Research And Precision Measurement On Critical Dimension Of Photomask Navigated By Micro Vision

In the manufacture process of integrated circuit(IC), lithography occupy a very important step, and the quality of photomask used in lithography affects the yield of LSI. With the narrow of geometric graphics of IC, it put higher requirements in the manufacturing quality of photomask. So the measurement and control in the feature size of photomask can reduce the reject of IC and research on this area is very meaningful.In this paper, micro vision was used to make measurements on the feature size of photomask. At first, in order to slow the error, the graphic lines keep in vertical or horizontal by controlling the motion platform. With the help of study in interaction between light and photomask and analysis on photomask's illumination model under coaxial light, ring light and back light, clear images of photomask were obtained that help measurement most under diffuse back light. Then, with the help of auto focus technology, clear images of photomask were obtained by using an searching algorithm that combines traversal and mountain-climb algorithm. It realizes auto focus and avoids falling into local minimum. After that, the pixel edges of photomask were find by using edge inspect algorithm, and a precision location was determined by using sub-pixel technology. Error analysis was carried through on measurements too.At last, Experimental study results show that with the study on diffraction of light, the measurement system can complete precision measurement on feature dimension in micron and to some extent expands the range of optical microscopy.