Focused ion beam micromachined three-dimensional features by means of a digital scan

Focused ion beam micromachining (FIBM) is a promising new technique capable of forming optical quality surfaces in semiconductor laser materials. A beam of 25 keV Ga+ ions focused to a 50-250 nm spot can sputter materials from a wafer surface providing a method for fabricating submicron features, such as diode laser output mirrors and coupled cavity oscillating mirrors. To date, all mirrors fabricated by traditional FIBM have been made up of lines or rectangles (i.e., fabricated by straight line scans). However, straight line scans cannot be satisfactorily used for many kinds of applications. In order to fabricate arbitrary structures such as curves and intersecting lines, a fully digitized, nonlinear, three-dimensional (3D) and variable-speed scan strategy, which can produce desired structures with arbitrarily curved paths in a plane and arbitrary depth profiles, has been developed. This strategy has been implemented using a FIB system with an IBM-compatible computer to fabricate "V", and micro-"V" and parabolic mirrors in GaAs lasers. A simple computer simulation of FIBM in 3D space, which is based upon a Gaussian current distribution for the ion beam, has been developed to demonstrate the difference between the two scan strategies, i.e., with and without variable-scan speed. The aim of the 3D simulation is software support for the computer controlled FIB micromachining of various 3D structures on semiconductor diode laser devices.