Active solid-state devices (e.g. – transistors – solid-state diode – Non-single crystal – or recrystallized – semiconductor... – Non-single crystal – or recrystallized – material with...
Reexamination Certificate
1998-11-06
2001-01-09
Mintel, William (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Non-single crystal, or recrystallized, semiconductor...
Non-single crystal, or recrystallized, material with...
C065S066000, C065S070000, C065S075000, C065S077000, C065S431000, C065S431000, C438S149000, C438S150000, C438S535000
Reexamination Certificate
active
06172380
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a semiconductor material especially suitable for use in forming a semiconductor layer on an insulator, for example, to make a device using the semiconductor layer.
2. Description of the Related Art
In the field of MOSLSI, technologies on SOI (silicon on insulator) are now being actively developed to meet the requirement of the use for lower source voltages. Heretofore, various methods for fabricating SOI substrates have been proposed, and some have been brought into practice. Today's typical methods for fabricating SOI substrates include a SIMOX process and a bonding process, but all involve the problems that it is difficult to control the thickness of the silicon (Si) film uniformly under 60 nm and the cost for fabricating the substrate is high, and these problems impede their wider practical use.
On the other hand, it is possible to make Si crystalline thin films on various kinds of substrates such as glass substrates by using the bonding process, but it becomes more and more difficult to ensure a uniform thickness of a film as the area for making the film becomes larger.
Moreover, although polycrystalline Si films can be readily formed on glass substrates or other various kinds of substrates, their electric characteristics are not satisfactory because of variance in grain size of crystal grains, existence of grain boundaries, randomness in orientation of crystal grains, and so forth.
OBJECTS AND SUMMARY OF THE INVENTION
It is therefore an object of the invention to overcome the problems involved in the conventional technologies. That is, an object of the invention is to provide a semiconductor material that excels in its electrical characteristics relative to polycrystalline semiconductor materials and can be easily formed on various kinds of substrates.
According to the invention, there is provided a semiconductor material comprising a plurality of substantially single-crystalline crystal grains of a semiconductor, these crystal grains being preferentially oriented in a common surface orientation, and adjacent ones of the crystal grains being substantially in lattice matching with each other at least in a part of grain boundaries thereof.
Since the crystallographic property of the semiconductor material according to the invention is similar to that of a single crystal, it is called “quasi-static single crystal” in the present specification.
In the present invention, typical semiconductors forming crystal grains are covalent bonding type semiconductors having diamond-type crystalline structures. In this case, a plurality of crystal grains are preferentially {100}-oriented, {111}-oriented or {110}-oriented. When the crystal grains are preferentially {100}-oriented, individual crystal grains are approximately square when viewed from a direction, and they are closely aligned in rows and columns. When the crystal grains are preferentially {111}-oriented, individual crystal grains are approximately hexagonal when viewed from a direction, and they are closely aligned to form an equilateral turtle shell pattern. When the crystal grains are preferentially {110}-oriented, individual grains are approximately hexagonal when viewed from a direction, and they are closely aligned to form a turtle shell pattern.
In the present invention, the degree of orientation of crystal grains in the preferential orientation is preferably not less than 20%, and more preferably not less than 30%. However, crystal grains in the preferential orientation involve those in orientations offset within ±5° from one orientation.
In the present invention, the mean grain size of crystal grains is not smaller than 0.1 &mgr;m and not larger than 10 &mgr;m. The crystal grains are preferably equal in grain size.
In the present invention, typical covalent bonding type semiconductors having diamond-type crystal structures are group IV semiconductors, namely, element semiconductors such as silicon (Si), germanium (Ge) and carbon (C), and compound semiconductors containing Si and at least one selected from the group consisting of Si, Ge and C, such as SiGe and SiC.
In the present invention, the semiconductor material is typically made in the form of a thin film on a substrate. The thickness of the quasi-static single crystalline semiconductor thin film made in this manner is 10 nm to 100 nm, for example, although it depends on where and how it is used.
The semiconductor material having the above-explained structure according to the invention is excellent in electric characteristics as compared with conventional polycrystalline semiconductor materials because crystal grains are substantially single crystals and preferentially oriented in a common orientation, and because adjacent crystal grains are substantially lattice-matching at least in a part of their grain boundaries where, therefore, the electric barrier is less. Additionally, the semiconductor material can be readily made on a glass substrate or any of other various kinds of substrates by combining deposition process such as a CVD, laser annealing using an excimer laser, solid-phase crystallization, or other appropriate technologies.
The above, and other, objects, features and advantage of the present invention will become readily apparent from the following detailed description thereof which is to be read in connection with the accompanying drawings.
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Ikeda et al., “Crystallization Mechanism of Compulsive Localized Nucleation by ELA,”Proceedings of the 44thSymposium on Semiconductors and Integrated Circuits Technology, Tokyo, Jun. 17-18, 1993, pp. 187-192.
Kim et al., “Hexagonal silicon formation by pulsed laser beam annealing,”Materials Letters, v. 27, Aug. 1996, pp. 275-279.
Ikeda Yuji
Noguchi Takashi
Kananen Ronald P.
Mintel William
Rader Fishman & Grauer
Sony Corporation
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