US20150014175A1

US20150014175A1 - Electroplating apparatus having scroll pump

Info

Publication number: US20150014175A1
Application number: US13/937,866
Authority: US
Inventors: Raymon F. Thompson
Original assignee: Individual
Current assignee: Individual
Priority date: 2013-07-09
Filing date: 2013-07-09
Publication date: 2015-01-15

Abstract

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 including the scroll pump, a catholyte chamber, and a membrane separating the anolyte chamber from the catholyte chamber.

Description

BACKGROUND

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.

SUMMARY

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.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-3 show an apparatus for electroplating a metal onto a surface of a wafer, where a wafer head of the apparatus is various operational positions.

FIGS. 4A, 4B, and 4C are cross-sectional views of one example of a processing base.

FIG. 5 is an example of a processing base of the type shown in FIGS. 4A-4B, but without an intermediate membrane.

FIGS. 6A and 6B illustrate one manner in which the perpendicular pumping operation of the scroll pump may assist in electroplating wafer features having high aspect ratios.

FIG. 7 is a flowchart showing one method for plating a wafer.

DETAILED DESCRIPTION

FIG. 1 shows an apparatus 10 for electroplating a metal onto a surface of a wafer 15. Apparatus 10 includes a wafer head 20 and a processing base 25. The wafer head 20 may be configured with a motor 23 to rotate the wafer 15 about axis 27 from a first position in which the wafer 15 is received by the wafer head 20 in a face up orientation (FIG. 1), and a second position in which the wafer 15 is disposed in a face down orientation (FIG. 2). A further motor 30 of the wafer head 20 is configured with a wafer support 35 (e.g., a vacuum chuck) to rotate the wafer 15 about a substantially vertical axis 40.
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 FIG. 2 and the processing position shown in FIG. 3.
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.
FIGS. 4A, 4B, and 4C are cross-sectional views of one example of a processing base 25. As shown, the processing base 25 includes an outer shell 125, an inner shell 130, a lower plate 135, and an upper annulus 137. The outer shell 125, the inner shell 130, and the lower plate 135 come together to define one or more fluid passages.
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 FIG. 4C, the rotation of the cam 175 results in radial movement of the oscillating scroll 145 with respect to the fixed scroll 140, such as shown by arrows 177, to generate the pumping action resulting inflow of the plating solution in the direction of arrow 163. In an alternate arrangement, the first scroll 140 and second scroll 145 may both be moving scrolls and configured to co-rotate in synchronous motion at offset centers of rotation.
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 FIGS. 4A-4C employs an anolyte chamber 210 and a catholyte chamber 215. The wafer 15 is placed in contact with catholyte solution in the catholyte chamber 215 by the wafer support 35 (not shown in FIGS. 4A and 4B) during plating. The catholyte solution is provided through one or more conduits in the processing base 25 to one or more outlets 220 disposed about a periphery of the upper annulus 137, and exits through, for example, vertical conduits 230.
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 FIG. 5.
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.
FIGS. 6A and 6B illustrate one manner in which the perpendicular pumping operation of the scroll pump 75 may assist in electroplating wafer features having high aspect ratios (i.e., the depth D of the structure is substantially greater than the width W). In FIGS. 6A, a wafer feature 300 is formed, for example, in a dielectric layer 305 of the wafer 15. A seed layer 310 is formed over the surface of the dielectric layer 305, where the seed layer 310 extends into the wafer feature 300. While the plating potential is applied between the seed layer 310 and the anode of scroll pump 75, the scroll pump 75 concurrently pumps the plating solution toward the membrane, which, in turn, may cause a corresponding agitated motion of the of anolyte at the boundary of the membrane contacting the anolyte. This may promote transfer of copper ions from the anolyte to the catholyte through the membrane. Further, given that the membrane is generally perpendicular to the surface of the wafer, the agitation provided to the membrane by the scroll pump 75 may be transferred to the catholyte. The resulting agitation of the catholyte may assist in providing an agitated flow of catholyte into the wafer feature 300. Further, when the scroll pump 75 has a diameter that is generally equal to or larger than the surface of the wafer, the agitated flow of the catholyte into other wafer features disposed across the diameter of the wafer is substantially the same for every wafer feature. The flow of copper ions with respect to the wafer feature 300 is shown by arrows 315. Since the pumping of the copper ions has components that are substantially perpendicular to the surface of the wafer 15, the ions may conformally plate the interior of wafer feature 300, thereby filling the feature with copper as shown in FIG. 6B.
FIG. 7 is a flowchart showing one method for plating a wafer. In operation 400 the wafer is received on a wafer support and driven to a processing position in operation 405. In operation 410, the plating solution is pumped in a direction substantially perpendicular to the surface of the wafer using a scroll pump disposed in a plating chamber. A plating potential is applied between at least one scroll of the scroll pump and a surface of the wafer 15 having a seed layer to plate the wafer surface at operation 415. Optionally, the wafer may be rotated at operation 420 while plating, or during a spinoff process that removes residual plating solution from the wafer surface under centrifugal force. At operation 425, the wafer support is driven to place the wafer in a position for removal by, for example, a robot.
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.

Claims

1. An electroplating apparatus for plating a metal onto a surface of a wafer, the apparatus comprising:

a wafer support configured to support a wafer; and

a processing base having a scroll pump oriented to pump a plating solution in a substantially perpendicular direction with respect to the surface of the wafer, wherein the scroll pump includes a first scroll and a second scroll, at least one scroll of the first and second scrolls being configured as an anode.

2. The electroplating apparatus of claim 1, wherein the diameter of the scroll pump is substantially the same as the diameter of the wafer.

3. The electroplating apparatus of claim 1, wherein the first scroll is fixed and the second scroll oscillates with respect to the first scroll.

4. The electroplating apparatus of claim 3, wherein the first scroll is configured as the anode.

5. The electroplating apparatus of claim 3, wherein the processing base includes a motor including a rotor having a cam, wherein the cam is configured to engage a cam follower disposed at a bottom portion of the second scroll to oscillate the second scroll with respect to the first scroll.

6. The electroplating apparatus of claim 1, wherein the first scroll and second scroll are configured to co-rotate in synchronous motion at offset centers of rotation.

7. The electroplating apparatus of claim 1, wherein the anode is a movable scroll.

8. The electroplating apparatus of claim 1, wherein the anode is a fixed scroll.

9. The electroplating apparatus of claim 1, wherein the processing base is configured to selectively provide the plating solution to the scroll pump from either a fresh supply path or a recirculation supply path.

10. The electroplating apparatus of claim 1, wherein the processing base comprises:

a catholyte chamber; and

an anolyte chamber, wherein the scroll pump is disposed in the anolyte chamber;

a membrane disposed between the anolyte chamber and the catholyte chamber; and

11. The electroplating apparatus of claim 1, further comprising a motor configured to rotate the wafer support.

12. The electroplating apparatus of claim 1, wherein processing base is configured so that plating solution from the scroll pump is driven to the surface of the wafer without an intermediate membrane.

13. The electroplating apparatus of claim 12, further comprising a porous element disposed between an upper portion of the scroll pump and the surface of the wafer.

14. The electroplating apparatus of claim 1, wherein both the first scroll and second scroll are configured as anodes.

15. A processing base for a wafer electroplating apparatus, the processing base comprising:

a scroll pump oriented to pump a plating solution in a substantially perpendicular direction with respect to a surface of the wafer, wherein the scroll pump includes a first scroll and a second scroll, at least one scroll of the first and second scrolls being configured as an anode; and

a scroll pump drive configured to operate the scroll pump.

16. The processing base of claim 15, wherein the diameter of the scroll pump is substantially the same as the diameter of the wafer.

17. The processing base of claim 15, wherein the scroll pump drive comprises a motor including a rotor having a cam, wherein the cam is configured to engage a cam follower disposed at a bottom portion of the second scroll to oscillate the second scroll with respect to the first scroll.

18. The processing base of claim 15, wherein the first scroll and second scroll are configured to co-rotate in synchronous motion at offset centers of rotation.

19. The processing base of claim 15, wherein the anode is a movable scroll.

20. The processing base of claim 15, wherein the anode is a fixed scroll.

21. The processing base of claim 15, wherein the processing base includes solution paths configured to selectively provide the plating solution from a fresh plating supply or recirculated plating supply pumped by the scroll pump.

22. The processing base of claim 15, further comprising:

a catholyte chamber; and

an anolyte chamber, wherein the scroll pump is disposed in the anolyte chamber; and

a membrane disposed between the anolyte chamber and the catholyte chamber.

23. The processing base of claim 15, wherein processing base is configured so plating solution from the scroll pump is driven to the surface of the wafer without an intermediate membrane.

24. A method for electroplating a surface of a wafer comprising:

placing the wafer in a processing position;

pumping plating solution in a direction substantially perpendicular to the wafer surface using a scroll pump; and

applying an electrical potential between at least one scroll of the scroll pump and the wafer surface.

25. The method of claim 24, further comprising rotating the wafer in the plating solution while in the processing position.

26. The method of claim 24, further comprising co-rotating scrolls of the scroll pump in synchronous motion at offset centers of rotation.

27. The method of claim 24, further comprising linearly oscillating a first scroll of the scroll pump with respect to a second scroll of the scroll pump.