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1 Background Statement for SEMI Draft Document 4844A 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 The trace metal information has been reported in the specification of semiconductor grade silicon. On this account, a guide for the trace metal analysis is necessary. However, there has been no document for trace metal analysis 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 Related information was drafted from September 2008 to December This document was drafted and improved until October 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 Doc.4844 does not match description of the classification of clean room and so on. Working Group 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 The voting result of Doc.4844A will be reviewed by the Chemical Analysis Working Group under the Japan Test Method Task Force and will be adjudicated by the Japan Silicon Wafer Committee during their meeting at SEMICON Japan at Makuhari Messe, Chiba, Japan If you have any questions, please contact to the Chemical Analysis Working Group leader and the Test Method TF co-leader as shown below: Ryuji Takeda/ Covalent Silicon at ryuji@covalent.co.jp, and Masaharu Watanabe/ Nuflare Technology at WatanabeNFT@aol.com, or Akiko Yamamoto, SEMI Japan staff at ayamamoto@semi.org.

2 SEMI Draft Document 4844A 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 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 8.3). 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 % (See and ). Here, the scanning solution consists of hydrofluoric acid and hydrogen peroxide or nitric acid. 2.5 This guide uses only ICP-MS (See 9.1) 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 Referenced Standards and Documents 3.1 SEMI Standards SEMI C1 Guide for Analysis of Liquid Chemicals SEMI E45 Test Method for the Determination of Inorganic Contamination from Minenvironments 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) Page 1 Doc. 4844A SEMI

3 3.2 ISO Standards 1 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 :1999. Clean rooms and associated controlled environments Part 1: Classification of air cleanliness 3.3 JIS Standards 2 JIS K0133 General rules for frequency plasma mass spectrometry NOTICE: Unless otherwise indicated, all documents cited shall be the latest published versions. 4 Terminology 4.1 Abbreviations and Acronyms ICP-MS Inductively Coupled Plasma Mass Spectrometry VPD Vapor Phase Decomposition DADD Direct Acid Droplet Decomposition 4.2 Definitions 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 VPD box the VPD box is an airtight container composed of acid-resisting materials (e.g., polytetrafluoroethylene and polyfluoroalkoxyethylene) and equipped with wafer stands 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 Summary 5.1 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: ; Fax: ; 2 Japanese Industrial Standards, Available through the Japanese Standards Association, 1-24, Akasaka 4-Chome, Minato-ku, Tokyo , Japan. Telephone: ; Fax: ; Page 2 Doc. 4844A SEMI

4 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 5.2 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. 5.3 Measurement After the sample preparation, the trace metal contamination in the sample solution is determined by ICP-MS. 6 Reagents and Materials 6.1 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 ISO 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. 6.3 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. 6.4 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. 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. 7 Equipment and Tool Usage 7.1 Equipment and tool usage in this method is as follows: Page 3 Doc. 4844A SEMI

5 7.1.1 ICP-MS Clean Booth VPD Box Automatic Scanning Equipment Tweezers: Vacuum Tweezers and Manual Tweezers Micro pipette 8 Sample Preparation 8.1 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 ) 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. 8.2 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). 8.3 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 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 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 2 Outline of Sample Preparation in VPD Method Page 4 Doc. 4844A SEMI

6 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 ISO 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 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 the recovery rate is should be between 75% and 125%, and 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 Decomposition of Native Oxide and Thermal Oxide A silicon wafer is placed in the VPD box such that the surface for analysis is exposed to hydrofluoric acid vapor under clean environments such as the interior of a clean draft. When the wafer is placed in the VPD box, it should be handled using vacuum tweezers for the wafer backside without contamination from the apparatus and handling processes. Additionally, a processing time that is sufficient for completely decomposing native and thermal oxides should be determined properly Collection of Trace Metal Contamination The trace metals should be collected by scanning a droplet of the scanning solution on the analytical surface manually or using automatic scanning equipment. The automatic equipment can be expected to have a better repeatability than the manual collection because of the presence of reducing contaminations from 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 Post-collection Process The scanning solution collected from the silicon wafer contains the silicon matrix. Therefore the standard addition method, the internal standard method, a collision cell or high-resolution ICP- MS etc should be utilized; measurements without interference by the silicon matrix would then be possible. In the case of the removal of the silicon matrix to reduce the background level, considerable attention should be paid to loss by volatilization, production of precipitates, and contaminations from the environment Method Blank For the preparation of the method blank, the same processes with the sample solution for the monitoring of contamination from the analytical environment, scanning solutions and periphery analytical tools should be performed. Here, the method blank solutions are prepared by scanning high-purity wafers. Otherwise, the scanning solutions are used as the method blank solutions. NOTE 4: The method blank is an important parameter for comparison of measurement data between facilities. It should be referred to if necessary 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. Page 5 Doc. 4844A SEMI

7 Silicon oxide Pipette Silicon wafer Self-recovery Figure 3 Outline of Sample Preparation in DADD Method Pipette 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. The preparation procedure is described in 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. The droplet would automatically sweep the target elements on the surface with a reaction between the silicon oxide and hydrofluoric acid Collection of Trace Metal Contamination Once the droplet has stopped sweeping, scan the surface with the droplet using a reproducible pattern; the entire surface should be covered in order to ensure complete collection of the target elements. The scanning solution would be collected using a micropipette. If the droplet of the scanning solution is too small to be collected, the scanning solution would be collected after ultra-pure water is added Post-collection Process Same as Method Blank Same as NOTE 5: 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. 9 Procedure 9.1 In this section, the measurement of the sample solution by ICP-MS is described Measurement Principle of ICP-MS The ICP-MS structure is shown in Figure 4. Page 6 Doc. 4844A SEMI

8 Plasma gas Auxiliary gas Carrier gas Sample Torch Plasma Spray chamber Nebulizer Interface Ion lens Figure 4 Schematic Diagram of ICP-MS Instrument Typical System of Quadruple ICP-MS Quadrupole Detector The plasma is produced from inert gas; the energy is supplied by electrical currents that are produced by electromagnetic induction. When the solution is measured, an aerosol is formed from a sample solution by using a nebulizer. The aerosol is ionized by its introduction into plasma. The ions are separated on the basis of the mass-tocharge ratio in a mass spectrometer, and they are counted using a detector Interference of Polyatomic Ions Since argon gas is primarily used for forming inductively coupled plasma, polyatomic ions of argon 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, 40 Ar 16 O on 56 Fe, 38 ArH on 39 K, and 29 Si 19 F on 48 Ti. Therefore, the interference of polyatomic ions should be suppressed by the cool plasma method or the collision/reaction cell On the other hand, because the sensitivity of ICP-MS decreases when the sample solution contains highconcentration silicon matrix, the internal standard method would be applied to the measurement Confirmation of ICP-MS Instrument Performance 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 Measurement Procedure 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 Page 7 Doc. 4844A SEMI

9 measured ion counts are plotted on the vertical axis. The composition of the calibration standard solutions and calibration blank solution should be the same as that of the sample solution. NOTE 6: The calibration curve is an important parameter for comparison of measurement data between the facilities. It should be referred to if necessary 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 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/cm 2 ): w v N A N = M (1) S 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; N A, the Avogadro constant; and S, the measurement area of the silicon wafer surface. 10 Calculation 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 Determination of detection limit and quantification limit 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 7: Detection limit is an important parameter for comparison of measurement data between facilities. It should be referred to if necessary 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. Page 8 Doc. 4844A SEMI

10 NOTE 8: Quantification limit is an important parameter for comparison of measurement data between the facilities. It should be referred to if necessary. 11 Report 11.1 The following information should be reported: Sample identification Decomposition of silicon oxide Method (VPD or DADD) Decomposition time Collection of surface metal contamination Method (Manual or Auto) Collection area Analysis results (unit: atoms/cm 2 ) Analysis date Values of target metals Detection limit of each target metal The report details should be determined between the related parties Page 9 Doc. 4844A SEMI

11 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 C 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 SEMIC 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. Page 10 Doc. 4844A SEMI

12 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 R The scanning solution comprises acid for collecting collect 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% + H 2 O 2 2% HF 1% + H 2 O 2 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 Review of Current Technology Procedure R 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. Page 11 Doc. 4844A SEMI

13 Table R1-1 Scanning Solutions Used in Review of Current Technology solution composition 1 HF 2% + H 2 O 2 2% 2 HF 1% + H 2 O 2 3% 3 Original of each site R1-2.3 Preparation of Intentionally Contaminated Wafers and Blank Wafers R 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 atoms/cm 3 of doped boron. The wafers had a thickness of 725 μm and a single polished surface. An interstitial oxygen concentration of atoms/cm 3 was obtained by Fourier transform infrared spectroscopy (FT-IR) analysis by assuming the conversion coefficient to be atoms/cm 3. Iron and copper were chosen as the intentional contamination elements. The target surface concentration level was fixed to atoms/cm 2. 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 Fe Cu 1 batch slot batch slot batches slot batches slot batches slot batches slot (x10 10 atoms/cm 2 ) From this result, it was found that the concentration of iron reached atoms/cm 2 (actual value: atoms/cm 2 ) 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. Page 12 Doc. 4844A SEMI

14 Cu/Fe consentrations (atoms/cm 2 ) Cu Figure R1-1 Change to Depend in Time of Concentration of Surface Contaminations Fe Storage time (Days) 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 R E+11 Surface concentration (atoms/cm 2 ) 1.E+10 1.E+09 1.E+08 Cu Fe A B C D E F G J Site name 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 atoms/cm 2. From these results, it was concluded that the actual cleanliness level of the blank wafers was relatively lower than the intentional contamination level. Page 13 Doc. 4844A SEMI

15 R1-2.4 Measurement Results of Iron R 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. Surface concentration (atoms/cm 2 ) 1.E+12 1.E+11 A B E G I J Site name Figure R1-3 Measurement Results of Fe Concentration by VPD Method Scanning solution 1 Scanning solution 2 Scanning solution 3 Surface concentration (atoms/cm 2 ) 1.E+12 Scanning solution 1 Scanning solution 2 Scanning solution 3 1.E+11 C D F Site name Figure R1-4 Measurement Results of Fe Concentration by DADD Method 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. Page 14 Doc. 4844A SEMI

16 R1-2.5 Measurement Results of Copper R 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. Surface concentration (atoms/cm 2 ) 1.E+11 1.E+10 Scanning solution 1 Scanning solution 2 Scanning solution 3 A B E G I J Site name Figure R1-5 Measurement Results of Cu Concentration by VPD Method Surface concentration (atoms/cm 2 ) 1.E+11 Scanning solution 1 Scanning solution 2 Scanning solution 3 1.E+10 C D F Site name Figure R1-6 Measurement Results of Cu Concentration by DADD Method 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 Page 15 Doc. 4844A SEMI

17 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 R 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. Page 16 Doc. 4844A SEMI

18 RELATED INFORMATION 2 DEFINITION OF CLEAN ROOM CLASSIFICAION 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 Definition of Classification R2-1.1 The definition of classification of a clean room is given in Table R2-1. This refers to ISO :1999. Table R2-1 Standards of Environmental Cleanliness Classification of Standard (Number/cft = 28.3L) cleanliness 0.1 μm 0.2 μm 0.3 μm 0.5 μm 1.0 μm 5.0 μm ISO Class 1 0 ISO Class ISO Class ISO Class ISO Class 5 2, ISO Class 6 28,300 6, , ISO Class 7 10,000 2, ISO Class 8 100,000 23, ISO Class 9 1,000, ,000 8,290 Page 17 Doc. 4844A SEMI

19 RELATED INFORMATION 3 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). R3-1 R3-1.1 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. R3-2 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 ICP- MS in the semiconductor industry Materials Science and Engineering B102 (2003): pp Table R3-1 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) Isobar (isotopic abundance ratio) 40 Ca (96.97), K (0.01) Ar (99.6) 41 K (6.91) 42 Ca (0.64) 43 Ca (0.14) 44 Ca (2.06) 46 Ca (0.003) Ti (7.99) 48 Ca (0.19) Ti (73.98) 50 Cr (4.35) Ti (5.25), V (0.24) 52 Cr (83.76) 53 Cr (9.51) 54 Fe (5.82), Cr (2.38) 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 Ni (1.25) 62 Ni (3.66) 63 Cu (69.1) 64 Zn (48.89), Ni (1.16) 65 Cu (30.83) 66 Zn (27.81) Polyatomic ions 38 ArH 40 Ar 40 ArH 40 ArH 2 12 C 16 O 16 O, 28 Si 16 O 14 N 16 O 16 O, 30 Si 16 O, 29 Si 16 OH, 28 Si 16 OH 2 30 Si 16 OH 2, 29 Si 16 OH 3, 28 Si 19 FH, 29 Si 19 F 36 Ar 14 N, 30 Si 19 FH, 29 Si 19 FH 2 36 Ar 16 O 40 Ar 14 N 40 Ar 14 NH 40 Ar 16 O 40 Ar 16 OH 28 Si 16 O 16 O 29 Si 16 O 16 O, 28 Si 16 O 16 OH 30 Si 16 O 16 O, 29 Si 16 O 16 OH, 28 Si 16 O 16 OH 2 30 Si 16 O 16 OH, 29 Si 16 O 16 OH 2, 28 S 16 OH 3, 28 Si 16 O 19 F 30 Si 16 O 16 OH 2, 29 Si 16 O 16 OH 3, 29 Si 16 O 19 F, 29 Si 16 O 19 FH 30 Si 16 O 16 OH 3, 30 Si 16 O 19 F, 29 Si 16 O 19 FH, 29 Si 16 O 19 FH 2 30 Si 16 O 19 FH, 29 Si 16 O 19 FH 2 Page 18 Doc. 4844A SEMI

20 67 Zn (4.11) 68 Zn (18.57) 40 Ar 14 N 14 N, 40 Ar 28 Si 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. By publication of this standard, Semiconductor Equipment and Materials International (SEMI) takes no position respecting the validity of any patent rights or copyrights asserted in connection with any items 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 19 Doc. 4844A SEMI