EXCIMER LASER TECHNOLOGY
Some of the state of the art technology in GAM Laser excimer laser
- Corona preionization.
All GAM lasers are preionized with a soft corona
discharge. Unlike lasers which utilize outdated UV spark preionization
or sliding spark preionization, true corona discharge preionization is a
uniform, low current, distributed glow gas discharge which does not
produce electrode erosion or consume the active laser gas. Spark
discharge is the opposite, a high current, localized, intense spark,
which vaporizes electrode material and consumes and contaminates the
active laser gas. Spark preionization also produces high EMI and
generates high dust levels within the laser chamber. The corona
discharge system in GAM LASER excimer lasers shows minimal wear after
billions of pulses and unlike spark preionized lasers, never requires
replacement. Corona discharge provides a long term stable preionization
method which gives increased gas lifetime and increased optics lifetime
due to low dust levels. Additionally, due to the high uniformity of
corona preionization the laser output gives excellent (<2% standard
deviation) pulse stability. Older technology spark preionized lasers can
usually be identified by the poor pulse to pulse stability, typically
+/-4% or worse.
- Pointing Stability.
The pointing stability of all lasers is maintained by a
proprietary control technology which actively stabilizes the laser
pointing to within +/-20ÁRad/C. The stabilization is active under all
operating conditions. This technology avoids power fluctuations due to
changes in mirror pointing and allows for precise, long term pointing of
the laser output under changing ambient and operating conditions. The
laser alignment remains constant over the long term without tweaking.
Additionally the low divergence of GAM LASER excimer lasers, typically a
factor of 3-5 less than large beam lasers, allows tight focusing of the
output beam for precision cutting and machining.
The EX50 and EX100 lasers produce very low divergence with the
standard stable resonators, this gives excellent focus ability. The
divergence is sufficiently low to produce air breakdown. Normally this
requires unstable resonator configurations for most excimer lasers.
EX50 laser breaking down air with 30mJ at 193nm using a standard
stable resonator configuration
Gas Lifetime. Gas lifetime is one of the most
important parameters of an excimer laser. The total metal/ceramic design
of GAM Laser products and the careful choice of pure metals, ceramics
and coatings in the laser chamber, produces the longest static and
dynamic gas lifetimes of any excimer lasers. The static gas fill
lifetime with a single gas fill and no halogen injections or
cryogenic add on's, of GAM lasers with XeCl is up to 2 years. KrF
gives up to 12 weeks of static gas lifetime. Dynamic gas lifetimes of
greater than 20 million pulses can be obtained with ArF at 193nm. Total
metal/ceramic design also results in maximum optics lifetime and high
pulse stability, better than 2% standard deviation.
Vacuum ultraviolet Fluorine operation at 157nm poses the stiffest
lifetime test for any excimer laser, lifetimes as short as 100,000
pulses were obtained from most lasers until recently, and typical static
gas lifetime for most F2 lasers at present is only 24 hours. The total
metal/ceramic design of GAM LASER excimers gives 10 times longer gas
life at 157nm than all other excimer lasers. For example, the EX50F
laser gives over 15 million pulses to 50% energy at 157nm with a static
gas lifetime of greater than 15 days.
High laser efficiency also increases the gas lifetime. The advanced
design of the Pulse Power Driver in the EX series of lasers results in
very high laser efficiency, over 5% with KrF. This greatly increases gas
lifetime and decreases electrode wear.
Coherence The temporal coherence length of the
EX10 laser with KrF at 248nm is 210m
FWHM and 90m
FWHM at 193nm with ArF. The relatively long coherence length makes the
laser ideal for writing fiber Bragg gratings. Spatial coherence length
of up to 1800 mM
at 248nm can be obtained with the unstable resonator optics option.
Standard lasers have a temporal coherence of 170 microns at 248nm and
120 microns at 193nm. Much
longer temporal coherence lengths can be obtained from line narrowed
lasers. The EX50LN has a temporal coherence length of approximately 7cm
FBG Fabrication A special version of the EX10
laser is available for FBG fabrication. The EX10BM laser offers
substantially longer spatial and temporal coherence than a standard EX10
excimer laser. The EX10BM produces better than 1% standard deviation
pulse to pulse stability and a long term pointing stability of 50
mRad , The laser is
packaged in a single table top air cooled unit including the internal
vacuum pump and halogen filter.
Internal Vacuum Pump and Halogen Filter
All laser models feature an internal vacuum pump, solenoid valve
manifold and Halogen filter. The vacuum pump is used when the active
laser gas in the laser chamber is replaced. The used gas is passed
through a high capacity Halogen filter and all Fluorine or Chlorine is
removed. The Halogen filter is rated for approximately 1000 refills of
the laser head, and is replaced during laser head service. The internal
vacuum pump system and computer control insures reliable, hands off,
repeatable gas refills without the use of any external vacuum components
and bulky stand alone vacuum pumps or halogen filters. Additionally the
internal vacuum pump allows for a complete contamination free gas
replacement, unlike excimer lasers which use gas flow through only to
replace the active laser gas. The vacuum pump provides a more reliable
method of gas exchange than simple flow through.
In normal operation a single cylinder of premix gas is attached to
the appropriate laser gas port. Refill of the laser, including pumping
out the old gas and refilling with fresh gas from the premix cylinder is
accomplished completely automatically from software.
Total Metal/Ceramic Design
Total Metal/Ceramic design means that all laser components are either
chemically stable ceramics or carefully selected pure metals. No plastic
is used anywhere in the laser chamber. Plastics were used extensively in
early excimer lasers and are still used today in a number of lasers.
Many lasers claiming to use a metal/ceramic design still in fact use
numerous plastic parts. Lasers containing plastics show poor gas dynamic
lifetime and can be easily identified by the very poor static gas
lifetime. Even if a laser containing plastics is left unused, the gas
still need s replacement every few days, the exact lifetime depending
upon the excimer gas used. XeCl gas fill is more tolerant of plastic
components and can last a week or more even with plastic components in a
laser. Compare this with the GAM Laser total metal/ceramic design where
XeCl static gas lifetime is over 2 years.
Plastics also reduce the optics lifetime of excimer lasers.
Fluorocarbons and Chlorocarbons produced in chemical reactions with the
plastic materials are photo deposited on the internal optical surfaces
and rapidly reduce the laser output energy and damage the optics. Lasers
with plastic components typically require optics service an order of
magnitude more frequently than metal/ceramic lasers.
The unique total Metal/Ceramic design of GAM lasers gives the longest
dynamic and static gas lifetimes of any excimer lasers and produces long
The output spectrum of free running KrF and ArF excimer lasers is a
broad spectral band a few hundred pm wide. This broad spectral output
can be narrowed using a resonator with wavelength disperive elements to
produce a linewidth of less than 1pm. The narrow line output gives a
longer coherence length, 7cm at 248nmand a much higher spectral
intensity than standard excimer lasers. The EX50LN produces stable
linewidths of less than 1pm over wide tuning ranges centered at 193.3nm
Internal Energy Monitor
All GAM LASER excimer lasers are equipped with an internal energy
monitor. The energy detector is used to measure the energy of every
laser pulse and is used in conjunction with the EXLASER software package
to monitor the output energy and average power of the laser. Long term
energy stabilization is maintained with the internal energy monitor and
software feedback control. The energy stabilization range is
approximately 40% to 95% of specified maximum energy output.
An optional feature allows automatic NIST traceable calibration of
the internal energy monitor.
Industrial Version Industrial versions of
higher repetition rate laser products are available. The industrial
versions are designed to operate continuously. The lasers offer much
longer dynamic gas lifetime than standard lasers. The longer gas
lifetime substantially reduces operating costs
Clean Room Version A clean room version of all
EX10, EX50 and EX100 lasers is available. The clean room package is a
completely hard anodized laser package to eliminate organic solvent residues.
GAM LASER, INC. excimer lasers are designed to minimize service events.
Service considerations common to all excimer lasers and the order of
a) Gas Replacement: The active gas in the laser chamber requires
replacement. The interval between gas replacements depends upon the
number of pulses obtained per gas fill, for example with KrF gas,
replacement is required every 30 Million pulses with the EX50 Laser.
This gas replacement procedure is handled automatically by software.
b) Optics Service: This is the cleaning or replacement of the laser
mirrors. The mirrors acquire dust on the internal surfaces and can also
be damaged by the UV laser light. The interval between optics cleaning
or replacement depends upon the laser active gas, for example is greater
than 500 Million pulses with the EX10, EX50 and EX100 lasers operating
on KrF. During optics service the laser optics are removed from the
laser chamber for cleaning or replacement.
c) Gas cylinder replacement: This is required approximately every 1
billion pulses with a 2000 liter gas cylinder on an EX50 with KrF.
Larger cylinders are available.
d) Chamber Service: This is required approximately every 2 billion
pulses. The chamber is rebuilt at the factory and returned to "as new"
Unstable Resonator Optics
Unstable resonator optics provide greatly reduced beam divergence.
The decreased beam divergence produces smaller focused spot sizes and
much increased laser intensity.
The unstable resonator optics produce divergences of less than 100
microradians. This allows air breakdown (a measure of the focused
intensity of the beam) at very low energy output. For example 8mJ causes
air breakdown with an EX10 laser equipped with unstable resonator optics
The unstable resonator optics also give the exceptional pointing
stability of better than +/-20 microradians shown with all GAM Laser,
Excimer laser products.
For Fiber Bragg (FBG) applications, unstable resonator optics also
give increased coherence properties. The spatial coherence length at
248nm and 193nm is increased by an order of magnitude to approximately
2mm and 1mm respectively.
Unstable resonator optics can be rapidly retrofitted to all laser
products in the field. Output energy at all wavelengths is reduced to
approximately 70% of stable energy output in the near field. Unstable
resonator optics are available for 157nm, 193nm, 248nm, 308nm and 351nm.
Versatile Software Control. All GAM lasers are
controlled from a PC. The EXLASER software package allows the user to
program and remotely control all laser functions. The laser is
controlled through a high speed link which allows pulse to pulse control
at the highest laser repetition rates. The entire EXLASER software
control package can be updated directly over the internet or through
phone lines. The laser can be operated remotely and allows for remote
diagnostics. EXLASER software provides complete laser operational
control from the WindowsTM 9x/2000/NT environment. The
software gives complete "on the fly" control of the laser, displays
graphical information on the laser performance, allows controlled burst
mode operation, controls gas handling, calibrates energy output and can
be set for long term automatic operation. A 32 bit DLL (Active X) is
also available for OEM users or those who wish to create custom laser
software or to incorporate the EXLASER software into a larger software
package for the WindowsTM 9x/2000/NT operating environment.
All lasers can be externally triggered by a user supplied trigger
pulse. A sync out pulse provides a timing reference for triggering
EXLASER software requires a PC with a 486 processor or better, 10MB
of hard drive space and 32MB RAM and a CD ROM.
VIDEO, unstable resonator optics focused in air. The lens is moved in
and out of the beam.