The Critical Role of Optical Systems in Semiconductor Manufacturing

Semiconductor manufacturing relies on optical systems in two key areas: lithography and inspection. In the lithography process, the light beam emitted by the light source must pass through a complex optical shaping and homogenization system before being precisely scaled and exposed onto the wafer surface via a projection objective lens. The numerical aperture, level of aberration correction, and transmittance of the optical system directly determine the resolution and overlay accuracy of the lithography system. In the inspection stage—ranging from critical dimension measurement to wafer surface defect detection—the performance of the microscope objective determines how small a defect or how fine a structure the equipment can “see.”

Take the measurement of key dimensions on masks in the deep ultraviolet (DUV) wavelength band as an example: a 248-nm water-immersion objective with a numerical aperture as high as 1.25. Comprising 19 fused quartz and calcium fluoride monolithic lenses, this objective has a total length of only about 72 millimeters. Yet it must achieve near-diffraction-limited imaging quality within a bandwidth of 248 ± 8 nm, while also being compatible with visible-light objectives and a 903-nm laser autofocus module mounted on the same turret. This optical design, subject to multiple constraints, tests the company’s capabilities across the entire supply chain—from material selection to assembly processes.

Technical Depth from Materials to Coatings

The performance limits of semiconductor optical components are primarily determined by the materials used. Fused quartz and calcium fluoride are the materials of choice for DUV optical systems due to their high transmittance and low absorption characteristics in the deep ultraviolet (DUV) wavelength range. In detection applications covering a broader spectral range, the design of wide-spectrum microscopy objectives—spanning from the near-ultraviolet to the near-infrared—requires the use of dispersion vector analysis to guide the selection of glass materials, thereby achieving flat-field apochromatic correction.

Coating technology represents another critical factor in the performance of optical components. Anti-reflection coatings, high-reflectance coatings, bandpass filters, and notch filters—these functional coatings directly determine the signal-to-noise ratio and measurement accuracy of optical systems. Take band-stop filters as an example: they must reflect specific wavelength bands (such as laser excitation lines) while efficiently transmitting all other wavelengths, with an optical density (OD) of 4 or higher. This places extremely high demands on the control of the number of coating layers and thickness precision. Bandpass filters, on the other hand, act as wavelength selectors in fluorescence microscopy, spectrometers, and machine vision inspection; narrow-band products can compress the bandwidth to 2–5 nm.