Stitching error reduction in electron beam lithography with in-situ feedback using self-developing resist

In electron beam lithography (EBL), a large area pattern is divided into smaller writing fields, which are then stitched together by stage movement to generate the large area pattern. Precise stage movement is essential to minimize the stitching error, and this can be achieved by using laser interferometer-controlled stage. In addition, electron beam deflection must be adjusted to match the stage movement, which is referred to as "writing field alignment." To expose large area nanostructures, a large writing field must be used; otherwise, the stage movement time would be impractically long. However, writing field alignment accuracy decreases with a larger writing field owing to its low magnification. Here, the authors report that self-developing resist (for which the pattern shows up immediately after exposure, thus eliminating the need for ex-situ development) can provide in-situ feedback for writing field alignment accuracy, which in turn can be used to optimize the alignment. After several iterations using the exposed test pattern in nitrocellulose (self-developing) resist as feedback, the authors reproducibly achieved nearly perfect (<50 nm stitching error) alignment with writing field of 1 mm2 using a Raith EBL system.