Accuracy of Strain in Strain Maps Improved by Averaging Multiple Maps

Several methods have been proposed and tried for strain analysis of a crystal on nano-scale. Diffractometry such as nano-beam diffraction [1] and convergent-beam electron diffraction [2][3], and the phase imaging methods such as dark-filed electron holography [4] and high-resolution electron microscopy [5] have been applied to this issue. In scanning transmission electron microscopy (STEM), when the raster spacing is close to the one of a crystal lattice or the multiple of it and the probe size is smaller than the crystal lattice spacing, we sometimes observe the moiré fringes due to the under-sampling effect. We applied the fringe to detect strain in practical semiconductor devices and succeeded to map and quantify the strain [6]. However, the required accuracy of the strain measurement in the semiconductor industry is as high as or better than 0.2 %. In this paper, we report how we improve the accuracy of the strain measurement by using multiple strain maps.