JPH0964347A - Semiconductor device and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the breakdown strength of a gate oxide film at a field edge part from decreasing by setting (100) face of silicon substrate to a main flat surface and forming gate oxide film on a surface which is inclined for the main flat surface of silicon substrate at the boundary part between the field oxide film and the gate oxide film. SOLUTION: An underlay oxide film 2 is formed on silicon substrate 1 with (100) face as a main surface and further nitrogen film 3 is subjected to patterning. Then, with the nitride film 3 as a mask, field oxide film 4 is formed on the main surface of the silicon substrate 1 with (100) face as a main surface and the nitride film 3 is eliminated. Then, the field oxide film 4 is partially etched and removed. A silicon crystal surface 1a which is slightly inclined from the (100) face is formed at a field edge part 6 of the silicon substrate 1. The inclination surface is set to an angle of 5-30 degrees for the main flat surface of the silicon substrate 1. Then, a gate oxide film 5 and a gate electrode 7 are formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a gate electrode portion of a MOS type semiconductor device, and more particularly to a structure of a gate oxide film and a manufacturing method thereof.

[0002]

2. Description of the Related Art In recent years, miniaturization of element dimensions has been advanced along with high integration of semiconductor devices. Also in the MOS type semiconductor device, the gate oxide film is becoming thinner along with the miniaturization of the element size. At present, a gate oxide film thickness of about 10 nm has been put into practical use, but the gate voltage applied to the gate oxide film does not decrease in response to the reduction in the gate oxide film thickness, but rather increases. The demand for stabilizing the gate oxide film breakdown voltage is becoming more and more severe.

FIG. 6 is a sectional view showing the structure of a gate electrode portion of a conventional MOS semiconductor device, and FIGS. 7 (a) to 7 (d).
FIG. 4A is a process sectional view showing the manufacturing method. The description will be made sequentially according to the drawing. First, as shown in FIG. 7A, after forming an underlying oxide film 2 on a silicon substrate 1, a nitride film 3 is formed.
Pattern.

Next, as shown in FIG. 7B, a known LOCOS film is formed by using the patterned nitride film 3 as a mask.
(LOCal Oxidation of Silic
on) method or the like to form a field oxide film 4 on the main surface of the silicon substrate 1 and remove the nitride film 3. Next, FIG.
As shown in (c), the underlying oxide film 2 is removed.

Next, as shown in FIG. 7D, a gate oxide film 5 is formed. Then, as shown in FIG.
(Chemical Vapor Deposition
n) method, etc. is used to deposit a polysilicon film. The polysilicon film is patterned by using the known photolithography technique and etching technique to form the gate electrode 7.

As shown in FIG. 6, the phenomenon in which the thickness of the gate oxide film 5 is locally thinned at a field edge portion 6 which is a boundary portion between the thick field oxide film 4 and the thin gate oxide film 5 (hereinafter referred to as Thinning). Happens. The effect of this thinning on the MOS capacitor will be described with reference to FIG.

FIG. 8 is a diagram showing a gate electric field Eg-gate current density Jg characteristic in a conventional MOS capacitor. The gate electric field Eg is the voltage V applied to the gate oxide film.
g is divided by the gate oxide film thickness Tox, and the gate current density Jg is obtained by dividing the gate current Ig flowing by the application of the gate voltage Vg by the area S of the gate oxide film. In the figure, the current observed at an electric field of 8 MV / cm or more is a tunnel current component called a Fowler-Nordoheime current due to the application of a strong electric field (hereinafter,
Referred to as F-N current). This F-N current is J = AE ² e
^It is expressed as ^{-B / E} (A and B are constants and E is an electric field), and is strongly influenced by the electric field.

Capacitor A and capacitor B in FIG. 8 are those shown in FIG. 9A is a plan view of the capacitor A, FIG. 9B is a cross-sectional view of the AA ′ portion of FIG. 9A, and FIG. 9C is a plan view of the capacitor B.
FIG. 9D is a cross-sectional view of the BB 'portion of FIG. 9C.
As can be seen from FIG. 9, the capacitor A and the capacitor B have the same area of the gate oxide film 5, but the field edge length of the capacitor B is 1000 times that of the capacitor A.
Has doubled.

It can be seen from FIG. 8 that more current is flowing in the capacitor B than in the capacitor A. This is because the capacitor B has a field edge length that is 1000 times longer than that of the capacitor A.
This is because the gate oxide film 5 is thinned by 1000 times more than the capacitor A, and a large amount of F-N current flows.

Therefore, in the case of the gate oxide film 5 having such thinning, the quality of the gate oxide film 5 is deteriorated because the electric field is concentrated in the narrow region of the field edge portion 6. Further, in an element such as a tunnel oxide film used for an EEPROM or a flash memory in which an F-N type current is positively flowed, the current concentrates on the thin film portion of the field edge portion 6 due to thinning, so that the tunnel oxide film The life was shortened.

The reason why the thinning occurs is that in the step of FIG. 7B, N or NH ₃ generated by the oxidation of the nitride film 3 at the time of LOCOS oxidation diffuses on the surface of the silicon substrate 1 and reacts with silicon to generate nitriding. To form a silicon film or an oxynitride film, FIG.
In the step of (d), in order to prevent silicon from being oxidized at the time of gate oxidation, in the field edge portion 6 which is a boundary portion between the field oxide film 4 and the gate oxide film 5, the oxidizer from the lateral direction is removed. It is known that the supply is restricted by the thick field oxide film 4 and the oxidation rate in the lateral direction of the silicon substrate 1 is reduced.

To solve these problems, Thinn
For the former, various measures have been taken, and for the former, the sacrifice of once removing the gate oxide film 5 and forming the gate oxide film 5 again in the step of FIG. 7D. The removal of the silicon nitride film and the oxynitride film by oxidation is performed. Further, with respect to the latter, also in the step of FIG. 7D, the oxidation conditions at the time of gate oxidation have been optimized. However, under the present circumstances where the gate oxide film 5 is becoming thinner, the present situation is that it is not a sufficient countermeasure.

[0013]

The structure and manufacturing method of the gate oxide film of the conventional MOS semiconductor device are as described above. As shown in FIG. 6, the boundary between the field oxide film 4 and the gate oxide film 5 is as shown in FIG. There is a problem that thinning occurs in the field edge portion 6 which is a portion, and the breakdown voltage of the gate oxide film is likely to be unstable. Also, this T
As shown in FIG. 8, the high electric field is concentrated in a limited region due to the thinning, which causes a problem that the reliability of the gate oxide film is deteriorated. These problems have become more apparent as the gate oxide film becomes thinner.

The present invention has been made to solve the above problems, and even if the gate oxide film is thinned,
A semiconductor device capable of preventing thinning at a field edge portion, which is a boundary portion between a field oxide film and a gate oxide film, preventing a breakdown voltage of the gate oxide film at the field edge portion, and improving reliability of the gate oxide film, and a manufacturing method thereof. It is intended to provide a way.

[0015]

In a semiconductor device according to claim 1 of the present invention, a silicon substrate has a (100) plane as a main plane, and the gate oxide film is formed at a boundary portion between a field oxide film and a gate oxide film. It is formed on a surface inclined with respect to the main plane of the silicon substrate.

According to a second aspect of the present invention, there is provided a semiconductor device comprising:
The inclined surface is inclined 5 degrees to 30 degrees with respect to the main plane of the silicon substrate.

According to a third aspect of the present invention, there is provided a method of manufacturing a semiconductor device in which a field oxide film is formed on a silicon substrate having a (100) plane as a main plane, and the surface of the field oxide film is partially etched. Thus, a step of exposing the surface of the silicon substrate inclined with respect to the main plane to the field edge portion and a step of forming a gate oxide film on the silicon substrate by thermal oxidation are provided.

According to a fourth aspect of the present invention, there is provided a method of manufacturing a semiconductor device, wherein a tilted silicon substrate surface is tilted by 5 to 30 degrees with respect to a main plane of the silicon substrate.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. The same parts as those of the conventional technique are designated by the same reference numerals, and detailed description thereof will be omitted. Embodiment 1. FIG. 1 is a cross-sectional view showing the structure of the gate electrode portion of the semiconductor device of the present invention, and FIGS. 2A to 2E are process cross-sectional views showing the manufacturing method thereof. The description will be made sequentially according to the drawing.

First, as shown in FIG.
After forming the underlying oxide film 2 on the silicon substrate 1 whose main surface is the (0) plane, the nitride film 3 is patterned. here,
The silicon substrate 1 having the (100) plane as the main surface has the smallest fixed electric charge at the interface and can reduce the variation in the threshold voltage, and is therefore a semiconductor substrate that is generally widely used in the manufacture of MOS transistors. . Next, FIG.
As shown in (b), the well-known LOCOS method or the like is used with the patterned nitride film 3 as a mask (100).
A field oxide film 4 is formed on the main surface of the silicon substrate 1 whose main surface is the main surface, and the nitride film 3 is removed. At this time, the film thickness of the field oxide film 4 is made thicker than the required film thickness by taking into account the decrease in film thickness in the next step of etching.

Next, as shown in FIG. 2C, the field oxide film 4 is etched away by about 1000 angstroms using an aqueous solution of hydrofluoric acid. As a result, the oxidized shape of the field oxide film 4 exposes the silicon crystal plane 1a slightly inclined from the (100) plane in the silicon substrate 1 at the field edge portion 6.

Here, FIG. 3 shows (10
It is a schematic diagram of the silicon crystal which looked at the main surface of (0) plane from the perpendicular direction. FIG. 4 is a schematic view of a silicon crystal in which the principal surface of the (100) plane of the silicon substrate 1 is tilted 8 degrees with respect to the normal line. As is clear from a comparison between FIG. 3 and FIG. 4, since the silicon atoms are overlapped in FIG. 3, the number of silicon atoms exposed per unit area is larger in FIG.

Next, as shown in FIG. 2D, a gate oxide film 5 is formed by a thermal oxidation method. At this time, thermal oxidation proceeds by the reaction between silicon atoms and oxygen, and thus the oxidation rate depends on the rate at which silicon atoms are taken into the oxide film and depends on the surface density of silicon atoms. Further, since the surface density of silicon atoms depends on the plane orientation, the surface where a large amount of silicon atoms per unit surface area is exposed has a higher oxidation rate, and the oxidation rate has a plane orientation dependence. . Therefore, in order to reduce the influence of other oxidative rate determining factors and emphasize the plane orientation dependence of the oxidative rate, the oxidative rate may be slowly performed at an oxidative rate of about 4 Å / min.

When oxidation is carried out in this way, as shown in FIGS. 3 and 4, the oxidation rate of the plane inclined from the (100) plane becomes faster than that of the (100) plane. As a result, the gate oxide film 5 is formed thick at the field edge portion 6 where the silicon crystal plane 1a slightly tilted from the (100) plane is exposed, and even if the gate oxide film 5 is thinned, T
Hinning can be prevented. The gate oxide film 5 can be formed in a single oxidation step without the need for double gate oxidation or photolithography process for the gate oxide film 5, the process is not complicated, and the quality of the gate oxide film 5 is not deteriorated. .

Thereafter, as shown in FIG. 1, a polysilicon film is deposited by using the CVD method or the like. The polysilicon film is patterned by using the known photolithography technique and etching technique to form the gate electrode 7.

FIG. 5 shows the Eg-Jg characteristics of the MOS type capacitor manufactured as described above. In the figure, a capacitor A and a capacitor B are shown in FIG. 9 and are the same as the conventional one. As compared with the conventional MOS type capacitor shown in FIG. 8, it can be seen that the difference between the capacitors A and B is reduced. This is the gate oxide film 5
The phenomenon in which the current was increased in the thin film portion of the field edge portion 6 was reduced.
It shows that there is a sufficient effect on ng. Here, the lower limit of the angle of the inclined silicon crystal plane 1a is about 5 degrees at which the effect of increasing the number of silicon atoms appears, and the upper limit thereof is the field edge portion due to the restriction due to the process for forming LOCOS or the excessive inclination. In consideration of the breakdown voltage deterioration of the oxide film in No. 6, up to about 30 degrees.

[0027]

As described above, according to the present invention, the silicon substrate has the (100) plane as the main plane, and the gate oxide film is formed on the main plane of the silicon substrate at the boundary between the field oxide film and the gate oxide film. Since it is formed on a surface inclined with respect to the surface, the oxidation rate at the time of forming the gate oxide film is faster on the surface inclined from the (100) surface than on the (100) surface, and the field oxide film and the gate oxide film are formed. Since the gate oxide film at the boundary with the gate oxide film is formed thicker than the gate oxide film in other portions, it is possible to prevent thinning, prevent breakdown of the gate oxide film from deteriorating and quality deterioration, and obtain a highly reliable semiconductor device. There is an effect that can be done.

Further, since the inclined surface is inclined by 5 to 30 degrees with respect to the main plane of the silicon substrate, the gate oxide film at the boundary portion between the field oxide film and the gate oxide film is gate oxidized at another portion. There is an effect that it can be surely formed thicker than the film.

Further, a step of forming a field oxide film on a silicon substrate having a (100) plane as a main surface, and a part of the surface of the field oxide film being etched, a field edge portion is inclined with respect to the main plane. Since the step of exposing the surface of the silicon substrate and the step of forming the gate oxide film on the silicon substrate by thermal oxidation are provided, the oxidation rate at the time of forming the gate oxide film is higher than that of the (100) surface. The surface inclined from the (100) surface becomes faster, and the gate oxide film at the field edge is formed thicker than the gate oxide film in other parts in one oxidation process, preventing thinning without making the process complicated. Can prevent the breakdown voltage of the gate oxide film from deteriorating and the quality from deteriorating.
There is an effect that a highly reliable semiconductor device can be manufactured.

Further, since the inclined silicon substrate surface is formed so as to be inclined at 5 to 30 degrees with respect to the main plane of the silicon substrate, the gate oxide film at the field edge portion can be changed to another by a single oxidation process. There is an effect that it can be formed surely thicker than the gate oxide film in a part.

[Brief description of drawings]

FIG. 1 is a sectional view showing a structure of a gate electrode portion of a semiconductor device of the present invention.

2A to 2D are process cross-sectional views showing a method of manufacturing the semiconductor device of FIG.

FIG. 3 is a schematic diagram of a silicon crystal when a main surface of a silicon substrate is viewed from a vertical direction thereof.

FIG. 4 is a schematic view of a silicon crystal in which the main surface of the silicon substrate 1 is tilted 8 degrees with respect to the normal line.

FIG. 5: Eg-Jg of MOS type capacitor of this invention
It is a figure which shows a characteristic.

FIG. 6 is a sectional view showing a structure of a gate electrode portion of a conventional semiconductor device.

7A to 7C are process cross-sectional views showing a method of manufacturing the semiconductor device of FIG.

FIG. 8 is a diagram showing Eg-Jg characteristics of a conventional MOS capacitor.

9A and 9B are a plan view and a cross-sectional view showing the structure of a MOS type capacitor used for the characteristic evaluation of FIGS.

[Explanation of symbols]

1 silicon substrate, 1a inclined silicon crystal plane, 4
Field oxide film, 5 gate oxide film, 6 field edge part.

Claims (4)

[Claims] 1. A semiconductor device comprising a field oxide film and a gate oxide film on a silicon substrate, wherein the silicon substrate has a (100) plane as a main plane, and a boundary portion between the field oxide film and the gate oxide film is formed. A semiconductor device, wherein the gate oxide film is formed on a surface inclined with respect to a main plane of the silicon substrate. 2. The semiconductor device according to claim 1, wherein the inclined surface is inclined 5 degrees to 30 degrees with respect to the main plane of the silicon substrate. 3. A step of forming a field oxide film on a silicon substrate having a (100) plane as a main plane, and a portion of the surface of the field oxide film is etched so that a field edge portion is inclined with respect to the main plane. A method of manufacturing a semiconductor device, comprising: exposing the surface of the silicon substrate, and forming a gate oxide film on the silicon substrate by thermal oxidation. 4. The method of manufacturing a semiconductor device according to claim 3, wherein the inclined silicon substrate surface is formed with an inclination of 5 to 30 degrees with respect to the main plane of the silicon substrate.