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 SiO₂ 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 wafer (Bruel, 1995), there are limits to how thin Si films can be made in 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 SC1 surface cleaning procedure for adjusting silicon film thickness. We also note that silicon removal during cleaning steps must be taken into account when processing thin SOI films.