- Email: [email protected]
Effect of high-temperature H2-anneals on the slow-trapping instability of MOS structures
566
World Abstracts on Microelectronics and Reliability
A case for large Auger recombination cross sections associated with deep centers in semiconductors. M. JAROS. Solid St. Commun. 25, 1071 (1978). It is argued that the recent quantitative results concerning localized defects in semiconductors (e.g. GaAs) are consistent with the possibility of large Auger-type cross sections associated with recombination at these centers. It is proposed that many of the capture cross sections reported to be in the range 10 ~3 10 ~~' cm 2, which exhibit only weak temperature dependence, and which do not depend on carrier concentration, might be explained by this mechanism. Hydrogen states in amorphous Gc. F. C. CHOO and B. Y. TONG. Solid St. Commun. 25, 385 (1978). The removal of dangling bond states from the energy gaps of tetrahedrally bonded a m o r p h o u s semiconductor is not the only effect when hydrogen is introduced. In addition to the bonding states deep in the valence band, we found that there are anti-bonding states appearing in the conduction band and near the bottom of the conduction band and, in some cases, even in the gap, as first conjectured by Paul et al. These latter states affect transport properties significantly as observed in photoconductivity. The one-lump Linviil model of a semiconductor region with arbitrary doping profile and recombination. Application for a model of lateral transistor. GVULA PASZTOR. Solid-St. Electron. 21,449 (1978). The current space-dependent due to recombination, and likewise the concentration of minority carriers exceeding equilibrium can be described as function series in a particular case when the carrier concentration is zero at one boundary of the examined region. By superimposing two series where this requirement is fulfilled at the two opposite boundaries, the general solutions of current and the minority carrier concentration are demonstrated. Using the general solution of the current, the one-lump Linvill model of a region with arbitrary doping profile is determined. As an example of this method, the one-lump model of the p-n-p lateral transistor was developed. By calculating the currents in the model arms, the d.c. current gain, the frequency limit f~ and I ..... are determined. EPR spectra of heat-treatment centers in oxygen-rich silicon. S. H. MULLER,M. SPRENGER, E. G. SIEVERTS and C. A. J. AMMERLAAN. Solid St. Commun. 25, 987 (1978). After heattreatment of oxygen-rich silicon at 410-550°C ten different EPR spectra were observed. Nine of these are new spectra, seven of them reveal 2 m m symmetry for the corresponding heat-treatment center, thereby reducing considerably the number of possible atomic configurations. In some cases the number of paramagnetic centers could account for the observed changes in carrier concentration. On the interpretation of electrical measurements on the G a A s - M O S system. E. KOHN and H. L. HARTNAGEL. Solid St. Electron. 21,409 (1978). Detailed evidence is presented which shows that previously published analyses of various investigations regarding the electrical characteristics of the GaAs M O S system lead to incorrect conclusions. Primarily the results were interpreted in terms of models which were developed to fit the Si-SiO2 interface properties. However, detailed I V and admittance measurements show that there are basic differences between the two systems, as the one with GaAs exhibits a charge injection p h e n o m e n o n across the interface barrier, oxide conduction and a complicated tup to now insufficiently understood) interface behaviour. All these effects prevent the determination of interface state densities by conventional methods. The conclusion, that simply because of a high density of interface states neither accumulation nor inversion are possible, is not justified.
Energy and momentum relaxation of charge carriers in Ge and Si under uniaxial stress. M. SWEtD, K. HESS and K SEEGER. J. Phy.s. Chem. Solids 39, 393 {1978). Measurements of the piezoresistance and the energy relaxation lime 7, in Ge and Si under uniaxial stress up to 4 kb are reported in the temperature range 30 K < T < 300 K. The measuremenls of r~ have been performed in the warm carrier range using the harmonic mixing technique. The experimental results for the piezoresistance and energy relaxation time in n-type material can roughly be understood in terms of carrier redistribution m the conduction band wflleys whose degeneracy is lifted by the stress. Information is obtained from these measurements about the relative strength of ! and ~/ type intervalley scattering in n-St: we lind nearly equal coupling strength for both scattering types. For the p-type material the experiments show convincingly that the main effect of stress on transport quantities is also caused b~ the lifted degeneracy of the heavy and light hole bands, as predicted already by Adams, and by Pikus and Bit. The nonlinear dependence of the piezoresistance and r on the stress can very well be explained by approximating the heavy and light hole bands as spherical and parabolical and using the deformation potential constant b as a parameter. The value of >~2 eV obtained for Jhl is in good agreemenl with curlier results for p-Ge. A contribution to the current gain temperature dependence of bipolar transistors. H.-M. REIN, H. v. ROHR and P WENNEKFRS. Solid-St. Electron. 21,439 (1978). In this paper it is demonstrated by a simple calculation that the temperatare dependence of current gain may be signilicantly influenced by both the different freeze-out rates of mobile carriers in emitter and base and the different temperature dependences of mobilities in these two regions. These effects can considerably reduce the decrease of current gain towards low temperatures, caused by the effective bandgap difference between the emitter and base region. Determination of surface state density from gm ti~ characteristics of MOSFETs. H KATrO and S. MUm~XMArSt Solid-St. Electrml. 21,459 (1978). The ,qm V,~characteristics of a M O S F E T measured at the room temperature in the transition region between the normal and the low level current regions are compared with the theoretical curve to obtain the surface state density, pss, within a small surface potential interval near the threshold voltage. It is further shown theoretically that the peak wdue of #,,, ~/,,,o, reduces against the increase of psx by the factor 1/11 + ~t*sx) where ;, is a constant, and good agreement is obtained between theory and experiment by using the devices in which surface states are produced by the RE sputter coating with SiO> The gate voltage corresponding to ~/,,o or ~1,.o/10 is shown to be linearly dependent on pss, but the gate voltage shift is considerably small at the lower current level, indicating ihe surface stale density increasing sharply towards the \alcnce band edge. Effect of high-temperature H2-anneals on the slow-trapping instability of M O S structures, A. K. SINHA, H. J. LEVINS]'EIN, L. P. ADDA, E. N. FULS and E. 1. Povlt,ONlS. Solid-St. ElectrmL 21,531 (t978). It is shown that the slow-trapping instability upon negative bias-temperature aging of MOS structures (poly-Si and Al-gate) can be significantly reduced by it high temperature (800-900'C) H2-anneal prior to AI metallization. Additional data are presented on the effects of high (700 900'C) and low temperature (450 CI [t2 annealing of MOS structures containing u-{l 1 l) St, dry HCI oxideand B-doped poly-Si. The midgap N~ (range: 8 × II,)I1 to 1.5 × 101°crn 2eV i) is reduced by both high and low temperature H2 anneals whereas the Q~ (range: 7 < I() ~ to I x 10 j ~ cm a eV ~) is reduced mainly by the high-temperarare H2-anneals. Presence of B near the interface is believed to cause an abnormal vohage asymmetry of the sloxx-
World Abstracts on Microelectronics and Reliability trapping drift, i.e. A VF~(- BT) < A VF~(+ BT). These effects are discussed in the light of Deal's model of the structure of the Si/SiO2 interface.
Influence of Se atoms on the properties of amorphous Ge. M. KUMEDA. M. ISHIKAWA, M. SUZUKI and T. SHIMIZU. Solid St. Commun. 25, 933 (1978). Electron spin resonance (ESR), electrical and optical measurements have been made for Gel .~Sex(0 =
8. T H I C K -
AND
THIN-FILM AND
567
heavy electron hybrid mode and thus produces hybridhybrid interaction. The diffusion-incorporated dispersion relation has been derived, taking into account the appropriate scattering mechanisms at 300°K. It is analysed to look for instability for real k and complex ¢~ (= ~o~ + i~t)i). One of the modes becomes unstable and propagates with a phase velocity equal to the transverse drift velocity of the light electrons. Instability is possible in the range of the magnetic field 2.5 < Bo < 6.0Tesla. The instability is observed only for small values of k. At large k the modes are damped, even at comparatively lower values of Bo.
Resistivity measurement of thin doped semiconductor layers by means of four point-contacts arbitrarily spaced on a circumference of arbitrary radius. EGBERT HESSE. Solid-St. Electron. 21, 637 (1978). The resistivity of a thin doped semiconductor layer or wafer measured in the vicinity of four point contacts placed on the semiconductor surface is shown to be independent of the relative distance between the contacts, provided the contacts are located on a circumference, and the distance to the boundary of the surface will not fall short of the greatest actual spacing between contacts. This method combines the advantage of the four probe resistivity measurement originally proposed by Valdes, that is the determination of p in a restricted layer region, with the advantage of arbitrary spacing of the probes, which characterizes van der Pauw's method. Experiments are in agreement with results obtained by the measuring methods of Valdbs and van der Pauw. Recombination-generation currents in degenerate semiconductors. OLDWIG VON ROBS. Solid-St. Electron. 21, 633 (1978). The classical Shockley-Read-Hall theory of free carrier recombination and generation via traps is extended to degenerate semiconductors. A concise and simple expression is found which avoids completely the concept of a Fermi level, a concept which is alien to non-equilibrium situations. Assumptions made in deriving the recombination generation current are carefully delineated and are found to be basically identical to those made in the original theory applicable to nondegencrate semiconductors.
COMPONENTS,
HYBRID
CIRCUITS
MATERIALS
The development of precision thin film resistors for submerged repeater applications. D. O. SeILLER. Electrocomp. Sci. Technol. 5, 9 (1978). The paper describes development of a low inductance thin film resistor series with a stability of +0.15% change in resistance, over a 25 year life, in a submerged repeater environment. (40% RH maximum and 0 to 30°C ambient temperature.) It was first necessary to establish an appropriate mathematical model relating resistor stability with time and temperature. This was devised from experimental data based on measured resistor drift at various temperatures, and enabled acceleration of resistor drift to be carried out to ensure that each resistor possessed the required stability. Deposition of a secondary nichrome layer protects the gold/nichrome interface and promotes SiO2 adhesion, This results in an improvement in the basic elevated temperature resistor stability by minimising diffusion effects of nichrome into the conductor, and protection against electrochemical corrosion as demonstrated by 10,000 hours life test at 83°; RH at 28°C on 5 mW load and by elevated temperature tests under electrical loading. Hybrid realisation of high precision analog conversion modules. L. KUN. Electrocomp. Sci. Technol. 5, 49 (1978). High precision analog modules are manufactured using film
technologies. Components which are critical as regards operation and stability are made by thin film technology, additional elements and interconnection of active components are made using thick film technology. Using these two separate manufacturing methods to obtain high stability and accuracy, optimum cost and yield can be achieved. To illustrate these facts, two circuits are discussed in detail, a voltage to frequency converter and a log amplifier.
A thick film base metal resistor and compatible hybrid system. F. E. BUZAN, J. D. GRIER, SR, B. E. BERTSCH and H. THORYK. Electrocomp. Sci. Technol. 5, 15 (1978). Nonnoble metal thick film materials have been the topic of several recent papers. This paper will focus on the first non-noble metal thick film system comprising conductors, dielectrics and most important, resistors for commercial use. Processing and performance data are presented in detail to illustrate the capabilities of these new materials. Circuit applications information is presented wherever possible. This new class of materials will enable the microelectronics industry to exploit new market opportunities previously unavailable due to the high costs of precious metal materials.
World Abstracts on Microelectronics and Reliability
A case for large Auger recombination cross sections associated with deep centers in semiconductors. M. JAROS. Solid St. Commun. 25, 1071 (1978). It is argued that the recent quantitative results concerning localized defects in semiconductors (e.g. GaAs) are consistent with the possibility of large Auger-type cross sections associated with recombination at these centers. It is proposed that many of the capture cross sections reported to be in the range 10 ~3 10 ~~' cm 2, which exhibit only weak temperature dependence, and which do not depend on carrier concentration, might be explained by this mechanism. Hydrogen states in amorphous Gc. F. C. CHOO and B. Y. TONG. Solid St. Commun. 25, 385 (1978). The removal of dangling bond states from the energy gaps of tetrahedrally bonded a m o r p h o u s semiconductor is not the only effect when hydrogen is introduced. In addition to the bonding states deep in the valence band, we found that there are anti-bonding states appearing in the conduction band and near the bottom of the conduction band and, in some cases, even in the gap, as first conjectured by Paul et al. These latter states affect transport properties significantly as observed in photoconductivity. The one-lump Linviil model of a semiconductor region with arbitrary doping profile and recombination. Application for a model of lateral transistor. GVULA PASZTOR. Solid-St. Electron. 21,449 (1978). The current space-dependent due to recombination, and likewise the concentration of minority carriers exceeding equilibrium can be described as function series in a particular case when the carrier concentration is zero at one boundary of the examined region. By superimposing two series where this requirement is fulfilled at the two opposite boundaries, the general solutions of current and the minority carrier concentration are demonstrated. Using the general solution of the current, the one-lump Linvill model of a region with arbitrary doping profile is determined. As an example of this method, the one-lump model of the p-n-p lateral transistor was developed. By calculating the currents in the model arms, the d.c. current gain, the frequency limit f~ and I ..... are determined. EPR spectra of heat-treatment centers in oxygen-rich silicon. S. H. MULLER,M. SPRENGER, E. G. SIEVERTS and C. A. J. AMMERLAAN. Solid St. Commun. 25, 987 (1978). After heattreatment of oxygen-rich silicon at 410-550°C ten different EPR spectra were observed. Nine of these are new spectra, seven of them reveal 2 m m symmetry for the corresponding heat-treatment center, thereby reducing considerably the number of possible atomic configurations. In some cases the number of paramagnetic centers could account for the observed changes in carrier concentration. On the interpretation of electrical measurements on the G a A s - M O S system. E. KOHN and H. L. HARTNAGEL. Solid St. Electron. 21,409 (1978). Detailed evidence is presented which shows that previously published analyses of various investigations regarding the electrical characteristics of the GaAs M O S system lead to incorrect conclusions. Primarily the results were interpreted in terms of models which were developed to fit the Si-SiO2 interface properties. However, detailed I V and admittance measurements show that there are basic differences between the two systems, as the one with GaAs exhibits a charge injection p h e n o m e n o n across the interface barrier, oxide conduction and a complicated tup to now insufficiently understood) interface behaviour. All these effects prevent the determination of interface state densities by conventional methods. The conclusion, that simply because of a high density of interface states neither accumulation nor inversion are possible, is not justified.
Energy and momentum relaxation of charge carriers in Ge and Si under uniaxial stress. M. SWEtD, K. HESS and K SEEGER. J. Phy.s. Chem. Solids 39, 393 {1978). Measurements of the piezoresistance and the energy relaxation lime 7, in Ge and Si under uniaxial stress up to 4 kb are reported in the temperature range 30 K < T < 300 K. The measuremenls of r~ have been performed in the warm carrier range using the harmonic mixing technique. The experimental results for the piezoresistance and energy relaxation time in n-type material can roughly be understood in terms of carrier redistribution m the conduction band wflleys whose degeneracy is lifted by the stress. Information is obtained from these measurements about the relative strength of ! and ~/ type intervalley scattering in n-St: we lind nearly equal coupling strength for both scattering types. For the p-type material the experiments show convincingly that the main effect of stress on transport quantities is also caused b~ the lifted degeneracy of the heavy and light hole bands, as predicted already by Adams, and by Pikus and Bit. The nonlinear dependence of the piezoresistance and r on the stress can very well be explained by approximating the heavy and light hole bands as spherical and parabolical and using the deformation potential constant b as a parameter. The value of >~2 eV obtained for Jhl is in good agreemenl with curlier results for p-Ge. A contribution to the current gain temperature dependence of bipolar transistors. H.-M. REIN, H. v. ROHR and P WENNEKFRS. Solid-St. Electron. 21,439 (1978). In this paper it is demonstrated by a simple calculation that the temperatare dependence of current gain may be signilicantly influenced by both the different freeze-out rates of mobile carriers in emitter and base and the different temperature dependences of mobilities in these two regions. These effects can considerably reduce the decrease of current gain towards low temperatures, caused by the effective bandgap difference between the emitter and base region. Determination of surface state density from gm ti~ characteristics of MOSFETs. H KATrO and S. MUm~XMArSt Solid-St. Electrml. 21,459 (1978). The ,qm V,~characteristics of a M O S F E T measured at the room temperature in the transition region between the normal and the low level current regions are compared with the theoretical curve to obtain the surface state density, pss, within a small surface potential interval near the threshold voltage. It is further shown theoretically that the peak wdue of #,,, ~/,,,o, reduces against the increase of psx by the factor 1/11 + ~t*sx) where ;, is a constant, and good agreement is obtained between theory and experiment by using the devices in which surface states are produced by the RE sputter coating with SiO> The gate voltage corresponding to ~/,,o or ~1,.o/10 is shown to be linearly dependent on pss, but the gate voltage shift is considerably small at the lower current level, indicating ihe surface stale density increasing sharply towards the \alcnce band edge. Effect of high-temperature H2-anneals on the slow-trapping instability of M O S structures, A. K. SINHA, H. J. LEVINS]'EIN, L. P. ADDA, E. N. FULS and E. 1. Povlt,ONlS. Solid-St. ElectrmL 21,531 (t978). It is shown that the slow-trapping instability upon negative bias-temperature aging of MOS structures (poly-Si and Al-gate) can be significantly reduced by it high temperature (800-900'C) H2-anneal prior to AI metallization. Additional data are presented on the effects of high (700 900'C) and low temperature (450 CI [t2 annealing of MOS structures containing u-{l 1 l) St, dry HCI oxideand B-doped poly-Si. The midgap N~ (range: 8 × II,)I1 to 1.5 × 101°crn 2eV i) is reduced by both high and low temperature H2 anneals whereas the Q~ (range: 7 < I() ~ to I x 10 j ~ cm a eV ~) is reduced mainly by the high-temperarare H2-anneals. Presence of B near the interface is believed to cause an abnormal vohage asymmetry of the sloxx-
World Abstracts on Microelectronics and Reliability trapping drift, i.e. A VF~(- BT) < A VF~(+ BT). These effects are discussed in the light of Deal's model of the structure of the Si/SiO2 interface.
Influence of Se atoms on the properties of amorphous Ge. M. KUMEDA. M. ISHIKAWA, M. SUZUKI and T. SHIMIZU. Solid St. Commun. 25, 933 (1978). Electron spin resonance (ESR), electrical and optical measurements have been made for Gel .~Sex(0 =
8. T H I C K -
AND
THIN-FILM AND
567
heavy electron hybrid mode and thus produces hybridhybrid interaction. The diffusion-incorporated dispersion relation has been derived, taking into account the appropriate scattering mechanisms at 300°K. It is analysed to look for instability for real k and complex ¢~ (= ~o~ + i~t)i). One of the modes becomes unstable and propagates with a phase velocity equal to the transverse drift velocity of the light electrons. Instability is possible in the range of the magnetic field 2.5 < Bo < 6.0Tesla. The instability is observed only for small values of k. At large k the modes are damped, even at comparatively lower values of Bo.
Resistivity measurement of thin doped semiconductor layers by means of four point-contacts arbitrarily spaced on a circumference of arbitrary radius. EGBERT HESSE. Solid-St. Electron. 21, 637 (1978). The resistivity of a thin doped semiconductor layer or wafer measured in the vicinity of four point contacts placed on the semiconductor surface is shown to be independent of the relative distance between the contacts, provided the contacts are located on a circumference, and the distance to the boundary of the surface will not fall short of the greatest actual spacing between contacts. This method combines the advantage of the four probe resistivity measurement originally proposed by Valdes, that is the determination of p in a restricted layer region, with the advantage of arbitrary spacing of the probes, which characterizes van der Pauw's method. Experiments are in agreement with results obtained by the measuring methods of Valdbs and van der Pauw. Recombination-generation currents in degenerate semiconductors. OLDWIG VON ROBS. Solid-St. Electron. 21, 633 (1978). The classical Shockley-Read-Hall theory of free carrier recombination and generation via traps is extended to degenerate semiconductors. A concise and simple expression is found which avoids completely the concept of a Fermi level, a concept which is alien to non-equilibrium situations. Assumptions made in deriving the recombination generation current are carefully delineated and are found to be basically identical to those made in the original theory applicable to nondegencrate semiconductors.
COMPONENTS,
HYBRID
CIRCUITS
MATERIALS
The development of precision thin film resistors for submerged repeater applications. D. O. SeILLER. Electrocomp. Sci. Technol. 5, 9 (1978). The paper describes development of a low inductance thin film resistor series with a stability of +0.15% change in resistance, over a 25 year life, in a submerged repeater environment. (40% RH maximum and 0 to 30°C ambient temperature.) It was first necessary to establish an appropriate mathematical model relating resistor stability with time and temperature. This was devised from experimental data based on measured resistor drift at various temperatures, and enabled acceleration of resistor drift to be carried out to ensure that each resistor possessed the required stability. Deposition of a secondary nichrome layer protects the gold/nichrome interface and promotes SiO2 adhesion, This results in an improvement in the basic elevated temperature resistor stability by minimising diffusion effects of nichrome into the conductor, and protection against electrochemical corrosion as demonstrated by 10,000 hours life test at 83°; RH at 28°C on 5 mW load and by elevated temperature tests under electrical loading. Hybrid realisation of high precision analog conversion modules. L. KUN. Electrocomp. Sci. Technol. 5, 49 (1978). High precision analog modules are manufactured using film
technologies. Components which are critical as regards operation and stability are made by thin film technology, additional elements and interconnection of active components are made using thick film technology. Using these two separate manufacturing methods to obtain high stability and accuracy, optimum cost and yield can be achieved. To illustrate these facts, two circuits are discussed in detail, a voltage to frequency converter and a log amplifier.
A thick film base metal resistor and compatible hybrid system. F. E. BUZAN, J. D. GRIER, SR, B. E. BERTSCH and H. THORYK. Electrocomp. Sci. Technol. 5, 15 (1978). Nonnoble metal thick film materials have been the topic of several recent papers. This paper will focus on the first non-noble metal thick film system comprising conductors, dielectrics and most important, resistors for commercial use. Processing and performance data are presented in detail to illustrate the capabilities of these new materials. Circuit applications information is presented wherever possible. This new class of materials will enable the microelectronics industry to exploit new market opportunities previously unavailable due to the high costs of precious metal materials.