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.

We discuss an approach to iron concentration determination in silicon, based on wafer-scale surface photovoltage measurement of the minority carrier diffusion length in the millimeter range. The approach combines two novel aspects: it overcomes the diffusion length to wafer thickness ratio limitation of previous SPV methods, and it employs iron separation from other recombination centers using rapid photo-dissociation of iron-boron pairs. The wafer thickness limitation was eliminated by using the correct theoretical SPV wavelength dependence instead of simplified asymptotic diffusion length form adopted in all previous treatments and valid only for diffusion lengths much shorter than the wafer thickness. Photo-dissociation of Fe-B pairs and measurement of the corresponding decrease of the L value (caused by creation of iron intersticials) enables iron detection in typical silicon wafers in times of seconds with a sensitivity in the low 108 atoms/cm3 range.

This work reports on the theoretical modeling and experimental investigation of isothermal SPV-DLTS based on the rate window concept. Experimental implementation of the technique is done using computer analysis of the SPV transients after ceasing the illumination. The transient involves two processes – a recombination of excess minority carriers and a thermal emission of carriers trapped by surface states and bulk defects. The later process is the key one for deep level defect determination.The upper limit for the measurable deep level emission rate is provided by the recombination lifetime. This limit often exceeds, by orders of magnitude, the standard 103 s−1 limit in capacitance DLTS. The sensitivity of SPV-DLTS is of the same order as that of optical capacitance DLTS.