FIB direct write of ALD Al₂O₃ mask for silicon DRIE

Abstract

The focussed ion beam mill rate of ALD AlOx has been measured and found to be 0.147µm3/nC. Standard FIB milling of the AlOx is conjectured to result in re-deposition of the AlOx material on the milled surfaces hindering the subsequent DRIE etching of the underlying silicon. The use of the enhanced etch gas iodine in the FIB system has been shown to remove this re-deposition and allows the subsequent etch to progress unhindered. Optimisation of the mill gas pressure and beam current density has also been shown to be essential for consistent pattern transfer into the underlying silicon