Abstract:
An atomic deposition (ALD) thin film deposition apparatus includes a deposition chamber configured to deposit a thin film on a wafer mounted within a space defined therein. The deposition chamber comprises a gas inlet that is in communication with the space. A gas system is configured to deliver gas to the gas inlet of the deposition chamber. At least a portion of the gas system is positioned above the deposition chamber. The gas system includes a mixer configured to mix a plurality of gas streams. A transfer member is in fluid communication with the mixer and the gas inlet. The transfer member comprising a pair of horizontally divergent walls configured to spread the gas in a horizontal direction before entering the gas inlet.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the priority benefit under 35 U.S.C. §120 to U.S. application Ser. No. 11/333,127, filed on Jan. 17, 2006, issued Jun. 26, 2012 as U.S. Pat. No. 8,211,230 and under 35 U.S.C. §119(e) of Provisional Application No. 60/645,581, filed on Jan. 18, 2005 and Provisional Application No. 60/656,832, filed Feb. 24, 2005, the entire contents of these applications are hereby incorporated herein by reference in their entirety 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to equipment for chemical processes. In particular, the present invention relates to equipment for growing a thin film in a reaction chamber. 
       DESCRIPTION OF THE RELATED ART 
       [0003]    There are several vapor deposition methods for depositing thin films on the surface of substrates. These methods include vacuum evaporation deposition, Molecular Beam Epitaxy (MBE), different variants of Chemical Vapor Deposition (CVD) (including low-pressure and organometallic CVD and plasma-enhanced CVD), and Atomic Layer Epitaxy (ALE), which is more recently referred to as Atomic Layer Deposition (ALD). 
         [0004]    ALD is a known process in the semiconductor industry for forming thin films of materials on substrates such as silicon wafers. ALD is a type of vapor deposition wherein a film is built up through self-saturating reactions performed in cycles. The thickness of the film is determined by the number of cycles performed. In an ALD process, gaseous precursors are supplied, alternatingly and repeatedly, to the substrate or wafer to form a thin film of material on the wafer. One reactant adsorbs in a self-limiting process on the wafer. A subsequent reactant pulse reacts with the adsorbed material to form a single molecular layer of the desired material. Decomposition may occur through reaction with an appropriately selected reagent, such as in a ligand exchange or a gettering reaction. In a typical ALD reaction, no more than a molecular monolayer forms per cycle. Thicker films are produced through repeated growth cycles until the target thickness is achieved. 
         [0005]    In an ALD process, one or more substrates with at least one surface to be coated and reactants for forming a desired product are introduced into the reactor or deposition chamber. The one or more substrates are typically placed on a wafer support or susceptor. The wafer support is located inside a chamber defined within the reactor. The wafer is heated to a desired temperature above the condensation temperatures of the reactant gases and below the thermal decomposition temperatures of the reactant gases. 
         [0006]    A characteristic feature of ALD is that each reactant is delivered to the substrate in a pulse until a saturated surface condition is reached. As noted above, one reactant typically adsorbs on the substrate surface and a second reactant subsequently reacts with the adsorbed species. As the growth rate is self-limiting, the rate of growth is proportional to the repetition rate of the reaction sequences, rather than to the temperature or flux of reactant as in CVD. 
         [0007]    To obtain self-limiting growth, vapor phase reactants are kept separated by purge or other removal steps between sequential reactant pulses. Since growth of the desired material does not occur during the purge step, it can be advantageous to limit the duration of the purge step. A shorter duration purge step can increase the available time for adsorption and reaction of the reactants within the reactor, but because the reactants are often mutually reactive, mixing of the vapor phase reactants should be avoided to reduce the risk of CVD reactions destroying the self-limiting nature of the deposition. Even mixing on shared lines immediately upstream or downstream of the reaction chamber can contaminate the process through parasitic CVD and subsequent particulate generation. 
       SUMMARY OF THE INVENTION 
       [0008]    To prevent the vapor phase reactants from mixing, ALD reactors may include an “inert gas valving” or a “diffusion barrier” arrangement in a portion of a supply conduit to prevent flow of reactant from a reactant source to the reaction chamber during the purge step. Inert gas valving involves forming a gas phase, convective barrier of a gas flowing in the opposite direction to the normal reactant flow in the supply conduit. See T. Suntola,  Handbook of Crystal Growth III, Thin Films and Epitaxy, Part B: Growth Mechanisms and Dynamics , ch. 14,  Atomic Layer Epitaxy , edited by D. T. J. Hurle, Elsevier Science V.B. (1994), pp. 601-663, the disclosure of which is incorporated herein by reference. See especially, pp. 624-626. Although such prior art arrangements have been successful in preventing vapor phase reactants from mixing, there is still room for improvement. In particular, experimental studies have indicated that within the reactor chamber there are dead pockets and/or recirculation cells that are difficult to purge. Accordingly, a portion of previous reactant pulse may remain in the reaction chamber during the subsequent reactant pulse. This may disadvantageously lead to CVD growth within the reaction chamber and on the substrate itself. CVD growth within the reaction chamber may disadvantageously lead to increased particle emissions. 
         [0009]    A need therefore exists for an improved reactor design which is easier to purge and eliminates or significantly reduces dead pockets in which reactants may remain after a purging step. 
         [0010]    Accordingly, one embodiment of the present invention comprises an atomic deposition (ALD) thin film deposition apparatus that includes a deposition chamber configured to deposit a thin film on a wafer mounted within a space defined therein. The deposition chamber comprises a gas inlet that is in communication with the space. A gas system is configured to deliver gas to the gas inlet of the deposition chamber. At least a portion of the gas system is positioned above the deposition chamber. The gas system includes a mixer configured to mix a plurality of gas streams. A transfer member is in fluid communication with the mixer and the gas inlet. The transfer member comprising a pair of horizontally divergent walls configured to spread the gas in a horizontal direction before entering the gas inlet. 
         [0011]    Another embodiment of the present invention comprises an atomic layer deposition (ALD) thin film deposition apparatus that comprises a deposition chamber configured to deposit a thin film on a wafer mounted within a space defined therein. The deposition chamber includes a gas inlet that is in communication with the space. The deposition chamber further comprising a sealing portion that includes a sealing surface. A susceptor is configured to support the wafer within the space. The susceptor configured to move vertically with respect to the deposition chamber between a first position in which the susceptor seals against the sealing surface and a second, lower position in which the susceptor no longer seals against the sealing surface. In the first position, a vertical distance between the interface between the sealing surface and the susceptor and the wafer positioned on the susceptor is less than about 2 millimeters. 
         [0012]    Another embodiment of the present invention comprises a substrate support for processing semiconductor substrates. The substrate support comprises a top surface with a recess. The recess is configured such that the top surface of the substrate support only contacts the substrate along an edge portion of the substrate. 
         [0013]    Another embodiment of the present invention comprises an deposition (ALD) thin film deposition apparatus that includes a deposition chamber configured to deposit a thin film on a wafer mounted within a space defined therein. The deposition chamber comprises a gas inlet that is in communication with the space. The deposition chamber further comprises a sealing portion that includes a sealing surface. A susceptor is configured to support the wafer within the space. The susceptor is configured to move vertically with respect to the deposition chamber between a first position in which the susceptor seals against the sealing surface and a second, lower position in which the susceptor no longer seals against the sealing surface. The susceptor is configured such that when the wafer is positioned on the susceptor in the first position, the leading edge of the wafer, with respect to gas flow, is positioned further from the sealing surface as compared to the trailing edge of the wafer. 
         [0014]    These and other objects, together with the advantages thereof over known processes and apparatuses which shall become apparent from the following specification, are accomplished by the invention as hereinafter described and claimed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1A  is front, top and left side a perspective view of an atomic layer deposition (ALD) device. 
           [0016]      FIG. 1B  is a bottom, back and left side perspective view of the ALD device from  FIG. 1A . 
           [0017]      FIG. 2  is a cut-away perspective of the ALD device of  FIG. 1 , cut along lines  2 - 2 . 
           [0018]      FIG. 3  is a perspective view of the gas distribution system within the ALD device of  FIG. 1A  (partially visible in  FIG. 2 ). 
           [0019]      FIG. 4  is a top plan view of the reactant gas lines coupled to an upstream member of the mixer assembly of the gas distribution system from  FIG. 3  showing a buffer region in each reactant gas line. 
           [0020]      FIG. 5  is a schematic cross-sectional view through a portion of the gas-distribution system and reactor chamber of the ALD device of  FIG. 1A . 
           [0021]      FIG. 6  is a perspective view of a portion of a modified embodiment of a gas distribution system that is coupled to a top plate of a reaction chamber within an ALD device. 
           [0022]      FIG. 7  is a top plan view of the gas distribution system of  FIG. 6 . 
           [0023]      FIG. 8  is a top plan view of the top plate of  FIG. 6  with the gas distribution system removed. 
           [0024]      FIG. 9  is a cross-sectional view taken along line  9 - 9  of  FIG. 7 . 
           [0025]      FIG. 9A  is an enlarged view of a portion of  FIG. 9 . 
           [0026]      FIG. 10  is a schematic illustration of a susceptor, a substrate and a bottom plate of a reactor within the ALD system of  FIG. 1 . 
           [0027]      FIG. 11  is a cross-sectional view similar to  FIG. 9  but also illustrating a susceptor and bottom plate of the ALD device. 
           [0028]      FIG. 12  is a partial top perspective view of the susceptor and bottom plate of  FIG. 11 . 
           [0029]      FIG. 13  is a top perspective view of the susceptor of  FIG. 11  rotated 180 degrees. 
           [0030]      FIG. 14  is a cross-sectional view taken through line  14 - 14  of  FIG. 13  and further illustrating a substrate positioned on the susceptor. 
           [0031]      FIG. 15  is a schematic cross-sectional illustration of an edge portion of an embodiment of a lift pin and susceptor arrangement. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0032]      FIG. 1A  is a perspective view of an embodiment of an ALD device  100 . The ALD device  100  comprises a top member  110 , a bottom member  112 , and a front member  118 , which together form a portion of a housing for the ALD device  100 . In the embodiment illustrated in  FIG. 1A , an upper heater  114  extends through the top member  110 . The upper heater  114  is configured to maintain the temperature in the upper portion of the ALD device  100 . Similarly, a lower heater  116  extends through the bottom member  112 . The lower heater is configured to maintain the temperature in the lower portion of the ALD device  100 . 
         [0033]    The front member  118 , which serves as a gate valve, of the ALD device  100  covers an opening  120 . A dashed line outlines the opening  120  in  FIG. 1A . Once the front member  118  is removed, the opening  120  can receive a wafer to be processed by the ALD device  100 . In this way, the received wafer is placed in a deposition chamber within the ALD device  100 . Once processing is complete, the wafer can be removed from the deposition chamber via the same opening  120 . 
         [0034]    An ALD control system (not shown) is configured to control the ALD device  100  during processing of the wafer. For example, the ALD control system can include a computer control system and electrically controlled valves to control the flow of reactant and buffer gases into and out of the ALD device  100 . The ALD control system can include modules such as a software or hardware component, such as a FPGA or ASIC, which performs certain tasks. A module may advantageously be configured to reside on the addressable storage medium of the computer control system and be configured to execute on one or more processors. 
         [0035]      FIG. 1B  is a perspective view of the ALD device  100  showing the bottom member  112 . The ALD device  100  further comprises a set of couplings  102 ( a ),  102 ( b ),  104 ( a )-( d ). In this exemplary configuration, ALD device  100  includes four separate reactant vapor sources. Two of these reactant vapor sources are connected to the ALD device  100  via couplings  102 ( a ),  102 ( b ). These gas sources can be pressurized or not. These vapor sources can be, for example, solid sublimation vessels, liquid bubblers or gas bombs. The third and fourth reactant vapor sources are connected to the ALD device  100  via couplings  104 ( b ),  104 ( c ). 
         [0036]    In one embodiment, each reactant vapor source has an associated inert gas source, which can be used to purge the reactant vapor lines after pulsing the reactant. For example, the inert gas sources that are associated with the reactant vapor sources connected to couplings  102 ( a ) and  102 ( b ) can be connected to couplings  104 ( a ) and  104 ( d ), respectively. The inert gas sources associated with the reactant vapor sources connected to couplings  104 ( b ) and  104 ( c ) can also connected to couplings  104 ( b ) and  104 ( c ), respectively. These inert gas sources can be pressurized or not. These inert gas sources can, be, for example, noble or nitrogen gas sources. The ALD control system (not shown) controls one or more valves to selectively allow or prevent the various gases from reaching the ALD device  100 . 
         [0037]    The ALD device  100  can be configured to deposit a thin film on the wafer when the wafer is inserted in the deposition chamber. In general, the ALD device  100  can receive a first reactant gas via one of the couplings  102 ( a ),  102 ( b ) or one of the couplings  104 ( b ),  104 ( c ). The ALD device  100  can also receive inert gas via the couplings  104 ( a )- 104 ( d ). In one embodiment, the inert gas enters the deposition chamber with the first reactant gas to adsorb no more than a monolayer of the first reactant on the wafer. By switching the appropriate valves (not shown), the flow of the first reactant gas is stopped preferably via an inert gas valving (IGV) arrangement and the deposition chamber and the gas lines are then purged with the inert gas from couplings  104 ( a ),  104 ( b ),  104 ( c ), and  104 ( d ). After the deposition chamber and gas lines are purged, the deposition cycle is continued with one or more of the other reactant gases. In one embodiment, the reactants from alternated pulses react with each other on the substrate or wafer surface to form no more than a single monolayer of the desired product in each cycle. It should be noted that variations of true ALD operation can increase deposition speed above one monolayer per cycle with some sacrifice to uniformity. 
         [0038]    In embodiments of the ALD device  100 , more than two reactant gases can be sequentially flowed (separated by periods of purging) through the ALD device  100  in each cycle to form compound materials on the wafer. Excess of each reactant gas can be subsequently exhausted via gas exit  106  ( FIG. 1B ) after adsorbing or reacting in the deposition chamber. The gas exit  106  may be connected to a vacuum pump to assist in the removal of the gases from the deposition chamber and provide a low pressure condition in the deposition chamber. Furthermore, the entire ALD device  100  can be pumped down to a low pressure by connecting any of the other couplings on the bottom member  112  to a vacuum pump. 
         [0039]      FIG. 2  is a cut-away section view of the ALD device  100  from  FIG. 1A  taken along line  2 - 2 . Within the ALD device  100  is a gas distribution system  202  (shown in more detail in  FIG. 4 ) and a deposition chamber  200 , which is formed by a top or cover plate  314 , bottom or base plate  206 , susceptor or wafer support  204  and exhaust launder  316 . Located on upper and lower sides of the gas distribution system  202  and the deposition chamber  200  are one or more reflector plates  208 ,  210 . The ALD device  100  further includes a wafer support  204 , a wafer support heater  216 , and a thermal switch  218 . 
         [0040]    The wafer support  204  is located within the ALD device and is configured to support a substrate or wafer during the deposition process. The wafer support  204  can be adapted to rotate within the deposition chamber  200 . The wafer support heater  216  can be configured to heat the wafer support  204 . The thermal switch  218  can be provided on the top member  110 . The thermal switch  218  can be configured to monitor the temperature of the top member  110 . It will be understood that the system  100  includes other temperature sensor and control mechanisms to maintain various surfaces of the system at desired temperatures. 
         [0041]    The illustrated embodiment includes upper reflector plates  208  that provide a thermal barrier between the upper portion of the gas distribution system  202  and the top member  110 . Similarly, lower reflector plates  210  provide a thermal barrier between the lower portion of the deposition chamber  200  and the bottom member  112 . The reflector plates  208  and  210  are also used to assist in radiatively heating the deposition chamber within a low pressure environment. As illustrated in  FIG. 2 , the upper heater  114  is coupled to coils  212  which extend through the upper reflector plates  208 . The coils  212  are configured to provide heat through radiation to the upper portion of the gas distribution system  202 . Similarly, the lower heater  116  is coupled to coils  214  which extend through the lower reflector plates  210  and heat the lower portion of the deposition chamber  200 . Alternatively, other heating systems can be employed. 
         [0042]    The gas distribution system  202  is configured to route reactant gases entering via the couplings  102 ( a ),  102 ( b ),  104 ( b ),  104 ( c ) and inert gases entering via couplings  104 ( a )-( d ) through the ALD device  100  (see  FIG. 1B ). The gas distribution system  202  is further configured to selectively mix one or more of the inert gases entering via couplings  104 ( a )-( d ) with one of reactant gases entering via couplings  102 ( a ),  102 ( b ),  104 ( b ),  104 ( c ) during a given pulse. The resulting mixture enters the deposition chamber  200 . After each pulse, the gas distribution system  202  exhausts any unreacted reactant and inert gases from the deposition chamber via gas exit  106 , such as through purging. The term coupling is used to describe a gas flow connection between one or more gas lines. The locations of the couplings shown herein are for illustrative purposes only and can be located at different locations along a gas line. Moreover, a gas line associated with a given coupling can be configured to flow gas into or out of the gas distribution system  202 . As will be described below, the various couplings in the exemplary embodiments described herein are designated to flow gases into or out of the gas distribution system  202 . However, the invention is not limited to the exemplary embodiments disclosed herein. 
         [0043]    The order that the reactant gases are cycled through the ALD device  100  depends on the desired product. To minimize any interaction between one or more reactant gases prior to each gas entering the deposition chamber  200 , the inert gas entering via couplings  104 ( a )-( d ) is periodically cycled or continuously flowed through the ALD device  100  between pulses of the reactant gases. In this way, the inert gases purge the deposition chamber  200 . As will be explained below, various reactant gases and inert gases are systematically cycled through the ALD device  100  so as to form a deposit on the wafer inserted through the opening  120 . 
         [0044]      FIG. 3  is a perspective view of the deposition chamber  200  and the gas distribution system  202  from the ALD device  100  of  FIG. 1A . The gas distribution system  202  comprises a plurality of gas lines, a mixer assembly  304 , a transfer tube  310 , and an intake plenum or manifold  312 . The deposition chamber  200  includes a cover plate  314 , a base plate  206 , and an exhaust launder  316 . The gas distribution system  202  is connected to the deposition chamber  200  at the intake plenum  312   
         [0045]    As best seen in  FIG. 4 , in this example, the plurality of gas lines include four reactant lines  300 ,  303 ,  309 ,  315  and eight buffer lines  301 ,  302 ,  305 ,  307 ,  311 ,  313 ,  317 , and  319 . Each reactant line is coupled with two of the buffer lines. Reactant line  300  is coupled to buffer lines  301 ,  302 . Reactant line  303  is coupled to buffer lines  305 ,  307 . Reactant line  307  is coupled to buffer lines  311 ,  313 . Reactant line  315  is coupled to buffer lines  317 ,  319 . The gas distribution system  202  can include greater or fewer reactant lines and buffer lines depending on the configuration of the ALD device  100 . Moreover, each reactant line may or may not be coupled to two buffer lines. For example, one or more of the reactant lines may be coupled to the buffer lines while another reactant line is not. The reactant line that is not coupled to buffer lines could be shut off by other means. 
         [0046]    Each reactant gas line includes four couplings within the gas distribution system  202 . Reactant gas line  300  comprises couplings  300 ( a ),  300 ( b ),  300 ( c ), and  300 ( d ). Reactant gas line  303  comprises couplings  303 ( a ),  303 ( b ),  303 ( c ), and  303 ( d ). Reactant gas line  309  comprises couplings  309 ( a ),  309 ( b ),  309 ( c ), and  309 ( d ). Reactant gas line  315  comprises couplings  315 ( a ),  315 ( b ),  315 ( c ), and  315 ( d ). The couplings for each reactant gas line are described below. 
         [0047]    Coupling  300 ( a ) couples the reactant gas line  300  with the coupling  102 ( b ) that leads to a reactant source (see  FIG. 1B ). Coupling  300 ( b ) couples the reactant gas line  300  with the buffer line  302 . Coupling  300 ( c ) couples the reactant gas line  300  with the buffer line  301 . Coupling  300 ( d ) couples the reactant gas line  300  with the mixer assembly  304 . 
         [0048]    Coupling  303 ( a ) couples the reactant gas line  303  with the coupling  104 ( b ) that leads to another reactant source (see  FIG. 1B ). Coupling  303 ( b ) couples the reactant gas line  303  with the buffer line  307 . Coupling  303 ( c ) couples the reactant gas line  303  with the buffer line  305 . Coupling  303 ( d ) couples the reactant gas line  303  with the mixer assembly  304 . 
         [0049]    Coupling  309 ( a ) couples the reactant gas line  309  with the coupling  104 ( c ) that leads to another reactant source. (see  FIG. 1B ). Coupling  309 ( b ) couples the reactant gas line  309  with the buffer line  313 . Coupling  309 ( c ) couples the reactant gas line  309  with the buffer line  311 . Coupling  309 ( d ) couples the reactant gas line  309  with the mixer assembly  304 . 
         [0050]    Coupling  315 ( a ) couples the reactant gas line  315  with the coupling source  102 ( a ) that leads to still another reactant source (see  FIG. 1B ). Coupling  315 ( b ) couples the reactant gas line  315  with the buffer line  319 . Coupling  315 ( c ) couples the reactant gas line  315  with the buffer line  317 . Coupling  315 ( d ) couples the reactant gas line  315  with the mixer assembly  304 . 
         [0051]    Buffer lines  301 ,  302 ,  305 ,  307 ,  311 ,  313 ,  317 , and  319  comprise couplings  301 ( a ),  302 ( a ),  305 ( a ),  307 ( a ),  311 ( a ),  313 ( a ),  317 ( a ), and  319 ( a ), respectively. 
         [0052]    In the embodiment illustrated in  FIGS. 3 and 4 , each coupling  301 ( a ),  305 ( a ),  311 ( a ), and  317 ( a ) provides a flow path into the gas distribution system  202 . The coupling  301 ( a ) couples the buffer line  301  with the coupling  104 ( a ) (see  FIG. 1B ). The coupling  305 ( a ) couples the buffer line  305  with the coupling  104 ( b ) (see  FIG. 1B ). The coupling  311 ( a ) couples the buffer line  311  with the coupling  104 ( c ) (see  FIG. 1B ). The coupling  317 ( a ) couples the buffer line  317  with the coupling  104 ( d ) (see  FIG. 1B ). 
         [0053]    Each coupling  302 ( a ),  307 ( a ),  313 ( a ), and  319 ( a ) provides a flow path between the gas distribution system  202  and the exhaust launder  316  via connectors  320 ( a )-( d ). Connector  320 ( a ) connects coupling  302 ( a ) with the exhaust launder  316 . Connector  320 ( b ) connects coupling  307 ( a ) with the exhaust launder  316 . Connector  320 ( c ) connects coupling  313 ( a ) with the exhaust launder  316 . Connector  320 ( d ) connects coupling  319 ( a ) with the exhaust launder  316 . These connections contribute to the operation of inert gas valving (IGV). 
         [0054]    In the embodiment shown in  FIG. 3 , the reactant gas lines  300 ,  303 ,  309 , and  315  route reactant gases to the mixer assembly  304 . The buffer lines  301 ,  305 ,  311 , and  317  route inert gases to the mixer assembly  304 . The resulting mixture (one reactant at a time with an inert gas) flows through a transfer tube  310  to an intake plenum  312 . The intake plenum  312  distributes the mixture in a transverse direction with respect to the flow path through the transfer tube  310 . The mixture exits the intake plenum  312  into the deposition chamber  200  through the cover plate  314 . As shown in  FIGS. 2 and 3 , the cover plate  314  lies adjacent to the base plate  206  and the two plates form a flow path there between for the mixture to flow over the substrate or wafer placed on the wafer support  204 . The base plate  206  and the cover plate  314  have substantially rectangular outer perimeters. 
         [0055]    While traversing the deposition chamber  200 , the mixture pulse saturates the surface of the substrate. Adsorption or reaction occurs between the current mixture and the surface of the substrate as left by the previous pulse may occur. After passing through the deposition chamber  200 , the mixture flows towards the exhaust launder  316 . The exhaust launder  316  is configured to collect excess of the mixture and any byproduct after the mixture has saturated the wafer. In an embodiment, a region within the exhaust launder  316  is at a lower pressure than the pressure in the deposition chamber  200 . A negative pressure source or vacuum can be in flow communication with the exhaust launder  316  and/or gas exit  106  to draw the mixture from the deposition chamber  200 . The exhaust launder  316  is in flow communication with the gas exit  106 . The collected mixture exits the deposition chamber  200  via the gas exit  106 . 
         [0056]    Still referring to  FIG. 3 , the mixer assembly  304  includes an upstream member  306  and a downstream member  308 . The upstream member  306  is in flow communication with the reactant gas lines and the buffer lines. The upstream member  306  is configured to mix the reactant gas with the inert gas prior to the mixture entering the downstream member  308 . The downstream member  308  funnels the mixture between the upstream member  306  and the transfer tube  310 . the downstream member  308  is generally configured to minimize the tendency of the mixture to re-circulate within the downstream member  308  by continually reducing cross-sectional area of the flow path for the mixture. 
         [0057]      FIG. 4  is a top plan view of the reactant gas lines coupled to the buffer lines and the upstream member  306  of the mixer assembly. Between couplings  300 ( c ) and  300 ( b ), a buffer region  400 ( a ) is formed in the reactant gas line  300 . Between couplings  303 ( c ) and  303 ( b ), a buffer region  400 ( b ) is formed in the reactant gas line  303 . Between couplings  309 ( c ) and  309 ( b ), a buffer region  400 ( c ) is formed in the reactant gas line  309 . Between couplings  315 ( c ) and  315 ( b ), a buffer region  400 ( d ) is formed in the reactant gas line  315 . The buffer lines  301 ,  305 ,  311 , and  317 , which form flow paths into the gas distribution system  202 , couple to their associated gas lines downstream of couplings  300 ( b )  303 ( b ),  309 ( b ), and  315 ( b ). In this way, gas entering via couplings  301 ( a ),  305 ( a ),  311 ( a ), and  317 ( a ) enters the reactant lines  300 ,  303 ,  309 ,  315  downstream of the reactant lines couplings with the buffer lines  302 ,  307 ,  311 , and  319 . Fixed orifices can be placed at couplings  302 ( a ),  307 ( a ),  313 ( a ) and  319 ( a ). 
         [0058]    As seen in  FIG. 3 , couplings  302 ( a ),  307 ( a ),  313 ( a ) and  319 ( a ) are in communication with the exhaust launder  316 . The orifices create a higher resistance path for the gases to flow to the exhaust launder  316  and bypass the deposition chamber  200 . In this way, during the pulse of a reactant gas, a small portion of the reactant gas entering via couplings  300 ( a ),  303 ( a ),  309 ( a ) or  315 ( a ) bypasses the deposition chamber and flows directly to the exhaust launder  316 . The restriction created by the orifice limits the amount of shunted reactant. During the purge step, at least a portion of the inert gas entering via couplings  301 ( a ),  305 ( a ),  311 ( a ), and  317 ( a ) creates a reverse flow towards couplings  300 ( b )  303 ( b ),  309 ( b ), and  315 ( b ) to form the buffer regions  400 ( a )-( d ) within the reactant gas line. The buffer regions keep the reactant gases from diffusing into the reactor during the purge steps or during reactant flow of a reactant from one of the other reactant lines into the mixer assembly  304 . 
         [0059]    For example, during an ALD processing step, reactant gas flows through reactant line  300  towards the upstream member  306  of the mixer assembly. A small amount of this reactant gas is diverted to the buffer line  302  and out through coupling  302 ( a ) into the exhaust launder  316 . The amount of gas that is diverted to the buffer line is dependent of the size of the fixed orifice at coupling  302 ( a ). The size of the fixed orifice can be changed to divert more or less of the gas into the exhaust launder  316 . The remaining reactant gas flows through the buffer region  400 ( a ) to the coupling  300 ( c ). 
         [0060]    Inert gas may or may not be introduced through coupling  301 ( a ) to push the reactant gas into the upstream member  306 . If inert gas is introduced through coupling  301 ( a ), the inert gas joins the reactant gas at coupling  300 ( c ) and flows to the upstream member  306 . After the pulse step, the reactant gas is purged from the gas line. Purging of the gas line can be accomplished by, for example, shutting off the flow of the reactant gas from coupling  300 ( a ) and/or using the inert gas to impede the diffusion of any remaining reactant gas into the upstream member  306 . The shutoff valve can be located outside of the heated area and can be used to shut off the flow of the reactant gas. The inert gas can be introduced through coupling  301 ( a ) in an inert gas valving (IGV) process as described generally in U.S. patent publication number 2001/0054377, published on Dec. 27, 2001, the disclosure of which is hereby incorporated herein by reference. 
         [0061]    A first portion of the stream of inert gas flow enters the buffer region  400 ( a ) and flows upstream or backwards towards the coupling  300 ( b ). A second portion of the stream of gas flows downstream towards the upstream member  306 . The first portion exits the reactant line  300  at the end of the buffer region  400 ( a ) and enters the buffer line  302 . While the first portion is flowing through the buffer region  400 ( a ), the remaining reactant gas between the shutoff valve upstream of coupling  300 ( a ) and coupling  300 ( b ) is blocked from flowing or diffusing to the upstream member  306  without subjecting physical valves (which are remote) to the wear caused by high temperatures. The first portion forms a buffer or diffusion barrier (or inert gas valve) that impedes the flow of the reactant gas through the reactant line  300  to the mixer assembly  304 . By cycling the shutoff valve upstream of coupling  300 ( a ), the ALD control system is able to control between flowing and not flowing the inert gas in the buffer line  301 . In this way, the ALD control system is able to quickly control whether the reactant gas entering the reactant line  300  via coupling  300 ( a ) reaches the upstream member  306 . Furthermore, during the purge step and subsequent pulses of other reactant gases, the reactant gas in a “dead space” which is located between the shutoff valve upstream of the coupling  300 ( a ) and coupling  300 ( b ) can be kept from diffusing into the upstream member  306 . This may be advantageous for ALD since the different reactant gases are kept separated and only react on the surface of the substrate and not in the gas phase. 
         [0062]    Whether the reactant gas entering the gas distribution system  202  via the coupling  303 ( a ) reaches the upstream member  306  is similarly controlled by flowing a gas through the buffer line  305  and into the reactant line  303  at coupling  303 ( c ) and using a shutoff valve upstream of coupling  303 ( a ). A first portion of the gas entering the reactant line at coupling  303 ( c ) forms the buffer  400 ( b ). In this way, the first portion of the gas impedes the reactant gas entering via the reactant line  303  from entering the upstream member  306 . A second portion of the gas entering the reactant line at coupling  303 ( c ) flows away from the buffer region  400 ( b ) and towards the upstream member  306 . 
         [0063]    Whether the reactant gas entering the gas distribution system  202  via the coupling  309 ( a ) reaches the upstream member  306  is similarly controlled by flowing a gas through the buffer line  311  and into the reactant line  309  at coupling  309 ( c ) and using a shutoff valve upstream of coupling  309 ( a ). A first portion of the gas entering the reactant line at coupling  309 ( c ) forms the buffer  400 ( c ). In this way, the first portion of the gas impedes the reactant gas entering via the reactant line  309  from entering the upstream member  306 . A second portion of the gas entering the reactant line at coupling  309 ( c ) flows away from the buffer region  400 ( c ) and towards the upstream member  306 . 
         [0064]    Whether the reactant gas entering the gas distribution system  202  via the coupling  315 ( a ) reaches the upstream member  306  is similarly controlled by flowing a gas through the buffer line  317  and into the reactant line  315  at coupling  315 ( c ) and a shutoff valve upstream of coupling  315 ( a ). A first portion of the gas entering the reactant line at coupling  315 ( c ) forms the buffer  400 ( d ). In this way, the first portion of the gas impedes the reactant gas entering via the reactant line  315  from entering the upstream member  306 . A second portion of the gas entering the reactant line at coupling  315 ( c ) flows away from the buffer region  400 ( d ) and towards the upstream member  306 . 
         [0065]    As mentioned above, the first portions of the gases which enter the gas distribution system  202  via buffer lines  301 ,  305 ,  311 , and  317  and form the buffer regions  400 ( a )-( d ), exit via buffer lines  302 ,  307 ,  313 , and  319 . The gas exiting via buffer lines  302 ,  307 ,  313 , and  319  enter the exhaust launder  316  without passing through the deposition chamber  200 . In this way, the first portions of the inert gases bypass the deposition chamber  200  and are collected by the exhaust launder  316  downstream of the deposition chamber  200 . 
         [0066]    As mentioned above, the second portions of each gas which enter the gas distribution system  202  via buffer lines  301 ,  305 ,  311 , and  317  flow away from the buffer regions  400 ( a )-( d ) and enter the mixer assembly  304 . During reactant pulses, the second portions mix with one or more reactant gases from other reactant lines, which reach the mixer assembly  304 . Thus, the second portions flow through the deposition chamber  200 . Depending on the current ALD processing step, gases may periodically flow through their respective buffer lines  301 ,  305 ,  311 , and  317 . 
         [0067]    A reactant gas which the ALD control system desires to reach the deposition chamber  200  flows through its respective reactant line and into the mixer assembly  304 . The ALD control system forms buffer regions  400  in the reactant lines associated with the reactant gases which the ALD control system does not want to reach the deposition chamber  200 . The reactant gas which flows through the reactant line which does not have a buffer region  400  mixes with the second portions of the one or more inert gases which are simultaneously flowing through the other reactant lines and into the mixer assembly  304 . As explained above, the first portions of these gases form buffer regions in the other reactant lines and bypass the deposition chamber  200 . 
         [0068]    In one embodiment of the ALD device  100  which comprises four reactant gas lines, each reactant gas alternates in reaching the mixer assembly  304 . In this embodiment the reactant gas selected by ALD control system flows into the mixer assembly  304  while inert or “buffer” gas flows in the remaining three reactant lines. Continuing with this embodiment, the second portions of the gases flowing away from the buffer regions enter the mixer assembly  304 . The reactant gas of the pulse of interest then mixes with the inert gas of the second portions in the mixer assembly  304 . 
         [0069]    Further aspects and feature of the illustrated embodiment of the ALD device  100  can be found in U.S. patent application Ser. No. 10/841585, filed May 7, 2004, the entirety of which is hereby incorporated by reference herein. 
         [0070]      FIG. 5  is a cross-sectional view of an embodiment of the transfer tube  310 , the plenum  312 , the top plate  314  and the bottom plate  206  described above. In particular, this figure shows the gas path from the mixer assembly  304  to the deposition chamber  200 . As shown in  FIG. 5 , a shim  500  can be positioned between the plenum  312  and the top plate  314 . The shim  500  can be provided with a series of small injection holes  501 , which are provided to create sufficient back pressure in the plenum  312  to provide uniform flow across the deposition chamber  200 . However, as shown in  FIG. 5 , this design can result in numerous recirculation cells  502  between the deposition chamber  200  and transfer tube  310 . Within these recirculation cells  502 , reactants from the subsequent pulses may collect. This may lead to CVD deposition within the deposition chamber  200 . Such CVD deposition is generally undesirable and can lead to particle buildup within the deposition chamber  200 . In addition, the shim  500  can produce a sharp contraction and then expansion of the gas flow. This can cause a sharp decrease in the temperature of the gas leading to condensation of the precursors in the gas stream. 
         [0071]      FIGS. 6-9A  illustrate an embodiment of a transfer member  510  and top (cover) plate  514 . This embodiment seeks to reduce or eliminate the recirculation cells in the gas path by smoothing out the expansion and contraction of the gas flow.  FIGS. 6 and 7  are top perspective and plan views of the transfer member  510  and the top plate  514 , respectively.  FIG. 8  is a top plan view of the top plate  514  with the transfer member  510  removed.  FIG. 9  is a cross-sectional view taken through line  9 - 9  of  FIG. 7  and  FIG. 9A  is an enlarged view of a portion of  FIG. 9 . 
         [0072]    As shown, the transfer member  510  forms a generally triangular shaped flow path that provides for gradual expansion of the gas from the mixer  304 . As best seen in  FIGS. 8-9 , the transfer member  510  in the illustrated embodiment includes a first portion  518  that is generally adjacent to the mixer  304  and a second portion  520  that is generally adjacent an opening  522  in the top plate  514 . As shown in  FIGS. 7 and 8 , the first portion  518  includes a pair of horizontally divergent walls  519  that expand in the horizontal direction at an angle A while the second portion  520  includes a pair of horizontally divergent walls  521  that expand in the horizontal direction at an angle B. In one embodiment, angle B is larger than angle A. In one embodiment, A is between about 5 to 45 degrees and B is between about 30 to 75 degrees. In the illustrated embodiment, the horizontally divergent walls are substantially straight. However, in a modified embodiment, the horizontally divergent walls can be curved, arced, continuously varying and/or segmented. In such an embodiment, the divergent walls can have average or mean divergent angle in the ranges described above. 
         [0073]    As shown in  FIG. 9 , the transfer member  510  includes a top wall  523  which defines, in part, the height of a gas passage  511  defined by the walls  519 ,  521 , the top wall  523  and a top surface  525  of the top plate  514 . In one embodiment, in the first portion  518 , the height h 1  of a gas passage  511  is preferably substantially constant. In the second portion  520 , the height h 2  of the gas passage  511  gradually decreases in the direction of the gas flow. In this manner, the volume of the second portion  520  adjacent the opening  522  can be reduced as compared to the plenum  312  of  FIG. 5 . In addition, as the transfer member  510  expands in the horizontal direction, the height of the gas path is reduced to smooth out the expansion of the gas flow and increase back pressure which aid in spreading the gas flow across the chamber width. In the illustrated embodiment, the gas path defined by the passage  211  is generally parallel and opposite to the gas path in the deposition chamber  200  (see e.g.,  FIG. 11 ). 
         [0074]    Another advantage of the illustrated embodiment is that the gas passage  511  is formed between the transfer member  510  and a top surface  525  of the top plate  514 . This “clamshell” arrangement makes it easier to clean and refurbish the transfer member  511  as compared, for example, to a tube. Specifically, when removed from the top plate  514 , a large opening is created, which exposes the inner surfaces of the transfer member  511  facilitating cleaning and refurbishing. 
         [0075]    With reference now to  FIGS. 8 ,  9  and  9 A, the top plate  514  is provided with the opening  522  to receive gas from transfer member  510 . In one embodiment, the opening  522  has a cross-sectional area that is substantially equal to the cross-sectional area (with respect to gas flow) of the end of the second portion  520 . In this manner, a smooth gas flow from the transfer member  510  into the top plate  514  is promoted. The opening  522  can have a generally elongated rectangular shape. See  FIG. 8 . 
         [0076]    As shown in  FIG. 9A , from the opening  522 , the top plate  514  includes a gradual contraction portion  524  that is connected to a narrowed region  526 . The contraction portion  524  includes a tapered or sloped wall  525 , which gradually reduces the cross-sectional area of the gas flow. In the illustrate embodiment, the narrowed region  526  comprises a generally rectangular slit of substantially constant cross-sectional area that extends in a generally vertical direction down through the top plate  514 . The narrowed region  526  is the portion of the gas flow between the mixer  304  and the deposition chamber  200  with the smallest cross-sectional area (with respect to gas flow). The narrowed region  526  is configured to create sufficient back pressure to provide uniform flow, particularly along the width w (see  FIG. 8 ) of the deposition chamber  200 . The end of the narrowed  526  is in communication with an expansion portion  528 . The expansion portion  528  includes a slowed or tapered wall  529  that is configured to increase the cross-sectional area of the gas flow such that the gas gradually expands as it enters the deposition chamber  200 . The outlet  530  of the expansion portion  528  is in communication with deposition chamber  200 . 
         [0077]    Advantageously, the narrowed region  526  is vertically and horizontally elongated (a three-dimensional path) across the deposition chamber  200  (see  FIG. 8 ) as compared to individual holes (a substantially two-dimension path) in the shim  500  described with reference to  FIG. 5 . For example, as compared to the individual holes, recirculation cells and dead spaces in the x-plane (i.e. between holes) and in the z-direction (i.e., beneath the holes) are eliminated or reduced. Advantageously, this arrangement of the transfer member  510 , plenum  512  and top plate  514  also takes the gas from the mixer  304  and extends it over a portion of the deposition chamber  200 . The gas flow is then turned  180  degrees as it flows into deposition chamber  200 . 
         [0078]    Within the deposition chamber  200 , dead volumes and/or recirculation cells can also be formed. For example,  FIG. 10  is a schematic illustration of the substrate S and susceptor plate  204  of the deposition chamber  200  of  FIG. 1-4 . As shown, there exists a gap g 2  between the substrate S and the susceptor plate  204  and a gap g 1  between the susceptor plate  204  and the base plate  206 . In certain circumstances, these gaps g 1 , g 2  can be difficult to purge and may harbor recirculation cells and/or be dead volumes. 
         [0079]      FIG. 11  is a partial cross-sectional view of a modified embodiment of the bottom plate  600  and susceptor  602  of the deposition chamber  200  taken along a line similar to line  9 - 9  of  FIG. 7 .  FIG. 12  is a partial perspective view of the bottom plate  600  and susceptor  602 . As shown, in this embodiment, the base plate  600  has a sealing portion  604  with a thickness t. The lower surface  605  of the sealing portion  604  seals against the susceptor  602  to seal the reaction chamber. In one embodiment, the end  606  of the sealing portion  604  has a thickness t that is approximately equal to the thickness of the substrate positioned on the susceptor  602 . Depending on the thickness of the substrate, the sealing portion  604  can have a thickness in the range from about 0.5 to about 3 millimeters. In this manner, as the gas flows over the bottom plate  600  towards the substrate, the gas is only exposed to a shallow step, which has a depth approximately equal to the thickness of the substrate. This reduces the size of or eliminates recirculation zones and facilitates purging the deposition chamber  200 . 
         [0080]    Another advantage of the bottom plate  600  and susceptor  602  arrangement illustrated in  FIGS. 11 and 12  is that the seal or contact surface between the bottom plate  600  and the susceptor  602  is elevated as compared the arrangement of  FIG. 10 . For example, in the illustrated embodiment, the lower surface  605  of the sealing portion  604  and the substrate are positioned substantially at the same vertical elevation. In one embodiment, the difference in elevation between the lower surface  605  and the substrate is between about 0 to about 2 millimeters. This arrangement advantageously reduces the volume of the dead space between the substrate and the bottom plate  604  and prevents or reduces the formation of recirculation cells in the deposition chamber  200 . 
         [0081]      FIGS. 13 and 14  illustrates in more detail the susceptor  602 .  FIG. 13  is a top perspective view of the susceptor  602 , which has been rotated 180 degrees with respect to the orientation shown in  FIGS. 11 and 12 .  FIG. 14  is a cross-sectional view of the susceptor  602  with a substrate positioned thereon. 
         [0082]    In this embodiment, the susceptor  602  is configured such that the substrate S can be positioned off-center with respect deposition chamber  200 . In this manner, the gap g 3  between the substrate and the interface between the susceptor  602  and the bottom plate  600  can be displaced further away from the leading edge (with respect to gas flow) of the substrate S. In general, the leading edge of the substrate is positioned near the inlet into the deposition chamber  200  as compared to a trailing edge of the substrate, which is positioned near on outlet (exhaust) of the deposition chamber  200 . 
         [0083]    In another embodiment, the substrate can be centered (or substantially centered) on the susceptor. In such an embodiment, the susceptor can be oversized to increase the distance between the interface between susceptor  602  and the bottom plate  600  and the edge of the substrate. In one embodiment, the susceptor  602  has a diameter that is at least about 10% greater than the diameter of the substrate. In another embodiment, this diameter of the susceptor is at least about 25% greater than the diameter of the substrate. In another embodiment, the diameter of the susceptor is between about 10% and about 25% greater than the diameter of the substrate. Such embodiments also provide for more space between the leading edge of the substrate and the interface between the susceptor and sealing surface. The oversized susceptor described above can also be used alone or in combination with the offset features described in this paragraph to provide even more space the leading edge of the substrate and the interface between the susceptor and sealing surface. 
         [0084]    Advantageously, for a susceptor of equivalent width and/or size, the gap g 3  between the leading edge of the substrate and the interface between the susceptor  602  and the bottom plate  600  can be increased. In this manner, any recirculation cells caused by discontinuities between the susceptor  602  and the bottom plate  600  are displaced further from the leading edge of the substrate S. Thus, in one embodiment, the center of the substrate positioned on the susceptor  602  is positioned asymmetrically and/or off-center with respect to the interface or seal between the susceptor  602  and the bottom plate  600 . In a modified embodiment, the susceptor can have a non-round or asymmetrical shape to further distance the leading edge of the substrate from discontinuities between the susceptor  602  and the bottom plate  600 . 
         [0085]    As shown in  FIG. 11 , the susceptor  602  can include a plurality of pins  609  that extend from the top surface of the susceptor  602  to constrain or confine movement of the substrate on the susceptor. The pins  609  can replace shoulders or ridges (see e.g., the shoulder that creates the gap g 2  in  FIG. 10 ) that are sometimes used to constrain or confine movement of the substrate. Such shoulders or ridges can disadvantageously create recirculation and/or dead zones. Thus, in one embodiment, a top area of the susceptor between the interface between the sealing surface and the susceptor is substantially flat and does not include such shoulders or ridges. Such an arrangement can eliminate or recirculation and/or dead zones. 
         [0086]    With continued reference to  FIG. 13  and with reference to  FIG. 14 , the susceptor can include a recessed region  610 , which is configured such that the substrate is only (or substantially only) contacted on its edges (see  FIG. 14 ). This embodiment helps to reduce wafer curvature and/or susceptor doming from becoming problematic. In particular, wafer curvature and/or doming can cause a gap to form between the edge of the substrate and the susceptor. Gases can become trapped in this gap making purging inefficient and causing backside deposition. By contacting the substrate along its edges as shown in  FIG. 14 , wafer curvature and/or doming will not cause a gap to form between the edge of the substrate S and the susceptor  602 . This eliminates or reduces the tendency for gases to become trapped between the substrate and the susceptor. In one embodiment, the recess region  610  has a depth between about 0.2 to 0.5 millimeters. In another embodiment, the substrate S and susceptor  602  are configured such that a continuous or substantially continuous seal is formed along the edge of the substrate S. 
         [0087]    With continued reference to  FIG. 13 , the recess  610  can have a generally circular shape such that the seal between the susceptor  602  and the substrate is also generally circular. In addition, as shown, the center c of the recess  610  can be positioned “off-center” with respect to the outer edge of the generally circular susceptor  602 . In this manner, the leading (with respect to gas flow) edge of the substrate can be distanced from the sealing portion  604  of the bottom plate  600  as compared to the trailing edge as described above. This allows the wafer to be placed a greater distance from the recirculation cells in front of the wafer. Since the gas is swept across the wafer in a cross flow reactor, re-circulation cells on the rear seal between the susceptor and base plate do not affect deposition uniformity as much. 
         [0088]      FIG. 15  illustrates partial cross-sectional view of embodiment of an edge contact lift pin  620  that could be used in combination with the susceptor  602  described above. As shown, the pin  620  can include a pin head  622  that includes a notch  624  or beveled edge for securing the substrate S. The pin head  622  is configured to contact the edge of the substrate and lies generally at the interface between the susceptor  602  and the recess region  610 . The pin head  622  can be coupled to a pin shaft  626 , which extends through openings  628  in the susceptor. 
         [0089]    The pin  620  can be configured such that when the susceptor  602  is raised into the deposition chamber  200 , the pin head  622  becomes recessed within a recessed region  630  formed in the susceptor  602 . As the susceptor is lowered, the pin head  622  can be raised with respect to the susceptor  602 . For example, as described in co-pending U.S. patent application No. ___/___,___, filed on Jan. __, 2006 under Attorney Docket No. ASMEX.532A (the entirety of which is incorporated by reference herein), in one embodiment, to the raise the pin  620  from a “lowered” position seated in the recess  630 , the substrate is moved downward by a lifting mechanism. This downward movement causes the bottom surface the support pin  620  to contact a connector (not shown) positioned below the susceptor  602 . The contact of the pin  620  with the connector compresses a spring (not shown) surrounding a lower portion of the shaft  626 . As the spring is compressed while the susceptor  602  is moved downward, the spring attains a restoring force that will facilitate relative “lowering” of the pin  620  when the susceptor  620  is lifted next time. Accordingly, the combination of the spring and the platform or “floor” for downward pin movement provided by the connector permits the pin to remain relatively fixed while the susceptor  602  moves up and down, without requiring the pin to be fixed relative to the deposition chamber  200 . 
         [0090]    Although this invention has been disclosed in the context of certain preferred embodiments and examples, it will be understood by those skilled in the art that the present invention extends beyond the specifically disclosed embodiments to other alternative embodiments and/or uses of the invention and obvious modifications and equivalents thereof. In addition, while a number of variations of the invention have been shown and described in detail, other modifications, which are within the scope of this invention, will be readily apparent to those of skill in the art based upon this disclosure. It is also contemplated that various combinations or sub-combinations of the specific features and aspects of the embodiments may be made and still fall within the scope of the invention. Accordingly, it should be understood that various features and aspects of the disclosed embodiments can be combine with or substituted for one another in order to form varying modes of the disclosed invention. Thus, it is intended that the scope of the present invention herein disclosed should not be limited by the particular disclosed embodiments described above, but should be determined only by a fair reading of the claims that follow.