An investigation of a new generation of progressive mask defects on the pattern side of advanced photomasks

Progressive mask defect problems such as crystal growth or haze are key yield limiters at DUV lithography, especially in 300mm fabs. With the high energy photons involved in DUV lithography and large wafer size requiring longer continuous exposure of masks, chances of photochemical reaction increases significantly on the masks. Most of the work published on this subject so far has been focused on defect growth on clear area (on the pattern surface) and on the back-glass of the mask. But there is a new generation of growing defects: crystals that grow on the half-tone (MoSi) film or on the chrome film, on the pattern side of the mask. It is believed that the formation mechanisms and rates are different for these new types of crystals. In light of this instability of masks in volume production, it becomes more important to understand the nature of such defects. The purpose of this investigation is to characterize the nature of these new defect growths and to understand the possible formation mechanisms involved in such problems.