Copper trace analysis using Transient Ion Drift (TID) combined with a Rapid Thermal Annealing (RT... more Copper trace analysis using Transient Ion Drift (TID) combined with a Rapid Thermal Annealing (RTA) process is investigated. A double pulse method is implemented to allow unambiguous identification of the copper-induced capacitance signal. Use of a mercury probe as sensing Schottky barrier enhances the flexibility of the method and allows mapping of the contaminant. The method is evaluated on quantitatively contaminated silicon wafers and compared to Total X-ray fluorescence (TXRF).It is shown that in Czochralski grown material, the RTA is sufficient to dissolve most copper atoms into interstitial sites independently of their initial configuration. As a result, both, the surface and bulk contamination can be monitored by RTA/TID with a bulk detection limit close to 1011cm-3.In Float Zone material mapping of the quenched interstitial copper revealed the existence of defect reactions involving presumably vacancy clusters.
Electrical measurements carried out on copper-diffused and quenched p-type silicon indicate that ... more Electrical measurements carried out on copper-diffused and quenched p-type silicon indicate that a large acceptor deactivation occurs throughout the material. The passivation stability, limited to subambient temperatures, is shown to be dopant dependent, thus confirming previous results. The measurements also provide information on the generation of Cu-related defects and copper behavior. One of the observed defects, labeled an M center, exhibits metastability. It is shown that this can be understood as a pairing mechanism between the M defect and free Cu atoms, with the pair being electrically inactive. Kinetic studies reveal a correlation between the dopant-copper binding energy and the M-Cu reaction. The available mobile copper ions result from dissociation of acceptor-copper pairs leading to a dopantdependent association frequency of the MCu; complex. On the basis of these results, certain recent data related to copper-defect reactions in silicon are reanalyzed. In particular, the so-called X-defect diffusion coefficient is reconsidered, taking into account the internal built-in electric field. The results support identification of the X defect as interstitial copper.
The behavior of iron in silicon during low-temperature annealing was studied. The influence of el... more The behavior of iron in silicon during low-temperature annealing was studied. The influence of electric fields on the underlying defect reactions is detailed. The depth profiles reveal Fe; outdiffusion and no precipitation in the bulk up to 470 K. In the presence of electric fields, the kinetics differ considerably and can be understood in terms of carrier-emission-limited iron drift. Consequences of this mechanism are discussed. The outdiffusion and drift data indicate a charge-state-dependent diffusion mechanism, in contrast to the generally accepted lack of any charge-state effect.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1996
ABSTRACT Cross-sectional Transmission Electron Microscopy (XTEM) and infrared (IR) absorption hav... more ABSTRACT Cross-sectional Transmission Electron Microscopy (XTEM) and infrared (IR) absorption have been used to study the morphology of silicon carbide (β-SiC) layers synthesized by 50 keV carbon implantation in silicon as a function of implantation temperature and dose. Particular attention was devoted to relate the IR parameters (strength of the 794 cm−1 absorption line, damping factor) to the XTEM observations. The evolution with dose is particularly discussed on two samples implanted at 700°C, respectively at 1018 and 2 × 1018 cm−2. The effect of post implantation annealing at 1200°C is also investigated on samples implanted at 600 and 900°C. The major feature of this study is the demonstration that silicon can accommodate a limited amount of implanted carbon to form a β-SiC phase.
The electronic properties of organic semiconductors depend strongly on the nature of the molecule... more The electronic properties of organic semiconductors depend strongly on the nature of the molecules, their conjugation and conformation, their mutual distance and the orientation between adjacent molecules. Variations of intramolecular distances and conformation disturb the conjugation and perturb the delocalization of charges. As a result, the mobility considerably decreases compared to that of a covalently well-organized crystal. Here, we present electrical characterization of large single crystals made of the regioregular octamer of 3-hexyl-thiophene (3HT)8 using a conductive-atomic force microscope (C-AFM) in air. We find a large anisotropy in the conduction with charge mobility values depending on the crystallographic orientation of the single crystal. The smaller conduction is in the direction of π-π stacking (along the long axis of the single crystal) with a mobility value in the order of 10(-3) cm(2) V(-1) s(-1), and the larger one is along the molecular axis (in the direction normal to the single crystal surface) with a mobility value in the order of 0.5 cm(2) V(-1) s(-1). The measured current-voltage (I-V) curves showed that along the molecular axis, the current followed an exponential dependence corresponding to an injection mode. In the π-π stacking direction, the current exhibits a space charge limited current (SCLC) behavior, which allows us to estimate the charge carrier mobility.
Abstract The diffusion barrier behaviour of 20 to 200 nm thin Ta(N,O) films in the Cu/Si contact ... more Abstract The diffusion barrier behaviour of 20 to 200 nm thin Ta(N,O) films in the Cu/Si contact system was evaluated by materials and transient ion drift analysis. Using high resolution transmission electron microscopy, grazing incidence X-ray diffractometry, Auger electron spectroscopy and secondary ion mass spectrometry depth profiling it was revealed that the as-deposited amorphous-like Ta(N,O) diffusion barriers tend to partially recrystallize after annealing at 1 h/500°C without any detectable diffusion and/or reaction of Cu and Si up to at least 1 h/600°C. By making use of the newly developed transient ion drift technique for trace element analysis down to 5 × 10 11 cm −3 of interstitially dissolved Cu in Si, an exponential decrease of the Cu concentration on the Ta(N,O) barrier thickness is observed.
The transient ion drift (TID) technique has been recently proposed for copper trace detection in ... more The transient ion drift (TID) technique has been recently proposed for copper trace detection in silicon. Cu atoms may be present either in the vicinity of the Si surface or within the volume. In the latter case they are either gathered at secondary defects or form precipitates believed to be silicides. In order to become detectable by TID Cu atoms must be put into the highly mobile interstitial state. Depending on the initial configuration of the Cu/Si system different physical mechanisms may enable Cu atoms to become 'TID active'. In this work we study the Cu activation process using rapid thermal processing (RTP) in an attempt to minimise the thermal budget required to achieve a complete activation. Both, surface and volume contaminated samples are investigated. During RTP treatments the activation of surface Cu atoms is found to proceed significantly faster than during standard furnace anneal. We tentatively attribute this behaviour to the UV light exposure associated with the RTP, which may enhance the release of copper atoms from the surface. The dissolution kinetics of the Cu precipitates occurring during RTPs are found to be only limited by Cu diffusion. The RTP/TID process is used to study the low temperature reaction path of supersaturated Cu. If prior to the RTP process, Cu atoms are chemically removed from the surface or near surface region, TID measures only the residual bulk Cu atoms. Our results show that out-diffusion and near-surface precipitation are reducing mostly the copper supersaturation.
... Res., 8 (1993) 535. [16] M. Born and K. Huang, in DH Wilkinson and W. Marshall (eds.), Dynami... more ... Res., 8 (1993) 535. [16] M. Born and K. Huang, in DH Wilkinson and W. Marshall (eds.), Dynamical Theory of Crystal Lattices, International Series of Monographs on Physics, Oxford University Press, Oxford, 1954. [17] E Durupt, Thesis, Lyon, 1983. [18] BW Berreman, Phys. ...
ABSTRACT A scanning minority‐carrier transient spectroscopy with optical injection and full trans... more ABSTRACT A scanning minority‐carrier transient spectroscopy with optical injection and full transient analysis is developed. The continuity equation is solved with adequate injection and boundary conditions in order to determine the optimum experimental conditions and the corresponding optimum spatial resolution. A numerical treatment is implemented which filters out the noise component of the transient, improving the sensitivity of the technique. It allows us to make a fit to the transient, to check its exponential character and to treat certain cases of nonexponential behavior. The technique is applied first to a step distribution of laser‐induced defects and results can be obtained which are in good agreement with theoretical predictions. Finally, the gettering of gold to dislocations during a rapid thermal annealing is illustrated using this technique.
ABSTRACT The kinetics of interstitial iron precipitation in p‐type silicon are investigated. Duri... more ABSTRACT The kinetics of interstitial iron precipitation in p‐type silicon are investigated. During annealing, the iron charge state is controlled by the applied reverse voltage and its effect on the precipitation is studied. We observe that iron in the neutral charge state (Fe0 i ) precipitates preferentially in three‐dimensional nucleation centers while Fe+ i vanishes in the dislocation lines (rod‐like nucleation centers). These centers are created during the fast cooling procedure necessary to dissolve iron in the silicon matrix.
ABSTRACT We use the transient ion drift in a depletion region of a Schottky barrier to determine ... more ABSTRACT We use the transient ion drift in a depletion region of a Schottky barrier to determine ion diffusivities at moderate temperatures. The pulsed reverse bias leads to temperature dependent capacitance transients similar to deep level carrier emission transients. A simple theoretical model together with classical transient signal analysis provide the means to extract the ion diffusion constant. When applied to copper in silicon, diffusion data are obtained in a not yet investigated temperature range (280–400 K) which agree well with both low and high temperature diffusion data.
Over the last decade, halogenated semiconducting polymers have attracted considerable interest du... more Over the last decade, halogenated semiconducting polymers have attracted considerable interest due to their outstanding optoelectronic properties. Thus, most today's OPV benchmark organic semiconductors are halogenated materials, either electron donor polymers or non-fullerene acceptor (NFA) small molecules. However, the nature and position of the substituted halogen atoms in halogenated semiconducting polymers impact, through self-assembly modification, on their optoelectronic properties in a way which is difficult to predict. Yet, the solid-state self-assembling of this materials has been shown to be a key parameter towards high charge transport properties and photovoltaic efficiencies. In this context, there is still a need to develop analytical methods that will enable an atomicscale structural characterization of these materials as function of the halogenation. In this manuscript, we explore the solid-state nuclear magnetic resonance (NMR) under magic angle spinning (MAS) as a tool to investigate the local structure and supramolecular organization of a series of conjugated polymers, specially designed for this study. Through a comprehensive study using complementary techniques including MAS-NMR, small and wideangle X-ray scattering (SWAXS) and molecular modelling investigations, we have definitely succeeded in determining the molecular conformation of these polymers in relation to their chemical composition.
Organic Electronics and Photonics: Fundamentals and Devices III
Organic semiconductor materials such as planar conjugated small molecules are of great interest t... more Organic semiconductor materials such as planar conjugated small molecules are of great interest to the photovoltaic community. In thin films, the exciton and charge carrier dynamics, which are crucial to photovoltaic device operation, depend in a non-trivial way on the organic molecular structure and on the molecular organization in the solid state. Recently, the exciton diffusion has been found to strongly depend on the crystalline order of the organic thin films. This work presents the study of the exciton lifetime in an innovative class of molecular semiconductors able to present different crystalline order. This family of molecules has a "dumbbell-shaped" structure based on triazatruxene units that act as a π-stacking platform. Such molecules with different side-chains have been found to self-assemble into various crystalline and liquid crystalline phases. We have studied the steady-state photoluminescence and the exciton lifetime for several triazatruxene-based derivatives with different side-chains, in solution and in thin films for different solid state phases. In solution, the fluorescence lifetime corresponds to the reference value that can be obtained without intermolecular interaction. In thin films, we measured the exciton lifetime for different molecular structures in order to correlate the exciton dynamics with the molecular stacking. The results reveal a significant increase in the exciton lifetime with the enhancement of the structural order.
We report the influence of positional isomerism on the electronic, photophysical, physical and ch... more We report the influence of positional isomerism on the electronic, photophysical, physical and charge transport properties of dispiroacridine-indacenobisthiophene positional isomers.
Most organic semiconductor materials dewet on silicon wafers with thermal oxide layers. While Siw... more Most organic semiconductor materials dewet on silicon wafers with thermal oxide layers. While Siwafers represent convenient substrates for building a field effect transistor (FET), dewetting largely destroys the possibility for obtaining a compact and continuous crystalline thin organic semiconductor film and thus limits the mobility in these systems. Using oligothiophenes, we present an approach where the initial dewetting process can be turned into an advantage for generating very thin but large crystalline domains of a size up to the millimetres with all molecules sharing a single orientation. Our approach can be easily extended to other molecules, which have strongly differing growth velocities in the various directions of the crystal, for example due to directional π-stacking interactions. FETs devices based on such large crystalline domains showed charge carrier mobilities that were two orders of magnitude higher compared to non-crystallized films.
Copper trace analysis using Transient Ion Drift (TID) combined with a Rapid Thermal Annealing (RT... more Copper trace analysis using Transient Ion Drift (TID) combined with a Rapid Thermal Annealing (RTA) process is investigated. A double pulse method is implemented to allow unambiguous identification of the copper-induced capacitance signal. Use of a mercury probe as sensing Schottky barrier enhances the flexibility of the method and allows mapping of the contaminant. The method is evaluated on quantitatively contaminated silicon wafers and compared to Total X-ray fluorescence (TXRF).It is shown that in Czochralski grown material, the RTA is sufficient to dissolve most copper atoms into interstitial sites independently of their initial configuration. As a result, both, the surface and bulk contamination can be monitored by RTA/TID with a bulk detection limit close to 1011cm-3.In Float Zone material mapping of the quenched interstitial copper revealed the existence of defect reactions involving presumably vacancy clusters.
Electrical measurements carried out on copper-diffused and quenched p-type silicon indicate that ... more Electrical measurements carried out on copper-diffused and quenched p-type silicon indicate that a large acceptor deactivation occurs throughout the material. The passivation stability, limited to subambient temperatures, is shown to be dopant dependent, thus confirming previous results. The measurements also provide information on the generation of Cu-related defects and copper behavior. One of the observed defects, labeled an M center, exhibits metastability. It is shown that this can be understood as a pairing mechanism between the M defect and free Cu atoms, with the pair being electrically inactive. Kinetic studies reveal a correlation between the dopant-copper binding energy and the M-Cu reaction. The available mobile copper ions result from dissociation of acceptor-copper pairs leading to a dopantdependent association frequency of the MCu; complex. On the basis of these results, certain recent data related to copper-defect reactions in silicon are reanalyzed. In particular, the so-called X-defect diffusion coefficient is reconsidered, taking into account the internal built-in electric field. The results support identification of the X defect as interstitial copper.
The behavior of iron in silicon during low-temperature annealing was studied. The influence of el... more The behavior of iron in silicon during low-temperature annealing was studied. The influence of electric fields on the underlying defect reactions is detailed. The depth profiles reveal Fe; outdiffusion and no precipitation in the bulk up to 470 K. In the presence of electric fields, the kinetics differ considerably and can be understood in terms of carrier-emission-limited iron drift. Consequences of this mechanism are discussed. The outdiffusion and drift data indicate a charge-state-dependent diffusion mechanism, in contrast to the generally accepted lack of any charge-state effect.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1996
ABSTRACT Cross-sectional Transmission Electron Microscopy (XTEM) and infrared (IR) absorption hav... more ABSTRACT Cross-sectional Transmission Electron Microscopy (XTEM) and infrared (IR) absorption have been used to study the morphology of silicon carbide (β-SiC) layers synthesized by 50 keV carbon implantation in silicon as a function of implantation temperature and dose. Particular attention was devoted to relate the IR parameters (strength of the 794 cm−1 absorption line, damping factor) to the XTEM observations. The evolution with dose is particularly discussed on two samples implanted at 700°C, respectively at 1018 and 2 × 1018 cm−2. The effect of post implantation annealing at 1200°C is also investigated on samples implanted at 600 and 900°C. The major feature of this study is the demonstration that silicon can accommodate a limited amount of implanted carbon to form a β-SiC phase.
The electronic properties of organic semiconductors depend strongly on the nature of the molecule... more The electronic properties of organic semiconductors depend strongly on the nature of the molecules, their conjugation and conformation, their mutual distance and the orientation between adjacent molecules. Variations of intramolecular distances and conformation disturb the conjugation and perturb the delocalization of charges. As a result, the mobility considerably decreases compared to that of a covalently well-organized crystal. Here, we present electrical characterization of large single crystals made of the regioregular octamer of 3-hexyl-thiophene (3HT)8 using a conductive-atomic force microscope (C-AFM) in air. We find a large anisotropy in the conduction with charge mobility values depending on the crystallographic orientation of the single crystal. The smaller conduction is in the direction of π-π stacking (along the long axis of the single crystal) with a mobility value in the order of 10(-3) cm(2) V(-1) s(-1), and the larger one is along the molecular axis (in the direction normal to the single crystal surface) with a mobility value in the order of 0.5 cm(2) V(-1) s(-1). The measured current-voltage (I-V) curves showed that along the molecular axis, the current followed an exponential dependence corresponding to an injection mode. In the π-π stacking direction, the current exhibits a space charge limited current (SCLC) behavior, which allows us to estimate the charge carrier mobility.
Abstract The diffusion barrier behaviour of 20 to 200 nm thin Ta(N,O) films in the Cu/Si contact ... more Abstract The diffusion barrier behaviour of 20 to 200 nm thin Ta(N,O) films in the Cu/Si contact system was evaluated by materials and transient ion drift analysis. Using high resolution transmission electron microscopy, grazing incidence X-ray diffractometry, Auger electron spectroscopy and secondary ion mass spectrometry depth profiling it was revealed that the as-deposited amorphous-like Ta(N,O) diffusion barriers tend to partially recrystallize after annealing at 1 h/500°C without any detectable diffusion and/or reaction of Cu and Si up to at least 1 h/600°C. By making use of the newly developed transient ion drift technique for trace element analysis down to 5 × 10 11 cm −3 of interstitially dissolved Cu in Si, an exponential decrease of the Cu concentration on the Ta(N,O) barrier thickness is observed.
The transient ion drift (TID) technique has been recently proposed for copper trace detection in ... more The transient ion drift (TID) technique has been recently proposed for copper trace detection in silicon. Cu atoms may be present either in the vicinity of the Si surface or within the volume. In the latter case they are either gathered at secondary defects or form precipitates believed to be silicides. In order to become detectable by TID Cu atoms must be put into the highly mobile interstitial state. Depending on the initial configuration of the Cu/Si system different physical mechanisms may enable Cu atoms to become 'TID active'. In this work we study the Cu activation process using rapid thermal processing (RTP) in an attempt to minimise the thermal budget required to achieve a complete activation. Both, surface and volume contaminated samples are investigated. During RTP treatments the activation of surface Cu atoms is found to proceed significantly faster than during standard furnace anneal. We tentatively attribute this behaviour to the UV light exposure associated with the RTP, which may enhance the release of copper atoms from the surface. The dissolution kinetics of the Cu precipitates occurring during RTPs are found to be only limited by Cu diffusion. The RTP/TID process is used to study the low temperature reaction path of supersaturated Cu. If prior to the RTP process, Cu atoms are chemically removed from the surface or near surface region, TID measures only the residual bulk Cu atoms. Our results show that out-diffusion and near-surface precipitation are reducing mostly the copper supersaturation.
... Res., 8 (1993) 535. [16] M. Born and K. Huang, in DH Wilkinson and W. Marshall (eds.), Dynami... more ... Res., 8 (1993) 535. [16] M. Born and K. Huang, in DH Wilkinson and W. Marshall (eds.), Dynamical Theory of Crystal Lattices, International Series of Monographs on Physics, Oxford University Press, Oxford, 1954. [17] E Durupt, Thesis, Lyon, 1983. [18] BW Berreman, Phys. ...
ABSTRACT A scanning minority‐carrier transient spectroscopy with optical injection and full trans... more ABSTRACT A scanning minority‐carrier transient spectroscopy with optical injection and full transient analysis is developed. The continuity equation is solved with adequate injection and boundary conditions in order to determine the optimum experimental conditions and the corresponding optimum spatial resolution. A numerical treatment is implemented which filters out the noise component of the transient, improving the sensitivity of the technique. It allows us to make a fit to the transient, to check its exponential character and to treat certain cases of nonexponential behavior. The technique is applied first to a step distribution of laser‐induced defects and results can be obtained which are in good agreement with theoretical predictions. Finally, the gettering of gold to dislocations during a rapid thermal annealing is illustrated using this technique.
ABSTRACT The kinetics of interstitial iron precipitation in p‐type silicon are investigated. Duri... more ABSTRACT The kinetics of interstitial iron precipitation in p‐type silicon are investigated. During annealing, the iron charge state is controlled by the applied reverse voltage and its effect on the precipitation is studied. We observe that iron in the neutral charge state (Fe0 i ) precipitates preferentially in three‐dimensional nucleation centers while Fe+ i vanishes in the dislocation lines (rod‐like nucleation centers). These centers are created during the fast cooling procedure necessary to dissolve iron in the silicon matrix.
ABSTRACT We use the transient ion drift in a depletion region of a Schottky barrier to determine ... more ABSTRACT We use the transient ion drift in a depletion region of a Schottky barrier to determine ion diffusivities at moderate temperatures. The pulsed reverse bias leads to temperature dependent capacitance transients similar to deep level carrier emission transients. A simple theoretical model together with classical transient signal analysis provide the means to extract the ion diffusion constant. When applied to copper in silicon, diffusion data are obtained in a not yet investigated temperature range (280–400 K) which agree well with both low and high temperature diffusion data.
Over the last decade, halogenated semiconducting polymers have attracted considerable interest du... more Over the last decade, halogenated semiconducting polymers have attracted considerable interest due to their outstanding optoelectronic properties. Thus, most today's OPV benchmark organic semiconductors are halogenated materials, either electron donor polymers or non-fullerene acceptor (NFA) small molecules. However, the nature and position of the substituted halogen atoms in halogenated semiconducting polymers impact, through self-assembly modification, on their optoelectronic properties in a way which is difficult to predict. Yet, the solid-state self-assembling of this materials has been shown to be a key parameter towards high charge transport properties and photovoltaic efficiencies. In this context, there is still a need to develop analytical methods that will enable an atomicscale structural characterization of these materials as function of the halogenation. In this manuscript, we explore the solid-state nuclear magnetic resonance (NMR) under magic angle spinning (MAS) as a tool to investigate the local structure and supramolecular organization of a series of conjugated polymers, specially designed for this study. Through a comprehensive study using complementary techniques including MAS-NMR, small and wideangle X-ray scattering (SWAXS) and molecular modelling investigations, we have definitely succeeded in determining the molecular conformation of these polymers in relation to their chemical composition.
Organic Electronics and Photonics: Fundamentals and Devices III
Organic semiconductor materials such as planar conjugated small molecules are of great interest t... more Organic semiconductor materials such as planar conjugated small molecules are of great interest to the photovoltaic community. In thin films, the exciton and charge carrier dynamics, which are crucial to photovoltaic device operation, depend in a non-trivial way on the organic molecular structure and on the molecular organization in the solid state. Recently, the exciton diffusion has been found to strongly depend on the crystalline order of the organic thin films. This work presents the study of the exciton lifetime in an innovative class of molecular semiconductors able to present different crystalline order. This family of molecules has a "dumbbell-shaped" structure based on triazatruxene units that act as a π-stacking platform. Such molecules with different side-chains have been found to self-assemble into various crystalline and liquid crystalline phases. We have studied the steady-state photoluminescence and the exciton lifetime for several triazatruxene-based derivatives with different side-chains, in solution and in thin films for different solid state phases. In solution, the fluorescence lifetime corresponds to the reference value that can be obtained without intermolecular interaction. In thin films, we measured the exciton lifetime for different molecular structures in order to correlate the exciton dynamics with the molecular stacking. The results reveal a significant increase in the exciton lifetime with the enhancement of the structural order.
We report the influence of positional isomerism on the electronic, photophysical, physical and ch... more We report the influence of positional isomerism on the electronic, photophysical, physical and charge transport properties of dispiroacridine-indacenobisthiophene positional isomers.
Most organic semiconductor materials dewet on silicon wafers with thermal oxide layers. While Siw... more Most organic semiconductor materials dewet on silicon wafers with thermal oxide layers. While Siwafers represent convenient substrates for building a field effect transistor (FET), dewetting largely destroys the possibility for obtaining a compact and continuous crystalline thin organic semiconductor film and thus limits the mobility in these systems. Using oligothiophenes, we present an approach where the initial dewetting process can be turned into an advantage for generating very thin but large crystalline domains of a size up to the millimetres with all molecules sharing a single orientation. Our approach can be easily extended to other molecules, which have strongly differing growth velocities in the various directions of the crystal, for example due to directional π-stacking interactions. FETs devices based on such large crystalline domains showed charge carrier mobilities that were two orders of magnitude higher compared to non-crystallized films.
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Papers by Thomas Heiser