Diffuser for uniform gas delivery in cross-flow reactor

Abstract

To provide a diffuser design improved for managing a material flow.SOLUTION: A diffuser includes a top surface 242 and a bottom surface 246 that extend from an inlet 152 to a wall 180. The top and the bottom are separated by a separation distance. The separation distance includes at least a first separation distance H1 at the inlet of the diffuser and a second separation distance at the wall such that the first separation distance is greater than the second separation distance. That is, at least a part of the top surface is tapered.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates generally to fabricating semiconductor devices. More specifically, the present disclosure relates to crossflow reactors and components, systems including the reactors and components, and methods of using the reactors, components, and systems. [Background technology]

[0002] Gas-phase reactors, such as chemical vapor deposition (CVD) reactors, including atomic layer deposition (ALD) reactors, can be used for a variety of applications, including forming layers on substrate surfaces. Such reactors can be used, for example, to deposit, etch, clean, and / or process layers on substrates to form semiconductor devices, flat panel display devices, photovoltaic devices, microelectromechanical systems (MEMS), and the like.

[0003] A typical gas phase reactor system includes a reactor including a reaction chamber, one or more precursor gas sources fluidly connected to the reaction chamber, one or more carrier or purge gas sources fluidly connected to the reaction chamber, a gas distribution system for delivering gases (e.g., precursor gases and / or carrier or purge gases) to the surface of the substrate, and an exhaust source fluidly connected to the reaction chamber.

[0004] A crossflow reactor is a type of gas-phase reactor that is particularly useful when rapid throughput and / or rapid purging of the reaction chamber is desired, such as in ALD deposition. In a crossflow reactor, gas generally enters the reaction chamber at one end of the reaction chamber, flows laterally across the substrate within the reaction chamber, and exits at a second end of the reaction chamber. The gas typically enters the reaction chamber through a diffuser, which attempts to distribute and / or mix the precursors before the flow enters the reaction chamber.

[0005] Diffusers in conventional systems are typically constant; that is, gas enters the diffuser and is distributed across the width of the reactor in a fixed manner that depends on the diffuser's geometry. This redistribution creates a specific flow velocity profile as the gas enters the reaction chamber. The resulting film thickness deposited on the substrate is then non-uniform. Material accumulates along the edges, such that the thickness of material deposited along the outer edge of one half of the substrate is greater than the thickness deposited elsewhere on the substrate. Therefore, improved diffuser designs for managing material flow are desirable. Summary of the Invention

[0006] The diffuser includes an inlet, and the process material enters the diffuser at the inlet before flowing through the reaction chamber. The inlet is at the intersection of a first axis, a second axis, and a third axis, the first axis, the second axis, and the third axis being perpendicular to one another. A wall is connected to the diffuser and the reaction chamber, and the process material flowing through the diffuser bends at the wall and enters the reaction chamber. The diffuser further includes a top surface extending from the inlet to the wall and a bottom surface extending from the inlet to the wall. The bottom surface is separated by a separation distance by the top surface, the separation distance being parallel to the third axis. The separation distance further includes a first separation distance at the inlet and a second separation distance at the wall, the first separation distance being greater than the second separation distance.

[0007] A method of manufacturing a diffuser is provided. The method includes defining an inlet on a first axis, a second axis, and a third axis, the first axis, the second axis, and the third axis being perpendicular to one another. The method further includes connecting a wall of the diffuser to the inlet by connecting a top surface of the diffuser to the inlet and the wall such that it extends from the inlet to the wall, and by connecting a bottom surface of the diffuser to the inlet and the wall such that it extends from the inlet to the wall. The bottom surface extends along a plane parallel to the plane defined by the first and second axes. The method also includes connecting the wall to the inlet by connecting a right surface extending from the inlet to the wall such that it is further connected to the bottom and top surfaces, and by connecting a left surface extending from the inlet to the wall such that it is further connected to the bottom and top surfaces. The right and left surfaces define a separation distance between the bottom and top surfaces, the separation distance being parallel to the third axis such that the separation distance at the inlet is greater than the separation distance at the wall.

[0008] The reactor system includes a material source configured to provide a material to be deposited on a substrate. The diffuser is fluidly connected to the material source, the diffuser having a top surface and a bottom surface. The reactor system also includes a cross-flow reaction chamber fluidly connected to the diffuser, the reaction chamber configured to deposit the material on the surface of the substrate. The system further includes a wall fluidly connected to the diffuser and the reaction chamber, such that material flowing from the material source through the diffuser flows through the wall into the reaction chamber. The top surface and the bottom surface are separated by a separation distance, the separation distance tapering from an inlet connected to the material source to the wall.

[0009] This Summary is provided to introduce a selection of concepts in a simplified form that are described in more detail below in the Detailed Description of Examples of the Disclosure. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. [Brief explanation of the drawings]

[0010] These and other features, aspects, and advantages of the inventions disclosed herein are described below with reference to drawings of certain specific embodiments, which are intended to be illustrative of the invention and not limiting of the invention.

[0011] [Figure 1] FIG. 1 is a perspective view of a diffuser in a reactor system according to an exemplary embodiment of the present disclosure. [Figure 2] FIG. 2 is a side view of the diffuser of FIG. 1 according to an exemplary embodiment of the present disclosure. [Figure 3] FIG. 2 is a front view of the left side of the diffuser of FIG. 1 in accordance with an exemplary embodiment of the present disclosure. [Figure 4] 2 is a cross-sectional view of the diffuser of FIG. 1 according to an exemplary embodiment of the present disclosure. [Figure 5] FIG. 2 is a flow diagram of a method for manufacturing a diffuser such as the diffuser of FIG. 1 according to an exemplary embodiment of the present disclosure.

[0012] It will be understood that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the relative size of some of the elements in the figures may be exaggerated compared to other elements to help to improve understanding of the illustrated embodiments of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0013] The descriptions of exemplary embodiments provided below are merely exemplary and intended for illustrative purposes only, and the following descriptions are not intended to limit the scope of the present disclosure or the claims. Moreover, the recitation of multiple embodiments having described features is not intended to exclude other embodiments having additional features or other embodiments incorporating different combinations of the described features.

[0014] As described in more detail below, various embodiments of the present disclosure relate to gas-phase reactors and reactor systems that include variable-height reaction chambers and / or spacers that help define a gap between the susceptor and base plate of the reactor.

[0015] 1-4 show sections of a gas-phase reactor system 100 according to an exemplary embodiment of the present disclosure. The system 100 includes a reactor 110. The reactor 110 may be used to deposit material on a surface of a substrate, etch material from a surface of a substrate, clean the surface of a substrate, treat the surface of a substrate, deposit material on a surface in a reaction chamber, clean a surface in a reaction chamber, etch a surface in a reaction chamber, and / or treat a surface in a reaction chamber 402 (see FIG. 4). The reactor 110 may be a stand-alone reactor or part of a cluster tool. Furthermore, the reactor 110 may be dedicated to a deposition, etching, cleaning, or treatment process, or the reactor 110 may be used for multiple processes, e.g., any combination of deposition, etching, cleaning, and treatment processes. As an example, the reactor 202 may include a reactor typically used for a chemical vapor deposition (CVD) process, such as an atomic layer deposition (ALD) process.

[0016] The reaction chamber 402 is a cross-flow reaction chamber. During operation, gas enters the reaction chamber 402 through the diffuser 120 and flows horizontally through the reaction chamber 402 to an exhaust conduit. As seen in FIG. 1 , gas flowing through the reaction chamber 402 enters the diffuser 120 at the inlet 152, impinges on the wall 180, and is output into the reaction chamber 402. The inlet 152 is aligned along axes 150, 156, and 158. As seen in FIG. 4 (a cross-sectional view of the diffuser 120), the diffuser 120 includes a tapered distance between the top surface 242 and the bottom surface 246 of the diffuser 120. In the exemplary embodiment, the height of the diffuser 120 between the top surface 242 and the bottom surface 246 tapers from a greater height at the inlet 152 to a smaller height as the top surface 242 and the bottom surface 246 meet the wall 180.

[0017] In the exemplary embodiment, diffuser 120 includes aft section 140. In the exemplary embodiment, diffuser 120 includes left section 142a and right section 142b. In the exemplary embodiment, diffuser 120 includes center section 130. In the exemplary embodiment, center section 130 further includes center left section 134a and center right section 134b. In the exemplary embodiment, center section 130 further includes center left section 132a and center right section 132b. In the exemplary embodiment, center section 130 includes center left end (point) 136a and center right end (point) 136b. In the exemplary embodiment, diffuser 120 includes front section 160.

[0018] In exemplary embodiments, the distance (H1) between the top surface 242 and the bottom surface 246 at the inlet 152 is greater than 4 mm. In some exemplary embodiments, the distance H1 at the inlet 152 is greater than 10 mm. In exemplary embodiments, the distance (H2) between the top surface 242 and the bottom surface 246 at the intersection 134 where the rear section 140, the center section 130, and the left and right sections 142a and 142b intersect is equal to or less than the distance H1. In exemplary embodiments, the distance H2 at the intersection 134 is between approximately 3 mm and 12 mm. In exemplary embodiments, the distance H2 is between approximately 4 mm and 10 mm. In some exemplary embodiments, the distance H2 is approximately 4 mm. In some exemplary embodiments, the distance H2 is approximately 7.75 mm. In some exemplary embodiments, the distance H2 is approximately 10 mm.

[0019] Similarly, in exemplary embodiments, the distance (H3) between top surface 242 and bottom surface 246 extending along intersecting edge 172a between rear section 140 and left section 142a and along intersecting edge 172b between rear section 140 and right section 142b is less than or equal to distance H1. In exemplary embodiments, distance H3 may be equal to distance H2. In exemplary embodiments, distance H3 may be slightly less than distance H2. For example, in some exemplary embodiments, the difference between distances H2 and H3 may be 1 mm or less.

[0020] Furthermore, in the exemplary embodiment, the distance between top surface 242 and bottom surface 246 along intersecting edge 174a (including edge 178a) between left section 142a and central section 130, and the distance between top surface 242 and bottom surface 246 along intersecting edge 174b (including edge 178b) between right section 142b and central section 130 are less than distance H3. In the exemplary embodiment, top surface 242 slopes downward from intersecting edge 172b of section 142b to intersecting edge 174b to abut bottom surface 246. Similarly, in the exemplary embodiment, top surface 242 slopes downward from intersecting edge 172a of section 142a to intersecting edge 174a to abut bottom surface 246.

[0021] In the exemplary embodiment, central section 130 includes a center left section 134a defined from edge 190 to edge 194a, and further defined from edge 178a to edge 170. Similarly, in the exemplary embodiment, central section 130 further includes a center right section 134b defined from edge 190 to edge 194b, and further defined from edge 178b to edge 170. In the exemplary embodiment, central section 130 includes a center left section 132a defined from edge 194a to 196a, and further defined from edge 174a to edge 170. Similarly, in the exemplary embodiment, central section 130 further includes a center right section 132b defined from edge 194b to edge 196b, and further defined from edge 174b to edge 170.

[0022] As shown in FIGS. 1-4, in exemplary embodiments, edge 190 extends from intersection 134 to edge 170. As shown in FIG. 1, edge 190 is aligned along axis 156. In exemplary embodiments, the distance (H5) between top surface 242 and bottom surface 246 at the intersection of edge 190 and edge 170 is between 2 mm and 12 mm. In some exemplary embodiments, distance H5 is approximately 2.24 mm. In some exemplary embodiments, distance H5 is approximately 4 mm. In some exemplary embodiments, distance H5 is approximately 7.75 mm. In some exemplary embodiments, distance H5 is approximately 10 mm.

[0023] 1-4, central section 130 of diffuser 120 extends from center edge 190 on the right side of diffuser 120 to terminal point 136b and further extends from center edge 190 on the left side of diffuser 120 to terminal point 136a. Terminal point 136a is located at the intersection of a first terminal axis and a second terminal axis, where the first terminal axis is parallel to axis 154 and the second terminal axis is parallel to axis 156. Similarly, terminal point 136b is located at the intersection of the first terminal axis and a third terminal axis, where the third terminal axis is parallel to axis 156.

[0024] As shown in FIG. 3 , in the exemplary embodiment, the distance between the top surface 242 and the bottom surface 246 of section 130 decreases as section 130 extends from central edge 190 to end points 136a and 136b. Central edge 190 is aligned along axis 156. Further end points 196a and 196b are equidistant from central edge 190. In the exemplary embodiment, the distance (H7) between top surface 242 and bottom surface 246 at edge 196a and between top surface 242 and bottom surface 246 at edge 196b is less than distance H5. In the exemplary embodiment, distance H7 is between 1 mm and 4 mm. In the exemplary embodiment, distance H7 is at least one of 1.12 mm, 2.14 mm, or 2.24 mm. In an exemplary embodiment (not shown), distance H7 may be equal to distance H5. As shown in FIG. 2, endpoints 136 a and 136 b are aligned along an axis 158 that is parallel to axis 154 .

[0025] 1-4, the upper surface 242 of the diffuser 120 in section 130 extends from the central edge 190 to edge 196a and further extends from the central edge 190 to edge 196b such that distance H7 is less than distance H5. In the exemplary embodiment, the upper surface 242 may extend linearly from the central edge 190 to edge 196a and from the central edge 190 to edge 196a such that the slope of the upper surface 242 between edge 190 and edge 196a remains constant. Similarly, the slope of the upper surface 242 between edge 190 and edge 196b remains constant.

[0026] In an exemplary embodiment, top surface 242 may extend nonlinearly from center edge 190 to edge 196a. As discussed herein, nonlinear is defined to mean that the slope of top surface 242 between two points is not necessarily constant. As shown in FIGS. 1-4 , in an exemplary embodiment, section 130 further includes edge 194a, which divides section 130 into center left section 134a and center left extreme section 132a. Similarly, in an exemplary embodiment, section 130 further includes edge 194b, which divides section 130 into center right section 134b and center right extreme section 132b. The distance (H6) between top surface 242 and bottom surface 246 at edges 194a and 194b is less than distance H5. In an exemplary embodiment, distance H6 may be greater than distance H7. In an exemplary embodiment, distance H6 is between 3 mm and 5 mm. In an exemplary embodiment, distance H6 is 3.7 mm.

[0027] In the exemplary embodiment, the top surface 242 of the diffuser 120 further tapers from edge 170 to edge 184, forming a tapered section 160. Thus, edge 184 is formed at the intersection of tapered section 160 and wall 180. As shown in FIG. 4 , any material flowing through the diffuser 120 is focused through tapered section 160 and further through wall 180. Thus, the variation in the distance between top surfaces 242 and 246 at different portions (162a, 162b, 164a, 164b, 166) through section 160 allows the material flow to be reoriented to its center, providing a higher velocity as it passes through wall 180. Wall shear then increases as the material bends along edge 184 and flows through wall 180. This arrangement then provides a more uniform application of material as it flows through the reaction chamber 402 and then onto the wafer. Therefore, material buildup on the wafer is significantly less than in conventional systems.

[0028] 5 illustrates a method for manufacturing a diffuser for a reactor system, such as diffuser 120 (shown in FIGS. 1-4). Method 500 includes defining a first axis, a second axis, and a third axis, such as axes 156, 157, and 158, as shown in box 502. These three axes are perpendicular to one another. Method 500 further includes providing inlets (e.g., inlet 152) on the first axis, the second axis, and the third axis, as shown in box 504.

[0029] Method 500 also includes connecting a wall (e.g., wall 180) to the inlet by connecting a top surface (e.g., surface 242) of the diffuser to the inlet and the wall so that it extends from the inlet to the wall, and by connecting a bottom surface (e.g., surface 246) of the diffuser to the inlet and the wall, as shown in box 506 (see Figures 1-4). Method 500 further includes connecting the wall to the inlet by connecting a right surface extending from the inlet to the wall and by connecting a left surface extending from the inlet to the wall, as shown in box 508. The right surface is connected to the bottom and top surfaces, and the left surface is connected to the bottom and top surfaces. Thus, method 500 further includes defining a separation distance between the bottom and top surfaces, the separation distance being parallel to a third axis such that the separation distance at the inlet is greater than the separation distance at the wall, as shown in box 510.

[0030] In an exemplary embodiment, the method 500 further includes providing a first edge (e.g., 170) separating the upper surface into a rear section (e.g., 140, 142a, 142b, 130) and a front section (e.g., 160) such that the difference between the separation distance at the inlet and the separation distance at the first edge is less than the difference between the separation distance at the first edge and the wall. Furthermore, in an exemplary embodiment, the method 500 includes tapering the separation distance from the first edge to the wall. Furthermore, in an exemplary embodiment, the method 500 includes defining a separation distance of the upper surface from the first edge to the wall within a range of 2 mm to 12 mm. In a further exemplary embodiment of the method 500, the separation distance may vary in different sections of the diffuser. For example, the separation distance in different portions of the section 130 may be different.

[0031] While exemplary embodiments of the present disclosure are described herein, it should be understood that the disclosure is not so limited. For example, while reactors and systems are described with reference to various specific configurations, the disclosure is not necessarily limited to these examples. Various modifications, variations, and enhancements may be made to the exemplary systems and methods described herein without departing from the spirit and scope of the disclosure.

[0032] Unless otherwise indicated, the subject matter of the present disclosure includes all novel and non-obvious combinations and subcombinations of the various systems, components, and configurations, and other features, functions, operations, and / or properties disclosed herein, and all equivalents thereof. Moreover, the headings provided herein (if any) are for convenience only and do not necessarily affect the scope or meaning of the devices and methods disclosed herein. [Explanation of symbols]

[0033] 100 Gas Phase Reactor System 110 Reactor 120 Diffuser 130 Central Section 130 Section 140 rear section 150 axes 152 Entrance 160 Front Section 170 Edge 190 Edge 202 Reactor 242 Top surface 246 bottom 402 Reaction Chamber

Claims

1. A diffuser, an inlet where a process material enters the diffuser before flowing through a reaction chamber, the inlet being at an intersection of a first axis, a second axis, and a third axis, the first axis, the second axis, and the third axis being perpendicular to one another; a wall connected to the diffuser and the reaction chamber, wherein a process material flowing through the diffuser bends at the wall and enters the reaction chamber; an upper surface extending from the inlet to the wall; a bottom surface extending from the inlet to the wall, the bottom surface being separated by the top surface by a separation distance; Equipped with a diffuser, wherein the separation distance is parallel to the third axis, the separation distance further comprising a first separation distance at the inlet and a second separation distance at the wall, the first separation distance being greater than the second separation distance;

2. 2. The diffuser of claim 1, wherein the upper surface further comprises a first edge between the inlet and the wall, whereby the separation distance includes a third separation distance at the first edge, and wherein a difference between the third separation distance and the second separation distance is greater than a difference between the first separation distance and the third separation distance.

3. a first endpoint at an intersection of a first endpoint axis and a second endpoint axis, the first endpoint axis being parallel to the first axis and the second endpoint axis being parallel to the second axis; a second endpoint at an intersection of the first endpoint axis and a third endpoint axis, the third endpoint axis being parallel to the second endpoint axis and the second axis; a central edge, the central edge being aligned along the second axis, the first end point and the second end point being equidistant from the central edge; the third separation distance comprises a fourth separation distance, the fourth separation distance being the separation distance at an intersection of the first edge and the central edge; the third separation distance further comprises a fifth separation distance, the fifth separation distance being the separation distance at an intersection of the first endpoint and the first edge; the third separation distance further comprises a sixth separation distance, the sixth separation distance being the separation distance at an intersection of the second endpoint and the first edge; The diffuser of claim 2 , wherein the fourth separation distance is greater than the fifth separation distance, and the fourth separation distance is greater than the sixth separation distance.

4. The diffuser of claim 3, wherein the fourth separation distance is between 2 mm and 12 mm.

5. The diffuser of claim 3, wherein the fifth separation distance and the sixth separation distance are between 2 mm and 4 mm.

6. The upper surface is a first tapered section connected to the central edge, the first edge, and the first end point, the first tapered section tapering from the central edge to the first end point; 4. The diffuser of claim 3, comprising: a second tapered section connected to the central edge, the first edge, and the second terminal point, the second tapered section tapering from the central edge to the second terminal point.

7. The diffuser of claim 6 , wherein the first tapered section has a linear slope and the second tapered section has a linear slope.

8. a right edge parallel to the second axis; a left edge parallel to the second axis; Furthermore, the right edge and the left edge are equidistant from the central edge, and the distance between the right edge and the first end point is the same as the distance between the left edge and the second end point; 7. The diffuser of claim 6, wherein the third separation distance includes a seventh separation distance at an intersection of the first edge and the right edge, the third separation distance includes an eighth separation distance at an intersection of the first edge and the left edge, the fourth separation distance is greater than the seventh separation distance, and the fourth separation distance is greater than the eighth separation distance.

9. The diffuser of claim 8 , wherein the seventh separation distance is greater than the fifth separation distance and the eighth separation distance is greater than the sixth separation distance.

10. The diffuser of claim 9, wherein the seventh separation distance and the eighth separation distance are between 3 mm and 5 mm.

11. 9. The diffuser of claim 8, wherein the fourth separation distance is 10 mm, the fifth and sixth separation distances are 2.14 mm, and the seventh and eighth separation distances are 3.7 mm.

12. the first tapered section includes a fourth tapered section connected to the central edge, the first edge, and the right edge, the fourth tapered section tapering from the central edge to the right edge; the first tapered section includes a fifth tapered section connected to the right edge, the first edge, and the first end point, the fifth tapered section tapering from the right edge to the first end point; the second tapered section includes a sixth tapered section connected to the central edge, the first edge, and the left edge, the sixth tapered section tapering from the central edge to the left edge; 9. The diffuser of claim 8, wherein the second tapered section includes a seventh tapered section connected to the first edge, the left edge, and the second terminal point, the seventh tapered section tapering from the left edge to the second terminal point.

13. The diffuser of claim 2 , wherein the upper surface comprises a front tapered section connected to the first edge and the wall, the front tapered section tapering from the first edge to the wall.

14. The diffuser of claim 13 , wherein the upper surface comprises a plurality of tapered sections.

15. the plurality of tapered sections: an aft section connected to the inlet and the aft edge, the aft section tapering from the inlet to the aft edge; a right side section connected to the rear section at the rear edge and further connected to an intermediate right side edge, at least a portion of the right side section tapering from the rear edge to the intermediate right side edge; a left side section connected to the rear section at the rear edge and further connected to an intermediate left side edge, at least a portion of the left side section tapering from the rear edge to the intermediate left side edge; The diffuser of claim 14 further comprising:

16. 1. A method of manufacturing a diffuser, comprising: defining an inlet on a first axis, a second axis, and a third axis, the first axis, the second axis, and the third axis being perpendicular to one another; connecting the wall of the diffuser to the inlet by connecting a top surface of the diffuser to the inlet and to the wall such that the top surface extends from the inlet to the wall of the diffuser, and by connecting a bottom surface of the diffuser to the inlet and to the wall such that the bottom surface extends from the inlet to the wall, wherein the bottom surface extends along a plane parallel to a plane defined by the first axis and the second axis; connecting the wall to the entrance by connecting a right surface extending from the entrance to the wall, the right surface being further connected to the bottom surface and the top surface, and by connecting a left surface extending from the entrance to the wall, the left surface being further connected to the bottom surface and the top surface, the left surface being further connected to the bottom surface and the top surface such that the right surface and the left surface define a separation distance between the bottom surface and the top surface, the separation distance being parallel to the third axis such that the separation distance at the entrance is greater than the separation distance at the wall; A method comprising:

17. 17. The method of claim 16, wherein connecting the upper surface to the inlet and the wall further comprises providing a first edge separating the upper surface into a rear section and a front section, such that a difference in separation distance at the inlet and the first edge is less than a difference in separation distance at the first edge and the wall.

18. 18. The method of claim 17, wherein coupling the top surface to the inlet and the wall further comprises tapering the separation distance from the first edge to the wall.

19. 19. The method of claim 18, wherein the separation distance of the top surface from the first edge to the wall is between 2 mm and 12 mm.

20. 1. A reactor system comprising: a material source configured to provide a material to be deposited on the substrate; a diffuser fluidly connected to the material source, the diffuser having a top surface and a bottom surface; a cross-flow reaction chamber fluidly connected to the diffuser, the cross-flow reaction chamber configured to deposit the material onto a surface of a substrate; a wall fluidly connected to the diffuser and the crossflow reaction chamber, wherein the material flowing from the material source through the diffuser flows through the wall into the crossflow reaction chamber; Equipped with The reactor system, wherein the top and bottom surfaces are separated by a separation distance, the separation distance tapering from an inlet connected to the material source to the wall.

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