Abstract:
A liquid delivery system for a substrate processing system includes a liquid ampoule to store liquid precursor. A pressure adjusting system adjusts pressure in the liquid ampoule. A pressure sensor senses a pressure in the liquid ampoule. A capillary injector includes a capillary tube in fluid communication with an output of the liquid ampoule. A temperature control device controls a temperature of the capillary tube. A first valve has an input connected to the capillary tube. A controller is configured to determine a predetermined pressure in the liquid ampoule corresponding a desired flow rate and a predetermined temperature of the capillary tube, maintain the temperature of the capillary tube at the predetermined temperature, communicate with the pressure sensor and the pressure adjusting system, and control the pressure in the liquid ampoule to the predetermined pressure to provide the desired flow rate.

Description:
FIELD 
       [0001]    The present disclosure relates to liquid flow control, and more particularly to systems and methods for supplying liquid in substrate processing systems. 
       BACKGROUND 
       [0002]    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. 
         [0003]    Substrate processing systems are used to deposit and etch film on a substrate. For example for the substrate processing system may perform chemical vapor deposition (CVD), plasma-enhanced (PE) CVD, atomic layer deposition (ALD), PEALD, etc. Deposition and/or etching may be performed by supplying a gas mixture to a processing chamber. The gas mixture may include one or more gases that are mixed together. In some situations, one or more of the gases may be generated from a liquid precursor that is vaporized. Precise metering of the liquid precursor is performed to ensure that the correct gas mixture is formed in the processing chamber. 
         [0004]    Thermal or Coriolis flow controllers are typically used to meter the liquid precursor flowing to the vaporizer. Liquid flow controllers are fully opened until a metering tube is filled. As a result, the liquid flow controllers typically overshoot a desired flow rate. In these types of systems, settling time for the flow rate can be greater than 10 seconds. Some substrate processing systems with long settling times divert the liquid or vaporized precursor until liquid flow is stabilized. Occasionally, a bubble will become trapped in the metering tube and inaccurate or no flow will persist until the liquid delivery system is serviced. 
       SUMMARY 
       [0005]    A liquid delivery system for a substrate processing system includes a liquid ampoule to store liquid precursor. A pressure adjusting system adjusts pressure in the liquid ampoule. A pressure sensor senses a pressure in the liquid ampoule. A capillary injector includes a capillary tube in fluid communication with an output of the liquid ampoule. A temperature control device controls a temperature of the capillary tube. A first valve has an input connected to the capillary tube. A controller is configured to determine a predetermined pressure in the liquid ampoule corresponding a desired flow rate and a predetermined temperature of the capillary tube, maintain the temperature of the capillary tube at the predetermined temperature, communicate with the pressure sensor and the pressure adjusting system, and control the pressure in the liquid ampoule to the predetermined pressure to provide the desired flow rate. 
         [0006]    In other features, a vaporizer has a first input in fluid communication with an output of the first valve. A liquid flow meter, in fluid communication with an output of the liquid ampoule and an input of the capillary tube, measures an actual flow rate. When the actual flow rate is not equal to the desired flow rate, the controller adjusts the pressure in the liquid ampoule using the pressure adjusting system. 
         [0007]    In other features, when the actual flow rate is equal to the desired flow rate after the adjustment, the controller updates the predetermined pressure corresponding to the desired flow rate based on the adjustment. The pressure adjusting system comprises a vacuum source and a second valve in fluid communication with the liquid ampoule to selectively reduce the pressure in the liquid ampoule. A push gas source and a third valve in fluid communication with the liquid ampoule selectively increase the pressure in the liquid ampoule. 
         [0008]    In other features, a first restricted orifice is arranged between the vacuum source and the second valve. A second restricted orifice is arranged between the vacuum source and the third valve. A filter is arranged between outputs of the second valve and the third valve and the liquid ampoule. The temperature control device comprises a Peltier device. 
         [0009]    In other features, a second valve is arranged between the liquid flow meter and the capillary injector. The second valve selectively injects purge gas into the capillary tube. 
         [0010]    In other features, an output end of the capillary tube is located less than 1 inch from a diaphragm of the first valve. The controller generates and stores a table including a plurality of predetermined pressures for the liquid ampoule and a corresponding plurality of desired flow rates. 
         [0011]    A method for liquid delivery in a substrate processing system includes storing liquid precursor in a liquid ampoule; providing a capillary injector that includes a capillary tube and a first valve having an input connected to the capillary tube; determining a predetermined pressure in the liquid ampoule that corresponds to a desired flow rate and a predetermined temperature of the capillary tube; maintaining a temperature of the capillary tube at the predetermined temperature; and controlling pressure in the liquid ampoule to the predetermined pressure to achieve the desired flow rate. 
         [0012]    In other features, the method includes vaporizing liquid received from an output of the first valve. The method includes measuring an actual flow rate at an output of the liquid ampoule using a liquid flow meter; and adjusting the pressure in the liquid ampoule when the actual flow rate is not equal to the desired flow rate. 
         [0013]    In other features, the method includes updating the predetermined pressure corresponding to the desired flow rate based on the adjustment when the actual flow rate is equal to the desired flow rate after the adjustment. 
         [0014]    In other features, adjusting the pressure comprises selectively opening a second valve to a vacuum source to reduce the pressure in the liquid ampoule; and selectively opening a third valve to a push gas source to increase the pressure in the liquid ampoule. 
         [0015]    In other features, the method includes arranging a first restricted orifice between the vacuum source and the second valve; and arranging a second restricted orifice between the vacuum source and the third valve. The method includes arranging a filter between outputs of the second valve and the third valve and the liquid ampoule. The method includes adjusting the temperature of the capillary tube using a Peltier device. 
         [0016]    In other features, the method includes arranging a second valve between the liquid flow meter and the capillary injector. The second valve selectively injects purge gas into the capillary tube. An output end of the capillary tube is located less than 1 inch from a diaphragm of the first valve. The method includes generating a table including a plurality of predetermined pressures for the liquid ampoule and a corresponding plurality of desired flow rates. 
         [0017]    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 
         [0018]    The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0019]      FIG. 1  is a functional block diagram of an example pressure-based liquid flow control system according to the present disclosure; 
           [0020]      FIG. 2  illustrates an example method for operating the pressure-based liquid flow control system according to the present disclosure; 
           [0021]      FIG. 3  illustrates an example method for generating values for desired flow rates and corresponding desired pressures; and 
           [0022]      FIG. 4  is a functional block diagram of an example of a substrate processing system used in conjunction with the pressure-based liquid flow control system. 
       
    
    
       [0023]    In the drawings, reference numbers may be reused to identify similar and/or identical elements. 
       DETAILED DESCRIPTION 
       [0024]    The present disclosure relates to systems and methods for pressure-based liquid flow control of liquid precursor from a liquid ampoule. The liquid precursor is delivered using a capillary tube. Isothermal flow through the capillary tube is consistent for a given pressure drop. Before the systems and methods described herein deliver the liquid precursor, pressure in the liquid ampoule is set to a predetermined pressure corresponding to a predetermined flow rate. The pressure in the liquid ampoule is maintained at the predetermined pressure during delivery of the liquid precursor from the liquid ampoule. 
         [0025]    When flow of the liquid precursor is required, a valve is opened and liquid precursor from a capillary tube flows through the valve. Liquid flow at a desired flow rate will occur quickly (e.g. within a fraction of a second) after the valve is opened. In some examples, the distance between a diaphragm of the valve and an output end of the capillary tube is relatively short to reduce the time to the desired flow rate. Both the temperature of the liquid in the capillary tube and the push pressure are maintained at controlled values to generate and maintain the desired flow rate. 
         [0026]    A controller may be used to maintain the constant pressure in the liquid ampoule by pulsing one or more valves. Pressure under the desired set point is adjusted by increasing head pressure in the liquid ampoule by pulsing the inert push gas through a valve. Pressure over the desired set point is adjusted by reducing head pressure in the liquid ampoule by pulsing another valve to vacuum. Initial pressure requirements may be determined by slowly ramping the pressure up or down in the liquid ampoule and storing a corresponding flow rate for the pressure in memory associated with the controller. 
         [0027]    Alternately, a digital pressure controller that maintains a pressure set point based on an analog or bus signal maybe used in place of the pulsing valves to set and control the ampoule pressure. The digital pressure controller will receive a control signal from the controller. The digital pressure controller may vent excess pressure to atmosphere, which may be suitable for non-reactive and non-toxic liquids. 
         [0028]    When the desired flow rate changes, the controller changes the pressure to a pressure value corresponding to a new desired flow rate. The controller monitors the flow rate during liquid precursor delivery. For example only, the controller may monitor the flow rate during liquid precursor delivery using a thermal or Coriolis device. The controller compares the actual flow rate to the desired flow rate and adjusts the pressure in the liquid ampoule as needed. The adjusted pressure can be used to update or replace the pressure value stored in the memory array for the desired flow rate. 
         [0029]    Referring now to  FIG. 1 , an example of a pressure-based liquid flow control system  10  is shown. The pressure-based liquid flow control system  10  includes a liquid ampoule  12  and a pressure adjusting system  14 . The pressure adjusting system  14  adjusts the pressure in the liquid ampoule  12 . The pressure adjusting system  14  includes a vacuum source  20  that communicates with a restricted orifice  22 . An output of the restricted orifice  22  flows to a valve  24  to selectively provide vacuum pressure to the liquid ampoule  12  to reduce a pressure in the liquid ampoule  12  as needed. The pressure adjusting system  14  also includes a gas source  30  that communicates with a restricted orifice  32  and a valve  34  to selectively provide push gas to increase pressure in the liquid ampoule  12 . 
         [0030]    Outputs of the valves  24  and  34  are input to a filter  36 . An output of the filter  36  is input to the liquid ampoule  12 . The filter  36  acts as a snubber to reduce the impact of pressure changes as the valves  24  and  34  are modulated. A pressure sensor  37  monitors pressure in the liquid ampoule  12 . 
         [0031]    When downstream valves are open, liquid precursor flows out of the liquid ampoule  12  through a valve  38  to a liquid flow meter (LFM)  40 . For example only, the LFM  40  may include a thermal or Coriolis device. An output of the liquid flow meter  40  flows through valves  42  and  48  to a capillary injector  50 . One input of the valve  48  is connected to an output of the valve  42 . Another input of the valve  48  may be connected to a purge gas source  46 . The valve  48  may be used to selectively supply purge gas to purge liquid precursor in the capillary injector  50  as needed while the valve  42  is closed to prevent purge gas flow back to the liquid ampoule  12 . 
         [0032]    In some examples, the capillary injector  50  is temperature controlled to control a temperature of the liquid precursor. The capillary injector  50  includes a capillary tube  52 , a temperature adjusting device  54 , and a valve  56 . One input of the valve  56  is connected to an output of the capillary tube  52 . An output of the valve  56  is connected to a vaporizer  58 . Another input of the valve  56  may be connected to a carrier gas source. A temperature sensor  57  may be used to monitor a temperature of the capillary tube  52  if closed loop control is desired. Open loop control may also be used. The temperature adjusting device  54  may include a resistive heater, a Peltier device or other temperature adjusting device. 
         [0033]    A controller  60  may be used to monitor process parameters such as the pressure in the liquid ampoule  12  as measured by the pressure sensor  37  and an actual flow rate of the liquid as measured by the liquid flow meter  40 . The controller  60  may also control set points for the pressure control valves  22  and  32  and opening and closing operation of the valves  24 ,  34 ,  38 ,  42 ,  48  and  56 . Vaporized gas output by the vaporizer  58  is input to a substrate processing system  90 . The controller  60  may also control operation of the temperature adjusting device  54 . 
         [0034]    Referring now to  FIG. 2 , an example of a method  150  for operating the pressure-based liquid flow control system is shown. At  160 , control determines whether there is a flow request for the liquid precursor. If not, control returns to  160 . Otherwise, control continues at  162  and determines whether the temperature of the capillary tube T cap  is equal to a desired temperature T cap     —     des . If not, control adjusts T cap  to T cap     —     des . At  168 , control measures pressure in the liquid ampoule. At  172 , control adjusts the pressure P act  in the liquid ampoule to a desired pressure P des  corresponding to the desired flow rate FR des . 
         [0035]    At  176 , control determines whether the pressure P act  in the liquid ampoule is equal to the desired pressure P des . If  176  is true, control continues at  180  and opens the valve to supply liquid to the vaporizer. 
         [0036]    At  182 , control optionally waits a stabilization period. At  184 , control determines whether P act =P des . As can be appreciated, this condition may be met if P act  is within a predetermined range of P des . If not, control continues with  186  and adjusts P act  to P des . If  184  is true, control continues with  190  and determines whether T cap =T cap     —     des . As can be appreciated, this condition may be met if T cap  is within a predetermined range of T cap     —     des . If not, control continues with  192  and adjusts T cap  to T cap     —     des . If  190  is true, control continues with  196  and determines whether FR act =FR des . As can be appreciated, this condition may be met if FR act  is within a predetermined range of FR des . If not, control continues with  200  and adjusts P act  as needed to achieve FR des . At  204 , control stores the new P act  as P des  corresponding to FR des . 
         [0037]    At  208 , control determines whether the flow request for liquid precursor has ended. If not, control continues with  184 . Otherwise, control closes the valve at  212  and continues with  160 . 
         [0038]    Referring now to  FIG. 3 , an example of a method for determining a relationship between one or more desired flow rates and desired pressures within the liquid ampoule is shown. As can be appreciated, the capillary tube is kept at a predetermined temperature for each data set. The process can be repeated for one or more different capillary tube temperatures and the desired flow rate and desired pressure values can be stored by each of the selected capillary temperatures. 
         [0039]    At  230 , control determines whether there is a request to set initial values for the desired flow rates and desired pressures. If  230  is true, control continues with  231  and sets the capillary tube temperature to one of the desired capillary tube temperatures. At  232 , a desired pressure P des  is set to an initial value such as a lowest or highest pressure. At  234 , control sets pressure in the liquid ampoule to the desired pressure P des . At  238 , control waits a settling period. At  242 , control measures the actual flow rate FR act . At  246 , control sets the desired flow rate FR des  equal to the actual flow rate FR act  for the desired pressure P des . At  250 , control determines whether flow rates for all of the desired pressure values P des  have been determined. If not, control continues with  254  and increments the desired pressure to the next desired pressure (or decrements if starting from the highest desired pressure P des ) and continues with  234 . The process may be repeated for other capillary tube temperatures. 
         [0040]    In some examples, a Peltier-type device is used to maintain the capillary tube at a constant temperature. The Peltier-type device typically includes first and second sides. When DC current flows through the device, heat flows from one side to the other. In other words, one side cools while the other side heats up. Either the hot side (or the cool side) is attached to a heat sink so that it remains at ambient temperature, while the cool side or the hot side goes below (or above) room temperature. In some applications, multiple Peltier-type devices can be cascaded together for lower or higher temperatures. 
         [0041]    In some examples, the capillary tube is incorporated into the valve so that the output end of the capillary tube is just below the diaphragm of the valve. In some examples, the output end of the capillary tube is arranged within close proximity of the diaphragm of the valve. For example only, the output end of the capillary tube may be arranged within 1″ of the diaphragm. The calibrated orifices may be used to achieve consistent flows to vacuum to relieve pressure and consistent flows from the inert push gas to raise pressure. The filter acts as a snubber to minimize the effects of the push gas and vacuum valves opening and closing. 
         [0042]    The controller uses control loops to control the temperature of the capillary tube. The calibration loop varies the pressure of the liquid ampoule and records the resultant flow rate. Another control loop maintains a last pressure set point by cycling the vacuum or pressure valves on or off. Another control loop reads the actual flow rate from the LFM, compares the actual flow rate to the desired flow rate and adjusts the pressure. The pressure is stored for the corresponding flow rate and may be used to adjust or replace the pressure set point previously stored in the controller. A delay can be implemented to isolate the system from initial flow rate spikes from the LFM. 
         [0043]    The purge gas valve provides for periodic purging of the capillary tube. Some types of liquid precursor are not stable and may clog the capillary tube if the liquid is left in the capillary tube too long. 
         [0044]    In some examples, the valves include valves that are normally used for atomic layer deposition (ALD) processes. While the action of the ALD valve can influence repeatability since movement of a diaphragm during opening acts like a pump, a size of the capillary tube can be selected to help minimize this affect. For lower flow rates, a stroke of the ALD valve can be reduced. In some examples, a turn down ratio from maximum to minimum stable flow is around 5:1. In other examples, multiple valve/capillary tube assemblies may be used to extend the turn down ratio. 
         [0045]    In some examples, surface tension may result in small quantities of liquid adhering to the valve. Introduction of a carrier gas can be used to move liquid out of the valve and into the vaporizer as needed. 
         [0046]    Referring now to  FIG. 4 , an example of a substrate processing system used in conjunction with the pressure-based liquid flow control system is shown. In some examples, the substrate processing system is used to perform atomic layer deposition (ALD), plasma-enhanced (PE) ALD, chemical vapor deposition (CVD), or PECVD. 
         [0047]    A substrate processing system  310  is shown to include a processing chamber  312 . Gas may be supplied to the processing chamber using a gas distribution device  314  such as showerhead or other device. A substrate  318  such as a semiconductor wafer may be arranged on a pedestal  316  during processing. The pedestal  316  may be an electrostatic chuck, a mechanical chuck or other type of chuck. 
         [0048]    A gas delivery system  320  may include one or more gas sources  322 - 2 ,  322 - 2 , . . . , and  322 -N (collectively gas sources  322 ), where N is an integer greater than one. Valves  324 - 1 ,  324 - 2 , . . . , and  324 -N, mass flow controllers  326 - 1 ,  326 - 2 , . . . , and  326 -N, or other flow control devices may be used to controllably supply a selected gas mixture to a manifold  330 , which supplies the gas mixture to the processing chamber  312 . The manifold  330  also receives an output of the vaporizer  58  that vaporizes liquid supplied by the pressure-based liquid flow control system  10 . 
         [0049]    A controller  340  may be used to monitor process parameters such as temperature, pressure and process timing. The controller  340  may be implemented by the controller  60  or as a separate controller. The controller  340  may also be used to control process devices such as the gas delivery system  320 , a pedestal heater  342 , a plasma generator  346 , and/or evacuation of the processing chamber  312 . In some examples, a valve  350  and pump  352  may be used to remove reactants from the processing chamber  312 . The RF plasma generator  346  may generate the RF plasma in the processing chamber. The RF plasma generator  346  may be an inductive or capacitive-type RF plasma generator. The RF plasma generator  346  may include a high frequency RF generator, a low frequency RF generator and a matching network (not shown). 
         [0050]    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. 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. 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. 
         [0051]    In this application, including the definitions below, the term controller may be replaced with the term circuit. The term controller may refer to, be part of, or include an Application Specific Integrated Circuit (ASIC); a digital, analog, or mixed analog/digital discrete circuit; a digital, analog, or mixed analog/digital integrated circuit; a combinational logic circuit; a field programmable gate array (FPGA); a processor (shared, dedicated, or group) that executes code; memory (shared, dedicated, or group) that stores code executed by a processor; other suitable hardware components that provide the described functionality; or a combination of some or all of the above, such as in a system-on-chip. 
         [0052]    The term code, as used above, may include software, firmware, and/or microcode, and may refer to programs, routines, functions, classes, and/or objects. The term shared processor encompasses a single processor that executes some or all code from multiple controllers. The term group processor encompasses a processor that, in combination with additional processors, executes some or all code from one or more controllers. The term shared memory encompasses a single memory that stores some or all code from multiple controllers. The term group memory encompasses a memory that, in combination with additional memories, stores some or all code from one or more controllers. The term memory may be a subset of the term computer-readable medium. The term computer-readable medium does not encompass transitory electrical and electromagnetic signals propagating through a medium, and may therefore be considered tangible and non-transitory. Non-limiting examples of a non-transitory tangible computer readable medium include nonvolatile memory, volatile memory, magnetic storage, and optical storage. 
         [0053]    The apparatuses and methods described in this application may be partially or fully implemented by one or more computer programs executed by one or more processors. The computer programs include processor-executable instructions that are stored on at least one non-transitory tangible computer readable medium. The computer programs may also include and/or rely on stored data.