Analysis clean room

IMS can be used for chemical analysis of vapours from electronics packaging [287]. IMS-QMS has been used to analyse headspace vapours in sealed electronic packages [275,288] and to follow outgassing of polymers [287]. Various types of photoresist solvents, phtha-late plasticisers and other polymer additives, such as BHT, were detected. Other applications of IMS in semiconductor technology involve failure analysis control of the efficiency of cleaning and etching steps characterisation of process media and surveillance of the atmosphere of clean rooms. 

Sample preparation is rather involved. A sample of urine or fecal matter is obtained and treated with calcium phosphate to precipitate the plutonium from solution. This mixture is then centrifuged, and the solids that separate are dissolved in 8 M nitric acid and heated to convert the plutonium to the +4 oxidation state. This nitric acid solution is passed through an anion exchange column, and the plutonium is eluted from the column with a hydrochloric-hydroiodic acid solution. The solution is evaporated to dryness, and the sample is redissolved in a sodium sulfate solution and electroplated onto a stainless steel planchette. The alpha particles emitted from this electroplated material are measured by the alpha spectroscopy system, and the quantity of radioactive plutonium ingested is calculated. Approximately 2000 samples per year are prepared for alpha spectroscopy analysis. The work is performed in a clean room environment like that described in Workplace Scene 1.2. 

Stephanie Boone, a technician at Los Alamos National Laboratory, Chemistry Division Bioassay Program, prepares samples to be electroplated for alpha spectroscopy analysis. The hair net and special lab coat are required for a clean room environment. 

The analysis of tetramethylammonium hydroxide (TMAH) solutions manufactured by SACHEM Inc. of Cleburne, Texas, includes the determination of trace elements. These elements cause less-than-optimum performance of integrated circuit boards manufactured by SACHEM s customers that use these solutions in their processes. Alkali and alkaline earth metals (e.g., Li, Na, K, Mg, Ca, and Ba) can reduce the oxide breakdown voltage of the devices. In addition, transition and heavy metal elements (e.g., Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ag, Au, and Pb) can produce higher dark current. Doping elements (e.g., B, Al, Si, P, As, and Sn) can alter the operating characteristics of the devices. In SACHEM s quality control laboratory, ICP coupled to mass spectrometry is used to simultaneously analyze multiple trace elements in one sample in just 1 to 4 min. This ICP-MS instrument is a state-of-the-art instrument that can provide high throughput and low detection Emits at the parts per thousand level. Trace elemental determination at the parts per thousand level must be performed in a clean room so that trace elemental contamination from airborne particles can be minimized. 

SACHEM Inc., located in Cleburne, Texas, is a producer of high-purity bulk chemicals for companies that have high-purity requirements in their chemical processing. As stated in Workplace Scene 1.2, one of their products is tetramethylammonium hydroxide (TMAH), which is sold to semiconductor industries. The analysis of TMAH for trace anions such as chloride, nitrate, nitrite, and carbonate is critical for SACHEM s quality control laboratory. If these ions are present on the integrated circuit boards manufactured by one of their semiconductor customers, they may cause corrosion severe enough to affect the functionality and performance of the electronic devices in which the circuit boards are used. In SACHEM s quality control laboratory, ion chromatography procedures have been developed to measure the anion concentrations in TMAH. Because the concentration levels are trace levels, a clean room environment, like that described in Workplace Scene 1.2, is used. A special procedure for carbonate analysis is required so that the absorption of carbon dioxide from the atmosphere can be minimized. 

A study of mercury in Lake Michigan found levels near 1.6 pM (1.6 X 10 12 M), which is two orders of magnitude below concentrations observed in many earlier studies.5 Previous investigators apparently unknowingly contaminated their samples. A study of handling techniques for the analysis of lead in rivers investigated variations in sample collection, sample containers, protection during transportation from the field to the lab, filtration techniques, chemical preservatives, and preconcentration procedures.6 Each individual step that deviated from best practice doubled the apparent concentration of lead in stream water. Clean rooms with filtered air supplies are essential in trace analysis. Even with the best precautions, the precision of trace analysis becomes poorer as the concentration of analyte decreases (Box 5-2). 

Environmental microbial monitoring and analysis of data by qualified personnel will permit the status of control to be maintained in clean rooms and other controlled environments. The environment should be sampled during normal operations to allow for the collection of meaningful data. Microbial sampling should occur when materials are in the area, processing activities are ongoing, and a full complement of operating personnel is on site. 

To prevent trace level contamination, the EPA established special sampling techniques for trace elements in ambient water in Method 1669 (EPA, 1996c). The EPA also provided the guidance for clean room laboratory analysis and for documentation and evaluation of trace element data (EPA, 1996d EPA, 1996e). 

Other than isotopes separation for uranium enrichment described in Chapter 2, inorganic membranes are commercially used for particulate filtration of air or other gases in clean room applications, airborne contaminant analysis and high-purity hydrogen production. In addition, some inorganic membranes are us in pH and ion selective electrodes. 

The well-established photon correlation spectroscopy (PCS) uses highly diluted suspensions to avoid multiple scattering. The low concentration of particles makes this method sensitive to impurities in the liquid. So usually very pure liquids and a clean-room environment have to be used for the preparation and operation (ISO 13321 1996, Particle Size Analysis—Photon Correlation Spectroscopy). 

Off-Gas Analysis. Gas samples are initially cleaned of particulates and dried to 2% moisture before analysis. Carbon monoxide and carbon dioxide are measured continuously using a Horiba Mexa-300 CO analyzer and a Horiba Mexa-200 CO2 analyzer. Syringe samples are taken downstream of the CO2 analyzer for gas chromatographic analysis, A room temperature molecular sieve 13X column is used to analyze for carbon monoxide, oxygen, and nitrogen, A Poropak Q column at 130°C is used to analyze for carbon dioxide, methane, ethane, ethylene, sulfur dioxide, and hydrogen sulfide. 

A sample should be prepared properly and then placed in a container before it is irradiated. The person who prepares the sample should be extremely careful not to contaminate it. Activation analysis is so sensitive that it can determine traces of elements undetectable by chemical methods. If the sample is left on a table for a certain period of time, it collects dust that acts as a contaminant. Touch by hand may transfer enough salt to cause the irradiated sample to show the presence of sodium and chlorine. To avoid contamination, samples should be handled in dry boxes or in clean rooms. The person who prepares the sample should use clean instruments (knife, file, tweezers, etc.) and also wear clean plastic gloves. 

Contamination. Contamination of samples by external sources can be a serious source of error and may be extremely variable. An excellent example of how serious this can be has been documented in the analysis of samples for polychlorinated biphenyls (PCBs). PCBs are synthetic mixtures of organochlorine compounds that were first manufactured in 1929 and have become of concern as significant environmental pollutants. It has been demonstrated that samples archived since 1914, before PCBs were manufactured, picked up measurable amounts of PCBs in a few hours just sitting in a modem laboratory (Erickson). Aluminum levels in the dust in a normal laboratory are so high that dust prohibits the determination of low ppb levels of aluminum in samples. A special dust-free clean lab or clean bench with a filter to remove small dust particles may be required, similar to the clean rooms needed in the semiconductor industry, for determination of traces of aluminum, silicon, and other common elements such as iron. When trace (inorganic analysis is required, the laboratory environment can be a significant source of contamination. 

A main requirement for a polymeric candidate is its biocompatibility with biological tissues and fluids. Biocompatibility will depend on the polymer intrinsic chemical nature and the additives present. It is a complex issue not dealt with here. It is not always possible to distinguish the medical-grade polymers from the conventional polymers. They may come from a batch intended for general purposes, but are selected on the basis of clean condition or trace element analysis or mechanical properties. Subsequent processing requires clean room conditions and care to avoid any contamination. There is still some inherent uncertainty about constituents unless there has been complete disclosure and/or only a pure polymer is used. With new developments in polymeric biomaterials, the situation should improve. 

Particle analysis of environmental samples by secondary ion mass spectrometry (SIMS, see Sect. 63.5.6.3) or scanning electron microscopy in combination with X-ray spectrometry (SEM-XRS, see Sect. 63.5.6.4). The SEM-XRS instrument and its sample-preparation area are located in the clean laboratory, but the SIMS instrument is not. Sample preparation for SIMS can be carried out in the CL, but a small dedicated clean-room at US Class-lOO/ISO-Class 5 cleanliness level is colocated with the instrument to avoid potential cross contamination when transporting the prepared sample planchets to the instrument. The SEM-XRS method is also supported in the CL by an array of optical microscopes equipped with micromanipulation systems for picking up particles of interest prior to further treatment such as chemical analysis and isotopic measurement by TIMS or ICP-MS. 

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