Patent Application
20150090599
The disclosed embodiment relates generally to a method and apparatus for electrochemical deposition, and more particularly to a method and apparatus for electrochemical deposition using an insoluble anode.
Electrochemical deposition, among other processes, is used as a manufacturing technique for the application of films, for example, tin, tin silver, nickel, copper or otherwise to various structures and surfaces, such as semiconductor wafers and silicon work pieces or substrates. An important feature of systems used for such processes is their ability to produce films with uniform and repeatable characteristics such as film thickness, composition, and profile relative to the underlying workpiece profile. Electrochemical deposition systems may utilize an anode to provide current to an electroplating solution that is in contact with the substrate. The characteristics of the film may be influenced by a variety of factors that result in thickness profile across the substrate. For example, the film may be thicker near the substrate edge than in the center or vice versa. The thickness variation may impact the electrical characteristics of the devices being formed on the substrate. Thickness variations may vary from substrate to substrate and process to process and may require hardware reconfigurations of the hardware. Such reconfiguration can be expensive and can require significant down time of the electrochemical deposition tool or sub module for service and process requalification that adversely affects the cost of ownership of the deposition tool. Accordingly, there is a desire for new and improved methods and apparatuses for controlling film thickness in electrochemical deposition tools.
Broadly, electrochemical deposition may include the transfer of metal ions from a metal source (e.g., anode) in a chemical solution to a substrate (e.g., cathode) that may also be immersed in the solution. The metal ion transfer may be enabled by applying current to the metal source causing metal ions to dissolve into the chemical solution. The metal ions may migrate through the solution and may plate or couple to the substrate. It is sometimes preferable to use an insoluble anode for electrochemical deposition. When this is used, the electrochemical deposition process works as previously described except the metal ions deposited onto the wafer are not replenished by dissolution of the anode. In some instances, the metal ions may not plate uniformly across the substrate due to various chemical, electrical, and mechanical aspects of the plating bath that includes the metal source, substrate, and the chemical solution.
One aspect of the thickness variation may be related to the current density within the plating bath or the solution. The current density may be non-uniformly distributed across the anode due to the physical characteristics of the plating bath, substrate, and/or the anode. Hence, the anode may be designed to control or influence current density at the cathode by optimizing current density uniformity at localized regions of the anode.
In one instance, the anode assembly may be designed to provide current uniformly across the anode by incorporating a plurality of anodes uniformly throughout a surface of the anode assembly. Current density across the anode assembly may be controlled or optimized by selectively turning on or off one or more of the plurality of anodes. The anodes may be controlled by electrical switches that may turn an anode on or off by allowing or restricting current flow from a single power source. The control resolution of the current density may be related to the size or diameter of the anode assembly and the diameter and arrangement of the anodes. Mounting height of each anode with respect to the insulating support piece can also be used to optimize near-anode interactions. The control resolution will be higher as the diameter of the anode decreases and the distribution of the anodes becomes denser. Near-anode interaction can be adjusted by mounting the anodes in a protruded, recessed, or planar fashion with respect to the insulating mounting piece. The higher control resolution and tuned near-anode interaction may enable a more uniform current density across the anode assembly which may result in a more uniform thickness on the substrate.
In one embodiment, the anodes may be coupled to a single power source that can provide a substantially similar amount of current to each of the anodes. However, other chemical, electrical, and/or mechanical factors may result in non-uniform current distribution at the substrate. These non-uniformities result in deposition non-uniformity on the substrate. High edge thickness is the most common deposition non-uniformity pattern observed. Accordingly, a select group of anodes proximate to the edge of the anode assembly may be turned off to decrease the current density at the edge without decreasing current density at the center of the anode assembly.
In another embodiment, one portion of the anodes may be collectively controlled by a single electrical switch and another portion of the anodes may each be individually controlled by a corresponding switch. In this way, at least one group of anodes may be turned on or off at the same time by a single switch while at least one or more individual anodes may be turned on or off by an electrical switch dedicated to that individual anode. The groups of anodes may be covering an area of the anode assembly that may inherently have uniform current density. While the individual anodes may be covering another area of the anode assembly that has a higher degree of current density non-uniformity. For example, a group anodes located near the center of the anode assembly may be controlled by a single switch and anodes near the edge of the anode assembly may be controlled by individual switches. Accordingly, the anodes near the edge may be selectively turned off to minimize the amount of current flowing into the solution. This may compensate for other factors contributing to deposition thickness non-uniformity resulting in a more evenly distributed deposit across the substrate. Hence, the arrangement or location of the anodes can have an impact on current density and deposition distribution across a substrate.
For example, the arrangement of the anodes within the anode assembly may enable various current density control profiles that may impact thickness on the substrate. The control profiles may include, but are not limited to, radial control, quadrant control, and/or top-to-bottom control. Briefly, radial control may include turning off groups of anodes that may be a certain distance from the center of the anode assembly. In this instance, the turned off anodes may form a circle or quasi-circle around the center of the assembly. By forming a circle off turned off anodes, the impact of the turned off anodes can result in relatively uniform deposition across the substrate surface. Radial control may also enable one or more circles of turned off anodes, the circles may be close together or they may be separated by circles of turned on anodes. In another instance, one or more circles of anodes may be so close that they form a single ring of anodes around the center of the anode assembly.
Another form of control may be quadrant control that may organize specific locations or regions to turn off or on at the same time. The geometry or arrangement of the turned off/on anodes is merely limited by the density of the anodes. For example, quadrant control may enable on/off anodes to be arranged in various geometries that may include, but are not limited to, circles, rectangles, lines, triangles, or rhombuses. In short, quadrant control may be used to impact current density in a relatively non-uniform way across the anode assembly. This may include creating localized regions of on or off anodes to account for substrate features. For example, the anodes located above specific die or devices on the substrate may be turned on to impact current density above one or more die. Likewise, the anodes located above the gaps between die may be turned off at the same time.
In another instance, quadrant control may impact current density across a continuous region of the anode assembly. The anode assembly or bath may be configured in way that creates pockets or regions of high or low current density. The anodes in the regions may be turned on or off to raise or lower the current density in that region. For example, the anodes within a certain distance of the anode assembly's edge may be turned off while the remaining anodes may be turned on. Under quadrant control, the on and off anodes may vary by any pattern that may improve current density control or thickness uniformity on the plated substrate.
Another form of anode control can be Top-to-bottom control. For example, the anode assembly may vary the amount of “on” anodes to “off” anodes in a systematic way to control the current density from top to bottom or from side to side of the anode assembly. In one embodiment, this may include having more anodes turned on at the top than at the bottom of the anode assembly. This type of control may be used to address substrate thickness profiles that vary from high to low across the substrate.
Described herein are several embodiments related to the current density control across the anode assembly. Note that this summary section does not specify every embodiment and/or incrementally novel aspect of the present disclosure or claimed invention. Instead, this summary only provides a preliminary discussion of different embodiments and corresponding points of novelty over conventional techniques. For additional details and/or possible perspectives of the invention and embodiments, the reader is directed to the Detailed Description section and corresponding figures of the present disclosure as further discussed below.
The features within the drawings are numbered and are cross-referenced with the written description. Generally, the first numeral reflects the drawing number where the feature was first introduced, and the remaining numerals are intended to distinguish the feature from the other notated features within that drawing. However, if a feature is used across several drawings, the number used to identify the feature in the drawing where the feature first appeared will be used. Reference will now be made to the accompanying drawings, which are not necessarily drawn to scale and wherein:
Techniques disclosed herein include methods and systems for electrochemical deposition (ECD), as well as sub systems, auxiliary modules, and processes that support ECD systems.
Of course, the order of discussion of the different steps as described herein has been presented for clarity sake. In general, these steps can be performed in any suitable order. Additionally, although each of the different features, techniques, configurations, etc. herein may be discussed in different places of this disclosure, it is intended that each of the concepts can be executed independently of each other or in combination with each other. Accordingly, the concepts described in this application can be embodied and viewed in many different ways. For example, techniques for electrochemical deposition can include, but are not limited to, a primary ECD unit, and one or more modules or cells that can generate various chemicals and metal ions to assist with the plating process. There can be various configurations among the different modules. Such modules assist with plating bath controls and provide a set of components that can be combined in various ways depending on specifications of a particular plating application or treatment process.
Two-Compartment Cell with Metal-Concentrate Dosing.
Using an insoluble anode results in different benefits. By way of a particular example, in some implementations (notably the plating of Sn or Sn-containing alloys) the anolytes (in reservoir 2004 and compartment 2002) can be selected so as to have differing compositions. By way of a specific example, anolyte in reservoir 2004 receives metal ions upon electrodissolution of anode 2001, and may also use a cross-bleed to ensure that all dissolved metal ions cross-over to the plating solution in reservoir 2030. Dosing unit 2018 is then used for supplemental dosing. A given plating solution can be recirculated, via conduits 2016 and 2015, through the ECD cell using pump 2008. Another benefit can be that insoluble anode system does not need to rely on the anolyte in compartment 2002 as a metal ion source. The cell in
In the
The anode assembly 2001 may be made of a dielectric material or a conductive material that may or may not be the same conductive material used in the anodes 3001. In one specific embodiment, the anode assembly 2001 may be made of, but is not limited to, niobium, titanium, platinum, gold, carbon, PVDF, PTFE, PP, FFPM, FKM or FFKM. In other embodiments, the conductive material may be copper, tin, silver, or any other metal that may be plated onto a substrate 2009. The anode assembly 2001 can have a diameter that enables metal plating on substrates with diameters of 200 mm or higher.
The anodes 3001 can be placed within the anode assembly 2001 and can be secured by a push-fit tolerance that keeps the anode in position within the anode assembly 2001. The diameter of the anodes 3001 may range between 1 mm to 5 mm. In one specific embodiment, the diameter of the anodes 3001 may be 4.5 mm. The anodes 3001 can be spaced evenly across the anode assembly 2001. A higher anode density provides greater resolution for controlling current density in the plating bath 2002. The
In one embodiment, the anodes 3001 may have a surface that is substantially flush with anode assembly 2001. This may mean that the surface of anodes 3001 and a surface of the anode assembly 2001 may be in the same plane. In this way, the current interaction between nearby anodes 3001 may be relatively uniform when they are in the same position. However, the current interaction between nearby anodes 3001 may be varied based, at least part, on the relative positions of the anodes 3001 with respect to the surface of the anode assembly 2001. For example, the surface of the anodes 3001 may be recessed into the anode assembly 2001 so that the surfaces anodes 3001 and the anode assembly 3001 may not be substantially flush. This embodiment may decrease the current interaction between the anodes 3001. In yet another embodiment, the anodes 3001 may be protruding from the anode assembly 2001 which can increase the current interaction between nearby anodes 3001. In some instances, the anodes 3001 may vary in distance from the cathode 1002 across the anode assembly 2001. For example, at least one of the anodes 3001 may be flush with the anode assembly 2001 and at least one other anode 3001 may be recessed into or protruding from the anode assembly 2001. Further, two or more portions of the anodes 3001 may be positioned in flush, recessed, and/or protruding positions with respect to the anode assembly 2001 or in any combination thereof.
The anodes 3001 can be made of a conductive material, preferably a metal, which can be plated onto a substrate 2009. The anodes 3001 may comprise, but are not limited to, Sn (tin) (various alpha-particle grades), Pb (lead) (various alpha particle grades), SnPb, Cu (copper), Ni (nickel), Ag (silver), Bi (bismuth), etc. The metal anodes 3001 can provide the metal ions that can be plated onto the substrate 2009.
In one embodiment, the each of the anodes 3001 can coupled to an electrical switch (not shown) that is electrically coupled to the power supply 2007. The electrical switches can act as a gate for the current flow to the anode and can be programmed to be on or off during processing. The selection of which anodes 3001 that are on or off can impact the current density profile along the anode assembly and/or the plating bath 2002.
In another embodiment, an electrical switch can be coupled to more than one anode 3001 and can turn the anodes 3001 on or off collectively. This grouping arrangement may be done on certain areas of the anode assembly 2001 that are known to have at least a relatively uniform current density. Accordingly, the anodes 3001 in these uniform regions are not likely to be turned on or off without the surrounding anodes 3002 being in the same state. In this way, the number of electrical switches can be reduced to provide some cost savings. However, each of the anodes 3001 in the other non-uniform regions can continue to be controlled by individual switches. As noted above, a single power supply 2007 can provide power to the anodes instead of using multiple power supplies to power each or a group of anodes 3001 in the anode assembly 2001.
The grouping of anodes to a single switch along with additional anodes that have their own switch reduces the number of switches. There is a tradeoff between equipment cost and equipment capability. For example, in certain instances the high resolution capability of using all individually controlled anodes 3001 may not be required to control current density to desired levels. In view of the capability to control individual anodes 3001, the arrangement of “on” or “off” anodes 3001 may vary widely from process to process to obtain a relatively uniform current density. Hence, the anode control strategy may vary from process to process. Broadly, the control strategies can be classified by, but are not limited to, radial control, quadrant control, and/or top-to-bottom control.
Turning now to one radial control embodiment,
Broadly, radial control can apply to controlling a group of anodes that can form a radial pattern around the center of the anode assembly 2001 when they are turned on or off. The group of anodes 4003 may be immediately adjacent to each other, such that there no intervening anodes that between them that are in a different state (e.g., on or off). However, in other embodiments the group of anodes 4004 may form a radial pattern, but they may have intervening anodes that have a different state. Further, there may be more than one radial pattern assigned to the anode assembly 2001 at the same time. The plurality of radial patterns can be used to control the current density in a cooperative manner. In that, the current density profile may be adjusted by one group of anodes or two or more groups of anodes working together.
In this embodiment, the radial control strategy targets an outer segment of anodes 4003 and an inner segment of anodes 4004. The outer segment of anodes 4003 form the outer ring of the anodes 3001, in that each of the outermost anodes can be turned off to control current density at the edge of the anode assembly 2001 or the substrate 2009. Additionally, an inner segment of anodes 4004 that are turned off can also be used to control current density in conjunction with the outer segment 4003.
This arrangement can be used to address higher current density around the substrate perimeter. Decreasing the flow of current by turning off the outer segment anodes 4003, the current density can be reduced at the edge of the anode assembly 2001 so that outer edge current density can be closer in magnitude to the current density in other areas of the anode assembly 2001.
Additionally, the current density may also be optimized by turning off the inner segment anodes 4004. In this embodiment, there is a gap of on anodes 4002 that intervene between the inner segment anodes 4004 and the outer segment anodes 4004. Also, the inner segment anodes 4004 may also include intervening anodes 4002 that are turned on as shown in
In other embodiments, the inner segment anodes 4004 and the outer segment anodes 4003 may be varied radially from the center of the substrate. Such that, the distance from the center of the anode assembly 2001 can vary in distance. For example, the pattern of the outer anode segment 4003 or the inner anode segment 4004 can be moved, radially, closer to the center of the anode assembly 2001.
In addition to radial control, the anodes may be turned on and off based, at least in part, on particular x-y coordinates that may correlate to device features on the substrate 2009 or to a known region of high current density.
In this embodiment, the incoming substrate 2009 can be aligned to the anode assembly prior to being placed in the plating solution 2002. The alignment can be done using alignment features on the devices on the substrate 2009 or notch alignment using a notch etched into the substrate or aligning based on the position of the wafer identification scribed into the surface of the substrate 2009.
In other embodiments, determining which anodes can be turned on or off can be based on the size and pitch of the device substrates and the size and pitch of the anodes 5001, 5002. However, when the pitch and size of the devices are relatively small compared to the pitch and size of the anodes 5001, 5002, the interior anodes may be turned on and the edge anodes may be turned off as shown in
In another embodiment (not shown), select anodes 6001 may be turned off to lower the deposition rate of the metal on the substrate across the substrate. This may enable a plating process that deposits metal at different deposition rates. The select anodes 6001 can be selected based, at least in part, on lowering the current density evenly across the substrate 2009 and thereby lowering the metal deposition rate. The select anodes 6001 may include a pattern, in which every other anode is turned off, or every second anode is turned off, or every third anode is turned off. In another embodiment, an entire row or column may be turned off to lower the current density across the substrate 2009. Further, more than one row and/or column may be turned off at the same time to achieve the lower deposition rate. In fact, at least one row and at least one column of anodes may be turned off to achieve the lower deposition rate. This may be in addition to the anodes 6002 that may have been turned off during the higher deposition rate step at the edge of the substrate 2009.
One way to implement a top-to-bottom current density profile can be to increase or decrease the number of on or off anodes across the anode assembly 2001. As shown in
In another embodiment, the top-to-bottom control strategy may be combined with the radial and/or quadrant strategy to customize the current density profile across the anode assembly 2001. For example, the top-to-bottom anode arrangement in
The power supply 8001 can be configured to provide current to one or more switches (not shown) in the switch assembly 8002. Current may be provided in the direct current or alternating current format. Preferably, the direct current can be used to provide a relatively constant current to the plating solution 1003, 2001. The power supply 8001 can regulate the current flow to a target condition and can maintain that target condition to within a tolerance threshold. The power supply can be a battery or receive power from an outside source such as a power outlet or a power distribution box. The power supply can regulate and/transform the incoming power to provide current to the switch assembly 8002 in a manner that is conducive to electrochemical plating. In one specific embodiment, a single power supply 8002 can provide all of the current to the switch assembly 8002 and the anodes 3001.
The switch assembly 8002 can include electrical switches (not shown) that can provide or restrict current from the power supply 8001 to the anodes 3001. The electrical switches may be controlled by switch controller 8003 to turn off or on during substrate 2009 processing. In another embodiment, the electrical switches may regulate the amount of current that can be provided to the anodes 3001 in a more nuanced manner than passing all the current or none of the current. For example, the current regulation may enable each anode to receive three or more amounts of current. In one instance, the first amount may be zero, the second amount may be the maximum current that can be provided by the power supply 8002, and the third amount may be a value between the first and second amounts. In other embodiments, the amount of current provided to the anodes 3001 may vary so that several individual anodes 3001 or several groups of anodes 3001 may be providing different amounts of current at the same time.
In one embodiment, each of the anodes 3001 may be controlled by a single electrical switch. In this way, each of the anodes may be turned on or off independently from other anodes 3001. Accordingly, in this embodiment, the number anodes and the number of electrical switches should be similar. In another embodiment, a group of anodes may be turned on or off by a single electrical switch. For example, the current density near the center of the anode assembly 2001 may be relatively constant and may not require a high degree of anode resolution to maintain uniform current density. Accordingly, a single electrical switch may be coupled to two or more anodes. In one embodiment, the anodes 3001 located within 5 cm of the center of the anode assembly 2001 can be coupled to the single electrical switch. However, each the remaining anodes outside of the 5 cm diameter may be coupled to individual electrical switches.
In other embodiments, a portion of the anodes 3001 may be grouped into two or more groups that can be controlled by a single electrical switch, while each of the remaining anodes may be controlled by a single electrical switch. Generally, the groups of anodes would correspond to regions of the anode assembly 3001 that are likely to have relatively uniform current density. As mentioned above, the individually controlled anodes 3001 may be located in regions in which the current density is not likely to be uniform. For example, the non-uniform regions may be near the edge of the anode assembly 3001 and the uniform regions may be near the center of the anode assembly 3001.
In one embodiment, the switch assembly 8002 may include DIN (Deutsches Institut fur Normung) rail relays that enable each of the electrical switches to be controlled by one signal from the power supply 8001. In this way, the electrical switches that are designated to be turned on will be closed and the electrical switches that are designated to be turned off will be closed. The on/off designation may be enabled by the switch controller 8006. In another embodiment, the switch assembly 8002 may include Double Pole Single Throw electrical switches that can also be controlled by a single signal to turn on/off the electrical switches.
The switch controller 8006 will direct which electrical switches will be open or closed and the duration of when the electrical switches will be opened or closed. The switch controller may include a processor (not shown) and memory (not shown) that contains computer-executable instructions that may be executed by the processor. The switch controller 8006 may also include a communications interface that can send signals to the switch assembly 8002 that specify which electrical switch(s) will be opened or closes.
The memory herein may be provided as a tangible machine-readable medium storing machine-executable instructions that, if executed by a machine, cause the machine to perform the methods and/or operations described herein. The tangible machine-readable medium may include, but is not limited to, any type of disk including floppy disks, optical disks, compact disk read-only memories (CD-ROMs), compact disk rewritables (CD-RWs), magneto-optical disks, semiconductor devices such as read-only memories (ROMs), random access memories (RAMs) such as dynamic and static RAMs, erasable programmable read-only memories (EPROMs), electrically erasable programmable read-only memories (EEPROMs), flash memories, magnetic or optical cards, or any type of tangible media suitable for storing electronic instructions. The machine may include any suitable processing or computing platform, device or system and may be implemented using any suitable combination of hardware and/or software. The instructions may include any suitable type of code and may be implemented using any suitable programming language. In other embodiments, machine-executable instructions for performing the methods and/or operations described herein may be embodied in firmware.
The processor herein may be provided as a computer processor or other logic device that can process computer-executable instructions to render a result that can be provided to memory or other components of the ECD system 9000. The processor may operate as a reduced instruction set computing (RISC) or complex instruction set computing (CISC). However, the processor may be any device that may include one or more arithmetic logic unit(s) (ALU) to generate instructions that can be communicated to the switch assembly 8002.
At block 9001, the method 9000 may be implemented by disposing an anode structure 2001 in an electrochemical deposition system 2000 opposite a substrate 2009. The anode structure 2001 can be placed in contact with an electrochemical medium 2002 contained between the anode structure 2001 and the substrate 2009. In one embodiment, the anode structure may be configured with a plurality of anodes 3001 that can provide current to the electrochemical medium 2002. In one embodiment, the anodes 3001 may be arranged uniformly across the anode structure 2001, as shown in
At block 9002, the method 9000 may be further implemented by providing a plurality of electrically controlled switches (e.g., switch assembly 8002) coupled between a power source 8001 and said plurality of anodes 3001. The electrically controlled switches can couple electrical current from the power source 8001 to one or more of said plurality of anodes 3001. The electrical switches may be configured to be an open circuit during a portion of the electrochemical process and a closed circuit during the plating portion of the electrochemical process implemented on the electro chemical deposition system 2000.
In one embodiment, the plurality of anodes 3001 is coupled exclusively to a corresponding electrical switch. In this way, each of the anodes 3001 may be controlled independently of the other anodes 3001 in the anode structure 2001.
In another embodiment, plurality of anodes 3001 comprises at least one group of anodes 3001 that are coupled to one electrical switch and a portion of anodes that are exclusively coupled to their own electrical switch. For example, anodes 3001 located near the center of the anode structure 2001 may be grouped to the same electrical switch. The grouping enables those anodes 2001 coupled to that single electrical switch to be turned on or off collectively at substantially the same time. The grouping may be based, at least in part, on the regions of the anode structure that typically have a relatively uniform current density during electrochemical processing.
At block 9003, the ECD system 8000 can be enabled to set a first configuration of an on and off state for each of the plurality of anodes 3001. For example, the configuration can be based, at least in part, but is not limited to, a radial control strategy, a quadrant strategy, and/or a top-to-bottom strategy as described above in the description of
In other embodiments, the electrochemical process may have a multi-step deposition process that can use different power settings for depositing a metal layer on the substrate 2009. The multi-step process may be used to accommodate features on the substrate 2009. For example, different power settings may be used during deposition step to account for via (e.g., hole on the surface of the substrate 2009) aspect ratios or to assist in initiating plating for thin or high resistance seed substrates. In another example, the current density profile or the deposition rate may change as the metal layer grows thicker or that a process condition or hardware feature may change the thickness uniformity over time. Although different power settings may be used to control uniformity, the anodes 3001 on/off configuration may also be reconfigured to account for changes in deposition uniformity over time. For example, the first configuration may similar to the arrangement shown in
In another embodiment, switching between the first configuration and the second configuration may be based, at least in part, on when another substrate 2009 is placed into the chemical plating solution 2010. For example, the first configuration may be used with a first type of substrate and the second configuration may be used with a second type of substrate. In this way, the anode assembly 2001 can be configured for different substrates without having to remove and modify the anode assembly 2001.
At block 9004, the anode arrangement discussed immediately above may be implemented by spatially controlling an anode current from the anode structure 2001 by setting the plurality of electrically controlled switches to the first configuration. As noted above, one embodiment can have the first configuration arranged in the manner as shown in
At block 9005, the substrate 2009 in may receive an electrochemically deposited film when the power is applied to the anodes in the first configuration and the substrate is exposed to a chemical plating solution (e.g., chemical solution 2010).
Although only certain embodiments of this application have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention.
