Lubek Jastrzebski

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.

BAND-TAIL PHOTOLUMINESCENCE IN POLYCRYSTALLINE SILICON THIN FILMS

We have found a new photoluminescence (PL) band with a maximum at 0.9 eV and a halfwidth of 0.1 eV at 4.2 K in polycrystalline Si thin films deposited on glass at 625 °C. The PL band strongly shifts toward low energy with increasing the temperature (1.3 meV/K) and toward high energy with increasing the excitation intensity. Hydrogenation of polycrystalline Si enhances the PL intensity by factor of 3 to 5. The luminescence characteristics are consistent with radiative recombination of electrons and holes trapped in tail states of the conduction and the valence band, respectively. Excellent agreement is achieved between the 0.9 eV band shape and theoretical calculations based on a band‐tail recombination. It is also argued that a corresponding luminescence spectroscopy provides a new possibility for band‐tail diagnostics in polycrystalline Si thin films.

The Present Status and Recent Advancements in Corona-Kelvin Non-Contact Electrical Metrology of Dielectrics for IC-Manufacturing

Non-contact electrical metrology offers a fast and cost saving monitoring of dielectrics in IC manufacturing process. This corona-Kelvin measuring technique has entered the maturity stage with about 400 tools installed in silicon IC-fabs. We discuss recent advancements that broaden the spectrum of monitoring parameters and enhance the precision of these measurements. We also discuss the current ongoing extension of corona-Kelvin metrology to the micro scale measurement on sites as small as 30µm x 30µm. This opens new possibilities for non-contact electrical testing of product wafers, rather than expensive process monitor wafers. Micro-measurement is illustrated using flash memory ONO structures and corona induced programming and erasing.

COCOS (corona oxide characterization of semiconductor) non-contact metrology for gate dielectrics

COCOS metrology enables gate dielectrics to be quickly monitored in a non-contact manner for all wafer sizes including 300mm. This approach has been developed during the last five years and is already implemented in many microelectronic fablines. The method uses corona charging in air to deposit an electric charge on a dielectric thus changing the electric field in the dielectric and in the semiconductor. The response is measured in a non-contact manner by using a contact potential difference, VCPD, in the dark and under strong illumination. This measurement gives the voltage drop across the oxide. VOX and the surface barrier, VSB, as a function of the corona charge dose, ΔQC. These basic relationships are then used in a very straightforward manner to determine the flat band voltage, VFB, the total charge required to achieve the flat band condition, QTOT and the interface trap spectra, DIT, across the silicon bandgap in an energy range from flat band to deep inversion. Measurements of VCPD vs. ΔQC under a...

Monitoring of SIMOX layer properties and implantation temperature by optical measurements

Infrared absorption and Raman scattering measurements of SIMOX structures implanted at various temperatures yield information on the structure and the strain in both the top silicon and the buried oxide layers. Both techniques can also be used to monitor the implant temperature after the implantation.

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.

INCREASING SHORT MINORITY CARRIER DIFFUSION LENGTHS IN SOLAR-GRADE POLYCRYSTALLINE SILICON BY ULTRASOUND TREATMENT

We have found that ultrasound treatment (UST) has a profound effect on the recombination rate in as‐grown, B‐doped cast polycrystalline silicon wafers for photovoltaic applications. As determined by surface photovoltage measurements of the minority carrier diffusion length L, the UST increases the corresponding lifetime by almost an order of magnitude. The maximum enhancement takes place in the wafer regions with the shortest L values. For L≳20 μm, both positive and negative changes of L after UST are revealed at different wafer regions. The UST effect is temperature dependent and exhibits maximum influence at about 60 °C. Enhanced dissociation of Fe‐B pairs by UST is identified as a mechanism which leads to a negative change of large L values, and a complex post‐treatment relaxation. A positive change of L is attributed to the influence of ultrasound vibrations on crystallographic defects.

ENHANCED HYDROGENATION IN POLYCRYSTALLINE SILICON THIN FILMS USING LOW-TEMPERATURE ULTRASOUND TREATMENT

Ultrasound treatment (UST) was applied to improve electronic properties of polycrystalline silicon films on silica‐based substrates. A strong decrease of sheet resistance by a factor of two orders of magnitude was observed in hydrogenated films at UST temperatures lower than 100 °C. This is accompanied by improvement of a film homogeneity as confirmed by spatially resolved photoluminescence study. The UST effect on sheet resistance demonstrates both stable and metastable behavior. A stable UST effect can be accomplished using consecutive cycles of UST and relaxation. An enhanced passivation of grain boundary defects after UST is directly measured by nanoscale contact potential difference with atomic force microscope. Two specific UST processes based on interaction between the ultrasound and atomic hydrogen are suggested: enhanced passivation of grain boundary defects and UST induced metastability of hydrogen related defects.

Change of minority carrier diffusion length in polycrystalline silicon by ultrasound treatment

We present a new approach for defect engineering by ultrasound treatment (UST) in solar-grade polycrystalline silicon wafers, leading to significant enhancement of minority carrier diffusion length (L) in wafer regions with short L. The maximum value of the UST effect is a 2.7 times increase of the diffusion length in regions of the sample with L=10 to 25 mu m. Using the surface photovoltage (SPV) method for non-contact mapping of the diffusion length, we have found both a positive and negative variation of L after UST in different wafer regions. The UST effect depends upon temperature, showing an activation energy of about 0.17 eV. A relaxation study of the UST effect shows two different behaviours: (i) stable result versus post-UST holding time, and (ii) partial or complete recovery of the diffusion length. Process (ii) is linked to the ultrasound-enhanced dissociation of FeB pairs followed by pairing kinetics.