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Photolithography Technologyand Application
Jeff TsaiDirector, Graduate Institute of Electro-Optical
Engineering Tatung University
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Art or Science?
HP processor, 1977.
Lind width = 100 to 5micron meter!!
Resolution = ~ 3 micron
Can you image the latest
transistor size? 22nm,
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Human fine art
magnified 500x, top metal(M2) is covering DUAL 2-Input AND gate
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Intel 32 nm technology from the
Core i5 660 Microprocessor
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How it works
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Wiki say Photolithography (or "optical lithography")
is a process used in microfabrication toselectively remove parts of a thin film orthe bulk of a substrate. It uses light to
transfer a geometric pattern from a photomask to a light-sensitive chemical photoresist, or simply "resist," on the substrate.
A series of chemical treatments thenengraves the exposure pattern into thematerial underneath the photo resist.
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Function of photolithography Generate all layers of patterns
Transistor
Define STI, well implant mask,, define gate
W/L, generate LDD, BPSG via, W plug tosource/drain,
Interconnections
Contact hole, island, dualdamascene, metalline
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Process flow Singe and Prime: 150C, hexamethyldisilazane (HMDS).
Spin coat: solvent dispensed on the wafer backside, in order to ensurethe wafer backside is clear of resist, and on the frontside wafer edge,to remove resist on the edge (Edge Bead Removal or EBR).
Pre-bake: drives off excess solvent and turns the resist from a liquidinto a film.
Expose/Align: patterned by exposure to UV illumination. Exposure isperformed through a "mask",
Post-expose bake: finer features and smoother vertical-wall profiles
achieved
Develop:
Post-develop bake:
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Spin coating Coater, Track,
http://www.apexicindia.com/SpinCoatingTheory.htm
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Photoresist Spin Coater
Vacuum
PR
EBR
Wafer
Chuck
WaterSleeve
Drain Exhaust
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Relationship of Photoresist Thickness to Spin Rate
and Viscosity
Thickness
(mm)
Spin Rate (rpm)
07k2k 3k 4k 5k 6k
0.5
1.0
1.5
2.0
2.5
3.0
3.5100 cst
50 cst
27 cst
20 cst
10 cst
5 cst
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Exposure
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I-line? G-line? DUV?? Light source vs. resolution
Wavelength improvement
436nm365nm248nm193nm
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Spectrum of the Mercury Lamp
G-line
(436)
H-line
(405)
I-line
(365)
300 400 500 600
Wavelength (nm)
Inten
sity(a.u
)
Deep UV
(
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Photolithography Light
SourcesName Wavelength (nm) Application feature
size ( m)
G-line 436 0.50
Mercury Lamp H-line 405
I-line 365 0.35 to 0.25
XeF 351
XeCl 308
Excimer Laser KrF (DUV) 248 0.25 to 0.15
ArF 193 0.18 to 0.13
Fluorine Laser F2 157 0.13 to 0.1
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Mask design
Computed intensity patterns at the wafer for themasks (NAo = 0.6, M= 1/5, s = 0.7). (a) BIM, (b)PSM, (c) cross-sections of the intensity patterns inthe images of the BIM (dashed) and the PSM(solid).
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Comparison of exposure systems
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Development
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Development: Immersion
Spin DrySpin DryDevelop Rinse
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Development Profiles
PR PR
Substrate Substrate
PR
Substrate
PR
Substrate
Normal Development
Under Development Over Development
Incomplete Development
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Pattern Inspection Inspection, stripped PR and rework
Photoresist pattern is temporary Etch or ion implantation pattern is permanent.
Photolithography process can rework
Cant rework after etch or implantation.
Scanning electron microscope (SEM) for
small feature size (< 0.5 um) Optical microscope for large feature size
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Pattern Inspection Overlay or alignment
run-out, run-in, reticle rotation, wafer rotation,misplacement in X-direction, andmisplacement in Y-direction
Critical dimension (CD) loss
Surface irregularities such as scratches,
pin holes, stains, contamination, etc.
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Other nanolithography AFM
Ink print
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Electron Beam Lithography
System
Wafer
Blanking Plate
Lens
Lens
Lens
Electron Gun
Deflection
Coils
Stigmator
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Thank you for your attention