Optical inspection apparatus and method
Performing modulation spectroscopy by directing a probe beam and a pump beam at a strained semiconductor sample, modulating the pump beam, and reflecting the probe beam into a detector. The detector produces a direct current signal proportional to reflectance R of the probe beam and an alternating current signal proportional to the modulation of the reflectance ΔR of the probe beam. Both R and ΔR are measured at a multiplicity of probe beam photon energies, to provide a spectrum having at least one line shape. The spectrum is analyzed to measure energy differences between interband electronic transitions of the sample, and the strain of the sample is determined from the energy differences.
1. A method for modulation spectroscopy of a semiconductor sample, the method comprising the steps of:
irradiating for an irradiation time at least a location on the sample at a radiation intensity and a radiation wavelength sufficient to cause a change in the sample for at least an enhanced measurement time,
halting the irradiation of the sample at the end of the irradiation time,
directing an incident probe beam at the location on the sample during the enhanced measurement time to produce a reflected probe beam,
directing a modulated pump beam at the location on the sample during the enhanced measurement time, thereby causing a modulation of the reflected probe beam,
receiving the reflected probe beam with a detector that generates as output a direct current signal that is proportional to an intensity of the reflected probe beam and an alternating current signal that is proportional to the modulation of the reflected probe beam, and
analyzing at least a portion of the output generated during the enhanced measurement time but not during the irradiation time to determine properties of the sample.
2. The method of claim 1 , wherein the sample is irradiated during the irradiation time by at least one of the probe beam, the pump beam, and a beam other than either the probe beam or the pump beam.
3. The method of claim 1 , wherein the changes are transient.
4. The method of claim 1 , wherein the changes are permanent.
5. The method of claim 1 , wherein the sample is irradiated with at least one of ultraviolet, infrared, and visible radiation.