Photoresist spray coating for 3D MEMS/NEMS

Spray coating of a photoresist was investigated for three-dimensional (3D) MEMS/NEMS. To improve the uniformity of photoresist deposition onto a sample with 3D surface structure, the gas flow in the vicinity of the sample was numerically analyzed to understand the physics for uniform photoresist deposition. The numerical analysis revealed that the gas flow that flowed horizontally in the vicinity of the sample degraded the uniformity of the resist deposition. The horizontal flow could be blocked by setting a shield plate with an aperture over the sample. Moreover, using the shield plate enhanced vertical velocity component in the aperture area, which could improve uniformity of the resist deposition on trench bottom, trench top. Angled exposure technique enabled photoresist patterning on the sidewall. With this “3D photolithography”, 3D MEMS/NEMS devices can be fabricated. For the demonstration, 100 photo cells of pn junction were connected in series by 3D wirings to achieve 10V.