LATERAL METROLOGY USING SCANNING PROBE MICROSCOPES, 2D PITCH STANDARDS AND IMAGE-PROCESSING

To use SPM as a metrological tool it is necessary to have traceable re ference standards and image processing tools that can calculate correc tion parameters and produce accurate measurements. We describe new rel iable methods for accurate characterization of SPM by imaging traceabl e 2D pitch standards and automated image processing. The scanning proc esses of the microscopes are characterized by correction parameters fo r lateral non-linearity, linear correction factors for the x- and y-ax es and an x-y coupling factor. To obtain high accuracy we have improve d a previously reported algorithm for calculation of the unit cell by subpixel Fourier analysis. We characterize the linearity by a new meth od where the positions of individual features associated with the unit cell are detected by a correlation technique and compared with predic ted positions based on the calculated unit cell. The differences betwe en the actual and predicted locations reflect the non-linearity. We ar e able to measure the non-linearity at sub-pixel level, i.e. smaller t han 0.2% of the scan range for a 512 x 512 pixel image. Evaluation of the linearity has given us a tool that can confirm the unit cell measu rements based on Fourier analysis to within 0.3% of the repeat distanc es. When analyzing a series of images acquired over a time frame of 6 months, we find a reproducibility of better than 0.7% for the calibrat ion parameters. We demonstrate that we are able to measure angular dis tortions smaller than 0.2 degrees and that corrections of small residu al non-linearities have a positive influence on the accuracy of the pi tch measurements. The developed software is made freely available.