Patent Publication Number: US-2013243971-A1

Title: Apparatus and Process for Atomic Layer Deposition with Horizontal Laser

Description:
BACKGROUND 
     Embodiments of the invention generally relate to an apparatus and a method for depositing materials. More specifically, embodiments of the invention are directed to a atomic layer deposition chambers with linear reciprocal motion. 
     In the field of semiconductor processing, flat-panel display processing or other electronic device processing, vapor deposition processes have played an important role in depositing materials on substrates. As the geometries of electronic devices continue to shrink and the density of devices continues to increase, the size and aspect ratio of the features are becoming more aggressive, e.g., feature sizes of 0.07 μm and aspect ratios of 10 or greater. Accordingly, conformal deposition of materials to form these devices is becoming increasingly important. 
     During an atomic layer deposition (ALD) process, reactant gases are introduced into a process chamber containing a substrate. Generally, a first reactant is introduced into a process chamber and is adsorbed onto the substrate surface. A second reactant is introduced into the process chamber and reacts with the first reactant to form a deposited material. A purge step may be carried out to ensure that the only reactions that occur are on the substrate surface. The purge step may be a continuous purge with a carrier gas or a pulse purge between the delivery of the reactant gases. 
     There is an ongoing need in the art for improved apparatuses and methods for processing substrates by atomic layer deposition. 
     SUMMARY 
     One or more embodiments of the invention are directed to deposition systems comprising a processing chamber, a gas distribution plate in the processing chamber and at least one laser source. The gas distribution plate has a plurality of elongate gas ports that direct flows of gases toward a surface of a substrate. The at least one laser source emits a laser beam directed along at least one of the elongate gas ports between the gas distribution plate and the substrate. 
     In some embodiments, the gas distribution plate comprises a plurality of first reactive gas injectors that direct flows of a first reactive gas toward a substrate and at least one second reactive gas injector that directs a flow of a second reactive gas different from the first reactive gas toward a substrate. In one or more embodiments, the at least one laser beam is directed along the length of one or more of each of the first reactive gas injectors and the at least one second reactive gas injectors. 
     In some embodiments, there is one laser source. In one or more embodiments, the one laser source emits a beam that is split with at least one beam splitter to direct the one laser beam along multiple elongate gas injector. 
     In some embodiments, there are at least two laser sources emitting laser beams and each laser beam is directed along a different elongate gas injector. 
     In some embodiments, the laser source is located outside of the processing chamber and the laser beam is directed through a window in a wall of the processing chamber. In one or more embodiments, the window is heated. Some embodiments further comprise a purge gas flow between the window and the gas distribution plate. 
     Additional embodiments of the invention are directed to deposition systems comprising a processing chamber, a gas distribution plate in the processing chamber and at least one laser source. The gas distribution plate directs flows of gases toward a surface of a substrate. The at least one laser source has a laser beam directed along a path adjacent to the gas distribution plate between the gas distribution plate and the substrate. 
     In some embodiments, there is one laser source and the system further comprises at least one beam splitter that directs the one laser beam along multiple paths. 
     In some embodiments, there are at least two lasers sources emitting at least two laser beams. One or more embodiments further comprise at least one beam splitter that directs at least one of the at least two lasers beams along multiple paths. 
     In some embodiments, the at least one laser source is positioned so that when a substrate is present in the system, the laser beam is up to about 50 mm from the substrate. 
     In some embodiments, the laser beam is one of a continuous laser and a pulsed laser. 
     Further embodiments of the invention are directed to methods of processing a substrate. The substrate is sequentially contacted with a flow of a first precursor and a flow of a second precursor from a gas distribution plate to form a layer on the substrate. At least one of the first precursor and the second precursor is activated with at least one laser beam directed adjacent the gas distribution plate. 
     In some embodiments, each of the first precursor and second precursor flow from separate elongate gas ports and the at least one laser beam is directed along a length of at least one of the elongate gas ports. 
     Some embodiments further comprise pulsing the laser beam to coincide with the flow of one or more of the first precursor and the second precursor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
         FIG. 1  shows a schematic side view of an atomic layer deposition chamber according to one or more embodiments of the invention; 
         FIG. 2  shows a susceptor in accordance with one or more embodiments of the invention; 
         FIG. 3  show a partial perspective view of an atomic layer deposition chamber in accordance with one or more embodiments of the invention; 
         FIG. 4  shows a schematic cross-sectional view of a gas distribution plate in accordance with one or more embodiments of the invention; 
         FIG. 5  shows a schematic cross-sectional view of a gas distribution plate and horizontal lasers in accordance with one or more embodiments of the invention; 
         FIG. 6  shows a schematic cross-sectional view of a gas distribution plate and horizontal lasers in accordance with one or more embodiments of the invention; 
         FIG. 7  shows a schematic cross-sectional view of a gas distribution plate and horizontal lasers in accordance with one or more embodiments of the invention; 
         FIG. 8  shows a schematic cross-sectional view of a gas distribution plate and horizontal lasers in accordance with one or more embodiments of the invention; 
         FIG. 9  shows a schematic cross-sectional view of a gas distribution plate in accordance with one or more embodiments of the invention; 
         FIG. 10  shows a schematic view showing the arrangement of lasers with respect to a gas distribution plate in accordance with one or more embodiments of the invention; 
         FIG. 11  shows a schematic view showing the arrangement of lasers with respect to a gas distribution plate in accordance with one or more embodiments of the invention; 
         FIG. 12  shows a schematic view showing the arrangement of lasers with respect to a gas distribution plate in accordance with one or more embodiments of the invention; and 
         FIG. 13  shows a cluster tool in accordance with one or more embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the invention are directed to atomic layer deposition apparatus and methods which provide improved movement of substrates. Some embodiments of the invention are directed to atomic layer deposition apparatuses (also called cyclical deposition) incorporating a gas distribution plate, reciprocal linear motion and a horizontal laser. 
     Embodiments of the invention use one or more lasers to stimulate gaseous precursors in and ALD reactor where the precursors are introduced horizontally separated. This may have the advantage of increasing the efficiency of precursor decomposition, increase the rate of saturation and/or initiate/catalyze the reaction. Current ALD processes are challenged by process speed with delays due to time consumed in emptying and refilling of the two precursors which are sequentially introduced to the reactor. Embodiments of invention apply to the use of pyrolitic (thermal) and photolytic assist using lasers of different wavelength (IR, UV-excimer lasers) to effectively dissociate through direct dissociation or catalytic decomposition of precursors. 
       FIG. 1  is a schematic cross-sectional view of an atomic layer deposition system  100  or reactor in accordance with one or more embodiments of the invention. The system  100  includes a load lock chamber  10  and a processing chamber  20 . The processing chamber  20  is generally a sealable enclosure, which is operated under vacuum, or at least low pressure. The processing chamber  20  is isolated from the load lock chamber  10  by an isolation valve  15 . The isolation valve  15  seals the processing chamber  20  from the load lock chamber  10  in a closed position and allows a substrate  60  to be transferred from the load lock chamber  10  through the valve to the processing chamber  20  and vice versa in an open position. 
     The system  100  includes a gas distribution plate  30  capable of distributing one or more gases across a substrate  60 . The gas distribution plate  30  can be any suitable distribution plate known to those skilled in the art, and specific gas distribution plates described should not be taken as limiting the scope of the invention. The output face of the gas distribution plate  30  faces the first surface  61  of the substrate  60 . 
     Substrates for use with the embodiments of the invention can be any suitable substrate. In some embodiments, the substrate is a rigid, discrete, generally planar substrate. As used in this specification and the appended claims, the term “discrete” when referring to a substrate means that the substrate has a fixed dimension. The substrate of some embodiments is a semiconductor wafer, such as a 200 mm or 300 mm diameter silicon wafer. 
     The gas distribution plate  30  comprises a plurality of gas ports that transmit one or more gas streams to the substrate  60  and a plurality of vacuum ports disposed between each gas port that transmit the gas streams out of the processing chamber  20 . In the embodiment of  FIG. 1 , the gas distribution plate  30  comprises a first precursor injector  120 , a second precursor injector  130  and a purge gas injector  140 . The injectors  120 ,  130 ,  140  may be controlled by a system computer (not shown), such as a mainframe, or by a chamber-specific controller, such as a programmable logic controller. The precursor injector  120  is configured to inject a continuous (or pulse) stream of a reactive precursor of compound A into the processing chamber  20  through a plurality of gas ports  125 . The precursor injector  130  is configured to inject a continuous (or pulse) stream of a reactive precursor of compound B into the processing chamber  20  through a plurality of gas ports  135 . The purge gas injector  140  is configured to inject a continuous (or pulse) stream of a non-reactive or purge gas into the processing chamber  20  through a plurality of gas ports  145 . The purge gas helps remove reactive material and reactive by-products from the processing chamber  20 . The purge gas is typically an inert gas, such as, nitrogen, argon and helium. Gas ports  145  are disposed in between gas ports  125  and gas ports  135  so as to separate the precursor of compound A from the precursor of compound B, thereby avoiding cross-contamination between the precursors and prevent gas-phase reactions. 
     In another aspect, a remote plasma source (not shown) may be connected to the precursor injector  120  and the precursor injector  130  prior to injecting the precursors into the chamber  20 . The plasma of reactive species may be generated by applying an electric field to a compound within the remote plasma source. Any power source that is capable of activating the intended compounds may be used. For example, power sources using DC, radio frequency (RF), and microwave (MW) based discharge techniques may be used. If an RF power source is used, it can be either capacitively or inductively coupled. The activation may also be generated by a thermally based technique, a gas breakdown technique, a high intensity light source (e.g., UV energy), or exposure to an x-ray source. Exemplary remote plasma sources are available from vendors such as MKS Instruments, Inc. and Advanced Energy Industries, Inc. 
     The system  100  further includes a pumping system  150  connected to the processing chamber  20 . The pumping system  150  is generally configured to evacuate the gas streams out of the processing chamber  20  through one or more vacuum ports  155 . The vacuum ports  155  are disposed between each gas port so as to evacuate the gas streams out of the processing chamber  20  after the gas streams react with the substrate surface and to further limit cross-contamination between the precursors. 
     The system  100  includes a plurality of partitions  160  disposed on the processing chamber  20  between each port. A lower portion of each partition extends close to the first surface  61  of substrate  60 , for example about 0.5 mm from the first surface  61 , This distance should be such that the lower portions of the partitions  160  are separated from the substrate surface by a distance sufficient to allow the gas streams to flow around the lower portions toward the vacuum ports  155  after the gas streams react with the substrate surface. Arrows  198  indicate the direction of the gas streams. Since the partitions  160  operate as a physical barrier to the gas streams, they also limit cross-contamination between the precursors. The arrangement shown is merely illustrative and should not be taken as limiting the scope of the invention. It will be understood by those skilled in the art that the gas distribution system shown is merely one possible distribution system and the other types of showerheads and gas distribution systems may be employed. 
     In operation, a substrate  60  is delivered (e.g., by a robot) to the load lock chamber  10  and is placed on a carrier  65 . After the isolation valve  15  is opened, the carrier  65  is moved along the track  70 , which may be a rail or frame system. Once the carrier  65  enters in the processing chamber  20 , the isolation valve  15  closes, sealing the processing chamber  20 . The carrier  65  is then moved through the processing chamber  20  for processing. In one embodiment, the carrier  65  is moved in a linear path through the chamber. 
     As the substrate  60  moves through the processing chamber  20 , the first surface  61  of substrate  60  is repeatedly exposed to the precursor of compound A coming from gas ports  125  and the precursor of compound B coming from gas ports  135 , with the purge gas coming from gas ports  145  in between. Injection of the purge gas is designed to remove unreacted material from the previous precursor prior to exposing the substrate surface  110  to the next precursor. After each exposure to the various gas streams (e.g., the precursors or the purge gas), the gas streams are evacuated through the vacuum ports  155  by the pumping system  150 . Since a vacuum port may be disposed on both sides of each gas port, the gas streams are evacuated through the vacuum ports  155  on both sides. Thus, the gas streams flow from the respective gas ports vertically downward toward the first surface  61  of the substrate  60 , across the first surface  110  and around the lower portions of the partitions  160 , and finally upward toward the vacuum ports  155 . In this manner, each gas may be uniformly distributed across the substrate surface  110 . Arrows  198  indicate the direction of the gas flow. 
     Substrate  60  may also be rotated while being exposed to the various gas streams. Rotation of the substrate may be useful in preventing the formation of strips in the formed layers. Rotation of the substrate can be continuous or in discrete steps. Where discrete rotational steps are used, it may be advantageous to rotate the substrate when it is in a position before and/or after the gas distribution plate. 
     Sufficient space is generally provided at the end of the processing chamber  20  so as to ensure complete exposure by the last gas port in the processing chamber  20 . Once the substrate  60  reaches the end of the processing chamber  20  (i.e., the first surface  61  has completely been exposed to every gas port in the chamber  20 ), the substrate  60  returns back in a direction toward the load lock chamber  10 . As the substrate  60  moves back toward the load lock chamber  10 , the substrate surface may be exposed again to the precursor of compound A, the purge gas, and the precursor of compound B, in reverse order from the first exposure. 
     The extent to which the substrate surface  110  is exposed to each gas may be determined by, for example, the flow rates of each gas coming out of the gas port and the rate of movement of the substrate  60 . In one embodiment, the flow rates of each gas are configured so as not to remove adsorbed precursors from the substrate surface  110 . The width between each partition, the number of gas ports disposed on the processing chamber  20 , and the number of times the substrate is passed back and forth may also determine the extent to which the substrate surface  110  is exposed to the various gases. Consequently, the quantity and quality of a deposited film may be optimized by varying the above-referenced factors. 
     In some embodiments, the system  100  may include a precursor injector  120  and a precursor injector  130 , without a purge gas injector  140 . Consequently, as the substrate  60  moves through the processing chamber  20 , the substrate surface  110  will be alternately exposed to the precursor of compound A and the precursor of compound B, without being exposed to purge gas in between. 
     The embodiment shown in  FIG. 1  has the gas distribution plate  30  above the substrate. While the embodiments have been described and shown with respect to this upright orientation, it will be understood that the inverted orientation is also possible. In that situation, the first surface  61  of the substrate  60  will face downward, while the gas flows toward the substrate will be directed upward. 
     In one or more embodiments, the system  100  may be configured to process a plurality of substrates. In such an embodiment, the system  100  may include a second load lock chamber (disposed at an opposite end of the load lock chamber  10 ) and a plurality of substrates  60 . The substrates  60  may be delivered to the load lock chamber  10  and retrieved from the second load lock chamber. 
     The embodiments of  FIG. 1  includes at least one laser  171  with a beam of collimated light which is directed along at least one of the elongate gas ports between the gas distribution plate  30  and the substrate  60 . As used in this specification and the appended claims, the terms “laser”, “laser beam”, “collimated light”, and the like, are used to describe both the physical hardware associated with generating a laser beam as well as the laser beam itself, depending on the context. As will be well understood by those skilled in the art, stating that the “laser” is directed along the at least one elongate gas ports means that the laser light is directed along the gas ports. 
     The deposition system  100  includes at least one laser source (not shown) which emits a laser beam. As used in this specification and the appended claims, the term “laser source” means any device capable of emitting a collimated beam of light. Suitable laser sources include, but are not limited to, laser diodes. As used in this specification and the appended claims, the term “laser beam” means a beam of coherent light that that produced from a laser source. The terms “laser beam”, “laser”, “light beam”, “collimated light”, “coherent light”, and the like, are used interchangeably to describe a beam of light emitted by a laser source. 
     Some precursors require activation before they can be useful in ALD processes. Activation can be as simple as forming an excited species which can react with the substrate surface (or film on the surface) with a lower activation energy barrier. Some precursors require a catalyst for activation and the catalyst can be activated by the laser increasing the catalytic effect. In some embodiments, the laser has sufficient power and frequency to initiate a local plasma. The laser can be used to photolytically produce a useful precursor in the chamber by laser assisted activation of the reactant gases in a region parallel to and adjacent the substrate surface. In some embodiments, the laser light is used to photolytically produce a catalyst species that assists in the activation of reactant gases by directing the laser light parallel to and adjacent the substrate. 
     Suitable lasers can be continuous wave or pulsed lasers (e.g., nanosecond and femptosecond lasers). The wavelength of the laser can be varied to correspond to the activation energies required by the specific precursors. Ultraviolet, visible, infrared, near-infrared lasers, and others, can be used. For example an argon fluoride (ArF) laser, which emits light at about 193 nm (6.4 eV) may be used to activate ammonia by photolysis to produce NH and NH 2  species. Other exemplary lasers include CO 2  lasers. Additionally, more than one laser type can be employed simultaneously at the same gas injector, or at different gas injectors. 
     The laser source can be positioned to direct one or more beams of light along any or all of the elongate gas ports. The laser source can be located within the chamber or outside of the chamber. In some embodiments, the laser source is located outside of the chamber to avoid material depositing on the laser&#39;s lens. When the laser source is located outside of the chamber, there is a window in at least one wall of the chamber to allow the light beam to enter the processing area. The size and shape of the window can vary depending on the arrangement of laser(s) in the system and the desired path of the laser beam. 
     Depending on the mode of activation, the precursors being used and the desired film, amongst others, the position of the laser within the chamber. The laser beam can be directed along the length of any of the elongate gas injectors to activate gaseous species flowing from the injector. For example, if the first precursor requires activation, the laser beam can be directed along the front of the first precursor injector, or along the front of all of the first precursor injectors, if there are more than, and it is desired. The laser beam can be directed along any of the precursors injectors, purge gas injectors and vacuum ports as needed. In some embodiments, the laser(s) is directed along the length of one or more of each of the first reactive gas injectors and the at least one second reactive gas injectors. 
     The laser can be directed along the length of a purge gas injector to convert the otherwise inert gas into a state useful in the formation of a film. For example, a first precursor can be deposited on the substrate surface and then the otherwise inert gas flowing across the surface can activate the surface species before exposure to the second precursor. 
     The laser beam can be directed in front of the gas distribution plate a distance from the surface of the substrate. The distance from the substrate surface can be varied depending on the precursors. For example, the lifetime of the radicals (activated species) generated by the laser can be a factor in the useful distance from the substrate. When the activated species has a shorter lifetime, the laser beam will be more useful located closer to the substrate surface. In some embodiments, the laser beam is positioned so that when the substrate is present in the system, the laser beam is up to about 100 mm from the substrate surface, or up to about 50 mm from the substrate surface. In some embodiments, the laser beam is up to about 45 mm, 40 mm, 35 mm, 30 mm, 25 mm, 20 mm, 15 mm, 10 mm, 9 mm, 8 mm, 7 mm, 6 mm, 5 mm, 4 mm, 3 mm, 2 mm, 1 mm, or 0.5 mm from the substrate surface. In some embodiments, the laser beam has a width in the range of about 0.5 mm to about 1 m. In one or more embodiments, the laser beam has a width in the range of about 1 mm to about 0.5 m. The width of the beam can be static or dynamic throughout processing. A plurality of lasers can be employed to make the beam wider. The beam can be shaped or manipulated using any known technique including, but not limited to, cylindrical or diffracting optics. 
     The laser power can be controlled by a separate controller (not shown). The controller can be used to change the power of the laser, including turning the laser on and off, during processing of the substrate. For example, it may be useful to only use the laser for the deposition of the first few ALD layers, at which point the laser can be turned off. Additionally, the controller can power and coordinate multiple lasers, allowing for the rapid switching between lasers during processing. For example, hydrazine can be activated by a UV laser or a hydrogen radical can be generated by an IR laser. The controller is capable of rapidly switching between the UV laser and IR laser to generate both species. 
     In some embodiments, the carrier  65  is a susceptor  66  for carrying the substrate  60 . Generally, the susceptor  66  is a carrier which helps to form a uniform temperature across the substrate. The susceptor  66  is movable in both directions (left-to-right and right-to-left, relative to the arrangement of  FIG. 1 ) between the load lock chamber  10  and the processing chamber  20 . The susceptor  66  has a top surface  67  for carrying the substrate  60 . The susceptor  66  may be a heated susceptor so that the substrate  60  may be heated for processing. As an example, the susceptor  66  may be heated by radiant heat lamps  90 , a heating plate, resistive coils, or other heating devices, disposed underneath the susceptor  66 . 
     In one or more embodiments, the top surface  67  of the susceptor  66  includes a recess  68  configured to accept the substrate  60 , as shown in  FIG. 2 . The susceptor  66  is generally thicker than the thickness of the substrate so that there is susceptor material beneath the substrate. In some embodiments, the recess  68  is configured such that when the substrate  60  is disposed inside the recess  68 , the first surface  61  of substrate  60  is level with the top surface  67  of the susceptor  66 . Stated differently, the recess  68  of some embodiments is configured such that when a substrate  60  is disposed therein, the first surface  61  of the substrate  60  does not protrude above the top surface  67  of the susceptor  66 . 
       FIG. 3  shows a partial cross-sectional view of a processing chamber  20  in accordance with one or more embodiments of the invention. The processing chamber  20  has at least one gas distribution plate  30 , a window  177  and at least one laser source  171  located outside the chamber  20  directing laser light  172  through the window  177  into the processing chamber  20 . 
     In embodiments with a window  177  there is potential for film deposition on the window  177 , as with any other part of the processing chamber. However, deposition on the window  177  could result in, for example, decreased laser intensity reaching the target area (i.e., the gas distribution plate  30 ), no laser intensity reaching the target area and laser scattering. Therefore, the window  177  of some embodiments is heated to minimize deposition thereon. The window  177  can be heated by any suitable means including, but not limited to, heating lamps directed at the window, heating elements (e.g., ceramic heaters, resistive heaters) located around the edges of the window and ceramic heats directed at the window. 
     Another embodiment includes a purge gas flow between the window  177  and the gas distribution plate  30 . The purge gas flow may help isolate the window  177  from reactive gases from the gas distribution plate  30 . To include a purge gas flow, the processing chamber may include one or more of a purge gas source, a purge gas flow controller and a purge gas injector. The flow of the purge gas can be continuous or pulsed. In some embodiments, to maximize the benefit of a purge gas isolating the window, the purge gas flow is continuous. The purge gas flow can be directed anywhere throughout the processing chamber, not just in the area of the window. For example, there can be one or more purge gas flows (i.e., different purge gas injectors) spaced around the entire chamber body to help form a barrier between the gases from the gas distribution plate and the walls of the chamber. 
     In some embodiments, the processing chamber  20  includes a substrate carrier  65  that moves a substrate along a linear reciprocal path along an axis perpendicular to the elongate gas injectors. As used in this specification and the appended claims, the term “linear reciprocal path” refers to either a straight or slightly curved path in which the substrate can be moved back and forth. Stated differently, the substrate carrier may be configured to move a substrate reciprocally with respect to the gas injector unit in a back and forth motion perpendicular to the axis of the elongate gas injectors. As shown in  FIG. 3 , the carrier  65  is supported on rails  74  which are capable of moving the carrier  65  reciprocally from left-to-right and right-to-left, or capable of supporting the carrier  65  during movement. Movement can be accomplished by many mechanisms known to those skilled in the art. For example, a stepper motor may drive one of the rails, which in turn can interact with the carrier  65 , to result in reciprocal motion of the substrate  60 . In some embodiments, the substrate carrier is configured to move a substrate  60  along a linear reciprocal path along an axis perpendicular to and beneath the elongate gas injectors  32 . In some embodiments, the substrate carrier  65  is configured to transport the substrate  60  from a region  76  in front of the gas distribution plate  30  to a region  77  after the gas distribution plate  30  so that the entire substrate  60  surface passes through a region  78  occupied by the gas distribution plate  30 . 
       FIGS. 4-9  show side, partial cross-sectional views of gas distribution plates  30  in accordance with one or more embodiments of the invention. The letters used in these drawings represent some of the different gases which may be used in the system. As a reference, A is a first reactive gas, B is a second reactive gas, C is a third reactive gas, P is a purge gas and V is vacuum. As used in this specification and the appended claims, the term “reactive gas” refers to any gas which may react with either the substrate, a film or partial film on the substrate surface. Non-limiting examples of reactive gases include hafnium precursors, tantalum precursors, water, cerium precursors, peroxide, titanium precursors, ozone, plasmas, Groups III-V elements, ammonia and hydrazine. Purge gases are any gas which is non-reactive with the species or surface it comes into contact with. Non-limiting examples of purge gases include argon, nitrogen and helium. 
     In some embodiments, the reactive gas injectors on either end of the gas distribution plate  30  are the same so that the first and last reactive gas seen by a substrate passing the gas distribution plate  30  is the same. For example, if the first reactive gas is A, then the last reactive gas will also be A. If gas A and B are switched, then the first and last gas seen by the substrate will be gas B. 
     Referring to  FIG. 4 , the gas distribution plate  30  of some embodiments comprises a plurality of elongate gas injectors including at least two first reactive gas injectors A and at least one second reactive gas injector B which is a different gas than that of the first reactive gas injectors. The first reactive gas injectors A are in fluid communication with a first reactive gas, and the second reactive gas injectors B are in fluid communication with a second reactive gas which is different from the first reactive gas. Laser beams  172  are directed through the path of the second reactive gas injectors B to activate the gaseous species from these injectors. The at least two first reactive gas injectors A surround the at least one second reactive gas injector B so that a substrate moving from left-to-right will see, in order, the leading first reactive gas A, the second reactive gas B and the trailing first reactive gas A, resulting in a full layer being formed on the substrate. A substrate returning along the same path will see the opposite order of reactive gases, resulting in two layers for each full cycle. As a useful abbreviation, this configuration may be referred to at an ABA injector configuration. A substrate moved back and forth across this gas distribution plate  30  would see a pulse sequence of
     AB AAB AAB (AAB) n  . . . AABA
 
forming a uniform film composition of B. Exposure to the first reactive gas A at the end of the sequence is not important as there is no follow-up by a second reactive gas B. It will be understood by those skilled in the art that while the film composition is referred to as B, it is really a product of the surface reaction products of reactive gas A and reactive gas B and that use of just B is for convenience in describing the films.
   

       FIG. 5  shows another embodiment similar to that of  FIG. 5  in which there are two second reactive gas B injectors, each surrounded by a first reactive gas A injector. A substrate moved back and forth across this gas distribution plate  30  would see a pulse sequence of
     ABAB AABAB (AABAB) n  . . . AABABA
 
forming a uniform film composition of B. As in the embodiment of  FIG. 4 , laser beams  172  are directed along the path of the second reactive gas B injectors. But it will be understood that the laser beam  172  can be directed along only one of the second reactive gas B injectors or any or all of the first reactive gas A injectors. The main difference between the embodiment of  FIG. 6  and  FIG. 5  is that each full cycle (one back and forth movement) will result in four layers.
   

     Similarly,  FIGS. 6-7  show embodiments of the gas distribution plate  30  without a trailing first reactive gas A injector. In  FIG. 6 , the laser beams  172  are shown in the path of the gas from the first reactive gas A injectors. In  FIG. 7 , there are shown laser beams  172  in the path of the first reactive gas A injector and a second laser beam  173  in the path of the second reactive gas B injector 
       FIG. 8  shows another embodiment of the invention in which the plurality of gas injectors  32  further comprise at least one third gas injector for a third reactive gas C. At least two first reactive gas A injectors surround the at least one third gas reactive gas injector. A substrate moved back and forth across this gas distribution plate  30  would see a pulse sequence of
     AB AC AB AAB AC AB (AAB AC AB) n  . . . AAB AC ABA
 
resulting in a film composition of BCB(BCB) n  . . . BCB. Again, the final exposure to the first reactive gas A is not important. Here, a laser beam  172  is shown activating the second reactive gas B and a second laser beam  173 , which can be different or the same as the laser beam  172 , is shown activating the third reactive gas C. Again, this is merely an example and should not be taken as limiting the scope of the invention.
   

       FIG. 9  shows a gas distribution plate  30  comprising purge gas P injectors and outside vacuum V ports. In the embodiment shown, the gas distribution plate  30  comprises at least two pumping plenums connected to the pumping system  150 . The first pumping plenum  150   a  is in flow communication with the vacuum ports  155  adjacent to (on either side of) the gas ports  125  associated with the first reactive gas A injectors  32   a,    32   c.  The first pumping plenum  150   a  is connected to the vacuum ports  155  through two vacuum channels  151   a.  The second pumping plenum  150   b  is in flow communication with the vacuum ports  155  adjacent to (on either side of) the gas port  135  associated with the second reactive gas B injector  32   b.  The second pumping plenum  150   b  is connected to the vacuum ports  155  through two vacuum channels  152   a.  In this manner, the first reactive gas A and the second reactive gas B are substantially prevented from reacting in the gas phase. The vacuum channels in flow communication with the end vacuum ports  155  can be either the first vacuum channel  150   a  or the second vacuum channel  150   b,  or a third vacuum channel. The pumping plenums  150 ,  150   a,    150   b  can have any suitable dimensions. The vacuum channels  151   a,    152   a  can be any suitable dimension. In some embodiments, the vacuum channels  151   a,    152   a  have a diameter of about 22 mm. The end vacuum plenums  150  collect substantially only purge gases. An additional vacuum line collects gases from within the chamber. These four exhausts (A, B, purge gas and chamber) can be exhausted separately or combined downstream to one or more pumps, or in any combination with two separate pumps. 
     Some embodiments of the invention are directed to an atomic layer deposition system comprising a processing chamber with a gas distribution plate therein. The gas distribution plate comprises a plurality of gas injectors consisting essentially of, in order, a vacuum port, a purge gas injector, a vacuum port, a first reactive gas injector, a vacuum port, a purge port, a vacuum port, a second reactive gas injector, a vacuum port, a purge port, a vacuum port, a first reactive gas injector, a vacuum port, a purge port and a vacuum port. As used in this specification and the appended claims, the term “consisting essentially of”, and the like, mean that the gas injector excludes additional reactive gas injectors, but does not exclude non-reactive gas injectors like purge gases and vacuum lines. Therefore, in the embodiment shown in  FIG. 4 , the addition of purge gases and/or vacuum ports (see e.g.,  FIG. 9 ) would still consist essentially of ABA, while the addition of a third reactive gas C injector (see e.g.,  FIG. 8 ) would not consist essentially of ABA. 
     The number and arrangement of the laser sources  171  can vary depending on the specific processing requirement.  FIG. 10  shows an embodiment in which there are two separate laser sources  171  emitting two separate laser beams  172  across the gas distribution plate  30 .  FIG. 11  shows an embodiment in which there is one laser source  171  emitting a single laser beam  172  which is split by beam splitter  174  and one of the split beams if redirected with mirror  175 . Both of the split beams  172  are different gas injectors, resulting in a single laser beam being directed along multiple gas injectors by aid of beam splitter. It will be understood by those skilled in the art that the laser power may be adjusted to maintain sufficient energy upon splitting. It will also be understood that there can be additional lenses, mirrors and splitters than what has been illustrated without deviating from the scope of the invention. 
       FIG. 12  shows another embodiment in which there is a first laser source  171  emitting a first laser beam  172  which is split by splitter  174  and redirected by mirror  175 . A second laser source  171   b  emits a second laser beam  173  which is redirected by mirror  175   b.  The first and second laser beams  172 ,  173  are directed across the gas distribution plate at different gas injectors. In some embodiments, the first laser beam  172  and second laser beam  173  are directed along the path of the same gas injector. 
     Additional embodiments of the invention are directed to cluster tools comprising at least one atomic layer deposition system described. The cluster tool has a central portion with one or more branches extending therefrom. The branches being deposition, or processing apparatuses. Cluster tools require substantially less space than stand-alone tools. The central portion of the cluster tool may include at least one robot arm capable of moving substrates from a load lock chamber into the processing chamber and back to the load lock chamber after processing. Referring to  FIG. 13 , an illustrative cluster tool  300  includes a central transfer chamber  304  generally including a multi-substrate robot  310  adapted to transfer a plurality of substrates in and out of the load lock chamber  320  and the various process chambers  20 . Although the cluster tool  300  is shown with three processing chambers  20 , it will be understood by those skilled in the art that there can be more or less than 3 processing chambers. Additionally, the processing chambers can be for different types (e.g., ALD, CVD, PVD) of substrate processing techniques. 
     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 will be apparent to those skilled in the art that various modifications and variations can be made to the method and apparatus of the present invention without departing from the spirit and scope of the invention. Thus, it is intended that the present invention include modifications and variations that are within the scope of the appended claims and their equivalents.