METHOD OF PREPARING AN ELECTRICALLY INSULATING FILM AND APPLICATION FOR THE METALLIZATION OF VIAS

• US 20100003808A1
• Filed: 06/30/2009
• Published: 01/07/2010
• Est. Priority Date: 07/01/2008
• Status: Active Grant

• Current Assignee: Alchimer S.A.
• Original Assignee: Alchimer S.A.
• Inventors: SUHR, Dominique, GONZALES, José, MEVELLEC, Vincent
• Granted Patent: US 8,119,542 B2
• Time in Patent Office: Days
• US Class Current: 438/469
• CPC Class Codes: C25D 13/18 using modulated, pulsed, or reversing current
• CPC Class Codes: C25D 7/123 Semiconductors first coated with a seed layer or a conductive layer
• CPC Class Codes: H01L 21/02118 carbon based polymeric organic or inorganic material, e.g. polyimides, poly cyclobutene or PVC polymers per se C08G, photoresist per se G03F
• CPC Class Codes: H01L 21/02282 liquid deposition, e.g. spin-coating, sol-gel techniques, spray coating
• CPC Class Codes: H01L 21/288 from a liquid, e.g. electrolytic deposition
• CPC Class Codes: H01L 21/312 Organic layers, e.g. photoresist H01L21/3105, H01L21/32 take precedence; photoresists per se G03C
• CPC Class Codes: H01L 21/76843 formed in openings in a dielectric
• CPC Class Codes: H01L 21/76898 formed through a semiconductor substrate
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00

Abstract

The present invention essentially relates to a method of preparing an electrically insulating film at the surface of an electrical conductor or semiconductor substrate, such as a silicon substrate.

According to the invention, this method comprises:

• • a) bringing said surface into contact with a liquid solution comprising:
    • a protic solvent;
    • at least one diazonium salt;
    • at least one monomer that is chain-polymerizable and soluble in said protic solvent;
    • at least one acid in a sufficient quantity to stabilize said diazonium salt by adjusting the pH of said solution to a value less than 7, preferably less than 2.5;
  • b) the polarization of said surface according to a potentio- or galvano-pulsed mode for a duration sufficient to form a film having a thickness of at least 60 nanometres, and preferably between 80 and 500 nanometres.
    Application: Metallization of through-vias, especially of 3D integrated circuits.

Claims

1. Method of preparing an electrically insulating film at the surface of an electrical conductor or semiconductor substrate which comprises:

a) bringing said surface into contact with a liquid solution comprising;

a protic solvent;

at least one diazonium salt;

at least one monomer that is chain-polymerizable and soluble in said protic solvent;

at least one acid in a sufficient quantity to stabilize said diazonium salt by adjusting the pH of said solution to a value less than 7;

b) the polarization of said surface according to a potentio- or galvano-pulsed mode for a duration sufficient to form a film having a thickness of at least 60 nanometres.

2. Method according to claim 1, wherein said substrate is a silicon substrate, wherein said at least one acid is comprised in said liquid solution in a sufficient quantity to stabilize said diazonium salt by adjusting the pH of said solution to a value less than 2.5;

and wherein the polarization of said surface is carried out for a duration sufficient to form a film having a thickness of between 80 and 500 nanometres.

3. Method according to claim 1, wherein said protic solvent is selected from the group consisting of water, hydroxylated solvents, carboxylic acids having 2 to 4 carbon atoms, and mixtures thereof.

4. Method according to claim 1, wherein said protic solvent is selected from the group consisting of deionized water, distilled water, alcohols having 1 to 4 carbon atoms;

formic acid, acetic acid, and mixtures thereof.

5. Method according to claim 1, wherein said diazonium salt is an aryldiazonium salt selected from the group consisting of the compounds of formula (I):

R—

N₂⁺,A⁻

 

 

(I)

in which;

A represents a monovalent anion,

R represents an aryl group.

6. Method according to claim 1, wherein said chain-polymerizable monomer is selected from the group consisting of vinyl monomers chosen from the monomers of formula (II):

7. Method according to claim 5, wherein said chain-polymerizable monomer is soluble in the protic solvent and is selected from the group consisting of vinyl monomers chosen from the monomers of formula (II):

8. Method according to claim 1, wherein said liquid solution comprises:

at least 0.3M of polymerizable monomer(s),

at least 5×

10<sup>−

3</sup>M of diazonium salt(s),

the molar ratio of the polymerizable monomer(s) to the diazonium salt(s) being between 10 and 300.

9. Method according to claim 1, wherein the polarization of said surface is produced in a pulsed mode, each cycle of which being characterized by:

a total period P of between 10 ms and 2 s;

a polarization time T_on of between 0.01 and 1 s, during which a potential difference or a current is applied to the surface of the substrate; and

an idle period with zero potential or current of a duration of between 0.01 and 1 s.

10. Method according to claim 7, wherein the polarization of said surface is produced in a pulsed mode, each cycle of which is characterized by:

a total period P of around 0.6 s;

a polarization time T_on of around 0.36 s, during which a potential difference or a current is applied to the surface of the substrate; and

an idle period with zero potential or current of a duration of around 0.24 s.

11. Method of preparing a coating of an electrical conductor or semiconductor substrate, said coating consisting of an internal layer forming an electrically insulating film and an external layer forming a copper diffusion barrier, wherein:

A. said internal layer is produced by employing the method according to claim 1;

B. said external layer is produced by;

a) the formation by wet process, at the surface of the internal layer thus obtained, of an organic film containing particles of metals or metal alloys;

b) bringing the film thus formed into contact with a liquid solution containing at least one metal salt, a stabilizing agent, and at least one reducing agent under conditions enabling the formation of a metal film having a thickness of at least 100 nm.

12. Method of preparing a coating of a silicon substrate, said coating consisting of an internal layer forming an electrically insulating film and an external layer forming a copper diffusion barrier, wherein:

A. said internal layer is produced by employing the method according to claim 2;

B. said external layer is produced by;

a) the formation by wet process, at the surface of the internal layer thus obtained, of an organic film containing nanoparticles of nickel or cobalt;

b) bringing the film thus formed into contact with a liquid solution containing at least one metal salt, a stabilizing agent, and at least one reducing agent under conditions enabling the formation of a metal film having a thickness of at least 100 nm.

13. Method according to claim 11, wherein said aforementioned step B.a) is carried out in non-electrochemical conditions by bringing the free surface of the aforementioned internal layer into contact with a liquid solution containing:

at least one solvent;

at least one diazonium salt;

at least one monomer that is chain-polymerizable by free radical methods and soluble in said solvent; and

at least one chemical initiator enabling the formation of radical entities from said diazonium salt.

14. Method according to claims 11, wherein said chain-polymerizable monomer used in step A.a) is a vinylpyridine or a methacrylate and said monomer which is chain-polymerizable by free radical methods used in step B.a) is 2-hydroxyethyl methacrylate.

15. Method according to claim 14, wherein said chain-polymerizable monomer used in step A.a) is 4-vinylpyridine or 2-hydroxyethyl methacrylate, and said monomer which is chain-polymerizable by free radical methods used in step B.a) is 2-hydroxyethyl methacrylate.

16. Method according to claim 13, wherein said chemical initiator is selected from the group consisting of a metal reducing agent in finely divided form, an organic base and an inorganic base in sufficient proportions for the pH of the liquid solution to be greater than or equal to 4.

17. Method according to claim 11, wherein said chain-polymerizable monomer used in step A.a) is a vinylpyridine and wherein step B.a) is carried out by bringing the free surface of the internal layer of polyvinylpyridine into contact with a liquid solution comprising:

at least one solvent;

at least one polymer that is soluble in said solvent and comprising functional groups capable of bonding with the functional groups of the polyvinylpyridine by hydrogen bonds or Van der Waals bonds, said polymer containing one or more functional groups selected from the group consisting of hydroxyl, (primary or secondary) amine, ammonium, carboxylic acid, carboxylic acid salts, (cyclic or linear) carboxylic anhydride, amide;

C(═

O)NHR where R represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, an amino acid, phosphonic acid, phosphonic acid salts, phosphoric acid, phosphoric acid salts, sulphonic acid, sulphonic acid salts, sulphuric acid, sulphuric acid salts, succinamic acid, succinamic acid salts, phthalimide, phthalimide salts, Si(OH)_n where n is an integer between 1 and 3;

for a sufficient duration to enable the formation of said hydrogen or Van der Waals bonds.

18. Method according to claim 17, wherein said chain-polymerizable monomer used in step A.a) is 4-vinylpyridine and said soluble polymer used in step B.a) is an acrylic polyacid.

19. Method according to claim 11, wherein said salt of said metal salt is selected from the group consisting of the acetate, acetylacetonate, hexafluorophosphate, nitrate, perchlorate, sulphate and tetrafluoroborate.

20. Method according to claim 11, wherein said reducing agent is selected from the group consisting of hypophosphorous acid, hypophosphorous salts, borane derivatives, glucose, formaldehyde and hydrazine.

21. Method of preparing a coating of an electrical conductor or semiconductor substrate, said coating consisting of an internal layer forming an electrically insulating film, an intermediate layer forming a copper diffusion barrier, and an external layer forming a copper seed layer, wherein:

A. said internal layer is produced by implementing the method according to claim 1;

B. said intermediate layer is produced by implementing the method according to claim 11;

C. said external layer is produced by;

a) bringing the free surface of the intermediate layer into contact with a liquid solution comprising;

at least one solvent;

copper ions in a concentration of between 14 and 120 mM;

ethylenediamine;

the molar ratio of ethylenediamine to copper being between 1.80 and 2.03;

the pH of said composition being between 6.6 and 7.5;

b) polarization of said free surface of the second layer for a sufficient duration to form said external layer.

22. Method according to claim 21, wherein said liquid solution used in the aforementioned step C.a) comprises cupric ions coming from copper sulphate in an amount between 16 and 64 mM and the molar ratio of ethylenediamine to the copper ions is between 1.96 and 2.0.

23. Wafer of a conductor or semiconductor material comprising one or more vias, wherein the walls of each via are covered with an internal layer made of poly-4-vinylpyridine with a thickness of between 200 and 400 nanometres forming an electrical insulator, which is itself coated with a layer of nickel or of nickel alloyed with boron, with a thickness of between 100 and 300 nanometres forming a copper diffusion barrier, which is itself covered with a copper layer with a thickness of between 200 and 500 nanometres forming a seed layer.

24. Wafer of a conductor or semiconductor material comprising one or more vias, wherein the walls of each via are covered with an internal layer made of poly-2-hydroxyethyl methacrylate with a thickness of between 200 and 400 nanometres forming an electrical insulator, which is itself coated with a layer of nickel or of nickel alloyed with boron, with a thickness of between 100 and 300 nanometres forming a copper diffusion barrier, which is itself covered with a copper layer with a thickness of between 200 and 500 nanometres forming a seed layer.