Abstract:
The present invention relates to an apparatus and method for heating a semiconductor processing chamber. One embodiment of the present invention provides a furnace for heating a semiconductor processing chamber. The furnace comprises a heater surrounding side walls of the semiconductor processing chamber, wherein the heater comprises a plurality of heating elements connected in at least two independently controlled zones, and a shell surrounding the heater.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   Embodiments of the present invention generally relate to apparatus and method for heating a semiconductor processing chamber. Particularly, the present invention relates to a furnace having a multizone heater for heating a semiconductor processing chamber. 
   2. Description of the Related Art 
   Some processes during semiconductor processing are performed in a furnace where on or more substrates are processed in an elevated temperature. It is essential to heat the substrate or substrates uniformly, especially in a batch processing, a commonly used process step that can process two or more substrates simultaneously in one region. Batch processing has been proven to be effective in increasing device yield and reducing cost of ownership. A batch processing chamber generally processes a batch of vertically stacked substrates within a chamber volume. Process steps performed in a batch processing chamber, such as atomic layer deposition (ALD) and chemical vapor deposition (CVD), generally require substrates to be heated uniformly. Therefore, a batch processing chamber generally comprises a heating system configured to heat a batch of substrates. However, it is challenging to heat a batch of substrate uniformly and such a heating system may be complicated, difficult to maintain and costly to repair. 
     FIGS. 1 and 2  illustrate a heated batch processing chamber known in the art.  FIG. 1  illustrates a batch processing chamber  100  in a processing condition. In this condition, a batch of substrates  102  supported by a substrate boat  101  is processed in a process volume  103  defined by a top  104 , sidewalls  105 , and a bottom  106 . An aperture  122  formed in the bottom  106  provides a means for the substrate boat to be inserted into the process volume  103  or removed from the process volume  103 . A seal plate  107  is provided to seal off the aperture  122  during a process. 
   Heating structures  110  are generally mounted on exterior surfaces of each of the sidewalls  105 . Each of the heating structures  110  contains a plurality of halogen lamps  119  which are used to provide energy to the substrates  102  in the process volume  103  through a quartz window  109  mounted on the sidewall  105 . Thermal shield plates  108  mounted on an inside surface of the sidewalls  105  are added to the process volume  103  to diffuse the energy emitted from the heating structures  110  to provide a uniform distribution of heat energy to the substrates  102 . 
   The sidewalls  105  and the top  104  are generally temperature controlled by milled channels  116  (shown in  FIG. 2 ) formed in the sidewalls  105  to avoid unwanted deposition and for safety reasons as well. When the quartz windows  109  are hot and the process volume  103  is under vacuum, undue stress would cause an implosion if the quartz windows  109  were in direct contact with the temperature controlled sidewalls  105 . Therefore, O-ring type gaskets  124  (constructed of a suitable material such as, for instance, viton, silicon rubber, or cal-rez graphite fiber) and strip gaskets  123  of a similar suitable material are provided between the quartz windows  109  and sidewalls  105  to ensure that the quartz windows  109  do not come in direct contact with the sidewalls  105 . The thermal shield plates  108  are generally mounted on the sidewalls  105  by insulating strips  125  and retaining clamps  126 . The thermal shield plates  108  and the insulating strips  125  are made of a suitable high temperature material such as, for instance, graphite or silicon carbide. The retaining clamps  126  are made from suitable high temperature material such as titanium. The milled channels  116  formed in the sidewalls  105  may be temperature controlled by use of a heat exchanging fluid that is continually flowing through the milled channels  116 . 
   The heating structures  110  are further described in U.S. Pat. No. 6,352,593, entitled “Mini-batch Process Chamber” filed Aug. 11, 1997, and U.S. patent application Ser. No. 10/216,079, entitled “High Rate Deposition At Low Pressure In A Small Batch Reactor” filed Aug. 9, 2002 which are incorporated herein by reference. 
   Referring now to  FIG. 2 , process gases used in depositing layers on substrates  102  are provided via a gas injection assembly  114 . The gas injection assembly  114  is vacuum sealed to the sidewalls  105  via an O-ring  127 . An exhaust assembly  115  is disposed on an opposite side of the gas injection assembly  114 . The sidewalls  105 , the top  104  and the bottom  106  are typically made of metals, such as aluminum. 
   The batch processing chamber  100  contains complicated system for heating, vacuum seal and thermal isolation. The heating structures  110  are difficult to assemble and service because special fixtures are required for removal and replacement. Furthermore, it would be difficult to control the heating uniformity using the heating structure  110 . 
   Therefore, there is a need for a simplified heating system to heat a batch of substrates uniformly in a semiconductor processing chamber. 
   SUMMARY OF THE INVENTION 
   The present invention generally provides a method and apparatus for heating a batch processing chamber. 
   One embodiment of the present invention provides a furnace for heating a semiconductor processing chamber. The furnace comprises a heater surrounding the semiconductor processing chamber, wherein the heater comprises a plurality of heating elements connected in at least two independently controlled zones, and a shell surrounding the heater, wherein the heater is secured to the shell. 
   Another embodiment of the present invention provides a semiconductor processing system. The system comprises a chamber for processing substrates therein, a heater surrounding the chamber, wherein the heater has multiple independently controlled zones, a shell covering the heater, and a first reflector element disposed between the heater and the shell, wherein the heater, the first reflector element, and the shell are secured together. 
   Yet another embodiment of the present invention provides a furnace for a semiconductor processing chamber. The furnace comprises a printed circuit heater having multiple independently controlled zones configured to heat the semiconductor processing chamber, a reflector disposed outside the printed circuit heater, and a shell disposed outside the reflector, wherein the printed circuit heater, the reflector and the shell are secured together. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
       FIG. 1  illustrates a sectional top view of a state of the art processing system. 
       FIG. 2  illustrates a sectional side view the processing system of  FIG. 1 . 
       FIG. 3  is a sectional top view of an exemplary processing system in accordance with the present invention. 
       FIG. 4  is a sectional side view of the exemplary substrate processing system of  FIG. 3 . 
       FIG. 5A  is a schematic sectional view of a heating element in accordance with the present invention. 
       FIG. 5B  is a schematic back view of the heating element of  FIG. 5A . 
       FIG. 6  is a top view of an exemplary processing system in accordance with the present invention. 
       FIG. 7  is a perspective view of the processing system of  FIG. 6 . 
   

   DETAILED DESCRIPTION 
   The present invention generally provides a semiconductor processing system having a multizone heater. The heater of in the present invention can accommodate a variety of control and wattage requirements depending on process temperatures and provide different heating power to different zones in a batch processing chamber. The invention is illustratively described below in reference to modification of a FLEXSTAR™ system, available from Applied Materials, Inc., Santa Clara, Calif. 
     FIGS. 3 and 4  illustrate one embodiment of a semiconductor processing system  200  of the present invention. The semiconductor processing system  200  may be configured to process a batch of substrate in an elevated temperature, for example to perform an atomic layer deposition (ALD) or chemical vapor deposition (CVD). 
   The semiconductor processing system  200  comprises a processing chamber  205  configured to process on or more substrates in an inner volume  212  enclosed therein. In one embodiment, the processing chamber  205  may be a cylindrical quartz chamber. The processing chamber  205  may have an exhaust port  211  positioned in one side and an inlet port  206  positioned in an opposite side of the exhaust port  211 . The inlet port  206  is configured to supply one or more processing gas into the inner volume  212  of the processing chamber  205 . The exhaust port  211  is generally adapted to a vacuum source and configured to pump processing gases from the inner volume  212 . The substrates being processed may be disposed in a substrate boat in a vertically stacked manner and are generally rotated during the process to be acquire uniform exposure to heat and processing gases. A detailed description of the processing chamber  205  may be found in a co-pending U.S. patent application Ser. No. 11/249,555, filed on Oct. 13, 2005, entitled “Reaction Chamber with Opposing Pockets for Injection and Exhaust”, which is incorporated herein as reference. 
   A heater  202  is disposed outside the processing chamber  205  and configured to heat the processing chamber  205  during process. The heater  202  may be a resistive heater. In one embodiment, the heater  202  may have substantially the same shape as the processing chamber  205  to provide a uniform heating effect around a circumference of the processing chamber  205 . The heater  202  comprises multiple independently controlled zones to achieve desired heating profile, for example a uniform heating along vertical level. In one embodiment, the heater  202  may comprise multiple independently controlled zones  202   i  (where i=1, 2, . . . n) that are vertically stacked together, as shown in  FIG. 4 . During a batch processing, substrates positioned near the top and the bottom of the substrate boat are usually less heated than the substrates positioned near the center of the substrate boat resulting in different processing effects among a batch of substrates. The vertically stacked configuration is particularly useful in reducing or eliminating uneven heating at different vertical levels inside the inner volume  212  in the processing chamber  205 . Other configurations of the multiple zones, such as vertical zones, combination of vertical and horizontal zones, and zones corresponding to thermal profile of the processing chamber  205 , may also be contemplated by the present invention. 
   In one embodiment, the heater  202  may be formed by a plurality of resistive heating elements.  FIG. 5A  illustrates a schematic sectional view of a heating element  220  that may be used to form the heater  202  of the  FIGS. 3 and 4 .  FIG. 5B  illustrates a backside (the side usually positioned away from heating target) view of the heating element  220 . In one embodiment, the heating element  220  may be manufactured from a graphite disk, or graphite material of other shape. A layer of pyrolytic boron nitride (PBN) is first coated on the graphite disk. The coated graphite disk is then machined to a desired pattern from the back side. Another coat of pyrolytic boron nitride. As shown in  FIGS. 5A and 5B , a channel  224  is machined on a graphite disk defining a resistive element  221  of the heating element  220 . A layer of pyrolytic boron nitride coat  223  serves as an insulating material of the heating element  220 . Pyrolytic boron nitride is anisotropic high temperature ceramic which has high electric resistance and good thermal conductivity. The heating element  220  may be connected to a power source via graphite posts  222 . The heating element  220  is chemically inert to most gases and liquids, mechanically and thermally uniform, shock resistance, with ultra fast response. Different designs of the resistive element  221  provide different heating effect to the heating element  220 . Therefore, the heater  202  made of one or more heating elements  220  may also have the flexibility of forming one or more zones of different heating effects. It should be noted that other suitable type of heating elements, such as other ceramic heaters, may also be used to form the heater  202 . 
   Referring to  FIG. 4 , each of the independently controlled zones  202   i  may comprise at least one heating element, such as the heating element  220  of  FIG. 5 . Each of the independently controlled zones  220   i  may be connected to an individually controlled power source via a pair of graphite posts  207 . 
   Referring to  FIG. 3 , the semiconductor processing system  200  further comprises an outer shell  201  configured to enclose the heater  202  therein. The outer shell  201  may be a metal shell. In one embodiment, the outer shell  201  may be made from stainless steel and may have a thickness of about 1.5 mm. In one embodiment, the outer shell  201  may have several feet  210  configured to secure the semiconductor processing system  200  to a base or a load lock. The heater  202  may be secured to the outer shell  201 . In one embodiment, the heater  202  may be fastened to the outer shell  201  by a plurality of bolts and nuts  208 . In another embodiment, the heater  202  may be directly secured to a base to which the semiconductor processing system  200  is attached. 
   A reflector  203  may be disposed between the heater  202  and the outer shell  201 . The reflector  203  is configured to reflect radiation heat back to the heater  202  and keep the outer shell  201  from getting hot. The reflector  203  may be made from metal, such as hastelloy or stainless steel. In one embodiment, a second reflector  204  may be positioned near the exhaust port  211 . 
   In one embodiment, the heater  202  may comprise two arced sections surrounding the processing chamber  205  and leaving the exhaust port and the inlet port uncovered. In one embodiment, the two arced sections may have the same zone configuration and counter part zones may be connected to each other forming an all around controlled zone. 
     FIGS. 6 and 7  schematically illustrate another embodiment of a semiconductor processing system  300  in accordance with the present invention. The semiconductor processing system  300  comprises a processing chamber  305  defining an inner volume  312  configured to process one or more substrates  310  positioned therein. The processing chamber  305  having an exhaust port  311  positioned in one side and an inject port  306  positioned on an opposite side of the exhaust port  311 . The semiconductor processing system  300  further comprises an outer shell  301  surrounding the processing chamber  305 . The inject port  306  may be sealed against an opening  314  formed in the outer shell  301 . 
   A heater  302  is disposed inside the outer shell  301  and outside the processing chamber  305 . The heater  302  is configured to heat the processing chamber  305 . In one embodiment, the heater  320  has a substantial similar shape as the processing chamber  305  wrapping around the processing chamber  305 . In one embodiment, the heater  302  may comprise two heater sections  302   a  and  302   b  leaving the exhaust port  311  and the inject port  306  uncovered. 
     FIG. 7  illustrates the semiconductor processing system  300  without the outer shell  301 . The two heater sections  302   a  and  302   b  may be connected by one or more brackets  304 . On or more graphite posts  313  may be positioned in the brackets  304  and configured to connect the heater sections  302   a  and  302   b  electronically. Each of the heater section  302   a  and  302   b  may further comprise one or more individually controlled zones  302   i . In one embodiment, the individually controlled zones  302   i  may be vertically stacked. The heater sections  302   a  and  302   b  may have identical configuration hence forming individually controlled zones at different vertical level across the processing chamber  305 . 
   Each of the one or more individually controlled zones  302   i  may have one or more heating elements, such as the heating elements  220  shown in  FIG. 5 . 
   The one or more brackets  304  may be connected together by a post  315 . One or more posts  308  may be also attached to the heater sections  302   a  and  302   b . The posts  315  and  308  may be further secured to a base hence securing the heater  302 . 
   While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.