improving the quality of pvd cu seed layer for
TRANSCRIPT
Improving the Quality of PVD Cu seed Improving the Quality of PVD Cu seed Improving the Quality of PVD Cu seed Improving the Quality of PVD Cu seed Improving the Quality of PVD Cu seed Improving the Quality of PVD Cu seed layer for Interconnect Metallizationlayer for Interconnect Metallization
Improving the Quality of PVD Cu seed Improving the Quality of PVD Cu seed layer for Interconnect Metallizationlayer for Interconnect Metallization
A. Dulkin, E. Ko, A. Dulkin, E. Ko, L. WuL. Wu, I. Karim, K. Leeser, and K.J. Park, I. Karim, K. Leeser, and K.J. ParkNovellus Systems, Inc.Novellus Systems, Inc.L. Meng, D.N. L. Meng, D.N. RuzicRuzic
Center for PlasmaCenter for Plasma--Material Interactions, University of Illinois at UrbanaMaterial Interactions, University of Illinois at Urbana--ChampaignChampaign
[email protected]@novellus.com408408--953953--46374637
OutlineOutline
Ø IntroductionØPVD in interconnect metallizationØPVD challenges, evolution of PVD to iPVDØHollow Cathode Magnetron (HCM)
Ø Objective and approaches of the researchØAdvantages and capabilities of HCM
Ø Plasma diagnostic methods and results
2
P. P. 22
Ø Plasma diagnostic methods and resultsØLangmuir probeØGridded Energy Analyzer (GEA)ØQuartz crystal microbalance (QCM)
Ø Process improvement resultsØFilm morphology, stability, filling capability, etc
Ø Conclusions
Interconnect MetallizationInterconnect MetallizationDual Damascene ProcessDual Damascene Process
A)SiN Cu Barrier DepVia Diel Oxide Dep* CMP Diel (buff)
B)SiN Etch Stop DepLine Diel DepARL Dep
C)Resist Via Pattern
D)Via Etch(2 Step)
E)Resist Strip
SiliconSilicon Cu
OxideOxide
SiliconSilicon Cu
OxideOxide
Resist Resist
SiliconSilicon Cu
OxideOxide
Resist Resist
SiliconSilicon Cu
OxideOxideOxide
Resist Resist
OxideOxide OxideOxide
OxideOxide OxideOxide
OxideOxide
SiliconSilicon Cu
OxideOxide OxideOxide
OxideOxide OxideOxide
Resist Resist Resist Resist
OxideOxide OxideOxide
P. P. 33 33
H)Resist Strip
SiN Cu Barrier Etch
F)Resist Line Pattern
G)Line Oxide Etch
I)Ta(N) Barrier Dep
J)Cu Seed Dep
K)Electrofill
L)Cu-CMP
M)SiN Cu Barrier Dep
SiliconSilicon Cu
OxideOxide
OxideOxide OxideOxide
OxideOxide
Cu
SiliconSilicon Cu
OxideOxide
OxideOxide OxideOxide
OxideOxide
Cu
SiliconSilicon Cu
OxideOxide
OxideOxide OxideOxide
OxideOxide
Cu
SiliconSilicon Cu
OxideOxide OxideOxide
OxideOxide OxideOxide
SiliconSilicon Cu
OxideOxide
OxideOxide OxideOxide
OxideOxide
SiliconSilicon Cu
OxideOxide
OxideOxide OxideOxide
OxideOxide
SiliconSilicon Cu
OxideOxide
OxideOxide OxideOxide
OxideOxide
SiliconSilicon Cu
OxideOxide OxideOxide
OxideOxide OxideOxide
PVD Realm
PVD Cu/barrier seed is PVD Cu/barrier seed is critical for defect free critical for defect free
interconnect metallizationinterconnect metallization
Challenges for PVD ExtendibilityChallenges for PVD Extendibility
è Overhang• Amplified by barrier/seed • Causes “pinch-off” voiding during electrofill
è Sidewall coverage• Thin or discontinuous (agglomerated) lower sidewall coverage can cause bottom voiding.
• Limited due to light-of-sight deposition and overhang growth
è Edge asymmetry
Example
P. P. 44
è Edge asymmetry• Asymmetry and “thinning” of films near wafer edge can cause voiding or barrier breakdown
• Critical with thinner sidewall coverage
è High aspect ratio• Becomes higher after B/S deposition presenting challenges for plating
è Aggressive structure• Dielectrics undercut/OH• Low-k dielectric, damage to dielectric• Rough dielectric surface
è …
Significant challenge to extend PVD to subSignificant challenge to extend PVD to sub--22nm technology22nm technology
Example
Example
Copper Barrier/Seed
Weak Spots
44
Evolution of PVD Evolution of PVD -- Ionized PVD Ionized PVD
M Ar+ M+
Metal neutral depositionPoor Coverage, Shadows, Overhang
formation
Metal ion depositionBetter Nucleation & Surface Mobility, Coverage
enhancement due to Resputtering, Overhang Reduction
P. P. 55
iPVDiPVD addresses some inherent limitations of PVDaddresses some inherent limitations of PVD
Conventional PVD Ionized PVD
55
OutlineOutline
Ø IntroductionØPVD in interconnect metallizationØPVD challenges, evolution of PVD to iPVDØHollow Cathode Magnetron (HCM)
Ø Objective and approaches of the researchØAdvantages and capabilities of HCM
Ø Plasma diagnostic methods and results
6
P. P. 66
Ø Plasma diagnostic methods and resultsØLangmuir probeØGridded Energy Analyzer (GEA)ØQuartz crystal microbalance (QCM)
Ø Process improvement resultsØFilm morphology, stability, filling capability, etc
Ø Conclusions
Objective of Research, Hypothesis, and SolutionsObjective of Research, Hypothesis, and Solutions7
Existing problems Hypothesis Solutions
Discontinuous Cu coverage on sidewall
Neutrals with wide angular distribution build Overhang
Film continuity requires thick film.
Overhang increases to shadow sidewall
deposition
Narrow angular distribution by long
throw
Increase ion/neutral ratio
Cu island growth on Ta. Film continuity can be improved by promoting
Minimize scattering
P. P. 77
coverage on sidewall when film is thin ratio
improved by promoting 2D growth
Shift ion balance in the flux to Cu+ from Ar+Cu/Ta adhesion is
easy to compromise
Immiscible metals. Interface can be strengthened by
intermixing of materials Increase number of nucleation sites, implant deposition
species
Increase ion energy
Cu solubility in plating bath, creating voids
Rough, discontinuous film is easy attacked by
plating solution
Hollow Cathode Magnetron
è HCM combines magnetron action with electrostatic confinement of hollowcathode, and magnetic mirror to create very high density plasma in aconcave target
è High density plasma produces high ionization fraction in the depositionmetal flux
e-
Hollow Cathode Magnetron (HCM) Hollow Cathode Magnetron (HCM) iPVDiPVDGeneral Principles of OperationGeneral Principles of Operation
P. P. 88 88
Hollow Cathode Magnetron
e-
ExB
B
E
e-
EM coil
Magnetic separatrix
ions
Magnetic mirror
HCM generates high density plasma source and high metal HCM generates high density plasma source and high metal ion fractionion fraction
A magnetic cusp near the target opening acts as an aperture for plasma extraction into the downstream region
è The target erosion profile can be changed by
changing magnetic field
è Electrical and magnetic fields in the module
modulate the plasma fluxEM Coils
Rotating Magnet
Advantages of HCMAdvantages of HCM9
P. P. 99
è Ion energy can be controlled by changing plasma density which defines the potential drop in the wafer sheath
EM Coils
Deposition flux with high ion fraction
Wafer
Uniform and energetic ion component in deposition flux can be Uniform and energetic ion component in deposition flux can be achieved achieved
ApproachesApproaches
è Increase neutral directionality to improve stepcoverage:§ Long throw mode of deposition by shifting target erosionfrom sidewall to corner by changing magnetic confinement
§ Low pressure to minimize scattering: reduced from0.4mTorr to 0.1mTorr
è Change the primary ion species from Ar to CuErosion
Old process
P. P. 1010
New process
Both plasma diagnostics and film characteristics were performed to Both plasma diagnostics and film characteristics were performed to confirm the Cu seed improvement by modified processconfirm the Cu seed improvement by modified process
è Change the primary ion species from Ar to Cu§By decreasing Ar pressure and utilizing Cu self-sputtering
è Increase the Cu ion/neutral ratio§By increasing ionization via increase of the plasmadensity
è Improve ion flux uniformity and increase ion energy atwafer level§By changing magnetic field configuration at the wafer level
1010
OutlineOutline
Ø IntroductionØPVD in interconnect metallizationØPVD challenges, evolution of PVD to iPVDØHollow Cathode Magnetron (HCM)
Ø Objective and approaches of the researchØAdvantages and capabilities of HCM
Ø Plasma diagnostic methods and results
11
P. P. 1111
Ø Plasma diagnostic methods and resultsØLangmuir probeØGridded Energy Analyzer (GEA)ØQuartz crystal microbalance (QCM)
Ø Process improvement resultsØFilm morphology, stability, filling capability, etc
Ø Conclusions
Plasma DiagnosticsPlasma DiagnosticsPlanar Langmuir ProbePlanar Langmuir Probe
Old process New Process
30
40
50
(V)
Vp-Vf
30
40
50
(V)
Vp-Vf
è Planar Langmuir probes developed and placed on wafer level
è ne, Te, ni, Vp and Vf were measured
è Ion energy (estimated as sheath potential Vp-Vf) increased about twice and became more uniform
P. P. 1212
0
10
20
30
0 50 100 150
Vp-V
f(V)
Position (mm)
0
10
20
30
0 50 100 150Vp-V
f(V)
Position (mm)
0
0.2
0.4
0.6
0.8
1
1.2
0 50 100 150
Ion den
sity (a.u.)
Position (mm)
Ion density
-0.3
0.2
0.7
1.2
0 50 100 150Ion den
sity (a.u.)
Position (mm)
Ion density
twice and became more uniform across the wafer
è Ion density increased by one order of magnitude on wafer level
New process has higher plasma New process has higher plasma density and ion energy with better density and ion energy with better
uniformity across the waferuniformity across the wafer
1212
No biasing needed
L. Wu, E. Ko, A. Dulkin, K.J. Park, S. Fields, K. Leeser, L. Meng, and D.N. Ruzic,, Rev. Sci. Instrum. November 10, 2010.
è Gridded energy analyzer (GEA) / QCM
� Measure ionization fraction of Cu
� Measure Ar+/Cu+ flux ratio
Plasma DiagnosticsPlasma DiagnosticsGridded Energy Analyzer/QCMGridded Energy Analyzer/QCM
PedestalWater cool
300mm
75mm
Ceramic plate
150mm
QCM
Grids
-+
Ceramic disk 3.2 mm
2.7 mm
3.9 mm
Electron repeller grid
Ion repeller grid
22.2 mm
-+
Ceramic disk 3.2 mm
2.7 mm
3.9 mm
Electron repeller grid
Ion repeller grid
22.2 mm
+
+
+≡
MMM
fractionionMetal0
P. P. 1313
� Measure ion energy distribution
è Typical Bias Setup
� Top grid floating
� Electron repelling grid -45 V (lowerthan Vf)
� Ion repelling grid -75 to 75 V
� QCM to record the metal dep rate
QCMA A
22.2 mm
QCMAA AA
22.2 mm
DeconvolutionDeconvolution of of ArAr++, Cu, Cu++ and Cuand Cu00 fluxesfluxes was achieved by measuring the ion current, Cu was achieved by measuring the ion current, Cu neutral neutral depdep rate and total Cu rate and total Cu depdep rate using the GEA/QCM assembly. rate using the GEA/QCM assembly.
1313L. Wu, E. Ko, A. Dulkin, K.J. Park, S. Fields, K. Leeser, L. Meng, and D.N. Ruzic,,
Rev. Sci. Instrum. November 10, 2010.
Plasma Diagnostics ResultsPlasma Diagnostics ResultsFluxes of Different SpeciesFluxes of Different Species
New processOld process
Cu+ Cu0Cu+&Ar+
P. P. 1414
è Fluxes of different species� Total ion flux (Ar+ and Cu+) increases (higher plasma density)
� Improved ion flux uniformity
� New process has lower Cu0 flux while higher Cu+ flux. More Cu atoms are ionized
1414
New process has higher ion density and Cu ion fluxNew process has higher ion density and Cu ion flux
Plasma Diagnostics ResultsPlasma Diagnostics ResultsIonization FractionIonization Fraction
Ar+/Cu+
Relative Cu ionization fraction
P. P. 1515
New process has higher Cu ionization and lower New process has higher Cu ionization and lower ArAr+/Cu+ ratio+/Cu+ ratio1515
è Cu ionization fraction increases more than twice and is more uniform� Lower at edge due to the diffusion process from source axis (separatrix opening)
è Decreased Ar+/Cu+ ratio.� Energetic Cu ions are preferred over Ar ions for transferring energy to Cu atoms onsurface
Plasma Diagnostics ResultsPlasma Diagnostics ResultsIon Energy DistributionIon Energy Distribution
è Ion energy distribution was resolved with the use of GEA
è The average ion energies agree with the Vp-Vf measurement
è At the center and middle radius, narrow ion energy distributions were observed.
è At the edge, the IED was IED obtained by taking the derivative of the collected current with respect to the energy.
Old process New Process
0
10
20
30
40
50
0 50 100 150
Vp-V
f(V)
Position (mm)
Vp-Vf
0
10
20
30
40
50
0 50 100 150
Vp-V
f(V)
Position (mm)
Vp-Vf
P. P. 1616
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
20 40 60 80
Ion energy distribution
Ion energy on wafer (eV)
Center
Middle
Edge
è At the edge, the IED was broadened and extended to the low energy side. This is caused by the non-perpendicular ion incident angles and the direction of magnetic field lines.
New process
collected current with respect to the energy.
Increased ion energies in the Increased ion energies in the new process were confirmed new process were confirmed with GEA measurementswith GEA measurements 1616
OutlineOutline
Ø IntroductionØPVD in interconnect metallizationØPVD challenges, evolution of PVD to iPVDØHollow Cathode Magnetron (HCM)
Ø Objective and approaches of the researchØAdvantages and capabilities of HCM
Ø Plasma diagnostic methods and results
17
P. P. 1717
Ø Plasma diagnostic methods and resultsØLangmuir probeØGridded Energy Analyzer (GEA)ØQuartz crystal microbalance (QCM)
Ø Process improvement resultsØFilm morphology, stability, filling capability, etc
Ø Conclusions
18
Area of
Improvement in Cu film CharacteristicsImprovement in Cu film CharacteristicsFilm MorphologyFilm Morphology
New processOld process
P. P. 1818
• Backwall of the seeded via was used as the test structure.
• Continuous seed is required for electrofill.
• Smooth film becomes continuous at the smaller thickness.
Area ofinterest
Improved seed morphology can result in continuous film Improved seed morphology can result in continuous film with lower thicknesswith lower thickness
~100 nm ~100 nm
19
40
Oxide
Improvement in Resistance to oxidation
Oxidation plasma grown oxide
Improvement in Cu film CharacteristicsImprovement in Cu film CharacteristicsFilm StabilityFilm Stability
P. P. 1919
20
Oxidethickness (A)
Old New
Smooth film with the less defined grains demonstrates Smooth film with the less defined grains demonstrates improved resistance to oxidationimproved resistance to oxidation
0
Resistance to dewetting
Barrier/seed interface wassubjected to H2 anneal totest the adhesion andstability of it.
Wafer Center: No Cu
Old process New process
Improvement of Cu SeedImprovement of Cu SeedInterface Stability and AdhesionInterface Stability and Adhesion
center center
500 nm
P. P. 2020
Wafer Center: No Cudewetting from the barrierfor both processes
Wafer Edge: Cu dewettedand agglomerated in oldprocess case while the newone demonstrated adhesionsimilar to the center
New process ensures that seed adhesion is uniform across New process ensures that seed adhesion is uniform across the waferthe wafer 2020
edge
r
edge
500 nm
4s 6s4s6sCold plating stability
DD features with seed layer
Old New
Improvement of Cu seedImprovement of Cu seedSeed StabilitySeed Stability
21
center
center
P. P. 2121
6s4s 4s 6s
DD features with seed layer(800A field thickness) were“cold” plated with variabledelay time.
New seed demonstratedlonger “life” in the platingbath as a result of betterfilm continuity
Better stability in the plating bath indicates improved seed Better stability in the plating bath indicates improved seed continuity and results in the wider continuity and results in the wider electrofillelectrofill process windowprocess window
edge
edge
Improvement of Cu seedImprovement of Cu seedElectrofillElectrofill of High Aspect Ratio of High Aspect Ratio ViasVias
Center
1488A 665A643A1453A
Edge Center Edge
Old New
P. P. 2222
1388A 1367A 542A 543A
The new process ensures The new process ensures electrofillelectrofill with 2x thinner seed. with 2x thinner seed. Uniformity is improved across the waferUniformity is improved across the wafer
2222
ConclusionsConclusions
Ø The emphasis of research was placed on improving Ta/Cubarrier/seed interface characteristics such as stability, adhesion, andmorphology on feature sidewalls with good uniformity across thewafer.
Ø Deposition flux was alternated by simple changing of magneticconfinement and operating pressure.• Planar Langmuir probe, GEA and QCM diagnostics have been utilized in assistingof changing the parameters in desired direction.
23
P. P. 2323
Ø Improved deposition was achieved due to• Long throw effect for the neutral flux• Increased plasma density and high metal ion fraction in the total deposition flux• Increased ion energy• Improved uniformity of plasma parameters• Enhanced Cu ion fraction in total ion flux
Ø Resulting seed demonstrated improved performance, which allowedfor better and more uniform electrofill with less seed thickness, aswell as better resistance to oxidation and agglomeration, which cantransform into better resistance to electro and stress migration.
ReferencesReferences
q L. Wu, E. Ko, A. Dulkin, K.J. Park, S. Fields, K. Leeser, L. Meng, and D.N. Ruzic, “Flux and Energy Analysis of Species in Hollow Cathode Magnetron Ionized Physical Vapor Deposition of Copper”, The Review of Scientific Instruments, 81, 123502, (2010)
q L. Meng, R. Raju, R. Flauta, H. Shin, D.N. Ruzic, and D.B. Hayden, J. Vac. Sci. Technol. A 28, 112 (2010)
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Thanks for your attention!
Old process New process
53% 64%
Improvement in Cu film CharacteristicsImprovement in Cu film CharacteristicsStep CoverageStep Coverage
Backup slide
P. P. 2525 2525
53%
12%
12%
14%
45%
64%
12%
28%
16%
76%
Improved step coverage as a result of more directional Improved step coverage as a result of more directional deposition fluxdeposition flux