Passivation of silicon wafer patterned by aluminum for micromachining

Low-pressure chemical vapor deposition (LPCVD) and plasma-enhanced chemical vapor deposition (PECVD) have been used for depositing silicon nitride (SiN) as passivation layer in microfabrications. SiN deposited by LPCVD and optimized PECVD can perfectly mask Si from etching attack in TMAH-water solution. After Al metallization, pinholes are always formed on SiN because of the Al crystal hillocks. Due to poor step coverage of PECVD SiN on Al, the edge etching of the Al patterns is the main reason for Si etching underneath of the Al patterns although the Al etching via the pinholes on SiN contributes. By structure designing and process tuning, we have achieved passivation techniques for micromachining after Al metallization.