Patent ID: 6922067

Claim:
An apparatus for determining the diffusion length of semiconductor wafers comprising: a probe for directing radiation on an area of back side wafer surface to excite charge carriers, create and detect a surface photovoltage, said probe including an electrode, including a transparent element placed on surface of the electrode in the path of said radiation and a non transparent element surrounding said transparent element, said electrode is placed in proximity to the back side of the wafer, means for illuminating of the surface at different wavelengths, including two or more different sources of monochromatic light driven by light drivers controlled by a computer, means for directing light flux onto said electrode of the probe and a photo detector, means for measuring surface photovoltage (SPV) signals picked up by said electrode, said means for measuring including SPV pre-amplifier and lock-in amplifier with said electrode connected to the input of said SPV pre-amplifier, the output of said SPV pre-amplifier connected to the output of said lock-in amplifier and the output of said lock-in amplifier connected to said computer, means for measuring light flux including pre-amplifier with said photo detector connected to the input of said pre-amplifier and the output of said pre-amplifier connected to said computer, an optical system installed from the front surface of the wafer coaxially with said electrode, said optical system being designed for pattern recognition, said optical system including objective lens and CCD matrix with said CCD matrix output connected to said computer, means for positioning said optical system coaxially with said electrode, and means for wafer positioning using for measurements in different locations including one or more linear stages and a rotary stage, said linear stages and said rotary stage controlled by said computer.