METHOD OF DIAMOND NUCLEATION AND STRUCTURE FORMED THEREOF

Abstract

The present invention relates to a method of diamond nucleation, comprising the following steps: providing a substrate and forming a metal layer on the substrate, wherein the metal layer comprises a catalyst and a transitional metal, the catalyst is copper, nickel or a combination. thereof, and the transitional metal is tungsten, molybdenum or a combination thereof; providing a reaction chamber and disposing the substrate in the reaction chamber; providing a gas mixture in the reaction chamber, wherein the gas mixture includes a carbon-containing gas and hydrogen gas; causing the carbon-containing gas to react and form a graphene layer on the metal layer; and causing the graphene to react with the transitional metal and the carbon-containing gas to form diamond nuclei on the metal layer at a border between the graphene layer and the metal layer. The present invention also relates to a structure formed by the aforesaid method.

Claims

1. A method of diamond nucleation, comprising the following steps: providing a substrate and forming a metal layer on a surface of the substrate, wherein the metal layer comprises a catalyst and a transitional metal, the catalyst is copper, nickel or a combination thereof, and the transitional metal is tungsten, molybdenum or a combination thereof; providing a reaction chamber and disposing the substrate with the metal layer formed thereon in the reaction chamber; providing a gas mixture in the reaction chamber, wherein the gas mixture includes a carbon-containing gas and hydrogen gas; causing the carbon-containing gas to react and form a graphene layer on a surface of the metal layer; and causing the graphene layer to react with the transitional metal and the gas mixture of the hydrogen gas and the carbon-containing gas to form diamond nuclei on the metal layer at a border between the graphene layer and the metal layer.

2. The method as claimed in claim 1, wherein no diamond seed is disposed on the substrate nor on the graphene layer.

3. The method as claimed in claim 1, wherein no negative bias is externally applied to the substrate.

4. The method as claimed in claim 1, wherein plasma is formed in the reaction chamber and the graphene layer is formed by plasma enhanced. chemical vapor deposition.

5. The method as claimed in claim 1, wherein plasma is formed in the reaction chamber and the diamond nuclei are formed by plasma enhanced chemical vapor deposition.

6. The method as claimed in claim 1, further comprising a step of causing the gas mixture of the hydrogen gas and the carbon-containing gas to react and form a diamond film from the diamond nuclei,

7. The method as claimed in claim 1, wherein the carbon-containing gas is a hydrocarbon gas.

8. The method as claimed in claim 7, wherein the hydrocarbon gas is methane.

9. The method as claimed in claim 1, wherein the gas mixture farther includes argon.

10. The method as claimed in claim 1, wherein the metal layer is a single layer comprising the catalyst and the transitional metal.

11. The method as claimed in claim 1, wherein the catalyst is copper.

12. The method as claimed in claim 1, wherein the transitional metal is tungsten.

13. The method as claimed in claim 1, wherein the substrate is a silicon substrate, a silicon dioxide substrate, a silicon wafer, a copper substrate, a nickel substrate, a tungsten substrate, a molybdenum substrate, a titanium substrate, or a metal or ceramic substrate coated by copper, nickel, tungsten, molybdenum, titanium, silicon or a combination thereof.

14. A structure formed by the method as claimed in claim 1 comprising: a substrate; a metal layer disposed on the substrate, wherein the metal layer comprises a catalyst and a transitional metal, the catalyst is copper, nickel or a combination thereof, and the transitional metal is tungsten, molybdenum or a combination thereof; a graphene layer formed on the metal layer; and a plurality of diamond nuclei formed on the metal layer at a border between the graphene layer and the metal layer.

15. The structure as claimed in claim 14, wherein the catalyst is copper.

16. The structure as claimed in claim 14, wherein the transitional metal is tungsten.

17. A structure formed by the method as claimed in claim 1 comprising: a substrate; a metal layer disposed on the substrate, wherein the metal layer comprises a catalyst and a transitional metal, the catalyst is copper, nickel or a combination thereof, and the transitional metal is tungsten, molybdenum or a combination thereof, a graphene layer formed on the metal layer; and a diamond film formed by merging diamond islands grown from diamond nuclei formed on the metal layer at a border between the graphene layer and the metal layer.

18. The structure as claimed in claim 17, wherein the catalyst is copper.

19. The structure as claimed in claim 17, wherein the transitional metal is tungsten.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] FIG. 1 is a schematic diagram showing a structure including a substrate, a tungsten-copper layer, a graphene layer, and diamond nuclei according to Embodiment 1 of the present invention.

[0044] FIG. 2 shows a Raman spectrum of diamond crystals formed in Embodiment 1 of the present invention.

[0045] FIG. 3 is an optical microscope image of diamond crystals formed in Embodiment 1 of the present invention.

[0046] FIG. 4 shows a Raman spectrum of graphene in area of the substrate where the surface is not covered by diamond nuclei in Embodiment 1 of the present invention.

[0047] FIG. 5 shows a Raman spectrum of diamond crystals formed in Embodiment 2 of the present invention.

DETAILED DESCRIPTION OF EMBODIMENT

[0048] The following embodiments when read with the accompanying drawings are made to clearly exhibit the above-mentioned and other technical contents, features and/or effects of the present disclosure. Through the exposition by means of the specific embodiments, people would further understand the technical means and effects the present disclosure adopts to achieve the above-indicated objectives. Moreover, as the contents disclosed herein should be readily understood and can be implemented by a person skilled in the art, all equivalent changes or modifications which do not depart from the concept of the present disclosure should be encompassed by the appended claims.

[0049] Furthermore, when a value is in a range from a first value to a second value, the value can be the first value, the second value, or another value between the first value and the second value.

Embodiment 1

[0050] FIG. 1 is a schematic diagram showing a structure of the present embodiment.

[0051] In the present embodiment, a substrate 11 is provided, which is a silicon substrate. A metal layer 12, which is a tungsten-copper film, is co-sputtered on a surface 111 of the substrate 11. In the present embodiment, the metal layer 12 (i.e. the tungsten copper film) is co-sputtered on the substrate 11 (i.e. the silicon substrate) in an argon environment by RF magnetron sputtering. The sputtering power is 90 W at a gas pressure of 210.sup.2 ton, under 30 sccm flow of argon. The sputtering process lasts for 15 mins,

[0052] Next, the substrate 11 coated with the metal layer 12 (i.e. the to film) is placed into a reaction chamber (not shown in the figure), and a gas mixture containing methane gas, hydrogen gas, and argon gas is provided into the reaction chamber to carry out a plasma enhanced chemical vapor deposition process. A graphene layer or discrete graphene island 13 is formed on the metal layer 12 (i.e. the tungsten-copper film) by the copper catalyst and the plasma enhanced CVD reacts with both graphene and tungsten to produce sp3 bond structure which is favorable for diamond nucleation.

[0053] In the reaction chamber, the gas mixture containing 1% methane diluted by the hydrogen gas and the argon gas reacts to form a plurality of diamond nuclei 14 on a surface of the metal layer 12 (i.e. the tungsten-copper film) where the graphene layer 13 is formed in-situ before diamond nuclei are formed. Specifically, a total flow of the gas mixture of 5 sccm of the methane gas and 500 sccm of the hydrogen gas in the reaction chamber of 50 liters volume is reacted for 2 hr under conditions such as a microwave power of 4000 W, a deposition pressure of 55 Torr, and a substrate temperature of 710C.

[0054] In the present embodiment, no diamond seed is disposed on the substrate 11 nor on the metal layer 12 (i.e. the tungsten-copper film). Both the substrate 11 and the metal layer 12 (i,e. the tungsten-copper film) are not processed by bias-enhanced diamond nucleation.

[0055] After the aforesaid process, as shown in FIG. 1, the structure is formed by synthesizing diamond nuclei 14 through reactions by the Diamond CVD plasma with the graphene layer 13 and the transitional metal predominantly along edges of in-situ formed graphene layer 13 on the substrate 11 coated with the metal layer 12 (i.e. the tungsten-copper film). More specifically, the structure of the present embodiment comprises: a substrate 11; a metal layer 12 (i.e. the tungsten-copper film) disposed on the substrate 11; a graphene layer 13 formed on the metal layer 12; and a plurality of diamond nuclei 14 formed on the metal layer 12 at a border between graphene layer 13 and the metal layer 12.

[0056] FIG. 2 shows a Raman spectrum (excited by a 532 m laser) of diamond crystals formed in the present embodiment. Specifically, diamond crystals are formed on a graphene-tungsten-copper layer, on which graphene is formed with copper as a catalyst before diamond nuclei are fanned.

[0057] As shown in FIG. 2, the signal intensity of the diamond Raman peak at 1332 cm.sup.1 is clear and sharp. Besides the diamond peak, G-band (around 1600 cm.sup.1), D-band between the diamond peak and the G-band (around 1450 cm.sup.1), and 2-D band (around 2700 cm.sup.4) originating from graphene are also clearly displayed. The silicon peak comes from the silicon substrate. This result demonstrates that diamond crystals have been formed on the graphene-tungsten-copper layer.

[0058] FIG. 3 is an optical microscope image (1000) of diamond crystals formed in the present embodiment. As shown in FIG. 3, individual diamond crystals are clearly seen. The density of diamond crystals is so high that a continuous diamond film can be formed after those diamond crystals grow larger both vertically and laterally. A silicon substrate coated with tungsten-copper by RF magnetron co-sputter from a tungsten target with 40% of the surface of a tungsten target having been covered by a copper foil. Tungsten atoms and copper atoms are knocked out of the target by energetic ions and diffuse and become mixed when they arrive at the substrate to deposit a thin film containing both tungsten and copper. The copper is used as a catalyst for forming graphene by-plasma enhanced CVD in 1% methane gas diluted by hydrogen. Graphene reacts with the plasma and the tungsten for promoting the formation of sp3 bonded graphene edges and defective sites, where carbon containing radicals are attached to form diamond nuclei.

[0059] FIG. 4 shows a Raman spectrum of exposed graphene which is formed on the tungsten-copper film in the present embodiment. The strong D-band at 1340 cm.sup.1, fig-band at 1600 cm.sup.1, and 2-D band at 2680 cm.sup.1 are clearly displayed and characteristic of graphene islands with abundant edges. It demonstrates that copper in the tungsten-copper film serves well as a catalyst to form graphene on the tungsten-copper film in-situ under plasma excitation in a gas mixture of 1% methane diluted by hydrogen, and synthesis of a continuous diamond film is then induced. In another word, the graphene synthesis, diamond nucleation, and diamond growth processes are integrated in one process without changing the plasma chemistry. However, this does not limit the further optimization of the integrated diamond nucleation and growth process for the fabrication of diamond films of different grain sizes. Ultrananocrystalline diamond films with grain sizes of few to several nanometers in size need the process gas mixture to he diluted mainly by argon gas so as to promote secondary nucleation, Microcrystalline diamond films with grain sizes of one hundred nanometers to multiple micrometers require the process gas mixture to be diluted by abundant hydrogen gas to suppress secondary nucleation and to enhance the diamond growth rate. Nanocrystalline diamond films need gas mixture between those for ultra-nanocrystalline diamond films and for microcrystalline diamond films.

Embodiment 2

[0060] The process and the structure of the present embodiment are similar to those of Embodiment 1, except for the conditions of the plasma enhanced CVD.

[0061] In the present embodiment, the diamond. films are grown at a higher substrate temperature of 850 C. at 65 Torr gas pressure in 1% methane diluted by hydrogen under 4000 W microwave excitation for two hours.

[0062] FIG. 5 shows a Raman spectrum of diamond crystals formed in the present embodiment. The signal strength of diamond Raman peaks at 1332 cm.sup.1 shown in FIG. 5 is much stronger than that in FIG. 2. This is consistent with commonly known diamond CVD art. In the Raman spectrum, the signal strength of the D-band (at around 1450 cm.sup.1) from dis-ordered carbon phase is much weaker than that in FIG. 2. The G-hand (at around 1600 cm) and the 2-D band (at around 2686 cm.sup.1) are clear indicating better quality of graphene having been formed on the tungsten-copper thin film at a high substrate temperature of 850 C.

[0063] Although the present invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the invention as hereinafter claimed.