Method and apparatus for pressure control in vacuum processors

A method for controlling pressure in an evacuated processing chamber comprising the steps of:

• retrieving from electronic memory a desired pressure value reflecting a desired pressure level for the processing chamber;
• retrieving from electronic memory a desired gas flow value representing a desired gas flow rate through the processing chamber;
• retrieving the current valve position;
• retrieving from electronic memory a constant, .beta., equal to standard pressure, divided by the volume of the chamber, divided by standard temperature;
• accessing from electronic memory a mathematical function having a domain comprising pressures in the processing chamber and gas flow rates into the processing chamber, and having a range comprising positions of the throttle valve;
• positioning a throttle valve to an initial position, the throttle valve used to control pressure in the processing chamber;
• measuring pressure and temperature within the processing chamber;
• calculating the change in pressure with respect to the change in time, dP/dt;
• calculating an outflow by applying the current valve position to the inverse of the mathematical function accessed from electronic memory and multiplying the result by the measured pressure;
• calculating an effective in-flow equal to the change in pressure with respect to the change in time multiplied by the constant, multiplied by the temperature of the chamber plus the outflow,
• Q.sub.in.sup.eff =[(dP/dt).times..beta..times.T.sub.chamber ]+Q.sub.out ;
• calculating a conductance which is substantially equal to the effective in-flow divided by the measured pressure;
• and
• positioning the throttle valve according to the mathematical function by applying the conductance to the inverse of the mathematical function accessed from electronic memory.

A method for controlling pressure in an evacuated processing chamber comprising the steps of:

• retrieving from electronic memory a desired pressure value reflecting a desired pressure level for the processing chamber;
• retrieving from electronic memory a desired gas flow value representing a desired gas flow rate through the processing chamber;
• positioning a throttle valve to an initial position, the throttle valve used to control pressure in the processing chamber;
• measuring pressure within the processing chamber;
• calculating the difference between the desired pressure and the measured pressure;
• calculating the change in pressure with respect to the change in time;
• storing in electronic memory the change in pressure with respect to the change in time;
• selecting the maximum absolute value of the change in pressure with respect to the change in time;
• and
• subsequent to said positioning step, repositioning the throttle valve based on the difference between the desired pressure and the measured pressure using proportional and integral control, wherein integral control is delayed until the absolute value of the change in pressure with respect to the change in time has decreased to below a preset threshold percentage of the selected maximum absolute value.

An apparatus for processing materials under a controlled low pressure environment comprising:

• a processing chamber;
• a gas introduction system in fluid communication with said processing chamber;
• a vacuum pump in fluid communication with said processing chamber configured to remove gas from said processing chamber;
• a throttle valve mounted between said processing chamber and said vacuum pump, said throttle valve positionable to regulate the rate of gas removed from said processing chamber by said vacuum pump;
• a controller for controlling the pressure in said processing chamber by directing the throttle valve to a plurality of throttle positions selected by said controller, wherein a first throttle position is pre-selected and wherein subsequent throttle positions are selected by the controller based on the difference between a desired pressure and a measured pressure using proportional and integral control, wherein the integral control is delayed for a predetermined period.

A method for controlling pressure in an evacuated processing chamber comprising the steps of:

• retrieving from electronic memory a desired pressure value reflecting a desired pressure level for the processing chamber;
• retrieving from electronic memory a desired gas flow value representing a desired gas flow rate through the processing chamber;
• accessing from electronic memory a mathematical function having a domain comprising pressures in the processing chamber and gas flow rates into the processing chamber, and having a range comprising positions of the throttle valve;
• measuring pressure within the processing chamber;
• calculating a pressure error equal to the difference between the desired pressure and the measured pressure;
• and
• positioning the throttle valve by repeating the steps:
• (a) retrieving from electronic memory proportional, integral and derivative gains, wherein at least one of said gains is not equal to zero;
• (b) calculating a proportional compensation of the valve position, an integral compensation of the valve position and a derivative compensation of the valve position by applying the pressure error to the proportional gain, the integral gain and the derivative gain respectively;
• (c) summing the outputs from step (b) to provide a value representing volumetric flow rate;
• (d) dividing the volumetric flow rate value by a pressure value to give a quotient representing flow/pressure;
• (e) applying the quotient to the inverse of the mathematical function accessed from electronic memory to provide a new valve position;
• and
• (f) repositioning the valve position to the new valve position.