Thinning of Si in SOI Wafers by the SC1 Standard Clean

SOI structures are becoming progressively thinner as device dimensions are scaled down. Although thinner layers of Si and SiO sub 2 can be made directly by (a) reducing the dose and energy of oxygen ions in the SIMOX process and (b) using lower H+ implant energy in the SmartCut(TM) wafers, there are limits to how thin Si Films can be made that way. Therefore, direct thinning methods are often used to obtain the final thickness of Si on the buried oxide (BOX) layer. Sacrificial oxidation is frequently used, a process in which oxidation consumes Si and the oxide is removed by wet etching in a HF solution. Direct wet etching of Si is not used since the etch rates are not as well controlled as oxidation rates, and significant roughening of the surface may occur. In this paper, we discuss application of a conventional surface cleaning procedure for adjusting silicon film thickness. We also want to point out that silicon removal during cleaning steps has to be taken into account when processing thin SOI films.