Abstract:
Methods and apparatus for forming thin films are described. A semiconductor processing chamber includes a substrate support, an electrode opposite the substrate support, the electrode having a gas inlet in a peripheral region thereof, and an edge ring disposed around a peripheral region of the substrate support, the edge ring having a first barrier and a second barrier, wherein each of the first barrier and the second barrier mates with a recess in the electrode. The edge ring provides a gas flow path through a processing zone between the substrate support and the electrode that is substantially parallel to the upper surface of the substrate support. The electrode may be powered to enhance formation of a film on a substrate.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims benefit of U.S. Provisional Patent Application Ser. No. 61/780,224, filed Mar. 13, 2013, which is incorporated herein by reference. 
     
    
     FIELD 
       [0002]    Embodiments described herein generally relate to methods and apparatus for atomic layer deposition. More specifically, embodiments described herein provide methods and apparatus for rapid cycling in an atomic layer deposition process. 
       BACKGROUND 
       [0003]    Atomic layer deposition is a process commonly used to form thin films in the semiconductor industry. A typical process includes positioning a substrate in a reactor and providing a first precursor to the reactor. The first precursor deposits a first species on the substrate surface until the surface is saturated with the first species, after which deposition stops. A second precursor is then provided to the chamber. The second precursor reacts with the first species lining the surface of the substrate until no more of the first species is available to react, after which deposition stops. Such cycles are repeated until a desired thickness of the layer is formed. The chamber is typically purged between precursors to provide controlled layering on the substrate. 
         [0004]    The atomic layer deposition process is useful for forming layers having very uniform thickness and composition because the deposition reaction is controlled at the molecular, or atomic, level. The first species only adheres to the substrate surface if an adhesion site is available. Every instance of the first species adheres to the substrate surface in exactly the same way, so that it can participate in the reaction with the second precursor in exactly the same way. 
         [0005]    The layer deposited in each deposition operation is monomolecular or monatomic. Typically, the species deposited are no larger than small molecules. Thus, each layer deposited typically has a thickness of 5 Å or less. Each cycle consisting of two precursor operations and two purge operations may take up to a minute to execute. More complex cycles involving more than two precursors may take longer. Forming layers 50-100 Å thick may take 10-20 minutes. To improve rates in ALD processes, one or more precursors may be activated, for example by forming a plasma. The precursor is flowed into the chamber, and then plasma is formed to activate deposition. Plasma is typically discontinued when deposition from the precursor is complete. Fast cycling of gases promotes high throughput. Thus, there is a continuing need for apparatus and methods for fast cycling in PEALD processes. 
       SUMMARY OF THE INVENTION 
       [0006]    Embodiments described herein include a semiconductor processing chamber having a substrate support, an electrode opposite the substrate support, the electrode having a gas inlet in a peripheral region thereof, and an edge ring disposed around a peripheral region of the substrate support, the edge ring having a first barrier and a second barrier, wherein each of the first barrier and the second barrier mates with a recess in the electrode. The edge ring provides a gas flow path through a processing zone between the substrate support and the electrode that is substantially parallel to the upper surface of the substrate support. The electrode may be powered to enhance formation of a film on a substrate. 
         [0007]    A plurality of high speed valves may be coupled to the gas inlet to provide rapid switching of precursors and/or reactants into the gas inlet. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical 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. 
           [0009]      FIG. 1  is a cross-sectional view of a processing chamber according to one embodiment. 
           [0010]      FIGS. 2A and 2B  are detailed views of portions of the chamber of  FIG. 1 . 
           [0011]      FIG. 3  is a cross-sectional view of the processing chamber of  FIG. 1  in another configuration. 
           [0012]      FIG. 4  is a perspective view of an edge ring according to another embodiment. 
           [0013]      FIG. 5  is a top view of the processing chamber of  FIG. 1 . 
       
    
    
       [0014]    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. 
       DETAILED DESCRIPTION 
       [0015]      FIG. 1  is a cross-sectional view of a processing chamber  100  according to one embodiment. The processing chamber  100  has a chamber body  102  and a chamber lid  104  that couples to the chamber body  102  to define an interior  150 . A substrate support  106  is disposed in the interior  150  of the chamber  100 . An upper surface  166  of the substrate support  106  and a lower surface  168  of the chamber lid  104  define a processing region  108  in which a substrate disposed in a substrate contact area  176  on the upper surface  166  of the substrate support  106  is exposed to a processing environment. 
         [0016]    Substrates enter and exit the processing chamber  100  through a substrate passage  110  in the chamber body  102 . In the cross-sectional view of  FIG. 1 , the substrate passage  110  is behind the cross-section plane, in the “back” of the chamber  100 . The substrate support  106  is movable along a longitudinal axis, for example a vertical axis, of the chamber  100  to position the substrate support  106  alternately in a substrate handling position, with the upper surface  166  of the substrate support  106  proximate the opening  110 , and a substrate processing position, with the upper surface  166  of the substrate support  106  proximate the lower surface  168  of the chamber lid  104 . In the view of  FIG. 1 , the substrate support  106  is shown in the substrate processing position. When the substrate support  106  is located in the substrate processing position, a distance between the upper surface  166  of the substrate support  106  and the lower surface  168  of the chamber lid  104  is about 2 mm to about 8 mm. A shaft  172  of the substrate support  106  typically extends through an opening  120  in a lower wall  170  of the chamber body  102  and couples to a lift mechanism (not shown) to actuate movement of the substrate support  106 . 
         [0017]    A substrate elevator  112  is disposed through the substrate support  106 . The substrate elevator  112  has a base  114  that contacts an actuator  116  disposed in a lower area of the interior  150  of the chamber  100 . The actuator  116  is supported from the lower wall  170  by a support member  118 . The actuator  116  may be an annular member, such as a ring, and the support member  118  may be an annular protrusion from the actuator  116 . The actuator  116 , the support member  118 , or both may alternately be segmented. For example, either or both may be a segmented annular member, or the actuator  116  may be a pad, post, or spindle positioned to engage the base  114  of the substrate elevator  112 . 
         [0018]    The support member  118  maintains the actuator  116  in a substantially parallel relation to the upper surface  166  of the substrate support  106 . When the substrate support  106  is moved from the processing position to the substrate handling position, the base  114  of the substrate elevator  112  contacts the actuator  116 , causing the substrate elevator  112  to protrude through the upper surface  116  of the substrate support  106  and lift a substrate disposed thereon above the upper surface  116  for access by a substrate handling robot (not shown) through the opening  110 . Only two substrate elevators  112  are visible in the view of  FIG. 1 , but a typical embodiment will have three or more substrate elevators  112  distributed to provide stable stationing for substrate handling. 
         [0019]    The chamber lid  104  may be an electrode, and may be coupled to a source of RF power  174 . If the chamber lid  104  is an electrode, the chamber lid  104  will typically include a conductive material. The chamber lid  104  may be entirely or substantially made of a conductive material, or may be coated with a conductive material to any convenient degree. If the chamber lid  104  is used as an electrode, the lower surface  168  of the chamber lid  104  will be conductive to provide RF coupling into the processing region  108  proximate the upper surface  166  of the substrate support  106 . In one embodiment, the chamber lid  104  is aluminum. 
         [0020]    A gas manifold  124  is coupled to the chamber lid  104  at a port  194 . Process gases are delivered to the chamber through a gas line  128 . A plurality of high speed valves  126 A-C control flow of gases through the gas line  128  into the chamber  100 . The high speed valves may be ALD valves, and in some embodiments may be capable of opening or closing in less than 1 second, and in some cases less than 0.25 seconds. A precursor line  130  is coupled to one of the high speed valves  126 A-C. The other high speed valves may be used to join other precursor lines, not visible in  FIG. 1 , to deliver gases through the gas line  128 . Operation of the high speed valves enables fast switch of gas flows as needed for chamber operations, such as ALD deposition cycles. 
         [0021]    The chamber lid  104  has a gas inlet  122  located in a peripheral region of the chamber lid  104  and in fluid communication with the port  194  and the gas manifold  124 . The gas inlet  122  may be located outside the substrate contact area  176  of the substrate support  106 . An edge ring  136  is disposed around a peripheral region of the substrate support  106 . The edge ring  136  may be an annular member having an inner dimension and an outer dimension. The inner dimension of the edge ring  136  may be substantially the same as a dimension of the substrate contact area  176  such that a substrate disposed on the substrate support nests inside the edge ring  136 , as shown in  FIG. 1 . The inner dimension of the edge ring  136  may also be larger than the dimension of the substrate contact area  176 . The inner dimension of the edge ring  136  may also be smaller than the substrate contact area  176  so that a portion of the edge ring  136  extends over an edge of the substrate. The edge ring  136  of  FIG. 1  rests on the substrate support  106  when the substrate support  106  is in the processing position. Thus, the substrate support  106  also supports the edge ring  136  when in the processing position. 
         [0022]    A pumping plenum  132  is located in a side wall  178  of the chamber body  102  proximate the processing position of the substrate support  106 . The pumping plenum  132  is an annular passage around the processing region  108  where processing gases are evacuated from the processing region  108 . A liner  134  separates the pumping plenum  132  from the processing region  108 . The liner  134  has an opening  180  that allows process gases to flow from the processing region  108  into the pumping plenum  132 . The opening  180  is typically located below the upper surface  166  of the substrate support  106  when the substrate support  106  is in the processing position. 
         [0023]      FIG. 2A  is a detailed view of a portion of the apparatus of  FIG. 1 . The substrate support  106  and the gas inlet  122  are visible in the view of  FIG. 2A . The edge ring  136  has a first barrier  138  and a second barrier  142 , each of which extend away from the rest of the edge ring  136 . The first barrier  138  and the second barrier  142  extend at least partly around the edge ring  136  and define an inlet channel  182  that registers with the gas inlet  122 . Gas flows through the gas inlet  122  into the channel  182  and into the processing zone  108  through openings formed in the second barrier  142 . The gas flows across a substrate disposed on the substrate support  106  in a substantially laminar fashion. The first barrier  138  prevents gas flow around the edge of the substrate support  106 . 
         [0024]    The first barrier  138  mates with a first recess  140  formed in the lower surface  168  of the electrode  104 , and the second barrier  142  mates with a second recess  144  formed in the lower surface  168  of the electrode  104 . The two recesses  140 ,  142  are formed on opposite sides of the gas inlet  122 , and help seal the channel  182  so gas does not escape. Each of the recesses  140 ,  144  has a seal member  146 , such as an o-ring, to seal the interface between the barriers  138 ,  142  and the recesses  140 ,  144 . 
         [0025]      FIG. 2B  is a detailed view of another portion of the apparatus of  FIG. 1 . The view of  FIG. 2B  is of the edge ring at a point opposite the view of  FIG. 2A . The recesses  140 ,  144  and the sealing members  146  are visible. A gas outlet channel  184  allows gas flowing across the upper surface  166  of the substrate support  106  to flow over the edge of the substrate support  106  into the opening  180  and the pumping plenum  132 , as shown by arrow  186 . 
         [0026]    When the substrate support  106  is in the processing position, the edge ring  136  rests on the substrate support  106 . Referring again to  FIG. 2A , the edge ring  136  has a contact point  188  where the edge ring  136  contacts the substrate support  106 . As shown in  FIG. 2A , the contact point  188  may be a notch in the edge ring  136  that mates with a corner or shoulder of the substrate support  106 . The contact point  188  is not visible in  FIG. 2B  because the contact point  188  is not continuous around the full extent of the edge ring  136  so that gas may flow off the edge of the substrate support  106  through the outlet channel  184 . 
         [0027]    When the edge ring  136  engages with the electrode  104 , the edge ring  136  forms a minimum volume reaction space around the substrate consisting of a space less than about 10 mm directly above the substrate. For a 300 mm circular substrate, the reaction volume is no more than about 225 mL, promoting fast switching of gases for an ALD process. When the edge ring  136  disengages from the electrode  104  and the substrate support  106 , the substrate may be accessed, removed through the opening  110 , and then replaced. 
         [0028]    An extension  190  of the edge ring  136  extends radially outward of the substrate support  106  and provides a means for the edge ring  136  to be supported above the substrate support  106  on a support shelf  192  of the liner  134  as the substrate support  106  moves into the substrate handling position proximate the substrate passage  110 . When the substrate support  106  is in the processing position, the extension  190  is spaced apart from the support shelf  192  by a gap of about 0.1 mm to about 5 mm. As the substrate support  106  moves to the substrate handling position, the extension  190  engages the support shelf  192 , and the edge ring  136  stops moving while the substrate support  106  continues to the substrate handling position. When the substrate support  106  moves from the substrate handling position to the processing position, the substrate support  106  engages the edge ring  136  at the contact point  188  and then the edge ring  136  moves with the substrate support  106 . When the substrate support  106  reaches the processing position, the barriers  138 ,  142  engage the recesses  140 ,  144  to seal the inlet channel  182 . 
         [0029]      FIG. 3  is a cross-sectional view of the processing chamber of  FIG. 1  with the substrate support  106  in the substrate handling position. The edge ring  136  is shown resting on the liner  134 , as described above, with the edge ring  136  spaced apart from the electrode  104 . The barriers  138 ,  142  are disengaged from the recesses  140 ,  144 , and the substrate elevator  112  is extended by operation of the actuator  116  on the base  114 , so the substrate is spaced apart from the substrate support  106  for movement through the substrate passage  110 . In the view of  FIG. 3 , the opening  180  is visible extending in an angular fashion partway around the “back” of the chamber  100 . 
         [0030]      FIG. 4  is a perspective view of the lower surface of the edge ring  136  of  FIGS. 1-3  showing the gas flow features thereof. The inlet channel  182  and outlet channel  184  are visible. A port  200  in the inlet channel  182  registers with the gas inlet  122  ( FIGS. 1-3 ) to maintain fluid communication between the gas inlet and the inlet channel  182 . The inlet channel  182  extends partway around the circumference of the edge ring  136 , and in the embodiment of  FIG. 4  subtends an angle θ that is selected to produce a gas flow field across the substrate support  106  ( FIGS. 1-3 ) that substantially covers the substrate contact area  176  of the substrate support  106 . The angle θ may be any convenient angle, but is typically between about 90° and about 140°, such as about 120°. 
         [0031]    The inlet channel  182  has a substantially constant width from the port  200  to either extremity  202  of the channel. The inlet channel  182  has a depth, defined as the distance from a surface  204  of the extension  190  to a floor  206  of the inlet channel  182 , measured in a direction perpendicular to the surface  204 , that increases from the port  200  to either extremity  202 . The increase in depth may be substantially linear with linear distance along the inlet channel  182 . The increasing depth profile of the inlet channel  182  toward either extremity  202  encourages distribution of gas from the port  200  toward the extremities  202 , promoting uniform distribution of gas to the flow field emerging from the edge ring  136 . 
         [0032]    The inlet channel  182  has an outer wall  208  and an inner wall  210 , in which a plurality of openings  212  are formed to provide gas flow into the processing zone  108  ( FIGS. 1-3 ) and across the substrate support  106 . The openings  212  are oriented to provide a substantially laminar, unidirectional, planar gas flow across a substrate disposed on the substrate support  106 . As noted above, the edge ring  136  rests on the substrate support  106  when the substrate support is in the processing position, so the channel  182  is enclosed by the outer wall  208 , the substrate support  106 , and the inner wall  210  with openings  212 . Gas thus flows from the gas inlet  122  through the port  200 , along the inlet channel  182  and through the openings  212  to reach the processing zone  108 . 
         [0033]      FIG. 5  is a top view of the processing chamber  100  of  FIG. 1 . The chamber lid  104  is visible with the port  194  into the gas inlet  122  ( FIG. 1 ). The gas manifold  124  is shown with the precursor line  130  coupled to the high speed valve  126 C. A second precursor line  152  and a third precursor line  154  are coupled to the other high speed valves  126 A,  126 B, respectively. The process gases are delivered to the port  194  through the gas line  128 . A first divert line  156  couples the high speed valve  126 A to a first divert valve  160 . A second divert line  158  couples the high speed valve  126 B to a second divert valve  162 . A divert exhaust line  164  couples to the divert valves  160 ,  162  to carry gas away from the gas manifold  124 . 
         [0034]    The high speed valves  126 A,  126 B are four-way valves that, when operated, direct one inlet stream to one or another outlet while constantly flowing another inlet stream through the valve. In the case of the high speed valve  126 B, precursors flowing through the third precursor line  154  may be directed to a blend line  131  or to the second divert line  158 , depending on the setting of the high speed valve  126 B, while precursors flowing through the precursor line  130  flow through the high speed valve  126 B to the blend line  131 . Thus, the high speed valve  126 B may be a divert valve. In the case of the high speed valve  126 A, precursors flowing through the second precursor line  152  may be directed to the gas line  128  or to the first divert line  156 , depending on the setting of the high speed valve  126 A, while precursors flowing through the blend line  131  flow through the high speed valve  126 A to the gas line  128 . Thus, the high speed valve  126 A may be a divert valve. Using the high speed valves  126 A,  126 B, precursors may be individually directed to flow into the chamber  100  through the port  194 , or may be diverted around the chamber through the divert exhaust line  164 . 
         [0035]    High speed valves are useful in such a configuration because precision deposition processes are best performed when flows of precursors and purge gases are switched quickly with minimal transition. Undesired blends of precursors are minimized, and time spent lining up the various precursors is also minimized. It should be noted that any number of precursor lines may be added to the gas manifold  124  by adding a four-way high speed valve, such as the valves  126 A, 126 B, between the high speed valve  126  and the high speed valve  126 C, connecting a precursor line to the additional high speed valve, and connecting a divert line and divert valve from the additional high speed valve to the divert exhaust line  164 . 
         [0036]    The chamber  100  may be used to perform a plasma-enhanced ALD process. A purge gas may be directed through the precursor line  130 , a first precursor may be directed through the first precursor line  152 , and a second precursor may be directed through the second precursor line  154 . The purge gas may be blended with a reagent, if desired, to perform an ALD process using three precursors. 
         [0037]    When using two precursors, the precursors may be alternately provided to the chamber through the port  194  using the high speed valves  126 A,  126 B while constantly flowing purge gas through the high speed valve  126 C. The first precursor may be provided to the port  194  by opening the high speed valve  126 A to perform a first half-reaction that deposits the first precursor on available sites of a substrate in the chamber  100 . The first precursor may then be diverted to the first divert line  156  by closing the high speed valve  126 A, and the second precursor may be directed to flow into the chamber by opening the second high speed valve  126 B to perform a second half-reaction in which the second precursor reacts with the first precursor deposited on the substrate. The second high speed valve  126 B may then be closed, and the cycle repeated, alternately opening the high speed valves  126 A,  126 B until a layer of desired thickness is formed on the substrate. Purge gas is constantly flowed through the precursor line  130  into the chamber while the high speed valves  126 A,  126 B are switched. 
         [0038]    RF power may be applied to the chamber lid  104  using the RF source  174  ( FIG. 1 ), if desired, to activate one or more of the precursors during any half-reaction. 
         [0039]    If desired, one or more precursors may be provided in a blend with a purge gas through the precursor line  130 , and one or more precursors may be provided through the first precursor line  152  and the second precursor line  154 . In such a configuration, it is preferred that the precursor blended with the purge gas is a precursor that does not react under normal circumstances, but may react when activated by RF power. In such an embodiment, the precursor and purge gas blend provided through the precursor line  130  acts as a carrier gas for a first precursor delivered through the first precursor line  152  for a first partial reaction, and then the first precursor is diverted while RF is applied to the precursor and purge gas blend to perform a second partial reaction. The precursor blended with the purge gas is activated by the RF power and reacts with the first precursor deposited on the substrate. A second precursor may be sequentially, concurrently, or alternately provided through the second precursor line  154  to perform a third partial reaction, if desired. 
         [0040]    The terms “upper”, “lower”, “top”, and “bottom”, as may be encountered throughout this description, are descriptions of directions relative to the orientation of the apparatus being described, and are not intended to limit the apparatus so described to any absolute orientation. 
         [0041]    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.