Exploring Cryogenic Focused Ion Beam Milling as a Group III-V Device Fabrication Tool

The studies reported here were carried out in order to explore the potential applications of cryogenic focused ion beam (cryo-FIB) milling as a Group III-V device fabrication tool. Cryogenic cooling of III-V semiconductor material during Ga+ FIB irradiation has recently been reported to suppress the reactions between the Ga ions in the FIB and the III-V elements in the material, yielding patterned features that are cleaner than comparable features defined by FIB milling at room temperature. In this paper, we compare the features observed on our III-V strained layer superlattice (SLS) materials system as a result of room temperature FIB milling to the features observed as a result of cryo-FIB milling (at -135°C) under the same beam conditions (30 kV:1 nA). The features on the cryo-FIB milled material were observed both when the material was still cold and after it returned to room temperature. We found that both room temperature FIB milling and cryo-FIB milling with subsequent sample warm-up resulted in the formation of Group III enriched features which are similar in some aspects to features observed on other FIB milled III-V materials as reported in the literature. However, we speculate that the features observed on cryo-FIB milled III-V materials after warm-up will be materialdependent, and in light of recent studies [3], dependent upon the sample warm-up conditions (i.e., rate and environment). The suggestion that the structural and chemical properties of features fabricated by cryo-FIB milling are temperature- and atmosphere-dependent is an important consideration when it comes to device fabrication, and these dependencies will need to be better​ understood and controllable if cryo-FIB milling is to have future applications in this area.​