lecture 13.0
DESCRIPTION
Lecture 13.0. Chemical Mechanical Polishing. What is CMP?. Polishing of Layer to Remove a Specific Material, e.g. Metal, dielectric Planarization of IC Surface Topology. CMP Tooling. Rotating Multi-head Wafer Carriage Rotating Pad Wafer Rests on Film of Slurry - PowerPoint PPT PresentationTRANSCRIPT
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Lecture 13.0Lecture 13.0
Chemical Mechanical Polishing
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What is CMP?What is CMP?
Polishing of Layer to Remove a Specific Material, e.g. Metal, dielectric
Planarization of IC Surface Topology
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CMP ToolingCMP Tooling Rotating Multi-head
Wafer Carriage Rotating Pad Wafer Rests on Film
of Slurry Velocity= -
(WtRcc)–[Rh(Wh –Wt)] when Wh=Wt
Velocity = const.
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SlurrySlurry
Aqueous Chemical Mixture– Material to be removed is soluble in liquid– Material to be removed reacts to form an oxide
layer which is abraded by abrasive Abrasive
– 5-20% wgt of ~200±50nm particles• Narrow PSD, high purity(<100ppm)• Fumed particle = fractal aggregates of spherical
primary particles (15-30nm)
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Pad PropertiesPad Properties
Rodel Suba IV Polyurethane
– tough polymer• Hardness = 55
– Fiber Pile• Specific Gravity = 0.3• Compressibility=16%• rms Roughness =
30μm
– Conditioned
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Heuristic Understanding of CMPHeuristic Understanding of CMP Preston Equation(Preston, F., J. Soc. Glass Technol., 11,247,(1927).
– Removal Rate = Kp*V*P• V = Velocity, P = pressure and Kp is the proportionality constant.
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CMP Pad ModelingCMP Pad Modeling Pad Mechanical Model - Planar Pad
• Warnock,J.,J. Electrochemical Soc.138(8)2398-402(1991).
Does not account for Pad Microstructure
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CMP ModelingCMP Modeling
Numerical Model of Flow under Wafer– 3D-Runnels, S.R. and Eyman, L.M., J. Electrochemical
Soc. 141,1698(1994).– 2-D-Sundararajan, S., Thakurta, D.G., Schwendeman,
D.W., Muraraka, S.P. and Gill, W.N., J. Electrochemical Soc. 146(2),761-766(1999).
PadU
Pappliedy
x
h(x)
Wafer
Slurry
D
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Abrasive in 2D Flow ModelAbrasive in 2D Flow Model
Aw CAbrasiveoutwithRatePolishing
AbrasivewithRatePolishing 1
In the 2-D approach the effect of the slurry and specifically the particles in the slurry is reduced to that of an unknown constant, , determined by experimental measurements
where w is the shear stress at the wafer surface and CA is the concentration of abrasive.
Sundararajan, Thakurta, Schwendeman, Mararka and Gill, J. Electro Chemical Soc. 146(2),761-766(1999).
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Copper DissolutionCopper Dissolution
Solution Chemistry– Must Dissolve
Surface Slowly without Pitting
Supersaturation
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Effect of Particles on CMP is Unknown.Effect of Particles on CMP is Unknown.
Effect of Particles on CMP– Particle Density– Particle Shape &
Morphology– Crystal Phase– Particle Hardness &
Mechanical Properties– Particle Size Distribution– Particle Concentration– Colloid Stability
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Particle EffectsParticle Effects-Aggregated Particles are used-Aggregated Particles are used
SSA(m2/gm) Phase(%alpha) Primary Diameter(nm)Agg. Diameter(nm)W Rate(nm/min.) Selectivity(W/SiO2)55 80% 27.5 86 485 5085 40% 17.8 88 390 110
100 20% 15.1 87 370 NA
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Layer Hardness EffectsLayer Hardness Effects Effect of Mechanical
Properties of Materials to be polished
Relationship of pad, abrasive and slurry chemistry needed for the materials being polished.
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Pad ConditioningPad Conditioning Effect of Pad on CMP
• Roughness increases Polishing Rate
– Effect of Pad Hardness &Mechanical Properties
– Effect of Conditioning
– Reason for Wear-out Rate
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Mass Transfer-Mass Transfer-Bohner, M. Lemaitre, J. and Bohner, M. Lemaitre, J. and Ring, T.ARing, T.A., "Kinetics of Dissolution of ., "Kinetics of Dissolution of --tricalcium phosphate," J. Colloid Interface Sci. 190,37-48(1997).tricalcium phosphate," J. Colloid Interface Sci. 190,37-48(1997).
Driving Force for dissolution, Ceq(1-S) S=C/Ceq Different Rate Determining Steps
– Diffusion - J(Flux) (1-S)– Surface Nucleation
• Mono - J exp(1-S) • Poly - J (1-S)2/3 exp(1-S)
– Spiral(Screw Dislocation) - J (1-S)2
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Solution Complexation-Solution Complexation-Chen, Y. and Chen, Y. and Ring, T.A.Ring, T.A., "Forced Hydrolysis of In(OH)3- Comparison of , "Forced Hydrolysis of In(OH)3- Comparison of Model with Experiments" J. Dispersion Sci. Tech., 19,229-247(1998).Model with Experiments" J. Dispersion Sci. Tech., 19,229-247(1998).
Solutions are Not Simple but Complex Complexation Equilibria
– i M+m + j A-a [Mi Aj](im-ja) – Kij ={[Mi Aj](im-ja)}/{M+m}i {A-a }j {}=Activity
– Multiple Anions - A, e.g. NO3-, OH-
– Multiple Metals - M, e.g. M+m, NH4+, H+
Complexation Needed to Determine the Equilibrium and Species Activity,{}i=ai
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Silica Dissolution - Solution ComplexationSilica Dissolution - Solution Complexation
SiO2(c) + H2O <---> Si(OH)4 Amorphous SiO2 dissolution Si(OH)4 + H+1 <---> Si(OH)3·H2O+1 pKo= -2.44 ΔHo= -16.9 kJ/mole Si(OH)4 + OH-1 <---> H3SiO4
-1 + H2O pK1= -4.2 ΔH1= -5.6 kJ/mole Si(OH)4 + 2 OH-1 <---> H2SiO4
-2 + 2 H2O pK2= -7.1 ΔH2= -6.3 kJ/mole 4Si(OH)4 + 2 OH-1 <---> Si4O6(OH)6
-2 + 6 H2O pK3= -12.0 ΔH3= -12 kJ/mole 4Si(OH)4 + 4 OH-1 <---> Si4O4(OH)4
-4 + 8 H2O pK4=~ -27
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Solution ComplexationSolution Complexation
Si(OH)40
H3SiO4-1
Si(OH)3·H2O+1
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Copper CMP uses a More Copper CMP uses a More Complex Solution ChemistryComplex Solution ChemistryK3Fe(CN)6 + NH4OH
– Cu+2 Complexes• OH- - i:j= 1:1, 1:2, 1:3, 1:4, 2:2, 3:4• NO3
- -weak• NH3 - i:j= 1:1, 1:2, 1:3, 1:4, 2:2, 2:4• Fe(CN)6
-3 - i:j=1:1(weak) • Fe(CN)6
-4 - i:j=1:1(weak) – Cu+1 Complexes
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Copper Electro-ChemistryCopper Electro-ChemistryReaction-Sainio, C.A., Duquette, D.J., Steigerwald, J.M., Murarka, J. Electron. Mater.,
25,1593(1996).
Activity Based Reaction Rate-Gutman, E.M., “Mechanochemistry at Solid Surfaces,” World Scientific Publishing, Singapore, 1994.
– k”=reaction rate constant 1=forward,2=reverse
– aj=activity, j=stociometry, μj =chemical potential
– Ã =Σνjμj =Overall Reaction Affinity
46233
36 )()(2)( CNFeNHCuNHCNFeCu EQK
j g
jproductsj
jtsreacjj TR
AakakakFluxJ jjj )1~
exp()( 2tan
21
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Chemical PotentialChemical Potential
Mineral Dissolution
Metal Dissolution
ø=Electrode Potential=Faraday’s Constant
iigioigioi cTRaTR lnln
iiigioiigioi zcTRzaTR lnln
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Fluid FlowFluid FlowMomentum BalanceMomentum Balance Newtonian
Lubrication Theory
Non-Newtonian Fluids
PadU
Pappliedy
x
h(x)
Wafer
Slurry
D
),(0 2 yxuP
),()(0 2 yxuP
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CMP Flow Analogous to Tape CMP Flow Analogous to Tape CastingCasting--RING T.A.,RING T.A., Advances in Ceramics vol. 26", M.F. Yan, K. Niwa, H.M. O'Bryan and W. S. Young, editors ,p. 269-576, Advances in Ceramics vol. 26", M.F. Yan, K. Niwa, H.M. O'Bryan and W. S. Young, editors ,p. 269-576, (1988).(1988).Newtonian Yc=0,
– Flow Profile depends upon PressureBingham Plastic, Yc0
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Wall Shear Rate, Wall Shear Rate, ww
Product of– Viscosity at wall shear stress– Velocity Gradient at wall
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Slurries are Non-Newtonian FluidsSlurries are Non-Newtonian Fluids
Crossian Fluid- Shear Thinning
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Mass Transfer into SlurriesMass Transfer into Slurries
No Known Theories!
2-D CMP Model gives this Heuristic
Wall Shear Stress, w and Abrasive Concentration, CA are Important!
AwCAbrasiveatewithoutPolishingRasiveatewithAbrPolishingR 1
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Mechanical PropertiesMechanical Properties
Elastic DeformationPlastic DamagePlastic Deformation
– Scratching
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Abrasive Particles Cause Surface StressAbrasive Particles Cause Surface StressA. Evans “Mechanical Abrasion”A. Evans “Mechanical Abrasion”
Collisions with Wafer Surface Cause Hertzian Stress
Collision Rate ?
Stress Due To Collision P[ =(H tan2 )1/3 Uk
2/3] is the peak load (N) due to the incident kinetic energy of the particles, Uk,The load is spread over the contact area
Hertzian Stress, sigma/Po
N
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Mechanical Effects on Mass Mechanical Effects on Mass TransferTransferChemical Potential-Gutman, E.M., “Mechanochemistry at
Solid Surfaces,” World Scientific Publishing, Singapore, 1994.
– Mineral Dissolution
– Metal Dissolution
migioi VaTR ln
miigioi VzaTR ln
TRVVX
g
mii
T
i )ˆ()ln( ,
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Effect of Stress on DissolutionEffect of Stress on DissolutionMetals Mineral-CaCOMetals Mineral-CaCO33
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Mechano-Chemical EffectMechano-Chemical Effect
– Effect on Chemical Potential of solid– Effect of Activity of Solid
As a result, Dissolution Rate of Metal and Mineral are Enhanced by Stress.
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Oxidation of Metal Causes StressOxidation of Metal Causes Stress
Stress, i = E i (P-B i – 1)/(1 - i)• P-Bi is the Pilling-Bedworth ratio for the
oxide
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Hertzian Hertzian Shear StressShear Stress
Delatches the Oxide LayerWeak Interface Bond
CL=0.096 (E/H)2/5 Kc-1/2 H-1/8 [ 1- (Po/P)1/4]1/2 P5/8
• A. Evans, UC Berkeley.
h
Lateral Cracks
b
CL
Hertzian Shear Stress, Tau/Po
M