Title:
Counter-electrode for electrodeposition and electroetching of resistive substrates
Kind Code:
A1


Abstract:
Various counter-electrodes for electroplating, electrodeposition or anodizing of substrates are disclosed. According to certain embodiments, multi-segmented counter-electrodes are provided. According to additional embodiments, counter-electrodes having concave or convex top surfaces are provided. The disclosed counter-electrodes enable greater control over electrodeposition, electroetching and anodizing processes for resistive substrates, as well as more uniform plating and etching of resistive substrates. Methods for electroplating, electrodeposition or anodizing of resistive substrates using multi-segmented counter-electrodes are also provided.



Inventors:
Andricacos, Panayotis C. (Croton-On-Hudson, NY, US)
Cooper, Emanuel I. (Scarsdale, NY, US)
Cotte, John M. (New Fairfield, CT, US)
Deligianni, Hariklia (Tenafly, NJ, US)
Andricacos, Caliopo (Chicago, IL, US)
Application Number:
11/155495
Publication Date:
12/21/2006
Filing Date:
06/20/2005
Assignee:
International Business Machines Corporation (Armonk, NY, US)
Primary Class:
Other Classes:
204/280
International Classes:
C25C7/02
View Patent Images:



Primary Examiner:
LEADER, WILLIAM T
Attorney, Agent or Firm:
INACTIVE - NOVAK DRUCE CONNOLLY BOVE (YOR) (Endicott, NY, US)
Claims:
We claim:

1. A multi-segmented counter-electrode for electrodeposition, electroetching or anodizing of resistive substrates, said multi-segmented counter-electrode comprising: a series of vertically stacked counter-electrode segments comprising a center counter-electrode segment, at least one middle counter-electrode segment disposed beneath said center electrode, and an outer counter-electrode segment disposed beneath said at least one middle electrode.

2. The multi-segmented counter-electrode of claim 1, wherein said center counter-electrode segment, said at least one middle counter-electrode segment and said outer counter-electrode segment are cylindrical in shape.

3. The multi-segmented counter-electrode of claim 2, wherein said at least one middle counter-electrode segment has a diameter that is larger than a diameter of said center counter-electrode segment and said outer counter-electrode segment has a diameter that is larger than the diameter of said at least one middle counter-electrode segment.

4. The multi-segmented counter-electrode of claim 1, wherein said at least one middle counter-electrode segment has a width that is larger than a width of said center counter-electrode segment and said outer counter-electrode segment has a width that is larger than the width of said at least one middle counter-electrode segment.

5. The multi-segmented counter-electrode of claim 1, wherein said at least one middle counter-electrode segment comprises two or more middle counter-electrode segments.

6. The multi-segmented counter-electrode of claim 1, wherein said center counter-electrode segment, said at least one middle counter-electrode segment, and said outer counter-electrode segment are constructed of a non-conductive material, and wherein an exposed portions of a top surface of each of said center counter-electrode segment, said at least one middle counter-electrode segment, and said outer counter-electrode segment is covered by a conductive layer.

7. A system comprising the multi-segmented counter-electrode of claim 1 and separate power supplies for each of said center counter-electrode segment, said at least one middle counter-electrode segment, and said outer counter-electrode segment.

8. A multi-segmented counter-electrode for electrodeposition, electroetching or anodizing of resistive substrates, said multi-segmented counter-electrode comprising: a center counter-electrode segment; at least one middle counter-electrode segment concentric with said center counter-electrode segment; an outer counter-electrode segment concentric with said center counter-electrode segment and said at least one middle counter-electrode segment; and a height-adjusting means arranged to individually adjust a height of at least one of the following: said center counter-electrode segment, said at least one middle counter-electrode segment and said outer counter-electrode segment.

9. The multi-segmented counter-electrode of claim 8, wherein said height-adjusting means comprises at least one shim disposed beneath at least one of the following: said center counter-electrode segment, said at least one middle counter-electrode segment, and said outer counter-electrode segment.

10. The multi-segmented counter-electrode of claim 8, wherein said height-adjusting means comprises at least one remotely-controlled element disposed beneath at least one of the following: said center counter-electrode segment, said at least one middle counter-electrode segment, and said outer counter-electrode segment.

11. The multi-segmented counter-electrode of claim 10, wherein said remotely controlled element comprises a pneumatic support.

12. The multi-segmented counter-electrode of claim 11, wherein the pneumatic support is connected to an air tube positioned along internal edges of an electrochemical cell.

13. The multi-segmented counter-electrode of claim 8, wherein adjacent counter-electrode segments among said center counter-electrode segment, said at least one middle counter-electrode segment, and said outer counter-electrode segment contact each other at low-friction vertical interfaces.

14. The multi-segmented counter-electrode of claim 8, wherein adjacent counter-electrode segments among said center counter-electrode segment, said at least one middle counter-electrode segment, and said outer counter-electrode segment are separated by a gap.

15. The multi-segmented counter-electrode of claim 8, wherein said center counter-electrode segment is cylindrical in shape, and wherein said at least one middle counter-electrode segment and said outer counter-electrode segment are annular in shape.

16. The multi-segmented counter-electrode of claim 15, wherein said at least one middle counter-electrode segment has an outer diameter that is larger than an outer diameter of said center counter-electrode segment and said outer counter-electrode segment has a diameter that is larger than the outer diameter of said at least one middle counter-electrode segment.

17. The multi-segmented counter-electrode of claim 8, wherein said center counter-electrode segment, said at least one middle counter-electrode segment, and said outer counter-electrode segment are constructed of a non-conductive material, and wherein an exposed portion of a top surface of each of said center counter-electrode segment, said at least one middle counter-electrode segment, and said outer counter-electrode segment is covered by a conductive layer.

18. The multi-segmented counter-electrode of claim 8, wherein said at least one middle counter-electrode segment comprises two or more middle counter-electrode segments.

19. A system comprising the multi-segmented counter-electrode of claim 8 and separate power supplies for each of said center counter-electrode segment, said at least one middle counter-electrode segment, and said outer counter-electrode segment.

20. A counter-electrode for electrodeposition, electroetching or anodizing of resistive substrates, wherein said counter-electrode comprises a concave or convex top surface.

21. A method for electroplating, electrodeposition or anodizing of resistive substrates, comprising: providing a multi-segmented counter-electrode comprising a series of vertically stacked counter-electrode segments; and selectively powering at least one of the counter-electrode segments.

22. The method of claim 21, wherein selectively powering at least one of the counter-electrode segments comprises powering at least two counter-electrode segments at equal current density.

23. The method of claim 21, wherein selectively powering at least one of the counter-electrode segments comprises powering at least two counter-electrode segments at different current densities.

24. A method for electroplating, electrodeposition or anodizing of resistive substrates, comprising: providing a multi-segmented counter-electrode comprising a series of concentric counter-electrode segments; and independently varying a height of at least one of the counter-electrode segments.

25. The method of claim 24, comprising selectively powering at least one of the counter-electrode segments.

26. The method of claim 25, wherein selectively powering at least one of the counter-electrode segments comprises powering at least two counter-electrode segments at equal current densities.

27. The method of claim 25, wherein selectively powering at least one of the counter-electrode segments comprises powering at least two counter-electrode segments at different current densities.

28. The method of claim 24, wherein the counter-electrode comprises at least one shim for independently varying the height of at least one of the counter-electrode segments.

29. The method of claim 24, wherein the counter-electrode comprises at least one remotely controlled element for independently varying the height of at least one of the selected counter-electrode segments.

30. The method of claim 24, wherein the at least one remotely controlled element comprises a pneumatic support.

Description:

BACKGROUND

In recent applications of electroplating such as Damascene plating of on-chip interconnects, the need for smaller electronic devices has resulted in the tendency to use thinner conductive seed layers, or the tendency to eliminate the conductive layer and plate on a high resistivity layer. The high active area density in Damascene plating, along with trends towards larger wafers, higher plating rates and stringent requirements of thickness uniformity have increased the need to control what is known as the “terminal effect.” The terminal effect, which is caused by the high ohmic drop within the seed layer and the plated deposit, results in highly non-uniform current distribution in the vicinity of electrical contacts during plating. The highly non-uniform current distribution can cause tremendous non-uniformity in thickness of the electrodeposited metal between areas in the vicinity of the electrical contacts and areas remote from these contacts. Similar effects are seen when the reversed polarity is used and the electrochemical process is one of electroetching or anodizing.

FIG. 1 shows a cross-section of a conventional electrolytic cell 10, which exhibits the terminal effect. The electrolytic cell 10 has a thin conductive layer electrode (cathode in the electrodeposition case), or seed layer 12, and a contact terminal 14 for contact at one end of the working electrode. The cell 10 further includes a non-conductive substrate or wafer 16 supporting the electrode 12, a counter-electrode (anode in the electrodeposition case) 18 and an electrolyte 20 disposed between the electrode 12 and the anode or counter-electrode 18. Exemplary current lines 22-32 in the cell 10 are shown in FIG. 1. As shown in FIG. 1, the current lines 22-32 are closely spaced near the contact terminal 14 on both the electrolyte side and within the conductive seed layer electrode 12. The spacing of the current lines 22-32 indicates that the local current density is high near the contact terminal 14. FIG. 2 shows the potential drop corresponding to current line 31, with reference to points A-D. As shown in FIG. 2, the potential drop is linear within the electrolyte 20. There is a sudden drop in potential at the interface of the electrolyte 20 and the electrode 12 because there is charge transfer and concentration overpotential on the electrolyte side of the interface and there is metal potential on the other side of the interface. The potential drop between points A and B is non-linear.

In many cases, the seed layer is of high resistivity and the resistance to passing current through the full distance between the terminal and the center of the electroprocessed substrate is very high. In such cases, the current lines will concentrate near the terminal and almost nothing will deposit at the substrate center because the high resistance of the electrode dominates the overall resistance of the electroplating circuit.

One known way to overcome the above-described terminal effect is to use current deflectors, known as “thieves”, that drive the current outward and away from the edges of the substrate and thus increase the relative current density to the substrate center and overall current uniformity. However, the use of current thieves in manufacturing significantly raises the cost of equipment processes and maintenance, because a current thief will deposit (or oxidize) the same metal or material as the workpiece, while consuming additional plating solution, and furthermore will need to be periodically stripped.

In view of the above, there remains a need for devices and methods for reducing the terminal effect and thereby promoting greater thickness uniformity in the electroprocessing of substrates.

SUMMARY

Various embodiments of novel counter-electrodes are disclosed herein. The novel counter-electrodes allow greater control over electrodeposition and electroetching processes for resistive substrates and enable more uniform plating and etching of resistive substrates as compared to known counter-electrodes.

According to one embodiment, a multi-segmented counter-electrode for electrodeposition, electroetching or anodizing of resistive substrates is provided, wherein the multi-segmented counter-electrode comprises: a series of vertically stacked counter-electrode segments comprising a center counter-electrode segment, at least one middle counter-electrode segment disposed beneath said center electrode, and an outer counter-electrode segment disposed beneath said at least one middle electrode.

According to another embodiment, a multi-segmented counter-electrode for electrodeposition, electroetching or anodizing of resistive substrates is provided, wherein the multi-segmented counter-electrode comprises: a center counter-electrode segment; at least one middle counter-electrode segment concentric with said center counter-electrode segment; an outer counter-electrode segment concentric with said center counter-electrode segment and said at least one middle counter-electrode segment; and a height-adjusting means arranged to individually adjust a height of at least one of the following: said center counter-electrode segment, said at least one middle counter-electrode segment and said outer counter-electrode segment.

According to further embodiments, counter-electrodes comprising concave or convex top surfaces are provided.

According to an additional embodiment, a method for electroplating, electrodeposition or anodizing of resistive substrates is provided, wherein said method comprises: providing a multi-segmented counter-electrode comprising a series of vertically stacked counter-electrode segments; and selectively powering at least one of the counter-electrode segments.

According to yet another embodiment, a method for electroplating, electrodeposition or anodizing of resistive substrates is provided, wherein said method comprises: providing a multi-segmented counter-electrode comprising a series of concentric counter-electrode segments; and independently varying a height of at least one of the counter-electrode segments.

Those skilled in the art will appreciate the above stated advantages and other advantages and benefits of various embodiments upon reading the following detailed description of the embodiments with reference to the below-listed drawings.

According to common practice, the various features of the drawings are not necessarily drawn to scale. Dimensions of various features may be expanded or reduced to more clearly illustrate the embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a traditional electrolytic cell for electroplating.

FIG. 2 is a plot of potential drops along a current line of FIG. 1.

FIG. 3 is a perspective view of a multi-segmented counter-electrode for electrodeposition and electroetching of resistive substrates, according to one embodiment.

FIG. 4 is a cross-sectional view of the counter-electrode of FIG. 3.

FIG. 5 is a cross-sectional view showing variable dimensions of the counter-electrode of FIG. 3.

FIG. 6 is a perspective view of a multi-segmented counter-electrode according to another embodiment, wherein the height of each segment of the counter-electrode is variable.

FIG. 7 is a cross-sectional view of a multi-segmented counter-electrode according to another embodiment.

FIG. 8 is a cross-sectional view of a counter-electrode having a concave top surface, according to another embodiment.

FIG. 9 is a cross-sectional view of a counter-electrode having a convex top surface, according to another embodiment.

FIG. 10A is a three-dimensional diagram of local sheet resistance of an electroplated surface produced by powering the center, middle and outer segments of a three-segment counter-electrode.

FIG. 10B is a three-dimensional diagram of local sheet resistance of an electroplated surface produced by powering only the center segment of three-segment counter-electrode.

FIG. 10C is a three-dimensional diagram of local sheet resistance of an electroplated surface produced by powering only the center and middle segments of three-segment counter-electrode.

FIG. 11A is a three-dimensional diagram of local sheet resistance of an electroplated surface produced on a relatively conductive substrate by powering only the center and middle segments of three-segment counter-electrode.

FIG. 11B is a three-dimensional diagram of local sheet resistance of an electroplated surface produced on a relatively resistive substrate by powering only the center and middle segments of three-segment counter-electrode.

DETAILED DESCRIPTION

FIGS. 3 and 4 show a novel, multi-segmented counter-electrode (anode) 100 including a series of vertically stacked, concentric counter-electrode segments 110, 120, 130. The design of the counter-electrode 100 may be referred to as a “layer cake” design. More specifically, the counter-electrode 100 includes an initial, or center segment 110, a second, or middle segment 120, and a final, or outer segment 130. The segments 110, 120, 130 may be made from any suitable resistive material, such as poly(propylene), poly(tetrafluoroethylyne) (PTFE), or poly(etheretherketone) (PEEK). Each counter-electrode segment 110, 120, 130 includes a side wall 112, 122, 132, a top surface 114, 124, 134 and a bottom surface 116, 126, 136. Conductive layers 118, 128, 138 cover exposed portions of the top surfaces 114, 124, 134 (i.e., portions that are not in contact with, and therefore are not covered by, the bottom surface of an adjacent counter-electrode segment). The conductive layers 118, 128, 138 may include a noble metal such as platinum, a structural metal coated with a noble metal, such as platinized titanium, or other metals that are essentially inert under the process conditions, or other suitable conductive materials including the metal being electrodeposited (or electroetched) at the working electrode. Each of the conductive layers 118, 128, 138 is fitted with at least one electrical contact (not shown) wired to an external power supply, preferably a separate power supply for each conductive layer. As can be seen in FIGS. 3 and 4, the entire top surface 114 of the center segment 110 is exposed, since there is no segment stacked on top of the center segment 110. Annular portions of the top surfaces 124 and 134 of the middle and outer segments 120 and 130 are exposed, because the central portions of top surfaces 124 and 134 are in contact with the respective bottom surfaces 116 and 126 of respective adjacent counter-electrode segments 110 and 120. As shown in FIGS. 3 and 4, the bottom surface 116 of segment 110 is in physical contact with the center portion of adjacent top surface 124 of the middle counter-electrode segment 120. Similarly, the bottom surface 126 of the middle counter-electrode segment 120 is in physical contact with the center portion of adjacent top surface 134 of the outer counter-electrode segment 130. Bottom faces 116 and 126 may be adhesively bonded to, or otherwise secured to top surfaces 124 and 134, respectively. As shown in FIGS. 3 and 4, the counter-electrode segments 110, 120, 130 may be cylindrical, so that they are suitable for electrodeposition or electroetching of rotating circular wafers. However, additional embodiments may include counter-electrode segments having various other geometric shapes, such as polygon shapes, for plating wafers of various planar shapes.

The center counter-electrode segment 110 has the smallest diameter (or width, in cases in which non-cylindrical counter-electrode segments are used) as compared to the diameters of segments 120 and 130, and is referred to as a “center” segment because its top face 114, and therefore its conductive layer 118, is exposed in the vicinity of the central axis Y of the counter-electrode 100. The middle counter-electrode segment 120 has a diameter larger than the diameter of the initial segment 110, and is referred to as the “middle” segment, because its top face 124, and thus its conductive layer 128, is exposed at a middle radial region of the counter-electrode 100. The outer counter-electrode segment 130 has the largest diameter as compared to the diameters of the segments 110 and 120, and is referred to as the “outer” segment because its top face 134, and therefore its conductive layer 138, is exposed at the outermost radial region of the counter-electrode 100.

FIG. 5 shows exemplary dimensions of the counter-electrode 100. Counter-electrode segments 110, 120 and 130 have respective radii r1, r2 and r3 and respective vertical heights h1, h2 and h3. It is noted that the differences in vertical height between adjacent counter-electrode segments (h1-h2, h2-h3) need not be uniform. Additionally, the differences in radii between adjacent counter-electrode segments (r1-r2, r2-r3) need not be uniform. In fact, the overall shape of a counter-electrode, such as counter-electrode 100, as well as the shape and dimensions of individual counter-electrode segments can be optimized for a given plating run. For example, a desired overall shape of a counter-electrode can first be calculated in a simulation model based on a set of global parameters (e.g., solution resistivity, distance between the center segment and the cathode, expected total current, seed layer resistivity) expected for an average plating run. Then, a multi-segmented counter-electrode, such as counter-electrode 100, can be constructed that approximates the shape predicted by the simulation model. Ideally, since the shape of the resultant counter-electrode has been optimized, the counter-electrode can be powered at equal current density across all counter-electrode segments, in which case a common power supply can be used. However, due to practical considerations, such as limits on the total height of the counter-electrode, it may not be possible to obtain an optimized shape of the counter-electrode for plating or etching with all counter-electrode segments powered at equal current density.

In order to provide greater control over an etching or deposition process, one or more of the counter-electrode segments 110, 120 and 130 may be individually powered. In order to individually power the segments 110, 120, 130, each segment 110, 120, 130 may be provided with an individual power supply (not shown). Thus, by selectively powering one or more counter-electrode segments, one can exercise greater control over the current field in the plating/etching circuit in order to achieve a uniform deposition or etching.

Greater control over an electrodeposition or electroetching process can be obtained by providing a multi-segmented counter-electrode having counter-electrode segments with variable interelectrode distances (i.e., variable heights), as shown in the embodiment of FIG. 6. With reference to FIG. 6, the counter-electrode 200 includes a cylindrical center counter-electrode segment 210 surrounded by a series of concentric annular counter-electrode segments including a middle counter-electrode segments 220, 230 and an outer counter-electrode segment 240. The design of the counter-electrode 200 may be referred to as a “scallion” design. Each of the exposed top surfaces 214, 224, 234, 244 of respective counter-electrode segments 210, 220, 230, 240 is covered with a respective conductive layer 218, 228, 238, 248, which may include any known conductive material suitable for electroetching or electrodeposition. The counter-electrode 200 further includes a respective height-adjusting means 250, 260, 270, 280 under each counter-electrode segment 210, 220, 230, 240 for independently adjusting the heights of the counter-electrode segments 210, 220, 230, 240. The height-adjusting means 250, 260, 270, 280 may comprise shims of various heights having diameters similar to the diameters of their respective counter-electrode segment. For example, a shim for the center segment 210 would be cylindrical, while shims for the middle segments 220, 230 and the outer segment 240 would be annular. When shims are used, each counter-electrode segment 210, 220, 230, 240 may be manually adjusted upward or downward between plating or etching runs by inserting or removing a respective shim. Alternatively, the height-adjusting means 250, 260, 270, 280 may comprise remotely controlled elements, such as pneumatic supports connected to air tubes (not shown) that are positioned along the internal edges of the electrochemical cell (not shown) so as to minimize interference with current lines in the electrochemical cell. When remotely controlled elements are used, the height of each counter-electrode segment 210, 220, 230, 240 can be controlled more rapidly and efficiently.

In order to allow the counter-electrode segments 210, 220, 230, 240 to move independently with respect to each other, adjacent counter-electrode segments must not be fixed together. Therefore, if the counter-electrode 200 is constructed such that adjacent anode sections contact each other, the vertical interfaces 202, 204, 206 of adjacent counter-electrode segments should be low-friction interfaces. Beyond polishing, low-friction interfaces may be achieved by applying a low-friction coating to contacting surfaces of adjacent counter-electrode segments, or by constructing the counter-electrode segments 210, 220, 230, 240 from a smooth low-friction material such as PTFE. Alternatively, the counter-electrode 200 should be constructed such that a solution-filled annular gap is provided between adjacent counter-electrode segments in lieu of the low-friction interfaces 202, 204, 206.

One way to compensate for the terminal effect during plating or etching processes, and therefore achieve more uniform plating or etching, is to increase the interelectrode distance (i.e., reduce the height of) of the counter-electrode segments that are closer to the workpiece edge (one or more of segments 220, 230 and 240) and to decrease the interelectrode distance (i.e., increase the height of) of the center counter-electrode segment 210, such that the center electrode 210 is brought vertically closer to the workpiece, while the counter-electrode segments that are closer to the workpiece edge are moved vertically further away from the workpiece.

Additionally, each segment 210, 220, 230, 240 of the counter-electrode 200 may be independently powered. Thus, the optimal conditions for achieving a uniform plating/deposition for a given plating/etching run (e.g., plating a particular type of substrate, at a particular plating rate, out of a particular plating solution, etc.) can then be defined by a combination of current profile and height profile of the segments 210, 220, 230, 240.

The counter-electrode 200 provides a very flexible solution to plating/etching. The use of counter-electrode segments 210, 220, 230, 240 that are independently height-adjustable increases the feasibility of connecting more than one segment to the same power supply, since it is possible to achieve more uniform plating/etching just based on varying the height of each segment 210, 220, 230, 240.

Although the counter-electrode 200 includes cylindrical and annular counter-electrode segments, other embodiments are possible which include counter-electrode segments of different shapes. For example, the center counter-electrode segment may have any given geometric shape, and the middle and outer counter-electrode segments may have similar shapes with hollow center portions.

FIG. 7 shows another multi-segmented counter-electrode 300, which includes a total of seven counter-electrode segments. The design of counter-electrode 300 is similar to that of counter-electrode 100, except that counter-electrode 300 includes more counter-electrode segments. As shown in FIG. 7, the counter-electrode 300 includes a center counter-electrode segment 310, middle counter-electrode segments 320, 330, 340, 350, 360, and outer counter-electrode segment 370. The counter-electrode segments 310, 320, 330, 340, 350, 360, 370 include respective conductive layers 318, 328, 338, 348, 358, 368, 378. In similar fashion to the embodiment of FIG. 4, the center counter-electrode segment 310 has the smallest diameter among the counter-electrode segments, while the outer counter-electrode segment 370 has the largest diameter among the counter-electrode segments. Proceeding vertically downward towards the outer segment 370, each middle counter-electrode segment 320, 330, 340, 350, 360 has a larger diameter than the preceding counter-electrode segment. As with the other embodiments discussed herein, the counter-electrode segments 310, 320, 330, 340, 350, 360, 370 may be individually powered, and/or may include means for independently adjusting their heights.

Although the multi-segmented counter-electrodes discussed in the preceding embodiments are shown having certain numbers of counter-electrode segments, it is possible to include any number of counter-electrode segments in the disclosed counter-electrodes. The number counter-electrode segments used will be determined based on the nature of the application.

FIG. 8 illustrates another novel counter-electrode 400. Counter-electrode 400 includes a concave top surface 410. The degree of concavity of the top-surface 410 can be varied to tailor current distribution in an electrolytic cell in order to achieve desired plating/etching results.

FIG. 9 illustrates yet another novel counter-electrode 500. The counter-electrode 500 includes a convex top surface 510. The degree of convexity of the top-surface 510 can be varied to tailor current distribution in an electrolytic cell in order to achieve desired plating/etching results. The current distribution of the counter-electrode 500 is inverse to the current distribution of the counter-electrode 400.

The advantages of certain embodiments disclosed herein are illustrated in the following examples:

EXAMPLES

In the following Examples 1-3, the results of which are illustrated in FIGS. 10A-10C, a platinized titanium, segmented counter-electrode having a construction similar to the construction shown in the embodiment of FIG. 5, was used to electroplate on a thin resistive seed layer having a thickness of 60 nm and a resistivity (μ) of 27 μohm·cm. Thus, the total sheet resistance (resistivity divided by thickness) of the seed layer was 4.5 ohm/square. Referring to FIG. 5, the respective dimensions were r1=37.5 mm; r2=70 mm, r3=102.5 m; h1=67 mm, h2=47 mm, h3=27 mm. Each segment was independently powered. The counter-electrode was positioned at the bottom of a cylindrical plating cell 250 mm in internal diameter and 150 mm high, which was filled with plating solution to a height of about 100 mm. Wafers 200 mm in diameter were held in a rotation-capable device, inserted into the solution face-down from above, positioned about 15 mm above the top of the counter-electrode, and plated at a cathodic current density of about 10 mA/cm2.

Example 1

The center, middle and outer counter-electrode segments were all powered at the same current density to form a deposit on the seed layer. The 3-D diagram of FIG. 10A maps the local sheet resistance of the resultant deposit. As shown in FIG. 10A, the local resistance of the deposit was highest towards the center of the deposit and lowest towards the edges of the deposit. The local sheet resistance is inversely proportional to the thickness of the deposit. Thus, it can be seen that the resultant deposit was edge thick. This example illustrates the previously discussed terminal effect.

Example 2

The center counter-electrode segment only was powered. The local sheet resistance of the resulting deposit is mapped in FIG. 10B. FIG. 10B shows that the local resistance of the deposit was highest towards the edges of the deposit and lowest at the center of the deposit. Thus, the deposit was center thick. This example illustrates that the thickness distribution can be nearly reversed when powering the center electrode only.

Example 3

The center and middle counter-electrode segments only were powered, to the same current density. The local sheet resistance of the resulting deposit is mapped in FIG. 10C. As shown in FIG. 10C, the local resistance of the deposit was highest part way towards the edges of the deposit, lower in the center of the deposit, and lowest at the very edge of the deposit. Thus, the deposit was center and edge thick, but more uniform than in the two previous examples.

Example 4

In this example, the same counter-electrode configuration and current distribution from the previous examples was used to electroplate two 200-mm wafers having widely different seed layer sheet resistances. In the case depicted in FIG. 11A, a 1-micron plated copper seed layer was used, having a sheet resistivity of about 0.02 ohm/square. Since the dominant resistance was through the electrolyte, the center-heavy current distribution resulted in a center-thick (lowest resistance at the center) plated sample. In the case depicted in FIG. 11B, on the other hand, a very thin seed layer of a more resistive metal was used, having a sheet resistivity of about 5 ohm/square. In this case the dominant resistance is through the seed layer, and as a result the plated sample was edge thick despite the mild corrective applied by means of the segmented anode (center and middle segments powered with identical current density). It is worth noting, however, that with the same high-resistance seed layer, the use of a non-segmented flat counter-electrode resulted in no plating at all in the central portion of the wafer (not shown). This example helps to demonstrate the inherent problem in using high resistance seed layers in large substrates, as well as the relative advantage of this invention's approach for such cases.

From the above examples, it is clear that the mere selective powering of different segments makes it possible to radically modify the thickness of the deposit. The uniformity can be further improved by fine-tuning the fractional current sent to each segment, by increasing the number of segments, and by modifying the dimensions of the segments.

The foregoing description illustrates and describes only selected embodiments, but it is to be understood that modifications within the scope of the inventive concept as expressed herein are possible, commensurate with the above teachings, and/or within the skill or knowledge of the relevant art. Accordingly, the description is not intended to limit the invention to the form disclosed herein. Also, it is intended that the appended claims be construed to include alternative embodiments, not explicitly defined in the detailed description.