Abstract:
A microwave antenna includes a first spiral conduit having a first conduit end, first plural ports in a floor of the first spiral conduit spaced apart along the length of the first spiral conduit; an axial conduit coupled to a rotatable stage; and a distributor waveguide comprising an input coupled to the axial conduit and a first output coupled to the first conduit end.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims benefit of U.S. Provisional Application Ser. No. 62/100,595, filed Jan. 7, 2015 entitled WORKPIECE PROCESSING CHAMBER HAVING A ROTARY MICROWAVE PLASMA ANTENNA WITH SLOTTED SPIRAL WAVEGUIDE, by Michael W. Stowell. 
     
    
     BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The disclosure concerns a chamber or reactor for processing a workpiece such as a semiconductor wafer using microwave power. 
         [0004]    2. Description of Related Art 
         [0005]    Processing of a workpiece such as a semiconductor wafer can be carried out using a form of electromagnetic energy, such as RF power or microwave power, for example. The power may be employed, for example, to generate a plasma, for carrying out a plasma-based process such as plasma enhanced chemical vapor deposition (PECVD) or plasma enhanced reactive ion etching (PERIE). Some processes need extremely high plasma ion densities with extremely low plasma ion energies. This is true for processes such as deposition of diamond-like carbon (DLC) films, where the time required to deposit some type of DLC films can be on the order of hours, depending upon the desired thickness and upon the plasma ion density. A higher plasma density requires higher source power and generally translates to a shorter deposition time. 
         [0006]    A microwave source typically produces a very high plasma ion density while producing a plasma ion energy that is less than that of other sources (e.g., an inductively coupled RF plasma source or a capacitively coupled RF plasma source). For this reason, a microwave source would be ideal. However, a microwave source cannot meet the stringent uniformity required for distribution across the workpiece of deposition rate or etch rate. The minimum uniformity may correspond to a process rate variation across a 300 mm diameter workpiece of less than 1%. The microwave power is delivered into the chamber through a microwave antenna such as a waveguide having slots facing a dielectric window of the chamber. Microwaves propagate into the chamber through the slots. The antenna has a periodic power deposition pattern reflecting the wave pattern of the microwave emission and the slot layout, rendering the process rate distribution non-uniform. This prevents attainment of the desired process rate uniformity across the workpiece. 
         [0007]    A limitation on processing rate is the amount of microwave power that can be delivered to a process chamber without damaging or overheating the microwave window of the chamber. Currently, a microwave window, such as a quartz plate, can withstand only low microwave power levels at which DLC deposition processes can require hours to reach a desired DLC film thickness. The microwave window provides a vacuum boundary of the chamber and is consequently subject to significant mechanical stress, rendering it vulnerable to damage from overheating. 
       SUMMARY 
       [0008]    A reactor for processing a workpiece comprises: a chamber and a workpiece support surface in the chamber; a rotary coupling comprising a stationary stage and a rotatable stage having an axis of rotation; a microwave source coupled to the stationary stage; a rotation actuator; a microwave antenna coupled to the rotation actuator and overlying the workpiece process chamber, the microwave antenna comprising: a floor and a ceiling; a first spiral wall extending between the floor and the ceiling and having a spiral axis corresponding to the axis of rotation, the first spiral wall defining a first spiral conduit having a first conduit end; first plural ports in the floor spaced apart along the length of the first spiral conduit; an axial conduit coupled to the rotatable stage; and a distributor waveguide comprising an input coupled to the axial conduit and a first output coupled to the first conduit end. 
         [0009]    In one embodiment, the microwave antenna further comprises: a second spiral wall extending between the floor and the ceiling and aligned with the spiral axis, the second spiral wall defining a second spiral conduit having a second conduit end; second plural ports in the floor spaced apart along the length of the second spiral conduit; wherein the distributor waveguide further comprises a second output coupled to the second conduit end. 
         [0010]    In one embodiment, the distributor waveguide comprises: a waveguide chamber overlying the microwave antenna and having respective openings aligned with respective ones of the first and second conduit ends; and a first pair of reflective surfaces angled to deflect radiation in the waveguide chamber into the respective openings. In one embodiment, the microwave antenna further comprises: a second pair of reflective surfaces angled to deflect radiation from the respective openings to respective ones of the first and second conduit ends. 
         [0011]    In one embodiment, the first pair of reflective surfaces are oriented at 45 degrees relative to the axis of symmetry. In one embodiment, the second pair of reflective surfaces are oriented at 45 degrees relative to the axis of symmetry. 
         [0012]    In one embodiment, the first and second conduit ends are at a periphery of the microwave antenna, the distributor waveguide spanning a diameter of the microwave antenna. In a related embodiment, the respective openings are displaced from one another by 180 degrees along the periphery. 
         [0013]    In accordance with a further aspect, a microwave source comprises: a floor and a ceiling; a first spiral wall defining a first spiral conduit and extending between the floor and the ceiling and having a spiral axis and a first conduit end; first plural ports in the floor spaced apart along the length of the first spiral conduit; an axial conduit; and, a distributor waveguide comprising an input coupled to the axial conduit and a first output coupled to the first conduit end. 
         [0014]    In one embodiment, the source further comprises: a rotary coupling comprising a stationary stage and a rotatable stage having an axis of rotation coinciding with the spiral axis; a microwave source coupled to the stationary stage, the axial conduit coupled to the rotatable stage; and a rotation actuator coupled to the rotatable stage. 
         [0015]    In one embodiment, the source further comprises: a second spiral wall extending between the floor and the ceiling and aligned with the spiral axis, the second spiral wall defining a second spiral conduit having a second conduit end; second plural ports in the floor spaced apart along the length of the second spiral conduit; and wherein the distributor waveguide further comprises a second output coupled to the second conduit end. 
         [0016]    In one embodiment, the distributor waveguide comprises: a waveguide chamber having respective openings aligned with respective ones of the first and second conduit ends; and a first pair of reflective surfaces angled to deflect radiation in the waveguide chamber into the respective openings. 
         [0017]    In one embodiment, the source further comprises: a second pair of reflective surfaces angled to deflect radiation from the respective openings to respective ones of the first and second conduit ends. 
         [0018]    In one embodiment, the first pair of reflective surfaces are oriented at 45 degrees relative to the axis of symmetry, and the second pair of reflective surfaces are oriented at 45 degrees relative to the axis of symmetry. 
         [0019]    In one embodiment, the first and second conduit ends are one opposite sides of a periphery of the source. In one embodiment, the respective openings are displaced from one another by 180 degrees along the periphery. 
         [0020]    In accordance with another aspect, a reactor comprises: a workpiece processing chamber; a first spiral waveguide conduit overlying the workpiece processing chamber and having a spiral axis and a first conduit end; first plural ports in the first spiral waveguide conduit facing the workpiece processing chamber and spaced apart along the length of the first spiral waveguide conduit; an axial conduit; and a distributor waveguide comprising an input coupled to the axial conduit and a first output coupled to the first conduit end. 
         [0021]    In one embodiment, the reactor further comprises: a rotary coupling comprising a stationary stage and a rotatable stage having an axis of rotation coinciding with the spiral axis; a microwave source coupled to the stationary stage, the axial conduit coupled to the rotatable stage; and a rotation actuator coupled to the rotatable stage. 
         [0022]    In one embodiment, the reactor further comprises: a second spiral waveguide conduit aligned with the spiral axis, the second spiral conduit having a second conduit end; second plural ports in the second spiral waveguide conduit spaced apart along the length of the second spiral conduit; and wherein the distributor waveguide further comprises a second output coupled to the second conduit end. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    So that the manner in which the exemplary embodiments of the present invention are attained can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. It is to be appreciated that certain well known processes are not discussed herein in order to not obscure the invention. 
           [0024]      FIG. 1A  is a cut-away elevational view of a first embodiment. 
           [0025]      FIG. 1B  is an enlarged view of a microwave antenna in the embodiment of  FIG. 1A . 
           [0026]      FIG. 2  is a cut-away plan view taken along line  2 - 2  of  FIG. 1B . 
           [0027]      FIG. 3  is a plan view of the embodiment of  FIG. 1B . 
           [0028]      FIG. 4  is a cut-away orthographic projection corresponding to  FIG. 3 . 
       
    
    
       [0029]    To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
       DETAILED DESCRIPTION 
       [0030]    Referring now to  FIGS. 1A and 1B , a workpiece processing reactor includes a chamber  100  containing a workpiece support  102 . The chamber  100  is enclosed by a side wall  104  and a ceiling  106  formed of a microwave transparent material such as a dielectric material. In one embodiment, the ceiling  106  may be implemented as a dielectric window  108  formed in the shape of a disk. A rotating microwave antenna  114  overlies the dielectric window  108 . The microwave antenna  114  is enclosed by a conductive shield  122  consisting of a cylindrical side wall  124  and a disk-shaped cap  126 . In one embodiment depicted in  FIG. 2 , the microwave antenna  114  is disk-shaped. 
         [0031]    As shown in  FIG. 1A , the microwave antenna  114  is fed by an axial waveguide  116 . The axial waveguide  116  is coupled through an overlying rotary microwave coupling  118  to a stationary microwave feed  120 . The rotary coupling  118  includes a stationary member  118 - 1  and a rotatable member  118 - 2 . The stationary member  118 - 1  is stationary relative to the chamber  100  and is connected to the microwave feed  120 . The rotatable member  118 - 2  is connected to the axial waveguide  116  and has an axis of rotation coinciding with the axis of symmetry  114   a  of the microwave antenna  114 . The rotary microwave coupling  118  permits microwave energy to flow from the stationary member  118 - 1  to the rotatable member  118 - 2  with negligible loss or leakage. As one possible example, a slip-ring RF seal (not shown) may be placed at the interface between the stationary and rotatable members  118 - 1  and  118 - 2 . 
         [0032]    A rotation actuator  140  is stationary relative to the chamber  100  and includes a rotation motor  140 - 1  and a rotating drive gear  140 - 2  driven by the rotation motor  140 - 1 . A driven gear  118 - 3  bonded or fastened to the rotatable member  118 - 2  is engaged with the drive gear  140 - 2 , so that the motor  140 - 1  causes rotation of the rotatable member  118 - 2  about the axis of symmetry  114   a.  The driven gear  118 - 3  may be implemented, for example, as a circular array of teeth on the bottom surface of the rotatable member  118 - 2 . 
         [0033]    In one embodiment, a gas distribution plate (GDP)  144  is disposed beneath the ceiling  106 , and has an array of gas injection orifices  145  extending through it and receives process gas from a process gas supply  147 . 
         [0034]    As shown in  FIG. 1A , a remote microwave source or generator  150  is coupled to the rotary coupling  118  by the microwave feed  120 . 
         [0035]    The microwave antenna  114  is depicted in detail in  FIGS. 1B through 4 , and includes an antenna floor  160 , an antenna ceiling  162 , and a pair parallel spiral waveguide side walls  164 ,  166  extending between the floor  160  and the ceiling  162 . The pair of parallel spiral waveguide side walls  164 ,  166  form a pair of parallel spiral waveguide cavities  168 ,  169 . In the illustrated embodiment, the pair of parallel spiral waveguide cavities  168 ,  169  form spirals of Archimedes, in which the radius of each spiral increases with the angle of rotation. Small slots  175 , or openings through the antenna floor  160 , serve as microwave radiation ports and are disposed at locations periodically spaced along the length of each spiral waveguide cavity  168 ,  169 . The slots  175  may be of any suitable shape and have an opening size, in one embodiment, a small fraction (e.g., one tenth or less) of a wavelength of the microwave generator  150 . In one embodiment, the distance S between neighboring slots  175  along the length of each spiral conduit  168 ,  169  is a fraction (e.g., about one-half) of a wavelength of the microwave source  150 . Microwave energy radiates through the slots  175  into the chamber  100 . A pair of feed openings  180 ,  182  in the ceiling  162  are disposed on opposing sides of the axis of symmetry  114   a  and provide respective paths for microwave energy to be fed into respective peripheral (radially outward) open ends  168   a,    169   a  of the spiral waveguide cavities  168 ,  169 . The peripheral open ends  168   a,    169   a  are displaced from one another by an angle of 180 degrees along the periphery of the microwave antenna  114 . Likewise, the pair of feed openings  180 ,  182  are displaced from one another by an angle of 180 degrees along the periphery of the microwave antenna  114 . 
         [0036]    A distributor waveguide  200  depicted in  FIGS. 3 and 4  overlies the ceiling  162  and distributes microwave energy from the axial waveguide  116  to the pair of feed openings  180 ,  182 . The distributor waveguide  200  includes a waveguide top  202  overlying and facing the ceiling  162  and a pair of slanted end walls  204 ,  206  extending between the waveguide top  202  and the ceiling  162 . The pair of slanted end walls  204 ,  206  reflect microwave energy flowing radially within the distributor waveguide  200  to flow axially into the feed openings  180 ,  182  respectively. A first slanted reflector surface  184  in registration with the feed opening  180  is disposed at an angle (e.g., 45 degrees) relative to the axis of symmetry  114   a.  A second slanted reflector surface  186  in registration with the feed opening  182  is disposed at an angle (e.g., 45 degrees) relative to the axis of symmetry  114   a.  The first and second slanted reflector surfaces  184 ,  186  reflect microwave energy flowing axially from the feed openings  180 ,  182  to flow azimuthally through the spiral waveguide cavities  168 ,  169  respectively. In one embodiment, the length of each of the slanted surfaces  184 ,  186 ,  204 ,  206  along the direction of wave propagation is one-quarter wavelength of the microwave generator  150 . The slanted surfaces  184 ,  186 ,  204 ,  206  may be referred to as reflective surfaces. 
         [0037]    Referring to  FIG. 3 , the distributor waveguide  200  has a length L corresponding to the diameter of the chamber  100 , and a width W of several inches, in one embodiment. Axial flat side walls  200 - 1 ,  200 - 2  along the length L enclose the interior of the distributor waveguide  200 . The height of the side walls  200 - 1 ,  200 - 2  corresponds to the distance between the ceiling  162  and the waveguide top  202 . In one embodiment, this distance may be on the order one or a few inches. Optionally, plural microwave stub tuners  300  are placed at periodic locations along the length of the distributor waveguide  200 . 
         [0038]    An advantage of the embodiments of  FIGS. 1B-4  is that microwave energy is uniformly distributed along the lengths of each spiral waveguide cavity  168 ,  169 , so as to radiate in uniformly distributed intervals corresponding to the periodic locations of the slots  175 . A further advantage is that power distribution among the pair of spiral waveguide cavities  168 ,  169  can be balanced by adjustment of the plural stub tuners  300 . 
         [0039]    While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.