JPH11168212A - Semiconductor device - Google Patents

Abstract

(57) Abstract: The present invention provides a device structure for changing the surface of a metal gate electrode to a metal insulating film at a low temperature to improve the reliability of a device, that is, a circuit / system, and a method of manufacturing the same. The purpose is to do. SOLUTION: The semiconductor device according to the present invention is characterized in that a gate electrode of a MOS device is formed using a metal, and a side wall thereof is modified into a metal insulating film to improve the reliability of the device. Further, a high-quality metal insulating film is formed at a low temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device having a new structure for improving the reliability of a MOS transistor having a metal gate electrode for realizing high-speed operation.

[0002]

2. Description of the Related Art Over the past thirty years, the operating speed of a semiconductor integrated circuit has been increased due to the reduction in element size of a semiconductor device. Until now, the reduction in device dimensions, such as the channel length of semiconductor devices, has made it possible to increase the current drive capability of the device, that is, increase the circuit speed.However, the device dimensions have entered the sub-quarter micron range, and the circuit speed has increased. It is being determined by parasitic resistance and parasitic capacitance.

In order to avoid these problems, a salicide technique in which the gate, source and drain regions of a MOS device are silicided in a self-aligned manner, or in order to further reduce the sheet resistance of the gate, a gate electrode having a high concentration is used. Polycide technology has been developed which has a laminated structure of polycrystalline silicon and metal silicide doped with undoped silicon.
Also in the wiring structure, copper wiring is being introduced for lowering resistance, and low dielectric constant interlayer insulating film is being introduced for lowering load capacity. However, in order to increase the speed of the next-generation MOS device, the parasitic resistance must be further reduced. As a solution to that problem, in recent years, a MOS device structure using a metal for a gate electrode has attracted attention.

[0004] However, although the use of a metal as a gate electrode material can increase the speed, there is a problem that the reliability is deteriorated, and there is a strong demand for a solution to this problem.

A particularly serious problem is a decrease in the breakdown voltage between the gate and the source or between the gate and the drain. When polycrystalline silicon is used as the gate electrode material, after the gate electrode is formed by anisotropic etching, heat treatment is performed in an oxidizing atmosphere (generally called a re-oxidation step), and the edge of the gate electrode is rounded. And the silicon oxide film SiO at the edge of the gate electrode
₂ By increasing the thickness of the gate insulating film, the breakdown voltage between the gate and source and between the gate and drain
It was possible to increase the breakdown voltage between the substrates (channels). However, when a metal is used for the gate electrode, a thin and high-quality insulating film cannot be formed.

[0006]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art by changing the surface of a metal gate electrode to a metal insulating film at a low temperature to improve the reliability of a device, that is, the reliability of a circuit / system. It is an object of the present invention to provide a device structure and a manufacturing method thereof.

[0007]

According to the present invention, there is provided a semiconductor device comprising:
A gate electrode of a MOS device is formed by using a metal, and a side wall thereof is modified to a metal insulating film to improve device reliability. Further, a high-quality metal insulating film is formed at a low temperature.

[0008]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is a schematic diagram of a manufacturing flow of a device of the present invention, and FIG. 2 shows a part of a cluster tool used for manufacturing. Element isolation is performed by the field oxide film 102, and wet cleaning at room temperature is performed on a single wafer cleaning apparatus 202.
After that, the substrate is transferred to the loading chamber 203 of the cluster tool via the transfer path 201 in a dry air atmosphere having an impurity concentration of water, hydrocarbon, or the like of 10 ppb or less. In this cluster tool, all chambers are maintained at a pressure of several mTorr by flowing an appropriate amount of nitrogen, and a small amount of gas is always supplied to suppress impurity back-diffusion from the gas exhaust system. After a gate insulating film Ta ₂ O ₅ is formed to a thickness of 8 nm by chemical vapor deposition (MOCVD) using an organic metal gas source in the process chamber 204, the Ta ₂ O ₅ thin film is modified in the process chamber 205 by Xe / It is performed using He (20%) / O ₂ (3%) plasma.

The film of Ta ₂ O ₅ is formed of Ta (OC ₂ H ₅ ) ₅ / O ₂
/ Ar was used at a substrate temperature of 450 ° C. and a pressure of 1 Torr. However, the film forming conditions are not limited to these, and TaCl ₅ , Ta (N (C
_{H 3) 2) 5, H} 3 Ta (C 2 H 5) may be used ₂ or the like.
Also, instead of Ta ₂ O ₅ , SiO ₂ , Si ₃ N ₄ , Ti
It goes without saying that another insulating film such as O ₂ or BST [(Ba, Sr) TiO ₃ ] or a ferroelectric thin film such as PZT may be used. Further, O ₂ is used as an oxidizing species at the time of film formation / reforming, but H ₂ O.H ₂ O / H ₂ .N ₂
· NO Similar results with an oxidizing species such as ₂ is of course obtained.

FIG. 3 is a schematic view of a plasma apparatus used for modifying a Ta ₂ O ₅ thin film. The plasma apparatus includes a vacuum vessel 301, an inlet 302 for a source gas necessary for generating plasma in the vessel, and a vacuum pump 303 for exhausting the source gas introduced into the vessel. A part of the constituting wall is a dielectric plate 304 made of a material capable of transmitting microwaves with almost no loss, and an antenna 305 for radiating microwaves is installed outside the container with the dielectric plate interposed therebetween. ing. Inside the container,
An electrode 306 for mounting a substrate 308 to be processed is provided, and the microwave radiating surface of the antenna and the surface of the substrate on which plasma processing is performed are arranged substantially parallel to each other. The electrode 306 is provided with a heating mechanism so that the substrate temperature can be increased during the process. A reflector 309 is provided for the purpose of preventing the microwave radiated from the antenna from propagating to the exhaust port side and uniformly generating plasma only on the substrate.
Further, in order to make the introduction of the source gas uniform, the source gas of the present apparatus is introduced into the process space through the shower plate 307 from a number of small holes. This source gas is exhausted from the plurality of vacuum pumps 303 to the outside. A relatively large space is provided at the upper part of each vacuum pump so as not to lower the conductance of the gas. By evacuating from a plurality of vacuum pumps arranged at substantially equal intervals on the side of the base as described above, a uniform gas flow on the base in the rotation direction can be realized without substantially reducing the conductance of the gas.

In this embodiment, a radial line slot antenna is used as a microwave antenna, and a substrate temperature of 500 ° C.
I went in. The feature of this microwave plasma is that the electron temperature is as low as about 1 eV and the energy of
The point is that it can be controlled to eV or less. In addition, heavy Xe
The use of ions makes it possible to transmit energy only to the vicinity of the surface without causing defects in the underlying Si substrate. A commonly used atomic radius of Ar is 1.8.
Compared with 8 °, the atomic radius of Xe is as large as 2.17 °, so that Xe is hard to be implanted into the substrate and energy can be efficiently transmitted only to the substrate surface. Also,
The atomic weights of Ar and Xe are 39.95 and 13 respectively.
Xe is 1.3, which is heavier than Ar or the like, has a low energy and momentum transfer efficiency to the substrate surface, and has the effect of making it difficult to form defects. Suitable when using irradiation. When Ta ₂ O ₅ formed by MOCVD is not modified, a leak current of about 10 ⁻⁶ A / cm ² flows, but Xe / He (20%) / O ₂ (3%) plasma is generated. When used for reforming, the leakage current can be reduced to 10 ⁻⁹ A / cm ² . This is because oxygen deficiency in the film has disappeared. While the O / Ta ratio before the reforming was 2.43, the O / Ta ratio could be made stoichiometric to 2.50 by the reforming. This is because the addition of He into the gas improves the generation rate of oxygen radicals, and the higher pressure increases the efficiency of intermolecular collisions and the more efficient generation of oxygen radicals. This is because only the vicinity of the surface can be activated without damaging the base by irradiation with low energy Xe ions.

After forming the gate insulating film, Ta used as a gate electrode in the process chamber 206 without being exposed to the atmosphere.
The thin film 104 was formed by the sputtering method. Xe plasma is used to irradiate the surface of the film with Xe ions in an amount 25 times that of the incident Ta atoms, and the ion irradiation energy is increased by 40%.
The film thickness was controlled to eV, and a Ta film having a bcc structure was formed. The specific resistance of the formed bcc-Ta is 14 μΩcm, and β-T
a (a specific resistance of about 160 μΩcm) could be obtained by one digit or more, and a low sheet resistance of 0.7 / □ was realized at a thickness of 200 nm.

After depositing the gate electrode, in order to prevent oxidation of the metal surface, nitriding of the Ta surface is performed in the process chamber 207 by microwave plasma using the radial line slot antenna shown in FIG.
An N layer 105 was formed. At this time, the gas used was Ar /
N ₂ (5%). Then, the SiO ₂ film 10 for the mask is used.
No. 6 was deposited and unloaded from the cluster chamber.

A resist mask for the gate was formed by a lithography process, and a gate processing and a re-oxidation process for the side wall of the gate electrode were performed in the cluster chamber shown in FIG.
The substrate is loaded from the loading chamber 401, the mask SiO ₂ film 106 is anisotropically etched by C ₄ F ₈ / CO / Ar / O ₂ plasma in the etching chamber 402, and the resist is ashed in the process chamber 403 by Xe. / O ₂ plasma. Subsequently, the anisotropic etching of the Ta thin film 104 was performed in the etching chamber 404 by using SiCl ₄ plasma.

The reoxidation step of the side wall of the Ta gate electrode, which is a feature of the present invention, was performed in the process chamber 405. The process apparatus used in this process is a microwave-excited plasma apparatus using a radial line slot antenna similar to that shown in FIG. The processing conditions at that time were the gas used Xe / H
e / O ₂ , gas pressure 500 mTorr, partial pressure ratio Xe: H
e: O ₂ = 68%: 30%: 2%, microwave power is 1
200 W, oxidation time: 15 minutes, the substrate is kept electrically floating, the temperature of the object to be processed is 450 ° C.
And However, the film forming conditions are not limited to this, and Ar may be used instead of Xe, but Xe is more preferably used.

As in the case of reforming Ta ₂ O ₅ , oxygen radicals can be efficiently generated by adding He, and the gate can be formed without introducing defects into the gate oxide film by using Xe plasma. Ta ₂ O ₅ was formed on the side wall of the electrode, and the gate edge was rounded to reduce the electric field concentration. By oxidizing the side wall of the gate electrode using a gas plasma containing Xe, the breakdown voltage between the gate and the source and between the gate and the drain (current density 100 mA /
(voltage at cm ² ) could be changed from 3V to 5V.

Thereafter, using the conventional process, the source
Drain layers 108 and 109 and side walls 110 were formed. In the Ta gate SiO ₂ gate insulating film, 7
For those having a history of 000 ° C. or more, the electrical oxide film thickness measured by the high frequency CV characteristic is 2-3 times the actual film thickness.
Double. From the viewpoint of leakage current, a history of 800 ° C. is allowed, but considering long-term reliability and the like, it is necessary to set the upper limit of the process temperature to 700 ° C. In addition, in-plane uniformity and process time for large-diameter wafers are reduced,
In consideration of the process time, the minimum reaction temperature, and the like in processes such as silicide formation in addition to the process margin in mass production, it is more preferable to perform the process at 600 ° C. or lower.

The film forming conditions described above are not limited to the above, and other plasma sources and process conditions may be used as long as similar results can be obtained. The gate may be processed without depositing the mask SiO ₂ film 106. However, when the source / drain layers are formed by ion implantation, impurities are also implanted in the gate Ta film, and Cause the sheet resistance to rise,
It is preferable to use a mask SiO ₂ film. When the SiO ₂ film for mask is not used, the Ta thin film 104 is etched with a resist mask, and then the resist ashing step and the Ta re-oxidation step are performed simultaneously, so that Ta ₂ O _{5 on the} side wall of the Ta gate electrode is used. The properties of the film are degraded as compared to the above process. Therefore, when ashing is performed, it can be improved by setting the microwave power to 500 W, thereafter setting the microwave power to 1200 W, and oxidizing the side wall of the Ta gate electrode. Breakdown voltage between drains (current density 1
The voltage at the time of 00 mA / cm ^{2 was} 4.7 V.

(Embodiment 2) FIG. 5 shows a schematic diagram of another device manufacturing flow of the present invention. The difference from the first embodiment is that Ta
_{The point that the 2} O ₅ film was formed by direct oxidation of Ta and that the non-doped polysilicon 5
5 is formed by a plasma CVD method (PECVD) to a thickness of 5 nm, and thereafter, a mask SiO ₂ film 505 is deposited.

The Ta ₂ O ₅ film is formed by first forming a Ta film of 6 nm.
After forming the thick film, direct oxidation of Ta was performed using XeHe / O ₂ plasma. The process apparatus used in this process is a microwave-excited plasma apparatus using a radial line slot antenna similar to that shown in FIG. The processing conditions at that time were: Xe / He / O ₂ gas used, gas pressure 500 m
Torr, partial pressure ratio: Xe: He: O ₂ = 68%: 30
%: 2%, microwave power: 1200 W, oxidation time: 15 minutes, the substrate was kept electrically floating, and the temperature of the object to be processed was 450 ° C. However, the film forming conditions are not limited to these, and instead of Xe, Ar
May be used, but it is more preferable to use Xe.

The film formation of the non-doped polycrystalline silicon is as follows:
Ar / SiH ₄ (1%), gas pressure 100 mTorr
r, at a substrate temperature of 300 ° C. This time, polycrystalline silicon was used, but amorphous silicon or doped silicon may be used. These silicon layers are used to prevent oxidation of the underlying gate metal. This silicon layer or Example 1
In the absence of the TaN layer described in (1), there arises a problem that the contact resistance between the gate and the wiring metal increases. However, when there is no contact between the gate and the wiring metal, that is, when applying the present invention to a floating gate,
The silicon layer or TaN layer may not be provided,
It is better to use it to suppress the rise in gate resistance.

Since the non-doped silicon layer becomes Ta ₅ Si ₃ or TaSi ₂ by a silicide reaction with the base Ta during activation annealing of the source / drain regions, for example, there is a problem that the contact resistance with the wiring metal is increased. There is no.

[0024]

According to the present invention, the surface of a metal gate electrode is changed to a metal insulating film at a low temperature, and a device
A device structure for improving the reliability of the system and a method for manufacturing the same can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a manufacturing flow of a device of Example 1.

FIG. 2 is a diagram showing a part of a cluster tool used for manufacturing.

FIG. 3 is a schematic view of a plasma apparatus used for modifying a Ta ₂ O ₅ thin film.

FIG. 4 is a diagram illustrating a cluster chamber according to the first embodiment.

FIG. 5 is a schematic flow chart of manufacturing a device of Example 2.

[Description of Signs] 102 field oxide film, 201 transfer path, 202 single wafer cleaning device, 203 loading chamber, 204 process chamber, 205 process chamber, 301 vacuum vessel, 302 inlet, 303 vacuum pump, 304 dielectric plate, 305 Antenna, 306 electrode, 307 shower plate, 309 reflector, 401 loading chamber, 402 etching chamber, 403 process chamber, 404 etching chamber, 405 process chamber.

Continuing from the front page (72) Inventor Yuhisa Nitta Ultra Clean Technology Development Laboratory 4-1-1 Hongo, Bunkyo-ku, Tokyo (72) Inventor Kazuhide Ino Aoba Aramaki Aoba-ku, Aoba-ku, Sendai, Miyagi No.) Tohoku University (72) Inventor Toshihisa Shinohara Aoba-ku, Aoba-ku, Aoba-ku, Sendai City, Miyagi Prefecture (No address) Inside Tohoku University

Claims (8)

[Claims] An electrically conductive substrate of a first type and a second type of electrical conductivity opposite to that of said substrate, spaced apart from each other in or on said substrate. A first source and drain region disposed between the first source and drain regions to define a channel in the substrate therebetween and to form an electrical connection with the substrate, and between the first source and drain regions;
A semiconductor device having a metal gate electrode placed over the channel via a first insulating layer so as not to make direct electrical contact with the first source and drain regions or with any of the regions; A semiconductor device, wherein at least a part of a metal gate electrode other than a surface in contact with the channel is covered with an insulating film containing the metal. 2. The semiconductor device according to claim 1, wherein only a side wall of said metal gate electrode is covered with an insulating film containing said metal.
3. The semiconductor device according to claim 1. 3. The metal gate electrode is made of Ta,
3. The semiconductor device according to claim 1, wherein a surface of the Ta gate electrode other than the surface in contact with the channel is covered with a tantalum oxide film. 4. The method according to claim 1, wherein the insulating film containing the metal is formed by modifying the surface of the metal gate while maintaining the temperature of the substrate at 700 ° C. or lower.
The semiconductor device according to claim 1. 5. The method according to claim 1, wherein the insulating film containing the metal is formed by modifying the surface of the metal gate while keeping the temperature of the base at 600 ° C. or less.
The semiconductor device according to claim 1. 6. The method according to claim 1, wherein the insulating film containing the metal is formed by maintaining the temperature of the substrate at 600 ° C. or lower and modifying the surface of the metal gate by means using plasma. 6. The semiconductor device according to any one of 1 to 5. 7. The method according to claim 1, wherein the insulating film containing the metal is formed by maintaining the temperature of the base at 600 ° C. or lower and modifying the surface of the metal gate by means using plasma containing Xe. Any one of claims 1 to 6
13. The semiconductor device according to item 9. 8. The method according to claim 1, wherein the insulating film containing the metal is formed by oxidizing the surface of the metal gate using a gas containing oxygen radicals while keeping the temperature of the base at 600 ° C. or less. Item 8. The semiconductor device according to any one of Items 1 to 7.