Abstract:
Methods and systems for depositing a film on a substrate are disclosed. In one embodiment, a method includes converting a non-gaseous precursor into vapor phase. Converting the precursor includes: forming a fluidized bed by flowing gas at a sufficiently high flow rate to suspend and stir a plurality of solid particles, and converting the phase of the non-gaseous precursor into vapor phase in the fluidized bed. The method also includes transferring the precursor in vapor phase through a passage; and performing deposition on one or more substrates with the transferred precursor in vapor phase.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a non-provisional of U.S. Provisional Patent Application No. 61/079,584, filed Jul. 10, 2008, which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to semiconductor processing equipment and, more particularly, to apparatus for providing vapor-phase precursor from solid or liquid sources for semiconductor processing. 
     BACKGROUND OF THE INVENTION 
     In the fabrication of integrated circuits on substrates, such as semiconductor wafers, the vapor deposition of chemicals, such as chemical vapor deposition (“CVD”) and atomic layer deposition (ALD), is often desirable. The expansion of suitable source chemicals has increasingly led to use of precursor materials that are naturally liquid or solid at room temperature and atmospheric pressure. 
     In order to effectively deposit using precursors from a solid or liquid source material, the solid or liquid source material must be vaporized first. In pursuit of this goal, evaporation apparatuses are used to effectuate the vaporization of a solid or liquid source material. In addition, heat sources are often employed in conjunction with such an apparatus in order to increase the vapor pressure above the solid or liquid source material. 
     Unfortunately, existing semiconductor processing systems, of which an evaporation apparatus is a component, have a number of shortcomings. For example, an evaporation apparatus for subliming a solid source material or vaporizing a liquid source material may offer both an inadequate ratio of solid or liquid source surface area to the desired vapor volume, and poor carrier gas/source material contact time. Often, current processing systems can allow a carrier gas to flow from inlet to outlet without intimately contacting the source material, thus preventing the carrier gas from becoming saturated with precursor vapor. 
     In certain instances, a large amount of precursor vapor is needed for deposition, such as batch-type deposition. In addition, deposition on a substrate having three-dimensional topology needs a large amount of precursor for a short period of time. Thus, there is a need for an evaporation apparatus that efficiently converts a solid or liquid source material into gas phase. 
     SUMMARY OF THE INVENTION 
     According to one embodiment, a method of depositing a film on a substrate includes converting a non-gaseous precursor into vapor phase. Converting the precursor includes forming a fluidized bed by flowing gas at a sufficiently high flow rate to suspend and stir a plurality of solid particles, and vaporizing the non-gaseous precursor in the fluidized bed. The method of depositing also includes transferring the precursor in vapor phase through a passage, and performing deposition on one or more substrates with the transferred precursor in vapor phase. 
     According to another embodiment, a deposition system includes: a vapor deposition reactor; a first passage; and a fluidized bed evaporator in fluid communication with the reactor via the first passage. 
     According to yet another embodiment, an apparatus for providing a vapor phase precursor for deposition is provided. The apparatus includes a fluidized bed evaporator, which includes a vessel body and a distributor plate positioned inside the vessel body. The distributor plate includes a plurality of holes formed therethrough. The fluidized bed evaporator further includes a precursor outlet formed through the vessel body above the distributor plate and a carrier gas inlet formed through the vessel body below the distributor plate. The carrier gas inlet is in fluid communication with the precursor outlet through the distributor plate. The apparatus further includes a fluidized bed condenser in fluid communication with the fluidized bed evaporator. The fluidized bed condenser includes a condenser vessel and a condenser distributor plate inside the condenser vessel. The condenser distributor plate includes a plurality of openings. 
     According to yet another embodiment, an apparatus for providing a vapor phase precursor for deposition is provided. The apparatus includes a fluidized bed evaporator which includes a vessel body and a distributor plate positioned inside the vessel body. The distributor plate includes a plurality of holes formed therethrough. The fluidized bed evaporator also includes a precursor gas outlet formed through the vessel body above the distributor plate, and a carrier gas inlet formed through the vessel body below the distributor plate. The carrier gas inlet is configured to flow a carrier gas through the distributor plate to the precursor gas outlet. The apparatus further includes a heated pipe in fluid communication with the precursor gas outlet. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood from the detailed description of the preferred embodiments and from the appended drawings, which are meant to illustrate and not to limit the invention and wherein like numerals refer to like parts throughout. 
         FIG. 1  is a block diagram of one embodiment of a deposition system including a fluidized bed evaporator. 
         FIG. 2A  is a cross-section of one embodiment of a fluidized bed evaporator before operation. 
         FIG. 2B  is a cross-section of the fluidized bed evaporator of  FIG. 2A  during operation. 
         FIG. 3  is a cross-section of another embodiment of a fluidized bed evaporator. 
         FIG. 4A  is a block diagram of one embodiment of a fluidized bed evaporation system using precursor-coated inert granules to form a fluidized bed and an integrated coating apparatus for coating the granules. 
         FIG. 4B  is a block diagram of an apparatus for coating inert granules with a solid precursor according to one embodiment, for use in an evaporation system such as that of  FIG. 4A . 
         FIG. 5  is a flow chart illustrating a method of automated recharging for an evaporation system, such as that of  FIG. 4A . 
         FIG. 6  is a block diagram of another embodiment of a deposition system including a fluidized bed evaporator. 
         FIG. 7  is a block diagram of yet another embodiment of a deposition system including a fluidized bed evaporator. 
         FIG. 8  is a block diagram of yet another embodiment of a deposition system including a fluidized bed evaporator, employing a circulated vaporized precursor path. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In one embodiment, a deposition system includes a reactor, a gas passage, and a fluidized bed evaporator. The fluidized bed evaporator is in fluid communication with the reactor via the gas passage. The fluidized bed evaporator may vaporize one or more non-gaseous (liquid or solid) precursor using a fluidized bed formed by solid particles. The solid particles, levitated and stirred by a high carrier gas flow, create a heated high surface contact area for precursor, and the fluidized bed provides an almost liquid-like medium that very efficiently transfers heat from a heat source to the particles. In one embodiment, the solid particles are inert solid granules, and the precursor either coats the granules or is mixed, in solid or liquid form, with the granules in the fluidized bed during operation. In another embodiment, the solid particles are solid precursor particles (e.g., powder) in the fluidized bed in the fluidized bed evaporator, and at least portion of the solid precursor particles may be vaporized by the fluidized bed evaporator. 
     Referring to  FIG. 1 , one embodiment of a deposition system  100  using a fluidized bed evaporator will be described below. The illustrated deposition system  100  includes a vapor deposition reactor  110 , a fluidized bed evaporator  120 , a carrier gas source  130 , a precursor container  140 , a gas line  150 , and a valve  160 . The system  100  also includes a controller  170  for controlling the operation of the system  100 , and various other components for the operation of the system  100 . 
     The reactor  110  defines a reaction space in which one or more substrates are processed. The reactor  110  can be a batch-type reactor that can process multiple substrates simultaneously, or a single-wafer reactor. The reactor  110  may operate continuously, and precursor supply for the fluidized bed evaporator  120  can be refreshed or recharged on the fly or between deposition runs. In some embodiments, the reactor  110  may be a chemical vapor deposition (CVD) reactor or an atomic layer deposition (ALD) reactor. In certain embodiments, the reactor  110  may also be configured to provide in-situ or remote plasma. A skilled artisan will appreciate that various types of reactors can be adapted for use as the reactor  110  for use in combination with fluidized bed evaporators, as described herein. 
     The fluidized bed evaporator  120  serves to change a non-gaseous precursor into vapor phase. The non-gaseous precursor may be either liquid or solid. The fluidized bed evaporator  120  may contain a fluidized bed formed by solid granules or particles. The solid granules or particles can be in a form of at least one of powder, bead, cylinder, rod, filament, fiber, ring, etc. 
     The term “fluidized bed” refers to a bed of solid particles, such as precursor particles or inert granules, with a flow of gas passing upward through the granules at a rate that is great enough to set the granules in motion. Gravity balances with the viscous forces in the flow to form a fluid-like state where intermixing between the granules and the gas is intense. An expanded bed may be formed when the gas flow rate increases and granules move apart. A few of the granules may visibly vibrate and move about in restricted regions. At higher velocities of gas flow, all the granules may be suspended. A skilled artisan will appreciate that the gas flow rate can vary widely, depending on the shape, size, and density of the solid particles, the design of the fluidized bed, gas viscosity, and so on. Solid particles in a fluidized bed can have properties and characteristics of normal fluids, such as the ability to free-flow under gravity, or to be pumped using fluid type technologies. A skilled artisan will also appreciate that the controller  170  can control various conditions (e.g., the gas flow rate, the amount of solid particles, and the like) for generating a desired fluidized bed. 
     The solid particles may have any suitable shape, weight, and size as long as they can form a fluidized bed. In one embodiment, inert granules are provided and have an average size of about 10 nm to about 10 mm, and optionally about 100 nm to about 0.1 mm. In one embodiment, a suitable carrier gas flow rate for forming a fluidized bed with the solid particles of the above average size may be between about 100 sccm and about 100 slm, and optionally between about 100 sccm to about 10 slm. For a given amount of precursor particles, the smaller the solid granules forming a fluidized bed are, the larger is the overall evaporation surface area provided by the fluidized bed. Table 1 shows the relationship between the average size of the granules and the evaporation surface area. 
     
       
         
               
               
             
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                 Particle 
               
               
                   
                 average 
               
               
                   
                 size (μm) 
               
             
          
           
               
                   
                 50 
                 20 
                 10 
               
               
                   
                   
               
             
          
           
               
                   
                 surface area/evaporation volume (m 2 /cc) 
                 0.1 
                 0.3 
                 0.6 
               
               
                   
                   
               
             
          
         
       
     
     However, smaller particles may have a higher chance of escaping from the fluidized bed evaporator together with the vapor phase precursor, entailing more complex filtering needs. A skilled artisan will appreciate that the size of the particles can vary widely depending on the design of the fluidized bed evaporator. 
     In one embodiment where the non-gaseous precursor is liquid, the solid particles for forming the fluidized bed may be inert solid granules. The inert granules can be formed of a material that is thermally conductive and chemically inert to the precursor and carrier gas under the conditions during evaporation of the precursor. Examples of materials for the inert granules include, but are not limited to, alumina (Al 2 O 3 ), fused silica, stainless steel, Hastelloy™, nickel, boron nitride (BN), and silicon carbide (SiC). 
     In another embodiment where the non-gaseous precursor is solid, the inert granules described above can form a fluidized bed for evaporating such a solid precursor. The solid precursor can coat the inert granules or the solid precursor can be a powder mixed and stirred with the inert granules. In yet another embodiment, the solid precursor itself may form a fluidized bed in the absence of inert granules. In such an embodiment, the solid precursor can have a form (for example, powder) suitable for forming a fluidized bed. A skilled artisan will appreciate that various forms of materials can form a fluidized bed. In the embodiments described above, a mixture of two or more precursor materials (liquid or solid) may be fed to the fluidized bed evaporator for evaporation. The two or more precursor materials in their gaseous state may be chosen to have substantially equal vapor pressures at a given temperature. 
     The carrier gas source  130  provides a high volumetric flow of an inert gas to the fluidized bed evaporator  120 . Examples of the inert gas include, but are not limited to, argon gas (Ar), nitrogen gas (N 2 ), helium gas (He), and a combination of two or more of the foregoing. In certain embodiments, oxygen gas (O 2 ) can be used as long as it does not react with the precursor at the temperature and pressure in the fluidized bed. The inert gas supplied from the carrier gas source  130  may have a pressure that is sufficient to form a fluidized bed in the fluidized bed evaporator  120 . A skilled artisan will appreciate that the controller  170  can control the carrier gas flow rate, pressure, and any other parameters for generating a fluidized bed in the evaporator  120 . 
     The precursor container  140  serves to provide a precursor to the fluidized bed evaporator  120 . The precursor may be liquid and/or solid as described above. In one embodiment, the precursor container  140  may provide the fluidized bed evaporator  120  with a solid precursor in a form of powder. In another embodiment, the precursor container  140  may supply inert granules coated with a solid precursor. A skilled artisan will appreciate that the precursor container  140  can provide any suitable form of precursor, depending on the design of the fluidized bed evaporator  120 . In one embodiment, a solid precursor may be provided to the fluidized bed evaporator  120  between operations or deposition “runs.” In another embodiment, a liquid precursor may be provided to the fluidized bed evaporator  120  between operations or during operation of the device. A skilled artisan will also appreciate that the controller  170  can control the supply of the precursor and/or inert granules, and any other parameters for generating a fluidized bed in the evaporator  120 . 
     The gas line  150  serves as a passage for the vaporized precursor. The gas line  150  is in fluid communication with the reactor  110  and the fluidized bed evaporator  120 . The gas line  150  may include filters to keep the solid or liquid precursor from being supplied to the reactor  110 . In one embodiment, the gas line  150  may be heated to prevent condensation of the precursor on the gas line  150 . A skilled artisan will appreciate that various configurations of heaters can be used to prevent the condensation of the precursor on the gas line  150 . A skilled artisan will also appreciate that the controller  170  can be configured to control the temperature of the gas line  150 . 
     The valve  160  or other types of meter serves to control the flow of the precursor into the reactor  110 . The valve  160  may also shut off the flow of the precursor into the reactor  110 . A skilled artisan will appreciate that various types of valves can be adapted for the valve  160 . A skilled artisan will also appreciate that the controller  170  can be configured to control the operation of the valve  160 . 
     The controller  170  serves to control the operation of the system  100 . The controller  170  may control the operation of one or more of the vapor deposition reactor  110 , the fluidized bed evaporator  120 , the carrier gas source  130 , the precursor container  140 , the gas line  150 , and the valve  160 , and may be in communication with the foregoing components. The controller  170  may include a processor, a memory, a storage device, and a user interface. A skilled artisan will appreciate that the controller  170  can include any other components necessary for controlling the operation of the system  100 . 
     In an embodiment, the fluidized bed evaporator  120  may provide a vapor phase precursor in a substantially continuous manner. In such an embodiment, the fluidized bed evaporator  120  may receive a liquid precursor substantially continuously or periodically, and supply a vapor phase precursor in a continuous manner to the reactor  110 . In other words, the evaporator  120  can be supplied with fresh precursor without stopping evaporation. 
     Referring to  FIGS. 2A and 2B , one embodiment of a fluidized bed evaporator for a liquid precursor will be described below. Examples of liquid precursors include, but are not limited to, alkylaluminum compounds such as trimethyl aluminum ((CH 3 ) 3 Al), also known as TMA, metal halides such as titanium tetrachloride (TiCl 4 ), boron compounds such as triethyl boron ((CH 3 CH 2 ) 3 B), also known as TEB, silicon compounds such as trisilane (Si 3 H 8 ), alcohols such as ethanol, and water (H 2 O). The illustrated fluidized bed evaporator  200  includes a vessel body  210 , an evaporation space  220 , a filter  230 , a distributor plate  240 , a precursor inlet  250 , a precursor gas outlet  260 , a carrier gas inlet  270 , and a heater  280 . A portion of the inner wall of the vessel body  210 , the filter  230 , and the distributor plate  240  together define the evaporation space  220 . 
     The vessel body  210  contains inert granules  215  for forming a fluidized bed in the evaporation space  220  thereof. The details of the inert granules  215  can be as described above with respect to the inert granules in reference to  FIG. 1 . The illustrated vessel body  210  includes a sidewall  211 , a top plate  212 , and a bottom plate  213 . The sidewall  211  surrounds the evaporation space  220 . The illustrated vessel body  210  has a vertically conical shape with the area of the bottom plate  213  being narrower than the area of the top plate  212 . A lower portion of the vessel body  210  between the distributor plate  240  and the bottom plate  213  may have a cylindrical shape. An upper portion of the vessel body  210  between the filter  230  and the top plate  212  may have a cylindrical shape. A skilled artisan will appreciate that the vessel body  210  can have various other shapes. 
     The filter  230  serves to prevent the inert granules  215  or precursor in liquid form from escaping from the vessel body  210  to the precursor outlet  260 . The filter  230  includes openings that are smaller in size than the inert granules  215 . In other embodiments, the filter  230  may be omitted, and a filter may be positioned outside the fluidized bed evaporator  200 , for example, at a passage leading to a reactor. 
     The distributor plate  240  serves to support the inert granules  215  and allow a carrier gas to flow therethrough into the evaporation space  220  in an upward direction. The distributor plate  240  includes holes that are smaller in size than the inert granules  215  to prevent the inert granules  215  from passing therethrough. The holes are distributed and configured to allow the carrier gas to flow therethrough such that at least some of the inert granules  215  are suspended in the evaporation space  220  to form a fluidized bed. In certain embodiments, the distributor plate  240  may represent a porous frit. 
     The precursor inlet  250  serves as an inlet for a liquid precursor into the evaporation space  220 . In the illustrated embodiment, the precursor inlet  250  is formed through the sidewall of the vessel body  210 , and is in fluid communication with a precursor container (not shown) via a precursor inlet line  251 . A valve  252  or other flow control device is on the precursor inlet line  251 . In other embodiments, the precursor inlet may be at any suitable location. 
     The precursor gas outlet  260  serves as an outlet for an evaporated precursor. In the illustrated embodiment, the precursor gas outlet  260  is formed through the top plate  212  of the vessel body  210 , and is in fluid communication with a reactor (not shown) via a gas line  265 . In other embodiments, the precursor gas outlet may be at any suitable location. In certain embodiments, the precursor gas outlet  260  may be provided with a monitoring device to measure and/or control the concentration of a vapor phase precursor. The monitoring device may be, e.g., an infrared device. 
     The carrier gas inlet  270  serves as an inlet for the carrier gas supplied into the evaporation space  220 . In the illustrated embodiment, the carrier gas inlet  270  is formed through the bottom plate and is in fluid communication with a carrier gas source (not shown) via a carrier gas line  271 . In other embodiments, the carrier gas inlet may be at any suitable location. The carrier gas source provides a pressurized inert gas into the vessel body  210  through the carrier gas inlet  270 . In certain embodiments, the carrier gas inlet  270  may be consolidated with the precursor inlet  250 . 
     The heater  280  serves to heat the evaporation space  220  and the sidewall  211  of the vessel body  210  to a temperature at which evaporation of the liquid precursor is facilitated, but the liquid precursor is not decomposed. The heater  280  may be a radiant and/or resistive heater. In the illustrated embodiment, a resistant wire helically winds the sidewall  211  of the vessel body  210 . In another embodiment, the heater  280  may include heater rods or other internal heating mechanisms that are positioned inside the evaporation space  220 . In yet another embodiment, the fluidized bed evaporator  200  may include a heater between the distributor plate  240  and the carrier gas inlet  270 . In yet another embodiment, the fluidized bed evaporator  200  may use induction, microwave, and/or light to heat the fluidized bed within the evaporation space  220 . A skilled artisan will appreciate that a combination of the foregoing or various other types of heaters can be adapted for heating the fluidized bed evaporator  200 . Whether the heater heats the walls of the vessel body  210  or more directly heats the fluidized bed, the fluidized bed and thermally conductive granules  215  facilitate efficient distribution of heat to the precursor. The high surface area of the heated precursor facilitates efficient vaporization rates and greater ease of saturation of the carrier gas with vaporized precursor. 
       FIG. 2A  illustrates a state in which the fluidized bed evaporator  200  is ready for operation. The inert granules  215  are supported on the distributor plate  240 , and are stationary.  FIG. 2B  illustrates a state in which the fluidized bed evaporator  200  is in operation. A carrier gas is provided at a high flow rate through the carrier gas inlet  270 , and is provided upward through the holes of the distributor plate  240 . The carrier gas moves at least some of the inert granules  215  upward, and suspends and stirs them in the evaporation space  220 , forming a fluidized bed. The movement of the inert granules  215  above the evaporation space  220  is restricted by the filter  230 . 
     The heater  280  is turned on to heat the sidewall  211  of the vessel body  210  such that the temperature of the granules  215  in the evaporation space  220  is suitable for the evaporation, but not decomposition, of the liquid precursor. A skilled artisan will appreciate that the temperature of the fluidized bed in the evaporation space  220  can vary widely depending on the types of the precursor. 
     While the inert granules  215  form a fluidized bed, the liquid precursor is provided into the evaporation space  220  through the precursor inlet  250 . In certain embodiments, the liquid precursor may be in a form of mist. The liquid precursor contacts the surfaces of the heated inert granules  215 , and evaporates into gas. Because the levitated inert granules  215  provide a greater evaporation surface area than when there are no inert granules, or when granules are not levitated, the evaporation of the liquid precursor is facilitated. 
     In addition, the fluidized bed has good thermal conductance, and efficiently heats the liquid precursor to vaporize into a gaseous state. Granules forming the fluidized bed are moved substantially continuously in substantially all directions. In other words, the granules behave like a fluid. This results in an intense thermal contact between the heated sidewalls  211  of the vessel body  210  and the granules  215 . Thus, the fluidized bed has good thermal conductance. Good thermal conductance of the fluidized bed significantly contributes to the evaporation of the precursor. In other embodiments, the fluidized bed can thermally conduct from an internal heater to the granules or can suscept externally generated inductive or microwave energy. 
     Referring to  FIG. 3 , another embodiment of a fluidized bed evaporator for a solid precursor will be described below. Examples of solid precursors include, but are not limited to, ZrCl 4 , HfCl 4 , and cyclopentadienyl compounds of barium or strontium. Cyclopentadienyl compounds of barium or strontium are described in U.S. Pat. No. 7,108,747, the disclosure of which is incorporated herein by reference. Mixtures of precursors may also be used, provided that the vapor pressures at the temperature of this fluidized bed are closely matched. 
     The illustrated fluidized bed evaporator  300  includes a vessel body  310 , an evaporation space  320 , a filter  330 , a distributor plate  340 , a precursor inlet  350 , a solid discharge outlet  355 , a precursor gas outlet  360 , a carrier gas inlet  370 , and a heater  380 . The inner walls of the vessel body  310 , the filter  330 , and the distributor plate  340  together define the evaporation space  320 . The configurations of the vessel body  310 , the evaporation space  320 , the filter  330 , the distributor plate  340 , the precursor inlet  350 , the precursor gas outlet  360 , the carrier gas inlet  370 , and the heater  380  can be as described above with respect to  FIG. 2A , including described alternatives. The fluidized bed evaporator  300  can be connected to a carrier gas line  371  at the carrier gas inlet  370  to receive an inert gas. The fluidized bed evaporator  300  can be connected to a precursor gas line  365  at the precursor gas outlet  360  to provide a precursor in vapor phase to a reactor. 
     The vessel body  310  serves to produce a fluidized bed in the evaporation space  320  thereof. In one embodiment, the fluidized bed may be formed by solid precursor particles in a form suitable for sublimation in the evaporation space  320 . The solid precursor particles may be in a form of powder. 
     In another embodiment, the fluidized bed is formed by inert granules, such as those described above in connection with  FIG. 1 . In such an embodiment, solid precursor particles in a form of, for example, powder, may be provided into the evaporation space  320 , levitated and stirred among the inert granules in the fluidized bed for sublimation. 
     In yet another embodiment, the fluidized bed may be formed by inert granules coated with a solid precursor. In such an embodiment, the inert granules coated with the solid precursor are provided into the evaporation space  320  such that the solid precursor is sublimed into a gaseous state. The other details of the vessel body  310  can be as described in connection with  FIG. 2A . 
     The precursor inlet  350  serves as an inlet for a solid precursor in a form of powder or inert granules coated with a solid precursor. The precursor inlet  350  is in fluid communication with a precursor container (not shown) via a precursor inlet line  351 . The solid precursor or coated inert granules may be carried by an inert carrier gas. The precursor inlet line  351  can have a valve  352  to control the flow of the precursor. 
     The solid discharge outlet  355  serves as an outlet for a used or partly used solid precursor and/or inert granules. In an embodiment where a solid powder precursor is provided into the evaporation space  320 , when particles of the solid powder precursor decrease in size by sublimation and approach a size of the openings of the filter  330 , the solid precursor particles may be discharged through the solid discharge outlet  355  to a discharge line  356 . The discharge line  356  can have a valve  357  to control the flow of the used solid precursor. This configuration prevents the solid precursor particles from being supplied to a reactor (not shown) along with a vapor phase precursor. In another embodiment where inert granules coated with a solid precursor are provided into the evaporation space  320 , substantially bare inert granules may be discharged through the solid discharge outlet  355  after the coated solid precursor has sublimed into a gaseous state. 
     Referring still to  FIG. 3 , one embodiment of a method of operating the fluidized bed evaporator  300  will be described below. As described above, in one embodiment, a fluidized bed may be formed by solid precursor particles in a powder form. In such an embodiment, the solid precursor particles may be provided along with a carrier gas, forming a gas-borne flow of particles into the evaporation space  320 . The particles form a fluidized bed while being sublimed into a gaseous state. 
     As the solid precursor particles stay longer in the evaporation space  320 , at least a portion of them sublimes, and the particles become smaller in size, or the thickness of precursor coating over inert granules shrinks. The solid precursor particles or coated granules may be automatically discharged through a filter over the discharge outlet  355  before they become smaller in size than the size of the openings of the filter  330 . 
     In another embodiment, the solid precursor particles may be provided as a batch into the evaporation space  320 , and sublimed into the vapor phase. In such an embodiment, the entire portion of the solid precursor particles may be discharged in a batch through an automated or manually-operated door at a lower portion  317  of the fluidized bed evaporator  300  when at least some of the precursor particles reach a certain size. 
     In yet another embodiment, the fluidized bed evaporator  300  contains a fluidized bed formed by inert granules. A solid precursor in a powder form may be provided as a batch into the evaporation space  320 , and sublimed into a gaseous state. The solid precursor may be discharged through the filter in the discharge outlet  355  when it reaches a certain average size or in a batch. 
     In yet another embodiment, the fluidized bed evaporator  300  is provided with inert granules coated with a solid precursor. Such inert granules coated with the solid precursor can be provided in a batch into the evaporation space  320 . Inert granules left after the precursor has sublimed may be recycled, as will be described below. 
     Referring to  FIG. 4A , one embodiment of a fluidized bed system using inert granules coated with a solid precursor will be described below. The illustrated system  400  includes a fluidized bed evaporator  410 , a coated granule container  420 , a precursor coating apparatus  430 , and an inert granule collector  440 . The configuration of the fluidized bed evaporator  410  can be as described above with respect to the fluidized bed evaporator  300  of  FIG. 3 . 
     The system  400  also includes a first line  451 , a second line  452 , a third line  453 , a fourth line  454 , a fifth line  455 , a sixth line  456 , and a seventh line  457 . The first line  451  runs from a first carrier gas source (not shown) into the fluidized bed evaporator  410 . The first line  451  may have a first valve  461  and a first mass flow controller (MFC)  471  to control a flow therethrough. 
     The second line  452  extends from a first connection point of the first line  451  between the first MFC  471  and the first valve  461 , and extends to the coated granule container  420 . The second line  452  may be provided with a second valve  462 . 
     The third line  453  extends from inside of the coated granule container  420  and connects to a second connection point of the first line  451  between the first valve  461  and the fluidized bed evaporator  410 . The third line  453  may be provided with a mass flow meter (MFM)  472  to measure a total amount of the precursor and the carrier gas flowing through the third line  453 . The third line  453  may also be provided with a third valve  463 . 
     The fourth line  454  extends from the precursor coating apparatus  430  to the coated granule container  420 . The fourth line  454  may be provided with a fourth valve  464 . The fifth line  455  extends from inside of the fluidized bed evaporator  410  to the inert granule collector  440 . The fifth line  455  may be provided with a fifth valve  465 . 
     The sixth line  456  runs from a second carrier gas source (not shown) to a connection point of the fifth line  455  between the fluidized bed evaporator  410  and the inert granule collector  440 . The sixth line  456  may be equipped with a sixth valve  466 , and a second mass flow controller  473  to control a flow therethrough. The seventh line  457  runs from the inert granule collector  440  to the precursor coating apparatus  430 . The seventh line  457  may be provided with a seventh valve  467 . 
     Referring to  FIGS. 4A and 5 , the operation of the system  400  will be described below. The coated granule container  420  contains inert granules coated with a solid precursor (hereinafter, “coated granules”). The second and third valves  462 ,  463  are opened, and the other valves are closed to supply the coated granules to the fluidized bed evaporator  410 . A carrier gas, for example, an inert gas, is provided into the coated granule container  420  through the second line  452 . The carrier gas entrains and carries the coated granules through the third line  453  and the first line  451  to the evaporator  410 . A selected amount of the coated granule may be supplied into the evaporator  410  in this manner (step  510 ), and then the second valve  462  is closed. During this step, the evaporator  410  is off. 
     Subsequently, the first and sixth valves  461 ,  466  are opened to supply the carrier gas into the evaporator  410  while the other valves are closed. The carrier gas moves the coated granules upward in the evaporator  410 , thereby forming a fluidized bed. This step is continued until a substantial portion of coated solid on the inert granules has sublimed into a gaseous state (step  520 ). The sublimed precursor is supplied to the reactor, as described above in connection with  FIG. 1 . 
     After a substantial portion of coated solid on the inert granules has sublimed into a gaseous state, depleted inert granules with thin or no precursor coating are discharged to the inert granule collector  440  (step  530 ), for example, through the fifth line  455  by opening the first and fifth valves  461 ,  465  and closing the second, fourth, sixth, and seventh valves  462 ,  464 ,  466 ,  467 . During this step, the third valve  463  may be opened or closed. The inert granules are collected by the inert granule collector  440  and are supplied to the precursor coating apparatus  430  via the seventh line  457 , such as by entraining and carrying the granules in a carrier gas flow. The precursor coating apparatus  430  is configured to coat the inert granules with a solid precursor (step  540 ), and supplies the coated granules to the coated granule container  420  via the fourth line  454  (step  510 ). In certain embodiments, the inert granule collector  440  may be omitted. In such embodiments, depleted inert granules may be transferred directly to the precursor coating apparatus  430 . 
     Referring now to  FIG. 4B , one embodiment of the precursor coating apparatus  430  of  FIG. 4A  will be described below. The illustrated coating apparatus  430  includes a fluidized bed condenser  431 , a solid precursor container  435 , and a carrier gas line  436 . 
     The fluidized bed condenser  431  includes a condenser vessel  432 , a condenser filter  433 , and a condenser distributor plate  434 . The condenser vessel  432  provides a condensation space for condensing a vaporized precursor on depleted inert granules  438  that form a fluidized bed therein. The temperature of the inert granules  438  in the condensation space  432  is maintained below the condensation temperature of a precursor being processed by the condenser  431 , and the fluidized bed ensures good heat distribution among the inert granules  438  for maintaining temperatures below the condensation temperature throughout the fluidized bed. 
     The bare or depleted inert granules  438  are provided into the condenser vessel  432  through the seventh line  457  from the inert granule collector  440  ( FIG. 4A ). In other embodiments, the inert granules  438  may be provided by another source, not by the inert granule collector  440 . The configurations of the condenser filter  433  and the condenser distributor plate  434  can be as described above with respect to the filter  230  and distributor plate  240  of the fluidized bed evaporator  200  of  FIG. 2A . 
     The solid precursor container  435  contains bulk solid precursor  439  therein. The solid precursor container  435  is provided with a carrier gas through the carrier gas line  436 , and is configured to provide the carrier gas to the bottom (as shown) or upper space of the condenser vessel  432 . The solid precursor container  435  also includes a heater configured to heat the bulk solid precursor  439  such that at least a portion of the bulk solid precursor  439  sublimes into a gaseous state. The carrier gas, while being supplied to the condenser  431 , moves the vapor phase precursor into the condenser vessel  432 . 
     During operation, the condenser  431  may receive bare or depleted inert granules  438  in a batch, such as by entraining granules in a carrier gas flow. In the condenser  431 , the inert granules  438  are moved upward by the carrier gas, thereby forming a fluidized bed. The vapor phase precursor is supplied from the bottom of the condenser  431  along with the carrier gas. 
     The vapor phase precursor is condensed on the surfaces of the inert granules  438  because the temperature of the granules  438  in the condensation space is kept below the condensation temperature of the precursor by a temperature control system. During this step, the inert granules are stirred by the high flow of carrier gas. Substantially the entire surface of each inert granule may contact with the vapor phase precursor, and is coated with the precursor. During this step, the fourth line  454  is closed. 
     After the granules are coated with the precursor, they are discharged through the fourth line  454  to the coated granule container  420  ( FIG. 4A ). The coated granules can be supplied to the fluidized bed evaporator, as described above in connection with  FIG. 4A . In another embodiment, the precursor coating apparatus may be a separate apparatus, and the coated granules may be transported to the deposition system in transport containers. 
     Referring to  FIG. 6 , another embodiment of a deposition system including a fluidized bed evaporator will be described below. The illustrated system  600  includes a reactor  610 , a fluidized bed evaporator  620 , first to third gas lines  631 ,  632 ,  633 , and an outlet line  640 . In other embodiments where two or more co-reactants are used, the system can include more lines for providing passages for the co-reactants. 
     Although not illustrated, the system  600  may also include a controller (for example, a computer) that controls the operation of the system  600 , as described herein. A skilled artisan will appreciate that the system can include any other components necessary for the operation of the system  600 . 
     In the embodiments described below, at least some of lines or gas passages are provided with mechanical valves. In other embodiments, at least one of the mechanical valves may be replaced with or combined with so-called “inert gas valving” or “transition valving,” which involves controlling the direction of an inert gas flowing through the line and containing a vapor phase precursor. Details of inert gas valving are described in U.S. Pat. No. 6,783,590, the entire disclosure of which is incorporated herein by reference. 
     The reactor  610  may be a chemical vapor deposition (CVD) reactor for housing one or more substrates (e.g., wafers) on which deposition will take place. A skilled artisan will appreciate that the reactor  610  can be any type of reactor that uses a naturally liquid or solid precursor suitable for evaporation by the fluidized bed evaporator  620 . 
     The fluidized bed evaporator  620  provides a vapor phase precursor to the reactor  610 . The details of the evaporator  620  can be one of those described above in connection with  FIGS. 2A ,  2 B, and  3 - 5 . 
     The first line  631  extends from the fluidized bed evaporator  620  to the reactor  610 , providing a passage for the vapor phase precursor. The first line  631  may include a first valve  651  to open, close, or control the flow therethrough. 
     The second line  632  extends from a second reactant source (not shown), and merges with the first line  631  at a first connection point near the reactor  610 . The second line  632  forms a passage for the second reactant. The second line  632  may include a second valve  652  to open, close, or control the flow therethrough. 
     The third line  633  extends from a second connection point of the first line  631  between the fluidized bed evaporator  620  and the first valve  651 . The third line  633  serves as an exhaust passage or vent for the vapor phase precursor. The third line  633  may include a third valve  653  to open, close, or control the flow therethrough. 
     The outlet line  640  extends from the reactor  610  to an evacuation pump (not shown). The outlet line  640  serves as an exhaust passage for an unused precursor, unused co-reactants, and any by-products produced in the reactor  610  during a process therein. The outlet line  640  may include an exhaust valve  655  to open, close, or control the flow therethrough. The exhaust lines  633 ,  640  can connect to the same pump or different pumps. 
     During the operation, the third valve  653  may be opened and the first valve  651  is closed until the fluidized bed evaporator  610  produces a stable flow of a vapor phase precursor. When the fluidized bed evaporator  610  produces a stable flow of a vapor phase precursor, the third valve  653  may be closed. The precursor may be provided into the reactor  610  to perform a CVD process by opening the first valve  651 . The precursor may be provided simultaneously or sequentially with co-reactant(s), such as from the second line  632 , into the reactor  610  to perform the CVD process. The precursor and co-reactant(s) are in the vapor phase, and are carried by a carrier gas. The first and second valves  651 ,  652  may be opened simultaneously or sequentially during the process. A skilled artisan will appreciate that the operation of the system  600  can vary widely, depending on the types and numbers of reactants. 
     Referring to  FIG. 7 , yet another embodiment of a deposition system including a fluidized bed evaporator will be described below. The illustrated system  700  includes a reactor  710 , a fluidized bed evaporator  720 , first to fourth lines  731 ,  732 ,  733 ,  734  and an outlet line  740 . In other embodiments where two or more additional reactants are used, the system can include more lines for providing passages for the additional reactants. 
     Although not illustrated, the system  700  may also include a controller (for example, a computer) that controls the operation of the system  700 , as described herein. A skilled artisan will appreciate that the system can include any other components necessary for the operation of the system  700 . 
     The reactor  710  may be an atomic layer deposition (ALD) reactor for housing one or more substrates (e.g., wafers) on which deposition will take place. A skilled artisan will appreciate that the reactor  710  can be any type of reactor that uses a naturally liquid or solid precursor suitable for evaporation by the fluidized bed evaporator  720 . 
     The fluidized bed evaporator  720  provides a vapor phase precursor to the reactor  710 . The details of the evaporator  720  can be one of those described above in connection with  FIGS. 2A ,  2 B, and  3 - 5 . 
     The first line  731  extends from the fluidized bed evaporator  720  to the reactor  710 , providing a passage for the vapor phase precursor. The first line  731  may include a first valve  751  to open, close, or control the flow therethrough. 
     The second line  732  extends from another reactant source (not shown) to the reactor  710 . The second line  732  forms a passage for the other reactant. The second line  732  may include a second valve  752  to open, close, or control the flow therethrough. 
     The third line  733  extends from a connection point of the first line  731  between the fluidized bed evaporator  720  and the first valve  751 . The third line  733  serves as an exhaust or vent passage for the vapor phase precursor. The third line  733  may include a third valve  753  to open, close, or control the flow therethrough. 
     The fourth line  734  extends from a connection point of the second line  732  between the co-reactant source and the second valve  752 , and merges with the third line  733 . The fourth line  734  serves as an exhaust or vent passage for the other reactant. The fourth line  734  may include a fourth valve  754  to open, close, or control the flow therethrough. 
     The outlet line  740  extends from the reactor  710  to an evacuation pump (not shown). The outlet line  740  serves as an exhaust passage for unused precursor, unused other reactants, purge gas, and any by-products produced in the reactor  710  during a process therein. The outlet line  740  may include an exhaust valve  755  to open, close, or control the flow therethrough. 
     During the operation, the third valve  753  may be opened and the first valve  751  is closed until the fluidized bed evaporator  710  produces a stable flow of a vapor phase precursor. When the fluidized bed evaporator  710  produces a stable flow of a vapor phase precursor, the third valve  753  may be closed. Similarly, the fourth valve  754  may be opened and the second valve  752  is closed until a stable flow of the other reactant is produced by another fluidized bed evaporator (not shown) for providing the other reactant in gas state from solid. When a stable flow of the other reactant is supplied, the fourth valve  754  may be closed. More typically, the second reactant is a naturally gaseous material. 
     The precursor and the other reactant may be provided alternately into the reactor  710  to perform an ALD process. The first and second valve  751 ,  752  are opened alternately during the process while the other valves are closed. During or after the ALD process, the first and second valves  751 ,  752  may be closed, and the exhaust valve  755  may be opened to purge the reactor  710  with a source of purge gas (not shown). A skilled artisan will appreciate that the operation of the system  700  can vary widely, depending on the types and numbers of reactants. 
     Referring to  FIG. 8 , yet another embodiment of a deposition system including a fluidized bed evaporator will be described below. In contrast to the vented lines of  FIGS. 6 and 7 ,  FIG. 8  employs a continuous loop for evaporated precursor, from which vapor can be drawn periodically for use in deposition. The illustrated system  800  includes a reactor  810 , a fluidized bed evaporator  820 , a first line  831 , a second line  832 , a third line  833 , and an outlet line  840 . The system  800  also includes a first heating system  870  and a second heating system  880 . In other embodiments where one or more additional reactants are used, the system can include more lines for providing passages for the additional reactants to the reactor  810 , as described above in connection with  FIGS. 6 and 7 . 
     Although not illustrated, the system  800  may also include a controller (for example, a computer) that controls the operation of the system  800 , as described herein. A skilled artisan will appreciate that the system can include any other components necessary for the operation of the system  800 . 
     The reactor  810  may be a chemical vapor deposition (CVD) reactor. In another embodiment, the reactor  810  may be an atomic layer deposition (ALD) reactor. A skilled artisan will appreciate that the reactor  810  can be any type of reactor that uses a naturally liquid or solid precursor suitable for evaporation by the fluidized bed evaporator  820 . 
     The fluidized bed evaporator  820  provides a vapor phase precursor to the reactor  810 . The details of the evaporator  820  can be for one of those described above in connection with  FIGS. 2A ,  2 B, and  3 - 5 . 
     The first line  831  extends from the fluidized bed evaporator  820  to the reactor  810 , providing a passage for the evaporated precursor. The first line  831  may include a first valve  851  to open, close, or control the flow therethrough. In addition, the first line  831  may contain restrictions to regulate the flow. In certain embodiments, the restrictions can be provided in conjunction with inert gas valving, as described in the incorporated &#39;590 patent, referenced in the description above of  FIG. 6 . 
     The second line  832  extends from a connection point of the first line between the evaporator  820  and the first valve  851 , and merges with the third line  833 , forming a loop for a vapor phase precursor with the first and third lines  831 ,  833  and the evaporator  820 . At least a portion of the loop may be heated to prevent the evaporated precursor from condensing, schematically indicated by a heating system  870  creating a hot zone for the evaporator  820  and its associated lines  831 ,  832 ,  833 . The second line  832  may include a pressure meter  862  and a pump  863 . The pressure meter  862  is configured to measure the pressure of the precursor flowing through the second line  832 . In certain embodiments, the pressure meter  862  may provide a feedback signal to the pump  863 . The pump  863  maintains the pressure and flow of the precursor. In certain embodiments, the pump  863  may adjust the pressure and flow of the precursor, based at least partly on the feedback signal from the pressure meter  862 . 
     The third line  833  extends from a carrier gas source (not shown) to the fluidized bed evaporator  820 . The third line  833  serves as a passage for the carrier gas and the evaporated precursor circulating the loop. The third line  833  may include a carrier gas valve  861  to open, close, or control the flow therethrough. 
     The outlet line  840  extends from the reactor  810  to an evacuation pump (not shown). The outlet line  840  serves as an exhaust passage for an unused precursor, unused other reactants, purge gas and any by-products produced in the reactor  810  during a process therein. The outlet line  840  may include an exhaust valve  855  to open, close, or control the flow therethrough. 
     The first heater  870  may be a heated oven enclosing the continuous loop. The heated oven may include a low pressure box with a reflective interior and radiant heating elements or lamps within the low pressure box. Such a low pressure box prevents heat losses from the solid source vessel. Examples of heated ovens are disclosed in U.S. Pat. No. 6,699,524 and U.S. Patent Application Publication No. 2005/0000428, the entire disclosures of which are incorporated herein by reference. While the incorporated disclosures employ radiant heating, other types of heating can maintain a uniform temperature for the evaporator  820  and related components. The second heater  880  is configured to heat the first line  831  and the first valve  851  and may be implemented, e.g., as blanket heaters. The first and second heaters  870 ,  880  are configured to prevent condensation of vaporized precursor. 
     During the operation, the precursor is supplied into the reactor  810  to perform a CVD or ALD process. The first valve  851  is opened periodically during the process when the evaporated precursor is needed. In the illustrated embodiment, during the process, the first valve  851  may be closed when the evaporator  820  does not need the precursor, for example, at purge steps. At such times, the vapor phase precursor produced by the evaporator  820  can circulate the loop, and the evaporator  820  can keep producing the vapor phase precursor. At such steps, the pump is on to maintain the circulation of the precursor in the loop including the evaporator  820 . In this manner, the system can provide a sufficient amount of the precursor (sufficiently high partial pressure) for the next step. In some embodiments, the circulation permits saturation of the carrier gas with the precursor. Ideally, all wetted parts (exposed to the vaporized precursor) of the loop with the fluidized bed and the pump are at the same, possibly elevated, temperature. To uniformly elevate the temperature of the loop, the entire loop may be placed in an oven to create a hot zone. The evaporator  820  may be equipped with a precursor inlet and a precursor exhaust similar to the precursor inlet  350  and the solid (or liquid) precursor exhaust  355  as described in connection with  FIG. 3 . 
     Switching between provision of the precursor to the reactor and circulation of the precursor may be achieved by so-called “inert gas valving” or “transition valving,” which involves controlling the direction of an inert gas flowing through the line, containing the precursor, creating an inert gas barrier. A more detailed description is provided in the incorporated &#39;590 patent referenced in the description above of  FIG. 6 . An advantage of such an arrangement is that gas flow can be quickly switched without leaving a large volume of precursor in communication with the reactor to diffuse in. At the same time, sensitive valves, prone to breakdown or high contamination when exposed to high temperatures, can be moved outside the hot zone. Pipes can thus be kept free of condensation without sacrificing fast and abrupt switching ability. In other embodiments, the switching may be achieved by a simple valve. 
     The embodiments described above use various forms of fluidized beds for converting a liquid or solid precursor into gas phase. The fluidized beds have good thermal conductivity and high surface area/volume ratio. Such characteristics permit a relatively small sized evaporator with high flow capability. 
     Accordingly, it will be appreciated by those skilled in the art that various omissions, additions and modifications can be made to the processes described above without departing from the scope of the invention, and all such modifications and changes are intended to fall within the scope of the invention, as defined by the appended claims.