Effect of protective layer deposition in cross-sectional analysis of focused ion beam in germanium substrate

Abstract

In this work, a single micro-size circular and rectangular holes were fabricated in phosphorus/tin implanted germanium substrate using ion milling of FIB, for potential application in photonic crystal and FINFET. One of the important analysis that need to be done in the future is a cross-sectional analysis in order to evaluate the milling rate of material, redeposition of milled material, and the quality of the milled surface in the pattern structure. However, a well-known practise in preparing a cross-sectional sample for transmission electron microscope analysis using FIB involves a deposition of protective layer on the substrate surface before performing the cross-sectional ion milling, in order to prevent the surface damage. Taking this into consideration, this work performed a preliminary study to analyze the effect of depositing a protective layer onto the hole for performing FIB cross-sectional analysis of the fabricated hole structures. Two-step deposition technique of platinum layer involving electron beam, followed by ion beam was performed on the hole prior to the cross-sectional milling. Hole structure without protective layer was also prepared as a comparison. It is found that although the depth of the milled area can be evaluated in both cross-sectioned holes with/without protective layer, an evaluation on roughness and redeposition are difficult, specifically in the one with protective layer. While the existence of secondary damage might affect the quality of milled surface during the cross-sectional milling in the sample without protective layer.