CHEMICAL SURFACE MODIFICATION OF POROUS SILICON

Resistance to room temperature oxidation and control over wetting prop erties can be achieved by chemical modification of a porous-silicon su rface. Fourier transform infrared spectroscopy was used in the transmi ssion mode to monitor the surface chemistry of both treated and untrea ted porous-silicon samples before and after exposure to humid air at r oom temperature. Surface modification methods investigated include: (i ) vapor-phase silation using either hexamethyldisilazane or trimethylc hlorosilane, and (ii) rapid thermal annealing in nitrogen, ammonia, or argon ambients. The silation treatments, carried out in the presence of trace moisture, were successful both in creating surf ace trimethyl silyl groups and m suppressing room temperature oxidation. Rapid therm al annealing at temperatures as low as 500-degrees-C for 30 s eliminat es all silicon hydrides. Nitrided porous-silicon layers are formed at 1100-degrees-C in either ammonia or nitrogen; in both cases the silico n nitride infrared absorption peaks scale with the porous layer thickn ess, indicating that the compounds are distributed throughout the poro us layer.