JP2001007422A - Fluorine laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a fluorine laser device which can reduce a waiting time necessary for starting laser oscillation. SOLUTION: He is filled into a laser chamber 13 by opening a valve V1 until a desired pressure is attained, then the valve V1 is closed and a valve V2 is opened. A mixture gas of F2 and He from an F2/He cylinder 20B is filled into the laser chamber 13 through pouring tubes 14a and 14 until a desired pressure is attained. Further, the valve V1 once closed is opened and He from a He cylinder 20A is filled into the laser chamber 13. In this way, no fluorine F2 remains in the pouring tube 14. After these operations have been completed, the valve V1 is closed once again. Then discharge in the laser chamber 13 becomes possible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a fluorine laser device for supplying a laser beam of a fluorine laser as an exposure light source of an exposure device.

[0002]

2. Description of the Related Art The performance required of an exposure machine (stepper) for lithography includes resolution, alignment accuracy, and the like.
There are various things such as processing capacity and device reliability. Among them, the resolution R directly leading to the miniaturization of patterns 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 an i-line exposure machine and a KrF
It is called an exposure machine. 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.

An etalon or the like is known as a band-narrowing element for narrowing the wavelength width of an ArF excimer laser to about 0.6 pm.

Further, as a next-generation lithography exposure apparatus of the above-mentioned ArF exposure apparatus, the light source has a wavelength of about 157 nm.
A fluorine exposure machine using a fluorine laser has been studied.

In this fluorine laser, there are two strong oscillation lines (also called oscillation lines) having different wavelengths and light intensities, and the wavelengths are 157.6299 nm and 1 respectively.
It is said that the wavelength width of each oscillation line is 1 to 2 pm.

In order to use such a fluorine laser for exposure, a wavelength having a large intensity is generally 157.6299 nm.
(Hereinafter referred to as a strong line and the other as a weak line) is selectively used (hereinafter referred to as one-line). Thus, conventionally, one or two prisms are used for one line.

However, in the case of a fluorine exposure apparatus, it is difficult to apply a refraction type reduction projection optical system using only a lens which has been generally used in an exposure apparatus up to that time (ie, an exposure apparatus up to an ArF exposure apparatus), and chromatic aberration It is said that a strong catadioptric type (also called a catadioptric type) must be applied.

[0010] The reason is that in the case of a fluorine laser having 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. 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.

[0011] It should be noted that one of the fluorine lasers for a fluorine exposure machine is used.
Regarding the line conversion, for example, “SPIE 24th
International Symposium o
n Microlithography, Feb. 199
9. ", The experimental results are reported.

[0012]

By the way, the laser beam having a wavelength of 157 nm in a fluorine laser is hardly absorbed by oxygen molecules and hardly passes through the air. Therefore, conventionally, the optical path of the laser beam in the fluorine laser device has been covered with a closed container, and the closed container has been filled with nitrogen. That is, laser oscillation is performed after the air inside the closed container is replaced with nitrogen. However, since the specific gravity of nitrogen is 0.967, which is almost equal to that of air, replacement with air (nitrogen) is performed. Replacement) takes several tens of minutes (for example, 30 minutes to 1 hour), which requires a long preparation time (standby time) until laser oscillation.

This is because it is necessary to exhaust air to an oxygen concentration of about 10 ppm or less at which the absorption of laser light having a wavelength of 157 nm is negligible. Because it is not
This is because the air was pushed out with nitrogen injected later without drawing the air into a vacuum.

In order to make the inside of the sealed container vacuum, a structure having high rigidity is required, which increases the cost.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a fluorine laser device capable of shortening a waiting time until laser oscillation.

[0016]

In order to achieve the above object, a first aspect of the present invention is to provide a laser chamber for oscillating a laser beam of a fluorine laser, and use the laser beam for exposure by an exposure apparatus. In a fluorine laser device to be supplied as a light source, an airtight container that shields an optical path of laser light emitted from the laser chamber and the outside is provided, and the airtight container is filled with a gas containing helium as a main component. It is characterized by the following.

According to a second aspect of the present invention, in the first aspect, a helium-filled second container for injecting the helium into the laser chamber is further provided, and the helium in the second container is filled with the helium. It is characterized by being injected into an airtight container.

According to a third aspect of the present invention, in the first aspect, the airtight container is provided with an exhaust pipe for discharging gas inside the airtight container at a position lower than the optical path of the laser beam. Features.

According to a fourth aspect of the present invention, in any one of the first to third aspects of the present invention, the apparatus further comprises a band-narrowing element for narrowing a band of the laser light oscillated from the laser chamber. I do.

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

An etalon 16 for narrowing the band of the laser light is disposed between the optical path between the laser window 13b and the total reflection mirror 12.

The etalon 16 has a function as a band narrowing element, and narrows the band of the fluorine laser beam emitted from the laser window 13b.

The optical path from the laser window 13a to the output mirror 11 (portion indicated by a dotted line in the figure) and the optical path from the output mirror 11 to a predetermined distance are covered by a closed container 17a. The optical path up to the total reflection mirror 12 (portion indicated by a dotted line in the figure) is covered by a closed container 17b.

One end of each of exhaust pipes 18a, 18b for discharging air from the inside of each of the two closed containers 17a, 17b is connected to a position lower than the optical path in each of the two closed containers 17a, 17b. , 17b, one end of an injection tube 19a, 19b for injecting helium (He) into each closed container is connected to a position higher than the optical path.

The other end of each of these injection pipes 19a and 19b is connected to the other end of a T-shaped injection pipe 21 whose one end is connected to a He cylinder 20A filled with He. As is well known, He has a specific gravity of 0.138 with air, which is as light as about 1/7 of air.

When filling the laser chamber 13 with the laser gas while the valves V1 to V4 are closed, first, when the valve V1 is opened, the He cylinder 20A is opened.
After that, He is injected into the laser chamber 13 through the injection pipe 21 and the injection pipe 14.

Next, after He is injected until a desired volume, for example, a desired pressure is reached, the valve V1 is closed and the valve V2 is opened, and a mixed gas of F2 and He is supplied from the F2 / He cylinder 20B. Is injected into the laser chamber 13 through the injection tubes 14a and 14.

When the mixed gas is injected into the laser chamber 13 until a desired volume, for example, a desired pressure is reached, the valve V2 is closed. Here, once again, the closed valve V1 is opened, and the H
e is preferably injected, so that no fluorine (F2) remains in the injection tube 14. When this process is completed, the valve V1 is closed again.

In the above procedure, when the mixed gas of fluorine and He is filled in the laser chamber 13 until the gas reaches a predetermined pressure, discharge becomes possible in the laser chamber 13.

As described above, according to the first to fourth aspects of the present invention, He (specific gravity: 0.138) having a specific gravity of 1/7 that of air is used as an airtight container in which an optical path of laser light is formed. And the air in the airtight container is exhausted by an exhaust pipe provided at a position lower than the optical path, so that the time for replacing the air with He is reduced as in the conventional case. Can be significantly reduced as compared with the time for replacing with nitrogen.

For this reason, the time required for the laser oscillation to reach the standby state can be greatly reduced as compared with the conventional case.

Further, the He required for the replacement does not need to be provided with a new He cylinder, and He used in a He cylinder conventionally used as a laser gas may be used. Cost and space can be reduced.

In the fluorine laser device, since the band narrowing element is provided, the oscillation line of the fluorine laser can be narrowed to about 0.2 pm.

Further, since the inside of the airtight container is filled with He, even when the temperature of He is increased by the laser operation, the change in the refractive index of He is about 1 compared to that of nitrogen.
Since /8.5 is also small, the change in the refractive index due to the temperature change is about 1 / 8.5, and as a result, the fluctuation of the oscillation wavelength can be reduced.

Therefore, according to the first to fourth aspects of the present invention, it is possible to operate the laser at a stable wavelength for a long time without performing control for stabilizing the wavelength.

[0036]

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 the fluorine laser device 100.

As shown in FIG.
At 0, the output mirror 11 and the total reflection mirror 12 form a stable resonator. A laser chamber 13 is provided in the stable resonator. One end of an injection pipe 14 for injecting a laser gas is provided in the laser chamber 13,
Exhaust pipe 1 for exhausting gas from laser chamber 13
5 is connected to one end.

On both sides of the laser chamber 13 in the direction of the optical path, a laser formed of a material that transmits laser light so that gas inside the laser chamber 13 is not exhausted (not leaked) from a portion other than the exhaust pipe 15. Windows 13a, 13
b is adhered.

An etalon 16 for narrowing the band of the laser beam is disposed between the optical path between the laser window 13b and the total reflection mirror 12.

The etalon 16 has a function as a band narrowing element, and narrows the band of the fluorine laser beam emitted from the laser window 13b.

That is, the etalon 16 has a wavelength width of 1 to 2 pm and a wavelength λ 1 of 157.629 among two strong oscillation lines of a fluorine laser having different wavelengths and light intensities.
An oscillation line of 9 nm is selected, and the wavelength width of the oscillation line is set to be narrowed to about 0.2 pm.

The optical path of the laser light between the output mirror 11 and the total reflection mirror 12 and the optical path of the laser light up to a predetermined distance from the output mirror 11 are covered with an airtight sealed container.

That is, the optical path from the laser window 13a to the output mirror 11 (the portion indicated by the dotted line in the figure) and the optical path from the output mirror 11 to a predetermined distance are covered by the closed container 17a. An optical path from 13b to the total reflection mirror 12 (portion indicated by a dotted line in the figure) is covered by a closed container 17b.

One end of each of exhaust pipes 18a and 18b for discharging air from the inside of each of the sealed containers is connected to the lower side of the two sealed containers 17a and 17b. That is, the exhaust pipes 18a and 18b are connected to positions lower than the optical path in the closed containers 17a and 17b, respectively.

Further, one end of injection pipes 19a and 19b for injecting helium (He) into the respective sealed containers is connected to a position higher than the optical path in the two sealed containers 17a and 17b.

The other end of each of these injection pipes 19a and 19b is connected to the other end of a T-shaped injection pipe 21 whose one end is connected to a He cylinder 20A filled with He. As is well known, He has a specific gravity of 0.138 with air, which is as light as about 1/7 of air.

In this embodiment, the He cylinder 20A is filled with 100% He gas. Thus H
Although a gas having e of 100% is preferable, a slight amount of nitrogen may be contained. However, it is necessary to use a gas containing almost no oxygen or moisture.

The other end of the injection pipe 14 is connected to a middle part of the injection pipe 21, and the middle part of the injection pipe 14 is filled with a mixed gas of fluorine (F 2) and He / F 2. He cylinder 20B and L-shaped injection pipe 14a
Connected through.

The injection tubes 14, 14a and the injection tubes 19a, 19
b are provided with valves V1 to V4, respectively.

Next, the fluorine laser device 100 having the above-described configuration will be described.
The process up to the standby state where laser oscillation is possible will be described in detail with reference to FIG.

Here, the valves V1 to V
Numeral 4 is set to a closed state to shut off the flow of gas.

When filling the laser chamber 13 with the laser gas, first, when the valve V1 is opened, the He cylinder 20A is opened.
After that, He is injected into the laser chamber 13 through the injection pipe 21 and the injection pipe 14.

Next, after He is injected until a desired volume, for example, a desired pressure is reached, the valve V1 is closed and the valve V2 is opened, and the mixed gas flows from the F2 / He cylinder 20B into the injection pipe 14a, 14 through the laser chamber 13
Injected into.

When the mixed gas is injected into the laser chamber 13 until a desired volume, for example, a desired pressure is reached, the valve V2 is closed. Here, once again, the closed valve V1 is opened, and the H
e is preferably injected, so that no fluorine (F2) remains in the injection tube 14. When this process is completed, the valve V1 is closed again.

In the above procedure, when the mixed gas of fluorine and He is filled in the laser chamber 13 until a predetermined pressure is reached, discharge becomes possible in the laser chamber 13.

However, in this state, the power of the laser beam L1 becomes so low that it cannot be detected. That is,
At first, since air exists between the laser window 13a of the laser chamber 13 and the output mirror 11 and between the laser window 13b and the total reflection mirror 12, respectively, a laser having a wavelength of 157 nm is generated by oxygen contained therein. This is because light is strongly absorbed.

Therefore, in the present embodiment, as described above, the closed container 17 is enclosed so as to surround the output mirror 11 and the total reflection mirror 12.
a and 17b are attached, and the structure is such that air in these closed containers can be removed.

That is, by opening the valves V3 and V4, the He gas in the He cylinder 20A used as the laser gas is opened.
Is filled in the closed containers 17a and 17b via the injection pipe 21 and the injection pipes 19a and 19b. As a result, the time until the oxygen concentration becomes 10 ppm or less can be reduced to several minutes (for example, about 5 minutes).

The reason is that He has a specific gravity (0.138) which is 1/7 smaller than that of air.
He injected from 19b into the sealed containers 17a, 17b
Is gradually filled from above in these closed containers. At the same time, these closed containers 19a, 19b
This is because the air is exhausted from the exhaust pipes 18a and 18b attached to the lower part of the vehicle.

That is, since the exhaust pipes 18a and 18b are attached below the optical path of the laser beam,
a, 17b, at least the exhaust pipe 18
He is filled with He at the height of the connection portion with a and 18b, and the optical path of the laser beam is filled with He.

By the way, conventionally, the exhaust pipe 18
a, while discharging air from the injection pipes 19a, 1b.
From 9b, nitrogen replacement was performed by injecting nitrogen, so it took about one hour to sufficiently exhaust air (that is, until the oxygen concentration became 10 ppm or less).

The reason is that it is necessary to exhaust air to an oxygen concentration of about 10 ppm or less, at which the absorption of laser light having a wavelength of 157 nm is negligible.
A structure in which the inside of 7b can be evacuated (that is, a structure with high rigidity)
This is because the air was not pumped down to a vacuum, but was extruded with nitrogen to be injected later.

Conventionally, when nitrogen is injected, since the specific gravity of nitrogen and air is 0.967, the injected nitrogen and the air existing in the closed container from the beginning are initially used. Are mixed almost uniformly, and as a result, much time is required until the nitrogen concentration is sufficiently reduced.

It is needless to say that conventionally, it is necessary to prepare a nitrogen cylinder in addition to the F2 / He cylinder 20B and the He cylinder 20A.

In the fluorine laser device 100, since the oscillation line of 1 to 2 pm is further narrowed by the etalon 16, it is necessary to stabilize the narrowed wavelength. That is, when the etalon 16 is an air gap etalon, generally, the temperature of the gas filling the gap rises due to the heat of the laser beam, so that the optical path length changes and the selected wavelength in the etalon changes. This is because the refractive index of the gas in the gap has temperature dependence.

However, by using He, it is possible to suppress a wavelength change due to a temperature change (that is, to stabilize the wavelength). Next, the stabilization of the wavelength will be described in detail.

In general, for a gas having a refractive index of n, the value of (n−1) is proportional to the density. However, for an ideal gas, the density is inversely proportional to the temperature T. Equation 1 is established.

[0069]

(N-1) = k / T Then, the temperature change of (n-1) is expressed by Expression 2.

[0070]

D (n-1) / dT = -k / T ＝ 2 where T ＾ 2 means the square of T.

When the proportional coefficient k is deleted from the above equation 2 based on the above equation 1, the following equation 3 is obtained.

[0072]

## EQU3 ## d (n-1) / dT =-(n-1) / T As can be seen from Equation 3, the temperature change of the refractive index (the left side of Equation 3) is (n-1). Will be proportional to

On the other hand, the value of (n-1) is "0.000297" for nitrogen in the case of 0 degree Celsius and 1 atm.
It is known that e is “0.000035”. That is, since He has a value of (n-1) that is about 1 / 8.5 smaller than that of nitrogen, (n-
The change in the value of 1) is about 1 / 8.5.

As described above, in the fluorine laser apparatus 100, by filling the optical path of the laser beam with He, not only the time for purging air is greatly shortened compared to nitrogen replacement, but also the temperature change of the filled He. , The change in the selected wavelength of the etalon 16 can be reduced by almost one digit.

Moreover, in practice, the closed containers 17a, 17
The temperature rise of He filled in b is smaller than in He. It is also known that the thermal conductivity of He is about six times larger than that of nitrogen. As a result, the effect that He collides with the inner walls of the sealed containers 17a and 17b and is cooled is large.

As described above, according to the present embodiment,
He whose specific gravity is 1/7 that of air (specific gravity 0.13
8) is injected from the injection pipes 19a, 19b and the air is exhausted from the discharge pipes 18a, 18b, so that the time for replacing the air with He is replaced with the time for replacing the air with nitrogen as in the conventional case. Time can be significantly reduced.

For this reason, it is possible to shorten the time required for the laser oscillation to enter the standby state by one digit as compared with the conventional case.

Further, for the He required for the replacement, it is not necessary to newly provide a He cylinder, and He used in a He cylinder conventionally used as a laser gas may be used. Further, the cost and space can be reduced because a new He cylinder is not required.

This is because it relates to a fluorine laser, and is generally different from an excimer laser using Ne as a buffer gas.

In the fluorine laser device 100,
Since the etalon 16 is disposed in the resonator, the oscillation line of the fluorine laser can be narrowed to about 0.2 pm.

Further, even when the temperature of He is increased by the laser operation, He is compared with nitrogen by (n−
Since the value of 1) is as small as about 1 / 8.5, the change in the value of (n-1) due to a temperature change is about 1 / 8.5, and as a result, it is possible to reduce the fluctuation of the oscillation wavelength. it can.

Therefore, according to this embodiment, laser operation can be performed at a stable wavelength for a long time without special wavelength control.

[Second Embodiment] FIG. 2 is a configuration diagram showing a configuration of a fluorine exposure apparatus 300 according to a second embodiment.

In this embodiment, the fluorine exposure machine 300
Assumes that the narrow band laser light from the fluorine laser device shown in FIG. 1 is used as an exposure light source.

Now, as shown in FIG.
Reference numeral 0 roughly comprises an exposure machine main body 200 and the fluorine laser device 100 shown in FIG.

The exposure apparatus main body 200 is arranged on a grating 23 in a clean room, and the fluorine laser apparatus 100 is arranged on a floor 24 below the grating 23 (a floor generally called a floor).

The laser beam L1 of only a strong line with a wavelength width of about 0.2 pm taken out of the fluorine laser device 100
Is reflected by the mirror 25a, travels upward, passes through the opening 26 in the grating 23, and
Go inside.

The laser beam L1 is converged by the lens 27, travels through the glass rod 28 made of calcium fluoride, and further undergoes total reflection inside the glass rod 28, so that the beam intensity distribution from the glass rod 28 is uniform. The converted laser light L2 is emitted.

The laser beam L2 is reflected by the mirror 25b and passes through the beam shaper 29 composed of the lenses 29a and 29b, so that the beam cross section is expanded. Further, the laser beam L2 is reflected by the mirror 25c and passes through the condenser lens 30. The reticle 31 passes through and is irradiated on the reticle 31.

The laser beam L3 emitted from the reticle 31
Passes through a reduction projection lens 32 composed of a monochromatic lens of calcium fluoride and strikes a wafer 33. That is, the pattern in the reticle 31 is
2 is transferred onto the wafer 33. The wafer 33 is mounted on a stage 34.

A window 35 separates the fluorine laser device 100 and the exposure machine main body 200 from each other.
He filled in a does not proceed to the exposure apparatus main body 200. However, when the exposure apparatus main body 200 is also filled with He, the window 35 becomes unnecessary. In that case, He for filling the inside of the exposure apparatus main body 200 is used.
If a cylinder is separately provided, He may be guided from the He cylinder to the vicinity of the laser beam path of the fluorine laser device 100.

As described above, according to the second embodiment, the time for replacing air with He is greatly reduced as compared with the conventional time for replacing air with nitrogen. Since the laser light from the fluorine laser device 100 capable of being used is used as an exposure light source, the waiting time before performing the exposure processing is compared with the conventional case where the air is replaced with nitrogen as in the conventional case. As a result, it is possible to greatly reduce the time (for example, the time for one digit).

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a configuration of a fluorine laser device according to a first embodiment.

FIG. 2 is a configuration diagram showing a configuration of a fluorine exposure apparatus according to a second embodiment.

[Explanation of symbols]

 Reference Signs List 11 output mirror 12 total reflection mirror 13 laser chamber 14, 14a, 19a, 19b, 21 injection pipe 15, 18a, 18b exhaust pipe 16 etalon 17a, 17b sealed container 20A He cylinder 20B F2 / He cylinder V1, V2, V3, V4 valve

Claims (4)

[Claims] 1. A fluorine laser apparatus comprising: a laser chamber for oscillating laser light of a fluorine laser; and supplying the laser light as an exposure light source of an exposure apparatus. A fluorine laser device comprising an airtight container for shielding, wherein the inside of the airtight container is filled with a gas containing helium as a main component. 2. The apparatus of claim 2, further comprising a second container filled with helium for injecting the helium into the laser chamber, wherein the helium in the second container is injected into the hermetic container. The fluorine laser device according to claim 1, wherein: 3. The fluorine according to claim 1, wherein an exhaust pipe for discharging gas inside the airtight container is provided at a position lower than an optical path of the laser beam. Laser device. 4. The fluorine laser device according to claim 1, further comprising a band-narrowing element for narrowing a band of the laser light oscillated from the laser chamber.