This paper proposes a technique for simultaneously mapping the thickness and surface profile of large-area patterned wafers with high density, as required in semiconductor and display manufacturing processes, using spectral interferometry. Conventional spectrometer-based metrology techniques suffer from reduced measurement accuracy due to limited wavelength resolution, which makes it difficult to clearly separate thickness and surface profile signals. In addition, their limited acquisition speed leads to degraded spatial resolution when measurements are performed under high-speed translation.
To overcome these limitations, a high-resolution, high-speed near-infrared spectrometer with a wavelength resolution of 0.1 nm, a wide optical path difference measurement range of up to 5 mm, and an acquisition speed of 40 kHz was employed. In the proposed measurement system, the surface profile signal is intentionally positioned in an optical path difference region that does not overlap with the thickness signal or its harmonics. This enables complete separation of thickness and surface profile signals using a single optical system without mutual interference.
To verify the system performance, a 100 mm × 55 mm area of a rapidly translated wafer was measured. As a result, wafer thickness maps and three-dimensional surface profile maps of patterned structures were simultaneously acquired with a high density of 552k measurement points. Furthermore, owing to the eightfold higher acquisition speed compared to conventional commercial spectrometers, high-density pattern images were obtained without undersampling or motion blur, even under high-speed scanning conditions. These results demonstrate the effectiveness of the proposed technique as a next-generation large-area metrology solution that resolves the trade-off between measurement speed and spatial resolution.
