Method and apparatus for eliminating displacement current from current measurements in a plasma processing system

An apparatus for measuring ion current in a plasma processing system for implanting ions into a target in a plasma processing chamber, said plasma processing system including first and second electrodes, wherein a voltage pulse is applied across the first and second electrodes, the apparatus comprising:

• a capacitive device coupled to the first and second electrodes to receive the voltage pulse, the capacitive device comprising a capacitor having a capacitance value the same or nearly the same as a capacitance between the first and second electrodes;
• first means for measuring a first current supplied to the first and second electrodes during the voltage pulse and for providing a first current signal representative of the first current;
• second means for measuring a second current supplied to the capacitive device during the voltage pulse and for providing a second current signal representative of the second current;
• and
• means for subtracting the second current signal from the first current signal to provide a measurement of the ion current in the plasma processing system.

An apparatus for measuring ion current in a plasma processing system for implanting ions into a target in a plasma processing chamber, said plasma processing system including first and second electrodes, wherein a voltage pulse is applied across the first and second electrodes, the apparatus comprising:

• a capacitive device coupled to the first and second electrodes to receive the voltage pulse, the capacitive device comprising a capacitor having a capacitance value the same or nearly the same as a capacitance between the first and second electrodes;
• a first current measuring device to measure a first current provided to the first and second electrodes during the voltage pulse and to output a first current signal representative of the first current;
• a second current measuring device, coupled to the capacitive device, to measure a second current provided thereto during the voltage pulse and to output a second current signal representative of the second current;
• and
• a subtractor to receive the first and second current signals and to subtract the second current signal from the first current signal to provide a measurement of the ion current.

A method of measuring an ion current in a plasma processing system for implanting ions into a target in a plasma processing chamber, said plasma processing system including first and second electrodes, wherein a voltage pulse is applied across the first and second electrodes, the method comprising:

• (a) electrically coupling a capacitor between the first and second electrodes to receive the voltage pulse and selecting the capacitor to have a capacitance different from a first capacitance between the first and second electrodes;
• (b) measuring a first current supplied to the first and second electrodes during the voltage pulse and providing a first current signal representative of the first current;
• (c) measuring a second current supplied to the capacitor during the voltage pulse and providing a second current signal representative of the second current;
• and
• (e) subtracting the second current signal from the first current signal to provide an ion current signal representative of the ion current.

A method of measuring an ion current in a plasma processing system for implanting ions into a target in a plasma processing chamber, said plasma processing system including first and second electrodes, wherein a voltage pulse is applied across the first and second electrodes and a target is disposed on the first electrode, the method comprising:

• (a) electrically coupling a capacitor between the first and second electrodes to receive the voltage pulse;
• (b) measuring a first current supplied to the first and second electrodes during the voltage pulse and providing a first current signal representative of the first current, the step of providing the first current signal comprising placing an ion detecting device adjacent the target to generate the first current signal;
• (c) measuring a second current supplied to the capacitor during the voltage pulse and providing a second current signal representative of the second current;
• (d) selecting the capacitor to have a capacitance different from a capacitance of the ion detecting device;
• and
• (f) subtracting the second current signal from the first current signal to provide an ion current signal representative of the ion current.

A method of measuring an ion current in a plasma processing system for implanting ions into a target in a plasma processing chamber, said plasma processing system including first and second electrodes, wherein a voltage pulse is applied across the first and second electrodes, the method comprising:

• (a) electrically coupling a capacitor between the first and second electrodes to receive the voltage pulse;
• (b) measuring a first current supplied to the first and second electrodes during the voltage pulse and providing a first current signal representative of the first current, the step of providing the first current signal comprising placing an ion detecting device adjacent the target to generate the first current signal;
• (c) measuring a second current supplied to the capacitor during the voltage pulse and providing a second current signal representative of the second current;
• (d) selecting the capacitor to have a capacitance substantially the same as a capacitance of the ion detecting device;
• and
• (e) subtracting the second current signal from the first current signal to provide an ion current signal representative of the ion current.

An apparatus for measuring ion current in a plasma processing system for implanting ions into a target in a plasma processing chamber, said plasma processing system including first and second electrodes, wherein a voltage pulse is applied across the first and second electrodes, the apparatus comprising:

• a capacitive device coupled to the first and second electrodes to receive the voltage pulse, the capacitive device comprising a capacitor having a capacitance different from a capacitance between the first and second electrodes;
• first means for measuring a first current supplied to the first and second electrodes during the voltage pulse and for providing a first current signal representative of the first current;
• second means for measuring a second current supplied to the capacitive device during the voltage pulse and for providing a second current signal representative of the second current;
• and
• means for subtracting the second current signal from the first current signal to provide a measurement of the ion current in the plasma processing system.

An apparatus for measuring ion current in a plasma processing system for implanting ions into a target in a plasma processing chamber, said plasma processing system including first and second electrodes, wherein a voltage pulse is applied across the first and second electrodes, the apparatus comprising:

• a capacitive device coupled to the first and second electrodes to receive the voltage pulse;
• first means for measuring a first current supplied to the first and second electrodes during the voltage pulse and for providing a first current signal representative of the first current, the capacitive device comprising a capacitor having a capacitance value the same or nearly the same as a capacitance of the first means for measuring the first current;
• second means for measuring a second current supplied to the capacitive device during the voltage pulse and for providing a second current signal representative of the second current;
• and
• means for subtracting the second current signal from the first current signal to provide a measurement of the ion current in the plasma processing system.

An apparatus for measuring ion current in a plasma processing system for implanting ions into a target in a plasma processing chamber, said plasma processing system including first and second electrodes, wherein a voltage pulse is applied across the first and second electrodes, the apparatus comprising:

• a capacitive device coupled to the first and second electrodes to receive the voltage pulse, the capacitive device comprising a capacitor having a capacitance value different from a capacitance of the first and second electrodes;
• a first current measuring device to measure a first current provided to the first and second electrodes during the voltage pulse and to output a first current signal representative of the first current;
• a second current measuring device, coupled to the capacitive device, to measure a second current provided thereto during the voltage pulse and to output a second current signal representative of the second current;
• and
• a subtractor to receive the first and second current signals and to subtract the second current signal from the first current signal to provide a measurement of the ion current, the subtractor comprising means for compensating for the difference in capacitance values.

An apparatus for measuring ion current in a plasma processing system for implanting ions into a target in a plasma processing chamber, said plasma processing system including first and second electrodes, wherein a voltage pulse is applied across the first and second electrodes, the apparatus comprising:

• a capacitive device coupled to the first and second electrodes to receive the voltage pulse;
• a first current measuring device to measure a first current provided to the first and second electrodes during the voltage pulse and to output a first current signal representative of the first current, the capacitive device having a capacitance different from a capacitance of the first current measuring device;
• a second current measuring device, coupled to the capacitive device, to measure a second current provided thereto during the voltage pulse and to output a second current signal representative of the second current;
• and
• a subtractor to receive the first and second current signals and to subtract the second current signal from the first current signal to provide a measurement of the ion current, the subtractor comprising means for compensating for the difference in capacitance values.

An apparatus for measuring ion current in a plasma processing system for implanting ions into a target in a plasma processing chamber, said plasma processing system including first and second electrodes, wherein a voltage pulse is applied across the first and second electrodes, the apparatus comprising:

• a capacitive device coupled to the first and second electrodes to receive the voltage pulse;
• a first current measuring device to measure a first current provided to the first and second electrodes during the voltage pulse and to output a first current signal representative of the first current, the capacitive device having a capacitance substantially the same as a capacitance of the first current measuring device;
• a second current measuring device, coupled to the capacitive device, to measure a second current provided thereto during the voltage pulse and to output a second current signal representative of the second current;
• and
• a subtractor to receive the first and second current signals and to subtract the second current signal from the first current signal to provide a measurement of the ion current.