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High-Pressure Gas Analysis System Disclosure Number: IPCOM000131216D
Publication Date: 2005-Nov-10
Document File: 12 page(s) / 78K

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The Prior Art Database

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Many applications of high-pressure CO2 (supercritical CO2) are emerging which require ultra-high purity (UHP) CO2. For example, new applications of supercritical CO2 are under development for the semiconductor industry for applications such as stripping of photoresist, synthesis of low-k materials, and deposition, among others. Other applications requiring very high-purity CO2 at high pressures are in the pharmaceutical industry, to make micro and nano particles, for example.

A major requirement for these applications is very high purity of CO2. Conventional CO2 analysis is performed at low pressures, typically close to the manufacturing site. Because of the possibility of CO2 contamination during transportation and conditioning (process of changing low pressure CO2 to supercritical CO2 by increasing pressure and temperature), it will be required to perform CO2 analysis at point-of-use, i.e., just before the conditioned CO2 is injected in a process chamber.

For large scale systems requiring substantial quantities of CO2, recycling of CO2 will be necessary. During the processing in the semiconductor applications, additives and co-solvents are added which need to be separated before the CO2 can be recycled. One of the approaches is to purify CO2 in supercritical or liquid phase to reduce cost of recompression. For such as approach, CO2 analysis under high-pressure can prove to be a useful tool to make sure that CO2 is purified sufficiently before it is recycled.

Supercritical chromatography is a well-known analysis technique which employs a supercritical fluid as a mobile phase. A supercritical fluid is defined as a fluid above its critical temperature and pressure. For example, CO2 has a critical temperature and pressure of 31.1 0C and 73 bar, respectively. CO2 above its critical temperature cannot be liquefied, irrespective of the pressure. A supercritical fluid exhibits viscosities and densities between those of gases and liquids, and solvating powers similar to liquids. The advantages of supercritical chromatography include greater speed in separations, greater resolution in complex mixtures and low temperature operation. So far, the application of this technique has been limited to compounds which are liquid at ambient conditions (solid compounds can also be dissolved in a liquid solvent and analyzed using this method).

Bürck et al describe a method to analyze supercritical CO2 using near-infrared spectroscopy (J. Bürck, G. Wiegand, S. Roth, H. Mathieu, K. Krämer, “Quantitative in-line analysis in supercritical CO2 using fiber-optic NIR spectroscopy and multivariate calibration: a potential method for monitoring continuous flow processes”, Journal of Near Infrared Spectroscopy, 12, 29-36 (2004)). Brantley et al describe the use of near-IR spectroscopy as a method to measure CO2 sorption kinetics and solubility at elevated pressures (N. Brantley, S. Kazarian, c. Eckert, “In situ FTIR mea...