Detailed analysis of capability and limitations of CD scatterometry measurements for 65- and 45-nm nodes

Control of critical dimension (CD) of 65nm and beyond nodes is the hot issue now. As feature size reduces it becomes difficult to measure CD precisely. A lot of factors can influence on accuracy of measurement. Scatterometry method is applicable for both production and development purpose, and can be used for in-situ or ex-situ control. In this work we study influence of CD non-uniformity and sidewall angle as well as influence of parameters of measurement system on precision of result. TE, TM and unpolarized light with different angle of incidence on grating structure is considered to find the best conditions for CD measurements of 65 and 45nm nodes. Rigorous coupled-wave analysis (RCWA) is used for theoretical spectra calculation and least square method for results extraction. Reflected spectrum from structures containing non-uniform or uniform CDs with variation of sidewall angle is compared with the set of theoretical spectra, and CD value with layer thickness is extracted in the same way as in the real experiment. It is shown that CD non-uniformity and sidewall angle can be estimated through comparison of results obtained with different polarization state of light. Best choice of polarization, angle of light incidence, range of wavelength for spectrum measurement and parameters of library for spectrum analysis are obtained in order to provide precise and fast scatterometry measurement for 65 and 45nm nodes mask structures.