Patent Application
20150014175
Production of semiconductor integrated circuits and other microelectronic devices from workpieces such as semiconductor wafers typically requires formation of one or more metal layers on the wafer. These metal layers are used, for example, to electrically interconnect the devices of an integrated circuit. Such metal layers also find use in the formation of the devices themselves, such as read/write heads of a disk drive.
The microelectronic manufacturing industry has applied a wide range of metals to form such structures. These metals include, for example, nickel, tungsten, solder, platinum, and copper. Further, wide ranges of processing techniques have been used to deposit such metals. One such process used to deposit a metal onto semiconductor wafers is referred to as “damascene” processing. In such processing holes, commonly called “vias”, trenches and/or other recesses are formed onto a workpiece and filled with a metal, such as copper. In the damascene process, the wafer is first provided with a metallic seed layer used to conduct electrical current during a subsequent metal electroplating step. The seed layer is a very thin layer of metal which can be applied using one or more of several processes.
As greater demands are placed on scaling down the size of microelectronic circuits, the aspect ratio of the vias, trenches, and other recesses of the wafer increase. More particularly, the opening of the structure into which the electroplating chemistry enters is significantly smaller than the depth of the structure to be filled. If the structure is not completely filled, voids develop that can render the associated microelectronics useless or increase the likelihood that the microelectronic devices will fail.
An electroplating apparatus for plating a metal onto a surface of a wafer is disclosed. The apparatus comprises a wafer support configured to support a wafer and a processing base. The processing base has a scroll pump oriented to pump a plating solution in a substantially perpendicular direction with respect to the surface of the wafer. Further, the scroll pump includes a first scroll and a second scroll, at least one of which is configured as an anode. In one embodiment, the processing base includes an anolyte chamber, which has the scroll pump, and a catholyte chamber, and a membrane separating the anolyte chamber from the catholyte chamber.
The wafer head 20 may also be driven along axis 45 by a still further motor 50. In this example, motor 50 is configured to drive the wafer head 20 and wafer support 35 between the elevated position shown in
The processing base 25 includes a shell assembly 55 that surrounds a processing space 60. Fluid passages are disposed through the processing base 25 and provide means for conducting plating solutions therethrough. In one example, the fluid passages may be configured to selectively recirculate and/or remove plating solution from the processing 60.
The processing space 60 is surrounded by the outer shell assembly 55 and contains a scroll pump 75. The scroll pump 75 is oriented to pump the plating solution in a direction substantially perpendicular to the surface of the wafer 15. In order to promote even plating across the entire diameter of the wafer, the scroll pump 75 may have a diameter that is approximately equal to or greater than the diameter of the surface of the wafer that is to be plated. As set forth in further detail below, the scroll pump 75 includes a first scroll and a second scroll, at least one of which is configured as an anode.
The processing base 25 also includes a scroll pump drive 80. The scroll pump drive 80 includes a motor 85 including a rotor 90 having a cam 95. The cam 95 is configured to engage a cam follower disposed at a bottom, central portion of a moving scroll of the scroll pump 75 to oscillate the moving scroll with respect to a fixed scroll.
A control system 100 may govern the operation of the apparatus 10. In one example, the control system 100 includes a drive/valve controller 105, a plating controller 110, and a chemistry controller 115. The drive/valve controller 105 may direct operation of the various motors of the apparatus 10. For example, the drive/valve controller may: 1) elevate the wafer head 20 along axis 45 and rotate it to a wafer face-up orientation about axis 27 to receive the wafer 15 on the wafer support 35; 2) rotate the wafer head 20 about axis 27 to a wafer face-down orientation and drive it along axis 45 to place the wafer in a processing position in contact with a plating solution in the processing base 25; and 3) drive the scroll pump 75. The drive/valve controller 105 may also direct the valves of the apparatus 10 to various states during processing to govern fluid flow into, through, and from the processing base 25. The plating controller 110 may be configured to control the plating potential between the surface of the wafer 15 and the scroll(s) that is configured as the anode.
The chemistry controller 115 governs the supply of various processing chemistries to the processing base 25 in cooperation with the drive/valve controller 105. For example, the chemistry controller 115 may operate to: 1) regulate the content of the mixture of the plating solution; 2) monitor properties of the plating solution; 3) add constituents to the plating solution; 4) regenerate used plating solution for further use; and/or 5) regulate recirculation, waste treatment, and/or disposal of the plating solution.
The interior of the inner shell 130 defines the processing space 60, which is used to hold the scroll pump 75 and the plating solution. The scroll pump 75 includes a first scroll 140, which is fixed, and a second scroll 145 which oscillates with respect to the first scroll 140. One or both of the scrolls 140, 145 are configured for connection to a negative terminal of a power supply to operate as an anode. When the metal to be electroplated is copper, the scroll operating as the anode is copper. However, both scrolls may be copper. Further, both scrolls may be configured as anodes. Still further, the fixed scroll 140 may be configured as a heater to provide localized heating of the plating solution and/or second scroll 145.
Here, the oscillating scroll 145 is connected to the negative terminal of the power supply at electrical posts 150 and 155. Electrical posts 150 and 155 extend through channels 160 and 165 of the inner shell 130 and lower plate 135. The channels 160 and 165 are dimensioned so as not to restrict the motion of the oscillating scroll 145.
For plating to occur there must be a plating potential between the surface of the wafer to be plated and the scroll(s) configured as the anode. To this end, a conductive seed layer is deposited on the surface of the wafer, a periphery of the wafer 15 having the seed layer may be configured to engage a contact for connection with a positive terminal of the power supply. In this manner, the surface of the wafer functions as a cathode.
The scroll pump drive 80 includes a motor 85 that drives a rotor 90. The rotor 90 extends into a common chamber 170 and terminates at a cam 175 that engages a cam follower 180. In turn, the cam follower 180 is in fixed engagement with respect to a lower, central portion of the oscillating scroll 145. Referring to
The common chamber 170 includes an inlet 179 and an outlet 187. The plating solution at the inlet 179 may be received through a recirculation path from the processing space 60, or from an inlet 183 connected to receive fresh plating solution. The recirculation path includes a vertical conduit 190 opening to the inlet 179 of the common chamber 170, and a horizontal conduit 195 extending from the outlet 187 to vertical conduit 200. Another horizontal conduit 205 extends between the vertical conduit 200 and an inlet 207 of the processing space 60. During processing, upon reaching a predetermined number of wafers that are to be plated with the recirculated plating solution, the plating solution is passed through the recirculation path. Once the plating solution the predetermined number of wafers have been plated, however, the scroll pump 75 is directed by the control system 100 to empty the processing space 60 instead of recirculating the solution, after which a fresh supply of plating solution is provided through inlet 183 and pumped into the processing space 60 by the scroll pump 75.
The embodiment of the processing base 25 shown in
A membrane 235 is disposed between the anolyte chamber 210 and the catholyte chamber 215. Membrane 235 may be a Nafion®-type membrane manufactured by Dupont Corporation. Nafion® is an example of a poly (tetrafluoroethylene) based ionomer. Nafion® has several desirable characteristics for electrochemical plating applications, such as its thermal and chemical resistance, ion-exchange properties, selectivity, mechanical strength, and insolubility in water. Nafion® is also a cationic membrane based on a fluorized polymer matrix.
Alternatively, membrane 235 may be a porous membrane that includes microporous chemical transport barriers, which limit chemical transport of most species, while allowing migration of anion and cation species, and hence passage of current. Examples of porous membranes include porous glass, porous ceramics, silica aerogels, organic aerogels, porous polymeric materials, and filter membranes. Specific membranes include carbon filter layers, Kynar layers, or polypropylene membranes. The intent of this configuration is to prevent additives in the plating solution from contacting the anode and depleting or degrading. An embodiment of a processing base 25 without such an intermediate membrane, however, is shown in
Once the wafer 15 is in contact with the plating solution, which generally contains copper sulfate, chlorine, and one or more of a plurality of organic plating additives (levelers, suppressors, accelerators, etc.) added to control plating parameters, a plating potential is applied between a seed layer on the wafer 15 and the scroll(s) of the scroll pump 75 that function as the anode. The electrical potential operates to cause metal ions in the plating solution to deposit on the cathodic wafer surface.
During plating, applying the plating potential between the anode of the scroll and the cathodic wafer causes a breakdown of the anolyte solution contained within the anolyte chamber 210. More particularly, applying the plating potential generates multiple hydrodynamic or Newtonian layers of the copper sulfate solution within the anolyte chamber 210. The hydrodynamic layers generally include a layer of concentrated copper sulfate positioned proximate the scroll operating as the anode, an intermediate layer of less concentrated copper sulfate, and a top layer of lighter and depleted copper sulfate proximate the membrane. The depleted layer is a less dense and lighter layer of copper sulfate than the copper sulfate originally supplied to the anolyte chamber 210, while the concentrated layer is a heavier and denser layer of copper sulfate having a very viscous consistency. The dense consistency of the concentrated layer proximate the anode may cause electrical conductivity problems and disrupt conformal deposition of the copper layer. Further, as the plating process proceeds, contaminants may accumulate on the membrane 235, which likewise disrupt conformal deposition.
Using a scroll pump 75 to pump the plating solution may improve electroplating performance and conformal coating of the copper on the wafer 15. More particularly, since the flow of anolyte from the scroll pump 75 is pumped in a direction substantially perpendicular to the surface of the wafer 15, the anolyte flow agitates the membrane 235. Agitation of the membrane 235 may assist in loosening membrane deposits, which can then be removed, for example, by a filter in the recirculation path, thereby enhancing transmission of copper ions through the membrane to the catholyte. Further, the agitation of plating solution between the scrolls while pumping may assist in reducing the buildup of anode passivation layers that would otherwise form on the scrolls.
While the foregoing is directed to various embodiments of analog show plating apparatus, other and further embodiments may be devised without departing from the basic teachings herein, and the scope of the invention is determined, without limitation, by the following claims.
