JP2005331804A - Cylindrical microlens array - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cylindrical microlens array having an alignment mark which is usable for alignment in a two-dimensional direction. <P>SOLUTION: A resist 2 is applied on the surface of a substrate 1 having a cylindrical microlens pattern of high sag accurately formed by using a plurality of gray scale masks (f). The resist 2 is then photo-sensed through the mask 5 with an alignment mark pattern 5a formed (g), and the resist 2 is developed, then, the resist 2 on a part 2a corresponding to the alignment mark is removed (h). And a chrome thin film 6 is deposited on the resist 2 by sputtering (i). Next, when the resist 2 is dissolved, the chrome thin film 6 on the resist 2 is removed, and the alignment mark 7 of the chrome thin film is formed on the part with no resist 2 (j). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a cylindrical microlens array suitable for use in a fly-eye lens or the like for producing uniform illumination light in an illumination optical system of an exposure apparatus.

  In a lithography process, which is a process for manufacturing a semiconductor device or a liquid crystal device, an exposure apparatus is used to transfer a pattern formed on a mask to a resist applied on a wafer. Recently, with the miniaturization of patterns of these semiconductor devices and liquid crystal devices, the wavelength of light used in the exposure apparatus has become shorter, and exposure apparatuses using an excimer laser light source having a wavelength of about 200 nm have come to be used. ing.

  In an exposure apparatus using such an excimer laser, a fly-eye lens is used in order to ensure illumination uniformity of illumination light that illuminates the mask. However, when a normal micro fly's eye lens is used, sufficient illumination uniformity cannot be obtained, and two cylindrical microlens arrays are combined so that their axial directions are orthogonal to each other, and the microscopic lens as a whole is combined. A method is employed that plays the role of a fly-eye lens.

  Examples of a method of manufacturing a microlens using photolithography are described in, for example, Japanese Patent Application Laid-Open No. 9-8266 (Patent Document 1) and Japanese Patent Application Laid-Open No. 8-504515 (Patent Document 2). Among these, the method described in Patent Document 1 forms the shape of the microlens by resist reflow, and cannot produce a microlens that requires high accuracy. The method described in Patent Document 2 uses a gray scale mask to control the resist shape, and can produce microlenses with higher accuracy than the method described in Patent Document 1. .

  However, since the cylindrical microlens array used for the light source of the exposure apparatus as described above requires a large amount of sag and very high shape accuracy, even when the method described in Patent Document 2 is used. Production was impossible.

    Therefore, conventionally, the cylindrical microlens array used for the light source of the exposure apparatus as described above has been manufactured by a method using grinding and polishing. A manufacturing method of the cylindrical microlens array by the grinding / polishing method is shown in FIG.

  As shown in (b), a grinding die 21 having a cross-sectional shape in which the concave-convex relationship is opposite to the shape of the cylindrical microlens to be manufactured is prepared and pressed against the glass substrate 22 with an appropriate load, as shown in (c). In addition, the grinding substrate 21 or the glass substrate 22 is reciprocated many times in the ridge line direction (arrow direction) of the lens cross-sectional shape formed in the grinding die 21, as shown in FIG. Create a cylindrical microlens shape.

  The created cylindrical microlens is not yet a polished surface and has a rough surface. Therefore, a polishing die having a cross-sectional shape similar to that of the grinding die is used, and polishing is performed in the same manner as in the grinding step to obtain the surface roughness and lens shape accuracy required for the cylindrical lens. After polishing, the shape of the created cylindrical microlens may be corrected by means such as heating and electron beam irradiation as necessary.

Japanese Patent Laid-Open No. 9-8266 JP-T 8-504515

  As described above, the cylindrical microlens array used in the illumination optical system of the exposure apparatus is used by combining two with their axial directions (length directions) being perpendicular. Therefore, it is necessary to align the two cylindrical microlens arrays, and the alignment needs to be performed with an accuracy of about ± 1 μm.

  In the case of a cylindrical microlens manufactured by a grinding / polishing method, grinding and polishing are performed by sliding the grinding mold and the polishing mold in the axial direction of the cylindrical lens. Therefore, as shown by reference numeral 23 in FIG. An alignment mark parallel to the axial direction can be created simultaneously with the creation of the cylindrical microlens array.

  However, such an alignment mark can be used for alignment in one direction on the plane (left and right in FIG. 4A), but alignment in a direction perpendicular to it (up and down in FIG. 4A). Cannot be used. In particular, as described above, when two cylindrical microlens arrays are used in combination so that their axes are orthogonal, such an alignment mark cannot serve as an alignment mark. .

  The present invention has been made in view of such circumstances, and an object thereof is to provide a cylindrical microlens array having an alignment mark that can be used for alignment in a two-dimensional direction.

  The first means for achieving the above object is to use two or more grayscale masks, sequentially transfer the grayscale mask pattern to a resist provided on an optical substrate, develop the resist, and then remain. Etching the resist and the optical base material to transfer a pattern of the resist corresponding to the gray scale mask to the optical base material to manufacture a microlens. Among the exposure times for exposure using each grayscale mask, in at least one grayscale mask, the exposure time for exposure using it is different from the exposure time for exposure using another grayscale mask. A cylindrical microlens array manufactured by a lens manufacturing method, A cylindrical microlens array characterized in that an alignment mark that can be used as a reference for a position in a two-dimensional direction is formed on a flat portion other than a portion where the lens shape of the optical substrate is formed. ).

The inventor's colleagues improved the technique described in Patent Document 2 and combined a plurality of grayscale masks to expose the resist, thereby making it possible to produce a high-sag, high-precision sag that was previously impossible to manufacture. Invented a method of manufacturing a microlens of a certain amount and filed patent applications as Japanese Patent Application Nos. 2003-82207 and 2004-86813 (referred to as “prior invention”).
According to the prior invention, since the step of exposing the resist using each grayscale mask using two or more grayscale masks is provided, it is more flexible than the method using one grayscale mask. A wide variety of exposure methods can be employed, whereby a microlens with good shape accuracy can be manufactured. In the present specification and claims, the term “optical substrate” refers to a substrate having a high transmittance for light used in an optical system to which a microlens is applied, such as glass and quartz.

  Further, when the exposure time is long, even if the transmittance of the gray scale mask is slightly different, the difference in the film thickness of the resist dissolved by development is large, which is suitable for rough adjustment of the microlens shape. On the other hand, when the exposure time is short, even if the transmittance of the gray scale mask is greatly different, the difference in the amount of film slip of the resist is small, which is suitable for fine adjustment of the shape of the microlens. In the prior invention, a microlens with good shape accuracy can be manufactured by utilizing this property.

  Cylindrical microlens arrays can be manufactured by such a microlens manufacturing method, but as a two-dimensional alignment mark such as a cross mark or a ring shape, this manufacturing method uses lithography. The alignment mark which can be used can be made in the flat part other than the location in which the lens shape of the optical base material was formed.

  Cylindrical microlens arrays having an alignment mark that can be used as such a two-dimensional alignment mark are aligned with respect to the alignment mark when two are used in pairs with the axis direction perpendicular to each other. Can be easily done.

  The second means for solving the problem is the first means, wherein the microlens array manufacturing method determines at least one of the gray scale masks to have a rough microlens shape. And at least one of them has a gray scale pattern for finely adjusting the shape of the coarsely determined microlens (claim 2).

  In this means, the shape of the microlens is roughly determined by exposure with a gray scale pattern for roughly determining the shape of the microlens. That is, the exposure of the gray scale pattern increases the amount of resist film slip and determines the rough shape of the microlens. Then, an exposure with a gray scale pattern for finely adjusting the shape of the coarsely determined microlens corrects the error of the coarse shape, and finally forms a highly accurate resist pattern. Produces high-precision microlenses. In actual exposure, either exposure using a gray scale pattern for coarsely determining the shape of the microlens or exposure using a grayscale pattern for finely adjusting the shape of the microlens that has been roughly determined is performed first. May be. This is because the superposition theorem holds for the energy stored in the resist. In this manner, the resist is developed after the exposure with each gray scale pattern.

  The third means for solving the problem is the first means or the second means, wherein the alignment mark is formed by etching the optical base material, or the optical base material It is characterized by being formed by etching a metal thin film formed on the substrate (claim 3).

  When the alignment mark is formed by etching the optical base material, the alignment mark pattern may be formed on the same mask as that used for forming the cylindrical microlens array, and the exposure may be performed. Simple. However, since the alignment mark is only formed in a state where the optical substrate is etched, there is a problem that it is difficult to visually recognize the alignment mark.

  In the case of an alignment mark formed by etching a metal thin film, a resist is applied after the cylindrical microlens array is formed, the alignment mark is exposed to remove the resist, and the metal thin film is sputtered. The resist is removed and then formed on the portion where the resist has been removed by vapor deposition or the like. Therefore, although the photolithography process is increased by one process, it is possible to form an alignment mark that is easy to see and has high positional accuracy.

  A fourth means for solving the problem is any one of the first to third means, wherein the flat portion where the alignment mark is formed is the portion where the cylindrical lens is actually formed. (Claim 4).

  In this means, the flat portion is formed so as to envelop the region where the cylindrical lens array is formed. Therefore, even when the position for forming the alignment mark is designated for various reasons, such as providing the alignment mark at a position where it can be easily confirmed when the cylindrical microlens array is incorporated in the lens barrel, it can be flexibly handled. A cylindrical microlens array can be obtained.

  A fifth means for solving the above-mentioned problem is the fourth means, wherein the alignment mark is formed so as to extend in the length direction of the cylindrical lens. 5).

  In this means, when forming the cylindrical lens by grinding, polishing, etc., the alignment mark is formed in the length direction of the cylindrical lens where the alignment mark could not be formed. Space is not required, and the cylindrical microlens array is not increased in size.

  According to the present invention, it is possible to provide a cylindrical microlens array having alignment marks that can be used for alignment in a two-dimensional direction.

  Hereinafter, a method for manufacturing a cylindrical microlens array according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 and FIG. 2 are diagrams showing an outline of the manufacturing process of the cylindrical microlens array according to the first embodiment of the present invention.

  First, a resist 2 is applied on a substrate (optical base material) 1 made of quartz or glass (a). Then, the resist 2 is exposed using the gray scale mask 3 for rough adjustment, and when the resist 2 is developed, a predetermined cylindrical microlens array is obtained (b). This exposure is performed for a relatively long time, whereby the shape of the cylindrical microlens array is roughly determined.

  Next, the resist 2 is exposed using the fine-adjustment gray scale mask 4 to adjust the shape of the cylindrical microlens array obtained by the exposure using the coarse adjustment gray-scale mask 3 (c ). The pattern of the fine adjustment grayscale mask 4 is obtained by measuring the shape of the cylindrical microlens array obtained by exposure of only the coarse adjustment grayscale mask 3, and based on the result, the difference from the target shape. Is determined so as to correct the pattern. This process is a characteristic part of the invention of the prior application.

  Next, when the exposed resist 2 is developed, the resist 2 is formed into a cylindrical microlens array pattern (d). When the resist 2 and the substrate 1 thus obtained are dry-etched to remove the resist 2, the pattern of the resist 2 is transferred to the substrate 1, and the substrate 1 having the shape of a cylindrical microlens array on the surface is obtained ( e). At this time, due to the difference in etching rate between the substrate 1 and the resist 2, the pattern shape of the resist 2 and the pattern shape of the surface of the substrate 1 are not equal, but the resist pattern is obtained so that the desired pattern shape can be obtained on the surface of the substrate 1. The pattern shape of 2 is determined in advance. A cylindrical microlens array is completed through the above steps.

  The exposure using the fine adjustment grayscale mask 4 may be performed before the exposure using the coarse adjustment grayscale mask 3, and in some cases, a more accurate microlens array may be formed. Can be manufactured.

  Thereafter, alignment marks are formed on the substrate 1. In FIG. 2, the substrate shown in FIG. 1 (e) is used as a starting material. First, a resist 2 is applied to the surface of the substrate 1 (f). Then, the resist 2 is exposed through the mask 5 on which the alignment mark pattern 5a is formed (g), and the resist 2 is developed to remove the resist 2 in the portion 2a corresponding to the alignment mark (h).

  Then, a chromium thin film 6 is formed thereon by sputtering (i). Subsequently, when the resist 2 is dissolved, the chromium thin film 6 on the resist 2 is removed, and an alignment mark 7 made of a chromium thin film is formed in a portion where the resist 2 does not exist (j).

  In the above process, since the exposure is performed three times, the alignment of the mask and the substrate 1 in each exposure is necessary. This is because the alignment mark for alignment is placed on each mask and the substrate 1. It can be realized by a method performed in a normal lithography process.

  In the above process, the chromium thin film 6 is formed after the process shown in (h). However, dry etching is performed from the state shown in (h), which corresponds to the alignment mark. The portion 2a can be engraved in the substrate 1 to form the substrate 1 with a recess, and this recess can be used as an alignment mark. According to this method, the process of forming and removing a metal thin film such as the chromium thin film 6 can be omitted, but the formed alignment mark is difficult to see unlike those formed of a metal thin film such as a chromium thin film. Has disadvantages.

  In FIG. 1 and FIG. 2, for simplification of description, each microlens is shown as being independent and protruding from the substrate 1, but the actually formed cylindrical microlens array is as follows. As shown in FIG. 3A is a plan view, and FIG. 3B is a cross-sectional view taken along line AA in FIG. The cylindrical microlens array portion is entirely recessed from the surface of the substrate 1, and the alignment mark 7 is formed on the surface portion of the substrate.

  In the example shown in FIG. 3, the length of each cylindrical lens is formed in accordance with a circular part that is actually used, so that the alignment mark 7 can be formed at a position close to the part that is actually used. . That is, the alignment mark 7 is a rectangle that envelops a portion where the cylindrical lens array is formed, and one side is formed in a direction that coincides with the length direction of the cylindrical lens. In this way, it is not necessary to enlarge the substrate 1 to form the alignment mark 7, and no special space for the alignment mark is required as can be seen from comparison with FIG. Can be miniaturized.

  The surface portion of the substrate is present in the completed cylindrical lens array so as to surround the cylindrical lens array, but an alignment mark may be formed on any portion of the surface portion. The formation position of the alignment mark may be determined according to the purpose of use of the alignment mark and the conditions during use.

  As described above, since the portion where the cylindrical microlens array is not formed remains the prototype of the substrate 1, the masks 3 and 5 used in the steps of FIGS. 1B and 1C are actually in this portion. The pattern is such that the corresponding exposure light is shielded. Therefore, by forming an exposed portion of the pattern corresponding to the alignment mark in this portion of either of the masks 3 and 5, formation of the cylindrical microlens array pattern in the steps (d) and (e). At the same time, alignment marks can be formed.

  A cylindrical microlens array as shown in FIG. 3 was manufactured by the steps shown in FIGS. The sag amount of this cylindrical microlens is about 70 μm. As an alignment mark, a chrome thin cross wire (length: 1 mm) having a line width of about 2 μm was formed. Since it is a crosshair, it can be aligned two-dimensionally using this mark (that is, when the horizontal direction is the X direction and the vertical direction is the Y direction in FIG. 3A), both the X and Y directions are aligned. . In this example, a cross line is formed. However, an alignment mark shape other than the cross line, for example, a ring shape, can be easily realized by preparing a mask according to the shape.

It is a figure which shows the outline | summary of the manufacturing process of the cylindrical microlens array which is the 1st Embodiment of this invention. It is a figure which shows the outline | summary of the manufacturing process of the cylindrical microlens array which is the 1st Embodiment of this invention. It is a figure which shows the example of the cylindrical microlens array which is embodiment of this invention. It is a figure which shows the manufacturing method of the cylindrical microlens array by a grinding / polishing method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Board | substrate, 2 ... Resist, 2a ... Part corresponding to alignment mark, 3 ... Coarse adjustment gray scale mask, 4 ... Fine adjustment gray scale mask, 5 ... Mask, 5a ... Alignment mark pattern, 6 ... Chromium thin film 7 Alignment mark

Claims (5)

Using two or more grayscale masks, sequentially transferring a grayscale mask pattern to a resist provided on an optical substrate, developing the resist, and then etching the remaining resist and the optical substrate The method of manufacturing a microlens includes a step of manufacturing a microlens by transferring a pattern of the resist corresponding to the grayscale mask to the optical base material, and exposure time of exposure using each grayscale mask Among them, a cylindrical microlens array manufactured by a microlens manufacturing method in which at least one grayscale mask has an exposure time different from that used to expose another grayscale mask. The lens shape of the optical substrate was formed The flat portion other than Tokoro, cylindrical microlens array alignment mark is formed can be used as a basis for the two-dimensional direction position. 2. The cylindrical microlens array according to claim 1, wherein at least one of the grayscale masks has a grayscale pattern for coarsely determining the shape of the microlens. The cylindrical microlens array is characterized in that at least one has a gray scale pattern for finely adjusting the shape of the microlens determined roughly. 3. The cylindrical microlens array according to claim 1, wherein the alignment mark is formed by etching the optical substrate, or a metal thin film formed on the optical substrate. A cylindrical microlens array formed by etching. The cylindrical microlens array according to any one of claims 1 to 3, wherein the flat portion on which the alignment mark is formed envelops the portion on which the cylindrical lens is actually formed. Cylindrical microlens array characterized by 5. The cylindrical microlens array according to claim 4, wherein the alignment mark is formed on an extension line in the longitudinal direction of the cylindrical lens.

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