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Anisotropic boron diffusion in silicon under oxidizing atmospheres
416
WORLD
ABSTRACTS
ON
MICROELECTRONICS
coefficient. Furthermore, under the assumption of a Maxwellian form of the isotropic part of the distribution function, the obtained expressions are simplified. Generalized Einstein relations between the transport coefficients are derived and the boundary-value problem is formulated which has to be solved in order to determine quantitatively the behavior of a device if the carriers become hot or cold. Finally, a discussion is given of a similar theory by Stratton as well as of limitations, advantages and possibilities of applications of the present theory. The present synthesis is not available elsewhere. A new type of charge trapping in MOS systems. D. J. BREED and R. P. KRAMER. Philips Res. Repts 28 (1973), pp. 75-79. It appears that the shift of the C - V curve of a p-MOS capacitor that occurs after cooling from room temperature to 77 K increases if a negative bias is applied to the capacitor during cooling. This extra shift can easily be observed in "standard" MOS capacitors when the bias during cooling is large enough. Extra shifts up to 30 V arc observed in samples that have received a heat treatment that also causes a large fixed oxide charge. It is shown that these shifts observed at 77 K are due to charge trapping at room temperature. These shifts can be explained neither by fixed oxide charge nor by fast interface states while the traps causing these shifts cannot be described as "slow states" in the usual way. An improvement on structure of charge coupled devices. MIFUNE, OCHI, KANO and SHIBATA. Proceedinos 4th Conference on Solid State Devices, Tokyo, 30-31 August (1972) Japan Soc. Appl. Phys. 42 (1973) Suppl., p. 207. A CCD structure having a resistive layer over the oxide film at the interelectrode gaps was studied. Polycrystalline silicon was used as the resistive material. The present structure allowed the use of a gap length of up to 12,tim without appreciable decrease in the charge transfer efficiency. The use of a large gap length removed the severe requirement of the resolution on the photolithographic technology in the conventional CCD structures. The resistivity of the resistive layer was analyzed on the basis of a distributed constant circuit of parallel planes. Test devices of 2- and 3-phase CCDs were fabricated and evaluated based on the present analysis. A 3-phase CCD was used as an image sensor which gave permissible character reproduction. Semiconductor characterization by measurements of nonequilibrium current in MOS capacitors. M. CONTI,F. CONTI and G. CORDA. Alta Frequenza XLII, No. 2, February (1973), p. 93. A method for measuring the generationrecombination properties of a semiconductor is described. It employs a M.O.S. capacitor which is taken to nonequilibrium by a voltage step. Under these conditions the current crossing the capacitor is controlled by generation mechanisms in the semiconductor and along the semiconductor surface. This method is non-destructive and differs from the others reported by literature by the fact that measurements are taken on the current thereby resulting in better accuracy and smaller instrumentation cost. A theory is developed which applies both to defect-free and defective silicon. In the case of defective material the
AND
RELIABILITY
voltage current characteristic of an equivalent diode is derived. This prediction is confirmed by the results obtained on diodes made on the same wafer. Additional interesting aspects include the possibility of obtaining non-equilibrium CV plot and therefore doping profile, and characterization of oxide-silicon interface highly affected by cleanings, diffusion of hard metals, etc. Trap structure of pyrolytic A1203 in MOS capacitors. E. HARARI and B. S. H. ROYCE. Princeton Univ. Solid State + Materials Lab., N.J. USA. 11 (1972) PSSL-141172. The trap structure of the pyrolytic A1203 layer of MOS capacitors was investigated by a technique in which the capacitor was used as an integral detector of the charge trapped in the oxide. In all the samples studied, five trap levels were found to exist extending from 2.2 eV to 4.5 eV below the oxide conduction band. The spatial distribution of these traps was inferred from complementary photoconductivity measurements. This method is applicable to the study of the effects of radiation damage and ion implantation on the trap structure of this and other thin film insulators. Polycrystalline silicon resistors for integrated circuits. F. D. KING, J. SHEWCHUN, D. A. THOMPSON, H. D. BARBER and W. A. PIECZONKA. Solid St. Electron. 16 (1973), p. 701. The suitability of thin films of doped polycrystalline silicon on SiO 2 substrates for the production of high value resistors for monolithic integrated circuits is considered. Resistors fabricated from this material posses the advantages of high sheet resistivity and dielectric isolation while still preserving an all silicon technology compatible with conventional production techniques. Relevant structural and electrical properties of doped polycrystalline films produced by both vacuum evaporation onto hot substrates with gas-doping and by diffusionannealing of amorphous films have been investigated. Sheet resistivities and TCR values measured on 2500 A polycrystalline films have proved superior to those encountered with conventional diffused resistors. Typically films with sheet resistivities of 1 kf//U] had TCR's of - 1000 ppm/°C while conventional diffused resistors are generally made from material of 200 f~/I~ and +2000 ppm/°C TCR. Etched resistor line widths of 0.25 mil. have been obtained in the polycrystalline material employing conventional photolithographic techniques. The temperature stability and linearity of doped polycrystalline resistors have been investigated. Anisotropic boron diffusion in silicon under oxidizing atmospheres. G. MASETTI,S. SOLMI and G. SONCINI. Solid St. Comm. 12, (1973) p. 1299. The anisotropy of boron diffusion into silicon under oxidizing atmospheres has been experimentally analysed, and the results interpreted by using a modified form of the Kato and Nishi theoretical model. Explanations based on redistribution phenomena and on dislocations induced at the oxide silicon interface are critically discussed. Polysilicon-fiiled notch produces fiat, well-isolated bipolar memory. THOMAS J. SANDERS and WILLIAM R. MORCOM.
WORLD
ABSTRACTS
ON
MICROELECTRONICS
coefficient. Furthermore, under the assumption of a Maxwellian form of the isotropic part of the distribution function, the obtained expressions are simplified. Generalized Einstein relations between the transport coefficients are derived and the boundary-value problem is formulated which has to be solved in order to determine quantitatively the behavior of a device if the carriers become hot or cold. Finally, a discussion is given of a similar theory by Stratton as well as of limitations, advantages and possibilities of applications of the present theory. The present synthesis is not available elsewhere. A new type of charge trapping in MOS systems. D. J. BREED and R. P. KRAMER. Philips Res. Repts 28 (1973), pp. 75-79. It appears that the shift of the C - V curve of a p-MOS capacitor that occurs after cooling from room temperature to 77 K increases if a negative bias is applied to the capacitor during cooling. This extra shift can easily be observed in "standard" MOS capacitors when the bias during cooling is large enough. Extra shifts up to 30 V arc observed in samples that have received a heat treatment that also causes a large fixed oxide charge. It is shown that these shifts observed at 77 K are due to charge trapping at room temperature. These shifts can be explained neither by fixed oxide charge nor by fast interface states while the traps causing these shifts cannot be described as "slow states" in the usual way. An improvement on structure of charge coupled devices. MIFUNE, OCHI, KANO and SHIBATA. Proceedinos 4th Conference on Solid State Devices, Tokyo, 30-31 August (1972) Japan Soc. Appl. Phys. 42 (1973) Suppl., p. 207. A CCD structure having a resistive layer over the oxide film at the interelectrode gaps was studied. Polycrystalline silicon was used as the resistive material. The present structure allowed the use of a gap length of up to 12,tim without appreciable decrease in the charge transfer efficiency. The use of a large gap length removed the severe requirement of the resolution on the photolithographic technology in the conventional CCD structures. The resistivity of the resistive layer was analyzed on the basis of a distributed constant circuit of parallel planes. Test devices of 2- and 3-phase CCDs were fabricated and evaluated based on the present analysis. A 3-phase CCD was used as an image sensor which gave permissible character reproduction. Semiconductor characterization by measurements of nonequilibrium current in MOS capacitors. M. CONTI,F. CONTI and G. CORDA. Alta Frequenza XLII, No. 2, February (1973), p. 93. A method for measuring the generationrecombination properties of a semiconductor is described. It employs a M.O.S. capacitor which is taken to nonequilibrium by a voltage step. Under these conditions the current crossing the capacitor is controlled by generation mechanisms in the semiconductor and along the semiconductor surface. This method is non-destructive and differs from the others reported by literature by the fact that measurements are taken on the current thereby resulting in better accuracy and smaller instrumentation cost. A theory is developed which applies both to defect-free and defective silicon. In the case of defective material the
AND
RELIABILITY
voltage current characteristic of an equivalent diode is derived. This prediction is confirmed by the results obtained on diodes made on the same wafer. Additional interesting aspects include the possibility of obtaining non-equilibrium CV plot and therefore doping profile, and characterization of oxide-silicon interface highly affected by cleanings, diffusion of hard metals, etc. Trap structure of pyrolytic A1203 in MOS capacitors. E. HARARI and B. S. H. ROYCE. Princeton Univ. Solid State + Materials Lab., N.J. USA. 11 (1972) PSSL-141172. The trap structure of the pyrolytic A1203 layer of MOS capacitors was investigated by a technique in which the capacitor was used as an integral detector of the charge trapped in the oxide. In all the samples studied, five trap levels were found to exist extending from 2.2 eV to 4.5 eV below the oxide conduction band. The spatial distribution of these traps was inferred from complementary photoconductivity measurements. This method is applicable to the study of the effects of radiation damage and ion implantation on the trap structure of this and other thin film insulators. Polycrystalline silicon resistors for integrated circuits. F. D. KING, J. SHEWCHUN, D. A. THOMPSON, H. D. BARBER and W. A. PIECZONKA. Solid St. Electron. 16 (1973), p. 701. The suitability of thin films of doped polycrystalline silicon on SiO 2 substrates for the production of high value resistors for monolithic integrated circuits is considered. Resistors fabricated from this material posses the advantages of high sheet resistivity and dielectric isolation while still preserving an all silicon technology compatible with conventional production techniques. Relevant structural and electrical properties of doped polycrystalline films produced by both vacuum evaporation onto hot substrates with gas-doping and by diffusionannealing of amorphous films have been investigated. Sheet resistivities and TCR values measured on 2500 A polycrystalline films have proved superior to those encountered with conventional diffused resistors. Typically films with sheet resistivities of 1 kf//U] had TCR's of - 1000 ppm/°C while conventional diffused resistors are generally made from material of 200 f~/I~ and +2000 ppm/°C TCR. Etched resistor line widths of 0.25 mil. have been obtained in the polycrystalline material employing conventional photolithographic techniques. The temperature stability and linearity of doped polycrystalline resistors have been investigated. Anisotropic boron diffusion in silicon under oxidizing atmospheres. G. MASETTI,S. SOLMI and G. SONCINI. Solid St. Comm. 12, (1973) p. 1299. The anisotropy of boron diffusion into silicon under oxidizing atmospheres has been experimentally analysed, and the results interpreted by using a modified form of the Kato and Nishi theoretical model. Explanations based on redistribution phenomena and on dislocations induced at the oxide silicon interface are critically discussed. Polysilicon-fiiled notch produces fiat, well-isolated bipolar memory. THOMAS J. SANDERS and WILLIAM R. MORCOM.