ELECTROLYTE AND PROCESS FOR ELECTROPLATING COPPER ONTO A BARRIER LAYER

• US 20150218724A1
• Filed: 08/28/2013
• Published: 08/06/2015
• Est. Priority Date: 09/24/2012
• Status: Active Grant

• Current Assignee: Alchimer S.A.
• Original Assignee: Alchimer S.A.
• Inventors: Mevellec, Vincent, Suhr, Dominique, Religieux, Laurianne
• Granted Patent: US 10,472,726 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: C25D 3/38 of copper
• CPC Class Codes: C25D 7/12 Semiconductors
• CPC Class Codes: C25D 7/123 Semiconductors first coated with a seed layer or a conductive layer

Abstract

The subject of the present invention is an electrolyte composition for depositing copper on semiconductor substrates covered with a barrier layer.

This electrolyte contains the combination of imidazole and 2,2′-bipyridine, used as suppressor, and of thiodiglycolic acid, used as accelerator.

The combination of these additives makes it possible to obtain a bottom-up filling on trenches of very small width, typically of less than 100 nm.

Claims

1. Electrolyte for electroplating copper onto a copper-diffusion barrier layer, the electrolyte comprising a source of copper ions, a solvent, and the combination of a suppressor and an accelerator, characterized in that the suppressor comprises the combination of bipyridine and imidazole, and the accelerator is thiodiglycolic acid.

2. Electrolyte according to claim 1, wherein its pH is greater than 6.7, preferably between 7.5 and 8.5, and more preferably of the order of 8.

3. Electrolyte according to claim 1, wherein the copper ions are derived from a compound chosen from copper sulphate, copper chloride, copper nitrate and copper acetate.

4. Electrolyte according to claim 1, which comprises less than 50 ppm of chlorine ions, and that it is preferably free of chlorine ions.

5. Electrolyte according to claim 1, wherein the bipyridine is in the form of 2,2′

-bipyridine.

6. Electrolyte according to claim 1, additionally comprising a leveller and/or a brightener, such as for example a polypyridine.

7. Electrolyte according to claim 1, wherein the concentration of copper ions is between 0.4 and 40 mM, the concentration of bipyridine is between 0.4 and 40 mM, the concentration of imidazole is between 1.2 and 120 mM, and the concentration of thiodiglycolic acid is between 1 and 500 mg/l.

8. Electrolyte according to claim 1, wherein the solvent predominantly comprises water.

9. Process for electroplating copper onto a copper-diffusion barrier layer, and which is optionally covered with a copper seed layer, said barrier layer covering one surface of a semiconductor substrate, the surface of the substrate having a flat part and a set of at least one trench having a width of less than 200 nm, the process being characterized in that it comprises the steps of:

bringing the barrier layer into contact with an electrolyte according to claim 1,

biasing of the surface of the barrier layer at an electric potential that enables the electroplating of copper onto the barrier layer or the copper seed layer, so as to form a copper deposit on said barrier layer.

10. Process according to claim 9, wherein the bias step is carried out so as to form a copper seed layer on said barrier layer.

11. Process according to claim 9, wherein the bias step is carried out so as to completely fill the volume of the trench with copper.

12. Process according to claim 9, wherein the barrier layer comprises at least one of the materials chosen from cobalt (Co), ruthenium (Ru), tantalum (Ta), titanium (Ti), tantalum nitride (TaN), titanium nitride (TiN), tungsten (W), titanium tungsten (TiW) and tungsten carbonitride (WCN).

13. Process according to claim 9, wherein, during the filling of the cavity, the substrate is rotated at a speed between 20 and 600 rpm, preferably at a rotational speed between 30 and 240 rpm.

14. Process according to claim 9, wherein the trench has an aspect ratio of greater than 2/1, preferably of greater than 3/1.

15. Process according to claim 9, wherein the bias of the surface is carried out in DC mode by applying a current per unit area within a range from 0.2 mA/cm² to 50 mA/cm², preferably from 0.5 mA/cm² to 5 mA/cm², and in that the bias time is at least 5 seconds, preferably between 10 seconds and 10 minutes.

16. Process according to claim 9, wherein the bias of the surface is carried out in galvano-pulsed mode such that the frequency of the bias periods is between 0.1 kHz and 50 kHz, for example between 5 kHz and 15 kHz.

17. Process according to claim 16, wherein the bias periods are spaced apart by rest times at zero current, the frequency of which is between 0.1 kHz and 50 kHz, for example between 1 kHz and 10 kHz.

18. Process according to claim 17, wherein the frequency of the bias periods is equal to 10 kHz approximately, and the frequency of the rest times is equal to 5 kHz approximately.

19. Process according to claim 16, wherein the bias of the surface is carried out with a current having a maximum intensity of between 0.01 and 10 mA/cm².