Semiconductor Equipment and Materials International
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Background Statement for SEMI Draft Document 5080B
REVISION OFSEMI F51-0200, GUIDEFOR ELASTOMETRICSEALINGTECHNOLOGY
Notice: This background statement is not part of the balloted item. It is provided solely to assist the recipient in reaching an informed decision based on the rationale of the activity that preceded the creation of this Document.
Notice: Recipients of this Document are invited to submit, with their comments, notification of any relevant patented technology or copyrighted items of which they are aware and to provide supporting documentation. In this context, “patented technology” is defined as technology for which a patent has issued or has been applied for. In the latter case, only publicly available information on the contents of the patent application is to be provided.
NOTICE:ThisDocumentwascompletelyrewritten.PertheProcedureManual(March2015)¶3.5.1.1acompleterewriteisappropriate whentheuseofunderlineandstrikethroughwouldbeexcessive.
Background
SEMIF51,GuideforElastomericSealingTechnology,islongoverdueforitsfiveyearreview.Toprovidestandardsforo-ringsandsealsusedinSemiconductorProcessEquipmentthismethodshouldbereviewedandupdatedasnecessarysothatitcancontinuetobeused forspecifyingsealingcompoundsandtheirapplications.Duetothemyriadofdifferentchemicalandphysicalpropertiesofbothsealsandprocessesupdatingthe standardizedapproachforspecifyingsealingcompoundsandsealconfigurationsisneeded.Themis-applicationofo-ringsandsealscreatessignificantcostsanddowntime.
Sealingtechnologyisanareacontinuingtoplayandeverincreasingroleinhighyieldingmanufacturingprocesses,yettheMicroelectronicIndustry’ssealingrequirementsarepoorlydefined.Complicatingtheissueisthatsomesealsused weredevelopedforunrelatedindustries.Thus,theexistingparametersthatdefinegoodsealingcharacteristicsareverydifferentthanthoserequiredbymicroelectronicsmanufacturing;i.e.:cleanliness,particulationseallife.
The ballot results will be reviewed and adjudicated at the meetings indicated in the table below. Check under Calendar of Events for the latest update.
Ballot Adjudication Information
TaskForceReview / CommitteeAdjudicationGroup: / SEMIF51(Perfluoroelastomer)RevisionTF / NAFacilities TC Chapter
Date: / Monday, July 13, 2015 / Tuesday, July 14, 2015
TimeTimezone: / 12:30 – 14:00 Pacific Time (Tentative) / 9:00 – 12:00 Pacific Time
Location: / San Francisco Marriott Marquis Hotel in conjunction with the NA Standards Meetings at SEMICON West 2015 / San Francisco Marriott Marquis Hotel in conjunction with the NA Standards Meetings at SEMICON West 2015
City,State/Country: / San Francisco, California/USA / San Francisco, California/USA
Leader(s): / DaliaVernikovsky(AppliedGlobalSeal) / SteveLewis(DPSEngineering)
StandardsStaff: / MichaelTran408.943.7019
/ MichaelTran408.943.7019
SEMI Draft Document 5080B
REVISION OFSEMI F51-0200, GUIDEFOR ELASTOMETRICSEALINGTECHNOLOGY
NOTICE: This Document was completely rewritten. Per the Procedure Manual (March 2015) ¶3.5.1.1 a complete rewrite is appropriate when the use of underline and strikethrough would be excessive.
1 Purpose
1.1 This Document is a basic guide for the use of seals in semiconductor fabrication equipment. The document is also an introduction of the diverse chemical and physical requirements for the many process applications and how choosing appropriate sealing materials is helpful to reduce cost of ownership and to improve up-time. It is important that equipment users, suppliers, OEMs, and seal manufacturers follow the same terminology so that communication can take place with alignment when the actual performance of the equipment is being discussed.
2 Scope
2.1 This Guide is applicable to the use of seals in operating environments used in the fabrication of semiconductor devices. O-rings were originally developed in 1896, for industrial markets and much later for aerospace, but were never developed to meet semiconductor needs. Current ASTM standards do not specifically relate to semiconductor seal performance. This guide will aid in defining the criteria by which sealing performance can be judged in comparable measurements and seal materials can be chosen.
2.2 Seal performance in semiconductor equipment and components consists of but not limited to the specifications shown in Table 1.
NOTICE:SEMI Standards and Safety Guidelines do not purport to address all safety issues associated with their use. It is the responsibility of the users of the documents to establish appropriate safety and health practices, and determine the applicability of regulatory or other limitations prior to use.
Table 1 Relative importance of seal performance criteria in several applications/process areas.
(Rate 1-5, 1: most important; 5: least important)
/ Process areas Properties
Specifications / Wet Etch / Dry Etch / CVD / PVD / Diffusion / Sub-Fab
Sealing Requirements
Seal Etch Rate / 5 / 1 / 3 / 5 / 2
Sealing Force Retention / 1 / 1 / 1 / 1 / 1
Impurities
Leachable / 1 / 5 / 5 / 5 / 3
Ash / 5 / 1 / 1 / 1 / 2
Outgassing / 5 / 2 / 1 / 3 / 5
Permeation / 5 / 1 / 1 / 3 / 3
TOC / 1 / 5 / 5 / 2 / 5
3 Limitations
3.1 The application of this Guide is limited to elastomeric seals that are used in semiconductor manufacturing and related process equipment.
4 Referenced Standards and Documents
4.1 SEMI Standards
SEMI C3 — Specifications for Gases
SEMI D9 — Definitions for Flat Panel Display Substrates
SEMI E45 — Test Method for the Determination of Inorganic Contamination from minienvironments
SEMI E49 — Guide for High Purity and Ultrahigh Purity Piping Performance, Subassemblies, and final Assemblies.
SEMI F21 — Classification of Airborne Molecular Contaminant Levels in Clean Environments
SEMI F57 — Specification of Polymer Materials and Components used in Ultrapure Water and Liquid Chemical Distribution Systems
SEMI F61 — Guide for Ultrapure Water Systems Used in Semiconductor Processing
SEMI F75 — Guide for Quality Monitoring of Ultrapure Water Used in Semiconductor
SEMI P5 — Specification for Pellicles
SEMI S4 — Safety Guideline for the Segregation/Separation of Gas Cylinders Contained in Cabinets
4.2 ASTM Standards[1]
ASTM D1414 —Standard Test Methods for Rubber O-Rings
ASTM D1415 —Standard Test Method for Rubber Property - International Hardness
ASTM D2000 —Standard Classification for Rubber Products in Automotive Application
ASTM D2240 —Standard Test Method for Rubber Property - Durometer Hardness
ASTM D395 —Standard Test Methods for Rubber Property - Compression Set
ASTM D412 —Standard Test Methods for Vulcanized Rubber and Thermoplastic Elastomers-Tension
ASTM D575 —Standard Test Methods for Rubber Properties in Compression
ASTM D5904 — Standard Test Method for Total Carbon, Inorganic Carbon, and Organic Carbon in Water by Ultraviolet, Per sulfate Oxidation, and Membrane Conductivity Detection
ASTM D6317 —Standard Test Methods for Low Level Determination of Total Carbon; Inorganic Carbon and Organic Carbon in Water by Ultraviolet, Per sulfate Oxidation, andMembrane Conductivity Detection.
4.3 IEST Standards[2]
IEST-RP-CC031.3 — Method for Characterizing Outgassed Organic Compounds from Cleanroom Materials and Components
4.4 ISO Standards[3]
ISO37 —Rubber, vulcanized or thermoplastic -- Determination of tensile stress-strain properties
ISO48 —Rubber, vulcanized or thermoplastic -- Determination of hardness (hardness between 10 IRHD and 100 IRHD)
ISO7619 —Rubber, vulcanized or thermoplastic -- Determination of indentation hardness -- Part 1: Durometer Method (Shore hardness)
ISO7743 —Rubber, vulcanized or thermoplastic -- Determination of compression stress-strain properties
ISO815—Rubber, vulcanized or thermoplastic -- Determination of compression set -- Part 1: At ambientor elevated Temperatures
NOTICE: Unless otherwise indicated, all documents cited shall be the latest published versions.
5 Terminology
5.1 Abbreviations and Acronyms
5.1.1 Five and Four Letter Acronyms:
5.1.1.1 LPCVD — Low Pressure Chemical Vapor Deposition
5.1.1.2 MOCVD —Metal Organic Chemical Vapor Deposition
5.1.1.3 UPDI—Ultra Pure De-ionized
5.1.2 Three and Two Letter Acronyms:
5.1.2.1 ATM — Atmospheric
5.1.2.2 BCDS— Bulk Chemical Dispensing System
5.1.2.3 CVD — Chemical Vapor Deposition
5.1.2.4 HDP — High Density Plasma
5.1.2.5 OEM — Original Equipment Manufacturer
5.1.2.6 PPB — Parts per Billion
5.1.2.7 PVD — Physical Vapor Deposition
5.1.2.8 RTP — Rapid Thermal Process
5.1.2.9 TOC —Total Oxidizable (organic) Carbon
5.1.2.10 DI — Deionized
5.1.2.11 HF —Hydrofluoric Acid
5.1.2.12 RF —Radio Frequency
5.1.2.13 UV — Ultraviolet
5.2 Definitions
5.2.1 Acid — a corrosive material whose chemical reaction characteristic is that of an electron acceptor. [SEMI F21, SEMI S4]
5.2.2 Anion — a negatively charged ion that is attracted to an anode in electrolysis.
5.2.3 Cation — a positively charged ion; an ion that is attracted to the cathode in electrolysis. These are typically ions of metallic elements.
5.2.4 Chemically assisted elastomeric degradation – the breakdown process of a seal surface caused by polymer degradationthat involves a change of the polymerproperties due to a chemical reaction with the polymer’s surroundings.[4]
5.2.5 Mechanical deformation — the alteration of a seal caused by mechanical means, such as abrasion, rubbing, and compression.
5.2.6 Chemical property — chemical durability is a measure of corrosion or attack of a glass surface when subjected to a specific reagent, such as acid, base, or water at a specific concentration for a specific time and temperature. [SEMI D9]
5.2.7 Chemical reaction — a process that involves change in the structure of ions or molecules.
5.2.8 Seal Chemical Compatibility — the ability of the molecules of a seal to coexist with process chemistries without the degradation of either.
5.2.9 Corrosives — a chemical that causes visible destruction of, or irreversible alterations in, living tissue by chemical action at the site of contact. A chemical is considered to be corrosive if, when tested on the intact skin of albino rabbits by the method described in the U.S. Department of Transportation in Appendix A to 49 CFR 173, it destroys or changes irreversibly the structure of the tissue at the site of contact following an exposure period of four hours. This term shall not refer to action on inanimate surfaces. [SEMI S4]
5.2.10 Deionized water — (specified with resistivity ≥18 MΩ/cm, cations: Na, Fe, Ca ≤0.2 µg/l).
[SEMI E45]
5.2.11 Degradation — a chemical reaction leading to the reduction to a simpler molecular structure. See also chemical breakdown.
5.2.12 Ion — an atom or group of atoms that has lost or gained one or more electrons.
5.2.13 Leak rate — rate at which an environment loses a vacuum (Millitorr liters/second).
5.2.14 Outgassing — a vacuum phenomenon wherein a substance spontaneously releases volatile constituents in the form of vapors or gases. In rubber compounds, these constituents may include water vapor, plasticizers, air, inhibitors, etc.[5]
5.2.15 Oxidizer gas — a gas which will support combustion or increase the burning rate of a combustible material with which it may come in contact. [SEMI S4]
5.2.16 Particle — a minute fragment or quantity of matter.[6]
5.2.17 Particle generation — molecules of material generated, in most cases, due to degradation of a material.
5.2.18 Permeation — process by which a gas or liquid to pass through a seal structure by diffusion.
5.2.19 Silica — silicon dioxide, occurring as quartz, etc.
5.2.20 Swell resistance — the ability of a material to resist increasing its volume when it has been immersed in a liquid or exposed to vapor.
5.2.21 Weight loss — reduction in mass of a sealing compound through the result of a chemical or physical reaction.
6 Measuring Methodology / Sample Preparation
6.1 Total Organic Carbon (TOC) Testing
6.1.1 General:
6.1.1.1 Reference documents: SEMI F40 and SEMI F57.
6.1.2 Sample preparation and leaching conditions: Follow SEMI F40 and SEMI F57.
6.1.2.1 It is important to maintain sufficient surface area to liquid volume ratio to satisfy the detection limit and specification requirements of SEMI F57 or other applicable specification.
6.1.2.2 TOC leaching test should be conducted using high purity materials for container in order to maintain detection limits within criteria of SEMI F57.
6.1.3 Testing: Analyze per ASTM D6317. If carbon content exceeds the limits of ASTM D6317 use ASTM D5904.
6.1.4 TOC reporting:
6.1.4.1 The reporting units are microgram per m2.
6.1.4.2 A complete sample description including manufacturer, material type, part number, lot number, processing conditions, surface treatment, cutting or other sample manipulation for testing, and other sample history should be included.
6.2 Surface Extractable Metallic Contamination
6.2.1 General: The extraction and analysis are per SEMI F57 for Surface Extractable Contamination. Alternate media such as 2% nitric acid for one hour may be used, if specified by end-use condition.
6.2.2 Sample preparation:
6.2.2.1 Samples should be prepared per SEMI F40 and SEMI F57.
6.2.2.2 Record the weight and dimensions of all samples prior to testing.
6.2.3 Surface extraction:
6.2.3.1 No UHPW or other rinsing should be performed prior to the analysis.
6.2.3.1.1 Extraction:
6.2.3.1.1.1 UPW – Follow SEMI F57.
6.2.3.1.1.2 Acids (HF and Piranha; or specified) - 1 hour in concentrated acid as defined in requirements at ambient temperature.
6.2.3.1.1.3 Conditions should be consistent for comparison and quality assessments.
6.2.4 Metals testing:
6.2.4.1 ICP-MS per SEMI F57.
6.2.4.2 Typical elements quantified are: Al, B, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Mo, Na, Ni, P, Pb, Sb, Sn, Sr, Ti, V, Zn, and Zr.
6.2.5 Reporting: Report units as µg/m2. Sample identification, dimensions and weight should be included in the report.
6.3 Ash Metal Analysis
6.3.1 General:
6.3.1.1 Analysis of metals contents of the ash is reported per weight of the pre-ashed sample.
6.3.2 Sample Preparation:
6.3.2.1 Samples size should be limited to 2 grams.
6.3.2.2 No UPW rinse or pre-acid clean should be performed prior to the analysis unless it is needed to remove potential surface contaminants that are not part of the bulk material.
6.3.3 Ashing condition: Ash in a muffle-type furnace until the material is fully ashed.
6.3.4 Metals testing:
6.3.4.1 ICP-MS.
6.3.4.1.1 Typical elements quantified are: Al, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Mo, Na, Ni, P, Pb, Sb, Sn, Sr, Ti, V, Zn, and Zr.
6.3.5 Reporting: Report as ng/gram or ppb of sample prior to ash.
6.4 Outgassing Test
6.4.1 General:
6.4.1.1 The outgassing test should be performed per IEST-RP-CC031.3.
6.4.1.1.1 Sample and test variables that should be consistent when performing comparison assessment include: sample size, sample exposed area, outgas time and temperature, gas flow rate, linear velocity of the gas over the sample, and geometry/size and orientation of the sample and vessel.
6.4.2 Sample Preparation:
6.4.2.1 It is important to maintain consistent exposed surface areas to improve reproducibility and comparative results. Very low outgassing materials may require the material to be cut to increase surface area during outgassing.
6.4.2.1.1 Cutting the material into very small pieces that are less than 1 mm in any dimension is preferred.
6.4.2.1.2 Samples should be delivered in a clean packaging to the lab.
6.4.2.1.3 Do not pre-clean the sample prior to placement in the sample vessel unless otherwise instructed by the customer.
6.4.2.1.4 Appropriate handling techniques should be used that will not contaminate the sample during handling.
6.4.2.1.5 Record the weight and dimensions of all samples prior to testing. If the material is cut into very small pieces, this should be noted in the report rather than recording dimensions.
6.4.2.1.6 Follow IEST-RP-CC031.3 instructions regarding analyzing blanks for each vessel used.
6.4.3 Testing: dynamic headspace/thermal desorption with cold trap and GC/MS system.
6.4.3.1 Outgas in baked quartz, SS or PFA sample vessel.
6.4.3.2 Separate outgas samples at two temperatures (100 °C, and 150 °C) for 30 minutes each. If the maximum projected use temperature is greater than 150°C, it is recommended to have a third test at a temperature that is 25°C greater than the maximum use temperature.
6.4.3.3 Utilize UHP He or N2 as the carrier gas at 100 mL/min flow rate.
6.4.3.4 Cryotrap temperature is 0-2°C.
6.4.3.5 Reference external standard such as hexadecane is to be used and documented in the reporting.
6.4.3.5.1 Follow IEST-RP-CC031.3 instructions regarding analyzing response of external standard.
6.4.4 Outgas Reporting
6.4.4.1 Results should be reported in ng/cm2 or ppmw for small cut up pieces or ng/part for parts with indeterminate surface areas of the outgassing material.
6.4.4.2 A complete sample description including manufacturer, material type, processing conditions, surface treatment, cutting or other sample manipulation for testing, and other sample features per IEST-RP-CC31.3 should be included.
6.4.4.3 Instrument/system information should be reported per IEST-RP-CC31.3.
6.5 Ionics
6.5.1 Ionics should be determined per SEMI F57.
6.6 Permeability
6.6.1 General: Reference document: ISO 15105-1 and ASTM D1434.
6.6.1.1 Permeability is analyzed by volume of gas passing through a material with specified thickness, per unit area and unit time, under unit partial pressure difference between the two sides of material. Test can be processed on single-layer film or sheet of material or multi-layer structures under a differential pressure.
7 Consideration for Perfluorooctanoic Acid (PFOA) and Fluorinated Telomers[7]
7.1 Perfluorooctanoic acid (PFOA) is a perfluorinated chemical (LCPFC) that does not occur naturally in the environment. LCPFCs are synthetic chemical substances with special properties and hundreds of manufacturing and industrial applications.
7.2 EPA has been investigating PFOA because:
7.2.1 It is very persistent in the environment
7.2.2 It is found at very low levels both in the environment and in the blood of the general U.S. population
7.2.3 It remains in people for a very long time
7.2.4 It causes developmental and other adverse effects in laboratory animals.
7.3 Major pathways that enable PFOA, in very small quantities, to get into human blood are not yet fully understood. PFOA is used to make fluoropolymers and can also be released by the transformation of some fluorinated telomers. However, consumer products made with fluoropolymers and fluorinated telomers, including Teflon® and other trademark products, are not PFOA. Rather, some of them may contain trace amounts of PFOA and other related perfluorinated chemicals as impurities. The information that EPA has available does not indicate that the routine use of consumer products poses a concern. At present, there are no steps that EPA recommends that consumers take to reduce exposures to PFOA.
7.4 EPA remains concerned about LCPFCs being produced by companies that are not participating in the stewardship program and intends to take action to address those concerns. On December 30, 2009, EPA postedfour action plans, including anaction plan on long-chain perfluorinated chemicals (LPFCs). The LCPFCs action plan outlines actions that would further reduce exposure to LCPFCs by addressing their use in products from sources other than the eight companies participating in the stewardship program. As these actions begin, there will be opportunities for public and stakeholder comment and involvement.
8 Considerations for Use in Ultrapure Deionized Water
8.1 Deionized water is used in many wafer processing steps and should not contribute any contaminants to the processes. The most common sealing requirements in DI water systems are for filters, valves, flow and pressure regulators, and fittings.
8.2 Contaminants in DI water fall primarily into three categories. They are: ion contamination, TOCs and bacterial growth. Contaminant levels are usually expressed in parts per billion (PPB).
8.3 Ion contamination problems are caused by anionic and cationic elements in DI water such as fluorides, chlorides, sulfates, etc. These can be leached from seals as well as the DI plumbing.
8.4 In order to kill bacteria which have a propensity to grow in DI water, the water is either heated (>80°C+), ozonized, or exposed to high levels of UV light (typically 254 nanometer wavelength), or possibly a combination of these three elements. These treatments pose unique problems for seals used in the DI system such as: contamination of the DI water by TOCs being leached from the seals; leaking of the DI plumbing due to temperature changes; seal failure due to exposure to strong oxidizing agents; and seal failure due to UV exposure. Ozone and UV deterioration of the seals usually leads to particulate contamination.
8.5 Considerations:
8.5.1 What method of sterilization (i.e., chemical, thermal or radiation)?
8.5.2 Concerns for cations, anions, or TOCs?
8.5.3 Seal life expectation?
9 Considerations for Use in Corrosives (Acids, Bases), Oxidizers, and Solvents
9.1 Inorganic wet chemicals at high concentration levels and in some cases at elevated temperatures are often used in front-end semiconductor processing. Most common sealing requirements are in acid recirculation and bulk chemical distribution systems (BCDS). Component systems include pumps, filters, mega sonic seals, gaskets for pipeline interfaces and valves.