Pressure control device for low pressure processing chamber

A method of controlling a pressure in a processing chamber having a gas inlet arranged to inlet gas into the chamber, an exhaust valve arranged to exhaust gas from the chamber, and a pressure gauge arranged to measure a gas pressure in the chamber, the method comprising:

• supplying gas to the chamber, via the gas inlet;
• exhausting gas from the chamber, via the exhaust valve;
• measuring the gas pressure in the chamber, via the pressure gauge;
• and
• automatically adjusting the gas pressure in the chamber to a target pressure, using a Proportional-Integral-Derivative (PID) control, based on an exhaust speed of gas leaving the chamber, via the exhaust valve, and the gas pressure from the pressure measured, via the pressure gauge,
• wherein the PID control is calculated for each control cycle to adjust an opening of the exhaust valve corresponding to a change in the exhaust speed, using gain values obtained for each control cycle based on the exhaust speed of gas and the target pressure, and
• wherein the gain values used in said PID control include an integral gain that has a positive correlation with the exhaust speed of gas calculated with the opening of the exhaust valve in each control cycle and a negative correlation with the target pressure and varies from one control cycle to another control cycle, a proportional gain that has a negative correlation with the target pressure and varies from one control cycle to another control cycle, and a differential gain that is a fixed constant.