Reference to Related Application This is a continuation-in-part of prior copending application serial No. 08/276,965, filed July 19, 1994. Technical Field ofthe Invention

The present invention relates to equipment and methods for plating metals onto substrates within a plating solution bath, and particularly to plating of semiconductor circuits.

Background ofthe Invention The manufacture of integrated circuit semiconductor chips requires the plating of conductive leads about the periphery of the chip. Typically, a semiconductor rod is cut into disk-like wafers having a diameter ranging from 3 to 8 inches. The formation of integrated circuit patterns on the wafer to define a plurality of circuit "chips" involves the application of a photoresist layer to one surface of the wafer. Conductive leads are then formed about each of the circuits, typically by plating gold or copper onto the wafer.

The photoresist coating is applied to the wafer during formation so as to leave a narrow band of non-coated surface exposed about the perimeter of the circuit surface of the wafer. Conventional processes for forming the leads about these circuit chips include "bump plating" methods. The wafer is immersed in an electrolyte bath, such as, for example, a cyanide gold solution for plating gold leads. The wafer is contacted on the non-coated periphery, and current is applied across the wafer and an anode, also immersed in the electrolytic bath, such as a platinum anode

for gold plating. Current is applied until the desired thickness of plating builds up on the wafer.

Traditional bump plating methods do not provide for uniformity in the plating thickness over the exposed surfaces of the wafer, however. The thickness of the plated leads may vary up to 200% across the width of the wafer. This results in a large rate of unacceptable chips being produced from each wafer.

Summary Qf he Invention The present invention provides an apparatus for use in plating of a substrate within an electrolytic bath. The apparatus includes a tank structure for containing an electrolyte and an anode. A shaft is rotatably mounted within the tank to rotate about a first axis. An arm is mounted on the shaft, and a fixture for receiving the substrate is rotatably mounted on the arm to rotate about a second axis, so that the substrate is both revolved about the first axis and rotated about the second axis. Electrical contact is maintained between the rotating substrate and a stationary power supply for plating.

In a further aspect ofthe present invention, the apparatus includes a plurality of electrical contacts on the fixture for contacting the substrate to be plated. Power is supplied from a multichannel power supply to the electrical contacts, so that each contact is separately supplied by a corresponding individual channel. A process for electrolytic plating of substrates is disclosed and involves revolving a cathodic substrate having a surface defining a width around a first axis within an electrolytic bath, while rotating the substrate about a second axis. Current is applied across the substrate and an anode, also immersed within the electrolytic bath. Metal is plated onto the surface of the substrate to develop a thickness that is uniform within ±5% over the width ofthe substrate.

The present invention thus provides a method for plating integrated circuit chips and other articles with a highly uniform plating thickness. The apparatus and method are useful for plating not only circuit chips, but ceramic packages, thick or thin substrates, dimensional printed circuit boards, parts with "blind" recesses, and parts with through holes. Various metals, including gold, nickel, silver, tin, palladium, and copper can be plated onto substrates using the method.

In particular, for the plating of integrated circuit chips on a wafer, the percentage of acceptably plated integrated circuits on each wafer increases significantly due to the plating thickness being maintained with a ±5% deviation over the width of the wafer.

Problems with prior plating techniques that involve applying current to multiple electrical contacts on a substrate wafer are avoided. In such prior techniques, the current actually supplied to each individual contact may vary due to the strength ofthe contact made at a particular point. The present invention provides an apparatus and method making it possible to supply each of a plurality of electrical contacts with current from a corresponding separate power supply channel. The invention thus allows for monitoring for even distribution of current among the contacts. Lack of uniformity in current supply can be adjusted by repositioning the electrical contact or adjusting the power supply distribution amongst the channels. In a further embodiment of the present invention, the apparatus includes a fixture assembly for use in plating substrates within an electrolytic tank, the tank including a powered rotary drive shaft that rotates about a first axis. The fixture assembly includes at least a first fixture arm, and preferably a plurality of fixture arms, that are secured to a fixture hub which is securable to the drive shaft to rotate with the drive shaft. A fixture member for receiving a substrate to be plated is rotatably mounted on each fixture arm at a position spaced radially from the drive shaft to rotate about a second axis. A motor is carried on each fixture arm and is coupled to the fixture member mounted on that fixture arm to rotate the fixture member about the second axis. This enables the fixture members to be rotated independently ofthe central drive shaft.

In a further aspect of the alternate embodiment of the invention, a plating power circuit is mounted in each fixture arm and is electrically coupled to the fixture member to deliver electroplating current across the received substrate to be plated. A first electrical connector is mounted on the fixture hub to which the fixture arm is secured, and is electrically coupled to the plating power circuit. A second electrical connector is mounted on the drive shaft and is electrically coupled to a power supply. The second connector on the drive shaft is disposed for automatic mating with the first connector on the fixture hub when the fixture hub is secured to the drive shaft. This enables removal ofthe fixture assembly from the central drive shaft for a change of substrates without requiring the rewiring ofthe electrical circuits which power the plating ofthe substrates, and also preferably powers the motors carried on the fixture arms.

In a still further aspect of the alternate embodiment of the present invention, the rotatable fixture members on the fixture arms are configured as fixture wheels. A fixture ring is securable to each fixture wheel to receive the substrate to be plated therebetween. Bias springs are coupled between the fixture ring and fixture wheel to

bias the fixture ring towards the fixture wheel. This enables securement of a substrate to be plated on the fixture wheel while also aiding sealing of the substrate against the fixture wheel to prevent leakage of plating solution onto the back surface ofthe substrate. This arrangement also facilitates automatic changeover of substrates on the fixture wheels.

Brief Description ofthe Drawings The foregoing aspects and many ofthe attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:

FIGURE 1 provides a perspective view of a plating apparatus of the present invention;

FIGURE 2 provides a detailed perspective view of the electrolyte tank and rotary/reciprocating fixture assembly, with portions ofthe tank removed for clarity; FIGURE 3 provides a cross-sectional view of the rotary/reciprocating fixture assembly and tank of FIGURE 2, taken substantially along a plane defined by the longitudinal axis ofthe structure and tank;

FIGURE 4 provides a perspective exploded view ofthe fixture arm and wheel ofthe apparatus of FIGURE 1; FIGURE 5 provides a detailed cross-sectional view of the fixture wheel mounted on the distal end of the fixture arm taken substantially along a plan aligned with the central axis ofthe fixture wheel;

FIGURE 6 provides an isometric view of an alternate multi-substrate fixture assembly ofthe present invention, with a central drive shaft and hub assembly shown exploded below the fixture assembly, the drive shaft being shown broken below the hub assembly;

FIGURE 7 provide a top elevation view of the fixture assembly of FIGURE 6, with the motor cover plates removed;

FIGURE 8 provides a bottom view of the fixture assembly of FIGURE 6, illustrating the fixture electrical connectors and fixture shaft assemblies;

FIGURE 9 provides a side elevation view of the fixture assembly of FIGURE 6 with the drive chain cover plate removed from one arm, and the fixture wheels shown in phantom;

FIGURE 10 illustrates a schematic, partial cross-sectional view of the fixture assembly ofthe present invention mounted in an electrolytic plating tank;

FIGURE 11 provides an enlarged schematic partial cross-sectional view of the fixture assembly and drive shaft hub assembly of FIGURE 10;

FIGURE 12 provides a side elevation view of the connector cover of the hub assembly of FIGURE 11 ; FIGURE 13 provides a top elevation view of the connector cover of

FIGURE 12;

FIGURE 14 provides a top elevation view ofthe fixture hub of FIGURE 11 ; FIGURE 15 provides a cross-sectional view of the hub of FIGURE 14, taken substantially along line A-A; FIGURE 16 provides a partial cross-sectional view ofthe hub of FIGURE 14 taken substantially along line B-B;

FIGURE 17 provides an enlarged schematic partial cross-sectional side elevation view ofthe fixture wheel assembly of FIGURE 10;

FIGURE 18 provides a cross-sectional side elevation view of the fixture wheel of FIGURE 17;

FIGURE 19 provides a cross-sectional view ofthe backing plate ofthe fixture wheel assembly of FIGURE 18, taken substantially along line A-A of FIGURE 20;

FIGURE 20 provides a front elevation view of the backing plate of FIGURE 19; FIGURE 21 provides a front elevation view of the fixture ring assembly of the fixture wheel assembly of FIGURE 17;

FIGURE 22 provides a cross-sectional view of the fixture ring assembly of FIGURE 21, taken substantially along the line A-A; and

FIGURE 23 provides an enlarged cross-sectional view ofthe bottom segment ofthe fixture ring assembly shown in the cross-section of FIGURE 22.

Detailed Description ofthe Preferred Embodiment

A first preferred embodiment of a plating apparatus 10 constructed in accordance with the present invention is shown in FIGURE 1. The apparatus includes a housing 12 that supports a plating tank 14 for containing an electrolyte solution, in which is mounted a rotary/reciprocating fixture assembly 16 that carries articles to be plated. A control console 18 mounted on the housing 12 includes a user interface 20 and control circuitry (not shown). The control circuitry controls operation of the rotary/reciprocating fixture assembly 16 and of a multichannel power supply 22, housed within the housing 12, that supplies current through the rotary/reciprocating fixture assembly 16 during plating.

The tank 14 and rotary/reciprocating fixture assembly 16 are shown in greater detail in FIGURE 2. The open topped tank 14 is cylindrical, having a bottom wall 24, a sidewall 26 and a central axis 28. The upper edge of the sidewall 26 is sealed about an opening formed in a support plate 29 of the housing 12. A drive shaft 30 is rotatably mounted within the tank 14 on the central axis 28, projecting orthogonally upward through the bottom wall 24. The drive shaft 30 is surrounded by an annular electrolyte reservoir assembly 32 that sparges recirculating electrolyte solution tlirough the tank 14 during plating. The reservoir assembly 32 also supports an anode support ring 34 from which extend downwardly a plurality of anode assemblies 36.

A fixture mounting plate 38 is non-rotatably secured to the upper end of the drive shaft 30, above the reservoir assembly 32. A fixture arm 40 is connected to the fixture mounting plate 38, and projects radially and then downwardly into the interior ofthe tank 14. A fixture wheel 42 is rotatably secured to the distal end ofthe fixture arm 40. The fixture wheel 42 carries the article to be plated, such as the semiconductor wafer 44 illustrated, which is mounted by three spring loaded electrical contacts 46. The electrical contacts 46 both retain the semiconductor wafer 44 and carry current from coπesponding channels of the multichannel power supply 22 through coπesponding electrical leads 48 to the semiconductor wafer 44. An annular track 50 is secured within the tank 14 on the upper surface of the bottom wall 24, and is centered about the central axis 28. A series of pins 52 are secured within longitudinal passages in the track 50 and project upwardly therefrom to create a periodic series of protuberances around the track 50. The perimeter 54 of the fixture wheel 42 rests on the track 50. A series of longitudinally oriented slots 56 is formed about the perimeter 54 of the fixture wheel 42, and are dimensioned and spaced to engage with the tops ofthe pins 52 ofthe track 50.

The drive shaft 30 is rotated by a motor 58 (FIGURE 3) mounted within the housing 12 below the bottom wall 24 of the tank 14. A drive pulley 59 on the motor 58 is connected to a driven pulley 60 secured on the projecting bottom end of the drive shaft 30 by a belt 62. The drive shaft 30 is rotated in a reciprocating fashion about the central axis 28, and carries with it the fixture mounting plate 38, fixture arm 40, fixture wheel 42, and thus the semiconductor wafer 44. As the semiconductor wafer 44 revolves in a reciprocating manner about the central axis 28, the fixture wheel 42, and thus the semiconductor wafer 44, rotate about the rotary axis 64 (FIGURE 3) of the fixture wheel 42. The cathodic semiconductor wafer 44 thus both revolves and rotates relative to the anode assemblies 36 during plating to

enhance the uniformity of plated coated thickness across the face of the semiconductor wafer 44.

Referring to FIGURE 3, the construction of the apparatus 10 will now be described in greater detail, beginning with the reservoir assembly 32. The reservoir assembly 32 is constructed from an outer tube 66 and an inner tube 68, which are coaxially installed and centered on the central axis 28. The tank 14 and structural components contained therein are constructed from a metal or polymeric material that is resistant to the plating solutions being utilized, such as polypropylene, TEFLON™ or stainless steel. The inner tube 68 passes upwardly through and is joined to an aperture in the bottom wall 24 of the tank 14. A round bottom plate 70 is received within and seals the interior of the bottom end of the inner tube 68. The upper end of the inner tube 68 extends nearly the full height of the tank 14. The upper edge of the inner tube 68 is received within and sealed to an annular groove formed in the bottom surface ofa round cap plate 72. The outer tube 66 is larger than the inner tube 68, and has an internal diameter sized to slide over the cap plate 72. The outer tube 66 extends from the bottom wall 24 of the tank 14 up to and suπounding the cap plate 72. An annular reservoir space 74 is defined between the inner tube 68 and the outer tube 66. A plurality of vertical anays of apertures 76 are formed at periodic radially spaced intervals through the outer tube 66. During plating with the apparatus 10, the plating solution, i.e., electrolyte, is supplied to the annular reservoir space 74 through a supply tube 78. The solution flows from the reservoir space 74, and is sparged through the apertures 76 into the interior of the tank 14. The apertures 76 are arranged in the outer tube 66 such that the solution is substantially evenly dispersed at all depths and radially locations within the tank 14. Solution overflows the tank from an outlet 80 near the top ofthe tank, flows to a sump pump (not shown), and is re-supplied to the tank 14 via the supply tube 78. Solution is thus recirculated throughout the tank 14 during use, ensuring that the anode assemblies 36 and wafer 44 are exposed to fresh electrolyte, and so that local deficiencies within the tank 14 are avoided.

The reservoir assembly 32 also provides support for the anode support ring 34. The anode support ring 34 rests on top of the upper edge of the outer tube 66. The anode support ring 34 is constructed from a conductive material such as copper or stainless steel. The anode support ring 34 is electrically connected to one side of the plating power supply 22. A conductor rod 82 is connected to a point on the inner diameter of the annular anode support ring 34, and is inserted radially into

the cap plate 72 to a point extending above the interior of the inner tube 68. The inner end of the conductor rod 82 is connected to a second conductor rod 86. The conductor rod 86 extends longitudinally from the cap plate 72, down through the interior of the inner tube 68, exiting through the bottom plate 70. An electrical lead 84 is connected from the bottom end of the conductor rod 86 to the power supply 22. In this manner power is supplied to the anode support ring 34 from the multichannel power supply 22.

The anode support ring 34 supports at least one, and preferably a plurality of anode assemblies 36. In the prefeπed embodiment ofthe apparatus 10 illustrated in FIGURES 2 and 3, four anode assemblies 36 are arranged radially around the reservoir assembly 32. Each anode assembly 36 includes a conductor rod 88 that is secured at its upper end to the outer diameter of the anode support ring 34, and that depends downwardly a majority ofthe depth ofthe tank 14. The conductor rod 88 is constructed from a conductive material such as stainless steel or copper, and is sheathed in an insulative sleeve 90, such as a polyvinyl chloride sleeve. The conductor rod 88 and insulative sleeve 90 are preferably mutually threaded for assembly.

Each anode assembly 36 includes an anode 92 of the appropriate material for the plating process at hand. For example, to apply gold plating to the semiconductor wafer 44, a suitable anode 92 is a platinum plated square section of metallic mesh, which is utilized with an electrolyte solution such as a cyanide gold solution. The anode 92 is mounted to the anode assembly 36 and placed in electrical contact with the power supply 22 by a bolt 94. The bolt 94 is inserted through the center of the anode 92, through an aperture in the insulative sleeve 90, and is threaded into the conductor rod 88. A current path thus exists from the power supply 22, through the electrical lead 84 to the conductor rod 82, the anode support ring 34, the conductor rod 88, the bolt 94 and to the anode 92. While a solid conductor rod 88 has been described for mounting the anodes 92, it should be apparent that other constructions are possible, such as the use of a hollow mounting tube through which electrical leads are threaded.

Each anode 92 is positioned at a height within the tank 14 approximately equal to the positioning of the semiconductor wafer 44 when mounted on the fixture wheel 42. As the fixture arm 40 reciprocates, the fixture wheel 42 sequentially passes each of the anodes 92, such that there is always an anode 92 in close proximity to the semiconductor wafer 44.

Referring still to FIGURE 3, the drive shaft 30 is journalled within upper and lower bearings 96 within the bottom plate 70 and cap plate 72 on the central axis 28. A shaft collar 98 is mounted on the bottom end of the drive shaft 30, which extends below the bottom plate 70. The driven pulley 60 is mounted on the bottom end ofthe drive shaft 30 below the shaft collar 98. One end of an elongate actuator 100 is secured on the bottom end of the drive shaft 30 below the driven pulley 60. The other end ofthe actuator 100 projects radially outward from the drive shaft 30.

The radial distal end ofthe actuator 100 aligns with a switch arm 102 so that each approximate 360 degree rotation ofthe drive shaft 30 causes the actuator 100 to move the switch arm 102. The switch arm 102 triggers a switch 104, which operates to reverse direction of the motor 58 upon each approximate 360 degree (i.e., 330° -350°) rotation of the drive shaft 30. This causes the drive shaft 30, and thus the fixture arm 40 and fixture wheel 42, to automatically reciprocate, first rotating clockwise approximately 360 degrees about the central axis 28, followed by immediate reversal and rotation approximately 360 degrees counterclockwise about the central axis 28, and so forth. The speed of rotation of the drive shaft 30 is selected for a particular process, and typically is between 1 and 13 revolutions per minute. The prefeπed operation speed is 3 revolutions per minute.

A low friction wear disc 106 is slid over the upper end of the drive shaft 30, and rests on top of the cap plate 72. The wear disc 106 is sandwiched between the cap plate 72 and the fixture mounting plate 38, and is constructed from a material such as ultra high molecular weight polyethylene, TEFLON™ fluorocarbon, or nylon that provides a smooth, low friction surface for the fixture mounting plate 38 to travel on as it rotates with the shaft 30. The fixture mounting plate 38 is retained on the shaft 30 by a nut 108. The interior ofthe central shaft 30 is hollow, and the electrical leads 48 that supply power to the fixture wheel 42 are threaded through the interior of the central shaft 30.

The fixture arm 40 shall now be described with reference to FIGURES 3 and 4. The apparatus 10 has been illustrated and described as including one fixture arm 40 and fixture wheel 42. The use of a single fixture arm and fixture wheel has been illustrated for clarity and because it is a suitable configuration for the apparatus 10. However, it is typically preferable to utilize a plurality of fixture arms 40 and fixture wheels 42, in order to enable the simultaneous plating of multiple semiconductor wafers 44 or other substrates.. When multiple fixture arms 40 and fixture wheels 42 are utilized, they are spaced evenly in radial disposition about the drive shaft 30. The use of up to eight fixture arms 40 and

fixture wheels 42 has been found suitable, with a typical number of fixture arms 40 and fixture wheels 42 utilized being four.

The fixture arm 40 is detachably mounted to the fixture mounting plate 38 in order to provide for easy removal of the entire fixture arm 40, fixture wheel 42 and semiconductor wafer 44. This provides for installation and removal of the semiconductor wafer outside of the tank 14. The fixture arm 40 has an overall 90 degree angled configuration, having a first leg 110 and a second leg 112. When mounted in the tank 14, the first leg 110 is horizontally disposed and substantially perpendicular to the central axis 28. The first leg 110 extends radially outward from the reservoir assembly 32. The second leg 112 depends downward from the first leg 110, and is oriented substantially parallel to the central axis 28. A hand-hold aperture 114 is formed through the first leg 110 to allow for gripping and removal of the fixture arm 40. The arm 40 is hollow, including an elongate passage 116 that is formed through both the first leg 110 and second leg 112 to allow for passage ofthe electric leads 48 through the interior ofthe fixture arm 40.

Referring to FIGURE 4, the first leg 110 of the fixture arm 40 is mounted between two flanges 118, a short distance from the radially innermost end ofthe first leg 110, to the fixture mounting plate 38. The flanges 118 are secured in spaced parallel disposition and project upwardly from the fixture mounting plate 38. A keyhole aperture 120 is formed transversely through the first leg 110 of the fixture arm 40 for mounting to the flanges 118. The keyhole aperture 120 is configured as a round transverse passage formed crosswise through the first leg 110, and which extends into a narrower slot to the bottom edge of the first leg 110. A retaining shaft 122 is received within the keyhole aperture 120 to secure the fixture arm 40 to the fixture mounting plate 38. The retaining shaft 122 is configured as a cylinder that is flattened on two opposing sides.

The retaining shaft 122 is non-rotatably secured on a pin 124 between the flanges 118. The pin 124 passes through aligned apertures formed in the flanges 118, the retaining shaft 122, and bearings 126 which are mounted between the ends ofthe retaining shaft 122 and the flanges 118. The pin 124 and thus the retaining shaft 122 can be rotated by pressing on a lever 128 that projects radially from one end of the pin 124. When the retaining shaft 122 is positioned as it is shown in FIGURE 4, with the flat sides of the shaft vertically disposed, the shaft 122 can be inserted from the bottom edge of the first leg 110 of the fixture arm 40 into the keyhole aperture 120. When the pin 124 and retaining shaft 122 are then rotated so that the flat sides of the shaft 122 are horizontally positioned, the retaining shaft 122 no

longer fits through the slotted portion of the keyhole aperture 120, and the fixture arm 40 is locked onto the fixture mounting plate 38. It should be readily apparent to one of skill in the art that an alternate selective locking mechanism rather than the retaining shaft 122 and keyhole aperture 120 could be utilized, such as a spring loaded retention pin.

The fixture arm 40 is also provided with an adjustment mechanism that enables the arm to pivot on the retaining shaft 122 to adjust the loading ofthe fixture wheel 42 against the track 50. A threaded passage 130 is formed vertically through the radially innermost end ofthe first leg 110 ofthe fixture arm 40. The passage 130 receives a stacked spring-loaded ball plunger 132 and a set screw 133. The ball plunger 132 projects from the bottom of the threaded passage 130 and bears against the fixture mounting plate 38. The position of the ball plunger 132 can be adjusted for the desired degree of loading of the fixture wheel 42 onto the track 50 by tightening the set screw 133 against the ball plunger 132. This adjustment can be made if, after some usage and wear of the apparatus 10, it is found that the fixture wheel 42 begins to slip relative to the track 50.

The electrical leads 48 from the multichannel power supply 22 are preferably fitted with a plug 134 that mates with a socket 136 that is mounted within the opening to the passage 116 within the first leg 110 of the fixture arm 40. The electrical leads 48 may be bundled for ease of threading through the passage 116.

Attention is now directed to FIGURES 4 and 5 to describe the mounting of the fixture wheel 42 onto the fixture arm 40. The second leg 112 of the fixture arm 40 includes a shaft portion 138 that projects perpendicularly from the lower end of the second leg 112, toward the reservoir assembly 32. The shaft portion 138 is cylindrically configured and defines the rotary axis 64 of the fixture wheel 42. All annular components of the fixture wheel 42 and the shaft portion 138 are coaxially aligned on the rotary axis 64. The shaft portion 138 includes a longitudinal slot 140 which provides for exit ofthe electrical leads 48.

The fixture arm 40, shaft 138 and the fixture wheel 42 are constructed from a non-conductive material, such as ultra high molecular weight polyethylene. A conductive path is formed from the electrical leads 48 to the electrical contacts 46. This path includes three tubular conductive contact bushings 142 that are slid onto the shaft portion 138 of the fixture arm 40. The contact bushings 142 are separated from each other by three annular non-conductive o-rings 144. There are thus three conductive bands formed around the shaft portion 138 that are isolated electrically from each other. A radial passage 148 is formed in each of the conductive contact

bushings 142. An end of a coπesponding electrical lead 48 is soldered into each of the passages 148 to connect each separate electrical lead 48 to a coπesponding conductive contact bushing 142.

When the contact bushings 142 are slid onto the shaft portion 138 of the fixture arm 40, the leads 48 pass through the slot 140 in the fixture arm 40. Prior to placement of the fixture wheel 42, an annular seal 150 is slid over the contact bushings 142 and up against the second leg 112 of the fixture arm 40, to provide a fluid tight seal between the fixture wheel 42 and the fixture arm 40.

The fixture wheel 42 includes a central cylindrical recess 152 that rotatably receives the shaft portion 138 of the fixture arm 40. An annular groove 154 is formed around the distal end of the shaft portion 138 of the fixture arm 40. A tangential bore 156 is formed into the fixture wheel 42 and aligns with the groove 154 when the fixture wheel 42 is fully inserted onto the shaft portion 138. A low friction locking rod 158, which may be suitably constructed from a fluorinated hydrocarbon polymer, is inserted into the bore 156 and thus passes tangentially into the groove 154. This locking rod 158 travels about the groove 154 as the fixture wheel 42 rotates on the shaft portion 138, and prevents the fixture wheel 42 from coming loose from the shaft portion 138.

A separate conductive path is provided from each conductive contact bushing 142 to a coπesponding electrical contact 46. Three radial passages 160 are formed into the perimeter 54 of the fixture wheel 42 and extend to the internal recess 152 of the fixture wheel 42. The radial passages 160 are staggered longitudinally along the longitudinal width of the fixture wheel 42, such that each radial passage 160 aligns with a coπesponding one of the conductive contact bushings 142 when the fixture wheel 42 is installed on the shaft portion 138.

An elongate brush assembly 162 is installed into each radial passage 160. Each brush assembly includes a conductive contact tip 164 connected by an internal lead 166 and a coil spring 168 to a plug 170. The contact tip 164 is constructed from a relatively soft conductive material, such as silver carbide, and rides on the coπesponding contact bushing 142 as the fixture wheel 42 rotates. Cuπent is conducted from the contact bushing 142 to the contact tip 164, through the lead 166 to the plug 170. The coil spring 168 biases the contact tip 164 against the contact bushing 142, so that electrical contact is maintained despite wear of the contact tip 164. Each electrical contact 46 is connected to a coπesponding brush assembly 162 by a conductive rod 172 that is inserted longitudinally into the front

face 174 ofthe fixture wheel 42. The radially distal end ofthe lead 166 ofthe brush assembly 162 is secured to one end of the conductive rod 172, and the other end of the conductive rod 172 is received within a body 176 of the electrical contact 46. (FIGURE 5). Each electrical contact 46 includes a conductive spring contact 178 that has a first end inserted radially into the body 176 and that is threaded onto the conductive rod 172. The spring contact 178 twists into a loop for tension and then forms a 90 degree angled portion, the tip of which is biased against the outer surface 180 ofthe wafer 44.

Conventional semiconductor wafers 44 are thin discs, typically from 3 to 8 inches in diameter. The semiconductor is conventionally coated with a photoresist material except for a narrow band around the perimeter of the outer surface 180 of the semiconductor wafer 44. The semiconductor wafer 44 is positioned over the front face 174 ofthe fixture wheel 42. Because it is not desired to have plating form on the opposite side ofthe semiconductor wafer 44, a gasket is provided between the wafer 44 and the front face 174 of the fixture wheel 42. In the embodiment of FIGURE 5, a flat annular gasket 182 is received within an annular recess formed in the front face 174 of the fixture wheel 42 to seal the back face of the wafer 44. It should be apparent to those of skill in the art that a solid sheet gasket or another type of seal such as an o-ring seal could instead be utilized. The electrical contacts 46 are turned after placement of the wafer 44 so that the tips of the spring contacts 178 contact a non-photoresist coated point of the semiconductor wafer 44. A cuπent path is thus provided from the electrical leads 48 through the conductive bushings 142 to the brush assemblies 162, electrical contacts 46 and to the wafer 44. In the preferred embodiment illustrated, three electrical contacts 46 are carried on the fixture wheel 42. The use of three contacts is found suitable to evenly distribute current to the semiconductor wafer 44. However, it should be readily apparent that differing numbers of electrical contacts could be utilized as desired. Further, the term electrical contact as used herein is intended to include not only the spring loaded electrical contacts 46 illustrated, but other electrical contacts. For example, an annular holding ring with segmented electrical portions could be utilized to retain and contact the wafer 44..

A critical aspect of the present invention is the multichannel delivery of cuπent to the wafer 44 via separate cuπent delivery circuits. One side of the multichannel power supply 22 is connected to the anodes 92, as previously described. The other side of the multichannel power supply is connected to the wafer 44 which

serves as the cathode, and current passes from the anodes 92 to the wafer 44 through the electrolyte solution. The power supply 22 is a multichannel power supply, which as used herein is intended to mean either a power supply with multiple channels or collectively to a plurality of single channel power supplies. The distribution of current delivered from the multichannel power supply 22 may be adjusted by adjusting the channels relative to each other. A separate individual current circuit is provided from each channel of the power supply 22 to a coπesponding electrical contact 46. This cuπent path is provided through the coπesponding separate leads 48 passing through the fixture arm 40 to the coπesponding electrically isolated conductive contact bushings 142. The individual paths are then continued through the coπesponding individual brush assemblies 162 to the corresponding electrical contacts 46.

During plating, the cuπent delivery through each channel of the power supply 22 can be monitored via the control console 18. If power supply to the individual contacts 46 is uneven, the electrical contacts 46 can be manually adjusted to coπect for any poor contact being made with the wafer 44, by repositioning the spring contacts 178. If an uneven power distribution is still found, the multichannel power supply 22 itself can be adjusted to coπect the distribution. This prevents the thickness of the plated coating being formed on the semiconductor wafer 44 from building up more heavily in the vicinity of one electrical contact 46 relative to another electrical contact 46.

As previously discussed, the perimeter 54 ofthe fixture wheel 42 rides on the track 50. The tips of the pins 52, which are preferably constructed of a polyethylene polymer, are received within coπesponding slots 56 fonned in the perimeter 54 of the fixture wheel 42 as the fixture wheel 42 rotates on the track 50. The positive mechanical engagement ofthe pins 52 and the slots 56 forces the fixture wheel 42 to continuously turn about the rotary axis 64 without slippage during revolution of the fixture wheel 42 around the central axis 28. The slippage that could occur with two smooth low friction surfaces is thus avoided. This mechanical engagement of the fixture wheel 42 and track 50 could alternately be otherwise obtained, such as by providing gear teeth on the fixture wheel which mesh with coπesponding teeth on the track 50. The result is that the fixture wheel 44 must necessarily rotate about the rotary axis 64 in direct proportion to the extent of rotation of the shaft 30 about the central axis 28. The rotary axis 64 of the fixture wheel 42 is oriented perpendicularly to the central axis 28 of a tank 14. Any individual point on the wafer 44 being plated thus

simultaneously revolves in reciprocal fashion around the central axis 28 while rotating about the rotary axis 64. All points on the outer surface 180 ofthe wafer 44 are thus exposed equally to the anodes 92. This multi-axis rotation provides for an even degree of plating across the wafer 44. This uniformity of plating could be lost if the fixture wheel 42 were to slip relative to the track 50, which is avoided due to the positive drive engagement of the pins 52 and slots 56. Further, the uniformity of plating thickness is also greatly affected if the distribution of current is not uniform across the wafer 44, which is avoided by the provision of multichannel power paths. Conventional bump plating methods result in wafers 44 having plating thicknesses varying as much as 200% across the width of the wafer. The multi-axis rotary/reciprocating revolving motion ofthe wafer provided by the present invention yields a plating uniformity of ±10% deviation across the width of the wafer. By including the independently adjustable electrical contact circuits of the present invention and the positive drive ofthe fixture wheel 42 and track 50 provided by the mating pins 52 and slots 56, the present invention provides for a deviation in plating thickness of less than or equal to ±5% for 5 to 8 inch diameter wafers, and of less than or equal to ±3% for 3 to 4 inch diameter wafers. Preferably, plating uniformity of at least ±1 to 2 percent deviation across the width of a 3 to 4 inch wafer is obtained. These low deviations have been measured when gold plating is applied using the present invention to a thickness of 8 to 35 microns through application of cuπent of 15 to 100 milliamps for a period of time of 20 minutes to 1 hour and 50 minutes. These low deviations have also been obtained from plating copper in accordance with the present invention to a thickness of approximately 3.75 microns by application of 300 milliamps of power. In general, plating thicknesses obtained with the present invention are found to vary no more than 0.25 microns over a distance of 1,000 microns across the width ofa wafer being plated.

An alternate embodiment of a rotary/reciprocating fixture assembly 200 is shown in FIGURES 6-23. Like the previously described fixture assembly 16 used in the plating apparatus 10, the fixture assembly 200 is mounted on a central drive shaft which rotates in a reciprocating fashion about a vertical axis. The fixture assembly 200 is suitable for use in a housing 12 and plating tank 14 as previously described, and operates in conjunction with an anode assembly 36 mounted on a central drive shaft as previously described. However, the fixture assembly 200 differs from the fixture assembly 16 in four primary ways. First, a plurality of fixture wheels are utilized. Secondly, each fixture wheel is rotatably driven by a dedicated

motor, rather than being driven on an annular track 50 as previously described. Third, the fixture assembly 200 is selectively detachable from the drive shaft as a complete assembly, and includes electrical connectors that allow breaking of electrical circuits between the drive shaft and the fixture assembly 200. Finally, the manner in which the semi-conductor wafers 44 are mounted on the fixture wheels differs. These aspects ofthe alternate embodiment will be described in detail, while those aspects in common with the prior embodiment are not discussed.

The fixture assembly 200 includes a fixture body 202 that is selectively securable to a hub 204 that is in turn secured on the upper end of a central drive shaft 206. The central drive shaft 206 is powered by a motor to rotate in a 360° reciprocating fashion as previously described. The fixture body 202 carries four fixture arms 208 that are mounted radially outwardly from the axis 210 of rotation of the central drive shaft 206. The fixture wheel assemblies 212 are oriented radially at even 90° intervals about the drive shaft 206. Each fixture arm 208 depends downwardly in parallel disposition to the drive shaft 206. A fixture wheel assembly 212 is rotatably mounted on the end of each of the fixture arms 208. Each fixture wheel assembly 212 is mounted to rotate about a second axis that extends perpendicularly i.e., radially from the axis 210 of rotation of the central drive shaft 206. The fixture wheel assemblies 212 each are capable of receiving a semi- conductor wafer 44 to be plated.

Referring to FIGURE 7, the fixture body 202 carries four motors 214, each of which is protected by a removable cover 216 (shown in FIGURE 6). Each motor 214 powers the rotation of a coπesponding fixture wheel assembly 212. Each fixture wheel assembly 212 includes an annular fixture ring 218 that is biased against a fixture wheel 220 to secure a semi-conductor wafer 44 (not shown) therebetween.

Referring to FIGURE 8, four electrical connectors 222 are mounted on the underside of the fixture body 202. These engage with mating electrical connectors 224 (FIGURE 6) that are mounted on the top ofthe hub 204 ofthe central drive shaft 206. This enables supply of power for both the motors 214 and for plating current across the semi-conductor wafers 44, as shall be described subsequently in greater detail.

The fixture assembly 200 is suited for use in both manual and automatic plating systems. Thus the fixture assembly 200 can be removed either manually or by an automatic manipulator from the hub 204 of the drive shaft 206. Electrical connectors 222 and 224 automatically mate and unmate upon placement and removal of the fixture assembly 200. The fixture rings 218 can be pulled apart from the

fixture wheels 212 to create a space permitting the semi-conductor wafers 44 to be either manually or robotically removed therefrom and reloaded. After reloading of the semi-conductor wafers 44, the entire fixture assembly 200 is remounted onto the hub 204 ofthe central drive shaft 206. Attention is now directed to FIGURES 6-10 to describe the construction of the fixture body 202. The fixture body 202 has a cylindrical center portion 226 (FIGURE 6 and 10) that is hollow, defining an internal cylindrical cavity that axially receives a conesponding cylindrical upper portion of the hub 204, as shall be described subsequently. Beneath the center portion 226 of the body 202 extends a slightly-frustoconical disc shaped base portion 228 (FIGURE 6). Radially oriented extension portions 230 project at 90° intervals from the base portion 228. The extension portions 230 each include an elongate radially oriented recess 232 (FIGURE 7) in which a conesponding motor 214 is received in radial disposition. These recesses 232 are selectively covered by the cover plates 216 to protect the motors from exposure to plating solution. The radial ends of the extension portions 230 are joined by an annular ring portion 234 that is aligned axially with the axis 210 of rotation of the drive shaft 206. The four fixture arms 208 depend downwardly from the ring portion 234, with each fixture arm 208 being aligned with an extension portion 230 and spaced at 90° intervals around the periphery of the body 202. The fixture arms 208 are further stabilized by being attached to an annular support ring 235 disposed below the ring portion 234 of the fixture body 202. A gripping attachment 236 is secured to and projects axially upwardly from the center portion 226 of the body 202, and allows grasping and lifting of the fixture assembly 200 by an automated manipulator or manually. Referring to the top view of FIGURE 7 and the bottom view of FIGURE 8, each motor 214 receives power through an electrical lead 238 that is electrically connected to a conesponding connector 222. A motor drive shaft 240 projects radially outward from the end of each motor 214 (FIGURE 7) for coupling with the fixture wheel assembly 212, as shall be described subsequently. Referring to FIGURE 9, each fixture arm 208 includes an elongate recess formed in the outer face of the arm that is selectively covered by fixture arm covers 242 (FIGURE 6). These protective covers can be removed (FIGURE 9) to expose a looped drive chain 244 that is trained about a drive sprocket 246 secured to the end of the motor drive shaft 240. The drive chain 244 then extends down within the recess of the fixture arm 208 to engage the end of a driven sprocket 248. The driven sprocket 248 is mounted on a radially outer end of a shaft journalled axially

within a fixture wheel shaft assembly 250 that is mounted within the lowermost end ofthe fixture arm 208. Each ofthe fixture wheel shaft assemblies 250 is oriented on an axis that is radially and perpendicularly disposed relative to the axis of rotation 210 of the drive shaft 206. The fixture wheel assemblies 212 are secured axially to the opposite, radially innermost end of the shaft within the fixture wheel shaft assembly 250. Each motor 214 independently drives rotation of a conesponding fixture wheel assembly 212 through the conesponding chain 244. While the use of a drive chain 244 and sprockets 246 and 248 has been described, it will be readily apparent to those of ordinary skill in the art that other force transmission mechanisms such as a cable and pulleys can be utilized.

This independent drive of the fixture wheel assembly 212 rotation has been found preferable to the track drive previously described above, because it is not subject to variations in level of the plating tank that could effect engagement of the fixture wheels. Additionally, each fixture wheel assembly 212 rotates continuously in the same direction, rather than reversing the direction with each reversal of the direction of rotation ofthe central drive shaft 206.

Attention is now directed to FIGURES 6 and 8 to describe the mating of the electrical connectors 222 and 224. The base portion 228 of the fixture body 202 defines a concave frustoconical bottom surface in which four radially oriented elongate recesses 252 are formed. In each recess 252 is mounted a conesponding connector 222, which projects downwardly from the recess 252 below the bottom surface ofthe base portion 228. Each ofthese connectors 222 is oriented in line with the conesponding extension portion 230 and fixture arm 208. These connectors 222 each include a plurality of prongs which supply power to a coπesponding motor 214, and to plating circuit leads (not shown) that are fed through the recesses within the arms 208 to the fixture wheel assemblies 212 to provide plating cuπent to the received semi-conductor wafers (not shown).

Referring to FIGURE 6, the hub 204 is secured by two screws 254 to the top ofthe drive shaft 206. The mating connectors 224 are mounted in recesses formed in the upper surface of the hub 204, in radial alignment with the connectors 222 on the fixture body 202. In this way when the fixture body 202 is installed on the hub 204, the connectors 222 automatically mate with the mating connectors 224 to supply power from leads fed through the interior ofthe drive shaft 206 from a power supply (not shown) to the motors 214 and plating circuits. The construction of the hub 204 is better understood with reference to

FIGURE 6 and the enlarged detail assembly of FIGURE 11, as well as

FIGURES 12-16 which illustrate components of the hub 204. The hub 204 includes a hollow cylindrical upper portion 256 (FIGURES 6, 14 and 15) that is slid onto the upper end of the drive shaft 206. From the bottom ofthe upper portion 256 flares a frustoconical base portion 258 that is contoured conespondingly to the base portion 228 of the fixture body 202. The recesses 260 that receive the mating connectors 224 are formed in this base portion 258 on radial lines that run at 90° relative to each other (FIGURE 14). A groove 262 formed longitudinally in the bottom of each recess 260 receives power leads 264 from the interior of the drive shaft 206 (FIGURES 14-16). The upper portion 256 of the hub 204 also includes two longitudinally oriented slots 264 (FIGURES 6 and 14) that are engaged by cylindrical cam followers 266 which are mounted in diametric opposition on the interior sidewall of the center portion 226 of the fixture body 202 (FIGURE 8) and project radially inward thereinto. The engagement ofthe cam followers 266 ofthe fixture body 202 and the slots 264 of the hub 204 helps to orient the fixture body 202 relative to the hub 204.

The cam followers 266 also enable operation of an automatic connector cover 268 which is best seen in FIGURES 6, 11, 12 and 13. The connector cover 268 has a contour which generally follows the upper surface contour of the hub 204. Thus, the connector cover 268 has a tubular upper portion 270 and a frustoconical base portion 272. The connector cover 268 is open at the upper end of the upper portion 270 and is retained nested on top of the hub 204 by a disc-like retaining plate 274 secured to the top ofthe hub 204 by the screws 254 (FIGURES 6 and 11). Once so secured, the connector cover 268 is able to freely rotate about the axis 210 of the drive shaft 206 on top of the fixture hub 204.

Referring to FIGURES 6, 12, and 13, four radially oriented slots 276 are formed through the base portion 272 of the connector cover 268. The slots are arranged in the same orientation and have the same width as the connectors 224 of the underlying hub 204. The connector cover 268 can be rotated between an open position, in which the slots 276 are aligned with and expose the underlying connectors 224, and a closed position in which the slots 276 are misaligned with the connectors 224, thus shielding the connectors 224 and preventing plating solution or other contaminants from falling into the connectors 224.

To facilitate automatic rotation ofthe connector cover 268, two diametrically opposed dog-legged cam grooves 278 are formed through the side walls ofthe upper portion 270 of the connector cover 268. These cam grooves 278 engage the cam

followers 266 mounted in the underside ofthe fixture body 202 (FIGURE 8). When the fixture body 202 is mounted onto the fixture hub 204, the cam followers 266 travel downwardly within the cam grooves 278, causing the connector cover 268 to rotate as the fixture body 202 moves downwardly. The cam grooves 278 are oriented such that as the fixture body 202 is lowered onto the fixture hub 204, the connector cover 268 moves to the open position to expose the connectors 224. As the fixture body 202 is withdrawn upwardly off of the fixture hub 204 for removal ofthe fixture body 202 and interchange of the semi-conductor wafers, the connector cover automatically moves to the closed position to shield the connectors 224. Attention is now directed to FIGURES 17-23 to describe construction of the fixture wheel assemblies 212. Each fixture wheel assembly 212 includes the fixture wheel 220 (FIGURES 17 and 18) which is mounted on the fixture wheel shaft assembly 250 to rotate with the drive shaft of the fixture wheel shaft assembly 250. Electrical brush contacts assembled within the interior of the fixture wheel 220 maintain contact with stationary annular electrical contacts which are carried on a stationary component of the fixture wheel shaft assembly 250, in a manner similar to the brush contact connection described in the previous embodiment above. The fixture wheel 220 is mated to a disc-like base plate 280, shown in FIGURES 17, 19 and 20. The base plate 280 is secured to the fixture wheel 220 by a plurality of screws 282 inserted through apertures 284 formed radially about the periphery ofthe base plate 280. A circular recess is formed in the front face of the base plate 280, covering all but an outer peripheral portion of the base plate 280. This recess 286 is undercut along its circular edge. This undercut recess 280 is filled with an elastomeric gasket, such as a silicone elastomer gasket, that fills the recess 280 to be flush with the front face ofthe base plate 280, for purposes of cushioning a received semi-conductor wafer.

Referring to FIGURES 17 and 21, an annular fixture ring assembly 288 is secured to the front face ofthe base plate 280. The annular fixture ring assembly 288 is further illustrated in FIGURES 22 and 23, and is assembled from a sandwich of a first annular ring 290 and a second annular ring 292. The first annular ring 290 (closest to the base plate 280) includes an annular recess 294 formed in the side facing the base plate 280 about the ring's inner circumference. This recess 294 is dimensioned to receive the edge of a semi-conductor wafer 44. The semi-conductor wafer 44 is placed within the recess 294 of the assembled fixture ring assembly 288, and can then be sandwiched between the fixture ring assembly 288 and the elastomeric gasket ofthe base plate 280.

Channels 296 formed within the interfacing surfaces of the first ring 290 and second ring 292 provide for placement of electrical leads into the fixture ring assembly 288 for delivery of cunent to the semi-conductor wafer.

Referring to FIGURES 17 and 22, the fixture ring 288 is secured to the base plate 280 by a plurality of spring-loaded pin assemblies 298. Each spring-pin assembly 298 includes a central pin 300 that is oriented axially within a longitudinal passage 301 formed through the base plate 280 and into the fixture wheel 220. A stop 302 is secured to the iniiermost end ofthe pin 300. The pin 300 then receives a coil spring 304. The spring 304 and pin 300 are retained within the passage by a threaded plug 306 secured into a threaded outer portion ofthe passage 301 within the base plate 280. The projecting end 308 of the pin 300 extends into a passage 310 (FIGURES 22 and 23) formed through the first ring 290 and into the adjacent second ring 292 of the fixture ring assembly 288. An electrical contact pin 312 (FIGURE 17) is secured to the end 308 of the pin 300 and passes through the channel 296 of the fixture ring assembly 288 to complete delivery of power to the received semi-conductor wafer.

The spring-pin assemblies 298 act to bias the fixture ring 288 toward the fixture wheel 220. Preferably three spring-pin assemblies 298 are utilized, and are oriented at 120° radial positions about the perimeter ofthe fixture ring assembly 288, as indicated by the anangement of the passages 301 within the base plate 280 (FIGURE 20). The length ofthese spring-pin assemblies 298 may vary dependent on the positioning of the brush contacts (not shown) within the interior of the fixture wheel 220.

The spring force of the springs 304 utilizing the spring-pin assemblies 298 is selected so that fixture ring assembly 288 can be forcibly retracted from the base plate 280 and fixture wheel 220, creating a space of approximately 1/2" therebetween to allow removal and insertion of semi-conductor wafers. The spring force is further selected at a predetermined value so that when this force is relieved from the fixture ring assembly 288, the fixture ring assembly 288 returns inwardly towards the base plate 280, securely gripping the semi-conductor wafer therebetween without damaging the semi-conductor wafer yet ensuring that a good seal is maintained between the semi-conductor wafer and the underlying elastomeric gasket to prevent leakage of plating solution to the back face of the semi-conductor wafer. The front face of the wafer is exposed through the center opening of the fixture ring assembly 288. An outer edge 316 of the fixture ring assembly 288 facilitates gripping by either manual or automated means for displacing the fixture ring

assembly 288 relative to the fixture wheel 220. The present fixture assembly 200 thus provides a process that is well adapted for either manual or automatic loading and unloading of semi-conductor wafers.

While the prefened embodiment of the invention has been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope ofthe invention.