Semiconductor Equipment and Materials International
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Phone: 408.943.6900, Fax: 408.943.7943
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Background Statement for SEMI Draft Document 5640A
REVISION TO SEMI C23-0708, SPECIFICATIONS FOR BUFFERED OXIDE ETCHANTS
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: Additions are indicated by underline and deletions are indicated by strikethrough.
Background
The document will be revised for its five year review and updated per the committee agreed upon changes.
Ballot Adjudication Information
Task Force Review / Committee AdjudicationGroup: / Analytical Methods TF / NA Liquid Chemicals Committee
Date: / Tuesday, April 1, 2014 / Tuesday, April 1, 2014
Time & Timezone: / 10:00 AM to 12:00 PM Noon (PST) / 1:00 PM to 4:00 PM (PST)
Location: / SEMI Headquarters / SEMI Headquarters
City, State/Country: / San Jose, CA / USA / San Jose, CA / USA
Leader(s): / Frank Parker / ICL
Frank Flowers / FMC / Frank Parker / ICL
Frank Flowers / FMC
Standards Staff: / Michael Tran
408.943.7019
/ Michael Tran
408.943.7019
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 1 Doc. 5640 ã SEMIâ
Semiconductor Equipment and Materials International
3081 Zanker Road
San Jose, CA 95134-2127
Phone: 408.943.6900, Fax: 408.943.7943
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This meeting’s details are subject to change, and additional review sessions may be scheduled if necessary. Contact Standards staff for confirmation.
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Notice: Additions are indicated by underline and deletions are indicated by strikethrough.
SEMI Draft Document 5640A
Revision to SEMI C23-0708, SPECIFICATIONS FOR BUFFERED OXIDE ETCHANTS
1 Purpose
1.1 The purpose of this document is to standardize requirements for buffered oxide etchants used in the semiconductor industry and testing procedures to support those standards. Test methods have been shown to give statistically valid results. Alternative methods may be used as long as they comply with SEMI C1 requirements for method validation. This document also provides guidelines for grades of buffered oxide etchants for which a need has been identified. In the case of the guidelines, the test methods may not have been statistically validated yet.
2 Scope
2.1 The scope of this document is all grades of buffered oxide etchants 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 Limitations
3.1 None.
4 Referenced Standards and Documents
4.1 SEMI Standards and Safety Guidelines
SEMI C1 — Guide for the Analysis of Liquid Chemicals
SEMI C35 — Specifications and Guides for Nitric Acid
4.2 ASTM Standard[1]
ASTM D5127 — Standard Guide for Ultra Pure Water Used in the Electronics and Semiconductor Industry
NOTICE: Unless otherwise indicated, all documents cited shall be the latest published versions.
5 Terminology
5.1 Definition
5.1.1 buffered oxide etchant — any combination of ammonium fluoride and hydrofluoric acid in which the concentrations are expressed in terms of the equivalent relative volumes of 40% ammonium fluoride solution and 49% hydrofluoric acid. In the expression, the relative volumes shall be reduced to a ratio of the smallest whole numbers which properly describes the composition. For example, a 7:1 buffered oxide etchant contains the equivalent of 7 volumes of 40.0% ammonium fluoride and 1 volume of 49% hydrofluoric acid.
6 Composition
6.1 For analytical purposes, the absolute concentrations of ammonium fluoride and hydrofluoric acid corresponding to the above definition shall be calculated according to the following equations.
(1)
(2)
where volume and density are expressed in consistent units and concentration is in weight percent to three significant figures.
6.2 Sample calculation for 7:1 buffered oxide etchant using 40.0% ammonium fluoride, density 1.111 g/mL, and 49.0% hydrofluoric acid, density 1.153 g/mL. The absolute percentage concentration of each component follows:
(3)
7 Tolerances
7.1 The tolerances allowed for the absolute percentage of each of the components of a buffered oxide etchant shall be:
Ammonium Fluoride: / ±0.5%Hydrofluoric Acid: / ±0.15%
7.2 For the example above, the permissible range of concentration for ammonium fluoride shall be 34.8 ± 0.5% and for hydrofluoric acid 6.33 ± 0.15%.
8 Requirements
8.1 The requirements for buffered oxide etchants for Grades 1 and 2 are listed in Table 1.
9 Grade 1 Procedures
9.1 Hydrofluoric Acid — Weigh accurately approximately 4.0 g of sample, transfer to a polyethylene beaker, and dilute with water to about 100 mL. Titrate with standardized 1 N sodium hydroxide. The endpoint may be detected colorimetrically by adding 3 drops of methyl red indicator solution and titrating to a definite yellow (no orange) endpoint. As an alternate method, the endpoint may be detected potentiometrically using an HF resistant pH electrode previously standardized in pH 4 and pH 7 buffers. Titrate to pH 6.5 with continuous stirring. Save the solution for the determination of ammonium fluoride.
(4)
9.2 Ammonium Fluoride — Add 40 mL of neutralized formaldehyde solution (see ¶ 9.2.1) to the solution from the preceding test and stir magnetically for 30 minutes. Titrate with standardized 1 N sodium hydroxide. The endpoint may be detected colorimetrically using 10 drops of phenolphthalein indicator and titrating to a stable pink end point. As an alternative method, the endpoint may be detected potentiometrically using an HF resistant electrode previously standardized in pH 7 and 9 buffers. Titrate to pH 8.5 with continuous stirring.
(5)
9.2.1 Neutralized Formaldehyde Solution — Dilute 20 mL of 37% formaldehyde solution with 20 mL of water and neutralize with 0.1 N sodium hydroxide solution to the phenolphthalein endpoint.
9.3 Trace Elements Contents — Determine the levels of specified trace elements and establish they do not exceed the specification limits using Inductively Coupled Plasma Optical Emission Spectrometry procedure (see SEMI C1).
10 Grade 2 Procedures
NOTE 1: Each laboratory is responsible for verifying the validity of the method within its own operation.Alternative methods may be used as long as they comply with SEMI C1 requirements for method validation
10.1 Hydrofluoric Acid — Weigh accurately approximately 4.0 g of sample, transfer to a polyethylene beaker, and dilute with water to about 100 mL. Titrate with standardized 1 N sodium hydroxide. The endpoint may be detected colorimetrically by adding 3 drops of methyl red indicator solution and titrating to a definite yellow (no orange) endpoint. As an alternate method, the endpoint may be detected potentiometrically using an HF resistant pH electrode previously standardized in pH 4 and pH 7 buffers. Titrate to pH 6.5 with continuous stirring. Save the solution for the determination of ammonium fluoride.
(6)
10.2 Ammonium Fluoride — Add 40 mL of neutralized formaldehyde solution (see ¶ 10.2.1) to the solution from the preceding test and stir magnetically for 30 minutes. Titrate with standardized 1 N sodium hydroxide. The endpoint may be detected colorimetrically using 10 drops of phenolphthalein indicator and titrating to a stable pink endpoint. As an alternative method, the endpoint may be detected potentiometrically using an HF resistant electrode previously standardized in pH 7 and 9 buffers. Titrate to pH 8.5 with continuous stirring.
(7)
10.2.1 Neutralized Formaldehyde Solution — Dilute 20 mL of 37% formaldehyde solution with 20 mL of water and neutralize with 0.1 N sodium hydroxide solution to the phenolphthalein endpoint.
10.3 Chloride — Mix 2.2 mL (2.5 g) of sample with 20 mL of water containing 0.5 g of boric acid. Add 1 mL of nitric acid and 1 mL of silver nitrate reagent solution (see SEMI C1), and allow to stand for 5 minutes. Any turbidity produced shouldshall be no greater than that produced when 0.01 mg of chloride ion (Cl) (see SEMI C1) is treated as the sample.
10.4 Nitrate — To 2 mL of water in a white plastic beaker, add 0.9 mL (1 g) of sample, 1 mL of sulfuric acid,
0.05 mL of 0.01 N (0.002 M) potassium permanganate, mix, and decolorize with sodium arsenite reagent solution (see SEMI C1). Dilute to 50 mL with brucine sulfate reagent solution (see SEMI C1) and mix. Heat the solution in a preheated (boiling water) bath for 10 minutes. Cool rapidly in an ice bath to room temperature. The yellow color of the sample shouldshall be no greater than that produced when 0.01 mg of nitrate ion (NO3) (see SEMI C1) is treated as the sample.
10.5 Phosphate — To a 9 mL (10 g) sample in a platinum dish, add 1 mL of sodium carbonate reagent solution (see SEMI C1) and 40 mL of nitric acid. Evaporate carefully, to prevent spattering, to near dryness. Cool, wash down the sides of the dish with 5 mL of nitric acid, and evaporate to dryness. Repeat the evaporation with nitric acid two times to ensure complete removal of all the fluoride. To the cooled dish, add 25 mL of 0.5 N sulfuric acid to dissolve the residue, warming if necessary. Cool, transfer to a color comparison tube, and add 1 mL of ammonium molybdate reagent solution (see SEMI C1), 1 mL of p-(methylamino)phenol sulfate reagent solution (see SEMI C1), and allow to stand at room temperature for 2 hours. Any blue color shouldshall be no greater than that produced when 0.01 mg of phosphate ion (PO4) (see SEMI C1) is treated as the sample.
10.6 Sulfate — To 23 mL (25 g) of sample, add 10 mL of sodium carbonate reagent solution (see SEMI C1) and heat gently until sample has been volatilized. To the residue, add 5 mL of hydrochloric acid and evaporate to dryness in a hood. Dissolve the residue in 10 mL of water and 1 mL of dilute hydrochloric acid (1 + 19); filter if necessary. Add 1 mL of barium chloride reagent solution (see SEMI C1), mix, and allow to stand for 10 minutes. Any turbidity developed shouldshall be no greater than that produced when 0.05 mg of sulfate ion (SO4) (see SEMI C1) solution is treated as the sample.
10.7 Trace Metals Analysis
10.7.1 The following method has given satisfactory results in determining metal ion impurities at the values specified for each of the following metals: aluminum (Al), antimony (Sb), arsenic (As), boron (B), calcium (Ca), chromium (Cr), copper (Cu), iron (Fe), lead (Pb), magnesium (Mg), manganese (Mn), nickel (Ni), potassium (K), sodium (Na), tin (Sn), titanium (Ti), and zinc (Zn). Alternative methods may be used as long as appropriate method validation as per SEMI C1 can be demonstrated.
10.7.2 Special Reagents
10.7.2.1 Nitric Acid, (SEMI C35, Grade 2)Ultrapure — Use nitric acid specified for low metal ion content.
10.7.2.2 4% Nitric Acid Solution — Dilute 40 mL of ultrapure nitric acid (see § 10.7.2.1) to 1 L using water meeting the criteria for Type E1.1 in ASTM D5127 with regards to metal content.
10.7.2.3 Water — The water used for all the dilution, calibration, and standards shouldshall meet at a minimum the criteria for Type E1.1 in ASTM D5127 in regard to cation analysismetal content.
10.7.2.4 Indium Internal Standard — Make up an indium internal standard solution to a concentration of 20 µg/mL (ppm) from an appropriate concentrated indium standard solution.
10.7.3 Sample Preparation
10.7.3.1 In a clean environment, weigh 10.0 g sample into a cleaned Teflon beaker and evaporate the sample on a 250°C hotplate to near dryness. Carefully add 1 mL of the ultrapure nitric acid (see § 10.7.2.1) and 3 mL of water and gently warm for several minutes. Cool to room temperature, add 25 µL of the indium internal standard, and dilute with Type E1.1 water to a final weight of 25.0 g.
10.7.4 Analysis
10.7.4.1 Using the prepared solutions and blanks, analyze sodium, potassium, calcium, and iron by graphite furnace atomic absorption (GFAA) and the remaining elements by inductively coupled plasma mass spectrometry (ICP/MS). For calibration, the standards are made up in 4% nitric acid solution (see § 10.7.2.2) with final concentration of 20 ng/g of the indium internal standard. Run a reagent blank.
11 Grade 3 Procedures
11.1 This section does not apply to this chemical.
12 Grade 4 Procedures
12.1 This section does not apply to this chemical.
13 Grade 5 Procedures
13.1 This section does not apply to this chemical.
14 Tier A Procedures
14.1 This section does not apply to this chemical.
15 Tier B Procedures
15.1 This section does not apply to this chemical.