Coherent light generators – Particular beam control device – Tuning
Reexamination Certificate
2001-03-29
2004-11-02
Wong, Don (Department: 2828)
Coherent light generators
Particular beam control device
Tuning
C372S032000, C372S099000, C372S102000, C372S107000
Reexamination Certificate
active
06813287
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a wavelength control device for controlling a center wavelength by band narrowing of a laser light.
BACKGROUND ART
A band narrowing art for narrowing a band of a laser light oscillated from an excimer laser device and the like and controlling its center wavelength to be a desired value is conventionally known, and it is shown, for example, in Japanese Patent Application Laid-open No. 5-283785.
FIG. 10
shows a configuration of a laser device disclosed in Japanese Patent Application Laid-open No. 5-283785, and the prior art will be explained hereinafter based on FIG.
10
.
In
FIG. 10
, an excimer laser device
11
includes a laser chamber
12
for containing a laser gas being a laser medium, with windows
17
and
19
for transmitting a laser light
21
being attached at both end portions thereof. Inside the laser chamber
12
, high voltage is applied between discharge electrodes not shown to excite the laser gas by electric discharge and to thereby generate the laser light
21
.
The generated laser light
21
enters a band narrowing unit
30
, expanded by a prism
32
, reflected by a wavelength selection mirror
34
, and is incident on a grating
33
being a band narrowing optical component. At the grating
33
, only the laser light
21
having a wavelength close to a predetermined center wavelength &lgr;c is reflected by diffraction. This is called band narrowing.
In this situation, the wavelength selection mirror
34
is mounted on a movable holder
36
the angle of which with respect to the laser light
21
is changeable by a pulse motor
40
. Changing the orientation of the wavelength selection mirror
34
changes an incident angle of the laser light
21
with respect to the grating
33
, which changes the center wavelength &lgr;c of the laser light
21
diffracted by the grating
33
. Specifically, by changing the orientation of the wavelength selection mirror
34
, the center wavelength &lgr;c of the laser light
21
oscillated can be controlled to be a desired target wavelength &lgr;
0
.
Further, the excimer laser device
11
takes out part of the laser light
21
by means of a beam splitter
22
, and monitors the center wavelength &lgr;c of the laser light
21
by means of a wavelength monitor
37
. A laser controller
13
outputs a command signal to the pulse motor
40
based on the monitored center wavelength &lgr;c to rotate the wavelength selection mirror
34
, thereby controlling the center wavelength &lgr;c of the laser light
21
to be the desired target wavelength &lgr;
0
.
The laser light
21
the band of which is narrowed inside the band narrowing unit
30
is amplified inside the laser chamber
12
while reciprocating several times between the band narrowing unit
30
and the front mirror
16
for partly reflecting the laser light
21
. Subsequently, it is radiated toward the front (leftward in
FIG. 10
) as the laser light
21
having the center wavelength &lgr;c.
However, the aforementioned prior art has the following disadvantages.
Specifically, when the excimer laser device
11
is used as a light source for exposure of a processing machine such as a stepper, it is sometimes necessary to suspend the discharge and stop laser oscillation for a fixed period of time for replacement of a wafer and reticle. In such a case, a property of an optical component itself such as the prism
32
changes, or fixture components (not shown) for fixing the optical components is extended or contracted due to reduction in temperature around the optical components, thus causing the center wavelength &lgr;c to deviate. Further, after the discharge is stopped for a while, a drift of the center wavelength &lgr;c occurs due to a change in a state of the discharge electrodes and the laser gas. This drift is called chirping. Furthermore, the processing machine (not shown) sometimes sends a command to change the target wavelength &lgr;
0
in response to a change in the temperature, atmospheric pressure and the like of the surrounding atmosphere.
When the center wavelength &lgr;c has to be changed as described above, the laser controller
13
outputs a command signal to the pulse motor
40
and thereby changes the angle of the wavelength selection mirror
34
to change the center wavelength &lgr;c. However, response time of the pulse motor
40
is generally long, and it takes about a few and a few tens of m sec to reach a desired stroke length of the pulse motor
40
after receiving a command signal. Thus, by the time the center wavelength &lgr;c reaches the target wavelength &lgr;
0
after the laser controller
13
issues a command, a few pulses or a few tens of pulses of the laser light
21
are radiated if the laser light
21
is oscillated at a high pulse frequency of, for example, a few kHz.
As the result, the laser light
21
with the center wavelength &lgr;c unsuitable for exposure is incident on the processing machine, and defective exposure occurs. In order to avoid the above, the laser light
21
has to be blocked by, for example, a shutter or the like, but due to the time required to open and close the shutter, waiting time until the processing starts becomes longer, thus causing the disadvantage of reducing the availability of the processing machine.
SUMMARY OF THE INVENTION
The present invention is made to eliminate the disadvantages of the above art, and its object is to provide a wavelength control device for a laser device capable of controlling a center wavelength of a laser light to be a target wavelength in a short time.
In order to attain the above-described object, the wavelength control device for a laser device according to the present invention is a wavelength control device for a laser device including a movable holder for making an optical component movable with respect to a laser optical axis, and a laser controller for moving the optical component with respect to the laser optical axis and changing an incident angle of laser light on a band narrowing optical component to thereby control a center wavelength of the laser light to be a target wavelength, and is characterized in that
the movable holder comprises a first drive mechanism moving by a very short distance and a second drive mechanism moving by longer distance than the first drive mechanism.
According to the above configuration, when the center wavelength is finely controlled, the movable holder is driven by the first drive mechanism capable of moving by a very small distance, and when the center wavelength is moved to a large extent, it is driven by the second drive mechanism. Consequently, a wavelength control with high precision over a wide range is made possible.
Further, in the wavelength control device for the laser device,
the first drive mechanism may comprise a piezoelectric element unit, and
the second drive mechanism may comprise a pulse motor unit.
According to the above configuration, the piezoelectric element unit quick in response and the pulse motor unit with a long stroke are included. When the center wavelength has to be controlled in a short time, it is controlled with the piezoelectric element unit, and when it has to be controlled to a large extent, it is controlled with the pulse motor unit, thus making it possible to control the wavelength quickly over a wide range.
Further, in the wavelength control device for the laser device,
on moving the optical component, the laser controller may move the optical component by means of the piezoelectric element unit, and
thereafter, may move the optical component by means of the pulse motor unit.
According to the above configuration, since the optical component is initially moved by the piezoelectric element unit quick in response, the center wavelength quickly reaches the target wavelength. Thereafter, the control is performed by means of the pulse motor unit with a long stroke, and therefore the center wavelength can be changed to a large extent when the target wavelength is changed, thus facilitating response.
Further, in the wavelength control device for the laser device,
the laser c
Bushida Satoru
Nakane Motoharu
Tanaka Hiroshi
Gigaphoton Inc.
Menefee James
Westerman Hattori Daniels & Adrian LLP
Wong Don
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