SEMI Test Methods under Development Peter Wagner Test Methods... · SEMI Test Methods under...

SEMI Test Methods under Development

for Si Feedstock Materials, Bricks and

Wafers Peter Wagner

Background

• SEMI Test Methods are an essential part of SEMI

Standards.

• They are referenced in material specifications.

• They help to establish common understanding

• of metrics,

• of measurement procedures and

• of measurement results.

• So far, 7 out of 33 published SEMI PV Standards are Test Methods

• Several new test methods are currently developed

Workshop on Test Methods for Si Feedstock

Materials, Bricks and Wafers, Munich, June 2012 2

Published SEMI Test Methods

• SEMI PV1-0211, Test Method for Measuring Trace Elements in PV-Grade Si by

High-Mass Resolution Glow Discharge Mass Spectrometry

• SEMI PV9-0611, Test Method for Excess Charge Carrier Decay in PV Si

Materials by Non-Contact Measurement of Microwave Reflectance after a Short

Illumination Pulse

• SEMI PV10-1110, Test Method for Instrumental Neutron Activation Analysis

• SEMI PV13-1111, Test Method for Contactless Excess-Charge-Carrier

recombination Lifetime Measurement in Si Wafers, Ingots, and Bricks Using an

Eddy-Current Sensor

• SEMI PV23-1011, Test Method for Mechanical Vibration of Crystalline Si PV

Modules in Shipping Environment

• SEMI PV25-1011, Test Method for Simultaneously Measuring Oxygen, Carbon,

Boron and Phosphorous in Solar Si Wafers and Feedstock by Secondary Ion

Mass Spectrometry

• SEMI PV28-0212, Test Method for Measuring Resistivity or Sheet Resistance

with a Single-Sided Noncontact Eddy-Current Gauge



Test Methods under Development(1)

• Doc 5330, NEW STANDARD: TEST METHOD FOR IN-LINE MEASUREMENT

OF CRACKS IN PV SILICON WAFERS BY DARK FIELD INFRARED IMAGING

(EU, passed technical review)

• Doc 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 (EU, passed technical

review)

• Doc 5332A, NEW STANDARD: TEST METHOD FOR IN-LINE MEASUREMENT

OF THICKNESS AND THICKNESS VARIATION OF SILICON WAFERS FOR

PV APPLICATIONS USING CAPACITIVE PROBES (EU, passed technical

review)

• Doc 5333, NEW STANDARD: TEST METHOD FOR IN-LINE MEASUREMENT

OF WAVINESS OF PV SILICON WAFERS BY A LIGHT SECTIONING

TECHNIQUE (EU, ballot planned for July 2012)



Test Methods under Development(2)

• Doc 4675B, NEW STANDARD: TEST METHOD FOR THE MEASUREMENT OF

ELEMENTAL IMPURITY CONCENTRATIONS IN SILICON FEEDSTOCK FOR

SILICON SOLAR CELLS BY BULK DIGESTION, INDUCTIVELY COUPLED-

PLASMA MASS SPECTROMETRY (NA, drafting)

• Doc 5394, NEW STANDARD: TEST METHOD FOR QSS MICROWAVE PCD

MEASUREMENTS OF CARRIER DECAY AND LIFETIME (NA, drafting)



Planned New Activities

• Doc xxxx, NEW STANDARD, TEST METHOD FOR IN-LINE

CHARACTERIZATION OF PV SI WAFERS BY USING

PHOTOLUMINESCNCE( EU, drafting)

• Doc xxxx, NEW STANDARD, TEST METHOD FOR IN-INE

MEASUREMENT OF LATERAL DIMENSIONS OF SILICON WAFERS FOR

PV APPLICATIONS (EU, drafting)

• Doc xxxx, NEW STANDARD; TEST METHOD FOR IN-LINE

CHARACTERIZATION OF PV SILICON WAFERS REGARDING GRAIN

SIZE (EU, drafting)



Doc 5330, Purpose

• Silicon (Si) for PV applications contains a variety of micro- and macroscopic

crystallographic defects and flaws that may impact the efficiency of a solar

cells or the yield of a manufacturing line.

• Two categories of defects:

• Grown-in defects consisting of point defects (impurities, vacancies, self-

interstitials and their complexes), dislocations, grain boundaries, and

precipitates/inclusions.

• Process induced defects consisting of chips/indents (surface and edge) and

cracks (not to mention the surface itself).

• Inclusions, chips and cracks are detrimental for solar cell processing as they

may enhance stress in the wafer bulk and the region surrounding them and

trigger the breakage of a wafer.

• Defining a test method for reproducibly detecting and characterizing cracks

and distinguishing them from other defects to avoid quality issues and

improve claim handling.



Doc 5330, Scope

• This test method characterizes cracks in single or multi-crystalline Si

wafers.

• It covers an in-line, non-contacting and non-destructive method that

determines the number of cracks per wafer and crack length of clean, dry

as-cut Si wafers that are supported by two belts that move the test

specimen through the measurement equipment.

• This test method covers square and pseudo-square PV Si wafers, with a

nominal edge length ≥ 125 mm and a thickness ≥ 100 µm.

• Because this test method is intended for in-line high throughput

measurements it is mandatory to operate the measurement system under a

tight SPC (e.g. ISO 11462) for obtaining reliable, repeatable and

reproducible measurement data.



Doc 5330, Apparatus



digital line cameras

wafer transport direction

wafer

projector below wafer

projected light stripa

surface normal and line of sight of camera

projector besides waferprojector

besides wafer

Schematic drawing of the Set-up

for Measuring Cracks Showing

Projector Positions for Method A

(Projector below Wafer) and

Method B (Projectors besides

Wafer)

Doc 5330, Image Processing Steps



Edge detection and filtering

Detection of potential defects

Identification and

classification

of defects

SegmentationComparison

and final decision

Step 1 Step 2 Step 3 Step 4 Step 5

Outline of the Flow of the

Image Processing Steps


Materials, Bricks and Wafers, Munich, June 2012

Doc 5331, Purpose

• 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.

• 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.

• 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.

• Standardized test methods providing reproducible values for saw marks

are required to specify this aspect of wafer quality.

• Process and quality control during manufacturing of wafers requires

continuous monitoring of saw marks with a non-contact method that

supports high throughput.

11



Doc 5331, Scope

• Determining maximum peak-to-valley of saw marks that typically run

across the entire wafer surface and along the wire direction.

• Applying to square and pseudo-square PV Si wafers, single and

multicrystalline, with a nominal edge length ≥ 125 mm and a nominal

thickness ≥ 100 µm.

• Intended for in-line, non-conctact, non-destructive 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.

• Based on a light sectioning technique where the saw marks are oriented

perpendicular to the direction of wafer transport.

12



Doc 5331, Apparatus

13

digital cameras


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

a

transport belts

D

Schematic View of the Upper

Part of the Measurement Set-

Up



Doc 5331, Data Processing

14

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-valley

tth

Illustration of the Processing

Steps for Evaluating the Peak-to-

valley Value from the Digital

Image of the Light Line Trace



Doc 5332, Purpose

• Wafer thickness and its variation across a wafer are important

parameters for solar cell manufacturing. Excessive thickness variations

within a lot from wafer to wafer or within a wafer may negatively impact

process yield and solar cell efficiency.

• Both parameters are part of the specification for solar cell wafers (SEMI

PV22), which define a thickness range as well as an upper limit for the

total thickness variation (TTV).

• In addition, careful process and quality control of the wafer thickness and

its variation during wafer and solar cell manufacturing requires

continuous monitoring of thickness by the supplier of wafers for PV

applications as well as by the user of such wafers.

• Therefore a standardized test method providing reproducible data for

thickness and its variation is required to establish agreement between

business partners regarding the specification of wafers.

15



Doc 5332, Scope

• In-line, non-contact, non-destructive measurement of the thickness and

the TTV of clean, dry silicon (Si) wafers supported on two belts that

move the test specimen through the measurement equipment.

• Applicable to square or pseudo-square multi- as well as single-crystalline

Si wafers in the resistivity range 10-3 W·cm to 105 W·cm with edge length

≥ 125 mm and with thickness ≥ 100 µm.

• Based on simultaneously measuring the capacitance between an aligned

pair of capacitive probes and the wafer surfaces when the wafer passes

through the gap formed between the capacitive probe pair.

• The test method does not cover measurement of surface flatness, warp,

bow or sori of wafers.

• The test method is intended for in-line high throughput measurements.

Therefore it is mandatory to operate system under tight statistical

process control (SPC), e.g. ISO 11462, in order to obtain reliable,

repeatable and reproducible measurement data.

16


Materials, Bricks and Wafers, Munich, June

2012

Doc 5332, Apparatus(1)

17

capacitive probe A

capacitive probe B

capacitive probe C

light sensors or emitters, respectively



waferwafer transport direction

CL = SL b

l1 l1

SL a

l3

l3

l2 l2

SL c

Schematic Drawing of

the Set-Up of the

Capacitive Probes, Top

View of the Bottom

Probes. The Gray

Areas Depict the Active

Areas of the Capacitive

Probes.



Doc 5332, Apparatus(2)

18


l3+e l3+e

l3+e l3+e

l3

l3

CL = SL b

SL a

CL

l2l2

SL c

OD

OD

OD

OD

OD

OD

Measurement Positions for 5- Point

(Triangles) and 9- Point (Circles)

Measurements. The Crosses Depict the

First and Last Measurement Points as

well as the Center Points on the Scan

Lines.



Doc 5332, Metrics

19

L3TA

Area

Measure Measure

thicknessthickness variation

entire line selected points

L3T5

Number of

points

L3TC

L3T9

thicknessthickness variation

L3VANumber

of points

L3V5 L3V9

5 59 9

1

Offset distance OD3 line scans

Thickness Metrics

Decision Tree



THANK YOU FOR YOUR KIND ATTENTION

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