Patent Publication Number: US-2023151490-A1

Title: Gas diffuser housings, devices, and related methods

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit under 35 USC 119 of U.S. Provisional Patent Application No. 63/280,283, filed Nov. 17, 2021, the disclosure of which is hereby incorporated herein by reference in its entirety. 
    
    
     FIELD 
     The description relates to gas diffuser devices, specifically directional gas diffuser devices and a housing component thereof, systems that include the gas diffuser devices, methods of using the gas diffuser devices, and methods of manufacturing gas diffuser devices. 
     BACKGROUND 
     Various industrial processes and manufacturing systems involve process steps and equipment that dispense a gas into an enclosed interior space of a chamber that is used to process, store, transport, or handle one or more semiconductor wafers during manufacturing. Example systems include systems for processing semiconductor and microelectronic devices, that supply a gas that is used in a process of cleaning, etching, or a material deposition step (e.g., chemical vapor deposition, atomic vapor deposition, etc.). Gases supplied to these systems include reactive gases, corrosive gases, e.g., hydrogen bromide (HBr) and other halide-containing gases, and inert gases. 
     Other systems include equipment that is used to contain, handle, transfer, or move multiple semiconductor wafers, examples being devices referred to as wafer transfer chambers, wafer carriers (“FOUPs”), and the like. These pieces of equipment include an enclosed interior space that is adapted to contain multiple semiconductor wafers while the wafers are being processed. The enclosed space of the device contains the wafers and may contain an atmosphere that is evacuated (i.e., that is under reduced pressure) or contains a gas different from air, e.g., an inert gas. 
     As one example, a wafer transfer station is a device that contains a chamber with an enclosed interior that is evacuated during use, while multiple in-process semiconductor wafer are held at the interior. Before opening the evacuated chamber to remove the wafers, gas can be returned to the enclosed interior to equalize the pressure of the interior with an exterior (ambient) pressure. The gas may be an inert gas, and is typically introduced into the enclosed interior through a device referred to as a diffuser. The diffuser introduces the gas into the interior of the transfer station in a steady and diffused manner, to avoid disrupting any contaminant particles that may be present at the interior, which if disrupted may settle at a surface of a wafer. Another device that includes an enclosed space that is adapted to contain multiple semiconductor wafers is a wafer carrier, sometimes referred to as a “FOUP,” which may stand for “Front Opening Unified Pod” or Front Opening Universal Pod.” A FOUP contains multiple semiconductor wafers at an enclosed interior, to transport the wafers. During use, while containing the wafers at the chamber interior, the interior is filled with an inert gas atmosphere, as opposed to an air atmosphere. The inert gas is typically added to the enclosed chamber interior by a diffuser. The diffuser introduces the inert gas into the interior of the wafer carrier as a steady and diffused flow, to avoid disrupting contaminant particles that may be present at the interior, which if disrupted may settle at a surface of a wafer. 
     SUMMARY 
     Described are diffuser housings for a directional gas diffuser, that are useful to dispense a gaseous raw material into an enclosed interior of a chamber of a semiconductor handling or processing device, or other reaction chamber, vacuum chamber, or the like. Also described are diffuser assemblies that include the housing and other components of a diffuser such as a diffuser membrane, methods of making the housing and diffuser assemblies, processing systems that include the diffuser assembly, and methods of using the housing and diffuser assemblies. 
     According to example diffuser housings, the housing comprises an elongate body that includes an inlet at one end, a second end that is closed, and a diffuser outlet (e.g., “opening”) that extends over a face of the body along the length between the inlet end and the closed end. A channel at the interior of the housing extends along the length, between the inlet end and the closed end, and is connected to the inlet and to the diffuser outlet. The channel can have varied dimensions along the length of the diffuser housing to improve uniformity of flow through the diffuser outlet. For example, a channel may have a varied cross-sectional area, depth, or both, when viewed in a direction along the longitudinal axis, at different locations along the length. The cross-sectional area or depth of the channel may be reduced at locations closer to the closed end to improve uniformity of flow of a gas through the diffuser outlet, along the length. 
     A diffuser body as described may be prepared by any useful method, with certain useful or presently preferred methods including additive manufacturing techniques, which include methods that are commonly referred to as “3-D printing” techniques. The method generally involves a series of individual layer-forming steps that sequentially form multiple layers of solidified feedstock composition derived from a layer of feedstock, to form a diffuser housing. Some specific examples of general types of additive manufacturing techniques include those commonly referred to as “powder-bed” additive manufacturing methods, which include various “binder jet printing” techniques. Other examples include stereolithography techniques (SLS) and “feedstock dispensing methods” (FDMs). Still others are referred to as “laser metal deposition,” “direct metal deposition,” and direct energy deposition.” Diffuser bodies as described may be prepared by any of these additive manufacturing methods, as well as others that may be currently known or developed at a future time. 
     In one aspect, the invention relates to a directional gas diffuser that includes an elongate housing. The housing includes: an inlet end, a closed end, a length between the inlet end and the closed end, an opening that extends along the length on a front side of the housing, a channel extending between the inlet end and the closed end. The channel is defined along the length by: the opening extending along the front side, an elongate back surface, and elongate side surfaces. The channel has a length, a width, a depth, and a varied cross-sectional area along the channel length. 
     In another aspect, the invention relates to a directional gas diffuser that includes an elongate housing that includes: an inlet end that comprises an inlet, a closed end, a length between the inlet end and the closed end, an opening that extends along the length on a front side of the housing, an interior channel extending between the inlet and the closed end, the channel defined along the length by: the opening on the front side; an elongate, non-porous back surface; and, elongate non-porous side surfaces. 
     In yet another aspect, the invention relates to a method of making a directional gas diffuser as described, by additive manufacturing. The method includes: forming a first feedstock layer on a surface, the feedstock layer comprising inorganic particles; forming solidified feedstock from the first feedstock layer; forming a second feedstock layer over the first feedstock layer, the second feedstock layer comprising inorganic particles; and forming second solidified feedstock from second feedstock layer; wherein the solidified feedstock layers are part of a directional gas diffuser. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    shows an example of a diffuser housing and diffuser assembly as described. 
         FIGS.  2 A and  2 B  show an example of a chamber and diffuser assembly as described. 
         FIGS.  3 A  (side-perspective view),  3 B (top view), and  3 C (side cut-away view) show an example of a diffuser housing as described. 
         FIG.  4    is a side cut-away view of a diffuser housing as described. 
         FIGS.  5 A and  5 B  show a comparison of flow of a gas through diffuser devices as described. 
         FIG.  6    is a photograph that shows laminar flow of water through a diffuser as described. 
     
    
    
     All figures are schematic and not necessarily to scale. 
     DETAILED DESCRIPTION 
     The disclosure relates to diffuser housings (or, simply “housings”) for a directional gas diffuser, that are useful to dispense a gaseous raw material (e.g., a “reagent gas”) into an enclosed interior of a semiconductor processing chamber, or of other type of vacuum chamber, reaction chamber, etc. The disclosure also relates to: diffuser assemblies that include the housing and other components of a diffuser such as a diffuser membrane, to methods of making the housing and diffuser assemblies, to processing systems that include the diffuser assembly, and to various methods of using the housing and diffuser assemblies. 
     A diffuser assembly as described is of a type sometimes referred to as a “directional diffuser,” which is different from other general types of diffusers, such as “showerhead” diffusers, “tube” diffusers, “disk” diffusers, and “plate” diffusers. A directional diffuser has a form that includes an elongate diffuser body between two ends of an elongate diffuser housing, with one end being a fluid inlet end and the second end being a closed end. The directional diffuser includes a diffuser opening that extends along the length of the elongate diffuser housing between the inlet end and the closed end on only one side of the diffuser body, with a diffuser membrane that covers the opening. The diffuser membrane is porous and semi-resistant to a flow of a gas, allowing gas under moderate pressure to flow through the membrane as a dispersed or “diffused” stream directed from only one side of the housing. The gas flows into the diffuser housing at the inlet end, flows along the length of the housing, and then exits the housing through the membrane in a lateral direction relative to the flow through the housing, and from only a portion (e.g., from one side) of the housing laterally, e.g., perpendicular to the direction of flow of the gas into and within the housing. On the remaining portions of the housing (the sides that don&#39;t include the opening and the diffuser membrane), the housing includes non-porous surfaces that enclose an interior channel that extends from the inlet, along the length of the housing, to the closed end, and that contacts the diffuser membrane. 
     A gaseous fluid can flow into the inlet and into the inlet end of the interior channel. The fluid then flows along the length of the interior channel, which is also along the length of diffuser membrane held in the length-wise opening on one side of the housing. As the fluid flows along the length of the housing within the interior channel a portion of the fluid also passes laterally (relative to the direction of flow along the channel) through the diffuser membrane over the entire length of the membrane. The diffuser membrane functions as a diffuser outlet that extends along the length of the diffuser and allows gas that flows along the length of the diffuser body, within the interior channel, to flow laterally (perpendicular to the length-wise direction of the interior channel) and exit the housing on one (and only one) side of the diffuser housing, with the flow of the gaseous fluid from the housing being predominantly in a direction that is perpendicular to the flow of fluid through the interior channel of the housing, with the fluid entering the channel at the inlet. 
     The diffuser is described as “directional” because the lateral flow occurs directionally relative to a circumference of the diffuser. The diffuser has a circumference when viewed in a direction of the length. The lateral flow does not occur in all directions of the circumference (i.e., at all 360 degrees of the circumference). Instead, the opening in the housing through which the gas flows is over a portion of the circumference, sometimes referred to as a “side” of the housing. The portion of the housing through which the lateral flow occurs may be less than half of the entire circumference, e.g., flow may occur over less than 180 degrees of the circumference, e.g., over a range from 10 to 170 degrees, or from 20 to 150 degrees, or from 40 to 120 degrees. 
     A benefit of directional flow from the diffuser over less than the entire circumference is an ability to control direction and placement of direct gas flow into a chamber. The flow may be directed for a purpose of avoiding a direct flow of gas into an area of a chamber at which particle contamination may exist. Direct flow of gas toward particles that have become settled at areas of a chamber can disrupt and disperse the particles within the chamber, which is preferably avoided. More generally, flow may be directed to provide uniform or thorough contact of the gas with a wafer or workpiece within a chamber. 
     The directional diffuser has a length dimension between the inlet end and the closed end, a width that is transverse to the length, and a depth that is transverse to the length and width. The directional diffuser is elongate, having a length that is greater than the width and that is greater than the depth. Example directional diffusers may have a length that is at least 2, 4, 5, 10, 12, 15, 20, or 30 time the magnitude of the depth, or the width, or both, measured at exterior surfaces of the housing. 
     Referring to  FIG.  1   , example directional diffuser  100  is illustrated. Directional diffuser  100  includes housing  112 , which has a length (L), a width (w), and a depth (d). Housing  112  includes inlet  102  at inlet end  106 , a second end (“closed end”)  104 , with the length L extending between inlet end  106  and closed end  104 . On front side  108  (the top side, as illustrated) of housing  112 , openings  118  extend along length L and width w, between inlet end  106  and closed end  104 . As illustrated, two separate lengthwise openings  118  are illustrated, but the two openings  118  could alternately be formed as a single opening that is not interrupted along length L. A porous diffuser membrane  120  is held within each of the two openings  118 . 
     In further detail, inlet  102  leads to an interior channel (not shown) that is defined by porous diffuser membrane  120  on one side, and by three elongate non-porous sidewalls on three other sides, including left and right sidewalls  114  (not visible) and  116 , and bottom or back sidewall  122  (not visible). Each sidewall  114 ,  116 , and  122 , is non-porous, i.e., not permeable to a flow of gas; each sidewall  114 ,  116 , and  122  includes a non-porous inner surface that defines the interior channel that extends along length L of housing  100 . 
     Generally, when positioned for use inside of an enclosed chamber of a semiconductor handling or processing device (“chamber” or “enclosed chamber”), a directional diffuser extends from a sidewall, top, or bottom of the chamber with the length of the diffuser extending from the sidewall, top, or bottom into the interior space of the chamber. Optionally, the directional diffuser can be mounted within the chamber on a rotating mount that allows the diffuser to be rotated about an axis that extends along the length of the diffuser. 
     Referring to  FIG.  2 A , illustrated is a side view of a chamber  220  that includes directional diffuser  200  as described herein. Directional diffuser  200  is mounted within an enclosed interior space  220  of chamber  202 , and is used to dispense a uniform flow of gas from a gas source (not shown) into interior  220  of chamber  202 , which contains wafers  218 . 
     Chamber  202  includes bottom  206 , top  204 , and (left and right) sidewalls  208  and  210 , which define enclosed chamber interior  220 . Directional diffuser  200  includes housing  230 , inlet end  222 , closed end  224 , and a length between the two ends. On front side  226  (facing to the left, as illustrated) of housing  230 , opening  232  extends along length L and width w between inlet end  222  and closed end  224  and directionally from a portion of a circumference of housing  230  (see  FIG.  2 B ). A porous diffuser membrane (not shown) is held within the opening. 
     A gaseous fluid enters diffuser  200  at inlet end  222  and flows in a direction of the arrows of  FIG.  2 A  along the length of diffuser  200 . As the fluid passes along the length, a portion of the fluid passes laterally (see arrows at  FIG.  2 A ) through the porous diffuser membrane that extends along front face  226 . The fluid passes through the porous diffuser membrane and enters interior  220  of enclosed chamber  202 . 
       FIG.  2 B  shows a top, cut-away view of diffuser  200  and chamber  202 . Details shown at  FIG.  2 B  include: front and back sidewalls  212  and  214  of chamber  202 ; sidewalls  242  and  244 , and back wall  246 , of diffuser housing  230 ; and interior channel  240  at the interior of diffuser housing  230 . Interior channel  240  is defined by a porous diffuser membrane (not shown) that is located at front face  226 , and by three elongate non-porous sidewalls on three other sides, including left and right sidewalls  242  and  244 , and back sidewall  246 . Each sidewall  242 ,  244 , and  246  is non-porous, i.e., not permeable to a flow of gas; each sidewall  242 ,  244 , and  246  includes a non-porous inner surface that defines interior channel  240  that extends along length L of housing  230 . 
     Chamber  202  may be a component of a device or apparatus used in manufacturing, storing, transporting, or handling multiple semiconductor wafers. Example types of devices that contain a chamber  202 , e.g., as illustrated at  FIGS.  2 A and  2 B , include devices and apparatuses commonly known as wafer carriers (“FOUPs”) and wafer transfer stations. Other examples include deposition chambers (e.g., chemical vapor deposition chambers, atomic layer deposition chambers, etc.), as well as etching chambers, among others. Example gases that may be dispensed for any of these processes include inert gases, reactive or corrosive gases (e.g., halogen or halogen-containing gases such as hydrogen bromide), as well as others. 
     Referring to  FIG.  2 A , diffuser  200  may be used to deliver a gas, such as an inert gas, from an external source to interior  220  of chamber  202 . According to example diffuser housings and diffuser assemblies, the diffuser housing includes a channel as described, defined within an interior of a housing by non-porous sidewalls (the term “sidewall” referring to sidewalls and backwalls), that is designed with size and shape features that will control a flow of a gaseous fluid through the diffuser membrane to produce useful, desired, or improved flow properties, including with desired uniformity of flow (based on flow pressure, flow rate, or both) through the diffuser membrane, along the diffuser length. 
     A purpose of a directional diffuser is to dispense a gaseous fluid into a chamber as a uniform flow of the gas. Toward that end, a diffuser assembly as described can be designed to include an interior channel that includes a shape or dimensions that vary along the length of the channel in a manner that provides for added control of the flow of the gas through the diffuser, for example by improving uniformity of flow through the diffuser membrane, at different locations along the length of the diffuser membrane. See e.g.,  FIG.  5 A . 
     As one mode of providing desired control of flow through a diffuser to achieve improved uniformity of flow along a length of the diffuser, an interior channel may exhibit a varied cross-sectional size (area, having a width component and a depth component, both transverse to a length of a diffuser housing, as shown at  FIG.  1   ) or dimension (e.g., depth or width) along the length. During use, as a gaseous fluid is caused under pressure to enter the interior channel and flow from the inlet end to the closed end of the diffuser assembly, the pressure of the fluid will vary along the length of the diffuser. The pressure of the gas within the channel will normally decrease at locations of the channel that are farther from the source of pressurization of the gas, i.e., farther from the inlet end and closer to the closed end. 
     To adjust for (e.g., reduce or prevent) a reduction in gas pressure along the length of the interior channel, as gas flows from the inlet end to the closed end of the channel, the channel can be adjusted in size, i.e., in cross-sectional area, in depth, in width, or a combination of these, along the length. To improve uniformity of a flow of gas through the diffuser membrane, meaning to provide more uniform flow of gas (based on flow rate or gas pressure) through the diffuser membrane measured at different locations along the length of the diffuser membrane, the interior channel can have a cross-sectional area, a depth, or both, that decrease along the length of the channel, with the channel having greater cross-sectional area, depth, or both, at locations nearer to the inlet end and reduced cross-sectional area, depth, or both, at locations nearer to the closed end. 
     An example of a diffuser ( 300 ) that includes an interior channel that has a depth and cross-sectional area that vary along the length of the interior channel is shown at  FIGS.  3 A,  3 B , and  3 C.  FIG.  3 A  shows a side-perspective view,  FIG.  3 B  is a top view, and  FIG.  3 C  is a side cut-away view of directional diffuser  300 . Referring to  FIG.  3 A , example directional diffuser  300  is illustrated. Directional diffuser  300  includes housing  312 , which has a length (L), a width (w), and a depth (d). Housing  312  includes inlet  302  at inlet end  306 , a second end (“closed end”)  304 , with the length L extending between inlet end  306  and closed end  304 . On front side  308  of housing  312 , opening  318  extends along length L and width w, between inlet end  306  and closed end  304 . A porous diffuser membrane (not shown) may be held within opening  318  as part of a diffuser assembly. 
     Inlet  302  leads to interior channel  310 , defined by opening  318  on one side, and by three elongate (in the length direction) non-porous sidewalls on three other sides, including left and right sidewalls  314  and  316 , and bottom or back sidewall  322 . The sidewalls are not discrete, but blend together as a single curved surface. Each of sidewalls  314 ,  316 , and  322 , is non-porous, i.e., not permeable to a flow of gas; each sidewall  314 ,  316 , and  322  includes a non-porous inner surface  324  that defines the interior channel that extends along length L of housing  300 . 
     As best illustrated by  FIG.  3 C , interior channel  314  has a cross-sectional area, and a depth (d), that vary along the length (L) of channel  310 . In specific with regard to the depth, near inlet end  306 , a non-porous lower or back surface  324 , which defines a portion of interior channel  310 , meets channel  302   a  of inlet  302 . Surface  324  defines a depth (d) of channel  310  between opening  318  and surface  324  of sidewalls  314 ,  316 , and  322 . The depth (d) is greatest at the approximate midpoint  330  of channel  324 , between distal end  334  of channel  310  and proximal end  332  of channel  310 . 
     Another example of a diffuser ( 400 ) that includes an interior channel that has a cross-sectional area and a depth that each vary along the length of the interior channel is shown at  FIG.  4   .  FIG.  4    shows a side cut-away view of directional diffuser  400 , which includes diffuser housing  412 , which has a length (L), a width (w), and a depth (d). Housing  412  includes inlet  402  at inlet end  406 , a second end (“closed end”)  404 , with the length L extending between inlet end  406  and closed end  404 . On front side  408  of housing  412 , openings  418  extend along length L and width w between inlet end  406  and closed end  404 . A porous diffuser membrane (not shown) may be held within each elongate opening  418  as part of a diffuser assembly. 
     Inlet  402  leads to interior channel  414 , defined by openings  418  on one side, and by elongate (in the length direction) non-porous sidewalls on the remaining sides. As shown, interior channel  414  has a depth (d) that varies along the length (L) of channel  414 , between inlet end  406  and closed end  404 ; the steady and gradual reduction in depth of interior channel  414  at the distal portion of housing  412  may be referred to as a “tapered” depth or a “tapered” or “gradual” reduction in depth. In specific, near inlet end  406 , surface  324  defines a depth (d) of channel  414 , between opening  418  and back surface  424 . The depth (d) is greatest at d-max, and becomes gradually reduced along length L in the direction toward closed end  404 . 
     According to specific example diffusers of the present description, a diffuser can be designed to have an interior channel that controls a flow of fluid through the length of the diffuser housing and through the diffuser membrane at different locations along the length of the housing, to produce an improved evenness or uniformity of flow through the membrane at locations along the length of the diffuser. Typically, in a directional diffuser that includes an interior channel that is uniform in cross section and dimensions along a length of the diffuser, the flow of gas through the diffuser membrane (at locations along the length of the diffuser) is un-even by having greater flow (or pressure) of fluid at the inlet end and lower flow (or pressure) at the outlet end. 
       FIGS.  5 A and  5 B  graphically illustrate gas flow rate (velocity) of flow of gaseous fluid through a membranes  510  and  610  of diffusers  500  and  600  as described. Referring to  FIG.  5 A , diffuser  500 , which includes membrane  510 , has an internal channel (not shown) that is uniform in cross-sectional area and dimensions along the length of diffuser  500 , from inlet end  512  to closed end  514 . Gaseous fluid flows into inlet end  512  and passes along the length of diffuser  500  toward closed end  514 . Along this path, pressure of the fluid within the interior channel gradually decreases, causing gradually reduced levels of flowthrough membrane  510 . 
       FIGS.  5 A and  5 B  depict higher and lower rates of flow of fluid through diffuser membrane  510  and membrane  610  as a range of shades of grey. Different relative rates of flow are shown in grey-scale. Flows of  FIGS.  5 A and  5 B  are lowest at the outer perimeter edges ( 518 ,  618 ) of diffuser membrane  510 . A slightly higher relative rate of flow occurs at locations  524  and  624 , and areas of the same grey shade. A still slightly higher relative rate of flow occurs at locations  522  and  622  and areas of the same grey shade. The highest relative rate of flow are the darkest areas, locations  520  and  620  and areas of the same dark grey shade. 
       FIG.  5 A  shows that a flow of fluid through diffuser membrane  510  is greatest at region  502  near inlet end  512 , is gradually reduced along the length of diffuser  500  toward closed end  514 , and has a lowest rate of flow near closed end  514 . The lack of uniformity of the rate of flow through membrane  510  may not precisely correlate to distance from the inlet, but in a general sense the fluid pressure within the internal channel and the rate of flow of fluid through membrane  510  are greatest near inlet end  512  and lowest near closed end  514  of diffuser  500 . 
     In contrast,  FIG.  5 B  shows a reduction in the variability of flow rate of fluid through a diffuser membrane of a diffuser as described, along the length of the diffuser. Referring to  FIG.  5 B , diffuser  600 , which includes membrane  610 , has an internal channel (not shown) that exhibits a gradually reduced depth and cross-sectional area along a length of the diffuser, with a greater depth and cross-sectional area being near inlet end  610 , and a lower (e.g., minimum) depth and cross-sectional area being near closed end  614 . Gaseous fluid flows into inlet end  612  and passes along the length of diffuser  600  toward closed end  614 . Along this path, the cross-sectional area and depth of the internal channel of diffuser  600  are gradually reduced. 
       FIG.  5 B  shows a flow of fluid through diffuser membrane  610  that is more uniform along the length of diffuser  600  in comparison to flow of fluid through diffuser membrane  510  of diffuser  500 , which does not have a variable depth or cross-sectional area along the length of diffuser  500 . The improved uniformity of the rate of flow through membrane  610  can be observed as the relatively even rate of flow of fluid through membrane  610  at region  602  near inlet end  612 , compared to the rate of flow of fluid through membrane  610  at region  604  near closed end  614 . The rate of flow of gas through membrane  610  may not precisely correlate to a distance from inlet end  612 , but in a general sense the rate of flow of gaseous fluid through membrane  610  is not significantly different at region  602 , compared to the rate of flow of fluid through membrane  610  at region  604 . Some amount of variability in flow rate of gaseous fluid still remains along the length of diffuser  600  and membrane  610 , but the variability is reduced relative to the diffuser of  FIG.  5 A  and does not include a significant or distinct maximum flow near inlet end  612  or a significant or distinct minimum level of pressure or flow near closed end  614 . 
     A diffuser assembly includes a diffuser housing as described, and can include one or more diffuser membranes attached to and contained within an opening or openings that extend along the length of the housing on one side of the housing. In use, for a gas to pass from the interior channel to an exterior of the directional diffuser, the gas must pass through the diffuser membrane. The diffuser membrane is located with one surface facing the interior channel of the housing, and a second surface facing a space that is external to the housing, which in use is an enclosed interior space of a chamber. 
     Various different types of diffuser membranes are known, including various porous or apertured sheet-like structures (“membranes”) that allow for a flow of a gaseous fluid through the structure. The membrane diffuser is effective to dispense an even flow of reagent gas from a gas source, that passes through the interior channel of the housing, through the diffuser membrane, and into an interior space of a chamber, with the diffuser assembly extending into an interior space of the chamber. The diffuser membrane is designed to cause the reagent gas to flow evenly into the reaction chamber to distribute the gas uniformly within the chamber in a diffused form, to prevent the flow from disrupting and moving any particulate contaminants that may be present in the interior space. 
     Examples of diffuser membranes formed from sintered porous bodies are described in United States Patent Publication Number 2013/0305673, the entirety of which is incorporated herein by reference. 
     According to preferred examples of diffuser assemblies, a directional diffuser as described comprises a flat or slightly curved sheet-type diffuser membrane that is capable of producing a flow of water through the diffuser assembly that exits the diffuser membrane in the form of substantially laminar flow that is relatively even along the length of the diffuser membrane, and that falls from the diffuser membrane as a film or curtain.  FIG.  6    is a photograph of an example of a directional diffuser that exhibits this preferred type of laminar flow of water through the diffuser at test conditions. 
     A diffuser assembly of the present description can be tested for this type of desired laminar flow property, using water, by allowing water (e.g., de-ionized water) to flow through the diffuser assembly by passing into the inlet, flowing through the interior channel, and then flowing through the diffuser membrane located at one surface of the assembly. With the diffuser assembly oriented horizontally, with the length and the width being in a common horizontal plane, and with the diffuser membrane facing down and the depth oriented vertically, water at low to moderate pressure is caused to flow into the inlet and is allowed to pass through the diffuser membrane. Desirably, when tested at ambient pressure and temperature, the water will flow relatively evenly through the diffuser membrane, preferably in the form of a thin film or “curtain” that forms from the flowing water along a length of the diffuser membrane. The water flowing from the membrane preferably retains the form of the film or curtain for as long as the flow is maintained. See  FIG.  6   . 
     The diffuser housings described herein, having the described elongate form, input end, closed end, and internal channel, are not limited in terms of any particular method used for preparing a housing. A housing as described may be prepared by any current or future manufacturing method that will is effective to form a diffuser housing as described. 
     Certain particular methods may be useful to form different examples of the described diffuser housings. For example, diffuser housings that include an interior channel that has a variable cross-sectional area or depth, or both, along the length of the channel, may be difficult to form on a commercial scale, in a cost effective manner, by using only machining, molding, or CNC (computer numerical control) equipment and techniques. 
     According to example methods and to example diffuser housings, techniques that have been found to be effective for preparing a diffuser housing or a component of a diffuser housing include additive manufacturing techniques, including methods that are commonly referred to as “3-D printing” techniques. 
     Many different versions of additive manufacturing techniques are known. Additive manufacturing methods generally involve a series of individual layer-forming steps that sequentially form layer-upon-layer of solidified feedstock composition derived from a feedstock composition. Some specific examples of general types of additive manufacturing techniques include those commonly referred to as “powder-bed” additive manufacturing methods, which include various “binder jet printing” techniques. Other examples include stereolithography techniques (SLS) and “feedstock dispensing methods” (FDMs). Still others, referred to as “laser metal deposition,” or “direct metal deposition,” or “direct energy deposition,” involve the use of a laser and feedstock composition (as powder or wire) to continuously form a “weld pool” on surface, which continuously solidifies, to continuously form multiple layers of a multi-layer body. 
     Diffuser bodies as described may be prepared by any of these additive manufacturing methods, as well as others, any of which may be currently known or developed in the future. 
     Using a series of additive manufacturing steps, each step forming a single layer of a structure, multiple layers of solidified feedstock are sequentially formed into a structure that is referred to herein as a multi-layer composite (or “composite”). As used herein, the term “composite” (or “multi-layer composite”) refers to a structure formed by additive manufacturing by sequentially forming a series of multiple individual and individually-formed layers of solidified feedstock. The composite takes the form of a diffuser housing, or a component of a diffuser housing of the present description, which includes: an inlet end that comprises an inlet; a closed end; a length between the inlet end and the closed end; an opening on a front side; and an interior channel extending between the inlet and the closed end, with the channel defined along the length by the opening on the front side, an elongate, non-porous back surface, and elongate non-porous side surfaces. The housing has dimensions referred to as a length, a width, and a depth, as described herein. In certain embodiments, the cross-sectional area, the depth, or both, of the channel, varies along the length of the channel. 
     According to example diffuser bodies, prepared by an additive manufacturing technique, the entire housing, between the two ends and from the front face to a back side, can be formed and held together exclusively as a structure of multiple layers formed by multiple layer-forming steps of an additive manufacturing method, and without using a bonding step such as a vacuum brazing step, to bond together two separately-produced pieces. A diffuser housing that is formed as a multi-layer composite by an additive manufacturing method, without bonding (by vacuum brazing, or the like), may be referred to herein as a “continuous” diffuser housing. 
     The term “continuous” in this context means that a complete housing is formed as a single-piece composite structure from multiple sequentially-formed layers. The term “continuous” does not refer to a structure that is prepared by separately forming two individual pieces and then bonding the two separately-formed pieces together, for example by a vacuum brazing technique or by a different type of bonding technique. A continuous diffuser housing will not include a seam or a boundary that results from a bonding step, especially a seam or boundary that is made of a bonding or filler material that has a composition that is different from the materials of the diffuser housing. 
     One specific example of an additive manufacturing technique is the technique commonly referred to as “selective laser melting.” Selective laser melting (SLM), also known as direct metal laser melting (DMLM) or laser powder bed fusion (LPBF), is a three-dimensional printing method that uses a high power-density laser to melt solid particles of a feedstock material, which allows the melted (liquid) material of the particles to flow to form a layer of the melted material, and then allows the layer to cool and solidify to form solidified feedstock. According to certain particular example methods, the particles of the feedstock can be fully melted to form a liquid (i.e., liquefied), and the liquid material is allowed to flow to form a substantially continuous, substantially non-porous (e.g., less than 80, 85, 90, or 95 percent porosity) film that then cools and hardens as a solidified feedstock layer of a multi-layer composite. 
     Additive manufacturing techniques may be useful for forming diffuser housings made from a broad range of materials, including metal materials (including alloys), metal matrix composite materials, ceramic materials, polymers, and combinations of these. 
     With additive manufacturing techniques, including selective laser melting techniques, the range of possible metals, alloys, and metal matrix composites that can be used to form a diffuser housing can advantageously include materials that are not easily formed into a useful diffuser housing by previous techniques such as machining techniques. The range of materials available with additive manufacturing techniques includes metals and metal alloys that can be melted by laser energy, such as aluminum alloys, iron-based alloys (stainless steel alloys) titanium alloys, nickel and nickel-based alloys, and various metal matrix composite materials, some of which are not easily processed by machining. Example materials may exhibit such high hardness that the materials can be difficult to process by machining techniques to form precise structures of a diffuser housing, including precise dimensions and varied dimensions (e.g., a varied depth). Using additive manufacturing techniques, these materials can be processed to form a diffuser housing that includes an interior channel that has variable dimensions, e.g., variable cross-sectional area, variable depth, or both, along the length of the channel, even from materials that would be difficult to similarly form by using standard machining techniques. 
     The material that is used to prepare the diffuser housing may be any material that is useful for preparing a diffuser housing, for example inorganic materials that include various metals (including alloys), metal matrix composites, ceramic materials, and polymers. 
     Examples of useful polymers may include polyethylene, polystyrene, and fluoropolymers, which includes hydro-fluoropolymers and perfluoropolymers, such as polytetrafluoroethylene (PTFE) and perfluoroalkyl polymers (PFAs). 
     The term “metal” is used herein in a manner that is consistent with the meaning of the term “metal” within the metal, chemical, and additive manufacturing arts, and refers to any metallic or metalloid chemical element or an alloy of two or more of these elements. 
     The term “metal matrix composite” (“MMC”) refers to a composite material that has been prepared to include at least two constituent parts or two phases, one phase being a metal or metal alloy and another phase that is a different metal or another non-metal material such as a fiber, particle, or whisker, that is dispersed through a metallic matrix. The non-metal material may be carbon-base, inorganic, ceramic, etc. Some example metal matrix composite materials are made of combinations of: an aluminum alloy with alumina particles; an aluminum alloy with carbon; an aluminum alloy with silicon; an aluminum alloy with silicon carbide (SiC); a titanium alloy with TiB 2 ; a titanium alloy with silicon; a titanium alloy with silicon carbide (SiC). 
     Metal and metal alloys that may be useful according to methods of the present description include metal and metal alloys that have in the past been used for preparing diffuser structures, and, additionally, other materials that have not. Useful or preferred materials include metals such as iron alloys (e.g., stainless steel and other types of steel), titanium and titanium alloys, nickel and nickel alloys (e.g., Hastelloy C22, Hastelloy C276), aluminum and aluminum alloys, molybdenum and molybdenum alloys, and various metal matrix composite materials. 
     By an additive manufacturing method, a complete (or substantially complete) functional diffuser housing can be prepared using a single manufacturing process (a single additive manufacturing “step”), which offers high manufacturing efficiency in a reduced amount of time per unit (high manufacturing throughput). A diffuser housing that is complete with substantially all required structures (e.g., an inlet end, closed end, front face, sidewalls, and an interior channel) may be prepared by a single series of additive manufacturing steps. For example, what can be referred to as a “one-step” additive manufacturing process to form a diffuser structure can form many, most, or all required structures of the diffuser housing (e.g., an inlet end, closed end, front face, sidewalls, and an interior channel) as a single, multi-layer composite as described. A one-step additive manufacturing process avoids the need to form multiple separate pieces individually by separate steps, followed by a still additional step of bonding the multiple, separately-formed pieces together to form a functional diffuser structure. 
     Still further, additive manufacturing techniques can be used to form a diffuser housing that has high-precision dimensions, or varied dimensions or shapes, including shapes or varied dimensions that are difficult to form by conventional techniques, including a varied dimension (cross-sectional area, depth, width, or a combination of these) of an interior channel along the length of the interior channel. 
     Each layer of a composite may be formed as desired, from a desired material, and with a desired thickness, to produce a diffuser housing in the form of a multi-layer composite that has a design as described. By exemplary additive manufacturing methods, each layer is prepared from a collection of particles (referred to as “feedstock”) that is generally in the form of a powder. A feedstock contains small particles made of one or a variety of different inorganic materials that can be melted by a high energy laser to liquefy and flow to form a layer of the melted material, then cool to solidify to form a layer of a multi-layer composite. 
     Particles that are useful according to the present description may be any particles that can be processed to form a useful multi-layer composite as described. Examples of useful particles include inorganic particles that are capable of being completely melted, partially melted (e.g., sintered), or liquefied, by laser energy to form a layer of a diffuser housing as described. Examples of such particles include inorganic particles that are made of metals (including alloys), ceramic, or metal matrix composites. Some useful examples, generally, include metals and metal alloys such as stainless steel, nickel-based alloys, aluminum and aluminum alloys, and titanium and titanium alloys, as well as metal matrix composites. 
     Useful particles of a feedstock can be of any size (e.g., mean particle size) or size range that is effective, including small or relatively small particles on a scale of microns (e.g., having an average size of less than 500 microns, less than 100 microns, less than 50 microns, 10 microns, or less than 5 microns). 
     The particles can be selected to achieve effectiveness in processing as described, to be capable of being contained in a feedstock, formed into a feedstock layer, and fully melted or partially melted (e.g., sintered) to form a layer that contains the melted particles, that can cool to form solidified feedstock as a layer of a multi-layer composite. The size, shape, and chemical makeup of the particles can be any that are effective for these purposes. 
     The particles can be in the form of a feedstock composition that can be used in an additive manufacturing process of the present description. According to examples, feedstock useful in an additive manufacturing process may contain particles that are capable of being heated to be partially melted or fully melted then cooled to form a layer of a multi-layer composite. The feedstock material is not required to contain any other material, but may if desired optionally contain amounts of other materials. 
     Example feedstock compositions for use in selective laser melting or selective laser sintering techniques may contain at least 80, 90, or 95, 98, or 99 percent inorganic particles by weight, based on total weigh of a feedstock composition. Other ingredients may be present if desired, at low amounts, such as one or more of a flow aid, surfactant, lubricant, leveling agent, or the like. 
     Each layer of a multi-layer composite may be formed to have any useful thickness. A thickness of a layer of a multi-layer composite is measured of a layer of the composite after the layer has been formed by melting particles of a feedstock layer to form a melted feedstock layer, and then cooled to form a solidified feedstock layer of the composite. Example thicknesses of a solidified layer of a composite may be in a range from 30 microns to 100, 200, or more microns, e.g., from 30 to 50, 60, 70, 80, microns up to 90, 100, 150, 200, 300, 400, or 500 microns. In example composite structures, all layers of the composite may have the same thickness or substantially the same thickness. In other example composite structures, the layers may not all have the same thickness, but different layers of the composite may each have different thicknesses. 
     A diffuser housing as described can be prepared by additive manufacturing methods that form a dense metal or metal matrix composite multi-layer composite structure, using a series of individual layer-forming steps. As one example, techniques referred to laser additive manufacturing techniques (LAMTs) may be used to form a multi-layer composite in a layer-by-layer, “additive manufacturing” fashion. Laser additive manufacturing techniques use a high-power laser energy to selectively cause metal or metal matrix composite particles of a feedstock layer to be heated, melt (at least partially), flow, and form a substantially solidified feedstock layer. By one specific example, referred to as selective laser melting (SLM), the feedstock layer is melted to form a substantially continuous, non-porous, melted layer, which solidifies as a substantially continuous, non-porous solidified feedstock layer. By a different specific example, referred to as selective laser sintering (SLS), the feedstock layer is sintered (partially melted) to form layer of partially melted feedstock particles, which cools to form a solidified feedstock layer that may contain a certain level of space between the melted particles, as pore space. 
     More specifically, a multi-layer composite may be built by sequential steps of producing many thin cross sections (“solidified feedstock” of a “layer,” herein) of a larger three-dimensional structure (composite). A layer of feedstock is formed, and includes many particles of metal or metal matrix composite. Laser energy is selectively applied to the feedstock layer over a portion of a layer of the feedstock. The portion of a feedstock layer that receives laser energy is a portion that will be formed as the diffuser housing. 
     The laser energy at least partially melts particles at the portion of the feedstock that are exposed to the laser energy. The melted material of the particles liquefies and flows to contact other melted particles, and the melted particles cool to solidify as a layer of solidified feedstock. 
     After an initial layer of solidified feedstock is formed, an additional thin layer of the feedstock is deposited over the top surface of the completed layer that contains the solidified feedstock. The process is repeated to form multiple layers of the solidified feedstock, each layer being formed on top of and adhering to a top surface of a previous layer. Multiple layers are deposited, successively, one over each completed layer, to form a multi-layer composite that is a composite of multiple layers of successively-formed solidified feedstock. The multiple layers may be of the same composition and thickness, or may be of different compositions and different layer thicknesses. 
     Binder jet additive manufacturing methods involve a polymer for forming a solidified feedstock layer, the formation of a “green body” that contains the polymer, and post-processing steps such as debinding to remove the polymer and heat treatment (e.g., sintering). Many laser-based additive manufacturing methods such as those described generally and specifically herein avoid the need for a polymer during formation of solidified feedstock layers. These laser-based methods also do not require a debinding step or a sintering step to form a final multi-layer composite. 
     A first aspect is directed to a directional gas diffuser comprising: an elongate housing, the housing comprising: an inlet end, a closed end, a length between the inlet end and the closed end, an opening extending along the length on a front side of the housing, and a channel extending between the inlet end and the closed end, the channel defined along the length by: the opening extending along the front side, an elongate back surface, and elongate side surfaces, wherein the channel has a length, a width, a depth, and a varied cross-sectional area along the channel length. 
     In a second aspect according the first aspect, the length is greater than the width, and the width is greater than a maximum depth of the channel. 
     In a third aspect according to any preceding aspect, the depth decreases along a portion of the length as the channel extends toward the closed end. 
     In a fourth aspect according to any preceding aspect, the elongate back surface is non-porous and the two elongate side surfaces are non-porous. 
     In a fifth aspect according to any preceding aspect, the housing further comprising a multi-layer composite that extends from the elongate back surface to the front side. 
     In a sixth aspect according to any preceding aspect, the multi-layer composite comprises: a metal or metal alloy, a metal composite matrix, a ceramic, or a polymer. 
     In a seventh aspect according to any preceding aspect, the multi-layer composite does not contain a seam. 
     In an eighth aspect according to any preceding aspect, the diffuser further comprising a diffuser membrane secured to the opening. 
     In a ninth aspect according to the eighth aspect, relative to an otherwise comparable diffuser having a channel with a uniform cross-sectional area, the varied cross-sectional area along the length produces a more uniform rate of flow of fluid through the diffuser membrane along the length of the diffuser membrane. 
     In a tenth aspect according to the eighth or ninth aspect, the diffuser is capable of producing a laminar flow of water through the diffuser membrane, whereby with the diffuser situated horizontally with the diffuser membrane facing down, water passing through the diffuser is capable of producing a continuous thin water film that forms from the flowing water along a length of the diffuser membrane. 
     An eleventh aspect is directed to a directional gas diffuser comprising: an elongate housing, the housing comprising: an inlet end that comprises an inlet, a closed end, a length between the inlet end and the closed end, an opening extending along the length on a front face of the housing, and an interior channel extending between the inlet and the closed end, the channel defined along the length by: the opening on the front side, an elongate, non-porous back surface, and elongate non-porous side surfaces. 
     In a twelfth aspect according to the eleventh aspect, the length is greater than the width, and the width is greater than a maximum depth of the channel. 
     In a thirteenth aspect according to the eleventh or twelfth aspect, the depth decreases along a portion of the length as the channel extends toward the closed end. 
     In a fourteenth aspect according to any of the eleventh through thirteenth aspects, the elongate back surface is non-porous and the two elongate side surfaces are non-porous. 
     In a fifteenth aspect according to any of the eleventh through fourteenth aspects, the housing further comprising a multi-layer composite that extends from the elongate back surface to the front side. 
     In a sixteenth aspect according to the fifteenth aspect, the multi-layer composite comprises: a metal or metal alloy, a metal composite matrix, a ceramic, or a polymer. 
     In a seventeenth aspect according to any of the eleventh through sixteenth aspects, the multi-layer composite does not contain a seam. 
     An eighteenth aspect is direct to an apparatus comprising a chamber that includes an interior adapted to contain one or more semiconductor wafers, the chamber comprising the directional gas diffuser of any the preceding aspects at the interior, connected to a source of inert gas. 
     A nineteenth aspect according to the eighteenth aspect selected from a wafer carrier and a wafer transfer station. 
     A twentieth aspect directed to a method of equalizing pressure in a chamber of the wafer transfer station of the nineteenth aspect, the method comprising: with the chamber containing multiple semiconductor wafers, with the chamber closed and containing an interior at below atmosphere pressure, dispensing inert gas through the diffuser to increase the pressure within the interior. 
     A twenty-first aspect directed to a method of displacing a gaseous atmosphere in a chamber of the wafer carrier of the nineteenth aspect, the method comprising: with the chamber containing multiple semiconductor wafers in the gaseous atmosphere, dispensing inert gas through the diffuser to add the inert gas to the interior. 
     In a twenty-second aspect according to the twenty-first aspect, the gaseous atmosphere in the chamber is air, and the inert gas displaces the air. 
     A twenty-third aspect is directed to a method of making housing of a directional gas diffuser of any of the first through seventeenth aspects, by additive manufacturing, the method comprising: forming a first layer of solidified feedstock, forming a second layer of solidified feedstock on a surface of the first layer of solidified feedstock, wherein the layers of solidified feedstock are part of the housing. 
     A twenty-fourth aspect according to the twenty-third aspect further comprising: forming a first feedstock layer on a surface, the feedstock layer comprising inorganic particles; forming solidified feedstock from the first feedstock layer; forming a second feedstock layer over the first feedstock layer, the second feedstock layer comprising inorganic particles; and forming second solidified feedstock from second feedstock layer, wherein the solidified feedstock layers are part of a housing of a directional gas diffuser. 
     A twenty-fifth aspect according to the twenty-third aspect further comprising forming solidified feedstock by melting inorganic particles using a laser. 
     In a twenty-sixth aspect according to any of the twenty-third through twenty-fifth aspects, the solidified feedstock layers comprise particles selected from: metal or metal alloy particles, metal composite matrix particles, ceramic particles, and polymer particles.