A novel method to measure duty cycles of rectangular gratings and evaluate the spa-tial uniformity of duty cycles was presented on the basis of top-down scanning electron micro-scope(SEM ) images .This method first conducts image grayscale profile preprocessing on tar-get images ,then performs border detection based on dynamic programming and least-squares spline approximation ,and finally computes the mean and standard deviations of duty cycles in the target area in light of the provided evaluation standards .Using this method ,we can not only quickly and accurately measure grating duty cycles and perform quantitative analysis on the spatial uniformity of duty cycles , but also avoid damaging sample preparation process , w hich greatly make up the deficiency of traditional method .A top-dow n SEM image processing software ,GradUI ,for detecting duty cycles of rectangular gratings was developed .The top-down SEM images of several 1 200 lines/mm self-made gratings were processed with the soft-ware ,and the root-mean-square deviation of the average duty cycle and the estimated value was 0 .017 3 .T he results show that the approach to calculate duty cycles based on top-dow n SEM images is feasible and of high efficiency ,and the software is robust .%提出了一种利用俯视SEM 图像检测矩形光栅占宽比的新方法。对目标检测图像进行灰度轮廓预处理，接着进行基于动态规划和最小二乘样条逼近的边缘检测，最后按照设定的量化评价标准，计算出目标区域内的光栅占宽比的平均值和标准偏差。使用该方法不仅可以快速准确地计算出目标区域内的光栅占宽比和量化评价占宽比空间分布均匀性，也避免了具有破坏性的制样过程，弥补了传统断面测量方法的不足。编写了用于矩形光栅占宽比检测的图像处理软件GradUI。使用此软件对一组1200线/mm矩形光栅的俯视SEM 图像进行检测分析，发现平均占宽比与灰度轮廓估算值的均方根偏差为0．0173。结果表明，基于俯视SEM 图像的矩形光栅占宽比检测方法是有效可行的，同时，也验证了软件的可靠性。
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