 |
 |
 |
 |
|
Comments? Suggestions? Send us your feedback.
MicroMagazine.com |
GREEN AND CLEANExamining purification and certification strategies for high-purity C2F6 process gasCharles C. Allgood and Jeremy D. Blanks, DuPont Fluoroproducts As the semiconductor industry shifts to using more-complex devices and finer geometries, the need grows for higher-purity process materials and gases. While manufacturing process improvements have provided the capability to consistently produce higher-purity material at higher rates, this improved purity has led to tighter specifications and the need for better analytical instrumentation and methods. Thus, developing new manufacturing and purification processes along with the associated packaging and analytical technologies is necessary to keep pace with increasingly demanding industry requirements. Hexafluoroethane (C2F6) is a high-purity product used in plasma-based semiconductor process applications as both a thin-film dry etching gas and a cleaning gas for chemical vapor deposition tools. In recent years, the use of hexafluoroethane as a process gas has grown significantly, and this high use level is expected to continue for some time. This article presents DuPont's approach to analytical methodology and instrumentation (both on-line and final product) required to support a state-of-the-art manufacturing facility for production of C2F6 to more than 99.9999% organic purity. The article outlines standard methodology and discusses supplemental testing methodology developed for benchmarking C2F6 quality beyond the current specifications. Ways that emerging methodologies may provide a standard on which to base future process improvements are addressed, and the recertification process is examined. Recovery and recycling are key issues in the semiconductor industry's effort to reduce or eliminate emissions of perfluorocompounds (PFCs) from process tools. A strategy and analytical methodology is provided for handling recovered C2F6 and its subsequent purification and recertification to virgin quality specifications. Certification Techniques During the years that Dupont Fluoroproducts (Deepwater, NJ) has been producing its Zyron 116.N5 high-purity C2F6 product, the company has evaluated the analytical technology in support of the production of hexafluoroethane for use in the semiconductor industry. Table I shows the current specifications for high-purity hexafluoroethane. To better determine product quality and to prepare for future product upgrades, analytical instrumentation was selected that would provide the lowest detection limits as well as the greatest operating efficiency. Based on this approach, the following analytical techniques were chosen:
These methods provide both accurate and precise determinations of the components of interest at concentrations well below the product specification levels.
Table I: Current specifications for the high-purity hexafluoroethane product.
Table II: Approximate lower limits of detection for C2F6 final product certification. Because of its superior detection limits, the HP 5973 GC-MS unit (Hewlett-Packard, Palo Alto, CA) was selected to perform the analyses for organic impurities. In the selected ion monitoring (SIM) mode, the tool can detect organic impurities in C2F6 down to the 1-ppbv level, and to pptv levels in most cases. This technique can be applied for the determination of a wide variety of species, including PFCs, chlorofluorocarbons, hydrochlorofluorocarbons, and hydrofluorocarbons. Figure 1 shows a total ion chromatogram of a calibration standard, which illustrates the capability of the GC-MS technique. Table II details the lower limits of detection for all of the final product certification methods.
Figure 1: A total ion chromatogram of a 1-ppmv standard using the GC-MS-SIM analysis technique. Potential organic impurities in hexafluoroethane are analyzed by injecting a sample through a six-port sampling valve (Valco, Houston). Components of the hexafluoroethane are separated via a 50-m PLOT column using a temperature-programmed run. The individual components are then analyzed by the mass selective detector (MSD) operating in the SIM mode. HP Chemstation software gathers data and generates a report. The software controls the GC-MS operation through a sequence, which allows the instrument to be used by laboratory personnel on a routine basis. The computer also controls the mass spectrometer tuning, which is carried out every 12 hours. Results from the analysis of C2F6 show that total organic impurities are typically <50 ppbv versus a specification of 500 ppbv. A GC-DID 590 System 3 (Gow-Mac, Bethlehem, PA) with a helium purifier was chosen to analyze for inert gases (N2, O2, CO, and CO2) primarily because of its excellent lower limits of detection. The DID produces a helium discharge that ionizes the gaseous species as they enter the detector chamber. The detector is universal, with additional advantages including a nonradioactive source, a stable baseline, extreme sensitivity, simplicity, and reliability. In contrast, previous experience with a GC-USD (ultrasonic detector) showed that tool to be more difficult to operate and to suffer from significant downtime. The GC-DID instrument can easily detect the desired gases (CF4, N2, O2, CO, and CO2) down to the low levels required by C2F6 specifications. Figures 2 and 3 contain chromatograms from the analyses of various inert gases and CF4 in hexafluoroethane.
The GC-DID is constructed of stainless steel with bellows-type valves. VCR-type fittings were used for connections in the carrier gas stream as well as in the sampling system to prevent leaks. Experience has shown that VCR-type fittings can be resealed (with new washers) many times without detectable leaks. Because of resealing problems, standard compression fittings were unacceptable for this application. To further minimize atmospheric leaks, the GC-DID has a helium purge in its oven. The inert gases and CF4 are analyzed by the GC-DID during an isothermal run in which the components are sent through a precolumn and then directed to one of two columns for their respective analyses. The precolumn is a 2-ft x 1/8-in. Haysep DB (made by Gow-Mac), which separates inert gases and CF4 from hexafluoroethane. The components are then guided either to an 8-ft x 1/8-in. molecular sieve column for N2, O2, and CO analyses, or to an 8-ft x 1/8-in. Haysep DB for CF4 and CO2 analyses. These columns were selected because they offer VCR-type fittings and orbital welding, which provides additional leak prevention. For ease of use, a valve was installed into the GC-DID to allow rapid change between columns. The GC-DID is controlled by a digital valve sequence controller and a lab automation system that generates the report. The Model 5900 UHP (Ametek, Feasterville, PA) was used for the oscillating crystal technology method because of its fast response time to changes in the moisture level and its low limits of detection.1 The 5900 UHP has been found to have a much faster response time (15 minutes to reach 95% of the change value) than older models, such as the 5700 (approximately 1 hour to adequately respond to a change). The tool also demonstrates a somewhat faster time than the Ametek 5800 (approximately 30 minutes to see a 90—95% change). The new instrument has cut the run time required from nearly an hour to less than 30 minutes in most instances. The 5900 does have a major drawback in that its upper limit of detection for water is 1 ppmv, and it is easily overloaded. If this point presents a problem in an application, the 5800 generally can perform the desired analyses. With any moisture measurement method, the sampling system must be constructed of electropolished tubing and heated, preferably to 60°C. In addition, the system must be maintained in a dry atmosphere to minimize the time required to adequately flush it. Electropolished tubing minimizes problems with water trapped in the sampling system. The polar characteristics of water cause it to cling to the rough surface of standard stainless-steel tubing, making such tubing unsuitable for sampling systems. A temperature of 60°C was chosen to minimize moisture holdup time and to match the temperature of the Ametek oven. Hexafluoroethane is analyzed for moisture by supplying a sample to the instrument at a flow rate of 200 ml/min for a preset time period, which was established through the analyses of standards and samples of known water content. Operation is controlled locally via the instrument's front panel. These analytical tools have self-calibrating capabilities through the use of permeation tubes, which greatly reduces problems associated with the use of external standards. The analytical technique for measuring acidity as HCl is a conductivity method. Although this procedure offers simplicity, the results can be misunderstood and, as with any conductivity method, there is a possibility that interfering species may be present. The proper steps must be followed and an adequate sample amount must be available to minimize outside contamination problems. This method can be used successfully as long as the specification stays well above 20-ppbw HCl. Analyses for acidity are carried out by bubbling at least 100 g (preferably 150 g) of sample through a known amount of deionized (DI) water (at least 16 M‡) in a polyethylene container. The solution's conductivity is measured via a probe, and the results are compared to the measured conductivity of the DI water alone. Then, using a previously determined calibration factor for HCl, the concentration of HCl is then calculated from this conductivity difference. For this method, the polyethylene containers must be kept clean and the quality of the DI water must be high. Finally, the possible presence of other ionizable species and their impact on the analyses must be considered. On-Line Process Monitoring The requirements for C2F6 (as shown in Table I) led to the installation of on-line monitoring systems to ensure that the manufacturing and purification processes were performing to the required levels. Based on this need, an HP gas chromatography detector (GCD) and ion mobility spectrometer (IMS) were installed on-line in the final product stream. These instruments provide rapid and accurate analyses for both organic purity and acidity on the final hexafluoroethane product before storage and packaging. Final product line samples are taken through 10-port sampling valves for the GCD and fed directly into the IMS after the appropriate flow control and pressure reduction. A distributed control system directs sampling of the final product. The GCD and IMS offer a level of automation that does not require an operator and needs only occasional maintenance. The on-line instruments for organic and HCl analyses provide real-time data for early warnings of potential process problems and also minimize the number of grab samples required. For the organic analyses, the GCD offered the best combination of detection limits and automation at the time of purchase. The GCD, operating in the SIM mode, is capable of detection limits in the 50-ppbv range for the potential organic impurities. The high signal-to-noise ratio and these low detection limits are illustrated by the total ion chromatogram of a 500-ppbv standard shown in Figure 4 where a variety of impurities have been added to a high-purity C2F6 background. In addition, the GCD offers automated tuning and sequencing for maximum automation.
Samples from the hexafluoroethane final product line are injected hourly into the GCD through gas sampling valves. The sample components are separated on a 40-m alumina column during a temperature-programmed run and then detected via the MSD operating in the SIM mode. The data are collected by Chemstation software, which identifies and quantitates the components and transmits the results to the distributed control system. The GCD is automatically tuned daily via the software. An IMS was chosen to perform the acidity analyses because of its automation capabilities, low limits of detection for hydrogen halides, and specificity for HCl. An IMS functions similarly to a time-of-flight mass spectrometer but has a lower limit of detection of 1 ppbw for HCl.2 The instrument is a flow-through device, which can respond to level changes in <5 minutes. It does have an upper limit of detection of 50 ppbw for HCl. Above the 50-ppbw level, the response of the IMS is generally nonlinear for the hydrogen halides. The IMS analyses are conducted hourly for about 15 minutes while a sample stream from the final product line is diverted to the IMS flow-through cell. The results are continuously transmitted to the distributed control system on a real-time basis. Supplemental Testing In addition to the standard analytical techniques discussed earlier, supplementary analyses were developed to examine impurities that are not specified in the final product specifications but may be of interest in the future. The purpose of these additional analyses is twofold: to "fingerprint" the current product quality and to provide a benchmark to gauge the effect of future process upgrades. To accomplish these tasks, a combination of methods was chosen to provide a wide-ranging analytical examination of the hexafluoroethane product: GC-MS (scan and SIM modes); GC—flame ionization detection (GC-FID); inductively coupled plasma—mass spectrometry (ICP-MS); and ICP—atomic emission spectrometry (ICP-AES). GC-MS was used to search for additional organic species because of its ability to rapidly and accurately provide qualitative and quantitative information. The combination of both scan and SIM mode operation further enhanced the system's ability to detect low-level impurities that might otherwise be overlooked. The mass spectrometer, operating in the scan mode (m/z 10—250 and m/z 45—250 in this case), is a useful tool for the identification and confirmation of organic impurities based on different compounds' unique mass-spectral fragmentation patterns and the use of computer-based library searches for unknown peaks. Figure 5 shows a typical GC-MS total ion chromatogram (scan mode) of the C2F6 product. To date, no additional organic impurities (that have not specifically been analyzed by the previously described specification methods) have been identified using these GC-MS techniques.
Figure 5: A GC-MS total ion chromatogram of C2F6 product. The MS is off during the elution of the C2F6 peak. The GC-MS analyses are performed with an HP 5971 equipped with a six-port sampling valve and a jet separator to allow the use of packed columns. Samples are injected through the six-port valve and separated by either a 12-ft x 1/8-in. SP-1000 or a Krytox column (made by DuPont) during a temperature programmed run. Chemstation software collects data and reviews them for the presence of impurities.
In addition to the GC-MS methods, a GC equipped with a flame ionization detector is used. The FID detects a wide range of volatile compounds and is especially sensitive to hydrocarbons, providing additional information on overall hexafluoroethane purity. Figure 6 shows the GC-FID analysis of a sample of C2F6. Figure 7 contains a chromatogram of a C1-C6 hydrocarbon standard for comparative purposes where a variety of hydrocarbons have been added to a high-purity C2F6 background. As with the GC-MS methods, no impurities other than those specifically analyzed by the specification methods have been identified by the GC-FID method to date. The GC-FID analyses are performed with an HP 6890 GC equipped with a six-port sampling valve. Samples are injected through that valve and separated on a 105-m Rtx-1 column during a temperature-programmed run. The Chemstation software collects data. The presence of inorganic materials, particularly metals, is an important purity measurement for semiconductor process gases. Methods of choice for the analysis of metal contamination at low parts-per-billion levels are ICP-MS and ICP-AES. Prior to ICP analysis, hexafluoroethane gas is purged through a dilute acid solution which dissolves and concentrates the metals. For these analyses, 1000 g of hexafluoroethane are slowly bubbled through 100 ml of a 5% ultrapure nitric acid solution. The dilute acid solution is then introduced directly into the ICP instrument, which can detect a number of elements with parts-per-billion level detection limits. A list of elements analyzed with the ICP-based techniques is shown in Table III. The average detection limits for the elements listed is 1 ppbw.
Table III: Elements selected for ICP-MS and ICP-AES analysis of C2F6 material. Recertifying Recycled C2F6 During recent years, there has been an industrywide effort to reduce emissions of PFCs from semiconductor manufacturing processes because of the long atmospheric lifetimes and high global warming potentials of PFCs. As part of this effort, which includes process optimization, alternative chemical development, and point-of-use abatement technologies, there has been significant focus on developing effective means to capture and recover PFCs from fab tool exhaust streams, with the ultimate goal of recycle and reuse.3 Several capture and recovery systems that are being developed and tested are able to recover the majority of PFCs from the tool exhaust and produce a C2F6-rich gas stream. In addition to the unreacted process gas (C2F6), this stream contains CF4 and other major by-products, additional process gases (N2), and trace contaminants that find their way downstream and into the recovery system. To close the product life-cycle loop (by purifying the recovered PFC mixture back to a C2F6 product indistinguishable from virgin product and recertifying it for use), careful analytical testing must be performed before and after the purification process. As shown in Table IV, initial predictions (based on current semiconductor manufacturing chemistries) of impurity types and amounts indicate that many organic species expected in the reclaim stream are also present as coproducts in the crude C2F6 stream being fed to the existing manufacturing process from which an extremely high-purity C2F6 product is produced.4 Thus, purification steps for the removal of these species have already been developed and are operational during purification of the virgin product. In this case, a straightforward approach to handling reclaimed product would be to treat it as crude C2F6 feedstock, for purification along with virgin crude produced under normal operating conditions.
Table IV: Predicted composition of a recovered PFC stream. There is a caveat to this approach to handling recovered C2F6 . Any new (i.e., not previously present in the manufacturing process) impurities introduced solely from the reclaimed material (e.g., SF6, NF3) need to be identified. Furthermore, any new species' impact on the purification process, as well as the process's adequacy for effectively removing these impurities, must be established. There may also be certain impurities that it is desirable to keep out of the repurification process; hence segregation of certain recovered material lots for alternative disposition may be appropriate. Based on this strategy, developing analytical methodologies and protocols for screening and quantitation of all impurities in hexafluoroethane-rich streams returned to the manufacturer, along with the analytical package already in place for virgin product certification, is a key to the successful implementation of a total C2F6 recycling program. Determination of Bulk C2F6 Content. After a visual inspection of a container (cylinder, ton tank, tube trailer) of recovered C2F6 received for processing, the net weight, temperature, and pressure of the contents should be documented. A quick semiquantitative determination of the bulk C2F6 content is also desirable, as well as a determination of CF4 and N2 levels, since these components are expected to be the highest concentration species typically encountered. An assay method that measures C2F6 is especially important if the incoming materials will be segregated and processed differently depending on the bulk C2F6 content. For example, it is expected that mixtures containing <90—95 vol.% C2F6 will require some type of preprocessing prior to introduction into the standard purification unit. A GC method with a thermal conductivity detector capable of resolving the C2F6, CF4, and N2 components and measuring them to within ±0.5 vol.% accuracy has been developed. This GC method is also easily adaptable to portable instrumentation for field use and for on-site testing at the recovery unit. Screening Organic Compounds. To exhaustively screen for organic compounds and other impurities in recovered hexafluoroethane, a variety of separation and detection techniques are needed. The combination of gas chromatography with mass spectrometry is a powerful analytical technique for analyzing complex mixtures and identifying unknown organic compounds. The separating power of gas chromatography (preferably by packed, capillary, PLOT, and a variety of other column types with stationary phases of different polarities and retention properties) is useful in ensuring that very small impurities are not masked by coeluting peaks of larger impurities or the bulk gas itself. The methods described earlier in this article provide good examples of how this technology can be used to screen reclaimed C2F6 material. In addition to scan mode operation, mass spectrometers can be operated in the SIM mode to detect specific compounds by monitoring selected fragment ions. For example, SF6 coelutes from the GC with C2F6 for many GC columns and conditions, complicating detection of low levels of SF6 in C2F6. By operating the mass spectrometer in the SIM mode and monitoring the SF5+ ion at m/z 127 (unique to SF6), the MSD can selectively monitor for SF6 and ignore the bulk C2F6 that would otherwise overwhelm a normal scan mode. Figure 8 illustrates the analysis results of a standard containing SF6 in hexafluoroethane by the GC-MS-SIM method.
The SIM mode offers increased sensitivity and lower detection limits but does not provide the total mass spectrum, or fingerprint, for identification. In practice, a combination of scan and SIM operation along with GC-FID analysis is valuable for assessing the impurity profile of recovered hexafluoroethane. Infrared analysis is useful for identifying impurities in fluorocarbon gases. The main advantage of this method is its ability to detect compounds that are more reactive than (not as stable as) perfluorocompounds such as SiF4, COF2, or HF since the sample can be introduced directly into an infrared cell for analysis. Interpretation is complicated because all components are detected simultaneously, and therefore their infrared spectra are superimposed. By their nature, homonuclear molecules (helium, argon) as well as symmetrical diatomic molecules (H2, N2) are infrared inactive and therefore not detectable by this technique. Nonetheless, infrared analysis is an important complement to the chromatography-based techniques discussed earlier. Inorganic Impurities. As mentioned previously, inorganic materials, particularly metals, are an important purity measure for semiconductor process gases. Since semiconductor processes use tungsten, aluminum, copper, and similar metals, trace levels of them may show up in a reclaimed gas stream. Furthermore, as semiconductor performance demands increase, lower levels of all metals, particularly those affecting device reliability, will be required. The previously discussed ICP-MS and ICP-AES methods for analyzing low-level metal contamination can be applied as effectively to reclaimed material as they can to virgin product. Nonvolatile Residue. Nonvolatile residue analysis of reclaimed C2F6 is a difficult task because the contamination is not a unique chemical species but rather mixtures of rust, oil, dirt, and the like. Although the fluorocarbons are not good solvents, other residue sources may include cutting and machine oils, lubricants, additives, and other substances that can be extracted from seals, O-rings and other internal parts of the process tools, recovery equipment, piping, or storage containers. A standard technique employing a Goetz bulb can indicate whether large amounts of residue are present, providing a gross assessment of contamination that may occur, for example, by loading recovered material into a dirty cylinder. During this technique, a large amount of gas is allowed to evaporate from a glass bulb, leaving behind any nonvolatile species that are then detected visually. The drawbacks of this method are poor detection limits and sampling difficulties with high-pressure gases. The demanding purity requirements of the semiconductor industry require techniques capable of parts-per-billion-level detection limits and the speciation of various residues to determine, and eliminate, any contamination source. To avoid transfer of contamination brought back in containers along with the recovered gases, it is important to screen reclaimed material for nonvolatile residue prior to unloading. A method using low-temperature trapping of residues, followed by GC-MS analysis, has been developed to detect common residue types including hydrocarbon-type, chlorotrifluoroethylene-type (CTFE), and fluorinated-type oils at low levels. The first part of the analysis involves sampling and trapping the residue contamination using a 0.005-in. pressure-reduction orifice tube and cold trap coil apparatus shown in Figure 9. The pressure reducer/trap is connected directly to the high-pressure gas source to be analyzed. The chances of external contamination must be minimized with this very sensitive analysis by keeping the equipment extremely clean and using the minimum number of fittings between the gas container and cold trap. Between analyses, all parts should be cleaned with a solvent and baked in a 300°C oven while being purged with inert gas.
A sufficiently large sample of gas (>30 L) is allowed to pass through the trap (which is placed in a container of dry ice) where any residues will accumulate (see Figure 9a). A flow rate of approximately 0.5 L/min is sufficient for adequate trapping and reasonable sample times. After the sampling has been completed, the trap is disconnected from the gas supply and the oils are back-flushed from the trap by filling the rinse reservoir with solvent and connecting the outlet to a source of high-purity, high-pressure gas, such as helium, nitrogen, or C2F6 . This step forces the solvent and dissolved residues into the sample collection vial (see Figure 9b), and it is repeated three times to ensure that all residue collected in the trap has been transferred to the vial. The solvent flushes are then evaporated by passing a gentle stream of clean helium over the vial. Prior to GC-MS analysis, the residue in the vial is redissolved by adding a measured amount of fresh solvent containing an internal standard (such as dodecane). The GC-MS is operated in the SIM mode for this analysis (m/z 57 for hydrocarbons, m/z 101 for the CTFE-type oils, and m/z 169 for the fluorinated oils). The chromatograph uses a splitless injection, and the chromatography is carried out on a standard 12-m methyl silicone—type column (Figure 10). Because of the detection method's selectivity, it is not necessary to get a complete chromatographic resolution of the oils. The individual oils are quantitated by integrating the entire peak area for the individual ion traces and calculating the concentration based on response factors generated from analyses of standard mixtures.
Inert Gases and Moisture. It is also desirable to understand the moisture and inert gas content of recovered material. High levels of contamination by inert gases in reclaimed C2F6 will be detected by the C2F6 assay method described earlier. The methods used to analyze low-level inert gases and moisture analyses are also applicable to the recovered material. Reactive Species. While current-generation recovery systems are expected to remove reactive species by combinations of wet and dry scrubbing, one must still screen for their presence in recovered C2F6 prior to purification. Many fluorine-containing species (SiF4, COF2, HF) can be detected indirectly by measuring the fluoride ion concentration [F-] of an aqueous solution that has had the sample gas bubbled through it. A variety of wet chemical techniques as well as ion chromatography have been developed for measuring [F-] as well as [Cl-] but will not be discussed here.5 Aqueous conductivity is the standard measure for detecting HCl in gas samples prepared similarly to the aforementioned fluoride ion analysis. This method will be useful for screening reclaimed C2F6 material for the presence of HCl as well as any other easily ionized species. As mentioned in the section on organic analysis, infrared analysis can also be useful for detecting reactive species, provided they do not react with the infrared-cell materials. Since the sample is introduced directly into the cell and analyzed at room temperature, there is less chance for reactive species to decompose. Conclusion A series of sensitive analytical methods have been developed to support the production of high-purity hexafluoroethane for use by the semiconductor industry. In addition, supplemental techniques have been developed for analysis of a wide range of species not covered under current product specifications. Furthermore, an analytical protocol and associated methodology have been established to support a C2F6-recycling program. By examining recycling and recovery concerns as well as refining purification and certification processes, production of high-purity hexafluorethane will continue to meet even the tightest industry requirements. The combination of analytical technologies evaluated here provides detailed and comprehensive quality assurance for the continued supply of high-purity C2F6 to meet the semiconductor industry's current and future needs. Acknowledgments The authors gratefully acknowledge the assistance provided by Joseph Shekiro and Dominic Barsotti of DuPont's Chambers Works in the development of the metals and residue analyses. References 1. Wei J, Pillion J, King S, et al., "Using an In-Line Monitor to Obtain Real-Time Moisture Measurements," MICRO, 15(2): 31—36, 1997. 2. Bacon T, Reategui J, and Getz R, Acid Gas Monitor Based on Ion Mobility Spectrometry, U.S. Patent 5,032,721, 1991. 3. Cummins W, Dupuis G, Keasari S, et al., "The Future of Perfluorocarbon Capture and Recycling: Membrane Technology," Semiconductor International, 20(8):265, 1997. 4. Mocella M, "DuPont Studies of Higher Order Solutions for PFC Emission Reductions," in Proceedings of a Partnership for PFC Reductions, Semicon West, San Francisco, 1997. 5. Blanks J, "Part I: Studies of Alkali Metal Fluorides through the Use of a Fluidized Bed Reactor. Part II: The Analysis of Fluorophosphate Anions by Ion Chromatography," dissertation, University of Alabama, 1995. Charles C. Allgood, PhD, is a technical services chemist for the Zyron Electronic Gases unit of DuPont Fluoroproducts in Deepwater, NJ. His primary area of responsibility is providing technical support to the semiconductor industry regarding the analysis, properties, uses, safety, and handling of fluorinated gases as well as in the development of new gases for emerging applications and PFC emission reduction efforts including recycling. Before joining DuPont in 1991, Allgood was a research chemist with the National Institute of Standards and Technology (Gaithersburg, MD). He received a BS in chemistry from Albright College and a PhD in analytical chemistry from the University of Delaware. He has published more than a dozen papers dealing with analytical chemistry and the applications and properties of fluorochemicals. (Allgood can be reached at 609/540-3170 or at Charles.C.Allgood@ USA.dupont.com) Jeremy D. Blanks, PhD, is an R&D chemist at DuPont Fluoroproducts. His recent work has focused on the analyses of trace-level impurities, improvements in quality control, and on-line applications of techniques such as GC-MS, IMS, and GC-DID. Blanks received a BS in chemistry from the University of Alabama, where he also obtained a PhD, specializing in the areas of analytical and inorganic fluorine chemistry. He is a member of the American Chemical Society as well as the fluorine chemistry division of ACS, and he has written or coauthored 10 technical publications. (Blanks can be reached at 609/540-4423 or Jeremy.D.Blanks@usa.dupont. com)
MicroHome |
Search | Current Issue | MicroArchives Questions/comments about MICRO Magazine? E-mail us at cheynman@gmail.com. © 2007 Tom Cheyney |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Figure 2: A chromatogram from the analyses of oxygen, nitrogen, and carbon monoxide (CO) in C2F6 using GC-DID.
Figure 3: A chromatogram from the analyses for carbon tetrafluoride (CF4) and carbon dioxide (CO2) in C2F6 using GC-DID.
Figure 4: Total ion chromatogram from the GCD-SIM analyses of a high-purity C2F6 sample spiked with 500 ppbv of various organic species.
Figure 6: A GC-FID chromatogram of C2F6.
Figure 7: A GC-FID chromatogram of a high-purity C2F6 sample spiked with C1-C6 hydrocarbons.
Figure 8: A selected ion chromatogram of the SF5+ fragment ion (m/z 127) from the GC-MS-SIM analysis of a C2F6 standard spiked with SF6. 
Figure 9: A schematic diagram of nonvolatile residue cold trap apparatus configured for (a) gas sampling/residue trapping and (b) residue flushing and collection.
Figure 10: Selected GC-MS ion chromatograms from the nonvolatile residue analysis of an oil standard.