IEST revises RP on outgassed organic compounds
IEST-RP-CC031.1, Method for Characterizing Outgassed Organic Compounds from Cleanroom Materials and Components, will include revisions for new RP in 2008
By Jim Ohlsen, PhD, Entegris, Inc., and Chair of IEST Working Group CC031
The Institute of Environmental Sciences and Technology (IEST) is responsible for the origination, publishing, and revision of 36 recommended practices (RPs) on topics of interest and of value to the contamination control industry. Currently, IEST has 59 working groups (WGs) engaged in RP production. The contamination control (CC) division of IEST is involved with the detection, measurement, and control of all forms of contamination in cleanrooms and other controlled environments. The CC division is divided into seven related Standards and Practices Committees (SPCs) covering the general categories of filtration, operational products, procedural issues, facilities, environmental control, reference documents, and nanotechnologies. Each SPC is further organized into WGs that are responsible for publishing RPs-a vital tool when establishing a comprehensive contamination control program. WG-CC031 is a working group within the environmental control SPC. This article will focus on IEST-RP-CC031.1 and recent revisions that, when published in early 2008, will become IEST-RP-CC031.2.
Background of WG-CC031
Working Group CC031 was first organized in the late 1990s to establish outgassing performance criteria for cleanroom materials. Members of the WG then and now include scores of engineers, scientists, and educators expert in contamination control for contamination-sensitive industries such as aerospace, data storage, and microelectronics. In April 2003, IEST-RP-CC031.1 was published, and that May, the first four-hour tutorial on this RP was presented at ESTECH 2003 to more than 25 people. Since then, two additional tutorials have been presented at ESTECH annual meetings of the IEST. The RP-CC031.1 tutorial provides in-depth analysis of each section of the RP, including numerous examples and plenty of time for questions. Attendees representing industries such as aerospace; cleanroom construction, supplies, and equipment; data storage; and microelectronics have shown great interest in this RP and its tutorials because it offers an approach to characterizing cleanroom materials and components using a test method that permits direct comparison of test data to evaluate the same product manufactured by different vendors. Furthermore, the test method described in this RP instructs manufacturers and suppliers to select materials, finishes, and assembly techniques that result in a final product that outgasses low levels of airborne molecular contamination (AMC).
Organization and section revisions
Section 1 covers the scope and limitations. The RP describes a test method appropriate for semiquantitative determination and semiqualitative characterization of organic compounds outgassed from materials or components exposed to air in cleanrooms or other controlled environments. This RP specifies four outgassing temperatures-50°C (122°F), 75°C (167°F), 100°C (212°F), and 150°C (302°F)-to baseline cleanroom materials and components. This recognition that different temperatures can be used to characterize different outgassing conditions that cleanroom materials and components may be subjected to, and thus introduce different levels of outgassing AMCs, is as significant today as in 2003 when the RP was first published.
Section 1 goes on to state that the test method described “...is designed to screen primarily cleanroom materials but can also be applied to materials used in other controlled environments for identification of outgassed compounds detectable by dynamic headspace gas chromatography-mass spectrometry (GC-MS). The method described is not designed to provide absolute quantitative results. Information on the composition of the materials under test may be useful in selecting the appropriate outgassing temperature to use.” Thus the test method described is centered on thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS). This analytical technique utilizes state-of-the-art instrumentation that is sensitive to detecting outgassing species down to parts per billion levels. Companies that do not have in-house laboratories equipped with a TD-GC-MS can utilize contract laboratories. Thus, the test method of this RP can be used by anyone.
Sections 2 and 3 cover references and terms and definitions, respectively. Only minor additions and/or changes have been made to the terms gate oxide integrity, n-dope, outgassing, and volatile organic compound.
Section 4 addresses the background and purpose of the RP. Several excerpts are noteworthy: “This document is relevant to industries that may experience adverse production yields as a result of gaseous organic contamination, also known as volatile organic compounds (VOCs) and semi-volatile organic compounds (SVOCs). The deposition of outgassed compounds on hardware, products, and wafer surfaces is recognized as a source of processing problems and hardware failures.” “The method described in this RP is designed to focus on medium- and low-vapor-pressure organic compounds. These compounds tend to adsorb on critical surfaces, including hardware, wafers, and optics and may potentially lead to processing problems.” The RP “...recommends several key test method conditions, such as outgassing time and temperature of analysis and reporting parameters, in order to obtain similar results from different laboratories.” Finally, “...the method in this RP is believed to be the most appropriate analysis to provide chemical information for a large range of organic compounds that may outgas under ambient or higher temperature conditions.”
In addition, Section 4 is composed of three sub-sections, namely, “Materials of Interest,” “Organic Compounds of Concern,” and “Using the Test Results.” The first sub-section has been updated to include more than 50 materials, components of construction, and polymers that may outgas organic compounds in cleanrooms or other controlled environments under certain conditions. In addition to the original list of compounds of concern, this sub-section now references ISO 14644-8:2006(E), Annex B for an extensive list of contaminating chemicals that can be of concern to a microelectronics product or process. The “Using the Test Results” sub-section remains unchanged.
Section 5 discusses the test method and consists of five sub-sections. In the introduction, the dynamic headspace GC-MS method is described, why it is preferred over a static headspace procedure is noted, and it concludes with a list of parameters that affect the concentration level and types of compounds outgassed from a material: “Material variables include material history and cure conditions. Sample variables include sample size, thickness, and exposed surface area. Analytical method variables include outgassing time and temperature, gas flow rate, and linear velocity over the sample, which is affected by the geometry and orientation of both the sample and the sample chamber. These factors should be considered in the analysis of materials under this RP.”
Sub-section 5.1, “Test Material and Sample Preparation,” has been expanded to include more examples of sample preparation. Sub-section 5.2, “Apparatus,” is unchanged and lists the equipment required to carry out the method, namely, thermal desorption (TD) unit, GC-MS system, GC column, inert gas for purging the sample and the GC, sample holders, and external standard. Sub-section 5.3 describes the thermal desorption conditions in detail and emphasizes that the outgassing temperature be based on the operating temperature of the cleanroom components. Sub-sections 5.4 and 5.5, “System Cleanliness and Validation” and “Data Processing and Calculation,” respectively, are unchanged. Finally, sub-section 5.6, “Extensions of Outgas Testing Beyond this RP,” has been added to address testing the outgassing of a large part, assembly, or complete system that may be in operation.
Section 6 discusses reporting, which lists the elements necessary to provide information about material identification, sample description, instrument/system information, compounds detected, and GC-MS chromatograms. Section 7, “Bibliography,” has been updated and contains three new references.
In conclusion, the revised RP-CC031.2 has been approved by the voting members of WG-CC031, and its publication is anticipated in early 2008.
The author wishes to thank CC-WG031 officers Kevin Seguin (vice chair), Ellen Westenburg (secretary), and their fellow voting members for their expert help in updating and revising this RP.
Jim Ohlsen is director of the Materials Characterization Group at Entegris, Inc., where he is responsible for three global materials technology laboratories and one technology characterization laboratory. He has a PhD in chemistry from Texas A&M University. As an active member of IEST, Ohlsen represents Entegris, Inc. as a corporate sponsor, and serves as director of Standards and Practices Committee 3: Procedural and as a reviewer for the editorial board of the Journal of the IEST. He is the 2007 recipient of the IEST Monroe Seligman Award, has presented three tutorials on IEST-RP-CC031.1, and serves as chair of WG-CC031.