Image quality improvement in focused ion beam photomask repair system

Focused ion beam (FIB) technology has widely been adopted as a defect repair tool on photomasks for semiconductor manufacturing. In the FIB mask repair process, scanning ion image (FIB image) is used for the defect area recognition. Quality of the FIB images is one of the most important factors in order to improve the repair accuracy. Precise imaging of the small features on the photomasks, however, is a challenging subject due to the surface charge buildup induced by FIB scanning, even though simultaneous electron beam irradiation is used for the charge compensation. The authors have developed new method of the FIB scanning for better image quality. This method utilizes software accumulation of multiple images with different scan directions and results in higher peak-to-background ratio and higher contrast images with isolated mask patterns on the quartz substrate, compared to the images acquired from conventional single scanning. The images also show better uniformity and symmetry of the secondary electron intensity.