Patent Application
20060180465
1. Field of the Invention
Embodiments of the invention generally relate to a contact assembly for electrochemical processing.
2. Description of the Related Art
Electrochemical Mechanical Processing (ECMP) is a technique used to deposit or remove conductive materials from a substrate surface. For example, in an ECMP polishing process, conductive materials are removed from the surface of a substrate by electrochemical dissolution while concurrently polishing the substrate with reduced mechanical abrasion as compared to conventional Chemical Mechanical Polishing (CMP) processes.
Electrochemical dissolution is performed by applying a bias between a cathode and a substrate surface to remove conductive materials from the substrate surface into a surrounding electrolyte. The bias may be applied to the substrate surface by a conductive contact disposed on or through a polishing material upon which the substrate is processed. A mechanical component of the polishing process is performed by providing relative motion between the substrate and the polishing material that enhances the removal of the conductive material from the substrate. ECMP systems may generally be adapted for deposition of conductive material on the substrate by reversing the polarity of the bias.
The energization, or biasing of the conductive material may be accomplished through the use of conductive balls that contact the conductive material during processing. However, although conductive balls as contact elements for biasing the conductive layer have demonstrated good results, service life and cost has made a search for an alternative contact element desirable.
Thus, there is a need for an improved apparatus for electrochemical mechanical polishing.
In one embodiment, a contact element for electrically biasing a substrate is provided. The electrical contact includes a conductive base. At least one conductive flat spring is coupled to the base. A contact is coupled to each flat spring and is suitable for slidably engaging a processed face of the substrate during processing.
In another embodiment, a processing pad assembly for electrically assisted processing of a substrate includes a processing pad having a processing surface. A contact element is laterally disposed therewith and is configured to contact a surface of the substrate opposing the processing surface at least contemporaneously with the processing surface. The contact element includes a conductive base. At least one conductive flat spring is coupled to the base. A contact is coupled to each flat spring and is suitable for slidably engaging a processed face of the substrate during processing.
In another embodiment, an electrically assisted substrate processing system includes a platen and a processing pad disposed on the platen. The processing pad has a processing surface. A contact element is laterally disposed with respect to the processing pad and is adapted to contact the surface of a substrate during processing at least contemporaneously with the processing surface of the processing pad. The contact element includes a conductive base. At least one conductive flat spring is coupled to the base. A contact is coupled to each flat spring and is suitable for slidably engaging a processed face of the substrate during processing.
So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures.
In one embodiment, the carrier head assembly 118 may be positioned over the platen assembly 142 by an arm 164 coupled to a column 130. The carrier head assembly 118 generally includes a drive system 102 coupled to a carrier head 122. The drive system 102 generally provides at least rotational motion to the carrier head 122. The carrier head 122 additionally may be actuated toward the platen assembly 142 such that the substrate 120 retained in the carrier head 122 may be disposed against a processing surface 104 of the pad assembly 106 during processing.
In one embodiment, the carrier head 122 may be a TITAN HEAD™ or TITAN PROFILER™ wafer carrier manufactured by Applied Materials, Inc., of Santa Clara, Calif. Generally, the carrier head 122 comprises a housing 124 and retaining ring 126 that define a center recess in which the substrate 120 is retained while leaving a feature side of the substrate exposed. The retaining ring 126 circumscribes the substrate 120 disposed within the carrier head 122 to prevent the substrate 120 from slipping out from under the carrier head 122 during processing. It is contemplated that other carrier heads may be utilized.
The platen assembly 142 is rotationally disposed on a base 158. A bearing 154 is disposed between the platen assembly 142 and the base 158 to facilitate rotation of the platen assembly 142 relative to the base 158. A motor 160 is coupled to the platen assembly 142 to provide rotational motion.
In one embodiment, the platen assembly 142 includes an upper platen 114 and a lower platen 148. The upper platen 114 may be fabricated from a rigid material, such as a metal or rigid plastic, and in one embodiment, is fabricated from or coated with a dielectric material, such as chlorinated polyvinyl chloride (CPVC). The upper platen 114 may have a circular, rectangular or other geometric form with a planar top surface 116. A top surface 116 of the upper platen 114 supports the pad assembly 106 thereon. The pad assembly 106 may be held to the upper platen 114 of the platen assembly 142 by magnetic attraction, static attraction, vacuum, adhesives, or the like.
The lower platen 148 is generally fabricated from a rigid material, such as aluminum and may be coupled to the upper platen 114 by any conventional means, such as a plurality of fasteners (not shown). Generally, a plurality of locating pins 146 (one is shown in
A plenum 138 may be optionally defined in the platen assembly 142 and may be partially formed in at least one of the upper or lower platens 114, 148. In the embodiment depicted in
The pad assembly 106 and at least one contact element 134 are disposed on the platen assembly 142. The contact element 134 is adapted to electrically couple the substrate 120 to a power source 166. The pad assembly 106 and the contact element 134 are configured for slidably engaging the substrate 120 on a side that is to be processed. The contact element 134 is configured to apply a substantially normal force against the substrate 120 during processing and is suitable for moving relative to the substrate without scratching or damaging the substrate 120.
It is contemplated that a plurality of contact elements 134 may be advantageously utilized to process a substrate 120 by providing multiple distributed electrical contact points along the surface of the substrate 120. Although a single contact element 134 is shown in the center of the pad assembly 106 in
As such, multiple contact elements 134 may be arranged in the pad assembly 106 to form any desired pattern of electrical contact points over the surface of the substrate. For example, multiple contact elements 134 may be arranged in a grid, triangular, random, or other pattern. Alternatively or in combination, multiple contact elements 134 may be distributed, with respect to the pad assembly 106, near the center, near the middle, near the edge, along the perimeter, asymmetrically, symmetrically, concentrically, in a star or asterisk pattern, or in any combination of the above. The contact elements 134 are all arranged to deflect in the same direction—away from the surface of the substrate to be processed—and thereby provide a normal contact force against the face of the substrate being processed while allowing the substrate to move over the contact elements 134 and the pad assembly 106.
In one embodiment, wires or other conductive elements (not shown) may couple one terminal of the power source 166 to the contact element 134, such that the substrate 120 may be electrically biased upon engaging the contact element 134. The pad assembly 106 may include an electrode 105 that is insulated from the contact element 134 and coupled to a different terminal of the power source 166 such that an electrical potential may be established between the substrate 120 and the electrode 105 of the pad assembly 106. The contact element 134 is generally insulated from the electrode 105. Electrolyte, which is introduced from the electrolyte source 170 and disposed on the pad assembly 106, completes an electrical circuit between the substrate 120 and the electrode 105, which assists in the deposition or removal of material from the surface of the substrate 120, depending on the polarity of the circuit.
Alternatively, the pad assembly 106 may be configured without an electrode, in which case the electrode may be disposed upon or within the platen assembly 142. It is contemplated that multiple contact elements and/or electrodes 105 may be used. The multiple contact elements 134 and/or electrodes 105 may be independently biased with respect to each other, e.g., multiple power sources may be utilized.
Pad assemblies suitable for use with the contact element 134 of the present invention are described in more detail in copending U.S. patent application Ser. No. 10/642,128, filed Aug. 15, 2003, U.S. patent application Ser. No. 10/727,724, filed Dec. 3, 2003, U.S. patent application Ser. No. 10/744,904, filed Dec. 23, 2003, U.S. patent application Ser. No. 10/880,752, filed Jun. 30, 2004, and U.S. patent application Ser. No. not yet assigned (Attorney Docket No. 4100P12), filed Nov. 3, 2004, each of which is hereby incorporated by reference to the extent not inconsistent with the teachings disclosed herein.
The contact element 134 may optionally be disposed above an actuator (not shown) formed in, or disposed on, the platen assembly 142. The contact element 134 may be either coupled to the actuator, part of the pad assembly 106, or a separate element. The actuator is adapted to selectively adjust the position of the contact element 134 in order to maintain contact with the substrate 120 at a desired pressure during processing, independent of the pressure applied by the pad assembly 106. Multiple actuators may be utilized in embodiments having multiple contact elements 134. Alternatively, a single actuator may control the position of each of the contact elements 134.
The actuator may comprise an elastic membrane, such as ethylene propylene diene monomer (EPDM) or other suitable material, coupled to a fluid supply (not shown). Alternatively, the actuator may comprise one or more of a fluid actuator, a linear actuator, a stepper or other motor, one or more springs, a lead or ball screw or a cam, or any other mechanism for incrementally adjusting the height or position of the contact element 134 and/or controlling the pressure exerted by the contact element 134 against the substrate 120.
To facilitate control of the processing station 100 as described above, a controller 180 is coupled to the processing station 100. The controller 180 is utilized to control power supplies, motors, drives, fluid supplies, valves, actuators, and other processing components of the processing station 100. The controller 180 comprises a central processing unit (CPU) 182, support circuits 186 and memory 184. The CPU 182 may be one of any form of computer processor that can be used in an industrial setting for controlling various chambers and sub-processors. The memory 184 is coupled to the CPU 182. The memory 184, or computer-readable medium, may be one or more of readily available memory such as random access memory (RAM), read only memory (ROM), floppy disk, hard disk, or any other form of digital storage, local or remote. The support circuits 186 are coupled to the CPU 182 for supporting the processor in a conventional manner. These circuits include cache, power supplies, clock circuits, input/output circuitry, subsystems, and the like.
The controller 180 may receive a metric indicative of processing performance for closed-loop process control of the processing station 100. For example, material removal in a polishing operation may be monitored by measuring and/or calculating the thickness of conductive material remaining on the substrate 120. The thickness of the material remaining on the substrate 120 may be measured and/or determined by, for example, optical measurement, interferometric end point, process voltage, process current, charge removed from the conductive material on the substrate, effluent component analysis, and other known means for detecting process attributes. The controller 180 may then adjust one or more processing parameters in response to the received metric, such as adjusting the pressure applied to the substrate 120, the rotational speed of the pad assembly 106, pressure applied by the contact element 134, or ending the polishing process.
The desired quantity of contacts 204 formed on each contact element 134 depends upon the desired contact area and electrical and/or process requirements for the particular substrate or material being processed. In addition, forming multiple contacts 204 on a single base 202 advantageously reduces the effect of high current density on the contact element 134. In one embodiment, the contact element 134 has about 20 or more contacts 204 formed thereon. In one embodiment, the contact element 134 has about 36 to 40 or more contacts 204 formed thereon.
Each contact 204 is coupled to a flat spring 210 that is formed in or coupled to the base 202. In one embodiment, the flat spring 210 is formed in the base 202 by one or more slots 212 that extend completely through the base 202. The slots 212 are formed around the contact 204, for example, by etching, laser machining, stamping, waterjet, electrical discharge machining (EDM), and the like. Each slot 212 leaves a relatively small, flexible, and conductive bridge 214 of material connecting the flat spring 210 to the remainder of the base 202. In the embodiment, depicted in
The flat spring 210 resists lateral deflection in the plane of the base 202. As such, the deflection of the flat spring 210 when the contact 204 is pressed against the substrate 120 (shown in
In addition, the geometry and number of slots 212 and bridges 214, may be selected to produce a flat spring 210 having a desired flexibility. As such, the amount of deflection of the flat spring 210 and the force applied by the contact 204 against the substrate may be adjusted and balanced as desired by base 202 material selection and thickness, the number of slots 212 and bridges 214, the size of the slots 212 and the bridges 214, the orientation, or geometry of the slots 212 and the bridges 214, and the like.
As such, the deflection and force applied by the contact 204 against the substrate may be pre-selected according to known process conditions. For example, in one process embodiment, the processing pressure is about 0.3 psi and the contacts 204 have a deflection in the range of from about 10 to about 30 mil. In one embodiment, the force applied is about 2 grams force or less per contact 204. In another embodiment, the force applied per contact is about 1 gram force or less. It is contemplated that other processes having other processing parameters may have varying deflection of the flat spring 210 and varying force applied by the contact 204.
The base 202 generally comprises a material compatible with process conditions and possessing the flexibility, resiliency, conductivity, and other characteristics necessary to form the flat spring 210. Generally, any material or combination of materials providing the desired combination of spring force and conductivity may be utilized. In one embodiment, the base 202 is fabricated from a copper-beryllium alloy. Optionally, the base 202 may be fabricated from one material possessing the desired spring characteristics and coated with another material possessing the desired conductivity. In one embodiment, the base 202 may comprise a dielectric or conductive material that is coated with a conductor, such as a copper-beryllium alloy. It is contemplated that the base 202 and flat spring 210 may be separate elements.
The base 202 and/or the flat spring 210 may optionally further comprise an upper coating 208 to protect the base 202 and/or the flat spring 210 from oxidation or other damage due to the process chemistries. The upper coating 208 may be formed by conventional techniques, such as chemical vapor deposition (CVD), electrochemical plating (ECP), and the like. For example, the coating 208 may comprise a tin or a copper coating formed over the base 202. Alternatively, any suitable metal, such as a noble metal, or a metal alloy that is process chemistry neutral may be utilized for the coating 208. The material of the coating 208 may further be selected based upon the specific process being performed (e.g., specific material being processed). For example, the coating 208 may comprise copper for processing copper, tungsten for processing tungsten, or other materials suitable for particular processing operations. It is contemplated that the most suitable material may be selected to protect the base 202 and/or the flat spring 210 for any particular application.
In one embodiment, the contact 204 generally has a domed, or rounded geometry suitable for slidably engaging the substrate without scratching or otherwise damaging the substrate. The contact 204 should be sufficiently wide as to provide stable contact over a large deflection range. In one embodiment, the contact 204 has a radius of about 50 to about 200 mils. In one embodiment, the contact 204 has a radius of about 0.2 inches. The contact 204 should have a height suitable for the range of deflection of the contact 204 and motion of the contact element 134. In one embodiment, the contact 204 has a height in the range of from about 50 mils to about 200 mils above the base 202. In one embodiment, the contact 204 has a height of greater than about 0.1 inch above the base 202.
The contact 204 is further adapted to provide electrical contact to the surface of a substrate being processed and generally comprises a suitable conductive material for providing satisfactory electrical contact that is soft enough to not damage the substrate. As such, the selection of material from which the contact 204 is made may depend upon the substrate being processed and is essentially independent of the material that forms the base 202. For example, the contact 204 may be fabricated from copper or tin for polishing or plating copper substrates. Alternatively, the contact 204 may comprise tungsten for processing tungsten substrates. Alternatively, the contact 204 may comprise other materials suitable for other particular processes. It is contemplate that the most suitable contact material for a particular application may be selected as described above. It is further contemplated that the contact 204 may be fabricated from any material having suitable characteristics for conducting electricity to the processed substrate without damaging the substrate while being compatible with processing conditions. Alternatively, the contact 204 may be fabricated from other materials that are coated with a suitable contact material as described above. It is contemplated that the contacts 204 and flat spring 210 may be separate elements coupled together. It is also contemplated that the contacts 204 and flat spring 210 may be formed in the flat spring 210 itself—i.e., formed together from a single piece of spring stock.
In the embodiment depicted in
In the embodiment depicted in
The diameter of the balls 502 may be selected to provide a desired flat spring 210 to substrate distance or flat spring 210 deflection distance. The ball 502 may be press-fit or otherwise attached to an aperture 508 formed in the base 202 in the center of the flat spring 210. In one embodiment, the diameter of the balls 502 is from about 0.05 to about 0.2 inches. In one embodiment, the diameter of the balls 502 is about 0.2 inches.
The base 202 and the balls 502, or any other embodiments of the contact 204, may optionally be coated, for example by flash coating, with a layer of material (not shown) similar to the coatings 305, 405 described above. The thickness of the coating may range from fractions of a micron to about a few microns, so long as the coated film continuously covers the upper surfaces of the base 202 and the contacts 204. In one embodiment, the thickness of the coating may range from about 0.1 to about 3 mils. In one embodiment, the base 202 and balls 502 are coated with 0.4 mils of copper.
A cover plate 510 may optionally be disposed on the base 202 to protect the contacts 204 and to control the exposed height of the ball 502. As such, the exposed height of the ball 502 should be in accordance with the operational range of the contact 204, e.g., the deflection of the contact 204. The cover plate 510 has an aperture 512 coincident with each contact 204. The aperture 512 is wider than the flat spring 210 so as not to impede deflection of the spring 210. The cover plate is fabricated from materials similar to the base 202 and may optionally be coated with a material similar to the coating 208 describe above. The cover plate 510 may optionally be utilized in other embodiments of the contacts 204 described herein.
Returning back to
The holder 206 may be fabricated from a conductive material or may have a conductive element (not shown) for electrically coupling the base 202 to the power source 166 as discussed above with respect to
Thus, various embodiments of a contact element suitable for use in electrically assisted processing of substrates have been provided. The contact element decouples the conductive and the mechanical properties of the contact. Contact materials may be chosen as most suitable for particular materials being processed while the flexible spring materials may be independently chosen for their desired mechanical properties. As such, the contact elements provide independent control over the deflection and force applied by the contact element to promote reliable uniform electrical contact that enhances processing performance. Moreover, the contact elements are configured to minimize scratching while processing, advantageously reducing defect generation and thereby lowering the unit cost of processing.
While the foregoing is directed to the illustrative embodiment of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
