JP4162730B2 - Continuous emission excimer laser oscillation apparatus and oscillation method, and laser chamber - Google Patents

Description

[0001]
[Technical field to which the invention belongs]
The present invention is a continuous emission excimer laser oscillation apparatus and an oscillation method capable of continuous emission, a laser chamber in parallel beauty.
[0002]
[Prior art]
Excimer lasers are attracting attention as the only high-power lasers that oscillate in the ultraviolet region, and are expected to be applied in the electronics, chemical, and energy industries.
[0003]
Specifically, it is used for processing, chemical reaction, etc. of metals, resins, glass, ceramics, semiconductors and the like.
[0004]
An apparatus that generates excimer laser light is known as an excimer laser oscillation apparatus. A laser gas such as Ar, Kr, Ne, or F ₂ filled in the manifold is excited by electron beam irradiation or discharge. Then, the excited F atoms are combined with inactive KrF ^* and ArF ^* atoms in the ground state to generate molecules that exist only in the excited state. This molecule is called an excimer. Since excimer is unstable, it immediately emits ultraviolet light and falls to the ground state. This is called bond-free transition or spontaneous light emission. Excimer laser oscillation is the one that uses this excited molecule to amplify it as phase-matched light in an optical resonator composed of a pair of reflectors and extract it as laser light. Device.
[0005]
By the way, conventionally, it is considered that excimer laser oscillators have a very short excimer life of a laser medium, so that continuous excitation is impossible, and a pulse current (about 10 nsec) with a fast rise is intermittently applied. Pulse excitation is applied.
[0006]
Therefore, the electrode in the conventional excimer laser oscillation device has a life of about half a year.
[0007]
In addition, when a chemically amplified resist is exposed using a pulsed oscillation type continuous-emitting excimer laser oscillation apparatus having a repetition rate of 100 Hz to 1 kHz in a semiconductor processing process, the lifetime of the lens material and the non-reflective multilayer film on the surface thereof is reduced. There is a problem that it is extremely short.
[0008]
This point will be described in detail below.
[0009]
The sensitivity of the chemically amplified resist is about 20 mJ / cm ² . Therefore, an exposure of 0.2 sec is sufficient for 0.1 W / cm ² light. In the case of 1 W / cm ² light, it is 0.02 sec. Considering a considerable loss in the optical system, a light output of about 10 W is sufficient.
[0010]
However, in the current pulse emission (1 kHz), pulse light of about 10 nsec is generated about 1,000 times per second. If the exposure time is 0.2 sec, 20 mJ / cm ^{2 is} required for 200 pulses. If the energy drops to 1/100 due to loss due to the optical system, the emission intensity I ₀ of each pulse is as follows in consideration of the pulse duty as shown in FIG.
[0011]
I ₀ (watt) x 10 (nsec) x 2 x 10 ² (pulse) x 10 ^-2 (efficiency)
= 2 × 10 ^-2 (Joul)
I ₀ = 2 × 10 ⁻² / 10 ⁻⁸ × 2
= 1 × 10 ⁶ (watt)
Assuming that a constant optical output is obtained for 10 nsec, the pulse light becomes 1 MW. Actually, it is as shown in FIG.
[0012]
Since the pulse waveform is actually as shown in FIG. 3, the intensity of the optical pulse is a peak power of 2 to 3 MW. Since light having a short wavelength of several MW is incident intermittently, the durability of the lens material and the non-reflective multilayer film on the surface thereof becomes extremely severe.
[0013]
Further, in the era of excimer laser lithography, exposure at the time of step and repeat is not performed all at once, but scanning exposure by scanning of a mirror or a lens. With pulse light of about 1000 shots per second and 0.2 second exposure, only about 200 pulses can be used in one exposure. Thus, for example, when trying to uniformly irradiate an exposure of 25 × 35 mm ² area, the relative relationship between mirror or lens scanning and pulsed light must be controlled very strictly, and an extremely complicated control system is applied to the optical element. Required. At present, the output of the pulsed light fluctuates by about 10%. Therefore, there is a problem that the control system of the mirror or the lens scan has to be extremely complicated, and the excimer laser exposure apparatus is also complicated and expensive.
[0014]
Furthermore, the conventional excimer laser oscillation device has the following problems. That is, among excimer laser light, KrF laser and ArF laser use highly reactive fluorine gas as the laser gas, so that the concentration of fluorine in the laser chamber for containing the laser gas and giving discharge energy to the gas is high. Decrease. Therefore, it is controlled to increase the supply voltage to the laser chamber so that a predetermined output can be obtained. If it is difficult to obtain an output even with such control, the oscillation is stopped once and the fluorine gas is Replenish. Furthermore, if oscillation continues, even if fluorine replenishment is performed, a predetermined laser output cannot be obtained. If this happens, the laser chamber must be replaced.
[0015]
In addition, in the case of an excimer laser light emitting device that emits light by a pulse voltage and emits light for about several tens of ns, since the light emission time is too short, the half-value width of the emission spectrum of the output light is as wide as about 300 pm. For this reason, a wavelength half-value width of 1 pm or less is obtained for the first time by monochromatization using a narrowband module such as grating.
[0016]
In the current technology, it is necessary to oscillate while increasing the applied voltage by replenishing fluorine gas every predetermined period. In other words, the fluorine gas decreases with time due to reaction with the inner surface of the chamber. Therefore, in terms of the lifetime of the laser chamber, the lifetime of the chamber is important for improving the manufacturing throughput of the processed article, particularly when the laser is used for a long period of time for processing the article. It is a factor.
[0017]
In addition, it is now possible to obtain a half-value width of 1 pm or less by monochromatization using a narrowing band module such as grating. On the other hand, emission of output light by narrowing band using grating or the like. The strength has decreased, which has been a major impediment to improving the manufacturing throughput of processed articles.
[0018]
[Problems to be solved by the invention]
The present invention is a continuous light emitting excimer that can reduce the load on the lens material and its surface, can simplify the mirror or lens scanning control system, and has a sufficiently long excimer laser life to withstand mass production use. and to provide a laser oscillating device and the oscillating how.
[0019]
It is another object of the present invention to provide an excimer laser oscillating device and an oscillating method capable of realizing a narrow band while increasing the intensity of output light.
[0020]
Reference invention, without using a narrowing module can achieve a narrow spectral wavelength width, and to provide an excimer laser exposure apparatus miniaturization and simplification of the device is achieved.
[0021]
[Means for Solving the Problems]
The continuous emission excimer laser oscillation device of the present invention comprises at least one inert gas selected from Kr, Ar, Ne and F _2. A laser chamber for storing a laser gas composed of a mixed gas with a gas, wherein the reflectance of light with a desired wavelength of 248 nm, 193 nm, and 157 nm on the inner surface is reduced to 50% or less, and the outermost surface of the inner surface is An optical resonator comprising a laser chamber composed of a compound and a pair of reflecting mirrors sandwiched between the laser chambers, wherein the reflectance of the reflecting mirror on the output side is 90% or more, and It has a microwave introduction means for continuously exciting the laser gas in the laser chamber .
[0022]
In the continuous emission excimer laser oscillation method of the present invention, the inner surface has a reflectance with respect to light of a desired wavelength of 248 nm, 193 nm, and 157 nm of 50% or less, and the outermost surface of the inner surface is made of fluoride. A laser gas composed of a mixed gas of at least one inert gas selected from Kr, Ar, and Ne and F ₂ gas is continuously supplied into the chamber,
Continuously exciting the laser gas by introducing microwaves into the laser chamber;
Reflectivity of the output side of the reflector, characterized in that to continuous light emission by resonating the light emitted from the laser gas raised該励 by a pair of reflecting mirrors is 90% or more.
[0025]
[Operation and embodiment]
The operation of the present invention will be described below together with the knowledge and embodiments obtained in making the invention.
[0026]
In the present invention, since continuous light emission is performed, it is not necessary to control the relative relationship between the scan of the mirror or lens and the pulse described above, and the control of the optical system becomes extremely simple.
[0027]
Further, as analyzed by the present inventors, 0.2 sec exposure is sufficient for 0.1 W / cm ² light, and 0.02 sec for 1 W / cm ² light. Considering the loss of light in the optical system , an output of about 10 W is sufficient, and the life of the lens material and its surface can be extended.
Further, the following actions are achieved.
[0028]
First, damage to optical materials such as glass is reduced. A normal excimer laser such as KrF or ArF emits a short pulse of 10 to 20 nsec, whereas the pulse repetition frequency is only about 1000 Hz. Therefore, the light intensity at the peak of this pulse is 10,000 times or more that of continuous light emission at the same intensity even if the problem of the efficiency of the optical system is excluded. It is known that the main cause of material damage that occurs in the excimer region is two-photon absorption, and the light damage in the current excimer laser, which is proportional to the square of the light peak intensity, is estimated to be less than in continuous light emission. Even 10 ⁸ times more severe. The durability of the glass material is a problem in the ArF region for the above reasons. Therefore, the realization of the continuous light emission light source solves the material problems in the ultraviolet region including ArF at a stretch.
[0029]
Second, it is easy to suppress the occurrence of speckle, a phenomenon peculiar to narrow-band light. In the case of pulsed light emission, in order to effectively erase speckles that are random interference fringes, it is necessary to synchronize the light emission timing of each pulse with known speckle removing means with high accuracy. On the other hand, if it is continuous oscillation, the speckle can be easily removed by a known means such as, for example, a rotating diffusion plate, without requiring any special synchronizing means. Therefore, the configuration of the optical system can be simplified, and the cost can be reduced.
[0030]
Third, exposure amount control is easy. When performing discrete exposure such as pulsed light emission, the minimum unit for controlling the exposure amount basically depends on the number of pulses, although it depends on the controllability of the exposure amount of one pulse. When the exposure is performed with 100 pulses in total, the next unit is 99 pulses or 101 pulses, and the control accuracy is ± 1%. Of course, various means have been proposed for the control of the last pulse, but for controllability or control there is no resolution due to such discreteness, and finer exposure control is desirable. As the line width becomes narrower, the continuous light source has a great effect in spite of demanding strict exposure control.
[0031]
By the way, as described above, conventionally, in the excimer laser, the energy level in the excimer state has a short lifetime, so it is impossible to keep atoms at the excitation level for a certain period of time, and continuous excitation is impossible. Therefore, pulse excitation with a fast rise was unavoidable.
[0032]
In the present invention, the inner surface of the laser chamber for housing the laser gas is a non-reflecting surface for light having a desired wavelength such as 248 nm, 193 nm, and 157 nm.
[0033]
The reason why the inner surface of the laser chamber is made a non-reflective surface is to prevent spontaneously emitted light from returning to the gas excited by being reflected by the inner surface, thereby causing KrF ^* or ArF ^* to transition from the excited state to the ground state. Because.
[0034]
Here, the term “non-reflection” refers to not only 100% transmission or absorption but also a certain degree of reflectance. The reflectance is preferably 50% or less, more preferably 20% or less, and further preferably 5% or less. What is necessary is just to select suitably so that a uniform laser beam can be obtained continuously with a specific apparatus.
[0035]
In addition, the inner surface of the laser chamber is made of fluoride to prevent the F ₂ from decreasing due to reaction with the laser chamber. In particular, the surface of a stainless steel that is stable against F ₂ is formed with an FeF ₂ layer, the surface of which is plated with nickel and further formed with an NiF ₂ layer, or aluminum. It is composed of any one of AlF ₃ and MgF ₂ layers formed on an alloy.
[0036]
In the present invention, the reflectance of the output-side reflecting mirror is 90% or more.
[0037]
The current resonator configuration is 100% reflection on one side, while the output side reflection is about 10%.
[0038]
By the way, the laser gas composition of the conventional KrF ^* excimer is, for example, as follows.
Kr / Ne / F ₂ = 0. Several%: 98%: 0. number%
[0039]
The concentration of F ₂ is as low as 1% or less. This is because if F ₂ is increased too much, electrons are attracted to F and become negative ions, and the discharge is not stable. On the other hand, the pressure is 3 to 4 atmospheres. The reason for this pressure is to make as much KrF ^* as possible to compensate for the reduced F ₂ concentration.
[0040]
In the case of continuous light emission, an output of about 10 W is sufficient. Infer an allowable gain α ₂ .
[0041]
-Unless the laser is operated at an intensity of about the laser beam intensity saturation intensity Is in the resonator, the upper level excimer is almost extinguished by collision. The saturation intensity is an intensity at which the gain g is ½ of the small signal gain g0. In the case of the KrF excimer, the saturation intensity is obtained as follows (“excimer laser development and applied technology / example” (supervised by Shuntaro Watanabe)).
Is = hν / στ
= 1.3 MW / cm ²
h: Planck's constant 6.63 × 10 ⁻³⁴ J · s
ν: Frequency 3 × 10 ⁸ /0.248×10 ⁻⁶ = 1.2 × 10 ¹⁵
σ: stimulated emission cross section 2 × 10 ⁻¹⁶ cm ²
τ: upper level lifetime 3 ns
(Including de-excitation due to collision)
Since the upper level lifetime τ is less likely to cause collision when the gas pressure is low, the maximum level lifetime τ increases up to the radiation lifetime (free space lifetime). In this case, the lifetime is 6.7 ns, and the saturation intensity Is is
Is = 0.6 MW / cm ² .
[0042]
Laser extraction efficiency: The ratio of the number of photons extracted per second from the unit volume to the number of excimers generated. The laser extraction efficiency η _ex is obtained as follows.
η _ex = (I / Is) (1− (1 + I / Is) −α _n / g ₀ )
I: laser light intensity Is: saturation intensity α _n : unsaturated absorption coefficient g ₀ : small signal gain Since α _n > 0,
η _ex <(I / Is) / (1 + I / Is)
When the laser light intensity I is less than Is, the laser oscillation becomes inefficient. For example, when the laser light intensity I in the resonator is 500 W / cm ² ,
η _ex = 1/2600 or less (laser extraction efficiency η _ex is very small)
Therefore, in order to perform laser oscillation efficiently, a saturation intensity of about 1.3 MW / cm ² is required.
[0043]
Hereinafter, preferred embodiments of the present invention will be described.
[0044]
(Laser gas)
In the present invention, the laser gas that is a laser medium is composed of a mixed gas of at least one inert gas selected from Kr, Ar, and Ne and F ₂ gas.
[0045]
Among these, gas types may be appropriately combined depending on the wavelength to be used. For example, in the case of a wavelength of 248nm is set to Kr / Ne / F _2, the Ar / Ne / F ₂ in the case of 193 nm, in the case of 157nm may be set to Ne / F _2.
[0046]
In the present invention, it is preferable to continuously supply the laser gas into the laser chamber. A more specific example of a laser gas supply system for this purpose is shown in FIG.
[0047]
In FIG. 7, reference numerals 21a and 21b denote gas inlets. The gas introduction ports 21 a and 21 b are provided at both ends of the laser chamber 20, and a gas discharge port 22 is provided at approximately the center of the laser chamber 20. If necessary, a vacuum pump or the like may be provided at the gas discharge port. The laser gas is supplied from the gas inlets 21a and 21b at both ends at the same flow rate through the gas inlets 21a and 21b, and is discharged from the gas outlet 22 provided substantially at the center. The reason is that it also serves as surface protection for the light reflecting plate at the output end. That is, since the outermost surface of the light reflecting plate is always covered with a thin film of a fluoride film, it does not react to F ₂ and F ^* . Further, it is desirable that the gas inlets 21a and 21b and the gas outlet 22 have a slit shape in the direction in which the microwave current flows.
[0048]
On the other hand, in FIG. 7, 25a, 25b, 26, 27a, 27b are valves. At the initial introduction of the laser gas, the valve 25a is closed 27a, the valves 25b and 27b are opened, and the piping from the laser gas source to the vicinity of the valves 25a and 27a is purged. After purging the pipe, the valves 25b and 27b are closed and 26 is opened to introduce the laser gas into the laser chamber 20, and after purging the laser chamber 20, the laser gas is introduced as it is to perform laser oscillation. Of course, when purging or the like is unnecessary, the above valve need not be provided. In FIG. 19, 28 is a mass flow controller (MFC) or pressure flow controller (PFC) for controlling the flow rate. PFC is preferred. 29 is a filter.
[0049]
In the present invention, in order to obtain stable continuous oscillation, the F ₂ concentration in the laser gas is 0.1 atomic% or more and 6 atomic% or less, and preferably 1 to 6 atomic%. 4 to 6% is more preferable.
[0050]
The laser gas pressure is preferably 10 Torr to 1 atm. 50 Torr to 1 atm is more preferable. That is, in the present invention, a stable discharge can be obtained even at such a low pressure, and thus stable continuous oscillation and continuous light emission can be obtained. In the prior art, the pressure of the laser gas was 3 to 4 atmospheres. In the prior art, if the F ₂ concentration is increased, F ⁻ becomes electrons and electrons are lost and the discharge becomes unstable. Therefore, the F ₂ concentration is set to 1% or less (actually lower than that), and 3 to compensate for it. It had to be -4 atm. However, in the present invention, even if the F ₂ concentration is increased, a stable discharge by such microwaves can be obtained, and therefore it is not necessary to increase the pressure to compensate. Of course, if it is necessary to increase the pressure for some reason, it may be increased.
[0051]
FIG. 26 shows a reaction formula, a reaction occurring in the laser tube of a KrF excimer laser. Noteworthy here is (3). It can be seen that F ⁻ and F ₂ are required to produce the KrF ^* excimer. On the other hand, the excimer emitting light from (4) returns to the base rare gas atom (Kr) and halogen (F), and does not become F ₂ or F ⁻ which is directly necessary for the production of KrF ^* excimer.
[0052]
Moreover, the reaction in which the halogen atom (F) generates a halogen molecule (F ₂ ) is much slower than (5).
[0053]
From the above, it is important to substitute halogen atoms (F ⁻ ) or halogen molecules (F ₂ ) that have returned to the ground state by emitting light in the discharge space.
[0054]
(Laser tube)
The laser tube 40 (FIGS. 8 and 9) is a tube constituting a laser chamber and has a window portion 44 for introducing a microwave. The laser tube 40 is connected to the waveguide 42 on the window 44 side. The inside of the laser tube 40 and the inside of the waveguide 42 are sealed, and sealing is performed by providing an insulating plate 41 on the window 44 of the laser tube 40. The insulating plate 41 will be described later.
[0055]
The cross-sectional shape of the end of the plasma excitation section, that is, the cross-sectional shape of the laser tube 40 constituting the laser chamber is substantially semi-cylindrical (or semi-elliptical) (FIG. 8A), cylindrical as shown in FIG. (FIG. 8B), elliptical shape (FIG. 8C), etc.
[0056]
Furthermore, a more preferable shape is the elliptical shape shown in FIG. 9A, and the minor axis direction of this ellipse is the microwave introduction direction. Therefore, in the case of the cross-sectional shape shown in FIG. 9A, the microwave is uniformly introduced into the laser gas that is the laser medium in the laser tube. In addition, a laser with higher density per unit area can be obtained and output to the outside.
[0057]
Further, the window 44 of the laser tube 40 may be provided with a taper that widens the laser tube 40 side as shown in FIG. 9B. The taper may be reversed.
[0058]
For the connection between the laser tube 40 and the waveguide 42, for example, as shown in FIG. 8 or FIG.
[0059]
In the present invention, it is not necessary to incorporate components such as electrodes inside the laser tube 40. That is, it is not necessary to incorporate an electrode or the like inside later. Therefore, the insulating plate 41 may be attached to the laser tube 40 in advance by a manufacturing process. The insulating plate 41 may be attached by shrink fitting, for example. In the case shown in FIG. 9B, the insulating plate 41 may be fitted from the inside of the laser tube 40.
[0060]
The laser tube 40 constitutes a laser chamber, and as described above, its outermost surface is made of fluoride to suppress reaction with F ^* , KrF ^* , and ArF ^* .
[0061]
Further, when the base material of the laser tube 40 is a metal, the fabrication becomes easy and the cooling efficiency is improved. In particular, it is preferable to use a metal having almost zero thermal expansion coefficient in order to prevent the optical resonator length from changing due to temperature change. In addition, it is desirable that the inner surface be made at least thicker than the skin depth of the microwave and provided with a metal having high electrical conductivity such as copper or silver by means such as plating.
[0062]
As a preferred embodiment of the insulating plate 41, a multilayer film (for example, SiO ₂ , Al ₂ O ₃ , CaF ₂ , MgF ₂ , LaF ₂ film) is formed on at least the surface in contact with plasma (the surface on the laser tube 40 side). ), And a fluoride thin film (for example, CaF ₂ , MgF ₂ , LaF ₂ or other fluoride thin film) is formed on the outermost surface.
[0063]
Furthermore, the insulating plate 41 has conditions such that the loss is overwhelmingly small with respect to the microwave supplied as a material requirement, is mechanically strong, and does not dissolve in water.
[0064]
Moreover, the thickness should just be the integral multiple of the half wavelength of the wavelength (in-tube wavelength) of a microwave, or the thickness of an integral multiple approximately.
[0065]
(Microwave)
In the present invention, microwaves are used as laser gas excitation means. By using microwaves, the laser gas is continuously excited to achieve continuous light emission.
[0066]
As a microwave supply source, for example, a trade name gyrotron may be used.
[0067]
The frequency and power of the microwave may be appropriately determined depending on the partial pressure of the component gas of the laser gas. Generally, the frequency of the microwave is preferably 1 GHz to 50 GHz, more preferably 5 to 40 GHz, and further preferably 20 to 35 GHz. The microwave power is preferably several hundred watts to several kW.
[0068]
When the frequency ω of the microwave for excitation is, for example, 35 GHz, the collision frequency ω _c of the electron determined with the Ne cross-section with the electron of Ne that is the main component of the plasma excitation gas is equal to the excitation microwave frequency. The gas pressure becomes 160 Torr.
[0069]
In this state, plasma excitation with the same power is most efficient.
[0070]
δ = (2 / ωμ ₀ σ) ^1/2
The skin depth determined by is the depth at which plasma excitation occurs efficiently. ω is the microwave angular frequency, μ ₀ is the vacuum permeability, and σ is the plasma conductivity.
[0071]
When a 35 GHz microwave is used with a gas pressure of 160 Torr and an electron density of 10 ¹⁴ cm ⁻³ ,
ω = 2π × 35 × 10 ⁹ [s ⁻¹ ]
μ ₀ = 4π × 10 ⁻⁷ [H / m]
σ = 12.8 [Ω ⁻¹ m ⁻¹ ]
And
δ = 750 μm
It becomes.
[0072]
For example, a 35 GHz microwave is guided by an oversized waveguide having a height of 5 mm and a width of 10 cm.
[0073]
The waveguide section and plasma excitation section are confidentially shielded with an insulating plate such as SiO ₂ , CaF ₂ , or MgF ₂ . The thickness of the insulating plate is approximately an integral multiple of the half length of the guide wavelength λg, taking into account the dielectric constant of the insulating plate.
[0074]
Therefore, in the 17.5 GHz microwave, the gas pressure of 80 Torr is equal to the collision frequency. Assuming that 35 GHz is the plasma frequency, the electron density at that time is 5 × 10 ¹³ cm ⁻³ . F ^* , KrF ^* and ArF ^{* at} a concentration of 10 ¹⁴ cm ⁻³ can be reliably realized by generating a gas plasma of about 70 to 80 Torr to about atmospheric pressure (1 atm) with a power of about 100 W to 1 kW at 35 GHz.
[0075]
In addition, when supplying the microwave, it is preferable that the surfaces of the waveguide and the insulating plate in contact with the plasma excitation portion are non-reflective plates with respect to a wavelength such as 248 nm.
[0076]
On the other hand, the interval between the waveguide and the insulating plate may be λg / 2 as shown in FIG. 10 or 11A, or may be λg as shown in FIG. 11B. Alternatively, 3λg / 2 may be used.
[0077]
In order to prevent discharge in the waveguide, a vacuum is preferably used in the waveguide. As the degree of vacuum is about 10 ⁻⁴ Torr or less, discharge can be prevented.
[0078]
Note that the inner surface of the waveguide 42 in the vicinity of the connection portion with the laser tube 40 is preferably a non-reflective surface, similar to the inner surface of the laser tube 40. This is to prevent the reflected light on the inner surface of the waveguide 42 from returning into the laser tube 40.
[0079]
Further, in order to cause a stable discharge, it is preferable to apply a magnetic field by an electromagnet or a permanent magnet as shown in FIG.
[0080]
(Microwave introduction means)
Moreover, structural examples of microwave introduction means are shown in FIGS.
[0081]
In the example shown in FIG. 13, the waveguide 1 which is a microwave introduction unit is a slot waveguide having a plurality of slots S. The slot waveguide 1 is connected to the outer periphery of the laser tube 2 in parallel to the axial direction. An electromagnetic wave of several GHz to several tens GHz is introduced from the upper part of the slot waveguide 1, and this electromagnetic wave propagates in the waveguide 1 as a TE10 mode in which the electric field is directed perpendicular to the paper surface.
[0082]
As shown in FIG. 14, a number of elongated slots 11 are opened on the lower surface of the slot waveguide 1 in the drawing, and electromagnetic waves propagate through the waveguide 1. Is released.
[0083]
The electromagnetic wave emitted from the slot S is introduced into the laser tube 2 through the dielectric plate 3, and the laser gas in the laser tube 2 is ionized to generate plasma. The magnetic field generator 10 is a permanent magnet or an electromagnet for introducing a vertical magnetic field to the laser tube 2. As the permanent magnet used here, an iron vanadium magnet or an Nb / Fe / B magnet having a strong magnetic force is suitable.
[0084]
By introducing a magnetic field into the laser tube 2, electrons in the plasma can be trapped to reduce loss on the wall surface, and a higher density plasma can be obtained. If the magnetic field strength is selected appropriately, a higher density plasma can be obtained by electron cyclotron resonance.
[0085]
Of course, when a sufficiently high density plasma can be obtained without applying a magnetic field, the magnetic field generator 10 is not necessary.
[0086]
For example, Kr, Ne, F ₂ gas is introduced / exhausted into the laser tube 2 from the gas inlet 8. If it is not necessary to replace the gas when the plasma is generated, the gas inlet 8 is not necessary because the gas only needs to be sealed in the laser tube 2. In plasma, radicals such as KrF having a lifetime of about 10 nsec are continuously generated, and light is emitted when dissociated into Kr and F. This light promotes stimulated emission while reciprocating in the optical resonator formed by the output side mirror 5 and the reflection side mirror 6, and is amplified by stimulated emission. The reflectance of the output side mirror 5 is 90% or more, and the light transmitted through the output side mirror is emitted to the outside as laser light.
[0087]
In the example shown in FIG. 13, but the material of the laser tube main body may be an aluminum alloy, the laser body inner surface and the inner surface of the dielectric 3 for efficiency are formed a dielectric multilayer film, the oscillation wave The reflectivity in the length is non-reflective.
[0088]
In order to cool the laser tube 2 and the waveguide 1, a coolant container 7 having a coolant inlet 9 and a coolant such as coolant, air, N ₂ gas, etc. can flow between them. . The slot waveguide 1 has a structure that can be evacuated in order to prevent discharge from occurring in the waveguide 1.
[0089]
FIG. 14 is a view of the slot waveguide 1 as viewed from below.
[0090]
In FIG. 14A, slots S oriented in a direction perpendicular to the axis of the waveguide 1 are arranged at an interval equal to the wavelength of the electromagnetic wave in the waveguide 1. From each slot, linearly polarized electromagnetic waves polarized in the axial direction of the waveguide with the same phase are emitted.
[0091]
In FIG. 14B, slots inclined by 45 degrees with respect to the waveguide axis are arranged at intervals equal to the wavelength of the electromagnetic wave in the waveguide. Each slot emits a linearly polarized electromagnetic wave polarized in a direction inclined by 45 degrees with respect to the waveguide axis direction having the same phase.
[0092]
FIG. 11C shows a pair of two slots inclined at an angle of 45 degrees with respect to the waveguide axis and arranged at intervals equal to the wavelength of the electromagnetic wave in the waveguide. From each slot, circularly polarized electromagnetic waves with uniform phases are emitted.
[0093]
The length of these slots is determined according to the electromagnetic wave intensity distribution in the waveguide so that the intensity of the electromagnetic waves emitted from each slot becomes substantially equal. Further, the angle of the slot and the interval between the slots may be other than the above.
[0094]
In the structure of FIG. 15, an electromagnetic wave of several GHz to several tens of GHz is introduced from the upper part of the tapered waveguide 11, and the electromagnetic wave is spread at the tapered portion and then introduced into the laser tube 2 through the dielectric plate 3. In the example shown in FIG. 15, the electric field propagates in the TE10 mode in the vicinity of the electromagnetic wave introduction portion of the tapered waveguide 11 in the horizontal direction on the paper surface. However, the electric field may face in the vertical direction on the paper surface. Others are the same as those shown in FIG.
[0095]
16 and 17 show examples in which microwaves are introduced as surface waves. In the structure shown in FIG. 16, electromagnetic waves of several GHz to several tens GHz are introduced from the upper part of the waveguide 12 with a gap using a cylindrical induction tube. This electromagnetic wave propagates in the tube as a TE10 mode in which the electric field is directed horizontally to the paper surface. An electric field in the tube axis direction of the dielectric tube 14 is applied from the gap portion of the waveguide 12 with a gap. The microwave thus introduced becomes a surface wave propagating in the left and right tube axis directions from the gap portion in the dielectric tube 14. Electrons in the plasma are accelerated by this surface wave electric field, and a high-density plasma is maintained.
[0096]
Since a surface wave with a mode that gently attenuates propagates from the center of the laser tube, the local microwave electric field cannot be strengthened or weakened. Therefore, since uniform plasma excitation is performed on the plasma surface, high-density plasma can be generated efficiently. Further, since the microwave electric field only needs to be applied to the gap part, the microwave circuit is very simple. This plasma generation method is optimal for oscillating a thin laser because it can efficiently generate a long, high-density plasma as thin as several mm or less. The dielectric tube 14 is CaF ₂ in the example shown in FIG. The movable short-circuit plate 13 is provided in order to suppress reflection to the electromagnetic wave generation unit by adjusting the position of the short-circuit, but need not be particularly movable. Further, when the frequency of the electromagnetic wave is high and the waveguide dimension is sufficiently small, the gap portion of the waveguide is not particularly necessary. The magnetic field generator 10 is a permanent magnet or an electromagnet, and generates a magnetic field in the tube axis direction of the dielectric tube 14. Others are the same as the structure shown in FIG.
[0097]
FIG. 17 shows an example using a guide plate 14a, which is the same in principle as when a cylindrical dielectric tube is used. It is suitable for generating a plasma having a wide width and a small thickness. Since the lower part of the plasma has nothing to do with plasma generation, it is easy to create a high-speed gas flow perpendicular to the laser tube axis.
[0098]
In the structure shown in FIG. 18, an electromagnetic wave of several GHz to several tens of GHz is introduced from the upper part of the coaxial conversion waveguide 16, and this electromagnetic wave propagates in the tube as a TE10 mode in which the electric field is directed in the horizontal direction on the paper surface. This electromagnetic wave is propagated by changing the mode to a left-right electromagnetic wave propagating between the shield plate 15 and the plasma in the dielectric tube 14. High-density plasma is generated by the high-frequency current flowing on the plasma surface. Other configurations are the same as those shown in FIGS.
[0099]
In the structure shown in FIG. 19, an electromagnetic wave of several GHz to several tens of GHz is introduced from the upper part of the coaxial conversion waveguide 16, and this electromagnetic wave propagates in the tube as a TE mode in which the electric field is directed in the horizontal direction on the paper surface. This electromagnetic wave is propagated by changing the mode to a right electromagnetic wave propagating between the shield plate 15 and the plasma in the dielectric tube 14. Others are the same as the structure shown in FIG.
[0100]
(Laser gas introduction mode)
FIG. 24 shows an excimer laser oscillation apparatus according to another embodiment of the present invention. The microwave introduction method and configuration are the same as those of the excimer laser oscillation apparatus shown in FIG. 13, and a microwave from a gyrotron, which is a microwave power source (not shown), is supplied to the slot plate via the rectangular waveguide 1. 3 is introduced into the laser tube 2.
[0101]
On the other hand, the apparatus described with reference to FIG. 13 employs a configuration in which laser gas can be introduced from the end portion in the longitudinal direction of the laser tube and discharged from the other end portion in the longitudinal direction. On the other hand, in the excimer laser oscillation device according to the present embodiment, a long hole is provided along the longitudinal direction of the laser tube 2 to serve as a laser gas discharge port 22. As a result, the laser gas introduced from the introduction port 21 is discharged from the discharge ports 22 on both sides thereof through the discharge space in the laser tube.
[0102]
In order to obtain a stable continuous emission excimer laser beam, the beam may be narrowed into one. For example, it has been found that in order to obtain 1 kW at a laser light intensity of 1.3 MW / cm ^2, it is sufficient to obtain plasma in a region having a diameter of about 0.3 mm. In the above-described apparatus shown in FIG. 24, plasma can be concentrated and generated in such a narrow region, so that an excimer laser beam of continuous emission with a narrow beam can be obtained.
[0103]
At this time, the reflectance of the mirror 6 is preferably 100%, and the reflectance of the output side mirror is preferably 99%.
[0104]
In addition, in order to obtain a continuous emission excimer laser beam stably, fluorine molecules (F ₂ ) and fluorine ions (F ⁻ ) exist in the discharge space, and excimer (KrF ^* ) can be sufficiently formed. Must be. For this purpose, it is desirable to introduce a large amount of fresh fluorine gas (F ₂ ) into the discharge space at a high speed, and to discharge the fluorine atoms (F) that have returned to the ground state by laser light emission from the discharge space.
[0105]
In this embodiment, in order to perform the above-described circulation replacement of the laser gas at a high speed, a new laser gas is introduced from a direction intersecting with the longitudinal direction of the laser tube (longitudinal direction of the discharge space), and the laser gas is introduced so as to be discharged. There is a mouth and an outlet.
[0106]
In addition, such high-speed circulation of gas replaces the gas and plasma in the discharge space at high speed, and thus has an effect of cooling the laser tube.
[0107]
FIG. 27 shows a mode that enables further high-speed circulation of laser gas. Compared with the gas inlet 23 and the gas outlet 24, the gas flow is narrower in the discharge space. Gas circulation and replacement are performed.
[0108]
Further, the magnet 10 for confining the plasma in a narrow region is not limited to the configuration in which the magnetic field lines crossing the longitudinal direction of the laser tube are generated as shown in FIG. 24, but the magnetic field lines are generated along the longitudinal direction of the laser tube. It can also be arranged.
[0109]
FIG. 25 shows an excimer laser oscillation apparatus according to another embodiment of the present invention.
[0110]
The microwave introduction method and configuration are the same as those of the excimer laser oscillation device shown in FIG. 16, and microwaves from a gyrotron, which is a microwave power source (not shown), are passed through a gap through a rectangular waveguide 12. Are introduced into the laser tube 14. The microwave propagates along the wall of the laser tube and travels in the longitudinal direction, and discharge occurs in the laser tube 14 to generate laser gas plasma.
[0111]
The apparatus shown in FIG. 24 is different from the apparatus shown in FIG. 16 in the laser gas introduction method.
[0112]
The apparatus of FIG. 16 introduced laser gas from the longitudinal end of the laser tube to form a gas flow along the longitudinal direction, whereas the apparatus of FIG. 25 has a slot in the side wall of the laser tube in the longitudinal direction. Are arranged so as to be parallel to the longitudinal direction of the laser tube, the laser gas is introduced from one side, and the laser gas is discharged from the other side.
[0113]
As a result, the laser gas flows through the laser tube so as to cross its longitudinal direction. As described above, also in the present embodiment, the gas and / or plasma in the discharge space is replaced at high speed, so that the excimer can be stably generated in the discharge space. It also has the effect of cooling the laser tube.
[0114]
Such gas introduction and discharge methods can be applied to all the apparatuses described with reference to FIGS.
[0115]
(cooling)
Since a laser beam of about 10 W that receives a microwave of about 100 W to 1 kW is obtained, considerable heat generation occurs. Precise cooling is necessary because the wavelength changes when it expands. It is better to use copper or silver plating on the inner surface using a metal with no thermal expansion.
[0116]
The reason why the plasma excitation part is made of metal is to increase the cooling efficiency. Water cooling is performed while controlling the cooling water temperature, the cooling water flow rate, and the cooling water pressure, for example, as shown in FIG. Cooling is preferably performed by a cooling device, and it is preferable that the gas is degassed from the cooling water and the pumping pressure is about 1 kg / cm ² so that vibration associated with the cooling water pumping does not occur.
[0117]
(Resonator)
By arranging a pair of reflecting mirrors on the optical axis of the laser tube, the laser light can be extracted by stimulated emission.
[0118]
As will be described later, when obtaining a continuously emitting excimer laser beam by reducing the beam diameter and maintaining the light intensity, the reflectance of one of the reflecting mirrors is 100%, and the reflecting mirror of the output side that extracts the laser beam is used. The reflectivity is preferably 99.0%.
[0119]
If the cross-sectional area of the plasma light emitting portion is 5 mm × 0.2 mm = 1 × 10 ⁻² cm ² , the power of the laser traveling in the resonator is 1 MW / cm ² × 10 ⁻² cm ² = 10 kW. Therefore, when the reflectance of the output mirror is 99.0%, the laser power output to the outside is 100 W, and when it is 99.9%, it is 10 W. Since the output of the microwave power source and the gyrotron is 0.5 to 10 kW, even 100 W in the case of a 99.0% reflecting mirror can be sufficiently realized. Of the 100 W that is output, 1 W, which is 1%, will reach the wafer and can be exposed in 0.02 sec. This is because the resist exposure requires 20 mJ / cm ² .
[0120]
Also, when the light intensity is maintained by extremely reducing the loss in the resonator, the reflectance of one of the reflecting mirrors is preferably 100% and the reflectance of the reflecting mirror on the output side is more preferably 99.5% or more. Is preferably 99.9% or more.
[0121]
FIG. 28 shows a configuration of a resonator in which the reflectance at both ends is 100% using a prism. The incident angle to the total reflection prisms 202 and 203 is a Brewster angle, and no light loss occurs at the time of incidence. Further, the reflection inside the total reflection prisms 202 and 203 uses total reflection, and no light loss occurs at the time of reflection. Therefore, the reflectance at both ends of the resonator is 100%. The output light can be set to reflectivity from 0% to several percent by adjusting the incident angle at the output light extraction plate 204 installed between the laser tube 201 and the total reflection prism 202.
[0122]
In the example shown in FIG. 28, since the left and right traveling waves are reflected on both the front and back surfaces in two places on the output light extraction plate, the number of output beams increases to eight. The processing of these output beams complicates the device. A modification shown in FIG. 29 is given as an example for reducing the number of output beams and preventing the apparatus from becoming complicated.
[0123]
In the example shown in FIG. 29A, two output light extraction plates a and b are provided for each beam in the resonator, and one (b) is set to the Brewster angle. Since the beam in the resonator is linearly polarized, no reflected light is generated at the output light extraction plate b set at the Brewster angle. Therefore, the number of output beams is four. The reason why the output light extraction plate b is provided is to correct a beam position shift caused by the output light extraction plate b.
[0124]
In the modification shown in FIG. 29B, output light is extracted by using diffraction of the beam in the resonator, and the output mirror is arranged so as to be in contact with one of the beams in the resonator, and is provided on one side or both sides. A highly reflective coat is applied. The diffracted light that has leaked to the output mirror is reflected by the surface on which the highly reflective coating is applied, and becomes an output beam. The number of output beams is two.
[0125]
In the modification shown in FIG. 29 (c), output light is extracted using an evanescent wave, and leakage is caused by installing the evanescent wave extraction prisms on the total reflection surface of the total reflection prism 202 or 203 at a distance of about a wavelength. Light (called evanescent wave) is taken out as output light. The number of output beams is two.
[0126]
(Exposure equipment)
FIG. 1 shows an exposure apparatus using an excimer laser oscillation apparatus.
[0127]
The light emitted from the oscillation device A1 is guided to the scanning optical system via the mirror and the lens A2.
[0128]
The scanning optical system has a scanning lens A4 and a scanning mirror A3 whose angle can be changed. Light emitted from the scanning optical system is irradiated onto a reticle A6 having a mask pattern via a condenser lens A5. The above is the configuration of the illumination optical system of the exposure apparatus.
[0129]
Light having a light and dark distribution corresponding to a predetermined mask pattern is formed on the wafer A8 placed on the stage by the imaging optical system having the objective lens 7 by the reticle A6, and a latent image corresponding to the mask pattern is formed on the wafer A8. It is formed on the photosensitive resist on the surface.
[0130]
As described above, the exposure apparatus shown in FIG. 1 includes the excimer laser oscillation apparatus A1, the illumination optical system, the imaging optical system, and the stage A9 for holding the wafer A8.
[0131]
In this device, a narrowing module (not shown) is provided between the oscillation device A1 and the scanning optical system. The oscillation device A1 itself is a pulse oscillation type.
[0132]
(Example of exposure device output method)
The following methods can be considered to turn on / off the use of the output light of the continuous oscillation excimer.
(1) A blocking means is provided outside the excimer laser device.
(2) Turn on / off the continuous excitation means.
[0133]
However, in the method (1), since the excimer laser is Deep UV light and its output is higher than that of other lasers, damage to the blocking means is large and the life of the blocking means is short. The life of the blocking means using the highly responsive AO element (acousto-optic element) is particularly short. Further, since the oscillation continues inside the laser even if the output light is cut off, the optical system inside the laser is unnecessarily damaged and the life is shortened.
[0134]
In the method (2), since a certain amount of time is required to form a stable excited state, the desired continuous oscillation light cannot be obtained immediately even if the continuous excitation means is turned on.
[0135]
The present invention will be described in detail based on the embodiments shown in the drawings.
[0136]
FIG. 22 is a schematic view of a continuous wave excimer laser according to the present invention. 101 is a laser chamber filled with Kr, Ne, and F ₂ gas, 102 is an output mirror that outputs light from the laser, 103 is a dielectric that introduces the microwave into the laser chamber, and 104 is a microwave guide. A slot waveguide 105 for wave generation is a microwave oscillation source for supplying microwaves. Reference numeral 106 denotes a wavelength selection unit that selects a wavelength to oscillate. The wavelength selection unit 106 includes a pair of prisms, an enlargement prism 106-1 that expands the beam diameter, and a diffraction grating 106-2 that extracts an arbitrary wavelength.
[0137]
Reference numeral 107 denotes a spatial filter that includes a pair of lenses and is provided at the focal position of the laser side lens of the beam shaping optical system 108, and controls the spread angle of the output light from the laser. Reference numeral 109 denotes a shutter, and 110 denotes a control system that controls the wavelength selection unit 106, the microwave oscillation source 105, and the shutter 109.
[0138]
Here, the output mirror 102 and the diffraction grating 106-2 constitute an excimer laser resonator.
[0139]
(Description of operation)
The microwave from the microwave oscillation source 105 is guided by the slot waveguide 104 and continuously excites the excimer laser gas in the laser chamber 101 via the dielectric 3. The light from the excited excimer laser gas enters the diffraction grating 106-2 via the magnifying prism 106-1. Only light in a predetermined wavelength region from the diffraction grating returns to the laser chamber 101 again through the magnifying prism 106-1, and undergoes induction excitation light emission with the excited excimer laser gas, and the light is output mirror 102 and the diffraction grating 106-. By sequentially stimulated emission while reciprocating in the optical resonator constituted by 2, only light in a predetermined wavelength region selected by the diffraction grating is amplified. A part of the amplified light is output via the output mirror 102.
[0140]
Next, the operation for turning on / off the use of the output light of the continuous wave excimer laser will be described.
[0141]
When blocking the output light of the continuous wave excimer laser, the control system 110 operates the shutter 109 while continuously supplying the microwave to block the light from the excimer laser gas from going to the output mirror 102. Close the shutter as shown. Then, the light oscillated in the optical resonator can no longer oscillate, and the output light from the continuous wave excimer laser can be cut off rapidly.
[0142]
When the output light of the continuous wave excimer laser is reused, the control system 110 operates the shutter 9 while continuously supplying the microwave, and the light from the excimer laser gas goes to the output mirror 102. Open the shutter so that. Light spontaneously emitted by the excimer laser gas is immediately and stably oscillated in the optical resonator, and stable output light can be obtained from the continuous wave excimer laser with good response.
[0143]
Next, another operation for turning on / off the use of the output light of the continuous wave excimer laser will be described.
[0144]
When blocking the output light of the continuous wave excimer laser, the control system 110 rotates the diffraction grating 106-2 while continuously supplying the microwave. Then, the light in the predetermined wavelength region selected by the diffraction grating is changed, and only the light in the changed wavelength region returns to the laser chamber 101 again through the magnifying prism 106-1. At this time, since the changed wavelength region is set to be the wavelength of the oscillating region determined by the excimer laser gas, the excited excimer laser gas does not emit induced excitation light, and thus light cannot oscillate. Output light from the continuous wave excimer laser can be blocked. This phenomenon will be described with reference to FIG.
[0145]
Normally, the excimer laser has a gain with respect to wavelength determined by the gas. The relationship is the gain curve GC of FIG. At this time, when light (G) in a wavelength region with a gain (λ−δλ to λ + δλ) is incident on the excited excimer laser gas, stimulated excitation light is emitted, and the excimer laser oscillates. On the other hand, when light in a region (NG) different from a wavelength region with a gain (λ−δλ to λ + δλ) is incident on the excited excimer laser gas, induction excitation light is not emitted, and the excimer laser does not oscillate. In this embodiment, when the output light of the continuous wave excimer laser is cut off by utilizing this phenomenon, the wavelength region (λ−δλ to λ + δλ) having a gain as the light returned to the laser chamber by the diffraction grating 106-2. Choose a different area of light.
[0146]
At this time, although light is not oscillated, light corresponding to spontaneous emission is output, but the light is not directional, and is almost blocked by the spatial filter 107.
[0147]
Further, when the output light of the continuous wave excimer laser is reused, the control system 110 rotates the diffraction grating 106-2 while continuously supplying the microwaves, and the oscillation grating can be oscillated by the diffraction grating. The wavelength is selected and only that light returns again to the laser chamber 101 via the magnifying prism 106-1. Then, stimulated excitation light is emitted by the immediately excited excimer laser gas and oscillates in the optical resonator, and stable output light can be obtained from the continuous wave excimer laser with good responsiveness.
[0148]
【Example】
FIG. 20 shows a continuous emission excimer laser oscillation apparatus used in this example.
[0149]
In this example, a cylindrical optical resonator is used.
[0150]
An antireflective film was formed on the inner surface. The outermost surface was made of fluoride.
[0151]
A jacket-like cooling device was provided on the outer periphery. The outermost surface was covered with a heat insulating material, and means for controlling the temperature of the inflowing cooling water to be lower than the ambient temperature and to substantially match the temperature of the outflowing cooling water was provided. As a result, the temperature fluctuation of the optical resonator can be made extremely small.
[0152]
As the waveguide, the one shown in FIG. 17 (oversized waveguide having a height of 5 mm and a width of 10 cm) was used, and the inside thereof was evacuated to a level of 10 ⁻⁴ Torr.
[0153]
On the other hand, in this example as well, a stable magnetic excitation was achieved by forming a magnetic field with a magnet.
[0154]
The insulating plate 44 is formed with a multilayer-coated non-reflective film made of CaF ₂ and MgF ₂ on the resonator side. A film made of fluoride was formed on the outermost surface.
[0155]
The microwave used was the trade name Gyrotron, the supply frequency was 35 GHz, and the gas composition was Kr / Ne / F ₂ (3%: 92%: 5%).
[0156]
The pressure was atmospheric pressure. Therefore, ω _c = 4.5Ω, and the electrons collide 4.5 times during one period of the excitation frequency.
ω _c : Photoelectron collision angular frequency
In this example, as shown in FIG. 20, gas inlets 21a and 21b are provided at both ends of the laser chamber 20, and a gas outlet 22 is further provided at the center thereof. Thus, the laser gas to be supplied is configured to flow toward the center. The reason is that, as described above, it also serves as the surface protection of the output end light reflecting plate. That is, the outermost surface of the light reflecting plate is always covered with a thin film of a fluoride film, so that it reacts to F ₂ and F ^* .
[0158]
The reflectance of the light reflecting plate was set to 99% or more.
[0159]
In this example, the magnet 51 is arranged so that a DC magnetic field is applied in a direction substantially perpendicular to the microwave electric field, and discharge start and discharge maintenance can be performed extremely stably.
[0160]
The optical oscillator is made of a metal cylinder having an inner diameter of several mm to several cm. The inner surface of the metal cylinder was coated with an antireflective multilayer film. A fluoride film was formed on the outermost surface.
[0161]
Seal bonding between the light reflection plate 31 and the laser tube (in this example, the metal cylinder 31) constituting the laser chamber was performed as shown in FIG.
[0162]
That is, a Teflon plate ring 33a is interposed between the light reflecting plate 31 and the flange 32a of the metal cylinder 32, and the outside of the light reflecting 31 is tightened by a bolt 34 with a Teflon plate ring 33b and a metal plate ring 35 interposed. Was pressed. Sealing was performed with an O-ring 36. Of course, you may attach with the screw using a bearing, without using the volt | bolt 34. FIG.
[0163]
When light was emitted with the above configuration, continuous light emission with sufficient output was achieved.
[0164]
Further, when the stepper was constructed using this continuous emission excimer laser oscillation device, the construction was simplified and the life of the lens material and the like was improved.
[0165]
(Other examples)
By using the apparatus shown in FIG. 24 and FIG. 25 and making the loss in the resonator extremely small, it was possible to obtain a stable continuous emission excimer laser beam.
[0166]
For example, the pressure of the laser gas is 65 Torr, and the energy loss due to the gas is suppressed to 1%. Along with this, a stable resonator was constructed by setting the reflectance of one reflected light to 100% and the reflectance of the reflecting mirror on the output side to 99.5% or more. As a result, the gain required for laser oscillation can be made 2% or more in a round trip, and the gain can be made larger than the loss.
[0167]
Note that when 35 GHz is used as the microwave energy and the pressure in the laser tube is set to 160 Torr, the loss due to the gas slightly increases, so it is desirable to set the reflectance of the output-side reflecting mirror to 99.9% or more.
[0168]
【The invention's effect】
According to the present invention, less load on the lens material and the surface, and the control system of the mirror or lens scanning can provide a continuous emission excimer laser oscillation equipment, which can be simplified.
[0169]
First, damage to optical materials such as glass is reduced. A normal excimer laser such as KrF or ArF emits a short pulse of 10 to 20 nsec, whereas the pulse repetition frequency is only about 1000 Hz. Therefore, the light intensity at the peak of this pulse is 10,000 times or more that of continuous light emission at the same intensity even if the problem of the efficiency of the optical system is excluded. It is known that the main cause of material damage that occurs in the excimer region is two-photon absorption, and the light damage in the current excimer laser, which is proportional to the square of the light peak intensity, is estimated to be less than in continuous light emission. Even 10 ⁸ times more severe. The durability of the glass material is a problem in the ArF region for the above reasons. Therefore, the realization of the continuous light emission light source solves the material problems in the ultraviolet region including ArF at a stretch.
[0170]
Second, it is easy to suppress the occurrence of speckle, a phenomenon peculiar to narrow-band light. In the case of pulsed light emission, in order to effectively erase speckles that are random interference fringes, it is necessary to synchronize the light emission timing of each pulse with known speckle removing means with high accuracy. On the other hand, if it is continuous oscillation, the speckle can be easily removed by a known means such as, for example, a rotating diffusion plate, without requiring any special synchronizing means. Therefore, the configuration of the optical system can be simplified, and the cost can be reduced.
[0171]
Third, exposure amount control is easy. When performing discrete exposure such as pulsed light emission, the minimum unit for controlling the exposure amount basically depends on the number of pulses, although it depends on the controllability of the exposure amount of one pulse. When the exposure is performed with 100 pulses in total, the next unit is 99 pulses or 101 pulses, and the control accuracy is ± 1%. Of course, various means have been proposed for the control of the last pulse, but there is no resolution due to such discreteness for controllability or control, and finer exposure amount control is possible. As the line width becomes narrower, the continuous light source has a great effect in spite of demanding strict exposure control.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram of an excimer laser exposure apparatus.
FIG. 2 is a conceptual diagram showing a pulse state.
FIG. 3 is a conceptual diagram showing an actual pulse state.
FIG. 4 is a diagram illustrating a decay state of spontaneous light emission.
FIG. 5 is a diagram illustrating a gain width and a mode state.
FIG. 6 is a graph showing how light is focused in an excimer laser.
FIG. 7 is a conceptual diagram showing a gas supply system to a laser chamber.
FIG. 8 is a cross-sectional view showing a shape example of a laser tube.
FIG. 9 is a cross-sectional view showing another example of the shape of a laser tube.
FIG. 10 is a perspective view showing the distance between the end of the waveguide and the insulating plate.
FIG. 11 is a perspective view showing the distance between the end of the waveguide and the insulating plate.
FIG. 12 is a perspective view showing application of a magnetic field.
FIGS. 13A and 13B are a cross-sectional view and a cross-sectional view taken along line AA of an example of a continuous light emitting excimer laser oscillation device having a microwave supply device.
14 is a bottom view of the waveguide 1 in FIG.
FIGS. 15A and 15B are a cross-sectional view and a BB cross-sectional view of a continuous light emitting excimer laser oscillation device having a microwave supply device. FIGS.
FIG. 16 is a cross-sectional view of a continuous light emitting excimer laser oscillation device having a microwave supply device.
FIG. 17 is a cross-sectional view of another continuous light excimer laser oscillation device having a microwave supply device.
FIG. 18 is a cross-sectional view of a continuous light emitting excimer laser oscillation device having a microwave supply device.
FIG. 19 is a cross-sectional view of a continuous light emitting excimer laser oscillation device having a microwave supply device.
FIG. 20 is a side view and a front view of an excimer laser oscillation device according to an example.
FIG. 21 is a cross-sectional view showing a seal structure between a light reflection plate and a laser tube (metal cylinder) in the excimer laser oscillation apparatus according to the embodiment.
FIG. 22 is a conceptual diagram of an excimer laser according to an embodiment of the present invention.
FIG. 23 is a graph showing a gain curve in an excimer laser according to an embodiment of the present invention.
FIG. 24 is a conceptual diagram of an excimer laser oscillation device according to an embodiment of the present invention.
FIG. 25 is a conceptual diagram of an excimer laser oscillation device according to another embodiment of the present invention.
FIG. 26 is a diagram showing a reaction formula of excimer.
FIG. 27 is a cross-sectional view of another continuous emission excimer laser oscillation device having a microwave supply device.
FIGS. 28A and 28B are a front view and a side view of a resonator in which the reflectance at both ends becomes 100% using a prism. FIGS.
29 is a side view showing a modification of FIG. 28. FIG.
[Explanation of symbols]
A1 oscillator,
A3 scanning mirror,
A4 scanning lens,
A5 condenser lens,
A6 reticle,
A7 objective lens,
A8 wafer,
A9 stage,
1 slot waveguide,
2 laser tube,
3 dielectric plate,
5 Output mirror
6 Reflective side mirror,
8 Gas inlet,
9 Refrigerant container,
10 Magnetic field generator,
11 slots,
12 waveguide with gap,
14 Dielectric tube,
14a dielectric plate,
13 Movable short-circuit plate,
15 Shield plate,
16 coaxial conversion waveguide,
20 laser chamber (laser tube),
21a, 21b gas inlet,
22 Gas outlet,
25a, 25b, 26, 27a, 27b valves,
28 MFC, PFC,
29 filters,
31 Reflector,
32 metal cylinder (laser tube),
32a flange,
33a, 33b Teflon plate ring,
34 volts,
35 Metal plate ring,
36 O-ring,
40 laser tube,
41 insulation plate,
42 waveguides,
50 temperature control device,
51 magnets,
101 laser chamber,
102 output mirror,
103 dielectric,
104 slot waveguide,
105 microwave oscillation source,
106 wavelength selection unit,
106-1 magnifying prism,
106-2 diffraction grating,
107 beam shaping optical system,
108 spatial filter,
109 shutter,
110 Control system.

Claims (40)

A laser chamber containing a laser gas composed of a mixed gas of at least one inert gas selected from Kr, Ar, and Ne and F ₂ gas, and having a desired wavelength of 248 nm, 193 nm, and 157 nm on the inner surface A laser chamber in which the reflectance to light is 50% or less and the outermost surface of the inner surface is made of fluoride;
An optical resonator comprising a pair of reflecting mirrors provided across the laser chamber, wherein the reflectance of the reflecting mirror on the output side is 90% or more;
A continuous light emitting excimer laser oscillating device comprising microwave introducing means for continuously exciting the laser gas in the laser chamber. The inner surface of the laser chamber has a structure in which a layer of FeF ₂ is formed on a stainless steel surface, or nickel is plated on a metal and a layer of NiF ₂ is formed on the surface thereof, or AlF ₃ is formed on an aluminum alloy. The continuous emission excimer laser oscillation device according to claim 1, wherein a layer of MgF ₂ is formed.   3. The continuous emission excimer laser oscillation apparatus according to claim 1, further comprising means for continuously supplying a laser gas into the chamber. Said laser gas consists of Kr / Ne / _{F 2,} Kr is 1-6%: A (atomic% or less the same), one of claims 1 to 3, characterized in that _{F 2} is 1-6% 2. A continuous light emission excimer laser oscillation device according to item 1. Said laser gas consists of Ar / Ne / _{F 2,} Ar is 1-6%, the continuous emission excimer laser oscillation according to any one of claims 1 to 3 _{F 2} is characterized in that it is a 1-6% apparatus. The continuous emission excimer laser oscillation apparatus according to any one of claims 1 to 3, wherein the laser gas is made of Ne / F ₂ and F ₂ is 1 to 6%.   The continuous emission excimer laser oscillation apparatus according to any one of claims 1 to 6, wherein the laser gas is introduced from both ends of the laser chamber and discharged from a central portion of the laser chamber.   The continuous wave excimer laser oscillation device according to any one of claims 1 to 7, wherein the frequency of the microwave is 1 GHz to 50 GHz.   9. The continuous light emitting excimer laser oscillation device according to claim 1, wherein the microwave introduction means is a waveguide, and the inside of the waveguide is in a vacuum.   10. The continuous light emission excimer laser oscillation device according to claim 1, wherein a vertical cross section of the laser chamber is elliptical.   The continuous emission excimer laser oscillation device according to claim 10, wherein the ellipse has a minor axis direction that is a microwave introduction direction.   The continuous light emitting excimer laser oscillation apparatus according to claim 1, wherein a magnetic field is applied to the laser chamber.   13. The continuous emission excimer laser oscillation apparatus according to claim 12, wherein the means for applying the magnetic field is an iron vanadium magnet or an Nb / Fe / B magnet.   The continuous emission excimer laser oscillation device according to any one of claims 1 to 13, wherein a gas pressure of the laser gas is set to several tens of Torr to 1 atm. The outer periphery of the laser chamber is covered with a jacket-like cooling device, and cooling means for controlling the temperature of the laser chamber is provided.
5. The continuous light emission excimer laser oscillation device according to any one of 4 above.   The inside of the microwave introduction means and the inside of the laser chamber are separated from each other by an insulating plate, and a fluoride thin film is formed on the outermost surface of the insulating plate on the laser chamber side. The continuous light emission excimer laser oscillation device according to any one of 15.   The continuous emission excimer laser oscillation apparatus according to any one of claims 1 to 16, wherein a plurality of slots are formed in the microwave introduction means, and microwaves are introduced into the laser chamber from these slots.   18. The continuous emission excimer laser oscillation according to claim 17, wherein the interval between the slots is equal to the wavelength of the microwaves in the microwave introduction means, and microwaves having the same phase are emitted from each slot. apparatus.   The continuous emission excimer laser according to any one of claims 1 to 16, wherein the microwave emitting portion of the microwave introducing means has a tapered shape that is widened in the length direction of the laser chamber. Oscillator.   The continuous emission excimer laser according to any one of claims 1 to 19, wherein the microwave emitting portion of the microwave introducing means has a gap for emitting a microwave having an electric field in the axial direction of the laser chamber. Oscillator. The inner surface is selected from Kr, Ar, and Ne in a laser chamber in which the reflectance of light with a desired wavelength of 248 nm, 193 nm, and 157 nm is 50% or less and the outermost surface of the inner surface is made of fluoride. Continuously supplying a laser gas composed of a mixed gas of at least one inert gas and F ₂ gas,
Continuously exciting the laser gas by introducing microwaves into the laser chamber;
A continuous light emitting excimer laser oscillation method, wherein light emitted from the excited laser gas is caused to resonate by a pair of reflecting mirrors having a reflectance of 90% or more on the output side reflecting mirror, thereby causing continuous emission. Said laser gas consists of Kr / Ne / _{F 2,} Kr is 1-6%, the continuous emission excimer laser oscillation method according to claim 21, wherein the _{F 2} is 0.1 to 6%. Said laser gas consists of Ar / Ne / _{F 2,} Ar is 1-6%, the continuous emission excimer laser oscillation method according to claim 21, wherein the _{F 2} is 0.1 to 6%. The continuous emission excimer laser oscillation method according to claim 21, wherein the laser gas is Ne / F ₂ , Ne is 94 to 99%, and F ₂ is 0.1 to 6%.   25. The continuous emission excimer laser oscillation method according to any one of claims 21 to 24, wherein the laser gas is introduced from both ends of the laser chamber and discharged from a central portion of the laser chamber.   The continuous wave excimer laser oscillation method according to any one of claims 21 to 25, wherein a frequency of the microwave is 1 GHz to 50 GHz.   27. The continuous emission excimer laser oscillation method according to any one of claims 21 to 26, wherein the microwave introduction means is a waveguide, and the inside of the waveguide is evacuated.   28. The continuous emission excimer laser oscillation method according to any one of claims 21 to 27, wherein an optical path vertical section of the laser chamber is elliptical.   29. The continuous emission excimer laser oscillation method according to claim 28, wherein a short axis direction of the ellipse is a microwave introduction direction.   30. The continuous emission excimer laser oscillation method according to any one of claims 21 to 29, wherein a magnetic field is applied to the laser chamber.   31. The continuous emission excimer laser oscillation method according to claim 21, wherein a distance between the pair of reflecting mirrors is 15 cm or less.   32. The continuous emission excimer laser oscillation method according to claim 21, wherein a gas pressure of the laser gas is set to several tens of Torr to 1 atm.   The continuous emission excimer laser oscillation method according to any one of claims 21 to 32, wherein an outer periphery of the laser chamber is covered with a jacket-like cooling device, and the temperature of the laser chamber is controlled. Light generated by exciting a laser gas composed of a mixed gas of at least one kind of inert gas selected from Kr, Ar, and Ne and F ₂ gas with electromagnetic waves, and comprising a pair of reflecting mirrors installed outside In a laser chamber that uses a resonator as laser light, the inner surface has a reflectance of 50% or less for light of a desired wavelength of 248 nm, 193 nm, and 157 nm, and the outermost surface of the inner surface is made of fluoride. A laser chamber comprising a window made of an insulator for introducing a microwave, wherein the reflectance of the window made of the insulator is 50% or less.   The laser chamber according to claim 34, wherein the window made of an insulator is provided by shrink fitting.   21. An excimer laser exposure apparatus comprising: the continuous-emitting excimer laser oscillation apparatus according to claim 1; an illumination optical system; an imaging optical system; and a stage for holding a wafer.   21. The continuous emission excimer laser oscillation device according to claim 1, wherein a reflectance of the output side reflecting mirror is 95% or more. 38. The continuous emission excimer laser oscillation device according to claim 37, wherein the reflectance of the output-side reflecting mirror is 99.5% or more. 38. The continuous emission excimer laser oscillation device according to claim 37, wherein the reflectance of the output side reflecting mirror is 99.95%, and the reflectance of the other reflecting mirror is 100%.   The continuous emission excimer laser oscillation device according to claim 1, wherein the laser gas is caused to flow so as to cross an optical axis direction of laser light in the laser chamber.

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