Dry film process development for electroplating and lift-off of metal layers

Abstract

A dry film photoresist (MX 5020 from DuPont Electronic Technologies) was selected to fabricate microstructures with high sidewall verticality. Sidewall verticality of dry film is very important for better pattern transfer and sharp features. A fractional factorial design (FFD) method was used to identify the significant process variables for sidewall optimization. The most significant factor was determined to be exposure energy, as other factors were not significant in improving sidewall verticality. It was found that the sidewall slope increased with a decrease in exposure energy. The fabricated dry film molds with nearly vertical sidewalls (86°) were used for copper electroplating and sputter deposited Ti lift-off applications. The electroplating process was also optimized using a fractional factorial design. A lower plating current density resulted in a smoother, fine grained deposit compared to the higher current density, and the dry film resist was able to withstand a very acidic (pH ~1) copper sulfate plating solution. Sputtered titanium films with a thickness of 200 nm were also successfully lifted-off using dry film patterning.

Soft lithographic printing and transfer of photosensitive polymers: facile fabrication of free-standing structures and patterning fragile and unconventional substrates

“…Soft lithographic printing and transfer of photosensitive polymers: facile fabrication of free-standing structures and patterning fragile and unconventional substrates and MEMS packaging [3][4][5][6][7][8][9], roll-to-roll photolithographic processes for flexible electronics [10][11][12], micromolds as electroplating and fast prototyping masters [13][14][15][16][17], patterning on curved surfaces [18], wafer adhesive bonding [19,20], and structural materials for microfluidic chips [21][22][23][24][25]. However, the thickness of most DF PRs is 20-50 µm [26], and as the minimum feature size is closely related to the PR thickness, features smaller than 10 µm would be difficult to resolve.…”

Homebrew Photolithography for the Rapid and Low-Cost, “Do It Yourself” Prototyping of Microfluidic Devices

“…Another caveat to the use of SU8 is the uneven flatness even following spin coating, which is characterized by a so-called “edge bead” at the outer edges, which if not removed correctly can prevent the photomask sitting flat atop the photoresist, resulting in reduced resolution of the resulting pattern. Such a high cost also warrants the search for alternatives, and indeed various dry-film resists (DFRs), and photosensitive polymer films were developed for the fabrication of printed circuit boards that have the benefit of good-flatness/no edge-bead occurrence; they are also simpler/more straightforward to manipulate and apply . In this work, we demonstrate the production of a range of microfluidic master molds of various shapes and dimensions using inkjet-printed photomasks on acetate sheets from a standard home and office printer in combination with photosensitive DFR film applied to copper clad epoxy tiles using a typical laminator appliance.…”

“…Such a high cost also warrants the search for alternatives, and indeed various dry-film resists (DFRs), and photosensitive polymer films were developed for the fabrication of printed circuit boards that have the benefit of good-flatness/no edge-bead occurrence; they are also simpler/more straightforward to manipulate and apply. 10 In this work, we demonstrate the production of a range of microfluidic master molds of various shapes and dimensions using inkjet-printed photomasks on acetate sheets from a standard home and office printer in combination with photosensitive DFR film applied to copper clad epoxy tiles using a typical laminator appliance. We expose the photoresist through the homemade photomasks by using a UV LED black-light floodlight, much like those used in aquariums, rave parties, or used to cure resins.…”