We present the principles and application examples of a recently refined, computerised, surface photovoltage (SPV) method. This new method is capable of wafer-scale, non-contact mapping of metal contaminants in the bulk and on the surface with sensitivities as high at 10'aatomscm-3. W e demonstrate the unique abilityofsw to measure product wafers with finished integratedcircuits.

The photodissociation of iron-boron pairs in p-type silicon produces lifetime killing interstitial iron and may be combined with noncontact surface photovoltage (SPV) measurement of the minority carrier diffusion length to achieve fast detection of iron. We found that, for iron concentrations ranging from 8×108 to 1×1013 atoms/cm3, the pair dissociation using a white light (10 W/cm2) was completed within 15 s. Surface recombination was a major rate limiting factor. Passivation of the surface enhanced the rate by as much as a factor of 20. The photodissociation rate increased with increasing temperature, however, the increase was smaller than that of the thermal dissociation rate. These characteristics are consistent with a previously proposed recombination enhanced dissociation mechanism. For practical iron detection, it is important that the detection limit of the approach is close to one part per quadrillion.

A procedure is presented for determining long minority carrier diffusion lengths, L, from the measurement of the surface photovoltage (SPV) as a function of the light penetration depth. The procedure uses explicit SPV formulas adopted for diffusion lengths longer than the light penetration 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 signal measurement. The procedure does not have the fundamental limitations of previous SPV methods in which the diffusion lengths were limited to about 70% of the wafer thickness.

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We present an overview of the physics and practical issues related to surface photovoltage measurement of the minority carrier diffusion length and its application to monitoring recombination center defects in silicon. A tutorial description is given of the role of pertinent processes like injection, recombination and trapping. The evolution of the SPV method is presented followed by a description of most recent refinements addressing the measurement of long diffusion lengths in silicon wafers with emphasis on accuracy, measuring speed, tool-to-tool reproducibility and, practically the most important question of monitoring, iron concentration.