Advanced edge roughness measurement application for mask metrology

With decreasing Critical Dimensions (CD), the negative influence of line edge roughness (LER) and line-width roughness (LWR) on CD uniformity and mean-to-target CD becomes more pronounced, since there is no corresponding reduction of roughness with dimension reduction. This applies to wafer metrology as well as to mask metrology. In order to better understand the types of roughness as well as the impact of the CD-SEM roughness measurement capabilities on the control of the mask process, the sensitivity and accuracy of the roughness analysis were qualified by comparing the measured mask roughness to the design for a dedicated LER test mask. This comparison is done for different LER amplitude and periodicity values and for reference structures without nominal LER using the built-in CD-SEM algorithms for LER characterization.