7 July 1997 Single-feature metrology by means of light scatter analysis
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During the last years, the prospects ofthe angle resolved optical scatterometry as an alternate and supplementary measuring technique in micrometrology were discussed. In a series of publications, the potential of the method was shown to be able to meet the challenges of quarter micron technology and beyond. However, until now, to our knowledge the applications were mainly confmed to periodic patterns. In this paper, the extension of the method to the characterization of single features is outlined by means of a theoretical simulation of the simple one-dimensional case. Therefore, we assume that a laser beam focussed down to about one micron in one dimension illuminates the target under investigation, e.g., a resist line on silicon. Because of the fmite spot diameter of the light probe, the method may be named as focussed beam optical scatterometry (FBOS). Then, quite similar to the angle-resolved scatterometry (ARS), the diffracted far field intensity is calculated in dependence on the angle. The paper shows that the basic tools of the grating theory can be taken over. Additionally, only the convolution of the calculated transfer functions, i.e., reflection and transmission coefficients for plane wave incidence, with the angular spectrum ofthe incident focussed beam has to be carried out. The selected grating period and accordingly the stepwidth of the angular spectrum can be chosen properly to prevent numerical artefacts. In this paper, the diffraction calculation will be done by means ofthe rigorous coupled wave approach (RCWA). Based on this model, several one-dimensional measuring problems have been investigated by means of multivariate regression and cross validation with the fmal goal to assess the measurement accuracy. To emulate real conditions, the computed light scatter distribution was degraded by a Gaussian noise and a certain depth of focus was admitted by shifting the focus of the laser spot vertically. In conclusion, it may be claimed that the FBOS may be able to enhance the resolution limit as well as the measurement accuracy in comparison to imaging optical microscopy.
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Joerg Bischoff, Joerg Bischoff, Karl Hehl, Karl Hehl, } "Single-feature metrology by means of light scatter analysis", Proc. SPIE 3050, Metrology, Inspection, and Process Control for Microlithography XI, (7 July 1997); doi: 10.1117/12.275951; https://doi.org/10.1117/12.275951

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