SEM observation of dopant striae in silicon

Dopant striae in high-resistivity [?1000Ω cm n- and p-type crystals as well as phosphorus-doped (2–0.1Ω cm)] floating-zone silicon crystals have been investigated in the scanning electron microscope by Schottky barrier charge collection microscopy. The variation of (residual) dopant concentration (striae) produce a spatial variation in the collected current. The sensitivity of this technique for striation detection is found to increase with decreasing doping level. For doped material, good agreement exists between this technique and others (e.g., preferential etching). For resistivities below 0.1Ω cm striation contrast is absent. Striae contrast formation and its dependence on doping level and imaging conditions may be understood by consideration of the charge collection process and its dependence upon the diode depletion layer width.