US20070261964A1

US20070261964A1 - Reactors, systems, and methods for electroplating microfeature workpieces

Info

Publication number: US20070261964A1
Application number: US11/432,164
Authority: US
Inventors: Gregory Wilson; Paul McHugh; Kyle Hanson; Rajesh Baskaran
Original assignee: Semitool Inc
Current assignee: Semitool Inc
Priority date: 2006-05-10
Filing date: 2006-05-10
Publication date: 2007-11-15

Abstract

Reactors, systems and methods for electroplating and/or electro-etching microfeature workpieces. Reactors in accordance with the invention have a first chamber configured to direct a first processing solution to a processing zone, a second chamber configured to contain a second processing solution different than the first processing solution, and an ion exchange membrane between the first chamber and the second chamber. The reactors also include (a) a support member in the first chamber that contacts the ion exchange membrane across the surface of the membrane, and (b) a counter electrode in the second chamber. The ion exchange membrane enables a low conductivity catholyte to be used in the first chamber and an inert counter electrode in the second chamber. More specifically, the ion exchange membrane prevents nascent oxygen that evolves from the inert counter electrode from reaching the catholyte to reduce oxidation of constituents of the catholyte, consumption of organic additives in the anolyte, and/or accumulation of bubbles and particulates at the workpiece.

Description

TECHNICAL FIELD

This application relates to reactors, systems, and methods for electroplating microfeature workpieces having a plurality of microdevices integrated in and/or on the workpieces. Particular aspects of the present invention are directed toward electroplating workpieces using a low-profile reactor.

BACKGROUND

Microfeature devices, such as semiconductor devices, imagers, displays, and micromechanical components, are generally fabricated on and/or in microfeature workpieces using a number of machines that deposit and/or etch materials from the workpieces. Many current microfeature devices have interconnects and other very small sub-micron sized features (e.g., 45-110 nanometers) formed by depositing materials into small trenches or holes. One particularly useful process for depositing materials into small trenches and/or vias is electroplating. Typical electroplating techniques include plating processes that deposit copper, solder, permalloy, gold, silver, platinum, electrophoretic resist, and other materials onto the workpieces.
One challenge of plating metals into narrow, deep trenches or holes is that it is very difficult to completely fill the very small features without creating voids or other non-uniformities in the metal. For example, an ultra thin seed layer must be used to deposit a metal into a trench having a dimension of 45 nm to 250 nm so that the trench has sufficient vacant space for the subsequently plated metal. Ultra thin seed layers, however, are problematic because they may not cover the workpiece uniformly. For example, ultra thin seed layers may have voids or other non-uniform physical properties that can result in non-uniformities in the plated material. This is particularly common on the side walls of such small features. These challenges can be overcome by plating onto the seed layers or plating a seed layer directly on a barrier layer to provide competent seed layers that are well-suited for bulk plating metals into trenches or holes with small critical dimensions. One particularly useful method is to plate a material using a processing solution with a low conductivity. Suitable electrochemical processes for forming competent seed layers are disclosed in U.S. Pat. No. 6,197,181, which is herein incorporated by reference.
One problem with low conductivity baths, however, is that they require more power to plate the material onto the workpieces compared to acidic plating solutions with high conductivities. As a result, conventional reactors require larger power supplies to operate with the low conductivity baths used for plating onto seed layers or plating directly onto barrier layers. This increases the operating costs of conventional reactors because they consume more power, and it may be inconvenient because the facility may need to be renovated to provide high-voltage power outlets. Another challenge of using low conductivity baths is that they are generally more sensitive to shielding and geometries of the system. As such, non-uniformities in the electrical field near the anode are more likely to cause non-uniformities on the workpiece compared to highly conductive baths.
Plating onto seed layers or plating materials directly onto barrier layers in high pH processing solutions presents additional challenges. For example, inert anodes are generally required in high pH processing solutions because the high pH passivates consumable copper anodes. This generally produces copper hydroxide particles and/or flakes that may create defects on the wafer. However, one drawback of using inert anodes is that the deposited material exhibits a significant increase in resistivity over a relatively small number of plating cycles (e.g., short bath life). The resistivity of the deposited layers can be maintained in a desired range by frequently changing the processing solution, but this increases the operating costs of electrochemically processing seed layers and/or depositing materials directly onto barrier layers.
As a result, there is a need for a reactor that reduces power consumption, enables the use of inert anodes in low conductivity processing solutions, and enables use of high pH processing solutions.

SUMMARY OF THE INVENTION

The present invention provides electroplating reactors for processing seed layers, depositing materials directly onto barrier layers, and/or depositing materials onto microfeature workpieces in other applications. The reactors enable the use of an inert anode and a low conductivity processing solutions so that the reactors of the invention are not plagued by the flaking problems associated with using consumable anodes in high pH solutions. The reactors achieve this result by significantly reducing or eliminating oxidation of certain constituents of the processing solution to prolong its operating life. This reduces the operating costs of using the reactor because the tool does not need to be frequently shut down to change out the processing solution. A further benefit of reactors in accordance with the invention is that they are designed to operate within conventional power consumption ranges and still plate a uniform layer of material on a seed layer or directly on a barrier layer. The reactors also enable the use of high pH processing solutions in the same system. As a result, reactors in accordance with the invention are expected to further reduce the operating costs of electroplating seed layers, depositing materials directly onto barrier layers using low conductivity processing solutions, and/or using high pH processing solutions.
One aspect of reactors in accordance with the invention is that they have a first chamber configured to direct a first processing solution to a processing zone, a second chamber configured to contain a second processing solution different than the first processing solution, and an ion exchange membrane between the first chamber and the second chamber. The reactors also include (a) a support member in the first chamber that contacts the ion exchange membrane across the surface of the membrane, and (b) a counter electrode in the second chamber. The ion exchange membrane enables a low conductivity catholyte to be used in the first chamber and an inert counter electrode in the second chamber. More specifically, the ion exchange membrane prevents nascent oxygen that evolves from the inert counter electrode from reaching the catholyte. This reduces oxidation of constituents of the catholyte, which results in good quality deposits over a long bath life. The ion exchange membrane is also quite useful in applications that use a low conductivity, high pH catholyte. Therefore, reactors of the invention provide a platform for using inert counter electrodes for precision plating processes.
The support member provides several advantages for using a low-profile reactor. The support member contacts the ion exchange membrane to impart the desired contour or profile to the membrane. This prevents the membrane from having a shape that disturbs the electrical field or traps bubbles. The support member also directs a flow of the first processing solution over the ion exchange membrane and toward the processing zone, and the support member configures the electrical field in the first chamber. The support member enables the reactors to reduce the distance between the processing zone and the electrode in the second chamber so that less power is required to establish a sufficient electrical field compared to conventional reactors. Reactors in accordance with the invention accordingly enable the use of low conductivity, high pH processing solutions with conventional power supplies that are already widely used in plating tools.
Several other features of the reactors in accordance with the invention enhance the uniformity of the layers deposited onto the workpieces. For example, the electrode in the second chamber can be shaped to further enhance the uniformity of the electrical field at the processing zone. Therefore, several embodiments of reactors in accordance with the invention also enable the uniform deposition of materials onto workpieces using low conductivity, high pH processing solutions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a reactor for electrochemically processing microfeature workpieces in accordance with an embodiment of the invention.
FIG. 2 is a schematic diagram illustrating the operation of a reactor in accordance with an embodiment of the invention.
FIG. 3 is a graph illustrating the resistivity of deposited layers as a function of bath age using a conventional reactor and a reactor in accordance with an embodiment of the invention.
FIG. 4 is a schematic illustration showing the operation of a reactor in accordance with another embodiment of the invention.
FIG. 5 is a cross-sectional view of a specific embodiment of a reactor for electrochemically processing microfeature workpieces in accordance with the invention.
FIG. 6 is a cross-sectional view illustrating a portion of the reactor shown in FIG. 5.
FIG. 7A is a cross-sectional view of a support member for use in a reactor in accordance with an embodiment of the invention.
FIG. 7B is a bottom plan view of the support member shown in FIG. 7A.
FIG. 7C is a detail view of a portion of the support member shown in FIG. 7B.
FIG. 8 is a cross-sectional view of a counter electrode for use in a reactor in accordance with an embodiment of the invention.
FIG. 9 is an isometric view of a seal for use in a reactor in accordance with an embodiment of the invention.

DETAILED DESCRIPTION

FIGS. 1-9 illustrate several embodiments of reactors, methods, and systems for electrochemically processing seed layers, plating directly onto barrier layers, and depositing materials in other applications. Several specific details of the invention are set forth in the following description and in FIGS. 1-9 to provide a thorough understanding of certain embodiments of the invention. One skilled in the art, however, will understand that the present invention may have additional embodiments, or that other embodiments of the invention may be practiced without several of the specific features explained in the following description.
FIG. 1 schematically illustrates a reactor 100 for plating onto seed layers, directly onto barrier layers, or otherwise depositing other materials onto workpieces. The reactor 100 includes a vessel 102, a first chamber 110 configured to direct a flow of first processing solution to a processing zone 112, and a second chamber 120 configured to contain a second processing solution separate from the first processing solution. An ion exchange membrane 130 separates the first processing solution in the first chamber 110 from the second processing solution in the second chamber 120, but selected ions can pass through the ion exchange membrane 130. The ion exchange membrane 130 may be an anion selective membrane in applications in which it is desirable to allow anions to pass between the first and second chambers 110 and 120, or the ion exchange membrane 130 may be a cation selective membrane in applications in which it is desirable to allow cations to move between the first and second chambers 110 and 120. The ion exchange membrane 130 enables the use of an inert counter electrode with an anolyte in the second chamber 120 and a catholyte in the first chamber 110. More specifically, because the ion exchange membrane 130 prevents oxygen that evolves from an inert electrode from affecting the conductivity of the catholyte in the first chamber 110, counter electrode 160 may be an inert electrode. Moreover, the ion exchange membrane 130 also prolongs bath life and prevents bubbles from accumulating at the wafer. The reactor 100, therefore, reduces the operating costs associated with using an inert counter electrode because the inert counter electrode does not affect the operating life of the catholyte in the first chamber 110.
The reactor 100 further includes a workpiece holder 140 having a plurality of electrical contacts 142 for applying an electrical potential to a workpiece W mounted to the workpiece holder 140. The workpiece holder 140 can be a movable head configured to position the workpiece W in the processing zone 112 of the first chamber 110, and the workpiece holder 140 can further be configured to rotate the workpiece W in the processing zone 112. Suitable workpiece holders are disclosed in U.S. Pat. Nos. 6,080,291; 6,309,520; 6,527,925; 6,773,560; and U.S. patent application Ser. No. 10/497,460; all of which are incorporated herein by reference. In applications that use low conductivity baths, it is expected that “dry” contact assemblies that seal against the perimeter of the workpiece are efficacious. Suitable dry contact assemblies are disclosed in U.S. Pat. Nos. 6,773,560 and 6,309,520. Such dry contact assemblies are also useful for plating onto high resistance layers (e.g., seed layer enhancement or direct-on-barrier plating).
The reactor 100 further includes (a) a support member 150 in the first chamber 110 that contacts a first surface 132 of the membrane 130, and (b) a counter electrode 160 in the second chamber 120. The support member 150 spaces the ion exchange membrane 130 apart from the workpiece processing zone 112 by a controlled distance. This feature provides better control of the electrical field at the processing zone 112 because the distance between the ion exchange membrane 130 and the workpiece processing zone 112 affects the electrical field at the processing zone 112. The support member 150 generally contacts the first surface 132 of the ion exchange membrane 130 such that the distance between the first surface 132 and the processing zone 112 is substantially the same across the first chamber 110. Another feature of the support member 150 is that it also shapes the ion exchange membrane 130 so that bubbles do not collect along a second side 134 of the membrane 130. The support member 150 can also be configured to impart a slanted or non-planar contour to the ion exchange membrane 130 for increasing/decreasing the strength of the electrical field in local regions of the processing zone 112 or providing additional bubble control.
The support member 150 is further configured to direct a flow F₁of the first processing solution laterally across the first surface 132 of the ion exchange membrane 130 and vertically to the processing zone 112. The support member 150 accordingly controls the flow F₁of the first processing solution in the first chamber 110 to provide the desired mass-transfer characteristics in the processing zone 112. The support member 150 also shapes the electrical field in the first chamber 110. The upper surface of the support member 150, for example, can be contoured to shape the electrical field within the reactor or otherwise control the electrical field of the workpiece. These features of the support member 150 enable the reactor 100 to provide good electrical and mass-transfer properties at the processing zone 112 with a relatively short distance D₁between the processing zone 112 and the counter electrode 160. As a result, the reactor 100 is particularly well suited for use with low conductivity processing solutions because less power is required to establish the desired electrical field at the processing zone 112 over the relatively short distance D₁compared to conventional reactors in which the space in between the workpiece W and the counter electrode is significantly larger.
The counter electrode 160 is spaced apart from the second surface 134 of the ion exchange membrane 130 by a gap distance D₂such that a flow F₂of the second processing solution moves radially outward across the second surface 134 of the ion exchange membrane 130 at a relatively high velocity. The flow F₂of the second processing solution accordingly sweeps oxygen bubbles and/or particles from the ion exchange membrane 130. The short distance D₂also limits the volume of the second processing solution in the second chamber 120 so that the second processing solution can be quickly withdrawn from the second chamber 120. The reactor 100 further includes a flow restrictor 170 around the counter electrode 160. The flow restrictor 170 is a porous material that creates a back pressure in the second chamber 120 to provide a uniform flow between the counter electrode 160 and the second surface 134 of the ion exchange membrane 130. As a result, the electrical field can be consistently maintained because the flow restrictor 170 mitigates velocity gradients in the second processing solution where bubbles and/or particles can collect. The configuration of the counter electrode 160 and the flow restrictor 170 also maintains a pressure in the second chamber during plating that presses the ion exchange membrane 130 against the support member 150 to impart the desired contour to the ion exchange membrane 130.
The reactor 100 operates by positioning the workpiece W in the processing zone 112, directing the flow F₁of the first processing solution through the first chamber 110, and directing the flow F₂of the second processing solution through the second chamber 120. As the first and second processing solutions flow through the reactor 100, an electrical potential is applied to the workpiece W via the electrical contacts 142 and the counter electrode 160 to establish an electrical field in the first and second chambers 110 and 120. When the counter electrode 160 is inert, the ion exchange membrane 130 prevents bubbles and particles from entering the first chamber 110. As such, the bubbles that evolve from the counter electrode 160 are carried out of the second chamber 120 by the flow F₂of the second processing solution.
The reactor 100 enables the efficient use of inert electrodes and/or low conductivity solutions for several reasons. First, the ion exchange membrane 130 mitigates oxidation of constituents in the first processing solution(e.g., chelating agents or other organic/inorganic species). Second, the total distance D₁between the workpiece W and the counter electrode 160 is significantly less than conventional reactors. This reduces the power necessary to establish the requisite electrical field through low conductivity processing solutions, which reduces the operating costs of the reactor 100 compared to conventional reactors. Third, the support member 150 controls the shape of the ion exchange membrane 130 and the flow F₁of the first processing solution in the first chamber to provide the desired electrical field and mass-transfer characteristics in the processing zone 112. The support member 150 enables the total distance D₁between the processing zone 112 and the counter electrode 160 to be relatively short without unduly sacrificing the desired electrical and mass-transfer properties at the processing zone 112.
The reactor 100 illustrated in FIG. 1 is particularly useful for processing ultra thin seed layers and/or plating materials directly on barrier layers because it is well suited for using an inert anode and a low conductivity, high pH processing solution that provides the necessary nucleation for seed layer processing and direct-on-barrier plating. More specifically, the ion exchange membrane allows an inert anode to be used because the membrane prevents nascent oxygen produced by inert anodes in such solutions from oxidizing constituents in the catholyte and/or accumulating at the workpiece. This arrangement accordingly improves the bath life of the catholyte to improve the operating costs of the reactor. The support member enhances control of the catholyte flow and the electrical field near the workpiece processing zone so that the low conductivity of the processing solution does not affect the quality of the plated layer. The reactor 100 is accordingly well suited for plating onto ultra-thin seed layers and/or directly onto a barrier layer.
Furthermore, gold plating or plating other precious metal or other metals that depend on use of an inert anode are plating processes that are candidates for membrane reactors employing an anion exchange membrane because the anodic process can be separated from the catholyte by the ion exchange membrane. Properties of gold deposits (such as roughness) will be fairly constant over the bath life. The bath stability and bath life of these plating processes can be greatly improved by isolating the plating species from the rest of the bath solutions. The anodic oxidation reaction in the anolyte of these plating baths does not influence the chelating agents or other organic agents for precious metal plating in the catholyte. The reactor can be operated in a continuous fashion indefinitely with no anode maintenance as the metal salt is added as a solution to the catholyte side and the metal ions are plated. The counter ions move across the membrane and pass into solution in the anolyte—where hydroxyl ions are lost due to the inert anodic reaction of oxygen production.
Furthermore, there are advantages in using an anion exchange membrane reactor plating for Sn (and other metals with multiple valence states). Any metal with multiple valence states can be plated from most of their stable states. Since the charge required to deposit any metal is directly proportional to the electrons required for their reduction, metals in their valence states closest to their neutral states consume less energy for reduction to metal. However most of the metals in their closest state with their valence are inherently unstable, and therefore production worthy plating is not feasible. With the reactor of this invention inherently unstable plating solutions can still be applied for a production worthy process because the separation of the anodic and cathodic process results in lesser oxidation of the inherently unstable metal species.
Most Sn—Ag—Cu alloy plating solutions prefer Sn(II) as the species for Sn plating. For such alloy plating systems, the control of Sn, Ag and Cu ions needs to be tight and the use of Sn, Ag, Cu as an anode is ruled out. These anode systems could not only cause stability issues by plating/reacting with the anodes, but also pose a problem for uniform metal replenishment. The use of inert anodes, however, causes nascent oxygen which not only oxidizes any organics in the plating bath, but also oxidizes Sn(II) to a stable Sn((V) ion. To prevent problems from occurring in such baths, the use of an inert anode anionic membrane reactor in accordance with this invention can greatly simplify replenishment schemes, and does not oxidize any organic agents or any metal species. This separation between catholyte and anolyte is ideal to solve such problems encountered in plating baths. The baths are relatively more stable, and the bath life can be extended.
Furthermore, for systems that use chelated baths, high pH, or other systems where inert anodes are used, the reactor of this invention can be very beneficial. First and foremost the advantages of using the membrane reactor of this invention for a high pH Cu bath with a chelating agent are: (a) the conductivity and pH of the catholyte is fairly constant; (b) the properties of deposit (eg. resistivity) are constant with bath age; (c) the chelating agent is not oxidized at the inert anode; (d) bubbles from the inert anode reaction are removed and therefore do not cause problems to the cathode; and (e) changes in the conductivity and pH of the anolyte are isolated from the catholyte and therefore the impact of such changes on the catholyte are minimized.
FIG. 2 schematically illustrates an example of the operation of the reactor 100 using an anion exchange membrane in a high pH environment suitable for processing seed layers and/or plating directly onto barrier layers. In this example, the first processing solution in the first chamber 110 is a catholyte having a low concentration of copper ions (e.g., copper sulfate-CuSO₄), a complexing agent (e.g., ethylenediamine-En) chelated with the copper ions, boric acid (H₂BO₃ ⁻) as a pH buffer, and tetramethylammonium hydroxide (TMAH) to adjust the pH of the solution to be alkaline (e.g., approximately 9-10). The second processing solution in the second chamber 120 is an anolyte. The anolyte has a pH approximately equal to the catholyte (e.g., 9-10), and the anolyte includes H₂BO₃ ⁻, TMAH, and other constituents.
During a plating cycle, the second processing chamber 120 is filled with the anolyte and an electrical potential is applied to the workpiece W and the counter electrode 160. As the copper ions are removed from the catholyte and plated onto the workpiece, sulfate ions SO₄ ²⁻ accumulate in the catholyte near the first surface 132 of the ion exchange membrane 130. Additionally, the positively charged counter electrode 160 causes hydroxyl ions OH⁻ at the inert counter electrode 160 to liberate oxygen and produce water. This creates a charge gradient that causes the negatively charged sulfate ions to move from the first surface 132 to the second surface 134 of the ion exchange membrane 130. The transfer of negatively charged sulfate ions from the catholyte to the anolyte during a plating cycle maintains the charge and mass balance of the system. Additionally, to maintain the concentration of boric acid in the catholyte during plating, the concentration of boric acid in the anolyte is significantly greater than that of the catholyte to prevent the boric acid in the catholyte from moving to the anolyte during plating. It should be noted that during an idle state the anolyte level is dropped to separate the anolyte from the ion exchange membrane to prevent boric acid from crossing the ion exchange membrane 130. The hydroxyl ions could also move from the catholyte to the anolyte during plating, but they are inhibited from moving by maintaining the at least approximately the same pH level in both solutions.
The operation of the reactor 100 in the example set forth in FIG. 2 significantly increases the operating life of the catholyte compared to conventional reactors without the ion exchange membrane 130. FIG. 3 is a graph illustrating test results showing the resistivity of several 20 nanometer seed layers deposited using a conventional reactor (line A) and the reactor 100 (line B) relative to the bath age measured in Amp-minutes. As shown in FIG. 3, the resistivity of seed layers deposited using a reactor without the ion exchange membrane 130 (line A) increases rapidly with the age of the bath. The example shown in FIG. 3 indicates that the bath life in reactors without the ion exchange membrane is less than 2000 Amp-minutes. The resistivity of seed layers deposited in the reactor 100 with the ion exchange membrane 130 (line B), however, only increases gradually over time such that little change was observed even at 10,000 Amp-minutes. These results can be achieved with the reactor 100 because the nascent oxygen generated at the inert anode in the second chamber 120 is prevented from passing to the first chamber 110 where it can oxidize the ethylenediamine. Moreover, because the ethylenediamine does not cross the ion exchange barrier 130, there is no oxidation of this complexing agent in the anolyte. As a result, the pre-anneal resistivity of electrochemically deposited films using the reactor 100 is only minimally affected by using an inert anode in a high pH solution. The significant increase in the operating life of the anolyte and the catholyte compared to reactors without an ion exchange membrane reduces the operating costs of the reactor 100 because the reactor does not need to be removed from production to frequently change the processing solution.
Another feature of the operation of the reactor 100 in the example illustrated in FIG. 2 is that pH does not drop significantly in the catholyte solution. As a result, tetramethylammonium hydroxide is not added to the catholyte, and therefore tetramethylammonium hydroxide does not accumulate in the catholyte. This simplifies the maintenance of both the catholyte and the anolyte to further prolong the operational life of the first and second processing solutions. Therefore, the reactor 100 maintains the catholyte composition, eliminates oxidation problems associated with using an inert anode, and maintains consistent electrical properties of the deposited layer over a long bath life.
FIG. 4 illustrates an example of the operation of the reactor 100 using a cation membrane. In this embodiment, the anolyte has a low pH (e.g., 1.4) and the catholyte has a high pH (e.g., 9.5). This causes proton migration (H⁺) from the anolyte to the catholyte through the ion exchange membrane 130. The protons replace the charge of the copper cations that are plated from the catholyte to the workpiece. The reaction at the counter electrode produces the protons by evolving oxygen via the consumption of water. To maintain the high pH in the catholyte, tetramethylammonium hydroxide is added to the catholyte. The cation exchange membrane used in the example of FIG. 4 also prevents oxygen produced at the counter electrode from oxidizing constituents (e.g., ethylenediamine) in the catholyte to provide a suitably long bath life in a manner similar to that described above with reference to FIGS. 2 and 3. However, tetramethylammonium (TMA⁺) and sulphate ions (SO₄) build up in the catholyte as the bath ages. This can limit the life of the bath to a certain extent, but by no means to the extent caused by oxidation of the ethylenediamine in the catholyte. Therefore, the reactor 100 with a cation exchange membrane is also advantageous compared to reactors without an ion exchange membrane.
FIG. 5 is a cross-sectional view illustrating a reactor 500 in accordance with a specific embodiment of the invention. The reactor 500 is similar to the reactor 100, and thus it is particularly well suited for operating with inert anodes. The reactor 500 includes a vessel 502, a first chamber 510 for containing a first processing solution, and a second chamber 520 for containing a second processing solution. The reactor 500 further includes the ion exchange membrane 130 between the first chamber 510 and the second chamber 520, a support member 550 in the first chamber 510, and a counter electrode 560 in the second chamber 520. The first processing solution can be a catholyte and the second processing solution can be an anolyte to achieve the results explained above with reference to the reactor 100. Additional aspects of the reactor 500 are further directed toward specific embodiments of components that provide the desired electrical field and/or mass transfer properties at the workpiece processing zone in a low-profile reactor. Therefore, in addition to providing a prolonged bath life for applications using an inert electrode, the reactor 500 further provides good electrical and mass transfer properties at the processing zone in low-profile reactors that consume less power.
The first chamber 510 illustrated in FIG. 5 has an inner vessel 512 within the vessel 502, and the inner vessel 512 has an inner wall 513 and a rim 514 at the top of the wall. The wall 513 guides the flow F₁of the first processing solution to a workpiece processing zone near the rim 514 and shapes the perimeter of the electrical field. In the reactor 500 shown in FIG. 5, the wall 513 defines an opening slightly smaller than the diameter of the workpiece to shield a peripheral portion of the workpiece from the electrical field.
FIG. 6 is a detailed cross-sectional view of the portion of the reactor 500 identified in FIG. 5. The inner vessel 512 can further include an inlet 516 through which the first processing solution flows into the first chamber 510. The inlet 516 of the first chamber initially passes upwardly through the inner vessel 512 and then flows downwardly toward the support member 550. The inner vessel 512 can also include a vent 517 near the apex of the inlet 516 for venting bubbles in the flow F₁of the processing solution. As explained in more detail below with reference to the support member 550, the support member 550 directs or otherwise distributes the flow relative to the ion exchange membrane 130 and/or a processing zone near the rim 514. The support member 550, for example, can distribute the flow F₁of the first processing solution across the first surface of the ion exchange membrane 130 and direct the flow F₁upwardly through the inner vessel 512 toward the processing zone. The flow F₁of the first processing solution proceeds to pass over the rim 514 and exit through a chamber 518 between the inner vessel 512 and the vessel 502. In low profile applications for plating onto ultra-thin seed layers and/or directly onto barrier layers, the depth of the first chamber between the upper surface of the ion exchange membrane 130 and the processing zone is approximately 1 inch to 6 inches. Other depths, however, may be used in other applications. For applications using low conductivity processing solutions, the depth and geometry of the processing chamber is desirably configured to use relatively low cell potentials. In a specific example, the depth and geometry of the processing chamber can be configured so that a cell potential of less than approximately 20V can be used with processing solutions having conductivities of about 0.5 mS/cm to about 50 mS/cm, or more specifically about 3 mS/cm to about 10 mS/cm, or still more specifically about 5 mS/cm. The chamber, however, need not be limited for use with such low cell potentials and low conductivity solutions in many applications.
FIG. 7A is a cross-sectional view of the support member 550, FIG. 7B is a bottom plan view of the support member 550, and FIG. 7C is a detailed view of a portion of FIG. 7B. Referring to FIGS. 5-7C together, the support member 550 is a dielectric member defining a flow director that receives the flow F₁of the first processing fluid from the inlet 516 (shown in FIG. 6). The support member 550 includes a plurality of standoffs 552 that contact the upper surface of the ion membrane 130 to impart the desired contour to the ion membrane 130 during processing. The standoffs 552, for example, can be lands with bearing surfaces that contact the upper surface of the ion exchange membrane 130 to control the profile of the ion exchange membrane 130. The standoffs 552 are spaced apart from one another to form a plenum 554 in a lower portion of the support member 550 through which the flow F₁of the first processing solution passes across the upper surface of the ion membrane 130. One aspect of the support member 550 is that the plenum 554 provides a desired flow distribution across the ion membrane 130. For example, the standoffs 552 can be posts arranged such that the plenum 554 provides a flow across the upper surface of the ion exchange membrane 130. The standoffs 552 can be arranged to restrict the flow through selected regions of the plenum 554 in other embodiments to provide different flow rates across in different areas of the support member 550.
The support member 550 further includes a plurality of openings 556 that direct the flow F₁of the first processing solution upwardly toward a processing zone near the rim 514 of the inner vessel 512. The openings 556 are generally arranged in a pattern to provide a generally uniform flow of the first processing solution in a direction normal to a plane at the rim 514 of the inner vessel 512, but the openings 556 can be arranged to provide a non-uniform flow toward the workpiece. For example, the openings 556 can have a uniform size and distribution across the support member 550, or the support member 550 can have a first region with first openings and a second region with second openings that are configured to provide different flow rates and/or different field components of the electric field. The first and second openings can have different sizes and/or be arranged in different patterns. The openings 556 also act as virtual electrodes that define the shape of the electrical field in the lower portion of the inner vessel 512. To avoid creating high magnitude points in the electrical field at the processing zone, the spacing between the openings 556 can be correlated with the distance to the processing zone. For example, the distance to the processing zone can be at least the distance between the openings 556. In operation, the workpiece holder (not shown in FIGS. 5-7B) rotates the workpiece in the processing zone to mitigate the affect of local non-uniformities in the flow and the electric field.
In an alternative embodiment, the support member in the first chamber 510 is a porous material that provides a highly uniform distribution of the electrical field and the flow of the first processing solution. The porous material can be a porous ceramic, a porous plastic, or any other suitable porous material. Although porous support members may provide a highly controlled distribution of the processing solution in the electrical field, they may also be a source of particles that can contaminate the workpiece. In still additional embodiments of the support member, the upper surface of the support member 550 can be contoured to shape the electrical field in the first chamber 510. For example, the center of the support member 550 can have a thickness that is less than the thickness at the perimeter to provide a higher current at the center of the wafer relative to the perimeter. This may enable more uniform plating on high resistance seed layers or allow a desired non-uniform plating shape (e.g., a dome or dish) for subsequent chemical-mechanical planarization. Additional embodiments of the support member 550 can include a non-uniform pattern of openings 556 to provide different flow rates and current densities in the first chamber 510. For example, the density or size of the openings can be greater at a center region of the support member 550 than at a perimeter region to increase the deposition rate at the center of the region relative to the perimeter region.
Referring back to FIGS. 5 and 6, the second chamber 520 is under the ion membrane 130, and the counter electrode 560 in the second chamber 520 is spaced apart from the ion membrane 130 by a small gap to provide a small channel for the flow F₂of the second processing solution (as shown in FIG. 6). More specifically, the flow F₂enters the second chamber 560 through an inlet 563 (FIG. 5) and progresses radially outwardly through a small gap 564 (FIG. 6) between an upper surface of the counter electrode 560 and the lower surface of the ion exchange membrane 130 (FIG. 6). The flow F₂of the second processing solution also passes through an annular flow restrictor 570 around the perimeter of the counter electrode 560 and into a channel in the lower part of the second chamber 520. The flow restrictor 570 is a ring of a porous polymeric material or other porous dielectric material. Referring to FIG. 6, the counter electrode 560 is surrounded by a dielectric strap 568 to electrically separate the counter electrode 560 from the flow restrictor 570. This provides better control of the shape of the electrical field at the counter electrode 560. The depth of the second chamber 520 can be less than that of the first chamber 510. For example, in applications for plating onto ultra-thin seed layers and/or directly onto barrier layer, the gap between the ion exchange membrane 130 and the upper surface of the counter electrode 560 can be approximately 0.05 inch to 2 inches. This gap, however, is not limited to these dimensions in other applications.
In operation, the second processing solution level can be lowered during an idle state to separate the second processing solution from the ion exchange membrane so that ions do not pass through the ion exchange membrane. For example, when the reactor 500 is operated using an anion membrane as described above with reference to FIG. 2, the anolyte is lowered so that H₂BO₃ ⁻ ions do not pass from the anolyte to the catholyte. During a plating cycle, the flow F₂of the second processing solution passes through the gap 564 (FIG. 6) so that the anolyte in the second processing chamber 520 is at a higher pressure than the catholyte in the first processing chamber 510. This drives the ion exchange membrane 130 against the standoffs 552 of the support member 550 to impart the desired contour to the ion exchange membrane 130 during a plating cycle. The small volume of anolyte in the gap 564 allows the second chamber 520 to be quickly drained/filled so that only a short period of time is spent transitioning between the idle state and a plating cycle.
FIG. 8 is a cross-sectional view of an embodiment of the counter electrode 560 used in the second chamber 520 of the reactor 500 shown in FIG. 5. The counter electrode 560 can have an exposed surface 565 with a curved central region 567 a and a generally planer upper region 567 b. The curved central region 567 a has a slope that avoids flow separation as the flow turns from an axial flow to a radial flow and along at least a portion of the radial flow. The curved region 567 a also provides added electrical current flow in the region of the opening. This feature, for example, reduces the impacton the electrical field caused by having a central inlet through the counter electrode. The counter electrode can alternatively have conventional shapes with straight side walls at the inlet and a planer upper region in other embodiments.
Referring to FIGS. 5 and 6, the reactor 500 further includes a seal 900 for sealing the ion exchange membrane 130 in a manner that prevents leakage between the first and second processing solutions. FIG. 9 is an isometric view illustrating the seal 900 in greater detail. The seal 900 can have a C-shape with a slot 910 between a lower flange 912 and an upper flange 914. Referring to FIG. 6, the perimeter of the ion exchange membrane 130 is received in the slot 910 and a lock-ring 920 with teeth 922 is pressed against the seal 900 to clamp the ion exchange membrane 130 in the slot 910. The seal 900 is expected to provide significant advantages over using conventional O-ring seals because many types of ion exchange membranes wick fluids to the perimeter region of the membranes. The seal 900 captures fluids that wick through the ion exchange membrane 130 in the slot 910 when the teeth 922 of the lock-ring 920 are pressed against the seal 900. As a result, the seal 900 prevents leakage between the first and second processing solutions that occurs in conventional systems with O-ring seals.
The term “microfeature workpiece” is used throughout to include substrates upon which and/or in which microelectronic devices, micromechanical devices, data storage elements, micro-optics, and other features are fabricated. For example, microfeature workpieces can be semiconductor wafers, glass substrates, dielectric substrates, or many other types of substrates. Microfeature workpieces generally have at least several features with critical dimensions less than or equal to one micron, and in many applications the critical dimensions of the smaller features on microfeature workpieces are less than 0.25 micron or even less than 100 nanometers. Furthermore, the terms “electrochemical processing” and “electrochemical deposition” include both electroplating processes and electroless plating processes. Where the context permits, singular or plural terms may also include the plural or singular term, respectively. Moreover, unless the word “or” is expressly limited to mean only a single item exclusive from other items in reference to a list of at least two items, then the use of “or” in such a list is to be interpreted as including (a) any single item in the list, (b) all of the items in the list, or (c) any combination of the items in the list. Additionally, the term “comprising” is used throughout to mean including at least the recited feature(s) such that any greater number of the same features and/or types of other features and components are not precluded.
From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the spirit and scope of the invention. For example, the reactors and systems disclosed herein are not limited for use with low conductivity, high pH solutions. In many applications, the processing solution can have only a low conductivity, only a high pH, or neither a low conductivity nor a high pH. Accordingly, the invention is not limited except as by the appended claims.

Claims

1. A reactor for electrochemical processing of microfeature workpieces, comprising:

a vessel;

a workpiece holder having an electrical contact to apply an electrical potential to a workpiece, wherein the workpiece holder is configured to position a workpiece in a processing zone relative to the vessel;

a first chamber in the vessel configured to direct a first processing solution to the processing zone;

an inlet at the first chamber;

a second chamber in the vessel configured to contain a second processing solution different than the first processing solution;

an ion exchange membrane between the first chamber and the second chamber, the ion exchange membrane having a first surface facing the first chamber and a second surface facing the second chamber;

a support member in the first chamber at the inlet, wherein the support member contacts the ion exchange membrane across the first surface of the ion exchange membrane and directs a flow of the first processing solution from the inlet toward the processing zone; and

an electrode in the second chamber.

2. The reactor of claim 1 wherein the support member comprises a flow distributor having plate, standoffs projecting from the plate and contacting the first surface of the ion exchange membrane, and openings through the plate.

3. The reactor of claim 2 wherein the standoffs and the openings are configured to direct a flow of the first processing solution across the first surface of the ion exchange membrane and upwardly through the openings.

4. The reactor of claim 2 wherein the plate has a first region and a second region, and wherein the openings include first openings in the first region and second openings in the second region that are configured to provide a first electrical field component relative to the first region and a second electrical field component relative to the second region.

5. The reactor of claim 1 wherein the support member spans across the first surface of the ion exchange membrane, and wherein the support member has a plenum over the first surface of ion exchange membrane and outlets above the plenum through which a flow of the first processing solution passes toward the workpiece processing zone.

6. The reactor of claim 1 wherein the support member comprises a plate having a first side contacting the first surface of the ion exchange membrane to control a profile of the ion exchange membrane across the vessel and a second side facing the processing zone.

7. The reactor of claim 6 wherein the plate has lands with bearing surfaces at the first side in contact with the ion exchange membrane and a flow channel configured to distribute a flow of the first processing solution across the first surface of the ion exchange membrane.

8. The reactor of claim 1 wherein the electrode in the second chamber comprises an inert anode.

9. The reactor of claim 1 wherein the electrode in the second chamber has a planar upper region and a curved central region with a slope that provides at least a substantially constant area of electrode surface relative to a radial position across the processing zone.

10. The reactor of claim 1, further comprising a seal encompassing a peripheral edge of the ion exchange membrane.

11. The reactor of claim 10 wherein the seal comprises a ring having a C-shaped cross-section with a slot configured to receive a peripheral portion of the ion-exchange membrane.

12. The reactor of claim 11, further comprises a clamp engaged with the seal to press a first portion of the seal against the first surface of the ion exchange membrane and a second portion of the seal against the second surface of the ion exchange membrane.

13. The reactor of claim 1, further comprising a flow diffuser around the perimeter of the electrode.

14. The reactor of claim 13, further comprising a dielectric strap between the perimeter of the electrode and the flow diffuser.

15. The reactor of claim 1 wherein the first chamber comprises a catholyte compartment and the second chamber comprises an anolyte compartment.

16. The reactor of claim 1 wherein the ion exchange membrane comprise at least one of an anion exchange membrane and a cation exchange membrane.

17. The reactor of claim 1 wherein the first chamber has a first depth between the ion exchange membrane and the processing zone of approximately 0.5 inch to 6 inches and the second chamber has a gap between a perimeter portion of the electrode and the ion exchange membrane of approximately 0.05 inch to 2 inches.

18. The reactor of claim 1 wherein:

the plate has lands with bearing surfaces at the first side in contact with the ion exchange membrane and a flow channel configured to distribute a flow of the first processing solution across the first surface of the ion exchange membrane;

the electrode in the second chamber comprises an inert anode; and

the first chamber comprises a catholyte compartment and the second chamber comprises an anolyte compartment.

19. The reactor of claim 1 wherein:

the support member spans across the first surface of the ion exchange membrane, and wherein the support member has a plenum over the first surface of ion exchange membrane and outlets above the plenum through which a flow of the first processing solution passes toward the workpiece processing zone;

the electrode in the second chamber comprises an inert anode; and

the ion exchange membrane comprise at least one of an anion exchange membrane and a cation exchange membrane.

20. The reactor of claim 1 wherein:

the electrode in the second chamber comprises an inert anode;

the ion exchange membrane comprise at least one of an anion exchange membrane and a cation exchange membrane; and

the first chamber has a first depth between the ion exchange membrane and the processing zone of approximately 0.5 inch to 6 inches and the second chamber has a gap between a perimeter portion of the electrode and the ion exchange membrane of approximately 0.05 inch to 2 inches.

21. A reactor for electrochemical processing of microfeature workpieces, comprising:

a vessel;

a flow director in the first chamber juxtaposed to the first surface of the ion exchange membrane, the flow director being configured to (a) distribute the first processing solution across the first surface of the ion exchange membrane and (b) direct the first processing fluid to the processing zone; and

an electrode in the second chamber.

22. The reactor of claim 21 wherein the flow director comprises support member having plate, standoffs projecting from the plate and contacting the first surface of the ion exchange membrane, and openings through the plate.

23. The reactor of claim 22 wherein the standoffs and the openings are configured to direct a flow of the first processing solution across the first surface of the ion exchange membrane and upwardly through the openings.

24. The reactor of claim 22 wherein the plate has a first region and a second region, and wherein the openings include first openings in the first region and second openings in the second region that are configured to provide a first electrical field component relative to the first region and a second electrical field component relative to the second region.

25. The reactor of claim 22 wherein the flow director comprises a support member that spans across the first surface of the ion exchange membrane, and wherein the support member has a plenum over the first surface of ion exchange membrane and outlets above the plenum through which a flow of the first processing solution passes toward the workpiece processing zone.

26. The reactor of claim 21 wherein the flow director comprises a plate having a first side contacting the first surface of the ion exchange membrane to control a profile of the ion exchange membrane across the vessel and a second side facing the processing zone.

27. A reactor for electrochemical processing of microfeature workpieces, comprising:

a workpiece holder having an electrical contact to apply an electrical potential to a workpiece, wherein the workpiece holder is configured to position a workpiece in a processing zone;

an ion exchange membrane having a first side and a second side;

a first flow cell on the first side of the ion exchange membrane configured to contain a first processing fluid, the first flow cell having a first inlet through which the first processing solution can flow;

a first flow distributor in the first flow cell configured to (a) direct a flow of the first processing solution from the inlet to the first side of the ion exchange membrane and (b) shape the first side of the ion exchange membrane;

a second flow cell on the second side of the ion exchange membrane configured to contain a second processing solution separately from the first processing solution; and

an electrode in the second flow cell, wherein the electrode is spaced apart from the ion exchange membrane by a gap through which a flow of the second processing solution can move radially outwardly across the second side of the ion exchange membrane.

28. The reactor of claim 27, further comprising a flow diffuser around the perimeter of the electrode.

29. The reactor of claim 28, further comprising a dielectric strap between the perimeter of the electrode and the flow diffuser.

30. The reactor of claim 27 wherein the first flow cell comprises a catholyte compartment and the second flow cell comprises an anolyte compartment.

31. The reactor of claim 27 wherein the ion exchange membrane comprise at least one of an anion exchange membrane and a cation exchange membrane.

32. The reactor of claim 27 wherein the first flow cell has a first depth between the ion exchange membrane and the processing zone of approximately 0.5 inch to 6 inches and the gap between the electrode and the ion exchange membrane is approximately 0.05 inch to 2 inches.

33. An apparatus for electrochemically processing a seed layer on a microfeature workpiece, comprising:

a vessel;

an ion exchange membrane between the first chamber and the second chamber, the ion exchange membrane having a first surface facing the first chamber and a second surface facing the second chamber; and

an inert electrode in the second chamber, wherein the electrode is spaced apart from the processing zone by a distance to provide a sufficient electrical field in a high pH processing solution suitable for seed layer processing using 120V power.

34. The apparatus of claim 33 wherein the distance between the electrode and the processing zone is approximately 1 inch to 6 inches.

35. The apparatus of claim 33 wherein the distance between the electrode and the processing zone is approximately 1.5-4 inches.

36. An apparatus for electrochemically processing a microfeature workpiece, comprising:

a vessel;

a seal encompassing a peripheral edge of the ion exchange membrane.

37. The apparatus of claim 36 wherein the seal comprises a ring having a C-shaped cross-section with a slot configured to receive a peripheral portion of the ion-exchange membrane.

38. The apparatus of claim 36, further comprising a clamp engaged with the seal to press a first portion of the seal against the first surface of the ion exchange membrane and a second portion of the seal against the second surface of the ion exchange membrane.

39. A method of electrochemically processing microfeature workpieces, comprising:

directing a flow of a first processing solution across a first surface of an ion exchange membrane and to a workpiece processing zone in a first flow cell of a vessel;

directing a flow of a second processing solution across a second surface of the ion exchange membrane facing a second flow cell of the vessel, wherein the first processing solution is different than the second processing solution; and

supporting a middle portion of the first surface of the ion exchange membrane while directing the flow of the second processing solution across the second surface of the ion exchange membrane.

40. The method of claim 39, further comprising providing a support member extending across the first flow cell, wherein the support member has a first side contacting a middle portion of the first surface of the ion exchange membrane and a flow channel through which the flow of first processing solution flows across the first surface of the ion exchange membrane.

41. The method of claim 40, wherein the support member further comprises openings facing the processing zone, and wherein directing the flow of the first processing solution comprises passing the first processing solution through the openings to the workpiece processing zone.

42. The method of claim 39 wherein the first processing solution comprises a catholyte and the second processing solution comprises an anolyte.

43. The method of claim 42, further comprising passing an electrical current between an electrode in the second flow cell and a workpiece at the processing zone in the first flow cell.

44. The method of claim 42, further comprising passing an electrical current between an inert electrode in the second flow cell and a workpiece at the processing zone in the first flow cell.

45. The method of claim 44, further comprising using the first processing solution for more than 2,000 Amp-minutes before changing out the first processing solution.

46. The method of claim 44, further comprising using the first processing solution for more than 8,000 Amp-minutes before changing out the first processing solution.

47. The method of claim 39, further comprising:

raising the second processing solution to contact the second surface of the ion exchange membrane;

passing an electrical current between an inert electrode in the second flow cell and a workpiece at the processing zone in the first flow cell while the second processing solution contacts the second surface of the ion exchange membrane; and

lowering the second processing solution from the second surface of the ion exchange membrane after processing a surface of the workpiece.

48. The method of claim 39, further comprising:

providing a first processing solution comprising a low conductivity, high pH catholyte;

49. The method of claim 48, further comprising using the first processing solution for more than 2,000 Amp-minutes before changing out the first processing solution.

50. The method of claim 48, further comprising using the first processing solution for more than 8,000 Amp-minutes before changing out the first processing solution.

51. The method of claim 48, further comprising plating material onto an ultra-thin seed layer while passing the electrical current between the inert electrode and the workpiece.

52. The method of claim 48, further comprising plating material onto an ultra-thin seed layer and exposed portions of a barrier layer under the seed layer while passing the electrical current between the inert electrode and the workpiece.

53. The method of claim 48, further comprising plating material directly onto a barrier layer while passing the electrical current between the inert electrode and the workpiece.

54. The method of claim 39 wherein the first processing solution comprises a catholyte and the second processing solution comprises an anolyte, and wherein the method further comprises using the second processing solution for a cycle period before changing out the second processing solution such that a desired conductivity and ion concentration gradient are maintained in the first processing solution.

55. The method of claim 39 wherein the first processing solution comprises a catholyte and the second processing solution comprises an anolyte, and wherein the method further comprises using the second processing solution for at least 400 Amp-minutes before changing out the second processing solution.