1

Structured wire in

multi-crystalline silicon

wafer mass production:

An efficient alternative to

diamond wire

Oliver Anspach

PV Crystalox Solar Silicon

GmbH, Germany

5th Annual c-Si PVMC

workshop

at Intersolar NA -

Wednesday July 13, 2016

2 5th Annual c-Si PVMC workshop

July 13, San Francisco, USA

England

Ingot / Block

Production

in Oxfordshire

Germany

Wafer

Production

in Erfurt

Clear focus on the crystalline silicon wafer technology

Independent Si-wafer manufacturer with European content and

low carbon foot-print

3 5th Annual c-Si PVMC workshop

July 13, San Francisco, USA

$0,50

$0,55

$0,60

$0,65

$0,70

$0,75

$0,80

$0,85

$0,90

$0,95

$1,00

Aug-12 Mar-13 Oct-13 Apr-14 Nov-14 May-15 Dec-15 Jun-16

Wafer price 2012 - 2016

Motivation

Average spot market price for

156 mm Multi-Si Solar Wafer

1) Source: PVinsights.com

1)

Wafer price 2011 - 2013

4 5th Annual c-Si PVMC workshop

July 13, San Francisco, USA

Challenges in Wafering

Thinner wires

Thinner wafers

Higher throuhput

Less consumables

Fixed Abrasives Diamond wire

Loose Abrasives Structured wire

Higher yield

Higher precision

Less breakage

• Only coolant needed – no loose abrasives

necessary

• High cutting speeds

• Wafer surface structure / breakage / texture

• New wire saws mandatory

• Differences in cutting of mono- or multi-Si

• Conventional slurry / wire system

• Higher cutting speeds / less wire

• Less slurry

• Less kerf loss

• Conventional wire saws

2) D. Heppner et al.; AMAT; 26th EUPVSEC, Hamburg, 2011.

2)

5 5th Annual c-Si PVMC workshop

July 13, San Francisco, USA

Structured wire

Wafering Squaring

6 5th Annual c-Si PVMC workshop

July 13, San Francisco, USA

Structured wire

Patents

Charles Hauser, 1990, WO 90/12670

„wire with active surface“

NV Bekaert S.A., 1999, WO 99/28547

„wire with waved elements“

NV Bekaert S.A., 2012,

WO 2012/069314

„structured wire with

helicoidal shape“

Sodetal, 2013,

WO 2013/076400

„twisted wire with a helix“

Trefilarbed (Arcelor), HCT Shaping

Systems (AMAT), 2006,

WO 2006/067062

„monofilament metal wire with crimps“

7 5th Annual c-Si PVMC workshop

July 13, San Francisco, USA

Structured wire – wafer mass production

Progress in wafer mass production using structured wire

121%

273%

0%

50%

100%

150%

200%

250%

300%

mo

nth

01

mon

th 0

2

mon

th 0

3

mo

nth

04

mon

th 0

5

mon

th 0

6

mo

nth

07

mon

th 0

8

mon

th 0

9

mon

th 1

0

mon

th 1

1

mon

th 1

2

mon

th 1

3

tod

ay

R&

D

table speed

Structured wire

production process:

• More than 150 % higher

throughput possible

• Similar throughput to

diamond wire process

possible

Vertical force

Diamond wire

process table

speed range

Straight wire process = 100 %

3) Anspach et al., Solar Energy Materials & Solar Cells 131 (2014) 58–63.

3)

8 5th Annual c-Si PVMC workshop

July 13, San Francisco, USA

Structured wire – wafer mass production

Progress in wafer mass production using structured wire

Structured wire

production process:

• More than 150 % higher

throughput possible

• More than 50 % less wire

consumption possible

Vertical force

121%

273%

84% 46%

0%

50%

100%

150%

200%

250%

300%

mo

nth

01

mon

th 0

2

mon

th 0

3

mo

nth

04

mon

th 0

5

mon

th 0

6

mo

nth

07

mon

th 0

8

mon

th 0

9

mon

th 1

0

mon

th 1

1

mon

th 1

2

mon

th 1

3

tod

ay

R&

D

table speed

wire consumption

Straight wire process = 100 %

3) Anspach et al., Solar Energy Materials & Solar Cells 131 (2014) 58–63.

3)

9 5th Annual c-Si PVMC workshop

July 13, San Francisco, USA

Structured wire – wafer mass production

The faster the cutting process the less power is needed!

0

100

200

300

400

500

600

Su

m p

ow

er

co

nsu

mp

tio

n [

kW

h]

time

straight wire process

structured wireprocess

Structured wire

production process:

• More than 150 % higher

throughput possible

• More than 50 % less wire

consumption possible

• Less power consumption

needed (3rd main cost

driver)

10 5th Annual c-Si PVMC workshop

July 13, San Francisco, USA

Structured wire – wafer mass production

Progress in wafer mass production using structured wire

121%

273%

39%

84% 46%

0%

50%

100%

150%

200%

250%

300%

mo

nth

01

mon

th 0

2

mon

th 0

3

mo

nth

04

mon

th 0

5

mon

th 0

6

mo

nth

07

mon

th 0

8

mon

th 0

9

mon

th 1

0

mon

th 1

1

mon

th 1

2

mon

th 1

3

tod

ay

R&

D

table speed

slurry consumption

wire consumption

Structured wire

production process:

• More than 150 % higher

throughput possible

• More than 50 % less wire

consumption possible

• Less power consumption

• More than 50 % less

slurry consumption

possible

Roughness

0,0

0,5

0 50 100 150 200 250

Ra

[µ

m]

distance from wire entry [mm]

straight wirestructured wire

Straight wire process = 100 %

3) Anspach et al., Solar Energy Materials & Solar Cells 131 (2014) 58–63.

3)

11 5th Annual c-Si PVMC workshop

July 13, San Francisco, USA

Structured wire – wafer mass production

Structured wire does not use small particles for cutting!

0,0

0,5

0 50 100 150 200 250

Ra [

µm

]

distance from wire entry [mm]

straight wirestructured wire

Roughness

0

0,2

0,4

0,6

0,8

1

0,1 1 10 100Freq

uen

cy d

istr

ibu

tio

n

Geometric particle diameter in µm

SiC-particlesSi-particlessum

wire

large particles

cut at the

wire entry

small particles

cut at the

wire exit

Particle size

entry both

wires

3) Anspach et al., Solar Energy Materials & Solar Cells 131 (2014) 58–63.

4) Anspach et al., Proceedings of the 24th EUPVSEC (2009).

3)

4)

12 5th Annual c-Si PVMC workshop

July 13, San Francisco, USA

Structured wire – wafer mass production

Structured wire does not use small particles for cutting!

0,0

0,5

0 50 100 150 200 250

Ra [

µm

]

distance from wire entry [mm]

straight wirestructured wire

Roughness

wire

large particles

cut at the

wire entry

small particles

cut at the

wire exit

Particle size classifi-

cation straight wire

Particle size

entry both

wires

0

0,2

0,4

0,6

0,8

1

0,1 1 10 100Freq

uen

cy d

istr

ibu

tio

n

Geometric particle diameter in µm

SiC-particlesSi-particlessum

3) Anspach et al., Solar Energy Materials & Solar Cells 131 (2014) 58–63.

3)

3) Anspach et al., Solar Energy Materials & Solar Cells 131 (2014) 58–63.

4) Anspach et al., Proceedings of the 24th EUPVSEC (2009).

4)

13 5th Annual c-Si PVMC workshop

July 13, San Francisco, USA

Structured wire – wafer mass production

Structured wire does not use small particles for cutting!

0,0

0,5

0 50 100 150 200 250

Ra [

µm

]

distance from wire entry [mm]

straight wirestructured wire

Roughness

wire

large particles

cut at the

wire entry

small particles

cut at the

wire exit

Particle size classifi-

cation straight wire

Particle size

entry both

wires

Particle size class.

structured wire

0

0,2

0,4

0,6

0,8

1

0,1 1 10 100Freq

uen

cy d

istr

ibu

tio

n

Geometric particle diameter in µm

SiC-particlesSi-particlessum

3) Anspach et al., Solar Energy Materials & Solar Cells 131 (2014) 58–63.

4) Anspach et al., Proceedings of the 24th EUPVSEC (2009).

3)

4)

14 5th Annual c-Si PVMC workshop

July 13, San Francisco, USA

Structured wire – wafer mass production

Structured wire does not use small particles for cutting!

0,0

0,5

0 50 100 150 200 250

Ra [

µm

]

distance from wire entry [mm]

straight wirestructured wire

Roughness

wire

large particles

cut at the

wire entry

small particles

cut at the

wire exit

Particle size classifi-

cation straight wire

Particle size

entry both

wires

Particle size class.

structured wire

3) Anspach et al., Solar Energy Materials & Solar Cells 131 (2014) 58–63.

4) Anspach et al., Proceedings of the 24th EUPVSEC (2009).

3)

4)

15 5th Annual c-Si PVMC workshop

July 13, San Francisco, USA

Structured wire – wafer mass production

What about higher kerf loss with structured wire? Kerf loss

140

145

150

155

160

165

170

0 100 200

Slo

t w

idth

[µ

m]

structrured wire entry structured wire exit

straight wire entry straight wire exit

• In 2012 standard 120 µm straight wire

• 900 mm block length with 345 µm pitch

• Introduction of 115 µm structured wire

120

125

130

135

140

145

150

155

160

0 1000 2000

calc

. kerf

lo

ss [

µm

]

corresponding wafer #

pitch

new pitch

• 200 µm thin wafers

• New median pitch 4 µm

less than standard

• Pitch correction of wire

guiding rollers possible

today

3) Anspach et al., Solar Energy Materials & Solar Cells 131 (2014) 58–63.

3)

16 5th Annual c-Si PVMC workshop

July 13, San Francisco, USA

Structured wire – wafer mass production

Why such a decrease of more than 20 µm kerf loss?

• Straight wire showed around 5 µm diameter loss due to wire wear

• Structured wire kerf loss is defined by a combination of:

Fresh wire Used wire 0°

Used wire 90 °

Wire wear

• Non-uniform

wire wear

• Brass coating

partly evident

• 0 - >20 µm

diameter loss

17 5th Annual c-Si PVMC workshop

July 13, San Francisco, USA

Structured wire – wafer mass production

Why such a decrease of more than 20 µm kerf loss?

Straight wire showed around 5 µm diameter loss due to wire wear

Structured wire kerf loss is defined by a combination of:

Wire wear

• Non-uniform

wire wear

• Brass coating

partly evident

• 0 - >20 µm

diameter loss

Structure

amplitude

• Manufacturer

defines

amplitude

• Structure

(effective

amplitude)

looses with

increasing

wire wear

• Structure

stiffness

+

18 5th Annual c-Si PVMC workshop

July 13, San Francisco, USA

Structured wire – wafer mass production

Why such a decrease of more than 20 µm kerf loss?

• Straight wire showed around 5 µm diameter loss due to wire wear

• Structured wire kerf loss is defined by a combination of:

Wire wear

• Non-uniform

wire wear

• Brass coating

partly evident

• 0 - >20 µm

diameter loss

Structure

amplitude

• Manufacturer

defines

amplitude

• Structure

(effective

amplitude)

looses with

increasing

wire wear

• Structure

stiffness

Wire tension

• Wire tension

defines

effective

amplitude

• Loss of wire

tension in wire

web + +

0 µm

2 µm

4 µm

6 µm

8 µm

10 µm

12 µm

14 µm

16 µm

18 µm

20 µm

0 N 10 N 20 N

Eff

ec

tive

am

pli

tud

e

19 5th Annual c-Si PVMC workshop

July 13, San Francisco, USA

Structured wire – wafer mass production

Why such a decrease of more than 20 µm kerf loss?

• Straight wire showed around 5 µm diameter loss due to wire wear

• Structured wire kerf loss is defined by a combination of:

Wire wear

• Non-uniform

wire wear

• Brass coating

partly evident

• 0 - >20 µm

diameter loss

Structure

amplitude

• Manufacturer

defines

amplitude

• Structure

(effective

amplitude)

looses with

increasing

wire wear

• Structure

stiffness

Wire tension

• Wire tension

defines

effective

amplitude

• Loss of wire

tension in wire

web

Speed ratio

• The higher the

speed ratio …

• … the higher

wire wear

• … the higher

wire tension

• … the less

effective

amplitude

+ + +

20 5th Annual c-Si PVMC workshop

July 13, San Francisco, USA

Structured wire – wafer mass production

High table to wire speed ratios cause loss of effective amplitude!

182

184

186

188

190

192

194

196

0 20 40 60

Cen

ter

wafe

r th

ickn

ess [

µm

]

Speed ratio [µm/min * (m/s)-1]

21 5th Annual c-Si PVMC workshop

July 13, San Francisco, USA

Structured wire – summary

Structured wire shows still high cost

reduction potential

Save cost in the short + mid term range

without invest

Still standard wire sawing equipment ready

for even thinner wires

One has to take care with the structure of

the wire

Balance between wire wear and wire tension

and effective amplitude

What is the best structure and why?

Where is the physical and economical limit

of Si load in slurry?

22 5th Annual c-Si PVMC workshop

July 13, San Francisco, USA

Wafering – near term challenges (1-3 years)

Reduce cost by 15-20 % per year

Reduce wire diameter down to less than 100 µm

Find optimal and stiff structure for thin wires

< 100 µm (take state of wear into account)

Steel wire with high breaking load

Structure wire

Reduce cost by 15-20 % per year

Reduce wire diameter down to 60 µm and get it work

in mass production

Very thin steel wire with high breaking load

Diamond wire

23 5th Annual c-Si PVMC workshop

July 13, San Francisco, USA

Wafering – long term challenges (4+ years)

Reduce cost by 15-20 % per year

Be aware of …

Conventional wire sawing

Show mass production capability

Show cost advantage after

development phase

Mono: Very high

performance n-type Si

needed

… New technologies

24 5th Annual c-Si PVMC workshop

July 13, San Francisco, USA

Slurry

Thank you for your attention!

wire

Si-block

Acknowledgement:

R&D + Engineering Team at PV Crystalox Solar Silicon GmbH