Investigation of Factors Causing Watermark Defect on Hydrophobic Silicon Surface

Watermark defect has been known to occur in HF (Hydrofluoric acid) last wet clean process due to the Hydrophobic nature of the exposed Silicon surface. Some water mark causing factors such as HF concentration, humidity, presence of megasonic in rinse etc. are well known to the industry. In this paper, new factors causing watermark defect on silicon surface and the recommended solutions are proposed. HF chemical bath batch life, HF dip duration and DI water rinse duration are identified as the factors that promote watermark defects. Avoiding running wafer in fresh HF chemical batch, reducing HF dip duration and DI water rinse duration are very important to prevent watermark defect on sensitive silicon surfaces.