Microelectronic workpiece holders and contact assemblies for use therewith

The invention provides an improved contact ring and an improved workpiece support, each of which is useful alone or jointly with the other in a workpiece holder for electrochemically treating microelectronic workpieces. Several embodiments of the invention provide a composite contact ring having a dielectric base carrying a conductor which delivers electric power to a microelectronic workpiece. The dielectric base may be rigid and define a plurality of rigid fingers, each of which carries a separate electrical contact of the conductor. Such a contact ring is expected to have a long service life and enhance uniformity of electrochemical treatment. Several embodiments of the invention provide a workpiece support which induces a control the flexure of a microelectronic workpiece without damaging the workpiece. This controlled flexure can ensure more uniform contact between the workpiece and a contact assembly despite variations in the workpiece and/or the contact assembly.

TECHNICAL FIELD

The present invention generally relates to electrochemically treating microelectronic workpieces and specifically relates to improved workpiece holders and contact assemblies for use in electrochemically treating microelectronic workpieces.

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. 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.

Another type of contact assembly is a “wet-contact” assembly wherein the electrical contacts are permitted to contact the electroplating solution. One problem associated with such contacts is “thieving” of metal intended for the front face of the workpiece. This “thieved” metal is commonly deposited on the surface of the contact rather than the surface of the workpiece. This fouls the contact and changes its electrical conductivity over time. Particularly where thieving occurs more at one location than at another, this can adversely impact uniformity of the current density across the workpiece, leading to non-uniform plated metal layers.

Dry-contact assemblies can minimize thieving by keeping the electrical contacts outside of the plating solution. However, the seals required to isolate the electrical contacts occupy valuable real estate on the front face of the microelectronic workpiece. In addition, the presence and thickness of the seal can induce turbulence in the flow of the electroplating solution at the workpiece surface and trap bubbles at the interior perimeter of the seal during operation. Increased in turbulence and bubbles can both adversely impact plating uniformity.

SUMMARY

The present invention is generally directed toward microelectronic workpiece holders, contact assemblies, and support plates for microelectronic workpiece holders. In one embodiment of the invention, the workpiece holder can include both a novel contact assembly in accordance with one aspect of the invention and a novel support plate in accordance with another aspect of the invention. Several embodiments of such workpiece holders facilitate uniform electrical contact with a microelectronic workpiece with reduced thieving, enhancing product uniformity. Several embodiments of the invention provide workpiece holders well-suited for wet-contact applications with enhanced service life and reduced thieving.

A workpiece holder in accordance with one embodiment of the invention is useful for supporting a microelectronic workpiece for electrochemical treatment, such as electroplating or deplating. This workpiece holder includes a contact ring and a support. The contact ring has a central opening and is adapted to deliver electrical power to the workpiece front surface. The support is adapted to urge the workpiece front surface against the contact ring while contacting the back surface of the workpiece. In particular, the support contacts an inner location on the workpiece back surface at a first height with respect to the contact ring and contacts an outer location on the workpiece back surface at a second height with respect to the contact ring. The first height is greater than the second height. When the support forces the workpiece toward the contact ring, this height differential can induce a controlled flexure of the workpiece, facilitating good electrical contact between the contact ring and the workpiece front surface. If so desired, both the contact ring and the support plate may be rigid, which can materially enhance the useful life of the workpiece holder.

Other embodiments of the invention provide composite contact rings and contact assemblies employing composite contact rings. These novel contact rings can be used in flexure-inducing workpiece holders in accordance with several embodiments of the invention. However, these contact rings can be used in a variety of other applications, including more conventional workpiece holder constructions.

In one embodiment of the invention useful in wet-contact assemblies, a composite contact ring includes a dielectric base, a conductor, and a dielectric coating. The dielectric base has a contact face and an interior opening through which an electrolyte might pass to contact a surface of a microelectronic workpiece. A conductor is carried by the contact face of the base. The conductor includes an outer busbar and a plurality of spaced-apart contacts extending inwardly from and electrically coupled to the busbar. The dielectric coating covers at least a portion of the busbar, with at least a portion of each of the contacts remaining exposed for electrically contacting the workpiece. In this embodiment, the dielectric base and dielectric coating can enhance operation of the contact ring in wet-contact applications.

A composite electrochemistry contact ring in accordance with another embodiment to the invention employs a rigid dielectric base having a peripheral member and a plurality of fingers extending inwardly from the peripheral member. A plurality of electrical contacts are provided, with each electrical contact being carried on a finger of the base. Each contact also has an exposed contact pad adapted to electrically contact a conductive surface of a microelectronic workpiece. A busbar is carried by the peripheral member of the base. The busbar is adapted to electrically couple the electrical contacts to an electroplating power source. If so desired, the electrical contacts and the busbar may be applied as a conductive metal trace on a ceramic base, providing a durable, dimensionally stable contact ring.

DETAILED DESCRIPTION

Various embodiments of the present invention provide contact assemblies, and methods of making contact assemblies and electroplating machines with contact assemblies for electroplating materials onto microelectronic workpieces. The following description provides specific details of certain embodiments of the invention illustrated in the drawings to provide a thorough understanding of those embodiments. It should be recognized, however, that the present invention can be reflected in additional embodiments and the invention may be practiced without some of the details in the following description.

The operation and features of the contact assemblies are best understood in light of the environment and equipment in which they can be used to electroplate workpieces. As such, several embodiments of electroplating tools and reaction chambers that can be used with the contact assemblies will be described with reference toFIGS. 1 and 2. The details and features of several embodiments of wafer holders, contact assemblies, and support plates will then be described with reference toFIGS. 3-13.

A. Selected Embodiments of Electrochemical Processing Machines and Reactor Chambers for Use With Workpiece Holders

FIG. 1is a front isometric view of an electrochemical processing machine1in which workpiece holders in accordance with embodiments of the invention can be used. The machine1can include a cabinet2, a load/unload mechanism4at one end of the cabinet2, and a plurality of chambers10in the cabinet2. The chambers10can include electrochemical processing chambers12, electroless plating chambers14, rapid thermal annealing chambers18, and/or cleaning chambers. The electrochemical processing machine1can also include a transfer mechanism20having a rail or track22and a plurality of robots24that move along the track22. The robots24include arms26that can carry a microelectronic workpiece30between the chambers10. In operation, the load/unload mechanism4positions a cassette or pod holding a plurality of workpieces either in the cabinet2or at an opening of the cabinet, and the transfer mechanism20handles the individual workpieces30inside the cabinet2. The transfer mechanism20, for example, can initially place the workpiece30in an electroless plating chamber14to repair or enhance the seed-layer on the workpiece. The transfer mechanism20can then remove the workpiece30from the electroless plating chamber14and place it in the electrochemical treatment chamber12for forming a blanket layer or a patterned layer on the front face of the workpiece30by electroplating. After the electroplating cycle, the transfer mechanism20can remove the workpiece30from the electrochemical treatment chamber12and transfer it to another processing station in the machine1(e.g., a standard rinser-dryer, a rinse/etch capsule, etc.) or place it in the cassette. In an alternative embodiment, the transfer mechanism can be a radial system such as in the EQUINOX® machines manufactured by Semitool, Inc. of Kalispell, Mont.

FIG. 2is a partial cross-sectional view of an electrochemical treatment chamber12having a workpiece holder100in accordance with one embodiment of the invention for supporting and providing an electrical connection to the workpiece30. For the purposes of brevity, several components of the electrochemical treatment chamber12are shown schematically or by line drawings. Many of the particular features of the components shown schematically are described more detail in the patent applications incorporated by reference above. The chamber12can include a bowl40configured to contain an electrochemical solution, e.g., an electroplating solution, an electrode50in the bowl40, and a head assembly70that carries the wafer holder100. The head assembly70is movable with respect to the bowl40to position the workpiece30in the electrochemical solution (not shown). When the head assembly70is fully inserted into the bowl40, a beveled surface72of the head assembly70is superimposed over a corresponding beveled surface42of the bowl40, and the workpiece holder100holds the workpiece30in a desired position relative to the plating solution.

The bowl40can include a cup44having an overflow weir46. The electrode50is positioned in the cup44, and the electrode50can be carried by an electrode support assembly52. In one embodiment, the electrode support assembly52has a channel54through which the electrochemical solution flows and is discharged into the cup44, but in other embodiments the electrochemical solution can flow into the cup44separately from the electrode support assembly52. The electrode support assembly52can be electrically conductive, or it can include a conductor to electrically couple the electrode50to an electrical power supply (shown schematically as58inFIG. 1). In operation, a flow of electrochemical solution (identified schematically by arrows “S”) flows past the electrode50, over the weir46, and into a lower portion of the bowl40. As the flow of electrochemical solution passes over the weir46, it forms a meniscus at the top of the cup44. The electrochemical solution flow S can then pass out of the bowl40where it is filtered and reconditioned so that the electrochemical solution can be re-circulated through the cup44. Suitable embodiments of bowls40, cups44, electrodes50and electrode support assemblies52are described in PCT Application Nos. PCT/US99/15430, PCT/US00/10120, and PCT/US00/10210, all of which are herein incorporated in their entirety by reference.

The head assembly70can further include a motor74and a rotor80that carries the workpiece holder100. The motor74is coupled to the rotor80to rotate the workpiece holder100and the workpiece30during a plating cycle (Arrow R). The workpiece holder100can include a movable support plate200and a seal84. The support plate200can move transverse to the workpiece30(Arrow T) between a first position in which the support plate200engages the back surface of the workpiece30(shown in solid lines inFIG. 2) and a second position in which it is spaced apart from the back surface of the workpiece30(shown in broken lines inFIG. 2). In this embodiment, the workpiece holder100is coupled to the rotor80by a plurality of shafts112that are received in quick-release mechanisms114. The shafts112can be rigid, conductive members that electrically couple a contact assembly110of the workpiece holder100to an electrical power supply (58inFIG. 1) to establish an electrical potential with respect to the electrode50. For example, the seed-layer on the workpiece30may function as a cathode and the electrode50may function as an anode for plating or the seed layer may function as an anode and the electrode50may function as a cathode for electropolishing.

In operation, the head assembly70can be initially raised above the bowl40and rotated about a relatively horizontal axis so the workpiece holder100faces upward away from the bowl40. The support plate200is moved to the second position in which it is spaced apart from the contact assembly110to load the workpiece30into the head assembly70. The robot24(FIG. 1) inserts the workpiece30face-up into the workpiece holder100, and then the support plate200moves to the first position in which it forces the workpiece30against the contact assembly110. The head assembly70then rotates about the horizontal axis to position the workpiece holder100face downward and lowers at least a portion of the loaded workpiece30and a portion of the contact assembly110into the electrochemical solution proximate to the overflow weir46. The motor74rotates the rotor80to move the workpiece30in the electrochemical solution during the treatment cycle. After the electrochemical treatment is complete, the head assembly70removes the workpiece30from the electrochemical solution so that it can be rinsed and/or transferred to another processing chamber or machine. In an alternative embodiment, the head assembly does not rotate about the horizontal axis to position the contact assembly100face-up during a load/unload sequence such that the workpiece is loaded into the contact assembly face-down toward the bowl40.

The foregoing description of the electrochemical processing machine100and the electrochemical processing chamber12provides examples of the types of devices in which workpiece holders, contact assemblies, and workpiece supports in accordance with embodiments of the invention can be used to plate metal layers onto microelectronic workpieces. It will be appreciated that the workpiece holder100, and other embodiments of workpiece holders, described in more detail below, can be used with other electrochemical processing machines and reaction chambers.

B. Selected Embodiments of Workpiece Holders for Electrochemical Processing of Microelectronic Workpieces

FIGS. 3-13illustrate several embodiments of workpiece holders, contact assemblies, and workpiece supports that can be used in the electrochemical processing chamber12of the electrochemical processing machine1. The structures and operation of the embodiments shown inFIGS. 3-13are generally described with reference to electroplating applications. It will be appreciated, however, that they can also be configured for use in connection with other electrochemical treatments or for use as non-electrical workpiece support assemblies in electroless plating applications, for example.

FIG. 3is a schematic, exploded view of selected components of a workpiece holder100in accordance with one embodiment of the invention. The workpiece holder100generally includes a coupling member120, a guide ring130, a contact ring140and a support plate200. The coupling member120, guide ring130, and contact ring140may remain stationary with respect to one another during operation of the workpiece holder100and together define a contact assembly110. The workpiece support200is movable with respect to the contact assembly110, as noted above and discussed in more detail in connection withFIGS. 11-13.

The guide ring130may include a plurality of tabs134extending radially outwardly to rest on a rear surface123of the coupling member120. These tabs may have through-holes to facilitate attachment of the guide ring130to the coupling member120. The guide ring130also includes an inclined guide surface132which slopes radially inwardly toward the contact ring140(see, e.g.,FIG. 5). The guide surface132can help guide a workpiece so it is properly positioned with respect to the contact ring140. The contact ring130may be formed of a dielectric material, such as a dielectric plastic compatible with the workpiece and the electrochemical solution.

The contact ring140is electrically coupled to and may be carried by the coupling member120. Coupling member120should be formed of a conductive material, such as a solid ring of metal, and may be electrically coupled to the electrical power supply58(FIG. 1) via the conductive shafts112(FIG. 2). The contact ring140may be attached to the coupling member120in any suitable fashion. In the illustrated embodiment, the coupling member120includes a plurality of bosses124arranged equilangularly about the forward surface122of the coupling member120. A plurality of bolts126may be passed through the contact ring140and threaded into the bosses124to attach the contact ring140to the coupling member120. If so desired, an O-ring128may be positioned about each of the bosses124and extend between the contact ring140and the coupling member120(see, e.g.,FIGS. 5 and 6).

1. Selected Embodiments of Contact Rings

The contact ring140shown inFIGS. 3-5includes a base142having a front face144, which may be oriented toward the electrochemical solution in the bowl40(FIG. 2), and a contact face146oriented toward the forward surface122of the coupling member120. The base142generally includes an annular peripheral member150and a plurality of fingers152. The peripheral member150may include holes148through which the bolts126may be passed to couple the contact ring140to the coupling member120. The number, spacing and orientation of the fingers can be varied as desired. In the illustrated embodiment, each of the fingers152extends generally radially inwardly from the annular peripheral member150. The fingers152may be spaced equilangularly about the central opening116of the contact ring140to enhance uniformity of the current density. In the embodiment ofFIG. 4A, the base142includes 72 fingers152, each spaced 5 degrees from each next adjacent finger but more or fewer fingers could be used instead.

As best seen inFIG. 5, in one embodiment of the invention each finger may taper somewhat between the peripheral member150and the nose154. This provides the nose154of each finger with a reduced profile. This reduced profile can improve the fluid dynamics of an electrochemical solution flowing outwardly over the overflow weir46as the rotor80rotates the workpiece holder100. The entire length of each finger152may be tapered in a uniform fashion. In another embodiment, shown inFIG. 5, only a distal length156of each finger152is tapered.

The contact ring140also includes a conductor160carried on, and which may be bonded directly to, the contact face146of the base142. The conductor160generally includes a busbar162and a plurality of contacts166. A separate contact166may be carried by each finger152, with the contact166being positioned adjacent a nose154of the finger152. The contact166is electrically coupled to the busbar162, such as by a lead164extending radially inwardly from the busbar162. When the busbar162is operatively coupled to the electrical power source (58inFIG. 1) and the electrical power source58is energized, electrical power carried by the busbar162, can be delivered to each of the contacts166by a separate lead164.

Each of the leads164may have the same width as the associated contact166, i.e., the contact166may simply comprise an undifferentiated length of the lead164. In the embodiment shown inFIG. 4B, however, the lead has a width which is less than the width of the contact166. If the lead164and the contact166each have the same thickness, this reduced width will give the lead164a reduced cross-sectional area, reducing total conductivity of the lead164. By appropriately controlling the cross-sectional area of the lead164, the lead164can function as a resistor disposed between the busbar162and the contact pad166. This “resistor” can help reduce variations in the current delivered by the busbar162to the various contacts166of the contact ring140, enhancing current density uniformly on the seed layer of the microelectronic workpiece.

As explained below, the conductor160is desirably a relatively thin layer of a conductive material bonded directly to the contact face146of the base142. With the relatively thin leads164, smaller variations in the thickness of the lead164during manufacture can lead to varying currents delivered to the contacts166. To minimize these production variations, a resistor168may be included in each of the leads164. The resistor168may comprise a length of the lead164having an increased resistance. The increased resistance can be provided in a variety of manners. In one embodiment, the resistor168comprises a length of the lead164formed of a material having a resistivity greater than the resistivity of the material of which the rest of the lead164is formed. For example, the busbar162, the contact pads166and the majority of each lead164may comprise a highly conductive noble metal, such as gold or platinum. A predetermined length of each lead164can be formed of a different material having a higher resistivity. The material of the resistor168may be a metal alloy, a mixture of a metal and a silicide or a mixture of metal and a metal oxide.

The contact face146of each finger152may be generally flat, leaving the lead164and contact166carried by the finger with a generally linear profile. As shown inFIG. 5, however, the nose154may have a non-linear profile. In particular, it may be angled with respect to a plane perpendicular to an axis of the interior opening116of the contact ring140. This will provide the contact166with a non-linear profile, as well, defining a preferred line of contact167of the contact166with a curved microelectronic workpiece30. If the microelectronic workpiece30is substantially flat, the length of the contact166extending radially outwardly beyond the line of contact167will contact the face of the microelectronic workpiece.

The contact ring140may also include a dielectric coating175. If the contact ring140is to be used in a dry contact operation wherein it is effectively sealed from the electrochemical solution in the bowl40during use, the dielectric coating175likely is unnecessary. If the contact assembly100is used in a wet-contact operation, the dielectric coating175can reduce thieving by the contact ring140and avoid any undue fouling of the contacts166due to reaction with the electrochemical solution.

The dielectric coating175may cover a majority of the busbar162and may also cover a length of each of the leads164. This leaves the contacts166exposed to promote electrical contact between the contacts166and the microelectronic workpiece30in use. In one embodiment, the dielectric coating175covers the entire lead164, leaving only the contact166exposed. This is schematically illustrated inFIG. 5. In an alternative embodiment of the invention, the dielectric coating175may be spaced radially outwardly from the contact166, leaving a length of each of the leads164exposed, as suggested inFIG. 4B.

The dielectric coating175of the contact ring140may be provided with a plurality of openings176, with each opening176being positioned concentrically about a hole148through the peripheral member50of the base for receiving a bolt126. This permits the bosses124of the coupling member120to which the bolts126are connected to electrically contact the busbar162of the conductor160. As a consequence, electrical power delivered to the coupling member120can be delivered to the contacts166of the contact ring140via the busbar162and leads164.

The materials used in forming the contact ring140can be selected to achieve a variety of different design objectives. As noted above, however, the base142of the contact ring140is desirably formed of a dielectric material. In one embodiment, the dielectric material of the base142comprises a resilient material which may deform when a microelectronic workpiece30is forced against the fingers152. This allows the fingers152to flex to accommodate any irregularities in the microelectronic workpiece30without unduly stressing the workpiece30.

In an alternative embodiment of the invention, the base142of the contact ring140is formed of a rigid dielectric material, such as a dielectric ceramic. To facilitate manufacture, outlined below, and to reduce dimensional variations with any changes in temperature, the ceramic material may also be a refractory. Suitable ceramic materials include alumina and silicon carbide. Forming the base142of a rigid material minimizes the fatigue and wear associated with contacts which must repeatedly flex in use. This can significantly extend the useful life of the contact ring. Whereas metal contacts in use today sometimes must be replaced after electroplating 3,000-5,000 semiconductor wafers, it is anticipated that a contact ring140of the invention employing a rigid dielectric base142will have a service life in excess of 10,000 semiconductor wafers. The conductor160may be formed of any suitably conductive material which bonds well to the dielectric base142. If the dielectric base142comprises a ceramic, the conductor160may comprise a metal which is bonded directly to the contact face146of the base142. Metal can be bonded to a ceramic material fairly readily, yielding a structurally stable conductor with a relatively long service life. The conductor may, for example, comprise copper or gold.

The dielectric coating175may be formed of any suitable dielectric. In one embodiment, the dielectric coating175comprises a coating of a dielectric plastic which bonds well to both the dielectric base142and the conductor160. In an alternative embodiment, the dielectric coating175instead comprises an inorganic dielectric material, such as a ceramic or glass, such as water glass. This can provide a more durable, wear-resistant dielectric coating175. The bond of an inorganic dielectric coating175to a ceramic base142is also anticipated to be relatively strong and durable.

The contact ring140can be formed in any suitable fashion and the method of manufacture may vary somewhat depending on the nature of the materials selected for the base142, conductor160, and dielectric coating175. If the base142is formed of a ceramic material, a rough blank of the base142may be formed using conventional ceramic forming processes, e.g., by slip casting or sol gel techniques. This rough blank may be bisque fired (if necessary to improve its raw structural strength in the green state) then initially machined to approximate the final desired shape. The blank may then be sintered at an elevated temperature then subjected to a final machining process. If the ceramic is a refractory ceramic, the machining may be performed using laser machining equipment to yield a precise shape, even with relatively complex finger profiles, without fear of overheating the base142.

Once the base142is formed, a conductive material may be applied in a predetermined pattern on the base. This predetermined pattern may define a busbar162on the peripheral member150of the base142and a plurality of electrical contacts166on the fingers152of the base142. The predetermined pattern of conductive material may be applied in any suitable technique. It is anticipated that precision screen printing and/or lithographic techniques commonly used to deposit conductive traces in printed circuit board manufacture may be advantageously employed here. After the conductive material is applied, the conductive material may be thermally treated to define a conductive trace bonded to the base142. This thermal treatment may simply comprise heating the entire device in an oven or the like. In an alternative embodiment, a mask may be applied over the base142and the conductive material can be deposited on the base via CVD or PVD processes. If a resistor168is included in the leads164, the resistors168can be applied in a separate step before or after the rest of the conductor160is applied.

If so desired, the contact ring140may be used in this state. As noted above, however, one embodiment of the contact ring140also includes a dielectric coating175. This dielectric coating may be applied over a portion of the conductive trace, leaving at least a portion of each contact166exposed for electrical contact with a microelectronic workpiece. As noted above, the dielectric coating may comprise a plastic or an inorganic material, such as glass. In either circumstance, the dielectric material may be initially applied using screen painting or lithographic techniques analogous to those used to deposit the conductive material of the conductor160. The dielectric coating could instead be applied using CVD or PVD processes, e.g., by sputtering silicon through a mask applied over the base142. The coated device may be subjected to a second thermal treatment to better bond the dielectric coating to the dielectric base142and/or the conductor160. If so desired, the thermal treatment of the conductor160and the dielectric coating175may take place in the same heating step.

FIG. 6schematically illustrates a contact assembly110in accordance with another embodiment of the invention. The coupling member120and guide ring130may be substantially the same as that employed in the embodiment ofFIG. 5. The primary difference lies in a reduced thickness of a portion of the fingers152′ of the contact ring140′ inFIG. 6. The contact ring140ofFIG. 5has a substantially constant thickness radially outwardly from the tapered distal length156. InFIG. 6, an intermediate length157is disposed between the distal length156′ of each finger152′ and the peripheral member150. This intermediate length may have a reduced thickness. In the illustrated embodiment, the contact face146of each finger dips downwardly toward the front face144along the intermediate length157to yield this reduced thickness. The reduced thickness of the intermediate length157reduces the cross-sectional area of the fingers152′, thus reducing the thickness of the fingers152′. This can help control the degree of flexure of the fingers152′ in use if the dielectric base142is formed of a resilient material, such as a dielectric plastic.

FIGS. 7A-Billustrate a contact ring180in accordance with another embodiment of the invention. The contact ring180is similar to the contact ring140ofFIGS. 3-5in many respects. The contact ring180includes a peripheral member182having a plurality of fingers184extending radially inwardly therefrom. A plurality of mounting holes186may be spaced about the peripheral member182to mount the contact ring180to the coupling member120. The contact ring180includes a conductor190having a busbar192carried on the peripheral member182and a plurality of electrical contacts194, with each electrical contact being carried on a separate finger184. The fingers184inFIG. 7A-Bare wider than the fingers152of the contact ring140inFIGS. 3-5. As noted previously, the fingers152may have a reduced profile adjacent their inner ends to improve fluid dynamics as the electroplating solution flows radially outwardly across the fingers152. The fingers152of the contact ring140are spaced an appreciable distance from one another. Unless the interior edge of the peripheral member150is tapered between the fingers152, the relatively abrupt interior edge of the peripheral member150may increase turbulence somewhat. The contact ring180ofFIGS. 7A-Bemploys wider fingers184which occupy a larger percentage of the interior surface of the peripheral member150. The fingers184may have a reduced profile, similar to the shape discussed above in connection withFIG. 5orFIG. 6. Reducing the gap between adjacent fingers184reduces the area of the relatively abrupt inner edge of the peripheral member182in the path of the fluid flow. This can further improve fluid dynamics as the electrochemical solution flows outwardly over the peripheral member150.

As noted above, workpiece holders100in accordance with several embodiments of the invention also include a workpiece support200. The workpiece support200is adapted to hold a microelectronic workpiece30against the contact assembly110with sufficient force to ensure reliable electrical contact between the contact assembly110and a conductive layer on the microelectronic workpiece, such as a seed layer. In accordance with one embodiment of the invention, the workpiece support may comprise a flat plate which urges the microelectronic workpiece30against the contact assembly110such that a peripheral portion of the front face of the microelectronic workpiece30is urged into electrical contact with the contact assembly110. If the contact assembly110includes an improved contact ring in accordance with an embodiment of the invention (e.g., contact ring140or180ofFIGS. 3-5or7, respectively), this would involve urging a peripheral region of the front face of the workpiece30into engagement with the contacts166or194.

2. Selected Embodiments of Workpiece Supports for Microelectronic Workpiece Holders

In accordance with several alternative embodiments of the invention, the workpiece support200is adapted to induce a controlled flexure of the microelectronic workpiece30when the workpiece30is grasped between the support200and the contact assembly110. As explained below, inducing a controlled degree of curvature in the microelectronic workpiece30can improve contact with the contact assembly110, particularly if a rigid contact ring140is employed.

FIGS. 8-9illustrate two alternative workpiece supports adapted to induce controlled flexure of a microelectronic workpiece30. Turning first to the embodiment ofFIGS. 8A-B, this particular workpiece support200includes a body202having a rear face204and a forward face206. The forward face206includes a first abutment210aand a second abutment210b. The first abutment210aincludes a first control surface212aadapted to contact a back surface of a microelectronic workpiece at a first location. The second abutment210bincludes a second control surface212badapted to contact the back surface of the workpiece at a different location. The first and second control surfaces212a-bmay have a curved profile rather than defining sharp edges to minimize localized stress on the back surface of the microelectronic workpiece as it is flexed.

In one embodiment, the first and second control surfaces212a-bof the first and second abutments210a-bare contiguous to one another to define a more continuous control surface for the workpiece support200. In the illustrated embodiment, the second abutment210bis instead spaced radially outwardly from the first abutment210a. The first abutment210acomprises a raised annulus positioning the first control surface212aa radius R1from the center of the workpiece support200. The second abutment210bis also a raised annulus and positions the second control surface212ba larger radius R2from the same center of the workpiece.

The first and second control surfaces212a-bmay be formed with a high degree of precision to ensure that they contact the microelectronic workpiece at the desired relative positions. It is not necessary for the entire forward face206of the workpiece support200to be manufactured to a tight tolerance, though. Instead, the forward surface206may have a reduced height inside the first abutment210a, defining a generally circular first recessed surface214a. A generally annular second recessed surface214bmay extend between the concentric first and second abutments210a-b. As these recessed surfaces214do not contact the workpiece30, flaws or variations in these surfaces214will not affect precise control of the contact locations with the workpiece.

The first and second abutments210a-bmay have different heights. In the illustrated embodiment, the first control surface212aof the first abutment210ais spaced a height h1from the rear face204of the body202. The second control surface212bof the second abutment210bis spaced a second height h2from the rear face204. The first height h1is greater than the second height h2. This leaves a height difference Δh between the first control surface212aand the second control surface212b. By appropriate selection of the radii R1and R2of the first and second abutments210a-band this height difference Δh, the degree of flexure of a microelectronic workpiece induced by the workpiece support200can be controlled.

The desired degree of curvature of the microelectronic workpiece will depend on a number of factors, including the material of which the microelectronic workpiece is formed and the size of the microelectronic workpiece. In one embodiment of the invention suitable for use in connection with a 200 mm silicon-based semiconductor wafer, the radius R1of the first abutment210ais greater than one inch (about 25 mm), e.g., about 1.5 in. (about 38 mm). The second abutment210bmay extend about the outer periphery of the support200and the support200may have a diameter which is slightly less than the diameter of the microelectronic workpiece. Hence, the second radius R2in this embodiment may be about 3.85 in. (about 98 cm). The height difference Δh for this exemplary workpiece support200may range between about one mil (0.001 in., about 0.025 mm) to about 100 mils (about 2.5 mm). The height difference Δh may be selected to be as small as possible yet yield consistent, reliable electrical contact with the contact assembly110. Accordingly, in one useful embodiment of the invention, the height difference Δh is about 8-32 mils (about 0.2-0.8 mm). In one more particular embodiment, the height difference Δh is about 8-16 mils (about 0.2-0.4 mm).

Another exemplary embodiment of the workpiece support200is suited for use with a 300 mm silicon-based semiconductor wafer. In one such embodiment, the radius R1of the first abutment210ais greater than one inch, e.g., about 1.5 in. (about 38 mm); the radius R2of the second abutment210bis slightly less than the size of the wafer, e.g., about 5.85 in. (about 148 mm); and the height difference Δh between the first and second control surfaces212a-bis about 1-200 mils (about 0.03-5 mm), with a height difference of 8-50 mils (about 0.2-1.3 mm) being useful in a variety of applications and a range of 16-32 mils (about 0.4-0.8 mm) being well-suited for many applications.

FIGS. 9A-Billustrate a workpiece support250in accordance with an alternative embodiment of the invention. This workpiece support250shares many similarities with the workpiece support200ofFIGS. 8A-B. In particular, the workpiece support250includes a body252having a rear face254and a forward face256. The forward face256includes a plurality of abutments adapted to contact the back surface of a microelectronic workpiece at spaced-apart locations, namely, a central first abutment260a, an annular second abutment260b, and an annular third abutment260c. The first abutment260amay comprise a generally circular pedestal having a radius R1, defining a generally circular first control surface262a. The second abutment260bis spaced a radius R2from the center of the workpiece support250and defines an annular second control surface262b. The third abutment260cis spaced a radius R3from the center of the support250and defines an annular third control surface262cadjacent the periphery of the workpiece support250.

Each of the control surfaces262a-cmay have a different height. Hence, the first control surface262ais spaced a height h1from the rear face254of the support250, the second control surface262bis spaced a height h2from the rear face254, and the third control surface262cis spaced a height h3from the rear face254. In one embodiment of the invention, the height decreases moving radially outwardly from the center of the workpiece support250, i.e., h1>h2>h3. This yields a first height difference Δh1between the first and second control surfaces262a-band a second height difference Δh2between the second and third control surfaces262b-c. The degree and shape of the flexure of the microelectronic workpiece in response to the force of the support250against the back surface of the workpiece can be controlled by appropriate selection of the radii R1-R3and heights h1-h3.

The three control surfaces262a-cof the support250are spaced from one another, leaving a first annular recessed surface264abetween the first and second abutments260a-band a second annular recessed surface264bbetween the second and third abutments260b-c. This provides three discrete, spaced-apart control surfaces262a-c. It should be understood that four or more discrete control surfaces262could be used instead. In each of the embodiments, the control surfaces are shown as being continuous, such as circular or annular surfaces. If so desired, a series of appropriately spaced abutments having predetermined heights could be arranged on the surface of the support rather than using continuous annular or circular control surfaces as shown inFIGS. 8-9.

In one embodiment of the invention, the entire forward surface206or256of the support200or250may define a curved, continuous control surface. If the support could be made with appropriate control and manufacturing tolerances at a reasonable cost, this could yield good control over the shape of the flexed microelectronic component. Utilizing a series of spaced-apart control surfaces as shown inFIGS. 8-9with recessed surfaces therebetween facilitates cost effective manufacture, though. The abutments210or260can be manufactured with a high degree of precision with exacting tolerances while the recessed areas between the abutments can be much less precisely machined. Because the control surfaces210or260define the areas of contact between the support200or250and the back surface of the microelectronic workpiece, this should yield sufficient control over the flexure of the workpiece without unduly increasing manufacturing costs of the workpiece support.

FIGS. 10A-Billustrate a microelectronic workpiece support280in accordance with another embodiment of the invention. This workpiece support280includes a body282having a back face284and a forward face286. A generally dome-shaped first abutment290a having a first control surface292amay be centered on the circular forward face286. An outer rim290bof the forward face286may define a second control surface292bspaced radially outwardly from the first control surface292a. The first control surface292ahas a maximum height h1from the back face284. The second control surface292bmay have a lesser second height h2from the back face284, leaving a height difference Δh between the spaced-apart first and second control surfaces292a-bto induce the desired flexure of a microelectronic workpiece in contact with the support280. To reduce localization of stress on the periphery of the microelectronic workpiece, the rim290bmay be rounded or beveled to yield a second control surface292bwhich is curved (as shown) or angled.

The support200,250, or280can be formed of any desired material. In one embodiment, the support is formed of a material capable of high precision machining or other high precision forming techniques. The material may have a high Young's modulus to reduce flexing of the support in use. The material may also be relatively hard and wear-resistant to ensure greater dimensional uniformity of the support over time. Suitable materials for forming the support200or250include ceramics (e.g., aluminum or silicon carbide), metals (e.g., aluminum coated with diamond-like carbon via CVD or PVD), or hard, rigid plastics. If the support is formed of a ceramic, the general forming process for the support may be similar to that of forming the dielectric base142of the contact ring140discussed above.

C. Exemplary Methods of Operation of Selected Embodiments of Microelectronic Workpiece Holders

FIGS. 11-13illustrate the workpiece holder100ofFIG. 3in use. The workpiece holder100is shown inFIGS. 2 and 3with the contact assembly110oriented downwardly toward the electrochemical solution in the bowl40. As noted above, in one embodiment of the invention, the head assembly70may be pivoted about a generally horizontal axis to load and unload workpieces30from the workpiece holder100.FIGS. 11-13illustrate the workpiece holder100in this inverted position.

The workpiece holder100shown inFIG. 11includes a workpiece support200generally as shown inFIGS. 8A-Band a contact assembly100including a contact ring140generally as shown inFIGS. 3-5. InFIG. 11, the wafer support100is in an open configuration wherein the workpiece support200is spaced away from the contact ring140along the axis A-A of the opening116through the contact ring140. A workpiece (not shown inFIG. 11) can be positioned between the support200and the contact assembly110and the back surface of the workpiece may be placed upon the support200. Since the first abutment210ahas a height greater than the rest of the front surface206of the support200, the back surface of a planar workpiece may be supported essentially exclusively by the first control surface212a.

FIGS. 12 and 13show the workpiece holder100grasping a workpiece30. In moving from the arrangement ofFIG. 11to that ofFIGS. 12 and 13, the workpiece support200is moved with respect to the contact assembly110generally along the axis A-A (FIG. 11) of the opening in the contact ring140. The support200is moved toward the contact ring140until the front face32of the microelectronic workpiece30contacts the contact ring140. When the workpiece first contacts the contact ring140, the peripheral portion of the back surface34of the workpiece30will still be spaced above the control surface212bof the second abutment210b. InFIGS. 12 and 13, the support200has been moved further toward the contact ring140so that the second abutment210bof the support200also supportively engages the back surface34of the workpiece30.

Due to the height difference (Δh inFIG. 8B) between the first and second abutments210a-b, the microelectronic workpiece30, which may be substantially planar when in a relaxed state, may flex in a controlled fashion. In the illustrated embodiment, the height differential between the annular first control surface212aof the first abutment210aand the annular second control surface212bof the second abutment210bwill bow the microelectronic workpiece30such that the front face32of the workpiece30will have an outwardly convex shape while the back face34will have an outwardly concave face. The height difference Δh between the abutments210a-bmay be relatively small in comparison to the overall diameter of the microelectronic workpiece, so the curvature of the microelectronic workpiece30inFIGS. 11 and 12is not particularly pronounced. Nonetheless, this controlled flexure of the microelectronic component30is expected to ensure relatively uniform, consistent contact about the entire periphery of the front face32of the workpiece30.

As noted above, the noses154of the contact ring fingers152may have an angled bottom surface, yielding an angled shape to the contact166carried thereon. Due to the bending of the microelectronic workpiece30, the contact166is expected to contact the front face32of the workpiece30primarily along a line of contact (167inFIG. 4B) corresponding with the position where the nose154of the finger152is angled.

In the embodiment ofFIGS. 12 and 13, the support200has a diameter which is smaller than the diameter of the workpiece30and the fingers152of the contact ring140contact a peripheral region of the workpiece front surface32spaced radially outwardly from the outer edge of the support200. This can increase the bending force applied on the microelectronic component30. In an alternative embodiment of the invention, the second abutment210bis positioned opposite the point of contact between the front surface32of the workpiece30and the fingers152. This will reduce the stress on the peripheral portion of the workpiece30while still inducing bending due to the height difference Δh between the control surfaces212a-b.

It should be noted that supports in accordance with various embodiments of the invention (e.g., supports200,250, or280) need not be used with a composite contact ring140as shown in the drawings. Conventional electrical contacts having relatively flexible fingers which are brought into contact with the front surface32of the workpiece30may still provide sufficient force against the periphery of the workpiece30to bring it into supportive contact with each of the control surfaces212of the support200. This curvature of the microelectronic workpiece can, therefore, yield beneficial improvements in the contact uniformity between the workpiece front surface32and the contact ring.

It is anticipated that the workpiece holder100of various embodiments of the invention can be used beneficially in electrochemically treating semiconductor workpieces, such as in electroplating silicon-based semiconductor wafers. Out of fear of catastrophically damaging the wafer, such wafers conventionally are deemed too valuable and too brittle to bend. Supports (e.g., support200,250, or280) in accordance with embodiments of the present invention, however, supportively contact predefined locations on the back surface of the microelectronic workpiece. Forcing a peripheral region of the workpiece30against a contact ring (e.g., contact ring140, though other contacts could be used instead) will controllably deform the workpiece into a predefined configuration. By appropriate selection of the location and dimensions of the control surfaces and the height differential between the control surfaces, the flexure induced in the microelectronic workpiece can be fairly precisely controlled to mitigate the likelihood of damaging the workpiece30.

Inducing a controlled flexure of the workpiece30, however, promotes reliable contact between the workpiece front surface32and each of the fingers152of the contact ring140(or other contact system). Improving uniformity of electrical coupling minimizes variations in plating of semiconductor wafers which may otherwise arise due to imperfections in the planarity of the semiconductor wafer, the positions and dimensions of the fingers of a contact ring, and other variations which could lead to inconsistent contact force between the semiconductor wafer and the contact ring from one location to the next. Not only with such uniform electrical coupling materially improve plating uniformity across the surface of a single wafer, it can also reduce variations in plating results from one wafer to the next. This can enhance product yield and reduce the likelihood that a wafer will need to be plated with an excessively thick metal layer, which is removed in later polishing operations, to ensure at least minimum coverage across the entire wafer surface.