Ion-induced deposition for x-ray mask repair. Rate optimization using a time-dependent model

Focused ion beam (FIB) induced tungsten deposition is a very promising candidate for the repair of clear x-ray mask defects. However, it requires careful process control due to the sputtering which accompanies deposition. To improve our understanding of the process and to optimize its parameters in view of high-throughput mask repair, we developed a model of FIB induced deposition. It is based on a model reported previously, but additionally includes two parameters of outstanding importance for the process: the FIB's dwell time and its loop time. The model was tested by applying it to the results of deposition experiments in which the influence of various parameters on the growth rate was investigated. Based on that comparison between experiment and theory, we make a prediction on the achievable repair speed as a function of the defect size. In our experiments, we obtained deposition rates of up to 20nm/s. The x-ray opacity of the deposited layers is in the order of 80% of the tungsten bulk value.