Silicon wafer etching is frequently used in micromachining and microelectronic fabrication processes. How to precisely control the thickness of etched silicon membrane is very challenging. Controlling the etching depth by controlling the etching time can result in large errors due to fluctuation of etching rate. A more accurate in-situ silicon membrane thickness monitoring system during silicon wafer etching is very necessary. In this poster, we proposed a silicon membrane thickness in-situ monitoring system based on optical sensing. A halogen lamp generates light to be passed through the silicon membrane. The light is partially absorbed while transmitting the silicon wafer depending on the thickness of the membrane. Two photodiodes are used to detect the lights passing through the silicon membrane at different wavelengths. The difference of the readings is used to cancel out the common errors, hence leading to improved accuracy. The system is designed and simulated to verify its optical responses. The experimental setup of the system is implemented and the results are analyzed. The proposed Silicon membrane thickness monitoring system can be used to monitor and control the etching depth to achieve precise silicon membrane thickness as needed
