JP5607592B2 - Narrow band laser equipment - Google Patents

Description

  The present invention relates to a narrow-band laser device, and in particular, in a narrow-band excimer laser device or a narrow-band F2 laser device as a light source of a reduction projection exposure apparatus used for manufacturing a semiconductor, the spectral purity of the laser light. The present invention relates to an apparatus for controlling spectral index values such as width.

  The prior art of the narrow-band laser apparatus used as the light source of the reduced projection exposure apparatus will be described below for each item.

(Light source for exposure)
As semiconductor integrated circuits are miniaturized and highly integrated, improvement in resolving power is demanded in semiconductor exposure apparatuses. For this reason, the wavelength of light emitted from the exposure light source is being shortened, and a gas laser device is used as the exposure light source in place of the conventional mercury lamp. As the current gas laser apparatus for exposure, a KrF excimer laser apparatus that emits ultraviolet light with a wavelength of 248 nm and an ArF excimer laser apparatus that emits ultraviolet light with a wavelength of 193 nm are used. As a next-generation exposure technique, it is conceivable to apply an immersion technique for ArF exposure, which shortens the apparent wavelength of the exposure light source by filling the space between the exposure lens and the wafer with liquid and changing the refractive index. ing. In ArF immersion, the apparent wavelength is as short as 134 nm. As a next-generation light source for exposure, an F2 laser device that emits ultraviolet light having a wavelength of 157 nm is promising, and F2 laser immersion exposure may be adopted. In F2 immersion, it is said that the wavelength is shortened to 115 nm.

(Exposure optics and chromatic aberration)
A projection optical system is adopted as an optical system of many semiconductor exposure apparatuses. In the projection optical system, chromatic aberration correction is performed by combining optical elements such as lenses having different refractive indexes. At present, there are no optical materials other than synthetic quartz and CaF2 suitable for use as the lens material of the projection optical system in the wavelength range of 248 nm to 115 nm of the laser wavelength which is an exposure light source. For this reason, as the projection lens for the KrF excimer laser, an all-refractive type monochromatic lens composed only of synthetic quartz is adopted, and as the projection lens for the ArF excimer laser, an all-refractive type composed of synthetic quartz and CaF 2 is adopted. Partially achromatic lens is used. However, since the spontaneous amplitudes of KrF and ArF excimer lasers are as wide as about 350 to 400 pm, when these projection lenses are used, chromatic aberration occurs and the resolving power decreases. Therefore, it is necessary to narrow the spectral line width of the laser light emitted from the gas laser device before chromatic aberration can be ignored. For this reason, the laser device is provided with a narrow-band module having a narrow-band element (such as an etalon or a grating) in the optical resonator to narrow the spectral line width.

(Spectral purity range)
The imaging performance of the exposure apparatus is greatly influenced not only by the full width at half maximum of the spectral waveform of the laser light but also by the skirt component of the spectral waveform. Therefore, a new index value of a spectrum called a so-called spectral purity range has been introduced. This spectral purity range is evaluated by, for example, a spectral width (E95) in which 95% of the total energy is included.

  In order to guarantee the quality of the integrated circuit, it is required to suppress this spectral purity range to 0.5 pm or less, for example.

(Reason to stabilize spectral purity range)
However, in recent years, it has begun to be said that even if the spectral purity range is a value that is significantly narrower than the value designed in the optical system, the quality of the integrated circuit may deteriorate. This is described in Patent Documents 1 (US6721340) and 2 (Japanese Patent Laid-Open No. 2001-267673). For this reason, the spectral purity range needs to be controlled so as to be stable within a certain predetermined allowable range (hereinafter referred to as stabilization control as appropriate).

(Prior art of spectral purity range control)
As a technique for controlling the spectral purity range, a method based on wavelength oscillation and a method based on grating bending control are disclosed.

  Patent Documents 1 and 2 describe a technique for stabilizing and controlling the spectral purity range by changing the wavelength. In Patent Document 2, a wavelength detector is provided, and a high-speed tuning mechanism is provided in the narrow-band unit, and the wavelength is oscillated minutely and at high speed for each pulse based on the detected wavelength. Describes an invention in which the apparent spectral purity range is controlled to fall within the allowable range. Here, “apparent spectral purity range control” refers to control for artificially obtaining a spectral purity range corresponding to the amplitude by oscillating the center wavelength at each moment and integrating the time.

  A technique for stabilizing and controlling the spectral line width (including the purity width) by grating bending control is described in Patent Document 3 (Japanese Patent Laid-Open No. 2000-312048). This Patent Document 3 relates to a precise grating bending mechanism of a wavelength selection element in a narrowband module, and a two-way spectral width control grating assembly is proposed. This technique will be described with reference to the drawings.

FIG. 26 shows a grating bending mechanism for controlling the spectral purity range.
The spring housing 91 is connected to one end plate 92 of the two end plates 92 and 93 extending away from the line surface of the grating 90. The adjustment rod 94 is screwed into the other end plate 93 and is inserted into the spring housing 91. Further, the adjustment rod 94 is fixed to a piston 95 provided in the spring housing 91. Inside the spring housing 91 are a compression spring 96 attached between one pressure surface 91a in the spring housing 91 and one surface of the piston 95, and the other pressure surface 91b in the spring housing 91 and the piston 95. There is a compression spring 97 attached between the other side of the two. When the adjustment rod 94 is turned in one direction, the concave shape of the line surface of the grating 90 becomes larger (or the convex shape is smaller), and when the adjustment rod 94 is turned in the other direction, the convex shape of the line surface of the grating 90 becomes larger. Becomes larger (or smaller concave). With this grating bending mechanism, the spectral line width and the spectral purity width E95 can be controlled within a certain range.

US67221340 JP 2001-267673 A JP 2000-312048 A

However, in the conventional technique described in Patent Document 2, the center wavelength also changes accompanying with the control of the spectral purity range. For this reason, it is difficult to independently perform the center wavelength control for matching the center wavelength with a desired value and the spectrum line width control for keeping the spectrum purity width within a predetermined allowable width. For this reason, the following problems occur.
(1) Although it is desirable to control the center wavelength for each pulse, this is a complicated control.
(2) In the situation where the center wavelength is stable, the accuracy of the center wavelength control is not a problem, but it is necessary to dynamically control the wavelength when an instruction to change the target wavelength is issued from the exposure apparatus. In some cases, the accuracy of the center wavelength control may be affected.
(3) At the initial stage of burst oscillation, a chirping phenomenon in which the center wavelength is greatly shifted occurs.

Further, in the conventional technique described in Patent Document 3, the following problem occurs when the spectral line width is controlled to the target spectral purity width E95 by controlling the grating bending.
(1) The control range of the spectral purity range E95 that can maintain the state in which the laser output is maintained is about 0.4 to 0.6 pm, and the dynamic range is small. For this reason, the target value of the spectral purity range E95 can only be set around 0.5 pm (details of this point will be described later). Moreover, it is difficult to stabilize the spectral purity range E95 when the range of ± 0.1 pm is exceeded due to the effects of heat load, acoustic waves, and the like.
(2) Since the bending of the grating for changing the spectral purity range is greatly expanded by the prism beam expander, it is necessary to bend the arc very neatly with a long curvature radius (for example, about several km). . If it cannot be bent neatly, it greatly affects the shape of the spectrum. For example, a plurality of peaks may occur.
(3) The size of the grating used in the narrow-band excimer laser apparatus for the exposure apparatus is very large (length: 200 mm to 350 mm), and the bending mechanism of the grating is very precise. Therefore, it is not suitable for fast control of the spectral purity range E95.

  As described above, there are various problems in controlling the spectral purity range by changing the wavelength or bending the grating, and the spectral purity range E95 is controlled in a wide control range with little influence on the control of the central wavelength. That was difficult.

  The present invention has been made in view of such circumstances, and the spectral purity range E95 can be controlled in a wide control range with little influence on the control of the center wavelength, and the spectral purity range E95 is stabilized. This is a problem to be solved.

The first invention is
A laser chamber enclosing a laser medium and provided with windows on both ends ;
An excitation source for exciting the laser medium;
A previous SL on the optical axis of a and the optical resonator due to the excitation of the laser medium to resonate the output light, the inside of the optical resonator, the one rear side of the window of said laser chamber comprising a line narrowing module and the other front side of the window of the laser chamber, characterized by comprising a wavefront adjuster for adjusting the wavefront of the light output from the laser medium.

  The first invention will be described with reference to FIG. For example, a laser gas 1 is sealed as a laser medium in a laser chamber 10 and discharge electrodes 11 and 12 are provided as excitation sources. The voltages of the discharge electrodes 11 and 12 are controlled by a power supply circuit. When the laser gas 1 is excited by a discharge generated between the discharge electrodes 11 and 12, light is emitted. In order to narrow the light band, a wavelength dispersion element such as a grating 21 is provided on the rear side of the laser chamber 10 to disperse the light for each wavelength. On the front side of the laser chamber 10, a partially transmissive output coupler 31 that reflects a part of incident light and transmits the remaining light is provided. The grating 21 and the output coupler 31 constitute an optical resonator. A wavefront adjuster 32 is provided on the output side in the optical resonator, that is, on the output coupler 31 side. The light passes through the wavefront adjuster 32 from the laser chamber 10 side and reaches the output coupler 31. The wavefront adjuster 32 is adjusted so as to obtain a desired spectral purity range E95. Then, when the light passes through the wavefront adjuster 32, it is adjusted to a desired wavefront.

The second invention is the first invention,
It has a partially transmissive output coupler that reflects part of the incident light and transmits the rest,
It further comprises a wavefront adjuster controller that samples the light output from the partially transmissive output coupler and feedback-controls the wavefront adjuster to obtain a desired spectral width.

The second invention will be described with reference to FIG. In the second invention, the wavefront adjuster controller, that is, the laser controller 50 and the wavefront adjustment driver 52 perform feedback control of the wavefront adjuster 32. That is, the light output from the output coupler 31 is sampled, and the spectral purity range E95 is detected. The laser controller 50 controls the wavefront adjuster 32 via the wavefront adjustment driver 52 so as to obtain a desired spectral purity range E95 based on the detected spectral purity range E95.

The third invention is the first invention,
The wavefront adjuster includes a cylindrical concave lens and a cylindrical convex lens arranged on an optical path, and a lens that adjusts an interval between the cylindrical concave lens and the cylindrical convex lens by moving at least one of the cylindrical concave lens and the cylindrical convex lens on the optical path. And an interval adjusting mechanism.

  The third invention will be described with reference to FIG. In the third aspect of the invention, the wavefront adjuster includes a lens interval adjustment mechanism that moves at least one of the cylindrical concave / convex lenses 33 and 34 and the cylindrical concave / convex lenses 33 and 34, that is, a linear stage 35. When the distance between the principal points of the cylindrical concave / convex lenses 33 and 34 is adjusted, the wavefront of the light changes.

A fourth invention is the first to fourth inventions,
The laser medium is a laser gas, and the excitation source has a pair of discharge electrodes facing each other and a power supply circuit for applying a high voltage between the discharge electrodes, and the laser gas and the discharge electrode are connected to each other in a laser chamber. It is characterized by being provided inside.

  The fourth invention is as described in the first invention.

According to the present invention, the following effects can be obtained.
(1) The dynamic range of the spectral purity range E95 can be increased while maintaining the laser pulse energy. Thereby, the spectral purity range E95 can be set in a wide range, and can be stabilized with a desired spectral purity range E95.

Furthermore, according to the third invention, the following effects can be obtained.
(2) Since the wavefront is changed independently of the central wavelength control by changing the distance between the concave and convex lenses, the wavefront control with a fast response is possible, and accordingly, the response of the control of the spectral purity range E95 is also a wavelength. It is faster than the swing method or the grating bending method.
(3) Since the wavefront is changed by changing the distance between the concave and convex lenses, the wavefront aberration is smaller than that of the grating bending method, so that the spectral purity width is changed with a clean waveform having a substantially single peak. Is possible. This is because it is difficult to bend the grating without distortion.
(4) The spectral purity range E95 can be actively controlled simply by installing a wavefront adjustment module on the front side of the conventional narrow-band laser (easy to handle options).

FIG. 1A is a diagram illustrating the configuration of the narrow-band laser device according to the first embodiment from the top, and FIG. 1B is a diagram illustrating the configuration of the narrow-band laser device including the wavefront adjuster from the side. It is. FIG. 2 is a diagram showing a grating bending mechanism. FIGS. 3A and 3B are diagrams showing characteristics when the wavefront is adjusted with a grating. FIGS. 4A and 4B are diagrams showing characteristics when the wavefront is adjusted with a cylindrical concave-convex lens. FIG. 5A is a side view showing the configuration of the narrow-band laser device that performs wavefront adjustment by the grating provided on the rear side, and FIG. 5B is the wavefront adjustment by the concave and convex lens provided on the front side. The structure of the narrow-band laser apparatus which performs is shown from the side. FIG. FIG. 6 is a side view of the configuration of the narrow-band laser apparatus according to the second embodiment. FIG. 7 is a side view of the configuration of the narrow-band laser apparatus according to the third embodiment. FIG. 8 is a view showing a cross section taken along the line AA of FIG. FIG. 9 shows a wavefront adjuster according to the fourth embodiment. FIG. 10 is a diagram illustrating the configuration of the control system for the spectral purity range E95 according to the fifth embodiment. FIG. 11 is a diagram showing the configuration of the monitor module. FIG. 12 is a flowchart of a main routine performed in the laser system according to the fifth embodiment. FIG. 13 is a flowchart of a subroutine of “spectral purity range E95 and E95 actuator calibration”. FIG. 14 is a flowchart of the “E95 measurement” subroutine. FIG. 15 is a flowchart of the “E95 control” subroutine. FIG. 16 is a view showing a flowchart of a subroutine of “E95 actuator control”. FIG. 17 is a flowchart of the “energy control” subroutine. FIG. 18 is a flowchart of the “center wavelength control” subroutine. FIG. 19 is a diagram showing the relationship between the position of the concave lens, the spectral purity width E95 of the laser, and the pulse energy E. FIG. 20 is a diagram illustrating a configuration of a control system for the spectral purity range E95 according to the sixth embodiment. FIG. 21A is a diagram illustrating a configuration of a beam divergence monitor, and FIG. 21B is a diagram illustrating a configuration of a Shack-Hartmann wavefront meter. FIG. 22 is a diagram showing a flowchart of beam correction control. FIG. 23 is a diagram showing a flowchart of beam correction control. FIG. 24 is a diagram showing the configuration of a laser system when Example 6 is applied to a double chamber system. It is a figure which shows the combination pattern of an uneven | corrugated lens. FIG. 26 is a diagram showing a grating bending mechanism for controlling the spectral purity range.

Embodiments of a narrow-band laser device according to the present invention will be described below with reference to the drawings.

FIG. 1A shows the configuration of the narrow-band laser apparatus according to the first embodiment from the top, and FIG. 1B shows the configuration of the narrow-band laser apparatus having a wavefront corrector from the side.
As shown in FIG. 1, a normal band-narrowing module 20 is disposed on the rear side (right side of the drawing) of the laser chamber 10, and a wavefront adjusting module 30 is disposed on the front side (left side of the drawing).

  Inside the laser chamber 10, a pair of discharge electrodes 11 and 12 are provided that are separated by a predetermined distance, are parallel to each other in the longitudinal direction, and face the discharge surfaces. Further, windows 13 and 14 are provided on the laser beam output portion on the optical axis of the laser beam in the laser chamber 10. The windows 13 and 14 are made of a material having transparency to laser light, such as CaF2. Both windows 13 and 14 are arranged with their outer surfaces arranged parallel to each other and at a Brewster angle to reduce reflection loss with respect to the laser beam.

  A laser gas 1 is sealed in the laser chamber 10 as a laser medium. In the case of the F2 laser, the laser gas 1 is a mixed gas of F2 gas and a buffer gas made of He, Ne or the like. In the case of a KrF excimer laser, the laser gas 1 is a mixed gas of Kr gas and F2 gas and a buffer gas made of He, Ne or the like. In the case of an ArF excimer laser, the laser gas 1 is a mixed gas of Ar gas and F2 gas and a buffer gas made of He, Ne or the like. Supply and discharge of each gas is controlled by a gas supply / discharge mechanism (not shown).

  A high voltage is applied to the discharge electrodes 11 and 12 provided in the laser chamber 10 by a power supply circuit (not shown). When the voltage between the discharge electrodes 11 and 12 exceeds a predetermined voltage, discharge occurs. Then, after the laser gas 1 is excited to move to a high energy level, the laser gas 1 moves to a low energy level. At this time, light is emitted.

  The band narrowing module 20 is provided with an optical element such as a prism beam expander 22 and a grating 21 which is a wavelength dispersion element. The band narrowing module 20 may be composed of an optical element such as an etalon that is a wavelength dispersion element and a total reflection mirror.

  The wavefront adjustment module 30 includes, for example, an output coupler 31 and a wavefront corrector 32. The output coupler 31 is an optical element that reflects a part of incident light and transmits the rest. The wavefront corrector 32 includes a cylindrical concave lens (hereinafter simply referred to as “concave lens”) 33, a cylindrical convex lens (hereinafter simply referred to as “convex lens”) 34, and a linear stage 35 that holds the concave lens 33. The concave lens 33 and the convex lens 34 are arranged on the output side optical axis in the optical resonator, and the concave lens 33 is movable along the optical axis according to the operation of the linear stage 35. The convex lens 34 may be held on the linear stage. The surfaces of the convex lens 34 and the concave lens 33 are coated with an antireflection film (AR film) for reducing reflection loss. The surface on the optical resonator side of the output coupler 31 is coated with a partial reflection film (PR film), and the output side surface is coated with an AR film.

  The output coupler 31 in the wavefront adjustment module 30 and the grating 21 in the narrowband module 20 constitute an optical resonator.

  The wavefront adjusting module 30 has a function of adjusting the radius of curvature of the wavefront on the front side in the optical resonator, and a function of outputting a part of the laser light and returning a part of it to the optical resonator. For example, the wavefront can be adjusted by moving the concave lens 33 along the optical axis. For example, when converting a wavefront having no curvature (flat) into a flat wavefront, the focal positions of the convex lens 34 and the concave lens 33 are the same. The distance between the convex lens 34 and the concave lens 33 at this time is D0. When converting a flat wavefront to a convex wavefront, the position of the concave lens 33 is adjusted so that the distance between the convex lens 34 and the concave lens 33 is greater than D0. Conversely, when converting a flat wavefront to a concave wavefront, the position of the concave lens 33 is adjusted so that the distance between the convex lens 34 and the concave lens 33 is smaller than D0. In this manner, the wavefront of light in the optical resonator can be adjusted by changing the distance between the convex lens 34 and the concave lens 33.

  Here, the relative positional relationship between the wavefront adjusting module 30 and the narrowband module 20 with respect to the discharge electrodes 11 and 12 in the laser chamber 10 will be described.

  In general, the narrowing of the band by the wavelength dispersion element (grating and dispersion prism) is efficiently performed by narrowing the beam divergence angle of the laser light incident on the wavelength dispersion element. Therefore, in the reference (Japanese Patent Laid-Open No. 2-3303178), the laser beam divergence angle in the direction perpendicular to the laser discharge direction (vertical direction in the drawing) is narrow (because the beam width is narrow). By arranging the optical element and the laser chamber (discharge direction) so that the plane including each wavelength dispersion direction (wavelength dispersion plane) and the plane of the discharge direction of the electrode are substantially perpendicular, the spectrum of the laser beam is narrowed and increased. A technique that can be output is disclosed. In this embodiment, by optimizing the direction of the wavefront of the wavefront adjusting module 30 in addition to the optical element in the narrowband module 20 and the laser chamber 10, a high variable output range and a wide variable range of E95 can be realized.

  In the laser chamber 10, a high voltage is applied between the discharge electrodes 11 and 12 by a high voltage power supply circuit (not shown) to perform discharge. In the discharge area between the discharge electrodes 11 and 12, a laser gain region is formed. When a discharge is made between the discharge electrodes 11 and 12, the light passes through the rear window 13 and the slit 5, and the beam is expanded in a direction substantially perpendicular to the discharge direction by the prism beam expander 22. The light expanded by this beam is incident on the diffraction surface of the grating 21 at a predetermined angle α, and light within a predetermined wavelength range is diffracted at the same diffraction angle α. This angular arrangement of the grating 21 is called a Littrow arrangement. That is, the grating 21 is disposed so that its wavelength dispersion plane is substantially orthogonal to the discharge direction between the discharge electrodes 11 and 12. The light diffracted by the grating 21 passes through the prism beam expander 22 again. The slit 5 transmits only light of the selected wavelength, and the light of the selected wavelength passes through the rear side window 13 and enters the discharge area. The light of the selected wavelength is amplified by passing through the discharge area. The amplified light passes through the window 14 on the front side, enters the wavefront adjustment module 30, and passes through the cylindrical concave and convex lenses 33 and 34, thereby adjusting the wavefront. The concavo-convex lens 33, 34 so that the straight line connecting the convex or concave vertices of the cylindrical surfaces of the concavo-convex lenses 33, 34 is parallel to the discharge direction between the discharge electrodes 11, 12 and substantially perpendicular to the wavelength dispersion plane of the grating 21. 34 is arranged. Then, a part of the laser light is extracted as output light of the laser by the output coupler 31, a part of the laser light is reflected, and the wavefront is adjusted by passing through the concave and convex lenses 33 and 34 again. This light again passes through the discharge area through the front window 14 and is amplified. Laser oscillation is generated by the optical resonator having such a configuration, and laser light having a predetermined spectral width of E95 is output. The wavelength selection characteristics of the wavelength dispersion element (grating and dispersion prism) can be changed by changing the wavefront of the wavelength dispersion surface. Therefore, as described above, the concave and convex lenses 33 and 34 and the grating 21 are arranged such that the cylindrical surfaces of the concave and convex lenses 33 and 34 and the wavelength dispersion surface of the grating 21 are substantially perpendicular to each other. In this embodiment, the wavefront adjusting module 30 having the cylindrical concave and convex lenses 33 and 34 is shown. However, without being limited to this, the wavefront adjusted by the wavefront adjusting module 30 is substantially perpendicular to the wavelength dispersion plane. It suffices to be configured. In other words, when a plane wave is transmitted through the wavefront adjusting module 30, the wavefront is converted into a cylindrical shape, and the cylindrical surface of the wavefront may be substantially perpendicular to the wavelength dispersion plane.

  Next, the characteristics of this embodiment, that is, the characteristics when the wavefront is adjusted by the wavefront adjusting module 30 disposed on the front side of the laser chamber 10, and the conventional characteristics, that is, the case where the wavefront is adjusted by the grating disposed on the rear side of the laser chamber. Compare the characteristics of

  FIG. 2 shows a grating bending mechanism. 3A and 3B show the characteristics when the wavefront is adjusted with a grating. FIG. 3A shows the relative value dependency between the relative value of the laser pulse energy and the curvature radius of the grating, and FIG. 3B shows the relative value dependency between the spectral purity range E95 and the curvature radius of the grating. .

  The grating bending mechanism 24 shown in FIG. 2 adjusts the curvature radius of the grating 21 by gripping both ends of the grating 21 and pushing and pulling the center.

  The inventors change the radius of curvature of the grating 21 using the grating bending mechanism 24 shown in FIG. 2 and measure the pulse energy and spectral purity width E95 of the laser beam to be output. The relationship between the pulse energy of the laser beam and the spectral purity range E95 was determined.

  As shown in FIG. 3A, the relationship between the relative value of the pulse energy of the laser and the relative value of the radius of curvature of the grating 21 is an upwardly convex curve. Assuming that the relative value of the required pulse energy is 800 or more, the relative value of the radius of curvature of the grating 21 in this case is in the range of −3 to +4.

  As shown in FIG. 3B, the relationship between the spectral purity (E95) and the relative value of the curvature radius of the grating is a downwardly convex curve. When the relative value of the radius of curvature of the grating 21 was in the range of −3 to +4, the range of change in spectral purity (E95) was about 0.4 to about 0.6 pm. In order to control the spectral purity range E95, it is necessary to control the radius of curvature of the grating 21 in the region of the monotone decreasing curve or the monotone increasing curve. Therefore, as indicated by the broken line a in FIG. 3B, the spectral purity range E95 is reduced from about 0.6 pm to about 0.4 pm by changing the relative value of the radius of curvature of the grating 21 from −3 to 0. be able to.

  From the above, in a narrow-band laser that controls the spectral width by grating bending, the change range of the spectral purity range E95 cannot be increased so much while the laser pulse energy is maintained, and the dynamic range cannot be increased too much. It was revealed.

  4A and 4B show characteristics when the wavefront is adjusted with a cylindrical concave-convex lens. 4A shows the relative value dependency between the relative value of the laser pulse energy and the curvature radius of the grating, and FIG. 4B shows the relative value dependency between the spectral purity range E95 and the curvature radius of the grating. .

  The inventors changed the distance between principal points of the concave and convex lenses 33 and 34 using the linear stage 35 shown in FIG. 1 and measured the pulse energy and spectral purity width E95 of the laser beam to be output. The relationship between the distance between the principal points of 34, the pulse energy of the laser beam, and the spectral purity range E95 was determined.

  As shown in FIG. 4A, the relationship between the relative value of the laser pulse energy and the distance between the lens principal points is an upwardly convex curve. Assuming that the relative value of the necessary pulse energy is 800 or more, the distance between the concave and convex lenses 33 and 34 in this case is in the range of 27 mm to 34 mm.

  As shown in FIG. 4B, the relationship between the spectral purity (E95) and the distance between the principal points of the concave and convex lenses 33 and 34 is a downward convex curve. When the distance between the principal points of the concave and convex lenses 33 and 34 is in the range of 27 mm to 34 mm, the range of change in spectral purity (E95) is about 0.4 pm to about 1.2 pm. In order to control the spectral purity range E95, it is necessary to control the distance between the principal points of the concave and convex lenses 33 and 34 in the region of the monotone decreasing curve or the monotone increasing curve. Therefore, as shown by the broken line b in FIG. 4B, the spectral purity range E95 is increased from about 0.4 pm to about 1.2 pm by changing the distance between the principal points of the concave and convex lenses 33 and 34 from 27 mm to 34 mm. Can be made.

  From the above, in the narrow-band laser that controls the spectral width by adjusting the distance between the principal points of the concave and convex lenses 33 and 34, even when the pulse energy of the laser is maintained, compared with the case shown in FIG. It was revealed that the change range of the spectral purity range E95 can be increased, and the dynamic range can be greatly increased.

The present inventor found that the laser discharge area is more effective when the wavefront adjustment is performed on the front side than when the wavefront adjustment is performed on the rear side of the laser chamber. It is presumed that this is because it can be used. Details will be described below.

FIG. 5A shows a configuration of a narrow-band laser device that performs wavefront adjustment by a grating provided on the rear side, and FIG. 5B shows a narrowband that performs wavefront adjustment by an uneven lens provided on the front side. The configuration of the banded laser device is shown from the side.

  First, the case where the wavefront adjustment is performed on the rear side of the laser chamber 10 will be described. Here, as shown in FIG. 5A, the grating bending mechanism 24 is disposed in the narrow band module 20 on the rear side of the laser chamber 10, and the wavefront is adjusted by the grating bending mechanism 24 and the grating 21. The light emitted by the discharge generated in the discharge area is transmitted through the rear window 13 and the slit 5, and the beam is expanded in a direction substantially perpendicular to the discharge direction by the prism beam expander 22. The light with the expanded beam is incident and diffracted on the grating 21 at a predetermined angle. Here, the wavelength dispersion plane of the grating 21 and the discharge direction of the discharge electrodes 11 and 12 are substantially perpendicular. The light diffracted by the grating 21 passes through the prism beam expander 22 again. The slit 5 transmits only light having a selected wavelength, and the light having the selected wavelength passes through the window 13 and enters the discharge area between the discharge electrodes 11 and 12. By passing through the discharge area, the light of the selected wavelength is amplified. However, since the width of the light transmitted through the slit 5 is significantly narrower than the width of the discharge area (the width of the discharge electrodes 11 and 12), the light of the selected wavelength is not efficiently amplified. The light amplified in the discharge area passes through the front-side window 14 and is partly extracted as output light of the laser by the output coupler 31 and partly reflected. The reflected light passes through the window 14 again, enters the discharge area, and is amplified. By configuring the optical resonator so that the operation described above can be performed, laser oscillation occurs, and laser light having a predetermined spectral width of E95 is output. As described above, when the wavefront is adjusted on the rear side of the laser chamber 10, since the light of the selected wavelength is not efficiently filled in the discharge area, the variable range of E95 cannot be increased while maintaining the laser output. .

  Next, the case where the wavefront is adjusted on the front side of the laser chamber 10 will be described. Here, as shown in FIG. 5B, it is assumed that the concave and convex lenses 33 and 34 are arranged in the wavefront adjusting module 30 on the front side of the laser chamber 10 and the wavefront is adjusted by the concave and convex lenses 33 and 34. The light emitted by the discharge generated in the discharge area is transmitted through the rear window 13 and the slit 5, and the beam is expanded in a direction substantially perpendicular to the discharge direction by the prism beam expander 22. The light with the expanded beam is incident and diffracted on the grating 21 at a predetermined angle. Here, the wavelength dispersion plane of the grating 21 and the discharge direction of the discharge electrodes 11 and 12 are substantially perpendicular. The light diffracted by the grating 21 passes through the prism beam expander 22 again. The slit 5 transmits only light having a selected wavelength, and the light having the selected wavelength passes through the window 13 and enters the discharge area between the discharge electrodes 11 and 12. By passing through the discharge area, the light of the selected wavelength is amplified. Here, although the width of the light transmitted through the slit 5 is narrower than the width of the discharge area (the width of the discharge electrodes 11 and 12), the light of the selected wavelength becomes a spherical wave having a predetermined spread and passes through the discharge area. Since it is transmitted, it is efficiently amplified. The light amplified in the discharge area passes through the front-side window 14, passes through the concave and convex lenses 33 and 34, and is converted into a predetermined wavefront. A part of the amplified light is extracted as output light of the laser by the output coupler 31, and a part of the light is reflected. The reflected light passes through the window 14 again, enters the discharge area, and is amplified. By configuring the optical resonator so that the operation described above can be performed, laser oscillation occurs, and laser light having a predetermined spectral width of E95 is output. As described above, when the wavefront is adjusted on the front side of the laser chamber 10, since the light of the selected wavelength is efficiently filled in the discharge area, the variable range of E95 can be increased while maintaining the laser output. .

The following effects (1) to (4) can be given as effects of the present embodiment.
(1) The dynamic range of the spectral purity range E95 can be increased while maintaining the laser pulse energy. Thereby, the spectral purity range E95 can be set in a wide range, and can be stabilized with a desired spectral purity range E95.
(2) Since the wavefront is changed by changing the distance between the concave and convex lenses, wavefront control with fast response becomes possible, and accordingly, the response of control of the spectral purity range E95 becomes faster than the grating bending method. .
(3) Since the wavefront is changed by changing the distance between the concave and convex lenses, the wavefront aberration is smaller than that of the grating bending method, so that the spectral purity width is changed with a clean waveform having a substantially single peak. Is possible. This is because it is difficult to bend the grating without distortion.
(4) The spectral purity range E95 can be actively controlled simply by installing a wavefront adjustment module on the front side of the conventional narrow-band laser (easy to handle options).

  The optical element for adjusting the wavefront is most preferably one that adjusts a cylindrical wavefront, but even if it adjusts a spherical wavefront, substantially the same function can be achieved. Therefore, for example, a spherical concave and convex lens may be combined as an optical element for wavefront adjustment.

  In the present embodiment, another embodiment of the first embodiment will be described.

  FIG. 6 shows the configuration of the narrow-band laser apparatus according to the second embodiment from the side. The difference between the first embodiment and the second embodiment is the configuration in the wavefront adjustment module.

  As shown in FIG. 6, the wavefront adjustment module 30 includes a wavefront adjuster 32. The wavefront adjuster 32 includes a cylindrical convex lens 37, a cylindrical concave lens 36, and a linear stage 35 that holds the concave lens 36. One surface of the convex lens 37 is processed into a flat shape, and the other surface is processed into a cylindrical shape. The concave lens 36 has one surface processed into a flat shape and the other surface processed into a cylindrical shape. The convex lens 37 and the concave lens are arranged such that the cylindrical convex surface of the convex lens 37 and the cylindrical concave surface of the concave lens 36 face each other, the flat surface of the convex lens 37 faces the laser output side, and the flat surface of the concave lens 36 faces the laser chamber 10 side. 36 is arranged on the optical axis. The flat surface of the convex lens 37 is coated with a PR film, and the cylindrical convex surface of the convex lens 37 and the cylindrical concave surface and flat surface of the concave lens 36 are coated with an AR film. The convex lens 37 of this embodiment also has the function of an output coupler.

  In this embodiment, a convex lens 37 having the function of an output coupler is fixed on the optical axis, and a wavefront adjustment is performed by driving a concave lens 36 coated with an AR film on both surfaces along the optical axis.

The following effects (1) to (3) are given as effects of the second embodiment.
(1) Since the number of optical elements can be reduced, the cost can be reduced.
(2) Since the number of surfaces in the resonator is reduced as compared with the first embodiment, the laser efficiency is improved.
(3) Since the cylindrical convex lens having the function of the output coupler is fixed, the optical axis of the laser beam hardly changes.

  In this embodiment, the wavefront adjuster 32 has a PR film coated on the flat surface of the convex lens 37 and an AR film coated on the cylindrical convex surface, but is not limited thereto. Even if the cylindrical convex surface of the convex lens 37 is coated with a PR film and the flat surface is coated with an AR film, both the wavefront adjustment and the function of the output coupler can be provided.

  As in the first embodiment, the most suitable optical element for adjusting the wavefront is one that adjusts a cylindrical wavefront, but even if it adjusts a spherical wavefront, it performs substantially the same function. Can do. Therefore, for example, a spherical concave and convex lens may be combined as an optical element for wavefront adjustment.

FIG. 25 shows patterns other than the combination of the concave and convex lenses shown in Examples 1 and 2.
As shown in FIG. 25 (a), a wavefront adjuster includes a concave lens 36 having a cylindrical surface on one surface and a flat surface on the other surface, a convex lens 34 having a cylindrical surface on both surfaces, and an output coupler 31. The cylindrical surface of the concave lens 36 and the cylindrical surface of the convex lens 34 may be opposed to each other, or the flat surface of the concave lens 36 and the cylindrical surface of the convex lens 34 may be opposed to each other as shown in FIG.

  Further, as shown in FIG. 25C, a concave lens 36 having a cylindrical surface on one surface and a flat surface on the other surface, and a flat surface on the other surface having a cylindrical surface on the other surface. A wavefront adjuster may be configured by the convex lens 37 having a flat surface coated with a PR film, and the flat surface of the concave lens 36 and the cylindrical surface of the convex lens 37 may face each other.

  Further, as shown in FIG. 25 (d), a concave lens 33 having a cylindrical surface on both surfaces, and a convex lens 37 having a cylindrical surface on one surface, a flat surface on the other surface, and a PR film coated on the flat surface. The wave front adjuster may be configured, and the cylindrical surface of the concave lens 33 and the cylindrical surface of the convex lens 37 may face each other.

  In the present embodiment, another embodiment of the first embodiment will be described.

  FIG. 7 shows the configuration of the narrow-band laser apparatus according to the third embodiment from the side. FIG. 8 shows an AA cross section of FIG. The difference between the first embodiment and the third embodiment is the configuration on the front side of the laser.

  As shown in FIG. 7, a deformable mirror 70 that is an end mirror is disposed on the front side of the laser chamber 10. In this embodiment, the shape of the total reflection surface of the deformable mirror 70 is shaped to change (correct) the laser wavefront.

  A laser resonator is configured between the grating 21 disposed on the rear side of the laser chamber 10 and a deformable mirror 70 on the front side. On the optical path between the laser chamber 10 and the deformable mirror 70 on the front side, a 45-degree incident beam splitter 71 is disposed. The beam splitter 71 functions as an output coupler. That is, part of the light output from the laser chamber 10 is reflected by the beam splitter 71 and output as laser light.

  On the other hand, the light transmitted through the beam splitter 71 is incident on the beam splitter 71 again with the reflected wavefront changed by the deformable mirror 70. The light transmitted through the beam splitter 71 passes through the laser chamber 10 and is amplified. The light transmitted through the laser chamber 10 and amplified is narrowed by the prism beam expander 22 and the grating 21. The diffracted light is again transmitted through the laser chamber 10 and amplified. Then, again, the light that has been transmitted through the laser chamber 10 and amplified is incident on the beam splitter 71 and laser-oscillated. The wavefront of the laser light generated in the laser chamber 10 is ideally a cylindrical wavefront.

  The deformable mirror 70 is mechanically pushed and pulled by a plurality of portions of the reflecting surface by an actuator 73. 7 and 8 show a line-type deformable mirror 70 and actuators 73 provided at three points on the reflecting surface of the deformable mirror 70. FIG. For example, a piezo element is used as the actuator 73. By extending and contracting each actuator 73 (piezo element), the rear surface of the deformable mirror 70 is pushed and pulled. As a result, each part of the reflective surface of the deformable mirror 70 is pushed and pulled, so that the radius of curvature of the deformable mirror 70 is adjusted. 7 and 8 illustrate the case where the number of actuators 73 is three, the present invention is not limited to this, and the number of actuators 73 is arbitrary. Increasing the number of actuators 73 enables more accurate wavefront correction. Further, the actuator 73 that pushes and pulls the reflecting surface of the deformable mirror 70 is not limited to a piezo element, and an arbitrary one can be used.

For example, in addition to the piezo element, an actuator that pushes and pulls the reflective surface of the deformable mirror 70 using thermal expansion due to temperature change may be used.

  The effects peculiar to this embodiment are shown below. The deformable mirror can be converted into a wavefront having an arbitrary shape by arranging a large number of actuators. For example, it is possible to correct a complex wavefront of light generated by an acoustic wave generated by a discharge in a laser chamber that occurs during high repetition. In addition, it is possible to adjust complex wavefront distortion of light generated from heat in the narrowband module.

  FIG. 9 shows a wavefront adjuster according to the fourth embodiment.

  In general, the refractive index of an optical material such as CaF2 varies with temperature. Therefore, a refractive index distribution can be generated by intentionally giving a temperature distribution to the optical element. Therefore, as shown in FIG. 9, a heating / cooling device 42 such as a thermoelectric element capable of heating and cooling is installed on each side surface of the CaF2 substrate 41 of the optical material. The temperature of the CaF2 substrate 41 in the vicinity where the heating / cooling device 42 is installed is detected by the temperature sensor 42a, and each heating / cooling device 42 is based on the detected value of the temperature sensor 42a so that the CaF2 substrate 41 has a predetermined temperature distribution. Is controlled to give a desired refractive index distribution to the CaF2 substrate 41 and change the wavefront of the laser beam.

  This wavefront adjuster can function as a wavefront adjusting module by being installed between the laser chamber and the output coupler. An AR film is coated on both surfaces of the CaF2 substrate 41. Further, in order to share the function with the output coupler, the output side surface may be coated with a PR film, and the optical resonator side surface may be coated with an AR film. In this case, the function of the present invention can be realized with one element, and the efficiency of the laser is improved.

  In this embodiment, a laser system including the laser apparatus described in Embodiment 1 and its control will be described. In addition, the laser apparatus of Examples 2-4 is applicable to the laser system of a present Example.

  FIG. 10 shows the configuration of the control system for the spectral purity range E95 according to the fifth embodiment.

  The laser system of this embodiment includes a wavefront adjustment module 30 that is arranged on the front side of the laser chamber 10 and adjusts the wavefront in the optical resonator, and a narrower that is arranged on the rear side of the laser chamber 10 and narrows the spectral line width. The banding module 20, the monitor module 39 for detecting the light output from the output coupler, the shutter 6 for switching off and outputting the output laser light, the laser controller 50 for controlling the entire laser system, and the laser controller The center wavelength adjustment driver 51 that outputs the wavelength control signal output from 50 as an operation signal of an actuator (for example, the rotary stage 23) provided in the narrowband module 20, and the wavefront control signal output from the laser controller 50 Actuator provided in the wavefront adjustment module 30 (For example, a linear stage 35) having a work wavefront adjusting driver 52 a signal to and outputs of a laser power source 53 to control the pulse energy of the laser, the. In this embodiment, the laser beam output from the laser device is guided to the exposure device 3 and used for exposure of the semiconductor wafer.

  FIG. 11 shows the configuration of the monitor module.

  The monitor module 39 includes a beam splitter 391, an etalon spectroscope 393, and a photodiode 392.

  In the etalon spectroscope 393, a spectral index value such as the spectral purity range E95 is measured, and the laser output energy is measured in the photodiode 392. The etalon spectroscope 393 includes a beam diffusing unit 394 such as a diffusing plate or a lens array, an etalon 395, a lens 396, and a sensor array 397. As the sensor array 397, for example, a line sensor in which a plurality of photodiode arrays are arranged in one dimension can be used. In this case, the plurality of photodiodes are arranged in the order of channels (ch: integer).

  In the monitor module 39, a part of the laser light is sampled by the beam splitter 391 and incident on the etalon spectroscope 393. The laser light incident on the etalon spectroscope 393 is diffused by the beam diffusion means 394 and incident on the etalon 395. The laser light that has passed through the etalon 395 enters the lens 396. A sensor array 397 is installed on the focal plane of the lens 396. Therefore, when the laser light is transmitted through the lens 396, interference fringes are generated on the sensor array 397. From the fringe data on the sensor array 397, linear data of the wavelength and light amount of the laser beam is obtained as a spectrum waveform, and the spectrum purity range E95 is calculated.

  Note that although the etalon spectroscope 393 is used in the configuration of FIG. 11, an angular dispersion type optical element may be used as the spectroscope. For example, a Czerny-Turner type spectroscope, a spectroscope using a plurality of gratings, or a multipass spectroscope may be used.

  The operation of this embodiment will be described with reference to FIGS. The laser controller 50 indicates a signal indicating an external command value of the spectral purity range E95 (from the exposure apparatus 3 or laser paddle input), the laser pulse energy output from the monitor module 39, and the spectral purity range E95 of the laser. Signal. Further, the laser controller 50 outputs a control signal of the spectral purity range E95 to the wavefront adjustment module 30 via the wavefront adjustment driver 51, and supplies a laser charge voltage control signal to the laser power source in order to control the pulse energy. In addition, the control signal of the center wavelength is output to the band narrowing module 20 via the center wavelength adjustment driver 52. For example, the concave lens 33 installed in the wavefront adjustment module 30 is held by a uniaxial linear stage 35. The linear stage 35 inputs the control signal output from the laser controller 50 via the wavefront adjustment driver 51, and moves the concave lens 33 in the optical axis direction (left-right direction in the drawing) according to the input signal. Further, the grating 21 arranged in the band narrowing module 20 is held on the rotary stage 23. The rotation stage 23 inputs the control signal output from the laser controller 50 via the center wavelength adjustment driver 52, and rotates the grating 21 according to the input signal. Note that wavelength control is possible even when any one of the prism beam expanders 22 is attached to the rotary stage 23 instead of the grating 21.

Here, the flow of processing according to the present embodiment will be roughly described first, and then the specific flow of processing will be described with reference to the drawings.
First, the target value of the spectral purity range E95 is input from the outside and set in the laser controller 50. The laser controller 50 closes the shutter 6, outputs a signal to the wavefront adjustment module 30, and moves the concave lens 33 to the position of the origin (which is a reference position when moving the concave lens 33 and is determined as any arbitrary position). In addition, a signal is output to the laser power source 53 to cause laser oscillation at a predetermined charging voltage. Then, the pulse energy of the laser is detected by the pin photodiode 392 in the monitor module 39, and the spectral purity width E95 and the center wavelength of the laser are detected by the etalon spectroscope 393. The laser controller 50 stores the detected pulse energy and the spectral purity range E95. Next, a signal is output to the wavefront adjustment module 30 to the laser controller 50, and the concave lens 33 is moved to a predetermined position to cause laser oscillation. Then, the pulse energy of the laser is detected again by the pin photodiode 392 in the monitor module 39, and the spectral purity range E95 and the center wavelength of the laser are detected by the etalon spectroscope 393. The laser controller 50 stores the detected pulse energy and the spectral purity range E95. The laser controller 50 repeats the above operation a predetermined number of times and stores the lens position dependency of the laser pulse energy and the spectral purity range E95.

  Next, the laser controller 50 determines a lens position for setting the concave lens 33 to the target spectral purity range E95 based on the stored lens position dependency data, and outputs an instruction signal to the wavefront adjustment driver 51. The wavefront adjustment driver 51 outputs a position signal to the linear stage 35. The linear stage 35 moves the concave lens 33 according to the position signal. Thus, the laser controller 50 performs feedback control in order to make the measured value of the spectral purity range E95 coincide with the target value. Further, the laser controller 50 controls the laser power source in order to set the pulse energy to the target energy. Further, the laser controller 50 outputs an instruction signal for setting the laser oscillation wavelength to the target wavelength to the center wavelength adjustment driver 52. The center wavelength adjustment driver 52 outputs a rotation signal to the rotation stage 23. The rotary stage 23 rotates the grating 21 according to the rotation signal. Thus, the laser controller 50 performs feedback control in order to make the measured value of the center wavelength coincide with the target wavelength.

  The laser controller 50 opens the shutter 6 after confirming that the laser pulse energy, the spectral purity range E95, and the center wavelength are controlled within the allowable ranges. The laser light is incident on the exposure device 3 and the semiconductor wafer is exposed.

  FIG. 12 is a flowchart of a main routine performed in the laser system according to the fifth embodiment.

  First, the shutter 6 is closed before the spectral purity range E95 is controlled by the laser controller 50 (step 1201). Due to the closure of the shutter 6, the laser light generated by the adjustment oscillation operation is not input to the exposure device 3. In this state, the target pulse energy, the spectral purity range E95 and the set value of the center wavelength output from the external device (exposure device 3 or paddle) are read into the laser controller 50 (step 1202). Then, the process proceeds to a subroutine of “spectral purity range E95 and E95 actuator calibration” (step 1203). In this subroutine, the dependency of the correction value of the wavefront adjustment (for example, the distance D between the lens principal points) on the laser pulse energy and the spectral purity range E95 is stored. Specific contents of the subroutine of “spectral purity range E95 and E95 actuator calibration” will be described later (FIG. 13).

  When the processing ends in the subroutine of “spectral purity range E95 and E95 actuator calibration”, the laser controller 50 sends an output signal indicating the repetition frequency fc and the charging voltage Vc to the laser power source 53 in order to set the laser oscillation conditions. (Step 1204). Then, a trigger signal is sent to the laser power source 53 to cause discharge between the discharge electrodes 11 and 12 in the laser chamber 10, and laser oscillation is started (step 1205).

  Here, an “E95 control” subroutine (step 1206) for setting the spectral purity range E95 to the target value, an “energy control” subroutine (step 1207) for setting the pulse energy E to the target value, and the center wavelength λ are set. The process proceeds to the “center wavelength control” subroutine (step 1208) for setting the target value. In each subroutine, the process is terminated when the control target (spectral purity range E95, pulse energy E, center wavelength λ) is within the allowable range, and the process is repeated when the target is not entered. Specific contents of each subroutine will be described later (FIGS. 15, 17, and 18).

  When each control target is within the allowable range, an OK signal for exposure preparation is sent from the laser controller 50 to the exposure apparatus 3, and the shutter 6 is opened (Yes in Step 1209, Step 1210). The laser beam is guided to the exposure apparatus 3 and exposure of the semiconductor wafer is started. At the time of exposure, the process proceeds to a subroutine for “E95 control” (step 1211), a subroutine for “energy control” (step 1212), and a subroutine for “center wavelength control” (step 1213). E95, feedback control is performed to set the center wavelength λ to the target value. An error signal is generated when an error of at least the spectral purity range E95 occurs during exposure. If an error signal is raised, the laser controller 50 notifies the exposure apparatus 3 of an abnormality, and the processing after Step 1201 is performed again (Yes at Step 1214).

  FIG. 13 shows a flowchart of a subroutine of “spectral purity range E95 and E95 actuator calibration”.

  First, an output signal indicating the repetition frequency fc and the charging voltage Vc is sent from the laser controller 50 to the laser power source 53 in order to set the laser oscillation conditions (step 1301). Then, a trigger signal is sent to the laser power source 53 in order to discharge between the discharge electrodes 11 and 12 in the laser chamber 10, and laser oscillation is started (step 1302).

  Next, in order to set the position of the concave lens 33 to the initial value Xn, a signal is output from the laser controller 50 to the wavefront adjustment driver 51 (step 1303). The wavefront adjustment driver 51 controls the linear stage 35 (step 1304). Here, the process proceeds to the “E95 measurement” subroutine (step 1305). The specific contents of the “E95 measurement” subroutine will be described later (FIG. 14). After the “E95 measurement” subroutine, the pulse energy E of the laser is measured by the monitor module 39 (step 1306). At this time, the position Xn of the concave lens 33, the spectral purity range E95n, and the pulse energy En of the laser are stored (step 1307). Further, the next position Xn + 1 = Xn + ΔX0 of the concave lens 33 is calculated (step 1308). This ΔX0 is a predetermined movement pitch of the linear stage 35.

  When the next position Xn + 1 of the concave lens 33 is smaller than the limit position XLM of the concave lens 33, Xn + 1 is set to Xn, and the processing after Step 1304 is repeated (Yes in Step 1309). When the position Xn + 1 of the concave lens 33 exceeds the limit position XLM of the concave lens 33, the laser oscillation is stopped and the process returns to the main routine shown in FIG. 12 (No in Step 1309, Step 1310).

  FIG. 14 shows a flowchart of the subroutine “E95 measurement”.

  After the subroutine starts, the spectrum waveform is measured by the monitor module 39 (step 1401). The measured spectral waveform is deconvolved to calculate a true spectral waveform (step 1402). Next, an average value or a moving average value of the spectral purity range E95 is obtained by calculation (step 1403). After the above processing, the process returns to the subroutine (FIG. 13 or FIG. 15 to be described later) before the transition to this subroutine.

  FIG. 15 is a flowchart of the “E95 control” subroutine.

  As shown in FIG. 15, simultaneously with laser oscillation, the routine proceeds to step 1501 where the “E95 measurement” subroutine (FIG. 14) is executed, and the monitor module 39 measures the spectral purity range E95. The spectral purity range E95 is measured for each pulse. However, the spectral purity range E95 may be evaluated by an average value over n pulses or a moving average value in consideration of the calculation time.

  The value of the target spectral purity range of the spectral purity range E95 is set to E950, and the first allowable range for the target spectral purity range E950 is set to E950 ± dE95 (s) (first control threshold dE95 (s)). The first allowable width E950 ± dE95 (s) for the target spectral purity width E950 is set according to the specifications required by the exposure apparatus 3. It is necessary to perform control so as not to exceed the first allowable width range by exceeding the upper limit value E950 + dE95 (s) required by the exposure apparatus 3 or falling below the lower limit value E950-dE95 (s). is there. Therefore, a second control threshold dE95 having a certain predetermined margin (dE95 (s) −dE95), that is, a second allowable width E950 ± dE95 with respect to the target spectral purity width E95 is set. The range of the second control threshold dE95 is 0 ≦ dE95 <dE95 (s). When dE95 = 0, when the measured value of the spectral purity range E95 slightly deviates from the target value E950, the linear stage 35 operates in accordance with an instruction from the laser controller 50 so that the measured value E95 matches the target value E950. Thus, the stabilization control is executed.

  After the actual spectral purity range E95 is measured, whether or not the absolute value of the difference between the measured value E95 and the target value E950 is equal to or smaller than the second control threshold dE95, that is, the measured spectral purity range E95 is 2 It is calculated whether or not it is within the allowable width E950 ± dE95 (step 1502).

  If the absolute value of the difference between the measured value E95 and the target value E950 is equal to or smaller than the second control threshold dE95, that is, | E95−E950 | ≦ dE95, the stabilization control of the spectral purity range E95 is not executed (Step 1502). Decision Yes). On the other hand, if the absolute value of the difference between the measured value E95 and the target value E950 exceeds the second control threshold dE95, that is, | E95−E950 |> dE95 (determination No in step 1502), then the measurement is performed. It is determined whether or not the absolute value of the difference between the value E95 and the target value E950 is below the first control threshold dE95 (s) (| E95−E950 | <dE95 (s)) (step 1503). As a result, when the absolute value of the difference between the measured value E95 and the target value E950 is equal to or greater than the first control threshold value dE95 (s) (determination No in step 1503), an error signal is sent to the exposure apparatus 3. The laser oscillation is stopped or the shutter 6 existing between the exposure device 3 and the laser device 2 is stopped so as to prevent laser light having a spectral purity width deviating from the first allowable width from entering the exposure device 3. (Step 1506).

  On the other hand, when the absolute value of the difference between the measured value E95 and the target value E950 is below the first control threshold dE95 (s) (determination Yes in step 1503), the measured value E95 is made to coincide with the target value E950. Then, the process proceeds to a subroutine of “E95 actuator control”, where the E95 actuator is operated and the stabilization control is executed (step 1504). The specific contents of the “E95 actuator control” subroutine will be described later (FIG. 16).

  If the spectral purity range E95 falls within the allowable range as a result of the processing of the “E95 actuator control” subroutine, the process returns to the main routine of FIG. 12 (Yes in step 1505). If the spectral purity range E95 does not fall within the allowable range, the processing after step 1501 is repeated (determination No in step 1505).

  FIG. 16 shows a flowchart of a subroutine of “E95 actuator control”.

  First, the difference ΔE95 (= E95−E950) between the measured value of the spectral purity range E95 and the target value is calculated (step 1601). Here, based on the relationship between the spectral purity range E95 stored in the “spectral purity range E95 and E95 actuator calibration” subroutine shown in FIG. 13 and the position X of the concave lens 33, the lens position ΔX required to change by ΔE95. Is calculated (step 1602). The “relation between the spectral purity range E95 and the position X of the concave lens 33” and the “specific calculation example of the lens position X” will be described later with reference to FIG.

  Next, the target position X (= X + ΔX) of the concave lens 33 is calculated (step 1603). Then, it is determined whether or not the calculated position X of the concave lens 33 is within an allowable range (step 1604). If the position X of the concave lens 33 is within the allowable range, a signal is output from the laser controller 50 to the linear stage 35 of the wavefront adjustment module 30 via the wavefront adjustment driver 51. The linear stage 35 actually controls the concave lens 33 to the position X (Yes in Step 1604, Step 1605). On the other hand, if the position X of the concave lens 33 is not within the allowable range, an error signal is generated (No in Step 1604, Step 1606). The allowable range of the position X of the concave lens 33 will be described later with reference to FIG. After the above processing, the process returns to the “E95 control” subroutine shown in FIG.

  FIG. 17 shows a flowchart of an “energy control” subroutine.

  First, the pulse energy E of the laser is detected by the pin photodiode 392 provided in the monitor module 39 (step 1701). Next, a difference ΔE (= E−E0) between the detected pulse energy E and the target energy E0 is calculated (step 1702). Then, the charging voltage V of the laser power source 53 is controlled from the laser controller 50 so that the pulse energy of the laser changes by ΔE (step 1703). When the above process ends, the process returns to the main routine shown in FIG.

  FIG. 18 shows a flowchart of the “center wavelength control” subroutine.

  First, the center wavelength λ of the laser is detected by the etalon spectroscope 393 provided in the monitor module 39 (step 1801). Next, a difference Δλ (= λ−λ0) between the detected center wavelength λ and the target center wavelength λ0 is calculated (step 1802). Then, a signal is output from the laser controller 50 to the rotary stage 23 in the narrowband module 20 via the center wavelength adjustment driver 52 so that the center wavelength of the laser changes by Δλ. The rotary stage 23 controls the installation angle of the grating 21 (step 1803). When the above process ends, the process returns to the main routine shown in FIG.

  FIG. 19 shows the relationship between the position of the concave lens, the spectral purity range E95 of the laser, and the pulse energy E, and is the relationship stored in the “spectral purity range E95 and E95 actuator calibration” subroutine shown in FIG. In FIG. 19, the broken line A represents the pulse energy E, and the solid line B represents the spectral purity range E95.

  As shown in FIG. 19, when the necessary pulse energy EL is set, the lower limit XLLM and the upper limit XMLM of the position X of the concave lens 33 of the wavefront adjustment module 102 are obtained. The upper and lower limit values XLLM and XLMM of the position X of the concave lens 33 are stored as an allowable range of the position X of the concave lens 33. This allowable range is used in the “E95 actuator control” subroutine shown in FIG.

  When the upper and lower limit values XLLM and XLMM of the position X of the concave lens 33 are obtained, the range of the spectral purity range E95 is also obtained. In FIG. 19, the range of the broken line C is the variable range of the spectral purity E95. In this range, the gradient value ΔE95 / ΔX at the position X of the concave lens 33 is stored. This gradient value is used when the lens position ΔX is calculated in the “E95 actuator control” subroutine shown in FIG.

  In the sixth embodiment, another embodiment of the fifth embodiment will be described.

FIG. 20 shows the configuration of the control system for the spectral purity range E95 according to the sixth embodiment, and shows an example in which a beam correction module is added to the configuration shown in FIG.
Since the configuration of the sixth embodiment is almost the same as the configuration of the fifth embodiment, only a different configuration will be described here.

  When the linear scale 35 provided in the wavefront adjusting module 30 is operated, the spectral purity range E95 changes, and at the same time, the beam profile and beam divergence of the output laser light change. Therefore, in this embodiment, the beam correction module 60 is arranged on the output side of the wavefront adjustment module 30. A beam correction driver 55 for controlling the beam correction module 60 is provided, and a beam monitor 399 is provided in the monitor module 39. Based on the signal detected by the beam monitor 399, the laser controller 50 sends a signal to the beam correction module 60 via the beam correction driver 55 to control the quality of the laser light incident on the exposure apparatus 3 to be within a predetermined range. To do.

  In this embodiment, concave and convex lenses 61 and 62 are used as the beam correction module 60. The concave lens 61 is held by a linear stage 63 so as to be movable on the optical axis. The convex lens 62 may be held by a linear stage. Beam correction can be performed by controlling the distance between the concave and convex lenses 61 and 62.

A specific example of the beam monitor 399 will be described with reference to FIGS.
FIG. 21A shows the configuration of the beam divergence monitor.

  A beam splitter 3991 is disposed on the optical axis of the laser light, a condensing lens 3992 is disposed on the optical axis of the light sampled by the beam splitter 3991, and a CCD 3993 is disposed at the focal position of the condensing lens 3992. The A part of the laser light is sampled by the beam splitter 3991, passes through the condenser lens 3992, and is irradiated on the CCD 3993. By measuring the diameter P of the spot light on the CCD 3993, the beam divergence D of the laser light can be measured. The beam cybergence D can be calculated from the focal length F of the condenser lens 3992 and the spot light diameter P (D = P / F).

  FIG. 21B shows the configuration of the Shack-Hartmann wavefront meter.

  A beam splitter 3991 is disposed on the optical axis of the laser light, a microlens array 3994 is disposed on the optical axis of the light sampled by the beam splitter 3991, and a CCD 3993 is disposed at the focal position of the microlens array 3994. The A part of the laser light is sampled by the beam splitter 3991, passes through the microlens array 3994, and is irradiated on the CCD 3993. By measuring the position of each spot light on the CCD 3993, the shape of the wavefront of the laser light can be measured.

  Further, although not shown, a laser beam profiler is installed as the beam monitor 399, the size of the laser beam is detected, and the beam width of the laser is stabilized based on the detected value via a beam correction actuator. A signal may be sent to the beam correction module.

  FIG. 22 shows a flowchart of beam correction control. FIG. 22 is an example of a flow when the beam divergence monitor shown in FIG. 21A is used as the beam monitor 399.

  First, the beam divergence D is detected, and the difference ΔD (= D−D0) between the detected beam divergence D and the target beam divergence D0 is calculated (step 2201). A signal is output from the laser controller 50 to the linear stage 263 of the beam correction module 60 via the beam correction driver 55 so that the laser beam divergence changes by ΔD. The linear stage 263 controls the position of the concave lens 61 (step 2202).

  FIG. 23 shows a flowchart of beam correction control. FIG. 23 shows an example of a flow when the Shack-Hartmann wavefront meter shown in FIG. 21B is used as the beam monitor 399.

  First, the curvature radius R of the wavefront of the laser output light is detected, and a difference ΔR (= R−R0) between the detected curvature radius R and the target curvature radius R0 is calculated (step 2301). Then, a signal is output from the laser controller 50 to the linear stage 263 of the beam correction module 60 via the beam correction driver 55 so that the curvature radius R of the laser wavefront changes by ΔR. The linear stage 263 controls the position of the concave lens 61 (step 2302).

  According to this embodiment, the beam quality of light output to the exposure apparatus is stabilized. Therefore, it is possible to stably control exposure spots and exposure amount of the semiconductor wafer.

  In this embodiment, the laser beam is monitored and feedback control is performed by sending a control signal to the beam correction module. However, the present invention is not limited to this, and the change in the beam is detected from the control value output to the wavefront adjustment module. The beam may be controlled by calculating a prediction and inputting a control signal to the beam correction module.

  In this embodiment, a mode in which the laser system described in Embodiment 6 is applied to a double chamber laser system will be described.

  FIG. 24 shows the configuration of a laser system when Example 6 is applied to a double chamber system.

  The double chamber system shown in FIG. 24 has a Master Oscilator (MO) that oscillates narrowed light and a Power Oscilator (PO) that amplifies and oscillates the narrowed light as seed light. This method is called the MOPO method.

  In the present embodiment, the configuration of the sixth embodiment is applied to the MO side. In the MO, the narrowband module 20 is disposed on the rear side and the wavefront adjusting module 30 is disposed on the front side of the MO laser chamber 10-1. On the output side of the wavefront adjusting module 30, a high reflection film (HR film) is coated on the surface, and a mirror 81 that reflects the seed light output from the wavefront adjusting module 30 at a right angle is disposed. A beam correction module 60 is arranged on the side. Further, an MO monitor module 39-1 is disposed on the output side of the beam correction module 60. On the output side of the MO monitor module 39-1, an HR film is coated on the surface, and a mirror 82 that reflects the seed light output from the MO monitor module 39-1 at a right angle is disposed. PO is configured. In PO, a rear mirror 7 is disposed on the rear side of the PO laser chamber 10-2, and a PO output coupler 8 is disposed on the front side. On the output side of the PO output coupler 8, a beam splitter 9 is disposed, and a PO monitor module 39-2 is further disposed. The rear mirror 7 may be a mirror coated with a PR film, or a mirror that partially transmits light.

  The MO outputs light having a predetermined spectral purity range E95. The light is reflected by the mirror 81, passes through the wavefront adjustment module 60, and enters the MO monitor module 39-1. Although a part of the light is transmitted by the MO monitor module 39-1, a part of the light is sampled to detect the MO pulse energy and the beam. The light transmitted through the MO monitor module 39-1 is reflected by the mirror 82 and input as seed light from the rear mirror 7 of the PO. The seed light is amplified and oscillated with the spectrum maintained by the PO laser chamber 10-2 and the output coupler 8, and is output as laser light. Part of the laser light is transmitted through the beam splitter 9, and part of the laser light is reflected and enters the PO monitor module 39-2. The PO monitor module 39-2 detects the pulse energy and the spectral purity range E95.

  The MO controller module 39-1 receives the MO pulse energy and the beam detection value, and the PO monitor module 39-2 receives the PO pulse energy, E95, and center wavelength detection values. . The laser controller 50 performs feedback control based on each input detection value. Based on the detection results of the MO pulse energy and the PO pulse energy, the laser controller 50 supplies the MO and PO discharge timings and charges to the MO laser power source 53-1 and the PO laser power source 53-2 via the synchronous controller 57. Send voltage value control signal. Further, the laser controller 50 sends a control signal to the wavefront adjustment module 30 via the MO wavefront adjustment driver 51 based on the detection result of the spectral purity range E95. Further, the laser controller 50 sends a control signal to the beam correction module 60 via the beam correction driver 54 based on the detection value of the beam monitor. Further, the laser controller 50 sends a control signal to the narrowband module 20 via the center wavelength driver 51 based on the detected value of the center wavelength. Each actuator provided in the narrowband module 20, the wavefront adjustment module 30, and the beam correction module 60 operates according to the control signal.

  In the present embodiment, an example of the MOPO system has been shown. However, the present invention is not limited to this, and the same control can be performed even when the power amplifier is operated as a power amplifier without the PO resonator. Furthermore, in order to control the spectral purity range E95, only the MO wavefront adjustment module 30 is controlled. However, the present invention is not limited to this and may be combined with other means for changing the spectral purity range E95. As a means for changing the spectral purity range E95, for example, there is a method of changing the synchronization timing of MO and PO.

DESCRIPTION OF SYMBOLS 1 Laser gas 10 Laser chamber 11, 12 Discharge electrode 13, 14 Window 20 Narrow-band module 21 Grating 22 Prism beam expander 23 Rotation stage 30 Wavefront adjustment module 31 Output coupler 32 Wavefront adjuster 33 Concave lens 34 Convex lens 35 Linear stage

Claims (4)

A laser chamber enclosing a laser medium and provided with windows on both ends ;
An excitation source for exciting the laser medium;
A previous SL on the optical axis of a and the optical resonator due to the excitation of the laser medium to resonate the output light, the inside of the optical resonator, the one rear side of the window of said laser chamber comprising a line narrowing module and the other front side of the window of said laser chamber, a narrow-band laser, characterized in that it comprises a wavefront adjuster for adjusting the wavefront of the light output from the laser medium apparatus. It has a partially transmissive output coupler that reflects part of the incident light and transmits the rest,
2. The narrow wave front adjuster according to claim 1, further comprising a wavefront adjuster control unit that samples light output from the partially transmissive output coupler and feedback-controls the wavefront adjuster to obtain a desired spectral width. Banded laser device. The wavefront adjuster includes a cylindrical concave lens and a cylindrical convex lens arranged on an optical path, and a lens that adjusts an interval between the cylindrical concave lens and the cylindrical convex lens by moving at least one of the cylindrical concave lens and the cylindrical convex lens on the optical path. The narrow-band laser device according to claim 1, further comprising an interval adjusting mechanism. The laser medium is a laser gas, and the excitation source has a pair of discharge electrodes facing each other and a power supply circuit for applying a high voltage between the discharge electrodes, and the laser gas and the discharge electrode are connected to each other in a laser chamber. The narrow-band laser device according to claim 1, wherein the narrow-band laser device is provided inside.

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