A Comparative Analysis of Semiconductor Electroplating Bath Additives by Calibration Verification...

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Paul VoelkerVertical Marketing Manager– Environmental & Industrial MarketsThermo Fisher Scientific, Sunnyvale, CA

Marc Plante, PhDSenior Applications ScientistThermo Fisher Scientific, Chelmsford, MA

Stewart FairlieStaff EngineerSeagate Technologies, Bloomington, MN

A Comparative Analysis of Semiconductor Electroplating Bath Additives by CVS and HPLC

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

Electroplating Bath Workflows

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 informationand 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

An Analytical Challenge

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

High-Performance Liquid Chromatography (HPLC)

Mobile Phase

Agenda

The Determination of

Accelerator and Suppressor

by HPLC and Charged Aerosol Detection

Thermo Scientific™ Dionex™ Corona™ Veo™ Charged Aerosol Detector

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

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

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 mmMobile Phase A: 10 mM Diethylamine* / Acetic Acid in Water, pH 5-6Mobile Phase B: MethanolMobile Phase C: n-PropanolDetector: Corona Veo RS

Filter: 3.6 sPower Function: 2Evap. Temp.: 50 °C

Sample Temperature: 20 °CFlow Rate Pump: 1.0–1.2 mL/minColumn Temperature: 40 °CInjection 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

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.

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

9 - Accelerator - 5.576

12 - Suppressor-1 - 7.316

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

150154

2 - Suppressor - 5.922

Triplicate injections at six concentrations.

200 %-Nominal

100 %-Nominal

50 %-Nominal

25 %-Nominal

12.5 %-Nominal

Calibration Curves — Accelerator

Linear fit, R2 = 0.999

Each standard injected in triplicate.

Conc.(mL/L)

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 2400.0

Calibration Curves – Suppressor

Linear fit, R2 = 0.998

Each standard injected in triplicate.

Conc.(mL/L)

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 2400.00

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

150154

2 - Suppressor - 5.922

0 Ah/L

5 Ah/L

12 Ah/L

20 Ah/L25 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

Suppressor Degradation

0 5 10 15 20 25 300%

Usage (Ah/L)

Suppressor quality can be measured by HPLC as a fraction of smaller molecular weight analytes—peak areas of earlier eluting suppressor.

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 -203.59R² = 0.8612

0 20 40 60 80 100 120

CVS Value (%-Nominal)

Suppressor HPLC vs. CVS Data

y = 1.6736x -98.883R² = 0.9799

0 30 60 90 120 150 CVS Value (%-Nominal)

Accelerator HPLC vs. CVS

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

Agenda

Determination of Accelerator and Leveller by

HPLC and Electrochemical Detection

Thermo Scientific™ Dionex™ UltiMate™ 3000 ECD-3000RS Electrochemical Detector

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

B B BBBB

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)

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

B Q + e-

E2E1A P + e-650

mV900 mV

B Q QB

Electrochemistry – Serial Coulometric Electrodes

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 9.34-0.90.0

2 - Leveller - 7.030

The leveller is a polymeric amine with oxidizable groups and detectable at +650 mV

Leveller by ECD

• Correlation is linear from 10-200% nominal

• R2 = 0.9945

%-Nominal Conc.

Replicates, n

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 2200.00

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

Degradant

4.9335.000 5.125 5.250 5.375 5.500 5.625 5.750 5.875 6.000 6.144-16

100104

25 Ah/L20 Ah/L12 Ah/L

5 Ah/L

0 Ah/L

Accelerator by Charged Aerosol Detection and ECD

Two measurements trend well, providing similar values.

Correlation Coefficient of ECD vs. Charged Aerosol Detection was 0.9661 0

0 5 10 15 20 25 30

Usage (Ah/L)

Accelerator – Charged Aerosol Detection Accelerator – ECD

Agenda

HPLC Method Conditions – Nickel additives

HPLC System:Column:

UltiMate 3000 RS with dual-gradient pumpThermo 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 acidB: Acetonitrile

Column Temperature: 30°CInjection volume: 10.0 LDetector 1: DAD, 230 nmDetector 2: Corona Veo RS Filter: 3.6 s Power Function: Data Rate:Sample Preparation:

1.0010 Hzneat

Gradient:Time (min)

Flow (mL/min)

-5 1 98 2

0 1 98 2

15 1 5 95

20 1 5 95

20 1 98 2

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

1 - 0.532

2 - 1.199

3 - 10.647

Saccharin2 – 2.935

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.

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 - - -

Saccharin

Impurity 1

Impurity 2

Degradents ?

Degradents

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.

Agenda

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.

Gage Results – Nickel Additives

HPLC-UV

SaccharinSV/T = 10.56%

SaccharinSV/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

Gage Study – Accelerator by CVS and Electrochemical Detection

Two CVS experiments showed SV/T of 35.84 – 44.90%.

The HPLC-Electrochemical Detection experimental result showed excellent capability, with an SV/T value of 9.69%

Gage Study – Suppressor by CVS and HPLC-Charged Aerosol Detection

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%

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

Thank you for yourAttention

Marc.Plante@thermofisher.com

A Comparative Analysis of Semiconductor Electroplating Bath Additives by Calibration Verification...

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