Distortion reduction by load release for imprint lithography

Due to the light source limitation and prohibitive cost inherent in conventional photolithography, various nontraditional patterning technologies, such as imprint lithography, electron beam or X-ray lithography have been attempted over the past 10 years. In this paper, a UV imprint lithography process is introduced for patterning sub-micrometer structures by using a soft PDMS mould, and an imprint experimental device with a loading mechanism driven by PZT for generating a time-variant load is described. As shown experimentally, an increased pressing load will reduce the thickness of the resist layer, leading to a reliable etching-through of the resist. It is found, however, that the mechanical pressing can generate geometrical distortion on the patterned resist mainly due to the elasticity. Incorporated with the use of a low viscosity photo-curable resist, a loading process with a load release step is proposed to reduce the geometrical distortion on the resist patterns. In the loading process, the loading force is partially released after the press peak but before the resist curing. Such a loading process can reduce the elastic distortion while attaining a thin remained resist layer. It is shown that this loading process, called Distortion Reduction by Load Release or DRLR simply can be combined with an imprint process for different patterning areas and feature sizes.