JPH07326660A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To improve the withstand voltage of a field shield gate oxide film, by depositing a polysilicon film on a semiconductor substrate, and forming an oxide film for the field shield gate oxide film by thermally oxidizing only the polysilicon film. CONSTITUTION:A P-type well 2 is formed on a semiconductor substrate 1, and a polysilicon film 3 is deposited by a CVD method. An oxide film 4 for a field shield gate is formed by thermally oxidizing only the polysilicon film 3. A polysilicon film 5 for a field shield gate electrode is deposited, on which an oxide film 6 for a field cap is deposited. A field shield gate electrode 7 and a field shield cap oxide film 8 are obtained on the oxide film 6, and a side wall 9 for the field gate electrode is formed. A field gate oxide film 10 is formed, and an element isolation region 11 is obtained. Thereby withstand voltage can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of manufacturing a semiconductor device suitable for manufacturing a semiconductor device of a type in which elements are separated by a field shield method.

[0002]

2. Description of the Related Art Conventionally, as one of means for electrically isolating a semiconductor element, a LOCOS method of forming an element isolation region made of a thick oxide film between elements has been known. It is difficult to reduce the size of the element isolation region because it is not possible to reduce the so-called bird's beak where the oxide film spreads in the isolation region.

In order to solve the above-mentioned problems, a field shield method of forming a field shield gate oxide film between elements has recently attracted attention. This method not only has the effect of reducing the size of the element isolation region, but also fixes the field shield electrode to 0 (V) to cut the potential of the semiconductor substrate below it, thus suppressing the generation of parasitic channels. It is excellent in electrical characteristics such as the fact that it has and that it can be expected to reduce the junction leak current due to crystal defects under the bird's beak.

[0004]

When the element isolation region is formed by using the field shield method, it is necessary to oxidize the semiconductor substrate by thermal oxidation to form the field shield gate oxide film. At that time, the semiconductor substrate is used. Oxygen precipitates present inside are taken into the oxide film, which causes a problem that the breakdown voltage of the oxide film is lowered.

Therefore, a first object of the present invention is to provide a semiconductor device in which elements are separated by using the field shield method.
It is to improve the withstand voltage of the field shield gate oxide film. A second object of the present invention is to improve the withstand voltage of the gate oxide film of the transistor element formed on the semiconductor substrate.

[0006]

According to the present invention, there is provided a field shield gate electrode and a field shield gate oxide film between adjacent elements formed on a semiconductor substrate so as to separate adjacent elements from each other. A method of manufacturing a semiconductor device, which comprises a step of depositing a polysilicon film on a silicon semiconductor substrate, and a step of thermally oxidizing only the polysilicon film to form an oxide film for the field shield gate oxide film. This is achieved by providing a method of manufacturing a semiconductor device characterized by the above.

[0007]

According to the above method, the semiconductor substrate containing the oxygen precipitates is not oxidized by the thermal oxidation method, but the polysilicon film not containing the oxygen precipitates is oxidized by the thermal oxidation method to perform the field shield gate oxidation. From forming a film,
There is no concern that oxygen precipitates in the semiconductor substrate will be taken into the gate oxide film.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

FIGS. 1A to 1F are flow charts showing the manufacturing process of the field shield gate oxide film of the semiconductor device according to the present invention, and FIGS. 2A to 2F or FIG. 3A to 3E are flow charts showing the subsequent transistor manufacturing process. In this embodiment, the case where an N-channel transistor is formed on the p-type well 2 of the semiconductor substrate 1 will be described as an example.

First, the p-type well 2 is formed in the silicon semiconductor substrate 1, and then the target field shield gate oxide film thickness (usually about 500 Å) is about 45.
A polysilicon film 3 having a thickness of about 10% is deposited by the CVD method (FIG. 1A).

Next, only the deposited polysilicon film 3 is oxidized by a thermal oxidation method to form an oxide film 4 for a field shield gate (FIG. 1 (b)). Here, the oxide film 4 becomes 2.2 times as thick as the original polysilicon film 3 due to volume expansion. That is, when the polysilicon film 3 is deposited to 100 nm, the thickness of the oxide film formed by thermal oxidation becomes about 220 nm. During the thermal oxidation, only the polysilicon film 3 is oxidized, and the semiconductor substrate 1 is not oxidized. This is to prevent oxygen precipitates in the semiconductor substrate 1 from being taken into the field shield gate oxide film. Further, since the p-type well 2 is not oxidized by doing so, the film thickness of the well is reduced as much as in the conventional case because a part of the well becomes an oxide film and spreads in the semiconductor substrate 1. Don't worry.

Next, the polysilicon film 5 for the field shield gate electrode is formed to 200 nm to 300 nm by the CVD method.
To a thickness of about 200 nm to 300 nm, and the oxide film 6 for the field shield cap is deposited on the top by a CVD method.
To some extent (FIG. 1 (c)).

Next, by using photolithography, patterning is performed so as to cover only the field shield element isolation region on the oxide film 6 formed in the step of FIG. 1C (not shown), and the exposed portion is exposed. Figure 1 after etching
A field shield gate electrode 7 and a field shield cap oxide film 8 are obtained by forming a pattern as shown in FIG.

Then, an oxide film for the side wall of the field shield gate electrode is deposited by the CVD method (not shown), and then etched back to form the side wall 9 for the field shield gate electrode (FIG. 1). (E)). Then, the oxide film 4 is etched to form the field shield gate oxide film 10 to complete the element isolation region (structure) 11 (FIG. 1).
(F)).

Next, the manufacturing process of the p-type transistor of the active portion will be described. First, a polysilicon film 13 having a film thickness of about 45% of a target gate oxide film thickness of a transistor (usually about 150 angstrom) is deposited on the semiconductor substrate 1 by the CVD method (FIG. 2A), and deposited. Only the polysilicon film 13 thus formed is oxidized by the thermal oxidation method to form the oxide film 14 for the gate of the transistor (FIG. 2).
(B)). Here, in the same manner as described above, only the polysilicon film 13 is oxidized at the time of thermal oxidation, and the semiconductor substrate 1 is not oxidized, so that oxygen precipitates in the semiconductor substrate 1 are taken into the gate oxide film of the transistor. Absent. After that,
In the ion implantation process, N-type impurities are implanted into the entire surface of the semiconductor substrate 1 to form shallow impurity diffusion regions 22.

Next, a polysilicon film 15 for the gate electrode and an oxide film 16 for the gate electrode cap are deposited by the CVD method (FIG. 2C) and patterned so as to cover only the transistor region (not shown). ), The exposed portion is etched to form the pattern shown in FIG. 2D, thereby obtaining the gate oxide film 20, the gate electrode 17, and the gate electrode cap oxide film 18.

Subsequently, an oxide film for a side wall is deposited by a CVD method (not shown), and then etched back to form a side wall 19 (FIG. 2).
(E)). Then, in the ion implantation step, impurities are implanted into the entire surface of the semiconductor substrate 1 to form the n-type impurity diffusion region 21 to complete the p-type transistor (FIG. 2 (f)).

On the other hand, the p-type transistor in the active portion may be manufactured by the steps shown in FIGS. 3 (a) to 3 (e). That is, first, the semiconductor substrate 1 is thermally oxidized from the state of FIG. 1F to form the oxide film 24 for the gate of the transistor (FIG. 3A).

Next, a polysilicon film 25 for the gate electrode and an oxide film 26 for the gate electrode cap are deposited by the CVD method (FIG. 3B) and patterned so as to cover only the transistor region (not shown). ), The exposed portion is etched to form the pattern shown in FIG. 3C, thereby obtaining the gate oxide film 30, the gate electrode 27, and the gate electrode cap oxide film 28. Then, in the ion implantation step, N-type impurities are implanted into the entire surface of the semiconductor substrate 1 to form shallow impurity diffusion regions 32.

Then, a sidewall oxide film is deposited by a CVD method (not shown), and then etched back to form a sidewall 29 (FIG. 3).
(D)). Then, in the ion implantation step, N-type impurities are implanted into the entire surface of the semiconductor substrate 1 to form the impurity diffusion region 31 to complete the p-type transistor (FIG. 3E).

[0021]

As is apparent from the above description, according to the method of manufacturing a semiconductor device of the present invention, a polysilicon film is deposited on a substrate, and the polysilicon film is thermally oxidized to oxidize the field shield gate. By forming a film, the field shield gate oxide film can be formed without incorporating oxygen precipitates existing inside the semiconductor substrate, and the film shield has a large film thickness, and it is easy to capture oxygen precipitates when a normal substrate is thermally oxidized. The breakdown voltage of the gate oxide film is not deteriorated. Further, there is an effect of preventing the thickness of the well from being reduced because the portion where the well is formed is taken by the gate oxide film.

[Brief description of drawings]

1A to 1F are flow charts showing a manufacturing process of an element isolation region of a semiconductor device to which the present invention is applied.

2A to 2F are flowcharts showing a manufacturing process of a transistor of a semiconductor device.

3A to 3E are flowcharts showing another manufacturing process of a transistor of a semiconductor device.

[Explanation of symbols]

1 semiconductor substrate 2 p-type well 3 polysilicon film by CVD method 4 oxide film obtained by thermal oxidation of polysilicon film 5 polysilicon film for field shield gate electrode 6 oxide film for cap of field shield gate electrode 7 field shield gate electrode 8 Cap Oxide Film of Field Shield Gate Electrode 9 Sidewall of Field Shield Gate Electrode 10 Field Shield Gate Oxide Film 11 Element Isolation Area 13 Polysilicon Film by CVD Method 14 Oxide Film of Thermally Oxidized Polysilicon Film 15 For Gate Electrode of Transistor Polysilicon film 16 Oxide film for cap of transistor gate electrode 17 Gate electrode of transistor 18 Cap oxide film of transistor gate electrode 19 Sidewall of transistor gate electrode 20 Trans Gate oxide film of transistor 21 Impurity diffusion layer 22 Shallow impurity diffusion layer 24 Oxide film for transistor gate 25 Polysilicon film for gate electrode of transistor 26 Oxide film for cap of transistor gate electrode 27 Gate electrode of transistor 28 Gate electrode of transistor Cap oxide film 29 side wall of transistor gate electrode 30 transistor gate oxide film 31 impurity diffusion layer 32 shallow impurity diffusion layer

Claims (1)

[Claims] 1. A method of manufacturing a semiconductor device having a field shield gate electrode and a field shield gate oxide film between elements for separating adjacent elements formed on the semiconductor substrate, the method comprising: A method of manufacturing a semiconductor device, comprising: a step of depositing a polysilicon film; and a step of thermally oxidizing only the polysilicon film to form an oxide film for the field shield gate oxide film.