JP5120924B2 - Method for producing amorphous carbon film - Google Patents

Description

  The present invention relates to a method and an apparatus for manufacturing an amorphous carbon film.

At present, a thin film of amorphous carbon (also called diamond-like carbon: DLC) is mainly used as a coating for improving wear resistance of mechanical parts and the like. As a method for producing an amorphous carbon thin film, a microwave plasma CVD method is generally used. For example, Patent Document 1 describes a method for producing an amorphous carbon thin film by a microwave plasma CVD method.
JP-A-8-165194

  Amorphous carbon has attracted attention as a semiconductor material in addition to the above-described coating applications. There are two types of carbon bonding, sp2 bonding and sp3 bonding. When it is composed of only sp2 bonds, it becomes a layered graphite, and when it is composed of only sp3 bonds, it becomes diamond. Graphite is a conductor with a band gap energy of 0, while diamond is an insulator with a band gap energy of about 5.5 [eV]. Amorphous carbon has a configuration in which sp2 bonds and sp3 bonds are mixed, and the possibility of using it as a semiconductor material is being sought.

  In order to use amorphous carbon as a semiconductor, it is necessary to control its band gap energy to a desired value. However, in the amorphous state (non-crystalline), since the structure is not regular, it is difficult to predict the influence of the structural change on the band gap energy. Therefore, conventionally, manufacturing parameters that can realize a desired band gap energy are specified after trying various manufacturing parameters, which is extremely inefficient.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide an amorphous carbon film manufacturing method and manufacturing apparatus that can easily realize desired band gap energy.

  In order to solve the above-described problems, a first method for producing an amorphous carbon film according to the present invention generates a plasma of the source gas by irradiating a source gas for growing the amorphous carbon film with microwaves. The method includes a step of forming an amorphous carbon film on a material, and the source gas is irradiated with microwaves while periodically changing the output intensity of the microwaves.

  A first amorphous carbon film manufacturing apparatus according to the present invention includes a source gas source for supplying a source gas for growing an amorphous carbon film, a chamber for providing a region in which source gas plasma is generated, and a source material And a microwave generation unit that outputs a microwave for converting the gas into a plasma to the chamber, and the microwave generation unit outputs the microwave to the chamber while periodically changing the output intensity of the microwave. And

  When forming an amorphous carbon film by the microwave plasma CVD method, the inventor irradiates the source gas with microwaves while periodically changing the output intensity of the microwaves, thereby obtaining the band gap energy of the amorphous carbon film. It was found that can be controlled to an arbitrary value. As an example, there is a certain correlation between the duty ratio of the periodically changing microwave and the band gap energy of the amorphous carbon film. In order to obtain a desired band gap energy, It is better to set the microwave to the corresponding duty ratio. Therefore, according to the manufacturing method and manufacturing apparatus of the first amorphous carbon film described above, a desired band gap energy can be easily realized.

  Further, in the above-described first amorphous carbon film manufacturing method and manufacturing apparatus, when the microwave output intensity is periodically changed, the operation of intermittently stopping the microwave irradiation, and the pulsed micro More preferably, at least one of the operations of intermittently irradiating the wave is performed. The first amorphous carbon film manufacturing apparatus described above preferably further includes means for changing the duty ratio of the pulsed microwave.

A second amorphous carbon film manufacturing method according to the present invention is a method for manufacturing an amorphous carbon film as a semiconductor film having a predetermined band gap energy, and is a source gas for growing an amorphous carbon film. In addition, pulsed microwaves are intermittently irradiated with a duty ratio corresponding to a predetermined band gap energy to generate plasma of the source gas, thereby forming an amorphous carbon film on the substrate.

  A second amorphous carbon film manufacturing apparatus according to the present invention is an apparatus for manufacturing an amorphous carbon film having a predetermined band gap energy, and is a raw material for supplying a source gas for growing an amorphous carbon film. A gas source, a chamber that provides a region where plasma of the source gas is generated, and a microwave generator that outputs a microwave for converting the source gas into plasma are output to the chamber. The microwave is intermittently output to the chamber at a duty ratio corresponding to a predetermined band gap energy.

  As described above, there is a certain correlation between the duty ratio of the microwave and the band gap energy of the amorphous carbon film. In order to obtain a desired band gap energy, the duty ratio corresponding to the band gap energy is obtained. Set the microwave to. Therefore, according to the above-described second amorphous carbon manufacturing method and manufacturing apparatus, desired band gap energy can be easily realized.

  According to the method and apparatus for producing an amorphous carbon film according to the present invention, a desired band gap energy can be easily realized.

  Embodiments of an amorphous carbon film manufacturing method and manufacturing apparatus according to the present invention will be described below in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a side sectional view showing a configuration of a microwave plasma CVD apparatus 10 as an embodiment of an apparatus for producing an amorphous carbon film according to the present invention. As shown in FIG. 1, the microwave plasma CVD apparatus 10 includes a chamber 11, a source gas source 12, a waveguide 14, and a microwave generator 15.

  The chamber 11 is an airtight container that provides a region where the plasma P of the source gas G is generated. The chamber 11 is connected to the source gas source 12 via a pipe. A source gas source 12 supplies a source gas G to the chamber 11. On the other hand, the exhaust port 19 of the chamber 11 is provided with an exhaust means 13 comprising an exhaust pump. Prior to growing the amorphous carbon film, the exhaust means 13 depressurizes the inside of the chamber 11 by evacuation. In the chamber 11, a substrate stage 18 is provided for supporting the substrate B that is an object for forming an amorphous carbon film.

  The microwave generation unit 15 outputs the microwave W for converting the raw material gas G introduced into the chamber 11 into plasma through the waveguide 14 to the chamber 11 and irradiates the raw material gas G. The microwave generation unit 15 generates, for example, a microwave W having an output of 600 to 1400 [W] and a frequency of 2.45 GHz by a magnetron or the like.

Further, the microwave generator 15 irradiates the source gas G with the microwave W while periodically changing the output intensity of the microwave W. Here, periodically changing the output intensity of the microwave W refers to an operation of intermittently stopping the irradiation of the microwave W or irradiating the pulsed microwave W intermittently, for example. FIG. 2 is a diagram illustrating an example of a waveform of the microwave W output from the microwave generation unit 15. As shown in FIG. 2, the microwave generation unit 15 periodically outputs a microwave pulse WP to the chamber 11. That is, the microwave generation unit 15 stops the irradiation of the microwave W to the source gas G in the intermittent period T1 shown in FIG. 2, and the microwave having the peak intensity W ₀ in the intermittent period T2 shown in FIG. The source gas G is irradiated with the wave pulse WP.

FIG. 3 is a diagram schematically showing the relationship between the band gap energy Eg of the amorphous carbon film and the duty ratio d = T1 / (T1 + T2) of the microwave pulse WP. As shown in FIG. 3, one to the size of the duty ratio d ₁ is the band gap energy Eg of the more amorphous carbon film duty ratio d becomes large decreases. Then, the band gap energy Eg becomes minimum at a duty ratio d _1, when the duty ratio exceeds d _1, the band gap energy Eg as the duty ratio d becomes larger increases. The microwave generator 15 outputs the microwave pulse WP to the chamber 11 with a duty ratio corresponding to the predetermined band gap energy in order to produce an amorphous carbon film having the predetermined band gap energy. In order to manufacture amorphous carbon films having various band gap energies, it is preferable that the microwave generator 15 has means for making the duty ratio of the microwave pulse WP variable.

  Here, an example of the configuration of the microwave generator 15 is shown in FIG. The microwave generation unit 15 includes a magnetron device 21, a power supply unit 22, an oscillator 23, a modulator 24, and an oscilloscope 25. The magnetron device 21 is a device that generates a microwave W and outputs the microwave W to the chamber 11 (see FIG. 1). The power supply unit 22 provides power for generating the microwave W to the magnetron device 21. The oscillator 23 generates a periodic pulse signal P1. The modulator 24 adjusts the duty ratio of the pulse signal P1 from the oscillator 23 and outputs the pulse signal P2. The oscilloscope 25 displays the waveform of the pulse signal P2 from the modulator 24 and outputs a control signal P3 corresponding to the pulse signal P2 to the power supply unit 22. The power supply unit 22 provides power to the magnetron device 21 in accordance with the control signal P3 from the oscilloscope 25. A line 26 shown in the figure is a reference potential line connecting the oscilloscope 25 and the magnetron device 21. In the configuration shown in FIG. 4, the modulator 24 functions as a means for changing the duty ratio of the microwave pulse WP.

  Refer to FIG. 1 again. The waveguide 14 guides the microwave W output from the microwave generator 15 and provides it to the interior of the chamber 11. The waveguide 14 is provided on the chamber 11 via a quartz window 16. A slot antenna 17 is provided on the surface of the waveguide 14 facing the chamber 11, and the microwave W is irradiated to the source gas G inside the chamber 11 through the slot antenna 17. A cooling fan 20 for cooling the waveguide 14 is installed on the waveguide 14.

The source gas source 12 supplies a source gas G for growing an amorphous carbon film to the chamber 11. The source gas source 12 includes at least one of a methane (CH ₄ ) source, an ethylene (C ₂ H ₄ ) source, and an acetylene (C ₂ H ₂ ) source as a carbon source gas source. The source gas source 12 includes, for example, a nitrogen (N ₂ ) source as a dopant gas source for supplying impurity atoms (dopants) added to the amorphous carbon film. The source gas source 12 includes an inert gas source such as an argon (Ar) source as a carrier gas source for supplying a carrier gas. These gas sources are connected to the chamber 11 via a mass flow controller (MFC: Mass Flow Controller) (not shown) for adjusting the gas flow rate, and the raw material gases are mixed after passing through the mass flow controller to be the raw material gas G. Is supplied to the chamber 11.

  A method for producing an amorphous carbon film using the microwave plasma CVD apparatus 10 having the above-described configuration will be described. First, after the base material B is installed on the base material stage 18 of the chamber 11, the inside of the chamber 11 is decompressed. Then, a source gas G containing a carbon source gas such as methane, ethylene, acetylene, a dopant gas such as nitrogen, and a carrier gas such as argon is supplied from the source gas source 12 into the chamber 11 while generating microwaves. The microwave W is output from the unit 15, and the source gas G in the chamber 11 is irradiated with the microwave W. At this time, for example, the source gas G is irradiated with the microwave W with the waveform shown in FIG. 2 while periodically changing the output intensity of the microwave W. At this time, in order to produce an amorphous carbon film having a predetermined band gap energy, the microwave pulse WP is intermittently generated with a duty ratio corresponding to the predetermined band gap energy based on the relationship shown in FIG. The raw material gas G is irradiated.

  Inside the chamber 11, surface wave plasma P is generated by the microwave W irradiated from the microwave generator 15 via the waveguide 14. As a result, the source gas G changes to radicals containing carbon, moves to the surface of the base material B, and is deposited. In this way, an amorphous carbon film having a predetermined band gap energy grows on the base material B.

  Hereinafter, the effect by the manufacturing method and manufacturing apparatus of an amorphous carbon film concerning this embodiment is explained. In manufacturing an amorphous carbon film using a microwave plasma CVD method, the present inventor has found the following matters. That is, as already described, the band gap energy of the amorphous carbon film can be controlled to an arbitrary value by irradiating the source gas G with the microwave W while periodically changing the output intensity of the microwave W. More specifically, an amorphous carbon film having a predetermined band gap energy is obtained by intermittently irradiating the source gas G with the microwave pulse WP at a duty ratio corresponding to the predetermined band gap energy.

  Here, the Example regarding manufacture of an amorphous carbon film is described. In this example, the microwave plasma CVD apparatus 10 shown in FIGS. 1 and 2 was used, and the change in the band gap energy of the amorphous carbon film was examined by changing the duty ratio of the microwave pulse WP. In the present embodiment, the frequency of the microwave W is 2.45 [GHz]. Also, acetylene (flow rate: 20 [ml] per minute) as the carbon source gas, nitrogen (flow rate: 5 [ml] per minute) as the dopant gas, and argon (flow rate: 200 [ml per minute: carrier gas) ]) Were supplied to the chambers 11 respectively. In addition, the pressure inside the chamber 11 when the source gas was introduced was set to 100 [Pa], and the frequency of the microwave pulse WP was set to 500 [Hz]. A quartz substrate and a Si substrate are used as the base material B, and the substrate is not heated.

また、図５に示すグラフＧＡは、本実施例において原料ガスＧに照射したマイクロ波Ｗの波形を示しており、グラフＧＢは、グラフＧＡに示した波形のマイクロ波Ｗを発生させる際に電源ユニット２２（図４参照）から出力された電力波形を示している。 The following Table 1 is a table showing the duty ratio of the microwave pulse WP implemented in the present embodiment and the microwave power at each duty ratio.

A graph GA shown in FIG. 5 shows a waveform of the microwave W irradiated to the source gas G in the present embodiment, and a graph GB shows a power source when the microwave W having the waveform shown in the graph GA is generated. The electric power waveform output from the unit 22 (refer FIG. 4) is shown.

FIG. 6 is a graph showing the correlation between the duty ratio of the microwave pulse WP and the band gap energy of the amorphous carbon film as a result of this example. FIG. 7 is a graph showing the film thickness of each of the prepared amorphous carbon films having respective duty ratios. The numerical values of the plots in FIGS. 6 and 7 are as shown in Table 2 below.

  Referring to FIG. 6 and Table 2, when the duty ratio of the microwave pulse WP is in the range of 20% to 70%, the band gap energy is increased from 0.8 [eV] to 2 as the duty ratio of the microwave pulse WP increases. It can be seen that it decreases monotonically in the range of .6 [eV]. On the contrary, in the range where the duty ratio of the microwave pulse WP is 70% or more and 100% or less, the band gap energy increases monotonously as the duty ratio of the microwave pulse WP increases.

  That is, if the output intensity of the microwave W is periodically changed and the duty ratio is determined according to the desired band gap energy, an amorphous carbon film having the band gap energy can be easily obtained. . Therefore, according to the amorphous carbon film manufacturing method and manufacturing apparatus of the present embodiment, a desired band gap energy can be easily realized.

  In addition, it is estimated that the band gap energy of an amorphous carbon film changes according to the change of the duty ratio of the microwave W for the following reason. That is, by pulsing the microwave W, a large amount of energy can be temporarily given to the source gas G, so that the generated plasma P has a higher energy state (high electron temperature and high ionization degree). Become. On the other hand, between the pulses (when off), the plasma state is not uniform, and an afterglow discharge state that cannot be realized by continuous oscillation occurs. Therefore, when the on / off time ratio (duty ratio) of the microwave W is changed, amorphous carbon films having different band gap energies grow.

  In addition, the amorphous carbon film produced according to the present embodiment is particularly suitable for applications such as solar cells and light receiving elements. For example, a solar cell called a tandem type is configured by optically connecting a plurality of types of pn junction layers having different band gaps. If these layers are formed as amorphous carbon by the method of this embodiment, The band gap of each layer can be easily varied.

  The method and apparatus for producing an amorphous carbon film according to the present invention are not limited to the above-described embodiments, and various other modifications are possible. For example, in the above embodiment, the source gas is irradiated with a microwave pulse having a constant waveform, but the pulse waveform may not be constant, and different waveforms may be arranged with intermittent pauses. Further, it is not necessary to pause the microwave output between pulses, and the microwave output intensity (> 0) at the time of ON and OFF may be set respectively.

  In the example in the above embodiment, as shown in FIG. 6, the band gap energy is minimum when the duty ratio is 70%. However, the duty ratio at which the band gap energy is minimum depends on the film forming conditions and the like. It is thought to fluctuate.

It is side surface sectional drawing which shows the structure of a microwave plasma CVD apparatus as one Embodiment of the manufacturing apparatus of the amorphous carbon film by this invention. It is a figure which shows an example of the waveform of the microwave output from a microwave generation part. It is a figure which shows roughly the relationship between the band gap energy of an amorphous carbon film, and the duty ratio of a microwave pulse. It is a figure which shows an example of a structure of a microwave generation part. Graph GA shows the waveform of the microwave irradiated to the source gas in the example, and graph GB shows the power waveform output from the power supply unit when generating the microwave of the waveform shown in graph GA. Yes. It is a graph which shows the correlation with the duty ratio of a microwave pulse, and the band gap energy of an amorphous carbon film as a result in an Example. It is a graph which shows the film thickness of each amorphous carbon film of each duty ratio created in the example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Microwave plasma CVD apparatus, 11 ... Chamber, 12 ... Source gas source, 13 ... Exhaust means, 14 ... Waveguide, 15 ... Microwave generator, 16 ... Quartz window, 17 ... Slot antenna, 18 ... Base material stage , 19 ... discharge port, 20 ... cooling fan, 21 ... magnetron device, 22 ... power supply unit, 23 ... oscillator, 24 ... modulator, 25 ... oscilloscope, B ... base material, G ... source gas, P ... surface wave plasma, W ... microwave.

Claims (1)

A method for producing an amorphous carbon film as a semiconductor film having a predetermined band gap energy,
The source gas for growing the amorphous carbon film is intermittently irradiated with pulsed microwaves at a duty ratio corresponding to the predetermined band gap energy to generate plasma of the source gas, and on the substrate A method for producing an amorphous carbon film, comprising forming the amorphous carbon film.

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