Thin diamond film bonding providing low vapor pressure at high temperature

Patent metadata

Field	Value
Publication number	US-9238349-B2
Application number	US-201414306062-A
Country	US
Kind code	B2
Filing date	Jun 16, 2014
Priority date	Aug 12, 2013
Publication date	Jan 19, 2016
Grant date	Jan 19, 2016

Abstract

This disclosure concerns bonding a thin film of diamond to a second thick diamond substrate in a way that does not cause the exposed (un-bonded) diamond surface to become contaminated by the bonding process or when the bonded diamond is held at high temperature for many hours in vacuum.

First claim

What we claim is:

1. A method of bonding for thin diamond film providing low vapor pressure at high temperature comprising:
heating a diamond substrate inside a vacuum chamber to about 500° C.;
cooling the diamond substrate to a temperature of about 200° C.;
coating a first surface of the diamond substrate with an adhesion layer of chromium;
depositing an initial layer of palladium on the adhesion layer of chromium;
heating the diamond substrate to a temperature of about 600° C.;
allowing the chromium and the diamond substrate to form a chemical bond;
inter-diffusing the adhesion layer of chromium and the initial layer of palladium;
cooling the diamond substrate to about 200° C.;
depositing a second layer of palladium;
placing a shadow mask on a thin diamond film;
degassing the vacuum at about 200° C. and minimizing sublimation of the deposited chromium;
depositing a tin layer onto the thin diamond film;
assembling the tin layer on the thin diamond film with the second palladium layer;
heating the tin layer on the thin diamond film and the second palladium layer;
melting the tin layer; and
bonding the thin diamond film to the diamond substrate.

2. The method of bonding for thin diamond film providing low vapor pressure at high temperature of claim 1 wherein the step of heating a diamond substrate inside a vacuum chamber further includes the step of removing adsorbed gases from the diamond substrate.

3. The method of bonding for thin diamond film providing low vapor pressure at high temperature of claim 2 wherein the step of heating a diamond substrate inside a vacuum chamber further includes the step of heating inside the vacuum chamber to about 500° C. until the pressure drops below about 2×10 −7 torr.

4. The method of bonding for thin diamond film providing low vapor pressure at high temperature of claim 1 wherein the step of coating a first surface of the diamond substrate with an adhesion layer of chromium further includes the step of using a shadow mask to coat the chromium on the diamond substrate.

5. The method of bonding for thin diamond film providing low vapor pressure at high temperature of claim 1 wherein the step of coating a first surface of the diamond substrate with an adhesion layer of chromium results in an adhesion layer of chromium that is about 20 nm.

6. The method of bonding for thin diamond film providing low vapor pressure at high temperature of claim 1 further including the step of forming an electric contact between the chromium layer and the thin diamond film.

7. The method of bonding for thin diamond film providing low vapor pressure at high temperature of claim 1 wherein the step of depositing palladium further includes the step of using a shadow mask and is completed without breaking the vacuum.

8. The method of bonding for thin diamond film providing low vapor pressure at high temperature of claim 1 wherein the step of depositing palladium further includes the step of depositing an initial layer of about 300 nm of palladium on the adhesion layer of chromium.

9. The method of bonding for thin diamond film providing low vapor pressure at high temperature of claim 1 wherein the step of depositing a second layer of palladium further includes the step of depositing about 2200 nm of palladium and thereby resulting in a total palladium thickness of about 2500 nm.

10. The method of bonding for thin diamond film providing low vapor pressure at high temperature of claim 1 further including the step of removing excess palladium with a nitric acid etch.

11. The method of bonding for thin diamond film providing low vapor pressure at high temperature of claim 1 wherein the tin layer deposited has a thickness of about 500 nm.

12. The method of bonding for thin diamond film providing low vapor pressure at high temperature of claim 11 wherein the step of depositing a tin layer occurs within about 8 hours before bonding.

13. The method of bonding for thin diamond film providing low vapor pressure at high temperature of claim 1 further including the steps of storing under vacuum or inert gas after the step of depositing a tin layer and preventing exposure to air or oxidation.

14. The method of bonding for thin diamond film providing low vapor pressure at high temperature of claim 1 further including the steps of;
evacuating the chamber below about 2×10 −7 torr;
maintaining a temperature of about 100° C. until the pressure is below about 2×10 −7 torr; and
cooling in vacuum.

15. The method of bonding for thin diamond film providing low vapor pressure at high temperature of claim 14 further including the steps of:
back-filling the chamber with Ar gas to about 78 torr prior to the step of heating the tin layer;
heating at a rate of about 10° C./s or about 600° C. in about 60 seconds;
cooling to about 450° C.;
holding the temperature at about 450° C. for about 1 hour; and
cooling to room temperature.

Assignees

• Shaw Jonathan L
• Hanna Jeremy
• Us Navy

Inventors

• Shaw Jonathan L
• Hanna Jeremy

Classifications

• H01J1/34 Primary

  Photo-emissive cathodes (H01J1/35 takes precedence) · CPC title

• B32B2311/00

  Metals, their alloys or their compounds · CPC title

• B32B2311/09

  Palladium · CPC title

• B32B38/0036

  Heat treatment (for heating or cooling of layers during lamination B32B37/06, B32B37/08) · CPC title

• B32B37/24

  with at least one layer not being coherent before laminating, e.g. made up from granular material sprinkled onto a substrate (B32B37/15 takes precedence) · CPC title