JPH10321620A - Oxynitride film and its forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the electrical properties of an oxynitride film and the barrier quality of its impurity, by forming an oxide film on a substrate, and by fluorinating thereafter the surface of the oxide film through a fluoride, and further, by nitrifying thereafter the surface of the resultant film through a nitrogen compound. SOLUTION: After growing an oxide film on a silicon substrate 1, the silicon substrate 1 is attached to a substrate holder in a reaction chamber 2. Then, passing an argon gas through a quartz tube 3, it is introduced into the reaction chamber 2. In the course thereof, the plasma of the argon gas is generated through a microwave power in a resonator 4. Also, an F2 gas diluted by a helium gas is introduced into the reaction chamber 2 from an introduction tube provided between the reaction chamber 2 and the resonator 4. After completing a fluorinating, interrupting the introductions of the gases and holding the silicon substrate 1 at a predetermined temperature, a nitrogen gas is introduced into the quartz tube 3 inserted of the argon gas to nitride the silicon substrate 1 by generating the plasma of the nitrogen gas through the microwave power. Thereby, the electrical properties of an oxynitride film and the barrier quality of its impurity 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 a nitrided oxide film which is a useful insulating film in the manufacture of semiconductor integrated circuits such as LSIs and TFTs.

[0002]

2. Description of the Related Art In recent years, gate oxide films (silicon oxide films) have become thinner with the increase in the density of integrated circuits. There is a problem of penetration of impurities into the semiconductor and deterioration of hot carrier resistance. In addition, a silicon oxynitride film is expected as a gate insulating film replacing a silicon oxide film. Furthermore, the improvement of electrical characteristics such as dielectric breakdown charge and hot carrier resistance is due to the nitrogen present at the interface. To prevent impurity diffusion from the silicon gate electrode, the surface of the gate oxide film is nitrided to achieve a dense structure. Can be prevented. At present, methods of forming a nitrided oxide film include a light assisted process, a plasma assisted process, and a heat treatment of a silicon oxide film using NH ₃ , and a heat treatment after ion implantation of nitrogen into a gate polysilicon film. There are a method in which nitrogen is introduced into a silicon oxide film, a method in which a silicon substrate is heated with an electric furnace or a lamp using a nitrous oxide gas, and a nitrided oxide film is directly formed. However, the method has an advantage that nitrogen of 10 atomic% or more can be introduced. However, at the same time, hydrogen is also mixed in to form an electron trap, a high-temperature treatment must be performed for its removal, and the method has a problem of defect recovery. Therefore, high-temperature heat treatment is required, nitrogen cannot be introduced into the surface, and the barrier properties of impurities are insufficient, and the method has a low nitrogen content, improves electrical characteristics, and has insufficient barrier properties of impurities. Problems.

Further, application of a nitrided oxide film to a capacitor or an interlayer insulating film has been studied, and the above-described method and a method of forming the film by a CVD method have been proposed. Although the problem of the method has already been described, the method has a problem that the interface characteristics are inferior to other methods.

[0004]

As a result of intensive studies, the present inventor has found a method of nitriding to a specific depth from the surface by subjecting an oxide film to surface treatment with a fluoride and then nitriding, and arrived at the present invention. did.

That is, the present invention provides a method for forming a nitrided oxide film, comprising forming an oxide film, fluorinating the oxide film surface with a fluoride, and nitriding with a nitrogen compound. .

Examples of the oxide film used in the present invention include a silicon oxide film and a tantalum oxide film. In the present invention, after forming the above oxide film, first, the surface of the oxide film is fluorinated with a fluoride. The fluoride used is fluorine,
Hydrogen fluoride, hydrofluoric acid, chlorine fluoride, bromine fluoride,
One of iodine fluoride, xenon fluoride, krypton fluoride, nitrogen fluoride, sulfur fluoride, carbon fluoride, and oxygen fluoride, or a mixture thereof.

As a method of performing the fluorination treatment, it is only necessary to bring a fluoride into contact with the oxide film surface. The temperature conditions, pressure conditions, concentration conditions, and the like are not particularly limited as long as the fluoride does not deteriorate the surface state of the oxide film in either gas or liquid. In addition, when an excitation method such as light, plasma, or heat is used, any method may be used as long as it does not deteriorate the surface state of the oxide film.

Next, the fluorinated oxide film is nitrided. Examples of the nitrogen compound used include N ₂ , NH ₃ and hydrazine. As a method of the nitriding treatment, an excitation method such as light, plasma, or heat is used. Any method may be selected as long as it does not deteriorate the surface state of the oxide film, and conditions such as temperature, pressure, and concentration are not limited, and may be selected as appropriate according to the concentration of nitrogen to be introduced into the film. As more preferable conditions, in the plasma method, the temperature is 10 to 100.
Preferably, the treatment is performed at a temperature of 0 ° C. and a pressure of 0.01 to 10 Torr. Further, even if the film is treated with a compound containing hydrogen such as NH ₃ , the diffusion of hydrogen into the film does not occur due to the hydrogen trapping effect of fluorine performed in the first fluorination treatment.

According to this method, a nitrided oxide film having a concentration gradient gradually decreasing from the surface in the depth direction and having an increased nitrogen concentration near the surface can be obtained. For example, a nitrogen concentration at a depth of 0 nm is 2 to 3 atoms. % Or more.
The nitrided oxide film is a nitrided oxide film in which diffusion of impurities is prevented and electrical characteristics are improved.

[0010]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited to these examples.

Example 1 After an oxide film was grown on a silicon substrate to a thickness of 10 nm, the oxide film was subjected to surface treatment with excited fluorine under the following conditions, followed by nitriding. FIG. 1 is a schematic diagram of the remote plasma device used.

First, a silicon substrate 1 on which an oxide film is grown to a thickness of 10 nm is mounted on a substrate holder in a reaction chamber 2 and then introduced into the reaction chamber 2 while passing argon gas (300 SCCM) through a quartz tube 3. In the middle of the resonator 4, plasma of argon gas was generated with microwave power of 60W. Further, helium gas-diluted F ₂ gas (88.5 SCCM) was introduced from an introduction pipe between the reaction chamber 2 and the resonator 4. Here, F ₂ gas partial pressure 0.01Torr processing time is 2 minutes. After completion of the fluoridation treatment, introduction of F ₂ gas was stopped, the substrate was kept at 550 ° C., nitrogen (600 SCCM) was introduced instead of argon gas, plasma was generated with microwave power of 80 W, and total pressure was increased. The nitriding treatment was completed at 1 Torr for 60 minutes.

FIG. 2 shows the distribution of F and N in the depth direction in the sample after the excitation fluorination treatment and the nitridation treatment. F in the film
And N concentrations were measured with an X-ray photoelectron spectrometer.
The vertical axis indicates the atomic% concentrations of F and N. 0 depth from FIG.
The concentration of nm is about 2.8 atomic%, the concentration of 1.5 nm at a depth of about 0.4 atomic%, and it can be seen that N is introduced at a high concentration from the surface to a shallow layer inside the film. . As characteristics of the film, electric breakdown characteristics and barrier properties against boron diffusion were measured. Electrical breakdown electrical properties are 8 C / cm ²
(About 5 C / cm ^{2 in} the case of a silicon oxide film), and the barrier property was 0.1 V or less as a result of examining the change in threshold voltage after implanting BF ²⁺ ions. The barrier properties against boron diffusion were significantly improved.

Embodiment 2 FIG. After an oxide film was grown in the same manner as in Example 1, the oxide film was subjected to a surface treatment with non-excited fluorine, followed by a nitriding treatment. [Fluorine treatment conditions] Total pressure: 1 Torr, F ₂ partial pressure 0.01
Torr (Carrier gas Ar + He) [Nitriding conditions] Total pressure: 1 Torr, Processing time: 60 minutes, Nitrogen flow rate: 60
0SCCM, substrate temperature: 550 ° C, microwave power: 8
FIG. 3 shows the distribution of N in the depth direction in the sample after the 0W nitriding treatment. The concentration of N in the film was measured with an X-ray photoelectron spectrometer. The vertical axis indicates the atomic% concentration of N. From FIG. 3, the concentration at the depth of 0 nm is about 2.7 atomic%, and the density at the depth of 2.5 n
m, and it is understood that N is introduced at a high concentration from the surface to a shallow layer inside the film. The electrical properties of the film and the barrier properties against boron diffusion were measured in the same manner as in Example 1. As a result, the electrical properties and the barrier properties against boron diffusion were significantly improved.

Embodiments 3-1 to 19-3 A silicon oxide film is formed by the same operation as in Embodiment 1, and a silicon oxynitride film (SiON) is formed by changing the fluoridation method and the nitriding method. Tables 1 and 2 show the results of the evaluation of the film quality and the results of the evaluation of the film quality obtained by subjecting a sample having a tantalum pentoxide film formed on a silicon wafer to a fluorination treatment and a nitriding treatment. The fluoridation treatment was excited by a plasma treatment. The nitriding was performed by plasma processing at a microwave power of 80 W. The concentration of N in the film was measured with an X-ray photoelectron spectrometer. N only in the shallow layer inside the film from the surface
Had been introduced. As a result of measuring the electric breakdown characteristics of the film and the barrier property against boron diffusion in the same manner as in Example 1,
The electrical properties and the barrier properties against boron diffusion were significantly improved.

[0016]

[Table 1]

[0017]

[Table 2]

Example 20 After a silicon oxide film was grown on a silicon wafer, the sample was immersed in a dilute aqueous hydrofluoric acid solution (water: HF = 50: 1) to perform a fluorination treatment. Further, after that, a nitriding treatment was performed under the same conditions as in Example 2, and the electrical breakdown characteristics and the barrier property against boron diffusion of the film were measured in the same manner as in Example 1. Improved.

Example 21 After a tantalum oxide film was grown on a silicon wafer, the sample was immersed in a dilute aqueous hydrofluoric acid solution (water: HF = 50: 1) to perform a fluorination treatment. Further, after that, a nitriding treatment was performed under the same conditions as in Example 2, and the electrical breakdown characteristics and the barrier property against boron diffusion of the film were measured in the same manner as in Example 1. Improved.

Comparative Example 1 Oxide film on silicon substrate
After the growth of nm, a nitridation oxidation treatment was performed by a remote plasma method without performing the fluoridation treatment. [Oxynitriding conditions] Total pressure: 1 Torr, flow rate ratio (N ₂ : O ₂ ) = 200 SCC
M: 1 SCCM, processing time: 90 minutes, microwave power:
150W, temperature: 550 ° C, 650 ° C, 750 ° C, 85
The concentration of N in the 0 ° C. film was measured with an X-ray photoelectron spectrometer. 750 ° C, 850 ° C
In this case, introduction of nitrogen was recognized, but nitrogen could hardly be observed at a temperature of 650 ° C. or less. Further, almost no nitrogen could be introduced into the film surface, and the barrier property of boron was poor. Further, it was confirmed that the film thickness was increased as compared with the initial film thickness.

Comparative Example 2 Oxide film on silicon substrate
After the growth of nm, a nitriding treatment was performed by a remote plasma method without performing the fluoridation treatment. [Nitriding conditions] Total pressure: 1 Torr, flow rate (N ₂ ): 200 SCCM, processing time: 90 minutes, microwave power: 150 W, temperature: 8
50 ° C. The concentration of N in the film was measured with an X-ray photoelectron spectrometer. As a result of performing under the above processing conditions, the amount of nitrogen introduced in the depth direction was small, and nitrogen was not introduced into the surface.

[0022]

According to the method of the present invention, it is possible to obtain a nitrided oxide film having an increased nitrogen concentration near the surface, and to manufacture a nitrided oxide film in which diffusion of impurities is prevented and electrical characteristics are improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a remote plasma device used in the present invention.

FIG. 2 shows the relationship between the depth direction and the concentration of F and N in a sample after excitation fluorine treatment and after nitriding treatment in Example 1.

FIG. 3 shows the relationship between the depth direction and the concentration of N in a sample after nitriding in Example 2.

[Explanation of symbols]

 1. Substrate 2. Reaction chamber 3. Quartz tube 4. Resonator

Claims (3)

[Claims] 1. A nitrided oxide film having a concentration gradient gradually decreasing from a surface to a depth direction and having an increased nitrogen concentration near the surface. 2. A nitrided oxide film containing fluorine, having a concentration gradient gradually decreasing from the surface in the depth direction and having an increased nitrogen concentration near the surface. 3. The method for forming a nitrided oxide film according to claim 1, wherein the surface of the oxide film is fluorinated with a fluoride and then nitrided with a nitrogen compound.