3D measurement using SEM technology

The evolution of 3D NAND memory devices is increasing the depth of HAR (High Aspect Ratio) hole structure. Consequently the technology to measure the shape of the structure is also becoming more difficult. In general, optical measurement method such as OCD (Optical Critical Dimension) is mainly used for measurement of the HAR structure, but optic technology has limitation in measurement of hole structure independently. To overcome this, SEM (Scanning Electron Microscopy) with high acceleration voltage of electron beam can be used for the measurement of bottom CD (Critical Dimension, diameter of a hole) of the hole structure. However this technology also has challenge in that the measured CD does not always represent the exact bottom CD of the structure. In order to solve this problem, we propose a method of inferring the actual depth where the measured CD is located by examining the change of the acceleration voltage and the angle of incident electron beam. The CDs of real product hole pattern were measured according to the change of landing energy of electron beam and the measured depth was calculated using proposed method. After inferring the CD measured from the actual hole structure, the method is verified in a sample having known structure figures. The proposed method can be used for 3D microstructure measurements using SEM technology in the future.