Abstract:
A chemical vapor deposition reactor and a method of wafer processing are provided. The reactor includes a reaction chamber having an interior, a gas inlet manifold communicating with the interior of the chamber, an exhaust system including an exhaust manifold having a passage and one or more ports, and one or more cleaning elements mounted within the chamber. The gas inlet manifold can admit process gasses to form a deposit on substrates held within the interior. The passage can communicate with the interior of the chamber through the one or more ports. The one or more cleaning elements are movable between (i) a run position in which the cleaning elements are remote from the one or more ports and (ii) a cleaning position in which the one or more cleaning elements are engaged in the one or more ports.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to wafer processing apparatus, to exhaust systems for use in such processing apparatus, and to methods of cleaning the exhaust systems. 
         [0002]    Many semiconductor devices are formed by processes performed on a substrate. The substrate typically is slab of a crystalline material, commonly referred to as a “wafer.” Typically, a wafer is formed by depositing a crystalline material and is in the form of a disc. One common process for forming such a wafer is epitaxial growth. 
         [0003]    For example, devices formed from compound semiconductors such as III-V semiconductors typically are formed by growing successive layers of the compound semiconductor using metal organic chemical vapor deposition or “MOCVD.” In this process, the wafers are exposed to a combination of gases, typically including a metal organic compound as a source of a group III metal, and also including a source of a group V element which flow over the surface of the wafer while the wafer is maintained at an elevated temperature. Typically, the metal organic compound and group V source are combined with a carrier gas which does not participate appreciably in the reaction as, for example, nitrogen. One example of a III-V semiconductor is gallium nitride, which can be formed by reaction of an organo gallium compound and ammonia on a substrate having a suitable crystal lattice spacing, as for example, a sapphire wafer. Typically, the wafer is maintained at a temperature on the order of 500-1100° C. during deposition of gallium nitride and related compounds. 
         [0004]    Composite devices can be fabricated by depositing numerous layers in succession on the surface of the wafer under slightly different reaction conditions, as for example, additions of other group III or group V elements to vary the crystal structure and bandgap of the semiconductor. For example, in a gallium nitride based semiconductor, indium, aluminum or both can be used in varying proportion to vary the bandgap of the semiconductor. Also, p-type or n-type dopants can be added to control the conductivity of each layer. After all of the semiconductor layers have been formed and, typically, after appropriate electric contacts have been applied, the wafer is cut into individual devices. Devices such as light-emitting diodes (“LEDs”), lasers, and other electronic and optoelectronic devices can be fabricated in this way. 
         [0005]    In a typical chemical vapor deposition process, numerous wafers are held on a component commonly referred to as a wafer carrier so that a top surface of each wafer is exposed at the top surface of the wafer carrier. The wafer carrier is then placed into a reaction chamber and maintained at the desired temperature while the gas mixture flows over the surface of the wafer carrier. It is important to maintain uniform conditions at all points on the top surfaces of the various wafers on the carrier during the process. Minor variations in composition of the reactive gases and in the temperature of the wafer surfaces cause undesired variations in the properties of the resulting semiconductor devices. 
         [0006]    For example, if a gallium indium nitride layer is deposited, variations in wafer surface temperature or concentrations of reactive gasses will cause variations in the composition and bandgap of the deposited layer. Because indium has a relatively high vapor pressure, the deposited layer will have a lower proportion of indium and a greater bandgap in those regions of the wafer where the surface temperature is higher. If the deposited layer is an active, light-emitting layer of an LED structure, the emission wavelength of the LEDs formed from the wafer will also vary. Thus, considerable effort has been devoted in the art heretofore towards maintaining uniform conditions. 
         [0007]    One type of CVD apparatus which has been widely accepted in the industry uses a wafer carrier in the form of a large disc with numerous wafer-holding regions, each adapted to hold one wafer. The wafer carrier is supported on a spindle within the reaction chamber so that the top surface of the wafer carrier having the exposed surfaces of the wafers faces upwardly toward a gas distribution element. While the spindle is rotated, the gas is directed downwardly onto the top surface of the wafer carrier and flows across the top surface toward the periphery of the wafer carrier. 
         [0008]    The wafer carrier is maintained at the desired elevated temperature by heating elements, typically electrical resistive heating elements disposed below the bottom surface of the wafer carrier. These heating elements are maintained at a temperature above the desired temperature of the wafer surfaces, whereas the gas distribution element typically is maintained at a temperature well below the desired reaction temperature so as to prevent premature reaction of the gases. Therefore, heat is transferred from the heating elements to the bottom surface of the wafer carrier and flows upwardly through the wafer carrier to the individual wafers. 
         [0009]    The used gas is evacuated from the reaction chamber through exhaust ports disposed below the wafer carrier and distributed around the axis of the spindle, typically near the periphery of the chamber. The exhaust ports may have features that restrict the flow of gas into each port, which promotes a uniform flow of gas into the ports. In a conventional CVD reactor, parasitic deposition of products of the reactants can form on the exhaust ports. Such parasitic deposition can be periodically removed so that the reactant flow can remain as uniform as possible, thereby improving the uniformity of the process at the wafer surfaces. However, such removal typically requires disassembly of the reactor and thus lost production time. 
         [0010]    Although considerable effort has been devoted in the art heretofore to optimization of such systems, still further improvement would be desirable. In particular, it would be desirable to provide better methods of cleaning the exhaust systems. 
       SUMMARY OF THE INVENTION 
       [0011]    A chemical vapor deposition reactor and a method of wafer processing are provided. One aspect of the invention provides a chemical vapor deposition reactor. The reactor includes a reaction chamber having an interior, a gas inlet manifold communicating with the interior of the chamber, an exhaust system including an exhaust manifold having a passage and one or more ports, and one or more cleaning elements mounted within the chamber. The gas inlet manifold can admit process gasses to form a deposit on substrates held within the interior. The passage can communicate with the interior of the chamber through the one or more ports. The one or more cleaning elements can be movable between (i) a run position in which the cleaning elements are remote from the one or more ports and (ii) a cleaning position in which the one or more cleaning elements are engaged in the one or more ports. 
         [0012]    In a particular embodiment, the chamber can have an entry port for insertion and removal of substrates and a shutter mounted to the chamber. In one example, the shutter can be movable between (i) an open position in which the shutter is clear of the entry port and (ii) a closed position in which the shutter blocks the entry port. In an exemplary embodiment, the one or more cleaning elements can be mounted to the shutter for movement therewith. In a particular example, the cleaning elements can be (i) in the run position when the shutter is in the closed position and (ii) in the cleaning position when the shutter is in the open position. Where the shutter moves vertically, the shutter typically is lowered to open it and raised to close it, and thus the open position can also be referred to as the “down” position and the closed position can also be referred to as the “up” position. 
         [0013]    Another aspect of the invention provides a method of wafer processing. The method includes the steps of providing a reaction chamber, holding one or more wafers on a wafer carrier so that a top surface of each wafer is exposed at a top surface of the wafer carrier, applying one or more process gasses to the exposed top surfaces of the wafers, removing a portion of the process gasses through an exhaust system, moving one or more cleaning elements mounted within the chamber downward, and inserting at least a portion of each cleaning element into the exhaust manifold so as to clean the exhaust manifold. The reaction chamber can define an interior and can include an entry port for insertion and removal of wafer carriers. The exhaust system can include an exhaust manifold. The exhaust manifold can have having a passage and one or more ports. The passage can communicate with the interior of the chamber through the one or more ports. 
         [0014]    In a particular embodiment, the method can include the step of moving a shutter mounted to the chamber from (i) an open position in which the shutter is clear of the entry port to (ii) a closed position in which the shutter blocks the entry port. In one example, the one or more cleaning elements can be directly joined to the shutter for movement therewith. In an exemplary embodiment, the step of moving a shutter can include moving the cleaning elements to (i) a run position when the shutter is in the closed position and (ii) a cleaning position when the shutter is in the open position. 
     
    
     
       BRIEF DESCRIPTION OF TEE DRAWINGS 
         [0015]      FIG. 1  is a perspective sectional view depicting chemical vapor deposition apparatus in accordance with one embodiment of the invention. 
           [0016]      FIG. 2  is a fragmentary perspective sectional view depicting an embodiment of elements of the chemical vapor deposition apparatus illustrated in  FIG. 1 . 
           [0017]      FIG. 3  is a top sectional view of the chemical vapor deposition apparatus illustrated in  FIG. 1 . 
           [0018]      FIG. 4  is a fragmentary perspective sectional view depicting another embodiment of the elements shown in  FIG. 2 . 
           [0019]      FIG. 5A  is a fragmentary side sectional view depicting portions of an apparatus according to a further embodiment of the invention in one position. 
           [0020]      FIG. 5B  is a fragmentary side sectional view of the apparatus of  FIG. 5A , shown in a different position. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    Referring to  FIGS. 1-3 , a chemical vapor deposition apparatus  10  in accordance with one embodiment of the invention includes a reaction chamber  12  having a gas inlet manifold  14  arranged at one end of the chamber  12 . The end of the chamber  12  having the gas inlet manifold  14  is referred to herein as the “top” end of the chamber  12 . This end of the chamber typically, but not necessarily, is disposed at the top of the chamber in the normal gravitational frame of reference. Thus, the downward direction as used herein refers to the direction away from the gas inlet manifold  14 ; whereas the upward direction refers to the direction within the chamber, toward the gas inlet manifold  14 , regardless of whether these directions are aligned with the gravitational upward and downward directions. Similarly, the “top” and “bottom” surfaces of elements are described herein with reference to the frame of reference of chamber  12  and manifold  14 . 
         [0022]    The chamber  12  has a cylindrical wall  20  that extends between a top flange  22  at the top end of the chamber and a base plate  24  at the bottom end of the chamber. The wall  20 , the flange  22 , and the base plate  24  define an air-tight sealed interior region  26  therebetween that can contain gasses emitted from the gas inlet manifold  14 . Although the chamber  12  is shown as cylindrical, other embodiments can include a chamber having another shape, including, for example, a cone or other surface of revolution, a square, a hexagon, an octagon, or any other appropriate shape. 
         [0023]    The gas inlet manifold  14  is connected to sources for supplying process gases to be used in the wafer treatment process, such as a carrier gas and reactant gases such as a metalorganic compound and a source of a group V metal. In a typical chemical vapor deposition process, the carrier gas can be nitrogen, hydrogen, or a mixture of nitrogen and hydrogen, and hence the process gas at the top surface of a wafer carrier can be predominantly composed of nitrogen and/or hydrogen with some amount of the reactive gas components. The gas inlet manifold  14  is arranged to receive the various gases and direct a flow of process gasses generally in the downward direction. 
         [0024]    The gas inlet manifold  14  can also be connected to a coolant system (not shown) arranged to circulate a liquid through the gas distribution element so as to maintain the temperature of the element at a desired temperature during operation. A similar coolant arrangement (not shown) can be provided for cooling the walls of chamber  12 . 
         [0025]    The chamber  12  is also provided with an entry opening  30  leading to an antechamber  32 , and a shutter  34  for closing and opening the entry opening  30 . The shutter  34  is movable between a closed position or up position shown in solid lines in  FIG. 1 , in which the door isolates the interior region  26  of the chamber  12  from the antechamber  32 , and an open position or down position as shown in broken lines at  34 ′ in  FIG. 1 . 
         [0026]    The shutter  34  can be moveable by a control and actuation mechanism  41  (schematically depicted in  FIG. 2 ) that is coupled to the shutter  34  by a linkage  35  (shown in  FIG. 2 ). The control and actuation mechanism  41  can move the shutter  34  between the closed position shown in  FIG. 1  and the open position shown as  34 ′. The control and actuation mechanism can include any type of actuator capable of moving linkage  35  and shutter  34  as for example, mechanical, electro-mechanical, hydraulic, or pneumatic actuators. As can be seen in  FIG. 2 , the shutter  34  defines an upper surface  36  facing the gas inlet manifold  14  and a lower edge  37  facing the exhaust manifold  72 . 
         [0027]    The shutter  34  can be configured as disclosed, for example, in U.S. Pat. No. 7,276,124, the disclosure of which is hereby incorporated by reference herein. Although the shutter  34  is shown as cylindrical, other embodiments can include a shutter having another shape, including, for example, a square, a hexagon, an octagon, or any other appropriate shape. 
         [0028]    Referring again to  FIG. 1 , a spindle  40  is arranged within the chamber so that the central axis  42  of the spindle  40  extends in the upward and downward directions. The spindle is mounted to the chamber by a conventional rotary pass-through device  44  incorporating bearings and seals (not shown) so that the spindle can rotate about the central axis  42 , while maintaining a seal between the spindle  40  and the base plate  24  of the chamber  12 . The spindle  40  has a fitting  46  at its top end, i.e., at the end of the spindle closest to the gas inlet manifold  14 . The fitting  46  is adapted to releasably engage a wafer carrier  50 . In the particular embodiment depicted, the fitting  46  is a generally frustoconical element tapering toward the top end of the spindle  40  and terminating at a flat top surface. 
         [0029]    The spindle  40  is connected to a rotary drive mechanism  48  such as an electric motor drive, which is arranged to rotate the spindle about the central axis  42 . The spindle  40  can also be provided with internal coolant passages extending generally in the axial directions of the spindle within the gas passageway. The internal coolant passages can be connected to a coolant source, so that a fluid coolant can be circulated by the source through the coolant passages and back to the coolant source. 
         [0030]    The wafer carrier  50  includes a body  52  which is substantially in the form of a circular disc having a central axis  54 . In the operative position shown in  FIGS. 1 and 3 , the central axis  54  of the wafer carrier body  52  is coincident with the axis  42  of the spindle. The body  52  can be formed as a single piece or as a composite of plural pieces. For example, as disclosed in U.S. Published Patent Application No. 20090155028, the disclosure of which is hereby incorporated by reference herein, the wafer carrier body may include a hub defining a small region of the body  62  surrounding the central axis  54  and a larger portion defining the remainder of the disc-like body. 
         [0031]    The wafer carrier body  52  can be formed from materials which do not contaminate the CVD process and which can withstand the temperatures encountered in the process. For example, the larger portion of the disc may be formed largely or entirely from materials such as graphite, silicon carbide, or other refractory materials. The body  52  has generally planar top and bottom surfaces extending generally parallel to one another and generally perpendicular to the central axis  54  of the disc. The body  52  also has a plurality of generally circular wafer-holding pockets  56  extending downwardly into the body  52  from the top surface thereof, each pocket adapted to hold a wafer  58 . In one example, the wafer carrier body  52  can be about 500 mm to about 1000 mm in diameter. 
         [0032]    A wafer  58 , such as a disc-like wafer formed from sapphire, silicon carbide, or other crystalline substrate, is disposed within each pocket  56  of the wafer carrier  50 . Typically, each wafer  58  has a thickness which is small in comparison to the dimensions of its major surfaces. For example, a circular wafer  58  about 2 inches (50 mm) in diameter may be about 430 μm thick or less. Each wafer  58  is disposed with a top surface thereof facing upwardly, so that the top surface is exposed at the top of the wafer carrier  50 . 
         [0033]    The apparatus  10  can further include a loading mechanism (not shown) capable of moving the wafer carrier  50  from the antechamber  32  into the chamber  12  and engaging the wafer carrier  50  with the spindle  40  in the operative condition, and also capable of moving the wafer carrier  50  off of the spindle  40  and into the antechamber  32 . 
         [0034]    A heating element  60  is mounted within the chamber  12  and surrounds the spindle  40  below the fitting  46 . The heating element  60  can transfer heat to the bottom surface of the wafer carrier  50 , principally by radiant heat transfer. Heat applied to the bottom surface of the wafer carrier  50  can flow upwardly through the body  52  of the wafer carrier  50  to the top surface thereof. Heat can pass upwardly to the bottom surface of each wafer  58 , and upwardly through the wafer  58  to the top surface thereof. Heat can be radiated from the top surface of the wafer carrier  50  and from the top surfaces of the wafers  58  to the colder elements of the process chamber  12  as, for example, to the walls  20  of the process chamber  12  and to the gas inlet manifold  14 . Heat can also be transferred from the top surface of the wafer carrier  50  and the top surfaces of the wafers  58  to the process gas passing over these surfaces. The chamber  12  also includes an outer liner  28  that reduces process gas penetration into the area of the chamber containing the heating element  60 . In an example embodiment, heat shields (not shown) can be provided below the heating element  60 , for example, disposed parallel to the wafer carrier  50 , to help direct heat from the heating element upwards towards the wafer carrier  50  and not downwards towards the base plate  24  at the bottom end of the chamber  12 . 
         [0035]    The chamber  12  is also equipped with an exhaust system  70  arranged to remove spent gases from the interior region  26  of the chamber. The exhaust system  70  includes an exhaust manifold  72  at or near the bottom of the chamber  12 . The exhaust manifold  72  is coupled to an exhaust conduit  74  that extends downward through the base plate  24  and is configured to carry spent gasses out of the reaction chamber  12 . 
         [0036]    As shown in  FIG. 1 , the exhaust manifold  72  extends around the periphery of the chamber  12  below the top of the spindle  40  and below the wafer carrier  50 . The exhaust manifold  72  defines a channel  78 . Although the channel  78  is shown as cylindrical or ring-shaped, other embodiments can include a channel  78  having another shape, including, for example, a square, a hexagon, an octagon, or any other appropriate shape. 
         [0037]    The exhaust manifold  72  includes a plurality of ports in the form of round apertures  76  extending through a top surface  77  of the manifold  72  from the interior region  26  of the chamber  12  into the channel  78 . The channel  78  is coupled to two exhaust ports  79  at diametrically opposed locations. Each exhaust port  79  extends between the channel  78  and the exhaust conduit  74 . The conduit  74  in turn is connected to a pump  75  or other vacuum source. 
         [0038]    The ports  76  are of relatively small diameter, as for example, about 0.5″ to about 0.75″. The ports  76  provide a low fluid conductance element that creates a flow rate restriction between the interior region  26  of the chamber  12  and the channel  78  of the exhaust manifold  72 . The exhaust manifold  72  thus provides a pressure barrier between the interior region  26  of the chamber  12  and the exhaust ports  79 , thereby providing increased uniformity of the flow of reactants inside of the chamber  12 . Because the flow resistance within the channel  78  is small, the flows through all of the ports  76  are substantially equal. This provides a substantially uniform flow of waste gas into the channel  78  around the periphery of the chamber  12 . 
         [0039]    In a particular example, the exhaust manifold  72  can include approximately ten ports  76 , each port  76  located approximately 36° apart from each adjacent port  76 . In other embodiments, the exhaust manifold can include any number of ports, each port located any distance apart from each adjacent port. For example, there can be 6, 8, 12, 16, 20, 24, or 32 ports, each spaced equidistantly about the top surface of the exhaust manifold  72 . 
         [0040]    As shown, the exhaust manifold  72  includes ports  76  that are circular in shape. In other embodiments, the apertures in the exhaust manifold can define any shape, including for example, oval, parabolic, square, rectangular, triangular, hexagonal, octagonal, crescent-shaped, or S-shaped. 
         [0041]    As shown, each port  76  extends horizontally across approximately three-quarters of the width of the top surface  77 , in a radial direction from the central axis of the reaction chamber. In other embodiments, each port can extend across any portion of the width of the top surface of the exhaust manifold, including approximately half, two-thirds, four-fifths, or nine-tenths of the width of the top surface. 
         [0042]    If a low fluid conductance element such as the ports  76  of the exhaust manifold  72  was not included in the chamber  12 , the location of the two diametrically opposed exhaust ports  79  could cause a pressure gradient around the circumference of the chamber  12 , thereby producing non-uniform gas flow across the wafer carrier  50 , which can cause undesired variations in the properties of the resulting semiconductor wafers  58 . 
         [0043]    Use of the exhaust manifold  72  to provide flow rate restriction can result in parasitic deposition of solid particles (e.g., products of the reactants) formed in and around the ports  76  during operation of the apparatus  10 . Such solid particles can reduce the size of or completely block some or all of the ports  76 , which can cause non-uniform flow rates among various ports  76 , which can result in undesired variations in the gas flow and thus affect the properties of the wafers  58  formed by the apparatus  10 . Partial blockage of one or more of the ports  76  can also cause a non-uniform growth rate of the wafers  58 . 
         [0044]    The apparatus  10  further includes a plurality of cleaning elements in the form of plungers  80 , each plunger extending downward from the shutter  34  from a location at or near the lower edge  37  thereof, such that the plungers  80  translate up and down with the shutter  34  relative to the exhaust manifold  72 . Each plunger  80  is configured to clean solid particles from a respective port  76 . Each plunger  80  can define a diameter that is approximately equal to or slightly smaller than a respective port  76 , such that each plunger  80  can scrape solid particles off of the inside edge of the respective port  76  as the plunger  80  is translated up and down relative to the top surface  77  of the exhaust manifold  72 . 
         [0045]    As best shown in  FIG. 2 , each plunger  80  is attached to the shutter  34  at an outer surface  38  thereof, and each plunger  80  includes a shaft  81  that is bent inward and downward and a contact element in the form of a conical tip  82  at a lower end thereof. Having a conical tip  82  may allow the pluralities of plungers to self-locate relative to the respective ports  76  as the shutter  34  is moved downward, such that if the conical tips  82  are misaligned with the respective ports  76 , the contact between the conical tips  82  and the top surface  77  can cause the plungers  80  to move the shutter  34  slightly horizontally until the plungers  80  can slide downward into the respective ports  76 . The plunger shafts  81  desirably have sufficient flexibility in the horizontal direction to allow such self-centering. 
         [0046]    As shown, each cleaning element  80  includes a tip  82  that is conical in shape, having a circular profile. In other embodiments, the contact element of each cleaning element can define any shape, including for example, oval, parabolic, square, rectangular, triangular, hexagonal, octagonal, crescent-shaped, or S-shaped. 
         [0047]    As shown, the conical tip  82  is located at the lower end of each cleaning element  80 . In other embodiments, the contact element of each cleaning element need not be located at a lower end thereof. In one example, each cleaning element can have a shaft and tip that have the same diameter and sectional profile, such that any part of the shaft can serve as a cleaning element. In another example, each cleaning element can have a contact element in the form of a radially-extending disc that is located between an upper and lower end thereof. In such an example, the lower end of the cleaning element can be moved downward into a port until the disc-shaped contact element contacts the port, thereby scraping solid particles off of the port. 
         [0048]    Depending on the relative diameters of each tip  82  and a respective port  76 , each plunger  80  can be fully inserted into a respective port  76  (e.g., wherein the diameter of the tip is less than or equal to the diameter of the port), or each plunger  80  can be partially inserted into a respective port  76  (e.g., wherein the diameter of the tip is greater than the diameter of the port). In embodiments where the diameter of the tip  82  is greater than the diameter of the respective port  76 , the tip  82  can be lowered into the aperture until the periphery of the tip  82  contacts the top surface  77  of the exhaust manifold  72 . Such a partial penetration of the tip  82  into a respective port  76  can effectively remove some or all of the solid particles that have become deposited in the port  76 . 
         [0049]    As shown in  FIG. 2 , each port  76  can have a chamfered edge. The angle of the chamfered edge of each port  76  can be any angle, but in some embodiments, the angle may approximately match the angle of the respective tip  82  (e.g., the angle of the chamfered edge of each port and the cone of each tip can be approximately 45 degrees. In such embodiments, where the diameter of the respective tip  82  is greater than the diameter of the port, the mating surfaces between the chamfered edge of the port and the conical tip can allow a greater surface area contact between the port and the tip, thereby allowing for the dislodging of a greater amount of solid particles from the port  76 . 
         [0050]    In operation, in a process according to an embodiment of the invention, the entry opening  30  is opened by lowering the shutter  34  to the open position  34 ′, thereby lowering a plurality of plungers  80  into respective ports  76 , thereby removing solid particles that may have deposited in the ports during a previous operation cycle of the apparatus. 
         [0051]    Then, a wafer carrier  50  with wafers  58  loaded thereon is loaded from the antechamber  32  into the chamber  12  and is placed in the operative position shown in  FIGS. 1 and 3 . In this condition, the top surfaces of the wafers  58  face upwardly, towards the gas inlet manifold  14 . The entry opening  30  is closed by raising the shutter  34  to the closed position depicted in solid lines in  FIG. 1 , thereby withdrawing the plungers  80  from the ports  76 . The heating element  60  is actuated, and the rotary drive  48  operates to turn the spindle  40  and hence the wafer carrier  50  around central axis  42 . Typically, the spindle  40  is rotated at a rotational speed from about 50-1500 revolutions per minute. 
         [0052]    Process gas supply units (not shown) are actuated to supply gases through the gas inlet manifold  14 . The gases pass downwardly toward the wafer carrier  50 , over the top surface of the wafer carrier  50  and the top surfaces of the wafers  58 , and downwardly around a periphery of the wafer carrier to the exhaust system  70  (which can result in solid particles being deposited in the ports  76 ). Thus, the top surface of the wafer carrier  50  and the top surfaces of the wafers  58  are exposed to a process gas including a mixture of the various gases supplied by the various process gas supply units. Most typically, the process gas at the top surface is predominantly composed of the carrier gas supplied by a carrier gas supply unit (not shown). 
         [0053]    The process continues until the desired treatment of the wafers  58  has been completed. Once the process has been completed, the entry opening  30  is opened by lowering the shutter  34  to position  34 ′, thereby lowering the plurality of plungers  80  into the respective ports  76 , thereby removing solid particles that may have deposited in the ports  76  during the just-completed operation cycle of the apparatus. Once the entry opening  30  is open, the wafer carrier  50  can be removed from the spindle  40  and can be replaced with a new wafer carrier  50  for the next operational cycle. The structure and method described above provide effective cleaning of the flow-restriction ports  76  of the exhaust system  70  during the normal operational cycle. This avoids or minimizes the need to disassemble the system in order to clean the ports  76 . 
         [0054]    In other embodiments (not shown), the plungers can move up and down relative to the exhaust manifold independently of the shutter. For example, the plungers can be attached to a bracket (e.g., a cylindrical bracket) that is located between the shutter and the exhaust manifold. The bracket can be moved up and down by a control and actuation mechanism that is coupled to the reaction chamber by a linkage similar to the linkage  35  shown in  FIG. 2 . However, use of the shutter itself to move the cleaning elements as discussed above considerably simplifies the design and operation of the reactor. 
         [0055]    In embodiments where the plungers can move up and down relative to the exhaust manifold independently of the shutter, it is not necessary that the plungers be moved into the apertures of the exhaust manifold following each operational cycle. In such embodiments, the plungers can moved downward to clean the apertures after any number of cycles, including for example, after two, three, four, five, eight, ten, fifteen, or twenty operational cycles. 
         [0056]    In a further variation, the plungers  80  may be mounted to the shutter  34 , but the shutter  34  and the control and actuation mechanism  41  are arranged so that in the normal open position of the shutter  34 , the plungers  80  remain above the ports  76 . The control and actuation mechanism  41  can be arranged to move the shutter  34  downwardly beyond its normal open position to a special port-cleaning position, where the plungers  80  are engaged in the ports  76 . Movement to the cleaning position can be used as needed, either in every cycle or intermittently. 
         [0057]    The shutter  134  shown in  FIG. 4  can be used in place of the shutter  34  shown in  FIGS. 1-3 . The shutter  134  is the same as the shutter  34  except that the plunger  180  extending downward near the lower edge  137  is attached to the shutter  134  at an inner surface  139  thereof, rather than at an outer surface  138 . The plunger  180  includes a shaft  181  that extends straight down along the inner surface  139 , and the shaft  181  terminates in a contact element shown in the form of a conical tip  182 . 
         [0058]    As shown in  FIGS. 1 ,  2 , and  4 , the plungers  80  and  180  extend downward from the shutters  34  and  134  for contact with respective ports. However, in other embodiments, the lower edge of the shutter can be shaped to function as the plungers, such that the plungers are integrated into the shape of the lower edge of the shutter as a single component. For example, the lower edge of the shutter can include plunger-like protrusions extending downward towards respective ports, such that when the shutter is moved downward to clean solid particles from the ports, a portion or all of each plunger-like protrusion can be inserted into a respective port, thereby scraping solid particles from the respective port. 
         [0059]    Referring now to  FIGS. 5A and 5B , a chemical vapor deposition apparatus  210  in accordance with an embodiment of the invention includes a shutter  234  to be used in a wafer treatment process in a reaction chamber such as the reaction chamber  12  shown in  FIG. 1 . The shutter  234  shown in  FIGS. 5A  (open shutter position) and  5 B (closed shutter position) is similar to the shutter  34  shown in  FIGS. 1-3 , except that the shutter  234  does not include plungers extending downward from an edge thereof, and the exhaust system includes a labyrinth having a single ring-shaped port rather than a manifold having plurality of round ports. 
         [0060]    The apparatus  210  includes a shutter  234  for closing and opening an entry opening such as the entry opening  30  shown in  FIGS. 1 and 3 . The shutter  234  defines an upper surface  236  facing a gas inlet manifold (not shown) and a lower edge  237  facing an exhaust labyrinth  272 . 
         [0061]    The exhaust labyrinth  272  includes a single port  276  (e.g., a ring-shaped port) extending through a top surface  277  of the labyrinth  272  into a channel  278  (e.g., a ring-shaped channel) having a plurality of baffles  283  that are coupled together by a bolt  284 . The channel  278  is coupled to an exhaust conduit  274  and exhaust ports configured to remove spent gases from the interior region of the chamber. 
         [0062]    The exhaust labyrinth  272  and the included baffles  283  are configured to provide a low fluid conductance element that creates a flow rate restriction between the interior region of the reaction chamber and the exhaust conduit  274 . The exhaust labyrinth  272  and the included baffles  283  can provide a pressure barrier between the interior region of the chamber and the exhaust conduit  274 , thereby providing increased uniformity of the flow of reactants inside of the chamber. 
         [0063]    Rather than having individual plungers coupled to the shutter (as shown in  FIGS. 1-4 ), the lower edge  237  of the shutter  234  is moveable relative to the exhaust labyrinth  272 , and is configured to contact the single port  276  of the exhaust labyrinth  272  to dislodge, clean, or scrape solid particles therefrom. 
         [0064]    The lower edge  237  of the shutter  234  is configured such that when the shutter  234  is lowered (e.g., to open the reaction chamber for insertion or removal of a wafer carrier), a portion of the shutter  234  can be inserted into the single port  276 , thereby scraping solid particles therefrom. The lower edge  237  can define a width (in a direction perpendicular to the central axis of the reaction chamber) that is approximately equal to or slightly smaller than the width of the port  276 . In such an embodiment, the lower edge  237  can partially fit inside of the port  276  and can scrape solid particles off of the inside edges of the port  276  as the shutter  234  is translated up and down relative to the top surface  277  of the labyrinth  272 . 
         [0065]    Having a chamfered inner edge  285  adjacent the lower edge  237  of the shutter  234 , and having a chamfered inner edge  286  of the port  276  may allow the shutter  234  to self-locate relative to the port  276  as the shutter  234  is moved downward. In such an embodiment, if the shutter  234  is misaligned with the port  276 , the contact between the chamfered inner edges  285  and  286  can cause the shutter  234  to move slightly horizontally until lower edge  237  thereof can slide downward partially into the port  276 . 
         [0066]    The angle of the chamfered inner edge  285  of the shutter  234  and the chamfered inner edge  286  of the port  276  can be any angles, but in some embodiments, the angle of the chamfered inner edges  285  and  286  may approximately match each other (e.g., the angle of the chamfered inner edges  285  and  286  can be approximately 45 degrees to the central axis of the chamber). In such embodiments, the mating chamfer inner edges  285  and  286  can allow a greater surface area contact between the shutter  234  and the port  276 , thereby allowing for the dislodging of a greater amount of solid particles from the port  276 . 
         [0067]    As shown, the exhaust labyrinth  272  includes a single port  276  extending around the entire exhaust labyrinth  272 . In other embodiments, the exhaust labyrinth can include a plurality of spaced apart arc-shaped ports extending around the labyrinth. For example, the exhaust labyrinth can include ten spaced apart arc-shaped ports, each spanning approximately 30 degrees, and each separated by 6 degrees of the top surface of the exhaust labyrinth. In such an embodiment, the lower edge of the shutter may include ten lowered portions, each lowered portion configured to fit into a corresponding arc-shaped port, such that the shutter can clean solid particles from the arc-shaped ports when the shutter contacts the exhaust labyrinth. 
         [0068]    As shown, the port  276  extends horizontally across approximately one-quarter of the width of the top surface  277 , in a radial direction from the central axis of the reaction chamber. In other embodiments, the port can extend across any portion of the width of the top surface of the exhaust manifold, including approximately half, two-thirds, four-fifths, or nine-tenths of the width of the top surface. 
         [0069]    As shown in  FIGS. 5A and 5B , the shutter  234  translates up and down relative to the exhaust labyrinth  272  for contact therewith and dislodging of solid particles. In other embodiments (not shown), a separate cleaning element (e.g., a cylindrical-shaped cleaning element) can move up and down relative to the exhaust labyrinth independently of the shutter. For example, a cylindrical bracket that is located between the shutter and the exhaust labyrinth can move up and down and contact the exhaust labyrinth to dislodge sold particles. The bracket can be moved by a control and actuation mechanism that is coupled to the reaction chamber by a linkage such as the linkage  35  shown in  FIG. 2 . 
         [0070]    As shown, the shutter  234  has a width greater than the width of the port  276 , such that only the lower edge  277  and part of the chamfered inner edge  285  can be inserted into the aperture  276  to dislodge solid particles therefrom. In other embodiments (not shown), the entire lower edge and chamfered inner edge of the shutter may be able to be inserted into the port (e.g., wherein the width of the shutter is less than or equal to the width of the aperture). 
         [0071]    As shown, there are three baffles  283  located inside of the exhaust labyrinth  272 . In other embodiments, there can be any number of baffles located inside of the exhaust labyrinth, depending on the degree of gas flow restriction between the inner region of the reaction chamber and the exhaust conduit that is desired. 
         [0072]    The invention can be applied in various wafer treatment processes as, for example, chemical vapor deposition, chemical etching of wafers, and the like. 
         [0073]    Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It will be appreciated that the various dependent claims and the features set forth therein can be combined in different ways than presented in the initial claims. It will also be appreciated that the features described in connection with individual embodiments may be shared with others of the described embodiments.