Abstract: The invention represents an improved method of measuring trenches on semiconductor wafers with optical spectroscopy. According to the described method, it is possible to characterize not only depth but also shape of the trench. The advancement is achieved by improved Effective Medium Approximation-based modeling of the optical response of trench structures.

Abstract: The penetration depth of surface acoustic wave scales with wavelength. To measure thinner films using impulse stimulated thermal scattering (ISTS) it is advantageous to reduce the measurement wavelength to on the order of 1 micron. One way to reduce the measurement wavelength is to employ a high numerical aperture lens to converge an excitation and probe laser beam in an optical system at wider angles. While doing this, the increased optical/mechanical tolerances can be reduced by fine-tuning the phase between an excitation laser pattern and a probe laser pattern by adjusting either a neutral-density filter or matching plate for a particular wavelength. Blocking unwanted diffraction order beams generated by the optical system with a specialized design beam block plate is needed to retain the long wavelength capability.

Abstract: The present invention uses ISTS to measure trenches with near- or sub-micron width. The trenches can be etched in a thin film on in a silicon substrate. One step of the method is exciting the structure by irradiating it with a spatially periodic laser intensity pattern in order to generate surface acoustic waves. Other steps are diffracting a probe laser beam off the thermal grating to form a signal beam; detecting the signal beam as a function of time to generate a signal waveform; determining surface acoustic wave phase velocity from the waveform; and determining at least one property of the trench structures based on the dependence of surface acoustic wave phase velocity on the parameters of the structure.

Abstract: The present invention measures a structure including multiple narrow metallic regions, each being disposed between neighboring regions comprising a second, non-metallic material. One step of the method is exciting the structure by irradiating it with a spatially periodic excitation field made up of excitation stripes in order to generate a thermal grating. Other steps are diffracting a probe laser beam off the thermal grating to form a signal beam; detecting the signal beam as a function of time to generate a signal waveform; and determining at least one property of the structure based on a thermal component of the signal waveform.

Abstract: In an opto-acoustic measuring device for thin films and solid surfaces, the probe beam is split into a first probe beam portion and a second reference beam portion. The splitting of the probe beam is achieved using a phase mask that also splits the excitation beam. The probe beam is aligned using a retro-reflector on a motorized stage to control the beam angle. Excitation and probe/reference beams are overlapped at the sample surface. The first probe beam portion gets diffracted by material disturbances generated by excitation beams. The diffracted part of the first probe beam portion is collinear with the second reference beam portion, resulting in heterodyning. The heterodyne signal measured by the detector is analyzed in order to determine thickness and/or other properties of a thin film or solid surface. The invention improves magnitude and reproducibility of the opto-acoustic signal which results in enhanced precision of measurements.