Measurement precision improvement for excimer laser pulse energy sensor based on a special finite impulse response filter
In deep ultraviolet lithographic tools, precise measurement of excimer laser pulse energy is essential. However, system noises of the energy sensor, which is used to monitor laser pulse during exposure dose control, complicate pulse energy measurement. To improve measurement precision, a specific finite impulse response filter is proposed for signal denoising. Particularly, the convolution kernel of the specific finite impulse response filter is derived from the nonlinear fitting of the energy sensor output. Experimental results show that measurement precision of the energy sensor improves 2-3 times with the specific finite impulse response filter. To verify the effectiveness of the energy sensor, it is used for transmittance measurement; the measurement result of a Corning 7980 witness sample is consistent with that measured by a commercial ultraviolet spectrophotometer and the measurement accuracy is 0.11% (k = 2).