KR20180040840A - Method for deposition of diamond thin film using hot filament chemical vapor deposition - Google Patents

Abstract

The present invention relates to a diamond deposition method using a hot filament chemical vapor deposition (HFCVD) method capable of increasing the rate of diamond deposition by increasing the degree of supersaturation in a substrate of a gaseous species in the growth of diamond by using the HFCVD method. The diamond deposition method using the HFCVD method according to the present invention is the diamond deposition method using an HFCVD device. The HFCVD device comprises: a chamber which provides a reaction space for diamond synthesis; a water-cooling block which is provided in the chamber for providing a mounting space for a substrate and controlling the temperature of the substrate; a high melting point filament which is provided at a position spaced apart from the upper part of the substrate; and a mixed gas supply pipe which supplies a mixed gas of hydrogen and methane into the chamber. The flow rate of the mixed gas is controlled to be 0.7-1.2 slm/cm^2 for 1 cm^2 of the substrate.

Description

[0001] The present invention relates to a method for depositing a diamond by a HFCVD method,

More particularly, the present invention relates to a diamond deposition method using a HFCVD method, and more particularly, to a diamond deposition method using an HFCVD (hot filament chemical vapor deposition) And more particularly, to a diamond deposition method using an HFCVD method capable of improving the diamond deposition.

Diamonds have a variety of excellent physical properties. Among the existing materials, it has the highest hardness, thermal conductivity and light transmittance, so it can be applied to various fields. The artificial synthesis of diamond can be performed by high pressure high temperature synthesis (HPHT) and chemical vapor deposition (CVD) (K. Kobashi, Diamond Films: Chemical Vapor Deposition for Oriented and Heteroepitaxial Growth, Elsevier, 2005 Reference). In the case of the former, the synthesized diamond is in powder form, and in the latter case, it is in the form of a film coated on the substrate. Therefore, the latter case is suitable for various industrial applications.

In the case of meteoric composite diamond, applications can be divided into two types. One is a case in which a film with a thickness of several 탆 is coated on a part or the like, and the other is a case in which a diamond film itself is used by being synthesized with a thick film having a thickness of several hundred 탆 or more. In both cases, the growth rate of diamond is an important factor in manufacturing cost. Particularly, when the thick film itself is used as a product, the growth rate of the diamond is an important part of the manufacturing cost.

As a method of synthesizing diamond, it is the simplest and easiest method for large-area deposition, which is a hot filament chemical vapor deposition (HFCVD) method (Korean Patent No. 382943). The diamond synthesis method using the HFCVD method will be briefly described as follows. When a filament made of a high melting point metal such as tungsten is heated and a mixed gas of hydrocarbon and hydrogen is supplied and decomposed, the diamond is grown by the chemical reaction of the decomposed gas on the substrate provided under the filament. Thus, the HFCVD process is very simple and is widely used as a manufacturing method of diamond coating tools and the like. However, the diamond deposition rate is as low as 1 mu m / h or less, and is applied only to the coating field of diamond thin films.

Korea Patent No. 382943

K. Kobashi, Diamond Films: Chemical Vapor Deposition for Oriented and Heteroepitaxial Growth, Elsevier, 2005 S. Matsumoto, S. Sato, M. Kamo and N. Setaka Jpn. J. Appl. Phys., 21 (1982) L183-L185

DISCLOSURE Technical Problem The present invention has been devised to solve the problems described above, and it is an object of the present invention to improve the rate of diamond deposition by increasing the degree of supersaturation of a gas species on a substrate in growing diamond using a hot filament chemical vapor deposition (HFCVD) The present invention provides a diamond deposition method using the HFCVD method.

According to an aspect of the present invention, there is provided a diamond deposition method using a HFCVD (HFCVD) apparatus, wherein the HFCVD apparatus includes a chamber for providing a reaction space for diamond synthesis, A water-cooling block provided in the chamber to provide a mounting space for a substrate and controlling a temperature of the substrate; a high-melting point filament disposed at a spaced-apart position above the substrate; and a mixed gas of hydrogen and methane And a flow rate of the mixed gas is controlled to 0.7 to 1.2 slm / cm ² per cm ² of the substrate.

The methane concentration in the mixed gas is 0.1 to 0.5 vol%.

The temperature applied to the high melting point filament is 2400 to 2800 ° C.

The diamond deposition method using the HFCVD method according to the present invention has the following effects.

By increasing the flow rate of the mixed gas composed of hydrogen and methane and lowering the methane concentration in the mixed gas, the concentration of the hydrocarbon radical and the concentration of hydrogen in the vicinity of the substrate surface on which the diamond thin film is grown are increased, The speed can be improved.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a block diagram of an HFCVD apparatus for implementing a diamond deposition method using an HFCVD method according to an embodiment of the present invention; FIG.
2 is a SEM photograph of a diamond film deposited according to each flow rate (1 to 5 slm) of the mixed gas.
FIG. 3 shows Raman spectra results of the diamond films deposited according to the respective flow rates (1 to 5 slm) of the mixed gas.
Fig. 4 shows the deposition rate of the diamond thin film according to the methane ratio and the flow rate of the mixed gas.
FIG. 5 shows Raman spectra results of deposited diamond films with a methane concentration of 3%. FIG.

The present invention relates to a method of growing a diamond using a hot filament chemical vapor deposition (HFCVD) method, in which the concentration of hydrocarbon radicals and atomic hydrogen on the substrate surface on which diamond is grown is increased to improve the deposition rate of the diamond I suggest a technique that can be done.

It is obvious that the higher the hydrocarbon radical concentration on the substrate surface during the vapor deposition of diamond, that is, the higher the degree of supersaturation of the hydrocarbon radical on the substrate surface, the higher the deposition rate of the diamond. To increase the hydrocarbon radical concentration at the substrate surface can be considered to increase the ratio of methane (CH ₄₎ in the mixed gas of hydrogen (H ₂₎ and methane (CH _4). However, not only when the methane (CH ₄₎ the rate of increase in the gas mixture of hydrogen and methane (CH ₄₎ the formation of the graphite is subject to acceleration rate limit of methane (CH ₄₎ contained in the mixed gas.

The present applicant has proposed a method of using a graphite substrate or graphite structure in Korean Patent No. 1252669 as a method for increasing the degree of supersaturation of a carbon source. Specifically, a method has been proposed in which the graphite substrate or the graphite structure is etched by atomic hydrogen and the etched graphite reacts with hydrogen to increase the degree of supersaturation of the carbon source.

In the present invention, a method for increasing the mixed gas flow rate per unit area and raising the temperature applied to the high melting point filament of the HFCVD apparatus is proposed as a method for increasing the hydrocarbon radical concentration on the substrate surface. A method of increasing the flow rate of the mixed gas is proposed. Mixer refers to a mixed gas of hydrogen (H ₂ ) and methane (CH ₄ ) as described above.

In the growth of diamond using HFCVD equipment, a mixed gas of methane (CH ₄ ) and hydrogen (H ₂ ) is converted into hydrocarbon radical and elemental hydrogen while passing through a hot filament. In order to increase the deposition rate of diamond, the concentration of hydrocarbon radical on the surface of the substrate must be high as described above, and the atomic hydrogen reacts with graphite, not diamond, to suppress the formation of graphite.

In order to increase the diamond deposition rate, the concentration of the hydrocarbon radicals and the concentration of the hydrogen atoms on the surface of the substrate must be high. The hydrocarbon radicals and the atomic hydrogen that have passed through the filaments collide with each other , Recombination occurs due to collision. Recombination by collision and collision of hydrocarbon radical and atomic hydrogen means reduction of hydrocarbon radical concentration and atomic hydrogen concentration on the substrate surface.

In order to suppress the collision between the hydrocarbon radical and the atomic hydrogen and the recombination phenomenon, the present invention applies a method of increasing the mixed gas flow rate per unit area and raising the temperature applied to the high melting point filament of the HFCVD apparatus.

In the case of supplying the mixed gas (mixed gas of H ₂ and CH ₄ ) into the HFCVD apparatus equipped with the substrate on which the diamond thin film is grown, when the flow rate supplied per unit area of the substrate is increased, As the amount of spontaneous hydrogen increases, the collision between the hydrocarbon radical and the atomic hydrogen, and hence the recombination, is canceled by the increased flow rate, and the amount of hydrocarbon radical and atomic hydrogen finally reaching the substrate surface . Further, the increase in the flow rate means an increase in the flow rate, and the collision between the hydrocarbon radical and the atomic hydrogen due to the increase of the flow rate and hence the recombination phenomenon can be additionally suppressed.

Also, the mixed gas supplied to the HFCVD apparatus is decomposed and activated while passing through the high melting point filament. By increasing the temperature applied to the high melting point filament, the amount of hydrocarbon radical and atomic hydrogen supplied to the surface portion of the substrate can be increased.

On the other hand, the present invention applies to lowering the methane (CH ₄ ) ratio in the mixed gas by another method for increasing the concentration of the hydrocarbon radical and the concentration of the hydrogen atom in the substrate surface. As it described above, when the ratio of methane (CH ₄₎ increases in the mixed gas of hydrogen (H ₂₎ and methane (CH ₄₎ the formation of the graphite is accelerated in the way of diamond growth.

The present invention relates to a method of increasing the flow rate of the mixed gas to increase the concentration of hydrocarbon radicals and the concentration of hydrogen in the surface of the substrate, a method of raising the temperature applied to the high melting point filament of the HFCVD apparatus, A method of lowering the methane (CH ₄ ) ratio in the mixed gas is applied, thereby improving the deposition rate of the diamond.

The flow rate of the mixed gas for increasing the concentration of hydrocarbon radicals and atomic hydrogen on the substrate surface should be designed so that mixed gas of 0.7 to 1.2 slm (standard liter per minute) per 1 cm ² of the unit area of the substrate is supplied. When the flow rate of the mixed gas is less than 0.7 slm / cm ² , recombination phenomenon occurs due to collision of hydrocarbon radical and atomic hydrogen, which limits the concentration of hydrocarbon radical and atomic hydrogen concentration on the surface of the substrate. In addition, when the flow rate of the mixed gas exceeds 1.2 slm / cm ² , the gas species on the surface of the substrate becomes excessively supersaturated and the growth of the diamond may be rather disturbed. 2, 3, and 5, the total flow rate of the mixed gas to be supplied to the HFCVD apparatus is set to 1 to 5 slm, and the total mixed gas flow rate of 1 to 5 slm in FIGS. 2, 3, When converted to 1 cm ² area, it corresponds to 0.7 to 1.2 slm. The results of FIGS. 2, 3 and 5 show that when the mixed gas is supplied at 0.7 to 1.2 slm per 1 cm ² of the substrate area, the diamond crystallinity is secured and the diamond deposition rate is improved.

In the deposition of diamond using the HFCVD apparatus, the high melting point filament of the HFCVD apparatus is generally controlled to a temperature of about 2000 ° C. In the present invention, the temperature applied to the high melting point filament is controlled to 2400 to 2800 ° C. It is possible to maximize the decomposition rate of the mixed gas at a temperature in the range of 2400 to 2800 ° C and maximize the decomposition rate of the mixed gas to increase the concentration of the hydrocarbon radical and the concentration of the atomic hydrogen on the substrate surface. In one embodiment, when the high-melting-point filament is formed of tungsten, the temperature applied to the filament can be controlled to 2400 to 2500 ° C. When the high-melting-point filament is made of tantalum, Lt; 0 > C.

On the other hand, the ratio of methane (CH ₄ ) in the mixed gas for increasing the concentration of the hydrocarbon radical and the concentration of the hydrogen atom on the surface of the substrate should be controlled to 0.1 to 0.5 vol% based on the total mixed gas volume. As described above, the lower the hydrocarbon ratio, the higher the hydrocarbon radical concentration and the atomic hydrogen concentration, but if the hydrocarbon ratio is lower than 0.1 vol%, the absolute amount of the carbon source becomes smaller and the diamond deposition rate becomes lower, If it is larger than 0.5 vol%, there is a problem that the ratio of black image in the thin film increases.

The HFCVD apparatus in which the diamond deposition method according to the present invention is implemented is constituted as follows. The HFCVD apparatus includes a chamber 110 for providing a reaction space as shown in FIG. 1, a water cooling block (cooling) 120 provided inside the chamber 110 for providing a mounting space for the substrate 10, block 120, as shown in FIG. The mixed gas of hydrogen (H ₂ ) and methane (CH ₄ ) is supplied to the interior of the chamber 110 through the mixed gas supply pipe 140. The high melting point filament 130 is heated by power application.

In such an HFCVD apparatus, the filament is spaced about 1 cm from the substrate and heated to 2400 to 2800 ° C to activate a mixed gas of hydrogen and hydrocarbon. The activated gas moves toward the substrate and recombination occurs between the gases due to the interaction between the elements due to the collision between the elements during movement. As a result, the degree of activation of the gas is greatly reduced and the concentration of the atomic hydrogen It also decreases. Therefore, when the distance between the substrate and the filament reaches a predetermined value or more, the diamond is not synthesized. In addition, it has been reported that as the distance decreases, the deposition rate of diamond and the content of graphite become smaller (Kim JW, Ph.D. dissertation, Korea Advanced Institute of Science and Technology, 1992).

The pressure used in the diamond synthesis in the HFCVD process is generally between 10 and 60 torr. The mean free path in this pressure range is several micrometers (A user's guide to vacuum technology, John Wiley & Sons, 1989, p 11). Thus, sufficient contact and collision between gas elements occurs while the activated gas moves from the filament to the substrate. If this collision results in a thermodynamic equilibrium of the gas at the substrate temperature, only graphite should be deposited. However, it can be seen from experimental deposition of diamond that atomic hydrogen is supersaturated.

These results are inferred to be due to two possibilities. One is that the collision between gas elements occurs at a synthesis pressure of several tens of torr, but the activated gas species are continuously supplied from the filament, and the reaction time is not sufficient for thermodynamic equilibrium between the gas elements, to be. The other is the case where the temperature gradient from the filament to the substrate does not form a linearly gentle slope but forms a sharp gradient on the surface of the substrate. In this case, there is a possibility that the thermodynamic equilibrium between the gas species corresponding to the abrupt temperature gradient of the surface portion of the substrate is difficult to be formed, so that the activation degree of the gas can be maintained.

Movement of the gas species into the substrate in the chamber of the HFCVD apparatus proceeds by diffusion. Increasing the rate of movement of gas elements artificially in such an HFCVD apparatus can reduce the number of collisions between gas elements during movement from the filament to the substrate. The reduction in the number of collisions reduces the reaction rate between the gas elements, so that the activation of the gas generated in the filament can be maintained at a higher level, and the concentration of the elemental hydrogen in the substrate region can be maintained at a high level. For example, if the flow rate of the substrate is increased to increase the flow rate of the gas several times, the rate of reduction of the gas activation rate at the substrate site can be reduced accordingly. This effect of reducing the collision between gas species through gas velocity control is similar to reducing the distance between the filament and the substrate and can also increase the rate of deposition of the film while reducing the formation of graphite in the deposited film. The present invention controls the flow rate of the mixed gas to 0.7 to 1.2 slm / cm < ² > per unit area of the substrate.

The diamond deposition method using the HFCVD method according to the present invention has been described above. Hereinafter, the present invention will be described in more detail with reference to experimental examples.

EXPERIMENTAL EXAMPLE 1: Deposition Behavior of Diamond by Increasing Mixture Gas Flow Rate [

1% of methane-99% of hydrogen was supplied to the HFCVD apparatus to perform diamond deposition. The distance between the substrate and the filament was maintained at 1 cm, the synthesis pressure was 40 torr, and the filament and substrate temperatures were fixed at 2400 ° C and 950 ° C, respectively. Further, diamond deposition was carried out while changing the flow rate of the precursor gas from 1 slm (0.7 slm / cm ² ) to 5 slm (1.2 slm / cm ² ).

2 is an SEM photograph of a diamond thin film deposited according to each flow rate (1 to 5 slm, 0.7 to slm / cm ² ) of a mixed gas. Referring to FIG. 2, the crystallinity of the diamond thin film decreases slightly as the flow rate increases, but diamond crystals are well formed.

FIG. 3 is a Raman Spectra result of a diamond thin film deposited according to each flow rate (1 to 5 slm, 0.7 to slm / cm ² ) of a mixed gas. Referring to FIG. 3, it can be seen that a scattering peak at 1332 cm ^-1 , which represents a diamond crystal, is clearly observed regardless of the flow rate of the mixed gas.

EXPERIMENTAL EXAMPLE 2 Deposition Rate of Diamond Thin Film with Increasing Mixture Gas Flow Rate [

The rate of methane in the mixed gas was set to 0.5 to 3.0%, and the flow rate of the mixed gas was changed from 1 slm (0.7 slm / cm ² ) to 5 slm (1.2 slm / cm ² ). The other experimental conditions were the same as in Experimental Example 1.

4 shows the deposition rate of the diamond thin film according to the methane ratio and the flow rate of the mixed gas. Referring to FIG. 4, although the deposition rate tends to increase as the flow rate of the mixed gas increases, the tendency to increase the deposition rate is remarkably decreased as the concentration of methane increases. In the case of 0.5% methane, the deposition rate increased by 10 times as compared to 1 slm (0.7 slm / cm ² ) at a flow rate of 5 slm (1.2 slm / cm ² ). The difference in the rate of deposition rate with methane concentration seems to be related to the crystallinity of the deposited diamond film. FIG. 5 is a Raman Spectra result of the deposited diamond thin film when the methane concentration is 3%. As shown in FIG. 5, no diamond scattering peak of 1332 cm ^-1 is seen. Instead, the nano-crystal diamond scattering band (nano-crystalline diamond scatter band) and a band of amorphous carbon in the vicinity of 1500cm ^-1 1140cm ^-1 are observed in the vicinity. This means that the deposited thin film contains a lot of graphite phase and the crystal size of the diamond is also very small. Therefore, the effect of increasing the deposition rate with the increase of the flow rate of the mixed gas is considered to be large under conditions in which atomic hydrogen concentration is high (ie, the methane concentration is as small as 0.1 to 0.5%) and the synthesis of crystalline diamond is easy .

10: substrate 110: chamber
120: water cooling block 130: filament
140: Mixed gas supply pipe

Claims (3)

A diamond deposition method using a hot filament chemical vapor deposition (HFCVD)
The HFCVD apparatus includes:
A water-cooling block provided in the chamber for controlling the temperature of the substrate and providing a mounting space for the substrate, a high-melting-point filament disposed at a spaced-apart position above the substrate, And a mixed gas supply pipe for supplying a mixed gas of hydrogen and methane therein,
The flow rate of the gas mixture are diamond deposition method using the HFCVD characterized in that the control in 0.7~1.2slm / cm ² per 1cm ² of the substrate.
The diamond deposition method according to claim 1, wherein the concentration of methane in the mixed gas is 0.1 to 0.5 vol%.
The diamond deposition method according to claim 1, wherein a temperature applied to the high-melting point filament is in a range of 2400 to 2800 ° C.

Images