3.155J/6.152J Lecture 10: Lithography – Part...
Transcript of 3.155J/6.152J Lecture 10: Lithography – Part...
3.155J/6.152J Lecture 10: Lithography – Part 1
Prof. Martin A. Schmidt
Massachusetts Institute of Technology
10/8/2003
Outline
The Lithographic Process Basic Process
Definitions
Fundamentals of Exposure
Exposure Systems
Resists
Advanced Lithography
Recommended reading Plummer, Chapter 5
Other: Campbell, Chapter 7,8,9
Fall 2003 – M.A. Schmidt 3.155J/6.152J – Lecture 10 – Slide 2
IC Process
Circuit Design Process Simulation Device Simulation
Layout BOXES
Mask Shop
Design Rules
Wafers Wafer Fab
Fall 2003 – M.A. Schmidt 3.155J/6.152J – Lecture 10 – Slide 3
An idea A file
Wafer Fab - Lithography
Most Common Measure of Complexity # of Masks, Minimum Feature (examples)
Approximately 50% of the Process Steps
Litho Etch Oxidation/Deposition Litho Etch Implant
Anneal Metal DepositionLitho Etch Litho Etch Sinter
Oxidation
Drives Infrastructure Cleanliness
Vibration
Temperature and Humidity
Fall 2003 – M.A. Schmidt 3.155J/6.152J – Lecture 10 – Slide 4
Semiconductor Roadmap
Fall 2003 – M.A. Schmidt 3.155J/6.152J – Lecture 10 – Slide 5
Pattern Transfer Steps
Mask
Coat with photoresist
Develop
Strip resist
Expose
Etch*
*Wet etch
Fall 2003 – M.A. Schmidt 3.155J/6.152J – Lecture 10 – Slide 6
Definitions
Metrics Resolution
Throughtput
Registration (Alignment)
Exposure Systems - UV Projection - Fraunhofer
Proximity - Fresnel
Contact - Fresnel
Advanced
DUV, E-Beam, X-Ray, Nano-imprint
Resists Positive/Negative
Contrast
CMTF
Fall 2003 – M.A. Schmidt 3.155J/6.152J – Lecture 10 – Slide 7
Lithography Systems
Proximity Contact Projection
Mask
Wafer
Fall 2003 – M.A. Schmidt 3.155J/6.152J – Lecture 10 – Slide 8
Contact/Proximity Printing
Fall 2003 – M.A. Schmidt 3.155J/6.152J – Lecture 10 – Slide 9
Contact/Proximity Printing
Fall 2003 – M.A. Schmidt 3.155J/6.152J – Lecture 10 – Slide 9
Applies when < g < W2/
Minimum resolvable feature = ( g)1/2
Proximity Printing Limits
Minimum resolvable feature = ( g)1/2
Gap = 20 m and Source = 436 nm
3.0 m
Fall 2003 – M.A. Schmidt 3.155J/6.152J – Lecture 10 – Slide 11
Projection Printing
Fall 2003 – M.A. Schmidt 3.155J/6.152J – Lecture 10 – Slide 12
Image from a Circular Opening
Note limit of d Fall 2003 – M.A. Schmidt 3.155J/6.152J – Lecture 10 – Slide 13
Resolving Features
Fall 2003 – M.A. Schmidt 3.155J/6.152J – Lecture 10 – Slide 14
: When the peak of one projection lands on the first zero of the other.
Rayleigh Limit
Rayleigh Criterion
S. Wolf, Microchip Manufacturing, Lattice Press
Fall 2003 – M.A. Schmidt 3.155J/6.152J – Lecture 10 – Slide 15
R
n=1 (air)
The Rayleigh Criterion
R = 1.22 f/d = 1.22 f/n(2fsin ) = 0.61 /nsin
NA = nsin Range from 0.16-0.76 )
R = 0.61 /NA = k1 /NA (practical k1 = 0.6-0.8)
Fall 2003 – M.A. Schmidt 3.155J/6.152J – Lecture 10 – Slide 16
Modulation Transfer Function (MTF)
Fall 2003 – M.A. Schmidt 3.155J/6.152J – Lecture 10 – Slide 17
Inte
nsi
ty
Inte
nsi
ty
Modulation Transfer Function (MTF) Mask
MTF =
Imax - Imin
Distance Imax + IminWafer
Imax
Imin
Fall 2003 – M.A. Schmidt Distance 3.155J/6.152J – Lecture 10 – Slide 18
MTF vs Feature Size
Fall 2003 – M.A. Schmidt 3.155J/6.152J – Lecture 10 – Slide 19
Depth of Focus
f
d
/4 = - cos
Small : /4 = 2/2
= sin = d/2f = NA
Depth of Focus = = /2(NA)2
= k2 /(NA)2
R = 0.61 /NA = k1 /NA
Fall 2003 – M.A. Schmidt 3.155J/6.152J – Lecture 10 – Slide 21
Resist Contrast Dose = Intensity (W/cm-2) x time (s)
Positive Negative
Develo
ped T
hic
kness
Q0
Qf
Develo
ped T
hic
kness
Q0
Qf
Exposure Dose (log scale) Exposure Dose (log scale) mJ cm-2 mJ cm-2
= 1 / log10(Qf/Q0)
Fall 2003 – M.A. Schmidt 3.155J/6.152J – Lecture 10 – Slide 22
Ideal Exposure – Ideal Resist
Dose
Distance
Resi
st T
hic
kness
Distance
Fall 2003 – M.A. Schmidt 3.155J/6.152J – Lecture 10 – Slide 23
Dose
Qf
Real Exposure – Ideal Resist
Distance
Resi
st T
hic
kness
Increase Time
Fall 2003 – M.A. Schmidt 3.155J/6.152J – Lecture 10 – Slide 24
Dose Qf
Q0
Real Exposure – Real Resist
Distance
Resi
st T
hic
kness
Increase Time
Decrease Contrast
Fall 2003 – M.A. Schmidt 3.155J/6.152J – Lecture 10 – Slide 25
Decreasing ‘Pitch’ D
ose
Qf
Q0
Dose
Distance Distance
Resi
st T
hic
kness
Resi
st T
hic
kness
Distance
Fall 2003 – M.A. Schmidt 3.155J/6.152J – Lecture 10 – Slide 26
Critical Modulation Transfer Function (CMTF) D
evelo
ped T
hic
kness
Q0
Qf
Q
CMTF =
f – Q0 10 – 1 =
Qf + Q0 10 + 1
If = 3, CMTF = 0.37= 1 / log10(Qf/Q0)
If = 2, CMTF = 0.52
Fall 2003 – M.A. Schmidt 3.155J/6.152J – Lecture 10 – Slide 28
Effect of Coherence on MTF
CMTF
CMTF
Fall 2003 – M.A. Schmidt 3.155J/6.152J – Lecture 10 – Slide 30