The objective for this project was to investigate the feasibility of making high aspect ratio SU8 structures via contact lithography with a target of 10:1 and line width resolution of about 2μm. Factors investigated include exposure dose of 150mJ/cm2, 200mJ/cm2, 250mJ/cm2 and PEB times of 1.5mm, 3mm and 4.5mm. The responses were line width CD and sidewall angle. The approach was first to optimize the thickness of the resist coated. This was done by generating a spin speed curve for the SU8 formulation used. Secondly, was to optimize the line width CD. A 32 full factorial experiment was performed. From earlier screening experiments, the center point treatment combination was using a dose of 200mJ/cm2, and PEB time of 3mm. Statistical analysis showed a large residual error in the response data and thus unexplained variation in the process as it pertains to controlling line width CD and sidewall angle. The treatment combination with the smallest 8μm line width was dose of 200 mJ/cm2, PEB time of 1.5mm and the measured feature width was 7.1μm to give an aspect ratio of approximately 3:1. Across all treatment combinations, dose of 250mJ/cm2, PEB time of 4.5mm gave the smallest line width CD resolved with a CD of 5.1 μm giving approximately 4:1 aspect ratio.
"Investigation into the Use of SU8 in High Aspect Ratio Applications,"
Journal of the Microelectronic Engineering Conference: Vol. 16
, Article 14.
Available at: http://scholarworks.rit.edu/ritamec/vol16/iss1/14