Airborne molecular contaminants

While the holes in the pellicle frame are effective in preventing particles from entering the space between the pellicle and mask, they are not effective in preventing airborne molecular contaminants such as ammonia, sulfur dioxide, water vapor, etc. from reaching this space. Under DUV illumination, these contaminants react together to form ammonium sulfate crystals on the reticle, discussed in Section 13.3.4. In addition, molecular contaminants can outgas from pellicle adhesives and from degradation products of the interaction of pellicles with DUV radiation. 

Topcoats also provide a protective function against airborne molecular contaminants such as amines. Figure 13.53 shows PEB delay stabilty of up to 15 minutes obtained on a resist film protected with a topcoat. Following the indicated PEB delay times, the resist film was postexposure baked and developed. Even after 15 minutes, the CD values of the 80-nm and 90-nm lines/space features remained remarkably stable. This is considerably better performance than that achieved when topcoat is not used. 

Another challenge faced by SCALPEL technology is related to the fact that the SCALPEL mask is not protected by pellicles, making particulate and airborne molecular contamination a major issue. In particular, many components of the SCALPEL tool are sensitive to the presence of charged particulates these include electrostatic chucks, electrostatic optics, and apertures. The fact that the SCALPEL tool is designed to operate in a vacuum environment (10 torr) has been reasonably effective in limiting the amount of particulate and molecular contamination, but has not eliminated them entirely. 

Potential hazards caused by some airborne molecular contaminations in production of semiconductor devices [46, 219]... 

M+W Zander Facility Engineering GmbH, Airborne Molecular Contamination, Information Brochure, http //www.mw-zander.com/en/leistungen/leistungen p l 2.htm (last retrieved... 

The results also showed that the amount of absorbed NMP, or for that matter any airborne molecular base, depends on the solubility parameter of the polymer, on the nature of the contaminant, and on the Tg of the polymer. This was a remarkable result because it suggested that the environmental sensitivity of a resist polymer could be controlled by merely changing the Tg or the solubility parameter of the resist polymer. A verification of this result was obtained when the environmental stability of two polymers synthesized from two different isomers of BOCST monomers—the 3-BOCST and the 5-BOCST isomers—were found to have their environmental stability very well correlated with their Tg. The polymer with the significantly lower 7g—the 3- BOCST isomer—showed the least sensitivity to exposure to low levels of NMP. 

Because SPMDs have high sampling rates (Rs s) for vapor phase contaminants, all SPMDs are assembled in an environmentally controlled room equipped with an activated carbon air filtration system for the removal of airborne contaminants. SPMDs of almost any length can be prepared after allowance of space for the molecular welds or heat seals (i.e., 2.5 cm for each end). However, different... 

Rain may also wash some of the spray off the leaves. Most pesticides are not compounds with high molecular weights. They can evaporate in the heat of the sun. Once airborne, they can travel to remote parts of the world, where rain can bring them to the surface again.52 This long-range aerial transport explains how remote lakes in the Arctic and remote islands in the oceans have become contaminated. The preemergence herbicide, acetochlor (11.12),... 

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