JP2002151013A - Reference light source for fluorine laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reference light source for a fluorine laser device emitting light with the wavelength of 157 nm, which can be used as a projection aligner including a stepper, a scan exposure or the like in a practical sense. SOLUTION: This is the reference light source used to stabilize the wavelength of a laser beam with the wavelength of 157 nm oscillated from the fluorine laser device, wherein 0.005 to 0.040 μmol/cc of bromine atom that is a light emitting substance is sealed in a discharge container. Only bromine atom is sealed as the light emitting substance in the discharge container. Furthermore, 0.3 to 3.5 kPa (at room temperature) of at least one kind of rare gas selected from among argon(Ar), xenon(Xe), and krypton(Kr) is sealed as a buffer gas for a startup in the discharge container. Bromine atoms are also sealed in the form of hydrogen bromide(HBr) or ammonium bromide (NH4Br).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reference light source for a fluorine laser device, and more particularly, to an oscillation wavelength of a laser beam of a fluorine (molecule) laser device used as a light source of a projection exposure apparatus such as a stepper or scan exposure. The present invention relates to a wavelength stabilizing reference light source for preventing fluctuation during operation.

[0002]

2. Description of the Related Art As semiconductor circuits become finer and more highly integrated,
The projection exposure apparatus is required to improve the resolution. For this reason, the exposure light emitted from the light source has been shortened in wavelength, and as a light source for semiconductor lithography, an ArF excimer laser device that emits light having a wavelength shorter than the emission wavelength (365 nm) of a conventional mercury lamp has been used. Has been adopted. Although this ArF excimer laser device has an oscillation wavelength of 193 nm and a spectrum width of 0.5 pm, a fluorine laser device having a shorter oscillation wavelength and a narrower spectrum width has attracted attention as a next-generation light source. This fluorine (molecular) laser device has an oscillation wavelength of 157 nm (strictly, 157.6 nm).
299 nm) and a spectral width of 0.2 pm.

Since the oscillation wavelength of the ArF excimer laser device and the fluorine laser device fluctuate during the discharge operation, the laser device needs wavelength stabilization control for maintaining the oscillation wavelength at a predetermined value. Become. In order to perform this control, a means for measuring the oscillation wavelength from the laser device is required. Normally, by using a reference light source whose emission light is stable (the emission wavelength does not fluctuate) and comparing the emission light from this reference light source with the light to be detected (laser light), the wavelength of the light to be detected is shifted. Is used.

FIG. 8 shows a wavelength measuring device of an ArF excimer laser device as a conventional example. Reference light, which is a reference light source, is emitted. This reference light enters the beam splitter via the shutter A, is reflected there, and enters the linear sensor (CCD) via the etalon and the condenser lens. An interference fringe (fringe) is formed on the linear sensor, and the line width of the reference light is recognized from the position data of the fringe. Since the wavelength of the reference light source hardly fluctuates, if it is measured only once, or if it is previously recognized by a computer or the like in the apparatus, it is considered that the measurement after the start of the laser operation is unnecessary. However, since the refractive index of the etalon fluctuates in air and the mirror position slightly fluctuates, the position of the interference fringes on the linear sensor also slightly fluctuates as the laser operation elapses. For this reason, it is necessary to measure the reference light source periodically or frequently, and the state of the etalon or the mirror at that time is grasped based on the measurement value from the reference light source.

Next, the shutter A is closed, and the light to be measured (laser light) having a wavelength of about 193.4 nm from the ArF excimer laser is guided through the entrance aperture, the shutter B, and the reflecting mirror, and further to the concave reflecting mirror and the etalon. . Then, the light to be measured, which is multiply interfered by the etalon, is irradiated on a linear sensor (CCD) via a condenser lens. On this linear sensor, a fringe is formed as in the case of the reference light source, and the wavelength of the light to be measured is calculated from position data formed on the CCD as in the case of the reference light source. In other words, even if the state of the etalon or the mirror has changed, the position data formed by the reference light source in that state and the position data formed by the laser light of the ArF laser device are compared to determine the oscillation wavelength of the laser light. The displacement can be measured.

Although the above-mentioned conventional example has been described for the case of an ArF excimer laser device, the same applies to a fluorine laser device, and control using a reference light source is required to stabilize the wavelength of the oscillating laser light. In particular, for a fluorine laser device, the oscillation wavelength is a vacuum ultraviolet light shorter than that of an ArF excimer laser, and the wavelength slightly changes due to a change in the refractive index caused by density fluctuation due to the temperature of a gas medium passing therethrough. That they may be observed,
Since the line width is small and the tolerance for deviation of the oscillation wavelength is small, a reference light source that emits light having a wavelength very close to the oscillation wavelength is required.

Here, the reference light source of the fluorine laser device is described in, for example, Japanese Patent Application Laid-Open No. 2000-249600. In this document, carbon (C), iron (Fe), sodium (Na) ), Fluorine (F), magnesium (Mg), aluminum (A
l), argon (Ar), calcium (Ca), scandium (Sc), chromium (Cr), manganese (Mn),
Nickel (Ni), copper (Cu), germanium (G
e), arsenic (As), bromine (Br), and platinum (Pt) are disclosed.

[0008] However, the disclosure of this document discloses that the wavelength 1
It is merely a list of atoms that have a possibility of emitting light even at a small wavelength of 57 nm, and does not specify a practically effective light emitting atom in consideration of the light emission intensity. In other words, even if a reference light source is made by selecting the atoms disclosed herein as a light emitting substance, the light emission intensity at a wavelength of 157 nm is practically too low, or the relative intensity with another wavelength is low. However, it is not industrially applicable to a projection exposure apparatus (stepper or scan exposure) which is a semiconductor manufacturing apparatus.

[0009]

An object to be solved by the present invention is a reference light source for a fluorine laser device which emits light having a wavelength of 157 nm, which is practically used as a light source for a projection exposure apparatus such as a stepper or scan exposure. It is to provide a reference light source that can be used in a technical sense.

[0010]

In order to solve the above-mentioned problems, a wavelength 1 oscillated from the fluorine laser device of the present invention is used.
It is a reference light source used for stabilizing the wavelength of a laser beam of 57 nm, and a bromine atom, which is a light-emitting substance, is placed in a discharge vessel in an amount of 0.
005 μmol / cc to 0.040 μmol / cc. As described above, in the present invention, when a fluorine laser device is used as a light source for an exposure apparatus for manufacturing a semiconductor, it is optimal to use bromine as a light-emitting atom in the sense that it is sufficiently effective from a practical viewpoint. And the amount of bromine enclosed is specified. In particular, the emission spectrum of the bromine atom is 157.
6387 nm, which is the oscillation wavelength of the fluorine laser.
It is extremely close to 57.6299 nm, and bromine atoms have a higher light intensity at a wavelength closer to the oscillation wavelength of this fluorine laser than other atoms, and are effective in a practical sense.

Further, according to claim 2, the discharge vessel includes:
It is characterized in that only a bromine atom is enclosed as a luminescent substance. There are many lamps in which a bromine atom is sealed, but these are intended for a halogen cycle, and are not positively sealed as a main luminescent material. For example, in some cases, bromine is sealed with an incandescent lamp or the like. This is a lamp that uses light emission from a tungsten filament to prevent tungsten from evaporating in a halogen (bromine) cycle to achieve a long life. is there. In some cases, bromine is sealed with a discharge lamp such as a mercury lamp. However, this is a lamp that uses light emission of mercury atoms, and bromine does not function as a light-emitting substance. The invention according to claim 2 clarifies such a difference from the conventional lamp, and is characterized in that only bromine is used as a luminescent material.

Further, according to claim 3, the discharge vessel includes:
Argon (Ar), Xenon (Xe), Krypton (K
r) at least one rare gas selected from the group consisting of 0.3 k
It is characterized in that it is sealed as a buffer gas for starting at Pa to 3.5 kPa (at room temperature). As described above, the reference light source for the fluorine laser device of the present invention encloses a rare gas such as argon as a starting buffer gas in addition to bromine as a light emitting substance. The purpose of the rare gas is to make it easy to start lighting like a general discharge lamp. However, the present inventors have assiduously studied and found that encapsulating this rare gas has an effect on the emission of bromine atoms depending on the encapsulation amount, in addition to the effect of starting properties.

Further, in claim 4, the bromine atom is hydrogen bromide (HBr), ammonium bromide (NH ₄ Br),
Ethylene bromide (CH ₂ Br ₂ ), methyl bromide (CH ₃ B
It is characterized by being enclosed in the form of r).

[0014]

FIG. 1 shows a reference light source for controlling the oscillation laser light of a fluorine laser device according to the present invention. The discharge vessel 1 includes a main body case 2 and a window member 3. The main body case 2 has a substantially cylindrical shape and is made of, for example, borosilicate glass. The window member 3 is for extracting vacuum ultraviolet light generated inside the container, and is attached so that a substantially disk-shaped member made of synthetic quartz glass closes one end of the main body case 2. Here, one end 2a of the main body case 2 is connected to a step joint of glass whose thermal expansion coefficient is slightly changed to facilitate adhesion to the window member 3. In addition,
The main body case 2 can be formed of synthetic quartz glass. In this case, since the main body case 2 is made of the same material as the window member 3, the hermetic sealing structure can be formed by directly bonding without employing a step joint structure. . Further, the window member 3 can employ magnesium fluoride other than the synthetic quartz glass. To give a numerical example, the discharge vessel is 150m long
m, outer diameter 20 mm.

Two generally ring-shaped electrodes 4 (4a, 4b) are wound around the outer surface of the main body case 2, and connection lines from the electrodes 4 (4a, 4b) are connected to an AC power supply. The electrode 4 is made of, for example, copper or aluminum, and is wound in such a manner that a thin-film electrode is in close contact with the main body case 2. To give a numerical example, the width of the electrode 4 is 10 mm, the distance between the electrode 4 a and the end of the discharge vessel is 20 mm, and the distance between the electrode 4 b and the window member 3 is 50 mm.

The discharge vessel 1 is filled with a bromine atom as a light-emitting component and xenon as a buffer gas for starting lighting. As will be described later, the bromine atom as a light emitting component is 0.1%.
005 μmol / cc to 0.040 μmol / cc, more preferably 0.005 μmol / cc to 0.0
Encapsulated in the range of 15 μmol / cc. On the other hand, as the rare gas, at least one kind of gas selected from xenon, argon, and krypton is adopted, and 0.3 kPa to 3.5 kP is used.
a (at room temperature), more preferably 0.67
It is sealed in the range of kPa to 2.67 kPa (normal temperature).
Here, the discharge vessel 1 does not require anything other than bromine atoms as a luminescent substance. For example, a common mercury lamp is filled with mercury, and a metal halide lamp is filled with various metal atoms.However, since this lamp requires light emission by bromine atoms, such other luminescent materials are required. It does not mean that.

Next, the amount of bromine atoms and the wavelength of 157 nm
The relationship with the radiation intensity will be described. We have:
It has been found that the intensity of vacuum ultraviolet light having a wavelength of 157 nm decreases as the amount of bromine atoms increases. It is considered that the cause is that self-absorption occurs with an increase in the concentration of bromine atoms, thereby reducing the intensity of vacuum ultraviolet light.
If the amount of bromine atoms enclosed, that is, the concentration is too small, the absolute intensity of the luminescent substance as a seed is small, so that the emission intensity of vacuum ultraviolet light similarly decreases. That is, it was found that there is an optimum range for the amount of bromine atoms enclosed.

It has also been found that the pressure of the noble gas (argon gas) is too low or too high, like bromine atoms, to affect the emission intensity of vacuum ultraviolet light. The electrons supplied from the argon gas to the discharge space excite the bromine atoms and emit light.However, if the amount of the filled argon gas is too low, the electron density in the discharge space becomes low, and the excitation of the bromine atoms occurs with sufficient frequency. Probably because it does not happen. On the other hand, if it is too high, it is considered that the excitation of the argon atoms by the electrons in the discharge space increases, and on the other hand, the frequency of the excitation of the bromine atoms decreases.

An experiment on this point will be described. 0.4 kPa (normal temperature) of argon is charged as a rare gas, and the amount of bromine atoms charged in this case is 0.005 μmol / cc,
0.015 μmol / cc, 0.025 μmol / cc,
0.040 μmol / cc, 0.050 μmol / cc,
The emission intensity of vacuum ultraviolet light having a wavelength of 157 nm was measured for each of the samples while changing the concentration to 0.100 μmol / cc. The measured value was measured as a relative value with the intensity when the molar amount of bromine atoms was 0.005 μmol / cc as 100.

Further, in order to consider the relationship with the amount of rare gas (argon) charged, the amount of argon charged is set to 0 kPa,
0.13 kPa, 0.67 kPa, 1.33 kPa,
2.00 kPa, 2.67 kPa, 3.33 kPa,
4.00 kPa and 6.67 kPa, and the bromine atom encapsulation amount for each of them was also 0.005 μmol / cc, 0.015 μmol / cc, 0.025 μmol / cc, 0.040 μmol / cc. cc, 0.050 μmol /
cc, 0.100 μmol / cc, and the wavelength 15
The emission intensity of 7 nm vacuum ultraviolet light was measured. All the measured values are relative values, with the molar amount of bromine atoms being 0.005 μmol / cc, and the intensity at the time of an argon sealing pressure of 0.4 kPa being 100.

The results are shown in FIG. 2 as numerical values, and based on the numerical results, FIG. 3 is a graph showing the relationship between bromine atoms and the emission intensity of vacuum ultraviolet light.
The graph shows the relationship between the argon filling pressure and the radiation hardness of vacuum ultraviolet light. From the results shown in FIG. 3, as the amount of bromine atoms increases, the emission intensity of the vacuum ultraviolet light decreases, and when the amount of bromine atoms increases to 0.040 μmol / cc or more, the relative value generally falls below 50. I have. That is, 0.0
In the range of 0.05 to 0.040 μmol / cc, a sufficient intensity of vacuum ultraviolet light can be obtained,
It can be seen that high strength with a relative value of 70 or more can be obtained in the range of 15 μmol / cc. In this experiment, the amount of bromine atoms was set to 0.005 μmol / cc as the minimum value. This is because when the amount is less than this, sufficient emission cannot be performed because the absolute amount of the luminescent material is small. The present inventors have confirmed that if the relative value is 50 or more, it can be sufficiently used as a reference light source for the oscillation laser light of the fluorine laser device. Here, the emission spectrum of the bromine atom is 15
7.6387 nm, which is very close to the fluorine laser oscillation wavelength of 157.6299 nm, and bromine atoms have a higher light intensity at a wavelength closer to the fluorine laser oscillation wavelength than other atoms and are practically used. It is found to be effective in a technical sense.

From the results shown in FIGS. 2 and 4, if the argon filling pressure is 0.4 to 3.33 kPa, the relative value is 50.
A high vacuum ultraviolet intensity as described above can be obtained.
It can be seen that the radiation intensity of the vacuum ultraviolet light as high as 70 was obtained when the pressure was 67 to 2.67 kPa.

Here, the bromine atom is hydrogen bromide (HB
r), ammonium bromide (NH ₄ Br), ethylene bromide (CH ₂ Br ₂ ), and methyl bromide (CH ₃ Br). This is because encapsulating bromine alone has problems such as toxicity and corrosiveness to metal piping of manufacturing equipment, and encapsulating in these forms alleviates such problems. Further, since hydrogen bromide (HBr) and ammonium bromide (NH ₄ Br) do not contain carbon, when they are decomposed by discharge in the discharge space, the light extraction efficiency of the discharge vessel and the light extraction window does not decrease due to the adhesion of carbon. It also has the advantage.

Next, the overall structure of a fluorine laser device using such a reference light source will be described with reference to FIG. The fluorine laser device includes a laser chamber 10, a narrow-band module 20, a waveform detection optical system 30, and a control circuit 40 as main components, and emits light having a wavelength of 157 nm to function as a light source for a projection exposure apparatus. Windows are provided at both ends of the laser chamber 10, and a fluorine gas and a buffer gas such as neon are sealed in the chamber. A pair of discharge electrodes facing each other are provided inside the laser chamber 10 at a predetermined interval, and when a high-voltage pulse is applied from a high-voltage generator (not shown), a discharge is generated between the discharge electrodes to generate a laser gas. A certain fluorine gas is excited. Although the laser light is generated by this excitation, the narrowing module 20 is provided with a prism or a diffraction grating for narrowing the spectrum width of the laser light. An output mirror is provided outside the other window of the laser chamber 10 and a beam splitter 31 is provided ahead of the output mirror, from which a part of detection light for calibrating the laser light is extracted. Waveform detection optical system 30 receiving this detection light
Has a structure shown in FIG. 8, that is, a signal from the linear sensor in FIG.

On the other hand, the light emitted from the reference light source 50 having a bromine atom as a light-emitting substance similarly enters the waveform detection optical system 30. This description can be similarly applied only by applying a lamp containing bromine to the reference light source in FIG. Then, the radiation light from the reference light source 50 is also transmitted to the control circuit 40 as a signal from the linear sensor. As an actual operation, the laser light from the fluorine laser device is periodically measured, and before and after the measurement, the light emitted from the reference light source 50 is measured. The reason for this is as described above, because the state of the optical components such as the etalon and the mirror included in the waveform detection circuit 30 is slightly changed. Each time, both lights are detected and the laser light of the fluorine laser device in that state is detected. Is measured with reference to the wavelength of the reference light source. If there is a deviation in the oscillation spectrum of the laser light from the fluorine laser device, a signal is sent from the control circuit 40 to the narrow band module 20, and the optimization is performed by moving the diffraction grating or the like.

FIG. 6 shows the spectrum of the reference light source of the present invention. The vertical axis indicates the relative intensity of light of each wavelength among the total radiation light radiated from this reference light source. Wavelength 15 from the figure
It can be seen that a high radiation intensity is shown at 7.6387 nm (in the figure, there is a wavelength showing a higher intensity near 163 nm, but 157.637 nm also has a subsequent peak). The reference light source was bromine 0.025 μmol / cc, and argon was used as a rare gas.
The lamp is filled with 60 kPa.

The reference light source of the present invention is not limited to the structure shown in FIG. 1, and the structures shown in FIGS. 7A to 7C can be applied. In FIG. 7, the AC power supply 5 and the discharge plasma 6 are omitted.

[0028]

As described above, according to the reference light source of the present invention, bromine atoms as a luminescent substance are contained in a discharge vessel in an amount of 0.005 μmol.
/ Cc to 0.040 μmol / cc, it is sufficiently effective from a practical viewpoint when the fluorine laser device is used as a light source for an exposure apparatus for manufacturing a semiconductor. Further, at least one rare gas selected from argon (Ar), xenon (Xe), and krypton (Kr) is used as a starting buffer gas sealed together with bromine atoms at a pressure of 0.3 kPa to 3.5 kPa (at room temperature). ) By encapsulating, not only the startability can be improved but also the light intensity can be increased, so that a more practical reference light source for a fluorine laser device can be provided.

[Brief description of the drawings]

FIG. 1 shows the entire structure of a reference light source for a fluorine laser device of the present invention.

FIG. 2 shows the effect of a reference light source for a fluorine laser device of the present invention.

FIG. 3 shows the relationship between the atomic weight of bromine and the radiation intensity of the reference light source of the present invention.

FIG. 4 shows the relationship between the argon filling pressure and the radiation intensity of the reference light source of the present invention.

FIG. 5 shows an overall structure of a fluorine laser device and a reference light source of the present invention.

FIG. 6 shows an example of a spectral distribution by the reference light source of the present invention.

FIG. 7 shows another structure of the reference light source of the present invention.

FIG. 8 shows a schematic configuration of a wavelength measuring device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Discharge container 2 Body casing 3 Window member 4 Electrode 5 AC power supply 6 Discharge plasma

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H097 CA13 LA10 5F046 BA03 CA03 CA08 DA01 5F071 AA04 JJ10 5F072 AA04 JJ20 KK15 KK30 YY09

Claims (4)

[Claims] 1. A wavelength 15 emitted from a fluorine laser device.
A reference light source used for stabilizing the wavelength of a 7.6299 nm laser beam.
A reference light source for a fluorine laser device, wherein the reference light source is encapsulated in an amount of μmol / cc to 0.040 μmol / cc. 2. The reference light source for a fluorine laser device according to claim 1, wherein only the bromine atom is sealed as a luminescent substance in said discharge vessel. 3. The discharge vessel contains at least one rare gas selected from argon (Ar), xenon (Xe), and krypton (Kr) as a starting buffer gas.
3. The reference light source for a fluorine laser device according to claim 1, wherein 0.3 kPa to 3.5 kPa (pressure at normal temperature) is sealed. 4. The method according to claim 1, wherein the bromine atom is encapsulated in the form of hydrogen bromide (HBr), ammonium bromide (NH ₄ Br), ethylene bromide (CH ₂ Br ₂ ), or methyl bromide (CH ₃ Br). The reference light source for a fluorine laser device according to claim 1, wherein