In order to create a crystal resonator with a high clock frequency, a new magnetron plasma etching method has been developed. Generation of a stable plasma over a wide range of plasma characteristics was achieved for an external magnetic field type magnetron plasma apparatus based on investigation of the relationship of discharge current and voltage of CF4 plasmas with and without Ar and O-2 as additive gases. By using such plasmas, the etching characteristics of cultured quartz crystals (SiO2) were studied. The etching rates were approximately 80 nm/min for CF(4 )plasmas and 14 nm/min for Ar plasmas. By mixing Ar and CF4 gases, it was confirmed that ion-assist-etching took place by both chemical and physical means. Furthermore, it was found that etching rates increased up to a maximum of 105 nm/min in a plasma mixture containing 20% O-2 Etched crystal blanks (resonators) were obtained with a thickness of less than 10 mu m and with a resonant frequency with a fundamental mode of about 187 MHz.