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As dimension of device shrinks to 1X nm node, an extreme control of critical dimension uniformity (CDU) of masks
becomes one of key techniques for mask and wafer fabrication. For memory devices, a large number of optical
techniques have been studied and applied to mask production so far. The advantages of these methods are to eliminate
the sampling dependency due to their high throughput, to minimize the local CD errors due to their large field of view
(FOV) and to improve the correlation with wafer infield uniformity if they have scanner-like optics.
For logic devices, however, CD-SEM has been a single solution to characterize CD performance of logic masks for a
long time and simple monitoring patterns, instead of the cell patterns, have been measured to monitor the CD quality of
masks. Therefore a global CDU of the mask tends to show its ambiguity because of the limited number of measurement
sites and large local CD errors. An application of optical metrology for logic mask is a challenging task because patterns
are more complex and random in shape and because there is no guarantee of finding patterns for CDU everywhere on the
mask. CDU map still consists of the results from the indirect measurements and the traditional definition of uniformity, a
statistical deviation of a typical pattern, seems to be unsuitable for logic CDU. A new definition of CDU is required in
order to maximize the coverage area on a mask.
In this study, we have focused of the possibility of measuring cell patterns and of using an inspection tool with data
base handling capability, KLA Teron617, to find the areas and positions where the repeating patterns exist and the
patterns which satisfy a certain set of condition and we have devised a new definition of CDU, which can handle
multiple target CDs. Then we have checked the feasibility and validity of our new methodology through evaluation its
fundamental performance such as accuracy, repeatability, and correlation with other CD metrology tools with a set of
logic masks.
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