Processing apparatus including a reactor for electrochemically etching microelectronic workpiece

Although there are several inventions disclosed herein, the present application is directed to a reactor for electrochemically processing a microelectronic workpiece. The reactor comprises a movable electrode assembly that is disposed for movement along a motion path. The motion path includes at least a portion thereof over which the electrode assembly is positioned for processing at least one surface of the microelectronic workpiece. A cleaning electrode is located along the motion path of the movable electrode assembly. In one embodiment, a programmable controller is connected to direct the movable electrode assembly to move to the cleaning electrode during a cleaning cycle. At that time, the programmable controller connects the movable electrode assembly as an anode and the cleaning electrode as a cathode for cleaning of the movable electrode assembly. The cleaning electrode may be disposed along a position of the motion path that is beyond the range of motion required to process the microelectronic workpiece so that the programmable controller may be programmed to conduct a cleaning cycle while a microelectronic workpiece is present in the reactor for processing.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH R DEVELOPMENT

Not Applicable

BACKGROUND OF THE INVENTION

The present invention generally relates to an apparatus for processing a microelectronic workpiece. More particularly, the present invention is directed to a processing tool that includes an improved electrochemical processing reactor that may be used to electrochernically etch one or more layers from a microelectronic workpiece. For purposes of the present application, a microelectronic workpiece is defined to include a workpiece formed from a substrate upon which microelectronic circuits or components, data storage elements or layers, and/or micro-mechanical elements are formed. Although the present invention will be described with respect to electrochemical etching, it will be recognized that many of the principles set forth herein are also applicable to other electrochemical tools and reactors.

FIG. 1, labeled “prior art,” illustrates the background art of electrochemical etching. The apparatus shown is a basic electrochemical etching cell. A tank T holds liquid electrolyte E, which is typically an aqueous solution of a salt. Two electrodes, the anode A and the cathode C, are wired to a voltage source such as a battery B. When the apparatus is electrified, metal atoms in the anode A are ionized by the electricity and forced out of the metal into the solution, which, in turn, causes the metal anode A to dissolve into the aqueous solution. The rate of dissolution is proportional to the electric current, according to Faraday's law. Depending on the chemistry of the metals and salt, the metal ions from the cathode either plate the cathode, fall out as precipitate, or stay in solution.

Different types of electrochemical etching apparatus are described in the literature, but most are based on the foregoing principles. In conventional electrochemical etching reactors, the cathode is a shaped tool held close to the anode. The cathode is slowly moved over the face of the workpiece while electrolyte is pumped into the interstitial gap between the cathode and the workpiece, which is connected as the anode. Due to electrical field effects, the highest dissolution rates on the workpiece surface are in those places where the cathode has closely approached the anode surface. The rate falls off as the distance between the anode and the cathode increases.

By choosing proper electrolyte and electrical conditions electropolished surfaces can be achieved in electrochemical etching. As the name implies, electropolishing creates a very smooth mirror-like surface, said to be specular or bright, whose roughness is smaller than a wavelength of light. Unlike a mechanically polished surface, an electropolished surface has no built-up stress left by the high pressures of machining and mechanical polishing. The conductive metal may be selectively or completely etched from the surface of the workpiece. In the microelectronic industry, for example, electrochemical etching is used for through-mask patterning and for removal of continuous thin film conducting metals, such as seed layers, from the surface of a workpiece, such as a semiconductor wafer.

In electrochemical etching processes, the material being removed provides the conductive path for supplying a necessary portion of the processing power. As a result, the removal of material must be performed in a generally controlled manner. Attempts to concurrently remove the entire conductive surface of the workpiece may result in the etching away of portions of the conductive layer located proximate the source of processing power before areas located remote from the processing power source are removed. Remote areas would therefore become electrically isolated from the processing power prior to the completion of the electrochemical etch in those areas. By selectively applying the etching process, the likelihood of the day at a region will be electrically isolated is significantly reduced.

In the foregoing apparatus, material that is removed from surface of the workpiece will migrate to conductive surfaces of the electrode that is used to etch the workpiece material (“the etching electrode”). As the number of workpieces processed increases, the amount of material that collects on the etching electrode will likewise increase. This buildup of conductive material may have a significant effect on the uniformity of the surface of the etching electrode. Additionally, the buildup of material may interfere with the free-flow of electrolyte through nozzle openings of the etching electrode that are provided to supply a flow of electrolyte to the surface of the workpiece.

The non-uniformity resulting from the material build-up alters the gap distance between the anode, formed by the surface of the workpiece, and the cathode formed by the etching electrode. These non-uniformities, in turn, result in a corresponding non-uniformity in the electric field between the workpiece and etching electrode. The electric field variations give rise to uneven etch rates. As the variations in the uniformity of the etch rate increase, so does the chance that portions of the workpiece surface may become electrically isolated from the source of processing power prior to completion of the etching process in those areas. Further, such variations cannot be tolerated in processes that require highly uniform etched surfaces, such as in electrochemical planarization.

Another factor that can affect the uniformity of the current density and, consequently, the uniformity of the etching rate, is the change in the area of the workpiece that is exposed to the etching electrode as the etching electrode is swept across the workpiece. The degree to which this changing area affects the etching rate is dependent on the relative shape of both the workpiece and etching electrode. For example, this etching rate dependency occurs when a circular wafer is swept by a paddle-shaped etching electrode assembly having a rectangular etching electrode. Initially, as the rectangular etching electrode begins to move across the surface of the workpiece, it intersects a first edge of the wafer. In most reactors, the rectangular etching electrode assembly intersects the workpiece at a point that is approximately at the center of the rectangular electrode. As the rectangular etching electrode moves toward the center of the workpiece, the area over which the etching electrode and the workpiece surface are exposed to one another increases. When the rectangular etching electrode is positioned proximate the center of the workpiece, the area of exposure is typically at its maximum value. As the etching electrode continues to move across the workpiece, away from the center of the workpiece, the area of exposure again begins to decrease until the etching electrode completes it movement to the opposite edge of the workpiece. The varying area of exposure between the workpiece and the etching electrode can have a significant detrimental effect on current densities and etch rates and, thus, have a corresponding detrimental effect on the desired results of the etching process.

The present inventors have recognized many of the problems associated with electrochemical etching reactors and processes employing existing microfabrication facilities. One or more of these problems are addressed in the exemplary processing tool set forth herein that includes an improved electrochemical etching reactor.

BRIEF SUMMARY OF THE INVENTION

Although there are several inventions disclosed herein, the present application is directed to a reactor for electrochemically processing a microelectronic workpiece. The reactor comprises a movable electrode assembly that is disposed for movement along a motion path. The motion path includes at least a portion thereof over which the electrode assembly is positioned for processing at least one surface of the microelectronic workpiece. A cleaning electrode is located along the motion path of the movable electrode assembly. In one embodiment, a programmable controller is connected to direct the movable electrode assembly to move to the cleaning electrode during a cleaning cycle. At that time, the programmable controller connects the movable electrode assembly as an anode and the cleaning electrode as a cathode for cleaning of the movable electrode assembly. The cleaning electrode may be disposed along a position of the motion path that is beyond the range of motion required to process the microelectronic workpiece so that the programmable controller may be programmed to conduct a cleaning cycle while a microelectronic workpiece is present in the reactor for processing.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2illustrates an electrochemical etching reactor constructed in accordance with one embodiment of the present invention. The reactor, shown generally at1, includes a reactor head assembly345and a reactor base315. The reactor my be incorporated in an integrated tool with other reactors that execute the same or ancillary processes used in the microfabrication of micro-sized devices and/or components. For example, the reactor may be included in a multiple station tool such as the LT-210C™ or EquinoX™ tools available from Semitool, Inc. of Kalsipell, Mont.

The reactor head assembly345may be connected to a lift mechanism703to drive the reactor head vertically in the directions noted by the arrows704. For example, lift mechanism3may drive the reactor head assembly345between a first position (not illustrated) in which it cooperates with the reactor base assembly345to define the controlled processing environment and a second position (illustrated inFIG. 2) in which the reactor head assembly345is separated from the reactor base assembly315. In the second position, a workpiece that is to be processed or that has been processed may be loaded or unloaded from the reactor head assembly345. To facilitate the loading and/or unloading process, the lift mechanism703may also include one or more actuators that rotate the reactor head assembly345in the directions noted by arrows706about the horizontal axis illustrated at arrows705.

In the illustrated embodiment, the reactor head assembly345includes the principal components that are used to load and unload the workpiece as well as those components that are used to provide processing power to the workpiece. To this end, reactor head assembly345includes an actuator section710and a workpiece contact section715. As will be set forth in further detail below, the actuator section710includes those components that are used to open and close the components of the contact section715for loading and unloading the workpiece, while workpiece contact section715includes those components that are used to support the workpiece and conduct electrical power to it during processing. The actuator section710may also include electrical circuits used to test the resistance of the surface that is to be electrochemically etched to either set the electrical parameters that are to be used for the processing and/or to insure that the workpiece meets certain parameters before it is processed.

Depending on the particular process requirements, reactor base315may serve as a reservoir that is filled with an electrolyte. In such instances, the reactor head assembly345is driven to a processing position in which at least one surface of the workpiece makes contact with the fluid surface of the electrolyte. In the embodiment shown here, however, reactor base315is not filled with electrolyte. Rather, it cooperates with the reactor head assembly345to provide a controlled processing environment in which electrochemical etching may take place. It may also include a drain to remove the electrolyte after it has been utilized in the etching process.

Generally stated, the reactor base assembly315of the illustrated embodiment comprised of a chamber portion720and a head engagement portion725. The head engagement portion725includes an etch assembly, shown generally at10, having an electrode assembly20that is driven linearly in the directions noted by arrows721. As will be set forth in further detail below, the electrode assembly20includes at least one conductive plate that serves as the cathode during electrochemical etching. Further, the electrode assembly20of the disclosed embodiment serves to provide a flow of electrolyte that spans the interstitial region between the conductive plate and the workpiece. In this arrangement, the surface of the workpiece that is to be electrochemically etched serves as the anode.

As noted above in connection with known electrochemical etching reactors, the spacing between the cathode and the surface of the workpiece is often critical to the uniformity of the etching process. As such, the etch assembly10is provided with one or more gap adjustment mechanisms, shown generally at200. In operation, the contact portion715of the reactor head assembly345includes structures that align with end portions of the gap adjustment mechanisms200so that the contact portion715and the etch assembly10properly register with one another. Since the workpiece is carried by the contact portion715and the electrode assembly20is carried by the etch assembly10, the gap adjustment mechanisms200serve to initially provide and thereafter maintain the electrode of the electrode assembly20and the surface of the workpiece at a predetermined distance from one another.

To ensure that the gap adjustment mechanisms200do not deviate to any substantial degree from their predetermined positions when the etch assembly10and the reactor head assembly345are registered with one another, head engagement portion725of the reactor base assembly315is compliantly mounted to the chamber portion720. In the illustrated embodiment, this compliant mounting is provided by cooperating float mechanism/pin pairs. With reference toFIG. 2, the reactor includes one or more float mechanisms260in fixed engagement with the chamber portion720that engage respective pins255that are in fixed engagement with the head engagement portion725. The specific details relating to one embodiment of a float mechanism260and corresponding pin255are set forth below.

During electrochemical etching, the etch material may build-up on the cathode thereby altering the desired distance between the cathode and the surface of the workpiece. This becomes a particularly onerous problem when the reactor is used to electrochemically etch, large volumes of workpieces in a production environment. Accordingly, etch assembly10is provided with a cleaning electrode35and may be programmed to execute a cleaning cycle after processing a single workpiece, after processing a predetermined number of workpieces, or during a single processing cycle. During a cleaning cycle, electrode assembly20is driven to a position in which the conductive plate thereof is adjacent the cleaning electrode35. Electrical power is then provided between the conductive plate and the cleaning electrode while a flow of electrolyte or other electrically conductive solution is maintained between them. The electrical power is provided during this cleaning cycle so that the cleaning electrode35operates as a cathode and the conductive plate of the electrode assembly20operates as an anode. In this operation, the material at the surface of the conductive plate is removed thereby leaving the conductive plate in a state in which workpiece-to-workpiece processing is substantially uniform and is not generally dependent on the total number of workpieces processed by the reactor. The cleaning electrode may, for example, be formed from platinum plated titanium or some other inert material.

FIG. 3Ais an exploded view of one embodiment of the head engagement portion725of the reactor base assembly315that is suitable for use in the reactor ofFIG. 2. As shown inFIG. 3A, the head engagement portion725includes a top cover740having a rectangular flange742and an upstanding circular rim744that defines a central aperture. The rim744and central aperture has a diameter that is large enough to allow at least the contact portion715of the reactor head345to extend therethrough so that the workpiece may be placed proximate the electrode assembly20for processing.

The top cover740is secured to an upper surface of an intermediate cover746. The intermediate cover746includes a plurality of downward depending sidewalls748that extend into engagement with a bottom cover752. Together, the intermediate cover746and bottom cover752cooperate to define one or more chambers that hold the components used to drive the electrode assembly20. Such an arrangement assists in isolating the components from the reactive chemicals that are typically used for processing. Further, this arrangement assists in preventing contaminants generated by the drive components from entering and fouling the processing of the workpiece.

FIG. 3Bis a perspective view of one embodiment of an etch assembly10, the components of which are also shown in an expanded form inFIG. 3A.

In the illustrated embodiment, the etch assembly10includes an electrode assembly20having a rectangular plan surface730that faces a lower surface of a microelectronic workpiece25, shown here by dashed lines as a disk-shaped semiconductor wafer. Although reference is made to one particular shape of workpiece, one skilled in the art will readily appreciate, that workpieces having alternative shapes could also be used without departing from the teachings of the present invention.

As shown in bothFIGS. 3A and 3B, three gap adjustment mechanisms200are spaced at equal angular distances with respect to the workpiece25. When the contact portion715of the reactor head assembly345engages the gap adjustment mechanisms200, the workpiece25rests along a plane that is parallel to the plane defined by these three points of engagement. Alternatively, the contact portion715may be designed so that the portions thereof that are engaged by the gap adjustment mechanisms200are recessed a sufficient distance so that the workpiece rests directly along the plane defined by these three points of engagement. In either instance, this ensures that the planar face of the electrode assembly20and the lower surface of the workpiece25are properly spaced from one another.

The electrode assembly20may be driven across the surface of the workpiece in a variety of manners. Here, the electrode assembly is driven linearly along the entire diameter of the workpiece25in order to process substantially the entire workpiece surface. With reference toFIGS. 3A,3B and3C, the electrode assembly20of the illustrated embodiment includes one or more connection tabs30that are connected to the drive mechanism. A first portion of each of the connection tabs30is connected to a corresponding drive belt185, the details of which will be discussed below. A second portion of each of the connection tabs30engages a corresponding guide rod195along which the electrode assembly20is driven during processing. In operation, the guide rods195assist in ensuring fluid and accurate motion of the electrode assembly20along its motion path. The guide rods195additionally help to maintain a consistent relative spacing between the surface of an electrode assembly20and the nearby workpiece25.

With particular reference toFIG. 3C, the electrode assembly20is driven along guide rods195by a drive mechanism that includes a set of four pulleys170a-b, each pulley being located at a respective corner of the etch assembly10. The pulleys170a-cride upon corresponding pulley rods175aand175b, with pulleys170aand170bsharing common pulley175a. Pulley170is connected so that it is directly driven by a motor180.

The pulleys170band170dare coupled to one another by drive belt185awhile pulleys170aand170care coupled to one another by drive belt185b. As such, the rotational motion imposed on pulley170dby motor180is imparted to all of the remaining pulleys170a-c. This motion, in turn, is imparted as a linear movement of the electrode assembly20since it is attached at connection tabs30to the drive belts185. In the illustrated embodiment, the gear ratios of the pulleys are one to one with respect to one another. As such, the relative rates of movement of the pulleys170a-dand the corresponding movement of the drive belts185aand185bare substantially identical.

The position of the electrode assembly20along its motion path may be detected and controlled in a variety of manners. In the illustrated embodiment, a position sensor190is attached to one of the connection tabs30so that it moves linearly along the motion path with the electrode assembly20. As the electrode assembly is driven along the motion path, the position sensor190provides an encoded signal whose value corresponds to the electrode assembly's absolute position. By decoding the signal received from the position sensor190, the position of the electrode assembly20can be tracked. Such decoding may be accomplished by providing the encoded signal to a programmable control system, shown generally at780ofFIG. 3B. A programmable control system780, in turn, may be connected to drive the motor180in response to the decoded position of the electrode assembly.20.

The cleaning electrode35of the illustrated embodiment is disposed along the motion path of the electrode assembly20and is positioned beyond the range of movement required to process the workpiece25. This allows the electrode assembly20to be cleaned even when a workpiece25is present. Further, depending on the processing requirements, the programmable control system780may be programmed so that cleaning operations are conducted as part of the processing of a single workpiece. For example, if the material that is electrochemically etched from the surface of the workpiece builds up quickly as a single workpiece is processed, a cleaning cycle may be scheduled mid-way (or at some other predetermined point) through the processing of the single workpiece.

The particular construction of one embodiment of an electrode assembly20suitable for use in the reactor ofFIG. 2is illustrated inFIGS. 4A through 4D. As shown, the electrode assembly20includes a top portion45and a bottom portion50. The top portion45includes a top surface having one or more conductive segments40. The bottom portion50is adapted for coupling to one or more fluid and/or electrical supply lines. For example, the bottom portion50may be coupled to one or more fluid sources or drains, electrical sources for receiving processing power, and/or vacuum sources for inducing pressure differentials at the surface of the electrode assembly20. In the illustrated embodiment, a number of different lines are provided to the bottom portion50. A first source of fluid is supplied to the electrode assembly20via a flexible tube55that is coupled proximate the center of the bottom portion50. A second source of fluid is provided by a pair of fluid supply lines60located near a first end of the electrode assembly20. A source of vacuum is coupled to a second end of the electrode assembly20by a pair of vacuum supply lines65. Finally, an electrical source providing processing power is coupled to the electrode assembly20via an electrical connection70located proximate the vacuum supply lines65.

The flexible tube55is connected to a reservoir containing processing fluid through a pump for supplying the processing fluid to the surface of the electrode assembly20. Processing fluid provided through the flexible tube55is received by a central chamber75located within the bottom portion50of the electrode assembly20. The central chamber75distributes the fluid lengthwise across the electrode assembly20. From the central chamber75, the fluid enters the top portion45of the electrode assembly20through a diffuser plate80(FIGS. 4C and 4D). As particularly shown inFIG. 4D, the top portion45includes a protrusion85, sized and shaped to correspond to the top opening of the central chamber75, that is received by the central chamber, and upon which the diffuser plate80is connected. A gasket90located around the periphery of the protrusion85seals against the internal sidewall surface of the central chamber75, thereby effectively restricting fluid flow between the peripheral surface of the protrusion85and the sidewall surface of the central chamber75.

In the illustrated embodiment, the diffuser plate80, as shown inFIG. 4D, includes a series of openings that span the length of the electrode assembly20. These openings are smaller proximate the center of the electrode assembly20compared to the size of the openings at the end portions thereof. As such, the fluid flow from the bottom portion50to the top portion45is more restricted proximate the point where the fluid is supplied to the electrode assembly20(here, the point of connection with flexible tube55) and less restricted further away from the initial source of the fluid. This assists in ensuring a generally uniform fluid pressure through chamber75thereby providing for an even distribution of the fluid flow to the workpiece across the entire length of the electrode assembly20.

After the fluid flows through the diffuser plate80, it enters one of the supply channels100located within a distribution portion105of the electrode assembly20. From the supply channel100, the fluid travels through openings120in a gasket110and exits the electrode assembly20through one or more fluid delivery ports115located at the upper surface of the electrode assembly20.

A source of de-ionized water and a source of vacuum pressure are also provided through openings at the surface of the electrode assembly20in a manner that is somewhat similar to that described above for the processing fluid. The fluid supply lines60supply the de-ionized water and are connected to a pump that, in turn, is coupled to a reservoir containing de-ionized water. The supply lines65are connected to a source of vacuum pressure. For example, the supply lines65may be connected to an air aspirator through a fluid separator. In this manner, the fluids and the gases that are drawn in through the electrode assembly20from the processing environment may be separated from one another.

With reference toFIGS. 4A and 4C, the de-ionized water and the vacuum pressure are supplied through vertical passageways125and130, respectively. As shown, the vertical passageways125and130are disposed at opposite ends of the electrode assembly20. The passageways125,130each begin where the respective supply lines60and65connect to the electrode assembly20and extend through the bottom portion50, into the top portion45where they open to a corresponding manifold channel103,107in the fluid distribution portion105of the electrode assembly20. At the point where passageways125,130transition between the bottom portion50and the top portion45, O-ring seals135are provided to limit leakage outside of the passageways125,130prior to opening into the corresponding manifold channel103,107.

The manifold channels103,107distribute the de-ionized water and the vacuum supply respectively to one or more fluid delivery ports140and one or more fluid recovery ports145. In the illustrated embodiment, the electrode assembly20includes two sets of fluid delivery ports140for de-ionized water, and two sets of fluid recovery ports145.

The surface of the electrode assembly20may be in the form of a single, continuous electrode. However, the surface of the electrode assembly20of the illustrated embodiment is comprised of a plurality of individual conductive segments40A through40E that are electrically isolated from one another (in the absence of an electrolyte or other conductive liquid). Electrical power is provided from an external power supply to these segments through respective conductive rods150A through150E. As will be explained in further detail below, electrical power to these individual segments may be controlled during processing based on the area of the electrode assembly20surface that is exposed to the surface of the workpiece under process.

FIG. 5illustrates operation of the electrode assembly20when it is proximate a surface, such as the surface of the workpiece25or the surface of the cleaning electrode35. As shown, a fluid155is provided from the electrode assembly20and fills the interstitial region between the workpiece25and the surface of the electrode assembly20. This fluid155may be, for example, electrolyte (used in an electrochemical etch process or electrochemical deposition), de-ionized water, etc.

The fluid155may be handled in a variety of different manners after it has contacted the surface of the workpiece25or the surface of the cleaning electrode35. For example, the fluid may be allowed to enter the chamber of the base assembly315. Alternatively, the fluid may be recovered via the suction force provided by the fluid recovery ports145. This can be especially useful where multiple types of fluids are employed for processing and/or contact cleaning. In such instances, mixing of the various fluid types in the base assembly315may be undesirable. Further, it may be desirable to recover the fluid through ports145for replenishment, recycling, etc.

Given the manner in which the operation of the electrode assembly20is shown inFIG. 5, it is clear that the electrode assembly is in motion and proceeding to the right hand side of the drawing. However, arrows160indicate the potential for bi-directional movement of the electrode assembly20during processing. In order to facilitate fluid recovery regardless of the direction in which the electrode assembly20travels, two sets of fluid recovery ports145are employed in the illustrated embodiment. The fluid recovery port sets are located exterior to and on opposite sides of the fluid delivery ports140.

Generally stated, the fluid is retained within the gap between the surface of the electrode assembly20and the corresponding surface of the workpiece or cleaning electrode when the volume of processing fluid provided to the surface does not exceed the volume of fluid that can be supported by the surface tension forces. With this in mind, it will be recognized that the rate at which the de-ionized water, or any other fluid, is recovered through the fluid recovery ports145should take account of the rate at which the de-ionized water is provided through the fluid delivery ports140.

FIG. 6illustrates the relative area of engagement between electrode assembly20and a disk-shaped microelectronic workpiece25as the electrode assembly20is moved during workpiece processing. At each position, designated by the electrode assembly positions20A-20C, it can be seen that the area of the electrode assembly20that overlies the surface of the workpiece25varies as the electrode assembly20is moved along the length of the workpiece. If a single, continuous conductive element is used at the surface of the electrode assembly20, processing power is provided across the entire length of the assembly regardless of the area of exposure. This can create electric field fringe effects that vary as the electrode assembly20is moved across the workpiece during processing. Depending on the processing requirements, such fringe effect may have a detrimental effect on the overall uniformity of the process. To avoid or otherwise control these fringe effects, each of the conductive segments40A through40E may be connected to individually controlled outputs of a power control system, shown schematically at792. Power control system792may take any number of forms. For example, power control system792may include a programmable controller, a standard power supply, and a power distribution circuit that is controlled by the programmable controller. Other configurations are likewise suitable.

The manner in which power is controlled for each of the segments40A through40E is process dependent. However, some of the ways in which power may be controlled are set forth in Table 1 below.

TABLE 1POSITIONPOWER20ASegment 40A and Segment 40E have no exposure to theworkpiece. No processing power to these segments.20BSegment 40B and Segment 40D have minimal exposureto the workpiece. At least three possible alternatives exist:1 - No processing power is provided to segments 40Band 40D, as the amount of exposure is very limited.2 - Full processing power is provided to segments 40Band 40D since they at least partially overlie the workpiece.3 - A limited level of processing power is provided tosegments 40D and 40B to account for the limited exposurethat these segments have with the workpiece 25.20CSegment 40C, similar to Segments 40B and 40D, is onlypartially exposed, consequently the specific level ofprocessing power which would be most beneficial maysimilarly vary

As opposed to altering the amount of electroplating power provided to the electrode of the court to assembly, it may be possible to compensate for the electric field variations by altering the motion profile that is used by the electrode assembly as it moves across the face of the workpiece. For example, the electrode assembly may be moved quickly along the end portions of its motion path when compared to its motion as it traverses the middle portions of the workpiece.

A specific embodiment of the gap adjustment mechanisms200is illustrated inFIGS. 7A and 7B. As shown, the gap adjustment mechanisms200each include a base portion205having a pair of mounting holes210for attachment to the etch assembly10. Each gap adjustment assembly200further includes an arm215that has a first end attached to an axle22, and a second end connected to a pin240that terminates at a spherical head245. It is the spherical head245advance in cages the appropriate portion of the contact portion of the reactor head assembly345. As such, the particular shape and size of arm215is dependent on where and how far it must span to engage the corresponding section of the contact portion715of the reactor head assembly345.

Axle220cooperates with the base portion205to form a fulcrum about which arm215may pivot. The other end of the axle220is coupled to a first end of a lever arm225. Lever arm225is engaged at a second end thereof by an adjustable tip of a micrometer230. The micrometer230is adjusted to pivot the lever arm225about axle220and thereby produce a corresponding raising and lowering of the spherical head245. This allows the position of the contact portion715of the head assembly345(and, thus, the workpiece) to be spaced from the upper surface of the electrode assembly20with a high degree of accuracy.

A specific embodiment of the float assemblies260is illustrated in FIGS.8A and8B. As shown, each float assembly260includes a housing265having a central passageway270, within which a spring float shaft275is received. One end of the spring float shaft275terminates at a flange280that is wider than the upper portion of the central passageway270thereby restricting motion of the shaft275past point285. The shaft275is biased toward this point285by a spring290similarly located within the central passageway270of the housing265. The end of the spring290opposite the point of contact with the shaft275is fixed with respect to the housing265by a retainer295. In some instances a second retainer295can be used to further increase the compression of the spring290.

The retainer295, in turn, is held in place by a snap ring300. The snap ring300is a discontinuous circular ring that may be squeezed to reduce its diameter. When deformed in this manner, the snap ring300can slide into the bottom opening305of the housing265past the more restrictive shaft diameter, and expand and fit within a groove310located in the wall of the central passageway270having a larger diameter, which is proximate to the opening305.

While the spring float assembly260can be a separate assembly, as illustrated in connection withFIGS. 8A and 8B, the spring float assembly260can also be integrated as part of the reactor base assembly315or as part of the base plate of the processing station (not shown). Various other configurations can also be employed to provide a compliant connection between the head engagement portion725and the base portion720of the reactor base assembly315.

FIG. 9illustrates one embodiment of a contact assembly910that may be used in the contact portion715apparatus ofFIG. 2. Generally stated, contact assembly910includes an exteriorly disposed dielectric rim915and an interiorly disposed conductive ring920having a plurality of sawtooth-shaped contact925. The contact assembly910may also inclu de one or more connection members930that a used to secure the contact ring assembly910to the other components of the contact portion715. Further details of this exemplary interconnection as well as of the contact assembly construction can be found in U.S. Ser. No. ______ filed Nov. 20, 2000, entitled “______”, which is hereby incorporated by reference.

Dielectric rim915includes a plurality of cut-out section935that are disposed for alignment with the spherical heads245of the gap adjustment mechanisms200. Each cut-out section935is provided with a corresponding insert940. It is the inserts940that are used to directly engage the spherical heads245. Since the inserts940are formed as pieces that are separate from the rim915, it is possible to form the dielectric rim915from a material that is less durable than would otherwise be required to sustain the wear and tear associated with frequent engagement of the gap adjustment mechanisms200.

FIG. 10illustrates a further contact assembly, shown generally at340, that may be used in the contact portion715of the reactor head assembly345. As illustrated, the contact assembly340includes a plurality of contacts350that are used to supply processing power to the surface of the workpiece25. Unlike contact assembly910, however, the contacts350of contact assembly340are formed as two groups355and360that are electrically isolated from one another (in the absence of an electrolyte). By electrically isolating the contact groups, it becomes possible to check the resistance across the workpiece25.

A schematic diagram of one embodiment of a contact resistance sensing circuit that may be used to check the resistance across the workpiece25is shown generally at485inFIG. 11. Circuit485is based on precise generation of a constant current by current source487. As illustrated, precision current source487is referenced to a precision bandgap voltage reference489. Bandgap voltage reference489also serves as a reference for the generation of upper and lower threshold voltages by circuits491and493, respectively. The upper and lower threshold voltages are used to determine whether the current from the constant current source487is within a predetermined range before a measurement of the contact and workpiece resistance is conducted. During this pre-measurement cycle, current source487is switched to drive a constant current through a series-connected circuit including low resistance resistor495(i.e., 2 ohm), the workpiece25and contacts350and, optionally, a pair of switching circuits497and499that are used to enable current flow through the workpiece and contacts. The voltage drop across the resistor495is proportional to the current flowing through it. Accordingly, this voltage drop is used to determine whether the current provided by the current source487falls within a predetermined acceptable range. As shown, the voltage drop across resistor495is provided to a pair of individual amplifier circuits501and503. The output signals of the amplifier circuits501and503, in turn, are each provided to the input of a respective comparator circuit507and509. Comparator circuit507compares the output voltage provided from amplifier501with a high current threshold reference voltage provided by reference circuit491. Similarly, comparator circuit509compares the output voltage provided from amplifier503with a low current threshold reference voltage provided by reference circuit493. The output signals from the competitors507and509are connected together in a wired-OR configuration. The output of this wired-OR configuration is used to determine whether the constant current flow provided by current source487is within a predetermined acceptable range, and is labeled as “current source okay” reflecting its function. As noted above, circuits491and493generate their respective threshold voltages with reference to the precision bandgap voltage reference489and, as such, these threshold values are highly stable. Each of circuits491and493, as well as the voltage reference492that generates threshold voltage Vmax, may include adjustable precision resistors or the like to set the minimum and maximum threshold values manually. Alternatively, these values may be set using a precision digital-to-analog converter that is connected to receive voltage data values from a programmable control circuit or the like.

Provided that the current measurement falls within the predetermined range as indicated by the output of comparator circuits507and509, the voltage drop across the contacts and workpiece is indicative of the resistance of the workpiece and contacts and, as such, may be measured. In the illustrated embodiment, the voltage across the contacts and workpiece is provided to a pair of amplifier circuits511and513. The output signals of the amplifier circuits511and513are provided as input signals to a differential amplifier515, which may also provide for some amplification of the signal. The output of the differential amplifier515, in turn, is provided for comparison to an upper voltage threshold value at comparator circuit517. Since the upper voltage threshold value is generated with respect to the precision bandgap voltage reference489, it is highly stable and accurate. If the voltage provided at the output of differential amplifier515exceeds the voltage Vmax, the output of comparator517will be at a corresponding logic state and processing of the workpiece will not continue. However, if the voltage provided at the output of differential amplifier515is below the voltage Vmax, electrochemical processing of the workpiece may proceed.

Given the low resistances and high currents that must necessarily be used in the foregoing circuit, circuit stability and measurement repeatability, although strongly desired, are difficult to obtain. To overcome many of the problems associated with this stability and repeatability of circuit485, one or more precision bandgap voltage references are used to generate the constant current as noted above. Further, current flow through the current source487is maintained at all times, even when no measurements are being made. This is done to insure the thermal stability of the measurement circuits, including the precision bandgap voltage reference489. To accomplish this, a switch (either mechanical or semiconductor) may be used to switch the constant current source between a first circuit that includes the contacts and workpiece and a second circuit that directs the current into a current sink.

The embodiment of the contact portion715illustrated inFIG. 12is adapted to load and unload the workpiece25using a workpiece tray. To this end, the contact portion715includes a tray slot365through which a tray370may be inserted and extracted. Tray370, is shown, is adapted for receiving a workpiece25, and provides a degree of protection for the workpiece as it is loaded onto the contact portion711of the head assembly345through the tray slot365. Once inserted into the tray slot365, the workpiece25can make a connection with the contacts350of the contact assembly340for processing.

FIGS. 13A and 13Billustrate both top and bottom isometric views of a tray370adapted for receiving such a workpiece25. As shown inFIG. 13A, the top of the tray370includes a circular depression375corresponding to the shape of the workpiece25to be received. At one end of the tray is a slot380through which a vacuum wand (not shown) may be inserted or removed, to facilitate placement and removal of a workpiece25onto the tray370. The top of the tray further includes a series of markings385located around the periphery of the workpiece depression375that enable the operator to visually verify the proper angular positioning of the workpiece as it is loaded onto the tray370.

The tray370may be manually loaded and removed from the head assembly345. As shown inFIG. 13B, the bottom of the tray370includes a depression390for facilitating gripping the tray370with a handle assembly400(FIGS. 14A, B and C) proximate the slot380through which an air wand, or similar instrument, can be inserted.

As can be seen inFIGS. 14A-14C, the handle assembly400includes both a first piece405and second piece410. The first piece405and the second piece410are coupled together by a pair of screws415and slide pins420. The slide pins420reside within a pair of slots425located within the first piece405. This construction allows the first piece405to slide with respect to the second piece410. The handle assembly400further includes a plunger pin430. The plunger pin430is adapted for moving within a slot435formed within the second piece410. The plunger pin430is further adapted for engaging a detent440at one end of the slot435. Once engaged plunger pin430and detent440provide a slight retaining force.

When the top piece405is shifted forward with respect to the second piece410, a protrusion445at the front of the handle located at the second of the top piece is exposed. The protrusion445is sized and shaped to correspond to depression390included in the bottom of tray370. By sliding the first piece405even with the second piece410, the front450of the second piece410extends over the protrusion445. If the protrusion445of the top piece405of handle assembly400has been received into the depression390of tray370, the engagement serves to fix the handle assembly400to the tray370. The tray370may then be carried by the handle assembly400and readily inserted into the tray slot365. By subsequently sliding the first piece405forward with respect to the bottom piece410, the handle assembly400may be disengaged from the tray370. The first piece405and second piece410each include a corresponding indentation455,460, which can be gripped by the operator to facilitate movement of the first piece405with respect to the second piece410.

Numerous modifications may be made to the foregoing system without departing from the basic teachings thereof. Although the present invention has been described in substantial detail with reference to one or more specific embodiments, those of skill in the wart will recognize that changes may be made thereto without departing from the scope and spirit of the invention as set forth in the appended claims.