JPH1041564A - Excimer laser oscillation device and aligner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prolong the life of one pair of electrodes and to make it possible to obtain a desired output for a long time by a control only of an applying electrode in an excimer laser oscillation device, by a method in which all the parts or the almost parts, which do not face one pair of reflecting mirrors, out of the surface of the interior of a laser chamber are formed of multilayer dielectric films having different refractive indexes. SOLUTION: Multilayer dielectric films 29 and 30 having different refractive indexes are formed on almost all the parts, which do not face reflecting mirrors 22 and 23, out of the surface of the interior of a chamber. The films 29 and 30 having the different refractive indexes are formed of an alternating multilayer film of a center wavelength of 1/4 of the thickness of an optical film and have roughly 100% of a reflectivity to a laser beam of a single-core wavelength. The surface of the interior of the chamber is formed of the multilayer film of a reflectivity of 100%, by which it becomes possible to return all lights emitted in directions other than the directions of one pair of the reflecting mirrors 22 and 23 to a discharge part. As a result, the efficiency to excite laser gas is enhanced and a desired output can be obtained for a long time by a control only of an applying electrode, wastage of a discharge electrode is also decreased and the life of one pair of electrodes provided in the chamber is also prolonged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the technical field of an excimer laser oscillation device used for processing various articles.

[0002]

2. Description of the Related Art Excimer lasers have attracted attention as the only high-power lasers that oscillate in the ultraviolet region, and are expected to be used in the electronics, chemical, and energy industries. Specifically, it is used for processing of metal, resin, glass, ceramics, semiconductor and the like, chemical reaction, and the like.

An apparatus for generating excimer laser light is:
It is known as an excimer laser oscillation device. A laser gas such as Ar, Kr, Xe, or F ₂ filled in the manifold is excited by electron beam irradiation, discharge, or the like. Then, the excited atoms combine with atoms in the ground state to generate molecules that exist only in the excited state. This molecule is called excimer. Since the excimer is unstable, it immediately emits ultraviolet light and falls to the ground state. This is called a bond-free transition. An excimer laser oscillation device amplifies the ultraviolet light obtained by this transition in an optical resonator composed of a pair of reflecting mirrors and extracts it as laser light.

[0004] Among the excimer laser beams, the KrF laser and the ArF laser contain a laser gas because a highly reactive fluorine gas is used as the laser gas.
The concentration of fluorine in the laser chamber for providing discharge energy to the gas is reduced. Therefore, control is performed so that a predetermined output can be obtained by increasing the supply voltage to the laser chamber.If it is difficult to obtain the output even with such control, the oscillation is stopped once and the fluorine gas is discharged. Replenish. Further, if oscillation is continued, a predetermined laser output cannot be obtained even when replenishment of fluorine is performed. In this case, the laser chamber must be replaced.
FIG. 1 is a graph showing the relationship between the number of oscillations of the pulse laser, the filling of fluorine gas, and the displacement of the supply voltage.
(William Parilo et al., "A Low Cost of Ownership K
rF Excimer Laser Using a NovelPulse Power and Cham
ber Configuration "), a technique to extend laser life by replenishing fluorine gas and controlling the supply voltage.

In the case of an excimer laser light emitting device which emits light by pulse voltage and emits light for about several tens of nanoseconds, the emission time is too short, so that the emission due to stimulated emission is much larger than the emission due to spontaneous emission. And the half width of the wavelength of the emission spectrum of the output light is
It is as wide as 300 pm. Therefore, for the first time, monochromatization by a narrow-banding module type such as grating,
A wavelength half width of less than pm is obtained.

As shown in FIG. 1, in the current technology, it is necessary to replenish fluorine gas at predetermined intervals and to oscillate while increasing the applied voltage. In other words, the fluorine gas decreases with time due to a reaction with the inner surface of the chamber. Therefore, the life of the laser chamber is not yet sufficient, and particularly when the laser is used for a long time for processing an article, the life of the chamber is important for improving the production throughput of the processed article. Is a factor.

Although it is now possible to obtain a wavelength half width of 1 pm or less by monochromatization using a band narrowing module such as grating, on the other hand, the output is reduced by band narrowing using grating or the like. The light emission intensity is decreasing, which is a great hindrance to improving the production throughput of processed articles.

[0008]

SUMMARY OF THE INVENTION The present invention provides an excimer laser which has a long life (that is, the replenishment period of fluorine gas can be lengthened) and a desired output can be obtained for a long time only by adjusting the applied electrode. It is an object to provide an oscillation device. In addition, the consumption of the discharge electrode can be reduced, and the life of the electrode can be prolonged.

It is a further object of the present invention to provide an excimer laser device capable of narrowing the band while increasing the intensity of output light. An object of the present invention is to provide an excimer laser exposure apparatus capable of achieving a spectrum with a narrow wavelength width without using a band narrowing module, and realizing miniaturization and simplification of the apparatus.

[0010]

According to the present invention, there is provided an excimer laser oscillation apparatus comprising: a laser chamber for containing a laser gas; a pair of electrodes provided in the chamber;
In an excimer laser oscillation device that applies a voltage to the pair of electrodes to excite a laser gas to emit light and cause laser oscillation by a pair of reflecting mirrors, the excimer laser oscillation device includes: All or most of the parts that do not face are formed of a multilayer dielectric film having a different refractive index.

[0011]

FIG. 2 is a schematic sectional view for explaining the structure of an excimer laser oscillation device according to the present invention. 1 is a laser chamber, 2 and 3 are a pair of reflecting mirrors constituting an optical resonator, and 3 is an output mirror. 4,5
Is an electrode to which a voltage for exciting the laser gas is applied, 6 is a blower for circulating the laser gas in the chamber, and 7 and 8 are windows for transmitting the laser light.

The excimer laser according to the present invention has four, five,
Is characterized in that the electrode surface is formed of a fluoride passivation film. For example, when NiF _2, which can be used for both an Al alloy surface and a stainless steel surface, is formed on a 20-nm thick electrode surface, the electrode life is increased 1.5 times as compared with the case where no fluoride passivation film is formed. did. This is because the formation of a fluorinated passivation film on the electrode surface completely suppresses the reaction between fluorine and the electrode material during discharge, thereby reducing the consumption of fluorine gas and the consumption of the electrode.

Further, by suppressing the reaction between fluorine and the electrode material during discharge, generation of particles and deposition of reaction by-products on the window surface can be reduced. This effect is further enhanced by covering not only the electrode surface but also the inner surface of the chamber with a fluorinated passivation film such as NiF ₂ , FeF ₂ , AlF ₃ / MgF ₂ . As a result, the window cleaning interval could be 1.5 times longer than before.

However, the current value, the capacitance of the fluorinated passivation film, and the like must be determined so that the fluorinated passivation film does not break down when a voltage is applied. That is, the current value flowing between the discharge electrodes is I, the capacitance of the fluorinated passivation film is C,
When the angular frequency of the applied voltage is ω, the dielectric breakdown electric field of the fluorinated passivation film is E _BD , and the film thickness is t, it is necessary to set these parameters so as to satisfy I / (ωC) <E _BD t. is there. FIG. 3 shows the results of current-voltage characteristics measured with an electrode of about 1 mmφ provided on a NiF ₂ film having a thickness of 200 nm.
The green breakdown voltage is 80V or more, and the withstand voltage is 4MV /
cm or more. Thus, it can be seen that the NiF ₂ film is an extremely excellent insulating film electrically.

FIG. 4 shows the direction of the current flowing between the discharge electrodes.
(A), the or case and the current value in the other direction immediately after the first current i ₁ flows in one direction is shed approximately equal a second current i _2, or FIG. 4 ( As shown in b), after a current i1 in _one direction flows, a predetermined period I
If and the current value in the other direction from spaced NT shed approximately equal a second current i _2, always compared to when the flow in the same direction, the life of the electrode is increased two-fold. This is because the deterioration of the discharge electrode is vertically symmetric, and the deterioration of the electrode is suppressed as compared with the conventional device.

As shown in FIG. 4A or FIG.
In order to flow a current as shown in FIG.
Alternatively, a circuit shown in FIG. 10 may be used. FIG. 9 is a circuit configuration diagram of a laser oscillation device for achieving FIG. 4A. 1 is a 1 kV high voltage power supply, 2 is a charging resistor,
Reference numeral 3 denotes a capacitor for accumulating electric charge, 4 denotes a magnetic switch for narrowing a pulse width, and 5 denotes a thyristor for starting laser oscillation. These are power supply 1, resistance 2, capacitance 3,
The magnetic switch 4 and the thyristor 5 constitute the primary coil side of the transformer 6. The turns ratio of the transformer 6 is, for example, 1: 2.
At 0, the winding direction is reversed. The same circuit as the capacitor 3 and the magnetic switch 4 may be connected in multiple stages to further reduce the pulse width.

On the secondary coil side of the transformer 6, a capacity 8,
9, _Cp and the magnetic switch 7 are connected. A circuit 16 including the capacitances 8, 9, _Cp and the magnetic switch 7 is connected to the discharge electrodes 10a, 10b of the laser chamber 10. Reference numeral 11 denotes a play onizer used for stably causing discharge. The features of this circuit are spark gap 12, capacitance C _i , coil 13, resistance 1
Fourth, a circuit 17 including a high-voltage power supply 15 is provided.

First, the charge storage capacitor 3 is charged to 1 kV using the high voltage power supply 1. Also, charge to 15kV using a high-voltage power supply 15 to charge storage capacitor C _i. Thereafter, when a trigger is applied to the thyristor 5 and the thyristor is turned on, the charge stored in the capacitor 3 is discharged.
At this time, a pulse voltage of about −15 kV is applied to both ends of the capacitor 8.

At both ends of the capacitor C _p , a voltage whose pulse width is reduced to about 150 ns by the magnetic switch 7 appears as shown in FIG. When the voltage applied to both ends of the capacitance Cp is -1
When the voltage changes from 5 kV to 0 V, first, the preionizer 11 starts discharging, and 10 ⁶ −1 in the laser chamber.
Free electrons having a density of about 0 ⁷ cm ^-3 are generated. Thereafter, a uniform discharge occurs between the discharge electrodes 10a and 10b, and a laser is oscillated. If there is no circuit 17, -15k
Although the voltage only increases from V to 0 V, the circuit 17
If there is, the voltage rises to +15 kV.

The operation at this time will be described below. When the voltage applied to both ends of the capacitance C _p changes abruptly, the high frequency voltage is almost applied to the coil 13. This is because the impedance of the coil 13 is set to be larger than that of the resistor 14. When a large voltage is applied to both ends of the coil 13, the spark gap 12 sparks and conducts. This will charge stored in the capacitor C _i is discharged, the discharge electrode 10a, the voltage applied between b rises to approximately 15kV. At this time, the discharge electrode 10
Discharge occurs again between a and b, this time with the current flowing in the opposite direction.

As described above, in this configuration, since the circuit 17 is provided, current flows alternately between positive and negative. FIG. 6 shows FIG.
5 is an example of a circuit for achieving the current of (b). As in the case where the circuit configuration of FIG. 9 is used, first, the charge storage capacitors 3 and 3 ′ are charged to 1 kV using the high-voltage power supply 1. Thereafter, when a trigger is applied to the thyristor 5 ′ and the thyristor 5 ′ is turned on, the electric charge stored in the capacitor 3 ′ is discharged. At this time, -1 is applied to both ends of the capacitor 8.
A pulse voltage of about 5 kV will be applied.

Further, the both ends of the capacitor C _p, the pulse width in the magnetic switch 7 appears the voltage was reduced to about 150ns. 0V voltage across the capacitance C _p is from -15kV
, First, the preionizer 11 starts discharging to generate free electrons having a density of about 10 ⁶ -10 ⁷ cm ^-3 in the laser chamber. Then, discharge electrode 1
A uniform discharge occurs between Oa and b, and a laser is oscillated. Next, by using the high-voltage power supply 1, the charge storage capacitor 3 ', which has lost its charge by discharging, is charged to 1 kV within 1 ms. This time, when a trigger is applied to the thyristor 5 and the thyristor 5 is turned on, the charge stored in the capacitor 3 is discharged. At this time, the capacitor 8 has + 15k
A pulse voltage of about V is applied.

At both ends of the capacitor Cp, a voltage whose pulse width is reduced to about 15 ns by the magnetic switch 7 appears as shown in FIG. 7, thereby oscillating the laser. Similarly, by applying a trigger to the thyristors 5 and 5 'alternately at 1 ms intervals, a pulse voltage can be generated at both ends of the capacitance Cp. However, by adding the circuit 21, the withstand voltage of the thyristors 5 and 5 'is twice that of the case where the circuit 21 is not provided, that is, at least 2kV is required.

As described above, in this circuit, since the circuit 21 is provided, the current can flow alternately between positive and negative. FIG. 5 is a schematic view of a laser oscillation device according to another preferred embodiment of the present invention, and shows a cross-sectional top view. 21 is a laser chamber, 22 and 23 are a pair of reflecting mirrors forming an optical resonator, and 23 is an output mirror. Reference numeral 24 denotes an electrode to which a voltage for exciting the laser gas is applied. Reference numerals 29 and 30 denote multilayer dielectric films having different refractive indexes.
Are formed in almost all parts not facing the reflector. Reference numerals 27 and 28 denote windows for transmitting laser light.

The multilayer dielectric films having different refractive indices shown in FIG. 5 are formed by alternating multilayer films having an optical film thickness of 中心 center wavelength, and are almost 100% with respect to a single core wavelength.
Has a reflectance of For example, La as a high refractive index material
F ₃ , NdF ₃ , Al ₂ O _{3 and the} like, and low refractive index materials include AlF ₃ , MgF ₂ and SiO ₂ . FIG.
The graph shows the reflectance with respect to wavelength when LaF ₃ as a high-refractive-index material and MgF ₂ as a low-refractive-index material are formed in multiple layers on the Al surface. At this time, the formation of the alternate multilayer film
First, a MgF ₂ / LaF ₃ alternate film was formed on Al with an optical film thickness of 1
15 times at 93/4 nm (48.25 nm) and M
The gF ₂ / LaF ₃ alternate film was coated with an optical film thickness of 248/4 nm (6
(2 nm) 13 times.

As described above, by forming the multilayer dielectric film having different refraction portions by an alternate multilayer film having an optical film thickness of 中心 center wavelength, as shown in FIG.
The reflectivity at m and 248 nm can be nearly 100%. The wavelength of 193 nm is the center wavelength of the ArF excimer laser, and the wavelength of 248 nm is the center wavelength of the KrF excimer laser. FIG. 7 also shows that MgF
_{The 2} / LaF ₃ alternating film was formed with an optical film thickness of 193/4 nm (48.
25 shows the reflectance with respect to the wavelength when the MgF ₂ / LaF ₃ alternate film was formed 22 times with an optical film thickness of 248/4 nm (62 nm) 23 times at 25 nm) and 22 times. As in the case of the Al substrate shown in FIG. 6, the reflectance can be made almost 100% at the wavelengths of 193 nm and 248 nm.

By forming the inner surface of the chamber with a multilayer film having a reflectivity of 100% as described above, it is possible to return all light emitted in directions other than the pair of reflecting mirrors to the discharge portion. As a result, the efficiency of exciting an excimer such as ArF ^* or KrF ^* is improved. Furthermore, the 8atm inner pressure of the chamber from a conventional 3 atm, 3% of the F ₂ concentration from conventional 0.1%, the Kr concentration from 1% 5
%, The same output was obtained even if the resonator length was reduced from 75 cm to 15 cm.

Shortening the resonator length has the effect of narrowing the half-width of the emission spectrum when one discharge time is as short as several tens of ns. For example, when the resonator length is 75 cm, the time required for light to make a round trip through the resonator is 5 nm. Therefore, when the discharge time is 10 ns, light can make only two round trips through the resonator at the maximum. Under such circumstances, the emission due to stimulated emission cannot be made sufficiently higher than the emission due to spontaneous emission, and as a result, the half-value width of the emission spectrum becomes 300 as shown in FIG.
pm. Therefore, at present, for the first time, 1p is achieved by monochromaticization using a band narrowing module such as grating.
m or less is obtained. However, when the band is narrowed using grating or the like, there is a problem that the light emission intensity decreases.

On the other hand, if the resonator length is reduced to 15 cm,
The time required for light to make a round trip through the resonator is 1 ns. Therefore, when the discharge time is 10 ns, the light makes a maximum of 10 round trips in the resonator, so that the emission by dielectric emission can be made sufficiently larger than the emission by spontaneous emission. The half width of the emission spectrum at this time is shown in FIG.
As shown in FIG.

As described above, according to the present invention, the resonator length is set to 15c.
shortened and m, 3 a chamber inner wall surface formed by alternate multilayer film having an optical thickness of 1/4 the center wavelength, further to 8atm inner pressure of the chamber from a conventional 3 atm, the F ₂ concentration from conventional 0.1% By increasing the Kr concentration from 1% to 5% to about%, the following effects are obtained. First, there is an effect that the half width of the emission spectrum is narrowed, and as a result, a half width of 1 pm or less was obtained. Further, by forming the inner surface of the chamber with a multilayer film having a reflectivity of 100%, it is possible to return all the light emitted in directions other than the pair of reflecting mirrors to the discharge portion, and to use an excimer such as ArF ^* or KrF ^*. The efficiency of exciting is improved. Further, the pressure in the chamber is increased from 3 atm to 8 a.
tm, and the F ₂ concentration from about 0.1% to about 3%,
By increasing the Kr concentration from 1% to 5%, a similar output can be obtained even if the resonator length is reduced from 75 cm to 15 cm. Since the band narrowing module such as grating is not used, the final output light can be made larger than that of the conventional one. Further, the device volume can be reduced to half or less by greatly shortening the resonator length in this way.

FIG. 11 shows an exposure apparatus using an excimer laser oscillation apparatus. Light emitted from the oscillation device A1 is guided to a scanning optical system via a mirror. 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 applied to 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.

Light having a light / dark distribution corresponding to a predetermined mask pattern by the reticle A6 is imaged on a wafer A8 mounted on a stage by an imaging optical system having an objective lens 7, and a latent image corresponding to the mask pattern is formed. Is formed on the photosensitive resist on the surface of the wafer A8. As described above, the exposure apparatus shown in FIG. 1 can be constituted only by the excimer laser oscillation device A1, the illumination optical system, the imaging optical system, and the stage A9 for holding the wafer A8. That is, the half width can be reduced without providing a band narrowing module between the oscillation device A1 and the scanning optical system, and a compact exposure apparatus can be achieved.

[0033]

According to the present invention, the life of the laser chamber can be extended. That is, the replenishment period of the fluorine gas can be lengthened, and a desired output can be obtained for a long time only by adjusting the applied electrode. In addition, the consumption of the discharge electrode can be reduced, and the life of the electrode can be prolonged. Further, a narrow band is realized while increasing the intensity of the output light.

[Brief description of the drawings]

FIG. 1 is a graph described in the literature showing the relationship between replenishment of fluorine gas and supply voltage.

FIG. 2 is a conceptual diagram of an excimer laser oscillation device.

FIG. 3 is a graph showing the results of current-voltage characteristics measured by providing an electrode of about 1 mmφ on a NiF ₂ film having a thickness of 200 nm.

FIG. 4 is a diagram showing an example of a current flowing between discharge electrodes.

FIG. 5 is a conceptual diagram of an excimer laser oscillation device according to an embodiment of the present invention.

FIG. 6 is a graph showing a relationship between wavelength and reflectance when a high refractive index layer and a low refractive index layer are formed in multiple layers on an Al surface.

FIG. 7 is a graph showing the relationship between the wavelength and the reflectance when a high refractive index layer and a low refractive index layer are formed in multiple layers on the SUS surface.

FIG. 8 is a graph showing a half width of an emission spectrum.
(A) is a conventional example, and (b) is an example of the present invention.

FIG. 9 is a circuit diagram showing a circuit example for flowing the current shown in FIG.

FIG. 10 is a circuit diagram showing an example of a circuit for flowing the current shown in FIG.

FIG. 11 is a conceptual diagram showing an exposure apparatus according to the present invention.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazuhide Ino Aoba, Aoba-ku, Aoba-ku, Sendai-shi, Miyagi (No address) Inside the Department of Electronic Engineering, Tohoku University (72) Inventor Nobuyoshi Tanaka 3- 30-2 Shimomaruko, Ota-ku, Tokyo No. Canon Inc.

Claims (7)

[Claims] 1. A laser chamber for containing a laser gas, a pair of electrodes provided in the chamber,
In an excimer laser oscillation device that applies a voltage to the pair of electrodes to excite a laser gas to emit light and cause laser oscillation by a pair of reflecting mirrors, the excimer laser oscillation device includes: An excimer laser oscillation device characterized in that all or most of the parts not facing are formed of a multilayer dielectric film having a different refractive index. 2. The excimer laser oscillation device according to claim 1, wherein currents flowing through the pair of electrodes on which the fluorinated passivation film is formed alternately flow in positive and negative directions. 3. The multi-layer dielectric film according to claim 1, wherein the multi-layer dielectric film is formed of an alternating multi-layer film having an optical film thickness of 中心 center wavelength and has a reflectance of about 100% with respect to the center wavelength. An excimer laser oscillation device as described in the above. 4. The excimer laser oscillation device according to claim 1, wherein the length of the resonator is approximately 15 cm or less. 5. The excimer laser oscillation device according to claim 1, wherein the pressure in the chamber is set to 5 atm or more. 6. The excimer laser oscillation device according to claim 1, wherein a fluorinated passivation film is formed on the electrode surface. 7. An excimer laser oscillation device according to claim 1, further comprising an illumination optical system, an imaging optical system,
An excimer laser exposure apparatus, comprising: a stage for holding a wafer.