Progressive mask defect problems such as crystal growth or haze are key yield limiters for DUV lithography, especially in 300mm fabs. Even if the incoming mask quality is good, there is no guarantee that the mask will remain clean during its production usage in the wafer fab. These progressive defects must be caught in advance during production in the fabs. The ideal reticle quality control goal should be to detect any nascent progressive defects before they become yield limiting. So, a high-resolution mask inspection is absolutely needed, but the big question is: “how often do fabs need to re-inspect their masks”? This re-inspection frequency should ideally be the most cost-effective frequency at which there is minimum threat for a yield loss.
Previous work towards finding a cost effective mask re-qualification frequency was done prior to the above mentioned progressive defect problem that industry started to see at a much higher rate during just the last few years. Other related recent work was done 2004 BACUS conference which is dedicated to DRAM fab data.
In this paper a realistic mask re-qualification frequency model has been developed based on a large volume of data from an advanced logic fab. This work will compliment previous work in this area done with the data from a DRAM fab. Statistical methods are used to analyze mask inspection and product data, which are combined in a stochastic model.
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.
DUV lithography has introduced a progressive mask defect growth problem widely known as crystal growth or haze. Even when incoming mask quality is high, there is no guarantee that the mask will remain clean during its production usage in the wafer fab. These progressive defects must be caught early during production in the fabs. In the absence of a solution for the defect’s root cause, the ideal reticle quality control goal should be to detect and monitor any nascent progressive defects before they become yield limiting.
Most of the work published so far has been focused on crystals 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. This work becomes more important with the impact of such defects’ instability on masks in volume production. The purpose of this investigation is to improve manufacturability of PSM’s through haze contamination reduction and to understand the impact and dependency of this contamination on die yield, on reticle lifetime, and on usage patterns.
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