16 August 2004 Real-time monitoring of thickness of silicon membrane during wet etching using a novel surface acoustic wave sensor
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Abstract
This study presents a novel method based on the surface acoustic wave (SAW) sensor, for monitoring the thickness of a silicon membrane in real time during wet etching. Similar to accelerometers and pressure sensors, some micro-electro-mechanical systems (MEMS) devices require the thickness of silicon membranes to be known precisely. Precisely controlling the thickness of a silicon membrane during wet etching is important, because the thickness strongly affects post-processing and device performance. Moreover, the proposed surface acoustic wave sensor allows the thickness of a silicon membrane to be monitored from a few μm to hundreds of μm in situ, which depends on the periodicity of interdigital transducers (IDT). A novel method, which differs from any in previous work on etch-stop techniques, is developed in-situ for monitoring the thickness of a silicon membrane during wet etching. In summary, the proposed method for measuring the thickness of a silicon membrane in real time, is highly accurate; is simple to implement, and can be mass-produced. This work also describes the principles of the method used, detailed process flows, the method of taking measurements and the simulated and experimental results. The theoretical and measured values differ by an error of less than 2.50μm, so the results closely agree with each other.
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Chi-Yuan Lee, Chi-Yuan Lee, Tsung-Tsong Wu, Tsung-Tsong Wu, Yung-Yu Chen, Yung-Yu Chen, Ying-Chou Cheng, Ying-Chou Cheng, Wen-Jong Chen, Wen-Jong Chen, Shih-Yung Pao, Shih-Yung Pao, Pei-Zen Chang, Pei-Zen Chang, Ping-Hei Chen, Ping-Hei Chen, Kai-Hsiang Yen, Kai-Hsiang Yen, Fu-Yuan Xiao, Fu-Yuan Xiao, } "Real-time monitoring of thickness of silicon membrane during wet etching using a novel surface acoustic wave sensor", Proc. SPIE 5455, MEMS, MOEMS, and Micromachining, (16 August 2004); doi: 10.1117/12.544959; https://doi.org/10.1117/12.544959
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