TECHNICAL FIELD
The present invention is directed toward methods and apparatus for filling features in microfeature workpieces. For example, many embodiments of such methods and apparatus fill different features that have different critical dimensions in a manner that improves the ability to subsequently process the workpiece.
BACKGROUND
Microelectronic devices, such as semiconductor devices, imagers, and displays, are generally fabricated on and/or in microelectronic workpieces using several different types of machines (“tools”). Many such processing machines have a single processing station that performs one or more procedures on the workpieces. Other processing machines have a plurality of processing stations that perform a series of different procedures on individual workpieces or batches of workpieces. In a typical fabrication process, one or more layers of conductive materials are formed on the workpieces during deposition stages. The workpieces are then typically subject to etching and/or polishing procedures (i.e., planarization) to remove a portion of the deposited conductive layers for forming electrically isolated contacts and/or conductive lines.
Tools that plate metals or other materials on the workpieces are becoming an increasingly useful type of tool. Electroplating and electroless plating techniques can be used to deposit copper, solder, permalloy, gold, silver, platinum, electrophoretic resist, and other materials onto workpieces for forming blanket layers or patterned layers. A typical copper plating process involves depositing a copper seed layer onto the surface of the workpiece using chemical vapor deposition (CVD), physical vapor deposition (PVD), electroless plating processes, or other suitable methods. After forming the seed layer, a blanket layer or patterned layer of copper is plated onto the workpiece by applying an appropriate electrical potential between the seed layer and an anode in the presence of an electroprocessing solution. The workpiece is then cleaned, etched, and/or annealed in subsequent procedures before transferring the workpiece to another processing machine.
Electroplating tools can have a single-wafer processing station that includes a container for receiving a flow of electroplating solution from a fluid inlet at a lower portion of the container. The processing station can include an anode, a plate-type diffuser having a plurality of apertures, and a workpiece holder for carrying a workpiece. The workpiece holder can include a plurality of electrical contacts for providing electrical current to a seed layer on the surface of the workpiece. When the seed layer is biased with a negative potential relative to the anode, it acts as a cathode. In operation, the electroplating fluid flows around the anode, through the apertures in the diffuser, and against the plating surface of the workpiece. The electroplating solution is an electrolyte that conducts electrical current between the anode and the cathodic seed layer on the surface of the workpiece. Therefore, ions in the electroplating solution plate onto the workpiece.
The plating machines used in fabricating microelectronic devices must meet many specific performance criteria. For example, many plating processes must be able to form small contacts in vias or trenches that are less than 0.5 μm wide, and often less than 0.1 μm wide. A combination of organic additives such as “accelerators,” “suppressors,” and “levelers” are often added to the electroplating solution to promote bottom-up plating in the trenches. Accelerators, more specifically, cause higher plating rates in the bottom of a trench than along the sides of the trench to avoid pinching off the opening and forming voids in the trench.
One drawback of conventional plating processes is that the finished layer may have bumps or other raised features on the plated layer directly over the trenches. These bumps can make it more difficult to planarize the workpiece because more time is required to remove the excess material plated over the trenches, and the additional height of the bumps may adversely affect the final surface of the workpiece. Moreover, the bumps also cause more consumables to be used in the planarizing process. The use of accelerators, therefore, may adversely affect the throughput, product quality, and operating costs of subsequent planarizing processes.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A-1E are schematic side cross-sectional views illustrating stages of filling first and second features on a workpiece.
FIG. 2 is a flow chart illustrating a method in accordance with an embodiment of the invention.
FIGS. 3A-3D are schematic side cross-sectional views illustrating stages of filling features on microfeature workpieces in accordance with an embodiment of the invention.
FIG. 4 is a schematic side cross-sectional view of a stage of a method in accordance with another embodiment of the invention.
FIG. 5 is a schematic side cross-sectional view illustrating a plating machine for filling features on microfeature workpieces in accordance with an embodiment of the invention.
DETAILED DESCRIPTION
A. Overview
The present invention is directed toward methods and apparatus for filling features on microfeature workpieces. One aspect related to the invention is that plating processes tend to form bumps directly above trenches or other small depressions in the workpiece. Referring to FIG. 1A, microfeature devices are often formed on a workpiece 10 that has a plurality of first features 12 with a first size and at least one second feature 14 with a second size larger than the first size. The first features 12 can be trenches for forming damascene lines, vias for forming plugs or interconnects in the workpiece 10, or other depressions in the workpiece 10. The first features 12 are typically formed in the array regions of the workpiece 10 and have relatively small critical dimensions. The second feature 14 can be a trench, void, alignment mark, or another depression on the workpiece 10 that has a significantly larger opening or dimension than the first features 12. The second feature 14 can be located in the array region with the first features 12, but in many applications the second feature 14 is located in a peripheral region of a die. The first features 12 and the second feature 14, therefore, are not necessarily adjacent to each other as shown in the figures.
FIGS. 1B-1E illustrate the problems of plating processes that are resolved by several embodiments of the methods and apparatus in accordance with the invention. Referring to FIG. 1B, a typical plating process initially deposits a conformal layer 16 onto the workpiece 10 such that the conformal layer 16 lines the first features 12 and the second feature 14. FIG. 1C illustrates a subsequent stage of the plating process in which additional material has been plated onto the workpiece 10 so that the layer 16 fills the first features 12 but does not completely fill the second feature 14. Although the plating process could terminate at the stage illustrated in FIG. 1C, it is difficult to planarize the workpiece 10 at this point because planarizing pads tend to “dish” in the region of the second feature 14. As such, many plating processes continue to deposit additional material until the second feature 14 is completely filled.
FIGS. 1D and 1E illustrate subsequent stages in which the second feature 14 is filled with the material. FIG. 1D illustrates a subsequent stage in which bumps 17 or other projections grow directly above the first features 12 as additional material is deposited onto the workpiece 10. As more material is deposited onto the workpiece 10 to fill the second feature 14, the bumps 17 continue to grow. Referring to FIG. 1E, for example, the bumps 17 tend to grow at an accelerated rate until the layer 16 completely fills the second feature 14.
Several embodiments of methods and apparatus for filling features on microfeature workpieces in accordance with the invention at least mitigate the size of projections aligned with trenches or other types of depressions on a workpiece. The inventors discovered that non-uniform accumulations of accelerators on the plated surface typically cause more material to be deposited in direct alignment with the first features 12 than on other areas of the workpiece 10. Referring to FIG. 1B, the surface area of the portion of the layer 16 within the first features 12 is significantly larger than the area of the opening at the top of the first features 12. As the material continually deposits onto the workpiece 10, the surface area of the deposited layer 16 within the first features 12 continually decreases until it is flat or at least substantially flat as shown by the areas 18 in FIG. 1C. The inventors believe that this causes higher concentrations of the accelerator to accumulate over the first features 12 compared to other areas on the workpiece 10. The higher concentration of the accelerator over the first features 12 accordingly promotes faster deposition rates at these areas compared to other areas across the workpiece 10. As explained in more detail below, several embodiments of the methods and apparatus for filling features on microfeature workpieces eliminate or at least mitigate this problem to produce workpieces 10 that are better suited for planarization or other processes after the features have been filled.
One embodiment of a method for filling features on microfeature workpieces in accordance with the invention comprises contacting a surface of a microfeature workpiece with a plating solution that includes a plating species and an accelerator for enhancing deposition of the plating species in depressions on the workpiece. This method continues by filling first depressions on the workpiece via electrochemically depositing the plating species onto the workpiece to form a first portion of a plated layer that at least substantially fills the first depressions on the workpiece. The embodiment of this method further includes reducing a concentration of the accelerator on a surface of the plated layer after the plated layer at least substantially fills the first depressions, and then electroplating more of the plating species onto the workpiece after reducing the concentration of the accelerator on the surface of the plated layer.
Another embodiment of a method for filling features on microfeature workpieces is directed toward workpieces having first features with a first dimension and second features with a second dimension greater than the first dimension. In this embodiment, the method comprises contacting a surface of a microfeature workpiece with a plating solution having a plating species and an accelerator, and electrochemically depositing the plating species onto the workpiece to form a layer that at least substantially occupies the first features of the workpiece. This method further includes removing accumulations of the accelerator from a surface of the layer, and subsequently electroplating more of the plating species onto the workpiece after removing the accumulations of the accelerator to bulk plate the plating species into the second features.
Another embodiment of a method for filling features on a microfeature workpiece comprises contacting a surface of the microfeature workpiece with a plating solution having a plating species and an accelerator, and electrochemically depositing the plating species onto the workpiece until the plating species at least substantially fills first depressions on the workpiece. The electrochemical species forms a plated layer on the workpiece, and this method further includes changing the concentration of the accelerator on a surface of the plated layer at locations aligned with the first depressions. The method continues by electroplating more of the plating species onto the workpiece after changing the concentration of the accelerator on the plated layer to further deposit the plating species into a second depression on the microfeature workpiece that is larger than the first depression.
Still another embodiment of a method for filling features on microfeature workpieces in accordance with the invention includes contacting a surface of the microfeature workpieces with a plating solution having a plating species and an accelerator, and electrochemically depositing the plating species onto the workpiece until the plating species fills first depressions on the workpiece to form a plated layer on the workpiece. In this embodiment, the method further includes electrochemically removing (a) accumulations of the accelerator from a surface of the plated layer and (b) a portion of the plated layer to produce a restored surface on the plated layer. This method can further include electroplating more of the plating species onto the restored surface of the plated layer to increase the thickness of the plated layer.
Another aspect of the invention is directed toward systems for filling features on microfeature workpieces having first features with a first size and a second feature with a second size greater than the first size. One embodiment of such a system comprises a workpiece holder having electrical contacts configured to contact a surface of the workpiece, a plating vessel configured to contain a plating solution, a counter electrode in the plating vessel, and a power source coupled to the electrical contacts and the counter electrode to establish an electrical field through the plating solution in the plating vessel for electrochemically processing the workpiece. The system can further include a controller coupled to the power source. The controller can include a computer-operable medium that contains instructions which cause the power source to (a) electrochemically deposit a plating species in the plating solution onto the workpiece until the plating species at least substantially fills the first features, (b) change the concentration of the accelerator on a surface of a plated layer at locations aligned with the first features, and (c) electroplate more of the plating species onto the workpiece after changing the concentration of the accelerator on the plated layer.
FIGS. 2A-5 illustrate several methods and apparatus for filling features on microfeature workpieces in accordance with embodiments of the invention. Several specific details of the invention are set forth in the following description and in FIGS. 2A-5 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. The term “microfeature workpiece” is used throughout to include substrates upon which and/or in which microelectronic devices, micromechanical devices, data storage elements, 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 1 μm, and in many applications the critical dimensions of the smaller features on microfeature workpieces are less than 0.25 μm or even less than 0.1 μm. Furthermore, the terms “planarization” and “planarizing” mean forming a planar surface, forming a smooth surface (e.g., “polishing”), or otherwise removing materials from workpieces. 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.
B. Embodiments of Methods for Filling Features on Microfeature Workpieces
FIG. 2 is a flow chart illustrating a method 200 for filling features on microfeature workpieces in accordance with an embodiment of the invention. The method 200 includes a preliminary stage 210 in which a surface of a microfeature workpiece is contacted with a plating solution that includes a plating species and an accelerator for enhancing deposition of the plating species into depressions or other features on the workpiece. The workpiece can be similar to the workpiece 10 shown in FIG. 1A, and thus the workpiece can include first depressions having a first size and a second depression having a second size greater than the first size. The method 200 continues with a first plating stage 220 that includes at least partially filling the first depressions on the workpiece with the plating species by electrochemically depositing the plating species onto the workpiece to form a plated layer. The electrochemical process can be an electroless procedure and/or an electroplating procedure that deposits the plating species onto the workpiece. The first plating stage 220 generally plates the plating species onto the workpiece until the plated layer completely fills, or at least substantially fills, the first depressions.
The method 200 further includes a reconditioning stage 230 that includes changing the concentration of the accelerator or other additive on a surface of the plated layer after the first plating stage 220. As explained in more detail below, the reconditioning stage 230 can be accomplished by removing the accelerator from the plated layer or otherwise changing the concentration of the accelerator on the surface of the plated layer. The method 200 further includes a second plating stage 240 that comprises electroplating more of the plating species onto the workpiece after the reconditioning stage 230. The second plating stage 240 can comprise further filling the second depressions on the workpiece with additional material. FIGS. 3A-3E illustrate various embodiments of the stages 210-240 in further detail.
FIG. 3A illustrates the workpiece 10 being processed in accordance with an embodiment of the preliminary stage 210 of the method 200 illustrated in FIG. 2. At this stage, the workpiece 10 is placed in contact with a plating solution 310 that includes the plating species for plating a layer onto the workpiece and an accelerator for promoting deposition of the plating species in the closed ends 13 of the first features 12. The plating solution 310 can also include levelers, brighteners, suppressors, and/or other additives for controlling the deposition of the plating species. The plating species are generally metal ions, suitable electrophoretic photoresist materials, or other materials that can be plated onto the workpiece 10 using electroless plating and/or electroplating processes. In the embodiment illustrated in FIG. 3A, the workpiece 10 is coupled to a power supply 320 to define a working electrode, and a counter electrode 330 is also coupled to the power supply 320. When electroplating metals onto the workpiece 10, the workpiece 10 is a cathode biased at a negative potential and the counter electrode 330 is an anode biased at a positive potential to plate metal ions onto the workpiece 10. When electroplating electrophoretic photoresist materials, the workpiece 10 is typically an anode biased at a positive potential and the counter electrode 330 is typically a cathode biased at a negative potential to plate negatively charged electrophoretic resist molecules onto the workpiece 10. In either situation, the bias that plates the plating species onto the workpiece 10 is a forward bias or forward potential, and the bias that de-plates the plating species from the workpiece 10 is a reverse bias or reverse potential.
FIG. 3B illustrates an embodiment of the first plating stage 220 of the method 200 illustrated in FIG. 2. In this particular embodiment, the plating species has been electroplated onto the workpiece 10 to form the layer 16 and partially fill the first features 12. The layer 16 is a conformal layer that follows the topography of the workpiece 10 at this point in the method 200. The accelerator in the plating solution 310 causes the plating rate to be higher in the closed ends 13 of the first features 12 than at an exterior 19 of the workpiece 10. The first features 12 accordingly fill in a “bottom-up” manner to prevent producing voids within the first features 12. The first features 12 also fill up faster than the second feature 14 even when the depth of the first features 12 is the same as the second feature 14. The first plating stage 220 can use a continuous forward plating process in which the workpiece is a cathode and the counter electrode 330 is an anode. The first plating stage 220 can also use a pulsed plating process including only forward biased pulses and/or a combination of forward- and reverse-biased pulses.
FIG. 3C illustrates the workpiece 10 at the end of the first plating stage 220 and during the reconditioning stage 230 of the method 200 illustrated in FIG. 2. At the end of the first plating stage 220, the layer 16 at least substantially fills the first features 12, but the layer 16 does not need to substantially fill the second feature 14. In the particular embodiment illustrated in FIG. 3C, the plated layer 16 completely fills the first features 12, but not the second feature 14. The first plating stage 220 is terminated to form a surface 26a on the layer 16. As explained above, there is typically a non-uniform distribution of the accelerator on the surface 26a. The areas 18 in direct alignment with the first features 12, for example, can have a higher concentration of the accelerator than other areas of the surface 26a. The reconditioning stage 230 is then executed to reduce or otherwise change the concentration of the accelerator on the layer 16. One particular embodiment of the reconditioning stage 230 includes removing the accumulations of the accelerator from the layer 16 by de-plating a portion of the layer 16. For example, when the layer 16 is formed by an electroplating process in which the workpiece 10 is a cathode as shown in FIG. 3B, the accelerator can be removed from the layer 16 by applying a reverse bias so that the workpiece 10 is an anode and the counter electrode 330 is a cathode. This removes additives that have accumulated on the surface 26a and some of the layer 16 to form a restored or reconditioned surface 26b on the layer 16. It is expected that the reconditioned surface 26b is substantially free of any accelerators such that the distribution of the accelerator should be substantially constant across the layer 16 after the reconditioning stage 230.
In one embodiment of the reconditioning stage 230 of the method 200, the reverse bias is applied to the workpiece 10 for a period of time sufficient to de-plate approximately 1-100 angstroms of the layer 16. Several embodiments can de-plate more or less than this amount, such as removing only 2-5 angstroms of the layer 16 using a reverse bias for a short period of time (e.g., 100 milliseconds) or even up to 100 angstroms of material by applying the reverse bias for a longer period of time (e.g., 1-3 seconds). The reverse bias for changing the concentration of the accelerator on the layer 16 can be achieved by modifying typical reverse pulsed plating processes such that the reverse bias is applied for a significantly longer period of time (e.g., 4-10 times longer than a typical reverse pulse) and reducing the amp-minutes from approximately 7 amp-minutes to approximately 0.001 amp-minute.
FIG. 3D illustrates an embodiment of the second plating stage 240 of the method 200 illustrated in FIG. 2 in accordance with the invention. The second plating stage 240 includes bulk plating additional material from the plating solution 310 to the layer 16 until a finished surface 26c is formed at a desired thickness. In the embodiment shown in FIG. 3D, the plating species is bulk plated onto the workpiece 10 by applying a forward bias between the workpiece 10 and the counter electrode 330. The bulk plating process can continue until the layer 16 at least approximately fills the second feature 14 to mitigate dishing over the second feature 14 during subsequent chemical-mechanical planarization of the workpiece 10.
As illustrated in FIG. 3D, the finished surface 26c does not have bumps or projections directly aligned with the first features 12. This result is achieved because the reconditioning stage cleans the surface of the layer 16 so that the distributions of the accelerators, suppressors, and/or levelers is more uniform. The concentrations of these additives are expected to be at least substantially the same in the array areas and the periphery areas, and thus the plating rate in the second plating stage 240 is expected to be substantially the same across the workpiece 10. As a result, the second plating stage 240 should not form bumps or projections in alignment with the first features 12.
FIG. 4 is a schematic side cross-sectional view of the workpiece 10 illustrating another embodiment of the first plating stage 220 and reconditioning stage 230 of the method 200 illustrated in FIG. 2. In this embodiment, the first plating stage 220 includes terminating the electrochemical deposition of the plating species before the layer 16 completely fills the first features 12. At this point, the reconditioning stage 230 (FIG. 2) can be executed by reducing or otherwise changing the concentration of the accelerator and other additives that have adsorbed onto the surface of the workpiece 10. The reconditioning stage 230 of this embodiment can include de-plating a portion of the layer 16 in situ as described above with reference to FIG. 3C. After the concentration of the accelerator and/or other additives has been changed to recondition the surface of the layer 16, the second plating stage 240 can commence to increase the thickness of the layer 16 as described above with reference to FIG. 3D. Referring to both FIGS. 3C and 4, filling the first depressions to form a plated layer of material that at least substantially fills the first features 12 includes either completely filling the first features 12 (FIG. 3C) or nearly filling the first features 12 (FIG. 4) before removing the accelerator and/or other additives from the surface of the plated layer.
FIG. 5 is a schematic side cross-sectional view of a system 500 for filling features on microfeature workpieces in accordance with an embodiment of the invention. In this embodiment, the system 500 includes a workpiece holder 510 having electrical contacts configured to contact a surface of the workpiece 10, a plating vessel 520 having an inlet 522 through which a plating solution 524 can flow into the vessel 520, and a counter electrode 530. The system 500 optionally can include a flow distributor 540 having a plurality of openings 542 for conditioning the flow of the plating solution 524 upstream from the workpiece 10. The system 500 can further include a power supply 550 operatively coupled to the workpiece holder 510 and the counter electrode 530. As explained above, the power supply 550 establishes an electrical field in the plating vessel 520 for electrochemically processing the workpiece 10 by plating and/or de-plating the plating species to/from the workpiece 10.
The system 500 further includes a controller 560 coupled to the power supply 550. The controller 560 includes a computer operable medium that contains instructions to effectuate any of the methods for filling features on microfeature workpieces set forth above. The computer operable medium of the controller 560, for example, can contain instructions that cause the power supply 550 to (a) electrochemically deposit the plating species onto the workpiece 10 until the plating species at least substantially fills first features on the workpiece, (b) change the concentration of the accelerator and/or another additive on a surface of a plated layer of the plating species aligned with the first features, and (c) electroplate more of the plating species onto the workpiece after changing the concentration of the accelerator and/or other additives on the surface of the plated layer. In another embodiment, the computer operable medium can contain instructions that cause the power source to (a) electrochemically deposit the plating species onto the workpiece to form a plated layer that fills first depressions on the workpiece, (b) electrochemically remove accumulations of the accelerator and a portion of the plated layer to produce a reconditioned surface on the plated layer, and (c) electroplate more of the plating species onto the reconditioned surface of the plated layer.
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. Accordingly, the invention is not limited except as by the appended claims.
Patent Application
20070045120
