New fabrication techniques of SU-8 fiber holder with cantilever-type elastic microclips by inclined UV lithography in water using single Mylar mask

In contact UV lithography, a pair of cantilever beams fabricated by two inclined exposures at +/- 45A degrees in SU-8 using a single mask will form a connected end on the top of SU-8 layer. These beams made of SU-8 with fixed-end have been used as optical fiber holders (Ling and Lian in Microsyst Technol 13(3-4):245-251, 2007). Recently, a two-mask, two-step process to fabricate free-end cantilever beams from SU-8 using inclined UV lithography has been developed (Ling et al. in Microsyst Technol 15(3):429-435, 2009), which has been successfully applied to fabricate SU-8 optical fiber holders with long free-end cantilever beams. In this process, two masks are needed in order to obtain free-end beams and the alignment between two exposures is always time consuming with limited accuracy. Two new techniques, inclined UV shadow mask lithography and inclined UV proximity lithography, have been illustrated here for fabricating free-end SU-8 cantilever beams, which eliminate the precise alignment step required in our previous work (Ling et al. in Microsyst Technol 15(3):429-435, 2009). In the inclined UV shadow mask lithography approach, the SU-8 cantilever beams without connected ends are formed by using one main mask and two shadow masks. Each shadow mask is used to selectively transfer one of the two separated patterns on main mask into SU-8 layer at +45A degrees and -45A degrees, respectively. In the inclined UV proximity lithography approach, a proper proximity gap between mask and SU-8 surface is obtained by using a 50 mu m thick Mylar sheet, so that the exposing light paths that formed connected beam ends will fall inside the proximity layer instead of the SU-8. In this way, the desired open-end cantilever structures can be achieved. In this paper, the principles and the fabrication procedures of the proposed techniques are demonstrated and the preliminary results are discussed.