Improving the measurement accuracy of pattern width and position of x-ray masks

Abstract

Precise measurement of the pattern position and width of x- ray masks is very important for producing highly accurate masks. When the position and width are measured by an optical system while moving the mask on an x-y stage in air, degradation of measurement accuracy or unstable focusing can sometimes occur. To investigate these phenomena, we estimated the measurement accuracy of pattern width and position. A comparison of the measurement accuracy of the width and position of patterns on an x-ray mask with that on a Si wafer showed the measurement accuracy of the pattern width in the membrane is worse than that on the wafer. Moreover, we found that pattern position in the membrane can be measured on the same order as that on the wafer. To improve measurement accuracy, we developed a new technique that involves covering the space in the back side of the membrane and confirmed that the measurement accuracy of pattern width in the membrane is on the same order as that on the wafer.