Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2000-03-10
2001-12-04
Lee, Eddie (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S410000, C257S406000, C257S368000, C257S369000, C257S388000
Reexamination Certificate
active
06326670
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device, and in particular, to a structure of a transistor using a metallic oxide film as a gate insulating film and a method for manufacturing the same.
2. Description of the Related Art
Finer processing of a MOS transistor seems to have no bounds, and a gate length of 0.1 &mgr;m will become a reality in the near future. This finer processing increases the speed of a device and reduces the power consumption and the area of the device. Also in recent years, this finer processing enables many devices to be mounted on the same chip area and hence can realize a multi-function LSI.
It is thought, however, that the pursuit of the finer processing runs into big barriers at a gate length of 0.1 &mgr;m. One of the barriers is the limit of thinning of a gate oxide film. A conventional gate insulating film uses SiO
2
because SiO
2
can satisfy two characteristics indispensable to the action of the device, that is, the SiO
2
includes few fixed electric charges and hardly forms an interface level at the interface between the gate insulating film and the Si of a channel portion. Also, since SiO
2
can form a thin film simply with good controllability, it is also effective in the finer processing of the device. However, the relative dielectric constant of the SiO
2
is small (3.9) and hence the SiO
2
film is made less than 3 nanometers thick so as to satisfy the performance of the transistor in the generation of a gate length of 0.1 &mgr;m or less. It is predicted that this thin film thickness presents a problem that carriers directly tunnel through the film and increase the leakage current between the gate and the substrate.
Therefore, research aimed at forming a thick gate insulating film and at preventing a tunneling phenomenon has been conducted by using a material having a larger relative dielectric constant than SiO
2
. A metallic oxide film made of Ta
2
O
5
or TiO
2
is used as a material having a large relative dielectric constant. It is thought that these are promising materials for preventing the tunneling phenomenon because they have a large relative dielectric constant of about 20 or 90 and hence the thickness thereof can be made about 5 to 20 times as large as the thickness of the SiO
2
in order to produce the same gate capacitance.
However, a problem has been pointed out that when a metallic oxide film is formed on a Si substrate by the use of a usual process flow, a Si oxide film having a low dielectric constant is formed with a thickness of about 1 nanometer to 2 nanometers between the metallic oxide film and the Si substrate by a heat treatment in each process. As a heat treatment after the formation of the metallic oxide film, there is an annealing treatment for activating impurities in source/drain regions after the formation of gate side walls (typically, annealing at 800° C. for 60 minutes in a nitrogen atmosphere), an oxidizing process after forming a gate electrode (about 700° C. to 900° C.), a heating process when the gate side wall is deposited (about 600° C. to 800° C.), a heating process for densifying a highly dielectric film (about 600° C. to 1000° C.), and a sintering process (about 300° C. to 500° C.).
The Si oxide film formed by the heat treatment after the formation of the metallic oxide film has a small relative dielectric constant; therefore, it reduces the capacitance of the gate and the substrate and hence reduces the driving force of a MOS transistor. Also, a transistor having a short gate length markedly produces “a short channel effect” of reducing a gate voltage threshold for turning on.
As described above, in a case where a metallic oxide film having a high dielectric constant is used as a gate insulating film, there is a problem that a Si oxide film having a low dielectric constant is formed between the metallic oxide film and a Si substrate by a heat treatment performed after the formation of the metallic oxide film. This reduces the capacitance of the gate and the substrate and hence reduces the driving force of a MOS transistor. Also, a transistor having a short gate length presents a problem that it markedly produces “a short channel effect” of reducing a gate voltage threshold for turning on.
SUMMARY OF THE INVENTION
The present invention has been made to solve the problems described above. It is the object of the present invention to provide a semiconductor device in which a Si oxide film formed between a metallic oxide film and a Si substrate is prevented from growing when the Si substrate is subjected to an annealing treatment after the metallic oxide film is formed and a method for manufacturing the same.
In order to accomplish the object described above, the present invention provides a semiconductor device comprising a silicon substrate; a gate insulating film made of a metallic oxide film and formed over the silicon substrate; and a gate electrode formed over the gate insulating film, wherein an interface film formed between the gate insulating film and the silicon substrate is thinner at the edges of the gate insulating film than at the center thereof.
Also, the present invention provides a semiconductor device comprising a silicon substrate; a gate insulating film made of a metallic oxide film and formed over the silicon substrate; and a gate electrode formed over the gate insulating film, wherein, in a part of the gate insulating film, the ratio of metal to oxygen is larger than a stoichiometric ratio.
Also, the present invention provides a method for manufacturing a semiconductor device that comprises forming a metallic oxide film over a main surface of a silicon substrate surrounded by a device-isolating region; forming a material to be oxidized directly on the metallic oxide film or on the film which is formed on the metallic oxide film and in which an oxidizing agent can diffuse; and performing a heat treatment.
Also, the present invention provides a method for manufacturing a semiconductor device that comprises forming a device-isolating region on the main surface of a silicon substrate; forming a metallic oxide film in which the ratio of metal to oxygen is larger than a stoichiometric ratio and a metallic oxide film in which the ratio of metal to oxygen is nearly equal to a stoichiometric ratio over the main surface of the silicon substrate surrounded by the device-isolating region; and performing a heat treatment.
Also, the present invention provides a method for manufacturing, a semiconductor device that comprises forming a metallic oxide film over a main surface of a silicon substrate surrounded by a device-isolating region; cutting a metal-to-oxygen bond in the metallic oxide film; and performing a heat treatment.
Also, the present invention provides a method for manufacturing a semiconductor device that comprises forming a metallic oxide film over a main surface of a silicon substrate surrounded by a device-isolating region; and performing a heat treatment at 500° C. or more in a reducing gas atmosphere.
Also, the present invention provides a method for manufacturing a semiconductor device, wherein the metallic oxide film is a Ti oxide film.
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Koike Masahiro
Nishiyama Akira
Diaz José R
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Kabushiki Kaisha Toshiba
Lee Eddie
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