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Space-charge model for surface potential shifts in silicon passivated with thin insulating layers
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A B S T R A C TON S MICROELECTRONICS AND RELIABILITY
The heating in vacuum of silicon substrates to temperatures greater than 800°C. J. WALESand A. J. J~,L, Journal of Scientific Instruments 41, 521 (1964). A technique is described for heating substrates to temperatures in excess of 1200°C by means of art electron gun heater. The electron gun consists of two stainless steel current electrodes mounted in a molybdenum lid which clips on to the inner of two concentric molybdenum cylinders. The cathode is a molybdenum spiral painted with lanthanum boride. The substrate is placed in a 0.01 in. thick tantalum spoon. A supply of 100 rm~kat 900 V has been found sufficient to heat a silicon substrate to a temperature of 1200°C, at a distance of 1 cm from the electron source. Basic considerations in integrated circuit design. L. STERN. Electro-Technology 7, 91 (1964). Optimum design of integrated circuits is dependent to a large extent on familiarity with the economics as well as the design freedoms and limitations of the technology. This article relates these basic considerations by discussing what can be integrated, what type of packaging is best, and what type of integrated circuit is most economical. Space-charge model for surface potential shifts in silicon passivated with thin insulating layers. J. E. THOMAS, JR. and D. R. YOUNG,IBM Journal 8, 368 (1964). Semipermanent changes in the semiconductor surface potantial occur in insulator-covered semiconductors when external fields are applied for long times, particularly at elevated temperatures. An attempt to explain these changes in terms of the charging and discharging of interface states leads to conclusions that disagree with many of the experimental facts. Specifically, the semipermanent effects of interface-state charges can always be overcome by the application of a field smaller than that which is used to induce the effect, and of the same sign, while the experiments described in the accompanying papers generally show that a field much larger than the inducing field, and of the opposite sign, is required to return the insulator covered surface to its initial status. The accumulation of space charge in the insulating layer can give rise to very large fields at the semiconductor surface that persist after the removal of an external inducing field. The size and sign of such space-charge fields agree with the experimental observations. Measurements made after treatment of temperatures above 125°C show that the surface of silicon passivated with silicon dioxide can become strongly n-type as a result of such a positive space-charge layer formed at the interface. A model is presented based on the concept that this space charge arises from oxygen vacancies in the silicon dioxide. It is suggested that the improvement resulting from the use of phosphorus pent toxide on the outside surface is due to the elimination of vacancies by the oxidizing action of the phosphorus pentoxide. Stabilization o f SiO.., passivation layers with P,,O 5. D. R. KERR, J. S. LOCaN, P. J. BURKHA~a~Tand W. A. PLISKIN, IBM Journal 8, 376 (1964). Measurements are reported of planar, npn silicon transistors with and without a phosphosilicate glass layer over the SiO2 passivation layer. The phosphosilicate layer forms during the emitter diffusion from a P2Os source, and the data show that, to insure stability, it must not be removed in subsequent processing steps. The units tested were of conventional geometry except for a gate electrode over the base region, which provided additional information on the surface condition. The transistors were subjected to temperatures of 150 and 200°C with either gate-bias or junction reverse-bias. Production transistors without gates, which had failed on life test were shown to have no phosphosilicate layer because it had been removed by excessive etching during fabrication. Additional evidence for the stabilization by P20 5 has been obtained by using metal-oxide-silicon capacitors with and without PoO~ treatment of the SiO2 layer. Both d.e. conduction through the insulator and stability of the capacitance-voltage characteristic were measured. These experiments suggest that the transistor degradation with unstabilized SiO2 is caused by an accumulation of positive space-charge in the silicon dioxide. This charge accumulates when an electric field (directed toward the silicon) is applied to the SiOz at temperatures in the range of 150°C. Effect of temperature and bias on glass-silicon interfaces. D. R. KEaR, IBM Journal 8, 385 (1964). New technologies for deposition of thin glass on silicon substrates have generated interest in the resulting glass-silicon interface potentials and the interface stability under conditions of bias and
A B S T R A C TON S MICROELECTRONICS AND RELIABILITY
The heating in vacuum of silicon substrates to temperatures greater than 800°C. J. WALESand A. J. J~,L, Journal of Scientific Instruments 41, 521 (1964). A technique is described for heating substrates to temperatures in excess of 1200°C by means of art electron gun heater. The electron gun consists of two stainless steel current electrodes mounted in a molybdenum lid which clips on to the inner of two concentric molybdenum cylinders. The cathode is a molybdenum spiral painted with lanthanum boride. The substrate is placed in a 0.01 in. thick tantalum spoon. A supply of 100 rm~kat 900 V has been found sufficient to heat a silicon substrate to a temperature of 1200°C, at a distance of 1 cm from the electron source. Basic considerations in integrated circuit design. L. STERN. Electro-Technology 7, 91 (1964). Optimum design of integrated circuits is dependent to a large extent on familiarity with the economics as well as the design freedoms and limitations of the technology. This article relates these basic considerations by discussing what can be integrated, what type of packaging is best, and what type of integrated circuit is most economical. Space-charge model for surface potential shifts in silicon passivated with thin insulating layers. J. E. THOMAS, JR. and D. R. YOUNG,IBM Journal 8, 368 (1964). Semipermanent changes in the semiconductor surface potantial occur in insulator-covered semiconductors when external fields are applied for long times, particularly at elevated temperatures. An attempt to explain these changes in terms of the charging and discharging of interface states leads to conclusions that disagree with many of the experimental facts. Specifically, the semipermanent effects of interface-state charges can always be overcome by the application of a field smaller than that which is used to induce the effect, and of the same sign, while the experiments described in the accompanying papers generally show that a field much larger than the inducing field, and of the opposite sign, is required to return the insulator covered surface to its initial status. The accumulation of space charge in the insulating layer can give rise to very large fields at the semiconductor surface that persist after the removal of an external inducing field. The size and sign of such space-charge fields agree with the experimental observations. Measurements made after treatment of temperatures above 125°C show that the surface of silicon passivated with silicon dioxide can become strongly n-type as a result of such a positive space-charge layer formed at the interface. A model is presented based on the concept that this space charge arises from oxygen vacancies in the silicon dioxide. It is suggested that the improvement resulting from the use of phosphorus pent toxide on the outside surface is due to the elimination of vacancies by the oxidizing action of the phosphorus pentoxide. Stabilization o f SiO.., passivation layers with P,,O 5. D. R. KERR, J. S. LOCaN, P. J. BURKHA~a~Tand W. A. PLISKIN, IBM Journal 8, 376 (1964). Measurements are reported of planar, npn silicon transistors with and without a phosphosilicate glass layer over the SiO2 passivation layer. The phosphosilicate layer forms during the emitter diffusion from a P2Os source, and the data show that, to insure stability, it must not be removed in subsequent processing steps. The units tested were of conventional geometry except for a gate electrode over the base region, which provided additional information on the surface condition. The transistors were subjected to temperatures of 150 and 200°C with either gate-bias or junction reverse-bias. Production transistors without gates, which had failed on life test were shown to have no phosphosilicate layer because it had been removed by excessive etching during fabrication. Additional evidence for the stabilization by P20 5 has been obtained by using metal-oxide-silicon capacitors with and without PoO~ treatment of the SiO2 layer. Both d.e. conduction through the insulator and stability of the capacitance-voltage characteristic were measured. These experiments suggest that the transistor degradation with unstabilized SiO2 is caused by an accumulation of positive space-charge in the silicon dioxide. This charge accumulates when an electric field (directed toward the silicon) is applied to the SiOz at temperatures in the range of 150°C. Effect of temperature and bias on glass-silicon interfaces. D. R. KEaR, IBM Journal 8, 385 (1964). New technologies for deposition of thin glass on silicon substrates have generated interest in the resulting glass-silicon interface potentials and the interface stability under conditions of bias and