JPH10178170A - Semiconductor device and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor device and its manufacturing method, which can reduce the boundary level or fixed charge at the boundary between two layers constituting the gate and the boundary between a semiconductor substrate and a gate insulating film, and is applicable for refined MOS transistor with a gate length of at most about 0.1μm. SOLUTION: The surface of a silicon semiconductor substrate 11 is dipped in a nitric acid, so as to form a silicon oxide film 13. Then it is annealed in an atmosphere of nitrogen to refine the film 13. Next, a Ta2 O5 film 14 is formed on the entire surface of the substrate 11. In this case, the total thickness of the films 13 and 14 is set to be about 2nm in terms of the silicon oxide film. Then a gate electrode 15 is formed on the film 14, and an impurity diffusion area 17 is formed on the surface layer of the substrate 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a miniaturized MO.
The present invention relates to a semiconductor device including an S transistor and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, further integration and miniaturization of semiconductor devices have been promoted, and practical use of MOS transistors having a gate length of 0.1 μm or less has been demanded. In such a fine MOS transistor, the thickness of the gate oxide film is expected to be about 2 nm.

However, when the thickness of the gate oxide film is 3n
Below m, the direct tunnel phenomenon becomes remarkable, and the gate leakage current increases rapidly. When the gate leakage current increases, not only does the reliability of the transistor decrease, but also the increase in power consumption cannot be ignored. Conventionally, a gate oxide film is usually formed by thermally oxidizing a substrate surface. However, it is difficult to form a gate oxide film having a thickness of 3 nm or less with good controllability by thermal oxidation. In the case of a MOS transistor having a gate length of 0.1 μm or less, characteristics such as a threshold voltage Vth and a gate leak current of the transistor greatly change due to a slight fluctuation in the thickness of the gate oxide film.

Accordingly, in order to form a fine MOS transistor having a gate length of 0.1 μm or less, it is necessary to use a high dielectric constant material as a material for a gate insulating film and increase the actual film thickness. Conventionally, Ta ₂ O ₅ (tantalum oxide) has been regarded as a promising material for a gate insulating film of a fine MOS transistor having a high dielectric constant. In addition, Ta ₂
O ₅ has also been studied as a capacitor material for gigabit DRAMs, and it has been found that leakage current can be improved by forming a two-layer structure with a nitride film.

[0005]

[SUMMARY OF THE INVENTION However, when forming a two-layer film with the Ta ₂ O ₅ film or a nitride film and the Ta ₂ O ₅ film on a silicon substrate as the gate insulating film, silicon substrate and the Ta ₂ O ₅ film A large amount of interface states and fixed charges are present at the interface with the silicon substrate, the interface between the silicon substrate and the nitride film, or the interface between the nitride film and the Ta ₂ O ₅ film, so that the threshold voltage Vth of the transistor becomes unstable, There is a problem that the characteristics such as (g _m ) vary.

The present invention has been made in view of the above-described problems of the conventional example, and has an interface state such as an interface between a semiconductor substrate and a gate insulating film and an interface between two layers constituting the gate insulating film. It is an object of the present invention to provide a semiconductor device and a method for manufacturing the same, which can reduce fixed charges and can be applied to a fine MOS transistor having a gate length of about 0.1 μm or less.

[0007]

SUMMARY OF THE INVENTION The object of the present invention is to provide a semiconductor substrate having a surface layer made of silicon, a pair of impurity diffusion regions formed on the surface layer of the semiconductor substrate so as to be separated from each other, and
A silicon oxide film formed on the semiconductor substrate between the pair of impurity diffusion regions, a Ta ₂ O ₅ film formed on the silicon oxide film, and a gate formed on the Ta ₂ O ₅ film The problem is solved by a semiconductor device having electrodes.

[0008] The above-mentioned object is to provide a semiconductor substrate whose surface layer is made of silicon, a pair of impurity diffusion regions formed in the surface layer of the semiconductor substrate so as to be separated from each other, and the semiconductor substrate between the pair of impurity diffusion regions. An extremely thin silicon oxide film formed on the silicon oxide film;
The problem is solved by a semiconductor device having an a ₂ O ₅ film and a gate electrode formed on the Ta ₂ O ₅ film.

[0009] The above-described problems include a step of forming a silicon oxide film by oxidizing a surface of a semiconductor substrate whose surface layer is made of silicon with an oxidizing agent, a step of annealing the silicon oxide film in an inert gas atmosphere, The problem is solved by a method for manufacturing a semiconductor device, comprising: a step of forming a Ta ₂ O ₅ film on a silicon oxide film; and a step of forming a gate electrode on the Ta ₂ O ₅ film.

[0010] The above-mentioned problems are to form a silicon oxynitride film by oxynitriding the surface of a semiconductor substrate whose surface layer is made of silicon with a gas containing nitrogen, and to form a Ta ₂ O ₅ film on the silicon oxynitride film. The problem is solved by a method of manufacturing a semiconductor device, comprising a step of forming and a step of forming a gate electrode on the Ta ₂ O ₅ film. Hereinafter, the operation of the present invention will be described.

In the present invention, a silicon oxide film or a silicon oxynitride film is interposed between a semiconductor substrate whose surface layer is made of silicon and a Ta ₂ O ₅ film thereon. In the case where a silicon oxide film or a silicon oxynitride film is formed on a semiconductor substrate, interface states and fixed charges generated at the interface with the silicon substrate are extremely reduced, and a silicon oxide film or a silicon oxynitride film and Ta ₂ Interface levels and fixed charges are less likely to be generated at the interface with the O ₅ film. Thereby, characteristics such as the threshold voltage Vth and the amplification factor of the MOS transistor are stabilized.

In the method of the present invention, the semiconductor substrate
Of the surface is oxidized using an oxidizing agent such as nitric acid, and then
Annealing in an inert gas atmosphere such as
A recon oxide film is formed. In this way, silicon oxidation
By forming a film, a thin and uniform thickness silicon
A con oxide film can be formed. Also the above method
Instead of the surface of the silicon substrate_TwoOr nitrogen such as NO
Contains a trace amount of nitrogen by oxynitriding with a gas containing
Thin and uniform silicon made of silicon oxide
An oxynitride film is formed, and Ta is formed on the silicon oxynitride film. _Two
O_FiveA film may be formed.

[0013]

Embodiments of the present invention will be described below with reference to the accompanying drawings. (First Embodiment) FIGS. 1 to 3 are sectional views showing a method of manufacturing a semiconductor device according to an embodiment of the present invention in the order of steps.

First, as shown in FIG. 1, the surface of the silicon semiconductor substrate 11 is selectively oxidized by a usual method,
LOCOS for separating semiconductor substrate 11 into a plurality of element regions
(Local Oxidation of Silicon) film 12 is formed. Next, as shown in FIG. 2, the surface of the semiconductor substrate 11 is immersed in nitric acid and the surface is chemically oxidized to form a silicon oxide film (SiO ₂ film) 13. This silicon oxide film 1
No. 3 has relatively low density and poor characteristics. Therefore, in the present embodiment, next, the substrate 11 is
Anneal by heating to 0 to 800 ° C. and holding for about 10 to 20 minutes. Thereby, the silicon oxide film 1
The structure of No. 3 is densified, and a stable oxide film close to a thermal oxide film is obtained. Further, under the above conditions, the thickness of the silicon oxide 13 becomes about 1 nm. It is preferable that the silicon oxide film 13 be formed as thin as possible. According to the above-described method, a silicon oxide film having a thinner and uniform thickness can be formed as compared with a silicon oxide film formed by a thermal oxidation method.

Thereafter, the entire surface of the substrate 11 is
Ta on the surface_TwoO_FiveTo a thickness of about 5 nm of Ta._TwoO
_FiveThe film 14 is formed. The silicon oxide film 13 and Ta
_TwoO _FiveThe thickness of the gate insulating film constituted by the film 14
Is equivalent to silicon oxide film (the relative permittivity of silicon oxide film is
3 nm or less in terms of film thickness (when 3.9)
Preferably, the thickness is about 2 nm.

Next, as shown in FIG. 3, as a gate electrode, TiN having a work function substantially in the middle of the band gap between p-type Si and n-type Si is deposited by CVD, and then TiN is deposited by a photolithography process. The gate electrode 15 is formed by patterning into a predetermined shape. After that, as shown in FIG.
Forming sidewalls 16 on both sides of the gate electrode 15;
Impurities are selectively introduced into the surface layer of the silicon substrate 11 to form impurity diffusion regions 17 serving as source / drain regions. Thereby, the semiconductor device of the present embodiment is completed.

In this embodiment, the gate insulating film and
And silicon oxide film 13 and Ta_TwoO _FiveTwo-layer structure with film 14
The formation of a structured film suppresses the generation of interface states and fixed charges.
Can be controlled. This allows the threshold voltage
Vth is stable, and variations in characteristics can be avoided.
Fine MOS transistor with gate length less than 0.1μm
Can be formed.

The semiconductor device thus formed is
The gate insulating film is a silicon oxide film 13 and a Ta ₂ O ₅ film 14
, The gate leakage current is small, and the semiconductor substrate 11 and the silicon oxide film 1 are formed.
3 and the silicon oxide film 13 and the Ta ₂ O ₅ film 14
There are few interface states and fixed charges at the interface with the substrate, deterioration of carrier mobility is suppressed, and good and small device characteristics are obtained.

In the above example, nitric acid is used as the oxidizing agent. However, an oxidizing agent may be used to form an oxide film on the surface of the silicon substrate. In the above-described example, the annealing is performed in the nitrogen atmosphere, but another inert gas such as argon may be used. (Second Embodiment) FIGS. 5 and 6 are sectional views showing a method of manufacturing a semiconductor device according to a second embodiment of the present invention in the order of steps.

First, as shown in FIG. 5, LOCOS is applied to the surface of the silicon substrate 11 in the same manner as in the first embodiment.
The film 12 is selectively formed, and the silicon substrate 11 is separated into a plurality of element regions. Next, the substrate 11 is placed in an NO gas atmosphere.
Is heated to about 800 ° C., and a thickness of about 1
A silicon oxynitride film 23 of nm or less is formed. The silicon oxynitride film 23 has a structure in which a trace amount of nitrogen is contained in an oxide film, and exhibits almost the same characteristics as a silicon oxide film. Note that the same oxynitride film can be formed on the surface of the silicon substrate 11 even if the silicon substrate 11 is heated in an atmosphere of N ₂ gas or another gas containing nitrogen instead of the NO gas atmosphere. .

Next, Ta ₂ O ₅ is deposited by CVD to form a Ta ₂ O ₅ film 14 having a thickness of 5 nm. Next, as shown in FIG. 6, a gate electrode 15 made of TiN is selectively formed on the Ta ₂ O ₅ film 14. Thereafter, sidewalls 16 are formed on both sides of the gate electrode 15 and impurities are selectively introduced into the surface layer of the silicon substrate 11 to form impurity diffusion regions 17 serving as source / drain regions, as in the conventional case. Thereby, the semiconductor device of the present embodiment is completed.

Also in this embodiment, since a film having a two-layer structure of the oxynitride film 23 and the Ta ₂ O ₅ film 14 is formed as a gate insulating film, it is possible to suppress the generation of interface states and fixed charges. it can. As a result, similarly to the first embodiment, the threshold voltage Vth is stable, the variation in characteristics can be avoided, and a fine MOS transistor having a gate length of 0.1 μm or less can be formed.

In the first and second embodiments, after the Ta ₂ O ₅ film 14 is formed, the Ta ₂ O ₅ film 14 is annealed using O ₃ or oxygen plasma. Good. Thus, the oxygen enters in the Ta ₂ O ₅ film 14, the Ta ₂ O ₅ film 14 and the oxide film 13 or oxynitride film 2
The interface state at the interface with No. 3 and the fixed charge are further reduced.

[0024]

As described above, in the present invention, since the silicon oxide film or the silicon oxynitride film is interposed between the surface of the semiconductor substrate and the Ta ₂ O ₅ film, it exists at each interface. Interface levels and fixed charges are significantly reduced.
As a result, characteristics such as a threshold voltage and an amplification factor are stabilized, and a MOS transistor having a gate length as small as about 0.1 μm can be obtained, which has the effect of contributing to higher integration of a semiconductor device.

In the method of the present invention, the surface of the semiconductor substrate is oxidized using an oxidizing agent such as nitric acid and then annealed in an inert gas atmosphere, or the surface of the semiconductor substrate is oxidized with a gas containing nitrogen. By nitriding, a silicon oxide film or a silicon oxynitride film having a thin and uniform thickness is formed, and a Ta ₂ O ₅ film is formed thereon, so that an interface state such as an interface between a semiconductor substrate and a gate insulating film is formed. Fine MOS with good characteristics that can reduce the position and fixed charge
A semiconductor device including a transistor can be manufactured.

[Brief description of the drawings]

FIG. 1 is a sectional view (part 1) illustrating a method for manufacturing a semiconductor device according to a first embodiment of the present invention;

FIG. 2 is a sectional view (part 2) illustrating the method for manufacturing the semiconductor device according to the first embodiment of the present invention;

FIG. 3 is a sectional view (part 3) illustrating the method for manufacturing the semiconductor device according to the first embodiment of the present invention;

FIG. 4 is a sectional view (part 4) illustrating the method for manufacturing the semiconductor device according to the first embodiment of the present invention;

FIG. 5 is a sectional view (part 1) illustrating the method for manufacturing the semiconductor device according to the second embodiment of the present invention.

FIG. 6 is a sectional view (part 2) illustrating the method for manufacturing the semiconductor device according to the second embodiment of the present invention.

[Explanation of symbols]

Reference Signs List 11 silicon semiconductor substrate 12 LOCOS film 13 silicon oxide film 14, 24 Ta ₂ O ₅ film 15 gate electrode 16 sidewall 17 impurity diffusion region 23 silicon oxynitride film

Claims (7)

[Claims] A semiconductor substrate having a surface layer made of silicon; a pair of impurity diffusion regions formed in the surface layer of the semiconductor substrate so as to be separated from each other; and a semiconductor substrate formed between the pair of impurity diffusion regions. A semiconductor device comprising: a silicon oxide film formed; a Ta ₂ O ₅ film formed on the silicon oxide film; and a gate electrode formed on the Ta ₂ O ₅ film. 2. The semiconductor device according to claim 1, wherein the total thickness of the silicon oxide film and the Ta ₂ O ₅ film is 3 nm or less in terms of a silicon oxide film. 3. A semiconductor substrate having a surface layer made of silicon; a pair of impurity diffusion regions formed in the surface layer of the semiconductor substrate so as to be separated from each other; and a semiconductor substrate formed on the semiconductor substrate between the pair of impurity diffusion regions. A semiconductor device comprising: a silicon oxynitride film formed; a Ta ₂ O ₅ film formed on the silicon oxynitride film; and a gate electrode formed on the Ta ₂ O ₅ film. 4. The silicon oxynitride film and the Ta ₂ O ₅
4. The semiconductor device according to claim 3, wherein the total thickness of the film and the film is 3 nm or less in terms of a silicon oxide film. 5. A step of oxidizing a surface of a semiconductor substrate whose surface layer is made of silicon with an oxidizing agent to form a silicon oxide film; a step of annealing the silicon oxide film in an inert gas atmosphere; the method of manufacturing a semiconductor device, characterized in that it comprises a step of forming a the Ta ₂ O ₅ film on, and forming a gate electrode on the the Ta ₂ O ₅ film. 6. A step of forming a silicon oxynitride film by oxynitriding a surface of a semiconductor substrate whose surface layer is made of silicon with a gas containing nitrogen, and a step of forming a Ta ₂ O ₅ film on the silicon oxynitride film. And a step of forming a gate electrode on the Ta ₂ O ₅ film. 7. After forming the the Ta ₂ O ₅ film, a semiconductor device according to claim 5 or 6, comprising a step of annealing said the Ta ₂ O ₅ film with O ₃ or oxygen plasma Manufacturing method.