JP3335762B2 - Plasma cleaning method - 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 cleaning a plasma CVD apparatus.

[0002]

2. Description of the Related Art A plasma CVD method capable of forming a film at a low temperature is known as a method of depositing a silicon nitride film or a silicon oxide film in a process after formation of a wiring made of aluminum in a process of manufacturing a semiconductor integrated circuit. I have. FIG. 1 is a schematic view of a plasma CVD apparatus used for manufacturing a semiconductor integrated circuit. In FIG. 1, an upper electrode 1 and a lower electrode 2 are arranged in parallel in a vacuum vessel 3 with a distance 8 between the electrodes. The semiconductor substrate 7 is placed on the lower electrode 2. On the lower electrode 2 side of the upper electrode 1, a gas inlet 4 having an infinite number of holes having an inner diameter of 0.4 to 1.0 mm is provided. The upper electrode 1 is connected to a high frequency power supply 5 for the upper electrode, and the lower electrode 2 is connected to a high frequency power supply 6 for the lower electrode. The reaction gas is introduced from the gas inlet 4 into the vacuum vessel 3.

[0003] Reference numeral 9 denotes a vacuum exhaust port for maintaining the inside of the vacuum vessel 3 at a predetermined pressure. The high-frequency power supply 5 for the upper electrode has a frequency of 13.56 MHz, the frequency of the high-frequency power supply 6 for the lower electrode has a frequency of 1 MHz or more on one side, and a power of a frequency of 200 kHz or more and 1 MHz or less on the other side. It is common to apply. The capacitor 10 is supplied from the upper electrode 1 and flows to the lower electrode 2.
When a high-frequency current of 1 MHz or less supplied from the high-frequency power source for lower electrode 6 does not directly flow to the ground when a high-frequency current of not less than 1 MHz flows to the ground,
A current of a frequency of 1 MHz or more flowing from the upper electrode 1 flows, and 1 MH supplied from the lower electrode high-frequency power supply 6
The capacity is set so that a current having a frequency of z or less does not flow. The coil 11 is supplied from the lower electrode 2 to the upper electrode 1
1MH supplied from the high-frequency power supply 5 for the upper electrode when a high-frequency current of a frequency of 1 MHz or less flowing through
1 MHz to prevent a high frequency current of z or more from flowing directly to the ground.
The inductance is adjusted so that a current of the following frequency flows and a current of 1 MHz or more supplied from the high frequency power supply 5 for the upper electrode does not flow.

When an insulating film is deposited on a substrate by a plasma CVD method, the film is deposited also on the upper electrode 1, the lower electrode 2, and the inner wall of the vacuum vessel 3. The deposits fall off during the reaction or during the transfer of the substrate and become dust. Further, if the deposits in the holes of the gas inlets 4 provided in the upper electrode 1 are clogged, the uniformity of the deposition rate in the substrate deteriorates.

Therefore, after the film deposition step by the plasma CVD method is completed, the substrate 7 is taken out of the vacuum vessel 3 and then
A plasma cleaning method is employed in which an etching gas is introduced into the vacuum vessel 3 to generate plasma, thereby removing films deposited on the upper electrode 1, the lower electrode 2, and the inner wall of the vacuum vessel 3. In this cleaning method, the etching gas is excited by the thermal electrons in the plasma to generate an etchant that has become a reactive gas, and the etching proceeds with the etchant. After the end of etching, the emission spectrum is significantly different from that during etching,
The light emitting state changes.

In the plasma cleaning method, when the distance 8 between the electrodes is shortened (for example, the maximum diameter of the upper electrode and the lower electrode 2 is set to be 1/10 or less of the maximum diameter of the smaller electrode), the height is increased. Since the plasma of the density is confined between the two electrodes 1, 2, the rate of etching the film deposited on the electrodes 1, 2 is significantly increased. This cleaning method is hereinafter referred to as narrow gap plasma cleaning. In the narrow gap plasma cleaning, the film deposited on the electrodes 1 and 2 can be removed at a high speed, but the density of the plasma existing in the space other than between the electrodes 1 and 2 in the vacuum vessel 3 is low, so the inner wall of the vacuum vessel 3 Film cannot be removed.

On the other hand, when plasma cleaning is performed in a state where the distance between the electrodes is long (for example, in a state where the maximum diameter of the smaller one of the upper electrode 1 and the lower electrode 2 is 1/10 or more of the maximum diameter). The density of the plasma between the electrodes 1 and 2 is reduced, and the plasma spreads over the entire vacuum vessel 3, and the film deposited inside the vacuum vessel 3 can be removed.
Since the plasma density between the electrodes 1 and 2 is low, the etching rate for the deposits on the electrodes 1 and 2 becomes low. Therefore, if the film deposited on the electrodes 1 and 2 is removed by wide gap plasma cleaning, a long cleaning is required.

Due to the above-described features of both the narrow gap plasma cleaning and the wide gap plasma cleaning, the two cleaning methods are used in combination to clean the inside of the vacuum vessel 3 at high speed and completely.

First, when switching to narrow gap plasma cleaning after performing wide gap plasma cleaning, it is difficult to determine when to switch to narrow gap plasma cleaning. As mentioned above,
When the substance to be etched is exhausted, the emission state of the plasma of the etching gas changes. There is a possibility that a film deposited on a portion other than the electrode, such as the inner wall, may not be completely removed, and there is a problem that it is not removed even after that. Conversely, if wide-gap plasma cleaning is performed until the light emission state of the plasma changes, there is a problem that cleaning takes a long time, and narrow gap plasma cleaning is not necessary.

Therefore, when both cleaning methods are used in combination, if the cleaning is to be performed completely in the minimum necessary cleaning time, narrow gap plasma cleaning is performed first, and after the plasma emission state changes. That is, the wide gap plasma cleaning is performed after all the deposits on the electrodes to be removed by the narrow gap plasma cleaning are removed.

[0011]

When the complete cleaning is performed only by the wide gap plasma cleaning, the cleaning is performed by about two times as compared with the two-stage cleaning method in which the narrow gap plasma cleaning is performed and then the wide gap plasma cleaning is performed. There is a problem that double cleaning time is required.

When a two-stage cleaning method in which narrow-gap plasma cleaning is performed, and wide-gap plasma cleaning is performed after the emission state of the plasma is changed, the cleaning time is shortened, but the particle size called dust is reduced to 0.1. There is a problem that many particles of about 3 μm are generated in the vacuum vessel, and this dust is taken into the film deposited by the plasma CVD method.

The present invention solves the above-mentioned problems in the conventional method, uses both narrow gap plasma cleaning and wide gap plasma cleaning, and changes the state of power application in the middle, thereby achieving high speed and low dust generation. An object of the present invention is to provide a plasma cleaning method.

[0014]

SUMMARY OF THE INVENTION In order to achieve the above-mentioned object, the present invention provides two electrodes arranged in a vacuum vessel with a high frequency.
Plasma was generated by applying a microwave power, 1MHz using plasma of the etching gas, when performing cleaning of the electrode and the inner wall of the vacuum vessel, at least one electrode by narrowing the distance between the two electrodes a first step of performing cleaning by applying a power of frequencies below, before the light-emitting state of the plasma in the first step is greatly changed, it is applied to the electrode for mounting a substrate of the two electrodes
That power stops, by applying a power of 1MHz or more frequencies only the other electrode, and a second step of performing cleaning to the point where light emission state of the flop plasma is greatly changed, the
After wide distance between the two electrodes, and having a third step of performing chestnut Ningu by applying a high frequency power to the electrode.

The first step and the second step are performed by setting the distance between the two electrodes to 1/10 or less of the maximum diameter of the electrode having the smaller maximum diameter of the two electrodes.
It is preferable that the third step be performed by setting the distance between the two electrodes to be at least 1/10 of the maximum diameter of the electrode having the smaller maximum diameter of the two electrodes.

In the first and third steps , cleaning is preferably performed by supplying power of 1 MHz or more to the first electrode and power of 1 MHz or less to the second electrode.

[0017]

As described above, when the narrow gap plasma cleaning is used and the two-stage cleaning method of performing the wide gap plasma cleaning after the light emission state of the plasma is changed, a large amount of dust is generated, and the dust is deposited by the plasma CVD method. This dust was known to be incorporated into the film, but the cause of dust generation was not clear. We have developed the plasma CVD of FIG.
The process of dust generation was clarified by performing a narrow gap plasma cleaning after depositing a film on the substrate using an apparatus and observing the state of dust generation.
As a result, during the narrow gap plasma cleaning, a phenomenon was observed in which a large amount of dust began to be generated in the vacuum vessel immediately before the emission state of the plasma changed significantly. In addition, in the cleaning using only the wide gap plasma cleaning, the phenomenon of dust generation was hardly observed.

The mechanism of this dust generation is considered as follows.

In the narrow gap plasma cleaning, since the electrodes are close to each other, the electric field due to the applied high-frequency power is strong in the space between the electrodes, but weak at the edges of the electrodes, and further in other spaces. become weak. Therefore, the plasma of the etching gas is collected in the space between the electrodes, the plasma density in the peripheral portion is low, and the kinetic energy of the plasma particles is weak. When the electrode has a large amount of deposits to be etched, most of the etchant is consumed for etching the electrode surface in contact with the region having a high plasma density, so that the amount of the etchant in the plasma diffused to the peripheral portion is small. Therefore, the peripheral portion is hardly etched. However, when there is no deposit to be etched on the electrode surface in contact with the region having a high plasma density, the etchant is not consumed for etching the electrode. The amount increases. Therefore, the etching of the edge of the electrode proceeds.

However, in the etching of the edge of the electrode by the etchant, the plasma density is low and the kinetic energy of the plasma particles is low, so that the weak film quality is selectively etched. The portion having a high film quality is also impacted by the plasma, and the fixing force is reduced. For this reason, it turned out that the strong film | membrane part surrounded by the weak film | membrane part peeled off and became dust. It was also found that most of the dust came from the edge of the electrode where the amount of the etchant diffused was large.

On the other hand, in the wide gap plasma cleaning, the plasma spreads throughout the vacuum chamber, and the plasma density and the kinetic energy of the plasma particles are lower than in the narrow gap plasma cleaning. It is higher than the density of plasma diffused to the edge of the electrode or the kinetic energy of plasma particles. Therefore, in the wide gap plasma cleaning, the selective etching as described above is not performed, and no dust is generated.

It has been experimentally confirmed that particles are difficult to diffuse when the particles in the plasma vibrate with a large amplitude. When a high frequency power of 1 MHz or less is applied, both electrons and ions oscillate with sufficient amplitude. However, when only high-frequency power of 1 MHz or more is applied, electrons oscillate following this power because their mass is light, so that sufficient amplitude can be obtained, but ions oscillate following this power because their mass is heavy. However, the amplitude is very small. Because
When only high-frequency power of 1 MHz or more is applied, electrons do not diffuse from between the electrodes, but ions diffuse from between the electrodes because of their small amplitude.

Based on the above findings, the operation of the present invention will be described below.

In the first step of the present invention, if the distance between the electrodes is narrowed, a strong electric field is limited between the electrodes, and the electric field becomes weak in other spaces, so that plasma is generated in this narrow area. . When a high frequency power of 1 MHz or less is applied, both electrons and ions have a sufficient amplitude, so that diffusion from a region having a strong electric field is suppressed. Even if power of 1 MHz or more and power of 1 MHz or less are applied simultaneously,
The ions are hardly diffused because a sufficient amplitude is obtained by power of 1 MHz or less.

Further, in the second step, if only electric power having a frequency of 1 MHz or more is applied, a sufficient amplitude cannot be obtained for ions, so that the ions are also diffused into a weak electric field region. However, electrons are hardly diffused, and if only ions are diffused, the charge distribution becomes non-uniform and is pulled back by Coulomb force, so that the diffusion of ions is limited to the vicinity where electrons are confined. Since the etchant to be etched is ionized by turning the etching gas into plasma, when only power having a frequency of 1 MHz or more is applied, the etchant spreads to the edge of the electrode and performs etching.
At this time, since the plasma density of the etching gas and the kinetic energy of the plasma particles are sufficiently high, selective etching is not performed on a portion having a low film quality, and the etching is uniformly performed on a portion having a high film quality. No outbreak occurs. By applying only high frequency power of 1 MHz or more before the emission state of the plasma changes, that is, before the generation of dust due to peeling, the electrode edge, which is the largest dust generation source, is not accompanied by generation of dust. Cleaning can be performed.

Also, in the third step, when high-frequency power is applied by widening the gap between the electrodes, the electric field spreads at the edge of the electrode, so that the plasma spreads widely in the vacuum vessel, and the wide gap cleaning covers a wide range in the vacuum vessel. It is done over. The density of the plasma spread in the vacuum vessel is lower than that in the case of the narrow gap plasma cleaning. However, the plasma is not diluted until the selective etching is performed, and etching is performed without generating dust.
Therefore, the inner wall of the vacuum vessel and the electrodes can be etched without generating dust.

Therefore, according to the method of the present invention, when cleaning is performed, high-speed electrode cleaning, which is a feature of narrow-gap plasma cleaning, and wide-area cleaning in a vacuum vessel, which is a feature of wide-gap plasma cleaning, are both compatible. It has a feature that can solve the problem of dust generation in the final stage of narrow gap plasma cleaning. Therefore, the inside of the vacuum container can be completely cleaned at high speed.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, in a manufacturing process of a semiconductor integrated circuit,
Plasma C used for depositing silicon nitride film for protective film
A description will be given of a cleaning process after the film deposition process by the VD method as an example. The apparatus used in the experiment was a plasma CVD apparatus for a 6-inch semiconductor substrate. The configuration of the device is the same as that of the conventional example, and therefore will not be described.

With respect to the plasma CVD apparatus thus configured, formation of a silicon nitride film and cleaning of the apparatus will be described. With the substrate 7 placed on the lower electrode 2 as shown in FIG.
While exhausting from the vacuum exhaust port 9 while introducing 00 SCCM and 150 SCCM of ammonia into the vacuum container 3 from the gas inlet 4, 300 W is applied to the upper electrode 1 and 100 W to the lower electrode 2 while maintaining the pressure in the vacuum container 3 at 4 Torr. When the high frequency power is applied, plasma is generated in the vacuum vessel 3 and a silicon nitride film can be deposited on the substrate 7.

The plasma C configured as described above is used.
A plasma cleaning method after depositing a silicon nitride film on the substrate 7 in the VD apparatus as described above will be described below.

As a first step, the following cleaning was performed. After the thin film is deposited on the substrate as described above, the distance 8 between the electrodes is set to 13 m while the substrate 7 is not on the lower electrode 2.
m, that is, the maximum diameter 1 of the upper electrode having the smaller maximum diameter
Reduce to 1/10 or less of 60 mm, sulfur hexafluoride 200S
The gas was exhausted while introducing CCM and 50 SCCM of oxygen from the gas inlet 4 into the vacuum vessel 3. 13.
500 MHz high frequency power of 56 MHz and 4 for lower electrode 2
When a high-frequency power of 200 W of 50 kHz is applied, plasma is generated in the vacuum chamber 3 and narrow gap plasma cleaning can be performed.

Subsequently, as a second step, the following cleaning was performed. 2 minutes and 30 seconds after the start of the first step, that is, 2 seconds after the start of the first step confirmed in a comparative example described later.
The application of the high-frequency power to the lower electrode 2 is stopped before the emission state of the plasma significantly changes after 50 minutes. At this time, the power applied to the electrode is only 13.56 MHz applied to the upper electrode 1, that is, only the power of 1 MHz or less. As a result, the ions diffused, the light emitting region of the plasma also spread to the edge of the electrode, and it was confirmed that the film deposited on the edge of the electrode was etched. However, since the plasma emission region does not extend to the inner wall of the vacuum vessel 3, the inner wall of the vacuum vessel is not cleaned. The light emission state is 2 minutes 55 after the start of cleaning.
The light emission state of the plasma changed greatly in seconds, and the spectrum of fluorine atoms reached a peak. At this point, the cleaning of the electrode surface has been completed in addition to the cleaning of the electrode surface originally performed by the narrow gap plasma cleaning.
After the application of the high-frequency power to the lower electrode 2 is stopped, the plasma density between the electrodes is slightly reduced because the etchant is diffused to the edge of the electrode, and the electrode edge is also cleaned. Slightly longer.

Then, as a cleaning in the third step,
At 2 minutes and 55 seconds after the start of the first step, that is, when the light emission state of the plasma between the electrodes significantly changes, the application of the high-frequency power applied to the upper electrode 1 is also stopped, and the narrow gap plasma cleaning is terminated. Thereafter, similarly to the above, the distance between the electrodes was changed to 28 mm, that is, 1/10 or more of the maximum diameter of the upper electrode having a smaller maximum diameter of 160 mm, and the pressure in the vacuum vessel was set to 200 mTorr, and then the discharge was performed again. Was started, wide-gap plasma cleaning was performed, and continued until the light emission state of the plasma in the vacuum vessel changed significantly. In this stage of cleaning, the region with a strong electric field extends to the periphery of the electrode, so that the plasma emission region also reaches the vacuum vessel wall, and the cleaning is performed not only on the electrode periphery such as the vacuum vessel wall, but also over a considerably wide area. Done. In this cleaning, the emission state of the plasma changes, and when the cleaning is completed, the deposited film in the vacuum vessel has been almost completely removed.

After the completion of this cleaning, as described above,
When a silicon nitride film was deposited on a substrate by a plasma CVD method, the number of dusts incorporated in the silicon nitride film was 20 or less, and the number of dusts was significantly reduced as compared with an experiment of a comparative example described later. did. The number of dusts confirmed here is almost equal to the number of dusts generated even when cleaning is performed only by the wide gap plasma cleaning, and it is considered that the number of dusts is not dust due to the separation of the deposits.

The total time required from the start to the end of the cleaning was 2 minutes and 30 seconds after the start of the cleaning, compared with the comparative example in which the application of power to the lower electrode was not stopped in the narrow gap plasma cleaning. When the application of the electric power was stopped, it was only about 5 seconds longer. That is, plasma cleaning was performed at high speed with little generation of dust.

For comparison with the above-described embodiment of the present invention, the following comparative experiment was conducted by a conventional plasma cleaning method.

First, narrow gap plasma cleaning is performed in the same manner as in the first step of this embodiment, and after the start,
It was confirmed that the emission state of the plasma between the electrodes changed in 50 minutes and the color of the discharge changed from blue-white to red. Here, the discharge is temporarily stopped, the distance between the electrodes is changed to 28 mm, and the pressure in the vacuum vessel is set to 200 m as in the third step of the present embodiment.
After Torr, discharge was started again, wide gap plasma cleaning was performed, and the process was continued until the light emission state of the plasma changed significantly. After this cleaning, when a silicon nitride film was deposited on the substrate by a plasma CVD method, it was found that 200 or more dusts were taken in the deposited silicon nitride film.

In order to examine the relationship between the light emission state and the light emission spectrum, in this experiment, when the spectroscopic analysis was performed on a fluorine atom (wavelength: 704 nm), the spectrum of the fluorine atom was changed immediately before the light emission state of the plasma changed significantly. The emission spectrum of fluorine atoms gradually increased and the emission spectrum of fluorine atoms reached a peak when the emission state changed significantly. In other words, it can be seen that the etching of the electrodes has already been completed when the light emitting state changes significantly.

In the above embodiment, the plasma cleaning step after the film deposition step by the plasma CVD method used for manufacturing the semiconductor integrated circuit has been described.
The present invention relates to a plasma CVD used for manufacturing a liquid crystal substrate.
The present invention is also applicable to a cleaning method in another plasma CVD apparatus such as an apparatus.

In the above embodiment, the cleaning step after the film deposition step by the plasma CVD method used for depositing the silicon nitride film for the protective film has been described as an example. However, other films, for example, a silicon oxide film or the like may be used. The present invention is also applicable to a cleaning process after the film deposition process by the plasma CVD method used for deposition.

Further, in the above-described embodiment, an example in which sulfur hexafluoride and oxygen are used as the etching gas has been described, but the etching gas may be another gas. For example, for a silicon nitride film, various gases such as dicarbon hexafluoride and nitrogen trifluoride can be used.

In the above-described embodiment, the case where the distance between the electrodes in the narrow gap plasma cleaning is 13 mm and the distance between the electrodes in the wide gap plasma cleaning is 28 mm is described. If the distance is less than or equal to 1/10 of the maximum diameter of the smaller electrode of the two electrodes, the density of plasma generated between the electrodes is sufficiently high,
Since the etching of the electrodes is performed at a high speed, it is regarded as narrow gap plasma cleaning. Similarly, the distance between the electrodes is one of the maximum diameter of the smaller one of the two electrodes.
If the value is / 10 or more, the plasma is diffused into the vacuum vessel, so that it can be regarded as wide gap plasma cleaning.

In the above embodiment, 13.
Although the frequency is set to 56 MHz and 450 kHz to the lower electrode 2, the high-frequency power of 450 kHz to the lower electrode 2 may be within a range of 1 MHz or less so that ions in the plasma can follow the high-frequency vibration and be confined between the electrodes. . Conversely, the upper electrode 1 is 1 MH such that ions cannot follow and vibrate.
It suffices if it is at least z. Further, the lower limit of the frequency is desirably 200 kHz or more in consideration of the stress controllability of the film formation. This critical value of 1 MHz is a value found by the present inventors in experiments.

[0044]

According to the present invention, a vacuum is generated by a plasma.
The inner wall of the container and the two electrodes placed in the vacuum container
It is possible to provide a plasma cleaning method with high speed and little generation of dust for the attached deposit .

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating an example of a plasma CVD apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Upper electrode 2 Lower electrode 3 Vacuum container 4 Gas inlet 5 High frequency power supply for upper electrode 6 High frequency power supply for lower electrode 7 Substrate 8 Distance between electrodes 9 Vacuum exhaust port

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-100925 (JP, A) JP-A-6-61219 (JP, A) JP-A-63-76434 (JP, A) JP-A-63-76434 221620 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01L 21/3065 C23C 16/507

Claims (3)

(57) [Claims] A high voltage is applied to two electrodes arranged in a vacuum vessel.
Plasma was generated by applying a frequency power, 1MHz using plasma of the etching gas, when performing cleaning of the electrode and the inner wall of the vacuum vessel, at least one electrode by narrowing the distance between the two electrodes a first step of performing cleaning by applying a power of frequencies below,
Before the light emission state of the plasma is largely changed in the first step, the voltage is applied to one of the two electrodes on which the substrate is mounted.
To power down, by applying a power of 1MHz or more frequencies only the other electrode, and a second step of performing cleaning to the point where light emission state of the flop plasma is greatly changed, before
After wide distance between serial two electrodes, the plasma cleaning method characterized in that it comprises a third step of performing chestnut Ningu by applying a high frequency power to the electrode. 2. The first step and the second step are performed by setting a distance between two electrodes to be 1/10 or less of a maximum diameter of an electrode having a smaller maximum diameter among the two electrodes, thereby performing the first step and the second step. The plasma cleaning method according to claim 1, wherein the third step is performed by setting a distance between the two electrodes to be at least 1/10 of a maximum diameter of an electrode having a small maximum diameter. 3. The cleaning according to claim 1, wherein the first step and the third step are performed by supplying power of 1 MHz or more to the first electrode and power of 1 MHz or less to the second electrode. Item 3. The plasma cleaning method according to Item 2.