EE143 F2010 Lecture 4 Photolithography - University of …ee143/fa10/lectures/Lec_… · ·...
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Transcript of EE143 F2010 Lecture 4 Photolithography - University of …ee143/fa10/lectures/Lec_… · ·...
Professor N. Cheung, U.C. Berkeley
Lecture 4EE143 F2010
1
Photolithography
• Minimum FeatureResolution
• Depth of Focus• Overlay Errors• Photoresist Response• E-beam and EUV lithography
Key Topics:Photo = s = (through) lightLitho = s = stoneGraphy = = writing
Professor N. Cheung, U.C. Berkeley
Lecture 4EE143 F2010
2
•Slow• several nm resolution
•High throughput
Professor N. Cheung, U.C. Berkeley
Lecture 4EE143 F2010
3
Professor N. Cheung, U.C. Berkeley
Lecture 4EE143 F2010
4
Contact Printing
wafer
hv
photoresist
Resolution R < 0.5m
mask plate is easily damagedor accumulates defects
PhotoMaskPlate
Professor N. Cheung, U.C. Berkeley
Lecture 4EE143 F2010
5
Proximity Printing
wafer
hv
g~20m
exposed
Photoresist
x
R = k ( g ) 1/2
~ 1 m for visible photons,much smaller for X-ray lithography
Professor N. Cheung, U.C. Berkeley
Lecture 4EE143 F2010
6
Projection Printing
hv
lens
wafer
P.R.focal plane
~0.2 m resolution (deep UV photons)tradeoff: optics complicated and expensive
De-Magnification: nX
10X stepper4X stepper1X stepper
Professor N. Cheung, U.C. Berkeley
Lecture 4EE143 F2010
7
Photon sources
Hg Arc lamps 436(G-line), 405(H-line), 365(I-line) nm Excimer lasers: KrF (248nm) and ArF (193nm) Laser pulsed plasma (13nm, EUV)
Source Monitoring
Filters can be used to limit exposure wavelengths Intensity uniformity has to be better than several % over the collection area Needs spectral exposure meter for routine calibration due to aging
Professor N. Cheung, U.C. Berkeley
Lecture 4EE143 F2010
8
Excimer Laser Stepper
Professor N. Cheung, U.C. Berkeley
Lecture 4EE143 F2010
9
Optical Stepper
wafer
scribe line
1 2
Imagefield
field size increaseswith future ICs
Translationalmotion
Professor N. Cheung, U.C. Berkeley
Lecture 4EE143 F2010
10
Aerial Images formed by Contact Printing, ProximityPrinting and Projection Printing
Professor N. Cheung, U.C. Berkeley
Lecture 4EE143 F2010
11
Professor N. Cheung, U.C. Berkeley
Lecture 4EE143 F2010
12
Line Patterns to illustrate principle of Projection Printing
Professor N. Cheung, U.C. Berkeley
Lecture 4EE143 F2010
13
Professor N. Cheung, U.C. Berkeley
Lecture 4EE143 F2010
14
waferplane
parallelopticalbeam
Line grating withspatial frequency 1/P
P P=L+S
...,2,1,0sin
nnP
-1
-2
+1
+2Mask lens
L S
0
sin = NA of lens
Qualitative Explanation of image degradation by lens
Professor N. Cheung, U.C. Berkeley
Lecture 4EE143 F2010
15x
x
Image on wafer After optical system
Mask Intensity
Imax
O
O
Imax
Professor N. Cheung, U.C. Berkeley
Lecture 4EE143 F2010
16
n=0
n=0 + n=1
n=0 + n=1 + n=3
n=0 + n=1 + n=3 + n=5
Effect of Fourier Components on aerial image of arectangular waveform
n=0
Source: Chapter 8 , iSheats and Smith,Microlithography
Professor N. Cheung, U.C. Berkeley
Lecture 4EE143 F2010
17
Why lNAm ?
The lens has to collect at least the n =1 diffracted beamsto show any spatially varying intensity on wafer.
Therefore printable Pminimum = /sin = /NA
For lm (L+S)/2 = Pm/2 /NA
Professor N. Cheung, U.C. Berkeley
Lecture 4EE143 F2010
18
point
best
off
Depth of Focus (DOF)
Professor N. Cheung, U.C. Berkeley
Lecture 4EE143 F2010
19
No defocus
Defocus increases
Note degradation ofimage contrastand image slope
Simulated aerial images with various degree of defocus
Professor N. Cheung, U.C. Berkeley
Lecture 4EE143 F2010
20
FieldOxide
Photo mask
Different optical images
Example of DOF problem
Step height > DOF
Professor N. Cheung, U.C. Berkeley
Lecture 4EE143 F2010
21
For Reference onlyFor Reference onlyBest focus Extreme Defocus
Large P features
Small P features
Focus versus Extreme Defocus (an illustration)
Professor N. Cheung, U.C. Berkeley
Lecture 4EE143 F2010
EE243 S2010 Lec 1122
First-Order Projection Printing Considerations
1) Minimum feature resolution lm = k1 (/NA)
2) Depth of Focus DOF = k2 / (NA)2
•NOTE: NA has contradictory effects on lm and DOF
where k1 and k2 are the technology factors
Professor N. Cheung, U.C. Berkeley
Lecture 4EE143 F2010
23
Image Quality Metric: (a) Image Contrast
Prefer high Contrast
Professor N. Cheung, U.C. Berkeley
Lecture 4EE143 F2010
24
* simulated aerial image of an isolated line
Image Quality metric: (b) Slope of Image Intensity
Prefer large Slope
Professor N. Cheung, U.C. Berkeley
Lecture 4EE143 F2010
EE243 S2010 Lec 11
Aerial Image Intensity on wafer
Photomask Pattern
Photomask Layout Pattern is 2D; Needs 2D Fourier Transform