Abstract:
An exposure apparatus includes plural light modulators that are arranged in parallel, each of which includes an element for modulating a phase distribution of incident light by providing the incident light with a phase difference, and plural projection optical systems that are arranged in parallel, each of which corresponds to each light modulator and projects a pattern formed by a corresponding one of the light modulators onto an object to be exposed.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to maskless exposure that dispenses with a photo-mask or reticle as an original, and utilizes a light modulator (also referred to as a spatial light modulator) that provides the incident light with plural phase differences modifies the light. The present invention is, suitable for example, for an exposure apparatus that exposes a large screen, such as a liquid crystal panel.  
         [0002]     A projection optical system has been conventionally used to expose a mask pattern onto a substrate on which a photosensitive agent is applied in manufacturing a semiconductor device and a liquid crystal panel. However, as the finer processing to the mask pattern and a larger mask size are demanded with the improved integration and increased area of the device, an increase of the mask cost becomes problematic. Accordingly, the maskless exposure that dispenses with the mask for exposure has called attentions.  
         [0003]     One exemplary attractive maskless exposure is a method for projecting a pattern image onto a substrate using a phase-modulation type light modulator. The light modulator is a parallel-connected type device, and the number of pixels per unit time may possibly be increased enormously. The phase modulation needs a minute displacement of a mirror, and thus is suitable for high-speed operation. In particular, a grating light valve (“GLV”) type light modulator that uses a modulated pattern of a diffraction grating is suitable for a large amount of data transfers, and a maskless exposure apparatus that transfers enormous data amount. The maskless exposure apparatus that uses the light modulator instead of the mask to modulate the exposure light in accordance with a desired pattern, and condenses the pattern via a projection optical system, and forms the pattern on the substrate. GLV is disclosed, for example, in Optics Letters, Vol. 17, pp. 688-690 (1992).  
         [0004]     Referring now to  FIGS. 10A and 10B , a description will be given of an operational principle of a conventional GLV  20 . Here,  FIG. 10A  shows a relationship between the section of the GLV  20  and a phase difference when the GLV  20  turns off.  FIG. 10B  shows a relationship between the section of the GLV  20  and a phase difference when the GLV  20  turns on.  
         [0005]     Each element in the GLV  20  has a pair of catoptric bands or ribbons  21 , and each pixel  23  includes three elements  22 . The GLV  20  is a reflection-type phase modulator that has plural pixels  23  arranged in parallel. One of ribbons  21  in each element  22  is connected to a switch (not shown), and configured to vary its level, for example, when the voltage is applied to it.  
         [0006]     When the switch turns off, as shown in  FIG. 10A , all the ribbons  22  have the same level. When the switch turns on, as shown in  FIG. 10B , the ribbons  21  fall alternately by a quarter of the irradiation wavelength, and the reflected light have a phase difference of 180° between two adjacent ribbons  21 . When the switch turns off, only the 0th order diffracted light is reflected since the reflected light is reflected while its phase is not modulated. On the other hand, when the switch turns on, the reflected light is phase-modulated and the ±1st order diffracted lights are reflected.  
         [0007]     Referring to  FIGS. 11A and 11B , a description will be given of control over the diffracted light using the GLV  20 . Here,  FIG. 11A  is a schematic view for explaining the control over the diffraction light using the GLV  20 . As shown in  FIG. 11A , a filter  32  that blocks the 0th order light is provided between a lens  31  and the GLV  20 . When the switch turns off, no light is incident upon the lens  31 . When the switch turns on, the ±1st order diffracted lights are incident upon the lens  31 . A maskless exposure apparatus that controls the exposure light is configured when it installs the GLB  20  instead of the mask and the lens  31  is regarded as the projection optical system.  
         [0008]     In the maskless exposure apparatus equipped with the GLV  20  shown in  FIG. 11A , the projection optical system  31  should have a wide diameter to accept the ±1st order diffracted lights, causing a big apparatus. In addition, two lights incident upon the projection optical system  31  may interfere with each other and result in an unnecessary pattern. On the other hand, in a conceivable combination of the GLV  20  and an oblique incident illumination shown in  FIG. 11B , when the switch turns off, this configuration does not supply the light to the lens  31  since only the 0th order light occurs. When the switch turns on, the ±1st order diffracted lights occur and one of them, which is the −1st order diffracted light in  FIG. 11B , enters the lens  31  by adjusting the irradiation angle onto the GLV. As a result, a small size is enough for the projection optical system  31 . In addition, only one light entering the projection optical system  31  realizes the high-quality exposure that resolves only a predetermined pattern. However, a problem of reduced exposure dose and thus lowered throughput occurs because one of the ±1st order diffracted lights is not used.  
         [0009]     Other prior art include U.S. Pat. No. 6,025,859, and J. W. Goodman, Introduction to Fourier Optics 2nd ed., ISBN 0-07-114257-6.  
         [0010]     There is a demand for large area exposure using the GLV, for example, for a liquid crystal panel, so as to increase the throughput. Even in this case, a smaller size of the exposure apparatus is preferable.  
       BRIEF SUMMARY OF THE INVENTION  
       [0011]     Accordingly, it is an exemplary object of the present invention to provide an exposure apparatus that utilizes a light modulator, preferably has a small size, and improves the throughput, and a device manufacturing method using the same.  
         [0012]     An exposure apparatus according to one aspect of the present invention includes plural light modulators that are arranged in parallel, each of which includes an element for modulating a phase distribution of incident light by providing the incident light with a phase difference, and plural projection optical systems that are arranged in parallel, each of which corresponds to each light modulator and projects a pattern formed by a corresponding one of the light modulators onto an object to be exposed.  
         [0013]     A device manufacturing method according to still another aspect of the present invention includes the steps of exposing an object using the above exposure apparatus, and developing the object that has been exposed. Claims for a device manufacturing method for performing operations similar to that of the above exposure apparatus cover devices as intermediate and final products. Such devices include semiconductor chips like an LSI and VLSI, CCDs, LCDs, magnetic sensors, thin film magnetic heads, and the like.  
         [0014]     Other objects and further features of the present invention will become readily apparent from the following description of the preferred embodiments with reference to the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]      FIG. 1  is a schematic block diagram of an exposure apparatus according to one embodiment of the present invention.  
         [0016]      FIG. 2  is a detailed schematic perspective view between GLVs and projection optical systems in the exposure apparatus shown in  FIG. 1 .  
         [0017]      FIG. 3  is a schematic plane view showing a relationship between the projection lenses and the exposure areas in the projection optical systems shown in  FIG. 2 .  
         [0018]      FIG. 4  is a schematic plane view showing an arrangement of the projection lenses in the projection optical system shown in  FIG. 2 .  
         [0019]      FIG. 5  is a schematic perspective view showing a relationship between one GLV and the projection lens in one projection optical system shown in  FIG. 2 .  
         [0020]      FIG. 6A  is a schematic plane view for explaining a cutout of the projection lens shown in  FIG. 5  near the pupil surface in the projection optical system.  
         [0021]      FIG. 6B  is a schematic plane view of the projection lens shown in  FIG. 5  that has been cut.  
         [0022]      FIG. 7  is a schematic plane view for explaining a relationship between the diffracted light and the projection lens arranged outside the pupil surface of the projection optical system shown in  FIG. 2 .  
         [0023]      FIG. 8  is a flowchart for explaining a device manufacturing method using the exposure apparatus shown in  FIG. 1 .  
         [0024]      FIG. 9  is a detailed flowchart for Step  4  of wafer process shown in  FIG. 8 .  
         [0025]      FIG. 10A  shows a relationship between the section of a conventional GLV that turns off and the phase differences.  
         [0026]      FIG. 10B  shows a relationship between the section of a conventional GLV that turns on and the phase differences.  
         [0027]      FIG. 11A  is a schematic view for explaining control of the diffracted light using the conventional GLV.  
         [0028]      FIG. 11B  is a schematic view for explaining control of the diffracted light using the conventional GLV. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]     Referring to  FIG. 1 , a description will be given of the exposure apparatus  100  according to one embodiment of the present invention.  FIG. 1  is a schematic block diagram of the illustrative exposure apparatus  100 . The exposure apparatus  100  includes an illumination apparatus  110  that illuminates a GLV  120 , the GLV  120  that has a similar structure as that of the GLV  20  shown in  FIGS. 10A and 10B , a projection apparatus  130  that projects onto a plate  140  the diffracted light generated from the illuminated GLV  120 , and a stage  145  that supports the plate  140 .  
         [0030]     The exposure apparatus  100  is suitable for a submicron or quarter-micron lithography process, and this embodiment discusses a step-and-scan exposure apparatus (also referred to as a “scanner”). The “step-and-scan manner”, as used herein, is an exposure method that exposes a pattern onto a wafer by continuously scanning the wafer relative to the GLV  120 , and by moving, after a shot of exposure, the wafer stepwise to the next exposure area to be shot. Of course, the exposure apparatus  100  is applicable to a step-and-repeat exposure apparatus (also referred to as a “stepper”).  
         [0031]     The illumination apparatus  110  includes a light source section  112  and an illumination optical system  114 , and illuminates the GLV  120  that is controlled in accordance with a circuit pattern to be transferred.  
         [0032]     The light source section  112  uses, for example, a light source such as an ArF excimer laser with a wavelength of approximately 193 nm, a KrF excimer laser with a wavelength of approximately 248 nm, and an an F 2  laser having a wavelength of about 157 nm. However, the type of the light source is not limited or the number of light sources is not limited. When using a laser, the light source section  112  preferably uses a light shaping optical system that turns the collimated light from the laser light source into a desired beam shape, and an incoherently turning optical system that turns a coherent laser beam into an incoherent one.  
         [0033]     The illumination optical system  114  is an optical system that illuminates the GVL  120 , and includes a lens, a mirror, an optical integrator, a stop and the like, for example, a condenser lens, a fly-eye lens, an aperture stop, a condenser lens, a slit, and an imaging optical system in this order. The illumination optical system  114  can use any light regardless of whether it is axial or non-axial light. The light integrator may include a fly-eye lens or an integrator formed by stacking two sets of cylindrical lens array plates (or lenticular lenses), and can be replaced with an optical rod or a diffractive optics. A method for illuminating the GLV may be perpendicular irradiation shown in  FIG. 11A , or the oblique irradiation shown in  FIG. 11B . This embodiment uses the perpendicular irradiation.  
         [0034]     The GLV  120  whose switch is electrically turned on and off from the outside controls the diffracted light, and is supported and driven by a GLV stage (not shown). The diffracted light is projected onto the plate  140  through the projection optical system  130 . The GLV  120  and the plate  140  have an optically conjugate relationship. Since the exposure apparatus  100  of this embodiment is a scanner, the GLV  120  repeats turning on and off while the exposure apparatus scans the plate  140  at a speed ratio corresponding to a reduction ratio, transferring the pattern of the GLV  120  onto the plate  140 . As described later with reference to  FIG. 2 , this embodiment provides N pieces of GLVs.  
         [0035]     Each projection optical system  130  may use a dioptric optical system that includes only plural lens elements, a catadioptric optical system comprised of a plurality of lens elements with at least one concave mirror, and a catoptric optical system including only mirrors, and so on. Any necessary correction of a chromatic aberration in the projection optical system  130  can use a plurality of lens elements made from glass materials having different dispersion or Abbe values, or arrange a diffraction optical element such that it disperses in a direction opposite to that of the lens element.  
         [0036]      FIG. 2  is a schematic perspective view showing a relationship between the GLVs  120  and the projection optical systems  130 . This embodiment arranges plural projection optical systems  130  for a block of scanning. This embodiment defines a scan direction SD as a row direction and a direction perpendicular to the scan direction SD as a column direction. The projection optical systems  130  are aligned with the row direction, but slightly shifted in the column direction. In the parallel exposure, an exposure area EA is defined as an area that one projection optical system  130  can expose by one scan. Two adjacent exposure areas EA should overlap each other. Therefore, as shown in  FIG. 3 , each line of the projection lenses  132  aligned with the row direction shifts by a width of the exposure area EA perpendicular to the scan direction SD. When the width of the exposure area EA is 1/M times the maximum diameter of the projection optical system  130  including the lens support mechanism, and M is the number of rows of projection optical systems  130  in the row direction, the projection lenses  132  adjacent in the column direction have overlapping exposure areas EA. M is a natural number in this embodiment. As a result, the projection lenses  132  are arranged like bricks as shown in  FIG. 4 . The number of projection lenses  132  in the row direction may be arbitrary.  
         [0037]     This embodiment attempts to miniaturize the exposure apparatus  100  by partially eliminating a nonuse area upon which no diffracted lights are incident from each projection lens  132  that has originally a circular shape when viewed from the top, and by reducing the size of each projection optical system  130 . In this embodiment, the size of the projection lens  132  should accept the ±1st order diffracted lights. All the lenses in the projection optical system  130  should have maximum diameters when the 0th order diffracted light is spatially separated from the ±1st order diffracted lights on the pupil of the projection lens  132  and the 0th order diffracted light is blocked while the 1st order diffracted light are transmitted during switching. In this case, the lens near the pupil should be about three times as large as the effective light diameter D of the diffracted light. The effective light diameter D of the diffracted light is a diameter of an area that obtains 90% or greater of the light intensity of each diffracted light. Therefore, the exposure apparatus  100  solves the problem of the large size of the exposure apparatus that uses the GLV  120  for the parallel exposure.  
         [0038]     Since the 0th order diffracted light and the ±1st order diffracted lights generated from the GLV  120  spread in one direction, the area in the lens  132 , which uses the lights has a linear shape. Therefore, there are many nonuse areas in the lens  132 , upon which no lights are incident. The lens  132  from which the nonuse area is eliminated is configured as shown in  FIG. 5 . The projection optical system  130  of this embodiment spatially separates the 0th order diffracted light from the ±1st order diffracted lights, and includes both the ±1st order diffracted lights. Therefore, the nonuse areas area removed by cut lines C shown in  FIGS. 6A and 7 . Here,  FIG. 6A  is a schematic plane view of the projection lens  132  near the pupil surface, while  FIG. 7  is a schematic plane view of the projection lens  132  slightly apart from the pupil surface.  
         [0039]      FIG. 6B  is a schematic plane view of the projection lens  132  cut by the cut lines C shown in  FIG. 6A . As illustrated, the length L: the width W=3: 1 is met in the cut projection lens  132 . The scan exposure that uses the parallel-arranged plural projection optical system  130  each equipped with such a projection lenses  132  can efficiently expose a large area while maintaining the size of the exposure apparatus  100 .  
         [0040]     Assume, in  FIG. 6B , the scan direction SD and the diffraction direction DD, with which centers of the diffracted lights are aligned (or the diffraction direction DD which is perpendicular to the scan direction SD). The width of the scan direction SD may be between the effective light diameter D of the 1st order diffracted light and the diameter shown in  FIG. 6A , such as about 3.3 times the effective light diameter D, which is slightly greater than a sum of three effective light diameters of the three diffracted lights (it is preferably “slightly greater” for a practical margin). Similarly, in this embodiment the width L of the diffraction direction DD may be the diameter shown in  FIG. 6A , such as about 3.3 times the effective light diameter D, which is slightly greater than a sum of three effective light diameters of the three diffracted lights (it is preferably “slightly greater” for a practical margin). When the oblique incidence is considered, it may be equal to or greater than the effective light diameter D of the 1st order diffracted light if there is a proper blocking means. For example, the length L may be slightly greater than a sum of the effective light diameter D of two diffracted lights, e.g., the 0th and 1st order diffracted lights, such as about 2.2 times the effective light diameter D, which is slightly greater than a sum of three effective light diameters of the three diffracted lights (it is preferably “slightly greater” for a practical margin).  
         [0041]     The plate  140  is an exemplary object to be exposed, such as a wafer and a LCD, and photoresist is applied to the plate  140 . A photoresist application step includes a pretreatment, an adhesion accelerator application treatment, a photoresist application treatment, and a pre-bake treatment. The pretreatment includes cleaning, drying, etc. The adhesion accelerator application treatment is a surface reforming process so as to enhance the adhesion between the photoresist and a base (i.e., a process to increase the hydrophobicity by applying a surface active agent), through a coat or vaporous process using an organic film such as HMDS (Hexamethyl-disilazane) The pre-bake treatment is a baking (or burning) step, softer than that after development, which removes the solvent.  
         [0042]     The stage  145  supports the plate  140 . The stage  145  may use any structure known in the art, and a detailed description of its structure and operations will be omitted. For example, the stage  145  uses a linear motor to move the plate  140  in the XY directions orthogonal to the optical axis. The GLV  120  and plate  140  are, for example, scanned synchronously, and positions of the GLV stage (not shown) and stage  145  are monitored, for example, by a laser interferometer and the like. The GLV  120  is turned on and off in accordance with driving of the stage  145 . The stage  145  is installed on a stage stool supported on the floor and the like, for example, via a damper. The GLV stage and the projection optical system  130  are provided, for example, on a barrel stool (not shown) that is supported on a base frame placed on the floor, for example, via a damper.  
         [0043]     In exposure, the light emitted from the light source section  112 , for example, Koehler-illuminates the GLV  120  through the illumination optical system  114 . The light that has been reflected by the GLV  120  and reflects the pattern forms an image on the plate  140  through the projection optical system  130 . The GLV  120  in the exposure apparatus  100  does not restricts the NA or loses the light intensity. Therefore, the exposure apparatus  100  can provide high-quality devices (such as semiconductor devices, LCD devices, image pick-up devices (such as CCDs), and thin film magnetic heads) with excellent work efficiency.  
         [0044]     While this embodiment introduces the step-and-scan manner, another manner is applicable. For example, rather than the wafer is stepped after exposure to one shot ends, the other manner 1) exposes only first part within the one shot and steps the wafer, 2) similarly exposes only the first part in the next shot and repeats this procedure for all the shots, and 3) returns to the initial shot, and repeats the similar action for second part different from the first part.  
         [0045]     A description will now be given of an embodiment of a device manufacturing method using the exposure apparatus  100 .  FIG. 8  is a flowchart for explaining a manufacturing method of a liquid crystal panel. Step  1  (array design) designs a liquid crystal array circuit. Step  2  (mask manufacture) sets the GLV exposure operation or an input signal to the GLV in order to form a designed circuit pattern. Step  3  (plate manufacture) manufactures a glass plate. Step  4  (array manufacture), which is also referred to as a “pretreatment”, forms actual circuitry on the glass plate through the photolithography using the GLV and plate that have been prepared. Step  5  (panel manufacture), which is also referred to as a “posttreatment”, seals a back peripheral that has been pasted together with a color filter that has been manufactured by a separate step, and implants liquid crystal. Step  6  (inspection) performs various tests, such as a performance test and a durability test, for a liquid crystal panel module that has assembled tabs and backlight and aged after Step  5 . A liquid crystal panel is finished and shipped through these steps (Step  7 ).  
         [0046]      FIG. 9  is a detailed flowchart for the array manufacture in Step  4 . Step  11  (cleaning before thin-film formation) cleanses the glass plate as a pretreatment prior to forming a thin film on its surface. Step  12  (PCVD) forms a thin film on the surface of the glass plate. Step  13  (resist application) applies desired resist to the surface of the glass plate, and bakes it. Step  14  (exposure) exposes the array pattern onto the glass plate using the exposure apparatus  100 . Step  15  (development) develops the exposed glass plate. Step  16  (etching) etches out parts other than developed resist images. Step  17  (resist stripping) strips disused resist after etching. These steps repeat until multi-layer circuit patterns are formed onto the plate.  
         [0047]     Furthermore, the present invention is not limited to these preferred embodiments and various variations and modifications may be made without departing from the scope of the present invention.  
         [0048]     The present invention can provide an exposure apparatus that improves the throughput by using the light modulator and a device manufacturing method using the exposure apparatus.  
         [0049]     This application claims a foreign priority benefit based on Japanese Patent Applications No. 2004-289736, filed on Oct. 1, 2004, which is hereby incorporated by reference herein in its entirety as if fully set forth herein.