Abstract:
An upper limit and a lower limit are preliminarily set for a spectral line width common to a plurality of narrow-band laser devices. When delivered or subjected to maintenance, the narrow-band laser device is caused to laser oscillate to detect its spectral line width before it is used as a light source for semiconductor exposure. A spectral line width adjustment unit provided in the narrow-band laser device is adjusted so that the spectral line width assumes a value between the upper limit and the lower limit. The present invention is able to suppress the variation in spectral line width such as E95 bandwidth caused by machine differences during the manufacture of the laser device, or by replacement or maintenance of the laser device, whereby the quality of integrated circuit patterns formed by the semiconductor exposure tool can be stabilized.

Description:
[0001]    This application is a divisional of Ser. No. 11/822,126, filed Jul. 2, 2007, which is hereby incorporated by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field the Invention 
         [0003]    The present invention relates to a method for adjusting a spectral line width such as E95 bandwidth of a narrow-band laser when using a narrow-band laser as a light source to expose a semiconductor. The E95 bandwidth means a spectral line width of the spectral area of laser light where 95% energy is concentrated. The present invention particularly relates to a method for reducing the deviation in spectral line width such as E95 bandwidth among a plurality of narrow-band laser devices. 
         [0004]    2. Description of the Related Art 
         [0005]    The recent trend of refining the configuration and increasing the degree of integration of semiconductor integrated circuits has increased the demand for improvement in resolution of a semiconductor exposure tool (hereafter, referred to as the “exposure tool”). For this purpose, the related art tries to decrease the wavelength of light emitted by an exposure light source. Recently, a gas laser device has replaced a traditional mercury lamp as an exposure light source. Such a gas laser device for exposure is for example a KrF excimer laser emitting vacuum vacuum ultraviolet light with a wavelength of 248 nm or an ArF excimer laser emitting vacuum vacuum ultraviolet light with a wavelength of 193 nm. 
         [0006]    Studies are being conducted for next-generation exposure technologies, represented by an immersion exposure technique in which space between a wafer and an exposure lens of an exposure tool is filled with liquid to change the index of refraction to thereby decrease the apparent wavelength of the exposure light source. When the immersion exposure is performed by using an ArF excimer laser as an exposure light source, the wafer is irradiated with vacuum ultraviolet light with a wavelength of 134 nm in the liquid. This technique is referred to as the ArF immersion exposure (or ArF immersion lithography). 
         [0007]    A next-next generation exposure light source which is viewed with high degree of expectation is an F2 laser emitting vacuum ultraviolet light with a wavelength of 157 nm. Further, the F2 laser is possibly used as an exposure light source to perform the immersion technique as described above. It is believed that, in this case, a wafer is irradiated with vacuum ultraviolet light with a wavelength of 115 nm. 
         [0008]    KrF and ArF excimer lasers have a free running line width as wide as about 350 to 400 pm. The use of these projection lens will cause occurrence of chromatic aberration, resulting in lose of resolution. Therefore, it is necessary to narrow the spectral line width of laser light emitted by the gas laser device until the chromatic aberration is reduced to a negligible level. For this reason, a line narrowing module having a line narrowing element (e.g. etalon or grating) is provided in a laser resonator of the gas laser device, so that the spectral line width is narrowed. A laser whose spectral line width is narrowed is referred to as the “narrow-band laser”. In general, a laser spectral line width is represented by a full width at half maximum. As shown in  FIG. 22(   a ), the term “full width at half maximum (FWHM)” refers to a spectral line width of a part of the laser light spectral where the light intensity is a half of the peak value. 
         [0009]    The image formation performance of an exposure tool can be accurately evaluated by an optical simulation calculation method using optical system data of the exposure tool and laser spectral profile. It is known from the results of the optical simulation calculation that the image formation performance of an exposure tool is greatly affected not only by the full width at half maximum of laser light spectral but also by components in the spectral skirts. Therefore, a new definition called E95 bandwidth (also referred to as spectral purity width) has been introduced to define a spectral line width. As shown in  FIG. 22(   b ), the E95 bandwidth is an index indicating a spectral line width of a part of spectral area of laser light where 95% of energy is concentrated. There is a correlation between the E95 bandwidth and image formation performance of an optical system of the exposure tool. The E95 bandwidth is thus required to be suppressed to 0.5 pm or less in order to guarantee a high quality for integrated circuits produced. 
         [0010]    The E95 bandwidth and the spectral line width at full width at half maximum can be varied for example by changing the wavefront of laser light. One of techniques to change the laser light wavefront is disclosed in the Patent Document 1 (Japanese Patent Application Laid-Open No. 2000-312048) which relates to a device for changing the curvature of a grating. 
         [0011]    However, it has recently been made known that if the value of the E95 bandwidth or the spectral line width at full width at half maximum is either too large or too small in comparison with a designed value for the optical system of the exposure tool, the quality of the integrated circuit pattern is deteriorated. This is described in the Patent Document 2 (U.S. Pat. No. 6,721,340) and the Patent Document 3 (Japanese Patent Application Laid-Open No. 2001-267673). 
         [0012]    When a plurality of laser devices are compared, those laser devices do not necessarily have an equivalent spectral line width such as E95 bandwidth even if they have the same configuration. It is rather common that the spectral line width such as E95 bandwidth differs among the plurality of laser devices.  FIG. 23  is a histogram showing the E95 bandwidths in a plurality of conventional laser devices. As shown in  FIG. 23 , the maximum value of E95 bandwidth was 0.450 pm, the minimum value 0.210 pm, the mean value 0.340 pm, and the standard deviation was 0.061 pm. Five out of twenty devices exhibited a variation in the E95 bandwidth exceeding an allowable range of the E95 bandwidth for an optical system of an exposure tool, for example a range of from 0.350 to 0.450 pm. The result revealed that if these five laser devices having an E95 bandwidth exceeding the allowable range were used as an exposure light source, the quality of integrated circuit patterns was deteriorated to such an extent that it is impossible to produce a semiconductor device. 
         [0013]    It is believed that the spectral line width such as E95 bandwidth differs among laser devices due to machine differences thereof The machine differences among laser devices include the followings. 
         [0014]    (1) Individual differences among optical elements (line narrowing elements) such as:
       i) variation in diffractive wavefront of gratings;   ii) variation in transmission wavefront of prisms; and   iii) variation in position and optical axis among optical elements in a line narrowing module;       
 
         [0018]    (2) Machine differences in adjustment of laser optical axis such as:
       i) variation in chamber discharge position and optical axis when chambers are replaced;   ii) variation in position and optical axis among line narrowing modules;   iii) variation in optical axis among laser resonators;       
 
         [0022]    (3) Machine differences of laser chambers such as:
       i) variation in discharge position   ii) variation in discharge position and discharge state.       
 
         [0025]    In a practical exposure process of semiconductor device manufacture, laser devices or modules are replaced due to failure or end of service life of the devices. Due to the machine differences as described above, a replacing laser device will have a different spectral line width such as E95 bandwidth from that of a replaced laser device even if they are of a same type. Moreover, the spectral line width such as E95 bandwidth will vary even in a same laser device between before and after maintenance thereof This means that the spectral line width such as E95 bandwidth is changed as a result of replacement or maintenance of the laser device, and if such change exceeds an allowable range of the spectral line width such as E95 bandwidth for an optical system of the exposure tool, the quality of integrated circuit patterns is deteriorated to such an extent that it is impossible to manufacture a semiconductor device. 
         [0026]    The present invention has been made in view of the circumstances described above. It is an object of the prevent invention to suppress variation in spectral line width such as E95 bandwidth due to machine differences caused during manufacture of laser devices and variation in spectral line width such as E95 bandwidth caused by replacement of maintenance of a laser device, and thus to stabilize the quality of integrated circuit patterns formed by a semiconductor exposure tool. 
       SUMMARY OF THE INVENTION 
       [0027]    A first aspect of the invention provides a narrow-band laser spectral line width adjustment method for adjusting the spectral line width of laser light when a narrow-band laser is used as a light source for semiconductor exposure, the method comprising the steps of: setting an upper limit and a lower limit for a spectral line width common to a plurality of narrow-band laser devices; causing the narrow-band laser device to laser oscillate prior to semiconductor exposure to detect a spectral line width; and adjusting a spectral line width adjustment unit provided in the narrow-band laser device to adjust the spectral line width to be a value between the upper limit and the lower limit. 
         [0028]    According to the first aspect of the invention, an upper limit and a lower limit are preliminarily set for a spectral line width common to a plurality of narrow-band laser devices. When delivered or subjected to maintenance, the narrow-band laser device is caused to laser oscillate to detect its spectral line width before it is used as a light source for semiconductor exposure. A spectral line width adjustment unit provided in the narrow-band laser device is adjusted so that the spectral line width assumes a value between the upper limit and the lower limit. This makes it possible, even if the narrow-band laser device is replaced with another one before semiconductor exposure, to minimize the difference in spectral line width between the replaced narrow-band laser device and the replacing narrow-band laser device. Further, even if the narrow-band laser device is subjected to maintenance before conducting semiconductor exposure, the difference in spectral line width of the narrow-band laser device between before and after the maintenance can be minimized. 
         [0029]    In a second aspect of the invention according to the first aspect, the spectral line width adjustment unit has a wavefront adjuster which is arranged on an optical path inside a laser resonator of the narrow-band laser device, and is designed to adjust the curvature radius of an optical wavefront with a straight line connecting the apex of the cylindrical shape of the optical wavefront being set substantially perpendicular to the wavefront dispersion surface of a wavelength selection element arranged inside the laser resonator of the narrow-band laser device, and the wavefront adjuster is adjusted so that the spectral line width assumes a value between the upper limit and the lower limit. 
         [0030]    In a third aspect of the invention according to the second aspect, the spectral line width adjustment unit includes: a cylindrical concave lens and cylindrical convex lens whose central axes are arranged on the optical path inside the laser resonator of the narrow-band laser device and whose mechanical axes are arranged substantially perpendicular to the wavefront dispersion surface of the wavelength selection element arranged inside the laser resonator; and a lens distance variable mechanism for varying the distance between the cylindrical concave lens and the cylindrical convex lens along the optical path, and the lens distance variable mechanism is adjusted so that the spectral line width assumes a value between the upper limit and the lower limit. 
         [0031]    In a fourth aspect of the invention according to the second aspect, the spectral line width adjustment unit includes: a cylindrical mirror whose central axis is arranged on the optical path inside the laser resonator of the narrow-band laser device, and whose mechanical axis is arranged substantially perpendicular to the wavefront dispersion surface of the wavelength selection element arranged inside the laser resonator; and a mirror curvature variable mechanism for varying a curvature of the cylindrical mirror, and the mirror curvature variable mechanism is adjusted so that the spectral line width assumes a value between the upper limit and the lower limit. 
         [0032]    In a fifth aspect of the invention according to the second aspect, the spectral line width adjustment unit includes: a grating used as the wavelength selection element; and a grating curvature variable mechanism for varying a curvature of the grating while keeping a linear shape of a multiplicity of grooves of the grating, and the grating curvature variable mechanism is adjusted so that the spectral line width assumes a value between the upper limit and the lower limit. 
         [0033]    In a sixth aspect of the invention according to the first aspect, the spectral line width adjustment unit includes: two or more prisms arranged on an optical path inside a laser resonator of the narrow-band laser device for expanding a beam in a direction substantially perpendicular to the wavefront dispersion surface of a wavelength selection element arranged inside the laser resonator; and a prism angle variable mechanism for varying a rotation angle of the two or more prisms to change a beam expansion factor, and the prism angle variable mechanism is adjusted so that the spectral line width assumes a value between the upper limit and the lower limit. 
         [0034]    The third to sixth aspects of the invention each relate to a specific method of adjusting the spectral line width in the first aspect of the invention. 
         [0035]    In a seventh aspect of the invention according to the first aspect, the narrow-band laser device includes an oscillation stage laser for generating and outputting seed light, and one or more amplification stage chambers or amplification stage lasers for receiving and amplifying the laser light output from a previous stage laser, and outputting the amplified laser light; and the spectral line width adjustment unit includes a spectral line width variable mechanism arranged on a laser optical path between the oscillation stage laser and the amplification stage chamber or the amplification stage laser, and the spectral line width variable mechanism is adjusted so that the spectral line width assumes a value between the upper limit and the lower limit. 
         [0036]    The seventh aspect of the invention relates to a specific method of adjusting the spectral line width when the narrow-band laser device is a double-chamber system having an oscillation stage and an amplification stage in the first aspect. 
         [0037]    In an eighth aspect of the invention according to the first aspect, the narrow-band laser device includes an oscillation stage laser for generating and outputting seed light, and one or more amplification stage chambers or amplification stage lasers for receiving and amplifying the laser light output from a previous stage laser, and outputting the amplified laser light; and the spectral line width adjustment unit includes a spectral line width variable mechanism arranged on a laser optical path inside a laser resonator of the oscillation stage laser, and the spectral line width variable mechanism is adjusted so that the spectral line width assumes a value between the upper limit and the lower limit. 
         [0038]    The eighth aspect of the invention relates to a specific method for adjusting the spectral line width when the narrow-band laser device is a double-chamber system having an oscillation stage and an amplification stage in the first aspect. 
         [0039]    The present invention is able to minimize the deviation in spectral line width such as E95 bandwidth among laser devices can be minimized, and the deviation in spectral line width such as E95 bandwidth of a same laser device between before and after it is subjected to maintenance. Therefore, the spectral line width of laser light output by the laser device does not exceed the allowable range of spectral line width such as E95 bandwidth for an optical system of the exposure tool. This makes it possible to stabilize the quality of integrated circuit patterns formed by the semiconductor exposure tool and thus improves the yield of semiconductor devices. Furthermore, the yield of laser production and the yield in maintenance are improved, whereby the laser production cost and the maintenance cost can be reduced effectively. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0040]      FIG. 1  is a diagram showing an example of a device configuration for adjusting a spectral line width of a narrow-band laser device; 
           [0041]      FIGS. 2(   a ) and  2 ( b ) are diagrams showing a configuration of an E95 bandwidth adjustment unit and the positional relationship among an output coupler, the E95 bandwidth adjustment unit, a laser chamber, and a line narrowing module, according to a first embodiment of the invention; 
           [0042]      FIGS. 3(   a ) and  3 ( b ) are diagrams showing a configuration of an E95 bandwidth adjustment unit according to a second embodiment of the invention; 
           [0043]      FIG. 4  is a diagram showing the relationship between a micrometer relative scale, an E95 bandwidth, and a laser output relative value when the E95 bandwidth adjustment unit according to the second embodiment is used; 
           [0044]      FIG. 5  is a histogram of E95 bandwidths due to laser machine differences when the E95 bandwidth adjustment unit according to the second embodiment is employed; 
           [0045]      FIG. 6  is a diagram showing a configuration of an E95 bandwidth adjustment unit according to a third embodiment and positional relationship among the E95 bandwidth adjustment unit, a laser chamber and a line narrowing module; 
           [0046]      FIG. 7  is a diagram showing a state in which the E95 bandwidth adjustment unit is attached to the rear side of the laser chamber; 
           [0047]      FIGS. 8(   a ) and  8 ( b ) are diagrams showing a configuration of an E95 bandwidth adjustment unit according to a fourth embodiment of the invention; 
           [0048]      FIG. 9  is a diagram showing a state in which the E95 bandwidth adjustment unit according to the fourth embodiment is provided in a line narrowing module; 
           [0049]      FIGS. 10(   a ) and  10 ( b ) are diagrams showing a configuration of an E95 bandwidth adjustment unit according to a fifth embodiment of the invention; 
           [0050]      FIG. 11  is a diagram showing a state in which the E95 bandwidth adjustment unit according to the fifth embodiment is provided in a line narrowing module; 
           [0051]      FIG. 12  is a diagram showing a configuration of an E95 bandwidth adjustment unit according to a sixth embodiment of the invention; 
           [0052]      FIG. 13  is a diagram showing a relationship among a micrometer relative scale, an E95 bandwidth, and a laser output relative value when the E95 bandwidth adjustment unit according to the sixth embodiment is employed; 
           [0053]      FIG. 14  is a diagram showing a configuration of an E95 bandwidth adjustment unit according to a seventh embodiment of the invention; 
           [0054]      FIG. 15  is a diagram showing a state in which the E95 bandwidth adjustment unit is provided in a PO (amplification stage laser) of a double-chamber system; 
           [0055]      FIG. 16  is a diagram showing positional relationship among an E95 bandwidth adjustment unit, a laser chamber, and a line narrowing module according to an eighth embodiment of the invention; 
           [0056]      FIGS. 17(   a ) and  17 ( b ) are diagrams showing a configuration of the E95 bandwidth adjustment unit according to the eighth embodiment; 
           [0057]      FIG. 18  is a diagram showing a state in which the E95 bandwidth adjustment unit is provided between a PO and an MO (oscillation stage laser) of a double-chamber system; 
           [0058]      FIG. 19  is a diagram showing a state in which a cylindrical lens is arranged between the MO and the PO; 
           [0059]      FIG. 20  is a diagram showing a state in which a prism is arranged between the MO and the PO; 
           [0060]      FIG. 21  is a diagram showing a state in which a slit is arranged between the MO and the PO; 
           [0061]      FIGS. 22(   a ) and  22 ( b ) are diagrams for explaining the FWHM and the E95 bandwidth; and 
           [0062]      FIG. 23  is a histogram of E95 bandwidths due to laser machine differences according to conventional techniques. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0063]    Preferred embodiments of the present invention will be described with reference to the accompanying drawings. While the spectral line width includes several types such as FWHM and E95, the following description will be made taking the E95 bandwidth as an example. 
         [0064]      FIG. 1  shows an example of a device configuration for adjusting the spectral line width of a narrow-band laser device. 
         [0065]    In a narrow-band laser device  1  as shown in  FIG. 1 , a slit  90   r  and a line narrowing module  30  are arranged on an optical path on the rear side (the right side in the drawing) of a laser chamber  20 , and a slit  90   f  and an E95 bandwidth adjustment unit  40  are arranged on an optical path on the front side (on the left side in the drawing) of the laser chamber  20 . Further, a monitor module  60  and an output coupler  50  having an incidence surface coated with a PR film and an emission surface coated with an AR film are arranged on an optical path on the front side (the left side in the drawing) of the E95 bandwidth adjustment unit  40 . The line narrowing module  30  and the output coupler  50  together form a resonator. 
         [0066]    A pair of discharge electrodes  21  and  22  are provided in the inside of the laser chamber  20 . The discharge electrodes  21  and  22  are arranged parallel to each other in the longitudinal direction thereof, and such that the discharge surfaces thereof face each other, being spaced from each other by a predetermined distance. Further, windows  23  and  24  are provided in a laser light output portion on the optical axis of laser light in the laser chamber  20 . The windows  23  and  24  are made of a material having transparency to laser light such as CaF2. The windows  23  and  24  are arranged such that the outer surfaces thereof are parallel to each other, and arranged at a Brewster angle to reduce the reflection loss of laser light. 
         [0067]    Laser gas is sealed inside the laser chamber  20  as a laser medium. The laser gas used in the case of F2 laser is gas mixture composed of F2 gas and a buffer gas such as He or Ne. The laser gas used in the case of KrF excimer laser is gas mixture composed of Kr gas, F2 gas, and a buffer gas such as He or Ne. The laser gas used in the case of ArF excimer laser is gas mixture composed of Ar gas, F2 gas, and a buffer gas such as He or Ne. The supply and discharge of the laser gas is controlled by a gas supply/discharge mechanism (not shown). 
         [0068]    High voltage is applied by a power supply circuit  70  to the discharge electrodes  21  and  22  provided in the laser chamber  20 . Electric discharge occurs when the voltage between the discharge electrodes  21  and  22  exceeds a predetermined voltage. The laser gas in the laser chamber  20  is excited by the electric discharge to shift to a high energy level and then to a low energy level, resulting in emission of light. 
         [0069]    There are provided in the line narrowing module  30  optical elements such as prism beam expanders (hereafter, each referred to as the “prism”)  32  and  33  and a grating  31  serving as a wavelength dispersive element. Although two prisms are provided in the example shown in  FIG. 1 , the number of the prisms can be determined arbitrarily. The grating  31  and the prisms  32  and  33  are usually fixed to a casing of the line narrowing module  30  by means of a fixing member. However, in some cases, they may be fixed rotatably. In such a case, the prisms  32  and  33  and the grating  31  are fixed to a rotation mechanism not shown in the drawing. The incident angle of laser light to the grating  31  and the prisms  32  and  33  is changed by driving the rotation mechanism. Further, the line narrowing module  30  may be formed of optical elements such as a total reflection mirror and an etalon serving as a wavelength dispersive element. 
         [0070]    The E95 bandwidth adjustment unit  40  is composed of optical elements for adjusting the E95 bandwidth of laser light. The E95 bandwidth adjustment unit  40  can be configured in several manners, which will be described later with reference to  FIGS. 2(   a ) and  2 ( b ) to  FIG. 21 . 
         [0071]    The monitor module  60  is provided with a beam splitter  61  and a monitor  62 . The monitor  62  is comprised of a monitor for detecting an E95 bandwidth or central wavelength and a monitor for detecting laser light energy. The monitor for detecting an E95 bandwidth or central wavelength includes a spectrometer having, for example, a diffuser panel, an etalon, a condenser lens, a line sensor and so on. Laser light entering the monitor module  60  is split by the beam splitter  61  so that part of the laser light enters the monitor  62  while the rest is emitted to the outside. 
         [0072]    A laser controller  80  calculates energy, wavelength, and spectral line width of laser light based on a spectral detected by the monitor  62  of the monitor module  60 . Based on the calculation results, the laser controller  80  outputs a command signal indicating a charging voltage of the power supply circuit  70 , and a command signal for driving the rotation mechanism to which the optical elements of the line narrowing module  30  are fixed. 
         [0073]    There are provided, in the outside of the narrow-band laser device  1 , a high resolution spectrometer  4  for detecting the spectral of laser light output by the narrow-band laser device  1 , a condenser lens  2  and an optical fiber  3  for guiding laser light from the narrow-band laser device to the high resolution spectrometer  4 , and a personal computer  9  for retrieving the detection result from the high resolution spectrometer  4  and displaying the spectral of the laser light on a display device. 
         [0074]    The laser light emitted by the narrow-band laser device  1  is collected by the condenser lens  2 . The light emitted by the condenser lens  2  passes through the optical fiber  3  and enters the high resolution spectrometer  4 . In the high resolution spectrometer  4 , the light passes through the condenser lens  5  and illuminates an entrance slit  11 . Light transmitted through the entrance slit is reflected by a concave mirror  6   a , diffracted by a grating  7 , and reflected by a concave mirror  6   b . A diffraction image is thus formed on a CCD line sensor  8 . This diffraction image changes its image forming position according to the diffraction angle at the grating  7  that is changed depending on a wavelength. The CCD line sensor  8  is thus enabled to detect the spectral of the light. The spectral detected by the CCD line sensor  8  is converted into a signal which is introduced into the personal computer  9 . The personal computer  9  has a display device  10  connected thereto, and the spectral detected by the CCD line sensor  8  is displayed on this display device  10 . Although the description of the high resolution spectrometer  4  has been made taking an example of a commonly used Czerny-Turner spectrometer, any other high resolution spectrometer may be used as long as it is capable of measuring E95 bandwidth sufficiently. 
         [0075]    Description will be made of procedures of a spectral line width adjusting method. 
         [0076]    In the first place, an upper limit ΔλHL and a lower limit ΔλLL are set for the E95 bandwidth common to narrow-band lasers used for semiconductor exposure. The upper limit ΔλHL and the lower limit ΔλLL are set within a range of E95 bandwidth allowed for the optical system of the semiconductor exposure tool. 
         [0077]    Before using the narrow-band laser device  1  as a light source for the exposure tool, for example after the assembly of the narrow-band laser device  1  or directly after maintenance of the narrow-band laser device  1 , the condenser lens  2 , the optical fiber  3 , the high resolution spectrometer  4 , the personal computer  9 , and the display device  10  are arranged outside the narrow-band laser device  1 , as shown in  FIG. 1 . The narrow-band laser device  1  is then laser oscillated. During the laser oscillation, a spectral of the laser light is detected by the high resolution spectrometer  4 , and is displayed on the display device  10 . 
         [0078]    Looking at the display device  10 , the operator adjusts the E95 bandwidth adjustment unit  40  of the narrow-band laser device  1  such that the E95 bandwidth takes a value between the upper limit ΔλHL and the lower limit ΔλLL. The E95 bandwidth varies in accordance with the adjustment of the E95 bandwidth adjustment unit  40 . When the E95 bandwidth becomes a value between the upper limit ΔλHL and the lower limit ΔλLL, the E95 adjustment unit  40  is fixed to terminate the adjustment of the E95 bandwidth. 
         [0079]    Although, according to the embodiment shown in  FIG. 1 , the high resolution spectrometer  4  provided outside the narrow-band laser device  1  is used, a small-sized spectral detector may be used, providing the same within the narrow-band laser device  1 . Further, the monitor  62  of the monitor module  60  provided in the narrow-band laser device  1  may be used. 
         [0080]    Description will be made of specific configuration of the E95 bandwidth adjustment unit  40 . 
         [0081]      FIGS. 2(   a ) and  2 ( b ) show configuration of the E95 bandwidth adjustment unit and positional relationship among the output coupler, the E95 bandwidth adjustment unit, the laser chamber, and the line narrowing module, according to the first embodiment.  FIG. 2(   a ) is a plan view and  FIG. 2(   b ) is a side view. The first embodiment is designed to adjust the optical wavefront by changing the distance between two lenses. The optical wavefront has a cylindrical shape. A straight line connecting the apex of the cylindrical shape is set approximately perpendicular to the wavefront dispersion surface of a wavelength selection element (grating) in the laser resonator, and the curvature of the cylindrical optical wavefront is varied, whereby the laser E95 bandwidth can be changed. The wavefront dispersion surface corresponds to an x-z plane in  FIGS. 2(   a ) and  2 ( b ), where the direction orthogonal to a multiplicity of grooves formed in the diffraction surface of the grating  31  is defined as the x axis, the direction parallel to the grooves formed in the diffraction surface of the grating  31  is defined as the y axis, and the direction orthogonal to the diffraction surface of the grating  31  is defined as the z axis. 
         [0082]    The E95 bandwidth adjustment unit  40  shown in  FIGS. 2(   a ) and  2 ( b ) has a cylindrical concave lens  41  and a cylindrical convex lens  42  which face each other with a distance therebetween, the distance being freely adjustable. The cylindrical concave lens  41  and the cylindrical convex lens  42  are arranged such that central axes thereof are located on the optical path in the laser resonator, and such that mechanical axes thereof are approximately perpendicular to the wavefront dispersion surface of the grating  31 . The central axes of the cylindrical concave lens  41  and cylindrical convex lens  42  are defined by a straight line connecting the centers of curvature radii of the cylindrical surfaces. The mechanical axis of the cylindrical concave lens  41  is defined by a straight line connecting the most recessed points in the lens. The mechanical axis of the cylindrical convex lens  42  is defined by a straight line connecting the most protruding point in the lens. The cylindrical concave lens  41  is fixed to the upper surface of a movable plate  43 . The movable plate  43  is movable along a linear guide  45  formed on a uniaxial stage  44 . The uniaxial stage  44  is arranged such that the direction in which the linear guide  45  is extended is parallel to the optical axis. 
         [0083]    A convex portion  43   a  is formed on one side face of the movable plate  43  so as to protrude therefrom. The head of the micrometer  46  abuts on the front side of the convex portion  43   a , while the head of a protrusion  47  abuts on the rear side of the convex portion  43   a . The micrometer  46  is extendable and retractable in the direction in which the linear guide  45  is extended, and the extension of the micrometer  46  applies a pressing force to the convex portion  43   a  in the direction toward the protrusion  47 . A spring which is extendable and retractable in the direction in which the linear guide  45  is extended is connected to the head of the protrusion  47 , so that the spring applies an urging force to the convex portion  43   a  in the direction toward the micrometer  46 . Consequently, the movable plate  43  is moved along linear guide  45  by extension or retraction of the micrometer  46 . 
         [0084]    A fixing screw  48  is provided on the other side of the movable plate  43 . The fixing screw  48  is screwed in a through hole formed in the movable plate  43  so that the tip end thereof abuts on the linear guide  45 . The movable plate  43  is fastened to the uniaxial stage  43  by tightening the fixing screw  48 . The movable plate  43  is released by loosening the fixing screw  48 . It should be understood that the fixing screw  48  may be omitted as long as the movable plate  43  can be sufficiently fixed to the uniaxial stage  43  by means of the micrometer  46  and the protrusion  47 . 
         [0085]    The E95 bandwidth adjustment unit  40 , the laser chamber  20 , and the line narrowing module  30  are arranged in orientation as shown in  FIGS. 2(   a ) and  2 ( b ). More specifically, the E95 bandwidth adjustment unit  40 , the laser chamber  20 , and the line narrowing module  30  are arranged such that the centers of the curvature radii of the cylindrical surfaces of the cylindrical concave lens  41  and cylindrical convex lens  42  provided in the line narrowing module  30  are located on the laser optical axis, and such that the mechanical axes of the cylindrical concave lens  41  and cylindrical convex lens  42  are parallel to the multiplicity of grooves formed in the diffraction surface of the grating  31 . 
         [0086]      FIGS. 3(   a ) and  3 ( b ) show configuration of an E95 bandwidth adjustment unit according to a second embodiment.  FIG. 3(   a ) is a plan view and  FIG. 3(   b ) is a side view. In the second embodiment, a planoconcave cylindrical lens  101  and a planoconvex cylindrical lens  102  are provided respectively in place of the cylindrical concave lens  41  and the cylindrical convex lens  42  shown in  FIGS. 2(   a ) and  2 ( b ). Configuration of the second embodiment is identical with that of the first embodiment shown in  FIGS. 2(   a ) and  2 ( b ), except for the planoconcave cylindrical lens  101  and the planoconvex cylindrical lens  102 . In the second embodiment, the output coupler  50  shown in  FIG. 1  is not required since the planoconvex cylindrical lens  102  functions as an output coupler. The incidence surface (the surface closer to the laser chamber) of the planoconvex cylindrical lens  102  is coated with an anti-reflection (AR) film, while the emission surface (the surface further from the laser chamber) is coated with a partial-reflection (PR) film. Similarly to the configuration shown in  FIGS. 2(   a ) and  2 ( b ), the centers of the curvature radii of the planoconcave cylindrical lens  101  and planoconvex cylindrical lens  102  are located on the laser optical axis, and the mechanical axes of the planoconcave cylindrical lens  101  and planoconvex cylindrical lens  102  are parallel to a multiplicity of grooves formed on the diffraction surface of the grating  31 . 
         [0087]      FIG. 4  shows relationship among a micrometer relative scale, an E95 bandwidth, and a laser output relative value when the E95 bandwidth adjustment unit according to the second embodiment is used. In  FIG. 4 , the relative scale of the micrometer  46  (the axis of abscissa) of “1” corresponds to a state in which the planoconcave cylindrical lens  101  and the planoconvex cylindrical lens  102  are separated from each other by a predetermined distance. As the relative scale of the micrometer  46  increases, the planoconcave cylindrical lens  101  is separated further from the planoconvex cylindrical lens  102 . 
         [0088]    As seen from  FIG. 4 , the E95 bandwidth monotonically increases from 0.23 pm to 1.2 pm along with the increase of the micrometer relative scale. On the other hand, as the micrometer relative scale increases from 1 to 9, the laser output relative value monotonically increases from 0.42 to 1.63. As the micrometer relative scale increases from 9 to 11, the laser output monotonically decreases from 1.63 to 1.2. 
         [0089]    When the target value of E95 bandwidth is set to 0.4 pm, for example, adjustment is made such that the relative scale of the micrometer  46  becomes 4.2. The laser output relative value is 0.95 in this state. Once the E95 bandwidth attains the target value, the fixing screw  48  is tightened to fix the movable plate  43 . 
         [0090]      FIG. 5  is a histogram showing the E95 bandwidth varied due to laser machine differences when the E95 bandwidth adjustment unit according to the second embodiment is used. 
         [0091]    A plurality of narrow-band laser devices were prepared as test samples. The lower limit ΔλLL of the E95 bandwidth was set to 0.30 pm, while the upper limit ΔλHL is set to 0.50 pm. The narrow-band laser devices were oscillated and the E95 bandwidth adjustment unit was adjusted so that the E95 bandwidth assumed a value between the upper limit ΔλHL and the lower limit ΔλLL. The maximum value of the E95 bandwidth was 0.440 pm, the minimum value 0.360 pm, the mean value 0.405 pm, and the standard deviation was 0.029 pm. These variations due to the machine differences were effectively contained in the allowable E95 bandwidth range of from 0.350 pm to 0.450 pm. 
         [0092]      FIG. 6  shows configuration of an E95 bandwidth adjustment unit according to a third embodiment and positional relationship among the E95 bandwidth adjustment unit, a laser chamber, and a line narrowing module.  FIG. 6  is a plan view. The third embodiment is designed to adjust the optical wavefront by changing the curvature of a cylindrical mirror. 
         [0093]    An E95 bandwidth adjustment unit  40  shown in  FIG. 6  has a cylindrical mirror  111  the curvature of which is adjustable. In the third embodiment, a beam splitter  117  is arranged between the cylindrical mirror  111  and a laser chamber  20 . The beam splitter  117  functions as an output coupler. Two rods  112  are connected, at one end thereof, to the opposite edges of the rear face of the cylindrical mirror  111 . One end of a spring  113  is connected to the center of the rear face of the cylindrical mirror  111 . The other ends of the two rods  112  are connected to a plate  114  arranged behind the cylindrical mirror  111 , and the other end of the spring  113  is connected to the head of a micrometer  115  arranged behind the cylindrical mirror  111 . The micrometer  115  is fixed to the plate  114 . The micrometer  115  is provided with a fixing screw  116  for fixing the extension or retraction. 
         [0094]    The cylindrical mirror  111  is arranged such that the center of the curvature radius of its cylindrical surface is located on the laser optical axis, and the mechanical axis of the cylindrical surface is parallel to a multiplicity of grooves formed in a diffraction surface of a grating  31  (i.e. substantially perpendicular to a wavefront dispersion surface of the grating  31 ). The definition of the mechanical axis of the cylindrical surface is the same as the definition of the mechanical axis of the cylindrical concave lens  41  described above. 
         [0095]    When extended, the micrometer  115  pushes the center of the cylindrical mirror  111  by way of the spring  113 . When retracted, the micrometer  115  pulls the center of the cylindrical mirror  111  by way of the spring  113 . The curvature of the cylindrical surface of the cylindrical mirror  111  is adjusted in this manner. 
         [0096]    The description so far has been made regarding the configuration in which the E95 bandwidth adjustment unit is arranged on the front side of the laser chamber. However, as shown in  FIG. 7 , the E95 bandwidth adjustment unit may be arranged on the rear side of the laser chamber to adjust the E95 bandwidth. Description will be made of this embodiment. 
         [0097]      FIGS. 8(   a ) and  8 ( b ) show a configuration of an E95 bandwidth adjustment unit according to a fourth embodiment.  FIGS. 8(   a ) and  8 ( b ) show a same E95 bandwidth adjustment unit but different patterns of wavefront adjustment. The configuration of the E95 bandwidth adjustment unit  40 ′ shown in  FIGS. 8(   a ) and  8 ( b ) coincides, in many aspects, with that of the E95 bandwidth adjustment unit  40  shown in  FIGS. 2(   a ) and  2 ( b ). They are different only in that a cylindrical concave lens  121  is not fixed to a movable plate but a cylindrical convex lens  122  is fixed to the movable plate. 
         [0098]    The E95 bandwidth adjustment unit  40 ′ shown in  FIGS. 8(   a ) and  8 ( b ) has a cylindrical concave lens  121  and a cylindrical convex lens  122  facing each other with a distance which is adjustable. The cylindrical convex lens  122  is arranged on the rear side of the laser chamber  20  such that the center of the curvature radius of the cylindrical surface is located on the laser optical axis, and the mechanical axis of the cylindrical surface is parallel with a multiplicity of grooves formed on a diffraction surface of a grating  31  (i.e. such that the mechanical axis is substantially orthogonal to the wavefront dispersion surface). The cylindrical concave lens  121  is arranged on the rear side of the cylindrical convex lens  122  such that the center of the curvature radius of the cylindrical surface is located on the laser optical axis and the mechanical axis of the cylindrical surface is parallel with the multiplicity of grooves formed on the diffraction surface of the grating  31  (i.e., such that the mechanical axis is substantially orthogonal to the wavefront dispersion surface). The cylindrical convex lens  122  is fixed to the upper surface of a movable plate  123 . The movable plate  123  is movable along a linear guide  125  formed on a uniaxial stage  124 . The uniaxial stage  124  is arranged such that the direction in which the linear guide  125  extends is parallel to the optical axis. 
         [0099]    A convex portion  123   a  is formed on one side of movable plate  123  so as to protrude therefrom. The head of a micrometer  126  abuts on the front face of the convex portion  123   a , and the head of a protrusion  127  abuts on the rear face of the convex portion  123   a . The micrometer  126  is extendable and retractable in the direction in which the linear guide  125  extends, and extension of the micrometer  126  applies a pressing force to the convex portion  123   a  in the direction towards the protrusion  127 . The head of the protrusion  127  is connected to a spring which is extendable and retractable in the direction in which the linear guide  125  extends. This spring applies an urging force to the convex portion  123   a  in the direction towards the micrometer  126 . Accordingly, the movable plate  123  is moved along the linear guide  125  by extension or retraction of the micrometer  126 . 
         [0100]    A fixing screw  128  is provided on the other side of the movable plate  123 . The fixing screw  128  is screwed into a through hole formed in the movable plate  123  and the tip end of the screw abuts on the linear guide  125 . The movable plate  123  is fixed to the uniaxial stage  123  by tightening the fixing screw  128 . The movable plate  123  is released by loosening the fixing screw  128 . It should be understood that the fixing screw  128  may be omitted as long as the movable plate  123  can be effectively fixed to the uniaxial stage  123  by means of the micrometer  126  and the protrusion  127 . 
         [0101]    As shown in  FIG. 9 , the E95 bandwidth adjustment unit  40 ′ shown in  FIGS. 8(   a ) and  8 ( b ) may be provided between a grating  31  and a prism  33  provided in the line narrowing module  30 . 
         [0102]      FIGS. 10(   a ) and  10 ( b ) show configuration of an E95 bandwidth adjustment unit according to a fifth embodiment.  FIGS. 10(   a ) and  10 ( b ) show a same E95 bandwidth adjustment unit but different patterns of wavefront adjustment. The configuration of the E95 bandwidth adjustment unit  40 ′ shown in  FIGS. 10(   a ) and  10 ( b ) coincides, in many aspects, with that of the E95 bandwidth adjustment unit  40  shown in  FIG. 6 . They are different only in that no beam splitter is provided and the optical incident direction is different from the reflection direction in the E95 bandwidth adjustment unit  40 ′. 
         [0103]    The E95 bandwidth adjustment unit  40 ′ shown in  FIGS. 10(   a ) and  10 ( b ) has a cylindrical mirror  131  the curvature of which is adjustable. Two rods  132  are connected, at one ends thereof, to the opposite edges of the rear face of the cylindrical mirror  131 . One end of a spring  133  is connected to the center of the rear face of the cylindrical mirror  131 . The other ends of the two rods  132  are connected to a plate  134  arranged behind the cylindrical mirror  131 , and the other end of the spring  133  is connected to the head of a micrometer  135  arranged behind the cylindrical mirror  131 . The micrometer  135  is fixed to the plate  134 . The micrometer  135  is provided with a fixing screw  136  for fixing the extension or retraction. 
         [0104]    The cylindrical mirror  131  is arranged in such an orientation that the incident direction of laser light is different from the reflection direction. The cylindrical mirror  131  is arranged such that the mechanical axis of the cylindrical surface is parallel with a multiplicity of grooves formed in the diffraction surface of a grating  31 . The definition of the mechanical axis of the cylindrical surface is the same as the definition of the mechanical axis of the cylindrical concave lens  41  described above. 
         [0105]    When extended, the micrometer  135  pushes the center of the cylindrical mirror  131  by way of the spring  133 , and when retracted the micrometer  135  pulls the center of the cylindrical mirror  131  by way of the spring  133 . The curvature of the cylindrical surface of the cylindrical mirror  131  is adjusted in this manner. 
         [0106]    As shown in  FIG. 11 , the E95 bandwidth adjustment unit  40 ′ shown in  FIGS. 10(   a ) and  10 ( b ) may be provided between a prism  32  and a prism  33  provided in the line narrowing module  30 . In this case, it is desirable to provide an operating portion of the micrometer  135  outside the casing of the line narrowing module  30 . 
         [0107]      FIG. 12  shows configuration of an E95 bandwidth adjustment unit according to a sixth embodiment. The sixth embodiment is designed to adjust the optical wavefront by changing the curvature of a grating provided in a line narrowing module. The configuration of the micrometer or the like used in the third and fifth embodiments is applied to the adjustment of the curvature of the grating. 
         [0108]    Two rods  142  are connected, at one ends thereof, to the opposite edges of the rear face of the grating  31 . One end of a spring  143  is connected to the center of the rear face of the grating  31 . The other ends of the two rods  142  are connected to a plate  144  arranged behind the grating  31 , and the other end of the spring  143  is connected to the head of a micrometer  145  arranged behind the grating  31 . The micrometer  145  is fixed to the plate  144 . The micrometer  145  is provided with a fixing screw  146  for fixing the extension or retraction. 
         [0109]    When extended, the micrometer  145  pushes the center of the grating  31  by way of the spring  143 , and when retracted, the micrometer  145  pulls the center of the grating  31  by way of the spring  143 . In this manner, the curvature of the diffraction surface is adjusted while keeping the multiplicity of the grooves of the grating  31  in linear shape. 
         [0110]      FIG. 13  shows relationship among a micrometer relative scale, an E95 bandwidth, and a laser output relative value when the E95 bandwidth adjustment unit according to the sixth embodiment is used. In  FIG. 13 , the relative scale of the micrometer  145  (the axis of abscissa) of “1” corresponds to a state in which the grating  31  has a predetermined curvature. As the relative scale of the micrometer  146  increases, the center of the grating  31  is pushed further out. 
         [0111]    As seen from  FIG. 13 , as the micrometer relative scale increases from one to six, the E95 bandwidth monotonically decreases from 0.40 pm to 0.23 pm. As the micrometer relative scale increases from six to eleven, the E95 bandwidth monotonically increases from 0.23 pm to 0.5 pm. On the other hand, as the micrometer relative scale increases from one to six, the laser output relative value monotonically increases from 0.1 to 0.5, and as the micrometer relative scale increases from six to eleven, the laser output relative value monotonically decreases from 0.5 to 0.1. 
         [0112]    When the target value of the E95 bandwidth is set to 0.4 pm, for example, the adjustment is made such that the relative scale of the micrometer  145  becomes one. The laser output relative value in this state is 0.1. Once the E95 bandwidth attains the target value, the fixing screw  146  is tightened to fix the micrometer  145 . 
         [0113]    It will be examined, on the basis of the result shown in  FIG. 4  and the result shown in  FIG. 13 , which is more advantageous when the adjustment of the E95 bandwidth is made on the front side of the laser chamber or when made on the rear side. The laser output relative values in  FIG. 4  and  FIG. 13  are indicated on the same scale so that the laser output values can be compared relatively. 
         [0114]    According to the configuration in which the E95 bandwidth adjustment unit is arranged on the front side of the laser chamber, as shown in  FIG. 4 , an advantageous characteristic is obtained that the E95 bandwidth monotonically increases along with the increase of the micrometer scale reading. Accordingly, it can be seen that the E95 bandwidth can be enlarged simply by extending the micrometer, whereas the E95 bandwidth can be narrowed simply by retracting the micrometer. 
         [0115]    On the other hand, when the E95 bandwidth adjustment unit is arranged on the rear side of the laser chamber, as shown in  FIG. 13 , the E95 bandwidth monotonically increases along with the increase of the scale reading of the micrometer. However, once the scale reading of the micrometer has increased to some extent, the E95 bandwidth thereafter monotonically decreases along with the increase of the scale reading. Accordingly, it is impossible to determine how to operate the micrometer for enlarging or narrowing the E95 bandwidth, until the micrometer is actually operated to observe how the E95 bandwidth varies. 
         [0116]    As a result, it can be concluded that the adjustment can be done easier when the E95 adjustment unit is arranged on the front side than on the rear side of the laser chamber. Further, comparing the laser output relative values of  FIG. 4  and  FIG. 13 , it can be seen that greater laser output can be obtained when the E95 adjustment unit is arranged on the front side than on the rear side of the laser chamber. Thus, it can be concluded that it is more advantageous to perform adjustment of the E95 bandwidth on the front side of the laser chamber. 
         [0117]      FIG. 14  shows configuration of an E95 bandwidth adjustment unit according to a seventh embodiment. The seventh embodiment is designed to adjust the expansion ratio of a beam entering a grating  31  by changing the rotation angle of a prism provided in a line narrowing module. When the incident beam is expanded in a direction perpendicular to the wavefront dispersion surface of the grating  31 , the spread angle of the beam is reduced and hence the spectral line width is narrowed. 
         [0118]    A prism  32  is fixed to a rotary plate  151 , and the rotary plate  151  is rotatably supported by a rotary stage  152 . A convex portion  151   a  is formed on a side face of the rotary plate  151  so as to protrude therefrom. The head of a micrometer  153  abuts on the front face of the convex portion  151   a , and the head of a protrusion  154  abuts on the rear face of the convex portion  151   a . The extension of the micrometer  153  gives a pressing force to the convex portion  151   a  in the direction towards the protrusion  154 . A spring which is extendable and retractable is connected to the head of the protrusion  154 , so that the urging force is given to the convex portion  151   a  by means of this spring in the direction towards the micrometer  153 . Accordingly, the rotary plate  151  is rotated by extension and retraction of the micrometer  153 . 
         [0119]    A prism  33  is fixed to the rotary plate  156  in the same manner as the prism  32  is fixed to the rotary plate  151 . Therefore, description thereof will be omitted. 
         [0120]    In order to adjust the E95 bandwidth, the micrometer  153  is adjusted to rotate the rotary plate  151  and the prism  32 , and the micrometer  158  is adjusted to rotate the rotary plate  156  and the prism  33 , while ensuring not to change the laser oscillation wavelength. During this operation, the rotary plate  151  and the prism  32  are rotated in the opposite direction to the direction in which the rotary plate  156  and the prism  33  are rotated, while matching the rotation angles thereof, whereby the beam expansion ratio by the prisms  32  and  33  is changed. The E95 bandwidth becomes greater as the expansion ratio increases, and the E95 bandwidth becomes smaller as the expansion ratio decreases. 
         [0121]    It should be understood that, as shown in  FIG. 15 , the present invention is also applicable to adjustment of the E95 bandwidth in a narrow-band laser device having two laser chambers, so-called double-chamber system. Description will be made of configuration of an E95 bandwidth adjustment unit used in a double-chamber system. 
         [0122]    For example, a double-chamber system includes an MO (oscillation stage laser)  200  for generating seed laser light and a PO (amplification stage laser)  300  for amplifying laser light output from the MO  200 . In the MO  200 , a line narrowing module  230  is arranged on the rear side of a laser chamber  220 , and an output coupler  250  is arranged on the front side. The line narrowing module  230  is provided with a grating  231  and prisms  232  and  233 . In the PO  300 , a rear mirror  331  is arranged on the rear side of a laser chamber  320 , and an output coupler  350  is arranged on the front side. In this embodiment, a rear mirror  331  is coated with a partial-reflection (PR) film having a reflectance of 80 to 90%, for example. 
         [0123]    The MO  200  according to this embodiment has the output coupler  250 , an E95 bandwidth adjustment unit, the laser chamber  220 , and a line narrowing module  230 . Laser light output by the MO  200  and having a narrow spectral line width is reflected by mirrors  501  and  502 , and injected into the PO  300 . In the PO  300 , the seed laser light is introduced into the rear mirror  331  from the rear side thereof, and a part of the seed laser light is transmitted through the rear mirror  331 . The transmitted seed light is amplified between the rear mirror  331 , the laser chamber  320 , and the output coupler  350  of the laser amplification stage to cause laser oscillation. Laser light output from the PO  300  is split by a beam splitter  503 . One part of the laser light is output to the outside while the other part of the laser light is input to a monitor module  560 . In the monitor module  560 , the laser light is split by a beam splitter  561 , an E95 bandwidth or a central wavelength is detected by a wavelength monitor  562 , and pulse energy is detected by an energy monitor  563 . 
         [0124]    The configuration described above in relation to the first to seventh embodiments may be provided on the front side or rear side of the laser chamber  220  provided in the MO  200 .  FIG. 15  shows an arrangement in which the configuration of the first to third embodiments is applied to the double-chamber system. 
         [0125]      FIG. 16  shows positional relationship among an E95 bandwidth adjustment unit, a laser chamber, and a line narrowing module according to an eighth embodiment.  FIGS. 17(   a ) and  17 ( b ) show configuration of an E95 bandwidth adjustment unit according to the eighth embodiment, as viewed in the direction indicated by A in  FIG. 16 . The eighth embodiment is designed to adjust a width of a slit. 
         [0126]    The E95 bandwidth adjustment unit  240  has a slit formed by two blades  401  and  402  which are movable in the dispersion direction of a grating  231 . The blades  401  and  402  are movably attached to a linear guide rail (not shown). The blade  401  is given an urging force in a direction toward the blade  402  by a plunger screw  403  having a spring incorporated therein. The blade  402  is given an urging force in a direction toward the blade  401  by a plunger screw  404  having a spring incorporated therein. The head of a triangular member  405  is inserted between the blade  401  and the blade  402 . The triangular member  405  is a planar member having a thickness equivalent to that of the blades  401  and  402 , and is movable in the direction parallel to the discharge direction of the laser chamber  220 . The side faces of the triangular member  405  are slidably in contact with the blades  401  and  402 , while the bottom face of the triangular member  405  is in contact with the head of a micrometer  406 . 
         [0127]    When the micrometer  406  is extended as shown in  FIG. 17(   b ), the triangular member  405  advances between the blades  401  and  402 . This causes the blades  401  and  402  to move in the directions separating from each other along the side faces of the triangular member  405 . When the micrometer  406  is retracted as shown  FIG. 17(   a ), the triangular member  405  is retracted from between the blades  401  and  402 . This causes the blades  401  and  402  to move in the directions approaching to each other along the side faces of the triangular member  405 . The slit width is varied in this manner. 
         [0128]    Since the grating  231  is an angular dispersive element, the E95 bandwidth of the MO  200  can be adjusted by adjusting the region in which the MO  200  laser oscillates with respect to the dispersion direction. Although in the configuration shown in  FIG. 16 , the E95 bandwidth adjustment unit  240  according to the eighth embodiment is arranged on the front side of the laser chamber  220 , the E95 bandwidth adjustment unit  240  according to the eighth embodiment may be arranged on the rear side of the laser chamber  220  or in the interior of the line narrowing module  230 . 
         [0129]    In the double-chamber system, as shown in  FIGS. 18(   a ) and  2 ( b ), the E95 bandwidth adjustment unit may be arranged on an optical path between the MO  200  and the PO  300 . 
         [0130]      FIG. 19  shows an arrangement in which cylindrical lenses are arranged between the MO and the PO. 
         [0131]    A planoconvex cylindrical lens  411  and a planoconcave cylindrical lens  412  are arranged on an optical path between the MO  200  and the PO  300  so as to face each other. Either the planoconvex cylindrical lens  411  or the planoconcave cylindrical lens  412  is movable along the optical axis. A moving mechanism for moving the lens may be the same as the one shown in  FIGS. 2(   a ) and  2 ( b ), for example. Further, a cylindrical convex lens and a cylindrical concave lens may be used in place of the planoconvex cylindrical lens  411  and the planoconcave cylindrical lens  412 . 
         [0132]    The spread of a beam injected into the PO  300  in the dispersion direction of a dispersive element (grating  231 ) mounted in the MO  200  can be adjusted by adjusting the distance between the planoconvex cylindrical lens  411  and the planoconcave cylindrical lens  412 . As a result, the E95 bandwidth of laser light amplified and oscillated by the PO  300  can be varied. The E95 bandwidth becomes smaller when the beam is spread wider in the dispersion direction by adjusting the distance between the planoconvex cylindrical lens  411  and the planoconcave cylindrical lens  412 . In contrast, the E95 bandwidth becomes greater when the beam spread is reduced with respect to the dispersion direction of the grating  231  by adjusting the distance between the planoconvex cylindrical lens  411  and the planoconcave cylindrical lens  412 . 
         [0133]      FIG. 20  shows an arrangement in which prisms are arranged between the MO and the PO. 
         [0134]    Two prisms  421  and  422  are arranged on an optical path between the MO  200  and the PO  300 . The two prisms  421  and  422  are rotatable. A rotation mechanism for rotating the prisms may be the same as the mechanism shown in  FIG. 14 , for example. 
         [0135]    The prisms  421  and  422  are rotated in opposite direction while matching the rotation angles thereof Thus, the beam expansion ratio is varied by the prisms  421  and  422 . The adjustment of the beam expansion ratio makes it possible to adjust the width of a beam injected into the PO  300  in the dispersion direction of a dispersive element (grating  231 ) mounted in the MO  200 . As a result, the E95 bandwidth of laser light amplified and oscillated by the PO  300  can be varied. Specifically, the E95 bandwidth becomes smaller when the beam expansion ratio is increased by adjusting the rotation angle of the prisms  421  and  422 . In contrast, the E95 bandwidth becomes greater when the beam expansion ratio is reduced with respect to the dispersion direction of the grating  231  by adjusting the rotation angle of the prisms  421  and  422 . 
         [0136]      FIG. 21  shows an arrangement in which a slit is arranged between the MO and the PO. 
         [0137]    A slit  431  is arranged on an optical path between the MO  200  and the PO  300 . The slit  431  may be the same one as shown in  FIGS. 17(   a ) and  17 ( b ), for example. 
         [0138]    The E95 bandwidth of laser light amplified and oscillated by the PO  300  can be varied by adjusting the width of the slit  431 . The E95 bandwidth becomes greater when the width of the slit  431  is increased. In contrast, the E95 bandwidth becomes smaller when the width of the slit  431  is reduced. Even if a beam injected into the PO  300  is narrower than a discharge width, output laser light can be spread out by causing the light to reciprocate through an optical resonator of the PO  300  as long as the beam has a spread angle. 
         [0139]    It should be understood that the present invention is also applicable to a narrow-band laser device having three or more laser chambers. In this case as well, the E95 bandwidth adjustment unit may be provided in the MO or between the stages. Further, although the description above of the embodiments has been made taking the MOPO system as an example of the double-chamber system, the present invention is also applicable to an MOPA-type double-chamber system in which no laser resonator is provided in the amplification stage so that seed light is directly amplified. 
         [0140]    According to the present invention, the deviation in spectral line width such as E95 bandwidth among the laser devices can be minimized. Further, also in a same laser device, the deviation in spectral line width such as E95 bandwidth before and after the maintenance of the device can be minimized. Therefore, the spectral line width of laser light output from the laser device will not exceed the allowable range of the spectral line width such as E95 bandwidth for an optical system of the exposure tool. This makes it possible to stabilize the quality of integrated circuit patterns formed by the semiconductor exposure tool, and thus the yield of semiconductor devices can be improved. Furthermore, the yield of laser production and the yield in maintenance are improved, whereby the laser production cost and the maintenance cost can be reduced effectively.