US20070170066A1

US20070170066A1 - Method for planarization during plating

Info

Publication number: US20070170066A1
Application number: US11/620,436
Authority: US
Inventors: Christopher Beaudry; Aron Rosenfeld; Michael Yang
Original assignee: Individual
Current assignee: Applied Materials Inc
Priority date: 2006-01-06
Filing date: 2007-01-05
Publication date: 2007-07-26

Abstract

A method and apparatus are provided for plating metal onto a substrate. The method generally includes applying a plating solution comprising at least a leveler to a substrate; substantially filling features in the substrate by plating metal ions from the plating solution onto the substrate, and applying sonic energy to the plating solution across a surface of the substrate prior to completely filling the features.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. provisional patent application Ser. No. 60/757,124 (APPM/009153L), filed Jan. 6, 2006, which is herein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention generally relates to a method for electrochemical plating of a metal onto a substrate.
2. Description of the Related Art
Metallization for sub-quarter micron sized features is a foundational technology for present and future generations of integrated circuit manufacturing processes. In devices such as ultra large scale integration-type devices, i.e., devices having integrated circuits with more than a million logic gates, the multilevel interconnects that lie at the heart of these devices are generally formed by filling high aspect ratio interconnect features with a conductive material, such as copper or aluminum, for example. Conventionally, deposition techniques such as chemical vapor deposition (CVD) and physical vapor deposition (PVD), for example, have been used to fill these interconnect features. However, as interconnect sizes decrease and aspect ratios increase, void-free interconnect feature fill via conventional metallization techniques becomes increasingly difficult. As a result, plating techniques, such as electrochemical plating (ECP) and electroless plating have emerged as viable processes for filling sub-quarter micron sized high aspect ratio interconnect features in integrated circuit manufacturing processes.
In an ECP process, for example, sub-quarter micron sized high aspect ratio features formed in the surface of a substrate may be efficiently filled with a conductive material, such as copper. ECP plating processes are generally two stage processes, wherein a seed layer is first formed over the surface features of the substrate, and then the surface features of the substrate are exposed to an electrolyte solution while an electrical bias is simultaneously applied between the substrate and an anode positioned within the electrolyte solution. The electrolyte solution is generally rich in ions to be plated onto the surface of the substrate. The application of the electrical bias causes these ions to be urged out of the electrolyte solution and to be plated onto the seed layer.
In general, ECP chemistry uses sulfuric acid containing copper sulfate, chloride ions, and a system of organic additives balanced to induce superfilling of features. In practice, the organic additives are named according to their general function during plating. Accelerators are organic sulfur containing compounds that tend to locally accelerate current and enhance deposition rates. Suppressors are polymers that tend to adsorb at the surface and locally suppress current and reduce local deposition rates. The presence of the chloride ion is important for the adsorption of these polymers. Levelers are also current suppressing polymers. They differ from the suppressors in that the concentration at the deposition surface is mass transfer dependent and thus suppresses more efficiently at regions of the interface that are more accessible. A chemical system is named by the number of organic additives it contains. Two component chemistries typically contain only the accelerator and suppressing additives and three component chemistries also contain a leveler additive.
For semiconductor manufacturing, the electroplating chemistry must satisfy the requirement of void free filling in high aspect ratio features which in turn implies the necessity of superfilling. Following the filling of a small feature, the bottom up speed enhanced by the locally concentrated accelerator will continue to promote faster deposition above the feature resulting in bump formation. In fact, bump formation indicates that superfilling has occurred. When such small features are arranged in a dense array, the locally concentrated accelerator will result in “overplating” in these regions.
The bump formation is subsequently removed by a planarization process wherein the excess metal is removed from the entire surface of the substrate to form an even, planar surface. During the planarization process, uneven substrate topography may lead to substrate defects, such as excess shear and incompatibility with non-abrading removal processes, e.g., electropolishing and chemical dissolution. Thus, the pattern or topography dependence of plating thickness results in non-planar film deposition potentially leading to issues in the chemical mechanical planarization (CMP) process.
The general approach to overplating reduction is through chemical means by the use of leveler additives to reduce the local overplating and “level” the film thickness in this region. As expected, the higher the concentration of leveler the more effective the additive system is in overplating reduction. Unfortunately, the relative concentration of leveler also impacts the superfilling phenomena during feature filling. Generally, top center voids are typical when the leveler concentration is too high and although three component chemistries can potentially reduce overplating in comparison with two component chemistries, their benefit is limited by the impact on superfilling.
Another method for reducing overplating is by increasing the rotation rate of the substrate during plating. The exact mechanism is not known but it is believed that increasing the RPM decreases the boundary layer thus increasing the effective amount of leveler at the plating surface. Although this method results in overplating reduction at a given leveler concentration a high rotation rate can result in increased defect density.
Another approach to reducing overplating divides the plating process into two steps. First plating in a chemistry designed for filling (low concentration of leveler) and then by plating in another chemistry tailored for leveling (high concentration of leveler). The strong leveling capability of the second bath is intended to inhibit the locally accelerated plating over the dense features without impacting filling. Disadvantages of this method include exposure of the plated surface between the respective steps and the cost and complexity of having different plating chemistries in the same plating system.
Therefore, a need exists for a method and apparatus for plating processes designed to promote void free filling while reducing overplating.

SUMMARY OF THE INVENTION

Embodiments of the invention generally relate to a method for plating metal onto a substrate. The method generally includes applying a plating solution to a substrate, the plating solution comprising at least a leveler, substantially filling features in the substrate by plating metal ions from the plating solution onto the substrate, and applying sonic energy to the plating solution across a surface of the substrate prior to completely filling the features. In one embodiment the feature comprises at least one opening and a field surrounding the opening. In another embodiment the opening has a width less than 2.0 μm.
Embodiments of the invention further include a method for plating a metal onto a substrate. The method generally includes applying a plating solution to a substrate, the plating solution comprising a leveler, a copper ion source, and a supporting electrolyte. Sonic energy is applied to the plating solution and features in the substrate are substantially filled by plating copper ions from the plating solution onto the substrate.
Embodiments of the invention further include an apparatus comprising an anolyte chamber configured to contain an anolyte solution, a catholyte chamber configured to contain a catholyte solution for plating metal onto a substrate, and a membrane positioned to separate the catholyte chamber from the anolyte chamber. An anode is positioned in the anolyte chamber, and a sonic transducer is positioned in the catholyte chamber to direct sonic energy toward the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
FIG. 1 is a flow diagram depicting an embodiment of the invention.
FIG. 2 is a flow diagram depicting another embodiment of the invention.
FIG. 3 is a top plan view of one embodiment of an electrochemical plating system of the invention.
FIG. 4 is a partial sectional view of one embodiment of an electrochemical processing cell containing a sonic transducer.
FIG. 5 is a graph depicting Overplating (Å) vs. leveler amount (ml/L) for 0 Watts (no sonic energy) and 300 Watts (application of sonic energy).
To facilitate understanding, identical reference numerals have been used, wherever possible, to designate identical elements that are common to the figures. It is contemplated that elements and/or process steps of one embodiment may be beneficially incorporated in other embodiments without additional recitation.

DETAILED DESCRIPTION

The words and phrases used herein should be given their ordinary and customary meaning by one skilled in the art, unless otherwise further defined herein.
Embodiments of the invention include plating methods and apparatus configured to reduce, prevent, and/or eliminate overplating on a substrate through the use of a leveler and sonic energy prior to substantially filling substrate features. Embodiments of the invention contemplate use with other diffusion rate limited additives. Embodiments of the invention contemplate use during all phases of the plating process alone or in combination, for example, the immersion phase, the gapfill phase, and the bulkfill phase. Embodiments of the invention also contemplate use for tuning film properties after the bulkfill phase.
FIG. 1 is a flow chart illustrating an exemplary method 100 of the invention to reduce overplating when plating a metal onto a substrate. The method 100 includes applying a plating solution to a substrate, the plating solution comprising at least a leveler at step 110. The plating solution is generally a copper plating solution having copper sulfate at a concentration between about 5 g/L and about 100 g/L, an acid at a concentration between about 5 g/L and about 200 g/L, and halide ions, such as chloride, at a concentration between about 10 ppm and about 200 ppm. The acid generally includes sulfuric acid, phosphoric acid, and/or derivatives thereof. In addition to copper sulfate, the electroplating solution generally includes other copper salts, such as copper fluoborate, copper gluconate, copper sulfamate, copper sulfonate, copper pyrophosphate, copper chloride, or copper cyanide. Application of the plating solution to the substrate may occur by immersion of the substrate into the plating solution, spraying the plating solution onto the substrate, or any other suitable method of application.
The plating solution may further include one or more additives. Additives, which may be, for example, levelers, inhibitors, suppressors, brighteners, accelerators, or other additives known in the art, are typically organic materials that adsorb onto the surface of the substrate being plated. Useful suppressors typically include polyethers, such as polyethylene glycol, or other polymers, such as polypropylene oxides, which adsorb on the substrate surface and slow down copper deposition in the adsorbed areas. Useful accelerators typically include sulfides or disulfides, such as bis(3-sulfopropyl) disulfide, which compete with suppressors for adsorption sites and accelerate copper deposition in adsorbed areas. Useful inhibitors typically include sodium benzoate and sodium sulfite, which inhibit the rate of copper deposition on the substrate. Useful levelers generally include thiadiazole, imidazole, and other nitrogen containing organics. Other useful levelers include, e.g., organic acid amides and amine compounds, such as acetamide, propyl amide, benz amide, acrylic amide, methacrylic amide, N,N-dimethylacrylic amide, N,N-diethyl methacrylic amide, N,N-diethyl acrylic amide, N,N-dimethyl methacrylic amide, N-(hydroxymethyl) acrylic amide, poly acrylic acid amide, hydrolytic product of poly acrylic acid amide, thioflavine, and safranine. The levelers can be used singly or with combination. During plating, the additives are consumed at the substrate surface, but are being constantly replenished by the electroplating solution. However, differences in diffusion rates of the various additives result in different surface concentrations at the top and the bottom of the features, thereby setting up different plating rates in the features. Ideally, these plating rates should be higher at the bottom of the feature for bottom-up fill. Thus, an appropriate composition of additives in the plating solution is required to achieve a void-free fill of the features. Examples of copper plating chemistries and processes can be found in commonly assigned U.S. patent application Ser. No. 10/616,097, titled “Multiple-Step Electrodeposition Process For Direct Copper Plating On Barrier Metals,” filed on Jul. 8, 2003, now published as U.S. 2005-0006245 on Jan. 13, 2005, and U.S. patent application No. 60/510,190, titled “Methods And Chemistry For Providing Initial Conformal Electrochemical Deposition Of Copper In Sub-Micron Features,” filed on Oct. 10, 2003, conventionally filed as U.S. patent application Ser. No. 10/962,236 on Oct. 8, 2004, now published as U.S. 2005-0109627, all of which are incorporated herein by reference to the extent not inconsistent with the present invention.
The plating solutions of the present invention are typically used at current densities ranging from about 10 mA/cm²to about 60 mA/cm². Current densities as high as 100 mA/cm²and as low as 5 mA/cm²can also be employed under appropriate conditions. In plating conditions where a pulsed current or periodic reverse current is used, current densities in the range of about 5 mA/cm²to about 400 mA/cm²can be used periodically.
In step 120, metal ions from the plating solution are plated onto the substrate to substantially fill features on the substrate. The metal ion source of step 120 may be salts generally required for plating a desired metal onto a substrate. The metal salts may include any of the suitable metal salts for the material to be plated on the substrate, such as copper salts, noble metal salts, semi-noble metal salts, Group IV metal salts, etc. Typical materials to be plated that can be used herein include, but are not limited to copper, nickel, gold, silver, and tungsten.
In step 130, sonic energy is applied to the plating solution across a surface of the substrate prior to completely filling the features. The sonic energy may be in a range of about 400 kHz to about 9 MHz. The sonic energy may have a power density in a range of 0.1 watts per square centimeter and 10 watts per square centimeter. In another embodiment, sonic energy is applied to other diffusion rate limited additives.
FIG. 2 is a flow diagram depicting another embodiment of the method to reduce overplating when plating a metal onto a substrate. The method 200 includes applying an electrolyte solution to a substrate, the plating solution comprising a leveler, a copper ion source, and a supporting electrolyte in step 210. In step 220, sonic energy is applied to the electrolyte solution. Finally, the features in the substrate are filled by plating copper ions from the electrolyte solution onto the substrate in step 230.
Embodiments of the invention can also be used to increase the limiting current (i_L). In electrochemical processes it is important to understand that charge neutrality in the electrolyte must be conserved (in a non-transient process or process step) and thus for every metal ion removed from the anode, a corresponding number of electrons are accepted at the cathode by a positive ion(s). At low to moderate electrochemical currents, the process will typically cause the metal ions in the electrolyte solution to be plated onto the cathode surface. Although, if the rate at which the metal ions are removed from the anode surface is increased, the reaction at the cathode can become limited since the fluid near the surface of the cathode becomes depleted of the metal ions. The electrochemical reaction, therefore, becomes rate limited by the process of diffusion of the metal ions across the depleted region around the cathode. Since the current is limited by the diffusion process of the ions, this state is commonly known as the limiting current (i_L). The depleted region near the surface of the cathode is commonly known as the diffusion boundary layer, or Nernst diffusion boundary layer, which is related to the hydrodynamic boundary layer. The Nernst diffusion boundary layer is inversely proportional to the limiting current (i_L). Application of sonic energy during the plating process decreases the Nernst diffusion boundary layer thus allowing for an increase in the limiting current and a corresponding increase in plating throughput.
Plating System:
FIG. 3 is a top plan view of one embodiment of an electrochemical processing system (ECP) 300 of the present invention. ECP system 300 generally includes a processing mainframe 313 having a mainframe robot 320 centrally positioned thereon. The mainframe robot 320 generally includes one or more robot arms 322, 324 configured to support substrates. Additionally, the mainframe robot 320 and the accompanying robot arms 322, 324 are generally configured to extend, rotate, and vertically move so that the robot 320 may insert and remove substrates to and from a plurality of processing locations 302, 304, 306, 308, 310, 312, 314, 316 positioned on the mainframe 313.
ECP system 300 further includes a factory interface (FI) 330. FI 330 generally includes at least one FI robot 332 positioned adjacent a side of the FI 330 that is adjacent the processing mainframe 313. This position of robot 332 allows the robot to access substrate cassette locations 334 to retrieve a substrate 326 therefrom and then deliver the substrate 326 to one of processing locations 314, 316 to initiate a processing sequence. Similarly, robot 332 may be used to retrieve substrates from one of the processing cells 314, 316 after a substrate processing sequence is complete. In this situation robot 332 may deliver the substrate 326 back to one of the cassette locations 334 for removal of the substrate 326 from system 300 via insertion of the substrate 326 into a cassette positioned at location 334. Additionally, robot 332 is also configured to access an anneal chamber 335 positioned in communication with FI 330. The anneal chamber 335 generally includes a two position annealing chamber, wherein a cooling plate or position 336 and a heating plate or position 337 are positioned adjacently with a substrate transfer robot 340 positioned proximate thereto, e.g., between the two stations. The robot 340 is generally configured to move substrates between the respective heating 337 and cooling plates 336. An exemplary annealing chamber 335 may be found in commonly assigned U.S. patent application Ser. No. 10/823,849, filed on Apr. 13, 2004 and entitled Two Position Anneal Chamber, now published as U.S. 2004-0209414, on Oct. 21, 2004, which is hereby incorporated by reference in its entirety to the extent not inconsistent with the present invention.
Generally, process locations 302, 304, 306, 308, 310, 312, 314, 316 may be any number of processing cells utilized in an electrochemical plating platform. More particularly, the process locations may be configured as electrochemical plating cells, rinsing cells, bevel clean cells, spin rinse dry cells, substrate surface cleaning cells, electroless plating cells, metrology inspection stations, and other cells or processes that may be beneficially used in conjunction with a plating platform.
FIG. 4 is a cross sectional view of one embodiment of a processing cell (FIG. 4 illustrates an exemplary electrochemical plating cell) that may be implemented in any one of processing locations 302, 304, 306, 308, 310, 312, 314, 316 of processing system 300. Generally, however, the exemplary processing system 300 is configured to include four electrochemical plating cells at processing locations 302, 304, 310, and 312. An exemplary plating cell that may be used in embodiments of the invention may be found in commonly assigned U.S. patent application Ser. No. 10/627,336, filed on Jul. 24, 2003, now published as U.S. 2004-0134775, and entitled Electrochemical Processing Cell, which is hereby incorporated by reference in its entirety to the extent not inconsistent with the present invention. Processing locations 306 and 308 are generally configured as edge bead removal or bevel clean chambers. An exemplary edge bead removal or bevel clean chamber that may be used in embodiments of the invention may be found in commonly assigned U.S. patent application Ser. No. 10/826,492, filed on Apr. 16, 2004, now published as U.S. 2004-0206375 on Oct. 21, 2004, and entitled Integrated Bevel Clean Chamber, which is hereby incorporated by reference in its entirety to the extent not inconsistent with the present invention. Further, processing locations 314 and 316 are generally configured as substrate surface cleaning chambers and spin rinse dry chambers, which may be positioned in a stacked manner, i.e., one above the other. An exemplary spin rinse dry chamber that may be used in embodiments of the invention may be found in commonly assigned U.S. patent application Ser. No. 10/680,616, filed on Oct. 6, 2003, now published as U.S. 2004-0206373 on Oct. 21, 2004, and entitled Spin Rinse Dry Cell, which is hereby incorporated by reference in its entirety to the extent not inconsistent with the present invention. However, the invention is not intended to be limited to any particular order or arrangement of cells, as various combinations and arrangements may be implemented without departing from the scope of the invention.
The electrochemical plating cell 400 generally includes an outer basin 401 and an inner basin 402 positioned within outer basin 401. Inner basin 402 is generally configured to contain a plating solution that is used to plate a metal, e.g., copper, onto a substrate during an electrochemical plating process.
During the plating process, the plating solution is generally continuously supplied to inner basin 402 (at about 1 gallon per minute for a 10 liter plating cell, for example), and therefore, the plating solution continually overflows the uppermost point of inner basin 402 and runs into outer basin 401. The overflow plating solution is then collected by outer basin 401 and drained therefrom for recirculation into inner basin 402. Plating cell 400 is generally positioned at a tilt angle, i.e., the frame member 403 of plating cell 400 is generally elevated on one side such that the components of plating cell 400 are tilted between about 3° and about 30°. Therefore, in order to contain an adequate depth of plating solution within inner basin 402 during plating operations, the uppermost portion of basin 402 may be extended upward on one side of plating cell 400, such that the uppermost point of inner basin 402 is generally horizontal and allows for contiguous overflow of the plating solution supplied thereto around the perimeter of basin 402.
The frame member 403 of plating cell 400 generally includes an annular base member 404 secured to frame member 403. Since frame member 403 is elevated on one side, the upper surface of base member 404 is generally tilted from the horizontal at an angle that corresponds to the angle of frame member 403 relative to a horizontal position. Base member 404 includes an annular or disk shaped recess formed therein, the annular recess being configured to receive a disk shaped anode member 405. Base member 404 further includes a plurality of fluid inlets/drains 409 positioned on a lower surface thereof. Each of the fluid inlets/drains 409 are generally configured to individually supply or drain a fluid to or from either the anode compartment or the cathode compartment of plating cell 400. Anode member 405 generally includes a plurality of slots 407 formed therethrough, wherein the slots 407 are generally positioned in parallel orientation with each other across the surface of the anode 405. The parallel orientation allows for dense fluids generated at the anode surface to flow downwardly across the anode surface and into one of the slots 407. Plating cell 400 further includes a membrane support assembly 406. Membrane support assembly 406 is generally secured at an outer periphery thereof to base member 404, and includes an interior region configured to allow fluids to pass therethrough. A membrane 408 is stretched across the support 406 and operates to fluidly separate a catholyte chamber and anolyte chamber portions of the plating cell. The membrane support assembly may include an o-ring type seal positioned near a perimeter of the membrane, wherein the seal is configured to prevent fluids from traveling from one side of the membrane secured on the membrane support 406 to the other side of the membrane. A diffusion plate 410 is positioned above the membrane 408.
In operation, assuming a tilted implementation is utilized, the plating cell 400 will generally immerse a substrate into a plating solution contained within inner basin 402. Once the substrate is immersed in the plating solution, which generally contains copper sulfate, chlorine, and one or more of a plurality of organic plating additives (levelers, suppressors, accelerators, etc.) configured to control plating parameters, an electrical bias is applied between a seed layer on the substrate and the anode 405 positioned in the plating cell. The electrical bias is generally configured to cause metal ions moving through the plating solution to deposit on the cathodic substrate surface. In this embodiment of the plating cell 400, separate fluid solutions are supplied to the volume above the membrane 408 and the volume below the membrane 408. Generally, the volume above the membrane is designated the cathode compartment or region, as this region is where the cathode electrode or plating electrode is positioned. Similarly, the volume below the membrane 408 is generally designated the anode compartment or region, as this is the region where the anode is located. The respective anode and cathode regions are generally fluidly isolated from each other via membrane 408 (which is generally an ionic membrane). Thus, the fluid supplied to the cathode compartment is generally a plating solution containing all the required constituents to support plating operations, while the fluid supplied to the anode compartment is generally a solution that does not contain the plating solution additives that are present in the cathode chamber, e.g., copper sulfate solutions, for example. Additional detail with respect to the configuration and operation of the exemplary plating cell illustrated in FIG. 4 may be found in commonly assigned U.S. patent application Ser. No. 10/268,284, entitled “ELECTROCHEMICAL PROCESSING CELL,” filed on Oct. 9, 2002, now published as U.S. 2004-0016636 on Jan. 29, 2004, which is hereby incorporated by reference in its entirety to the extent not inconsistent with the present invention. The plating cell 400 includes a transducer 412 connected to a power source (not shown), which may include a single transducer or an array of multiple transducers, oriented to direct sonic energy toward the wafer. When the transducer(s) direct sonic energy into fluid in the chamber, they induce acoustic streaming within the fluid.
In another embodiment, the transducer 412 is placed in the anode compartment. In yet another embodiment, the transducer 412 is placed outside of the plating cell 400. In yet another embodiment, the transducer 412 is placed in a non-compartmentalized processing cell.
The transducer 412 is preferably positioned such that the energy beam interacts with the substrate surface at or just below the gas/liquid interface, e.g., at a level within the top 0-20% of the liquid in the inner basin. The transducer 412 may be configured to direct megasonic energy in a direction normal to the substrate surface or at an angle from normal. Preferably, energy is directed at an angle of approximately 0-80 degrees from normal, and most preferably approximately 50-80 degrees from normal. Directing the megasonic energy from transducer 412 at an angle from normal to the substrate surface can have several advantages. For example, directing the energy towards the substrate at an angle minimizes interference between the emitted energy and return waves of energy reflected off the substrate surface, thus allowing power transfer to the solution to be maximized. It also allows greater control over the power delivered to the solution. It has been found that when the transducers are parallel to the substrate surface, the power delivered to the solution is highly sensitive to variations in the distance between the substrate surface and the transducer. Angling the transducers reduces this sensitivity and thus allows the power level to be tuned more accurately. The angled transducers are further beneficial in that their energy is not blocked by the contact ring 505.
It may be desirable to provide the transducer 412 to be independently adjustable in terms of angle relative to normal and/or power. Providing the transducer 412 to have an adjustable angle permits the angle to be changed depending on the nature of the substrate (e.g. fine features) and also depending on the process step being carried out. In some instances it may also be desirable to have more than one transducer 412.
The transducer 412 may be of any shape such as circular, hexagonal, square, etc. The transducer 412 is connected to a high frequency power source (not shown). The transducer 412 comprises a piezoelectric material, such as, for example, lead zirconate titanate (PZT) among other piezoelectric materials. The transducers 412 are sized to generate acoustic waves at a particular frequency in response to an applied high frequency power. The transducers 412 are capable of emitting sonic radiation. The sonic energy may be in a range of about 400 kHz to about 9 MHz. The sonic energy may have a power density in a range of 0.1 watts per square centimeter and 10 watts per square centimeter.
Performance of the Sonic Transducer
FIG. 5 demonstrates the effect of various concentrations of leveler (ml/L) on overplating (Å) with the addition of megasonic energy (300 W) and without the addition of megasonic energy (0 W). The overplating was measured with profilmetry above 0.18/0.18×0.5 μm (trench/space×depth) array of trenches (1.2 mm×1.2 mm), (9/4/Z) which is based on (X/Y/Z) where X/Y/Z represents the ratio of accelerator/suppressor/accelerator, 0.8 μm plated. At 0 ml/L of leveler the amount of overplating is identical for both the 0 W and the 300 W case. At 2 ml/L of leveler, the overplating for the 300 W case has been reduced by approximately 1100 Å more than the 0 W case. At 4 ml/L of leveler, the overplating for the 300 W case has been reduced by approximately 800 Å more than the 0 W case. At 6 ml/L of leveler, the overplating for the 300 W case has been reduced by approximately 800 Å more than the 0 W case. At 8 ml/L of leveler, the overplating for the 300 W case has been reduced by approximately 500 Å more than the 0 W case. These results demonstrate that the use of leveler with megasonic energy achieves a greater reduction in overplating than the use of leveler without megasonic energy.
SEM photographs of two samples show copper plated to 150 Å at a current of 5 Amperes at 20 rpm with 0 Watts (no megasonic energy) and 300 Watts (with megasonic energy). The photo shows trenches that are 0.214 μm×1 μm in (9/4/6). Photographs representing the first sample, the 0 W case, show that the wafer center fills at a faster rate than the edge of the wafer. This demonstrates that without the combination of sonic energy and leveler, the center and edge will fill at different rates. SEM photographs representing the second sample demonstrate that the combination of megasonic energy and leveler suppresses growth at the center leading to the center and edge filling at similar rates.
Although not wishing to be bound by theory, as plating occurs on the wafer, ions in solution plate (deposit) from the solution onto the substrate. To provide additional plating material, ions must diffuse through a diffusion boundary layer adjacent the plating surface. It is believed that when the use of ultrasonic (<400 kHz) and megasonic (>400 kHz) energy is applied to a chemical solution the effective boundary layer is significantly reduced. Minimizing the boundary layer promotes particle removal by higher chemical refresh rates and increasing chemical access to the surface. The boundary layer thickness is a function of frequency, acoustic intensity, and fluid properties. In general in aqueous chemistries increasing the frequency of the megasonic range reduces the boundary layer to submicron dimensions compared to a few microns in the ultrasonic frequency range. This reduction of the boundary layer offers the opportunity to increase the limiting current. Increasing the applied energy also can decrease the boundary layer. Pulsed wave operation of megasonic system is more effective in transmitting energy to the solution resulting in high applied energy than continuous operation.
The advantage of this approach is the ability to independently control the effective boundary layer thickness and therefore the “leveling” power during the plating process. Benefits include the reduction of overplating at a given leveler concentration (similar to the rotation rate effect) and the reduction of the amount of leveling additives (reliance on the suppressor) required to achieve similar overplating performance. This approach also allows a combination of additives in the same bath chemistry that will dominate the overplating behavior depending on the resultant effective boundary layer. The acoustic streaming velocity aspect of applying sonic energy during plating also reduces the amount of additive incorporation by “sweeping” away the additive during plating. With proper hardware design a sonic energy waveform may be designed to modulate the boundary layer thickness to favor the copper plating rate over the diffusion characteristics of respective additives leading to less additive incorporation which generally leads to lower resistivity (less inhibited grain growth during annealing) and a longer bath life.
Embodiments of the invention may also be used with other forms of agitation including but not limited to wiping brushes, blades, pads, rotational and/or linear motion and high pressure jets.
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

1. A method for plating a metal onto a substrate, comprising:

applying a plating solution to a substrate, wherein the plating solution comprises at least a leveler;

substantially filling features in the substrate by plating metal ions from the plating solution onto the substrate; and

applying sonic energy to the plating solution across a surface of the substrate prior to completely filling the features.

2. The method of claim 1, wherein the sonic energy has a frequency in a range of about 400 kilohertz (kHz) to about 9 megahertz (MHz).

3. The method of claim 1, wherein the applying sonic energy to the plating solution comprises applying a power of about 300 W.

4. The method of claim 1, wherein the applying sonic energy to the plating solution comprises applying a current of about 40 Amperes.

5. The method of claim 1, wherein the leveler is selected from the group consisting of thiadiazole, imidazole, nitrogen containing organics, organic acid amides, amine compounds, and combinations thereof.

6. The method of claim 1, wherein the feature comprises at least one opening and a field surrounding the opening.

7. The method of claim 6, wherein the opening has a width less than 2.0 μm.

8. The method of claim 1, wherein the metal ions comprise copper ions.

9. The method of claim 1, further comprising providing a plating cell comprising at least one anode and cathode, wherein the cathode comprises at least a portion of the conductive surface of the substrate.

10. The method of claim 9, further comprising applying current between the at least one anode and the cathode to generate an electroplating current density, wherein the current density is about 60 mA/cm².

11. A method for plating a metal onto a substrate, comprising:

applying a plating solution to a substrate, wherein the plating solution comprises a leveler, a copper ion source, and a supporting electrolyte;

applying uniform agitation to the plating solution; and

substantially filling features in the substrate by plating copper ions from the plating solution onto the substrate.

12. The method of claim 11, wherein the supporting electrolyte comprises acid and water.

13. The method of claim 11, wherein the uniform agitation comprises applying sonic energy.

14. The method of claim 13, wherein the sonic energy has a frequency in a range of about 400 kilohertz (kHz) to about 9 megahertz (MHz).

15. The method of claim 14, wherein the applying sonic energy to the plating solution comprises applying a power of about 300 W.

16. The method of claim 11, wherein the leveler is selected from a group comprising organic acid amides and amine compounds.

17. An electrochemical plating cell, comprising:

an anolyte chamber configured to contain an anolyte solution;

a catholyte chamber configured to contain a catholyte solution for plating a metal onto a substrate;

a membrane positioned to separate the catholyte chamber from the anolyte chamber;

an anode positioned in the anolyte chamber; and

at least one sonic transducer positioned in the catholyte chamber to direct sonic energy toward the substrate.

18. The electrochemical plating cell of claim 17, wherein the sonic transducer produces sonic energy between about 400 kHz and about 9 MHz.

19. The electrochemical plating cell of claim 18, wherein the sonic transducer produces sonic energy between about 0.1 watts/cm²and about 10 watts/cm².

20. The electrochemical plating cell of claim 17, wherein the sonic transducer is configured to direct sonic energy toward a surface of the substrate at an angle from approximately 50 to 80 degrees from normal to the substrate surface.