JP2002305196A - Method for manufacturing semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease concentration of nitrogen in an interface between a silicon substrate and a silicon oxidizing and nitriding film and increase concentration of nitrogen in the surface of the silicon oxidizing and nitriding film. SOLUTION: A silicon oxidizing film is formed on the silicon substrate and treated thermally in an NH3 gas atmosphere at a pressure of at most 50 Torrs, at a temperature of at least 1,000 deg.C for at most 60 sec, so that nitrogen is introduced in the silicon oxidizing film, and the silicon oxidizing and nitriding film is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a method for manufacturing a semiconductor device, and more particularly, to a MIS field effect transistor (M
The present invention relates to a method for forming an oxynitride film used as a gate insulating film of an ISFET.

[0002]

2. Description of the Related Art Large-scale integrated circuits (LSI: Large)
Scale Integrated circuit
With the advance of miniaturization and high integration of s), it is necessary to reduce the thickness of a silicon oxide film used as a gate insulating film.

However, as the silicon oxide film becomes thinner, the barrier property against impurities (for example, boron) introduced into the gate polysilicon electrode is lost. This phenomenon causes a variation in threshold voltage and an increase in interface state, and causes a problem of an increase in variation in device characteristics.

Further, as the gate insulating film becomes thinner, the gate current depending on the film thickness increases. It is known that this phenomenon theoretically increases exponentially with decreasing film thickness.

Therefore, in order to solve the above problems,
As the gate insulating film, a silicon oxynitride film may be used instead of the silicon oxide film. The introduction of nitrogen atoms makes the molecular structure of the gate insulating film dense, and prevents diffusion of boron atoms, which are impurities in the gate electrode, into the silicon substrate.

Further, since the average dielectric constant of the gate insulating film is increased by the introduction of nitrogen atoms, it is possible to form a gate insulating film having the same electrical thickness and a larger physical thickness than the silicon oxide film. There is also an advantage that the above-mentioned phenomenon of an increase in gate current can be suppressed.

For forming the silicon oxynitride film, a method of forming a silicon oxide film on a semiconductor substrate and then performing a heat treatment in a NO, N ₂ O or NH ₃ gas atmosphere is used.

[0008]

[Problems to be Solved by the Invention] However, especially 5 nm
When nitrogen is introduced into the following thin silicon oxide film, N
When O or N ₂ O gas is used, nitrogen is introduced near the interface between the silicon substrate and the silicon oxynitride film as shown in FIG. As a result, fixed charges and interface states increase, causing problems such as a decrease in mobility and an increase in 1 / f noise, which leads to deterioration of device characteristics.

When NH ₃ gas is used, when the silicon oxynitride film is thinner than 5 nm, the nitrogen concentration distribution in the oxynitride film becomes almost uniform as shown in FIG. Like the NO or N ₂ O gas, the nitrogen concentration near the interface between the silicon substrate and the oxynitride film increases. Therefore, also in this case, the device characteristics deteriorate.

Accordingly, the present invention provides a method of manufacturing a semiconductor device in which the nitrogen concentration near the interface between the silicon oxynitride film and the silicon substrate is kept low and the nitrogen concentration on the surface of the silicon oxynitride film is increased.

[0011]

The object of the present invention is to form a silicon oxide film having a thickness of 5 nm or less on a silicon substrate, and to apply a pressure of 50 T to the silicon substrate on which the oxide film is formed.
forming a silicon oxynitride film by introducing nitrogen into the silicon oxide film by performing a heat treatment at a temperature of not less than 1000 ° C. and at a temperature of not less than 1000 ° C. in an atmosphere of NH ₃ or less of orr. The problem is solved by a method for manufacturing a semiconductor device.

According to the present invention, by performing the heat treatment under the above conditions, the nitriding reaction near the interface between the silicon substrate and the silicon oxynitride film is suppressed, and the nitrogen concentration near the surface of the silicon oxynitride film can be increased. it can.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment First Embodiment of the Present Invention
The manufacturing process of the semiconductor device according to the embodiment will be described. FIG.
FIG. 3 is a diagram showing a manufacturing process of the MIS semiconductor device according to the first embodiment of the present invention.

Referring to FIG. 1A, a silicon substrate 1
An element isolation region 2 is formed, and a 2.5 nm silicon oxide film 3 is formed on the silicon substrate 1 by a thermal oxidation method.

Next, as shown in FIG. 1B, the silicon oxide film 3 is subjected to a heat treatment at a temperature of 1050 ° C. for 60 seconds in an NH ₃ gas atmosphere at a pressure of 10 Torr. As a result, nitrogen is introduced into the silicon oxide film 3 to form a silicon oxynitride film 4.

Here, the nitrogen concentration profile from the surface of the silicon oxynitride film 4 formed by the above process to the interface with the silicon substrate is shown by a solid line in FIG. The dotted line in FIG. 2 shows the nitrogen concentration profile when the heat treatment is performed in the NO gas atmosphere instead of the NH ₃ gas in the above step.

The dotted line indicates that the surface of the silicon oxynitride film (hereinafter referred to as “oxynitride film surface”) has a low nitrogen concentration and is near the interface between the silicon substrate and the silicon oxynitride film (hereinafter referred to as “silicon substrate interface”). Nitrogen concentration is high. On the other hand, the solid line indicates that the nitrogen concentration on the surface of the oxynitride film is high, and conversely, the nitrogen concentration near the silicon substrate interface is low.

Therefore, as is apparent from FIG.
The nitrogen concentration of the silicon oxynitride film treated in the ₃ gas atmosphere is high near the oxynitride film surface, low near the silicon substrate interface, and can keep fixed charges and interface levels low.
It is possible to suppress a decrease in mobility and an increase in 1 / f noise.

Subsequently, as shown in FIG. 1C, polysilicon serving as a gate electrode is deposited on the silicon oxynitride film 4 and processed by photolithography and etching to form a gate electrode 5. Further, an impurity is diffused in a region between the gate electrode 5 and the element isolation region 2 to form a diffusion layer 6, whereby an MIS type semiconductor device is formed. Here, a description will be given of an embodiment of the present invention in which the effects of the present invention can be exhibited.

FIG. 3 is a graph showing the relationship between the processing time in an NH ₃ -containing gas atmosphere at a pressure of 30 Torr and the nitrogen concentration on the surface of the oxynitride film at different processing temperatures. From FIG.
It can be seen that the higher the processing temperature, the higher the nitrogen concentration on the oxynitride film surface can be increased in a shorter time, and the longer the processing time, the higher the nitrogen concentration on the oxynitride film surface.

However, if the treatment time is lengthened, the nitrogen concentration on the surface of the oxynitride film increases, but at the same time, the nitrogen concentration on the interface of the silicon substrate also increases. FIG. 4 is a graph showing this phenomenon. FIG. 4 is a graph showing the relationship between the processing time in an NH ₃ -containing gas atmosphere at a pressure of 30 Torr and the nitrogen concentration at the silicon substrate interface for each processing temperature. FIG. 4 shows that the longer the processing time, the higher the nitrogen concentration at the silicon substrate interface. Since the present invention aims at suppressing the nitrogen concentration at the silicon substrate interface low and preventing the deterioration of device characteristics due to problems such as a decrease in mobility and an increase in 1 / f noise, the nitrogen concentration at the silicon substrate interface is low. Is more desirable. In order to obtain good interface characteristics, it is necessary to keep the nitrogen concentration at the silicon substrate interface within 2 atomic%. That is, as shown in FIG.
At ℃, it is necessary to shorten the time within 10 minutes.

However, when the treatment is carried out at a treatment temperature of 900 ° C. or 800 ° C., the nitrogen concentration at the silicon substrate interface can be suppressed within 2 atomic% under the above conditions. 4.5 atomic%
(See FIG. 3). On the other hand, when the processing temperature is 1000 ° C., the nitrogen concentration at the silicon substrate interface is 2%.
The nitrogen concentration on the surface of the oxynitride film can be increased to about 6.6 atomic% with respect to atomic% (see FIG. 3). Therefore, by performing the processing at a high temperature of 1000 ° C. or more and for a short time of 60 seconds or less, it is possible to suppress the nitridation at the silicon substrate interface and increase the nitrogen concentration on the oxynitride film surface.

Next, the relationship with the pressure will be considered. FIG.
Is a graph showing the relationship between the pressure and the nitrogen concentration at the interface of the silicon substrate when the heat treatment is performed at a temperature of 1000 ° C. for 60 seconds.
From FIG. 5, the nitrogen concentration at the interface of the silicon substrate was set to 2 atom.
In order to keep the pressure within c%, the pressure must be 50 Torr or less.

[Second Embodiment] Next, a manufacturing process of a semiconductor device according to a second embodiment of the present invention will be described. FIG. 6 is a sectional view showing the manufacturing process of the MIS semiconductor device according to the second embodiment of the present invention. However, in FIG. 6, the parts described above are denoted by the same reference numerals, and description thereof will be omitted.

Referring to FIG. 6A, the silicon substrate 1
Then, an element isolation region 2 is formed, and a silicon oxide film having a thickness of 0.5 to 1.5 nm is formed on the silicon substrate by a thermal oxidation method. Next, as in the first embodiment, NH at a pressure of 10 Torr was used.
_The silicon oxynitride film 7 is formed by performing a heat treatment at a temperature of 1050 ° C. for 60 seconds in a _three- gas atmosphere.

Subsequently, as shown in FIG. 6B, a Si ₃ N ₄ is formed on the silicon oxynitride film 7 as a high dielectric insulating film 8.
And the like, and further, polysilicon serving as a gate electrode is deposited on the high dielectric insulating film 8.

Next, as in the first embodiment, the gate electrode 9 is formed by processing the silicon oxynitride film, Si ₃ N ₄ and polysilicon by photolithography and etching techniques. Further, an impurity is diffused in a region between the gate electrode 9 and the element isolation region 2 to form a diffusion layer 6, whereby a MIS type semiconductor device is formed.

Since the Si ₃ N ₄ deposited between the silicon oxynitride film 7 and the gate electrode 9 is a high dielectric substance, the average dielectric constant of the gate insulating film is higher than that of the silicon oxynitride film alone. As a result, the physical thickness of the gate insulating film can be increased while maintaining the electrical thickness, so that an increase in gate current can be suppressed.

Further, since the surface of the silicon oxynitride film 7 formed in the embodiment of the present invention has a high nitrogen concentration, the average dielectric constant of the oxynitride film is also high. Therefore, the average dielectric constant of the entire gate insulating film is higher than when the silicon oxide film is used as an interface layer with the high dielectric insulating film 8.

Although polysilicon is used for the gate electrode and Si ₃ N ₄ is used for the high dielectric insulating film, the gate electrode is made of an electrode material such as tungsten or aluminum, and the high dielectric insulating film is made of Ta ₂ O ₅ or TiO _2. It is also possible to use a high-dielectric insulating material such as ₂ .

Therefore, the present invention is not limited to the specific embodiment, and various modifications and changes can be made within the gist of the claims.

[0032]

As described above, according to the present invention, the nitrogen concentration at the interface between the silicon substrate and the silicon oxynitride film can be suppressed low, and the nitrogen concentration at the surface of the silicon oxynitride film can be increased. As a result, the fixed charge and the interface state can be kept low.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a manufacturing process of a semiconductor device according to a first embodiment.

FIG. 2 is a diagram showing a nitrogen concentration profile of a silicon oxynitride film manufactured according to the first embodiment and a nitrogen concentration profile when heat-treated in an NO gas atmosphere.

FIG. 3 is a diagram showing a relationship between a processing time in an NH ₃ gas atmosphere at a pressure of 30 Torr and a nitrogen concentration on the surface of a silicon oxynitride film.

FIG. 4 is a diagram showing a relationship between a processing time in an NH ₃ gas atmosphere at a pressure of 30 Torr and a nitrogen concentration at an interface between a silicon oxynitride film and a silicon substrate.

FIG. 5 shows a temperature of 1000 ° C. in an NH ₃ gas atmosphere.
FIG. 4 is a diagram showing a relationship between pressure and a nitrogen concentration at an interface between a silicon oxynitride film and a silicon substrate when heat treatment is performed for 60 seconds.

FIG. 6 is a diagram showing a manufacturing process of the semiconductor device according to the second embodiment.

FIG. 7 is a nitrogen concentration profile of a silicon oxynitride film manufactured by a conventional technique.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Silicon substrate, 2 ... Element isolation region, 3 ... Silicon oxide film, 4, 7 ... Silicon oxynitride film, 5, 9 ... Gate electrode, 6 ... Diffusion layer, 8 ... High dielectric insulating film

Continued on the front page F term (reference) 5F058 BC11 BD01 BD15 BD18 BF64 BJ01 5F140 AA00 AA01 AA03 AA06 AA24 BD01 BD07 BD09 BD11 BD12 BD15 BE07 BE08 BE19 BF01 BF04 BF05 BF07 BG37 CB04

Claims (2)

[Claims] A step of forming a silicon oxide film having a thickness of 5 nm or less on a silicon substrate;
Forming a silicon oxynitride film by introducing nitrogen into the silicon oxide film by performing a heat treatment at a temperature of 1000 ° C. or higher in an atmosphere of an NH ₃ -containing gas of Torr or less for 60 seconds or less. A method for manufacturing a semiconductor device. 2. The method according to claim 1, further comprising, after the step of forming the silicon oxynitride film, a step of forming a high dielectric insulating film on the silicon oxynitride film. .