Al-Cu Pattern Wafer Study on Metal Corrosion Due to Chloride Ion Contaminants

Abstract

Chloride ions (Cl(-)) in the cleanroom environment induce metal corrosion of integrated circuits, and cause wafer scrap events. In this paper, pattern wafers were designed to monitor critical Cl(-) concentration which leads to metal corrosion effects in a simulated airborne molecular contamination (AMC) environment. The simulated Cl(-) contamination environment was established by placing different numbers of preventive maintenance (PM) wipers in wafer pods and monitored simultaneously by ion mobility spectrometer (IMS) and impinger+ion chromatography (IC) instruments. The exposed Al-Cu pattern wafers were analyzed by the KLA surface scanner and the scanning electron microscope/energy dispersive X-ray spectroscopy analyzer. The results indicate that the IMS and the impinger+IC instruments provide consistent HCl monitoring data. Furthermore, they suggest that pattern wafer exposure tests can be an effective method to monitor metal corrosion. The PM wipers are a simple and effective method to establish simulated source of HCl for studying the AMC effect in ppbv levels. The critical HCl concentration where particles could be found on the wafer surface is around 2.0-3.5 ppbv, and the critical HCl concentration that results in metal corrosion defects is around 4.1-6.4 ppbv.