TEM validation of CD AFM image reconstruction

An extensive test series was undertaken to validate image reconstruction algorithms used with critical dimension atomic force microscopy (CD AFM). Transmission electron microscopy (TEM) was used as the reference metrology system (RMS) with careful attention devoted to both calibration and fiducial marking of TEM sample extraction sites. Shape measurements for the CD probe tips used in the study were acquired both through the use of reentrant image reconstruction and independent (non-destructive) TEM micrographs of the probe tips. TEM images of the tips were acquired using a sample holder that provided the same projection of the tip as presented to the sample surface during AFM scanning. In order to provide meaningful validation of the CD AFM image reconstruction algorithm, widely varying sample morphologies and probe tip shapes were selected for the study. The results indicate a 1 - 2 nm bias between the TEM and CD AFM that is within the uncertainty of the measurements given the Line Width Variation (LWV) of the samples and accuracy of the measurement systems. Moreover, each TEM sample consisted of a grid with multiple features (i.e., 21 to 22 features). High density CD AFM pre-screening of the sample allowed precise locating of the TEM extraction site by correlating multiple feature profile shapes. In this way, the LWV and height of the sample were used to match measurement location for the two independent metrology systems.