KR101318236B1 - Method and apparatus for grain size control in the diamond synthesis - Google Patents

Abstract

PURPOSE: A method for controlling the particle size of a diamond crystal and an apparatus using the same are provided to selectively control the intensity of the electric field between anode and cathode by controlling an inter-electrode distance, thereby easily controlling the particle size of the diamond crystal. CONSTITUTION: A method for controlling the particle size of a diamond crystal controls an interelectrode electric field by converting a precursor gas to electrons and ions for synthesizing the diamond crystal after by supplying power to cathode and anode. The particle size of the diamond crystal becomes smaller if the electric field between the anode and the cathode becomes larger. The particle size of the diamond crystal becomes larger if the electric field between the anode and the cathode becomes smaller.

Description

Method and apparatus for controlling grain size of diamond crystals {Method and apparatus for grain size control in the diamond synthesis}

The present invention relates to a method and apparatus for controlling a particle size of diamond crystals, and more particularly, in a vapor phase diamond crystal synthesis method of inducing electron collisions with ions to form a diamond crystal thin film, the cathode of the apparatus implementing the method ( The present invention relates to a method and apparatus for controlling a particle size of a diamond crystal capable of controlling the particle size of the diamond crystal by controlling an interelectrode electric field between a cathode and an anode.

Diamond synthesis technology using chemical vapor deposition process has been developed to enable the synthesis of ultra-nanocrystalline diamond (UNCD, ultra-nanocrystalline diamond). Ultra-nanocrystalline diamond (UNCD) is a combination of the characteristics of diamond and ultra-nanocrystalline thin film, and can be applied to various fields.

Ultra-nanocrystalline diamonds can be synthesized using an innovative method using microwave plasma-assisted chemical vapor deposition (MW-PACVD) under an Ar-rich atmosphere. In addition, the synthesis of ultra-nanocrystalline diamond is possible through a conventional method using MW-PACVD in a hydrogen excess atmosphere. In the case of the MW-PACVD method in a hydrogen excess atmosphere, a process is performed in a manner that a negative power is applied to a substrate and positive ions collide with a growth surface of the substrate.

Synthesis of ultra-nanocrystalline diamond (UNCD) is also possible through direct current plasma-assisted chemical vapor deposition (DC-PACVD), in which case the process is carried out under a hydrogen excess atmosphere without applying negative power to the substrate ( H.-J. Lee, H. Jeon, and W.-S. Lee, J. Appl. Phys. 109, 023303 (2011)).

The diamond synthesis method using the BEG (bias enhanced growth) method such as MW-PACVD is a method of applying a negative power to the substrate and the positive ions collide with the substrate, whereas the DC-PACVD method is a substrate This is a method in which electrons collide with the substrate by applying a positive power to the substrate. Compared with ion bombardment, electron bombardment has little effect on substrate damage, so the DC-PACVD method is advantageous for diamond crystal thin film synthesis.

Diamond crystal thin films are classified into nanocrystalline diamond (NCD) thin films and microcrystalline diamond thin films in addition to the ultra-nanocrystalline diamond (UNCD) thin film as described above according to the crystal grain size. Accordingly, the particle size of the diamond crystal thin film is optionally required. Therefore, the technique of controlling the particle size of the diamond crystal thin film is very useful in commercial as well as academic aspects.

However, in the DC-PACVD method of synthesizing a diamond crystal thin film by inducing electron collision, a technique for controlling the size of diamond crystal grains has not been proposed until now.

H.-J. Lee, H. Jeon, and W.-S. Lee, J. Appl. Phys. 109, 023303 (2011)

The present invention has been made to solve the above problems, in the vapor phase diamond crystal synthesis method of forming a diamond crystal thin film by inducing ion collision with electrons, the cathode (cathode) and the anode ( It is an object of the present invention to provide a method and apparatus for controlling the particle size of a diamond crystal which can control the particle size of the diamond crystal by controlling the interelectrode electric field between the anodes.

In the method for controlling the particle size of diamond crystals according to the present invention for achieving the above object, in the synthesis of diamond crystals by converting a precursor gas into electrons and ions by applying power to a cathode and an anode, between the cathode and the anode The larger the interelectrode electric field (IEEF), the smaller the grain size of the diamond crystal, and the smaller the interelectrode electric field (IEEF), the larger the grain size of the diamond crystal.

When the interelectrode distance IED between the cathode and the anode increases, the intensity of the interelectrode electric field IIEF decreases, and when the interelectrode distance IED decreases, the intensity of the interelectrode electric field IIEF increases.

A substrate on which diamond crystals are grown is provided on the anode, and the cathode is provided at a spaced position above the substrate, and electrons generated by applying power from the cathode and the anode are moved toward the substrate, and ions are moved to the cathode. Is moved towards.

Diamond crystal particle size control apparatus according to the present invention is provided with a chamber to provide a precursor space to the diamond crystal synthesis precursor gas, and is provided at the lower and upper portions of the chamber respectively to convert the precursor gas electrons and ions by applying power Comprising a positive electrode and a negative electrode and a substrate provided on the anode to provide a space for growing diamond crystals, the distance between the electrode (IED) between the anode and the cathode is adjustable, the distance between the electrodes ( Increasing IED) decreases the strength of the inter-electrode electric field (IEEF) to increase the grain size of the diamond crystal, and decreasing the inter-electrode distance (IED) increases the intensity of the inter-electrode electric field (IEEF) It is characterized in that the particle size is reduced.

The particle size control method and apparatus of the diamond crystal according to the present invention has the following effects.

It is possible to selectively control the intensity of the interelectrode electric field (IEEF) by adjusting the interelectrode distance (IED) between the cathode and the anode, thereby easily controlling the particle size of the diamond crystal.

(A), (b) and (c) of FIG. 1 are photographs of the discharge state when the inter-electrode distance (IED) is 5 mm, 25 mm, and 35 mm, respectively, and FIG. 1 (d) shows the inter-electrode distance (IED). And graph showing the correlation between the electric field (IEEF) and the electrode.
(A), (b) and (c) of FIG. 2 are HR-TEM photographs and SAED pattern results of diamond crystals grown when the inter-electrode distance (IED) is 5 mm, 25 mm, and 35 mm, respectively.
(A), (b) and (c) of FIG. 3 are light emission spectrum results during discharge of the anode region, the positive column region and the cathode region, respectively.
4 is a graph showing I _CH / I _Hα according to an interelectrode electric field (IEEF) for each region of FIG. 3.

In the method of synthesizing diamond crystals using electrons and ions, the particle size of the diamond crystals is controlled by controlling the intensity of an interelectrode electric field (hereinafter referred to as 'IEEF') between the cathode and the anode. It is possible to synthesize ultra-nanocrystalline diamond (UNCD), nanocrystalline diamond (NCD), microcrystalline diamond (MCD) through this.

The method of synthesizing diamond crystals using electrons and ions refers to a method in which diamond crystals are synthesized by electrons and ions generated from precursors of diamond crystal synthesis in a space (for example, a chamber) where diamond crystals are synthesized. And ions are generated by applying power to a cathode and an anode provided in the chamber. CH ₄ , H _2, etc. may be used as a precursor of diamond crystal synthesis, and electrons and ions may exist in a plasma state. In addition, in the present invention, it is assumed that a positive power is applied to the substrate side where the diamond crystal is grown. That is, the substrate is provided on the anode, and the cathode is provided on the opposite side of the substrate.

The reason why the substrate is provided on the anode is to allow electrons generated by the application of power to be moved toward the substrate, and ions, ie, positive ions, to be moved toward the cathode. Electrons moving toward the anode, ie, the substrate, collide with gas species within the substrate or chamber, and cations traveling toward the cathode collide with the gas within the chamber.

The collision of electrons serves to enhance the reactivity of the substrate growth front and the reactivity of gas phase radicals. Specifically, due to the collision of electrons, the kinetic energy of the electrons is applied to the bound electrons of the molecular bonds of the surface radical sites located on the substrate surface, thereby improving reactivity in growth. In addition, the collision of the electrons with the gas in the chamber leads to an improvement in the reactivity of the gaseous radicals around the growth surface due to the kinetic energy transfer of the electrons. That is, the collision between the electron and the substrate or the collision between the electron and the gas improves the reactivity of the substrate growth surface and its surroundings, thereby enhancing renucleation activity on the substrate surface. The collision strength of the electrons increases as the interelectrode electric field (IEEF) increases, and as the interelectrode electric field increases, the nucleation of the substrate surface also increases. The collision of electrons is a form of inelastic collision which increases the internal energy of the collision body, ie, the substrate and the gas.

Collision of ions means precisely that ions collide with atoms (or molecules) of the gas. When ions collide with the gas, kinetic energy of ions is applied to each atom of the gas, so that the gas is decomposed and hydrocarbon radicals Is generated. Recombination of hydrocarbon radicals by the constant collision of ions is suppressed, whereby the CH _x / H ratio around the growth surface is kept high. Like the collision strength of electrons, the collision strength of ions increases as the interelectrode electric field (IEEF) increases, and the CH _x / H ratio increases as the interelectrode electric field increases. The collision of ions, unlike the collision of electrons, is in the form of an elastic manner, whereby a portion of the ion bombardment energy is converted into kinetic energy of atoms / molecules.

As mentioned above, the collision strength of electrons or ions is proportional to the intensity of the interelectrode electric field (IEEF), and the interelectrode electric field (IEEF) is inversely proportional to the interelectrode distance (IED). That is, the smaller the interelectrode distance IED, the greater the collision strength of electrons and ions, and the larger the interelectrode distance IED, the smaller the collision intensity of electrons and ions. In addition, as the collision strength of electrons and ions increases, the nucleation rate increases on the substrate growth surface, and the particle size of diamond crystals decreases. The grain size of the diamond crystals is increased.

The collision of electrons and ions has a close relationship with the control of the particle size of the diamond crystals, which is supported by experimental results such as optical emission spectrum results described later.

On the other hand, the diamond crystal synthesis method according to the present invention that can selectively control the particle size of the diamond crystal through the control of the inter-electrode electric field (IEEF), it is applicable to both vapor phase diamond synthesis method using electrons and ions, It is assumed that a positive power is applied to the electrode on which the substrate is mounted.

Next, experimental examples and experimental results of the particle size control method of the diamond crystal according to the present invention will be described.

<Example: Experimental Conditions>

Diamond crystals were synthesized using a DC-PACVD apparatus. A mixed gas of 3% CH ₄ and 97% H ₂ was used as the precursor, and the process pressure, gas flow rate, and discharge current were 150 Torr, 150 sccm, and 35 ± 2 A, respectively, and a 4 inch silicon wafer was used as the substrate. It was mounted on a substrate holder made of material. Growth temperature was maintained at about 800 ℃. Detailed experimental conditions are as shown in Table 1, and the experiments were conducted in the state of adjusting the inter-electrode distance (IED) to 5, 10, 15, 25, and 35 mm.

The discharge state was photographed with a digital camera, and the light emission during discharge was analyzed by optical emission spectroscopy (OES). In addition, HR-TEM, XRD, HR-SEM were used for particle size, microstructure, crystal structure analysis, the results are shown in Table 1.

<Table 1> Experimental conditions and results

<Example: Experimental Results>

1 (a) to 1 (c) show the development of DC discharge according to the inter-electrode distance IED. It can be seen that a positive column appears and expands as the inter-electrode distance IED increases (FIGS. 1B and 1C). FIG. 1 (d) shows the interelectrode electric field (IEEF) according to the interelectrode distance (IED). As the interelectrode distance (IED) decreased from 35 mm to 5 mm, the interelectrode electric field (IEEF) increased from 263 V / cm to 940 V / cm. This trend is explained by the thermal electron emission of the cathode. When the interelectrode electric field (IEEF) is increased, the particle size of the diamond crystals is significantly reduced (see Table 1), which can be confirmed by HR-TEM analysis results as shown in FIG.

A typical UNCD structure is obtained when the IED with the largest interelectrode electric field (IEEF) is 5 mm (Fig. 2 (a)), while a diamond grain structure with a large particle size is obtained as the inter-electrode distance (IED) is increased (Fig. 2). (b), (c)). Selected area electron diffraction (SAED) patterns, interplanar spacing (see FIG. 2), and NEXAFS analysis results support these findings. The close relationship between the interelectrode electric field (IEEF) and the diamond grain size means that electrons and ions play an important role in controlling the grain size during discharge.

The role of electrons and ions in particle size control can be confirmed by the results of optical emission optics (OES) analysis for various discharge regions. In FIG. 3, the emission peaks at 388.8 nm, 486.7 nm, and 656.3 nm are emission peaks of CH [B ² Σ-X ² π], H _β , H _α , and FIG. 4 using the results of FIG. 3. It shows I _CH / I _Hα according to the electric field (IEEF).

Since CH emission occurs at a lower wavelength (ie higher energy) than H _α emission, an increase in I _CH / I _Hα means that the kinetic energy distribution of free electrons is shifted to the higher side. _Referring to FIG. 4, I _CH / I _Hα (kinetic energy of free electrons) is the most positive in the anode region, that is, the substrate growth surface among the anode region, the positive column, and the cathode region. high. This is a natural result as free electrons accelerate towards the anode. Further, in the anode region, I _CH / I _Hα increases with increasing interelectrode electric field (IEEF). This result is consistent with the smallest particle size at the highest interelectrode electric field (IEEF) (see Tables 1 and 2), and the association between the interelectrode electric field (IEEF) and particle size depends on the role of free electrons / ions. It means to depend. In other words, electrons and ions play a role of strengthening the nucleation in the synthesis of diamond crystals, and nucleation is enhanced or reduced according to the collision strength of electrons and ions.

Claims (4)

In synthesizing diamond crystals by applying power to the cathode and anode to convert the precursor gas into electrons and ions,
The grain size of the diamond crystal is characterized in that the grain size of the diamond crystal becomes smaller as the interelectrode electric field (IEEF) between the cathode and the anode becomes larger, and the grain size of the diamond crystal becomes larger when the interelectrode electric field (IEEF) becomes smaller. .
The method of claim 1, wherein the strength of the interelectrode electric field (IEEF) decreases when the interelectrode distance (IED) between the cathode and the anode increases, and when the interelectrode distance (IED) decreases, the interelectrode electric field (IEEF). The particle size control method of diamond crystals, characterized in that the strength of the increase.
The method of claim 1, wherein the substrate on which the diamond crystal is grown is provided on the anode, the cathode is provided at a spaced position above the substrate,
Electron generated by the application of the power supply of the cathode and the anode is moved toward the substrate, the ion is moved toward the cathode, the particle size control method of the diamond crystals.
A chamber supplied with a precursor gas to provide a diamond crystal synthesis space;
An anode and a cathode provided at the lower and upper portions of the chamber, respectively, to convert the precursor gas into electrons and ions by applying power; And
It is provided on the anode and comprises a substrate that provides a space for growing diamond crystals,
The interelectrode distance (IED) between the anode and the cathode is adjustable,
As the inter-electrode distance IED increases, the intensity of the inter-electrode electric field IIEF decreases to increase the grain size of the diamond crystal. When the inter-electrode distance IED decreases, the intensity of the inter-electrode electric field IEEF increases. An apparatus for controlling diamond grain size, characterized in that the grain size of the diamond crystal is increased to decrease.

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