A physical model based on the statistics of silicon point defects is proposed to explain the commonly observed enhanced oxidation rates of heavily doped silicon. The physical effect of the high doping levels on the Si/SiO2 interface oxidation kinetics is postulated to be primarily electrical in nature. The high doping levels shift the position of the Fermi level toward the conduction band (n-type) or toward the valence band (p-type) even at oxidation temperatures, causing an increase in the equilibrium concentration of point defects (vacancies) in the silicon substrate. These point defects may provide reaction sites for the chemical reaction converting Si to SiQ and thereby increase the rate at which this reaction occurs. This paper describes the theoretical basis for this model and predicts quantitatively the expected oxidation rates for n +-and p+-doped silicon under a wide range of oxidation conditions. Integrated circuit structures and technologies continue to make extensive use of thermally grown silicon dioxide. It is well known that silicon heavily doped with donor or acceptor impurities, as commonly encountered in such device regions as bipolar emitter and MOS source/drain areas, may exhibit oxidation rates significantly enhanced relative to those observed for lightly doped silicon (1). An understanding of such dopant effects on oxidation kinetics, therefore, becomes of obvious importance to device process design and optimization.Some indication of the nature of these effects is contained in a considerable body of kinetic data recently reported for the thermal oxidation of heavily phosphorus-doped (111) oriented silicon in a dry oxygen ambient, in the temperature range 800~176(2). The observed enhancement of oxidation rate with increasing substrate doping levels, as shown for example in Fig. 1 from Ref. (2), is substantial, particularly at the lower oxidation temperatures studied. Oxide thickness vs. oxidation time is shown for six substrate types with the average electrically active phosphorus doping levels indicated. When reduced to the effective rate constants B and B/A of the Deal and Grove oxidation model (3), this enhancement is manifested primarily in a substantial increase in the linear rate constant B/A with increasing substrate doping. Apparently, however, there is only a relatively slight effect on the associated activation energy, as illustrated in Fig. 2 also taken from Ref. (2). Samples A through F in Fig. 2 have the same phosphorus doping levels as in Fig. 1.Analysis of these effects has led to the development of a physical model that may explain these observa-* Electrochemical Society Active Member.

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Ultrathin silicon nitride films prepared by combining rapid thermal nitridation with lowpressure chemical vapor deposition Appl.Stability of hydrogen in silicon nitride films deposited by lowpressure and plasma enhanced chemical vapor deposition techniques J. Vac. Sci. Technol. B 7, 150 (1989); 10.1116/1.584707Hopping conduction in undoped lowpressure chemically vapor deposited polycrystalline silicon films in relation to the film deposition conditionsThe effect of stress in silicon nitride films, deposited by the low-pressure chemical vapor deposition process, on the point defect concentrations in silicon has been studied. The stress level in the nitride film is varied by controlling the ratio offiow rates of reactant gases R = fSiII,ClJfNH" from 1/6 to 6. The stress in the nitride film is tensile and its magnitude increases with decreasing R. During anneals at 1100 °C in Ar with a high stress in the nitride, phosphorus diffusion in silicon is retarded, antimony diffusion is enhanced, and extrinsic stacking faults shrink faster than with a low stress. These results suggest that a vacancy supersaturation and a self-interstitia! undersaturation exist under the nitride and that the deviation from the equilibrium point defect concentrations are closely related to the stress level in the silicon nitride film. From the phosphorus junction profiles with varying shape width, an effective vacancy diffusivity of 3 X 10 -10 eml/s has been obtained.

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We show that a straightforward account of dielectric relaxation current in glasses follows from a semiclassical treatment of the double-well model [P. W. Anderson, B. I. Halperin, and C. M. Varma, Philos. Mag. 25, 1 (1972) and W. A. Phillips, J. Low Temp. Phys. 7, 351 (1972)] explaining the linear specific heat of glasses at low temperature. The current is obtained from the field-induced tunneling of the glass between the minima of its potential energy surface, and is found to have the experimentally observed linear dependence on field and inverse dependence on time. The effects of temperature and prior biases are briefly discussed, as well as the relation of the model to the theory of charge trapping. No dielectric relaxation is expected in a perfect insulating crystal, raising the important technological question of how perfect high-k dielectrics like HfO2 and ZrO2 must be in order to serve as gate dielectrics in transistors.