Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – Having insulated gate
Reexamination Certificate
2003-01-10
2004-11-02
Wille, Douglas (Department: 2814)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
Having insulated gate
C257S410000
Reexamination Certificate
active
06812101
ABSTRACT:
TECHNICAL FIELD
The present invention relates to semiconductor devices having gate insulating films made of a high dielectric constant material, and to methods for fabricating the same.
BACKGROUND ART
With recent advances in techniques for enabling increased degrees of integration in and high-speed operation of semiconductor devices, MOSFETs (metal oxide semiconductor field effect transistors) have decreased in size. Along with this decrease in MOSFET size, gate insulating films have become progressively thinner, and as a result, the problem of enlarged gate leakage current due to tunnel current has become manifest. To address the problem, techniques have been studied for realizing a gate insulating film having a capacity equivalent to that of a thin SiO
2
film (that is, a small equivalent oxide (SiO
2
) thickness, hereinafter referred to as “EOT”) and having a large physical film thickness (meaning a small leakage current), by using, as a material for the gate insulating film, a high-k material having a dielectric constant higher than that of SiO
2
(hereinafter referred to as a “high-dielectric-constant material”). Specific examples of such a high-dielectric-constant material include an insulating metal oxide such as HfO
2
or ZrO
2
.
In addition, lately, multi-function circuits, such as internal circuits for performing computational operations, peripheral circuits for carrying out input and output, and DRAMs (dynamic random access memories), have been generally integrated on a single chip set out as a system LSI. As components of such a system LSI, MOSFETs that, in accordance with their functions, have enhanced driving power even though their leakage current is large, or have decreased leakage current even though their driving power is low are being sought. Being used in this regard is technology by which the SiO
2
films that serve as gate insulating films in MOSFETs are varied in thickness on the basis of the MOSFET functions,—specifically, multi-gate insulating film technology for forming gate insulating films with differing thicknesses.
When a high-dielectric-constant material is used as a material for a gate insulating film, however, it is difficult to obtain a desired EOT even though increase in the gate leakage current can be prevented.
Further, there is also a problem with the multi-gate insulating film technology, in that the gate leakage current is increased owing to the small thickness of the gate insulating films.
DISCLOSURE OF INVENTION
In view of the foregoing, a first object of the present invention is to realize a gate insulating film with small EOT and small leakage current, and a second object thereof is to prevent increase in gate leakage current when multi-gate insulating film technology is used.
To achieve the objects, the present inventors investigated the cause of the failure to realize a desired EOT even when a high-dielectric-constant material (specifically, a metal oxide) is used as a material for a gate insulating film, and the following has been made clear.
Specifically, when a metal oxide layer which serves as a gate insulating film is formed on a silicon substrate, an insulating compound layer (hereinafter, referred to as a “metal silicate layer) made of the three elements of silicon, oxygen and a metal contained in the metal oxide layer forms between the silicon substrate and the metal oxide layer. In other words, a gate insulating film is formed out of the multilayer structure of the metal silicate layer and the metal oxide layer. In this case, the dielectric constant of the metal silicate layer is lower than the dielectric constant of the metal oxide layer, thus decreasing the effective dielectric constant of the entire gate insulating film. As a result, a gate insulating film having a desired EOT cannot be formed, and therefore a MOSFET having such high driving power as expected cannot be realized, that is, the performance of the MOSFET cannot be enhanced.
FIG. 6
is a cross-sectional view illustrating a known semiconductor device, specifically a known MOSFET in which zirconium oxide (ZrO
2
) is used as a high-dielectric-constant material constituting a gate insulating film.
As shown in
FIG. 6
, a zirconium oxide layer
11
, which serves as a gate insulating film, is formed on a silicon substrate
10
. At this time, however, a zirconium silicate layer
12
forms between the silicon substrate
10
and the zirconium oxide layer
11
. Accordingly, a gate electrode
13
will be formed on the gate insulating film made of the multilayer structure of the zirconium oxide layer
11
and the zirconium silicate layer
12
.
Meanwhile, the present inventors found that when a metal oxide layer, which acts as a high-dielectric-constant material layer, is formed on a silicon substrate by, e.g., reactive sputtering, a metal silicate layer having a uniform thickness of about 2 through 3 nm and having a dielectric constant higher than the dielectric constant of a SiO
2
film can be formed between the silicon substrate and the metal oxide layer by controlling particles sputtered from the target and implanted into the substrate surface, or by controlling the O
2
plasma generated during the sputtering. They also found that by using the metal silicate layer as a gate insulating film, that is, by forming the metal oxide layer and the metal silicate layer and subsequently removing the metal oxide layer, the first object can be achieved, that is, a gate insulating film with small EOT and small leakage current can be realized. Note that when chemical vapor deposition, for example, is used instead of the reactive sputtering to form a metal silicate layer, such a quality metal silicate layer as mentioned above can also be formed.
The present inventors also found the following. When another metal oxide layer is formed on the metal silicate layer after the metal oxide layer has been removed, said another metal oxide layer can be formed as designed without taking reaction with the substrate into account; thus by using the multilayer structure of the metal silicate layer and said another metal oxide layer as a gate insulating film, the first object can also be achieved.
The present inventors further found that by forming a metal oxide layer and a metal silicate layer, and then partially removing the metal oxide layer, multi-gate insulating film technology in which the single layer structure of the metal silicate layer is used as a thin gate insulating film and the multilayer structure of the metal silicate layer and the metal oxide layer is used as a thick gate insulating film can be realized. This enables the second object to be achieved, that is, the gate leakage current can be controlled when the multi-gate insulating film technology is used. In this case, the multilayer structure of the metal silicate layer and another metal oxide layer may also be used as a thin gate insulating film.
The present invention was made based on the above-described findings. Specifically, in order to achieve the first object, a first inventive method for fabricating a semiconductor device includes the steps of: (a) forming a metal silicate layer containing at least a first metal on a silicon substrate, and also forming a metal oxide layer containing the first metal on the metal silicate layer; (b) removing the metal oxide layer, thereby forming a gate insulating film made of the metal silicate layer; and (c) forming a gate electrode on the gate insulating film.
According to the first inventive method for fabricating a semiconductor device, a metal silicate layer and a metal oxide layer both containing a first metal are sequentially formed on a silicon substrate, and the metal oxide layer is then removed, thereby forming a gate insulating film made of the metal silicate layer. In this method, a metal silicate layer with a uniform thickness and a dielectric constant higher than that of SiO
2
can be formed by a reactive sputtering method or by a chemical vapor deposition method, for example, and the thickness of the metal silicate layer can be easily adjusted by controlling the sputtering
Kubota Masafumi
Moriwaki Masaru
Niwa Masaaki
Matsushita Electric - Industrial Co., Ltd.
McDermott Will & Emery LLP
Wille Douglas
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