Background Statement for SEMI Draft document 4657B NEW STANDARD: SPECIFICATIONS FOR TUNGSTEN HEXAFLUORIDE (WF 6 ) 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 knguyen@semi.org
SEMI Draft Document 4657B NEW STANDARD: SPECIFICATIONS FOR TUNGSTEN HEXAFLUORIDE (WF 6 ) 1 Purpose 1.1 The purpose of this document is to provide specifications for tungsten hexafluoride (WF 6 ) 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. Page 1 Doc. 4657B SEMI
Table 1 Impurity and Other Requirements for Tungsten Hexafluoride (WF 6 ) Previous SEMI Reference # C3.26-0301 (Specification) C3.52-0200 (Specification) Grade 99.9% 99.997% Impurities Maximum Acceptable Level (ppm) #1 Carbon Tetrafluoride (CF 4 ) 10 1 Carbon Dioxide (CO 2 ) -- 1 Carbon Monoxide (CO) -- 1 Hydrogen Fluoride (HF) 1000 20 Nitrogen (N 2 ) 50 5 Oxygen (O 2 ) + Argon (Ar) 50 1 Sulfur Hexafluoride (SF 6 ) 10 1 Silicon Tetrafluoride (SiF 4 ) 10 1 TOTAL LISTED IMPURITIES 1130 31 Impurities Maximum Acceptable Level (ppm w) Cobalt (Co) & Manganese (Mn) -- 0.01 Lead (Pb) -- Chromium (Cr), Zinc (Zn), & Uranium (U) -- 0.02 0.05 Calcium (Ca) & Magnesium (Mg) -- 0.10 Nickel (Ni), Copper (Cu), Sodium (Na), & Potassium (K) -- 0.15 Iron (Fe) -- Thorium (Th) -- Molybdenum (Mo) -- 0.02 0.1 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 (WF 6 ) Table 2 Properties of Tungsten Hexafluoride (for information only) Metric Units US Units CAS # 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/m 3 0.805 lb/ft 3 Specific gravity of gas 10.8 10.8 Density of liquid at boiling point 3440 kg/m 3 214.8 lb/ft 3 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. Page 2 Doc. 4657B SEMI
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 Run Time 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. Sample Peak Area Standard Peak Area Concentration of Standard = Concentration of Sample (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. Page 3 Doc. 4657B SEMI
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 Chemicals Component Wavenumber (cm -1 ) Carbon Tetraflouride (CF 4 ) 1283 Hydrogen Fluoride (HF) 4076 Silicon Tetrafluoride (SiF 4 ) 1029 Sulfur Hexafluoride (SF 6 ) 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. Measured Absorbance of the Sample Measured Absorbance of the Standard Concentration Concentration = of Standard of Sample (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. Page 4 Doc. 4657B SEMI
Figure 1 Setup for Position 1 Helium Carrier Porapak Column Vent MS5A Column Sample Out Sample In T.C. DET Position Position 2: 1: V1 Sample is turned is purging through loop Sample Porapak flows S column through is backflushing sample loop to the Porapak MS5A column S column connected and then to to detector MS5A column Figure 2 Setup for Position 2 Page 5 Doc. 4657B SEMI
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 WF 6 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 WF 6 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 WF 6 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 Page 6 Doc. 4657B SEMI
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 WF 6 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). 10.2.3 Operating Procedure 10.2.3.1 Attach a suitable pressure regulator to the standard cylinder. Connect the regulator to the dedicated WF 6 handling system, which is connected to the chromatographic sampling valve. 10.2.3.2 Purge the sampling lines with the standard for at least one minute. 10.2.3.3 Inject the standard into the gas chromatograph. Switch the valves in order to operate in the same conditions as the WF 6 sample analysis. Record the retention times and peak areas. Order of elution for the above mentioned standard is oxygen and argon, nitrogen, and carbon monoxide. 10.2.3.4 Inject the WF 6 sample in the same manner as the calibration standard. Record the retention times and peak areas. 10.2.3.5 Compare the average peak areas of the calibration standard to that of the detected peak in the tungsten hexafluoride. Calculate the concentration of each impurity using the standard and sample areas and the standard concentration. The results may not exceed the specifications in table 1. 10.3 Hydrogen Fluoride This procedure is for the determination of hydrogen fluoride in tungsten hexafluoride using Fourier Transform Infra Red (FTIR) analyzer. 10.3.1 Detection Limit 0.5 ppm (mole/mole). 10.3.2 Instrument Parameters cell with CaF 2 windows HF band: 4038,8 cm -1 resolution: 2 cm -1 path length: 12 cm 10.3.3 Calibration Standard 20 40 ppm (mol/mol) hydrogen fluoride. Calibrate with low vapor pressure hydrogen fluoride or permeation device. 10.3.4 Operating Procedure Carefully dry the cell before sampling tungsten hexafluoride. Then purge it with tungsten hexafluoride and record the concentration. When it is steady, that means the line is purged and the true hydrogen fluoride concentration is obtained. 10.4 Elemental Impurities This procedure is for the determination of Ca, Co, Cr, Cu, Fe, K, Mg, Mn, Mo, Na, Ni, Pb, Th, U, and Zn in the nonvolatile residue of liquid phases tungsten hexafluoride (WF 6 ) and analyzed by Inductively Coupled Plasma Mass Spectrometry (ICPMS). Page 7 Doc. 4657B SEMI
10.4.1 Detection Limits (ppb wt/wt) Ca: 1.5; Co: 0.1; Cr: 0.8, Cu: 0.5; Fe: 1; K: 1.5; Mg: 0.1, Mn: 0.1, Mo: 0.5; Na: 0.6; Ni: 1; Pb: 0.1; Th, U: 0.01; and Zn: 0.8. 10.4.2 Sampling Apparatus Figure 7 shows the sampling apparatus used for obtaining a liquid phase sample of WF 6. The sampling apparatus consists of: Cylinder Inverter, PFA Vessels, PFA Valves, and PFA Tubing. The whole sampling system is placed inside a hood. 10.4.3 Water At least 18 MΩ DI water should be used for all dilutions, blanks, and washing. 10.4.4 Reagents All reagents are of the highest purity available minimizing background metal contamination. The following reagents are needed to prepare the sample and standards: Aqueous Ammonia, Aqueous HNO 3, Aqueous HF, and NIST traceable ICP standards. 10.4.5 Sampling Liquid Tungsten Hexafluoride 10.4.5.1 Place about 400 ml of DI water in each of the hydrolysis vessels. Obtain the weight of each of the hydrolysis vessels. 10.4.5.2 Assemble the apparatus as shown in Figure 3. Do not tighten the cylinder CGA connection. All PFA parts should be clean and dried prior to assembly. 10.4.5.3 Open valves V2, V3, V4 and V5. Set the house nitrogen pressure to approximately 15 psig (205 kpa). Purge the system with nitrogen for about 15 minutes. TIGHTEN THE CYLINDER CGA CONNECTION. 10.4.5.4 Close V2. The system should now be under pressure. Check for leaks and repair if necessary. 10.4.5.5 Open V1 and evacuate the system for approximately 10 minutes. 10.4.5.6 Close all valves. 10.4.5.7 Fill sample vessel by opening cylinder valve and valve V5. Fill the sample vessel approximately 2/3 full. Close cylinder valve. 10.4.5.8 Close V5. Open V2, V4, and V6. This will carry the WF 6 vapors to the hydrolysis vessel. 10.4.5.9 Purge the system with nitrogen for a few minutes after the WF 6 liquid in the sample cup has totally evaporated. 10.4.5.10 Close all valves. Remove the hydrolysis vessels and weigh the vessels. 10.4.5.11 The weight gain in the hydrolysis vessel will give the weight of the sampled WF 6. Typically the weight gain of the second and third vessels will be less than 1% of the weight gain of the first hydrolysis vessel. 10.4.5.12 Remove the sample vessel and dissolve the residue. 10.4.6 Sample Preparation 10.4.6.1 Add 20 ml DI water to a 100 ml volumetric flask. 10.4.6.2 Open the sample cup and add 5 ml of aqueous ammonia to the cup. 10.4.6.3 Swirl in the cup and place in a 100 ml volumetric flask. Page 8 Doc. 4657B SEMI
10.4.6.4 Add 5 ml Nitric Acid to the cup. 10.4.6.5 Swirl and place in the same 100 ml volumetric flask. 10.4.6.6 Add 5 ml Hydrofluoric Acid to the cup. 10.4.6.7 Swirl and place in the same 100 ml volumetric flask as before. 10.4.6.8 Dilute the solution with DI water up to the mark of the 100 ml volumetric flask. 10.4.6.9 Analyze for metals in the sample. 10.4.7 ICPMS Analysis Procedure 10.4.7.1 This procedure is used to analyze for trace Na, K, Cr, Fe, Th and U using multi point calibration. Other elements can be analyzed using a single point calibration. Elements for which stable standards can not be obtained, can be analyzed using interpolation and a knowledge of the instrument response function. The ICPMS should be calibrated using matrix matched multi-element standards. At least one spiked sample should be analyzed as part of the analytical procedure. The recovery of the spikes should be within ± 25%. At least three standards and a blank should be used for the calibration. Regression based approach should be used to calculate the response factors. The limit of detection (LOD) should be calculated following SEMI C10, Guide for Determination of Method Detection Limits. 10.4.7.2 The concentration of impurities in gas phase WF 6 is given by Conc. in Solution Wt.of Solution Conc. in WF6 = (3) Weight of Sampled WF 6 Figure 3 CF 4 and SF 6 Standards in He Page 9 Doc. 4657B SEMI
Figure 4 CO 2 Standards in He Figure 5 SiF 4 Standard in He Page 10 Doc. 4657B SEMI
Figure 6 O 2, N 2, and CO Standards in He Page 11 Doc. 4657B SEMI
To Vent Hydrolysis Vessels Anti Suckback Vessel V6 V4 PFA Vessel Figure 7 Sampling System for WF 6 V5 V3 V2 V1 Vacuum Pump House Nitrogen NOTICE: SEMI makes no warranties or representations as to the suitability of the standards set forth herein for any particular application. The determination of the suitability of the standard 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. These standards are subject to change without notice. The user s attention is called to the possibility that compliance with this standard may require use of copyrighted material or of an invention covered by patent rights. By publication of this standard, SEMI takes no position respecting the validity of any patent rights or copyrights asserted in connection with any item mentioned in this standard. Users of this standard 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. Page 12 Doc. 4657B SEMI