Automated aerial image based CD metrology initiated by pattern marking with photomask layout data

Abstract

The photomask is a critical element in the lithographic image transfer process from the drawn layout to the final structures on the wafer. The non-linearity of the imaging process and the related MEEF impose a tight control requirement on the photomask critical dimensions.Critical dimensions can be measured in aerial images with hardware emulation. This is a more recent complement to the standard scanning electron microscope measurement of wafers and photomasks. Aerial image measurement includes non-linear, 3-dimensional, and materials effects on imaging that cannot be observed directly by SEM measurement of the mask. Aerial image measurement excludes the processing effects of printing and etching on the wafer. This presents a unique contribution to the difficult process control and modeling tasks in mask making.In the past, aerial image measurements have been used mainly to characterize the printability of mask repair sites. Development of photomask CD characterization with the AIMS™ tool was motivated by the benefit of MEEF sensitivity and the shorter feedback loop compared to wafer exposures. This paper describes a new application that includes: an improved interface for the selection of meaningful locations using the photomask and design layout data with the Calibre™ Metrology Interface, an automated recipe generation process, an automated measurement process, and automated analysis and result reporting on a Carl Zeiss AIMS™ system.

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.…”

Wafer level CD metrology on photomasks using aerial imaging technology

“…These features have to be accurately controlled during the photomask manufacturing process to make sure that the desired CD is printed on the wafer. Small features or regions where the Mask Error Enhancement Factor (MEEF) is high are extremely sensitive to process variations [1]. Small process variations on the mask level can lead to large CD variations on the printed wafer.…”