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The shrinkage of semiconductor devices creates demand for micronization in the photolithographic process. As a result, problems are arising in photolithography in the semiconductor manufacturing process. Focus latitude in photolithography becomes smaller as micronization advances and therefore the flatness of the mask can no longer be ignored. In the previous work, we clarified what the specification of mask flatness should be from the standpoint of its warpage in vacuum chucking of an exposure tool. A two-dimensional approach was applied for the prediction of mask surface after chucking. The approach was simple analytical calculation distinguishing between x-direction and y-direction. Warpage of mask surface after chucking had two modes depending on the directions. On was leverage caused by interaction of mask surface and chucking stage. Another one was warpage along chucking stage surface. The prediction of mask flatness showed good agreement with the actual surface of chucked mask.
In this study, influence of pellicle mounting to the prediction was investigated furthermore. Difference of flatness about 0.1-0.2 μm at the pellicle mounting process was observed. This value of the flatness change is not negligible in order to contrl mask flatness for hp65 nm technology node. However, the difference between the chucked mask surface with the pellicle and that without the pellicle decreased. In order to understand the cause of the change of flatness by pellicle mounting reduced by the vacuum chucking, a simulation analysis by a FEM was performed. The simulation showed that the vacuum chucking reduces the difference of flatness to permissible value. The vacuum chucking of an exposure tool negates the warpage caused by the pellicle mounting. Since the power of the leverage caused by chuck stage is overwhelmingly large as compared with the warpage power of the pellicle, this phenomenon is observed. As a conclusion, the prediction of mask flatness with the vacuum chucking has no influence of the pellicle mounting.
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