Bonding process with inhibited oxide formation

• US 10,541,224 B1
• Filed: 12/17/2018
• Issued: 01/21/2020
• Est. Priority Date: 09/19/2016
• Status: Active Grant

• Current Assignee: SiTime Corporation (Megachips Corporation)
• Original Assignee: SiTime Corporation (Megachips Corporation)
• Inventors: Hagelin, Paul M., Grosjean, Charles I.
• Primary Examiner(s): Fernandes, Errol V
• Application Number:
  US16/222,939
• Time in Patent Office: 400 Days
• CPC Class Codes: H01L 2224/0346 Plating
• CPC Class Codes: H01L 2224/0381 Cleaning, e.g. oxide removal step, desmearing
• CPC Class Codes: H01L 2224/03826 Physical vapour deposition [PVD], e.g. evaporation, or sputtering
• CPC Class Codes: H01L 2224/05124 Aluminium [Al] as principal constituent
• CPC Class Codes: H01L 2224/056 with a principal constituent of the material being a metal or a metalloid, e.g. boron [B], silicon [Si], germanium [Ge], arsenic [As], antimony [Sb], tellurium [Te] and polonium [Po], and alloys thereof
• CPC Class Codes: H01L 2224/05609 Indium [In] as principal constituent
• CPC Class Codes: H01L 2224/05611 Tin [Sn] as principal constituent
• CPC Class Codes: H01L 2224/05618 Zinc [Zn] as principal constituent
• CPC Class Codes: H01L 2224/05639 Silver [Ag] as principal constituent
• CPC Class Codes: H01L 2224/05644 Gold [Au] as principal constituent
• CPC Class Codes: H01L 2224/05655 Nickel [Ni] as principal constituent
• CPC Class Codes: H01L 2224/05664 Palladium [Pd] as principal constituent
• CPC Class Codes: H01L 2224/05666 Titanium [Ti] as principal constituent
• CPC Class Codes: H01L 2224/05669 Platinum [Pt] as principal constituent
• CPC Class Codes: H01L 2224/05673 Rhodium [Rh] as principal constituent
• CPC Class Codes: H01L 2224/05676 Ruthenium [Ru] as principal constituent
• CPC Class Codes: H01L 2224/05678 Iridium [Ir] as principal constituent
• CPC Class Codes: H01L 2224/05683 Rhenium [Re] as principal constituent
• CPC Class Codes: H01L 2224/08148 the bonding area connecting to a bonding area protruding from the surface of the body
• CPC Class Codes: H01L 2224/80 Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected
• CPC Class Codes: H01L 2224/80048 : Thermal treatments, e.g. annealing, controlled pre-heating or pre-cooling
• CPC Class Codes: H01L 2224/80097 : Heating
• CPC Class Codes: H01L 2224/80805 : involving forming a eutectic alloy at the bonding interface
• CPC Class Codes: H01L 2224/83048 : Thermal treatments, e.g. annealing, controlled pre-heating or pre-cooling
• CPC Class Codes: H01L 2224/83143 : Passive alignment, i.e. self alignment, e.g. using surface energy, chemical reactions, thermal equilibrium
• CPC Class Codes: H01L 2224/83355 : having an external coating, e.g. protective bond-through coating
• CPC Class Codes: H01L 2224/83895 : between electrically conductive surfaces, e.g. copper-copper direct bonding, surface activated bonding
• CPC Class Codes: H01L 2224/83911 : Chemical cleaning, e.g. etching, flux
• CPC Class Codes: H01L 2224/94 : at wafer-level, i.e. with connecting carried out on a wafer comprising a plurality of undiced individual devices
• CPC Class Codes: H01L 2225/06513 : Bump or bump-like direct electrical connections between devices, e.g. flip-chip connection, solder bumps
• CPC Class Codes: H01L 24/03 : Manufacturing methods
• CPC Class Codes: H01L 24/05 : of an individual bonding area
• CPC Class Codes: H01L 24/80 : Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected
• CPC Class Codes: H01L 24/83 : using a layer connector
• CPC Class Codes: H01L 25/50 : Multistep manufacturing processes of assemblies consisting of devices, each device being of a type provided for in group H01L27/00 or H01L29/00 H01L21/50 takes precedence
• CPC Class Codes: H01L 2924/01014 : Silicon [Si]
• CPC Class Codes: H01L 2924/01029 : Copper [Cu]
• CPC Class Codes: H01L 2924/01032 : Germanium [Ge]
• CPC Class Codes: H01L 2924/01047 : Silver [Ag]
• CPC Class Codes: H01L 2924/01079 : Gold [Au]
• CPC Class Codes: H01L 2924/10252 : Germanium [Ge]
• CPC Class Codes: H01L 2924/10253 : Silicon [Si]
• CPC Class Codes: H01L 2924/10271 : Silicon-germanium [SiGe]
• CPC Class Codes: H01L 2924/1461 : MEMS

Abstract

First and second contacts are formed on first and second wafers from disparate first and second conductive materials, at least one of which is subject to surface oxidation when exposed to air. A layer of oxide-inhibiting material is disposed over a bonding surface of the first contact and the first and second wafers are positioned relative to one another such that a bonding surface of the second contact is in physical contact with the layer of oxide-inhibiting material. Thereafter, the first and second contacts and the layer of oxide-inhibiting material are heated to a temperature that renders the first and second contacts and the layer of oxide-inhibiting material to liquid phases such that at least the first and second contacts alloy into a eutectic bond.

Claims

1. A method of forming a wafer-to-wafer bond, the method comprising:

forming, on a first wafer, a first contact from a first conductive material subject to surface oxidation when exposed to air;

disposing a layer of oxide-inhibiting material over a bonding surface of the first contact;

forming, on a second wafer, a second contact from a second conductive material that, upon heating while in physical contact with the first conductive material, will form a eutectic bond;

positioning the first and second wafers relative to one another such that a bonding surface of the second contact is in physical contact with the layer of oxide-inhibiting material; and

heating the first and second contacts and the layer of oxide-inhibiting material to one or more temperatures that render the first and second contacts and the layer of oxide-inhibiting material to liquid phases such that the first and second contacts and the layer of oxide-inhibiting material alloy into a ternary eutectic bond;

wherein

forming the first contact from the first conductive material subject to surface oxidation comprises forming the first contact from at least one of silicon, germanium or a silicon-germanium alloy, and

forming the second contact from the second conductive material comprises forming the second contact from at least one of aluminum, aluminum-silicon alloy, aluminum-copper alloy or aluminum-silicon-copper alloy.

2. The method of claim 1 wherein at least one of the first and second wafers is a complementary metal oxide semiconductor (CMOS) wafer.

3. The method of claim 2 wherein one of the first and second wafers is a microelectromechanical-system (MEMS) wafer.

4. The method of claim 1 wherein disposing the layer of oxide-inhibiting material over the bonding surface of the first contact comprises disposing a layer of noble metal over the bonding surface of the first contact.

5. The method of claim 4 wherein disposing a layer of noble metal over the bonding surface of the first contact comprises disposing a layer of gold over the bonding surface of the first contact.

6. The method of claim 1 wherein disposing the layer of oxide-inhibiting material over the bonding surface of the first contact comprises disposing the layer of oxide-inhibiting material over the bonding surface of the first contact with such limited exposure to an oxidizing environment that the bonding surface of the first contact remains primarily that of the first conductive material.

7. The method of claim 1 wherein positioning the first and second wafers relative to one another such that a bonding surface of the second contact is in physical contact with the layer of oxide-inhibiting material comprises pressing the second contact against the layer of oxide-inhibiting material to establish a pressure therebetween within a predetermined range.

8. The method of claim 7 wherein pressing the second contact against the layer of oxide-inhibiting material to establish a pressure therebetween within a predetermined range comprises pressing the second contact against the layer of oxide-inhibiting material with sufficient force to crush the layer of oxide-inhibiting material.

9. The method of claim 1 wherein positioning the first and second wafers relative to one another such that a bonding surface of the second contact is in physical contact with the layer of oxide-inhibiting material comprises pressing the second contact against the layer of oxide-inhibiting material, and wherein heating the first and second contacts and the layer of oxide-inhibiting material to the one or more temperatures comprises heating the first and second contacts and the layer of oxide-inhibiting material while pressing the second contact against the layer of oxide-inhibiting material.

10. The method of claim 1 wherein heating the first and second contacts and the layer of oxide-inhibiting material to one or more temperatures that render the first and second contacts and the layer of oxide-inhibiting material to liquid phases such that the first and second contacts and the layer of oxide-inhibiting material alloy into a ternary eutectic bond comprises, prior to positioning the first and second wafers relative to one another, heating the first contact and the layer of oxide-inhibiting material to a first temperature that renders the first contact and the layer of oxide-inhibiting material to liquid phases such that the first contact and the layer of oxide-inhibiting material form an alloy.

11. The method of claim 10 further comprising, after heating the first contact and the layer of oxide-inhibiting material to the first temperature and prior to positioning the first and second wafers relative to one another, cooling the first contact and the layer of oxide-inhibiting material to a solid-phase alloy of the first contact layer and the oxide-inhibiting material.

12. The method of claim 11 wherein heating the first and second contacts and the layer of oxide-inhibiting material to one or more temperatures that render the first and second contacts and the layer of oxide-inhibiting material to liquid phases such that the first and second contacts and the layer of oxide-inhibiting material alloy into a ternary eutectic bond comprises heating the second contact and the solid-phase alloy of the first contact and the oxide-inhibiting material to a second temperature that renders both the second contact and the solid-phase alloy of the first contact and the oxide-inhibiting material to a liquid phase.

13. The method of claim 12 wherein the second temperature is higher than the first temperature.

14. The method of claim 12 wherein the second temperature is lower than the first temperature.

15. The method of claim 1 wherein the layer of oxide-inhibiting material disposed over the bonding surface of the first contact constitutes a first layer of oxide-inhibiting material, the method further comprising, prior to positioning the first and second wafers relative to one another and prior to heating the first and second contacts and the first layer of oxide-inhibiting material to the one or more temperatures, disposing a second layer of the oxide-inhibiting material over the bonding surface of the second contact.

16. The method of claim 15 wherein heating the first and second contacts and the first layer of oxide-inhibiting material to one or more temperatures comprises heating to liquid phases the first and second contacts and the first and second layers of the oxide-inhibiting material disposed respectively over the bonding surfaces of the first and second contacts.

17. The method of claim 16 wherein heating the first and second contacts and the first and second layers of the oxide-inhibiting material to liquid phases comprises heating the first contact and the first layer of oxide-inhibiting material disposed thereon to liquid phase and heating the second contact and the second layer of oxide-inhibiting material disposed thereon to liquid phase prior to positioning the first and second wafers relative to one another.

18. A method of forming a wafer-to-wafer bond, the method comprising:

forming, on a first wafer, a first contact from a first conductive material subject to surface oxidation when exposed to air;

disposing a layer of oxide-inhibiting material over a bonding surface of the first contact;

forming, on a second wafer, a second contact from a second conductive material that, upon heating while in physical contact with the first conductive material, will form a eutectic bond;

positioning the first and second wafers relative to one another such that a bonding surface of the second contact is in physical contact with the layer of oxide-inhibiting material; and

heating the first and second contacts and the layer of oxide-inhibiting material to one or more temperatures that render the first and second contacts and the layer of oxide-inhibiting material to liquid phases such that the first and second contacts and the layer of oxide-inhibiting material alloy into a ternary eutectic bond;

wherein heating the first and second contacts and the layer of oxide-inhibiting material comprises, prior to positioning the first and second wafers relative to one another, heating the first contact and the layer of oxide-inhibiting material to a first temperature that renders the first contact and the layer of oxide-inhibiting material to liquid phases such that the first contact and the layer of oxide-inhibiting material form an alloy.

19. The method of claim 18 further comprising, after heating the first contact and the layer of oxide-inhibiting material to the first temperature and prior to positioning the first and second wafers relative to one another, cooling the first contact and the layer of oxide-inhibiting material to a solid-phase alloy of the first contact layer and the oxide-inhibiting material.

20. The method of claim 19 wherein heating the first and second contacts and the layer of oxide-inhibiting material to one or more temperatures that render the first and second contacts and the layer of oxide-inhibiting material to liquid phases such that the first and second contacts and the layer of oxide-inhibiting material alloy into a ternary eutectic bond comprises heating the second contact and the solid-phase alloy of the first contact and the oxide-inhibiting material to a second temperature that renders both the second contact and the solid-phase alloy of the first contact and the oxide-inhibiting material to a liquid phase.

21. The method of claim 20 wherein the second temperature is higher than the first temperature.

22. The method of claim 20 wherein the second temperature is lower than the first temperature.

23. The method of claim 18 wherein one of the first and second wafers is a microelectromechanical-system (MEMS) wafer.

24. A method of forming a wafer-to-wafer bond, the method comprising:

forming, on a first wafer, a first contact from a first conductive material subject to surface oxidation when exposed to air;

disposing a layer of oxide-inhibiting material over a bonding surface of the first contact;

forming, on a second wafer, a second contact from a second conductive material that, upon heating while in physical contact with the first conductive material, will form a eutectic bond;

positioning the first and second wafers relative to one another such that a bonding surface of the second contact is in physical contact with the layer of oxide-inhibiting material; and

heating the first and second contacts and the layer of oxide-inhibiting material to one or more temperatures that render the first and second contacts and the layer of oxide-inhibiting material to liquid phases such that the first and second contacts and the layer of oxide-inhibiting material alloy into a ternary eutectic bond;

wherein heating the first and second contacts and the first and second layers of the oxide-inhibiting material to liquid phases comprises heating the first contact and the first layer of oxide-inhibiting material disposed thereon to liquid phase and heating the second contact and the second layer of oxide-inhibiting material disposed thereon to liquid phase prior to positioning the first and second wafers relative to one another.

25. The method of claim 24 wherein forming the second contact from the second conductive material comprises forming the second contact from at least one of silicon, germanium or a silicon-germanium alloy.

26. The method of claim 24 wherein disposing the layer of oxide-inhibiting material over the bonding surface of the first contact comprises disposing a layer of noble metal over the bonding surface of the first contact.

27. The method of claim 24 wherein one of the first and second wafers is a microelectromechanical-system (MEMS) wafer.