Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
2002-10-18
2004-11-09
Zarneke, David A. (Department: 2829)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
Reexamination Certificate
active
06815349
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to apparatus and methods for electroless plating on substrates. More specifically, the invention relates to improved apparatus for controlling engaging substrates during electroless plating in order to provide good plating performance at relatively high temperatures.
BACKGROUND
The Damascene process provides inlaid copper lines in dielectric layers of integrated circuits. The copper lines provide electrical routing (metal interconnects) between circuit elements in the integrated circuit. Damascene copper lines are rapidly replacing traditional aluminum etched lines in high-performance integrated circuitry.
Currently, a preferred method of metal-interconnect layer deposition is electroplating. This is in part due to the success of “bottom-up” copper filling methods for damascene features. The process typically involves formation of a barrier layer (typically composed of Ta, TiN or TiSiN) and a seed layer (typically copper) over the wafer, followed by plating the wafer to fill embedded structures from the bottom-up. A number of problems occur when trying to accomplish this task. Such problems include corrosion of the seed layer and associated reactions in the plating bath, poor structures (morphology) of PVD-deposited seed layers, non-uniform deposition of the metal over and into features, and shrinking of feature volume (and associated increase in aspect ratio) when seeded.
As features become smaller, the seed layer must become thinner (otherwise the feature will be closed off by the generally non-conformal PVD seeding process). However, most useful electroplating tool designs require supplying current to the wafer from the wafer's outer edge via the seed layer. When attempting to electroplate using ever thinner seed layers for supplying plating current, the current distribution becomes increasingly dominated by the resistance in the seed layer. This phenomenon is commonly referred to as the “terminal effect.”
Thus, the need exists to find methods of depositing seed layers in a more conformal manner. This is because conformal seed layers reduce resistance by providing a greater average thickness in comparison to non-conformal layers deposited by PVD, for example. As a result, the terminal effect is mitigated during electroplating.
Electroless plating can provide highly conformal seed layers. And in some cases, electroless plating can replace not only PVD seed deposition, but electroplating as well, thereby dispensing with the need for a plating current and a seed layer. This, of course, circumvents the problems of the terminal effect and poor seed layer step coverage.
General process requirements for wafer plating include global and local plating uniformity, defect free process, and high throughput. In order to produce plating equipment for high-volume manufacturing (e.g., damascene copper processing) meeting these requirements, advances in electroless plating hardware design are required.
There are problems associated with available and proposed electroless plating apparatus. Most of these are due to heating. Electroless plating can take place at temperatures near room temperature, but to realize good performance for integrated circuit fabrication applications, it is preferably performed at higher temperatures, in the range of about 50 to 90 degrees C. As a consequence, electroless plating baths decompose to some degree during the plating process. In addition, conventional plating equipment can expand, deform, and/or stick to components during plating.
Some wafer electroplating apparatus can provide most of the functionality required for electroless plating. One example is the SABRE™ “clamshell” electroplating apparatus available from Novellus Systems, Inc. of San Jose, Calif. and described in U.S. Pat. Nos. 6,156,167 and 6,139,712, which are herein incorporated by reference in their entireties. The clamshell apparatus provides many advantages for wafer throughput and uniformity; most notably, wafer backside protection from contamination during electroplating, wafer rotation during the electroplating process, and a relatively small footprint for wafer delivery to the electroplating bath (vertical immersion path). During plating, it compresses the wafer between a “cup” and a “cone,” thereby sealing off the backside of the wafer from contact with plating solution.
Modifications to the “clamshell” and its associated plating environment for improved wafer uniformity and quality have been described in U.S. Pat. Nos. 6,074,544, 6,110,346, 6,162,344, and 6,159,354 which are herein incorporated by reference in their entirety. The described modifications relate to methods for using variable currents, improved mass transfer, and electric potential shaping. Other documents providing details of the clamshell design include the following: U.S. patent application Ser. No. 09/927,741, filed Aug. 10, 2001, titled “Clamshell Apparatus For Electrochemically Treating Wafers”, and naming Reid, et al. as the inventors; U.S. patent application Ser. No. 09/872,340, filed May 31, 2001, titled “Methods and Apparatus for Bubble Removal in Wafer Wet Processing”, and naming Patton, et al. as the inventors; U.S. patent application Ser. No. 09/872,341, filed May 31, 2001, titled “Methods and Apparatus for Controlled-Angle Wafer Immersion”, and naming Reid, et al. as the inventors; and U.S. patent application Ser. No. 09/927,740, filed Aug. 10, 2001, titled “Methods and Apparatus for Controlling Electrolyte Flow for Uniform Plating”, and naming Mayer, et al. as the inventors.
Many features of the basic clamshell apparatus are suitable for electroless plating. However, some features must be modified to account for the relatively high temperatures required for electroless plating.
SUMMARY
The present invention addresses these needs by providing certain improved features of a clamshell plating apparatus designed for use at relatively high temperatures (e.g., at least about 50 degrees C.). It accomplishes this with judicious choices of construction materials and feature positioning. For example, the clamshell cup and cone components that engage the work piece are made from dimensionally stable materials with relatively low coefficients of thermal expansion. Further, O-rings are removed from positions that come in contact with the work piece. This avoids the difficulty caused by O-rings sticking to work piece surfaces during high temperature processing. In place of the O-ring, a cantilever member is provided on the portion of the cone that contacts the work piece. Still further, the invention may employ a heat transfer system for controlling the temperature of the work piece backside during plating.
One aspect of the invention pertains to apparatus for engaging a work piece during plating. Such apparatus may be characterized by the following features: (a) a cup having a circumferential side wall defining an interior region and a lip within the interior region arranged such that lip can support the work piece while the work piece remains within the interior region; (b) a cone having a work piece contact surface that fits within the cup's interior and can contact the work piece in a manner that holds the work piece in a fixed position against the cup's lip; and (c) a circumferential cantilever member provided on the contact surface, which cantilever member elastically deflects holding the work piece in the fixed position. Preferably, the cone's circumferential cantilever member and the work piece contact surface form a monolithic element. That is, they are formed from a single piece of material.
Preferably, the cantilever member has certain associated features such as a contact feature and a backing O-ring. The contact feature protrudes from a distal end region of the circumferential cantilever member and points toward the cup. Thus, the contact feature is the first portion of the cone to contact the work piece during engagement of the work piece. Typically, the contact feature is implemented as a circumferential ridge on the circumferential cantil
Biggs Kevin
Fetters Wayne
Minshall Edmund B.
Stowell R. Marshall
Beyer Weaver & Thomas LLP
Harrison Monica D.
Novellus Systems Inc.
Zarneke David A.
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