Plasma processing apparatus using capacitance manometer and pressure control method thereof

A plasma processing apparatus comprising:

• plasma processing means for processing an object by use of plasma at a predetermined pressure in a plasma processing container;
• a capacitance manometer for detecting a pressure in said plasma processing container as a pressure detection signal, which indicates the pressure and includes erroneous components;
• vacuum creating means for creating a predetermined pressure in said plasma processing container;
• pressure instruction means for, when plasma processing is performed by said plasma processing means, providing a first pressure instruction signal to said vacuum-creating means to set a pressure in said plasma processing container at a predetermined first pressure on the other of several 10 m torr as said predetermined pressure, and when said capacitance manometer is calibrated before plasma processing is performed, providing a second pressure instruction signal to said vacuum-creating means to set the pressure in said plasma processing container at a predetermined second pressure on the order of 10.sup.-4 Torr at which said capacitance manometer cannot operate correctly;
• correction value calculating means for, when the pressure in said plasma processing container is set at said predetermined second pressure in order to calibrate said capacitance manometer in accordance with said second pressure instruction from said pressure instruction means, receiving said pressure detection signal from said capacitance manometer, and calculating a correction value used for canceling said erroneous components previously included in said pressure detection signal;
• correcting means for, when the pressure in said plasma-processing container is set at said predetermined first pressure, correcting said pressure detection signal output from said capacitance manometer on the basis of said correction value calculated by said correction value calculating means, thereby to cancel said erroneous components previously included in said pressure detection signal;
• and
• pressure controlling means for maintaining said predetermined first pressure in said plasma processing container so that plasma processing is performed in accordance with said pressure detection signal from which said erroneous components have been canceled, wherein said correction value calculating means comprises:
• a multiplier for multiplying a signal, a, output from said capacitance manometer by a predetermined multiplier value N;
• a first A/D converting means for converting an output signal N.multidot.a into a digital signal;
• a signal processing means for receiving the digital signal from said first A/D converting means, and outputting a digital signal -N.multidot.a corresponding to the output signal N.multidot.a;
• D/A converting means for converting a digital signal corresponding to the signal -N.multidot.a output from said signal processing means into an analog signal;
• and
• a divider for dividing said analog signal output from said D/A converting means by N, and outputting a signal, -a', as said correction value.