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Characterization of Se implanted layers for GaAs FETS
824
World Abstracts on Microelectronics and Reliability
power MOSFET devices can be used to significantly improve the reverse recovery characteristics of their integral reverse conducting diodes without adversely affecting the MOSFET characteristics. By using 3 MeV electron irradiation at room temperature it was found that the reverse recovery charge in the integral diode could be continuously reduced in a well controlled manner from over 500nC to less than 100nC without any significant increase in the forward voltage drop of the integral diode under typical operating peak currents. The reverse recovery time was also observed to decrease from 3 microseconds to less than 200 nsec when the radiation dose was increased from 0 to 16 Megarads. The damage produced in gate oxide of the MOSFET due to the electron radiation damage was found to cause an undesirable decrease in the gate threshold voltage. This resulted in excessive channel leakage current flow in the MOSFET at zero gate bias. It was found that this channel leakage current was substantially reduced by annealing the devices at 140°C without influencing the integral diode reverse recovery speed. Thus, the electron irradiation technique was found to be effective in controlling the integral diode reverse recovery characteristics without any degradation of the power MOSFET characteristics. Focused ion beams in microelectronic fabrication. JOHN A. DOHERTY, BILL W. WARD and EDWIN M. KELLOGG. IEEE Trans. Components Hybrids Mf# Technol. Chmt-6 (3), 329 (September 1983). For more than 20yr the designers and fabricators of integrated circuits and microstructure devices have striven toward smaller features as a means of achieving higher packing density, better performance, and lower cost. The new field of microlithography has emerged as a result of these pressures. The results of these efforts are a wide array of advanced development and production techniques using photooptics, electrons, and X-rays as energy sources for pattern generation and replication. Over the past 3-4yr a new technique, focused ion beam lithography, has emerged as a challenger to these lithography tools for very large-scale integration (VLSI) research and production applications. A number of significant advantages exist when using focused beams in microelectronic fabrication that are not available in the technologies mentioned above. For example, the focused ion beam (FIB) may allow manufacturers to eliminate many of the process steps associated with conventional implantation since FIB implants can be performed without lithography and chemical processes. Special implant steps can also be done that are neither practical nor even possible with conventional photomasking techniques. Characterization of Se implanted layers for GaAs FETS. B. R. SINGH, MADHU KOCHHAR, O. P. DAGA and W. S. KHOKLE. Microelectron. Reliab. 23 (5), 857 (1983). Results on doping profile, uniformity of doping and mobility for Se implanted LEC grown semi-insulating GaAs substrates are presented as a function of Se ion energy and annealing temperature. SiO 2, RF sputtered Si3N 4 and G a 2 0 3 +AI are used as encapsulating layers. Surface effects (stress and damage) on doping efficiency of implanted Se ions are also included. Diffusion, ion implantation and annealing. PIETER S. BURGGRAAF. Semiconductor Int. 100 (November 1983). Equipment for semiconductor doping processes and associated annealing operations were enhanced this year to enable the fabrication of higher density VLSI ICs. Silicon film recrystallization using e-beam line source. D. B. RENSCI-I and J. Y. CrtEN. Microelectron. J. 14 (6), 66 (1983). Lateral zone melting from a fast-scanning (50 to 30 cm s-1) E-beam line source has been used to grow single-crystal films with an area limited only by the E-beam scan field. Electron backscattering contrast and etch pit techniques have been used to study the crystallographic orientation and extent of
single crystal silicon film growth on SiO2--coated silicon wafers. (100) textured films have been grown on these (0.35 to 1.0tim thick) SiO 2 layers containing periodic openings to permit seeding during recrystallization. Recrystallization of non-seeded polysilicon produced (111)-textured films. Enhancement mode n-channel MOSFETs have been made in both types of films. Channel mobility as high as 600cm2/ V-see has been measured in the (100) textured films. Beam-recrystallized silicon-on-insulator films: can devices live with grain boundaries? JEAN-PIERRECOLINGE. Microelectron. J. 14 (6), 58 (1983). Current techniques in which polysilicon films deposited on an insulator are recrystallized have not yet shown the ability to produce large areas of grain boundaryfree material. Grain boundaries have been demonstrated to be paths of rapid dopant diffusion, giving rise to shorts in devices. Grain boundaries occurring in the channel of transistors shift the device threshold voltage in an uncontrolled manner. It is, however, possible to control the location of these defects with accuracy and to place them where they will not preclude circuit operation, i.e., in the field area of the circuits. Single-crystal stripes of silicon-on-insulator can be obtained, with no other defects than the localized ones. Good device performances have been obtained using this material, in which the mobility is the same as in bulk silicon. The time resolved electron beam induced current method applied to P N junctions. A. GEORGES and G. JACOB. Acto Electron. 25 (3), 211 (1983). In French. The Time Resolved Electron Beam Induced Current (TREBIC) method is a nondestructive technique which allows to visualize the position of P - N junctions, with a spatial resolution of 0.1 lam, and to measure their depth with a sensitivity better than 5 %. The principle of TREBIC is described and some experimental results are reported. EBIC and LBIC techniques for characterization of reverse biased power devices. J. N. SANDOE and J. R. HUGHES. Acta Electron. 25 (3), 201 (1983). In French. This paper describes and compares the Electron Beam Induced Current (EBIC) and Laser Beam Induced Current (LBIC) techniques as used to observe depletion region formation in silicon devices. A range of practical examples demonstrate use of the techniques to elucidate problems associated with the passivation of high voltage power devices. These include diffusion faults, inhomogeneity of surface layers, and the effect of surface conductors on the spread of depletion regions in reverse biased devices. Semiconducting surface layers lead to depletion region formation in the silicon surface at low applied bias and give corresponding relief of high field regions at high voltages. The behaviour of concentric field relief rings is shown to be affected by surface conducting layers. Silicon-on-insulator structures using high dose oxygen implantation to form buried oxide films. K. DAS, G. SHORTHOUSE, J. BUTCHER and K. V. ANAND. Microelectron. J. 14 (6), 88 (1983). The feasibility of growing epitaxial layers of silicon on silicon substrates with a buried oxide layer formed by the implantation of oxygen ions, has been studied. Buried implanted oxide layers have been formed by high dose implantation of oxygen ions in silicon. The effect of dose at a given energy for a given peak concentration on the distribution profile of oxygen has been studied. An approximately Gaussian distribution is observed at doses contributing less than the stoichiometric requirement of oxygen for the formation of silicon dioxide. A saturation in the peak oxygen concentration is reached when the stoichiometric requirement is exceeded. A consequent reduction in the interface damage is also observed. Other parameters being equal, at higher substrate temperatures the interface damage is decreased. It has been attempted to optimize conditions for a dose of 1.4 x 1018 cm 2 at 200 keV which provided the stoichiometric concentration only at the peak of the distribution.
World Abstracts on Microelectronics and Reliability
power MOSFET devices can be used to significantly improve the reverse recovery characteristics of their integral reverse conducting diodes without adversely affecting the MOSFET characteristics. By using 3 MeV electron irradiation at room temperature it was found that the reverse recovery charge in the integral diode could be continuously reduced in a well controlled manner from over 500nC to less than 100nC without any significant increase in the forward voltage drop of the integral diode under typical operating peak currents. The reverse recovery time was also observed to decrease from 3 microseconds to less than 200 nsec when the radiation dose was increased from 0 to 16 Megarads. The damage produced in gate oxide of the MOSFET due to the electron radiation damage was found to cause an undesirable decrease in the gate threshold voltage. This resulted in excessive channel leakage current flow in the MOSFET at zero gate bias. It was found that this channel leakage current was substantially reduced by annealing the devices at 140°C without influencing the integral diode reverse recovery speed. Thus, the electron irradiation technique was found to be effective in controlling the integral diode reverse recovery characteristics without any degradation of the power MOSFET characteristics. Focused ion beams in microelectronic fabrication. JOHN A. DOHERTY, BILL W. WARD and EDWIN M. KELLOGG. IEEE Trans. Components Hybrids Mf# Technol. Chmt-6 (3), 329 (September 1983). For more than 20yr the designers and fabricators of integrated circuits and microstructure devices have striven toward smaller features as a means of achieving higher packing density, better performance, and lower cost. The new field of microlithography has emerged as a result of these pressures. The results of these efforts are a wide array of advanced development and production techniques using photooptics, electrons, and X-rays as energy sources for pattern generation and replication. Over the past 3-4yr a new technique, focused ion beam lithography, has emerged as a challenger to these lithography tools for very large-scale integration (VLSI) research and production applications. A number of significant advantages exist when using focused beams in microelectronic fabrication that are not available in the technologies mentioned above. For example, the focused ion beam (FIB) may allow manufacturers to eliminate many of the process steps associated with conventional implantation since FIB implants can be performed without lithography and chemical processes. Special implant steps can also be done that are neither practical nor even possible with conventional photomasking techniques. Characterization of Se implanted layers for GaAs FETS. B. R. SINGH, MADHU KOCHHAR, O. P. DAGA and W. S. KHOKLE. Microelectron. Reliab. 23 (5), 857 (1983). Results on doping profile, uniformity of doping and mobility for Se implanted LEC grown semi-insulating GaAs substrates are presented as a function of Se ion energy and annealing temperature. SiO 2, RF sputtered Si3N 4 and G a 2 0 3 +AI are used as encapsulating layers. Surface effects (stress and damage) on doping efficiency of implanted Se ions are also included. Diffusion, ion implantation and annealing. PIETER S. BURGGRAAF. Semiconductor Int. 100 (November 1983). Equipment for semiconductor doping processes and associated annealing operations were enhanced this year to enable the fabrication of higher density VLSI ICs. Silicon film recrystallization using e-beam line source. D. B. RENSCI-I and J. Y. CrtEN. Microelectron. J. 14 (6), 66 (1983). Lateral zone melting from a fast-scanning (50 to 30 cm s-1) E-beam line source has been used to grow single-crystal films with an area limited only by the E-beam scan field. Electron backscattering contrast and etch pit techniques have been used to study the crystallographic orientation and extent of
single crystal silicon film growth on SiO2--coated silicon wafers. (100) textured films have been grown on these (0.35 to 1.0tim thick) SiO 2 layers containing periodic openings to permit seeding during recrystallization. Recrystallization of non-seeded polysilicon produced (111)-textured films. Enhancement mode n-channel MOSFETs have been made in both types of films. Channel mobility as high as 600cm2/ V-see has been measured in the (100) textured films. Beam-recrystallized silicon-on-insulator films: can devices live with grain boundaries? JEAN-PIERRECOLINGE. Microelectron. J. 14 (6), 58 (1983). Current techniques in which polysilicon films deposited on an insulator are recrystallized have not yet shown the ability to produce large areas of grain boundaryfree material. Grain boundaries have been demonstrated to be paths of rapid dopant diffusion, giving rise to shorts in devices. Grain boundaries occurring in the channel of transistors shift the device threshold voltage in an uncontrolled manner. It is, however, possible to control the location of these defects with accuracy and to place them where they will not preclude circuit operation, i.e., in the field area of the circuits. Single-crystal stripes of silicon-on-insulator can be obtained, with no other defects than the localized ones. Good device performances have been obtained using this material, in which the mobility is the same as in bulk silicon. The time resolved electron beam induced current method applied to P N junctions. A. GEORGES and G. JACOB. Acto Electron. 25 (3), 211 (1983). In French. The Time Resolved Electron Beam Induced Current (TREBIC) method is a nondestructive technique which allows to visualize the position of P - N junctions, with a spatial resolution of 0.1 lam, and to measure their depth with a sensitivity better than 5 %. The principle of TREBIC is described and some experimental results are reported. EBIC and LBIC techniques for characterization of reverse biased power devices. J. N. SANDOE and J. R. HUGHES. Acta Electron. 25 (3), 201 (1983). In French. This paper describes and compares the Electron Beam Induced Current (EBIC) and Laser Beam Induced Current (LBIC) techniques as used to observe depletion region formation in silicon devices. A range of practical examples demonstrate use of the techniques to elucidate problems associated with the passivation of high voltage power devices. These include diffusion faults, inhomogeneity of surface layers, and the effect of surface conductors on the spread of depletion regions in reverse biased devices. Semiconducting surface layers lead to depletion region formation in the silicon surface at low applied bias and give corresponding relief of high field regions at high voltages. The behaviour of concentric field relief rings is shown to be affected by surface conducting layers. Silicon-on-insulator structures using high dose oxygen implantation to form buried oxide films. K. DAS, G. SHORTHOUSE, J. BUTCHER and K. V. ANAND. Microelectron. J. 14 (6), 88 (1983). The feasibility of growing epitaxial layers of silicon on silicon substrates with a buried oxide layer formed by the implantation of oxygen ions, has been studied. Buried implanted oxide layers have been formed by high dose implantation of oxygen ions in silicon. The effect of dose at a given energy for a given peak concentration on the distribution profile of oxygen has been studied. An approximately Gaussian distribution is observed at doses contributing less than the stoichiometric requirement of oxygen for the formation of silicon dioxide. A saturation in the peak oxygen concentration is reached when the stoichiometric requirement is exceeded. A consequent reduction in the interface damage is also observed. Other parameters being equal, at higher substrate temperatures the interface damage is decreased. It has been attempted to optimize conditions for a dose of 1.4 x 1018 cm 2 at 200 keV which provided the stoichiometric concentration only at the peak of the distribution.