Metal mask

As with any other fabrication process, masks are needed to define the features to be etched. It is common that the etch used for the semiconductor also etches the masking material. For this reason many different masks are used in etching, including photoresist, dielectric films, and metals. Masking can be a complex issue, especially when very deep etches (>5 fim) are performed with high aspect ratios (148). 

FIGURE 2.3 Sequence for fabrication of the glass microfluidic chip, (a) Cr and Au masked glass plate coated with photoresist (b) sample exposed to UV light through a photomask (c) photoresist developed (d) exposed metal mask etched (e) exposed glass etched (f) resist and metal stripped (g) glass cover plate bonded to form sealed capillary [102]. Reprinted with permission from American Chemical Society. 

When poly(ethylene oxide) (PEO) silane was grafted onto oxidized PDMS stamps it acts as a protein repellent layer. This property was utilized to design a flat stamp with regions that can attract proteins (nonmodified PDMS) and regions modified with PEO that have protein-repellent properties. The local modification of native PDMS was conducted by oxidation in 02-plasma with the application of a metal mask (areas that were covered by the mask were not oxidized and not modified). Proteins (immunoglobulin G, IgG) were transferred successfully to the glass substrates... 

The channel layer is 50-nm-thick pentacene deposited in the vacuum sublimation system at ambient substrate temperature with fine metal masks. After deposition of pentacene thin film, 30-nm-thick gold layers are deposited as source and drain though fine metal masks. 

For these reasons uniform thickness films are deposited on all surfaces. Unique features which result are the deposition of uniform thickness coatings on sharp edges, in crevices, and around the inside of holes. A metallizing mask was coated with 1.5 mils of poly(chloro-p-xylylene). Figures 2 and 3 are magnifications of the coated saw tooth and coated... 

Okano and coworkers have patterned poly(N-isopropylacryl-amide) (PNIPAAm), a material similar to BSA and PEG in that it does not adhere to cells at room temperature. In this experiment, a composite solution of PNIPAAm dissolved in propanol (55 wt%) was uniformly coated inside a commercial cell culture dish. The polymer was then patterned, using standard e-beam lithography, onto the surface of a cell culture dish to test the dynamic behavior of cells for potential clinical applications. A metal mask (60 mm o.d. 

Capacitance of the anodicTa205 films was measured on test MDM structures (Al/Ta205/Al). Upper electrode was deposited through metal mask with diameter of holes 1 and 0.5 mm. Surface structure was analyzed with an atomic force microscope (AFM). 

The grafting of poly(acrylic acid) and poly(allylamine) from the previous example was also conducted in the presence of a metallic mask... 

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