Background Statement for SEMI Draft Document 5749
NEW STANDARD: TEST METHOD FOR MEASUREMENT OF
WAVINESS OF CRYSTALLINE SAPPHIRE WAFERS BY USING
OPTICAL PROBES
Notice: This background statement is not part of the balloted item. It is provided solely to assist the recipient in
reaching an informed decision based on the rationale of the activity that preceded the creation of this Document.
Notice: Recipients of this Document are invited to submit, with their comments, notification of any relevant
patented technology or copyrighted items of which they are aware and to provide supporting documentation. In this
context, “patented technology” is defined as technology for which a patent has issued or has been applied for. In the
latter case, only publicly available information on the contents of the patent application is to be provided.
Background
The market for sapphire wafers and substrates is rapidly growing and specifications for sapphire wafers to
be used as substrates for HB-LED were recently standardized in SEMI HB1. Verifying the requirements
specified in this document requires customers and suppliers agreement on measurement methods. So far
only few such methods are standardized in the HB-LED and sapphire wafer industry. In particular
standardized test methods are missing for the basic geometrical characteristics of sapphire wafers or
substrates. Therefore, a standardized test method for these characteristics would be of great benefit for the
involved industries for establishing a common understanding of measurements equipment capabilities,
limits and performance and for avoiding unnecessary discussions on quality or specification issues.
This document describes a test method for measuring and characterizing the waviness of crystalline
sapphire wafers. It also defines related metrics and terms. Test methods for measuring thickness, shape
and saw marks of such wafers are currently under development.
Review and Adjudication Information
Task Force Review
Committee Adjudication
Group:
HB-LED Test Methods TF
N.A HB-LED TC Chapter
Date:
April 02, 2015
April 02, 2015
Time & Time zone:
8:00 am – 9:00 am (Pacific Time)
1:30 pm – 4:30 pm (Pacific Time)
Location:
SEMI Headquarters in conjunction with the
N.A. Standards Spring 2015 Meetings
SEMI Headquarters in conjunction with the
N.A. Standards Spring 2015 Meetings
City, State/Country: San Jose, CA/USA
San Jose, CA/USA
Leader(s):
Peter Wagner (Self)
Iain Black (Philips Lumileds), Mike Feng
(Silian), Chris Moore (BayTech-Resor)
Standards Staff:
Michael Tran
408.943.7019
[email protected]
Michael Tran
408.943.7019
[email protected]
*This meeting’s details are subject to change, and additional review sessions may be scheduled if necessary.
Contact the task force leaders or Standards staff for confirmation.
Telephone and web information will be distributed to interested parties as the meeting date approaches. If you will
not be able to attend these meetings in person but would like to participate by telephone/web, please contact
Standards staff.
Semiconductor Equipment and Materials International
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DRAFT
SEMI Draft Document 5749
NEW STANDARD: TEST METHOD FOR MEASUREMENT OF
WAVINESS OF CRYSTALLINE SAPPHIRE WAFERS BY USING
OPTICAL PROBES
1 Purpose
1.1 Crystalline sapphire wafers (CSW) are used as substrates for manufacturing compound semiconductor devices,
in particular HB-LED (High Brightness Light Emitting Diodes).
1.2 In SEMI HB1 a multitude of requirements is defined for CSW qualified for device production, including
geometry and surface characteristics.
1.3 Waviness and other surface features are important characteristics for depositing layers of III-V compound on
CSW during HB-LED manufacturing.
1.4 In addition, careful process and quality control of the wafer waviness during CSW and device manufacturing
requires continuous monitoring of waviness by the supplier as well as by the user of CSW.
1.5 An understanding of the measurements methods used for the qualification of CSW is required to enable
agreement on specifications. Such an understanding is provided by standardized test methods for the wafer
characteristics.
1.6 This Document provides a standardized test method for measuring one of the most basic characteristics of CSW,
waviness. In addition, this document defines terms and metrics needed for quantifying the waviness of CSW.
2 Scope
2.1 This Test Method covers the non-contact, non-destructive measurement of waviness of clean CSW used for
manufacturing semiconductor devices.
2.2 The thickness range of the CSW to be measured with this Test Method depends on details of the specific set-up
used.
2.3 The surface condition of the CSW may be as cut or lapped.
2.4 This Test Method does not cover any measurements in the wafer edge profile.
2.5 This Test Method may also be applied to wafers of other materials within the constraints of diameter, thickness
and surface condition.
NOTICE: SEMI Standards and Safety Guidelines do not purport to address all safety issues associated with their
use. It is the responsibility of the users of the Documents to establish appropriate safety and health practices, and
determine the applicability of regulatory or other limitations prior to use.
3 Limitations
3.1 The spatial resolution of the test method depends on a) the diameter of the light spot of the optical probes used,
b) the pitch of the measurement points and c) the cut-off wavelength of the filter used.
3.2 Vibrations of wafer, wafer support or probes may adversely impact the measurement results.
3.3 Precision of the test method depends critically on the precision of the position of the line scans on the wafer
faces.
4 Referenced Standards and Documents
4.1 SEMI Standards and Safety Guidelines
SEMI E89 –– Guide for Measurement System Analysis (MSA)
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
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Document Number: 5749
Date: 1/7/2015
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DRAFT
SEMI HB1 — Specifications for Sapphire Wafers Intended for Use for Manufacturing High Brightness-Light
Emitting Diode Devices.
SEMI M1 — Specification for Polished Single Crystal Silicon Wafers
SEMI M20 –– Practice for Establishing a Wafer Coordinate System
SEMI MF1569 –– Guide for Generation of Consensus Reference Materials for Semiconductor Technology
4.2 ISO Standards 1
ISO 11462-1 — Guidelines for implementation of statistical process control (SPC) – Part 1: Elements of SPC
ISO 11462-2 –– Guidelines for implementation of statistical process control (SPC) – Part 2: Catalogue of tools and
techniques
NOTICE: Unless otherwise indicated, all documents cited shall be the latest published versions.
5 Terminology
(Refer to the SEMI Standards Compilation of Terms (CoTs) for a list of the current Abbreviations, Acronyms,
Definitions, and Symbols.)
5.1 Abbreviations and Acronyms
5.1.1 CRM –– certified reference material
5.1.2 CSW — crystalline sapphire wafer(s)
5.1.3 FQA –– fixed quality area
5.2 Definitions
5.2.1 Back face, of CSW –– that face of a CSW that is not intended for manufacturing a semiconductor device.
5.2.2 Center line, of a CSW –– an imaginary line through the wafer center traverse to the waviness direction.
5.2.3 Front face, of CSW –– that face of a CSW that is intended for manufacturing a semiconductor device.
5.2.4 Maximum wafer back face waviness WMB, of a CSW –– the maximum waviness measured on the wafer back
face.
5.2.5 Maximum wafer front face waviness WMF, of a CSW –– the maximum waviness measured on the wafer front
face.
5.2.6 Maximum waviness WMT, of a CSW –– the maximum of WMF and WMB.
6 Summary of Test Method
6.1 A line scan of the wafer is performed by moving the wafer between a pair of fixed, opposing optical probes.
6.2 The wafer is supported at 3 points around its circumference at its edge during measurement.
6.3 The wafer is scanned along imaginary horizontal lines parallel to or on the center line and traversing across the
waviness direction across and within the FQA of the CSW.
6.3.1 The measurement point pitch l for the line scan is adjusted according to the required resolution for the
waviness measurement.
6.3.2 The distances between the probes and the respective wafer faces are measured and recorded providing line
scans of the surface heights of both surfaces.
6.3.3 The line scans’ data are processed to determine the waviness depth and width.
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
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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Document Number: 5749
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DRAFT
7 Coordinate System
7.1 The origin of the coordinate system is at the wafer center and the y-axis is aligned perpendicular to the fiducial
orientation flat or bisects the fiducial orientation notch as described in SEMI M20. This document assumes that the
wafer rests horizontally on its support.
7.2 The origin of the z-axis is assumed at the beginning of the measurement range.
7.3 In case that the wafer is held in an upright position during the measurement the coordinate system shall be
adjusted accordingly.
8 Apparatus
8.1 Optical probe set — a pair of opposing probes spaced a distance w apart that measure the distances to the
respective wafer faces by using an optical technique the light spot of which has a diameter D (see Figure 1).
8.2 x-y stage — supports the wafer at three points around its periphery so that a) the wafer is not contaminated and
b) the measurement is not impacted. Stage lateral motion provides appropriate horizontal and vertical positioning.
8.3 Electronics –– controlled by a computer that is equipped with software for recording and processing the
measured data according to §14 The computer controls also wafer handling and movement of the wafer support.
9 Safety Precautions
9.1 In case equipment with automated wafer handling is used then the entire equipment has to be placed in a closed
housing and has to be secured with a safety lock that stops the robot and safely switches the tool off when the
housing is opened.
10 Test Specimens
10.1 Clean, dry sapphire wafers.
11 Preparation of Apparatus
11.1 The suitability of the equipment is determined by performing a statistically based MSA to ascertain whether
the equipment is operating within the manufacture’s stated specification e.g. according to SEMI E89.
11.2 Verify that the probes and the wafer support are aligned and adjusted according to the manufacturer’s
specifications.
11.3 Verify that the equipment is operating within its specified temperature range.
11.4 Define the control limits for SPC for the measurement equipment with a set of selected wafers (ISO 11462).
12 Calibration and Standardization
12.1 The measurement equipment is calibrated by using reference material (RM), preferably CRM, the waviness of
which is known.
12.2 The RM may either be a CSW the waviness and its uncertainty are known at marked positions, or gauge
blocks with steps of known height.
12.3 Calibration is established only for the specified linear range of the optical probe pair about the gap position
used during this calibration.
12.4 Large changes in product-specified wafer thickness may require changing the calibration.
12.5 Calibration has to be performed under the same ambient conditions (temperature, humidity) as the
measurements of the test specimens and within the ranges specified by the supplier of the measurement equipment.
13 Procedure
13.1 Place the wafer on the x-y-stage.
13.2 Choose the number N of line scans and their distances dn to the center line (n = 1, 2, …, N) as well as pitch l
and the lengths Ln of the scan lines to be used for the waviness measurement and report l, N, all Ln and dn.
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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Document Number: 5749
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DRAFT
13.3 Define the pitch l and the length of the scan L to be used for the waviness measurement and report l and L.
13.3.1 Perform the line scans across the wafer within the FQA traverse to the direction of the waviness and parallel
to or on the center line.
13.3.2 Record the distances hikn between both probes and the respective wafer faces (i = f, b for front and back face,
k = 1, 2, …, Kn ≤ Ln/l) at Kn points along the line.
13.3.3 Calculate the metrics for waviness according to §14
13.3.4 Report the metrics.
14 Calculations and Data Processing
14.1 The following calculations are performed automatically within the instrument. The data shall be processed
and the metrics be calculated as outlined in the following.
14.2 Filter the set of hikn for each line scan optionally with a smoothing filter. Report filter type and filter details.
14.3 Determine the peak-to-valley values Wikn of the hikn for each line scan within a sliding window of r
measurement points for k = floor(r/2), …, Kn-floor(r/2) and i = f, b, where floor(x) is defined as the largest integer
less than x.
14.4 Report r.
14.5 Determine the maximum waviness amplitude WMF of all line scans on the wafer front face as
WMF  max( W fkn )
(1)
14.5.1.1 Determine the maximum waviness amplitude WMB of all line scans on the wafer back face as
WMB  max( Wbkn )
(2)
14.5.1.2 Determine the total maximum waviness amplitude WMT of all line scans on the wafer back face as
WMT  max( WMF , WMB )
(3)
14.5.1.3 Report WMF, WMB and WMT.
15 Report
15.1 The report shall contain the following elements.
15.2 General Information
15.2.1 Date and time of test.
15.2.2 Identification number of measurement equipment.
15.2.3 Equipment software revision.
15.2.4 Calibration and SPC status of measurement equipment.
15.2.5 Date of calibration.
15.2.6 ID of reference material.
15.2.7 Lot identification, including each wafer's ID if available.
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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15.2.8 Ambient temperature.
15.3 Specifics of Measurement Equipment
15.3.1 Diameter D of the measurement light spot.
15.3.2 Filter type and details (spatial cut-off wavelength).
15.3.3 Scan lengths Ln.
15.3.4 Number N of line scans.
15.3.5 Distances ds of the line scans from the center line.
15.3.6 Point pitch l of the scan lines.
15.3.7 Filter type and details (spatial cut-off wavelength).
15.3.8 Sliding window width r.
15.4 Characteristics of CSW
15.4.1 Waviness metrics WMF, WMB and WMT.
16 Precision and Bias
16.1 The precision of the method has been determined experimentally by performing a MSA with one wafer with
as-cut faces providing the summarized results regarding repeatability and reproducibility as shown in Table 1.
16.2 Details of the MSA are reported in Related Information 1.
16.3 No certified reference materials in the shape of a CSW currently exist for establishing the accuracy of
measurement equipment that can be used with equipment as described in this test method. Therefore, bias of
equipment performing these measurements has not been developed.
16.4 Provisional reference materials may be qualified by using appropriate equipment that is capable measuring
certified reference materials as well as silicon wafers (SEMI MF1569).
Table 1 Results of MAS for Waviness Metrics
Waviness Metrics
r/µm, wafer A#1
WMF
WMB
WMT
0.302
0.270
0.292
#1 Total standard deviation, combined for repeatability and reproducibility.
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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DRAFT
NOTE: The relative dimensions are not to scale.
Figure 1
Schematic side view of the set-up with a CSW between a pair of optical probes
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Document Number: 5749
Date: 1/7/2015
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DRAFT
RELATED INFORMATION 1
DETAILS OF MSA
NOTICE: This Related Information is not an official part of SEMI [designation number] and was derived from the
work of the [committee name] Global Technical Committee. This Related Information was approved for publication
by full letter ballot procedures on [A&R approval date].
R1-1 Purpose
R1-1.1 The MSA was performed for establishing the capability of the test method for usage in large volume
sapphire wafer production.
R1-1.2 The measurements were performed on standard production equipment.
R1-2 Parameter Settings
R1-2.1 The following settings for the parameters were used:








Light spot diameter D = 12 µm
Number of line scans N = 1
Scan Lengths L1 = 98 mm
Distances of the scan lines from the center line d1 = 0
Point pitch of scan lines l = 3.75 µm
Filter type: none
Filter cut-off wavelength: not applicable
Sliding window width r = 4 mm
R1-3 Results of MSA
R1-3.1 Test specimen –– a sapphire wafers, 100 mm diameter.
R1-3.2 Surface condition –– both faces as cut.
R1-3.3 Test conditions –– two runs of 5 repeats on three successive days.
R1-3.4 Results –– the standard deviations per day are reported in Table R1-1 and the overall standard deviations in
Table R1-2 for the waviness metrics WMF, WMB and WMT. The results of the individual measurements per day,
per run and per repeat are displayed in Figure R1-1.
Table R1-1 MSA Results, Standard Deviation of the
Waviness Metrics WMF, WMB and WMT per Day
Day
WMF
std.dev./µm
WMB
std.dev./µm
WMT
std.dev./µm
1
0.322
0.249
0.310
2
0.300
0.177
0.300
3
0.294
0.325
0.268
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LETTER (YELLOW) BALLOT
Document Number: 5749
Date: 1/7/2015
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DRAFT
Document Number: 5749
Date: 1/7/2015
WMF
std.dev./µm
WMB
std.dev./µm
WMT
std.dev./µm
0302
0.270
0.292
LETTER (YELLOW) BALLOT
Table R1-2 MSA Results, Standard Deviation
of the Waviness Metrics WMF, WMB and WMT
10
9
8
WMF, WMB / µm
7
6
5
WMF
4
WMB
3
2
1
0
1 1 1 1 1 2 2 2 2 2 1 1 1 1 1 2 2 2 2 2 1 1 1 1 1 2 2 2 2 2
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 3
Run / Day
Figure R1-1
MSA Results for the Waviness Metrics WMF and WMB.
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to the suitability of the Standards and Safety Guidelines set forth herein for any particular application. The
determination of the suitability of the Standard or Safety Guideline 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. Standards and Safety Guidelines are subject to change
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