Thick polycrystalline synthetic diamond wafers for heat spreading applications and microwave plasma chemical vapour depositon synthesis techniques

Patent metadata

Field	Value
Publication number	US-9478938-B2
Application number	US-201314419340-A
Country	US
Kind code	B2
Filing date	Aug 9, 2013
Priority date	Aug 13, 2012
Publication date	Oct 25, 2016
Grant date	Oct 25, 2016

Abstract

A method of fabricating a polycrystalline CVD synthetic diamond material having an average thermal conductivity at room temperature through a thickness of the polycrystalline CVD synthetic diamond material of at least 2000 Wm −1 K −1 , the method comprising: loading a refractory metal substrate into a CVD reactor; locating a refractory metal guard ring around a peripheral region of the refractory metal substrate, the refractory metal guard ring defining a gap between an edge of the refractory metal substrate and the refractory metal guard ring having a width 1.5 mm to 5.0 mm; introducing microwaves into the CVD reactor at a power such that the power density in terms of power per unit area of the refractory metal substrate is in a range 2.5 to 4.5 W mm −2 ; introducing process gas into the CVD reactor wherein the process gas within the CVD reactor comprises a nitrogen concentration in a range 600 ppb to 1500 ppb calculated as molecular nitrogen N2, a carbon containing gas concentration in a range 0.5% to 3.0% by volume, and a hydrogen concentration in a range 92% to 98.5% by volume; controlling an average temperature of the refractory metal substrate to lie in a range 750° C. to 950° C. and to maintain a temperature difference between an edge and a centre point on the refractory metal substrate of no more than 80° C. growing polycrystalline CVD synthetic diamond material to a thickness of at least 1.3 mm on the refractory metal substrate; and cooling the polycrystalline CVD synthetic diamond material to yield a polycrystalline CVD synthetic diamond material having a thickness of at least 1.3 mm, an average thermal conductivity at room temperature through the thickness of the polycrystalline CVD synthetic diamond material of at least 2000 Wm −1 K −1 over at least a central area of the polycrystalline CVD synthetic diamond material, wherein the central area is at least 70% of a total area of the polycrystalline CVD synthetic diamond material, a single substitutional nitrogen concentration no more than 0.80 ppm over at least the central area of the polycrystalline CVD synthetic diamond material, and wherein the polycrystalline CVD synthetic diamond material is substantially crack free over at least the central area thereof such that the central area has no cracks which intersect both external major faces of the polycrystalline CVD synthetic diamond material and extend greater than 2 mm in length.

First claim

The invention claimed is:

1. A method of fabricating a polycrystalline CVD synthetic diamond material having an average thermal conductivity at room temperature through a thickness of the polycrystalline CVD synthetic diamond material of at least 2000 Wm −1 K −1 , the method comprising:
loading a refractory metal substrate into a CVD reactor;
locating a refractory metal guard ring around a peripheral region of the refractory metal substrate, the refractory metal guard ring defining a gap between an edge of the refractory metal substrate and the refractory metal guard ring having a width 1.5 mm to 5.0 mm;
introducing microwaves into the CVD reactor at a power such that the power density in terms of power per unit area of the refractory metal substrate is in a range 2.5 to 4.5 W mm −2 ;
introducing process gas into the CVD reactor wherein the process gas within the CVD reactor comprises a nitrogen concentration in a range 600 ppb to 1500 ppb calculated as molecular nitrogen N 2 , a carbon containing gas concentration in a range 1.5% to 3.0% by volume, and a hydrogen concentration in a range 92% to 98.5% by volume;
controlling an average temperature of the refractory metal substrate to lie in a range 750° C. to 950° C. and to maintain a temperature difference between an edge and a centre point on the refractory metal substrate of no more than 80° C.
growing polycrystalline CVD synthetic diamond material to a thickness of at least 1.3 mm on the refractory metal substrate; and
cooling the polycrystalline CVD synthetic diamond material to yield a polycrystalline CVD synthetic diamond material having a thickness of at least 1.3 mm, an average thermal conductivity at room temperature through the thickness of the polycrystalline CVD synthetic diamond material of at least 2000 Wm −1 K −1 over at least a central area of the polycrystalline CVD synthetic diamond material, wherein the central area is at least 70% of a total area of the polycrystalline CVD synthetic diamond material, a single substitutional nitrogen concentration no more than 0.80 ppm and no less than 0.10 ppm over at least the central area of the polycrystalline CVD synthetic diamond material, and wherein the polycrystalline CVD synthetic diamond material is substantially crack free over at least the central area thereof such that the central area has no cracks which intersect both external major faces of the polycrystalline CVD synthetic diamond material and extend greater than 2 mm in length.

2. A method according to claim 1 , wherein the refractory metal substrate has a diameter which lies in a range 60 mm to 120 mm, 80 mm to 110 mm, 90 mm to 110 mm, or 95 mm to 105 mm.

3. A method according to claim 1 , wherein the gap between the edge of the refractory metal substrate and the refractory metal guard ring has a width in a range 2.0 mm to 4.0 mm, or 2.5 mm to 3.5 mm.

4. A method according to claim 1 , wherein the nitrogen concentration in the process gas within the CVD reactor, calculated as molecular nitrogen N 2 , lies in a range 700 ppb to 1300 ppb, 800 ppb to 1200 ppb, or 900 ppb to 1100 ppb.

5. A method according to claim 1 , wherein the carbon containing gas concentration of the process gas within the CVD reactor lies in a range 1.6% to 2.5%, 1.7% to 2.3%, or 1.8 to 2.1% by volume.

6. A method according to claim 1 , wherein the hydrogen concentration of the process gas within the CVD reactor lies in a range 94% to 97%, or 95% to 96% by volume.

7. A method according to claim 1 , wherein the average temperature of the refractory metal substrate is controlled to lie in a range 775° C. to 900° C., 800° C. to 875° C., or 820° C. to 860° C.

8. A method according to claim 1 , wherein the temperature difference between the edge and the centre point on the refractory metal substrate is no more than 60° C., 40° C., 20° C., or 10° C.

9. A method according to claim 1 , wherein the power density is in a range 2.75 to 4.25 W mm −2 , 3.0 to 4.0 W mm −2 , 3.2 to 3.8 W mm −2 , or 3.3 to 3.6 W mm −2 .

10. A method according to claim 1 , wherein an operating pressure during growth of the polycrystalline CVD synthetic diamond material is controlled within a range 100 to 300 torr, 150 to 250 torr, 175 to 225 Torr, or 195 to 205 Torr.

11. A polycrystalline CVD synthetic diamond material comprising:
an average thermal conductivity at room temperature through a thickness of the polycrystalline CVD synthetic diamond material of at least 2000 Wm −1 K −1 over at least a central area of the polycrystalline CVD synthetic diamond material, wherein the central area is at least 70% of a total area of the polycrystalline CVD synthetic diamond material; and
a single substitutional nitrogen concentration no more than 0.80 ppm and no less than 0.10 ppm over at least the central area of the polycrystalline CVD synthetic diamond material;
wherein the thickness of the polycrystalline CVD synthetic diamond material is at least 1.3 mm; and
wherein the polycrystalline CVD synthetic diamond material is substantially crack free over at least the central area such that the central area has no cracks which intersect both external major faces of the polycrystalline CVD synthetic diamond material and extend greater than 2 mm in length.

12. A polycrystalline CVD synthetic diamond material according to claim 11 , wherein the average thermal conductivity at room temperature through the thickness of the polycrystalline CVD synthetic diamond material is at least 2025 Wm −1 K −1 , 2050 Wm −1 K −1 , 2075 Wm −1 K −1 , 2100 Wm −1 K −1 , 2125 Wm −1 K −1 , or 2150 Wm −1 K −1 .

13. A polycrystalline CVD synthetic diamond material according to claim 11 , wherein the average thermal conductivity at room temperature through the thickness of the polycrystalline CVD synthetic diamond material is less than 2200 Wm −1 K − , 2180 Wm −1 K −1 2175 Wm −1 K −1 , or 2160 Wm −1 K −1 .

14. A polycrystalline CVD synthetic diamond material according to claim 11 , wherein the polycrystalline CVD synthetic diamond material has an as-grown diameter in the range 60 mm to 120 mm, 80 mm to 110 mm, 90 mm to 110 mm, or 95 mm to 105 mm.

15. A polycrystalline CVD synthetic diamond material according to claim 11 , wherein the thickness is at least 1.5 mm, 1.7 mm, 1.8 mm, 1.9 mm, 2.0 mm, 2.2 mm, 2.5 mm, 2.75 mm, 3.0 mm, 3.25 mm, or 3.5 mm.

16. A polycrystalline CVD synthetic diamond material according to claim 11 , wherein the single substitutional nitrogen concentration is no more than 0.70 ppm, 0.60 ppm, 0.50 ppm, or 0.45 ppm.

17. A polycrystalline CVD synthetic diamond material according to claim 11 , wherein the single substitutional nitrogen concentration is no less than 0.20 ppm, 0.30 ppm, or 0.35 ppm.

18. A polycrystalline CVD synthetic diamond material according to claim 11 , wherein the diameter of the central area is at least 75%, 80%, 85%, 90%, 95%, or 99% of the as-grown diameter of the polycrystalline CVD synthetic diamond material.

Assignees

• Element Six Tech Ltd

Inventors

• Williams Gruffudd Trefor
• Dodson Joseph Michael
• Inglis Paul Nicolas
• Kelly Christopher John

Classifications

• C30B25/18

  characterised by the substrate · CPC title

• C30B25/16

  Controlling or regulating (controlling or regulating in general G05) · CPC title

• C01B32/26

  Preparation (by using ultra-high pressure B01J3/06; by crystal growth C30B29/04) · CPC title

• Y10T428/21

  Circular sheet or circular blank · CPC title

• C30B25/105

  by irradiation or electric discharge · CPC title