JP2001077453A - Super narrow band width laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a super narrow band width laser device which can narrow the band of the laser beam from a fluorine laser or a laser, having a wavelength shorter than the fluorine laser has by using a diffraction grating as a band- narrowing element. SOLUTION: A laser resonator is constituted of a total reflection mirror 10 and a mirror 11. A diffraction grating 13 is set up at an incident angle of 80 deg. or larger so that the grating 13 functions an oblique-incident diffraction grating. In the grating 13, undo diffraction and reflection are produced, and the diffracted laser beam returns to the grating 13, after being reflected by the mirror 11. The reflected laser beam L10, however, is made incident to a prism 14. Since the grating 13 is of the oblique-incidence type, although the grating 13 and mirror 11 function as an output mirror, having high transmittance though the diffraction efficiency of the grating 13 being as low as 10-20%, because the grating 13 is applied on a fluorine (F2) laser or argon dimer (F2) laser.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a narrow-band laser device having a laser chamber for oscillating laser light, narrowing a band of laser light from the laser chamber, and supplying the narrow band to an exposure apparatus as an exposure light source. Ultra narrow band laser device for ultra narrow band.

[0002]

2. Description of the Related Art There are various types of performance required for an exposure apparatus for lithography, such as resolution, alignment accuracy, processing capability, and apparatus reliability. Among them, the resolution R directly leading to the miniaturization of the pattern is R = k · λ /
NA (k: constant, λ: exposure wavelength, NA: numerical aperture of the projection lens). Therefore, in order to obtain good resolution, the shorter the exposure wavelength λ, the more advantageous.

Therefore, in a conventional exposure apparatus, the i-line (wavelength: 365 nm) of a mercury lamp and the wavelength of 248 nm
Krypton fluorine (KrF) excimer laser is used as a light source for an exposure machine. These are called an i-line exposure machine and a KrF exposure machine, respectively. As the projection optical system used in the i-line exposure machine and the KrF exposure machine, a reduction projection lens combining a large number of lenses made of quartz glass is used. Widely used.

As a next-generation exposure apparatus for performing fine processing, argon fluorine (ArF) having a wavelength of 193 nm is used.
An exposure machine using an excimer laser as an exposure light source has begun to be used, and is called an ArF exposure machine. In the ArF exposure apparatus, the ArF exposure device narrows the wavelength band to about 0.6 pm.
An F excimer laser is used, and an achromatic lens made of two kinds of materials is used in the reduction projection optical system.

Here, the configuration of a conventional laser device such as an ArF excimer laser device is shown in FIGS. 9 and 10. FIG.

FIG. 9 is a configuration diagram showing the configuration of a conventional narrow-band laser device.

In this narrow band laser device, a laser resonator is constituted by the output mirror 1 and the diffraction grating 2, and a laser chamber 3 and a prism beam expander 4 are arranged in the laser resonator.

In such a narrow band laser device, the laser beam emitted from the laser chamber 3 passes through the prism beam expander 4, so that the laser beam whose beam width has been expanded impinges on the diffraction grating 2.

The laser light from the diffraction grating 2 disposed in the Littrow arrangement passes through the prism beam expander 4 and the laser chamber 3 and is incident on the output mirror 1, so that the laser light is output between the output mirror 1 and the diffraction grating 2. The laser light resonates to narrow the band. Then, the output mirror 1 outputs the laser light L1 having a narrow band.

FIG. 10 is a configuration diagram showing the configuration of a conventional oscillation amplifier laser device.

In this oscillation amplifier laser device, a total-reflection mirror 5 and an output mirror 6 constitute a laser resonator in an oscillation stage, and a laser chamber 7 and an etalon 8 are arranged in the laser resonator.

In the oscillation stage, the wavelength of the laser light emitted from the laser chamber 7 is selected by passing through the etalon 8, and the laser light of the selected wavelength is reflected on the total reflection mirror 5, and When the laser beam passes through the laser chamber 7 and enters the output mirror 6, the laser light resonates between the output mirror 6 and the total reflection mirror 5 to narrow the band.

In the amplifying stage, the narrowed laser light L2a output from the output mirror 5 is applied to the mirror 9a.
The laser beam L2b is amplified by being reflected by the mirror 9b and passing through the laser chamber 7, and output as an amplified laser beam L2b.

Incidentally, as in the laser device shown in FIG.
Another example of a laser device having both an oscillation stage and an amplification stage in one laser chamber is disclosed in Japanese Patent No. 2673.
There is a laser device described in the '510 patent.

As a next-generation lithography exposure apparatus of the above-mentioned ArF exposure apparatus, the light source has a wavelength of about 15 nm.
A fluorine exposure machine using a 7 nm fluorine laser is being studied.

In this fluorine laser, there are two oscillation lines (also called oscillation lines) having different wavelengths and light intensities.
The wavelengths are 157.5233 nm and 157.629, respectively.
9 nm, and the wavelength width of each oscillation line is 1-2 pm
It is said to be about.

To use the fluorine laser for exposure,
In general, it is advantageous to select and use only one line of a wavelength (157.6299 nm) having a high intensity (hereinafter, referred to as one line). ~ 2 are used.

The two lines of the fluorine laser are described in, for example, "CAN.J.PHYS.VOL.63,
1985, pp. 217-218 ".

For one line of the fluorine laser, for example, “SPIE, 24th International
onal Symposium on Microlio
thography, February. 1999. The experimental results are reported in

[0020]

However, in the case of a fluorine exposure apparatus, it becomes difficult to apply a refraction-type reduction projection optical system using only a lens, which has been generally used in conventional exposure apparatuses (that is, up to an ArF exposure apparatus).

The reason is that at a wavelength of 157 nm, the transmittance of quartz glass becomes extremely low, and only a very limited material such as calcium fluoride can be used.

Therefore, when a reduction projection lens is formed by using a monochromatic lens made of only calcium fluoride,
It is said that narrowing the band is insufficient even if the fluorine laser is made into one line, and it is necessary to narrow the band to one-tenth of the wavelength width (about 0.2 pm) for one line. ing.

As described above, since it was difficult to narrow the band to 0.2 pm or less for one line of the fluorine laser,
As a reduction projection optical system, it is necessary to apply a catadioptric reduction projection optical system (also called a catadioptric type), which is said to be usable in a wavelength width that is 10 times wider than a total refractive optical system using only a lens. It is considered.

Conventionally, in a fluorine laser, in order to further narrow a band of laser light which has been made into one line, the use of an etalon or a diffraction grating which can be narrower than a prism is as follows. It was difficult for a reason.

First, when an etalon is used, it is necessary to form a partial reflection film.
At a wavelength of m, it was difficult to form a partially reflective film having high light resistance.

That is, in the vacuum ultraviolet region having a wavelength of 157 nm, since the optical absorptivity of many optical materials is high, the partial reflection film is likely to be damaged due to a rise in temperature due to the absorption of laser light in these optical materials.

In the case of a fluorine laser, the pulse width is 5 to 5.
10 ns, which is as short as about half that of an excimer laser, so that the peak power of the pulsed laser light is high. Therefore, damage is likely to occur in the dielectric multilayer film constituting the partial reflection film.

On the other hand, in a general narrow-band laser device using a Littrow diffraction grating, in order to make the beam width of the laser beam impinging on the diffraction grating as wide as possible, FIG.
As in the conventional narrow-band laser device shown in (1), it is widely practiced to widen the beam width of laser light by using a prism expander 4.

This is because, in the diffraction grating 2, the effect of narrowing the band increases in proportion to the total number of groove lines irradiated with laser light.

However, when the prism beam expander 4, which is widely used to widen the beam width of the laser beam, is used, particularly when the band width of the fluorine laser is narrowed, the following two problems occur.

First, the first problem is that the wavelength of the laser light whose band is narrowed fluctuates.

That is, when the wavelength is short as in the case of a fluorine laser, heat absorption occurs inside the prism of the prism beam expander 4 because the absorptance of laser light in the optical material increases. As a result, since the refractive index in the prism changes, the optical axis of the laser light may be slightly shifted, which may be a factor for changing the wavelength of the laser light to be narrowed.

The second problem is that the coating film applied to the prism is easily damaged.

That is, in each prism in the prism beam expander 4, the side where the beam width is widened, that is, the surface 4
It is necessary to apply an anti-reflection coating to a and 4b.

The reason for this is that, particularly, on the side (surfaces 4a and 4b) of each of the prisms where the beam width is widened, the laser beam enters or exits at a substantially perpendicular incident angle or exit angle. For this reason, in order to suppress Fresnel reflection having a reflectivity of 4 to 5%, an anti-reflection coating is applied.

However, in the case of a fluorine laser, the coating film is liable to be damaged due to a rise in temperature due to the absorption of the laser beam by the prism. Therefore, it is not possible to use a prism beam expander to widen the beam width of the laser beam. Not preferred.

Conventionally, as described above, a diffraction grating is used as an oblique incidence type diffraction grating without using an optical element such as an etalon or a prism as a band narrowing element (optical element). A configuration for banding has also been proposed.

Regarding the oblique incidence type diffraction grating, for example, “Journal of Applied Physi
cs, Vol. 48, no. 11, November,
1977, pp. 4495-4497 ".

Conventionally, the problem with the use of the grazing incidence type diffraction grating is that the efficiency is lower than that of a normal Littrow type. That is, the efficiency with which the diffracted light of the laser beam incident on the diffraction grating strikes the mirror and is returned to the diffraction grating is 1
It is as low as 0 to 20%, and almost all is radiated from the laser resonator to the outside. Therefore, it is said that since the reflectance as an output mirror is low, no feedback is applied and laser oscillation is difficult.

Further, in a system in which one laser chamber has both an oscillation stage and an amplification stage as in the oscillation amplifier laser device shown in FIG. 10, although it is possible to narrow the band of the fluorine laser, the following method is used. Such a problem occurs.

That is, as shown in FIG. 10, a normal mirror is used as the output mirror 6 of the oscillation stage.
Immediately before laser oscillation, of the weak light having a wide spectral width (spontaneous emission light) generated in the amplification stage, the light traveling in the opposite direction to the extracted laser beam L2b strikes the output mirror 6 of the oscillation stage and is reflected there. And returned to the amplification stage.

That is, of the spontaneous emission light generated in the amplification stage, the spontaneous emission light traveling to the oscillation stage side is reflected by the mirror 9b and the mirror 9a and reflected by the output mirror 6, and then further reflected by the mirror 9a and the mirror 9b And returns to the laser chamber 7.

For this reason, the spontaneous emission light returned to the laser chamber 7 is strengthened and the ASE (Amplified Spontaneous
Light with a wide spectrum width called emission is strongly generated. As a result, there is a problem that the wavelength width of the laser light (the laser light L2b in FIG. 10) extracted from the amplification stage is widened.

As described above, in a system in which one laser chamber has both an oscillation stage and an amplification stage as in the oscillation amplifier laser device shown in FIG. 10, the ASE is generated from the amplifier because the laser operation timings are equal. It was easy.

In the case of a laser device in which the oscillator and the amplifier are independent from each other, generally, the laser operation in the amplifier is slightly delayed so that the laser light from the oscillator is incident on the amplifier and then the amplifier is excited. Thus, it was possible to suppress the occurrence of the ASE.

Accordingly, an object of the present invention is to use a diffraction grating instead of an etalon or a prism as an optical element such as a fluorine laser, Another object of the present invention is to provide an ultra-narrow band laser device capable of narrowing a band of a laser beam having a short wavelength.

Another object of the present invention is to provide a laser beam having a narrow band which does not include ASE (light having a wide spectral width) even in a system having both an oscillation stage and an amplification stage in one laser chamber. It is an object of the present invention to provide an ultra-narrow band laser device capable of generating a laser beam.

[0048]

In order to achieve the above object, a first aspect of the present invention is to provide a laser chamber which oscillates a laser beam of a fluorine laser or a laser having a shorter wavelength than this laser. An ultra-narrow band laser device which narrows a band of a laser beam from a chamber and supplies it to an exposure apparatus as an exposure light source, wherein a total reflection means for totally reflecting incident light, and a laser oscillated by the laser chamber An oblique incidence type diffraction grating that disperses the wavelength of light, and an optical element that totally reflects the diffracted light diffracted by the oblique incidence type diffraction grating, wherein the total reflection means, the oblique incidence type diffraction grating and the optical element, Wherein the laser chamber is disposed between the optical element and the total reflection means and the optical element.

According to a second aspect of the present invention, in the first aspect, the oblique incidence type diffraction grating has a heat radiation plate disposed on a surface opposite to a surface having a groove formed in the diffraction grating. It is characterized by the following.

In a third aspect based on the first aspect, the optical element is a mirror or a diffraction grating.

The first to third inventions will be described with reference to FIG.

As shown in FIG. 2, in the ultra-narrow band laser device 200, a laser resonator is constituted by the total reflection mirror 10 and the mirror 11, and a laser chamber 12 is arranged between the laser resonators. ing.

The diffraction grating 13 is arranged so as to bend the optical axis of the laser light emitted from the laser chamber 12.

The diffraction grating 13 is arranged so that the incident angle is about 80 degrees or more so as to function as an oblique incidence diffraction grating. The diffraction grating 13 performs diffraction and reflection, and the diffracted laser light is reflected by the mirror 11 and returns to the diffraction grating 13, while the reflected laser light is incident on the prism 14.

The reason for making the diffraction grating 13 function as an oblique incidence diffraction grating and totally reflecting the diffracted light by the mirror 11 is that the laser light from the laser chamber 12 is supplied to a plurality of grooves formed in the diffraction grating 13. This is because the light is emitted to the plurality of groove lines and the reflected light (emitted light) from the mirror 11 is also applied to the plurality of groove lines. As a result, the band can be further narrowed.

The diffraction grating 13 and the mirror 11 function as an output mirror, and the laser beam whose band is actually narrowed is output from the diffraction grating 13.

Since the diffraction grating 13 from which the laser beam L10 is extracted is of the oblique incidence type, the diffraction efficiency is 10-2.
Although it is as low as 0%, since it is applied to a fluorine (F2) laser or an argon dimer (Ar2) laser,
The diffraction grating 13 and the mirror 11 function as an output mirror having a high transmittance.

The heat radiating plate 15 is provided on the back surface of the diffraction grating 13, that is, on the surface opposite to the surface on which the groove lines are formed, and is used to suppress a temperature rise.

As described above, according to the first to third aspects of the present invention, an oblique incidence type diffraction grating is used as the band narrowing element without using an optical element such as an etalon or a prism. Alternatively, the laser light of a laser having a shorter wavelength than this laser can be narrowed.

Further, since optical elements such as etalons and prisms are not used in the laser resonator, there is no heat generation due to absorption of laser light by these optical elements, and there is no change in wavelength due to this thermal change. As a result, the center wavelength of the narrowed laser beam can be stabilized.

Further, since the temperature rise of the grazing incidence type diffraction grating can be suppressed by the heat radiating plate, the wavelength fluctuation due to the thermal expansion of the grazing incidence type diffraction grating itself, that is, the change of the wavelength width and the change of the center wavelength are reduced. Accordingly, the wavelength of the laser light having a narrow band can be stabilized.

According to a fourth aspect, in the first aspect, an output mirror for emitting laser light from the laser chamber, a convex mirror for reflecting laser light oscillated by the laser chamber, and A concave mirror for reflecting the laser light, and a diffraction grating disposed in Littrow corresponding to the concave mirror and dispersing the wavelength of the laser light from the concave mirror, between the convex mirror, the concave mirror and the diffraction grating and the output mirror. Wherein the laser chamber is disposed in the laser cavity, and the diffraction grating and the output mirror constitute a laser resonator.

The fourth invention will be described with reference to FIG.

As shown in FIG. 7, in this embodiment, the diffraction grating 72, the convex mirror 74 and the concave mirror 75 function as a total reflection mirror. Further, the convex mirror 74 and the concave mirror 7
Laser chamber 1 using only five reflective optical elements
2, the beam width of the laser beam emitted from the laser beam 2 is increased.

For this reason, in the diffraction grating 72, the laser beam (parallel light) from the concave mirror 75 is applied to a wide area, that is, to many groove lines, so that the band can be further narrowed.

In the above laser resonator, an optical element such as a prism is not used for expanding the laser beam, so that heat is not generated by absorption of the laser light by this optical element, so that a narrow band is used. The fluctuation of the wavelength of the laser light to be converted can be suppressed.

As described above, according to the fourth aspect, even when the diffraction grating is used as the total reflection mirror, the prism optical element is used in the laser resonator as in the related art. Without using the reflective optical elements of the convex mirror and the concave mirror, the beam width of the laser light emitted from the laser chamber can be expanded.

Therefore, the fluctuation of the narrowed wavelength due to heat generation due to the absorption of the laser light by the prism does not occur, and the center wavelength of the narrowed laser light can be stabilized.

A fifth aspect of the present invention includes an oscillation stage and an amplification stage including one laser chamber, and the oscillation stage narrows a laser beam of a fluorine laser or a laser having a shorter wavelength than this laser. Ultra-band narrowing laser for outputting the band-passed laser beam, and amplifying and outputting the laser beam narrowed by the oscillation stage, and supplying the amplified laser beam to an exposure apparatus as an exposure light source. The apparatus is characterized in that a grazing incidence type diffraction grating for dispersing the wavelength of laser light oscillated by the laser chamber is arranged on the output side of the oscillation stage.

According to a sixth aspect, in the fifth aspect, a total reflection means for totally reflecting incident light and an optical element for totally reflecting the diffracted light diffracted by the oblique incidence type diffraction grating are further provided. Wherein the laser chamber is disposed between the total reflection means and the oblique incidence type diffraction grating and the optical element, and the total reflection means and the optical element constitute a laser resonator. And

The fifth and sixth inventions will be described with reference to FIG.

As shown in FIG. 4, the ultra-narrow band laser device 400 has an oscillation stage and an amplification stage in one laser chamber 43. The laser resonator of the oscillation stage is composed of a total reflection mirror 41 and a mirror 44, and a diffraction grating 42 is arranged between the laser resonators.

The oscillation stage comprises a total reflection mirror 41, a laser chamber 43, a diffraction grating 42 and a mirror 44, and the amplification stage comprises a mirror 45 and a laser chamber 43.

The diffraction grating 42 is a grazing incidence type diffraction grating, and is arranged so that the laser beam is incident at an incident angle of about 80 degrees or more.

Since the diffracted light from the diffraction grating 42 is totally reflected by the mirror 44, in the diffraction grating 42, as in the case of the diffraction grating 13, many groove lines are irradiated with laser light.

The diffraction grating 42 and the mirror 44 have a function as an output mirror, and the laser beam whose band is actually narrowed is output from the diffraction grating 42.

The mirror 45 applies the laser light reflected by the diffraction grating 42, that is, the narrowed laser light to the diffraction grating 4.
2 so as to reflect the light to the laser chamber 43 without returning the light to the laser chamber 43.

As described above, the fifth invention and the sixth invention
According to the invention of the above, even in a system having both an oscillation stage and an amplification stage in one laser chamber, the grazing incidence type diffraction grating arranged on the output side of the oscillation stage functions as an output mirror, Even if the generated weak light (spontaneous emission light) strikes the grazing incidence type diffraction grating, this light is reflected in the opposite direction (amplification stage side) and is not returned to the amplification stage.

Therefore, it is possible to provide an ultra-narrow band laser device capable of generating a narrow-band laser beam which does not include the ASE (light having a wide spectrum width).

Further, according to a seventh aspect based on the sixth aspect, the narrowed band laser light emitted from the laser chamber and oscillated from the oscillation stage is transmitted to the optical axis of the laser light in the laser chamber. And a reflecting means for reflecting the light so that an optical axis is formed at a position different from the above, and the laser light from the reflecting means is further amplified by passing through the laser chamber.

The seventh invention will be described with reference to FIG.

In this embodiment, the oscillation stage is a total reflection mirror 4
1. Laser chamber 43, diffraction grating 42 and mirror 44
The amplification stage includes a mirror 45, a laser chamber 43, and a folding mirror 61.

This amplification stage has a two-pass or two-stage configuration. Specifically, the mirror 45 and the laser chamber 4
3 and a first amplification stage composed of the reflection surface 61a of the folding mirror 61, and a second amplification stage composed of the reflection surface 61b of the folding mirror 61 and the laser chamber 43.

Then, the laser light having a narrow band output from the diffraction grating 42 oscillated by the laser in the oscillation stage is
When the laser light first enters the first amplification stage, the laser light is reflected by the mirror 45 and amplified by passing through the laser chamber 43, and is output from the laser chamber 43 as a laser light L60a.

The laser beam L60a is reflected by the turning mirror 6
When the laser beam L is reflected by the first amplification stage 1a and enters the second amplification stage,
The laser beam 60a is reflected by the folding mirror 61b, amplified by passing through the laser chamber 43 again, and output from the laser chamber 43 as a laser beam L60. This laser beam L60 is used for exposure in a fluorine exposure machine (not shown).

As described above, according to the seventh aspect,
Of course, the effects of the fifth and sixth aspects of the invention can be expected, and since the amplification stage has a two-stage configuration, the amplification coefficient is large, and in particular, a fluorine laser having a large gain or this laser can be used. Are also suitable for short wavelength lasers.

Then, with this fluorine laser or a laser having a shorter wavelength than this laser, a sufficiently high output can be obtained.

[0088]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

In the ultra-narrow band laser device of the present invention, a laser beam is narrowed by using a diffraction grating as a band narrowing element without using a band narrowing element such as an etalon or a prism in a laser resonator. In addition, it is assumed that a band of a fluorine (F2) laser having a wavelength of 157 nm or a laser having a wavelength shorter than this wavelength, for example, a rare gas molecule laser = argon dimer (Ar2) laser having a wavelength of 126 nm is narrowed. In the following embodiment, a case will be described in which the band of the fluorine laser is narrowed.

FIG. 1 is a configuration diagram showing a configuration of an ultra-narrow band laser device 100 according to this embodiment.

As shown in FIG. 1, in the ultra-narrow band laser apparatus 100, a laser resonator is constituted by the total reflection mirror 10 and the mirror 11, and a laser chamber 12 is arranged between the laser resonators. ing.

A diffraction grating 13 is arranged to bend the optical axis of the laser light emitted from the laser chamber 12, and a mirror 11 is arranged to totally reflect the diffracted light diffracted by the diffraction grating 13. Have been.

Further, the diffraction grating 13 is arranged so that incident light is incident at an angle of about 80 degrees or more so as to function as a grazing incidence type diffraction grating. The diffraction grating 13 performs diffraction and reflection, and the diffracted laser light is reflected by the mirror 11 and returns to the diffraction grating 13, while the reflected laser light is incident on the prism 14.

The reason that the diffraction grating 13 functions as an oblique incidence type diffraction grating and the mirror 11 totally reflects the diffracted light is that the laser light from the laser chamber 12 This is because the groove lines are irradiated, and the reflected light (outgoing light) from the mirror 11 is also irradiated on the plurality of groove lines.

That is, in general, the narrower the band is, the more the laser light applied to the diffraction grating hits the many groove lines, so that the laser light (reflected light) from the mirror 11 is Irradiation is performed over a wide area, that is, many groove lines.

The diffraction grating 13 and the mirror 11 function as an output mirror, and the laser beam whose band is actually narrowed is output from the diffraction grating 13. Further, the diffraction grating 13 from which the laser beam L10 is extracted is of a grazing incidence type, and has a low diffraction efficiency of 10 to 20%, but is applied to a fluorine (F2) laser.
The diffraction grating 13 and the mirror 11 function as an output mirror having a high transmittance.

The prism 14 is formed in a wedge shape having an apex angle of about 10 degrees, is disposed outside the laser resonator, and has an incident angle of the narrow band laser light L10 from the diffraction grating 13. The laser beam L10 is disposed so as to have a Brewster angle, and is used to make the optical axis of the laser beam L10 parallel to the optical axis of the laser beam emitted from the laser chamber 12.

By the way, since the prism 14 is arranged outside the laser resonator so that the incident angle becomes the Brewster angle, the wavelength of the narrowed laser light does not fluctuate, but the reflection loss Occurs about 2%.

However, if a mirror is used instead of a prism in order to return the traveling direction of the laser beam L10, the reflection loss of the mirror generally occurs about 7 to 8%. Clearly, it is better to use a prism.

The above-described total reflection mirror 10, mirror 11
The diffraction grating 13 is coated with a total reflection film.

Ultra-narrow band laser apparatus 100 having such a configuration
Will be described with reference to FIG.

As shown in FIG. 1, when the laser light emitted from the laser chamber 12 enters the diffraction grating 13, a part of the laser light is diffracted and the other laser light is reflected on the diffraction grating 13.

The laser light (diffracted light) diffracted by the diffraction grating 13 strikes the mirror 11, and the laser light reflected by the mirror 11 is incident on the diffraction grating 13 again. The incident laser light returns to the laser chamber 12, passes through the laser chamber 12, and hits the total reflection mirror 10, so that the laser light resonates between the total reflection mirror 10 and the mirror 11 to narrow the band. .

On the other hand, the laser light L reflected by the diffraction grating 13
The laser beam 10 passes through the prism 14, and the transmitted laser beam travels in a direction parallel to the optical axis of the laser beam emitted from the laser chamber 12. This laser light L10 is used as exposure light (exposure light source) of a fluorine exposure machine (not shown).

In the above embodiment, the wavelength is 157 nm.
However, the present invention is not limited to this, and the present invention is not limited to this. Also applicable to

As described above, according to the present embodiment, since a narrow band element (optical element) such as an etalon or a prism is not used in the laser resonator, the laser in these narrow band elements is used. No heat generation due to light absorption. For this reason, since there is no change in the wavelength due to a thermal change in the optical element that is the band-narrowing element, the center wavelength of the laser beam whose band has been narrowed can be stabilized.

The optical elements used in the ultra-narrow band laser device 100 include a total reflection mirror 10, a mirror 11,
And the diffraction grating 13, all of which need only be coated with a total reflection film, and do not require a coating such as a partial reflection film which is easily damaged. Therefore, this laser device is suitable for a fluorine (F2) laser or an argon dimer (Ar2) laser.

Further, since the laser beam is applied to a wide area (many groove lines) in the diffraction grating 13, the effect of narrowing the band is high.

Further, since the diffraction grating 13 is an oblique incidence type, it has a low diffraction efficiency of 10 to 20%, but is applied to a fluorine (F2) laser or an argon dimer (Ar2) laser having a short wavelength. It functions as an output mirror with high transmittance. Therefore, the laser light extraction efficiency is sufficiently high.

[Second Embodiment] FIG. 2 is a configuration diagram showing a configuration of an ultra-narrow band laser device 200 according to a second embodiment.

The ultra-narrow band laser device 200 shown in FIG.
Adds a heat sink 15 to the configuration shown in FIG.
The arrangement of the prism 14 is slightly changed.
Note that, in the same figure, portions that perform the same functions as the components shown in FIG. 1 are denoted by the same reference numerals.

The heat radiating plate 15 is provided on the surface (back surface) of the diffraction grating 13 opposite to the surface on which the groove lines are formed, and is used to suppress a rise in temperature.

The reason for using the heat radiating plate 15 is that an average output of 10 to 30 W is used as an exposure light source for lithography.
Is required, especially at a wavelength of a fluorine laser where the absorption of laser light by the reflection film is as large as several percent.
Heating at 3 is greater.

In particular, when the diffraction grating 13 is used in an oblique incidence type,
Since the place where the laser light intensified in the laser chamber 12 is extracted is the diffraction grating 13, the thermal load of the diffraction grating 13 is larger than that of a normal Littrow arrangement using the diffraction grating on the total reflection side. For this reason, by arranging the heat radiating plate 15 on the back surface of the diffraction grating 13, the temperature rise is suppressed.

In the dye laser apparatus using the conventional grazing incidence type diffraction grating, the temperature rise was hardly a problem because the dye laser normally operated at a low output of less than 1 W.

The prism 14 is formed of a thin prism having an apex angle of about 10 degrees, and is arranged so that the incident angle is about 65 degrees and the emission angle is about 48 degrees.

In the prism 14 arranged as described above, when the incident angle is about 65 degrees and the exit angle is about 48 degrees, the respective reflections on the entrance plane and the exit plane are about 0.9%, These two surfaces result in a reflection loss of less than about 2%. However, as described above, the reflection loss is smaller by about 1/4 than when a mirror is used.

The ultra-narrow band laser device 200 having the above configuration
Operates basically in the same manner as in the first embodiment, and the description of the operation is omitted here.

In the above embodiment, the wavelength is 157 nm.
However, the present invention is not limited to this, and the present invention is not limited to the case where a laser having a wavelength shorter than 157 nm, such as an argon dimer (Ar2) laser having a wavelength of 126 nm, is narrowed. Also applicable to

As described above, according to the second embodiment, the effect of the first embodiment can be expected, and the temperature rise of the diffraction grating 13 can be suppressed. The wavelength fluctuation due to the thermal expansion of the grating 13 itself, that is, the change in the wavelength width and the change in the center wavelength are reduced, and the wavelength of the laser light L10 having a narrower band than in the first embodiment is reduced. Can be further stabilized.

[Third Embodiment] FIG. 3 is a configuration diagram showing a configuration of an ultra-narrow band laser device 300 according to a third embodiment.

Ultra-narrow band laser device 300 shown in FIG.
Removes the mirror 11 in the configuration shown in FIG.
The configuration is such that a diffraction grating 30 is added. Note that, in the same figure, parts that perform the same functions as the components shown in FIG. 1 are denoted by the same reference numerals.

The third embodiment is different from the first embodiment in that a laser resonator is constituted by the total reflection mirror 10 and the diffraction grating 30 arranged in a Littrow arrangement.

When the diffraction grating 30 reflects the laser light (diffracted light) diffracted by the diffraction grating 13 back, the reflected light is dispersed according to the wavelength.

For this reason, the resolution is further improved as compared with the case where the mirror according to the first embodiment is used.
The wavelength of the resonating laser light is further narrowed.

Ultra-narrow band laser apparatus 300 having such a configuration
Operates basically in the same manner as in the first embodiment, and the description of the operation is omitted here.

In the above-described embodiment, as in the second embodiment, a heat radiating plate may be provided on the back surface of the diffraction grating 13 to suppress a rise in temperature.

In the above embodiment, the wavelength is 157.
nm fluorine (F2) laser
The present invention is not limited to this, and can be applied to the case where a laser having a wavelength shorter than the wavelength of 157 nm, for example, an argon dimer (Ar2) laser having a wavelength of 126 nm is narrowed.

As described above, according to the third embodiment, the function and effect of the first embodiment can be expected, and the diffraction grating 30 diffracts the light by the diffraction grating 13. When the laser light (diffracted light) is reflected and returned, the reflected light is dispersed according to the wavelength, so that the resolution is further increased, and compared with the case where the mirror in the first embodiment is used. As a result, the wavelength of the resonating laser light is further narrowed.

[Fourth Embodiment] FIG. 4 is a configuration diagram showing a configuration of an ultra-narrow band laser device 400 according to a fourth embodiment.

In the fourth embodiment, an ultra-narrow band laser device having both an oscillation stage and an amplification stage is assumed, and a narrow-band element such as an etalon or a prism is provided in a laser resonator in the oscillation stage. Instead of using a diffraction grating as a band-narrowing element, the band of the laser beam is narrowed and the wavelength is 157.
It is assumed that a narrow band of a fluorine (F2) laser of nm or a laser of a shorter wavelength than this wavelength, for example, a rare gas molecule laser = argon dimer (Ar2) laser having a wavelength of 126 nm is used. In the following embodiment, a case will be described in which the band of the fluorine laser is narrowed.

As shown in FIG. 4, the ultra-narrow band laser device 400 has an oscillation stage and an amplification stage in one laser chamber 43. The laser resonator of the oscillation stage is composed of a total reflection mirror 41 and a mirror 44, and a diffraction grating 42 is arranged between the laser resonators.

That is, the oscillation stage comprises a total reflection mirror 41, a laser chamber 43, a diffraction grating 42 and a mirror 44, and the amplification stage comprises a mirror 45 and a laser chamber 43.

The diffraction grating 42 is a grazing incidence type diffraction grating, and is arranged so that the laser beam enters at an angle of incidence of about 80 degrees or more.

Since the diffracted light from the diffraction grating 42 is totally reflected by the mirror 44, in the diffraction grating 42, as in the case of the diffraction grating 13, many groove lines are irradiated with laser light.

The diffraction grating 42 and the mirror 44 have a function as an output mirror, and the laser beam whose band is actually narrowed is output from the diffraction grating 42.

The mirror 45 transmits the laser light reflected by the diffraction grating 42, that is, the narrow band laser light to the diffraction grating 4.
2 so as to reflect the light to the laser chamber 43 without returning the light to the laser chamber 43.

Ultra-narrow band laser device 400 having such a configuration
Will be described with reference to FIG.

First, in the oscillation stage, when the laser light emitted from the laser chamber 43 enters the diffraction grating 42, a part of the laser light is diffracted and the other laser light is reflected on the diffraction grating 42. .

The laser light (diffracted light) diffracted by the diffraction grating 42 strikes a mirror 44, and the laser light reflected by the mirror 44 is incident on the diffraction grating 42 again.

The incident laser light is applied to the laser chamber 4.
Returning to step 3, the laser light passes through here and strikes the total reflection mirror 41, so that the laser light resonates between the total reflection mirror 41 and the mirror 44 to narrow the band.

On the other hand, the laser light reflected by the diffraction grating 42, that is, the laser light having a narrow band, enters the amplification stage.

In the amplifying stage, the narrow band laser light from the diffraction grating 42 is reflected by the mirror 45, enters the laser chamber 43, and is amplified by passing therethrough. That is, the amplified laser light L40 is emitted from the laser chamber 43. This laser beam L40
Is used as exposure light (exposure light source) of a fluorine exposure machine (not shown).

In the above embodiment, the wavelength is 15
Although a 7 nm fluorine (F2) laser has been described, the invention is not limited to
Laser having a wavelength shorter than the wavelength of, for example, 126 nm
It can also be applied to the case where the bandwidth of the argon dimer (Ar2) laser is narrowed.

As described above, according to the fourth embodiment, since the output mirror of the oscillation stage is an oblique incidence diffraction grating, spontaneous emission light (weak light) generated in the amplification stage is emitted from the oscillation stage. Even if the light returns to the direction, the light hits the diffraction grating 42, but since the diffraction grating 42 functions as an output mirror, the spontaneous emission light (weak light) is not reflected so as to return to the opposite direction (the amplification stage side). . Therefore, the spontaneous emission light reflected on the diffraction grating 42 is not returned to the amplification stage again and amplified, and the ASE (light having a wide spectrum width) is hardly generated.

[Fifth Embodiment] FIG. 5 is a configuration diagram showing a configuration of an ultra-narrow band laser device 500 according to a fifth embodiment.

Ultra-narrow band laser device 500 shown in FIG.
Differs from the configuration shown in FIG. 4 in that a mirror 51, a beam expander 52, and a shift prism 53 are added and the diffraction grating 4
2. The arrangement of the mirrors 44 and 45 is changed. Note that, in the same figure, parts that perform the same functions as those of the components shown in FIG. 4 are denoted by the same reference numerals.

In this embodiment, the oscillation stage includes the total reflection mirror 4
1. Laser chamber 43, diffraction grating 42 and mirror 44
The amplification stage includes mirrors 45 and 51, a beam expander 52, a shift prism 53, and a laser chamber 43.
It is composed of

The diffraction grating 42, two mirrors 44,
Since the mirror 45, the beam expander 52, and the shift prism 53 are additionally arranged, the arrangement 45 is arranged so as to be symmetric with respect to the Y axis in the arrangement shown in FIG.

Ultra-narrow band laser device 500 having such a configuration
Will be described with reference to FIG.

Since the operation of the oscillation stage is the same as that of the fourth embodiment, the description of the operation is omitted here.

In the amplifying stage, the laser beam L50, which is laser-oscillated in the oscillating stage and output from the diffraction grating 42, is folded back by the mirrors 45 and 51 and passes through the beam expander 52 to thereby obtain a beam width. Is enlarged.

The laser beam having the expanded beam width is translated in parallel through the shift prism 53, and then enters the laser chamber 43 and is amplified by passing therethrough.

The amplified laser light L51 is taken out of the laser chamber 43 as an element of the amplification stage, and is used for exposure in a fluorine exposure machine (not shown).

In the above embodiment, when the wavelength is 15
Although a 7 nm fluorine (F2) laser has been described, the invention is not limited to
Laser having a wavelength shorter than the wavelength of, for example, 126 nm
It can also be applied to the case where the bandwidth of the argon dimer (Ar2) laser is narrowed.

As described above, according to the fifth embodiment, as can be seen from FIG. 5, of the weak light (spontaneous emission light) generated in the optical path of the amplification stage in the laser chamber 43, as shown in FIG. The light traveling upward at 5 passes through a shift prism 53 and a beam expander 52 and passes through mirrors 51 and 4.
Although the light is reflected at 5 and hits the diffraction grating 42, it is not reflected so as to be returned to the diametrically opposite side (amplifying stage side). Therefore, the weak light (spontaneous emission light) reflected on the diffraction grating is not returned to the amplification stage again and is amplified.
The ASE hardly occurs.

[Sixth Embodiment] FIG. 6 is a configuration diagram showing a configuration of an ultra-narrow band laser device 600 according to a sixth embodiment.

The ultra-narrow band laser device 600 shown in FIG.
Has a configuration in which a folding mirror 61 is added to the configuration shown in FIG. Note that, in the same figure, parts that perform the same functions as those of the components shown in FIG. 4 are denoted by the same reference numerals.

In this embodiment, the oscillation stage includes the total reflection mirror 4
1. Laser chamber 43, diffraction grating 42 and mirror 44
The amplification stage includes a mirror 45, a laser chamber 43, and a folding mirror 61.

This amplification stage has a two-pass or two-stage configuration. Specifically, the mirror 45 and the laser chamber 4
3 and a first amplification stage composed of the reflection surface 61a of the folding mirror 61, and a second amplification stage composed of the reflection surface 61b of the folding mirror 61 and the laser chamber 43.

Ultra-narrow band laser device 600 having such a configuration
Will be described with reference to FIG.

Since the operation of the oscillation stage is the same as that of the fourth embodiment, the description of the operation is omitted here.

In the amplifying stage, when a narrow band laser beam oscillated by the laser in the oscillation stage and output from the diffraction grating 42 first enters the first amplifying stage, the laser beam is reflected by the mirror 45. The laser light is amplified by passing through the laser chamber 43 and output from the laser chamber 43 as a laser beam L60a.

The laser beam L60a is reflected by the turning mirror 6
When the laser light L60a is reflected by the first reflecting surface 61a and enters the second amplification stage, the laser beam L60a is reflected by the reflecting surface 6 of the folding mirror 61.
The laser light is reflected by the laser chamber 1b, further amplified by passing through the laser chamber 43 again, and output from the laser chamber 43 as laser light L60. This laser beam L60 is used for exposure in a fluorine exposure machine (not shown).

In the above-described embodiment, when the wavelength is 15
Although a 7 nm fluorine (F2) laser has been described, the invention is not limited to
Laser having a wavelength shorter than the wavelength of, for example, 126 nm
It can also be applied to the case where the bandwidth of the argon dimer (Ar2) laser is narrowed.

As described above, according to the sixth embodiment, not only the operation and effect of the fourth embodiment can be expected, but also because the amplification stage has a two-stage configuration, It has a large coefficient and is particularly suitable for a fluorine laser having a large gain. In this fluorine laser, enough
High output can be obtained.

[Seventh Embodiment] FIG. 7 is a configuration diagram showing a configuration of an ultra-narrow band laser device 700 according to a seventh embodiment.

As shown in the figure, in the ultra-narrow band laser device 700, a laser resonator is composed of an output mirror 71 and a diffraction grating 72 arranged in a Littrow arrangement, and between the laser resonators. A laser chamber 73, a convex mirror 74 and a concave mirror 75 are arranged.

In this embodiment, the mechanism including the diffraction grating 72, the convex mirror 74 and the concave mirror 75 functions as a total reflection mirror. In addition, the beam of the laser light emitted from the laser chamber 12 is expanded by using a reflective optical element having only the convex mirror 74 and the concave mirror 75.

For this reason, in the diffraction grating 72, the laser beam (parallel light) from the concave mirror 75 is applied to a wide area, that is, many groove lines, so that the band can be narrowed further.

In the above laser resonator, since an optical element such as a prism is not used for expanding the laser beam, heat is not generated due to absorption of the laser beam by this optical element, so that a narrow band is used. The fluctuation of the wavelength of the laser light to be converted can be suppressed.

Ultra-narrow band laser device 700 having such a configuration
Will be described with reference to FIG.

As shown in FIG. 7, when the laser light emitted from the laser chamber 73 strikes the convex mirror 74, the laser light is expanded in beam width and reflected by the concave mirror 75 to become parallel light, and then diffracted. The light is incident on the grating 72.

The laser light incident on the diffraction grating 74 arranged in the Littrow arrangement is again reflected on the concave mirror 75 and the convex mirror 74 and is incident on the laser chamber 73, and after passing therethrough, is incident on the output mirror 71.

In the output mirror 71, reflection and transmission are performed, and a part of the laser light is reflected by the output mirror 71 and re-enters the laser chamber 73. Resonance of the laser light is generated between the laser beam 72 and the laser beam 72 to narrow the band.

On the other hand, the laser beam transmitted through the output mirror 71 is
The light is output as a laser light L70 having a narrow band, and is used for exposure in a fluorine exposure machine (not shown).

In the above-described embodiment, when the wavelength is 15
Although a 7 nm fluorine (F2) laser has been described, the invention is not limited to
Laser having a wavelength shorter than the wavelength of, for example, 126 nm
It can also be applied to the case where the bandwidth of the argon dimer (Ar2) laser is narrowed.

As described above, according to the seventh embodiment, even when the diffraction grating is used as the total reflection mirror, the optical element of the prism is used as in the conventional laser device shown in FIG. , The beam width of the laser light emitted from the laser chamber 73 can be expanded by using the reflective optical elements of the convex mirror and the concave mirror.

Therefore, the wavelength of the narrowed band does not fluctuate due to the heat generated by the absorption of the laser light by the prism, and the center wavelength of the narrowed laser light can be stabilized.

[Eighth Embodiment] FIG. 8 is a configuration diagram showing a configuration of a fluorine exposure apparatus 800 using an ultra-narrow band laser device.

The fluorine exposure apparatus 800 is roughly composed of the ultra-narrow band laser apparatus 100 shown in FIG. 1 and an exposure apparatus main body 810.

The exposure apparatus main body 810 is arranged on a grating 81 in a clean room. Have been.

The laser beam L20 of only a strong line (oscillation line) having a wavelength width of about 0.2 pm extracted from the ultra-narrow band laser device 100 is reflected by the mirror 83a and travels upward, and the opening in the grating 81 is opened. After passing 84
The process proceeds to the inside of the exposure machine main body 810.

The laser beam L20 is focused by the lens 85,
Further, the laser light travels through a glass rod 86 made of calcium fluoride and repeats total reflection inside the glass rod 86, thereby emitting a laser beam L21 having a uniform beam intensity distribution.

The laser beam L21 is reflected by the mirror 83b, passes through the beam shaper 87 to expand the beam cross section, and is further reflected by the mirror 83c to irradiate the reticle 89 through the condenser lens 88.

Laser light L22 emitted from reticle 89
Passes through the reduction projection lens 90 and hits the wafer 91. That is, the pattern in the reticle 89 is transferred onto the wafer 91 by the reduction projection lens 90, so that the pattern is exposed on the reticle 89. In addition,
The wafer 91 is mounted on a stage 92.

In the fluorine exposure apparatus 800 of this embodiment,
As the reduction projection optical system, a reduction projection lens 90 is used, and the reduction projection lens 90 is configured by a monochromatic lens made of calcium fluoride.

As described above, the use of the reduced projection optical system including only the lens is enabled by the ultra-narrow band laser device 1.
00 has a wavelength width of about 0.2 mm.
Because it is as narrow as 2 pm, about 1/5 of the conventional fluorine laser,
This is because chromatic aberration in the reduction projection lens 90 can be ignored.

Therefore, the configuration of the exposure machine main body 810 is as follows.
It becomes equivalent to that of the conventional KrF exposure machine. The major difference is that the material of the lens is simply changed from quartz to calcium fluoride, so the design of the reduction projection lens is the same as the conventional one, and the design cost is greatly reduced. Can be.

As described above, according to the eighth embodiment, in the fluorine exposure apparatus, the price of the fluorine laser device (ultra-narrow band fluorine laser device) increases significantly and the efficiency of the laser increases. The all-refractive reduction projection optical system can be used without deterioration.

That is, as a reduction projection optical system, a conventional K
The design can be similar to that of the rF exposure machine. In other words, a simulation tool similar to the conventional one can be used, and a reduced projection optical system can be designed in a short time, and labor costs can be significantly reduced. A fluorine exposure machine can be provided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a configuration of an ultra-narrow band laser device 100 according to a first embodiment.

FIG. 2 is a configuration diagram showing a configuration of an ultra-narrow band laser device 200 according to a second embodiment.

FIG. 3 is a configuration diagram showing a configuration of an ultra-narrow band laser device 300 according to a third embodiment.

FIG. 4 is a configuration diagram showing a configuration of an ultra-narrow band laser device 400 according to a fourth embodiment.

FIG. 5 is a configuration diagram showing a configuration of an ultra-narrow band laser device 500 according to a fifth embodiment.

FIG. 6 is a configuration diagram showing a configuration of an ultra-narrow band laser device 600 according to a sixth embodiment.

FIG. 7 is a configuration diagram showing a configuration of an ultra-narrow band laser device 700 according to a seventh embodiment.

FIG. 8 is a fluorine exposure apparatus 80 according to an eighth embodiment.
FIG. 3 is a configuration diagram illustrating a configuration of a zero.

FIG. 9 is a configuration diagram showing a configuration of a conventional narrow-band laser device.

FIG. 10 is a configuration diagram showing a configuration of a conventional narrow-band laser device.

[Explanation of symbols]

 10, 41 Total reflection mirror 11, 44, 45, 51 Mirror 12, 43 Laser chamber 13, 30, 42, 72 Diffraction grating 14 Prism 15 Heat sink 52 Beam expander 53 Shift prism 61 Folding mirror 71 Output mirror 74 Convex mirror 75 Concave mirror 100-700 Ultra narrow band laser device 800 Fluorine exposure machine

Claims (7)

[Claims] A laser chamber for oscillating laser light of a fluorine laser or a laser having a shorter wavelength than the laser, and narrowing a band of the laser light from the laser chamber;
An ultra-narrow band laser device to be supplied as an exposure light source to an exposure device, comprising: total reflection means for totally reflecting incident light; and an oblique incidence type diffraction grating for dispersing a wavelength of laser light oscillated by the laser chamber. And an optical element that totally reflects the diffracted light diffracted by the grazing incidence diffraction grating, and disposing the laser chamber between the total reflection means and the grazing incidence diffraction grating and the optical element, An ultra-narrow band laser device, wherein a laser resonator is constituted by the total reflection means and the optical element. 2. The oblique incidence type diffraction grating according to claim 1, wherein a heat radiating plate is arranged on a surface opposite to a surface having a groove formed in said diffraction grating. Narrow band laser device. 3. The ultra-narrow band laser device according to claim 1, wherein said optical element is a mirror or a diffraction grating. An output mirror for emitting laser light from the laser chamber; a convex mirror for reflecting laser light oscillated by the laser chamber; a concave mirror for reflecting laser light from the convex mirror; A diffraction grating that is disposed in a Littrow corresponding manner and that disperses the wavelength of the laser light from the concave mirror, wherein the convex mirror, the concave mirror and the laser chamber are arranged between the diffraction grating and the output mirror, and the diffraction grating 2. The ultra-narrow band laser device according to claim 1, wherein a laser resonator is constituted by the output mirror and the output mirror. 5. An oscillating stage and an amplifying stage including one laser chamber, wherein the oscillating stage narrows and outputs a laser beam of a fluorine laser or a laser having a shorter wavelength than the laser. Wherein the amplification stage is an ultra-narrow band laser device that amplifies and outputs the laser beam narrowed by the oscillation stage and supplies the amplified laser light to an exposure device as an exposure light source; An ultra-narrow band laser device, wherein an oblique incidence type diffraction grating for dispersing the wavelength of laser light oscillated by a laser chamber is arranged on the output side of the oscillation stage. 6. A total reflection means for totally reflecting incident light, and an optical element for totally reflecting the diffracted light diffracted by said oblique incidence type diffraction grating, wherein said total reflection means and said oblique incidence type diffraction element are provided. 6. The ultra-narrow band laser according to claim 5, wherein said laser chamber is arranged between a grating and an optical element, and said total reflection means and said optical element constitute a laser resonator. apparatus. 7. A laser beam having a narrow band emitted from the laser chamber and oscillated from the oscillation stage, the optical axis of which is formed at a position different from the optical axis of the laser beam in the laser chamber. 7. The ultra-narrow band laser device according to claim 6, further comprising a reflection unit for reflecting the laser beam, wherein the laser beam from the reflection unit is further amplified by passing through the laser chamber.