GaAs and other III–V semiconductor integrated circuits (ICs) are fabricated on semi-insulating (SI) substrates, unlike silicon which are generally semi-conducting. Therefore, isolation ion implantation using elements such as helium (He) is performed after partial etching of the semiconducting layers to isolate adjacent devices and circuit elements (Pearton in Nucl Instrum Methods Phys Res B 59–60:970–977, 1991; Sharma et al. in Mater Sci Semicond Process 87:195–201, 2018). To precisely monitor such processes, a short-loop test structure for inline monitoring of multi-step isolation ion implantation was innovated. The short-loop test structure is used to measure the implanted base sheet resistance using the transmission line model (TLM) by utilizing metal deposition prior to implant for the test structure’s pads and interconnects. This development allows for the structure to be measured immediately after the implant process and give precise results, instead of waiting weeks for final DC parametric test data. It improves detection limits of dose and/or energy shifts in the implant process that has not yet been proven possible with other methods currently available. Graphical Abstract
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