Enhanced 28nm FD-SOI diffraction based overlay metrology based on holistic metrology qualification

Continuous tightening of the overlay control budget in the semiconductor industry drives the need for improved overlay metrology capabilities. In this context, measurement accuracy needs to be addressed. The first part this study shows that Diffraction Based Overlay metrology accuracy can be improved with a dedicated methodology. This methodology involves the use of target design simulation software in order to maximize stack sensitivity and to minimize processes non uniformity impact on the measurement. In the second part this study focuses on Holistic Metrology Qualification (HMQ) methodology that allows selecting the best on-wafer target. The methodology is explained and discussed. It is demonstrated that HMQ helps to reduce target asymmetry impact on measurement uncertainty and to select primary recipe parameters (wavelength, polarization, etc…). Finally CD-SEM measurements were used to validate methodology results.