Groove depth uniformization in [110] Si anisotropic etching by ultrasonic wave and application to accelerometer fabrication

We studied the use of ultrasonic waves to obtain uniform groove depth in (1 10) Si anisotropic etching. Using dynashock type ultrasonic waves, whose frequency is switched between 3 frequencies at very short intervals, grooves with uniform depth could be successfully formed with widths of 1-20 ~m independently of pattern width and pattern spacing. This technology was applied to the fabrication of an accelerometer with comb-type narrow gap electrodes. Comb electrodes with a minimum gap of 3.0 ~m and a height of 58 ~m could be formed uniformly, although they had different pattem widths and pattern spacings. The capacitance of this device has a high sensitivity to acceleration of 39 pF/g. By combining it with an output CV converter and amplifiers, we produced a sensor with good full-scale linearity of 0.63% over the acceleration range of -2 to +2 g.