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Mask defect printability at 0.18-μm design rules for 193-nm lithography

In this paper, the printability of mask defects at 0.18 micrometers design rule is studied via 193 nm top surface imaging (TSI) resist process. The mask defect printability is determined by taking into account the wafer process critical dimension (CD) variability. In the experiment, an 193 nm microstepper with 0.6 NA imaging lens was used to expose the programmed defect mask. The resist CD response to the mask defect area is measured under the different process conditions, i.e., different exposure dose or focus. It is found that similar to a single layer 248 nm DUV resist case that has been studied before, the TSI resist CD responds to the mask defect area linearly for the small mask defects. From such a set of CD-defect response lines, the allowable mask defect requirement is assessed via the statistical explanation of the printable mask defect size which is tied to the wafer process specifications and the actual wafer process CD controllability. Its printability is further verified by the process window measurements. Our results showed that for 193 nm exposure and TSI resist process, a mask defect as small as 0.13 micrometers (4X) is printable at 0.18 micrometers design rule. This printable mask defect size is approximately independent of mask bias in a linear CD region, i.e., a region in which the resist CD responds to the mask CD linearly. Although the above experimental results are obtained based on a TSI process, many characteristics of mask defect behavior can be generalized to the other resist processes. Based on the statistical defect printability analysis method that we have developed, the printable mask defect size can always be re-defined without additional data collection when the process control or the process specification changes.