JPH0684888A - Formation of insulation film - Google Patents

Abstract

PURPOSE:To acquire a formation method of an insulation film which has good film quality, especially good electrical properties by a plasma CVD method by stopping supply of organic silane material gas without discontinuing discharge after formation of the insulation film and by continuing plasma discharge of acid gas for a specified time. CONSTITUTION:A substrate 17 is set on a sample base 16 and oxygen is introduced into a film formation chamber 14 as acid gas. High frequency power of 250W of 13.56MHz is applied from a high frequency power source 19 Film formation of SiO2 is started. After a specified 1000Angstrom -thick film is formed, an opening/closing valve 21 is closed to stop supply of TEOS. Thereafter, acid gas alone is supplied into the film formation chamber 14 and plasma discharge is continued. High frequency power is stopped and an opening/closing valve 20 is closed. An interior of the film formation chamber 14 is evacuated to high vacuum and then made an atmospheric pressure. The film formation chamber 14 is opened and the substrate 17 wherein an insulation film is formed is taken out.

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 insulating film, and more particularly to a method very useful for forming a gate insulating film such as a thin film transistor.

[0002]

2. Description of the Related Art Generally, an insulating film is formed by a plasma CVD method using an organic silane material and an oxidizing gas by using a plasma CVD apparatus as shown in FIG. The oxidizing gas is introduced into the film forming chamber 14 through the opening / closing valve 20 and the mass flow controller 12 from the oxidizing gas inlet 10. On the other hand, the organosilane material gas is passed from the vaporizer 11 through the opening / closing valve 21 and the mass flow controller 13 and introduced into the film forming chamber 14 at the same time as the oxidizing gas. After the pressure is stabilized, the high-frequency plasma discharge decomposes and oxidizes the organic silane material gas to form Si on the substrate 17.
Form an oxide film. After the predetermined film thickness is formed, the discharge is stopped and the supply of both gases is stopped to form the Si oxide film. FIG. 4 is a time chart of main operations for explaining the conventional method of forming an insulating film. First, at time 6, the opening / closing valve 21 for the organic silane material gas and the opening / closing valve 20 for the oxidizing gas are simultaneously closed and opened, both gases are introduced into the film forming chamber 14, and for the pressure stabilization, After the lapse of time t ₀ , high-frequency power is applied from the high-frequency power source 19 at time 7, plasma discharge is started, and film formation is started on the substrate 17. After forming a film with a predetermined thickness, the high frequency power is turned off at time 8, and at the same time, the opening / closing valve 21 for the organic silane material gas is opened.
Then, the opening / closing valve 20 for the oxidizing gas is closed.

[0003]

However, according to the conventional method of forming an insulating film, at the initial stage of plasma discharge,
The amount of oxygen radicals and oxygen ions generated is small, the oxidation does not proceed sufficiently, and the intermediate reaction product of the organosilane material gas is Si.
Since the oxide film is deposited without becoming an oxide film, O
A large amount of impurities such as H group and C are included. Further, when the plasma discharge is stopped even after the film formation is completed, unreacted organic silane material gas existing in the film formation chamber 14 and its intermediate reaction product are deposited on the surface of the Si oxide film.
As described above, the Si film formed by the conventional insulating film forming method is formed.
A large amount of impurities such as OH groups and C were contained in the interface of the oxide film with the substrate 17 and on the surface thereof, and the film quality, particularly the electrical characteristics, deteriorated. In particular, when it is used for a gate insulating film such as TFT, it has been a serious problem. Therefore, an object of the present invention is to provide a method for forming an insulating film having good film quality, particularly excellent electrical characteristics, by a plasma CVD method using an organic silane material gas and an oxidizing gas.

[0004]

The object of the present invention is to supply an organic silane material gas and an oxidizing gas to a film forming chamber to form an insulating film by a plasma CVD method. First introduced, plasma discharge is generated, and after a lapse of a predetermined time t ₁ , an organosilane material gas is introduced without interrupting the discharge, an insulating film is formed, and then the organosilane material gas without interrupting the discharge. stopping the supply of, after this is solved the plasma discharge of the oxidizing gas at a predetermined time t ₂ Continue method.

Further, in a method of supplying an organic silane material gas and an oxidizing gas to a film forming chamber to form an insulating film by a plasma CVD method, the oxidizing gas is first introduced into the film forming chamber to perform plasma discharge. And the plasma discharge and the supply of oxidizing gas were not interrupted during film formation.
This is solved by a method of intermittently supplying the organosilane material gas.

The present invention will be described in detail below. FIG. 1 shows a time chart of main operations for explaining the first example of the method for forming an insulating film of the present invention. Figure 3 at time 1
The opening / closing valve 20 for the oxidizing gas of the plasma CVD apparatus shown in (4) is opened to closed, and the oxidizing gas is introduced into the film forming chamber 14. Then, after time t _{0 for} stabilizing the pressure, high frequency power is applied from the high frequency power supply 19 at time 2 to start plasma discharge. At time 3, when the opening / closing valve 21 for the organic silane material gas is opened and the organic silane material gas is introduced into the film forming chamber 14, the formation of the insulating film is started. After forming a film with a predetermined film thickness, at time 4, the opening / closing valve 21 for the organic silane material gas is closed, only the oxidizing gas is supplied into the film forming chamber 14, and the plasma discharge is continued. After a lapse of time t ₂ , the high frequency power is turned off at time 5, and at the same time, the oxidizing gas opening / closing valve 20 is closed.

The pressure stabilization time t ₀ is usually about 0.5 to 2 minutes. The plasma discharge times t ₁ and t ₂ in which only the oxidizing gas is supplied into the film forming chamber 14 are stable if each is 10 seconds or more, but preferably in a range of 0.5 to 20 minutes.

As the organic silane material, various organic silane materials such as tetraethylorthosilicate (hereinafter abbreviated as TEOS), diethylsilane, triethoxysilane and tetramethylcyclotetrasiloxane are used. As the oxidizing gas, oxygen, nitrous oxide, ozone-containing oxygen or the like is used.

Next, a second example of the method for forming an insulating film of the present invention will be described. FIG. 2 shows a time chart of main operations for explaining the insulating film forming method of the second example. The difference of this insulating film forming method from the first example is that between time 3 and time 4, the plasma discharge and the supply of the oxidizing gas are continuously supplied without interruption. Instead, the organic silane material gas is intermittently supplied.

As an example of the method, at time 3, the opening / closing valve 21 of the organic silane material gas is opened without interrupting the plasma discharge and the supply of the oxidizing gas, and the organic silane material gas is placed in the film forming chamber 14. Introduced
The formation of the insulating film is started. Then, after the lapse of time t _A ,
The opening / closing valve 21 for the organic silane material gas is closed, only the oxidizing gas is supplied into the film forming chamber 14, and the plasma discharge is continued. After the time t _{B has} elapsed, the opening / closing valve 21 for the organosilane material gas is opened again, and the organosilane material gas is introduced into the film forming chamber 14. As described above, the supply of the organic silane material gas is intermittently performed by repeating the opening / closing operation of the opening / closing valve 21 a plurality of times. After the film having a predetermined film thickness is formed, at time 4, the opening / closing valve 21 for the organic silane material gas is closed, only the oxidizing gas is supplied into the film forming chamber 14, and the plasma discharge is continued.

The discharge is stable when the supply time t _A and the supply stop time t _B of the organic silane material gas are each 10 seconds or more, but the range is preferably 0.5 to 10 minutes. The characteristics improve as the number of times of repeating the opening and closing operation increases, but it is preferable that the number of times of repeating the opening and closing operation is 2 to 10 times in actual film formation in consideration of the processing time.

In the method of forming an insulating film according to the present invention,
When unstable immediately after plasma discharge, the organic silane material gas is not supplied and oxygen radicals and oxygen ions are sufficiently generated,
Since the adsorbed molecules are reduced in the film forming chamber and on the substrate on which the insulating film is formed and the organic silane material gas is introduced to form a film in a state where oxygen radicals and oxygen ions are sufficiently generated, the film is formed at the initial stage of film formation Impurities such as OH groups and C in the insulating film are reduced.

Further, by intermittently supplying the organic silane material gas, when the organic silane material gas is first supplied into the film forming chamber, the organic silane material gas is decomposed by plasma discharge and the insulating film is formed. Is formed.
After that, when the supply of the organic silane material gas is stopped, oxygen radicals, oxygen ions, etc. generated by the plasma discharge of only the oxidizing gas cause impurities such as OH groups and C in the previously formed insulating film. Removal is performed efficiently.

Further, since the supply of the organosilane material gas is stopped before the plasma discharge is completed, the organosilane material gas or the like remaining due to the plasma of the oxidizing gas is sufficiently decomposed and oxidized to generate H ₂ O and CO. , CO _{2 and the} like can be exhausted as gas molecules, so that even if the plasma discharge is terminated, an intermediate reaction product which is insufficiently oxidized is not deposited on the formed insulating film, and impurities on the surface of the insulating film are removed. Decrease. Therefore, when the insulating film is formed by the method for forming an insulating film according to the present invention, not only impurities in the interface portion with the semiconductor and in the surface portion of the insulating film but also internal impurities can be efficiently removed. The film quality, especially the electrical characteristics are improved.

[0015]

EXAMPLES The present invention will be described below with reference to examples.
It does not limit the invention. Example 1 First, a plasma CVD apparatus similar to that shown in FIG. 3 was prepared. Then, the substrate 17 is set on the sample table 16 below the cathode electrode 15 in the film forming chamber 14 and constituting the anode of the parallel plate electrode, and the air inside the film forming chamber 14 is exhausted from the vacuum exhaust port 18. High vacuum was used. A heater was built in the sample stage 16 and the substrate 17 was controlled so as to be kept at 315 ° C. during the process.

Then, gas introduction and high frequency power application were controlled according to the time chart for explaining the first example of the method for forming an insulating film according to the present invention shown in FIG. First,
At time 1, the opening / closing valve 20 for the oxidizing gas was opened, and oxygen was introduced as the oxidizing gas into the film forming chamber 14 through the mass flow controller 12 from the oxidizing gas inlet 10. The flow rate of oxygen is 100 sccm (standard cc /
min). The pressure in the film forming chamber 14 was controlled to 1.0 Torr by changing the conductance valve 22 connected to the vacuum exhaust port 18.

Then, after a lapse of 1 minute as time t ₀ for pressure stabilization, at time 2, the high frequency power supply 19
250 W of high frequency power of 3.56 MHz was applied. Plasma discharge was continued by supplying only the oxidizing gas, and after 10 minutes at time t ₁ , the opening / closing valve 21 of the organosilane material gas was opened at time 3, and TEOS was introduced into the film forming chamber 14 through the mass flow controller 13. . The flow rate of TEOS is the mass flow controller 13
Was controlled to 8 sccm. At this time, TEOS in the vaporizer 11 is set to 70 ° C.
Was heated to 95 ° C.

Then, the film formation of SiO ₂ is started, and after the predetermined film thickness of 1000 Å has been formed, at the time 4, the opening / closing valve 2
1 was closed and the supply of TEOS was stopped. After this time t ₂
For 10 minutes, only the oxidizing gas is deposited in the film forming chamber 14
And then plasma discharge was continued. At time 5, the high frequency power was stopped and the on-off valve 20 was closed. And
The inside of the film forming chamber 14 was evacuated to a high vacuum, and then the atmospheric pressure was set, the film forming chamber 14 was opened, and the substrate 17 on which the insulating film was formed was taken out.

(Embodiment 2) A plasma CVD apparatus similar to that shown in FIG. 3 is prepared, and between time 3 and time 4, a second example of the method for forming an insulating film according to the present invention shown in FIG. An insulating film was formed on the substrate 17 in the same manner as in Example 1 except that gas introduction and high frequency power application were controlled as described below according to a time chart for explanation. At time 3, the open / close valve 21 for the organosilane material gas was opened without interrupting the plasma discharge and the supply of the oxidizing gas, and TEOS was introduced into the film forming chamber 14 through the mass flow controller 13. TE
The flow rate of OS is 8s by the mass flow controller 13.
Controlled to ccm. At this time, TEOS in the vaporizer 11 was heated to 70 ° C., and a pipe from the vaporizer 11 to the film forming chamber 14 was heated to 95 ° C. Then, the SiO ₂ film formation is started, and after a lapse of 2 minutes at time t _A , the opening / closing valve 21 of the organic silane material gas is closed, only the oxidizing gas is supplied into the film formation chamber 14, and the plasma discharge is continued. did. After the plasma discharge using only the oxidizing gas for 2 minutes at time t _B , the opening / closing valve 21 for the organic silane material gas is opened, the organic silane material gas is supplied into the film forming chamber 14, and the insulating film is formed. It was Such an opening / closing operation of the opening / closing valve 21 for the organic silane material gas was repeated four times at times t _A and t _B , respectively. After film formation with a predetermined film thickness of 1000Å, the opening / closing valve 21 was closed at time 4 to stop the supply of TEOS.

(Test Example) The deposition parameters (gas flow rate, pressure, high frequency power, substrate temperature, etc.) are the same between the first and second examples of the insulating film forming method of the present invention and the conventional insulating film forming method. Then, based on the time charts of FIG. 1, FIG. 2 and FIG. 4, respectively, a 1000 Å SiO ₂ film is formed on a Si wafer, and an Al having an area of 0.05 cm ^{2 is formed} thereon.
A MOS capacitor having electrodes was prepared and the characteristics were compared. The results are shown in Table 1.

[0021]

[Table 1]

In Table 1, the leak current is measured by applying an electric field of 2 MVcm ^-1 . As is clear from the results shown in Table 1, the insulating film formed by the first and second examples of the method for forming an insulating film of the present invention has a higher withstand voltage than that by the conventional forming method, Level density,
It was confirmed that the leak current was small and the electric characteristics were very good. This is a thin film transistor, MIS
It has sufficient characteristics as a gate insulating film for transistors and the like.

[0023]

As described in detail above, the method for forming an insulating film according to the present invention is applied to a case where an organic silane material gas and an oxidizing gas are supplied to a film forming chamber to form an insulating film by a plasma CVD method. In addition, the film quality of the insulating film, especially the electrical characteristics can be significantly improved. Therefore, a good-quality gate insulating film can be formed at a low temperature, and it is particularly effective for forming a gate insulating film of a thin film transistor using a substrate having a low melting point.

[Brief description of drawings]

FIG. 1 is a time chart for explaining a first example of a method for forming an insulating film of the present invention.

FIG. 2 is a time chart for explaining a second example of the insulating film forming method of the present invention.

FIG. 3 is a plasma CVD used in a method for forming an insulating film.
It is a schematic diagram of an apparatus.

FIG. 4 is a time chart for explaining a conventional method of forming an insulating film.

[Explanation of symbols]

 10 Gas Inlet Port 11 Vaporizer 12 Mass Flow Controller 13 Mass Flow Controller 14 Film Forming Chamber 15 Cathode Electrode 16 Sample Stage 17 Substrate 18 Vacuum Exhaust Port 19 High Frequency Power Supply 20 Open / Close Valve 21 Open / Close Valve 22 Conductance Valve

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H01L 29/784

Claims (7)

[Claims] 1. A method of supplying an organic silane material gas and an oxidizing gas to a film forming chamber to form an insulating film by a plasma CVD method, wherein the oxidizing gas is first introduced into the film forming chamber to perform plasma discharge. Wake up for a predetermined time t
After ₁ lapse of time, the organosilane material gas was introduced without interrupting the discharge to form the insulating film, and then the supply of the organosilane material gas was stopped without interrupting the discharge, after which the plasma discharge of the oxidizing gas was performed. Is continued for a predetermined time t _{2, a} method of forming an insulating film. 2. A method of supplying an organic silane material gas and an oxidizing gas to a film forming chamber to form an insulating film by a plasma CVD method, wherein the oxidizing gas is first introduced into the film forming chamber to perform plasma discharge. A method for forming an insulating film, characterized in that the plasma discharge and the supply of the oxidizing gas are not interrupted during the film formation and the supply of the organosilane material gas is intermittently performed. 3. The method for forming an insulating film according to claim 1, wherein the oxidizing gas discharge times t ₁ and t ₂ are each 0.5 to 20 minutes. 4. The method for forming an insulating film according to claim 2, wherein the supply of the organosilane material gas is intermittently performed twice or more during film formation. 5. The method for forming an insulating film according to claim 1, wherein the organic silane material gas is tetraethyl orthosilicate. 6. The organic silane material gas is one selected from triethoxysilane, diethylsilane, and tetramethylcyclotetrasiloxane, according to any one of claims 1 to 4. Method of forming insulating film. 7. The method for forming an insulating film according to claim 1, wherein the oxidizing gas is oxygen.