Do I need a wafer prober with a fully guarded chuck for use with my Agilent 4155A/B/C or Agilent 4156A/B/C?
The need for a fully guarded chuck depends upon the type of measurements you plan to make on your wafer prober. The chuck is the large metal plate onto which the user places the wafer. The chuck is insulated from ground and acts like a large capacitor connected to the backside of your wafer. This capacitance can be eliminated or significantly reduced by adding another conductor that surrounds the chuck (driven guard). This makes low level CV and IV measurements possible where there is an electrical path to the wafer backside. CMOS gate oxide or Fowler-Nordheim plots are examples. Low level CV measurements are degraded by the large stray capacitance of the chuck. The guarded chuck gives more consistent CV measurements across the wafer at ultra low-levels.