Apparatus for dry chemical etching caused by ion bombardment of a substrate placed in a vacuum chamber. The substrate is in contact with an electrode, connected to a high frequency bias voltage source having one terminal connected to a ground of the chamber. The etchants are produced in the form of plasma by an electrical discharge maintained in the chamber containing a gas or a suitable gaseous mixture. The plasma is produced by a microwave generator and the bias voltage by means of a high frequency source. The respective amplitudes and frequencies of the two sources enable the base of a groove on an electronic circuit to be etched without erosion of the groove.