Piotr Edelman

Non-contact mapping of heavy metal contamination for silicon IC fabrication

The authors 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 1010 atoms cm-3. They demonstrate the unique ability of SPV to measure product wafers with finished integrated circuits.

Iron detection in the part per quadrillion range in silicon using surface photovoltage and photodissociation of iron-boron pairs

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.

Method for the measurement of long minority carrier diffusion lengths exceeding wafer thickness

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.

New approach to measuring oxide charge and mobile ion concentration

We discuss the determination of oxide charge from simultaneous noncontact measurement of the surface potential barrier, Vs, (via surface photovoltage) and the voltage drop across the oxide, Vox, (via contact potential vibrating probe). These two measurements enable us to separate the contributions from total charge and oxide charge. In combination with corona charging and low temperature stress, this approach can be used for wafer-scale determination of the mobile Na+ concentration. The principles of the approach are presented and typical results are given which contrast the effects of ion drift and charge injection in the oxide. Experimental results also illustrate the noncontact, wafer-scale mapping of the mobile ion distribution.

Multifunction metrology platform for photovoltaics

Advanced characterization for PV is a complex process that must address bulk defects, interfaces, passivation, and degradation phenomena. It requires not only appropriate measurement techniques, but also a coupling of measurements with treatments altering defect/interface activity. Preferably, the metrology should be noncontact and cost effective. The purpose of this work was to provide such multifunction wafer scale characterization capability for silicon PV. In this paper we describe a multifunction metrology platform. Example applications are given that illustrate the importance of sequenced measurements for 1 — monitoring of the light induced degradation in PV wafers and solar cells; 2 — correlation between interface trap density and surface recombination and the role of surface barrier, and 3 — monitoring of the field-effect potential emitter passivation.

Non-contact deep level transient spectroscopy (DLTS) based on surface photovoltage

The authors present results of non-contact, wafer-scale measurement of the deep level thermal emission realised in GaAs on a native surface barrier using surface photovoltage (SPV) transients. The principle of corresponding optical deep level transient spectroscopy (DLTS) is discussed and the approach is applied to non-contact wafer mapping.

Non-Contact, No Wafer Preparation Deep Level Transient Spectroscopy Based on Surface Photovoltage

We discuss a novel approach to Deep Level Transient Spectroscopy (DLTS) in which the emission of trapped minority carriers is analyzed employing the surface photovoltage (SPV) transient as measured in a non-contact manner on the native depletion barrier on semiconductor surfaces. Optical excitation is used as the trap-filling pulse. Experiments done on n-type GaAs demonstrate that the SPV-DLTS is suitable for wafer-scale, non-contact determination of deep level defects on semiconductor surfaces. The SPV approach can monitor emission rates up to 106 s-1 which is 102 to 103 above the limit of standard capacitance DLTS. The sensitivity of the method is comparable to that of the oplical capacitance DLTS.

Energy levels of the SbGa heteroantisite defect in GaAs:Sb

A transient capacitance study of antimony‐doped bulk GaAs has led to the identification of two energy levels related to the SbGa heteroantisite defect. The levels with electron emission activation energies of 0.54 and 0.70 eV are typically overshadowed by omnipresent EL3 and EL2 traps related to oxygen defect and the arsenic antisite, respectively. Positive identification of the levels, and determination of their emission rate signatures, was made possible employing GaAs crystals with a defect structure especially engineered to achieve very low concentrations of background traps. Relationship of the levels to the SbGa defect is deduced from excellent agreement with previous electron paramagnetic resonance results.

Photoluminescence and minority carrier diffusion length imaging in silicon and GaAs

The correlation between the distribution of minority carrier diffusion lengths monitored using surface photovoltage measurements and the distribution of photoluminescence intensity has been investigated in silicon and III-V semiconductor materials. Photovoltage measurements have been performed using a non-contact probe and constant photon flux method at room temperature, while the scanning photoluminescence measurements have been done in the room to liquid helium temperature range. To demonstrate the combined capabilities of the two methods, assessments of a liquid phase electroepitaxial InxGa1-xAs single crystal and 450 degrees C annealed silicon have been performed. The discussion emphasises the effects of non-uniform carbon distribution in InGaAs and oxygen-related defects in silicon.

Non-Contact C-V Technique for high-k Applications.

This non-contact high-k monitoring technique is based on a differential quasistatic C-V that is generated using time- resolved metrology combining corona charging and contact potential difference (CPD) measurements. The technique incorporates transconductance corrections that enable measurements in the high field range (lOMV/cm) required for extraction of large dielectric capacitance corresponding to ultra-low equivalent electrical oxide thickness (EOT) down to the sub-nanometer range. It also provides a means for monitoring the flat band voltage, VFB, the interface trap spectra, DIT, and the total dielectric charge, dQTOT- This technique is seen as a replacement for not only MOS C-V measurements but also for mercury-probe C-V. EOT measurement by the differential corona C-V has a major advantage over optical methods because it is not affected by water adsorption and molecular airborne contamination, MAC. These effects have been a problem for optical metrology of ultra-thin dielectrics. The presented results illustrate the application of the technique to state of the art gate dielectrics, including Si-O-N and HfO2.