FOCUSED ION-BEAM MILLING - DEPTH CONTROL FOR 3-DIMENSIONAL MICROFABRICATION

Ion milling with a focused ion beam (FIB) is a potential method for ma king micromolds, which will then be the primary elements in the mass p roduction of micro-or mini-objects by embossing or injection molding. The challenge lies in controlling the ion milling to produce cavities with predefined, arbitrary geometric cross-sections. This work involve s programming variations as a function of position into the algorithm that generates the dwell times in the pixel address scheme of a FIB. T hese variations are done according to whether an axis of symmetry or a plane of symmetry determines the final geometry, and the result is 26 new cross-sectional shapes, such as hemispherical pits, parabolic pit s, hemispherical domes, etc. The ion milling control programs were use d to generate parabolic cross-section trenches, sinusoidal trenches, s inusoidal cross-section rings on an annulus, and hemispherical domes. We observed reasonable agreement between the shapes ion milled in Si(1 00) and the expected geometry. The dwell times are generated assuming each pixel has a unique dose and the ion yield is constant with angle of incidence. Deviations from ideality are ascribed to the variation i n sputter yield with changing angle of incidence, and to the dwell tim e control algorithm. Redeposition also compounds the deviation from id eality, but it is difficult to estimate the magnitude of this effect. (C) 1997 American Vacuum Society.