JPH1126766A - Mos field effect transistor and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an MOS field effect transistor having a high current driving power, without lowering the withstand voltage and manufacture thereof. SOLUTION: The transistor is structured such that an insulation film between a gate electrode 8 and lightly doped drain region is thicker than a gate oxide film, enough to store carrier due to the strong inversion of the drain region 2 surface due to application of a gate voltage, provided that the drain region 2 will not diffuse to below the gate electrode 8. The transistor is formed by thermally oxidizing a semiconductor region implanted with impurity ions through a nitride film of about 500 Å which forms an oxide film having large bird beaks, this increasing the oxidation rate owing to diffusion of the impurity ions to channels and hence always forming a thick oxide film on the drain region 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a MOS field effect transistor constituting a semiconductor integrated circuit, and more particularly to a MOS field effect transistor requiring a high breakdown voltage.

[0002]

2. Description of the Related Art FIG. 5 shows a conventional N-channel MOS field effect transistor having a high breakdown voltage structure. In the figure, 1 is P
Semiconductor region of a device forming region comprising a silicon substrate or a P-well region, 2 is a low-concentration drain region,
3 is a high-concentration drain region, 4 is a low-concentration source region, 5 is a high-concentration source region, 6 is a gate oxide film, 7 is a thick oxide film formed by thickening a part of a gate insulating film, 8 is a gate electrode,
9 is an insulating film, 10 is a drain electrode, and 11 is a source electrode.

As shown in FIG. 1, a conventional MOS field effect transistor surrounds a high-concentration source region 5 and a high-concentration drain region 3 with a low-concentration source region 4 and a low-concentration drain region 2 in order to increase the breakdown voltage. Had a structure.
Further, a thick oxide film 7 is formed between the gate electrode 8 and the lightly doped drain region 2 and lightly doped source region 4.

In order to simplify the manufacturing process, this thick oxide film 7 has been formed simultaneously with a very thick LOCOS oxide film of 5000 to 10000 angstroms used for element isolation. Generally, in the manufacturing process of the LOCOS oxide film, a thick nitride film having a thickness of 1000 Å or more is used as the oxidation-resistant film and thermal oxidation is performed for a long time in order to minimize bird's beak.

[0005]

SUMMARY OF THE INVENTION A conventional high withstand voltage M
The OS type field effect transistor has a structure in which the low-concentration drain region 2 and the low-concentration source region 4 are diffused below the gate oxide film 6 as a result of the long-time thermal oxidation process. In such a structure, the dimension between the high-concentration drain region 3 in contact with the drain electrode 10 and the channel region formed immediately below the gate oxide film 6 becomes particularly large. As a result, there is a problem that the drain resistance is increased and the current driving capability is reduced. The present invention solves the above-described problems, and does not cause a decrease in the withstand voltage.
It is an object of the present invention to provide a field effect transistor and a method of manufacturing the same.

[0006]

To achieve the above object, a MOS field effect transistor according to a first aspect of the present invention comprises a source and drain region of opposite conductivity type formed in a semiconductor region of one conductivity type. A MOS field effect transistor having a gate electrode disposed between the source region and the drain region with a gate insulating film interposed therebetween, wherein the drain region has a reverse conductivity type high-concentration diffusion region in contact with the drain electrode; A low-concentration diffusion region of a reverse conductivity type extending in the direction of the gate electrode, wherein an insulating film disposed between the low-concentration diffusion region and the gate electrode is thicker than the gate insulating film, and a voltage is applied to the gate electrode. Is applied, the electric field intensity applied to the low-concentration diffusion region below the insulating film is reduced, and the carrier concentration on the surface of the low-concentration diffusion region can be increased. It is characterized in that the.

The method of manufacturing a MOS field effect transistor according to the second aspect of the present invention is directed to a method of manufacturing a MOS type field effect transistor, comprising: a source region and a drain region of opposite conductivity type formed in a semiconductor region of one conductivity type; A gate electrode formed with a gate oxide film interposed therebetween, wherein at least the drain region is a high-concentration diffusion region of the opposite conductivity type in contact with the drain electrode and a low-concentration diffusion region of the opposite conductivity type extending in the direction of the gate electrode. A MOS type field effect transistor comprising an oxide film thicker than the gate oxide film between the low-concentration diffusion region and the gate electrode, wherein an oxidation-resistant film is formed on the gate electrode formation region. Forming an impurity for forming the low concentration diffusion region into the semiconductor region using the oxidation resistant film as a mask; Forming a thicker oxide film than the gate oxide film between the impurity diffusion region and the oxidation-resistant film by performing thermal oxidation using the mask as a mask, and applying a voltage to the gate electrode. In this case, the thickness is such that the electric field intensity applied to the low concentration diffusion region below the oxide film is reduced and the carrier concentration on the surface of the low concentration diffusion region can be increased.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The first and second embodiments of the present invention will be described below in accordance with a manufacturing process, taking an N-channel MOS type field effect transistor as an example. First, P
An oxide film 12 on the surface of the P-type semiconductor region 1 in a region where an element is to be formed, which is formed of a P-type silicon substrate or a P-type well region;
A nitride film 13 serving as an oxidation-resistant film is formed on the oxide film 12 by lamination. Here, the thickness of the nitride film 13 is a normal LOCOS
The thickness is smaller than the thickness of the nitride film used when forming the oxide film. Specifically, the thickness is larger than 300 Å which can be used as an oxidation-resistant film, and does not exceed 500 Å formed by an appropriate bird's beak. Thereafter, the nitride film 13 is etched away using the photoresist as a mask while leaving the channel formation region.

A photoresist is formed to open the low-concentration drain region and the low-concentration source region, and phosphorus ions are implanted into the regions shown by broken lines in FIG. 1 (FIG. 1). After removing the photoresist, the semiconductor region 1 is removed using the nitride film 13 as a mask.
The surface is thermally oxidized to form a thick oxide film 14 of about 1500 angstroms. The thickness of this thick oxide film 14 is
As will be described later, it is appropriately selected according to the operating conditions of the MOS field effect transistor. Simultaneously with the formation of the oxide film 14, the previously implanted phosphorus ions are thermally diffused to form the low-concentration drain region 2 and the low-concentration source region 4 having an impurity concentration of about 5.0 × 10 16 to 1.0 × 10 17 atoms / cm 3. (FIG. 2).

A major feature of the present invention is that a thick oxide film 14 is formed on the surface of the semiconductor region 1 into which phosphorus ions have been implanted by using the thin nitride film 13 as a mask. When thermal oxidation is performed using the thin nitride film 13, LOC
A bird's beak larger than that in the case of forming the OS oxide film is formed, and the growth rate of the oxide in the channel direction can be made higher than the diffusion rate of the impurity ions.
As described above, the conditions for increasing the growth rate of the bird's beak, specifically, the thickness of the oxidation-resistant film, the heat treatment temperature, and the time, and by appropriately selecting the combination of the diffused impurity ions, the low-concentration drain region 2 will always be located under the thick oxide film 14.

The nitride film 13 and the oxide film 12 remaining thereunder are removed by etching to form a P-type semiconductor region 1 in a channel formation region.
The surface is exposed. Again, thermal oxidation is performed to expose P
A gate oxide film 6 is formed on the surface of the type semiconductor region 1. With this etching step and thermal oxidation step, the gate oxide film 6 is formed.
The thickness of the thick oxide film 14 is 500 angstroms and 1000 angstroms, respectively. next,
Form a polysilicon film that constitutes the gate electrode on the entire surface,
Etching is performed using a photoresist as a mask to form a gate electrode 8. Here, the gate electrode 8 is formed so as to partially overlap the thick oxide film 14 (FIG. 3).

In the following, an insulating film 9 is formed and a thick oxide film 1 is formed in accordance with a normal MOS type field effect transistor manufacturing process.
4 is removed by etching to form a low-concentration drain region 2,
A high-concentration drain region 3 and a high-concentration source region 5 are formed in the low-concentration source region 4, respectively. Thereafter, a drain electrode 10 and a source electrode 11 connected to each other are formed, and a MOS field effect transistor is completed (FIG. 4).

In the MOS field effect transistor thus formed, the intensity of the electric field applied to the low-concentration drain region 2 can be reduced by the thick oxide film 14 between the low-concentration drain region 2 and the gate electrode 8. At the same time, carriers (electrons) are accumulated on the surface of the low-concentration drain region 2 by the voltage applied to the gate electrode 8. With this carrier, the drain resistance can be reduced. As a result, the MOS field intensity transistor can obtain a high current driving capability at the same time as a high breakdown voltage. Thick oxide film of the above structure is MOS of about 1000 Å
When the source-drain voltage Vds becomes larger than the gate-source voltage Vg in the type field effect transistor, carriers are accumulated on the surface of the low-concentration drain region 2 and the current driving capability is improved.

The thickness of the thick oxide film 14 between the low-concentration drain region 2 and the gate electrode 8 is not limited to the above conditions, but is appropriately set according to the voltage applied to the gate electrode 8. Become. That is, in order to reduce the electric field intensity applied to the low-concentration drain region 2, the thick oxide film 14 is preferably as thick as possible. At the same time, it is necessary to set the thickness so that carriers (electrons) can be accumulated on the surface of the low-concentration drain region 3 by the voltage applied to the gate electrode 8. That is, the larger the voltage applied to the gate electrode 8, the thicker the oxide film 14 can be formed.

As described above, in the MOS field-effect transistor of the present invention, carriers (electrons) accumulate on the surface of the low-concentration drain region 2 and, as a result, the high-concentration drain region 3 connected to the drain electrode 10 and immediately below the gate oxide film. , The drain resistance can be reduced, and the current driving capability can be improved. Further, the intensity of the electric field applied to the low-concentration drain region 2 is proportional to the thickness of the thick oxide film 14, and the greater the thickness, the more the magnitude is reduced. This has the effect of mitigating the band-to-band tunnel phenomenon, thereby preventing hot carriers from being injected into the gate oxide film. In addition, since the high-concentration drain region can be formed apart from the gate electrode, there is an effect that the impact ionization is reduced, and a decrease in withstand voltage can be prevented.

As a result of a simulation of the MOS field effect transistor having the above structure, when a source-drain voltage Vds = 20 V and a gate voltage Vg = 4 V, a thick oxide film of about 1000 angstroms where the gate electrode overlaps is obtained. In the low-concentration drain region 2 below 14, the electric field intensity was 6.0 × 10 5 V / cm in the absence of the thick oxide film 14, but increased to 3.0 × 10 5
V / cm. This result indicates that the inter-band tunnel phenomenon is reduced. The electric field strength near the boundary between the low-concentration drain region 2 and the channel below the gate oxide film 6 is 2.0 × 10 5 V / cm to 1.0 × 1 V / cm.
It has been reduced to less than 0.5 V / cm. This result indicates that the hot carrier resistance was improved.

In the manufacturing method of the present invention, a MOS field effect transistor having a desired structure can be easily obtained by selecting the thickness of the oxidation resistant film and the like. The manufacturing method of the present invention is a simple method, and can form a MOS field effect transistor with high yield.

The production method of the present invention is not limited to the above method, but can be variously modified. For example, FIG.
In order to form a field oxide film used for element isolation, a thick (3000 Å) nitride film is formed and a field oxide film is formed.
It can be used as an oxidation-resistant film for forming a thick oxide film by thinning and patterning to about 500 angstroms. Further, the impurity to be implanted is not limited to phosphorus, and an impurity ion having a desired diffusion coefficient such as arsenic may be appropriately selected according to the oxidation rate of the thick oxide film.

The N-channel MOS field-effect transistor has been described above. However, the P-channel MOS field-effect transistor can be formed according to the same manufacturing method, and it can be said that the same effect can be expected. Not even.

[0020]

As described above, the MO of the first invention is
The S-type field effect transistor has the effect of reducing the electric field intensity near the low-concentration drain region and the gate electrode or the channel region, improving interband tunneling and deterioration due to hot carriers, and improving leak characteristics and hot carrier resistance.

Further, since the gate electrode is formed on a thick oxide film, the gate capacitance can be reduced, and the high speed operation can be performed.

In the method of manufacturing a MOS field effect transistor according to the second invention, a large bird's beak can be formed by performing thermal oxidation using a thin oxidation-resistant film as a mask, and a desired shape can be complicated. It can be easily formed without going through a complicated manufacturing process.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of an embodiment of the present invention.

FIG. 3 is an explanatory diagram of an embodiment of the present invention.

FIG. 4 is an explanatory diagram of an embodiment of the present invention.

FIG. 5 is an explanatory diagram of a conventional MOS field effect transistor having a high breakdown voltage structure.

[Explanation of symbols]

 Reference Signs List 1 P-type semiconductor region 2 Low-concentration drain region 3 High-concentration drain region 4 Low-concentration source region 5 High-concentration source region 6 Gate oxide film 7 Thick oxide film 8 Gate electrode 9 Insulating film 10 Drain electrode 11 Source electrode 12 Oxide film 13 Nitriding Film 14 thick oxide film

Claims (2)

[Claims] 1. A semiconductor device comprising: a source region and a drain region of opposite conductivity type formed in a semiconductor region of one conductivity type; and a gate electrode disposed between the source region and the drain region via a gate insulating film. In the MOS field-effect transistor, the drain region includes a high-concentration diffusion region of a reverse conductivity type in contact with a drain electrode and a low-concentration diffusion region of a reverse conductivity type extending in a direction of the gate electrode; And an insulating film disposed between the gate electrodes, thicker than the gate insulating film, and when a voltage is applied to the gate electrode, reduces the intensity of the electric field applied to the low concentration diffusion region below the insulating film, A MOS field effect transistor characterized in that the thickness is such that the carrier concentration on the surface of the low concentration diffusion region can be increased. 2. A semiconductor device comprising: a source and drain region of opposite conductivity type formed in a semiconductor region of one conductivity type; and a gate electrode formed between the source and drain regions with a gate oxide film interposed therebetween. At least the drain region comprises a high-concentration diffusion region of the opposite conductivity type in contact with the drain electrode and a low-concentration diffusion region of the opposite conductivity type extending in the direction of the gate electrode, between the low-concentration diffusion region and the gate electrode. A method of manufacturing a MOS field-effect transistor having an oxide film thicker than the gate oxide film, comprising: forming an oxidation-resistant film on the gate electrode formation region; Introducing an impurity for forming a concentration diffusion region into the semiconductor region; and performing thermal oxidation using the oxidation resistant film as a mask to form the impurity diffusion region and the oxidation resistant film. Forming a thicker oxide film than the gate oxide film, the thick oxide film reduces the intensity of the electric field applied to the low concentration diffusion region below the oxide film when a voltage is applied to the gate electrode. And a thickness capable of increasing the carrier concentration on the surface of the low concentration diffusion region.
Of manufacturing a field-effect transistor.