TEM validation of CD AFM image reconstruction: Part II

The present paper is a continuation of an investigation to validate CD AFM image reconstruction using Transmission Electron Microscopy (TEM) as the Reference Metrology System (RMS).¹ In the present work, the validation of CD AFM with TEM is extended to include a 26 nm diameter carbon nanotube (CNT) tip for non-reentrant feature scans. The use of DT (deep trench) mode and a CNT tip provides detailed bottom feature resolution and close mid-CD agreement with both TEM and prior CD mode AFM scans (using a high resolution Trident tip). Averaging AFM scan lines within the ∼80 nm thickness region of the TEM sample² is found to reduce systematic error with the RMS. Similarly, errors in alignment between AFM scan lines and TEM sample are corrected by a moving average method. Next, the NanoCD standard³ is used for complete 2D tip shape reconstruction (non-reentrant) utilizing its traceable feature width and well-defined upper-corner radius. The shape of the NanoCD is morphologically removed from the tip/standard image, thus providing the tip's shape with bounded dimensional uncertainty. Finally, an update of the measurement uncertainty budget for the current generation CD AFM is also presented, thus extending the prior work by NIST.⁴.