Aluminum oxide hard mask fabrication by focused ion beam implantation and wet etching

Abstract

A novel aluminum oxide (Al2O3) hard mask fabrication process with nanoscale resolution is introduced in this work. The Al2O3 mask can be used for various purposes, and in this thesis it was utilized for silicon patterning using cryogenic deep reactive ion etching (DRIE). Patterning of Al2O3 is a two-step process utilizing focused ion beam (FIB) irradiation combined with wet etching. Ga+ FIB maskless patterning renders wet etch selectivity between the irradiated region and the non-irradiated region on the Al2O3 layer, and mask patterns can be easily revealed by wet etching. This method is a modification of direct Ga+ FIB implantation for silicon etch stop. Introducing an Al2O3 layer eliminates the lattice damage and doping to silicon substrate in critical devices, as an extra film protects the underlying silicon from Ga+ ions. Masking capacity is evaluated in terms of equal width line and space pairs amount per 1 µm in a nano-line array. 7 pairs per 1 µm is achieved in this work.