Fabrication techniques photoresist pattern

Figure 6 Cross-section of a switchable grating from photoresist (Strategy 3). By using standard semiconductor fabrication techniques, a cell can be constructed with a holographically patterned central electrode. After filling with LC, the cell can be switched on and off with an electric field applied between the outer unpatterned electrodes.

After the patterns on these polymer films are transferred into photoresist films coated on silicon substrates using photolithography, the developed photoresist patterns can serve as a master to make the required PDMS stamps. By combining this method of rapid prototyping with soft lithographic techniques, we can fabricate patterned microstructures of polymers and metals within 24 h of the time that the design is completed. Rapid prototyping makes it possible to produce substantial numbers of simple microstructures rapidly and inexpensively. 

In many cases it is necessary to synthesize porous materials in a well-defined preordered shape or within confined geometries, which introduces a pathway to fabricate hierarchically ordered porous materials. The techniques mentioned above have been shown to be capable of producing structured and well-ordered templates [61] within capillaries [50], thin plates [62], micromolds [63], or photoresist patterns [64,65]. Spatial adjustment of the surface functionality on the substrate and its wetting properties can yield patterned colloidal films [66,67]. Finally, confining the particle dispersion itself by printing techniques produces micropatterned arrays [68]. This was also shown to work without the necessity of preceding surface patterning steps [69]. 

Imprint and Exposure Phase-Shift Lithography To solve the contact problem between phase shift mask and substrate, a new combination method is suggested. By using thermal imprint technique, photoresist can be patterned with specific geometry and it can be roUed as phase shift mask structure and photoresist layer at the same time. A photoresist has different refractive index from transparent elastomer or quartz, height of imprint mold needs to be calculated again with the equation above. Fabrication process flow is explained in Fig. 5. 

A shadow-mask technique has been applied for the local metal deposition to exclude metal residues on other designs processed on the same wafer (Fig. 4.2b). Such metal residues may be caused by imperfections in the patterned resist due to topographical features on the processed CMOS wafers or dust particles. The metal film is only deposited in those areas on the wafer, where it is needed for electrode coverage on the microhotplates. This also renders the lift-off process easier since no closed metal film is formed on the wafer, so that the acetone has a large surface to attack the photoresist. Another advantage of the local metal lift-off process is its full compatibility with the fabrication sequence of chemical sensors based on other transducer principles [20]. 

The lift-off process is usually employed to fabricate metal electrodes. This method, as opposed to the wet-etch process, allows the dual-composition electrode to be patterned in a single step [747]. In order to achieve well-defined metal electrodes in a channel recess using the lift-off technique, the metal (Pt/Ta) will not be deposited onto the sidewalls of the photoresist structure (see Figure 2.32). This discontinuity of the deposited metal layer around the sidewalls allows metal on the resist to be removed cleanly from the surface without tearing away from the metal on the surface. Thus negative resists were used because they can be easily processed to produce negatively inclined sidewalls. To achieve this, the photoresist is subjected to underexposure, followed by overdevelopment [141]. 

A metal interconnect fabrication process is disclosed in US-A-5384267. A metal layer and a photoresist layer are formed on an array of HgCdTe detectors. The photoresist layer is patterned to form a positive mask and the metal interconnect is formed by using a dry etching technique. 

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