Semiconductor device manufacturing: process – Bonding of plural semiconductor substrates – Subsequent separation into plural bodies
Reexamination Certificate
1999-02-26
2003-02-18
Lee, Eddie (Department: 2815)
Semiconductor device manufacturing: process
Bonding of plural semiconductor substrates
Subsequent separation into plural bodies
C438S455000, C438S464000, C438S149000
Reexamination Certificate
active
06521511
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a thin film device transfer method, a thin film device, a thin film integrated circuit device, an active matrix board, a liquid crystal display, and an electronic apparatus.
BACKGROUND ART
In the manufacture of a liquid crystal display comprising thin film transistors (TFTs), for instance, thin film transistors are formed on a substrate through CVD or any other process. Since a fabrication process for forming thin film transistors on a substrate involves high-temperature treatment, a substrate made of a heat-resistant material is required, i.e., the substrate material must have a high softening point and a high melting point. At present, therefore, quartz glass is used as a material to provide a substrate capable of withstanding up to approx. 1000° C., or heat-resistant glass is used as a material to provide a substrate capable of withstanding up to approx. 500° C.
As mentioned above, the substrate on which thin film devices are to be mounted must satisfy conditions required for fabricating the thin film devices. Namely, the kind of substrate is determined to meet fabrication conditions required for the devices to be mounted thereon.
In view of a subsequent phase to be taken after thin film devices such as TFTs are formed, the substrate indicated above are not always preferable.
Where a fabrication process involving a high-temperature treatment is carried out, a quartz glass or heat-resistant glass substrate is used as exemplified above. However, the quartz glass or heat-resistant glass substrate is very expensive, resulting in an increase in product cost.
The glass substrate is also disadvantageous in that it is relatively heavy and fragile. A liquid crystal display for use in a portable electronic apparatus such as a palm-top computer or mobile telephone should be as inexpensive as possible, light in weight, resistant to deformation to a certain extent, and invulnerable to dropping. In actuality, however, the glass substrate is heavy, not resistant to deformation, and vulnerable to dropping.
In other words, there is a discrepancy between restrictive conditions required for a manufacturing process and characteristics desirable for a manufactured product. It has been extremely difficult to satisfy both of these required process conditions and desirable product characteristics.
The inventors, et al. have proposed a technique in which an object-of-transfer layer containing thin film devices is formed on a substrate through a conventional process and thereafter the object-of-transfer layer containing thin film devices is removed from the substrate for transference to a destination-of-transfer part (Japanese Patent Application No. 225643/1996). In this technique, a separation layer is formed between the substrate and a thin film device which is the object-of-transfer layer, and the separation layer is irradiated with light to cause exfoliation in an inner-layer part and/or interface of the separation layer. Thus, bonding strength between the substrate and the object-of-transfer layer is weakened to enable removal of the object-of-transfer layer from the substrate. In this manner, the object-of-transfer layer is transferred to the destination-or-transfer part. Where a fabrication process for forming thin film devices involves high-temperature treatment, a quartz glass or heat-resisting glass substrate is used. In the technique mentioned above, however, since the destination-of-transfer part is not exposed to high-temperature treatment, restrictive requirements imposed on the destination-of-transfer part are advantageously alleviated to a significant extent.
When the object-of-transfer layer containing thin film devices is removed from the substrate employed for thin film device formation so that the object-of-transfer layer is transferred to the destination-of-transfer part, the layering relationship of the object-of-transfer layer with respect to the destination-of-transfer part becomes opposite to that of the object-of-transfer layer with respect to the substrate. Namely, the side of the object-of-transfer layer which has faced the substrate originally does not face the destination-of-transfer part. For example, in the case where the object-of-transfer layer has first and second layers and is formed on the substrate in the order of the first and second layers, when the object-of-transfer layer is transferred to the destination-of-transfer part, the object-of-transfer layer is configured thereon in the order of the second and first sub-layers.
In the common practice of forming thin film devices on a substrate, electrodes are formed via an insulation layer after the formation of the element. Since the electrodes are disposed on the surface side, wiring connections or contacts can be arranged on the electrodes with ease. On the contrary, where the object-of-transfer layer containing thin film device and electrodes is transferred to the destination-of-transfer part, the electrodes are covered with the destination-of-transfer part, making it difficult to arrange wiring connections or contacts thereon.
DISCLOSURE OF THE INVENTION
In view of the foregoing, it is a general object of the present invention to provide a novel technique in which a substrate employed for thin film device formation and a substrate used as an actual element of a product (i.e., a substrate having characteristics desirable for usage of the product) can be selected individually and flexibly and in which thin film devices can be transferred to the substrate used as the actual product element while maintaining the layering relationship of the thin film devices with respect to the substrate employed for thin film device formation.
In accomplishing this object of the present invention and according to one aspect thereof, there is provided a thin film device transfer method comprising:
a first step of forming a first separation layer on a substrate;
a second step of forming an object-of-transfer layer containing a thin film device on the first separation layer;
a third step of forming a second separation layer on the object-of-transfer layer;
a fourth step of attaching a primary destination-of-transfer part to the second separation layer;
a fifth step of removing the substrate from the object-of-transfer layer using the first separation layer as a boundary;
a sixth step of attaching a secondary destination-of-transfer part to the bottom of the object-of-transfer layer; and
a seventh step of removing the primary destination-of-transfer part from the object-of-transfer layer using the second separation layer as a boundary,
whereby the object-of-transfer layer containing the thin film device is transferred to the secondary destination-of-transfer part.
The first separation layer to be separated later is provided on a substrate such as a quartz glass substrate having high reliability for device fabrication, and the object-of-transfer layer containing thin film devices such am TFTs is formed thereon. Then, the second separation layer to be separated later is formed on the object-of-transfer layer, and further the primary destination-of-transfer part is attached to the second separation layer. Thereafter, using the first separation layer as a boundary, the substrate employed for thin film device formation is removed from the object-of-transfer layer. In this state, however, layering relationship of the object-of-transfer layer with respect to the primary destination-of-transfer part is opposite to that of the object-of-transfer layer with respect to the substrate employed for thin film device formation.
It is therefore preferable that the first separation layer is removed from the bottom of the object-of-transfer layer, then the secondary destination-of-transfer part is attached to the bottom thereof. Thereafter, using the second separation layer as a boundary, the primary destination-of-transfer part is removed from the object-of-transfer layer. Thus, the secondary destination-of-transfer part is disposed at the position that has been occupied by the substrate employed for t
Inoue Satoshi
Miyazawa Wakao
Shimoda Tatsuya
Lee Eddie
Oliff & Berridg,e PLC
Richards N. Drew
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