Stepper with exposure time monitor

摘要

A method for detecting a degraded light source is provided. An exposure time associated with the light source is monitored. The exposure time is compared to at least one control limit. A degraded condition is identified based on the exposure time violating the control limit. A processing tool includes a stepper and an automatic process controller. The stepper has a light source and is adapted to illuminate a wafer for an exposure time. The automatic process controller is adapted to monitor the exposure time, compare the exposure time to at least one control limit, and identify a degraded condition based on the exposure time violating the control limit.