Programmable structured DUV illumination by coherent harmonic generation at crystalline solids for nanometer-resolution inspection of periodic samples

Abstract The continued narrowing of transistor pitch in semiconductor chips has boosted the demand for deep-ultraviolet (DUV, λ < 280 nm)-based high-resolution optical inspection and metrology. However, the lack of a beam control device for DUV wavelength due to the significant UV absorption in most optical materials has hindered the handy implementation of conventional high-resolution metrology techniques such as structured illumination microscopy (SIM) to the DUV regime. Here, we present a programmable DUV structured illumination for nanometer-resolution pitch and displacement inspection of periodic samples enabled by nonlinear third-harmonic generation. By manipulating a spatial phase of the near-infrared (NIR, λ = 800 nm) driving beam that is incident on crystalline solids, the emitted third harmonic beam at DUV (λ = 266 nm) can be spatially controlled so as to form a high-visibility sinusoidal distribution with a real-time adjustable pitch and orientation angle. The angle-tunable DUV structured beam allows observation of low-visibility periodic sample information in high-visibility frequency-down-converted Moiré patterns, with a magnification factor of up to 70 times. By analyzing the Moiré pattern pitch and orientation angle, the sample periods of 277.8 nm and 416.7 nm were reconstructed with an error of 1.9% (5.4 nm) and 0.5% (2.1 nm), respectively. Furthermore, a 20.0 nm lateral shift of the periodic sample – below Abbe’s diffraction limit – was measured with a repeatability of 5.3 nm via monitoring of the magnified Moiré pattern. Our DUV structured illumination will enable high-resolution monitoring of semiconductor processes such as transistor pitch variation and mask alignment.