Patent Application
20140001050
Electroplating has many applications. One important application is in plating copper onto semiconductor wafers to form conductive copper lines for “wiring” individual devices of the integrated circuit. Often, this electroplating process serves as a step in, for example, a Damascene fabrication procedure. Other important applications include through silicon via plating (TSV) and wafer level packaging (WLP). A continuing issue in modern wafer electroplating processing is the quality of the deposited metal film. Defects on the deposited metal film are of particular concern. Examples of such defects include defects resulting from pits, protrusions, and particles/agglomerates formed on the film. Electroplating is frequently performed at a late stage in the device fabrication procedure when the processed wafer is worth many thousands of dollars. Defects introduced at this stage can result in substantial losses for integrated circuit manufacturers.
End users of sophisticated electroplating tools typically collect defect information on a daily basis. They may accomplish this by electroplating on a monitor wafer and counting the plated defects. Defects that create pits in the electroplated layer are particularly problematic, but any defect can be detrimental. Assessing defectivity of an electroplating apparatus through use of a monitor wafer introduces various problems. First, monitor wafers are quite expensive. Additionally, the time spent plating onto a monitor wafer is down time for the apparatus. No production wafers can be plated while the monitor wafer is installed. Further the use of a monitor wafer cannot pinpoint where or when an apparatus is failing through particle generation.
This disclosure presents various implementations of liquid particle counter (LPC) modules as components of electroplating tools. LPC modules may help to detect particles in electrolyte, allowing designers and operators of electroplating apparatuses to address problematic conditions before they introduce significant defects in wafers. Implementations of LPC modules during the design stage, research and development stage, and wafer production stage have proven beneficial. For example, in some embodiments, continuous particle monitoring of various locations within an electroplating apparatus may provide a constant process signature so that the conditions of chosen on-tool/apparatus components are known during production. Additionally, monitoring of incoming chemicals and/or previously combined chemicals in the electrolyte can be provided at various locations. Moreover, LPC monitoring at locations chosen to address particular defect types can accurately predict on-wafer defect performance, a metric which is conventionally typically obtained only after a wafer is processed with stand-alone metrology tools. In some embodiments, the disclosed implementation of LPC modules on electroplating tools/apparatuses allows for a comprehensive monitoring and diagnostic scheme that reveals real-time tool conditions and aids timely system troubleshooting and maintenance. Additionally, LPC modules may be used to isolate particle generating hardware in the apparatus during research and design. In some cases, such hardware components can be replaced before production, thereby potentially reducing production wafer defects.
In some embodiments, LPC modules may use light scattering as a method of particle detection. Different particle types such as solid particles and bubbles may produce similar LPC scattering signatures. In some embodiments, LPC modules are connected to multiple sampling ports distributed throughout the apparatus. A single LPC module may detect particle concentrations from multiple different locations throughout the electroplating apparatus. The sample ports may be designed and located to capture or exclude certain types of particles. For example, a sampling port may be designed to exclude bubbles from reaching the LPC module.
Certain embodiments disclosed herein concern an apparatus for electroplating metal onto a substrate. The apparatus may be characterized by the following features: (a) an electroplating cell for electroplating metal onto a substrate; (b) an electrolyte circulation system connected to the electroplating cell; (c) one or more liquid particle counter modules for measuring particle concentration in an electrolyte solution; and (d) sampling ports for taking samples at two or more locations in the apparatus. In various embodiments, the apparatus is configured for electroplating copper.
A single liquid particle counter module may be configured to analyze samples from multiple sampling ports. To this end, the liquid particle counter module may be coupled to a manifold to enable selective monitoring of sampling ports. The manifold and associated apparatus may include a tap for each sampling port, one or more pumps to draw sample electrolyte to the LPC module, and one or more valves and associated controller for selectively delivering the sample from particular ports at particular times.
In some embodiments, a liquid particle counter module is designed to analyze electrolytes at a flow rate between about 2 and 250 mL/min, or at a flow rate between about 5 and 100 mL/min, or at a flow rate between about 5 and 50 mL/min, or at a flow rate between about 5 and 20 mL/min, or at a flow rate between about 9 and 11 mL/min. In some implementations, the liquid particle counter module may be coupled to a drain. Thus, in some embodiments, the measured sample may not necessarily be recycled to the plating apparatus.
In some implementations, the liquid particle counter module is configured to collect particles in size-based particle bins. Example of particle size ranges for separate bins include the following: between about 0.1 and about 0.15 μm in diameter, between about 0.15 and about 0.2 μm in diameter, between about 0.2 and about 0.3 μm in diameter, between about 0.3 and about 0.5 μm in diameter, and greater than about 0.5 μm in diameter.
In some implementations, the sampling ports may be strategically located on various points in the electrolyte circulation system and/or the electroplating cell. The electrolyte circulation system may include various types of fluidic elements such as pumps. Sampling ports may be provided directly upstream and/or directly downstream from a fluidic element under consideration. The term “directly” used herein indicates that no other processing fluidic element is located between the sampling port and the fluidic element under consideration.
In certain embodiments, at least one of the sampling ports is positioned directly downstream from a pump. Another sampling port may be located upstream of the same pump. In some apparatus designs, the electrolyte circulation system includes a second pump and optionally a third pump, where additional sampling ports are positioned directly downstream from the second pump and the optional third pump.
The electrolyte circulation system may include a bath reservoir, which may contain at least one of the sampling ports. The electrolyte circulation system may include one or more contactors (designed to degas electrolyte), and there may be a sampling port positioned directly downstream from the contactor. In certain embodiments, the electrolyte circulation system may include one or more particle filters, each with its own (or with an associated) sampling port positioned directly downstream from the corresponding filter.
In certain embodiments, at least one of the sampling ports may be positioned directly upstream from an electroplating cell. In certain embodiments, at least one of the sampling ports is located on the interior of at least one of the electroplating cells. In certain embodiments, at least one of the sampling ports is located proximate to a membrane in the interior of an electroplating cell. Such membrane may be part of a Separated Anode Chamber or SAC as further described below.
Certain aspects of the disclosure concern methods for determining particle concentrations in an electrolyte present in an electroplating apparatus including an electroplating cell, and an electrolyte circulation system. The method may be characterized by the following operations: (a) directing a sample of electrolyte from a sampling port in the apparatus to a liquid particle counter module; (b) determining the particle concentration at the sampling port using the liquid particle counter module; and (c) modifying operation of the electroplating apparatus to reduce the particle concentration. In certain embodiments, modifying the operation of the electroplating apparatus involves identifying a source of particle contamination and replacing the source with a tool, chemical, or component, as appropriate, to reduce the particle concentration.
Accordingly, disclosed herein are electroplating apparatuses for electroplating metal onto a semiconductor wafer. In some embodiments, the apparatuses may include an electroplating cell for containing an anode and an electrolyte during electroplating, an electrolyte circulation system connected to the cell for circulating electrolyte to and from the cell, one or more sampling ports, and one or more liquid particle counter modules connected to the one or more sampling ports for measuring particle concentration in the electrolyte. In some embodiments, the one or more sampling ports may include a first sampling port for taking a first sample of electrolyte at a first location in the apparatus, and a second sampling port for taking a second sample of electrolyte at a second location in the apparatus. In some embodiments, an apparatus may include a manifold connected to at least two sampling ports and to at least one liquid particle counter module, and in certain such embodiments, the apparatus may further include two or more valves for controlling the flow of electrolyte from the at least two sampling ports to the manifold, and in certain further embodiments, a controller including machine readable instructions for controlling the opening and closing of the two or more valves to control the flow of electrolyte from the at least two sampling ports to the manifold. In some embodiments, the apparatus may further include a drain and at least one liquid particle counter module may be connected to the drain.
In some embodiments, at least one of the LPC modules of the electroplating apparatus may include a size-selective particle collector having size-based bins for collecting particles. In certain such embodiments, the size-based bins may include a first bin for collecting particles between about 0.1 and 0.15 μm in diameter, a second bin for collecting particles between about 0.15 and 0.2 μm in diameter, a third bin for collecting particles between about 0.2 and 0.3 μm in diameter, a fourth bin for collecting particles between about 0.3 and 0.5 μm in diameter, and a fifth bin for collecting particles greater than about 0.5 μm in diameter.
In some embodiments, an electroplating apparatus may further include a pump, sampling ports located directly downstream and upstream of the pump, and the apparatus may also include a controller configured to (i) monitor the particle concentrations upstream and downstream from the pump, (ii) determine when the pump is producing more than a threshold amount of particles; and (iii) generate an alert and/or modify operation of the apparatus when the pump is producing more than the threshold amount of particles.
In some embodiments, there may be a sampling port located within the interior of the electroplating cell, and the electroplating apparatus may further include a controller configured to (i) monitor the particle concentration within the interior of the electroplating cell, (ii) determine when the particle concentration in the electroplating cell is greater than a threshold level; and (iii) generate an alert and/or modify operation of the apparatus when the particle concentration in the electroplating cell is greater than the threshold level.
In some embodiments, an electroplating apparatus having an electroplating cell, an electrolyte circulation system, first and second sampling ports for taking first and second samples of electrolyte at first and second locations in the apparatus, and one or more LPC modules connected to the sampling ports, may further include a controller configured to (i) determine the approximate particle concentration in the first sample using the one or more liquid particle counter modules, (ii) determine the approximate particle concentration in the second sample using the one or more liquid particle counter modules, and (iii) modify the operation of the electroplating apparatus to reduce particle concentration in the electrolyte circulating to and from the electroplating cell. In some embodiments, the controller may be further configured to identify a source of particle contamination in the apparatus based on the approximate particle concentrations in the first and second samples, and in certain such embodiments, modifying the operation of the electroplating apparatus may include diverting electrolyte away from the source of particle contamination. Furthermore, in certain such embodiments, the source of particle contamination may be another electroplating cell of the electroplating apparatus, and diverting electrolyte away from this cell may include closing one or more valves to isolate this cell from the electrolyte circulation system. In some embodiments, the controller may be configured to direct the first sample of electrolyte from the first sampling port to the one or more liquid particle counter modules, and direct the second sample of electrolyte from the second sampling port to the one or more liquid particle counter modules.
In some embodiments, an electroplating apparatus having an electroplating cell, an electrolyte circulation system, first and second sampling ports for taking first and second samples of electrolyte at first and second locations in the apparatus, and one or more LPC modules connected to the sampling ports, may further include a controller configured to (i) determine the approximate particle concentration in the first sample using the one or more liquid particle counter modules, (ii) determine the approximate particle concentration in the second sample using the one or more liquid particle counter modules, and (iii) send an alert to the operator of the electroplating apparatus if the approximate particle concentration in the first and/or second samples exceeds a threshold, and/or if the magnitude of the difference between the approximate particle concentrations in the first and second samples exceeds a threshold.
Also disclosed herein are methods for reducing particle concentration in an electrolyte present in an electroplating apparatus having an electroplating cell and an electrolyte circulation system for circulating electrolyte to and from the electroplating cell. In some embodiments, the methods may include (i) directing a first sample of electrolyte from a first sampling port in the apparatus to one or more liquid particle counter modules, (ii) determining the approximate particle concentration in the first sample using the one or more liquid particle counter modules, (iii) directing a second sample of electrolyte from a second sampling port in the apparatus to the one or more liquid particle counter modules, (iv) determining the approximate particle concentration in the second sample using the one or more liquid particle counter modules, and (v) modifying the operation of the electroplating apparatus to reduce particle concentration in the electrolyte present in the electroplating apparatus. In certain such embodiments, modifying the operation of the electroplating apparatus may include identifying a source of particle contamination based on the approximate particle concentrations in the first and second samples, and replacing the source of particle contamination. Depending on the embodiment, the source of particle contamination may be a chemical or a component within the electroplating apparatus. In other embodiments, modifying the operation of the electroplating apparatus may include diverting electrolyte away from the source of particle contamination, and in certain such embodiments, the source of particle contamination may be an electroplating cell, and diverting electrolyte away from the cell comprises closing one or more valves to isolate the cell from the electrolyte circulation system.
These and other features of the disclosure are presented in further detail below with reference to the associated drawings.
In the following description, numerous specific details are set forth in order to provide a thorough understanding of the presented embodiments. The disclosed embodiments may be practiced without some or all of these specific details. In other instances, well-known process operations have not been described in detail to not unnecessarily obscure the disclosed embodiments. While the disclosed embodiments will be described in conjunction with the specific embodiments, it will be understood that it is not intended to limit the disclosed embodiments.
In this application, the terms “semiconductor wafer,” “wafer,” “substrate,” “wafer substrate,” and “partially fabricated integrated circuit” are used interchangeably. One of ordinary skill in the art will understand that these terms can refer to a silicon wafer during any of many stages of integrated circuit fabrication thereon. The following detailed description assumes the disclosed implementations are implemented on a wafer substrate. However, the disclosed implementations are not so limited. The work piece may be of various shapes, sizes, and materials. In addition to semiconductor wafers, other work pieces that may take advantage of the disclosed implementations include various articles such as printed circuit boards and the like.
Further, in this application, the terms “plating solution,” “plating bath,” “bath,” “electrolyte solution,” and “electrolyte” are used interchangeably. One of ordinary skill in the art will understand that these terms can refer to a solution containing metal ions and possibly other additives for plating or electroplating a metal onto a work piece.
Implementations disclosed herein are related to configurations and methods of using plating tool hardware for reducing defects on a wafer substrate during electroplating. Implementations disclosed herein are applicable to electroplating apparatus and methods designed for, e.g., 300 millimeter or 450 millimeter wafers seeded with a thin conductive seed layer. In some embodiments, the methods and apparatuses described herein may be used as an upgrade for deployed electroplating apparatuses such as the Sabre™ tool available from Lam Research Corporation. In some embodiments, the apparatus may be installed on existing field tools and also on complete and/or newly manufactured electroplating systems. The disclosed liquid particle counter systems permit end users to monitor and maintain their electroplating apparatus's health by, e.g., preventing costly scrapping of electroplated wafers. In some embodiments, the disclosed system may also be used by apparatus designers to identify problematic components which introduce particles at levels that could introduce problematic defects in electroplated wafers.
Embodiments disclosed herein are able to detect various extraneous items in a liquid electrolyte. These items include bubbles as well as solid particles. Collectively, bubbles, solid particles, and other small defect producing items in an electrolyte are referred to herein as “particles.”
Particle detection may be performed in reference to various components or fluidic features fluidically connected via an electrolyte circulation system. The electrolyte circulation systems described herein may include various fluidic features. Such fluidic features may include, but are not limited to, fluid conduits (including lines and weirs), filters, pumps, fluid inlets, fluid outlets, valves, level sensors and flow meters. As can be appreciated, any of the valves may include manual valves, air controlled valves, needle valves, electronically controlled valves, bleed valves and/or any other suitable type of valve. Any one or more of these features can be a source of detrimental particles. To this end, electrolyte may be analyzed for particles before and/or after any one or more of these features.
Among the elements or components of electroplating apparatus 100 which may be monitored are plating cells 14 (individually labeled “Plating Cell” 1, 2, and 3 in the figure), pumps 120 (individually labeled “Pump” 1, 2, and 3 in the figure), and contactors 182 (individually labeled “Contactor” in the figure). Contactors are used to remove dissolved gases and/or bubbles from the electrolyte. Other elements that may be monitored in apparatus 100 include the plating solution bath reservoir 12 (labeled “Bath” in the figure), and filters 186 (individually labeled as “Filter” in the figure). Sampling ports 180 for each of these elements are connected to the LPC module by appropriate fluidic conduits as schematically illustrated in
The information on particle concentration and size distribution from individual sampling locations by itself or in conjunction with information from other sampling locations is used to assess apparatus conditions. The scope of electroplating apparatus condition assessment includes (but is not limited to) (1) on-tool component performance, (2) on-tool chemistry condition, and (3) on-wafer defect performance.
Categories of sampling port locations for LPC analysis include at least the following:
1. Electroplating cells
2. Bath reservoir—e.g., a reservoir for holding the electrolyte for one or more electroplating cells.
3. Pumps
4. Filters
5. Contactors
In certain embodiments, the sampling ports are positioned both upstream and downstream from a fluidic element under consideration. In this manner, the elements can be isolated to determine whether it is acting as a source of particles which are contaminating the electrolyte.
Thus, in some embodiments, an electroplating apparatus may have one or more pumps and may have one or more sampling ports located directly downstream of the pumps. For example, electroplating apparatus 100 shown in
Likewise, in some embodiments, an electroplating apparatus may have one or more particle filters and may have one or more sampling ports located directly downstream of the particle filters. For example, electroplating apparatus 100 shown in
Likewise, in some embodiments, an electroplating apparatus may have one or more contactors and may have one or more sampling ports located directly downstream of the contactors. In some embodiments, a sampling port may be located directly upstream of a contactor, or there may be sampling ports located both directly upstream and directly downstream of a contactor. The latter configuration, for instance, may allow a direct and unambiguous determination of the contactor's contribution to particle concentration in the electrolyte solution. For example, electroplating apparatus 100 shown in
Likewise, in some embodiments, an electroplating apparatus may include sampling ports located directly upstream and/or directly downstream of one or more of the electroplating apparatus's electroplating cells. However, sampling ports may be located at any convenient position within the interior of an electroplating cell as well. In certain such embodiments, a sampling port may be located as close to the wafer as possible. However, there are some specific locations in a SAC cell design that have been found to be particularly useful:
(a) Above the SAC (separated anode chamber) membrane in the wafer catholyte chamber. Such ports are useful for identifying filter-generated particles. They may additionally identify particles generated in situ in the cell by, e.g., precipitation. Thus, an electroplating apparatus configured with a separated anode chamber within an electroplating cell may have a sampling port located proximate to, and downstream from, the membrane which separates the separated anode chamber from the cathode chamber within this electroplating cell.
(b) Near an ionically resistive channeled element (sometimes called a HRVA and described below). In some embodiments, the sampling port is located near an outer perimeter of and slightly above the HRVA. Sampling ports in such locations are useful for detecting bubble-related particles.
Sampling ports may also be located within, and/or upstream, and/or downstream of the bath reservoir of an electroplating apparatus, such as, for instance, bath reservoir 12 schematically illustrated as part of electroplating apparatus 100 in
The individual sampling ports 180 can be configured to capture or exclude bubbles depending upon the location of the port. A pump which operates by cavitation is a potential source of bubble contamination. Therefore a sampling port located next to a pump might be configured to capture bubbles as well as solid particles. See for example, the A, B, and C sampling ports 180 directly downstream from the #1, #2, and #3 pumps 120 in
In certain embodiments, sampling ports designed to capture bubbles are positioned at locations where bubbles are likely to accumulate. For example, a sampling port may face downward and be located near the top of a conduit or other fluidic element where bubbles, through their natural buoyancy, tend to accumulate.
In other embodiments, where bubbles are to be excluded from the sampling port, the port may be located at the bottom of the fluidic element—or other location where bubbles are unlikely to accumulate. Some examples are as shown in
LPC modules for the embodiments described herein may be obtained from various sources. They may be specially constructed for the applications described herein or they may be general purpose tools. LPC modules are commercially available. In various embodiments, suitable LPC modules are those that are marketed to the chemical and medical industries. Particle Measuring Systems, Lighthouse, and RION are some examples of vendors that manufacture LPC modules. Of course, the disclosed embodiments are limited LPC modules provided by these vendors.
In some embodiments, LPC modules use an optical detection technique, which utilizes scattering effects to detect particles. In various embodiments, the LPC module employs a laser beam passing through a flowing or stagnant electrolyte sample. In some embodiments, the wavelength is near-infrared or red (e.g., 633 nm). The chosen wavelength is a function of the particle sizes to be detected. Particles in the nanometer size range are detectable using laser beams having relatively short wavelengths. Photodetectors are located around the volume element near the incident beam. Other particle detection mechanisms (i.e., those not relying on light scatting) may be used as well.
In some embodiments, the LPC module ranges between about 10 to 20 inches on each side. The LPC module can be placed at any convenient location on the electroplating apparatus, configured such that the LPC is attached to a damper or other vibration isolation mechanism.
An LPC module is fluidically connected to one or more sampling ports via appropriate connections. In various embodiments, the LPC module may be configured with a multiplex design where multiple sampling ports are interrogated by a single LPC module. In some implementations, one LPC module can only measure from one sampling port at a time. Therefore, LPC measurements of particle concentration at each of these ports are made serially. In some implementations, certain sampling ports may be fluidically connected to their own dedicated LPC modules which are devoted to measuring particle concentration in the electrolyte sampled from this sampling port.
Oftentimes however, LPC modules are basically shared between sampling ports. One way of accomplishing this is by way of a manifold. Thus, as shown in
If a manifold is used, the manifold may be connected to at least two sampling ports and to at least one LPC module. The manifold 188 shown in
As shown in
In many implementations, the sampling system associated with the LPC module contains different length conduits as necessary to deliver sample from each of multiple sampling ports to the LPC module for analysis. In some embodiments, short length conduits are desirable to monitor a source of time-dependent particle concentrations.
In one embodiment, the LPC module is configured to collect particles at least 0.1 μm in diameter. The LPC module also collects particles in size-based particle bins such that a distribution of the sizes of particles detected can be generated. Examples of particle size ranges collected in such bins include: between about 0.05 and 0.1 μm in diameter, between about 0.1 and about 0.15 μm in diameter, between about 0.15 and about 0.2 μm in diameter, between about 0.2 and about 0.3 μm in diameter, between about 0.3 and about 0.5 μm in diameter, and greater than about 0.5 μm in diameter. In other embodiments, the range of particle sizes detectable by the LPC module depend on the LPC module selected for use in the apparatus.
In one configuration, the electroplating apparatus can contain an LPC module connected to each sampling port. In another configuration, the electroplating apparatus contains two LPC modules, one arranged to continuously monitor the bath reservoir and the other arranged to continuously monitor the electroplating cell. The manifold or other LPC fluidic system is configured to adjust the fluid delivery as needed such that samples from other sampling ports in the electrolyte circulation system can be analyzed to isolate a potential source of particle generation or contamination or other defect cause. In some embodiments, at least one of the LPC modules can be shared by two or more electroplating cells, with the LPC fluidics system configured to deliver samples to the LPC module from each of the electroplating cells.
Depending on the embodiment, there will also typically be a computer program and/or coded logic (hereinafter referred to as just “logic”) associated with the one or more LPC modules which generally works to control particle measurement operations, process, store and analyze the measurements, and to generally operate the LPC module, etc. The logic may be hardcoded into an electronics unit or it may be implemented in software running on a processor. Likewise, the logic may be integrated into the LPC module itself, or it may be executed on a piece of hardware distinct from, but in electronic communication with, the LPC module.
In some embodiments, the logic associated with an LPC module may control various fluid sampling parameters. For instance, the logic may adjust sampling rate—e.g., the frequency at which particle concentrations are measured from electrolyte samples by the LPC module. Thus, in certain such embodiments, an LPC module and its associated logic may generate a process signature of particle concentrations in real time associated with a particular process module/component—albeit represented by data at discretely sampled points acquired at certain time intervals determined by the aforementioned sampling rate. This measured signature—associated with a particular component—may then be compared to one or more predetermined signatures characteristic of that component to determine whether the component is functioning within-spec as expected. A detected and significant deviation from the predetermined signature may then be treated as an alarm which may be used to alert the operator of the apparatus of the anomalous (or potentially anomalous) condition. Examples in the context of identification of defective tools (e.g., a defective pump or filter), detection of out-of-spec chemistries, etc. will be discussed in greater detail below.
It should be noted, however, that although in some embodiments this type of processing and analysis (or a portion thereof) may take place on logic integrated into an LPC module or modules, in other embodiments, some or all of this type of processing and analysis may take place via logic which is implemented on a system controller of the electroplating apparatus, which, more generally, operates to control the overall functioning of the electroplating system. System controllers will now be discussed in greater detail, and in conjunction therewith, various electroplating methods and apparatuses which modify their operation in response to particle concentrations measured by one or more LPC modules.
Nevertheless, it is to be understood that the data processing and analysis logic used to implement these techniques and methodologies may reside on the LPC module itself, or on the system controller, or on some other data processing module within the electroplating apparatus, or on an external data processing apparatus, or on any combination of the foregoing. Thus, for example, in a particular embodiment, various logic modules may be located on the one or more LPC modules themselves as well as on the system controller—which then operate in a cooperative manner to modify the operation of the electroplating apparatus or send an alert in response to out-of-spec particle concentrations measured by the one or more LPC modules.
System Controllers and Logic for Modifying Operations in Response to Particle Concentrations Measured by LPC Module(s)
Thus, various embodiments include a system controller having logic for controlling process operations in accordance with the present invention. For example, a system controller may be coupled to an electroplating apparatus and configured to control some or all aspects of electroplating operations including monitoring and reacting to particle concentration measurements made by one or more LPC modules, feeding anolyte and catholyte, bleeding the catholyte, delivering anolyte to catholyte, etc.
In some embodiments, the system controller is also configured to adjust parameters of the system in response to signals received from the various components of the system and, in particular, the one or more LPC modules. Such parameters may include, for example, flow rates in the electrolyte circulation system, timing of dosing, opening and closing of valves to control electrolyte flow, controlling opening and closing of valves relating to the manifold (see, e.g., manifold 188 in
Typically, a system controller will include one or more memory devices and one or more processors configured to implement and execute logic so that the apparatus may perform a method in accordance with the present disclosure. Machine-readable media containing instructions for controlling process operations in accordance with the present invention may be coupled to the system controller.
Various techniques, algorithms, and/or methodologies for modifying the operation of an electroplating apparatus in response to particle concentration measurements will now be disclosed in the context of a system controller—with the understanding (as discussed above) that the instant disclosure encompasses these concepts wherever the logic embodying and implementing these concepts happens to physically reside.
For example, in some embodiments, the system controller first directs one or more LPC modules to determine whether there are an excessive concentration of particles in the electroplating cell. This information may directly correlate with process performance because, as explained above, high particle concentration in the electroplating cell generally result in wafer defects and poor electroplating performance. The LPC module (or modules) used to determine particle concentration in the electroplating cell may be fluidically connected to a sampling port located in the electrolyte circulation system directly downstream from the electroplating cell, or the sampling port may be located within the interior of the electroplating cell. In some embodiments wherein the electroplating cell has a separated anode chamber (as described elsewhere herein), the sampling port may be located proximate to, and downstream from, a membrane separating the separated anode chamber from the cathode chamber within the electroplating cell. In any event, the system controller may be configured to monitor the particle concentration within the interior of the electroplating cell via one or more LPC modules connected to one or more of the aforementioned sampling ports, and determine when the particle concentration in the electroplating cell is greater than a threshold level. If a predetermined threshold is exceeded, the system controller may be configured to generate an alert and/or modify operation of the apparatus. Furthermore, in some embodiments, due to the importance of particle count in the electroplating cell itself, the one or more LPC modules and system controller may be configured to sample the particle concentration more frequently at the location of the wafer in the electroplating cell. (Sampling rates for particle concentration measurements are discussed above.)
Moreover, in some embodiments, if a high particle concentration is detected in an electroplating cell (as just described), the system controller may additionally be configured to direct the operation of various LPC modules located in the electrolyte circulation system to measure particle concentrations upstream and downstream from various components in an effort to determine which component in the apparatus is potentially most responsible for generating the high particle concentration. In this manner, the logic employed on the system controller may work at attempting to isolate the source of the problem. Certain aspects of this process are explained below in greater detail and in specific contexts.
I. LPC Monitoring of on-Tool Component Performance
Each module/component on an electroplating apparatus may be monitored in terms of particle performance (generation, filtration, accumulation, etc.). If a module/component is known or suspected to be generating an excessive amount of particles, one or more LPC modules may be assigned to monitor the particle concentrations of electrolyte samples from sampling ports located directly upstream and downstream of the suspect component. The particle generation rate can then be calculated based on the difference between the two LPC readings—e.g., if the magnitude of the difference between the approximate particle concentrations in the upstream and downstream samples exceeds a threshold value, an alert can be triggered or the operation of the apparatus modified. Similarly, for a component/module which is designed to (or known to) filter out particles, LPC modules can be assigned to monitor the particle concentrations upstream and downstream from the particular component/module respectively and the particle filtration rate can be calculated based on the difference between the two LPC readings. If a module is known or suspected to accumulate particles, LPC modules can be assigned to monitor the particle concentration before and after the particular module respectively and the particle retention rate can be calculated based on the difference between the two LPC readings. When the LPC monitoring shows a deviance from the acceptable baseline range the module or component needs to be repaired or replaced. This method can also be applied to compare performance of different brands or models of a given component so that a component of superior performance can be selected for use in the electroplating apparatus.
A pump is a useful example for illustrating how an LPC module is used to evaluate and screen pump performance.
A similar approach may be implemented in a system controller and used for monitoring the particle performance of pumps or other on-tool components (e.g., filter, degasser, contactor, etc.) over time. Such real-time component monitoring can identify performance issues before they mature and therefore prevent catastrophic failure events from occurring. For example, in conventional electroplating systems, pump performance is largely not monitored. Conventionally, pumps are replaced when the pumps fails or when it reaches its recommended life-span. For the former case, before a pump fails, it can generate elevated particle concentration for prolonged length of time, which negatively affects defect and yield performance of the electroplating tool. For the latter case, the recommended life-span is suggested for an average pump based on different criteria. For a particular pump, the recommended life-span can be too early or late. As shown in
Accordingly, in order to monitor individual components of an electroplating apparatus and to identify performance issues before they mature into severe failure events, in some embodiments, an electroplating apparatus may employ a sampling port located directly downstream of a component, a sampling port located directly upstream of the component, and a system controller configured to monitor the particle concentrations upstream and downstream from the component. By this monitoring, the system controller may be configured to determine if and when the component is producing more than a threshold amount of particles, and if so, having identified a source of particle contamination, generate an alert and/or modify the operation of the electroplating apparatus in response. Operational modification may be, for example, to execute logic which diverts electrolyte away from the source of particle contamination, logic which removes the offending component from the electrolyte circulation system, logic which sends an alert to the operator of the electroplating apparatus that the component requires replacement, or perhaps logic which shuts down the electroplating apparatus until maintenance can be performed to avoid potential destruction of valuable wafers. In some cases, the source of particle contamination may be another electroplating cell and diverting electrolyte away from this cell may include closing one or more valves to isolate the offending cell from the rest of the electrolyte circulation system.
As indicated above, the component may be a pump, but it may be another type of component as well, as described above. For instance, if the component is a filter, the relevant consideration may be whether or not the filter is sufficiently reducing the number of particles in the electrolyte passing through the filter. In such a case, with respect to monitoring the filter, the controller may be configured to monitor the particle concentrations upstream and downstream from the filter, and be configured to determine when the filter is failing to reduce the amount of particles below a threshold level or to reduce particle number such that the ratio of particles in the downstream electrolyte versus the upstream electrolyte is below a threshold ratio. If so determined, the controller may be configured to generate an alert and/or modify the operation of the electroplating apparatus in response. For example, by sending an alert to the operator of the electroplating apparatus to replace the offending filter.
II. LPC Monitoring of on-Tool Chemistry Condition
Various chemicals are delivered to an electroplating cell to enable the electroplating process. A major concern for electroplating is the presence of both minute particles in the incoming chemicals and particles generated from the interaction between chemicals in various chemical and ambient environments (air, temperature, etc.), and during the electroplating process. Chemistry conditions can be monitored in real-time by employing LPC sampling at proper locations.
III. LPC Monitoring and its Direct Matching to on-Wafer Defect Performance
On-wafer defect performance is a metric for electroplating tools. Minute particles are one of the main causes of on-wafer defects. A conventional method of obtaining on-wafer defect data is to measure processed wafers with various stand-alone metrology tools, typically hours after wafers have been plated in production. As a result, in the event of a defect excursion, the event would not be discovered until hours after a problem arose, during which both numerous wafers and tool time are wasted. However, by implementing LPC sampling at proper locations, particle data which qualitatively and quantitatively correlates to on-wafer defects in real-time as the wafers are plated can be obtained.
Example Electroplating Cells and Apparatuses with Recirculation Systems
Specific examples of electroplating cells and apparatuses with recirculation systems which may incorporate sampling ports and LPC modules as described above will now be presented in detail with reference to
One example of a suitable electroplating apparatus with a recirculation system is described in detail in U.S. application Ser. No. 13/051,822 titled “ELECTROLYTE LOOP FOR PRESSURE REGULATION FOR SEPARATED ANODE CHAMBER OF ELECTROPLATING SYSTEM” filed on Mar. 18, 2011 and naming Rash et al. as inventors, which is incorporated herein by reference in its entirety. Other suitable electroplating apparatus is described in U.S. application Ser. No. 13/305,384 titled “ELECTROPLATING APPARATUS AND PROCESS FOR WAFER LEVEL PACKAGING” filed on Nov. 28, 2011 and naming Mayer et al. as inventors, which is incorporated herein by reference in its entirety.
An example of an electroplating apparatus including an electroplating cell and an electrolyte circulation system will now be described. Referring to
For example only, the anode electrolyte delivery system 13-1 may be a closed loop system that circulates anode electrolyte. Excess anode electrolyte may be returned to the plating bath 12 as needed. The cathode electrolyte delivery system 13-2 may circulate and return plating solution from the plating bath 12 in the solution reservoir. As described further below, the anolyte delivery system may also be an open loop system.
Referring now to
Further, the membrane may be omitted in some implementations. In various embodiments, the electrolyte in the SAC is an aqueous solution of between about 10 and 50 gm/l copper and between 0 and about 200 gm/l H2SO4.
The membrane 24 may be supported by a membrane frame (not shown). For example only, the membrane 24 may be electrically dielectric and may include micro-porous media that is resistant to direct fluid transport. For example only, the membrane 24 may be a cationic membrane. For example only, the cationic membrane may include membranes sold under the trade name Nafion®, which are available from Dupont Corporation of Wilmington Del. Electroplating apparatuses having membranes for forming separated anode chambers are described in U.S. Pat. No. 6,527,920 issued to Mayer et al., and U.S. Pat. Nos. 6,126,798 and 6,569,299 issued to Reid et al., which are all herein incorporated by reference in their entireties.
The cathode and anode chambers 18 and 22 may include cathode electrolyte and anode electrolyte flow loops, respectively. The cathode electrolyte and anode electrolyte may have the same or different chemical compositions and properties. For example only, the anode electrolyte may be substantially free of organic bath additives while the cathode electrolyte may include organic bath additives.
An anode 28 is arranged in the anode chamber 22 and may include a metal or metal alloy. For example only, the metal or metal alloy may include copper, copper/phosphorous, lead, silver/tin or other suitable metals. In certain embodiments, anode 28 is an inert anode (sometimes referred to as a “dimensionally stable” anode). The anode 28 is electrically connected to a positive terminal of a power supply (not shown). A negative terminal of the power supply may be connected to a seed layer on the substrate 70.
Flow of anode electrolyte is fed into the anode chamber 22 as shown by arrow 38 via a central port and passing through anode 28. Optionally, one or more flow distribution tubes (not shown) are used to deliver anolyte. When used, the flow distribution tubes may supply anode electrolyte in a direction towards a surface of the anode 28 to increase convection of dissolved ions from the surface of the anode 28. Optionally, a second sampling port (not shown) may be connected to the central port or flow distribution tube (not shown) directly upstream of the electroplating cell 14 to deliver sample electrolyte to an LPC module (not shown).
The flow of anode electrolyte exits the anode chamber 22 at 30 via manifolds 32 and returns to an anode electrolyte bath (not shown) for recirculation. In some implementations, the membrane 24 may be conically-shaped to reduce collection of air bubbles at a central portion of the membrane 24. In other words, the anode chamber ceiling has a reverse conical shape. A return line for plating solution may be arranged adjacent to radially outer portions of the membrane.
While the anode 28 is shown as a solid, the anode 28 may also include a plurality of metal pieces such as spheres or another shape (not shown) arranged in a pile (not shown). When using this approach, an inlet flow manifold may be arranged at a bottom of the anode chamber 22. Flow of the electrolyte may be directed upward though a porous anode terminal plate.
The anode electrolyte may be optionally directed by one or more of the flow distribution tubes onto a surface of the anode 28 to reduce a voltage increase associated with the build-up or depletion of dissolved active species. This approach also tends to reduce anode passivation.
The anode chamber 22 and the cathode chamber 18 are separated by the membrane 24. Cations travel from the anode chamber 22 through the membrane 24 and the cathode chamber 18 to the substrate 70 under the influence of the applied electric field. The membrane 24 substantially blocks diffusion or convection of non-positively charged electrolyte components from traversing the anode chamber 22. For example, the membrane 24 may block anions and uncharged organic plating additives.
The cathode electrolyte supplied to the cathode chamber 18 may have different chemistry than the anode electrolyte. For example, the cathode electrolyte may include additives such as accelerators, suppressors, levelers, and the like. For example only, the cathode electrolyte may include chloride ions, plating bath organic compounds such as thiourea, benzotrazole, mercaptopropane sulphonic acid (MPS), dimercaptopropane sulphonic acid (SPS), polyethylene oxide, polyproplyene oxide, and/or other suitable additives.
Cathode electrolyte enters the cathode chamber 18 at 50 and travels through a manifold 54 to one or more flow distribution tubes 58. While flow distribution tubes 58 are shown, the flow distribution tubes 58 may be omitted in some implementations. For example only, the flow distribution tubes 58 may include a non-conducting tubular material, such as a polymer or ceramic. For example only, the flow distribution tubes 58 may include hollow tubes with walls composed of small sintered particles. For example only, the flow distribution tubes 58 may include a solid walled tube with holes drilled therein.
One or more of the flow distribution tubes 58 may be oriented with openings arranged to direct fluid flow at the membrane 24. A sampling port (not shown) may be located within chamber 18 and samples of the fluid flow are delivered to an LPC module (not shown) for analysis. The flow distribution tubes 58 may also be oriented to direct fluid flow to regions in the cathode chamber 18 other at the membrane 24. A discussion of plating apparatus having fluted flow distribution tubes is contained in U.S. patent application Ser. No. 12/640,992 filed Dec. 17, 2009 by Mayer et al. and incorporated herein by reference in its entirety.
The electrolyte eventually travels through a flow diffuser 60 and passes near a lower surface of a substrate 70. The electrolyte exits the cathode chamber 18 over a weir wall 74 as shown by arrows 72 and is returned to the plating bath.
For example only, the flow diffuser 60 may include a micro-porous diffuser, which is usually greater than about 20% porous. Alternately, the flow diffuser may include an ionically resistive channeled plate, also sometimes called a high resistance virtual anode (HRVA) plate, such as one shown in U.S. Pat. No. 7,622,024, issued Nov. 24, 2009, which is hereby incorporated by reference in its entirety. A sampling port can be located near the outer perimeter of and slightly above the ionically resistive channeled plate and connected to an LPC module for detecting particles. Placing sampling ports in such locations is useful for detecting bubble-related particles. The channeled plate is typically less than about 5% porous and imparts higher electrical resistance. In other implementations, the flow diffuser 60 may be omitted.
Various patents describe electroplating apparatus containing separated anode chambers (SAC) that may be suitable for practice with the embodiments disclosed herein. These patents include, for example, U.S. Pat. Nos. 6,126,798, 6,527,920, and 6,569,299, each previously incorporated by reference, as well as U.S. Pat. Nos. 6,821,407 issued Nov. 23, 2004, and 6,890,416 issued May 10, 2005, both incorporated herein by reference in their entireties. The disclosed embodiments may also be practiced with apparatus and methods designed for simultaneously depositing two or more elements (e.g., tin and silver) such as those described in U.S. patent application Ser. No. 13/305,384, filed Nov. 28, 2011, and titled “ELECTROPLATING APPARATUS AND PROCESS FOR WAFER LEVEL PACKAGING,” which is hereby incorporated by reference in its entirety for all purposes.
In various embodiments, the electroplating apparatus used with the systems described herein has a “clamshell” design. A general description of a clamshell-type plating apparatus having aspects suitable for use with this invention is described in detail in U.S. Pat. No. 6,156,167 issued on Dec. 5, 2000 to Patton et al., and U.S. Pat. No. 6,800,187 issued on Oct. 5, 2004 to Reid et al., which are incorporated herein by reference for all purposes.
Referring now to
Deionized (DI) water source 100 provides deionized water via a valve 112 to a conduit 114, which may include a sampling port. A plating solution source 104 provides plating solution or electrolyte via a valve 108 to the conduit 114. In some embodiments, the apparatus includes a sampling port immediately downstream from plating solution source. The plating solution may be virgin makeup solution (VMS). For a discussion of one implementation for dosing with VMS and DI water, see, e.g., U.S. patent application Ser. No. 11/590,413, filed Oct. 30, 2006, and naming Buckalew et al. as inventors, which is incorporated herein by reference in its entirety. A pump 120 has an input in fluid communication with the conduit 114. An output of the pump 120 communicates with an input of a filter (not shown) via conduit 121. A sampling port (not shown) may be connected to conduit 121 and delivers samples of fluid via conduit (not shown) to an LPC module (not shown) for particle detection. In many embodiments, this filter may be unnecessary as all the filtering is handled by a filter 164.
A conduit 124 connects to conduits 128 and 130, which are connected to the anode chambers 22-1 and 22-2, respectively. A drain valve 126 may be used to drain fluid from the conduit 124. As can be appreciated, the drain valve 126 may be positioned at other locations in the electroplating circulation system. For example, it may be incorporated into a variant of valve 108, which variant is a three-way valve. Conduits 132 and 134 receive electrolyte from the anode chambers 22-1 and 22-2, respectively. A conduit 136 connects the conduits 132 and 134 to a pressure regulating device 138. A sampling port (not shown) may be located on conduit 136 and connected to the LPC module.
The pressure regulating device 138 includes a housing 140 including an inlet 142 arranged on or near a bottom surface 141 thereof. The inlet 142 communicates with a vertical tubular member 144, which includes an inlet 145 and an outlet 146. The housing 140 further includes a first outlet 147 that is spaced from the inlet 142 on or near the bottom surface 141 of the housing 140. The housing 140 further includes a second outlet 152 near an upper portion 153 of the housing 140.
In various embodiments, the pressure regulating device is exposed to atmospheric pressure. In other words, it is “open” and thereby creates an open loop for anolyte recirculation. Exposure to atmospheric pressure may be accomplished by, for example, providing vent holes or other openings in housing 140. In other cases, an electrolyte outlet pipe (e.g., conduit 154) may have an opening to allow atmospheric contact with the electrolyte. In a specific embodiment, the outlet conduit delivers electrolyte into a trough, which is of course exposed to atmospheric pressure. Additional details of a pressure regulating device suitable for some implementations is described in U.S. patent application Ser. No. 13/051,822, filed on Mar. 18, 2011, which is incorporated herein by reference in its entirety.
In the depicted embodiment, the pressure regulating device 138 further includes filter medium 164. The filter medium 164 may include porous material that filters bubbles from the electrolyte. The filter medium 164 may be positioned in a horizontal position as shown or in any other suitable position to filter bubbles and/or particles from the anode electrolyte before the anode electrolyte returns to the anode chambers 22-1 and 22-2. More general, other forms of bubble separation devices may be employed. These include thin sheets of porous material such as “Porex”™ brand filtration products (Porex Technologies, Fairburn, Ga.), meshes, activated carbon, etc.
In some implementations, the filter medium 164 may be arranged outside of the housing 140 in line with the conduit 121 or another conduit. In other implementations, the filter medium 164 may be arranged at an angle between horizontal and vertical. In still other implementations, the filter medium 164 may be arranged in a vertical position and the outlet may be arranged on a side wall of the housing 140. Still other variations are contemplated.
In a specific embodiment, filter 164 has a sleeve shape and fits over tubular member 144. It may fit from top to bottom over the sleeve or over at least a substantial fraction of the height. In some cases, the filter includes a sealing member such as an o-ring disposed at a location on the inner circumference of the filter and mating with the tubular member 144. The filter is configured to remove particles and/or gas bubbles from the electrolyte before delivering the electrolyte to outlet 147. For bubble management, it may be sufficient that the filter have pores sized at approximately 40 micrometers or smaller, or in some cases sized at approximately 10 micrometers or smaller. In a specific embodiment, the average pore size is between about 5 and 10 micrometers. Such filters have the additional benefit of removing very large particles. As an example, suitable filters may be obtained from Parker Hannifin Corp., filtration division, Haverhill, Mass. (e.g., a 5 micron pore size pleated polypropylene filter part number PMG050-9FV-PR). In some designs, the outer diameter of the filter will be between about 2 and 3 inches. Further, the filter size may be chosen so that some space remains between the filter and the outer housing of the pressure regulator. Such a gap can allow easier and more reliable tuning of level sensors in the pressure regulator. In some embodiments, the regulator housing and the filter are sized so that a gap of about 0.2 to 0.5 inches remains between them.
The first outlet 147 communicates with a conduit 148, which returns anode electrolyte and completes an anode electrolyte flow loop. A sampling port (not shown) may be located on conduit 138 and connected to the LPC module. A conduit 154 connects the second outlet 152 to the plating bath 12 in a solution reservoir to handle overflow of anode electrolyte as needed. In some cases, as indicated above, the conduit 154 empties into a trough (not shown) prior to reaching a solution reservoir for holding plating bath 12.
In some implementations, the inlet 145 of the vertical tubular member 144 is vertically located below at least a portion of the membranes 24-1 and 24-2. The outlet 146 of the vertical tubular member 144 is located above the membranes 24-1 and 24-2.
In certain embodiments, the plating bath 12 in a solution reservoir provides catholyte to the cathode chambers. Because the electrolyte provided to the plating bath from pressure regulator 138 is anolyte, which may be without plating additives, the composition of electrolyte in the plating bath may require adjustment prior to delivering to the cathode chambers. For example, some plating additives may be dosed into the plating bath in while held in a solution reservoir.
In use, the anode chambers 22-1 and 22-2 may be initially filled with plating solution and/or deionized water. The pump 120 may be turned on to provide flow. In some implementations, the pump 120 may provide approximately 2-4 liters per minute. The pump 120 causes variations in the pressure of the electrolyte in the anode chambers 22. Additionally, delivery of fresh plating solution from source 104 may introduce transient increases in the anolyte pressure within chambers 22. As the pressure in the anode chamber 22 increases, electrolyte flows out of the vertical tubular member 144 and down an outer surface of the vertical tubular member 144. The electrolyte flows through the filter medium 164 (if present) and out the outlet 147.
Methods of Reducing Particle Concentration in Electroplating Apparatuses
Several methods will now be described for reducing particle concentration in an electrolyte present in an electroplating apparatus. These methods relate to the various techniques described above for modifying the operation of an electroplating apparatus in response to particle concentration measurements, which were discussed above within the context of logic implemented on an electroplating apparatus's system controller or other hardware. It should be appreciated, however, that in many cases, the methods described here could be implemented via logic (either as software or hard-coded) residing on an electroplating apparatus's system controller or another device in electronic communication with the LPC modules of an electroplating apparatus. Similarly, it should be appreciated that the techniques, methodologies, and/or algorithms described above with reference to a system controller could also be characterized as methods performable independent of the context of a system controller or other specific hardware.
Accordingly, some methods for reducing particle concentration in an electrolyte present in an electroplating apparatus are performed in the context of an apparatus having an electroplating cell and an electrolyte circulation system for circulating electrolyte to and from the cell as these components/modules are described herein.
The operation of the electroplating apparatus may be modified in various ways in order to reduce particle concentration depending on the methodology employed. In some embodiments, modifying the operation of the electroplating apparatus to reduce particle concentration may include identifying a source of particle contamination based on the approximate particle concentration in the first sample and the approximate particle concentration in the second sample, and replacing the source of particle contamination. For instance, a pump may be producing an excessive number of particles, as described above, and modification of the apparatus may include replacing the pump. In other embodiments, modifying the operation of the electroplating apparatus to reduce particle contamination may include identifying the source of the contamination as just described and diverting electrolyte away from the source of particle contamination. For instance, if one of several electroplating cells in an electroplating apparatus is generating excessive particle contamination, electrolyte may be diverted away from it by closing one or more valves to isolate the cell from the electrolyte circulation system (as described above).
Lithographic Patterning Tools and Processes
The apparatus and processes described hereinabove may be used in conjunction with lithographic patterning tools or processes, for example, for the fabrication or manufacture of semiconductor devices. Typically, though not necessarily, such tools/processes will be used or conducted together in a common fabrication facility. Lithographic patterning of a film typically comprises some or all of the following steps, each step enabled with a number of possible tools: (1) application of photoresist on a workpiece, i.e., substrate, using a spin-on or spray-on tool; (2) curing of photoresist using a hot plate or furnace or UV curing tool; (3) exposing the photoresist to visible or UV or x-ray light through a mask using a tool such as a wafer stepper; (4) developing the resist so as to selectively remove resist and thereby pattern it using a tool such as a wet bench; (5) transferring the resist pattern into an underlying film or workpiece by using a dry or plasma-assisted etching tool; and (6) removing the resist using a tool such as an RF or microwave plasma resist stripper. This process may provide a pattern of features such as Damascene, Through Silicon Via, or Wafer Level Packaging features that may be electrofilled with silver tin using the above-described apparatus. In some embodiments, electroplating occurs after the resist has been patterned but before the resist is removed (through resist plating).
Although the foregoing processes, systems, apparatuses, and compositions have been described in some detail for the purpose of promoting clarity of understanding, it will be apparent to one of ordinary skill in the art that certain changes and modifications may be practiced within the scope of the appended claims. It should be noted that there are many alternative ways of implementing the processes, systems, apparatuses, and compositions disclosed herein. Accordingly, the disclosed embodiments are to be considered as illustrative and not restrictive, and the scope of each appended claims is not to be limited to the specific details of the embodiments described herein.
This application claims priority to U.S. Provisional Pat. App. No. 61/662,853, filed Jun. 21, 2012, and titled “LIQUID PARTICLE COUNTER FOR ELECTROPLATING APPARATUS,” which is hereby incorporated by reference in its entirety for all purposes.
| Number | Date | Country | |
|---|---|---|---|
| 61662853 | Jun 2012 | US |
