Experimental research on resist filling behavior in microimprint lithography by using defocusing digital particle image velocimetry

The resist filling behavior is crucial to the quality of the final imprinted patterns in microimprint lithography. To achieve the microscale velocity field of resist, a 3-D defocusing digital particle image velocimetry (DDPIV) system was established. The spatial coordinates of 500 nm fluorescent tracer particles were inferred from their DDPIV images generated by a mask with three apertures forming an equilateral triangle. Time-resolved 3-D particle field inside the resist was obtained with the spatial coordinates of particles. Particle tracking velocimetry was utilized to derive the velocity field from the particle spatial position in the imprinting sequence. Velocity history of particles along the extracted track was described. The results showed that the maximum velocity of the resist was always located in the region between the mold corner and the supporting substrate; meanwhile, the velocity component of the resist in the vertical direction is approximate to zero. The volume transfer characteristics of resist was illustrated from the view of particle field and velocity field, which will help reveal the resist filling mechanism and provide useful guidance for the mold structure optimization.