Hydrogen Passivation of Oxygen Donors in Si
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HYDROGEN PASSIVATION OF OXYGEN DONORS IN Si L. C. KIMERLING, S. J. PEARTON, A. M. CHANTRE, and W. C. DAUTREMONT-SMITH AT & T Bell Laboratories, 600 Mountain Avenue, Murray Hill, NJ 07974
K. D. CUMMINGS
ABSTRACT The electrical activity of the oxygen-related thermal donors in heat-treated, P-doped, Czochralski grown Si is passivated by reaction with atomic hydrogen. Secondary ion mass spectrometry and spreading resistance profiles on deuterium plasma treated samples show a direct correlation between the deuterium incorporation depth and the distance over which the thermal donors are passivated. The donor activity is restored by annealing above 400"C, and comparison with other defect dehydrogenation data suggests that the thermal donors may contain Si dangling bonds. Results obtained from deep level transient spectroscopy measurements are used to illustrate the observed donor passivation and reactivation kinetics.
INTRODUCTION Oxygen aggregation phenomena in Si have been the focus of considerable attention over a long period. [ 1-3] Czochralski (CZ) grown Si contains concentrations of interstitial oxygen close to 1018 cm- 3, which, during low temperature (-450'C) heat treatment, form the well-known thermal donors. [1 ] While the formation and annihilation kinetics of these entities have been known and used in device fabrication processes for many years, the detailed microstructure of the thermal donors is still the subject of a degree of controversy. [3,41 In this paper we report the passivation by reaction with atomic hydrogen of electrical activity of thermal donors in 450"C heat treated Si. The depth of the passivation effect is limited by the diffusivity of atomic hydrogen in the Si at a particular donor density and is typically -0.5jm after a 1h, 120"C exposure of the sample to a low pressure hydrogen plasma. Isotopic substitution of the hydrogen by deuterium, combined with secondary ion mass spectrometry (SIMS) profiling shows a direct correlation of the thermal donor passivation depth with the deuterium incorporation distance.
EXPERIMENTAL Phosphorus-doped, (100), CZ grown Si wafers with starting resistivities in the range 210flcm were chemically cleaned and heat treated at 450°C for periods between 62-94h in Ar. Spreading resistance and capacitance-voltage data after the annealing cycle showed an increase in the net donor concentration in samples from different crystals, 6-20 X 1014 cm- 3 to 5-60 x 1015cm-3, depending on the actual duration of the anneal. The increase in donor concentration was uniform over the depth probed (0-10Mm from the surface) and is due to thermal donor introduction. Atomic hydrogen was incorporated into the Si by exposing the samples to a 750mtorr, 0.08W cm-2, 30kHz plasma for 1-3h with the sample held at -120"C. On some occasions a deuterium plasma was used in order to obtain quantitative profiles of the deuterium by SIMS. Those measurements were performed on a Cameca IMS 3f system using a C+ ion beam with detection of the D- secondary ions. [5] The ion intensities were converted
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