Molecular contamination

The analytical techniques covered in this chapter are typically used to measure trace-level elemental or molecular contaminants or dopants on surfaces, in thin films or bulk materials, or at interfaces. Several are also capable of providing quantitative measurements of major and minor components, though other analytical techniques, such as XRF, RBS, and EPMA, are more commonly used because of their better accuracy and reproducibility. Eight of the analytical techniques covered in this chapter use mass spectrometry to detect the trace-level components, while the ninth uses optical emission. All the techniques are destructive, involving the removal of some material from the sample, but many different methods are employed to remove material and introduce it into the analyzer. 

Characterization and Testing of Cell Banks Test for adventitious agents, endogenous agents, and molecular contaminants (toxins, antibiotics) to confirm identity, purity, and suitability for manufacturing use... 

Different kinds of anthropogenic compounds and their occurrence within the non-extractable matter are reported in a couple of studies. Most of the investigations are related to the occurrence and fate of associated low molecular contaminants, the so called "bound residues", and are published within the last 30 years (e.g. Li and Felbeck 1972 Kaufman et al. 1976 Liechtenstein et al. 1977 Wheeler et al. 1979 Liechtenstein 1980 Khan 1982, Boul et al. 1994 Lichtfouse 1997 Houot et al. 1997 Northcott and Jones 2000). Earlier investigations dealed especially with... 

At microflotation the process of deposition of disperse particles and molecular contaminants on a bubble surface proceed in parallel. If the rates of these processes are commensurable in the process of microflotation the level of impurities in the bulk decreases. It means that their adsorption on bubbles surfaces decreases too, leading to the increase of the residual mobility. 

Let us point out two more aspects of this problem, which contribute to the preservation of a noticeable mobility of the bubble surface. It is expected that in the development of microflotation technology, increasingly deeper purification from dispersed particles and therefore from molecular contaminations can be attained under the condition of a remarkable residual mobility. 

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. 

Although contamination control is implemented in these exposure tools with on-board purge control units, which are equipped with gas purifiers that remove contaminants such as H2O, O2, CO, CO2, hydrocarbons, H2, and sulfur compounds, these control units are oftentimes not 100% efficient. Typical benefits of molecular contamination control include improved process yield and greater process control. 

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]... 

Examples of molecular contaminants to be removed and carbon impregnating chemical used for purification of air for semiconductors production processes... 

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... 

A dramatic change in instriunental development for environmental chemical analysis and specifically for molecular contaminants has ocemred over recent years [205-218]. The following sections wiU review the different techniques and instrumental development currently used for the characterization of organic contaminants. 

Nanotechnology-based sensors have the potential to bring about a paradigm shift in revolutionizing the speed and accuracy with which industries or regulatory agencies detect the presence of molecular contaminants or adulterants in complex food matrices with color changes that occur to metal nanoparticle solutions in the presence of analytes... 

Ultrafitration is a rapid and protective technique, by which a P. solution is simultaneously concentrated and freed from small molecular contaminants. It is usually operated with excess, rather than reduced pressure. By using the appropriate membrane filter (pore sizes range from 15 pm upwards), P. mixtures can also be crudely fractionated according to M,. Biologically active P. can be prepared on an industrial scale by using tubular membranes with large surface areas and a daily throughput eapaeity of several thousand liters. 

Initial Studies of Molecular Contaminants Using Static Secondary Ion Mass Spectrometer (SIMS)... 

Tremendous efforts have been made in the development of nanotechnology-based sensors for the deteetion of molecular contaminants in complex food matrices. In this respect, nanosensors ean be defined as an array of thousands of nanoparticles that fluoresce on contact with food pathogens. On the other hand, tests for the detection of spoilage reveal modification of the color among the metal nanoparticles solution and analytes (Ai et al. 2009). 

In summary, observation of reduction in situ revealed that the hydroxylated ferric surface of the precursor is converted into a largely ferrous surface, free of water after a long induction period. Only a fraction of the surface iron is reduced to an ill-defined metallic state. Neither a film of chemisorbed water nor other molecular contaminants block the surface and prevent the reduction from proceeding. This is in contrast to the kinetic studies described in Section 2.5, which deal with the high-pressure reduction of iron oxides where, under identical conditions, ferrous ions are more easily reduced than ferric ions. 

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