JPH11330063A - Method for cleaning plasma processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the particle contamination of a substrate, for example, when a CF film is formed through the use of a plasma processor. SOLUTION: C4 F8 gas and C2 H4 gases are used as film forming gases, for example. For example, gases are made into plasma, and a CF film is formed on a semiconductor wafer by the active species. Then, cleaning is executed for removing the CF film adhered into a vacuum container. In cleaning, the CF film is removed by making a cleaning gas, O2 gas, for example, into plasma and causing the active species adhered to the CF film to react. When cleaning is executed whenever one wafer is formed, the CF film whose adhesion is inferior is prevented from being peeled off during a film forming processing. Thus, particle contamination of a wafer W is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma processing apparatus for forming a thin film such as a fluorine-added carbon film, which can be used as an interlayer insulating film of a semiconductor device, on a substrate such as a semiconductor wafer by plasma processing. The present invention relates to a cleaning method.

[0002]

2. Description of the Related Art In order to increase the degree of integration of semiconductor devices, techniques such as miniaturization of patterns and multi-layering of circuits have been devised. One of them is a technique of multi-layer wiring. In order to form a multilayer wiring structure, a conductive layer is connected between the nth wiring layer and the (n + 1) th wiring layer, and a thin film called an interlayer insulating film is formed in a region other than the conductive layer.

A typical example of this interlayer insulating film is Si
Although there is an O ₂ film, it has been required in recent years to lower the relative dielectric constant of the interlayer insulating film in order to further increase the operation speed of the device, and the material of the interlayer insulating film has been studied. . That is, SiO ₂ has a relative dielectric constant of about 4
The emphasis is on excavating smaller materials. One of them is Si whose relative dielectric constant is 3.5.
Although the realization of OF is being promoted, the present inventor has paid attention to a fluorine-added carbon film (hereinafter, referred to as a “CF film”) having a smaller relative dielectric constant.

[0004] Such a CF film is formed by, for example, electron cyclotron resonance (EC) which is an interaction between a microwave and a magnetic field.
It is formed by a plasma film forming process using R). An example of this film forming process will be described with reference to FIG. 4. When a microwave of 2.45 GHz is supplied into the plasma generation chamber 1A through the waveguide 11, a magnetic field of 875 gauss is applied by the electromagnetic coil 12 at the same time. Then, the Ar gas, which is a plasma generating gas, is converted into a high density plasma by the electromagnetic cyclotron resonance, and a film forming gas such as a C ₄ F ₈ gas and a C ₂ H ₄ gas introduced into the film forming chamber 1B by this plasma is formed. Activation is performed to form active species, and a CF film is formed on the surface of the semiconductor wafer (hereinafter, referred to as “wafer”) W on the mounting table 13.

In such a plasma processing apparatus, when a film forming process is performed, C.P.
The F film adheres, and if the film has a certain thickness, the adhered film is peeled off and causes particles. Therefore, after the film forming process, the film adhered in the apparatus is removed. Is subjected to a predetermined cleaning. For example, C
The cleaning for removing the F film is performed by introducing an O ₂ (oxygen) gas as a cleaning gas into a vacuum vessel, converting the gas into a plasma to generate O plasma, and reacting the plasma with the adhered film. Let it be removed.

[0006]

In the above-described plasma processing apparatus, an SiO ₂ film can be formed.
_In the case of _two films, the thickness of the thin film attached in the apparatus is 10 μm.
Cleaning is performed when the wafer W has grown to a thickness of about m. At this timing, the cleaning is performed every time about 10 wafers W are formed.

However, when forming a CF film, S
As in the case of the iO ₂ film, if cleaning is performed every time about 10 wafers W are formed, the number of particles immediately after the cleaning is not large, but as the number of film formation processing increases, the number of particles increases. Therefore, there is a problem that the number of particles attached to the wafer W increases, and the yield eventually decreases.

The present invention has been made under such circumstances, and an object of the present invention is to reduce particle contamination of a substrate when a thin film is formed using a plasma processing apparatus. An object of the present invention is to provide a cleaning method for a plasma processing apparatus.

[0009]

According to the present invention, a substrate is mounted on a mounting table provided in a vacuum vessel, and a film forming gas is turned into plasma. A film forming step of forming a thin film made of a bon film, and then a cleaning step of converting a cleaning gas into plasma in the vacuum vessel and removing the thin film adhered in the vacuum vessel by the plasma. The cleaning step is performed each time a film forming process is performed on one substrate. In this case, the film forming gas and the cleaning gas are converted into plasma by the interaction between the microwave and the magnetic field, for example.

[0010]

FIG. 1 shows an example of a plasma processing apparatus for carrying out the method of the present invention. This apparatus has a vacuum vessel 2 made of, for example, aluminum or the like. This vacuum vessel 2 is located above and communicates with a first cylindrical vacuum chamber 21 for generating plasma below the first vacuum chamber 21. The first vacuum chamber 21 is connected to a second vacuum chamber 22 having a larger diameter than the first vacuum chamber 21. The vacuum vessel 2 is grounded and has a zero potential.

An upper end of the vacuum vessel 2 is opened, and a transparent window 23 made of a material such as quartz, which transmits microwaves, is provided in this portion in an airtight manner. Is to be maintained. Outside the transmission window 23, a waveguide 25 connected to a high-frequency power supply unit 24 for generating a microwave of 2.45 GHz, for example.
The microwave generated in the high-frequency power supply unit 24 is guided by the waveguide 25 in, for example, the TE mode, or the microwave guided in the TE mode is converted into the TM mode by the waveguide 25. , Through the transmission window 23 into the first vacuum chamber 21.

A gas nozzle 31 is provided on a side wall of the first vacuum chamber 21 which is uniformly arranged, for example, along the circumferential direction. The nozzle 31 has a gas source (not shown) such as an Ar gas source and an O ₂ gas. A source is connected, and a gas for plasma generation, for example, an Ar gas or a cleaning gas, for example, an O ₂ gas, can be uniformly and uniformly supplied to an upper portion in the first vacuum chamber 21.

A wafer mounting table 4 is provided in the second vacuum chamber 22 so as to face the first vacuum chamber 21. The mounting table 4 is provided with an electrostatic chuck 41 on the surface thereof. The electrode of the electrostatic chuck 41 has a DC power supply (not shown) for attracting a wafer and a bias voltage for drawing ions into the wafer. The high frequency power supply unit 42 is connected so as to apply the voltage.

On the other hand, the upper part of the second vacuum chamber 22, that is, the first
A ring-shaped film-forming gas supply unit 5 is provided in a portion that communicates with the vacuum chamber 21.
Is formed, for example, from the gas supply pipes 51 and 52 through C
F-based gas such as C ₄ F ₈ gas and hydrocarbon gas such as C
₂ H ₄ gas is supplied, and the mixed gas is supplied into the vacuum chamber 2 from the gas hole 54 on the inner peripheral surface.

A ring-shaped main electromagnetic coil 26, for example, is disposed as a magnetic field forming means close to the outer periphery of the side wall which partitions the first vacuum chamber 21 and is disposed below the second vacuum chamber 22. On the side is a ring-shaped auxiliary electromagnetic coil 27
Is arranged. Exhaust pipes 28 are respectively connected to the bottom of the second vacuum chamber 22 at, for example, two positions symmetric with respect to the central axis of the vacuum chamber 22.

Next, the method of the present invention implemented by the above-described apparatus will be described by taking as an example a case where an interlayer insulating film made of a CF film is formed on a wafer W as a substrate. First, a gate valve (not shown) provided on the side wall of the vacuum vessel 2 is opened, and a wafer W having, for example, an aluminum wiring formed on its surface is carried in from a load lock chamber (not shown) by a transfer arm (not shown) and placed on the mounting table 4. Then, the wafer W is electrostatically attracted by the electrostatic chuck 41.

Subsequently, after closing the gate valve to seal the inside, the inside atmosphere is evacuated from the exhaust pipe 28 and evacuated to a predetermined degree of vacuum.
In addition to introducing Ar gas into the chamber 1, C ₄ F ₈ gas and C ₂ H ₄ gas are introduced into the second vacuum chamber 22 from the film forming gas supply unit 5 at a predetermined flow rate. Then, the inside of the vacuum vessel 2 is maintained at a predetermined process pressure, a bias voltage of 13.56 MHz, 1500 W is applied to the mounting table 4 by the high frequency power supply unit 42, and the surface temperature of the mounting table 4 is set to about 400 ° C.
Set to.

The high-frequency (microwave) of 2.45 GHz from the high-frequency power supply unit 24 reaches the ceiling of the vacuum vessel 2 through the waveguide 25, passes through the transmission window 23, and passes through the first vacuum chamber. 21 is introduced. On the other hand, a magnetic field from the upper part of the first vacuum chamber 21 to the lower part of the second vacuum chamber 22 is formed in the vacuum vessel 2 by the main electromagnetic coil 26 and the auxiliary electromagnetic coil 27. In the vicinity, the strength of the magnetic field becomes 875 Gauss. In this manner, electron cyclotron resonance is generated by the interaction between the magnetic field and the microwave, and the Ar gas is converted into plasma and the density is increased by the resonance. From the first vacuum chamber 21 to the second vacuum chamber 22
The plasma flow that has flowed into the
_{The 4} F ₈ gas and the C ₂ H ₄ gas are activated (plasma) to form active species (plasma), and a CF film is formed on the wafer W.

After the CF film is formed on one wafer W in this manner, the film forming process is performed in the vacuum vessel 2, around the mounting table 4, the inner wall of the film forming gas supply unit 5, and the second vacuum chamber 22. Clean the CF film attached to the inner wall and the like. That is, while the inside of the vacuum vessel 2 is maintained at a predetermined degree of vacuum by the exhaust pipe 28, O ₂ gas is introduced at a predetermined flow rate from the gas nozzle 31, and the microwaves are introduced into the first vacuum chamber 21 as described above. The O ₂ gas is turned into plasma by electron cyclotron resonance generated by the interaction between the O ₂ gas and the magnetic field.

In this way, the O plasma generated by the plasma reaction reacts with the adhered CF film to decompose the CF film into, for example, CO ₂ gas or F ₂ (fluorine) gas. The gas scatters outside the vacuum vessel 2 through the exhaust pipe 28. By performing such cleaning for about 15 seconds, the CF film adhered to the inside of the vacuum vessel 2 is removed.

If the cleaning is performed every time one wafer W is formed, the particle contamination of the wafer W can be reduced as will be understood from the experimental results described later. The reason is considered as follows. In other words, the CF film has a composition close to that of polytetrafluoroethylene, and does not have a very high adhesiveness to Al or the like constituting the vacuum vessel 2 or the like.

Therefore, if cleaning is performed every time a film forming process is performed on, for example, ten wafers W as in the prior art, as the film forming process progresses, C adhering to the inside of the vacuum vessel 2 is increased.
The amount of the F film increases, which is caused by the vacuum vessel 2 during the film forming process.
Peels off from the inner wall surface of the substrate and becomes particles. Therefore, the amount of particles increases as the film forming process proceeds, and the particle contamination of the wafer W progresses.

On the other hand, as in this embodiment, one wafer W
When cleaning is performed every time a film is formed,
The CF film adhered in the film forming process is sufficiently removed by the subsequent cleaning. For this reason, the film formation process is always performed in a state in which the generation of particles due to the CF film adhered in the vacuum vessel 2 is suppressed, so that the particle contamination of the wafer W can be significantly reduced. It is considered possible.

If cleaning is performed each time one wafer W is formed into a film, the throughput can be improved for the reasons described below. The first reason is that, as is clear from the experimental results described later, the total cleaning time when a predetermined number of wafers W are formed is reduced. This is because if the cleaning is performed after the wafer W is continuously formed, the amount of the CF film adhered to the vacuum vessel 2 increases, and the amount of the CF film adhered due to the change in the internal state of the vacuum vessel 2 increases. The film quality changes and the CF films adhere more firmly to each other, making it difficult to remove the CF films. On the other hand, if cleaning is performed every time one wafer W is formed, the vacuum vessel It is considered that this is because the amount of the CF film adhering to the inside 2 is small and the film quality of the CF film is hard to change, so that one cleaning time can be considerably shortened to, for example, about 15 seconds.

The second reason is that it is not necessary to perform the charge removal processing separately from the cleaning. Usually, in the film formation process,
Each time the film formation of one wafer W is completed, a charge removal process of, for example, O ₂ plasma is performed for about 10 seconds to remove the charge remaining on the mounting table 4. Therefore, when cleaning is performed after the wafer W is continuously formed into a film as in the related art, after the wafer W on which the film has been formed is unloaded, the charge elimination process is performed before the next wafer W is loaded. Will be
On the other hand, if the cleaning is performed every time one wafer W is formed, the cleaning time is longer than the static elimination time. Therefore, when the cleaning is performed, the static elimination processing is automatically performed. This eliminates the need to separately perform only the charge removal processing.

For this reason, the total static electricity elimination time when the same number of wafers W are processed is compared. When cleaning is performed after the wafers W are continuously formed into a film,
Compared to the method of the present embodiment, the simple calculation requires a longer time of (static elimination processing time) × (number of processed wafers W). When cleaning is performed every time one wafer W is formed as described above, the total processing time can be reduced, so that the throughput of the entire processing can be improved.

Here, an experimental example performed by the present inventors will be described. Using the plasma processing apparatus shown in FIG. 1, a process pressure of 0.2 Pa, microwave power (high-frequency power supply unit 2
4) 2700 W, bias power (high frequency power supply section 42) 1
Under 500 W, Ar gas as a plasma generation gas,
C ₄ F ₈ gas and C ₂ H ₄ gas are introduced as a film forming gas to form a 1 μm-thick CF film on an 8-inch wafer W. - O ₂ gas was introduced at a flow rate of 200sccm as Ningugasu, pressure 0.2 Pa, a microwave power 2700 W, chestnut under bias power 0 W - while training, the film forming process with respect to 10 sheets of wafers W went. The number of times of cleaning was 10 times in total.

Then, the particles adhering to the formed wafer W
The number of ticles was measured by Surfscan 6240 (Surfscan: manufactured by Tencor), and the total processing time was measured. In this case, the end point of the cleaning is
The emission intensity of the O plasma is measured by measuring the emission intensity of the O plasma. The emission intensity gradually increases as the cleaning proceeds, and becomes almost constant at the end of the cleaning. The time required for the intensity to reach a substantially constant value was defined as the cleaning time.

Similarly, when cleaning is performed every time five wafers W are formed while performing static elimination for 10 seconds when replacing the wafers W under the same conditions, the same applies.
The number of particles attached to the wafer W and the total processing time were measured. The number of times of cleaning is 2 in total.
It was times.

FIG. 2 shows a case where the measurement result of the number of particles is cleaned every time one wafer W is formed.
FIG. 3 shows a case where cleaning is performed each time a single wafer W is formed. In these figures, the vertical axis indicates the number of particles, and the horizontal axis indicates the integrated film thickness of the formed CF film.

According to this result, when cleaning is performed every time five wafers W are formed, the number of particles rapidly increases as the film formation process proceeds, and the number of particles increases to 75 or more in the fifth wafer W. On the other hand, when cleaning was performed every time one wafer W was formed, it was recognized that the number of particles was 10 or less on average. Thus, according to the method of the present embodiment, it is understood that particle contamination of the wafer W can be significantly reduced and a stable film forming process can be performed.

The total processing time is about 15 seconds on average when cleaning is performed every time one wafer W is formed, and the total processing time is 7 seconds.
When cleaning was performed every time five wafers W were formed, the cleaning time was 2 minutes.
30 minutes, and the total processing time is 11 minutes 40 minutes.
Because of the seconds, it was confirmed that according to the method of the present embodiment, the total processing time can be shortened and the throughput of the entire film forming process can be improved.

As described above, in the present embodiment, CF ₄ gas, C ₂ gas,
F ₆ , C ₃ F ₈ , C ₆ F ₆ can be used, and C and F
In addition, a gas containing C, F, and H, for example, a CHF ₃ gas may be used. As the hydrocarbon gas, CH ₄ , C
₂ H ₂ , C ₂ H ₆ , C ₃ H ₈ , C ₄ H _{8 and the} like can be used, but hydrogen gas may be used instead of hydrocarbon gas.

In the present invention, pre-coating may be performed after cleaning is completed. This pre-coat is
The precoat film is formed on the inner wall of the vacuum vessel 2 so as to cover the inner wall, and is performed as a pre-process of the film forming process. For example, in the case of forming a CF film, the precoat film is formed of a CF film. This pre-coating is performed in such a manner that the Ar gas is introduced at a predetermined flow rate from the gas nozzle 31 while the inside of the vacuum vessel 2 is maintained at a predetermined degree of vacuum, and that the C ₄ F ₈ gas and the C _{4 2} H
Each of the _four gases is introduced at a predetermined flow rate, and these gases are converted into plasma by the electron cyclotron resonance, whereby a CF film is formed on the inner wall of the vacuum vessel 2. When pre-coating is performed in this manner, a CF film is formed following the pre-coating.

When such pre-coating is performed, a pre-coat film (CF film) is formed on the inner wall of the vacuum vessel 2.
The effect is obtained that particle contamination of the wafer W can be further reduced. During the film forming process, a CF film is formed on the upper surface of the pre-coat film, but since the composition of the pre-coat film and the CF film formed by the film forming process are similar,
The adhesion between the two is great, and the vacuum vessel 2
This is because the adhered CF film is less likely to be peeled off as compared with the case where the CF film is directly adhered to the inner wall surface, and the generation of particles can be further suppressed. Further, by forming the pre-coat film, particles slightly remaining in the vacuum vessel 2 are sealed in the pre-coat film, and scattering of the particles during the subsequent film forming process is prevented. Because.

Further, in the present invention, the thin film formed in the plasma processing apparatus is not limited to the CF film, but may be a SiOF film or a SiO
_Although it can be applied to the case of forming _two films, a silicon nitride film, a silicon carbide film and the like, it is particularly suitable for forming a thin film having poor adhesion such as a CF film. Furthermore, the present invention is not limited to the generation of plasma by ECR, for example, ICP (Inductive Coupled).
The present invention can also be applied to a case where plasma is generated by a method of applying an electric field and a magnetic field to a processing gas from a coil wound around a dome-shaped container, which is called “Plasma”.

[0037]

As described above, according to the present invention, when a thin film is formed using a plasma processing apparatus, particle contamination of a substrate can be reduced and throughput can be improved. Can be.

[Brief description of the drawings]

FIG. 1 is a vertical sectional side view showing an example of a plasma processing apparatus for carrying out a method of the present invention.

FIG. 2 is a characteristic diagram showing the number of particles when cleaning is performed each time one wafer is formed.

FIG. 3 is a characteristic diagram showing the number of particles when cleaning is performed every time five wafers are formed.

FIG. 4 is a sectional view showing a conventional plasma processing apparatus.

[Explanation of symbols]

 2 Vacuum Vessel 21 First Vacuum Chamber 22 Second Vacuum Chamber 24 High-Frequency Power Supply 25 Waveguide 26, 27 Electromagnetic Coil 28 Exhaust Pipe 31 Gas Nozzle 4 Placement Table 5 Film Forming Gas Supply Section 51, 52 Gas Supply Pipe W Semiconductor Wafer

Claims (3)

[Claims] 1. A film forming step of mounting a substrate on a mounting table provided in a vacuum vessel, converting a film forming gas into plasma, and forming a thin film on the substrate by the plasma; And a cleaning step of converting a cleaning gas into plasma and removing a thin film adhered in the vacuum vessel by the plasma. The cleaning step is performed every time a film forming process is performed on one substrate. A cleaning method for a plasma processing apparatus, comprising: 2. A thin film formed on a substrate is a fluorine-added
2. The cleaning method for a plasma processing apparatus according to claim 1, wherein the cleaning method is a bonding film. 3. The cleaning method for a plasma processing apparatus according to claim 1, wherein the film forming gas and the cleaning gas are converted into plasma by interaction of a microwave and a magnetic field.