JP2000294663A - Method for forming oxide film and semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming an oxide film in which electrical characteristics are improved by decreasing the surface roughness of the film, and to provide a semiconductor device. SOLUTION: A method for forming an oxide film comprises a step for cleaning the surface of a silicon substrate 1, a step for annealing the silicon substrate 1 at a temperature higher than a temperature of thermal oxidation for forming a tunnel oxide film 3 in an atmosphere of Ar gas, and a step for forming the tunnel oxide film 3 through the thermal oxidation method. In this method, the surface roughness of the tunnel oxide film 3 can be decreased and accordingly the electrical characteristics of the tunnel oxide film 3 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 for forming an oxide film formed on a semiconductor substrate and a semiconductor device using the oxide film.

[0002]

2. Description of the Related Art An example of a conventional oxide film forming method is F
A method for forming a tunnel oxide film in an AMOS (nonvolatile memory) will be described.

First, before forming a tunnel oxide film, a silicon substrate surface is subjected to pre-oxidation cleaning. That is, the surface of the silicon substrate is cleaned by immersing the silicon substrate in a cleaning solution obtained by mixing ammonia and hydrogen peroxide solution. Next, the silicon substrate is washed with water and subjected to IPA drying (drying with isopropyl alcohol).

After that, 900
A tunnel oxide film is formed on a silicon substrate by performing thermal oxidation under a temperature condition of ° C.

Next, Ar or N ₂ is deposited on the tunnel oxide film.
Annealing is performed at a temperature of about 900 ° C. to 1000 ° C. for a predetermined time in an atmosphere. Thus, a tunnel oxide film is formed on the silicon substrate.

[0006]

In the above-mentioned conventional method for forming an oxide film, an oxide film is formed on a silicon substrate after cleaning before oxidation. This oxide film is a film formed during pre-oxidation cleaning or a natural oxide film formed after pre-oxidation cleaning. Since the surface of such an oxide film is rough, the surface of a tunnel oxide film subsequently formed thereon also becomes rough. As a result, the electrical characteristics of the tunnel oxide film are degraded.

The present invention has been made in view of the above circumstances, and has as its object to reduce the roughness of an oxide film surface, thereby improving the electrical characteristics of the oxide film. A method for forming a film and a semiconductor device are provided.

[0008]

In order to solve the above-mentioned problems, a method for forming an oxide film according to the present invention comprises the steps of: cleaning a surface of a semiconductor substrate; And a step of forming an oxide film on the semiconductor substrate by a thermal oxidation method at a temperature equal to or higher than the thermal oxidation temperature at the time of forming the oxide film.

In the above-described method for forming an oxide film, after cleaning before forming the oxide film, the semiconductor substrate is subjected to a heat treatment at a temperature equal to or higher than the thermal oxidation temperature at which the oxide film is formed in an inert gas atmosphere. I am giving. Thus, the oxide film formed on the surface of the semiconductor substrate can be burned during or after the pre-oxidation cleaning, and as a result, the roughness on the surface of the semiconductor substrate can be reduced. Therefore, when an oxide film is formed on the semiconductor substrate after this heat treatment, the roughness on the surface of the oxide film can be reduced. As a result, the quality of the oxide film can be improved, and the electrical characteristics of the oxide film can be improved.

In the above method for forming an oxide film,
The oxide film may be a tunnel oxide film or a gate oxide film.

A semiconductor device according to the present invention includes a source region diffusion layer formed on a semiconductor substrate, a drain region diffusion layer formed on the semiconductor substrate, and a semiconductor layer between the source region and the drain region. A tunnel oxide film formed on the substrate, a floating gate formed on the tunnel oxide film, and a control gate formed on the floating gate via an insulating film, wherein the tunnel oxide film is After the surface of the semiconductor substrate is cleaned and subjected to a heat treatment at a temperature higher than a thermal oxidation temperature at the time of forming an oxide film described below under an inert gas atmosphere on the semiconductor substrate, the semiconductor substrate is formed on the semiconductor substrate by a thermal oxidation method. It is characterized in that the oxide film is formed.

A semiconductor device according to the present invention includes a source region diffusion layer formed on a semiconductor substrate, a drain region diffusion layer formed on the semiconductor substrate, and a semiconductor between the source region and the drain region. A gate oxide film formed on the substrate; and a gate electrode formed on the gate oxide film. The gate oxide film cleans the surface of the semiconductor substrate and provides an inert gas atmosphere to the semiconductor substrate. An oxide film formed by performing a heat treatment at a temperature equal to or higher than a thermal oxidation temperature at the time of forming an oxide film below and then forming the oxide film on the semiconductor substrate by a thermal oxidation method.

In the above semiconductor device, the electrical characteristics of the tunnel oxide film or the gate oxide film can be improved.
Thereby, the quality of the semiconductor device is also improved.

[0014]

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

FIG. 1 is a sectional view showing a semiconductor device according to an embodiment of the present invention.

This semiconductor device is a FAMOS (non-volatile memory). An N ⁺ diffusion layer 11 in the source region and an N ⁺ diffusion layer 13 in the drain region are formed in the silicon substrate 1. A tunnel oxide film 3 is formed between the source region and the drain region. This tunnel oxide film 3
Is formed by thermally oxidizing the silicon substrate 1. A floating gate 5 is formed on the tunnel oxide film 3, and a control gate 9 is formed on the floating gate 5 via an insulating film 7.

Next, a method of forming the tunnel oxide film 3 in the FAMOS shown in FIG. 1 will be described.

Before forming the tunnel oxide film 3, the surface of the silicon substrate 1 is subjected to pre-oxidation cleaning. That is, the surface of the silicon substrate 1 is cleaned by immersing the silicon substrate 1 in a cleaning solution in which ammonia and hydrogen peroxide solution are mixed. Thereby, the oxide film on the silicon substrate 1 is removed. Next, the silicon substrate 1 is washed with water, and IPA drying (drying with isopropyl alcohol) is performed.

Thereafter, the silicon substrate 1 is annealed. The conditions at this time are as follows:
For example, a 100% Ar atmosphere is used, and the temperature is equal to or higher than the thermal oxidation temperature at the time of forming the tunnel oxide film, for example, 100.
The temperature is about 0 ° C., and the annealing time is 30 minutes.
Thereby, the roughness on the surface of the silicon substrate 1 is reduced. The reason for performing the annealing at a temperature higher than the thermal oxidation temperature is that if the oxidation temperature performed after the annealing is higher than the annealing temperature, it is considered that the roughness of the oxide film surface during the oxidation increases.

Next, a tunnel oxide film 3 is formed on the silicon substrate 1 by subjecting the surface of the silicon substrate 1 to thermal oxidation. The thermal oxidation conditions at this time are as follows:
And the atmosphere is 50% O ₂ /50% Ar.

Thereafter, the tunnel oxide film 3 is annealed at a temperature of about 900 ° C. to 1000 ° C. for a predetermined time in an Ar or N ₂ atmosphere. Thereby, tunnel oxide film 3 is baked.

According to the above embodiment, after the pre-oxidation cleaning before forming the tunnel oxide film of the FAMOS, the thermal oxidation temperature at the time of forming the oxide film on the silicon substrate 1 under an inert gas atmosphere. Annealing is performed at the above temperature.
Thus, the oxide film formed on the surface of the silicon substrate 1 by the pre-oxidation cleaning and the natural oxide film formed on the substrate 1 by exposing the silicon substrate 1 to the air after the pre-oxidation cleaning can be burned. As a result, the roughness on the surface of the silicon substrate 1 can be reduced. Therefore, when the tunnel oxide film 3 is formed on the silicon substrate 1 after the annealing, the surface roughness of the tunnel oxide film 3 generated on the surface of the substrate 1 can be reduced. Thus, the quality of the tunnel oxide film can be improved. Therefore, the electrical characteristics of the tunnel oxide film 3 can be improved.

FIG. 2 is a graph showing the relationship between the QBD of the tunnel oxide film and the cumulative failure rate when the tunnel oxide film is formed by three types of forming methods. Note that QBD is a constant current TDDB, which is the amount of charge injected until the oxide film is broken down when a constant current density is continuously applied to the oxide film.

The three types of forming methods are no annealing, annealing after oxidation, and annealing before oxidation.

The tunnel oxide film formed by the method without annealing treatment is obtained by cleaning the surface of the silicon substrate before forming the tunnel oxide film, and then thermally oxidizing the surface of the silicon substrate without performing annealing treatment with an inert gas. A tunnel oxide film was formed by a method, and thereafter, an annealing process with an inert gas was not performed.

The tunnel oxide film formed by the post-oxidation annealing treatment is formed by the above-described conventional method of forming a tunnel oxide film. The tunnel oxide film formed by the method of annealing before oxidation is formed by the method of forming a tunnel oxide film according to the above embodiment.

According to FIG. 2, QBD is plotted against the cumulative defect rate.
The tunnel oxide film formed by the pre-oxidation annealing method has the best value, and the tunnel oxide film formed by the post-oxidation annealing method has the next best QBD value.
It can be seen that the worst QBD value is the tunnel oxide film formed by the method without annealing. Therefore, the experimental results shown in FIG. 2 confirm that the effect of improving the electrical characteristics of the tunnel oxide film as described above can be obtained in the method for forming a tunnel oxide film according to the present embodiment.

The present invention is not limited to the above embodiment, but can be implemented with various modifications. For example,
In this embodiment mode, the above-described oxide film forming method
Although it is used for forming a tunnel oxide film of the OS, the present invention is not limited to this. For example, it can be used for forming a gate oxide film. In this case, the constant voltage TDDB value of the gate oxide film can be improved. Note that the constant voltage TDDB value is a lifetime until dielectric breakdown occurs when a constant voltage is continuously applied to the oxide film.

[0029]

As described above, according to the present invention, after cleaning before forming an oxide film, the semiconductor substrate is heated to a temperature not lower than the thermal oxidation temperature when forming the oxide film in an inert gas atmosphere. Heat treatment at the temperature of Therefore, it is possible to provide a method for forming an oxide film and a semiconductor device capable of improving the electrical characteristics of the oxide film by reducing the roughness of the oxide film surface.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a semiconductor device according to an embodiment of the present invention.

FIG. 2 is a graph showing the relationship between the QBD of the tunnel oxide film and the cumulative failure rate when the tunnel oxide film is formed by three types of forming methods.

[Explanation of symbols]

1 N ⁺ diffusion of the N ⁺ diffusion layer 13 drain region of the silicon substrate 3 tunnel oxide film 5 the floating gate 7 insulating film 9 control gate 11 source region

Claims (4)

[Claims] A step of cleaning the surface of the semiconductor substrate; a step of subjecting the semiconductor substrate to a heat treatment at a temperature equal to or higher than a thermal oxidation temperature when forming an oxide film described below in an inert gas atmosphere; Forming an oxide film by a thermal oxidation method. 2. The method according to claim 1, wherein the oxide film is a tunnel oxide film or a gate oxide film. 3. A diffusion layer of a source region formed on a semiconductor substrate, a diffusion layer of a drain region formed on the semiconductor substrate, and a diffusion layer formed on the semiconductor substrate between the source region and the drain region. A tunnel oxide film, a floating gate formed on the tunnel oxide film, and a control gate formed on the floating gate via an insulating film, wherein the tunnel oxide film covers the surface of the semiconductor substrate. Wash,
After performing a heat treatment at a temperature equal to or higher than the thermal oxidation temperature when forming the following oxide film under an inert gas atmosphere on the semiconductor substrate,
A semiconductor device comprising an oxide film formed on the semiconductor substrate by a thermal oxidation method. A source region diffusion layer formed on the semiconductor substrate; a drain region diffusion layer formed on the semiconductor substrate; and a drain region diffusion layer formed on the semiconductor substrate between the source region and the drain region. A gate oxide film, and a gate electrode formed on the gate oxide film, wherein the gate oxide film cleans the semiconductor substrate surface, and forms the following oxide film on the semiconductor substrate under an inert gas atmosphere. A semiconductor device comprising an oxide film formed by a thermal oxidation method on the semiconductor substrate after a heat treatment at a temperature higher than a thermal oxidation temperature at the time of formation.