Ion beam micromachining method

Abstract

Millimeter-wave electronic devices are produced first by micromachining an epitaxial layer on a substrate wafer to a precise thickness by directing an ion beam over the epitaxial layer. Any bombardment damage is removed by a light chemical etch. Thereafter, an insulative layer with a mask is placed over the micromachined epitaxial layer and the ion beam is broadly directed onto the masked wafer to micromachine precise holes through unmasked portions of the insulative layer. Micromachining may proceed until approximately 500 A thickness of the insulative layer remains, this remaining layer being removed by a brief chemical etch to expose the underlying epitaxial layer. Alternatively, in cases where a slight recess into the semiconductor is desired to alter the electric field lines at the interface between the oxide and the semiconductor, the ion beam may be permitted to etch completely through the oxide film and into the epitaxial layer to the desired depth. Precise thinning of the epitaxial layer is obtained by holding the wafer down by a metallic tab which serves to retain and act as a shield against sputtering by the normally incident ion beam. Following removal of the desired layer thickness, the wafer is removed from the system and the amount of the material which was removed is verified by measuring the step height produced at the edge of the masking tab. Removal of additional material may be required and the wafer may be reinserted into the system with the same masking retainer tab.