Detection system of multilayer coating microstructure defects based on differential interference contrast confocal microscopy

Defects in the multilayer extreme ultraviolet lithography (EUV) mask "whiteboard" have become an important issue to restrict the development of next-generation lithography. A detection system based on differential interference contrast(DIC) confocal microscopy is proposed in order to improve the ability of distinguishing the microstructure defects on the lithography mask "whiteboard". Based on the scalar diffraction theory, the lateral and axial resolution of the system are calculated. In the condition that numerical aperture of 0.65 and working wavelength of 405 nm, resolutions of DIC confocal microscopy, traditional microscopy and the confocal microscopy system are compared and analyzed using MATLAB. The results show that the DIC confocal microscopy has the ability of lateral resolution of 230 nm and resolution of axial step height difference of 25 nm (corresponding to defects such as scratches). In addition, the effect of factors such as the size of detector and the axial deviation of the sample are also simulated and analyzed. The experimental results show that the proposed system can detect multilayer coating microstructure defects with a width of 200 nm and a height of 10 nm, which has better detection ability than the other two systems.