US20050230262A1

US20050230262A1 - Electrochemical methods for the formation of protective features on metallized features

Info

Publication number: US20050230262A1
Application number: US10/828,011
Authority: US
Inventors: LinLin Chen
Original assignee: Semitool Inc
Current assignee: Semitool Inc
Priority date: 2004-04-20
Filing date: 2004-04-20
Publication date: 2005-10-20

Abstract

Electrochemical processes and apparatus are described for forming a protective feature on the exposed surface of a metallized feature. The protective feature provides a diffusion barrier and protects the metallized feature from corrosion and contamination. Protective features formed from nickel, cobalt, and alloys of these metals are described.

Description

FIELD OF THE INVENTION

The present invention relates to electrochemical methods for the formation of protective features on metallized features formed on microelectronic workpieces.

BACKGROUND OF THE INVENTION

A microelectronic workpiece can have repeating layers of insulating regions and conducting regions bonded to one another. An inherent problem when joining two dissimilar materials is a tendency of one or both materials to migrate or diffuse across the common interface into the other material. Thus, in order to be effective, the materials chosen to form the insulating regions and the conducting regions must be properly isolated from each other so that one material does not diffuse into the adjacent dissimilar material.
Typically, metals have been used as materials for conducting regions. Metals can be used to form interconnections between differing layers or regions, or they can be used to form intraconnections in the same layer. The newest generation of microelectronic devices relies more and more heavily upon copper-based interconnections.
While copper exhibits desirable conductivity and resistivity characteristics, it has been found to have a high tendency to diffuse into surrounding dielectric materials or corrode, which degrades the integrity of the interconnection features as well as the surrounding devices or dielectric structures. Typically, a copper feature will be formed on a “barrier layer,” which is interposed between the underlying structure and the copper feature. Such barrier layers are typically applied to the underlying structure prior to deposition of the copper. In situations where the copper is to be deposited into a trench or via the barrier layer serves to isolate the bottom and sidewalls of the copper from the dielectric. The resulting top surface of the copper feature can then be “capped” by a barrier material to isolate the top surface of the copper feature from subsequently applied layers of dielectric.
Conventional materials for applying barrier layers include sputter deposited or low-pressure chemical vapor deposited titanium or tantalum metals or alloys thereof. For example, in U.S. Pat. No. 5,256,274 to Poris, a diffusion barrier is applied to a silicone-based dielectric region before proceeding with an electrodeposition step. Poris also describes a thin, nonconductive silicon nitride layer which is applied to an exposed deposited metal feature to act as a diffusion barrier. Such nonconductive barrier layer must be removed prior to the deposition of a via or line onto the underlying metal feature.
Sputter deposition and physical or chemical vapor deposition, however, are costly because they involve time-consuming processing steps when compared to electrochemical deposition processes. Furthermore, such processes are nonselective and are less than desirable when it comes to deposition on vertically oriented features or features with high aspect ratios.
In Electrolessly Deposited Diffusion Barriers for Microelectronics, J. Research & Development, by E. J. O'Sullivan et al., electrolessly deposited capping layers for the top surface of copper interconnects are described as protecting the top surface of the copper feature from corrosion, preventing diffusion and to ensure adhesion to subsequent polyimide layers.
In certain process architectures, the top and/or sidewalls of a metallized feature such as copper lines or vias are exposed. When dielectric is deposited over these sidewalls, the possibility for diffusion of the copper into the dielectric and corrosion of the copper exists. Accordingly, there is a need for processes for providing protective features on exposed surfaces of conductive features, such as control top surface and/or sidewalls that have been deposited and are to come in contact with dielectric materials deposited after formation of the conductive feature.

SUMMARY OF THE INVENTION

The present invention provides electrochemical methods for encapsulating conductive features, such as copper features, to prevent diffusion of copper into surrounding structures such as dielectrics deposited over the conductive features and to prevent diffusion of undesired materials into the conductive features themselves. The present invention achieves this goal by encapsulating a metallized feature formed on a microelectronic workpiece with a conductive protective feature, wherein a surface of the metallized feature is covered by the conductive protective feature prior to deposition of a dielectric material over the metallized feature.
In one embodiment, the method involves forming a metallized feature on a microelectronic workpiece wherein the metallized feature has an exposed surface, such as a top surface or sidewalls. The conductive protective feature is provided by electrolytically depositing a metal such as nickel, cobalt, or alloys thereof on the exposed surface of the metallized feature.
In another embodiment, the conductive protective feature is provided by first forming a metallized feature on the front side of a microelectronic workpiece wherein the metallized feature has an exposed surface. The microelectronic workpiece carrying the metallized feature is then cleaned. Thereafter, at least the exposed surface of the metallized feature is activated, followed by the electroless deposition of the conductive protective feature on the exposed surface.
In the embodiments described above, the methods can also include deposition of a protective feature on at least an exposed sidewall.
A method carried out in accordance with the present invention provides a conductive feature on a microelectronic workpiece that comprises an electrochemically deposited metallized feature having an exposed surface and a conductive protective feature electrochemically deposited exterior to the top surface and optionally on at least one sidewall.
The present invention also provides an apparatus for carrying out processes in accordance with the present invention. Such an apparatus is suitable for use in a manufacturing line for providing conductive features on a microelectronic workpiece. The apparatus includes an input section for receiving a microelectronic workpiece which carries a barrier feature, a seed layer formed exterior to the barrier feature and a photoresist feature. Typically such microelectronic workpiece is processed in a tool separate from a tool formed in accordance with the present invention. The apparatus of the present invention also includes a bulk metallization station for electrochemically forming a metallized feature exterior to the seed layer. A photoresist removal station is provided for removing at least a portion of the photoresist feature. The removal of the photoresist results in a metallized feature on the workpiece with an exposed surface, e.g., a top surface and/or at least one exposed sidewall. A seed layer removal station removes those portions of the seed layer that are not covered by the metallized feature. In order to deposit a protective feature of the present invention, an electrochemical deposition station is included in the apparatus for electrochemically depositing a conductive protective feature on the exposed surface of the metallized feature. Finally, a barrier layer etching station is provided for removing at least a portion of the exposed barrier layer. The electrochemical deposition station for use in an apparatus formed in accordance with the present invention can be either an electrolytic deposition chamber or an electroless deposition chamber.
The methods and apparatuses of the present invention provide for the selective and controllable deposition of a conductive protective feature onto an exposed metallized feature that isolates the exposed top surface(s) from a layer of dielectric deposited after the metallized feature is formed. In a preferred embodiment, the metallized feature is encapsulated by the protective feature. The method of the present invention provides a protective feature on the metallized feature and does not suffer from the nonselective nature of prior processes for depositing diffusion barrier layers and is a more controllable and less costly alternative to sputter deposition, and physical or chemical vapor deposition techniques.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:
FIGS. 1-5 schematically illustrate a process architecture for forming a raised exposed metallized feature suitable for processing in accordance with the present invention;
FIGS. 6-8 schematically illustrate an alternative process architecture for providing a raised exposed metallized feature for processing in accordance with the present invention;
FIGS. 9-13 schematically illustrate another alternative process architecture for providing a raised metallized feature with exposed surfaces which can be processed in accordance with the present invention;
FIGS. 14-16 schematically illustrate a process carried out in accordance with the present invention;
FIG. 17 schematically illustrates a metallized feature which has a protective feature provided in accordance with the present invention; and
FIG. 18 schematically illustrates a manufacturing sequence including a tool for carrying out the formation of a protective feature in accordance with the present invention; and
FIG. 19 is a cross-section view of a reactor for carrying out electrochemical deposition of metals in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Prior to undertaking the description of the present invention, it is advantageous to describe the various terms used herein to signify deposition methods and other terms used in the present specification.
Electroplating, plating, or electrolytically depositing is a process for deposition of a conductive material using an applied current between a workpiece and an anode.
Electroless or electroless deposition is the autocatalytic deposition of a conductive material without the use of an applied current.
Electrochemical deposition as used herein refers to both methods of electroplating and electroless deposition.
Layer is any region of substantially similar composition, although it is not required to be constant throughout.
Microelectronic workpiece refers to workpieces having generally planar first and second surfaces that are relatively thin, including semiconductor wafers, ceramic workpieces, and other workpieces upon which microelectronic circuits or components, data storage elements, or layers, and/or micromechanical elements are formed.
The methods of the present invention are applicable to metallized features formed on a microelectronic workpiece, typically by an additive or through plating process architecture, such as photoresist pattern plating, template plating, or planar subtractive metallization techniques. These techniques result in a raised metallized feature such as the one described below having an exposed surface(s) such as its top surface, its top surface and at least one sidewall, and its top surface and two sidewalls.
An exemplary process architecture is illustrated and described below with reference to FIGS. 1-5. Referring to FIG. 1, a trench 100 is formed in a substrate 102 using conventional photolithographic and etching techniques. A barrier layer 104 is deposited onto the substrate and into trench 100 using physical vapor deposition, such as sputtering, or by chemical vapor deposition. Materials suitable for use as barrier layer 104 include tantalum, tantalum nitride, titanium, and titanium nitride. Suitable thicknesses for barrier layer 104 range from about 100 to 300 angstroms; however, the thickness may vary depending upon the particular architecture. A metal seed layer 106 is provided exterior to barrier layer 104 using known techniques, such as sputter or vapor deposition. Suitable metals for use as a seed layer 100 include, in addition to copper, metals such as chromium, cobalt, silver, tin, lead, cadmium, platinum, palladium, iridium, ruthenium, zinc, gold, nickel, alloys thereof, or any combination thereof. Referring to FIG. 2, a patterned and developed photoresist layer 108 is formed exterior to seed layer 106 providing a trench 109 centered over trench 100.
Referring to FIG. 3, a metallized feature 110 is deposited into trench 100 and trench 109 using known techniques such as electrochemical deposition. Suitable metals for use in the bulk metallization include, in addition to copper, metals such as chromium, cobalt, silver, tin, lead, cadmium, platinum, palladium, iridium, ruthenium, zinc, gold, nickel, alloys thereof or any combination thereof. Referring to FIG. 4, after metallized feature 110 is deposited, photoresist 108 is removed to provide raised metallized feature 110 with its top surface 101 and opposing sidewalls 103 and 105 exposed. As can be seen in FIG. 4, the term exposed refers to the top 101 and sidewall surfaces 103 and 105 that are exposed after removal of photoresist 108. In contrast, the sidewalls of the metallized feature formed in trench 100 are not exposed as such term is used herein. Subsequent to the removal of the photoresist 108, the portion of seed layer 106 not covered by metallized feature 105 is removed by etching or a similar technique to provide the structure illustrated in FIG. 5. A protective feature formed in accordance with the present invention can be applied to the structure illustrated in FIG. 5. Alternatively, the exposed portion of the barrier layer 104 can be removed before a protective feature formed in accordance with the present invention is formed.
Alternatively, a raised exposed metallized feature which can be treated in accordance with the present invention can be provided by an alternative process architecture described below with reference to FIGS. 6, 7, and 8.
Referring to FIG. 6, a trench 100 and trench 109 are provided with a barrier layer 104 as described above with respect to FIGS. 1-5; however, seed layer 106 has been omitted. In this process architecture, seed layer 106 is deposited onto the portion of barrier layer 104 which are not covered by the patterned photoresist layer 108. After deposition of seed layer 106, bulk metallization is carried out to deposit metallized feature 110 in trenches 100 and 109 as illustrated in FIG. 8. Thereafter, photoresist 108 can be removed to provide a metallized feature with an exposed top surface and sidewalls identical to that described above with reference to FIG. 5.
Finally, a raised metallized feature with exposed top surface and sidewalls can be provided by a process architecture described below with reference to FIGS. 9-13. In such a process architecture, a barrier feature 104 and seed layer 106 are sequentially deposited onto a substrate 102 to provide the structure as illustrated in FIG. 9. Thereafter, a photoresist layer 108 is deposited and patterned to provide a trench 100 as illustrated in FIG. 10. Subsequent to the formation of trench 100, bulk metallization is carried out to fill trench 100 to provide metallized feature 110 as illustrated in FIG. 11. Thereafter, photoresist 108 is removed, exposing sidewalls 103 and 105 of metallized feature 110. Thereafter, the portions of seed layer 106 and barrier feature 104 that are not covered by metal feature 110 can be removed by etching or other similar technique to provide the metallized feature illustrated in FIG. 13 with an exposed top surface and sidewalls.
It should be understood that while three different process architectures have been described above for providing raised metallized features with exposed top surface and sidewalls that can benefit from the present invention, it should be understood that the advantages of the present invention may be applicable to other process architectures not specifically described herein that provide similar structure. Examples of such alternative process architectures may include damascene and dual damascene processes.
The foregoing process architectures provide a metallized feature which is raised and exposed on its top surface as well as both sidewalls. In order to provide multilayer architectures, a dielectric will eventually be deposited over the raised metallized feature in order to form additional layers. In order to minimize the possibility of diffusion of the metal of the metallized feature into such dielectric layer, corrosion of the metallized feature, and diffusion of undesirable materials into the metallized features, a protective feature formed in accordance with the present invention is advantageously provided.
For purposes of the present specification, and for a better understanding of the present invention, a distinction is drawn between those barrier layers described above that are applied to a substrate prior to deposition of a metallized feature thereon and the protective features of the present invention. Such barrier layers serve to isolate the underlying substrate from the overlying metallized feature. In contrast, the protective features of the present invention are applied onto the exposed surfaces of an already deposited metallized feature, thus isolating the metallized feature from a subsequently deposited dielectric layer. For convenience and ease of understanding, “protective feature” will be used herein to refer to the layers of protective materials that are applied after deposition of a metallized feature and before deposition of a dielectric over the metallized feature.
Referring to FIG. 14, a conductive feature 120 formed in accordance with the present invention from the raised exposed metallized features described above with reference to FIGS. 1-8 includes a protective feature 112 which in the illustrated embodiment has been deposited on the top surface 101 of metallized feature 110 and the exposed sidewalls 103 and 105. The structure illustrated in FIG. 14 can be prepared for subsequent planarization by etching the exposed portions of barrier layer 104 to provide the structure illustrated in FIG. 15. Thereafter, a planarizing dielectric layer 114 can be deposited to provide the structure illustrated in FIG. 16.
With respect to the raised metallized feature described above with respect to FIGS. 9-13, a protective feature 112 can be provided on the exposed top surface 101 and exposed sidewalls 105 to provide the structure illustrated in FIG. 17. In view of the electrical isolation of metallized feature 110 in FIGS. 13 and 17, it is understood that in order to provide a protective feature 112 in accordance with the present invention, such protective feature 112 will need to be provided by an electroless process as described below in more detail. Since conductive feature 110 in FIG. 13 is electrically isolated, it would not be possible to electrolytically deposit a protective feature onto the exposed top and exposed sidewalls because no applied current can be established between conductive feature 110 and an anode. With respect to the raised and exposed metallized features described above with reference to FIGS. 1-5 and 6-8, current can be carried to metallized feature 110 through barrier layer 104 and therefore a protective feature 112 can be deposited onto metallized feature 110 in FIGS. 1-5 and 6-8 either electrolytically or electrolessly.
A protective feature formed in accordance with the present invention comprises metals such as nickel, its alloys, cobalt, and its alloys. Specific examples of nickel alloys include nickel-tungsten-phosphorus, nickel-molybdenum-phosphorus, nickel-molybdenum-boron, nickel-tungsten-boron, nickel-boron and nickel-phosphorus. Suitable alloys of cobalt include cobalt-phosphorus, cobalt-boron nickel-cobalt-phosphorus, nickel-cobalt-boron, cobalt-tungsten-phosphorus, cobalt-molybdenum-phosphorous, cobalt-molybdenum-boron, and cobalt-tungsten-boron. A protective feature can range in thickness from about 500 angstroms to about 2,500 angstroms. It should be understood that protective features that are less thick or more thick than the recited range fall within the scope of the present invention. Protective features that are thinner can be deposited more quickly; however, their ability to isolate the metallized feature from the overlying dielectric material may be less compared to protective features that are thicker. In contrast, thicker protective features will require longer extended processing times.
The composition of the protective feature can vary depending upon the particular architecture involved. The composition should be chosen so that adequate isolation between the underlying metallized feature and the overlying dielectric material is provided while at the same time providing satisfactory adhesion between the underlying metallized feature and overlying dielectric material. In addition, the particular metal or its alloy chosen for the protective feature should not have an undesirable effect on the resistivity of the underlying metallized feature.
In accordance with the present invention, the protective features of the present invention can be provided by electrochemical deposition processes such as an electrolytic or electroless process.
In an electrolytic process, the workpiece carrying the metallized feature with its exposed surfaces is contacted with an electroplating bath of a composition suitable for deposition of the desired metal for the protective feature when a current is applied between the workpiece and an anode in the bath. Specific metals suitable for the electrolytically deposited protective features have been described above, but it should be understood that other metals which can be electrolytically deposited and are conductive that provide the necessary diffusion barrier properties can also be used in accordance with the present invention.
The metal or metals that are to be deposited as a protective feature onto the exposed surfaces of the metallized features on the workpiece in accordance with the present invention are present in a solution as species of metal ions or complexed ions. The metal ions are deposited under alkaline or acidic process conditions that result in their preferential deposition on the raised and exposed surfaces of the metallized features as opposed to the surrounding field regions. Such electrolytic solutions advantageously include organic additives that encourage deposition onto the raised exposed features (i.e., accelerators) or that suppress deposition of metal ions onto the surrounding field surface areas (i.e., suppressors). In addition, the baths may include organic additives such as brighteners or levelers.
Examples of accelerators for use in electrolytic baths useful for carrying out the present invention include water-soluble salts of organic acids including mercapto or thiol functional groups, as well as other compounds that include the chemical structure S—R₁—S, wherein R₁is an alkyl or aryl moiety. Examples of suitable suppressors include polyethylene glycols and polyoxyethylene glycols having molecular weights of approximately 3,000 to 8,000. Such suppressor agents are available commercially from sources such as Shipley Company, Inc., Newton, Mass., and Enthone-OMI, New Haven, Conn.
Complexing agents that are suitable for use in electrolytic baths for depositing protective features in accordance with the present invention include ethylene diamine tetracetic acid (EDTA), ethylene diamine (ED), citric acid, and their salts. Such complexing agents can be used alone, in combination with one another, or in combination with one or more other complexing agents. The specific amount of complexing agent employed will be dependent upon the specific process conditions and composition of the electrolytic processing bath. It should be understood that other complexing agents may be employed depending upon the specific chemistry of the electrolytic bath.
The electrolytic deposition of a protective feature in accordance with the present invention can be carried out in an alkaline bath. An exemplary alkaline bath for depositing a nickel based protective feature includes a source of metal ions in the form of nickel, such as nickel sulfate, nickel chloride, nickel acetate or nickel sulfamate. Concentrations of 5-50 gm per liter of the nickel salt in the plating bath are useful. If the metal or alloy to be deposited is cobalt, the alkaline bath includes a source of metal ions in the form of cobalt such as cobalt sulfate, cobalt chloride, or cobalt acetate. Concentrations ranging from about 5-50 gm per liter of the cobalt salt in the plating bath are useful in accordance with the present invention. Other components of an alkaline plating bath useful in accordance with the present invention for depositing protective features of nickel or cobalt or its alloys include complexing agents such as citrate salt, ethylenediamine, glycine, oxalate salt, salicylate salt. As alternatives to these salts, their acids, such as citric acid, oxalic acid, salicylic acid, and bases, such as sodium hydroxide, potassium hydroxide, ammonium hydroxide, and tetramethylammonium hydroxide can be used. The complexing agents when used should be present in a stoichiometric excess with respect to the nickel or cobalt concentration in the bath. An exemplary range of concentration is about 5-50 gm per liter. The bath may also include a pH buffer such as boric acid in an amount ranging from about 10-30 gm per liter and a nonionic surfactant, such as Triton X-100 available from the Dow Chemical Company in an amount ranging from about 0.01-1 gm per liter.
When the protective feature is formed from an alloy of nickel or cobalt, the alloying metal is provided by including a source of metal ions in the form of the alloying material in the plating bath. When phosphorous is the alloying material, the bath can include a source of phosphorous ions. When boron is the alloying material, the bath can include a source of boron ions. When tungsten is the alloying material, a tungsten salt, such as sodium tungstate or ammonium tungstate can be present in the plating bath in an amount ranging from about 2-10 gm per liter. When molybdenum is the alloying material, the bath can include sodium molybdate or ammonium molybdate in an amount ranging from about 2-10 gm per liter.
The electrolytic deposition of a protective feature in accordance with the present invention can also be carried out in an acidic bath. An exemplary acidic bath for depositing a nickel based protective feature includes a source of metal ions in the form of nickel sulfate, an acid in the form of boric acid, and a citrate complexing agent. A suitable nonlimiting composition and range of concentrations for the various components of an electrolytic bath for depositing nickel boron on an exposed metallized feature on a workpiece according to the present invention include the following:

- 1. 0.25 M NiSO₄;
- 2. 0.5 M H₃BO₃;
- 3. 0.33 M Na₃C₃H₅O₇; and
- 4. pH of about 6.2.

The above-mentioned bath can also be used to plate nickel tungsten (20%) or nickel phosphorus (25%) alloys if tungstate (H₂WO₄) or H₂PHO₃is present in the bath. In addition, in view of the similar electroplating properties of nickel and cobalt, cobalt can be used in place of nickel and provided in the bath in the form of cobalt sulfate.
Other nickel or cobalt alloys can be selectively deposited through the selection of the specific components present within the electroplating bath. It should be understood that the aforementioned solutions are not intended to limit the use of the present invention to the specific baths. Solutions useful in accordance with the method of the present invention can include one or a plurality of metal ion source or sources, depending on whether the protective feature to be deposited is a binary or ternary alloy. Other sources of nickel ions or cobalt ions are also within the scope of the present invention.
The electrolytic deposition of the protective features of the present invention can be carried out in a tool designed to electrochemically deposit metals such as one available from Semitool, Inc., of Kalispell, Mont., under the trademark LT210™ ECD system. Other commercially available systems for the electrochemical deposition of metals include the Equinox™ model tool available from Semitool, Inc. as well.
An integrated tool can be provided to carry out a number of process steps carried out in accordance with the present invention. Below is described one possible combination of processing stations that could be embodied in a processing tool platform sold under the trademark EquinoX™ by Semitool, Inc. of Kalispell, Mont. It should be understood that other processing tool platforms could be configured in similar or different manners to carry out the metallization steps of the present invention. Referring to FIG. 18, an exemplary integrated processing tool includes various stations to carry out an optional seed layer deposition 122, a photoresist developing step 124, a bulk metallization step 126, a seed layer etch step 128, a barrier layer etch step 130, and a protective feature deposition step 132. The tool may also include a photoresist removal chamber 127 for removing developed photoresist. The chambers for carrying out such steps can be arranged in various configurations. Microelectronic workpieces are transferred between the stations through the use of robotics (not shown). In addition, other processing stations such as a rinse station identified by reference 134 can be provided in the processing tool 120. Processing tool 120 is capable of being programmed to implement user entered processing recipes and conditions.
The robotics for the tool 120 are designed to move along a linear track. Alternatively, the robotics can be centrally mounted and designed to rotate to access the input section 136 and the output section 138 of tool 120. Suitable chambers for use in tool 120 include those available for the modular configuration of an Equinox® brand processing tool from Semitool, Inc.
For example, the photoresist developing chamber 124, seed layer etch chamber 128, barrier layer etch chamber 130, can be of the type available from numerous manufacturers for carrying out such process steps. Examples of such chambers include spray processing modules and immersion processing modules available in conjunction with the Equinox™ system described above. The optional seed layer deposition chamber 122, bulk metallization chamber 126 and protective feature deposition chamber 132 can be provided by numerous electroplating and electroless deposition reactors such as those available as immersion processing modules and electroplating processing reactors for the Equinox™ processor specific examples of an electroplating processing reactor include the types described in International Application No. WO98/02911 (PCT/US97/12332) and International Application No. WO00/03067, the portions of the descriptions of these applications relating to the electroplating processing reactors are expressly incorporated herein by reference.
In general, a chamber for electroplating bulk metal or protective features in accordance with the present invention includes a reactor, a bath supply, an anode, a power supply, and a controller. The reactor receives the surface of the workpiece and exposes the surface to an electroplating bath. The bath supply includes a source of metal ions to be deposited on the surface of the workpiece. The anode is in electrical contact with the electroplating bath. The power supply supplies electroplating power between the surface of the workpiece and the anode to electroplate metal ions onto the surface. The controller controls the supply of electroplating power so that the metal ions are deposited on the workpiece surface. Referring to FIG. 19, the seed layer deposition chamber 122, bulk metallization chamber 126 and/or protective feature deposition chamber 132 can include a reactor vessel in which the electroplating bath is held and which receives at least one surface of the workpiece on which the metal to be deposited is contained.
Referring to FIG. 20, a suitable reactor 60 includes a processing head 62 and an electroplating bowl assembly 64. The electroplating bowl assembly includes a cup assembly 70 that is disposed within a reservoir container 72. The cup assembly 70 includes a fluid reactor 72 portion that holds the electroplating bath fluid. The cup assembly also includes a depending annular skirt 74 which extends below the cup bottom 76, and which includes apertures opening therethrough for fluid communication of the plating bath solution, and for release of any gases that might collect as the reactor of the reservoir assembly is filled with plating solution. The cup is preferably made from a material that is inert to plating solutions, such as polypropylene.
A lower opening in the bottom wall of the cup assembly 70 is connected to a polypropylene (or other material) riser tube 78, which preferably is adjusted in height relative to the cup assembly by a threaded connection. A first end of the riser tube 78 is secured to the rear portion of an anode shield 80, which supports an anode 82. A fluid inlet line 84 is disposed within the riser tube 78. Both the riser tube 78 and the fluid inlet line 84 are secured to the processing bowl assembly 64 by a fitting 86. The fitting 86 can accommodate height adjustment of both the riser tube 78 and the inlet line 84. As such, this connection provides for vertical adjustment of the anode 82. The inlet line 84 is preferably made from a conductive material, such as titanium, and is used to conduct electrical current to the anode 82 from the power supply, as well as to supply fluid to the cup assembly 70.
The metal that is to be plated onto the workpiece in accordance with the present invention is present in a plating solution as species of metal ions to be deposited onto the workpiece. Electroplating solution is provided to the cup assembly 70 through the fluid inlet line 84 and proceeds therefrom through a plurality of fluid inlet openings 88. The plating solution then fills the reactor 72 through openings 88, as supplied by a plating fluid pump (not shown) or other suitable supply. The metal ions are deposited under process conditions that preferentially deposit metal ions onto the metallized features as opposed to the surrounding field surfaces.
The upper edge of the cup sidewall 90 forms a weir, which limits the level of electroplating solution within the cup. This level is chosen so that only the bottom surface of a wafer W (or other workpiece) is contacted by the electroplating solution. Excess solution pours over this top edge into an overflow reactor 92.
The outflow liquid from the reactor 72 is preferably returned to a suitable reservoir where it can be treated with additional plating chemicals to adjust the levels of the constituents and then recycled through the plating reactor 72.
In one embodiment of the apparatus for electroplating metals, the anode 82 is an inert anode used in connection with the plating of metals onto the workpiece. The specific anode may alternatively be a consumable anode, with the anode used in reactor 60 varying depending upon the specifics of the plating liquid and process being used.
The reactor illustrated in FIG. 19 also employs a diffuser plate 93 that is disposed above the anode 82, providing an even distribution of the flow of fluid across the surface of wafer W. Fluid passages are provided over all or a portion of the diffuser plate 93, to allow fluid communication therethrough. The height of the diffuser plate within the cup assembly may be adjustable by using a height adjustment mechanism 94.
The anode shield 80 is secured to the underside of the anode 82 using anode shield fasteners 96, to prevent direct impingement by the plating solution as the solution passes into the processing reactor 72. The anode shield 80 and anode shield fasteners 96 are preferably made from a dielectric material, such as polyvinylidene fluoride or polypropylene. The anode shield serves to electrically isolate and physically protect the backside of the anode.
The processing head 62 holds a wafer W (or other workpiece) within the upper region of the processing reactor 72. In a preferred embodiment, the head 62 is constructed to rotate the wafer W within the reactor 72 about an axis R. To this end, the processing head 62 includes a rotor assembly 98 having a plurality of wafer W engaging contact fingers 200 that hold the wafer W against features of the rotor. Alternatively, the rotor assembly 98 includes a ring contact as described in International Application No. PCT/US99/15850 (WO 00/40779), which is incorporated herein by reference. The fingers 200 are for a ring contact assembly is preferably adapted to conduct current between the wafer W and an electrical power supply.
The processing head 62 is supported by a head operator (not shown) that is adjustable to adjust the height of the processing head. The head operator also has a head connection shaft 202 that is operable to pivot about a horizontal pivot axis. Pivotal action of the processing head using the operator allows the processing head to be placed in an open or face-up position (not shown) for loading and unloading of the wafer W. FIG. 19 illustrates the processing head pivoted into a face-down position in preparation for processing. The foregoing reactor can be readily adapted to carry out an electroless deposition which does not require the anode or a power supply for providing plating current.
Tool 120 can be incorporated into a manufacturing line that includes other tools for producing raised metallized features having an exposed top surface and exposed sidewalls. The additional tools will be capable of carrying out operations on the substrate that are not capable of being carried out in tool 120. For example, the manufacturing line can include a tool or tools for patterning a substrate and/or for depositing and exposing a dielectric layer deposited on the substrate. Referring to FIG. 18, a tool for patterning a substrate is schematically illustrated by block 140 and is arranged to receive the substrates and to provide a pattern in the surface of the substrate, for example through a series of photoresist deposition, photoresist patterning and etching steps. Upon formation of a pattern in the microelectronic workpiece substrate, the workpiece can be delivered to another tool 150 suitable for the deposition of a barrier layer within the features formed in tool 140. In addition, tool 150 can include chambers that can be used to deposit a seed layer onto the barrier layer. Typical chambers present in tool 150 will be those capable of physical vapor deposition techniques or chemical vapor deposition techniques. The patterned microelectronic workpiece with the deposited barrier layer and seed layer can be delivered to tool 160 where photoresist and dielectric can be deposited and exposed.
In tool 120, as an alternative to the vapor deposition of a seed layer in tool 150, a chamber 122 is provided which allows for the electrochemical deposition of the seed layer in tool 120. In an exemplary process architecture, after a seed layer has been deposited, the workpiece is removed from tool 120 and delivered to tool 160 designed to deposit photoresist or dielectric and to expose the photoresist. After deposition of the photoresist and its exposure, the microelectronic workpiece can be returned to tool 120 for development and patterning of the photoresist in chamber 124. Following the patterning of the photoresist in chamber 124, the microelectronic workpiece is delivered to reactor 126 where bulk metallization is carried out electrochemically. Subsequent to the bulk metallization, the microelectronic workpiece is delivered to reactor 127 where etching of the developed remaining photoresist is carried out. Subsequent to the removal of the remaining photoresist, the microelectronic workpiece is delivered to chamber 128 where the portion of the seed layer which is not covered by the bulk metallized feature is removed. Subsequent to the removal of seed layer in reactor 128, the microelectronic workpiece is delivered either to chamber 130 for removal of the exposed barrier layer or to chamber 132 where conductive protective features formed in accordance with the present invention is electrochemically deposited.
Tool 120 can also include a clean/rinse station 134 which can be used between the respective processing steps.
Tool 120 can be configured to include chambers capable of electrolytic deposition of metals or the electroless deposition of metals. The specific configuration of tool 120 will be dependent upon the specific process steps that the manufacturer chooses to carry out. The present invention is not limited to the particular sequence of process steps described above or the particular sequence of chambers described above.
The particular conditions for carrying out the electrolytic deposition of the protective feature will vary depending upon the composition of the electrolytic bath, the rate of deposition desired, and the thickness desired. Variables which can be controlled in the electrolytic deposition process include the temperature of the bath, its pH, concentration of the components in the bath, agitation of the bath or workpiece, time of deposition, and the current density.
The electrolytic plating of a protective feature on the exposed surfaces of a metallized feature in accordance with the present invention is carried out selectively on the metallized feature because the surrounding field surfaces are nonconductive and therefore are not suitable for electrolytic deposition of metals thereon. As a result thereof, the method of the present invention carried out using an electrolytic process results in the selective deposition of a protective feature on the exposed surfaces of a raised metallized feature.
In another embodiment, a protective feature can be selectively deposited on the exposed surfaces of the metallized feature without the application of an applied current, using an electroless deposition process. Electroless deposition is particularly useful when the metallized feature is electrically isolated prior to deposition of a protective feature. In accordance with this aspect of the present invention, the electroless deposition of a protective feature on the exposed surfaces of a metallized feature is carried out by first depositing a catalyst, such as palladium, onto the exposed surfaces of the metallized feature. The deposition of the palladium can be achieved by immersing the metallized feature in a dilute aqueous, acidic solution of palladium ions. Thereafter, the palladium “seeded” surfaces of the metallized feature are contacted with a bath containing nickel and/or cobalt, and alternatively including nonmetallic elements such as phosphorus or boron and a reducing agent. The reducing agent converts the metal ions to a zero valent metal on the seeded surface of the metallized feature to form a continuous metal film. Baths used for the electroless deposition of protective features formed in accordance with the present invention include those components described above with respect to the electrolytic baths and in addition, include a reducing agent such as a hypophosphite salt, e.g., sodium hypophosphite, potassium hypophosphite, or ammonium hypophosphite or dimethylamine borane. Two exemplary baths for the electroless deposition of a protective feature in accordance with the present invention are as follows:

Bath for Electroless Deposition of Cobalt-Tungsten-Phosphorus Protective



	Ammonium tungstate	10 g/l
	Cobalt chloride	30 g/l
	Sodium citrate	80 g/l
	Sodium hypophosphate	20 g/l
	Surfactant	0.05 g/l

Bath for Electroless Deposition of Nickel-Tungsten-Phosphorus Protective Feature



Nickel sulfate	30	g/l
Sodium hypophosphate	10	g/l
Sodium citrate	40	g/l
Ammonium chloride	40	g/l
Sodium tungstate	2-10	g/l

The bath compositions described herein are exemplary of baths suitable for electrolytically and electrolessly depositing protective features of the present invention. Bath compositions for other protective features can be readily formulated by one skilled in the art without undue experimentation. It should be understood that the present invention is not limited to the specific baths set forth above.
The electroless deposition of the metallized feature can be controlled through the manipulation of the temperature of the bath, the concentration of the respective components, and the pH. The thickness of the deposited protective feature can be controlled by adjusting the time of contact of the metallized feature with the metal-containing bath.
In certain situations, it is desirable to employ an electrolytic deposition process to provide protective features in accordance with the present invention. With an electrolytic bath, it is easier to control the composition of the bath, the bath is more stable, and electrolytic baths have fewer selectivity problems as compared to electroless plating processes.
While the present invention has been described above with reference to a dielectric/barrier/seed/metal layer structure, it should be understood that the present invention is not specifically limited to such structure. Fewer or a greater number of layers may form the structure to which a protective feature formed in accordance with the present invention is applied.
While the preferred embodiment of the invention has been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.

Claims

1. A method of forming a protective feature on a metallized feature formed on a microelectronic workpiece, the method comprising:

forming the metallized feature on the microelectronic workpiece, the metallized feature having an exposed surface; and

electrolytically depositing a conductive protective feature on the exposed surface of the metallized feature.

2. The method of claim 1 wherein the exposed surface is a top surface.

3. The method of claim 2, wherein the metallized feature has at least one exposed sidewall.

4. The method of claim 3, wherein the metallized feature has at least two exposed sidewalls.

5. The method of claim 4, wherein the electrolytically depositing step further comprises depositing the conductive protective feature on the exposed top surface and the at least two exposed sidewalls.

6. The method of claim 1, wherein the conductive protective feature comprises nickel, nickel alloys, cobalt, or cobalt alloys.

7. The method of claim 1, wherein the metallized feature includes metals selected from the group comprising copper, copper alloys, aluminum, aluminum alloys, gold, silver, platinum, platinum alloys, and combinations thereof.

8. The method of claim 7, wherein the metallized feature comprises copper.

9. The method of claim 1, wherein the step of forming the metallized feature further comprises forming the metallized feature on a barrier layer comprising tantalum or titanium.

10. The method of claim 9, wherein the step of forming the metallized feature further comprises depositing a seed layer on the barrier layer prior to formation of the metallized feature.

11. The method of claim 10, wherein after formation of the metallized feature, a portion of the seed layer is removed prior to electrolytically depositing the conductive protective feature.

12. A conductive feature on a microelectronic workpiece made by the method of claim 1.

13. A method of forming a conductive protective feature on a metallized feature formed on a microelectronic workpiece having a front side and a backside, the method comprising:

forming a barrier layer on the front side of the microelectronic workpiece;

forming a seed layer exterior to the barrier layer formed on the front side of the microelectronic workpiece;

forming the metallized feature on the front side of the microelectronic workpiece exterior to the seed layer, the metallized feature having an exposed surface;

removing exposed portions of the seed layer;

activating the exposed surface of the metallized feature; and

electrolessly depositing a conductive protective feature on the exposed surface of the metallized feature.

14. The method of claim 13, wherein the exposed surface is a top surface.

15. The method of claim 13, wherein the metallized feature has at least one exposed sidewall.

16. The method of claim 15, wherein the metallized feature has at least two exposed sidewalls.

17. The method of claim 16, wherein the electrolessly depositing step further comprises depositing the conductive protective feature on an exposed top surface and the at least two exposed sidewalls.

18. The method of claim 13, wherein the conductive protective feature comprises nickel, nickel alloys, cobalt, or cobalt alloys.

19. The method of claim 18, wherein the conductive protective feature comprises the alloys of nickel-tungsten-phosphorus, nickel-tungsten-boron, cobalt-tungsten-phosphorus, cobalt-tungsten-boron, nickel-molybdenum-phosphorous, cobalt-molybdenum-phosphorous, nickel-molybdenum-boron and cobalt-molybdenum-boron.

20. The method of claim 13, wherein the metallized feature comprises copper, copper alloys, aluminum, aluminum alloys, gold, silver, platinum, platinum alloys, and combinations thereof.

21. The method of claim 20, wherein the metallized feature comprises copper.

22. The method of claim 13, wherein the barrier layer comprises tantalum or titanium.

23. A microelectronic workpiece including a conductive feature formed by the method of claim 13.

24. A conductive feature on a microelectronic workpiece formed over a titanium or tantalum barrier layer comprising:

an electrochemically deposited metallized feature having an exposed surface; and

a conductive protective feature electrochemically deposited on the metallized feature exterior to the exposed surface.

25. The conductive feature of claim 21, wherein the conductive protective feature comprises nickel, nickel alloys, cobalt, or cobalt alloys.

26. An apparatus for use in a manufacturing line for providing conductive features on a microelectronic workpiece, the apparatus comprising:

an input section for receiving a microelectronic workpiece, a surface of the microelectronic workpiece comprising a barrier feature, a seed layer formed exterior to the barrier feature, and a photoresist feature;

a bulk metallization station for electrochemically forming a metallized feature exterior to the seed layer;

a photoresist removal station for removing at least a portion of the photoresist feature resulting in a raised metallized feature with an exposed surface;

a seed layer removal station for removing at least a portion of the seed layer;

an electrochemical deposition station for electrochemically depositing a conductive protective feature on the exposed surface of the metallized feature; and

a barrier layer etching station for removing at least a portion of the barrier layer.

27. The apparatus of claim 26, where the electrochemical deposition station comprises an electrolytic deposition chamber.

28. The apparatus of claim 26, wherein the electrochemical deposition station comprises an electroless deposition chamber.

29. The apparatus of claim 26, further comprising a photoresist developing station.