Selection of ESH solvents POS2008 - MST CONF Presentations/Particle11-TBearda.pdf · Selection of...

Selection of ESH solvents for cleaning applicationsin semiconductor manufacturing

E. Kesters1, M. Claes1, Q. T. Le1, K. Barthomeuf 2, M. Lux1, G. Vereecke1*, T. Bearda1, and J.B. Durkee3**

1 IMEC, Kapeldreef 75, 3001 Leuven, Belgium2 INSA, 20 av. A. Einstein, 69621 Villeurbanne, France3 Precisioncleaning, PO Box 847, Hunt TX 78024, USA* [email protected]** [email protected]

E. Kesters et al. imec 2008 2

11th POS 2008

Outline

• Introduction

• Materials & methods

• Results & first discussion

• Analysis of the Hansen “spherical” approach to solvent selection

• Conclusions


11th POS 2008

Micro-electronics

< 100 nm


11th POS 2008

Semiconductor manufacturing

• Introduction of new materials

• Cu wires

• Embedded in a porous dielectric

– SiOC, …

• Encapsulated in a barrier

– TaN/Ta, SiC, WCN, Ru, …

• Transistors, capacitors, etc…

• Novel gate dielectric materials

– HfO, HfSiON, LaO, DyO, …

• Novel gate electrode materials

– TiN, Ta2C, …

• On a substrate (wafer)

– Si, Ge, Ga/As, etc…


11th POS 2008

Uses of organic photoresist (PR) layers

• Transistor level

• Patterning of materials by etching

• Local modification of substrate conductivity by ion doping

– Protection of undoped areas

nFET pFET

poly-Si

metal gatehigh-k

resistcrust

As implantation


11th POS 2008

Uses of organic photoresist (PR) layers

• Cu wiring

• Patterning of dielectric layers by plasma etching

– Before Cu filling

substrate

dielectricetch

photoresist


11th POS 2008

Removal of used PR

• Issues with plasma ashing– Materials compatibility: damaging of exposed materials

� Degradation of properties

– E.g. porous dielectrics

� Material loss in subsequent process steps

�Renewed interest in wet organic stripping– Must meet new ESH criteria

– E.g. n-methyl pyrrolidone (NMP), a good solvent, will be re-classified as reprotoxin (cat. 2)


11th POS 2008

This work

• Find ESH replacement solvents– Making use of Hansen approach

• Focus on pristine PR– Model for bulk under crust

Crust

Bulk PR removed

Crust

Bulk PR removed


11th POS 2008

Outline

• Introduction

• Materials & methods– PR materials

– Solvents selection

– Experimentals



• Conclusions


11th POS 2008

PR materials: 193 nm DUV

• PR1: polymethacrylate (PMA)

• PR2: made from acrylate and methacrylate monomers

adamantane lactone

adamantane lactone

/H /H


11th POS 2008

ESH selection criteria

Criteria set according to EEC classification

• Safety: flash point FP > 55 °C– No F+, F, R10 solvents

• Health: no toxic solvents– T+ (very toxic) and T (toxic) discarded

• No R23-28, R39, R48 solvents

– Carcino/mutagenic & reprotoxic discarded (of all cat.; T, Xn)

• No R40, R45-46, R49, R60-63, R68 solvents

• Environment: no toxic solvents – Aquatic & non-aquatic environment

• No R50-R59 solvents

• No N label


11th POS 2008

Selection of solvents

• Method: based on Hansen theory– Hansen solubility parameters (HSP)

– General principle of use: “like dissolves like”

δd

δp δh

2 2 2

p d hδ δ δ δ= + +

Hydrogen bonds

Dispersive interactions (VdWaals)

Polar interactions


11th POS 2008

Experimental procedure

• Dissolution of pristine PR– Wafer pieces with PR films

– Beaker tests at RT, afo time

– Visual inspection for complete removal

– Final check by FTIR

0.18

0.2

0.22

0.24

0.26

0.28

0.3

0.32

0.34

5001000150020002500300035004000

Wavenumber (cm-1

)

0.26

0.27

0.28

0.29

0.3

0.31

0.32

5001000150020002500300035004000

Wavenumber (cm-1

)

CHx

lactone+ester

clean


11th POS 2008

Outline

• Introduction


• Results & first discussion– Selected solvents & mixtures

– Evaluation of organics solvents & mixtures


• Conclusions


11th POS 2008

0

5

10

15

20

0 5 10 15 20 25 30

Hydrogen bonding parameter

Polar parameter

NMP

Ac

PGMEDCM

MIBK

TCE

CHex

EATHF

PC

EG

Tex

BA

Selected solvents & mixtures (1)

• Mixtures of PC with:

–BA, Tex � NMP & Ac

–EG: used in commercial chemistries� good solvents from initial selection

Acronyms: see Annex

• Very few solvents meeting selection criteria & close to good solvents� mixtures

• HSPmixture = volume fraction weighted average of HSPcomponents


11th POS 2008

0

5

10

15

20

0 5 10 15 20


Polar parameter

NMP

Ac

PGMEDCM

MIBK

TCE

CHex

EATHF

THFA

DMSO

Cap

NP

? NEP

? HFE

? HFC

EHA

Selected solvents & mixtures (2)

• Mixtures of THFA with:

–Cap, NEP, NP � NMP

–CHex, EHA, MIBK� DCM

–EA, HFE, HFC � THF & TCE

• Mixtures of DMSO with:

–HFC, HFE � NMP, Ac, CHex, MIBK

� good solvents from initial selection

? Hansen parameters unknown

Acronyms: see Annex


11th POS 2008

Dissolution of PR1

Hansen plot

• All solvents & mixtures

–Acronyms: see annex

• Color scale for dissolution time

Discussion

• Hansen approach does not seem to work

–No well defined solubility domain

–Solvents & mixtures with similar parameters do not show same behavior

• See DCM & NMP

0

5

10

15

20

0 5 10 15 20


Polar parameter NMP

Ac

PGME

DCM

MIBK

TCE

CHex

EATHF

THFA

DMSO

Cap

NP

? NEP

? HFE

? HFC

EHA

PC

BATex

EG

H2O

� ≤ 0.5 min

� 0.5-1 min

� 1 - 2 min

� 2 - 5 min

� > 5 minunlabelled data points are mixtures



11th POS 2008

Reasons for apparent failure

• Hansen parameters are thermodynamics

↔ Dissolution tests data gives kinetics– Discrepancy points to kinetic factors

– Effect of size of solvent molecules ? • See later

– Microstructure of PR• PR is a (blend of) copolymer(s)

• PR contains additives

• Hansen parameters are 3-D↔ 2-D analysis– See later


11th POS 2008

0

5

10

15

20

0 5 10 15 20


Polar parameter NMP

Ac

DCM

MIBK

EATHF

THFA

DMSO

Cap

NP

? NEP

? HFE

? HFC

EHA

PC

BATex

EG

H2O

unlabelled data points are mixtures

� ≤ 0.5 min

� 0.5-1 min

� 1 - 2 min

� 2 - 5 min

� > 5 min

Dissolution of PR2

Hansen plot

• All solvents & mixtures

– Acronyms: see annex

• Color scale for dissolution time

Discussion

• Very large solubility domain

• Very different behavior compared to PR1

• Possible reasons

– Different copolymers

– Different additives in PR mixture



11th POS 2008

Summary of solubility tests on pristine PR

• Best pure solvents

– Benzyl alcohol

– (1-nitropropane)1

– NEP

– (NMP)2

– DMSO

– Propylene carbonate1 FP = 33 °C

2 Reprotoxin cat.2

• Mixtures with HFC & HFE

– Not miscible with DMSO (down to 10 %)

– Not miscible with THFA (down to 10 %)

• Ranking of the solvent mixtures

1. Propylene carbonate/benzyl alcohol

2. THFA/1-nitropropane

3. THFA/NEP

4. THFA/NMP2

5. THFA/MIBK

6. THFA/Cyclohexanone

7. THFA/Ethyl Acetate

8. Propylene carbonate/ethylene glycol

9. Propylene carbonate/texanol

10.THFA/2-ethylhexyl acrylate

11.THFA/ε-caprolactam


11th POS 2008

Outline

• Introduction




• Conclusions


11th POS 2008

Outline

• Review of Method– Based on matching impact of intermolecular forces between solvent and soil

– Presentation format is spherical geometry

– An optimization routine & a two-dimensional plot

• Application to PR1 and PR2 Data Sets– Analysis of specific results

• Key Learnings About “Spherical” Approach– Maintain realistic optimization goals

– Recognize / accept “false” results

– Beware of two-dimensional plots

• Conclusions


11th POS 2008

Hansen Approach to Solvent Selection

• For polymers, soils, or solvents [solutes]:

– One matches intermolecular forces of solvent & solute

• “Like dissolves like”

• Three intermolecular forces:

– Dispersed throughout the molecule

– Localized between poles of electrostatic charge

– Localized among hydrogen bonds

• Each force characterized by a thermodynamic parameter:

– δ disperse

– δ Polar

– δ H2-Bonding

• Total force characterized by the Hildebrand parameter:

σ =∆ Energy

Volume

δ δ δ δ2 2 2 2Hildebrand Polar Dispersion Hydrogen bonding= + + −


11th POS 2008

A Geometric Vision by Hansen & Coworker

• Each solubility parameter is independent– Impacting in one of three independent coordinates

• A polymer / soil / solvent is located in a three-dimensional space at the values of its solubility parameters.

• The limit of action with another chemical is a radial dimension called RO.

• There will be differentiable outcomes– GOOD and BAD solvency are binary outcomes

– Experimental data are of solution time

– “Solubility Grade” = solution time <> value


11th POS 2008

Not-Plain Geometry

• The separation between any two chemicals in three-dimensional “Hansen space” is another radial dimension called RA.

• In terms of solubility parameters for solvents and solute:

• Equation derived from data plots

– The “4” has theoretical and empirical significance

– Not RA ≠ ∆ δ Hildebrand

• Mutual solubility is expected when

– RO overlaps RA

– I.e., The data lies within the solubility sphere

{ }[ ] { }[ ] { }[ ]R A disperse disperse polar polar h bonding h bonding= × − + − + −

− −4 2 1 2 1 2 1

2 2

2 2

2

δ δ δ δ δ δ


11th POS 2008

The Meaning of Data Analysis

• Data analysis is to inquire:– When RA < RO, is there solubility?

• i.e., “Good” and IN?

– When RA > RO, is there not solubility?

• i.e.., “Bad” and OUT?

• “False Negatives” are:– When RO > RA, & there is solubility!

• i.e., “Good” and OUT?

• “False Positives” are:– When RO < RA, & there is not solubility?

• i.e., “Bad” and IN?


11th POS 2008

Data Processing

• Wanted are the parameters which characterize the material being solubilized

– Will allow selection of new solvents/mixtures

• Optimization identifies the solubility parameters which place all the data where it should be placed:

– So all are “Good” and IN; or “Bad” and OUT.

• The parameters are known for each solvent:

– δ disperse

– δ Polar

– δ H2-Bonding

– RA

{ }δ δany i iX= ×∑X Volume Fractioni =


11th POS 2008

Optimization Methodology; One Needs:

• To define an error:

– Dfi = 1 for “Good” and IN, or “Bad” and OUT, because then FACTOR = 0. For “False” results, FACTOR = 1

– Without regard to values of RA and RO

• To choose an error function:– The “Desirability Function” (DF)

• To choose an optimization routine– Linear (and non-linear) programming in spreadsheets

• To pay attention– To the distribution of outcomes

( ) { }[ ]df i R R FACTORO A i= − − ×exp

( ) { }[ ]{ } ( ) { }[ ]{ } ( ) { }[ ]{ }DF R R FACTOR R R FACTOR R R FACTOR iO A O A O Ai= − − × × − − × × − − ×exp exp ..... exp1 2

1


11th POS 2008

Distribution of Outcomes – PR1

0.730113124780.005.6525.5219.18<5

0.720714144390.0011.1921.9413.52<2

0.83849928340.0011.7619.7610.67<1

1.000008009.589.5222.4923.69>5

0.85405620490.0010.5618.929.35< 0.5

Optimized MPa^(1/2)

DFGood & OUT

Bad & IN

Good & IN

Bad & Out

ð H2 Bonding

ð Polar

ð Dispersion

RASolution Time, Min

HSP Optimization with PR1 Photoresist

• The goal optimum (DF = 1) includes all data, i.e.– No optimization being done

• A significant amount of data is properly considered @ < 0.5 min– 69 of 80 data points

• Targets were methylene chloride and n-methyl pyrrolidone


11th POS 2008

Analysis of the “False” Outcomes

• Molar volume is often a significant parameter in solubility performance:– Low volume solvents like methylene chloride, water, and acetone often perform better than expected.

• That’s not the case here.

• But, all but 3 of the “False” outcomes for PR1 are within ± 1 RA

unit of expected performance


11th POS 2008

Analysis of Four “False” Outcomes

Better (PR1)98.132.0311.309.2318.80'THFA & Cyclohexanone

@ 50 % THFA (0.17 min)

Poorer (PR1)96.87-2.3410.208.2017.80'Tetrahydrofurfuryl alcohol (THFA), (5 min)

Poorer (PR2)110.7-3.347.4015.0019.70Caprolactam (>100 min, but it’s a solid at room temperature…)

Better (PR1)103.585.0313.706.3018.40Benzyl Alcohol (0.17 min)

MPa^(1/2)

Vs Expectations

Molar Volume, cc/mole

Excess HSP RA

ð H2 Bonding

ð Polar

ð Dispersion

Solvents, or

Mixtures

Solvent Combinations Performing Considerably Outside of Expectations

• Benzyl alcohol is far outside the sphere and performed very well!

• The two Tetrahydrofurfuryl alcohol materials performed differently?

• THE REASONS FOR THIS ARE NOT KNOWN!


11th POS 2008

Distribution of Outcomes – PR2

0.9192227368.718.6822.5615.35<5

0.9544616779.466.4521.1912.96<2

0.9470226897.168.1120.4210.39<1

1.0000008109.6612.3621.5523.86>5

0.81035461115.908.6420.209.48< 0.5

Optimized MPa^(1/2)

DFGood & OUT

Bad & IN

Good & IN

Bad & Out

ð H2 Bonding

ð Polar

ð Dispersion

RASolution Time, Min

HSP Optimization with PR2 Photoresist

• All but three other “False” results are within ± 1 RA unit of expected performance

• 80 of 81 results are as expected

• There Are Fewer Anomolies With PR2


11th POS 2008

Solvents Selected for Low Molar Volume


11th POS 2008

Surprising Outcome

• Hydrogen-bonding HSP is about zero for PR1.– And not for PR2.

• It’s not clear, based on these structures, why this should be so.– Removal of the “False”outcomes doesn’t change this outcome.

adamantane lactone

adamantane lactone

/H /H


11th POS 2008

Beware Two-Dimensional HSP Plots

• Commonly used in analysis of solubility problems.

• Based on assumption that δ disperse doesn’t vary among solvents– But it does.

• Plot makes it appear that some “GOOD” & Out are actually in.– They’re not

– Plotted @ δ disperseoptimum = 18.9


11th POS 2008

A Two-Dimensional Plot Re-plotted

• Plot shows that some “GOOD” & Out are actually out.– Plotted @ HSP optimum + 4 = 22.9

– Shows just the “end” of the sphere

• Don’t use two-dimensional plots to make final judgments– Use them to select solvents for test


11th POS 2008

Outline

• Introduction




• Conclusions


11th POS 2008

Conclusions

• Several ESH solvents & mixtures identified that can dissolve the PRs

• Selection is dependent on PR– Kinetics vs. thermodynamics

– PR is a (blend of) different copolymer(s)

– PR is a complex mixture (with different additives)


11th POS 2008

Conclusions

• Hansen “spherical” approach shows measured solubility data set “thermodynamically”consistent.– 18 for PR1 (< 0.5 min solution time)

– 62 for PR2 (< 0.5 min solution time)

• The HSP and RA values are known for the PRs– For additional evaluations

• Care must be taken with the “spherical”approach.– It can produce unexplained outliers

– DF =1 is not the optimization target

• Properly-located assignments Vs Solubility Grades are

– Don’t make judgments from 2-D plots


11th POS 2008


11th POS 2008

Solvents acronyms

• Ac: acetone

• BA: benzyl alcohol

• Cap: ε-caprolactam

• CHex: cyclohexanone

• DCM: dichloromethane

• DMSO: dimethyl sulfoxide

• EA: ethylacetate

• EHA: 2-ethyl hexylacrylate

• EG: ethylene glycol

• HFC: Vertrel MCA

• HFE: HFE-7100DL

• MIBK: methyl-isobutyl-ketone

• NEP: n-ethyl pyrrolidone

• NMP: n-methyl pyrrolidone

• NP: 1-nitropropane

• PC: propylene carbonate

• PGME: 1-Methoxy-2-propanol

• TCE: trichloroethylene

• Tex: texanol

• THF: tetrahydrofuran

• THFA: tetrahydrofuranalcohol

Selection of ESH solvents POS2008 - MST CONF Presentations/Particle11-TBearda.pdf · Selection of...

Documents

Transcript of Selection of ESH solvents POS2008 - MST CONF Presentations/Particle11-TBearda.pdf · Selection of...