Patent Publication Number: US-2022228616-A1

Title: Flat head units for heavy load alignment

Description:
RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 63/139,858, filed Jan. 21, 2021, the entire contents of which are hereby incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The instant specification generally relates to electronic device fabrication. More specifically, the instant specification relates to flat head units for heavy load alignment. 
     BACKGROUND 
     An electronic device manufacturing apparatus can include multiple chambers, such as process chambers and load lock chambers. Such an electronic device manufacturing apparatus can employ a robot apparatus in the transfer chamber that is configured to transport substrates between the multiple chambers. In some instances, multiple substrates are transferred together. 
     SUMMARY 
     The following is a simplified summary of the disclosure in order to provide a basic understanding of some aspects of the disclosure. This summary is not an extensive overview of the disclosure. It is intended to neither identify key or critical elements of the disclosure, nor delineate any scope of the particular implementations of the disclosure or any scope of the claims. Its sole purpose is to present some concepts of the disclosure in a simplified form as a prelude to the more detailed description that is presented later. 
     In accordance with an embodiment, a mask frame support unit is provided. The mask frame support unit includes a case, a protruding body extending below the case, and a station having a flat head disposed above the case. The protruding body includes a tapered region and a cylindrical region. The tapered region includes a first end having a first diameter coupled to the case and comprising a second end having a second diameter opposite the first end. The second diameter is less than the first diameter, and the tapered region is coupled to the cylindrical region at the second end. The case houses a number of components including an upper receiving plate in contact with the station, a lower receiving plate disposed underneath the upper receiving plate, a flat head unit movement support mechanism disposed between the lower receiving plate and the body, and a centering component. 
     In accordance with another embodiment, an apparatus is provided. The apparatus includes a mask frame, an alignment shaft including a hollow cylinder having an opening, and a plurality of mask frame support units including a flat head unit. The flat head unit includes a case, a protruding body extending below the case and integrated into the alignment shaft via the opening, and a station having a flat head disposed above the case. The case houses a plurality of components including an upper receiving plate in contact with the station, a lower receiving plate disposed underneath the upper receiving plate, a flat head unit movement support mechanism disposed between the lower receiving plate and the body, and a centering component. 
     In accordance with yet another embodiment, a method of forming a mask frame support unit is provided. The method includes inserting an upper receiving plate and a lower receiving plate within a case, forming a centering component within the case, securing a protruding body to a bottom of the case, and securing a station having a flat head to a top of the case. The protruding body includes a tapered region and a cylindrical region. The tapered region includes a first end having a first diameter coupled to the case and comprising a second end having a second diameter opposite the first end. The second diameter is less than the first diameter, and the tapered region is coupled to the cylindrical region at the second end. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Aspects and implementations of the present disclosure will be understood more fully from the detailed description given below and from the accompanying drawings, which are intended to illustrate aspects and implementations by way of example and not limitation. 
         FIG. 1  is a perspective view of an apparatus including a flat head unit, in accordance with some embodiments. 
         FIG. 2  is a cross-sectional view of an apparatus including a flat head unit, in accordance with some embodiments. 
         FIG. 3  is a schematic diagram of a flat head unit, in accordance with some embodiments. 
         FIG. 4A  is a cross-sectional view of a flat head unit, in accordance with some embodiments. 
         FIG. 4B  is a cross-sectional view of the flat head unit of  FIG. 4A  after movement from a neutral position to an offset position, in accordance with some embodiments. 
         FIGS. 5A-5H  illustrate an example process flow of forming a flat head unit, in accordance with some embodiments. 
         FIG. 6  is a flow chart of a method for forming an apparatus including a flat head unit, in accordance with some embodiments. 
         FIGS. 7A-7C  are top-down views of a mask alignment system, in accordance with some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic device processing systems can include vision alignment technology, which can enable manufacturers to reduce production costs by reducing or eliminating photolithography and/or etch processing systems. For example, a conventional vision system can include a number of ball transfer units (BTUs) placed on the top of vision shafts to provide mask support during a vision alignment process. More specifically, each BTU includes a ball (e.g., a ceramic ball within a housing) on which a mask frame can sit to support the weight of the mask frame while still allowing for some movement of the mask frame. However, the small point of contact, or contact surface area, between the mask frame and the balls of the BTUs can result in the formation of undesirable deformations (e.g., dents) or markings (e.g., scratches) in the mask frame due to the concentrated pressure at the points of contact, particularly if the mask frame placed on the BTUs is sufficiently heavy. 
     Aspects and implementations of the present disclosure address these and other shortcomings of existing technologies by providing flat head units to provide (heavy) load alignment. For example, the flat head units described herein can be used provide load alignment while reducing or eliminating the occurrence of deformations (e.g., dents) or markings (e.g., scratches) on the load. More specifically, the flat head units described herein can provide a larger point of contact, or increased contact surface area, with the load, such as a mask frame, to enable the reduced or eliminated deformations (e.g., local deformations). The flat head units described herein can further support free range of motion of the load in the X-Y plane. For example, the flat head units described herein can be designed to move, e.g., about 7.5 millimeters (mm) from the center in any X-Y direction. To achieve such motion, the flat head units described herein can include flat head movement support mechanisms for supporting the load and enabling movement of the units. For example, the flat head units described herein can be embodied as flat head ball (FHB) units that include a set of balls disposed in a ball retainer. The flat head units described herein can further include a centering component or centering mechanism that can bring the flat head units back to the center when there is no load thereon. For example, the centering component can include a set of tension springs. 
     For the sake of simplicity and illustration, the embodiments described herein will reference embodiments in which a flat head unit is embodied having a circular surface. However, the surfaces of the flat head units described herein can have any suitable geometry to provide load alignment in accordance with the embodiments described herein. Examples of other suitable geometries for the surfaces of the flat head units include oval shape, polygonal shape (e.g., quadrilateral, hexagonal, octagonal), etc. 
     In some embodiments, a flat head unit can be implemented as a mask frame support unit within an apparatus including a mask frame. In such embodiments, the flat head unit can support the weight of a mask sheet placed thereon, thereby reducing or eliminating the occurrence of mask deformations (e.g., dents). For example, a number of flat head units can be utilized within a vision system, with each flat head unit being associated with a corresponding shaft (e.g., an idle vision shaft). Illustratively, the flat head units described herein can be implemented within electronic device processing systems including a thin-film encapsulation (TFE) system. A TFE system can be used form thin-film barriers during electronic device processing (e.g., organic light emitting diode (OLED) devices). For example, a TFE system can be used to enable the formation of flexible organic light emitting diode (OLED) devices having a thin-film barrier as a substrate material (as opposed to other materials such as glass), which can reduce cost and enable a lighter and thinner OLED display. A TFE system can be, e.g., a TFE chemical vapor deposition (CVD) (TFE CVD) system (e.g., a TFE plasma-enhanced CVD (TFE PECVD) system). 
     Aspects and implementations of the present disclosure result in technological advantages over other approaches. For example, as mentioned above, the flat head units described herein can prevent deformation and markings, and can reduce or eliminate the contact stress problem that may be present with BTUs and other similar units. Moreover, the flat head units described herein can enable mask frame movement that may be needed during mask frame alignment. The life cycle of the flat head units described herein can be greater than other units, e.g., BTUs with the same load and test conditions. For example, the flat head units described herein can be designed for a load of, e.g., about 100 kilograms (kg) at a temperature of, e.g., about 80° C. Accordingly, the flat head units described herein, when implemented as mask frame support units, can provide improved mask frame and/or vision alignment accuracy as compared to other units, e.g., BTUs. 
       FIG. 1  is a perspective view of an apparatus  100 , in accordance with some embodiments. In some embodiments, the apparatus  100  is included within a vision system of a thin-film encapsulation (TFE) system. Such embodiments should not be considered limiting, however, and the apparatus  100  can be implemented within any suitable system in accordance with the embodiments described herein. 
     As shown, the apparatus  100  includes a flat head unit (“unit”)  110 , a susceptor body  120  and an alignment shaft  130 . More specifically, as will be described in further detail herein, the unit  110  can be integrated into, or mated with, the alignment shaft  130  via an opening of the alignment shaft  130 . Any suitable mechanism can be used to integrate the unit  100  into the alignment shaft  130  in accordance with the embodiments described herein. 
     As will be described in further detail below with respect to  FIG. 2 , the unit  110  can provide support for a mask frame. That is, the unit  110  can be implemented as a mask frame support unit. For example, the unit  110  can be a TFE mask frame support unit. As will be described in further detail herein below, the unit  110  has a geometry designed to support the weight of a mask including the mask frame and a mask sheet in a manner that can reduce contact stress and thus reduce or eliminate mask deformation. For example, in this illustrative embodiment, the unit  110  has a circular surface. Further details regarding the unit  110  will now be described below with reference to  FIG. 2 . 
       FIG. 2  is a cross-sectional view of an apparatus  200 , in accordance with some embodiments. The apparatus  200  includes an alignment shaft  210  and a flat head unit (“unit)” integrated into, or mated with, the alignment shaft  210 . For example, the alignment shaft  210  can be an idle vision shaft of a vision system. The unit  220  includes a protruding body (“body”)  222 , a case  224 , and a station  226 . 
     As will be described in further detail herein, the body  222  includes a tapered region and a cylindrical region. The tapered region includes a first end having a first diameter coupled to the case  224  and includes a second end having a second diameter opposite the first end. The second diameter is less than the first diameter, and the tapered region is coupled to the cylindrical region at the second end. 
     As will be described in further detail herein, the case  224  houses a number of components including an upper receiving plate in contact with the station, a lower receiving plate disposed underneath the upper receiving plate, a flat head unit movement support mechanism disposed between the lower receiving plate and the body, and a centering component. 
     In this illustrative embodiment, the case  224  is a circular case and the station  226  has a circular flat head. The station  226  can have substantially free movement (e.g., X-Y movement) around the center by virtue of components formed within the case  224 , as will be described in further detail below with reference to  FIGS. 4A-4B . As further shown, one end of a mask frame  230  is placed on the station  226 . The apparatus  200  can include one or more other units (not shown) to support the mask frame  230 . Further details regarding the unit will now be described below with reference to  FIGS. 3 and 4 . 
       FIG. 3  is a schematic diagram showing dimensions of a flat head unit (“unit)  300 , in accordance with some embodiments. As shown, the unit  300  includes a protruding body (“body”)  310 , a case  320 , and a station  330  having a lower portion  332  and an upper portion  334 . The body  310  can be integrated within, or mated to, an opening within a shaft including a hollow cylinder. In some embodiments, the shaft is an alignment shaft of a vision system for mask frame alignment. 
     More specifically, the body  310  can include a cylindrical region  312  and a tapered region  314 . The tapered region  314  includes a first end  317 - 1  having a first diameter coupled to the case  320  and includes a second end  317 - 2  having a second diameter opposite the first end. The second diameter is less than the first diameter. The tapered region  314  is coupled to the cylindrical region  312  at the second end  317 - 2 . 
     The station  330  can be a moveable station with substantially free movement around the center. In this illustrative embodiment, the case  320  is a circular case and the station  330  has a circular flat head. 
     A distance from the left outside edge of the lower portion  332  to the left outside edge of the case  320 , “L1”, can be, e.g., between about 7 millimeters (mm) and about 8 mm. More specifically, L1 can be, e.g., about 7.5 mm. 
     Similarly, a distance from the right outside edge of the lower portion  332  to the right outside edge of the case  320 , “L2”, can be, e.g., between about 7 mm and about 8 mm. More specifically, L2 can be, e.g., about 7.5 mm. 
     A distance between the left and right outside edges of the lower portion  332 , “L3” (which also corresponds to a length of the lower portion  332  and a length of the station  330 ), can be, e.g., between about 52 mm and about 60 mm. More specifically, L3 can be, e.g., about 56 mm. 
     A length of the upper portion  334 , “L4”, can be, e.g., between about 35 mm and about 45 mm. More specifically, L4 can be, e.g., about 39 mm. 
     A height of the station  330 , “L5”, can be, e.g., between about 10 mm and about 16 mm. More specifically, L5 can be, e.g., about 13 mm. 
     A height of the upper portion  334 , “L6”, can be, e.g., between about 0.5 mm and about 4 mm. More specifically, L6 can be, e.g., about 2 mm. Accordingly, the height of the lower portion  332  (L5-L6) can be, e.g., between about 9.5 mm and about 12 mm, and more specifically, e.g., about 11 mm. 
     A length of the case  320 , “L7”, can be, e.g., between about 65 mm and about 75 mm. More specifically, L7 can be, e.g., about 70 mm. 
     A combined height of the case  320  and the station  330 , “L8”, can be, e.g., between about 44 mm and about 52 mm. More specifically, L8 can be, e.g., about 47.75 mm. Accordingly, the height of the case  320  (L8−L5) can be, e.g., between about 34 mm and about 36 mm, and more specifically, e.g., about 34.75 mm. 
     A height of the tapered region  314 , “L9”, can be, e.g., between about 12 mm and about 22 mm. More specifically, L9 can be, e.g., about 17.1 mm. 
     A height of the cylindrical region  312 , “L10”, can be, e.g., between about 18 mm and about 28 mm. More specifically, L10 can be, e.g., about 23 mm. Thus, a height of the body  310  (L9+L10) can be, e.g., between about 30 mm and about 50 mm, and more specifically, e.g., about 40.1 mm. Accordingly, a total height of the unit  300  (L8+L9+L10) can be, e.g., between about 74 mm and about 102 mm, and more specifically, e.g., about 87.85 mm. 
     As further shown, the cylindrical region  312  includes a plurality of edges including edge  316 . For example, the dimensions of the edge  316  can include a length of, e.g., between about 17 mm and about 27 mm, and a width of, e.g., between about 1 mm and about 4 mm. More specifically, the dimensions of the edge  316  can include a length of, e.g., about 22 mm and a width of, e.g., about 2.5 mm. 
     As further shown, the tapered region  314  includes a first upper edge  318 - 1  and a second upper edge  318 - 2 . An angle between the first upper edge  318 - 1  and the second upper edge  318 - 2 , “A”, can be, e.g., between about 80° and about 100°. More specifically, A can be, e.g., about 90°. 
     A length of the body  310  measured between the contact point of the first upper edge  318 - 1  to the case  320  and the contact point of the second upper edge  318 - 2  to the case  320 , “L11”, can be, e.g., between about 31.2 mm and about 41.2 mm. More specifically, L11 can be, e.g., about 36.2 mm. 
       FIG. 4A  is a cross-sectional view of a flat head unit (“unit”)  400 , in accordance with some embodiments. In this illustrative example, the unit  400  is embodied as a flat head ball (FHB) unit, in which the flat head unit movement support mechanism includes a set of balls. However, such embodiments should not be considered limiting. 
     As shown, the unit  400  includes a protruding body (“body”)  1 , a case  2  and a station  4 . As will be described in further detail below, the station  4  has a flat head with substantially free movement around the center (e.g., X-Y movement). In this illustrative embodiment, the case  2  is a circular case and the station  4  has a circular flat head. The body  1  can be integrated within, or mated to, an opening within a shaft including a hollow cylinder. In some embodiments, the shaft is an alignment shaft of a vision system for mask frame alignment. 
     The case  2  houses a number of components. For example, the case  2  houses a lower receiving plate  3 , a station  4 , a ball retainer  5 , a center structure  6 , a spring loaded flange  7 , an upper receiving plate  8 , a first screw  9 , a number of second screws including screw  10  (not visible in the cross-section), a number of third screws including screw  11 , a number of balls including ball  12  and a number of tension springs including tension spring  13 . More specifically, the second screws can include 2 screws, the third screws can include 3 screws, the balls can include 9 balls, and the tension springs can include 3 tension springs. 
     The station  4  is mounted into the upper receiving plate  8  and the lower receiving plate  3  with the second screws including screw  10 . The lower receiving plate  3  can sit inside a pocket within the upper receiving plate during assembly. The first screw  9  is inserted through the plates  3  and  8  and the center structure  6  to secure the plates  3  and  8  within the unit  400 . 
     The balls are used to support the load of the mask placed on the unit  400  and support movement of the unit  400 , and the ball retainer  5  is used to assure the location of the each of the balls in all situations. The spacing of the balls provides an approximately even distribution of a load placed on the unit  400 . More specifically, as will be described in further detail below with reference to  FIGS. 5A-5H , the respective sets of the balls are placed on the body  1  in respective regions between respective ones of the tension springs. For example, if the balls include 9 balls and the tension springs includes 3 springs, a first set of 3 balls can be placed in a first region (e.g., sector) defined between a first tension spring and a second tension spring, a second set of 3 balls can be placed in a second region defined between the second tension spring and a third tension spring, and a third set of 3 balls can be placed in a third region defined between the third tension spring and the first tension spring. Accordingly, in this illustrative embodiment, the unit  400  is a flat head ball (FHB) unit, in which the flat head unit movement support mechanism includes a set of balls. 
     The tension springs are part of a centering component or centering mechanism that brings the station  4  back to the center when there is no load on the unit  400 , as shown in  FIG. 4A . For example, as will be described in further detail below with reference to  FIGS. 5A-5H , each of the tension springs can have one end attached to the a centering ring of the center structure  6  using the spring loaded flange  7  and another end attached to the case  2 . For example, if there are 3 tension springs, each of the 3 tension springs can be placed at about a 120° angle relative to each other. Further details regarding the configuration of the tension springs within the unit  400  will be described below with reference to  FIGS. 5A-5H . 
     In this illustrative embodiment, the centering component is implemented using tension springs. However such an embodiment should not be considered limiting. For example, a magnetic-based mechanism can be used instead of the tension springs to bring the station  4  back to the center when there is no load on the unit  400 . 
     The case  2  is connected to the body  1  using the plurality of third screws including screw  11 . The body  1  can have a suitable thread feature for easy replacement of another mask frame support unit (e.g., BTU) with the unit  400 . 
     The components of the unit  400  can be formed from any suitable material(s) in accordance with the embodiments described herein. For example, the components  1 ,  3  and  4  can illustratively be formed from a suitable ceramic material. In some embodiments, the ceramic material can be aluminum oxide or alumina (Al 2 O 3 ). However, such embodiments should not be considered limiting. 
     The components  2  and  5 - 11  can be formed from an alloy or other suitable material. In some embodiments, the alloy is an aluminum (Al) alloy. For example, the Al alloy can be a 6061 Al alloy (e.g., a 6061-T6 Al alloy). 
     The plurality of balls, including ball  12 , can be formed from any suitable material in accordance with the embodiments described herein. For example, the plurality of balls can be formed from a ceramic material. In some embodiments, the plurality of balls can be formed from zirconium dioxide or zirconia (ZrO 2 ). Each of the plurality of balls can have a diameter of, e.g., between about 4 mm and about 8.5 mm. More specifically, each of the plurality of balls can have a diameter of, e.g., about 6.35 mm (or 0.25 inch). Further details regarding the configuration of the plurality of balls will be described below with reference to  FIGS. 5A-5H . 
     The plurality of tension springs can be formed from a suitable material (e.g., alloy) that has excellent mechanical strength, particularly at high temperatures, and is highly resistant to corrosive and/or oxidative effects. In some embodiments, the plurality of tension springs can be formed from a suitable nickel alloy. One example of a suitable nickel alloy is a nickel-molybdenum alloy. For example, the plurality of tension springs can be formed from a suitable nickel-molybdenum-chromium alloy. Such a nickel-molybdenum-chromium alloy can include a small amount of tungsten to provide additional corrosion-resistant properties. 
     The first screw  9 , the second screws including screw  10 , and the third screws including screw  11  can each have any suitable dimensions in accordance with the embodiments described herein. For example, the first screw  9  can have a diameter of, e.g., between about 2.5 mm and about 3.5 mm and a length of, e.g., between about 16 mm and about 20 mm (e.g., an M3×18 mm screw), the second screw  10  can have a diameter of, e.g., between about 3.5 mm and about 4.5 mm and a length of, e.g., between about 13 mm and about 17 mm (e.g., an M4×15 mm screw), and the third screw  11  can have a diameter of, e.g., between about 2.5 mm and about 3.5 mm and a length of, e.g., between about 4 mm and about 8 mm (e.g., an M3×6 mm screw). 
     The first screw  9 , the second screws including screw  10 , and the third screws including screw  11  can be formed from any suitable material in accordance with the embodiments described herein. One example of a suitable material is anodized Al. However, other similarly suitable materials are contemplated. 
     In  FIG. 4A , the unit  400  is in a neutral position in which a center position of the station  4 , the lower receiving plate  3 , the upper receiving plate  8 , etc., denoted by line A-A′, is collinear with a center position of the body  1 , denoted by line B-B′. However, as will be described below with reference to  FIG. 4B , line A-A′ can move in a direction away from the center position (e.g., in any X-Y direction) in response to a load placed on the unit  400 . 
       FIG. 4B  is another cross-sectional view of the unit  400  after a movement from the neutral position shown in  FIG. 4A  to an offset position. More particularly, in this illustrative example, the line A-A′ has moved to the right relative to the line B-B′ by at most a maximum distance “L.” In other embodiments, the line A-A′ can move to the left relative to the line B-B′ by at most the maximum distance L. In other embodiments, the line A-A′ can move “forward” or “backward” relative to the line B-B′ (e.g., into the page or out of the page) by at most the maximum distance L. Accordingly, the line A-A′ can move away from line B-B′ in any suitable X-Y direction by a distance of at most L. Upon removal of the load on the unit  400 , the centering component including the plurality of tension springs can revert the unit  400  from the offset position shown in  FIG. 4B  back to the neutral position shown in  FIG. 4A . That is, the centering component can automatically realign line A-A′ with line B-B′. 
     The maximum distance L is defined by the dimensions of the unit  400 , as described in further detail above with reference to  FIG. 3 . For example, in some embodiments, the maximum distance L is, e.g., about 7.5 mm from the center position, such that the unit  400  can move up to about 7.5 mm from the center position in any X-Y direction. 
       FIGS. 5A-5H  depict a process flow of fabricating a flat head unit  500 , in accordance with some embodiments. The flat head unit  500  can be a mask frame support unit for supporting a mask frame. In this illustrative embodiments, the flat head unit  500  is a flat head ball (FHB) unit. However, such embodiments should not be considered limiting. 
       FIG. 5A  shows a bottom view of the flat head unit  500  including a case  502 . An upper receiving plate  504  will be inserted within the region  503  defined within the top of the case  502 . The case  502  and the upper receiving plate  504  are similar to the cases and upper receiving plates described above with reference to  FIGS. 4A-4B . 
       FIG. 5B  shows the insertion of the upper receiving plate  504 , the insertion of a lower receiving plate  506  on the upper receiving plate  504 , and a ball retainer  508  that will be placed on the lower receiving plate  506 . The lower receiving plate  506  and the ball retainer  508  are similar to the lower receiving plate and the ball retainer described above with reference to  FIGS. 4A-4B . 
       FIG. 5C  shows the placement of the ball retainer  508  on the upper receiving plate  506 , the placement of a set of tension springs including tension spring  510  between respective gaps of the baller retainer  508 , and a centering ring  512  to be placed in the region  509  defined by the ball retainer  508 . The set of tension springs including tension spring  510  and the centering ring  512  are similar to the set of tension springs and the centering ring described above with reference to  FIGS. 4A-4B . 
       FIG. 5D  shows the attachment of the centering ring  512  to each tension spring of the set of tension springs within the region  509 , and a center pin  514  to be placed within the centering ring  512  to form a centering component or mechanism. The centering component is similar to the centering component described above with reference to  FIGS. 4A-4B . 
       FIG. 5E  depicts a top view of the flat head unit  500 , which shows a bolt or screw  518  that will be placed through a hole  519  disposed within a top of the case  502  to secure the center pin  514 . The screw  518  is similar to the first screw described above with reference to  FIGS. 4A-4B . 
       FIG. 5F  reverts back to a bottom view of the flat head unit  500 , which shows a set of balls including ball  520  each inserted within a respective location of the ball retainer  508 . In this illustrative embodiment, the set of balls includes 9 balls. As further shown, the end of the screw  518  can be visible and flush with respect to the center pin  514 . The set of balls including ball  520  is similar to the set of balls described above with reference to  FIGS. 4A-4B . 
       FIG. 5G  shows a protruding body (“body”)  522  secured to the bottom of the case  502  via a plurality of bolts or screws including bolt or screw  524 . The body  522  and the plurality of bolts or screws including bolt or screw  524  are similar to the body and the plurality of third screws, respectively, described above with reference to  FIGS. 4A-4B . As shown, the body  522  includes a tapered region  523  and a cylindrical region  525 . 
       FIG. 511  depicts a top view of the flat head unit  500 , which shows a station  526  secured to the top of the case  502  with screws including a screw  528 . The station  526  is similar to the station and the screws including screw  528  are similar to the plurality of second screws, respectively, described above with reference to  FIGS. 4A-4B . 
     The body  522  can be integrated into, or mated with, an opening within a hollow cylinder. In some embodiments, the hollow cylinder is an alignment shaft of a vision system for mask frame alignment. In this illustrative embodiment, cylindrical region  525  is designed with threads, such that the body  522  can be integrated into the hollow cylinder using a threaded locking mechanism (e.g., “screwed into” the hollow cylinder). However, any suitable integration mechanism can be used to integrate the body  522  within the hollow cylinder in accordance with the embodiments described herein. 
       FIG. 6  depicts a flow diagram of a method  600  of integrating a mask frame support unit within a mask alignment system, in accordance with some embodiments. For example, the unit assembly can be similar to the unit described above with reference to  FIGS. 2-5 . 
     At block  602 , a mask frame support unit having a flat head is formed. In some embodiments, the mask frame support unit is a flat head ball (FHB) unit. For example, the mask frame support unit can be formed in accordance with the process flow described above with reference to  FIGS. 5A-5H . 
     At block  604 , the mask frame support unit is installed within a mask alignment system. Installing the mask frame support unit can include integrating a protruding body of the mask frame support unit into an opening of an alignment shaft including a hollow cylinder. More specifically, the alignment shaft can be an idle vision shaft. 
     At block  606 , a mask frame is placed on the mask frame support unit. The mask frame support unit can support the weight of the mask frame while reducing or eliminating dents or other deformations. The mask frame support unit can also include a centering component or mechanism to enable movement of the mask frame. For example, upon removal of the mask, centering component can cause the flat head unit to re-center itself. 
     Further details regarding the method  600 , including the flat head unit and the mask frame, are described above with reference to  FIGS. 1-5 . 
       FIGS. 7A-7C  are top-down views of a mask alignment system  700 , in accordance with some embodiments. For example, the  700  can include a vision system. 
       FIG. 7A  shows an overview of the system  700 . As shown, the system  700  includes a chamber body  710 , a plurality of flat head units  720 - 1  through  720 - 6 , a plurality of ball transfer units (BTUs)  730 - 1  and  730 - 2 , and a mask frame  740  placed on the plurality of flat head units  720 - 1  through  720 - 6  and the plurality of BTUs  730 - 1  and  730 - 2 . Although 6 flat head units and 2 BTUs are shown, any suitable number of flat head units and/or BTUs can be used in accordance with the embodiments described herein. In some embodiments, the plurality of flat head units  720 - 1  through  720 - 6  include flat head ball (FHB) units. A region  750  corresponding to the flat head unit  720 - 1  and a region  760  corresponding to the BTU  730 - 1  are also depicted. A patterned mask sheet can be used to cover an area of a substrate during, e.g., a coating process. 
       FIG. 7B  shows a blown-up view of the system  700  corresponding to region  750  shown in  FIG. 7A .  FIG. 7C  shows a blown-up view of the system  700  corresponding to region  760  shown in  FIG. 7B . 
     The preceding description sets forth numerous specific details such as examples of specific systems, components, methods, and so forth, in order to provide a good understanding of several embodiments of the present invention. It will be apparent to one skilled in the art, however, that at least some embodiments of the present invention may be practiced without these specific details. In other instances, well-known components or methods are not described in detail or are presented in simple block diagram format in order to avoid unnecessarily obscuring the present invention. Thus, the specific details set forth are merely exemplary. Particular implementations may vary from these exemplary details and still be contemplated to be within the scope of the present invention. 
     Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrase “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. In addition, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or.” When the term “about” or “approximately” is used herein, this is intended to mean that the nominal value presented is precise within ±10%. 
     Although the operations of the methods herein are shown and described in a particular order, the order of the operations of each method may be altered so that certain operations may be performed in an inverse order or so that certain operation may be performed, at least in part, concurrently with other operations. In another embodiment, instructions or sub-operations of distinct operations may be in an intermittent and/or alternating manner. 
     It is to be understood that the above description is intended to be illustrative, and not restrictive. Many other implementation examples will be apparent to those of skill in the art upon reading and understanding the above description. Although the present disclosure describes specific examples, it will be recognized that the systems and methods of the present disclosure are not limited to the examples described herein, but may be practiced with modifications within the scope of the appended claims. Accordingly, the specification and drawings are to be regarded in an illustrative sense rather than a restrictive sense. The scope of the present disclosure should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.