JP2742381B2 - Method of forming insulating film - Google Patents

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 for forming a gate insulating film (hereinafter, referred to as an insulating film) such as a thin film transistor (TFT).

[0002]

2. Description of the Related Art Conventionally, a method of forming an insulating film by a plasma CVD method using an organic silane is generally performed based on a time chart shown in FIG. For example, in the case of depositing a silicon oxide film, for example, a source gas composed of an organic silane gas and an oxidizing gas is introduced into a chamber, and after a predetermined time t ₀ , high-frequency power is applied to start plasma discharge. . By this plasma discharge, the organic silane gas is decomposed and oxidized, and a silicon oxide film is deposited on the substrate. And before performing such an insulating film deposition step, usually, as pretreatment, boiling with concentrated sulfuric acid, washing with diluted hydrofluoric acid, washing with pure water and drying are performed.
Organic impurities and natural oxide films on the substrate and semiconductor are removed.

However, in the conventional method, the substrate is exposed to the air between the pretreatment and the deposition of the insulating film, so that atmospheric components are adsorbed on the substrate or a natural oxide film is generated. In the initial stage of the plasma discharge, the amount of generated oxygen radicals and oxygen ions is small, the oxidation does not proceed sufficiently, and the intermediate reaction product of the organic silane gas is deposited without completely forming the Si oxide film. OH on the interface
Impurities such as group and C were contained in large amounts. As described above, in the conventional formation method, the interface between the formed Si oxide film and the substrate contains a large amount of impurities such as OH groups and C, which deteriorates the film quality, particularly, the electrical characteristics, and particularly deteriorates the gate of a TFT or the like. This has been a major problem when used for an insulating film.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of these circumstances, and is intended to provide an insulating film having excellent film quality, particularly excellent electrical characteristics, by a plasma CVD method using an organic silane gas. It is intended to provide a forming method.

[0005]

The object of the present invention is to provide an organic sila
Gas using a plasma CVD method.BaseGame on board
In the method of forming an insulating film, fluorine is used as a constituent element.
Containing gas into the processing tank, apply high frequency power,
Rasma dischargeTo form a gate insulating film on the substrateStep
After performing the plasma treatment process, complete the gate insulating film formation.
Perform an edge deposition processA method of forming an insulating film,
Between the plasma treatment process and the subsequent insulating film deposition process
A method of forming an insulating film that does not interrupt dischargeBy solving
Wear. In addition, the above-mentioned plasma processing step and a subsequent insulating film
Between the deposition step, the inside of the processing tank may be evacuated.Ma
The high frequency power in the plasma processing step is 0.1 to
1.0W / cm^TwoAnd the substrate temperature is 250 to 400 ° C.
And the pressure in the processing tank is 20 to 150 Pa,
The processing time is preferably 2 to 10 minutes. Furthermore, before
The gas containing fluorine as a constituent element is F_Two, NF_Three, C_nF
_{2 (n + 1)} (Where n = 1, 2, 3, 4)
Is a gas containing one kind, and the organic silane gas is
Triethyl orthosilicate, diethylsilane, trie
Toxisilane, tetraethylcyclotetrasiloxane,
Tetramethylcyclotetrasiloxane, hexamethyldi
Siloxane, tetramethyldisilazane, hexamethyldi
Silazane, tetrakisdimethylaminosilane, hexame
One selected from tylcyclotrisilazane
Preferably.

[0006]

By performing a plasma treatment process using a gas containing fluorine as a constituent element before forming an insulating film on a substrate by a plasma CVD method, it is possible to remove atmospheric component impurities and a natural oxide film by fluorine radicals. Then, most of the unreacted products at the beginning of the subsequent plasma CVD are converted to gaseous products by the fluorine radicals or fluorine atoms adsorbed on the substrate, and are eliminated.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a method for forming an insulating film will be described in detail. Figure 1 is a first example embodiment of the method of forming the insulation Enmaku (hereinafter
Shows a time chart of the major operations for explaining say), FIG. 3 shows an example of an apparatus 10 used to implement the forming method.

In FIG. 3, reference numeral 11 denotes a processing bath, in which a cathode electrode 13 connected to a high-frequency power supply 12 is provided. Further, at a position below the cathode electrode 13 and facing the cathode electrode 13,
A sample stage 14 serving as an anode of the parallel plate electrode is installed,
Further thereon, a substrate 15 on which an insulating film is deposited is mounted. Further, one pipe serving as a vacuum exhaust port 17 is inserted into one surface of the processing tank 11, and the pipe is provided with a conductance valve 16. The gas inlets 18, 19, 20
The three pipes are inserted, and the valves 21, 22, and 23 are respectively provided outside the processing tank 11, and the mass flow controllers 24, 25, and 26 are further provided on the processing tank 11 side. Have been. further,
The high-frequency power supply 12 and the sample stage 14 are connected to ground.

Next, a method for forming an insulating film using such an apparatus 10 will be described with reference to FIG. First, time 1
In FIG. 3, the valve 23 shown in FIG. 3 is opened, and a gas containing fluorine as a constituent element is supplied into the processing tank 11. Then
At time 2 after the time t ₀ for stabilizing the pressure, high-frequency power is applied from the high-frequency power supply 12 to start plasma discharge. By doing so, fluorine radicals are generated in the processing bath 11, combined with atmospheric components and organic impurities on the substrate, turned into gas, exhausted out of the processing bath 11, and the surface of the substrate 15 is cleaned. .

The plasma processing step is performed for a predetermined processing time. After the processing time t _{1 has} elapsed, at time 3 the high frequency power supply 12 is turned off and the valve 23 is closed to supply high frequency power and a gas containing fluorine as a constituent element. Is stopped and the plasma discharge is terminated. Next, in order to make the inside of the processing tank 11 high vacuum, the conductance valve 16 is fully opened, and the vacuum exhaust port 1 is opened.
Exhaust from 7. At a time 4 after the elapse of the predetermined time t ₂ for evacuation, the valves 21 and 22 are opened to supply a source gas necessary for depositing the insulating film. afterwards,
After time t ₀ for pressure stabilization, high-frequency power is applied at time 5 to start plasma discharge. Then, after forming an insulating film having a predetermined thickness, at time 6, the high frequency power supply 12 is turned off, the valves 21 and 22 are closed, and the high frequency power
Stop supplying the source gas.

Here, the time t _{0 for} pressure stabilization may be omitted, but is usually about 0.1 to 2 minutes. The processing time t ₁ of the plasma processing step may be 0.5 minutes or more, but is preferably in the range of 2 to 10 minutes. Further, the predetermined time t ₂ for the evacuation, which may be at least 0.5 minutes, preferably in the range of 0.5 to 5 minutes.

The high frequency power to be applied is 0.1 to 1
W / cm ² It is preferable that This means that the high frequency power is 0.1 W / cm ² If it is less than 3, the generation of fluorine radicals is insufficient, it is difficult to sufficiently remove impurities, and the high frequency power is 1.0 W / cm ^2. This is because the amount of fluorine radicals does not increase so much even when the amount exceeds the above, and improvement of the effect cannot be expected. Further, the substrate temperature is preferably set to 250 ° C. to 400 ° C., and the pressure in the processing tank 11 is set to 20 to 150 Pa
It is preferable that

Here, among the raw material gases used for depositing the insulating film, the organic silane gas is a gas of an organic substance having a bond of silicon and oxygen or nitrogen in a molecule, and is formed on a substrate by a plasma CVD method. All the materials used when forming an insulating film are included, but when a silicon oxide film is formed as the insulating film, tetraethylorthosilicate, diethylsilane, triethoxysilane, tetramethylcyclotetrasiloxane, hexamethyldisiloxane It is preferably siloxane. As the oxidizing gas, oxygen, nitrous oxide, ozone-containing oxygen, or the like is used.

When a silicon nitride film is formed, an organic silane gas containing no oxygen in the molecule, such as tetramethyldisilazane, hexamethyldisilazane, tetrakisdimethylaminosilane, or hexamethylcyclotrisilazane, is preferable. As the nitriding gas, ammonia, nitrogen, or the like is used.

The gas containing fluorine as a constituent element includes all gases containing fluorine atoms in the molecule and capable of forming fluorine radicals in a plasma CVD environment, but include F ₂ , NF ₃ , C _n F _{2 (n + 1)} (where n = 1,
2, 3, 4) are preferably included.

Next, an example of a method for forming an insulating film according to the present invention.
(Hereinafter referred to as a second example) will be described. FIG. 2 shows a time chart of main operations for explaining the method of forming the insulating film of the second example. The difference between the method of forming the insulating film and the first example is that high-frequency power is continuously supplied without interrupting plasma discharge between the plasma processing step and the insulating film deposition step, and the fluorine in the processing bath 11 is reduced. The point is that the gas contained in the constituent elements is changed to the source gas necessary for depositing the insulating film. Others are the same as the first example.

A description will be given with reference to FIG. At time 1 in FIG. 2, the valve 23 shown in FIG.
A gas containing fluorine as a constituent element is supplied. After the time t ₀ for stabilizing the pressure, at time 2, high-frequency power is applied from the high-frequency power supply 12 to start plasma discharge.
Fluorine radicals are generated in the processing tank 11 and are combined with atmospheric components and organic impurities on the substrate 15 to form a gas, which is exhausted out of the processing tank 11 to clean the substrate surface.

Then, after a lapse of the plasma processing time t ₁ ,
At time 3, the valve 23 is closed, the supply of the gas containing fluorine as a constituent element is stopped, and at the same time, the valves 21 and 22 are opened to supply the source gas necessary for depositing the insulating film. At this time, the plasma discharge is continued without interruption, and after forming an insulating film having a predetermined thickness, the high frequency power supply 12 is turned off at time 6 and the valves 21 and 22 are turned off.
And shut off the supply of high frequency power and source gas.

In such a method of forming an insulating film, in a method of forming an insulating film on a substrate 15 by a plasma CVD method using an organic silane gas, a gas containing fluorine as a constituent element is supplied into the processing tank 11. After applying a high-frequency power and performing a plasma processing step of generating a plasma discharge, the method for forming an insulating film is characterized by performing an insulating film depositing step of forming an insulating film. The natural oxide film can be removed, and subsequently, most of the unreacted products at the beginning of the subsequent plasma CVD are converted into gaseous products by fluorine radicals or fluorine atoms adsorbed on the substrate, and are eliminated. The properties and interface characteristics are improved, and a high-quality insulating film can be obtained.

Hereinafter, specific examples will be shown to clarify the effects of the present invention. ( Test Example 1) First, a plasma CVD apparatus 1 similar to that shown in FIG.
0 was prepared. Then, the cathode electrode 1 in the processing tank 11
The substrate 15 was set on the sample stage 14 below the sample plate 3 and constituting the anode of the parallel plate electrode, and the air in the processing tank 11 was evacuated from the vacuum exhaust port 17 to create a high vacuum. A heater was built in the sample stage 14, and the substrate 15 was controlled to be maintained at 315 ° C. during the process.

[0021] Then, the method of forming the insulation Enmaku are shown in FIG. 1 (hereinafter
The supply of gas and the application of high-frequency power were controlled in accordance with a time chart for explaining the first example below . First, at time 1, as a gas containing fluorine as a constituent element, CF ₄ was supplied into the processing tank 11 from the gas inlet 20 through the mass flow controller 26 by opening the valve 23. The flow rate of CF ₄ is 100 sccm (standard cc) by the mass flow controller 26.
/ Min). The pressure in the processing tank 11 was controlled to 130 Pa by changing the conductance valve 16 connected to the vacuum exhaust port 17.

Next, after a lapse of one minute as time t ₀ for stabilizing the pressure, at time 2, the high frequency power supply 12
The high frequency power of 3.56 MHz is converted to 250 W (0.55 W /
cm ² ). At time 3 after the plasma discharge by CF _{4 was} continued for 5 minutes at time t ₁ , the high frequency power supply 12 was stopped, the valve 23 was closed, and the supply of CF ₄ was stopped. Next, the inside of the processing tank 11 was evacuated to a high vacuum.

As time t ₂ , after elapse of 5 minutes, at time 4, tetraethylorthosilicate (hereinafter referred to as TEOS) and oxygen are supplied as source gases for depositing an insulating film from gas inlets 18 and 19 through valves 21, 21, respectively. 22, the processing tank 1 through the mass flow controllers 24 and 25
1. The flow rate of TEOS was controlled to 6 sccm by the mass flow controller 24.

Further, the piping from the TEOS vaporizer (not shown) to the processing tank 11 was kept at 95 ° C. in order to prevent TEOS from resolidifying. The mass flow controller 25 controlled the flow rate of oxygen to 100 sccm. Processing tank 11
The internal pressure was controlled to 130 Pa by varying the conductance valve 16 connected to the vacuum exhaust port 17. Then, after a lapse of one minute as time t ₀ for pressure stabilization, at time 5, 13.56 from the high-frequency power source 12.
250 W (0.55 W / cm ² )
Applied. Here, the plasma discharge was started, and the deposition of the silicon oxide film was started. After forming a film having a predetermined thickness of 100 nm, the high frequency power supply 12 is stopped at time 6 and the valve 2
1 and 22 were closed to stop the supply of the raw material gas. And
The inside of the processing tank 11 was evacuated to a high vacuum, and then brought to atmospheric pressure, the processing tank 11 was opened, and the substrate 15 on which the insulating film was formed was taken out.

Test Example 2 A plasma CVD apparatus 10 similar to that shown in FIG. 3 was prepared. The sample stage 1 which is located below the cathode electrode 13 in the processing tank 11 and constitutes the anode of the parallel plate electrode
The substrate 15 was set on 4 and the air in the processing tank 11 was exhausted from the vacuum exhaust port 17 to make a high vacuum. A heater was built in the sample stage 14, and the substrate 15 was controlled to be kept at 315 ° C. during the process.

The supply of gas and the application of high-frequency power were controlled according to a time chart for explaining an example (hereinafter referred to as a second example) of the method of forming an insulating film according to the present invention shown in FIG. First, at time 1, as a gas containing fluorine as a constituent element, CF ₄ is opened by opening the valve 23, and the mass flow controller 26 is opened from the gas inlet 20.
And supplied into the processing tank 11. The flow rate of CF ₄ was controlled to 100 sccm (standard cc / min) by the mass flow controller 26. The pressure in the processing tank 11 was controlled to 130 Pa by changing the conductance valve 16 connected to the vacuum exhaust port 17.

Then, after a lapse of one minute as the time t ₀ for stabilizing the pressure,
The high frequency power of 3.56 MHz is converted to 250 W (0.55 W /
cm ² ). After the plasma discharge by CF ₄ was continued for 5 minutes at time t ₁ , at time 3 valve 2
3 and shut off the supply of CF ₄ ,
1, 22 are opened, and TEOS and oxygen are supplied as source gases from the gas inlets 18 and 19 through the valves 21, 22,
It was supplied into the processing tank 11 through the mass flow controllers 24 and 25. Here, the flow rate of TEOS was controlled to 6 sccm by the mass flow controller 24.

Further, the piping from the TEOS vaporizer (not shown) to the processing tank 11 was kept at 95 ° C. in order to prevent re-solidification of TEOS. In addition, during the gas switch,
The application of the high-frequency power was continued, and the plasma discharge was continued.
The flow rate of oxygen is 1 by the mass flow controller 25.
It was controlled at 00 sccm. The pressure in the processing tank 11 was controlled to 130 Pa by changing the conductance valve 16 connected to the vacuum exhaust port 17.

Here, the deposition of the silicon oxide film starts. After forming a film having a predetermined thickness of 100 nm, at time 6, the high-frequency power supply 12 was stopped, and the valves 21 and 22 were closed to stop supplying the source gas. Then, the inside of the processing tank 11 was evacuated to a high vacuum, and then the pressure was increased to the atmospheric pressure, and the processing tank 11 was opened to take out the substrate 15 on which the insulating film was formed.

[0030] The method of forming the first and second examples of the conventional insulating film forming method (Test Example 3) absolute Enmaku, deposition parameters (gas flow rate, pressure, RF power, substrate temperature, etc.) are the same And based on the time charts of FIGS. 1, 2 and 4, respectively,
A 100 nm silicon oxide film is deposited on a Si wafer, and an M electrode having an Al electrode having an area of 0.005 cm ² thereon is formed.
An OS capacitor was prepared and the characteristics were compared. In addition,
All Si wafers were treated with concentrated sulfuric acid 150
The treatment was performed at 5 ° C. for 10 minutes, 5% hydrofluoric acid for 7 minutes, washed with pure water, and dried, and an insulating film was formed in about 30 minutes. Table 1 shows the results.

[0031]

[Table 1]

In Table 1 , the leak current was measured by applying an electric field of 2 MVcm ^-1 . As is clear from the results shown in Table 1 , an example of the method for forming an insulating film of the present invention (second
An insulating film formed by the example), the conventional forming method 及
Further, it was confirmed that the dielectric breakdown voltage was higher, the interface state density and the leak current were smaller than those of the first example , and the electrical characteristics were very good. This is a thin film transistor, M
It has sufficient characteristics as a gate insulating film of an IS transistor or the like.

[0033] The method of forming the first and second examples of the conventional insulating film forming method (Test Example 4) insulation Enmaku, deposition parameters (gas flow rate, pressure, RF power, substrate temperature, etc.) are the same And based on the time charts of FIGS. 1, 2 and 4, respectively,
A 100 nm silicon oxide film is deposited on a Si wafer, and an M electrode having an Al electrode having an area of 0.005 cm ² thereon is formed.
An OS capacitor was prepared and the characteristics were compared. In addition, the insulating film was formed on all the Si wafers without performing the pretreatment. Table 2 shows the results.

[0034]

[Table 2]

In Table 2 , the leak current was measured by applying an electric field of 2 MVcm ^-1 . As is clear from the results shown in Table 2 , the insulating film forming method of the present invention (second method )
It can be seen that the cleaning as pretreatment can be omitted by using Example) .

[0036]

As described above, the method of forming an insulating film according to the present invention uses a method of forming an insulating film on a substrate by a plasma CVD method using an organic silane gas by treating a gas containing fluorine as a constituent element. is supplied to the tank, a high-frequency power is applied, after performing plasma processing step of causing a plasma discharge, a method of forming insulation Enmaku to facilities the insulating film deposition step of forming an insulating film, wherein the plasma treatment process And the following
Do not interrupt the plasma discharge between
Since the formation method of the insulating film, wherein the brewing, the fluorine radicals can be removed atmospheric components impurities and a natural oxide film, further followed by fluorine radicals or fluorine atoms adsorbed on the substrate, non-subsequent plasma CVD initial Most of the reaction products are converted to gaseous products,
Since it is excluded, the insulating properties and interface characteristics are improved, and the film quality of the insulating film, particularly, electrical characteristics can be significantly improved. Therefore, a high-quality gate insulating film can be formed at a low temperature, and is particularly effective for forming a gate insulating film of a thin film transistor using a substrate having a low melting point. In addition, since the surface of the substrate can be efficiently cleaned, it is possible to omit the usual cleaning of the pretreatment.

[Brief description of the drawings]

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

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

FIG. 3 shows a plasma CV used in a method of forming an insulating film.
It is a schematic diagram of D apparatus.

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

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Plasma CVD apparatus, 11 ... Processing tank, 12 ... High frequency power supply, 13 ... Cathode electrode, 14 ... Sample stand, 15 ... Substrate, 16 ... Conductance valve, 17 ... Vacuum exhaust port,
18, 19, 20 ... gas inlet, 21, 22, 23 ... valve, 24, 25, 26 ... mass flow controller

 ────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-110471 (JP, A) JP-A-63-53929 (JP, A) JP-A-1-296626 (JP, A) Sharp Technical Report No. 55 (1993-3-10) p. 27-31

Claims (10)

(57) [Claims] 1. A plasma CVD method using an organic silane gas.
In a method for forming a gate insulating film on a substrate by a method, a gas containing fluorine as a constituent element is supplied into a treatment tank,
The high-frequency power is applied, causes a plasma discharge, was subjected to a plasma treatment process on the substrate to form a gate insulating film, a method of forming insulation Enmaku to facilities the insulating film deposition step of forming a gate insulating film, The plasma treatment step and subsequent
A method for forming an insulating film, wherein plasma discharge is not interrupted between an edge film deposition step . 2. The method for forming an insulating film according to claim 1, wherein the inside of the processing tank is kept at a vacuum between the plasma processing step and a subsequent insulating film depositing step. 3. A forming method according to claim 1 or claim 2, wherein the insulating film, wherein the high-frequency power in the plasma treatment step is 0.1~1.0W / cm ^2. 4. The method of claim 1 the substrate temperature in the plasma treatment step is characterized in that it is a 250 to 400 ° C. ~
3. The method for forming an insulating film according to any one of 3 . Wherein the plasma processing method of forming a dielectric film according to any one of claims 1-4 in which the pressure in the treatment tank in the process is characterized in that it is a 20～150Pa. Wherein the plasma processing method of forming a dielectric film according to any one of claims 1-5 in which the processing time in the process is characterized in that 2 to 10 minutes. 7. The gas containing fluorine as a constituent element,
F ₂ , NF ₃ , C _n F _{2 (n + 1)} (where n = 1, 2, 3,
The method for forming an insulating film according to any one of claims 1 to 6 , wherein the gas is a gas containing at least one of 4). 8. The method according to claim 1, wherein the organic silane gas is tetraethylorthosilicate, diethylsilane, triethoxysilane, tetraethylcyclotetrasiloxane, tetramethylcyclotetrasiloxane, hexamethyldisiloxane, tetramethyldisilazane, hexamethyldisilazane, tetrakisdimethylaminosilane. method of forming a dielectric film according to any one of claims 1-7, characterized in that the one selected from among hexamethylcyclotrisilazane. 9. A method of forming a dielectric film according to any one of claims 1-8, characterized in that the gate insulating film is a silicon oxide film. 10. A method of forming a dielectric film according to any one of claims 1-8, characterized in that the gate insulating film is a silicon nitride film.