Patent ID: 9131170
Filing Date: 2015-09-08
Classification: G01N,H04N

Abstract:
1. A method of producing an optical carrierographic image of a semiconductor sample, the method comprising: a) generating a first modulation signal having a first modulation frequency and a second modulation signal having a second modulation frequency, wherein a beat frequency between the first modulation frequency and the second modulation frequency is substantially less than both the first modulation frequency and the second modulation frequency; b) generating a reference signal having a reference frequency equal to the beat frequency; c) providing a first optical beam and a second optical beam, the first optical beam and the second optical beam having wavelengths selected for excitation of carriers within the semiconductor sample; d) focusing and spatially overlapping the first optical beam and the second optical beam onto a location of the semiconductor sample; e) modulating the first optical beam according to the first modulation signal and modulating the second optical beam according to the second modulation signal; f) detecting, with an infrared detector, infrared radiation emitted from the semiconductor sample in response to absorption of the first optical beam and the second optical beam, and obtaining a plurality of carrierographic signals at different points in time during at least one beat period; and g) providing the reference signal to a lock-in amplifier and processing the carrierographic signals with the lock-in amplifier to obtain an amplitude signal and a phase signal.