EB metrology of Ge channel gate-all-around FET: buckling evaluation and EB damage assessment

Electron beam (EB) metrology of Ge channel gate-all-around (GAA) FET (field effect transistor) was investigated. Ge-GAA FET is one of the promising candidates for high performance pMOS device of future node. Ge is superior to Si in hole mobility which can be enhanced further by applying compressive channel strain in GAA structure with SiGe strain relaxed buffer (SRB). Coincide with this advantage, channel buckling could happen more easily. Thus, a monitoring method of channel buckling is required. Chemical instability of Ge is another issue in fabrication process. It is suspected that EB irradiation during SEM inspection could cause the deterioration of device performance. On this background, following two evaluations were performed. The first one is quantitative evaluation of channel buckling. It is found that the channel buckling can be quantified with a proposed buckling index. The second one is assessment of the EB-induced damage on the electrical properties. The results showed that EB irradiation on Ge channels does not affect the device performance when the device is annealed adequately. In conclusion, EB metrology is effective for the evaluation of channel buckling and applicable to Ge channels without deterioration of the device performance.