Considerable difficulties and limitations are associated with the patterning ofthick photoresist layers to generate high aspect ratio features in MEMS fabrication. Moreover, a large number of steps is needed to achieve the patterned MEMS structures.The PMOD methodology takes advantage of direct patterning of a photoirnageable, highly etch resistant inorganic metal oxide precursor to form the hard mask. A spin coated thin Ti02 film deposited onto a Novolac transfer layer has been evaluated. An etch ratio of 850: 1 between Novolac resin and Ti02 thin-film has been achieved by oxygen gas ME. One set of process parameters demonstrated vertical sidewalls on 1 0 jtm thick Novolac using a 20 urn patterned Ti02 thin film. Photo resolution ofthe Ti02 films as small as 0.5 im has been demonstrated using a contact aligner. In addition to applying our process to silicon substrates, we have also demonstrated the feasibility ofpatterning on ceramic alumina substrates. The plasma-etch residues and the PMOD film were removed by wet chemical cleaning solutions developed at EKC Technology.
PMOD (Photochemical Metal Organic Deposition)-based DTFI (Direct Thin Film Imaging) methodology is a demonstrated means for patterning organic materials on flexible (plastic) substrates. This process is used to pattern 1-micron features at an aspect ratio of 8:1 using contact lithography. Use of oxygen plasma RIE etch to transfer the hard mask pattern to the organic material allows for good sidewall angle control. High etch selectivity between the novolac polymer and PMOD TiOX hard mask (< 800:1) makes the use of very thin hard masks (∼ 200 angstroms) to pattern thick organic films (<10 microns) possible. Selective removal of the PMOD TiOX (TiO2) hard mask makes this process amenable to patterning of functional organic structures fabricated from materials chosen for their desired properties (e.g., glass transition temperature (Tg), etch resisitance, optical properties, mechanical properties, etc.) not their ability to be photopatterned (e.g., photoresist).
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