1.  Field of the Invention
The present invention relates to SMIF pods, and more particularly to a system including modular cartridges having breather filters, adsorbent media, and/or check valves, which cartridges may be removably inserted into a well in a bottom surface of a SMIF pod. 
2.  Description of Related Art
A SMIF system proposed by the Hewlett-Packard Company is disclosed in U.S. Pat.  Nos.  4,532,970 and 4,534,389.  The purpose of a SMIF system is to reduce particle fluxes onto semiconductor wafers during storage and transport of the wafers through the semiconductor fabrication process.  This purpose is accomplished, in part, by mechanically ensuring that during storage and transport, the gaseous media (such as air or nitrogen) Surrounding the wafers is essentially stationary relative to the wafers, and by ensuring that particles from the ambient environment do not enter the immediate wafer environment. 
A SMIF system has three main components: (1) minimum volume, sealed pods used for storing and transporting wafers and/or wafer cassettes; (2) an input/output (I/O) minienvironment located on a semiconductor processing tool to provide a miniature clean space (upon being filled with clean air) in which exposed wafers and/or wafer cassettes may be transferred to and from the interior of the processing tool; and (3) an interface for transferring the wafers and/or wafer cassettes between the SMIF pods and the SMIF minienvironment without exposure of the wafers or cassettes to particulates.  Further details of one proposed SMIF system are described in the paper entitled “SMIF: A TECHNOLOGY FOR WAFER CASSETTE TRANSFER IN VLSI MANUFACTURING” by Mihir Parikh and Ulrich Kaempf, Solid State Technology, Jul. 1984, pp.  111-115. 
Systems of the above type are concerned with particle sizes which range from below 0.02 microns (μm) to above 200 μm.  Particles with these sizes can be very damaging in semiconductor processing because of the small geometries employed in fabricating semiconductor devices.  Typical advanced semiconductor processes today employ geometries which are one-half μm and under.  Unwanted contamination particles which have geometries measuring greater than 0.1 μm substantially interfere with 1 μm geometry semiconductor devices.  The trend, of course, is to have smaller and smaller semiconductor processing geometries which today in research and development labs approach 0.1 μm and below.  In the future, geometries will become smaller and smaller and hence smaller and smaller contamination particles become of interest. 
In practice, a SMIF pod is set down on various support surfaces within a wafer fab, such as for example at a load port to a minienvironment, whereupon interface mechanisms in the load port open the pod door to allow access to the wafers within the pod.  Additionally, a pod may be supported at a storage location while awaiting processing at a particular tool.  Such storage locations may comprise a local tool buffer in the case of metrology or high throughput tools, or may alternatively comprise a stocker for storing large numbers of pods within a tool bay. 
Whether a tool load port, local tool buffer, stocker or stand alone purge station, the support surfaces typically include registration or kinematic pins protruding upward from the support surface.  In 200 mm pods, the support surface includes registration pins, and guide rails which guide the pod into the proper rotational and translational position onto the pins.  In 300 mm pods, a bottom surface of the pods includes radially extending grooves for receiving the pins.  Once the pod is positioned so that the grooves are mounted over their respective kinematic pins, the grooves settle over the pins to establish six points of contact between the pod and support platform (at the grooves and pins) to kinematically couple the pod to the support platform with fixed and repeatable accuracy.  Such a kinematic coupling is for example disclosed in U.S. Pat.  No.  5,683,118, entitled “Kinematic Coupling Fluid Couplings and Method”, to Slocum, which patent is hereby incorporated by reference herein in its entirety.  The size and location of the kinematic pins are standardized so that the pods of various suppliers are compatible with each other.  The industry standard for the location and dimensions of the kinematic coupling pins are set by Semiconductor Equipment and Materials International (“SEMI”). 
Occasionally, it is advantageous to purge a pod of contaminants and/or particulates by creating a current flow through a pod to carry away the contaminants and/or particulates.  It may also be beneficial to fill a pod with a non-reactive gas for longer term storage and certain processes.  Additionally it may be advantageous on occasion to provide the pod with a pressure higher or lower than ambient.  In order to accomplish such purging, it is known to provide one or more valves within a pod which allow fluid flow to and/or from the interior of the pod.  Inlet valves to the pod may be connected to a pressurized gas source to fill the pod with a desired gas, and outlet valves may be connected to a vacuum source to remove gas from the pod.  The inlet and outlet valves may be used to purge the pod, including filling the pod with a desired gas, or raising/lowering the pressure within the pod.  Such a system is disclosed in U.S. Pat.  No.  4,724,874, entitled “Sealable Transportable Container Having a Particle Filtering System”, to Parikh et al.,  which patent is assigned to the owner of the present application, and which patent is hereby incorporated by reference in its entirety.  Relative to systems which require opening of the pod for purging valve systems require less components and space, and in general operate more efficiently. 
In conventional purging systems, the gas flow lines terminate at the support surface at hollow pins that protrude above the support surface, which pins are received in the valves when the pod is placed on the support surface.  An interface seal in the form of an elastic member is typically provided between the flow pin and valve to ensure a tight fit of the flow pin with respect to the valve.  It is important that such interface seals provide a tight fit, and be durable to ensure that the tight fit does not deteriorate with use. 
As gas flowing into a pod will be in contact with the exposed wafers, such gas is typically filtered before entry into a pod.  For example, it is known to provide breather filters, such as for example high efficiency submicron particle filtering TEFLON® membranes for filtering gas injected or diffusing into a pod to remove particulates from the gas flow stream.  Moreover, as the components and/or wafers within the SMIF pod may generate contaminants through outgassing, it is further known to provide adsorbent filters, such as for example those containing activated carbon, within the pod to absorb contaminants diffusing around the interior of the pod.  Examples of various filters are disclosed in U.S. Pat.  No.  5,346,518 entitled “Vapor Drain System”, to Baseman et al.,  and U.S. Pat.  No.  4,724,874 entitled “Sealable Transportable Container Having a Particle Filtering System”, to Parikh et al.,  which patents are incorporated by reference herein in their entirety.  It is further known to provide a conditioning agent within a pod, such as for example those which emit vapors that reduce corrosion and/or electrostatic charges within the pod. 
SMIF pods may carry a variety of different substrates at different times, and may transport the substrates to a variety of different process stations.  It may be advantageous to condition the gas within the pod, both with respect to composition and pressure, differently for the various substrates and/or processes.  For example, certain processes may be more sensitive to certain particulates and contaminants.  For such processes, a particular type of breather filter, adsorbent filter and/or a conditioning agent may be preferred.  Additionally, it may be necessary to utilize a particular type of valve for a particular process or for a particular type of gas flow/removal system in the support surface.  For example, some valves must be actuated by a pin in the port before gas is allowed to pass therethrough.  Still others are self-actuating.  Different types of valves are disclosed in U.S. Pat.  No.  4,129,145 to Wynn, entitled “Check Valve Assembly”, which reference is incorporated herein in its entirety.  An additional type of valve is disclosed in U.S. Pat.  No.  5,988,233, previously incorporated by reference.  There may additionally be processes for which it is necessary to completely block off one or more of the inlet or outlet positions in a pod.  Further complicating the problem is that it may be necessary to utilize a particular type of valve with a particular type of filter, and/or with a particular type of conditioning agent. 
Cost and space considerations have to this point prevented wafer fabs from stocking SMIF pods with all combinations of valves, filters and/or conditioning agents.  Aside from the vast expense of providing the necessary number of pods having each such combination, the majority of such pods would sit idle and would take up valuable storage space in a cleanroom environment. 
While it is conceivable that an individual pod may be altered to include the desired valves, filters, and/or conditioning agents, such a process at present would require each of the wafers within a pod to be removed from the pod while the necessary pod configuration is manually assembled.  Moreover, filters used in pods become ineffective when clogged with particulates and/or contaminants.  Again, these filters may be removed and replaced by new ones.  At present, such processes for removing and replacing components are time consuming, labor intensive, and require hardware for transferring and storing the wafers while the components are being changed.