JP3416716B2 - Method for forming oxide film on semiconductor substrate surface - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal-oxide film-semiconductor device, that is, a MOS (metal oxide semiconductor) device used in semiconductor integrated circuits and the like, and more particularly to an ultrathin gate oxide film and a capacitor of a MOS transistor and a MOS capacitor. The present invention relates to a method of forming an oxide film on the surface of a semiconductor substrate, which can be applied to an oxide film and the like.

[0002]

2. Description of the Related Art Semiconductor devices, especially MOS transistors, MOS oxide gate oxide films, and capacitor oxide films are usually formed of a silicon dioxide film in the case of a silicon device.
(Hereinafter referred to as an oxide film) is used. These oxide films are required to have a high dielectric breakdown voltage and a high dielectric breakdown charge amount. Therefore, wafer cleaning is positioned as one of the very important steps.

At the same time that the wafer is washed,
High quality such as low fixed charge density and low interface state density is required. On the other hand, with the miniaturization and high integration of devices, the gate oxide film and the capacitive oxide film have become thinner. For example, a design rule of 0.1 μm or less requires an ultrathin gate oxide film of 4 nm or less. .

Conventionally, a method of forming a gate oxide film of a MOS transistor by exposing a semiconductor substrate to an oxidizing atmosphere such as dry oxygen or water vapor at a high temperature of 600 ° C. or higher has been adopted.

In addition to thermal oxidation, a chemical vapor deposition method in which monosilane is thermally decomposed and deposited on the surface of the substrate is also used.

Further, as a method of growing an oxide film at a low temperature, there is a method of forming a chemical oxide film by immersing a semiconductor substrate in a chemical solution such as nitric acid having a strong oxidizing property. However, there is a problem that an oxide film having a thickness of about 1 nm or more cannot be grown.
It cannot be used as a gate oxide film.

However, the conventional thermal oxidation at a relatively high temperature has a problem that the controllability of the film thickness is insufficient when forming an oxide film of 4 nm or less.

When oxidation is performed at a low temperature in order to improve the controllability of the film thickness, the quality of the oxide film formed is
There are problems such as high interface state density and high fixed charge density.

Furthermore, the oxide film deposited by the chemical vapor deposition method also has the same problems in terms of film thickness controllability and film quality.

Therefore, as a method for solving these problems, for example, a method for forming an oxide film is proposed in Japanese Patent Laid-Open No. 9-45679.

The outline of this method will be described with reference to FIG.

First, the isolation region 2 and the active region 4 are formed on the semiconductor substrate 1. A natural oxide film 9 is formed on the surface of the active region 4.
Exists (FIG. 4 (a)).

In this state, next, the wafer is mounted on a known RC.
A cleaning method (W. Kern, D.A. Plutien: RCA review 31, page 18, 1970) is used to clean the wafer, and then the wafer is immersed in a dilute HF solution to remove the native oxide film 8 on the silicon surface. (Fig. 4 (b)).

Then, after rinsing (washing) the wafer,
This is dipped in hot nitric acid to form a chemical oxide film (first oxide film) 5 having a surface thickness in the range of 0.1 to 1.5 nm on the silicon substrate 1 (FIG. 4 (c)).

Next, a metal thin film (for example, a platinum thin film) 6 having an oxidation catalyst function is formed on the first oxide film 5 by a vapor deposition method in a thickness range of 1 to 30 nm (FIG. 4 (d)).

Thereafter, heat treatment is performed at a temperature of 25 to 600 ° C. in an oxidizing atmosphere to form the second oxide film 7.
(Fig. 4 (e)).

At this time, the thickness of the second oxide film 7 is 1 to 2
At about 0 nm, the film thickness can be controlled by the heat treatment temperature and the heat treatment time.

[0018]

The method of the prior art shown in FIG. 4 has the advantage that a relatively low temperature of 600 ° C. or less and a thin oxide film of several nm can be formed with good controllability. , The following problems remain.

That is, although the interface state density of the oxide film formed by the method of FIG. 4 is lower than that of the oxide film formed by the low temperature thermal oxidation method or the chemical vapor deposition method, the required quality of the gate oxide film is required. Values below 1 × 10 ¹¹ eVcm ⁻² cannot be achieved.

When the value of the interface state density exceeds 1 × 10 ¹¹ eVcm ⁻² , not only the hot carrier characteristics of the transistor are deteriorated, but also the instability of the threshold voltage of the transistor and the mobility of carriers are increased. It causes fatal problems, especially in fine devices.

The present invention has been made in order to solve the above-mentioned problems, and by further improving the method shown in FIG. 4, the value of the interface state density is further lowered and a high quality is obtained on the surface of the semiconductor substrate. It is an object of the present invention to provide a method for forming an oxide film of the above.

[0022]

In order to solve the above problems, the present invention takes the following means in a method of treating an oxide film on the surface of a semiconductor substrate.

That is, according to the first aspect of the present invention, when forming the oxide film on the surface of the semiconductor substrate, the first oxide film having a thickness of 0.1 to 1.5 nm is formed on the semiconductor substrate, and then the first oxide film is formed. A metal thin film having an oxidation catalyst function is formed on the first oxide film in a thickness range of 1 to 30 nm.
The shape of the oxide film on the surface of the semiconductor substrate in which the first heat treatment is performed at a temperature of 00 ° C. or lower in an oxidizing atmosphere to form a second oxide film.
In the treatment method, after the first heat treatment, the oxidation catalyst function
On a metal thin film having a thickness of 1 to 1000 nm.
It is characterized in that the minium film is formed and the second heat treatment is performed at a temperature of 600 ° C. or lower in an atmosphere which is not an oxidizing atmosphere.

According to a second aspect of the invention, the surface of the semiconductor substrate
When forming an oxide film on the semiconductor substrate, the thickness of
Forming a first oxide film in the range of 1 to 1.5 nm, and then
A metal thin film having an oxidation catalyst function is formed on the first oxide film.
Formed in the range of 1 to 30 nm, and then 600 ° C.
Perform the first heat treatment in the oxidizing atmosphere at the following temperature
A method for forming an oxide film on the surface of a semiconductor substrate for forming a 2-oxide film, which has an oxidation catalyst function after the first heat treatment.
After removing the metal thin film with a thickness of 1-1000 nm
Form an aluminum film in an atmosphere that is not an oxidizing atmosphere
It is characterized in that the second heat treatment is performed at a temperature of 600 ° C. or lower .

According to a third aspect of the invention, in the method for forming an oxide film on the surface of a semiconductor substrate according to the first or second aspect, the second heat treatment is performed in an atmosphere containing hydrogen.
It is characterized by performing.

[0026]

[0027]

[0028]

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION In the method for treating an oxide film on the surface of a semiconductor substrate of the present invention, the following process is adopted.

(1) When forming an oxide film on the surface of a semiconductor substrate, a first oxide film having a thickness of 0.1 to 1.5 nm is formed on the semiconductor substrate, and then on the first oxide film. And forming a metal oxide film having an oxidation catalyst function in a thickness range of 1 to 30 nm, and then performing a first heat treatment in an oxidizing atmosphere at a temperature of 600 ° C. or less to form a second oxide film. Then, after this first heat treatment, a second heat treatment is performed at a temperature of 600 ° C. or lower in an atmosphere that is not an oxidizing atmosphere.
As a result, a thin oxide film having a low interface state density of about 1 to 20 nm can be realized.

(2) In particular, in the method (1), it is preferable to use the resistance heating vapor deposition method when forming the metal thin film having the oxidation catalyst function.

(3) In the above methods (1) and (2), the second heat treatment is performed particularly in an atmosphere containing hydrogen.

(4) In the method of any one of (1), (2), and (3) above, aluminum having a thickness of 1 to 10000 nm is formed on the metal thin film having an oxidation catalyst function before the second heat treatment. Form a film.

(5) In the above method (4), the metal thin film having an oxidation catalyst function is removed before the aluminum film is formed.

(6) Furthermore, even if the second heat treatment is not performed, the interface characteristics can be improved to some extent by using the resistance heating vapor deposition method when forming the metal thin film having the oxidation catalyst function.

[0036]

EXAMPLES The present invention will be described more specifically below based on examples.

Example 1 In Example 1, a silicon substrate is used as an example of a semiconductor substrate, and a process of forming a MOS capacitor will be described with reference to FIG.

First, the isolation region 2 and the active region 4 were formed on the silicon substrate 1. A natural oxide film 8 exists on the surface of the active region 4 (FIG. 1 (a)).

As a silicon substrate, p-type (100), 10
After using a substrate of 150 Ωcm and implanting a boron channel stopper, LOCOS (1 ocal oxidati
An oxide film was formed to a thickness of 500 nm.

Next, in order to clean the surface of the active region 4,
After cleaning the wafer by a known RCA cleaning method,
Immerse in dilute HF solution (0.5 vol.% HF aqueous solution) for 5 minutes,
The native oxide film 8 on the silicon surface was removed (FIG. 1 (b)). The removal of the natural oxide film 8 has an important role in forming the first oxide film 5 having clean and uniform characteristics thereafter.

In order to form a high quality ultra-thin oxide film on the silicon surface, a clean silicon surface 3 is necessary, and it is important to completely remove the natural oxide film 8 on the silicon surface and remove impurities on the silicon surface. .

Next, the wafer is rinsed with ultrapure water for 5 minutes.
After (washing), the wafer was immersed in hot nitric acid at 115 ° C. for 10 minutes to form a chemical oxide film having a surface thickness of 1.1 nm as the first oxide film 5 on the silicon substrate (FIG. 1 (c)). Thus, by using hot concentrated nitric acid, a clean and high-quality chemical oxide film (first oxide film) 5 containing no heavy metals can be formed.

As a treatment method for forming the chemical oxide film 5 on the semiconductor surface, in addition to the method of immersing in the hot concentrated nitric acid as in Example 1, the method of immersing in the mixed solution of sulfuric acid and hydrogen peroxide solution is used. Examples include a method, a method of immersing in a mixed solution of hydrochloric acid and hydrogen peroxide solution, a method of immersing in a mixed solution of ammonia water and hydrogen peroxide solution, a method of immersing in ozone water in which ozone is dissolved at 10 ppm. In addition, a method of performing heat treatment at 400 ° C. to room temperature while exposing the wafer to the ozone gas atmosphere, a method of exposing the wafer to the ozone gas atmosphere while irradiating the ultraviolet ray, and the like are also possible.

Next, on the first oxide thin film 5 on the silicon substrate, platinum 6 having a thickness of about 3 nm was vapor-deposited as a metal thin film having an oxidation catalyst function by an electron beam vapor deposition method (FIG. 1).
(d)).

At this time, platinum having a purity of 99.99% was used. The vapor deposition rate was 0.3 nm / min, the temperature of the silicon substrate during vapor deposition was 50 ° C., and the pressure was 1 × 10 ⁻⁴ Pa. In addition to platinum, palladium can be used as the metal film having an oxidation catalyst function.

Then, in an electric furnace in humidified oxygen at 300 ° C.
For 1 hour (first heat treatment). By this first heat treatment, the silicon oxide film 7 was grown to a thickness of 4.5 nm (see FIG. 1).
(e)).

At this time, an oxide film 7 having a thickness of 4.5 nm and platinum 6 having a thickness of 3 nm are formed on the silicon substrate 1.

Further, in Example 1, nitrogen gas having a purity of 99.9999% was used as an atmosphere gas to be flown in the electric furnace, and this gas was replaced while flowing at a rate of 10 liters per minute to obtain 400 Treated at ℃ for 1 hour (2nd
Heat treatment).

The atmosphere gas at this time is not particularly limited to nitrogen gas as long as it does not form an oxidizing atmosphere, and for example, an inert gas such as helium or argon may be used.

Further, the second oxide film 7 thus formed
In order to accurately measure the interfacial characteristics of Pt, the photoresist 10 is formed on the platinum thin film 6 (Fig. 1 (f)), and the platinum thin film 6 on the separation region 2 is removed with aqua regia (Fig. 1 (g)). ), And the photoresist 10 was removed by a remover (FIG. 1 (h)).

In the first embodiment, the photoresist 10 is formed in order to measure the interface characteristics. However, when the photoresist 10 is used as a MOS capacitor, it is not necessary to form the photoresist 10 and the platinum thin film 6 is used. You may directly form a metal thin film for a gate electrode or a circuit structure on it.

Table 1 compares the results of measuring the minimum interface state densities immediately after the first heat treatment and immediately after the second heat treatment using the platinum thin film 6 as the gate electrode.

[0053]

[Table 1]

The interface state density is based on Solid State in the United States.
eMeasurement SSM-490i CV SYSTE
Charge / voltage measurement (Q-V) was performed using M, and it was determined using the conversion program of the same system.

As is apparent from Table 1, it can be seen that, as in Example 1, the second interface heat treatment was performed in the nitrogen atmosphere, whereby the value of the minimum interface state density was lowered and the interface characteristics were improved. .

The reason is considered as follows.

As described above, when the oxide film (first oxide film) 5 is formed on the semiconductor silicon substrate 1, it is considered that the oxide film 5 terminates the dangling bonds of the semiconductor at the interface. When the platinum thin film 6 is formed on the oxide film 5 by the electron beam evaporation method or the sputtering method, ultraviolet rays and X-rays are emitted, and charged particles such as ions are generated. The unbonded hands of are separated. Since the subsequent first heat treatment is performed in an oxidizing atmosphere, the effect of recovering the ends of the dangling bonds separated by the formation of the thin film 6 is not sufficient, but as in the present invention, in the atmosphere not in an oxidizing atmosphere. When the second heat treatment is performed, the recovery effect becomes remarkable, and the second oxide film 7
It is speculated that the interfacial properties of the are improved.

Example 2 In Example 2, instead of using nitrogen gas alone as in Example 1 in the second heat treatment, nitrogen gas and hydrogen gas each having a purity of 99.9999% were mixed at 97: 3. A mixed gas mixed in proportion was used. Although the hydrogen content in the second heat treatment is 3% in the second embodiment, a hydrogen gas content of 100% may be used.

Other methods were performed in the same manner as in Example 1 to measure the minimum interface state density. The results are shown in Table 1 above.

Second Example in Nitrogen Atmosphere of Example 1 above
As compared with the heat treatment, it can be seen that when the heat treatment including the hydrogen atmosphere is performed as in Example 2, the value of the minimum interface state density is further reduced and the interface characteristics are further improved.

The reason is that, in the second heat treatment, if an atmosphere containing hydrogen gas is used, hydrogen penetrates to the interface, and this penetrating hydrogen promotes the termination of dangling bonds, and initially the second oxide film 7 is used. It is speculated that unbonded bonds that were not terminated will also be terminated by hydrogen.

Example 3 In this Example 3, the second oxide film 7 according to the above Example 2 was used.
After forming (FIG. 1 (e) and FIG. 2 (a)), subsequently, an aluminum film 9 having a thickness of 500 nm was formed on the platinum thin film 6 by electron beam evaporation (FIG. 2 (b)). As a method of forming the aluminum film 9 at this time, a resistance heating vapor deposition method, a sputtering method, an ion plating method or the like may be used in addition to the electron beam vapor deposition method of the third embodiment.

Further, the second heat treatment is performed in the mixed gas used in Example 2 to form the photoresist 10 in the same manner.
(Fig. 2 (c)) After boiling 5% phosphoric acid at 80 ° C to remove the aluminum film, and then removing platinum with aqua regia (Fig. 2).
(d)), the photoresist was removed by a remover (Fig. 2
(e)).

The results of the minimum interface state density measured in the same manner as in Example 1 are also shown in Table 1.

Compared to the values of Example 2, the heat treatment after forming the aluminum film 9 of Example 3 further reduced the value of the minimum interface state density, indicating that the interface characteristics were improved.

As described above, when the aluminum film 9 is formed on the platinum thin film 6 after the second oxide film 7 is formed, it is presumed that the hydrogen absorption efficiency is further increased, and the interface characteristics are further improved.

Example 4 In Example 2, after the second oxide film 7 was formed (FIG. 1 (e), FIG.
(a)), the platinum thin film 6 was removed with aqua regia (FIG. 3 (b)), and an aluminum film 9 of 500 nm was formed on the second oxide film 7 by electron beam evaporation (FIG. 3 (c)).

Further, the second heat treatment is performed in the mixed gas used in Example 2 to form the photoresist 10 in the same manner.
(FIG. 3 (d)) After boiling 5% phosphoric acid at 80 ° C. to remove the aluminum film 9 (FIG. 3 (e)), the photoresist was removed with a remover (FIG. 3 (f)).

The minimum interface state density of the oxide film produced by this method is also shown in Table 1.

When the second heat treatment is performed after the aluminum film 9 is directly formed on the second oxide film 7 as in the fourth embodiment, the minimum interface state density is lower than that in the third embodiment. Was decreased to 1 × 10 ¹¹ eVcm ⁻² or less, and the interface characteristics could be improved to such a quality that good characteristics were obtained as the gate oxide film of the transistor.

Thus, it is presumed that by removing the platinum thin film 6 in advance before forming the aluminum film 9, hydrogen can be more efficiently sent to the interface of the second oxide film 7 with the substrate 1, The interface characteristics are further improved.

[0072] forming processing method of an oxide film of Example 5 This example 5 is basically
It is similar to the process of Example 1, but is characterized by the method for forming the platinum thin film 6 having an oxidation catalyst function.

That is, in the fifth embodiment, similarly to the first embodiment, after the first oxide film 5 is formed on the silicon substrate 1, the resistance using the tungsten boat is formed on the first oxide film 5. A platinum thin film 6 having a thickness of about 3 nm was deposited by the heating deposition method (FIG. 1 (d)). At that time, 99.99% for platinum
The one with the purity of was used. The vapor deposition rate is 0.1 nm / min, the temperature of the silicon substrate 1 during vapor deposition is 60 ° C., and the pressure is 1 ×.
It was set to 10 ⁻⁴ Pa.

Thereafter, as in the case of Example 1, a treatment was performed in an electric furnace in humidified oxygen at 300 ° C. for 1 hour (first heat treatment). By this first heat treatment, the silicon oxide film 7 was grown to a thickness of 4.5 nm (FIG. 1 (e)). Subsequently, a nitrogen gas having a purity of 99.9999% was used as an atmosphere gas, which was replaced in the electric furnace while flowing at a rate of 10 liters for 1 minute and treated at 400 ° C. for 1 hour (second heat treatment). .

Further, the photoresist 1 is formed on the platinum thin film 6.
0 (FIG. 1 (f)), the platinum thin film 6 on the separation region 2 was removed with aqua regia (FIG. 1 (g)), and the photoresist 10 was removed with a remover (FIG. 1 (h). )).

The minimum interface state density using the platinum thin film 6 as a gate electrode is also shown in Table 1.

By limiting the method of forming the platinum thin film to the resistance heating vapor deposition as in the fifth embodiment, the value of the minimum interface state density can be reduced as compared with the case of using the conventional electron beam vapor deposition or the like. It can be seen that the interfacial properties are reduced and the interface properties are improved.

When the platinum thin film 6 is formed by the resistance heating vapor deposition method as in the fifth embodiment, it is presumed that the adverse effect of ultraviolet rays or X-rays on the interface during the formation of the platinum thin film 6 is reduced.

Even when the methods of Examples 2 to 4 are adopted, it is effective to form the platinum thin film 6 by the resistance heating vapor deposition method. Further, as in Example 5, even if the second heat treatment is not performed, the interface characteristics can be improved to some extent even when the resistance heating vapor deposition method is used when the metal thin film having the oxidation catalyst function is formed. Is.

[0080]

The method of treating an oxide film on the surface of a semiconductor substrate of the present invention has the following effects.

(1) As described in claim 1, after the first heat treatment , 1 to 10 are formed on the metal thin film having an oxidation catalyst function.
By forming an aluminum film having a thickness of 00 nm and performing a second heat treatment in an atmosphere that is not an oxidizing atmosphere, the interface characteristics of the oxide film on the surface of the semiconductor substrate formed with good controllability without using high-temperature heating, It can be improved further.

(2) As in the invention described in claim 2, the metal thin film having an oxidation catalyst function is removed before the second heat treatment.
An aluminum film is formed on the second oxide film after the removal.
As a result, as in the invention according to claim 3 , the second
By including hydrogen in the heat treatment atmosphere, an oxide film having a quality that can be used as a gate oxide film can be realized by the oxide film on the surface of the semiconductor substrate that is formed with good controllability without using high temperature heating. be able to.

[0083]

[Brief description of drawings]

FIG. 1 is a diagram showing a process of an embodiment of a method for forming an oxide film on a semiconductor substrate according to the present invention.

FIG. 2 is a diagram showing a process of another embodiment of the method for forming an oxide film on a semiconductor substrate of the present invention.

FIG. 3 is a diagram showing a process of still another embodiment of the method for forming an oxide film on a semiconductor substrate of the present invention.

FIG. 4 is a diagram showing a process of a conventional example of a method for forming an oxide film on a semiconductor substrate.

[Explanation of symbols]

1 Semiconductor substrate 2 separation oxide film 3 Clean semiconductor substrate surface 4 Active area of semiconductor surface 5 lth oxide film 6 Metal thin film (platinum thin film) with oxidation catalyst function 7 Second oxide film 8 Natural oxide film 9 Aluminum thin film 10 photoresist

Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01L 21/312 H01L 21/314 H01L 21/316 H01L 21/318

Claims (3)

(57) [Claims] 1. When forming an oxide film on the surface of a semiconductor substrate, a first film having a thickness of 0.1 to 1.5 nm is formed on the semiconductor substrate.
An oxide film is formed, then a metal thin film having an oxidation catalyst function is formed on the first oxide film in a thickness range of 1 to 30 nm, and then the first thin film is formed at a temperature of 600 ° C. or less and in an oxidizing atmosphere. A method of forming an oxide film on a surface of a semiconductor substrate, which comprises performing a heat treatment to form a second oxide film, wherein an aluminum film having a thickness of 1 to 1000 nm is formed on a metal thin film having an oxidation catalyst function after the first heat treatment. Then, the second heat treatment is performed at a temperature of 600 ° C. or lower in an atmosphere that is not an oxidizing atmosphere, and a method for forming an oxide film on the surface of the semiconductor substrate. 2. When forming an oxide film on the surface of a semiconductor substrate
On the semiconductor substrate with a thickness in the range of 0.1 to 1.5 nm.
An oxide film is formed, and then an oxidation catalyst is formed on the first oxide film.
Forming a metal thin film having a function within a thickness range of 1 to 30 nm
Then, at a temperature below 600 ° C and in an oxidizing atmosphere
In the method for forming an oxide film on the surface of a semiconductor substrate, in which a first heat treatment is performed to form a second oxide film , a metal thin film having an oxidation catalyst function is removed after the first heat treatment.
After removal, aluminum film with a thickness of 1-1000 nm
In a non-oxidizing atmosphere.
A method for forming an oxide film on a surface of a semiconductor substrate, which comprises performing the second heat treatment at a temperature of not more than ° C. 3. The method of forming an oxide film on a surface of a semiconductor substrate according to claim 1, wherein the second heat treatment is performed in an atmosphere containing hydrogen. Method for forming film.