Method and apparatus for treating an electrostatic chuck

Abstract

As an example, techniques and equipment (apparatus) are described for treating an electrostatic chuck at controlled process conditions, including for treating the electrostatic chuck during a step of curing an adhesive that forms a bond between two layers of the electrostatic chuck.

Description

[Technical Field]

[0001] The following description relates, by way of example, to techniques and apparatus for processing an electrostatic chuck, including for processing an electrostatic chuck during a step of curing an adhesive that forms a bond between two layers of the electrostatic chuck. [Background technology]

[0002] Electrostatic chucks (also simply referred to as "chucks" for short) are used in semiconductor and microelectronic device processing. The chuck functions to hold a workpiece, such as a semiconductor wafer or microelectronic device substrate, in place for performing a process on the surface of the workpiece. The electrostatic chuck is adapted to support and secure the workpiece on its upper surface by creating an electrostatic attraction between the workpiece and the chuck. A voltage is applied to electrodes contained within the chuck to induce charges of opposite polarity in the workpiece and the chuck.

[0003] Chucks include various structures, devices, and designs that enable the chuck to function or improve its performance. A typical electrostatic chuck assembly is a multi-component, multi-layer structure that may include an upper layer having an upper surface for supporting a workpiece, a base layer supporting the upper layer, an adhesive that forms a bond between the upper and base layers, electrical components such as electrodes, conductive coatings, and ground connections for controlling the electrostatic charge on the chuck and the supported workpiece, and one or more cooling systems for controlling the temperature of the chuck and the supported workpiece. Various other components may include measurement probes, movable pins used to support or change the position of the workpiece relative to the chuck, and structures (e.g., "protrusions") on the upper surface for supporting the workpiece at a small height above the flat upper surface.

[0004] A common feature of electrostatic chucks is a base that includes a cooling system, which includes an array of channels or passages formed within the interior of the chuck that allow a cooling fluid (e.g., gas, water, or another liquid) to flow therethrough to remove heat from the chuck and control the temperature of the supported workpiece during processing.

[0005] According to a typical design of an electrostatic chuck, an adhesive layer is included as a layer of the chuck, such as to bond an upper layer to a lower base layer. The adhesive is generally of a chemically curable type. The adhesive is placed between two layers of the chuck in an uncured condition and then allowed or caused to cure for a period of time (the "cure time" or "cure period") to form a secure adhesive bond between the layers. Summary of the Invention

[0006] The following disclosure relates to techniques and apparatus for treating an electrostatic chuck, particularly for treating an electrostatic chuck during a step of curing an adhesive that forms a bond between two layers of the electrostatic chuck.

[0007] Applicant has determined that the conditions for curing the adhesive layer of an electrostatic chuck can affect the quality of the electrostatic chuck. Curing conditions maintained within a desired range can produce chucks of individually improved quality and reduced rejection rates and rework of chucks after the curing step. Curing conditions outside the desired range can produce chucks of individually lower quality, causing increased rejection rates and the need to rework individual chucks. One process condition that can affect chuck quality is the temperature of the adhesive during the step of curing the adhesive. The relative humidity in the curing atmosphere also affects the quality of an electrostatic chuck. Chucks cured in an atmosphere containing too much humidity can cause moisture (liquid water) to condense on the chuck surface during the curing step, especially if the temperature of the chuck is reduced during curing.

[0008] In one aspect, disclosed herein is an apparatus for treating an electrostatic chuck, the apparatus including a chamber containing a chamber atmosphere within the chamber, a source of chamber purge gas adapted to supply a chamber purge gas to the chamber, a source of temperature control fluid adapted to supply a temperature control fluid to the chamber, and a temperature sensor for measuring a temperature within the chamber.

[0009] In another aspect, disclosed herein is a method of treating an electrostatic chuck. The electrostatic chuck comprises a first layer, a second layer, and an adhesive between the first layer and the second layer. The method includes: ,blood In a sealed chamber equipped with a chamber atmosphere and a temperature sensor Chuck Placed In this state , including using an electronic controller to control the temperature of the chuck and to control the humidity in the chamber.

[0010] In yet another aspect, disclosed herein is an apparatus for treating an electrostatic chuck. The electrostatic chuck includes a first layer, a second layer, a fluid flow channel passing through at least one of the two layers, and an adhesive between the first and second layers. The apparatus includes a source of temperature-control fluid connected to the fluid flow channel and a source of purge gas connected to the fluid flow channel. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 shows an example of a chamber of the described apparatus. [Figure 2] FIG. 1 shows an example of the described apparatus including multiple chambers. [Figure 3] FIG. 1 illustrates exemplary components of the described apparatus and the electronic connections between some of the components. DETAILED DESCRIPTION OF THE INVENTION

[0012] The following disclosure relates to techniques and apparatus (devices) for processing electrostatic chucks in a sealed chamber and using controlled process conditions, such as a controlled temperature of the chuck and a controlled level of humidity. The techniques and apparatus enable the use of sensors, flow control, and electronic process control adapted to perform one or more of the following functions: setting or maintaining one or more process conditions, monitoring one or more process conditions, setting a time period for the process, and recording data of process conditions at the beginning and during the process.

[0013] Electrostatic chucks that can be processed using the apparatus can be of any design and construction; a particular example is an electrostatic chuck design that includes two layers bonded together by a chemically curable adhesive that can be effectively cured by maintaining the adhesive at a constant temperature. The adhesive can be a chemically curable adhesive, such as a thermosetting polymer adhesive; one example is an epoxy-based curable adhesive. When used to bond the layers of an electrostatic chuck, the adhesive can desirably be cured at a cure temperature below ambient temperature, and the temperatures of the chuck and adhesive are held at a reduced (below ambient) temperature during the adhesive curing period. Other adhesives can be best cured by maintaining the adhesive temperature at or above ambient temperature. The adhesive can be uncured (including partially cured) before the chuck is processed using the described apparatus and can be processed using the apparatus to allow the adhesive to cure under controlled process (cure) conditions provided by the apparatus, and the apparatus can be capable of setting, controlling, monitoring, or recording the conditions of the apparatus and the electrostatic chuck during the adhesive curing process.

[0014] One layer of the chuck can be the upper layer of the electrostatic chuck, which includes a surface that is positioned adjacent to the lower surface of the supported workpiece during use of the chuck. The second layer can be a lower layer, e.g., a base layer, which supports multiple layers above the base layer, including the upper layer. A curable adhesive is between the upper and lower layers. One or more additional layers or devices (e.g., electrodes) can also be positioned between the upper and base layers.

[0015] Each of these layers can be made from a material that is useful as an upper or lower (base) layer in an electrostatic chuck. Exemplary materials for either layer include metals (including metal alloys) and ceramic materials. Preferably, and as described herein as a prime example of a chuck that can be effectively processed using the described apparatus, the base layer can include cooling channels running through its interior, the base layer can be made from a metal such as aluminum or an aluminum alloy, the upper layer can be made from a ceramic, and an adhesive contacts both the base layer and the upper layer to form an adhesive bond between the two layers.

[0016] According to exemplary methods herein, an electrostatic chuck may be treated at process conditions that are set, controlled, or both, and optionally and preferably monitored and recorded during the treatment of the electrostatic chuck. The process conditions may include any one or more of the temperature of the chuck, the humidity in the chamber, and the amount of time allowed to perform the process or individual distinct portions of the process.

[0017] The process for preparing an electrostatic chuck is carried out in the chamber of the described apparatus for a desired amount of time sufficient to allow the process to be initiated and completed, and at desired process conditions, such as the temperature of the chuck and the humidity of the curing atmosphere. The process conditions may be created at the beginning or early part of the process and then maintained (controlled) during all or part of the process, and optionally and preferably monitored and recorded during the process until the process is completed. The amount of time the process is carried out, i.e., the duration of the process and the amount of time for particular steps of the overall process, may be the desired predetermined time period for the adhesive curing process.

[0018] During processing of the electrostatic chuck, for example, during curing of an adhesive that is part of the chuck, the electrostatic chuck is held at a desired constant processing temperature (the "cure temperature"), and may be held below a maximum temperature or above a minimum temperature, or within a range of temperatures. The processing temperature may be any temperature, which may be ambient, above ambient (elevated), or below ambient (cooled).

[0019] For the specific example of an electrostatic chuck and a process for curing a chuck adhesive, a useful process temperature (cure temperature) may be a temperature that allows for complete and effective curing of the adhesive during the curing period. For adhesives of different chemistries, the cure temperature may vary, with widely useful cure temperatures ranging from minus 25 degrees Celsius (-25°C) to 100°C. For some epoxy adhesives currently useful or preferred for bonding electrostatic chucks, the cure temperature may be below ambient (room) temperature, such as below 25°C or 20°C, for example, in the range of 5°C to 25°C, or 10°C to 20°C.

[0020] In some examples of electrostatic chucks used in operating conditions that include sub-ambient chuck temperatures, the chuck adhesive is designed to be stable at sub-ambient operating conditions. According to the described methods, the chuck adhesive can be cured at a temperature that may be below ambient, the same temperature at which the chuck will be maintained during use. As another advantage, the sub-ambient curing temperature can also create a desired shape of the surface of the electrostatic chuck.

[0021] The particular temperature for the process of curing the adhesive of the electrostatic chuck may be selected based on the type of adhesive being cured, the temperature at which the chuck and adhesive are designed to operate, and other characteristics of the curing step, such as the amount of time the curing temperature is maintained during the curing step.

[0022] To control the temperature of the chuck and maintain the desired temperature of the chuck during processing, a temperature-control fluid is provided inside the chamber and used to maintain the temperature of the chuck, which is also held in the chamber, by bringing the temperature-control fluid into thermal contact with the electrostatic chuck. In a preferred embodiment, the temperature-control fluid may be a liquid, such as water, that is flowed into the chamber by any useful method and brought into direct contact with the chuck. In certain exemplary embodiments, the temperature-control fluid may be used to control the chuck temperature by flowing it through channels through the interior of a layer of the chuck (e.g., through a base layer of the chuck). The temperature-control fluid may be flowed in thermal contact with the chuck at a flow rate and temperature that maintains the chuck at a desired temperature for processing, e.g., for curing an adhesive, where the desired temperature will be approximately the same as the temperature of the cooling fluid.

[0023] A temperature-control fluid (e.g., a cooling fluid) may be provided inside the chamber from a temperature-control fluid source, such as a “chiller” or “heater.” The temperature-control fluid may flow through a conduit leading from the temperature-control fluid source and into the chamber, where the temperature-control fluid may be in thermal contact with the chuck. In an exemplary method, the conduit connects to an opening in the electrostatic chuck (“inlet”), which connects to a channel (sometimes called a “fluid flow channel” or “cooling channel”) through a layer of the electrostatic chuck. The channel includes a second opening (“outlet”). The second conduit has one end that connects to the second opening of the channel (to the channel “outlet”) and a second end disposed outside the chamber. During operation, the temperature-control fluid flows through the first conduit, through the inlet, and through the entire path of the channel within the chuck, exits the channel through the outlet, and is received by the second conduit. A second conduit carries the temperature control fluid from within the chamber, for example, back to a source of the temperature control fluid.

[0024] The apparatus includes one or more temperature sensors (e.g., thermocouples or other temperature-sensing devices) inside the chamber that can be used to measure and optionally monitor the temperature within the chamber during processing. The measured and optionally monitored temperature can be related to the electrostatic chuck and can be measured directly or indirectly during processing of the chuck to determine whether the chuck is at a desired processing temperature, such as within a temperature range above and below a desired curing temperature, which can be equal to or approximately equal to the temperature of a temperature-control fluid (e.g., a cooling fluid).

[0025] The temperature measurement location and manner in which the temperature is measured may be desired and useful for a particular process, electrostatic chuck, apparatus, chamber, etc. A temperature sensor may, for example, measure the surface temperature of the chuck by being placed on the surface of the chuck or by reading the temperature at the surface of the chuck. Alternatively, a temperature sensor may measure the temperature of a temperature-control fluid in thermal contact with the chuck, for example, as the temperature-control fluid passes into, through, or out of the fluid flow channels of the electrostatic chuck. Multiple temperature sensors may be useful.

[0026] According to presently preferred exemplary apparatus and methods, the apparatus may include two temperature sensors disposed within the chamber. One temperature sensor may be positioned and configured to measure the temperature of a temperature-control fluid (e.g., cooling water) as it flows through an inlet (including a nearby conduit) of a cooling channel of the electrostatic chuck. A second temperature sensor may be positioned and configured to measure the temperature of the temperature-control fluid (e.g., cooling water) as it flows from the cooling channel, for example, through an outlet (including a nearby conduit) of the cooling channel of the electrostatic chuck.

[0027] Optionally, the chamber may also include one or more pressure sensors for monitoring the pressure of a temperature-control fluid (e.g., a liquid cooling fluid) flowing within the chamber. According to a presently preferred exemplary apparatus and method, the apparatus may include two pressure sensors disposed within the chamber for monitoring the pressure of the temperature-control fluid at two locations. One pressure sensor may be positioned and configured to measure the pressure of the temperature-control fluid (e.g., cooling water) as it flows through an inlet (including a nearby conduit) of a cooling channel of the electrostatic chuck. A second pressure sensor may be positioned and configured to measure the pressure of the temperature-control fluid (e.g., cooling water) as it flows through an outlet (including a nearby conduit) of a cooling channel of the electrostatic chuck.

[0028] Another process condition that can be controlled, and optionally monitored and recorded, during use of an apparatus to process an electrostatic chuck is the relative humidity of the chamber atmosphere contained within the sealed chamber. The terms "controlling" humidity and humidity "control" broadly refer to any method of maintaining the relative humidity of the chamber atmosphere low enough to prevent moisture contained in the gaseous atmosphere from forming on the surface of a cooled electrostatic chuck within the atmosphere. A method of "controlling" humidity does not require that a specific humidity level (i.e., percent relative humidity at a specific temperature) or maximum humidity level be measured and maintained within the sealed chamber during a process step. "Controlling" humidity does not specifically require (but may optionally include, if desired) a feedback-type control system or step that quantitatively measures and adjusts the amount of gaseous moisture in the chamber atmosphere, such as by measuring and maintaining the humidity of the chamber atmosphere within a specified or predetermined range of relative humidity, or at a desired relative humidity "set point," or below a maximum relative humidity value.

[0029] Controlling humidity to prevent condensation of moisture on the chuck surface can be achieved in a non-feedback manner, e.g., by qualitatively controlling the amount of moisture contained in the chamber atmosphere. In certain exemplary methods, controlling the humidity of the chamber atmosphere can be achieved by adding a dry gas (purge gas) to the chamber during processing. Humidity control can include maintaining a consistent (e.g., continuous or semi-continuous) flow of dry purge gas into the chamber during a process step. The amount (volume, volumetric flow rate) of purge gas delivered to the chamber can be determined empirically (e.g., by trial and error) or based on calculations. The purge gas can be delivered to the chamber, and the amount of purge gas can be controlled and optionally monitored through the use of a flow meter connected to a process controller (described herein).

[0030] In certain exemplary methods, at the start of the process, a sealed chamber initially contains an electrostatic chuck contained (e.g., supported) within a chamber atmosphere consisting entirely of ambient air, e.g., the ambient air contained in the clean room in which the chamber is housed. The air initially contained within the sealed chamber will have a typical clean room relative humidity and temperature, which may be in the range of less than 10 percent to about 50 percent relative humidity, such as 30 percent to 40 percent relative humidity, at ambient temperatures (e.g., 20 to 23 degrees Celsius). With a relative humidity within this range, the ambient air comprising the chamber atmosphere contains a sufficient concentration of moisture (gaseous water) such that when the electrostatic chuck is cooled to a temperature sufficiently reduced below ambient temperature, such as during a process of curing a chuck adhesive at below ambient temperatures, the moisture contained in the air will condense as liquid water on the surface of the chuck.

[0031] To prevent condensation of moisture as liquid water on the surface of the electrostatic chuck when cooling the electrostatic chuck within the chamber, the concentration of moisture in the chamber atmosphere during the processing step can be controlled. At the start of a process step, the chamber atmosphere can be presented to or adjusted within the chamber to exhibit a relative humidity that will not result in condensation of liquid water on the chuck surface during processing, including reducing the temperature of the chuck.

[0032] When the chamber atmosphere in a chamber is made from ambient air, e.g., the air contained in a clean room, the moisture concentration in the ambient air atmosphere can be reduced to prevent condensation on the surface of a chuck cooled below ambient temperature. For example, during electrostatic chuck processing, the relative humidity of the chamber atmosphere contained in a sealed chamber can be reduced and controlled to a level that does not cause condensation on the chuck surface by adding an amount of additional gas to the air to reduce the concentration of water vapor in the air that makes up the chamber atmosphere. The added gas is called a "chamber purge gas" and contains a reduced amount of water relative to ambient air, preferably no water, e.g., less than 5, 2, or 1 volume percent water vapor, and is considered a "dry" gas. The chamber purge gas can be any type of gas that, when added to the chamber atmosphere (e.g., ambient air), will reduce the moisture (water vapor) concentration in the chamber atmosphere. Examples include dry (low moisture) gases such as dry nitrogen and clean dry air (CDA).

[0033] The chamber purge gas may be added to the chamber in a continuous or semi-continuous manner during and throughout the process. The amount of chamber purge gas added to the chamber, e.g., volumetric flow or flow rate, may be an amount that will maintain the relative humidity level of the chamber atmosphere at a level that does not result in condensation of liquid water on the surface of the electrostatic chuck being processed in the chamber at the processing temperature (e.g., curing temperature) of the electrostatic chuck.

[0034] Chamber purge gas can be added to the chamber during chuck processing after the electrostatic chuck is placed in the chamber and the chamber is closed. The amount and type of chamber purge gas added to the chamber atmosphere increases the concentration of chamber purge gas in the chamber and reduces the concentration of water vapor in the chamber atmosphere. With an effective flow of chamber purge gas into the chamber during processing, the electrostatic chuck in the chamber can be processed through steps that reduce the temperature of the chuck without causing moisture (water vapor) contained in the chamber atmosphere to condense as liquid water on the cooled chuck surface. The process does not require that the relative humidity of the chamber atmosphere be measured and used in a feedback control loop during the process, or specifically set or maintained at a specific (quantitative) level or maintained below a set maximum. Humidity control can be achieved by adding an amount of purge gas to the chamber during processing (e.g., as a measured and controlled flow rate) sufficient to create and maintain a chamber atmosphere that does not result in moisture condensation on the cooled chuck surface.

[0035] A useful amount of chamber purge gas can be added to the chamber by controlling or metering the flow of chamber purge gas into the chamber during a process, and the amount of chamber purge gas can be any amount that will prevent condensation on the surface of the chuck during the particular process being performed on the chuck in the chamber.

[0036] By one method of adding chamber purge gas to the chamber, the chamber purge gas can be added to the chamber in a continuous or semi-continuous manner during the process through a flow meter that measures the amount of fluid (by volume, mass, or otherwise) going into the chamber. The amount of gas added inside the chamber is a calculated or empirically determined amount to reduce the relative humidity of the chamber atmosphere to a desired relative humidity level that will not cause condensation during processing.

[0037] Optionally, but not as a requirement of the described method or apparatus, a pressure sensor can be included inside the chamber to measure the pressure of the gaseous chamber atmosphere when purge gas is added to the chamber. The amount of chamber purge gas added to the chamber can be an amount to create a desired positive pressure within the closed chamber, such as a pressure within the range of 1.2 atmospheres (absolute) to 4.0 atmospheres (absolute), for example, 1.5 atmospheres (absolute) to 3.5 atmospheres (absolute).

[0038] Another process condition that can be set and monitored is the amount of time a process or process step is performed. In the case of a process for curing an adhesive, various individual steps are performed for different time periods during the overall process. Exemplary steps include, among others, controlling the temperature of the chuck by contacting the chuck with a temperature-controlling fluid, flowing a purge gas inside the chamber, and passing a channel purge gas through the channels of the chuck. In an exemplary method, the amount of time the chuck is held in the chamber under controlled or monitored process conditions can be measured or controlled using a timer. Processes performed on the electrostatic chuck within the chamber and the controlled chamber environment can be performed with steps that each are in effect for a predetermined period of time.

[0039] During an exemplary process of curing an adhesive on an electrostatic chuck, the electronic controller may control, among other things, one or more of the amount of time the temperature of the chuck is in contact with the temperature control fluid, the flow rate of the temperature control fluid, the temperature of the temperature control fluid, the amount of time to flow a chamber purge gas inside the chamber, the flow rate of the chamber purge gas, the amount of time to pass a channel purge gas through the channels of the chuck, and the flow rate of the channel purge gas.

[0040] For an exemplary process involving curing a chemically curable adhesive in the chamber of the described apparatus under uniform conditions, exemplary curing periods and amounts of time that cooling fluid passes through the chuck's cooling channels can be at least 30, 60, or 90 minutes, at least 3, 5, or 10 hours, or up to or exceeding 12, 16, or 24 hours. During the curing period, the chuck remains in the sealed chamber, the chamber atmosphere is controlled to prevent condensation on the cooled chuck surface (e.g., by flow of chamber purge gas into the chamber), and the chuck temperature is controlled and optionally monitored using a temperature control fluid to ensure that the chuck temperature remains within the desired curing temperature range, e.g., below a maximum temperature.

[0041] After the process has been carried out under controlled conditions for a desired amount of time, the flow of temperature-control fluid through the chamber and through the channels of the chuck can be stopped. With the chuck still held inside the chamber, the temperature-control fluid, which is in liquid form, such as liquid water, can be removed, i.e., "purged," from the channels, and the channels can be dried. Removing the temperature-control fluid from the channels and drying the channels can be carried out in any manner and by one or more steps. By an exemplary method, the temperature-control fluid can be removed from the channels and the channels can be dried by passing a channel purge gas through the channels. The amount of time that the channel purge gas is passed through the channels and the flow rate of the channel purge gas can be controlled by an electronic processor.

[0042] The channel purge gas can be routed through the same flow conduit used to route temperature-control fluid through the channels of the electrostatic chuck. For example, the channel purge gas can flow from a channel purge gas source and through a conduit leading into the chamber, which connects to an opening in the electrostatic chuck (the "inlet") that connects to a channel through the layers of the electrostatic chuck (sometimes called a "fluid flow channel" or "cooling channel"). The channel includes a second opening (the "outlet"). The second conduit connects to the second opening at one end of the conduit and to the exterior of the chamber at the second end of the conduit. The channel purge gas can flow through the first conduit, through the inlet, and throughout the entire path of the channel within the chuck, eventually causing it to exit the channel through the outlet and be received by the second conduit. The second conduit carries the channel purge gas back to the chamber, e.g., to a source of the channel purge gas. The inlet and outlet may be located on either surface of the electrostatic chuck (top or bottom, upper or lower), and the inlet and outlet may both be on the same surface or on different surfaces.

[0043] The channel purge gas can be any gas capable of removing liquid from the channels of the chuck or drying the channels of the chuck, and preferably removing traces of moisture from the surfaces of the channels, leaving dry channels. The channel chamber purge gas preferably contains a low amount of water (moisture), and preferably is water-free, e.g., less than 5, 2, or 1 volume percent moisture vapor, and is considered a "dry" gas. Examples of channel purge gases include dry (low-moisture) gases such as dry nitrogen and clean dry air (CDA). The source of the channel purge gas can be the same as the source of the chamber purge gas for the described chamber or apparatus.

[0044] During a process performed on an electrostatic chuck in a chamber under controlled conditions, the process conditions present during the process can be monitored and recorded. The purpose of monitoring the conditions occurring during the process is to ensure that the process conditions are within a desired range and to allow the process to be adjusted or stopped if the conditions are outside of a set range. For example, if the chuck temperature is monitored during a curing process and the temperature is outside of a desired range (e.g., exceeding a maximum or minimum temperature), the device (e.g., via an electronic controller) can sound a warning or alarm to notify the device operator that the temperature is out of range. An out-of-range temperature can indicate a malfunction of the device, such as a temperature control fluid leak or a malfunctioning source of temperature control fluid (e.g., a "chiller").

[0045] Alternatively or additionally, an optional but not required relative humidity sensor can monitor the relative humidity of the chamber atmosphere while the chamber is in use. If the relative humidity in the chamber is outside of a desired range, the apparatus (e.g., via electronic process control) can sound a warning or alarm to notify an operator of the apparatus that the relative humidity is out of range. A relative humidity that is out of range can indicate an apparatus malfunction, such as a malfunctioning or depleted source of chamber purge gas.

[0046] Similarly, other sensors, such as a pressure sensor in the chamber, may be monitored, and if the pressure is outside a desired (pre-set) range, the device may produce a signal, e.g., a warning or alarm, to notify an operator of the device that the pressure or other condition is out of range.

[0047] The process conditions monitored during a process performed on a particular electronic chuck can preferably be recorded. If the chuck is subsequently tested or used and found to be defective, the conditions established in the chamber when the particular chuck was processed (e.g., chuck temperature, relative humidity) can be examined to determine whether the conditions were proper or out of range during the processing of the particular chuck.

[0048] According to a specific example, a method can be implemented in the described apparatus for curing an adhesive of an electrostatic chuck under controlled and monitored process conditions. The method can include placing an electrostatic chuck in the described chamber. The electrostatic chuck can be designed to include a chemically curable adhesive that bonds two layers of the chuck together. The chuck can include a first layer, a second layer, and an adhesive that bonds the first layer to the second layer. The adhesive can be uncured, meaning completely uncured or partially cured (pre-cured). A partially cured adhesive can be allowed to cure for a short period of time that allows the adhesive to partially solidify. An exemplary time period for pre-curing can range from 30 minutes to 3 hours, depending on the adhesive.

[0049] The process of curing the adhesive is carried out in a chamber of the described apparatus while setting, controlling, or maintaining one or more process conditions in the chamber while the adhesive cures. The process conditions can include maintaining the chuck at a temperature below ambient temperature (e.g., below 20 degrees Celsius). The method can also include providing a chamber atmosphere having a relative humidity low enough to avoid condensation of moisture (water) from the chamber atmosphere onto the reduced temperature surface of the cooled electrostatic chuck.

[0050] Exemplary methods may include placing a chuck in a chamber and closing an access port of the chamber. The chamber will be closed, sealing the chamber interior, but the chamber is not necessarily and is not required to be sealed in an airtight manner for use herein. In some exemplary methods of curing an adhesive for an electrostatic chuck, a flat, weighted surface, such as a ceramic plate, is placed on the top surface of the electrostatic chuck during the adhesive curing step to maintain the position of the upper layer during the curing step.

[0051] In an exemplary method, when the chamber is first closed at the start of the process, it will contain an initial atmosphere of ambient air from the environment of the apparatus, which may be a clean room. After the chamber is closed, an amount of chamber purge gas may be added to the chamber to reduce the humidity of the chamber atmosphere to prevent condensation of water on the chuck surface as it cools. Chamber purge gas may be added to the chamber in a continuous or semi-continuous manner during the process to maintain a relatively dry chamber atmosphere that does not result in condensation of moisture on the surface of the cooled electrostatic chuck at any time during the process.

[0052] The curing process can be carried out by maintaining the temperature of the chuck in the chamber at a suitable curing temperature for a desired amount of time. The temperature can be controlled to be constant, i.e., uniform, throughout the process, or at least controlled so as not to exceed a predetermined maximum chuck temperature. By a preferred method, a cooling fluid (chilled water) is flowed through cooling channels passing through the layers of the chuck to control the temperature of the chuck during the process.

[0053] Using the electronic controller during the curing process, the apparatus can perform one or more of: measuring the temperature of the chuck (e.g., directly at the surface of the chuck, by measuring coolant flowing through channels in the chuck, or otherwise); measuring the humidity in the chamber using a relative humidity sensor; measuring the pressure of the chamber atmosphere within the chamber using a pressure sensor; and using a timer to control the amount of time the curing step is performed. If, during the curing process, a condition, such as the temperature, pressure, or relative humidity of the atmosphere, is outside of a predetermined operating range, the electronic controller can issue a signal, such as a warning, to be detected by an operator of the apparatus.

[0054] After completing the curing process, while the chuck is still in the chamber, a channel purge gas can be flowed through the channels of the chuck to remove liquid from the channels, dry the channels, or both. After the liquid has been removed from the channels and the channels have been dried, the chuck is removed from the chamber.

[0055] To carry out the described processes, a useful apparatus includes one or more chambers, various sensors located in each of the chambers (to measure the relative humidity, temperature, and pressure of the liquid or gas), fluid supplies and flows to the chambers (chamber purge gas, channel purge gas, temperature control fluids), and an electronic controller for receiving electronic signals from the sensors or system components. The chambers, sensors, fluid sources, fluid flow controls such as valves and flow meters, and electronic controller work together to process one or more electrostatic chucks under controlled, and preferably monitored and recorded, process conditions.

[0056] Useful controllers can be any electronic device, e.g., an electronic control or computing device, capable of electronically receiving and transmitting control signals between devices or components of the described apparatus. The controller can be a computerized control system including a central processing unit and programmable control software, such as a programmable or process logic controller ("PLC"), a laptop computer, a desktop computer, a tablet computer, a smartphone, or the like. A controller for an apparatus including multiple chambers, each with a chamber atmosphere, one or more sources of temperature-control fluid, and one or more sources of purge fluid (chamber purge fluid or channel purge fluid), can be programmed to run different processes in each chamber. The temperature-control fluid delivered to one chamber of the apparatus can have a different temperature than the temperature-control fluid delivered to different chambers of the apparatus, and these temperature-control fluids can be received from two different temperature-control fluid sources, each delivering fluids at different temperatures to the two chambers.

[0057] The controller can also control the flow of cooling fluid through a bypass loop in the chamber, which flows the cooling fluid through the chamber but not through the electrostatic chuck. The controller can flow the cooling fluid through the bypass loop, for example, when the chamber does not contain an electrostatic chuck to be processed or when the flow of cooling fluid through the electrostatic chuck in the chamber is stopped, such as during a channel purge using a purge gas. The flow conduit of the bypass loop contains cooling fluid flowing at a rate that can be the same as the rate that flows through the cooling channels of the electrostatic chuck during a process step, such as an adhesive curing step. The cooling fluid can flow through the conduit of the bypass loop and back to the source of the cooling fluid, and can be recirculated through the system. The bypass loop functions to maintain a controlled flow rate of cooling fluid in a chamber that receives cooling fluid all from a single source. The bypass loop also allows the introduction and removal of an electrostatic chuck from the chamber without interrupting the cooling fluid and provides a consistent flow of water through the system when the chiller is on.

[0058] More specifically, a useful or preferred apparatus includes one or more chambers, each of which includes a chamber interior capable of containing an electrostatic chuck during processing. The chamber is defined by optionally insulated sidewalls, at least one of which includes a panel or door that can be opened or closed to allow access to the chamber's interior space (also known as the "chamber interior"), and while open, allows the electrostatic chuck to be advanced into the interior space, held by a support, or removed from the interior space. After placing a substrate in the chamber interior, the panel or door can be closed to seal the chamber interior.

[0059] Useful chamber interiors can be sealed, but need not be "sealed." A "sealed" chamber interior refers to an interior that defines a closed space on all sides. A sealed chamber can be non-sealed, meaning that the chamber is not airtight but allows some movement of air between the chamber interior and the chamber exterior, such as through small openings or minute passages located in the chamber structure. The air pressure within the chamber is approximately equal to the air pressure in the device's surrounding environment, e.g., a clean room, or in some cases greater due to the flow of purge gas into the chamber. The chamber is not required to be sealed in an airtight manner that substantially prevents gas from entering or leaving the interior space during use. A sealed chamber useful according to the present specification can specifically be sealed, but neither airtight nor sealed.

[0060] Each chamber defines an interior space that can be closed to contain a sealed atmosphere ("chamber atmosphere"). Characteristics such as the relative humidity and pressure of each of the one or more chamber atmospheres can be controlled, monitored, or recorded as needed during operation of the apparatus for processing the electrostatic chuck. The temperature of the electrostatic chuck (e.g., as measured by a temperature-control fluid (e.g., cooling water) in thermal contact with the electrostatic chuck) can be controlled, monitored, or recorded during operation of the apparatus for processing the electrostatic chuck. A single chuck can be contained in each of the one or more chambers, and any one or more process conditions within each of the one or more chambers can preferably be controlled separately from the process conditions of different ones of the one or more chambers.

[0061] In an exemplary apparatus and process, an electronic controller receives separate electronic inputs from sensors in each of one or more chambers. The controller can monitor and record each of the separate electronic inputs while the electrostatic chuck is being processed in the chamber. The controller can independently supply each chamber with different fluids from different sources, the different fluids being delivered at different flow rates, in different amounts, at different temperatures, etc.

[0062] The apparatus can include a source of cooling fluid that can be used to contact the electrostatic chuck during processing to maintain a desired temperature of the chuck. Optionally, the apparatus can include two different sources of cooling fluid for delivering different flows of cooling fluid to two different chambers of the apparatus. The different sources of cooling fluid can be maintained at different temperatures.

[0063] The apparatus can include a source of a gas, referred to as a chamber purge gas, that is useful for providing a chamber purge gas inside the chamber.

[0064] The apparatus can include a source of a gas, referred to as a cooling channel purge gas, that is useful for supplying a channel purge gas to the channels of the electrostatic chuck to purge or dry the channels. The source of the channel purge gas can be the same as or different from the source of the chamber purge gas.

[0065] 1, an example of the described apparatus is shown. The apparatus 100 includes a chamber 102 having a chamber interior volume 104. The chamber interior volume 104 is closed ("sealed") during use, but is not sealed in an airtight manner. The interior volume 104 houses an electrostatic chuck 110 within the sealed chamber atmosphere.

[0066] The electrostatic chuck 110 includes an upper layer 112, a base layer 114, and an adhesive layer 116. At least one of the base layer 114 or the upper layer 112 includes fluid flow channels (not specifically shown), e.g., cooling channels, that extend in an array within the layer through which a fluid (e.g., a liquid such as a coolant) can be flowed to control the temperature of the chuck 110. An inlet 120 connects to one end of the channel, and an outlet 122 connects to a second end of the channel.

[0067] A conduit 124 is connected to the inlet 120 and allows a fluid, such as a temperature control fluid or a channel purge gas, to be flowed from an external location to the inlet 120. The external location of the conduit 124 may be connected to a source 140 of the temperature control fluid (e.g., a chiller providing chilled water), to a source 142 of the channel purge gas, or both. A flow meter 144 may be used to control, meter, and measure the amount of purge gas added to the space 104.

[0068] A conduit 126 is connected to the outlet 122 and allows a fluid, such as a temperature control fluid or a channel purge gas, to be flowed from the outlet 122 to an external location. The external location of the conduit 126 can be connected using switches or valves (146, 148) to a source 140 of temperature control fluid (e.g., a chiller providing chilled water), to a source 142 of channel purge gas, or both.

[0069] Sensors that may (but are not required to) be present in chamber 102 may include a temperature sensor, a gas pressure sensor, a relative humidity sensor, a liquid pressure sensor, or combinations thereof. Apparatus 100 also includes an electronic controller 128, which is connected to the sensors, to fluid sources such as 140, 142, to a flow meter 144, and to switches or valves 146 and 148. Electronic connections between controller 128 and devices or components of apparatus 100 are shown by dashed lines. Connections may be direct, wired, wireless (e.g., Bluetooth), through a local area network, a virtual private network (VPN), an Ethernet connection, an internet connection, etc.

[0070] In the exemplary apparatus 100 shown, one or more relative humidity sensors 130 (optional and not required) are present within the chamber interior volume 104, each capable of sending an electronic signal to the controller 128 to indicate the relative humidity of the chamber atmosphere within the volume 104. One or more gas pressure sensors (not shown) may also be present within the volume 104, each capable of sending an electronic signal to the controller 128 to indicate the pressure of the gaseous chamber atmosphere within the volume 104.

[0071] Also in the exemplary apparatus 100, temperature and liquid pressure sensors measure and monitor the temperature and pressure of the temperature-control fluid passing through the conduits 124, 126 and the cooling channels of the chuck 110. Specifically, the temperature sensor 134 measures the temperature of the temperature-control fluid as it travels from the conduit 124 into the cooling channels (not shown) at the input 120. The second temperature sensor 134 measures the temperature of the temperature-control fluid as it travels from the cooling channels through the output 122 to the conduit 126. The temperature measurements are transmitted to the processor 128. The liquid pressure sensor 136 measures the pressure of the temperature-control fluid as it travels from the conduit 124 into the cooling channels (not shown) at the input 120, or alternatively, the liquid pressure sensor can measure the pressure of the temperature-control fluid as it enters the chamber 102. The second liquid pressure sensor 136 measures the pressure of the temperature-control fluid as it travels from the cooling channels through the output 122 to the conduit 126. The liquid pressure measurement is sent to the processor 128 .

[0072] Also shown as part of the apparatus 100 is a purge gas source 142 adapted to cooperate with the controller 128 and a flow meter 144 to supply a chamber purge gas to the space 104 of the chamber 102 in a continuous or discontinuous manner during the process.

[0073] 2, an apparatus 200 is shown that includes three separate chambers 102 in a vertically stacked configuration. The stacked chambers 102 may be supported as part of a single apparatus, for example, connected and supported by a single frame, rack, chassis, or carrier (not shown). In a useful or preferred exemplary apparatus, the chambers may be vertically stacked and supported.

[0074] 2 shows an apparatus 200 including three different chambers 102, each adapted to contain a single electrostatic chuck 100 for processing in a controlled atmosphere within a sealed chamber interior volume 104. The apparatus includes one source 162 of purge gas (more sources can be used if desired) and one or more sources 160 of temperature-controlling fluid. In FIG. 2, each chamber 102 of apparatus 200 and its component components (volume 104, chuck 110, sensors, etc.) have similar structures and numerical designations to those in FIG. 1, except for sources 140 and 142.

[0075] Each of the three illustrated chambers 102 is connected to a source of temperature-controlled fluid. The source 160 for each chamber can be the same or a different source. In an exemplary apparatus and method, the source 160 supplies cooling water at a cooling water temperature to each of the three chambers 102, with the cooling water to all three chambers derived from a single source 160 and delivered at the same cooling water temperature. In an alternative exemplary apparatus and method, one source 160 supplies cooling water at a cooling water temperature to one of the three chambers 102 at a first cooling water temperature, and a second source 160 supplies cooling water to one or two other chambers at a second cooling water temperature. In this manner, one of the three chambers can process chucks at a first cooling water temperature, and a second and optionally a third of the three chambers can process chucks at a second cooling water temperature. Optionally, a third chamber may process the chuck at the first chuck temperature, at a second chuck temperature, or, by using a third cooling water source 160, at a third cooling water temperature different from the first and second cooling water temperatures.

[0076] Each of the three illustrated chambers 102 is connected to a source of chamber purge gas 162. The source 162 for each chamber can be the same source or different sources.

[0077] Each of the three depicted chambers 102 is also connected to a source 162 of cooling channel purge gas. In the exemplary apparatus and method, for any single one of the chambers 102, the source 162 supplying purge gas to the cooling channels of the chuck 110 can be the same as or different from the source 162 supplying chamber purge gas to the space 104. For the three different chambers, some or all of the different chambers can receive chamber purge gas or cooling gas, or both, from a single source 162, or alternatively, from two or more different sources of purge gas; that is, although shown as three separate units, the source 162 can be a single unit that supplies source gas to each of the three different chambers, supplying each chamber both as cooling purge gas and as chamber purge gas.

[0078] Referring to FIG. 3, an example of an arrangement of electronic components that may be included as part of or adapted to work with an apparatus (e.g., 200) herein is shown. In FIG. 3, electronic controller 300 is a PLC in electronic communication with apparatus 200 (represented by a box surrounding controller 300 and switch 320), such as apparatus 200 (e.g., of FIG. 2). Apparatus 200 may include two or more individual chambers, sensors associated with each chamber, flow controls (e.g., flow meters), and fluid sources for apparatus 200, including one or two chillers 304a and 304b (temperature-controlled fluid sources) and purge gas source 306. As shown, controller 300 is in electronic communication with electronic switch 320. While controller 300 is a PLC-type controller, other electronic control devices including a central processing unit (CPU) and programmable control software may also be useful.

[0079] A laptop 300 and connected barcode scanner 302 may be located near the apparatus, in electronic communication with the apparatus and a switch 320, which communicates with the controller 300. When a chuck is to be processed, the scanner 302 can scan the barcode or other identifying feature of the chuck to be processed, and the laptop 300 is used to record the location, placement, and timing of when the chuck is placed in the chamber of the apparatus for processing. Also shown in Figure 3A is network hardware (server) 310 in communication with the controller 300, and one or more remote computers 312 that can access the network hardware 310 through a virtual private network (VPN).

[0080] In a first aspect, an apparatus for processing an electrostatic chuck includes a chamber containing a chamber atmosphere within the chamber, a source of chamber purge gas adapted to supply a chamber purge gas within the chamber, a source of temperature control fluid adapted to supply a temperature control fluid within the chamber, and a temperature sensor for measuring a temperature within the chamber.

[0081] The second aspect according to the first aspect further comprises a humidity sensor for measuring the humidity of the chamber atmosphere.

[0082] A third aspect according to the first or second aspect further comprises a first conduit for providing a temperature control fluid to the chamber, a second conduit for removing the temperature control fluid from the chamber, the second conduit having a temperature sensor adapted to measure a temperature of the temperature control fluid in the first conduit, and a second temperature sensor adapted to measure a temperature of the temperature control fluid in the second conduit.

[0083] A fourth aspect according to any one of the first to third aspects further comprises a flow meter for controlling an amount of chamber purge gas supplied to the chamber from a source of chamber purge gas.

[0084] A fifth aspect according to any one of the first to fourth aspects further comprises a pressure sensor within the chamber adapted to measure a pressure of the temperature control fluid within the chamber.

[0085] A sixth aspect according to any one of the first to fifth aspects further comprises an electronic controller in communication with one or more sensors in the chamber, a source of chamber purge gas, and a source of temperature control fluid.

[0086] A seventh aspect according to the sixth aspect, wherein the electronic controller includes a timer for controlling one or more of a time period during which the temperature control fluid is supplied to the chamber, a time period during which the chamber purge gas is supplied to the chamber, or both.

[0087] An eighth aspect according to the sixth or seventh aspect, wherein the electronic controller is adapted to record data during operation of the apparatus, the data including temperature data from one or more temperature sensors within the chamber interior, humidity data from a humidity sensor within the chamber interior.

[0088] A ninth aspect according to any one of the first to eighth aspects further includes an electrostatic chuck contained within the chamber interior, the electrostatic chuck comprising a first layer, a second layer, a fluid flow channel passing through at least one of the two layers, and an adhesive between the first layer and the second layer, and a source of temperature control fluid connected to the fluid flow channel.

[0089] A tenth aspect according to the ninth aspect further comprises a conduit for providing a temperature control fluid to an inlet of the fluid flow channel and a conduit for receiving a temperature control fluid from an outlet of the fluid flow channel.

[0090] An eleventh aspect according to the ninth or tenth aspect further comprises a pressure sensor for measuring a pressure of the temperature control fluid.

[0091] A twelfth aspect according to any one of the ninth to eleventh aspects further comprises a source of purge gas adapted to supply a channel purge gas to the fluid flow channels.

[0092] A thirteenth aspect according to any one of the first to twelfth aspects further comprises a second chamber containing a second chamber atmosphere within the second chamber, a source of chamber purge gas adapted to supply the chamber purge gas to the second chamber, a source of temperature control fluid adapted to supply the temperature control fluid to the second chamber, and a temperature sensor for measuring a temperature within the second chamber.

[0093] A fourteenth aspect according to the thirteenth aspect further comprises an electronic controller in communication with the one or more sensors of the chamber, the one or more sensors of the second chamber, the source of chamber purge gas, and the source of temperature control fluid.

[0094] A fifteenth aspect according to the thirteenth or fourteenth aspects further comprises a second source of temperature-control fluid, the source of temperature-control fluid adapted to supply temperature-control fluid to the chamber, and the second source of temperature-control fluid adapted to supply temperature-control fluid to the second chamber.

[0095] A sixteenth aspect according to any one of the thirteenth to fifteenth aspects further comprises a chassis supporting the chamber and the second chamber in a vertically stacked orientation, and an electronic controller in communication with one or more sensors in the first chamber, one or more sensors in the second chamber, a source of chamber purge gas, and a source of temperature control fluid.

[0096] In a seventeenth aspect, there is provided a method of treating an electrostatic chuck, the electrostatic chuck comprising a first layer, a second layer, and an adhesive between the first layer and the second layer; Ha, Chi Chamber atmosphere and warm Equipped with a temperature sensor Ruchi In the chamber Chuck Placed In this stateA method is disclosed that includes using an electronic controller to control the temperature of the chuck and to control the humidity in the chamber.

[0097] An eighteenth aspect according to the seventeenth aspect further includes controlling the temperature of the chuck to maintain the temperature below 15 degrees Celsius, and controlling humidity in the chamber by adding a dry gas to the chamber in an amount that prevents condensation from forming on the surface of the chuck.

[0098] A nineteenth aspect according to the seventeenth or eighteenth aspects further includes controlling the temperature of the chuck for a period of time sufficient to allow the adhesive to cure.

[0099] A twentieth aspect according to any one of the seventeenth to nineteenth aspects further includes placing the chuck in a chamber while the adhesive is uncured, and controlling the temperature of the chuck in the chamber to allow the adhesive to cure for a period of at least 40 minutes.

[0100] A 21st aspect according to any one of the 17th to 20th aspects, wherein the chuck includes a cooling channel passing through at least one of the two layers, the chamber includes a source of temperature-control fluid adapted to supply the temperature-control fluid to the cooling channel, and a temperature sensor measures the temperature of the temperature-control fluid.

[0101] A twenty-second aspect according to the twenty-first aspect further includes passing a channel purge gas through the cooling channels to remove liquid from the cooling channels.

[0102] A twenty-third aspect according to any one of the seventeenth to twenty-second aspects further includes recording the temperature of the chuck.

[0103] A twenty-fourth aspect according to any one of the seventeenth to twenty-third aspects further includes delivering a chamber purge gas to the chamber to reduce the relative humidity of the chamber atmosphere.

[0104] A 25th aspect according to any one of the 17th to 24th aspects, wherein the first layer is ceramic, the second layer is aluminum, and the adhesive is an epoxy adhesive.

[0105] A 26th aspect according to any one of the 17th to 25th aspects further includes treating the electrostatic chuck and a second electrostatic chuck disposed in a second chamber, the second electrostatic chuck comprising a first layer, a second layer, a fluid flow channel passing through at least one of the two layers, and an adhesive between the first layer and the second layer, the second chamber comprising a second chamber atmosphere and a temperature sensor for measuring a temperature of the second electrostatic chuck, the method further comprising treating the second chuck disposed in the second chamber. In this state , controlling the temperature of the second chuck and controlling the humidity in the second chamber using an electronic controller.

[0106] In a 27th aspect, an apparatus for processing an electrostatic chuck comprises a chamber containing a chamber atmosphere inside the chamber and an electrostatic chuck, the electrostatic chuck comprising a first layer, a second layer, a fluid flow channel passing through at least one of the two layers, and an adhesive between the first layer and the second layer; a source of temperature control fluid connected to the fluid flow channel; and a source of purge gas connected to the fluid flow channel.

[0107] A twenty-eighth aspect according to the twenty-seventh aspect further comprises a source of chamber purge gas adapted to supply a chamber purge gas to the chamber, and a temperature sensor for measuring a temperature of the electrostatic chuck.

[0108] A twenty-ninth aspect according to the twenty-seventh or twenty-eighth aspect further comprises a humidity sensor for measuring humidity of the chamber atmosphere.

[0109] A thirtieth aspect according to any one of the twenty-seventh to twenty-ninth aspects further comprises an electronic controller in communication with a source of temperature control fluid and a source of chamber purge gas.

Claims

1. 1. An apparatus for processing an electrostatic chuck, said apparatus comprising: a chamber containing a chamber atmosphere within the chamber; a source of chamber purge gas adapted to supply a chamber purge gas inside the chamber; a source of temperature-control fluid adapted to supply a temperature-control fluid inside the chamber; a first conduit for providing the temperature control fluid to the chamber; a second conduit for removing the temperature control fluid from the chamber; a temperature sensor for measuring a temperature inside the chamber, the temperature sensor adapted to measure the temperature of the temperature control fluid in the first conduit; a second temperature sensor adapted to measure the temperature of the temperature control fluid in the second conduit; An apparatus comprising:

2. The apparatus of claim 1 , further comprising a humidity sensor for measuring humidity within the chamber.

3. further comprising an electrostatic chuck contained within the chamber interior, the electrostatic chuck comprising: a first layer; and a second layer; and a fluid flow channel passing through at least one of the two layers; an adhesive between the first layer and the second layer; Equipped with the source of temperature-controlled fluid is connected to the fluid flow channel; 10. The apparatus of claim 1.

4. 1. A method of treating an electrostatic chuck, comprising: a first layer; and a second layer; and an adhesive between the first layer and the second layer; Equipped with The method comprises: With the electrostatic chuck disposed within the chamber, an electronic controller is used to controlling the temperature of the electrostatic chuck; controlling humidity in the chamber; [0033] The chamber a chamber atmosphere; a first conduit for providing a temperature control fluid to the chamber; a second conduit for removing the temperature control fluid from the chamber; a temperature sensor adapted to measure the temperature of the temperature control fluid in the first conduit; a second temperature sensor adapted to measure the temperature of the temperature control fluid in the second conduit; A method comprising:

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