WO2022164695A1

WO2022164695A1 - Spatially and dimensionally non-uniform channelled plate for tailored hydrodynamics during electroplating

Info

Publication number: WO2022164695A1
Application number: PCT/US2022/012969
Authority: WO
Inventors: Stephen J. Ii Banik; Gabriel Hay Graham; Bryan L. Buckalew; Robert Rash; Lee Peng Chua; Frederick Dean Wilmot; Chien-Chieh LIN
Original assignee: Lam Research Corporation
Priority date: 2021-02-01
Filing date: 2022-01-19
Publication date: 2022-08-04
Also published as: KR20230136017A; US20240076795A1; CN115803480A; TW202248466A

Abstract

An ionically resistive ionically permeable element for use in an electroplating apparatus includes ribs to tailor hydrodynamic environment proximate a substrate during electroplating. In one implementation, the ionically resistive ionically permeable element includes a channeled portion that is at least coextensive with a plating face of the substrate, and a plurality of ribs extending from the substrate-facing surface of the channeled portion towards the substrate. Ribs include a first plurality of ribs of full maximum height and a second plurality of ribs of smaller maximum height than the full maximum height. In one implementation the ribs of smaller maximum height are disposed such that the maximum height of the ribs gradually increases in a direction from one edge of the element to the center of the element.

Description

SPATIALLY AND DIMENSIONALLY NON-UNIFORM CHANNELLED PLATE FOR TAILORED HYDRODYNAMICS DURING ELECTROPLATING INCORPORATION BY REFERENCE A PCT Request Form is filed concurrently with this specification as part of the present application. Each application that the present application claims benefit of or priority to as identified in the concurrently filed PCT Request Form is incorporated by reference herein in its entirety and for all purposes. FIELD OF THE INVENTION The disclosed embodiments relate to methods and apparatus for controlling electrolyte hydrodynamics during electroplating. More particularly, methods and apparatus described herein are particularly useful for plating metals onto semiconductor wafer substrates, especially those having a plurality of recessed features. BACKGROUND In semiconductor device fabrication, deposition and etching techniques are used for forming patterns of materials, such as for forming metal lines embedded in dielectric layers. Electrochemical deposition processes are well-established in modern integrated circuit fabrication. The transition from aluminum to copper metal line interconnections in the early years of the twenty-first century drove a need for increasingly sophisticated electrodeposition processes and plating tools. Much of the sophistication evolved in response to the need for ever smaller current carrying lines in device metallization layers. These copper lines are formed by electroplating metal into very thin, high- aspect ratio trenches and vias in a methodology commonly referred to as “damascene” processing (pre-passivation metallization). Electrochemical deposition is now poised to fill a commercial need for sophisticated packaging and multichip interconnection technologies known generally and colloquially as wafer level packaging (WLP) and through silicon via (TSV) electrical connection technology. These technologies present their own very significant challenges due in part to the generally larger feature sizes (compared to Front End of Line (FEOL) interconnects) and high aspect ratios. The background description provided herein is for the purposes of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. SUMMARY In one aspect, an electroplating apparatus is provided. In some embodiments, the electroplating apparatus includes: (a) an electroplating chamber configured to contain an electrolyte and an anode while electroplating metal onto a substrate; (b) a substrate holder configured to hold the substrate such that a plating face of the substrate is separated from the anode during electroplating; and an ionically resistive element. The ionically resistive element includes: (i) a channeled plate adapted to provide ionic transport through the ionically resistive element during electroplating; (ii) a substrate- facing side that is parallel to the plating face of the substrate and separated from the plating face of the substrate by a gap; and (iii) a plurality of ribs positioned on the substrate-facing side of the ionically resistive element, wherein the plurality of ribs comprises a first plurality of ribs of full maximum height and a second plurality of ribs of smaller maximum height than the full maximum height. The electroplating apparatus further includes: an inlet to the gap for introducing cross flowing electrolyte to the gap; and an outlet to the gap for receiving cross flowing electrolyte flowing in the gap, wherein the inlet and outlet are positioned proximate azimuthally opposing perimeter locations on the plating face of the substrate during electroplating. In some embodiments, the ionically resistive element is positioned such that the second plurality of ribs of smaller maximum height is proximate the inlet to the gap. In some embodiments all ribs are parallel to each other, and are perpendicular to a direction of a flow of the cross flowing electrolyte in the gap. In some embodiments the second plurality of ribs comprises at least two ribs of different maximum heights. In some embodiments the ribs in the second plurality of ribs are arranged such that the maximum rib height increases in a direction from an edge to the center of the ionically resistive plate, and wherein the second plurality of ribs of lower height are disposed only on one side of the ionically resistive element. In some embodiments, the total number of ribs is between about 15 and about 30, and the second plurality of ribs of lower maximum height has between about 2 and about10 ribs. In some embodiments the full maximum height of the ribs is less than about 5 mm. For example, in some embodiments the full maximum height of the ribs is about 1 - 3 mm. In some embodiments, the gap between the bottom portion of the substrate holder and the ionically resistive element is less than about 20 mm. In some embodiments, at least some of the ribs have variable height. In some embodiments, at least some of the ribs have variable height, and rib height in a rib having variable height, decreases gradually in a direction toward an edge of the rib. In some embodiments, the ionically resistive element includes a region, where rib height is lower than the full maximum height, and wherein the region is generally crescent-shaped. In some implementations this region is located proximate either the inlet or the outlet from the gap. In some embodiments, the ionically resistive element includes a region, where rib height is lower than the full maximum height, and where the region is generally ring-shaped. In some embodiments, the ionically resistive element includes a region where rib height is lower than the full maximum height, and where the region has a martini glass shape. In some embodiments, the ionically resistive element includes a plurality of non-communicating channels. In other embodiments, the ionically resistive element includes a three-dimensional network of communicating channels. In some embodiments, the electroplating apparatus further includes a cross flow injection manifold fluidically coupled to the inlet. In some implementations, the cross flow injection manifold is at least partially defined by a cavity in the ionically resistive element. In some embodiments, the electroplating apparatus further includes a flow confinement ring positioned over a peripheral portion of the ionically resistive element. In some embodiments, the inlet spans an arc between about 90-180° proximate the perimeter of the plating face of the substrate. In another aspect, an ionically resistive plate for use in an electroplating apparatus is provided, where the resistive plate may be adapted to plate material on a semiconductor wafer of a standard diameter, In some embodiments, the plate includes: a circular portion that has a plurality of channels that is coextensive with a plating face of the semiconductor wafer, wherein the plate has a thickness between about 2-25 mm; and a plurality of ribs extending from the circular portion, wherein the plurality of ribs comprises a first plurality of ribs of full maximum height and a second plurality of ribs of smaller maximum height than the full maximum height. In another aspect, a method for electroplating a substrate is provided. In some embodiments, the method includes: (a) receiving a substrate in a substrate holder, wherein a plating face of the substrate is exposed, and wherein the substrate holder is configured to hold the substrate such that the plating face of the substrate is separated from an anode during electroplating; (b) immersing the substrate in an electrolyte, wherein a gap is formed between the plating face of the substrate and an ionically resistive element plane, wherein the ionically resistive element is at least about coextensive with the plating face of the substrate, wherein the ionically resistive element comprises a channeled plate adapted to provide ionic transport through the ionically resistive element during electroplating, and wherein the ionically resistive element includes a plurality of ribs positioned on the substrate-facing side of the ionically resistive element, wherein the plurality of ribs includes a first plurality of ribs of full maximum height and a second plurality of ribs of smaller maximum height than the full maximum height; (c) flowing electrolyte in contact with the substrate in the substrate holder from a side inlet, into the gap, and out a side outlet, wherein the side inlet and side outlet are designed or configured to generate cross flowing electrolyte in the gap during electroplating; (d) rotating the substrate holder; and (e) electroplating material onto the plating face of the substrate while flowing the electrolyte as in (c). In some embodiments, the electroplated material includes tin and silver. In some embodiments, the electroplated material includes copper. In some embodiments the electrodepositions methods provided herein are used in conjunction with photolithographic patterning, and provided methods further include the steps of: applying photoresist to the semiconductor substrate; exposing the photoresist to light; patterning the photoresist and transferring the pattern to the semiconductor substrate; and selectively removing the photoresist from the semiconductor substrate. In another spect, a non-transitory computer machine-readable medium is provided, where the non-transitory computer machine-readable medium includes program instructions for control of an apparatus configured for substrate processing, wherein the program instructions comprise code configured to effect electrodeposition of material in accordance with the methods provided herein. These and other aspects of implementations of the subject matter described in this specification are set forth in the accompanying drawings and the description below. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic cross-sectional view of an electroplating apparatus having an ionically resistive element according to an embodiment provided herein. Figure 2 is a view of an ionically resistive element according to an embodiment provided herein. Figure 3A is a top view of a portion of the ionically resistive element illustrated in Figure 2. Figure 3B is another view of a portion of the ionically resistive element illustrated in Figure 2. Figure 3C is a cross-sectional view of a portion of the ionically resistive element illustrated in Figure 2. Figure 3D is a different cross-sectional view of a portion of the ionically resistive element illustrated in Figure 2. Figure 4 is an experimental plot illustrating silver content (in %) in the electrodeposited tin silver layer as a function of radial profile (in mm) for a uniform rib CIRP (top curve) and a CIRP of Embodiment 1. Figure 5 is an experimental plot illustrating thickness of the electrodeposited tin silver layer (bump height) as a function of radial position (in mm) for a uniform rib CIRP and a CIRP of Embodiment 1. Figure 6A is a top view of a resistive element according to an embodiment provided herein. Figure 6B is a view of a portion of a resistive element according to an embodiment provided herein. Figure 6C is a cross-sectional view of a portion of a resistive element according to an embodiment provided herein. Figure 7 illustrates top view of different ionically resistive elements according to embodiments provided herein. Figure 8 is schematic presentation of an integrated tool configured for electrodeposition of metals according to an embodiment provided herein. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Methods and apparatuses for electrodeposition of a metal on a semiconductor substrate with improved control over electrolyte hydrodynamics are provided. Due to greater control over electrolyte hydrodynamics, uniformity of electrodeposition can be improved. The methods are particularly useful for electroplating metal onto a semiconductor substrate having a plurality of recessed features. For example, provided methods can be used to fill recessed features, e.g., in WLP processing. The methods make use of an ionically resistive ionically permeable element, which includes an ionically permeable channeled plate and a plurality of ribs extending from the substrate- facing surface of the plate toward the substrate, where ribs have different maximum heights, or where individual ribs have variable heights (e.g. tapered ribs), or both. In some embodiments the electrolyte is injected into a gap between the ionically resistive element and the surface of the substrate, creating electrolyte cross-flow (lateral electrolyte flow parallel to the surface of the substrate). In some embodiments, the ribs (referring to “length” dimension of the ribs) are substantially perpendicular to electrolyte cross-flow direction. In one implementation the ribs proximate the inlet to the gap (e.g., within 50 mm of the inlet) have lower maximum height than ribs further away from the inlet. For example, the ionically resistive element may include a first rib (or a first plurality of ribs) and a second rib (or a second plurality of ribs), where the ionically resistive element is positioned such that the first rib (or a first plurality of ribs) is closer to the inlet to the gap than the second rib (or the second plurality of ribs) and where the first rib (or a first plurality of ribs) has a smaller maximum height than the second rib (or the second plurality of ribs). In some embodiments maximum rib height increases gradually in a direction from the edge of the element towards the center of the element. In some embodiments the ionically resistive element has ribs of various sizes distributed in a spatially non-uniform pattern. This produces tailored convection at a substrate surface for improved plating performance. By tailoring the rib height, tapering, and distributing the ribs at certain locations across the ionically resistive element, the hydrodynamics at the wafer surface can be modulated to improve plating performance. The term “a metal” as used herein, refers to one or more metals, and “electrodeposition of a metal” is not limited to electrodeposition of a single metal. For example, “a metal” can be a combination of tin and silver. In some embodiments, the methods are used for electrodeposition of copper (Cu). In some embodiments, the methods are used for electrodeposition of nickel (Ni), tin (Sn), or tin silver alloy (SnAg). The term “semiconductor substrate” as used herein refers to a substrate at any stage of semiconductor device fabrication containing a semiconductor material anywhere within its structure. It is understood that the semiconductor material in the semiconductor substrate does not need to be exposed. Semiconductor wafers having a plurality of layers of other materials (e.g., dielectrics) covering the semiconductor material, are examples of semiconductor substrates. The following detailed description assumes the disclosed implementations are implemented on a semiconductor wafer, such as on a 200 mm, 300 mm, or 450 mm semiconductor wafer. However, the disclosed implementations are not so limited. The work piece may be of various shapes, sizes, and materials. In addition to semiconductor wafers, other work pieces that may take advantage of the disclosed implementations include various articles such as printed circuit boards and the like. The term “about” when used in reference to numerical values includes a range of ±10% of the recited numerical value, unless otherwise specified. The term “ribs” refer to protrusions on the substrate-facing side of the ionically resistive ionically permeable element. The ribs in many embodiments have length to height ratios of greater at least 3:1. The rib lengths are usually at least coextensive with the channeled portion of the ionically resistive ionically permeable element. In some embodiments the ionically resistive ionically permeable element is machined from a single piece of a non-conductive material, e.g., polycarbonate. In other embodiments, the ribs may be removeable and may be inserted into slots on the channeled portion of the ionically resistive element. The terms “ionically resistive element”, “ionically resistive ionically permeable element”, and “channeled ionically resistive plate” are used herein interchangeably and refer to an element that is made of an electrically non-conductive material that has a plurality of channels that allow for passage of electrolyte. The element in some embodiments introduces a resistance to the ionic current between the anode and the cathodically biased wafer substrate. The term “maximum height” refers to the greatest height of a rib. For example, a rib that is tapered at the edges will have maximum height outside of the tapered region. If a rib has a constant height, its maximum height is equal to its constant height. The term “full maximum height” for a plurality of ribs refers to the greatest maximum height of a plurality of ribs. For example is a plurality of ribs has a plurality of ribs, where each rib has a maximum height of 5 mm, and a plurality of ribs where each rib has a maximum height of 3 mm, the “full maximum height” will be 5 mm. Provided methods make use of a channeled ionically resistive plate (CIRP), which is also referred to as ionically resistive ionically permeable element to control electrolyte hydrodynamics proximate the substrate. CIRP provides a small channel (a cross flow manifold) between the plating surface of the wafer substrate and the top of the CIRP. The CIRP can serve many functions, which may include at least one of 1) allowing ionic current to flow from an anode generally located below the CIRP and to the wafer, 2) allowing fluid to flow through the CIRP upwards and generally towards the wafer surface and 3) confining and resisting the flow of electrolyte away from and out of the cross flow manifold region. The electrolyte flow in the cross flow manifold region in some embodiments is comprised of fluid that comes up through holes in the CIRP as well as fluid that comes in from a cross flow injection manifold, typically located on the CIRP and to one side of the wafer, which creates transverse electrolyte flow. In certain embodiments, the apparatus is configured to operate under conditions that produce an average transverse electrolyte velocity of about 3 cm/sec or greater (e.g., about 5 cm/s or greater, about 10 cm/s or greater, about 15 cm/s or greater, or about 20 cm/s or greater) across the center point of the plating face of the substrate. When CIRP with uniform rib elements (thin protrusions of same height) is used, it should provide uniform flow disturbance across the CIRP. However, in some cases inlet or outlet effects can interact with the rib elements, creating a highly turbulent zone, leading to non-uniform plating performance. According to some embodiments provided herein, spatially distributing the ribs can counteract and minimize inlet/outlet turbulence and produce a more uniformly plated substrate. In one aspect, an electroplating apparatus is provided, where the electroplating apparatus includes: (a) an electroplating chamber configured to contain an electrolyte and an anode while electroplating metal onto a substrate; (b) a substrate holder configured to hold the substrate such that a plating face of the substrate is separated from the anode during electroplating; and an ionically resistive ionically permeable element positioned such that there is a gap between a working surface of the substrate and a substrate-facing surface of the element. The ionically resistive element includes a channeled plate adapted to provide ionic transport through the ionically resistive element during electroplating; a substrate-facing side that is parallel to the plating face of the substrate and separated from the plating face of the substrate by a gap; and a plurality of ribs positioned on the substrate-facing side of the ionically resistive element, wherein the plurality of ribs comprises a first plurality of ribs of full maximum height and a second plurality of ribs of smaller maximum height than the full maximum height. In some embodiments, the apparatus further includes an inlet to the gap for introducing cross flowing electrolyte to the gap; and an outlet to the gap for receiving cross flowing electrolyte flowing in the gap, wherein the inlet and outlet are positioned proximate azimuthally opposing perimeter locations on the plating face of the substrate during electroplating. The non-uniform ribs on the ionically resistive ionically permeable element are used to tailor the hydrodynamic environment at the substrate, by adjusting convection of electrolyte in the gap (also known as cross-flow manifold or CIRP chamber). An example of an electroplating apparatus 100 having a CIRP 101 with ribs of different maximum heights, as described above, is shown in Figure 1, which depicts a schematic cross-sectional view of the apparatus 100. The electroplating apparatus 100 includes a plating chamber 102 filled with electrolyte (which includes ions of a metal that is being electroplated, and, optionally, an acid and electroplating additives), which houses an anode 103 at the bottom. The anode 103 may be an active or an inert anode, which is electrically connected to a power supply and is configured to be positively biased. The wafer substrate 105 is held by a substrate holder 107 in a face-down orientation in the depicted embodiment and is configured to be negatively biased and immersed into the electrolyte during electroplating. In the depicted embodiment the apparatus further includes a membrane frame 109 and a membrane mounted on the membrane frame 109 between the anode 103 and the cathodically biased wafer substrate 105. The membrane may be an ion selective membrane, which may be used to maintain different compositions in the anode chamber 111 below the membrane, and the cathode chamber 113 above the membrane. For example, during concurrent tin silver plating when an active tin anode is used, the membrane may be used to inhibit or prevent silver ions in catholyte from being transferred to the anolyte chamber. In the depicted embodiment, CIRP 101 resides in the cathode chamber 113 and includes a channeled plate 114, where channels (not shown) allow the electrolyte to flow through the CIRP 101, and a plurality of ribs 115 (the ribs themselves are not channeled in this embodiment), where the ribs 115 include a first plurality of ribs of full maximum height (schematically depicted as seven ribs to the right) and a second plurality of ribs of lower maximum height (schematically depicted as four lower ribs to the left). The electrolyte is injected into an inlet 117 into the cross-flow manifold (CIRP chamber) 119 as shown by the arrow and flows after encountering ribs 115 that are gradually increasing in height without undergoing undesired levels of turbulence to the outlet 121 from the CIRP chamber 119 proximate azimuthally opposing perimeter location of the plating face of the substrate (relative to the inlet). The flow path for delivering cross flowing electrolyte begins in a vertically upward direction as it passes through the cross flow feed channel in the plate. Next, this flow path enters a cross flow injection manifold formed within the body of the channeled ionically resistive plate. The cross flow injection manifold is an azimuthal cavity which may be a dug out channel within the plate that can distribute the fluid from the various individual feed channels (e.g., from each of 6 individual cross flow feed channels) to the various multiple flow distribution holes of a cross flow showerhead plate. This cross flow injection manifold may be located along an angular section of the peripheral or edge region of the channeled ionically resistive plate 101. In certain embodiments, the cross flow injection manifold forms a C-shaped structure over an angle of about 90-180° of the plate’s perimeter region. The details of the cross-flow injection manifold are not shown in Figure 1 to preserve clarity. It is understood that the depiction of apparatus in Figure 1 is schematic, and that, in actual CIRPs a larger number of ribs may be used. In some embodiments the full maximum height of the ribs is less than about 5 mm, such as between about 1 – 3 mm. In some embodiments, the total number of ribs is between about 15 – 30, and the number of ribs of lower maximum height than the full maximum height is between about 2-10 ribs. It is noted that in the depicted embodiment the use of lower rib heights proximate the electrolyte inlet 117 is associated with marked decrease in turbulence as compared to a CIRP having all ribs of same maximum heights. The decrease in turbulence, in turn, leads to improved plating uniformity. Further in those embodiments where tin and silver are electroplated concurrently the use of the CIRP as shown in Figure 1 leads to more uniform content of silver in the tin silver layer throughout the wafer surface. In various cases, the CIRP is a disc made of a solid, non-porous dielectric material that is ionically and electrically resistive. The material is also chemically stable in the plating solution of use. In certain cases the CIRP is made of a ceramic material (e.g., aluminum oxide, stannic oxide, titanium oxide, or mixtures of metal oxides) or a plastic material (e.g., polyethylene, polypropylene, polyvinylidene difluoride (PVDF), polytetrafluoroethylene, polysulphone, polyvinyl chloride (PVC), polycarbonate, and the like), having between about 6,000 – 12,000 non-communicating through-holes. The channeled portion of the disc, in many embodiments, is at least substantially coextensive with the plating surface of the wafer (e.g., the CIRP disc has a diameter of about 300 mm when used with a 300 mm wafer) and resides in close proximity to the wafer, e.g., just below the wafer in a wafer-facing-down electroplating apparatus. Preferably, the plated surface of the wafer resides within about 20 mm, more preferably within about 5 mm of the closest CIRP surface. Another feature of the CIRP is the diameter or principal dimension of the through-holes and its relation to the distance between the CIRP and the substrate. In certain embodiments, the diameter of each through-hole (or of a majority of through- holes, or the average diameter of the through-holes) is no more than about the distance from the plated wafer surface to the closest surface of the CIRP. Thus, in such embodiments, the diameter or principal dimension of the through-holes should not exceed about 5 mm, when the CIRP is placed within about 5 mm of the plated wafer surface. As above, the overall ionic and flow resistance of the plate is dependent on the thickness of the plate and both the overall porosity (fraction of area available for flow through the plate) and the size/diameter of the holes. Plates of lower porosities will have higher impinging flow velocities and ionic resistances. Comparing plates of the same porosity, one having smaller diameter 1-D holes (and therefore a larger number of 1-D holes) will have a more micro-uniform distribution of current on the wafer because there are more individual current sources, which act more as point sources that can spread over the same gap, and will also have a higher total pressure drop (high viscous flow resistance). In certain cases, however, the ionically resistive plate is porous, as mentioned above. The pores in the plate may not form independent 1-D channels, but may instead form a mesh of through-holes which may or may not interconnect. For example, the plate may include a three-dimensional network of interconnecting channels. It should be understood that as used herein, the terms channeled ionically resistive plate (CIRP) and channeled ionically resistive element are intended to include this embodiment, unless otherwise noted. Rib Tapering In some embodiments, individual ribs of the CIRP have variable height, and, for example, may be tapered at the edges. Such tapering can improve electrolyte hydrodynamics at the substrate proximate the rib edges, and can also lead to more uniform electroplating. Rib height variation for individual ribs may be used either alone or in combination with using ribs of different maximum height as discussed above. Figure 2, and Figures 3A-3D show several views of a CIRP 200, which includes both ribs of different maximum height and ribs with tapered edges, which can be used as shown in the apparatus of Figure 1. Figure 2 illustrates a CIRP 200, which has 27 parallel ribs, of which ribs at one side of the CIRP have lower maximum heights than the maximum heights of the remaining ribs. Further, in addition, a portion of the ribs are tapered at the edges (have smaller height at the edges of a rib than at a center of the rib). Tapered ribs may be ribs of the full maximum height, ribs of lower maximum height or both. For example, full maximum height may be about 3 mm, und such ribs may or may not be tapered at the edges. For example, referring to Figure 2, the CIRP 200 includes non-tapered ribs 201 of full maximum height at one side of the CIRP 200, tapered ribs 203 of lower maximum height at an opposite side of the CIRP 200, and tapered ribs 205 having full maximum height. Figure 3A illustrates a top view of a portion of the CIRP 200 that was depicted in Figure 2, where a crescent-like region 310 is shown, in which rib height is lower than full maximum height. The region is formed by a combination of tapered portions at the edges (where height of individual ribs is reduced towards the edges) and by ribs that have maximum height that is smaller than the full maximum height. In the portion of the CIRP 200 that is outside of the crexcent- shaped region 310, which is referred as region 320, the ribs have full height. Figure 3B shows an isometric view of a portion of such CIRP 200, where tapering of ribs at the edges is more clearly depicted. Figure 3C depicts a cross-section of a portion of the same CIRP 200, which more clearly illustrates a gradual increase in maximum heights of consecutive ribs. Figure 3D illustrates a different cross-sectional view of a portion of the same CIRP 200, where rib tapering at the edges is illustrated. The CIRP shown in Figures 2, and 3A-3D (also referred to as Embodiment 1) was used in tin-silver plating in an apparatus as shown in Figure 1, and the results were compared to plating with a CIRP having uniform ribs (all ribs of the same height and without tapering). Figure 4 is an experimental plot 400 illustrating silver content (in %) in the electrodeposited tin silver layer as a function of radial profile (in mm) for a uniform rib CIRP (black diamonds) and for a CIRP of Embodiment 1 (white diamonds). It can be seen that the use of a uniform rib CIRP results in increased incorporation of silver into the film near the edge of the wafer as compared to wafer center. When the CIRP of Embodiment 1 is used the silver content variation as a function of radial position is advantageously reduced, and silver content remains substantially constant at all radial positions. Figure 5 is an experimental plot 500 illustrating thickness of the electrodeposited tin silver layer (bump height) as a function of radial position (in mm) for a uniform rib CIRP (black diamonds) and a CIRP of Embodiment 1 (white diamonds). It can be seen that the use of a uniform rib CIRP results in a drastic reduction of layer thickness at the edge of the wafer as compared to the center. When the CIRP of Embodiment 1 is used, the thickness uniformity is advantageously restored, and tin silver bump thickness remains substantially constant at all radial positions. It is believed that both improvements in silver content variation, and deposited layer uniformity are attributable to reduced turbulence that is achieved with the CIRP of Embodiment 1. When tin silver is plated, silver is provided in a small amount in the electrolyte relative to tin in this embodiment and silver concentration in the deposited film is limited by convection. With increased turbulence at the edge (encountered with uniform rib CIRP due to electrolyte flow disruption by full-height first ribs encountered at the electrolyte inlet), larger amounts of silver will be incorporated into the tin silver film at the edge of the wafer. This is addressed by providing a CIRP with gradually increasing height of consecutive ribs at the electrolyte inlet, and by rib tapering at the edges provided by the CIRP of Embodiment 1. With respect to increased plating at the edge with the use of a uniform-rib CIRP, the increased turbulence in this case results in increased function of an electroplating leveler, which is added to the tin silver electroplating electrolyte. Similarly, the use of CIRP of Embodiment 1 reduces the turbulence at electrolyte inlet and edges, leading to a substantially uniform plating profile. Figures 6A, 6B, and 6C provide different views of a CIRP 600 in accordance with the Embodiment 2. Embodiment 2 is similar to Embodiment 1 but differs from Embodiment 1 in that the crescent-like region 610 that includes regions with lower rib height than the full maximum height (including both shorter ribs and tapered rib portions) has a larger area than in the CIRP 200 of Embodiment 1. Specifically, it can be seen from Figure 6A that this region has an area that is about 50% of the total area of the channeled portion of the CIRP. The remaining area 620 is a region of ribs having full height. In some embodiments the area of this region is between about 40-60% of the total area of the channeled substrate-facing surface of the CIRP. The CIRPs with non-uniform ribs can be used to improve electrolyte hydrodynamics and to improve plating uniformity in a variety of other embodiments. They are particularly useful when used in an electroplating apparatus having electrolyte cross flow between an inlet and outlet in the cross flow manifold. A number of CIRP embodiments are illustrated in Figure 7, which schematically illustrates top views of CIRPs, where gray area represents an area where rib height is smaller than the full maximum height (tapered regions and/or ribs that have smaller maximum height than full maximum height) . Full maximum height region is shown as a white area. The direction of electrolyte flow over the CIRP is shown by an arrow. In Embodiment 3, the region of lower rib height has a crescent shape as in Embodiment 1, but the CIRP in Embodiment 3 is positioned such that this crescent region is positioned proximate to the outlet from the cross flow manifold rather than the inlet. This can be used to reduce any non-uniformities due to turbulences at the outlet. In Embodiment 4 the region of lower rib height is located at the right and left edges of the CIRP (relative to the direction of electrolyte flow). For example, substantially all of the ribs may be tapered at the edges in this embodiment. In Embodiment 5, the region of lower rib height has an annular shape (also referred to as bullseye embodiment). In Embodiment 6, the region of lower rib height has a horseshoe shape and is disposed proximate the inlet to the cross-flow manifold. In Embodiment 7, the region of lower rib height has a martini glass shape, with a larger area closer to the inlet into the cross-flow manifold. In another aspect, a method for electroplating a metal on a substrate is provided, where the method includes: (a) receiving a substrate in a substrate holder, wherein a plating face of the substrate is exposed, and wherein the substrate holder is configured to hold the substrate such that the plating face of the substrate is separated from an anode during electroplating; (b) immersing the substrate in an electrolyte, wherein a gap is formed between the plating face of the substrate and an ionically resistive element plane, wherein the ionically resistive element is at least about coextensive with the plating face of the substrate, wherein the ionically resistive element comprises a channeled plate adapted to provide ionic transport through the ionically resistive element during electroplating, and wherein the ionically resistive element comprises a plurality of ribs positioned on the substrate-facing side of the ionically resistive element, wherein the plurality of ribs comprises a first plurality of ribs of full maximum height and a second plurality of ribs of smaller maximum height than the full maximum height. The method further includes: (c) flowing electrolyte in contact with the substrate in the substrate holder (i) from a side inlet, into the gap, and out a side outlet, wherein the side inlet and side outlet are designed or configured to generate cross flowing electrolyte in the gap during electroplating; (d) rotating the substrate holder; and (e) electroplating material onto the plating face of the substrate while flowing the electrolyte as in (c). In another aspect an ionically resistive plate for use in an electroplating apparatus to plate material on a semiconductor wafer of standard diameter is provided, comprising: a circular portion that has a plurality of channels that is coextensive with a plating face of the semiconductor wafer, wherein the plate has a thickness between about 2-25 mm; and a plurality of ribs extending from the circular portion, wherein the plurality of ribs comprises a first plurality of ribs of full maximum height and a second plurality of ribs of smaller maximum height than the full maximum height. In some embodiments full maximum rib height is about 5 mm or less, such as about 3 mm or less. SYSTEM The deposition methods described herein can be carried out in a variety of electroplating apparatuses that are configured to include provided CIRPs. A suitable apparatus for deposition of a metal includes a plating chamber configured for holding an electrolyte and an anode, and a substrate holder having contacts for cathodically biasing the substrate. The apparatus may be configured for rotating the substrate during electroplating. Deposition can be conducted in a face-up or a face-down orientation. Some plating tools may be also run vertically. An example of a suitable apparatus is a SABRE 3D tool available from Lam Research Corp. of Fremont, CA. In some embodiments the electroplating tool includes multiple plating cells (for electrodepositing identical or different metals), where at least one plating cell includes a CIRP with non-uniform ribs as described herein, and a robotic tool for transferring the substrate between the individual plating cells. In some embodiments the apparatus further includes a controller that includes program instructions for causing performance of any of the methods described herein. An integrated apparatus configured for electrodeposition of metals is illustrated in Figure 8. In this embodiment, the apparatus 800 has a set of electroplating cells 807, each containing an electrolyte-containing bath, in a paired or multiple “duet” configuration. In addition to electroplating per se, the apparatus 800 may perform a variety of other electroplating or electroplanarization related processes and sub-steps, such as spin-rinsing, spin-drying, metal and silicon wet etching, electroless deposition, pre-wetting and pre-chemical treating, reducing, annealing, photoresist stripping, and surface pre-activation, for example. The apparatus 800 is shown schematically looking top down in Figure 8, and only a single level or “floor” is revealed in the figure, but it is to be readily understood by one having ordinary skill in the art that such an apparatus, e.g. the Lam Research Sabre^TM 3D tool, can have two or more levels “stacked” on top of each other, each potentially having identical or different types of processing stations. In some embodiments electroplating stations for different metals are arranged on different levels of the tool. In other embodiments a single level may include stations for electroplating both a first and a second metal. Referring once again to Figure 8, the substrates 806 that are to be electroplated are generally fed to the apparatus 800 through a front end loading FOUP (front loading unified pod) 801 and, in this example, are brought from the FOUP to the main substrate processing area of the apparatus 800 via a front-end robot 802 that can retract and move a substrate 806 driven by a spindle 803 in multiple dimensions from one station to another of the accessible stations - two front-end accessible stations 804 and also two front-end accessible stations 808 are shown in this example. The front-end accessible stations 804 and 808 may include, for example, pre-treatment stations, and spin rinse drying (SRD) stations. Lateral movement from side-to-side of the front-end robot 802 is accomplished utilizing robot track 802a. Each of the substrates 806 may be held by a cup/cone assembly (not shown) driven by a spindle connected to a motor (not shown), and the motor may be attached to a mounting bracket 809. Also shown in this example are the four “duets” of electroplating cells 807, for a total of eight cells 807. The electroplating cells 807 may be used for electroplating different metals. After a first metal has been electroplated in one of the plating stations 807, the substrate is transferred to a plating cell configured for electroplating of a second metal either on the same level of the apparatus or on a different level of the apparatus 800. A system controller (not shown) may be coupled to the electrodeposition apparatus 800 to control some or all of the properties of the electrodeposition apparatus 800. The system controller may be programmed or otherwise configured to execute instructions according to processes described earlier herein. The system controller will typically include one or more memory devices and one or more processors configured to execute the instructions so that the apparatus will perform a method in accordance with the present invention. Machine-readable media containing instructions for controlling process operations in accordance with the present invention may be coupled to the system controller. In some implementations, a controller is part of a system, which may be part of the above-described examples. Such systems can include semiconductor processing equipment, including a processing tool or tools, chamber or chambers, a platform or platforms for processing, and/or specific processing components (a wafer pedestal, a gas flow system, etc.). These systems may be integrated with electronics for controlling their operation before, during, and after processing of a semiconductor wafer or substrate. The electronics may be referred to as the “controller,” which may control various components or subparts of the system or systems. The controller, depending on the processing requirements and/or the type of system, may be programmed to control any of the processes disclosed herein, including the delivery of electrolytes, temperature settings (e.g., heating and/or cooling), voltage delivered to the cathode, wafer transfers into and out of a tool and other transfer tools and/or load locks connected to or interfaced with a specific system. Broadly speaking, the controller may be defined as electronics having various integrated circuits, logic, memory, and/or software that receive instructions, issue instructions, control operation, enable cleaning operations, enable endpoint measurements, and the like. The integrated circuits may include chips in the form of firmware that store program instructions, digital signal processors (DSPs), chips defined as application specific integrated circuits (ASICs), and/or one or more microprocessors, or microcontrollers that execute program instructions (e.g., software). Program instructions may be instructions communicated to the controller in the form of various individual settings (or program files), defining operational parameters for carrying out a particular process on or for a semiconductor wafer or to a system. The operational parameters may, in some embodiments, be part of a recipe defined by process engineers to accomplish one or more processing steps during the fabrication of one or more layers, materials, metals, oxides, silicon, silicon dioxide, surfaces, circuits, and/or dies of a wafer. The controller, in some implementations, may be a part of or coupled to a computer that is integrated with, coupled to the system, otherwise networked to the system, or a combination thereof. For example, the controller may be in the “cloud” or all or a part of a fab host computer system, which can allow for remote access of the wafer processing. The computer may enable remote access to the system to monitor current progress of fabrication operations, examine a history of past fabrication operations, examine trends or performance metrics from a plurality of fabrication operations, to change parameters of current processing, to set processing steps to follow a current processing, or to start a new process. In some examples, a remote computer (e.g. a server) can provide process recipes to a system over a network, which may include a local network or the Internet. The remote computer may include a user interface that enables entry or programming of parameters and/or settings, which are then communicated to the system from the remote computer. In some examples, the controller receives instructions in the form of data, which specify parameters for each of the processing steps to be performed during one or more operations. It should be understood that the parameters may be specific to the type of process to be performed and the type of tool that the controller is configured to interface with or control. Thus as described above, the controller may be distributed, such as by comprising one or more discrete controllers that are networked together and working towards a common purpose, such as the processes and controls described herein. An example of a distributed controller for such purposes would be one or more integrated circuits on a chamber in communication with one or more integrated circuits located remotely (such as at the platform level or as part of a remote computer) that combine to control a process on the chamber. Without limitation, example systems may include a plasma etch chamber or module, a deposition chamber or module, a spin-rinse chamber or module, a metal plating chamber or module, a clean chamber or module, a bevel edge etch chamber or module, a physical vapor deposition (PVD) chamber or module, a chemical vapor deposition (CVD) chamber or module, an atomic layer deposition (ALD) chamber or module, an atomic layer etch (ALE) chamber or module, an ion implantation chamber or module, a track chamber or module, and any other semiconductor processing systems that may be associated or used in the fabrication and/or manufacturing of semiconductor wafers. As noted above, depending on the process step or steps to be performed by the tool, the controller might communicate with one or more of other tool circuits or modules, other tool components, cluster tools, other tool interfaces, adjacent tools, neighboring tools, tools located throughout a factory, a main computer, another controller, or tools used in material transport that bring containers of wafers to and from tool locations and/or load ports in a semiconductor manufacturing factory. Patterning Method/Apparatus: The apparatus/process described hereinabove may be used in conjunction with lithographic patterning tools or processes, for example, for the fabrication or manufacture of semiconductor devices, displays, LEDs, photovoltaic panels and the like. Typically, though not necessarily, such tools/processes will be used or conducted together in a common fabrication facility. Lithographic patterning of a film typically comprises some or all of the following steps, each step enabled with a number of possible tools: (1) application of photoresist on a workpiece, i.e., substrate, using a spin-on or spray-on tool; (2) curing of photoresist using a hot plate or furnace or UV curing tool; (3) exposing the photoresist to visible or UV or EUV or x-ray light with a tool such as a wafer stepper; (4) developing the resist so as to selectively remove resist and thereby pattern it using a tool such as a wet bench; (5) transferring the resist pattern into an underlying film or workpiece by using a dry or plasma-assisted etching tool; and (6) removing the resist using a tool such as an RF or microwave plasma resist stripper.

Claims

CLAIMS What is claimed is: 1. An electroplating apparatus comprising: (a) an electroplating chamber configured to contain an electrolyte and an anode while electroplating metal onto a substrate; (b) a substrate holder configured to hold the substrate such that a plating face of the substrate is separated from the anode during electroplating; (c) an ionically resistive element comprising: (i) a channeled plate adapted to provide ionic transport through the ionically resistive element during electroplating; (ii) a substrate-facing side that is parallel to the plating face of the substrate and separated from the plating face of the substrate by a gap; and (iii) a plurality of ribs positioned on the substrate-facing side of the ionically resistive element, wherein the plurality of ribs comprises a first plurality of ribs of full maximum height and a second plurality of ribs of smaller maximum height than the full maximum height; (d) an inlet to the gap for introducing cross flowing electrolyte to the gap; and (e) an outlet to the gap for receiving cross flowing electrolyte flowing in the gap, wherein the inlet and outlet are positioned proximate azimuthally opposing perimeter locations on the plating face of the substrate during electroplating.

2. The electroplating apparatus of claim 1, wherein the ionically resistive element is positioned such that the second plurality of ribs of smaller maximum height is proximate the inlet to the gap.

3. The electroplating apparatus of claim 1, wherein all ribs are parallel to each other and are perpendicular to a direction of a flow of the cross flowing electrolyte in the gap.

4. The electroplating apparatus of claim 1, wherein the second plurality of ribs comprises at least two ribs of different maximum heights.

5. The electroplating apparatus as in any of the claims 1, wherein the ribs in the second plurality of ribs are arranged such that the maximum rib height increases in a direction from an edge to the center of the ionically resistive plate, and wherein the second plurality of ribs of lower height are disposed only on one side of the ionically resistive plate.

6. The electroplating apparatus as in any of the claims 1-5, wherein the total number of ribs is between about 15 – 30, and the second plurality of ribs of lower maximum height has between about 2-10 ribs.

7. The electroplating apparatus as in any of the claims 1-5, wherein the full maximum height of the ribs is less than about 5 mm.

8. The electroplating apparatus as in any of the claims 1-5, wherein the full maximum height of the ribs is about 1 – 3 mm.

9. The electroplating apparatus as in any of the claims 1-5, wherein the gap between the bottom portion of the substrate holder and the ionically resistive element is less than about 20 mm.

10. The electroplating apparatus as in any of the claims 1-5, wherein at least some of the ribs have variable height.

11. The electroplating apparatus as in any of the claims 1-5, wherein at least some of the ribs have variable height, and wherein rib height decreases gradually in a direction toward an edge of the rib.

12. The electroplating apparatus of claim 1, wherein the ionically resistive element comprises a region, where rib height is lower than the full maximum height, and wherein the region is generally crescent-shaped.

13. The electroplating apparatus of claim 12, wherein the region is located proximate either the inlet or the outlet from the gap.

14. The electroplating apparatus of claim 1, wherein the ionically resistive element comprises a region, where rib height is lower than the full maximum height, and wherein the region is generally annular.

15. The electroplating apparatus of claim 1, wherein the ionically resistive element comprises a region, where rib height is lower than the full maximum height, and wherein the region has a martini glass shape.

16. The electroplating apparatus of claim 1, wherein the ionically resistive element comprises a plurality of non-communicating channels.

17. The electroplating apparatus of claim 1, wherein the ionically resistive element comprises a 3-D network of communicating channels.

18. The electroplating apparatus of claim 1, further comprising a cross flow injection manifold fluidically coupled to the inlet.

19. The electroplating apparatus of claim 18, wherein the cross flow injection manifold is at least partially defined by a cavity in the ionically resistive element.

20. The electroplating apparatus of claim 1, further comprising a flow confinement ring positioned over a peripheral portion of the ionically resistive element.

21. The electroplating apparatus of claim 1, wherein the inlet spans an arc between about 90-180° proximate the perimeter of the plating face of the substrate.

22. An ionically resistive plate for use in an electroplating apparatus to plate material on a semiconductor wafer of standard diameter, comprising: a circular portion that has a plurality of channels that is coextensive with a plating face of the semiconductor wafer, wherein the plate has a thickness between about 2-25 mm; a plurality of ribs extending from the circular portion, wherein the plurality of ribs comprises a first plurality of ribs of full maximum height and a second plurality of ribs of smaller maximum height than the full maximum height.

23. A method for electroplating a substrate comprising: (a) receiving a substrate in a substrate holder, wherein a plating face of the substrate is exposed, and wherein the substrate holder is configured to hold the substrate such that the plating face of the substrate is separated from an anode during electroplating; (b) immersing the substrate in an electrolyte, wherein a gap is formed between the plating face of the substrate and an ionically resistive element plane, wherein the ionically resistive element is at least about coextensive with the plating face of the substrate, wherein the ionically resistive element comprises a channeled plate adapted to provide ionic transport through the ionically resistive element during electroplating, and wherein the ionically resistive element comprises a plurality of ribs positioned on the substrate-facing side of the ionically resistive element, wherein the plurality of ribs comprises a first plurality of ribs of full maximum height and a second plurality of ribs of smaller maximum height than the full maximum height; (c) flowing electrolyte in contact with the substrate in the substrate holder (i) from a side inlet, into the gap, and out a side outlet, wherein the side inlet and side outlet are designed or configured to generate cross flowing electrolyte in the gap during electroplating; (d) rotating the substrate holder; and (e) electroplating material onto the plating face of the substrate while flowing the electrolyte as in (c).

24. The method of claim 23, wherein the electroplated material comprises tin and silver.

25. The method of claim 23, wherein the electroplated material comprises copper.

26. The method of claim 23, further comprising the steps of: applying photoresist to the semiconductor substrate; exposing the photoresist to light; patterning the photoresist and transferring the pattern to the semiconductor substrate; and selectively removing the photoresist from the semiconductor substrate.

27. A non-transitory computer machine-readable medium comprising program instructions for control of an apparatus configured for substrate processing, wherein the program instructions comprise code configured to effect electrodeposition of material in accordance with the method of claim 23.