Semiconductor Equipment and Materials International
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Phone: 408.943.6900, Fax: 408.943.7943
Background Statement for SEMI Draft Document 5876
New Standard: Test Method for Determining the Critical Pitting
Temperature of Stainless Steel Surfaces Used in Corrosive Gas
Systems by Use of a Ferric Chloride Solution
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.
Background
A simple Test Method is needed for comparing corrosion resistance of stainless steels intended for fabrication of
semiconductor gas supply components. The Test Method is a chemical procedure that does not require expensive
analytical equipment.
This Test Method describes a procedure that may be used to rank the pitting corrosion resistance of wetted surfaces
of tubing or components of finished surfaces intended for use in corrosive gas systems. Pitting corrosion is believed
to be a major corrosion failure mode in semiconductor gas delivery systems, particularly in components and tubing
welded and exposed to corrosive gases and moisture.
This Test Method is an adaptation of ASTM G48 Method E, Critical Pitting Temperature Test for Stainless Steel.
The adaptation describes a method for performing the Test Method on coupons or wetted surface sections cut from
gas supply system components or tubing. It is an aqueous immersion method in an acidified ferric chloride solution.
This Test Method is reproducible and provides a metric (i.e., critical pitting temperature) in addition to a qualitative
(i.e., visual) evaluation of corrosion resistance.
The ballot results will be reviewed and adjudicated at the meetings indicated in the table below. Check
http://www.semi.org/standards under Calendar of Events for the latest update.
Review and Adjudication Information
Task Force Review
Materials of Construction of Gas Delivery
Systems Task Force
Date:
Monday, November 2, 2015
Time & Time Zone: 08:00 – 09:30 Pacific Time (Tentative)
Location:
SEMI Headquarters in conjunction with the
Fall NA Standards Meetings
Group:
City, State/Country: San Jose, California/USA
Tim Volin (Parker Hannifin)
Leader(s):
Standards Staff:
TC Chapter Adjudication
NA Gases TC Chapter
Tuesday, November 3, 2015
9:00 – 12:00 Pacific Time
SEMI Headquarters in conjunction with the
Fall NA Standards Meetings
San Jose, California/USA
Tim Volin (Parker Hannifin)
Mohamed Saleem (Fujikin)
David Bouldin
972.965.0340
dbouldin@semi.org
David Bouldin
972.965.0340/
dbouldin@semi.org
This is a Draft Document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted Standard or Safety Guideline.
Permission is granted to reproduce and/or distribute this document, in whole or in part, only within the scope of SEMI International Standards committee (document development)
activity. All other reproduction and/or distribution without the prior written consent of SEMI is prohibited.
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Doc. 5876  SEMI
LETTER BALLOT
DRAFT
Document Number: 5876
Date: 2/9/2016
Semiconductor Equipment and Materials International
3081 Zanker Road
San Jose, CA 95134-2127
Phone: 408.943.6900, Fax: 408.943.7943
*This meeting’s details are subject to change, and additional review sessions may be scheduled if necessary. Contact
the task force leaders or Standards staff for confirmation.
Telephone and web information will be distributed to interested parties as the meeting date approaches. If you will
not be able to attend these meetings in person but would like to participate by telephone/web, please contact Standards
staff.
This is a Draft Document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted Standard or Safety Guideline.
Permission is granted to reproduce and/or distribute this document, in whole or in part, only within the scope of SEMI International Standards committee (document development)
activity. All other reproduction and/or distribution without the prior written consent of SEMI is prohibited.
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Doc. 5876  SEMI
LETTER BALLOT
DRAFT
Document Number: 5876
Date: 2/9/2016
Semiconductor Equipment and Materials International
3081 Zanker Road
San Jose, CA 95134-2127
Phone: 408.943.6900, Fax: 408.943.7943
SEMI Draft Document 5876
New Standard: Test Method for Determining the Critical Pitting
Temperature of Stainless Steel Surfaces Used in Corrosive Gas
Systems by Use of a Ferric Chloride Solution
1 Purpose
1.1 The purpose of this Test Method is to determine the relative resistance to pitting corrosion of the wetted surfaces
of components intended for use in corrosive gas distribution systems for semiconductor manufacturing. This Test
Method is an adaptation of American Society for Testing and Materials (ASTM) G48 and is intended to differentiate
between alloy compositions or processing that may affect the corrosion performance of the wetted surfaces. Detailed
information on the method is found in ASTM G48.
2 Scope
2.1 This Test Method describes a procedure which may be used to rank the pitting corrosion resistance of wetted
surfaces of tubing or components of finished surfaces intended for use in corrosive gas systems. Pitting corrosion is
believed to be a potential corrosion failure mechanism in semiconductor gas delivery systems, particularly in
components and tubing welded and exposed to corrosive gases with moisture present.
2.2 This Test Method is an adaptation of ASTM G48 Method E, Critical Pitting Temperature Test for Stainless Steel.
The adaptation describes a method for performing the Test Method on coupons or wetted surface sections cut from
gas supply system components or tubing. It is an aqueous immersion method in an acidified ferric chloride solution.
2.3 This Test Method is reproducible and provides a metric (i.e., critical pitting temperature) in addition to a
qualitative (i.e., visual) evaluation of corrosion resistance.
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.
3 Limitations
3.1 The test conditions of this Test Method do not simulate actual service in a corrosive gas supply system. Thus the
test results may not correlate to relative corrosion resistance in a specific corrosive gas or corrosive gas supply system.
3.2 The Critical Pitting Temperature (CPT) is valid only in a range of 10°C to 95°C. A CPT result greater than 95°C
is not considered to be valid since it is approaching the boiling point of the solution. A critical pitting temperature
(CPT) below 10°C shall only be reported as <10°C and may be an indication of crevice corrosion, which renders the
test invalid.
3.3 Since alloy composition and surface parameters can affect the results of the test, all variables other than the one
being tested must be fixed during the test in order to obtain reproducible and comparable results.
3.4 The test is destructive of the component tested. The component should not be placed in service following test.
This is a Draft Document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted Standard or Safety Guideline.
Permission is granted to reproduce and/or distribute this document, in whole or in part, only within the scope of SEMI International Standards committee (document development)
activity. All other reproduction and/or distribution without the prior written consent of SEMI is prohibited.
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Document Number: 5876
Date: 2/9/2016
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Phone: 408.943.6900, Fax: 408.943.7943
4 Referenced Standards and Documents
4.1 SEMI Standards
SEMI F19 — Specification for the Surface Condition of the Wetted Surfaces of Stainless Steel Components
4.2 ASTM Standards1
ASTM G15 — Standard Terminology Relating to Corrosion and Corrosion Testing
ASTM G48 — Standard Test Methods for Pitting and Crevice Corrosion Resistance of Stainless Steels and Related
Alloys by Use of Ferric Chloride Solution
NOTICE: Unless otherwise indicated, all documents cited shall be the latest published versions.
5 Terminology
NOTE 1: Unless otherwise stated, the terminology relating to corrosion and corrosion testing is as defined in ASTM G15.
5.1 Abbreviations and Acronyms
5.1.1 AISI — American Iron and Steel Institute
5.1.2 ASTM — American Society for Testing and Materials
5.1.3 CPT — critical pitting temperature
5.1.4 GP — general purity [GP]
5.1.5 HP — high purity
5.1.6 UHP — ultra-high purity
5.2 Definitions
5.2.1 crevice corrosion — corrosion at a cavity between adjoining pieces or at the edge of a seal or masking paint.
The chemical mechanism of crevice corrosion is similar to that of pitting, the cavity being a ‘preformed’ pit. As
corrosion is initiated at the cavity, the critical temperature for crevice corrosion is always lower than the critical pitting
temperature (CPT).
5.2.2 critical pitting temperature (CPT) — the lowest temperature at which pitting occurs on the test surface under
the specified test conditions.
5.2.3 pitting — corrosion of a metal surface, confined to a point or small area, that takes the form of cavities.
5.2.4 wetted surface — surfaces of a component in contact with the contained fluids.
6 Summary of Test Method
6.1 The test specimen is immersed in a solution of 6 % FeCl3 by mass and 1 % HCl at 10°C for 24 hours followed by
visual examination for pitting. If pitting is not present the test is repeated at 5°C higher temperature increments until
pitting is observed. The temperature at which pitting is observed is reported as the critical pitting temperature (CPT).
7 Possible Interferences
7.1 A possible interference is failure by crevice corrosion in which case the test is considered invalid.
7.2 Crevice corrosion can occur at any point of contact of the area under test with another object, such as a specimen
holder or container, or at the edge of the masking media. The crevice corrosion sites exist at the contact sites or the
masking boundaries. Figure 1 gives an example of the typical appearance of crevice corrosion sites from a critical
pitting test performed on type 316 stainless steel using masking.
1
American Society for Testing and Materials, 100 Barr Harbor Drive, West Conshohocken, Pennsylvania 19428-2959, USA. Telephone:
610.832.9585; Fax: 610.832.9555; http://www.astm.org
This is a Draft Document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted Standard or Safety Guideline.
Permission is granted to reproduce and/or distribute this document, in whole or in part, only within the scope of SEMI International Standards committee (document development)
activity. All other reproduction and/or distribution without the prior written consent of SEMI is prohibited.
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Document Number: 5876
Date: 2/9/2016
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Phone: 408.943.6900, Fax: 408.943.7943
7.3 Crevice corrosion also has a critical temperature that is always less than the CPT. The critical crevice corrosion
temperature for American Iron and Steel Institute (AISI) 316L is less than 10C. Test results for AISI 316L less than
10C achieved by the use of this Test Method are likely due to crevice corrosion and are considered invalid.
Figure 1
Examples of Pitting and Crevice Corrosion (Dashed Circles) on Type 316
Stainless Steel After a Pitting Test
7.4 Sulfur is added to stainless steel to improve machinability and welding penetration and exists as manganese
sulfide precipitate inclusions. These precipitates are preferred sites for the initiation of pitting when revealed on the
surface under test. Surfaces that are not parallel to the mechanical working direction of the stainless steel may intersect
a large number of the inclusions elongated by the mechanical working and therefore exhibit high pitting densities and
deep pitting.
8 Apparatus
8.1 The apparatus necessary for this Test Method consists of a test container, a constant temperature bath, and a
specimen holder.
8.1.1 Test container – glass flask or test tube
8.1.1.1 Glass flask requirements – 1,000 mL wide-mouth laboratory flask
8.1.1.2 Test tube requirements – If the test specimens are small, a test tube may be used of sufficient size to completely
immerse the test surface of the test specimen and have a solution volume of at least 150 mL and 5 mL/cm2 (30 mL/in.2)
of the test surface area.
8.1.2 Constant temperature bath – A water or oil bath having the capability of maintaining a constant temperature
between 5°C and 85°C ± 1°C.
8.1.3 Specimen holder – If an unmasked test specimen is used, it can be supported on cradles or hooks as described
in ASTM G48. A test specimen that is masked per ¶ 9.6 can be placed on the bottom of the test container as long as
the unmasked area of test interest is not touching the container, such that crevice corrosion may be induced.
This is a Draft Document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted Standard or Safety Guideline.
Permission is granted to reproduce and/or distribute this document, in whole or in part, only within the scope of SEMI International Standards committee (document development)
activity. All other reproduction and/or distribution without the prior written consent of SEMI is prohibited.
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Document Number: 5876
Date: 2/9/2016
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3081 Zanker Road
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Phone: 408.943.6900, Fax: 408.943.7943
9 Test Specimens
9.1 Test specimens are required to be representative of a product or process lot.
9.2 Specimen preparation should preferably be done by the component manufacturer. The specimen(s) are to be
cleaned and packaged per the manufacturer’s standard final cleaning and packaging procedures.
9.3 If specimen preparation is done by a party other than the manufacturer, the specimen(s) may be cleaned by
degreasing with a suitable detergent, rinsing in deionized water, followed by ethanol or similar solvent, and air drying.
After degreasing, the specimen must be handled with clean gloves, soft clean tongs, or equivalent preventive measures,
to avoid surface contamination. If the specimen(s) are not to be analyzed immediately, they should be packaged by
wrapping in clean metal foil or sealing in cleanroom quality nylon bags. If specimen preparation is done by a party
other than the manufacturer, this shall be stated in the report narrative and the analytical results are not to be interpreted
as indicative of the manufacturer’s quality of cleaning and packaging procedures. A note to this effect shall be included
in the reported results.
9.4 After preparation, specimens should be analyzed promptly, with allowance for shipping times and queuing time
at the analyst.
9.5 Tubing specimens shall consist of 5.0 cm (2.0 in.) lengths of tubing sectioned axially. Other types of components
shall be sectioned to expose the surface of interest to the test solution. The cut surfaces shall be smoothed sufficiently
to be effectively masked per ¶ 9.6.
9.6 All specimens should be masked to isolate the test to the surface of interest only. This can be accomplished by
masking with a nonreactive lacquer, which can be baked to ensure optimum adhesion. Alternately, plater’s tape can
be used.
9.7 The finish of the surface to be tested shall be consistent with the requirements of the surface roughness and surface
defects of the intended specification grade (i.e., general purity [GP], high purity [HP], or ultrahigh purity [UHP]) of
SEMI F19. Since surface finish can affect the CPT results, surface finishing should be done as consistently as possible
within a specimen set. Details of the surface finishing process, parameters, and characterization should be provided in
the test report as outlined in ¶ 13.
9.8 A minimum of three specimens shall be tested, and preferably five or more to obtain statistical significance in the
testing results.
9.9 The minimum test area is 1 cm2. This minimum test area is required for both flat specimens and tubing specimens.
Certain types of components may not have sufficient test area to meet this requirement. This should be noted in the
test report and the calculated test area reported.
10 Reagents And Materials
10.1 Reagent grade chemicals and deionized water shall be used in the preparation of test solutions.
10.2 The ferric chloride test solution is prepared by dissolving 68.72 g of reagent grade ferric chloride (FeCl3·6H2O)
in 600 mL of deionized water and adding 16 mL of reagent grade concentrated (36.5–38.0%) hydrochloric acid (HCl).
The solution can be made up in bulk and stored in a sealed container for up to five days at room temperature.
11 Procedure
11.1 Transfer 600 mL of the test solution to a flask or the amount required per ¶ 8.1.1.2 to a test tube. Cover with a
watch glass and place in the constant temperature bath set at 10°C. Allow the test solution to equilibrate to the set
temperature.
11.2 Immerse one or more test specimens in the test solution and cover the container with a watch glass for the
duration of the test.
11.3 After 24 hours, remove the specimen(s) from the test solution, rinse thoroughly in deionized water followed by
methanol, and dry.
11.4 Examine the specimen(s) for pitting. If pitting is observed, the test temperature shall be reported as the CPT.
11.5 If pitting has not occurred, repeat ¶¶ 11.1 through 11.4 at 5°C higher temperature increments until pitting is
observed.
This is a Draft Document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted Standard or Safety Guideline.
Permission is granted to reproduce and/or distribute this document, in whole or in part, only within the scope of SEMI International Standards committee (document development)
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11.6 When test is completed, remove the specimen(s) from the test solution and rinse with deionized water.
11.7 Examine the test area of the specimen(s) under an optical microscope at 20X magnification.
11.8 Confirm the existence of pits and the absence of crevice corrosion, as indicated by the absence of pits touching
the masked-off or lacquered area (see ¶ 7.1 and Figure 1). Any crevice corrosion observed on the specimen after
testing means that the test results are invalid and must be discarded.
12 Data Analysis
12.1 The CPT is the lowest temperature at which pitting without crevice corrosion is observed by visual examination.
13 Reporting Results
13.1 Information Required in the Test Report
13.1.1 Test specimens(s) identification
13.1.1.1 Manufacturer
13.1.1.2 Part number (if applicable).
13.1.1.3 Lot number
13.1.1.4 Specification Grade per F19 or surface processing history (e.g., mechanical polish, electropolish,
passivation).
13.1.1.5 Welded specimens must be identified and the welding process specified.
13.1.1.6 Tubing diameter for tubing specimens.
13.1.2 Test identification number and date of test.
13.1.3 Critical pitting temperature (CPT). CPTs below 10°C shall only be reported as below 10°C.
13.1.4 Number of specimens in which pitting is observed, if more than one specimen is tested.
13.1.5 The scatter or deviation in the CPT values based on multiple runs, if performed
14 Related Documents
14.1 SEMI Standards
SEMI F20 — Specification for 316L Stainless Steel Bar, Forgings, Extruded Shapes, Plate, and Tubing for
Components Used in General Purpose, High Purity and Ultra-High Purity Semiconductor Manufacturing Applications
NOTICE: SEMI makes no warranties or representations as to the suitability of the Standards and Safety Guidelines
set forth herein for any particular application. The determination of the suitability of the Standard or Safety Guideline
is solely the responsibility of the user. Users are cautioned to refer to manufacturer’s instructions, product labels,
product data sheets, and other relevant literature, respecting any materials or equipment mentioned herein. Standards
and Safety Guidelines are subject to change without notice.
By publication of this Standard or Safety Guideline, SEMI takes no position respecting the validity of any patent
rights or copyrights asserted in connection with any items mentioned in this Standard or Safety Guideline. Users of
this Standard or Safety Guideline are expressly advised that determination of any such patent rights or copyrights
and the risk of infringement of such rights are entirely their own responsibility.
This is a Draft Document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted Standard or Safety Guideline.
Permission is granted to reproduce and/or distribute this document, in whole or in part, only within the scope of SEMI International Standards committee (document development)
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