JP3562592B2 - Exposure equipment - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to an exposure apparatus, and more particularly, to an exposure apparatus for a wafer, a mask, an LCD substrate, or the like, or to an exposure machine for high-definition photolithography, which can provide a uniform exposure surface over a wide range and The present invention relates to an exposure apparatus that does not require an illumination unevenness correction filter for uniformizing exposure.
[0002]
[Prior art]
FIG. 5 is a schematic diagram showing the configuration of a conventional LCD substrate exposure apparatus.
Reference numeral 1 denotes a light source, and a mercury lamp, a halogen lamp, or the like is usually used. The mercury lamp is arranged upright. Reference numeral 2 denotes a condensing mirror, which is usually constituted by a part of an elliptical mirror. 3a and 3b are reflection mirrors, and 4 is an integrator, which smoothes light. It consists of a number of small-diameter rod-shaped lenses, usually called fly's eyes. Reference numeral 5 denotes an illuminance non-uniformity correction filter for further uniformizing the light applied to the exposure plane. Reference numeral 6 denotes a collimator lens, 7 denotes a mask, 8 denotes an LCD substrate to be exposed, and 9 denotes a substrate mounting table.
[0003]
As shown in the figure, in this type of exposure apparatus, an optical system combining a Koehler illumination system for obtaining a planarly uniform exposure surface and a telecentric illumination system in which an illumination light beam is vertically incident at all points in the exposure surface. Is adopted. The light beam emitted from the mercury lamp (light source) 1 is incident on the integrator lens 4 as a parallel light beam by the input lens 6a via the reflection mirror 3a by the elliptical mirror 2. Since the entrance surface corresponds to the pupil plane of the light source, the illuminance is relatively uniform, but the central portion is high and the peripheral portion has a low illuminance distribution. A plurality of integrator entrance surfaces are conjugated to an exposure surface 7 by an integrator lens 4 (individual integrator lens) and a collimator lens 6b, and a plurality of entrance surfaces are overlapped to form an image on one exposure surface to form a Koehler illumination system. are doing. In addition, a light source image is formed on the exit surface of each integrator 4, and this is set as the front focal position of the collimator lens 6 b, so that the telecentric optics in which the illumination light flux is vertically incident on all surfaces of the exposure surface 7. Realize the system.
[0004]
However, depending on the orientation pattern of the light source, the light in the central part is usually strong and the peripheral part is weak. Therefore, in this type of exposure apparatus used in the field of semiconductor manufacturing technology, in order to obtain exposure light that is uniform in a plane so as to meet the demand, it is inevitable to lower the transmittance of light at the center and to weaken it. Therefore, it is necessary to provide a correction filter 5 that corrects the illuminance unevenness such that the transmittance increases toward the periphery.
[0005]
[Problems to be solved by the invention]
In recent years, in semiconductor technology, formed patterns have been highly miniaturized, and there has been a higher demand for uniformity of exposure light in a planar sense than ever before. In such a situation, a physically fixed illuminance non-uniformity correction filter is no longer sufficient. This is because the illuminance distribution changes according to the state of the light source and the state of the illumination system. In order to obtain a flat and uniform illuminance exposure surface that meets the requirements of the semiconductor manufacturing technology field, illuminance unevenness must be corrected in accordance with the aging of the light source and the light distribution changed by adjusting the optical system. Must. Therefore, in order to change the correction filter each time, it is necessary to measure the current illuminance portion, and a corresponding illuminance non-uniformity correction filter must be prepared and arranged each time.
The correction filter is a method of dropping the luminous flux reaching the center of the exposure surface with high illuminance by scattering or absorption, and thus has a disadvantage of light amount loss. Normally, a correction of about 10% causes a loss of about 10%.
Such an operation is troublesome, and all filters created in the past are useless.
[0006]
Now, the technology of photoengraving is widely used as a technology for producing plates required for various types of printing. Printing technology can be broadly classified into relief printing, intaglio printing, stencil printing, lithographic printing, etc.A plate is required in any system, and film exposure in photolithography is a technology for producing high-precision printing. Process improvements have been made.
In the plate making process, the fineness of the mesh of the netting film determines the fineness, that is, the resolution of the resulting print. That is, if the mesh is coarse, a jagged halftone dot shape is visually recognized at the boundary portion where the contour and the color of the pattern change in the finished printed matter. Except in newspaper printing, such jagged halftone dots are not visible in normal printing.However, in order to achieve higher precision printing, it is possible to use halftone halftone dots. Has been requested. In particular, for high-quality printing such as art reproduction, high-definition printing using halftone dots having a screen ruling of 200 lines or more has attracted attention, but there is also the problem of uniformity of exposure. In other words, the finer the dots, the more difficult it is to transfer the image of the dots faithfully, and the pattern exposed by the photosensitive layer of the photoreceptor film can be reproduced faithfully as the dots become finer. Disappears.
[0007]
Therefore, prior to this application, a technique similar to the present invention described later has been developed, and a photolithography technique has already been filed. However, in this application, since the uniform exposure with high precision enough to be used in the semiconductor manufacturing process is not taken into consideration, it is possible to achieve the uniformization of the entire exposure plane enough to meet the demands of the semiconductor technical field. The analysis of facts alone and the examination of technology were insufficient.
It is an object of the present invention to provide an exposure apparatus which analyzes this fact and can be sufficiently applied to semiconductor manufacturing techniques, including the manufacture of LCD substrates, and which does not require the use of a filter for correcting uneven illuminance for uniform exposure. To provide.
[0008]
[Means for Solving the Problems]
The features of the present invention for achieving such an object include a single rod integrator that receives an exposure light source image on an incident surface side, a first lens that receives light from an exit surface of the rod integrator, and a first lens that receives the light from the exit surface . And a second lens disposed at a predetermined distance away from the lens of the rod integrator and having the exit surface of the rod integrator as an object point to form an image on the exposure surface in a conjugate relationship and changing the predetermined distance to form an exit surface of the rod integrator. and illuminance correction lens system to distort in the direction of greater contracted with respect to the central portion of the peripheral portion of the image, the composite focal position or its vicinity of the arranged and illuminance correction lens system between the illuminance correction lens system and the exposure surface A concave mirror having a focal point disposed therein and maintaining a conjugate relationship is provided, and by adjusting a predetermined distance, an exposure plane having uniform illuminance is formed in an image on the exposure plane.
[0009]
[Action]
The light of the light source image incident on the single rod integrator propagates through the rod integrator and is emitted from the emission surface. However, since the single rod integrator is used, the light emission surface is substantially uniform. A simple surface light source can be obtained. However, from the characteristics of the light source and the characteristics of the lens, the illuminance unevenness in which the central part is strong and the peripheral part is weak remains. Here, this slight illuminance unevenness is eliminated by correction due to image distortion of the illuminance correction lens system. That is, the illuminance correction lens system forms a conjugate image on the exposure surface using the emission surface as an object point, and performs distortion correction for contracting the peripheral portion with respect to the central portion. As a result, the illuminance density at the peripheral portion is increased with respect to the central portion, and a uniform exposure surface without uneven illuminance is realized inside the image on the exposure surface.
This eliminates the need for a correction filter, so that the loss of the exposure light beam can be substantially reduced.
[0010]
【Example】
FIG. 1 is a sectional view showing a schematic configuration of an embodiment to which the exposure apparatus of the present invention is applied. The same components as those in FIG. 5 are denoted by the same reference numerals.
In FIG. 1, a single rod integrator 10 is provided in place of the integrator 4 of FIG. 5, and a concave mirror 11 is provided in place of the collimator lens 6. Further, an uneven illuminance correction lens system 12 (hereinafter referred to as a correction lens 12) is provided in place of the uneven illuminance correction filter 5.
The rod integrator 10 includes a single rod lens having a rectangular cross section. The entrance surface of this lens is arranged so as to come to the other focal point of the ellipse with respect to the focal point where the light source 1 is placed. Therefore, the light from the light source image projected on the entrance surface is transferred to the exit surface and is made uniform. In addition, the image of the emission surface is one light source image here.
[0011]
The exit surface of the rod integrator 10 (hereinafter, the integrator 10) is disposed at or near the focal position on the near side of the combined focal point of the correction lens 12. The concave mirror 11 is arranged further behind the composite focus on the rear side. Here, the image of the exit surface of the integrators 10, in front of the concave mirror 11, positioned or focused in the vicinity of the synthesis focal point behind the correcting lens 12. This imaging position is at or near the focal point of the concave mirror 11. The image formed at this position is radiated through the concave mirror 11 onto the exposure surface corresponding to the position of the mask 7. The position of the exposure surface is substantially equal to the focal length fo of the concave mirror 11, thereby forming a telecentric optical system. Illumination light beams are vertically incident on all surfaces of the exposure surface 7, and the illuminance is made uniform by multiple reflection. the exit surface of the made the integrators 10 is imaged on the exposed surface as a Koehler illumination system by correcting lens 12 and the concave mirror 11.
[0012]
Figure 2 is a diagram illustrating the integration action of a single integrators 10 shows the paths of light rays propagating in the rod integrator.
The light from the light source 1 enters from one end face of the integrator 10, a part of the light is totally reflected on the side face of the rod lens, and is emitted from the other end face. At this time, the light beam incident on a certain point on the incident end face of the rod lens is dispersed to each point on the exit end face of the integrator 10 according to the incident angle. As a result, the illuminance distribution is made uniform.
[0013]
This will be described in more detail with reference to FIG. FIG. 2A illustrates the trajectory of a light beam incident on the integrator 10 from the center of the incident end face (point on the optical axis). 2B, 2C, 2D, and 2E are diagrams in which the light beam of FIG. 2A is separated according to the number of total reflections on the side surface of the integrator 10.
First, as shown in FIG. 2B, when the incident angle is small within a predetermined range, the light beam spreads over the entire exit end face without being totally reflected, and is emitted directly from the exit end face. If the angle of incidence is small, as in (B), it depends, of course, on the length of the integrator 10 and the cross-sectional area perpendicular thereto. Here, a rod lens having a length of about 300 mm and a cross section of about 22 mm × 27 mm is used. Next, a light beam having a predetermined incident angle as a center and a light beam whose incident angle slightly deviates from the plus or minus direction is totally reflected once by the side surface of the integrator 10 as shown in FIG. This light beam also spreads out the entire exit end face of the rod lens and exits.
[0014]
A light beam having an incident angle larger than that of FIG. 2C and whose incident angle slightly deviates from the light beam within a predetermined range by plus or minus is totally twice on the side surface of the integrator 10 as shown in FIG. reflect. Again, this light beam spreads out the entire exit end face of the integrator 10 and exits. Further, a light beam having a predetermined incident angle larger than that of (D) as a center and a light beam whose incident angle deviates slightly to plus or minus from the light beam is totally three times on the side surface of the integrator 10 as shown in FIG. reflect. Again, this light beam spreads out the entire exit end face of the integrator 10 and exits.
As described above, as the angle of incidence on the incident surface increases, the number of times of total reflection increases, and the light also spreads and exits the entire exit surface of the integrator 10.
[0015]
In this manner, light rays incident from a certain point at the center of the incident end face are all spread and dispersed throughout the output end face. This situation is better understood by (A), which superimposes (B), (C), (D), and (E).
Such dispersion of light over the entire exit end face occurs similarly for light incident from another point on the entrance end face. That is, at each point on the incident end face, the incident light beam is dispersed to the exit end face. As a result, the uniformity of the illuminance distribution is almost achieved, and the image of the light source is transferred to the exit surface in a uniform form.
That is, even if there is an illuminance distribution on the entrance surface of the integrator 10, the incident light at each point is similarly dispersed on the exit surface, so that the illuminance distribution on the exit surface becomes uniform. However, even if the light from such an integrator 10 is integrated and averaged, as an exposure apparatus used in a semiconductor manufacturing process, the influence of the intensity at the center of the light source still appears, and the influence from the center toward the periphery is still present. Thus, the uneven illuminance phenomenon in which the illuminance is reduced is not completely eliminated, and it cannot be said that sufficiently uniform exposure light is still obtained in a planar view from the viewpoint of exposure.
[0016]
Here, the correction lens 12 plays an important role. As shown in FIG. 3, this lens system has three combined convex lenses 12a, 12b, and 12c as a first lens group, and two convex lenses as a second lens group disposed at a distance d1 from the combined convex lenses. 12d and 12e. The distance between the first lens group and the exit surface SO of the integrator 10 is d2.
As shown in FIG. 2A, the light from the emission surface SO 2 spreads at the center at the center and at the periphery at the periphery, and is condensed by the concave mirror 11 via the correction lens 12. . Then, an image of the emission surface SO 2 is projected on the exposure surface. Therefore, for the combined optical system of the lens system 12 and the concave mirror 11, the emission surface SO 1 of the integrator 10 is the object point, and the exposure surface (in FIG. 1, the back surface corresponding to the substrate side of the mask 7) is the image point. Then, the image on the exit surface of the integrator 10 is projected on the exposure surface. That is, here, the object point image on the emission surface SO 2 and the projected image on the exposure surface have a conjugate relationship.
[0017]
Next, a description will be given of illuminance unevenness correction. The distortion amount of the peripheral portion with respect to the central portion of the image is adjusted by the distance d1 between the first lens system and the second lens system. Then, by adjusting the distance d2, the emission surface of the integrator 10 is set near the combined focus on the front side of the correction lens 12, and the image is positioned near the combined focus on the rear side. Adjust so that the position of does not move too much. Thereby, the conditions of the telecentric system shown in FIG. 1 can be maintained as much as possible to achieve uniform light in a plane on the exposure surface.
That is, by changing the distances d1 and d2, the image of the exit surface SO 2 of the integrator 10 is distorted at or near the combined focal point behind the correction lens 12 disposed at or near the focal point of the concave mirror 11. By projecting, the luminous flux density in the peripheral portion is improved, and the light on the exposed surface is made uniform by substantially maintaining the conditions of the Koehler illumination and the telecentric system on the exposed surface.
[0018]
The size of the image on the exposure surface is designed in advance so that this image is larger than the mask surface on which the image is exposed. Then, by adjusting the distance d1, this image causes the peripheral portion to be greatly distorted with respect to the central portion and is reduced. As a result, the image projected on the exposure surface is also distorted such that the peripheral portion is greatly reduced from the central portion.
This distortion has such a characteristic that the reduction rate decreases as the lens approaches the optical axis from the function of the lens. The lightness per unit area of the greatly reduced peripheral portion increases, and its influence disappears as it approaches the central portion. However, when the distance d1 is adjusted, the projected image on the exit surface also moves back and forth from the focal position of the combined focal point. The relationship between Koehler illumination and telecentric systems cannot be maintained unless this movement is kept as close as possible to the focal position.
That is, the range in which the correction lens 12 can be corrected is performed under the condition of maintaining the Koehler illumination and the telecentric system, and the image of the emission surface formed near the rear combined focal position is positioned. Must be. Therefore, the range that can be adjusted by the distortion is somewhat limited. The integrator 10 plays a role in equalizing the light at the preceding stage so that the distortion is limited in the adjustment limitation range.
[0019]
A specific example will be described.
The area of the exit surface SO 2 of the integrator 10 is 22 mm × 27 mm, and the length is 300 mm. In this case, the size of the light source 1 as an object point (object point image on the emission surface) is about 25 mmφ. The distance between the convex lens 12a and the emission surface SO of the first lens group is 25 mm, the distance between the convex lens 12e and the concave mirror 11 is 2000 mm, and the distance between the first lens group and the second lens group is 70 mm. The convex lens 12a is a quartz meniscus lens having an aperture of about 80 mmφ, a curvature R1 = 94 mm, R2 = 273 mm, and n = 1.47455. , N = 1.47455. The convex lenses 12d and 12e of the second lens group are quartz plano-convex lenses each having an aperture of about 100 mmφ, a curvature R1 = 144, R2 = ∞, and n = 1.47455. Finally, the combined focal length of the correction lens 12 is about 93 mm.
[0020]
In this example, the object point image on the exit surface is projected onto the exposure surface at approximately 20 times . FIG. 4 illustrates the relationship between the peripheral distortion and the amount of light in each case with respect to the exposure surface S in the form of blocks, and FIG. This represents the amount of distortion for the block. The ratio between the area of the exposure surface S and the area of each block of the distorted surface D behind it is the amount of increase in light of each block on the exposure surface S.
Here, for example, assuming that the size of the exposed surface is 420 × 540 mm in length and width, the distortion amount in the central portion is 0% and 1.47% in the corner portion in the peripheral portion under the condition of the correction lens. About 1.48%, about 0.37% to 0.45% at the center of the peripheral part in the vertical direction, and about 0.79 to 0.83% at the center of the peripheral part in the horizontal direction. The light amount is corrected according to the distortion amount.
[0021]
When projecting the image of the exit surface onto the exposure surface at a magnification of about 20 times, the actual correction lens 12 has a distance d2 between the convex lens 12a and the exit surface of 10 to 30 mm, the first lens group and the second lens group. Distance d1 = 60 to 100 mm, and the combined focal length f varies from about 85 to 115 mm.
The above condition is an example in which the projection magnification of the object point is about 20 times , and the numerical value is appropriately selected by changing the magnification. The above-mentioned numerical values are also changed depending on the area of the exit surface of the integrator 10, and these are design items.
[0022]
Incidentally, it goes without saying that a collimator lens as shown in FIG. 5 may be used for the concave mirror 11. Further, it goes without saying that a reflection mirror, a fixed integrator lens, and the like may be provided between the correction lens and the exposure surface.
Further, in the embodiment, an example is given in which conditions such as Koehler illumination are set, but it is not necessary to fully satisfy all of these conditions depending on the degree of uniformity of exposure light. Therefore, particularly in the case of uniform exposure, which does not require high accuracy, or in the case of photolithography technology, it is not always necessary to adjust the distance between the exit surface of the integrator and the correction lens.
Further, the exposure light source does not even need to be projected by an elliptical mirror.
[0023]
【The invention's effect】
As can be understood from the above description, according to the present invention, a substantially uniform light source image is obtained as an object point image using a single integrator, and the central part of the object point image is strong, and the peripheral part is strong. Distortion that causes the illuminance unevenness to weaken, forms an image conjugate to the illuminance unevenness correction lens system on the exposure surface through the illuminance unevenness correction lens system using the exit surface of the integrator as an object point, and shrinks the periphery to the center Since the correction is performed by the correction lens, it is possible to increase the illuminance density in the peripheral portion with respect to the central portion, thereby realizing a surface without uneven illuminance inside the image.
As a result, an exposure surface with more uniform illuminance than before can be obtained without using a conventional correction filter. Moreover, since a correction filter is not required, the loss of the exposure light beam can be almost reduced.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view of the configuration of an exposure apparatus according to an embodiment to which the exposure apparatus of the present invention is applied.
FIG. 2 is an explanatory diagram of an operation of the integrator of FIG. 1;
FIG. 3 is an explanatory diagram of a relationship between the integrator of FIG. 1 and a correction lens system.
FIG. 4 is an explanatory diagram of a distortion amount on an exposure surface by a correction lens.
FIG. 5 is a schematic sectional view of a configuration of a conventional exposure apparatus.
[Explanation of symbols]
1 light source, 2 condensing mirror, 3 mirror, 4 integrator,
5: correction filter, 6: collimator lens,
7 ... mask, 8 ... LCD substrate,
10: rod integrator, 11: concave mirror,
12: Illumination unevenness correction lens system.

Claims (4)

A single rod integrator that receives the exposure light source image on the incident surface side, a first lens that receives light from the exit surface of the rod integrator, and a second lens that is disposed at a predetermined distance from the first lens With the lens and the exit surface of the rod integrator as an object point, an image is formed in a conjugate relationship on the exposure surface and the peripheral portion of the image of the exit surface formed by changing the predetermined distance is larger than the center portion. An illuminance correction lens system for distorting in the direction of contraction, and a conjugate relationship in which the focal point is disposed between the illuminance correction lens system and the exposure surface and at or near a composite focal position of the illuminance correction lens system. And a concave mirror for holding an image, and forming an exposure plane having uniform illuminance in an image on the exposure surface by adjusting the predetermined distance. An exposure light source, a condenser mirror that arranges the exposure light source at or near a first focal position and forms a part of an elliptical mirror that projects an image to a second focal position, and the second focal position or A single rod integrator having a rectangular cross section in which the incident surface side is disposed at the projection position of the exposure light source in the vicinity thereof, and an illuminance correction lens system that forms an image on the exposure surface in a conjugate relationship with the emission surface of the rod integrator as an object point. A concave mirror that is disposed between the illuminance correction lens system and the exposure surface and whose focus is disposed at or near a combined focal position of the illuminance correction lens system and maintains the conjugate relationship, system, Toka second lens group and the first lens group that receives light from the first lens group are arranged in a position at a predetermined distance from the exit surface of the rod integrator It is to distort the peripheral portion of the image of the exit surface formed by changing the predetermined distance in a direction to shrink more greatly with respect to the center, and by adjusting the predetermined distance, An exposure apparatus for forming an exposure plane with uniform illuminance in an image on an exposure surface. The distance between the exit surface of the rod integrator and the correction lens system is adjustable, and the exit surface is disposed at or near a focal position before the composite focal point, and the adjustment of the predetermined distance The focal position behind the combined focal point is located near the focal position where the Kera illumination and the telecentric illumination are maintained or almost in the vicinity of the focal position where the Kayla illumination and the telecentric illumination are maintained in relation to the distance of the exposure surface. 3. The exposure apparatus according to claim 2, wherein the relationship is maintained. The exposure apparatus according to claim 3, wherein a collimator lens is used instead of the concave mirror.

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