Note: Descriptions are shown in the official language in which they were submitted.
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SPECIFICATION
LASER DEVICE
FIELD OF AKT
The present invention relates to a technique which is
effectively applied to the control of oscillation wavelength
and oscillation output in a laser device.
BACKGROUND ;~
..~ :. .
A laser light itself has features such as high
coherent wavelength purity, high output, etc., and is
promising as a light source capable of irradiating an intense -
light. Under these circumstances, there is a narrow band
excimer laser which has been studied f~or use as a light
source in the step of lithography in t;he manufacture of a
semiconductor.
For obtaining a narrow band laser light, there has
been known a laser resonator composed of wavelength selection
elements such as a grating, a prism, a birefringent filter,
etalon, etc.
Furthermore, ~or a laser medium which~has a laser
gain in a wide band such as an excimer laser or a dye laser,
the technic has been known in which one or more etalons are
lnserted into a laser resonator for a narrower band.
The etalon will be briefly described. The etalon is
a wavelength selection element which applies multi-reflection ;
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and interference phenomenon of a light generated between two
reflective films of high flatness held parallel with each
other at predetermined distances.
A laser device using such an etalon as described
above is shown in Fig. 6, in which a multiple narrow band is
realized by a pair of first and second etalons 25a and 25b.
That is, the first etalon 25a has a function for rough
adJustment of the narrower band, and the second etalon 25b `
has a function for fine adjustment thereof. More
partlcular]y, a laser light irradiated from a laser medium 26
is reflected by a rear mirror 27, after which an original j ;
laser oscillation wavelength is roughly formed into a
, narrower band by the first etalon 25a, and said narrower
band is further narrowed, as an output, to the band width as
desired by the second etalon 25b. The light is irradiated
from a laser resonator 29 via a front mirror 28.
The following method has been employed in order to
; stabilize the wavelength of the laser light irradiated from
, the laser resonator 29.
: :.
The light path of a laser light irradiated from the
laser resonator 29 is branched by a beam splitter 30, and the
branched laser light is introduced into a wavelength
measuring portion 33 via an optical fiber cable 32. The
center wavelength is measured by the wavelength measuring
portion 33, and the thus obtained measured signal is released ~`
to a main controller 34. In the main controller 34,
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predetermined arithmetic processing is execu~ed accordin~ to
the measured signal, and actuators 36a and 36b for changing
air pressure, oil pressure or spring pressure are driven by a
predetermined amount through a driving interface 35 to adJust
the etalons 25a and ~5b to an optimum position.
Accordingly, it has been necessary to positively
fine-ad~ust both the etalons 25a and 25b in order to
stabilize the center wavelength of the laser light irradiated
from the laser resonator 29.
Incidentally, in the field requiring superfine
processing such as the manufacture of semiconductors, high- `
degree wavelength stability is required in the continuous
irradiation for a long period of time, and a variation in ;;
center wavelength of light has to be suppressed within a
range as small as possible in the narrow band. `
However, the actuators 36a and 36b relying upon the
air pressure, oil pressure or spring pressure is rough in
minimum operation unit. That is, it :Ls difficult to fine~
adJust an angle of inclination of the etalons 25a and 25b,
thus making it difficult to obtain high-degree stability of ;,
laser wavelength.
The present invention has been achieved in view of
the foregoing. An object of the present invention is to
provide an arrangement wherein adjustment of an angle of
inclination of wavelength selection elements such as etalons
is effected with high accuracy, and a laser output
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wavelength from a laser resonator is always stabili~ed.
Further, it is desired in the laser device that the ;
laser output i5 highly stabilized. However, it is necessary
to positively measure the laser output on the premise of
feedback control for the stabilization of laser output.
Moreover, for the stabilization of laser output, it
is necessary to cutoff noises from a power source portion,
and further necessary to properly control the entire
apparatus.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a
~ :,
laser device which can response to the demands as noted
above. For achieving the aforesaid obJect, the present
invention (a first invention) provides a laser device having
at least first and second wavelength selection elements which
are arranged in series on a light path and in which a laser
light from a laser medium is made into a narrow band by
adJusting an angle of inclination of at least one wavelength
selection element, said laser device comprising an automatic
micrometer head for finelY ad~usting said inclination angle.
According to the aforementioned means, fine
adjustment of an angle of inclination of the wavelength
selection element with respect to the light path can be made
by the use of an automatic micrometer head capable of finely
controlling a movement amount. Therefore, the wavelength of
the laser light outputted from the laser resonator can be
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always stabilized.
The aforementioned automatic micrometer head is an
actuator having a construction in which for example, a ~C --
motor, a pulse motor, etc. is used, and the rotation of such
a motor is converted into linear movement to move the head.
As the wavelength selection element used in the
present invention, there can be used, other than the etalon,
a diffraction grating, a birefringent filter, etc.
Further, a combination of said diffraction grating and said ~- ~
etalon or a combination of the birefringent filter and the ~-
etalon can be also used.
Lasers suitable for the control o~ laser oscillation
output and wavelength according to the present invention
include, other than excimer lasers such as KrF, ArF, etc.,
carbon dioxide gas laser, copper vapor laser, alexandrite
laser, Ti-saphire laser, dye laser, etc.
Next, a second invention wtll be described which is
intended to improve reliability of measurement of detection of
laser oscillation output. An obJect of the present
invention is to provide a laser device which enables accurate
measurement of laser oscillation output without being
affected by electromagnetlc noises from laser medium or the
like, and which enables stabilized laser oscillation.
The second invention provides a laser osclllation
output detection device comprising a light receiving portion
arranged in the neighbourhood of a laser medium, an optical
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~iber having one end connected to said light receiving
portion to transmit a detected light from the laser medium, a
light release portion connected to the other end of the
optical fiber, a photoelectric conversion element arranged
opposedly of said light release portion, and a main
controller which calculates an oscillation output of said
laser light on the basis of a detected signal from the
photoelectric conversion element to generate a control signal
to said laser medium.
Lasers used herein may include not only lasers which
oscillate pulses such as excimer laser such as KrF, ArF,
etc., carbon dioxide gas laser, copper vapor laser, dye
laser, YAG laser, alexandrite laser, etc. but also lasers for
continuous oscillation such as helium~neon laser, argon ion
laser, etc.
The light receiving portion arld the light release
portion connected to the opposite ends of the optical fiber
are provided with optical lenses, respectively, to improve
in-light efficiency and out-light efficiency.
The photoelectric conversion element is, for example,
an element such as a photodiode. An element having a
photoelectric ef-fect which generates an electric signal
corresponding to light quantities received will suffice.
According to the aforementioned means, the detected
light received at the light receiving portion arranged in the
neighbourhood of the laser medium is guided in the state o-f
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light to the optical fiber. Light is emitted from ~he light
release portion provided at a position not affected by the
electromagnetic noise of the laser medium, and said light is
received by the photoelectric conversion elemen*.
As described above, in the present invention, the -
optical flber is used to thereby determine the distance :-
between the laser medium and the photoelectrlc conversion
ele~ent, and a photodiode is arranged close to a drive and
detection portion, whereby the influence of the
electromagnetic noise from the laser medium can be suppressed.
Moreover, electric wiring from the photoelectric conversion
element to the drive and detection portion can be
considerably shortened.
As the result, a level of a noise signal mixed into an
output signal of the photoelectric conversion element can be
lowered to detect a signal not impaired by the noise. It is
possible to positively control the laser device on the basis
of the detected result as Just mentioned.
For the purpose of measuring a laser emission
intensity of high reliability, a third invention provides a
laser oscillation output detection device comprising a light
receiving element for receiving a laser light, an A/D
conversion portion for converting a detected electric signal
sub~ected to photoelectric-conversion by the light receiving
element into a digital signal, and arithmetic means for
analyzing a singnal from the A/D conversion portion to
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' " ' . ' " ' ' " ' . ' ' . ' , ' . ~ , '; ' ' . ' ' ' . " ' ' ' " ' . '
3 ~
calculate a laser oscillation output, characterized in that
an integrating circuit provided at least a multistage
integrator is interposed between said light receiving element
and the A~D converter.
Laser used herein may include not only pulse
oscillation lasers such as excimer laser, carbon dioxide gas
laser, copper vapor laser, dye laser, YAG laser, alexandrite
laser, etc. but also continuous oscillation lasers such as
helium/neon laser, argon ion laser, etc.
The light receiving element is a photoelectric
element, for example, such as a photodiode and will suffice
to be an element which generates an electric signal
corresponding to received light quantities.
As the integrating circuit, an integrator can be
realized by a circuit structure in which, for example, OP
amplifiers are connected in a multi-stage manner.
Preferably, oscillation wavelength of at least scores of ns
can be extended to approximately scores o~ ~ s.
According to the aforementioned means, paying
attention to the fact that the output waveform of the light ~-
recelving element represents the time distribution o~ light
intensity, this value is integrated by time to detect the ~`~
light intensity as light quantities. Therefore, more
accurate detection of the light intensity can be made. ~
A fourth invention has lts ob~ect to provide a laser ;;;;
device which does not diffuse noises externally of a casing
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or toward a power source, and which can considerablY improve ; :
an isolation particularly between a computer and a high ~-
voltage system to prevent an abnormal operation of the
computer.
The fourth invention provides a laser device having
a high voltage generator for supplying a high voltage to a
discharge electrode within a gas laser chamber and a computer
for controlling said high voltage ~enerator, said laser
device comprising the following configuration.
That is, a first shield is provided on a first power
source line for connecting said high voltage generator and a
power source.
A noise filter is interposed halfway of the first
power source line.
A second shield is provided on a second power source
line for connecting a power source 3 and a computer.
A third shield is provided on a high voltage cord
between said high voltage generator and the discharge
electrode.
Moreover, a control llne for connecting said high
voltage generator and the computer is used as an optical
cable to provide a laser device.
As suitable shields as described above, there can be
mentioned metal nettings and flexible convex tubes of high
shieldability, which are preferably grounded.
As the noise filter, an lnsulated transformer or a
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lowpass filter is suitable. Preferably, a shielding or
fllterlng is applied to parts from which noise tends to leak.
The reflective wave from the high voltage generator
is cut by a noise filter and never moves into the power
source. Accordingly, spurious or pulsewise noises are not
entered into the computer or other circuits through the power
source. The shields are provided to prevent the noises
caused by electromagnetic induction from being induced into
the power source llne.
Since the computer uses the optical cable for input
and output of data, isolation from noises is complete, and no -
possible erroneous operation occurs.
A fifth invention has its obJect to prevent an
erroneous operation during the control of a laser gas supply
and exhaust system to reali2e the gas supply and exhaust
control of high reliability.
The fi~th invention provides a laser-gas supply and
,.
exhaust device for supplying and exhausting a laser gas into
a laser chamber, comprising a main pipe connected between a
gas~source and a laser chamber to introduce the laser gas
..::
within said gas source into the chamber, a fluid pressure ~ ~-
: .
driving valve provided on said main pipe and driven by fluid
, ~ :
pressure via a control pipe from a remote position to open
and close the main pipe, an electromagnetic valve device
connected to the end of said control pipe, a pressure
detector connected to the end of a branch pipe from said main ~
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pipe, and a control portion connected by electric wiring to
said electromagnetic valve device and said pressure detector
to electrically control them, the piPing distance of said
control pipe and said branch pipe being determined to have a
sufficient length so that said electric wiring is not
affected by electromagnetic noises generated in the laser
chamber.
This invention is particularly characterized in
that a valve for controlling the opening and closing of
the main pipe is made to constitute a fluid pressure
driving valve, a control pipe for supplying and e~hausting
said driving fluid pressure and an electromagnetic valve
device are provided, and the pressure detector is connected
to the end of the branch pipe.
According to the aforesaid means, the valve for
controlling the opening and closing of the main pipe is of
the type driven by fluid pressure such as air not affected by
the electromagnetic no~se, and the pressure detector is
arranged at a position away from the laser chamber by
arrangement of the branch pipe, whereby all electric wirings
of the control system can be parted from the laser chamber.
Therefore, the accuracy of the detected value by the
pressure detector is secured without being affected by the
electromagnetic noise generated in the laser chamber.
Similarly, the valve for opening and closing the main pipe is
prevented from being erroneously operated.
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The gas supply and exhaust device having the above-
described features can be generally used for the gas laser
device which is not of the seal-off type.
A sixth invention has its object to provide a gas
laser control device having a plurality of control items
different in processing speed, in which a plurality of
control items can be executed side by side by a single
control device.
The sixth invention provides a gas laser control
device comprising at least a high speed processing system
requiring a high speed processing and a low speed processing
system requiring a low speed processing, characterized in
that processing timings are independently determined by a
high speed timer counter for producing a reference clock for
said high speed processing and a low speed timer counter for
producing a reference clock for the low speed processlng.
According to the aforesaid means, a control device ~;~
is built up on the basis of an exclusive-use microprocessor
(CPU), and two or more timer counters for synthesizing -
optional frequencies ~rom a clock signal are freely used to
thereby response to the high speed arithmetic processing as
weIl as the low speed arithmetic processing. To this are
added, for example, parallel input and output, I/O of
digital-analog conversion and analog-digital conversion and
light input and output ports to constitute a system.
Further, a time-division system is incorporated in a software
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and a low speed control processing is incorporated into a
high speed control processing, whereby the side by side
processing of a plurallty of control items can be made. As
the result, for example, the laser oscilla~ion required for
the high speed processing is not stopped, and other low speed
controls such as the exchange of gas can be executed.
In the sixth invention, the control items in the high
speed processing system include at least an output of a
discharge start signal, an output for detection of a laser
output and a control signal for the stabilization thereof,
and an output of detection of a laser wavelength and a
control signal for the stabilization thereof. The control
items in the low speed processing system desirably includes
at least an output of a signal for controlling the opening
and closing of a gas valve in the exchange of gas.
Two or more of first to sixth inventions described
above are selectively combined and can be incorporated into
the laser device.
BRIEF DESCRIPTION OF THE DRAWINGS
Figs. 1 to 5 show one embodiment of the present
invention (a first invention). Fig. 1 is a block diagram
showing the whole structure of a laser device, Fig. 2(a)
shows an etalon holder for explaining adjusting means of
a wavelength selection element as viewed ln a direction
of A of Fig. 2(b), Fig. 2(b) is a side view of the same,
and Fig. 3 is an explanatory view showing the stabilizing
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control of a center wavelength. Fig. 4 is a view showing
one example of an automatic micrometer head. Fig. 5 is a
block diagram of a main control section. Fig. 6 is a block
diagram showing the whole structure of a laser device
according to prior art.
Fig. 7 is a block diagram showing the structure of a
laser oscillation output detection device according to one
embodiment of a second invention. -
Figs. 8 to 10 show one embodiment according to a
third invention. Eig. 8 is a block diagram showing the
structure of a laser oscillation output detection device,
Figs. 9(a) and 9(b) are respectively explanatory views
showing a li~ht receiving element and an output waveform in
an integrating circuit, and Fig. 10 is a circuit view showing
the detailed structure of the integrating circuit.
; Figs. 11 and 12 ~how an embodiment according to a
fourth invention. Fig. 11 is a block diagram of the whole
structure, and Fig. 12 is a block diagram of a computer
section.
Fig. 13 is a block diagram showing a laser gas supply
and exhaust device according to one embodiment of a fifth
invention.
Fig. 14 is a block diagram showing the structure of a
gas laser control device according to one embodiment of a
sixth in~ention.
BEST MODE FOR CARRYING OUT THE INVENTION
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Embodiments of the present invention will be described
hereinbelow with reference to the drawings.
In the present invention (a first invention), a
roughly adJusting etalon 3 and a finely adjusting etalon 4 as
a wavelength selection element are arranged outwardly of one
end of a laser medium 2, as shown in Fig. 1. A rear mirror 5
is arranged on the outermost side of the laser medium so that
a laser light produced by the laser medium 2 is reflected by
the rear mirror 5 and thereafter narrowed into a wavelength
band of approximately ljlO by the roughly adjusting etalon 3
and further narrowed into approximately 1/10 thereof by the
finely adjusting etalon 4. The light then radiated outside
via a front mirror 1.
The thus radiated laser light is branched in light
path by a beam splitter 6 arranged on the light path, and the
light enters a wavelength measuring section 8 from an optical
fiber cable 7, and the oscillation wavelength thereof is
detected. A main control section 10 for receiving the
detected signal performs a predetermined arithmetic
processing to output a control signal to a DC motor driver 11. `:
The DC motor driver 11 finely adJusts the roughly ad~usting ~ :
etalon 3 and the finely adJusting etalon 4 in accordance with
the control signal. Such a fine adjustment as described is
accomplished by driving automatic micrometer heads 14a to
14d.
The aforesaid fine ad~ustment technique will be
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described with re~erence to Fig. 2.
Each pair of the automatic micrometer heads 14a to
14d are arranged on one diagonal line on planes o~ and wi$h
respect to rectangular etalon holders 15 and 16 for holding
the eta]ons 3 and 4, comprising the automatic micrometer
heads 14a and 14d for -finely ad~usting a lateral deviation -
o~ the etalons 3 and 4 and the automatic micrometer heads
14b and 14c ~or finely ad~usting an angle of inclination
with respect to the light path of the etalon. The
automatic micrometer heads 14a to 14d are independently
driven by the DC motor driver 11 according to the control
signal from the main control section 10.
The automatic micrometer heads 14a to 14d will be -
brlefly explained. The automatic micrometer head is
internally provided with a supersmall DC motor DC drive
means and a gear head o~ high resolving power, said gear head
being connected to a lead screw rotated by a motor, and the
rotation of the motor 1s converted into the movement in a
linear direction o~ the lead screw.
For example, as shown in Fig. 4, a casé 20a for the
automatic micrometer head is interiorly provided with a
linear slide head 20b, a lead screw 20c, a gear head 20d of
h~gh resolving power, and a supersmall DC motor 20e, said
supersmall DC motor 20e being controlled by the main control
section 10.
The linear slide head 20b has a rod-like portion 20
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at one end thereof which proJects from ~he case 20a and a
cylindrical portion 20g at the other end thereof which is
internally formed with internal threads 20h. The lead screw
20c is in the form of a rod, which is inserted into a
cylindrical portion 20g of the linear slide head 20b and -
formed in its peripheral surface with external threads 20i
meshed with the external threads 20h.
The gcar head 20d oY high resolving power performs
the torque conversion of the DC motor 20e with a combination
of gears not shown. The main control section 10 controls the
rotational amount and rotational speed of the DC motor 20e.
More specifically, as shown in Fig. 5, the main control
section 10 comprises a target value setting means 21 for
setting a reference ce~ter wavelength of a narrower band
spectrum, a deviation detection means 22 for detecting a
deviation of the measured center wavelength detected by the
wavelength measuring section 8 to the reference center
wavelength set by the target value setting means 21, and
control means 23 for sending a signal for controlling the
rotatlonal amount and rotational speed of the DC motor to
the automatic micrometer head in a direction of negating
the deviation detected by the deviation detection means 22.
As previously mentioned. the automatic micrometer
head is composed of the automatic micrometer heads 14a and
14d for finely ad~usting the lateral deviation and the
automatic micrometer heads 14b and 14c for finely adjusting
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the angle o-~ inclination. The fine adJustment of the angle
of inclination comprises an important element for the
stabilizing control o~ the wavelength. The use of the
a~oresaid automatic micrometer heads enables the highly ~;
accurate fine ad~ustment of the angle of inclination, say,
0.04 mrad/sec.
Next, the concrete stabilizing control of the
wavelength using the present device will be described.
In the stabilizing control of the wavelength
according to the present embodiment, first, the target value
setting means 21 determines a reference center wavelength of
a narrower spectrum as a target. In the case where the
measured center wavelength detected by the wavelength
measuring section 8 is deviated ~rom the aforesaid reference
center wavelength, the deviation detection means 22 detects
the deviation, and it is controlled so that the deviation
is overcome by a control signal (a feedback signal) -from the
control means 23 of the main control section 10.
That is, as shown in Fig. 3, a reference center
wavelength lo as desired of the laser light ls determined ;~
while monitoring the wavelength measuring section 8, and ~ ;
under this condition, the DC motor driver 11 is locked to ~`~
temporarily fix both the etalons 3 and 4.
Next, the laser light irradiated from a laser resonator
9 is measured with the lapse o~ time by the wavelength
measuring section 8. When the measured center wavelength is
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deviated by ~ l from the reference center wave:length, the
main control section 10 outputs a control signal for finely
ad~usting the position on the light path to the etalons 3
and 4 to the DC motor driver 11. That is, out of four
automatic micrometer heads 14a to 14d, the automatic
micrometer head 14d for controlling an angle of inclination
of the finely ad~usting etalon 4 is principally driven to
finely adJust the angle of inclination.
At this time, the DC motor within the automatic
micrometer head 14d is rotated through a predetermined amount -
clockwise or counterclockwise depending on the fact that said
deviation of ~ A is on the short wavelength side
(- direction) or on the long wavelength side (+ direction).
Control parameters in the main control section 10, for
example, such as the rotational direction, driving speed and
driving time of the DC motor are registered in advance in a
predetermined address of a memory area of the main control
section 10.
The stabilizing experiment for the center wavelength
by the aforementloned apparatus was conducted using one
dimensional photodiode array in the procedure in which the -
apparatus is operated for one hour at 80 Hz to measure the
state of variation of the measured center wavelength. As the
result, the wavelength stability whose variation width of the
center wavelength is + 0.57 pm.
An automatic micrometer head with an encoder for
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detecting the rotational amount of the motor may be used.
In this automatic micrometer head, an encoder is arranged
between a spindle and a gear head so as not to count lost
motion (unnecessary movement) or backlash (reverse rotation). ~ `
An example o~ a second invention, which is intended
to improve the reliability of measurement in the detection of
laser oscillation output, will be described below.
In Fig. 7, a laser light 103 emitted from an outlet
102 o~ a laser resonator 101 having a laser medium is partly
branched by a beam splitter 104, and the branched light
enters a light receiving section 105. The laser light 103 is
guided to a light release section 107 at a position of a
predetermined distance ~ via an optical fiber 106 connected
to the light receiving section 105.
Pre~erably, the predetermined distance ~ is
determined by, for example, the outpu1; standard of the laser
medium 2 itself.
A photodiode as a photoelectric conversion element
110 is arranged at a position opposed to the light release ~;
section 107 through an ND ~ilter 108. At the photodiode, an
output voltage is varied according to the light intensity
~rom the light release section 107.
In a drive and detection section 111, a voltage
signal from the photodlode is sub~ecSed to signal processing ~ -
such as A/D conversion and outputted to a control section
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112.
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The control section 112 is composed of a micro-
processor, a memory, etc. so that predetermined arithmetic
processing is carried out according to a measured signal from
the drive and detection section 111 to produce a control
signal for a laser resonator 101. This control signal is
delivered to the laser resonator 101 or a laser control
meehanism not shown through a control line 113 to eontrol the
intensity of the laser light emitted from the laser resonator
101 .
As the method for produeing a eontrol signal, there
ean be mentioned a method which eomprises storing in a memory
ideal control parameters obtained by sampling ln advance to
be paired with the light intensity, and sequentially changing
said eontrol parameters in response to the signal from the
drive and deteetion seetion 111.
In the present embodiment, the distance between the
laser resonator 101 and the photoeleetrie eonversion element
110 ean be sufficiently secured by the optieal fiber 106, and
therefore, the photoelectrie conversion element 110 ean be
arranged in the proximity of the drive and detection section
111. Thus, the in~luence of the electromagnetic noise
generated in the laser resonator 101 can be minimized.
Moreover, an electric wiring 114 from the photoelectric
conversion element 110 to the drive and detection section 111
ean be eonsiderably shortened.
As the result, a level of the noise signal mixed into
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the output signal of the photoelectric conversion element 110
can be lowered to detect a signal not impeded by the noise,
and a precise control signal can be produced in the control
section 112.
According to the present invention, the signal not
impeded by the noise can be detected with the result that a
stabilized laser output can be obtained by the control of
$he laser device.
A third invention will be described hereinbelow.
As shown in Fig. 8, a laser light 203 emitted from an
outlet 202 of a laser resonator 201 having a laser medium is
partly branched by a beam splitter 204, and the branched
light enters a light receiving element 205. A pulse
detection signal sub~ected to photoelectr~c conversion by
the light receiving element 205 is converted into a digital
signal by an A/D conversion section 207 and enters a control
section 208 after the pulse detection signal is sub~ected to
ad~ustment of wavelength by an integrating circuit 206. The
control section 208 is composedr for example, of a CPU
provided with arithmetic means, a register, etc., and an
external memor~ device such as a memory, so that
predetermined arithmetlc processing has been executed on
the basis of a pulse detection signal, after which a control
signal with respect to the laser resonator 201 is produced.
This control signal is outputted to the laser resonator 201
or a laser control mechanism not shown through a control
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line 2]0 to control the intensitY of the laser light emitted
from the laser resonator 201.
The eonerete strueture of the integrating circuit 206
which eonstitutes a feature of the present embodiment will be
deseribed hereinafter.
The integrating cireuit 206 is eomposed principally of
four OP amplifiers 211a, 211b, 211c and 211d as shown in Fig.
10, among which the first OP amplifier 211a has a function as
an amplification stage whose amplification degree is varied
by seleeting a resistance value between (-) input and earth.
A pulse detection signal is integrated by th~ second
to fourth OP amplifiers 211b, 211c and 211d.-
In the second and third OP amplifiers 211b and 211cin Fig. 10, an input terminal is in an imaglnary short state,
and condensers of 150 pF are charged to an input voltage and
initial values are applied to the respective integrators to
e~eet ealeulation.
As the above-deseribed OP amplifiers, those having a
band width of 8.0 MHz and having a responsiveness whose
through rate is about 25 V/~ s can be used.
The integrating eireuit 206 ls eonstituted by the multi-
stage integrator as described above to thereby provlde a
signal shown in Flg. 9(b) obtained by extending
rise/attenuation time of a detection pulse signal of the
order of scores o~ ns as shown in Fig. 9(a) to the order o~
seores of ~ s. Aecordingly, a pulse deteetion signal
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corresponding to the responsive speed to the A/D conversion
section 7 can be obtained to enable accurate detection of
light intensity.
According to the present embodiment, since four OP
amplifiers are used to constitute the integating circuit 206,
the integration of the pulse detection signal can be made
without degrading the temperature characteristics of the
integrating circuit 206 even in use for long periods.
According to the present invention, paying attention
to the fact that the output waveform of the light receiving
element represents the time distribution of light intensity,
this value is integrated with respect to time to detect the
light intensity as light quantities, and therefore, accurate
detection of light intensity can be made.
An embodiment o~ a fourth invention will be described
hereinafter with reference to Figs. 11 and 12.
A gas laser chamber 310 is interiorly provided with a
discharge electrode 311. A gas control device 321 is
connected to the gas laser chamber 310 through a pipe 320,
and a gas cylinder 323 is connected to the gas control device
321 through a pipe 322. Thereby, a mixed gas composed of the
aforementioned components is filled into the gas laser ~;
chamber 310. A high voltage generator 301 is connected to
the discharge electrode 311 through a high voltage cord 312,
and a third shield 313 is provided around the high voltage
cord 312. The voltage o~ the high voltage generator 301 is
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controlled by a computer 302. The high voltage generator
301 is connected to a power source 303 through a first
power source line 304, and a ~irst shield 305 is provided
on the first power source line 304. An insulating
trans~ormer as a noise filter 306 is provided halfway o~
the first power source line 304.
Furthermore, a second shield 308 is provided on
second power source line 7 for connecting the power source
3 and a computer 302.
A control line between the high voltage generator
301 and the computer 302 is comprised of an optical cable
9. An interface between the optical cable 309 and the
computer 302 is as shown in Fig. 2, in which the optical
cable 309 is first inputted into an optical MODEM 302a and
connected to an MPU 302c through an input and output circuit
302b. RAM 302d and ROM 302e are connected to the MPU 302c.
The MPU 302c is shielded by a single Imember.
A valve actuator (not shown) within the gas control
device 321 is also controlled by the computer 302, and a
control line 324 also is comprised of an optical cable. A
shield 326 is applied also to a power source line 325 for
connecting the gas control device 321 and the power
source 303. ; -
The gas laser chamber 310. high voltage generator
301, computer 302, noise filter 306 and gas control device
321 are encased in a casing (K), said casing K and said
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shields being grounded at GND.
With the structure as described above, a noise in a
power source line system and a noise in a radiation system
can be suppressed and prevented. That is, the noise in the
power source line system enters the power source 303 with a
reflective voltage wave generated in the discharge electrode
311 passing through the high voltage generator 301, from
which power source the noise leaks toward various parts but
the reflected component is absorbed by the noise filter 306
and does not reach the power source 303. The noise in the
radiation system does not reach the power source line due to
the provision o-~ the shields.
As describe~ above, the stability and reliability of
operation can be secured.
According to the present invention, the shield is
applied to the power source line to be a noise source and the
noise filter is provided on the high voltage power source
line. Therefore, noises which leak into the external portion
of the casing and into the power source can be considerably
suppressed.
Furthermore, since the high voltage generator and the
computer for controlling the same are connected by the
optical chble, the isolation therebetween is improved, and
the abnormal operation of the computer can be prevented.
A ~ifth invention will be described hereinafter.
- Fi~. 13 is a structural view of a laser gas supply
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and exhaust device according to an embodiment of the present t
invention. In this figure, an examp:Le of a device in
connection with an excimer laser is illustrated for an
explanation.
In Fig. 13, a laser chamber 401 is connected to a gas
source 402 by a main pipe 403, and buffer gas, rare gas and
halogen gas etc. can be supplied into the laser chamber 401.
Valves 404a to 404c driven by ~luid pressure are provided
halfway of the main pipe 403 for supplying the gases so as to
adjust the mixing ratio of the gases. An exhaust pipe 406
connected to a vacuum 405 is branched from the main pipe 403,
and a valve 404d driven by fluid pressure ls provided halfway
of the exhaust pipe 406 The aforesaid valves 404a to 404d
driven by fluid pressure are driven by the pressure of a
fluld such as air to open and close~the main pipe 403 and
the exhaust pipe 406. The valves are designed so that a
linear motion caused by increase or decrease of air pressure
1s converted into a rotational motion o~ the valve by, Eor
example, an actuator or the ~ike.
Control pipes 407a to 407d for supplying air pressure
are connected to the valves 404a to 404d, respectively, said
control pipes 407a to 407d being moved by a predetermined
distance L and connected to an electromagnetic unit 8 for
controlling a supply of air.
A branched pipe 410 is extended in the midst of the
main pipe 403 from the valves 404a to 404d to the laser
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chamber 401. The branched pipe 410 is moved by a
predetermined distance L and connected to a pressure detector
411. The pressure detector 411 can detect the state of
pressure within the main pipe 403, that is, within the laser
chamber 401.
The vacuum pump 405, the electromagnetic valve unit
408 and the pressure detector 411 are connected to the
control section 412 so that their operation is controlled. .
The control section 412 is composed of a microprocessor
provided with, for example, a memory or the like, in which the
electromagnetic unit 408 is controlled on the basis of the
detected value of the pressure detector 411 to adjust the
opening and closing degree of the valves 404a.to 404d so as
to control the state of pressure within the laser chamber 401.
As described above, according to the present .
embodiment, the valve mechanism for opening and closing the
main pipe 403 ls of the fluid pressure drive and the pressure
detector 411 is connected to the branched pipe 410 which is ;
branched and moved by from the main pipe 403 whereby the .
control system for the vacuum pump 405, the electromagnetic
valve unit 408, the pressure detector 411 and the like can be
parted from the laser chamber 401, and all the ele:ctric
wirings can be executed at a position away -from the laser
chamber 401. Therefore, the control of gas supply and `~
exhaust can be made without being affected by the :.
electromagnetic noise generated in the laser chamber 401.
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Preferably, the distance L parted from the e~haust
pipe 406, the control pipes 407a to 407d and the branched
pipe 410 is the distance as short as possible as needed to
such a degree that the vacuum pump 405, the electromagnetic
valve unit 408 and the pressure detector 411 are not affected
by the electromagnetic noise from the laser chamber 401.
That is, when the distance is long, lowering of detection
accuracy, lowering of drive response or the like possibly
occur.
According to the present invention, the lnfluence of
the electromagnetic noise in the gas laser can be reduced to
prevent malfunction of the gas supply and exhaust system.
An embodiment of a sixth invention will be described
hereinbelow w1th reference to a block dia~ram shown in Fig.
14 showing the structure of a gas laser control device.
In Fig. 14, reference numeral 501 designates CPU o~
16 bit system or 32 bit system. A high speed processing
system such as an output wavelength monitor device 509, a
laser high voltage power source 510, etc. and a low speed
processing system such as a gas processing system 511 are
controlled according to the command ~rom the CPU 501. j, ,
An output signal from the CPU 501 is outputted to a
high speed timer counter 502 and a low speed timer counter ~-
503. These timer counters 502 and 503 independently count
clock signals CL from the CPU 501 to produce a predetermined
high speed clock signal and low speed clock signal.
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A wavelength monitor control signal and a voltage
settlng eontrol signal out of outputs o-f the high speed timer
counter 502 are converted into digital optical signals via
D/A eonverters 504 and 505 and photoelectric converters 507a
and 507b, and the digital optieal signals are again eonverted
into digital electric signals v~a optical fiber cables 508a
and 608b and photoeleetrie eonverters 507a and 507b to
eontrol the output wavelength monitor deviee 509 and the
laser output high voltage power souree 510. The eontrol
timing therefor is given by a timing trigger signal whieh is
produeed by a parallel TTL output deviee 508a on the basis of
a high speed eloek signal from the high speed timer eounter
502 and passing through the photoeleetric eonverter 507e, the
optieal fiber eable 508e and the photoelectric converter 507c
in named order.
On the other hand, an output from the low speed timer
counter 503 is converted into a digital optical signal via a
parallel TTL output deviee 506b and a photoeleetric converter
507d and is again converted into a digital electric signal
via an optieal fiber eable 508d and a photoelectric converter
507d and thenee delivered to a gas proeessing system 511
ineluding a laser ehamber. The gas proeessing system 511
executes the gas replaeing wor~ or the like with a gas valve
opening and elosing signal or a vaeuum pump ON/OFF signal.
As described above, in the present embodiment, a time
reference of monitor eontrol of an output waveform and
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laser output control requiring high speed arithmetic
processing is produced by the high speed processing timer
counter 502, whereas a time re~erence of gas replacing
control or the like requiring low speed arithmetic processing
is produced by the low speed processing timer counter 503.
As described above, two kinds of time references whlch are
greatly different from each other are independently counted by
the individual timer counters to enable realization of a
plurality of parallel controls without stopping any of
controls. -
Moreover, according to the present embodiment, there
is an effect in that the control slgnal is made to pass
through the optical fiber cables 508a to 508d whereby the
influence of the electromagnetic noises generated *rom the
laser chamber or other driving systems can be reduced to
prevent malfunction of the control system.
According to the present invention, the control on
the basis of a plurality of time references can be made by a
single control device.
INDUSTRIAL APPLICABILITY
According to the present invention, the fine
ad~ustment of the wavelength selection element can be made
with high accuracy, and as a result, the output waveform in
the laser resonator can be greatly stabilized.
Accordingly, the present invention can be effectively
utilized for uses such as a light source in a lithography
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step ln the manufacture of a semiconductor.
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