CHEMICAL SURFACE MODIFICATION OF POROUS SILICON

Resistance to room temperature oxidation and control over wetting properties can be achieved by chemical modification of a porous-silicon surface. Fourier transform infrared spectroscopy was used in the transmission mode to monitor the surface chemistry of both treated and untreated porous-silicon samples before and after exposure to humid air at room temperature. Surface modification methods investigated include: (i) vapor-phase silation using either hexamethyldisilazane or trimethylchlorosilane, 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 trimethylsilyl groups and m suppressing room temperature oxidation. Rapid thermal annealing at temperatures as low as 500-degrees-C for 30 s eliminates all silicon hydrides. Nitrided porous-silicon layers are formed at 1100-degrees-C in either ammonia or nitrogen; in both cases the silicon nitride infrared absorption peaks scale with the porous layer thickness, indicating that the compounds are distributed throughout the porous layer.