METHOD FOR INTERCONNECTING COMPONENTS OF AN ELECTRONIC SYSTEM BY SINTERING

Abstract

Method for interconnecting components of an electronic system comprising the steps of: a) depositing a sintering solution onto a first component in order to form an interconnection layer, the sintering solution comprising a solvent, metal nanoparticles dispersed in the solvent, and a stabilizing agent adsorbed onto the metal nanoparticles, more than 95.0%, preferably more than 99.0% of the mass of the metal nanoparticles comprising a metal selected from silver, gold, copper and alloys thereof and having a polyhedral shape with an aspect ratio of more than 0.8, b) eliminating, at least partially, the solvent from the interconnection layer such as to form at least one ordered agglomerate in which the metal nanoparticles are regularly disposed in three axes, the stabilizing agent binding them together and maintaining at least a portion of the metal nanoparticles at a distance from each other, c) debinding and sintering the interconnection layer, and d) depositing a second component in contact with the interconnection layer before or during debinding or sintering.

Claims

1. Method for interconnecting components of an electronic system, the method comprising the steps of: a) depositing a sintering solution onto a first component in order to form an interconnection layer, the sintering solution comprising a solvent, metal nanoparticles dispersed in the solvent, and a stabilizing agent adsorbed onto the metal nanoparticles, the metal nanoparticles comprising for more than 95.0% of their mass a metal selected from silver, gold, copper and alloys thereof and having a polyhedral shape with an aspect ratio of more than 0.8, b) eliminating, at least partially, the solvent from the interconnection layer such as to form at least one ordered agglomerate in which the metal nanoparticles are regularly disposed in three axes, the stabilizing agent binding them together and maintaining at least a portion of the metal nanoparticles at a distance from each other, c) debinding and sintering the interconnection layer, and d) depositing a second component in contact with the interconnection layer before or during debinding or sintering.

2. Method according to claim 1, the metal nanoparticles comprising for more than 99.0% of their mass a metal selected from silver, gold, copper and alloys thereof.

3. Method according to claim 1, the sintered interconnection layer having a density that is greater than or equal to 90% of the density of said metal.

4. Method according to claim 1, more than 95.0% of the mass of the metal nanoparticles being constituted by silver.

5. Method according to claim 1, the metal nanoparticles being cubic in shape, optionally truncated.

6. Method according to claim 1, the granular assembly formed by the metal nanoparticles being monodisperse in size.

7. Method according to claim 1, the sintering solution comprising, as percentages by weight expressed on the basis of the mass of the sintering solution: between 5.0% and 50.0% of metal nanoparticles, between 0.1% and 4.0% of stabilizing agent, and between 46.0% and 94.9% of solvent.

8. Method according to claim 1, the solvent being selected from water, ethanol, 1,2-propanediol, ethylene glycol, diethylene glycol and mixtures thereof.

9. Method according to claim 1, the stabilizing agent being selected from cetyltrimethylammonium chloride, dodecyltrimethylammonium chloride, decyltrimethylammonium chloride, trimethylammonium chloride and mixtures thereof.

10. Method according to claim 9, the stabilizing agent being cetyltrimethylammonium chloride.

11. Method according to claim 1, the elimination of solvent in step b) comprising evaporation and/or decomposition of the solvent.

12. Method according to claim 1, step b) for eliminating the solvent being carried out at a temperature of less than 200° C.

13. Method according to claim 1, debinding and sintering in step c) being carried out by bringing the agglomerate into contact with at least one destabilizing agent configured to desorb the stabilizing agent from the metal nanoparticles in order to aggregate and coalesce said metal nanoparticles between themselves.

14. Method according to claim 13, the destabilizing agent being selected from an alcohol, sodium styrene sulfonate, sodium polystyrene sulfonate and mixtures thereof.

15. Method according to claim 1, the agglomerate being defined by regular repetition of an elementary pattern comprising metal nanoparticles along three axes, the elementary pattern being simple cubic, centered cubic or face centered cubic.

16. Method according to claim 1, step c) for debinding and sintering being carried out at a temperature of less than 200° C.

17. Method according to claim 1, in which the first component and/or the second component of the electronic system are selected from a support, a chip produced from a semiconductor material, a light emitting diode, a component of an electronic power system.

18. Sintering solution comprising a solvent, metal nanoparticles dispersed in the solvent, and a stabilizing agent adsorbed onto the metal nanoparticles, the metal nanoparticles comprising for more than 95.0% of their mass a metal selected from silver, gold, copper and alloys thereof and having a polyhedral shape with an aspect ratio of more than 0.8, the sintering solution comprising, as percentages by weight: between 5.0% and 50.0% of metal nanoparticles, between 0.1% and 4.0% of stabilizing agent, and between 46.0% and 94.9% of solvent.

19. Sintering solution according to claim 18, the metal nanoparticles comprising for more than 99.0% of their mass a metal selected from silver, gold, copper and alloys thereof.

20. Sintering solution according to claim 18, in which more than 95.0% of the mass of the metal nanoparticles is constituted by silver.

21. Sintering solution according to claim 18, in which the stabilizing agent is selected from cetyltrimethylammonium chloride, dodecyltrimethylammonium chloride, decyltrimethylammonium chloride, trimethylammonium chloride and mixtures thereof and the solvent is selected from water, ethanol, 1,2-propanediol, ethylene glycol, diethylene glycol and mixtures thereof.

Description

[0129] The invention will now be illustrated by means of the examples below and the accompanying drawings, in which

[0130] FIG. 1 schematically represents an exemplary embodiment of the method in accordance with the invention,

[0131] FIG. 2 is a photograph acquired by electron microscopy of an agglomerate of nanoparticles of silver obtained from an exemplary embodiment of the method, and

[0132] FIG. 3 is a photograph acquired by electron microscopy of an agglomerate of nanoparticles of silver obtained from another exemplary embodiment of the method.

EXAMPLE 1

[0133] FIG. 1 schematically illustrates an exemplary embodiment of the method in accordance with the invention.

[0134] Prior to step a), a base solution comprising cubic silver nanoparticles 5 with a size of less than 30 nm dispersed in 18.2 MΩ demineralized water and stabilized with CTAC, 10, was prepared using the method described in Chem. Eur. J. 2016, 22, 2326-2332, doi: 10.1002/chem.201504303, which was modified as follows. A germination solution containing silver seeds was initially prepared in a 50 mL flask, with stirring. 10 mL of a 0.5 mM aqueous solution of CTAC and 25 μL of an aqueous 0.1 M silver nitrate solution were introduced into the flask in order to form a reaction medium. After homogenizing for 10 minutes, 0.45 mL of an aqueous 0.08 M sodium borohydride solution was added to the reaction medium. The germination solution obtained thereby was maintained at 30° C., with stirring, for 1 h. Two distinct volumes of the germination solution were then used to grow cubic silver nanoparticles with sizes equal to 32 nm and 21 nm respectively. A first volume of 43 mL and a second volume of 39.5 mL respectively of 18.2 MΩ demineralized water were introduced into two distinct 100 mL flasks at a temperature of 60° C. 200 mg of CTAC was introduced into each of the flasks. Volumes of 1.5 mL and 5 mL of the germination solution were respectively added to the flasks. 500 μL of a 0.1 M aqueous silver trifluoroacetate solution was then added to each flask. After homogenizing for 20 minutes, 5 mL of 0.1 M aqueous ascorbic acid solution was introduced and added to each flask. The growth solutions obtained in this manner were maintained at 60° C., with stirring, for 1.5 h. The cubic nanoparticles synthesized in this manner were washed several times with 18.2 MΩ demineralized water by centrifuging and redispersed in a reduced volume of 18.2 MΩ demineralized water. The base solution was then concentrated by solvent evaporation, by vacuum evaporation or in a stream of argon in order to constitute a sintering solution comprising the desired percentage by weight of aqueous solvent.

[0135] The base solution was washed with 18.2 MΩ demineralized water by centrifuging in order to eliminate the excess CTAC.

[0136] The nanoparticles were then dispersed in a small volume of 18.2 MΩ demineralized water. A sintering solution comprising, as percentages by weight, 5% of cubic silver nanoparticles, 0.4% of CTAC and 94.6% of water was then obtained, as illustrated in FIG. 1.

[0137] A droplet of sintering solution with a volume of 15 μL was then deposited onto a dielectric substrate coated with a 30 nm thick layer of gold. The layer of gold had been functionalized using hexadecanethiol, which is an aliphatic thiol, in order to minimize the wettability of the substrate and spreading of the sintering solution.

[0138] The substrate had already been cleaned with a plasma in order to eliminate organic pollutants on the surface of the substrate.

[0139] The sintering solution was then evaporated for 2 hours at a temperature of 30° C. under a bell jar. Another test was carried out by evaporating the solution over 3 hours at a temperature of 20° C. The rate of evaporation was controlled by the temperature prevailing in the bell jar.

[0140] Ordered agglomerates 15 were then produced; the silver nanoparticles organized themselves into the form of a super-crystal with a simple cubic structure, as can be observed in FIGS. 2 and 3. The agglomerates forming in the water were then deposited onto the substrate by sedimentation. The agglomerates had a generally cubic shape and a size comprised between 500 nm and 3000 nm.

[0141] FIGS. 2 and 3 are photographs acquired by scanning microscopy of ordered agglomerates formed at 22° C. from cubic silver nanoparticles with a size equal to 31 nm and 21 nm respectively. The adjacent nanoparticles are spaced apart by approximately 3±1 nm.

[0142] Thus, the agglomerates form a 3D film which covers the substrate. They comprise approximately 8.0% by weight CTAC and have a density comprised between 70% and 80% of the density of silver. The CTAC content was measured by thermogravimetric analysis.

[0143] Debinding of the agglomerates of Example 1 was carried out by depositing a droplet of ethanol with a volume of 5 μL onto the interconnection layer as a destabilizing agent 20, at a temperature of 25° C.

[0144] After a period of 2 hours so that the ethanol had sufficiently desorbed the CTAC from the surface of the nanoparticles, a conventional heat treatment under argon was carried out as follows: a temperature ramp-up of 45 min, a constant temperature stage maintaining the temperature at 185° C. for 2 h, followed by cooling for a period of 1 h in order to sinter the interconnection layer by aggregation and coalescence of nanoparticles of silver in the form of sintered aggregates 30.

[0145] An interconnection layer was thus obtained that had a density of more than 90% of the density of silver.

[0146] Clearly, the invention is not limited to the exemplary embodiments of the method presented above by way of illustration.