Microlithography Lens Wavefront Correction Model

The model coefficients are segmented into three groups (offset coefficients, linear coefficients, and quadratic coefficients) with different calibration frequencies. Offset coefficients are calibrated most frequently, linear coefficients less frequently, and quadratic coefficients least frequently. This segmentation allows the system to maintain high correction accuracy by frequently updating the most critical parameters while preserving operational efficiency by calibrating less critical parameters less often.

The patent implements periodic calibration of model coefficients at different frequencies. Offset coefficients undergo periodic calibration before each substrate exposure, linear coefficients are calibrated periodically but less frequently than offset coefficients, and quadratic coefficients are calibrated periodically with the longest interval. This periodic action ensures accuracy is maintained when most needed while minimizing overall calibration time.

Different calibration frequencies are assigned to different groups of coefficients based on their relative importance and sensitivity. Offset coefficients, which have the greatest impact on correction accuracy, are calibrated most frequently (before each substrate). Linear coefficients are calibrated with moderate frequency, and quadratic coefficients with the lowest frequency. This local quality approach ensures that time is invested proportionally to the impact each coefficient group has on overall accuracy.

The patent applies partial calibration action by selectively calibrating only the most critical coefficients (offset coefficients) before each substrate exposure, rather than calibrating all coefficients equally. This partial action provides sufficient correction accuracy for each exposure cycle without the time penalty of full system recalibration, while less critical coefficients are updated less frequently.