(120b) Microstencils for Patterning of Nontraditional Materials

MEMS devices have relied on photolithography and thin film processing techniques optimized by the semiconductor industry to form micro- and nano-structures. This photolithographic patterning of structures typically involves cyclic processing steps such as photoresist coating, thermal treatment, UV exposure, chemical development, and wet/dry etching. As MEMS technology is harnessed for newer applications, particularly related to biology, some classes of materials and surfaces used may be incompatible with the chemical or thermal process steps associated with standard microfabrication. In response to this increasing need to pattern non-traditional materials several novel microfabrication techniques have been developed the most prominent of which are imprinting and shadow masking.

Imprinting is a pattern transfer technique that has been successfully used for patterning non-traditional materials. The imprinting process uses a mold with the desired pattern made by standard lithography. This mold is then brought in contact with the material that needs to be patterned. The wetted mold is then contacted to another substrate to transfer the material onto that substrate. Adjusting the surface properties can control the wetting and de-wetting of the mold and the substrate. The imprinting modes have been used to pattern a variety of materials and substrates including 3-dimensional multi-layer patterning. Shadow masking uses rigid silicon wafers that were etched through to transfer pattern. These silicon shadow masks can be cleaned and re-used making their use relatively low-cost. However, the problem with this method is that an air gap always exists between the mask and the substrate giving rise to features larger than the mask openings due to lateral leakage and oblique deposition.

We present a photo-lithographically patterned parylene-SU8 bi-layer microstencil that can be used for micropatterning. The parylene layer enables mechanical peeling of the hybrid film from a hydrophilic substrate and eliminates the use of harsh chemicals typically required for releasing the resist. The SU8 layer is photo-lithographically patterned ensuring alignment with existing features. The role of the SU8 layer is to provide a mask for parylene etching as well as provide height to the microstencil for controlling the amount of material patterned. Alternatively, the amount of material patterned can be externally controlled using a variety of techniques including spin coating and thin film deposition. The microstencils were defined on silicon, glass, and polymer substrates, and then used to pattern chemically and thermally sensitive compounds including cells, wax, sol, and CYTOP^TM. Especially, photolithographically aligned wax column can be used for various applications that require patterned paraffins such as phase-change valve, which helps the system integration.