CROSS-REFERENCE TO RELATED APPLICATIONS
BACKGROUND OF THE INVENTION
This application claims benefit of U.S. Provisional Patent Application No. 60/580,255, filed Jun. 15, 2004, which is herein incorporated by reference.
1. Field of the Invention
Embodiments of the invention generally relate to a metal plating apparatus and process, namely for the replenishment of chemical components used to electroplate copper.
2. Description of the Related Art
Semiconductor substrates can be plated with copper by electroplating or electroless plating processes. During the electroplating, an anode is usually placed into an electrolyte solution and the substrate is conductively coupled to a cathode. As current flows, dissolved copper ions from the electrolyte solution are reduced and plated (or deposited) on the surface of the substrate as copper metal. Traditionally, the anode is made from consumable copper metal and is continuously oxidized to provide copper ions to the plating process. Due to the consumption of the copper anode, the dimension of the copper anode is changed. Therefore, the directional electrical fields produced by the anode also change accordingly. This alteration in the electric field presents a challenge to precisely control the electroplating process, especially within vias with high aspect ratios.
Another electroplating process utilizes an inert or stable anode in place of a consumable anode. The use of an inert anode provides excellent control for precision plating since the anode is not consumed during the plating process. However, the inert anode does not supply a source of copper into the electrolyte solution. As the copper ions are reduced and plated from the electrolyte solution to the substrate surface, the copper ion concentration in the electrolyte solution is diminished. Therefore, as the plating process progresses, a copper source, namely copper ions, must be added to the electrolyte solution in order to continue the plating process. Copper sources are generally chosen from a variety of copper salts that include copper sulfate, copper hydroxide, copper oxide and copper phosphate.
The prior art discloses a method to maintain an alkaline copper plating solution with a desired concentration of copper ions and hydroxide ions. Generally, copper hydroxide powder is added from a conduit to a dissolving tank containing an alkaline, pyrophosphate solution. Once the solution has been heated and agitated to insure that the copper hydroxide has been dissolved, the pyrophosphate solution is transferred via a pump to the plating solution. The plating solution is monitored with a pH meter and maintained with a basic pH between 7 and 10 by adding the alkaline, pyrophosphate solution. Though the addition of copper hydroxide powder is adequate in the realm of electroplating wires, this technique is unacceptable in a clean environment, such as a semiconductor fabrication room equipped to plate substrates. The dumping of a powdery precursor into a solution would present contamination issues for semiconductor processing in a cleanroom environment.
Other prior art realizes the shortcomings of using copper hydroxide as a copper source in a cleanroom and discloses a method to replenish copper ions in a plating solution by dissolving metallic copper wires in an acidic solution. The plating solution also contains iron ions (Fe3+/2+) used as an oxidizing/reducing agent. While the iron ions are useful electron donors/receivers, there are several undesirable characteristics to have iron ions in copper plating solutions. Iron ions can not be used with cation-exchange membranes since the ions will poison the membranes causing a dramatic performance drop to their selectivity and conductivity. Also, iron ions in plating solutions may be undesirable during many semiconductor processes due interfering with various organic additives as well as causing iron contamination in the deposited films.
- SUMMARY OF THE INVENTION
Therefore, there is a need for an apparatus and method to replenish chemical compounds, including copper ions and/or a pH adjusting agent, within an electrolyte solution in a consistent and reliable manner.
In one example, an apparatus for dispensing copper into a plating solution is provided which includes a cartridge containing an inlet and an outlet and comprising a copper metal source therein, a dosing device containing an oxidizing agent in fluid communication with the inlet, a tank for containing the plating solution in fluid communication with the outlet, a pH electrode adapted to contact the plating solution, and a system controller which receives input from the pH electrode and sends output to the dosing device.
In another example, an apparatus for dispensing metal ions into a plating solution is provided which includes a cartridge containing an inlet and an outlet and comprising a metal source therein, a dosing device containing an oxidizing agent in fluid communication with the inlet, a tank for containing the plating solution in fluid communication with the outlet, a sensor adapted to contact the plating solution, and a system controller which receives input from the sensor and sends output to the dosing device.
In another example, a method for replenishing copper in a plating solution is provided which includes flowing the plating solution from a plating cell to a replenishing system comprising a dosing device and a cartridge, dosing an oxidizing agent from the dosing device to the plating solution, exposing the plating solution to a copper metal source contained in the cartridge, enriching the plating solution with copper ions derived from the copper metal source, and flowing the enriched plating solution to the plating cell.
BRIEF DESCRIPTION OF THE DRAWINGS
In another example, a method for monitoring and controlling a pH setting of a plating solution in an electroplating system is provided which includes electroplating a substrate with the plating solution within a first pH range, monitoring the plating solution to determine when the plating solution is within a second pH range, dosing an oxidizing agent into the plating solution, exposing a copper metal source to the plating solution to form an enriched plating solution, and ceasing the doses of the oxidizing agent once the plating solution is within the first pH range.
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 shows a flow diagram for a two-sectional electrochemical cell with catholyte and anolyte, as described in the prior art;
FIG. 2 shows a system to replenish chemicals in a plating solution according to one embodiment described herein;
FIG. 3 shows a cartridge for replenishing chemicals according to one embodiment described herein;
FIG. 4 shows a metal bundle for use in a cartridge for replenishing chemicals as described according to one embodiment described herein; and
FIG. 5 shows another system to replenish chemicals in a plating solution according to one embodiment described herein.
The present invention comprises apparatuses and methods to replenish chemical compounds, such as copper ions, in plating solutions in a consistent and reliable manner while overcoming the shortcomings of the related art as described in the background. Therefore, by utilizing the various embodiments of the apparatuses and methods of the present invention, each substrate experiences more consistent plating times and anolyte chemical concentrations.
Embodiments of the present invention are useful in a variety of plating systems, including electroplating and electroless plating systems. Further, various embodiments are also applicable to electroplating with soluble anodes and with insoluble anodes. FIG. 1 shows a schematic arrangement of an electroplating system 10 with a cell 11 containing an insoluble anode 12. The insoluble anode 12 is made from relatively inert materials, such as platinum, titanium, titanium with a Pt-coating, palladium, nickel, stainless steel and/or carbon. The material of the insoluble anode 12 is generally configured to withstand the various process conditions involved while plating to a wafer or substrate 14. Process conditions may have acidic or basic pH, oxidative/reductive potentials and an assortment of chemical compounds throughout the solution. In one embodiment, the insoluble anode 12 endures process conditions such as acidic plating solutions and an oxidative potential. The substrate 14 is attached to the cathode 13, usually by a contact ring, pins, and the like (not pictured).
The insoluble anode 12 and the cathode 13 are separated by a membrane 16 extending through cell 11. The membrane 16 is an electroconductive membrane, such as an ion-exchange membrane, nano-filtration membrane, ultra-filtration membrane and others known in the art. The portion of the cell 11 containing the cathode 13 is in fluid communication with the catholyte tank 17 to recirculate the catholyte within. The catholyte is a mixture of compounds for copper plating may be a sulfuric copper plating electrolyte or a pyrophosphoric copper plating electrolyte. A sulfuric copper plating electrolyte will generally include a mixture of copper sulfate, sulfuric acid, water and various organic and inorganic additives including suppressors, accelerators, levelers and brighteners. Catholyte may pass through a diffuser 15 to be more evenly distributed while flowing towards the substrate 14.
The portion of the cell 11 containing the insoluble anode 12 is in fluid communication with the anolyte tank 18 and recirculates the anolyte within. For copper plating, the anolyte is usually an aqueous solution containing copper ions, often derived from dissolved copper salts, such as copper sulfate. Other copper ion sources include copper hydroxide, copper carbonate, copper oxide and copper phosphate.
Under copper plating electrolysis, the half reaction in scheme (i) occurs on the insoluble anode 12:
H2O→2H++2e −+ŻO2(g), (i)
while Cu2+ ions migrate through the membrane 16 from the anolyte to the catholyte and are reduced according to the half reaction shown in scheme (ii):
The combined half reactions in schemes (i) and (ii) are represented in reaction scheme (iii):
Therefore, as the electroplating process proceeds, the anolyte becomes depleted of copper ions due to the precipitation of metallic copper from the reduced copper salt, as well as more acidic due to the production of sulfuric acid. Also, water is consumed making the electrolyte more concentrated.
The sulfuric acid formed in the anolyte increases the acidity of the catholyte due to protons penetrating membrane 16. Therefore, the sulfuric acid in the anolyte lowers the pH of the catholyte. The more acidic anolyte and catholyte is not desirable since the unbalanced chemical concentrations are not constant and adversely effect the plating process. To prevent the lowering of the pH of the catholyte and to maintain a substantially constant copper concentration, an oxidizing agent is dosed into the anolyte upstream from a metallic copper source. The reaction between the metallic copper source, an oxidizing agent (e.g., H2O2) and sulfuric acid generates copper ions (e.g., CuSO4) while neutralizing the sulfuric acid, as shown by the reaction scheme (iv):
Therefore, the half reactions shown in schemes (iii) and (iv) are combined and the summed reaction is depicted by scheme (v), such as:
where metallic (source) copper is consistently oxidized to form copper ions enriching the anolyte and subsequently reduced to form metallic (deposited) copper. Also, scheme (v) reveals that hydrogen peroxide is consumed while water and oxygen are formed as byproducts. Sulfuric acid is formed and consumed in situ, therefore does not appear in scheme (v).
In one embodiment, the plating solution is a copper sulfate based plating solution with a copper concentration from about 50 mM to about 1.5 M, preferably from about 100 mM to about 1.0 M. However, other plating solutions may be used, such as copper phosphate, copper chloride, copper acetate and combinations thereof. For example, as a copper phosphate or copper sulfate plating solution is used to electroplate, copper ions are depleted as the acidity increases, therefore an oxidizing agent may be pulsed into the system. The excess acid that is formed in situ (e.g., phosphoric or sulfuric) reacts with the metallic copper and the oxidizing agent to consume some of the acid while forming copper ions. Therefore, the copper ion concentration is increased and the acid concentration or acidity of the plating solution is decreased.
The term plating solution herein may refer to the catholyte and/or the anolyte in an electroplating solution. In one example, the plating solution (e.g., anolyte) has a pH from about 2.5 to about 4.5, preferably from about 2.8 to about 3.5. In another example, the plating solution (e.g., catholyte) has a pH from about −0.5 to about 3, preferably from about 0 to about 1.5. Plating solutions with other non-acid pH ranges are anticipated to work with the present invention, including neutral and basic.
FIG. 2 shows system 100 that may be used to replenish chemical components, such as copper ions, within a plating solution. System 100 may be used to replenish chemical components in electroless plating solutions, as well as electroplating solutions, including anolyte and/or catholyte solutions. In the preferred embodiment, system 100 is used on an anolyte portion an electroplating system.
System 100 includes cell 111, dosing device 130, cartridge 120 and anolyte tank 118, each in fluid communication by conduit 102, such as pipes, tubes, hoses and the like. Cell 111 is used to plate materials to substrate surfaces, such as copper or copper-containing alloys during an electroplating process. For example, cell 111 may be the electroplating cell 11 shown in FIG. 1. The anolyte flows from anolyte tank 118 to cell 111. A pump 114 may be situated between tank 118 and cell 111, as shown, or pump 114 may be positioned in other sections of system 100. After or during an electroplating process, depleted anolyte flows into the cartridge 120 via dosing device 130. The dosing device 130 may be directly connected in-line to system 100 or fluidly connected on a spur 103. The anolyte flows from cartridge 120 to anolyte tank 118 to complete the cycle.
A system controller 124 communicates with dosing device 130 and a pH electrode 122. System controller 124 may be a computer or connected to a computer and monitors the pH value of the anolyte that accumulates in anolyte tank 118 via pH electrode 122. The pH electrode 122 is usually continuously exposed to the anolyte such that system controller 124 can determine the anolyte pH at any time during processing of the substrate. System controller 124 may be connected with other pH electrodes or sensors positioned throughout system 100 (not shown).
The system controller 124 may pulse an oxidizing agent via the dosing device 130 as the pH value of the plating solution reaches a predetermined pH range. For example, if the anolyte is a copper sulfate based solution, then the preferred pH value of the anolyte is in the range from about 2.5 to about 4.0, preferably from about 2.8 to about 3.5. In one embodiment, the system controller 124 is preset to start administering an oxidizing agent, such as H2O2, when the pH value of the anolyte reaches about 2.7 or less. The system controller 124 is preset to stop administering the oxidizing agent when the pH value of the anolyte reaches about 3.0 or higher. In another example, once the anolyte has a pH value in the range from about 2.0 to about 2.7, the oxidizing agent may be administered until the anolyte has an increased pH value, such as in the range from about 2.8 to about 3.5. The exact point at which to start and/or stop the administration of an oxidizing agent is determined with routine experimentation and dependant to the plating solution composition as well as the desired plated material. In one embodiment, a system controller 124 is a pH controller and may be selected from a variety of commercially available models, such as the dTRANSpH 01 from JUMO Process Control Inc., DP24-E Process Meter from Omega, the EMIT-pH from Pathfinder Instruments, and the LED pH/ORP indicator/controller from Kemko Instruments.
Dosing device 130 is triggered to administer the oxidizing agent by the system controller 124. In some configurations, dosing device 130 may be serially connected with the pH electrode 122 and the system controller 124. Dosing device 130 is an apparatus commonly used to administer chemicals in a controlled manner, such as a syringe pump or dosing pump, for example the CERAMPUMP«, available from Fluid Metering, Inc., located in Syosset, N.Y.
Dosing device 130 administers an oxidizing agent as a solid, liquid or gas, but preferably a liquid. The oxidizing agent may be stored in a reservoir within the dosing device 130 or stored nearby, such as an external reservoir or supplied by in-house feed lines, and plumbed to dosing device 130 by piping or tubing. Oxidizing agents may include hydrogen peroxide, carbamide peroxide, organic peroxides, inorganic peroxides (e.g., calcium peroxide), various metal compounds (e.g., Fe2+/3+ or cobaltocene), ozone solutions, chlorites (e.g., hypochlorites), bromites, derivatives thereof, and combinations thereof. Organic peroxides useful as oxidizing agents are described with the formula ROOR′, wherein R and R′ are each independently an organic group, such as methyl, ethyl, propyl, butyl, penta, alkyl, benzyl, aryl, and derivatives thereof, for example, benzoyl peroxide, tert-butyl peroxide, di-tert-amyl peroxide. The oxidizing agent may be a solution comprising an active oxidizer dissolved in a solvent and may contain an optional stabilizer. For example, benzoyl peroxide may be dissolved in an aqueous solution. The oxidizing agent is usually within the plating solution at a concentration in the range from about 0.01 vol % to about 5.0 vol %, preferably, from about 0.03 vol % to about 3.0 vol %. In the preferred embodiment, the oxidizing agent is hydrogen peroxide at a concentration in the plating solution in the range from about 0.03 vol % to about 3.0 vol %.
FIG. 3 depicts one embodiment of the plating solution flowing along a pathway from inlet 121 to outlet 123 through cartridge 120. The plating solution may also flow from the top to the bottom through cartridge 520, as depicted in FIG. 5. Cartridges may be horizontally or vertically positioned. Cartridge 120 contains a metal bundle 125, such as a copper bundle. In FIG. 4, a metal bundle 125 comprises at least one sheet of metal foil 126 and a separator 127 a. The metal foil 126 is preferably copper or a copper-containing alloy. Separator 127 a is used to maintain metal foil 126 from touching itself while being rolled to form metal bundle 125. Therefore, metal bundle 125 maintains metal foil 126 with high surface area and assures a consistent exposure of plating solution across metal foil 126. In order to allow plating solution to pass freely, separator 127 a has ridges 128 protruding against metal foil 126 while separator 127 b has squared geometries 129 protruding against metal foil 126. Separators are usually composed of materials that do not react with the plating solution, such as plastics, polymers, elastomers, rubbers, and inert metals, for example, polyethylene, polypropylene, nylon, PVC, fluoropolymers and PTFE and may include geometries such as meshing, screening and netting. Separators are commercially available from InterNet, Inc., located in Minneapolis, Minn.
In one example of the embodiment, metal foil 126 is the preferred geometry for a metal source due to the high surface area as well as the ability to evenly dissolve into solution upon oxidation. In other examples, cartridge 120 contains metal sources with alternative geometries, such as sheets, spheres, beads, powder, granules, wires, springs, mesh, derivatives thereof and combinations thereof. In the preferred embodiment, a copper-containing foil is rolled with a meshing to form metal bundle 125 and supplied to cartridge 120.
However, in other examples, supplemental copper reagents may be useful for copper ion replenishment in a plating solution as described herein. Supplemental copper reagents include copper hydroxide, copper oxides, copper carbonate, copper sulfate and copper phosphate and combinations thereof, preferably copper hydroxide. Generally, plating solutions, enriched or depleted, have a copper ion concentration in a range from about 50 mM to about 1.5 M.
FIG. 5 depicts a system 500 useful to replenish chemical components, such as copper ions, to a plating solution. System 500 includes cell 511, dosing device 530, cartridge 520 and anolyte tank 518, each in fluid communication by conduit 502, such as pipes, tubes, hoses and the alike. System 500 also contains a bypass line 503 and valves 531 and 532. Valves 531 and 532 may be three-way valves which are positioned to segregate dosing device 530 and cartridge 520 from cell 511 and anolyte tank 518. In one embodiment, valves 531 and 532 are positioned to allow anolyte to flow through dosing device 530 and cartridge 520 and not flow through bypass line 503. In another embodiment, valves 531 and 532 are positioned to not allow anolyte to flow through dosing device 530 and cartridge 520, but allow anolyte to flow through bypass line 503.
Cell 511 is used to plate materials to substrate surfaces, such as copper or copper-containing alloys during an electroplating process. Anolyte flows from anolyte tank 518 to cell 511. A pump 514 may be situated between tank 518 and cell 511, as shown, or pump 514 may be positioned in other sections of system 500. After or during electroplating, depleted anolyte may flow from cell 511 through dosing device 530, through cartridge 520 and into anolyte tank 518. Alternatively, the depleted anolyte may flow from cell 511 through bypass 503 and into the anolyte tank 518. The dosing device 530 may be directly connected in-line to system 500, as shown, or fluidly connected on a spur.
A system controller 524 communicates with dosing device 530, valves 531 and 532, and sensor 523, such as a pH electrode, a photo sensor (FT-IR or UV-vis spectrometers), or other sensors commonly used to measure chemical concentrations. System controller 524 may be a computer or connected to a computer and monitors chemical concentrations of the anolyte composition that accumulates within anolyte tank 518 via sensor 523, such as monitoring acidity with a pH electrode. The sensor 523 may be continuously exposed to the anolyte such that system controller 524 can determine chemical concentrations of the anolyte composition at any time during processing of the substrate. System controller 523 may be connected with other sensors, such as pH electrodes (not shown), positioned throughout system 500.
The system controller 524 may pulse an oxidizing agent via the dosing device 530 as the pH of the plating solution reaches a preset pH range. For example, if the anolyte is a copper sulfate based solution, the preferred pH value to maintain the anolyte is in the range from about 2.5 to about 4.0, preferably from about 2.8 to about 3.5. In one embodiment, the system controller 524 is preset to start administering an oxidizing agent, such as H2O2, when the pH value of the anolyte reaches about 2.7 or less. The system controller 524 is preset to stop administering the oxidizing agent when the pH of the anolyte reaches about 3.0 or higher. In another example, once the anolyte has a pH value in the range from about 2.0 to about 2.7, the oxidizing agent may be administered until the anolyte has an increased pH value, such as in the range from about 2.8 to about 3.5. The exact point at which to start and/or stop the administration of an oxidizing agent is determined with routine experimentation and dependant to the plating solution composition as well as the desired plated material. In one embodiment, a system controller 524 is a pH controller and may be selected from a variety of commercially available models, such as the dTRANSpH 01 from JUMO Process Control Inc., the DP24-E Process Meter from Omega, EMIT-pH from Pathfinder Instruments, and the LED pH/ORP indicator/controller from Kemko Instruments.
Dosing device 530 is triggered to administer the oxidizing agent by the system controller 524. In some configurations, dosing device 530 may be serially connected with the sensor 523 and the system controller 524. Dosing device 530 is an apparatus commonly used to administer chemicals in a controlled manner, such as a syringe pump or dosing pump, for example the CERAMPUMP«, available from Fluid Metering, Inc., located in Syosset, N.Y. Dosing device 530 administer an oxidizing agent as a solid, liquid or gas, but preferably a liquid. In one example, the oxidizing agent is in a liquid state, such as hydrogen peroxide. In another example, the oxidizing agent is in a solid state, such as benzoyl peroxide.
System 500, containing bypass line 503 and valves 531 and 532, function similar to system 100 when valves 531 and 532 are positioned to exclude anolyte circulation from bypass line 503, herein, “full mode.” However, valves 531 and 532 may be positioned to exclude anolyte circulation through dosing device 530 and cartridge 520 and direct all anolyte through the bypass line 503, herein, “bypass mode.” The full or bypass modes are controlled by positioning valves 531 and 532 via the system controller 524. System 500 may be placed in bypass mode to replace the copper source and/or the oxidizing agent while continuing to operate the plating system. Also, system 500 may provide additional control to administer the oxidizing agent and copper ion concentration. For example, an oxidizing agent may be dispensed from the dosing device 530 by flowing anolyte in full mode and then switching to bypass mode to cease the administration of the oxidizing agent. This latter example may be applied to an oxidizing agent in the solid state that slowly dissolves into the anolyte.
The above apparatus and process describes replenishing metal ions in a plating solution as well as decreasing the acidity (e.g., increasing pH) of the plating solutions. In the preferred embodiment, the plating solution is an anolyte within an electroplating system used to plate copper or copper-containing alloy. However, plating with other metals are within the scope of the present invention, such as zinc, cadmium, tungsten, nickel, platinum, palladium, gold, silver, vanadium, cobalt, alloys thereof, as well as other metals. In an alternative example, at least one secondary element may be added with a copper-containing material as a metal source to be plated. The above apparatus and process anticipate that one skilled in the art can easily replace the plating solution composition to deposit a variety of metals by applying routine experimentation to the basic scope of the present invention. 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.