Design and fabrication of microlens and spatial filter array by self-alignment

Abstract

For typically small volume production of MEMS, MOEMS, fine feature PCB, high density chip packaging and display panels, especially for lab tests, low cost and the capability to change the original design easily and quickly are very important for customers and researchers. BALL Semiconductor Inc.'s Maskless Lithography Systems (MLS) feature the Digital Mirror Device (DMD) as the pattern generator to replace photo-masks. This can remove masks from UV lithography, and dramatically reduce the running cost and save time for lab tests and small volume production. At Ball Semiconductor Inc, 1.5µm line/space, 10µm line/space, and 20µm line/space Maskless Lithography Systems were developed.In our MLS, an 848×600 microlens and spatial filter array (MLSFA) was used to focus the light and to filter the noise. In order to produce smaller line-space than 16 µm the MLSFA was used to get smaller UV light pad (compared with the SVGA DMD's micro-mirror: 17µm×17µm) and to filter the noise produced from the DMD, optical lens system, and micro lens array. This MLSFA is one of the key devices for our Maskless Lithography System, and determines the resolution and quality of maskless lithography.A novel design and fabrication process of a single-package MLSFA for our Maskless Lithography System will be introduced. To avoid problems produced by misalignment between a two-piece spatial filter and microlens array, MEMS processing is used to integrate the microlens array with the spatial filter array. In this paper, the selfalignment method used to fabricate exactly matched MLSFA will be presented.

High-resolution maskless lithography

“…The micromir-rors on the DMD can be instructed to produce a pattern by way of tilting them Ϯ 10 deg off their normal position. Light reflected off the micromirrors is projected into the low-NA 1:3 magnifying lens, forming a DMD image coplanar to the back plane of the integrated microlens and spatial filter array 13,14 ͑MLSFA͒. This is the first image plane where the individual DMD pixel image is focused by the corresponding microlens onto a second surface coplanar with the spatial filter array.…”

“…Background illumination due to optical scattering or noise, crosstalk, high-spatial-frequency components, as well as imperfect focusing by the microlens array are eliminated at the foci with a corresponding array of spatial filters. This array filtering technique 12,14 increases the system contrast and produces better lithographic results. With the 5:1 reduction lens, the focal points or point array carrying the DMD pattern is projected onto the surface of the substrate.…”

“…After lithographic exposure with the Hi-Res MLS, the substrate was further treated through a series of semiconductor processes before the concave microlens array was produced as shown. 13,14…”