JP3256082B2 - 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.

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.

For this reason, after the film deposition step by the plasma CVD method is completed, after the substrate 7 is taken out of the vacuum vessel 3,
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 the etching, the emission of the reaction product due to the etching is not observed, so that the emission spectrum is significantly different from that during the etching, and the emission 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, if 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-mentioned 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, the narrow gap plasma cleaning is performed first, and after the light emission state of the plasma is changed. 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.

[0010]

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-step cleaning method in which the narrow gap plasma cleaning is performed and the wide gap plasma cleaning is performed after the emission state of the plasma is changed, the cleaning time is reduced, 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.

An object of the present invention is to solve the above-mentioned problems in the conventional method, and to provide a plasma cleaning method which is high-speed and generates less dust by using both narrow-gap plasma cleaning and wide-gap plasma cleaning. I do.

[0013]

According to the present invention, there is provided a plasma CVD apparatus comprising the steps of:
After that, when cleaning the two electrodes in the vacuum vessel and the inner wall of the vacuum vessel using plasma, a first step of performing a narrow gap plasma cleaning by setting a distance between the two electrodes to L ₁ and a first step Following the plasma cleaning method and a second step of the distance between the two electrodes performing the wide gap plasma cleaning with the large of L ₂ from the L _1, the first step, pre-plasma emission state is larger It is characterized in that a change time is obtained in advance, and the first step is terminated before the previously obtained time.

The first step is 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, and the distance between the two electrodes is set to two electrodes. It is preferable to perform the second step by setting the maximum diameter of the electrode having a smaller maximum diameter to 1/10 or more.

[0015]

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, if there is no deposit to be etched on the electrode surface in contact with the region having a high plasma density, the amount of unreacted etchant in the plasma diffused to the edge of the electrode is reduced because the etchant is not consumed for etching the electrode. To increase. Therefore, the etching of the edge of the electrode proceeds. However, the etching of the edge of the electrode by the etchant has a low plasma density and a low kinetic energy of the plasma particles, and thus selectively etches the weak film portion. 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.

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. . Therefore, since the plasma density between the electrodes is increased, high-speed cleaning between the electrodes can be performed.

Furthermore, if this cleaning is stopped before the emission state of the plasma changes, that is, before the generation of dust due to peeling, the electrode may not be sufficiently cleaned yet. Is suppressed.

Next, in the second step, when the wide gap plasma cleaning with the electrodes spread is performed, the electric field is widened, so that the plasma spreads widely in the vacuum vessel and the wide gap cleaning is performed over a wide range in the vacuum vessel. Done. Even if the electrodes are not completely cleaned by the narrow gap plasma cleaning, the electrodes can be cleaned simultaneously with the peripheral portion by the wide gap plasma cleaning. Therefore, the electrodes are completely cleaned by the wide gap plasma cleaning. can do. Further, 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, in the method of the present invention, when cleaning is performed, high-speed cleaning of the electrode, which is a feature of narrow gap plasma cleaning, and cleaning over a wide area in a vacuum vessel, which is a feature of wide gap plasma cleaning, are both compatible. It has the feature of suppressing the generation of dust, which is the interruption of narrow gap plasma cleaning. Therefore, the inside of the vacuum container can be completely cleaned at high speed.

[0024]

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.
The high-frequency power is supplied to the upper electrode 1 and the lower electrode 2 while maintaining the pressure in the vacuum vessel 3 at 4 Torr while exhausting the vacuum vessel 3 while introducing 00 SCCM and 150 SCCM of ammonia into the vacuum vessel 3 from the gas introduction port 4. When it is charged, plasma is generated in the vacuum vessel 3 and a silicon nitride film can be deposited on the substrate 7.

The plasma C constructed as described above
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 depositing the thin film on the substrate as described above,
The distance between the electrodes is 13 m when the substrate 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.

Two and a half minutes after the start of the first step, that is,
2 minutes and 5 minutes after the start of the first step confirmed in a comparative example described later.
The narrow gap plasma cleaning is terminated before the emission state of the plasma changes significantly after 0 seconds. At this stage, the electrodes are not sufficiently cleaned by narrow gap plasma cleaning. Further, it can be seen that light emission is limited between the electrodes and plasma is limited between the electrodes during the cleaning in the first step.

Thereafter, the following cleaning was performed as a second step.

The distance between the electrodes is 28 mm, that is, 1/10 of the maximum diameter 160 mm of the upper electrode having the smaller maximum diameter.
With the above changes, the discharge was started again after the pressure in the vacuum vessel was set to 200 mTorr, wide gap plasma cleaning was performed, and the process was continued until the light emission state of the plasma significantly changed. 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. Therefore, the deposited film of the electrode remaining in the narrow gap plasma cleaning can be removed by this cleaning. 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 the same as the number of dusts generated even when cleaning is performed only by the wide gap plasma cleaning, and it is considered that the dusts are not dusts due to the separation of the deposits.

The total time required from the start to the end of the cleaning is also 2 minutes and 50 minutes by the narrow gap plasma cleaning.
Compared to the experiment of the following comparative example, in which the application of power to the lower electrode was stopped 2 minutes and 30 seconds after the start of cleaning, the time was only increased by about 5 seconds. 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.

In the comparative example, the operation of depositing a silicon nitride film having a thickness of 1 μm on the substrate 7 was repeated five times in the same manner as in the above example, and then the cleaning was performed. First, when the narrow gap plasma cleaning is performed by the above method, the light emission state of the plasma changes 2 minutes and 50 seconds after the start,
A phenomenon in which the color of the discharge changed from blue-white to red was confirmed. Here, the discharge is temporarily stopped, the distance between the electrodes is changed to 28 mm, the pressure in the vacuum vessel is set to 200 mTorr, the discharge is started again, wide-gap plasma cleaning is performed, and the emission state of the plasma changes significantly. Continued. 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. Further, in order to examine the relationship between the light emission state and the light emission spectrum, if the spectroscopic analysis is performed in the cleaning step of this experiment and the light emission state is performed on fluorine atoms (wavelength: 704 nm), the spectrum of the fluorine atoms is changed immediately before the light emission state of the plasma changes significantly. The emission spectrum of the fluorine atom reaches a peak when the emission state gradually increases and the emission state greatly changes, and narrow gap plasma cleaning is first performed in the above-described configuration using the above environment in the same manner as in the above experiment.

The following experiment was conducted as a method of the present invention for comparison with the experiment of the conventional example.

In the above embodiment, the plasma cleaning step after the film deposition step by the plasma CVD method used for manufacturing a 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 end of 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. The present invention is also applicable to a cleaning process after the film deposition process by the plasma CVD method used for deposition.

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

Further, in the above 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.

[0041]

According to the present invention, plasma cleaning can be performed at high speed with little dust.

[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

Continuation of the front page (56) References JP-A-6-97154 (JP, A) JP-A-6-77143 (JP, A) JP-A-58-46639 (JP, A) (58) Fields investigated (Int) .Cl. ⁷ , DB name) H01L 21/205 H01L 21/3065

Claims (2)

(57) [Claims] 1. A film deposition step in a plasma CVD apparatus
After completion, when cleaning the two electrodes and the inner wall of the vacuum vessel of the vacuum vessel by using plasma, a first step of performing a narrow gap plasma cleaning by the distance between the two electrodes to L _1, the first step Following the plasma cleaning method and a second step of the distance between the two electrodes performing the wide gap plasma cleaning with the large of L ₂ from the L _1, the first step, pre-plasma emission state is larger A plasma cleaning method, wherein a time point of change is obtained, and the first step is completed before the time point obtained in advance. 2. The first step is performed by setting the distance between the two electrodes to be 1/10 or less of the maximum diameter of the electrode having the smaller maximum diameter of the two electrodes, wherein the distance between the two electrodes is two electrodes. 2. The plasma cleaning method according to claim 1, wherein the second step is performed by setting the maximum diameter of the electrode having a smaller maximum diameter to 1/10 or more.