Real-time, in-situ particle monitoring in a high current ion implantation production bay

Abstract

This work shows how end station particle levels can be made a real-time process control variable, using sensors that measure the local particle flux and particle size distribution. These sensors are passive and vacuum-compatible, and operate continuously. A typical installation is in the end station in very close proximity to the front of the spinning wheel that holds the wafers during processing. This provides immediate response when moving particles are present in front of the wafer during the process. Sensors in the end station of implanters from different manufacturers were linked to a central computer that logs particle activity during each production batch. This provides real-time warning of major particle generating events; such as, wafer breakage and excess photoresist debris generation. The article focuses on the use of real-time monitoring for measurement and control of particle levels. Examples show how the system can detect lot-to-lot variations and major particle generating events, and how autocleaning can be optimized with real-time feedback to aid in running an implanter consistently clean. Correlation between the particle counts and wafer surface counts is also addressed.