Background Statement for SEMI Draft Document 5331A NEW ...downloads.semi.org/web/wstdsbal.nsf/890bac27e9c14...opto-electronic noise level, and the calibration of measured signal to

Background Statement for SEMI Draft Document 5331A NEW STANDARD: TEST METHOD FOR IN-LINE MEASUREMENT OF SAW MARKS ON PV SILICON WAFERS BY A LIGHT SECTIONING TECHNIQUE USING MULTIPLE LINE SEGMENTS

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.

Today the dominant technology for slicing bricks to produce silicon wafers for photovoltaic solar cells is multiple

wire sawing. With this technology it is possible to reliably produce wafers with thicknesses between 100 – 300 µm.

Wire sawing is a mechanical process where steel wires with a diameter between 100 and 160 um are used to

transport slurry into the cutting zone of the silicon brick or, in the case of diamond wire saws, cut the silicon directly

using only a lubricant but not slurry. The slurry typically contains SiC particles, which remove the silicon material

in an abrasive process. In case of a diamond wire small diamond pieces are attached to the steel wire. In both cases

the abrasive process generates grooves and steps along the wire direction in the surface of the Si wafers. These

grooves and steps, called saw marks, negatively impact the quality of the wafers and subsequently the quality of the

solar cell made from these wafers. The maximum depth/height of saw marks is part of the wafer specifications.

Therefore these saw marks need to be reproducibly characterized regarding their depth/height by an in-line high

throughput measurement method. This document proposes such a measurement method.

The corresponding SNARF was approved by the PV Committee in its meeting in Dresden on October 11, 2011. The

draft document was approved for yellow letter ballot in cycle 1 of 2012 by the PV Committee in its meeting in

Dresden on October 11 to be adjudicated in Berlin in March 2012 where it failed. Immediate re-ballot of the

document in cycle 3 2012 was approved to be adjudicated in the PV Materials Committee meetings in Munich in

June 2012 in conjunction with Intersolar Europe 2012.

Check www.semi.org/standards under Calendar of Events for the latest update.

Review and Adjudication Information

Task Force Review Committee Adjudication

Group: PV Silicon Materials TF Europe PV Materials Committee

Date: Wednesday, June 13, 2012 Wednesday, June 13, 2012

Time & Timezone: 11:00 to 13:00 CET 16:00 to 18:00 CET

Location: International Congress Centre Munich (ICM) International Congress Centre Munich (ICM)

City, State/Country: Munich, Germany Munich, Germany

Leader(s): Peter Wagner

Peter Wagner

Hubert Aulich (PV Crystalox)

Standards Staff: Kevin Nguyen (SEMI NA)

408.943.7997

[email protected]

Kevin Nguyen (SEMI NA)

408.943.7997

[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.

This is a Draft Document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted Standard or Safety Guideline. Permission is granted to reproduce and/or distribute this document, in whole or in part, only within the scope of SEMI International Standards committee (document development) activity. All other reproduction and/or distribution without the prior written consent of SEMI is prohibited.

Page 1 Doc. 5331A SEMI

Semiconductor Equipment and Materials International 3081 Zanker Road San Jose, CA 95134-2127 Phone: 408.943.6900, Fax: 408.943.7943

LETTER (YELLOW) BALLOT

DRAFTDocument Number: 5331A

Date: 4/16/2012

SEMI Draft Document 5331A NEW STANDARD: TEST METHOD FOR IN-LINE MEASUREMENT OF SAW MARKS ON PV SILICON WAFERS BYA LIGHT SECTIONING TECHNIQUE USING MULTIPLE LINE SEGMENTS

1 Purpose

1.1 Silicon (Si) wafers for PV applications cut from a Si ingot or Si brick by multiple-wire sawing contain artifacts

characteristic for this cutting process, so called saw marks.

1.2 The saw marks consist of topographic features, such as grooves, steps (see R2), on or in the Si wafer surface

and that extend along the wire direction.

1.3 Saw marks may significantly impact the quality of wafers. They interfere with printing the contact fingers on

solar cells. Extreme saw mark dimensions may interrupt the contact fingers or create too wide fingers.

1.4 Saw marks are frequently specified for Si wafers for solar cells with respect to their maximum peak-to-valley

within a finite distance, or window.

1.5 Standardized test methods providing reproducible values for saw marks are required to specify this aspect of

wafer quality.

1.6 Process and quality control during manufacturing of wafers requires continuous monitoring of saw marks with a

non-contact method that supports high throughput.

2 Scope

2.1 This test method determines maximum peak-to-valley of saw marks of multi or single crystal Si wafers that

typically run across the entire wafer surface and along the wire direction.

2.2 It describes an in-line, non-contacting and non-destructive method that determines the height changes of steps

and grooves of clean, dry as-cut silicon wafers supported by two belts that move the test specimen through the

measurement equipment.

2.3 This test method covers square and pseudo-square PV Si wafers, with a nominal edge length ≥ 125 mm and a

nominal thickness ≥ 100 µm. It applies to both single-crystalline and multi-crystalline Si wafers.

2.4 The test method is intended for in-line high throughput measurements. Therefore it is mandatory to operate the

measurement system under statistical process control (SPC, e.g. ISO 11462) in order to obtain reliable, repeatable

and reproducible measurement data.

2.5 The test method is based on a light sectioning technique (see R1) where patterns of line segments or spots of

light are projected onto a wafer surface and the saw marks are oriented perpendicular to the direction of wafer

transport.

2.6 Other measurement techniques may also provide similar information about saw marks of a wafer as compared

to this test method, but they are not the subject of this test method.

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 Loading of wafers onto the measurement system must ensure that the saw marks are transverse, not parallel, to

the direction of travel through the measurement system. Measurements made on wafers loaded with saw marks

parallel to the direction of travel will not be suitable for specifying the wafers’ saw mark topography.

3.2 Wafer surface height vibration caused by transport during measurement may adversely impact measurements.

3.3 The transverse locations where the measurements are taken on the wafer surface are critical. When comparing

measurement results obtained by different equipment or by subsequent measurements on the same equipment it

should be verified that the measurements are taken at the same transverse locations on the wafer surface.

3.4 Measurement of saw mark height change depends on the physical setup of the measurement equipment, its

opto-electronic noise level, and the calibration of measured signal to height.






Date: 4/16/2012

3.5 Variations of the projected light line image due to optical imperfections, including those of the wafer surface

(such as grain boundaries or stains), may affect the measurement result.

3.6 Wafer surface waviness may impact the saw mark measurement precision.

4 Referenced Standards and Document

4.1 SEMI Standards and Safety Guidelines

SEMI E89 –– Guide for Measurement System Analysis (MSA)

SEMI M59 –– Terminology for Silicon Technology

SEMI MF1569 –– Guide for Generation of Consensus Reference Materials for Semiconductor Technology

4.2 ISO Standards1

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

NOTE 1: Refer to SEMI’s Compilation of Terms (COT) for a list of the most current terms and their definitions.

5.1 Terms and acronyms relating to silicon and other semiconductor technology are defined in SEMI M59.

5.2 Other Abbreviations and Acronyms

5.2.1 AOI –– angle of incidence

5.2.2 COB –– center of brightness

5.3 Other Terms Used in this Standard

5.3.1 angle of incidence, of projected light line –– the angle between the line of sight of the projector and the

surface normal (of the wafer).

5.3.2 center line, CL — an imaginary straight line bisecting a square or pseudo-square wafer surface. It is

equidistant from opposing edges of the wafer surface.

5.3.3 center-of-brightness (COB) line –– a line fitted through a multiple pixel image representing the weighted

average of the pixel values transverse to the projected line direction.

5.3.4 pixel width and height, effective –– the distances on the wafer surface imaged by one picture element, or pixel,

of the image sensor in perpendicular directions.

5.3.5 saw mark –– a topographic step or groove along the sawing wire direction on the surface of a wafer, generated

by the wire of the multiple wire saw.

5.3.6 scan line –– an imaginary line parallel to a wafer edge and parallel to the wafer transport direction along

which measurements are performed.

5.3.7 waviness –– a surface height variation with spatial wavelengths of typically a few millimeters.

6 Summary of Test Method

6.1 Four patterns of light line segments are projected on the wafer surface at an AOI α as the wafer, resting on belts,

is moved along in the x- direction, the direction of belt travel. These segments provide illumination for image

acquisition along four scan lines.

6.1.1 The four scan lines are front-left (FL), back-left (BL), front-right (FR) and back-right (BR).

6.1.2 Each of these four projected light patterns are used identically to sample wafer topography at discrete

transverse locations y, the direction perpendicular to the x-direction, ultimately producing N times four surface

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






Date: 4/16/2012

height variation profiles: H(x, yFL), H(x, yBL), H(x, yFR) and H(x, yBR), where N is the number of line segments in a

pattern.

6.2 When loaded onto the conveyor belt system the wafer is oriented such that:

6.2.1 The wafer’s saw marks are perpendicular to the direction of belt travel.

6.2.2 Each projected light pattern illuminates the wafer surface at a distance ∆ from the nearest wafer edge.

6.3 Each projected pattern’s scattered light from the wafer surface is imaged by a camera system viewing the wafer

surface at normal incidence. Alternatively the positions of projector and camera may be interchanged.

6.4 Overlapping images of the projected light pattern scattered from the wafer surface are acquired during wafer

transit.

6.5 Height deviations from planar, along each scan line of the wafer surface, due to steps, grooves or waviness!!

result in small transverse translations of the projected light pattern on the wafer surface that are recorded by the

image of the projected light line segment (see R1).

6.6 The images are processed and evaluated by an algorithm according to § 14 .

6.6.1 A calibration factor for each of the four projected light patterns image acquisition systems is determined using

reference material with known step heights.

6.6.1.1 Small variations in the optical systems, such as the AOI of the projection and the actual viewing angle of the

camera being slightly off-normal, make a purely geometrical calculation based on AOI less precise than is possible

through calibration.

6.6.1.2 Calibration factors therefore are used to more precisely quantify surface height variation and reduce system-

to-system measurement variation.

7 Interferences

7.1 Vibrations of the test specimen relative to the probe-measuring axis may produce errors. Internal system

monitoring may also be used to detect non-repetitive and repetitive system mechanical translations.

7.2 Substantial variations in wafer surface properties may negatively impact the measurement result or possibly

prevent measurement of some wafers.

7.2.1 Wafer surface roughness variation, along a scan line within a single wafer or between wafers, may impose

signal to noise constraints on the optical system when imaging the light scatter from a nominally diffuse scattering

surface.

7.2.2 Surface waviness variations may also negatively impact the measurement result.

7.3 Variation of pixel height and width within a camera system may not be corrected through the calibration.

7.4 Mechanical variations in equipment adjustment may introduce errors.

7.5 Temperature gradients across the measurement set-up may affect the measurement performance.

7.6 Large surface defects, such as pits or chips, or contamination, such as slurry residue or particles, also may

impact the measurement result.

8 Apparatus (see Figure 1)

8.1 Wafer transport device –– consisting of two belts, which transport the wafer continuously through the

measurement apparatus without obstructing the projected light line or the line of sight of the cameras. The material

of the belts shall not leave traces or residue on the wafer surface.

8.2 Projector –– projecting one of the following patterns at an AOI α onto the wafer surface at a distance ∆ from

the wafer edge during transport.

8.2.1 Pattern A: N closely adjacent and equidistant parallel line segments that are oriented nominally parallel to the

direction of belt travel. Typically N = 1 or N = 2, but more are possible. The distance between two adjacent line

segments is denoted as δ.

8.2.2 Pattern B: N adjacent light spots (to be understood as limit of short line segments). Typically N = 1 or N = 2,

but more are possible. The distance between two adjacent spots is denoted as δ.






Date: 4/16/2012

8.2.3 The distance ∆ is measured from the wafer edges to the outmost part of the pattern.

8.3 In total four projectors are used, two above the wafer and two below the wafer.

8.4 Sensor –– an imaging digital camera system with an effective pixel width sw and an effective pixel height sh. It

is set-up with its line of sight normal to the wafer surface, recording images of the projected light pattern on the

wafer surface while in transit. In total four cameras are used, two above the wafer and two below the wafer.

8.5 Computer –– for controlling the measurement system and equipped with software for synchronously acquiring

and processing the camera images according to § 14.

8.6 The positions of projectors and corresponding cameras may be interchanged, meaning that the projector AOI is

normal and the camera views the wafer surface at an oblique angle.

9 Test Specimen

9.1 Clean, dry Si wafers with an as-cut surface condition.

10 Safety Precautions

10.1 The entire equipment has to be placed in a closed housing and has to be secured with a safety lock that stops

the belts and safely switches the tool off when the housing is opened.

10.2 If required by local, national or international safety requirements, eye protection goggles have to be used by

operators and maintenance personnel.

11 Preparation of Apparatus

11.1 The suitability of the equipment is determined by performing statistically based instrument repeatability and

reproducibility study to ascertain whether the equipment is operating within the manufacture’s stated specification,

e.g. according to SEMI E89.

11.2 Adjust the sensitivity of the camera and the light intensity of projected light pattern so that the intensity profile

of the image of the light pattern in the camera extends over at least three digital intensity levels above the noise level

of the camera while avoiding saturation and image bloom.

11.3 Define the control limits for SPC for the measurement equipment with a set of selected wafers.

NOTE 2: As this test method is intended for a high throughput, high volume measurement the equipment cannot be calibrated for

measuring each individual wafer. Therefore careful SPC has to be performed.

12 Calibration and Standardization

12.1 Each projection and camera imaging system is calibrated by using one or more reference wafers.

12.2 The reference wafers contain topographic surface features, called reference marks, with known step heights or

groove depths.

12.2.1 Care has to be taken selecting a tool for establishing the surface feature heights or depths of the reference

wafers. This tool has to be calibrated with traceable reference materials and be non-destructive, typically non-

contact.

12.3 Measure the reference wafer(s) according to the procedure given in § 13.

12.4 Determine for each reference mark k the calibration factor fk by dividing the known step height/groove depth

by the corresponding tk.

12.5 Determine the mean calibration factor f for that imaging system for several surface features k from one or

several wafers.

13 Procedure

13.1 Adjust the equipment and calibrate it according to the instructions of the supplier.

13.2 Determine the calibration factors f for each projection and camera imaging system.

13.3 Verify the equipment is within SPC limits.

13.4 Measure the wafer.

13.4.1 Place a wafer horizontally on the transport belts.






Date: 4/16/2012

13.4.1.1 Align the wafer so that two of its edges are parallel to, and the saw marks are oriented perpendicular to, the

direction of transport so that ∆ is within the range of 5 mm to 1/6 of wafer side length with a tolerance of ± 2 mm.

13.4.2 Move the wafer through the measurement set-up.

13.4.3 Scan the entire length of the wafer.

13.4.4 For pattern A record successive, overlapping images Hj(x, yi,) of each projected pattern during the scan so

that 100% wafer coverage across the four scan lines is ensured, where i denotes the scan line (FL, FR, BL and BR), j

denotes the image recorded.

13.4.5 For pattern B, combine successive images of the spot pattern so that images of line segments Hj(x, yi,) are

obtained that cover 100% of the wafer across the four scan lines.

13.4.6 Process each Hj(x, yi) from all four projection and camera imaging systems according to § 14.

13.4.7 Report the heights/depths of all saw marks identified as well as the maximum saw mark height/depth of the

wafer according to § 15.

13.5 Repeat with the next wafer.

14 Calculations

14.1 The following calculations are performed automatically within the instrument. An outline of the calculation

structure is provided here to indicate the nature of the procedure.

14.2 The projected light pattern and its image recorded by the digital camera have a finite width extending over

several pixels. Therefore the image of the light pattern consists of an array of pixels that has to be processed to

generate a line representing the surface profile that can be evaluated with respect to saw marks.

14.3 Define sampling points as follows for each line segment in Hj(x, yi) in order to calculate the saw mark step

height/groove depth from the scanned measurement points.

14.3.1 Assign a rectangular coordinate system to each Hj(x, yi) so that the x-axis is along the length of the line

image(s) and the y-axis is perpendicular to the x-axis (Figure 2).

14.3.2 For each line image in a light pattern identify each pixel by a pair (x, yi) of integer index numbers, e.g. (215,

30), corresponding to the indices of the pixel in line 30 of column 215 of the pixel array.

14.3.3 Identify the gray-scale image brightness of the pixel at (x, yi) by In(x, yi) with n denoting the number of lines

in the light pattern.

14.3.4 Image values typically range from 0 to 2M

– 1, where M is the bit-depth of the image. Typical cameras use 8-

bit images in unsigned integer format. In this case image brightness values span the range from 0 to 255 and use

only 1 byte of data storage.

14.3.5 For each x-index value determine three yi-index values for each line image as follows:

14.3.5.1 Select a brightness threshold Ith that defines the signal level threshold clearly above noise level.

14.3.5.2 Determine ym,n(x) where In(x,yi) has its maximum.

14.3.5.3 Determine yl,n(x), the last y-index value where In(x ,yi) > Ith starting at ym,n(x) and going to increasing y-

values.

14.3.5.4 Determine yu,n(x), the last y-index value where In(x, yi) > Ith starting at ym,n(x) and going to decreasing y-

values.

14.3.6 Calculate the COB lines yCOB,n(x) for each line in the pattern by

∑

∑=

)(,

)(,

)(,

)(.

,

),(

),()(

xy

xy in

xy

xy ini

nCOBnu

nl

nu

nl

yxI

yxIyxy (1)

with array indices x and yi, and the image brightness In(x, yi) at point (x, yi) of line n in the pattern with N lines in

total.






Date: 4/16/2012

14.4 Perform a segmented polynomial spline fit2 to each COB line. Each polynomial spline fit segment consists of

a fixed number of p sampling points (Figure 4).

14.5 Subtract the spline-fitted line from each COB line (Figure 4).

14.6 Apply a moving-average filter of a fixed width of q sampling points to this line to smooth the resulting line3

(Figure 4).

14.7 Calculate the peak-to-valley values ti,j,n(x) within a sliding window of a width of r sampling points for the

smoothed line (Figure 4).

14.8 Define a saw mark threshold tth.

14.9 Identify each peak as saw mark where ti,j,n(x) ≥ tth.

14.10 Calculate the height/depth hi,j,n(x) of the saw mark by

(2)

14.11 Assign to hi,j(x) the mean of all lines of a pattern by

(3)

if a saw mark is identified in all lines at the same position and add it to the list of saw marks found on the wafer.

14.12 If N > 1 discard hi,j,n(x) if only one line of a pattern identifies a saw mark at the same position x.

14.13 If N = 1 then hi,j(x) = hi,j,1(x).

14.14 Determine hmax as

(4)

and report it.

15 Report

15.1 The report shall contain the following elements.

15.1.1 Date and time of test.

15.1.2 Identification number of measurement equipment.

15.1.3 Software revision.

15.1.4 Calibration and SPC status of measurement equipment.

15.1.5 Ambient temperature.

15.1.6 Lot identification, including each wafer ID if available

15.1.7 Angle of incidence (AOI) α.

15.1.8 Line segment pattern used, A or B.

15.1.9 Number of lines segments or spots used.

15.1.10 Distance δ, if multiple line segments of spots are used.

15.1.11 Effective pixel width sw and height sh.

15.1.12 Smoothing filter length q.

2 See e.g. http://en.wikipedia.org/wiki/Smoothing_spline and reference therein. 3 See e.g. E.L. Church et al., Optical Engineering 24 (1985) 388 for theory of filtering.

fxtxh njinji )()( ,,,, =

N

xh

xh n

nji

ji

∑=

)(

)(,,

,

)max( ,max jihh =






Date: 4/16/2012

15.1.13 Evaluation window width r.

15.1.14 Saw mark threshold value tth.

15.1.15 Number of saw marks found.

15.1.16 List of saw marks and their height/depth in micrometers.

15.1.17 Maximum height/depth of saw marks hmax in micrometers.

16 Precision and Accuracy

16.1 The precision of the method has been determined experimentally by performing a MSA that provided the

summarized results regarding repeatability and reproducibility shown in Table 1. Details of the MSA are reported in

Related Information 1.

16.2 No certified reference materials currently exist to establish the accuracy of measurement equipment for

measuring saw mark dimensions that can be used with equipment as described in this test method.

16.3 Provisional reference materials may be qualified by using appropriate measurement equipment that is capable

measuring certified reference materials as well as silicon wafers (SEMI MF1569).

16.4 In the absence of inter-laboratory test data to establish repeatability and reproducibility this test method should

be used for materials specification and acceptance only after the parties to the test have established reproducibility

and correlation.

Table 1 Results of MSA

Metric hmax

σr/µm#1 0.86

P/T#2,#3 6.5 %

#1 Total standard deviation, combined for repeatability and reproducibility

#2 Precision over tolerance ratio (SEMI E89), tolerance for hmax was assumed to be +20 µm

#3 Precision was defined as 3 σr






Date: 4/16/2012

NOTE: The lower part is mirror symmetric to the upper part with respect to the plane of

the wafer. Light line pattern A with a single line segment is shown on the left side of

the wafer and line pattern A with a pair of line segments on its right side.

Figure 1

Schematic View of the Upper Part of the Measurement Set-Up

NOTE: The white dashed rectangle indicates the expanded section of the light line shown

in Figure 3.

Figure 2

Assignment of Coordinate Axes to Image of Light Line Segment on Wafer Surface

digital cameras

wafer transport

direction

projector

wafer

projector

projected light line

segment pattern A

with two parallel

line segments

projected light line

segment pattern A

with a single line

segment

saw marks

scan line FLscan line FR

α

transport belts

∆

x (parallel to scanned line)

y






Date: 4/16/2012

Figure 3

Enhanced section of Pixel Image of the Light Line on the Wafer Surface of Figure 2, Illustrating the Choice of

yu,x and yl,x.

yu,x1

yu,x2

yu,x3

yl,x1

yl,x2 , yl,x3

x1 x2 x3 x

ypixels with largest

y where intensity

is above threshold

pixels with smallest y

where intensity is

above threshold

COB line






Date: 4/16/2012

Figure 4

Illustration of the Processing Steps for Evaluating the Peak-to-valley Value from the Digital Image of the

Light Line Trace

x/a.u.

y/a

.u.

Image of light line

segment

COB line and spline fit

(dashed)

subtraction of spline fit

from COB line

moving average

filter

peak-to-valley

evaluation -> ti,j,n(x)maximum

peak-to-valleytth






Date: 4/16/2012

RELATED INFORMATION 1 RECOMMENDED PARAMETER SETTINGS AND MSA

NOTICE: This Related Information is not an official part of SEMI doc. 5331A and was derived from the work of

the global PV Materials 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 settings of parameters α, p, q, r, s significantly impact the outcome of a saw mark measurement.

Therefore a set of parameters is provided that enables reproducible measurements and that is widely used.

R1-2 Parameter Settings

R1-2.1 The following settings for the parameters are recommended:

• α = 76°

• p = 400

• q = 5

• r = 25

• sh = 20 µm

R1-3 Geometrical Resolution

R1-3.1 The fundamental relation between the saw mark height/depth (h), the AOI α (with respect to surface

normal) and the measured offset a of the light trace due to the higher/lower surface of the saw mark as compared to

the adjacent surface is as follows (see Figure R1-1):

αtanha = . (R1-1)

R1-3.2 A change in height/depth (∆h) results then in a change ∆a based on equation R1-1 and assuming a constant

angle α:

αtanha ∆=∆ . (R1-2)

R1-3.3 Assuming that the minimum ∆a that can be detected by the system equals the effective pixel height sh one

obtains with the parameters settings of R1-2.1 a height/depth resolution of the measurement set-up of

µmµms

h h 0.576tan

20

tan=

°==∆

α. (R1-3)






Date: 4/16/2012

h

a

α

projector

camera

projected line

projected line

wafer surface

Figure R1-1

Schematic Drawing of Basics of Light Sectioning Technique

R1-3.4 Therefore the minimum saw mark height/step that can be detected based on geometrical considerations is

5.0 µm.

R1-3.5 However, the light trace on the wafer surface is a line the image of which is several pixels wide in the y-

direction (see Figures 3 and 4) displaying an intensity profile. Therefore smaller saw marks heights/depths changes

may be detected with the techniques as described in § 14 by evaluating the intensity profile of the line image.

R1-4 Results of MSA

R1-4.1 Test specimen –– 3 wafers 156 × 156 mm2.

R1-4.2 Test conditions –– 27 repeats per day on 4 days, performed with the settings as described in R1-2.1.

R1-4.3 Light pattern used –– Pattern A with a single line segment.

R1-4.4 Results –– in Table R1-1 the mean values and standard deviations per day and per wafer are reported for

hmax. The mean and the standard deviation per wafer (over 4 days) are reported in Table R1-2. The results of the

individual measurements per day and per repeat are displayed in Figure R1-2.

Table R1-1 Results of MSA, Mean and Standard Deviation Per Wafer and Per Day

Wafer Day hmax mean/µm hmax std.dev./µm

1 1 25.481 0.580

1 2 25.222 0.751

1 3 25.296 1.068

1 4 25.111 0.641

2 1 18.630 0.792

2 2 18.148 0.456

2 3 18.370 0.839

2 4 18.074 0.781

3 1 22.370 0.884

3 2 22.778 0.934

3 3 22.963 1.091

3 4 23.000 0.920






Date: 4/16/2012

Table R1-2 Results of MSA, Mean and Standard Deviation Per Wafer

Wafer hmax mean/µm hmax std.dev/µm

1 25.278 0.783

2 18.306 0.755

3 22.778 0.980

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

1 11 21 1 11 21 1 11 21 1 11 21

hm

ax/

μm

Day and Repeat

Wafer_1 Wafer_2 Wafer_3

Day 1 Day 2 Day 3 Day 4

Figure R1-2

Results of Daily Measurements of Saw Marks






Date: 4/16/2012

RELATED INFORMATION 2

SCHEMATIC ILLUSTRATIONS OF SAW MARK TYPES

NOTICE: This Related Information is not an official part of SEMI doc. 5331A and was derived from the work of

the global PV Materials Technical Committee. This Related Information was approved for publication by full letter

ballot procedures on [A&R approval date].

Figure R2-1

Schematic Cross Section of a Wafer Displaying a Groove Type Saw Mark With Width b and Depth t.

Figure R2-2

Schematic Cross Section of a Wafer Displaying a Step Type Saw Mark with Height t.

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