Impact of Averaging of CD-SEM Measurements on Process Stability in a Full Volume DRAM Production Environment

摘要

In our work we investigate the influence of averaging varying numbers of measurement structures on process stability and CD uniformity. Measurements are performed on an Applied Materials VeritySEM CD-SEM system which provides the possibility to measure several lines or contact hole structures and to yield the average and 3 sigma value of all measured structures. We show that averaging significantly improves the single tool precision up to 30%. Additionally, a long term pilot test has shown that the range of the CD distribution of selected production layers is significantly decreased reducing the contribution of the measurement to the total CD budget resulting in a yield enhancement. Further, we discuss the influence of averaging on the contribution of short-range random CD variations for CD uniformity measurements. This is done by investigating the distribution of the CD difference between adjacent structures across the wafer. We show that increased averaging significantly reduces the contribution of random CD variations to the CD budget.