STUDYING LOW-PRESSURE CHEMICAL-VAPOR-DEPOSITION A-SI-B ALLOYS BY OPTICAL SPECTROSCOPY

As-deposited and wet oxidized a-Si:B alloys deposited by low-pressure chemical vapor deposition with various boron content were studied by v isible optical spectroscopy and Fourier transform infrared spectroscop y. It is found that the optical band gap of a-Si:B varies with respect to the boron content. This effect is associated with the structure ch ange induced by B content. After oxidation, the Si-O stretching peak a t 1108 cm(-1) shifted to 1079 cm(-1). The oxidation behaviors of films with boron content 3%-25% are different from those with boron content exceeding 30%. For B content between 3% and 25%, besides the remarkab le change around 1100 cm-(1), there are also notable changes around 16 00-1300 cm(-1), and 1000-500 cm(-1), which indicate the increase of B- O bonds and decrease of B-B bonds. However, when the B content exceede d 30%, the change of Si-O bonds was enhanced while the change of B-O b onds and B-B bonds was suppressed. A possible structure and oxidation mechanism for different boron content a-Si:B films is proposed. (C) 19 98 American Vacuum Society. [S0734-2101 (98)05804-7].