JPH05259154A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To enable the formation of a silicon oxide film having a uniform film thickness and less impurities with high accuracy by using a liquid phase growth method to form the silicon oxide film on a polycrystalline silicon film formed on a semiconductor substrate. CONSTITUTION:A polycrystalline silicon film 4 is formed on a semiconductor substrate 1, and a silicon oxide film 6 is formed on the surface thereof using a liquid phase growth method. A process for annealing in an inert gas atmosphere is provided after these processes above. The liquid phase growth method includes a method, for example, that boric acid is added to fluorosilicic acid aqueous solution, and a silicon oxide film is deposited from silicon oxide supersaturated in the resultant solution. Moreover, a second polycrystalline silicon film 7, for example, is deposited on the silicon oxide film 6, and impurities are diffused. Subsequently, the second polycrystalline silicon film 7, silicon oxide film 6, and polycrystalline silicon film 4 are selectively etched one by one to form floating and control gate electrodes on an EPROM element.

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 forming a silicon oxide film provided on a polycrystalline silicon film.

[0002]

2. Description of the Related Art A method of forming a silicon oxide film on a polycrystalline silicon film provided on a semiconductor substrate to form a part of a semiconductor device is widely used.

FIGS. 3A to 3D are cross-sectional views of a semiconductor chip shown in the order of steps for explaining a conventional method for manufacturing a semiconductor device.

First, as shown in FIG. 3 (a), a field oxide film 2 for element isolation for selectively providing an element formation region on the surface of a silicon substrate 1 and an element formation area is provided. A first polycrystalline silicon film 4 is deposited on the surface including the gate oxide film 3 by a chemical vapor deposition (hereinafter referred to as CVD) method, impurities are diffused in order to reduce electric resistance, and photolithography technology and etching technology are used. Patterning by.

Next, as shown in FIG. 3B, a thermal oxide film 5 is formed on the surface of the polycrystalline silicon film 4 by heating in an oxygen atmosphere.

Next, as shown in FIG. 3C, a second polycrystalline silicon film 7 is deposited on the surface including the thermal oxide film 5 by the CVD method and impurities are diffused in order to reduce the electric resistance.

Next, as shown in FIG. 3D, the polycrystalline silicon film 7 is formed by the photolithography technique and the etching technique.
Then, the thermal oxide film 5 and the polycrystalline silicon film 4 are selectively and sequentially etched to form a floating gate electrode and a control gate electrode of the EPROM element.

The polycrystal silicon film 7, the thermal oxide film 5 and the polycrystal silicon film 4 are etched by anisotropic dry etching in three steps. The first step and the third step are etching of the silicon film. On the other hand, the second step is performed under the condition that the etching selection ratio of the silicon oxide film is large, and the etching selection ratio of the silicon film is large with respect to the etching of the silicon oxide film.

[0009]

In this conventional method for manufacturing a semiconductor device, the surface orientation of each crystal grain of the polycrystalline silicon film has a thermal oxidation rate when the surface of the first polycrystalline silicon film is thermally oxidized. Since the grain boundaries are different from each other, there is a problem that the formed thermal oxide film has a local non-uniformity in the film thickness distribution and has a weak point with respect to the electrostatic breakdown voltage.

Further, since the surface of the polycrystalline silicon film in which the impurities are diffused is thermally oxidized, the formed thermal oxide film contains a large amount of impurities, which causes a problem that the reliability of the oxide film is lowered. It was

Such local non-uniformity of the film thickness distribution is
This is a factor that lowers the reliability of the capacitance element having the thermal oxide film on the polycrystalline silicon film as a dielectric.

[0012]

A method of manufacturing a semiconductor device according to the present invention comprises a step of forming a polycrystalline silicon film on a semiconductor substrate, and a silicon oxide film formed on the surface of the polycrystalline silicon film by liquid phase epitaxy. It comprises a step of forming and a step of annealing the silicon oxide film in an inert gas atmosphere.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

FIGS. 1A to 1D are cross-sectional views of a semiconductor chip showing the order of steps for explaining the manufacturing method of the first embodiment of the present invention.

First, as shown in FIG. 1 (a), the surface of a silicon substrate 1 is selectively thermally oxidized to form a field oxide film 2 for element isolation, and an element formed by the field oxide film 2 is formed. Gate oxide film 3 by thermally oxidizing the surface of the region
To form. Next, CVD is performed on the surface including the gate oxide film 3.
The first polycrystalline silicon film 4 is deposited by the method and impurities are diffused in order to reduce the electric resistance, and then patterned by the photolithography technique and the etching technique.

Next, as shown in FIG. 1B, a silicon oxide film 6 is formed on the surface including the polycrystalline silicon film 4 by a liquid phase growth method, and annealed at 900 ° C. or higher in an inert gas atmosphere. To do.

Next, as shown in FIG. 1C, a second polycrystalline silicon film 7 is deposited on the silicon oxide film 6 by the CVD method and impurities are diffused in order to reduce the electric resistance.

Next, as shown in FIG. 1D, the polycrystalline silicon film 7 is formed by the photolithography technique and the etching technique.
Then, the silicon oxide film 6 and the polycrystalline silicon film 4 are selectively and sequentially etched to form a floating gate electrode and a control gate electrode of the EPROM element. In addition,
Etching of the polycrystalline silicon film 7, the silicon oxide film 6, and the polycrystalline silicon film 4 is performed by three-step anisotropic dry etching similar to the conventional example.

Further, the growth of the silicon oxide film 6 is performed by using a hydrosilicofluoric acid (H ₂ SiF ₆ ) solution.

[0020]

By maintaining the equilibrium state of and adding boric acid (H ₃ BO ₃ ) to the place where a saturated state of SiO ₂ is formed,

[0022]

The reaction HF is consumed by the supersaturation state of SiO ₂ is achieved, it takes place in that the SiO ₂ is precipitated.

The conditions for establishing liquid phase growth are about 33
% H ₂ SiF ₆ aqueous solution, H ₃ BO in the aqueous solution
₃ Concentration Growth at 50 × 10 ^-3 mol / l can be more starts.

As an example, H ₃ BO ₃ is used at a liquid temperature of 23 ° C.
When the concentration is 100 × 10 ^-3 mol / l, it is about 0.1n.
A silicon oxide film growth rate of m / min is obtained.
At this time, the film thickness uniformity is ± 2% for a 4-inch diameter wafer, and the film shrinkage ratio during annealing is 900% at 900 ° C. Annealing, and a film having good film thickness uniformity and a small film shrinkage ratio can be obtained. In addition, the silicon oxide film formed is a non-doped film, and the diffusion of impurities is only thermal diffusion during annealing. Therefore, by adopting short-time high-temperature annealing such as lamp annealing,
A silicon oxide film containing less impurities can be formed.

2 (a) to 2 (d) are sectional views of the semiconductor chip in the order of steps for explaining the manufacturing method of the second embodiment of the present invention.

First, as shown in FIG. 2A, a first polycrystalline silicon film 4 is deposited on a field oxide film 2 for element isolation provided on a silicon substrate 1 by a CVD method, and an electric field is formed. Impurities are diffused to reduce resistance.

Next, as shown in FIG. 2B, a silicon oxide film 6 is formed on the polycrystalline silicon film 4 by liquid phase growth and annealed in an inert gas atmosphere at a temperature of 900 ° C. A silicon nitride film 8 is formed on the silicon oxide film 6 by a CVD method, and the surface thereof is thermally oxidized to form a thermal oxide film 9 to form a three-layer structure of silicon oxide film / silicon nitride film / silicon oxide film. (Hereinafter referred to as ONO structure).

Next, as shown in FIG. 2C, a second polycrystalline silicon film 7 is deposited on the thermal oxide film 9 by the CVD method, and impurities are diffused in order to reduce the electric resistance.

Next, as shown in FIG. 2D, the polycrystalline silicon film 7 is formed by the photolithography technique and the etching technique.
Then, the ONO structure and the polycrystalline silicon film 4 are selectively subjected to anisotropic dry etching in order to form a capacitive element.

Here, when an ONO structure is formed as a dielectric film on a polycrystalline silicon film formed on a semiconductor substrate, not only the quality of the intermediate silicon nitride film,
Thickness of several nm formed prior to the formation of the silicon nitride film
The quality of the silicon oxide film is also an important factor in terms of reliability, but by using a silicon oxide film formed by liquid phase epitaxy on this, high quality without being affected by the quality of the underlying silicon film. A silicon oxide film can be formed.

[0032]

As described above, according to the present invention, a silicon oxide film formed on a polycrystalline silicon film formed on a semiconductor substrate is formed by a liquid phase epitaxy method.
It has an effect that a film thickness uniformity is good and a silicon oxide film with few impurities can be formed with high precision.

[Brief description of drawings]

1A to 1C are sectional views showing a process sequence for explaining a first embodiment of the present invention.

2A to 2D are sectional views showing a process sequence for explaining a second embodiment of the present invention.

3A to 3C are cross-sectional views showing the order of steps for explaining a conventional method for manufacturing a semiconductor device.

[Explanation of symbols]

 1 Silicon substrate 2 Field oxide film 3 Gate oxide film 4,7 Polycrystalline silicon film 5,9 Thermal oxide film 6 Silicon oxide film 8 Silicon nitride film

Claims (2)

[Claims] 1. A step of forming a polycrystalline silicon film on a semiconductor substrate, a step of forming a silicon oxide film on a surface of the polycrystalline silicon film by a liquid phase growth method, and a step of forming the silicon oxide film in an inert gas atmosphere. And a step of annealing in the semiconductor device. 2. The liquid phase epitaxy method is hydrofluoric acid (H ₂ Si).
_{2. The} method for manufacturing a semiconductor device according to claim 1, further comprising a method of adding boric acid (H ₃ BO ₃ ) to an F ₆ ) aqueous solution to deposit a silicon oxide film from a supersaturated state of silicon oxide (SiO ₂ ) generated in the aqueous solution. ..