JP2009266884A - Cleaning method of plasma film forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent occurrence of abnormal film formation by reducing occurrence of arcing and preventing various parts in a chamber from being damaged when cleaning is performed by plasma treatment, using gas mixture of hydrofluorocarbon gas and oxygen as cleaning gas, in order to remove deposits deposited in the chamber and the exhaust pipe of a plasma CVD film forming apparatus. <P>SOLUTION: Plasma treatment is carried out using gas mixture containing hydrofluorocarbon gas, oxygen and dissociative gas, where the proportion of dissociative gas is 5-10 vol.% of the total amount of hydrofluorocarbon gas and oxygen, as the cleaning gas. Pentafluoroethane gas is desirable as the hydrofluorocarbon gas, and any one or more sorts of CF<SB>4</SB>, C<SB>2</SB>F<SB>6</SB>, C<SB>3</SB>F<SB>8</SB>, c-C<SB>4</SB>F<SB>8</SB>, NF<SB>3</SB>, and N<SB>2</SB>O are desirable as the dissociative gas. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a cleaning method for a plasma film forming apparatus, and relates to a method for forming a thin film using a film-forming gas containing silicon and then cleaning the gas containing fluorine into a plasma.

  In the electronic device manufacturing process, there are many processes for 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 (PECVD) is often used. In this process, a solid deposit mainly composed of film-forming components accumulates in the chamber and the exhaust pipe along with the film-forming process.

Since this solid deposit causes abnormal film formation, generation of particles, and blockage of the exhaust pipe, it is necessary to clean the inside of the chamber and the exhaust pipe according to the accumulated film thickness and film formation frequency. .
As this cleaning method, dry cleaning in which the solid deposit is chemically changed to a volatile fluoride such as silicon tetrafluoride (SiF ₄ ) by active fluorine atoms to remove the exhaust gas 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 (Non-patent Document 1).
However, these PFC gases are global warming gases (Non-patent Document 2).

The semiconductor industry has set a goal of reducing these global warming substances by 10% by 2010, based on 1995 (Non-patent Document 3).
As a cleaning method for reducing the emission amount of PFC gas, a method of performing plasma treatment using a so-called alternative gas such as a hydrofluorocarbon gas having a hydrogen atom in a molecule has been filed by the present applicant.

The cleaning method disclosed in this prior invention uses a mixed gas of an alternative gas composed of a hydrofluorocarbon gas such as ethane tetrafluoride and ethane pentafluoride and an oxygen-containing gas such as oxygen as a cleaning gas. This is a cleaning method.
However, when this type of alternative gas is used, generally, the discharge voltage (Vpp) during plasma processing is increased or the self-bias voltage (Vdc) is increased due to the physical properties of the alternative gas itself or the relationship between the mixture ratio of the alternative gas and oxygen. ) Tends to fluctuate on the negative side.

The discharge voltage refers to a peak-to-peak voltage between a positive potential and a negative potential of a high-frequency voltage applied between electrodes, and is a voltage necessary for plasma discharge. The self-bias voltage refers to a voltage at a position that is 1/2 of the discharge voltage.
If the discharge voltage becomes extremely higher than the conventional conditions or if the self-bias voltage takes a negative large value, a local abnormal discharge of plasma called arcing is likely to occur during plasma generation.

  Arcing does not occur because it is difficult to promote the plasma-assisted chemical reaction for normal cleaning, damages various parts in the chamber, shortens the service life, and causes abnormal film formation. It is necessary to control as follows.

It is desirable that the discharge voltage has a value equivalent to that in the conventional cleaning method, and it is desirable that the plasma be maintained so that the self-bias voltage does not become a large negative potential as well.
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, “About the results of the 9th World Semiconductor Conference (WSC)” http: // semicon. jeita. or. jp / docs / wsc. pdf (2005). JP 2004-6554 A JP 2006-24709 A

  Therefore, the problem in the present invention is that, when cleaning is performed by plasma treatment using a mixed gas of hydrofluorocarbon gas and oxygen as a cleaning gas, the occurrence of arcing is suppressed, and various parts in the chamber are not damaged. The purpose is to prevent film abnormalities.

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,
A plasma treatment is performed using a mixed gas containing a hydrofluorocarbon gas, oxygen, and a dissociative gas as a cleaning gas, and the ratio of the dissociative gas being 5 to 10 vol% of the total amount of the hydrofluorocarbon gas and oxygen. This is a cleaning method of the plasma film forming apparatus.

The invention according to claim 2 is the cleaning method for a plasma film forming apparatus according to claim 1, wherein the hydrofluorocarbon gas is pentafluoroethane gas.
In the invention according to claim 3, the dissociative gas is at least one of CF ₄ , C ₂ F ₆ , C ₃ F ₈ , c-C ₄ F ₈ , NF ₃ , and N ₂ O. Alternatively, the cleaning method of the plasma film forming apparatus described in 2.

According to the present invention, by using a mixed gas containing a hydrofluorocarbon gas, oxygen, and a dissociative gas as a cleaning gas, and the proportion of the dissociative gas being 5 to 10 vol% of the total amount of the hydrofluorocarbon gas and oxygen. In the plasma processing, the discharge voltage is almost the same as that in the case of using the conventional cleaning gas, so that the discharge voltage does not increase unnecessarily, and the self-bias voltage does not become a large negative value.
For this reason, the occurrence of local abnormal discharge of plasma called arcing is suppressed, various parts in the chamber are not damaged, and film formation abnormality does not occur.
In addition, emissions of global warming substances are reduced.

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 2 that generates a plasma by applying a high frequency power from a high frequency power source 1 and forms a thin film such as silicon oxide on a substrate in a plasma atmosphere. Chamber 3, a raw material gas introduction pipe 4 for introducing a film forming gas into the chamber 3, a first introduction pipe 5 for feeding a hydrofluorocarbon gas constituting the cleaning gas into the chamber 3, and a cleaning gas A second introduction pipe 6 for sending the oxygen gas formed into the chamber 3; a third introduction pipe 7 for sending the dissociative gas forming the cleaning gas into the chamber 3; and an exhaust pump 9 for exhausting the gas in the chamber 3. And an exhaust pipe 8.

The plasma generating means 2 includes a shower head 21 through which a deposition gas and a cleaning gas flow out and a susceptor 22 on which a substrate is placed, and high frequency power from the high frequency power source 1 is applied between the shower head 21 and the susceptor 22. It has come to be.
The source gas introduction pipe 4, the first introduction pipe 5, the second introduction pipe 6, and the third introduction pipe 7 communicate with the shower head 21, and the film forming gas and the cleaning gas are transferred from the shower head 21 to the substrate. It is designed to flow toward

  In film formation by this film formation apparatus, a substrate such as a silicon substrate is disposed on the susceptor 22 in the chamber 3, and a source gas containing tetraethoxysilane, oxygen, nitrogen, ammonia, or the like is supplied from the source gas introduction pipe 4 to the chamber 3. Then, the plasma generating means 2 is operated and a thin film such as an oxide film is formed on the substrate by plasma CVD reaction. The gas in the chamber 3 is sucked by the exhaust pump 9 and discharged from the exhaust pipe 8.

  In cleaning the inside of the chamber 3 and the exhaust pipe 8 of the plasma CVD film forming apparatus, a predetermined amount of hydrofluorocarbon gas is fed into the chamber 3 from the first introduction pipe 5 through the mass flow meter 10, 2 A predetermined amount of oxygen gas is fed from the introduction pipe 6 into the chamber 1 through the mass flow meter 11, and a dissociative gas is fed from the third introduction pipe 7 through the mass flow meter 12.

  A high frequency power of a predetermined power from the high frequency power source 1 is applied between the shower head 21 and the susceptor 22 to excite the cleaning gas in the chamber 3 to generate plasma. The gas in the chamber 3 is sucked by the exhaust pump 9 so as to maintain a predetermined pressure and is discharged from the exhaust pipe 8.

As the cleaning gas used in the present invention, a mixed gas of hydrofluorocarbon gas, oxygen gas and dissociative gas is used.
As hydrofluorocarbon gas, a part of hydrogen of saturated lower hydrocarbons such as C ₂ HxFy (x = 1, 2, y = 4, 5), C ₃ HxFy (x = 1, 2, y = 6, 7), etc. One kind or a mixture of two or more kinds of fluorinated hydrocarbon gas in which is substituted with fluorine is used, and suitable hydrofluorocarbons include C ₂ HF ₅ and C ₃ HF ₇ .
These hydrofluorocarbon gases are gases having a high allowable concentration value and a smaller global warming potential than C ₂ F ₆ .

  The mixing ratio of hydrofluorocarbon gas and oxygen gas is 400 to 900 parts of oxygen gas with respect to 100 parts of hydrofluorocarbon gas in a volume ratio. There is a shortage of active fluorine atoms generated by the reaction in the plasma atmosphere. On the other hand, when it exceeds 900 parts, the discharge voltage (Vpp) becomes remarkably high.

The dissociative gas refers to a gas having a chemical bond with molecules composed of two or more atoms. Specific examples of the dissociative gas include C ₂ F ₆ (dissociation energy (C—C): 4.28 eV) c—C ₄ F ₈ (dissociation energy (C—C): 2.26 eV), NF ₃ ( Dissociation energy (N—F): one or two or more mixed gases such as 2.63 eV) may be mentioned, and in addition, C ₃ F ₈ (dissociation energy (C—C): 4.10 eV), N ₂ O (dissociation energy (N—O): 1.73 eV) can also be used.
As a gas not included in the category of such a dissociative gas, there is a rare gas such as argon, helium, or neon.

  The amount of such dissociative gas used is 5 to 10% by volume with respect to the total amount of hydrofluorocarbon gas and oxygen gas, and the occurrence of arcing in which the proportion of dissociative gas is outside this range is suppressed. I can't do that.

The plasma discharge conditions during the cleaning process are, for example, a high frequency power of 3 W / cm ^{2 to} 6 W / cm ² , a temperature of 300 to 500 ° C., a pressure of 4 to 10 Torr, and a total gas flow rate of 400 to 1000 sccm, but are limited to this range. It is practical that it is determined by experimental trial and error.

  In the cleaning method of the present invention, the hydrofluorocarbon gas and the oxygen gas in the cleaning gas react in a plasma atmosphere to generate active fluorine atoms, and the active fluorine atoms are generated on the inner wall surfaces of the chamber 3 and the exhaust pipe 8. The solid deposit made of silicon oxide or the like adhering to the gas is changed to a gaseous compound such as silicon tetrafluoride and discharged from the exhaust pipe 8 to the outside of the system.

At this time, by the coexistence of dissociative gas, plasma is generated with lower energy, and the generated plasma has less high energy components, and the plasma potential is considered to be neutral (0 V), and the discharge voltage is increased. It is expected that the self-bias voltage will not take a negative high voltage.
On the other hand, when excessively dissociative gas is added, the electron density of the plasma becomes too low, and the plasma discharge is sustained, so that the characteristics change so that the energy of electrons per one becomes high, the discharge voltage becomes high, It is predicted that an unstable plasma will be formed when the self-bias voltage takes a high negative value.

  Therefore, by adding an appropriate amount of dissociative gas, it is possible to prevent the discharge voltage from increasing excessively, and the self-bias voltage does not become a large negative value, thereby preventing the occurrence of arcing. . For this reason, various parts in the chamber 3 are not damaged, and there is no occurrence of defects such as film formation abnormality.

Specific examples are shown below.
(Conventional example)
Mixing of hexafluoroethane and oxygen used as standard cleaning gas using a parallel plate plasma device (Precision 5000, 5 inch wafer manufactured by Applied Materials) for silicon oxide film formation using tetraethoxysilane (TEOS) The chamber cleaning performance by gas system was evaluated.
For the state evaluation during cleaning, a high voltage probe was attached to the RF waveguide in the chamber lid, and the discharge voltage (Vpp) and the self-bias voltage (Vdc) were monitored. Cleaning was performed after the silicon oxide film was grown to about 800 nm.
The cleaning conditions were as follows.

・ High frequency applied power: 750w
・ In-chamber pressure (high pressure cleaning): 3.5 torr, 70 sec
-Substrate temperature: 400 ° C
・ Gas flow rate: ethane hexafluoride (C ₂ F ₆ ) 500 sccm + oxygen 600 sccm
・ Distance between electrodes: 999 mils

  The results of Vpp and Vdc measured during cleaning are shown in FIG. Vpp changes at about 500V, and Vdc changes from -2.5V to -0.5V.

Example 1
A mixed gas composed of C ₂ HF ₅ and O ₂ as a hydrofluorocarbon gas and C ₂ F ₆ as a dissociating gas was used as a cleaning gas, and the state of Vpp and Vdc was measured.
The total flow of C ₂ HF ₅ and _{O 2} is 600 sccm, RF power 750W, electrode distance to the fixed _999Mils, the concentration of _{C 2 HF 5 ([C 2} HF 5] / [C 2 HF 5 + O 2]) Is 10% to 20%, the pressure is 3 Torr to 5 Torr, and the concentration of dissociable gas ([dissociable gas] / [C ₂ HF ₅ + O ₂ ]) is varied from 0 to 10%. Condition dependency was analyzed. The results are shown in FIG.

In the graph of FIG. 3, the discharge voltage Vpp is separately taken on the upper stage of the vertical axis, the self-bias voltage Vdc is taken separately on the lower stage, the concentration (%) of the hydrofluorocarbon gas on the left side of the horizontal axis, and the pressure in the chamber (Torr) in the middle. The right side shows the dissociative gas concentration (%), and shows the influence of changes in hydrofluorocarbon gas concentration, pressure and dissociative gas concentration on the discharge voltage and self-bias voltage. The same applies to the graphs of FIGS.
The values of the discharge voltage and the self-bias voltage when the dissociative gas concentration on the horizontal axis in the graphs of FIGS. 3 to 6 is 0% are those of the above-mentioned prior application of the present applicant.

The higher the Vpp is, the higher the negative value of Vdc is, the higher the arcing risk is. From the analysis results shown in FIG. 3, the conditions under which Vpp is lower and Vdc is positively increased are those in which 8.2% of C ₂ F ₆ that is a dissociative gas is added.
At this time, Vpp was 543 V, and Vdc was +0.1 V, which was equivalent to the conventional cleaning method using C ₂ F ₆ gas as the cleaning gas. Under conditions where the flow rate of the additive gas was lower or higher, Vpp was higher and Vdc was lower.

(Example 2)
In the same manner as in Example 1, it was measured in the case of using a c-C ₄ F ₈ in the dissociative gas. The analysis results are shown in FIG. Also in this case, the condition with the addition of 6.9% of c-C ₄ F ₈ which is a dissociative gas was the condition with the lowest arcing risk.
At this time, Vpp was 544 V, and Vdc was +1.8 V, which was equivalent to the conventional cleaning method using C ₂ F ₆ gas as the cleaning gas.

(Example 3)
By the same method as in Example 1, measurement was performed when NF ₃ was used as the dissociative gas. The analysis results are shown in FIG. Also in this case, the condition where 8% of NF ₃ which is a dissociative gas was added became the condition with the lowest arcing risk.
At this time, Vpp was 489 V, and Vdc was +4.7 V, and the arcing risk was low as compared with the conventional cleaning method using C ₂ F ₆ gas as a cleaning gas.

(Comparative Example 1)
In the same manner as in Example 3, measurement was performed when c-C ₄ F ₈ , oxygen, and NF ₃ as a dissociative gas were added instead of the hydrofluorocarbon gas. The analysis results are shown in FIG.
Also in this case, the condition where 4.7% of NF ₃ as a dissociating gas was added became the condition with the lowest arcing risk. However, in this case, as the flow rate of the dissociable gas is increased, Vdc tends to take a large negative value, and the effect of the dissociative gas is not recognized.

(Comparative Example 2)
In the same manner as in Example 1, measurement was performed when cleaning was performed using a mixed gas obtained by mixing C ₂ HF ₅ , oxygen, and helium (He) having no dissociation property as a cleaning gas.
The measurement pressure was fixed at 5 Torr. The measurement results are shown in Table 1.
As is apparent from the results in Table 1, when non-dissociable He was used, Vpp tended to increase, Vdc remained almost unchanged, and the effect of helium gas was not obtained.

It is a schematic block diagram which shows the example of the plasma processing apparatus used for the cleaning method of this invention. It is a graph which shows the result of a prior art example. 3 is a graph showing the results of Example 1. 10 is a graph showing the results of Example 2. 10 is a graph showing the results of Example 3. 6 is a graph showing the results of Comparative Example 1.

Explanation of symbols

1 .... high frequency power supply, 2 .... plasma generating means, 3 .... chamber, 4 .... source gas introduction pipe, 5 .... first introduction pipe, 6 .... second introduction pipe, 7 .... third introduction pipe, 8 .. Exhaust pipe, 9 .. Exhaust pump, 21 .. Shower head, 22 .. Susceptor 22

Claims (3)

A method for removing deposits deposited in a chamber and an exhaust pipe of a plasma CVD film forming apparatus,
A plasma treatment is performed using a mixed gas containing a hydrofluorocarbon gas, oxygen, and a dissociative gas as a cleaning gas, and the ratio of the dissociative gas being 5 to 10 vol% of the total amount of the hydrofluorocarbon gas and oxygen. A method for cleaning a plasma film forming apparatus.   The method for cleaning a plasma film forming apparatus according to claim 1, wherein the hydrofluorocarbon gas is pentafluoroethane gas. Dissociative _{gas, CF 4, C 2 F 6} , C 3 F 8, c-C 4 F 8, NF 3, N 2 plasma deposition of O claim 1 or 2 is either 1 or more How to clean the device.

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