Systematic Measurement Uncertainty of Critical Dimension Scanning Electron Microscope

Critical dimension (CD) bias between a critical dimension scanning electron microscope (CD-SEM) and a reference tool is the most important error factor for more accurate CD measurement. The systematic measurement uncertainty was evaluated by experiment and electron beam simulation. The CD bias varia...

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Published inJapanese Journal of Applied Physics Vol. 49; no. 6; pp. 06GD03 - 06GD03-5
Main Authors Abe, Hideaki, Kadowaki, Motoki, Hamaguchi, Akira, Ikeda, Takahiro, Yamazaki, Yuichiro
Format Journal Article
LanguageEnglish
Published The Japan Society of Applied Physics 01.06.2010
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Summary:Critical dimension (CD) bias between a critical dimension scanning electron microscope (CD-SEM) and a reference tool is the most important error factor for more accurate CD measurement. The systematic measurement uncertainty was evaluated by experiment and electron beam simulation. The CD bias variation is caused by the change in secondary electron signal intensity. CD bias variation of an isolated 150 nm silicon substrate space pattern with space width change is 1.7 nm per 10 nm space width. The CD bias difference of the silicon substrate between with and without the native oxide layer is 30 nm at 150 nm space width. The CD bias change is 1.4 nm per 10 nm pattern height. This is caused by an interaction between space width and pattern height. We identified that measurement uncertainty includes not only random error but also systematic error in actual pattern shape, material, and layout variation quantitatively. The impact of systematic error on CD bias is very large compared with the metrology requirement for next-generation devices.
Bibliography:Measurement uncertainty of CD-SEM. Measurement uncertainty is defined as the deviation from linear regression. Cross-sectional TEM images (upper) and top-down CD-SEM images (lower). (a) Space width = 80 nm. (b) Space width = 300 nm. The material of the specimen is silicon. Grayscale profiles of CD-SEM images (solid curve) are overwritten on CD-SEM images. Grayscale profiles of the right pattern edge. Space widths of these profiles are 80, 150, 300 nm. Space width dependence on CD bias. CD bias is defined as the difference between CD-SEM value at the 50% grayscale level and TEM value at the 50% height level. Space width was set from 50 to 500 nm. (a) SEM image of the silicon substrate with the native oxide layer. (b) SEM image of the silicon substrate without the native oxide layer. (c) Grayscale profile of CD-SEM images with and without native oxide layer on silicon surface. The space width was set at 300 nm. (a) Space width dependence of CD bias with and without native oxide layer. (b) Grayscale profiles of the right pattern edge with and without native oxide layer. The grayscale profile without the native oxide layer is modified to fit at the top and bottom peak levels. Procedure of electron beam simulation. (a) TEM image. (b) Edge extraction from the TEM image by image processing. (c) Extracted edge data is imported to the electron beam simulator. (d) Simulated SEM image. Secondary electron behavior is calculated by Monte Carlo simulation without charging effects. (a) Simulated secondary electron emission coefficient of 150 nm space width. The profile of silicon is modified to fit at the top and bottom peak levels of the profile of the silicon dioxide layer on the silicon substrate. (b) Simulated space width dependence of CD bias for silicon and silicon dioxide layer on the silicon substrate. (a) Secondary electrons enter the bottom and the sidewall of the space pattern. Re-incident electron number in the specimen is calculated. (b) Re-incident electron count of silicon and the silicon dioxide layer on the silicon substrate. (a) Interaction between space width and pattern height by electron beam simulation. Pattern height is set at 50, 150, and 290 nm. The pattern shape is set as trapezoid. The taper width is 20 nm. (b) Pattern height dependence of CD bias. Space width is set from 60 to 100 nm.
ISSN:0021-4922
1347-4065
DOI:10.1143/JJAP.49.06GD03