Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – Having insulated gate
Reexamination Certificate
2002-09-11
2004-05-11
Whitehead, Jr., Carl (Department: 2813)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
Having insulated gate
C438S591000, C438S785000
Reexamination Certificate
active
06734069
ABSTRACT:
TECHNICAL FIELD
The present invention relates to methods and apparatuses for fabricating semiconductor devices and more particularly relates to a method for forming a very thin gate insulating film having a high dielectric constant.
BACKGROUND ART
Recently, with a great progress in a high degree of integration of semiconductor integrated circuits, attempts have been made at reducing the size of transistor devices and increasing the performance thereof in MOS semiconductor devices. Specifically, as the size of devices such as transistors has been reduced, achievement of highly reliable MOS devices is required. In order to increase the reliability of MOS devices, each member composing a MOS device should be highly reliable. Specifically, as for gate insulating films used in MOS devices, the thickness thereof has been rapidly reduced and it is expected that very thin gate insulating films having a thickness of 2 nm or less will be commonly used during the 21
st
century. As the thickness of a gate insulating film becomes thinner, a higher degree of uniformity in properties of the gate insulating film is required. Therefore, the achievement of gate insulating films having excellent properties has been regarded as important so that properties of a gate insulating film are said to determine characteristics of a MOS transistor and even electric properties of a semiconductor integrated circuit.
Currently, SiO
2
films are used as gate insulating films in most cases. When an SiO
2
film is used as a gate insulating film, there have been big problems, in very thin regions having a thickness of 2 nm or less, of reduced reliability of the insulating film and increased gate leakage current which is directly caused by a tunnel phenomenon current. In fact, the gate leakage current has to be suppressed to achieve an LSI having low power consumption. However, such gate leakage current due to the tunnel phenomenon is a phenomenon that is governed by physical rules and is strongly influenced by the physical characteristics of SiO
2
films. Therefore, it is no longer possible to achieve the LSIs having low power consumption by the very thin SiO
2
films.
Then, there have been increased efforts to adopt a film having a higher dielectric constant than the SiO
2
film, thereby ensuring as great a capacitance as that of the very thin SiO
2
film while increasing the thickness of the insulating film to suppress leakage current, for example, as described in a reference material (Lee et al. IEEE/International Electron Device Meeting 99, p. 133). For example, by using an HfO
2
film (a high dielectric film) as a gate insulating film, it is possible to achieve a transistor which has a capacitance corresponding to a thickness of 2 nm or less in terms of the SiO
2
film and which occurs three orders of smaller leakage current than the SiO
2
film. For example, if the gate insulating film is composed of HfO
2
, a method for depositing films using reactive sputtering is generally adopted.
FIGS.
18
(
a
) through
18
(
c
) are cross-sectional views illustrating process steps of forming a gate insulating film composed of an HfO
2
film by a plasma CVD method.
A p-type Si substrate
501
shown in FIG.
18
(
a
) is first prepared, and then in the process step shown in FIG.
18
(
b
), an HfO
2
target is bombarded with Ar ions to sputter the Hf atoms, thereby injecting the Hf atoms into an Ar plasma
504
. An HfO
2
activated species
503
is generated in the Ar plasma
504
, and the HfO
2
activated species
503
is deposited on the Si substrate
501
to form an HfO
2
film
502
. Then, in the process step shown in FIG.
18
(
c
), a polysilicon film
505
is deposited on the HfO
2
film
502
. Thereafter, the polysilicon film
505
and the HfO
2
film are patterned, and thereby a gate insulating film and a gate electrode can be formed, though they are not shown.
As for system LSIs, LSIs in which multiple types of MIS devices including gate insulating films with different thicknesses are mounted are utilized. Conventionally, an LSI in which two types of devices, i.e., an MIS device of a 3.3 V system including a thick gate insulating film and provided in an I/O section and an MIS device including a thin gate insulating film provided in a logic core section, are mounted has been well known. Nowadays, however, the thin gate oxide film being provided in the logic core section is subdivided into more types, and in order to reduce the gate leakage current in a stand-by state, an MIS device in which the thickness of an gate insulating film has been physically increased is provided only in a specific part of an LSI. In this case, a film forming method in which ions, such as F ions, have been implanted in advance into a substrate region on which a thick gate insulating film is to be formed, and gate insulating films having different thicknesses are simultaneously formed on the same substrate by using the difference in oxidation speed between the ion-implanted region and the remaining region, or like methods are adopted.
Problems to be Solved
It has been pointed that when the HfO
2
film or a ZrO
2
film which has a high dielectric constant is used as the gate insulating film of a MOS transistor, the interface between the gate insulating film and an Si substrate has poor properties relative to the case of using an SiO
2
film and therefore that characteristics of the MOS transistor can not be expectedly improved. In the case of a sputtering method concerns arise about damages to the Si substrate
501
due to ion attacks. Thus, there have been more cases in which not the HfO
2
film or the ZrO
2
film but so-called silicate materials such as HfSiO-based materials or ZrSiO-based materials are introduced. However, the silicate materials have problems, such as difficulties in controlling the composition of a film containing a silicate material or great difficulties in controlling the thickness of an SiO
2
layer around the surface of the Si substrate in forming a silicate layer. Accordingly, when a silicate material is used as the gate insulating film, the level of the gate leakage current varies widely, and therefore the silicate material is not suitable for mass production.
Furthermore, when multiple types of gate insulating films composed of an oxide film (or an oxynitride film) and having different thicknesses are provided on a substrate in accordance with desired characteristics of the transistor, it is difficult to control the thicknesses of the insulating films with high accuracy in the known method in which the oxidation speed is varied by implanting F ions, and therefore the capacitance between the gate and the substrate unwantedly varies widely. On the other hand, when a step of partially removing the oxide film is repeatedly performed to form three oxide films or oxynitride films having different thicknesses, problems caused by etching a silicon substrate surface for many times might become noticeable.
DISCLOSURE OF INVENTION
An object of the present invention is to provide a method for easily forming a gate insulating film in which good properties of an SiO
2
film on an Si substrate is maintained and which has a high dielectric constant, and a method for fabricating a semiconductor device including the gate insulating film so as to accommodate size reduction of transistors.
A first method for forming an insulating film according to the present invention includes the steps of: a) introducing at least oxygen into a surface region of a semiconductor substrate, thereby forming an initial insulating film; b) introducing at least one type of metal into at least part of the initial insulating film; and c) performing heat treatment to diffuse the metal in the initial insulating film, thereby forming at least one high dielectric film having a higher dielectric constant than the initial insulating film on at least part of the semiconductor substrate.
According to the method, a metal that has been introduced into at least part of an initial insulating film is diffused, thereby forming from the initial insulating film a high
Jr. Carl Whitehead
Smoot Stephen W.
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