Microelectronic circuits generally include conductive features such as via plugs, metal lines, and the like to interconnect various portions or layers of the circuit. The conductive features of the microelectronic circuits include conductive material such as metal and often include a barrier material to reduce unwanted diffusion of the conductive material and promote adhesion between the conductive material and an adjacent layer of the circuit.
Aluminum is often used to form conductive features because aluminum features are relatively easy to manufacture using conventional deposition (e.g., chemical vapor deposition) and etch (e.g., reactive ion etch) techniques. While use of aluminum to form conductive features is adequate for some circuits, the use of aluminum to form conductive features becomes increasingly problematic as the size of the conductive feature decreases. In particular, as the size of the conductive feature decreases, the current density through the feature generally increases and thus the feature becomes increasingly susceptible to electromigration, i.e., the mass transport of metal due to the current flow. Electromigration may cause short circuits where the metal accumulates, opens where the metal has been depleted, or other circuit failures. Similarly, increased conductive feature resistance may cause unwanted device problems such as excess power consumption or heat generation.
Recently, techniques have been developed to form conductive features comprising copper, which is less susceptible to electromigration and which exhibits a lower resistivity than aluminum. Because copper does not readily form volatile or soluble compounds, the copper conductive features are often formed using damascene technology. More particularly, the copper conductive features are formed by creating a via within an insulating material, blanket depositing a barrier layer onto the surface of the insulating material and into the via, blanket depositing a seed layer of copper onto the barrier layer, electrodepositing a copper layer onto the seed layer to fill the via, and removing any excess barrier material and copper from the surface of the insulating material using chemical mechanical polishing. During the electrodeposition process, additives such as leveling agents are continuously or regularly added to the plating bath to reduce formation of voids within the conductive features. Such leveling agents may affect the grain boundaries of the deposited material, necessitating a subsequent anneal process to obtain the desired material properties.
Forming copper conductive features according to the method described above can be relatively expensive, in part, because each material deposition and removal step is typically carried out using dedicated equipment. Further, once conductive features are formed, it may be necessary to subject the wafer to further processing. Again, however, such additional processing is often conducted at remote, dedicated equipment stations. A system configuration that requires that stages of processing be carried out at remote stations on dedicated equipment may result in higher costs and loss of throughput.
Accordingly, an improved apparatus for electrochemically depositing a metal film is needed. There is also a need for an apparatus that provides for electrochemical deposition and polishing of a workpiece and additional multi-stage processing.