JPH0212980A - Narrow band laser oscillator - Google Patents

Abstract

PURPOSE:To obtain a laser output having stable narrowed spectral width, to reduce a special coherence and to eliminate a speckle in case of a lithography by forming the laser medium of a main oscillator of a slablike solid material, forming the sectional shape of an oscillated laser light in an optical axis direction in a slit state, and exciting and amplifying it as it is. CONSTITUTION:A main oscillator 17 has a slablike alexandrite 19 as a laser medium and a pair of Xe lamps 20, 21 oppositely provided on the opposite surface parts of the alexandrite 19. An optically pumping light source driver 22 controls the light emission of the lamps 20, 21. First slit plate 25 and a prism beam expander 26 are sequentially provided between a diffraction grating 23 and the alexandrite 19. First and second slit plates 25, 28 are formed with slits 25a, 28a passed continuously laterally. A laser light emitted from the mirror 24 of the oscillator 17 is incident to an amplifier 18.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a narrowband laser oscillation device used as a light source of a semiconductor exposure apparatus, for example.

(Prior Art) Narrowband excimer lasers are being used as light sources in reduction projection exposure systems for semiconductor exposure, but in this case, in order to obtain high output, an amplification section is required to amplify the output of the laser light emitted from the laser light oscillator. Injection lock technology is used.

FIG. 5 shows a conventional injection lock type narrowband laser oscillation device.

This laser oscillation device 1 consists of a main oscillation section 2 and an amplification section 3, both of which use an excimer gas laser medium. The main oscillator 2 is provided with a diffraction grating 5 and an output mirror 6 that face each other across a discharge tube 4 that excites an excimer gas laser medium to emit laser light.

Between the diffraction grating 5 and the discharge tube 4, there is a plate 8 having a pinhole 7 on the discharge tube 4 side, and a wavelength selection element 9 provided on the diffraction grating 5 side and constituted by a prism, an etalon, etc. (not shown). is provided to form a stable laser resonator.

The laser beam oscillated from the main oscillation section 2 is then
The optical axis is bent by the second high-reflection mirror 10.11, and the light is incident on the amplifying section 3.

As described above, the amplifying section 3 includes a discharge tube 12 in which an excimer gas laser medium is sealed, and a convex mirror 13 and a concave mirror 14 facing each other so as to sandwich the discharge tube 12 therebetween. Here, a through hole 15 having a diameter of about 1 u is bored in the center of the concave mirror 14, and the laser beam oscillated by the main oscillation section 2 is incident on the through hole 15. ing.

The laser oscillation device 1 configured as described above first oscillates a laser beam with a spectral width of 0.003 na+ and an average output of 0.01 W using the main oscillation section 2. This transfers the light emitted from the discharge tube 4 to the diffraction grating 5 and the wavelength selection element 9.
By passing through the pinhole 7 etc. of the plate 8, the single light is made into an oscillating state and a predetermined output (0, Olw
) from the output mirror 6 to the first high reflection mirror 10
Aim the laser beam at the target. Then, the laser beam reflected by the first high reflection mirror 10 is transferred to the second high reflection mirror 1.
1 and enters the amplification section 3. The laser beam that enters the amplifying section 3 enters between the unstable resonators 13 and 14 from the through hole 15 of the concave mirror 14, and is reflected multiple times while expanding the beam between the resonators 13 and 14. Then, the injection is locked and the output is amplified while maintaining a narrow spectrum width, and is finally emitted from the convex mirror 13 side. Due to this amplification effect, the spectrum width is 0.00, which is the same as when oscillated from the main oscillator 2.
At 3 nm, a narrow band laser beam with an average output of 50 W can be obtained.

However, such a narrowband laser oscillation device has the following drawbacks.

First, the single transverse mode laser beam output from the main oscillator 2 is directly amplified by the injection lock, resulting in high spatial coherence, which causes speckles on the exposed surface when used for lithography in semiconductor manufacturing. do.

Further, the stimulated emission time of the excimer gas laser medium is extremely short, about 10 to 40 ns, and therefore the timing of excitation of the medium in the main oscillation section 2 and the amplification section 3 must be precisely matched with an accuracy of 1 to 3 ns. However, this timing may sometimes shift due to instability of the discharge for excitation, jitter in the electric circuit, etc. In this case, injection locking is not performed sufficiently, and a laser beam with a wide spectrum width is output, resulting in a decrease in laser output. It was sometimes unstable. Furthermore, the laser beam output from the main oscillator 2 passes through the pinhole 7, so that the laser beam itself has an extremely thin cylindrical shape, and only a small portion of the emitted laser beam is extracted. Therefore, the utilization efficiency of the excitation volume was low.

(Problem to be solved by the invention) A narrowband laser oscillation device that uses an excimer gas laser oscillator for both the main oscillation part and the amplification part and passes the laser light through a pinhole has high spatial coherence and is used for exposure in semiconductor lithography, etc. Speckles may appear on the surface. Furthermore, since the induced discharge period of the excimer gas laser medium is extremely short, it is extremely difficult to match the timings of the main oscillation section and the amplification section. Furthermore, since the band can be narrowed by passing through a pinhole, there is a drawback that the utilization efficiency of the excitation volume is low.

The present invention was made in view of the above problems, and it is possible to obtain a stable laser output with a narrow band spectral width, low spatial coherence, and no speckles occur during lithography. (The purpose is to provide a narrowband laser oscillation device that can oscillate laser light that can perform homogeneous exposure.

[Structure of the invention]

(Means for solving the problem) An excitation section that has a slab-shaped solid-state laser medium and oscillates a laser beam is provided, and the laser beam from this excitation section is connected to a diffraction grating and a luminous flux thickness in the thickness direction of the solid-state laser medium. A main oscillation part is provided that outputs a slit-shaped laser beam whose frequency is narrowed to the ultraviolet region, and the laser beam outputted from the slit is introduced into the excitation part having an excimer gas laser medium. A narrowband gas laser oscillation device includes an amplification section that amplifies laser light.

(Function) By using a slab-like solid as a laser medium, the laser beam has a slit-like cross section, so it is possible to oscillate a multi-mode single wavelength laser beam, and the spatial coherence is lowered, making it suitable for use in semiconductor lamination lithography. This can prevent the occurrence of errors. Furthermore, by using a slab-like solid state as the laser medium of the main oscillation section, the stimulated emission period is long, and it becomes easy to synchronize the excitation timing of the amplification section, making it possible to obtain stable laser output. Furthermore, the laser beam emitted from the slab-like solid has a slit-like cross-sectional shape in the optical axis direction, and is pumped and amplified with this cross-sectional shape, resulting in high utilization efficiency of the excitation volume.

(Embodiment) An embodiment of the present invention will be described with reference to FIGS. 1 to 4. The narrowband laser oscillation device 16 shown in the figure consists of a main oscillation section 17 and an amplification section 18. First, the configuration of the main oscillation section 17 will be explained. The main oscillator 17 has a width, length, and height of 20II11×
A slab-shaped alexandrite 19 formed in a 100M 1×5 cell is provided as a laser medium, and a pair of Xe lamps 20 and 21 are provided facing each other on opposing surface portions of the slab-shaped alexandrite 19. An excitation light source driver 22 is connected to each of these Xe lamps 20, 21. This excitation light source driver 22
is for controlling the light emission of the Xe lamps 20 and 21.

Further, a diffraction grating 23 is provided on one end surface side in the longitudinal direction of the alexandrite 19, and an output mirror 24 is provided on the other end surface side. A first slit plate 25 and a prism beam expander 26 are sequentially provided between the diffraction grating 23 and the alexandrite 19 from the alexandrite 19 side.

Further, between the alexandrite 19 and the output mirror 24, a laser beam frequency multiplication unit 27 consisting of a nonlinear optical element or the like is installed from the alexandrite 19 side.
A second slit plate 28 is sequentially provided. Here, the first and second slit plates 25.2
Both slits 8 are provided with slits 25a and 28a that are continuously penetrated in the width direction so as to face each other across the width direction dimension 20M of the alexandrite 19. These slits 25 a s 2 (y a ) have a width dimension of 22 m and a height dimension of 11111.

Output mirror 24 of main oscillator 17 configured as described above
The laser beam emitted from the first and second high-reflection mirrors 29 and 30 is sequentially reflected, and the optical axis is bent, so that the laser beam is incident on the amplifying section 18.

This amplification section 18 includes an excimer laser excitation section 31 that excites an excimer gas laser medium by discharge, and an excimer laser excitation section 31 that excites an excimer gas laser medium by discharge.
It has an amplification resonator 31a consisting of a cylindrical concave mirror 32 and a cylindrical convex mirror 33 facing each other with the excimer gas laser medium in between. An excimer laser excitation unit driver 35 is provided for generating discharge. That is, a discharge electrode (not shown) is provided in the discharge tube 34 to amplify the laser light passing therethrough, and the excitation driver 35 is electrically connected to this discharge electrode. This excitation driver 35 is connected to a delay circuit 36, and is operated under control from this delay circuit 36. Here, the delay circuit 36 is also connected to the excitation light source driver 22 of the main oscillation section 17,
The main oscillation section 17 and the amplification section 18 are arranged so that the amplification section 18 operates in a timely manner in response to the laser beam oscillated by the main oscillation section 17.
It is designed to control both.

Further, the cylindrical concave mirror 32 is disposed on the optical axis of the laser beam between the second high reflection mirror 30 and the discharge tube 34, and the reflective surface 37 faces the discharge tube 34. This reflective surface 37 is formed into a cylindrical shape that is curved only in the height direction and has no curvature in the width direction.
An anti-reflection coating area 38 is formed as an incident part at the center in the height direction so that the laser beam can pass through.
A high reflection coating region 39 is formed in other parts. The anti-reflection coating area 38 has a height of 111% and a width of 20w1.

On the other hand, the cylindrical convex mirror 33 is arranged such that a reflecting surface 40 curved only in the height direction faces the discharge tube 34, and the height dimension is 2 ms and the width dimension is 20 m in the central part in the height direction.
A high reflection coating region 41 is formed in the size range of rx. In addition, a non-reflective coating area 42 is formed on the other part of the high-reflection coating area 41 of the reflective surface 40. Furthermore, the back surface 43 is coated with a non-reflective coating and has a meniscus shape with the same curvature as the front surface.

Here, both the concave cylindrical mirror and the convex cylindrical mirror 32 and 33 are made of a material that transmits laser light.

When the narrowband laser oscillation device configured as described above is operated, first, the Xe lamps 20 and 21 emit light under the control of the excitation light source driver 22, and the alexandrite 19 of the main oscillation section 17 emits light at a wavelength of 750 nm. Laser light is oscillated in the range of ±5OnIg. The wavelength of this laser beam is reduced to, for example, 1/3 by passing through the laser frequency multiplication unit 27, and then the slit plate 25.
28, prism beam expander 26, diffraction grating 23
The center wavelength is 248.4 nm and the spectral width is 0.00.
3 nm. The cross-sectional shape of the laser beam emitted from the output mirror 24 in the optical axis direction is in the order of height,
It has a slit-shaped rectangular shape with a width of 20 m.

Here, the alexandrite 19 is formed into a slab shape, and the laser beam emitted by exciting the alexandrite 19 has a cross-sectional shape extremely similar to the slit-shaped laser beam output, so that the excitation volume can be used with high efficiency. can do.

Here, the average output of the laser beam oscillated by the main oscillation section 17 is about 0.2 W, which is more than 10 times the output of the main oscillation section using a conventional excimer laser oscillation device, so it is relatively large. Sufficient injection locking can be achieved even when outputting in terms of area.

As described above, the laser light output from the main oscillation section 17 is input into the amplification resonator 31a of the amplification section 32 from the non-reflection coating region 38 of the cylindrical concave mirror 32 of the amplification section 18. After passing through the cylindrical concave mirror 32, this laser light passes through the discharge tube 34, is reflected by the high reflection coating area 41 of the cylindrical convex mirror 33, and passes through the discharge tube 34 again. The light is then reflected by the high reflection coating area 39 of the cylindrical concave mirror 32, repeatedly passes through the discharge tube 34, and is reflected by the high reflection coating area 41 of the cylindrical convex mirror 33. By being reflected between the cylindrical concave mirror 32 and the cylindrical convex mirror 33 in this way, the light is expanded and amplified only in the curvature direction of the cylindrical surface. As a result, the outer portion of the cylindrical convex mirror 33 outputs a laser beam having an optical cross section of 10 B in height and 20 m in the width direction. Here, the emitted laser beam has a shadow having a heightwise dimension of 2u formed by the high reflection coating region 42 of the cylindrical convex mirror 33 at the center in the heightwise direction. That is, since the laser beam is emitted only from the non-reflection coating area 42 of the cylindrical convex mirror 33, the cross section of the laser beam is divided into two parts, an upper side and a lower side. At this time, the delay circuit 36 controls the excitation light source driver 22 and the excitation section driver 35 in order for the amplification section 18 to pump and amplify the laser beam output from the main oscillation section 17 efficiently and stably. There is.

The laser beam emitted in this way can obtain an average output of 50 W, and this laser beam has a spectral width of 0.0
03no+i has a narrow band, but since the laser light passes through the slits 25a and 28a instead of the pinhole in the main oscillator 17, the transverse mode becomes a multi-mode, so the spatial coherence can be lowered, making it easy to apply to semiconductors etc. The occurrence of speckles during lithography can be reduced.

In addition, the pulse width of the alexandrite laser is about 1 μs, which is 5 μs compared to the conventional excimer laser.
It is about 0 times longer, and it is easy to prevent injection lock deviation due to a difference in excitation timing between the main oscillation section 17 and the amplification section 18.

Note that the present invention is not limited to the above-mentioned embodiment. For example, in the above embodiment, the material of the slab-shaped solid laser medium is alexandrite 19, but is not limited to this, and is a slab-shaped solid medium that can oscillate a laser compatible with the wavelength of the excimer laser excited in the amplification section. That's fine.

〔Effect of the invention〕

By using a slab-shaped solid-state laser medium in the main oscillation part, the cross section of the laser beam in the optical axis direction becomes long in the width direction, and the mode in the width direction becomes a multi-mode, making it possible to meet specifications when used in lithography, etc. It is possible to prevent the occurrence of errors. In addition, by using a solid laser medium for the main oscillator,
It is now possible to extend the stimulated emission time of the laser beam, and it is now possible to reliably synchronize the excitation timing in the amplification section.
Can oscillate stable laser light. Furthermore, the slab-like solid medium of the main oscillator section emits light with a slit-shaped cross section in the optical axis direction, and is amplified in the amplification section while maintaining a state close to this cross-sectional shape. Utilization efficiency can be increased.

[Brief explanation of the drawing]

FIGS. 1 to 4 show an embodiment of this invention,
Fig. 1 is a block diagram showing a schematic configuration of a narrowband laser oscillation device, Fig. 2 is a perspective view showing the shape of a slab-like solid, Fig. 3 is a perspective view showing a cylindrical concave mirror, and Fig. 4 is a cylindrical convex mirror. FIG. 5 is a perspective view showing a mirror and a configuration diagram showing a schematic configuration of a conventional narrow band laser oscillation device. 17... Main oscillation part, 18... Amplification part, 19... Alexandrite (slab-like solid), 23... Diffraction grating, 25a... Slit, 28a... Slit, 2
7... Optical frequency multiplication unit, 32... Cylindrical concave mirror 33... Cylindrical convex mirror Patent attorney Takehiko Suzue

Claims (1)

[Claims] Laser light generated in an excitation section having a slab-shaped solid-state laser medium is narrow-banded using a diffraction grating and an aperture plate formed with a slit that narrows the thickness of the light beam in the thickness direction of the solid-state laser medium. A main oscillation section that changes the frequency of the slit-shaped laser beam to the ultraviolet region and outputs it, and an excitation section that introduces the outputted slit-shaped laser beam and has an excimer gas laser medium to amplify the introduced laser beam. What is claimed is: 1. A narrowband laser oscillation device comprising: an amplifier section for outputting an output.