Patent Publication Number: US-2017350038-A1

Title: Vacuum platform with process chambers for removing carbon contaminants and surface oxide from semiconductor substrates

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. provisional patent application Ser. No. 62/345,160, filed Jun. 3, 2016, which is herein incorporated by reference. 
    
    
     FIELD 
     Implementations of the present disclosure generally relate to an apparatus and a method for cleaning a surface of a substrate. 
     BACKGROUND 
     Integrated circuits are formed in and on silicon and other semiconductor substrates. In the case of single crystal silicon, substrates are made by growing an ingot from a bath of molten silicon, and then sawing the solidified ingot into multiple substrates. An epitaxial silicon layer may then be formed on the monocrystalline silicon substrate to form a defect free silicon layer that may be doped or undoped. Semiconductor devices, such as transistors, may be manufactured from the epitaxial silicon layer. The electrical properties of the formed epitaxial silicon layer are generally better than the properties of the monocrystalline silicon substrate. 
     Surfaces of the monocrystalline silicon and the epitaxial silicon layer are susceptible to contamination when exposed to typical substrate fabrication facility ambient conditions. For example, a native oxide layer may form on the monocrystalline silicon surface prior to deposition of the epitaxial layer due to handling of the substrates and/or exposure to ambient environment in the substrate processing facility. Additionally, foreign contaminants such as carbon and oxygen species present in the ambient environment may deposit on the monocrystalline surface. The presence of a native oxide layer or contaminants on the monocrystalline silicon surface negatively affects the quality of an epitaxial layer subsequently formed on the monocrystalline surface. It is therefore desirable to pre-clean the substrates in order to remove the surface oxidation and other contaminants before epitaxial layers are grown on the substrates. However, pre-clean processes are often carried out in one or more standalone vacuum process chambers, which may increase substrate handling time and chances of exposing substrates to ambient environment. 
     Therefore, there is a need in the art to provide an improved substrate processing system for cleaning a substrate surface prior to performing an epitaxial deposition process that minimizes substrate handling time and exposure to ambient environment. 
     SUMMARY 
     Implementations of the present disclosure generally relate to an improved vacuum processing system and a method for removing contaminants and native oxides from a surface of a substrate. In one implementation, the vacuum processing system includes a first transfer chamber coupled to at least one processing chamber, a second transfer chamber, a transition station disposed between, and connected to, the first transfer chamber and the second transfer chamber, the transition station comprising a first plasma-cleaning chamber, a second plasma-cleaning chamber coupled to the second transfer chamber, and a load lock chamber coupled to the second transfer chamber. 
     In another implementation, the vacuum processing system includes a first transfer chamber comprising a first substrate handling mechanism, a transition station coupled to the first transfer chamber, the transition station having a first plasma-cleaning chamber coupled to or disposed therein, and at least one process chamber coupled to the first transfer chamber, wherein the at least one process chamber is an epitaxy chamber. 
     In yet another implementation, a method for processing a substrate within a vacuum processing system is provided. The method includes transferring a substrate from a load lock chamber to a first cleaning chamber using a first robotic transport mechanism disposed within a first transfer chamber, the first cleaning chamber using a plasma formed from a cleaning gas comprising a hydrogen-containing gas and a fluorine containing gas to remove oxides from a surface of the substrate, transferring the substrate from the first cleaning chamber to a transition station by the first robotic transport mechanism, the transition station has a second cleaning chamber disposed therein, the second cleaning chamber using a hydrogen containing plasma to remove carbon-containing contaminants from the surface of the substrate, and transferring the substrate from the second cleaning chamber to at least an epitaxy process chamber coupled to a second transfer chamber using a second robotic transport mechanism disposed within the second transfer chamber, wherein the transition station is connected to the first transfer chamber and the second transfer chamber, and wherein the substrate is transferred among the load lock chamber, the first transfer chamber, the first cleaning chamber, the second cleaning chamber, the second transfer chamber, and the epitaxy process chamber without breaking vacuum in the vacuum processing system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Implementations of the present disclosure, briefly summarized above and discussed in greater detail below, can be understood by reference to the illustrative implementations of the disclosure depicted in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical implementations of this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective implementations. 
         FIG. 1  illustrates a processing sequence in accordance with one implementation of the present disclosure. 
         FIG. 2  is a cross-sectional view of a cleaning chamber used to perform a cleaning process of  FIG. 1  in accordance with one implementation of the present disclosure. 
         FIG. 3  is a cross-sectional view of a cleaning chamber used to perform a reducing process of  FIG. 1  in accordance with one implementation of the present disclosure. 
         FIG. 4  illustrates a vacuum processing system that can be used to complete the processing sequence of  FIG. 1  according to implementations 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. The figures are not drawn to scale and may be simplified for clarity. It is contemplated that elements and features of one implementation may be beneficially incorporated in other implementations without further recitation. 
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a processing sequence  100  in accordance with one implementation of the present disclosure. In box  102 , oxides are removed from a surface of a semiconductor substrate using a cleaning process. The substrate may include a silicon containing material and the surface may include a material, such as silicon (Si), germanium (Ge) or silicon germanium alloys (SiGe). In some implementations, the Si, Ge, or SiGe surface may have an oxide layer, such as a native oxide layer, and contaminants disposed thereon. Due to the sensitivity of epitaxial deposition processes to oxides and contaminants, such as carbon containing contaminants, surface contamination resulting from exposure to most typical cleanroom environments for a few hours can become significant enough for the accumulated oxides and contaminants to affect the quality of a subsequently formed epitaxial layer. 
     The substrate surface may be cleaned by performing an oxides removal process and a contaminant removal process. In one implementation, the oxides are removed from the surface of the substrate using a cleaning process (box  102 ), and the contaminants, such as carbon containing contaminants, are removed from the surface of the substrate using a reducing process (box  104 ). The cleaning process may include a plasma etching process. The plasma etching process may use a plasma formed form a cleaning gas including hydrogen (H 2 ), helium (He), argon (Ar), ammonia (NH 3 ), a fluorine containing gas such as NF 3 , or any combination of these gases. The plasma may be inductively or capacitively coupled, or the plasma may be energized by a microwave source in a processing chamber. The processing chamber may be a remote plasma chamber that is spatially separated from a processing region in which the substrate is disposed. The term “spatially separated” described herein may refer to a plasma generation region that is separated from a substrate processing region by one or more chamber components such as a blocker plate  228  and a gas distribution plate  230  shown in  FIG. 2 , or even a conduit between a remote plasma chamber and a substrate processing chamber. 
     In one implementation, the plasma is generated using a capacitively coupled plasma source. Radicals from the plasma may pass through a gas distribution plate disposed above the substrate, which is positioned on a support at a temperature of about 25 degrees Celsius to about 100 degrees Celsius. The processing pressure may be at subatmospheric pressure, for example about 20 mTorr to about 25 mTorr. Radicals reach the substrate and then react with the surface oxides. Exemplary processing chambers that can be adapted to perform the plasma etching process include the Siconi™ or Selectra™ chambers, which are available from Applied Materials, Inc., of Santa Clara, Calif. Chambers from other manufacturers may also be used. 
     In one exemplary implementation, the plasma etch process is a remote plasma assisted dry etch process which involves the concurrent exposure of a substrate to NF 3  and NH 3  plasma by-products. In one example, the plasma etch process may be similar to or may include a SiCoNi™ etch process that is available from Applied Materials, Inc., of Santa Clara, Calif. The remote plasma etch can be largely conformal and selective towards silicon oxide layers, and thus does not readily etch silicon regardless of whether the silicon is amorphous, crystalline or polycrystalline. The remote plasma process will generally produce solid by-products which grow on the surface of the substrate as substrate oxide material is consumed. The solid by-products can be subsequently removed via sublimation when the temperature of the substrate is raised. The plasma etch process results in a substrate surface having silicon-hydrogen (Si—H) bonds thereon. 
     In box  104 , after removing oxides from the surface of the substrate, any remaining contaminants on the surface of the substrate are removed. In one implementation of box  104 , contaminants such as carbon or hydrocarbons are removed from the surface of the substrate using a reducing process. The reducing process may use a hydrogen containing plasma to remove contaminants. The plasma may be formed from a cleaning gas containing hydrogen gas (H 2 ), helium (He), argon (Ar), ammonia (NH 3 ), or any combination of these gases. The plasma may be inductively or capacitively coupled, or the plasma may be energized by a microwave source in a processing chamber. The processing chamber may be a remote plasma chamber that is physically separated from the processing chamber where the substrate is disposed. 
     In one implementation, the plasma is generated using an inductively coupled plasma source that is a remote plasma source (RPS) to perform the reducing process  104 . Radicals from the plasma may pass through a passage tube and a gas distribution plate disposed above the substrate. The substrate is positioned on a support at a temperature of about 25 degrees Celsius to about 400 degrees Celsius. The processing pressure may be at subatmospheric pressure, for example about 20 mTorr to about 300 Torr, for example about 100 mTorr to about 300 mTorr, for example about 150 mTorr. Radicals reach the substrate and then react with the surface contaminants. Exemplary processing chambers that can be adapted to perform a reducing process include AKTIV Pre-Clean™, Siconi™, PCxT Reactive Preclean™ (RPC), or Selectra™ chambers, available from Applied Materials, Inc., of Santa Clara, Calif. Chambers from other manufacturers may also be used. 
     In box  106 , an epitaxial layer is formed on the surface of the substrate. If cleaned prior, as described above, the surface of the substrate is oxide and contaminant free which improves the quality of the epitaxial layer subsequently formed on the surface of the substrate. An exemplary epitaxial process may be a selective epitaxial process performed at a temperature that is less than about 800 degrees Celsius, for example about 450 to 650 degrees Celsius. The epitaxial layer may be formed using a high temperature chemical vapor deposition (CVD) process. The epitaxial layer may be a crystalline silicon, germanium, or silicon germanium, or any suitable semiconductor material such as a Group III-V compound. In one exemplary thermal CVD process, processing gases such as dichlorosilane, silane, disilane, germane, hydrogen chloride, or combinations thereof are used to form the epitaxial layer. The processing temperature is under 800 degrees Celsius and the processing pressure is between 5 Torr and 600 Torr. An exemplary processing chamber that can be used to perform the epitaxial deposition process is the Centura™ Epi chamber, which is available from Applied Materials, Inc., of Santa Clara, Calif. Chambers from other manufacturers may also be used. 
     Boxes  102 ,  104  and  106  may be performed in one processing system, such as a vacuum processing system illustrated in  FIG. 4 . It is contemplated that processes described in boxes  102  and  104  may be reversed. In addition, the processes described in boxes  102  and  104  may be repeated as many times as necessary. 
       FIG. 2  is a cross sectional view of a processing chamber  200  that is adapted to perform at least some of the processes found in box  102 , and thus removes oxides from a surface of a substrate. The processing chamber  200  may be particularly useful for performing a thermal or plasma-based cleaning process and/or a plasma assisted dry etch process. The processing chamber  200  includes a chamber body  212 , a lid assembly  214 , and a support assembly  216 . The lid assembly  214  is disposed at an upper end of the chamber body  212 , and the support assembly  216  is at least partially disposed within the chamber body  212 . A vacuum system can be used to remove gases from processing chamber  200 . The vacuum system includes a vacuum pump  218  coupled to a vacuum port  221  disposed in the chamber body  212 . The processing chamber  200  also includes a controller  202  for controlling processes within the processing chamber  200 . 
     The lid assembly  214  includes at least two stacked components configured to form a plasma volume or cavity. A first electrode  220  is disposed vertically above a second electrode  222  to define a plasma volume. The first electrode  220  is connected to a power source  224 , such as a radio frequency (RF) power supply, and the second electrode  222  is connected to ground or a reference potential, forming a capacitance between the first electrode  220  and the second electrode  222 . The lid assembly  214  also includes one or more gas inlets  226  for providing a cleaning gas to a substrate surface through a blocker plate  228  and a gas distribution plate  230 , such as a showerhead. The cleaning gas may use radicals of a plasma formed form a cleaning gas including hydrogen (H 2 ), helium (He), argon (Ar), ammonia (NH 3 ), a fluorine containing gas such as NF 3 , or any combination of these gases. 
     Alternatively, a different cleaning process may be utilized to clean the substrate surface. For example, a remote plasma containing He and NF 3  may be introduced into the processing chamber  200  through the gas distribution plate  230 , while NH 3  may be directly injected into the processing chamber  200  via a separate gas inlet  225  that is disposed at a side of the chamber body  212 . 
     The support assembly  216  may include a substrate support  232  to support a substrate  210  thereon during processing. The substrate support  232  may be coupled to an actuator  234  by a shaft  236  which extends through a centrally-located opening formed in a bottom of the chamber body  212 . The actuator  234  may be flexibly sealed to the chamber body  212  by bellows (not shown) that prevent vacuum leakage around the shaft  236 . The actuator  234  allows the substrate support  232  to be moved vertically within the chamber body  212  between a processing position and a loading position. The loading position is slightly below the opening of a slit valve formed in a sidewall of the chamber body  212 . 
     The substrate support  232  has a flat, or a substantially flat, substrate supporting surface for supporting a substrate to be processed thereon. The substrate support  232  may be moved vertically within the chamber body  212  by actuator  234 , which is coupled to the substrate support  232  by shaft  236 . In operation, the substrate support  232  may be elevated to a position in close proximity to the lid assembly  214  to control the temperature of the substrate  210  being processed. As such, the substrate  210  may be heated via radiation emitted or convection from the distribution plate  230 . 
       FIG. 3  is a cross sectional view of a processing chamber  300  that is adapted to perform at least some of the processes found in box  104 , and thus removes contaminants, such as carbon or hydrocarbons accumulated on a surface of a substrate. The processing chamber  300  has a chamber body  310 , which includes a chamber enclosure  316 , a process kit housing  318 , and a lid  340 . The chamber enclosure  316  and the lid  340  may be fabricated from aluminum, stainless steel or other suitable materials. The process kit housing  318  may be fabricated from aluminum alloy or other suitable materials. The lid  340  is removably coupled to the chamber enclosure  316  through the process kit housing  318 . 
     The process kit housing  318  may be a ring-shaped housing having a top surface that couples to the lid  340  and a bottom surface that couples to the chamber enclosure  316 . The process kit housing  318  has a shield portion  329  extending down from an inner surface  331  of the process kit housing  318 . The inner surface  331  of the process kit housing  318  surrounds and supports a gas distribution plate  326  thereon. The gas distribution plate  326  may be a quartz showerhead. A plenum  348  is defined between the gas distribution plate  326  and the lid  340 . The gas distribution plate  326  includes a plurality of apertures  327  formed through the thickness of the gas distribution plate  326  to allow gases flowing into the plenum  348  through a port  342 . The apertures  327  are evenly distributed across the diameter of the gas distribution plate  326  to ensure uniform distribution of the gases or radicals to the substrate  308 . The gases flowing through the apertures  327  are distributed across the substrate  308  disposed in a process region  330  defined between the gas distribution plate  326  and a heater  314 . The shield portion  329  also helps confine electrically neutral radicals within the process region  330 . In one example, the shield portion  329  is extended to a location adjacent or below the edge of the heater  314 . 
     The processing chamber  300  includes a remote plasma source  350  that is coupled to the port  342  by a passage tube  360 . The port  342  is formed in the lid  340 . The passage tube  360  defines a conduit  356 , which may have a first inner diameter and a second inner diameter that is larger than the first inner diameter. The first inner diameter may be disposed adjacent to the remote plasma source  350  and the second inner diameter may be disposed adjacent to the lid  340 . In one example, first inner diameter is about 12 mm to about 30 mm, for example about 20 mm, and the second inner diameter is about 35 mm to about 60 mm, for example about 40 mm. 
     The passage tube  360  is configured to filter ions generated in the remote plasma source  350  before entering the process region  330 , while allowing electrically neutral radicals to enter the process region  330 . The relative concentration of ions in the process region  330  is thus reduced. In one implementation, the gases flowing through the conduit  356  are filtered by a magnetic field generated by one or more magnets disposed adjacent to the passage tube  360 . The magnets generate a magnetic field across the passage tube  360  to filter charged particles entrained with the reactive radicals flowing from the remote plasma source  350 . 
     In the implementation depicted in  FIG. 3 , a first magnet  352  and a second magnet  354  are disposed adjacent to the passage tube  360 . The first magnet  352  and second magnets  354  may be permanent magnets or electromagnets. The magnets  352 ,  354  may be disposed to oppose to each other across the first inner diameter of the passage tube  360 . For example, the magnets  352 ,  354  may be adhered or secured on opposite sides of an outer periphery of the passage tube  360 . It is also contemplated that the magnets  352 ,  354  may be secured to the chamber lid  340  or other components of the chamber body  310 . The relative distance between the opposed magnet and the conduit  356  formed within the passage tube  360  affects the strength of the magnetic field passing through the conduit  356 , and thereby affects the filtering efficiency. The magnetic field may also be adjusted by using different magnets, i.e., replacing magnets  352 ,  354  with different strength. The passing charged particles are drawn in contact with an inner surface  370  of the passage tube  360  and become electrically neutral, non-ionic species. As such, the filtered, electrically neutral radicals are delivered to the surface of the substrate to react with and clean contaminants thereon. 
     In some implementations, the ions may be further filtered by providing a quartz surface in the flow path of the process gases (i.e., radicals) passing into the chamber body  310 . For example, the inner surface  370  of the passage tube  360  defining the conduit  356  may be entirely or partially coated or fabricated from quartz. Additionally, the surfaces defining the plenum  348  and/or gas distribution plate  326  may also be entirely or at least partially coated or fabricated from quartz. For example, in the implementation of  FIG. 3 , a top liner  324  may be disposed along the inner surface  331  of the process kit housing  318 . The top liner  324  may have a ring-shaped body surrounding the plenum  348 , an inner surface thereof defining the outer boundary of the plenum  348 . The top liner  324  may be made of quartz. The top liner  324  may rest on the gas distribution plate  326 , or may be supported by any other suitable securing approach. 
     A liner plate  344  may be disposed along the bottom surface of the lid  340 . The liner plate  344  may be coated with, or fabricated from, quartz. The liner plate  344  defines the upper boundary of the plenum  348 . Therefore, the liner plate  344 , the top liner  324 , and the gas distribution plate  326  define the plenum  348  therein. A bottom liner  325  may be disposed along the inner surface  331  of the process kit housing  318 . The bottom liner  325  may have a ring-shaped body surrounding the process region  330 , an inner surface thereof defining the outer boundary of the process region  330 . The bottom liner  325  may be coated with, or fabricated from, quartz. The bottom liner  325  may be supported by the shield portion  329 . In one example as shown, a ledge  303  extends radially inward at an end of the shield portion  329  to support the bottom liner  325 . Therefore, the passage tube  360 , the liner plate  344 , the top liner  324 , the bottom liner  325 , and the gas distribution plate together provide a quartz surface in the flow path of the process gases. These components reduce the recombination of radicals as compared to other chamber materials (e.g., aluminum). As such, only electrically neutral radicals are flowed through the gas distribution plate or presented in a process region defined between the gas distribution plate and a substrate support of the processing chamber. These electrically neutral radicals will remain reactive when they reach and react with a surface of the substrate disposed on the substrate support the substrate to remove unwanted materials, for example native oxides, from the surface of the substrate 
     A heater (or substrate support)  314  is disposed in the process region  330  of the chamber body  310 . The heater  314  is coupled to a bottom of the chamber enclosure  316  through a central shaft  341 . The heater  314  has a substrate supporting surface for supporting the substrate  308  thereon during a process, such as the processes described above with respect to boxes  102  and  104 . An optional focus ring  338  may be disposed on the heater  314  around the outer periphery of the substrate supporting surface. The focus ring  338  confines plasma or neutral species in an area above the substrate  308  during process. The focus ring  338  may be fabricated from quartz. 
     The heater  314  may be fabricated from bare aluminum with a plurality of sapphire contacts (not shown) disposed on the substrate supporting surface to minimize contact between the substrate supporting surface and a substrate disposed on the sapphire contacts. The heater  314  is actuated by a driving unit  337  to move vertically between a loading position and a processing position. The heater  314  may have one or more heating elements  335  embedded therein to provide uniform thermal energy to the substrate supporting surface. Suitable heating elements  335  may include resistive heaters, thermoelectric devices, or conduits for flowing heat transfer fluid, among other heating devices. The heating elements  335  allow the temperature of the substrate  308  to be maintained at a temperature range of about 200° C. to about 700° C., or greater, for example about 300° C. to about 350° C., about 350° C. to about 450° C., about 450° C. to about 550° C., about 550° C. to about 650° C., or about 650° C. to about 750° C. In some implementations, the heater  314  may have cutouts formed through the peripheral edge of the substrate supporting surface so that a substrate handler (not shown) can manipulate the substrate  308  from the edge of the substrate when the heater  314  is positioned at the loading position. During the cleaning process, the heater  314 , with substrate  308  disposed thereon, is positioned at the processing position, which is a desired position for processing the substrate  308 . 
     The processing chamber  300  includes a pump  317 . The pump  317  is connected to the chamber body  310  through a foreline  361 . The foreline  361  connects to the chamber body  310  at an opening  315  formed at the bottom of the enclosure  316 . The chamber  300  also includes a throttle valve  363  disposed in the foreline  361 . The throttle valve  363  is operated to open and close to whatever extent is necessary to maintain the pressure in the processing chamber  300  in a desired vacuum range for the plasma cleaning process being run. The pump  317  and the throttle valve  363  control the pressure inside the chamber body  310  from between about 0.005 Torr and 750 Torr, for example about 40 Torr to about 500 Torr. In one example, the pump  317  is a dry pump that maintains the pressure inside the processing chamber  300  at an exemplary pressure range of about 0.1 Torr to about 40 Torr, for example about 30 Torr. In one example, the pump  317  is a low pressure pump that maintains the pressure inside the processing chamber  300  at an exemplary pressure range of about 100 mTorr to about 500 mTorr, for example about 150 mTorr. In some examples, the pump  317  is a turbo pump that maintains the pressure inside the processing chamber  300  at an exemplary pressure range of about 20 mTorr to 50 mTorr. 
       FIG. 4  illustrates an exemplary vacuum processing system  400  that can be used to complete the processing sequence  100  illustrated in  FIG. 1 , according to implementations of the present disclosure. As shown in  FIG. 4 , a plurality of processing chambers  402   a ,  402   b ,  402   c ,  402   d  are coupled to a first transfer chamber  404 . The processing chambers  402   a - 402   d  may be used to perform any substrate related processes, such as annealing, chemical vapor deposition, physical vapor deposition, epitaxial process, etching process, thermal oxidation or thermal nitridation process, degassing etc. In one implementation, the processing chamber  402   a  may be an epitaxy deposition chamber, for example a Centura˜ Epi chamber available from Applied Materials, Santa Clara, Calif., that is capable of forming a crystalline silicon or silicon germanium. The processing chamber  402   b  may be a rapid thermal processing chamber (RTP). The processing chamber  402   c  is a plasma etching chamber. The processing chamber  402   d  may be a degassing chamber. The first transfer chamber  404  is also coupled to at least one transition station, for example a pair of pass-through stations  406 ,  408 . The pass-through stations  406 ,  408  maintain vacuum conditions while allowing substrates to be transferred between the first transfer chamber  404  and a second transfer chamber  410 . The first transfer chamber  404  has a robotic substrate handling mechanism (not shown) for transferring substrates between the pass-through stations  406 ,  408  and any of the processing chambers  402   a - 402   d.    
     One end of the pass-through stations  406 ,  408  is coupled to the second transfer chamber  410 . Therefore, the first transfer chamber  404  and the second transfer chamber  410  are separated and connected by the pass-through stations  406 ,  408 . The second transfer chamber  410  is coupled to a first plasma-cleaning chamber  414 , which can be a plasma chamber such as the processing chamber  200  ( FIG. 2 ) that is adapted to perform at least some of the processes found in box  102  for removing oxides from a surface of a substrate. In one implementation, the first plasma-cleaning chamber  414  is a Siconi™ or Selectra™ chamber, which is available from Applied Materials, Santa Clara, Calif. 
     In one implementation, the at least one transition station, for example one of the pass-through stations  406 ,  408 , is configured to be a plasma-cleaning chamber. Alternatively, a plasma-cleaning chamber may be coupled to one of the pass-through stations  406 ,  408  for removing contaminants from the surface of the substrate. Thus, the processing system  400  may have a second plasma-cleaning chamber that is, or is connected to, one of the pass-through stations  406 ,  408 . In one implementation shown in  FIG. 4 , the pass-through station  406  includes a second plasma-cleaning chamber  416 . The second plasma-cleaning chamber  416  may be a version of the processing chamber  300  ( FIG. 3 ) that is adapted to perform at least some of the processes found in box  104  for removing contaminants from the surface of the substrate. It should be noted that, although only one plasma-cleaning chamber  416  is shown coupled to a pass-through station, in this case the pass-through station  406 , a plasma-cleaning chamber (e.g., a version of the processing chamber  300 ) may be coupled to both the pass-through stations  406  and  408 . 
     The second transfer chamber  410  also has a robotic substrate handling mechanism (not shown) for transferring substrates between a set of load lock chamber  412  and the first plasma-cleaning chamber  414  or the second plasma-cleaning chamber  416 . A factory interface  420  is connected to the second transfer chamber  410  by the load lock chambers  412 . The factory interface  420  is coupled to one or more pods  430  on the opposite side of the load lock chambers  412 . The pods  430  typically are front opening unified pods (FOUP) that are accessible from a clean room (not shown). 
     While two transfer chambers are shown, it is contemplated that any of the transfer chambers may be omitted. In one implementation where the second transfer chamber  410  is omitted, the second plasma-cleaning chamber  416  may be disposed within or coupled to the first transfer chamber  404  at the loation currently shown as occupied by the pass-through stations  406  or  408 . The first transfer chamber  404  may be coupled to one or more processing chambers capable of forming crystalline silicon or silicon germanium, such as an epitaxy chamber, for example a Centura™ Epi chamber available from Applied Materials, Inc., of Santa Clara, Calif. Alternatively, the first transfer chamber  404  may be omitted and the second plasma-cleaning chamber  416  may be disposed within or coupled to the pass-through station  406 , which is coupled to the second transfer chamber  410 . In such a case, the second transfer chamber  410  may be configured to be coupled to one or more processing chambers capable of forming crystalline silicon or silicon germanium. 
     In operation, substrates are carried from pods  430  to the vacuum processing system  400  in a transport cassette (not shown) that is placed within one of the load lock chambers  412 . The robotic transport mechanism within the second transfer chamber  410  transports the substrates, one at a time, from the load lock chambers  412  to the first plasma-cleaning chamber  414  where the a cleaning process, e.g., processes found in box  102 , is performed to remove oxides from a surface of a substrate. Once the oxides have been removed from the substrate surface, the robotic transport mechanism disposed within the second transfer chamber  410  transfers the substrate from the first plasma-cleaning chamber  414  to the second plasma-cleaning chamber  416  where a reducing process, e.g., processes found in box  104 , is performed to remove contaminants such as carbon or hydrocarbons from the substrate surface. It is contemplated that the steps here may also be performed in the reverse order, i.e., using the robotic transport mechanism to transfer the substrate from the second plasma-cleaning chamber  416  to the first plasma-cleaning chamber  414 . In either case, the clean substrates are then transferred by the robotic transport mechanism disposed within the first transfer chamber  404  from the second plasma-cleaning chamber  416  (or the first plasma-cleaning chamber  414 ) to one or more processing chambers  402   a - 402   d . The one or more processing chambers  402   a - 402   d  may include an epitaxy process chamber where a layer formation process, such as the epitaxial deposition described in box  106 , is performed. 
     Upon completion of processing in the one or more processing chambers  402   a - 402   d , the robotic transport mechanism disposed within the first transfer chamber  404  moves the substrate from either one of the processing chambers  402  to the pass-through station  408 . The substrate is then removed from the pass-through station  408  by the robotic transport mechanism disposed within the second transfer chamber  410  and transferred to the other load lock chamber  412  through which it is withdrawn from the vacuum processing system  400 . 
     Since the processes of all three boxes  102 ,  104  and  106  are performed within the same vacuum processing system  400 , vacuum is not broken as the substrate is transferred among various chambers, which decreases the chance of contamination and improves the quality of the deposited epitaxial film. It should be understood that the movement of the substrates is described herein for illustration purposes. A controller (not shown) may be used to schedule the movement of the substrates through the vacuum processing system  400  in accordance with a desired sequencing program, which may vary depending upon the application. 
     Benefits of the present disclosure include an improved vacuum processing system integrating two different types of pre-clean process chambers with the epitaxial process chamber on the same vacuum processing system. The pre-clean process chambers may include a first plasma-cleaning process chamber and a second plasma-cleaning process chamber. Co-existence of two types of surface materials removal chamber on the same vacuum processing system allows substrates to remain in vacuum between surface preparation and epitaxial deposition, which reduces the time the substrates are exposed to ambient and eliminates the need to prepare the substrates on a separate processing chamber or system. This architecture also maximizes the number of process chambers on a vacuum system because the pass-through station between two transfer chambers also functions as a pre-clean process chamber, which also reduces overall handling time of the substrates. 
     While the foregoing is directed to implementations of the present disclosure, other and further implementations of the disclosure may be devised without departing from the basic scope thereof.