Methods for verifying gas flow rates from a gas supply system into a plasma processing chamber

Abstract

Methods of measuring gas flow rates in a gas supply system for supplying gas to a plasma processing chamber are provided. In a differential flow method, a flow controller is operated at different set flow rates, and upstream orifice pressures are measured for the set flow rates at ambient conditions. The measured orifice pressures are referenced to a secondary flow verification method that generates corresponding actual gas flow rates for the different set flow rates. The upstream orifice pressures can be used as a differential comparison for subsequent orifice pressure measurements taken at any temperature condition of the chamber. In an absolute flow method, some parameters of a selected gas and orifice are predetermined, and other parameters of the gas are measured while the gas is being flowed from a flow controller at a set flow rate through an orifice. In this method, any flow controller set point can be flowed at any time and at any chamber condition, such as during plasma processing operations. Gas supply systems are also disclosed.

1 . A method for verifying process gas flow rates from a gas supply system to a plasma processing chamber, the method comprising: 
 a) setting a first flow controller to a first set point and flowing a gas at a first set flow rate from the first flow controller, the gas flowing through a first orifice of an orifice array into a plasma processing chamber which is at ambient temperature;    b) setting the first flow controller to a second set point and flowing the gas at a second set flow rate from the first flow controller, the gas flowing through the first orifice or a second orifice of the orifice array into the plasma processing chamber which is at ambient temperature;    c) for each of the first and second set flow rates, measuring the actual flow rate of the gas into the plasma processing chamber;    d) determining a relationship between the first and second set flow rates and the actual flow rates for the first flow controller;    e) measuring the pressure of the gas upstream of the first and second orifices at the first and second set flow rates, respectively, with the chamber at ambient temperature;    f) determining an empirical factor K d  for the first flow controller for each of the first and second orifices using the actual flow rates and the measured upstream gas pressures for the first and second set flow rates;    g) setting the first flow controller to a third set point and flowing the gas at a third set flow rate from the first flow controller, the gas flowing through the first or second orifice into the plasma processing chamber;    h) measuring the pressure of the gas upstream of the first or second orifice at the third set flow rate; and    i) determining the flow rate of the gas through the first or second orifice at the third set flow rate using the measured gas pressure and K d  for the respective first or second orifice.    
   
   
       2 . The method of  claim 1 , wherein the gas is flowed through the first and second orifices at a viscous sonic flow rate.  
   
   
       3 . The method of  claim 1 , wherein the actual flow rate of the gas is determined by measuring the rate of pressure increase in the plasma processing chamber as the gas is flowed into the plasma processing chamber at each of the first set flow rate and second set flow rate.  
   
   
       4 . The method of  claim 1 , wherein for g), the plasma processing chamber is at a temperature above ambient temperature.  
   
   
       5 . The method of  claim 4 , wherein g) is performed before or during plasma processing of a semiconductor substrate in the plasma processing chamber.  
   
   
       6 . The method of  claim 1 , comprising repeating a)-i) for a second flow controller and the same or a different gas.  
   
   
       7 . The method of  claim 1 , wherein the plasma processing chamber comprises inner and outer zones through which process gas is supplied by a showerhead electrode via the orifice array.  
   
   
       8 . The method of  claim 1 , comprising performing e) subsequent to a)-c).  
   
   
       9 . The method of  claim 1 , comprising performing e) simultaneously with a)-c).  
   
   
       10 . The method of  claim 1 , comprising, for a), b) and g), automatically determining with a control section of the gas supply system the first or second orifice of the orifice array to which the gas is flowed from the first flow controller, the gas being flowed through the first orifice and/or second orifice at a viscous sonic flow rate for each of the first, second and third set flow rates.  
   
   
       11 . The method of  claim 1 , wherein the first and second flow controllers are mass flow controllers.  
   
   
       12 . The method of  claim 1 , wherein the gas is a tuning gas.  
   
   
       13 . The method of  claim 1 , comprising replacing the first flow controller and/or the second flow controller with a respective replacement flow controller, and repeating a)-f).  
   
   
       14 . The method of  claim 1 , comprising repeating a)-f) using a different gas.  
   
   
       15 . A computer readable medium having a computer readable program code stored thereon, the computer readable medium implementing the method of  claim 1 .  
   
   
       16 . A method for verifying process gas flow rates from a gas supply system to a plasma processing chamber, the method comprising: 
 a) setting a first flow controller to a first set point and flowing a first gas at a first flow rate from the first flow controller, the first gas flowing at a viscous sonic flow rate through a first orifice of an orifice array into a plasma processing chamber;    b) measuring a pressure (P 1 ) and temperature (T 1 ) of the first gas upstream of the first orifice at the first flow rate;    c) measuring a cross-sectional flow area (A) of the first orifice;    d) determining for the first gas, the specific heat at constant volume (C v ), the specific heat at constant pressure (C p ), the molecular weight (M) and the absolute flow empirical factor (K a ); and    e) calculating the flow rate Q of the first gas through the first orifice using the following equations (i)-(iii):                  Q   ⁢           =           ⁢           AP   1     ⁡     (       P   2       P   1       )         1   /   γ       ⁢           ⁢         {       (       2   ⁢           ⁢   γ       γ   ⁢           -           ⁢   1       )     ⁢           ⁢           R   0     ⁢           ⁢     T   1       M     ⁡     [     1   ⁢           -           ⁢       (       P   2       P   1       )         (     γ   ⁢           -           ⁢   1     )     /   γ         ]         }       1   /   2       ·     K   a                 (   i   )                 where R 0  is the universal gas constant:      γ= C   p   /C   v , and  (ii)    P   2   /P   1   =[2 /(γ+1)] γ/(γ−1)   =r   c .  (iii)    
   
   
       17 . The method of  claim 16 , wherein the plasma processing chamber comprises inner and outer zones through process gas is supplied by a showerhead electrode via the orifice array.  
   
   
       18 . The method of  claim 16 , wherein the first flow controller is a mass flow controller.  
   
   
       19 . The method of  claim 16 , comprising: 
 setting the first flow controller to a second set point and flowing the first gas at a second flow rate from the first flow controller, the first gas flowing at a viscous sonic flow rate through the first orifice or a second orifice of the orifice array into the plasma processing chamber;    repeating b)-e) for the second set point of the first flow controller.    
   
   
       20 . The method of  claim 16 , repeating a)-e) for at least a second flow controller.  
   
   
       21 . A computer readable medium having a computer readable program code stored thereon, the computer readable medium implementing the method of  claim 16 .  
   
   
       22 . A method for verifying process gas flow rates from a gas supply system to a plasma processing chamber, the method comprising: 
 a) setting a first flow controller to a first set point and flowing a carrier gas at a first flow rate from the first flow controller, the carrier gas flowing at a viscous sonic flow rate through a first orifice of an orifice array into a plasma processing chamber;    b) measuring a pressure (P 1 ) and temperature (T 1 ) of the carrier gas upstream of the first orifice at the first flow rate;    c) measuring a cross-sectional flow area (A) of the orifice;    d) determining for the carrier gas, the specific heat at constant volume (C v ), the specific heat at constant pressure (C p ), the molecular weight (M) and the absolute flow empirical factor (K a );    e) calculating the flow rate Q of the carrier gas through the orifice using the following equations (i)-(iii):                  Q   ⁢           =           ⁢           AP   1     ⁡     (       P   2       P   1       )         1   /   γ       ⁢           ⁢         {       (       2   ⁢           ⁢   γ       γ   ⁢           -           ⁢   1       )     ⁢           ⁢           R   0     ⁢           ⁢     T   1       M     ⁡     [     1   ⁢           -           ⁢       (       P   2       P   1       )         (     γ   ⁢           -           ⁢   1     )     /   γ         ]         }       1   /   2       ·     K   a                 (   i   )                 where R 0  is the universal gas constant:      γ= C   p   /C   v , and  (ii)    P   2   /P   1 =[2/(γ+1)] γ/(γ−1)   =r   c .  (iii)    e) then setting a second flow controller to a second set point and flowing a seed gas at a second flow rate from the second flow controller, the seed gas being mixed with the carrier gas to form a gas mixture which is flowed through the first orifice and into the plasma processing chamber, the second flow rate being subsonic and/or non-viscous when the seed gas alone is flowed through the first orifice;    f) measuring the pressure (P 1 ) and temperature (T 1 ) of the gas mixture upstream of the first orifice;    g) calculating the flow rate Q of the gas mixture through the first orifice using equation (i) and C v , C p , M and K a  for the carrier gas; and    h) comparing the value of Q of the carrier gas to the value of Q of the gas mixture to determine the flow rate of the seed gas through the first orifice.    
   
   
       23 . The method of  claim 22 , wherein the plasma processing chamber comprises inner and outer zones through which process gas is supplied by a showerhead electrode.  
   
   
       24 . The method of  claim 22 , wherein the first flow controller is a mass flow controller.  
   
   
       25 . A computer readable medium having a computer readable program code stored thereon, the computer readable medium implementing the method of  claim 22 .  
   
   
       26 . A gas supply system adapted to supply process gas into a plasma processing chamber, comprising: 
 a gas line adapted to be in flow communication with a gas supply section;    an orifice array in flow communication with the gas line, the orifice array comprising at least two orifices;    a first pressure sensor in flow communication with the orifice array, the first pressure sensor being adapted to measure a first range of gas pressure upstream of the orifice array; and    a second pressure sensor in flow communication with the orifice array, the second pressure sensor being adapted to measure a second range of gas pressure upstream of the orifice array, the second range of gas pressure having an upper value which is higher than an upper value of the first range of gas pressure.    
   
   
       27 . The gas supply system of  claim 26 , wherein further comprising the gas supply section including a plurality of gas sources.  
   
   
       28 . The gas supply system of  claim 26 , wherein the plasma processing chamber comprises inner and outer zones through which process gas is supplied by a showerhead electrode via the orifice array.  
   
   
       29 . The gas supply system of  claim 26 , further comprising: 
 a valve associated with each orifice to control flow of the gas through the orifice; and    a control section adapted to control operation of the first and second pressure sensors and each of the valves.