Integration the back-side inclined exposure technology to fabricate the 45° k-type prism with nanometer roughness

Abstract

This paper describes the design for a special k-type microprism structure for application in the lateral-type blu-ray semiconductor laser of an optical pickup head system. This design solves the current frontal type blu-ray semiconductor laser problem, and thus reduces the size of the optical pickup head. This study combines front- and back- inclined exposure technology to develop a k-type microprism structure. Thick film negative photoresist are used in this study as the main structural material. For obtaining the optimal structural surface roughness, the effect of solvent loss percentage of the polymer material was controlled. Besides, the bottom half of the k-type was generated through backside exposure to solve problems such as diffraction phenomena due to uneven photoresist surface during front-side inclined exposure. This design also avoids the problem of refractive index matching by omitting the step of filling the gap between the mask and the photo resistor with glycerol. For improving the roughness problem of the front-side inclined exposure, backside inclined exposure is implemented when fabricating a 45 ° polymer micro mirror. The use of front-side exposure for making the top half of the k-type solves the problem of undesirable surface roughness caused by insufficient light penetration during front-side inclined exposure. This paper utilizes front- and back-side inclined exposure technology to fabricate a 45 ° k-type polymer micro mirror with 15.2 and 12.4 nm (400 μm × 400 μm) roughness, respectively. The roughness level could meet the standards (λ/10, λ = 405 nm) of blue ray specifications. This type of micro prism can be used as a key component in Pico-projector, Interferometer, bio detection systems, data storage systems, and linear encoder optical systems. This novel technology also has the characteristics of high throughput and wafer-level assembly.