前言： 对用电子显微镜测量薄膜厚度的三种方法：双束衍射法、污斑法、污线法进行了实验及比较分析。

The experiments , comparison and analysis for the three thickness measurement methods :two-beam diffraction method , contamination spot method and contamination line method were carried out.

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对于实际光学系统，由于光的衍射和像差，使所成的点像为一弥散斑。

However, for the actual optical system, its point image become a speckle because of diffraction of light and aberration.

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散斑衍射晕能量分布合理，条纹清晰度好。

The intensity of speckle diffraction halo distributes more proper and the speckle fringes are clearer than conventional method.

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