JP2001220678A - Plasma cvd system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the working ratio of a plasma CVD system. SOLUTION: In this plasma CVD system in which high frequency electric power or d.c. electric power is applied on a cathode to generate plasma between the cathode and a substrate arranged oppositely thereto, and this plasma is utilized to deposit a thin film on the substrate, by allowing gas which does not deposit a film in a state of being a simple substance in the case of being exposed to plasma to exist relatively at a high concentration in the vicinity of the surface of the cathode, the concentration of reaction gas in the above vicinity is made relatively low.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an apparatus for forming a thin film by plasma CVD.

[0002]

2. Description of the Related Art Si thin films and DLC (Diamond Like Carbo)
n) Plasma CVD is used to form a thin film. Plasma CVD is a method of forming a thin film by converting a reaction gas into plasma and depositing active species such as ions and radicals in the plasma on the surface of a substrate.

As a plasma generation source used for plasma CVD, for example, a capacitively-coupled high-frequency plasma source using a frequency of 100 kHz to 200 MHz or JP-A-64-658 is known.
There is a device utilizing electron cyclotron resonance (ECR) as disclosed in Japanese Patent Publication No. 43-43. Among them, the capacitively-coupled high-frequency plasma source can perform large-area processing and stable discharge, and can be manufactured at a lower cost than an ECR plasma source.

The capacitively coupled high-frequency plasma processing apparatus generates plasma between a high-frequency electrode and a ground electrode, and applies a high-frequency voltage to the high-frequency electrode via a coupling capacitor. At this time, a deep negative bias is formed on average by the self-bias effect, so that the high-frequency electrode functions as a cathode. Then, a glow region is generated between the high-frequency electrode and the ground electrode. In this specification, the high-frequency electrode is called a cathode, and the ground electrode is called an anode.

[0005]

SUMMARY OF THE INVENTION In plasma CVD,
The active species generated near the substrate in the plasma space adhere to the surface of the substrate to form a thin film. However, a thin film is formed on the cathode surface by the same mechanism, and the thickness increases in proportion to the processing time. When the film formed on the cathode surface has a certain thickness, it is peeled off and becomes a flake shape, and a part thereof adheres to the substrate surface. Therefore, defects such as pinholes occur in the thin film formed on the substrate surface. To prevent such defects from occurring,
It is necessary to periodically clean the cathode surface. Si
In a plasma CVD apparatus used for forming a thin film, plasma is generally generated using a gas such as carbon tetrafluoride or nitrogen trifluoride, and cleaning is performed by so-called dry etching.

However, since cleaning lowers the operation rate of the plasma CVD apparatus, it is necessary to reduce the frequency of cleaning as much as possible.

An object of the present invention is to improve the operation rate of a plasma CVD apparatus.

[0008]

The above object is achieved by the following (1).
This is achieved by the present invention of (3). (1) Plasma is generated by applying high-frequency power or DC power to a cathode to generate a plasma between the substrate and a substrate disposed opposite to the cathode, and using the plasma to deposit a thin film on the substrate. In the CVD apparatus, in the vicinity of the cathode surface, a gas that does not form a film by itself when exposed to plasma is present at a relatively high concentration, so that the reaction gas concentration in the vicinity is relatively low. Plasma CVD apparatus. (2) The plasma CVD according to (1), wherein the surface of the cathode is formed of a porous material, and a gas that does not form a film by itself when ejected from the porous material is exposed from the porous material.
apparatus. (3) The plasma CVD apparatus according to (2), wherein the gas ejected from the porous body is heated.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a plasma CVD of the present invention.
1 shows a configuration example of an apparatus. FIG. 1 shows the inside of a reaction chamber (vacuum tank) of a plasma CVD apparatus, and the wall surface of the reaction chamber is not shown. In this apparatus, a cathode 2 and a substrate holder 31 functioning as an anode are arranged to face each other, and a substrate 3 is placed on the surface of the substrate holder 31. Cathode 2
Is connected to a high frequency power supply 5 via a coupling capacitor 4, and the substrate holder 31 is grounded.

In the present invention, a gas which does not form a film by itself when exposed to plasma is present at a relatively high concentration near the surface of the cathode 2. Therefore, in the device shown in FIG. 1, the cathode 2 is composed of the cathode body 21 and the porous body 22 that covers the surface of the cathode body 21 through the gap. The gas introduced from the back side (the lower side in the figure) of the cathode main body 21 into the gap between the cathode main body 21 and the porous body 22 (the gas that does not form a film by itself when exposed to plasma) The gas is ejected from the surface of the cathode 2 through a through hole provided in the porous body 22. On the other hand, the reactive gas supplied between the cathode 2 and the substrate 3 generates active species due to the plasma 6 and adheres to the surface of the substrate 3 to form a film. At this time, in the conventional plasma CVD apparatus, the active species also adhered to the surface of the cathode 2 to form a film, but in the present invention, the adhesion of the active species to the surface of the cathode 2 is greatly reduced. In the present invention, a gas that does not form a film by itself when it is exposed to plasma is ejected from the surface of the cathode 2, so that the concentration of this gas is relatively higher in the vicinity of the cathode 2 than in the vicinity of the substrate 3. Therefore, the concentration of the reaction gas near the surface of the cathode 2 becomes low, and the active species cannot approach the vicinity of the surface. As a result, the concentration of the reactive gas in the vicinity of the surface of the cathode 2 becomes relatively lower than that in the vicinity of the substrate 3, so that the attachment of active species to the surface of the cathode 2 is greatly reduced. Therefore, the frequency of cleaning the cathode 2 can be significantly reduced, so that the operation rate of the plasma CVD apparatus is greatly improved.

In addition to the configuration shown in FIG. 1, a cathode having no through-hole is used as in the prior art, and a gas which does not form a film by itself is sprayed on the surface of the cathode. By forming a gas flow not to be formed substantially parallel to the cathode surface, the concentration of the reaction gas in the vicinity of the cathode surface can be reduced. However, the structure shown in FIG. 1 is most preferable because the uniformity of the concentration of the gas that does not form a film by itself can be improved.

The reaction gas supplied between the cathode 2 and the substrate 3 may be a mixture of the reaction gas and a gas that does not form a film by itself. Although the substrate 3 is shown as a plate-like body in FIG. 1, a long substrate wound with a flexible film may be used.

Japanese Patent Application Laid-Open No. Hei 8-209349 discloses a plasma CVD apparatus for forming a thin film on the surface of a substrate to be processed by applying high-frequency power to upper and lower electrodes to generate plasma. It describes a configuration in which a shower plate made of a porous metal plate is provided on the lower surface of the upper electrode and a reaction gas introduced into the hollow portion is supplied between upper and lower electrodes via the shower plate. The CVD apparatus described in the publication is similar to the apparatus of the present invention in that a porous metal plate is provided on an electrode.

Japanese Patent Application Laid-Open No. Hei 10-242134 describes a plasma CVD apparatus having a high-frequency electrode provided with a gas outflow hole. The plasma CVD apparatus described in the publication is similar to the apparatus of the present invention in that a gas outflow hole is provided in a high-frequency electrode (cathode).

However, in the devices described in the above publications, the gas ejected from the porous metal plate or the gas outlet provided in the electrode is a reaction gas, which is completely different from the device of the present invention in this point. However, in Japanese Patent Application Laid-Open No. Hei 8-209349, since the reaction gas is uniformly supplied from the fine holes of the porous metal plate, no gas remains on the lower surface of the upper electrode, and the reaction gas flow It describes that no film is deposited on the upper electrode by the self-cleaning action. However, if the reactant gas is supplied through the electrode, film adhesion to the electrode cannot be avoided.

The gas used in the present invention that does not form a film by itself when exposed to plasma is generally a rare gas (any of He, Ne, Ar, Kr and Xe).
Alternatively, a mixed gas containing two or more rare gases can be used. For example, when an amorphous silicon film is formed, a hydrogen gas and a mixed gas of the hydrogen gas and the rare gas can also be used. The preferable flow rate of the gas ejected from the surface of the cathode differs depending on various conditions such as the area of the cathode surface and the flow rate of the reaction gas. The specific flow rate may be determined experimentally. Although the size of the cathode is not particularly limited, usually, the area is 1
It is about 00 to 10000 cm ² . When a cathode having such a size is used, the gas flow rate is usually 10 to 2000
What is necessary is just to select from the range of sccm.

Next, a more detailed configuration of the plasma CVD apparatus of the present invention will be described.

In FIG. 1, the porous body 22 is formed by processing a porous metal plate, and is fixed to the surface of the cathode main body 21 by screwing or bonding. For the porous metal plate, for example, a punching metal may be used, or a metal net may be used. In these cases, the diameter of the through-hole is usually 0.1 mm.
It is preferably about 3 to 5 mm. The arrangement density of the through-holes is preferably determined so as to be the maximum without significantly impairing the mechanical strength of the porous body 22, for example,
It is preferable to select from a range of about 4 to 600 / cm ² depending on the diameter of the through hole. If the diameter of the through-hole is too large or the arrangement density is too low, it becomes difficult to uniformly form a high gas concentration region near the surface of the cathode 2. On the other hand, it is difficult to form a through hole having a diameter smaller than the above range.

In order to uniformly form a high gas concentration region near the surface of the cathode 2, it is preferable that the through holes are as small as possible and the arrangement density is as high as possible.
Therefore, it is preferable to provide a coating layer made of a porous ceramic such as porous alumina on the surface of the substrate using a punching metal or a metal net as a substrate. However, even in this case, the uniformity of gas ejection is limited by the arrangement density of the through holes provided in the base.

Therefore, in the present invention, it is preferable to use a porous sintered metal for the porous body 22. The porous sintered metal is a metal in which countless capillaries (through holes) connected to each other are open on the surface, and is used for applications such as filtration, degassing, and foaming. When a sintered metal is used, there is no need to provide a base made of a punching metal or a metal net, and therefore, the openings contributing to gas ejection are present at a very high density and uniformly on the cathode surface. Therefore, a uniform high gas concentration region can be formed near the surface of the cathode. The diameter of the opening of the capillary in the sintered metal is usually about 10 to 1000 μm, and the arrangement density is 100 to 10 μm.
It is about 0000 / cm ² . Examples of the sintered metal preferably used in the present invention include stainless steel and copper alloy.

In the present invention, the cathode 2 can be formed only by fixing the porous body 22 to the surface of a conventional cathode as shown in the figure. However, the cathode may be composed only of the porous body.

Next, a preferred embodiment of the present invention will be described.
In the present invention, it is preferable that a heated gas is ejected from the through hole provided in the cathode. Since the heating gas has a high molecular temperature, it is possible to efficiently suppress the reaction gas from approaching the vicinity of the cathode. FIG. 2 shows a configuration example of a cathode capable of ejecting a heated gas. In this cathode, the cathode body 21 is a block heater in which a resistor 23 made of a nichrome wire or the like is built in a plate-shaped body made of a metal such as iron. The porous body 22 provided on the cathode body 21 is made of a sintered metal. When the cathode body 21 generates heat by energizing the resistor 23, the porous body 22 in contact with the cathode body 21 is heated. The gas introduced into the space between the cathode body 21 and the porous body 22 is heated while being in contact with each surface of the cathode body 21 and the porous body 22, and then from the opening of the porous body 22 to the plasma generation space. Gushing.

The temperature of the heater surface in contact with the gas is preferably 100 ° C. or higher, more preferably 150 ° C. or higher. If the surface temperature of the heater is too low, the gas temperature will not rise sufficiently and the effect of the heating will be insufficient. Although there is no particular upper limit on the surface temperature of the heater, considering the thermal effect on the members that are in contact with or near the heater, 400
C. or lower, particularly preferably 350.degree. C. or lower.

In order to efficiently heat the gas introduced into the space in the cathode, the surface area of one or both of the heating member and the heating member may be increased in the space. The cathode shown in FIG. 3 has a structure in which plate-like porous bodies 22A and 22B are provided in the space inside the cathode shown in FIG. The cathode main body 21 and the porous bodies 22A, 22B, and 22 are arranged in this order, and a gap is provided therebetween. Due to the heat generated by the cathode body 21,
The porous body 22 which is in direct or indirect contact with this
A, 22B and 22 are heated. The gas introduced into the cathode includes a cathode body 21, porous bodies 22A, 22B and 2B.
After contacting with No. 2, it is ejected out of the cathode. Therefore, in the cathode having the structure shown in FIG. 2, the gas heating efficiency is increased. In FIG. 2, the porous body 2 is viewed from the lamination direction of the porous body.
Both porous bodies are arranged so that the through-hole of 2A and the through-hole of porous body 22B do not overlap. Therefore, the residence time of the gas in the cathode becomes longer, and the gas heating efficiency becomes extremely high.

The cathode shown in FIG. 3 has a structure in which a porous body 22A made of a sintered metal is provided in a space inside the cathode shown in FIG. Since the sintered metal has a remarkably large surface area (including the inner surface of the capillary), the gas heating efficiency can be significantly increased.

In the above, the structure in which at least one porous body is provided in the space in the cathode has been described as an example. However, in order to increase the contact area with the gas, for example, the heater is directly or indirectly contacted with the heater. Fins (radiation fins) may be provided in the space inside the cathode.

Although the height of the space provided in the cathode in FIGS. 1 and 2 is not particularly limited, it is usually 0.5 to 5 mm.
It is preferable to set the degree. The height of the space provided between the porous bodies in FIGS. 3 and 4 may be set to this level.

The reaction gas used in the present invention is not particularly limited, and may be appropriately selected according to the composition of the film to be formed. For example, when forming a Si thin film, silane (S
iH ₄ ), higher order silane or the like is used. In addition to the Si thin film, the present invention can be used for forming a diamond thin film, a diamond-like carbon film, a silicon carbide film, a silicon oxide film, a silicon nitride film, an aluminum oxide film, an aluminum nitride film, and the like. In addition, in the plasma, in addition to the above reaction gas,
A rare gas, hydrogen gas, or the like is supplied as a diluting gas.

The pressure in the reaction vessel and the partial pressure of the reaction gas are not particularly limited, and may be the same as in a conventional plasma CVD apparatus.

Although the illustrated example is a capacitively coupled plasma processing apparatus, the present invention can also be applied to an apparatus using DC plasma.

[0031]

EXAMPLE A plasma CVD apparatus having the structure shown in FIG. 1 was prepared. As the cathode main body 21, a cathode in a usual plasma CVD apparatus was used. The porous body 22 was formed by processing a sintered metal plate (thickness: 2.3 mm) made of stainless steel. The openings of the capillaries existing on the surface of the porous body 22 had an average diameter of about 200 μm and an arrangement density of about 1300 / cm ² . The porous body 22 was fixed with screws so as to completely cover the surface of the cathode main body 21. The plane dimensions of the cathode body 21 are 36 cm x 46 cm,
The distance between the surface of the cathode main body 21 and the porous body 22 was 2 mm.

In this apparatus, near the surface of the substrate 3,
Supplying 50 sccm of silane gas and 500 sccm of hydrogen gas,
The pressure in the reaction vessel was set to 133 Pa. In addition, the cathode body 2
He gas is supplied to the space between
It was introduced at 0 sccm and was ejected from the surface of the porous body 22 through a capillary tube. In this state, a process of forming a Si film on the surface of the substrate 3 was continuously performed, and the time required until the surface of the porous body 22 needed to be cleaned was examined. For comparison, an Si film was formed on the surface of the substrate 3 in the same manner as described above except that the cathode from which the porous body 22 was removed was used, and the time until cleaning was required was examined. As a result, it was confirmed that the cleaning interval can be extended by the present invention.

When plasma CVD was performed using the cathodes having the structures shown in FIGS. 2 to 4 while ejecting a heating gas from the cathodes, deposition of a film on the surface of the porous body was further suppressed. .

[0034]

According to the present invention, when plasma CVD is performed, active species are unlikely to adhere to the surface of the cathode, so that the frequency of cleaning the cathode can be significantly reduced, and as a result, the operation rate of the apparatus is significantly improved. it can.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a main part of a plasma CVD apparatus according to the present invention.

FIG. 2 is a cross-sectional view illustrating a configuration example of a cathode used in the plasma CVD apparatus of the present invention.

FIG. 3 is a cross-sectional view illustrating a configuration example of a cathode used in the plasma CVD apparatus of the present invention.

FIG. 4 is a cross-sectional view illustrating a configuration example of a cathode used in the plasma CVD apparatus of the present invention.

[Explanation of symbols]

 2 Cathode 21 Cathode main body 22, 22A, 22B Porous body 23 Resistor 3 Substrate 31 Substrate holder 4 Coupling capacitor 5 High frequency power supply 6 Plasma

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4K030 AA06 AA16 AA17 BA28 BA30 BA37 BA38 BA43 BA44 EA06 FA03 JA06 KA17 KA25 KA46 5F045 AA08 AB02 AC01 AE25 BB08 BB10 DP04 DP22 EE14 EE20 EH04 EH05 EH08 EH14 EK08

Claims (3)

[Claims] A high-frequency power or a direct-current power is applied to a cathode to generate plasma between the cathode and a substrate arranged opposite to the cathode, and the plasma is used to deposit a thin film on the substrate. A plasma CVD apparatus for performing, in the vicinity of a cathode surface, a relatively high concentration of a gas that does not form a film by itself when exposed to plasma, thereby relatively increasing the reaction gas concentration in the vicinity. Plasma CVD equipment to lower the temperature. 2. The plasma C according to claim 1, wherein the surface of the cathode is made of a porous material, and a gas that does not form a film by itself when exposed to plasma is ejected from the porous material.
VD device. 3. The plasma CVD apparatus according to claim 2, wherein the gas ejected from said porous body is heated.