EPL stencil mask defect inspection system using a transmission electron beam

A new mask inspection system using transmission electron beam (0EB) technology is being developed to detect defects on electron projection lithography (00EPL) masks with design rules of 65-nm and below. In our new system, we use the transmission EB image, multi-line Time Delayed Integration (TDI)-CCD camera, and stage scanning. The transmission EB image can detect defects hidden in stencil patterns with a very high resolution. The scanning system, combined with a high-speed image acquisition system, enables high throughput. A magnified image of the mask stencil pattern is formed on an image sensor by the electron-optic system. The image of the stencil patterns is captured by a multi-line TDI-CCD camera and the image data is transferred to an image-processing unit composed of multi high-speed image processors. To capture an EB image, a special TDI-CCD camera was developed. The typical pixel size is 50-nm on the mask. To achieve the goal of high-speed image processing, multi-fiber cable is used to transfer the image data from the camera to the image-processor. Each image processor shares the inspection area in parallel, and performs a die-to-database comparison. Typical inspection time for a 200-nm EPL stencil mask is 4 to 5 hours. A defect of 50-nm was observed by the developing system. This inspection system will be completed in March 2004.