Method of manufacturing an electroluminescence display device

ABSTRACT

Substrates suitable to manufacture and products of a thin film semiconductor device are provide, by at first preparing a manufacturing substrate having a characteristic of being capable of enduring a process for forming a thin film transistor and a product substrate having a characteristic of being suitable to direct mounting of the thin film transistor in a preparatory step, then applying a bonding step to bond the manufacturing substrate to the product substrate for supporting the product substrate at the back, successively applying a formation step to form at least a thin film transistor to the surface of the product substrate in a state reinforced with the manufacturing substrate and, finally, applying a separation step to separate the manufacturing substrate after use from the product substrate.

INFORMATION

DETAILED DESCRIPTION OF THE INVENTION

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of this invention are to be described in detail with reference to the drawings. FIGS. 1A and 1B are an example of schematic step charts illustrating a method of manufacturing a thin film semiconductor device according to this invention. At first, as shown in FIG. 1A, a manufacturing substrate having characteristics durable to the process for forming a thin film transistor and a product substrate having characteristics suitable to direct mounting of a thin film transistor are prepared. In the preparatory step, a manufacturing substrate , for example, made of an inorganic material, such as glass, and a product substrate made of an organic material, such as plastic, are prepared. In this embodiment, non-alkali glass is used as the manufacturing substrate . The heat resistance of the non-alkali glass is about 500° C. The standard thickness for the manufacturing substrate is, for example, 0.7 mm. If it is reduced to 0.5 mm, there is no particular problem in view of the manufacturing process. In this embodiment, non-alkali glass is used but, instead, metal plate, such as of stainless steel, plastic plate, quartz and the like, can be also be used. On the other hand, for the product substrate , it is necessary to have a heat resistance capable of withstanding the processing temperature of a thin film transistor, and it is necessary that the substrate is thinner and lighter compared with the manufacturing substrate . In this embodiment, a plastic material is used with a thickness from about 0.1 mm to 0.5 mm. Particularly, polyether sulfone resin (PES), polyethylene terephthalate resin or ARTON resin of excellent heat resistance is used. The polyether sulfone resin has a heat resistance as high as about 250° C. (ARTON is a trademark of Japan Synthetic Rubber Co. Ltd.). The plastic film used for the product substrate may be a single layer and, depending on the case, has a laminate structure. Particularly, when this is used for a reflection type display and not a transmission type display, a metal plate can be used instead of the plastic material. However, when the metal plate is used, the surface has to be insulated. For example, when an aluminum plate is used for the product substrate , the surface has to be previously covered with alumina.

Successively, as shown in FIG. 1A, the manufacturing substrate is bonded to the product substrate in order to support the product substrate at the back. In the bonding step, the manufacturing substrate is bonded to the product substrate by using an adhesive coated, for example, in a releasable state. In this embodiment, a heat resistant resin is coated as the adhesive . Since the resin has to endure heat upon forming the thin film transistor, a polyimide, silicon or TEFLON-type resin is used (TEFLON is a trademark of DuPont). However, when the processing temperature for the thin film transistor is lowered, various adhesives can be used. Coating is conducted by spin coating or printing a liquid material. Instead, there is a method of appending a film-shaped adhesive to one of the substrate surfaces and then coating by heat melting the same. The adhesive is not restricted only to organic material, but silicon, germanium and, further, metal (lead, aluminum, molybdenum, nickel or tin) may also be used. When such a material is used, it is formed as a film by a sputtering or the like to one of the substrates and bonded to the other of the substrates while being melted under laser irradiation or the like. In the case of using an aluminum plate as the product substrate , a product substrate made of aluminum or the like and a manufacturing substrate made of glass can be bonded directly by using optical energy, such as that of laser.

Successively, as shown in FIG. 1B, a thin film device, such as a thin film transistor , is integrated and formed on the surface of the product substrate in a state reinforced with the manufacturing substrate . Specifically, after forming film of a metal, such as tantalum or molybdenum, by a sputtering method or the like at first, it is patterned by isotropic dry etching to fabricate into a gate electrode . Successively, SiO2 is deposited, for example, to a thickness of 100 to 200 nm by a plasma CVD method (PE-CVD method) to form a gate insulation film for covering the gate electrode . Amorphous silicon is deposited further thereon to a thickness, for example, of 20 to 60 nm to form a semiconductor thin film . The insulation film and the semiconductor thin film can be grown continuously without breaking vacuum in one identical film forming chamber. Subsequently, the semiconductor thin film is crystallized, for example, by irradiating an XeCl excimer laser beam at a wavelength of 308 nm for an extremely short period of time. The amorphous silicon is melted by the energy of the laser beam and forms polycrystal silicon when solidified. Since the irradiation time of the laser beam is extremely short, it causes no damages to the product substrate . Subsequently, resist is coated on the semiconductor thin film and back-face exposure is applied by using a light shielding gate electrode as a mask to obtain a mask aligned with the gate electrode in self-alignment. Then, impurities (for example, phosphorus) are implanted by way of the mask by an ion-doping method into the semiconductor thin film at a relatively low concentration. Further, after covering the mask and the peripheral thereof with another photoresist, impurities (for example, phosphorus) are implanted at a relatively high concentration by an ion doping method to the semiconductor thin film . A source region S and a drain region D are thus formed. Further, a channel region Ch previously implanted with P-type impurities (for example, boron) for threshold value control is left just above the gate electrode . Between the channel region Ch and the source region S or the drain region D, an LDD region implanted with N-type impurities, such as phosphorus, at a relatively low concentration is left. Subsequently, unnecessary photoresist is removed. The ion-doping method is a method of doping ions in a plasma state under electric field acceleration all at once into the semiconductor thin film that enables short time processing. Successively, a laser beam is irradiated again for activating the doped atoms. This is the same method as for crystallization, but a weak energy may suffice since there is no requirement for growing the crystals. Then, SiO2, for example, is deposited to form an interlayer film for insulation between interconnections. After making a contact hole in the interlayer film , metal aluminum or the like is deposited by sputtering, patterned to a predetermined shape and fabricated into interconnections . In the subsequent procedures, in a case of manufacturing a thin film semiconductor device for use in an active matrix type liquid crystal display, a protection film or a pixel electrode is formed optionally. Further, an assembling step is applied by bonding an opposing substrate previously formed with opposing electrodes to the product substrate formed with the pixel electrode at a predetermined distance and injecting liquid crystals into the gap. On the other hand, in the case of using the thin film semiconductor device for an active matrix type organic electroluminescence display, an organic electroluminescence device is previously formed on the pixel electrode .

Finally, as shown in FIG. 2, a separation step of separating the used manufacturing substrate from the product substrate is applied. Specifically, both of the substrates can be separated by dissolving adhesives interposed between the manufacturing substrate and the product substrate in a solvent. The solvent used is different depending on the material of the adhesives. Generally, the adhesive layer is extremely thin and takes much time until the solvent intrudes. Then, it is effective to promote the dissolution of the adhesives by using energy, such as supersonic waves or laser beams. In the previous bonding step, it is not necessary to uniformly coat the adhesive over the entire surface of the substrate. Rather, dissolution using the solvent is facilitated by coating the adhesives discretely. As described above, since only the product substrate made of the plastic material or the like is left to the final product, a display light in weight and reduced in the thickness can be obtained. In the case of preparing a liquid crystal display, the assembling step described above may be applied after separation of the manufacturing substrate .

In the embodiment described above, a thin film transistor of the bottom gate structure has been formed on the product substrate . Instead, a thin film transistor of a top gate structure may also be integrated and formed. FIG. 3 shows this embodiment. For easy understanding, corresponding reference numerals are attached to those portions corresponding to the previous embodiment shown in FIG. and FIG. . As shown in the drawing, in the thin film transistor of the top gate structure, the gate electrode is formed by way of the gate insulation film on the semiconductor thin film . In this embodiment, a moisture proof buffer film is formed between the product substrate and the thin film transistor. The buffer film comprises a silicon oxide film or a silicon nitride film formed by a chemical vapor deposition (CVD) or sputtering method, which stops water passing through the product substrate and suppresses impurities from intruding into the product substrate . In the case of using a plastic material for the product substrate , it is sometimes preferred to form a buffer film particularly as a moisture proof countermeasure.

FIG. 4 is a schematic perspective view illustrating an example of an active matrix type liquid crystal display device assembled by using a thin film semiconductor device according to this invention as a driving substrate. The liquid crystal display device has a panel structure possessing liquid crystals between a product substrate and an opposed substrate . A pixel array area and a peripheral circuit area are integrated and formed by the same thin film transistor as described above on the product substrate . The peripheral circuit area is divided into a vertical scanning circuit and a horizontal scanning circuit . Further, terminal electrodes for external connection are also formed on the upper end of the product substrate . Each of the terminal electrodes is connected by way of interconnections to the vertical scanning circuit and the horizontal scanning circuit . Gate interconnections and signal interconnections crossing to each other are formed in the pixel array area. The gate electrode is connected with the vertical scanning circuit while the signal interconnection is connected with the horizontal scanning circuit . A pixel electrode and a thin film transistor for driving the same are formed at the intersection between both of the interconnections and . On the other hand, counter electrodes are formed although not illustrated to the inner surface of the opposing substrate. When plastic material is used for the product substrate and identical plastic material is used as the opposing substrate , a panel extremely light in weight and resistant to damages can be obtained.

FIG. 5 is a schematic fragmentary cross-sectional view illustrating an active matrix type electroluminescence display device assembled using a thin film semiconductor device according to this invention as a driving substrate. In this embodiment, an organic electroluminescence device OLED is used as a pixel. The OLED comprises an anode A, an organic layer and a cathode K stacked successively. The anode A is isolated on every pixel made, for example, of chromium and basically is light reflecting. The cathode K is connected in common between each of the pixels, has a laminate structure, for example, of a metal layer and a transparent conduction layer and is basically light permeable. When a forward voltage (at about 10 V) is applied between the anode A and the cathode K of the OLED of such a structure, injection of carriers, such as electrons or positive holes, occurs and light emission is observed. It is considered that the operation of the OLED is light emission caused by exciters formed with holes injected from the anode A and electrons injected from the cathode K.

On the other hand, a thin film transistor for driving the OLED comprises a gate electrode formed on a product substrate made, for example, of a plastic material, a gate insulation film stacked thereon and a semiconductor thin film stacked above the gate electrode by way of the gate insulation film . The semiconductor thin film comprises, for example, a silicon thin film crystallized by laser annealing. The thin film transistor comprises a source region S, a channel region Ch and a drain region D as a passage for the current supply to the OLED. The channel region Ch situates just above the gate electrode . The thin film transistor having the bottom gate structure is covered with an interlayer film , on which interconnections are formed. The film of the OLED described above is formed on them by way of another interlayer film . The anode A of the OLED is electrically connected by way of the interconnections to the thin film transistor .

As has been described above, this invention comprises a structure in which a manufacturing substrate having the characteristic of being able to endure the process for forming the thin film transistor and a product substrate having the characteristic of being suitable to direct mounting of the thin film transistor are used, the manufacturing substrate is bonded to the product substrate for supporting the product substrate at the back, at least the thin film transistor is formed on the surface of the product substrate in a state reinforced with the manufacturing substrate, and the manufacturing substrate after use is separated from the product substrate. In the manufacturing steps, since the thin film transistor is integrated and formed on the substrate reinforced with bonding, handling for the substrate, etc. can be facilitated to contribute to the stablization of the process. On the other hand, since the manufacturing substrate after use is separated in a stage where the product is completed, the product itself is reduced in weight and thickness. In addition, the separated manufacturing substrate can further be utilized again in the thin film transistor manufacturing process, making it possible for recycling of resources.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are step charts illustrating a method of manufacturing a thin film semiconductor device according to this invention;

FIG. 2 is a step chart illustrating a method of manufacturing a thin film semiconductor device according to this invention;

FIG. 3 is a fragmentary cross-sectional view illustrating another embodiment of a thin film semiconductor device according to this invention;

FIG. 4 is a perspective view illustrating a liquid crystal display device according to this invention; and

FIG. 5 is a schematic cross-sectional view illustrating an electroluminescence display device according to this invention.

RELATED APPLICATION

This application is a divisional application of application Ser. No. 10/259,454, filed on Sep. 30, 2002, which in turn is a divisional application of application Ser. No. 09/808,957, filed on Mar. 16, 2001.

CLAIMS

1. A method of manufacturing an electroluminescence display device comprising: a preparatory step of preparing a manufacturing substrate having a characteristic capable of enduring a process for forming a thin film transistor and a product substrate having a characteristic suitable to direct mounting of the thin film transistor, said manufacturing substrate being made of an inorganic material and said product substrate being made of an organic substrate, a bonding step of bonding the manufacturing substrate to the product substrate for supporting the product substrate, a formation step of forming at least a thin film transistor and an electroluminescence device to surface of the product substrate in a state bonded with the manufacturing substrate, a moisture proof film being formed on the surface of the product substrate and the thin film transistor and electroluminescence device being formed on the moisture proof film, and a separation step of separating the manufacturing substrate from the product substrate after the formation step.

2. A method of manufacturing an electroluminescence display device as claimed in claim 1, wherein the bonding step comprises bonding the manufacturing substrate to the product substrate by using adhesives coated in a releasable state.

3. A method of manufacturing an electroluminescence display device as claimed in claim 1, wherein said manufacturing substrate is a glass substrate.

4. A method of manufacturing an electroluminescence display device as claimed in claim 1, wherein said metal is aluminum.

5. A method of manufacturing an electroluminescence display device as claimed in claim 1, wherein said organic material is a plastic.

6. A method of manufacturing an electroluminescence display device as claimed in claim 1, wherein a moisture-proof buffer film is formed between said product substrate and said thin film transistor.

7. A method of manufacturing an electroluminescence display device as claimed in claim 1, wherein said plastic is from the group comprising polyether sulfone resin, polyethylene terephthalate resin and ARTON resin.

8. A method of manufacturing an electroluminescence display device as claimed in claim 1, wherein said adhesive layer is from the group comprising a polyimide, TEFLON resin, silicon, germanium and metal.

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