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

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.