Abstract:
An active matrix substrate comprises a substrate, a position control member provided on the substrate and surrounding a specific space by a sidewall thereof to expose a surface of the substrate and whose inner side face inclines at a specific angle with respect to the substrate, an active element provided so as to engage with the inner side face of the position control member and whose outer side face has at least a part that inclines at substantially the same angle as the specific angle of the inner side face of the position control member with respect to the substrate, and an adhesion section which bonds the active element to the substrate or the position control member and whose wettability with the position control member is lower than that of the adhesive with the substrate.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-208724, filed Jul. 10, 2001, the entire contents of which are incorporated herein by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention relates to an active matrix substrate and a method of manufacturing active matrix substrates  
           [0004]    2. Description of the Related Art  
           [0005]    Liquid-crystal displays (LCDs) have been widely used as display terminals for mobile information units, such as notebook personal computers, televisions, mobile phones, or mobile information terminals (or PDAs). For example, an active matrix LCD is formed as follows: thin film transistors (TFTs), which use amorphous silicon or polycrystalline silicon as an active layer, are formed in a matrix on a glass substrate and secured with an approximately 5-μm gap between the TFTs and an opposite glass substrate, the gap being filled with liquid crystal, thereby completing an active matrix LCD. This type of active matrix LCD is used as a thin display unit that provides high-quality, full-color display.  
           [0006]    On the other hand, there have been demands that LCDs should consume less electric power, have a larger number of pixels, be larger in size, weigh less, help decrease manufacturing costs, assure high-quality display, etc.  
           [0007]    Active elements, such as TFTs, are formed by repeating the following processes: electrodes, an insulating layer, etc. are formed on a glass substrate by vacuum processes, including CVD and sputtering techniques, and then are subjected to photolithography and dry etching or wet etching, thereby forming a pattern. Therefore, to obtain a large display unit, it is necessary to make the apparatus for vacuum processes larger, resulting in higher manufacturing costs. Since the percentage of the area of the display unit taken up by the active elements is small, it is wasteful to use a large apparatus for vacuum processes.  
           [0008]    To make a display unit lighter, the formation of TFTs on a plastic substrate or a film substrate has been studied. Forming TFTs on those substrates requires the process temperature to be lowered. However, it is conceivable that a drop in the process temperature will degrade the TFT performance and therefore impose a limitation on the picture quality, the number of pixels, etc. Moreover, since those substrates have high thermal expansion coefficients and are deformed plastically at low temperature, a higher definition design is expected to be impossible, which leads to a decline in the quality of display.  
           [0009]    A method of solving those problems has been disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2001-7340. In the method, active elements, such as TFTs, are formed on an element formation substrate made of glass, silicon, or the like and then selectively transferred to another display substrate (or a final substrate) made of plastic, film, or the like. Thereafter, the active elements are interconnected.  
           [0010]    [0010]FIG. 1 shows one step in the method of transferring and forming active elements disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2001-7340. In this method, active elements  2701 , such as TFTs, are formed on an element formation substrate (not shown) and then transferred to an intermediate substrate  2702 . The active elements  2701  on the intermediate substrate  2702  are further transferred to a final substrate  2703 .  
           [0011]    In this method, the active elements  2701  and the intermediate substrate  2702  are bonded together via a temporary adhesion layer  2704 . The temporary adhesion layer  2704  is made of a material that has adhesion and lowers in adhesion when being illuminated by light or heated. As shown in FIG. 1, adhesion layers  2705  are formed beforehand in regions on the final substrate  2703  where the active elements  2701  are to be transferred. The active elements  2701  are transferred in such a manner that light or heat is projected via a mask  276  onto only the active elements to be transferred, while the active elements  2071  are being pressed against the adhesion layers  2705 .  
           [0012]    In the method disclosed Jpn. Pat. Appln. KOKAI Publication No. 2001-7340, active elements have been formed on an element formation substrate with a high density and then selectively transferred to a final substrate, thereby improving the production efficiency. In this method, however, since the positions of the active elements are not determined on the surface of the final substrate, the accuracy of the alignment of the intermediate substrate with the final substrate determines the accuracy of the positions of the active elements. Therefore, when the final substrate is produced by a plurality of transfers, the positions of the active elements shift, resulting in variations in the shift. When interconnections are made after the process of transferring the active elements, a shift in the position causes variations in the parasitic capacitance between the active elements, interconnections, and electrodes, resulting in a decline in the quality of display.  
           [0013]    Furthermore, to increase the position accuracy in transferring the active elements, there is a method of making tapered hollows in a final substrate and transferring tapered active elements to the final substrate.  
           [0014]    In this method, since both of the active elements and the final substrate have been tapered, the active elements fit into the tapered hollows in the final substrate, achieving the transfer with high position accuracy. In this transfer, however, since the active elements are pushed into the hollows in the final substrate, thereby carrying out transfer, this makes it difficult to selectively transfer densely formed active elements to the final substrate.  
           [0015]    As described above, in forming an active matrix substrate, it was impossible to selectively transfer active elements with high position accuracy by a conventional method of transferring active elements. Therefore, there has been a need to realize an active matrix substrate which enables active elements to be selectively transferred with high position accuracy and a method of manufacturing such active matrix substrates.  
         BRIEF SUMMARY OF THE INVENTION  
         [0016]    According to a first aspect of the present invention, there is provided an active matrix substrate comprising: a substrate; a position control member provided on the substrate and surrounding a specific space by a sidewall thereof to expose a top surface of the substrate and whose inner side face inclines at a specific angle with respect to the substrate; an active element provided so as to engage with the inner side face of the position control member and whose outer side face has at least a part that inclines at substantially the same angle as the specific angle of the inner side face of the position control member with respect to the substrate; and an adhesion section which includes an adhesive that bonds the active element to the position control member and whose wettability with the position control member is lower than that of the adhesive with the substrate.  
           [0017]    According to a second aspect of the present invention, there is provided an active matrix substrate comprising: a substrate; a position control member provided on a top surface of the substrate and has a concave part that is made up of an inner side face inclining at a specific angle with respect to the substrate and a bottom part connecting to the inner side face; an active element provided so as to engage with the concave part of the position control member and whose outer side face has at least a part that inclines at substantially the same angle as the specific angle of the inner side face of the position control member; and an adhesion section which includes an adhesive that bonds the active element to the substrate or the position control member, with a contact angle of the adhesive to the position control member being 70° or more.  
           [0018]    According to a third aspect of the present invention, there is provided a method of manufacturing active matrix substrates, comprising: forming an active element on a first substrate; transferring the active element to a second substrate; processing the active element in such a manner that an outer side face of the active element has a first inclination with respect to a bottom surface thereof; forming on a third substrate a position control member which surrounds a specific space by a sidewall thereof and an inner side face of the position control member has a second inclination with respect to the third substrate; applying an adhesive to a face exposed to the specific space in the position control member, the wettability of the adhesive to the position control member being lower than that of the adhesive to the third substrate; and engaging the active element with the position control member at the specific space and bonding the active element with the adhesive. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0019]    [0019]FIG. 1 is a sectional view to help explain one process of a conventional method of manufacturing active matrix substrates;  
         [0020]    FIGS.  2  to  8  are sectional views to help explain stepwise a method of manufacturing active matrix substrates according to a first embodiment;  
         [0021]    [0021]FIG. 9 is a drawing to help explain a contact angle of adhesive;  
         [0022]    [0022]FIGS. 10A and 10B are a sectional view and a plan view, respectively, to help explain a process following the process in FIG. 8;  
         [0023]    [0023]FIG. 11 is a sectional view to help explain a shift in the position of the supply of adhesive in the process of FIG. 10A;  
         [0024]    FIGS.  12  to  16  are sectional views to help explain stepwise processes following the process of FIGS. 10A and 10B;  
         [0025]    FIGS.  17  to  20  are sectional views to help explain stepwise a method of manufacturing active matrix substrates according to a second embodiment;  
         [0026]    [0026]FIGS. 21 and 22 are plan views of modifications of the position control member in the first or second embodiment;  
         [0027]    [0027]FIG. 23 is a plan view of part of a liquid-crystal display according to a third embodiment;  
         [0028]    [0028]FIG. 24 is a plan view of an active element in the third embodiment;  
         [0029]    [0029]FIG. 25 is a sectional view taken along line  25 - 25  in FIG. 24;  
         [0030]    [0030]FIG. 26 is a plan view of part of an EL display according to a fourth embodiment; and  
         [0031]    [0031]FIG. 27 is a plan view of an active element in the fourth embodiment. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0032]    Hereinafter, referring to the accompanying drawings, embodiments of the present invention will be explained in detail.  
         [0033]    (First Embodiment)  
         [0034]    In a first embodiment, active elements are formed on an element formation substrate (or a first substrate). After the active elements on the element formation substrate are then transferred to an intermediate substrate (or a second substrate), they are processed so as to have a tapered shape. Then, tapered position control members are also formed on a final substrate (or a third substrate). The active elements are aligned with the tapered position control members and transferred to the final substrate, which completes an active matrix substrate. The position control members enable the active elements to be transferred at the proper positions.  
         [0035]    The configuration of an active matrix substrate will be explained by reference to FIG. 16. The active matrix substrate of the first embodiment includes tapered active elements  103  whose cross section inclines perpendicularly to the surface of the substrate, and position control members  108  whose inner side face is tapered so as to enclose the corresponding active element  103  on a final substrate  107 . Each active element  103  has an etching stopper layer  102  on its bottom surface. The etching stopper layer is bonded to the final substrate  107  via an adhesion section  109 .  
         [0036]    On the entire surfaces of these component parts, a post-transfer interlayer insulating layer (or post-transfer insulators)  111  is provided. Contact sections are provided in the regions of the post-transfer interlayer insulating layer corresponding to the electrodes of the active elements  103 . On each contact section, an interconnection  112  and a pixel electrode  113  are formed. In the first embodiment, although the etching stopper layer  102  is shown separately from the active element  103 , the active element  103  together with the etching stopper layer  102  might be called an active element  103 .  
         [0037]    A method of manufacturing active matrix substrates according to the first embodiment will be explained by reference to FIGS.  2  to  16 .  
         [0038]    As shown in FIG. 2, on the element formation substrate  101  made of silicon, alkali-free glass, quartz, or the like, an etching stopper layer  102  is formed to a thickness of about 0.1 to 10 μm using an insulating material, such as tantalum oxide (TaOx), alumina (AlOx), silicon oxide (SiOx), or silicon nitride (SiNx). In the first embodiment, the element formation substrate  102  is removed by grinding and etching as described later. Therefore, it is desirable that a material whose etching selection ratio to the element formation substrate  101  is high should be used as a material for the etching stopper layer  102 .  
         [0039]    On the etching stopper layer  102 , a plurality of active elements  103  are formed. Each active element  103  includes a polycrystalline silicon TFT or a circuit including a polycrystalline silicon TFT, an amorphous silicon TFT or a circuit including an amorphous silicon TFT, or a crystalline silicon TFT or a circuit including a crystalline silicon TFT. The number of elements constituting each active element is not limited to one. It is desirable that an active element should have one side of about 20 to 100 μm in length and a thickness of about 1 to 5 μm, and an inter-element distance of 3 to 20 μm. In the first embodiment, the thickness of the etching stopper layer  102  is set to about 1 μm, the size of an active element  103  is set as a square about 36 μm long, the distance between adjacent elements is set to about 6 μm, and the pitch in element arrangement is set to about 42 μm.  
         [0040]    Next, as shown in FIG. 3, the etching stopper layer  102  is separated into pieces in such a manner that the pieces correspond to the active elements  103  in a one-to-one ratio. The etching stopper layer  102  is processed as follows. A resist (not shown) is patterned into the shapes of active elements  103  using photolithographic techniques. With the resulting resist as a mask, the etching stopper layer  102  is etched by reactive ion etching (RIE) techniques or the like. The separation of the etching stopper layer  102  may be performed after the removal of the element formation substrate  101 , which will be explained later Next, as shown in FIG. 4, an intermediate substrate  105  made of glass, plastic, or the like is prepared. A temporary adhesion layer  104  is sandwiched between the surface of the element formation substrate  101  at which the active elements  103  have been formed and the intermediate substrate  105  and then laminated together. A material that has adhesion and is stimulated to peel in the presence of ultraviolet rays, such as an acrylic adhesive including benzophenone, may be used as the temporary adhesion layer  104 . The temporary adhesion layer  104  is applied to the intermediate substrate  105  and bonded to the element formation substrate  101 . In the first embodiment, the film thickness of the temporary adhesion layer  104  is set to about 4 μm.  
         [0041]    Next, as shown in FIG. 5, the element formation substrate  101  is removed. For example, when a glass substrate is used as the element formation substrate  101 , the element formation substrate  101  is made thinner by mechanical grinding. The resulting substrate is then etched with a mixed solution of hydrofluoric acid and surfactant, or the like. The material for and the layer quality of the etching stopper layer  102  and the material for the etchant are selected so that etching may stop at the etching stopper layer  102 .  
         [0042]    Next, as shown in FIG. 6, the etching stopper layer  102  and then the temporary adhesion layer  104  are etched into tapered shapes for each active element  103 , thereby making a cut  106  with a specific angle.  
         [0043]    The temporary adhesion layers  104  around the active elements  103  are not necessarily tapered, and all of the temporary adhesion layers around the active elements  103  may be etched away so that the individual active elements  103  are separated completely.  
         [0044]    Dry etching, wet etching, or the like may be used. Use of isotropic etching conditions enables tapered shapes to be obtained.  
         [0045]    It is desirable that the taper angle (the angle the cut surface makes to the bottom surface of the etching stopper layer) should be about 30 degrees or more and about 85 degrees or less. With the taper angle less than 30 degrees, the active elements are hard to move when they are pressed while deviating from their proper positions in a transfer process explained later, which makes it hard for them to fit into the desired positions. With the taper angle larger than about 85 degrees, the allowance of shifts in the positions of the active elements is too small in a transfer process explained later.  
         [0046]    The etching condition for etching the etching stopper layer  102  into a tapered shape may differ from the etching condition for etching the temporary adhesion layer  104  into a tapered shape or a shape other than a tapered shape. Even when the temporary adhesion layer  104  is tapered, the tapered shapes of the active elements  103  and etching stopper layers  102  may differ from the tapered shape of the temporary adhesion layer  104 .  
         [0047]    In the first embodiment, as shown in FIG. 7, the taper angle is set to about 45 degrees and the maximum width of the cut  106  in the etching stopper layer  102  is set to about 8 μm. As a result, the width of the bottom surface of the remaining part of the etched etching stopper layer  102  is about 34 μm.  
         [0048]    On the other hand, as shown in FIG. 8, position control members  108  have been formed in parts of the final substrate  107  to which the active elements (including the etching stopper layer) are to be transferred. The final substrate  107  is made of alkali-free glass, soda-lime, plastic, or metal foil. The position control members  108  are formed so as to enclose the corresponding active elements when the active elements are transferred, and to have a tapered shape with an inner side face in contact with the active element being inclined.  
         [0049]    In the first embodiment, photosensitive acrylic resin is applied to a thickness of about 2 μm and the resulting layer is patterned by photolithographic techniques, thereby forming the position control members  108 . The material for the position control members  108  is not limited to this. Another material may be used, provided the wettability with the adhesion section using adhesive is low.  
         [0050]    For example, an organic material with a low wettability with a normally used adhesive, such as silicon resin, styrene, polypropylene, or fluorine-based polymer, may be formed as the position control member  18  by spin coating techniques or the like. Moreover, an oxide such as SiO 2 , tantalum oxide, or alumina, or SiNx may be formed by sputtering, evaporation, spin coating techniques or the like and then coated with silicon or fluorine, thereby decreasing the wettability. In regions where adhesion sections are to be formed, the wettability may be increased by carrying out a primer coating process, followed by the selective formation of the adhesion sections.  
         [0051]    The wettability of the adhesion section with the position control member  108  indicates the degree of adhesion between them. With the wettability between them being low, when there is a slope, the adhesive tends to flow downward and is unlikely to stay in the same position. In a case where the adhesion section is placed on a certain member, when the contact angle of the surface of the adhesion section is large because of adhesion tension or the like, the wettability between the position control member  18  and the adhesion section is low. Therefore, to measure the degree of adhesion, for example, the contact angle of the adhesion section with the position control member  108  is measured.  
         [0052]    In this case, the contact angle is defined as an angle of α that the tangent to the end of liquid material B makes with the surface of plate-like material A when liquid material B is placed on the surface of plate-like material A. When plate-like material A is a glass substrate, the contact angle is measured according to, for example, Japanese Industrial Standard JIS R 3257 (1999).  
         [0053]    When the wettability, or the degree of adhesion, is low, the contact angle of the adhesion section with the position control member  108  is large. To lower the wettability of the adhesion section with the position control member  108 , the contact angle between them is preferably about 70° or more, and more preferably about 90° or more. As described above, the larger contact angle of the adhesion section with the position control member  108  and the low wettability of the adhesion with the position control member  108  allow the adhesion section to flow to the desired position, even if the adhesion section sticks to the tapered part of the position control member  108 . It is desirable that the wettability of the adhesion section with the final substrate  107  should be higher than the wettability of the adhesion section with the position control member  108 , because the adhesion section is kept stable. In the first embodiment, the contact angle of the adhesive section to the position control member  108  is about 140°.  
         [0054]    Furthermore, it is desirable that the height from the surface of the final substrate  107  to the top surface of the position control member  108  is about 0.3 μm or more and about 10 μm or less. One reason is that, when the height is less than about 0.3 μm, the active element goes over the position control member, which makes it impossible to control the position of the active element. The other reason is that, when the height is larger than about 10 μm, the position control member becomes too large, which deteriorates the high definition of the display element. Therefore, it is more desirable that the height should be 5 μm or less. In the first embodiment, the height from the surface of the final substrate  107  to the top surface of the position control member  108  is set to about 2 μm. To bond the active element to the adhesion layer well, the height from the surface of the final substrate  107  to the top surface of the active element is preferably equal to or larger than the height from the surface of the final substrate  107  to the top surface of the position control member.  
         [0055]    The taper angle of the inner side face where the position control member  108  contacts the active element is preferably almost the same taper angle given to the active element, that is, an angle equal to about 30 degrees or more and about 85 degrees or less. With the taper angel less than 30 degrees, when the active element is pressed, while deviating from its proper position, the element is unlikely to move in a transfer process explained later, which makes it difficult for the active element to fit into the desired position. When the taper angle is larger than about 85 degrees, the allowance of a shift in the position of the active element becomes too small in the transfer process explained later. In the first element, to cause the taper shapes of the etching stopper layer  102  and active elements  103  to coincide with the taper shapes of the position control members  108 , their taper angles are set to about 45 degrees.  
         [0056]    Next, as shown in FIG. 10A, an adhesion section  109  is formed on the inside of the position control member  108  by a screen printing method, a dropping method, or the like. A liquid adhesive, such as an ultraviolet-curing adhesive, epoxy resin, thermosetting adhesive, or acrylic adhesive, is used as the adhesion section  109 . At this time, the top surface of the adhesion section  109  is adjusted so as not to be higher than the top surface of the position control member  108 . In the embodiment, the height of the adhesion section  109  is set to about 1 μm and the height of the position control member  108  is set to about 2 μm. FIG. 10B is a plan view of the position control member  108  and adhesion section  109  viewed from above.  
         [0057]    In forming the adhesive section  109 , when the element size is small, there is a possibility that the adhesion section  109  will shift a little as shown in FIG. 11 and be formed on the side of the position control member  108 . In the first embodiment, however, since the tapered position control member  108  is made of a material whose wettability with the adhesion section  109  is low, the adhesion section  109  falls into the proper position even when being formed in such a position.  
         [0058]    Next, as shown in FIG. 12, the active element  103  on the intermediate substrate  105  is aligned with the position control member  108  on the final substrate  107 .  
         [0059]    Next, as shown in FIG. 13, ultraviolet rays are projected from the intermediate substrate  105  side via a mask  110  onto the active elements to be transferred, while a suitable pressure is being applied across the intermediate substrate  105  and the final substrate  107 . Being illuminated by ultraviolet rays, the temporary adhesion layer  104  corresponding to the chosen active elements  103  decreases in adhesion. At the same time, ultraviolet rays are also projected from the final substrate  107  side, thereby hardening the adhesion layers  109 , which bonds the active elements  103  to the final substrate  107 .  
         [0060]    At this time, since the position control member  108  and active element  103  have been tapered, even if the active element  103  deviates from the desired position to which the element  103  is to be transferred, the application of pressure across the intermediate substrate  105  and the final substrate  107  causes the active element  103  to shift to the proper position.  
         [0061]    In the first embodiment, the position control member  108  and active element  103  have the same tapered shape, the position accuracy of the active element  103  is high. It is preferable to cause both the active element and the active element to have the same tapered shape. Even if they do not have the same tapered shape, it is possible to increase the position accuracy of the active element  103 .  
         [0062]    Since the position control member  108  are formed into a convex shape on the final substrate  107 , only the active elements  103  to be transferred approach the final substrate  107  and the remaining active elements are held stable on the intermediate substrate  5  without being damaged due to contact.  
         [0063]    While in the embodiment, ultraviolet rays are selectively projected from the intermediate substrate  105  side onto the active elements  103  via the mask  110 , ultraviolet rays may be selectively projected by causing a laser beam in the ultraviolet region to scan.  
         [0064]    In the state where the adhesion of the temporary adhesion layer  104  is decreased and the adhesion of the adhesion section  109  is generated, the pressure applied across the intermediate substrate  105  and the final substrate  107  is removed, thereby separating the substrates, which causes only the chosen active elements  103  to be transferred to the final substrate  107  as shown in FIG. 14.  
         [0065]    As shown in FIG. 15, on the final substrate  401  to which the active elements  301  have been transferred, a post-transfer interlayer insulating layer (or post-transfer insulator)  111  is formed to a thickness of about 1 to 50 μm. Photosensitive acrylic resin or the like is used as a material for the post-transfer interlayer insulating layer  111 . Contact holes are made by photolithographic techniques in the regions of the post-transfer interlayer insulating layer  111  where the active elements  103  have to make contact.  
         [0066]    Next, as shown in FIG. 16, a conductive material, such as metal or ITO (Indium Tin Oxide), is sputtered or printed, thereby forming interconnections  112 , including signal lines and scanning lines, and pixel electrodes  113 . This completes an active matrix substrate of the first embodiment. These interconnections  112  and pixel electrodes  113  may be made of another material using other processes. Interconnections may be formed in a plurality of layers.  
         [0067]    As described above, in the first embodiment, the position control members  108  and active elements  103  have been tapered, which enables an active matrix substrate to be formed with high position accuracy. Since the convex position control members  108  are formed on the final substrate  107 , the active elements  103  on the intermediate substrate  105  are selectively transferred to the final substrate  107 . The remaining active elements  103  are held stable on the intermediate substrate  107  without being damaged. Furthermore, since the position control members  108  are made of a material whose wettability with the adhesion sections  109  is low, this enables the adhesion sections  109  to flow to the proper positions, which causes the active elements  103  to be bonded stably.  
         [0068]    (Second Embodiment)  
         [0069]    A second embodiment differs from the first embodiment in the shape of the position control member. The second embodiment will be explained, centering on the difference from the first embodiment. Explanation of the same parts as those of the first embodiment will be omitted.  
         [0070]    [0070]FIG. 20 is a sectional view of active element mounting sections of an active matrix substrate in the second embodiment. In FIG. 20, the configuration of the part above the active elements  103  is the same as that of the first embodiment and is not shown here. The active matrix substrate of the second embodiment is the same as that of the first embodiment in that tapered position control members  203  whose inner side face is inclined and tapered active elements  103  inclined so as to be enclosed by the position control members are formed on the final substrate  107 . However, the position control members  203  differ from those of the first embodiment in that they cover not only the sides of the active elements  103  but also their bottom surfaces so that they are concave. The active elements  103  are bonded to the position control members  203  via the adhesion sections  109 .  
         [0071]    A method of manufacturing the position control members  203  in the second embodiment will be explained by reference to FIGS.  17  to  29 . The remaining part of the manufacturing method is the same as that of the first embodiment.  
         [0072]    As shown in FIG. 17, position control member forming patterns  201  are formed in regions to which active elements are to be transferred and in areas around the regions on a final substrate  107 . Photosensitive acrylic resin, which is used as a material for the position control member forming patterns  201 , is applied to the entire surface to a thickness of about 5 μm and then patterned by photolithographic techniques.  
         [0073]    Next, as shown in FIG. 18, a pattern of photoresist  202  is formed which has openings in the regions to which the active elements of the position control member forming patterns  201  are to be transferred.  
         [0074]    Next, as shown in FIG. 19, after the regions to which the active elements of the position control member forming patterns  201  are to be transferred are made thinner than the areas around the regions, the photoresist  202  is removed, which completes the position control members  203 . At this time, the position control member forming patterns  201  are processed by an isotropic dry etching method, a wet etching method, or the like in such a manner that the inner side faces of the position control members  203  in contact with the active elements are tapered.  
         [0075]    In the second embodiment, the thickness of the position control member  203  in the region facing the bottom surface of the active element is set to about 2 μm and the thickness of the surrounding bank is set to about 5 μm. The taper angle is set to about 45 degrees (see FIG. 19).  
         [0076]    Next, as in the first embodiment, adhesive is supplied to the concave part of the position control member  203  to form adhesive section  109 . Choosing a suitable material for the adhesive so that the contact angle of the adhesive to the position control member may be 70° or more enables the adhesive to slide easily onto the bottom of the concave part of the position control member  203  to form adhesive section  109 .  
         [0077]    Next, as shown in FIG. 20, the active elements  103  are selectively engaged with the position control members  203 , thereby performing transfer. Since the position control members  203  whose wettability with the adhesion is low is placed over not only the sides of the active elements  103  but also their bottom surfaces, it is easy for the adhesive to flow and be formed in the proper position. After the adhesive is hardened, the active elements  301  are secured to the position control members  203  by the adhesive section  109  with a suitable strength.  
         [0078]    Furthermore, use of the position control members  203  with the bottom makes the adhesion surfaces of the active elements  103  higher. This reduces damage or the like caused by the contact of the untransferred active elements  103  with the final substrate  107  or the like.  
         [0079]    In the second embodiment, too, the tapered position control members  103  and active elements  103  enables the active elements  103  to be selectively transferred, which makes it possible to form an active matrix substrate having high position accuracy with respect to active elements.  
         [0080]    [0080]FIGS. 21 and 22 are plan views of modifications of the position control member in the first or second embodiment. For example, a position control member  301  may enclose an adhesion section  109  bonded to an active element (not shown) in such a manner that the position control member  301  has a cut in it as shown in FIG. 21. In addition, as shown in FIG. 22, a position control member  401  may enclose an adhesion section  109  bonded to an active element (not shown) in such a manner that the position control member  401  has a plurality of cuts in it as shown in FIG. 22. As in these modifications, even when the position control member encloses the active element with a cut in the member, its tapered shape enables the active elements to be selectively transferred with high position accuracy.  
         [0081]    Use of the position control member with a cut in it allows adhesive to escape through the cut even if the amount of adhesive is too large, which prevents the adhesive from adhering to the top surface of the active element. When the position control member with a cut in it is used, it is desirable to use a highly viscous adhesive to prevent the adhesive from running short because of outflow.  
         [0082]    The position control member may enclose only the side face of the active element as shown in the first embodiment. Alternatively, the position control member may enclose not only the side face of the active element but also its bottom surface as shown in the second embodiment. Furthermore, it is desirable that the shapes of the active element and position control member and their tapered shapes should not have rotation symmetry (have a shape out of rotation symmetry). The shape out of rotation symmetry prevents the active elements from being transferred in a different direction even if the transfer angle shifts a little in transferring them. Note that “a shape out of rotation symmetry” means the shape does not have rotation symmetry due to N times rotation with respect to all natural numbers N not less than two.  
         [0083]    (Third Embodiment)  
         [0084]    In a third embodiment, TFTs and storage capacitors are formed as active elements at an element formation substrate. After these active elements are transferred to an intermediate substrate, they are tapered. Then, the resulting active elements are transferred to a final substrate at which tapered position control members have been formed. Thereafter, interconnections and such are formed to make an active matrix substrate, thereby forming a liquid-crystal display.  
         [0085]    [0085]FIG. 23 is a sectional view of part of the liquid-crystal display in the third embodiment. A pixel of the liquid-crystal display of the third embodiment includes a signal line  501 , a scanning line  502 . a TFT  503 , a storage capacitor  504 , and a pixel electrode  505 . In the third embodiment, the TFT  503  and storage capacitor  504  constitute an active element  103 .  
         [0086]    The gate of the TFT  503 , which has a double gate structure to reduce off-leakage current, is connected to the scanning line  502 . One of the source and drain of the TFT  503  is connected to the signal line  501  and the other is connected to the pixel electrode  505 . The storage capacitor  504  has a gate overlap Cs structure that has a capacitance between the pixel electrode  505  and the neighboring scanning line  502  on the opposite side of the gate electrode  505 .  
         [0087]    In the pixel, to apply a voltage to a liquid crystal, a pulse on the scanning line  502  turns on the TFT  503  at a specific timing, thereby applying the image signal from the signal line  501  to the pixel electrode  505 . The storage capacitor  504  exists between the pixel electrode  505  and the above-mentioned neighboring scanning line in the off state, which enables a charge to be held.  
         [0088]    Next, a method of manufacturing active elements in the third embodiment will be explained by reference to FIGS. 24 and 25. FIG. 24 is a plan view of an active element. FIG. 25 is a sectional view taken along line  25 - 25  in FIG. 24.  
         [0089]    First, on an element formation substrate  506 , an etching stopper layer  507  is formed using alumina to a thickness of about 100 nm.  
         [0090]    On the entire surface of the etching stopper layer  507 , amorphous silicon is deposited by CVD techniques to a thickness of about 50 nm. The amorphous silicon is crystallized by excimer laser annealing techniques, thereby forming a polycrystalline silicon layer  508 . The polycrystalline silicon layer  508  is processed into island-like pieces by photolithographic techniques, thereby forming the active layers of the TFTs  503  and the lower electrodes of the storage capacitors  504 . In the polycrystalline silicon layer  508 , p-type impurities are doped.  
         [0091]    Next, a silicon oxide layer is formed on the entire surface by plasma TEOS techniques to a thickness of about 100 nm, thereby forming a gate insulating layer  509 .  
         [0092]    On the entire surface of the gate insulating layer  509 , an Mo—W alloy layer is formed by sputtering techniques to a thickness of about 300 nm. The resulting layer is patterned by photolithographic techniques, thereby forming the gate electrodes  510  of the TFTs  503 . The gate electrodes  510  is formed with the upper electrodes of the storage capacitors  504  at the same time, and is electrically connected thereto. In the polycrystalline silicon layer  508  to make the source and drain regions on both sides of the gate electrode  510 , n-type impurities are doped upto about 1×10 −12  cm −2  by ion doping techniques.  
         [0093]    On the entire surface of the gate electrode  510 , a silicon oxide layer is formed by plasma CVD techniques to a thickness of about 500 nm, thereby forming an interlayer insulating layer  511 . The interlayer insulating layer  511  in the regions corresponding to the source and drain regions of the TFT  503  and the lower electrode of the storage electrode  504 , and the interlayer insulating layer  511  in the regions corresponding to the gate insulating layer  509  and the gate electrode of the TFT  503  are patterned, thereby forming contact sections. Then, Al or the like is formed on the entire surface by sputtering techniques. The resulting layer is patterned by photolithographic techniques, thereby forming interconnections  512  to be connected to the source and drain regions and lower electrode via the contact sections.  
         [0094]    After the interconnections  512  are formed, an organic insulating layer, such as OPTMER (registered by JSR Corporation), is formed to a thickness of about 3 μm by spin coating techniques, thereby forming a protective layer  513 . The protective layer  513  in the regions corresponding to the interconnections  512  is patterned by dry etching techniques, thereby forming opening sections  514 . Thereafter, the layers around the active elements from the protective layer  513  to the etching stopper layer  507  or to the gate insulating film  509  are patterned by dry etching techniques, thereby separating the elements, which completes the active elements.  
         [0095]    The process of transferring the active elements to an intermediate substrate, tapering the side faces of the elements, and transferring the resulting elements to a final substrate at which tapered position control members have been formed is carried out as in the first embodiment. Therefore, explanation of the process will be omitted.  
         [0096]    Next, using FIGS.  23  to  25 , a method of providing interconnections on the final substrate to which the active elements have been transferred, thereby forming a liquid-crystal display will be explained.  
         [0097]    First, a first planarization layer (not shown) is formed using OPTMER by spin coating techniques on the entire surface of the final substrate to which the active elements have been transferred. The first planarization layer in the region corresponding to the opening section  514  above the gate electrode  510  is patterned, thereby making an opening. Then, a scanning line  502  to be connected to the gate electrode via the opening section  514  is formed using an Mo—W alloy by sputtering techniques.  
         [0098]    Next, on the entire surface of the first planarization layer, a second planarization layer (not shown) is formed using OPTMER by spin coating techniques. Then, the first planarization layer and second planarization layer in the regions corresponding to the source and drain regions of the TFT  503  and the opening section  514  of the lower electrode of the storage capacitor  504  are patterned, thereby making openings. Then, a signal line  501  to be connected via the opening section  514  to one of the source drain regions and a pixel electrode  505  to be connected to the other of the source and drain regions and the lower electrode are formed using Al by sputtering techniques.  
         [0099]    Then, the resulting substrate is coupled to an opposing substrate (not shown) on which an opposing electrode has been formed. Liquid crystal is injected into the couple, which is then sealed. This completes a liquid-crystal display of the third embodiment.  
         [0100]    In the third embodiment, the tapered position control members and the tapered active elements enable the active elements to be selectively transferred, which makes it possible to form a liquid-crystal display having high position accuracy with respect to active elements. Since the position control members have a low wettability with the adhesion section, the adhesion section flows to the proper position, which enables the active elements to be bonded in a good state.  
         [0101]    In the third embodiment, in the case where the ratio of the area taken up by the active elements to the total area of the final substrate is low, the active elements are formed on an element formation substrate with high density. Then, the active elements formed on the single element formation substrate are transferred to a plurality of final substrates, which makes the manufacturing processes more efficient.  
         [0102]    Furthermore, since the position accuracy is high, even when active elements are transferred to a final substrate through a plurality of transfer processes, a variation in the deviation of the storage capacitor from the proper position is small, which enables a high-image-quality liquid-crystal display with good uniformity.  
         [0103]    (Fourth Embodiment)  
         [0104]    In a fourth embodiment, sets of two TFTs are formed as active elements on an element formation substrate. After these active elements are transferred to an intermediate substrate, they are tapered. Then, the resulting active elements are transferred to a final substrate on which tapered position control members have been formed. Thereafter, interconnections and such are formed to make an active matrix substrate, which completes an organic EL display.  
         [0105]    [0105]FIG. 26 is a plan view of part of an organic EL display in the fourth embodiment. A pixel of the organic EL display of the fourth embodiment includes a signal line  601 , a scanning line  602 , a scanning TFT  603 , a driving TFT  604 , a pixel electrode  605 , an organic EL section  606 , and a power supply line  607 .  
         [0106]    In the fourth embodiment, an active element  103  has a scanning TFT  603  and a driving TFT  604 . The gate of the scanning TFT  603  is connected to the scanning line  602  and one of the source and drain of the scanning TFT  603  is connected to the signal line  601  and the other is connected to the gate of the driving TFT  604 . One of the source and drain of the driving TFT  604  is connected to the power supply line  607  and the other is connected to the pixel electrode  605 .  
         [0107]    With this pixel, to cause the organic EL section  606  to emit light, a pulse on the scanning line  602  turns on the scanning TFT  603  with specific timing, thereby applying the image signal from the signal line  601  to the gate of the driving TFT  604  via the scanning TFT  603 . Then, the current from the power supply line  607  is supplied from the pixel electrode  605  via the driving transistor  604  to the organic EL section  606 , which emits light with specific luminance.  
         [0108]    As shown in FIG. 27, each active element has two TFTs. The source and drain regions of the scanning TFT  603  and driving TFT  604  are made of a polycrystalline layer  608  by the same method as in the third embodiment. Moreover, the gate electrodes  609  of the scanning TFT  603  and driving TFT  604  are made of an Mo—W alloy or the like by the same method as in the third embodiment.  
         [0109]    In the fourth embodiment, it is possible to form an EL display which enables active elements to be selectively transferred and has high position accuracy with respect to the active elements as in the third embodiment.  
         [0110]    Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.