JULY 12 2017
Challenges in Cleaning Tungsten and Cobalt for Advanced Node Post CMP and Post Etch Residue Removal Applications
Michael White. Daniela White, Thomas Parson, Elizabeth Thomas, Shining Jeng, Ruben Lieten, Volley Wang, Sean Kim, Wisma Hsu and Steve Lippy
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01Cleaning requirements for Co and W at the advanced Node
02 Co cleaning mechanisms
03 Controlling corrosion on Co
04 Cobalt defectivity improvements
05 Cobalt wet etch & cleaning
06 W Cleaning mechanisms
07 Cleaning Si3N4 after W polishing
08 W wet etch & cleaning
09 Conclusions
AGENDA
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CLEANING CHALLENGES FOR BULK COBALT AND TUNGSTEN
• Replace more traditional copper cleaners with rationally designed Co cleaners
• Low/No Cobalt corrosion
• Low/no galvanic corrosion
• Low/no dendritic CoOx growth
• Low/no Co pitting
• Low/no organic residues
• Low/no silica particles or clusters
• No increased roughness
• Green chemistry (TMAH free)
• Market increasing challenged by W recess
• High pH commodities (SC1, dilNH3)
• Traditional low pH cleaners
• Low W etch rates (<2 Ǻ/min)
• Low/no Organic Residue
• Nitride cleaning is particularly problematic
• Low no silica particles or clusters
• No increased roughness
• Green chemistry.(TMAH free)
Post CMP Bulk Co Cleaners Post CMP W Cleaners Post Etch Residue Remover
• Post Etch Residue Remover.- Cu, W, Co
• Multi Function Cleaner - Clean + Etch etc…
• PERR for advanced FEOL application (Ge and SiGe)
• Green chemistry (TMAH free)
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THE RATIONAL DESIGN OF A POST CMP CLEANER PLANARCLEAN® AG COPPER CLEANING
PlanarClean® AG ‒ Advanced Generation Copper Cleaning Mechanism
Co(0)
CoO/Co2O3
O O
HO
H
Con+ Co
High pH leads to charge repulsion between negatively
charged silica and negative cobalt oxide surface
Corrosion inhibitor
package controls galvanic
corrosion
Cleaning additive disperses silica and organic residue and
prevents reprecipitation
Etchant for controlled, uniform CuOx
dissolution to undercut particles
Organic additive attacks and removes Co-organic residue
Q
SiO2
SiO2SiO2 SiO2
PLANARCLEAN AG PREVENTS SILICA AGGREGATION
◦ Particle adhesion mechanisms
◦ Physisorption (van der Waals attraction – increases with PS)
◦ Electrostatic attraction or repulsion (zeta potential)
◦ Chemisorption (chemical reaction particle-surface)
◦ Capillary condensation
AG-3XXX
Dispersed particlesHighly negatively charged
No particles agglomeration
OHOH
OH
OHOH
OH
OH
OH
SiO2
OHOH
OH
OHOH
OH
OH
OH
SiO2
OHOH
OH
OHOH
OH
OH
OH
SiO2
Post-CMP Co Post-CMP Co
O‒
OH
O‒
OHO‒
OH
O‒
O‒ SiO2
O‒
OH
O‒
OHO‒
OH
O‒
O‒ SiO2
O‒
OH
O‒
OHO‒
OH
O‒
O‒ SiO2
O+
Si Si
H
SiOH + HO- SiO- + H2O
IEP = 4
5
Zeta Potentialz = 4pg(n/E)/e
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SOME CHALLENGES ASSOCIATED WITH CO CLEANER DEVELOPMENT
• Ideal pH range for Silica slurry removal to prevent hydroxide precipitation
Mtn+Xn-
Co
CoO + Co2O3
Co
CoO + Co2O3
OHOH OH OH OH OH OH OH OH
Surface passivation
• Co passivation by both cobalt oxide/hydroxide and/or corrosion inhibitor
• Can result in CoOx(OH)y growth without the proper complexing agent
Co2+
OH2
OH2
H2O H2O
H2OH2O
2 HO-
[O]3 HO-
Co2+
OH2
OH2HO-
H2O
H2OHO-
Co3+
OH2
OH2HO-HO-
H2OHO-
Co2+
L
LLL
L
L
Ksp = 1.6 x 10-16
Ksp = 1.6 x 10-44
Ksp = soluble
6 L
Co Pourbaix Diagram
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SOME CHALLENGES ASSOCIATED WITH CO CLEANER DEVELOPMENT
• Well-passivated Co surfaceAFM, SEM – no CoOx surface precipitates,low surface roughness (Ra = 5 nm)
• Uniform, smooth etching (no pitting)
AFM
• Poorly passivated surface or insufficuentcomplexation
• Dendritic CoOx growth
SEM
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POTENTIODYNAMIC REDUCTION OF CO OXIDE LAYERS CAN MEASURE THE RELATIVE CONCENTRATIONS OF CO(II) AND CO(III) OXIDE/HYDROXIDES
-1.00 -0.75 -0.50 -0.25 0-0.000075
-0.000050
-0.000025
0
E (V vs. Ag/AgCl)
I (A
)
tsmc CVD Co in pH 11.5 KOH
Co2O3
Q = 0.0066 CoulThickness = 41.95Å
CoO
Q = 0.01268 CoulThickness = 43.94Å
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XPS FITTING SHOWS COBALT(II) AND COBALT(III) CAN BOTH BE PRESENT
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Ref: 1. Wang, et al. SPIE Beijing 2016 Conf. Proc.2. Bard, A. J. Faulkner, L. R. Electrochemical Methods: Fundamentals and Applications; Wiley and Sons 2001
NYQUIST PLOTS SHOW INFLUENCE OF PROPER INHIBITOR SELECTION AND CONCENTRATION ON COBALT PASSIVATION
22/12222/1
2/1
)()1(
=
ctdldl
ct
RCC
RRZ
High Inhibitor 2
No Inhibitor
When -> 0 aRCC
CRCZ
ctdldl
dlctdl
22/12222/1
2/1222/1
)()1(
)(
=
High Inhibitor 1
Low Inhibitor 2
Higher impedance storage and loss components
higher film integrity
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AG- CO FORMULATIONS SHOW UP TO A 2X IMPROVEMENT IN DEFECTIVITY OVER COMPETITOR
Silica particle
Organic residue
Judicious selection of cleaning additives leads to lower defectivity
Silica cluster
2.5x
12Mukherjee, T. Thesis N. Texas U., 2016
TITANKLEAN MECHANISM FOR REMOVING DRY ETCH RESIDUES WHILE PROTECTING COBALT
Organic/inorganic residues
Residues from dry process
Oxidization Degradation
Etchant
Swelling & dissolution
Solvent
Residues removal
Etchant
Metal inhibitor
M complex
XCo/ESL
Co/ESL protection
Co/ESL
Etchant M complexTK 162 M3+ M2+
Chelating agent
ESL/inorganic residues removal
low-ĸ
Etchant
residues
CoESL 2 Low
-ĸ
ESL 1
CoLow-ĸ
TitanKlean
Wet Cleaning
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PLANARCLEAN AG-W CLEAN MECHANISM FOR ALUMINA OR SURFACE TREATED SILICA (ST-SiO2)-Based CMP Slurries
Polishing produces many particles (slurry, metal, and organics)
W W W W W W W W W W W
OrganicParticle
MetalParticle
MetalParticle
Al2O3
ST(+)-SiO2
OrganicParticle
Al2O3
ST(+)-SiO2
MetalParticle
Comp B & D – modifies particles surface and creates negative surface charges
W
O
W
O
W
O
W
O
W
O
W
O
W
O
W
O
W
O
W
O
W
O
B
Al2O3
ST(+)-SiO2
B
B
B B
B
B
D
DD
D
D
DDB
Al2O3
ST(+)-SiO2
B
B
B B
B
B
D
DD
D
D
DD
Removed by DIW Rinse
W W W W W W W W W W W
B
Al2O3
ST(+)-SiO2
B
B
B B
B
B
D
DD
D
D
DD
Organicparticle
Metal Particle
Component A – Insures negative charges on W surface and organic particles.
Organicparticle
Metal Particle
Organicparticle
W
O
W
O
W
O
W
O
W
O
W
O
W
O
W
O
W
O
W
O
W
O
PC AG-W formulations:
◦ Inhibits W corrosion
◦ Controls the W etch rate
◦ Particle and surface modification
◦ Dielectric compatibility
◦ Non-TMAH additives fororganic residue removal
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HIGHER TUNGSTEN ETCH RATES WITH INCREASING pH DUE TO DISSOLUTION AS POLYOXOTUNGSTATE KEGGIN IONS
"Hetero and lacunary polyoxovanadate chemistry: Synthesis, reactivity and structural aspects". Coord. Chem. Rev. 255: 2270–2280. 2011.
Dil NH3 (1:2850)
SC1: 1:50 > 6 A/min
Liu, et al. J. Mater. Chem A, Issue 6, 2014
WO3 Negative at all pHs of interest
MECHANISMS FOR IMPROVING ORGANIC RESIDUE REMOVAL FROM SI3N4 STUDIED BY CONTACT ANGLE AND FTIR
1.
clean, hydrophilic
dirty dirty
Si3N4
Control clean clean
Cleaning additive removes cationic Contamination form dielectric
surface and disperses
FTIR
Contact Angle
Si3N4 surface typicallyHighly contaminatedby cationic dishing and
erosion control agents
AG- W Cleaner
Electrostatic Repulsion during CMP
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0
50
100
150
200
250
W100 SC1 W210 W210 #A W210 #B W210 P3 buff
slurry ball
slurry cluster
oxide
organic-silica
organic
# defects pareto (>= 65 nm defects)# defects pareto (≥ 65 nm defects)SiO2 – EDR Review – Defect Pareto
AG-W#1 SC-1 AG-W#3AG-W#2 AG-W#4
0
5
10
15
20
25
30
W100 W210 W210 #A W210 #B W210 P3 Buff
Slurry ball
Slurry cluster
Oxide
Organic
# defects pareto (>= 100 nm defects)# defects pareto (≥ 100 nm defects)W – EDR Review – Defect Pareto
AG-W#3 AG-W#40
5
10
15
20
25
30
W100 W210 W210 #A W210 #B W210 P3 Buff
Slurry ball
Slurry cluster
Oxide
Organic
# defects pareto (>= 100 nm defects)
AG-W#1
-10
10
30
50
70
90
110
130
150
W100 SC1 W210 W210 #A W210 #B
Slurry ball cluster
Slurry ball
Silica
Organic
# defects pareto (>= 60 nm defects)
9618 defects
# defects pareto (≥ 65 nm defects)Si3N4 – EDR Review – Defect Pareto
AG W#1 SC-1 AG-W#2 AG W#3 AG W#4
-10
10
30
50
70
90
110
130
150
W100 SC1 W210 W210 #A W210 #B
Slurry ball cluster
Slurry ball
Silica
Organic
# defects pareto (>= 60 nm defects)
9618 defects
PLANARCLEAN AG-W FORMULATIONS EXHIBIT LOWER DEFECTS AND ORGANIC RESIDUES OVER TRADITIONAL CLEANS
AG-W#2
9618 defects-SC1 or dil NH3
No cleaning on Si3N4
• PC AG-W Series show improved performance over SC-1 on all substrates
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1. White, M. L. et al, Materials Research Society Symposium Proceedings Volume 991Issue Advances and Challenges in Chemical Mechanical Planarization Pages 207-212Journal 2007
2. Hegde, Sharath; Babu, S. V. Electrochemical and Solid-State Letters (2004), 7(12), G316-G3183. White , M. L. et al. Mat. Sc. For. 1249 E04-07 (2010).
DEFECTIVITY CORRELATED TO CHARGE REPULSION BETWEEN SILICA PARTICLES
Additive increases negative charge on
particle surface
q 1 q 2
r
Coulomb’sLaw
𝐹 = 𝑘𝑞1 ∗ 𝑞2/r2
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TITANKLEAN® PERR AND SELECTIVE ETCH APPLICATIONS
Application: W vs. TiN selective etching
• Challenge and Requirements: Control selectivity of TiN/W; compatible with various dielectric materials
• W Etch rate controlled through selective W Inhibitors
Si substrate
Gate oxideTiN
W W
W/TiN Etch controllableetchant
W/TiN etching
Buried Wordline Formation
30.10
20.15 11.38
180.55
164.38
147.93
0.00
20.00
40.00
60.00
80.00
100.00
120.00
140.00
160.00
180.00
200.00
0215-5* 0215-6* 0215-7*
(A/m
in)
TiN ER(A/min) W ER(A/min)
6x8x
12x
Better W Inhibitors
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CONCLUSIONS
◦ Proper selection of Cobalt inhibitors and complexers can virtually eliminate cobalt corrosion
◦ Certain cobalt cleaning additives improve defectivity on cobalt
◦ Additives have been found that remove and disperse organic residue from silicon nitride after W CMP
◦ Tungsten etch rate and corrosion can be controlled through the proper selection of W inhibitors
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