Patent Publication Number: US-2022238312-A1

Title: Showerhead insert for uniformity tuning

Description:
CLAIM OF PRIORITY 
     This application claims the benefit of priority to U.S. Patent Application Ser. No. 62/854,193, filed on May 29, 2019, which is incorporated by reference herein in its entirety. 
    
    
     FIELD 
     The present disclosure relates to a showerhead insert and in some examples to a showerhead insert for a quad station process module (QSM) in semiconductor manufacturing applications. 
     BACKGROUND 
     The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. 
     Plasma systems are used to control plasma processes. A plasma system typically includes multiple radio frequency (RF) sources, an impedance match, and a plasma reactor. A workpiece (for example, a substrate or wafer) is placed inside the plasma chamber and plasma is generated within the plasma chamber to process the workpiece. It is often a key production goal for the workpiece to be processed in a uniform or repeatable manner. To this end, it can be important that electromagnetic field uniformity during wafer processing be achieved and consistently maintained. This can be particular challenging in asymmetric plasma chambers, for example. 
     SUMMARY 
     The present disclosure relates generally to a showerhead insert (also called a showerhead liner), and in some applications to a showerhead insert for a QSM. One or more of the processing modules or stations in a QSM may be asymmetric. A shaped insert above the showerhead is used to alter the electric fields near the wafer processing area and in some examples to correct or improve asymmetry in a QSM processing module. In some embodiments, an insert for a showerhead in a processing chamber is provided. An example showerhead insert for may comprise: a body shaped and configured to associate with the showerhead in the processing chamber, the body having at least one surface thereon that comprises a material for supporting electromagnetic coupling when energized by an RF power source; and a formation in the body sized to accommodate a stem of the showerhead. 
     In some examples, a configuration of the insert is selected to affect or correct an asymmetry of an electromagnetic field or plasma generated within the processing chamber in use. 
     In some examples, the at least one surface of the insert includes a rounded or curved portion. 
     In some examples, the asymmetry is caused at least in part by a disconformity between a wall of the processing chamber, or an adjacent processing chamber, and a substrate-support assembly disposed therein, and wherein a profile of the rounded or curved portion of the at least one surface bounding the chamber substantially matches a profile of the substrate-support assembly. 
     In some examples, the body is an annular body, the formation in the body including an annulus of the annular body sized to accommodate the stem of the showerhead. 
     In some examples, the at least one surface extends into the annulus of the annular body. 
     In some examples, the at least one surface does not extend into the annulus of the annular body. 
     In some examples, the at least one surface covers a substantial entirety of the body of the insert. 
     In some examples, the least one surface of the insert is aligned in use with a wall or surface of the processing chamber or the showerhead. 
     In some examples, the least one surface of the insert is planar and in use is inclined in relation to a wall or surface of the processing chamber or the showerhead. 
     In some examples, the at least one surface of the insert modifies an internal geometry or volume of the processing chamber. 
     In some examples, the insert induces a substantially uniform electromagnetic field around a substrate-support assembly disposed within the processing chamber. 
     In some examples, the insert induces a substantially non-uniform electromagnetic field around a substrate-support assembly disposed within the processing chamber. 
     In some examples, the showerhead insert can be adjusted, repositioned, or mechanically modulated in shape or position to alter the electromagnetic field profile within the processing chamber. 
     In some embodiments, an insert for a showerhead in a processing chamber comprises a body shaped and configured to associate with the showerhead in the processing chamber, the body having at least one surface thereon that comprises a material for supporting electromagnetic coupling when energized by an RF power source; a formation in the body sized to accommodate a stem of the showerhead; the showerhead insert including an upper surface through which the stem of the showerhead can pass when the showerhead insert is fitted to the showerhead; and the showerhead insert including a shaped, recessed lower surface including at least one curved profile disposed adjacent, at least in part, a surface of the showerhead. 
     In some examples, the body is an annular body, the formation in the body including an annulus of the annular body sized to accommodate the stem of the showerhead. 
     In some examples, the shaped, recessed lower surface of the showerhead insert defines, at least in part, a free volume sized and configured to accept and surround a substantial entirety of the showerhead. 
     In some examples, a spatial distance between the shaped, recessed lower surface of the showerhead and an upper surface of the showerhead insert increases from a radially inner location to a radially outer location of the showerhead insert. 
     In some examples, the upper surface of the showerhead insert is substantially flat. 
     In some examples, a spatial distance between a wall of the annulus of the annular body and the stem of the showerhead increases from a vertically higher location to a vertically lower location of the showerhead insert. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Some embodiments are illustrated by way of example and not limitation in the views of the accompanying drawing: 
         FIGS. 1-4  show schematic views of substrate processing tools in which an example showerhead insert of the present disclosure may be deployed. 
         FIG. 5  is a schematic view of an example substrate processing tool including a quad station process module in which an example showerhead insert of the present disclosure may be deployed. 
         FIGS. 6A-6C  depict an example electromagnetic field strength around a pedestal, according to an example embodiment. 
         FIG. 7  shows a simplified example of a plasma-based processing chamber, which can include a substrate-support assembly comprising an electrostatic chuck (ESC), having water-cooled components that may be used with the disclosed subject matter: 
         FIG. 8  shows a sectional side view of a showerhead, according to an example embodiment. 
         FIG. 9  shows a sectional side view of a showerhead to which a showerhead insert has been fitted, according to an example embodiment. 
         FIGS. 10A-10C  show RF current paths, according to example embodiments. 
         FIGS. 11A-11B  show top and underside pictorial views of a showerhead insert, according to an example embodiment. 
     
    
    
     DESCRIPTION 
     The description that follows includes systems, methods, techniques, instruction sequences, and computing machine program products that embody illustrative embodiments of the present disclosure. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of example embodiments. It will be evident, however, to one skilled in the art that the present disclosure may be practiced without these specific details. 
     A portion of the disclosure of this patent document may contain material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever. The following notice applies to any data as described below and in the drawings that form a part of this document: Copyright Lam Research Corporation, 2019, All Rights Reserved. Although a showerhead insert is described herein with particular reference to a QSM, this application is not limiting and, unless the context indicates otherwise, other applications are possible and are covered by the appended claims. 
     A substrate processing system may be used to perform deposition, etching and/or other treatment of substrates such as semiconductor wafers. During processing, a substrate is arranged on a substrate support in a processing chamber of the substrate processing system. During etching or deposition, gas mixtures including one or more etch gases or gas precursors, respectively, are introduced into the processing chamber and plasma may be struck to activate chemical reactions. 
     The substrate processing system may include a plurality of substrate processing tools arranged within a fabrication room. Each of the substrate processing tools may include a plurality of process modules. Typically, a substrate processing tool includes up to six process modules. 
     Referring now to  FIG. 1 , a top-down view of an example substrate processing tool  100  is shown. The substrate processing tool  100  includes a plurality of process modules  104 . In some examples, each of the process modules  104  may be configured to perform one or more respective processes on a substrate. Substrates to be processed are loaded into the substrate processing tool  100  via ports of a loading station of an equipment front end module (EFEM)  108  and then transferred into one or more of the process modules  104 . For example, a substrate may be loaded into each of the process modules  104  in succession. Referring now to  FIG. 2 , an example arrangement  200  of a fabrication room  204  including a plurality of substrate processing tools  208  is shown. 
       FIG. 3  shows a first example configuration  300  including a first substrate processing tool  304  and a second substrate processing tool  308 . The first substrate processing tool  304  and the second substrate processing tool  308  are arranged sequentially and are connected by a transfer stage  312 , which is under vacuum. As shown, the transfer stage  312  includes a pivoting transfer mechanism configured to transfer substrates between a vacuum transfer module (VTM)  316  of the first substrate processing tool  304  and a VTM  320  of the second substrate processing tool  308 . However, in other examples, the transfer stage  312  may include other suitable transfer mechanisms, such as a linear transfer mechanism. In some examples, a first robot (not shown) of the VTM  316  may place a substrate on a support  324  arranged in a first position, the support  324  is pivoted to a second position, and a second robot (not shown) of the VTM  320  retrieves the substrate from the support  324  in the second position. In some examples, the second substrate processing tool  308  may include a storage buffer  328  configured to store one or more substrates between processing stages. 
     The transfer mechanism may also be stacked to provide two or more transfer systems between the substrate processing tools  308  and  304 . Transfer stage  312  may also have multiple slots to transport or buffer multiple substrates at one time. 
     In the configuration  300 , the first substrate processing tool  304  and the second substrate processing tool  308  are configured to share a single equipment front end module (EFEM)  332 . 
       FIG. 4  shows a second example configuration  400  including a first substrate processing tool  404  and a second substrate processing tool  408  arranged sequentially and connected by a transfer stage  412 . The configuration  400  is similar to the configuration  300  of  FIG. 3  except that in the configuration  400 , the EFEM  332  is eliminated. Accordingly, substrates may be loaded into the first substrate processing tool  404  directly via airlock loading stations  416  (e.g., using a storage or transport carrier such as a vacuum wafer carrier, front opening unified pod (FOUP), an atmospheric (ATM) robot, etc., or other suitable mechanisms). 
     A showerhead insert of the present disclosure may be deployed in quad station process modules (QSMs). In some examples, as shown in  FIG. 5 , a quad station process module  500  is provided. A QSM  500  includes four process modules  508  disposed at respective corner stations in the substrate processing tool  500 . Each process module  508  may itself include four generally square corners, as shown. Each process module  508  has chamber walls enclosing four wafer processing stations  518  that may include generally round support pedestals, as shown. While various configurations of the process modules  508  are possible, in some examples the location of a round pedestal supporting a round wafer in a square (or non-matching) corner of a process module  508  is asymmetric and provides an asymmetric environment during wafer processing. This can present a significant challenge to electromagnetic uniformity and is at least one issue that embodiments of the present disclosure seek to address. 
     In this regard, reference is made to  FIGS. 6A-6C .  FIG. 6A  shows a representation of varying electromagnetic field strength surrounding a round wafer processing station  518  in one of the four processing modules  508  of a QSM  500 . The processing module  508  may have a chamber in an RF path (see for example,  FIGS. 10A-10C  below) that includes corners or other shapes. In the illustrated example, a wafer processing station  518  is not necessarily symmetric about the center of the wafer due to differing boundary conditions that may include a single chamber corner  604 , a spindle region  602 , and adjacent processing stations  608 . The curved configuration of the rounded chamber corner  604  may substantially match the curved profile of the wafer processing station  518 , but the adjacent stations  608  and spindle region  602  do not match the rounded pedestal profile. This uneven configuration can present an asymmetry in chamber geometry and cause the creation of an asymmetric electromagnetic field, as shown by contour lines  610 . The asymmetric field is discussed further below. 
     Three radial positions around an example processing station  518  are shown in  FIG. 6B  at 0°, 45°, and 225° positions, respectively. The example processing station includes a chamber corner and spindle region as shown. Corresponding electromagnetic field strengths are shown for each of these three radial positions in the graph of  FIG. 6C . The shape of the field strength line  606  indicates that the electromagnetic field strength fluctuates around the periphery of the pedestal  518 . This may be caused primarily by the asymmetric geometry and environment of the processing module  508 . This uneven or variable electromagnetic field distribution can present a significant challenge in obtaining uniform processing conditions across the surface of a wafer. 
     Returning to  FIG. 5 , the QSM  500  includes transfer robots  502  and  504 , referred to collectively as transfer robots  502 / 504 . The processing tool  500  is shown without mechanical indexers for example purposes. In other examples, the respective process modules  508  of the tool  500  may include mechanical indexers. A VTM  516  and an EFEM  510  may each include one of the transfer robots  502 / 504 . The transfer robots  502 / 504  may have the same or different configurations. In some examples, the transfer robot  502  is shown as having two arms, with each arm having two vertically stacked end effectors. The robot  502  of the VTM  516  selectively transfers substrates to and from the EFEM  510  and between the process modules  508 . The robot  504  of the EFEM  510  transfers substrates into and out of the EFEM  510 . In some examples, the robot  504  may have two arms, each arm having a single end effector or two vertically stacked end effectors. 
     A system controller  506  may control various operations of the illustrated substrate processing tool  500  and its components including, but not limited to, operation of the robots  502 / 504 , rotation of the respective indexers of the process modules  508 , and so forth. 
     The tool  500  is configured to interface with, for example, each of the four process modules  508 . Each process module  508  may have a single load station accessible via a respective slot  512 . In this example, sides  514  of the VTM  516  are not angled (i.e., the sides  514  are substantially straight or planar). Other arrangements are possible. In the illustrated manner, two of the process modules  508 , each having a single load station, are coupled to each of the sides  514  of the VTM  516 . Accordingly, the EFEM  510  may be arranged at least partially between two of the process modules  508 . 
     During substrate processing in a process module  508 , processing gases enter the module to assist in creating a plasma, for example. The gases then exit the process module  508 . The expulsion of exhaust gases may be performed by a vacuum or exhaust line. One of more exhaust lines may be situated underneath each processing module  508  and be connected to a vacuum source to expel gases from the process module  508 . 
     With reference now to  FIG. 7 , a simplified example of a plasma-based processing tool  700  is shown.  FIG. 7  is shown to include the plasma-based processing chamber  701 A in which a showerhead electrode (or for brevity simply called a showerhead)  703  and a substrate-support assembly  707 A are disposed. The substrate-support assembly  707 A may include a pedestal of the type discussed above. Typically, the substrate-support assembly  707 A provides a substantially-isothermal surface and may serve as both a heating element and a heat sink for a substrate  705 . The substrate-support assembly  707 A may comprise an ESC in which heating elements are included to aid in processing the substrate  705 , as described above. The substrate  705  may be a wafer comprising elemental semiconductors (e.g., silicon or germanium), a wafer comprising compound elements (e.g., gallium arsenide (GaAs) or gallium nitride (GaN)), or variety of other substrate types including conductive, semi conductive, and non-conductive substrates. The plasma-based processing chamber may have several water-cooled components. 
     In operation, the substrate  705  is loaded through a loading port  709  onto the substrate-support assembly  707 A. A gas line  713  supplies one or more process gases to the showerhead electrode  703 . In turn, the showerhead electrode  703  delivers the one or more process gases into the plasma-based processing chamber  701 A. A gas source  711  to supply the one or more process gases is coupled to the gas line  713 . An RF power source  715  is coupled to the showerhead electrode  703  or to the substrate-support assembly  707 A (see  FIGS. 10A-10C , for example). 
     In operation, the plasma-based processing chamber  701 A is evacuated by a vacuum pump  717 . RF power is capacitively coupled between the showerhead electrode  703  and a lower electrode (not shown explicitly) contained within or on the substrate-support assembly  707 A. The substrate-support assembly  707 A is typically supplied with two or more RF frequencies. For example, in various embodiments, the RF frequencies may be selected from at least one frequency at about 1 MHz, 2 MHz, 13.56 MHz, 27 MHz, 60 MHz, and other frequencies as desired. A coil to block or partially block a particular RF frequency can be designed as needed. Therefore, particular frequencies discussed herein are provided merely for ease in understanding. The RF power is used to energize the one or more process gases into a plasma in the space between the substrate  705  and the showerhead electrode  703 . The plasma can assist in depositing various layers (not shown) on the substrate  705 . In other applications, the plasma can be used to etch device features into the various layers on the substrate  705 . As noted above, the substrate-support assembly  707 A may have heaters (not shown) incorporated therein. RF power is coupled through at least the substrate-support assembly  707 A. 
       FIG. 8  shows a sectional side view of a showerhead  802 , for example a showerhead  703  as discussed above. The illustrated showerhead  802  is energized by an external RF power source to create a number of example electric field contours  804  around it. It will be seen that the distribution pattern of the field contours  804  on the left of the pedestal  802  is different to the pattern on the right of the pedestal  802 . The field contours on the left are more dispersed than their corresponding field contours on the right of the pedestal. This is an example of a non-uniform or asymmetric electromagnetic field. This processing chamber condition can significantly affect the creation of consistent semiconductor formations on the surface of a wafer. 
       FIG. 9  shows the showerhead  802  to which an annular showerhead insert (also called a showerhead liner)  902  has been fitted. In this example, the showerhead insert has been fitted around the showerhead stem  906 . Other arrangements are possible, for example by the insert  902  being supported by a wall of a processing chamber in which it is being used. Here, it will be noted that the distribution pattern of the field contours  904  is substantially the same on both the left and right sides of the showerhead  802 . The showerhead insert  902  can provide an electromagnetic boundary condition which results in a more uniform electromagnetic field around the showerhead  802 . Since the plasma in a processing chamber is created by an electromagnetic field generated in it, the resulting plasma is generally more uniform in distribution and effect. 
     In some examples, based on certain factors such as a processing chamber pressure, or a processing frequency, or a pedestal-to-showerhead gap, a gas composition, and other process parameters, the profile of a chamber surface (such as upper chamber wall, for example) can be configured by a showerhead insert. The size, shape and/or configuration of a showerhead insert may be selected and optimized to create or improve a more uniform and consistent formation creation on a wafer surface during processing. The use of a suitably shaped showerhead liner can enable consistent chamber conditions and allow wafer formation to be controlled and varied as desired. 
     In some examples, a showerhead insert  902  can induce a reduction in an undesired electromagnetic field above a showerhead which may otherwise ignite a parasitic plasma within a processing chamber. An appropriate insert shape or configuration can reduce the inductance of the RF path from the showerhead to the chamber walls which may reduce or alter a voltage of the showerhead relative to the chamber or a “ground” reference. A processing chamber geometry can be selected and adapted to impart a variety of processing conditions based on wafer processing needs. 
     In this regard, reference is now made to  FIGS. 10A-10C . In some instances, it may be desired to correct an asymmetry in a wafer processing chamber such as in a wafer processing module  508 , for example. In some examples, a specific asymmetry in a processing chamber may actually be desired. In each view, a wafer processing chamber  1002  is shown. The wafer processing chamber  1002  may be included in a processing module  508  in a QSM, for example. The processing chamber  1002  may be enclosed and defined by chamber walls  1006  including an upper chamber wall  1008  having an initially flat or unaltered surface or configuration. This configuration is shown in  FIG. 10A . 
     Each processing chamber  1002  includes a substrate-support assembly  1004  which may include a round shaped pedestal  518  for example ( FIG. 5-6 ), or  107 A ( FIG. 7 ). Each processing chamber  1002  further includes a showerhead  1010 , such as a showerhead  802  ( FIG. 8-9 ), or  703  ( FIG. 7 ). Each processing chamber  1002  is powered by an RF power source  1012  (for example, RF power source  715  in  FIG. 7 ) which can generate an electromagnetic field within each chamber  1002  to form a plasma  1018  between each substrate-support assembly  1004  and showerhead  1010 . The arrows  1014  in each view of  FIGS. 10A-10C  show an RF current path generating an electromagnetic field in each processing chamber  1002 . The RF current path proceeds from the RF power source  1012 , through the plasma  1018  and back through the chamber walls  1006  and  1008  to the RF power source  1012 . 
     A shape and strength of an electromagnetic field within the processing chamber  1002  may be configured by a showerhead insert. The showerhead insert may be configured appropriately to induce or adjust a symmetry or asymmetry of the electromagnetic field or plasma. In some examples, a chamber  1002  such as illustrated in  FIG. 10A  includes a pedestal-fed grounded showerhead  1010  which generates an RF current path, as shown. 
     In other examples, a chamber  1002  such as illustrated in  FIG. 10B  may include a pedestal-fed grounded showerhead  1010  and a symmetric annular showerhead insert  1016 . The showerhead insert  1016  affects the RF current path  1014  as shown and alters the electromagnetic field in a manner to provide the desired symmetry which may beneficially impact a wafer supported by the substrate-support assembly  1004 . In this example, the electromagnetic field is symmetric. 
     In further examples, a chamber  1002  such as illustrated in  FIG. 10C  includes a pedestal-fed grounded showerhead  1010  and an asymmetric showerhead insert  1016 . The asymmetric showerhead insert  1016  affects the RF current path  1014  unequally as shown could be used to compensate for other asymmetries which may be present in a given RF plasma chamber such as a QSM  500 . In this example, the electromagnetic field is asymmetric however it could be used to compensate for other asymmetries. 
       FIGS. 11A-11B  provide top and underside pictorial views of an example configuration of a showerhead insert  902  for configuring an electromagnetic field within a processing chamber. With reference to  FIGS. 11A-11B  and  FIG. 9 , the showerhead insert  902  comprises a body  908  shaped and configured to associate with the showerhead in the processing chamber, for example a showerhead  802  in  FIG. 9 . The body  908  has one or more surfaces  910  that comprise a material for supporting electromagnetic coupling when energized by an RF power source. A formation  912  in the body  908  is sized to accommodate a stem of the showerhead, for example the showerhead stem  906  in  FIG. 9 . The showerhead insert  902  includes an upper surface  914  through which the stem (for example stem  906 ) of the showerhead can pass when the showerhead insert  902  is fitted to the showerhead (for example, showerhead  802 ). In some examples, the upper surface  914  of the showerhead insert  902  is substantially flat, as shown. 
     The showerhead insert  902  includes a shaped, recessed lower surface  916 , also visible in sectional view in  FIG. 9 . The lower surface  916  includes at least one curved profile  918  disposed adjacent, at least in part, a surface of the showerhead  802 . This may be more clearly seen in  FIG. 9 . In some examples, the body  908  of the showerhead insert  902  is an annular body, and the formation  912  in the body  908  includes an annulus  912  of the annular body  908 . The annulus  912  is sized to accommodate the stem  906  of the showerhead  802 , as shown in  FIG. 9 , for example. 
     The shaped, recessed lower surface  916  of the showerhead insert  902  defines, at least in part, an interior or free volume  920  sized and configured to accept and surround a substantial entirety of the showerhead  802 , as shown more clearly in  FIG. 9 . In  FIG. 9 , it will be seen that in the illustrated example a spatial distance between the shaped, recessed lower surface  916  of the showerhead insert  902  and an upper surface  924  of the showerhead  802  increases from a radially inner location  922  to a radially outer location  926  of the showerhead insert  802  i.e. in the direction of arrow  930 . In some examples, a spatial distance between a wall of the annulus  912  of the annular body  908  and the stem  906  of the showerhead  802  increases from a vertically higher location to a vertically lower location of the showerhead insert  902  i.e. in the direction of arrow  932 . 
     Other showerhead insert  902  configurations are possible. Some example embodiments of a showerhead insert  902  may have one or more curved or rounded field-affecting surfaces. Other examples may further include one or more substantially planar field-affecting surfaces. A surface of a showerhead insert  902  may be aligned in use with a chamber wall or showerhead or be inclined with respect to these elements. 
     Although examples have been described with reference to specific example embodiments or methods, it will be evident that various modifications and changes may be made to these embodiments without departing from the broader scope of the embodiments. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense. The accompanying drawings that form a part hereof, show by way of illustration, and not of limitation, specific embodiments in which the subject matter may be practiced. The embodiments illustrated are described in sufficient detail to enable those skilled in the art to practice the teachings disclosed herein. Other embodiments may be utilized and derived therefrom, such that structural and logical substitutions and changes may be made without departing from the scope of this disclosure. This Detailed Description, therefore, is not to be taken in a limiting sense, and the scope of various embodiments is defined only by the appended claims, along with the full range of equivalents to which such claims are entitled. 
     Such embodiments of the inventive subject matter may be referred to herein, individually and/or collectively, by the term “invention” merely for convenience and without intending to voluntarily limit the scope of this application to any single invention or inventive concept if more than one is in fact disclosed. Thus, although specific embodiments have been illustrated and described herein, it should be appreciated that any arrangement calculated to achieve the same purpose may be substituted for the specific embodiments shown. This disclosure is intended to cover any and all adaptations or variations of various embodiments. Combinations of the above embodiments, and other embodiments not specifically described herein, will be apparent to those of skill in the art upon reviewing the above description.