During the chip manufacturing process, meeting overlay error requirements is essential to semiconductor yield. Measuring equipment of overlay error requires standard samples, which the double-layer grating with precise horizontal alignment can be used as, to verify its capability. Thus, we propose a novel alignment and processing method for layer separated processed double-layer gratings. Firstly, the bottom grating is obtained by holographic lithography . The upper and lower layers are aligned based on the homogeneous period of processing diffraction patten and the bottom grating, and manufactured simultaneously. We conducted an optical simulation of the alignment based on FDTD, setting the bottom grating as Ag material, 50 nm depth, 1μm period, and 50% duty cycle. Principally, the alignment accuracy is comparable with the linear encoder.
Pixelated micro-polarizer array is an attractive polarization imaging device because of its real-time fully detecting capability to Stokes parameters and high integration level. However, this micro-device is commonly fabricated by electron beam lithography, thus is often high-cost. Since periodic unit of this device is a 2×2 array of four types of one-dimensional (1D) gratings with different orientations (0°, 45°, 90°, 135°), a low-cost grating fabrication technique, interference lithography (IL), is possible to be used to fabricate this device. In this research, a four-steps exposure patterning method of micro-polarizer array based on single Lloyd’s mirror interferometer IL is developed. This interferometer is composed by two perpendicular parts: a mirror and a photoresist holder, and a 1D grating parallel with mirror can be fabricated in the exposure region on photoresist through lithography. A Cr-based mask, whose transparent pattern is a square array of square windows with 15×15 μm2 window size and 17 μm window spacing, is introduced and clamped onto the photoresist to cut exposure region. In four exposure steps, each 15×15 μm2 quadrant area of a polarizer array with 2 μm quadrant spacing will be exposed on photoresist, respectively. Between two exposure steps, mask and photoresist substrate need to be simultaneously horizontal rotated, to adjust the orientation of grating fabricated in next exposed quadrant on photoresist. Based on this method, we fabricated the single-state patterned micro-polarizer array, which effectively controls the cost and fabrication cycle. The experimental results show that the photoresist grating within a single window has stable structure, uniform period and good directivity.
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