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Excimer
refers to the bound excited upper state of a molecule that breaks apart
when a photon is emitted. Resonance excites Excimer emission from its
lamps with a proprietary RF power supply.
Some
of the UV emission wavelengths for various gas fill and window
combinations are shown below.
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Advantages of Excimer:
 | NON TOXIC - No
toxic mercury vapor in lamp.
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| NO HF- and other
acids, no toxic organic solvents result from lamp use.
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| PROCESS FRIENDLY-
Cannot harm vacuum process with mercury vapor.
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| NO FLUIDS- process
does not require fluids with consequent de-sorption and contamination
problems.
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| EMIT SINGLE PEAK
-(wavelength) radiation with high output in UV or VUV (Vacuum
ultraviolet)
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| CAN TARGET
SPECIFIC CHEMICAL
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| LOW ENERGY
CONSUMPTION- Can be greater than 10%.
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| BETTER THAN LASERS
- Excimer lasers are typically only 1 to 3 % efficient.
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| COOL OPERATION -
Low operating temperature (do not heat irradiated surface).
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| INSTANT START -
Typically start in less than 1 millisecond.
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| MINIMUM DAMAGE-UV
absorbed in 1 micron layer
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Excimer Cleaning:
Excimer systems use a UV cleaning
process referred to as Dry Cleaning. This process destroys and
removes organic compounds with minimum impact on the process stream.
This is superior to wet cleaning as it does not produce toxic liquids.
Excimer destruction of organic compounds takes place when contaminant
molecules (e.g. photoresists, resins, human skin oils, cleaning solvent
residues, silicone oils, soldering flux etc.) are broken down to simple
non-toxic volatile molecular fragments by the action of vacuum ultraviolet
light (pictured below).
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Terms to Know:
Photo-oxidation
refers
to the UV induced processes referenced above which result in the breakdown
of organic compounds.
Atomically
clean
refers
to a surface condition in which the substrate has a contaminating film
less than one molecule thick leaving the substrate directly exposed.
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Semiconductor
and Related
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| Dry
cleaning surface of silicon wafers and photo-resist films
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| Dry
cleaning lithography masks
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| Post CMP
dry cleaning
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| Surface
conditioning of high K materials
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| UV dry
cleaning of interlayer dielectric (SOG)
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| Optical
chemical vapor deposition (CVD)
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| PMMA
conditioning (resist smoothing)
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| Post
dicing dry cleaning of tape residues
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| Pre-wire
bonding dry cleaning
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| Dry
cleaning of backside of lead frames
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Plasma
Display Panels
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| Pre-photo-resist,
Pre-sputtering dry cleaning
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| Dry
cleaning before and after wet cleaning to improve yield
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| PDP
phosphor evaluation systems using Excimer lamps and fiber
optic UV delivery systems
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Environmental
and Medical
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| Toxic
waste (e.g. CFC's, PCB's, dioxin's, trichloroethylene)
destruction in air/water streams by photo-oxidation
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| Non
solvent cleaning: of mechanical parts
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| UV/Ozone
sterilization of medical instruments and medical supplies
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| Cleaning
glass boards, PDP Fluorescent light and LCD
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Other
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| Improvement
for non-exposed part surface of photo-resist film
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| Soft-Ashing
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| Pre-treatment
of disc surfaces, i.e., CD and DVD
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| Dry
cleaning ball bearings for hard disk drives
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| Igniter
and stabilizer for plasma etcher (Excimer used as an assist
light)
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| Post-process
treatment of CMP hardening of coatings and adhesives
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| Generation
of amorphous material, such as amorphous silicon solar cell
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| Printing
- textile printing, finishing, printed circuits
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| Reforming
surfaces - ceramics, surface etching
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| Environmental
CLEAN UP
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Contact Angle Measurements:
| A simple way to
measure the cleaning of certain surfaces.
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| Surface tension of
water droplets will depend on surface contamination.
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| The angle of
contact of a water drop will decrease as the surface tension decreases
due to removal of surface contamination (on a hydrophilic surfaces
that wet easily)
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The
images below show surface cleaning on a glass microscope slide with
Excimer UV
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Start of Exposure (0
seconds)
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After
30 Seconds of Exposure |
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contact angle method it can be seen that 172 nm Excimer light
rapidly removes contamination from glass surfaces in 30 seconds or
less.
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| The strong
dependence on distance to the sample results from the large absorbance
of O2 at 172 nm. This effect can be minimized by using a gas mixture
with a smaller O2 fraction than air.
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Example
Measurements
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Mercury
vs. Excimer on a Si surface Contact Angle Measurements (see
figure to left)
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Excimer Lamp takes 15 sec. to change the water contact angle
from 50.9 deg. to 2.6 deg.
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| The
Mercury Lamp takes 220 sec. at almost twice the power to
change the contact angle from 60 deg. to 8 deg.
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| Excimer
VUV cleaning is much faster than Mercury cleaning
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STEVEN SEPVEST CORP.
