Abstract
LIGA process, which combines x-ray deep lithography, electroforming and micromolding techniques, is a major method for fabricating microstructures with very high aspect ratio. However, the cost and accessibility of x-ray synchrotron radiation as well as the demanding mask-making technology hinder the pervasive exploitation of the process. Thus several analogous processes, including UV-LIGA and Laser-LIGA processes, have been developed to overpass the barrier.UV-LIGA process has been viewed as `poor man’s LIGA’ because it employs low cost exposure apparatus, and which is already used in IC industries. A negative-tone photoresist named SU-8 is the most popular photoresist used in UV-LIGA process because it can form several-hundred-micrometers thick layer easily by spin coating method and aspect ratio of photoresist structures after development can up to 20. Although SU-8 photoresist can fulfill most requirements for UV-LIGA process, it is very difficult to be removed after completing electroforming procedure because SU-8 is virtually insoluble in most chemicals after it is crosslinked. However, photoresists with positive-tone behavior can avoid this problem. Some researchers report using a positive-tone photoresist ma-P 100 in UV-LIGA process, but the attainable thickness is only up to 100 micrometers for a single spin coating process. Thus the demand for new photoresists is necessary.In our work, a novel positive-tone photoresist combining chemically amplified concept and casting technique has been developed for UV-LIGA process. Photoresist layers up to 500 micrometers thick can be fabricated easily. For a 100-500 micrometers thick layer, a dose of 75-100 mJ/cm2·μm is required to remove all the exposed photoresist. The microstructure with 150 micrometers tall and 15 micrometers wide has been realized and the calculated aspect ratio is around 10. At present, the resist microstructue with 500 micrometers tall has been made. Then the nickel microstructure has also realized by completing electroforming procedure and the residual resist has removed with usual organic solvent.