Patent ID: 6049220
Filing Date: 2000-04-11
Classification: G01N,G01R,H01L

Abstract:
An apparatus for evaluating a wafer, said apparatus comprising:a first source of a first beam of photons having a first intensity modulated at a frequency sufficiently low to avoid creation of a wave of charge carriers in a region of said wafer when said first beam is incident on said region;a second source of a second beam of photons, said photons in said second beam having energy sufficiently lower than said energy of said photons in said first beam to avoid creation of more than a negligible number of charge carriers in said region when said second beam is incident on said region; anda photosensitive element located in a path of a portion of said second beam, said portion being modulated at said frequency after reflection by said region, said photosensitive element generating a first signal indicative of a first concentration of said charge carriers created in said region by incidence of said first beam.