Patent Publication Number: US-2012034382-A1

Title: Substrate support material useful for screen printing processes

Description:
BACKGROUND OF THE DISCLOSURE 
     1. Field of the Invention 
     The present invention relates to a system used to deposit a patterned layer on a surface of a substrate, such as a screen printing process. In particular, the present invention relates to supporting material used to support a substrate during the screen printing process. 
     2. Description of the Background Art 
     Solar cells are photovoltaic (PV) devices that convert sunlight directly into electrical power. PV devices typically have one or more p-n junctions. Each junction comprises two different regions within a semiconductor material where one side is denoted as the p-type region and the other as the n-type region. When the p-n junction of the PV cell is exposed to sunlight (consisting of energy from photons), the sunlight is directly converted to electricity through the PV effect. PV solar cells generate a specific amount of electric power and cells are tiled into modules sized to deliver the desired amount of system power. PV modules are joined into panels with specific frames and connectors. The solar cells are commonly formed on a silicon substrate, which may be in form of single or multicrystalline silicon substrates. A typical PV cell includes a p type silicon wafer, substrate or sheet typically less than about 0.3 mm thick with a thin layer of n-type silicon on top of a p-type region formed in a substrate. 
     The photovoltaic market has experienced growth with annual growth rates exceeding above 30% for the last ten years. Some articles have suggested that solar cell power production worldwide may exceed 10 GWp in the near future. It has been estimated that more than 95% of all photovoltaic modules are silicon wafer based. The high market growth rate in combination with the need to substantially reduce solar electricity costs has resulted in a number of serious challenges for inexpensively forming high quality photovoltaic devices. 
     Therefore, one major component in making commercially viable solar cells is reducing the manufacturing costs required to form the solar cells, such as by improving the device yield and increasing the substrate throughput. 
     Screen printing has long been used in printing designs on objects, such as cloth, and is used in the electronics industry for printing electrical component designs, such as electrical contacts or interconnects on the surface of a substrate. State of the art solar cell fabrication processes also use screen printing processes. Misaligned, or inaccurately placed, screen printed patterns on an electronic device or solar cell can affect the device yield. Moreover, the accuracy of the placement of the screen printed pattern on a solar cell substrate can affect the cost to produce a solar cell device and the cost of ownership of a solar cell production line. Additionally, improving handling of solar cell substrates will aid accurate placement of the screen printed pattern and reduce substrate breakage. 
     Therefore, there is a need for a screen printing apparatus for the production of solar cells, electronic circuits or other useful devices that provides improved handling of substrates and an accurate placement of a screen printed material to improve the device yield and produce a lower cost of ownership (CoO) than other known apparatuses. 
     SUMMARY OF THE INVENTION 
     The present invention generally provides a supporting material comprising a non-woven material that supports a substrate during the screen printing process. The non-woven material comprises a top region and a bottom region, and has a first surface adjacent to the top region, and a first end and a second end, wherein the top region is less compliant than the bottom region. A plurality of features may be formed on a region of the first surface, which extends in a direction between the first end and the second end. The non-woven material has a sufficient thickness in a direction substantially perpendicular to the first surface to allow air to pass through the thickness when a vacuum is applied to a second surface opposite the first surface of the material. 
     Embodiments further provide an apparatus for processing a substrate, comprising a material conveyor assembly comprising a platen having a substrate supporting surface, a first material positioning mechanism that is adapted to provide a supporting material to the substrate supporting surface, the supporting material comprising a non-woven material having a top region and a bottom region, wherein the top region is less compliant than the bottom region, the supporting material having a first surface on which a plurality of features are formed, and a second material positioning mechanism that is adapted to receive the supporting material transferred across at least a portion of the substrate supporting surface from the first material positioning mechanism, a sensor assembly disposed over the first surface, wherein the sensor assembly is positioned to sense the change in position of the plurality of features formed on the first surface, and a controller adapted to receive a signal from the sensor assembly and control the position of the supporting material on the substrate supporting surface using an actuator coupled to the first material positioning mechanism or the second material positioning mechanism. 
     Embodiments of the invention further provide a method of processing a substrate, comprising receiving a substrate on a first surface of a non-woven support material that has top region and bottom region, wherein the top region is adjacent to the first surface and is less compliant than a bottom region, and the first surface has a plurality of features formed thereon, moving the support material across a surface of a substrate support, sensing the movement of the plurality of features past a sensor assembly, and controlling the position of the substrate on the surface of the substrate support based at least partially on the sensed movement of the plurality of features. 
     Embodiments of the invention further provide a method of processing a substrate, comprising receiving a substrate on a first surface of a non-woven support material that has top region and bottom region, wherein the top region is adjacent to the first surface and is less compliant than a bottom region, and the first surface has a plurality of features formed thereon, moving the support material across a surface of a substrate support, emitting electromagnetic radiation from a source onto the first surface of the support material, wherein the emitted radiation striking the first surface interacts with the plurality of features formed thereon, receiving an intensity of the electromagnetic radiation after the at least a portion of the electromagnetic radiation has interacted with the plurality of features, and monitoring the intensity of the received electromagnetic radiation to determine the position of the substrate on the surface of the substrate support. 
     Another embodiment of the invention includes a support material on a printing nest used to support a substrate during processing. The support material comprises a porous non-woven material having two different properties. The non-woven material comprises a bottom region and a top region, wherein the bottom region comprises a synthetic fabric and the top region comprises a smooth polymeric material more rigid than the bottom region. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. 
         FIG. 1  is an isometric view of a screen printing system according to one embodiment of the invention. 
         FIG. 2  is a plan view of the screen printing system illustrated in  FIG. 1  according to one embodiment of the invention. 
         FIG. 3  is an isometric view of a rotary actuator assembly according to one embodiment of the invention. 
         FIG. 4A  is an isometric view of a printing nest portion of the screen printing system according to one embodiment of the invention. 
         FIG. 4B  is a cross-sectional view of support material according to one embodiment of the invention. 
         FIG. 5A  is an isometric view of a printing nest according to one embodiment of the invention. 
         FIG. 5B  is a close-up isometric view of a region of the printing nest illustrated in  FIG. 5A  according to one embodiment of the invention. 
         FIG. 6A  is a side schematic cross-sectional view illustrating one embodiment of a printing nest according to one embodiment of the invention. 
         FIG. 6B  is a side schematic cross-sectional view illustrating one embodiment of a printing nest according to one embodiment of the invention. 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation. 
     It is to be noted, however, that the appended drawings illustrate only exemplary embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
     DETAILED DESCRIPTION 
     The present invention(s) provide an apparatus and method for processing substrates in a screen printing chamber that can deliver a repeatable and accurate screen printed pattern on one or more processed substrates. In one embodiment, the screen printing chamber is adapted to perform a screen printing process within a portion of a crystalline silicon solar cell production line in which a substrate is patterned with a desired material. In one embodiment, the screen printing chamber is a processing chamber positioned within the Rotary line tool or SoftlineTM tool available from Baccini S.p.A., which is owned by Applied Materials, Inc. of Santa Clara, Calif.. 
     Screen Printing System 
       FIGS. 1-2  illustrate a multiple screen printing chamber processing system, or system  100 , that may be used in conjunction with various embodiments of this invention. In one embodiment, the system  100  generally contains two incoming conveyors  111 , a rotary actuator assembly  130 , two screen printing heads  102 , and two outgoing conveyors  112 . Each of the two incoming conveyors  111  are configured in a parallel processing configuration so that they each can receive substrates from an input device, such as an input conveyor  113 , and transfer the substrate to a printing nest  131  coupled to the rotary actuator assembly  130 . Also, each of the outgoing conveyors  112  are configured to receive processed substrates from the printing nest  131  coupled to the rotary actuator assembly  130  and transfer each processed substrate to a substrate removal device, such as an exit conveyor  114 . The input conveyor  113  and exit conveyor  114  are generally an automated substrate handling devices that are part of a larger production line, for example the Rotary line tool or the SoftlineTM tool, that is connected to the system  100 . One will note that  FIGS. 1-4  are only intended to illustrate one possible processing system configuration that could benefit from the various embodiments described herein, and thus other conveyor configurations and other types of material deposition chambers could be used without deviating from the basic scope of the invention described herein. Examples of other system configurations that may be adapted to benefit from one or more of the embodiments described herein are further described in the commonly assigned U.S. Pat. No. 6,595,134, filed Dec. 11, 2001, and the commonly assigned U.S. patent application Ser. No. 11/590,500, filed Oct. 31, 2006, which are both incorporated by reference herein. 
       FIG. 2  is a plan view of the system  100  that schematically illustrates the position of the rotary actuator assembly  130  in which two of the printing nests  131  (e.g., reference numerals “ 1 ” and “ 3 ”) are oriented so that they can transfer a substrate  150  from each of the printing nests  131  to the outgoing conveyor  112  and each receive a substrate  150  from each of the incoming conveyors  111 . The substrate motion thus generally follows the path “A” shown in  FIGS. 1 and 2 . In this configuration the other two printing nests  131  (e.g., reference numerals “ 2 ” and “ 4 ”) are oriented so that a screen printing process can be performed on the substrates  150  that are positioned within the two screen printing chambers (i.e., screen printing heads  102  in  FIG. 1 ). Also, in this configuration, the printing nests  131  are oriented such that the direction of substrate movement on the nest is tangential to the rotary actuator assembly  131 , which is different from other commercially available systems that have a radially oriented substrate movement. A tangential orientation of the conveyors to the rotary actuator assembly  130  allows the substrates to be delivered and received from two locations, for example reference numerals “ 1 ” and “ 3 ” ( FIG. 2 ), without increasing the footprint of the system. 
     It is believed that when only one substrate is screen printed at a time, printing accuracy can remain very high, since the print head  102  only needs to be precisely aligned to a single substrate rather than two or more substrates at one time. This configuration thus is used to increase the system throughput and system uptime, without affecting the accuracy of the screen printing process. 
     The incoming conveyor  111  and outgoing conveyor  112  generally include at least one belt  116  that is able to support and transport the substrates  150  to a desired position within the system  100  by use of an actuator (not shown) that is in communication with the system controller  101 . While  FIGS. 1-2  generally illustrate a two belt  116  style substrate transferring system, other types of transferring mechanisms may be used to perform the same substrate transferring and positioning function(s) without varying from the basic scope of the invention. 
     The system controller  101  is generally designed to facilitate the control and automation of the overall system  100  and typically may include a central processing unit (CPU) (not shown), memory (not shown), and support circuits (or I/O) (not shown). The CPU may be one of any form of computer processors that are used in industrial settings for controlling various chamber processes and hardware (e.g., conveyors, detectors, motors, fluid delivery hardware, etc.) and monitor the system and chamber processes (e.g., substrate position, process time, detector signal, etc.). The memory is connected to the CPU, and may be one or more of a readily available memory, such as random access memory (RAM), read only memory (ROM), floppy disk, hard disk, or any other form of digital storage, local or remote. Software instructions and data can be coded and stored within the memory for instructing the CPU. The support circuits are also connected to the CPU for supporting the processor in a conventional manner. The support circuits may include cache, power supplies, clock circuits, input/output circuitry, subsystems, and the like. A program (or computer instructions) readable by the system controller  101  determines which tasks are performable on a substrate. Preferably, the program is software readable by the system controller  101 , which includes code to generate and store at least substrate positional information, the sequence of movement of the various controlled components, substrate inspection system information, and any combination thereof. 
     The two screen print heads  102  utilized in the system  100  may be conventional screen printing heads available from Baccini S.p.A. which are adapted to deposit material in a desired pattern on the surface of a substrate positioned on a printing nest  131  during the screen printing process. In one embodiment, the screen print heads  102  are adapted deposit a metal containing or dielectric containing material on a solar cell substrate. In one example, the substrate is a solar cell substrate that has a width between about 125 mm and 156 mm in size and a length between about 70 mm and 156 mm. 
     In one embodiment, the system  100  also contains an inspection assembly  200 , which are adapted to inspect the substrates  150  before or after the screen printing process has been performed. The inspection assembly  200  may contain one or more cameras  120  that are positioned to inspect an in-coming or processed substrate positioned in the positions “ 1 ” and “ 3 ,” as shown in  FIGS. 1 and 2 . The inspection assembly  200  generally contains at least one camera  120  (e.g., CCD camera) and other electronic components that are able to inspect and communicate the inspection results to the system controller  101  so that damaged or mis-processed substrates can be removed from the production line. In one embodiment, the printing nests  131  may each contain a lamp, or other similar optical radiation device, to illuminate a substrate  150  positioned over the support platen  138  ( FIG. 4 ) so that it can be more easily inspected by an inspection assembly  200 . 
     The inspection assembly  200  can also be used to determine the precise position of the substrates on each of the print nests  131 . The location data of each substrate  150  on each printing nest  131  can be used by the system controller  101  to position and orient the screen print head components in the screen print head  102  to improve the accuracy of the subsequent screen printing process. In this case the position of each of the print heads can be automatically adjusted to align the screen print head  102  to the exact position of the substrate positioned on the print nest  131  based on the data received during inspection process step(s). 
     In one embodiment, as shown in  FIGS. 1-3 , the rotary actuator assembly  130  contains four printing nests  131  that are each adapted to support a substrate  150  during the screen printing process performed within each of the screen print heads  102 .  FIG. 3  is an isometric view of the rotary actuator  130  that illustrates a configuration in which a substrate  150  disposed on each of the four printing nests  131 . The rotary actuator assembly  130  can be rotated and angularly positioned about the axis “B” by the use of a rotary actuator (not shown) and the system controller  101  so that the printing nests  131  can be desirably positioned within the system. The rotary actuator assembly  130  may also have one or more supporting components that facilitate the control of the printing nests  131  or other automated devices that are used to perform a substrate processing sequence in the system  100 . 
     Printing Nest Configuration 
     As illustrated in  FIG. 4A , each printing nest  131  generally has a conveyor assembly  139  that has a feed spool  135 , a take-up spool  136 , and one or more actuators (not shown), which are coupled to the feed spool  135  and/or take-up spool  136 , that are adapted to feed and retain a supporting material  137  positioned across a platen  138 . The platen  138  generally has a substrate supporting surface on which the substrate  150  and supporting material  137  are positioned during the screen printing process performed in the screen print head  102 . In one embodiment, the supporting material  137  is a porous material that allows a substrate  150 , which is disposed on one side of the supporting material  137 , on the first surface  141 A, to be retained on the platen  138  by a vacuum applied to the opposing side or second surface  141 B of the supporting material  137  by a conventional vacuum generating device (e.g., vacuum pump, vacuum ejector). In one embodiment, a vacuum is applied to vacuum ports (not shown) formed in the substrate supporting surface  138 A (see  FIGS. 6A-6B ) of the platen  138  so that the substrate can be “chucked” to the substrate supporting surface  138 A of the platen. In one embodiment, the supporting material  137  is a transpirable material that consists, for instance, of a transpirable paper of the type used for cigarettes or another analogous material, such as a plastic or textile material that performs the same function. In one example, the supporting material  137  is a cigarette paper that does not contain benzene lines. 
     Turning to  FIG. 4B , another embodiment of the supporting material  137  is illustrated. In one embodiment, the supporting material  137  comprises a non-woven material that is compliant and is adapted to support a substrate during the screen printing process. In one example, the non-woven material comprises a mix of resins and synthetic fibers. The supporting material  137  comprises a non-woven material comprising a top region and a bottom region, wherein the top region is less compliant than the bottom region. The non-woven material has a first surface  141 A adjacent to the top region and a second surface  141 B opposite the first surface and a first end  145 A and a second end  145 B, such as shown in  FIGS. 6A-6B . In one embodiment, and as discussed in greater detail below, a plurality of features may be formed on a region of the first surface which extends in a direction between the first end and the second end. The non-woven material has a thickness in a direction substantially perpendicular to the first surface to allow air or other gases to pass through when a vacuum is applied to a second surface opposite the first surface of the material. In one embodiment, the non-woven supporting material is formed from a mixture of resin and synthetic fibers that are pressed together. The resin and fibers can be formed from various natural or man made materials that are commonly used to form porous sheet like materials. In one embodiment, the top region and bottom region may each comprise separate homogenous layers, such as shown in  FIG. 4B . It should be noted that the regions may also comprise heterogeneous mixtures of materials that yield a top region that is less compliant than a bottom region. It should also be noted that although the embodiment illustrated in  FIG. 4B  and discussed below generally includes a supporting material that is formed from two different layers, this configuration is not intended to limiting as to the scope of the invention, since the top and bottom regions could be formed from the same material(s), but be further processed in such a way that the top and bottom regions have one or more different chemical and/or physical properties. 
     In one embodiment, the non-woven supporting material  137  may comprise a bottom layer  410  and a top layer  420  as shown in  FIG. 4B . The bottom layer  410  may be a soft synthetic fabric whereas the top layer  420  may be a polymeric material, such as a plastic having a flat, smooth surface. It is believed that the soft bottom layer  410  can help to compensate for any uneven surfaces found on the surface of the substrate  150  when the substrate is “chucked” to the substrate supporting surface  138 A by the vacuum generating device. It is also believed that a less compliant and/or smooth top layer  420  is useful to prevent the uneven surfaces on the substrate  150  from abrading or damaging the surface of the top layer  420 , thus increasing non-woven supporting material&#39;s useful life and preventing damage to the substrate. In general, the term compliant as used herein is used describe a material&#39;s surface hardness or its ability to resist bending or deformation due to the application of a force. This configuration can be especially useful when “ribbon” type solar cell substrates are processed using the printing nest  131 , which is discussed below. In one embodiment, the soft bottom region may be a translucent and porous material that has a cotton like texture that may be formed from a natural or a synthetic fiber. In one embodiment, the soft bottom region may be a translucent and porous material that has is formed from a polymeric material, such as polyethylene. 
     The top layer  420  of the non-woven supporting material  137  may be formed by treating the soft bottom layer  410  with a polymeric material. In one embodiment, the top layer  420  treatment may entail depositing or bonding a polyethylene material, or other similar material, over the bottom layer  410 . In one embodiment, the top layer  420  may be a translucent, porous, and less compliant than the material from which the bottom layer  410  is formed. The top layer  420  may provide a better grip of the substrate  150  whereas the bottom layer  410  may provide more of a structural support to the non-woven material. The two-layer non-woven material embodiment may have a thickness between about 40 and about 50 microns (μm). The non-woven supporting material has a porous structure that permits air or other gases to pass through the top layer  420  and bottom layer  410  so that a substrate  150  can be “chucked” to the surface of the top layer  420 . The non-woven structure may also decrease contamination of the substrate during processing by preventing chipping of raised regions formed on the surface of the substrate  150  when the substrate is “chucked” and also allow the non-woven supporting material  137  to be cleaned to prevent any loose particles generated in the screen printing system from migrating to the substrate surface. 
     Typical solar cell substrate processing techniques may stain the non-woven material with dyes, inks, polymers, etc. However, the non-woven supporting material  137  is washable rendering the non-woven supporting material  137  reusable, and thus reducing the screen printing system&#39;s cost-of-ownership (CoO). The two-layer non-woven material may have a basis weight lower than paper, thus requiring less torque to move and position the supporting material  137  over the substrate supporting surface  138 A on the screen print head  102  during the process of transporting a substrate  150 . More detail about moving the supporting material  137  across the platen  136  of the conveyor assembly  139  will be discussed below. 
     Some of the potential advantages of a supporting material  137  comprising a non-woven material may be best exhibited when ribbon wafers or substrates are used in the screen printing process to manufacture solar cells. Ribbon substrates tend to have an uneven surface due to characteristics of their manufacturing process and thus can be difficult to reliably retain during the screen printing process. For example, the surface roughness for ribbon substrates may be around  50  microns. During a typical screen printing process stress is applied to the substrate by the screen printing device components which can cause damage to the substrate, particularly when ribbon substrates that have uneven surfaces are used. It is believed that by using a two-layer non-woven supporting material, the process induced stress in the substrate  150  will be absorbed by the non-woven material, such as by the compliant bottom layer  410 . By using a non-woven material as described above, such as a two-layer non-woven polymeric material, the negative effects of an uneven substrate surface can be minimized during a screen printing process. 
     The non-woven material may also allow elastic extension, i.e. it may stretch, whereas paper type supporting material may tear more easily after use in one or more screen printing processes. If a substrate does break when using a less elastic material, such as paper, the substrate shards can easily cut the material, risking complete loss of the roll of material. Thus, less breakage of substrates may occur when using a roll of non-woven material and complete loss of the roll of supporting material is less likely should a substrate break during manufacturing. 
     The substrates  150  typically have a low mass and thus it is often difficult to precisely control the exact position of the substrate  150  when it is loaded onto the printing nest  131 . In some cases the substrate  150  may advance more than the supporting material  137  when the supporting material is moved across the platen  138 . Accurate identification of the substrate position improves screen printing accuracy and alignment during solar cell manufacturing. The top layer  420  may provide a smooth surface that has improved grip to allow better uniform support of the substrate  150  and more precise control of the exact position of the substrate  150 . This may also contribute to less substrate breakage, better force distribution on the substrate surface, and better grip during handling when compared to conventional supporting materials. Thus, non-woven supporting material  137  may provide better control of the actual wafer position when aligning the substrate in the printing nest  131  prior to screen printing. Additionally, the non-woven substrate support material is at least partially transparent for backlight illumination during the screen printing process. The non-woven material may also be configured to permit gases to pass through it with only limited lateral dispersion. As will be discussed below, marks on the support material  137  can help identify the position of the substrate during screen printing. 
     Another embodiment of the invention includes a support material  137  on a printing nest  131  used to support a substrate  150  during processing. The support material  137  comprises a porous non-woven material having two different properties. The non-woven material comprises a bottom layer  410  and a top layer  420 , wherein the bottom layer  410  comprises a soft, cotton like synthetic fabric and the top layer comprises a smooth polymeric material more rigid than the bottom layer. In one embodiment, the hardness of the surface of the top layer  420  is greater than the hardness of the material in the bottom layer  410 . 
     In one configuration, a nest drive mechanism  148  that is coupled to, or is adapted to engage with, the feed spool  135  and a take-up spool  136  so that the movement of a substrate  150  positioned on the supporting material  137  can be accurately controlled within the printing nest  131 . In one embodiment, feed spool  135  and the take-up spool  136  are each adapted to receive opposing ends of a length of the supporting material  137 . In one embodiment, the nest drive mechanism  148  contains one or more drive wheels  147  that are coupled to, or in contact with, the surface of the supporting material  137  positioned on the feed spool  135  and/or the take-up spool  136  to control the motion and position of the supporting material  137  across the platen  138 . 
       FIG. 6A  is a side schematic cross-sectional view illustrating one embodiment of a conveyor assembly  139  in a printing nest  131 . In this configuration the tension and motion of the supporting material  137  across the platen  138  is controlled by conventional actuators (not shown) in the nest drive mechanism  148  that are able to control the rotational movement of the feed spool  135  and/or the take-up spool  136 . In one embodiment as shown in  FIG. 6A , the supporting material  137  is guided and supported by a plurality of pulleys  140  as it is moved in either direction between the feed spool  135  and the take-up spool  136 . 
     One issue that arises in the transfer and positioning of substrates using a roll-to-roll type conveyor system as shown in FIGS.  4  and  6 A- 6 B is that the amount of supporting material  137  that is moved across the platen  138  due to the angular movement of the feed spool  135  or take-up spool  136  may vary thus affecting the system controller&#39;s ability to accurately and repeatably move a substrate disposed on the supporting material  137  to a desired processing position on the platen  138 . The variation in the actual position of a substrate on the platen  138  creates a need for a camera  120  in the inspection system  200  that has a field of view larger than what would be necessary to assure that all areas of a desirably aligned substrate  150  and camera  120  are viewed during the inspection process. Therefore, since the resolution of the camera is inversely related to the size of the field of view the ability of the inspection system to detect defects on the substrates and determine the substrate&#39;s position on the platen  138  is often worse than is desired. Therefore, to improve the inspection process it is desirable to minimize the variation in the processing position of substrates disposed on the platen  138  to allow a higher resolution camera to be used to better detect defects to improve device yield and the cost of ownership of the screen printing process. 
     One possible cause of variation in the position of the substrate on the supporting material  137  on the platen  138  can be caused by slippage between the actuating devices and the spool of supporting material  137  positioned on the feed spool  135  or the take-up spool  136 . To account for the variation in movement of supporting material  137  across the platen  138  it is possible to measure the diameter, or change in diameter, of one or more of the spools (e.g., feed spool  135  or the take-up spool  136 ). Alternately, it is possible to monitor the linear motion of the supporting material  137  by monitoring the rotation of one or more of the pulleys  140  or other similar supporting material  137  engaging devices. However, due to the general inaccuracy of these techniques and the possible slippage between the material engaging components (e.g., drive wheels  147 , pulleys  140 ) the positioning accuracy of a substrate on the surface of the platen  138  generally will not meet today&#39;s or future production needs. Another possible cause of the variation using these techniques is the variation in the amount of supporting material  137  that is transferred across the platen  138  per rotation of the driven feed spool  135  or the take-up spool  136  as material is transferred from one spool to another during processing. In one example, if the motion of the material across the platen  138  is controlled by the rotational motion of the take-up spool  136  then the movement of the material across the platen  138  is affected by the diameter, or amount, of supporting material  137  wound around the take-up spool  136 . Thus, the amount of supporting material  137  that passes linearly across the platen  138  will vary when the most of the supporting material  137  is wound around the feed spool  135  versus when the supporting material  137  is wound around the take-up spool  136 . Therefore, there is a need for a more direct measurement technique that is able to measure and feedback the supporting material  137  movement or position data to the system controller  101  so that the movement and position of a substrate disposed thereon can be more accurately controlled. The improved accuracy can allow a higher resolution camera  120  ( FIG. 1 ) to be used to detect defects in the incoming and/or outgoing substrates that are processed in the system  100 . The higher resolution camera can help to reduce the number of misprocessed substrates and improve the device yield. 
     Moreover, it is believed that by directly monitoring the movement of the supporting material  137 , the substrate can be conveyed at higher speeds to improve the system throughput. Higher substrate transfer speeds are generally achievable, since the increased likelihood that slippage between the supporting material  137  and the other conveyor assembly  139  components, due to the higher velocities or accelerations of the supporting material  137 , will not affect the accuracy and control of the supporting material  137  and substrate  150  ( FIG. 5A ) position on the platen  138 . 
       FIGS. 5A-5B  and  6 A- 6 B illustrate a printing nest  131  that contains a detection system  143  that is used to monitor and feedback the supporting material  137  movement and position data to the system controller  101 . In general, the movement and position of the supporting material  137  can be monitored by use of a sensor assembly  142  in the detection system  143  that is positioned to view one or more regions of the supporting material  137  that has a pattern  137 A formed thereon. The pattern  137 A of formed elements may include a regular pattern of deposited material or formed features that can be detected by the sensor assembly  142  as it passes through a detection region  142 C of the sensor assembly  142  ( FIG. 5B ). In one example, the pattern  137 A is a regular array of printed ink lines that are deposited on the surface of the supporting material  137 . In another example, the pattern  137 A is an array of embossed features in the support material  137 . In yet another example, the pattern  137 A is an array of regions of removed support material  137 , such as holes. The term holes as used herein may include but is not limited to round holes, oval holes, polygon shaped holes, slots, grooves, cuts or other similar feature that are formed in the support material  137 . 
       FIG. 5A  is an isometric view of a printing nest  131  that illustrates one embodiment of a pattern  137 A formed on one edge of the supporting material  137  and inspected by the detection system  143 .  FIG. 5B  is a close-up isometric view of the sensor assembly  142  and pattern  137 A formed on the supporting material  137 . In one embodiment, as shown in  FIGS. 5A-5B , the pattern  137 A comprises an array of equally spaced features (e.g., lines) that are disposed on or formed in the supporting material  137  that passes through and are sensed by the components in the sensor assembly  142 . 
     The sensor assembly  142  generally contains one or more components that are able monitor the movement of the pattern  137 A as it is moved by the components in the conveyor assembly  139 . The sensor assembly  142  may utilize optical monitoring techniques, capacitive measurement technique, eddy current measurement techniques, or other similar suitable technique that is able to detect the motion of a pattern  137 A or features within the pattern  137 A as it passes by the sensor assembly  142 . In one embodiment, the sensor assembly  142  includes a light source  142 A and a detector  142 B that are connected to the system controller  101 . Typically, the light source  142 A generally contains a source of some form of electromagnetic energy, such as light delivered from an LED or a laser that is directed at the surface of the supporting material  137 . Typically, the detector  142 B is conventional optical detector, such as a photoconductive sensor, thermoelectric detector, AC type optical sensor, DC type optical sensor, or other similar device that is adapted to detect the variation in intensity of the energy delivered by the light source  142 A due to the interaction of the energy with the features within pattern  137 A. 
     In one embodiment, each printing nest  131  contains two or more sensor assemblies  142  that are each positioned to detect the motion of the pattern  137 A, and are used in combination with the system controller  101  to determine the actual motion of the supporting material  137 . In one configuration, the two or more sensor assemblies  142  are positioned to monitor different portions of the pattern  137 A so that the actual position can be determined. 
     In one configuration, the shape or one or more materials in the formed pattern  137 A preferentially absorbs or reflects one or more wavelengths of light delivered from the light source  142 A that is sensed by the detector  142 B. In one case, an array of equally spaced lines of an ink material are deposited on a surface of the support material  137  which is seen as a series of signal intensity peaks and valleys by the detector  142 B and system controller  101  as the pattern  137 A is moved past the sensor assembly  142 . The system controller  101  may use the intensity peaks and valley information to determine how much support material  137  has been moved past the sensor assembly  142  or determine the actual position of a portion of the support material  137 . In some cases the shape of the features within the pattern  137 A may change from one region of the roll of support material  137  to another (i.e., start of the roll of support material to the end of the roll), thus providing some information about the actual position of a region of the support material  137  on the roll. One skilled in the art will appreciate that any known shaped or spaced pattern  137 A could be used to provide information to the system controller  101  about the supporting material and substrate movement without deviating from the basic scope of the invention described herein. Similarly, by positioning the sensor assembly  142  to view at least a portion of the surface of the substrate  150 , one or more features on the substrate  150  could also be used by the sensor assembly  142  and system controller  101  to help control the position and/or movement of the substrate and supporting material. 
       FIG. 6A  is a side cross-sectional view of the printing nest  131  that illustrates one embodiment of the sensor assembly  142  that uses reflected energy to monitor the movement of the supporting material  137  having a first surface  141 A and a second surface  141 B. The supporting material  137  also has a first end  145 A and a second end  145 B. In this configuration, the sensor assembly  142  generally consists of a light source  142 A that illuminates “B1” the detection region  142 C ( FIG. 5B ) on the supporting material  137  containing the pattern  137 A and receives an amount of reflected light “B2” at the detector  142 B that is altered by the interference or interaction with the pattern  137 A. The altered energy received by the detector  142 B due to the interaction with the pattern  137 A is fed back to the system controller  101  so that the movement and/or position of supporting material  137  can be controlled. In one case the electromagnetic energy delivered by the light source  142 A is designed to preferentially reflect from the surface of the supporting material  137  or the material from which that the pattern  137 A is formed, so that the movement of the pattern  137 A can be monitored by the system controller  101 . In another embodiment, the electromagnetic energy delivered by the light source  142 A is reflected off of the platen  138 , and thus the presence or absence of the supporting material  137  in the pattern  137 A is used to monitor the movement and/or position of the supporting material  137 . In yet another embodiment, the electromagnetic energy delivered by the light source  142 A is primarily reflected off of the platen  138  due to the opaque nature of the supporting material  137 , and thus the presence and absence of a material in the pattern  137 A (e.g., deposited ink regions) formed on the supporting material  137  surface is used to alter the reflected energy and thus provide information about the movement of the supporting material  137  past the sensor assembly  142 . In an alternate configuration, the sensor assembly  142  is positioned beneath the platen  138 , such as within the printing nest  131 . In this case, the pattern  137 A formed on a surface of the supporting material  137  may be viewed through a hole (not shown) formed in the platen  138 . 
       FIG. 6B  is a side cross-sectional view of the printing nest  131  that illustrates one embodiment of the sensor assembly  142  that uses through-beam sensor configuration to monitor the movement of the supporting material  137  having a first surface  141 A, and a second surface  141 B. The supporting material  137  also has a first end  145 A and a second end  145 B. In this configuration, the sensor assembly  142  generally consists of a light source  142 A that is positioned to provide light to a detector  142 B that is disposed on the opposite side of supporting material  137 . Therefore, the interference or interaction of the energy delivered by the light source  142 A with the pattern  137 A is received by the detector  142 B so that the movement and/or position of the material can be controlled. In one embodiment, the electromagnetic energy delivered by the light source  142 A is passed through an array of holes in the in the supporting material  137 , and thus the presence or absence of the supporting material  137  in the pattern  137 A is used to monitor the movement and/or position of the supporting material  137 . In another embodiment, the electromagnetic energy delivered by the light source  142 A primarily passes through the supporting material  137 , and thus the presence of a material in the pattern  137 A (e.g., ink) is used to alter the energy received by the detector  142 B to help provide information about the movement of the supporting material  137 . 
     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.