Method for Chemical Vapor Deposition and Preparation of Conformal Titanium-Based Films

US006090709A Ulllted States Patent [19] [11] Patent Number: Kal0yer0s et al. [45] [54] 62 218576 3-214734 9/1987 9/1991 Japan . Japan - WO 95/33866 12/1995 WIPO - METHODS FOR CHEMICAL VAPOR DEPOSITION AND PREPARATION OF CONFORMAL TITANIUM-BASED FILMS [75] Date of Patent: Inventors: Alain E. Kaloyeros, Slingerlands, N.Y.; Y. Inoue et al., “Behavior of TiN and Ti Barrier Metals in A1—Barrier—A1 Via Hole MetalliZation”, J. Electrochem. [73] Assignees: Gelest, Inc., TullytoWn, Pa.; The 50a 141;4 (Apr' 1994) pp_ 1()56_1()61~ Research FOllIldatiOIl Of State N. YoshikaWa et al., “Microstructures of Chemical—Vapour— University Of New York, Albany, NY Deposited TiN Films”, Mat. Res. Soc. Symp. Proc. 343 (1994) pp. 741—746. K. Glejbol et al., “Nucleation of CVD—TiN on Tungsten”,J. [21] Appl, No,: 08/989,553 [22] Flled: Mater: Res. 8:9, (Sep., 1993) pp. 2239—2244. Dec‘ 12’ 1997 A. Intermann et al., “Film Properties of CVD Titanium _ _ Nitride De osited With Or anometallic Precursors at LoW Related U'S‘ Apphcatlon Data Pressure UIsJing Inert Gasesg, Ammonia, or Remote Activa [63] Continuation of application NO‘ 08/322,020’ Oct‘ 11’ 1994’ 2Electrochem. Soc. 140—11 (Nov. 1993) pp. abandoned. ' [51] Int. c1.7 ................................................... .. H01L 21/44 [52] US. Cl. [58] Field of Search ................................... .. 438/656, 648, (List Continued on next page) .. 438/685; 438/656; 438/648; 438/680; 438/653 Primary Examiner_TI-ung Dang Attorney, Agent, or Firm—Akin, Gump, Strauss, Hauer & Feld, L_L_p_ 438/680, 683, 653, 685 [56] Jul. 18, 2000 OTHER PUBLICATIONS Barry C. Arkles, Dresher, Pa. _ 6,090,709 [57] References Clted US. PATENT DOCUMENTS ABSTRACT Titanium and titanium nitride layers can be produced by chemical vapor deposition (CVD) processes conducted at ggigg; temperatures below 475° C. The layers may serve as diffu """ sion and adhesion barriers for ultra-large scale integration 4:882:224 11/1989 M0r0 et aL 428/403 (ULSI) microelectronic applications. The processes use 21 478847123 437/192 titanium halide precursor, such as titanium tetraiodide, and 4,897,709 4,957,777 1/1990 Yokoyama et al. ................... .. 437/197 9/1990 Iiderem et a1. . hydrogen or hydrogen in Combination With nitrogen, argon, or ammonia to either produce pure titanium metal ?lms, 5,017,403 5/1991 Pang - titanium ?lms Which alloy With the underlying silicon, or 11/1989 Dixit et aL ______ __ 5,173,327 12/1992 Sandhu et a1- - titanium nitride ?lms. The deposition of titanium metal from 5,246,881 titanium halide and hydrogen or the deposition of titanium 9/1993 Sandhu et al. ........................ .. 437/192 5250367 10/1993 Santhanam et a1‘ ' 5,252,518 10/1993 nitride from titanium halide With nitrogen and hydrogen is Sandhu et al. . . 5 271 963 12/1993 Eichman et al. ................... .. 427/2481 5:326:404 5,466,971 7/1994 Sam . . achleved Wlth the asslstance of a 1W energy. Plasma‘ The 118/723 MR process alloWs smooth and reversible transition betWeen 11/1995 Higuchi ................................. .. 257/751 deposition of ?lms of either titanium metal or titanium nitride by introduction or elimination of nitrogen or ammo FOREIGN PATENT DOCUMENTS 0214734 11/1981 0218576 9/1987 nu Japan . Japan . 100 30 Claims, 8 Drawing Sheets I I I I I XRS Ti from PPCVD TiI4 1 l 1 | | | | | | | | | | 7‘ ‘w 0 10 20 30 40 50 SPU'l'l'ER TIME (MIN) 60 70 80 90 | | 6,090,709 Page 2 OTHER PUBLICATIONS K. Ikeda et al., “TiN Thin Film Prepared by CVD Method C. Winter et al., “A Single—Sources Precursor to Titanium Nitride Thin Films. Evidence for the Intermediacy of Imido Complexes in the Chemical Vapor Deposition Process”, J. Using Cp2Ti(N3)2”, Proceedings of the 1992 Dry Process Symposium, (1992), pp. 169—173. Am. Chem. Soc. 114 (1992) pp. 1095—1097. R. Andrievskii et al., “Structure, Hardness and Recrystalli E. Kobeda et al., “Diffusion Barrier Properties of TiN Films Zation of Alloyed Laminated Films Based on Titanium Nitride”, Institute of New Chemical Problems, Russian Academy of Sciences. Translated from Neorganicheskie Materialy, 28:2 (Feb., 1992) pp. 365—368. © 1992 Plenum Publishing Corporation (pp. 268—271). V. Ivanov et al, “Prediction of Inorganic Cationic Conduc tors AaBVm?X4(a=2,5,6) and A7B"Y4 According to Geo metrical Criteria for A3BVX4”, S. OrdZhonikidZe Novocherkassk Polytechnical Institute. Translated from Neorganicheskie Materialy, 28:2 (Feb., 1992) pp. 369—372. Original article submitted Mar. 5, 1991. © 1992 Plenum Publishing Corporation (pp. 271—274). Y. Lomnitskaya et al., “Interaction of Zirconium of Zirco nium or Hafnium With Vanadium and Phosphorous”, I. Franko L’vov State University. Translated from Neorgan icheskie Materialy, 28:2 (Feb., 1992) pp. 373—377. © 1992 Plenum Publishing Corporation 274). M. Rutten et al., “Failure of Titanium Nitride Diffusion Barriers During Tungsten Chemical Vapor Deposition: Theory and Practice” (Abstract, Fig. 1). for Submicron Silicon Bipolar Techno1ogies”,J.Appl. Phys. 72:7 (Oct., 1992) pp. 2743—2748. R. Joshi et al., “Collimated Sputtering of TiN/Ti Liners into Sub—Half—Micrometer High Aspect Ratio Contacts/Lines”, Appl. Phys. Lett. 61:21 (Nov., 1992) pp. 2613—2615. K. Gonsalves et al. “LoW—Temperature Deposition of Ti(C, O) on Polyimides via organometallic Precursors” J. Inorg. Orgmet. Polym. 1:1 (1991) pp. 131—134. R. FiX et al., “Chemical Vapor Deposition of Titanium, Zirconium, and Hafnium Nitride Thin Films”, Chem. Mater. 3:6 (1991) pp. 1138—1148. A. Kohlhase et al., “Performance and Failure Mechanisms of TiN Diffusion Barrier Layers in Submicron Devices,” J. Appl. Phys. 65:6 (Mar., 1989) pp. 2464—2467. J. Hillman et al., “Process for LPCVD Titanium Nitride K. Sugiyama et al., Temperature Deposition of Metal Nitrates by Thermal Decomposition of Organometalllic Compounds, J. Electrochem. Soc. 122:11 (Nov. 1975) pp. Deposition” (Abstract, Figs. 1—5). 1545—1549. Using Meta1—Organic Chemcial Vapor Deposition” R. Gordon, “Conformal TiN by LoW—Temperature CVD”. (Abstract, Figs. 1—3). Chou, W.B., et al., “Laser Chemical Vapor Deposition of Ti from TiBr4,” Journal ofApplied Physics, vol. 66, No. 1, pp. G. Sandhu, “Characterization for TiN Films Deposited Y. Shacham—Diamand et al., “ULSI Application of Spin—On Titanium—Nitride” (Abstract, Figs. 1—6), Submitted Oct. 8—10, 1991 to the Advanced Meta1liZation for ULSI Appli cations (1991). 191—195, (Jul. 1989). Yokoyama, N., et al., “LPCVD TiN as Barrier Layer in E. Travis et al., “An Intergrated CVD TiN Barrier and VLSI,” Journal of the Electrochemical Society, vol. 136, Se1f—A1igned Tungsten Plug Contact Technology for High Aspect Ratio Submicron Contracts” (Abstract, Figs. 1—9). No. 3, pp. 882—883, (Mar. 1989). P. Groning et al., “Interface Analysis of P1asma—Deposited Titanium Nitride on Stainless Steels”, Applied Surface Sci ence 62 (1992) pp. 209—216. Y. Massiani et al., “Photoelectrochemical CharacteriZation of OXidiZed Films of Titanium Nitride and Titanium Obtained by Reaction Sputtering”, Thin Solid Films 207 (1992) pp. 109—116. Database WPI, Abstract of “Embedding Metal Into Fine Through—Holes for VLSI Prodn.,” Abstract No. XP—002125911 (1990). Joshi, R.V., et al., “Collimated Sputtering of TiN/Ti Liners into Sub—Half—Micrometer High Aspect Ratio Contacts/ Lines,” Applied Physics Letters, vol. 61, No. 21, pp. 2613—2615, (Nov. 1992). U.S. Patent Jul. 18,2000 Sheet 2 018 6,090,709 a z _ 11 weZ;5GJ;E5#549MXa $1 E: £2 :2 2f @f :02 $2Q6 _- _ . 12$ _\g.vfiér§21xtoCds©!ujh_ .wm N 2 E g m a. Q a 3 Om f.-25 \@z257;2:8 _ 22% 12% 13% 12% 12? 10.3 -2 U.S. Patent Jul. 18,2000 Sheet 3 0f8 If] 6,090,709 M2%ma2t:; E2E 6%6%6% 5%z=6_6 |"./g‘kqvi. \.I!:4<110I_, o a 2 02 Q2 0: .5 m U.S. Patent Jul. 18,2000 Sheet 4 0f8 6,090,709 00w Hi ELNQHW J;E9:ZCLnomgmil“in _ _ _ _ _ OOmDO¢COMCONOm:O 2 _ 6:5w.20 E w 1l 0 D1 Q1 p 9 a. woN U.S. Patent Jul. 18,2000 Sheet 5 0f8 6,090,709 U.S. Patent Jul. 18,2000 Sheet 8 0f8 CSSEM Ti from P'PCVD Tilt; 6,090,709 6,090,709 1 2 METHODS FOR CHEMICAL VAPOR DEPOSITION AND PREPARATION OF CONFORMAL TITANIUM-BASED FILMS ers. See, e.g., S. Saitoh et al., ibid, p. 495; M. JimineZ et al., J. Vac. Sci. Tech. B9, p. 1492, 1991; and A. Noya et al.,Jpn. J. Appl. Phys, 30, p. L1760, 1991. Efforts to resolve these CROSS-REFERENCE TO RELATED APPLICATION vapor desorption techniques, such as collimated reactive sputtering, have been unsuccessful to date because of, for example, reduced throughput due to the use of a collimator, This is a continuation of application Ser. No. 08/322,020, ?led Oct. 11, 1994, noW abandoned. undesirable particulate generation, and increased sensitivity FIELD OF THE INVENTION problems through the development of modi?ed physical 10 The present invention relates to substrates having titanium-based coatings, and to methodology for preparing such coated substrates. More particularly, the present inven tion is directed to substrates having sub-micron features and conformal Ti and TiN layers and bilayers coated thereon, and to loW-temperature and plasma-promoted chemical surface of the substrate to be coated. It is this reactive process Which distinguishes CVD from physical deposition processes, such as sputtering or evaporation. CVD poten vapor deposition techniques to provide Ti and TiN coatings. BACKGROUND OF THE INVENTION Titanium (Ti) and titanium nitride (TiN) are refractory materials With ionic structure, covalent bonding and metallic conductivity. These characteristics lead to high speci?c strengths at elevated temperatures, excellent mechanical, chemical and thermal stabilities, and good resistance to corrosion. These properties have made titanium and titanium nitride important building blocks in the manufacture of very tially offers many intrinsically attractive features for fabri 20 25 large scale integrated (VLSI) circuitry, Where they function as, for example, adhesion layers and diffusion barriers. VLSI fabrication also makes use of Ti—TiN bilayers on silicon substrates, Where titanium functions as a getter for oxygen 30 40 Thin Solid Films, 139, p. 247, 1986, and T. Akahori et al., 45 50 chlorine contamination to the extent of several atomic percent. Early attempts at preparing titanium nitride ?lms using CVD mostly involved coreacting titanium tetrachloride 55 diffusion barriers Which may be met by Ti and TiN ?lms. Physical vapor deposition methods, such as sputtering, Which Were successfully used in manufacturing VLSI 60 micron range and beloW, sputtering techniques provide undesirably non-conformal coverage. For example, sputter (TiCl4) and ammonia (NH3) to yield TiN ?lms With resis tivities in the range of 50 to 100 nQcm. These early attempts provided ?lms having good step coverage and diffusion barrier properties. See, e.g., A. Sherman, J. Electrochem. Soc., 137, p. 1892, 1990. In addition, ?lms produced thereby had impurities, mainly chlorine, at a concentration of less than about one atomic percent. See, e.g., J. Hiollman et al. in Advanced Metallization for ULSI Applications, ed. V. Rana et al., Mat’l Res. Soc. Pittsburgh, Pa., p. 319, 1992. HoWever, the high processing temperatures involved in ing causes thinning at vias, hole edges and Walls, and keyholes in the vias and trenches. Further, the deposits trapped sputter gas and possess a columnar groWth structure Which seriously inhibits their usefulness as diffusion barri Proc. Int’l Conf on Solid State Devices and Materials, Yokohama, Japan, p. 180, 1991. These efforts led to an appreciable reduction in process temperature, to Within the desired range of about 350° C.—500° C. HoWever, ?lm step coverage Was only 30%—70% for features of loW aspect ratio, and the ?lms exhibited undesirably high resistivities of nearly 200 nQcm. In addition, the ?lms suffered from 3:1, sometimes 4:1 and sometimes even 6:1. provided by sputtering techniques frequently contain by atmospheric pressure CVD (APCVD) using TiCl4 and isopropylamine as coreactants. See, e.g., M. Hilton et al., ULSI circuitry, Will be referred to herein as sub-micron devices, are unable to meet the requirements of the neW ULSI devices. As feature siZes are reduced into the half about 500° C. It is knoWn to prepare titanium metal ?lms by use of nitrogen and hydrogen; by electron cyclotron resonance (ECR) plasma CVD of TiCl4 in a nitrogen atmosphere; and These ?nely patterned substrates that are typically used in Reliable methodology has not heretofore existed for the coating of conformal, high-quality Ti and TiN ?lms onto the ?nely patterned substrates used in ULSI circuitry. And yet there is a critical need for appropriate adhesion layers and ology fails to provide Ti and TiN coatings With conformal coverage for substrates having sub-micron features as typi cally found in ULSI circuitry. In addition, standard CVD methodology requires processing temperatures in excess of about 650° C., Which is higher than can typically be tolerated plasma-assisted CVD (PACVD) of TiCl4 in a mixture of interconnect layer. The advent of ultra-large scale integration (ULSI) multi substrates. The sub-micron substrates used in ULSI circuitry have features With aspect ratios, i.e., the ratio of the depth to the Width of a feature When vieWed in cross-section, of about catalysis interaction of the substrate With CVD source precursors can possibly lead to selective metal groWth. HoWever, as discussed beloW, recogniZed CVD method contacts effectively requires CVD temperatures of less than 35 for the subsequent aluminum- or copper-based plug or often less than 0.5 micron and even less than 0.25 micron. electronics. For example, CVD can generally provide a high groWth rate and conformal coating of substrates having a complex topography of trenches and vias. In addition, to provide the contacts for the circuit. The use of aluminum loWer and more stable contact resistance than a titanium level metalliZation (MLM) schemes (see, e.g., M. Rutten et al., in Advanced Metallization for ULSI Applications, ed. V. Rana et al., Mat’l Res. Soc. Pittsburgh, Pa., p. 227, 1992), has seen the development of substrates having features, such as holes, vias and trenches, of diameter less than 1 micron, cation of Ti and TiN ?lms as demanded by modern micro in ULSI fabrication When aluminum serves as the material at the silicon interface. Such a bilayer provides signi?cantly nitride single layer, and improved adhesion and diffusion barrier properties, compared to a titanium metal single layer, to processing conditions. Chemical vapor deposition (CVD) is a process Whereby a solid ?lm is synthesiZed from the reaction products of gaseous phase precursors. The energy necessary to activate the precursors and thereby start the chemical reactions Which lead to ?lm formation, may be thermal and/or electrical, and may be reduced by catalytic activity at the 65 producing these ?lms, typically in excess of 650° C., pro hibit this technology from being used to prepare ULSI devices, Which can tolerate temperatures not greater than about 500° C. 6,090,709 3 4 There are several reports of the use of organometallic precursors to prepare titanium and titanium nitride ?lms by CVD. For example, there are several recent reports on the ?rst layer. Current technology does not provide a single reaction chamber With the versatility to deposit both Ti and metal-organic CVD (MOCVD) of TiN from dialkylamino the chamber. As is knoWn in the art, a process for the in-situ TiN ?lms merely by controlling the operating parameters of derivatives of titanium of the type Ti(NR2)4, Where R is a methyl or ethyl group. See, e.g., R. Fix et al., MRS Symp. deposition of sequential bilayers of Ti and TiN is desirable in part because of the high af?nity of titanium for oxygen Proc., 168, p. 357, 1990; and K. Ishihara et al.,Jpn. J. Appl. Phys., 29, p. 2103, 1990. Additional MOCVD studies and Water. This affinity leads typically to contamination of the Ti ?lm surface during transfer to a second reaction chamber Where it is coated With TiN. involving the use of single source titanium precursors of the type TiCl2(NHR2) (NHZR) and TiCl4(NR3)2 have been reported. See, e.g., C. Winter et al. in Chemical Perspectives of Microelectronic Materials 111. ed. C. Abernathy et al., MRS, Pittsburgh, Pa. 1992; and K. Ikeda et al., Proceedings 10 of the 1992 Dry Process Symposium, p. 169, 1992 (using cyclopentadienyl titanium compounds, such as bis (cyclopentadienyl) titanium diaZide). The use of diimine analogs of [3-diketonates such as Ti(NH)2C2CHR2)2 in MOCVD has also been reported. See A. Weber, The Pro 15 20 nQcm, and a step coverage beloW 70% even for features of concentrations of up to 50 atomic percent, and a carbon nathy et al., MRS, Pittsburgh, Pa. 1992, for using MOCVD techniques With neopentyltitanium (Me3CCH2)4Ti and sila 25 compounds have also been explored as precursors to tita 01/290,771, 1989. HoWever, as in the case of TiN, the 35 embodiments, the compound of formula (I) is titanium tetraiodide and the molar ratio of nitrogen atoms in compo nent (c) to titanium atoms in component (a) is at least 1:1. The method is particularly useful When the substrate is a silicon or silicon dioxide Wafer useful in the manufacture of According to another aspect of the invention, a method is provided for the chemical vapor deposition of a is titanium based ?lm onto a substrate, Which comprises introducing to a deposition chamber the folloWing components: a) a sub strate; (b) vapor of a compound having the formula (I) as one gas selected from the group consisting of hydrogen; hydrogen and at least one of nitrogen, ammonia, argon and xenon; nitrogen and at least one of ammonia, argon and 40 xenon; ammonia and at least one of argon and xenon. The above components are maintained in said chamber at a temperature of about 200° C. to about 650° C., preferably Anorg. Allgem. Chem., 148, p. 345, 1925) occurs at such high temperatures that it is not useful for ULSI fabrication. There thus exists a need for technology to provide Ti and TiN ?lms suitable for ULSI fabrication. Such ?lms must be are maintained in the deposition chamber at a temperature of above, and preferably titanium tetraiodide; and (c) at least resulting Ti ?lms exhibited high resistivity, and carbon and hydrogen content in excess of 10 atomic percent, making them undesirable for use in ULSI circuitry fabrication. It is knoWn that titanium halides Will decompose to Ti at temperatures in excess of 1300° C. This reaction, Which is knoWn as the Van Arkel process (see, A. Van Arkle et al. Z. Wherein m is 0—4 and n is 0—2; (c) a ?rst gas selected from the group consisting of ammonia and hydra Zine; and (d) a second gas selected from the group consisting of hydrogen, nitrogen, argon and xenon. These components 30 a ULSI device. neopentyltitanium (Me3SiCH2)4Ti. Cyclopentadienyl-based nium ?lms. See, e.g., N. AWaya et al., Japanese Patent No. pound having the formula Ti(I4_m_n) (Brm) (Cln) (hereinafter about 200° C. to about 650° C., preferably about 350° C. to about 475° C., for a time sufficient to deposit a titanium based ?lm onto the substrate. According to preferred loW aspect ratio. In addition, the ?lms contained hydrogen concentration of several atomic percent. These impurities are highly detrimental to the performance of the resulting ?lms and effectively prohibit their use in ULSI devices. MOCVD has also been studied for the preparation of titanium ?lms. See, e.g., T. Groshens et al., in Chemical Perspectives of Microelectronic Materials 111 ed. C. Aber Which comprises introducing to a deposition chamber the folloWing components: (a) a substrate; (b) vapor of a com formula ceea'ings of the Schumacher Conference (San Diego, Calif., 1993). HoWever, the TiN ?lms produced by MOCVD exhibit relatively high resistivities of greater than 200 SUMMARY OF THE INVENTION One aspect of the invention is a method for the chemical vapor deposition of a titanium-based ?lm onto a substrate, 45 about 350° C. to about 475° C., in the presence of a plasma having a plasma poWer density of about 0.1 to about 0.5 W/cm2. The components are maintained under these condi tions for a time suf?cient to deposit a titanium-based ?lm concentrations Well beloW 1 atomic percent. Also, the ?lms onto the substrate. According to preferred embodiments, the gas component (c) is hydrogen or hydrogen in combination should desirably exhibit a non-columnar structure in order to With nitrogen or hydrogen in combination With at least one perform appropriately as a barrier layer. Further, the ?lms should be conformal to the complex topography of ULSI circuitry, and provide step coverage in excess of 70%. It is desirable that technology be developed Which can readily of argon and xenon. A preferred substrate is a silicon or of ultra-high quality, in terms of purity, With impurity silicon dioxide Wafer useful in the manufacture of ULSI devices. According to another aspect of the invention, a method is provided for depositing multiple layers of titanium-based prepare single ?lms containing either Ti or TiN, as Well as bilayer ?lms of Ti and TiN, and that such technology be 55 ?lm onto a substrate While the substrate remains ?xed in a amenable to process temperatures beloW about 500° C. in single deposition reactor. The method comprises the steps of order to prevent thermally induced device damage during introducing components, Wherein the components are a processing. It is especially desirable that a process be developed Which alloWs for the preparation of the above-mentioned substrate and a source precursor, into a CVD chamber, Where the source precursor is vapor of at least one com 60 ?lms sequentially and in-situ, i.e., Without the necessity of transferring a substrate coated With a single ?lm (Ti or TiN) to another reaction chamber to deposit the other ?lm. Thus, according to current technology, the production of a bilayer typically involves the laying doWn of a ?rst layer in a ?rst reaction chamber, and then transferring the substrate to a second reaction chamber Where a second layer is coated onto pound of formula (I) as above, and is preferably vapor of titanium tetraiodide. The method comprises sequentially depositing onto the substrate alternating layers of titanium metal ?lm and titanium nitride ?lm, Where either the tita nium metal ?lm or the titanium nitride ?lm may be deposited 65 ?rst onto the substrate. According to a preferred embodiment, a titanium metal ?lm is deposited onto a substrate to provide a coated 6,090,709 5 6 substrate, and a titanium nitride ?lm is deposited onto the coated substrate. The titanium metal ?lm and the titanium DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS nitride ?lm are formed as described above. Processes utiliZing chemical vapor deposition (CVD) Another aspect of the invention provides a substrate for have been developed Which can prepare titanium-based ?lms suitable as, for example, diffusion barriers and adhe integrated circuitry having a coating disposed thereon. The substrate has features, such as holes, vias and trenches as typically found on integrated circuits, With dimensions of less than one micron, and preferably less than about 0.5 microns and more preferably less than about 0.25 microns, and aspect ratios of at least about 3:1, preferably at least sion inter-layers in integrated circuit fabrication, and in particular, in ULSI fabrication. The processes of the inven tion direct carefully selected precursors into a CVD reactor, 10 about 4:1 and more preferably at least about 6: 1. The coating is a titanium-based ?lm that is conformally deposited onto the substrate With step coverage greater than about 70%. BRIEF DESCRIPTION OF THE DRAWINGS under carefully speci?ed reaction conditions, to achieve high quality titanium-based ?lms of the invention. As used herein, the term “titanium-based ?lm” refers to a ?lm containing titanium. Exemplary titanium-based ?lms include ?lms of titanium metal, titanium nitride, titanium 15 The foregoing summary, as Well as the folloWing detailed description of preferred embodiments of the invention, Will silicide and laminates thereof including a bilayer ?lm of titanium metal and titanium nitride. The titanium-based ?lms of the invention may be substantially pure, or may contain a mixture of phases of titanium-based materials, e. g., be better understood When read in conjunction With the a mixture of titanium metal phases With titanium nitride or appended draWings. For the purpose of illustrating the titanium silicide phases. In addition, the titanium-based invention, there are shoWn in the draWings embodiments Which are presently preferred. It should be understood, hoWever, that the invention is not limited to the precise arrangements and instrumentalities shoWn. In the draWings: FIG. 1 is a diagrammatic representation of a reaction apparatus used to achieve chemical vapor deposition accord ing to the present invention. FIG. 2 is an x-ray diffraction (XRD) pattern of a TiN ?lm produced by the TCVD reaction of TiI4 and NH3. XRD indicates a clean (111) TiN phase. 20 example, nitrogen. To prepare titanium-based ?lms according to the invention, thermal chemical vapor deposition (TCVD) or 25 process Wherein all reactants are introduced to the CVD reactor in gaseous form, and the energy necessary for bond cleavage is supplied entirely by thermal energy. As used 30 35 40 deposited by TCVD reaction of TiI4 and NH3. The coating damage, and alloW the formation of ?lms With reduced stress levels. PECVD operated at plasma poWer density greater 45 50 of the source precursor; a vacuum chamber and pumping system to maintain an appropriately reduced pressure as necessary; a poWer supply to create discharge as necessary; a temperature control system; and gas or vapor handling capabilities to meter and control the How of reactants and FIG. 6 is an x-ray diffraction (XRD) pattern of a Ti ?lm produced by the plasma-promoted CVD reaction of TiI4 and hydrogen in an argon plasma. The XRD spectrum indicates a clean hexagonal Ti phase. FIG. 7 is an x-ray photoelectron spectroscopy (XPS) spectrum of a Ti ?lm produced by plasma-promoted CVD reaction of TiI4 and hydrogen in an argon plasma. XPS results indicate a pure Ti phase, as documented by its 55 60 alloying With Si. FIG. 8 depicts a cross section, magni?ed by scanning electron microscopy, of a silicon substrate upon Which oxide via patterns, of diameter 0.2 pm and 6 to 1 aspect ratio, are formed and upon Which a conformal Ti coating has been deposited by plasma-promoted CVD reaction of TiI4 and hydrogen in an argon plasma. than 0.5 W/cm2 is not included Within PPCVD according to the invention. A deposition reactor suited for TCVD or PPCVD accord ing to the invention has several basic components: a pre cursor delivery system (also referred to as bubbler or sublimator) Which is used to store and control the delivery shoWn in the left-hand micrograph of FIG. 5 has a thickness of less than 100 nm, Which is a typical ?lm thickness for ULSI devices. The coating shoWn in the right-hand micro graph of FIG. 5 has a considerably thicker coating, and is shoWn to illustrate that conformal coatings are prepared even at extraordinarily high thickness. CVD (PECVD), Where PECVD is a Well-knoWn technique. HoWever, in contrast to PECVD, Which uses high plasma poWer densities, the loW poWer densities employed in PPCVD do not cause ion-induced substrate and ?lm FIG. 5 depicts cross sections, magni?ed by scanning electron microscopy, of silicon substrates upon Which oxide via patterns, of diameter 0.25 pm and 4 to 1 aspect ratio, are formed and upon Which conformal TiN coatings have been the high energy electrons formed in a gloW discharge or plasma having a plasma poWer density of beloW about 0.5 W/cm2. PPCVD takes advantage of the high energy elec trons present in gloW discharges to assist in the dissociation of gaseous molecules, as is the case With plasma-enhanced RBS results indicate a pure TiN phase With a stoichiometric Mn, etc.) contamination. herein, PPCVD refers to a CVD process Wherein all reac tants are introduced to the CVD reactor in gaseous form, and the energy necessary for bond cleavage is supplied in part by FIG. 4 is a Rutherford backscattering (RBS) spectrum of a TiN ?lm produced by the TCVD reaction of TiI4 and NH3. Ti to N ratio (1:1) and essentially no heavy element (e.g., Cr, plasma-promoted chemical vapor deposition (PPCVD), may be employed. As used herein, TCVD refers to a CVD FIG. 3 is an x-ray photoelectron spectroscopy (XPS) spectrum of a TiN ?lm produced by the TCVD reaction of TiI4 and NH3. XPS results indicate a pure TiN phase With a stoichiometric Ti to N ratio (1:1) and no light element (e.g., C, O, F, etc.) contamination. ?lms of the invention may contain gas molecules, for products that result from the process. According to one preferred embodiment for the deposi tion of titanium-based ?lms according to the invention, the deposition reactor shoWn in FIG. 1 is employed. The source precursor 10 is placed in the bubbler/sublimator 11 Which is heated by a combination of resistance heating tape and an associated poWer supply 12 to a desired temperature. The dashed lines in FIG. 1, labeled 12, encompass parts of the CVD reactor Which are heated by the resistance heating tape. A mass ?oW controller 13, Which can be isolated from the 65 bubbler by a high vacuum valve 14, controls the How of carrier gas 15 through feedthrough 16 into the bubbler. While a carrier gas need not be employed, it is preferable to 6,090,709 7 8 use a carrier gas in order to better control and accelerate the the carrier gas may also be a mixture of pure gases. rate of How of the source precursor vapor into the deposition chamber. In a preferred embodiment, the mixture of precursor vapor Hydrogen is a particularly preferred carrier gas for both TCVD and PPCVD according to the invention. The How rate of the carrier gas through the source precursor is controlled by the mass ?oW controller 13. The and carrier gas is transported through feedthrough 17, high How rate of the carrier gas is about 10 sccm to about 100 sccm, and preferably about 20 sccm to about 60 sccm. A How rate of about 20 sccm to about 60 sccm is preferred for vacuum isolation valves 18 and 19, and delivery line 20 into the deposition reactor 21. All transport and delivery lines and high vacuum isolation valves 17, 18, 19, and 20 are maintained at the same temperature as the bubbler/ sublimator 11, again using a combination resistance heating 10 both TCVD and PPCVD according to the invention. Under action of the carrier gas, the How rate of the vapor of the source precursor is about 0.001 sccm to about 1,000 sccm. Preferably, the How rate of source precursor vapor into the CVD chamber is about 0.1 sccm to about 200 sccm. tape and associated poWer supply 22. The dashed lines in FIG. 1 labeled 22 encompass parts of the CVD reactor heated by resistance heating tape, Where the heating tape The auxiliary gas is at least one of hydrogen, helium, heats the apparatus to prevent precursor recondensation. The reactor 21 is a cold-Wall stainless steel CVD reactor 15 nitrogen, ammonia, hydraZine, neon, chlorine, bromine, argon, krypton and xenon. As With the carrier gas, the of siZe suf?cient to hold an 8“ Wafer. It is equipped With a preferred auxiliary gases are non-halogenated. The How of diode-type parallel plate-type plasma con?guration made of the auxiliary gas, Which may be a pure gas or a mixture of tWo electrodes 23 and 24. The upper plate 23 serves as the active electrode and is driven by a plasma generator 25. This upper plate is constructed in a “mesh” type pattern to alloW gases, is preferably about 10 sccm to about 10,000 sccm, and 20 controller 13 is denoted herein as the carrier gas, and the 26 sits on the loWer, grounded plasma electrode 24. The substrate 26 is heated to a process temperature by an 8“ boron nitride (BN)-encapsulated graphite heater 27. A spe cially designed shoWer head 28 and associated pumping 25 may and typically does undergo reaction in the chamber during the deposition process. The auxiliary gas may be inert Evacuation of the deposition reactor is possible through of tWo pumping packages, Where the ?rst is cryogenic pump-based, and the second is roots bloWer pump-based. The pumping stack may be isolated from the reactor by the high vacuum gate valve 31. The cryogenic pump-based package is used to ensure high vacuum base pressure in the reactor, While the roots bloWer-based package is employed or include inert components, in Which case some or all of the 30 35 for appropriate handling of the high gas throughput during actual CVD runs. A high vacuum load lock system 32 is used for transport and loading of substrate into and out of the reactor. Finally, a side line 33 is employed to feed additional gaseous reactants, i.e., auxiliary gas, into the reactor. The side line gas How is controlled by the mass ?oW controller 34 and associated isolation valve 35. The source precursor 10 according to the invention is at gas(es) entering the mass ?oW controller 34 is denoted herein as the auxiliary gas, this terminology should not be misconstrued. In fact, in addition to carrying the vapor of the source precursor into the reaction chamber, the carrier gas lines 29 are employed to ensure proper reactant mixing and uniformity in reactant delivery and How over the substrate. use of a pumping stack 30. The pumping stack 30 consists is more preferably about 100 sccm to about 1,000 sccm. Although for convenience the gas(es) entering mass ?oW unrestricted reactant How to a substrate 26, Where substrate auxiliary gas serves merely to dilute the reactive atmosphere inside the deposition chamber. LikeWise, the carrier gas may be inert or contain inert components. The auxiliary gas may also undergo reaction in the CVD chamber. According to a preferred embodiment of PPCVD, hydro gen is the carrier gas and there is no auxiliary gas. According to another preferred embodiment for PPCVD, hydrogen is introduced into the deposition chamber simultaneously With an inert gas such as neon, argon, krypton or xenon. 40 Preferably, hydrogen is introduced as the carrier gas and at least one of argon and xenon is the auxiliary gas. HoWever, the inert gas may be introduced in admixture With hydrogen, Where the mixture serves as the carrier gas. It is also possible for the inert gas to serve as the carrier gas, and have 45 hydrogen introduced as the auxiliary gas. In each of the above instances, a titanium metal ?lm is produced. least one titanium containing compound of the formula (I) PPCVD according to the invention can also be used to prepare titanium nitride (TiN) ?lms. To prepare a TiN ?lm by PPCVD, a nitrogen-containing gas must be introduced Wherein m is an integer Within the range 0—4 and n is an into the reactor chamber. Nitrogen (N2), ammonia and hydraZine are exemplary nitrogen-containing gases accord ing to the invention. When nitrogen (N2) is the nitrogen integer Within the range 0—2. Preferably, the compound of formula (I) has n=0, i.e., there are no chlorine ligands. More preferably, the source precursor 10 is titanium tetraiodide, containing gas, it may be introduced as either a carrier or auxiliary gas, and hydrogen or an inert gas such as argon or xenon may be introduced simultaneously thereWith as either After being charged to the bubbler/sublimator 11, the source precursor is taken to a temperature Which is high 55 a carrier or auxiliary gas. Preferably, at least one of nitrogen, enough to ensure the precursor’s sublimation or hydrogen and an inert gas is a carrier gas. i.e., TiI4. When ammonia or hydraZine is the nitrogen-containing gas during PPCVD of a TiN ?lm, then it Will be introduced into the deposition chamber as an auxiliary gas, and hydro vaporiZation, but not too high to cause premature decom position. Preferably, the source precursor is heated to a temperature of about 90° C. to about 160° C. The carrier gas can be any gaseous substance Which is not 60 gen and/or an inert gas such as argon or xenon may be the 65 carrier gas. Hydrogen and/or an inert gas may also be co-introduced as the auxiliary gas, i.e., hydrogen and/or an inert gas may be in admixture With the ammonia or hydra Zine gas. Nitrogen in combination With at least one of ammonia and hydraZine may be the sole gases present in the reactive With compounds of formula Exemplary carrier gases are hydrogen, helium, nitrogen, neon, chlorine, bromine, argon, krypton and xenon. While halogenated gases can function as the carrier gas, non-halogenated gases are preferred because they cannot contribute any halogen contamination to the titanium-based ?lm. The preferred carrier gases are hydrogen, nitrogen and argon. Of course, deposition chamber during the preparation of TiN, in Which case nitrogen Will be the carrier gas. According to a pre 6,090,709 9 10 ferred embodiment to prepare TiN ?lm by PPCVD, hydro gas(es) present in the reactant chamber. The plasma has a plasma poWer density of about 0.1 to about 0.5 W/cm2, and preferably has a density of about 0.15 W/cm2 to about 0.3 W/cm2. As described above, When a titanium nitride ?lm is gen and nitrogen are introduced into the reactant chamber simultaneously With the source precursor. Titanium nitride ?lms may also be prepared using TCVD according to the invention. To prepare a TiN ?lm by TCVD, desirably deposited by PPCVD onto a substrate, or onto a ammonia and/or hydraZine is introduced to the deposition coated substrate, the gases nitrogen and hydrogen are pref chamber as an auxiliary gas, and at least one of hydrogen, erably present With the source precursor vapor, in the presence of a plasma. When a titanium metal ?lm is desir ably deposited onto the substrate, or onto a coated substrate, nitrogen or an inert gas such as argon or xenon serves as a carrier gas. According to a preferred embodiment, hydrogen is a carrier gas While ammonia is an auxiliary gas. Regardless of Whether TCVD or PPCVD is used to 10 argon and xenon are present With the source precursor, in the prepare the TiN ?lm, and regardless of the exact identities of the nitrogen-containing gas and the carrier and auxiliary presence of a plasma. The deposition rate of the ?lms of the invention is observed to be about 25 to about 2000 angstroms per minute gases, it is important to maintain at least one mole of nitrogen atoms in the reaction chamber for each mole of titanium in the reaction chamber. If insuf?cient nitrogen is 15 be deposited rather than titanium nitride, thereby alloWing of this invention, in instances Where a pure TiN ?lm is desired, i.e., a ?lm having a Ti:N molar ratio of about 1:1, preferred thickness of about 500 A to about 1500 The deposition time is therefore seen to be quite rapid, on the 20 next. It should be noted that the formation of titanium 25 silicide ?lms (TiSi), occurs only When the substrate is silicon or polysilicon and the titanium being deposited is particu larly pure titanium metal. In such cases, the substrate titanium interface can react to form a layer of TiSi. It has been observed that a silicon substrate can catalyZe the made With excess nitrogen may demonstrate enhanced dif 30 reaction(s) leading to the deposition of titanium metal. Titanium and titanium silicide ?lms Were prepared in the deposition reactor shoWn in FIG. 1, according to the PPCVD generated through use of radiofrequency (RF) gloW discharges, having frequencies in the MHZ range, although plasmas With frequencies ranging from kHZ to GHZ could be employed. See, generally, Hess, D. W. and Graves D. B., “Plasma-Assisted Chemical Vapor Deposition”, Chapter 7 in order of seconds or minutes. The appearance and composition of the titanium-based ?lms prepared according to the inventive methods, as Well as their structural and electrical properties, Will be described then an adequate supply of nitrogen atoms must be supplied to the deposition chamber. Excess nitrogen may enhance ?lm stability, and the diffusion barrier properties of a ?lm fusion barrier properties. According to the preferred PPCVD method, the plasma is (A/min). A typical deposition rate is about 400 A/min to about 500 A/min. The ?lms of the invention have a thickness of about 50 angstroms to about 2 microns, and have a present in the deposition chamber, then titanium metal may the formation of a mixed-phase ?lm, i.e., a ?lm having phases of titanium and phases of titanium nitride. While a mixed-phase ?lm may be desired for some applications, and methodology to prepare such titanium-based ?lms and sub strates having these ?lms coated thereon is Within the scope by PPCVD, hydrogen gas, optionally With at least one of method of the invention. The source precursor Was titanium tetraiodide and it Was sublimed at a temperature Within the 35 range of 120° C. to 160° C. Films Were prepared during reactions Wherein the Working pressure inside the deposition Chemical Vapor Deposition, Principles and Applications, reactor Was from 200 to 400 mtorr, the carrier gas Was Hitchman M. L. and Jensen, K. F. eds., Academic Press hydrogen With a How rate of from 10 to 60 sccm, the auxiliary gas Was argon With a How rate of 400 to 600 sccm and the substrate temperature Was from 300° C. to 450° C. The ?lms Were deposited onto a silicon Wafer. (1993). Apreferred frequency is about 1 to about 100 MHZ, With about 14 MHZ being particularly preferred. 40 Prior to beginning a sequence of deposition runs, and periodically betWeen depositions conducted during a The titanium and titanium silicide ?lms thus produced Were metallic, continuous, and silver colored. X-ray diffrac tion (XRD) analysis of a Ti ?lm groWn at 450° C. is shoWn sequence of runs the deposition reactor is baked under a nitrogen atmosphere to beloW 0.3 torr and then pumped doWn to beloW 10-7 torr for an hour at 150° C. This process 45 in FIG. 6 for a 1000 A-thick ?lm on Si. The XRD analysis shoWs that the ?lm has a hexagonal Ti phase. X-ray photo assures cleanliness of the reactor, and is conducted for both electron spectroscopy (XPS) Was performed using a Perkin TCVD and PPCVD runs. Elmer Physical Electronics Model 10-360 spherical capaci The substrate 26 is placed into the CVD reactor and then preferably exposed to a cleaning regime. Pre-deposition substrate cleaning is preferably accomplished by exposing tor analyZer. The gold f7/2 line at 83.8 eV Was taken as 50 reference line and the analyZer calibrated accordingly. All the substrate in situ to a hydrogen plasma having a plasma poWer density of about 0.1 to about 1.0 W/cm2. Substrate cleaning as described is performed for both TCVD and spectra Were obtained using a pass energy of 5 eV at a PPCVD. Prior to introducing the source precursor into the CVD pressure Was in the 10-10 torr range, and the results Were resolution of 0.8 eV. Aprimary x-ray beam (Mg Kot, 127 eV) of 15 keV and 300 W Was employed. The analysis chamber 55 standardiZed using a sputtered Ti sample. The XPS survey deposition chamber, the chamber atmosphere is evacuated, spectra (FIG. 7) indicated that, Within the detection limits of and the reactor is heated to a process temperature. XPS, the Ti ?lms produced beloW 400° C. contained less than 20 atomic percent oxygen, While Ti ?lms produced Preferably, the pressure in the chamber is about 0.001 torr to about 760 torr during the deposition process. More preferably, the atmosphere in the chamber during the depo 60 above 400° C. Were free of oxygen and exhibited signi?cant interactions With the Si substrate, Which requires pure Ti to sition has a pressure of about 0.1 torr to about 10 torr. The occur. No carbon or any other light element contaminants process temperature during deposition is less than about 650° C. Preferably, the process temperature is about 250° C. Were observed in the ?lms, regardless of substrate tempera ture. As used herein, light elements refer to elements having atomic number betWeen 3 and 13, inclusive. The presence of to about 500° C., and more preferably about 350° C. to about 475° C. 65 iodine Was detected at levels of about 0.4 to 1.5 atomic Aplasma may be present during the deposition process in percent. Four-point probe resistivity measurements found order to promote reaction of the source precursor With other that ?lm resistivities as loW as 90 nQcm could be obtained. 6,090,709 11 12 The ?lms prepared according to the inventive methods are The nature of the titanium and titanium silicide ?lms vis a-vis a silicon substrate Was next examined. The adherence seen to have very high purity, and thus are Well suited for use of the titanium ?lms to either silicon or silicon dioxide Was in, for example, microelectronic applications Where purity observed to be good. Cross-section SEM analysis Was SEM micrograph (FIG. 8) of a 1000 A-thick Ti ?lm shoWed demands are quite stringent. The ?lms of the invention have carbon and hydrogen impurity levels of less than about 15 atomic percent, preferably less than about 10 atomic percent and more preferably less than about 1 atomic percent. The conformal step coverage of 0.20 pm vias With aspect ratio of ?lms of the invention have minimal or no halogen 6. contamination, Where the halogens are iodine, bromine or chlorine. Thus, ?lms according to the invention Will have halogen contamination of less than about 15 atomic percent, preferably less than about 5 atomic percent, and more carried out on a Zeiss DSM940 microscope, employing a 20 keV primary electron beam and a beam current of 4 MA. An Titanium nitride ?lms Were prepared in the deposition reactor shoWn in FIG. 1, according to the TCVD method of 10 the invention. The source precursor Was either titanium tetraiodide or titanium tetrabromide, and the sublimation temperatures Were from 120° C. to 160° C. and from 90° C. to 140° C. respectively. Films Were prepared during reac tions Wherein the Working pressure inside the deposition preferably less than about 1 atomic percent. Due in part to their high purity, the titanium-based ?lms 15 of the invention are seen to have desirably loW resistivities. The inventive ?lms have a resistivity of about 40 to about reactor Was from 200 to 350 mtorr, the carrier gas Was 5,000 microOhm-centimeters (,uQcm), preferably about 40 hydrogen With a How rate of from 20 to 60 sccm, the auxiliary gas Was ammonia With a How rate of 400 to 600 sccm and the substrate temperature Was from 300° C. to 450° C. The ?lms Were deposited onto a silicon Wafer. The titanium nitride ?lms Were typically metallic, con to about 1,000 pQcm, and more preferably about 40 to about 150 pQcm. 20 tinuous and gold colored. X-ray diffraction (XRD) analysis lent adhesive properties When formulated into ULSI cir cuitry. of a TiN ?lm groWn at 350° C. from TiI4 is shoWn in FIG. 2 for a 1000 A-thick ?lm on Si. The ?lm shoWed a polycrystalline TiN phase With major diffraction peaks appearing at 20=36.66° (111), 42.59° (200), 61.81° (220), and The inventive titanium nitride ?lm, Whether prepared by 25 74.07° (311). Essentially the same spectrum Was observed When TiBr4 Was the source precursor. X-ray photoelectron spectroscopy (XPS) measurements Were performed using a Perkin-Elmer Physical Electronics Model 10-360 spherical capacitor analyZer. The gold f7/2 line at 83.8 eV Was taken PPCVD or TCVD according to the invention, typically has a titanium to nitrogen ratio of about 0.9—1.1:0.9—1.1, and more preferably have a titanium to nitrogen ratio of about 1:1. While our invention alloWs the separate and independent 30 production of titanium-based ?lms, and particularly ?lms 35 preferred embodiment, the inventive method provides for in situ sequential CVD in Which the deposition mode of a single precursor is smoothly and reversibly sWitched betWeen Ti and TiN by changing auxiliary gases that can comprising mainly titanium metal or titanium nitride, in a as reference line and the analyZer calibrated accordingly. All spectra Were obtained using a pass energy of 5 eV at a resolution of 0.8 eV. Aprimary x-ray beam (Mg Kot, 127 ev) of 15 keV and 300 W Was employed. The analysis chamber The titanium-based ?lms of the invention may advanta geously be tailored to columnar or non-columnar structure. The titanium-based ?lms of the invention also have excel pressure Was in the 10-10 torr range, and the results Were also act as carriers. standardiZed using a sputtered TiN sample. All samples Were sputter-cleaned before data acquisition. The XPS survey according to FIG. 1 is charged to contain vapor from a Thus, according to the inventive method, the reactor spectra (FIG. 3) indicated that, Within the detection limits of XPS, a TiN ?lm prepared from TiI4 as the source precursor Was free of oxygen, carbon, and similar light element compound of formula (I), and preferably titanium tetraio 40 dide vapor, in the presence of argon, hydrogen, and a plasma having a plasma poWer density of about 0.1 W/cm2 to about contaminants. In general, iodine concentrations, ranging 0.5 W/cm2. As described previously, these reaction condi from 0.4—1.5 atomic percent, Were detected in the ?lms. tions result in the formation of a titanium ?lm on a substrate. Rutherford backscattering (RBS) spectra Were taken using a 2 MeV HE2+ beam, and calibrated With a bulk sample of silicon. The RBS results, shoWn in FIG. 4 for a 1000 A-thick TiN ?lm on silicon, con?rmed the XPS ?ndings that the PPCVD process yields TiN ?lms With extremely loW iodine concentrations. In general, the TiN ?lms contained greater Then the plasma is turned off and the auxiliary gas is 45 changed from argon to ammonia. Under these revised reac tion conditions, a ?lm of titanium nitride is deposited on top of the previously laid doWn titanium ?lm, to provide a bilayer ?lm of the invention. It should be understood that the process could be reversed, than 99 atomic percent TiN, and this Was observed When i.e., the titanium nitride ?lm could be laid doWn ?rst on the either TiI4 or TiBr4 Was the source precursor. substrate, folloWed by deposition of titanium metal ?lm. Four-point probe resistivity measurements determined Preferably, the titanium ?lm is laid doWn so as to contact that ?lm resistivities as loW as 44 pQcm Were obtained When With the substrate, Which is preferably a silicon substrate. It the source precursor Was titanium tetraiodide. HoWever, should also be understood that more than tWo composition When the source precursor Was titanium tetrabromide, ?lm 55 ally diverse layers may be deposited on a substrate, Without resistivities as loW as 120 pQcm Were obtained. the need to remove the substrate from the reaction chamber. The nature of the titanium nitride ?lm vis-a-vis a silicon substrate Was next examined. Cross-section SEM analyses Were carried out on a Zeiss DSM940 microscope, employing a 20 keV primary electron beam and beam current of 4 MA. 60 The SEM micrograph (FIG. 5) of a 700 A-thick TiN ?lm prepared from titanium tetraiodide as the source precursor, shoWed conformal step coverage of 0.25 pm vias With aspect ratio of 4. The adherence of the titanium nitride to either silicon or silicon dioxide Was found to be good. Essentially the same results Were obtained When titanium tetrabromide Was the source precursor. 65 It should also be understood that in preparing bilayer ?lms, any method for preparing a titanium metal ?lm according to the invention could be folloWed or preceded by any method for preparing a titanium nitride ?lm according to the invention. For example, PPCVD With hydrogen carrier gas could be used to deposit a titanium metal ?lm, folloWed by PPCVD With hydrogen and nitrogen as carrier and/or auxiliary gases, to deposit a titanium nitride ?lm and thereby produce a bilayer. The in situ deposition of a titanium-based bilayer as described is very convenient for the preparation of ULSI 6,090,709 13 14 devices. The inventive method allows the formation of a determining the variation in the thickness of that coating. bilayer Without the necessity of transferring the partially According to the invention, sub-micron substrates are con coated substrate betWeen reaction chambers. That the bilayer can be made in a single reaction chamber greatly minimizes the risk of contamination of the ?lm, Which may occur during transfer of the partially coated substrate betWeen reaction chambers. Contamination is a particular formally coated, When the coating has a thickness, measured preferred embodiment, the variation in coating thickness is problem for the titanium-based ?lms of the invention, Within 10%, i.e., at no point is the thickness of the coating because these ?lms are often very reactive and even slight amounts of contamination can destroy their usefulness in ULSI devices. at any point normal to the surface of a Wall or ?oor of a hole in the surface of the substrate, Which is Within 25% of the thickness at any other point in the hole. According to a 10 The titanium-based ?lms of the invention may be depos ited onto a Wide range of substrates, in order to prepare materials useful in refractive, mechanical, microelectronic and decorative applications, to name a feW. There is really no limitation on the identity of the substrate, hoWever preferably the substrate is stable to the conditions used to deposit the ?lm or coating onto the substrate. That is, the substrate should be stable to temperatures of about 200° C. to about 650° C., preferably to about 350° C. to about 500° either 10% greater or 10% smaller than the average thick ness of the coating. The preferred coatings are titanium metal and titanium nitride, and the preferred substrate com prises at least one of silicon or silicon oxide. As used herein, the term step coverage refers to the ratio of the coating thickness at the bottom of a feature such as a 15 trench or via, to the thickness of the coating on the top surface of the substrate adjacent to the feature, Where the ratio is multiplied by 100 to provide a percent value. The processes of the invention provide conformally coated sub micron substrates having step coverage of greater than about 20 25% for features of high aspect ratios, Where high aspect C., and to pressures of about 0.1 torr to about 10 torr, preferably about 0.5 torr to about 5 torr. ratios are considered to be greater than about 3:1. FIG. 5 shoWs micrograph of tWo TiN ?lms Which Were The substrate of the invention may be metallic, that is, it may be comprised mainly of a metal. Exemplary metals deposited onto sub-micron substrates using TCVD accord ing to the invention. The micrograph on the left-hand side of include, Without limitation, aluminum, beryllium, cadmium, cerium, chromium, cobalt, copper, gallium, gold, iron, lead, manganese, molybdenum, nickel, palladium, platinum, rhenium, rhodium, silver, stainless steel, steel, strontium, tin, titanium, tungsten, Zinc, Zirconium, and alloys thereof. 25 In microelectronic applications, a preferred substrate is intended to become an integrated circuit, and has a complex 30 conformal to a via With a diameter of 0.25 micron and a 4:1 aspect ratio. The micrograph on the right-hand side of FIG. the necessary connections betWeen materials of various electrical conductivities that form a semiconductor device. titanium tetraiodide as the source precursor, and ammonia as 35 silicon dioxide, silicon nitride, or doped versions and mix The substrates of the invention are preferably intended for ultra-large scale integrated (ULSI) circuitry, and are pat accomplished by PPCVD according to the invention, With 40 titanium tetraiodide as the source precursor and hydrogen as 45 the carrier gas and an argon plasma. The coating is seen to be conformal. We have discovered that selected perhalogenated titanium compounds, in combination With argon, can be converted by means of mixed hydrogen-argon plasma in a CVD system, even 0.25 microns or less. Substrates having such small features are knoWn herein as sub-micron substrates. Sub micron substrates Which may be coated according to the invention also typically have features With high aspect ratios, from about 3:1 to about 6:1, Where the ratio of a feature’s depth to its diameter, as vieWed in cross-section, is termed the aspect ratio of the feature. As used herein, sub-micron substrate have feature diameters of less than about one micron and the aspect ratio of the features is larger than about 3:1. Features having an aspect ratio of about 4:1 into high quality titanium ?lms. Similarly, under thermal conditions, titanium nitride can be produced from reacting 50 circuitry. placed on sub-micron substrates having feature diameters as small as about 0.25 micron With aspect ratios as large as about 6:1. Conformal coatings of TiN or TiN/Ti bilayer may be placed on sub-micron substrates having feature diameters the same tetrahalotitanium compounds With ammonia, in the presence of a carrier gas. Exemplary reactions according to the invention can be summariZed by the folloWing equations, Wherein TiI4 is an exemplary tetrahalotitanium to about 6:1 are found on typical substrates for ULSI According to the chemical vapor deposition processes of the invention, conformal coatings may be placed on sub micron substrates. Conformal coatings of Ti or Ti/Si may be the auxiliary gas. FIG. 8 shoWs a micrograph of a Ti ?lm Which Was deposited onto a sub-micron substrate having a via diameter of 0.2 microns and a 6:1 aspect ratio. The deposition Was tures thereof. terned With holes, trenches and other features With diameters of less than 1.0 micron, often less than 0.50 microns, and 5 shoWs a very thick coating of TiN deposited onto a silicon substrate having the same feature dimensions as depicted in the micrograph on the right-hand side of FIG. 5, and it can be seen that even after an extended deposition time, TCVD according to the invention provides a conformal coating With high step coverage. The ?lms Were prepared from topography formed of holes, trenches, vias, etc., to provide The substrate is preferably formed of, for example, silicon, FIG. 5 shoWs that a TiN ?lm according to the invention is 55 compound. PPCVD: TiI4+H2—>Ti+HI (major byproduct) PPCVD: TiI4+N2+H2QTiN+HI (major byproduct) TCVD: TiI4+NH3+H2QTiN+NH4I (major byproduct) In contrast to prior art chemical vapor deposition methods, our invention provides ?lms of higher purity, due to the near or complete absence of carbon and chlorine contamination. In contrast to sputtering techniques, our by, for example, examining the thickness of the coating invention provides coatings on substrates suitable for ULSI fabrication. While not Wishing to be bound by theory, We offer the folloWing explanation for the ef?cacy of our processes. In our method, We have selected inorganic titanium compounds in Which the dissociation energy of primary bonds is rela tively loW, and thus We believe recombination can be along the Walls and bottom of a hole in the substrate, and interrupted by nitrogen radicals formed by interaction of 60 as small as about 0.25 micron With aspect ratios as large as about 4:1. As used herein, the term conformal coating refers to a coating that evenly covers a substrate having a complex topography. The evenness of the coating can be measured 65 6,090,709 15 16 diatomic nitrogen With a hydrogen plasma ?oW or by hydrogen radicals. The following Table 1, Which shoWs properties of selected titanium halides, indicates that the While no plasma Was employed during actual deposition. A bond energies of Ti—I and Ti—Br are much loWer than that of Ti—Cl, as indicated by their loWer heat of formation. and uniformity in reactant delivery and How over the 8“ Wafer. TABLE 1 The pumping stack 30 consisted of tWo pumping pack ages: the ?rst, cryogenic pump-based, and the second, roots specially designed shoWer head 28 and associated pumping lines 29 Were employed to ensure proper reactant mixing bloWer pump-based The pumping stack Was isolated from the reactor by the high vacuum gate valve 31. The cryogenic AHformation @ 298° C. TiF4 TiCl4 TiBr4 TiI4 m.p. b.p. Molecular Form kcal/mole ° C. ° C. Weight % Ti solid liquid Solid Solid 284 —24 38 155 sublimes 136 233 377 123.89 189.71 367.54 555.50 38.6 25.2 13.0 8.6 —394 —192 —148 —92 10 Was employed for appropriate handling of the high gas 15 We believe that, under the conditions of plasma-promoted chemical vapor deposition, titanium tetraiodide dissociates interrupted by the presence of plasma nitrogen, leading to 20 contrast to the reaction of titanium chloride With ammonia in EXAMPLE 2 25 Preparation of TiN ?lms by TCVD using TiBr4/H2/NH2 In the case of titanium metal deposition, We believe that the deposition involves the formation of a titanium hydride intermediate from the titanium tetraiodide, and that the intermediate dissociates to form titanium by eliminating either hydrogen or hydrogen iodide. The process as described in Example 1 Was essentially repeated, but the source precursor Was changed to titanium tetrabromide (TiBr4) instead of TiI4. The runs Were per 30 formed under processing conditions similar to those listed above for TiI4, except the temperature of the bubbler/ The folloWing examples are set forth as a means of sublimator 11 Was heated in this case to 100° C. during the illustrating the present invention and are not to be construed CVD process. All transport and delivery lines and high as a limitation thereon. EXAMPLE 1 ?oW controller 34 and associated isolation valve 35. Pro cessing pressure Was 0.2 torr. The resulting TiN ?lm Was metallic, continuous and gold-colored, and had properties typical of TiN ?lms accord ing to the invention, as previously described. the formation of titanium nitride. This is in signi?cant Which higher coordinate species must be involved in both transport and decomposition. See, e.g., R. T. CoWdell and G. P. A. FoWles, J. C. S. p. 2522, (1960). throughput during actual CVD runs. A high vacuum load lock system 32 Was used for transport and loading of 8“ Wafers into the reactor. Finally, a side line 33 Was employed to feed the ammonia (NH3) gas into the reactor. The NH3 How Was 425 liters/minute and Was controlled by the mass in a ?rst step to titanium triiodide and other loWer coordinate species, and that the reassociation of titanium With iodine is pump-based package Was used to ensure high vacuum base pressure in the reactor While the roots bloWer-based package vacuum isolation valves 17, 18, 19 and 20 Were maintained 35 Preparation of TiN ?lms by TCVD using TiI4/H2/NH3 Thermally promoted chemical vapor deposition (TCVD) at a temperature of 90° C., using a combination heating tape and associated poWer supply 22, to prevent precursor recon densation. The TiN ?lms produced by TCVD of TiBr4 Were again Was carried out With the reactor shoWn in FIG. 1, using TiI4 as the titanium source precursor. The tetraiodotitanium 40 (TiI4) precursor 10 Was placed in the bubbler/sublimator 11, and 11 Was heated by a combination of heating tape and an metallic, continuous, and gold colored. Analyses by x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), Rutherford backscattering (RBS), four-point probe, and cross-sectional SEM (CS-SEM), indicated that their structural, chemical, and electrical properties are equivalent to those produced by TCVD of TiI4 as in Example 1, except associated poWer supply 12, to 140° C. during the CVD process. A mass ?oW controller 13, Which can be isolated from the bubbler by a high vacuum valve 14, controlled a 45 for ?lm resistivity, Which Was 140 pQcm in this case. ?oW of 20 sccm hydrogen carrier gas 15 through feedthrough 16 into the bubbler. The mixture of precursor vapor and hydrogen carrier gas Was then transported through EXAMPLE 3 feedthrough 17, high vacuum isolation valves 18 and 19, and delivery line 20 into the CVD reactor 21. All transport and delivery lines and high vacuum isolation valves 17, 18, 19 Preparation of Ti ?lm by PPCVD using TiI4/H2/Ar The CVD reactor shoWn in FIG. 1 Was employed for the deposition of Ti by PPCVD. The tetraiodotitanium (TiI4) and 20 Were maintained at 120° C., using a combination precursor 10 Was placed in the bubbler/sublimator 11 Which Was heated by a combination heating tape and associated heating tape and associated poWer supply 22, to prevent precursor recondensation. poWer supply 12 to 140° C. during actual processing. Amass The reactor 21 Was a cold-Wall, stainless-steel CVD 55 ?oW controller 13, Which can be isolated from the bubbler reactor of siZe suf?cient to hold an 8“ Wafer. It Was equipped by a high vacuum valve 14, controlled a How of 28 sccm With a diode-type parallel plate-type plasma con?guration hydrogen carrier gas 15 through feedthrough 16 into the made of tWo electrodes 23 and 24. The upper plate 23 served as the active electrode and Was driven by the radio frequency (13.56 MHZ) poWer supply 25. It Was constructed in a “mesh” type pattern to alloW unrestricted reactant How to the substrate 26. The substrate (Wafer) 26 Was placed on the loWer, grounded plasma electrode 24, and Was heated to 425° C. by an 8“ boron nitride (BN)-encapsulated graphite heater 27. A bubbler. The mixture of precursor vapor and hydrogen hydrogen plasma Was used for in-situ pre-deposition sub strate cleaning at a plasma poWer density of 0.25 W/cm2, 60 65 carrier gas Was then transported through feedthrough 17, high vacuum isolation valves 18 and 19, and delivery line 20 into the CVD reactor 21. All transport and delivery lines and high vacuum isolation valves 17, 18, 19, and 20 Were maintained at temperatures in the range 120° to 160° C. using a combination heating tape and associated poWer supply 22, to prevent precursor recondensation. The reactor 21 Was equipped With a diode-type parallel plate-type plasma con?guration made of tWo electrodes 23 and 24. The 6,090,709 17 18 upper plate 23 served as the active electrode and Was driven by the radio frequency (13.56 MHZ) poWer supply 25. 4. The method according to claim 3, Wherein an inert gas selected from the group consisting of argon and xenon is In this case, plasma-promoted CVD (PPCVD) Was employed for the growth of Ti thin ?lms. Accordingly, a hydrogen plasma Was used for in situ pre-deposition sub strate cleaning at a plasma poWer density of about 0.25 W/cm2, While an argon plasma Was employed during actual deposition at a plasma poWer density of about 0.25 W/cm2. titanium metal ?lm. 5. The method according to claim 1, Wherein the source precursor is titanium tetraiodide vapor. 6. The method according to claim 1, Wherein a nitrogen containing gas is present in said chamber With said substrate and said vapor, and said chamber contains a plasma having The side line 33 Was employed to feed the argon gas into the reactor. The argon How of 500 liters/minute Was controlled by the mass ?oW controller 34 and associated isolation valve 35. The substrate (Wafer) 26 Was placed on additionally present in the chamber during deposition of the 10 7. The method according to claim 6, Wherein the nitrogen containing gas is selected from the group consisting of (a) hydrogen and at least one of nitrogen, ammonia or the loWer, grounded plasma electrode 24, and Was heated to 450° C. by an 8“ boron nitride (BN)-encapsulated graphite heater 27. The titanium metal ?lm thus produced Was metallic, continuous silver-colored and had physical and electrical 15 properties identical to those previously described for typical titanium metal ?lms made according to the invention. 20 EXAMPLE 4 The CVD reactor shoWn in FIG. 1 Was employed for the containing gas is hydrogen and nitrogen. 25 in-situ sequential deposition of a Ti/TiN bilayer from TiI4. The Ti layer Was ?rst groWn by the PPCVD described in Example 3. Then the plasma Was turned off and the auxiliary gas changed from argon to ammonia to form a TiN layer essentially as described in Example 1. ATiN layer Was thus groWn on top of the Ti layer to form a laminate bilayer. The changes could be made to the embodiments described above Without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modi?cations Within the spirit and scope of the present invention as de?ned by the appended claims. What is claimed is: 30 35 40 substrate is a microelectronics substrate. 14. The method according to claim 1, Wherein n in formula (I) is equal to Zero. 15. The method according to claim 1, Wherein the layers are deposited Without transfer of the substrate from the chamber so as to minimiZe contamination. 45 substrate and a source precursor into a CVD chamber, Wherein the source precursor is a vapor of at least one compound of formula (I): 50 Wherein m is 0—4 and n is 0—2; and sequentially depositing onto the substrate at a temperature of about 200—650° C. layers of titanium metal ?lm and titanium nitride ?lm, 55 least the titanium metal ?lm is deposited in the presence of a plasma, With hydrogen halides or ammonium halides being 16. A method for chemical vapor deposition (CVD) of a titanium metal ?lm onto a substrate, comprising introducing to a deposition chamber the folloWing components: (a) a microelectronics substrate; (b) a vapor of a compound having the formula (I): TiUMXBYm) (1) Wherein m is 0—4; and (c) at least one of a carrier gas and an auxiliary gas for said vapor; and maintaining the substrate at a temperature of about 200 to 650° C. in the presence of a plasma for a time suf?cient to deposit a titanium metal ?lm onto the substrate, With hydrogen halides or ammonium halides being major byproducts of the deposition. major byproducts of the deposition. 2. The method according to claim 1, Wherein a titanium metal ?lm is deposited onto a substrate to provide a coated substrate, and a titanium nitride ?lm is deposited onto the coated substrate. argon and xenon; and said substrate, said vapor, said ?rst gas and said second gas are reacted under thermal conditions in the absence of a plasma for a time suf?cient to deposit a titanium nitride ?lm onto the substrate. 11. The method according to claim 10, Wherein the ?rst gas is ammonia and the second gas is hydrogen. 12. The method according to claim 1, Wherein said 13. The method according to claim 12, Wherein said 1. A method for depositing multiple layers of titanium Wherein either the titanium metal ?lm or the titanium nitride ?lm may be deposited ?rst onto the substrate and Wherein at additionally contains a ?rst gas selected from the group consisting of ammonia and hydraZine; and a second gas substrate is silicon-containing. based ?lm onto a substrate by sequential chemical vapor deposition (CVD), comprising the steps of introducing a 10. The method according to claim 1, Wherein during deposition of titanium nitride ?lm the deposition chamber selected from the group consisting of hydrogen, nitrogen, Ti and TiN ?lms Were analyZed as described earlier and found to exhibit typical properties. It Will be appreciated by those skilled in the art that hydraZine; (b) nitrogen and at least one of ammonia, argon or xenon; and (c) ammonia and at least one of argon and xenon. 8. The method according to claim 6, Wherein the substrate is maintained at a temperature of about 350° C. to about 475° C. 9. The method according to claim 7, Wherein the nitrogen In-situ Sequential Preparation of Ti/TiN bilayers by PPCVD using TiI4/H2/Ar folloWed by TCVD using TiI4/H2/ NH3 a loW poWer density, for a time suf?cient to deposit a titanium nitride ?lm onto the substrate. 17. The method according to claim 16, Wherein the 60 substrate is maintained at a temperature of about 350° C. to about 475° C. 18. The method according to claim 16, Wherein the compound of formula (I) is titanium tetraiodide. 3. The method according to claim 1, Wherein hydrogen 19. The method according to claim 16, Wherein the gas is present in the chamber With said vapor and said substrate, and said chamber contains a plasma having a loW poWer density, for a time suf?cient to deposit a titanium metal ?lm onto the substrate. substrate is a silicon or silicon dioxide Wafer useful in the 65 manufacture of a ULSI device. 20. The method according to claim 16, Wherein the plasma has a loW poWer density. 6,090,709 19 20 providing a vapor of a compound containing TiI4; 21. A method for chemical vapor deposition (CVD) of a titanium nitride ?lm onto a substrate, comprising introduc ing to a deposition chamber the following components: (a) a microelectronics substrate; (b) a vapor of a compound having the formula: TiI4; and (c) at least one nitrogen-containing gas; and maintaining the substrate at a temperature of about 200 maintaining said silicon-containing substrate at a tem perature of about 200 to 650° for a selected period of time; and depositing on said sideWalls and said bottom Wall a substantially continuous titanium-based ?lm, With hydrogen iodides or ammonium iodides being major byproducts of the deposition. 27. The method according to claim 26, Wherein the step to 650° C. for a time sufficient to deposit a titanium nitride ?lm onto the substrate, With hydrogen iodides or ammonium iodides being major byproducts of the deposition. 22. The method according to claim 21, Wherein the nitrogen-containing gas is selected from the group consist ing of: (a) hydrogen and at least one of nitrogen and ammonia and at least one of argon and Xenon; (b) nitrogen and at least one of ammonia, argon and Xenon; and (c) ammonia and at least one of argon and Xenon. of maintaining said silicon containing substrate at a tem perature of about 200 to 650° C., includes the step of maintaining the silicon-containing substrate at a temperature of about 350 to 475° C. 15 23. The method according to claim 22, Wherein the nitrogen-containing gas is hydrogen and nitrogen. 24. The method according to claim 21, Wherein the deposition is carried out in the presence of a plasma. 25. The method according to claim 21, Wherein the 20 substrate is a silicon or silicon dioxide Wafer useful in the manufacture of ULSI devices. 26. Amethod for forming a conformal layer of a titanium containing compound, comprising the steps of providing a silicon-containing substrate having formed thereon a via having sideWalls and a bottom Wall, Wherein the sideWalls are spaced apart less than 0.1 microns; 25 28. The method according to claim 26, Wherein said step of depositing a substantially continuous titanium-based ?lm includes the step of forming a titanium-based ?lm having a thickness of betWeen about 50 angstroms and about 1500 anstroms. 29. The method according to claim 26, Wherein the step of providing a silicon-containing substrate includes the step of providing a substrate having formed thereon a via With an aspect ratio of betWeen about 3:1 and 6:1. 30. The method according to claim 21 Wherein the tem perature for maintaining the substrate is about 350—475° C.