Hydrogen Passivation of Polycrystalline Silicon

Abstract

Defects in polycrystalline silicon sheet which are associated with high angle grain boundaries, twin boundaries, and intragranular dislocation arrays have all been shown to be amenable to hydrogen passivation. Using the EBIC technique, it has been shown that nearly all the recombination producing defects can be passivated down to depths of 10–20 μm and that passivation depths of several hundred microns can sometimes occur. A model is advanced whereby the key defects being passivated are dislocations and where deep passivation is effected through rapid thermal diffusion down dislocation arrays, either in intragranular regions or in the grain boundaries themselves. Hydrogen diffusivity down grain boundaries and twin boundaries has been measured to be 10⁻⁸ to 10⁻¹⁰ cm²/sec. Diffusivity down intragranular dislocation arrays is < 10⁻⁸ cm²/sec. Surface recombination velocities, S, of the grain boundaries have been measured as a function of the passivation depth, X; and for X < 35 μm, ℓn S ∝ −X. Enhanced EBIC contrast at T = 100°K has been interpreted as due to shallow electron traps within ~0.1 eV of the conduction band edge. Such shallow traps do not seem to be subject to passivation while presumed deeper lying recombination levels at the same spatial location do respond to hydrogen passivation.