SLM lithography: printing down to k1=0.30 without previous OPC processing

摘要

SLM-based mask writers have high speed, good CD uniformity, good resolution [1], but they are limited by the resolution of the optics. Moreover the optical image is not perfectly neutral; it has certain artifacts due to the partially coherent nature of the light. It is possible to remove those if the mask data file is OPC processed for the mask writer optics before the data is sent to the mask writing tool, but not without an impact on cycle time and cost. In this work we have combined several elements to create a system for real-time OPC, i.e. the OPC processing of the mask data is embedded in the data path of the mask writer. In this way it adds neither time, nor cost to the mask production. First, the scheme uses the analog tilting mirrors of the Sigma mask writers which are pure amplitude (not phase) modulators which make the rasterisation simple and makes interpolation and summation of the mirror amplitudes possible. Secondly, the optics is optimized to minimize the optical interaction length, thereby reducing the number of operations needed. Third, an explicit perturbation formula is used to correct the intensity on every edge. The fourth element, is a reduction of the optical kernel based on the symmetries of the image. We show that the described OPC processing is suited to be implemented in state-of-the-art FPGA devices.