TWI415965B - Method of diamond nucleation - Google Patents

Abstract

The present invention relates to a method of diamond nucleation, including: providing a gas mixture, which includes a noble gas and a carbon-containing gas, in a reaction chamber; and forming a plasma in the reaction chamber to react the carbon-containing gas into a plurality of nuclei on an unseeded substrate without externally applied bias voltage. The plasma does not contact with the substrate. Accordingly, the present invention can achieve direct nucleation on a non-diamond substrate for subsequent diamond growth.

Description

Diamond nucleation method

The invention relates to a novel diamond nucleation method, in particular to a diamond nucleation method without direct nucleation under external bias.

Diamonds possess many excellent physical, chemical, optical, mechanical and electrical properties, such as high thermal conductivity, chemical inertness, highest hardness, high Young's modulus and low coefficient of friction, wide energy gap and wide optical wear. Through the frequency domain. Therefore, polycrystalline diamond (PCD) is a material widely used in the industrial field in recent years, and its advantages are in addition to the excellent mechanical properties of a single crystal diamond, and can be processed into a desired shape in accordance with the purpose. The use of chemical vapor deposition (CVD) to grow polycrystalline diamond films is a well-established and common method, mainly using precursor materials such as hydrogen, oxygen, hydrocarbons and other carbonaceous materials. The polycrystalline diamond film is grown by using various forms of energy application to free and excite the mixed gas containing the precursor material.

When diagnosing diamonds on non-diamond substrates, nucleation or seeding must be performed. Since self-nucleation can simplify the diamond deposition process, many studies are devoted to the self-nucleation of diamonds. method. The first heterogeneous nucleation method proposed is bias-enhanced nucleation, which increases the kinetic energy of the species by applying a negative bias to the substrate, and effectively attacks the substrate to form a nucleus, wherein The bias voltage can be a DC bias or an RF bias. In addition, related research indicates that additional coating layers (such as amorphous carbon layers) can facilitate subsequent nucleation processes.

On the other hand, related research has proposed a preparation method of a super nanocrystalline diamond film (UNCD), which is formed by using a mixed gas containing methane and argon without hydrogen or oxygen. Ultra-nanocrystalline diamond film with surface flatness (grain size about 2-5 nm). Compared with the conventional method for growing a diamond film under hydrogen-rich conditions, since the argon free energy is lower than that of hydrogen, the method can grow a super nanocrystalline diamond film at a lower microwave power and a lower substrate temperature. . However, this method must first perform the seeding process before growing the nano-crystal diamond film, so it is not conducive to simplifying the process.

The main object of the present invention is to provide a novel diamond nucleation method for diamond nucleation directly on a non-crystallized non-diamond substrate without external biasing.

In order to achieve the above object, the present invention provides a diamond nucleation method comprising: providing a mixed gas in a reaction chamber, wherein the mixed gas comprises an inert gas and a carbon-containing gas; and forming a plasma in the reaction chamber And reacting the carbon-containing gas on an uncrystallized substrate to form a plurality of core species without applying a bias voltage, wherein the plasma is not in contact with the substrate. Here, the present invention is preferably carried out in a microwave plasma chemical vapor deposition system for diamond nucleation.

Accordingly, compared with the conventional bias-assisted nucleation method, the present invention can achieve the purpose of diamond nucleation without applying a bias voltage under the condition that the substrate is not in contact with the plasma. In detail, due to the limited depth of the microwave penetrating plasma ball, the microwave energy is mostly absorbed by the outer layer of the plasma ball, and part of the plasma species is diffused to the inside by the outer layer of the plasma ball. The internal rate is slower, so the plasma density of the outer layer of the plasma ball will be greater than the internal plasma density; accordingly, in the present invention, since the substrate is very close to the plasma but not in contact with the plasma, the outer layer of the plasma ball will not Shielded by the substrate, therefore, compared with the conventional method of contacting the plasma with the substrate, the outer layer of the plasma ball not in contact with the substrate can effectively absorb the microwave energy to form a high-density plasma layer, which can be made by high density. Low energy ions collide to increase the surface temperature of the substrate to facilitate diamond nucleation. At the same time, the nucleation method of the present invention does not require an external bias except that the electron diffusion rate in the plasma is greater than the self-bias caused by the positive ions. (such as DC bias or RF bias), and some of the electrons with sufficient energy and excited state argon can pass through the plasma sheath between the substrate and the plasma ball to reach the vicinity of the substrate, and then generate a nucleation near the substrate. Needed plasm (E.g., carbon containing radical and the amount of atomic hydrogen), the substrate to serve as nucleation on the non-seed. Therefore, the present invention can be directly nucleated on a non-diamond substrate having no carbon coating even without applying a bias voltage.

In the present invention, the distance between the plasma and the substrate is preferably from 2 mm to 10 mm, more preferably from 3 mm to 6 mm, wherein the distance between the plasma and the substrate means a higher electron density and a higher The shortest distance from the surface of the plasma ball of brightness (ie, the outer layer of the plasma ball) to the surface of the substrate.

In the present invention, those skilled in the art can adjust the appropriate microwave power according to the microwave frequency and the reactor size. For example, if a substrate carrier of 5 cm to 7 cm diameter and a 2.45 GHz microwave are used, the microwave power is compared. Preferably, the process parameters of the diamond nucleation are: the substrate temperature is about 200 ° C to 900 ° C, and the deposition pressure (ie, the mixed gas pressure) is about 50 Torr to 300 Torr.

In addition, the present invention can improve the purity and quality of the synthetic diamond by controlling the flow rate of the mixed gas and avoiding excessive carbon-containing gas in the reaction chamber to form carbon soots. In detail, the conventional method often causes the plasma to form an unstable orange-red plasma region due to gas phase synthesis of carbon particles, thereby affecting the purity and quality of the diamond, resulting in process failure. However, the present invention can vary with the size of the reaction chamber. The size of the microwave power, the deposition pressure, and the content of the carbon-containing gas in the mixed gas, lowering the total flow rate of the mixed gas to prolong the residence time of the reaction gas in the reaction chamber, thereby making the amount of carbon in the reaction chamber It is slightly lower than the amount required for the synthesis of carbon particles in the gas phase to avoid the instability of the plasma caused by the gas phase synthesis of carbon particles, thereby improving the quality of diamond nucleation. Specifically, in actual operation, the operator can adjust the total mixed gas flow rate by observing whether an unstable orange-red plasma region is formed in the plasma; that is, in the present invention, preferably, By adjusting the total flow rate of the mixed gas, the plasma is prevented from forming an orange-red plasma region. Taking the volume of 4 liters of the reaction chamber as an example, the present invention preferably controls the total flow rate of the mixed gas at a flow rate of about 5 sccm to 100 sccm at a microwave power of 400 watts and a deposition pressure of 110 Torr (that is, based on the volume per liter of the reaction chamber. The flow rate is preferably from 1 sccm to 25 sccm), more preferably from 20 sccm to 40 sccm (i.e., the total flow rate is preferably from 5 sccm to 10 sccm per liter of the reaction chamber) to improve the quality of diamond nucleation. . Here, the volume percentage of the carbon-containing gas in the mixed gas is preferably from about 0.05% to 50%, more preferably from about 0.1% to 10%, most preferably from about 0.5% to 5%, for example, one of the present inventions. The embodiment uses methane as the carbon-containing gas, and the content thereof is preferably 0.1% to 10%; in addition, those having ordinary knowledge in the art can modulate the diamond nucleation by adjusting the content of the carbon-containing gas in the mixed gas. density. Accordingly, when the present invention performs diamond nucleation under conditions of microwave power of 200 W to 800 W, carbon-containing gas of 0.1% to 10%, and deposition pressure of 50 Torr to 300 Torr, based on the volume per liter of the reaction chamber, Preferably, the present invention controls the total flow rate of the mixed gas from about 1 sccm to 25 sccm to facilitate the formation of high purity and high quality synthetic diamond.

In the present invention, the carbon-containing gas is preferably reacted to nucleate without hydrogen doping, whereby the microwave power required for the free inert gas (such as argon) is compared to the conventional nucleation method rich in hydrogen. Smaller, and less hydrogen-containing, the atomic hydrogen produced is less, which is beneficial to low-temperature processes. In detail, the heat released by the combination of microwave energy and atomic hydrogen causes the substrate temperature to rise. Therefore, the process conditions of low microwave power and low atomic hydrogen content help to reduce the heat load of the substrate, and can be used at lower temperatures. Nucleation under process conditions is conducive to expanding the application of synthetic diamonds. In addition, nucleation under conditions of no hydrogen doping has the advantage of being safer in process. Of course, the present invention can also perform diamond nucleation under conditions of a small amount of hydrogen, but at this time, higher microwave power is required to generate plasma, and the substrate temperature is higher. In the present invention, the carbon-containing gas is not particularly limited, and may be any carbon-containing gas used in a conventional chemical vapor deposition method, but is preferably a hydrocarbon gas such as methane or acetylene.

In the present invention, the inert gas is preferably an inert gas other than helium, such as argon gas, helium gas, neon gas or a mixed gas thereof, and more preferably argon gas.

In the present invention, the substrate is not particularly limited except for temperature resistance, and it may be any target for depositing a diamond film. Here, the present invention can nucleate directly on a conductive substrate or an insulating substrate without applying a bias voltage (such as a DC bias or an RF bias); in particular, a carbon coating is additionally formed as a transition layer. The prior art can directly nucleate on the surface of the non-carbon phase without additionally forming a carbon coating as a transition layer, that is, the invention can directly be applied to a non-diamond substrate without a carbon coating (such as a germanium substrate or two). Nucleation on the ruthenium oxide substrate.

In summary, the present invention can directly form a nuclear species on a substrate that is not seeded without external bias, and can be grown into a diamond and a diamond film from a nuclear species that is self-nucleating. For example, in the embodiment of the present invention, the crystal grains are directly nucleated on the ruthenium substrate or the ruthenium dioxide substrate, and then the nano-crystal diamond (UNCD) is grown on the nucleus, and the grown grain size can be increased with the growth time. To 1000 nm or more. Moreover, as shown in another embodiment, those of ordinary skill in the art can also prepare diamonds having larger grain sizes by adjusting appropriate diamond growth parameters to different growth parameters than nucleation conditions. That is, the present invention can not only complete diamond nucleation and growth under the described process, but also can be combined with other diamond growth processes to prepare diamonds and diamond films of various structures. Compared with the conventional bias-assisted nucleation method, the present invention can achieve the purpose of diamond nucleation without applying a bias voltage under the condition that the substrate is not in contact with the plasma. In particular, the present invention can be directly nucleated on a non-diamond substrate without the need to additionally form a carbon coating, which has the advantage of simplifying the process. In addition, the present invention can improve the purity and quality of the synthetic diamond by controlling the flow rate of the mixed gas and avoiding excessive carbon-containing gas in the reaction chamber to form carbon particles.

The embodiments of the present invention are described by way of specific examples, and those skilled in the art can readily appreciate the other advantages and advantages of the present invention. The present invention may be embodied or applied in various other specific embodiments, and various modifications and changes can be made without departing from the spirit and scope of the invention.

Example 1

Please refer to FIG. 1 , which is a schematic diagram of diamond nucleation and growth using a quartz bell-type SEKI 1.5 kW microwave plasma chemical vapor deposition system in this embodiment.

As shown in FIG. 1, in this embodiment, the uncrystallized substrate 11 is placed on the substrate stage 211 of the reaction chamber 21, and the inert gas 41 is controlled by the mass flow controllers 31, 32, respectively. The flow rate of argon gas and carbon-containing gas 42 (methane used in the present embodiment) was used, and then a mixed gas containing about 98.7% of inert gas 41 and 1.3% of carbon-containing gas 42 was introduced into the reaction chamber 21. Here, in the embodiment, the mass flow controller 33 is used together with the vacuum pump 51 to extract a part of the mixed gas to control the total flow rate of the mixed gas entering the reaction chamber 21 to be about 25 sccm, and the reaction chamber 21 is prevented from being contained. Excess carbonaceous gas 42 forms carbon particles. Accordingly, the microwave power is about 400 W at 2.45 GHz, the deposition pressure is about 110 Torr (pressure is controlled by the pressure controller 61), and the substrate temperature is about 450 ° C (measured by a thermocouple temperature sensor inserted in the substrate stage). Under the conditions of the chamber, a disk-shaped plasma 71 is generated in the reaction chamber 21, and the carbon-containing gas 42 is reacted to form a nucleus on the substrate 11, and the nucleus formed by the nucleation is grown to form a super nanocrystalline diamond.

In detail, as shown in FIG. 1, the substrate 11 is disposed at a position not in contact with the plasma 71 (wherein, the distance D between the plasma 71 and the substrate 11 is about 5 mm, that is, between the plasma 71 and the substrate 11. Since the plasma sheath has a thickness of about 5 mm, the outer layer of the plasma 71 is not shielded by the substrate 11, and accordingly, it is not in contact with the substrate 11 as compared with the conventional method of bringing the plasma into contact with the substrate. The outer layer of the plasma 71 can effectively absorb the microwave energy to form a high-density plasma layer 711, and the surface temperature of the substrate can be increased by collision of high-density low-energy ions to facilitate the formation of nuclear species, and at the same time, in addition to the electron diffusion speed in the plasma. In addition to the self-bias caused by the positive ions, no additional bias is applied in this embodiment, and some of the electrons with sufficient energy and the excited state of argon can pass through the plasma sheath to reach the vicinity of the substrate. Further, a plasma species (such as an appropriate amount of atomic hydrogen) required for nucleation is generated in the vicinity of the substrate, a nucleus is formed on the uncrystallized substrate, and then a super nanocrystalline diamond (UNCD) is grown from the formed nucleus.

In this embodiment, a self-nucleated diamond particle morphology on a substrate is observed using a scanning electron microscope (SEM). As shown in FIG. 2, this embodiment is a self-nucleating nucleus grown with a nano-crystal diamond (UNCD) of about 4 In hours, the grain size is from 500 nm to 1200 nm.

In addition, this embodiment further uses a 325 nm laser excitation source for Raman spectroscopy, as shown in FIG. 3, which can find a diamond-specific signal peak at 1330 cm ^-1 .

Example 2

The process conditions of this embodiment are substantially the same as those of Embodiment 1, except that the carbon-containing gas content of the present embodiment is increased by 2% to increase the nucleation density, and the mixed gas flow rate is reduced to 15 sccm (ie, The total flow rate of the mixed gas is about 4 sccm based on the volume per liter of the reaction chamber. 4 is a SEM analysis diagram of a super nanocrystalline diamond formed in the present embodiment, and has an average grain size of about 500 nm to 1200 nm.

Example 3

The process conditions of this embodiment are substantially the same as those of the second embodiment except that the present embodiment is based on a ceria substrate for diamond nucleation and growth. Fig. 5 is a SEM analysis diagram of the super nanocrystalline diamond formed in the present embodiment, and has an average crystal grain size of about 500 nm to 1200 nm.

Example 4

The process conditions of this embodiment are substantially the same as those of the first embodiment except that the carbon-containing gas (i.e., methane) of the present embodiment is increased by 2%, and the remaining 98% is an inert gas (i.e., argon) to increase the nucleation density. The nucleation is carried out under the condition of a total flow rate of 20 sccm. The deposition pressure and microwave power are below the fixed total flow gas composition, and gradually increase to a deposition pressure of 110 Torr and a microwave power of 400 W to synthesize a diamond seed; subsequently, the argon gas is turned off. And hydrogen is turned on to 99sccm to grow large-grain diamonds on the diamond core in the conventional diamond growth conditions of 1 sccm methane and 99 sccm hydrogen. At this time, the deposition pressure is adjusted to 50 Torr and the microwave power is increased to 1300 W. A diamond with a clear diamond face can be obtained in 10 minutes, as shown in Figure 6. It can be seen that the diamond nucleation method of the present invention is suitable for growing diamonds and diamond films of various structures.

Accordingly, compared with the conventional bias-assisted nucleation method, the present invention can achieve the purpose of diamond nucleation without applying a bias voltage under the condition that the substrate is not in contact with the plasma. In particular, the present invention can directly nucleate on a non-conductive non-diamond substrate on which a DC bias is not applicable, without additionally forming a carbon coating, or applying a bias power such as RF, which has the advantage of simplifying the process. In addition, the present invention can not only complete diamond nucleation and growth under the described process, but also can be combined with other diamond growth processes to prepare diamonds and diamond films of various structures. Furthermore, the present invention can improve the purity and quality of the synthetic diamond by controlling the flow rate of the mixed gas and avoiding excessive carbon-containing gas in the reaction chamber to form carbon particles. The above-mentioned embodiments are merely examples for convenience of description, and the scope of the claims is intended to be limited to the above embodiments.

11. . . Substrate

twenty one. . . Reaction chamber

211. . . Substrate stage

31,32,33. . . Mass flow controller

41. . . Inert gas

42. . . Carbonaceous gas

51. . . Vacuum pump

61. . . pressure controller

71. . . Plasma

711. . . High density plasma layer

D. . . distance

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic illustration of diamond nucleation and growth in a microwave plasma chemical vapor deposition system in accordance with a preferred embodiment of the present invention.

2 is a top plan view of a super nanocrystalline diamond formed in accordance with a preferred embodiment of the present invention under a scanning electron microscope.

3 is a Raman spectrum of a super nanocrystalline diamond formed by a laser at 325 nm in accordance with a preferred embodiment of the present invention.

4 is a top plan view of a super nanocrystalline diamond formed by another preferred embodiment of the present invention under a scanning electron microscope.

Figure 5 is a plan view of a super nanocrystalline diamond formed in accordance with still another preferred embodiment of the present invention under a scanning electron microscope.

Figure 6 is a side elevational view of a large grain diamond formed in accordance with yet another preferred embodiment of the present invention under a scanning electron microscope.

11. . . Substrate

twenty one. . . Reaction chamber

211. . . Substrate stage

31,32,33. . . Mass flow controller

41. . . Inert gas

42. . . Carbonaceous gas

51. . . Vacuum pump

61. . . pressure controller

71. . . Plasma

711. . . High density plasma layer

D. . . distance

Claims (11)

A diamond nucleation method comprising: providing a mixed gas in a reaction chamber, wherein the mixed gas comprises an inert gas and a carbon-containing gas; and forming a plasma in the reaction chamber without biasing The carbon-containing gas is reacted on an uncrystallized substrate to form a plurality of core species, wherein the plasma is not in contact with the substrate. The diamond nucleation method according to claim 1, wherein the distance between the plasma and the substrate is 2 mm to 10 mm. The method of diamond nucleation according to claim 1, wherein the nucleus is formed under conditions of no hydrogen doping. The diamond nucleation method of claim 1, wherein the nucleus is formed in a microwave plasma chemical vapor deposition system. The diamond nucleation method according to claim 1, wherein the carbon-containing gas is methane, and the inert gas is argon. The diamond nucleation method according to claim 1, wherein the volume percentage of the carbon-containing gas in the mixed gas is 0.05% to 50%. The diamond nucleation method according to claim 5, wherein the volume percentage of the carbon-containing gas in the mixed gas is 0.1% to 10%. The diamond nucleation method according to claim 3, wherein the carbon-containing gas system is nucleated at a substrate temperature of 200 ° C to 900 ° C. The diamond nucleation method according to claim 1, wherein the carbon-containing gas system is nucleated at a deposition pressure of 50 Torr to 300 Torr. The diamond nucleation method according to claim 8, wherein the volume percentage of the carbon-containing gas in the mixed gas is 0.05% to 50%, and the carbon-containing gas system has a deposition pressure of 50 Torr to 300 The reaction nucleates under the conditions of Torr. The diamond nucleation method according to claim 7, wherein the carbon-containing gas system is nucleated under conditions of a microwave power of 200 W to 800 W and a deposition pressure of 50 Torr to 300 Torr, and the reaction chamber is used. The total flow rate of the mixed gas is from 1 sccm to 25 sccm based on the volume per liter.