Anisotropic Wet Etching Process Research Articles

Analysis and prevention of convex corner undercutting in bulk micromachined silicon microstructures

Convex corner undercutting in <100> silicon is an undesired phenomena during bulk micromachining of crystalline silicon substrate using anisotropic wet chemical etching process. The present investigation concentrates on the studies of convex corner undercutting at the free end of silicon cantilever beams released by anisotropic etching process. It also reports a simple, space efficient compensation design for complete prevention of corner deformation. Various compensation patterns such as square, rectangle and superposition of square and rectangular blocks of various dimensions have been employed at the free end corners of cantilever beam to protect corner deformation due to undercutting. The experiment was carried out in 44wt.% KOH at 70°C using <100> oriented silicon wafer. Both n-type and p-type silicon wafers were used to study the variations in the nature of corner deformation. A simple empirical relation has been obtained from the experimental data to calculate the lateral dimensions of the compensation layout from the total etch depth required to release the structure.

A novel micromachined vibrating rate-gyroscope with optical sensing and electrostatic actuation

This paper reports the fabrication and preliminary characterization of a novel vibratory rate-sensor. The sensor employs the modulated integrative differential optical sensing (MIDOS) to detect the output mode amplitude. The mechanical part of the sensor is fabricated by bulk micromachining using a double side anisotropic wet etching process. A CMOS chip containing the detecting photodiodes and their readout electronics is fabricated through MOSIS. Electrical and mechanical integration of the two parts is achieved by using the indium bumps technology. The proof mass is aligned with the detecting photodiodes, so that when at rest, equal portions of the two photodiodes are exposed. Several prototypes have been fabricated and tested on a rotating table. Good linearity (<1%) was shown on a −1000–1000°/s range and so far, a minimum detectable rate (MDR) below 1°/s was demonstrated. Future research will focus on lowering the MDR below 0.01°/s.

Wet Chemical Etching of High Quality V‐Grooves with {111} A Sidewalls on (001) InP

We have developed a novel anisotropic wet chemical etching process for V‐grooves on (001) InP substrates. The etching was carried out in three steps with solutions of 0.1 volume percent bromine in methanol and (3:1:1). The etching mask was a 30 nm thick film patterned with conventional photolithography and plasma enhanced chemical vapor deposition. It exhibited excellent properties with respect to undercutting. The resulting V‐grooves had very smooth {111} A sidewalls and a tip radius below 10 nm. The uniformity of the etched profile was excellent both along the groove axis and from groove to groove.