In the semiconductor fabrication arts, electroplating is typically performed in a single-wafer processor, with the wafer immersed in an electrolyte. During electroplating, the wafer is typically held in a wafer holder, at a negative, or ground potential, with respect to a positively charged plate (also immersed in the electrolyte) which acts as an anode. To form a copper layer, for example, the electrolyte is typically between about 0.3M and about 0.85M CuSO4, pH between about 0 and about 2 (adjusted by H2SO4), with trace levels (in ppm concentrations) of proprietary organic additives as well as Cl to enhance the deposit quality. During the plating process, the wafer is typically rotated to facilitate uniform plating. After a sufficient film thickness has been achieved during the plating process, the wafer is moved from the plating chamber to another chamber where it is rinsed in de-ionized (DI) water, to remove residual electrolyte from the wafer surface. Next the wafer is subjected to additional wet processing, to remove unwanted copper from the backside and bevel edge, and then another DI water rinse removes wet processing chemical residues. Then the wafer is dried and annealed before it is ready for the chemical mechanical planarization (CMP) operation.
During the plating process, the wafer acts as a cathode, which requires that the power supply be electrically connected to the wafer. Typically, numerous discrete contacts on the wafer holder connect the wafer holder electrically to the edge of the wafer. The current utilized to electroplate the wafers is provided through these contacts. Plating current is desired to be evenly distributed around the perimeter of the wafer to provide uniform deposition. Unfortunately, plating current is generally stronger in locations closer to the contacts. Therefore, uneven plating often occurs. In addition, when wafer is plated in a plating chamber, the time to plate the wafer can be lengthy.
What is needed is an electroplating system that produces uniform electroplating on wafers in an efficient and cost effective manner.