In - line Characterization of Photovoltaic Wafers
SEMI Workshop, June 2012, Dr. K. Herrmann
Agenda
- Introduction and Background
- Measurement System Analysis
- Measurement System Control and Product Yield
- Industry Standards
- Wafer Tracking
- Summary and Conclusion
2
Company Profile
1985
Engineering office Hennecke Ecker GBR, automation
engineering, design
1995
Changing of company‘s legal form in Hennecke
Systementwicklung - Office in Zülpich Germany (near Cologne),
projects in the field of measurement technology, automation and
process control
1999
Installation of the first wafer measurement and sorting system at
Bayer Solar AG (Deutsche Solar AG)
2008
Service Points in P.R. China, R.O.C. Taiwan, Freiberg
(Sachsen), USA, Japan
Hennecke Systems GmbH, Member of the Meyer Burger Group
2010
Meyer Burger 100 % shareholder of Hennecke
2011
Installed more than 400 machines worldwide
Key Trends in Solar Industry
4
Recent Trend in PV Industry
Dramatic Price Decline
⇒ need to reduce the manufacturing costs
⇒ need to improve cell efficiency
⇒ need to improve yield
5
How can Measurement Technology
contribute to these Needs ?
6
Measurement System Analysis
7
What about the Measurement System ?
Accuracy ?
Precision ?
Is the measurement system sufficiently capable enough to
collect appropriate data ?
8
What about the Measurement System ?
According to David C. Crosby, « If you don’t
know the capability of your measurement
system, you don’t know if your measurements,
or products, or services are good or bad »
David C. Crosby (1930 – 2010), Quality management, Zero Defect Strategy
9
Measurement System Analysis
Accurate and
precise
Accurate but not
precise
Precise but not
accurate
Not accurate or
precise
10
Measurement System Analysis
Important Reporting Ratios: Cp, Cpk
Process capability index Cp: => describes the variability of the
measurement process
Process capability index Cpk: => describes the variability of the process
with respect to a reference value of the
product specification
11
Measurement System Analysis
Process Capability Index
Definition of Cp and Cpk:
USL − LSL
T
=
6 ⋅σ
6 ⋅σ
 USL − xm xm − LSL 
= min 
;

3 ⋅σ 
 3 ⋅σ
Cp =
C pk
USL, LSL:
Upper / Lower Specification limit
T:
Tolerance limit
σ:
Variability of process
xm:
Reference value of process
12
Measurement System Analysis
Process Capability Index
Examples:
13
MSA Test Certificate
Measurement Equipment Ability(Cp/Cpk)
Date:
System
Data
30.09.2010
0 Hennecke Sys.
0
PASS
Measurement-system
Calibr.standard
Feature:
Sync
Eq.Name
Label
xxxx Des.Val Xdesired
ID
SAWMARK ID
without Tolerance T
Uncertainty
without USL
Reason
MSA Unit
µm LSL
Remark
Synchronization of each individual sensors
1
Meas.
Data
13,542
4,354
15,719
11,365
7
13
19
25
31
13,650
13,530
13,920
13,980
13,160
13,270
13,550
13,560
13,600
13,700
12,890
12,850
13,470
13,640
14,380
13,710
12,980
13,600
13,460
13,660
13,780
12,810
13,240
13,810
13,570
14,290
12,980
13,470
14,170
13,890
13,510
13,270
Hennecke provides
a MSA Certificate for
each System
18,00
1120,00
16,00
1100,00
14,00
M easurement
M essdat en
dat a
12,00
1080,00
Results +
Tolerance
limits
USLUSL
10,00
1060,00
8,00
LSL LSL
UCLUCL
= Xm+3*s
= X m+3*s
LCLLCL
= X m-3*s
= Xm-3*s
1040,00
6,00
Desired
Sollwert
value
4,00
1020,00
2,00
1000,00
0,00
0 0
5 5
Cp =
Cpl =
Cp, Cpk
Ratios
1010
Values from Spec
Xdesired
13,542
11,365
LSL=Xdes ire d+0.5*T
15,719
USL=Xdes ire d-0.5*T
2,177
Abw = 0.5*T
4,354
T
Cpu =
T
6 ∗ sM
15
15
20
20
25
25
30
30
Measured Values
x min
x max
Range
n
12,810
14,380
1,570
32
35
Statistical Values
XM
13,542
XM - 3*sM
12,360
XM + 3*sM
14,724
6*sM
2,364
sM
0,394
Cp
1
Cp
1,84
1
0,00
1,33
x M − LSL
Cpu
Cpl
3 * sM
USL − x M
1,84
1,84
2,66
3 * sM
Cpk = min [Cpl; Cpu]
Cpk
1,84
1,560
#BEZUG!
Cpk
1
0,00
1,33
Tmin/Cp
2,66
Tmin/Cpk
1,560
PASS
Criterion Cp:
0,66
Judgement
Criterion Cpk:
0,66
Date:
Remarks:
Synchronization of each individual sensors
30.09.2010
Sign:
14
How often should you do a MSA Test ?
- Before data collection
- Before new measurement system operation
- Before new measurement system launch
- Before improvement verification
- After system calibration
- After system maintenance
- After new procedure set up
15
Examples for MSA Tests
- Saw mark measurement
- Thickness / TTV measurement
16
Saw Marks Inspection
compatible with SEMI Standard
• 4 high resolution cameras
Resolution: 1400x1000 pixel
Visual field: 19mm x 25mm
• 4 lasers
• Resolution: 0,1µm
• Accuracy: +-1,5µm
• Detected types of saw marks:
Saw Marks Inspection
with light sectioning technique
Saw mark MSA Test Results
3 Wafers, 30 Repeats, 4 Days
19
Thickness / TTV Inspection
compatible with SEMI Standard
• Thickness:
Capacitive sensors for three rows
Resolution: 0,1µm
Accuracy: +-1µm
•TTV:
Resolution: 0,1µm
Accuracy: +-1µm
Thickness / TTV Inspection
Capacitive Sensors
Measuring principle:
For an ideal plate capacitor
the reactance is
proportional to the distance
of the plates.
Thickness T = DTotal - DTop - DBottom
8,4 mm
5,5 mm
Light sensor
Capacitive
sensor
1,2 mm
min 8 mm
Thickness / TTV MSA Test Results
3 Wafers, 30 Repeats, 4 Days
22
Measurement System Control
and Product Yield
23
What about the Product Yield ?
Nominal
value
Lower
specification
20
Good parts rejected ?
Upper
specification
25
30
Is it possible due to
measurement error ?
24
Influence of Measurement
Uncertainty on Product Yield
Product
attribute
Product out of Spec
Measurement
Uncertainty
USL
Product according
to Spec
Specification Width
Measurement
Uncertainty
LSL
Product out of Spec
After A. Weckenmann, 1999
25
Influence of Measurement
Uncertainty on Product Yield
Measurement Uncertainty
Production Statistics
without Measurement Uncertainty
Good parts
Bad parts
with Measurement Uncertainty
False positives
Product attribute
False negatives
Product attribute
26
Industry Standards
27
Same thing but not mutually agreed ?
Same thing but not mutually agreed, it must be something wrong with the system !
28
Industry Standards
- Bringing together suppliers and
customers by making measurement
results comparable
- Agreeing on common parameters
and terminology
- Necessary for an efficient claim
management
29
Wafer Tracking
30
Do you know what happens
with your Products ?
31
Wafer Tracking
Highly accurate wafer
tracking enables production
transparency and cost reduction relating cell
and module properties with
production processes
Faulty process equipment can be
identified easily
Quality claims can be managed
Production processes can be optimized
32
Summary and Conclusions
- Measurement process control means high - quality measurement
systems operating under a tight statistical process control (SPC)
- Measurement process control on individual systems enables
reliable product quality and improved production yield
- Measurement process control and industry standards enables
efficient claim management by mutually agreed and comparable
measurement procedures
- Measurement process control and wafer tracking enables
manufacturing transparency and process optimization
33
Thank you very much for your attention