Patent Application
20050121329
The present invention relates to electrochemical plating systems used in the deposition of metal layers on semiconductor wafer substrates in the fabrication of semiconductor integrated circuits. More particularly, the present invention relates to an electrochemical plating system having a thrust pad assembly which reduces the quantity of metal electroplated on the edge regions of a cathode/wafer by the application of variable pressure to the center and edge regions of the wafer.
In the fabrication of semiconductor integrated circuits, metal conductor lines are used to interconnect the multiple components in device circuits on a semiconductor wafer. A general process used in the deposition of metal conductor line patterns on semiconductor wafers includes deposition of a conducting layer on the silicon wafer substrate; formation of a photoresist or other mask such as titanium oxide or silicon oxide, in the form of the desired metal conductor line pattern, using standard lithographic techniques; subjecting the wafer substrate to a dry etching process to remove the conducting layer from the areas not covered by the mask, thereby leaving the metal layer in the form of the masked conductor line pattern; and removing the mask layer typically using reactive plasma and chlorine gas, thereby exposing the top surface of the metal conductor lines. Typically, multiple alternating layers of electrically conductive and insulative materials are sequentially deposited on the wafer substrate, and conductive layers at different levels on the wafer may be electrically connected to each other by etching vias, or openings, in the insulative layers and filling the vias using aluminum, tungsten or other metal to establish electrical connection between the conductive layers.
Deposition of conductive layers on the wafer substrate can be carried out using any of a variety of techniques. These include oxidation, LPCVD (low-pressure chemical vapor deposition), APCVD (atmospheric-pressure chemical vapor deposition), and PECVD (plasma-enhanced chemical vapor deposition). In general, chemical vapor deposition involves reacting vapor-phase chemicals that contain the required deposition constituents with each other to form a nonvolatile film on the wafer substrate. Chemical vapor deposition is the most widely-used method of depositing films on wafer substrates in the fabrication of integrated circuits on the substrates.
Due to the ever-decreasing size of semiconductor components and the ever-increasing density of integrated circuits on a wafer, the complexity of interconnecting the components in the circuits requires that the fabrication processes used to define the metal conductor line interconnect patterns be subjected to precise dimensional control. Advances in lithography and masking techniques and dry etching processes, such as RIE (Reactive Ion Etching) and other plasma etching processes, allow production of conducting patterns with widths and spacings in the submicron range. Electrodeposition or electroplating of metals on wafer substrates has recently been identified as a promising technique for depositing conductive layers on the substrates in the manufacture of integrated circuits and flat panel displays. Such electrodeposition processes have been used to achieve deposition of the copper or other metal layer with a smooth, level or uniform top surface. Consequently, much effort is currently focused on the design of electroplating hardware and chemistry to achieve high-quality films or layers which are uniform across the entire surface of the substrates and which are capable of filling or conforming to very small device features. Copper has been found to be particularly advantageous as an electroplating metal.
Electroplated copper provides several advantages over electroplated aluminum when used in integrated circuit (IC) applications. Copper is less electrically resistive than aluminum and is thus capable of higher frequencies of operation. Furthermore, copper is more resistant to electromigration (EM) than is aluminum. This provides an overall enhancement in the reliability of semiconductor devices because circuits which have higher current densities and/or lower resistance to EM have a tendency to develop voids or open circuits in their metallic interconnects. These voids or open circuits may cause device failure or burn-in.
In operation of the electroplating system 10, the current source 12 applies a selected voltage potential typically at room temperature between the anode 16 and the cathode/wafer 18. This potential creates a magnetic field around the anode 16 and the cathode/wafer 18, which magnetic field affects the distribution of the copper ions in the bath 20. In a typical copper electroplating application, a voltage potential of about 2 volts may be applied for about 2 minutes, and a current of about 4.5 amps flows between the anode 16 and the cathode/wafer 18. Consequently, copper is oxidized typically at the oxidizing surface 22 of the anode 16 as electrons from the copper anode 16 and reduce the ionic copper in the copper sulfate solution bath 20 to form a copper electroplate (not illustrated) at the interface between the cathode/wafer 18 and the copper sulfate bath 20.
The copper oxidation reaction which takes place at the oxidizing surface 22 of the anode 16 is illustrated by the following reaction formula (1):
Cu→Cu+++2e− (1)
The oxidized copper cation reaction product forms ionic copper sulfate in solution with the sulfate anion in the bath 20:
Cu+++SO4−−→Cu++SO4−− (2)
At the cathode/wafer 18, the electrons harvested from the anode 16 flow through the wiring 38 and reduce copper cations in solution in the copper sulfate bath 20 to electroplate the reduced copper onto the patterned surface 19a of the cathode/wafer 18:
Cu+++2e−→Cu (3)
As the anode 16 is consumed during the electroplating process, small quantities of solid copper sulfate or “anode fines” tend to precipitate at the interface between the copper sulfate bath 20 and the oxidizing surface 22 of the anode 16 to form a copper precipitate or sludge on the oxidizing surface 22.
As shown in
After the electroplating process, some excess electroplated metal must typically be removed from the edge regions 18b of the cathode/wafer 18 since excess metal in the edge regions 18b is potentially a significant source of contaminant particles during subsequent processing of the wafer 18. This excess metal removal process is typically carried out using an edge bevel clean process that is integrated into the electrochemical plating apparatus. However, such edge bevel cleaning of wafers required after electroplating is a common source of process flow bottlenecking and hinders orderly and efficient flow of the electroplating process sequence.
It has been found that the quantity of metal electroplated onto the edge region of a substrate can be reduced by the application of reduced-magnitude pressure to the edge region of the substrate during electrochemical plating, thus reducing the ohmic contact between the contact ring and the edge region of the substrate. This eliminates the need for edge bevel cleaning of substrates after electrochemical plating and facilitates efficient and orderly flow of substrates and increases throughput of electrochemically-plated substrates throughout a process flow sequence during the fabrication of semiconductor integrated circuits.
Accordingly, an object of the present invention is to provide a new and improved thrust pad assembly which can be adapted to an electrochemical plating system.
Another object of the present invention is to provide a new and improved thrust pad which is capable of applying pressure of reduced magnitude against the edge region of a substrate to reduce or eliminate the deposition of excess quantities of a metal on the edge region during electrochemical plating of the substrate.
Still another object of the present invention is to provide a new and improved thrust pad assembly which generates zones of variable pressure against a substrate in the electrochemical plating of the substrate.
Yet another object of the present invention is to provide a new and improved thrust pad assembly which is capable of reducing or eliminating the need for edge bevel cleaning of substrates after electrochemical plating.
A still further object of the present invention is to provide a new and improved thrust pad assembly which significantly increases throughput of substrates during electrochemical plating.
Another object of the present invention is to provide a novel method for electroplating a metal onto a substrate.
In accordance with these and other objects and advantages, the present invention is generally directed to a new and improved thrust pad assembly which is capable of reducing the quantity of metal electroplated onto the edge region of a substrate to eliminate or reduce the need for edge bevel cleaning or removal of excess metal from the substrate after the electroplating process. The thrust pad assembly typically includes an air platen through which air is applied at variable pressures to the central and edge regions, respectively, of a thrust pad. The thrust pad applies pressure to a contact ring connected to an electroplating voltage source. The contact ring applies relatively less pressure to the edge region than to the central region of the substrate, thereby reducing the ohmic contact between the contact ring and the edge region of the substrate. Therefore, excess electroplating of the metal onto the edge regions of the substrate is eliminated or substantially reduced.
The present invention further includes a method of electroplating a metal on a substrate. The method includes providing a substrate, providing a contact ring in contact with the substrate, providing the contact ring and the substrate in an electrolyte bath, providing an anode in the electrolyte bath, applying a voltage to the contact ring and the anode, applying a central pressure to a central region on the substrate, and applying a peripheral pressure which is less than the central pressure to an edge region on the substrate.
The invention will now be described, by way of example, with reference to the accompanying drawings, in which:
The present invention has particularly beneficial utility in the electroplating of copper or other metals onto a semiconductor wafer substrate in the fabrication of integrated circuits on the substrate. However, the invention is not so limited in application, and while references may be made to such semiconductor wafer substrate and integrated circuits, the invention may be more generally applicable to electroplating metals on substrates in a variety of industrial applications.
The present invention is generally directed to a new and improved thrust pad assembly which is suitable for preventing deposition of excess quantities of metal onto the edge or peripheral region of a substrate as copper or other metal is electroplated onto the substrate in the fabrication of semiconductor integrated circuits on the substrate. The thrust pad assembly eliminates the need for edge bevel cleaning or removal of excess metal from the edge region of the substrate after the electroplating process. The thrust pad assembly typically includes an air platen through which air is applied at variable pressures to the central and edge regions, respectively, of a thrust pad. The thrust pad, in turn, transmits this variable pressure to a contact ring which is electrically connected to the electroplating current source. The thrust pad applies relatively less pressure to the edge region than to the central region of the substrate, thus reducing ohmic contact between the contact ring and the edge region of the substrate. Electrical resistance between the anode and the edge region of the substrate is reduced with respect to the electrical resistance between the anode and the central region of the substrate. This variable pressure application to the substrate, and resulting disparity in electrical resistance, is used to control the substrate plating shape such that excess electroplating of the metal onto the edge region of the substrate is reduced or eliminated while electroplating of the metal onto the central region of the substrate remains optimal.
The present invention further contemplates a method of electroplating a metal on a substrate. The method includes providing a substrate, providing a contact ring in contact with the substrate, immersing the contact ring and the substrate in an electrolyte bath, immersing an anode in the electrolyte bath, applying a voltage to the contact ring and the anode, applying a central pressure to a central region on the substrate, and applying a peripheral pressure which is less than the central pressure to an edge region on the substrate.
Referring to
As further shown in
Referring to
Referring next to
As the metal layer 74 is electroplated onto the wafer 54, the contact ring 50 of the thrust pad assembly 40 applies pressure of variable magnitude against the backside 57 of the wafer 54, as follows. As shown in
It will be appreciated by those skilled in the art that because the thickness of the electroplated metal 74 at the edge region 54b of the wafer 54 is attenuated with respect to the thickness of the electroplated metal 74 at the center region 54a throughout the electroplating process, electroplating of excessive quantities of the metal layer 74 at the edge region 54b of the wafer 54 is prevented. Accordingly, there is no need to subject the wafer 54 to edge bevel clean methods which would otherwise be needed to remove excess electroplated metal from the edge region 54b. This eliminates process bottlenecking at the electroplating station and promotes an orderly and efficient flow of wafers through the electroplating process.
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.
