Semiconductor Equipment and Materials International
3081 Zanker Road
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Phone: 408.943.6900, Fax: 408.943.7943
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Background Statement for SEMI Draft Document #5389A
Revision to MF1982-1110, TEST METHODS FOR ANALYZING ORGANIC CONTAMINANTS ON SILICON WAFER SURFACES BY THERMAL DESORPTION GAS CHROMATOGRAPHY
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
SEMI standard document of MF1982 as description of the method of organic contamination measurement on the silicon wafer surface has wide influence over the user which is referred by ITRS road map. Now, TF had been decided to revise the MF1982 which was long time spending from establishment, problem for the measurement and immoderate description by TF reconsideration.
Regarding the points of revision are correction about affect of measurement, simplifying of the expression and conformity of the SEMI style manual. This revision will be expected to active use for long time with easily understanding.
The current standard document had been described the method for the measurement of organic contamination on the silicon wafer determined by GC-MS. And the expression of two methods (so-called A and B) for sample preparation had been described in this document by the deference of the shaping sample.
TF had considered the problem of the current document of MF1982. Then we reached at the conclusion of three matters as followed. All organic contamination is not covered by GC-MS. The sample preparation can be combined expression about A and B method. And this document shall be changed the structure by referring the SEMI style manual. Concretely, TF would be performed to revise for this document as below,
1.Regarding the important concern for the measurement, it is described at new section as “Limitation”.
2.Removing the A and B method expression.
3.Reconsidering the whole document structure using SEMI style manual.
This document had been revised from viewpoints of upper description. It was almost full alteration.
Doc.4846 was submitted for Cycle 1, 2010 and passed the committee review in March. However, the Minority Report citing language flaws and its conflict with SEMI MF1982 was submitted. Then, the Japan Silicon Wafer Committee in June decided to overturn the adjudication result based on the Silicon GCS recommendation, and the document was returned to the Test Method Task Force. Language was reviewed and substantially improved as well as clarification of the difference between SEMI MF1982 and the proposed document was made. Doc.4846A was then submitted for Cycle 72010, however it failed the committee review during SEMICON Japan. The Task Force reviewed all the negatives and comments, and revised the document as appropriate.Doc.4846B was failed again for Cycle 7, 2011. The proposal of new standard (Doc 4846B) gives up and revises MF1982.
Doc.5389 had been balloted in cycle 7 at 2012. However, this document had been failed. Because of the reject voters had pointed out the some beneficial comments. Then, Japan TF judged the “fail” for aim to better content. Japan TF had discussed about all reject voter’s comments. Also, TF had performed to continuously discussion with voters based on the TF comment by e-mail. Here, Japan TF decided to re-throw the Doc.5389A into the ballot cycle 7 at 2013.Doc.5389A was reached the consensus at the international Test Method Task Force at Aug. 28th and submitted in Japan Silicon Wafer Committee at Sep. 3rd.
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.
Page 1Doc. 5389 SEMI
Semiconductor Equipment and Materials International
3081 Zanker Road
San Jose, CA95134-2127
Phone: 408.943.6900, Fax: 408.943.7943
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Review and Adjudication Information
Task Force Review / Committee AdjudicationsGroup / International Test Method TF / Global Silicon Wafer Committee
Date / Dec 4th 2013 / Dec 5th2013
Time & Time zone / 3:00p.m.-5:00p.m.Japan Standard Time / 10:30a.m. - 6:00 p.m.
Japan Standard Time
Location / Makuhari Messe / Makuhari Messe
City, State/Country / Chiba/Japan / Chiba/Japan
Leaders / Ryuji Takeda ()
Peter Wagner ()
Dinesh Gupta () / Tetsuya Nakai ()
Naoyuki J. Kawai ()
Standard staff / Hirofumi Kanno () / Hirofumi Kanno ()
Note: Additions are indicated by underline and deletions are indicated by strikethrough.
SEMI Draft Document #5389A
Revision to SEMI MF1982-1110, TEST METHODS FOR ANALYZING ORGANIC CONTAMINANTS ON SILICON WAFER SURFACES BY THERMAL DESORPTION GAS CHROMATOGRAPHY
1 Purpose
1.1 Organics are present in many materials, such as plastics, lubricants, cleansers, soaps, and living tissues. Some of these compounds are volatile and others can become airborne through chemical reactions, heating, abrasion, or outgassing.Organic compounds are present in many materials such as parts and components for cleanrooms, carriers, FOUP, developers, and organic removers. Some of these organic compounds are volatile and some can be discharged into clean room environment through chemical reactions or by heating.Also they can transfer to wafers by direct contact or be left behind from solvent residues. Once present in clean facilities, they can deposit on wafer surfaces.The desorbed organic compounds can be transferred to wafers or reticles through the environment.Organics deposited on wafers can cause degradation haze, wafer surface tension changes, irregular oxidation rates, and other effects, such as counter-doping by organophosphorus compounds.Various organic compounds on wafer surfaces can cause a pseudo increase of the thickness of the native oxide film. Nonuniformity of the surface leads to nonuniform oxide on a wafer and causes degradation of the oxide breakdown voltage. It also causes not only wafers, but also the reticles or mirrors to haze.Identification of trace level organic contaminants is important in determining the source of the particular contamination. These test methods use the thermal desorption gas chromatographymass spectrometry(TD/GC-MSTD-GC)[1],[2]technique to characterize and quantify organics deposited on wafer surfaces.This is one of the reasons that control of organic compounds is required in a cleanroom environment or on wafer surfaces. This mandates test methods of organic compounds on wafer surfaces. TD/GC-MSis useful for qualitative and quantitative analysis of trace-level organic compounds adsorbed on wafer surfaces.
1.2 Monitoring of organic contamination on wafer surfaces also can be used to measure material outgassing for proper selection of cleanroom, construction, and wafer packaging materials.
2 Scope
2.1 These test methods cover the identification and quantification of organic contaminants on silicon wafer surfaces using a gas chromatograph interfaced to a mass spectrometer (GC-MS) or a phosphorus selective detector, or both. This test method covers the identification and quantification of organic compounds on wafer surfaces by using Gas Chromatography Mass Spectrometry(GC-MS).
2.2 These test methods describe the apparatus and related procedures for sample preparation and analyses by TD-GC.This test method describes the procedures for sample preparation and analyses by Thermal Desorption Gas Chromatography (TD-GC).
2.3 The range of detection limits of these test methods depends on the target organic compounds, for example, the range of detection limits is from the subpicogram to the nanogram level of hydrocarbons (C8 to C28) per square centimeter of silicon wafer surface.The range of lower detection limits of this test method depends on the species of organic compound. However, generally for organic compounds, it ranges from subpicogram to nanogram per square centimeter of silicon-wafer surface (pg/cm2 to ng/cm2). The lower detection limit when the molecular weight is assumed as 300 and carbon numbers as from 10 to 20 is in the range of 5e10–5e11 molecules/cm2, 1e12-1e13 C atoms/cm2.
2.4 These test methods can be used for polished silicon wafers, or silicon wafers with oxide films.This test method can be used for various materials depending on the purposes, but mainly for bare silicon wafers.
2.5 Two methods are described. Method A is performed on cleaved wafers. Method B is performed on full wafers. The detailed procedures of Method A and Method B as well as the differences between them, are described in §6 and §8.When testing wafers, full wafers are basically used. However, cleaved wafers can be accepted as long as it does not cause a significant drop in the sensitivity (from a quarter to a half of a wafer).
2.6 Suitable safety precautions must be followed when handling organic solvents and compounds, hot materials subjected to propane flame, the propane flame itself, wafer thermal desorption systems, rapid thermal annealer, or a high temperature furnace.
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]
3.1 Some organic compounds show difficulty in measuring by TD/GC-MS. These are volatile compounds, amines, polar compounds (fatty acids, etc.), and high-polymer organic compounds that degraded at 400°C or below. In the TD/GC-MS measurement above, high-polymer organic compounds or polar organic compounds tend to remain in the column or show themselves as broad peaks. Organic materials degraded at 400°C or below may be measured as other materials generated after the degradation. As organic phosphorus tends to remain and degrade, a combination of qualitative analysis by TOF-SIMS and quantitative analysis by Inductivity Coupled Plasma Mass Spectrometry(ICPMS) after organophosphorus degradation is desirable. For amines, qualitative and quantitative analysis by Capillary Electrophoresis (CE) or Capillary Electrophoresis Time-of-Flight Mass Spectrometry (CE/TOF-MS) is preferable.
4 Referenced Standards and Documents
4.1 SEMIStandard
SEMI M59 — Terminology for Silicon Technology
4.2 ASTMStandard
ASTM D6196 — Practice for Selection of Sorbents and Pumped Sampling/Thermal Desorption Analysis Procedures for Volatile Organic Compounds in Air3[4]
4.3 ISO Standard[5]
ISO/DIS 14644-8 Classification of air cleanliness by chemical concentration
ISO/FDIS 14644-10 Classification of surface cleanliness by chemical concentration
4.4 JACA Standard[6]
JACA No.43-2006 (Japan Air Cleaning Association Standard) Analysis of Surface Molecular Contaminants
NOTICE: Unless otherwise indicated, all documents cited shall be the latest published versions.
5 Terminology
5.1 General acronyms, terms, and symbols related to silicon technology are listed and defined in SEMI M59.
5.2 Abbreviations Specific to this Standard
5.2.1 AED— atomic emission detector C16―n-hexadecane, n-C16H34
5.2.2 C16 — n-hexadecane (n-C16H34) C20―n-eicosane, n-C20H42
5.2.3 FID— flame ionization detector CE―Capillary Electrophoresis
5.2.4 FPD— flame photometric detector CE/TOF-MS―Capillary Electrophoresis Time-of-Flight Mass Spectrometry
5.2.5 GC— gas chromatography GC―Gas Chromatography
5.2.6 GC-MS — gas chromatograph interfaced to a mass spectrometer GC-MS―Gas Chromatography Mass Spectrometry
5.2.7 MS— mass spectrometer ICPMS―Inductivity Coupled Plasma Mass Spectrometry
5.2.8 NPD— nitrogen/phosphorus thermionic ionization detector NA―Avogadro’s Constant
5.2.9 TBP— tributyl phosphate (C4H9O)3PO TD―Thermal Desorption
5.2.10 TCEP— tris (2-chloroethyl) phosphate (ClCH2CH2O)3PO TD-GC―Thermal Desorption Gas Chromatography
5.2.11 TD— thermal desorption TD/GC-MS―Thermal Desorption Gas Chromatography Mass Spectrometry
5.2.12 TP— total organophosphorus TOF-SIMS―Time-of-Flight Secondary Ionization Mass Spectrometry
5.3 Definitions of Term Specific to this Standard Definitions
5.3.1 blank wafer— a thermally-treated wafer desorbed of any surface organic contaminants equipment blank ―equipment (analyzer) background level
5.3.2 reference wafer ― a wafer surface which is organic contamination free
6 Summary of Test MethodsOverview
6.1 MethodAThermal Desorption and GC Analysis
6.1.1 Desorption and GC Analysis— The volatile organic contaminants on a wafer surface are desorbed thermally from the wafer surface in a wafer desorption oven and swept into a sample thermal desorption tube. The sample thermal desorption tube then is heated for a set period in the thermal desorption unit and the volatile organic contaminants desorbed from the sample thermal desorption tube are swept by a stream of helium to a cold trap where they are preconcentrated. At the end of this period, the cold trap is heated rapidly to release the trapped organics to the GC column head. Sample components then are separated and eluted out of the GC column. Then, a portion goes to a phosphorus selective detector and the remainder goes to a mass spectrometer (MS). Blank wafers are prepared by purging out any surface organic contaminants in a rapid thermal annealer or a high temperature furnace while a purge gas is flowing. The organic compounds on a wafer surface are thermally desorbed in a quartz chamber and trapped by absorbents.
6.1.2 Identification of Contaminants — Identification of individual unknown compounds is performed by correspondence of retention time of their peaks with that of known compounds. Correspondence of retention time on a single column should not be regarded as proof of identity. More precise identification of individual unknown compounds is performed with MS by matching their fragmentation patterns with mass spectra of known compounds in the spectral library.The absorbents are kept in an inert gas environment such as He or N2 for certain time to thermally desorb the organic compounds trapped in the absorbents and are then cooled down rapidly in a cold trap to condense the organic compounds.
6.1.3 Quantification — Quantification of total organics is based on the comparison of the integrated total peak area of the sample peaks with the area of the external standard compound, n-hexadecane (n-C16H34) [C16]. Total organophosphorus content in a sample is quantified by comparing the sample signal integrated from the phosphorus selective detector with the signal of the phosphorus standard compound, tris (2-chloroethyl) phosphate (TCEP) or tributyl phosphate (TBP). Specified range of standards is measured periodically, and the result is reported with blank wafer data.The cold trap is heated rapidly to release the trapped organic compounds into the GC column head.
6.1.4 Each component of the organic compounds is separated in the GC column.
6.1.5 Each separated component is lead to the mass spectrometer. Identification of individual unknown compounds is performed by matching patterns with mass-spectra library patterns.
6.1.6 Quantification is based on the integrated total peak area of each component compared with those of C16 or C20 as the standard.
6.1.7 Individual unknown organic compounds cannot be identified by retention time alone in the separation analysis by GC. It should be made by searching individual mass and library patterns.
6.2 MethodB
6.2.1 Desorption and GC Analysis — The volatile organic contaminants on a wafer surface are desorbed thermally from the wafer surface in a quartz chamber unit and swept into a glass TD tube. The glass TD tube then is heated for a set period and a stream of helium sweeps the volatile organic contaminants desorbed from the glass TD tube to a cold trap where they are preconcentrated. At the end of this period, the cold trap is heated rapidly to release the trapped organics to the GC column head. Sample components then are separated and eluted out of the GC column. Then, a portion goes to a phosphorus selective detector and the remainder goes to a MS. Blank wafers are prepared by purging out any surface organic contaminants in the heated quartz chamber unit, while helium gas is flowing as a purge gas.
6.2.2 Identification of Contaminants — Identification of individual unknown compounds is performed by correspondence of retention time of their peaks with that of known compounds. Correspondence of retention time on a single column should not be regarded as a proof of identity. More precise identification of individual unknown compounds is performed with MS by matching their fragmentation patterns with mass spectra of known compounds in the spectral library.
6.2.3 Quantification — Quantification of total organics is based on the comparison of the integrated total peak area of the sample peaks with the area of the external standard compound, C16. Total organophosphorus content in a sample is quantified by comparing the sample signal integrated from a phosphorus selective detector with the signal of the phosphorus standard compound, tris-(2-chloroethyl)-phosphate (TCEP) or tributyl phosphate (TBP). Specified range of standards is measured periodically, and the result is reported with blank wafer data.
7 Apparatus
7.1 MethodATD/GC-MS
7.1.1 GC Instrument utilizing a capillary column to separate a wide variety of organic compounds coupled to a MS, or a phosphorus selective detector, or both. Examples of phosphorus selective detectors are flame photometric detector (FPD), and atomic emission detector (AED). The nitrogen/phosphorus thermionic ionization detector (NPD) also responds to nitrogen containing compounds.GC-MS (e) column― uses a general-purpose fused-silica capillary column. As a liquid phase, nonpolar 100%-Dimethylpolysiloxane, less polar 5%-Phenyl 95%-Methylpolysiloxane, and polar 50%-Diphenyl 50%-Dimethylpolysilarylene can be used.
NOTE 1: A NPD may also be used as a phosphorus selective detector. This type of detector also responds to nitrogen containing compounds. If an NPD is used, the total organophosphorus reported should exclude any signals due to nitrogen containing compounds. Often, identification from the mass spectra can be used to determine whether compound contains nitrogen or phosphorus, or both.
7.1.2 Sample Thermal Desorption Tubes — Stainless-steel tubes packed with adsorbent medium, are used to trap compounds of interest and release them onto a thermal desorption unit.Chamber Unit (a) ― desorbs organic compounds on wafer surface and traps them in a trap tube.
NOTE 2: Note that stainless steel is catalytically active and can corrode with time, affecting recovery for some compounds. In this case, deactivated stainless steel, glass, or quartz tubes also can be used. Several adsorbent materials can be used for trapping organic compounds desorbed from silicon wafer samples. Some examples are activated carbon, graphitized carbon, and poly-(2,6-diphenyl-p-phenylene oxide).