JP2002314073A - Method for manufacturing semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a semiconductor device in which the breakdown voltage of a gate oxide film does not deteriorate even after long time heat treatment for impurity diffusion. SOLUTION: An LOCOS film 5 is formed on a semiconductor substrate 1, an oxide film 6 is formed on the resulting semiconductor substrate 1, impurities are introduced to the surface of the semiconductor substrate 1 through an oxide film 3 and then heat treatment is performed in order to diffuse introduced impurities under an atmosphere containing an oxidizing gas thus fabricating a semiconductor device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device, and more particularly, to a method for manufacturing a semiconductor device including steps of performing element isolation using a thermal oxide film, introducing impurities, and performing heat treatment.

[0002]

2. Description of the Related Art In recent years,
LOCOS (Local Oxdation)
of Silicon) method is widely used.

A conventional method for forming an element isolation film will be described below.

First, a first oxide film 2 is formed by thermally oxidizing the surface of a silicon substrate 1, and a nitride film 3 is deposited on the first oxide film 2. Next, the resist pattern 4 for element isolation formation
Is formed by a photolithography technique. Using the resist pattern 4 as a mask, the nitride film 3 is patterned (FIG. 4A).

After that, the resist pattern 4 is removed, and the silicon substrate 1 is cleaned. Next, the obtained silicon substrate 1 is oxidized to form a LOCOS oxide film 5, and the nitride film 3 is completely removed with hot phosphoric acid at about 150 ° C. (FIG. 4).
(B)).

Subsequently, the first oxide film 2 is removed using buffered hydrofluoric acid (FIG. 4C), and a second oxide film 6 is formed again by thermal oxidation (FIG. 4D). ).

Next, in order to form a P well, boron ions 7 are implanted into the entire surface of the silicon substrate 1 (FIG. 4).
(E)).

A resist pattern 8 for forming the N well 11 is formed by photolithography. Using this resist pattern 8 as a mask, phosphorus ions 9 are implanted (FIG. 4F). At this time, N
The boron ions 7 implanted into the region for forming the well are compensated by the phosphorus ions 9.

Subsequently, as shown in FIG.
A heat treatment is performed at 00 ° C. for 540 minutes to diffuse the impurities to form the P well 10 and the N well 11.

Next, the second oxide film 6 is removed using buffered hydrofluoric acid, and a gate oxide film is formed by gate oxidation.

After that, transistors and wirings are sequentially formed by a known method to complete a semiconductor device.

However, since the gate oxide film thus formed is thinned around the LOCOS oxide film 5,
There is a problem that the withstand voltage of the gate oxide film is deteriorated and the reliability of the device is reduced.

Therefore, as a method of solving the above problem,
For example, Japanese Patent Application Laid-Open No. Hei 8-203995 proposes a method in which an oxide film is formed after a heat treatment in a nitrogen atmosphere containing no oxygen that diffuses impurities introduced into a semiconductor substrate.

However, even in such a method, when a long heat treatment is required such as when a deep diffusion layer is required for a high withstand voltage device, the gate oxide film is increased with a long heat treatment time. However, since the breakdown electric field strength becomes small, the heat treatment has a time restriction, and the above problem has not always been solved.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and has as its object to provide a method of manufacturing a semiconductor device in which a gate oxide film does not deteriorate in breakdown voltage even after a long-time heat treatment for impurity diffusion. And

[0016]

The inventor of the present invention has studied the causes of the deterioration of the breakdown voltage of the gate oxide film.
As shown in FIG. 5A, the periphery of the LOCOS oxide film 5 and the surface of the silicon substrate 1 are nitrided during a heat treatment in a nitrogen gas atmosphere to form a nitride film 13 partially.
As shown in FIG. 5B, after an oxide film (not shown) is formed and further removed, the nitride film 13 remains only in the peripheral portion of the LOCOS oxide film 5, and as shown in FIG. ,
When a gate oxide film 14 is formed on the entire surface of such a silicon substrate 1, the LOCOS
The formation of the gate oxide film 14 formed around the oxide film 5 is hindered, and the gate oxide film 14 at that portion is reduced in thickness 14a.
And completed the present invention.

That is, according to the present invention, a LOCOS film is formed on a semiconductor substrate, an impurity is introduced into the surface of the obtained semiconductor substrate, and the impurity introduced in an atmosphere containing an oxidizing gas is diffused. And a method of manufacturing a semiconductor device for performing the method.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method of manufacturing a semiconductor device according to the present invention comprises forming a LOCOS film on a semiconductor substrate, introducing impurities into the surface of the obtained semiconductor substrate, and introducing the impurities in an atmosphere containing an oxidizing gas. And performing a heat treatment for diffusing the impurities.

Examples of the semiconductor substrate that can be used in the present invention include various substrates such as an element semiconductor substrate such as silicon and germanium, a substrate made of a compound semiconductor such as GaAs and InGaAs, an SOI substrate, and a multilayer SOI substrate. Can be used. Among them, a silicon substrate is preferable.

The LOCOS film is a film usually formed as an element isolation region, and can be formed by the LOCOS method. Specifically, a first oxide film is formed on a semiconductor substrate, a nitride film is selectively formed on the first oxide film, and oxidation is performed using the nitride film as a mask. it can. Here, the first oxide film is LOC
It is formed to relieve stress when an OS film is formed, and can be formed by thermal oxidation of a semiconductor substrate, a CVD method, or the like. It is appropriate that the oxide film has a thickness of, for example, about 5 to 20 nm. The nitride film is formed as an oxidation prevention film, and has a thickness of 100 to 30.
About 0 nm is appropriate. As a method for selectively forming a nitride film, a nitride film is formed on the entire surface of the first oxide film by a CVD method or the like, and then a resist pattern having a desired shape is formed by a photolithography and etching process. There is a method of etching using a pattern as a mask. By performing heat treatment in an oxidizing atmosphere using the nitride film as a mask, a LOCOS oxide film can be formed. The heat treatment here is performed, for example, in a temperature range of about 950 to 1150 ° C. and 20 to 20 °.
For example, about 0 minutes, and thus, for example, a film thickness of 30 minutes
A LOCOS oxide film of about 0 to 700 nm can be formed. After forming the LOCOS oxide film, it is preferable to completely remove the nitride film and the first oxide film by wet etching using an appropriate etchant or the like.

After the above steps, it is preferable to form an oxide film on the obtained semiconductor substrate. The oxide film here is formed as a protective film when impurities are introduced in a later step, and is suitably formed with a thickness of about 10 to 40 nm by the same method as described above.

Impurities are introduced into the surface of the semiconductor substrate without or through an oxide film formed on the semiconductor substrate. The impurities here are p-type or n-type impurities,
Although it can be introduced by various methods such as vapor phase diffusion and ion implantation, it is preferable to introduce it by ion implantation. The ion implantation is preferably performed by a known method by selecting an appropriate ion species, acceleration energy, and dose. The purpose of the impurity introduction here is not particularly limited as long as the impurity can be introduced before the formation of the gate oxide film, and the purpose is not particularly limited. It can be applied to various purposes such as formation. In particular, the present invention can be suitably applied to the introduction of impurities used in a process requiring a higher breakdown voltage than a normal logic process such as a flash memory and a liquid crystal driver. The introduction of the impurity may be either p-type or n-type ion implantation, may be both ion implantations, may be only one time or plural times, or may use an appropriate resist mask. Ion implantation may be used.

After introducing the impurities, a heat treatment is performed. In the case where an oxide film is formed in advance, the heat treatment may be performed with the oxide film attached or after removing the oxide film. Further, it is preferable to perform the heat treatment under an atmosphere containing an oxidizing gas, particularly under a nitrogen atmosphere containing an oxidizing gas. The oxidizing gas means a gas containing an oxygen atom, such as an oxygen gas and an ozone gas. The oxidizing gas is suitably contained in the atmosphere at a flow rate ratio (volume) of 0.5 to 5%. The heat treatment can be performed at a temperature in the range of about 1000 ° C. to 1300 ° C., preferably about 1100 ° C. to 1150 ° C.
The heat treatment time can be appropriately adjusted depending on the temperature of the heat treatment and the like, and is about 1 hour to 50 hours, preferably about 2 hours to 30 hours. By such a heat treatment, a new oxide film is formed on the entire surface of the semiconductor substrate. The thickness of the oxide film here varies depending on the heat treatment conditions. For example, if the oxide film was formed before the heat treatment, the total oxide film formed on the semiconductor substrate in addition to the oxide film Is preferably about 50 to 100 nm.

In the method of manufacturing a semiconductor device according to the present invention, the above-described steps are preferably performed in the above-described order. However, before and after each step, steps usually performed when forming a semiconductor device are added. May be. Further, after the above series of steps, steps necessary for forming various semiconductor devices are described.
It is preferable to carry out according to a known method.

For example, it is preferable that after the heat treatment, an oxide film other than the LOCOS oxide film formed on the entire surface of the semiconductor substrate is removed, and then a new gate oxide film is formed on the semiconductor substrate. Various known methods can be used to remove the oxide film here. For example, wet etching using an appropriate etchant is preferable. The gate oxide film can be formed by selecting an appropriate thickness by a method known in the art.

The method of manufacturing a semiconductor device according to the present invention will be described below with reference to the drawings.

First, the surface of the silicon substrate 1 is thermally oxidized,
A first oxide film 2 having a thickness of about 10 nm is formed to relieve stress in forming a LOCOS film, and a nitride film 3 is formed on the first oxide film 2 by LP.
Deposit about 170 nm by the CVD method. Next, an element isolation resist pattern 4 is formed by photolithography. Using the resist pattern 4 as a mask, the nitride film 3 is etched by a dry etching technique (FIG. 1A).

Thereafter, the resist pattern 4 is removed, and the silicon substrate 1 is cleaned. Next, the obtained silicon substrate 1 is oxidized to a LOCOS oxide film 5 of about 400 nm.
Is formed, and the nitride film 3 is completely removed with hot phosphoric acid at about 150 ° C. (FIG. 1B).

Next, the first oxide film 2 is removed using buffered hydrofluoric acid (FIG. 1C).

A second oxide film 6 having a thickness of about 20 nm is formed again by thermal oxidation (FIG. 1D).

Subsequently, in order to form a P well, boron ions 7 are applied at an energy of 150 keV to about 3 × 10
^At a dose of ¹² cm ^-2 , implantation is performed on the entire surface of the silicon substrate 1 (FIG. 1E).

Next, a resist pattern 8 for forming the N well 11 is formed by photolithography. Using this resist pattern 8 as a mask, phosphorus ions 9 are applied at an energy of 400 keV to about 2 × 10
^The implantation is performed at a dose of ¹³ cm ^-2 (FIG. 1F). On this occasion,
The boron ions 7 implanted in the region where the N well is formed in the previous step are compensated for by the phosphorus ions 9.

Subsequently, a heat treatment is performed at 1100 ° C. for 540 minutes to diffuse the impurities to form the P well 10 and the N well 11. The heat treatment at this time is performed under an atmosphere in which oxygen gas is mixed at a flow rate of 0.5% to 5% with respect to nitrogen.
Perform while maintaining this atmosphere. Thereby, the third oxide film 1 having a thickness of 50 nm to 100 nm is formed on the surface of the silicon substrate 1.
2 is formed (FIG. 1 (g)).

Thereafter, the third oxide film 12 is removed using buffered hydrofluoric acid, and a gate oxide film (not shown) is formed by gate oxidation.

Next, transistors and wirings are sequentially formed by a known method to complete a semiconductor device.

The breakdown voltage of the gate oxide film manufactured by the above method was evaluated. The result is shown in FIG. Note that the gate oxide film was formed by dry O ₂ oxidation with a thickness of 38 nm.

According to FIG. 2, it can be confirmed that, in the case of the method of the present invention, the deterioration of the withstand voltage of the obtained gate oxide film is completely eliminated in comparison with the conventional method.
That is, in the conventional method, the withstand voltage of the gate oxide film is 8 to 2
In the present embodiment, the voltage is distributed in the range of 9 V.
Since it is distributed in the range of 2 to 33 V, 8 MV / c
A physical breakdown electric field of the silicon oxide film of m (= 3.2 V / 38 nm) is realized, and the withstand voltage deterioration of the gate oxide film is completely eliminated.

As described above, in the method of the present invention, by adopting specific heat treatment conditions, as shown in FIG. 3A, depending on the heat treatment after impurity introduction, the surface of the silicon substrate 1 and the LOCOS oxidation No nitride film is generated near the film 5. As a result, as shown in FIG. 3B, after the oxide film is removed, no nitride film for suppressing oxidation does not remain, so that the gate oxide film is formed as shown in FIG. Also, the thickness of the peripheral portion of the LOCOS oxide film 5 is not reduced, and the breakdown voltage does not deteriorate.

[0039]

According to the method of manufacturing a semiconductor device of the present invention, the heat treatment after impurity introduction is performed under specific conditions, so that the surface of the semiconductor substrate around the LOCOS oxide film can be in an oxidizing atmosphere. In addition, generation of a nitride film can be suppressed. As a result, it is possible to prevent a gate oxide film to be formed in a later step from being thinned in the peripheral portion of the LOCOS oxide film, and to realize a method of manufacturing a semiconductor device in which the withstand voltage of the gate oxide film is prevented from deteriorating by a simple method. It becomes possible.

In particular, it is possible to provide a method of manufacturing a semiconductor device that reliably prevents the gate oxide film from deteriorating withstand voltage even when a long-time heat treatment is required.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional process drawing of a main part for describing a method for manufacturing a semiconductor device of the present invention.

FIG. 2 is a graph showing an evaluation of the withstand voltage degradation of a gate oxide film when the method of manufacturing a semiconductor device according to the present invention is applied.

FIG. 3 is a schematic cross-sectional view of a main part for explaining a mechanism of preventing a gate oxide film from deteriorating withstand voltage by applying a method of manufacturing a semiconductor device according to the present invention;

FIG. 4 is a schematic sectional view of a main part showing a conventional method for manufacturing a semiconductor device.

FIG. 5 is a schematic cross-sectional view for explaining a cause of a decrease in breakdown voltage of a gate oxide film in a conventional method.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 silicon substrate (semiconductor substrate) 2 first oxide film 3, 13 nitride film 4, 8 resist pattern 5 LOCOS oxide film 6 second oxide film (oxide film) 7 boron ion 9 phosphorus ion 10 P well 11 N well 12 second Oxide film 3 14 Gate oxide film 14a Thinned portion of gate oxide film

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5F048 AA07 AC03 BA15 BE03 BG12 5F058 BC02 BE07 BF56 BF62 BJ01 5F140 AA19 AB03 AC36 BA01 BA07 BA09 BC06 BC15 BC17 BD05 BE03 BE07 CB01 CB08 CB10

Claims (4)

[Claims] A LOCOS film formed on a semiconductor substrate;
A method for manufacturing a semiconductor device, in which an impurity is introduced into a surface of the obtained semiconductor substrate and a heat treatment for diffusing the introduced impurity in an atmosphere containing an oxidizing gas is performed. 2. The method according to claim 1, wherein an oxide film formed on the heat-treated semiconductor substrate is removed, and thereafter, a gate oxide film is formed on the semiconductor substrate surface. 3. A heat treatment at 1100 ° C. to 1150 ° C.
The method according to claim 1 or 2, which is performed for 2 hours to 30 hours. 4. The atmosphere containing an oxidizing gas is 0.5
The method according to any one of claims 1 to 3, wherein the atmosphere is a nitrogen gas atmosphere containing an oxidizing gas at a flow ratio of 5 to 5%.