Deep reactive ion etching of GaSb in Cl2/Ar-plasma discharges using single-layer soft mask technologies

Technologies for GaSb dry etching employing Cl 2 /Ar-plasma discharges are reported. Etch rates higher than 2 μm min −1 are achieved in a conventional reactive ion etching (RIE) chamber. To our knowledge these are the highest etch rates reported in GaSb dry-etch technology with conventional RIE. Also, three different single-layer soft mask processes are described and compared with respect to suitability for deep RIE of GaSb. Soft masks have many advantages over (metal) hard masks, such as easy and inexpensive processing, low pinhole density and high etching reproducibility. The well known AZ5214E resist from Clariant allows for GaSb etch depths of up to 6.4 μm keeping dimensional accuracy. Using TI 35ES photoresist, developed by MicroChemicals, GaSb etch profiles of up to 51 μm depth are obtained revealing considerable dimensional stability. This photoresist material is reported in the literature for the first time. By applying optimized GaSb dry-etch parameters, SU-8–50, an epoxy-type resist, developed by MicroChem Corp., will show an outstanding resist mask lifetime of up to 420 min, if SU-8–50 is spin-coated to a thickness of 80 μm. Thus it is possible to achieve GaSb etch depths beyond 100 μm. Deep dry etching of GaSb can be exploited to fabricate fiber or capillary connections, or to create substrate windows for backside-illuminated photodetectors for the mid-infrared (MIR) wavelength range.