Patent Publication Number: US-2012027921-A1

Title: Vapor deposition apparatus and process for continuous deposition of a thin film layer on a substrate

Description:
FIELD OF THE INVENTION 
     The subject matter disclosed herein relates generally to the field of thin film deposition processes wherein a thin film layer, such as a semiconductor material layer, is deposited on a substrate. More particularly, the subject matter is related to a vapor deposition apparatus and associated process for depositing a thin film layer of a photo-reactive material on a glass substrate in the formation of photovoltaic (PV) modules. 
     BACKGROUND OF THE INVENTION 
     Thin film photovoltaic (PV) modules (also referred to as “solar panels”) based on cadmium telluride (CdTe) paired with cadmium sulfide (CdS) as the photo-reactive components are gaining wide acceptance and interest in the industry. CdTe is a semiconductor material having characteristics particularly suited for conversion of solar energy (sunlight) to electricity. For example, CdTe has an energy bandgap of 1.45 eV, which enables it to convert more energy from the solar spectrum (sunlight) as compared to lower bandgap (1.1 eV) semiconductor materials historically used in solar cell applications. Also, CdTe converts light more efficiently in lower or diffuse light conditions as compared to the lower bandgap materials and, thus, has a longer effective conversion time over the course of a day or in low-light (i.e., cloudy) conditions as compared to other conventional materials. 
     Solar energy systems using CdTe PV modules are generally recognized as the most cost efficient of the commercially available systems in terms of cost per watt of power generated. However, the advantages of CdTe not withstanding, sustainable commercial exploitation and acceptance of solar power as a supplemental or primary source of industrial or residential power depends on the ability to produce efficient PV modules on a large scale and in a cost effective manner. 
     Certain factors greatly affect the efficiency of CdTe PV modules in terms of cost and power generation capacity. For example, CdTe is relatively expensive and, thus, efficient utilization (i.e., minimal waste) of the material is a primary cost factor. In addition, the energy conversion efficiency of the module is a factor of certain characteristics of the deposited CdTe film layer. Non-uniformity or defects in the film layer can significantly decrease the output of the module, thereby adding to the cost per unit of power. Also, the ability to process relatively large substrates on an economically sensible commercial scale is a crucial consideration. 
     CSS (Close Space Sublimation) is a known commercial vapor deposition process for production of CdTe modules. Reference is made, for example, to U.S. Pat. No. 6,444,043 and U.S. Pat. No. 6,423,565. Within the vapor deposition chamber in a CSS system, the substrate is brought to an opposed position at a relatively small distance (i.e., about 2-3 mm) opposite to a CdTe source. The CdTe material sublimes and deposits onto the surface of the substrate. In the CSS system of U.S. Pat. No. 6,444,043 cited above, the CdTe material is in granular form and is held in a heated receptacle within the vapor deposition chamber. The sublimated material moves through holes in a cover placed over the receptacle and deposits onto the stationary glass surface, which is held at the smallest possible distance (1-2 mm) above the cover frame. The cover is heated to a temperature greater than the receptacle. 
     While there are advantages to the CSS process, the related system is inherently a batch process wherein the glass substrate is indexed into a vapor deposition chamber, held in the chamber for a finite period of time in which the film layer is formed, and subsequently indexed out of the chamber. The system is more suited for batch processing of relatively small surface area substrates. The process must be periodically interrupted in order to replenish the CdTe source, which is detrimental to a large scale production process. In addition, the deposition process cannot readily be stopped and restarted in a controlled manner, resulting in significant non-utilization (i.e., waste) of the CdTe material during the indexing of the substrates into and out of the chamber, and during any steps needed to position the substrate within the chamber. 
     Accordingly, there exists an ongoing need in the industry for an improved vapor deposition apparatus and process for economically feasible large scale production of efficient PV modules, particularly CdTe modules. 
     BRIEF DESCRIPTION OF THE INVENTION 
     Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention. 
     An apparatus is generally provided for vapor deposition of a sublimated source material as a thin film on a photovoltaic (PV) module substrate. The apparatus includes at least one receptacle disposed in a deposition head. Each receptacle is configured for receipt of a granular source material (e.g., cadmium telluride). A heating system is configured to heat the receptacle(s) to sublimate the source material. A substantially vertical distribution plate is disposed between the receptacle(s) and a substrate conveyed through the apparatus. The distribution plate is positioned at a defined distance from a vertical conveyance plane of a deposition surface of the substrate. The distribution plate comprises a pattern of passages therethrough that distribute the sublimated source material for deposition onto the deposition surface of the substrate. 
     Variations and modifications to the embodiments of the vapor deposition apparatus discussed above are within the scope and spirit of the invention and may be further described herein. 
     A process is also generally provided for vapor deposition of a sublimated source material to form thin film on a photovoltaic (PV) module substrate. According to one embodiment, source material can be supplied to at least one receptacle within a deposition head. Each receptacle can be heated with a heating system to sublimate the source material, and the sublimated source material can be directed through a distribution plate having a substantially vertical orientation. Individual substrates can be conveyed in a substantially vertical arrangement past the distribution plate such that the sublimated source material passing through the distribution plate is deposited onto a deposition surface of the substrates. 
     Variations and modifications to the embodiment of the vapor deposition process discussed above are within the scope and spirit of the invention and may be further described herein. 
     These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and appended claims, or may be obvious from the description or claims, or may be learned through practice of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present invention, including the best mode thereof, is set forth in the specification, which makes reference to the appended drawings, in which: 
         FIG. 1  is a plan view of a system that may incorporate embodiments of a vapor deposition apparatus of the present invention; 
         FIG. 2  is a cross-sectional view of an embodiment of a vapor deposition apparatus according to aspects of the invention in a first operational configuration; 
         FIG. 3  is a cross-sectional view of the embodiment of  FIG. 2  in a second operational configuration; and, 
         FIG. 4  is a top view of the embodiment of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment, can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention encompass such modifications and variations as come within the scope of the appended claims and their equivalents. 
       FIG. 1  illustrates an embodiment of a system  10  that may incorporate a vapor deposition apparatus  100  ( FIGS. 2 and 3 ) in accordance with embodiments of the invention configured for deposition of a thin film layer on a photovoltaic (PV) module substrate  14  (referred to hereafter as a “substrate”). As shown, the system  10  and vapor deposition apparatus  100  are configured to deposit a thin film on the substrates  14  while in a substantially vertical orientation. The substantially vertical orientation can prevent particles from falling onto the substrate or apparatus. 
     The thin film may be, for example, a film layer of cadmium telluride (CdTe). As mentioned, it is generally recognized in the art that a “thin” film layer on a PV module substrate is generally less than about 10 microns (μm). It should be appreciated that the present vapor deposition apparatus  100  is not limited to use in the system  10  illustrated in  FIG. 1 , but may be incorporated into any suitable processing line configured for vapor deposition of a thin film layer onto a PV module substrate  14 . 
     For reference and an understanding of an environment in which the vapor deposition apparatus  100  may be used, the system  10  of  FIG. 1  is described below, followed by a detailed description of the apparatus  100 . 
     Referring to  FIG. 1 , the exemplary system  10  includes a process chamber  12  defined by a plurality of interconnected modules. Any combination of rough and fine vacuum pumps  40  may be configured with the modules to draw and maintain a vacuum within the chamber  12 . The process chamber  12  includes a plurality of heater modules  16  that define a pre-heat section of the vacuum chamber through which the substrates  14  are conveyed and heated to a desired temperature before being conveyed into the vapor deposition apparatus  100 . Each of the modules  16  may include a plurality of independently controlled heaters  18 , with the heaters defining a plurality of different heat zones. A particular heat zone may include more than one heater  18 . 
     The process chamber  12  also includes a plurality of interconnected cool-down modules  20  downstream of the vapor deposition apparatus  100 . The cool-down modules  20  define a cool-down section within the process chamber  12  through which the substrates  14  having the thin film of sublimated source material deposited thereon are conveyed and cooled at a controlled cool-down rate prior to the substrates  14  being removed from the system  10 . Each of the modules  20  may include a forced cooling system wherein a cooling medium, such as chilled water, refrigerant, gas, or other medium, is pumped through cooling coils (not illustrated) configured with the modules  20 . 
     In the illustrated embodiment of system  10 , at least one post-heat module  22  is located immediately downstream of the vapor deposition apparatus  100  and upstream of the cool-down modules  20  in a conveyance direction of the substrates. The post-heat module  22  maintains a controlled heating profile of the substrate  14  until the entire substrate is moved out of the vapor deposition apparatus  100  to prevent damage to the substrate, such as warping or breaking caused by uncontrolled or drastic thermal stresses. If the leading section of the substrate  14  were allowed to cool at an excessive rate as it exited the apparatus  100 , a potentially damaging temperature gradient would be generated longitudinally along the substrate  14 . This condition could result in breaking, cracking, or warping of the substrate from thermal stress. 
     As diagrammatically illustrated in  FIG. 1 , a feed device  24  is configured with the vapor deposition apparatus  100  to supply source material, such as granular CdTe. The feed device  24  may take on various configurations within the scope and spirit of the invention, and functions to supply the source material without interrupting the continuous vapor deposition process within the apparatus  100  or conveyance of the substrates  14  through the apparatus  100 . 
     Still referring to  FIG. 1 , the individual substrates  14  are initially placed onto a load conveyor  26 , and are subsequently moved into an entry vacuum lock station that includes a load module  28  and a buffer module  30 . A “rough” (i.e., initial) vacuum pump  32  is configured with the load module  28  to drawn an initial vacuum, and a “fine” (i.e., final) vacuum pump  38  is configured with the buffer module  30  to increase the vacuum in the buffer module  30  to essentially the vacuum pressure within the process chamber  12 . Valves  34  (e.g., gate-type slit valves or rotary-type flapper valves) are operably disposed between the load conveyor  26  and the load module  28 , between the load module  28  and the buffer module  30 , and between the buffer module  30  and the process chamber  12 . These valves  34  are sequentially actuated by a motor or other type of actuating mechanism  36  in order to introduce the substrates  14  into the process chamber  12  in a step-wise manner without affecting the vacuum within the chamber  12 . 
     In operation of the system  10 , an operational vacuum is maintained in the process chamber  12  by way of any combination of rough and/or fine vacuum pumps  40 . Additionally, one or more process gasses can be added to these chambers to control the atmosphere within. In order to introduce a substrate  14  into the process chamber  12 , the load module  28  and buffer module  30  are initially vented (with the valve  34  between the two modules in the open position). The valve  34  between the buffer module  30  and the first heater module  16  is closed. The valve  34  between the load module  28  and load conveyor  26  is opened and a substrate  14  is moved into the load module  28 . At this point, the first valve  34  is shut and the rough vacuum pump  32  then draws an initial vacuum in the load module  28  and buffer module  30 . The substrate  14  is then conveyed into the buffer module  30 , and the valve  34  between the load module  28  and buffer module  30  is closed. The fine vacuum pump  38  then increases the vacuum in the buffer module  30  to approximately the same vacuum in the process chamber  12 . In another embodiment, after pumping down the remaining atmosphere to a sufficiently low level so as to not contaminate the process chamber  12 , the buffer module  30  is then backfilled with a process gas or mixture of process gases to a pressure matched with that of the vacuum chamber. At this point, the valve  34  between the buffer module  30  and process chamber  12  is opened and the substrate  14  is conveyed into the first heater module  16 . 
     An exit vacuum lock station is configured downstream of the last cool-down module  20 , and operates essentially in reverse of the entry vacuum lock station described above. For example, the exit vacuum lock station may include an exit buffer module  42  and a downstream exit lock module  44 . Sequentially operated valves  34  are disposed between the buffer module  42  and the last one of the cool-down modules  20 , between the buffer module  42  and the exit lock module  44 , and between the exit lock module  44  and an exit conveyor  46 . A fine vacuum pump  38  is configured with the exit buffer module  42 , and a rough vacuum pump  32  is configured with the exit lock module  44 . The pumps  32 ,  38  and valves  34  are sequentially operated to move the substrates  14  out of the process chamber  12  in a step-wise fashion without loss of vacuum condition within the process chamber  12 . 
     System  10  also includes a conveyor system configured to move the substrates  14  into, through, and out of the process chamber  12 . In the illustrated embodiment, this conveyor system includes a plurality of individually controlled conveyors  48 , with each of the various modules including a respective one of the conveyors  48 . It should be appreciated that the type or configuration of the conveyors  48  may vary. In the illustrated embodiment, the conveyors  48  are roller conveyors having rotatably driven rollers that are controlled so as to achieve a desired conveyance rate of the substrates  14  through the respective module and the system  10  overall. 
     As described, each of the various modules and respective conveyors in the system  10  are independently controlled to perform a particular function. For such control, each of the individual modules may have an associated independent controller  50  configured therewith to control the individual functions of the respective module. The plurality of controllers  50  may, in turn, be in communication with a central system controller  52 , as diagrammatically illustrated in  FIG. 1 . The central system controller  52  can monitor and control (via the independent controllers  50 ) the functions of any one of the modules so as to achieve an overall desired heat-up rate, deposition rate, cool-down rate, conveyance rate, and so forth, in processing of the substrates  14  through the system  10 . 
     Referring to  FIG. 1 , for independent control of the individual respective conveyors  48 , each of the modules may include any manner of active or passive sensors  54  that detects the presence of the substrates  14  as they are conveyed through the module. The sensors  54  are in communication with the respective module controller  50 , which is in turn in communication with the central controller  52 . In this manner, the individual respective conveyor  48  may be controlled to ensure that a proper spacing between the substrates  14  is maintained and that the substrates  14  are conveyed at the desired conveyance rate through the process chamber  12 . 
       FIGS. 2 and 3  relate to a particular embodiment of the vapor deposition apparatus  100  configured to deposit a thin film on the substrates  14  while in a substantially vertical arrangement. The apparatus  100  includes a deposition head  110  defining an interior space in which a plurality of receptacles  116  are positioned. Although shown as including three receptacles  116 , any suitable number of receptacles  116  can by included in the deposition head  110 . For example, one or more receptacles  116  can be included, such as 2 to about 5 receptacles  116 . As such, some embodiments may only include a single receptacle  116 , while other embodiments may include a plurality of receptacles (i.e., more than one). 
     Each receptacle  116  is configured for receipt of a granular source material  117 . As shown, the three receptacles  116  are aligned substantially vertically within the deposition head  110 . This arrangement of the receptacles  116  can allow for a more uniform distribution of the source vapors  119  upon sublimation of the source material  117 . 
     A heating system can be positioned within the deposition head  110  to sublimate the source material  117  within each receptacle  116 . As shown, a plurality of heating elements  115  can be utilized in one particular embodiment. In one particular embodiment, a heating element  115  can be positioned in close proximity to each receptacle (e.g., underneath) such that each receptacle  116  is primarily heated via its respective heating element  115 . As such, the temperature of each receptacle  116  can be independently controlled by its respective heating element  115 . In the illustrated embodiment, at least one thermocouple  122  is operationally positioned to monitor temperature within or near each receptacle  116 . This independent control of the heating of each receptacle  116  can help control the vapor pressure of the sublimated source material within the deposition head  110  by allowing for independent adjustment of the temperature of each receptacle  116 , and thus the sublimation rate of the source material  117  within each receptacle  116 . This independent control of the temperature of each receptacle  116  can help control the vapor pressure of the source vapors within the deposition head  110  and lessen the vapor pressure gradient within the deposition head  110  before passing through the distribution manifold  124  and distribution plate  152 . 
     As mentioned, the granular source material may be supplied by a feed device or system  24  ( FIG. 1 ) via a plurality of feed tubes  148 . Each feed tube  148  is connected to a distributor  144  disposed above each receptacle, respectively, and is configured to distribute the granular source material  117  into each receptacle  116 . The receptacle  116  has an open top and may include any configuration of internal ribs (not shown) or other structural elements. 
     Referring to  FIG. 4 , the deposition head  110  also includes longitudinal end walls  112  and side walls  113 . The substrates  14  are transported by conveyors  48  through the deposition head  110  and past the distribution plate  152  through which source vapors are passed to deposit a thin film on the substrate  14 . 
     A distribution manifold  124  is disposed between the receptacles  116 . This distribution manifold  124  may take on various configurations within the scope and spirit of the invention, and serves to distribute the sublimated source material that flows from the receptacles  116 . 
     In the illustrated embodiment, the distribution manifold  124  can be heated to inhibit that source vapors from depositing thereon, and may also indirectly heat the receptacles  116 . As shown, the distribution manifold  124  has a clam-shell configuration that includes a first shell member  130  closer to the receptacles  116  and a second shell member  132  closer to the substrates  14 . Each of the shell members  130 ,  132  includes recesses therein that define cavities  134  when the shell members are mated together as depicted in  FIGS. 2 and 3 . Heater elements  128  are disposed within the cavities  134  and serve to heat the distribution manifold  124  to a degree sufficient inhibit the source vapors from depositing on or within the distribution manifold  124 . The heater elements  128  may be made of a material that reacts with the source material vapor and, in this regard, the shell members  130 ,  132  also serve to isolate the heater elements  128  from contact with the source material vapor. Thus, the heat generated by the distribution manifold  124  is sufficient to prevent the sublimated source material from plating out onto components of the head chamber  110 . Desirably, the coolest component in the head chamber  110  is the deposition surface of the substrates  14  conveyed therethrough so as to ensure that the sublimated source material plates onto the substrate, and not onto components of the head chamber  110 . 
     Still referring to  FIGS. 2 and 3 , the heated distribution manifold  124  includes a plurality of passages  126  defined therethrough. These passages have a shape and configuration so as to uniformly distribute the sublimated source material towards the substrates  14 . 
     In the illustrated embodiment, a distribution plate  152  is disposed between the distribution manifold  124  at a defined distance from the deposition surface of an underlying substrate  14  (i.e., the surface of the substrate  14  facing the distribution plate  152 ). This distance may be, for example, between about 0.3 cm to about 4.0 cm. In a particular embodiment, the distance is about 1.0 cm. The conveyance rate of the substrates past the distribution plate  152  may be in the range of, for example, about 10 mm/sec to about 40 mm/sec. In a particular embodiment, this rate may be, for example, about 20 mm/sec. The thickness of the CdTe film layer that deposits onto the deposition surface of the substrate  14  can vary within the scope and spirit of the invention, and may be, for example, between about 1 μm to about 5 μm. In a particular embodiment, the film thickness may be about 1.5 μm to about 4 μm. 
     The distribution plate  152  includes a pattern of passages, such as holes, slits, and the like, therethrough that further distribute the sublimated source material passing through the distribution manifold  124  such that the source material vapors are uninterrupted in the transverse direction. In other words, the pattern of passages are shaped and staggered or otherwise positioned to ensure that the sublimated source material is deposited completely over the substrate  14  in the transverse direction so that longitudinal streaks or stripes of “un-coated” regions on the substrate are avoided. In one embodiment, the distribution plate  152  can be heated, such as via the distribution manifold  124 , to inhibit the source material from depositing on the distribution plate. 
     As previously mentioned, a significant portion of the sublimated source material will flow out of the receptacles  116  source vapors (depicted by arrows  119 ). Although these curtains of vapor will diffuse to some extent in the longitudinal direction prior to passing through the distribution plate  152 , it should be appreciated that it is unlikely that a uniform distribution of the sublimated source material will be achieved as the vapors pass through the distribution manifold. However, the distribution plate  152  can aid in the further distribution of the source vapors contacting the substrate  14  to ensure substantially uniform deposition of the thin film layer. 
     As illustrated in the figures, it may be desired to include a debris shield  150  between the receptacle  116  and the distribution manifold  124 . This shield  150  includes holes defined therethrough (which may be larger or smaller than the size of the holes of the distribution plate  152 ) and primarily serves to retain any granular or particulate source material from passing through and potentially interfering with operation of the movable components of the distribution manifold  124 . In other words, the debris shield  150  can be configured to act as a breathable screen that inhibits the passage of particles without substantially interfering with vapors flowing through the shield  150 . Thus, this shield  150  can protect the distribution manifold  124 , the distribution plate  152 , and/or the substrate  14  from unvaporized source material that can be in the deposition head  110  (e.g., cracking and/or popping of the source material may occur during sublimation, resulting in unvaporized source material being ejected from the receptacle  116 ). 
     A cold trap  153  is positioned under the substrate  14  and within the deposition head  110  to collect errant source vapors  119 . As shown, the cold trap  153  is positioned along the lower surface of the deposition head  110 . For example, the cold trap  153  can have a trap temperature that is below the sublimation temperature of the source material (e.g., about 0° C. to about 300° C. for CdTe vapors). As such, any errant source vapors that contact the cold trap  153  will plate onto the surface of the cold trap  153 . Additionally, the cold trap can collect any particles that fall to the bottom of the chamber. This collected errant source vapors can be recycled as source material for later use. Although shown under only the substrate  14 , the cold trap can be extended to cover the entire lower surface of the deposition head  110  in certain embodiments. 
     Referring to  FIG. 4  in particular, apparatus  100  desirably includes transversely extending seals  154  at each longitudinal end of the head chamber  110 . In the illustrated embodiment, the seals define an entry slot  156  and an exit slot  158  at the longitudinal ends of the head chamber  110 . These seals  154  are disposed at a distance from the deposition surface of the substrates  14  that is less than the distance between the surface of the substrates  14  and the distribution plate  152 , as is depicted in  FIG. 4 . The seals  154  help to maintain the sublimated source material in the deposition area above the substrates  14 . In other words, the seals  154  prevent the sublimated source material from “leaking out” through the longitudinal ends of the apparatus  100 . It should be appreciated that the seals  154  may be defined by any suitable structure. In the illustrated embodiment, the seals  154  are actually defined by components of the first shell member  130  of the heated distribution manifold  124 . It should also be appreciated that the seals  154  may cooperate with other structure of the vapor deposition apparatus  100  to provide the sealing function. For example, the seals may engage against structure of the underlying conveyor assembly in the deposition area. 
     Referring to  FIGS. 2 and 3 , the illustrated embodiment includes a movable shutter plate  136  disposed above the distribution manifold  124 . This shutter plate  136  includes a plurality of passages  138  defined therethrough that align with the passages  126  in the distribution manifold  124  in a first operational position of the shutter plate  136  as depicted in  FIG. 2 . As can be readily appreciated from  FIG. 2 , in this operational position of the shutter plate  136 , the sublimated source material is free to flow through the shutter plate  136  and through the passages  126  in the distribution manifold  124  for subsequent distribution through the plate  152 . Referring to  FIG. 3 , the shutter plate  136  is movable to a second operational position relative to the surface of the distribution manifold  124  wherein the passages  138  in the shutter plate  136  are misaligned with the passages  126  in the distribution manifold  124 . In this configuration, the sublimated source material is blocked from passing through the distribution manifold  124 , and is essentially contained within the interior volume of the head chamber  110 . Any suitable actuation mechanism, generally  140 , may be configured for moving the shutter plate  136  between the first and second operational positions. In the illustrated embodiment, the actuation mechanism  140  includes a rod  142  and any manner of suitable linkage that connects the rod  142  to the shutter plate  136 . The rod  142  is rotated by any manner of mechanism located externally of the head chamber  110 . 
     The shutter plate  136  configuration illustrated in  FIGS. 2 and 3  is particularly beneficial in that, for whatever reason, the sublimated source material can be quickly and easily contained within the head chamber  110  and prevented from passing through to the deposition area above the conveying unit. This may be desired, for example, during start up of the system  10  while the concentration of vapors within the head chamber builds to a sufficient degree to start the deposition process. Likewise, during shutdown of the system, it may be desired to maintain the sublimated source material within the head chamber  110  to prevent the material from condensing on the conveyor or other components of the apparatus  100 . 
     The present invention also encompasses various process embodiments for vapor deposition of a sublimated source material to form a thin film on a PV module substrate. The various processes may be practiced with the system embodiments described above or by any other configuration of suitable system components. It should thus be appreciated that the process embodiments according to the invention are not limited to the system configuration described herein. 
     In a particular embodiment, the vapor deposition process includes supplying source material to a plurality of receptacles within a deposition head (e.g., vertically arranged receptacles), and heating each receptacle to sublimate the source material. The sublimated source material is directed out of the receptacle and through the distribution plate. Individual substrates are conveyed substantially vertically past the distribution plate. The sublimated source material that passes through the distribution plate and is distributed onto a deposition surface of the substrates. 
     In yet another unique process embodiment, the passages for the sublimated source material through the heat source may be blocked with an externally actuated blocking mechanism, as discussed above. 
     Desirably, the process embodiments include continuously conveying the substrates at a constant linear speed during the vapor deposition process. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.