JP2008235562A - Cleaning method for plasma CVD film forming apparatus - Google Patents

Abstract

The present invention provides a cleaning method in which deposits deposited in a plasma CVD film-forming apparatus are removed and cleaned, so that a discharge amount of a global warming substance is small and a new harmless treatment apparatus is not required.
SOLUTION: A mixed gas of a fluorinated hydrocarbon gas and an oxygen-containing gas having an allowable concentration of 200 ppm or more, a global warming coefficient of 1000 to 5000, and a vapor pressure at room temperature of 5 atm or more is used. Cleaning is performed under plasma discharge conditions such that the decomposition rate of the activated hydrocarbon gas is 90% or more. The fluorinated hydrocarbon is preferably one having 2 to 3 carbon atoms and 1 to 2 hydrogen atoms in the molecule.
[Selection figure] None

Description

  The present invention relates to a cleaning method for removing deposits adhering to the inside of a chamber and an exhaust pipe of a plasma CVD film forming apparatus, and in particular, after film formation is performed using a gas containing silicon as a film forming gas. The present invention relates to a method for cleaning by introducing a hydrocarbon gas.

In the electronic device manufacturing process, there are many steps of forming an insulating film such as a silicon oxide film or a silicon nitride film. As a method for forming these insulating films, a plasma CVD method is often used.
In the plasma CVD method, a solid deposit mainly composed of these film-forming components adheres to the inside of the chamber and the exhaust pipe along with the film-forming process.

This deposit causes problems such as abnormal film formation, generation of particles, and closure of the exhaust pipe system of the film forming apparatus. Therefore, the deposit needs to be cleaned according to the film forming frequency.
As this cleaning method, dry cleaning in which solid deposits are chemically changed to volatile fluorides such as silicon tetrafluoride (SiF ₄ ) by active fluorine atoms and exhausted is widely used.

In order to generate an active fluorine atom, a gas having a fluorine atom in the molecule is used. Generally, a perfluorinated compound such as tetrafluoromethane (CF ₄ ) or hexafluoroethane (C ₂ F ₆ ) is used. A method of converting (PFC) into plasma is used.
However, these PFC gases are global warming gases. The semiconductor industry has set a goal of reducing these greenhouse gases by 10% by 2010, based on 1995.

By using octafluoropropane (C ₃ F ₈ ) and cyclic butane octafluoride (c-C ₄ F ₈ ) as a method of reducing PFC gas emissions, gas consumption can be reduced or discharged. There are also known methods for reducing the total amount of global warming substances, but these gases also have a global warming potential (GWP) higher than CF ₄ and are not a radical solution.
On the other hand, although a method using a gas with extremely low GWP has been devised, generally, a low GWP gas is toxic to the human body, and thus conventionally a non-toxic inert gas such as CF ₄ or C ₂ F ₆ has been used. In the case of devices and equipment, new equipment for handling toxic gases is required.

In the High Pressure Gas Safety Law in Japan, gases whose allowable concentration values set by the American Society for Occupational Health are lower than 200 ppm are defined as toxic gases. Regarding the handling of these gases, gas leak detectors and gas containers are sealed in sealed rooms. It is necessary to provide a detoxifying device such as a combustion type detoxifying device which is housed in a container and exhausted to the environment, and which discharges the gas at an allowable concentration or less.
However, the addition of these devices leads to a significant cost increase. In particular, in order to introduce an abatement device, a large space is required, and it cannot be introduced when there is no new device introduction space with an existing device.
Table 1 shows the physical properties of generally known fluorine compounds for cleaning.

Mocella, M .; T.A. Mat. Res. Soc. Symp. Proc. 447 (Environmental, Safety and Health Issues in IC Production), 29 (1997). Ehalt, D.M. Prather, M .; International Panel on Climate Change (IPCC), Climate Change 2001: The Scientific Basis. Atmospheric Chemistry and Greenhouse Gases (2001) Japan Electronics and Information Technology Industries Association, press release, "9th World Semiconductor Conference (WSC) results" JP 2004-6554 A JP 2006-24709 A

  Therefore, the problem in the present invention is that when the deposit deposited in the plasma CVD film forming apparatus is removed and cleaned, the amount of emission of the global warming substance is small and it is not necessary to provide a new detoxification processing apparatus. There is to get a way.

To solve this problem,
The invention according to claim 1 is a method for removing deposits deposited in a chamber and an exhaust pipe of a plasma CVD film forming apparatus,
Using a mixed gas of a fluorinated hydrocarbon gas and an oxygen-containing gas having an allowable concentration of 200 ppm or more, a global warming coefficient of 1000 to 5000, and a vapor pressure at room temperature of 5 atm or more,
A cleaning method for a plasma CVD film-forming apparatus, wherein cleaning is performed under plasma discharge conditions such that the decomposition rate of the fluorinated hydrocarbon gas during cleaning is 90% or more.

  The invention according to claim 2 is characterized in that the fluorinated hydrocarbon has 2 to 3 carbon atoms and 1 to 2 hydrogen atoms in the molecule. Is the method.

  According to the present invention, the amount of emission of global warming substances is small, and it is not necessary to provide a new detoxification processing apparatus.

FIG. 1 shows an example of a plasma CVD film forming apparatus for carrying out the cleaning method of the present invention.
This plasma CVD film forming apparatus includes a parallel plate type plasma generating means (not shown) for generating plasma by applying high-frequency power, and for forming a thin film such as silicon oxide on a substrate in a plasma atmosphere. A chamber 1, a raw material gas introduction pipe 2 for introducing a film forming gas into the chamber 1, a first introduction pipe 3 for sending a fluorinated hydrocarbon gas forming a cleaning gas into the chamber 1, and a cleaning gas It is schematically constituted by a second introduction pipe 4 for sending the oxygen-containing gas formed into the chamber 1 and an exhaust pipe 6 provided with an exhaust pump 5 for exhausting the gas in the chamber 1.

  In film formation by this film formation apparatus, a substrate such as a silicon substrate is disposed in the chamber 1, and a source gas containing tetraethoxysilane, oxygen, nitrogen, ammonia, or the like is introduced into the chamber 1 from the source gas introduction pipe 2. Then, the plasma generating means is operated to form a thin film such as an oxide film on the substrate by plasma CVD reaction. The gas in the chamber 1 is sucked by the exhaust pump 5 and discharged from the exhaust pipe 6.

  In cleaning the chamber 1 and the exhaust pipe 6 of the plasma CVD film forming apparatus, a predetermined amount of fluorinated hydrocarbon gas is fed into the chamber 1 through the mass flow meter 7 from the first introduction pipe 3, 2 A predetermined amount of oxygen-containing gas is fed into the chamber 1 through the mass flow meter 8 from the introduction pipe 4. Then, a high frequency power of a predetermined power from a high frequency power source (not shown) is applied to the plasma generating means to excite the gas in the chamber 1 to generate plasma. The gas in the chamber 1 is sucked by the exhaust pump 5 so as to maintain a predetermined pressure and is discharged from the exhaust pipe 6.

The cleaning gas used in the present invention is a mixed gas of a fluorinated hydrocarbon gas and an oxygen-containing gas having an allowable concentration of 200 ppm or more, a global warming coefficient of 1000 to 5000, and a vapor pressure at room temperature of 5 atm or more. It is.
Specific examples of the fluorinated hydrocarbon gas include tetrafluoroethane (CF ₃ CH ₂ F, GWP: 1300, allowable concentration: 1000 ppm, vapor pressure: 6.6 atm), pentafluoroethane (CF ₃ CHF ₂ , GWP: 3400, allowable concentration: 1000 ppm, vapor pressure: 12.9 atm), heptafluoropropane (CF ₃ CHFCF ₃ , GWP: 3500, allowable concentration: 1000 ppm, vapor pressure: 5.8 atm) And fluorine compounds having 2 to 3 hydrogen atoms and 1 to 2 hydrogen atoms.

These fluorinated hydrocarbon gases have hydrogen atoms in their molecules, and these hydrogen atoms have reactivity with hydroxyl radicals in the atmosphere and have high infrared absorption ability, but GWP is relatively low. Value. In addition, since the decomposition reaction in the atmosphere proceeds slowly, the possibility of affecting the human body is extremely low and the allowable concentration value is high.
Under the High Pressure Gas Safety Law, these gases are classified as non-toxic and inert liquefied high pressure gases, and it is not necessary to install gas leak detectors or newly install a detoxifying device that decomposes these gases. It is possible to handle the gas with the same equipment as C ₂ F ₆ which is the gas for use.

Furthermore, these gases are in a liquefied state when they are filled in a gas container, but when removing the deposits deposited in the plasma CVD film forming apparatus and cleaning them, the vapor pressure is 5 atm or more at room temperature. Therefore, it is possible to use a common supply facility with CF ₄ and C ₂ F ₆ which are conventional cleaning gases.
If the permissible concentration of the fluorinated hydrocarbon gas is less than 200 ppm, the exhaust gas at the time of cleaning cannot be exhausted as it is, and a detoxification processing apparatus is required. When the global warming potential is less than 1000, the amount of toxic gas increases, and when it exceeds 5000, the amount of the global warming substance in the exhaust gas increases.

  Further, as the oxygen-containing gas, a gas containing oxygen atoms in a molecule such as oxygen or nitrogen oxide is used. Furthermore, a gas such as argon, helium, or nitrogen may be accompanied if necessary.

In order to perform the cleaning efficiently, it is necessary to efficiently release fluorine atoms in the molecule into the cleaning atmosphere under the condition that the decomposition rate of the fluorinated hydrocarbon gas is 90% or more. If this decomposition rate is less than 90%, active fluorine atoms cannot be generated efficiently, and undecomposed fluorinated hydrocarbon gas is discharged out of the system at a high concentration.
The concentration of oxygen required for plasma discharge in a mixed gas obtained by adding oxygen (O ₂ ) to the fluorinated hydrocarbon gas to oxidize carbon atoms in the molecule to carbon dioxide and release fluorine atoms is as follows: Assuming that the oxidation reaction (Equation 1) is completely dominant, it is obtained from the relationship of α = 2x.
CxHyFz + Oα → xCO ₂ + yHF + (z−y) F Equation 1

For example, in a mixed gas system of heptafluoropropane and oxygen, oxygen is 75% with respect to the total gas flow rate. Actually, the decomposition rate of the fluorinated hydrocarbon gas varies from 90 to 100%, and the side reaction generated by carbonyl difluoride (COF ₂ ) and CF ₄ proceeds simultaneously, such as N ₂ and Ar Therefore, the conditions may be optimized within a range of about 10% centering on the above concentration.

  When the number of carbon atoms contained in the cleaning gas molecule is not 2 to 3, for example, when it is 1, the number of fluorine atoms obtained from Formula 1 is small and the cleaning effect is remarkably reduced. In the case of four or more, cleaning performance can be expected, but the vapor pressure of the liquid is remarkably lowered, so that it cannot be used in the cleaning process. Similarly, when the number of hydrogen atoms contained in the molecule is 3 or more, the cleaning performance is remarkably lowered, so that it cannot be used in the cleaning process.

The plasma source used for plasma discharge may be any one of low frequency, high frequency, and microwave, and the applied power may be the same as when CF ₄ or C ₂ F ₆ that is a conventional cleaning gas is used. Since there is no need to use a high-density plasma source, there is no restriction on the plasma CVD film forming apparatus.

Incidentally, a fluorinated hydrocarbon gas having 2 to 3 carbon atoms and 1 to 2 hydrogen atoms in the molecule is known to be used in fields such as etching (Japanese Patent No. 2988455).
In both etching and cleaning, the object to be removed is changed to a gaseous compound such as SiF ₄ and discharged out of the system.
However, in etching, a protective film is formed on the side wall and the bottom to obtain a specific processing shape, and in order to obtain the vertical processability of the portion to be removed, the etching active species can be accelerated to an ion by an electromagnetic field. There is a need to.

On the other hand, neutral F atoms are necessary for cleaning, and in order to obtain F atoms efficiently, the gas pressure at the time of plasma discharge is raised above the etching conditions, proper applied power (power density), oxygen It is necessary to control the concentration and total flow rate, to increase the decomposition rate of the fluorine compound gas, and to make the conditions for high oxidation efficiency of intramolecular carbon.
These conditions are conditions for effectively obtaining F atoms, and are significantly different from known etching conditions. In the case of using the fluorinated hydrocarbon gas in the present invention, it is necessary to find conditions suitable for extracting the cleaning effect.

  Specifically, plasma discharge conditions for setting the decomposition rate to 90% or more include, for example, high frequency power of 3 W / cm 2 to 6 W / cm 2, temperature 300 to 500 ° C., pressure 4 to 10 torr, total gas flow rate 400 to 1000 sccm, Although it is possible by setting the concentration of the fluorinated hydrocarbon gas in the gas to 10 to 30% by volume, it is not limited to this range, and this condition is practically determined by experimental trial and error. .

In the present invention, since the decomposition rate of the fluorinated hydrocarbon gas is 90% or more, the undecomposed fluorinated hydrocarbon gas may be discharged from the plasma CVD film forming apparatus. However, as described above, this fluorinated hydrocarbon gas has a low GWP, has little adverse effect on the human body, and has a high allowable concentration. Therefore, even if it is released into the atmosphere as it is, there is no problem.
For example, when the total flow rate is 1000 sccm and the fluorinated hydrocarbon gas concentration is 30% by volume, the undecomposed gas may be discharged up to 30 sccm. However, in a dry pump that normally exhausts the inside of the CVD apparatus chamber, Since about 30 slm of nitrogen gas is added, the concentration of the fluorinated hydrocarbon gas immediately after the dry pump does not exceed the allowable concentration of 1000 ppm.

In the present invention, the global warming substances discharged during cleaning are the undecomposed fluorinated hydrocarbon gas and reaction byproducts such as CF ₄ , C ₂ F ₆ , and CO _2. The amount is small, so the total carbon dioxide equivalent emission weight is small.

Specific examples are shown below.
[Comparative example]
Using a parallel plate type plasma apparatus (Precision 5000, 5 inch wafer manufactured by Applied Materials) for forming a silicon oxide film with tetraethoxysilane (TEOS), using a mixed gas system of ethane hexafluoride (C ₂ F ₆ ) and oxygen Chamber cleaning performance was evaluated. The state of cleaning was monitored by the Fourier transform infrared spectrometer (FT-IR) installed at the rear stage of the exhaust pump and the components and concentration transition of the discharged gas.
Cleaning was performed after a silicon oxide film was grown to about 800 nm. The cleaning conditions were as follows.

・ High frequency applied power: 750w
・ In-chamber pressure: 3.5 torr
-Time: 70 seconds-Temperature: 400 ° C
・ Gas flow rate: ethane hexafluoride 500 sccm + oxygen 600 sccm
・ Distance between electrodes: 999 mils
The decomposition rate of C ₂ F ₆ in cleaning was 30%, and 70% of undecomposed gas was discharged. The warming substances discharged during cleaning were undecomposed C ₂ F ₆ and reaction byproducts CF ₄ and CO ₂ . Terms of CO ₂ emissions total weight obtained by multiplying the respective global warming potential of these discharge weight became 0.027 tons.

[Example 1]
In order to optimize the cleaning condition by the mixed gas system of CHF ₂ CF ₃ and O ₂ , the condition dependence of the cleaning condition was measured by using the experimental design method based on the response phase design of the three factor 3 level.
The variable factors were a total gas flow rate of 500 to 1,000 sccm, a CHF ₂ CF ₃ concentration with respect to the total flow rate of 20 to 40%, and a chamber internal pressure of 3 to 5 torr.
The fixed factors were an RF power of 750 W, an interelectrode distance of 999 mils, a temperature of 400 ° C., and the film formation conditions were the same as in the comparative example.

As a result of the analysis, it was found that the cleaning process speed was maximized when the total gas flow rate was 500 sccm, the CHF ₂ CF ₃ concentration was 20%, and the pressure was 5 Torr.
Further, within the above condition range, the decomposition rate of CHF ₂ CF ₃ during plasma discharge was 98% or more.
A similar experiment was performed on CF ₃ CHFCF ₃ , and the total flow rate was 500 sccm, the concentration of CF ₃ CHFCF ₃ was 14%, the pressure was 5 torr, and the cleaning processing speed was maximized. Also in this case, the decomposition rate of CF ₃ CHFCF ₃ during plasma discharge was 98% or more under all conditions.

In each case, the gas flow rate is up to about twice, and the pressure is in the range up to about 4 torr. The condition dependency is low, and the actual cleaning conditions are not fixed to the above conditions. When the pressure is 3 torr or less, or when the concentration of CHF ₂ CF ₃ is 30% or more, the gas decomposition rate is 90% or less, and carbonyl difluoride (COF ₂ ), which is a reaction byproduct, is used. As a result, the yield of C ₂ F ₆ was increased, and the cleaning processing speed was significantly reduced.
The known etching process pressure is set to 2 to 60 mtorr. As described above, when the fluorinated hydrocarbon gas is used for cleaning, a high oxygen concentration and a high pressure condition are necessary.

[Example 2]
The cleaning performance was evaluated by a mixed gas system of CHF ₂ CF ₃ and O ₂ by the same method as in the comparative example. Each flow rate was set to 100 sccm for CHF ₂ CF ₃ , 400 sccm for O ₂ , and a pressure of 5 Torr. The other conditions were the same as those in Example 1.
Warming substances discharged when cleaning was performed were undecomposed CHF ₂ CF ₃ (decomposition rate 99%) and reaction by-products CF ₄ , C ₂ F ₆ and CO ₂ . These terms of CO ₂ emissions total weight obtained by multiplying the respective global warming potential discharge weight becomes a 0.0027 t became compared to 90% reduction in the comparative example.

In this embodiment, the one-step cleaning does not change the pressure. However, in consideration of the cleaning effect of the exhaust system, in addition to the high-pressure cleaning as in this condition, a two-step cleaning with a pressure of 1 to 3 torr is added. Step cleaning can also be performed.
Under these conditions, even when 100 sccm of N ₂ , Ar, He, and N ₂ O was added, there was no change in the cleaning time and the discharge amount of warming substances. These additive gases are expected to increase the cleaning area and reduce the rate of progress of electrode degradation, so the maintenance frequency is reduced in mass production lines that process thousands of sheets in January. Can be expected.

[Example 3]
In the same manner as in the comparative example, performance evaluation was performed when a mixed gas of CF ₃ CHFCF ₃ and O ₂ was used as the cleaning gas. The flow rates of CF ₃ CHFCF ₃ were 80 sccm, O ₂ was 500 sccm, the pressure was 5 torr, and other conditions were the same as in the comparative example.
Warming substances discharged when cleaning was performed were undecomposed CF ₃ CHFCF ₃ (decomposition rate 99%) and reaction by-products CF ₄ , C ₂ F ₆ and CO ₂ . These terms of CO ₂ emissions total weight obtained by multiplying the respective global warming potential discharge weight becomes a 0.0022 t, became reduced to about 96% compared to the comparative example. Also in the gas system, as in CHF ₂ CF ₃ , two-step cleaning and N ₂ , Ar, He, and N ₂ O can be added as additive gases.

It is a schematic block diagram which shows the example of the film-forming apparatus for enforcing the cleaning method of this invention.

Explanation of symbols

1 .... chamber, 2 .... source gas introduction pipe, 3 .... first introduction pipe, 4 .... second introduction pipe, 5 .... exhaust pump, 6 .... exhaust pipe, 7 .... mass flow meter, ...・ Mass flow meter

Claims (2)

A method for removing deposits deposited in a chamber and an exhaust pipe of a plasma CVD film forming apparatus,
Using a mixed gas of a fluorinated hydrocarbon gas and an oxygen-containing gas having an allowable concentration of 200 ppm or more, a global warming coefficient of 1000 to 5000, and a vapor pressure at room temperature of 5 atm or more,
A cleaning method for a plasma CVD film-forming apparatus, wherein cleaning is performed under plasma discharge conditions such that the decomposition rate of the fluorinated hydrocarbon gas during cleaning is 90% or more.   The method of cleaning a plasma CVD film-forming apparatus according to claim 1, wherein the fluorinated hydrocarbon has 2 to 3 carbon atoms and 1 to 2 hydrogen atoms in the molecule.

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