Deposit morphology of electroplated copper

• US 7,879,218 B1
• Filed: 12/18/2003
• Issued: 02/01/2011
• Est. Priority Date: 12/18/2003
• Status: Active Grant

• Current Assignee: Novellus Systems Incorporated (Lam Research Corporation)
• Original Assignee: Novellus Systems Incorporated (Lam Research Corporation)
• Inventors: Webb, Eric, Reid, Jon, Takada, Yuichi, Archer, Timothy
• Primary Examiner(s): Nguyen; Nam X
• Assistant Examiner(s): Van; Luan V
• Application Number:
  US10/741,048
• Time in Patent Office: 2,602 Days
• Field of Search: 205/102, 205/103, 205/105, 205/118, 205/123, 205/291, 205295-298, 205/210
• US Class Current: 205/210
• CPC Class Codes: C25D 5/34 Pretreatment of metallic surfaces to be electroplated
• CPC Class Codes: C25D 7/123 Semiconductors first coated with a seed layer or a conductive layer
• CPC Class Codes: H01L 21/2885 using an external electrical current, i.e. electro-deposition
• CPC Class Codes: H01L 21/76877 Filling of holes, grooves or trenches, e.g. vias, with conductive material

Abstract

The present invention provides improved methods and devices for electroplating copper on a wafer. Some implementations of the present invention involve the pre-treatment of the wafer with a solution containing accelerator molecules. Preferably, the bath into which the wafer is subsequently placed for electroplating has a reduced concentration of accelerator molecules. The pre-treatment causes a reduction in roughness of the electroplated copper surface, particularly during the initial phases of copper growth.

Claims

1. A method of electroplating copper on a substrate, the method comprising:

depositing a copper seed layer on the substrate;

spraying the copper seed layer with a solution containing accelerator molecules; and

electroplating copper on the copper seed layer in plating solution comprising substantially no accelerator additive.

2. The method of claim 1, further comprising a drying step after the spraying step and prior to the electroplating step, and at least one rinse step prior to the electroplating step.

3. The method of claim 1, wherein the spraying step comprises spraying the copper seed layer with a solution containing surfactant molecules.

4. The method of claim 1, wherein the spraying step comprises spraying the copper seed layer with a solution containing CuSO₄.

5. The method of claim 1, wherein the spraying step comprises spraying the copper seed layer with a solution containing components for controlling pH to avoid significant dissolution of the copper seed layer.

6. The method of claim 1, wherein the plating solution includes leveler additives in the concentration range of approximately 1 ppm-7 ppm.

7. A method of electroplating copper on a substrate, the method comprising:

depositing a copper seed layer on the substrate;

spraying the copper seed layer with a solution containing accelerator molecules; and

electroplating copper on the copper seed layer in plating solution containing a leveler and substantially no accelerator.

8. A method of electroplating copper onto a surface comprising a field region and a plurality of recessed features, the recessed features having a range of aspect ratios, the surface having a copper seed layer, the method comprising:

spraying the surface with a solution comprising an accelerator additive;

immersing the surface in an electroplating solution comprising copper ions, substantially no accelerator additive and a leveler additive in a concentration in a range from 1 ppm to 7 ppm;

applying a DC cathodic current density through the surface, the current density having a first value that is sufficiently small that depletion of copper ions and the additives is absent at both the field region and the recessed features, to create a substantially conformal thin conductive metal film on the surface;

applying a DC cathodic current density having a second value through the surface, the second value such that electroplating occurs preferentially on bottoms of recessed features having the largest aspect ratios;

increasing the current density from the second value until all recessed features have aspect ratios less than about 0.5; and

further increasing the current density to a third value that provides a condition of conformal plating, filling said recessed features and plating metal onto the field region.

9. The method of claim 8, wherein the copper seed layer is cathodically polarized with respect to the electroplating solution prior to, or less than approximately 5 seconds following, the immersing step.

10. The method of claim 8, wherein said first value is between about 0.2 and about 10 milliamperes per square centimeter.

11. The method of claim 10, further comprising the step of superimposing cathodic current pulses on said DC cathodic current density.

12. The method of claim 10, further comprising the step of causing alternating cathodic and anodic pulses to be superimposed on said DC cathodic current density.

13. The method of claim 8, wherein the second value is between about 5 and about 15 milliamperes per square centimeter.

14. The method of claim 8, wherein the electroplating solution further comprises copper ions, a suppressor additive and a leveler additive.