Resist stripper

At present, with ICP-MS, many chemicals can be diluted with high-purity water and analyzed directly without any further sample preparation. This method, with its enormous sensitivity for many metals at levels of part per billion to part per trillion, is valuable for good quality control of incoming chemicals, particularly acids, buffered etches, and various resist strippers. 

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. 

When the wafer was dipped into this buffer solution, the amount of scum decreased sharply during the first ten seconds, but after 30 seconds the removal rate became extremely low and residue remained as shown in Figure 7. However, the remaining scum and resist layer were removed perfectly in a second step by dipping into conventional resist stripper S-502(Tokyo Ohka Co.), at 110°C for 7 to 10 minutes as shown in Figure 8. 

Two broad categories of resist strippers and cleaners are employed. These are solvent-based (wet) and plasma-based (dry) strippers. Depending on whether the wet stripping is to be done for the FEOL processes or BEOL processes, different types and combinations of resist strippers may be used in order not to damage the devices. 

Some of these strippers suffered from one or more drawbacks such as potential toxicity to workers exposed to them, environmental and pollution problems in disposal after use, volatility, corrosion of equipment, and the safety hazard of operating at temperatures above the flash point of the stripper. They were also plagued by difficulties and the high cost associated with disposing of them in an environmentally acceptable manner after use. The semiconductor industry has to a large extent migrated away from them for the aforementioned reasons, and some of the chlorinated resist strippers such as chloroform are now banned from the semiconductor industry. 

These modern resist strippers pose no significant toxicity hazard to qualified personnel handling them. The compositions are miscible with water and are therefore readily washed from the substrate after the stripping operation has been completed. The stripping bath is stable and can be reused many times over a prolonged period without losing its efficacy. Furthermore, the principal components of these strippers are readily recoverable by distillation and thus can be recycled. 

Molecular bases Ammonia Amines Amides CVD, HMDS, CMP slurries, wafer cleaning processes, TiN and Si3N4 films deposition, TMAH decomposition Resist strippers NMP, dimethyl acetaminde, polyimides Neutralizes photoacids in resists, reacts with molecular acids to form haze crystals on optical elements... 

Nonaqueous Waste Resists. One of the most exciting waste minimization techniques currently being tested is the elimination of the need for rinsing from both photoresist developing and stripping operations. This new process may eliminate spent developer wastes and wiU eliminate the spent resist stripper bath dnmp. 

N-Methyl-2-Pyrrolidone. N-methyl-2-pyrrolidone (commonly referred to as NMP or M-Pyrol) is used within the semiconductor industry as a degreaser, a resist stripper and as a solvent for phenolic die coat resins is known to cause skin irritation and to rapidly permeate through intact skin. The U.S. Environmental Protection Agency (EPA) in a final assessment document on NMP, found this material as a significant risk of reproductive and developmental effects for people working with NMP-based paint strippers. 

After this exemption, TBAC, non-HAP organic solvent is expected to have wider use in adhesives, inks, coatings, industrial cleaners, photo-resist strippers and other formulated products. TBAC can be substituted for more reactive solvents. The businesses using exempt VOCs like TBAC would be subject to fewer regulatory requirements thereby enjoying lower costs of production. For instance, such businesses may not need to operate air pollution control equipments to comply with the regulations. ... 

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