CN119302041A - Removal of metal salt deposits in electroplating tools - Google Patents

Abstract

The disclosed examples relate to the removal of metal salt deposits within a circulation loop of an electroplating tool. In an exemplary method, during a processing stage of operation, a metal salt solution is flowed through a recirculation loop at a process temperature to deposit metal on a substrate. The metal salt solution contains at least a metal cation and a counter ion. During the precipitate removal phase of operation, the metal salt solution is heated to a temperature higher than the process temperature. The heated metal salt solution then flows through the circulation loop for a period of time to dissolve metal salt precipitates of the metal salt solution in the circulation loop. The metal salt solution is then cooled to the process temperature.

Description

Removal of metal salt deposits from electroplating tools

Background Art

Electroplating can be used in the process of integrated circuits to deposit conductive films on substrates. Electroplating involves electrochemically reducing dissolved ions of a selected metal to an elemental state on a substrate to form a film of the selected metal. The electroplating system comprises: a cathode chamber through which a cathode electrolyte solution circulates; and an anode chamber through which an anolyte solution circulates. A cation exchange membrane is located between the cathode electrolyte chamber and the anode chamber electrolyte. The cation exchange membrane allows protons and ions of the selected metal to pass from the anode to the cathode and blocks the passage of anions and organic additives.

Summary of the invention

This summary is provided to introduce a selection of concepts in a simplified form, which will be further described in the following detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that address any or all of the disadvantages mentioned in any part of this disclosure.

Disclosed examples relate to the removal of metal precipitates from a circulation loop of an electroplating tool. In an exemplary method, during a treatment phase of operation, a metal salt solution flows through a circulation loop at a process temperature to deposit metal on a substrate. The metal salt solution contains at least metal cations and counter ions. During a precipitate removal phase of operation, the metal salt solution is heated to a temperature higher than the process temperature. The heated metal salt solution then flows through the circulation loop for a period of time to dissolve the metal salt precipitate of the metal salt solution in the circulation loop. The metal salt solution is then cooled to the process temperature.

In some such examples, the method further includes receiving an indication of accumulated metal salt precipitate of the metal salt solution within the circulation loop, and initiating a precipitate removal phase of operation in response to the received indication.

In some such examples, the system for indicating accumulated metal salt precipitates of the metal salt solution in the circulation loop alternatively or additionally includes an indication of passivation of the cation exchange membrane.

In some such examples, the indication of accumulated metal salt precipitate of the metal salt solution in the circulation loop alternatively or additionally includes a non-uniform current observed at the cathode.

In some such examples, initiating a deposit removal phase of operation alternatively or additionally includes monitoring a total coulomb of electroplating performed by the electroplating tool following a previous deposit removal phase of operation.

In some such examples, the method alternatively or additionally further includes, in response to the accumulated total coulombs being below a threshold when accumulation of metal salt precipitates is indicated, initiating a precipitate removal phase of operation during a next idle period.

In some such examples, the method alternatively or additionally further includes, in response to the accumulated total coulombs being above the threshold when accumulation of metal salt precipitates is indicated, initiating a precipitate removal phase of operation prior to a next idle period.

In some such examples, the metal salt solution alternatively or additionally comprises a catholyte or an anolyte.

In some such examples, the metal cation alternatively or additionally comprises Cu ²⁺ , and the counter ion alternatively or additionally comprises SO ₄ ²⁻ .

Another example provides an electroplating tool. The electroplating tool includes: a substrate, a circulation loop of a metal salt solution, the circulation loop includes: a heater, a logic machine, and a storage machine, the storage machine storing instructions that can be executed by the logic machine. The instructions can be executed to, during a processing phase of operation, control the flow of the metal salt solution through the circulation loop at a process temperature to deposit metal on the substrate, and during a precipitate removal phase of operation, control the heater to heat the metal salt solution to a temperature higher than the process temperature, control the flow of the metal salt solution through the circulation loop for a period of time to dissolve the metal salt precipitate in the circulation loop, and control the heater to cool the metal salt solution to the process temperature.

In some such examples, the circulation loop alternatively or additionally includes a cathode chamber or an anode chamber.

In some such examples, the cathode chamber is alternatively or additionally separated from the anode chamber by a cation exchange membrane.

In some such examples, the anode chamber alternatively or additionally contains a consumable anode.

In some such examples, the consumable anode alternatively or additionally comprises copper metal.

In some such examples, the metal cation alternatively or additionally comprises Cu ²⁺ , and the counter anion alternatively or additionally comprises SO ₄ ²⁻ .

In some such examples, the precipitate removal phase of the operation is alternatively or additionally initiated in response to an indication of accumulated metal salt precipitate in the circulation loop.

Another example provides a storage machine that also stores instructions that can be executed by the logic machine, the instructions being used to, in an electroplating tool, during a processing phase of operation, control the flow of a metal salt solution through a circulation loop at a process temperature to deposit metal on a substrate, and during a precipitate removal phase of operation, control a heater to heat the metal salt solution to a temperature higher than the process temperature, control the flow of the metal salt solution through the circulation loop for a period of time to dissolve metal salt precipitates in the metal salt solution in the circulation loop, and control the heater to cool the metal salt solution to the process temperature.

In some such examples, the memory machine alternatively or additionally stores instructions executable by the logic machine for receiving an indication of accumulated metal salt precipitate of the metal salt solution in the circulation loop and, in response to the received indication, initiating a precipitate removal phase of operation.

In some such examples, the memory engine alternatively or additionally stores instructions executable by the logic engine for initiating a precipitate removal phase of operation during a next idle period if the accumulated total coulomb count is below a threshold when accumulation of metal salt precipitates is indicated.

In some such examples, the memory engine alternatively or additionally stores instructions executable by the logic engine for initiating a precipitate removal phase of operation prior to a next idle period if the accumulated total coulomb count is above the threshold when accumulation of metal salt precipitates is indicated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of an exemplary electroplating tool.

FIG. 2 schematically depicts an exemplary electroplating cell of an electroplating tool.

3A and 3B schematically depict examples of cationic current flow in the electroplating tool of FIG. 2 without and with metal salt precipitation, respectively.

FIG. 4 shows a flow chart describing an example of a method of operating an electroplating tool.

FIG. 5 depicts an exemplary graph of metal salt solution temperature versus time for an exemplary implementation of the method of FIG. 4 .

FIG. 6 schematically depicts exemplary states of the electroplating tool of FIG. 2 over time while performing an exemplary implementation of the method of FIG. 4 .

FIG. 7 shows an exemplary computing system.

DETAILED DESCRIPTION

The term "anode" may generally refer to a conductive structure where electrochemical oxidation occurs during an electroplating process.

The term "anodic chamber" may generally refer to a physical structure configured to house at least one anode and anolyte and to provide selective separation from a cathodic chamber.

The term "anolyte" may generally refer to a solution used in the anode compartment of an electroplating process.

The term "anolyte bath" may generally refer to a liquid environment in the anode compartment.

The term "cathode" may generally refer to a conductive layer on a substrate that is grown by electrochemical reduction of ions during an electroplating process.

The term "cathode chamber" may generally refer to a physical structure configured to house at least one cathode and a catholyte and to provide selective separation from an anode chamber.

The term "catholyte" generally refers to a solution used in the cathode chamber of an electroplating process.

The term "catholyte bath" may generally refer to a liquid environment in the cathode chamber.

The term "circulation loop" may generally refer to a path through which a liquid is recirculated over time. The term circulation loop may generally refer to a circulation loop for the anolyte and may also generally refer to a circulation loop for the catholyte.

The term "consumable anode" may generally refer to an electrode material that is electrochemically oxidized during an electroplating process.

The term "electroplating coulombs" may generally refer to the quantification of the amount of charge, measured in coulombs, used to electrochemically reduce a metal on one or more substrates over time.

The term "counter anion" may generally refer to an anion that provides charge balance to a cation in a solution.

The terms "electroplating," "plating," "deposition," and variations thereof may generally refer to a process in which dissolved ions of one or more metals are reduced on a substrate surface to form a film of the one or more metals.

The term "electroplating tool" may generally refer to a machine configured to perform electroplating.

The term "high resistance virtual anode" (HRVA) may generally represent an ionically resistive structure positioned between the substrate holder and the anode of an electroplating tool through which ions flow from the anode to the cathode during electroplating. The HRVA approximates a reasonably constant and uniform current source adjacent to the cathode.

The term "idle period" may generally refer to a period of time during which an electroplating tool is not scheduled to perform electroplating on a substrate.

The term "cation exchange membrane" may generally refer to a membrane that selectively allows one or more cationic species to pass therethrough while blocking the passage of other species, such as anionic species and organic species.

The term "metal salt solution" may generally refer to a solution comprising dissolved metal ions and counter anions.

The term "metal cation" may generally refer to a metal atom in a positive oxidation state.

The term "metal salt precipitate" may generally refer to a solid metal salt precipitate produced from a solution.

The term "non-uniform current" may generally refer to an ion flow or current that contains different magnitudes in a region that intersects the direction of the current flow.

The term "passivation" when used with reference to a cation exchange membrane will generally refer to a coating of metal salt precipitates that reduces or inhibits transport through the cation exchange membrane.

The term "precipitate removal phase" may generally represent a period of operation of an electroplating tool during which metal salt precipitates are dissolved in the metal salt solution and the substrate is not treated.

The term "processing stage" may generally refer to the operating section of an electroplating tool when a substrate is undergoing processing.

The term "process temperature" generally refers to the temperature of the metal salt solution during the electroplating operation.

The term "substrate" refers to any object upon which a film can be deposited.

In the semiconductor processing industry, the demand for maintaining high uniformity while electroplating metal on substrates is increasing rapidly. To meet this demand, electroplating techniques tend to favor higher plating currents and chemicals that can help increase the plating rate. For example, the catholyte solution and the anolyte solution may contain metal salts close to saturation concentrations. However, this condition may cause the deposition of metal salt precipitates that form in the electroplating tool over time.

As a particular example, to achieve a relatively high copper electroplating growth rate, the electroplating current may exceed 10 amperes. In addition, the catholyte and anolyte may contain nearly saturated solutions of copper sulfate (CuSO ₄ ), sulfuric acid (H ₂ SO ₄ ) and other possible supporting additives. Copper electroplating uses a cation exchange membrane to separate the anolyte chamber and the catholyte chamber to prevent oxidation of organic additives at the anode. An exemplary cation exchange membrane may include a sulfonated tetrafluoroethylene-based fluoropolymer copolymer. The metal ions that reach the catholyte from the anolyte through the cation exchange membrane increase the concentration of metal ions in the catholyte adjacent to the cation exchange membrane. Such a local concentration increase may cause the cathode electrolyte solution at the cation exchange membrane to be supersaturated in some cases. This may cause metal salt precipitates to form at the cation exchange membrane and/or adjacent structures. Low convection in the catholyte at the exchange membrane may also cause precipitation to occur and crystal growth. Over time, the thickening of the precipitate may cause partial passivation of the cation exchange membrane. This may negatively impact the uniformity of the electroplated film on the substrate.

Currently, a major strategy for restoring a target substrate deposition profile to a tool that has experienced deposit buildup is manual intervention. Manual intervention may include removing/replacing the affected films and parts. Such intervention may be time-consuming and relatively expensive, at least due to the cost of the parts and the impact on tool availability. Other strategies, such as reducing the metal ion concentration and/or the current used for electroplating, may reduce the effectiveness of the tool.

Accordingly, an example is disclosed, which relates to using an in-situ heat treatment cycle to remove metal salt precipitates from the circulation loop of an electroplating tool. This disclosed example is a non-invasive, in-situ process, which uses a potential appropriate temperature increase of a circulating metal salt solution to dissolve the metal salt precipitates accumulated by electroplating tool parts. This disclosed example can help avoid the replacement of parts caused by precipitate accumulation, and can reduce the overall impact of precipitate removal on the tool usable time. Although the accumulation of copper electroplating tools and copper sulfate crystals at cation exchange membranes is mainly described herein, this method can be used together with any suitable chemical on any suitable electroplating tool. In addition, this disclosed example can even allow the improvement of severe crystal accumulation. In addition, because this disclosed process is non-invasive, this process can be performed without destroying the plane of the electroplating tool.

Before discussing these examples in more detail, FIG. 1 schematically depicts a block diagram of an exemplary electroplating tool 100. The electroplating tool 100 includes an electroplating cell 102, which includes an anode chamber 104 and a cathode chamber 106. The electroplating tool 100 also includes a cation exchange membrane 108 separating the anode chamber 104 and the cathode chamber 106, and a HRVA 109 in the cathode chamber 106. The anode chamber 104 includes an anode 110. The anode chamber 104 also includes an anolyte. The cathode chamber 106 includes a catholyte. The catholyte includes ionic species that are deposited in a metallic state by electrochemical reduction at the cathode layer of the substrate 111. The anode 110 may include a consumable anode formed from the deposited metal, or may include an inert anode. When the anode 110 includes the deposited metal, the electrochemical oxidation of the anode 110 can at least partially replenish the ionic species consumed by the electroplating process. Bulk anolyte solution and/or catholyte solution may sometimes be added to replenish the ionic species.

Cation exchange membrane 108 prevents organic and anionic species from passing between cathode chamber 106 and anode chamber 104, while allowing metal ions to pass from anode chamber 104 to cathode chamber 106. As described above, HRVA 109 comprises an ionically resistive element that approximates a reasonably constant and uniform current source adjacent to the substrate cathode.

The substrate holder 112 is coupled to a substrate holder movement system 113, which includes an elevator 114 configured to adjust the space between the substrate holder 112 and the HRVA 109. For example, the elevator 114 may lower the substrate holder 112 to position the substrate 111 in the catholyte for electroplating. The elevator 114 may also raise the substrate holder 112 from the catholyte after electroplating. The substrate holder movement system 113 may also include components to control the opening and closing of the substrate holder 112.

The catholyte may be circulated between the cathode chamber 106 and the catholyte reservoir 120 by a combination of gravity and one or more pumps 122. Likewise, the anolyte may be circulated between the anode chamber 104 and the anolyte reservoir 124 by a combination of gravity and one or more pumps 126. In-line heaters 127 and 128, such as heater/coolers, may be included to control the temperature of the catholyte and anolyte, respectively.

In some electroplating tools, the electroplating operation can be performed in parallel with multiple electroplating units on multiple substrates. In some such examples, a central catholyte and/or anolyte reservoir can supply catholyte and/or anolyte to multiple electroplating units. In other such examples, independent catholyte and/or anolyte reservoirs can be used to supply multiple electroplating units. In still other examples, the electroplating tool can include separate electroplating units. When the electroplating tool includes multiple electroplating units, a separate elevator can be configured to raise two or more substrate holders of two or more different electroplating units.

After the substrate 111 is loaded into the substrate holder 112, the substrate holder 112 is lowered toward the HRVA 109 by the elevator 114. The substrate 111 faces the surface of the HRVA 109 and is separated from the HRVA 109 by a plating gap during the electroplating process. An electric field is established between the anode 110 and the substrate 111. The electric field drives the dissolved metal cations from the anode chamber 104 into the cathode chamber 106. At the substrate 111, the metal cations are electrochemically reduced to be deposited on the substrate 111. The anode potential acts on the anode 110 through the charged plate 115 and the cathode potential is supplied to the cathode of the substrate 111 through the cathode electrical connection 116 to form a circuit. In some examples, the substrate holder 112 can be rotated by a rotation motor 117 during the electroplating process.

The electroplating tool 100 also includes a computing system 130, various aspects of which are described in more detail below with respect to FIG. 7. The computing system 130 may include executable instructions to control any suitable function of the electroplating tool 100. Examples of functions include electroplating processes, substrate loading/unloading processes, and precipitate dissolution processes. The precipitate dissolution process of the example is described in more detail below. In some examples, the computing system 130 may be configured to communicate with a remote computing system 140 via a suitable computer network. The remote computing system 140 may include any suitable computing system. Examples include network workstation computers, enterprise computing systems, and/or cloud computing systems. It is understood that in some examples the remote computing system 140 may communicate with and control multiple electroplating tools.

FIG2 schematically depicts an exemplary electroplating cell 202 of an electroplating tool. The electroplating cell 202 is an example of the electroplating cell 102 of FIG1 . The electroplating cell 202 includes an anode chamber 204 and a cathode chamber 206. The electroplating cell 202 also includes a cation exchange membrane 208 that separates the anode chamber 204 and the cathode chamber 206. The electroplating cell 202 also includes a HRVA 209 disposed in the cathode chamber 206.

The anode chamber 204 includes an anolyte bath 210 in which an anode 212 is configured. In this example, the anode 212 includes a copper metal anode. In other examples, the anode 212 may include an inert anode. The cathode chamber 206 includes a catholyte bath 214, which includes copper ions (Cu ²⁺ ) to be deposited on a substrate 216 that serves as a cathode. The catholyte bath 214 is located in a catholyte circulation loop 220. The catholyte enters the cathode chamber 206 from an inlet 222 and leaves from an outlet 224. The catholyte circulation loop 220 includes a heater 226 (e.g., a heater/cooler) that is configured to adjust and/or maintain the temperature of the catholyte flowing through the cathode electrolyte loop 220.

Similarly, the anolyte bath 210 is located in an anolyte circulation loop 230. Anolyte enters the anode chamber 204 through an inlet 232 and exits through an outlet 234. The anolyte circulation loop 230 includes a heater 236 (e.g., a heater/cooler) configured to adjust and/or maintain the temperature of the anolyte flowing through the anolyte circulation loop 220. A voltage source 240 applies a voltage across the substrate 216 and the anode 212 to drive the copper ions to flow for deposition on the substrate 216.

For copper electroplating, in some examples, anode 212 may include a copper block (e.g., a ball) or a copper plate. As mentioned above, in other examples, anode 212 may include an inert anode. In the described example, the applied voltage causes copper metal to oxidize to Cu ²⁺ at anode 212. Cation exchange membrane 208 allows Cu ²⁺ ions to flow from anolyte bath 210 to catholyte bath 214. The Cu ²⁺ ions passing through cation exchange membrane 208 replace at least some of the copper ions in catholyte bath 214 that are reduced to substrate 216.

Heater 226 can be controlled to maintain catholyte bath 214 at a predetermined process temperature during the electroplating process. Heater 236 can also be controlled to maintain anolyte bath 210 at a predetermined process temperature during the electroplating process. The process temperature may include relatively low temperatures in some processes. For example, a process temperature in the range of 22°C-26°C may be used in some copper deposition processes.

As mentioned above, some electroplating conditions may increase the concentration of dissolved copper ions in the catholyte near the surface of the cation exchange membrane. The resulting concentration may exceed the solubility limit of the cathode electrolyte solvent (e.g., water) at the process temperature. This may cause crystals to form on the cation exchange membrane. In the example of Figure 2, the Cu ²⁺ ions in the anolyte bath 210 pass through the cation exchange membrane 208 and enter the catholyte bath 214. Therefore, the catholyte just above the cation exchange membrane 208 contains ions from the catholyte in the catholyte bath 214 and additional Cu ²⁺ flowing in from the anolyte bath 210. The concentration of the additional Cu ²⁺ ions increases when the electroplating current increases. If there is no sufficient catholyte reflux to remove excess Cu ²⁺ ions, the solution above the membrane may precipitate solid copper salts on the membrane. CuSO ₄ may be the main component of the copper salt precipitate. The copper-containing catholyte may also contain chloride ions and sulfonate anions, which may also form copper precipitates. Metal salt precipitation may also occur in other electroplating chemistries. Examples include tin and tin-silver alloys. For tin-silver alloys, exemplary counter anions include methylsulfonicacid and organic acids. Precipitation may also occur for other electroplated metals, including cobalt, indium, and nickel.

The presence of metal salt precipitates on the cation exchange membrane 208 may block the distribution of fluid transmission and current. Such a situation can be called passivation. If the area on the membrane is partially or completely passivated, it may cause non-uniform current distribution. This may cause non-uniform metal plating on the substrate.

In some examples, one or more sensors may be located in or near the electroplating cell 202 to monitor the situation and provide a non-uniform indication of the accumulation that may indicate the metal salt precipitate. For example, the electroplating cell 202 may include a cathode current sensor array 242 and/or an optical sensor 246. The cathode current sensor array 242 may monitor the electric current at different positions on the substrate 216. The optical sensor 246 may be installed to provide visual monitoring of the accumulation of metal salt precipitates to observe the surface of the cation exchange membrane 208. The optical sensor 246 may include a photodiode, a camera and/or other suitable optical sensing devices. Except those shown, additional optical sensors, and/or other sensors may be installed in and near the electroplating cell 202.

3A and 3B schematically depict examples of current flow in electroplating cell 202. FIG3A shows current flow without metal salt precipitation on cation exchange membrane 208. FIG3B shows current flow with metal salt precipitation on cation exchange membrane 208. Referring first to FIG3A, ion flow 305 from anode 212 is uniform across anode 212, through cation exchange membrane 208, and through HRVA 209. This produces uniform current 310 and deposition on substrate 206.

3B, cation exchange membrane 208 is partially passivated by metal salt precipitates 325. Regions 322 of cation exchange membrane 208 having a higher degree of accumulation of metal salt precipitates 325 correspond to portions 327 of the substrate that experience a slower metal deposition rate than portions 330 of the substrate.

Returning to FIG. 2 , metal salt precipitates may deposit at other locations in the catholyte loop 220 and/or the anolyte loop 230. For example, the electroplating tool may use a water management and removal system in one or more of the catholyte loop 220 or the anolyte loop 230 to remove excess water. When solvent is removed from the bath, the ion concentration effectively increases. This can cause metal salts to precipitate in the water management and removal system. Precipitation may also occur at other locations near high volatility areas.

In some cases, metal salt precipitates may be generated in the anolyte circulation loop 230. For example, some electroplating processes may use high concentrations of copper in the anolyte bath 210 similar to the catholyte bath 214. When there is a low circulation condition in the anode compartment, metal salt precipitates may form. The metal salt precipitates in the anode compartment may cause performance problems similar to the passivation of cation exchange membranes. For example, when metal salt precipitates form in several areas of the anode, oxidation of copper may be prevented in these areas. This may cause non-uniformity of ion flow between the anode 212 and the substrate 216.

Metal salt deposits may also form between parts of the electroplating cell 202. For example, metal salt deposits may occur on the seal between the HRVA 209 and the membrane frame, as shown at 340. If the seal is not completely cleaned, the deposits may cause leakage current.

As mentioned above, manual intervention to remove metal salt deposits from an electroplating tool can be time consuming and expensive. Therefore, FIG. 4 shows a flow chart describing an exemplary method 400 for operating an electroplating tool in a manner that can remove metal salt deposits without manual intervention. The method 400 can be controlled by a computing system (such as computing system 130) of the electroplating tool. For example, the method 400 may be encoded as instructions stored in a storage device of the computing system that can be executed by a logic device of the computing system. The method 400 can also be manually controlled by an operator of the electroplating tool.

At 410, method 400 includes, during a process phase of operation, flowing a metal salt solution through a circulation loop including a cathode chamber in an electroplating process. The metal salt solution flows through the circulation loop at a process temperature. The metal salt solution includes at least a metal cation and a counter anion. The process temperature may be predetermined based on conditions during the process phase.

In some examples, the deposited metal includes copper and a metal cation including Cu ²⁺ . In such examples, an exemplary process temperature of the metal salt solution may include a temperature between 22-26°C. In other examples, the deposited metal may include tin, silver, indium, cobalt, nickel, or other conductive metals. In such examples, the metal cation may be a soluble cation of the corresponding metal. In some examples, the deposited metal may be an alloy or a solder material including two or more metals, such as a tin-silver alloy. In such examples, the metal salt solution may include two or more metal cations, such as Sn ²⁺ and Ag ⁺ . For more than one selected metal cation, any suitable relative anion or combination of relative anions can be used. Examples include SO ₄ ^2- , Cl ^- , hydroxide, sulfonate, and the like. In some examples, the metal salt solution includes a cathode electrolyte. In other examples, the metal salt solution may additionally or alternatively include an anolyte.

In some examples, visual inspection of the electroplating tool and its components may be periodically performed to detect metal salt deposits. Likewise, substrate analysis may be performed to sense metal film properties (eg, non-uniform growth) that may indicate the presence of inappropriate amounts of metal salt deposits.

Alternatively, in other examples, automatic sensing may be used to sense conditions that may indicate accumulation of metal salt precipitates. Thus, method 400 may include, at 420, receiving an indication of accumulation of metal salt precipitates in a circulation loop, and initiating a precipitate removal phase of operation in response to the indication received. For example, an indication of passivation of a cation exchange membrane may be received. For example, a current sensor configured to sense cathode current (e.g., cathode current sensing array 242) may sense non-uniform current flowing at different locations on a substrate. In another example, optical sensing (e.g., optical sensor 246) may be used to detect precipitates on structures that are prone to precipitate accumulation. In addition, a camera may be used to photograph an electroplating unit, and a trained machine learning classifier may be used to detect the presence of precipitates in image data obtained from a camera. Such a machine learning function may be trained by using a monitored learning program using labeled image data showing a range of precipitate conditions. Exemplary machine learning functions include suitable neural network classes, such as residual neural networks. Such a machine learning function may be trained using a back propagation algorithm and an appropriate cost function. Exemplary cost functions include a quadratic cost function, a cross entropy cost function, and an exponential cost function.

As another example, charge sensing can be used to detect the cumulative amount of electrochemical metal reduction performed by the electroplating tool since the last operational sediment removal phase. Such charge sensing can be performed by a current detector that monitors the cathode current. In some examples, the cumulative total coulomb count exceeding a threshold value can be used as a trigger to perform a sediment removal phase.

In other examples, when process conditions that may indicate an inappropriate amount of precipitate are detected, the cumulative total coulomb count is used to determine the action to be taken. For example, in section 430, method 400 optionally includes monitoring the total coulomb count of electroplating performed by the electroplating tool after the precipitate removal phase of the previous operation. In section 432, process conditions indicating a possible risk of precipitation are detected, as described above. In response, in 434, method 400 determines whether the cumulative total coulomb count is below or meets a threshold. When the cumulative coulomb count is below the threshold, the precipitate removal phase of the operation may be performed during the next idle period, as mentioned in 436. On the other hand, in section 438, when the cumulative coulomb count meets the threshold, the precipitate removal phase of the operation may be initiated before the next idle period (e.g., when any substrate currently awaiting processing at the tool is completed). After the precipitate removal phase is performed, the cumulative total coulomb count may be reset.

The cumulative coulomb threshold may be predetermined, or may vary based on operating conditions. For example, the cumulative coulomb threshold may automatically change over time based on changes in conditions such as metal salt solution composition and concentration, metal salt solution flow rate, plating gap distance, and/or plating current. In some examples, the user interface may be configured to alert the user when the precipitate removal phase of the operation should be performed (e.g., at the next idle period, or at a specific point before the next idle period, such as when all wafers in a current front opening pod (FOUP) or other substrate carrier have been processed).

Continuing with FIG. 2 , at section 430 , method 400 includes, during a precipitate removal phase of operation, heating the metal salt solution to a temperature higher than the process temperature. The precipitate removal phase of the operation also includes passing the metal salt solution through a circulation loop for a period of time to dissolve the metal salt precipitate of the metal salt solution in the circulation loop. The precipitate removal phase of the operation also includes, after passing the metal salt solution through the circulation loop for a period of time, cooling the metal salt solution to the process temperature. For example, when the process temperature is 25° C., the temperature of the metal salt solution may be heated to a temperature in the range of 34° C.-37° C. during the precipitate removal phase. The temperature of the metal salt solution may then be cooled back to the process temperature after the precipitate removal phase. The redissolved metal salt precipitate may have only a minor effect on the total number of metal cations and counterions in the metal salt solution when redissolved. Therefore, the concentration of the metal salt solution may not need to be adjusted after the precipitate removal phase.

In some examples, other operating conditions may be adjusted during the precipitate removal phase. For example, the concentration of metal cations may be reduced by temporarily diluting the metal salt solution. The concentration may then be restored to that used for electroplating on the substrate. The flow rate of the metal salt solution may also be adjusted.

The temperature and duration of the precipitate removal can be determined based on various factors. Exemplary factors include process temperature, metal salt solution flow rate, metal salt solution concentration and/or composition, current used for electroplating, non-uniformity of cathode current measured at different substrate locations, and/or the length of time since the last operational precipitate removal phase.

FIG5 shows a curve 500 depicting an example of a temperature variation of a metal salt solution over time for an exemplary implementation of method 400. At time _t0 , the electroplating tool is operating in a process phase of operation and the metal salt solution is circulating in a circulation loop at a process temperature (T1). At time _t1 , an indication of a metal salt precipitate in the circulation loop of the metal salt solution is received. At time _t2 , a precipitate removal phase is initiated and the temperature of the metal salt solution is increased until a selected temperature (T2) above the process temperature is reached at time _t3 .

The metal salt solution is then circulated in a circulation loop at an elevated temperature for a period of time (e.g., from time _t3 to time _t4 ). This allows the precipitate to redissolve. This also allows passive irrigation/convection to remove any concentrated solution produced from the membrane or other accumulation location. For example, the flow of catholyte across the cathode chamber establishes solution exchange across the HRVA, causing the catholyte to flow through the HRVA into the volume between the HRVA and the ion exchange membrane. The flow of catholyte across the HRVA also causes convection of the catholyte in the volume between the HRVA and the cation exchange membrane. In some examples, the duration may be approximately 2-4 hours. In other examples, the duration may be shorter or longer, depending on the operating conditions.

At time _t4 , the precipitate removal phase ends and the temperature of the metal salt solution drops to process temperature T1. There may be some temperature oscillations around T1 as the solution temperature stabilizes. At time _t5 , the metal salt solution temperature has stabilized and the electroplating tool can return to the processing phase.

Figure 6 depicts some example states over time when the electroplating tool of Figure 2 performs an example implementation of the method of Figure 4. At 600, the electroplating cell 202 is operating in a process stage of operation, and the catholyte is circulated in the circulation loop 220 at a process temperature of 25°C, passively flushing the HRVA 209, as shown at 602. As shown, the cation exchange membrane 208 is passivated by the metal salt precipitate 604, and the effect is observed at the substrate 216.

At 610, the electroplating cell 202 progresses to the precipitate removal phase of operation. The catholyte is heated to an elevated temperature (e.g., 35°C) by the heater 226. As the temperature increases, dissolution of the metal precipitate progresses, as shown at 612. In this case, the solid precipitate dissolves rapidly. The resulting concentrated metal salt solution is removed by passive irrigation (e.g., a catholyte flow rate of 70 liters per minute). At 620, the elevated temperature is maintained while all of the metal salt precipitate is dissolved and flushed from the cathode chamber 206. At 630, the electroplating chemistry is returned to the initial temperature to restart the electroplating operation.

The solubility limit of _CuSO4 in aqueous solution increases exponentially with temperature. Under the conditions where crystals are produced (e.g., low-temperature electroplating solutions), the concentration of dissolved copper sulfate is saturated at the cation exchange membrane interface. By temporarily increasing the temperature of the electroplating chemistry, even by a relatively small amount (e.g., 10°C-12°C), the ability of the solution to dissolve additional _CuSO4 is significantly increased.

Therefore, the disclosed example can allow the metal salt precipitate to be removed from the cathode electrolyte circulation loop and/or the anolyte circulation loop of the electroplating tool without manual intervention. The disclosed example can also help to restore the passivated cation exchange membrane. This can help reduce the replacement frequency of the cation exchange membrane. Therefore, the precipitate can be removed with shorter tool downtime and less cost compared to the manual intervention method.

In some embodiments, the methods and processes described herein may be combined with a computing system of one or more computing devices. Specifically, such methods and processes may be implemented as a computer application or service, an application programming interface (API), a library, and/or other computer program products.

FIG7 schematically illustrates a non-limiting embodiment of a computing system 700 that can perform one or more of the above methods and processes. The computing system 700 is shown in simplified form. The computing system 700 can take the form of one or more personal computers, workstations, computers integrated with wafer processing tools, and/or network accessible server computers.

Computing system 700 includes a logic machine 710 and a storage machine 720. Computing system 700 may optionally include a display subsystem 730, an input subsystem 740, a communication subsystem 750, and/or other components not shown in FIG7. Computing system 130 is an example of computing system 700.

Logic machine 710 includes one or more physical devices configured to execute instructions. For example, the logic machine can be configured to execute instructions that are part of one or more applications, services, programs, routines, libraries, objects, components, data structures, or other logical constructs. Such instructions can be implemented to perform tasks, implement data types, transform the state of one or more components, achieve technical effects, or otherwise achieve desired results.

The logic machine may include one or more processors configured to execute software instructions. Additionally or alternatively, the logic machine may include one or more hardware or firmware logic machines configured to execute hardware or firmware instructions. The processors of the logic machine may be single-core or multi-core, and the instructions executed thereon may be configured for sequential, parallel and/or distributed processing. The various components of the logic machine may optionally be distributed in two or more separate devices that may be remotely located and/or configured for coordinated processing. Various aspects of the logic machine may be virtualized and executed by a remotely accessible networked computing device configured in a cloud computing configuration.

The storage machine 720 includes one or more physical devices configured to store instructions 755 that can be executed by a logic machine to implement the methods and processes described herein. When such methods and processes are implemented, the state of the storage machine 720 can be transformed—for example, to store different data.

The storage machine 720 may include removable and/or built-in devices. The storage machine 720 may include optical storage (e.g., CD, DVD, HD-DVD, Blu-ray disc, etc.), semiconductor storage (e.g., RAM, EPROM, EEPROM, etc.), and/or magnetic storage (e.g., hard disk drive, floppy disk drive, tape drive, MRAM, etc.). The storage machine 720 may include volatile, non-volatile, dynamic, static, read/write, read-only, random access, sequential access, location addressable, file addressable, and/or content addressable devices.

It should be understood that storage 720 includes one or more physical devices. However, alternatively, aspects of the instructions described herein may be propagated via a communication medium (eg, electromagnetic signals, optical signals, etc.) that is not held for a finite duration by a physical device.

Aspects of the logic machine 710 and the storage machine 720 may be integrated together into one or more hardware logic components. For example, such hardware logic components may include field programmable gate arrays (FPGAs), program and application specific integrated circuits (PASIC/ASIC), program and application specific standard products (PSSP/ASSP), systems on chips (SOCs), and complex programmable logic devices (CPLDs).

When included, the display subsystem 730 can be used to present a visual representation of the data stored by the storage machine 720. This visual representation can take the form of a graphical user interface (GUI). Since the methods and processes described herein change the data held by the storage machine, and therefore change the state of the storage machine, the state of the display subsystem 730 can also be converted to visually represent the change of the underlying data. The display subsystem 730 can include one or more display devices using almost any type of technology. Such a display device can be combined with the logic machine 710 and/or the storage machine 720 in a shared cabinet (a shared enclosure), or such a display device can be a peripheral display device.

When included, the input subsystem 740 may include or may interact with one or more user input devices (e.g., a keyboard, mouse, or touch screen). In some embodiments, the input subsystem may include or interact with selected natural user input (NUI) components. Such components may be integrated or peripheral, and the conversion and/or processing of input actions may be handled on-board or off-board. Exemplary NUI components may include microphones for voice and/or sound recognition, and infrared, color, stereo, and/or depth cameras for machine vision and/or gesture recognition.

When included, the communication subsystem 750 can be configured to communicatively couple the computing system 700 with one or more other computing devices. The communication subsystem 750 can include wired and/or wireless communication devices compatible with one or more different communication protocols. As a non-limiting example, the communication subsystem can be configured to communicate using a wireless telephone network, or a wired or wireless local area network or wide area network. In some embodiments, the communication subsystem can allow the computing system 750 to send messages to other devices and/or receive messages from other devices through a network such as the Internet.

It should be understood that the configuration and/or method described herein is exemplary in nature, and these specific one or more embodiments should not be considered as restrictive, because many variations are possible. The specific routine or method described herein can represent one or more of any number of processing strategies. Therefore, the various actions shown and/or described can be performed in the order shown and/or described, in other orders, in parallel or omitted. Similarly, the order of the above-mentioned process can be changed.

The subject matter of the present disclosure includes all novel and nonobvious combinations and subcombinations of the various processes, systems and configurations, and other features, functions, acts, and/or properties disclosed herein, as well as any and all equivalents thereof.

Claims (20)

1. A method of operating an electroplating tool, the method comprising: During a process phase of operation, flowing a metal salt solution through a circulation loop at a process temperature to deposit metal on a substrate, the metal salt solution comprising at least a metal cation and a counter anion; and In the precipitate removal stage of operation, the metal salt solution is heated to a temperature above the process temperature, the metal salt solution is flowed through the circulation loop for a period of time to dissolve the metal salt precipitate of the metal salt solution in the circulation loop, and then the metal salt solution is cooled to the process temperature. 2. The method of claim 1 further comprising receiving an indication of accumulated metal salt precipitate of the metal salt solution within the circulation loop and initiating the precipitate removal phase of operation in response to the indication received. 3. The method of claim 2, wherein the indication of accumulated metal salt precipitate of the metal salt solution within the circulation loop comprises an indication of passivation of a cation exchange membrane. 4. The method of claim 2, wherein the indication of accumulated metal salt precipitate of the metal salt solution within the circulation loop comprises: a non-uniform current observed at a cathode. 5. The method of claim 2, wherein initiating the deposit removal phase of operation further comprises monitoring the total coulombs of electroplating performed by the electroplating tool after a previous deposit removal phase of operation. 6. The method of claim 5, further comprising, in response to the accumulated total coulombs being below a threshold when accumulation of metal salt precipitates is indicated, initiating the precipitate removal phase of operation during a next idle period. 7. The method of claim 6, further comprising, in response to the accumulated total coulombs being above the threshold when accumulation of metal salt precipitates is indicated, initiating the precipitate removal phase of operation prior to the next idle period. 8. The method of claim 2, wherein the metal salt solution comprises a catholyte. 9 . The method of claim 1 , wherein the metal cation comprises Cu ²⁺ , and wherein the counter anion comprises SO ₄ ²⁻ . 10. An electroplating tool, comprising: substrate; a circulation loop of a metal salt solution, the circulation loop comprising a heater; Logic Machine; and A storage machine storing instructions executable by the logic machine, the instructions being used to: During a processing phase of operation, controlling the flow of the metal salt solution through the circulation loop at a process temperature to deposit metal on the substrate; and During the precipitate removal stage of operation, the heater is controlled to heat the metal salt solution to a temperature above the process temperature, the flow of the metal salt solution through the circulation loop is controlled for a period of time to dissolve the metal salt precipitate in the circulation loop, and the heater is controlled to cool the metal salt solution to the process temperature. 11. The electroplating tool of claim 10, wherein the circulation loop comprises a cathode chamber. 12. The electroplating tool of claim 11, wherein the cathode chamber is separated from the anode chamber by a cation exchange membrane. 13. The electroplating tool of claim 12, wherein the anode chamber comprises a consumable anode. 14. The electroplating tool of claim 13, wherein the consumable anode comprises copper metal. 15. The electroplating tool according to claim 14, wherein the metal salt solution contains at least Cu ²⁺ and SO4 ^2- . 16. The electroplating tool of claim 10, wherein the precipitate removal phase of operation is initiated in response to an indication that metal salt precipitates have accumulated within the circulation loop. 17. A storage machine storing instructions executable by a logic machine, the instructions being used to: In an electroplating tool, during the process stage of operation, controlling the flow of a metal salt solution through a circulation loop at a process temperature to deposit metal on a substrate; and During the precipitate removal stage of operation, the heater is controlled to heat the metal salt solution to a temperature above the process temperature, the flow of the metal salt solution through the circulation loop is controlled for a period of time to dissolve the metal salt precipitate of the metal salt solution in the circulation loop, and the heater is controlled to cool the metal salt solution to the process temperature. 18. The storage machine according to claim 17, further storing instructions executable by the logic machine, the instructions being used to: An indication of accumulated metal salt precipitate of the metal salt solution in the circulation loop is received, and the precipitate removal phase of operation is initiated in response to the indication received. 19. The storage machine according to claim 18, further storing instructions executable by the logic machine, the instructions being used to: In the event that the accumulated total coulombs are below a threshold when accumulation of metal salt precipitates is indicated, the precipitate removal phase of operation is initiated during the next idle period. 20. The storage machine of claim 19, further storing instructions executable by the logic machine, the instructions being used to: In the event that the accumulated total coulombs are above the threshold when accumulation of metal salt precipitates is indicated, the precipitate removal phase of operation is initiated prior to the next idle period.