Patent ID: 6452400
Filing Date: 2002-09-17
Classification: H05H

Abstract:
A method of measuring negative ion density of a plasma, said method comprising the steps of:supplying a first gas, which is an inert gas, into a vacuum chamber and ionizing the first gas to produce a first plasma; bringing the first plasma into contact with a probe having a base end connected through a variable-voltage power supply to a ground; measuring a saturation current Ies1 at which current flowing through the probe is saturated when potential of the probe is changed by the variable-voltage power supply in a potential region where the potential of the probe is higher than a ground potential, and a saturation current Iis1 at which current flowing through the probe is saturated when potential of the probe is changed by the variable-voltage power supply in a potential region where the potential of the probe is lower than the ground potential; supplying a second gas containing a gas for producing negative ions into the vacuum chamber and ionizing the second gas to produce a second plasma; bringing the second plasma into contact with the probe having the base end connected through the variable-voltage power supply to the ground; measuring a saturation current Ies2 at which current flowing through the probe is saturated when potential of the probe is changed by the variable-voltage power supply in a potential region where the potential of the probe is higher than the ground potential, and a saturation current Iis2 at which current flowing through the probe is saturated when potential of the probe is changed by the variable-voltage power supply in a potential region where the potential of the probe is lower than the ground potential; and determining negative ion density ni1âˆ’ of the second plasma produced by ionizing the second gas by using Iis1/Iis2, Ies1/Ies2, mi1, mi2 and ne1, where mi1 is mass of positive ions of the first gas, mi2 is reduced mass of dominant positive ions among those of the second gas and ne1 is electron density of the first plasma.