Liquid crystal display panel manufacturing method and aligning apparatus

Abstract: A liquid crystal display panel manufacturing method and an aligning apparatus for use in the method make it possible to precisely align an active matrix substrate (11B) and a counter substrate (11A) with high precision even if the two alignment marks thereon are substantially apart from each other. A clear image is formed by focusing a microscope onto an alignment mark on a counter substrate, captured into a video camera and output as a first image signal. The first image signal output from the video camera is temporarily stored in an image memory. Next, a clear image is formed by focusing the microscope onto an alignment mark on an active matrix substrate, captured into the video camera and output as a second image signal. The second image signal output from the video camera and the first image signal temporarily stored in the image memory are synthesized by an image synthesizing circuit, and then, displayed clearly on a monitor.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display panel manufacturing method in accordance with the precharacterizing part of claim 1. A manufacturing method of that kind is known from US-A-4,655,600. Further the present invention relates to an alignment apparatus in accordance with the precharacterizing part of independent claim 5. An aligning apparatus of that kind is known from JP-A-1238668. 2. Description of the Related Art As electronic equipment provided with a liquid crystal display apparatus, which is represented by a liquid crystal projector, has become widely available in recent years, the need for higher performance of the liquid crystal display apparatus has grown and improvements have been made to enhance the definition and brightness of the liquid crystal display apparatus. A liquid crystal display panel used in the liquid crystal display apparatus is generally composed of an active matrix substrate provided with a matrix of pixels, a TFT (Thin Film Transistor) for pixel control and the like, and a counter substrate provided with a color filter, a black matrix and the like. These substrates are overlaid (aligned) relative to alignment marks, laminated and integrated into one. Fig. 4 shows a schematic structure of a conventional liquid crystal display panel in assembly. Referring to Fig. 4, a counter substrate 110A is located opposed and parallel to an active matrix substrate 110B, and an alignment mark a and an alignment mark b are formed on the counter substrate 110A and the active matrix substrate 110B, respectively. In laminating the active matrix substrate 110B and the counter substrate 110A in a conventional manner, the alignment marks a and b are simultaneously observed by a microscope 120, and the active matrix substrate 110B is shifted in a horizontal direction by an unillustrated shift table if the alignment marks a and b are displaced from each other, whereby the active matrix substrate 110B and the counter substrate 110A are aligned. A required distance d is provided between the active matrix substrate 110B and the counter substrate 110A because liquid crystal is required to be sealed therein in the later process. When the distance d is about several microns, since both the alignment marks a and b are within the focal depth of the microscope 120, sufficient visibility and precise alignment can be achieved. However, in such a conventional method, if the distance between the active matrix substrate and the counter substrate increases to about several hundreds of microns, the two alignment marks are out of the focal depth of the microscope, which makes it difficult to simultaneously observe the two alignment marks with high visibility and also lowers alignment precision. JP-A-1238668 is not specifically directed to a liquid crystal display manufacturing method, but to a high-precision positioning for alignment of two substrate plates. This document discloses a method of taking a first picture of a registration mark on a first substrate plate, storing said picture in a memory, then taking a second picture of a second registration mark on the second substrate by moving a camera by a predetermined distance and focusing the camera on the mark on the second substrate plate. Thereafter, the stored image is called and the data thereof is processed so as to match the real image with a virtual image, while simultaneously comparing the real image of the second registration mark with the virtual image of the first registration mark in the camera's view field and carrying out the positioning so that the two images are matching. A draw-back of this known precision positioning method is that the camera is not maintained at a fixed location, but is moved by a predetermined distance L which may generate errors, if the positioning of the camera causes parallaxes. US-A-4,655,600 discloses a method of aligning an object by which partial image information is captured with a video camera from V-shaped marks moving in correspondence with the position of the object, determining a position where this mark and a straight mark detection line crosses each other, and positioning this object on the basis of information on this predetermined position. SUMMARY OF THE INVENTION With such a problem in view, a first object of the present invention is to provide a liquid crystal display panel manufacturing method in which an active matrix substrate and a counter substrate are precisely aligned and laminated even if the two alignment marks thereon are substantially apart from each other. A second object of the present invention is to provide an aligning apparatus capable of precisely aligning and laminating two substrates even if the two alignment marks thereon are substantially apart from each other, and, particularly, suitable for use in manufacturing a liquid crystal display panel. According to one aspect of the invention, there is provided a liquid crystal display panel manufacturing method comprising the steps of: preparing a first substrate with a display portion including a matrix of pixels and a first alignment mark, preparing a second substrate with a second alignment mark to be located opposed to said first substrate, forming image signals of said first and second alignment marks by capturing them into a video camera, processing said image signals formed by said video camera separately to obtain image monitoring signals of said alignment marks to be displayed on monitoring means, shifting said first and said second substrates relatively so that the displayed images of said first and second alignment marks are overlaid at a reference position, and laminating said first and second substrates while maintaining a required distance therebetween, characterized in that the images taken by said video camera are selectively focused by means of a microscope and one of said image signals of said first or second alignment mark captured by said video camera is stored in a storage means to be displayed on said monitor as said reference position. The second substrate may have a plurality of microlenses for gathering light onto the display portion formed on the first substrate. Furthermore, the second substrate may have a transparent plate located over the microlenses. It is preferable that the space between the first and second alignment marks be set so as to include the thickness of the microlenses, the thickness of the transparent plate and the height of a cavity to be filled with liquid crystal. According to another aspect of the present invention, there is provided an aligning apparatus for aligning a first substrate having a first alignment mark and a second substrate having a second alignment mark serving as a reference for alignment of said second substrate with said first substrate while maintaining a required distance between said substrates, which apparatus comprises image forming means for selectively focusing said first alignment mark and said second alignment mark and forming clear images of said alignment marks, image input means for capturing the images of said first alignment mark and said second alignment mark formed by said image forming means and converting the images into first and second image signals, respectively, image memory means for temporarily storing the first image signal of said alignment mark first output from said image input means, and substrate shifting means for shifting said first and second substrates relatively so that the images of said first and second alignment marks are overlaid at a reference position, image synthesizing means for synthesizing the first image signal of said first alignment mark stored in said image memory means and the second image signal of the second alignment mark output later from said image input means, said apparatus being characterized by an image display monitor for simultaneously displaying the two images of said first alignment mark and said second alignment mark synthesized by said image synthesizing means, wherein said image forming means includes a microscope for selectively focusing to said first and second alignment marks and forming an enlarged image thereof. In the aligning apparatus of the present invention, the first alignment mark and the second alignment mark are focused selectively and clear images of the alignment marks are formed by the image forming means. The images of the first alignment mark and the second alignment mark formed by the image forming means are captured into the image input means and converted into image signals respectively therein. The image signal of the alignment mark first output from the image input means is temporarily stored in the image memory means. The image signal stored in the image memory means and the image signal of the alignment mark output later from the image input means are synthesized and output by the image synthesizing means, and the images are displayed simultaneously and clearly on the image display means. It is preferable that the first substrate be a matrix substrate with a display portion having a matrix of pixels and that the second substrate be a counter substrate provided with microlenses for gathering light onto the pixels. The image forming means include a microscope for forming an enlarged image of the alignment mark. The image input means may include a video camera. It is preferable that the second substrate be a matrix substrate with a display portion having a matrix of pixels and that the first substrate be a counter substrate provided with microlenses for gathering light onto the pixels. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram showing the schematic structure of an aligning apparatus according to an embodiment of the present invention. Fig. 2 is a view showing the relation between an active matrix substrate and a counter substrate in a liquid crystal display panel to be aligned. Fig. 3 is a view explaining a display state of two alignment marks on a monitor in the alignment apparatus shown in Fig. 1. Fig. 4 is a view explaining a method of aligning an active matrix substrate and a counter substrate in a conventional liquid crystal display panel. DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described in detail below with reference to the drawings. Fig. 1 shows a schematic structure of an aligning apparatus 10 according to an embodiment of the present invention. The aligning apparatus 10 comprises a microscope 12 serving as a clear image forming means for forming enlarged images of alignment marks A and B respectively formed on a counter substrate 11A and an active matrix substrate 11B which constitute a liquid crystal display panel 11, a video camera 13 serving as an image input means for capturing the images formed by the microscope 12 and outputting a first image signal corresponding to the alignment mark A on the counter substrate 11A and a second image signal corresponding to the alignment mark B on the active matrix substrate 11B, an image memory 14 serving as an image memory means for temporarily storing the first image signal of the image signals output from the video camera 13, an image synthesizing circuit 15 serving as an image synthesizing means for inputting the first image signal stored in the image memory 14 and the second image signal output from the video camera 13 and selecting and outputting these image signals alternately, a monitor 16 serving as a display means for simultaneously displaying the two image signals in response to the output from the image synthesizing circuit 15, and an X-Y- table 17 serving as a substrate shifting means for positioning the active matrix substrate 11B relative to the counter substrate 11A by slightly shifting the active matrix substrate 11B on the horizontal plane in two axial directions (X and Y) and the rotational direction (). The first and second image signals output from the video camera 13 each include one field of information, and constitute one frame. Fig. 2 is an enlarged view of the counter substrate 11A and the active matrix substrate 11B, which constitute the liquid crystal display panel 11, before aligned. On the counter substrate 11A, a color filter, a black matrix and the like are formed, and a plurality of, for example, semicircular microlenses 11a are integrally formed thereon. These microlenses 11a are integrally formed on the counter electrode 11A for the following reason. That is, though it is necessary to increase the number of pixels according to the request for downsizing and high definition of the liquid crystal display panel, if the number of pixels is increased, the area of regions other than the pixels relatively increases, which increases the area of a black mask for covering these regions, decreases the pixel area contributory to image display, and lowers the aperture ratio of the liquid crystal display panel. The lowering of the aperture ratio darkens the display plane of the liquid crystal display panel, and reduces image quality. In order to prevent such reduction in image quality resulting from the lowering of the aperture ratio, the microlenses 11a are integrally formed on the counter substrate 11A to gather incident light onto pixels on the active matrix substrate 11B. On the counter substrate 11A, for example, a square alignment mark A with a cross line 20 at the center thereof is formed as shown in an enlarged view of Fig. 3A. The alignment mark A is integrally formed, for example, in the same process as that of forming the microlenses 11a in order to simplify the manufacturing procedure. The microlenses 11a and the alignment mark A can be formed by, for example, selectively etching a parent material (glass substrate) of the counter substrate 11A. A cover glass plate 11b for evening a liquid crystal layer to be filled in a later process is laminated onto the microlenses 11a formed on the counter substrate 11A. The thickness of the cover glass plate 11b is determined by the refractive indices of the microlenses 11a and the counter substrate 11A, the pixel pitch of the liquid crystal display panel 11, and the like. On the other hand, a matrix of pixels, a TFT (Thin Film Transistor) and the like are formed on the active matrix substrate 11B, and, for example, a cross-shaped alignment mark B is further formed on the surface of the active matrix substrate 11B as shown in an enlarged view of Fig. 3B. The active matrix substrate 11B may have what is called an on-chip black and on-chip color filter structure in which a black matrix and a color filter are formed as well as pixels and a switching device, such as a TFT, for pixel control. In the liquid crystal display panel 11 used in this embodiment, a distance between the alignment mark A of the counter substrate 11A and the alignment mark B of the active matrix substrate 11B is longer than the conventional one by the thicknesses of the microlenses 11a and the cover glass plate 11b (several hundreds of microns). If the two alignment marks are thus apart from each other in the height direction thereof, they are out of the focal depth of the microscope as mentioned above and are made difficult to be simultaneously observed with high visibility, which lowers alignment precision. The aligning apparatus 10 according to this embodiment is used effectively in aligning the counter substrate 11A and the active matrix substrate 11B which are thus apart from each other by more than a predetermined distance in the height direction thereof. The action of the aligning apparatus 10 will be described below with reference to Figs. 1 to 3. First, a clear image shown in Fig. 3A is formed by focusing the microscope 12 onto the alignment mark A on the counter substrate 11A. The image of the alignment mark A is captured into the video camera 13, and output as a first image signal from the video camera 13. The first image signal output from the video camera 13 is temporarily stored in the image memory 14. Next, a clear image shown in Fig. 3B is formed in the similar manner to above by focusing the microscope 12 onto the alignment mark B on the active matrix substrate 11B. The image of the alignment mark B is captured into the video camera 13 and output as a second image signal from the video camera 13. The second image signal output from the video camera 13 is input to one input terminal of the image synthesizing circuit 15. At the same time, the first image signal temporarily stored in the image memory 14 is input to the other input terminal of the image synthesizing circuit 15. The image synthesizing circuit 15 alternately selects and outputs the first and second image signals to the monitor 16. Since the first and second image signals each have one field of information and constitute one frame, two images corresponding to the alignment marks A and B are simultaneously displayed on the monitor 16 as shown in Fig. 3C. In this state, if the alignment mark A of the counter substrate 11A and the alignment mark B of the active matrix substrate 11B are not aligned with each other, for example, as shown by a two-dot chained line in Fig. 3C, the X-Y- table 17 is so driven that the two alignment marks are aligned, thereby shifting the active matrix substrate 11B in this embodiment. After the two alignment marks A and B are aligned on the monitor 16, a required pressure is applied between the counter substrate 11A and the active matrix substrate 11B by, for example, an unillustrated pressing device, and sealing agent previously applied to an unillustrated portion (peripheral portion) of one substrate is hardened. The process of aligning (laminating) the active matrix substrate 11B and the counter substrate 11A is thereby completed. After that, liquid crystal is injected into a space between the active matrix substrate 11B and the counter substrate 11A by an unillustrated liquid crystal filling device. As mentioned above, in the aligning apparatus 10 according to this embodiment, when the alignment marks are observed by the microscope 12, the microscope 12 is focused onto the active matrix substrate 11A and the counter substrate 11B individually, and the image (alignment mark A) on the counter substrate 11A, which is focused first, is temporarily captured into the image memory 14 and simultaneously displayed on the monitor 16 in synchronization with the image (alignment mark B) of the active matrix substrate 11B which is focused later. Therefore, the images of the alignment marks A and B displayed on the monitor 16 are clear. In other words, in this embodiment, if the alignment marks A and B are substantially apart from each other in the height direction, the active matrix substrate 11B and the counter substrate 11A can be aligned with high precision. This increase in alignment precision makes it possible to sufficiently bring out the effect of gathering light onto the pixels on the active matrix substrate 11B by means of the microlenses 11a on the counter substrate 11A, and to thereby increase brightness. While the present invention has been described above with reference to the preferred embodiment thereof, the present invention is not limited to the foregoing embodiment, and various modifications may be made therein. For example, though the image (the first alignment mark A) corresponding to (the first alignment mark A) output from the video camera 13 is captured into the image memory 14 in the above embodiment, the image (the second alignment mark B) corresponding to the active matrix substrate 11B may be captured into the image memory 14 on the contrary. In this case, the counter substrate 11A is shifted for alignment. Furthermore, though the images corresponding to the counter substrate 11A and the active matrix substrate 11B output from the video camera 13 are alternately selected by the image synthesizing circuit 15 and displayed on the monitor 16 as they are, these images may be displayed after subjected to arithmetic processing. The shapes and positions of the alignment marks are not limited to those in the foregoing embodiment, but are arbitrary. Furthermore, though the object to be aligned is the liquid crystal display 11 composed of the counter substrate 11A integrally having the microlenses and the active matrix substrate 11B, the present invention is applicable to the devices, in general, composed of two substrates which are apart from each other to such an extent that they are not simultaneously within the focal depth. As mentioned above, according to the liquid crystal display panel manufacturing method of the invention, clear images corresponding to the first alignment mark on the counter substrate and the second alignment mark on the active matrix substrate are separately formed, and thereby displayed clearly on the display means. As a result, alignment can be performed with high precision even if the distance between the first alignment mark on the counter substrate and the second alignment mark on the active matrix substrate is long. Furthermore, the aligning apparatus of the present invention comprises an image forming means for individually focusing the first alignment mark on the first substrate and the second alignment mark on the second substrate and forming clear images of the alignment marks, an image input means for inputting the images of the first alignment mark and the second alignment mark formed by the clear image forming means and converting the images into image signals respectively, an image storing memory means for temporarily storing the first output image signal of the output alignment mark of the image signals output from the image input means, an image synthesizing means for synthesizing and outputting the image signal stored in the image memory means and the image signal of the alignment mark output later from the image input means, and an image display means for simultaneously displaying two images of the first alignment mark and the second alignment mark synthesized by the image synthesizing means. Consequently, precise alignment can be achieved even if the marks of the two substrates are positioned substantially apart from each other.

Claims: A liquid crystal display panel manufacturing method comprising the steps of: preparing a first substrate (11A) with a display portion including a matrix of pixels and a first alignment mark (A); preparing a second substrate (11B) with a second alignment mark (B) to be located opposed to said first substrate (11A); forming image signals of said first and second alignment marks (A, B) by capturing them into a video camera (13); processing said image signals formed by said video camera separately to obtain image monitoring signals of said alignment marks (A, B) to be displayed on monitoring means; shifting said first and said second substrates (11A, 11B) relatively so that the displayed images of said first and second alignment marks (A, B) are overlaid at a reference position; and laminating said first and second substrates (11A, 11B) while maintaining a required distance therebetween, characterized in that the images taken by said video camera are selectively focused by means of a microscope (12) and one of said image signals of said first or second alignment mark (A, B) captured by said video camera (13) is stored in a storage means (14) to be displayed on said monitor as said reference position. A liquid crystal display panel manufacturing method according to claim 1, wherein said second substrate has a plurality of microlenses for gathering light onto said pixels formed on said first substrate. A liquid crystal display panel manufacturing method according to claim 2, wherein said second substrate has a transparent plate located over said microlenses. A liquid crystal display panel manufacturing method according to claim 3, wherein a distance (D) between said first and second alignment marks is set so as to include the thickness of said microlenses, the thickness of said transparent plate and the height of a cavity to be filled with liquid crystal. An aligning apparatus for aligning a first substrate (11A) having a first alignment mark (A) and a second substrate (11B) having a second alignment mark (B) serving as a reference for alignment of said second substrate (11B) with said first substrate (11A) while maintaining a required distance (D) between said substrates (11A, 11B), which apparatus comprises: image forming means (12) for selectively focusing said first alignment mark (A) and said second alignment mark (B) and forming clear images of said alignment marks (A, B); image input means (13) comprising a video camera for capturing the images of said first alignment mark (A) and said second alignment mark (B) formed by said image forming means (12) and converting the images into first and second image signals, respectively; image memory means (14) for temporarily storing the first image signal of said alignment mark (A) first output from said image input means; and substrate shifting means (17) for shifting said first and second substrates (11A, 11B) relatively so that the images of said first and second alignment marks (A, B) are overlaid at a reference position, image synthesizing means (15) for synthesizing the first image signal of said first alignment mark (A) stored in said image memory means (14) and the second image signal of the second alignment mark (B) output later from said image input means; said apparatus being characterized by an image display monitor (16) for simultaneously displaying the two images of said first alignment mark (A) and said second alignment mark (B) synthesized by said image synthesizing means (15), wherein said image forming means (12) includes a microscope for selectively focusing to said first and second alignment marks (A, B) and forming an enlarged image thereof. An aligning apparatus according to claim 5, wherein said first substrate is a matrix substrate with a display portion having a matrix of pixels and said second substrate is a counter substrate provided with microlenses for gathering light onto said pixels. An aligning apparatus according to claim 5, wherein said second substrate is a matrix substrate with a display portion having a matrix of pixels and said first substrate is a counter substrate provided with microlenses for gathering light onto said pixels.

Inventors: HAZAMA YOSHIKAZU, HAZAMA, YOSHIKAZU
Applicants: SONY CORP, SONY CORPORATION
Application year: 1997
Main classification: G02F1
IPC codes: G02F1, G02B3