Real-Time Water Leak Detection and Preventing Yield Excursions in Lithography

Cooling water is extensively used in photolithography for temperature control of coating and developing[1]. Water leaks can cause failure in semiconductor manufacturing processes [2], resulting in significant wafer yield loss. Inspecting or replacing all water jackets periodically is time- consuming and costly. Due to a rapid flow of cooling water running at 5l/min in TEL Track [3], it is hard to detect bubbles in the TCU (temperature control unit) return line by ordinary bubble detection methods readily available on the market. A photoelectric sensor with a retro-reflective type can be used to detect high-speed liquid or bubbles in specific applications. When an object, such as a liquid or bubble, passes through the beam of light, the amount of light reflected in the sensor changes, which can trigger an output signal. This paper will present a cost- effective setup of fiber optic evanescent sensors for early detection of water jackets or tubing cracks to eliminate the risk of wafer defects due to potential liquid leaks.