Tool contamination

The third class of dry-developable resists involves heating the exposed resist films in a development step. This development method does not require expensive etching tools, is therefore economical, and could alleviate the potential problem of exposure tool contamination associated with the self-developing resist systems. Many of the plasma-developable resist systems involving a relief-bake step, as discussed in Section 3.2.4.1, have the thermal development characteristics to a certain extent. In the thermally developable resist scheme, development is minimal during irradiation but completed to the substrate upon postbaking. 

Solid radioactive waste results from the operation and maintenance of the nuclear power plant and its associated processing systems for gaseous and liquid radioactive waste. The nature of such waste varies considerably from plant to plant, as do the associated levels of activity. Sohd radioactive waste may consist of spent ion exchange resins (both bead and powder) cartridge filters and pre-coat filter cake particulate filters from ventilation systems charcoal beds tools contaminated metal scrap core components debris from fuel assemblies or in-reactor components and contaminated rags, clothing, paper and plastic. 

Although the process requires the addition of a phosphate donor, such as glycerol-2-phosphate, it may be a valuable tool for cleaning water contaminated with radionuchdes. An alternative mode of uranium precipitation is driven by sulfate-reducing bacteria such as Desulfovibrio desulfuricans which reduce U(VI) to insoluble U(IV). When combined with bicarbonate extraction of contaminated soil, this may provide an effective treatment for removing uranium from contaminated soil (85). 

Three approaches have been identified that reduce susceptibility of CA resists to airborne contamination. In the first, process engineering changes such as the addition of special activated carbon filters to the environmental chambers surrounding the exposure tools (76,79), overcoating the resist with a soluble protective film to isolate the resist from the environment (77,80,81), or modifications of the process flow to minimize the time interval between exposure and post-exposure bake have been shown to improve CA resist processibibty. 

Chemical Gas Detection. Spectral identification of gases in industrial processing and atmospheric contamination is becoming an important tool for process control and monitoring of air quaUty. The present optical method uses the ftir (Fourier transform infrared) interference spectrometer having high resolution (<1 cm ) capabiUty and excellent sensitivity (few ppb) with the use of cooled MCT (mercury—cadmium—teUuride) (2) detectors. 

Fig. 4. Examples of emission spectrometry as a diagnostic monitoring tool for plasma processing, (a) The removal of chlorine contamination from copper diode leads using a hydrogen—nitrogen plasma. Emissions are added together from several wavelengths, (b) The etching and eventual removal of a 50-p.m thick polyimide layer from an aluminum substrate, where (x ) and (° ) correspond to wavelengths (519.82 and 561.02 nm, respectively) for molecular CO2...

Historically, EELS is one of the oldest spectroscopic techniques based ancillary to the transmission electron microscope. In the early 1940s the principle of atomic level excitation for light element detection capability was demonstrated by using EELS to measure C, N, and O. Unfortunately, at that time the instruments were limited by detection capabilities (film) and extremely poor vacuum levels, which caused severe contamination of the specimens. Twenty-five years later the experimental technique was revived with the advent of modern instrumentation. The basis for quantification and its development as an analytical tool followed in the mid 1970s. Recent reviews can be found in the works by Joy, Maher and Silcox " Colliex and the excellent books by Raether and Egerton. ... 

PL measurements are generally nondestructive, and can be obtained in just about any configuration that allows some optically transparent access within several centimeters of the sample. This makes it adaptable as an in situ measurement tool. Little sample preparation is necessary other than to eliminate any contamination that may contribute its own luminescence. The sample may be in air, vacuum, or in any transparent, nonfluorescing medium. 

Because of the extreme surface sensitivity of static SIMS, care should always be exercised not to handle the samples. Clean tools and gloves should be used always to avoid the possibility of contaminating the surface. While it is possible to remove surface contamination with solvents like hexane, it is always desirable not to clean the surface to be analyzed. 

Design, maintain and operate machine tools to minimize fumes and mist generation, splashing and skin contamination... 

Anything that enters an exclusion zone should be evaluated as to its potential contamination. If not removed properly, these contaminants may permeate PPE, tools, instruments, and other equipment [2]. In addition, this potential contamination can be transferred to the clean zones if it is not controlled. If contamination does get into clean zones, anyone may be able to take the contamination home with them to affect themselves, family members, and the general population. 

EMGRESP is a source-term and dispersion emergency response screening tool for calculating downwind contours with a minimum of user input and computational expense in the event of a release of a hazardous chemical. The program provides hazardous contaminant information, calculates toxic concentrations at various distances downwind of a release, and c" the... 

When the zoning strategy is applied, the two-zone model is a useful and simple tool for the determination of the thermal, contaminant, and humidity accumulations. Principles of two-zone modeling are presented in Section 8.4. 

Most exhaust hoods are either integrated with the contaminant-generating process equipment or are independent of the process equipment. It is nearly always better to have an integrated hood. The advantages are that the hood is de-ro work with that specific tool, process, and contaminant its airflow rate... 

The more enclosed a process is, the easier it is to keep a low concentration in the workroom. It is usually necessary for the workers or for some equipment to have physical contact with the process, w hich could make it difficult to use complete enclosures. If it is possible to enclose the contaminant source and the tool, a total enclosure is recommended, especially if the workers only need to access the process during pauses in operation. Total enclosures may also be necessary for processes that generate highly toxic contaminants. Where total enclosures are not practicable, partial enclosures may be used. F xterior hoods are the least effective exhaust hood. 

This is usually not a problem with small exhausts. With large exhausts (opening area larger than 0.1 m-), parts of a worker or of tools could easily come between the source and the exhaust. This diminishes the efficiency and could also spread the contaminant in unwanted directions, even if the exhaust velocity is... 

I FIGURE 10.8 Schematic ideal placing of worker, tool, and contaminant source when using exterior hoods. 

Tools are normally close to the opening. One way to diminish tlie disturbances from a tool is to shape the opening around that part of the tool where contaminants are generated. Another is to size the opening specifically foi the source and place it very close to the source and away from disturbances front the tool. 

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