A Fully Automated VPD System for Noble Metal Control during CIS Manufacturing

Metallic contamination has long been reported as a source of defects for most semiconductor devices, and its impacts on complementary metal-oxide-semiconductor (CMOS) image sensors (CISs) are especially detrimental. These contaminants could be introduced during the CIS fabrication, such as ion implantation process [1-2]. Wafer surface concentration of certain noble metals, including Au, Ag, and Pt, needs to be controlled to no more than 0.05 to 0.2 ppt [6]. Conventional methods of metal trace analysis involve chemically collecting these elements into a scanning solution, and analyzing the diluted scanning solution by inductively coupled plasma mass spectroscopy (ICP-MS). However, detecting the concentration of noble metals on wafer surface has been particularly challenging, due to their low solubility in scanning solutions. In this paper, the authors proposed a method to effectively collect the noble metals, especially silver and gold, with an aqua regia (AR) based scanning solution to increase the collection efficiency (CE). Combined with a vapor phase decomposition (VPD) treatment of the wafer surface, and an integrated ICP-MS analysis, our fully automated method of AR based noble metal collection is of great importance to control the noble metal contamination for CIS manufacturing.