JP2006307251A - Method for producing diamond-like carbon thin film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a diamond-like carbon thin film where adhesion between a DLC film and a target substrate is improved, and in which deterioration in the quality of the DLC thin film caused by the intrusion of melted resolidified particles (droplets) and coarse particles such as the fragments of a solid target which becomes a problem in a laser ablation process can be evaded. <P>SOLUTION: A gaseous starting material introduction port is irradiated with a carbon dioxide laser, thus gaseous starting material molecules are dissociated into an atomic state, and an atom beam having translational energy of about 5eV equivalent to the interatomic bond energy of substrate composing atoms is generated. By using normal chain hydrocarbon gas such as methane, ethylene and acetylene, a carbon atom beam is generated, and a diamond-like carbon film is formed on the surface of a solid target such as a silicon substrate by a covalent bond. The deposition of the carbon based thin film is confirmed regarding the surface of the silicon substrate, and the fact that it is a DLC thin film is confirmed from an analysis result according to Raman spectroscopy. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technique for producing a diamond-like carbon thin film using a high-energy carbon atom beam formed by a laser detonation method.

Diamond-like carbon (DLC) is a general term for amorphous high-hardness carbon thin films, and generally used DLC is vague in structure and physical properties, and has a structure close to that of graphite and hydrocarbon polymers from a film having a structure close to diamond. There are a wide variety of films including
DLC is a mixed material of diamond with high wear resistance and graphite with good lubrication properties in the atmosphere, and since its first report by Aisenberg et al. In 1971, its excellent physical and chemical properties As a result, it is applied to various fields.

For example, DLC's insulation and low dielectric constant can be used for plasma display electron-emitting devices and LSI insulation films, and high infrared transmittance and high hardness can be used for infrared window protection films for chemical stability. It is widely applied to coatings and tools for various molds, and to various mechanical parts, faucets, and surface coatings of magnetic disks using its excellent sliding characteristics.
In addition, there is a movement to apply DLC to the tribology (wear and friction) field for the purpose of reducing the environmental load of lubricating oil and saving energy, and the use as a protective film for solid lubrication of automotive engine parts has also begun. Yes.

Currently, there are two main types of DLC thin film fabrication methods: physical vapor deposition (PVD) and chemical vapor deposition (CVD). Magnetron sputtering and ion beam deposition are often used for PVD, and plasma CVD is often used for CVD (for example, Patent Document 1).
However, in such a method for producing a DLC thin film, since the DLC thin film is formed by a dry process, there is a problem of adhesion to the target substrate. In addition, the characteristics of DLC thin films are strongly dependent on the fabrication method and fabrication conditions. Adhesion with the target substrate, uniformity on a three-dimensional substrate or large area substrate, deposition rate, and sliding environment dependency There are problems such as.

  In addition, as a method for producing a DLC thin film that improves adhesion to a target substrate, there is a thin film production method (laser ablation method) that utilizes an ablation phenomenon by a high energy beam such as a laser. Ablation is a phenomenon in which when a solid target surface is irradiated with a beam having a high energy density such as a laser, a substance that has absorbed the beam energy is scattered as a fragment having a large energy. However, there is a problem of film quality deterioration due to mixing of coarse particles such as molten re-solidified particles (droplets) of about micron or sub-micron accompanying the laser heating of the solid target and fragments of the solid target, and it has not been put into practical use.

JP 08-217596 A

  The present invention improves the adhesion between the DLC thin film and the target substrate, and the DLC thin film is caused by mixing of coarse particles such as molten re-solidified particles (droplets) and solid target fragments, which are problematic in the laser ablation method. An object of the present invention is to provide a method for producing a diamond-like carbon thin film capable of avoiding deterioration of quality.

The inventors of the present invention attempted to produce a DLC thin film by various methods, and as a result of repeated improvements to the production method, completed the method for producing a diamond-like carbon thin film according to the present invention.
From the viewpoint of the present invention, there is provided a method for producing a diamond-like carbon thin film characterized by irradiating a solid target with a superheated carbon atom beam to form a diamond-like carbon thin film on the surface of the solid target.
Here, the superheated carbon atom beam has a translational energy of about 1 to 10 eV corresponding to an interatomic bond energy, and an atomic carbon flux (flux) of about 10 ^13-15 atoms / cm ² s or more. A carbon atom beam.

According to the present invention, the superheated carbon atom beam is preferably generated by a laser detonation method.
In the laser detonation method, a carbon dioxide laser synchronized with the raw material gas is condensed at a nozzle-like raw material introduction nozzle port for introducing the raw material gas in pulses, and the raw material gas is dissociated to generate an atomic beam. Is the method.
By irradiating the raw material introduction nozzle port with a carbon dioxide laser, the raw material gas molecules can be dissociated into atoms and an atomic beam having a translational energy of about 5 eV corresponding to the interatomic bond energy of the substrate constituent atoms can be generated. It can be done.
Here, by using a straight chain hydrocarbon gas such as methane, ethylene, or acetylene as a raw material gas, a carbon atom beam is generated, and a diamond-like carbon thin film is formed on the surface of the solid target substrate.
In particular, a hydrogenated DLC thin film can be formed by using methane gas (CH ₄ ) as a raw material gas.

  The solid target to be irradiated with the superheated carbon atom beam is a semiconductor substrate such as silicon, a substrate such as glass, quartz or metal, a so-called flexible substrate made of a plastic film or a polymer fiber.

The method for producing a diamond-like carbon thin film according to the present invention forms a film by directly irradiating the surface of a solid target with a superheated carbon atom beam, and does not require a carrier gas. Compared with this, impurities can be prevented from being mixed into the film, and the quality of the DLC thin film can be improved.
Also, by dissociating the methane gas, which is the source gas, into an atomic form and generating a carbon atom beam, it is caused by the inclusion of coarse particles such as molten resolidified particles (droplets) and solid target fragments that are problematic in laser ablation methods, etc. Can prevent the degradation of DLC thin film quality.
Further, the method for producing a diamond-like carbon thin film according to the present invention improves the adhesion between the DLC thin film and the target substrate because the DLC thin film is generated by covalently bonding atoms and carbon atoms on the surface of the solid target. effective.

  Hereinafter, embodiments of a method for producing a diamond-like carbon thin film according to the present invention will be described in detail with reference to the drawings.

  As an example, a superheated carbon atom beam is generated using a laser detonation method, and a diamond-like carbon thin film is formed on the surface of the solid target by irradiating the generated superheated carbon atom beam to the solid target. Will be described. First, a laser detonation type atomic beam generator will be described with reference to the schematic diagram of FIG.

As shown in FIG. 1, the laser detonation type atomic beam generator is synchronized with a pulse in a raw material introduction nozzle port 1 into which a raw material gas is introduced in a pulse shape by a piezo-driven pulse valve 3 in a vacuum chamber. By condensing and irradiating the carbon dioxide laser beam, the surface of the solid target substrate 5 is irradiated as a carbon atom beam having a translational energy of about 5 eV by dissociating and accelerating the gas molecules in an atomic form. .
The vacuum chamber is connected to a vacuum exhaust apparatus (not shown), and the inside of the chamber can be set to a pressure of 10 ⁻³ Pa or less. Thereby, adhesion of impurities to the solid target substrate 5 can be prevented. In addition, since this film formation method forms a film by directly irradiating the surface of the solid target substrate 5 with a carbon atom beam, no carrier gas is required. This is also the reason why impurities do not adhere to the solid target substrate 5. Since there is no adhesion of impurities to the surface of the solid target substrate, the adhesion between the surface of the solid target substrate and the thin film to be formed is improved.

  As shown in the schematic diagram of FIG. 1, the atomic beam generating mechanism includes a raw material introduction pipe 2 for introducing a raw material gas into a vacuum chamber, a nozzle-shaped raw material introduction nozzle port 1, a carbon dioxide laser oscillation device (not shown), The carbon dioxide laser oscillated from the carbon dioxide laser oscillating device reflects the carbon dioxide laser and condenses it at the raw material gas inlet, and the concave mirror 4 is covered with gold. The reason why the carbon dioxide laser is reflected by the concave mirror 4 and focused on the raw material introduction nozzle port 1 is affected by the oscillation position of the carbon dioxide laser by adjusting the angle of the concave mirror 4 and the like. This is because the carbon dioxide laser can be focused on the raw material inlet without any problem. For this reason, the size of the vacuum chamber can be reduced by providing the concave mirror 4.

The atomic beam generation mechanism applies the principle of laser propulsion, that is, a pulsed raw material gas is introduced into the raw material introduction nozzle port 1 through the raw material introduction tube 2, and a carbon dioxide gas laser is synchronized with it. Irradiate. As a result, a detonation wave propagates from the breakdown generated in the nozzle, and an atomic beam of about 5 eV is generated. In this embodiment, a carbon atom beam is generated by using methane gas (CH ₄ ) as a source gas.

The generated carbon atom beam has a translational energy of 2 to 5 eV corresponding to the interatomic bond energy and a flux of 10 ^13-15 atoms / cm ² s. Here, the flux of the carbon atom beam is obtained by a quartz crystal microbalance (QCM) 6 coated with an Ag thin film, and the composition and translational kinetic energy of the carbon atom beam are obtained by a quadrupole mass spectrometer 7 (Quadrupole Mass Spectrometer). Measurement is performed using a time-of-flight spectrum using a spectrometer (QMS) as a detector.

In this embodiment, a silicon substrate Si (100) subjected to RCA cleaning is used as the solid target substrate 5. This laser detonation type atomic beam generator succeeded in forming a DLC thin film on a silicon substrate by irradiating the silicon substrate with the generated carbon atom beam.
That is, the deposition of a carbon-based thin film on a silicon substrate was confirmed, and from the analysis results by Raman spectroscopy, the carbon-based thin film on the silicon substrate is a DLC thin film containing about 58% of carbon atoms containing SP ³ bonds. I was able to confirm that.

  The carbon-based thin film is also deposited on the concave mirror 4 in the apparatus. However, since this carbon-based thin film is a DLC thin film, it is transparent (does not absorb) to infrared rays, and the performance of the concave mirror does not deteriorate. There is also a practical advantage that the film formation reaction can proceed continuously.

  In the pretreatment method for forming a carbon-based thin film on a silicon substrate, a pretreatment process such as a cleaning process by irradiation of hydrogen ions on the surface of the silicon substrate is performed before the thin film is formed on the silicon substrate. Thus, it is possible to further improve the adhesion between the DLC thin film and the silicon substrate surface.

Hereinafter, the measurement result of the carbon atom beam and the analysis result of the carbon-based thin film will be described in detail. First, FIG. 2 shows the result of measuring the composition and time-of-flight measurement of the carbon atom beam generated using the apparatus shown in FIG. FIG. 2 (a) shows a time-of-flight spectrum when the detected mass-to-charge ratio of the quadrupole mass spectrometer 7 is fixed at 16 (CH ₄ ⁺ ). The origin of the horizontal axis in FIG. 2 (a) is based on the trigger of the pulse valve. The line-shaped peak observed at the flight time of 220 μs is the emission peak of the carbon dioxide laser, and is the measurement reference point for the flight time. In FIG. 2A, it can be understood that there are two peaks at 700 μs and 2000 μs. Among them, the peak of 2000 μs is a component having thermal kinetic energy not accelerated by laser detonation, and the peak of 700 μs is a superheated molecular beam accelerated by a laser.

In the case of time-of-flight measurement using a quadrupole mass spectrometer as a detector, the ionization rate due to electron collision of molecules at the ion source is proportional to the reciprocal of the flight speed (residence time in the ion source), so correction is necessary. FIG. 2B shows the result of this correction. The spectrum of FIG. 2B is a time-of-flight spectrum with the laser irradiation time as the origin. From the area ratio of the peak of the time-of-flight spectrum in FIG. 2 (b), it can be understood that about 80% of CH ₄ is accelerated by the laser, and about 20% is not accelerated but flies at the thermal motion speed.

In addition, it can be calculated that the kinetic energy of CH ₄ which has superheat energy from the flight time is about 2.8 eV. Furthermore, the mass-to-charge ratio of the molecules detected by QMS was set to m / e = 1, 12, 13, 14, 15 and the same measurement was performed, and the time-of-flight spectrum was measured. The beam composition was examined by comparing the peak area ratios in these spectra. Table 1 below shows the atomic composition ratio of the beam component when CH ₄ measured from the time-of-flight spectrum is used as the source gas. The accuracy of this value is not high because it does not take into account the difference in ionization probability when each molecule is ionized by the electron impact ion source of QMS, which is the detector, but about 60% of the beam is CH ₄ It can be seen that it is suggested to contain about 40% CH _x radicals.

On the other hand, the flux of the carbon atom beam is estimated from the mass change of the quartz crystal microbalance. FIG. 3 shows a change in the resonance frequency of the crystal unit when the crystal unit microbalance 6 is irradiated with a carbon atom beam. In FIG. 3, the horizontal axis represents time, and the vertical axis represents the change in resonance frequency. Here, the decrease in the resonance frequency represents an increase in mass (deposition). In FIG. 3, introduction of CH ₄ is started at 80 s, and carbon dioxide laser irradiation is started at 100 s. Even if only CH ₄ is introduced, the resonance frequency does not change (thin film is not formed), but when the CO2 laser is started to irradiate, the resonance frequency decreases linearly. It is shown. This indicates that the carbon-based thin film is deposited at a constant deposition rate. Based on this change in resonance frequency, the mass of the carbon-based film deposited on the quartz crystal microbalance 6 was calculated and the deposition rate was calculated. The unit area and unit time were 3.9 × 10 ^-9 g / cm. ² / s can be calculated.

  4A to 4C show the broad spectrum and C1s, O1s high-resolution spectrum of X-ray photoelectron spectroscopy (XPS) of the DLC thin film prepared by the method of this example. For comparison, FIGS. 4D to 4F show the analysis results of a commercially available hydrogenated DLC produced by the plasma CVD method measured under the same conditions.

  From the broad spectrum shown in Fig. 4 (a), the surface composition of the thin film formed by the DLC thin film manufacturing method according to the present invention is 92% carbon and 8% oxygen, and is exposed to the atmosphere before XPS measurement. And it can be understood that there are few impurities when the sputter cleaning is not performed before the XPS measurement. Compared with commercially available hydrogenated DLC produced by the plasma CVD method, the surface composition is almost the same, and it can be understood that the composition is comparable to commercially available hydrogenated DLC.

  FIGS. 4B and 4C show high-resolution spectra of C1s and O1s. It can be understood that both spectra are formed from a single peak and contain almost no bonds such as C = C. Compared with the high-resolution spectrum of commercially available hydrogenated DLC (Fig. 4 (e), (f)), the peak shape is almost the same, but the peak position of C1s is 285.3 eV, Fig. 4 (b) in Fig. 4 (b). In e), the carbon-based thin film formed by the method for producing a DLC thin film according to the present invention is 284.4 eV, which is shifted to the higher energy side by about 0.9 eV. When comparing O1s as well, the difference in peak position is basically due to the surface charge-up because the shift in Fig. 4 (c) is about 0.6 eV. The possibility of gender differences is small. Therefore, it can be said from XPS that the DLC thin film formed by the method for producing a DLC thin film according to the present invention has the same composition as a commercially available DLC produced by the plasma CVD method.

Next, Raman scattering measurement was performed on the thin film formed by the method for producing a DLC thin film according to the present invention in order to clarify the bonding state of carbon. FIG. 5 shows a Raman spectrum as a result of the Raman scattering measurement. A broad peak that characterizes amorphous carbon is observed, and a typical D-band (1319 cm ^-1 ), which indicates irregularities in the crystal structure, coexists in addition to a G-band (1519 cm ^-1 ) that exhibits a graphite structure. A DLC Raman spectrum is shown.
The peak position and peak area of G-band and D-band are shown in Table 2 below.

The area intensity ratio of D-band and G-band is calculated to be 0.45. According to Robertson, it is reported that there is a correlation as shown in FIG. 6 between the peak area intensity ratio of G-band and D-band and the proportion of sp ³ structure in the DLC film. Here, the horizontal axis in FIG. 6 represents the proportion of the sp ³ structure, and the vertical axis represents the G-band peak position and the area intensity ratio. Since the values of the thin films formed by the DLC thin film manufacturing method according to the present invention are respectively the peak position 1519 cm ⁻¹ and I (D) / I (G) = 0.45, the ratio of sp ³ is estimated to be about 58%. is doing.

  On the other hand, in order to clarify the surface structure of the thin film prepared by laser detonation, we observed it with an atomic force microscope (AFM). FIG. 7 shows a topographic image and a phase image. From the topographic image shown in FIG. 7, it can be seen that the thin film produced in this example does not have a completely uniform layer-by-layer growth in the microscopic manner but an island growth. This suggests that the bonding force between the substrate and the first surface layer carbon is smaller than the bonding between the deposited carbons (surface diffusion is likely to occur).

  FIG. 8 shows cross-sectional shapes of the topographic image and the phase image in FIG. From this, it can be seen that the valley portion in FIG. 7 has a flat shape, and the mountain portion has a shape in which the central portion is raised. The phase image shows that the phase lag is small at the carbon-based thin film deposition position. The decrease in phase lag in the AFM tapping mode suggests that the deposited thin film has a high hardness or a small surface interaction force (adhesion force). These characteristics are typical characteristics of DLC, and it can be understood that the DLC thin film was formed on the silicon substrate by the DLC thin film manufacturing method according to the present invention.

  By using the method for producing a diamond-like carbon thin film according to the present invention, it is possible to produce a DLC thin film from the gas phase, avoiding droplets that are problematic in conventional solid targets, and charging that is problematic in the plasma method. Since a DLC thin film excellent in film quality free from damage by particles can be produced, it can be used in fields where DLC film quality such as coating of DLC film on a semiconductor substrate is regarded as important.

Schematic cross section of laser detonation type atomic beam generator (A) Time-of-flight spectrum of a typical CH4 beam, (b) Time-of-flight spectrum after correcting for ionization yield in the ionization chamber A graph showing the frequency change of the quartz crystal when the quartz crystal microbalance is irradiated with a carbon beam X-ray photoelectron spectroscopy spectrum of carbon-based thin film. Here, (a) the broad spectrum of the carbon film prepared by the laser detonation method, (b) the C1s high resolution spectrum of the carbon film prepared by the laser detonation method, (c) the high resolution O1s of the carbon film prepared by the laser detonation method Spectrum, (d) wide spectrum of commercially available hydrogenated DLC thin film, (e) C1s high resolution spectrum of commercially available hydrogenated DLC thin film, and (f) O1s high resolution spectrum of commercially available hydrogenated DLC thin film. Raman scattering spectrum of carbon-based thin film prepared by laser detonation method according to the present invention Graph showing the ratio of sp ³ bonds contained in carbon-based thin films, the peak position of Raman scattering, and the relative area intensity of G-band and D-band AFM image (a) topographic image, (b) phase image of carbon-based thin film prepared by laser detonation method according to the present invention Sectional shape of AFM image of carbon-based thin film prepared by laser detonation method according to the present invention (a) Topographic image, (b) Phase image

Explanation of symbols

1 Raw material introduction nozzle port
2 Raw material introduction pipe 3 Pulse valve
4 concave mirror
5 Solid target substrate 6 Quartz Crystal Microbalance (QCM)
7 Quadrupole Mass Spectrometer (QMS)
8 Orifice

Claims (6)

  A method for producing a diamond-like carbon thin film, comprising irradiating a solid target with a superheated carbon atom beam to form a diamond-like carbon thin film on the surface of the solid target.   The method for producing a diamond-like carbon thin film according to claim 1, wherein the superheated carbon atom beam is generated by a laser detonation method.   3. The method for producing a diamond-like carbon thin film according to claim 2, wherein the source gas is a hydrocarbon gas in the laser detonation method.   3. The method for producing a diamond-like carbon thin film according to claim 2, wherein the source gas is methane gas in the laser detonation method.   The method for producing a diamond-like carbon thin film according to any one of claims 1 to 4, wherein the solid target is a semiconductor substrate. The diamond-like carbon thin film according to any one of claims 1 to 4, wherein the solid target is any one selected from glass, quartz, metal, plastic film, and polymer fiber. Method.