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Background Statement for SEMI Draft document 4657B
NEW STANDARD: SPECIFICATIONS FOR TUNGSTEN HEXAFLUORIDE (WF6)
Note: 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.
Note: 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.
The Gases Committee has been combining the common SEMI Gases into single specifications to make it an orderly and efficient way that would facilitate ease of use or reference. The committee took advantage of the common traits in all the existing specifications to reduce the total volume of specs and to reinforce their commonalities.
In the past ballot cycles, the committee has successfully combined Oxygen, Hydrogen and Nitrogen gases below
SEMI C54-1103, SPECIFICATIONS AND GUIDELINES FOR OXYGEN
SEMI C58-0305, SPECIFICATIONS AND GUIDELINES FOR HYDROGEN
SEMI C59-1103, SPECIFICATIONS AND GUIDELINES FOR NITROGEN
In a continuing process, this ballot proposal is to combine
SEMI C3.26-0301 SPECIFICATION FOR TUNGSTEN HEXAFLUORIDE (WF6) IN CYLINDERS, 99.8% QUALITY and
SEMI C3.52-0200 STANDARD FOR TUNGSTEN HEXAFLUORIDE, 99.996% QUALITY
In this document, the committee carried out the following steps:
First, new Purpose, Scope sections and other mandatory sections were added to the ballot. Its purpose is to modify the titles of the combine standards for a given gases into a single stand-alone specification. This is being accomplished as follows:
1) Collect and group all gases standards and combined into one specification for each gases that includes all grades.
2) Combine all relevant gases tables into a single table in the consolidated specification
3) Re-designate the combined specifications with a single designation (C3.xx) for each gas.
4) Reference the previous SEMI designation numbers (C3.yy) for grades at the top of each column in the table.
This involves reformatting the standards, updating any technical information, format according to SEMI editorial guidelines, and obtaining approval of the committee by balloting.
NOTE: If this ballot is approved, SEMI C3.26 and C3.52 will be submitted for withdrawal in subsequent meeting.
The results of this ballot will be reviewed and adjudicated by NA Facilities and Gases Committee during their meetings late March 2011 in San Jose, CA. Check www.semi.org/standards for the latest meeting schedule.
For question on the ballot, contact SEMI Staff, Kevin Nguyen at
SEMI Draft Document 4657B
NEW STANDARD: SPECIFICATIONS FOR TUNGSTEN HEXAFLUORIDE (WF6)
1 Purpose
1.1 The purpose of this document is to provide specifications for tungsten hexafluoride (WF6) that are used in the semiconductor industry.
2 Scope
2.1 This document covers requirements for tungsten hexafluoride used in the semiconductor industry.
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 Description
3.1 Tungsten hexafluoride is a colorless gas or colorless liquid. It is shipped as a liquefied gas under its own vapor pressure.
4 Limitations
4.1 None
5 Referenced Standards and Documents
5.1 SEMI Standards
SEMI C1 — Guide for the Analysis of Liquid Chemicals
SEMI C3 — Specifications for Gases
SEMI C10 — Guide for Determination of Method Detection Limits
NOTICE: Unless otherwise indicated, all documents cited shall be the latest published versions.
6 Terminology
6.1 Terminology appropriate to this standard is defined in SEMI C3.
7 Requirements
7.1 Purity and other requirements for tungsten hexafluoride are given in Table 1.
Table 1 Impurity and Other Requirements for Tungsten Hexafluoride (WF6)
Previous SEMI Reference # / C3.26-0301(Specification) / C3.52-0200
(Specification)
Grade / 99.9% / 99.997%
Impurities / Maximum Acceptable Level (ppm) #1
Carbon Tetrafluoride (CF4) / 10 / 1
Carbon Dioxide (CO2) / -- / 1
Carbon Monoxide (CO) / -- / 1
Hydrogen Fluoride (HF) / 1000 / 20
Nitrogen (N2) / 50 / 5
Oxygen (O2) + Argon (Ar) / 50 / 1
Sulfur Hexafluoride (SF6) / 10 / 1
Silicon Tetrafluoride (SiF4) / 10 / 1
TOTAL LISTED IMPURITIES / 1130 / 31
Impurities / Maximum Acceptable Level (ppm w)
Cobalt (Co) & Manganese (Mn) / -- / 0.01
Lead (Pb) / -- / 0.02
Chromium (Cr), Zinc (Zn), & Uranium (U) / -- / 0.05
Calcium (Ca) & Magnesium (Mg) / -- / 0.10
Nickel (Ni), Copper (Cu), Sodium (Na), & Potassium (K) / -- / 0.15
Iron (Fe) / -- / 0.02
Thorium (Th) / -- / 0.1
Molybdenum (Mo) / -- / 1
#1: An analysis of significant figures has not been considered. The number of significant figures will be based on analytical accuracy and the precision of the provided procedure.
8 Properties of Tungsten Hexafluoride (WF6)
Table 2 Properties of Tungsten Hexafluoride (for information only)
Metric Units / US UnitsCAS # / 7783-82-6 / 7783-82-6
Molecular weight / 297.85 / 297.85
Boiling point at 1 atm / 17.1°C / 62.8°F
Density of gas at 22.8°C (73°F) and 1 atm / 12.9 kg/m3 / 0.805 lb/ft3
Specific gravity of gas / 10.8 / 10.8
Density of liquid at boiling point / 3440 kg/m3 / 214.8 lb/ft3
9 Analytical Procedures for Tungsten Hexafluoride, 99.9% Purity
9.1 Nitrogen and Oxygen + Argon — This procedure is for the determination of nitrogen and oxygen + argon in tungsten hexafluoride using a gas chromatograph with a thermal conductivity detector.
9.1.1 Detection Limits — 10 ppm (mol/mol) nitrogen, and 10 ppm (mol/mol) oxygen + argon.
9.1.2 Instrument Parameters
9.1.2.1 Columns: (See Figures 1, 2)
· Column 1: Porapak® S, 80/100 mesh, 1.5 m (5 ft) by 6.4 mm (1/4 in) OD, 5.1 mm (0.2 in) ID, ss or equivalent.
· Column 2: Molecular sieve 5A, 80/100 mesh, 1.8 m (6 ft) by 4.8 mm (3/16 in) OD, 3.7 mm (0.147 in) ID, ss or equivalent.
9.1.2.2 Column Flow: 30 mL/min helium.
9.1.2.3 Sample Volume: 2 mL
9.1.2.4 Temperatures
· Detector: 70°C
· Column: 40°C
9.1.3 Calibration Standard — 50 ppm (mol/mol) nitrogen, 50 ppm (mol/mol) oxygen, balance helium.
9.1.4 Operating Procedures
9.1.4.1 Determine the times for valve switching and signal changes, and enter into the run table. An example of a run table follows.
Table 3 Example of a RunTime / Position / Function
0 min. / 1 / Purge sample through loop. Backflush Porapak® column. Connect MS column to the TCD.
1 min. / 2 / Inject sample onto Porapak® column. Allow oxygen + argon and nitrogen to elute from the Porapak® column to the MS column. Sequentially elute the oxygen + argon and nitrogen from the MS column to the TCD.
4 min. / 1 / Backflush Porapak® column to vent for 8 minutes.
9.1.4.2 Set the valves in Position 1 (Figure 1).
9.1.4.3 Flow the calibration standard through the 10-port valve. Analyze standard using the conditions described above. Record retention times and peak areas.
9.1.4.4 Flow the sample to be tested through the 10-port valve for 1 minute. Analyze in the same manner as in ¶ 9.1.4.3.
9.1.4.5 The standard is again run as in ¶ 9.1.4.3.
9.1.4.6 Calculate the concentrations of nitrogen and oxygen + argon in the sample, using the formula below. The result may not exceed the specifications in table 1 of this Standard.
(1)
9.2 Carbon Tetrafluoride, Hydrogen Fluoride, Silicon Tetrafluoride, and Sulfur Hexafluoride — This procedure is for the determination of these gases in tungsten hexafluoride using infrared spectrophotometry.
NOTE 1: Actual detection limits will be determined by the noise level and the resolution of the spectrometer. One way is to reduce the noise level is to use a Fourier Transform Infrared Spectrometer.
9.2.1 Detection Limits — 10 ppm (mol/mol) carbon tetrafluoride, 1000 ppm (mol/mol) hydrogen fluoride, 10 ppm (mol/mol) silicon tetrafluoride and 10 ppm (mol/mol) sulfur hexafluoride.
9.2.2 Instrument Parameters
9.2.2.1 Cell path length: 10 cm
9.2.2.2 Sample Cell Pressure: 1 atmosphere
9.2.2.3 Wavenumbers:
Table 4 Wavenumber of ChemicalsComponent / Wavenumber (cm-1)
Carbon Tetraflouride (CF4) / 1283
Hydrogen Fluoride (HF) / 4076
Silicon Tetrafluoride (SiF4) / 1029
Sulfur Hexafluoride (SF6) / 948
9.2.3 Calibration Standards — 1% (mol/mol) hydrogen fluoride in tungsten hexafluoride, 20 ppm (mol/mol) silicon tetrafluoride in nitrogen, 20 ppm (mol/mol) each carbon tetrafluoride and sulfur hexafluoride in nitrogen.
9.2.4 Operating Procedures
9.2.4.1 Flow each calibration gas through the system for 1 minute. Pressurize the cell to 1 atmosphere. Record the absorbance of each calibration standard at the wavenumber listed in ¶ 9.2.2.3.
9.2.4.2 Flow the sample gas through the system for 1 minute. Pressurize the cell to 1 atmosphere. Record the absorbance at each of the appropriate wavenumbers. Calculate the concentration of each gas, using the formula below. The results may not exceed the specification in table 1 of this standard.
(2)
NOTE 2: Tungsten hexafluoride interferes with the direct absorbance reading for silicon tetrafluoride. The absorbance for silicon tetrafluoride is determined by compensating for the interfering absorbance from the tungsten hexafluoride. Compensation is made by subtracting the absorbance contributed to this band by tungsten hexafluoride band at 930 cm-1. This absorbance is halved and subtracted from the total peak absorbance at 1040 cm-1, resulting in the peak absorbance for silicon tetrafluoride.
NOTE 3: Actual detection limits will be determined by the noise level and the resolution of the spectrometer. One way is to reduce the noise level is to use a Fourier Transform Infrared Spectrometer.
NOTE 4: All gases used in the analysis of the sample should not contain more than 10% of the specified value of the component of interest, unless otherwise stated.
NOTE 5: As tungsten hexafluoride has a low vapor pressure, the cylinder should be kept at room temperature (20°C) for at least 8 hours prior to analysis.
NOTE 6: Observe proper safety procedures for handling and disposing of tungsten hexafluoride.
NOTE 7: Prior to introducing tungsten hexafluoride purge the sample lines and instrument tubing with helium to remove moisture.
NOTE 8: Upon completing the analysis, cap off the manifold and instrument lines or purge the system with helium.
Figure 1
Setup for Position 1
Figure 2
Setup for Position 2
10 Analytical Procedures for Tungsten Hexafluoride, 99.997% Purity
NOTE 9: All gases used in the analysis of the sample should contain not more than 10% of the specified value of the component of interest unless otherwise specified.
10.1 Carbon Tetrafluoride, Silicon Tetrafluoride, Carbon Dioxide, and Sulfur Hexafluoride — This procedure is for the determination of carbon tetrafluoride, silicon tetrafluoride, carbon dioxide, and sulfur hexafluoride in tungsten hexafluoride using a gas chromatograph equipped with a helium ionization detector. A backflush is used in order to protect the detector from the main component.
10.1.1 Detection Limits — 0.3 ppm (mole/mole) carbon tetrafluoride, 1 ppm (mole/mole) silicon tetrafluoride, 0.1 ppm (mole/mole) carbon dioxide, and 0.5 ppm (mole/mole) sulfur hexafluoride.
10.1.2 Instrument Parameters
10.1.2.1 Columns:
· Column 1: 10% Kel F Nr10 on Chromosorb® T, 4.0 m (13 ft) by 3.2 mm (1/8 in) nickel or equivalent,
· Column 2: Preconditioned HAYESEP® Q, 60/80 mesh, 3 m (10 ft) by 3.2 mm (1/8 in) or equivalent. The column should be treated by repeated WF6 sample injections at 125°C.
10.1.2.2 Carrier Flow — 26 mL/min helium, 6.0 grade.
10.1.2.3 Temperatures:
· Detector: 50°C
· Column Oven: 50°C
10.1.2.4 Sample Volume — 2 mL
10.1.2.5 Calibration Standards — 1 and 2 ppm (mole/mole) carbon tetrafluoride, carbon dioxide, and sulfur hexafluoride in helium (see Figures 3 and 4). 2 ppm silicon tetrafluoride in helium or permeation device (see Figure 5).
10.1.3 Operating Procedure
10.1.3.1 Attach a suitable pressure regulator to the standard cylinders. Connect the regulator to the dedicated WF6 handling system which is connected to the chromatographic sampling valve.
10.1.3.2 Purge the sampling lines with the standard for at least one minute.
10.1.3.3 Inject the standard into the gas chromatograph. Record the retention times and peak areas. Order of elution for the above mentioned standard is carbon tetrafluoride, silicon tetrafluoride, carbon dioxide, and sulfur hexafluoride.
10.1.3.4 Inject the WF6 sample to be analyzed in the same manner as the calibration standard. Record the retention times and peak areas.
10.1.3.5 Compare the average peak areas of the calibration standard to that of the detected peak in tungsten hexafluoride. Calculate the concentration of each impurity using the standard and sample peak areas and the standard concentration. The results may not exceed the specifications in table 1.
10.2 Oxygen and Argon, Nitrogen, and Carbon Monoxide — This procedure is for the determination of oxygen and argon, nitrogen, and carbon monoxide in tungsten hexafluoride using a gas chromatograph equipped with a helium ionization detector. A backflush is used in order to protect the detector from the main component.
10.2.1 Detection Limits — 5 ppm (mol/mol) oxygen + argon, 5 ppm (mol/mol) nitrogen, and 1 ppm (mol/mol) carbon monoxide.
10.2.2 Instrument Parameters
10.2.2.1 Columns:
· Column 1: 10% Kel F Nr 10 on Chromosorb® T, 4.0 m (13 ft) by 3.2 mm (1/8 in) nickel or equivalent.
· Column 2: Preconditioned HAYESEP® Q, 60/80 mesh, 3 m (10 ft) by 3.2 mm (1/8 in) or equivalent. The columns should be treated by repeated WF6 sample injections at 125°C.
· Column 3: Molecular sieve 5 A, 60/80 mesh, 2 m (6 ft) by 3.2 mm (1/8 in).
10.2.2.2 Carrier Flow — 26 mL/min helium, 6.0 grade.
10.2.2.3 Temperatures:
· Detector: 50°C
· Column Oven: 50°C
10.2.2.4 Sample Volume — 2 mL
10.2.2.5 Calibration Standards — 1 and 2 ppm (mole/mole) oxygen, nitrogen, and carbon monoxide in helium (see Figure 6).