Current collimation for thin seed and direct plating

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the invention generally relate to an electrochemical plating cell having an electric field collimator positioned between the anode and the substrate being plated.

2. Description of the Related Art

In semiconductor processing, electrochemical plating (ECP) is generally the preferred technique for filling features formed onto substrates with a conductive material. A typical ECP process generally includes immersing a substrate into an electrolyte solution that is rich in ions of the conductive material (generally copper), and then applying an electrical bias between a conductive seed layer formed on the surface of the substrate and an anode positioned in the electrolyte solution. The application of the electrical bias between the seed layer and the anode facilitates an electrochemical reaction that causes the ions of the conductive material to plate onto the seed layer.

However, with conventional ECP processes and systems, the conductive seed layer formed on the substrate is generally very thin, and as such, is highly resistive. The resistive characteristics of the seed layer causes the electric field traveling between the anode and the seed layer in a plating process to be much more dense near the perimeter of the substrate where electrical contact with the seed layer is generally made. This increased electric field density near the perimeter of the substrate causes the plating rate near the perimeter of the substrate to increase proportionally. This phenomenon is generally known as the “terminal effect”, and is an undesirable characteristic associated with conventional plating systems.

The terminal effect is of particular concern to semiconductor processing, because as the size of features continues to decrease and aspect ratios continue to increase, the seed layer thickness will inherently continue to decrease. This decrease in the thickness of the seed layer will further heighten the terminal effect, as the decreased thickness of the seed layer further increases the resistivity of the layer.

Therefore, there is a need for an electrochemical plating cell and method for plating onto semiconductor substrates, wherein the plating cell and method are configured to eliminate the terminal effect.

SUMMARY OF THE INVENTION

Embodiments of the invention generally provide an electrochemical plating cell having a collimator positioned between the anode of the cell and a substrate positioned in the cell for plating. The collimator operates to channel the electric field traveling from the anode to the substrate, such that the electric field travels in a substantially linear path. The plating cell of the invention further provides for a zoned anode, wherein each of the zones comprises a non-concentrically shaped anode element.

Embodiments of the invention may further provide a method and apparatus for plating a conductive material onto a substrate. The apparatus includes a fluid processing cell having a fluid basin configured to contain an electrolyte solution and having an opening configured to receive a substrate for processing, an anode assembly positioned in the fluid basin, and a collimator positioned in the fluid basin between the anode and the opening.

Embodiments of the invention may further provide an electrochemical plating cell having a cell body configured to contain a plating solution therein and having an opening configured to receive a substrate for plating. The cell further includes an anode assembly positioned in the cell body such that the anode assembly is in electrical communication with the plating solution, and an electric field collimator positioned in the cell body between the anode assembly and the opening, the collimator comprising a plurality of electrically insulative fluid conduits having substantially parallel longitudinal axes.

Embodiments of the invention may further provide a method for plating a conductive material onto a substrate, wherein the method includes generating an electric field between an anode positioned in a plating cell and a substrate being plated in the plating cell, collimating the electric field in a substantially linear direction between the anode and the substrate, and plating the conductive material onto the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

FIG. 1 illustrates a schematic view of a conventional plating cell and the electric field lines generated therein.

FIG. 2 illustrates a schematic sectional view of a plating cell of the invention having a collimator positioned therein.

FIG. 3A illustrates a plan view of an exemplary collimator of the invention using circular conduits

FIG. 3B illustrates a plan view of an exemplary collimator of the invention using octagonal conduits.

FIG. 3C illustrates a plan view of an exemplary collimator of the invention using hexagonal conduits.

FIG. 3D illustrates a plan view of an exemplary collimator of the invention using square conduits.

FIG. 3E illustrates a plan view of an exemplary collimator of the invention using triangular conduits.

FIG. 4 illustrates a sectional view of an exemplary plating cell of the invention having a collimator in the cell.

FIG. 5A illustrates a top perspective view of an exemplary anode assembly in the plating cell of the invention.

FIG. 5B illustrates a sectional view of the exemplary anode assembly of the plating cell of the invention.

FIG. 5C illustrates a sectional/schematic view of the anode assembly of the invention with schematic representation of the power supply connections to the individual anode members.

FIG. 5
d illustrates an electrical resistance schematic view of an exemplary plating cell of the invention.

FIG. 6 illustrates partial sectional view of the exemplary anode assembly of the invention including an anode adjustment member.

FIG. 7 illustrates a plating thickness plot for a plating cell incorporating the collimator of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates a schematic view of a conventional plating cell 100 and the electric field lines generated therein. The conventional plating cell 100 generally includes a fluid basin 101 configured to contain a fluid volume 102, which is generally an electrolyte plating solution. An anode 104 is positioned in a lower portion of the fluid basin 101 and a substrate 106 that is to be plated is generally positioned across an upper open portion of the cell 100. The substrate 106 is supported by a contact ring that is configured to electrically contact the plating surface 108 of the substrate 106 near the perimeter of the substrate 106 via one or more electric contact elements 110. The electric contact elements 110 are in electrical communication with a cathodic terminal of a power supply 114, while the anodic terminal of the power supply is in electrical communication with the anode 104. Further details of the conventional plating cell 100 may be found in commonly assigned U.S. Pat. No. 6,271,433, which is hereby incorporated by reference in its entirety to the extent not inconsistent with the present invention.

FIG. 1 also illustrates the electric field lines 112 generated during a plating process in the conventional plating cell 100. As noted above, the substrate plating surface 108 has a thin conductive seed layer deposited thereon and the electric field lines 112 inherently converge toward the electrical contact elements 110 as a result of the least resistive path between the anode and the cathode being toward the perimeter of the substrate proximate the contact elements 110. Several manufacturers of plating cells have attempted to solve the convergence problem by substantially increasing the resistivity of the electrolyte, however, it has been shown that this causes an unacceptable decrease in plating rates and does not sufficiently reduce the electric field convergence effect.

FIG. 2 illustrates a schematic sectional view of a fluid processing or plating cell 200 of the invention having a collimator 202 positioned therein. The plating cell 200 generally includes a fluid basin 206 that defines a fluid volume therein and has an open upper portion that is configured to receive a substrate 212 for plating. The basin 206 includes at least one fluid inlet/outlet 208 and an uppermost weir 210 that defines the opening that receives the substrate 212. The fluid inlets/outlets 208 may be configured to supply plating solutions, e.g., anolyte and/or catholyte solutions, to various regions or volumes within the fluid basin 206. The electrolyte (anolyte and/or catholyte solutions) supplied to the fluid basin generally overflows the uppermost weir 210, which is positioned above a processing position of the substrate 212 (so that the substrate plating surface 214 is immersed in the electrolyte contained in the fluid basin 206).

The lower portion of basin 206 includes an anode assembly 204. The anode electrode assembly 204, which may include several independently powered electrode elements, as will be further discussed herein, in electrical communication with an anodic terminal of a power supply 220. The cathodic terminal of the power supply 220 is in electrical communication with a substrate contact ring 222 that is configured to support and electrically contact the plating surface 214 of the substrate 212. Exemplary contact rings may be found in commonly assigned U.S. patent application Ser. No. 10/355,479, filed Jan. 31, 2003, entitled “Contact Ring with Embedded Flexible Contacts”, U.S. patent application Ser. No. 10/278,527, filed Oct. 22, 2002, entitled “Plating Uniformity Control by Contact Ring Shaping” and U.S. Pat. No. 6,251,236, all of which are hereby incorporated by reference in their entirety to the extent not inconsistent with the present invention. The plating cell 200 may optionally include a membrane 216, such as a cationic membrane, for example, positioned across the interior volume of the fluid basin 206 between the anode 204 and the substrate 212. When membrane 216 is implemented, the fluid basin inlet/outlets 208 may be configured to supply different electrolytes to the volumes above and below the membrane 216, i.e., a catholyte solution to the volume above the membrane and an anolyte solution to the volume below the membrane, for example. An exemplary plating cell incorporating the membrane separation noted above may be found in commonly assigned U.S. patent application Ser. No. 10/627,336, filed Jul. 24, 2003, entitled “Electrochemical Processing Cell”, which is hereby incorporated by reference in its entirety to the extend not inconsistent with the present invention.

The collimator 202 may be a single unit when no membrane 216 is implemented, or alternatively, when a membrane 216 is implemented, a first collimator may be positioned above the membrane 216 and a second collimator may be positioned below the membrane 216. Similarly, in embodiments where a membrane 216 is implemented, a single collimator may be positioned above the membrane 216, however, in this embodiment, it is desirable to have the membrane 216 positioned as close to the anode assembly 204 as possible to prevent electric field divergence (horizontal movement) from the center of the cell prior to the electric field entering the collimator 202, as will be further discussed herein.

The collimator 202, which is illustrated in plan view in FIG. 3A, generally includes a plurality of elongated conduits positioned adjacent to each other and having substantially parallel axes. The plurality of conduits 304 are generally manufactured from a dielectric material, such as ceramics, PVDF, plastic materials, Teflon®, or other electrically resistive or insulating materials that are non-reactive with electrochemical plating solutions. Each of the conduits 304 forms an elongated hollow interior region 302 that fluidly communicates one terminating end of the conduit 304 with an opposing terminating end of the conduit. The plurality of conduits 304 are affixed together such that the longitudinal axis of each of the conduits is generally parallel to each of the other axes of the conduits 304, and further, the axes of the conduits 304 are generally positioned orthogonal to the plating surface 214 of the substrate 212 being plated in the plating cell 200. As such, the longitudinal axes of conduits 304 are generally positioned orthogonal to both the upper surface of the anode assembly 204 and to the substrate plating surface 214. The conduits 304 may be affixed together via glue or epoxy process, via a heat treatment process, a sintering process, or other process suitable to affix the conduits 304 together such that the assembled collimator 202 is rigid and capable of supporting its own weight without substantial deflection or bowing.

Assembly of the collimator 202 in a manner that prevents substantial deflection or bowing in a plating process is important to the operation of the invention. More particularly, as noted herein, the upper surface 230 of the collimator 202 is preferably positioned between about 0.5 mm and about 20 mm, or more particularly, between about 1 mm and about 10 mm, or about 15 mm away from the plating surface 214 of the substrate 212. This spacing operates to prevent excessive lateral or horizontal divergence of the electric field exiting from the conduits 304 before the electric field contacts the plating surface 214. If the collimator 202 is manufactured in a manner that allows for bowing or vertical deflection, then the spacing between the collimator 202 and the plating surface 214 will be increased near the middle of the plating cell, and as a result thereof, horizontal or lateral movement of the electric filed will be more likely near the center of the cell as a result of the increased spacing. Allowing the electric field to diverge away from the center of the cell furthers the terminal effect, and as such, is undesirable in the present invention. Thus, vertical rigidity of the collimator 202, i.e., the ability to retain shape/remain planar under its own weight, and additionally, under processing conditions that include fluid flow, is an important aspect of the invention.

Further, the conduits 304 are generally affixed together in a manner such that the space 306 between the outer surfaces of the conduits 304 may also form a conduit from one side of the collimator 202 to the other side thereof. The space 306 shares a parallel axis with the other conduits 304, and as such, further facilitates the electric field channeling of the invention. In other embodiments of the invention, the collimator 202 may be manufactured from various shapes of conduits 304 that may or may not form space 306. For example, conduits 304 may be triangular, square, pentagonal, hexagonal, heptagonal, octagonal, nonagons, decagons, or other polygon shapes. For example, FIG. 3B illustrates a plan view of a collimator 202 of the invention manufactured from octagonal conduits; FIG. 3C illustrates a plan view of a collimator 202 of the invention manufactured from hexagonal conduits; FIG. 3D illustrates a plan view of a collimator 202 of the invention manufactured from square conduits; and FIG. 3E illustrates a plan view of an exemplary collimator of the invention using triangular shaped conduits.

Additionally, other embodiments of the invention contemplate that the collimator 202 may be formed by boring conduits of varying cross sectional shapes out of a solid disk of material. For example, a plurality of circular or other polygon shaped bores may be formed into a solid disk of material to generate a collimator 202.

FIGS. 3C, 3D, and 3E include polygon shaped conduits 302 that do not generate any vertical space 306 between the respective conduits, i.e., these embodiments eliminate the space 306 illustrated in FIGS. 3A and 3B by having the respective conduits abut directly against each other, and therefore, these embodiments of collimator 202 do not include the additional conduits formed by the spaces 306. As such, these embodiments of the collimator 202 provide conduits that are all symmetric and identically shaped, which may operate to provide a more uniform electric field at the substrate surface during plating operations as a result of the elimination of the spaces 306 that are not shaped identically to the shape of the conduits 302.

Collimator 202 is generally positioned such that an upper terminating surface 230 of the collimator 202 is positioned proximate to and in a generally parallel relationship with the plating surface 214, and such that a lower terminating surface 240 is positioned proximate to and generally parallel to an upper surface 235 of the anode assembly 204. The positioning of the upper and lower surfaces 230, 240 proximate the plating surface 214 and the upper surface 235 of the anode assembly 204 operates to restrict horizontal flow or dispersion of the electric field traveling from the anode 204 to the plating surface 214. The spacing of the lower surface 240 may be generally the same as the upper surface, e.g., the spacing between the anode 204 and the lower surface 204 may be as recited herein with respect to the spacing between the plating surface 214 and the upper surface 230. Arrows 222 in FIG. 2 illustrate the electric field flow in a plating cell 200 of the invention incorporating the collimator 202. The electric field flow 222 is substantially vertical and has minimal horizontal movement or dispersion, as the conduits of the collimator 202 prevent the electric field from traveling horizontally or dispersing while traveling therethrough. During the time period when the electric field is entering and exiting the collimator 202, e.g., when the electric field is traveling from the anode assembly 204 to the collimator 202 and when the electric field is traveling from the collimator 202 to the plating surface 214, the electric field is not prevented from dispersing. As such, it is desirable to minimize the vertical distance 208 between the collimator and the plating surface 214 and between the collimator 202 and the anode assembly 204, as these distances directly impact the dispersion ability of the electric field.

More particularly, in order to minimize horizontal electric field movement in the plating cell of the invention, the upper and lower terminating ends 230, 240 are positioned proximate the plating surface 214 and the upper surface 235 of the anode 204, respectively. More particularly, the inventors have found that when the upper terminating end 230 of the collimator 202 is positioned less than about 15 mm from the plating surface 214, and more particularly, within about 7 mm, or within about 3 mm from the plating surface 214, that horizontal electric field movement is essentially eliminated, i.e., the only area where the electric field can travel horizontally is in the space 209 between the upper terminating end 230 of the collimator 202 and the plating surface 214. Since the space 209 is very small as a result of the spacing between the collimator 202 and the substrate being in the range of about a 0.5 mm to about a 5 mm gap, there is little area for the electric field to travel or disperse horizontally. Further, although the inventors have determined that the closer the upper terminating end 230 of the collimator 202 is to the plating surface, the greater the reduction in the horizontal electric field movement, embodiments of the invention are not limited to configurations where the collimator 202 is positioned less than about 15 mm from the plating surface 214. Different processing conditions and plating requirements may allow for placement of the collimator 202 farther from the plating surface 214, e.g., between about 5 mm and about 25 mm away, for example, while still maintaining acceptable processing results for particular processing applications.

Similarly, the positioning of the lower surface 240 of the collimator 202 close to the membrane 402 also operates to minimize horizontal electric field movement. For example, in the plating cell of the invention, membrane 402 operates to transmit the electric field emitted from the anode 204 therethrough so that the electric field can travel to the substrate to facilitate the electrochemical plating process. Positioning the lower surface 240 of the collimator 202 within about 15 mm from the membrane 402 operates to capture the electric field being traveling through the membrane 402 before the electric field is able to travel horizontally. Once the electric field is captured by the conduits of the collimator 202, the electric field is vertically channeled toward the substrate plating surface. Positioning the collimator 202 closer, i.e., within about 10 mm, for example, from the anode 204 further assists with minimizing electric field divergence in the plating cell of the invention.

Another factor that impacts the ability of the invention to prevent horizontal dispersion of the electric field is the size, and in particular, the cross sectional width or diameter of the conduits 302. More particularly, when circular conduits 302 are implemented, for example, it is desirable to have the cross sectional diameter of each of the conduits 302 to be less than about 10 mm, and more particularly, between about 2 mm and about 10 mm, or between about 1 mm and about 5 mm, for example. Smaller diameters of conduits 302, i.e., less than about 10 mm, have been experimentally shown to provide improved electric field collimation and reduced electric field dispersion over larger diameter conduits 302, i.e., greater than about 15 mm for semiconductor processing. In embodiments of the invention where measurements of diameter are inapplicable, i.e., where some polygon or triangular shapes are implemented, then the cross sectional area of the conduit 302 should be minimized. For example, it is desirable to have the cross sectional area of the conduits to be between about 2 mm²and about 30 mm². Additionally, for a 300 mm substrate processing cell, for example, there will generally be more than about 250 of the fluid conduits 302 that are used to form the collimator 202. In embodiments where the inner diameter of the conduits 302 is smaller and the conduits 302 are closely packed, the number of conduits used for a 300 mm plating cell may be more than about 500, or more than about 1000, for example.

In another embodiment of the invention, the terminating ends of the conduits 302 may increase or decrease in diameter. For example, the lower end of the conduits, i.e., the end proximate the anode, may be funnel shaped in order to gather the electric field. Both the upper and lower ends may be sized in accordance with the plating characteristics desired. In this embodiment of the invention, the upper and lower portions of the conduits may be larger or smaller than the respective other end.

In another embodiment of the invention, the collimator 202 is sized and positioned such that the vertical size or height of the collimator 202 occupies between about 50% and about 99% of the vertical space between the anode 204 and the substrate 212 being plated. More particularly, embodiments of the invention contemplate that the collimator 202 will occupy between about 75% and about 95% of the vertical space between the anode 204 and the substrate 212, or between about 80% and about 99% of the space between the anode and the substrate being plated. These proportions of occupied space have been shown to substantially reduce terminal effect plating.

FIG. 4 illustrates a sectional view of an exemplary plating cell 400 of the invention having a collimator 202 in the cell 400. A general description of the components of plating cell 400 may be found in commonly assigned U.S. patent application Ser. No. 10/268,284, filed Oct. 9, 2002, entitled “Electrochemical Processing Cell”, which is hereby incorporated by reference in its entirety to the extent not inconsistent with the present invention. Plating cell 400 generally includes a catholyte volume and an anolyte volume, where the catholyte volume is generally defined as the fluid volume in the plating cell 400 that is above the ionic membrane 402, and where the anolyte volume is generally defined as the fluid volume in the plating cell 400 that is below the membrane 402 adjacent the anode assembly 404 positioned in the anode base member 406. However, plating cell 400 differs from the application cited above in that plating cell 400 does not include a diffusion member (illustrated as element 210 in the commonly assigned application). Rather, the diffusion member of the incorporated case is replaced in the present invention with the collimator 202, as described above.

Collimator 202 is generally positioned above the membrane 402 and below the substrate being plated in the catholyte volume (the fluid volume above the membrane 402) of the plating cell 400, i.e., between the substrate being plated and the membrane 402. The lower surface of the collimator 202 is generally positioned between about 0.1 mm and about 10 mm from the upper surface of the membrane 402. Preferably, the lower surface of the collimator 202 is positioned between about 0.1 mm and about 5 mm from the upper surface of the membrane 402, so that the electric field traveling from the anode toward the substrate being plated does not have sufficient vertical space to disperse horizontally or radially outward toward the perimeter or outer wall of the plating cell. Similarly, as discussed above, the upper surface of the collimator 202 is generally positioned as close as possible to the plating surface of a substrate positioned in the cell for plating. More particularly, the upper surface of the collimator 202 may be positioned between about 0.5 mm and about 10 mm, or between about 0.5 mm and about 5 mm from the plating surface of the substrate. This narrow spacing prevents the electric field exiting from the collimator 202 from traveling horizontally (dispersing) toward the edge of the substrate before contacting the plating surface of the substrate, i.e., prevents the electric field effects that are known to cause the terminal effect. Research has shown that placement of the collimator 202 within about 2 mm and about 10 mm from the plating surface is sufficient to substantially eliminate the terminal effect in semiconductor plating processes.

FIG. 5A illustrates a top perspective view of an exemplary anode assembly 404 of the plating cell 400 of the invention. The anode assembly 404, as noted above, is positioned in an anode base assembly 406 and is configured to work with the collimator 202 to control electric field density in the plating cell. The anode base assembly 406 is generally manufactured from an electrically insulative material that is not reactive with electrochemical plating solutions. Further details of the construction and operation of the anode base assembly 406 and surrounding components may be found in commonly assigned U.S. patent application Ser. No. 10/627,336, filed Jul. 24, 2003, entitled “Electrochemical Processing Cell”, which is incorporated by reference in its entirety to the extent not inconsistent with the present invention.

The anode assembly 404 of the invention generally includes a plurality of individual anode members 405 that cooperatively form the anode assembly 404. For example, embodiments of the invention may include between about 20 and about 200 individual anode members 405 that collectively form the anode assembly 404. The individual anode members 405 may be manufactured from a soluble conductive material, such as copper for a copper electrochemical plating system, or from another material that is soluble in an electrochemical plating solution. Alternatively, the individual anode members 405 may be manufactured from an insoluble conductive material, such as platinum, titanium, or other insoluble metals amenable to electrochemical plating solutions. Further, the conductive material of anode members 405 may be coated with another conductive material, such as platinum, for example. The individual anode members 405 may be manufactured as square shaped (in plan view) conductive members, wherein an electrically insulative spacer 408 may be positioned between the respective square shaped anode members 405 to electrically isolate the anode members 405 from each other, as illustrated in the sectional view of the anode member in FIG. 5B. The spacers 408 generally have a thickness of less than about 3 mm, and more particularly, less than about 1 mm, so that the surface area on the anode surface that is not electrically active is minimized, as inactive surface area on the anode has been shown to facilitate plating uniformity problems, such as the problems associated with concentric anode configurations where there is a small non-active space between the concentric rings of the anode member. The spacers 408 used in the present anode assembly 404 may be made from any insulative or dielectric material that is not reactive with electrochemical plating solutions, such as, PVDF, Teflon®-type materials, plastics, insulative oxides, anodized materials, the same material as the anode, etc. Additionally, the central portion of the anode assembly 404 may include a collection of anode members 405 that do not have insulative spacers 408 positioned therebetween, as the inventors have found that the spacers tend to create low plating areas on the substrate when positioned proximate the center of the anode assembly 404.

The upper surface of each of the respective anode members 405 are generally positioned in a substantially parallel orientation with each other such that a unitary planar upper anode surface is generated. Further, each of the respective anode members 405 is also generally in electrical communication with an anodic terminal of a power supply (as illustrated in FIG. 2). The electrical power or current applied to each of the respective anode members 405 may be individually controlled or regulated by a controller (not shown). The controller may be used to adjust the resistance of a variable resistor (not shown), for example, positioned in series electrical connection between each individual anode member 405 and the power supply. The controller may be a microprocessor type controller configured to control a processing sequence, as is generally known in the art. The controller may be modified, however, to allow for control of the individual anode members 405. The anode members 405 may further be controlled in groups or banks, e.g., regions of the anode assembly 404, such as a group of anode members 405 in the central portion of the anode assembly 404 and a surrounding group of anode members 405 near the perimeter of the anode assembly 404. The controlled banks or groups of anode members 405 may be in any shape, size, or number. For example, concentric or symmetrically shaped regions or banks may be used. In one embodiment of the invention, the anode assembly 404 is divided into at least two concentric regions, wherein a first region covers the center of the anode assembly 404 and at least one second region covers an annularly shaped region surrounding the center region. In this embodiment, the center region may be powered to generate a greater plating rate near the center of the substrate, which further minimizes the terminal effect.

FIG. 5C illustrates a sectional/schematic view of the anode assembly 404 of the invention with schematic representation of the power supply connections to the individual anode members 405. In this embodiment, each of the respective anode members 405 is in series electrical connection with a variable resistor 502. The plurality of variable resistors 502 (one resistor 502 for each anode member 405) are in parallel electrical connection with each other. The parallel relationship of variable resistors 502 is in series electrical communication with an anodic terminal of a power supply 503. The variable resistors 502 are generally controllable by a system controller configured to control the operation of the plating system of the invention. One advantage of this configuration is that only one power supply is needed to drive a plurality of anode members 405. For an anode member 405 that is square and has a side length of 10 mm, for example, a typical resistance value for the variable resistor is about 10 kΩ.

FIG. 5
d illustrates an electrical resistance schematic view of the plating cell of the invention. The power supply 503 is in parallel connection with each of the anode member circuits 506, as illustrated by the dashed line. Each anode member circuit 506 includes the variable resistor 502, resistance 506 (which represents the resistance of the anode member 405 and the electrolyte solution between the anode member 405 and the substrate being plated), and a horizontal resistance 505 that represents the resistance of the seed layer on the substrate. As noted above, typical resistance values for the 10 mm wide anode members 405 are 10 kΩ, and around 10 ohms for the seed resistors 505. However, note that the drawing does not illustrate a horizontal resistance for the electrolyte, as this resistance is in parallel with the seed resistance 505, and generally has a value of between about 5 and 10Ω when the anode members 405 are spaced from the substrate at a distance of about 2 mm. As such, the resistance for the electrolyte may be combined with resistance 505 or generally ignored.

By having the impedance of the variable resistor 502 be about 1000 times greater than the seed layer resistance 505, the anode resistors predominate in controlling the current distribution across the surface of the substrate being plated. Thus, as the copper thickness increases during plating, the seed layer resistance will decrease in value, and the anode resistors become more dominant in controlling the current distribution. In the present embodiment of the invention, the value of the variable resistors 502 will generally be inversely proportional to the top surface area of the corresponding anode member 405. For example, for the previously noted resistance value about 10 kΩ, the top surface area of the anode member 405 would be around 1 cm². In this configuration, the current passing through the resistors 502 would be substantial, and as such, the resistors 502 would inherently become heated. As such, the inventors contemplate that cooling (air, fluid, etc.) of the circuits 506 may be required.

FIG. 6 illustrates a partial sectional view of the exemplary anode assembly of the invention including an anode adjustment mechanism 610. The anode adjustment mechanism 610 is positioned below each of the respective anode segments 405 and above the anode base 406. The anode adjustment member 610 generally includes a mechanism that is configured to vertically move the anode segment 405 positioned thereon. The movement of the anode segment by the adjustment member 610 is calculated to maintain the upper surface of the anode assembly 204 in a substantially planar orientation with respect to the upper surface of the other anode segments 405. The adjustment member 610 may be configured to vertically move the associated anode segment 405 vertically in response to the changing weight of the anode segment 405, such as through a weight responsive spring mechanism that will raise the anode segment 405 in proportion to the quantity of material eroded from the segment. This particular embodiment of the invention is configured for use in plating systems incorporating soluble anodes, as soluble anodes are known to erode at varying rates, thus generating a non-planar upper anode surface. Use of the adjustment member 610 allows for individual vertical adjustment of the respective anode segments 405 such that the upper surfaces of the anode segments 405 continually remain coplanar, despite the varying erosion rates of the respective anode elements 405.

In operation, embodiments of the invention may be used to plate a conductive material onto a semiconductor substrate in a substantially uniform manner, i.e., substantially eliminating increased plating accumulation near the perimeter of the substrate as a result of the electrical contact being made near the perimeter of the substrate, e.g., the terminal effect. A plating process using embodiments of the invention generally begins with a substrate to be plated being immersed into a plating solution contained in a plating cell of the invention, such as plating cell 200 or 400 illustrated in FIGS. 2 and 4 respectively. The substrate may be electrically biased during the immersion process to prevent etching of any conductive material already deposited on the substrate prior to initiation of the plating process. Once immersed, the substrate may be positioned in a plating position, i.e., generally an orientation where the plating surface 214 of the substrate is positioned substantially parallel to an anode assembly 204 of the plating cell, as generally illustrated in FIG. 2.

Once the substrate is in the plating position, an electrical plating bias is applied between the anode assembly 204 (connected to an anodic terminal of the power supply) and the substrate plating surface 214 (connected to a cathodic terminal of the power supply) to drive the electrolytic reaction that causes copper ions in the plating solution to deposit onto the plating surface 214. The plating bias may be a constant current, constant voltage, a pulsed current or voltage, a ramped current or voltage, and may include reverse current or voltage step(s) and/or relaxation intervals between application of plating or deplating electrical bias steps. A more detailed description of the application of the plating bias may be found in commonly assigned U.S. Pat. No. 6,261,433, which is hereby incorporated by reference in its entirety, to the extent not inconsistent with the present invention.

The application of the plating bias generates a current flow between the anode 204 and the plating surface 214. The current flow inherently generates an electric field between the anode 204 and the plating surface. This electric field in a conventional plating cell, as shown in FIG. 2, tends to diverge toward the perimeter of the substrate where the electrical contact is generally made. This divergence of the electric field causes the deposition rate near the perimeter of the substrate to be greater than the deposition rate near the center of the substrate, as the electric field flux is known to be proportional to the deposition rate.

The present invention solves the challenges associated with diverging electric field in electrochemical plating cells by positioning the collimator 202 between the anode 204 and the plating surface 214. The electric field 222 is received by the lower surface of the collimator 202 just above the anode 204. The electric field 222 is then transmitted via the conduits 302 (shown in FIG. 3) of the collimator 202 toward the substrate plating surface 214. The conduits 302 channel the electric field 222 such that the electric field travels directly toward the plating surface 214, i.e., in a vertical direction, without horizontal divergence. The electric field is then emitted from the upper surface 230 of the collimator 202 proximate the substrate plating surface 214. More particularly, the upper surface 230 is generally. positioned less than about 20 mm from the plating surface, and as such, when the electric field is emitted from the conduits 302 of the collimator 202, the field has minimal opportunity to travel horizontally prior to intersecting with the plating surface. Since the inventors have found that the vertical spacing between the upper surface 230 and the plating surface 214 is controlling of the divergence (smaller spacing between the upper surface 230 and the plating surface 214 provides proportional reduction in horizontal field divergence), embodiments of the invention contemplate that the spacing between the upper surface 230 and the plating surface 214 may be less than about 25 mm, and more particularly, between about 0.5 mm and about 15 mm, as these spacing dimensions provide minimal vertical spacing for horizontal field dispersion.

FIG. 7 illustrates a plating thickness plot 700 for a plating cell incorporating the collimator of the invention. The plot was obtained in a plating cell having a plurality of anodes with the collimator positioned less than about 10 mm away from the plating surface of the substrate. The anodes were independently powered with the center anodes receiving more power than the surrounding anodes, and the outer anodes receiving more power than either of the inner anodes. The substrate plated had a diameter of 300 mm and had a 1000 Å thick seed layer formed thereon. A total of 7000 Å was plated onto the seed layer using an acidic copper sulfate based plating solution. The plot 700 illustrates that the collimator may be used to control the plating uniformity, i.e., the edge of the substrate has reduced plating thickness, as illustrated by 702. Additionally, the center of the substrate has reduced plating thickness 706, while the middle portion of the substrate between the center and edge has increased plating rate 704. This data illustrates that the collimator of the invention may be used to overcome edge high plating characteristics associated with the terminal effect.

While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Current collimation for thin seed and direct plating

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