| 摘要 |
PURPOSE:To monitor the etching state of a piezoelectric diaphragm by providing split electrodes in pairs to one side of the piezoelectric diaphragm and applying an AC current to the split electrodes to as to attain horizontal electric field excitation. CONSTITUTION:When a crystal resonator is used for the piezoelectric vibrator, since the resonance frequency is inversely proportional to the thickness of a crystal flat plate 2 in general, a resonance frequency (f) inversely proportional to the thickness (t) including the thin split electrode 3 provided on one side is expressed as f=K/t (where K is a thickness frequency constant). When the face opposite to the face having the split electrodes 3 is subject to, e.g., dry etching or reactive ion etching under vacuum, the increment DELTAf of the frequency corresponding to the decrement DELTAt of the thickness thereby is expressed as DELTAf=-K'f<2>DELTAt, and the etching amount DELTAf is can be known by monitoring the DELTAf. A loop oscillating circuit network known as the transmission method having a phase adjusting amplifier 8 is used for the purpose. |
