'Ruler' Promises Nano-Precise Litho Calibration

摘要

Metrology calibration has always been composed of two parts: precision and accuracy. As defined by Sematech, statistical process control accuracy is the compliance of the measured or observed value to the true value or accepted reference value, while precision is the measure of natural variation of repeated measurements. Obviously, the precision component has always had greater importance than accuracy for calibration purposes, particularly in the accurate matching of tools to ensure that there is as small a variation as is physically possible between the measurements made by various platforms. Therefore, it is not surprising that inspection as well as process equipment OEMs have continuously worked over the years to gradually improve precision.