Patent Publication Number: US-2015063957-A1

Title: Segmented substrate loading for multiple substrate processing

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of a co-pending U.S. patent application Ser. No. 13/052,725, filed Mar. 21, 2011, which claims benefit of the U.S. Provisional Patent Application Ser. No. 61/317,638, filed Mar. 25, 2010. Each of afore mentioned patent applications is incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Field 
     Embodiments of the present disclosure relate to apparatus and methods for handling substrates during processing. More particularly, embodiments of the present disclosure relate to apparatus and methods for loading substrates into processing chambers that simultaneously process multiple substrates, for example, processing chambers for manufacturing devices such as light emitting diodes (LEDs), laser diodes (LDs), and power electronics. 
     2. Description of the Related Art 
     When processing small substrates during semiconductor processing, a plurality of substrates are often loaded into substrate carriers then transferred in and out of processing chambers with substrate carriers. For example, sapphire substrates used in manufacturing of light emitting diodes (LED) are usually processed in a batch mode with a batch of sapphire substrates disposed and transferred in a substrate carrier during processing. 
     However, using substrate carriers affects repeatability of processing chambers since different substrate carriers affect performance of the processing chambers differently. Using substrate carriers also limits productivity in various ways. First, the size of substrate carriers is limited by method for manufacturing and the size of slit valve doors in a processing system. Since substrate carriers are usually formed from silicon carbide to obtain desired properties, it is difficult and expensive to manufacture substrate carriers beyond 0.5 meter in diameter. Therefore, even though chambers are capable of processing more substrates at the same time, the number of substrates processed is limited by the size of the substrate carriers used. Second, cost of production is increased because substrate carriers are subject to substantive wear during processing as substrate carriers are transferred with the substrates among various chambers, loading stations, load locks, and exposed to various environments. Additionally, using substrate carriers also requires robots for handling the substrates during loading, unloading, landing, and robots for handling the substrate carriers, thus, also increasing the cost of production. 
     Therefore, there is a need for method and apparatus for handling substrates during multiple substrate processing. 
     SUMMARY 
     Embodiments of the present disclosure relate to apparatus and methods for loading substrates into processing chambers that simultaneously process multiple substrates. More particularly, embodiments of the present disclosure provide apparatus and methods for loading and unloading a processing chamber in a segment by segment manner. 
     One embodiment of the present disclosure provides an apparatus for processing multiple substrates. The apparatus includes a chamber body defining a processing volume and a substrate supporting tray disposed in the processing volume. The chamber body has a first opening to allow passage of substrates therethrough. The substrate supporting tray has a plurality of substrate pockets formed on an upper surface. Each substrate pocket accommodates a substrate therein. The plurality of substrate pockets form a plurality of segments. The apparatus further includes a substrate handling assembly disposed in the processing volume. The substrate handling assembly moves relative to the substrate supporting tray to pick up and drop off substrates from and to a segment of substrate pockets in a loading position aligned with the substrate handling assembly. Each of the plurality of segments is alignable with the substrate handling assembly. 
     Another embodiment of the present disclosure provides a cluster tool for processing multiple substrates including a first processing chamber. The cluster tool also includes a transfer chamber selectively connected to the first processing chamber via a first opening of the first processing chamber, and a substrate transfer robot disposed in the transfer chamber to load and unload substrates in the first processing chamber. The substrate transfer robot includes a first robot blade having one or more substrate pockets. The one or more substrate pockets in the first robot blade are arranged in the same pattern as the one or more substrate pockets in each segment on a first substrate supporting tray of the first processing chamber. 
     Yet another embodiment of the present disclosure provides a method for handling substrates during multiple-substrate processing. The method includes receiving one or more substrates in a first segment of a substrate supporting tray in a multiple-substrate processing chamber from an exterior substrate transfer robot. The multiple-substrate processing chamber includes features as described above. The method also includes rotating the substrate supporting tray to align a second segment of the substrate supporting tray with the substrate handling assembly, and receiving one or more substrates in the second segment of the substrate supporting tray from the exterior substrate transfer robot. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments. 
         FIG. 1  is a plan view of a cluster tool including multiple-substrate processing chambers in accordance with one embodiment of the present disclosure. 
         FIG. 2A  is a schematic top view of a multiple-substrate processing chamber and a substrate transfer robot in accordance with one embodiment of the present disclosure. 
         FIG. 2B  is a schematic sectional view of the multiple-substrate processing chamber of  FIG. 2A  in a substrate transfer position. 
         FIG. 2C  is a schematic top view of the multiple-substrate processing chamber with a substrate carrier removed. 
         FIG. 2D  is a schematic sectional view of the multiple-substrate processing chamber of  FIG. 2A  in a segment switching position. 
         FIG. 3A  is a schematic perspective view of a substrate grabbing assembly according to one embodiment of the present disclosure. 
         FIG. 3B  is a partial top view of a substrate supporting tray in accordance with one embodiment of the present disclosure. 
         FIG. 4A  is a partial sectional view of a substrate supporting tray carrier according to one embodiment of the present disclosure. 
         FIG. 4B  is a partial sectional view of the substrate supporting tray of  FIG. 4A  receiving a lifting pin. 
         FIG. 5A  is a schematic top view of a substrate carrier using sub-carriers process smaller substrates. 
         FIG. 5B  is a partial sectional view of the substrate carrier of  FIG. 5A . 
         FIG. 6  is a schematic top view of a substrate processing system having a transfer robot adapted to transfer two substrates simultaneously in accordance with one embodiment of the present disclosure. 
         FIG. 7  is a schematic top view of a substrate processing system having a transfer robot adapted to transfer multiple substrates simultaneously in accordance with one embodiment of the present disclosure. 
         FIG. 8  is a plan view of a cluster tool including multiple-substrate processing chambers in accordance with one embodiment of the present disclosure. 
         FIG. 9  is a plan view of a cluster tool including multiple-substrate processing chambers in accordance with another embodiment of the present disclosure. 
         FIG. 10  is a plan view of a liner cluster tool for multiple-substrate processing in accordance with one embodiment of the present disclosure. 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation. 
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure provide apparatus and methods for loading and unloading a processing chamber configured to process multiple substrates. More particularly, embodiments of the present disclosure provide apparatus and methods for loading and unloading a processing chamber in a segment by segment manner. Embodiments of the present disclosure also provide apparatus and methods for transferring multiple substrates in and out a processing chamber without transferring substrate supporting trays in and out the processing chamber. 
       FIG. 1  is a plan view of a cluster tool  100  for multiple-substrate processing in accordance with one embodiment of the present disclosure. The cluster tool  100  generally creates a processing environment where various processes can be performed to a substrate. In one embodiment, the cluster tool  100  is to fabricate compound nitride semiconductor devices, such as light emitting diodes (LEDs), laser diodes (LDs), and power electronics. The cluster tool  100  generally include a system controller  102  programmed to carrier out various processes performed in the cluster tool  100 . 
     The cluster tool  100  includes a plurality of processing chambers  104 ,  106 ,  108 ,  110  coupled to a transfer chamber  112 . Each processing chamber  104 ,  106 ,  108 ,  110  is configured to process multiple substrates  126  simultaneously. The processing chamber  104 ,  106 ,  108 ,  110  may have different substrate processing capacities. For example, the processing chamber  104  can simultaneously process twice as many substrates as the other processing chambers  106 ,  108 ,  110 . 
     The cluster tool  100  also includes a load lock chamber  116  connected to the transfer chamber  112 . In one embodiment, the cluster tool  100  also includes one or more service chambers  124  coupled to the transfer chamber  112  for providing various functions for processing, for example, substrate orientation, substrate inspection, heating, cooling, degassing, or the like. The transfer chamber  112  defines a transfer volume  152 . A substrate transfer robot  114  is disposed in the transfer volume  152  for transferring substrates  126  among the processing chambers  104 ,  106 ,  108 ,  110 , the load lock chambers  116 , and optionally the service chamber  124 . The transfer volume  152  is in selective fluid communication with the processing chambers  104 ,  106 ,  108 ,  110 , the load lock chambers  116  via slit valves  144 ,  146 ,  148 ,  150 ,  142  respectively. 
     The cluster tool  100  includes a factory interface  118  connecting one or more pod loaders  122  and the load lock chamber  116 . The load lock chamber  116  provides a first vacuum interface between the factory interface  118  and the transfer chamber  112 , which may be maintained in a vacuum state during processing. Each pod loader  122  is configured to accommodate a cassette  128  for holding and transferring a plurality of substrates. The factory interface  118  includes a Fl robot  120  configured to shuttle substrates between the load lock chamber  116  and the one or more pod loaders  122 . 
     The substrate transfer robot  114  includes a robot blade  130  for carrying one or more substrates  126  among the processing chambers  104 ,  106 ,  108 ,  110 , the load lock chamber  116 , and the service chamber  124 , and loading/unloading each chamber. 
     Each processing chamber  104 ,  106 ,  108 ,  110  include a substrate supporting tray  132 ,  134 ,  136 ,  138  respectively. Each substrate supporting tray  132 ,  134 ,  136 ,  138  is configured to support multiple substrates  126  in the respectively processing chamber  104 ,  106 ,  108 ,  110  during processing. During processing, the substrate supporting trays  132 ,  134 ,  136 ,  138  remain in the respectively processing chambers and do not travel with the substrates  126  among the processing chambers. In one embodiment, the load lock chamber  116  may also include a stay-in substrate supporting tray  140  similar to the substrate supporting trays  132 ,  134 ,  136 ,  138  in the processing chambers  104 ,  106 ,  108 ,  110 . In the exemplary embodiment shown in  FIG. 1 , the substrate supporting tray  132  is configured to hold 8 substrates that are 6 inches in diameter, and the substrate supporting trays  134 ,  136 ,  138 ,  140  are configured to hold 4 substrates that are 6 inches in diameter. Different substrate supporting trays can be used when processing substrates of different sizes, such as substrates that are 2 inches in diameter, 4 inches in diameter or 8 inches in diameter. 
     According to embodiments of the present disclosure, each of the processing chambers  104 ,  106 ,  108 ,  110  can be loaded or unloaded by the substrate transfer robot  114  in a segmented manner. The substrate transfer robot  114  is configured to retrieve substrates  126  from or deliver substrates  126  to a segment of each the processing chambers  104 ,  106 ,  108 ,  110 . Particularly, the substrate transfer robot  114  can load or unload a segment of the substrate supporting trays  132 ,  134 ,  136 ,  138  in one trip. One or more substrates  126  may be in each segment of the substrate supporting trays  132 ,  134 ,  136 ,  138 . Each processing chambers  104 ,  106 ,  108 ,  110  is loaded or unloaded by multiple trips of the substrate transfer robot  114 . After loading and/or unloading one segment, the substrate supporting trays  132 ,  134 ,  136 ,  138  may move to align a new segment with the substrate transfer robot  114  to repeat the loading and/or unloading until the entire chamber is loaded and/or unloaded. Details on embodiments of processing chambers and substrate transfer robots that enable segmented loading are further described with  FIGS. 2-7  below. 
     Segmented loading allows the substrate transfer robot  114  to be compatible with processing chambers of different capacities. Each segment of the substrate supporting trays  132 ,  134 ,  136 ,  138  may include a number of substrates that can be transferred by the substrate transfer robot  114  at one time. For example, in the embodiment shown in  FIG. 1 , the robot blade  130  of the substrate transfer robot  114  carries one substrate at a time, and each segment in the substrate supporting trays  132 ,  134 ,  136 ,  138  includes one substrate, and the processing chambers  104 ,  106 ,  108 ,  110  are loaded/unloaded in 4 and 8 segments. However, chamber capacity and segment arrangement can be modified according to various factors, such as the size of the substrates being processed and the processing recipes. 
     In one embodiment, the cluster tool  100  is configured to manufacture light emitting diodes (LED) and the processing chambers  104 ,  106 ,  108 ,  110  are metal organic chemical vapor deposition (MOCD) chambers and/or hydride vapor phase epitaxy (HVPE) chambers configured to form group-III nitride films. 
     A LED device is generally formed by a stack of films including: an n-GaN (n-doped GaN) layer, a MQW (multi quantum well) layer, p-GaN layer (including p-doped AlGaN layer and a p-doped GaN layer) on a substrate. All layers can be formed by MOCVD. When using MOCVD, the n-GaN layer and the MQW layer take longer to form the p-GaN layer. Alternatively, the n-GaN layer may be formed using HVPE to achieve a fast growth rate. Embodiments of the present disclosure include arrangements of processing chambers in a cluster tool to achieve overall efficiency when fabricating LED devices. 
     In one embodiment, the cluster tool  100  is configured to form LED devices on substrates using MOCVD to consecutively form an n-GaN layer, a MQW layer, and p-GaN layer on a substrate. Particularly, the processing chamber  104 , which has twice the substrate processing capacity as the processing chambers  106 ,  108 ,  110 , is a MOCVD chamber configured to form n-GaN layers on the substrates  126 ; the processing chambers  106 ,  108  are MOCVD chambers configured to form MQW layers on the substrates  126 ; and the processing chamber  110  is a MOCVD chamber configured to form p-GaN layers on the substrates  126 . By assigning the large processing chamber  104  to the n-GaN deposition process and two processing chambers  106 ,  108  to the MQW deposition process, this arrangement reduces waiting time between processes and increases efficiency. 
     During processing, substrates  126  being processed in a cassette  128  is first loaded into one of the pod loaders  122 . The Fl robot  120  then picks up the substrates  126  from the pod loader  122  and transfers the substrate  126  to the substrate supporting tray  140  in the load lock chamber  116 . Alternatively, Fl robot  120  may transfer the cassette  128  into the load lock chamber  116  when the substrate supporting tray  140  is not present in the load lock chamber  116 . The load lock chamber  116  with the substrates  126  on the substrate supporting tray  140  or in the cassette  128  is sealed and pumped up to the environment close to that of the transfer chamber  112 . The slit valve  142  between the load lock chamber  116  and transfer chamber  112  is then opened so that the substrate transfer robot  114  can pick up the substrate  126  in the load lock chamber  116 . 
     The substrate transfer robot  114  extends the robot blade  130  into the load lock chamber  116 , picks up a substrate  126  therein, and retracts the robot blade  130  with the substrate  126  to the transfer volume  152 . The substrate transfer robot  114  then rotates and aligns the robot blade  130  with the processing chamber  104  to load the substrate  126  in the processing chamber  104 . Optionally, the substrate transfer robot  114  may first transfer the substrates  126  to the service chamber  124  for alignment, preheating, cleaning or inspection before loading the substrate  126  to the processing chamber  104 . 
     The robot blade  130  extends into the processing chamber  104  through the slit valve  144  which is open while the substrate supporting tray  132  rotates to align one segment with the substrate transfer robot  114  to receive the substrate  126 . One substrate is loaded in the processing chamber  104 . The substrate transfer robot  114  repeats picking up a substrate  126  from the load lock chamber  116  and loading the substrate  126  to the processing chamber  104  to load the processing chamber  104  segment by segment until the processing chamber  104  is full. 
     The slit valve  144  then closes and a process to deposit an n-GaN layer on the substrates  126  is performed in the processing chamber  104 . After the process in the processing chamber  104  is completed, the processing chamber  104  is pumped out and the slit valve  144  opens. The substrate transfer robot  114  retrieves the substrates  126  with the n-GaN layer from the processing chamber  104  and transfers the substrate  126  with the n-GaN layer to the processing chamber  106  and  108  segment by segment, or one by one in the configuration shown in  FIG. 1 . 
     After each processing chamber  106 ,  108  is loaded with substrates  126  having n-GaN layer, the slit valve  146 ,  148  closes and a process to deposit a MQW layer on the substrates  126  is performed in each processing chamber  106 ,  108 . While the MQW deposition is going in the processing chambers  106 ,  108 , the substrate transfer robot  114  can reload the processing chamber  104  with a new batch of substrates  126  to begin processing to the new batch of substrates  126 . 
     After the process in the processing chamber  106  is completed, the processing chamber  106  is pumped out and the slit valve  146  opens. The substrate transfer robot  114  retrieves the substrates  126  with the MQW layer from the processing chamber  106  and transfers the substrates  126  with the MQW layer to the processing chamber  110  segment by segment. 
     A process to deposit a p-GaN layer on the substrates  126  is then performed in the processing chamber  110 . After the p-GaN layer deposition is completed, the processing chamber  110  is pumped out and the substrate transfer robot  114  transfers the substrates  126  with the p-GaN layer to the load lock chamber  116 . Optionally, the substrates  126  may be transferred to the service chamber  124  for cooling, or examination before going back to the load lock chamber  116 . 
     The substrates  126  from the processing chamber  108  are then transferred to the processing chamber  110  for deposition of a p-GaN layer. The processed substrates  126  are then transferred out of the processing chamber  110  to the load lock chamber  116 . 
     The Fl robot  120  transfers the processed substrates  126  from the load lock chamber  116  to the pod loader  122 , where the processed substrates  126  can be transferred or stored for further processes. 
     It should be noted that the cluster tool  100  can be modified to perform various processes by exchanging or programming the one or more processing chambers. 
     For example, in an alternative embodiment, the processing chambers  104 ,  106 ,  108 ,  110  can be arranged to enable the cluster tool  100  to form GaN templates for LED devices by depositing an n-GaN layer on a substrate. 
     In another embodiment, the processing chambers  104 ,  106 ,  108 ,  110  can be arranged to enable the cluster tool  100  to form LED devices on n-GaN templates by forming a multi quantum well (MQW) layer, p-doped AlGaN layer, and a p-GaN (p-doped GaN) layer on GaN templates. 
     In yet another alternative embodiment, the processing chambers  106 ,  108  are MOCVD chambers configured to form n-GaN layer; the processing chamber  104  is a MOVCVD chamber configured to form MQW layers; and the processing chamber  110  is a MOCVD chamber configured to form p-GaN layers on the substrates  126 . 
       FIG. 2A  is a schematic top view of a multiple-substrate processing chamber  200  in accordance with one embodiment of the present disclosure.  FIG. 2B  is a schematic sectional view of the multiple-substrate processing chamber  200 . The multiple-substrate processing chamber  200  is configured to be loaded and unloaded in a segmented manner. The multiple substrate processing chamber  200  may be used in place of the one of the processing chambers  104 ,  106 ,  108 ,  110  in the cluster tool  100  of  FIG. 1 . 
     The multiple substrate processing chamber  200  comprises a chamber body  202  defining a processing volume  204 . The chamber body  202  has an opening  206  formed therethrough to allow passage of substrates to and from an processing volume  204 . The opening  206  may be selective closed, for example by a slit valve door  208 . A robot, such as the substrate transfer robot  114  can be used to transfer substrates  126  in and out the multiple substrate processing chamber  200 . 
     A substrate supporting assembly  210  is disposed in the processing volume  204  for supporting a plurality of substrates  126  during processing. The substrate support assembly  210  includes a rotating frame  212  and a substrate supporting tray  214  disposed on the rotating frame  212 . 
     In one embodiment, the multiple substrate processing chamber  200  is a MOCVD chamber having a showerhead assembly  224  disposed above the substrate supporting assembly  210  and a heat source  228  disposed below a quartz bottom  226 . 
     The rotating frame  212  includes a shaft  216  coupled to an actuator  218  configured to rotate and vertically move the shaft  216 . Two or more fingers  220  extend from the shaft  216  to a supporting ring  222  on which the substrate supporting tray  214  sits. The fingers  220  are usually slim, thus allowing a back side of the substrate supporting tray  214  exposed to the heat source  228  disposed below. 
     The substrate supporting tray  214  is a thin plate having a plurality of substrate pockets  230  formed on an upper surface  234 . Each substrate pocket  230  is configured to accommodate a substrate  126 . The plurality of substrate pockets  230  can be grouped in a plurality of segments, wherein the substrate pockets  230  in each segment are arranged in the same pattern to enable segmented loading/unloading. In one embodiment, each segment may include one substrate pocket  230 . 
     Each substrate pocket  230  is configured to accommodate one substrate. In one embodiment, the substrate supporting tray  214  is circular and shaft  216  rotates the substrate supporting tray  214  about a center axis  232 . The substrate pockets  230  are arranged on the upper surface  234  of the substrate supporting tray  214  so that every substrate pocket  230  can be positioned in a loading position  236  as the substrate supporting tray  214  rotates about the center axis  232 . The substrates  126  in the substrate pockets  230  are uniformly exposed to the processing environment as the substrate supporting tray  214  rotates. 
     In one embodiment, the substrate pockets  230  may be evenly distributed on the substrate supporting tray  214  in one circular pattern and one substrate pocket  230  can be aligned in the loading position  236  at a time as shown in  FIG. 2A . However, depending on the size of the processing volume  204  and the diameter of the substrates  126 , the substrate pockets  230  may be arranged accordingly to improve throughput and to insure process uniformity. 
     The substrate supporting tray  214  may be removably disposed on the rotating frame  212  and may be exchanged and removed for maintenance. In one embodiment, the substrate supporting tray  214  is formed from a silicon carbide for supporting sapphire substrates. 
     In one embodiment, the multiple substrate processing chamber  200  includes a sensor assembly  238  configured to detect the orientation of the substrate supporting tray  214  and align one or more substrate pockets  230  with the loading position  236 . The sensor assembly  238  may be optical sensors, or image sensors to detect a marker on the substrate supporting tray  214 . 
     The multiple substrate processing chamber  200  further includes a lift pin assembly  240  disposed below the substrate supporting tray  214 . The lift pin assembly  240  includes three or more lift pins  242  attached to a lift pin frame  244 . The lift pin frame  244  is mounted on a lift pin shaft  246  through a mounting arm  252 . In one embodiment, three or more pin holes  250  are formed through the substrate supporting tray  214  in each substrate pocket  230 . The pin holes  250  allows the lift pins  242  to be inserted therein for loading and unloading a substrate  126  when the substrate pocket  230  is in the loading position  236 . 
     The lift pin assembly  240  is positioned below the loading position  236  to so that the lift pins  242  can pick up a substrate  126  from and drop off a substrate  126  onto a substrate pocket  230  in the loading position  236  as shown in  FIG. 2B . The robot blade  130  includes supporting fingers  254  separated by slots  256  for accommodating lift pins  242  when the robot blade  130  enters the multiple substrate processing chamber  200 . The supporting fingers  254  form a substrate pocket for holding a substrate  126  therein. 
     At least one of the lift pin frame  244  and the substrate supporting tray  214  can move vertically to allow the lift pins  242  to be inserted in the substrate supporting tray  214 . In one embodiment, the lift pin assembly  240  is fixedly disposed in the processing volume  204  and the vertical motion of the substrate supporting tray  214  allows the lift pins  242  to move in and out the substrate supporting tray  214 . In another embodiment, the lift pin shaft  246  is coupled to an actuator  248  configured to move the lift pins  242  vertically relative to the substrate supporting tray  214 . 
     The loading position  236  may be near the opening  206  so that an exterior robot blade, such as the robot blade  130  of the substrate transfer robot  114  can pick up and drop off one or more substrates  126  from/into the substrate pockets  230  in the loading position  236 . Because each substrate pocket  230  can be rotated to the loading position  236 , the substrate transfer robot  114  only needs to have a range of motion to reach as far as the loading position  236  to have access to the entire substrate supporting tray  214 . Therefore, embodiments of the present disclosure allow the multiple substrate processing chamber  200  to have a size larger than the size limited by the robot range, therefore, enabling increase in throughput. 
     As shown in  FIG. 2A , since it is not necessary to move the substrate supporting tray  214  through the opening  206 , the substrate supporting tray  214  can have a diameter much larger than the width of the opening  206 , therefore, allowing increase in the number of substrates  126  being processed. 
       FIG. 2C  is a schematic top view of the multiple-substrate processing chamber  200  with the substrate supporting tray  214  removed. The lift pin frame  244  may be a ring having three lift pins  242  extending therefrom. 
       FIG. 2D  is a schematic sectional view of the multiple-substrate processing chamber  200  in a position where the substrate supporting tray  214  is above the lift pins  242 . In this position, the substrate supporting tray  214  can rotate about the central axis  232  to switch segment that aligns with the lift pin assembly  240 . The substrates  126  are also processed in the position shown in  FIG. 2D . 
     During substrate transferring, the shaft  216  rotates the substrate supporting tray  214  to position an empty substrate pocket  230  in the loading position  236 . The substrate transfer robot  114  extends the blade  130  to the multiple substrate processing chamber  200  and positions the substrate  126  above the empty substrate pocket  230  in the loading position  236 . The lift pins  242  moves up through the pin holes  250  in the substrate supporting tray  214  and the slots  256  in the blade  130  to pick up the substrate from a substrate pocket  258  of the blade  130 . The robot blade  130  retracts without the substrate. The lift pins  242  then lower down below the substrate supporting tray  214  dropping the substrate in the substrate pocket  230  in the loading position  236 . 
     The substrate transfer robot  114  may then go back to a load lock chamber or a different processing chamber to pick up a new substrate for processing in the multiple substrate processing chamber  200 . The substrate supporting tray  214  rotates to have another empty substrate pocket  230  aligned with the loading position  236 . The substrate transfer robot  114  then loads the substrate to the substrate supporting tray  214 . The process can be repeated until the substrate supporting tray  214  is full. The slit valve door  208  may then be closed and the substrates on the substrate supporting tray  214  will be processed in the closed environment of the processing volume  204  in the multiple substrate processing chamber  200 . During processing, the substrate supporting tray  214  may rotate constantly to ensure the multiple substrates on the substrate supporting tray  214  have uniform exposure to the processing environment, thus, being processed uniformly. 
     After the processing in the multiple substrate processing chamber  200  is completed, the multiple substrate processing chamber  200  is pumped out and the slit valve door  208  opens. The substrate supporting tray  214  positions one substrate pocket  230  in the loading position  236  and stops rotating. The lift pins  242  come through the pins holes  250  and pick up the substrate. The substrate transfer robot  114  then extends the robot blade  130  into the multiple substrate processing chamber  200  to below the substrate on the lift pins  242 . The lift pins  242  then retract to below the substrate supporting tray  214  dropping the substrate on the robot blade  130 . The robot blade  130  then retracts with the substrate and one substrate is unloaded from the multiple substrate processing chamber  200 . The unloaded substrate may be transferred to a load lock chamber or another processing chamber for further processing. The substrate supporting tray  214  then rotates to align another substrate pocket  230  with a substrate with the loading position  236  to unload another substrate. The process is repeated until the substrate supporting tray is empty. 
     Any suitable substrate handling mechanisms may be used in place of the lift pin assembly  240  in the multiple substrate processing chamber  200  to achieve segmented loading. For example, the multiple substrate processing chamber  200  may include a substrate handling mechanism that uses vacuum methods, Bernoulli chucks, electrostatic chucks, or edge grabbing to pick up one or more substrates  126  from the substrate pockets  230  and exchange substrates  126  with exterior substrate handler, such as the robot  114 . 
     In an alternative embodiment, the lift pin assembly  240  may be omitted in the multiple substrate processing chamber  200  wherein substrates  126  may be loaded and unloaded by an exterior substrate handler that can directly pick up the substrates  126  from the substrate pockets  230 . For example, exterior substrate handler using edge grabbing, vacuum methods, Bernoulli chucks, or electrostatic chucks can be used for loading and unloading the multiple substrate processing chamber  200  without the lift pin assembly  240 . 
       FIG. 3A  is a schematic perspective view of a substrate grabbing assembly  300  according to one embodiment of the present disclosure. The substrate grabbing assembly  300  may include three or more grabbing fingers  302  attached to a frame  312 . In one embodiment, the frame  312  may be attached to a shaft  316  through a mounting arm  314  for using in a processing chamber in which the area under the substrate grabbing assembly  300  is not available for mounting. 
     Each grabbing finger  302  may be extending vertically upwards from the frame  312 . A top portion  318  of each grabbing finger  302  has a supporting surface  304  and a substrate directing surface  306  extending upwards and outwards from the supporting surface  304 . The supporting surface  304  is configured for supporting a backside of a substrate near an edge area. The supporting surfaces  304  may be planar. The supporting surfaces  304  of the three or more grabbing fingers  302  form a substrate sitting area  308  where a substrate is supported by the three or more grabbing fingers  302 . The substrate directing surface  306  is configured for directing the substrate to the substrate sitting area  308 . 
     The grabbing fingers  302  may be arranged in a manner that each grabbing finger  302  contacts a substrate at the corresponding supporting surface  304  when a substrate is fully engaged with the substrate grabbing assembly  300 . The directing surface  306  may be a sloped surface that flares outwards and upwards. The directing surfaces  306  define a receiving area  310  that is larger than the substrate being received, and gently direct the substrate down to the substrate sitting area  308 . The substrate grabbing assembly  300  is especially usefully when in centering the substrate and aligning the substrate with a substrate pocket. 
       FIG. 3B  is a partial top view of a substrate supporting tray  330  to be used with the grabbing mechanism  300 . The substrate grabbing assembly  300  may be disposed under a substrate supporting tray  330  and the grabbing fingers  302  be actuated by an actuator and move relative to the substrate supporting tray  330 . 
     The substrate supporting tray  330  is similar to the substrate supporting tray  214  except that each substrate pocket  332  of the substrate supporting tray  330  has three or more through holes  334  formed one an edge  336  of each substrate pocket  332 . Each through hole  334  allows passage of one substrate grabbing finger  302 . As illustrated in  FIG. 3B , the substrate receiving area  310  defined by the grabbing fingers  302  is larger than the substrate pocket  332 , and the substrate sitting area  308  is within the substrate pocket  332 . Therefore, the substrate grabbing assembly  300  ensures that a substrate stays within the substrate pocket  332  when dropping a substrate into the substrate pocket  332 . 
     As discussed above, in some processing chambers, such as MOCVD and HVPE chambers, one or more heating element may be positioned above and/or below a substrate supporting tray to heat the substrate supporting tray  214  and the substrates during processing. In the case where heating lamps or other heating elements are used to heat a substrate supporting tray from underneath the substrate supporting tray, a cap may be used in each pin holes to avoid direct heating to the substrate being processed. 
       FIGS. 4A and 4B  are partial sectional side views of a substrate supporting tray  400  having cover caps  402  for covering through holes  404  in each substrate pocket  408 . The through holes  404 , similar to pin holes  250  in the substrate supporting tray  214  and through holes  334  in the substrate supporting tray  330 , are configured to allow passage of lift pins or grabbing fingers  406 . When a lift pin or grabbing finger  406  is lifted through the through hole  404 , the cover cap  402  is lifted away from the substrate supporting tray  400  for substrate exchange. During processing, the cover cap  402  plugs the through hole  404  and preventing the substrate  126  from direct heating in the areas exposed by the through holes  404 . In one embodiment, the cover cap  402  may be fabricated so that the thermal properties of the cover cap  402  with a thickness of t 1  are similar to the substrate supporting tray  400  with a thickness of t 2 . 
     While the substrate supporting trays  214 ,  330 , and  400  described above can be designed to use in a processing chamber for processing substrates with relatively large size, such as 4 inch, 6 inch, 8 inch or lager substrates, the substrate supporting trays according to embodiments of the present disclosure may be modified to backward compatible with small substrate processing. 
     In one embodiment, smaller substrates may be transferred with a sub-carrier.  FIG. 5A  is a schematic top view of a substrate supporting tray  500  with sub-carriers  504  to process small substrates  506 .  FIG. 5B  is a partial sectional view of the substrate supporting tray  500 . Each sub-carrier  504  is configured to support and secure a plurality of small substrates  506 . The sub-carrier  504  fits in substrate pockets  502  formed in the substrate supporting tray  500 . During processing, the sub-carrier  504  is transferred along with the small substrates  506 . 
     Substrate supporting trays and robot blades according to embodiments for the present disclosure may be changed to process substrates of different sizes. 
     Segmented loading/unloading according to embodiments of the present disclosure may be achieved using various substrate transfer robots. In one embodiment shown in  FIGS. 1 and 2A , the substrate transfer robot  114  in the transfer chamber  112  includes one robot blade  130  for handling one substrate. 
     In another embodiment, the substrate transfer robot  114  may include multiple robot blades each for carrying one substrate at a time. For example, the substrate transfer robot  114  may have two robot blades  130  positioned in two vertical levels. For example, in the substrate transfer robot  114  shown in  FIG. 2B , a second robot blade  260  (shown in dashed lines) may be used in combination of the robot blade  130 . Substrate pockets in the robot blades  130 ,  260  may have the same arrangement so that the substrate transfer robot  114  can unload and load a segment of a substrate supporting tray in one trip. 
     In one embodiment, the robot blades  130 ,  260  may enter the multiple substrate processing chamber  200  at a staggered manner so that lift pins  242  can have access to either robot blade  130 ,  260  without affecting the other. 
     During operation, one robot blade  130  or  260  carries one or more substrates to be loaded to the multiple substrate processing chamber  200  while the other blade remains empty. Usually, the robot blade that enters the processing chamber first remains empty so that the multiple substrate processing chamber  200  can be unloaded before loading. In the embodiment of  FIG. 2B , the upper robot blade  260  stays empty before operation and the lower robot blade  130  holds one or more substrates to be loaded. The multiple substrate processing chamber  200  has one segment of the substrate supporting tray  214  in the loading position  236 , and the lift pins  242  lift up the one or more substrates  126  to be unloaded. The empty robot blade  260  picks up the substrate from the lift pin  242  as the lift pins  242  drop down. The lower robot blade  130  then moves forward to the loading position  236 . The lift pins  242  rise to pick up the substrate on the lower robot blade  130  to complete loading of the segment. 
     Alternatively, the substrate transfer robot  114  may include one robot blade configured to carry two or more substrates at a time. 
       FIG. 6  is a schematic top view of a substrate processing system  600  having a substrate transfer robot  602  for transfer two substrates simultaneously in accordance with one embodiment of the present disclosure. The substrate processing system  600  may include a transfer chamber  604  having a transfer volume  606 . The substrate transfer robot  602  is disposed in the transfer volume  606 . 
     The substrate transfer robot  602  includes a robot blade  608  having two substrate pocket  610  for supporting two substrates thereon. The substrate transfer robot  602  operates to extend the robot blade  608  from the transfer volume  606  in the transfer chamber  604  to processing chambers  612 ,  614  attached to the transfer chamber  604  through the openings  616 ,  618  to pick up or drop off substrates. The substrate pockets  610  on the robot blade  608  are arranged to match the arrangement of lift pins  620 ,  622  in the processing chambers  612 ,  614 . 
     The processing chambers  612 ,  614  may have different configurations and capacities as long as each processing chamber  612 ,  614  includes segments having the same substrate pocket arrangement as of the robot blade  608 . The processing chambers  612 ,  614  include lift pins that match the robot blade  608 . The processing chambers  612 ,  614  may include substrate supporting trays  628 ,  630  respectively. The substrate supporting trays  628 ,  630  may include substrate pockets  624 ,  626 . The substrate pockets  624 ,  626  may be grouped into multiple segments and each segment includes substrate pockets  624 ,  626  formed in a pattern matching the pattern of the substrate pockets  610  of the robot blade. In the embodiment shown in  FIG. 6 , the substrate pockets  610  are arranged side by side. The substrate supporting tray  628  may include four segments separated by lines  632 ,  634 . The substrate supporting tray  630  may include two segments formed by line  636 . 
       FIG. 7  is a schematic top view of a substrate processing system  700  having a substrate transfer robot  702  for transfer three substrates simultaneously in accordance with one embodiment of the present disclosure. The transfer robot  702  has a robot blade  704  which includes three substrate pockets  706 . The substrate pockets  706  are arranged in the same pattern as substrate pockets  712  within a segment  714  of a substrate supporting tray  710  in a processing chamber  708 . 
     It should be noted that substrate supporting trays and robot blades may have other configurations to allow multiple substrate handling. Robot blades on a substrate transfer robot can be exchanged according to size of the substrates being processed. 
     Embodiment of the present disclosure also includes cluster tools of various configurations with segmented loading function for various process requirements.  FIGS. 8-10  illustrate a few exemplary cluster tools according to embodiments of the present disclosure. 
       FIG. 8  is a plan view of a cluster tool  800  in accordance with one embodiment of the present disclosure. The cluster tool  800  is similar to the cluster tool  100  of  FIG. 1  except that a HVPE chamber  810  is connected to the transfer chamber  112  in place of the processing chamber  110 , and a loading station  818  instead of the factory interface  118  is connected to the load lock chamber  116 . 
     The cluster tool  800  includes processing chambers  104 ,  106 ,  108  configured for performing MOCVD processes, and the HVPE chamber  810 . Each chamber  104 ,  106 ,  108 ,  810  can be segmented loaded by the substrate transfer robot  114  disposed in the transfer chamber  112 . 
     The HVPE chamber  810  and the processing chambers  106 ,  108  may have the same substrate processing capacities while the processing chamber  104  can process twice as many substrates as the chambers  810 ,  106 ,  108 . The HVPE chamber  810  increases the efficiency of the cluster tool by using a HVPE process to increase growth rate from the MOCVD deposition. The HVPE chamber  810  may be used in forming n-GaN layers in metal nitride devices. 
     According to one embodiment of the present disclosure, the cluster tool  800  is configured to form LED devices. The HVPE chamber  810  is configured to form n-GaN layers for LED devices; the processing chambers  106 ,  108  are MOCVD chambers configured to form MQW layers; and the processing chamber  104  is a MOCVD chamber configured to form p-GaN layers. 
       FIG. 9  is a plan view of a cluster tool  900  in accordance with another embodiment of the present disclosure. 
     The cluster tool  900  is similar to the cluster tool  100  of  FIG. 1  except that there is a fifth processing chamber  924  connected to the transfer chamber  112  in place of the service chamber  124 , all five processing chambers  106 ,  108 ,  110 ,  904 ,  924  have the same substrate processing capacity, and a loading station  818  instead of the factory interface  118  is connected to the load lock chamber  116 . 
     In one embodiment, all five processing chambers  106 ,  108 ,  110 ,  904 ,  924  are MOCVD chamber. The cluster tool  900  may be configured to form LED devices. For example, the processing chambers  110 ,  108  are configured to form n-GaN layers for LED devices; the processing chambers  106 ,  904  are configured to form MQW layers; and the processing chamber  924  is configured to form p-GaN layers. 
       FIG. 10  is a plan view of a linear cluster tool  1000  for multiple-substrate processing in accordance with one embodiment of the present disclosure. 
     The cluster tool  1000  includes two factory interfaces  1002   a,    1002   b  with a plurality of transfer chambers  1004   a,    1004   b,    1004   c  and processing chambers  1006   a ,  1006   b  connected in between. During processing, substrates being processed enter the cluster tool  1000  from the factory interface  1002   a,  go through the transfer chambers  1004   a,    1004   b,    1004   c  to be processed in the processing chambers  1006   a ,  1006   b  sequentially, and exit the cluster tool  1000  from the factory interface  1002   b . The processing chamber  1006   a,    1006   b  can be loaded/unloaded segmented by substrate transfer robots  1008   a,    1008   b,    1008   c  in the transfer chambers  1004   a ,  1004   b,    1004   c.    
     Each processing chamber  1006   a,    1006   b  in the cluster tool  1000  is connected to two transfer chambers. This configuration further increases loading and unloading efficiency because loading and unloading can be performed simultaneously by two substrate transfer robots in the two transfer chambers. The processing chamber  1006   a,    1006   b  may have two loading positions and two lift pin assemblies for the two robots. 
     The segmented loading arrangement according to embodiments of the present disclosure provides several advantages and improvements to cluster tools, such as the cluster tools  100 ,  800 ,  900 , and  1000 . 
     One advantage is improving repeatability of a multiple-substrate processing chamber. Because segmented loading allows the substrate supporting trays to become permanent structures in processing chambers, the stability of the processing environment in the processing chambers improves and performance repeatability also improves. 
     Another advantage of segmented loading arrangement is avoiding transferring substrate supporting trays with the substrates during processing. When transferring substrates in substrate supporting trays, the substrate supporting tray is usually designed to be suitable for various processing chambers simultaneously in a cluster tool since the substrate supporting tray travels through the various processing chambers with the substrates. Thus, designs of the substrate supporting tray may be compromised to fit different chambers. In the segmented loading arrangement, each substrate supporting tray remains in the corresponding processing chamber and can have individual designs to best suit the particular processing chamber. Furthermore, when transferring substrates in substrate supporting trays, process variation from load to load can be introduced by the manufacturing tolerance of the substrate supporting trays. Segmented loading arrangement eliminates process variations from load to load caused by the substrate supporting trays. 
     Another advantage is increasing productivity. By incorporating segmented loading/unloading without transferring substrate supporting trays with the substrates, larger processing chamber can be used since the chamber size is no longer limited by the size of the substrate supporting tray, or the size of the slit valve opening, or the range of motion of substrate transfer robots. Larger processing chambers process a larger number of substrates, thus increasing overall productivity of a cluster tool. 
     Using segmented loading also allows a cluster tool to include chambers of different dimensions or substrate processing capacities. A cluster tool may use a large processing chamber for a long process, and a small processing chamber for a short process, thus, optimizing the cluster tool between efficiency and cost. 
     Using segmented loading in a cluster tool also reduces cost by avoiding costs for manufacturing and maintaining substrate supporting trays that travel with substrates during processing. Additionally, using segmented loading also simplifies substrate handling systems by only using robots for handling substrates, and deleting the robots for handling substrate supporting trays, thus, further reduce operation costs. 
     Furthermore, segmented loading also reduces cross contamination among processing chambers caused by substrate supporting trays moving from chamber to chamber during operation. 
     Although, manufacturing LED is described above, other embodiments of the present disclosure are suitable for any processes where multiple-substrate process is performed. Embodiments of the present disclosure are also suitable of loading and unloading a standalone multiple-substrate processing chamber. 
     While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.