Scatterometry is an optical metrology technique designed for analyzing the changes of light intensity in a device. This technique is widely used for the wafer metrology of nanostructured surfaces in the semiconductor industry. There are two scatterometric approaches: angle-resolved and spectroscopic scatterometer.1, 2 Angle-resolved scatterometry involves single-wavelength readings at various angles, and measure both zeroth-order and first order diffractions. Spectroscopic systems work at a fixed angle of incidence but in broadband wavelengths range in the visible or UV, and measure only the zeroth-order diffraction. In contrast to angle-resolved and spectroscopic scatterometries, the proposed extreme ultraviolet (EUV) scatterometer is designed to measure the intensity of non-zero-order diffractions at a fixed incident angle and at multiple laser-like wavelengths. The short wavelengths of EUV, which give rise of several diffraction orders of scattering from nanoscale grating features. The well-separated higher-order diffraction beams are more informative than the zero-order diffraction beam, coupled with a very efficient rigorous coupled-wave analysis (RCWA), can achieve a detailed reconstruction of the profile of nanoscale periodic gratings. In this paper, however, describes the use of yet two more methods for breaking correlations and increasing sensitivity—include the use of non-zeroth order (m = + 1 and m = −1) diffracted light and polychromatic wavelengths of high harmonic generation (HHG). For many structures, this flexibility significantly increases parameter sensitivity and reduces parameter correlation.
We developed an extreme ultraviolet (EUV) scatterometer equipped with a table-top EUV source for the characterization of nanoscale grating lines. Appropriate orders of high-harmonic generation at wavelengths ranging from 25 to 35 nm are selected as the coherent light source for high-resolution spatial performance. It is shown that the grating surface profile significantly affects the scattered diffraction intensities and can be retrieved by the structure reconstruction algorithms using inverse modeling by rigorous coupled wave analysis.
We have developed a EUV scatterometer using a focused high-order harmonic generation (HHG) source for nano-scale
grating measurement. The coherent light source with multiple discrete wavelengths of 25-35 nm was pumped by a
tabletop Ti:sapphire laser system. A charge-couple-device (CCD) camera directly records the diffraction image of the
zero and the first order diffraction information from the grating samples. The grating structure can be reconstructed base
on the calculations from the location and the intensity distribution of diffraction pattern.
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