DEPOSITION OF TIN OXIDE INTO POROUS SILICON BY ATOMIC LAYER EPITAXY

The deposition of conformal coatings into porous silicon layers was su ccessfully demonstrated. Tin oxide films were formed from SnCl4 and H2 O precursors by atomic layer epitaxy. The influence of the porous subs trate structure on the deposition parameters was analyzed from the vie wpoint of formation mechanism growth rate, and layer composition. The SnOx covered porous substrates were characterized by means of Rutherfo rd backscattering, secondary ion mass spectrometry: cross-sectional tr ansmission electron microscopy, and ellipsometry. The mesoporous struc ture of the Si substrate uniquely determines the gas-phase diffusion a nd physisorption of the precursors. The processing parameters favoring chemisorption are more critical for porous silicon than those for a f lat surface. Even a small decrease in the deposition temperature resul ts in a considerable increase in the growth rate through gas-phase rea ctions, and the process becomes chemical vapor deposition-like. Confor mal step coverage was obtained on extremely high (140:1) aspect ratio pores if the deposition conditions were chosen such that chemisorption was the growth rate determining step in the process.