Patent Application
20080067076
The invention will be better understood, by way of example, with reference to the accompanying drawings, in which:
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
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
As indicated in step S2 of
Next, as indicated in step S3 and shown in
As indicated in step S4 of
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
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
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
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.
