lecture 10.0
DESCRIPTION
Lecture 10.0. Photoresists/Coating/Lithography. Semiconductor Fab. Land$0.05 Billion Building$0.15 Billion Tools & Equipment $1 Billion Air/Gas Handling Sys$0.2 Billion Chemical/Electrical Sys$0.1 Billion Total$1.5 Billion 10 year Amortization~$1 Million/day. - PowerPoint PPT PresentationTRANSCRIPT
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Lecture 10.0Lecture 10.0
Photoresists/Coating/Lithography
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Semiconductor FabSemiconductor Fab
Land $0.05 BillionBuilding $0.15 BillionTools & Equipment $1 BillionAir/Gas Handling Sys$0.2 BillionChemical/Electrical Sys $0.1 BillionTotal $1.5 Billion10 year Amortization ~$1 Million/day
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80nm Line width with 80nm Line width with =193 nm =193 nm LithographyLithography
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Photoresist -Photoresist -Sales $1.2 billion/yr. in 2001 Sales $1.2 billion/yr. in 2001 Resins– phenol-formaldehyde, I-line
SolventsPhotosensitive compounds
– Polymethylmethacrylate or poly acrylic acid = 638 nm RED LIGHT
– diazonaphthoquinone• Hg lamp, = 365 nm, I-line
– o-nitrobenzyl esters – acid generators• Deep UV, = 248 nm, KrF laser
– Cycloolefin-maleic anhydride copolymer– Poly hydroxystyrene
=193 nm gives lines 100 nm = 157 nm F laser
Additives
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PhotoresistPhotoresist
Spin Coat waferDry solvent out of filmExpose to LightDevelop Quench developmentDissolve resist (+) or developed
resist (-)
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Spin CoatingSpin Coating
Cylindrical Coordinates– Navier-Stokes– Continuity
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Navier-StokesNavier-Stokes
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Spin Coating DynamicsSpin Coating Dynamics
NewtonianrV
zV
rg
gzr
rzVV
rVV
tV
gzz
VVrVV
tV
StokesNavierzV
rrV
r
Continuity
zrrz
r
zrzz
zz
rz
rrzr
zr
rr
zr
,
)(1
0)()(1
2
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Newtonian Fluid-Newtonian Fluid-non-evaporatingnon-evaporating
2/12
2
322
32
0
22
2
341)(
)0(..3
1
)(3
),(@0
0@0.'.
thhth
solutionhthCB
hrrr
qrrrt
h
thdzvq
trhazv
zvsCB
rzv
oo
o
h
r
r
r
r
If hois a constant film is uniformFor thin films, h -1 t-1/2
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Evaporating Model - Evaporating Model - Heuristic ModelHeuristic Model
CN non-volatile, CV volatile
e= evaporationq= flow rate
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Spin Coater - Heuristic ModelSpin Coater - Heuristic Model
Flow Rate, h is thickness
Evaporation rate due to Mass Transfer
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Spin Coating SolutionSpin Coating Solution
Dimensionless Equations
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Viscosity increases with loss of Viscosity increases with loss of solventsolventViscosity of pure
Resin is very high
Viscosity of Solvent is low
0 0.02 0.041 10 5
1 10 4
1 10 3
0.01
Volume Fraction Vapor Component
Vis
cosi
ty(m
^2/s
ec) 1.521 10 3
1 10 5
x( )
x o0 x
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Spin CoatingSpin Coating
Thickness RPM-1/2 o1/4
Observed experimentally
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ResultsResultsEffect of Mass
Transfer = dimensionless
Mass transfer Coefficient
– Increase MT Increase in Film Thickness
– MT increases viscosity and slows flow leading to thicker film
Dimensionless Film Thickness
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Dissolve edge of photoresistDissolve edge of photoresist
So that no sticking of wafer to surfaces takes place
So that no dust or debris attaches to wafers
Wafer with Photoresist
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LithographyLithography
Light passes thru die mask
Light imaged on wafer
Stepper to new die location
Re-image Wafer with Photoresist
Mask
Light Source
ReductionLens
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LithographyLithographyAspect Ratio (AR)=3.5
– AR=Thickness/Critical Dimension • Critical Dimesion=line width• Thickness= photoresist thickness
Lateral Resolution (R)– R=k1 /NA
Numerical Apparature (NA)– NA is a design parameter of lens
Depth of Focus (DOF)– DOF= k2 /NA2
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Lithography - PhotoreactionLithography - Photoreaction
– Photo Reaction Kinetics• dC/dt = koexp(-EA/RT) C I(x,)
– Beer’s Law• I(x, )/Io=exp(- () C x)() = extinction coefficient
– Solution?• dC/dt = koexp(-EA/RT) C Io exp(- () C x)
– C=Co at t=0, 0<x<L
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Drying solvent out of LayerDrying solvent out of Layer
Removal of Solvent– Simultaneous Heat and Mass Transfer– In Heated oven– Some shrinkage of layer
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PhotoresistPhotoresist
Positive– Light induced reaction
• decomposes polymer into Acid + monomers
– Development• Organic Base (Tri
Methyl ammonium hydroxide) + Water
• neutralizes Acid group• Dissolves layer
– Salt + monomer
Negative– Light induced reaction
• Short polymers crosslink to produce an insoluble polymer layer
– No Development needed
– Dissolution of un- reacted material
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Photoresist DevelopmentPhotoresist Development
Boundary Layer Mass TransferPhotoresist DiffusionChemical ReactionProduct diffusion, etc.
Reaction Plane
Reactant ConcentrationProfileProduct
ConcentrationProfile
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Rate Determining StepsRate Determining Steps
X
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Dissolution of Uncrosslinked PhotoresistDissolution of Uncrosslinked Photoresist
Wafers in CarriagePlaced in SolventHow Long??Boundary Layer MT
is Rate Determining– Flow over a leading
edge for MT– Derivation & Mathcad
solutionAlso a C for theConcentration profile
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Mass transfer correlation Mass transfer correlation - flow over leading edge- flow over leading edge
Sh=Kgx/DAB Kg= DAB / C
Sc=/DAB Re=V x/
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Global Dissolution Rate/TimeGlobal Dissolution Rate/Time
Depends on–Mass Transfer• Diffusion Coefficient• Velocity along wafer surface• Size of wafer
– Solubility– Density of Photoresist Film
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Local Dissolution Rate/TimeLocal Dissolution Rate/Time
Depends on–Mass Transfer• Diffusion Coefficient• Velocity along wafer surface• Size of wafer
– Solubility– Density of Photoresist Film– Position on the wafer