Abstract:
A counterflow mixing device for a process chamber is disclosed, comprising an injection tube that introduces a fluid in a manner counter to a flow of a post-plasma gas mixture traveling downward from a plasma source. The invention allows for proper mixing of the fluid as well as avoiding recombination of generated ions and radicals.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 62/253,016, which was filed on Nov. 9, 2015 and is incorporated herein by reference. 
     
    
     FIELD OF INVENTION 
       [0002]    The present disclosure generally relates to semiconductor processing tools. More particularly, the disclosure relates to a low pressure mixer of gas travelling from a small flow tube into a large flow tube. 
       BACKGROUND OF THE DISCLOSURE 
       [0003]    Certain cleaning or other low vacuum processes require the mixing of a gas/vapor between a plasma source (PS) and the wafer processing chamber. For example, a NF 3 /NH 3  process can be used to remove SiO 2  from Si. In this process, Ar is mixed with NF 3  prior to being injected into a top PS. 
         [0004]    Plasma is produced in the PS, which, in addition to some ionization of the Ar/NF 3  mix, produces Fluorine radicals that are highly reactive. A relatively large diameter (˜25 mm to 50 mm diameter) with a relatively short length (˜100 mm to 300 mm) conductance tube is used between the PS and the chamber in order to minimize recombination of the Fluorine radicals. 
         [0005]    In the example process, NH 3  cannot be mixed with the Ar/NF 3  prior to the PS because disassociation of the NH 3  is undesirable. The NH 3  is typically injected into a side of the PS to chamber conductance tube. However, injection into the side of conductance tube that has a low length to diameter ratio (˜2:1 to 12:1) will not provide effective mixing and thus, will lead to an uneven distribution of the NH 3  on the wafer being processed. Uniformity of the distribution of the NH 3  over the wafer is required for a robust and repeatable process. 
         [0006]    Issues arising in the example process are attributable in part to: (1) insufficient diffusion time to ensure complete mixing; and (2) preservation of streamlines at required pressures. Mixing time is a function of a length and a diameter of a tube in which the gases flow viscously at a given velocity. To achieve complete mixing the tube must be long enough so that the time of the viscous flow from inlet to outlet exceeds the time for diffusion across the diameter. Generally, the tube length to tube diameter ratio may exceed 20:1 to achieve complete mixing. However, given the fact that the diameter must be large to preserve the formed F radicals, a 20:1 length to diameter ratio may not be feasible. 
         [0007]    Streamlines are capable of affecting mixing of gases. At particular pressures, if streamlines of a flowing gas remain undisturbed, a flow of introduced gases may not be able to be properly mixed. For example, pressures resulting from gases leaving the PS range between 1 to 10 Torr. At these pressures, the flow of gases is generally laminar. 
         [0008]    As a result, it is desired to create a system in which a gas is sufficiently mixed as well as minimization of radical/ion recombination from a plasma source. 
       SUMMARY OF THE DISCLOSURE 
       [0009]    In accordance with at least one embodiment of the invention, an apparatus is disclosed that comprises in part a plasma source, a conical member, a counterflow injector, and a configurable orifice plate. The conical member is configured to receive a first gas in a first direction and promotes a mixing of the first gas and the second gas. The counter flow injector introduces a second gas in a second direction, such that the first direction is opposite to the second direction. The apparatus includes a configurable orifice plate mounted at the bottom of the conical member, the adjustable orifice plate defining an opening through which the first gas and the second gas pass through, such that changing a size of the opening of the configurable orifice plate changes an extent of the mixing of the first gas and the second gas. 
         [0010]    In accordance with at least one embodiment of the invention, a reaction system is disclosed. The reaction system comprises: a plasma source, the plasma source generating a first gas; a conical member, the conical member configured to receive the first gas in a first direction; a counter flow injector, the counter flow injector introducing a second gas in a second direction, wherein the first direction is opposite to the second direction; an adjustable orifice plate mounted at the bottom of the conical member, the adjustable orifice plate defining an opening through which the plasma gas and the first fluid pass through; a reaction chamber that receives the first gas and the second gas, the reaction chamber comprising: a housing defining a plenum to receive the first gas and the second gas; and a showerhead with a plurality of holes for passing the first gas and the second gas onto a substrate to be processed; wherein the conical member promotes a mixing of the first gas and the second gas; and wherein adjusting a size of the opening of the adjustable orifice plate changes an extent of the mixing of the first gas and the second gas. 
         [0011]    For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been described herein above. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught or suggested herein without necessarily achieving other objects or advantages as may be taught or suggested herein. 
         [0012]    All of these embodiments are intended to be within the scope of the invention herein disclosed. These and other embodiments will become readily apparent to those skilled in the art from the following detailed description of certain embodiments having reference to the attached figures, the invention not being limited to any particular embodiment(s) disclosed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
         [0013]    These and other features, aspects, and advantages of the invention disclosed herein are described below with reference to the drawings of certain embodiments, which are intended to illustrate and not to limit the invention. 
           [0014]      FIG. 1  is a cross-sectional view of a reaction system in accordance with at least one embodiment of the invention. 
           [0015]      FIG. 2  is a cross-sectional view of a reaction system in accordance with at least one embodiment of the invention. 
           [0016]      FIG. 3  is a top perspective view of a component of the reaction system in accordance with at least one embodiment of the invention. 
           [0017]      FIG. 4  is a top perspective view of a component of the reaction system in accordance with at least one embodiment of the invention. 
           [0018]      FIG. 5  is a bottom perspective view of a component of the reaction system in accordance with at least one embodiment of the invention. 
           [0019]      FIG. 6  is a perspective view of a component of the reaction system in accordance with at least one embodiment of the invention. 
       
    
    
       [0020]    It will be appreciated that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of illustrated embodiments of the present disclosure. 
       DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0021]    Although certain embodiments and examples are disclosed below, it will be understood by those in the art that the invention extends beyond the specifically disclosed embodiments and/or uses of the invention and obvious modifications and equivalents thereof. Thus, it is intended that the scope of the invention disclosed should not be limited by the particular disclosed embodiments described below. 
         [0022]      FIG. 1  illustrates a cross-sectional view of a reaction system  100  in accordance with at least one embodiment of the invention. The reaction system  100  comprises a plasma source. The plasma source (“PS”, illustrated as “Plasma Gas Source” in  FIG. 1 ) generates a first gas  110  from a gaseous mixture using RF energy to excite gas. For example, the plasma source may receive a mixture of Argon and NF 3 , WF 6 , or other fluorine containing gas. The plasma source may partially ionize the gaseous mixture to form a glow discharge plasma and in the process form F radicals that are highly chemically reactive. Examples of PSs include the ASTRON® Paragon from MKS Instruments, Inc. and the Litmas from Advanced Energy Industries, Inc. Plasma sources may also be custom designed and built for the application. 
         [0023]    The first gas  110  flows and passes through a seal  120  to a conical funnel portion  130 . In one embodiment of the invention, the seal  120  may have a diameter of  50  mm. The conical funnel portion  130  is made of suitable material such as: aluminum; anodized aluminum; plasma electrolytic oxide (PEO) coated aluminum; alumina; aluminum nitride; silicon carbide; nickel; nickel plated aluminum; or nickel-plated stainless steel, for example. The conical funnel portion  130  may include a hole in which a counter flow injector  140  is disposed. The counter flow injector  140  comprises a small injection tube that turns upward toward the PS. The counter flow injector  140  may be made of suitable material such as nickel or nickel-plated stainless steel. Other materials that may be used include: anodized aluminum base material; PEO coated aluminum base material; ALD Al 2 O 3  coated aluminum base material; aluminum oxide ceramic; aluminum nitride ceramic; or silicon carbide, for example. 
         [0024]    The counter flow injector  140  introduces a second gas  150  that flows counter to the first gas  110  flowing down from PS. The fluid introduced through the counter flow injector  140  will flow upwards into the gas flowing down from the PS until the first gas  110  causes the second gas  150  to flow back downwards. When the fluid turns back, a streamline from the counter flow injector  140  is not preserved and in essence, mixture of the injected fluid into the plasma gas takes place. 
         [0025]    The second gas  150  is first generated by an injector gas source  160 . The injector gas source  160  may provide ammonia (NH 3 ), amines, or hydrogen (H 2 ), for example. For example, NH 3  gas may flow through the counter flow injector  140  and mix with the Argon and NF 3  post-plasma mixture. From the injector gas source  160 , the second gas  150  then passes through a set of valves  170 . The set of valves  170  may be valves manufactured by Swagelok Co., for example. 
         [0026]    The counter flow injector  140  also does not provide a significant blockage of a main tube defined in part by the seal  120 . By not providing a significant blockage of the main tube, recombination of the F radicals can be minimized within the gas mixture and on the walls. 
         [0027]    In an alternative embodiment of the invention, a plate  180  may be placed above the counter flow injector  140  to enhance the spread of the second gas  150  radially. As illustrated in  FIG. 3 , the plate  180  may be supported by three thin radial arms  190  to minimize the flow disruption. The plate  180  also shields the counter flow injector  140  from fluorine radicals that would otherwise recombine and heat the counter flow injector  140  beyond the maximum allowable temperature of the part. The plate  180  and the radial arms  190  may be made from a high temperature capable and high thermal conductivity material such as aluminum nitride or silicon carbide. This allows use of more easily fabricated materials such as stainless steel and aluminum for the counter flow injector  140  that do not have sufficient temperature capability to withstand the fluorine recombination on the surface. 
         [0028]    The gas mixture then proceeds through a configurable orifice plate  200 . By changing the size of the orifice, the configurable orifice plate  200  can change a mixing time of the gas mixture. A greater orifice size of the configurable orifice plate  200  may allow the gas mixture to flow downwards slower compared to a smaller orifice size. The orifice can also be changed to influence residence time above the orifice to control the completeness of a gas phase reaction. In an embodiment where the seal  120  has a diameter of 50 mm, the configurable orifice plate  180  may have a diameter of 9 mm. 
         [0029]    A faster rate of travel means that the gas mixture has lesser residence time in the conical funnel portion  130 , and thus, the injected fluid may not be as well mixed as a gas mixture that has a greater residence time in the conical funnel portion  130 . However, the increased residence time could potentially cause an issue as it may allow for the recombination of generated radicals. As a result, the size of the configurable orifice plate  200  may need to be adjusted accordingly. 
         [0030]    After passing the configurable orifice plate  200 , the gas mixture would travel into a lower tube  210 , where then it would enter into a reaction system  220  having a defined plenum  230 . 
         [0031]    Within the plenum  230 , the gas mixture may spread out along a showerhead plate  240 . The showerhead plate  240  serves the purpose of distributing the gas mixture evenly along a substrate (not pictured). The showerhead plate  240  comprises a plurality of injection holes  250 . 
         [0032]      FIG. 2  provides a zoomed-in view of an upper section of  FIG. 1 . The flow of the first gas  110  is to counter the second gas  150  in accordance with at least one embodiment of the invention. The second gas  150  may be able to spread out through a space defined by the seal  120  in order to allow for sufficient mixing of the injected fluid with the first gas  110 . The combined gas mixture would then flow in a direction defined by arrows  260  into the configurable orifice plate  200  and the lower tube  210 . 
         [0033]      FIGS. 4-5  illustrate a top view and a bottom view of the conical funnel portion  130  and the counter flow injector  140  in accordance with at least one embodiment of the invention. The conical funnel portion  130  may include a top portion  270  that mounts to a portion of the plasma source. The conical funnel portion  130  may also include a bottom portion  280  that interfaces with the configurable orifice plate  200 . Connected to the counter flow injector  140  is a portion of the set of valves  170 . 
         [0034]      FIG. 6  is a perspective view of the configurable orifice plate  200  in accordance with at least one embodiment of the invention. The configurable orifice plate  200  defines an opening  290  in which the gas mixture is allowed to pass through to the lower tube  210 . The size of the opening  290  may be adjusted by switching to a different configurable orifice plate  200 , which then may affect the flow velocity of the gas mixture  260  as well as the residence time of the gas mixture  260 . If the size of the opening  290  is larger, a lower flow velocity of the gas mixture may result in a higher residence time, as well as greater mixing of the introduced fluid  150  into the plasma gas  110 . On the other hand, if the size of the opening  290  is smaller, a greater flow velocity of the gas mixture  260  may result in a smaller residence time, as well as less mixing of the introduced fluid  150  into the plasma gas  110 . 
         [0035]    The particular implementations shown and described are illustrative of the invention and its best mode and are not intended to otherwise limit the scope of the aspects and implementations in any way. Indeed, for the sake of brevity, conventional manufacturing, connection, preparation, and other functional aspects of the system may not be described in detail. Furthermore, the connecting lines shown in the various figures are intended to represent exemplary functional relationships and/or physical couplings between the various elements. Many alternative or additional functional relationship or physical connections may be present in the practical system, and/or may be absent in some embodiments. 
         [0036]    It is to be understood that the configurations and/or approaches described herein are exemplary in nature, and that these specific embodiments or examples are not to be considered in a limiting sense, because numerous variations are possible. The specific routines or methods described herein may represent one or more of any number of processing strategies. Thus, the various acts illustrated may be performed in the sequence illustrated, in other sequences, or omitted in some cases. 
         [0037]    The subject matter of the present disclosure includes all novel and nonobvious combinations and subcombinations of the various processes, systems, and configurations, and other features, functions, acts, and/or properties disclosed herein, as well as any and all equivalents thereof.