JP2008231513A - Plasma cvd system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plasma CVD system where the phenomenon that temperature conditions are changed due to the state of a substrate as the object for film deposition, so as to generate variation in film deposition is suppressed. <P>SOLUTION: A stage 11 cooled by a cooling member 13 is mounted with an anode 12 composed of graphite. The graphite can transmit a large quantity of heat by the radiation of the heat. The contribution to the temperature of a substrate 1 by contact heat conduction depending on the contact area between the anode 12 and the substrate 1 and the contact area between the anode 12 and the stage 11 is relatively reduced; thus the temperature control of the substrate 1 can be facilitated. In this way, the phenomenon that cooling conditions are changed due to the state of the substrate 1, so as to generate variation in film deposition can be suppressed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a plasma CVD apparatus.

Patent Document 1 describes that an electrode such as molybdenum is applied to a conductive region of an electrode of a plasma processing apparatus.
JP 2005-63973 A

  As described above, when the plasma processing apparatus of Patent Document 1 is applied as a plasma CVD apparatus, a substrate to be deposited is placed directly on an electrode for generating plasma. However, the actual contact area between the substrate and the electrode is greatly influenced by the surface roughness of the facing surface where the substrate and the electrode are in contact, the shape, weight, flatness, etc. of the substrate. Very small value. Therefore, variations in heat flow propagation tend to occur. Therefore, even if the arrangement position of the substrate on the electrode is different, the actual contact area between the substrate and the electrode changes greatly, and the state of heat conduction between the electrode and the substrate changes significantly. In the case of plasma CVD in which the temperature of the substrate becomes high, the film formation conditions vary, which is an unstable factor.

  An object of this invention is to provide the plasma CVD apparatus which can suppress the dispersion | variation in the substrate temperature at the time of film-forming.

In order to achieve the above object, a plasma CVD apparatus according to the first aspect of the present invention comprises:
An electrode on which a substrate to be treated is placed, a surface formed of graphite,
Plasma generating means for generating a plasma on the electrode and performing a predetermined treatment on the substrate;
It is characterized by providing.

A stage for supporting the electrode;
A cooling means for cooling the electrode to lower the substrate temperature by cooling the stage may be further provided.

The cooling means may start cooling the substrate when the film is formed on the substrate.
The predetermined process performed by the plasma generating means may be to form a film on the substrate by converting the plasma into a hydrocarbon as a reaction gas.

  According to the present invention, variations in substrate temperature during film formation can be suppressed, and film formation is stabilized.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a configuration diagram showing an outline of a plasma CVD apparatus according to an embodiment of the present invention.

  This DC plasma CVD apparatus is an apparatus that forms a film on the surface of a substrate 1 to be processed, and includes a chamber 10 that is a reaction tank. The chamber 10 blocks the substrate 1 from the outside air.

A cylindrical steel stage 11 is disposed in the chamber 10, and a disk-shaped anode 12 is placed on the electrode placement surface 11 a on the upper side of the stage 11. For example, the rectangular substrate 1 is placed on the substrate placement surface 12 a on the upper side of the anode 12. The anode 12 is made of graphite, and its surface has an arithmetic average roughness Ra of about 5 μm.
The outer peripheral surface of the anode 12 is surrounded by a ring 14 made of an insulator such as quartz glass. The stage 11, the anode 12 and the ring 14 are set so as to rotate around the axis 11x.

The stage 11 below the anode 12 is provided with a closed columnar space 11b, and the electrode placement surface 11a of the stage 11 is plate-shaped.
A columnar cooling member 13 is disposed in the space 11 b of the stage 11. The cooling member 13 is provided to cool the substrate 1 as necessary, and is formed of a metal having high thermal conductivity such as copper. The cooling member 13 is configured to move up and down as indicated by an arrow by a moving mechanism (not shown).

  The upper end surface of the cooling member 13 is a facing surface 13a that faces a surface 11c opposite to the electrode mounting surface 11a of the stage 11 (hereinafter, this surface is referred to as a back surface), and has a large outer diameter. As the cooling member 13 moves upward, the facing surface 13a faces the back surface 11c of the stage 11 so as to come close to or come into contact therewith.

  Inside the cooling member 13, there is formed a flow path 13b through which a cooling medium such as cooled water or a calcium chloride aqueous solution flows. The flow path 13b passes from the side surface of the cooling member 13 through the vicinity of the facing surface 13a and reaches the side surface of the cooling member 13 again. The flow path 13b is connected to the cooler 15 via the pipelines 13c and 13d, and the cooling medium is cooled by the cooler 15 and flows between the flow path 13b and the cooler 15 in a circulating manner.

A vent 13e is opened at the center of the facing surface 13a of the cooling member 13. The ventilation hole 13 e penetrates the lower side surface of the cooling member 13. On the side surface below the cooling member 13, the vent 13 c is connected to the pipe line 16. The pipe line 16 is connected to a cylinder 19 via a valve 17 and a flow rate regulator 18. The cylinder 19 is filled with helium gas or nitrogen gas as a cooling gas. The cooling gas is filled in the space 11b, but is not filled on the substrate placement surface 12a side of the anode 12.
As described above, the cooling member 13 includes not only a mechanism for cooling the stage 11 with the cooling medium, but also a mechanism for cooling the stage 11 by blowing the cooling gas to the stage 11 from the vent 13e. Therefore, when the anode 12 and the substrate 1 are cooled, a method in which the facing surface 13a is partly or entirely brought into contact with the back surface 11c of the stage 11 or a cooling gas is blown onto the stage 11 with the facing surface 13a being brought close to the back surface 11c The method for cooling the stage 11 or both of them can be selected.

  The cathode 20 is supported so as to face the substrate mounting surface 12a of the anode 12. A power supply 21 for applying a voltage for generating plasma is connected between the cathode 20 and the anode 12.

  A gas introduction pipe 22 is provided at a position higher than the cathode 20 of the chamber 10 to introduce a source gas supplied from a source gas system (not shown) into the chamber 10. A gas exhaust pipe 23 for discharging the source gas is provided at the bottom of the chamber 10.

  The gas introduction pipe 22 and the gas exhaust pipe 23 pass through holes provided in the chamber 10, respectively, and a gap between each hole and the outer periphery of the gas introduction pipe 22 and the gas exhaust pipe 23 is sealed with a sealing material. Airtightness within 10 is ensured. Connected to the gas exhaust pipe 23 is an exhaust system (not shown) that discharges the source gas from the gas exhaust pipe 23 and adjusts the atmospheric pressure in the chamber 10.

  A window 25 for observing the inside of the chamber 10 may be formed on the side surface of the chamber 10. In this case, the window 25 is fitted with heat-resistant glass, and airtightness in the chamber 10 is ensured. A spectral radiance meter 26 for measuring the temperature of the substrate 1 through the heat-resistant glass of the window 25 is disposed outside the chamber 10.

  When forming a film on the substrate 1 using this DC plasma CVD apparatus, the substrate 1 is first mounted on the substrate mounting surface 12 a of the anode 12. When the placement of the substrate 1 is completed, the inside of the chamber 10 is then depressurized using an exhaust system, and then a source gas is introduced into the chamber 10 from the gas introduction pipe 22. The source gas is a mixture of a reaction gas such as methane that is a film forming material and a matrix gas (carrier gas) such as hydrogen that is not a film forming material at a predetermined ratio. For example, when a carbon film such as graphite or diamond fine particles is formed on the substrate 1, the reaction gas is a compound gas containing carbon.

  The introduction amount and the exhaust amount of the source gas are adjusted, and the atmospheric pressure in the chamber 10 is set so that a predetermined value or a deviation from the predetermined value is within an allowable range. Further, the stage 11 is rotated at, for example, 10 rpm to rotate the substrate 1 and the anode 12. In this state, a DC voltage is applied between the anode 12 and the cathode 20 to generate plasma. When plasma is generated, active species are generated from the reaction gas by the plasma, and film formation on the substrate 1 is started. By rotating the substrate 1 and the anode 12, temperature variations due to the position of the substrate 1 are reduced, and variations in film formation on the substrate 1 are prevented.

  Cooling incorporated in the cooling member 12 in order to prevent the temperature rise of the substrate 1 due to film formation and to secure a desired film quality, or to change the film quality by changing the temperature of the substrate 1 during film formation. The mechanism is appropriately selected and used. That is, the opposing surface 13a may be brought into contact with the back surface 11c while flowing the cooling medium cooled by the cooler 15 through the flow path 13b of the cooling member 13, or the opposing surface 13a is brought close to the back surface 11c and the cooling gas. May be sprayed on the back surface 11c, or a cooling gas may be sprayed on the back surface 11c by causing a part of the facing surface 13a to contact the back surface 11c while flowing a cooling medium through the flow path 13b.

  Since the surface temperature of the substrate 1 can be measured by the spectral radiance meter 26, the cooling timing of the substrate 1 and the voltage applied between the anode 12 and the cathode 20 can be controlled according to the surface temperature of the substrate 1 by plasma.

  When a predetermined time has elapsed since the start of film formation and when the film formation is in an end stage, the application of voltage between the anode 12 and the cathode 20 is stopped, and then the supply of the source gas is stopped, Nitrogen gas is supplied as a purge gas into the chamber 10 to return to normal pressure, and then the substrate 1 is taken out.

Next, advantages of this DC plasma CVD apparatus will be described.
When film formation is performed on the substrate 1, the substrate 1, the anode 12, and the cathode 20 are heated by being exposed to plasma generated between the anode 12 and the cathode 20. Although a part of the energy given to the substrate 1 is transmitted to the chamber 10 also by heat radiation, most of the energy is transmitted from the substrate 1 to the anode 12 and the stage 11 and also to the cooling member 12 via the stage 11. Thus, the temperature of the substrate 1 is kept constant by balancing the amount of heat transferred and the amount of heat transferred.

  Here, when the anode 12 is made of graphite (hereinafter, this electrode is referred to as a graphite electrode) and when it is made of molybdenum (hereinafter, this electrode is referred to as a molybdenum electrode), a comparison is made. .

As for the film forming conditions, in both the graphite electrode and the molybdenum electrode, a source gas having a flow rate of methane of the reaction gas of 50 sccm and a flow rate of hydrogen of the matrix gas of 500 sccm is introduced into the chamber 10 and the exhaust speed is adjusted. This maintained the overall pressure at 7999.32 Pa. Moreover, power was applied so that the current density between the cathode 20 and the graphite electrode and the molybdenum electrode was 0.15 A / cm ² (current / electrode area) to generate plasma.
The arithmetic average roughness Ra of the surface of the molybdenum electrode was 1.5 μm, and the thermal conductivity λ due to bulk movement was 132 W · m ⁻¹ · K ⁻¹ . The arithmetic average roughness Ra of the surface of the graphite serving as the anode 12 was 5 μm, and the bulk thermal conductivity λ was 120 W · m ⁻¹ · K ⁻¹ .

The substrate 1 is made of silicon having a thickness of 0.5 mm. In order to change the temperature of the substrate 1, the opposing surface 13 a and the back surface 11 c of the stage 11 in FIG. The distance x was set to 60 mm. In the meantime, in a plasma CVD apparatus using a graphite electrode, a carbon nanowall composed of a plurality of petal-shaped (fan-shaped) carbon flakes that are curved and connected in a random direction is formed on the substrate 1. Was filmed. Each carbon flake was a graphene sheet of several to several tens of layers with a lattice spacing of 0.34 nm. After that, the distance x was brought close to 0.5 mm. Then, the temperature of the substrate 1 was lowered by introducing helium gas as a cooling gas into the space 11b below the stage 11 at 500 sccm through the vent 13e. In the meantime, in a plasma CVD apparatus using a graphite electrode, a microcrystalline diamond film, which is a layer containing a plurality of microcrystalline diamond particles having a particle size of nanometer order (less than 1 μm), is deposited on the carbon nanowall on the substrate 1. As the microcrystalline diamond particles grow, a part of the carbon nanowall grows mainly, forming needle-like carbon rods that penetrate the gaps in the microcrystalline diamond film and protrude from the surface of the microcrystalline diamond film. It was. This carbon rod has carbon formed to the inside, and is not a cylindrical structure formed so as to be hollow with a thin carbon layer like a carbon nanotube, but is rigid and grows from the carbon nanowall. Therefore, mechanical strength is strong.
The spectral radiance meter 26 was used to measure the temperature of the substrate 1, the infrared radiation intensity from the substrate 1 was measured and the gray body approximation was applied to evaluate the temperature and emissivity of the substrate 1.

FIG. 2 is a graph showing the measured temperature of the substrate 1 due to the difference in the anode 12.
As shown in FIG. 2, in both electrodes, the temperature of the substrate 1 reaches the highest point within 30 minutes from the start of film formation, and thereafter the temperature of the substrate 1 tends to decrease with a constant current density. . The reason why the temperature of the substrate 1 tends to decrease is that carbon nanowalls, which are aggregates of graphene sheets, are deposited on the substrate 1, thereby increasing the emissivity of the upper surface of the substrate 1. This is because the amount of heat transfer due to radiation from the surface into the chamber increases. Furthermore, after the carbon nanowall is deposited on the substrate 1, the temperature of the substrate 1 is stable after the emissivity of the substrate 1 reaches a constant value. Such a phenomenon indicates that the peripheral emissivity greatly affects the temperature of the substrate 1 when the film is formed by CVD such that the temperature of the substrate 1 exceeds 900 ° C.

  Comparing the temperature of the substrate 1 with the electrodes, in the initial film formation region where the temperature of the substrate 1 greatly fluctuated, the temperature of the substrate 1 on the graphite electrode was lower than that on the molybdenum electrode by 100 ° C. or more. In a state where the temperature thereafter is stable, even when the distance x is 0.5 mm, the temperature of the substrate 1 in the case of the graphite electrode is 40 ° C. lower than the temperature of the substrate 1 in the case of the molybdenum electrode.

FIG. 3 is a graph showing a change in the power applied to the plasma in a state where the applied current is constant in the furnace of FIG.
During this film formation, the current density flowing between the anode 12 and the cathode 20 is controlled to be constant at 0.15 A / cm ² , and the applied voltage automatically varies depending on the gas state. . In practice, the applied voltage tends to decrease as the gas density between the electrodes decreases. In the case of the molybdenum electrode having a high temperature of the substrate 1, the ambient gas temperature is increased by the substrate 1 and the electrode, and the density is reduced accordingly. The voltage for passing the current density is reduced. For this reason, the power applied in the case of the molybdenum electrode is always smaller than that in the case of the graphite electrode, but the amount of change is 1.5% or less with respect to the applied power.

  Despite the fact that the applied power hardly changes, the difference in temperature of the substrate 1 between the molybdenum electrode and the graphite electrode is always 100 ° C. The reason why the graphite electrode heats more than the molybdenum electrode in this temperature region. It was because it was easy to escape. The fact that graphite electrodes with a lower thermal conductivity and a rougher surface than molybdenum tend to release heat has a greater contribution to heat conduction by thermal radiation in both electrodes than in heat conduction by contact. It can be explained that it is. If the thermal conductivity of the electrode material itself does not make sense because of the large contact thermal resistance, molybdenum has only an emissivity of about 0.3 due to reflection by the surface, compared to graphite with an emissivity of 0.9 or more. It can be easily explained that the temperature of the substrate 1 is smaller with the graphite electrode.

  Moreover, the tendency that the temperature difference between the molybdenum electrode and the graphite electrode becomes larger as the temperature of the substrate 1 becomes higher is that the heat transfer due to the contact changes in proportion to the temperature difference, whereas the heat transfer amount increases. With radiation, the amount of heat transfer increases in proportion to the fourth power of the absolute temperature. Therefore, as the temperature of the substrate 1 increases, the amount of heat transfer that is rapidly released increases, making it difficult to increase the temperature. These facts also suggest that the ratio of heat radiation is large in heat conduction during film formation.

Here, in order to estimate the amount of heat transfer by each heat transfer method, consider a case where a mirror-polished substrate is placed on the anode having a surface roughness Ra. If the front surface y is the back surface of the substrate, the front surface z is the surface of the anode, and the back surface y of the substrate is a mirror surface, the heat transfer due to the contact is of a length Ra. It is thought that it is transmitted through the projection of the anode. In this case, when the temperature of the substrate 1 is T ₁ and the anode temperature is T ₂ , the amount of heat transfer W _t1 per unit area flowing between the substrate and the anode by contact is:
It can be expressed as. Where λ is the thermal conductivity of the anode material, r is the ratio of the actual contact area between the substrate 1 and the anode 12 to the apparent contact area between the substrate 1 and the anode 12, and Ra is the arithmetic mean roughness of the surface. It is. A more accurate equation introduces a correction term for the distance between the substrate 1 and the electrode 12, but this is omitted in this case because it is intended to be approximate.

In addition to the above-described heat transfer by contact between solids, there is heat conduction that is transmitted through the gas in the gap between the substrate 1 and the anode 12. When considered simply as heat conduction through a stationary layer between two parallel flat plates of different temperatures, the average is obtained in an atmosphere of 0.1 atm or less, which is generally performed in plasma CVD when obtaining the data shown in FIG. Since the free path can be regarded as sufficiently larger than the surface roughness on the back side of the substrate, heat transfer can be considered as free molecular heat conduction. At this time, the heat transfer amount W _g1 is
It can be expressed as. Where Λ: free molecular thermal conductivity, α: adaptation coefficient, p: pressure, γ: specific heat ratio, k: Boltzmann constant, m: mass of gas molecule. As a simplification for rough estimation, the adaptation coefficient is set to 1 which is the largest, and the specific heat ratio and the mass of gas molecules are calculated as 7 / 5.3.3 × 10 ⁻²⁷ Kg of hydrogen molecules as the main gas of plasma.

Finally, the amount of heat transfer by radiation is considered. When the anode is considered as an infinite parallel plate, the heat transfer amount W _r1 transmitted from the surface y to the surface z by thermal radiation is
It is represented by Here, ε ₁ and ε ₂ are the emissivities of the surface y and the surface z, respectively, and σ is a Stefan-Boltzmann coefficient (5.67 × 10 ⁻⁸ Wm ⁻² K ⁻⁴ ).

  Regarding these three heat transfer mechanisms, the emissivity of silicon serving as a substrate is 0.6, the emissivity of molybdenum is 0.3, the emissivity of graphite is 0.9, and the appearance between the substrate 1 and the anode 12 is When the ratio of the real contact area between the substrate 1 and the anode 12 to the contact area of 1 / 1000,000, the substrate temperature is 920 ° C., the anode temperature is 860 ° C., and the substrate area □ 30 mm is calculated, In the case of a molybdenum electrode, the contact heat conduction with the substrate 1 is about 5 W, the heat conduction by free molecules between the molybdenum electrode and the substrate is about 10 W, and the heating by thermal radiation is about 5 W. Is about 1 W, thermal conduction by free molecules between the graphite electrode and the substrate 1 is about 10 W, and heating by thermal radiation is about 11 W. Thus, when no stress is applied to the interface and r becomes a very small value, the rate of heat transfer by heat radiation and free molecular heat conduction independent of r increases.

Consider a case where the heat transfer from the plasma to the substrate is constant when r is small. Even if the ratio r of the actual contact area between the substrate and the anode with respect to the apparent contact area between the substrate and the anode varies due to misalignment, the absolute value of r is small, so the change in the amount of heat transferred from the substrate to the anode Is almost independent of heat transfer by radiation, and only changes the amount of heat transfer by contact that changes in proportion to r. At this time, the greater the contribution of heat transfer by radiation, the greater the change in heat transfer due to contact changes in proportion to (T ₁ ⁴ -T ₂ ⁴ ). The amount of change in T ₁ can be made relatively small by compensating for the change in the amount of heat transfer due to radiation. As described above, the graphite electrode having a large contribution of heat conduction by radiation can suppress the variation in the substrate temperature due to the change of r with respect to the electrode having a smaller radiation rate, and can stabilize the film forming conditions.

In addition, it will be described below that unnecessary deposits can be prevented from being deposited on the anode 12 by using the anode 12 as a graphite electrode.
4 (a) and 4 (b) are photographs showing the states of the molybdenum electrode and the graphite electrode after film formation, respectively.

When the anode 12 was a molybdenum electrode, as shown in FIG. 4A, a carbonized film was formed on the portion where the substrate 1 was not placed after film formation. For this reason, when a new substrate is disposed on the molybdenum electrode on which the carbonized film is formed, the surface roughness at the position where the carbonized film is formed further varies, and temperature control becomes more difficult due to contact heat conduction.
On the other hand, in the graphite electrode, as shown in FIG. 4B, almost no deposit was present, so there was no variation in surface roughness, and more stable temperature control was possible.
The resistance between the carbonized film of the molybdenum electrode and the back surface of the molybdenum electrode is 3 MΩ or more, and the applied voltage itself varies between the anode and the cathode. The resistance between the back surface and the back surface was not changed from the state before film formation, and the applied voltage between the cathode and the cathode on the surface of the anode could be made uniform in the surface.

  Thus, since the anode 12 is made of a graphite electrode, a carbonized film serving as an insulator is hardly deposited on the anode 12, so that the substantial shape of the anode 12 does not change during the film formation process. Can be prevented, and stabilization of film formation can be expected.

In addition, this invention is not limited to the said embodiment, A various deformation | transformation is possible.
As shown in FIG. 5, in order to increase heat radiation, a recess that can accommodate the substrate 1 may be formed on the substrate mounting surface 12 a so as to widen the heat radiation surface of the anode 12.
In this case, in order to equalize the thickness of the anode 12 so that the temperature at the anode 12 is equal, the back side of the anode 12 may be a protruding portion that protrudes to the depth of the recessed portion of the anode 12. Preferably, a concave portion is formed on the electrode placement surface 11a of the stage 11 so as to match the convex portion of the anode 12, and the thickness of the stage 11 is made equal so that the temperature at the stage 11 is uniform. It is preferable that the electrode mounting surface 11a is a protruding portion that protrudes so as to meet the depth of the recessed portion. And it is preferable that a recessed part is formed in the opposing surface 13a so that it may fit in the back side of the stage 11. FIG.

Moreover, as shown in FIG. 6, even if the back surface of the substrate 1 is not smooth, a recess may be formed so that the substrate 1 can be fitted in accordance with the shape of the back surface of the substrate 1.
In this case, in order to equalize the thickness of the anode 12 so that the temperature at the anode 12 is equal, the back side of the anode 12 may be a protruding portion that protrudes to the depth of the recessed portion of the anode 12. Preferably, a concave portion is formed on the electrode placement surface 11a of the stage 11 so as to match the convex portion of the anode 12, and the thickness of the stage 11 is made equal so that the temperature at the stage 11 is uniform. It is preferable that the electrode mounting surface 11a is a protruding portion that protrudes so as to meet the depth of the recessed portion. And it is preferable that a recessed part is formed in the opposing surface 13a so that it may fit in the back side of the stage 11. FIG.

  Further, for example, the power source 21 may be a plasma CVD apparatus that applies a high frequency, instead of a configuration in which a DC voltage is applied between the anode 12 and the cathode 20. Also in this case, by using graphite as an electrode for cooling the substrate 1, the substrate can be cooled by heat radiation, and the film formation can be stabilized.

It is a lineblock diagram showing an outline of a plasma CVD apparatus concerning an embodiment of the present invention. It is a figure explaining the temperature difference of the graphite electrode and molybdenum electrode at the time of film-forming. It is a graph which shows the change of the electric power applied to plasma. It is a figure which shows the state of the anode after film-forming. It is a lineblock diagram showing an outline of a plasma CVD apparatus concerning an embodiment of the present invention. It is a lineblock diagram showing an outline of a plasma CVD apparatus concerning an embodiment of the present invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Board | substrate, 10 ... Chamber, 11 ... Stage, 11a ... Electrode mounting surface, 11b ... Space, 11c ... Back surface, 12 ... Anode, 12a ... Substrate Mounting surface, 13 ... Cooling member, 13a ... Opposing surface, 13b ... Channel, 13e ... Vent, 15 ... Cooling machine, 19 ... Cylinder, 20 ... Cathode , 21 ... power source, 22 ... gas introduction pipe, 23 ... gas exhaust pipe

Claims (4)

An electrode on which a substrate to be treated is placed, a surface formed of graphite,
Plasma generating means for generating a plasma on the electrode and performing a predetermined treatment on the substrate;
A plasma CVD apparatus comprising: A stage for supporting the electrode;
The plasma CVD apparatus according to claim 1, further comprising a cooling unit that cools the stage to cool the electrode to lower the substrate temperature.   The plasma CVD apparatus according to claim 2, wherein the cooling unit starts cooling the substrate when film formation is performed on the substrate.   2. The plasma CVD apparatus according to claim 1, wherein the predetermined process performed by the plasma generating unit is to form a film on the substrate by converting the plasma into a hydrocarbon as a reaction gas.