Evaluating both thickness and compositional variables in a thin film sample

A method for evaluating the thickness and compositional variables in a layered or thin film sample by analyzing thermal waves present in the sample, said thermal waves being generated by a periodic localized heating at the surface of the sample, said method comprising the steps of:

• A. detecting thermal wave signals within the periodically heated area on the surface of the sample that are a function primarily of the surface temperature, said detecting step being performed by
• directing a radiation probe beam within a portion of the periodically heated area on the surface of the sample in a manner such that the radiation probe beam reflects off the surface of the sample;
• and
• measuring the intensity variations of the reflected radiation probe beam resulting from the changes in optical reflectivity of the sample induced by said periodic heating with the measured variations being independent of changes of beam diameter and position;
• B. detecting thermal wave signals within the periodically heated area on the surface of the sample that are primarily a function of the integral of the temperature beneath the sample;
• and
• C. processing the measured thermal wave signals such that information about both layer thickness and compositional variables may be evaluated.

An apparatus for evaluating thickness and compositional variables in a layered or thin film sample by analyzing thermal waves present in the sample, said thermal waves being generated by a periodic localized heating at the surface of the sample, said apparatus comprising:

• a probe for emitting a radiation beam;
• means for directing the radiation probe beam within a portion of the periodically heated area on the sample surface in a manner such that the radiation probe beam reflects off the sample surface;
• first means for measuring the intensity variations of the reflected radiation probe beam resulting from changes in optical reflectivity of the sample induced by the periodic heating with the measured intensity variations being independent of changes in beam diameter and position, wherein said first means functions to generate output signals that are primarily a function of the surface temperature of the sample;
• second means for measuring the angular displacements of the reflected radiation probe beam resulting from angular deviations of the sample surface induced by the periodic heating and generating output signals that are primarily a function of the integral of the temperature beneath the sample surface;
• and
• means for processing the output signals from said first and second measuring means such that information about both layer thickness and compositional variables of the sample may be evaluated.

A method for evaluating thickness and compositional variables in a layered or thin film sample by analyzing thermal wave signals in the sample, said thermal waves being generated by a periodic localized heating at the surface of the sample, said method comprising the steps of:

• A. directing a radiation probe beam within a portion of the periodically heated area on the sample surface in a manner such that the radiation probe beam reflects off the sample surface;
• B. measuring the periodic intensity variations of the reflected radiation probe beam resulting from the changes in optical reflectivity of the sample induced by the periodic heating with the measured intensity variations being independent of beam diameter and position and generating output signals that are primarily a function of the surface temperature;
• C. measuring the periodic angular displacements of the reflected radiation probe beam resulting from angular deviations of the sample surface induced by the periodic heating and generating output signals that are primarily a function of the integral of the temperature beneath the sample;
• and
• D. processing the output signals measured in Steps B and C to derive information about both layer thickness and compositional variables of the sample.