JP2011099137A - Method for depositing diamond film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for depositing an excellent diamond film on dissimilar substrates formed of metal or the like by the laser ablation in the atmosphere of oxygen or hydrogen. <P>SOLUTION: In the method for depositing the diamond film on substrates, laser beam of the pulse width of ≤50 ns is irradiated to a carbon target consisting of graphite, amorphous carbon, glassy carbon or diamond in the atmosphere of oxygen or hydrogen; carbon particles are scattered from the target by the laser ablation and deposited on a substrate; a supersaturated state of the deposited particles is formed for each pulse to form a diamond film on the substrate; and a diamond film is deposited on the substrate. The laser beam is irradiated in a state in which the negative bias is applied to the substrate. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a technique for forming a diamond film suitable for an electronic device, a heat sink, a surface acoustic wave element, an X-ray window, an optical material, a hard coating material, and the like by a laser ablation method.

  Since diamond has the highest hardness and thermal conductivity among materials, and is excellent in translucency and chemical stability, it is expected to be applied to various industrial fields. Recently, it has been recognized as a new semiconductor material having a wide band gap, and has attracted attention from the viewpoint of application as an electronic device. In putting these to practical use, it is important to form a diamond film at a low cost.

  Diamond is a high-temperature and high-pressure phase, and conventionally high-pressure synthesis has been the main. However, in recent years, hydrocarbon gas (methane, etc.) diluted to about 1% with hydrogen by an excitation method such as μ-wave plasma, DC plasma, or hot filament is used. Chemical vapor deposition (CVD), in which diamond is deposited on a substrate that is decomposed and maintained at a temperature of about 1000 ° C., has been actively studied, and a diamond film can be obtained relatively easily.

On the other hand, a diamond film can also be formed by laser ablation which is physical vapor deposition (PVD). In the laser ablation method, a target material is instantaneously scattered and deposited on a substrate by irradiating the target material with a pulse laser at a power density of about 10 ¹⁰ W / cm ² using an excimer laser or a YAG laser. In recent years, it has been attracting attention because it is applied to various materials such as oxides and compound semiconductors, and a high-quality film can be obtained at a relatively low temperature.

  The characteristics of the laser ablation method are as follows: (1) The energy of scattered particles is high, and low temperature growth is possible as compared with the CVD method. (2) A metastable phase or non-equilibrium phase can be generated. ) Since there is little compositional deviation from the target and no impurities are mixed in principle, high-quality film formation is possible, and (4) the apparatus configuration is simple. These features are preferable for the creation of diamond films, and in particular, because they are low-temperature processes compared to CVD methods, the possibility of forming diamond films on materials that cannot be applied to high-temperature processes such as low-melting-point materials and plastic materials. Have.

  As an example of forming a diamond film by a laser ablation method, Patent Document 1 discloses a method of obtaining a diamond film having a desired particle diameter in an oxygen atmosphere. According to this, a diamond film is obtained on a diamond substrate by irradiating a graphite target with a laser in an atmosphere of oxygen 70 mTorr and setting the substrate temperature to 400 ° C. to 650 ° C., and the repetition frequency (0. It is described that the particle size of the diamond film is adjusted by setting 1 to 50 Hz).

  Patent Document 2 discloses a method for obtaining an ultra-flat diamond film in a hydrogen atmosphere. According to this, a microcrystalline diamond thin film having an average roughness of 2.2 nm is formed on a diamond substrate in an atmosphere of hydrogen 4 Torr at a substrate temperature of 450 ° C. to 650 ° C.

JP 2004-91250 A JP 2005-15325 A

  In forming a diamond film by laser ablation, an oxygen or hydrogen atmosphere plays an important role in determining the film quality. Since the thermodynamic stable phase of carbon is graphite, the film quality usually deposited by the laser ablation method is mainly composed of a graphite component (sp2 binding component). However, in an oxygen or hydrogen atmosphere, oxygen or hydrogen is activated by collision between the ablated carbon particles and gas molecules, and reacts with the film deposited on the substrate. Since the graphite component is more reactive than the diamond component, selective etching occurs, resulting in the diamond component being deposited on the substrate.

  However, under the gas atmosphere as described above, a new problem has arisen in that the high energy property, which is one of the features of the laser ablation method, is impaired by the collision between the ablated carbon particles and the gas molecules. When the energy of the carbon particles reaching the substrate is lowered, the probability of diamond nucleation at the initial growth stage is lowered. Therefore, even if film formation on a diamond substrate is possible, when different types of substrates are used, diamond nucleation is less likely to occur, and even if a diamond film is not formed, the initial nucleus density is not formed. However, there is a problem that it is difficult to form a continuous film.

  The present invention has been made in view of the above-described problems, and its purpose is good for different types of substrates such as metals while eliminating the graphite component by laser ablation in an oxygen or hydrogen atmosphere. The object is to provide a method capable of forming a diamond film.

  In order to achieve the above object, the present invention irradiates a laser target with a pulse width of 50 ns or less to a carbon target made of graphite, amorphous carbon, glassy carbon, or diamond in an oxygen or hydrogen atmosphere, and performs laser ablation. In the method in which carbon particles are scattered from the target and deposited on a substrate, and a supersaturated state of the deposited particles is formed for each pulse to form a diamond film on the substrate, the negative bias is applied to the substrate. It is characterized by irradiating with laser light.

  Since most of the particles scattered from the carbon target by laser ablation are positively charged ions, application of a negative bias to the substrate accelerates the carbon ions when they collide with the substrate. As a result, energy lost by collision with gas molecules in an oxygen or hydrogen atmosphere is compensated, and carbon particles can reach the substrate with high energy while suppressing generation of sp2 components.

  When the laser beam is incident on the target with a pulse width of 50 ns or less, the target material is instantaneously ablated and reaches the substrate. At this time, the deposited particles are supersaturated. In addition, since the high energy particles reach the substrate due to the substrate bias, the carbon particles on the substrate are in a pseudo high temperature and high pressure state. Therefore, nucleation of diamond, which is usually a thermodynamically unstable phase, is promoted.

  The diamond film forming method according to the present invention, as described above, effectively generates diamond nuclei on a different substrate by irradiating a target made of a carbon material with a negative bias applied to the substrate. It is possible to form a high-quality diamond film on various materials. In addition, because it only forms a high temperature and high pressure state in a pseudo manner, a diamond film can be formed even on materials that could not be applied with the conventional CVD method, which is a high temperature process, making a great contribution to diamond applications. Can be made.

  In the present invention, it is preferable to use a metal substrate for the substrate, or to use an insulating substrate or a nonmetallic conductive substrate with a conductive coating on the substrate. However, a negative bias can be applied and a good diamond film can be formed.

It is a schematic block diagram which shows the film-forming apparatus which enforces this invention method. It is a graph which shows the Raman spectrum of the film | membrane obtained by this invention method.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
In FIG. 1, a vacuum chamber 1 constituting a film forming apparatus is connected to a vacuum pump through a gate valve 2 and can exhaust the inside. A gas introduction pipe 4 having an on-off valve 3 is connected to the vacuum chamber 1 so that the atmosphere gas during film formation can be supplied into the vacuum chamber 1 through the gas introduction pipe 4 by opening the on-off valve 3. It is configured.

  A target holder 5 for holding the target 50 is disposed on one side in the vacuum chamber 1. As the target 50 for forming the diamond film, a carbon material such as graphite, amorphous carbon, glassy carbon, or diamond can be used.

  A laser optical system 6 for irradiating the target 50 with the laser beam 60 is attached to the other side of the vacuum chamber 1. The laser optical system 6 introduces laser light 60 generated from a laser light source 61 into the vacuum chamber 1 via a mirror 62, a condenser lens 63, and a laser introduction window 64, and is oblique to the target 50 (in the illustrated example). The laser ablation is performed on the target 50 by being incident on the target 50 and being focused on the target 50. As the laser light source 61, for example, an ArF excimer laser, a KrF excimer laser, a YAG laser, or the like can be used.

  A substrate holder 7 for holding a substrate 70 on which a diamond film is formed is disposed at a position facing the target 50 (target holder 5) in the vacuum chamber 1. A heater (not shown) that is electrically insulated from the substrate holder 7 is installed inside the substrate holder 7, and the substrate 70 can be heated to a predetermined temperature by the heater. The substrate holder 7 is supported by the vacuum chamber 1 via an insulating material 72 at the shaft portion 71, and is electrically insulated from the vacuum chamber 1. Further, the shaft portion 71 of the substrate holder 7 is connected to the variable voltage source 73 outside the vacuum chamber 1 so that a desired negative bias can be applied to the substrate holder 7.

  Next, the Example which implemented the formation method of the diamond film based on this invention using the said film-forming apparatus is described.

Example 1
Using a KrF laser as the laser light source (61), a laser with a pulse width of 20 ns is repeatedly incident on the surface of the target (50) made of graphite at a frequency of about 2 mm ² at a frequency of 5 Hz. 200 mJ.

  A Nb: STO substrate was used as the substrate (70), placed at a distance of 50 mm from the target (50), and a negative voltage of 150 V was applied to the substrate holder 7 using a variable voltage source 73 as a substrate bias. Since the Nb: STO substrate is electrically connected to the substrate holder 7, a negative bias is similarly applied to the Nb: STO substrate. The temperature of the substrate (70) was controlled to 600 ° C. using the heater in the substrate holder.

After evacuating the inside of the vacuum chamber 1 to 10 ⁻⁷ Torr or less using a vacuum pump (turbo molecular pump), a film is formed by irradiating the laser under the above-described conditions with oxygen introduced as an atmospheric gas at 20 mTorr. It was. FIG. 2 shows the Raman spectrum of the obtained polycrystalline diamond film measured at an excitation wavelength of 514 nm. sp2 D peak indicating the component (1300 cm ^-1 vicinity) and G peak (1600 cm around ^-1) was not observed, a sharp peak was observed at 1332 cm ^-1 indicating the diamond.

(Example 2)
Next, the film was formed under the same conditions as in Example 1 except that the atmosphere gas was 1 Torr of hydrogen. When the Raman spectrum of the obtained polycrystalline diamond film was measured under the same conditions as in Example 1, only a sharp diamond peak at 1332 cm ⁻¹ was obtained as in Example 1.

(Comparative Example 1)
Further, as Comparative Example 1, when a film was formed without applying a substrate bias under the conditions of the example, no film was obtained. This is because the carbon particles incident on the substrate have lost energy, so that diamond nucleation hardly occurs, and the sp2 component generated instead is etched in an oxygen atmosphere.

(Comparative Example 2)
Furthermore, as Comparative Example 2, film formation was performed under the conditions of Example 2 without applying a substrate bias. As in Comparative Example 1, no film was obtained. Also in this case, it seems that the sp2 component was etched in a hydrogen atmosphere as in Comparative Example 1.

  In the above embodiment, the pulse width of the laser beam is set to 20 ns. However, depending on other conditions, the deposited particles are in a supersaturated state, so that the pulse width can be set to about 50 ns. However, even if the pulse width is larger than 50 ns, not only does it contribute to the formation of the diamond film, but also the consumption of the target and the energy consumption increase.

  As mentioned above, although embodiment of this invention was described, this invention method is not limited to the said embodiment, In addition to the above, various deformation | transformation and a change are further possible based on the technical idea of this invention. .

DESCRIPTION OF SYMBOLS 1 Vacuum chamber 2 Gate valve 3 On-off valve 4 Gas introduction pipe 5 Target holder 50 Target 6 Laser optical system 60 Laser light 61 Laser light source 62 Mirror 63 Condensing lens 64 Laser introduction window 7 Substrate holder 70 Substrate 71 Shaft portion 72 Insulating material 73 Variable voltage source

Claims (3)

  In an oxygen or hydrogen atmosphere, a carbon target made of graphite, amorphous carbon, glassy carbon, or diamond is irradiated with laser light with a pulse width of 50 ns or less, and carbon particles are scattered from the target by laser ablation on the substrate. In the method of depositing and forming a diamond film on the substrate by forming a supersaturated state of deposited particles for each pulse, the diamond film is irradiated with a laser beam with a negative bias applied to the substrate Forming method.   The method for forming a diamond film according to claim 1, wherein a metal substrate is used as the substrate. 2. The method for forming a diamond film according to claim 1, wherein an insulating substrate or a nonmetallic conductive substrate obtained by applying a conductive coating to the substrate is used.

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