Patent Application
20070144118
The present invention relates to the purging of high purity environments to remove contamination. More specifically, the present invention provides a method for purging a standardized mechanical interface pod to ensure the quality of the environment therein. The invention particularly pertains to the purging of a container for semiconductor devices, wafers, flat panel displays, and other products requiring high purity environments while the container interfaces with a process tool or other sealed chamber.
In the fabrication of semiconductor devices the silicon wafers undergo many process steps to build the layers of material necessary for the device. Each process step requires a separate tool to perform the task and the wafers must be transported between these process tools. The reduction in feature dimensions on the wafers has driven the constantly increasing purity of the gases, chemicals, and environments that contact the wafers during each process step. Since the cleanroom environment is considerably less pure than the surface of the wafer, the exposure of the wafers to cleanroom air during transport is detrimental to the process, resulting in defects and wafer loss. The standardized mechanical interface (SMIF) system has provided a solution to the transport of wafers in the open cleanroom.
While impurity tolerance levels vary from process to process, in most process tools the advantage of point of use purification is clear. Process gases are often transported to the tool over long distances of piping throughout the fabrication facility, the greater the distance traveled the more likely that contaminants will become entrained in the stream. Furthermore, it is often not feasible for suppliers to provide gases of high enough purity to the fabrication facility. Even in cases where the production of gas of sufficient purity is practical, the likelihood of contamination during transport and installation often precludes the direct use of this gas. Therefore, many inventions exist in the prior art for the point of use purification of nearly all of the gases used in the process tools. The incorporation of these methods and devices into process tools has become standard practice in the industry.
To ensure cleanliness and for ease of transport, the wafers are typically contained within a standardized container as they travel to different process tools. The two most common types of these containers are standard mechanical interface (SMIF) pods and front opening unified pods (FOUPs). The SMIF system decreases wafer contamination by protecting the wafers from particulate contamination and providing a standardized and automated interface with the clean environment of the process tool. In the SMIF system the wafers or other sensitive devices, such as flat panel displays, are contained within the pod, which is composed of polycarbonate plastic. A typical FOUP has a capacity of 10-25 wafers, which are secured on individual shelves. The FOUP is connected to the process through an interface device or “port,” such as the Isoport® available from Asyst Technologies. The Isoport provides a kinematic coupling mechanism to align the FOUP with the tool and an automated door to open and close the FOUP for access to the wafers. Once opened, the FOUP environment comes into contact with the tool environment and the interface is generally purged by positive flow from the process tool.
Despite the purging of the interface between the FOUP and the process tool, the FOUP environment is still susceptible to impurities, both particulate and airborne molecular contaminants (AMCs), from a number of sources. The FOUP is made of a polycarbonate plastic body that is sealed to an aluminum base. The seals and resins used in the FOUP may outgas contaminants, especially contaminants absorbed during the wet rinse process in which FOUPs are cleaned. During the process step, the wafers are continuously removed from and returned to the FOUP. Depending upon the process occurring in the tool a variety of contaminants may be retained on the surface of the wafer. As the wafers rest in the FOUP, especially if they are stored for an extended time, these contaminants may be released into the FOUP environment and contaminate additional wafers or portions of the wafer. Also, as the wafers rest in the FOUP, outside air leaks into and contaminant the FOUP environment. For reasons of safety and handling, FOUPs are not constructed to be hermetically sealed.
A separate purge specifically for the FOUP has not been incorporated into the design of Isoport stations, because experimental evidence has supported the idea that purging the FOUP is detrimental to the wafers. Veillerot, et. al. (“Testing the use of purge gas in wafer storage and transport containers,” [online] 1997-2003; on the Internet at http://www.micromagazine.com/archive/03/08/verllerot.html) conducted a study in which they examined the effects of SMIF pod purging with clean dry air containing <2 ppb hydrocarbon contaminants and nitrogen containing 300 ppt hydrocarbon contaminants. Based on electrical measurements on wafers stored with and without purging, they concluded that a static environment is better than a purged container. Thus, purging of FOUPs with gas at this purity level is clearly undesirable.
In patents issued to Asyst Technologies a number of valve arrangements, sensors, and actuators have been disclosed for incorporating purge gas flow to the FOUP when it is present on the stage of the Isoport. The focus of these inventions is the introduction of purging to the Isoport without regard for control of the purge conditions. The conditions for administering purge gas are crucial to the success of the method. In addition to complications arising from gas that is not of a certain purity level, the starting and stopping of purge gas flow introduces new complications arising from the turbulent flow of gas within the FOUP. This turbulent flow, which occurs whenever gas is instantly made to flow across a pressure differential, causes particles that have settled on the bottom of the FOUP to become entrained in the stream and to subsequently settle on the surface of the wafers. As a result of purging the wafers become contaminated, resulting in defects and lost wafers. The Asyst patents clearly are a novel means to interface purge gas flow with the FOUP, but it is not practical without proper control of the purge conditions.
In U.S. Pat. No. 5,346,518 issued to IBM Corp. an elaborate system of adsorbents and filters is disclosed whereby contaminants, specifically hydrocarbons are removed from the environment within a SMIF pod. The invention involves many embodiments with alternative adsorbent arrangements to compensate for variables that might be encountered in different processes and SMIF pods. While the invention provides a novel means of protecting the FOUP environment, some major drawbacks exist when using this method. The vapor removal elements or adsorbents described in this invention rely on the diffusive transport of contaminants to them under static conditions. Therefore, the residence time of the contaminants within the FOUP may be long and certain contaminants that are irreversibly bound to the wafer surfaces will not be efficiently removed. Even if the contaminants are reversibly bound to the wafer surface, the wafer surface may still reach a quasi-steady level of contamination that is difficult to remove using a purely diffusive process. The adsorbents themselves typically rely on reversible equilibrium adsorption conditions to remove contaminants from the FOUP environment. Therefore, as contaminants become concentrated on the adsorbents they may be released into the FOUP environment. This complication is prevented by periodically replacing the adsorbents, thereby creating a new process step. Additionally, since replacement is dependant on time rather than contaminant concentration, the method is susceptible to the effects of process irregularities. For example, a system upset may result in a large amount of impure gas entering the FOUP, such as from process tool purge gas. The impurities in this gas may saturate the absorbents in the FOUP and result in their inoperability before their scheduled replacement. Since FOUPs are normally cleaned in a wet rinse process, the adsorbents must be removed or otherwise protected prior to this process. Thus, this method of contamination control possesses considerable disadvantages when compared to purging of FOUPs under the proper conditions, but the two methods are not mutually exclusive.
In one embodiment of the invention, a method of purifying a transfer container is described. The method comprises purging a non hermetically sealed transfer container with a gas having a contaminant concentration level no greater than about 100 parts per trillion (ppt), 10 ppt, or 1 ppt. The transfer container may include plastic, and may also be a standardized mechanical interface pod or a front opening unified pod. The contaminant in the gas used to purge the transfer container may be an organic contaminant, a hydrocarbon, an amines, an organophosphate, a siloxane, an inorganic acid, ammonia, or a combination of any of the aforementioned components. The gas used to purge the transfer container may include one or more of air, oxygen, nitrogen, water, and a noble gas. The gas may have a flow rate through the transfer container of less than about 300 standard liters per minute (slm), or the flow rate may be between about 5 slm and 200 slm. The gas may be introduced into the transfer container by ramping the flow rate starting at about 0 slm.
In another embodiment of the invention, a method of transferring an object from a non hermetically sealed transfer container to a sealed chamber is described. The method includes the steps of purging the transfer container with a gas, exposing the transfer container to the sealed chamber, and transferring the object between the transfer container and the sealed chamber. The gas used to purge the transfer container has a contaminant concentration no greater than about 100 ppt. The method may further include the step of detecting the contaminant concentration of gas that is purged from the transfer container, the transfer container being exposed to the sealed chamber only when the detected contaminant concentration is no higher than a threshold contaminant concentration. The object to be transferred may be a semiconductor device or a wafer. The transfer container may have at least one non hermetically sealed container within the transfer container that holds the object to be transferred. The gas used to purge the transfer container may have a flow rate between about 100 slm and 10000 slm.
Another embodiment of the invention is directed to another method of transferring an object from a non hermetically sealed transfer container to a sealed chamber. The method includes the steps of purging the transfer container with a gas, exposing the transfer container to the sealed chamber, and transferring the object between the transfer container and the sealed chamber. The gas used to purge the transfer container has a contaminant concentration below 2 parts per billion. The contaminant concentration is also low enough so that the sealed chamber has a lower concentration of contaminants upon being exposed to the transfer container than if the transfer container was not purged with the gas.
Another embodiment of the invention is directed to a system for transferring an object between two environments. The system comprises a non hermetically sealed transfer container and a sealed chamber. The transfer container contains an environment that is purged with a gas having a contaminant concentration no greater than 100 ppt. The sealed chamber is connected to the transfer container. A closeable door separates the environment of the transfer container from the environment of the sealed chamber when the door is shut. A detector is optionally included and configured to identify the contaminant concentration of gas that is purged from the transfer container. The detector is also configured to send a signal to a controller for opening the closeable door when the contaminant concentration of the purged gas is no greater than a threshold concentration.
One embodiment of the invention is directed to a transfer container. The container includes an enclosure, a purifier, and a fan. The purifier is attached to the enclosure and includes a purification material. The purifier is configured to purify fluid flowing into the enclosure. The fan, for propelling fluid through the purifier and into the enclosure, is attached to the enclosure.
In a related embodiment of the invention, the enclosure is non-hermetically sealed. In such an instance, the fan and purifier may be configured to propel a gas having a contaminant concentration no greater than 100 parts per trillion into the enclosure. In other related embodiments, the transfer container includes a front opening unified pod and/or the purification material is enclosed in a replaceable cartridge. In another related embodiment, the transfer container includes a power source, attached to the enclosure, to drive the fan. The power source may be chosen to last at least 24 hours. The power source may be a battery, a compressed gas source, a solar cell, or a fuel cell. A fuel cell may include the use of a replaceable fuel cartridge attached to the enclosure. A battery may include the use of a fan for recharging the battery.
Another embodiment of the invention is directed to a transfer container for transferring an object. The transfer container includes an enclosure and a purifier attached to the enclosure for purifying fluid flowing into the enclosure. The purifier includes a purification material enclosed in a replaceable cartridge. The enclosure may be non-hermetically sealed. The purifier may purify fluid to a contaminant concentration no greater than 100 parts per trillion.
Another embodiment of the invention is directed to a transfer container having an enclosure and a purifier. The purifier is attached to the enclosure and configured as a plurality of beds. The beds are configurable so that only one bed purifies fluid flowing into the enclosure. The beds may also be configured such that only one bed purifies fluid flowing into the enclosure while at least on other bed is being regenerated. Each bed may have purification material enclosed in a removable cartridge. The enclosure may be non-hermetically sealed. At least one bed may be configured to flow fluid into the enclosure having a contaminant concentration no greater than 100 parts per trillion.
The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.
A description of preferred embodiments of the invention follows.
The use of standardized mechanical interface (SMIF) systems to control the microenvironment of sensitive devices during storage and transport within a fabrication facility has greatly improved process control and reduced device contamination. These improvements have produced higher yields of the devices and allowed for technological improvements that could not have been achieved if the devices were left in contact with the cleanroom environment. SMIF systems have played a particularly important role in the contamination control that enabled 130 nm integrated circuits and 300 mm ULSI wafers. As process improvements continue with the further implementation of these technology nodes and the drive toward future sub-micron technology nodes, contamination control becomes more crucial to the processes of semiconductor fabrication. Therefore, enhancements of the SMIF system that enable technological advancements and increase wafer yields are necessary.
While purging of SMIF systems, specifically SMIF pods and front opening unified pods (FOUPs), has been previously disclosed, its application was impractical prior to the present invention. Alternatives to purging have also been disclosed, but lack of control in these passive systems makes them less desirable for contamination control. Additionally, these methods are compatible with and complementary to actively purging the FOUP.
Embodiments of present invention solve the problems associated with purging FOUPs and provide an enhancement to the SMIF system that will enable future technological developments. Embodiments of the present invention utilize extremely pure purge gases, ≦100 ppt total organic contamination, preferably ≦10 ppt. This purity level was not readily attainable in most prior art methods. However, innovations in gas purification technology by the applicant have facilitated the availability of gas of said purity. Other embodiments of the present invention introduce the purge gas flow in a non instantaneous manner into the FOUP. It is relevant to note that teachings of these embodiments are contradictory to the application of purging as described in the prior art.
In one embodiment of the present invention, exemplified in
A preferred embodiment of the present invention involves the following steps as depicted in
In
The present invention is not restricted to a specific purge gas. The nature of the gas used may vary according to the requirements of the manufacturing process and may be proprietary to the process or tool. Since SMIF pod purging has not been feasible prior to the present invention, the optimal purge gas may not be known to those skilled in the art. However, it is expected that the properties known to be optimal for gases used to purge similar environments will be applicable to the purging of FOUPs. Common purge gases used in other ultra high purity environments are nitrogen, argon, oxygen, air, and mixtures thereof. Recently, the applicant of the present invention has disclosed a novel purge gas found to possess considerable advantages over prior art practices for the purging of ultra high purity gas delivery lines and components. Furthermore, the use of said gas in the instant invention has been anticipated, although the methods of said use were unknown. Therefore, the preferred purge gas for use with the invention is extreme clean dry air (XCDA) as defined in U.S. patent application Ser. No. 10/683,903, U.S. patent application Ser. No. 10/683,904, and International Application Number PCT/US2004/017251, all of which are incorporated herein by reference.
According to another embodiment of the present invention, the purge gas is purified such that the wafers, or other contamination susceptible devices, are not contaminated by said purge gas. A broad definition of this is that the purge gas is more pure than the ambient gas of the SMIF pod environment. Embodiments of the present invention are restricted to purge gases that effectively remove contaminants from the environment of the SMIF pod (e.g., purge gases with ≦100 ppt total organic contaminants, more preferably ≦10 ppt).
As previously disclosed by the applicant, the addition of certain oxygen containing species to purge gases, improves the effectiveness of a purge gas. Specifically, the addition of pure oxygen or water to oxygen-free or dry purge gases decreases the time required to reach a desired purity level of the effluent gas from a purged environment. It is speculated that the physical and chemical properties of O2 and/or H2O assist in the desorption of organic and other contaminants from an impure surface. Additionally, it is known to those skilled in the art that these oxygen containing species are necessary compounds in certain processes, such as the proper curing of photoresist polymers. Therefore, in certain embodiments of the present invention, water and/or oxygen may be added to the purge gas post purification. In these embodiments, the addition of these species will not result in diminished purity of the purge gas within the stated limits.
Though previously described embodiments of the invention are directed to purging wafer transfer containers such as FOUPs and other SMIF pods, it should be understood that the present invention can be practiced with more breadth. For example, the methods described by embodiments of the invention are not limited to purifying wafers and the environments of SMIF pods. The methods can be practiced with any transfer chamber that is non hermetically sealed. As well, the objects that are transferred and cleansed in the transfer container may be any semiconductor device, electronics manufacturing component, flat panel display component, or other object needing to be transferred to a purified sealed chamber (e.g., components of a high vacuum system).
One method, in accord with an embodiment of the invention, is directed to purifying a transfer container that is non hermetically sealed. The method comprises the step of purging the transfer container with a gas that has a contaminant concentration no greater than about 100 ppt.
Another embodiment of the invention is directed to a method of transferring an object from a non hermetically sealed transfer container to a sealed chamber. The method includes purging the transfer container with a gas that has a contaminant concentration no greater than about 100 ppt. Next the transfer container is exposed to the sealed chamber (e.g., by interfacing a port with a connector to allow the environments of the transfer container and sealed chamber to be in fluid communication). Finally the object is transferred between the transfer container and the sealed chamber; the object may be transferred in either direction. Optionally, the method includes the step of detecting a contaminant concentration of gas that has been purged from the transfer container. The environment of the transfer container is not exposed to the environment of the sealed chamber until the purged gas contaminant concentration is equal to or lower than a threshold concentration level.
In another embodiment of the invention, similar to the transfer method described above, the transfer container is purged with a gas. The contaminant concentration in the gas is below 2 ppb. The contaminant concentration is also low enough such that the contaminant exposure concentration in the sealed chamber, after the sealed chamber is exposed to the transfer container, is below what would be expected if the transfer container was not purged.
Another embodiment of the invention is directed to a system for transferring a semiconductor device. The system includes a non hermetically sealed transfer container having been purged with a gas having a concentration of contaminants no greater than about 100 parts per trillion. The system also includes a sealed chamber in communication with the transfer container to allow the semiconductor device to be transferred between the sealed chamber and transfer container. Such an embodiment may also be practiced in a broadened context, wherein the object to be transferred between the transfer container and sealed chamber is not necessarily limited to a semiconductor device.
In another embodiment of the invention, a system for transferring an object between two environments comprises a transfer container and a sealed chamber. The transfer container is a non hermetically sealed container that is purged with a gas having a concentration of contaminants no greater than about 100 parts per trillion. The sealed chamber is connected with the transfer container. A closable door separates the environment of the sealed chamber from the environment of the transfer container when the door is closed. A detector is optionally included. The detector is configured to identify the contaminant concentration of the gas that is purged from the transfer container. When the contaminant concentration is equal to or below a threshold level, the detector is configured to send a signal to a controller that opens the closeable door. Subsequently, an object, such as a wafer or other semiconductor device, may be passed between the transfer container and sealed chamber.
Sealed chambers, used with the aforementioned embodiments, include chambers with an inner environment that is hermetically sealed from an exterior environment. Such chambers are constructed with walls that are gas impermeable (e.g., stainless steel). Thus, leakage of contaminants into the chamber is limited to where a port connects to another environment. Sealed chambers include semiconductor process tools (e.g., a photolithography tool) and other containment vessels, which may sustain a vacuum or other condition separate from the open atmosphere.
The transfer container used with embodiments of the invention are not limited to FOUPs or other types of SMIF pods. The transfer container may be constructed with materials such as plastics (e.g., polycarbonate or polypropylene). Since the transfer container is not hermetically sealed, contaminants may leech into the environment enclosed by the transfer container. As well, when plastics are utilized, off-gassing of the plastics may further contaminate the environment in the transfer container. Another source of contamination is the object transferred by the container. For examples, wafers may off-gas and desorb a substantial amount of contaminants to the transfer container environment while the wafer is being transferred. Thus, embodiments of the invention may enable purification of the environment of such transfer chambers as well as their contents.
Contaminants to be removed from a purge gas that is used with embodiments of the invention are not limited to organics, such as hydrocarbons, but include the range of contaminants of concern in high purity processing environments. Other examples include amines, organophosphates, siloxanes, inorganic acids, and ammonia. Any of these contaminants, or mixtures thereof, may need to be removed from a purge gas. As well, such contaminants may be removed during the purge of a transfer chamber.
Gases used to purge the transfer container in the above-described embodiments include any of the gases mentioned earlier in the SMIF pod and FOUP purifying embodiments. Types of purge gases include air (e.g., XCDA), oxygen, nitrogen, water, a noble gas (e.g., argon), and mixtures of such gases.
The concentration level of contaminants in the purge gas affects the ability of embodiments of the invention to purify transfer containers sufficiently to allow exposure to a sealed chamber without detrimentally contaminating the environment of the sealed chamber. Embodiments of the invention utilize purge gases with a contaminant concentration level no greater than about 100 ppt. In some embodiments of the invention, the contaminant concentration is no greater than about 10 ppt; no greater than about 1 ppt in another particular embodiment; and about 500 parts per quadrillion or lower in yet another particular embodiment.
The flow rate of a purge gas flowing into a transfer chamber also affects the purity of environment of the transfer container, and subsequently the purity of the sealed chamber after it is exposed to the contents of the transfer chamber. Embodiments of the invention utilize a purge gas flow rate less than about 300 standard liters per minute (slm), and a gas flow rate between about 3 slm and about 200 slm in a particular embodiment.
In related embodiments of the invention, when a transfer container is purged, the flow of purge gas may be introduced in a particular manner to suppress particulate contamination in the transfer container, and subsequently in the exposed sealed chamber. The flow of purge gas is ramped from a substantially no flow condition to the desired flow rate, as opposed to being introduced in a step-wise, or substantially instantaneous fashion. This flow may be achieved by utilizing a pressure compensating mass flow controller (MFC), or a pressure controller in conjunction with a calibrated orifice for gas introduction, or any other mechanism for controlling gas flow rates in high purity chambers as understood by those of ordinary skill in the art. Such controlled introduction of the purge gas helps suppress the development of turbulent gas flow and eddys that may enhance particulate transport and thus particulate contamination in the transfer chamber.
Embodiments of the invention directed to the transfer containers described herein may or may not utilize a mass flow controller. In some instances, it is preferable to forego the expense of a mass flow controller since acceptable purging performance is still achievable.
Alternate embodiments of the invention may utilize a transfer container that holds one or more non hermetically sealed transfer containers. For example, the transfer container may be a stocker 800 than contains one or more FOUPs or other types of SMIF pods as shown in
Some embodiments of the invention are directed to a transfer container that is configured to promote purging of the container. Because electronic fabrication facilities are heavily constrained by space and cost of equipment considerations, transfer containers that utilize purging as described herein are improved by features which decrease the size and cost of equipment necessary to enable purging. As well, specific features of transfer containers consistent with these embodiments may also allow the accrual of other advantages. Though some of these embodiments are described with specific reference to a FOUP, it should be understood that these features may also be incorporated into and/or onto other transfer containers (e.g., a SMIF pod, stocker, front opening shipping box (FOSB), isolation pods, or other containers for transporting wafers and/or electronic substrates). As well, these embodiments may or may not utilize features regarding purging conditions for transfer containers, as well as other embodiments of the invention, previously discussed herein.
Embodiments of the invention are depicted by features shown in the schematic of
The enclosure may be made of any type of material. In one embodiment, the enclosure is a non-hermetically sealed enclosure, as typically utilized in commercially available FOUPs. More tightly sealed enclosures, however, may also be utilized by some of the embodiments disclosed herein. In a particular embodiment of the invention, the enclosure is constructed with a low off-gassing or non off-gassing plastic such as perfluoroalkoxy fluorocarbon (PFA) or ultra high density polyethylene (UHDPE).
In one mode of operation, the fan unit 930 is configured to recirculate the fluid in the enclosure by drawing fluid out of the enclosure through line 920, pushing the fluid through the purifier 960, and back into the volume of the enclosure 910. Alternatively, the fan unit may draw fluid from another area (e.g., the inside of a clean room) through line 921, and push the fluid through the purifier 960 and into the volume of the enclosure 910. Fluid inside the enclosure 910 is purged out through line 922. The fan location can be altered from what is shown in
In a particular embodiment of the invention, a power source 950 is attached to the enclosure 910 for providing power to the fan unit 930 through an electrical connection 940. By including the power source and the purifier with the transfer container, the ability to purge the transfer container is self-contained. No additional transfer conduits or external equipment, which would hinder the use of the transfer container within the context of an electronics fab, is necessary.
The power source 950 can be any source of power compatible with the running the fan unit 930 at a sufficient rate to purge the enclosure 910 to at a desired rate, while being small enough to be portable with the transfer container (e.g., when the container is a FOUP in an electronics fab). For instance, a fan unit may draw tenths of watts of power to propel gas through the purifier and enclosure to sufficiently purge the enclosure. As well, the fan unit may need to operate for a time of at least about 24 hours, or at least about 48 hours, or at least about 72 hours in typical FOUP operation in a fab. Thus, a power source may be configured to meet one or more of these specifications. Some types of power sources include batteries, a solar cell, or a fuel cell. More than one type of power source may be utilized to create the desired power output.
When one or more batteries are used as a power source, the batteries may be configured to be easily replaced in a compartment or other holding device on the outside of the enclosure. Alternatively, the batteries may be rechargeable, either while installed in the power source or by removal from the power source before being subsequently recharged. In an alternate embodiment, the batteries are recharged using a fan unit to generate power to perform the recharging function. The fan unit can be driven by an external source of compressed gas. The same fan unit may be used to recharge the batteries and drive gas through the purifier and enclosure, using appropriate electrical connections to achieve the dual function. Alternatively, a plurality of separate fan units may be utilized.
When a solar cell is used as a power source, the solar cell may be embodied as a group of photovoltaic cells along one or more exterior walls of the enclosure. The solar cell may require supplementation from other power sources to meet the power requirements of the fan unit.
When a fuel cell is used as a power source, the fuel cell may include fuel cartridges that may be replaced upon consumption of the fuel without disturbing the contents of the enclosure of a transfer container. For example, the fuel cell may utilize a source of molecular hydrogen in a removable cartridge configuration. The hydrogen may be disposed in a pure form or diluted in a carrier to reduce the flammability danger.
In an alternative embodiment of the invention, a compressed gas source is used to purge the enclosure of a transfer container without the use of a fan unit. The source of compressed gas, either located on the transfer container or, more preferably, independent from the transfer container, is connected to a line that feeds the gas through the purifier and into the enclosure of the transfer container. A vent/outlet from the enclosure allows gas to be purged from the enclosure.
A purification material is incorporated into the purifier to remove contaminants from a fluid that subsequently purges the enclosure of a transfer container. One example of such a purification material is activated carbon fibers. In a particular embodiment, the purification material does not interact with water, i.e., the purification material does not substantially adsorb water and is not substantially degraded or deactivated by the presence of water. Thus, purge gases and fluids that contain appreciable amounts of water will not substantially reduce the working lifetime of the purification material.
Furthermore, gases that comprise water, oxygen, or water & oxygen mixtures may be especially preferred to remove contaminants within the enclosure of a transfer container, as discussed in International Application No. PCT/US2004/017251 filed Jun. 1, 2004, having International Publication No. WO2004/112117 published Dec. 23, 2004, and U.S. Pat. No. 6,913,654 issued Jul. 5, 2005; the entire contents of both documents are incorporated herein by reference. Thus various embodiments of the invention described herein may utilize a purge gas that comprises water, oxygen, or a mixture of water & oxygen, wherein the purge gas has a contamination level below about 1 part per billion on a volume basis, or preferably below about 100 parts per trillion (ppt), below about 10 ppt, or below about 1 ppt by volume. Furthermore, the purge gas may comprise between about 1% and about 25% oxygen on a volume basis, or preferably between 17% and 22% oxygen by volume. The purge gas may alternatively, or in addition, comprise more than about 100 parts per million water on a volume basis and/or less than about 2% water by volume. Also, the purge gas may comprise a sufficient amount of water, oxygen, or both components to purge contaminants, such as hydrocarbons, at a rate faster than purging with nitrogen gas.
In another particular embodiment of the invention, a transfer container includes an attached purifier 960 in which the purification material is enclosed in a replaceable cartridge 965, as depicted in
In another embodiment of the invention, a transfer container includes a purifier for purifying fluid that flows into an enclosure of the transfer container. The purifier is configured into two or more separate beds. Each bed contains purification material capable of retaining contaminants from a gas that is passed through the bed. The beds are configured such that each bed is capable of purifying the fluid to be delivered into the enclosure, while the other beds are isolated from the enclosure and/or inlet. This allows purging of an enclosure to continue while maintenance operations are performed on the unused beds.
An example of the flow of purging gas, from an inlet 1030, through a purifier 1000, and out through a line 1040 to the enclosure of the transfer container, is schematically depicted in
The dual bed configuration of a purifier mounted on a transfer container may be utilized with other embodiments of the invention disclosed herein. For example, one or more of the beds may each include a removable cartridge to easily exchange the purification material located within the bed. Such cartridges may be analyzed for historical contamination information, as described earlier.
Alternatively, one or more of the beds may each include a thermal source 1011, 1021 for thermally regenerating the bed when it is isolated and not in use. For example, with reference to
Purifier materials that are thermally regenerable, for use with these embodiments, are preferably exposed to relatively low heating temperatures (e.g., about 200° C.) in order to activate the bed to thermally regenerate.
Other embodiments of the invention utilize a transfer container, as described herein, that further comprises an electrostatic discharger for reducing the build up of static electricity in the transfer container. Particular purging environments utilized with a transfer container (e.g., the use of extra clean dry air) can promote the build up of static charge on substrates such as wafers. Given the sensitivity of some of these substrates, an electrical discharge can result is substantial damage to the substrate. By utilizing an electrostatic discharger with the transfer container, the potential damage to materials within the transfer container is decreased. In particular, it is desirable to keep static charge build up on surfaces of the transfer container below about ±150 volts/inch, consistent with the teachings for minienvironments in the paper Integrated Minienvironment Design Best Practices (International SEMATECH; Technology Transfer # 99033693A-ENG; available on the World Wide Web at ismi. sematech.org/docubase/document/3693aeng.pdf).
Electrostatic dischargers of any suitable type with transfer containers known to those of ordinary skill in the art may be utilized with various embodiments of the invention. In one example, a FOUP, or other transfer container, may be at least partially constructed of static dissipative or conductive materials. In general, it is desirable that portions of the transfer container that contact the carried substrates or wafers be constructed of such materials. Alternatively, other techniques for dissipating or preventing static electrical buildup may be utilized, including grounding and utilizing an ionization device within the transfer container environment.
Other related embodiments may also use the concept of static electrical discharge in other portions of the process beyond the transfer containers to maintain continuity of decreasing the risk of a discharge event.
The following examples are meant to illustrate particular aspects of some embodiments of the invention. The examples are not intended to limit the scope of any particular embodiment of the invention that is utilized.
FOUP Atmosphere Testing
The atmosphere of a FOUP 450 was examined for hydrocarbon contaminants under static conditions and with a XCDA purge. The experimental setup for the FOUP contamination test is shown in
The results from the FOUP experiment are shown in
Load Port and FOUP Test
The experimental system depicted in
A MFC was used to maintain a flow rate of the purge gas at 25 slm for locations 610, 620, 630 in
For measurement (i), the Teflon tubing was connected directly to the GC/FID. A backpressure regulator was used to maintain a pressure of 30 psig during this test and a MFC was used to maintain a sample flow rate of 0.75 slim Since a hard-plumbed connection could not be made to locations 620, 630, 640 of
The results from the load port and FOUP test are summarized in Table 1 in terms of the average concentration of contaminant hydrocarbons (CHCs) measured at the various locations. As shown in the table, location 610 was not a significant source of contamination.
Wafer Storage Experiment
MFCs 710, 711, 712 were used to maintain a flow rate of the air during the experiment. The air was purified with an Aeronex CE500KFO4R purifier 720, 721 to provide a XCDA gas stream having a contaminant concentration below 1 ppt. The gas stream to the instrument and for sample measurement was pressurized to 30 psig with a backpressure regulator 730. Since the FOUP 740 is not hermetically sealed, the gas stream to it was at atmospheric pressure. The wafer chamber 750 was composed of stainless steel, A rotameter 760 was used to determine the flow from the FOUP 740 to the wafer chamber 750. The wafer chamber's operating temperature was maintained with an environmental chamber 770. The GC/FID 780 was used to measure hydrocarbons in the gas samples. A cold trap was used to measure the hydrocarbons at ppt concentration levels. The lower detection limit (LDL) for the cold trap method is 1 ppt. A MFC 712 was used to maintain the sample flow rate through the GC/FID 780 at 0.75 slm. The tubing between the FOUP and the GC/FID and valves V1 through V5 was coated with Sulfinert.
Measurements of wafer contamination were made under three different conditions:
1. The FOUP under static conditions for seven days.
2. The FOUP under purge conditions for seven days using XCDA.
3. The FOUP under purge conditions for seven days using UHP CDA.
During all three measurements, valve V5 was left open to allow XCDA gas to purge the tubing downstream of valve V4. For measurement 1, the inlet to the FOUP was capped. Valve V1 was opened and valves V2, V3, and V4 were closed to expose the wafer chamber to the FOUP environment. For measurements 2 and 3, valves V1 and V3 were opened and valves V2 and V4 were closed to allow the purge gas to flow at 5 slm through the FOUP. The purge gas flow rate through the wafer chamber and out to vent was about 3.0 to about 3.5 slm. The rotameter was used to determine how much gas was actually flowing through the FOUP and to the wafer chamber. After the seven-day test period for each of the three measurements, the wafer chamber was isolated and heated to 150° C. Once this temperature reached, samples were collected by closing valve V5 and opening valves V2 and V4. Between sample collections, the wafer chamber was isolated so that all of the hydrocarbons released could be captured for measurement.
The results from all three measurements are summarized in Table 2 in terms of the total volume of non methane hydrocarbons (NMHCs) collected from the wafer.
The results indicate that XCDA purge gas conditions are more efficient at limiting and removing hydrocarbons from the wafer's surface than static and UHP CDA purge gas conditions. Due to the hydrocarbon's present in the UHP CDA purge gas, more hydrocarbons are loaded onto the wafer under this method than under static conditions. Prior to performing the UHP CDA purge conditions, the hydrocarbon concentration in the UHP CDA was measured at 15 ppt. Therefore, purging with an unpurified gas will add hydrocarbon contamination to the wafer and not prevent it.
While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.
This application is a continuation-in-part of U.S. application Ser. No. 11/196,791, filed Aug. 3, 2005 (converted to Provisional Application No. 60/______), which is a continuation-in-part of International Application No. PCT/US2005/003287 filed Feb. 3, 2005, which claims the benefit of U.S. Provisional Application No. 60/542,032 filed on Feb. 5, 2004. The entire teachings of the above applications are incorporated herein by reference.
