Background Statement for SEMI Draft Document 4844C
New Standard: Guide for the Measurement of Trace Metal
Contamination on Silicon Wafer Surface by Inductively Coupled
Plasma Mass Spectrometry
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.
Background
Information about the trace metal on wafer surface is reported in the specification of semiconductor grade silicon as
SEMI M1. On this account, a guide for the trace metal analysis is necessary. However, there has been no document
for trace metal analysis using ICP-MS of semiconductor grade so far. Therefore, this document is proposed. This
document was developed by taking the following steps:
1. Survey by questionnaire
2. Review of current technology
3. Drafting
The survey by questionnaire was conducted from November 2007 to March 2008, and current technology was
reviewed from May 2008 to September 2008. Related information was drafted from September 2008 to December
2008. This document was drafted and improved until October 2009.
The high sensitivity impurity analysis is very important for quality control of silicon wafers for semiconductor
devices. The metal impurities contaminating the silicon wafer surface affects reliability and the device yield. For this
reason, the trace metal analysis has been included in the specifications of the semiconductor grade wafer. Currently,
the Inductively Coupled-Plasma Mass Spectrometry (ICP-MS) technique is mainly utilized for the high sensitivity
impurity analysis. Technique outlined in this guide is intended to guide the measurement of elemental impurity
concentrations in high purity silicon wafer surface by ICP-MS. Also, this document would provide evaluation
technique for semiconductor grade silicon wafer surface quality.
Doc.4844 was submitted for Cycle 1, 2010 and was adjudicated by the Japan Silicon Wafer Committee at their
meeting on March 12, 2010 at SEMI Japan Office. The ballot failed as many reject votes were submitted. Some of
them pointed out that description of the classification of clean room and so on do not match in Doc.4844 . The Japan
Test Method TF had several meeting for discussion about clean room classification, description of relation to SEMI
E45, and change to optimized technical term from April 2010 to September 2010.
Doc.4844A was submitted for Cycle 7, 2010 and was adjudicated by the Japan Silicon Wafer Committee at their
meeting on November at SEMI Japan Office. The ballot failed as a reject vote was submitted. The reject vote
pointed out that the structure of the document is not adequate and the related information 2 is superfluous.
Furthermore, the vote pointed out that quantitative numerical results and brand of the ICP-MS equipment were
insufficient in the related information 1.
The TF had several meeting for revision of Doc.4844A. The structure of the document was changed and section
"limitation" "apparatus" and "calibration" were added. The related information 2 “definition of clean room
classification” was deleted. Then, original data, standard deviation etc. were added to the related information 1.
However, brand or type of the ICP-MS equipment was not described, because analysis conditions at each site were
closed and a description of the brand name was not recommended according to the SEMI standard style manual.
Similarity with SEMI E45 was pointed out at the reject votes in the first and the second vote. Regarding E45 issue,
the "Japan Silicon Wafer committee" had proposed a course of action which the ownership of E45 is moved from
"Metric Committee" to "Silicon Wafer Committee". However, The TF was given the answer the “Metric
Committee” of this issue, which was voted down in “Japan Metric Committee” meeting at April 11th. There were
mainly two reasons. One is the purpose, which is measured for evaluation of environment including the shipping
box (not for wafer quality). Another one is maintainability of document. The TF accepted this decision, because of
comprehension of large impact to Doc.4844 by difference purpose. Then, The TF had decided in the TF meeting to
move forward to establishment of the Doc.4844. Working group added note 1 to Doc.4844A, because a purpose of
Doc.4844 was different from SEMI E45 and more severe pureness of water is required in Doc.4844 than SEMI E45.
After deliberation in Japan Silicon Wafer Committee at September 3rd meeting, The TF will send International Test
Method TF a draft to ask comments not later than September. Doc.4844B was submitted for Cycle 7, 2013 and was
adjudicated by the Silicon Wafer Committee at their meeting on December at SEMI Japan. The ballot failed as a
reject vote was submitted. The reject vote pointed out that the mismatching of the SEMI style manual to use “shall”
for “Guide”. Silicon committee and Int’l Test Method TF member had adjudicated “Fail” for editorial persuasive.
Then, the TF was change the wording from “shall” to “should”.
TF will consider about timeline for Doc.4844C as below. The voting result of Doc.4844C will be reviewed by the
international test method TF and will be adjudicated by the Global Silicon Wafer Committee during their meeting at
SEMICON West 2014 at San Francisco NA.
Review and Adjudication Information
Task Force Review
Group
International Test Method TF
Date
June 2014 (TBD)
Time & Time zone TBD
Location
SEMI Japan Office
City, State/Country Tokyo, Japan
Committee Adjudications
Global Silicon Wafer Committee
Tuesday, July 8, 2014
2:00 p.m. to 5:30 p.m. US Pacific Time
San Francisco Marriott Marquis
San Francisco, CA
Leaders
Ryuji Takeda ([email protected])
Peter Wagner ([email protected])
Dinesh Gupta ([email protected])
Dinesh Gupta ([email protected])
Noel Poduje ([email protected])
Standard staff
Naoko Tejima ([email protected])
Kevin Nguyen ([email protected])
If you have any questions, please contact to the Test Method TF co-leader and its Chemical Analysis Working
Group leader as shown below:
Ryuji Takeda/ [email protected] or
Naoko Tejima, SEMI Japan staff at [email protected]
Semiconductor Equipment and Materials International
3081 Zanker Road
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Phone: 408.943.6900, Fax: 408.943.7943
SEMI Draft Document 4844C
New Standard: Guide for the Measurement of Trace Metal
Contamination on Silicon Wafer Surface by Inductively Coupled
Plasma Mass Spectrometry
1 Purpose
1.1 Reduction of surface metal contamination below a concentration in accordance with the ITRS road map is a key
issue for silicon wafer quality for most of the leading-edge technology applications. This document provides a guide
for a high-sensitivity measurement of trace metal contamination on the surface of a semiconductor grade silicon
wafer by using inductively coupled plasma mass spectrometry (ICP-MS).
1.2 This guide describes the procedure for trace metal measurement, including the metal impurity collection method
from a silicon wafer surface, scanning solution composition, and its optimization. In particularly, the procedure of
the collection method is described in detail because it influences the reliability of measurement data and
reproducibility of each facility.
2 Scope
2.1 This guide describes methods for the measurement of trace metal contamination on a silicon wafer surface. The
decomposition of silicon oxide on silicon wafer, the collection of trace metal contamination from a wafer surface
using mixture acid, measurements, and reports are described in this guide.
2.2 This guide covers an evaluated substrate wafer as a mirror-polished surface, annealed wafer, epitaxial growth
wafer, diffusion wafer, and bonding wafer, which are non-patterned surfaces. However, this document also
addresses the back side of a patterned wafer. Additionally, this guide covers wafers that form native oxides and
thermal oxides.
2.3 In the case of decomposition of silicon oxide on the silicon wafer and contamination collection from the wafer
surface, a procedure with the recommended technique for the vapor phase decomposition (VPD) and the direct acid
droplet decomposition (DADD) methods is presented (See ¶9.1).
2.4 In this document, a scanning solution for collecting metal contamination from wafer surfaces is recommended
for using the solution compositions optimized by ensuring recovery rate with 75-125% (See ¶5.2.3 and ¶9.1.1.1).
Here, the scanning solution consists of hydrofluoric acid and hydrogen peroxide or nitric acid.
2.5 This guide uses only ICP-MS (See ¶7.1) for the measurement of contamination on the wafer surface. The target
elements of this method are sodium, magnesium, aluminum, potassium, calcium, chromium, manganese, iron, cobalt,
nickel, copper, and zinc.
NOTE 1: In this analysis procedure, a mini environment such as a shipping box is used for temporary storage and
transfer of a silicon wafer. To evaluate the trace metal contamination from a mini environment, SEMI E45 should be
used.
NOTICE: This standard does not purport to address safety issues, if any, associated with its use. It is the
responsibility of the users of this standard to establish appropriate safety and health practices and determine the
applicability of regulatory or other limitations prior to use.
3 Limitations
3.1 Interference of Polyatomic Ions ― Polyatomic ions of atmospheric components, acid in the sample solution and
argon - since argon gas is used for forming inductively coupled plasma - are produced in the plasma. In addition,
polyatomic ions of silicon are produced when the sample solution contains a silicon matrix. These polyatomic ions
interfere with the measurement of the target element, for example, 40Ar16O on 56Fe, 38ArH on 39K, and 29Si19F on 48Ti.
Therefore, the interference of polyatomic ions should be suppressed by the cool plasma method, the
collision/reaction cell or a double focusing sector field ICP-MS (high resolution ICP-MS).
3.2 Matrix effects ―The scanning solution collected from the silicon wafer contains the silicon matrix. The
sensitivity of ICP-MS decreases when the sample solution contains too high-concentration silicon matrix. In that
case, the internal standard method, the standard addition method or the removal of the silicon matrix should be
utilized; measurements without the matrix effects would then be possible.
3.3 In the case of the removal of the silicon matrix, considerable attention should be paid to loss by volatilization,
production of precipitates, and contaminations from the environment.
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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4 Referenced Standards and Documents
4.1 SEMI Standards
SEMI C1 ― Guide for Analysis of Liquid Chemicals
SEMI E45 — Test Method for the Determination of Inorganic Contamination from Minienvironments using Vapor
Phase Decomposition-Total Reflection X-ray Spectroscopy (VPD/TXRF), VPD-Atomic Absorption Spectroscopy
(VPD/AAS), or VPD/Inductively Coupled Plasma-Mass Spectrometry (VPD/ICP-MS)
4.2 ISO Standards1
ISO 17331:2004. Surface chemical analysis — Chemical methods for the collection of elements from the surface of
silicon-wafer working reference materials and their determination by total-reflection X- ray fluorescence (TXRF)
spectroscopy
ISO 14644-1:1999. Clean rooms and associated controlled environments — Part 1: Classification of air cleanliness
ISO 8655-2 — Piston-operated volumetric apparatus — Part 2: Piston pipettes
ISO 8655-6 — Piston-operated volumetric apparatus — Part 6: Gravimetric methods for the determination of
measurement error
4.3 JIS Standards2
JIS K0133 — General rules for frequency plasma mass spectrometry
NOTICE: Unless otherwise indicated, all documents cited should be the latest published versions.
5 Terminology
5.1 Abbreviations and Acronyms
5.1.1 ICP-MS — Inductively Coupled Plasma Mass Spectrometry
5.1.2 VPD — Vapor Phase Decomposition
5.1.3 DADD — Direct Acid Droplet Decomposition
5.2 Definitions
5.2.1 scanning solution — scanning solution implies a solution for the collection of trace metals from a wafer
surface after the decomposition of silicon oxide by the VPD method. On the other hand, it also implies the solution
for the decomposition of silicon oxide and the collection of trace metals from a wafer surface by the DADD method.
5.2.2 VPD box — the VPD box is an airtight container composed of acid-resisting materials (e.g.,
polytetrafluoroethylene and polyfluoroalkoxyethylene) and equipped with wafer stands.
5.2.3 recovery rate — the recovery rate is the ratio (B/A) of the quantity (B) of the measured element to the
quantity (A) of the element that is included in a sample, i.e., the quantity (A) of the added element. The recovery
rate is expressed as a percentage.
5.2.4 cool plasma — the method to reduce interference of polyatomic ions of mainly argon origin by plasma
generated with the low high-frequency power or high carrier gas flow quantity.
5.2.5 collision/reaction cell — the collision/reaction cell is a system to reduce the interference that polyatomic ions
cause. Interference of polyatomic ions is reduced by the interaction between ions and gas (hydrogen, helium,
ammonia, etc.) introduced into a cell.
6 Summary
6.1 In this guide, sample preparation methods such as the collection of trace metal contamination from wafer
surface and measurement methods for the collected contamination are described. A simple flowchart of this guide is
shown in Figure 1.
1
International Organization for Standardization, ISO Central Secretariat, 1 rue de Varembé, Case postale 56, CH-1211 Geneva 20, Switzerland.
Telephone: 41.22.749.01.11; Fax: 41.22.733.34.30; http://www.iso.ch;
2
Japanese Industrial Standards, Available through the Japanese Standards Association, 1-24, Akasaka 4-Chome, Minato-ku, Tokyo 107-8440,
Japan. Telephone: 81.3.3583.8005; Fax: 81.3.3586.2014; http://www.jsa.or.jp
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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Wafer set up
Sample preparation
Decomposition of silicon oxide
Collection of contamination from wafer surface
Measurement
Calibration curve
Determination of trace metal by ICP-MS
Calculation
Report
Figure 1
Flowchart of Contamination Analysis Procedure of Silicon Wafer Surface
6.2 Sample Preparation — This guide specifies two methods for the collection of contamination; the VPD method
and the DADD method. In the VPD method, silicon oxide is decomposed by hydrofluoric acid vapor and the
contamination is collected from the wafer surface using the scanning solution droplet. On the other hand, in the
DADD method, silicon oxide is decomposed using the scanning solution droplet, and the contamination is collected
from the wafer surface using the droplet.
6.3 Measurement — After the sample preparation, the trace metal contamination in the sample solution is
determined by ICP-MS.
7 Apparatus
7.1 There are two types of the instruments of ICP-MS. One is a quadrupole ICP-MS and the other is a high
resolution ICP-MS. Either type of ICP-MS can be used for this guide.
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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Ion Source Interface Ion lens
Sample
Introduction
System
Mass
Spectrometer
Detector
Plasma
Carrier gas
Sample
Figure 2
Schematic Diagram of ICP-MS Instrument
Typical System of ICP-MS
7.2 ICP-MS consists of a sample introduction system, an ion source, a sampling interface, ion lens, a mass
spectrometer and a detector.
7.3 Clean Booth — The environment in a clean booth should be better than ISO class 5 (See ISO 14644-1). A clean
booth should have a local exhaust system.
7.4 VPD Box — see ¶5.2.2
7.5 Automatic Scanning Equipment — The automatic scanning equipment should have mechanism to hold and scan
a scanning solution droplet. Scan of a droplet can be carried out by manual operation instead of the automatic
equipment.
7.6 Tweezers: Vacuum Tweezers and Manual Tweezers — Particulate emission from the tweezers should be low.
7.7 Micro pipette — a micropipette should be validated according to ISO 8655-2, ISO 8655-6.
8 Reagents and Materials
8.1 Ultra-pure Water — Ultra-pure water containing less than 1 pg/ml of each of the impurities, i.e., sodium,
magnesium, aluminum, potassium, calcium, chromium, manganese, iron, cobalt, nickel, copper, and zinc, is used.
This is as per ISO17331.
8.2 Ultra-pure Acid — Acid for the scanning solution (e.g., hydrofluoric acid and hydrogen peroxide) containing
less than 10 pg/ml of each of the following impurities: sodium, magnesium, aluminum, potassium, calcium,
chromium, manganese, iron, cobalt, nickel, copper, and zinc, should be used.
8.3 Hydrofluoric Acid for VPD Process — The purity of hydrofluoric acid could be degraded to less than 100 pg/ml
for each of the impurities such as sodium, magnesium, aluminum, potassium, calcium, chromium, manganese, iron,
cobalt, nickel, copper, and zinc, because the hydrofluoric acid vapor used in the VPD process is purified after
vaporizing.
8.4 Commercial Scanning Solution — Recently, the scanning solution has been commercially traded for silicon
wafer surface analysis. When the commercial scanning solution is used, it should contain less than 10 pg/ml of each
of the following impurities: sodium, magnesium, aluminum, potassium, calcium, chromium, manganese, iron, cobalt,
nickel, copper, and zinc.
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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NOTE 2: As far as possible, acid of the highest purity should be used for the scanning solution with the aim of decreasing the
detection limit.
9 Principle of Collection Method
9.1 Decomposition of Silicon Oxide and Collection of Contamination — In this section, the VPD and DADD
methods are described. Each method should be selected on the basis of the purpose and analysis environment. The
consistency between both sides is described in Related Information 1.
9.1.1 VPD Method — In the VPD method, silicon oxide is decomposed by exposure to hydrofluoric acid vapor;
subsequently, trace metals are collected into a high-purity acid droplet that is scanned completely or through any
part of the silicon wafer. The droplet is scanned manually or using automatic scanning equipment. The automatic
equipment can be expected to have a better repeatability than the manual collection because of a reduced
contamination risk by the operator. Scanning condition such as the volume of the scanning solution, scanning speed,
and number of scans required should be optimized by using the intentionally contaminated sample in order to satisfy
the criterion of the recovery rate. The schematic illustration of the VPD method is shown in Figure 2.
Silicon oxide
Silicon wafer
HF vapor
Silicon oxide
with residual
Silicon wafer
Pipette
Silicon wafer
Pipette
Recovery by scanning
Silicon wafer
Figure 3
Outline of Sample Preparation in VPD Method
9.1.1.1 Preparation of Scanning Solution — Metal impurities are dissolved in the droplet of the scanning solution
on the silicon wafer surface after the VPD process. In this process, noble metals such as copper, which have weak
ionization tendencies, is easy to re-adhere to the silicon surface because of the oxidation-reduction interaction.
Therefore, a mixture of acid and an oxidizing agent should be used as the scanning solution in order to improve the
recovery rate by accelerating the ionization of copper with a high oxidation-reduction voltage of the solution. The
mixture of several percent hydrofluoric acid and several percent hydrogen peroxide, or the mixture of several
percent hydrofluoric acid and several percent nitric acid is a representative example of the scanning solution. For
example, a mixture of 2% hydrofluoric acid and 2% hydrogen peroxide is used for the collection of iron and nickel
in ISO17331. This composition was also used in the review of current technology in this guide, and the difference of
measurement values of iron among the sites was small (See Related Information 1). However, in the measurement of
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.
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noble metals such as copper, the scanning solution composition should be optimized carefully. In some cases,
increase in the concentration of an oxidizing agent such as hydrogen peroxide or nitric acid may be required, or a
change in other analysis conditions such as scanning speed may be required. Suitable analysis conditions depend on
the automatic scanning system, wafer surface condition, etc. The composition of the scanning solution should be
optimized to satisfy a defined criterion for the recovery rate of each measurement elements. The criterion for
recovery rate is fulfilled if the recovery rate is in the range of 75 - 125 %. The procedure for the determination of the
recovery rate is described in Appendix 1. The scanning solution can be prepared from commercial ultra-high purity
reagents. Contamination control for a clean room, vessels, and equipment should be performed routinely. In order to
determine the background level of trace metal contaminants, their amounts in the scanning solution should be
evaluated by the ICP-MS technique in the same manner as this test method.
NOTE 3: The composition of the scanning solution is an important parameter for the comparison of measurement data between
facilities. It should be referred to if necessary.
9.1.2 DADD Method — In the DADD method, silicon oxide is decomposed using a high purity acid droplet. Silicon
oxide and trace metals are simultaneously collected. In general, the droplet is scanned on the entire wafer surface
after decomposition. The schematic of the DADD method is shown in Figure 3.
Silicon oxide
Silicon wafer
Pipette
Pipette
Self-recovery
Figure 4
Outline of Sample Preparation in DADD Method
9.1.2.1 Preparation of Scanning Solution — The scanning solution for the DADD method should be composed of
hydrofluoric acid and other acids because of the decomposition of silicon oxide. The concentration of hydrofluoric
acid should be optimized along with the thickness of silicon oxide. Preparation except the concentration of
hydrofluoric acid is same as ¶9.1.1.1.
10 Procedure
10.1 VPD Method
10.1.1 Environment — The operation consists of sample preparation and measurement by using ICP-MS. Sample
preparation should be carried out in a clean draft having a local exhaust system. The wafer should be placed in the
environment that is better than ISO class 5 (See ISO 14644-1) during sample preparation, in order to eliminate
contamination from an environment. Furthermore, the sample solution should be placed in an environment that is
better than ISO class 5 during a measurement by ICP-MS.
10.1.2 Wafer Handling and Storage — The sample wafer should be handled with gloves by using metal-free
tweezers or vacuum tweezers to avoid contamination and direct contact. The sample wafer should be stored in
closed containers (e.g., wafer shipping box).
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.
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10.1.3 Decomposition of Native Oxide and Thermal Oxide — Take hold of a silicon wafer backside by a vacuum
tweezer. Place the silicon wafer in the VPD box under clean environments such as the interior of a clean draft.
Expose the surface of the silicon wafer to hydrofluoric acid vapor till native or thermal oxides were completely
decomposed. Determine a processing time for complete decomposition of silicon oxides in advance.
10.1.4 Collection of Trace Metal Contamination — Place the droplet of the scanning solution on the analytical
surface by a micro pipette or automatic scanning equipment. Scan the analytical surface with the droplet manually or
automatically. Collect the droplet by a micro pipette or automatic scanning equipment.
10.1.5 Post-collection Process
10.1.5.1 Put the scanning solution collected from the wafer surface into a sample cup by a micropipette or
automatic scanning equipment. If the volume of the scanning solution does not reach quantity to be necessary for the
measurement, add ultra-pure water or scanning solution of enough volume to a sample cup.
10.1.5.2 If the removal of the silicon matrix is required, put the scanning solution collected from the wafer surface
into a PTFE or PFA beaker, vessel, etc. Heat the scanning solution to dryness. Add a dilute acid, for example several
percent nitric acid, and resuspend. Transfer the solution to a sample cup.
10.1.6 Measurement — Introduce the solution into a nebulizer from a sample cup and measure the ion intensity by
ICP-MS.
10.1.7 Method Blank — For the monitoring of contamination from the analytical environment, scanning solutions
and periphery analytical tools, prepare the method blank solution through the same processes. Here, prepare the
method blank solutions by scanning high-purity wafers. Otherwise, use the scanning solutions as the method blank
solutions.
NOTE 4: In case of being a likelihood of the influence of silicon matrix on the measurement, this affect should be removed.
NOTE 5: The method blank is an important parameter for comparison of measurement data between facilities. It should be
referred to if necessary.
10.2 DADD Method
10.2.1 Environment — Same as ¶10.1.1.
10.2.2 Wafer Handling and Storage — Same as ¶10.1.2.
10.2.3 Decomposition of Native Oxide and Thermal Oxide — Place a sample wafer on the wafer stand in the clean
draft. Place a droplet of the scanning solution (approximately 100 μl-1000 μl) on the surface of the sample wafer
using a micropipette. Wait until oxides are completely decomposed and the droplet stops.
10.2.4 Collection of Trace Metal Contamination — After the droplet has stopped sweeping, scan the entire surface
with the droplet Collect the scanning solution using a micro pipette. If the droplet of the scanning solution is too
small to be collected, add ultra-pure water before collecting the scanning solution.
10.2.5 Post-collection Process — Same as ¶10.1.5.
10.2.6 Measurement — Same as ¶10.1.6
10.2.7 Method Blank — Same as ¶10.1.7
NOTE 6: The sample cup should be handled with gloves, and the sample solution after pretreatment should not be touched.
Since the amounts of liquid sample are reduced, and since trace metals adhere to the inside of the sample cup when stored, the
sample solution should not be stored for long durations, and it should be measured soon.
11 Calibration
11.1 The sensitivity of the ICP-MS instrument is confirmed using a chemical reagent that contains elements for
adjustment. A reagent for adjustment containing elements with low atomic weight (e.g., lithium, magnesium),
medium atomic weight (e.g., cobalt, indium, barium), and high atomic weight (e.g., lead, uranium) needs to be used.
In addition, it is desirable that potassium and iron are contained for the confirmation of the interface of polyatomic
ions. First, the plasma supply is started, and the reagent for adjustment is introduced after stabilization. The RF
power, blowtorch position, ion lenses, and gas flow quantity are optimized while monitoring the ion counts of the
element during the adjustment.
11.2 Calibration Curve ― Calibration standard solutions with several levels of concentration and containing the
measurement elements are prepared. Further, a calibration blank solution is prepared. Each of these calibration
standard solutions and calibration blank solution are then measured. Subsequently, the concentrations of the
elements in the solutions are plotted on the horizontal axis whereas the measured ion counts are plotted on the
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vertical axis. The composition of the calibration standard solutions and calibration blank solution should be the same
as that of the sample solution.
NOTE 7: The calibration curve is an important parameter for comparison of measurement data between the facilities. It should
be referred to if necessary.
12 Calculation
12.1 Quantification of Measurement Element ― The results of the ICP-MS measurement of a sample solution
collected from the wafer surface are provided as ion counts. The measured ion counts can be converted to the
concentration of the measurement elements using the related calibration curve.
12.1.1 The concentration of the sample solution should be included in the effective area of the calibration curve. In
particular, the concentration levels of the standard solution should be included in the concentration of the sample
solution. However, in many cases, the concentration of the trace metal on the silicon wafer surface is lower than the
detection limit. The concentration of the low level standard solution should be prepared as low a value as possible.
The calibration blank solution, calibration standard solution, and the sample solutions contain impurities from their
chemical reagents. In addition, the sample solutions are contaminated during sample preparation. Therefore, these
contaminations should be adequately deducted by using the method blank solutions.
12.2 Calculation Method ― Calculate the atomic surface density of the target elements by using the following
equation, which is expressed in atoms per square centimeter (atoms/cm2):
wv
 NA
M
N
S
(1)
Here, N is the atomic surface density, w; the concentration of the target elements in the sample solution that is
expressed in weight per unit volume; v, the volume of the sample solution; M, the atomic weight of the target
element; NA, the Avogadro constant; and S, the measurement area of the silicon wafer surface.
12.3 Determination of detection limit and quantification limit
12.3.1 The detection limit is determined using the following equation:
Detection Limit = k × SD/ s,
(2)
where,
SD is the standard deviation of the intensity of the method blank solutions. It is desirable to measure ten method
blank solutions.
s is the slope of the calibration curve.
k is a coefficient. In the past, several coefficients have been proposed. For example, k=3 has been used in JIS
K0133. On the other hand, k=3.29 has been recommended in the IUPAC Compendium of Chemical Terminology
2nd Edition. It is possible to use k=3, 3.29, or some other value. However, if a user requests, the calculation method
should be shown.
NOTE 8: Detection limit is an important parameter for comparison of measurement data between facilities. It should be referred
to if necessary.
12.3.2 Similarly, the quantification limit is determined by using the following equation:
Quantification Limit = k ×SD/ s,
(3)
where,
SD is the standard deviation of the intensity of the method blank solutions. It is desirable to measure ten method
blank solutions.
s is the slope of the calibration curve.
k is a coefficient. k=10 has been used in JIS K0133. Further, k=10 or some other value can be used. However, if a
user requests, the calculation method should be shown.
NOTE 9: Quantification limit is an important parameter for comparison of measurement data between the facilities. It should be
referred to if necessary.
13 Report
13.1 The following information should be reported:
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13.1.1 Sample identification
13.1.2 Decomposition of silicon oxide
13.1.2.1 Method (VPD or DADD)
13.1.2.2 Decomposition time
13.1.3 Collection of surface metal contamination
13.1.3.1 Method (Manual or Auto)
13.1.3.2 Collection area
13.1.4 Analysis results (unit: atoms/cm2)
13.1.4.1 Analysis date
13.1.4.2 Values of target metals
13.1.4.3 Detection limit of each target metal
13.2 The report details should be determined between the related parties
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APPENDIX 1
DETERMINATION OF RECOVERY RATE
NOTICE: The material in this appendix is an official part of SEMI (doc#) and was approved by full letter ballot
procedures on (date of approval).
A1-1 Methods for Determining the Recovery Rate
A1-1.1 The recovery rate is influenced by sample preparation conditions such as composition of the scanning
solution and scanning speed of a droplet. Therefore, the recovery rate should be confirmed in advance, and the
conditions for sample preparation should be adjusted such that the criterion for the recovery rate is satisfied; the
criterion is that the recovery rate should be within 75%–125%, according to SEMI C1-0705. Methods for
determining the recovery rate employ the following three procedures:
 Procedure A — Based on SEMI C1. Target elements of known concentration are spiked on the surface of clean
wafers. Element-spiked wafers and clean wafers are analyzed by using the proposed test method. The recovery
rate of the test method is determined using the following equation:
Recovery rate (%) = (Amount of target element on “spiked wafer” —Amount of target element on “clean
wafer”) / Spiked amount of target element × 100
(1)
Several methods are available for preparing a spiked wafer; for example, a droplet containing a known
concentration of the target elements is dropped on the wafer surface and dried. On the other hand, commercial
“element-spiked” wafers can also be used.
 Procedure B — Target elements of unknown concentrations are spiked on the surface of wafers. They are
collected from the surface of the spiked wafers and measured by ICP-MS using the proposed standard guide.
This collection is repeated N times. After the collection, the recovery rate of the guide is determined using the
following equation:
Recovery rate (%) = Amount of target element in “1st measurement” / Amount of target element in “total
amount of N times measurement” × 100
(2)
There exist some well-known methods for preparing a spiked wafer with a spiked wafer with unknown
concentrations of the target elements, for example, the IAP method. In this method, wafers are dipped in a
mixture of aqueous ammonia and hydrogen peroxide solution including the target element at a constant time.
Instead of dipping, spinner equipment could be used to spread the solution including the target element evenly
on the wafer surface.
 Procedure C — Target elements of unknown concentration are spiked on the surface of the wafers. The target
elements are collected from the surface of the spiked wafers and measured by ICP-MS using the proposed
standard guide. The collection is repeated twice. After the collection, the recovery rate of the guide is
determined using the following equation:
Recovery rate (%) = (Amount of target element in “1st measurement” — Amount of target element in “2nd
measurement”) / Amount of target element in “1st measurement” × 100
(3)
In procedure C, it is assumed that the second recovery rate is identical to the first one. Therefore, if the second
recovery rate is different from the first one, this procedure cannot be applied.
In procedures A, B and C, the recovery rates of all measurement elements should be determined because the
recovery rates of individual elements may differ.
NOTE 1: Procedures B and C are not according to SEMIC1-0705 and other SEMI standard. However, these procedures are
adopted in this guideline as well as in procedure A because they can generally be used in wafer surface analysis of trace metals.
NOTE 2: The recovery rate is an important parameter for comparison of measurement data between facilities. It should be
referred to if necessary.
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RELATED INFORMATION 1
QUESTIONNAIRE AND REVIEW OF CURRENT TECHNOLOGY
NOTICE: This related information is not an official part of SEMI (doc#) and was derived from (origin of
information). This related information was approved for publication by (method of authorization) on (date of
approval).
R1-1 Implementation of Questionnaire
R1-1.1 A technical questionnaire survey was conducted in various companies and institutions for an analysis aimed
at the effective preparation of this guide. The results of this survey demonstrated the necessity (around 80%) of
publishing a document related to the measurement of impurities on a silicon wafer surface. The outline of this
questionnaire lists both general and detailed items such as the nature of business, objective, analysis environment,
chemical solution, analytical data, and detection limit. Many questionnaire respondents were in good agreement over
several items (e.g., the level of cleanliness in the analysis environment and the ultra-pure water). Further, slightly
different viewpoints were found on decisions about the detection limit and method blanks. However, the basic
measurement procedure was unaffected by these differences. On the other hand, the responses about the composition
of the scanning solution were largely varying; this composition is discussed in the next section.
R1-2 Review of Current Technology
R1-2.1 Purpose of This Review
R1-2.1.1 The scanning solution comprises acid for collecting the impurities on the silicon wafer surface. Recently,
as a result of the development of an automatic scanning system, a commercial scanning solution came to be used
with the VPD method. As of April 2009, the available commercial scanning solutions are of the following two
types:

HF 2% + H2O2 2%
 HF 1% + H2O2 3%
Furthermore, improvements in the measurement of impurities on a wafer surface have been made at each site by
following the technical road map for semiconductors. For instance, because it was difficult to collect copper from
the wafer surface, valid scanning solutions were developed to improve the recovery rate at each site. Therefore, at
present various compositions for the scanning solution are used at each site. For establishing this guide, it had to be
investigated whether the differences in the scanning solution influenced the measurement result. Therefore, review
of current technology was performed by using intentionally contaminated wafers at several sites.
R1-2.2 Procedure of This Review
R1-2.2.1 This review was performed as described below. The types of scanning solutions used are listed in Table
R1-1. Three types of scanning solutions were adopted at each site - two typical commercial solutions (See ¶R1-2.1)
and the original solution. The composition of solution 3 was different at each site, and these compositions were
closed. The usual analysis conditions (e.g., decomposition time, volume of droplet of the scanning solution,
scanning speed, and repetition of scan) were adopted at each site in this review. Moreover, it was decided to
measure the impurities using ICP-MS with selecting the equipment maker freely. Eight laboratories participated in
this test. Intentionally contaminated samples were prepared and these samples were sent to each site. Further, the
time-dependence shift of the contamination level was monitored by measuring the contamination level of the
intentionally contaminated wafers at regular intervals. Furthermore, accidental contamination was confirmed by
measuring the blank wafers at each site.
Table R1-1 Scanning Solutions Used in Review of Current Technology
solution
1
2
3
composition
HF 2% + H2O2 2%
HF 1% + H2O2 3%
Original of each site
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R1-2.3 Preparation of Intentionally Contaminated Wafers and Blank Wafers
R1-2.3.1 This section describes the intentionally contaminated wafers. The samples used in this experiment were
prepared from P-type (100) CZ silicon wafers having a diameter of 200 mm. These wafers contained 1 × 1015
atoms/cm3 of doped boron. The wafers had a thickness of 725 m and a single polished surface. An interstitial
oxygen concentration of 1.1 × 1018 atoms/cm3 was obtained by Fourier transform infrared spectroscopy (FT-IR)
analysis by assuming the conversion coefficient to be 4.81 × 1017 atoms/cm3. Iron and copper were chosen as the
intentional contamination elements. The target surface concentration level was fixed to 1 × 1011 atoms/cm2. To
achieve intentional contamination, “IAP method”was used wherein the wafers were dipped in a mixture of aqueous
ammonia and hydrogen peroxide (SC-1 solution) containing iron and copper ions. After the contamination process
was completed, the wafers were rinsed in ultra-pure water for a few seconds and then spin-dried. The samples were
divided into three sets, and the contamination process was performed three times. Table R1-2 lists the iron and
copper contamination levels on the wafer surface for each batch after the process.
Table R1-2 Intentional Contamination Levels of Wafers of Each Batch
Contaminated batches
1 batch slot 2
1 batch slot 24
2 batches slot2
2 batches slot 24
3 batches slot 2
3 batches slot 3
Fe
16
18
14
14
12
12
Cu
5.5
7.0
4.7
3.0
4.2
4.1
(x1010atoms/cm2)
From this result, it was found that the concentration of iron reached 1 × 1011 atoms/cm2 (actual value: 1.2-1.6 × 1011
atoms/cm2) on the wafer surface. On the other hand, the concentration of copper was limited to 50% of the target
contamination level. However, this experiment was decided to be continued because of the practical contamination
level. Furthermore, the changes in the time-dependent surface concentration for evaluating the reliability of this
experiment were surveyed. The results are shown in Figure R1-1. In this figure, the concentration is expressed on
the vertical axis and the storage time is expressed on the horizontal axis. The iron data were plotted on the upper
side and the copper data on the lower side of the figure. From this result, it was found that the time-dependent
surface concentration shift was almost nil during a storage period of around 1 month. This result implies that no
analytical data was affected by the time-dependent shift of the contamination level because the operation of all the
sites was completed in less than 1 month.
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2
Cu/Fe consentrations (atoms/cm )
1.E+12
Fe
1.E+11
Cu
1.E+10
0
5
10
15
20
25
30
35
40
Storage time (Days)
Figure R1-1
Change to Depend in Time of Concentration of Surface Contaminations
In addition, the contamination of operation was confirmed by using non-contaminated wafers for monitoring
accidental contamination. The result for blank wafers at each site is shown in Figure R1-2.
Surface concentration (atoms/cm 2 )
1.E+11
Cu
Fe
1.E+10
1.E+09
1.E+08
A
B
C
D
E
Site name
F
G
J
Figure R1-2
Confirmation of Cleanliness Level of Blank Wafers at Each Site
In this figure, the concentration is expressed on the vertical axis and the site name is expressed on the horizontal
axis. Pink and blue plots represent Cu and Fe, respectively. The actual cleanliness level of the blank wafer was
around 2 × 109 atoms/cm2. From these results, it was concluded that the actual cleanliness level of the blank wafers
was relatively lower than the intentional contamination level.
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1.1.1 Measurement Results
Table R1-3 shows the original data, R1-4 shows the cell means, and R1-5 shows standard deviation. Because of bias
of the batch of intentional contamination, the repeatability and the reproducibility were not calculated.
Table R1-3 original data
collection
laboratory
method
A
B
VPD
E
G
J
C
DADD
D
F
Fe
batch of
10
2
intentional
×10 atoms/cm
contamination solution 1 solution 2 solution 3
1
20.3
18.7
18.6
1
19.3
19.4
1
16.4
16.1
16.4
1
16.4
16.2
16.5
2
12.5
13.1
12.8
2
12.7
12.8
12.6
2
16.4
15.1
11.2
2
17.1
15.8
13.2
3
16.8
13.4
12.9
3
13.4
13.1
13.1
1
16.0
16.1
16.5
1
16.2
16.3
16.3
1
16.1
16.5
16.2
2
13.8
14.1
14.1
2
13.9
13.9
14.2
2
14.8
13.8
14.3
Cu
10
2
×10 atoms/cm
solution 1 solution 2 solution 3
1.83
1.66
2.42
1.55
2.63
4.06
3.94
5.24
3.98
4.17
5.29
1.07
1.20
3.58
1.14
1.22
3.49
2.64
2.91
2.59
2.62
3.23
3.15
2.19
3.02
3.24
2.32
3.29
3.52
4.82
5.29
5.26
4.80
5.16
5.24
4.84
5.59
5.66
3.48
3.88
3.34
4.20
4.14
3.71
3.98
4.23
4.04
Table R1-4 cell mean
collection
laboratory
method
VPD
DADD
A
B
E
G
J
C
D
F
solution 1
19.8
16.4
12.6
16.8
15.1
16.1
15.0
14.4
Fe
mean
×1010atoms/cm2
solution 2
18.7
16.2
13.0
15.5
13.3
16.2
15.3
13.9
solution 3
19.0
16.5
12.7
12.2
13.0
16.4
15.2
14.3
solution 1
1.69
4.02
1.11
2.63
2.26
4.81
4.16
4.09
Cu
mean
×1010atoms/cm2
solution 2
1.66
4.06
1.21
3.07
3.16
5.23
4.74
4.19
solution 3
2.53
5.27
3.54
2.87
3.38
5.25
4.50
3.88
solution 1
0.20
0.06
0.05
0.01
0.09
0.01
0.96
0.16
Cu
standard deviation
×1010atoms/cm2
solution 2
-
0.16
0.01
0.23
0.19
0.09
1.21
0.06
solution 3
0.15
0.04
0.06
0.40
0.20
0.01
1.64
0.23
Table R1-5 standard deviation
collection
laboratory
method
VPD
DADD
A
B
E
G
J
C
D
F
solution 1
0.71
0.00
0.14
0.49
2.40
0.14
1.63
0.64
Fe
standard deviation
×1010atoms/cm2
solution 2
-
0.07
0.21
0.49
0.21
0.14
1.70
0.07
solution 3
0.57
0.07
0.14
1.41
0.14
0.14
1.48
0.07
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R1-2.4 Measurement Results of Iron
R1-2.4.1 Data obtained by a comparison of the measurement values at each site are presented. Measurement values
for iron at each site obtained with the VPD and DADD methods are shown in Figure R1-3 and Figure R1-4,
respectively. Further, mean and RSD of each solution are shown in Table R1-6.
1.E+12
Scanning solution 2
Scanning solution 3
2
(atoms/cm )
Surface concentration
Scanning solution 1
1.E+11
A
B
E
G
J
Site name
Figure R1-3
Measurement Results of Fe Concentration by VPD Method
1.E+12
Scanning solution 2
(atoms/cm )
Scanning solution 3
2
Surface concentration
Scanning solution 1
1.E+11
C
D
F
Site name
Figure R1-4
Measurement Results of Fe Concentration by DADD Method
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Table R1-6 mean and relative standard deviation of iron
mean
10
×10 atoms/cm2
VPD
DADD
Solution 1
Solution 2
Solution 3
Solution 1
Solution 2
Solution 3
16
15
15
15
15
15
relative standard
deviation
%
16
13
19
7.4
8.5
8.9
In both these figures, concentration of iron is expressed on the vertical axis and the site name is expressed on the
horizontal axis. In the analysis of iron, the variation among the three scanning solutions was found to be small at
almost all the sites in the cases of both the VPD and DADD methods. Further, when the difference in the intentional
contamination level shown in Table R1-1 was considered, the difference in the measurement values between any
two sites was sufficiently small. Similarly, the difference in the measurement values obtained by the VPD method
and the DADD method was small. Therefore, it was concluded that the difference in the composition of the scanning
solutions 1, 2, and 3 hardly influenced the analysis of iron on the wafer.
R1-2.5 Measurement Results of Copper
R1-2.5.1 Next, results of measurement of copper are presented. The description of the measurement is identical to
that of iron; the analytical values obtained using the VPD and DADD methods are shown in Figure R1-5 and Figure
R1-6, respectively. Further, mean and RSD of each solution are shown in Table R1-7.
1.E+11
Scanning solution 2
Scanning solution 3
2
(atoms/cm )
Surface concentration
Scanning solution 1
1.E+10
A
B
E
G
J
Site name
Figure R1-5
Measurement Results of Cu Concentration by VPD Method
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1.E+11
Scanning solution 2
Scanning solution 3
2
(atoms/cm )
Surface concentration
Scanning solution 1
1.E+10
C
D
F
Site name
Figure R1-6
Measurement Results of Cu Concentration by DADD Method
Table R1-7 mean and relative standard deviation of copper
mean
10
×10 atoms/cm2
VPD
DADD
Solution 1
Solution 2
Solution 3
Solution 1
Solution 2
Solution 3
2.3
2.7
3.5
4.4
4.7
4.6
relative standard
deviation
%
45
41
29
13
15
18
In the DADD method, the difference in the measurement values between scanning solutions of different
compositions was small; similarly, the difference in the measurement values between sites was also small. In the
case of the VPD method, a large bias of the measurement values existed between the scanning solutions of different
compositions. Except in the case of one site, the values for solutions 1 and 2 tended to be lower than that for solution
3. The value for solution 3 obtained by the VPD method agreed well with that obtained by the DADD method
except at some sites. In addition, in the case of solutions 1 and 2, the difference in the values between any two sites
was larger than that in the case of solution 3. The composition of solution 3 was devised to collect the measurement
element, including copper, at each site. Furthermore, the analysis conditions were optimized for obtaining the
original solution for each site. It is supposed that because the analysis conditions were not optimized in the cases of
solutions 1 and 2, the values for these solutions were low. Because the composition of solution 3 and analysis
conditions at each site were closed, the most suitable composition and detailed analysis conditions cannot be
provided. However, these results suggest that it is possible to analyze copper on a wafer surface by optimizing the
analysis conditions even if the composition of the scanning solution is not standardized. The bias of values of copper
may be decreased by optimizing the analysis conditions even if solution 1 or 2 is used.
R1-2.6 Summary of Review of Current Technology
R1-2.6.1 Good results were obtained for iron, the bias of the measurement values at each site was very low. The
bias of the values of copper was observed in the case of using solutions 1 and 2, but the difference between the sites,
as obtained by using solution 3, was small. It is considered to be important that the optimization of the analysis
conditions (e.g., scanning speed and repetition of scan) matches the scanning solution. Further, it is believed that the
determination of the recovery rate (see A1) by using intentionally contaminated wafers is effective for the
optimization of analysis conditions.
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RELATED INFORMATION 2
INTERFERENCE OF POLYATOMIC IONS
NOTICE: This related information is not an official part of SEMI (doc#) and was derived from (origin of
information). This related information was approved for publication by (method of authorization) on (date of
approval).
R2-1
R1-2.7 The interference of polyatomic ions for measurement element (see ¶2.5) is summarized in Table R3-1.
These polyatomic ions are produced when the sample solutions contain hydrofluoric acid and a silicon matrix.
However, the other polyatomic ions are produced when the sample solutions contain hydrochloric acid sulfuric acid
or phosphoric acid.
R2-2 Referenced Standards and Documents
JIS K0133 — General rules for frequency plasma mass spectrometry
Mohammad B. Shabani, Y. Shiina, F. G. Kirscht, Y. Shimanuki, “Recent advanced applications of AAS and ICPMS in the semiconductor industry” Materials Science and Engineering B102 (2003): pp. 238-246
Table R1-3 Interference of Polyatomic Ions
Mass
number
Maesurement Element
(isotopic abundance ratio)
23
Na (100)
24
Mg (78.8)
25
Mg (10.15)
26
Mg (11.05)
27
Al (100)
39
K (93.08)
40
Ca (96.97), K (0.01)
Isobar
(isotopic abundance ratio)
Polyatomic ions
38
41
K (6.91)
40
42
Ca (0.64)
40
43
Ca (0.14)
44
Ca (2.06)
46
Ca (0.003)
50
Cr (4.35)
Ti (5.25), V (0.24)
52
Cr (83.76)
Cr (9.51)
55
Mn (100)
56
Fe (91.66)
57
Fe (2.19)
58
Ni (66.77), Fe (0.33)
59
Co (100)
60
Ni (26.16)
61
62
14
Ti (7.99)
Ti (73.98)
Fe (5.82), Cr (2.38)
ArH
ArH2
C16O16O, 28Si16O
Ca (0.19)
54
Ar
12
48
53
ArH
40
Ar (99.6)
16
16
N O O,
30
16
30
Si16O, 29Si16OH, 28Si16OH2
29
Si OH2, Si16OH3, 28Si19FH, 29Si19F
36
Ar14N, 30Si19FH, 29Si19FH2
36
Ar16O
40
Ar14N
40
Ar14NH
40
Ar16O
40
Ar16OH
28
Si16O16O
29
Ni (1.25)
30
16
Si O O, 28Si16O16OH
Si O O, 29Si16O16OH, 28Si16O16OH2
Ni (3.66)
30
63
Cu (69.1)
64
Zn (48.89), Ni (1.16)
30
65
Cu (30.83)
30
66
Zn (27.81)
16
16
16
16
Si O16OH, 29Si16O16OH2, 28S16OH3, 28Si16O19F
Si16O16OH2, 29Si16O16OH3, 29Si16O19F, 29Si16O19FH
Si16O16OH3, 30Si16O19F, 29Si16O19FH, 29Si16O19FH2
30
Si16O19FH, 29Si16O19FH2
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Semiconductor Equipment and Materials International
3081 Zanker Road
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Zn (4.11)
68
Zn (18.57)
40
Ar14N14N, 40Ar28Si
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