Abstract
This paper analyzes the effect of polarization and the incident angle on the contrasts of interference patterns in three-beam interference lithography. A non-coplanar laser interference system was set up to simulate the relationship between contrast, beam polarization, and the incident angle. Different pattern periods require different incident angles, which means different contrast losses in interference lithography. Two different polarization modes were presented to study the effects of polarization with different incident angles based on theoretical analysis simulations. In the case of the co-directional component TE polarization mode, it was demonstrated that the pattern contrast decreases with the increase in the incident angle and the contrast loss caused by the polarization angle error also grew rapidly. By changing the mode to azimuthal (TE-TE-TE) polarization, the contrast of the interference pattern can be ensured to remain above 0.97 even though the incident angle is large. In addition, TE-TE-TE mode can accept larger polarization angle errors. This conclusion provides a theoretical basis for the generation of high-contrast light fields at different incident angles, and the conclusion is also applicable to multi-beam interference lithography.
Highlights
Many techniques have been developed for the fabrication of photonic crystals, of which the laser interference lithography (LIL) is a powerful technology due to its low cost, short time consumption, and lack of necessity for precise focusing
LIL, the same analysis of contrast loss and the beam polarization combination mode is applicable for N-beam (n > 3) interference lithography
It can be seen from Equation (15) that the polarization combination of the beams has a key effect on the contrast of the light field
Summary
LIL can write sub-diffraction-limited features in photoresist [12,13] This is possible because of the non-linear response of positive photoresist to the light dose. The feature size (line width) is reduced by overexposing the high-contrast sinusoidal energy distribution light field [14,15]. In order to obtain the smallest possible feature size, the contrast of the interference light field needs to be sufficiently high. For non-coplanar interference, the contrast of the interference light field is simultaneously affected by the azimuth angle, incident angle, and polarization state of each beam [22–24]. We calculate how to select the appropriate combination of beam polarization states to ensure sufficient contrast under different incident angles. According to the non-coplanar interference model, we demonstrate the specific beam polarization combinations that should be used for different pattern periods in three-beam LIL. LIL, the same analysis of contrast loss and the beam polarization combination mode is applicable for N-beam (n > 3) interference lithography
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