Accuracy and precision of scatterometer measurements relative to conventional CD metrology

Abstract

Scatterometry is an emerging metrology technique for measuring critical dimensions (CD), profiles, and thicknesses within diffraction gratings printed on semiconductor film stacks. A 2/spl theta/ scatterometer was used to measure diffraction gratings on two film stacks: (1) front end of line logic gate stack, and (2) resist on anti-reflective coating (ARC) on silicon. The CD measurements of the scatterometer were compared to critical dimension scanning electron microscope (CD-SEM), atomic force microscope (AFM), and cross-section scanning electron microscope (X-SEM) measurements. The correlation between scatterometer and CD-SEM measurements was analyzed using the Mandel technique of Archie and Banke where AFM and X-SEM measurements were used to characterize the "real" properties of the grating. Initial results indicated that the measured CD value by scatterometer and CD-SEM were linearly correlated with a sizeable offset. Further analysis of the correlation shows that the offset was pronounced at grating sidewall angles approaching 90/spl deg/. The effect of sidewall angle on CD-SEM to scatterometer correlation and results for precision and accuracy on the scatterometer are discussed relative to in-line stepper focus control.