Determination of Diffusion Characteristics Using Two

By the use of two- and four-point probe measurements, much can be learned about the characteristics of a doped silicon wafer. The two-point probe system (spreading resistance probe) will provide resistivity vs depth profiles while the four-point probe system will indicate the uniformity of the diffusion over the surface of the wafer. Both systems have the same equation as their basis. The development of each system from this equation is discussed. Applications and the strengths and weaknesses of each system are discussed. Solid state diffusion is a mechanism which dominates semiconductor fabrication processes. It permits the process engineer, within stringent limitations, to put dopants where they are wanted. Controlling diffusion is also essential to prevent doping where it is not wanted. Control requires measurement. Two methods of measuring dopant distribution resulting from solid state diffusion in silicon are discussed: spreading resistance analysis (SRA) and four-point probe analysis. Both methods are indirect in that they deal with electrica