Patent ID: 7148705

Claim:
A charging voltage measuring device apparatus for measuring a charging voltage Vs on the surface of a substrate held on a substrate holding unit, comprising: a measuring electrode, for forming an electrostatic capacity Cs with said substrate, being disposed on said substrate holding unit to make contact with or proximate to the back face of said held substrate, and said measuring electrode being electrically insulated from said substrate holding unit; a measuring capacitor connected between said measuring electrode and a ground potential portion, said measuring capacitor having an electrostatic capacity Cm; a voltage measuring unit for measuring a measuring voltage Vm between both ends of said measuring capacitor; and a calculator calculating unit for calculating said charging voltage Vs at time t 1 in accordance with a numerical expression Vs=K[Vm(t 1 )+{1/(Cm×Rm)}Ò0t 1 Vm(t)dt] where K=(Cs+Cm)/Cs or K=Cm/Cs (if Cm>>Cs) or its mathematically equivalent numerical expression on the basis of an inverse K of a voltage dividing ratio that is defined by the relation between said electrostatic capacities Cs and Cm, and said measuring voltage Vm(t 1 ) at time t 1 , and a resistance value Rm of a resistor including an internal resistor of said voltmeter and disposed in parallel to said measuring capacitor, when the time is t, the measurement start time is t=0, and the measurement time is t 1 .