JP5240978B2 - Method for producing diamond-like carbon film - Google Patents

Description

  The present invention relates to a method for producing a diamond-like carbon film.

Diamond Like Carbon (hereinafter also referred to as “DLC”) is a quasi-similar material that has properties similar to diamond rather than graphite, such as high hardness, transparency, electrical insulation, and corrosion resistance. It is a stable hard amorphous carbon. Researched since 1970, it has been found that DLC films with various properties can be obtained by the deposition method, but the definition is still unclear. There are a variety of applications that make use of the characteristics of DLC. Industrial applications include cutting tools for difficult-to-cut materials such as aluminum, precision molds such as lenses that require demolding, HDD magnetic heads, and protective films for disks. Automotive parts that make use of tribological (lubricating) characteristics and coatings on the inner wall of plastic bottles that make use of gas barrier properties are attracting attention and are being put to practical use. In addition, DLC is regarded as a next-generation semiconductor, and development utilizing the property of making it a variable bandgap semiconductor is also expected.

  As a current manufacturing method, a high-frequency plasma method and an ionized vapor deposition method are mainly used. In the high-frequency plasma method, methane gas is used as a raw material, and film formation is performed using a capacitively coupled plasma electrode. It is said that the film quality is smooth because it has a lot of hydrogen in the film, and it has excellent smoothness and a small coefficient of friction, but its hardness is slightly low.

On the other hand, in the ionized vapor deposition method, benzene is used as a raw material, and ionized hydrocarbons are accelerated by direct current. Therefore, hydrogen is blown out from the film and the film becomes hard, but it is said that the surface roughness is slightly deteriorated.

For this reason, the high-frequency plasma method is suitable for sliding applications, and the ionized vapor deposition method is used for dies and blades. However, depending on the application, the point considered to be these disadvantages is not a big problem, and many products are already used in mass production. In particular, when the base material is an insulator, the high-frequency plasma method is frequently used because it hardly causes charge-up.

  Note that a method for forming a DLC film by a high-frequency plasma method is described in Patent Document 1, for example. However, in the conventional DLC film forming methods such as the high-frequency plasma method and the ionization vapor deposition method, in order to form the DLC, the vicinity of the object to be formed must be in a high vacuum environment, which requires a large amount of equipment. Moreover, the productivity was not high.

Regarding the related art, Patent Document 2 describes that a hot filament deposition reactor is used to form a pseudo diamond film. This hot filament deposition reactor is also used in a vacuum atmosphere. Since it is a membrane, there is a problem that the equipment becomes large and the productivity is not high. Further, Patent Document 3 describes that diamond particles are formed by microwave plasma CVD using methane gas as a raw material gas. Since this microwave plasma CVD is also a film formation in a vacuum atmosphere, The equipment is large and the productivity is not high. Furthermore, Patent Document 4 describes that graphite or diamond particles are generated on the surface of a material to be processed by a hot filament CVD method. This hot filament CVD method is also used for film formation in a vacuum atmosphere. Therefore, the equipment becomes large and the productivity is not high.
JP-A-2005-002377 Japanese Patent No. 2939272 JP 2002-281991 A JP 2004-288460 A

As mentioned above, most conventional DLC fabrication methods use plasma under a low pressure of about 1 to 10 Pa, that is, a vacuum device is required. This is an issue for expanding and developing applications.

Thus, several years ago, the present inventors succeeded in trying to manufacture DLC with an inexpensive and small self-made device that does not require a vacuum device. Although this seems to have further expanded the possibilities of DLC, there are many problems such as low adhesion between the film and the substrate and the burden on the device due to the temperature required for this fabrication method. In addition, information on the produced film is not sufficient.

In the present invention, through experiments, changes in the structure of a film produced under various production conditions are analyzed and evaluated using Raman spectroscopy or the like, and more practical and excellent conditions for producing a DLC film are examined and proposed.

  Accordingly, the present invention has been made in view of the above problems, and its object is to produce DLC without using a catalyst, and thereby to produce a diamond having a smoother surface that is not affected by uneven deposition of the catalyst. The object is to provide a method for producing a like carbon film.

In order to achieve the above object, the invention according to claim 1 is directed to heating the substrate containing a sapphire single crystal to 1000 ° C. or higher in a normal pressure hydrocarbon gas-containing atmosphere without a catalyst. It has the process of forming the diamond-like carbon film by thermal decomposition of hydrocarbon gas on the surface.

The invention according to claim 2 is the method for producing a diamond-like carbon film according to claim 1, characterized in that the heating time is 60 minutes or more.

Invention of Claim 3 is a manufacturing method of the diamond-like carbon film of Claim 1 or 2, Comprising: After heating time progresses, supply of hydrocarbon gas is stopped, and gas for post-processing is supplied The method further includes a step of gradually lowering the temperature .

The invention of claim 4 is a method for producing a diamond-like carbon film of any one of claims 1 to 3, a hydrocarbon gas, characterized in that it is a gas containing propane.
A fifth aspect of the present invention is a method for producing a diamond-like carbon film according to the fourth aspect of the present invention, wherein hydrogen gas is mixed with hydrocarbon gas.

  According to the present invention, a diamond-like carbon film is formed on the surface of a substrate by thermal decomposition of the hydrocarbon gas by heating the substrate containing the sapphire single crystal to 1000 ° C. or higher in a hydrocarbon gas-containing atmosphere. Therefore, a smoother film that is not affected by uneven deposition of the catalyst can be produced.

(Embodiment)
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a film forming apparatus according to this embodiment.
In this film forming apparatus, a heating unit 1b is provided in the heating apparatus 1a, and a substrate S on which a film is to be formed is attached to a support device 1c for the substrate S in the heating apparatus 1a. The heating means 1b receives electric power from the power source 4 and heats the inside of the heating device 1a, and includes a heating wire, an induction heating device, an infrared irradiation device, and the like.

  A hydrocarbon gas-containing gas is continuously supplied from the gas supply source 2 to the heating device 1a at a predetermined flow rate. The gas flow rate is controlled by the flow rate control device 3. The flow control device 3 includes a flow meter, a control device that maintains the flow rate constant based on flow data from the flow meter, and a valve that adjusts the flow rate according to a command from the control device. This flow rate control can be omitted when the flow rate of the gas supplied from the gas supply source 2 is determined in advance.

  A temperature control device 5 is provided in the heating device 1a. The temperature control device 5 includes a thermometer and a control device that maintains the inside of the heating device at a constant temperature based on temperature data from the thermometer, and adjusts electric power according to a signal from the control device. The temperature in the heating device 1a is kept constant. In addition, the temperature adjustment and the temperature maintenance control in the heating device 1a can be simply performed manually, and in this case, the temperature control device 5 can be omitted.

(Experimental device)
Unlike the film formation by the plasma CVD apparatus and the film formation by the PLD method, there is no ready-made experimental apparatus dedicated to it. Therefore, in this experiment, the experimental apparatus was assembled and used by itself. The materials used to assemble are as follows. The assembled device is shown in FIG.
・ Quartz tube (length: 800mm, inner circle diameter: 18mm, outer circle diameter: 20mm)
・ Kanthal wire diameter 1.0 mm Made by Niraco Co., Ltd. ・ 2 tubes (for gas introduction and exhaust)
・ Novix (to eliminate the gap between the silicon stopper and the quartz tube)
・ Silicon stopper
・ Five heat insulation blocks ・ Slide transformer (voltage source)
・ Alumina glass wool (for heat insulation)

As shown in FIG. 2, a Kanthal wire 11b as a heating wire is wound around an outer peripheral surface of a quartz tube 11a serving as a heating device, and this Kanthal wire 11b is connected to a slide transformer 14 as a power source. Both end faces are connected to gas introduction and discharge tubes, respectively, and an Ar—CH ₄ mixed gas is continuously introduced from one tube into the quartz tube 11a, and the used gas is discharged from the other tube. A thermal insulation alumina glass wool is wound around the Kanthal wire 11b, and the apparatus is placed on a heat insulation block, thereby completing the experimental apparatus. The substrate S is placed in the quartz tube 11a and heated while flowing a gas.

(Samples and raw materials)
In this experiment, Ar—CH ₄ mixed gas (Ar 90%) was used as the hydrocarbon gas-containing gas.
, CH ₄ 10%), Ar—C ₃ H ₈ mixed gas (Ar 90%, C ₃ H ₈ 10%), a p-type Si (100) wafer, Al ₂ O ₃ (0001) as a substrate for film formation A wafer was used, and an aqueous nickel nitrate solution was used as a catalyst.

Nickel nitrate was used as a catalyst on the Si substrate. The amount suitable for use as a catalyst was about 1/10 of the number of Si atoms (about 10 ¹⁵ ) on the surface of the Si substrate 10 mm × 10 mm, and about 10 ¹⁴ nickel atoms were placed on the substrate. The calculation formula and work are as follows.
1. The average surface density of the Si substrate 10 mm × 10 mm was calculated.
Si atoms: 28.09, specific gravity: 2.33g / cm ³
2.33 ÷ 28.01 × (6.02 × 10 ²³ ) ≒ 4.99 × 10 ²² / cm ³ → number of Si atoms per 1 cm ³
(4.99 × 10 ²² ) ^2/3 ≒ 1.36 × 10 ¹⁵ / cm ² → Number of Si atoms per 1 cm ²
2. The concentration when the Ni nitrate aqueous solution xl placed on the Si substrate contains 1/10 Si atoms of Ni atoms was set to amol / l, and the relational expression was obtained.
From 1, 1/10 Si atoms = 1.36 x 10 ¹⁴
1.36 × 10 ¹⁴ ÷ (6.02 × 10 ²³ ) ≒ 2.26 × 10 ^-10 mol
∴ax = 2.26 × 10 ^-10 mol… (A)
3. Since the nickel nitrate aqueous solution was 0.128ml on the Si substrate 10mm x 10mm, the required concentration of nickel nitrate was calculated from the formula (A).
a = 2.26 × 10 ^-10 ÷ (0.128 × 10 ^-3 ) ≒ 1.76 × 10 ^-6 mol / l
Four. Nickel nitrate was dissolved in distilled water and diluted several times to prepare an aqueous solution having the concentration determined in Procedure 3.
Five. Drop 0.128 ml of the aqueous solution prepared in Step 4 on the ultrasonically cleaned Si substrate,
Water was evaporated and deposited at about 100 ° C. using PLATE.
The aqueous solution prepared here was also used on an Al ₂ O ₃ substrate.

(Experiment 1)
Methane (CH ₄ ) is decomposed into carbon and hydrogen as shown in the following equation by obtaining energy called heat.
CH ₄ → C + 2H ₂
The decomposed carbon takes various bond forms such as sp ² bond (graphite bond) and sp ³ bond (diamond bond), and it is considered that a DLC film can be produced by depositing these on the substrate. However, previous studies have shown that methane decomposition using only thermal energy is difficult due to temperature limitations in this experimental system. In addition, it has been reported that by using a catalyst, methane decomposition is promoted and a DLC film can be produced at a temperature that could not be produced only by thermal energy. Therefore, in Experiment 1, a reproduction experiment of the previous study is first performed.

(catalyst)
First, a catalyst is a substance that promotes a specific chemical reaction, and it continues to change during operation regardless of solid, gas, liquid, and form, but consumption and regeneration are repeated before and after the reaction. This means that there is no net increase or decrease. It may also refer to the action of the catalyst (catalysis). The catalyst forms a reaction intermediate with the reactant, thereby creating another reaction pathway with low activation energy required for the reaction. Thereby, reaction advances rather than the case where a catalyst does not exist. However, when the reaction is in equilibrium, the composition ratio is the same as when there is no catalyst.

(Nickel nitrate aqueous solution)
In this experiment, nickel nitrate was used as an example of the catalyst. When nickel nitrate is written in chemical formula, it becomes Ni (NO ₃ ) ₂ · 6H ₂ O, and the formula weight is 290.8. It is very soluble in water, and its solubility in water is 94.2g / 100g (25 ° C). It is also soluble in alcohol. When storing it, it is necessary to seal it in a place with low humidity. The characteristic is an endothermic reaction, and when used as a catalyst, carbon tends to be deposited on the surface. When a saturated hydrocarbon such as methane is directly decomposed using nickel nitrate as a catalyst, it is considered to be a reaction suitable for this experiment because it produces only hydrogen and carbon.

(Experiment)
A Si sample was introduced into the experimental apparatus, and an Ar—CH ₄ mixed gas was flowed at a flow rate of 200 ml / min. After judging that the quartz tube was filled with Ar—CH ₄ gas, a current was passed through the Kanthal wire using a slide transformer to generate heat. The temperature of the Kanthal wire was raised to 1350 ° C. and heated for 60 minutes. The temperature was measured using an optical pyrometer, and the flow rate was measured using a flow meter. After the experiment, the substrate was taken out from the apparatus and the XPS peak was measured. For comparison, the XPS peak of pure graphite was also measured.

(result)
A glossy film was produced on the part on which the catalyst was placed. The produced film does not break even when it is scratched with tweezers and has a thickness and elasticity that can be seen with eyes, but it seems that the adhesion to the Si substrate is low. Residual stress can be cited as a cause of this low adhesion. The residual stress is a stress inside the thin film that is generated even after the external force or heat is removed, and causes the thin film to crack or peel the film from the substrate. First, temperature is considered as the largest cause of residual stress. In this manufacturing method, film formation is performed in a very high temperature apparatus, so that the substrate and the manufactured film are also in a very high temperature state. After the film formation, residual stress is generated due to the difference in the coefficient of thermal expansion between the produced film and the substrate when cooled to room temperature. This residual stress is said to increase as the film becomes thicker and the hardness increases. Moreover, non-uniform deposition of the catalyst on the substrate can be considered as a means of promoting cracks in the produced film.

FIG. 3 and FIG. 4 show XPS spectra (270 to 300 eV) of carbon 1s electrons of the prepared film and pure graphite carbon, respectively. Moreover, each peak value is shown in FIG. 5, FIG. When FIG. 3 is seen, there are two peaks at 285.4 eV and 283.5 eV, and from the literature values, it seems to be peaks indicating sp ³ bond and sp ² bond, respectively. However, it can be seen from FIG. 4 that the spectrum of pure graphite has peaks at 285.3 eV and 283.8 eV, which are almost the same as the spectrum waveform of FIG. Therefore, it is considered difficult to determine DLC using XPS. From the next experiment, XPS measurement will not be performed, and Raman evaluation, which is most often used for DLC identification, will be performed. The reason why two peaks appear in pure graphite is considered to be a slight difference in binding energy due to two crystal forms (hexagonal graphite structure and rhombohedral graphite structure) existing in graphite. In Experiment 1, the evaluation by Raman spectroscopy is not performed, and it is judged that the film produced from the information of the carbon spectrum obtained from XPS is DLC by comparing the appearance with the film produced in the previous research.

(Experiment 2)
Previous studies have reported that the use of a catalyst accelerates the decomposition of the source gas and allows the production of a DLC film on the Si substrate. In Experiment 1, the reproduction experiment was performed. Therefore, in Experiment 2, a DLC film can be formed on Al ₂ O ₃ as a substrate other than Si under various conditions.

(substrate)
Sapphire single crystal has excellent mechanical strength, chemical stability, optical properties, electrical properties, and thermal conductivity, and is a material that can be replaced by silicon and ceramics in environments where high durability against heat is required. Yes. The main component is aluminum oxide containing 0.1 to 0.2% TiO ₂ and some Fe ₂ O ₃ . The structure of sapphire is shown in FIG.
Details of the sapphire substrate used this time are described below.
・ Production method: Czochralski method
・ Crystal structure: Hexagonal system a = 4.758Å c = 12.992Å
・ Crystal purity: 99.99%
・ Density: 3.98g / cm ³
Melting point: 2040 ° C
・ Thermal expansion coefficient: 7.5 (× 10 ^-6 / ℃)
-Plane orientation: <0001> C-plane
・ Surface gloss: Only on one side ・ Bumps on the surface: <5mm

(thermocouple)
If two different metal wires are connected and their contacts are kept at different temperatures, current flows through the circuit. This phenomenon is called the Seebeck effect. When a potentiometer is inserted and the electromotive force [mV] at this time is measured, the value is determined by the type of two metals and the temperature of both contacts. Therefore, if a constant metal wire is used, and the electromotive force is measured with reference to 0 ° C. and the temperatures at both contacts as various known temperatures, this can be used as a kind of thermometer. ^[13]

(K-type thermocouple (chromel-alumel thermocouple, CA thermocouple))
Chromel and alumel are alloys that are unlikely to oxidize each other and can be used in the range of -200 to 1100 ° C, so they are most often used for high temperature measurements. The thermoelectromotive force change for a change of 1 ℃ is about 0.041mV, and the relationship between temperature and electromotive force is close to a straight line. Since the electromotive force may change when used at a high temperature for a long time, it should be verified from time to time. Since alumel wire is weak and easily cut, it is unsuitable for 1 mmφ or less for regular use above 1000 ° C. When used at high temperatures, the chromel wire is + and the alumel wire is &#8722; and the alumel wire can be easily distinguished by attaching to the magnet.

In this experiment, a chromel-alumel thermocouple was made and used. The components of chromel and alumel are as follows. In the experiment, the potential difference was measured by converting the potential difference by connecting the chromel and alumel terminals to a digital micrometer.
(Chromel: Ni 89.0%, Cr 9.4%, Fe 1.0%, Mn 0.2%) Diameter 0.20mm
(Alumel: Ni 94.0%, Al 2.0%, Si 1.0%, Fe 0.5%, Mn 2.5%) Diameter 0.2mm Made by Nilaco Corporation

(Experiment)
In the same manner as in the Si substrate of Experiment 1, four conditions were prepared by changing the conditions such that the nickel nitrate aqueous solution was deposited on the Al ₂ O ₃ substrate ultrasonically cleaned and not deposited. The sample was then introduced into the experimental apparatus and Ar-CH ₄
The gas was flowed at a flow rate of 200 ml / min. After judging that the quartz tube was filled with Ar—CH ₄ gas, a current was passed through the Kanthal wire using a slide transformer. The temperature of the Kanthal wire was changed to 1300 ° C and 1200 ° C for each sample and heated for 60 minutes. After heating, Ar-CH ₄
While the gas was stopped and the current was gradually lowered, N ₂ gas and H ₂ gas were changed into the experimental apparatus for each sample and flowed at a flow rate of 100 ml / min. The temperature was measured using a chromel and alumel thermocouple, and the flow rate was measured using a flow meter. The conditions of the four samples (samples A to D) described above are summarized and shown below.
Sample A: Nickel nitrate Yes 1200 ° C. at 60 minutes post-deposition N ₂ gas treatment Sample B: Nickel nitrate Yes 1300 ° C. after 60 minutes deposition N ₂ gas treated sample C: Nickel nitrate Yes 1300 ° C. at 60 minutes post-deposition H ₂ gas Processed sample D: No nickel nitrate After deposition at 1300 ° C. for 60 minutes, after treatment with N ₂ gas and the experiment, the substrate was taken out from the apparatus, and each Raman spectrum was measured using a Raman spectrometer. At this time, for comparison, Raman spectra of pure graphite and diamond were also measured with the same spectrometer. The conditions for Raman measurement are shown below.

(Raman spectroscopy analysis conditions)
The analysis apparatus and measurement conditions by Raman spectroscopy are described below.
・ Analyzer Measuring device: JASCO Single Monochromator M50
Grating 1800 / mm
Focal length 500mm
Laser source: Ar ion laser Detector: LNCCD
・ Measurement conditions Laser power: 200Mw
Laser wavelength: 514.5nm
Measurement time: 0.5 seconds Integration count: 100 times Laser incident angle: 0 degrees

(result)
Blackish films were formed on both sides of the Al ₂ O ₃ substrates of all samples A to D. Even if each film is scratched with tweezers, it does not break, and there is a thickness and elasticity that can be seen with eyes, but it seems that the adhesion with the Al ₂ O ₃ substrate is low (the cause of the low adhesion is described above) Street). Also, the color of the film and the smoothness of the surface appear to be different between the smooth surface polished with Al ₂ O ₃ and the rough surface not polished on the back side.

Next, consider the results of Raman spectroscopy. First, the Raman spectra of pure graphite and diamond are shown in FIGS. 7 and 8, respectively. From the spectrum of FIG. 7, it can be seen that the peak of pure graphite is 1599 cm ⁻¹ . When evaluating DLC, this vibration mode of graphite is called G band. In addition, since no peak was observed at the position of the D band (1350 cm ^{-1 in the} literature value) composed of graphite defects, amorphous carbon, and nanoparticles, the measured graphite was pure graphite with no defects. It was confirmed that there was.

Next, it can be seen from the spectrum of FIG. 8 that the peak of pure diamond is 1333 cm ⁻¹ . Since the full width at half maximum is very narrow, it can be said that the crystallinity is very good. Next, Raman spectra of samples A to D produced under different conditions are summarized for each comparison target, and are shown as FIGS. 9, 10, 11, and 12, respectively. The compared samples and purposes are as follows.
Fig. 9: Sample A smooth surface / Sample B smooth surface ⇒ Comparison of membrane structure due to temperature difference (smooth surface)
Fig. 10: Rough surface of sample A / Rough surface of sample B ⇒ Comparison of film structure due to temperature difference (rough surface)
Fig. 11: Sample B / Sample C ⇒ Comparison of membrane structure due to differences in post-processing Fig. 12: Sample D smooth surface / Sample D rough surface ⇒ Can a DLC film be prepared without a catalyst?
From FIG. 9, the spectra of the prepared sample B smooth surface in Sample A smooth surface and 1300 ° C. made at 1200 ° C., a peak in each of 1350 cm ^-1 and 1610 cm ^-1, 1350 cm ^-1 and 1611cm ^-1 Is seen.

Further, from FIG. 10, the spectrum of the sample A rough surface and the sample B rough surface is 1367cm ^-1 and 1616cm ^-1, a peak is observed in 1347Cm ^-1 and 1611cm ^-1. The peak appearing in the vicinity of 1350 cm ^-1 is considered to be a Raman peak in the D band from the literature values. In addition, the peak that appears in the vicinity of 1610 cm ⁻¹ is considered to be a G-band Raman peak shifted to a higher wavenumber of 11 to 17 cm ⁻¹ than the measured value obtained from FIG. Therefore, the films produced on both surfaces of Sample A and Sample B can be judged to be DLC films because they show the characteristics of DLC having two Raman peaks. This means that the Al ₂ O ₃ film produced on the smooth and rough surface is the same DLC film even if it looks different. The surface of the produced DLC film depends on the substrate surface. It can be said that. In addition, comparing the Raman intensity of the D band and G band, the sample A produced at 1200 ° C has almost the same Raman intensity, whereas the sample B produced at 1300 ° C has a stronger G band. It can be seen that it is clearly greater than the intensity of the band. This is thought to be because the decomposition of the source gas progressed as the deposition temperature increased, and the proportion of carbon particles other than graphite constituting the D band increased in the film. And because these particles are partially crystallized at high temperature and the film quality becomes hard, the G band shifts to the high wavenumber side, and there are many things that perform uniform molecular vibration with D band particles, The D band is thought to be as sharp as the G band. However, details of the carbon particles constituting the D band are under investigation. In addition, although no data has been posted this time, no change occurred in the Al ₂ O ₃ substrate with catalyst previously heated at 1150 ° C for 60 minutes, so if the raw material gas is methane, use a catalyst. However, it can be said that a temperature of 1200 ° C or higher is necessary for the production of DLC film.

Next, look at FIG. Than 11, the spectrum of Sample C can be determined that because of its peaks of the same 1350 cm ^-1 and 1599cm ^-1 and the measured values with the literature values, fabricated film on the sample surface is DLC film. Unlike sample B, the Raman intensity of the D band and G band of sample C is almost the same. From this, it can be seen that the film structure changes even if the film is deposited at the same temperature depending on whether the post-treatment is nitrogen or hydrogen. Assuming that the inert gas nitrogen has little effect on the film, let us consider the effect of hydrogen on the film. The most probable thing is that various forms of carbon decomposed by the heat and catalyst that make up the D band, when placed in a hydrogen atmosphere, gained heat energy and flew again with hydrogen. That is. This seems to mean that the carbon particles constituting the D band are chemically unstable and have a weaker binding force than the graphite particles constituting the G band. In addition, sample C does not show a high-frequency shift of the G band as in sample B, and there is a peak at the same position as pure graphite. It was thought that the entire film was softened due to the loss of properties and hydrogen termination instead.

Finally, look at FIG. Shown in FIG. 12 is the Raman spectrum of sample D, a film made of Al ₂ O ₃ without a double-sided catalyst. Spectrum of rough surfaces and smooth surfaces, respectively 1350 cm ^-1 and 1611cm ^-1, it is found to have a peak at 1358cm ^-1 and 1618cm ^-1. These peaks are considered to be the D-band and G-band peaks, respectively, which means that a DLC film could be produced without a catalyst. However, according to previous studies, when this experimental apparatus was used with methane as the raw material gas, it was considered difficult to produce a DLC film without a catalyst at 1300 ° C. Moreover, as mentioned at the outset, the film produced is never brittle. Therefore, what is considered is that Al ₂ O ₃ itself has a catalytic function. So far, no literature has confirmed that Al ₂ O ₃ is a catalyst, but perhaps 0.1-0.2% TiO _{2 in} Al ₂ O ₃
And some Fe ₂ O ₃ is considered to promote methane decomposition as a catalyst. Therefore, when Al ₂ O ₃ is used as a substrate in the future, there is no need to hang the solution on the substrate as in the past, so there is no uneven catalyst deposition on the substrate, and the film cracks. One cause can be avoided. It is also considered advantageous for the low friction property of the DLC film.
In addition, the Raman peak value of D band and G band of the graph of FIGS. 9-12 and its intensity ratio are shown as FIGS. 13-16, respectively.

(Experiment 3)
Experiment 2 shows that when Al ₂ O ₃ is used as a substrate, DLC can be produced without a catalyst unlike Si substrate. This makes it possible to produce a smoother film that is not affected by non-uniform deposition of the catalyst. But there are still problems to be solved. The first is the temperature required for methane decomposition. In order to produce a DLC film by this experimental method, a temperature of 1200 ° C. or higher is required even if a catalyst is used. However, since the melting points of Kanthal wire and quartz tube are 1400 ° C and 1500 ° C, respectively, the production of DLC using methane as the source gas tends to cause damage to the experimental system.

Therefore, in Experiment 3, we tried to make a DLC film using propane instead of methane. Since propane has a lower intermolecular bond energy than methane, it may be decomposed at lower temperatures. The second problem is low adhesion between the produced film and the substrate. This problem is addressed with hydrogen. The film thickness is suppressed by flowing hydrogen gas together with hydrocarbon gas and recombining hydrogen molecules with extra carbon atoms. As a result, the residual stress is reduced, and an improvement in adhesion can be expected.

(propane)
Propane is one of the chain saturated hydrocarbons represented by the chemical formula C ₃ H ₈ . It has a molecular weight of 44, is colorless and heatable, and becomes propanol when oxidized at room temperature with a gas. Propane is one of the components of nature, but unlike other ingredients, propane is heavier than air. It is 1.5 times heavier than the specific gravity of air, and if propane leaks, it will stay on the floor. Liquid propane vaporizes instantaneously at atmospheric pressure. In order to remove heat from the atmosphere during vaporization, the water vapor condenses and produces a white mist.

_Two Al ₂ O ₃ substrates subjected to only ultrasonic cleaning were prepared. Each was introduced into the experimental apparatus and different source gases were allowed to flow. After judging that the inside of the quartz tube was filled with each source gas, a current was passed through the Kanthal wire using a slide transformer to generate heat. The temperature of the Kanthal wire was raised to 1000 ° C. and both samples were heated for 60 minutes. Ar-C ₃ H ₈ after heating
The gas was turned off, and H ₂ gas was flowed at different flow rates while gradually lowering the temperature. The temperature was measured using a chromel-alumel thermocouple, and the flow rate was measured using a flow meter. The different parts of the conditions of the two samples (samples 1 and 2) described above are shown below.
Sample 1: Raw material gas: Ar-C ₃ H ₈ mixed gas 100ml / min
After heating for 60 minutes ... H ₂ gas 100ml / min
Sample 2: Raw material gas: Ar-C ₃ H ₈ mixed gas 100 ml / min + H ₂ gas 35 ml / min
After heating for 60 minutes ... H ₂ gas 35ml / min
After the experiment, the substrate was taken out from the apparatus, and a Raman spectrum was measured using a Raman spectrometer. The measurement conditions by Raman spectroscopy are the same as in Experiment 2. The film was observed with FE-SEM.

(result)
Blackish films were formed on both the Al ₂ O ₃ substrates of Samples 1 and ₂ . Both sides depended on the surface of the Al ₂ O ₃ substrate, and a mirror film was formed on the polished smooth surface, and a rough film was formed on the non-polished surface on the back side. However, sample 1 is a brittle film that seems to break just by touching it with tweezers, whereas sample 2 film does not break even if it is strongly scratched by tweezers, and the adhesion to the Al ₂ O ₃ substrate has been tested so far. 1 and the film produced in Experiment 2 and the film of Sample 1 seem to be clearly different. This is because by mixing hydrogen gas with hydrocarbon gas, which is the raw material for carbon deposition, from the beginning of heating, chemically unstable carbon particles with weak bonding force recombine with hydrogen molecules and do not deposit on the substrate. Therefore, it is considered that the deposition of the entire substrate is completed with an appropriate amount of carbon particles, and the residual stress that seems to be the cause of the decrease in adhesion is reduced.

The results measured by Raman spectroscopy are shown in FIGS. 17 and 18, respectively. Peak 1350 cm ^-1 and 1609cm ^-1 of the spectrum of the smooth surface from FIG. 17, the peak is observed in 1350 cm ^-1 and 1605 cm ^-1 in the spectrum of the rough surface. The peak, a peak at 1350 cm ^-1 and 1614cm ^-1 of the spectrum of the rough surface can be seen in 1350 cm ^-1 and 1612 cm ^-1 in the spectrum of the smooth surface from FIG 18. (FIG. 19, FIG. 20 Raman peak value of D band and G band and intensity ratio (I (D) / I (G) are shown.)
Each peak is considered to represent the G band from the measured value (G band peak: 1598 cm ^-1 ) although it is slightly shifted to the D band from the literature value (D band peak: 1350 cm ^-1 ). Since the characteristics of DLC having both peaks are shown, it can be determined that the films prepared for both samples are DLC.

The cause of the shift of the G band peak to the high wavenumber side is considered to be the hardness of the film described above. The Raman spectrum is caused by the vibrational state of the molecule, and the vibrational energy of the molecule depends on the bonding force between the molecules. Therefore, the shift of the peak of the G band to the high wavenumber side means that the bonding force between crystals is strong, that is, the hardness of the film is increased. Here, when the spectra shown in FIGS. 17 and 18 are compared, the spectrum of sample 2 has a larger G peak shift amount and intensity ratio (I (D) / I (G)) than sample 1, and the D band. It can be seen that the shape of is also sharp. As described at the beginning of this section, this is not only a treatment after heating the hydrogen gas, but also because the raw material is mixed with the soot from the beginning of the heating, so that there are many carbon particles with strong bonding strength that did not recombine with hydrogen. It is considered that the hardness is increased by depositing on the top, and the peaks are sharp even in the D band, which is a collection of defects, due to the uniform molecular vibration of these particles during Raman measurement.

Next, the results by FE-SEM are shown in FIGS. First, as a result of the sample 1 (smooth surface), FIGS. FIG. 21 is an image of the DLC film viewed at 1000 times. Although there are conspicuous particles, it seems to be smooth overall. FIG. 22 focuses on one of the particles present in FIG. 23 and is magnified 10 times. From the scale, it can be seen that it is an aggregate of spherical particles having a diameter of 2.5 μm. FIG. 23 is an enlarged image of the location moved from FIG. From the scale of FIG. 24, which is further magnified 5 times, FIG. 23 shows that spherical particles having a diameter of 500 nm are aggregates. Moreover, it turns out that the particle | grains which are somewhat rugged with a size of 50-100 nm exist so that it may adhere to the particle | grains. In other words, the DLC film of Sample 1 has many smooth portions, but it is considered that uniformity is applied because particles of various sizes are mixed. Next, as a result of the sample 2 (smooth surface), FIGS. FIG. 25 is an image viewed at the same magnification as FIG. 21, but in comparison, it can be said that the number of particles observed is smaller than that of sample 1. Next, FIG. 26 is an image obtained by enlarging the central portion of FIG. By enlarging, we notice the presence of fine particles that are uniform and fairly dense throughout the film. These fine particles are rugged particles having a diameter of 50 to 100 nm from the scales of FIGS. 27 and 28, and the presence and deposition of these particles are greatly involved in improving the adhesion of the film by mixing H ₂ gas. I think.

The results of Raman spectroscopy and FE-SEM are integrated, and the cause of improved adhesion between the fabricated film and the substrate by H ₂ gas mixing is discussed as follows. Probably by mixing H ₂ gas with the source gas, chemically unstable and poorly crystalline particles recombined with hydrogen atoms and became stable and flowed out of the apparatus as exhaust gas. As a result, the adhesion to the substrate was enhanced by the uniform and dense deposition on the substrate centered on particles with good crystallinity.

(Conclusion)
The conclusion of this experiment is described below.
First, in order to produce a DLC film using Ar—CH ₄ as a raw material by this experimental method, a temperature of 1200 ° C. or higher is required even if a catalyst is used. Due to the temperature limit of the experimental system, the heating temperature is limited to 1350 ° C. However, the higher the raw material gas decomposition, the greater the proportion of carbon particles other than graphite in the film. As the film grows, the film hardness increases.
Further, the surface of the produced DLC film depends on the original substrate surface.
Furthermore, when an Al ₂ O ₃ substrate is used, it does not need to be newly coated because it has a catalytic function. This makes it possible to produce a uniform film regardless of the shape of the substrate.
Furthermore, when Ar—C ₃ H ₈ is used as a source gas, a DLC film can be produced even at 1000 ° C. This makes it possible to fabricate the DLC at low temperature in this experimental system and eliminates the risk of causing damage to the experimental system due to temperature. In addition, the production of a DLC film can be expected on a metal substrate having a low melting point.
Further, the adhesion between the film produced by introducing hydrogen into the source gas from the beginning of heating and the substrate is enhanced.

It is a block diagram which shows an example of the film-forming apparatus which forms the DLC film of this invention. It is a schematic diagram of the film-forming apparatus used in embodiment of this invention. It is a measurement result of an XPS spectrum when it experimented at 1350 degreeC (experiment 1). It is a measurement result of XPS spectrum of pure graphite (Experiment 1). It is the C1s electron XPS peak value of DLC (Experiment 1). This is the C1s electron XPS peak value of pure graphite (Experiment 1). It is a measurement result of Raman spectrum of pure graphite (Experiment 2) It is a measurement result of Raman spectrum of pure diamond (Experiment 2) It is the result of having compared the film | membrane by the difference in temperature (smooth surface) (Experiment 2). It is the result of having compared the film | membrane by the difference in temperature (Rough surface) (Experiment 2). It is the result of having compared the film | membrane by the difference in post-processing (experiment 2). It is the result of having compared the structure of the DLC film produced without the catalyst (Experiment 2). Raman peak value and intensity ratio of D band and G band (sample A smooth-sample B smooth) (Experiment 2) Raman peak value and intensity ratio of D band and G band (Sample A Roughness-Sample B Roughness) (Experiment 2) It is the Raman peak value and intensity ratio of D band and G band (Sample B-Sample C) (Experiment 2) Raman peak value and intensity ratio of D band and G band (sample D smooth-sample D rough) (Experiment 2) It is a measurement result of the Raman spectrum of Sample 1 (Experiment 3). It is a measurement result of Raman spectrum of sample 2 (Experiment 3). It is the Raman peak value and intensity ratio of D band and G band (Experiment 3) It is the Raman peak value and intensity ratio of D band and G band (Experiment 3) 2 is an FE-SEM image (× 1,000) of Sample 1. 2 is an FE-SEM image (× 10,000) of Sample 1. 2 is an FE-SEM image (× 10,000) of Sample 1. 2 is an FE-SEM image (× 50,000) of Sample 1. 2 is an FE-SEM image (× 1,000) of Sample 2. 2 is an FE-SEM image (× 10,000) of Sample 2. 2 is an FE-SEM image (× 50,000) of Sample 2. 2 is an FE-SEM image (× 100,000) of Sample 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1a Heating apparatus 1b Heating means 1c Support apparatus 2 Gas supply source 3 Flow control apparatus 4 Power supply 5 Temperature control apparatus 6 Base | substrate

Claims (5)

By heating the substrate containing the sapphire single crystal to 1000 ° C. or higher in an atmosphere containing hydrocarbon gas at atmospheric pressure without a catalyst, a diamond-like carbon film formed by pyrolysis of hydrocarbon gas is formed on the surface of the substrate. A method for producing a diamond-like carbon film, comprising the step of forming.   The method for producing a diamond-like carbon film according to claim 1, wherein the heating time is 60 minutes or more.   3. The diamond-like carbon according to claim 1, further comprising a step of, after the heating time elapses, stopping the supply of the hydrocarbon gas and gradually lowering the temperature while supplying a gas for post-treatment. A method for producing a membrane.   The method for producing a diamond-like carbon film according to any one of claims 1 to 3, wherein the hydrocarbon gas is a gas containing propane.   The method for producing a diamond-like carbon film according to claim 4, wherein hydrogen gas is mixed with the hydrocarbon gas.