- Email: [email protected]
Shallow doping in silicon
World Abstracts on Microelectronics and Reliability
819
understanding of some semiconductor surface reconstructions is given. These include the G a A s ( l l 0 ) surface and the (100) and (111) surfaces of Si and Ge. The strong correlation between atomic and electronic structure and the energies involved in structural rearrangements at the surface are discussed.
agreement is a substantial improvement by factors of 2 - 4 over the results of earlier theories such as first order Born and nondegenerate theories. The results of this work, particularly the inequality of minority and majority carrier mobilities, have implications for the modelling of both bipolar and field effect transistors.
Photoionization of impurity atoms in semiconductors in the presence of an applied electric field. D. D. COON and R. P. G. KARUNASIRI. Solid-St. Electron. 26 (12), 1151 (1983). An analytic expression for the photoionization cross-section of an impurity atom in an applied field is derived for photon energies below the zero-field photoionization threshold. The use of a q u a n t u m defect wave function for the impurity ground state permits impurity atoms to be conveniently characterized in terms of known ground state energies. The C o u l o m b Green's function and the W K B approximation in parabolic coordinates are used to calculate the wave function of photoexcited electrons or holes from which the photoioniation cross-section is obtained. The results apply to shallow or deep levels associated with carriers bound to charged impurity centres. Results for photodetachment of carriers bound to neutral impurities are obtained in the limit where the impurity charge goes to zero.
L E E D evaluation of three models of the Si(100) surface. G. J. R. JONES and B. W. HOLLAND. Vacuum 33 0 0 - 1 2 ) , 627 (1983). A strong body of opinion has recently favoured the buckled dimer type of model for the Si(100) surface and we compare LEED calculations for two such models with experiment. The first model is that of Yin and Cohen which was proposed on the basis of minimization of the H e l l m a n F e y n m a n forces using a self-consistent, local density, pseudopotential theory. The second model is that of Yang, Jona and Marcus which was found by varying structural parameters to obtain agreement with the LEED data. For comparison we also include the symmetric dimer model of Tong and Maldonado. Our calculations are fully dynamical and we treat the actual structures proposed without imposing any limitations to aid computation. We present visual comparisons of calculations and experimental data and also calculate the Pendry R factors. We find that the Yang, Jona and Marcus model is in best agreement with experiment, but the improvement over the other two models does not seem to be as great as one might expect if the structure were essentially correct. There is still some question therefore as to whether the model needs only minor modifications or significant changes.
Theory of the growth of SiO2 in an oxygen plasma. A. KIERMASZ, W. ECCLESTON and J. L. MORUZZI. Solid-St. Electron, 26 (12), 1167 (1983). Theory is presented for the anodization of silicon in a microwave, or r.f. plasma of oxygen. The electrons, and O - ions, are assumed to be accelerated towards the anode by a fixed bias applied between the electrodes. For small thicknesses the electric field in the oxide is uniform and constant with time. The growth rate is then constant, until a thickness is reached where the number of electrons in the film modifies the field and the current becomes space charge limited. There is then a strong variation of electron density with position, being a m a x i m u m at the oxide gas interface where the electric field strength is a minimum. The dependence of oxide thickness xt on time t is of the form x2ctt. The currents in both the linear and parabolic region of growth are calculated. The predictions have been checked experimentally and have been found to be accurately obeyed demonstrating that, as assumed, the electrons in the oxide dominate the current, and the oxidation process is limited by the drift of ions through the oxide. Semiconductor surfaces and interfaces. R. H. WILLIAMS. Vacuum 33 (10-12), 587 (1983). The development of modern techniques to probe surfaces on an atomic scale, coupled with parallel theoretical calculations of surface structures and electronic states has led to substantial progress in our understanding of semiconductor surfaces and their interfaces with metal contacts. Recent experiments are briefly reviewed and some recent theories relating to electrical barrier formation at metal-semiconductor interfaces considered. Hole and electron mobilities in heavily doped silicon: comparison of theory and experiment. HERBERT S BENNETT. Solid-St. Electron. 26 (12), 1157 (1983). Most device models for npn or pnp transistors assume that hole (electron) mobilities in n-type and p-type silicon are equal. Partialwave phase shift calculations for the contributions of carrierdopant ion scattering to the carrier mobilities lead to unequal minority hole (electron) and majority hole (electron) mobilities at the same doping density. These calculations are valid over the doping range of 2 x 1019 to 8 × 1019cm -3 in n-type and p-type silicon and contain the assumptions that the holes and electrons move in isotropic, parabolic energy bands and are scattered by the screened Coulomb potentials of the dopant ions. When the effects of carrier-acoustic p h o n o n and carrier-carrier scatterings are included, these calculations agree to within the spread of experimental value for the majority mobilities reported in the literature. This
Shallow doping in silicon. SCHYI-YI-Wu. IEEE Trans. Components Hybrids Mfg Technol. Chmt-6 (3), 309 (September 1983). In recent years liquid-state diffusion by laser melting has been instituted in device manufacture; and annealing of doped polysilicon and ion implantation damage by various lasers and incoherent radiation sources have been investigated. Continuous wave (CW) laser annealing was shown to be superior in the reduction of polysilicon sheet resistance due to increase in grain size. Incoherent radiation sources appear to be practical for dopant activation with m i n i m u m redistribution. The conventional furnace technology continues to play an important role while new technologies are introduced to complement it. These various technologies for shallow doping ( < 1 ~tm) in silicon are reviewed in terms of cost, throughput, special process requirements, dopant activation, dopant profile shift, and device characteristics.
An analytical method for determining intrinsic drain/source resistance of lightly doped drain (LDD) devices. CHARVAKA DUVVURY, DAVE BAGLEE, MICHAEL DUANE, ADIN HYSLOP, MICHAEL SMAYLINGand MIKE MAEKAWA.Solid-St. Electron. 27 (1), 89 (1984). M O S devices with double diffusion junctions containing Lightly Doped Drain/Source (LDD) regions have been built and analyzed. Comparison of current characteristics of the 2 lam L D D devices with conventional devices of same channel length indicates that the L D D devices, while displaying relatively good drain current gain, deviate from the M O S transistors in the linear region due to the intrinsic n drain/source resistance and thus have lower substrate current due to the reduced hot electron effects. An analytical method is developed where this intrinsic resistance can be extracted from curve fitting of I--V data. T h r o u g h curve fitting analysis the intrinsic resistance parameter is found to be an inverse function of transistor width as well as being dependent on temperature in the usual T 3/2 manner. Tunnelling of holes from acceptor levels in an applied field. HuI-QUAN N1E and D. D. COON. Solid-St. Electron. 27 (1), 53 (1984). A formula is derived for the rate of tunnelling of holes from bound acceptor levels into valence band states in the presence of an applied field. The rate of this q u a n t u m mechanical field ionization process is very strongly dependent
819
understanding of some semiconductor surface reconstructions is given. These include the G a A s ( l l 0 ) surface and the (100) and (111) surfaces of Si and Ge. The strong correlation between atomic and electronic structure and the energies involved in structural rearrangements at the surface are discussed.
agreement is a substantial improvement by factors of 2 - 4 over the results of earlier theories such as first order Born and nondegenerate theories. The results of this work, particularly the inequality of minority and majority carrier mobilities, have implications for the modelling of both bipolar and field effect transistors.
Photoionization of impurity atoms in semiconductors in the presence of an applied electric field. D. D. COON and R. P. G. KARUNASIRI. Solid-St. Electron. 26 (12), 1151 (1983). An analytic expression for the photoionization cross-section of an impurity atom in an applied field is derived for photon energies below the zero-field photoionization threshold. The use of a q u a n t u m defect wave function for the impurity ground state permits impurity atoms to be conveniently characterized in terms of known ground state energies. The C o u l o m b Green's function and the W K B approximation in parabolic coordinates are used to calculate the wave function of photoexcited electrons or holes from which the photoioniation cross-section is obtained. The results apply to shallow or deep levels associated with carriers bound to charged impurity centres. Results for photodetachment of carriers bound to neutral impurities are obtained in the limit where the impurity charge goes to zero.
L E E D evaluation of three models of the Si(100) surface. G. J. R. JONES and B. W. HOLLAND. Vacuum 33 0 0 - 1 2 ) , 627 (1983). A strong body of opinion has recently favoured the buckled dimer type of model for the Si(100) surface and we compare LEED calculations for two such models with experiment. The first model is that of Yin and Cohen which was proposed on the basis of minimization of the H e l l m a n F e y n m a n forces using a self-consistent, local density, pseudopotential theory. The second model is that of Yang, Jona and Marcus which was found by varying structural parameters to obtain agreement with the LEED data. For comparison we also include the symmetric dimer model of Tong and Maldonado. Our calculations are fully dynamical and we treat the actual structures proposed without imposing any limitations to aid computation. We present visual comparisons of calculations and experimental data and also calculate the Pendry R factors. We find that the Yang, Jona and Marcus model is in best agreement with experiment, but the improvement over the other two models does not seem to be as great as one might expect if the structure were essentially correct. There is still some question therefore as to whether the model needs only minor modifications or significant changes.
Theory of the growth of SiO2 in an oxygen plasma. A. KIERMASZ, W. ECCLESTON and J. L. MORUZZI. Solid-St. Electron, 26 (12), 1167 (1983). Theory is presented for the anodization of silicon in a microwave, or r.f. plasma of oxygen. The electrons, and O - ions, are assumed to be accelerated towards the anode by a fixed bias applied between the electrodes. For small thicknesses the electric field in the oxide is uniform and constant with time. The growth rate is then constant, until a thickness is reached where the number of electrons in the film modifies the field and the current becomes space charge limited. There is then a strong variation of electron density with position, being a m a x i m u m at the oxide gas interface where the electric field strength is a minimum. The dependence of oxide thickness xt on time t is of the form x2ctt. The currents in both the linear and parabolic region of growth are calculated. The predictions have been checked experimentally and have been found to be accurately obeyed demonstrating that, as assumed, the electrons in the oxide dominate the current, and the oxidation process is limited by the drift of ions through the oxide. Semiconductor surfaces and interfaces. R. H. WILLIAMS. Vacuum 33 (10-12), 587 (1983). The development of modern techniques to probe surfaces on an atomic scale, coupled with parallel theoretical calculations of surface structures and electronic states has led to substantial progress in our understanding of semiconductor surfaces and their interfaces with metal contacts. Recent experiments are briefly reviewed and some recent theories relating to electrical barrier formation at metal-semiconductor interfaces considered. Hole and electron mobilities in heavily doped silicon: comparison of theory and experiment. HERBERT S BENNETT. Solid-St. Electron. 26 (12), 1157 (1983). Most device models for npn or pnp transistors assume that hole (electron) mobilities in n-type and p-type silicon are equal. Partialwave phase shift calculations for the contributions of carrierdopant ion scattering to the carrier mobilities lead to unequal minority hole (electron) and majority hole (electron) mobilities at the same doping density. These calculations are valid over the doping range of 2 x 1019 to 8 × 1019cm -3 in n-type and p-type silicon and contain the assumptions that the holes and electrons move in isotropic, parabolic energy bands and are scattered by the screened Coulomb potentials of the dopant ions. When the effects of carrier-acoustic p h o n o n and carrier-carrier scatterings are included, these calculations agree to within the spread of experimental value for the majority mobilities reported in the literature. This
Shallow doping in silicon. SCHYI-YI-Wu. IEEE Trans. Components Hybrids Mfg Technol. Chmt-6 (3), 309 (September 1983). In recent years liquid-state diffusion by laser melting has been instituted in device manufacture; and annealing of doped polysilicon and ion implantation damage by various lasers and incoherent radiation sources have been investigated. Continuous wave (CW) laser annealing was shown to be superior in the reduction of polysilicon sheet resistance due to increase in grain size. Incoherent radiation sources appear to be practical for dopant activation with m i n i m u m redistribution. The conventional furnace technology continues to play an important role while new technologies are introduced to complement it. These various technologies for shallow doping ( < 1 ~tm) in silicon are reviewed in terms of cost, throughput, special process requirements, dopant activation, dopant profile shift, and device characteristics.
An analytical method for determining intrinsic drain/source resistance of lightly doped drain (LDD) devices. CHARVAKA DUVVURY, DAVE BAGLEE, MICHAEL DUANE, ADIN HYSLOP, MICHAEL SMAYLINGand MIKE MAEKAWA.Solid-St. Electron. 27 (1), 89 (1984). M O S devices with double diffusion junctions containing Lightly Doped Drain/Source (LDD) regions have been built and analyzed. Comparison of current characteristics of the 2 lam L D D devices with conventional devices of same channel length indicates that the L D D devices, while displaying relatively good drain current gain, deviate from the M O S transistors in the linear region due to the intrinsic n drain/source resistance and thus have lower substrate current due to the reduced hot electron effects. An analytical method is developed where this intrinsic resistance can be extracted from curve fitting of I--V data. T h r o u g h curve fitting analysis the intrinsic resistance parameter is found to be an inverse function of transistor width as well as being dependent on temperature in the usual T 3/2 manner. Tunnelling of holes from acceptor levels in an applied field. HuI-QUAN N1E and D. D. COON. Solid-St. Electron. 27 (1), 53 (1984). A formula is derived for the rate of tunnelling of holes from bound acceptor levels into valence band states in the presence of an applied field. The rate of this q u a n t u m mechanical field ionization process is very strongly dependent