Patent Publication Number: US-10774588-B2

Title: Cluster tool system with step ladder assembly

Description:
FIELD OF THE INVENTION 
     Implementations of the present disclosure relates to a step ladder for use in a fabrication facility, and related apparatus and systems. 
     DESCRIPTION OF THE RELATED ART 
     As space in semiconductor fabrication facilities is costly, manufacturers have sought to maximize space utilization by installing tools and equipment in close proximity to each other. However, access to equipment in fabrication facilities often requires workers to use ladders in order to reach elevated positions. Such ladders must be carried by workers around the fabrication facility floor and due to the tight spacing in the facility, this can be cumbersome and also poses the risk of collisions with equipment and potentially unwanted particulate generation. 
     SUMMARY 
     Implementations of the present disclosure provide a step ladder for use in a fabrication facility. The step ladder is configured to enable an operator to access equipment in the fabrication facility to, for example, monitor or service such equipment. The step ladder is mounted to a side of a module in the fabrication facility, and capable of being rotated/flipped up and over the module, thereby stowing the ladder above the module and providing access to areas beneath the module. The step ladder can be gas spring assisted, to facilitate raising the step ladder from the fabrication facility floor, and further can be held in place by over center gas spring geometry when raised and inverted over the module to which it is attached. Safety pins can also be used to lock the step ladder in place. 
     In some implementations, a ladder assembly is provided, including the following: a mounting plate that connects to a side surface of a module that handles, transfers, stores, and/or processes substrates in a fabrication facility; a step ladder, including, a ladder frame having an arm that connects to the mounting plate at a first joint, wherein the step ladder rotates about the first joint between a lowered position and a raised position, the lowered positioned defined by resting of the step ladder on a floor of the fabrication facility, and the raised position defined by suspension of the step ladder off of the floor and substantially over the module, wherein rotation of the step ladder from the lowered position to the raised position includes a movement of a center of gravity of the step ladder through a vertical plane that intersects an axis of rotation of the first joint; a plurality of step plates connected to the ladder frame, the step plates defining step surfaces for a user when the step ladder is in the lowered position. 
     In some implementations, rotation of the step ladder from the lowered position to the raised position includes a movement of the center of gravity of the step ladder from a location that is lateral to the module to a location that is over the module. 
     In some implementations, the ladder assembly further includes a gas spring connected between the mounting plate and the arm, the gas spring configured to exert an extension force that reduces an amount of force required to lift the step ladder from the lowered position to the raised position. 
     In some implementations, the extension force resists rotation of the step ladder towards the lowered position when the step ladder is in the raised position, and wherein the extension force resists rotation of the step ladder towards the raised position when the step ladder is in the lowered position. 
     In some implementations, as the step ladder rotates between the lowered position and the raised position, the gas spring rotates about a second joint that connects the gas spring and the mounting plate, wherein the second joint is horizontally offset from the first joint that connects the arm to the mounting plate. 
     In some implementations, as the step ladder rotates from the lowered position towards the raised position, the extension force of the gas spring rotates about the second joint, from being directed towards a first side of the first joint, through being directed towards and aligned with the first joint, to being directed towards a second side of the first joint that is opposite the first side of the first joint. 
     In some implementations, the arm includes a main length and a connector defined along the main length, the connector forming the second joint with the gas spring at a location that is offset from the main length of the arm. 
     In some implementations, the mounting plate includes a central opening that provides visibility access to a viewing window defined along the side surface of the module. 
     In some implementations, the ladder assembly further includes a sleeve connected to the ladder frame, the sleeve extending below one of the step plates of the step ladder, the sleeve configured to house electronic equipment used in the fabrication facility. 
     In some implementations, the one of the step plates below which the sleeve extends is defined from a substantially transparent material that allows viewing of the electronic equipment. 
     In some implementations, the electronic equipment includes at least one power supply for a process module in the fabrication facility. 
     In some implementations, the module is a buffer module that stores substrates. 
     In some implementations, a ladder assembly is provided, including the following: a mounting plate that connects to a side surface of a module that handles, transfers, stores, and/or processes substrates in a fabrication facility; a step ladder, including, a ladder frame having an arm that connects to the mounting plate at a first joint, wherein the step ladder rotates about the first joint between a lowered position and a raised position, the lowered positioned defined by resting of the step ladder on a floor of the fabrication facility, and the raised position defined by suspension of the step ladder off of the floor and substantially over the module, wherein rotation of the step ladder from the lowered position to the raised position includes a movement of a center of gravity of the step ladder through a vertical plane that intersects an axis of rotation of the first joint; a plurality of step plates connected to the ladder frame, the step plates defining step surfaces for a user when the step ladder is in the lowered position; a sleeve connected to the ladder frame, the sleeve extending below one of the step plates of the step ladder, the sleeve configured to house electronic equipment used in the fabrication facility; a gas spring connected between the mounting plate and the arm, the gas spring configured to exert an extension force that reduces an amount of force required to lift the step ladder from the lowered position to the raised position. 
     In some implementations, the extension force resists rotation of the step ladder towards the lowered position when the step ladder is in the raised position, and wherein the extension force resists rotation of the step ladder towards the raised position when the step ladder is in the lowered position. 
     In some implementations, as the step ladder rotates between the lowered position and the raised position, the gas spring rotates about a second joint that connects the gas spring and the mounting plate, wherein the second joint is horizontally offset from the first joint that connects the arm to the mounting plate. 
     In some implementations, as the step ladder rotates from the lowered position towards the raised position, the extension force of the gas spring rotates about the second joint, from being directed towards a first side of the first joint, through being directed towards and aligned with the first joint, to being directed towards a second side of the first joint that is opposite the first side of the first joint. 
     In some implementations, the arm includes a main length and a connector defined along the main length, the connector forming the second joint with the gas spring at a location that is offset from the main length of the arm. 
     In some implementations, the mounting plate includes a central opening that provides visibility access to a viewing window defined along the side surface of the module. 
     In some implementations, the one of the step plates below which the sleeve extends is defined from a substantially transparent material that allows viewing of the electronic equipment. 
     In some implementations, the electronic equipment includes at least one power supply for a process module in the fabrication facility. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a ladder assembly for use in a fabrication facility, in accordance with implementations of the disclosure. 
         FIG. 2A  is an overhead view conceptually illustrating a cluster tool system for processing substrates in a fabrication facility, in accordance with implementations of the disclosure. 
         FIG. 2B  is a perspective view of a portion of the cluster tool system in accordance with the implementation of  FIG. 2A , showing the step ladder in a lowered position, in accordance with implementations of the disclosure. 
         FIG. 2C  is a perspective view of a portion of the cluster tool system in accordance with the implementation of  FIG. 2A , showing the step ladder in a raised position, in accordance with implementations of the disclosure. 
         FIG. 3  is a perspective view of the ladder assembly showing the step ladder  100  in a raised position, in accordance with implementations of the disclosure. 
         FIG. 4A  illustrates a side view of an upper portion of the ladder assembly, in accordance with implementations of the disclosure. 
         FIG. 4B  illustrates a side view of the ladder assembly showing the step ladder  100  in a raised position, in accordance with implementations of the disclosure. 
         FIG. 5  illustrates a side view of the ladder assembly, showing the forces and resulting moments acting on the step ladder during operation, in accordance with implementations of the disclosure. 
         FIG. 6  is a graph illustrating the force required by an operator when lifting the step ladder from the lowered position to the raised position, demonstrating the effect of the gas springs of the ladder assembly, in accordance with implementations of the disclosure. 
         FIG. 7  is a perspective view of an upper portion of the step ladder  100 , in accordance with implementations of the disclosure. 
         FIG. 8  is a close-up view of the mounting plate  102 , in accordance with implementations of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous specific details are set forth to provide a thorough understanding of the presented embodiments. The disclosed embodiments may be practiced without some or all of these specific details. In other instances, well-known process operations have not been described in detail to not unnecessarily obscure the disclosed embodiments. While the disclosed embodiments will be described in conjunction with the specific embodiments, it will be understood that it is not intended to limit the disclosed embodiments. 
       FIG. 1  is a perspective view of a ladder assembly for use in a fabrication facility, in accordance with implementations of the disclosure. The ladder assembly includes a mounting plate  102  that mounts to a side surface of a module used in the processing of substrates in a fabrication facility, and a step ladder  100  that is connected to the mounting plate. The step ladder  100  further includes a ladder frame  104  that connects to the mounting plate  102  via a pair of connecting arms. In some implementations, the width (side-to-side) of the ladder frame  104  is approximately 0.3 to 1 meters. In some implementations, the width of the ladder frame is approximately 0.4 to 0.7 meters. In some implementations, the width of the ladder frame is approximately 0.5 meters. 
     More specifically, the ladder frame  104  includes a left arm  106   a  and a right arm  106   b . The left arm  106   a  is connected to the mounting plate  102  at a left hinge joint  108   a  (or revolute joint or pin joint). The right arm  106   b  is connected to the mounting plate  102  at a right hinge joint  108   b . It will be noted that the hinge joints establish an axis of rotation for the step ladder  100 , and that the step ladder  100  rotates about the hinge joints between a lowered position and a raised position. In the illustrated implementation, the step ladder  100  is shown in the lowered position. 
     The mounting plate  102  includes a central opening  103  that provides visibility access through the mounting plate. This is useful to, for example, enable viewing of a window that is on the side of the module to which the mounting plate  102  is connected. 
     The lateral portions of the ladder frame  104  include upper and lower side rails. A left upper side rail  110   a  is shown, as well as a right upper side rail  110   b . A left lower side rail  112   a  and a right lower side rail  112   b  are also shown. The lower two steps/rungs of the step ladder  100  are defined substantially between the upper side rails. In the illustrated implementation, the step ladder  100  includes four steps/rungs. The lower two steps are defined by step plates  114   a  and  114   b , which define step surfaces for a user to stand on. The step plates  114   a  and  114   b  are connected to the left and right upper side rails  110   a  and  110   b  as shown, e.g. by a plurality of screws or other fasteners. In some implementations, the depth of each of the lower steps is approximately 10 to 25 centimeters. In some implementations, the depth of each of the lower steps is approximately 15 to 20 centimeters. In some implementations, the depth of each of the lower steps is approximately 17 to 18 centimeters. 
     The ladder frame  104  further includes step frames  116   a  and  116   b , and connecting vertical side rails  117   a  and  117   b . A third step of the step ladder  100  is framed by the step frame  116   a  that defines a perimeter of the third step. Similarly, a fourth step of the step ladder  100  is framed by the step frame  116   b  that defines a perimeter of the fourth step. Step surfaces of the third and fourth steps (the upper steps) of the step ladder  100  are further defined by step plates  114   c  and  114   d , respectively, that are respectively disposed in and surrounded by the step frames  116   a  and  116   b . In the illustrated implementation, the step frames corresponding to the third and fourth steps substantially define the elevation contour of these steps. In some implementations, the depth of each of the upper steps is approximately 15 to 25 centimeters. In some implementations, the depth of each of the upper steps is approximately 20 centimeters. In some implementations, the depth of the upper steps is sized to accommodate a predefined number of power supplies, e.g. four power supplies. 
     The front corners of the step frame  116   a  are connected to the upper ends of the upper side rails  110   a  and  110   b . A pair of vertical side rails  117   a  and  117   b  are connected between the rear corners of the step frame  116   a  and the front corners of the step frame  116   b . The vertical side rails  117   a  and  117   b  define the elevation change between the third and fourth steps of the step ladder. 
     It will further be noted that the step plates  114   c  and  114   d  as shown are defined from a substantially transparent or translucent material that enables viewing of equipment stored underneath these third and fourth steps of the step ladder. The step plates  114   c  and  114   d  thus act as covers for the electronic equipment as well as step surfaces, thereby protecting the electronic equipment when users step/stand on the third or fourth steps of the step ladder  100 . 
     A sleeve  118   a  extends below the step frame  116   a  and/or the step plate  114   c , and is configured to house electronic equipment. In some implementations, the sleeve  118   a  is connected to the step frame  116   a . In some implementations, the electronic equipment is for one or more modules that are used in the processing of substrates in the fabrication facility. In some implementations, the electronic equipment can include power supplies for process chambers. 
     A second sleeve  118   b  extends below the step frame  116   b  and/or the step plate  114   d , and is also configured to house electronic equipment. In some implementations, the sleeve  118   b  is connected to the step frame  116   b . The sleeves  118   a  and  118   b  which are defined below the third and fourth steps of the step ladder provide an accessible storage location for electronic equipment. In some implementations, the sleeves  118   a  and  118   b  are formed from sheet metal. Electronic equipment that is housed by the sleeves can be secured to the sleeves, for example, via brackets, screws, and/or other hardware. In some implementations, power supplies are grounded through the sleeve, e.g. through a bracket or mounting flange of the sleeve. 
     The sleeves can define a component rack system in accordance with standard component mounting systems. In some implementations, the sleeves  118   a  and/or  118   b  are sized and configured to provide a standard 19 inch (482.6 mm) width rack mount system. In some implementations, a given sleeve can accommodate four rack-units (1.75 inches (44.45 mm) thickness per rack-unit). 
     The step ladder  100  includes feet  120   a  and  120   b  that are configured to contact the floor of the fabrication facility when the step ladder  100  is in the lowered position. 
     It will be appreciated that the various components of the ladder assembly can be defined from any suitable material known in the art, including, without limitation, metals, alloys, plastics, aluminum, stainless steel, etc. Also, the components of the ladder assembly can be connected to each other by any suitable technique, including without limitation, screws, bolts, pins, clips, welds, clamps, etc. 
       FIG. 2A  is an overhead view conceptually illustrating a cluster tool system for processing substrates in a fabrication facility, in accordance with implementations of the disclosure. An equipment front end module (EFEM)  200  receives substrates/wafers into the system. For example, substrates may be received through one or more load ports that are configured to enable loading and unloading of substrates from a substrate carrier device, such as a front opening unified pod (FOUP) or other substrate carrier, which may be moved about the fabrication facility by an automated material handling system. From the EFEM  200  substrates are transferred through a load lock  202  that isolates the process environment of the cluster tool from the external environment and/or contamination, and enables maintenance of, for example, a controlled gas environment or controlled vacuum environment for processing. A first wafer transfer module  204  is connected to the load lock  202 , and is configured to transfer substrates to and from either of process modules  210  or  212 . 
     The process modules are configured to perform any of a variety of process operations on substrates, including without limitation, a front end of line operation, a back end of line operation, etching, deposition, clean, plasma processing, annealing, or any other process operation. In some implementations, the process modules are multi-station process modules having a plurality of stations for processing multiple substrates simultaneously. Such multi-station process modules can be configured to migrate substrates internally from one station to the next. One example of a multi-station process module is the Strata process module manufactured by Lam Research Corporation. 
     As shown in the illustrated implementation, the wafer transfer module  204  is also connected to a buffer module  206 . Step ladders  100   a  and  100   b  are connected to the sides of the buffer module  206 , and are each configured as the step ladder  100  described with reference to  FIG. 1  above. A second wafer transfer module  208  is further connected to the buffer module  206 . It will be appreciated that the load lock  202 , the wafer transfer module  204 , the buffer module  206 , and the wafer transfer module  208  are linearly arranged in the illustrated implementation. However, in other implementations, other arrangements are possible. The second wafer transfer module  208  is configured to transfer substrates to and from either of process modules  214  or  216 . As has been noted, the process modules  214  and  216  can also be multi-station process modules in some implementations. 
     As shown, the step ladder  100   a  is connected to one side of the buffer module  206  in the space between the process modules  210  and  214 . Whereas the stepladder  100   b  is connected to the side of the buffer module  206  opposite that of the stepladder  100   a , and positioned in the space between the process modules  212  and  216 . The step ladder  100   a  provides access to elevated portions of the process modules  210  and  214 , while the stepladder  100   b  provides access to elevated portions of the process modules  212  and  216 . Both step ladders provide access to the top of the buffer module  206 , as well as the tops of the transfer modules  204  and  208 . The configuration of the step ladders thus efficiently utilizes the available space, while also providing a storage location for electronic equipment. The hinged configuration of the step ladders allows them to be stored at the point of use, while being able to easily and safely move them up and out of the way to provide access to areas underneath and behind the step ladders. 
       FIG. 2B  is a perspective view of a portion of the cluster tool system in accordance with the implementation of  FIG. 2A , showing the step ladder in a lowered position, in accordance with implementations of the disclosure. As shown, the step ladder  100   a  is connected to the buffer module  206  via the mounting plate, and shown in the lowered position, such that the step ladder is also resting on the floor  220  of the fabrication facility. As has been noted, the step ladder  100   a  is capable of being raised off of the fabrication facility floor  220  to a raised position that is substantially over the buffer module  206 . 
     In the illustrated implementation, a fabrication facility floor  220  is shown, upon which persons may stand. The fabrication facility floor  220  is defined as an elevated floor that is supported over an underlying subfloor  222 . The fabrication facility floor  220  can be perforated or vented to permit airflow through the floor  220  to remove particulates from the fab environment. In some implementations, the distance between the fabrication facility floor  220  and the subfloor  222  is approximately 2 feet (approximately 60 centimeters). In some implementations, the distance between the fabrication facility floor  220  and the subfloor  222  is in the range of approximately 1.5 to 2.5 feet (approximately 45 to 75 centimeters). In some implementations, the distance between the fabrication facility floor  220  and the subfloor  222  is in the range of approximately 1 to 4 feet (approximately 0.3 to 1.2 meters). 
     The subfloor space that is defined between the fabrication facility floor  220  and the subfloor  222  can be utilized for equipment storage, as well as passage of various facilities lines, such as process gas lines, vacuum lines, electrical/RF lines/feeds, data cables, liquid supply lines, etc. 
       FIG. 2C  is a perspective view of a portion of the cluster tool system in accordance with the implementation of  FIG. 2A , showing the step ladder in a raised position, in accordance with implementations of the disclosure. As shown, the step ladder  100   a  is in the raised position, so as to be suspended substantially over the buffer module  206 . By raising the step ladder  100   a  from the lowered position to the raised position, the step ladder  100   a  is rotated about its joints to the mounting plate. As the step ladder  100   a  is rotated, it is also substantially inverted in the process (rotated/turned upside-down). 
       FIG. 3  is a perspective view of the ladder assembly showing the step ladder  100  in a raised position, in accordance with implementations of the disclosure. In this view, additional components of the ladder assembly can be seen. Notably, gas springs  300   a  and  300   b  are shown in the Illustrated implementation, and are configured to exert an extension force that reduces the amount of force required by an operator to lift the step ladder  100  from the lowered position to the raised the position. To achieve this, each of the gas springs is connected to the mounting plate  102  and to one of the arms of the step ladder  100 . More specifically, the gas spring  300   a  connects to the left arm  106   a  at an upper hinge joint  306   a ; and the gas spring  300   b  connects to the right arm  106   b  at an upper hinge joint  306   b.    
     The gas spring  300   a  also connects to the mounting plate  102  at a lower hinge joint  302   a ; whereas the gas spring  300   b  connects to the mounting plate  102  at a corresponding lower hinge joint  302   b . More specifically, the gas spring  300   a  connects to an end of a lower extension  304   a  of the mounting plate  102 . The gas spring  300   b  connects to an end of a lower extension  304   b  of the mounting plate  102 . The lower extensions  304   a  and  304   b  each protrude laterally away from the side of the module to which the mounting plate  102  is mounted, thereby providing a connection point to the gas springs  300   a  and  300   b  so that the lower hinge joints formed are substantially horizontally offset from the side of the module. This is shown more clearly with reference to  FIGS. 4A and 4B , as described below. 
     With continued reference to  FIG. 3 , a chain  308  is shown disposed along the back side of the step ladder  100 . The chain  308  routes cables from the electronics equipment (stored beneath the third and fourth steps of the step ladder  100 ) underneath the module (e.g. buffer module  206 ) to which the mounting plate  102  is connected. The chain  308  consists of a number of articulating links that enable the chain  308  to move and change shape as the step ladder  100  is raised or lowered. 
       FIG. 4A  illustrates a side view of an upper portion of the ladder assembly, in accordance with implementations of the disclosure. In the illustrated implementation, the step ladder  100  is shown in the lowered position. As can be seen, the lower extension  304   a  extends laterally outward away from a vertical plane  400  defined by the side of the module  206  to which the mounting plate  102  is a fixed. The lower extension  304   a  is configured to position the lower hinge joint  302   a  (having a lateral position defined by the vertical plane  404  that intersects both lower hinge joints  302   a  ad  302   b ) so as to be laterally further away from the vertical plane  400  (i.e. from the side of the module  206 ) than the joint  108   a  (having a lateral position defined by the vertical plane  402  that intersects the hinge joints  108   a  and  108   b ; vertical plane  402  intersects the axis of rotation defined by the hinge joints  108   a  and  108   b ) between the arm  106   a  of the step ladder  100  and the mounting plate  102 . 
     The gas spring  300   a  connects to a connector  406   a  of the arm  106   a  of the step ladder  100 . The connector  406   a  is configured so as to place the hinge joint  306   a  at a position that is offset from the main length of the arm  106   a.    
     The positions of the upper hinge joint  306   a  and the lower hinge joint  302   a , which connect the gas spring  300   a  to the left arm  106   a  and the lower extension  302   a  of the mounting plate  102 , respectively, are configured so that the extension force of the gas spring, shown by the vector F gs , is directed behind the hinge joint  108   a  when the step ladder  100  is in the lowered position. That is, the alignment of the gas spring  300   a  when the step ladder  100  is in the lowered position and resting on the fabrication facility floor, is such that the gas spring&#39;s force of extension is directed to a side of the hinge joint  108   a  that is laterally toward the plane  400  that is defined by the side of the module to which the mounting plate  102  is attached. 
     It should be appreciated that due to the geometry of the above-described components and the alignment of the gas springs when the step ladder  100  is in the lowered position, the extension force of the gas springs actually promotes downward rotation of the step ladder  100 . That is, when the step ladder is in the lowered position and resting on the fabrication facility floor, the force of the gas springs initially resists rotation of the step ladder  100  away from the lowered position towards the raised position. This feature helps to secure the step ladder  100  in the lowered position and helps to prevent unwanted movement of the step ladder  100  when in the lowered position. However, once the step ladder  100  has been rotated away from the lowered position (and towards the raised position) to a certain extent, then the geometry of the components is such that the extension force of the gas springs promotes rotation towards the raised position (in other words, reducing the amount of force required to lift the step ladder towards the raised position). 
       FIG. 4B  illustrates a side view of the ladder assembly showing the step ladder  100  in a raised position, in accordance with implementations of the disclosure. In the right position, the stepladder  100  is suspended substantially over the module  206 . When raised from the lowered position to the raised position, the center of gravity of the step ladder  100 , which is shown by the indicator  410 , follows a circular path  414  centered around the axis of rotation defined by the hinge joint  108   a . Furthermore, the center of gravity moves from an initial (geographic) location that is lateral to the module  206  when the step ladder is in the lowered position, to a position that is over the module  206  when the ladder is in the raised position. It should be appreciated that as the step ladder  100  rotates to the raised position, its center of gravity moves horizontally past the hinge joint  108   a  from a location (shown at reference  412 ) that is directly over the floor of the fabrication facility (and not over the module  206 ) to a location that is directly over the module  206  as shown at reference  410 . That is, the center of gravity moves through and past the vertical plane  402  (that intersects the axis of rotation of the hinge joint  108   a ) by an angular amount θ. 
     When the step ladder  100  is in the raised position, the extension force of the gas springs act to maintain the step ladder&#39;s raised position. That is, the extension force of the gas springs resists movement of the step ladder  100  away from the raised position towards the lowered position. This acts as a safety measure to prevent accidental or unwanted lowering of the step ladder. 
     It will be appreciated that due to the side views specifically shown in  FIGS. 4A and 4B , the operational mechanisms noted above have been described with reference to components on one side of the ladder assembly, e.g. arm  106   a , hinge joint  108   a , gas spring  300   a , upper hinge joint  306   a , lower hinge joint  302   a , etc. However, it will be appreciated that similar operational mechanisms can be described for the other side of the ladder assembly, these being apparent to those skilled in the art and therefore not specifically described in the present disclosure for purposes of brevity. 
       FIG. 5  illustrates a side view of the ladder assembly, showing the forces and resulting moments acting on the step ladder during operation, in accordance with implementations of the disclosure. In the illustrated view, clockwise rotation of the step ladder  100  is associated with movement of the step ladder from the lowered position towards the raised position; whereas counterclockwise rotation is associated with movement of the step ladder from the raised position towards the lowered position. As shown, the step ladder  100  is in between the raised and lowered positions. The extension force of the gas springs, F gs , acts to produce a moment, M gs , in the clockwise direction. The force provided by an operator/user lifting the step ladder  100 , Fop, acts to produce a moment, M op , that is also in the clockwise direction. Whereas, the weight of the step ladder produces a force F w , that acts to produce a moment, M w , that is in the counterclockwise direction, and thereby opposes the moments M gs  and M op . 
       FIG. 6  is a graph illustrating the force required by an operator when lifting the step ladder from the lowered position to the raised position, demonstrating the effect of the gas springs of the ladder assembly, in accordance with implementations of the disclosure. 
     The curve  600  illustrates the amount of force required by an operator of the step ladder to raise/rotate the step ladder from the lowered position to the raised position, as a function of the angle of rotation of the step ladder. A ladder rotation angle of 0 degrees corresponds to the lowered position wherein the step ladder  100  is resting on the fabrication facility floor. As can be seen, the amount of force required by the operator rapidly increases from an initial amount of about 35 lbf (pound-force units) at 0 degrees to a peek amount over 70 lbf at approximately 60 degrees, before decreasing as the step ladder continues to be rotated upward. At approximately 150 degrees of rotation the force required by the operator reaches zero lbf, corresponding to the point at which the center of gravity of the step ladder is vertically aligned with the hinge joints (ref.  108   a  and  108   b ) around which the step ladder is being rotated. Beyond this point the amount of force required becomes negative, as the weight of the step ladder is now pulling the step ladder down. 
     The curve  602  illustrates the amount of force required by the operator when lifting/rotating the step ladder from the lowered position to the raised position, with the assistance of gas springs as have been described in the present disclosure. As can be seen, the initial amount of force required at 0 degrees of rotation is slightly above 40 lbf, which is greater than that required without the gas springs. As explained previously, this is due to the geometry of the gas springs when the step ladder  100  is in the lowered position, such that the extension force of the gas springs resists rotation of the step ladder away from the lowered position. However, once the step-ladder has been rotated past an initial amount, e.g. about 5 to 7 degrees in some implementations, then the extension force of the gas springs significantly reduces the amount of force that is required by the operator to rotate the step ladder toward the raised position. In contrast to the scenario without gas springs, the amount of force required by the operator crosses over from positive to negative at only approximately 110 degrees of rotation. 
     As can be seen from the illustrated graph, the force from the gas springs both enhances the stability of the step ladder when resting on the fabrication facility floor in the lowered position, and also greatly reduces the amount of force required by the operator when lifting the step ladder to the raised position. 
     It should be appreciated that the illustrated graph is provided by way of example only, without limitation, to demonstrate one particular implementation showing the effect of the gas springs. In other implementations, the specific forces required to lift the step ladder, both with and without gas springs, may differ from the specifically illustrated implementation of  FIG. 6 . 
       FIG. 7  is a perspective view of an upper portion of the step ladder  100 , in accordance with implementations of the disclosure. In the illustrated view, the fourth step (topmost step) of the step ladder  100  is shown. As previously noted, the perimeter of the step is defined by a step frame  116   b . The step&#39;s surface is defined by a step plate  114   d , which is defined from a substantially transparent material to enable viewing of electronic equipment stored beneath the step. Thus, the step plate  114   d  functions as both a protective cover for the electronic equipment and a step surface for an operator to step/stand on. The step plate  114   d  can be formed from any transparent or substantially transparent material providing suitable visibility and strength. By way of example, without limitation, the step plate  114   d  can be formed from a plastic or glass material, a transparent polymer, an acrylic polymer, Plexiglass, etc. In some implementations, the step plate  114   d  is defined in the form a grate having sufficient holes to enable suitable viewing of the electronic equipment disposed below. 
     As noted, the electronic equipment can include one or more power supplies housed within the sleeve  118   b  below the fourth step of the step ladder. In the illustrated implementation, the electronic equipment stored beneath the fourth step includes four power supplies  702   a ,  702   b ,  702   c , and  702   d . Power switches for the power supplies are accommodated by a plurality of recesses  700   a ,  700   b ,  700   c , and  700   d , defined in the underside of the step plate  114   d . This enables individual power supplies to be switched on or off with ease. 
     Furthermore, in some implementations, each power supply corresponds to an individual process station in a multi-station process module, such as one of the process modules  210 ,  212 ,  214 , or  216 . Thus, in implementations wherein a multi-station process module contains four stations, then the power supplies stored below a single step of the step ladder provide power for each of the stations in a single multi-station process module. Furthermore, then with reference to the cluster tool system of  FIG. 2A , each of the third and fourth steps of the step ladders  100   a  and  100   b  are configured to house power supplies for the process modules  210 ,  212 ,  214 , and  216 . For example, the third step of the step ladder  100  may house the power supplies for the stations of the process module  210 , whereas the fourth step of the step ladder  100  may house the power supplies for the stations of the process module  214 . And the third step of the step ladder  100   b  may house the power supplies for the stations of the process module  212 , whereas the fourth step of the step ladder  100   b  may house the power supplies for the stations of the process module  216 . 
     With continued reference to  FIG. 7 , in the illustrated implementation, the step plate  114   d  is defined by an assembly of components, including two cover plates  710   a  and  710   b , and a numbered crossbar  704 , having numbers inscribed thereon. The numbers identify the process stations of a given multi-station process module, to which the power supplies below the numbers respectively correspond. It will be appreciated that the step plate  114   c  may also be defined by a similar assembly configuration, in accordance with implementations of the disclosure. 
     Though the implementations described with reference to  FIG. 7  have been with reference to the fourth step of the step ladder  100 , it will be appreciated that similar description can be applied to the third step of the step ladder  100 , as well. 
       FIG. 8  is a close-up view of the mounting plate  102 , in accordance with implementations of the disclosure. As shown, the mounting plate  102  includes a pair of hinge joint bracket plates  800   a  and  800   b . The hinge joint bracket plates include holes  802   a  and  802   b . The upper end of the left arm  106   a  is disposed between the hinge joint bracket plates  800 A and  800 B, and the hinge joint  108   a  is formed by a connector pin that is inserted through the hole  802   a , a corresponding hole  706   a  of the left arm  106   a  which is shown at  FIG. 7 , and the hole  802   b.    
     Furthermore, the hinge joint bracket plates include holes  804   a ,  804   b ,  806   a , and  806   b , which accommodate a safety pin  806   a . When the step ladder  100  is in the lowered position, then a hole  708   a  (shown at  FIG. 7 ) of the arm  106   a  is aligned with the holes  806   a  and  806   b . In this position, the safety pin  806   a  can be inserted through the holes  806   a ,  708   a , and  806   b , to lock the step ladder in the lowered position. 
     When the step ladder  100  is in the raised position, then the hole  708   a  of the arm  106   a  is aligned with the holes  804   a  and  804   b . In this position, the safety pin  806   a  can be inserted through the holes  804   a ,  708   a , and  804   b , to lock the step ladder in the raised position. 
     It will be appreciated that similar componentry exists with respect to the other side of the mounting plate  102 , including hinge joint bracket plates  800   c  and  800   d , and a safety pin  806   b , which have similar operational mechanisms as described above, but for the right arm  106   b  and the right hinge joint  108   b.    
     In some implementations, the mounting plate  102  is attached to the side surface of the module by screws or bolts that are threaded through screw holes  810 . 
     Although the foregoing embodiments have been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the disclosed embodiments. It should be noted that there are many alternative ways of implementing the processes, systems, and apparatus of the present embodiments. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the embodiments are not to be limited to the details given herein.