PROJECT TITLE :
Experimental Analysis of Vapor HF Etch Rate and Its Wafer Level Uniformity on a CMOS-MEMS Process
This paper presents the characterization results of the discharge step with vapor hydrofluoric acid on a Complementary Metal Oxide Semiconductor-Microelectromechanical Systems (CMOS-MEMS) process obtained with a new methodology for controlling the release etch method of CMOS-MEMS devices. The effect of unleash hole size on etch rate and uniformity was investigated. No appreciable effects were observed for release hole sizes between zero.48 and 1 μm2. With-in-wafer uniformity higher than threepercent and wafer-to-wafer variability better than 2.five% were found, while achieving constant etch rates of ~zero.twenty five μmmin-one and maintaining the required selectivity. The new characterization methodology relies on monitoring capacitance values of a group of check structures distributed across the analyzed wafers instead of monitoring oxide undercuts. A brand new parameter defined as etch ratio greatly improved the accuracy of this system by removing undesirable contributions to the capacitance coming from sources not connected to the discharge method itself. Results showed that this methodology provides a characterization accuracy one order of magnitude better than what was achieved with a methodology based on optical measurements of oxide lateral undercuts.
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