Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
1999-10-22
2004-03-02
Dudek, James (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
Reexamination Certificate
active
06700631
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
present invention relates to a method of separating a thin film device, a method of transferring a thin film device, a thin film device, an active matrix substrate and a liquid crystal display device.
2. Background Art
For example, the production of a liquid crystal display using a thin film transistor (TFT) is carried out through the step of forming the thin film transistor on a substrate by CVD or the like. The step of forming the thin film transistor on the substrate is accompanied by high-temperature treatment, and it is thus necessary to use a substrate made of a material having excellent heat resistance, i.e., high softening point and melting point. Therefore, at present, quartz glass is used as a substrate which can resist a temperature of about 1000° C., and heat-resistant glass is used as a substrate which can resist a temperature of about 500° C.
As described above, the substrate on which the thin film is mounted must satisfy conditions for producing the thin film device. Namely, the substrate used is determined to necessarily satisfy conditions for producing the device mounted thereon.
However, in consideration of only steps after completion of the substrate on which the thin film device such as TFT is mounted, the above-described substrate is not necessarily preferred.
For example, in cases in which the substrate is passed through the production process accompanied with high-temperature treatment, as described above, a quartz substrate, a heat-resistant glass substrate, or the like is used. However, such a substrate is very expensive, and thus causes an increase in product cost.
A glass substrate also has the property that it is heavy and brittle. In a liquid crystal display used for a portable electronic device such as a palm top computer, a portable telephone, or the like, a substrate is preferably as inexpensive as possible, lightweight, resistant to deformation, and hard to break even by dropping. However, in fact, the glass substrate is heavy and weak against deformation, and has the possibility of breakage by dropping.
Namely, there is a gap between the limits caused by production conditions and the preferable characteristics required for products, thereby causing great difficulties in satisfying both the conditions and characteristics.
SUMMARY OF THE INVENTION
Therefore, a technique is proposed in which a thin film device is formed on a first substrate by a conventional process, then separated from the first substrate and transferred to a second substrate. Thus, a separation layer is formed between the first substrate and the thin film device as a layer to be transferred. For example, this separation layer is irradiated with light to separate, from the first substrate, the thin film device as the layer to be transferred, which is then transferred to the second substrate.
As a result of experiments, it was found that in some cases of separating the thin film device from the first substrate, a separation phenomenon does not sufficiently occur in the separation layer only by irradiating the separation layer with light, for example.
As a result of intensive research, it was also found that whether or not the separation phenomenon readily occurs depends upon the properties of the separation layer.
There was also a problem in which the laminate relation of the layer to be transferred to the first substrate used in production of the layer to be transferred differs from the laminate relation of the layer to be transferred to the second substrate to which the layer to be transferred is transferred.
Accordingly, an object of the present invention is to provide a method of separating a thin film device in which before the step of producing a separation phenomenon in a separation layer, the separation layer is securely brought in an easy-to-separate state to accelerate separation of the thin film device from a substrate, and a thin film device, an active matrix substrate and a liquid crystal display device, which use the separation method.
Another object of the present invention is to provide a method of transferring a thin film device which can make the laminate relationship of a layer to be transferred to a substrate used in producing the layer to be transferred coincide with the laminate relationship of the layer to be transferred to a transfer material to which the layer to be transferred is transferred.
(1) The present invention provides a method of separating a thin film device comprising:
the first step of forming a separation layer on a substrate;
the second step of forming a thin film device on the separation layer; and
the third step of producing a separation phenomenon in the separation layer and/or the interface to separate the substrate from the separation layer;
wherein the ion implantation step of implanting ions into the separation layer is provided before the third step.
The separation layer having, for example, the property of absorbing light is provided on the substrate, for example, such as a quartz substrate having high reliability in device manufacture, and the thin film device such as TFT is formed on the substrate. Preferably, the thin film device is then joined to a desired transfer material with, for example, an adhesive layer held therebetween. Then, the separation layer is irradiated with light, for example, to produce a separation phenomenon in the separation layer. As a result, the substrate can be peeled from the substrate, for example, by applying force to the substrate.
At this time, ions are implanted into the separation layer before the separation step to cause the significant separation phenomenon in the separation layer in the separation step, thereby permitting secure separation of the thin film device from the substrate.
In this method, ions are previously implanted into the separation layer to exert the action defined below in any one of (2) to (5), causing the significant separation phenomenon in the separation layer.
(2) The third step preferably includes the step of gasifying the ion implanted into the separation layer. This gasification of the ion in the separation layer causes internal pressure in the separation layer to accelerate the separation phenomenon.
(3) The third step described above in (2) preferably includes the step of irradiating the separation layer with light. This can gasify the separation ion by the light. At this time, irradiation of the substrate from the rear side thereof can decrease the quantity of light incident on the thin film device layer and prevent deterioration in characteristics thereof.
(4) In the ion implantation step, bonds of atoms or molecules which constitute the separation layer are preferably cut by the ions to previously damage the separation layer. This accelerates the separation phenomenon in the separation layer, which is caused in the subsequent separation step.
(5) In the ion implantation step, the characteristics of the separation layer are preferably changed to previously weaken adhesion between the separation layer and the substrate. This facilitates the separation phenomenon in the separation layer, which is caused in the subsequent separation step.
(6) The second step preferably includes the thin film transistor forming step of forming a thin film transistor, the thin film transistor forming step preferably includes a channel layer forming step, and the ion implantation step is preferably performed after the channel layer forming step.
The channel forming step is a high-temperature treatment step, as compared with the other steps. Therefore, if the ions for accelerating the separation phenomenon are implanted before the channel forming step, the ions are possibly released from the separation layer during subsequent high-temperature treatment.
(7) The thin film transistor forming step includes a channel pattern forming step after the channel layer forming step, and the ion implantation step is preferably performed after the channel pattern forming step.
For example, even when the ions for accelerating the separation phenomen
Inoue Satoshi
Shimoda Tatsuya
Dudek James
Seiko Epson Corporation
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