METHOD FOR THE MEASUREMENT OF LONG MINORITY-CARRIER DIFFUSION LENGTHSEXCEEDING WAFER THICKNESS

A procedure is presented for determining long minority carrier diffusi on lengths, L, from the measurement of the surface photovoltage (SPV) as a function of the light penetration depth. The procedure uses expli cit SPV formulas adopted for diffusion lengths longer than the light p enetration depths. Results obtained on high-purity silicon demonstrate new capability for noncontact wafer-scale measurement of L values in a mm range, exceeding the wafer thickness by as much as a factor of 2. 5. This factor can be increased by increasing the accuracy of SPV sign al measurement. The procedure does not have the fundamental limitation s of previous SPV methods in which the diffusion lengths were limited to about 70% of the wafer thickness.