Method of fabricating organic LED matrices

Abstract: Items (30, 32, 34) of material are patterned on a substrate (13) by forming a layer of photoresist (14) on the substrate (13) and a layer of metal (15) on the photoresist (14). The photoresist (14) is patterned to define an opening (20) exposing a portion of the substrate (13) and the metal (15) is patterned to define an aperture (19) smaller than the opening (20) so as to divide the exposed surface of the substrate (13) into shadow areas (22, 23) and a non-shadow area (21). A first material system (31) is evaporated generally perpendicular to the aperture (19) to form a first organic light emitting diode (30) on the surface of the substrate (13) in the non-shadow area (21) and second and third material systems (33, 35) are evaporated at angles (α, β) to the aperture (19) to form second and third organic light emitting diodes (32, 34) in the shadow areas (22, 23). Passivation material (70, 72, 74) is evaporated perpendicularly onto the first diode (30) and at the angle (α, β) onto the second diodes (32, 34).

Description: Field of the Invention The present invention pertains to methods of fabricating items of one or more material systems on a substrate and passivating the items. Background of the Invention At the present time, organic light emitting diodes (LED) are becoming very popular because of the large number of materials that are available as well as the relatively low cost of the organic materials and the ease of producing the materials in a workable form. However, one of the main difficulties with organic LED displays comes in the patterning of the organic material into separate LEDs. One proposed method of patterning to form strips of organic material includes the use of vertical shadow masks, or upright walls, with organic material evaporated and angularly directed at the walls to form the separate strips. Additional information on this method of fabricating organic LED displays is disclosed in U.S. Patents No. 5,276,380, 5,294,869, 5,294,870, 5,424,560, and 4,204,222. The problem with most of these fabricating methods is that they are only viable for crude dimensions. Also, the upright walls are relatively difficult to form and position correctly. Further, because all of the various color devices are fabricated in an integrated process, many of the steps in these fabricating processes produce overlapping layers that can reduce efficiency of the final devices. Also, organic light emitting diodes are sensitive to the presence of oxygen and water vapor in the ambient air and must, therefore, be hermetically sealed for proper operation and a useful longevity. Conventional hermetic seals, including metal cans, thick patterned metal and continuous insulating barrier layers are generally too large and cumbersome for large matrices. Further, once the organic materials are in place they are sensitive to high temperatures and it is generally difficult to find low temperature dielectrics that are a good hermetic seal. Accordingly, it would be desirable to devise a fabrication process in which an organic light emitting diode display, and especially a color display, can be easily, conveniently and accurately produced and passivated. It is a purpose of the present invention to provide a new and improved method of fabricating organic LED matrices. It is also a purpose of the present invention to provide a new and improved method of passivating organic LED matrices and the like. It is another purpose of the present invention to provide a new and improved method of fabricating and/or passivating organic LED matrices which is relatively easy and inexpensive. It is still another purpose of embodiments of the present invention to provide a new and improved method of fabricating organic LED matrices which is capable of producing relatively accurate items of material for high resolution displays. It is a further purpose of embodiments of the present invention to provide a new and improved method of fabricating and/or passivating organic LED matrices which is capable of producing matrices with reduced weight and thickness. It is a further purpose of embodiments of the present invention to provide a new and improved method of fabricating and passivating organic LED matrices in one lithography and using a single integrated mask. Summary of the Invention A method in accordance with the present invention is defined in claim 1. The above problems and others are at least partially solved and the above purposes and others are realized in a method of patterning items of material on a supporting substrate. The substrate includes a base with a conductive layer thereon covered by an insulating layer except for cavities therein exposing portions of the conductive layer. The method includes forming a first layer of material on the surface of a substrate overlying the cavities in the insulating layer and a second layer of material on the first layer of material. The first layer of material is formed to define an opening therein with a first transverse dimension exposing a portion of the surface of the substrate including the cavities and the second layer of material is formed to define an aperture therethrough with a second transverse dimension, smaller than the first transverse dimension and positioned generally coaxially with one of the cavities. The second layer of material is positioned to overlie a portion of the exposed surface of the substrate in the opening so as to divide the exposed surface of the substrate into a shadow area including one of the cavities and a non-shadow area including a second of the cavities. A first material system is deposited generally perpendicular to the aperture to form an item of the first material system on the surface of the substrate in the non-shadow area and overlying the one cavity and a second material system is deposited at an angle to the aperture to form an item of the second material system on the surface of the substrate in the shadow area and overlying the second cavity. The above substrate, including the deposited items and the shadow mask, are passivated in a similar fashion. Passivation material is evaporated from a distally located source, in a direction generally perpendicular to the aperture in the shadow mask, to form a passivation cover on the deposited items. When additional items are deposited in the shadowed areas, passivation material is evaporated at an angle to the aperture, to form a passivation cover on the additional items. Dithering one of the distally located source or the substrate about the perpendicular direction and/or the angle may be required to provide complete passivation. Brief Description of the Drawings Referring to the drawings: FIGS. 1 - 5 are simplified sectional views illustrating several steps in the preparation of a mask for use in a fabrication process in accordance with the present invention; FIG. 6 illustrates another embodiment of a mask similar to FIG. 5; FIG. 7 is a simplified sectional view illustrating the deposition of color diodes of organic material systems in accordance with the present invention; FIG. 8 is a simplified sectional view of a typical organic light emitting diode; FIG. 9 is a perspective view illustrating a simplified matrix of organic light emitting diodes, portions thereof broken away; FIG. 10 is a simplified sectional view of apparatus for the deposition of an item and the passivation of the deposited item in accordance with the present invention; and FIG. 11 is a simplified sectional view of apparatus for the passivation of color diodes of organic material systems, similar to those illustrated in FIG. 7, in accordance with the present invention. Description of the Preferred Embodiments Turning now to the drawings, FIGS. 1 - 5 illustrate a series of steps in a process of fabricating items of material on a supporting substrate, in accordance with the present invention. Referring specifically to FIG. 1, a substrate 10 or base is illustrated with an upper surface. A conductive layer is positioned on the surface of substrate 10 and is patterned into strips 11 or rows in any convenient manner, such as mask and etch, mask and deposit, selective deposit, etc. A plurality of strips 11 extend parallel and horizontally in rows and each serve as one terminal for all devices in the row in a well known manner. A layer 12 of dielectric material, such as a nitride or oxide, is deposited over strips 11 and may be, for example, a blanket layer over the entire base 10. Cavities 12A, 12B, and 12C are defined in layer 12 by masking and etching, or any other convenient method, to expose portions of the surface of strips 11. As will be explained in more detail presently, the size of cavities 12A, 12B, and 12C is a large factor in the current carrying characteristics of the items to be fabricated on the substrate. Accordingly, as will be understood, the size and shape of cavities 12A, 12B, and 12C can be adjusted during the definition to compensate for differences in conduction or emission characteristics-of the items to be fabricated. Cavities 12A, 12B, and 12C can have substantially any desired shape (in the plane of the layer 12), including round, square, oval, etc. In this specific embodiment, the entire structure illustrated in FIG. 1 is considered a supporting substrate 13 for purposes of the remaining disclosure. It should be understood that for purposes of this disclosure the term "supporting substrate" includes any structure provided to support the items being fabricated and may, for example, include a glass plate, a quartz plate, a plastic plate, a semiconductor chip, a semiconductor chip with integrated circuits formed thereon, a semiconductor chip with additional layers of material formed thereon, etc. Also, the structure of FIGS. 1- 5 represents a two dimensional matrix including rows and columns of devices (e.g. pixels) with a single device broken out and explained to simplify this disclosure. Those skilled in the art will also understand that the specific matrix illustrated is for purposes of explanation and many changes and modifications can be devised. Referring now to FIG. 2, a layer 14 of removable material, such as undeveloped photoresist or the like, is positioned on surface 11 of supporting substrate 13 by any convenient method. A layer 15 of sufficiently rigid material, such as metal, is positioned on layer 14. Generally, both layers 14 and 15 are simply blanket layers that cover supporting substrate 13 entirely and are deposited in any of the many well known methods which are compatible with the specific method and equipment being utilized. A layer 16 of photoresist is deposited on the surface of layer 15 and patterned by any convenient method to form a mask, illustrated in FIG. 3. Layer 16 has defined therein an opening 17 which exposes a portion of the surface of layer 15. The exposed portion of layer 15 is then etched to form an aperture 19 therein, as illustrated in FIG. 4, by any convenient etching material, which generally is determined by the material composing layer 15. Aperture 19 has a transverse dimension W 1 greater than the transverse dimension of cavity 12A and approximately equal to the width of one of the items of material to be deposited, which will be explained presently. The dimension perpendicular to the plane of the paper depends upon the shape of cavities 12A, 12B, and 12C and may be, for example, the same as W 1 if cavities 12A, 12B, and 12C are square. Once aperture 19 is properly defined in layer 15, layer 16 is exposed and developed away along with portions of layer 14 not covered by layer 15. Portions of layer 14 are then removed from under layer 15, as illustrated in FIG. 5, by any convenient method, such as oxygen plasma, chemical etching, expose and develop, etc. The lateral undercutting of layer 15 defines an opening 20 in layer 14, having a transverse dimension W 2 greater than the transverse dimension W 1 of aperture 19, exposing a portion of the surface of supporting substrate 13 including cavities 12A, 12B, and 12C. It should be noted that layer 15 must be sufficiently rigid to maintain the overhang therein and to withstand subsequent processing, to be explained. While layer 15 could be a variety of different metals or combinations of metals, one specific example of a metal that has adequate characteristics and is easy to work with is gold. In this embodiment, transverse dimension W 2 of opening 20 is chosen to provide a non-shadow area 21 surrounding cavity 12A, a shadow area 22 surrounding cavity 12B, and a shadow area 23 surrounding cavity 12C. Further, areas 22 and 23 are slightly larger than area 21 for purposes that will become apparent as this description proceeds. In a slightly different embodiment, a structure (not shown) similar to that of FIG. 5 can be constructed by laying down a portion of photoresist 20' approximately the dimensions of opening 20, as illustrated in FIG. 6. Metal is then plated on each side of the photoresist and partially over the upper surface to define an aperture 19'. Aperture 19' is conveniently defined because the metal will extend onto the upper surface of photoresist 20' a distance L approximately equal to the height (H+L) of the metal above photoresist 20'. Photoresist 20' is then exposed and developed away to leave an opening and overhang similar to that illustrated in FIG. 5. In this structure a first layer 14' of material defining the opening and a second layer 15' of overhanging material overhang defining aperture 19' are formed of the same material. Referring now to FIG. 7, continuing steps in a process of fabricating items of material on supporting substrate 13 are illustrated. Utilizing the shadow mask of FIG. 5, an item 30 of a first material system is deposited over cavity 12A in area 21 of opening 20 by directing the material from a source 31 generally perpendicular to aperture 19. Because aperture 19 is larger than cavity 12A, item 30 will extend outwardly beyond cavity 12A onto the surface of layer 12 and, therefore, if item 30 includes a plurality of layers of material (e.g. an organic diode) the layers will not be shorted by conductive layer 11. An item 32 of a second material system is deposited over cavity 12B in area 22 of opening 20 by directing the material from a source 33 at a first angle α to aperture 19. Also, an item 34 of a third material system is deposited over cavity 12C in area 23 of opening 20 by directing the material from a source 35 at a second angle β to aperture 19. In a specific example, the material of sources 31, 33, and 35 are evaporated in a vacuum chamber at a distance from aperture 19 sufficiently far so that the particles emanating from sources 31, 33, and 35 appear to move toward aperture 19 and the target (supporting substrate 13) in generally parallel lines (similar to a point or line light source, or collimated light). It will be understood by those skilled in the art that angles α and β can be accurately determined by knowing the transverse dimension W 1 of aperture 19 and the height h above the surface 11 of supporting substrate 13. Generally, angles α and β will be in a range of approximately 30° to 50°, although this range and/or the specific angle can be selected or predetermined by adjusting the thickness of layer 14. Also, the transverse dimension W 1 of aperture 19 determines the width of item 30 and it is desirable to make both items 32 and 34 approximately the same width as item 30, even though the dimensions of cavities 12A, 12B, and 12C may be different. Thus, it can be seen that by accurately determining the height h, items 30, 32, and 34 are positioned in opening 20 in parallel spaced apart relationship with a space therebetween sufficient to prevent electrical interconnection. It should be understood that the order in which items 30, 32, and 34 are deposited is not crucial and the order described either in this disclosure or in the claims in not intended in any way to limit the scope of this invention. In a preferred embodiment, each material system forming items 30, 32, and 34 includes materials to form an organic light emitting diode. A sectional view of an organic light emitting diode 35, which may be utilized for this purpose, is illustrated in FIG. 8. Light emitting diode 35 is formed on substrate 10 with conducting layer 11 as a first electrode. A hole transporting layer 36 is positioned on layer 11, a light emitting layer 37 is positioned on layer 36, an electron transporting layer 38 is positioned on layer 37, and a second terminal is formed by placing a conducting layer 39 on layer 38, to completes the diode. Those skilled in the field of organic light emitting diodes will understand that various combinations of hole injecting and transporting zones and electron injecting and transporting zones can be utilized to form diodes from different materials. It is, however, generally necessary to utilize as a minimum two electrodes and a light emitting layer therebetween. In the structure of FIG. 7, source 31 is utilized to deposit a material system resulting in a green light emitting organic diode. Similarly, source 33 is utilized to deposit a material system resulting in a red light emitting organic diode and source 35 is utilized to deposit a material system resulting in a blue light emitting organic diode. It will of course be understood that the various sources 31, 33, and 35 could be interchanged or substituted with other sources, if desired or convenient. Thus, the three items 30, 32 and 34 can be utilized as a single pixel in a full color display. A perspective view of the matrix is illustrated in FIG. 9, showing how such three color pixels are separated into columns. It will of course be understood that only two items and two colors could be used in simpler matrices or all of the items 30, 32, and 34 can be formed to generate the same color light (e.g. a monochrome display). As will be understood by those skilled in the art, the amount of electrical current which can be conducted through organic light emitting diode 35 (and many other electrical items) is dependent upon the area of layer 36 in contact with conductive layer 11. Also, it will be understood by those skilled in the art that all color light emitting diodes do not emit with the same intensity. Thus, it should be noted that the present invention is especially well adopted to compensate for such exigencies, since the horizontal dimensions of cavities 12A, 12B, and 12C can easily be selected to provide different amounts of current to each diode to allow for differences in emission intensity. Referring specifically to FIG. 10, a method of passivating an item of material positioned on a supporting substrate is illustrated. While the item to be passivated may be virtually any material or electronic device, in this specific example the item is a light emitting diode 50 formed on a supporting substrate 51, which in this embodiment is a light transmitting material such as glass or the like. Diode 50 includes a first conductive strip of material 52, which may be for example indium-tin-oxide (ITO) or the like, positioned on the upper surface of substrate 51. A dielectric layer 53, of some insulating material such as silicon nitride or the like, is positioned on material 52 and patterned to define a restraining opening for diode 50. As previously described in conjunction with FIG. 5 a shadow mask 60 is formed over the restraining opening. A first layer 61 of photoresist is deposited on layer 53 and a metal layer 62 is deposited on layer 61. A second layer of photoresist (not shown) is deposited on the surface of layer 62 and patterned by any convenient method to form a mask. The second layer of photoresist has defined therein an opening which is approximately the desired width of diode 50 and directly overlying the restraining opening in layer 53. The exposed portion of metal layer 62 is then etched to form an aperture 65 therein, as illustrated in FIG. 10. Once aperture 65 is properly defined in layer 62, the layer of photoresist is exposed and developed away along with portions of layer 61 not covered by layer 62. Portions of layer 61 are then removed from under layer 62, as illustrated in FIG. 10, by any convenient method, such as oxygen plasma, chemical etching, expose and develop, etc. Utilizing the shadow mask of FIG. 10, diode 50 is then formed by depositing a layer 54 of organic light emitting material on conductive material 52 in the restraining opening. A layer 55 of metal, generally n-type conductive metal, is positioned on layer 54 to complete diode 50. A layer 66 of passivation material is deposited on diode 50 by directing the material from a source 67 generally perpendicular to aperture 65. In a specific example, the material of source 67 is evaporated in a vacuum chamber at a distance from aperture 65 which may be similar to or somewhat closer than that described previously for depositing the parallel items. Also, source 67, or substrate 51 if convenient, is dithered transversely, as indicated by arrow 68, (or rotated) to ensure a complete coating of material over the entire surface of diode 50. The specific amount of dithering and the distance over which the dithering occurs depends upon the height of diode 50 and the transverse dimension of aperture 65. Thus, diode 50 is fabricated and passivated utilizing the same shadow mask and with no added alignment or masking requirements. Referring now to FIG. 11, the structure of FIG. 7 is illustrated with items 30, 32, and 34 already deposited. Utilizing the shadow mask which is already in place, a first passivation layer 70 is deposited over item 30 by directing the material from a distally positioned source 71 generally perpendicular to aperture 19. A passivation layer 72 is deposited over item 32 by directing the passivation material from a source 73 at a first angle α to aperture 19. Also, a passivation layer 74 is deposited over item 34 by directing the passivation material from a source 75 at a second angle β to aperture 19. It will of course be understood that passivation sources 71, 73, and 75 can simply replace green, red, and blue sources 31, 33, and 35. As described above, passivation sources 71, 73, and 75 are dithered slightly about the perpendicular, angle α, and angle β, respectively, to ensure complete coverage and passivation of items 30, 32, and 34. Once the passivation is complete, layer 14 can be partially or completely dissolved and layer 15 can simply be lifted off. In some applications, layers 14 and 15 can be lifted off simultaneously and with no dissolving required, by utilizing, for example, adhesive tape or the like. The single mask is utilized for both the patterning of the matrix of organic diodes onto the supporting substrate and the passivation of the organic diodes. Since the passivation layers 70, 72, and 74 do not contact each other, they can be formed of a hermetically sealing metal, which metal can also be used as the second electrical terminal for each organic diode. Thus, a new and improved method of fabricating single items or complete organic LED matrices has been disclosed and of passivating the single item or complete organic LED matrices with one lithographic step. The new and improved method of fabricating and/or passivating items or organic LED matrices is relatively easy and inexpensive, and is capable of producing relatively accurate items of material for high resolution displays. Further, the new and improved method of fabricating and/or passivating organic LED matrices is capable of producing matrices with reduced weight and thickness. As a further major advantage, the patterning and passivation allows the use of solvent for lift off of the single mask (or simply lift off) so that no complicated and damaging steps, such as etching and the like, are involved. Also, the complete fabrication and passivation is performed without involving any high temperature processes after the deposition of the organic materials. While we have shown and described specific embodiments of the present invention, further modifications and improvements will occur to those skilled in the art. We desire it to be understood, therefore, that this invention is not limited to the particular forms shown and we intend in the appended claims to cover all modifications that do not depart from the spirit and scope of this invention.

Claims: A method of forming, on a supporting substrate, items of material systems including organic light emitters, including the step of providing a supporting substrate (13), characterized by the steps of: forming a first layer of removable material (14) on the substrate (13) and a second layer of metal (15) on the layer of removable material (14), the layer of removable material (14) defining an opening (20) therein with a first transverse dimension (W 2 ) exposing a portion of the substrate and the layer of metal (15) defining an aperture (19) therethrough with a second transverse dimension (W 1 ), smaller than the first transverse dimension (W 2 ), the layer of metal (15) overlying a portion of the substrate (13) in the opening (20) so as to divide the exposed substrate into a shadow area (22, 23) and a non-shadow area (21); forming a first material system (31) generally perpendicular to the aperture (19) to form an item (30) of the first material system (31) including an organic light emitter on the substrate (13) in the non-shadow area (21) and forming a second material system (33, 35) at an angle (α, β) to the aperture (19) to form an item (32, 34) of the second material system (33, 35) including an organic light emitter on the substrate (13) in the shadow area (22, 23); and removing the first layer (14) of removable material and the second layer (15) of metal on the layer (14) of removable material. A method of forming items of material on a supporting substrate as claimed in claim 1 wherein the step of providing the supporting substrate (13) includes providing a base (10) with a conductive layer (11) positioned thereon and an insulating layer (12) positioned on the conducting layer (11) and having cavities (12A, 12B, 12C) with selected horizontal dimensions defined therethrough to expose portions of the conductive layer (11). A method of forming items of material on a supporting substrate as claimed in claim 2 wherein the step of providing the supporting substrate (13) further includes selecting the horizontal dimensions of the cavities (12A, 12B, 12C) to determine the relative amounts of electrical conduction of the items (30, 32, 34). A method of forming items of material on a supporting substrate as claimed in claim 3 wherein forming the items (30, 32, 34) each include depositing organic light emitter material (37) on the exposed portions of the conductive layer (11) in the cavities (12A, 12B, 12C) and portions of a second layer (39) of conductive material on the organic light emitter material (37) in overlying relationship to each of the cavities (12A, 12B, 12C). A method of forming items of material on a supporting substrate as claimed in claim 4 wherein depositing the organic light emitter material (37) on the exposed layer (11) of conductive material and the second layer (39) of conductive material on the organic light emitter material (37) further includes depositing one of a hole transport layer (36) between the exposed portions of conductive material (11) and a layer of organic electron emitter material or an electron transport layer (38) between the second layer (39) of conductive material and the layer (37) of organic light emitter material. A method of forming items of material on a supporting substrate as claimed in claim 1 including, subsequent to the step of forming items (30, 32, 34), the steps of depositing passivation material generally perpendicular to the aperture (19) to form a passivation cover (70) on the item (30) in the non-shadow area (21) and depositing passivation material (73,75) at an angle (α, β) to the aperture (19) to form a passivation cover (72, 74) on the items (32, 34) in the shadow area (22, 23). A method of forming items of material on a supporting substrate as claimed in claim 6 wherein the steps of depositing passivation material generally perpendicular to the aperture (19) and depositing passivation material at an angle (α, β) to the aperture (19) each include dithering deposition sources (71, 73, 75) about the perpendicular and the angle (α, β) to form the passivation covers (70, 72, 74). A method of forming items of material on a supporting substrate as claimed in claim 1 wherein the items comprise red, blue, and green organic material.

Inventors: LEE HSING-CHUNG, SHIEH CHAN-LONG, LEE, HSING-CHUNG, SHIEH, CHAN-LONG
Applicants: MOTOROLA INC, MOTOROLA, INC.
Application year: 1996
Main classification: H05B33
IPC codes: H01L51, G09F9