Low temperature direct copper-copper bonding

Patent metadata

Field	Value
Publication number	US-2022018036-A1
Application number	US-201917309567-A
Country	US
Kind code	A1
Filing date	Dec 7, 2019
Priority date	Dec 10, 2018
Publication date	Jan 20, 2022
Grant date	—

Abstract

Direct copper-copper bonding at low temperatures is achieved by electroplating copper features on a substrate followed by electroplanarizing the copper features. The copper features are electroplated on the substrate under conditions so that nanotwinned copper structures are formed. Electroplanarizing the copper features is performed by anodically biasing the substrate and contacting the copper features with an electrolyte so that copper is electrochemically removed. Such electrochemical removal is performed in a manner so that roughness is reduced in the copper features and substantial coplanarity is achieved among the copper features. Copper features having nanotwinned copper structures, reduced roughness, and better coplanarity enable direct copper-copper bonding at low temperatures.

First claim

1 . A method of preparing copper features for direct copper-copper bonding, the method comprising:
forming a plurality of first copper features on a first substrate, each of the plurality of first copper features having nanotwinned copper structures; and electroplanarizing the plurality of first copper features by electrochemically removing a portion of exposed copper from the first copper features prior to directly bonding the first substrate to a second substrate having a plurality of second copper features disposed on the second substrate.

2 . The method of claim 1 , further comprising:
forming the plurality of second copper features on the second substrate, each of the plurality of second copper features having nanotwinned copper structures; and electroplanarizing the plurality of second copper features by electrochemically removing a portion of exposed copper from the second copper features.

3 . The method of claim 1 , wherein electroplanarizing the plurality of first copper features comprises:
anodically biasing the first substrate and contacting the plurality of first copper features with an electrolyte.

4 . The method of claim 3 , wherein anodically biasing the first substrate and contacting the plurality of first copper features with the electrolyte comprises:
electroetching copper of the plurality of first copper features below a critical potential; and electropolishing the copper of the plurality of first copper features above a critical potential.

5 . The method of claim 4 , wherein electroetching occurs at a potential of between about 0.1 V and about 0.7 V, and wherein electropolishing occurs at a potential of between about 0.7 V and about 2.0 V, wherein the potential is measured relative to a copper reference electrode.

6 . The method of claim 3 , wherein the electrolyte includes copper ions and an acid, wherein a viscosity of the electrolyte is at least about 4 centipoise.

7 . The method of claim 6 , wherein the acid includes phosphoric acid, 1-hydroxyethylidene-1,1 diphosphonic acid (HEDP), or combinations thereof.

8 . The method of claim 6 , wherein a concentration of copper ions in the electrolyte is maintained at or near a target level such that the concentration does not fluctuate by more than 5% from the target level during electrochemical removal of the portion of the exposed copper from the first copper features.

9 . The method of claim 1 , wherein the electrochemical removal of the portion of the exposed copper from the first copper features improves both within die uniformity and within feature uniformity.

10 . The method of claim 1 , wherein the plurality of first copper features are provided in through mask features of the first substrate during electrochemical removal of the portion of the exposed copper from the plurality of first copper features.

11 . The method of claim 1 , further comprising:
directly bonding the plurality of first copper features with the plurality of second copper features on the second substrate to connect the first substrate and the second substrate.

12 . The method of claim 11 , wherein the plurality of first copper features and the plurality of second copper features are directly bonded at a temperature less than about 250° C.

13 . The method of claim 1 , wherein the plurality of first copper features and second copper features include copper pillars.

14 . The method of claim 1 , wherein forming the plurality of first copper features on the first substrate comprises:
contacting a surface of the first substrate with an electroplating solution; and applying a first current to the first substrate when the first substrate is contacted with the electroplating solution to deposit the plurality of first copper features having nanotwinned copper structures, wherein the first current comprises a pulsed current waveform that alternates between a constant current and no current.

15 . The method of claim 14 , further comprising:
forming, prior to contacting the first substrate with the electroplating solution, a mask layer on the first substrate having a plurality of through mask recessed features, wherein the plurality of first copper features are formed within the plurality of through mask recessed features.

16 . The method of claim 14 , wherein a duration of no current being applied in the pulsed current waveform is at least three times longer than a duration of constant current being applied in the pulsed current waveform.

17 . The method of claim 14 , wherein the pulsed current waveform alternates between the constant current being applied for a duration between about 0.1 seconds and about 2 seconds, and no current being applied for a duration between about 0.4 seconds and about 6 seconds.

18 . The method of claim 14 , further comprising:
applying, after applying the first current to the first substrate, a second current to the first substrate when the first substrate is contacted with the electroplating solution, wherein the second current comprises a constant current waveform.

19 . The method of claim 1 , wherein the first substrate comprises a copper seed layer on which the plurality of first copper features are formed, the copper seed layer having a plurality of <111> crystal grain structures.

20 . The method of claim 1 , wherein the first substrate comprises a diffusion barrier layer on which the plurality of first copper features are formed, the diffusion barrier layer having a plurality of columnar grain structures.

21 . The method of claim 1 , wherein the nanotwinned copper structures comprise a plurality of (111)-oriented nanotwinned crystal copper grains.

22 . The method of claim 1 , wherein forming the plurality of first copper features and electroplanarizing the plurality of first copper features are performed within the same tool.

23 . An apparatus comprising:
an electroplating cell for holding an electroplating solution; an electrochemical metal removal cell for holding an electrolyte; a power supply for applying current to one or more substrates during electroplating and during electrochemical metal removal; and a controller configured with instructions for performing the following operations:
form a plurality of first copper features on a first substrate in the electroplating cell, each of the plurality of first copper features having nanotwinned copper structures; and
electroplanarize the plurality of first copper features by electrochemically removing a portion of exposed copper from the first copper features in the electrochemical metal removal cell.

24 . The apparatus of claim 23 , wherein the controller is further configured with instructions for performing the following operations:
directly bond the plurality of first copper features with a plurality of second copper features on a second substrate to connect the first substrate and the second substrate.

25 . The apparatus of claim 24 , wherein the plurality of first copper features and the plurality of second copper features are directly bonded at a temperature less than about 250° C.

26 . The apparatus of claim 23 , wherein the controller is further configured with instructions for performing the following operations:
transfer the first substrate to a system configured to directly bond the first substrate with a second substrate having a plurality of second copper features disposed on the second substrate.

Assignees

• Lam Res Corp

Inventors

• Banik Ii Stephen J
• Oberst Justin
• Thorkelsson Kari
• Buckalew Bryan L
• Ponnuswamy Thomas Anand

Classifications

• H10W80/314

  characterized by direct bonding of pads or other interconnections · CPC title

• H10W72/01251

  Changing the shapes of bumps · CPC title

• H10W72/01235

  by plating, e.g. electroless plating or electroplating · CPC title

• H10W72/252

  comprising solid metals or solid metalloids, e.g. PbSn, Ag or Cu · CPC title

• H10W72/224

  Bumps having multiple side-by-side cores · CPC title