Depth profiling of semiconductor structures using multi-wavelength pump-probe technique

A pump-probe based system for depth-profiling of a patterned wafer sample, the system comprising:

• n probe sources each of the n probe sources configured to simultaneously emit light pulses at a different wavelength (λ1-λn), wherein λ1 is further used as a pump pulse for producing an acoustic pulse, which propagates within a target region of the sample;
• n detectors each configured to detect a different one of wavelengths λ1-λn;
• a pump modulator configured to modulate the pump pulse having the wavelength λ1 at a frequency f0;
• a probe modulator configured to modulate the probe pulse λ1 at a frequency f1;
• time delay configuration for generating a time delay between the pump pulse and the probe pulses;
• an optical setup configured to:
• direct the f0 modulated pump pulse on the target region of the sample to thereby produce an acoustic pulse propagating within the target region;
• direct the probe pulses to simultaneously impinge on the target region of the sample at the time delay relative to the pump pulse;
• and separate the light reflected from the sample, so that each of the λ1-λn wavelengths of the reflected probe pulses are detected as separate signals by a respective of the n detectors;
• a lock-in amplifier configured to demodulate the λ2-λn signals detected by the respective n detectors by locking in on f0, enabling detection of the acoustic effect generated by the pump pulse, while removing background optical signal;
• and, for the λ1 signal, to lock on frequencies f0±f1 thereby allowing to electronically separate the pump pulse λ1 from the probe pulse λ1;
• and
• a processor configured to receive the demodulated signals and to determine a 3D nanostructure of the target region of the sample based thereon.

A method for in-depth profiling of a patterned wafer sample, the method comprising:

• providing a patterned wafer sample comprising a target region;
• projecting an optical pump pulse on the sample, such as to produce an acoustic pulse, which propagates within the target region of the sample,
• projecting a plurality of optical probe pulses on the sample, such that the probe pulse undergoes Brillouin scattering off the acoustic pulse within the target region;
• wherein each of the plurality of probe pulses has a different wavelength (λ1-λn);
• passing each of the plurality of probe pulses through an optical setup configured to combine the plurality of probe pulses, such that they simultaneously reach the same target region of the sample and to separate the plurality of probe pulses upon their reflection from the sample, such that each of the plurality of probe pulses is detected by a separate detector;
• and
• analyzing the detected signals to obtain a 3D nanostructure of the target region of the sample.