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Superlattice and negative differential conductivity in semiconductors
WORLD
ABSTRACTS
ON MICROELECTRONICS
AND RELIABILITY
463
majority carriers only. For minority carriers, the limitations are far less severe in most cases of practical interest, and depend on the characteristics of the trapping centers involved.
Dielectric films for Ge planar devices. T. O. SEDGWICK,J. A. ABOAF and S. KRONGELB,I B M 3 t. Res. Dev. 14, January (1970), p. 2. A series of passivating and masking films was developed and evaluated for use in a Ge planar transistor technology. In the search for satisfactory films, silicon dioxide, aluminum oxide, silicon nitride and multilayer combinations of these films, as well as some doped and mixed-composition films, were studied. The films, formed by pyrolytic deposition or by sputtering, were evaluated and compared with respect to the following properties: etch rate; dopant masking; mechanical stress; oxygen, hydrogen and water permeability; stability with respect to elevated temperature electrical-bias stressing; and Ge-insulator interface electrical condition. The most important results of our experiments are the following: Silicon nitride appears to be the only satisfactory mask for Ga diffusions, although silicon dioxide is adequate for As, P and Sb diffusion masking. The dielectric properties of pyrolytically deposited SiO2 can be made to approach those of thermal SiO~ by high temperature densification. T h e surface electrical properties of the Ge-SiO2 interface are more stable to thermal annealing than is any other Ge-insulator combination. However, aluminum oxide has been shown to be much less permeable to oxygen, hydrogen and water vapor than is SiO 2. Since the Ge-insulator interface electrical properties are sensitive to these ambient gases, a satisfactory passivating film structure for Ge consists of an underlayer of SiOa and an overlayer of AltOs silicon nitride or other relatively impermeable film.
Superlattice and negative differential conductivity in semiconductors. L. ESAKI and R. Tsu. I B M J. Res. Dev. 14, January (1970), p. 61. We consider a one-dimensional periodic potential, or "superlattice," in monocrystalline semiconductors formed by a periodic variation of alloy composition or of impurity density introduced during epitaxial growth. If the period of a superlattice, of the order of 100A, is shorter than the electron mean free path, a series of narrow allowed and forbidden bands is expected due to the subdivision of the Brillouin zone into a series of minizones. If the scattering time of electrons meets a threshold condition, the combined effect of the narrow energy band and the narrow wave-vector zone makes it possible for electrons to be excited with moderate electric fields to an energy and momentum beyond an inflection point in the E-k relation; this results in a negative differential conductance in the direction of the superlattice. The study of superlattices and observations of quantum mechanical effects on a new physical scale may provide a valuable area of investigation in the field of semiconductors.
Analysis of surface and bulk impurities in silicon single crystal slices by neutron activation. G. LUNDE, Solid St. Technol., January (1970), p. 61. A method of separating and analyzing bulk and surface impurities in silicon single crystal slices has been developed. The method is based on etching the neutron-activated silicon with an etching agent in which inactive elements of the elements to be analyzed are dissolved. Analyses of the following impurities-zirconium, gold, copper, sodium and arsenic, performed on silicon material delivered from different producers are presented. T h e results indicate that most of the impurities are located on the surface of the silicon.
Bipolar compatible MOS ICs. C. CLIFFORD,Microelectronics, March (1970), p. 36. When MOS devices were first introduced, one of their main disadvantages was the need for relatively high power supply and operating voltages. This to a large extent precluded their use in systems requiring the higher power or speed capabilities of bipolar devices without complex interfacing circuitry. In the intervening period much development work has been carried out on a new or modified M O S fabrication process to allow direct compatibility. This article describes one such approach. Metal edge coverage and control of charge accumulation in r f shuttered insulators. J. S. LOGAN, F. S. MADDOCKSand P. D. DAVIDSE,I B M J . Res. Dev. 14, No. 2, March (1970), p. 182. The successful application of rf sputtered SiO~ in the passivation of silicon semiconductor devices depends in part on the proper control of ionic charge migration in the insulator during sputtering, and on the adequate coverage of metal line edges by the insulator. It is shown that an appropriate combination of target purity, substrate temperature control and phosphosilicate blocking layer thickness can be used to achieve ionic charge densities at the silicon-SiOz interface of less than 1 × 10 TM charges per square centimeter. The effects of argon ion bombardment are shown to be acceptably low for typical operating conditions. In a conventional system, the adequate coverage of metal line edges is shown to be influenced primarily by argon pressure and magnetic field. In a special system where the substrate potential can be varied, it has been shown that adequate edge coverage can be obtained at sufficiently negative potentials. These data are consistent with a mechanism requiring some resputtering to obtain the desired film coverage.
High-frequency properties and uses of MIS varactors. J. MARQUARDT,B. SCHIEK and H. G. UNGER, Nachrichtentech. 20, No. 3 (1970), p. 105 (In German). M I S varactors were made by means of the insulator-semiconductor combinations SiOe-Si, Si3N4-Si, Si~N~-SiO-Si4, and SisN4-GaAs. They show a linear capacity characteristic in pieces, exclusively because of majority carrier effects. Above 200 Mc/s the interfacial losses are smaller than the losses of path. Frequency triplers in the microwave range showed an efficiency of 50 per cent in the presence of an
ABSTRACTS
ON MICROELECTRONICS
AND RELIABILITY
463
majority carriers only. For minority carriers, the limitations are far less severe in most cases of practical interest, and depend on the characteristics of the trapping centers involved.
Dielectric films for Ge planar devices. T. O. SEDGWICK,J. A. ABOAF and S. KRONGELB,I B M 3 t. Res. Dev. 14, January (1970), p. 2. A series of passivating and masking films was developed and evaluated for use in a Ge planar transistor technology. In the search for satisfactory films, silicon dioxide, aluminum oxide, silicon nitride and multilayer combinations of these films, as well as some doped and mixed-composition films, were studied. The films, formed by pyrolytic deposition or by sputtering, were evaluated and compared with respect to the following properties: etch rate; dopant masking; mechanical stress; oxygen, hydrogen and water permeability; stability with respect to elevated temperature electrical-bias stressing; and Ge-insulator interface electrical condition. The most important results of our experiments are the following: Silicon nitride appears to be the only satisfactory mask for Ga diffusions, although silicon dioxide is adequate for As, P and Sb diffusion masking. The dielectric properties of pyrolytically deposited SiO2 can be made to approach those of thermal SiO~ by high temperature densification. T h e surface electrical properties of the Ge-SiO2 interface are more stable to thermal annealing than is any other Ge-insulator combination. However, aluminum oxide has been shown to be much less permeable to oxygen, hydrogen and water vapor than is SiO 2. Since the Ge-insulator interface electrical properties are sensitive to these ambient gases, a satisfactory passivating film structure for Ge consists of an underlayer of SiOa and an overlayer of AltOs silicon nitride or other relatively impermeable film.
Superlattice and negative differential conductivity in semiconductors. L. ESAKI and R. Tsu. I B M J. Res. Dev. 14, January (1970), p. 61. We consider a one-dimensional periodic potential, or "superlattice," in monocrystalline semiconductors formed by a periodic variation of alloy composition or of impurity density introduced during epitaxial growth. If the period of a superlattice, of the order of 100A, is shorter than the electron mean free path, a series of narrow allowed and forbidden bands is expected due to the subdivision of the Brillouin zone into a series of minizones. If the scattering time of electrons meets a threshold condition, the combined effect of the narrow energy band and the narrow wave-vector zone makes it possible for electrons to be excited with moderate electric fields to an energy and momentum beyond an inflection point in the E-k relation; this results in a negative differential conductance in the direction of the superlattice. The study of superlattices and observations of quantum mechanical effects on a new physical scale may provide a valuable area of investigation in the field of semiconductors.
Analysis of surface and bulk impurities in silicon single crystal slices by neutron activation. G. LUNDE, Solid St. Technol., January (1970), p. 61. A method of separating and analyzing bulk and surface impurities in silicon single crystal slices has been developed. The method is based on etching the neutron-activated silicon with an etching agent in which inactive elements of the elements to be analyzed are dissolved. Analyses of the following impurities-zirconium, gold, copper, sodium and arsenic, performed on silicon material delivered from different producers are presented. T h e results indicate that most of the impurities are located on the surface of the silicon.
Bipolar compatible MOS ICs. C. CLIFFORD,Microelectronics, March (1970), p. 36. When MOS devices were first introduced, one of their main disadvantages was the need for relatively high power supply and operating voltages. This to a large extent precluded their use in systems requiring the higher power or speed capabilities of bipolar devices without complex interfacing circuitry. In the intervening period much development work has been carried out on a new or modified M O S fabrication process to allow direct compatibility. This article describes one such approach. Metal edge coverage and control of charge accumulation in r f shuttered insulators. J. S. LOGAN, F. S. MADDOCKSand P. D. DAVIDSE,I B M J . Res. Dev. 14, No. 2, March (1970), p. 182. The successful application of rf sputtered SiO~ in the passivation of silicon semiconductor devices depends in part on the proper control of ionic charge migration in the insulator during sputtering, and on the adequate coverage of metal line edges by the insulator. It is shown that an appropriate combination of target purity, substrate temperature control and phosphosilicate blocking layer thickness can be used to achieve ionic charge densities at the silicon-SiOz interface of less than 1 × 10 TM charges per square centimeter. The effects of argon ion bombardment are shown to be acceptably low for typical operating conditions. In a conventional system, the adequate coverage of metal line edges is shown to be influenced primarily by argon pressure and magnetic field. In a special system where the substrate potential can be varied, it has been shown that adequate edge coverage can be obtained at sufficiently negative potentials. These data are consistent with a mechanism requiring some resputtering to obtain the desired film coverage.
High-frequency properties and uses of MIS varactors. J. MARQUARDT,B. SCHIEK and H. G. UNGER, Nachrichtentech. 20, No. 3 (1970), p. 105 (In German). M I S varactors were made by means of the insulator-semiconductor combinations SiOe-Si, Si3N4-Si, Si~N~-SiO-Si4, and SisN4-GaAs. They show a linear capacity characteristic in pieces, exclusively because of majority carrier effects. Above 200 Mc/s the interfacial losses are smaller than the losses of path. Frequency triplers in the microwave range showed an efficiency of 50 per cent in the presence of an