THERMAL YAVE CHARACTERIZATION OF SEMICONOUCTORS ANO SUPERCONOUCTORS

Thermal wave technology has proven to be a very effective means for investigating the near surface region of several different materials. Although there are many methods for generating and detecting thermal waves the most desirable for quantitative NOE are the noncontact and nondamaging laser methods. Yhen a material is excited with an intensity-modulated laser pump beam a thermal wave is generated within the near surface of the sample. Since the complex refractive index of most materials depends on temperature, the laser pump induced modulations in the local tempera ture of the sample will induce a corresponding modulat ion in the local refractive index. This variation in refractive index can in turn be detected through the modulat ion in the reflectance of a laser probe beam from the surface of the material [1,2). This method is not only a highly effective method for generat ing and detecting thermal waves, but also permits thermal wave measurements to be performed with micron scale spatial resolution by utilizing highly focused pump and probe laser beams. Semiconductors The laser pump generates thermal waves in alI materials. In semiconductors, such as silicon, a pump laser operating in the visible also generates electron-hole plasma waves which also modulate the reflectance of the probe laser [2,3). The thermal waves provide information about the local thermal transport properties while the plasma waves provide information about the local charge carrier transport properties. It is this latter sensitivity to local electrical properties that accounts for the success of the modulated reflectance method as a process control tool in the semiconductor industry for monitoring ion implant dose levels [4,5) and plasma-induced damage effects [6,7) in Si wafers. In these applications no attempt is made to perform thermal wave imaging of individual defect structures in the silicon wafer. Recently we have demonstrated that the modulated reflectance method can be used to image localized defects and structures by employing high-density raster scanning techniques [8]. Images with 1 ~m spatial resolution have been obtained of metallic precipitates, dislocations, dislocation clusters and stacking faults