Simulation of critical dimension and profile metrology based on scatterometry method

As the on-wafer transistor sizes shrink, and gate nodes reduce below 90 nm, it is becoming very important to precisely measure and control the critical dimension (CD) on the mask. Phase shift technology for masks is essential for decreasing of the feature size, therefore CD and profile metrology on the phase shifting materials becomes critical. Scatterometry provides fast and nondestructive method of profile and CD measurements. In this paper the conditions of determining of profile and CD measurement are analyzed. In the real experiment scattered spectrum from structure with unknown profile is measured. Before experiment the library of spectra is generated. Spectra in the library correspond to structures with various parameters (such us thickness, CD, sidewall angle, etc.). For calculation of this library rigorous coupled-wave analysis (RCWA) was used. This method allows us to get precise solution of Maxwell equations and find directly amplitude of zero diffraction order which is measured in the experiment. To determine the possibility of measurement of sidewall angle various spectra with different sidewall angle value were calculated. Calculated spectrum is changed by adding or deduction of random value. The randomly changed spectrum is compared with spectra in the library in order to find spectrum with best fit. Therefore sidewall angle and CD can be determined. Precision, possibility and maximum allowed error in the spectra measurements is obtained. Moreover, influence of polarization of incident light on precision of extracted results was found.