A Comparative Analysis of Semiconductor Electroplating Bath Additives by Calibration Verification Standard (CVS) and High Pressure Liquid Chromatography (HPLC)

1
The world leader in serving science
Paul Voelker
Vertical Marketing Manager– Environmental & Industrial Markets
Thermo Fisher Scientific, Sunnyvale, CA
Marc Plante, PhD
Senior Applications Scientist
Thermo Fisher Scientific, Chelmsford, MA
Stewart Fairlie
Staff Engineer
Seagate Technologies, Bloomington, MN
A Comparative Analysis of
Semiconductor Electroplating Bath
Additives by CVS and HPLC

2
Agenda
• Overview — Plating Baths and HPLC
• Determination of Accelerator and Suppressor by HPLC and
Charged Aerosol Detection
• Sample Preparation, Calibration, Measurements
• Comparisons to CVS data
• Determination of Accelerator and Leveller by HPLC and
Electrochemical Detection (ECD)
• Coulometric Detection Mechanism and Design
• Calibration and Measurements
• Nickel Additives, Saccharin and Sodium Alkylsulfate
• Gage Study Results
• Conclusions

3
Electroplating Bath Workflows

4
Electroplating for Electronic Packaging
• Modern Electroplating Issues
• Circuit density is increasing
• Uniform plating processes improves product quality, yield, and
performance
• High yields are desired to provide decent commercial profitability
• Current metrology (CVS) does not offer full quantitative information
and takes significant time to complete
CVS provides an indirect bath measurement since
it measures the “combined” effect of the additives
and by-products on the plating quality

6
Chromatographic Overview — Additives
• Copper plating baths are comprised of an aqueous solution of
• Copper sulfate and sulfuric acid
• Accelerator solution — a sodium (bis sulfoalkyl) disulfide
• Suppressor solution — a polyalkenylglycol
• Leveller solution – a nitrogen or sulfur-containing molecule or high
molecular weight polymer
• Nickel plating bath additives
• Sodium alkylsulfate (SAS)
• Saccharin
• Methods consist of reverse phase and ion-paring HPLC

7
High-Performance Liquid Chromatography (HPLC)
Mobile Phase

8
Agenda
• Conclusions

9
The Determination of
Accelerator and Suppressor
by HPLC and Charged Aerosol Detection
Thermo Scientific™ Dionex™ Corona™ Veo™
Charged Aerosol Detector

10
Charged Aerosol Detection — Schematic
• Non- and semi-volatile
analyte down to low
nanograms on column
• Lacking a chromophore
• In use since 2004
• The Corona Veo RS
detector provides linear
calibration fits, needed for
suppressor quantitation
1
2
3
4
5
6
7
8
9
101
2
3
4
5
6
7
8
9
10

11
Sample Preparation and Measurement
• Since acid-copper samples are too acidic to be measured
directly, samples are neutralized with N,N-
dimethylaminoethanol (DMEA) to a pH between 2 and 4
• Instrument is calibrated using standards that are diluted in
matrix and neutralized around targeted concentrations
• Samples are injected on to the HPLC instrument for analysis
• Results are obtained by comparing sample peak area against
calibration curve

12
HPLC System: Thermo Scientific™ Dionex™ UltiMate™ 3000 RSLC,
dual gradient, one 6-port valve
HPLC Software: Thermo Scientific™ Dionex™ Chromeleon™ Chromatography
Data System (CDS) 7.2 SR 1
HPLC Column: Thermo Scientific™ Accucore™ C18, 2.6 µm, 3.0 x 150 mm
Mobile Phase A: 10 mM Diethylamine* / Acetic Acid in Water, pH 5-6
Mobile Phase B: Methanol
Mobile Phase C: n-Propanol
Detector: Corona Veo RS
Filter: 3.6 s
Power Function: 2
Evap. Temp.: 50 °C
Sample Temperature: 20 °C
Flow Rate Pump: 1.0–1.2 mL/min
Column Temperature: 40 °C
Injection Volume: 50 µL
Sample Preparation: 980 µL Sample + 20 µL DMEA, cap, and shake.
* Diethylamine, Ethylamine, and Dimethylamine, can be used as ion-pairing, depending on
desired retention.
Method Conditions – Accelerator & Suppressor

13
Method Conditions – Corona Veo Detector
Flow Gradient: Valve Control:
Time
(min)
Flow
(mL/min)
%A %B %C
-5.0 1.0 98.0 2.0 0.0
1.0 1.0 98.0 2.0 0.0
3.0 1.0 98.0 2.0 0.0
3.8 1.2 15.0 85.0 0.0
4.5 1.2 13.0 87.0 0.0
5.5 1.2 10.0 0.0 90.0
7.0 1.2 0.0 0.0 100.0
8.0 1.2 0.0 0.0 100.0
10.0 1.2 0.0 0.0 100.0
10.0 1.2 98.0 2.0 0.0
11.0 1.0 98.0 2.0 0.0
Time
(min)
Detector
Valve
Right
Valve
Initial On 1-2
2.00 Off 6-1
4.00 On
Control of the organic solvent
content controls elution of the
additives from the HPLC
column.

14
4.7 4.8 5.0 5.2 5.4 5.6 5.8 6.0 6.2 6.4 6.6 6.8 7.0 7.2 7.4 7.6-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
9 - Accelerator - 5.576
12 - Suppressor-1 - 7.316
min
pA
6.25 %-Nominal
Accelerator and Suppressor Overlays
4.75 5.00 5.25 5.50 5.75 6.00 6.25 6.50 6.75 7.00 7.25 7.50 7.75 8.00 8.25 8.50 8.758.88
-6
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
154
2 - Suppressor - 5.922
min
pA
Triplicate injections at
six concentrations.
200 %-Nominal
100 %-Nominal
50 %-Nominal
25 %-Nominal
12.5 %-Nominal

15
Calibration Curves — Accelerator
Linear fit, R2 = 0.999
Each standard injected in
triplicate.
Conc.
(mL/L)
%RSD
20 0.44
10 1.09
5 1.36
2.5 0.28
1.25 0.97
0.625 2.35
Accelerator External CAD_1
%-Nominal
pA*min
0 20 40 60 80 100 120 140 160 180 200 220 240
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
3.2
3.4
3.6
3.8
4.0

16
Calibration Curves – Suppressor
Linear fit, R2 = 0.998
Each standard injected in
triplicate.
Conc.
(mL/L)
%RSD
20 0.22
10 0.20
5 0.87
2.5 0.27
1.25 0.14
0.625 0.03
Suppressor (Suppressor-1) External CAD_1
%-Nominal
pA*min
0 20 40 60 80 100 120 140 160 180 200 220 240
0.00
1.25
2.50
3.75
5.00
6.25
7.50
8.75
10.00
11.25
12.50
13.75
15.00
16.25
17.50
18.75
20.00
21.25
22.50
23.75
25.00
26.25
27.50
28.75
30.00

17
Bath Samples at 0, 5, 12, 20, and 25 Ah/L
4.75 5.00 5.25 5.50 5.75 6.00 6.25 6.50 6.75 7.00 7.25 7.50 7.75 8.00 8.25 8.50 8.88
-6
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
154
2 - Suppressor - 5.922
min
pA
0 Ah/L
5 Ah/L
12 Ah/L
20 Ah/L
25 Ah/L
• Amount of accelerator
and high molecular
weight suppressor
decrease with amount of
applied current
• Amount of low molecular
weight suppressor
degradents increases
with amount of applied
current
Degradents

18
Suppressor Degradation
0%
5%
10%
15%
20%
25%
30%
35%
40%
45%
0 5 10 15 20 25 30
Rel.MassSuppressorDegradants
Usage (Ah/L)
Suppressor quality
can be measured by
HPLC as a fraction
of smaller molecular
weight analytes—
peak areas of earlier
eluting suppressor.

19
Comparison Between HPLC and CVS Results
• Additives decrease with bath usage
• HPLC measures quantities of additives and
some degradants, separately
• CVS measures activities of additives
y = 3.1225x - 203.59
R² = 0.8612
0
2
40
60
80
100
120
140
0 20 40 60 80 100 120
CVS Value (%-Nominal)
Suppressor HPLC vs. CVS Data
y = 1.6736x - 98.883
R² = 0.9799
0
15
30
45
60
75
90
105
120
135
0 30 60 90 120 150
CVS Value (%-Nominal)
Accelerator HPLC vs. CVS

20
HPLC or CVS?
• HPLC methods can run between 16 – 30 minutes, per
sample total time
• CVS methods can take 2- 6 hours, depending on number of additives
• HPLC methods separate and quantify additives
• CVS methods provide composite results of all additives added to a
sample, requiring iterative measurements
• HPLC methods can also determine some degradents,
measured separately from actual additives
• CVS methods do not distinguish between additive and degradent

21
Agenda
• Conclusions

22
Determination of Accelerator and Leveller by
HPLC and Electrochemical Detection
Thermo Scientific™ Dionex™ UltiMate™ 3000
ECD-3000RS Electrochemical Detector

23
Electrochemical Detection
• Accelerator and leveller are electrochemically active to
oxidation and ECD is a suitable means of detection
• The accelerator disulfide bond is oxidizable
• The leveller, typically an amine molecule / polymer, often
used in very low concentrations.
• Levellers are typically electrochemically
active and most are retained on
reversed phase HPLC columns

24
Flow
A
A
B
B
A A
A
A
A
A
A
A
A
A
AA
A
A
B
B
B
B B
B
BB
B
B
B
B
B
B
B
B
B
A
A
A
A
B
A
B
A B + e-
Electrochemistry – Coulometric Cell
• A coulometric sensor is a highly efficient type of amperometric sensor in
which ~100% of the analyte undergoes electrolysis Lacking a
chromophore
• With 100% electrolysis, the peak area is related to the quantity of sample
injected by Faraday’s law: Q=nFN
Q = charge transferred (current over time – peak area)

25
Coulometric electrodes are both sensitive and, when used in series,
selective.
Leveller typically detected on E1 at +650 mV,
Accelerator on E2 at +900 mV
E1 E2
A P
A B Q
B Q
Flow
B Q + e-
E2E1
A P + e-650 mV 900 mV
P
P
P P
P
P
B
B Q QB
B
B
B
Electrochemistry – Serial Coulometric Electrodes

26
Leveller – Standards by HPLC-ECD,
10 – 200% Nominal Concentration
5.66 5.80 6.00 6.20 6.40 6.60 6.80 7.00 7.20 7.40 7.60 7.80 8.00 8.20 8.40 8.60 8.80 9.00 9.20 9.34
-0.9
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
18.0
20.0
22.0
24.0
26.0
28.0
30.0
32.0
34.0
36.0
38.1
2 - Leveller - 7.030
min
µA
The leveller is a
polymeric amine with
oxidizable groups
and detectable at
+650 mV

27
Leveller by ECD
• Correlation is linear
from 10-200%
nominal
• R2 = 0.9945
%-Nominal
Conc.
Replicates,
n
%RSD
200 3 4.9
150 3 3.6
100 5 6.2
75 3 3.5
50 3 5.2
25 3 11.0
10 3 18.6
Leveller External ECD_1
µA*min
0 20 40 60 80 100 120 140 160 180 200 220
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
1.10
1.20
1.30
1.40
1.50
1.60
1.70
1.80
1.90
2.00

28
Accelerator by HPLC-ECD with Usage
Detecting accelerator
by ECD is an
orthogonal
measurement to the
Corona detector.
Degradant (inset)
increases with bath
operation.
2.00 2.50 3.00 3.50 4.00 4.50 5.00 5.50 6.00 6.50 7.00 7.50 8.00 8.50 9.00
-40
-20
0
20
40
60
80
100
120
140
160
180
200
220
240
260
280
300
320
340
360
380
400
420
440
460
480
500
min
µA
Degradant
4.9335.000 5.125 5.250 5.375 5.500 5.625 5.750 5.875 6.000 6.144
-16
-10
0
10
20
30
40
50
60
70
80
90
100
104
min
µA
25 Ah/L
20 Ah/L
12 Ah/L
5 Ah/L
0 Ah/L

29
Accelerator by Charged Aerosol Detection and ECD
Two measurements
trend well, providing
similar values.
Correlation
Coefficient of ECD
vs. Charged Aerosol
Detection was
0.96610
5
10
15
20
25
30
35
40
45
0 5 10 15 20 25 30
Accelerator(Mass)
Usage (Ah/L)
Accelerator – Charged Aerosol Detection Accelerator – ECD

30
Agenda
• Conclusions

31
HPLC Method Conditions – Nickel additives
HPLC System:
Column:
UltiMate 3000 RS with dual-gradient pump
Thermo Scientific™ Acclaim™ Surfactant Plus 3 µm,
3.0 x 100 mm
Eluents: A: 100 mM Ammonium acetate in DI Water, pH
5.4 with acetic acid
B: Acetonitrile
Column Temperature: 30°C
Injection volume: 10.0 L
Detector 1: DAD, 230 nm
Detector 2: Corona Veo RS
Filter: 3.6 s
Power Function:
Data Rate:
Sample Preparation:
1.00
10 Hz
neat
Gradient:
Time (min)
Flow
(mL/min)
%A %B
-5 1 98 2
0 1 98 2
15 1 5 95
20 1 5 95
20 1 98 2

32
HPLC-Charged Aerosol Detection Chromatogram,
Saccharin & SAS
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0 14.0 15.0 16.0 17.0 18.0 19.0 20.0
-50
0
50
100
150
200
250
300
350
1 - 0.532
2 - 1.199
3 - 10.647
min
pA
-
SAS
Saccharin
2 – 2.935

33
Nickel Additives by HPLC
For simplicity, the same mobile phases and columns used for copper
additives by Charged Aerosol Detection can be used for saccharin and
SAS determinations for nickel additives, but gradient conditions may
need to be adjusted.
Saccharin and its degradents absorb UV well at 230 nm, but SAS does
not absorb.

34
Saccharin Impurities by HPLC-UV
0.06 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.11
-
-
-
min
mAU
Saccharin
Impurity 1
Impurity 2
Degradents ?
Degradents
153
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
10
20
26
Use of UV (230 nm) can be used to measure impurities in nickel
plating baths. Sample in blue, standards in black.
Some may be too volatile for Charged Aerosol Detection.

35
Agenda
• Conclusions

36
Gage Capability
• One gage study was performed for saccharin in a nickel
plating bath.
• Two gage studies were performed to determine the capability
of the method to reliably determine quantities of accelerator
and suppressor in acid-copper baths.
• Gage results are a measure of Standard Variance relative to
Tolerance, or SV/T.
• Values of SV/T < 30% show capability.
• Values of SV/T < 7% show superior capability.

37
Gage Results – Nickel Additives
HPLC-UV
Saccharin
SV/T = 10.56%
Saccharin
SV/T = 5.48%
SAS by HPLC-Charged Aerosol Detection had an
SV/T value of 4.5%.
No test for SAS was used previously.
Previous Metrology

38
Gage Study – Accelerator by CVS and
Two CVS experiments
showed SV/T of
35.84 – 44.90%.
The HPLC-
experimental result
showed excellent
capability, with an SV/T
value of 9.69%

39
Gage Study – Suppressor by CVS and HPLC-
Two CVS experiments
showed SV/T of 74 and
79%.
The HPLC-Charged
Aerosol Detection
experimental result
showed acceptable
capability, with an SV/T
value of 19%

40
Conclusions
• The current methods are gage-capable, and are able to
quantify the organic additives in both copper and nickel
plating chemistries
• The methods require minimal sample preparation, which may
only be acid-neutralization
• Analyses are shorter in time, and results are more accurate
and reliable than by traditional CVS metrology
• Methods are automated, meaning engineers are free for
other important work
• Better results means better efficiency

41
Marc.Plante@thermofisher.com

A Comparative Analysis of Semiconductor Electroplating Bath Additives by Calibration Verification Standard (CVS) and High Pressure Liquid Chromatography (HPLC)

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A Comparative Analysis of Semiconductor Electroplating Bath Additives by Calibration Verification Standard (CVS) and High Pressure Liquid Chromatography (HPLC)