| Popis: |
We report that, based on our experimental data, lens heating (LH) impact on wafer image can be effectively controlled by using a computational method (cASCAL) on critical device layers with no request on tool time. As design rule shrinks down, LH control plays a key role in preventing the image deterioration caused by the LH-induced wavefront distortion during exposure. To improve LH prediction accuracy, 3-dimension structure of mask stack (M3D) is considered in calculating the electro-magnetic (EM) field that passes through the mask for full chip. Additionally, lens specific calibration (LSC) is performed on individual scanners to take the lens-to-lens variation into account. In data comparisons, we show that cASCAL performs very well as an ASCAL substitute, and that M3D and LSC improve the LH prediction accuracy of cASCAL. |
