Wafer level CD metrology on photomasks using aerial imaging technology

Abstract

Recently more and more mask designs for critical layers involve strong OPC which increases the complexity for standard CD SEM mask measurements and conclusive interpretation of results. For wafer printing the wafer level CD is the crucial measure if the mask can be successfully used in production. Recent developments in the AIMS™ software have enabled the user to use the tool for wafer level CD metrology under scanner conditions. The advantage of this methodology is that AIMS™ does see the CD with scanner eyes. All lithographic relevant effects like OPC imaging which can not be measured by other tools like mask CD SEM will be captured optically by the AIMS™ principle. Therefore, measuring the CD uniformity of the mask by using AIMS™ will lead to added value in mask metrology. With decreasing feature sizes the requirements for CD metrology do increase. In this feasibility study a new prototype algorithm for measuring the lithographically relevant AIMS™ CD with sub pixel accuracy has been tested. It will be demonstrated that by using this algorithm line edge and line width roughness can be measured accurately by an AIMS™ image. Furthermore, CD repeatability and tool matching results will be shown.

In-die metrology on photomasks for low k 1 lithography

“…Recently, it has been shown in some case studies that Aerial Imaging Technology is per se able to measure the wafer level CD uniformity of a mask correctly [4][5][6][7]. Appling this technique to mask CD metrology can lead to added value for the mask shop and the wafer fab as the optical performance under scanner conditions can be already measured in the mask shop.…”