Leveraging LER to Minimize Linewidth Measurement Uncertainty in a Calibration Exercise
James Roberts, W Banke, Ronald G. Dixson
Many semiconductor metrologists are aware that the contribution of line edge roughness (LER), and thus linewidth variation (LWV), can be a significant contributor to measurement uncertainty budget. More generally, the impact of measurand variation and proper sampling is becoming a major player in nearly every area of semiconductor measurement. This paper describes a simple technique of using the LER of a linewidth as a fingerprint to uniquely characterize the measurement target in such a way to make the LER contribution negligible in a linewidth calibration exercise. A single crystal critical dimension reference material (SCCDRM) was the calibration artifact used to calibrate the tip width of a critical dimension atomic force microscope (CD-AFM). These samples were released by the National Institute of Standards and Technology (NIST) to SEMATECH member companies in 2004. The specific SCCDRM used for this work had six calibrated linewidths ranging from 100 nm to 270 nm. Our paper shows in detail the overlay of the CD-AFM linewidth data with that of the data used to calibrate the SCCDRM for each linewidth. With the aid of this linewidth fingerprinting, Mandel regression is used to assess the quality of correlation of the CD-AFM to that of the NIST-derived calibration data. As a final assessment, a NIST uncertainty budget analysis is presented as a conclusion of the tip width calibration exercise. An expanded uncertainty of less than 2 nm with a k =3 coverage factor was ultimately achieved.
Proceedings of SPIE
February 26, 2007
San Jose, CA, USA
Metrology, Inspection, and Process Control for Microlithography XXI