JP5030101B2 - Formation method of nano diamond / amorphous carbon composite film using plasma CVD method - Google Patents

Description

  The present invention relates to a method for forming a nanodiamond / amorphous carbon composite film using a plasma CVD method.

  In recent years, with the discovery of low-pressure synthesis technology of diamond thin films by chemical vapor deposition (CVD) using plasma, research on the use of diamond in the electronics field as well as silicon has been actively conducted. Diamond has the most excellent electrical characteristics as a single substance, and all applied research in the electronic field uses single crystals with increased integrity, such as silicon, or the use of large grain polycrystals. Is the premise. Normally, diamond obtained by the plasma CVD method has a micrometer particle size, but a diamond having a nanometer particle size can be obtained by controlling the plasma conditions. These nanodiamonds have advantages such as a smooth surface, a small friction coefficient, a low field emission threshold voltage, and good light transmission.

  There are roughly two methods for producing nanodiamond thin films. The first method is to apply a negative bias voltage of several hundred volts to the substrate in hydrogen-methane plasma. The second method is to add a rare gas such as argon with a high concentration (over 90%) to methane. The former is expected to lower the crystallinity of diamond due to ion bombardment induced by the substrate bias, while the latter does not require ion bombardment, and therefore a relatively high crystallinity is expected. Note that the nanodiamond thin film obtained by the above deposition method is a composite film in which nanodiamond particles are dispersed in an amorphous carbon matrix.

Before the formation of such a composite film, the surface of the silicon substrate is usually pretreated in order to improve the wettability of the surface of the silicon substrate (introducing nucleation sites). Conventionally, there are two types of pre-processing. The first pretreatment method is a method of carbonizing the surface of a silicon substrate as disclosed in, for example, Patent Document 1 (Japanese Patent Laid-Open No. 7-89793). The second pretreatment method is a method of scratching the surface of a silicon substrate using diamond particles as disclosed in Patent Document 2 (Japanese Patent Laid-Open No. 2005-41718).
JP-A-7-89793 (Claims 1 and 2) Japanese Patent Laying-Open No. 2005-41718 (column [0029])

  According to the inventor's research, the first pretreatment method for performing carbonization is effective for forming a nanodiamond / amorphous carbon composite film when methane is used as a main constituent raw material gas. It has been found that it is not effective when other rare gases such as gas are used. The second scratch treatment is also effective when methane is used as the main constituent raw material gas, but is not effective when other rare gases such as acetylene gas are used. Patent Document 2 also describes that acetylene can be used as the main constituent raw material gas. However, sufficient nanodiamonds can be obtained even when acetylene is actually used as the main constituent raw material gas and deposited for a long time. It is difficult to form an amorphous carbon composite film.

  An object of the present invention is to provide a method for forming a nanodiamond / amorphous carbon composite film using a plasma CVD method that makes it possible to reliably form a nanodiamond / amorphous carbon composite film using acetylene as a source gas. It is in.

  Another object of the present invention is to provide a method for forming a nanodiamond / amorphous carbon composite film using plasma CVD that makes it possible to form a nanodiamond / amorphous carbon composite film in a short time using acetylene as a source gas. It is to provide.

In the method for forming a nanodiamond / amorphous carbon composite film using the plasma CVD method of the present invention, the surface of a substrate (a silicon single crystal substrate, a silicon substrate, a Ti substrate, a Mo substrate, etc.) that can be carbonized in the pretreatment is firstly obtained. Is carbonized to form a carbonized layer, and then the surface of the carbonized layer is scratched using diamond particles. Then, a nanodiamond / amorphous carbon composite film is formed on the surface of the carbonized layer subjected to scratch treatment by plasma CVD using acetylene as a source gas. When carbonization treatment and scratch treatment are performed in the pretreatment as in the present invention, a silicon carbide layer in which a number of fine grooves are formed on the surface of the carbonization treatment layer subjected to the scratch treatment, and these A surface state in which diamond particles for scratch treatment remain inside the groove is formed. If such a surface state is formed, it is considered that at the beginning of the film formation by the plasma CVD method, the diamond particles remaining in the grooves are used as nuclei to start the film formation. When film formation is started from the inside of the groove, it is considered that a film is further formed so as to fill the groove thereafter. In such a state, a part of the film formed in the groove serves as an anchor, and the film surely grows thereafter. When acetylene is used as the source gas, the carbon supersaturation degree is high and the wettability of the substrate surface is good only by performing the above-described carbonization treatment, but diamond nuclei are hardly generated and film formation is hardly started. . Further, when only the scratch treatment using diamond particles is performed without carbonization, the remaining diamond particles become nuclei, and a film is partially formed from the nuclei. However, the situation around the remaining diamond particles is not always high in carbon supersaturation and good wettability when acetylene (C ₂ H ₂ ) is used as the source gas. Therefore, although the film partially grows, the film does not grow on the entire substrate surface. For this reason, the present invention can sufficiently use acetylene as a source gas as compared with the conventional method.

The method of carbonization treatment is arbitrary, but if carbonization treatment is performed using methane plasma, the surface of a substrate such as a silicon single crystal substrate can be carbonized reliably in a short time. In the carbonization treatment using methane plasma, methane plasma is generated by applying a high-frequency voltage from the waveguide to the gas in a methane (CH ₄ ) gas atmosphere. Then, a silicon carbide layer having a thickness of 10 angstroms to 300 angstroms is formed on the surface of a substrate such as a silicon single crystal substrate by high frequency discharge of methane plasma, and an amorphous carbon layer is formed on the silicon carbide layer. The lower limit value and the upper limit value of the film thickness of the silicon carbide layer are determined from experiments to ensure that a necessary amount of the silicon carbide layer remains even after the subsequent scratch treatment. Below the lower limit of this range, almost no silicon carbide layer remains after the scratch treatment. Above the upper limit of this range, a long scratch process is required. Further, when the amorphous carbon layer is formed, it is possible to prevent the silicon carbide layer from being excessively shaved by the subsequent scratch treatment. For this reason, the amorphous carbon layer preferably has a thickness of 1 μm to 10 μm. If the thickness of the amorphous carbon layer is smaller than the lower limit value, the silicon carbide layer is excessively shaved. If the thickness is larger than the upper limit value, only the scratch processing time is increased. The thickness of the amorphous carbon layer is determined by the average particle size of the diamond particles used in the scratch treatment and the time of the scratch treatment. As the average particle size of diamond particles increases, the thickness of the amorphous carbon layer needs to be increased, and as the time for scratching increases, the thickness of the amorphous carbon layer needs to be increased.

  For example, the scratch treatment is performed by applying a suspension of diamond particles to the surface of the amorphous carbon layer and applying ultrasonic vibration to the diamond suspension to remove most of the amorphous carbon layer by the diamond particles and carbonizing. The silicon layer may be scratched (many fine grooves are randomly formed on the surface of the silicon carbide layer). By using such a method, the scratch process can be performed easily and in a short time.

  When using the plasma CVD method to form a nanodiamond / amorphous carbon composite film in a short time and reliably using a source gas in which argon is added so that the concentration is 70% or more in acetylene. Can do. If the argon concentration is lower than 70%, the degree of carbon supersaturation is significantly reduced, and the diamond particle size increases to the micrometer order. Conversely, increasing the argon concentration decreases the film deposition rate, so the upper limit of this concentration is determined by the deposition rate.

  The nanodiamond / amorphous carbon composite film produced using the method of the present invention has a stable polymer-like structure having a high hydrogen density in the film and having etching resistance.

  According to the present invention, when acetylene is used as a source gas, a nanodiamond / amorphous carbon composite film can be reliably formed.

  Embodiments of the present invention will be described below.

  Here, FIG. 1 shows a configuration of a bell jar type microwave CVD apparatus which is a typical diamond film manufacturing apparatus. The microwave CVD apparatus 1 includes a gas introduction tube 3, a gas discharge tube 5, a reaction vessel 8 surrounded by a quartz tube 7, and a base 9. In order to generate plasma in the quartz tube 7, a microwave is input from a microwave power source (not shown) via the waveguide 10, and the microwave is radiated to the upper portion of the reaction vessel 8 via the antenna 11. The A silicon single crystal substrate 13, which can be easily obtained as a carbonizable substrate, is placed on the base 9. When microwaves are incident on this apparatus, ball-shaped plasma having a diameter of about 5-10 cm can be generated. The substrate 13 is heated by radiation from the plasma, but the temperature can be controlled by the base 9 having both water cooling and a heating mechanism. The temperature of the substrate 13 can be measured by a radiation thermometer (not shown).

  A hydrogen gas supply tank, an acetylene gas supply tank, and an argon gas supply tank are disposed upstream of the gas introduction pipe 3.

Hereinafter, an example of a method for producing a nanodiamond / amorphous carbon composite film on a silicon single crystal substrate 13 by a gas phase reaction will be described with reference to FIG. The crystal orientation of the silicon single crystal substrate 13 used here is (100). First, when the diamond / amorphous carbon composite film is formed on the substrate 13, the surface of the substrate 13 is carbonized to form a carbonized layer. In this example, carbonization was performed using a plasma CVD apparatus. In the carbonization treatment using methane plasma, hydrogen-diluted methane (CH ₄ ) gas having a volume ratio of 0 to 50% is used as the gas, the gas pressure is 0.1 to 100 Torr, and the substrate temperature is 700 to 1000 ° C. Carbonization treatment was performed by exposing the formed plasma to a substrate bias of 0 to -50 V for 30 to 60 minutes. If the substrate bias is 0V, a normal carbonization process is performed. When a negative bias is applied, carbonization can be performed in a shorter time, and the thickness of the silicon carbide layer is increased. As a result, a silicon carbide layer having a thickness that can withstand scratching can be easily obtained.

  FIG. 3B shows an example of a cross-sectional photograph of the carbonized layer formed on the surface of the substrate 13 in this way. As shown in FIG. 3B, a silicon carbide layer (SiC layer) of 10 angstroms to 300 angstroms and a silicon carbide layer (SiC layer) are formed on the surface of the silicon single crystal substrate (Si substrate) by high frequency discharge of methane plasma. ) Is formed on the amorphous carbon layer. When such an amorphous carbon layer is formed, it is possible to prevent the silicon carbide layer from being excessively shaved by subsequent scratch treatment. For this reason, the amorphous carbon layer preferably has a thickness of 1 μm to 10 μm. This carbonization treatment increases the degree of supersaturation of the surface of the substrate 13 shown in FIG. FIG. 3 (A) shows the result of evaluating the carbonized layer formed by the carbonization by the Raman spectrum. From this evaluation result, it can be seen that two peaks indicating amorphous carbon appear in the spectrum.

  Returning to FIG. 2, after the carbonization treatment, a scratch treatment using diamond particles is performed. This scratch treatment was performed based on the recognition that the presence of diamond particles on the surface of the substrate 13 can increase the nucleation density of diamond and facilitate the formation of a gas phase synthetic diamond film. First, a diamond suspension (or diamond slurry) is applied to the surface of the substrate 13, and then the diamond suspension is subjected to ultrasonic treatment to vibrate the diamond particles in the diamond suspension finely. went. Specifically, the substrate was placed in a suspension of diamond particles (particle diameter 100 to 1000 nm cluster diamond) diluted with an ethanol solution. Then, the substrate 13 was subjected to ultrasonic vibration for 10 to 60 minutes, and the suspension of the diamond particles on the surface was made into a uniform application state. After finishing this scratch treatment, the surface was cleaned with an ethanol solution as shown in FIG.

Almost no amorphous carbon formed by carbonization treatment remains on the surface of the substrate 13 after the surface cleaning. A large number of grooves having a depth of 100 nm to 1 μm are formed so as to extend from the surface of the silicon carbide layer to the inside of the surface of the substrate 13. In addition, a plurality of diamond particles used in the scratch treatment remain in a state where a part of the plurality of diamond particles has been encroached inside the numerous grooves. When such a surface state is formed, at the beginning of film formation using acetylene as a source gas by a later plasma CVD method, the diamond particles remaining in the grooves are used as nuclei to form a film. It is thought to start. When film formation is started from the inside of the groove, it is considered that a film is further formed so as to fill the groove thereafter. After that, a part of the film formed in the groove serves as an anchor, and thereafter the film grows reliably. In the case of using acetylene as a source gas, the carbon supersaturation degree is high and the wettability of the substrate surface is good only by performing the carbonization treatment described above, but diamond nuclei are hardly generated and film formation is hardly started. . Further, when only the scratch treatment using diamond particles is performed without carbonization, the remaining diamond particles become nuclei, and a film is partially formed from the nuclei. However, the situation around the remaining diamond particles is not always high in carbon supersaturation and good wettability when acetylene (C ₂ H ₂ ) is used as the source gas. Therefore, although the film partially grows, it is not formed on the entire substrate surface. These phenomena have been confirmed by the inventors' experiments. Therefore, in the present invention, carbonization treatment and scratch treatment are used in combination as pretreatment when acetylene is used as the source gas.

  A diamond / amorphous carbon composite film using a microwave CVD method was formed on the substrate subjected to such pretreatment. First, the substrate 13 pretreated as described above was placed on the base 9, and then the inside of the chamber was evacuated by a vacuum pump (not shown), and the inside of the chamber was set to about 100 Torr. And acetylene gas was used as source gas, and 53-94 vol. % Argon gas and 5-46 vol. % Hydrogen gas was added from the gas supply port 3. And the board | substrate 13 was heated to the temperature of 550-900 degree | times.

  Next, a microwave was applied to generate plasma on an 800 W ball having a diameter of about 5 to 10 cm inside the apparatus. The film formation time was about 1 hour. This film formation time is shorter than that in the case where the film is formed by performing only the scratch treatment, and is at a level where practical use is possible. In this way, a nanodiamond / amorphous composite film having a diamond particle diameter of 15 to 25 nm and a film thickness of 1 to 2 μm was obtained on the entire surface of the substrate 13.

Hereinafter, the advantages of using acetylene as a source gas will be described by comparing the case where methane is used as the source gas and the embodiment of the method of the present invention (when acetylene is used). FIG. 4 shows the relationship between the emission intensity of C ₂ (Swan band: 5165Å) and the argon concentration in Ar / H ₂ / CH ₄ and Ar / H ₂ / C ₂ H ₂ plasmas. From this figure, it is understood that the acetylene raw material emits C ₂ about three times stronger, and a lot of active C ₂ is generated. The main process for generating C ₂ from acetylene is C ₂ H ₂ + Ar → C ₂ + H ₂ + Ar (reaction with Ar), whereas in methane, C ₂ H _{2 is} reacted with Ar or metastable Ar. And finally C ₂ is formed by reaction with Ar. Meanwhile the main process _{of C 2} disappears is _{C 2 + H 2 → C 2} H + H ( reaction with _{H 2).} Therefore, it can be seen that an increase in the added argon concentration (decrease in the hydrogen concentration) increases the density of C ₂ due to the decrease in the annihilation rate in addition to the increase in the generation rate, which is consistent with the measurement trend of the emission intensity.

FIG. 5 shows Raman spectra of thin films obtained by Ar / H ₂ / CH ₄ and Ar / H ₂ / C ₂ H ₂ plasmas. In the case of methane, the nano particle size was obtained at an argon concentration of 94% or more, but the diamond peak is hidden by the amorphous “D” peak and is unclear. In the case of acetylene, the nano particle size was obtained at a lower argon concentration (71% or more) than methane, but the amorphous “D” peak intensity decreased and a diamond peak appeared. A slight peak of polyacetylene appears and an increase in the hydrogen concentration in the film is expected.

Next, FIG. 6 shows a typical FTIR spectrum corresponding to two gas systems. Absorption peaks corresponding to C—H bonds in the amorphous layer are present, and peaks at 2850, 2875, and 2920 cm ⁻¹ are stretches of sp ³ —CH ₂ , sp ³ —CH ₃ , and sp ³ —CH ₂ , respectively. It depends on the mode. The film obtained with acetylene has a higher overall absorption intensity and a higher hydrogen density in the film, which is consistent with the results of Raman scattering. From the above, it can be seen that when acetylene is used as a precursor, an increase in the diamond component is effective by suppressing the formation of the amorphous layer, and a stable polymer structure is formed in the amorphous layer by an increase in the hydrogen density in the film.

In the above embodiment, a silicon single crystal substrate is used as a substrate that can be carbonized. However, the substrate is not limited to a silicon single crystal substrate, but a silicon substrate, a Ti (titanium) substrate, a Mo (molybdenum) substrate, or an Nb (niobium) substrate. Even if a Zr (zirconium) substrate, a W (tungsten) substrate, a V (vanadium) substrate, an Hf (hafnium) substrate, or the like is used, the same result as in the above embodiment can be obtained. As a representative example of the metal substrate, test results performed using a Ti substrate and a Mo substrate will be described. The diamond film manufacturing apparatus used in the test is the same as the bell jar type microwave CVD apparatus shown in FIG. The method for producing the nanodiamond / amorphous carbon composite film on the Ti substrate and the Mo substrate by gas phase reaction is the same as the production process shown in FIG. That is, when the diamond / amorphous carbon composite film is formed on the Ti substrate and the Mo substrate, the surface of the substrate is carbonized to form a carbonized layer. Carbonization was performed using methane plasma. In the carbonization treatment using methane plasma, hydrogen-diluted methane (CH ₄ ) gas having a volume ratio of 0 to 50% is used as the gas, the gas pressure is 0.1 to 100 Torr, and the substrate temperature is 700 to 1000 ° C. Carbonization treatment was performed by exposing the formed plasma to a substrate bias of 0 to -50 V for 30 to 60 minutes.

  After the carbonization treatment, a scratch treatment using diamond particles was performed. First, a diamond suspension (or diamond slurry) is applied to the surface of the substrate, and then the diamond suspension is subjected to ultrasonic treatment to vibrate the diamond particles in the diamond suspension and scratching. It was. Specifically, the substrate was placed in a suspension of diamond particles (particle diameter 100 to 1000 nm cluster diamond) diluted with an ethanol solution. Then, the substrate 13 was subjected to ultrasonic vibration for 10 to 60 minutes, and the suspension of the diamond particles on the surface was made into a uniform application state. After the scratch treatment, the surface was cleaned with an ethanol solution.

  Next, a diamond / amorphous carbon composite film using a microwave CVD method was formed on the substrate subjected to such pretreatment. First, the Ti substrate and the Mo substrate pretreated as described above were placed on the base 9 in FIG. 1, and then the inside of the chamber was evacuated by a vacuum pump (not shown) to make the inside of the chamber about 100 Torr. And acetylene gas was used as source gas, and 53-94 vol. % Argon gas and 5-46 vol. % Hydrogen gas was added from the gas supply port 3. And the board | substrate 13 was heated to the temperature of 550-900 degree | times.

  Next, a microwave was applied to generate plasma on an 800 W ball having a diameter of about 5 to 10 cm inside the apparatus. The film formation time was about 1 hour. In this way, a nanodiamond / amorphous composite film having a diamond particle diameter of 15 to 25 nm and a film thickness of 1 to 2 μm was obtained on the entire surface of the Ti substrate and the Mo substrate.

FIG. 7 shows a Raman spectrum of a thin film obtained by Ar / H ₂ / C ₂ H ₂ plasma. As can be seen from a comparison between FIG. 5 and FIG. 7, a diamond peak appears near the amorphous “D” peak when using either the Ti substrate or the Mo substrate. In the case of the Ti substrate, the nano particle size was obtained at an argon concentration of 70% or more. In the case of the Mo substrate, the nano particle size was obtained at an argon concentration of 70% or more.

  In addition, if the method of the present invention is used, even if a substrate capable of carbonization such as other silicon substrate, Nb substrate, Zr substrate, W substrate, V substrate, Hf substrate, etc. is used, acetylene is used as the source gas. In, a nanodiamond / amorphous carbon composite film can be formed.

It is a figure which shows the structure of the bell jar type | mold microwave CVD apparatus which is a typical manufacturing apparatus of a diamond film. FIG. 3 is a diagram illustrating an example process of an embodiment of the method of the present invention. (A) is a figure which shows the evaluation result by the Raman spectrum of the amorphous carbon formed by carbonization, (B) is an example of the cross-sectional photograph of a carbonization process layer. It is a diagram showing a ratio of C ₂ emission intensities of the two gas system of methane and acetylene. It is a figure which shows the comparison of the Raman spectrum of the film | membrane obtained in two gas systems of methane and acetylene. It is a figure which shows the comparison result of the FTIR spectrum of the film | membrane obtained in two gas systems of methane and acetylene. It is a figure which shows the comparison of the Raman spectrum of the film | membrane obtained when the Ti board | substrate and Mo board | substrate are used as a board | substrate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Microwave CVD apparatus 3 Gas introduction pipe 5 Gas exhaust pipe 7 Quartz tube 8 Reaction vessel 9 Base 11 Antenna 13 Silicon single crystal substrate

Claims (8)

A method of forming a nanodiamond / amorphous carbon composite film using a plasma CVD method,
Carbonizing the surface of the silicon single crystal substrate to form a carbonized layer comprising a silicon carbide layer and an amorphous carbon layer formed on the silicon carbide layer on the surface of the silicon single crystal substrate ;
Thereafter, most of the amorphous carbon layer is removed using diamond particles on the surface of the carbonized layer , and the silicon carbide layer is scratched, and the diamond particles are formed in the grooves formed by the scratch processing. Forming a residual surface condition,
A nano diamond / amorphous carbon composite film is formed by plasma CVD using acetylene as a source gas on the surface of the carbonized layer subjected to the scratch treatment. A method for forming an amorphous carbon composite film. A method of forming a nanodiamond / amorphous carbon composite film using a plasma CVD method,
Carbonizing the surface of the substrate that can be carbonized to form a carbonized layer comprising a carbonized layer and an amorphous carbon layer formed on the carbonized layer on the surface of the substrate ;
Thereafter, most of the amorphous carbon layer is removed using diamond particles on the surface of the carbonized layer, and the carbonized layer is scratched, so that the diamond particles remain in the grooves formed by the scratch processing. Formed surface state,
A nano diamond / amorphous carbon composite film is formed by plasma CVD using acetylene as a source gas on the surface of the carbonized layer subjected to the scratch treatment. A method for forming an amorphous carbon composite film. 3. The method for forming a nanodiamond / amorphous carbon composite film using plasma CVD according to claim 1 or 2, wherein the carbonization is performed using methane plasma. The carbonization is performed using methane plasma,
Wherein in the carbonizing process using methane plasma, methane plasma generated in a methane gas atmosphere, the silicon carbide layer and the carbon of the surface 10 angstroms to 300 angstroms of the silicon single crystal substrate by a high frequency discharge of the methane plasma forming method of nanodiamond / amorphous carbon composite film using the plasma CVD method according to claim 1, characterized in that to form the amorphous carbon layer on the silicon layer. The method for forming a nanodiamond / amorphous carbon composite film using the plasma CVD method according to claim 4 , wherein the amorphous carbon layer has a thickness of 1 μm to 10 μm. In the scratch treatment, a diamond particle suspension is applied to the surface of the amorphous carbon layer, and ultrasonic vibration is applied to the diamond suspension to remove most of the amorphous carbon layer by the diamond particles. The method of forming a nanodiamond / amorphous carbon composite film using the plasma CVD method according to claim 1 , wherein the silicon carbide layer is scratched.   In the scratch treatment, a diamond particle suspension is applied to the surface of the amorphous carbon layer, and ultrasonic vibration is applied to the diamond suspension to remove most of the amorphous carbon layer by the diamond particles. The method for forming a nanodiamond / amorphous carbon composite film using the plasma CVD method according to claim 2, wherein the carbonized layer is scratched.   The plasma CVD method is a microwave plasma CVD method using a source gas in which argon is added to acetylene so as to have a concentration of 70% or more. Nanodiamonds using the plasma CVD method according to claim 1 or 2 A method for forming an amorphous carbon composite film.