Method of reducing oxygen content in ECP solution

Abstract

A novel method, which is suitable to substantially reduce the presence of oxygen micro-bubbles in an electroplating bath solution, is disclosed. The method includes the addition of aerobic bacteria to the electroplating bath solution to consume oxygen in the solution. Reduction of the oxygen content in the electroplating bath solution prevents oxygen micro-bubbles from forming in the solution and becoming trapped between the solution and the surface of a metal seed layer on a substrate to block the electroplating of a metal film onto the seed layer. Consequently, the presence of surface pits and other structural defects in the surface of the electroplated metal film is substantially reduced.

Description

FIELD OF THE INVENTION

The present invention relates to electrochemical plating (ECP) processes used to deposit metal layers on semiconductor wafer substrates in the fabrication of semiconductor integrated circuits. More particularly, the present invention relates to a method of reducing the oxygen content of an electroplating bath solution by adding aerobic bacteria to the solution in order to enhance the quality of an electroplated metal film.

BACKGROUND OF THE INVENTION

When a copper layer is deposited on a substrate, such as by electrochemical plating, the copper layer must be deposited on a metal seed layer such as copper, which is deposited on the substrate prior to the copper ECP process. Conventional electrochemical plating techniques typically use copper sulfate (CuSO₄) for the main electrolyte in the electroplating bath solution. The solution may further include additives such as chloride ion and levelers, as well as accelerators and suppressors, which increase and decrease, respectively, the rate of the electroplating process. The rate of deposition of copper on the substrate, and the quality and resulting electrical and mechanical properties of the metallization, are critically dependent on the concentration of these organic additives in the electroplating bath solution.

Throughout the electroplating process, the electroplating bath solution is continually circulated from and back to the bath container, respectively. This circulation of the solution often induces the formation of oxygen micro-bubbles in the solution. The micro-bubbles tend to become trapped at various locations on the seed layer deposited on the wafer and block deposition of the metal film onto the seed layer at those locations. As a result, the metal film is unevenly plated on the seed layer. During subsequent chemical mechanical planarization (CMP) of the electroplated metal film, this phenomenon is manifested by the presence of defects in the form of pits, voids, broken metal lines and other defects in device features on the wafer. The presence of pits, voids and broken metal lines in device features leads to unreliable, unpredictable and unuseable electronic devices in the electronic circuit containing the features. Accordingly, a novel method is needed to reduce the oxygen content in an electrochemical plating bath solution in order to prevent or at least reduce the formation of bubble-induced defects in a metal film or line electroplated onto a wafer.

SUMMARY OF THE INVENTION

In accordance with these and other objects and advantages, the present invention is generally directed to a novel method, which is suitable to substantially reduce the presence of oxygen micro-bubbles in an electroplating bath solution. The method includes the addition of aerobic bacteria to the electroplating bath solution to consume oxygen in the solution. Reduction of the oxygen content in the electroplating bath solution prevents oxygen micro-bubbles from forming in the solution and becoming trapped between the solution and the surface of a metal seed layer on a substrate to block the electroplating of a metal film onto the seed layer. Consequently, the presence of surface pits and other structural defects in the surface of the electroplated metal film is substantially reduced.

The present invention is further directed to a metal film having a substantially reduced number of surface pits, voids and other defects. The metal film is plated onto a substrate by providing an electrochemical plating solution, adding aerobic bacteria to the solution, immersing the substrate in the solution, and carrying out an electroplating process in the solution.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic of an electrochemical plating system in implementation of the present invention;

FIG. 1A is a cross-sectional view of a wafer substrate with a metal film electroplated thereon according to the method of the present invention;

FIG. 2 is a flow diagram illustrating a typical flow of process steps carried out according to the method of the present invention; and

FIG. 3 is a graph in which the concentration of dissolved oxygen (DO) in an electroplating bath solution to which aerobic bacteria have been added is compared to the concentration of dissolved oxygen in an electroplating bath solution devoid of aerobic bacteria.

DETAILED DESCRIPTION OF THE INVENTION

The present invention has particularly beneficial utility in the electrochemical plating of a high-quality copper film on a copper seed layer deposited on a semiconductor wafer substrate in the fabrication of semiconductor integrated circuits. However, the invention is more generally applicable to the electrochemical plating of metals including but not limited to copper on substrates in a variety of industrial applications including but not limited to semiconductor fabrication.

The present invention is generally directed to a novel method for substantially reducing the presence of oxygen micro-bubbles in an electroplating bath solution used to electroplate a metal film on a seed layer provided on a substrate. The method facilitates the electroplating of a metal film which is substantially devoid of voids and surface pits onto the seed layer. According to the method, an aerobic bacteria is added to the electroplating bath solution. The aerobic bacteria consumes all or most of the oxygen in the solution to prevent or reduce the formation of oxygen micro-bubbles in the solution typically as the solution is circulated through the bath container. Consequently, micro-bubble blockage of metal electroplated onto the seed layer is prevented or at least substantially reduced.

The present invention is further directed to a metal film having a substantially reduced number of surface pits, voids and other defects. The metal film is plated onto a substrate by providing an electrochemical plating solution, adding aerobic bacteria to the solution, immersing the substrate in the solution, and carrying out an electroplating process in the solution.

The method of the present invention may be used with any formulation for the electrochemical plating bath solution, such as copper, aluminum, nickel, chromium, zinc, tin, gold, silver, lead and cadmium electrochemical plating baths. The present invention is also suitable for use with electrochemical plating baths containing mixtures of metals to be plated onto a substrate.

It is preferred that the electroplating bath be a copper alloy electroplating bath, and more preferably, a copper electroplating bath. Typical copper electroplating bath formulations are well known to those skilled in the art and include, but are not limited to, an electrolyte and one or more sources of copper ions. Suitable electrolytes include, but are not limited to, sulfuric acid, acetic acid, fluoroboric acid, methane sulfonic acid, ethane sulfonic acid, trifluormethane sulfonic acid, phenyl sulfonic acid, methyl sulfonic acid, p-toluenesulfonic acid, hydrochloric acid, phosphoric acid and the like. The acids are typically present in the bath in a concentration in the range of from about 1 to about 300 g/L. The acids may further include a source of halide ions such as chloride ions.

Suitable sources of copper ions include, but are not limited to, copper sulfate, copper chloride, copper acetate, copper nitrate, copper fluoroborate, copper methane sulfonate, copper phenyl sulfonate and copper p-toluene sulfonate. Such copper ion sources are typically present in a concentration in the range of from about 10 to about 300 g/L of electroplating solution.

Aerobic bacteria which are suitable for implementation of the present invention include nitrifying bacterial agents, Bdellovibrio bacteriovorus, Acinetobacter calcoaceticus, Pseudamonas fluorescens, Arthrobacter globiformis, and Acetobacter pasteurianus. In a preferred embodiment of the present invention, the aerobic bacteria is a nitrifying bacterial agent. Preferably, the aerobic bacteria are present in the electroplating bath solution in a concentration of from typically about 1 ml/l to about 5 ml/l.

Other electrochemical plating process conditions suitable for implementation of the present invention include a plating rpm of from typically about 0 rpm to about 500 rpm; a plating current of from typically about 0.2 mA/cm² to about 20 mA/cm²; and a bath temperature of from typically about 10 degrees C. to about 35 degrees C. In cases in which planarity of the electroplated metal through chemical mechanical planarization (CMP) is necessary, a leveling agent may be added to the electroplating bath solution at a concentration of from typically about 5 mmol/L to about 5 mol/L.

Referring to FIG. 1, an electrochemical plating (ECP) system 10 which is suitable for implementation of the present invention is shown. The system 10 may be conventional and includes a standard electroplating cell having an adjustable current source 12, a bath container 14, a typically copper anode 16 and a cathode 18, which cathode 18 is the semiconductor wafer substrate that is to be electroplated with copper. The anode 16 and cathode/substrate 18 are connected to the current source 12 by means of suitable wiring 38. The bath container 14 holds an electrolyte electroplating bath solution 20. The system 10 may further include a mechanism for rotating the substrate 18 in the bath 20 during the electroplating process, as is known by those skilled in the art.

The ECP system 10 may further include a pair of bypass filter conduits 24, a bypass pump/filter 30, and an electrolyte holding tank 34. The bypass filter conduits 24 typically extend through the anode 16 and open to the upper, oxidizing surface 22 of the anode 16 at opposite ends of the anode 16. The bypass filter conduits 24 connect to the bypass pump/filter 30 located outside the bath container 14, and the bypass pump/filter 30 is further connected to the electrolyte holding tank 34 through a tank inlet line 32. The electrolyte holding tank 34 is, in turn, connected to the bath container 14 through a tank outlet line 36. It is understood that the ECP system 10 heretofore described represents just one example of a possible system which is suitable for implementation of the present invention, and other systems of alternative design may be used instead.

Referring to FIGS. 1, 1A and 2, according to the method of the present invention, a metal seed layer 19, such as copper, is deposited on a wafer substrate 18, as indicated in step S1 of FIG. 2. The metal seed layer 19 may be deposited on the substrate 18 using conventional chemical vapor deposition (CVD) or physical vapor deposition (PVD) techniques, for example, according to the knowledge of those skilled in the art. The seed layer 19 has a thickness of typically about 50˜1500 angstroms.

As indicated in step S2 of FIG. 2, the electrochemical plating (ECP) electrolyte bath solution 20 is prepared in the bath container 14. The electroplating bath solution 20 may include an accelerator having a concentration of from typically about 5 mmol/L to about 5 mol/L, and may include a leveling agent or additive in a concentration of from typically about 5 mmol/L to about 5 mol/L, as heretofore noted.

Next, as indicated in step S3 and shown in FIG. 1, the aerobic bacteria 25 of the present invention is added to the electroplating bath solution 20, which is then circulated from the bath container 14, through the electrolyte holding tank 34 and back to the bath container 14, by operation of the pump 30, to achieve an aerobic bacteria concentration of from typically about 1 ml/l to typically about 5 ml/l in the electroplating bath solution 20. The anode 16 and substrate 18 are then immersed in the bath solution 20 and connected to the adjustable current source 12, typically through wiring 38. Accordingly, the seed layer 19 on the substrate 18 contacts the bath solution 20. The entire surface of the seed layer 19, as well as gap features on the substrate 18, is thoroughly wetted by the bath solution 20.

As indicated in step S4 of FIG. 2, the bath 20 is continually circulated from the bath container 14 through the bypass filter conduits 24, electrolyte holding tank 34 and back into the bath container 14, respectively, by operation of the pump 30. This maintains the copper sulfate or other electrolyte in a dissolved state in the electroplating bath solution 20, and prevents or minimizes precipitation of the electrolyte onto the sides, bottom and other surfaces of the bath container 14, throughout the electroplating process.

During circulation of the bath solution 20 throughout the ECP system 10, as heretofore described, dissolved oxygen normally forms oxygen micro-bubbles (not shown) in the bath solution 20. Accordingly, the aerobic bacteria 25, having been previously added to the bath solution 20 at step S3 of FIG. 2, consume all or most of the oxygen present in the bath solution 20. This eliminates or substantially reduces the quantity of oxygen micro-bubbles which form in the solution 20. Consequently, the presence of micro-bubbles between the bath solution 20 and the seed layer 19 on the substrate 18 is eliminated or substantially reduced during the subsequent electroplating process, which will be hereinafter described.

As the electroplating bath solution 20 is circulated through the system 10, a metal film 21 is electroplated onto the seed layer 19, as shown in FIG. 1A and indicated in step S5 of FIG. 2, typically as follows. The electroplating bath solution 20 is maintained at a temperature of from typically about 10 degrees C. to about 35 degrees C. The plating rpm for the substrate 18 is typically about 0-500 rpm.

During the electrochemical plating process, the current source 12 applies a selected voltage potential, typically at room temperature, between the anode 16 and the cathode/substrate 18. This voltage potential creates a magnetic field around the anode 16 and the cathode/substrate 18, which magnetic field affects the distribution of the copper ions in the bath solution 20. In a typical copper electroplating application, a voltage potential of about 2 volts may be applied for about 2 minutes, and a plating current of from typically about 0.2 mA/cm² to about 20 mA/cm² flows between the anode 16 and the cathode/substrate 18.

Consequently, copper is oxidized typically at the oxidizing surface 22 of the anode 16 as electrons harvested from the copper anode 16 flow through the wiring 38 and reduce the ionic copper in the typically copper sulfate solution bath solution 20 to form a copper electroplate (not illustrated) at the interface between the cathode/substrate 18 and the copper sulfate bath 20. Due to the absence or paucity of oxygen micro-bubbles between the bath solution 20 and the surface of the seed layer 19, the electroplated metal film 21 deposited onto the seed layer 19 is substantially continuous and devoid of structural deformities such as voids, pits and broken metal lines. Accordingly, the electroplated metal film 21 on the substrate 18 contributes to the fabrication of high-quality IC devices that are characterized by high structural and operational integrity.

Referring next to the graph of FIG. 3, which illustrates a graph in which the concentration of dissolved oxygen (DO) in an electroplating bath solution to which aerobic bacteria have been added is compared to the concentration of dissolved oxygen in an electroplating bath solution devoid of aerobic bacteria. From a consideration of the graph, it can be seen that the addition of aerobic bacteria to an electroplating bath solution is capable of reducing the concentration of dissolved oxygen (DO) in the solution from about 5 mg/l to about 2 mg/l.

While the preferred embodiments of the invention have been described above, it will be recognized and understood that various modifications can be made in the invention and the appended claims are intended to cover all such modifications which may fall within the spirit and scope of the invention.

Claims

1. A method of electroplating a thin film onto a substrate, comprising:

providing an electroplating bath solution;

providing aerobic bacteria in said solution;

providing a current source in electrical contact with said substrate;

immersing said substrate in said solution; and

plating the thin film onto said substrate by applying a current to said substrate.

2. The method of claim 1 wherein said aerobic bacteria is a nitrifying bacterial agent, Bdellovibrio bacteriovorus, Acinetobacter calcoaceticus, Pseudamonas fluorescens, Arthrobacter globiformis, or Acetobacter pasteurianus.

3. The method of claim 1 wherein said solution comprises copper sulfate.

4. The method of claim 3 wherein said aerobic bacteria is a nitrifying bacterial agent, Bdellovibrio bacteriovorus, Acinetobacter calcoaceticus, Pseudamonas fluorescens, Arthrobacter globiformis, or Acetobacter pasteurianus.

5. The method of claim 1 wherein said aerobic bacteria is present in said solution in a concentration of about 1 ml/l to 5 ml/l.

6. The method of claim 5 wherein said aerobic bacteria is a nitrifying bacterial agent, Bdellovibrio bacteriovorus, Acinetobacter calcoaceticus, Pseudamonas fluorescens, Arthrobacter globiformis, or Acetobacter pasteurianus.

7. The method of claim 5 wherein said solution comprises copper sulfate.

8. The method of claim 7 wherein said aerobic bacteria is a nitrifying bacterial agent, Bdellovibrio bacteriovorus, Acinetobacter calcoaceticus, Pseudamonas fluorescens, Arthrobacter globiformis, or Acetobacter pasteurianus.

9. A method for forming a metal film onto a substrate by:

providing an electroplating bath solution comprising a metal;

providing aerobic bacteria in a concentration of from about 1 ml/l to about 5 ml/l;

providing a current source in electrical contact with said substrate;

immersing said substrate in said solution; and

applying a current of from about 0.2 mA/cm2 to about 20 mA/cm2 to said substrate.

10. The metal film of claim 9 wherein said aerobic bacteria is a nitrifying bacterial agent, Bdellovibrio bacteriovorus, Acinetobacter calcoaceticus, Pseudamonas fluorescens, Arthrobacter globiformis, or Acetobacter pasteurianus.

11. The metal film of claim 9 wherein said electroplating bath solution comprises copper sulfate.

12. An electrochemical plating solution comprising:

an electrolyte solution comprising metal; and

an aerobic bacteria provided in said electrolyte solution.

13. The electrochemical plating solution of claim 12 wherein said metal is copper, aluminum, nickel, chromium, zinc, tin, gold, silver, lead, or cadmium.

14. The electrochemical plating solution of claim 12 wherein said aerobic bacteria is a nitrifying bacterial agent, Bdellovibrio bacteriovorus, Acinetobacter calcoaceticus, Pseudamonas fluorescens, Arthrobacter globiformis, or Acetobacter pasteurianus.

15. The electrochemical plating solution of claim 12 wherein said aerobic bacteria is present in said electroplating bath solution in a concentration of about 1 ml/l to 5 ml/l.

16. The electrochemical plating solution of claim 12 wherein said electroplating bath solution comprises copper sulfate.