OPC model accuracy enhancement for asymmetrical layouts by incorporating 2D contour extraction methodology

Abstract

As the semiconductor device dimension continues to shrink, the tolerance of Critical Dimension (CD) variation has been dramatically reduced for whole chip area to ensure the good uniformity of device functionality. Accordingly, the Optical Proximity Correction (OPC) model accuracy has become extremely important for controlling across-chip CD variation. The traditional method relying on CD Scanning Electron Microscope (CD-SEM) measurement data from synthetic patterns, such as dense line/space and isolated line in various pitch biases, for OPC model calibration is no longer sufficient for accurately projecting the complex patterns such as asymmetrical layout environments. Alternatively, the 2D extracted contours from SEM images associated with user-specified cutline algorithm to get the dimensional information of complex patterns have been incorporated for OPC modeling as well as process qualification [1-3]. In this work, the 2D contour extraction methodology was incorporated to extract more comprehensive CD information of complex features for OPC model calibration of 39nm half-pitch process layer. Together with the use of CD-SEM based CD, the model calibration via MASK2D and MASK3D model forms were conducted for accuracy comparison. The OPC model validation results demonstrated the contour-based gauges helps to improve the OPC model projection accuracy by 40~60% for asymmetrical features comparing to the traditional OPC calibration method.