Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Utilizing magnet or magnetic field during coating
Reexamination Certificate
1999-09-03
2001-06-26
Gorgos, Kathryn (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Utilizing magnet or magnetic field during coating
C205S096000, C205S133000, C205S148000, C205S157000, C204S22400M, C204S273000, C204S230200, C204S275100
Reexamination Certificate
active
06251250
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the control of fluid flow in the wet processing of the surfaces of workpieces in such applications as electroplating and the like, where electric fields may also be involved, being more particularly, though not exclusively, directed to the processing of substantially thin or planar workpieces such as silicon semiconductor wafers and the like, by the automatic and controlled processing application and removal of fluid from such surfaces, as well as more generally the control of wet processing of other types of workpiece surfaces including wet processing without electric fields, as later discussed
BACKGROUND OF THE INVENTION
While, as above indicated, the invention has general application and usefulness in various types of wet processing of a myriad of workpiece surfaces, the principal thrust of the preferred embodiment and particular advantageous use of the invention resides in the field of electroplating, and more specifically for such applications as the electroplating of thin planar workpiece surfaces such as silicon semiconductor wafers and the like though the invention will therefore illustratively be described hereinafter as applied to such usage, it is to be understood that it has decided utility, also, for controlling flow or movement of processing fluids at workpiece surfaces more generally, including as further examples, in electroless plating processes, chemical etching, photo resist coating and stripping, spin-on glass and other dielectric coatings, wafer cleaning processes, and the like. While electro-etching processes and the like, similarly to electroplating, also require electric field control, other processes such as cleaning and the like do not involve the use of electric fields.
Turning, therefore, to electroplating applications as illustrative, such electroplating has been widely used for many years as a manufacturing technique for the application of metal films to many different kinds of structures and surfaces. It has been particularly advantageous in semiconductor or solid-state wafer workpiece manufacturing for the application of copper, gold, lead-tin, indium-tin, nickel-iron, and other types of metals or alloys of metals to the wafer workpiece surfaces. An important requirement of the machines used for such a process is that they be capable of depositing metal films with uniform and repeatable characteristics, such as metal thickness, alloy composition, metal purity, and metal profile relative to the underlying workpiece profile For high-volume manufacturing, it is economical to process workpieces using an automated robotic tool, in which a central robot distributes the workpieces to and from separate processing chambers—commonly referred to as a cluster tool that enables the processing of many workpieces per hour and many workpieces per unit of floor-space occupied by the tool. In the exemplary embodiment of such a cluster tool for electroplating in the field of integrated semiconductor circuit manufacturing, the electroplating is used to apply copper films to silicon workpieces for interconnection wiring, to apply lead-tin solder bumps to the workpieces, and also to apply gold to the workpieces. The process chamber designed for such an electroplating cluster tool addresses the various arts of electroplating, fluid mixing, and fluid control. Various features of such a processing chamber can make its integration into an automated wafer handling cluster tool more efficient and useful for manufacturing. It is to these applications as they relate more specifically to a manufacturing cluster tool wet processing chamber, that the present invention is primarily addressed.
At least three factors, however, make it difficult to design equipment that is capable of producing substantially uniform metal films. First, the plating current spreads out when passing from the anode to the cathode, usually resulting in thicker plated deposits near the outer edge of the workpiece. Secondly, the fluid distribution in the electroplating chamber, particularly at the anode and cathode surfaces, may not be uniform. Non-uniform fluid distribution at the cathode, for example, can cause variation of the diffusion boundary layer thickness across the workpiece surface, which, in turn, can lead to non-uniform plated metal thickness and non-uniform alloy composition. Thirdly, the ohmic potential drop from the point on the workpiece at which the electroplating current enters the workpiece may be non-uniform across the workpiece surface, leading to variation in plating current at the workpiece surface and consequently leading to non-uniform metal film deposition.
The prior art reveals several approaches that have been developed to try to minimize one or more of these sources of non-uniformity in the deposited films, particularly for thin and flat workpieces such as wafers and the like. A common arrangement, for example, is described as a fountain plating chamber, or a “fountain plater” as in Schuster et al U.S. Pat. No. 5,000, 827, embodying a fountain or cup plater wherein the water surface to be plated is positioned face down. To control non-uniformity due to edge effects, a method is disclosed wherein the reduction of deposition rate due to fluid effects and the increase in deposition rate due to electric field effects at the workpiece perimeter are balanced against one another to cause substantially uniform plating across the whole workpiece surface. Unfortunately, however, this arrangement is difficult to incorporate in a machine that automatically loads and unloads workpieces in and from the plating chamber. A patent to Stierman et al, U.S. Pat. No. 5,024, 746, as another example, describes a means of operating with a workpiece facing upward toward the cathode such that bubbles will float upwards from the growing plated metal surface to reduce the effect of entrapped air bubbles blocking metal deposition onto the workpiece. This approach, however, requires workpiece attachment means which are difficult to automate for manufacturing. Unlike either of such prior art approaches, the present invention is designed to provide fluid mixing near the growing metal surface which effectively washes entrapped air bubbles from the workpiece surface and carries them out of the plating chamber, as later more fully explained.
As known to those familiar in the art, the technique of fountain plating requires the providing of a distance between the fluid inlet and cathode workpiece which is similar to or greater than the radius or cross-dimension of the cathode workpiece being plated in order to cause acceptably uniform fluid flow at the workpiece surface. Fluid enters at the bottom of the chamber and flows through the anode toward the cathode workpiece surface. The position of fluid passages in the anode, the position of the anode between the fluid inlet and cathode, and the overall size of the fluid chamber are variables that can be changed to influence the uniformity of the electroplated film. The patent to Lytle et al, U.S Pa. No. 5,391, 285, for example, describes a fountain plating cell wherein the anode, the cathode workpiece and the fluid inlet separation distances can be adjusted to cause uniform flow at the cathode workpiece surface. In an article by T. Lee, W. Lytle, B. Hileman, entitled
Application of a CFD Tool in Designing a Fountain Plating Cell for Uniform Bump Plating of Semiconductor Wafers
, IEEE Trans. On Components, Packaging, and Manufacturing Technology, Part B. Vol. 19, No. 1, February 1996, p. 131, there is a description of how the fluid chamber size, along with the position of the anode in the chamber, can be optimized for producing the best uniformity of plated deposits on a cathodic wafer surface. An inlet to wafer spacing of 70% of the wafer diameter is shown to be. For a 300 mm wafer, as an illustration, this would be a 210 mm fluid chamber height. While in a cluster tool, the compactness of the plating chamber is important for maximizing the economy of the manufacturing process, such prior art fountain plating
Feely Michael J
Gorgos Kathryn
Rines and Rines
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