Abstract:
An apparatus for wafer processing that includes a wafer reaction chamber containing a heater within, the heater including an interior volume containing at least one heating element, a fluid inlet port, and a fluid vent port positioned to vent the fluid outside the wafer reaction chamber. Additionally, the interior volume has a seal that isolates it from the wafer reaction chamber.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to heating mechanisms for process chambers, and particularly, to heating mechanisms for chemical vapor deposition chambers. 
     2. Description of Related Art 
     Chemical vapor deposition (CVD) is a process for depositing various types of films on substrates and is used extensively in the manufacture of semiconductor-based integrated circuits such as, for example, the processing of semiconductor wafers (wafers) to form individual integrated circuit devices. In typical CVD processing, a wafer or wafers are placed in a deposition or reaction chamber and reactant gasses are introduced into the chamber that are decomposed and reacted at a heated surface to form a thin film on the wafer or wafers. 
     A CVD reactor vessel adds coatings to wafers using a multi-zone resistive heater (heater) to react the coating chemistry once applied to a wafer surface. The heater includes at least two resistive heating rods disposed within a tube to contact a spiral heater coil (coil) embedded within a heater disk (disk). The distinct heating rods are not equadistantly centered about the tube centerline nor the coil. Instead they are offset, the result being that areas of the heating disk can have a wide range of temperatures provided by varying the electrical power applied to the individual heating rods. A specially designed surface (susceptor) exists on one side of the heating disk upon which is supported the wafer. The wafer is heated conductively by heat transferred from the heating coil to the susceptor. Upon completion of the deposition of the film onto the wafer, the process gasses are removed, the reaction chamber purged with cleaning chemicals and inert gasses, and the wafer removed. 
     Initially at assembly, an interior volume of the heater assembly is exposed to atmosphere. Once the heater is assembled, atmosphere will remain contained within. Oxygen in the atmosphere that is contained within the heater assembly will attack the heater components at temperatures above 700° C. As a result, the mechanical strength of the heater components will degrade with use and the heater components will have to be replaced at a cost in parts, labor, and down time for the reactor vessel. 
     SUMMARY OF THE INVENTION 
     A wafer processing method, comprising processing a wafer in a reaction chamber comprising a heater having an interior space; heating the reaction chamber with the heater, purging an inert gas into the heater interior space, and venting the inert gas. 
    
    
     BRIEF DESERTION OF THE DRAWINGS 
     FIG. 1 is an illustration of a CVD reactor assembly; 
     FIG. 2 is an illustration of a portion of the CVD reactor assembly; 
     FIG. 3 is an illustration of a portion of the CVD reactor assembly; 
     FIG. 4 is an illustration of a portion of the CVD reactor assembly; 
     FIG. 5 is a an illustration of a resistive heater assembly; 
     FIG. 6 is an illustration of a spiral coil; 
     FIG. 7 is an illustration of the resistive heater assembly with purge; 
     FIG. 8 is an illustration of the resistive heater assembly with vacuum. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention generally relates to a method and an apparatus for removing reactive gasses from the interior of a multi resistive heater (heater) used in a semiconductor wafer processing reaction chamber. Wafer processing requires corrosive chemistry to be applied at high temperatures and the heater components that must withstand this environment are currently manufactured from a ceramic material, aluminum nitride (AlN). 
     While the heater interior is subject to the same heating conditions as the reaction chamber, it is sealed and not exposed to the processing gasses during operation of the reaction chamber. The heater interior is assembled and disassembled in atmosphere and therefore contains atmospheric gasses, in particular oxygen. At operating temperatures greater than 700° C., aluminum nitride when exposed to atmosphere, will react with the oxygen and the material strength of the AlN component will be reduced. As a result, the service life of the heater is reduced. 
     The heater interior surfaces, made of aluminum nitride, that are exposed to atmosphere and processing heat during wafer processing include; the inside surfaces of a tube, a portion of a heater disk that is covered by the tube, and a set heating rod insulators. A method and apparatus for reducing or eliminating the oxygen from these inner heater surfaces (heater interior) is disclosed. In an embodiment, the method comprises a continual flow of an inert fluid through the interior of the heater to maintain an oxygen free environment. The inert fluid can be a liquid or a gas or combination of gasses that are non-reactive at the operating conditions of the intended use. In another embodiment, a vacuum is placed within the heater interior to ensure no oxygen is present. 
     FIG. 1 is an illustration of a reactor vessel assembly (reactor)  100  that processes a film onto a semiconductor wafer. The reactor vessel assembly  100  is comprised of a chamber assembly  102  and a resistive heater assembly (heater)  104  for use in a chemical vapor deposition apparatus. Heater  104  is designed to move along an axis  105  relative to chamber assembly  102 . A chamber body  106  defines a reaction chamber  108  where the reaction between a process gas or gasses and the wafer takes place, e.g., a CVD reaction. Chamber body  106  is constructed, in an embodiment, of 6061-T6 aluminum and has passages  110  for water to flow through to cool chamber body  106 . Resident in reaction chamber  108  is resistive heater (heater)  104  that includes several heating elements (rods)  112  running the length of a heater tube (tube)  114  that are made of nickel. At the end of tube  114  is a heating disk (disk)  116  made of sintered AlN. Sintered within disk  116  is a spiral heating element (coil)  118  made of molybdenum. Rods  112  and coil  118  are joined with a brazing and are electrically conductive therein. Rods  112  are thermally insulated with AlN ceramic sleeves  120 . Coil  118  provides most of the electrical resistance and therefore most of reaction chamber  108  heating. At the end of heating disk  116  is a recess called a susceptor  122  within that is placed a wafer (not shown). In an embodiment, susceptor  122  has a surface area sufficient to support a 200 millimeter diameter semiconductor wafer (200 mm wafer) while in another embodiment, susceptor  122  has a surface area sufficient to support a 300 millimeter diameter semiconductor wafer (300 mm wafer). 
     Referring still to FIG. 1, heater  104  is retracted along an axis  105  and the wafer (not shown) is placed in reaction chamber  108  on susceptor  122  through an entry port  134  in a side portion of chamber body  106 . To accommodate the wafer for processing, heater  104  is retracted until a surface of susceptor  122  is below entry port  134 . A transfer blade (FIG. 2 below) places the wafer (not shown) into chamber body  106  within susceptor  122 . Once loaded, entry port  134  is sealed and heater  104  is advanced in a direction toward faceplate  130  by lifter assembly  136 . At this point, process gasses controlled by a gas panel (not shown) flow into chamber  108  through port  124 , through blocker plate  128 , through faceplate  130 , and typically react or are deposited onto the wafer (not shown) to form a film (not shown). Using a pressure controlled system (not shown), the pressure in chamber  108  is established and maintained by a pressure regulator or regulators (not shown) coupled to chamber  108 . 
     FIG. 2 is an embodiment of a simplified processing area around wafer  132  with many of the reactor  100  (FIG. 1) components removed for clarity. Process gasses  154  enter reaction chamber  108  through an opening  124  in a top surface of a chamber lid  126  of chamber body  106 . The process gases first pass through a blocker plate  128 . Blocker plate  128  is perforated with a set of holes (not shown) to radially distribute the process gas. The process gasses then pass through holes (not shown) of a second perforated plate known as a faceplate  130 . Faceplate  130  provides uniform distribution of the process gasses  154  onto wafer  132 . 
     A pump (not shown) draws on a pumping plate  138  at a collection channel  140 . As a result, after impacting wafer  132 , process gases  154  pass through radial holes  156  in pumping plate  138 , are collected in an annular channel  140 , and are then directed out of reaction chamber  108 . Chamber  108  may then be purged  155 , for example, with an inert gas, such as nitrogen. 
     In an embodiment, as shown in FIG. 3, after processing and purging, heater  104  is moved in a lower direction (away from a chamber lid  126 ) by a lifter assembly  136  lift pins  142  are positioned at the base of reaction chamber  108 . Lift pins  142  have one end positioned through holes in disk  116  to a contact lift plate  144 . As heater  104  moves in a lower direction along axis  105 , through the action of a lifter assembly  136 , lift pins  142  remain stationary and ultimately extend above the top surface of disk  116  to separate processed wafer  132  from the surface of susceptor  122 . 
     In an embodiment, as shown in FIG. 4, once processed, wafer  132  is separated from the surface of susceptor  122  by transfer blade  166  of a robotic mechanism (not shown) that is inserted through opening  134  to remove wafer  132 . The steps described above are reversed to bring wafer  132  into a process position. 
     In a high temperature operation such as low pressure CVD (LPCVD) processing of Si 3 N 4  or polysilicon, the reaction temperature inside the reaction chamber  108  can be as high as 750° C. or more. Accordingly, the exposed components in reaction chamber  108  must be compatible with such high temperature processing. Such component materials should also be compatible with the process gasses and other chemicals, such as the cleaning chemicals that may be introduced into reaction chamber  108 . 
     An exploded view of a dual-zone heater (heater) is shown in an embodiment as illustrated in FIG.  5 . In this embodiment, tube  214 , disk  216 , and heater rod insulators  220  are comprised of sintered and machined aluminum nitride (AlN). Heater disk  216  is sintered having heating coil  218  contained within. Heating coil  218  is bonded to tube  214  through diffusion bonding or brazing as such coupling will similarly withstand the environment of reaction chamber  108  (FIG.  1 ). Heater assembly  204  includes heater disk  216  having surface  258  with susceptor (not shown) to support a wafer (not shown) and opposite surface  260  to couple to tube  214 . Located within tube  214  is two pair of heating rods  212  equidistantly disposed about a common centerline  246 . Each heating element  212  is housed in ceramic sleeve (AlN)  220 . Each heating rod  212  is made of a material having thermal expansion properties similar to the material of tube  114 . In this embodiment, heating rods  212  are made of nickel (Ni), the heating rods  212  having a thermal expansion coefficient similar to aluminum nitride. The heating rods  212  pass through an end cap  250  and are attached to electrical connections (not shown) that enter the end cap  250  from the opposite side. A thermocouple  248  can be positioned within the tube  214  of the heater assembly  204  with the electrical connections placed at the end cap  250 . An end of the thermocouple  240  can contact the heater disk  216  to provide a temperature profile of the heater disk  216  during operation. 
     However, in an embodiment as illustrated in FIG. 6, heating rods  212  are not centered around the common centerline  217  of heater disk  216 , heater coil  218  (dashed line), and tube  214 . This non-centering of heating rods  212  to centerline  217  used by the other components, along with the individual electrical control to each heating rod  212 , provides the full temperature range required in CVD processing. 
     Referring now to an embodiment as illustrated in FIG. 7, atmospheric gasses are purged from the inside of dual-zone heater  304 . The purge may be accomplished with a constant flow of a fluid such as an inert gas at a flow rate of approximately 100 cubic centimeters per minute (ccm) through a connector base  355 , a connector adapter  350  and into tube  314 . For an embodiment, nitrogen may be used as the inert gas. The nitrogen gas pressure applied to the heater, along with the size of the inlet port  362  and vent port  364  should be such as to provide a desired flow rate through the heater  304 . 
     In one embodiment, the flow of nitrogen gas could be at a rate to maintain a pressure of 30 pounds per square inch (psi) when purged into an inlet port  362 . The nitrogen can vent out of heater  304  at a vent port  364 . The nitrogen used may be refrigerated to a temperature. Refrigerated nitrogen can maintain the temperature below 700° C. within the heater and further reduce AlN material degradation as a result of any small amount of oxygen remaining within the heater interior  366 . One method to refrigerate the nitrogen is to mix nitrogen at ambient temperature with nitrogen vapor evaporating off liquid nitrogen The purge may be continuous in that it can be started prior to beginning the wafer process cycle to ensure that oxygen is removed from heater interior  366  before the wafer process cycle begins. In addition, the purge into the heater may be continuous regardless of wafer processing and may only be stopped for heater disassembly to repair or discard. 
     In an embodiment, a connector assembly  370  connects to heater  304  at one end and provides a multitude of connections. Connector assembly  370  attaches to end cap  345 , to heater tube  314 , and to chamber body  106  (FIG.  1 ). Passing through connector assembly  370  is inlet port  362 , vent port  364 , electrical connections  372  for a thermocouple (not shown), and electrical connections for heater rods  312 . Connector assembly  370  includes a connector adapter  350  and a connector base  355 . Connector adapter  350  attaches electrical connections  372  to the ends of heater rods  312 . Attached to connector adapter  350  is connector base  355  that attaches to chamber body  106  (FIG.  1 ). Inlet port  362  passes through end cap  345  while venting past the end cap  345  may be accomplished with loose dimensional tolerancing. With this connector assembly  370  configuration, a single operation of attaching connector assembly  370  to heater  304  provides for all the electrical and fluid connections simultaneously. The heater  304  acts as a pressure vessel in that it has pressure integrity. This is accomplished by O-rings  375  placed between components: heater tube  314 , end cap  345 , connector assembly  370 , to reduce loss of inert gas into the reaction chamber  108  (FIG.  1 ). 
     Alternatively in an embodiment, as illustrated in FIG. 8, heater interior volume  466  within heater  404  may be evacuated with vacuum to remove the resident atmosphere. Connector assembly  470  connects to heater  404  at one end and provides a multitude of connections  474 . Connector assembly  470  attaches to end cap  445 , to heater tube  414 , and to chamber body  106  (FIG.  1 ). Passing through connector assembly  470  is vacuum port  462 , vent port  464 , electrical connections  472  for a thermocouple (not shown), and electrical connections for heater rods  412 . Connector assembly  470  includes a connector adapter  450  and a connector base  455 . Connector adapter  450  attaches electrical connections  472  to the ends of heater rods  412 . Attached to connector adapter  450  is connector base  455  that attaches to chamber body  106  (FIG.  1 ). Vacuum port  462  passes through end cap  445  to gain access to heater interior volume  466 . Attached to vent port  464  may be a vacuum or pressure gauge  476  to monitor vacuum levels. With this connector assembly  470  configuration, a single operation of attaching connector assembly  470  to heater  404  provides for all the electrical and fluid connections simultaneously. Heater  404  acts as a pressure vessel in that it has pressure integrity. This is accomplished with O-rings  475  that are placed between components: heater tube  414 , end cap  445 , and connector assembly  470 , to block vacuum from pulling into the heater interior volume  466  any of the reaction chamber chemistry. 
     When vacuum is applied to vacuum port  462 , the heater interior  466  is subjected to an approximate 5 torr vacuum. In this manner, a vacuum source is continuously applied to interior  466  of heater  404 . In addition to monitoring vacuum levels, vacuum gauge  476  may be used to leak check the vacuum integrity of heater interior  466 . The ability of heater  404  to hold sufficient vacuum may be confirmed by periodic leak checks that test heater  404  pressure integrity. The leak check may be performed by sealing off heater interior  466  from a vacuum source and monitoring a loss of vacuum over time for a rate of vacuum decay. An approximate vacuum decay rate in the range of 0-2.5 torr per five hours could be acceptable. 
     It should be appreciated for the described embodiments that modifications and adjustments to the invention might be accomplished. For instance, for the embodiment providing a vacuum in the heater interior  466 , it may be determined that for some process temperatures (below 700° C.), the vacuum requirement in the first embodiment may be of a range such as 2.5-10 torr. 
     It should be appreciated that for the embodiment performing a purge, that a variety of fluids may be used. In particular, any inert gas may be used in substitute for nitrogen such as halogen gases. The purge of inert gas through heater interior  466  may be accomplished at purge rates that vary from 100 ccm dependent on temperature of the inert gas going in and the desired temperature of the heater interior volume  466 . Purge pressures other than 30 psi may be applied to fine-tune the purge process. Along with varying the purge flow rate, the purge gas(es) may be cooled or refrigerated to control the temperature within the heater. In addition, instead of a purge port, dimensional tolerancing of the mating connector component could be specified to be a loose tolerance. Such loose tolerancing would provide spaces between components that may allow the purge gas to leak out between the components at a sufficient rate to eliminate the need for a vent port. It is also possible to purge continuously (non-stop) regardless of wafer processing to further insure that no atmosphere is present within the heater interior during operation. 
     In another embodiment, an inert gas is purged through the heater until the atmosphere has been removed. At a point, both purge and vent sides are shut off or blocked and the inert gas to a selected pressure would remain standing or static within the pressure vessel. A pressure gauge could be used to confirm that no discernable pressure change had occurred in the heater interior. A discernable pressure loss is any loss that is not acceptable for the design, operation, and useful life of the heater. 
     In another embodiment, vacuum may be applied to the heater interior volume until a particular vacuum level is reached and then the vacuum source may be shut off to the heater interior volume. A vacuum gauge that is in-line or attached to the vacuum system near or at the heater interior could monitor the vacuum level within the heater interior. This would allow for better notice of loss of vacuum integrity of the heater interior.