Resist Removal Stripping

The main goal of this step is the complete removal of the resist without affecting the wafer surface. Two methods are used wet stripping (the use of either solvents, which dissolve the resists, or oxidisers that transform the resist into carbon dioxide and waste) and plasma resist stripping. 

During this step very small amounts of impurities (e.g., boron, arsenic) diffuse into the stripped regions of the semiconductor substrates. The cycle described in this section has to be repeated several times to obtain the integrated circuit component. 

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Fig. 1. The hthographic process. A substrate is coated with a photosensitive polymer film called a resist. A mask with transparent and opaque areas directs radiation to preselected regions of the resist film. Depending on resist characteristics, exposed or unexposed portions of the film are removed using a developer solvent. The resulting pattern is then transferred to the substrate surface and the resist is stripped.

Stripping The resist was stripped or removed using a Chemcut stripper placed in tandem with the Chemcut etcher. The Model number was also 547-20. Potassium hydroxide solution was used as the stripping medium at a temperature of 150 F (ca. 66 C). The conveyor speed was 7.0 feet per minute. 

In order to remove the resist after the RIE treatment, wafers were immersed in phenolic-type resist stripper, but the resist as well as the scum could not be stripped. Since a thin silicon oxide layer is formed on the resist surface, and the composition of scum is thought to be silicon oxide as discussed above, it is necessary to remove this silicon oxide layer (scum) prior to the resist removal. Therefore, resist stripping was done in two steps. In a first step the wafer was immersed in buffered hydrofluoric acid solution to remove the silicon oxide and was then treated with conventional resist stripper. 

Plastic mold is fabricated by polydimethylsiloxane (PDMS). The chemical structure of PDMS is shown in Figure 4.20. A monolayer of DPE (4,4-diami-nodiphenylether) is coated on the plastic mold. The monolayer is transferred to the base plate. After stripping of the plastic mold, a multilayer of terephthaloyl chloride (TPC) and DPE is self-assembled on a monolayer by vapor deposition, as shown in Figure 4.21. The multilayer is then hardened by condensation polymerization. The reaction scheme of condensation polymerization is shown in Figure 4.22. The final pattern on the base plate is obtained after etching and resist removal. 

Plating. Plating is an additive process where the copper layer is first etched.Then the layer is catalyzed for electroless plating, and photoresist is applied. Resistor locations are imaged into the resist and the pattern developed. Exposed catalyst in the proper areas then initiates plating of the resistors. The resist is stripped, background catalyst is removed, and the resistors are in the proper locations. 

After image transfer, the patterned resist must be readily and completely removable without substrate damage. The pattern often can be stripped from the substrate with a mild organic solvent. Proprietary stripper formulations or plasma oxidation treatments are utilized when the imaging chemistry or image transfer process has iasolubilized the pattern. 

Resist stripping- Both wet and dry removal processes are used at this step in processing. Dry ashing removes the bulk of the photoresist and wet stripping removes remsuning residues. 

Steam stripping is capable of removing typically 90 to 99% H2S, 90 to 97% NH3 and 75 to 99% organic materials. It should be noted though, that some organic materials are resistant to steam stripping and it is thus not a universal solution to contamination with organic materials. 

The zinc ion cross-links with the polymer to create sufficient strength and cross-linking density for durability and resistance to abrasion and detergents. The floor finish is easily removed with ammonia cleansers to reform the stable complex with zinc. The action of pulling the zinc out of the polymer allows the polymer to dissolve in the stripping solution. 

Film Formation. A novel feature of these Au-organic solvent colloids is their film forming properties that can be induced simply by solvent stripping. In this sense they are "living" colloidal particles. Films formed in this way are conductive, but less so than pure metals. (in ) The higher resistance of the films is due to the incorporation of substantial portions of the organic solvent, which can partially be removed by heating, and resistivity then decreases.(M1)... 

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