Photoresist wafer fabrication

The whole system is constructed from two silicon wafers, fabricated using photoresist by deep reactive ion etching (DRIB) [21]. The wafers were thermally bonded. Thereafter, inlet and outlet ports were machined and the single reactors isolated by DRIB. 

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]. 

During the component fabrication process, CFC-113 and TCA are widely nsed for cleaning surfaces and for stripping negative photoresist. Nonhalogenated solvents are often nsed for stripping positive resist. Following fabrication, the chips are tested for defects and the wafers cnt into individual chips. 

Figure 11.6 Fabrication procedure of an IDA microelectrode. An oxidized silicon wafer (A) is coated with platinum (B). Carbon film is pyrolyzed on it (C). The substrate is coated with photoresist, which is exposed and developed (D) unnecessary portions are then removed by reactive ion etching (E). After removing the photoresist, an Si3N4 layer is deposited on the substrate (G). The substrate is coated with photoresist, which is exposed and developed (H) then the desired shape of the carbon electrode is exposed by reactive-ion etching (I). [Adapted from Ref. 36.]...

Fabrication aids include such applications as photoresists, planarization layers in multi-level photoresist schemes, and as ion implant masl. In these applications, the polymer is applied to the wafer or substrate, is suitably cured and/or patterned, but is removed after use. 

Photoresist—Photosensitive polymer that is used to pattern silicon wafers during integrated circuit fabrication. 

Today, a typical process flow for advanced ICs consists of 300 to 500 steps, 30% of which are wafer cleaning steps." Many process steps during IC fabrication may introduce contamination, which must be cleaned before the next process step. For example, in processes such as steam oxidation, resist etching, and ion implantation, metallic contamination typically introduces a surface concentration of 10 to lO Vcm. The need for wafer cleaning can be separated into three areas (1) preparation of the wafer surfaces for oxidation, diffusion, deposition, and metallization (2) preparation for the application of photoresist and (3) removal of photoresist after the etching process." ... 

Exposure of the photosensitive article. The exposure step photographically transfers a pattern from a reticle or photomask to the photoresist coated on the wafer surface. Photomasks are glass plates with patterns made of opaque and transparent areas. A photomask will typically have the pattern for a few dice and will be stepped across the wafer exposing the pattern after each step. In order to ease a task of a photomask fabrication and make the process less defect sensitive, photomask patterns are either 5x or 4x, the size of the desired feature on the wafer, and the photomask pattern is optically shrunk before reaching the wafer. 

Contact cuts were plasma etched through the polyimide (using a photoresist mask) and buffered HF was used to etch the silicon dioxide underneath. After aluminum was deposited and patterned, both test and control wafers were sintered in forming gas at 400°C for 10 minutes. A CPI strip was fabricated beside each FET with four aluminum contacts to allow CPI 4 point conductivity measurements. 

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