JP2000357836A - Super narrow frequency band fluorine laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a super narrow frequency band fluorine laser device which can oscillate only in one line, make the wavelength width of the line narrow to be about 0.2 pm, and restrain the decrease of laser output. SOLUTION: In an etalon 16, the maximum transmitted wavelength λa is made to coincide with the center of a strong oscillation line L1 of a wavelength λ1=157,629.9 pm. In this case, in the etalon, the center wavelength of a weak oscillation line L2 of a wavelength λ2=157,523.3 pm becomes almost intermediate between two adjacent maximum transmitted wavelengths λb and λc. As a result, the etalon 16 becomes large loss to the weak oscillation line L2, and the component of the strong oscillation line L1 of the fluorine laser light becomes 90% or higher in the wavelength width of about 0.2 pm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultra-narrow band fluorine laser apparatus for narrowing an oscillation laser beam of a fluorine laser used as a light source of a stepper such as a fluorine exposure apparatus.

[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.

In a conventional exposure apparatus, an i-line (wavelength: 365 nm) of a mercury lamp or a krypton fluorine (KrF) excimer laser having a wavelength of 248 nm is used as a light source of the exposure apparatus. These are called an i-line exposure machine and a KrF exposure machine, respectively. As a projection optical system used in these i-line exposure apparatuses and KrF exposure apparatuses, a reduction projection lens in which many lenses made of quartz glass are combined is widely used.

Further, as a next-generation lithography exposure apparatus, an exposure apparatus using an argon fluorine (ArF) excimer laser having a wavelength of 193 nm as a light source has been started to perform finer processing. This is called an ArF exposure machine. In this ArF exposure machine, a spectrum width (wavelength width) is used.
Uses an ArF excimer laser whose band is narrowed to about 0.6 pm, and an achromatic lens made of a double material is used for the reduction projection optical system.

[0005] As a band-narrowing element for narrowing the wavelength width of an ArF excimer laser to about 0.6 pm, elements such as an etalon, a grating, and a mode selector are known. Among these elements, regarding the mode selector, “PROCEEDING OF THE
IEEE, VOL. 60, NO. 4, APRIL 19
72, pp. 422-441 ".

An ArF excimer laser device has two
Some employ a single laser device. That is, seed light is generated by a first laser device, and the seed light is injected into an oscillator, which is a second laser device.
The so-called injection locking is applied to an ArF excimer laser device.

[0007] Such an injection-locked ArF excimer laser device is described in, for example, "59th Federation of Applied Physics-related Lectures, Proceedings, p. 950, 17-a-P2".
1, 1998 "is known.

In the next-generation lithography exposure apparatus of the above-mentioned ArF exposure apparatus, the light source has a wavelength of about 157 n.
A fluorine exposure machine using a fluorine laser of m is under study.

In this fluorine laser, there are two strong oscillation lines (also called oscillation lines) having different wavelengths and light intensities. The wavelengths are 157.6299 nm (this is referred to as a wavelength λ1) and 157.5233 nm (this is referred to as a wavelength λ1). Is the wavelength λ2), and the wavelength width of each oscillation line is said to be 1 to 2 pm.

In order to use such a fluorine laser for exposure, generally, a wavelength λ1 = 157.6299 having a large intensity is used.
One line of nm (hereinafter referred to as a strong line and the other is referred to as a weak line) is selected and used (hereinafter, 1 line).
This is called line conversion. ) Is considered advantageous. Therefore, conventionally, one or two prisms are used for one line.

It should be noted that one of the fluorine lasers for a fluorine exposure machine is
Regarding the line conversion, for example, “SPIE 24th
International Symposium o
n Microlithography, Feb. 199
9. ", The experimental results are reported.

Regarding the two lines of the fluorine laser, for example, “CAN.J.PHYS.VOL.63,
1985, pp. 217-218 ".

[0013]

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

The reason is that, in the case of a fluorine laser having a wavelength of 157 nm, the transmittance of quartz glass is extremely low, and only a very limited material such as calcium fluoride can be used. Even if the reduction projection lens is formed by using a monochromatic lens made of only calcium fluoride, and the fluorine laser is made into one line, the narrowing of the oscillation laser beam of the fluorine laser is insufficient. Although the wavelength width due to such narrowing is about 2 pm, in practice, it is necessary to further narrow the bandwidth to about 1/10 the wavelength width = about 0.2 pm for one line. It is said.

Therefore, conventionally, a fluorine laser 1
Since it was difficult to narrow the bandwidth to a line width of 0.2 pm or less, the reduction projection optical system can be used with a wavelength width 10 times wider than that of the all-refractive optical system using only a lens. It has been considered necessary to apply a catadioptric reduction projection optical system (hereinafter, referred to as a catadioptric type).

Conventionally, a fluorine laser having a wavelength width of 0.2
The reason why it is difficult to narrow the band to pm is that if one or two prisms for making one line are inserted into the laser resonator, the laser output drops to about 40%. In order to further narrow the wavelength width to 0.2 pm, the band can be further narrowed (that is, the reflectance is 80%).
% Of an etalon or the like, the insertion loss is further increased by about 50%. For this reason, laser oscillation becomes difficult or the laser output is greatly reduced.

Here, the reason why the laser output is significantly reduced particularly by the insertion of the etalon in the fluorine laser will be described.

That is, it is generally known that, in an etalon having a reflective film with a high reflectance, the lower the flatness, the lower the maximum transmittance. Wavelength = 157
When an etalon is formed using calcium fluoride, a typical optical material that can be used in nm, as a substrate, this etalon has a lower hardness than quartz and is difficult to polish because it is a crystal. , The flatness is 1 / the wavelength
You can only get up to about 20. If quartz is used,
It is known that an etalon that can obtain a flatness of about 1/100 of the wavelength can be used.

Therefore, for example, when an etalon of finesse 10 is used to narrow a laser beam having a wavelength width of 2 pm to a wavelength width of 0.2 pm, the etalon becomes 8
An etalon coated with a reflectance of 0% or more is required. If the flatness of the etalon is 1/20 of the wavelength, the maximum transmittance of the etalon is only about 50%.

Therefore, a first object of the present invention is to oscillate only on one line and to set the wavelength width of that line to about 0.2 pm.
It is an object of the present invention to provide an ultra-narrow band fluorine laser device capable of narrowing the band to an extent and suppressing a decrease in laser output.

A second object of the present invention is to provide an ultra-narrow band capable of supplying an oscillating laser beam of a fluorine laser as an exposure light source to a fluorine exposure apparatus utilizing a total refraction type reduction projection optical system having only a lens. An object of the present invention is to provide a fluorine fluoride laser device.

[0022]

In order to solve the above-mentioned first problem, a first invention of the present invention provides an ultra-narrow band fluorine which supplies an oscillation laser beam of a fluorine laser as a light source of an exposure apparatus. In a laser device, while the transmittance or the reflectance periodically changes according to the wavelength of the incident light,
A wavelength selection element for narrowing the oscillation laser light of the fluorine laser, wherein the wavelength selection element has a first oscillation line having a higher light intensity among two oscillation lines having different wavelengths and light intensities in the fluorine laser. Is located at one selected wavelength in its own element, the center wavelength of the second oscillation line whose light intensity is weaker than that of the first oscillation line is two adjacent selected wavelengths in its own element. The optical element is characterized by being formed of an optical element whose transmittance or reflectance changes periodically so as to be positioned between the optical elements.

According to a second aspect of the present invention, in the first aspect, the wavelength selection element has a transmittance at a center wavelength of the second oscillation line of 0.64 of a transmittance at a center wavelength of the first oscillation line. It is characterized in that it is formed to be twice or less.

In a third aspect based on the first aspect, the wavelength selection element is a mode selector formed by a dividing means having a beam dividing surface and two reflecting means having a reflecting surface. .

In a fourth aspect based on the first or second aspect, the apparatus further comprises an oscillation stage and an amplification stage for oscillating the laser light of the fluorine laser, wherein the oscillation stage and the amplification stage have an optical path between the oscillation stage and the amplification stage. A wavelength selection element is provided.

In order to solve the second problem, the fifth
According to the invention, in any one of the first to fourth inventions, the laser beam narrowed by the wavelength selection element is supplied to a fluorine exposure apparatus having a total refraction type reduction projection optical system having only a lens. It is characterized by doing so.

The first invention and the second invention will be described with reference to FIGS.

As shown in FIG. 1, the beam splitter 14
An etalon 16 which is a periodic wavelength selecting element as a band narrowing element is arranged between the optical path between the mirror and the mirror 15.
The period (FSR) of the etalon 16 is 3.0 pm and the finesse is 15.

In the etalon 16, as shown in FIG. 2, the maximum transmission wavelength λa is adjusted to the center of a strong line (oscillation line) L1 having a wavelength λ1 = 157.6299 nm.
As a result, when the laser beam L12 incident on the etalon 16 from the beam splitter 14 side passes through the etalon 16 (that is, in the laser beam L13), the strong line L1
, The peak power is about 50%, but the wavelength width is about 0.25, which is 1/15 of the original line width.
pm.

The wavelength difference between two lines in the fluorine laser (= 157,629.9 pm-157,523.3)
pm) is divided by the FSR of 3.0 pm to obtain 35.53, so that the wavelength λ2 = 157.52.
The transmittance at 33 nm is about several percent.

That is, the value of 106.6 / FSR (35
Since the decimal part of (53) is 0.53, the wavelength λ1 = 1
In the etalon 16 having the maximum transmittance at 57,629.9 pm, the wavelength λ2 = 157,523.3p
m is approximately halfway between two adjacent maximum transmission wavelengths λb and λc, as shown in FIG. Therefore, the wavelength λ2 = 15
Since the etalon 16 causes a large loss with respect to the weak line (oscillation line) L2 of 7.5233 nm, the laser beam L
In No. 13, the component of the strong line L1 having a wavelength width of about 0.2 pm is 90% or more.

The operation will be described again with reference to FIG. The laser light L13 is reflected by the mirror 15 and is returned to the etalon 16 again.
, And further reflected by the beam splitter 14,
Since the light enters the laser chamber 13, the ratio of the narrowed strong line L <b> 1 further increases. Therefore, laser oscillation occurs only on the strong line L1, and the laser beam L1 on only the strong line L1 having a wavelength width of about 0.2 pm
4 is taken out of the output mirror 11.

The two lines L1 and L2 of the fluorine laser
It is said that the intensity ratio of the weak line L2 is about 1/6 to about 1/7 of the strong line L1. In consideration of this intensity ratio, the weak light reciprocates at least two times through the periodic wavelength selection element such as the etalon so that the intensity at the center wavelength of the weak line L2 is 1% or less of the intensity at the center wavelength of the strong line L1. As a ratio of the transmittance at the periodic wavelength selection element, the transmittance at the center wavelength of the weak line L2 is (１ ／) の (1) of the transmittance at the center wavelength of the strong line L1. /4)=0.64 times or less.

That is, the characteristic (specification) of the periodic wavelength selection element is that the transmittance at the center wavelength of the weak line L2 is
About 0.64 of the transmittance at the center wavelength of the strong line L1
It is set to be less than double.

As described above, according to the first aspect, the wavelength selection element is such that the center wavelength of the oscillation line having the higher light intensity of the two oscillation lines of the fluorine laser having different wavelengths and light intensities is the same as that of the element itself. When located at the selected wavelength in,
Since the center wavelength of the oscillation line having a low light intensity is located between two adjacent selected wavelengths in its own element, the oscillation line is formed of an optical element whose transmittance or reflectance changes periodically. It is possible to efficiently generate laser light having a wavelength of 157.6299 nm and a narrow line of about 0.2 pm, without using a prism for changing the wavelength.

According to the second invention, the transmittance at the center wavelength of the second oscillation line (weak line L2) is about 0.64 of the transmittance at the center wavelength of the first oscillation line (strong line L1). Is set to be less than
The oscillation of the laser beam in the oscillation line can be suppressed.

Next, the third invention will be described with reference to FIG.

As shown in FIG. 5, in the ultra-narrow band fluorine laser apparatus 500, the resonator sandwiching the laser chamber 52 is composed of a total reflection mirror 51 and a mode selector 501. The mode selector 501 includes a beam splitter 53 having a beam splitting function and two reflecting mirrors 54a and 54a.
4b. The mode selector 501 is a periodic wavelength selection element, and has a function like an output mirror for extracting a laser beam of a selected wavelength.

The reflecting mirror 54 in the mode selector 501
"d" is the distance (precisely, the optical path length) between "a" and the reflecting mirror 54b.
FS, which is the cycle of the mode selector 501
R is represented by c / (2d). Here, “c” is the speed of light.

In this case, since d is set to 12.3 mm, FSR becomes 1.01 pm.
06.6 / 1.01 = 105.5.

In the mode selector 501 to which the laser light from the laser chamber 52 is incident, a part of the laser light passes through the beam splitter 53, and a part of the laser light is reflected by the beam splitter 53. Further, the light is reflected by the reflecting mirror 54b.

A part of the laser beam reflected by the reflecting mirror 54b is reflected by the beam splitter 53 and passes through the beam splitter 53. The laser light reflected by the beam splitter 53 is again incident on the laser chamber 52,
On the other hand, the laser light that has passed through the beam splitter 53 is reflected by the reflecting mirror 54a.

The laser light reflected by the reflecting mirror 54a is further reflected by the beam splitter 53 and output as a laser light L50, and a part of the laser light passes through the beam splitter 53 and is reflected by the reflecting mirror 54b. I do.

When the above operation is repeated, when the laser beam is incident on the laser chamber 52, the ratio of the narrow line strong line L1 of the laser beam is further increased. Is output.

That is, 106.6 / 1.01 = 10
Since it is 5.5, a strong line L1 having a wavelength λ1 = 157.6299 nm is obtained by the mode selector 501.
, The line L2 having the wavelength λ2 = 157.5233 nm is suppressed, and the laser beam L50 having the wavelength λ1 = 157.6299 nm is output from the beam splitter 53.
Is taken out.

As described above, according to the third aspect,
The mode selector as a wavelength selection element is formed by a splitting unit having a beam splitting surface (for example, a beam splitter) and two reflecting units having a reflecting surface (for example, a reflecting mirror). A mirror which can be formed on an uncoated (uncoated) substrate and has a total reflection film can be used as a means having a reflection surface.

Therefore, the wavelength selection element can be formed without using a half mirror using a partial reflection film used for the etalon which is one of the wavelength selection elements.

That is, since it is not necessary to use a wavelength selection element such as an etalon which needs to be provided with a partial reflection film which is liable to be damaged, in a ultra-narrow band fluorine laser apparatus using a mode selector, the mode selection is In addition, it is possible to narrow the band of the oscillated laser beam without damage and stably for a long period of time.

Next, the fourth invention will be described with reference to FIG.

As shown in FIG. 7, the ultra-narrow band fluorine laser device 700 is of the injection locking type, and comprises a seed laser 71 as an oscillation stage and an oscillator 72 as an amplification stage.

The seed laser 71 is provided in a laser chamber 75.
, An output mirror 73 and a total reflection mirror 74 are arranged on both sides to form a stabilizing resonator. In addition, between these resonators,
No band-narrowing element is included. Therefore, the laser beam L71 extracted from the seed laser 71 has
Lines L1 and L2 are included, and neither line has a narrow wavelength band of about 1 pm.

The laser light 71 is supplied to an etalon 7 which is a periodic wavelength selecting element disposed outside the seed laser 71.
Go through 6. The characteristics of this etalon 76 are such that the FSR is 3.0 pm and the finesse is 15. Etalon 7
The laser light L72 passing through 6 is narrowed to a wavelength width of 0.2 pm, and has only one line.

However, the energy of the laser light L72 is reduced to about 1/10 of that of the laser light L71. The narrowed laser light L72 proceeds to the oscillator 72, which is the second fluorine laser device. This laser light L72 is injected into the resonator from the hole of the concave mirror with a hole 78 as seed light. Then, when the laser beam L72 is discharged while passing through the laser chamber 79, the laser beam L73 having only the increased power while keeping the wavelength width is extracted.

As described above, according to the fourth aspect, the wavelength selection element is arranged between the oscillation stage and the amplification stage, so that the laser beam does not need to be narrowed in the oscillation stage. As a result, laser oscillation easily occurs in the oscillation stage, and laser light having a sufficiently long pulse width can be generated.

Therefore, in the super-bandwidth fluorine laser of the fourth invention, the laser light can be amplified with high efficiency even if there is some synchronization error between the oscillation stage and the amplification stage.

Next, the fifth invention will be described with reference to FIG.

As shown in FIG. 3, a fluorine exposure machine 300
Is roughly composed of an exposure machine main body 200 and an ultra-narrow band fluorine laser apparatus 100 (see FIG. 1).

The exposure apparatus main body 200 is disposed on a grating 21 in a clean room, and the ultra-narrow band fluorine laser apparatus 100 is disposed on a floor 22 below the grating 21 (a floor generally called a floor). Have been.

The laser beam L20 of only the strong line L1 having a wavelength width of about 0.2 pm, which is extracted from the ultra-narrow band fluorine laser apparatus 100, is reflected by the mirror 23a and travels upward to pass through the opening 24 in the grating 21. Go through,
The process proceeds into the exposure apparatus main body 200.

In the exposure apparatus main body 200, the laser beam L22 emitted from the reticle 29 passes through the reduction projection lens 30 and strikes the wafer 31. The reduction projection lens 30 as a reduction projection optical system is configured by a monochromatic lens made of calcium fluoride.

As described above, according to the fifth aspect, the laser beam output from the ultra-narrow band fluorine laser device is
Since it is supplied to a fluorine exposure apparatus having a total refraction type reduction projection optical system, in the fluorine exposure apparatus,
As a reduction projection optical system, conventional krypton fluorine (Kr
F) The design is the same as that of the exposure apparatus, so that it is possible to provide a commercially available fluorine exposure apparatus in a short period of time and at low cost.

[0062]

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

FIG. 1 is a configuration diagram showing the configuration of an ultra-narrow band fluorine laser device 100 according to the present invention.

In this ultra-narrow band fluorine laser device 100, it is assumed that the laser beam of the fluorine laser is narrowed by a periodic wavelength selection element (this will be described later). In this fluorine laser, there are two strong oscillation lines (oscillation lines) having different wavelengths and light intensities. That is, an oscillation line having a wavelength λ1 = 157.6299 nm (hereinafter referred to as a strong line L1) and a wavelength λ1
2 = 157.5233 nm oscillation line (hereinafter referred to as a weak strong line L2). Here, it is assumed that the strong line L1 is selected (hereinafter, referred to as one line) and the laser light is narrowed.

Here, the above-mentioned periodic wavelength selection element is an optical element which is a band narrowing element and whose transmittance (or reflectance) changes periodically at substantially constant wavelengths. That is, in the periodic wavelength selection element, for example, the maximum transmittance is periodically obtained for each fixed wavelength. The wavelength transmitted at the maximum transmittance is called the maximum transmission wavelength. Further, a period in which the maximum transmittance is obtained in the periodic wavelength selection element is referred to as “FSR”. Here, examples of the periodic wavelength selection element include an etalon and a mode selector. Further, the maximum transmission wavelength can be rephrased as a selected wavelength.

Now, description will be made with reference to FIG. In the ultra-narrow band fluorine laser device 100, a laser chamber 13 is disposed between a stable resonator constituted by an output mirror 11 and a total reflection mirror 12. An uncoated (uncoated) beam splitter 14 is inserted between the resonators, and the direction of an edge as a periodic wavelength selection element is opposite between optical paths of the beam splitter 14 and the mirror 15. An etalon 16 having two edge plates 16a and 16b is arranged. Period of etalon 16 (FS
R) is 3.0 pm and finesse is 15.

The edge plates 16a, 1a of the etalon 16
As the edge angle of 6b, a Brewster angle (about 57 °) on the surface of the etalon 16 where the laser beam is incident is preferable because the reflection loss can be ignored.

When the fluorine laser gas in the laser chamber 13 is excited by electric discharge, spontaneous emission light is generated mainly in two lines of strong and weak lines (lines having different wavelengths and light intensities), and these lights move inside the resonator. While the strength is strengthened.

A part of the laser light emitted from the laser chamber 13 is reflected by the beam splitter 14 and
6 and the transmitted laser beam L13 is reflected by the mirror 15
And again passes through the etalon 16. A part of the transmitted laser light is further reflected by the beam splitter 14 and enters the laser chamber 13, so that the ratio of the strong line L1 narrowed by the etalon 16 is further increased.

Therefore, laser oscillation occurs only on the strong line L 1, so that the laser beam L 14 of only the strong line L 1 having a wavelength width of about 0.2 pm is extracted from the output mirror 11.

In the etalon 16, as shown in FIG. 2, a strong line L 1 having a wavelength λ 1 = 157.6299 nm is used.
Is set to the center of the maximum transmission wavelength λa. As a result, when the laser beam L12 incident on the etalon 16 from the beam splitter 14 side passes through the etalon 16 (that is, in the laser beam L13), the peak power becomes about 50% at the center wavelength of the strong line L1. , The wavelength width (spectral width) is about 0.2 pm, which is 1/15 of the original line width (spectral width).

The wavelength difference between two lines in the fluorine laser (= 157, 629.9 pm-157, 523.3)
pm) is divided by the FSR of 3.0 pm to obtain 35.53, so that the wavelength λ2 = 157.52.
The transmittance at 33 nm is about several percent.

That is, the value of 106.6 / FSR (35
Since the decimal part of (53) is 0.53, the wavelength λ1 = 1
In the etalon 16 having the maximum transmittance at 57,629.9 pm, the wavelength λ2 = 157,523.3p
m is approximately halfway between two adjacent maximum transmission wavelengths λb and λc, as shown in FIG. Therefore, the wavelength λ2 = 15
Etalon 1 for 7.5233 nm weak line L2
6 causes a large loss, so that the laser beam L13 has a wavelength width of about 0.2 pm and the component of the strong line L1 is 90% or more.

The maximum transmission wavelengths λa, λb, λc
Are also the selected wavelengths.

Further, the etalon 16 which is the periodic wavelength selection element of the present embodiment may be used in place of the output mirror 11. In this case, at a wavelength where the transmittance of the etalon 16 is low, the reflectance increases and laser oscillation is easily performed. Therefore, although the selected wavelength is opposite to that of the arrangement of FIG. 1, when the laser is oscillated at the wavelength λ1, the wavelength λ is adjusted.
In No. 2, since the reflectance is lowered, the feedback control is not performed, and the laser oscillation can be suppressed.

However, when an etalon, which is a periodic wavelength selection element of the present invention, is used instead of the output mirror, an etalon having a transmittance close to 100% at a wavelength not to be selected is used to completely stop laser oscillation. Therefore, it is necessary to use a low finesse etalon having a minimum value of the transmittance of about 90% (a maximum value of the reflectance of about 10%). It is suitable that two uncoated substrates in which the reflection coating is not applied to the inner surface of the etalon are combined. As a result, long-term stability can be obtained because a reflective coating that is easily damaged is not required.

Next, quantitative specifications of the periodic wavelength selection element will be described.

In the fluorine laser, it takes about 20 ns from the start of the actual excitation of the fluorine laser gas to the start of laser oscillation (time from injection of discharge energy to observation of laser light). When this time is converted into a distance, it corresponds to a length that light travels about 6 m.

This is about four times the general resonator length of a fluorine laser device = 1 to 1.5 m, so that the weak light which is a seed of oscillation before the laser oscillation starts 2 to 3 reciprocations. Therefore, by the time of laser oscillation, the type of oscillation (weak light) reciprocates two or three times through a periodic wavelength selection element such as an etalon.

The intensity ratio of the two lines of the fluorine laser is such that the weak line L2 is about 1/6 of the strong line L1.
It is said to be about 1/7. In consideration of this intensity ratio, the weak light is transmitted through at least two periodic wavelength selection elements such as an etalon.
By reciprocating (ie, passing at least four times), the intensity at the center wavelength of the weak line L2 is 1% or less of the intensity at the center wavelength of the strong line L1 (in this case, negligible in actual exposure processing). In order to obtain the intensity, the transmittance at the center wavelength of the weak line L2 is (１ ／) of the transmittance at the center wavelength of the strong line L1 as the ratio of the transmittance at the periodic wavelength selection element. (1/4) = ｛(1/6) (1/4)
It is sufficient that the power 倍 = 0.64 times or less.

That is, the characteristic (specification) of the periodic wavelength selection element depends on the transmittance characteristic (in the case of an etalon, it is determined by the reflectance and flatness of the reflection film). The transmittance at the center wavelength of the weak line L2 is about 0.5% of the transmittance at the center wavelength of the strong line L1.
It is set to be 64 times or less.

Next, the ultra-narrow band fluorine laser device 1
A fluorine exposure machine using 00 will be described.

FIG. 3 is a configuration diagram showing the configuration of the fluorine exposure apparatus 300.

As shown in FIG.
Is roughly composed of the ultra-narrow band fluorine laser device 100 and the exposure machine main body 200 described with reference to FIG.

The exposure apparatus main body 200 is disposed on a grating 21 in a clean room, and the ultra-narrow band fluorine laser apparatus 100 is disposed on a floor 22 below the grating 21 (a floor generally called a floor). Have been.

The laser beam L20 of only the strong line L1 having a wavelength width of about 0.2 pm, which is extracted from the ultra-narrow band fluorine laser apparatus 100, is reflected by the mirror 23a and travels upward to pass through the opening 24 in the grating 21. Go through,
The process proceeds into the exposure apparatus main body 200.

The laser beam L20 is focused by the lens 25,
Proceed through a glass rod 26 made of calcium fluoride,
Further, by repeating total reflection inside the glass rod 26, the glass rod 26 emits a laser beam L21 having a uniform beam intensity distribution.

The laser beam L21 is reflected by the mirror 23b and passes through the beam shaper 27 composed of the lenses 27a and 27b, so that the beam cross section is expanded. Further, the laser beam L21 is reflected by the mirror 23c and passes through the condenser lens 28. The reticle 29 passes through and irradiates the reticle 29.

The laser beam L2 emitted from the reticle 29
2 passes through the reduction projection lens 30 and hits the wafer 31. That is, the pattern in the reticle 29 is transferred onto the wafer 31 by the reduction projection lens 30, so that the wafer 31 is exposed in a pattern on the reticle 29. The wafer 31 is mounted on a stage 32.

The reduction projection lens 30 as a reduction projection optical system is constituted by a monochromatic lens made of calcium fluoride.

As described above, in the fluorine exposure machine 300,
A reduction projection optical system using only a lens (that is, a reduction projection lens 3)
0) can be used because the wavelength width of the laser beam L20 extracted from the ultra-narrow band fluorine laser 100 is 0.2 pm, which is about 1/10 of that of the conventional fluorine laser. This is because the chromatic aberration at 30 can be ignored.

Therefore, the design of the reduction projection lens is the same as the conventional one, and the cost for this design can be greatly reduced. That is, the same simulation tool as that of the related art can be used, and design can be performed in a short period of time, so that labor costs can be greatly reduced.

In this embodiment, the wavelength difference between the two lines is 106.6 pm, and the FSR of the etalon 16 used is
The fractional part of the value divided by is 0.53, but in practice, the decimal part is an ideal value = 0.50 to 0.3 to
Even if they are separated by about 0.4 (that is, 0.50 ± 0.3 ~
0.4), and the wavelength width can be narrowed to about 0.2 pm.

As described above, according to the present embodiment,
In the ultra-narrow band fluorine laser apparatus 100, a strong line L1 having a wavelength λ1 = 157.6299 nm is used without using a prism for forming one line in the resonator.
With only this, laser light whose wavelength width is narrowed to about 0.2 pm can be generated with high efficiency.

The ultra-narrow band fluorine laser device 100
In the fluorine exposure apparatus 300 using
Compared with the F exposure apparatus, the material of the lens of the reduction projection optical system (reduction projection lens 30) is only changed from quartz to calcium fluoride.
It can be made equivalent to a conventional KrF exposure machine.

Therefore, it is possible to use the all-refractive reduction projection optical system without significantly increasing the price of the fluorine laser device or greatly reducing the efficiency of the laser.
Accordingly, since the reduction projection optical system has the same design as that of the conventional KrF exposure apparatus, it is possible to provide a fluorine exposure apparatus that can be commercialized in a short period of time and at low cost.

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

As shown in the figure, in the narrow-band fluorine laser apparatus 400, the output mirror 41 and the total reflection mirror 42 constitute a stable resonator. The laser cavity 43 and the etalon 16 shown in FIG.
And an etalon 44 having the same function as the above. However, the etalon 44 has two edge plates 44a,
44b, and these edge plates 44a, 44
Since the direction of the edge b is the same, it has the same function as the dispersing prism.

The narrow band fluorine laser device 40 having such a configuration
0, as in the first embodiment described above, when the laser gas in the laser chamber 43 is excited by electric discharge, spontaneous emission light is mainly generated in the two lines L1 and L2, and these lights are emitted from the resonator. Strength is strengthened while moving inside.

In the etalon 44, as shown in FIG. 2, a strong line L having a wavelength λ1 = 157.6299 nm is used.
Since the maximum transmission wavelength λa is set at the center of 1, the laser light emitted from the laser chamber 43 transmits through the etalon 44, is reflected by the total reflection mirror 42, and transmits through the etalon 44, Further again, the laser chamber 4
3 is incident.

As a result, the laser light has a wavelength width of about 0.2 pm at the center wavelength of the strong line L1 having a narrow band. The narrowed laser light passes through the laser chamber 43, passes through the output mirror 41, and is output as laser light L43.

Incidentally, since the etalon 44 has a function equivalent to a dispersion prism (that is, a function of wavelength dispersion),
The weak line L2 (see FIG. 2) can be further suppressed, so that the specification of one line by the etalon 44 can be relaxed.

That is, even when the transmittance at the center wavelength of the weak line L2 is set to about 0.8 times the transmittance at the center wavelength of the strong line L1 (it is originally preferable to set the transmittance to 0.64 times or less). Laser oscillation in the weak line L2 can be suppressed. Therefore, the reflectance of the reflection film of the etalon 44 can be as low as about 10%.

Further, an etalon combining a non-coated substrate not provided with a reflective coating may be used.

However, for example, in a normal etalon having a reflectance of 10%, the transmittance is about 60% even at the minimum transmission wavelength. Therefore, with this etalon alone, laser oscillation may occur to some extent even in the weak line L2 to be suppressed. In order to cope with this, it is necessary to add one prism, but this increases the insertion loss and also reduces the output of the strong line L1 to be generated.

However, in the second embodiment, since the etalon 44, which is a periodic wavelength selection element, has a wavelength dispersion function like a prism, it is necessary to suppress laser oscillation on the weak line L2. Can be.

For this reason, the ultra-narrow band fluorine laser device 10
0, low reflectance or uncoated etalon 44
Can be used, and the reflection film having a low reflectance has a feature that damage is unlikely to occur because the number of coating films is small or absent.

When the etalon 44 having such a low reflectance is not used, particularly when a fluorine laser is used,
At a wavelength of 157 nm, most coating materials have a high absorptance, so that the coating film is likely to be damaged.

As described above, according to the second embodiment, the etalon 44 having a wavelength dispersion function such as a prism narrows the oscillation laser light of a fluorine laser. The weaker line L2 can be suppressed as compared with the etalon 16 described in the first embodiment.

Further, the reflection film having a low reflectance applied to the etalon 44 is characterized by being hardly damaged, so that the long-term stability of the periodic wavelength selection element (that is, the etalon 44) can be improved.

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

As shown in the figure, in the ultra-narrow band fluorine laser device 500, the resonator sandwiching the laser chamber 52 is composed of a total reflection mirror 51 and a mode selector 501. The mode selector 501 includes a beam splitter 53 having a beam splitting function and two reflecting mirrors 54a and 54a.
4b. The mode selector 501 is a periodic wavelength selection element, and has a function like an output mirror for extracting a laser beam of a selected wavelength.

The reflecting mirror 54 in the mode selector 501
"d" is the distance (precisely, the optical path length) between "a" and the reflecting mirror 54b.
FS, which is the cycle of the mode selector 501
R is represented by c / (2d). Here, “c” is the speed of light.

In this embodiment, since d is set to 12.3 mm, FSR becomes 1.01 pm, and as a result, 106.6 / 1.01 becomes 105.5.

Ultra-narrow band fluorine laser device 5 having such a configuration
At 00, when the laser gas in the laser chamber 52 is excited by electric discharge, two lines L1 and L
2, spontaneous emission light is generated, and the intensity of these lights is increased while moving in the resonator.

In the mode selector 501 into which the laser light from the laser chamber 52 is incident, a part of the laser light passes through the beam splitter 53, and a part of the laser light is reflected by the beam splitter 53. ,
Further, the light is reflected by the reflecting mirror 54b.

A part of the laser beam reflected by the reflecting mirror 54b is reflected by the beam splitter 53 and passes through the beam splitter 53. The laser light reflected by the beam splitter 53 is again incident on the laser chamber 52,
On the other hand, the laser light that has passed through the beam splitter 53 is reflected by the reflecting mirror 54a.

The laser beam reflected by the reflecting mirror 54a is further reflected by the beam splitter 53 and output as a laser beam L50, and a part of the laser beam reflected by the reflecting mirror 54a passes through the beam splitter 53. Then, the light is reflected by the reflecting mirror 54b.

By repeating such an operation, when the laser beam is incident on the laser chamber 52, the ratio of the narrow line strong line L1 of the laser beam is further increased. Is output.

That is, 106.6 / 1.01 = 10
Since it is 5.5, a strong line L1 having a wavelength λ1 = 157.6299 nm is obtained by the mode selector 501.
, The line L2 of the wavelength λ2 = 157.5233 nm is suppressed, and therefore, the laser beam L50 of the wavelength λ1 = 157.6299 nm is output from the beam splitter 53.
Is taken out.

As described above, according to the third embodiment, a means having a beam splitting surface (beam splitter 53) and two means having reflecting surfaces (reflecting mirrors 54a and 54b) are used as the periodic wavelength selecting element. ) Can be used, and a member plate of uncoated calcium fluoride can be used as the mode selector 501.

For this reason, in the mode selector 501, the beam splitter 53 is hardly damaged, and a total reflection film is formed as a reflection film on the reflection mirrors 54a and 54b. Damage is less likely to occur as compared with the partial reflection film used in the above.

Accordingly, the mode selector 501 can stably narrow the oscillation laser beam for a long period of time without receiving any damage, and is less likely to cause damage to the optical system. It becomes easy to realize a banded fluorine laser device.

In particular, in a fluorine laser device which does not use such a mode selector, since the power is high, the wavelength is short, and most of the optical materials have a large absorption compared to the excimer laser device, the partial reflection When an etalon requiring a film was used, the partial reflection film was easily damaged.

Further, in the ultra-narrow band fluorine laser apparatus of the third embodiment, the fluorine exposure apparatus using the ultra-narrow band fluorine laser apparatus as an exposure light source is placed on an extension of the laser chamber in the ultra-narrow band fluorine laser apparatus in the longitudinal direction. This is effective in the case of arrangement.

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

As shown in the figure, in the ultra-narrow band fluorine laser apparatus 600, the resonator sandwiching the laser chamber 62 is composed of a total reflection mirror 61 and a mode selector 601. The mode selector 601 includes a beam splitter 63 and two reflecting mirrors 64a and 64b.

Here, the beam splitter 63 and the reflecting mirror 6
Assuming that the interval between the mode selector 601 and the beam splitter 63 and the reflecting mirror 64b is "d2", the FSR that is the cycle of the mode selector 601 is c / (2 (d1 + d).
2)).

In this embodiment, (d1 + d2) = 1
Since it is set to 2.3 mm, as a result, the third
FSR = 1.01 pm as in the embodiment.

The narrow band fluorine laser device 50 having the above-described structure is used.
0, when the laser gas in the laser chamber 62 is excited by discharge, the two lines L1 and L2
, Spontaneous emission light is generated, and the intensity of these lights is increased while moving in the resonator.

A part of the laser light entering the mode selector 601 from the laser chamber 62 is reflected by the beam splitter 63 and output as a laser light L60. Part of the laser light from the laser chamber 62 is
The light passes through the beam splitter 63 and is reflected by the reflecting mirror 64a.

A part of the laser light reflected by the reflecting mirror 64a passes through the beam splitter 63 and is again incident on the laser chamber 62, and at the same time, the beam splitter 63
To the reflecting mirror 64b. A part of the laser light reflected by the reflecting mirror 64b is reflected again by the beam splitter 63, and is directly reflected by the beam splitter 6b.
Pass 3 Hereinafter, such an operation is repeated.

That is, as described in the third embodiment, since 106.6 / 101.1 = 105.5, when tuning is performed with the line L1 having the wavelength λ1 = 157.6299 nm, the wavelength λ2 = 157. The line L2 of 0.5233 nm is suppressed, and the laser beam L60 of the wavelength λ1 = 157.6299 nm is extracted from the beam splitter 63.

As described above, according to the fourth embodiment, the same effects as those of the third embodiment can be expected. For example, the mode selector 601 is used as the periodic wavelength selection element, and the mode selector 6
As 01, it is possible to use an uncoated calcium fluoride member plate.

For this reason, the mode selector 601 can stably narrow the oscillation laser beam for a long time without being damaged. Therefore, damage to the optical system hardly occurs, and a practical ultra-narrow band fluorine laser device can be easily realized.

In the ultra-narrow band fluorine laser apparatus of the fourth embodiment, the fluorine exposure apparatus using the ultra-narrow band fluorine laser apparatus as an exposure light source is perpendicular to the longitudinal direction of the laser chamber in the ultra-narrow band fluorine laser apparatus. It is effective when it is arranged at

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

As shown in the figure, the ultra-narrow band fluorine laser device 700 is of the injection locking type, and comprises a seed laser 71 and an oscillator 72 as surrounded by a dotted line in the figure. .

In the seed laser 71, the laser chamber 7
The output mirror 73 and the total reflection mirror 74 arranged on both sides so as to sandwich the filter 5 constitute a stabilizing resonator. Note that no band-narrowing element is included between the stabilizing resonators. Accordingly, the laser beam L71 extracted from the seed laser 71 includes two lines L1 and L2, both of which are strong and weak, and the wavelength width of each line is not narrowed to about 1 pm.

This laser beam 71 is supplied to an etalon 7 which is a periodic wavelength selecting element disposed outside the seed laser 71.
Go through 6. The characteristics of the etalon 76 are the same as the etalon 16 described in the first embodiment, and the FSR is 3.0.
pm and finesse are 15.

Therefore, as described in the first embodiment, the wavelength of the laser beam L72 passing through the etalon 76 is narrowed to 0.2 pm, and is only one line. However, the energy of the laser light L72 is
It is reduced to about 1/10 compared to 71. The narrowed laser light L72 proceeds to the oscillator 72, which is the second fluorine laser device.

In the oscillator 72, an unstable resonator is constituted by a concave mirror 78 with a hole and a convex mirror 77 arranged so as to sandwich the laser chamber 79.

The laser beam L72 is injected as seed light into the cavity from the hole of the concave mirror 78 with holes. When the laser light L72 is discharged while passing through the laser chamber 79, the laser light L73 having only the increased power while keeping the wavelength width is extracted.

That is, the laser beam L72 injected into the resonator is reflected by the convex mirror 77, further reflected by the concave mirror 78 with holes, and then output as a laser beam L73.

Therefore, the laser beam L73 has a sufficient output with only one line having a wavelength width of about 0.2 pm. This is guided to the exposure machine main body as exposure light.

Here, the etalon 76 is the seed laser 71.
FIG. 8 shows the effect of being placed outside the
This will be described with reference to FIG.

The laser beams L71 to L73 shown in FIGS. 8B, 8C, and 8D correspond to the laser beams L71 to L73 shown in FIG. 7, respectively.

FIG. 8A shows the level of the excitation power in the laser chamber 75 of the seed laser 71, and shows that laser oscillation occurs when the laser oscillation threshold is exceeded.

Since the band narrowing element is not inserted in the seed laser 71, the internal loss is small. Therefore, FIG.
As shown in FIG. 8A, the laser beam L71 is generated during the period when the level of the pump power exceeds the threshold value 1 (see FIG. 8B). Here, the total pulse width is about 30 n
s.

When the laser beam L71 passes through the etalon 76 (becomes a laser beam L72), its peak power is reduced. Therefore, as shown in FIG. 8C, the laser beam L72 is compared with the laser beam L71. And energy is 1/10
become.

In this case, however, the output of the seed laser 71 may be reduced to some extent because the laser light L72 having reduced energy is not used for direct exposure but is used as seed light in the oscillator 72. .

That is, since the laser beam L73 actually used for exposure is generated by the oscillator 72, the laser beam L73 shown in FIG.
As shown in (d), sufficient energy is obtained as in the case of the laser beam L71.

On the other hand, if the seed laser 71 itself attempts to narrow the band until the wavelength width becomes 0.2 pm, it is necessary to insert an etalon or the like into the resonator. As a result, the threshold value of laser oscillation increases due to the insertion loss.

That is, since laser oscillation occurs only during the period exceeding the threshold value 2 shown in FIG. 8A, the pulse width becomes shorter than the pulse width in the case of the threshold value 1 as shown in FIG. 8E. (This is referred to as a laser beam L74).

When the laser beam L74 having such a reduced pulse width is made to enter the oscillator 72 as the seed beam, the laser beam L74 is hardly locked.
In the laser light extracted from the laser light, the wavelength width is widened to about 2 pm as in the case of the natural oscillation, and the laser light oscillates on two lines L1 and L2.

That is, when the oscillator 72 performs laser oscillation, the locking is performed only for a short time when the laser light L74 as the seed light passes. Note that rocking means that the spectrum of the laser light extracted from the second laser device is narrowed like the seed light.

On the other hand, in the fifth embodiment,
Since the non-narrowed laser light once extracted from the seed laser 71 is narrowed by the etalon 76, the power of the non-narrowed laser light is reduced, but the pulse duration is sufficiently long. It has become. Thereby, high locking efficiency is obtained in the oscillator 72.

In the ultra-narrow band fluorine laser device according to the fifth embodiment, an etalon is arranged between the oscillation stage and the amplification stage, that is, a so-called injection-locked type. The present invention is not limited to this, and can be applied to an oscillation amplifier or a fluorine laser device having an oscillation stage and an amplification stage in one discharge tube.

That is, in these laser devices,
An etalon may be arranged between the oscillation stage and the amplification stage.

As described above, according to the fifth embodiment, the oscillation stage (the seed laser 71) and the amplification stage (the oscillator 7)
2), the periodic wavelength selection element (etalon 76) is arranged between the oscillation stage and the amplification stage. It is possible to oscillate a laser beam which is not banded and has a sufficiently long pulse width. Therefore, energy can be extracted with high efficiency in the amplification stage.

That is, when the exposure light source of the fluorine exposure machine is constituted by the second fluorine laser device, the etalon which is a periodic wavelength selection element is arranged on the optical path outside the resonator of the first laser device. By doing so, from the etalon,
It is possible to generate seed light with a sufficiently long pulse width in one line and with a narrower wavelength width of about 0.2 pm. Further, by injecting the seed light into an oscillator, which is a second fluorine laser device, it is possible to increase the output of the laser light narrowed in one line.

[Brief description of the drawings]

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

FIG. 2 is an explanatory diagram for explaining a method of selecting an oscillation line.

FIG. 3 is a configuration diagram showing a configuration of a fluorine exposure machine using an ultra-narrow band fluorine laser device.

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

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

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

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

FIG. 8 is a pulse waveform diagram for explaining the operation of the ultra-narrow band fluorine laser device according to the fifth embodiment.

[Explanation of symbols]

16, 44, 76 Etalon 30 Reduction projection lens 100, 400, 500, 600, 700 Ultra-narrow band fluorine laser device 300 Fluorine exposure machine 501, 601 Mode selector

Claims (5)

[Claims] 1. An ultra-narrow band fluorine laser device for supplying an oscillation laser beam of a fluorine laser as a light source of an exposure device, wherein a transmittance or a reflectance is periodically changed according to a wavelength of incident light. A wavelength selecting element for narrowing an oscillation laser beam of the fluorine laser, wherein the wavelength selecting element has a first oscillation line having a higher light intensity among two oscillation lines having different wavelengths and light intensities in the fluorine laser. Is located at one selected wavelength in its own element, the center wavelength of the second oscillation line whose light intensity is weaker than that of the first oscillation line is two adjacent selected wavelengths in its own element. An ultra-narrow band fluorine laser device characterized by being formed of an optical element whose transmittance or reflectivity changes periodically so as to be positioned between them. 2. The wavelength selection element is formed such that the transmittance at the center wavelength of the second oscillation line is 0.64 times or less the transmittance at the center wavelength of the first oscillation line. 2. The ultra-narrow band fluorine laser device according to claim 1, wherein: 3. The ultra narrow band according to claim 1, wherein said wavelength selection element is a mode selector formed by a dividing means having a beam dividing surface and two reflecting means having a reflecting surface. Fluorine laser device. 4. An oscillating stage and an amplifying stage for oscillating laser light of the fluorine laser, wherein the wavelength selection element is disposed between an optical path between the oscillating stage and the amplifying stage. The ultra-narrow band fluorine laser device according to claim 1 or 2. 5. The apparatus according to claim 1, wherein a laser beam narrowed by said wavelength selection element is supplied to a fluorine exposure apparatus having a total refraction type reduction projection optical system having only a lens. 5. The ultra-narrow band fluorine laser device according to any one of 4.