Laser device

Details Laser device Laser device

2000-07-20

2004-05-04

Tran, Minh-Loan (Department: 2826)

Coherent light generators

Particular resonant cavity

Specified cavity component

C372S100000, C372S102000, C372S103000

Reexamination Certificate

active

06731666

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a laser device, and particularly relates to a laser device having an optical element for shaping a beam form of laser light into a desired form.
BACKGROUND ART
Conventionally, in a narrow band excimer laser device and fluorine laser device, a slit for shaping a sectional form of laser light into a predetermined form is known, and it is disclosed, for example, in Japanese Patent No. 2531788.
FIG. 13
shows a configuration of an excimer laser device according to the prior art. It should be noted that
FIG. 13
is made by being reversed horizontally relative to the drawing made in the aforementioned Patent. In
FIG. 13
, the excimer laser device
1
is seen from above, and in the explanation hereinafter, an up and down direction of the paper surface of
FIG. 13
is called a lateral direction, and a direction vertical to the paper surface is called a vertical direction.
In
FIG. 13
, an excimer laser device
1
includes a laser chamber
2
containing laser gas being a laser medium at a predetermined pressure ratio, and inside the laser chamber
2
, discharge electrodes
5
and
5
are placed to oppose to each other in the aforementioned vertical direction. High voltage is applied across the aforementioned discharge electrodes
5
and
5
from a high voltage power supply not illustrated to initiate discharge, and thereby the laser medium is excited in a discharge area
18
to oscillate laser light
11
.
The laser light
11
excited in the laser chamber
2
is outputted from a rear window
9
toward the rear (the left side in FIG.
13
), and its bandwidth is narrowed by a grating
23
so that a spectrum width of the laser light
11
become narrow. The laser light
11
with its bandwidth being narrowed enters the laser chamber
2
again from the rear window
9
, and it outputted from the excimer laser device
1
through a front window
7
and a front mirror
38
to become a light source for processing of a processing unit such as a stepper or the like not illustrated.
In this situation, partial reflection coating for partially reflecting part of the laser light
11
at a predetermined ratio and transmitting and outputting the rest of the laser light
11
is applied on an entire surface of the front mirror
38
to the side of the laser chamber
2
, and defines a partial reflecting element
26
. The laser light
11
which is partially reflected by the front mirror
38
returns to the inside of the laser chamber
2
, and is amplified again by discharge in the discharge area
18
.
In front of and behind the laser chamber
2
, placed are a front slit
16
and a rear slit
17
(described as “aperture” in the aforementioned Japanese Patent No. 2531788) having a rectangular front opening
16
A and rear opening
17
A respectively. In the above prior art, the front slit
16
and the rear slit
17
correspond to optical elements for shaping the beam form of the laser light
11
into a desired form.
In the excimer laser device
1
, part of the laser light
11
is cut by the aforementioned slits
16
and
17
, and the sectional form of the laser light
11
is shaped into the form of the openings
16
A and
17
A so that the sectional form of the laser light
11
corresponds to a form required by a processing unit. Hereinafter, the sectional form of the laser light
11
is called a beam form.
The rear slit
17
shapes the beam form of the laser light
11
traveling rearward, thereby preventing disturbance of the wave surface caused by the laser light
11
hitting an end portion of the grating
23
.
However, the aforementioned prior art has the disadvantage described below.
FIG. 14
shows a view taken along the
14
—
14
line in FIG.
13
. It should be noted that the aforementioned lateral direction is represented as the left and right direction in FIG.
14
. The illustration of the front window
7
is omitted.
FIG. 15
shows a detailed configuration of the area near the front and the rear windows
7
and
9
of the excimer laser device
1
.
As shown in
FIG. 14
, both the front opening
16
A and the rear opening
17
A according to the prior art are narrower than the discharge area
18
in which the laser medium is excited. As a result, even if the shape of the discharge area
18
is varied as a result of consumption of the discharge electrodes
5
and
5
, the laser light
11
passing through the openings
16
A and
17
A can obtain a stable beam form.
However, as a result that the openings
16
A and
17
A are made narrower than the discharge area
18
, as shown in
FIG. 15
, surplus laser light
11
A, which is oscillated at the outer peripheral side of the discharge area
18
than the openings
16
A and
17
A, is cut by the slits
16
and
17
. Thus, out of the discharge energy inputted into the discharge area
18
, a part of it becomes a loss such as heat or the like and is not taken out as the laser light
11
, which causes the disadvantage of reducing the efficiency of the excimer laser device
1
.
Further, as shown in
FIG. 15
, the surplus laser light
11
A is outputted to areas close to the openings
16
A and
17
A of the slits
16
and
17
. Thus, the temperature in the areas close to the openings
16
A and
17
A of the slits
16
and
17
rise and thereby refractive index of the gas inside the openings
16
A and
17
A is varied, thus causing the disadvantage of the wave surface of the laser light
11
being disturbed. Furthermore, heat occurs in the areas close to the openings
16
A and
17
A of the slits
16
and
17
causes the slits
16
and
17
to have heat, which causes the disadvantage that impurities occurring there stain and damage the other optical components.
Further, in the rear slit
17
, as shown in
FIG. 15
, the rear opening
17
A is made smaller than the front opening
16
A. Thereby, a part
11
C of the laser light
11
, which is partially reflected by the front mirror
38
, passes through the front opening
16
A, and returns to the discharge area
18
, cannot pass through the rear opening
17
A and is cut, thus further increasing the loss.
SUMMARY OF THE INVENTION
The present invention is made to eliminate the disadvantages of the above art, and its object is to provide a laser device capable of efficiently oscillating laser light and always obtaining a stable beam form.
In order to attain the above object, a first configuration of a laser device according to the present invention is in a laser device including an amplifying section in which a laser medium is amplified to oscillate laser light, and an optical element for separating part of the laser light oscillated in the amplifying section, and shaping a beam form of the laser light into a desired form to output the same,
the configuration in which the optical element has at least either one of a partial reflecting portion for partially reflecting the laser light or a non-reflective portion for transmitting the laser light at high transmissivity, each of which is provided on approximately a center portion, and a total reflecting portion which is provided outside a perimeter of said partial reflecting portion or said non-reflective portion, and which reflects the laser light at high reflectivity.
According to the above configuration, by allowing the laser light to pass through the partial reflecting portion or the non-reflective portion of the optical element, the beam form of the laser light to be outputted is shaped into the shape of the partial reflecting portion or the non-reflective portion. Recycle laser light separated by the optical element is reflected at the total reflecting portion with high reflectivity and returns to the amplifying section, where it contributes to laser oscillation. Accordingly, energy of the separated laser light is not lost, thus improving the energy efficiency of the laser device relative to the energy inputted for excitation.
A second configuration of the laser device according to the present invention is in a laser device including an amplifying section in which a laser medium is amplified to oscillate laser light,
the configuration inc

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