Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
2001-03-30
2004-08-10
Nguyen, Nam (Department: 1753)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S192380, C204S192380, C204S192380
Reexamination Certificate
active
06773560
ABSTRACT:
BACKGROUND
Processors, memory devices, field-emission-displays, read/write heads and other microelectronic devices generally have integrated circuits with microelectronic components. A large number of individual microelectronic devices are generally formed on a semiconductor wafer, a glass substrate, or another type microelectronic workpiece. In a typical fabrication process, one or more layers of metal are formed on the workpieces at different stages of fabricating the microelectronic devices to provide material for constructing interconnects between various components.
The metal layers can be applied to the workpieces using several techniques, such as chemical vapor deposition (CVD), physical vapor deposition (PVD), plasma-enhanced deposition processes, electroplating, and electroless plating. The particular technique for applying a metal to a workpiece is a function of the particular type of metal, the structure that is being formed on the workpiece, and several other processing parameters. For example, CVD and PVD techniques are often used to deposit aluminum, nickel, tungsten, solder, platinum and other metals. Electroplating and electroless plating techniques can be used deposit copper, solder, permalloy, gold, silver, platinum and other metals. Electroplating and electroless plating can be used to form blanket layers and patterned layers. In recent years, processes for plating copper have become increasingly important in fabricating microelectronic devices because copper interconnects provide several advantages compared to aluminum and tungsten for high-performance microelectronic devices.
Electroplating is typically performed by forming a thin seed-layer of metal on a front surface of a microelectronic workpiece, and then using the seed-layer as a cathode to plate a metal layer onto the workpiece. The seed-layer can be formed using PVD, CVD or electroless plating processes. The seed-layer is generally formed on a topographical surface having vias, trenches, and/or other features, and the seed-layer is approximately 500-1000 angstroms thick. The metal layer is then plated onto the seed-layer using an electroplating technique to a thickness of approximately 6,000 to 15,000 angstroms. As the size of interconnects and other microelectronic components decrease, it is becoming increasingly important that the plated metal layer (a) has a uniform thickness across the workpiece, (b) completely fills the vias/trenches, and (c) has an adequate grain size.
Electroplating machines for use in manufacturing microelectronic devices often have a number of single-wafer electroplating chambers. A typical chamber includes a container for holding an electroplating solution, an anode in the container to contact the electroplating solution, and a support mechanism having a contact assembly with electrical contacts that engage the seed-layer. The electrical contacts are coupled to a power supply to apply a voltage to the seed-layer. In operation, the front surface of the workpiece is immersed in the electroplating solution so that the anode and the seed-layer establish an electrical field that causes metal in a diffusion layer at the front surface of the workpiece to plate onto the seed-layer.
The structure of the contact assembly can significantly influence the uniformity of the plated metal layer because the plating rate across the surface of the microelectronic workpiece is influenced by the distribution of the current (the “current density”) across the seed-layer. One factor that affects the current density is the distribution of the electrical contacts around the perimeter of the workpiece. In general, a large number of discrete electrical contacts should contact the seed-layer proximate to the perimeter of the workpiece to provide a uniform distribution of current around the perimeter of the workpiece. Another factor that affects the current density is the formation of oxides on the seed-layer. Oxides are generally resistive, and thus oxides reduce the efficacy of the electrical connection between the contacts and the seed-layer. Still other factors that can influence the current density are (a) galvanic etching between the contacts and the seed-layer, (b) plating on the contacts during a plating cycle, (c) gas bubbles on the seed-layer, and (d) other aspects of electroplating that affect the quality of the connection between the contacts and the seed-layer or the fluid dynamics at the surface of the workpiece. The design of the contact assembly should address these factors to consistently provide a uniform current density across the workpiece.
One type of contact assembly is a “dry-contact” assembly having a plurality of electrical contacts that are sealed from the electroplating solution. For example, U.S. Pat. No. 5,227,041 issued to Brogden et al. discloses a dry contact electroplating structure having a base member for immersion into an electroplating solution, a seal ring positioned adjacent to an aperture in the base member, a plurality of contacts arranged in a circle around the seal ring, and a lid that attaches to the base member. The seal ring is placed in a channel of the base member. In operation, a workpiece is placed in the base member so that the front face of the workpiece engages the contacts and the seal ring. When the front face of the workpiece is immersed in the electroplating solution, the seal ring prevents the electroplating solution from engaging the contacts inside the base member.
U.S. Pat. No. 6,156,167 issued to Patton et al. (Patton) discloses another apparatus for electroplating the wafer surface. The devices disclosed in Patton include a cup having a center aperture defined by an inner perimeter, a compliant seal adjacent to the inner perimeter, contacts adjacent to the compliant seal, and a cone attached to a rotatable spindle. The cup can be formed of an electrically insulating material, such as polyvinylidene fluoride (PVDF) or chlorinated polyvinyl chloride (CPVC). Alternatively, the cup can be formed of an electrically conductive material, such as aluminum or stainless steel. The compliant seal engages a perimeter region of the wafer surface to prevent the plating solution from contaminating the wafer edge, the backside of the wafer, and the contacts. The compliant seal is formed of a relatively soft material, such as VITON (manufactured by DuPont®) or CHEMRAZ (manufactured by Green Tweed). In operation, a surface of the cone presses against the backside of the wafer to force a perimeter region of the wafer against the compliant seal.
The devices disclosed in Brogden and Patton may entrap bubbles on the plating surface of a wafer at the inner perimeter of the compliant seal. One feature of these devices that inhibits bubbles from flowing off of the plating surface is the “well-depth,” which is defined by the thickness of the seal and the base member that holds the seal. In Brogden, for example, the combined thickness of the seal and the base member appears to be quite large such that it is expected that bubbles will accumulate at the interior perimeter of the seal during operation. It appears that Patton is an improvement over Brogden, but Patton also appears to have a significant well-depth at the inner perimeter of its compliant seal. The depth of the inner perimeter of the cup and the compliant seal in Patton, for example, is disclosed as being approximately 0.147 inch. Therefore, the electroplating apparatus disclosed in Patton are also expected to allow bubbles to accumulate at the inner perimeter of the seal.
SUMMARY
The present invention is generally directed toward contact assemblies, electroplating machines with contact assemblies, and methods for making contact assemblies that are used in the fabrication of microelectronic workpieces. The contact assemblies are generally dry-contact assemblies that inhibit the electroplating solution from engaging the contacts or the backside of the workpieces. In one aspect of an embodiment, a contact assembly for use in an electroplating system comprises a support member and a contact system carried by
Pedersen John M.
Willey Jeremy
Woodruff Daniel J.
Mutschler Brian L
Nguyen Nam
Perkins Coie LLP
Semitool Inc.
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