Semiconductor device manufacturing: process – Making device or circuit responsive to nonelectrical signal – Responsive to electromagnetic radiation
Reexamination Certificate
1999-08-03
2001-05-15
Chaudhari, Chandra (Department: 2813)
Semiconductor device manufacturing: process
Making device or circuit responsive to nonelectrical signal
Responsive to electromagnetic radiation
C438S116000, C438S659000, C257S082000
Reexamination Certificate
active
06232142
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a technical field of semiconductor devices and methods for making the same. In particular, the present invention relates to a technical field of a method for making a semiconductor device including forming a single-crystal semiconductor thin film for constituting switching elements such as thin film transistors (hereinafter referred to as TFTs) on an insulating substrate, a semiconductor device produced by this method, a method for making an electro-optical device using the semiconductor device, an electro-optical device produced by this method, and an electronic apparatus using the electro-optical device.
2. Description of Related Art
Semiconductor technologies for forming a single-crystal silicon thin film on an insulating substrate and for forming semiconductor devices using the single-crystal silicon thin film are called silicon-on-insulator (SOI) technologies and have been widely studied because of their advantages, such as high-speed response, low electrical power consumption, and high integration density of pixels.
One of the SOI technologies is an SOI substrate production technology by adhesion of a single-crystal silicon substrate. This method, generally called an “adhesion process”, includes adhering a single-crystal silicon substrate to a supporting substrate (an insulating substrate) by a hydrogen bonding force, reinforcing the adhering strength by heat treatment, and then thinning the single-crystal silicon substrate by grinding , polishing, or etching to form a single-crystal silicon layer on the supporting substrate. This process can directly thin the single-crystal silicon substrate and enables production of high-performance devices with silicon thin films having high crystallinity.
Applied methods of this adhering process have also been known, for example, a method including implantation of hydrogen ions into a single-crystal silicon substrate, adhering this substrate to a supporting substrate, and then separating a thin film silicon layer from a hydrogen-implanted region of the single-crystal silicon substrate by heat treatment (U.S. Pat. No. 5,374,564), and a method for forming an epitaxial single-crystal silicon thin film on a supporting substrate which includes epitaxial growth of a single-crystal silicon layer on the silicon substrate with a porous surface, adhering this substrate to a supporting substrate, removing the silicon substrate, and then etching the porous silicon layer (Japanese Patent Laid-Open Application No. 4-346418).
SOI substrates formed by the adhesion methods have been used in production of various devices, as well as general bulk semiconductor substrates (semiconductor integrated circuits), and have an advantage in which various materials can be used as a supporting substrate different from an advantage of the conventional bulk substrate. Transparent quartz and glass substrates, in addition to general silicon substrates, can be used as supporting substrates. As a result, for example, formation of a single-crystal silicon thin film on a transparent substrate enables formation of high-performance transistor elements using single-crystal silicon having high crystallinity in devices requiring light transmissivity, such as electro-optical devices such as a transmissive liquid crystal display device.
SUMMARY OF THE INVENTION
According to production methods using SOI technologies by the above-mentioned adhering processes, by adhering a light-transmissive transparent supporting substrate with a single-crystal silicon thin film in SOI substrates, and particularly, an SOI substrate using glass including quartz as a supporting substrate, thermal conductivity of the quartz glass substrate will cause a problem during adhesion. For example, the thermal conductivity of quartz glass is in a range of 1 to 2 W/m·K and is two orders of magnitude lower than that of the single-crystal silicon substrate, hence, thermal distribution on the adhering face differs between the periphery and the center. Such a nonuniform thermal distribution on the adhering face produces a nonuniform bonding force distribution on the adhering face, and thus causes voids and defects on the adhering face.
When the method described in U.S. Pat. No. 5,374,564 is applied to a quartz glass substrate in which hydrogen ions are implanted into a single-crystal silicon substrate, which is adhered to the supporting substrate, and then a thin film silicon layer, is separated from the hydrogen-implanted region of the single-crystal silicon substrate, the thermal distribution in the hydrogen-implanted region becomes nonuniform during the substrate separation step, and the single-crystal silicon substrate will not be separated from the single-crystal silicon film in a partial region.
On the other hand, a semiconductor device produced by the above-mentioned method has a problem in that heat generated during the operation thereof is not adequately dissipated from the use of a supporting substrate having low thermal conductivity. When the semiconductor devices produced in such a method are used as switching elements in the pixel section or peripheral circuit section of an electro-optical device, such as a liquid crystal device, the temperature of the switching elements increases during the operation due to insufficient heat dissipation, resulting in some problems, including deterioration of switching element characteristics.
In such electro-optical devices, temperature rise is also caused by projected light which is incident on the electro-optical device (among the light emitted from a light source or the like), and reflected light (reflected by succeeding optical elements among the light emitted from the electro-optical device), as well as heating of the semiconductor device itself, hence, the above-described insufficient heat dissipation during the operation will become a more serious problem when it is used in a projector using intense projected light.
It is an object of the present invention, achieved in view of the above-described problems, to provide a method for making a semiconductor device having a highly uniform in-plane thermal distribution during the production process, a semiconductor device produced by this method, and high heat-dissipation characteristics during operation, and an electro-optical device, such as a liquid crystal device and an electronic apparatus, using the semiconductor device.
The object of the present invention is achieved by a method for making a semiconductor device including the steps of forming a thermally conductive film having thermal conductivity which is higher than that of the supporting substrate on one surface of the supporting substrate, forming a first insulating film on the thermally conductive film, and adhering a single-crystal semiconductor film onto the first insulating film by heat treatment.
According to the method for making a semiconductor device of the present invention, a thermally conductive film is first formed on one surface of a supporting substrate, and then a first insulating film is formed on the thermally conductive film. A single-crystal semiconductor film is formed on the first insulating film by heat treatment to produce a semiconductor device using an SOI technology by an adhesion method. Since the thermally conductive film is disposed between the first insulating film and the supporting substrate, the thermally conductive film conducts heat during the heat treatment in the adhesion step and the thermal distribution is made uniform in the substrate plane. Since the uniformity of the thermal distribution on the substrate plane by the heat treatment is high during the adhesion step, enhancement of the adhesion strength is achieved together with the uniformity of the adhesion in the substrate plane, and defects and deterioration of a semiconductor device which will be finally produced can be decreased. Even when a supporting substrate having a relatively large area is used, a semiconductor device showing high performance and stable reliability a
Blum David S.
Chaudhari Chandra
Oliff & Berridg,e PLC
Seiko Epson Corporation
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