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10 May 2005 The sidewall angle dependence of CDSEM measurements and its impact on CD process control
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The CD measurements from CDSEMs is a two-step process, the first being the pixel based electron emission signal intensity profile generation and the second the algorithm treatment on the generated intensity profile for the dimension determination. Secondary electron emission is currently the most common choice for signal intensity profile generation due to its relatively high signal-to-noise ratio at low landing energy range and the maturity of detector designs than the backscattered electron collections. It is known that the secondary electron emission depends on feature topography. The pixel based intensity profile bears the signature of feature topography. Therefore, the following algorithm processing for CD derivation cannot be free from the feature topographic influence. In this study, we elect isolated resist line as our feature with the resist sidewall angle the major topographical contributor. A set of FEM wafers are exposed at a fixed CD node and the process window is identified for sampling range identification. A profile CDAFM is used as a reference tool for resist height, CD, and sidewall angle measurement. The range of sidewall angle variation in the process window is identified by CDAFM as the reference. Various locations in the process window are measured by CDAFM and CDSEM, and the ratios of the same metrology information are plotted as function of sidewall angle deviation from vertical profile. In this paper, the sidewall angle dependence of derivative based CDSEM algorithm will be identified and the impact of CD measurement dependence on sidewall angle on process control will be discussed. This paper aims to generate a guide for process engineers to perform better process control through the quantification of sidewall angle influence. This paper will also address the need of the development of new CDSEM algorithm which compensates sidewall angle influence.
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Justin J. Hwu, Homayoun Kiamanesh, Sukhbir Dulay, and Peter Wilkens "The sidewall angle dependence of CDSEM measurements and its impact on CD process control", Proc. SPIE 5752, Metrology, Inspection, and Process Control for Microlithography XIX, (10 May 2005);


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