Patent Publication Number: US-2023141653-A1

Title: Frontside and backside pressure monitoring for substrate movement prevention

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 63/210,444, filed on Jun. 14, 2021. The entire disclosure of the application referenced above is incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to generally to substrate processing systems and more particularly to pressure control systems for preventing substrate movement. 
     BACKGROUND 
     The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. 
     Substrate processing systems may be used to deposit, etch, ash, clean or otherwise perform treatment of film on a substrate such as a semiconductor wafer. The substrate processing systems typically include a processing chamber, a gas distribution device, and a substrate support assembly. During processing, the substrate is arranged on the substrate support assembly. Different gas mixtures may be introduced into the processing chamber. Radio frequency (RF) plasma and/or heat may be used to activate chemical reactions. 
     Prior to processing, the substrate is transferred into the processing chamber and disposed on lift pins of a substrate support. The lift pins are then lowered to place the substrate on a body of the substrate support. The processing chamber is pressurized according to a process recipe. Subsequent to processing, the substrate is lifted from the substrate support via the lift pins and then the processing chamber is depressurized. The substrate is removed from the processing chamber after depressurization. 
     SUMMARY 
     A pressure control system is provided and includes a first sensor, a second sensor, an evacuation valve and a controller. The first sensor is configured to detect a frontside pressure within a processing chamber. The frontside pressure is indicative of a downforce on a substrate disposed on a substrate support within the processing chamber. The second sensor is configured to detect a backside pressure on a backside of the substrate. The controller is configured to: control the evacuation valve to remove gas from and reduce the frontside pressure of the processing chamber; and during the removal of gas from and reduction in the frontside pressure of the processing chamber and based on the frontside pressure and the backside pressure, regulate an opening of the evacuation valve such that the frontside pressure does not drop below the backside pressure. 
     In other features, the controller is configured to: during the removal of gas from and reduction in frontside pressure of the processing chamber, compare the frontside pressure to the backside pressure to provide a pressure differential value; transition the evacuation valve from a first open state to a second open state when at least one of a rate of change of the pressure differential value exceeds a first threshold or the pressure differential value is less than or equal to a second threshold, wherein the second open state is a more closed state than the first open state; and transition the evacuation valve from the first open state to a third open state, when at least one of the rate of change of the pressure differential value does not exceed the first threshold or the pressure differential value is greater than the second threshold, wherein the third open state is a more open state than the first open state. 
     In other features, the controller is configured to close the evacuation valve when the frontside pressure is less than or equal to the backside pressure. In other features, the controller is configured to remove gas from the processing chamber and regulate the opening of the evacuation valve at least one of during or subsequent to processing the substrate. 
     In other features, the pressure control system further includes a backside valve. The controller is configured to open the backside valve to continuously draw gas from the backside of the substrate during processing and removal of gas from the processing chamber. In other features, the controller is configured to regulate the evacuation valve to maintain at least a safety margin between the frontside pressure and the backside pressure. 
     In other features, the controller is configured to, during the removal of gas from and reduction in the frontside pressure of the processing chamber, maximize an opening of the evacuation valve to maximize a depressurization rate of the processing chamber while at least one of preventing the frontside pressure from dropping below the backside pressure or maintaining at least a safety margin between the frontside pressure and the backside pressure. 
     In other features, the controller is configured to: during the removal of gas from and reduction in the frontside pressure of the processing chamber, determine whether the frontside pressure is less than a predetermined pressure; and when the frontside pressure is less than the predetermined pressure, actuate lift pins to lift the substrate off a top surface of a body of the substrate support. In other features, the predetermined pressure is 4-5 Torr. 
     In other features, the controller is configured to: pressurize the processing chamber to provide a first frontside pressure; process the substrate according to a first portion of a recipe; remove gas from the processing chamber to provide a second frontside pressure that is less than the first frontside pressure; and process the substrate according to a second portion of the recipe. In other features, the first frontside pressure is greater than 4-5 Torr. 
     In other features, the substrate support is void of mechanical and electrical components to hold the substrate in place on the substrate support. The controller is configured to prevent the substrate from moving on the substrate support by pressuring the processing chamber. 
     In other features, the substrate support is implemented as an electrostatic chuck. The controller is configured to, during the removal of gas from and reduction in the frontside pressure of the processing chamber, cease electrostatic clamping of the substrate prior to lifting the substrate off a top surface of a body of the substrate support. 
     In other features, the controller is configured to remove gas from the processing chamber to at least partially depressurize the processing chamber prior to actuating lift pins of the substrate support to lift the substrate off a top surface of a body of the substrate support. In other features, the controller is configured to remove gas from the processing chamber to reduce the frontside pressure in the processing chamber to less than a predetermined pressure prior to actuating lift pins of the substrate support to lift the substrate off a top surface of a body of the substrate support. In other features, the pressure control system further includes a pump. The controller is configured to run the pump to draw gas from the processing chamber to depressurize the processing chamber. 
     In other features, the pressure control system further includes: an evacuation line extending from the processing chamber to the pump; a backside line extending from a channel in a body of the substrate support to the evacuation line; and a backside valve connected to the backside line and configured to control flow of gas through the backside line. The evacuation valve is attached to the evacuation line upstream from the backside line. In other features, the backside sensor detects pressure within the backside line. 
     In other features, a method of operating a pressure control system is provided. The method includes: detecting a frontside pressure within a processing chamber, wherein the frontside pressure is indicative of a downforce on a substrate disposed on a substrate support within the processing chamber; detecting a backside pressure on a backside of the substrate; controlling an evacuation valve to remove gas from and reduce the frontside pressure of the processing chamber; and during the removal of gas from and reduction in frontside pressure of the processing chamber and based on the frontside pressure and the backside pressure, regulate an opening of the evacuation valve such that the frontside pressure does not drop below the backside pressure. 
     In other features, the method further includes: during the removal of gas from and reduction in frontside pressure of the processing chamber, comparing the frontside pressure to the backside pressure to provide a pressure differential value; transitioning the evacuation valve from a first open state to a second open state when at least one of a rate of change of the pressure differential value exceeds a first threshold or the pressure differential value is less than or equal to a second threshold, where the second open state is a more closed state than the first open state; and transitioning the evacuation valve from the first open state to a third open state, when at least one of the rate of change of the pressure differential value does not exceed the first threshold or the pressure differential value is greater than the second threshold. The third open state is a more open state than the first open state. 
     In other features, the method further includes closing the evacuation valve when the frontside pressure is less than or equal to the backside pressure. In other features, the method further includes removing gas from the processing chamber and regulating the opening of the evacuation valve at least one of during or subsequent to processing the substrate. 
     In other features, the method further includes opening a backside valve to continuously draw gas from the backside of the substrate during processing and removal of gas from the processing chamber. In other features, the method further includes regulating the evacuation valve to maintain at least a safety margin between the frontside pressure and the backside pressure. 
     In other features, the method further includes, during the removal of gas from and reduction in the frontside pressure of the processing chamber, maximizing an opening of the evacuation valve to maximize a depressurization rate of the processing chamber while at least one of preventing the frontside pressure from dropping below the backside pressure or maintaining at least a safety margin between the frontside pressure and the backside pressure. 
     In other features, the method further includes: during the removal of gas from and reduction in the frontside pressure of the processing chamber, determining whether the frontside pressure is less than a predetermined pressure; and when the frontside pressure is less than the predetermined pressure, actuating lift pins to lift the substrate off a top surface of a body of the substrate support. In other features, the predetermined pressure is 4-5 Torr. 
     In other features, the method further includes: pressurizing the processing chamber to provide a first frontside pressure; processing the substrate according to a first portion of a recipe; removing gas from the processing chamber to depressurize the processing chamber and provide a second frontside pressure that is less than the first frontside pressure; and processing the substrate according to a second portion of the recipe. In other features, the first frontside pressure is greater than 4-5 Torr. 
     In other features, the method further includes preventing the substrate from moving on the substrate support by pressuring the processing chamber. The substrate support is void of mechanical and electrical components to hold the substrate in place on the substrate support. 
     In other features, the method further includes, during the removal of gas from and reduction in the frontside pressure of the processing chamber, ceasing electrostatic clamping of the substrate prior to lifting the substrate off a top surface of a body of the substrate support. In other features, the method further includes removing gas from the processing chamber to at least partially depressurize the processing chamber prior to actuating lift pins of the substrate support to lift the substrate off a top surface of a body of the substrate support. 
     In other features, the method further includes removing gas from the processing chamber to reduce the frontside pressure in the processing chamber to less than a predetermined pressure prior to actuating lift pins of the substrate support to lift the substrate off a top surface of a body of the substrate support. In other features, the method further includes running a pump to draw gas from the processing chamber to depressurize the processing chamber. 
     In other features, a pressure control system is provided and includes a first sensor, a second sensor, an evacuation valve and a controller. The first sensor is configured to detect a frontside pressure within a processing chamber. The frontside pressure is indicative of a downforce on a substrate disposed on a substrate support within the processing chamber. The second sensor is configured to detect a backside pressure on a backside of the substrate. The controller is configured to: control the evacuation valve to depressurize the processing chamber; and during the depressurization of the processing chamber and based on the frontside pressure and the backside pressure, regulate a position of the evacuation valve such that the frontside pressure does not drop below the backside pressure. 
     In other features, the controller is configured to: during the depressurization of the processing chamber, compare the frontside pressure to the backside pressure to provide a pressure differential value; transition the evacuation valve from a first position to a second position when at least one of a rate of change of the pressure differential value exceeds a first threshold or the pressure differential value is less than or equal to a second threshold, where the second position is a more closed position than the first position; and transition the evacuation valve from the first position to a third position, when at least one of the rate of change of the pressure differential value does not exceed the first threshold or the pressure differential value is greater than the second threshold, where the third position is a more open position than the first position. 
     In other features, the controller is configured to close the evacuation valve when the frontside pressure is less than or equal to the backside pressure. In other features, the controller is configured to depressurize the processing chamber and regulate the position of the evacuation valve at least one of during or subsequent to processing the substrate. 
     In other features, the pressure control system of further includes a backside valve. The controller is configured to open the backside valve to continuously draw gas from the backside of the substrate during processing and depressurization of the processing chamber. In other features, the controller is configured to regulate the evacuation valve to maintain at least a safety margin between the frontside pressure and the backside pressure. 
     In other features, the controller is configured to, during the depressurization of the processing chamber, maximize an opening of the evacuation valve to maximize a depressurization rate of the processing chamber while at least one of preventing the frontside pressure from dropping below the backside pressure or maintaining at least a safety margin between the frontside pressure and the backside pressure. 
     In other features, the controller is configured to: during the depressurization of the processing chamber, determine whether the frontside pressure is less than a predetermined pressure; and when the frontside pressure is less than the predetermined pressure, actuate lift pins to lift the substrate off a top surface of a body of the substrate support. In other features, the predetermined pressure is 4-5 Torr. 
     In other features, the controller is configured to: pressurize the processing chamber to provide a first frontside pressure; process the substrate according to a first portion of a recipe; depressurize the processing chamber to provide a second frontside pressure that is less than the first frontside pressure; and process the substrate according to a second portion of the recipe. In other features, the first frontside pressure is greater than 4-5 Torr. 
     In other features, the substrate support is void of mechanical and electrical components to hold the substrate in place on the substrate support; and the controller is configured to prevent the substrate from moving on the substrate support by pressuring the processing chamber. 
     In other features, the substrate support is implemented as an electrostatic chuck. The controller is configured to, during the depressurization of the processing chamber, cease electrostatic clamping of the substrate prior to lifting the substrate off a top surface of a body of the substrate support. 
     In other features, the controller is configured to at least partially depressurize the processing chamber prior to actuating lift pins of the substrate support to lift the substrate off a top surface of a body of the substrate support. In other features, the controller is configured to depressurize the processing chamber to less than a predetermined pressure prior to actuating lift pins of the substrate support to lift the substrate off a top surface of a body of the substrate support. 
     In other features, the pressure control system further includes a pump. The controller is configured to run the pump to draw gas from the processing chamber to depressurize the processing chamber. 
     In other features, the pressure control system further includes: an evacuation line extending from the processing chamber to the pump; a backside line extending from a channel in a body of the substrate support to the evacuation line; and a backside valve connected to the backside line and configured to control flow of gas through the backside line. The evacuation valve is attached to the evacuation line upstream from the backside line. In other features, the backside sensor detects pressure within the backside line. 
     In other features, a method of operating a pressure control system is provided. The method includes: detecting a frontside pressure within a processing chamber, where the frontside pressure is indicative of a downforce on a substrate disposed on a substrate support within the processing chamber; detecting a backside pressure on a backside of the substrate; controlling an evacuation valve to depressurize the processing chamber; and during the depressurization of the processing chamber and based on the frontside pressure and the backside pressure, regulate a position of the evacuation valve such that the frontside pressure does not drop below the backside pressure. 
     In other features, the method further includes: during the depressurization of the processing chamber, comparing the frontside pressure to the backside pressure to provide a pressure differential value; transitioning the evacuation valve from a first position to a second position when at least one of a rate of change of the pressure differential value exceeds a first threshold or the pressure differential value is less than or equal to a second threshold, where the second position is a more closed position than the first position; and transitioning the evacuation valve from the first position to a third position, when at least one of the rate of change of the pressure differential value does not exceed the first threshold or the pressure differential value is greater than the second threshold, where the third position is a more open position than the first position. 
     In other features, the method further includes closing the evacuation valve when the frontside pressure is less than or equal to the backside pressure. In other features, the method further includes depressurizing the processing chamber and regulating the position of the evacuation valve at least one of during or subsequent to processing the substrate. 
     In other features, the method further includes opening a backside valve to continuously draw gas from the backside of the substrate during processing and depressurization of the processing chamber. In other features, the method further includes regulating the evacuation valve to maintain at least a safety margin between the frontside pressure and the backside pressure. 
     In other features, the method further includes, during the depressurization of the processing chamber, maximizing an opening of the evacuation valve to maximize a depressurization rate of the processing chamber while at least one of preventing the frontside pressure from dropping below the backside pressure or maintaining at least a safety margin between the frontside pressure and the backside pressure. 
     In other features, the method further includes: during the depressurization of the processing chamber, determining whether the frontside pressure is less than a predetermined pressure; and when the frontside pressure is less than the predetermined pressure, actuating lift pins to lift the substrate off a top surface of a body of the substrate support. In other features, the predetermined pressure is 4-5 Torr. 
     In other features, the method further includes: pressurizing the processing chamber to provide a first frontside pressure; processing the substrate according to a first portion of a recipe; depressurizing the processing chamber to provide a second frontside pressure that is less than the first frontside pressure; and processing the substrate according to a second portion of the recipe. In other features, the first frontside pressure is greater than 4-5 Torr. 
     In other features, the method further includes preventing the substrate from moving on the substrate support by pressuring the processing chamber, where the substrate support is void of mechanical and electrical components to hold the substrate in place on the substrate support. 
     In other features, the method further includes, during the depressurization of the processing chamber, ceasing electrostatic clamping of the substrate prior to lifting the substrate off a top surface of a body of the substrate support. In other features, the method further includes at least partially depressurizing the processing chamber prior to actuating lift pins of the substrate support to lift the substrate off a top surface of a body of the substrate support. 
     In other features, the method further includes depressurizing the processing chamber to less than a predetermined pressure prior to actuating lift pins of the substrate support to lift the substrate off a top surface of a body of the substrate support. In other features, the method further includes running a pump to draw gas from the processing chamber to depressurize the processing chamber. 
     Further areas of applicability of the present disclosure will become apparent from the detailed description, the claims and the drawings. The detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG.  1    shows an example substrate processing system including a pressure control system in accordance with the present disclosure; 
         FIGS.  2 A- 2 B  shows an example of a substrate support assembly and lift pins used in the substrate processing system of  FIG.  1   ; 
         FIGS.  3 A- 3 B  illustrates a method for reducing pressure in a processing chamber including removing gas from the processing chamber in accordance with the present disclosure; 
         FIG.  4    is a timing diagram and plot illustrating portions of the method of  FIGS.  3 A- 3 B ; 
         FIGS.  5 A- 5 B  illustrates a method for reducing pressure within a processing chamber including removing gas to transition from a high-pressure traditionally associated with substrate movement in accordance with the present disclosure; and 
         FIGS.  6 A- 6 C  illustrates a multiple pressure transitioning process including removal of gas to depressurize a processing chamber in accordance with the present disclosure. 
     
    
    
     In the drawings, reference numbers may be reused to identify similar and/or identical elements. 
     DETAILED DESCRIPTION 
     Prior to processing, a substrate is disposed within a processing chamber and on a substrate support. The substrate support may not be configured with mechanical and/or electrical components to prevent movement of the substrate. For example, the substrate support may not include a mechanical fixture for holding the substrate and/or electrostatic clamping electrodes for clamping the substrate to a body of the substrate support. The substrate may instead be held in place due to a pressure differential created between opposing surfaces of the substrate. When gas is introduced into the processing chamber and pressure in the processing chamber increases, the substrate does not move due to pressure on the top side of the substrate being greater than pressure on the bottom side of the substrate. The pressure of the top side of the substrate is referred to as the frontside pressure and the pressure on the bottom side of the substrate is referred to as the backside pressure. The substrate is processed at a frontside pressure that is higher than a base pressure provided when under vacuum. 
     The processing chamber may be depressurized during processing and/or subsequent to processing and prior to removal of the substrate from the processing chamber. The terms “depressure”, “depressurized”, “depressurizing” and “depressurization” as used herein refers to the removal of gas from a processing chamber to reduce a frontside pressure and/or a backside pressure within the processing chamber. As an example, a recipe may call for the frontside pressure to decrease from a high pressure to a low pressure, which requires depressurization of the processing chamber. During depressurization, the frontside pressure may be reduced to a reduced pressure and/or a low pressure above a base pressure or may be reduced to the base pressure. During depressurization, there is a chance that the frontside pressure drops below the backside pressure, such that the backside pressure exceeds the frontside pressure. 
     The frontside pressure may drop below the backside pressure because a rate at which an area on the frontside of the substrate is depressurized is quicker than a rate at which an area on the backside of the substrate is depressurized. The gas evacuation line through which gas is pumped out of the processing chamber is typically significantly larger in diameter and/or cross-sectional area than a backside line through which gas is drawn from the area on the backside of the substrate. The gas flow rate (or gas conductance rate) through the backside line is significantly lower than the gas flow rate through the gas evacuation line. As a result, the frontside pressure drops quicker and can drop below the backside pressure. The higher the frontside pressure, the more likely this is to occur. At higher frontside pressures, the backside pressure tends to creep higher from a base pressure at vacuum to a pressure, for example, as high as 1-2 Torr. The substrate may move from a predetermined processing position when the backside pressure is greater than the frontside pressure. For this reason, conventional substrate processing, especially when a substrate is only held in place by the stated pressure differential, has been limited to recipes that do not call for depressurization due to the associated risk for substrate movement. 
     Traditionally and subsequent to processing a substrate within a processing chamber, lift pins of a substrate support are driven upward to overcome a downward pressure on the substrate. This occurs prior to the processing chamber being depressurized. Pressure within the processing chamber is maintained to maintain the downward pressure on the substrate until the substrate is lifted to prevent substrate movement. When the substrate is lifted, the frontside pressure quickly drops such that there is no longer a pressure differential between the frontside and the backside of the substrate. Gas within the chamber moves to an area on the backside, thereby equalizing the pressures on the frontside and the backside. 
     The higher the frontside pressure during processing, the more force needed subsequent to processing to drive the lift pins upward and overcome the frontside downward pressure on the substrate. The higher the frontside pressure, the greater the chances of the substrate “popping” and/or shifting when lifted. This is because of the quick change in pressure differential, which results in the substrate momentarily hopping off and/or shifting on the lift pins. The high frontside pressure causes a high downforce on the substrate and during a mechanical lift pins up operation the substrate “pops” or slides relative to a top surface of the body of the substrate support. Also, the higher the processing chamber pressure, the more movement of the substrate when lifted. This movement is not consistent and can be in different directions. Because of the potential for substrate movement as a result of processing at high pressures, processing pressures are typically limited to less than a predetermined pressure threshold (e.g., 4-5 Torr). Below the predetermined pressure threshold, the substrate tends not to experience a popping when lifting the substrate and there is typically negligible to no shifting in position. However, as chamber pressure increases above the predetermined pressure threshold, the amount of substrate movement increases. 
     The examples set forth herein include providing a controlled rapid pump down of a processing chamber including maintaining a pressure differential between a frontside and a backside of a substrate during and after processing. The pressure differential is such that the frontside pressure is greater than the backside pressure. The controlled rapid pump down prevents substrate movement during and after processing. This is unlike an uncontrolled rapid pump down, which risks movement of the substrate. By maintaining this pressure differential during and subsequent to processing, a corresponding processing chamber is able to be quickly depressurized, which decreases time associated with processing and allows for increased throughput. In an embodiment, the rate of depressurization is increased to a maximum rate at which if exceeded the frontside pressure would drop below the backside pressure and cause a wafer “slide” event. Depressurization of the processing chamber is able to occur prior to lifting the substrate off the top surface of the body of the substrate support, which allows the processing chamber to be depressurized within a shorter period of time. 
       FIG.  1    shows an example substrate processing system  100  including a pressure control system  102 . The pressure control system  102  controls a pressure differential between a frontside pressure (designated P 1 ) and a backside pressure (designated P 2 ) of a substrate  104 . The pressure control system  102  may control the pressure differential prior to, during, and subsequent to processing of the substrate  104 . 
     The substrate processing system  100  further includes a processing chamber  106  that encloses some components of the substrate processing system  100  and contains RF plasma (if used). The substrate processing system  100  includes a gas distribution plate (GDP)  108  (sometimes referred to as a showerhead) and a substrate support  110 . The substrate  104  is arranged on the substrate support  110 . The GDP  108  introduces and distributes process gases during processing of the substrate  104 . 
     If plasma is used, the plasma can be direct or remote plasma. In this example, an RF generating system  120  generates and outputs an RF voltage to either the GDP  108  or the substrate support  110  (the other may be DC grounded, AC grounded, or floating). For example only, the RF generating system  120  may include an RF voltage generator  122  that generates the RF voltage that is fed by a matching network  124  to the GDP  108  or the substrate support  110 . Alternately, the plasma may be delivered by a remote plasma source  126 . 
     A gas delivery system  140  includes one or more gas sources  142 - 1 ,  142 - 2 , . . . , and  142 -N (collectively gas sources  142 ), where N is a positive integer. The gas sources  142  supply one or more etch gas mixtures, precursor gas mixtures, cleaning gas mixtures, ashing gas mixtures, etc. to the processing chamber  106 . Vaporized precursor may also be used. The gas sources  142  are connected by valves  144 - 1 ,  144 - 2 , . . . , and  144 -N (collectively valves  144 ) and mass flow controllers  146 - 1 ,  146 - 2 , . . . , and  146 -N (collectively mass flow controllers  146 ) to a manifold  148 . An output of the manifold  148  is fed to the processing chamber  106 . For example only, the output of the manifold  148  is fed to the GDP  108 . In one embodiment, there is no flow of gas to the backside of the substrate  104 . For example, there is no flow of helium to the backside of the substrate  104 . 
     The substrate support  110  may be an electrostatic chuck including one or more electrodes  150  for electrostatically clamping the substrate  104  to a top surface  152  of a body  154  of the substrate support  110 . Although shown as an electrostatic chuck, the substrate support  110  may be implemented as a pedestal void of mechanical and/or electrical components for holding the substrate  104  in place on the body  154  of the substrate support  110 . The body  154  may include one or more plates. The substrate support  110  may include one or more heating elements  160  for heating the body  154 . As an example, the heating elements  160  may include one or more heating coils. 
     A controller  170  controls operation of the substrate processing system  100  including the pressure control system  102 . The controller  170  may control the pressure differential based on feedback signals from frontside (or chamber) pressure sensor  180  and backside pressure sensor  182 . The sensors  180 ,  182  may be implemented as manometers. The frontside pressure sensor  180  measures pressure within the processing chamber  106 . The backside pressure sensor  182  may measure pressure within a backside line  184  through which gas is drawn under vacuum from a backside (or bottom side)  186  of the substrate  104 . The pressure measurements are provided as feedback information that is used to control depressurization including the removal of gas and the rate of removal of the gas from the processing chamber  106 . The backside line  184  may extend through the body  154  of the substrate support to an area between the substrate  104  and the body  154 . 
     The backside line  184 , as shown, extends from the body  154  to an evacuation line  188  and may include a backside valve  190 . In an embodiment, the backside valve  190  is implemented as a two state valve having an ON (or fully open) state and an OFF (or fully closed) state. The backside line  184  extends from a channel  191  in the body  154  to a point downstream from an evacuation valve  192 . The channel  191  may extend vertically through one or more plates of the body  154  and to the top surface  152 . 
     The evacuation valve  192  is located within the evacuation line  188  and is used to control flow of gas out of the processing chamber  106 . The evacuation valve  192  may be adjusted between fully open, partially open, and closed states. As an example, the evacuation valve  192  may include a throttle plate  194  with variable (or infinite) position adjustability for regulating the opening of the evacuation valve  192  and thus regulating flow of gas from the processing chamber  106 . As another example, the evacuation valve  192  may be a butterfly valve and/or other suitable type of valve. In an embodiment, each position of a plate (or disc) of the valve has a corresponding opening state. As referred to herein, the position of the evacuation valve  192  may refer to a position of the plate (or disc) and/or other component of the evacuation valve  192  that is used to adjust the opening of the evacuation valve  192 . Although the evacuation line  188  is shown as extending from a bottom of the processing chamber  106 , the evacuation line  188  may be located elsewhere. As another example, the evacuation line  188  may extend from a side of the processing chamber  106 . The evacuation line  188  is used to draw gas from the processing chamber  106 . A pump  196  is connected to the evacuation line  188  and draws gas from the processing chamber  106  and from the backside line  184 . Gas can leak around edges of the substrate  104  between the substrate  104  and the body  154  and be drawn away from the backside  186  via the pump  196 . 
     The controller  170  controls operation of the valves  190 ,  192  and the pump  196 . In one embodiment, the pump  196  is continuously on during and subsequent to processing of the substrate  104  and continuously draws gas from the backside line  184  to maintain a low backside pressure. In one embodiment, the backside of the substrate  104  is pumped out constantly to maintain a minimum pressure on the backside of the substrate  104 . The minimum pressure may decrease during the removal of gas and depressurization of the processing chamber. 
     The backside valve  190  may be in an ON state during and subsequent to processing of the substrate  104 . The controller  170  may regulate and/or adjust position of the throttle plate  194  and/or opening state of the evacuation valve  192  to control the pressure differential between P 1  and P 2 , such that P 1  remains greater than P 2 . In one embodiment, the frontside pressure P 1  is greater than or equal to a sum of the backside pressure P 2  and a predetermined safety margin. The predetermined safety margin may be, for example, 5-30% of the frontside pressure P 1 . In one embodiment, the safety margin is at least 5% of the frontside pressure P 1 . In another embodiment, the safety margin is 5-15% of the frontside pressure P 1 . The safety margin is set to not be too large such that the substrate  104  is unable to be lifted off the top surface  152  of the body  154  via lift pins. 
     The controller  170  may control temperature of the substrate support by controlling an amount of current supplied to the heating elements  160 . This control may be based on temperature signals from one or more temperature sensors (e.g., a temperature sensor  198  is shown). The controller  170  may also control other components of the substrate processing system  100 . For example only, the controller  170  may: control the gas delivery system  140  to control flow of process gases; monitor process parameters such as temperature, pressure, power, etc.; and strike and extinguish plasma, remove reactants, etc. The controller  170  may further control a motor  199  for moving the GDP  108  and other upper chamber components relative to the substrate support  110  to adjust a size of a gap G between the GDP  108  and the substrate support  110 . The controller  170  moves the GDP  108  away from the substrate support  110  for placement of the substrate  104  on the substrate support  110  and removal of the substrate  104  from the processing chamber  106 . 
       FIGS.  2 A- 2 B  show an example substrate support assembly  200  and example lift pins  202  that may be used in the substrate processing system  100  of  FIG.  1   . Other lift pin assemblies may be included in the implementation of  FIG.  1   . The substrate support assembly  200  is provided as an example illustration including lift pins for: placing a substrate on a top surface of a body of a substrate support; and lifting the substrate off the body for removal from a corresponding processing chamber. The substrate support assembly  200  may be arranged in the processing chamber  106  of  FIG.  1    and include a substrate supporting plate (also called a top plate)  210 , a supporting column  212 , and a base  214 . The base  214  may include a ring shaped platform or structure (also called a lift ring) in which lift pins and lift pin holder assemblies are installed. The supporting column  212  may move relative to the base  214 . 
     Lift pin holder assemblies  220  are arranged below the substrate supporting plate  210  on the base  214 . Each of the lift pin holder assemblies  220  includes a base portion  226 , one of the lift pins  202 , and a lift pin holder  234 . In some examples, the lift pin holder assemblies  220  and the lift pins  202  are generally cylindrically shaped. The lift pins  202  include circular grooves  231 , which are useful in locking the lift pins  202  into the lift pin holder assemblies. 
     One or more guiding elements  240  may be used to guide the lift pins  202 . In some examples, the guiding elements  240  include cylindrical supports  243  that are attached to a bottom surface of the substrate supporting plate  210 . Each of the cylindrical supports  243  includes a bore  245  for receiving a middle portion the lift pin  202 . Likewise, the substrate supporting plate  210  includes bores  241  for receiving an upper portion of the lift pins  202 . 
     During use, the base  214  may be raised and lowered via a motor  246  relative to the substrate supporting plate  210  (e.g., using the controller  170  of  FIG.  1    and suitable actuators) to vary a height of the upper end of the lift pins  202  relative to an upper surface of the substrate supporting plate  210 . As a result, the lift pins  202  lift the substrate  222  above the substrate supporting plate  210  or are positioned to receive the substrate  222  to be loaded onto the substrate supporting plate  210 . Clearance is provided between the substrate  222  and the upper surface of the substrate supporting plate  210  as shown at  248 . The substrate supporting plate  210  may include a channel connected to a backside line, such as a channel similar to the channel  191  of  FIG.  1   , which is connected to the backside line  184 . 
       FIGS.  3 A- 3 B and  5 A- 6 C  show depressurization methods that may be implemented by the pressure control system  102  and controller  170  of  FIG.  1    and include use of the substrate support assembly of  FIG.  2 A . At least some of the operations of the methods may be iteratively performed. The methods include implementation of algorithms for quickly removing gas from the processing chamber and thus quickly depressurizing the processing chamber  106  during substrate processing and/or subsequent to substrate processing. The frontside pressure is reduced quickly without the frontside pressure dropping below the backside pressure. 
       FIGS.  3 A- 3 B  shows a depressurization method, which may begin at  300 . At  300 , the substrate  104  is disposed on the lift pins  202 . At  302 , the corresponding processing chamber is pumped down. This may include opening the evacuation valve  192  and operating the pump  196  to evacuate and reduce pressure in the processing chamber  106  and prevent a gas pocket beneath the substrate  104 . At  304 , the controller  170  moves the lift pins  202  down to place the substrate on, for example, the plate  210  or the body  154  of the corresponding substrate support  110 . If the substrate support  110  is an electrostatic chuck, then the controller  170  may electrostatically clamp the substrate  104  to the substrate support  110 . 
     At  306 , the controller  170  pressurizes the processing chamber to initial process pressure level according to a process recipe. The initial pressure level may be less than or equal to a low pressure. For example, the initial process pressure may be less than or equal to 4-5 Torr. At  308 , the controller  170  moves the GDP  108  down from, for example, a home position to a processing position. The processing position corresponds to a predetermined gap between the GDP  108  and the substrate support. Operation  308  may be performed while operation  306  is performed. 
     At  310 , the substrate  104  is processed according to the process recipe. During processing, the controller  170  may regulate the opening of the evacuation valve  192 , which may include regulating the position of the evacuation valve  192 , to maintain the frontside pressure at the process pressure level. This may include various processing operations, such as etch, deposition and/or cleaning operations. During processing, the pressure within the processing chamber  106  is less than or equal to the low pressure (e.g., less than or equal to 4-5 Torr). The substrate processing may include formation of features within and/or on the substrate  104 . 
     At  312 , subsequent to the processing of the substrate  104 , the controller  170  begins moving the GDP  108  up away from the substrate support. At  313 , the controller may start removing gas from the processing chamber  106  to depressurize the processing chamber  106  and control the pressure differential by controlling the opening of the evacuation valve  192 . The controller  170  may open the evacuation valve  192  to begin pump down of the processing chamber  106  to the base pressure or predetermined setpoint pressure. Operation  313  may be performed while operation  312  is performed. 
     At  314 , the sensors  180 ,  182  generate pressure signals, which are received at the controller  170 . At  315 , the controller  170  determines whether a differential pressure condition is satisfied, which may include determining whether the frontside pressure is (i) greater than the backside pressure, and/or (ii) more than a predetermined amount greater than the backside pressure. The predetermined amount may be equal to the predetermined safety margin described above. In one embodiment, the safety margin is maintained. As an example, the backside pressure may be subtracted from the frontside pressure and compared to the predetermined safety margin. If the difference is greater than or equal to the safety margin, then the differential pressure condition is satisfied, otherwise the differential pressure condition is not satisfied. In another embodiment, no safety margin is maintained and the controller  170  simply checks if the frontside pressure is greater than the backside pressure. If the frontside pressure is greater, than the differential pressure condition is satisfied. If the differential pressure condition is not satisfied, operation  316  may be performed, otherwise operation  317  is performed. 
     At  316 , the controller  170  may cease depressurizing the processing chamber  106  or slow the rate of depressurization by transitioning the valve  192  to a more closed state (or position). This may include closing the evacuation valve  192 . In one embodiment, the valve  192  is incrementally closed until the frontside pressure is greater than the backside pressure and/or greater than a sum of the backside pressure and the safety margin. Operation  314  may be performed subsequent to operation  316 . 
     At  317 , the controller  170  starts or continues to depressurize the processing chamber. This may include controlling the frontside pressure and the depressurization rate by regulating the opening of the evacuation valve  192  based on a difference in the frontside pressure and the backside pressure. The opening regulation prevents sharp drops in the frontside pressure. The controller  170  may monitor the rate of change in the difference between the frontside and backside pressures. If the difference is decreasing too fast, then the controller  170  may reduce a size of the opening through the evacuation valve  192  by partially closing the evacuation valve  192  to slow the rate of evacuation from the processing chamber  106 . If the rate of change in the differential pressure exceeds a predetermined threshold, then the evacuation valve  192  may be transitioned to a more closed state. If the difference is decreasing at less than a predetermined rate, is not changing, and/or is increasing, then the controller  170  may further open the evacuation valve  192  to increase flow of gas from the processing chamber  106 . If the rate of change in the differential pressure is does not exceed the predetermined threshold, then the evacuation valve  192  may be transitioned to a more open state. The controller  170 , during operations  313 ,  314 ,  315  and  317 , may maximize an opening of the evacuation valve  192  to maximize a depressurization rate of the processing chamber while preventing the frontside pressure from dropping below the backside pressure. This may also occur while maintaining the differential pressure safety margin. The controller  170  may continue to increase the opening of the evacuation valve  192  until one of the above-stated conditions is satisfied which prevents further opening the evacuation valve  192 . 
     Operations  314 - 317  may be performed in parallel with operations  318 - 320 . 
     At  318 , the controller  170  may determine whether the GDP  108  is up. If yes, operation  319  and  320  may be performed. At  319 , the controller  170  performs gas distribution plate homing. The motor  199  used to move the GDP  108  may be a stepper motor and the controller  170  may home to zero the position of the stepper motor. At  320 , the controller  170  may move the lift pins  202  up. This includes overcoming downward pressure remaining on the substrate  104 . Once the substrate  104  is not in contact with a plate or body of the substrate support, the frontside and backside pressures equalize. If the substrate support  110  is an electrostatic chuck, the controller  170  ceases clamping the substrate  104  to the substrate support  110  prior to lifting the substrate  104 . In one embodiment, operation  320  is performed when the frontside pressure is less than a first predetermined threshold (e.g., 2 Torr). In one embodiment, operation  320  is not performed until after operation  322 , as shown by operation  324 . Operation  322  may be performed subsequent to operations  317 ,  319  and  320 . 
     At  322 , the controller  170  may determine whether a first depressurization period has expired since starting depressurization at  320  and/or whether the frontside pressure is less than or equal to a first predetermined threshold. The first predetermined threshold may be 2000 milli-Torr (mT). In one embodiment, the controller  170  determines whether the frontside pressure is between 500-2000 mT prior to permitting upward movement of the lift pins  202 . If yes, operations  324  and  326  may be performed, otherwise operation  314  may be performed. 
     At  324 , the controller  170  may move the lift pins  202  up, as described above. At  326 , the controller  170  continues to depressurize the processing chamber. Once the substrate is lifted off the top surface  152  of the body  154  of the substrate support  110 , (i) the evacuation valve  192  may be fully opened, if not already fully open, to maximize the depressurization rate, and (ii) a pressure differential between the frontside and backside of the substrate  104  is no longer maintained. If the substrate support  110  is an electrostatic chuck, the controller  170  ceases clamping the substrate  104  to the substrate support  110  prior to lifting the substrate  104 . Operation  326  may be performed while operation  324  is performed. 
     At  328 , the controller  170  may determine whether the processing chamber pressure is less than or equal to a second predetermined threshold and/or at the base pressure. If yes, operation  330  may be performed to remove the substrate  104  from the processing chamber  106 . 
       FIG.  4    shows an example timing diagram  400  and plot  402  illustrating portions of the depressurization method of  FIGS.  3 A- 3 B . The timing diagram  400  illustrates four periods. The first period is shown, which corresponds to operation  310 . The second period is shown corresponding to operations  312 ,  313 ,  317 . The third period is shown and corresponds to operations  317 ,  319 ,  320 . Although the lift pins are shown as being moved up during the third period, the lift pins may be moved up during the fourth period as represented by operation  324 . The fourth period is shown and corresponds to at least operation  326 . As an example, the second period may be  3  seconds in length, the third period may be  2  seconds in length, and the fourth period may be  2  seconds in length. 
     The plot  402  includes a frontside pressure curve  404 , a backside pressure curve  406  and an evacuation valve opening curve  408 . As shown, the frontside pressure decreases during removal of gas from and as a result depressurization of the processing chamber  106  of  FIG.  1   . During depressurization of the processing chamber  106 , the backside pressure also decreases, but at a significantly slower rate than the frontside pressure. A differential pressure ΔP is shown. The differential pressure prevents undershoot of the frontside pressure relative to the backside pressure. The controller  170  of  FIG.  1    controls the position and thus the opening of the evacuation valve  192  to prevent the frontside pressure from decreasing below the backside pressure during at least the second and third periods. The frontside pressure may decrease below the backside pressure during the fourth period, as shown. 
       FIGS.  5 A- 5 B  shows a depressurization method for transitioning from a high-pressure traditionally associated with substrate movement. As an example, the high-pressure may be greater than 4-5 Torr. In an embodiment, the high-pressure is greater than 4 Torr. In another embodiment, the high-pressure is greater than 5 Torr. As another example, the high-pressure may be 4-8 Torr. The method may begin at  500 , which includes the substrate  104  being disposed on the lift pins  202 . At  502 , the corresponding processing chamber is pumped down. This may include opening the evacuation valve  192  and operating the pump  196  to evacuate and reduce pressure in the processing chamber  106  and prevent a gas pocket beneath the substrate  104 . At  504 , the controller  170  moves the lift pins  202  down to place the substrate  104  on, for example, the plate  210  or the body  154  of the corresponding substrate support  110 . If the substrate support  110  is an electrostatic chuck, then the controller  170  may electrostatically clamp the substrate  104  to the substrate support  110 . 
     At  506 , the controller  170  pressurizes the processing chamber to initial process pressure level according to a process recipe. The initial processing pressure or a subsequent pressure may be 4-8 Torr. At  508 , the controller  170  moves the GDP  108  down from, for example, a home position to a processing position. The processing position corresponds to a predetermined gap between the GDP  108  and the substrate support  110 . Operation  508  may be performed while operation  506  is performed. 
     At  510 , the substrate  104  is processed according to the process recipe. During processing, the controller  170  may regulate the opening of the evacuation valve  192  to maintain the frontside pressure at the process pressure level. This may include various processing operations, such as etch, deposition and/or cleaning operations. This may include forming features within and/or on the substrate  104 . 
     At  512 , subsequent to the processing of the substrate  104 , the controller  170  begins moving the GDP  108  up away from the substrate support. At  513 , the controller  170  may start removal of gas from and depressurization of the processing chamber  106  and control the pressure differential by controlling the opening of the evacuation valve  192 . Operation  513  may be performed while operation  512  is performed. 
     At  514 , the sensors  180 ,  182  generate pressure signals, which are received at the controller  170 . At  515 , the controller  170  determines whether a differential pressure condition is satisfied, which may include determining whether the frontside pressure is (i) greater than the backside pressure, and/or (ii) more than a predetermined amount greater than the backside pressure. The predetermined amount may be equal to the predetermined safety margin described above. In one embodiment, the safety margin is maintained. As an example, the backside pressure may be subtracted from the frontside pressure and compared to the predetermined safety margin. If the difference is greater than or equal to the safety margin, then the differential pressure condition is satisfied, otherwise the differential pressure condition is not satisfied. In another embodiment, no safety margin is maintained and the controller  170  simply checks if the frontside pressure is greater than the backside pressure. If the frontside pressure is greater, than the differential pressure condition is satisfied. If the differential pressure condition is not satisfied, operation  516  may be performed, otherwise operation  517  is performed. 
     At  516 , the controller  170  may cease depressurizing the processing chamber  106  or slow the rate of depressurization by transitioning the valve  192  to a more closed state. This may include closing the evacuation valve  192 . In one embodiment, the valve  192  is incrementally closed until the frontside pressure is greater than the backside pressure and/or greater than a sum of the backside pressure and the safety margin. Operation  514  may be performed subsequent to operation  516 . 
     At  517 , the controller  170  may perform operations similar to that performed at  317  and starts or continues to depressurize the processing chamber  106 . This may include controlling the frontside pressure and the depressurization rate by regulating the opening of the evacuation valve  192  based on a difference in the frontside pressure and the backside pressure. The controller  170  may monitor the rate of change in the difference between the frontside and backside pressures. If the difference is decreasing too fast, then the controller  170  may reduce a size of the opening through the evacuation valve  192  by partially closing the evacuation valve  192  to slow the rate of evacuation from the processing chamber  106 . If the difference is decreasing at less than a predetermined rate, is not changing, or is increasing, then the controller  170  may further open the evacuation valve  192  to increase flow of gas from the processing chamber  106 . 
     Operations  514 - 517  may be performed in parallel with operations  518 - 520 . 
     At  518 , the controller  170  may determine whether the GDP  108  is up. If yes, operation  519  and  520  may be performed. At  519 , the controller  170  performs gas distribution plate homing. At  520 , the controller  170  may move the lift pins  202  up as described above with respect to operation  320 . If the substrate support  110  is an electrostatic chuck, the controller  170  ceases clamping the substrate  104  to the substrate support  110  prior to lifting the substrate  104 . In one embodiment, operation  520  is not performed until after operation  522 , as shown by operation  524 . Operation  522  may be performed subsequent to operations  517 ,  519  and  520 . 
     At  522 , the controller  170  may determine whether the pressure within the processing chamber is less than or equal to a second predetermined threshold. The second predetermined threshold may refer to a pressure that is less than or equal to, for example, 4-5 Torr. This operation may be performed to minimize popping and/or shifting of the substrate  104  subsequent to processing and during depressurization. Although not shown in  FIG.  5 B , the controller  170  may also determine whether a second depressurization period has expired since starting depressurization at  520 . In one embodiment, if the frontside pressure is less than or equal to the second predetermined threshold, then operations  524  and  526  are performed, otherwise operation  514  is performed. In another embodiment, if the frontside pressure is less than or equal to the second predetermined threshold and the second depressurization period has expired, then operations  524  and  526  are performed, otherwise operation  514  is performed. 
     At  524 , the controller  170  may move the lift pins  202  up, as described above. At  526 , the controller  170  continues to depressurize the processing chamber. Once the substrate is lifted off the top surface  152  of the body  154  of the substrate support  110 , (i) the evacuation valve  192  may be fully opened, if not already fully open, to maximize the depressurization rate, and (ii) a pressure differential between the frontside and backside of the substrate  104  is no longer maintained. If the substrate support  110  is an electrostatic chuck, the controller  170  ceases clamping the substrate  104  to the substrate support  110  prior to lifting the substrate  104 . Operation  526  may be performed while operation  524  is performed. 
     At  528 , the controller  170  may determine whether the processing chamber pressure is less than or equal to a second predetermined threshold and/or at the base pressure. If yes, operation  530  may be performed to remove the substrate  104  from the processing chamber  106 . 
       FIGS.  6 A- 6 C  shows a multiple pressure transitioning process including depressurization. The method may begin at  600 , which includes the substrate  104  being disposed on the lift pins  202 . At  602 , the corresponding processing chamber is pumped down. This may include opening the evacuation valve  192  and operating the pump  196  to evacuate and reduce pressure in the processing chamber  106  and prevent a gas pocket beneath the substrate  104 . At  604 , the controller  170  moves the lift pins  202  down to place the substrate  104  on, for example, the plate  210  or the body  154  of the corresponding substrate support  110 . If the substrate support  110  is an electrostatic chuck, then the controller  170  may electrostatically clamp the substrate  104  to the substrate support  110 . 
     At  606 , the controller  170  pressurizes the processing chamber to initial process pressure level according to a process recipe. The initial pressure level may be a high-pressure (e.g., 4-8 Torr), or a low pressure (e.g., less than or equal to 4-5 Torr). At  608 , the controller  170  moves the GDP  108  down from, for example, a home position to a processing position. The processing position corresponds to a predetermined gap between the GDP  108  and the substrate support. Operation  608  may be performed while operation  606  is performed. 
     At  610 , the substrate  104  is processed according to the process recipe. During processing, the controller  170  may regulate the opening of the evacuation valve  192  to maintain the frontside pressure at the first process pressure level. This may include various processing operations, such as etch, deposition and/or cleaning operations. This may include forming features within and/or on the substrate  104 . 
     At  612 , the controller  170  determines whether there is another process step at a different processing chamber pressure that is different than a current processing chamber pressure. If no, operations  612  and  613  may be performed, otherwise operation  616  may be performed. 
     At  613 , the controller  170  begins moving the GDP  108  up away from the substrate support. At  614 , the controller  170  may start removal of gas from and as a result depressurization of the processing chamber and control the pressure differential by controlling the opening of the evacuation valve  192 . Operation  614  may be performed while operation  613  is performed. Operations  634  and  638  may be performed subsequent to operations  613  and  614 . 
     At  616 , the controller  170  may determine whether the next processing chamber pressure is less than the current processing chamber pressure. If no, operation  630  may be performed, otherwise operation  618  may be performed. 
     At  618 , the sensors  180 ,  182  generate pressure signals, which are received at the controller  170 . At  620 , the controller  170  determines whether a differential pressure condition is satisfied, which may include determining whether the frontside pressure is (i) greater than the backside pressure, and/or (ii) more than a predetermined amount greater than the backside pressure. The predetermined amount may be equal to the predetermined safety margin described above. In one embodiment, the safety margin is maintained. As an example, the backside pressure may be subtracted from the frontside pressure and compared to the predetermined safety margin. If the difference is greater than or equal to the safety margin, then the differential pressure condition is satisfied, otherwise the differential pressure condition is not satisfied. In another embodiment, no safety margin is maintained and the controller  170  simply checks if the frontside pressure is greater than the backside pressure. If the frontside pressure is greater, than the differential pressure condition is satisfied. If the differential pressure condition is not satisfied, operation  622  may be performed, otherwise operation  624  is performed. 
     At  622 , the controller  170  may cease depressurizing the processing chamber  106  or slow the rate of depressurization by transitioning the valve  192  to a more closed state. This may include closing the evacuation valve  192 . In one embodiment, the valve  192  is incrementally closed until the frontside pressure is greater than the backside pressure and/or greater than a sum of the backside pressure and the safety margin. Operation  618  may be performed subsequent to operation  622 . 
     At  624 , the controller  170  may perform operations similar to that performed at  317  and starts or continues to depressurize the processing chamber  106 . This may include controlling the frontside pressure and the depressurization rate by regulating opening of the evacuation valve  192  based on a difference in the frontside pressure and the backside pressure. The controller  170  may monitor the rate of change in the difference between the frontside and backside pressures. If the difference is decreasing too fast, then the controller  170  may reduce a size of the opening through the evacuation valve  192  by partially closing the evacuation valve  192  to slow the rate of evacuation from the processing chamber  106 . If the difference is decreasing at less than a predetermined rate, is being maintained, or is increasing, then the controller  170  may further open the evacuation valve  192  to increase flow of gas from the processing chamber  106 . 
     At  628 , the controller  170  may determine whether the process chamber pressure is at the next process pressure. If yes, operation  632  may be performed, otherwise operation  618  may be performed. 
     At  630 , the pressure within the processing chamber  106  is increased to the next processing pressure. 
     At  632 , the substrate  104  is processed at the next processing chamber pressure and according to the process recipe. During processing, the controller  170  may regulate the opening of the evacuation valve  192  to maintain the frontside pressure at the next process pressure level. This may include various processing operations, such as etch, deposition and/or cleaning operations. This may include forming features within and/or on the substrate  104 . 
     At  634 , the sensors  180 ,  182  generate pressure signals, which are received at the controller  170 . At  635 , the controller  170  determines whether a differential pressure condition is satisfied, which may include determining whether the frontside pressure is (i) greater than the backside pressure, and/or (ii) more than a predetermined amount greater than the backside pressure. The predetermined amount may be equal to the predetermined safety margin described above. In one embodiment, the safety margin is maintained. As an example, the backside pressure may be subtracted from the frontside pressure and compared to the predetermined safety margin. If the difference is greater than or equal to the safety margin, then the differential pressure condition is satisfied, otherwise the differential pressure condition is not satisfied. In another embodiment, no safety margin is maintained and the controller  170  simply checks if the frontside pressure is greater than the backside pressure. If the frontside pressure is greater, than the differential pressure condition is satisfied. If the differential pressure condition is not satisfied, operation  636  may be performed, otherwise operation  637  is performed. 
     At  636 , the controller  170  ceases depressurizing the processing chamber  638 . This may include closing the evacuation valve  192 . Operation  634  may be performed subsequent to operation  636 . 
     At  637 , the controller  170  may perform operations similar to that performed at  317  and starts or continues to depressurize the processing chamber  106 . This may include controlling the frontside pressure and the depressurization rate by regulating the opening of the evacuation valve  192  based on a difference in the frontside pressure and the backside pressure. The controller  170  may monitor the rate of change in the difference between the frontside and backside pressures. If the difference is decreasing too fast, then the controller  170  may reduce a size of the opening through the evacuation valve  192  by partially closing the evacuation valve  192  to slow the rate of evacuation from the processing chamber  106 . If the difference is decreasing at less than a predetermined rate, is not changing, or is increasing, then the controller  170  may further open the evacuation valve  192  to increase flow of gas from the processing chamber  106 . 
     Operations  634 - 637  may be performed in parallel with operations  638 - 640 . 
     At  638 , the controller  170  may determine whether the GDP  108  is up. If yes, operation  639  and  640  may be performed. At  639 , the controller  170  performs gas distribution plate homing. At  640 , the controller  170  may move the lift pins  202  up as described above with respect to operation  640 . In one embodiment, operation  640  is not performed until after operation  642 , as shown by operation  644 . If the substrate support  110  is an electrostatic chuck, the controller  170  ceases clamping the substrate  104  to the substrate support  110  prior to lifting the substrate  104 . Operation  642  may be performed subsequent to operations  637 ,  639 , and  640 . 
     At  642 , the controller  170  may determine whether a first depressurization period has expired since starting depressurization at  640  and/or whether the pressure within the processing chamber is less than or equal to the first predetermined threshold of operation  322  of  FIG.  3 B  and/or the second predetermined threshold  522  of  FIG.  5 B . If yes, operations  644  and  646  may be performed, otherwise operation  634  may be performed. 
     At  644 , the controller  170  may move the lift pins  202  up, as described above. At  646 , the controller  170  continues to depressurize the processing chamber. Once the substrate is lifted off the top surface  152  of the body  154  of the substrate support  110 , (i) the evacuation valve  192  may be fully opened, if not already fully open, to maximize the depressurization rate, and (ii) a pressure differential between the frontside and backside of the substrate  104  is no longer maintained. If the substrate support  110  is an electrostatic chuck, the controller  170  ceases clamping the substrate  104  to the substrate support  110  prior to lifting the substrate  104 . Operation  646  may be performed while operation  644  is performed. 
     At  648 , the controller  170  may determine whether the processing chamber pressure is less than or equal to a second predetermined threshold and/or at the base pressure. If yes, operation  650  may be performed to remove the substrate  104  from the processing chamber  106 . 
     The above-described operations of the methods of  FIGS.  3 A- 3 B  and  FIGS.  4 A- 6 C  are meant to be illustrative examples. The operations may be performed sequentially, synchronously, simultaneously, continuously, during overlapping time periods or in a different order depending upon the application. Also, any of the operations may not be performed or skipped depending on the implementation and/or sequence of events. 
     The foregoing description is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent upon a study of the drawings, the specification, and the following claims. It should be understood that one or more steps within a method may be executed in different order (or concurrently) without altering the principles of the present disclosure. Further, although each of the embodiments is described above as having certain features, any one or more of those features described with respect to any embodiment of the disclosure can be implemented in and/or combined with features of any of the other embodiments, even if that combination is not explicitly described. In other words, the described embodiments are not mutually exclusive, and permutations of one or more embodiments with one another remain within the scope of this disclosure. 
     Spatial and functional relationships between elements (for example, between modules, circuit elements, semiconductor layers, etc.) are described using various terms, including “connected,” “engaged,” “coupled,” “adjacent,” “next to,” “on top of,” “above,” “below,” and “disposed.” Unless explicitly described as being “direct,” when a relationship between first and second elements is described in the above disclosure, that relationship can be a direct relationship where no other intervening elements are present between the first and second elements, but can also be an indirect relationship where one or more intervening elements are present (either spatially or functionally) between the first and second elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A OR B OR C), using a non-exclusive logical OR, and should not be construed to mean “at least one of A, at least one of B, and at least one of C.” 
     In some implementations, a controller is part of a system, which may be part of the above-described examples. Such systems can comprise semiconductor processing equipment, including a processing tool or tools, chamber or chambers, a platform or platforms for processing, and/or specific processing components (a wafer pedestal, a gas flow system, etc.). These systems may be integrated with electronics for controlling their operation before, during, and after processing of a semiconductor wafer or substrate. The electronics may be referred to as the “controller,” which may control various components or subparts of the system or systems. The controller, depending on the processing requirements and/or the type of system, may be programmed to control any of the processes disclosed herein, including the delivery of processing gases, temperature settings (e.g., heating and/or cooling), pressure settings, vacuum settings, power settings, radio frequency (RF) generator settings, RF matching circuit settings, frequency settings, flow rate settings, fluid delivery settings, positional and operation settings, wafer transfers into and out of a tool and other transfer tools and/or load locks connected to or interfaced with a specific system. 
     Broadly speaking, the controller may be defined as electronics having various integrated circuits, logic, memory, and/or software that receive instructions, issue instructions, control operation, enable cleaning operations, enable endpoint measurements, and the like. The integrated circuits may include chips in the form of firmware that store program instructions, digital signal processors (DSPs), chips defined as application specific integrated circuits (ASICs), and/or one or more microprocessors, or microcontrollers that execute program instructions (e.g., software). Program instructions may be instructions communicated to the controller in the form of various individual settings (or program files), defining operational parameters for carrying out a particular process on or for a semiconductor wafer or to a system. The operational parameters may, in some embodiments, be part of a recipe defined by process engineers to accomplish one or more processing steps during the fabrication of one or more layers, materials, metals, oxides, silicon, silicon dioxide, surfaces, circuits, and/or dies of a wafer. 
     The controller, in some implementations, may be a part of or coupled to a computer that is integrated with the system, coupled to the system, otherwise networked to the system, or a combination thereof. For example, the controller may be in the “cloud” or all or a part of a fab host computer system, which can allow for remote access of the wafer processing. The computer may enable remote access to the system to monitor current progress of fabrication operations, examine a history of past fabrication operations, examine trends or performance metrics from a plurality of fabrication operations, to change parameters of current processing, to set processing steps to follow a current processing, or to start a new process. In some examples, a remote computer (e.g. a server) can provide process recipes to a system over a network, which may include a local network or the Internet. The remote computer may include a user interface that enables entry or programming of parameters and/or settings, which are then communicated to the system from the remote computer. In some examples, the controller receives instructions in the form of data, which specify parameters for each of the processing steps to be performed during one or more operations. It should be understood that the parameters may be specific to the type of process to be performed and the type of tool that the controller is configured to interface with or control. Thus as described above, the controller may be distributed, such as by comprising one or more discrete controllers that are networked together and working towards a common purpose, such as the processes and controls described herein. An example of a distributed controller for such purposes would be one or more integrated circuits on a chamber in communication with one or more integrated circuits located remotely (such as at the platform level or as part of a remote computer) that combine to control a process on the chamber. 
     Without limitation, example systems may include a plasma etch chamber or module, a deposition chamber or module, a spin-rinse chamber or module, a metal plating chamber or module, a clean chamber or module, a bevel edge etch chamber or module, a physical vapor deposition (PVD) chamber or module, a chemical vapor deposition (CVD) chamber or module, an atomic layer deposition (ALD) chamber or module, an atomic layer etch (ALE) chamber or module, an ion implantation chamber or module, a track chamber or module, and any other semiconductor processing systems that may be associated or used in the fabrication and/or manufacturing of semiconductor wafers. 
     As noted above, depending on the process step or steps to be performed by the tool, the controller might communicate with one or more of other tool circuits or modules, other tool components, cluster tools, other tool interfaces, adjacent tools, neighboring tools, tools located throughout a factory, a main computer, another controller, or tools used in material transport that bring containers of wafers to and from tool locations and/or load ports in a semiconductor manufacturing factory.