JPH08306797A - Fabrication of semiconductor device - Google Patents

Abstract

PURPOSE: To deposit a gate oxide having two kinds of thickness by forming an anti-oxidation layer covering only a semiconductor substrate in a first forming region and a gate electrode and forming a bird's beak between a second forming region and the gate electrode by wet oxidation. CONSTITUTION: Gate electrodes 12, 12' are formed in regions A, B. Insulating oxide layers 14, 14' are also formed around the gate electrodes 12, 12'. After depositing nitride 15 by about 100nm as an anti-oxidation layer, the nitride is removed selectively from the region B. Silicon oxide is then deposited on a semiconductor substrate 11 in the region B by wet oxidation. Consequently, the insulating oxide layer 14' becomes thick on the surface and side face of the gate electrode 12' but a bird's beak is formed between the gate electrode 12' and the semiconductor substrate 11 and thereby a gate oxide layer 16' has a thickness of 12-16nm. With such method, semiconductor elements having gate oxide layer of different thickness can be fabricated on a same semiconductor substrate.

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 including a semiconductor element having a gate oxide film, and more particularly to manufacturing a semiconductor device having an element having a gate oxide film having a different film thickness on the same semiconductor substrate. Regarding the method.

[0002]

2. Description of the Related Art Conventionally, as a method of manufacturing a semiconductor of this kind, there are some methods as disclosed in, for example, Japanese Patent Application Laid-Open No. 4-103162 or Japanese Patent Application Laid-Open No. 3-55876.

The first method is described in Japanese Patent Application Laid-Open No. 4-103162 as prior art (FIG. 4), and is constituted by the steps shown in FIG. First, FIG.
As shown in (a), the main surface of the N or P type semiconductor substrate 21 is thermally oxidized to form an insulating film (silicon oxide film) 22 having a film thickness t1 on the entire surface (regions A and B). next,
As shown in FIG. 2B, after the resist 23 as a mask is selectively formed on the insulating film 22 only in the region A, the insulating film 22 in the region B not covered with the resist 23 is wet-etched. To remove. Next, after removing the resist 23 in the region A, as shown in FIG. 2C, an insulating film 24 having a film thickness t2 is formed on the entire surface by thermal oxidation again.
As a result, a gate oxide film having a film thickness (t1 + t2) is formed in the region A and a film thickness t2 is formed in the region B. After this, the usual MOS manufacturing process is performed. That is, as shown in FIG. 2D, after forming a polysilicon (polycrystalline silicon) film 25 on the insulating film 24, the polysilicon film 25 is patterned to form a gate electrode, which is self-aligned with the gate electrode. Specifically, an impurity diffusion region is formed near the surface of the semiconductor substrate 21 to form a source / drain region.

The second method is the above-mentioned Japanese Patent Laid-Open No. 10316/1992.
This is the method shown in FIG. That is, a polysilicon film to be a gate electrode is formed on the gate oxide film having a film thickness t1, a resist as a mask is formed, and then the polysilicon film and the gate oxide film not covered with the resist are removed. Next, a gate oxide film having a film thickness t2 is formed by thermal oxidation, and polysilicon is formed thereon. The polysilicon and oxide film in the upper layer of the gate oxide film region having the film thickness t1 are removed. As a result, a MOS transistor having a gate oxide film with a film thickness of t1 and t2 can be formed.

The third method is the method disclosed in Japanese Patent Laid-Open No. 3-55876. That is, a nitride film is formed in a part of the transistor formation region before gate oxidation is performed. Oxidation causes bird's beak of an oxide film between the nitride film and the semiconductor substrate. After removing the nitride film, a gate oxide film electrode is formed on the bird's beak oxide film, whereby a MOS transistor having a thin gate oxide film is formed. If the gate oxide film electrode is formed in the region where the nitride film is not formed, a MOS transistor having a thick gate oxide film is formed.

[0006]

SUMMARY OF THE INVENTION In the first method,
When selectively removing the insulating film, a resist as a mask is directly formed on the insulating film. However, since the resist generally contains a large amount of alkali metals, heavy metals, etc., the insulating film with which the resist is in direct contact has the effect of deteriorating the initial breakdown voltage. Further, the removal of the resist is performed by an ashing process using oxygen (O ₂ ) plasma, and the insulating film is directly exposed to the plasma, so that the initial breakdown voltage is also deteriorated in this case. Therefore, there is a problem that the reliability as a device deteriorates in the long term.

The present invention has been made in view of the above problems, and an object thereof is to obtain gates of two kinds of film thickness without causing problems such as deterioration of initial withstand voltage of the gate oxide film and deterioration of long-term reliability. It is an object of the present invention to provide a semiconductor device manufacturing method capable of manufacturing a semiconductor device having an oxide film.

[0008]

A method of manufacturing a semiconductor device according to claim 1, wherein a semiconductor device having gate oxide films of different film thicknesses on the same semiconductor substrate is manufactured, A step of forming an insulating layer to be a gate oxide film, a step of forming a conductive layer to be a gate electrode over the entire surface of this insulating layer, and patterning this conductive layer to form a first formation region and a second formation region. By the step of forming the gate electrode in each formation region and the dry oxidation,
A step of forming an insulating film so as to cover the gate electrodes and the semiconductor substrate in the first and second formation regions, and a step of forming an oxidation resistant film so as to cover the semiconductor substrate and the gate electrode in the first formation region A wet oxidation treatment step for forming an oxide insulating film on the entire surface, and a step for removing the oxidation resistant film in the first formation region, the wet oxidation treatment step including the gate in the second formation region. The above-described object is achieved by generating a pars beak between the electrode and the semiconductor substrate and increasing the film thickness of the gate oxide film in the second formation region.

In the method of manufacturing a semiconductor device according to the second aspect, the object is achieved by forming the oxidation resistant film with a nitride film.

[0010]

In the method of manufacturing the semiconductor device according to the present invention, the gate electrode is formed in each of the first and second formation regions on the insulating film formed on the semiconductor substrate, and the insulating film is formed so as to cover all of them. In addition, an oxidation resistant film (nitride film) is formed so as to cover only the semiconductor substrate and the gate electrode in the first formation region, and wet oxidation treatment is further performed to form the gate electrode and the semiconductor substrate in the second formation region. By generating a purse beak between the two, the thickness of the gate oxide film in the second formation region can be increased. on the other hand,
The original film thickness of the gate oxide film in the first formation region is maintained due to the presence of the nitride film.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described in detail below with reference to FIG. FIG. 1 shows a method of manufacturing a semiconductor device according to an embodiment of the present invention. First, FIG.
As shown in (a), a silicon oxide film having a film thickness of 11 nm is formed on the entire surface (regions A and B) of an N or P type semiconductor substrate (silicon substrate) 11 by thermal oxidation, CV with the polysilicon film that becomes the gate electrode
A film thickness of about 350 nm is formed by D or the like, and the polysilicon film is doped with impurities such as phosphorus.

Then, the polysilicon film is patterned by photolithography to form gate electrodes 12 and 12 'in regions A and B, respectively. After that, a dry oxidation process is performed to form a film having the same thickness as the gate oxide film 1 on the semiconductor substrate 11.
1 nm silicon oxide films 13 and 13 '(insulating oxide film) are formed. At this time, the insulating oxide films 14 and 14 are also formed around the gate electrodes 12 and 12 '(top and side surfaces), respectively.
Is formed.

Next, as shown in FIG. 1 (b),
After depositing a nitride film (for example, Si ₃ N ₄ ) 15 as an oxidation resistant film to a thickness of about 100 nm, only the nitride film in the region B is selectively removed.

Next, a 30 nm silicon oxide film is further formed on the semiconductor substrate 11 in the region B by wet oxidation. At this time, in the region B, as shown in FIG. 1C, the insulating oxide film 14 ′ on and above the gate electrode 12 ′ is thickened by the wet oxidation process, but the gate electrode 12 ′ and the semiconductor substrate are thickened. Since bird's beaks are generated between the semiconductor substrate 11 and the gate electrode 1,
The film thickness of the gate oxide film 16 'sandwiched by 2'is 1
It becomes about 2 to 16 nm. On the other hand, the insulating oxide film 1 in the region A
Since 3 and the gate electrode 12 are covered with the nitride film 15 which is an oxidation resistant film, the semiconductor substrate 11 and the gate electrode 12 in the region A are not oxidized and the oxide film is not formed on the nitride film 15. Of course, the thickness of the gate oxide film 16 is
It remains 11 nm formed in the first step.

Next, by removing the nitride film 15 in the region A, the state shown in FIG. 1C is obtained. After that, a normal MOS transistor forming process is performed. That is, the semiconductor substrate 11 in contact with the gate electrodes 12 and 12 '
The impurity diffusion region is doped in a predetermined range near the surface of the gate electrode in a self-aligning manner to form a source / drain region, an interlayer insulating film is further formed, and then a contact is formed, a metal wiring layer is formed, and A MOS transistor is completed through steps such as patterning. The gate length (that is, the distance between the source and the drain) of the MOS transistor having the thick gate oxide film in the region B is preferably 0.8 μm or less.

As described above, according to the manufacturing method of this embodiment, since the resist is not directly applied to the silicon oxide film to be the gate oxide film, it is not affected by the alkali metal or heavy metal contained in the resist. It becomes possible to form MOS transistors having different gate oxide films on the same semiconductor substrate.

[0017]

As described above, according to the method of manufacturing the semiconductor device of the present invention, the gate electrode is formed in each of the first and second formation regions on the insulating film formed on the semiconductor substrate, An insulating film is formed so as to cover all of them, an oxidation resistant film (nitride film) is formed so as to cover only the semiconductor substrate and the gate electrode in the first formation region, and wet oxidation treatment is further performed to form a second film. Since the parse beak is generated between the gate electrode in the formation region of the second region and the semiconductor substrate, only the film thickness of the gate oxide film in the second formation region can be increased. In these steps, the resist does not come into direct contact with the gate oxide film,
It is not affected by the alkali metal or heavy metal in the resist, and the gate oxide film is not directly exposed to plasma. Therefore, it becomes possible to form semiconductor elements having gate oxide films of different thicknesses on the same semiconductor substrate while eliminating the problems of deterioration of initial breakdown voltage and deterioration of device reliability in the long term.

[Brief description of drawings]

FIG. 1 is a process chart showing a method for manufacturing a semiconductor device according to an embodiment of the present invention.

FIG. 2 is a process chart showing a conventional method of manufacturing a semiconductor device.

[Explanation of symbols]

 11 semiconductor substrate 12, 12 'gate electrode 13, 13' insulating oxide film 14, 14 'insulating oxide film 15 nitride film (oxidation resistant film) 16, 16' gate oxide film

Claims (2)

[Claims] 1. A method of manufacturing a semiconductor device having gate oxide films of different thicknesses on the same semiconductor substrate, the method comprising: forming an insulating layer to be a gate oxide film on the entire surface of the semiconductor substrate; A step of forming a conductive layer to be a gate electrode on the entire surface of the insulating layer; a step of patterning this conductive layer to form a gate electrode in each of the first formation region and the second formation region; and dry oxidation. A step of forming an insulating film so as to cover the gate electrodes and the semiconductor substrate in the first and second formation regions, and forming an oxidation resistant film so as to cover the semiconductor substrate and the gate electrode in the first formation region And a wet oxidation treatment step for forming an oxide insulating film on the entire surface, and a step of removing the oxidation resistant film in the first formation region. By generating a Pazubiku between the gate electrode and the semiconductor substrate region, a method of manufacturing a semiconductor device, wherein a thickness of the gate oxide film of the second forming region is thickened. 2. The method of manufacturing a semiconductor device according to claim 1, wherein the oxidation resistant film is a nitride film.