Mario E. Rodriguez

Computational Aspects of Laser Radiometric Multiparameter Fit for Carrier Transport Property Measurements in Si Wafers

A computational multiparameter fitting methodology that uses a three-dimensional laser photothermal radiometric model for semiconductors is presented in this study. One- and three-dimensional models of the free-carrier plasma-wave generation and response to laser photothermal (PT) excitation in a semiconductor have been reported in the literature. 1,2 The amplitude of PT response in these models has been used to measure carrier transport properties of electronic materials. The total radiation emitted from a silicon sample illuminated with a modulated laser beam arises from two sources: emission of IR radiation from the photoexcited carrier plasma-wave (injected excess carrier density) and from direct lattice photon absorption and optical-to-thermal (nonradiative) power conversion leading to temperature rise (a thermal wave). 1,3 Sheard and co-workers 1,2 observed experimentally that under infrared photothermal radiometric (PTR) detection, carrier emission dominates and the thermal-wave contribution can be neglected for some Si samples. This observation was addressed theoretically by Salnick et al. 4,5 These authors generated a composite plasma- and thermal-wave PTR model of semiconductors and showed that the plasma-wave signal component can dominate in high-quality materials virtually at all modulation frequencies. However, in this model the radial spatial variation of laser-generated excess carriers and of the temperature rise was not considered. Ikari et al. 6 have recently presented a general theoretical model for the laser-induced PTR signal from a semiconductor wafer of finite thickness using a three-dimensional geometry. In this model, carrier diffusion and recombination, as well as heat conduction, along the radial and axial directions in the sample were taken into account using cylindrical coordinates. A pair of conventional coupled plasma- and heat diffusion-wave equations were written and solved in Hankel space. In this theoretical framework, the plasma and thermal components can be written as follows

Minority carrier lifetime and iron concentration measurements on p-Si wafers by infrared photothermal radiometry and microwave photoconductance decay

A comparative study of electronic transport properties of p-Si wafers intentionally contaminated with Fe was performed using infrared photothermal radiometry (PTR) and microwave photoconductance decay (μ-PCD). Strong correlations were found between PTR and μ-PCD lifetimes in a lightly contaminated wafer with no significant PTR transient behavior. The absolute PTR lifetime values were larger than the local averaged μ-PCD values, due to the different excitation wavelengths and probe depths. In a heavily contaminated wafer the μ-PCD and PTR lifetime correlation was poorer. PTR measurements were highly sensitive to iron concentration, most likely due to the dependence of the bulk recombination lifetime on it. Rapid-scanned (nonsteady-state) PTR images of the wafer surface exhibited strong correlations with both μ-PCD lifetime and [Fe] concentration images in both heavily and lightly contaminated wafers. For the lightly and uniformly contaminated wafer, PTR scanning imaging was found to be more sensitive to ir...

Microelectronic circuit characterization via photothermal radiometry of scribeline recombination lifetime

Abstract Three-dimensional (3D) photothermal radiometric microscopic imaging and laser-intensity-modulation frequency scans have been used for the non-contact, non-intrusive measurement of electronic transport properties of integrated circuits in patterned 4″ Si wafers. The experimental data showed that carrier recombination lifetimes along each scribeline remain constant. However, variations in surface recombination velocities and carrier diffusion coefficients were found. It was further found that such variations are related to the presence of highly doped poly-Si structures adjacent to the scribeline. As a result of these measurements, it is concluded that scribeline photothermal radiometric probing can be used effectively for monitoring local values of the carrier recombination lifetime and, through those, wafer contamination and damage during device fabrication processing.

Infrared photothermal radiometry of deep subsurface defects in semiconductor materials

Photothermal radiometry (PTR) signals obtained with a highly focused laser beam, were used to obtain amplitude and phase PTR two-dimensional and three-dimensional images of a high-resistivity Si wafer with a mechanical damage on the backsurface, probed from the front (intact) surface. The frequency chosen was 5 kHz, corresponding to an optimal phase resolution of the defect. It is shown that the position of the underlying damage is well resolved in both images, with the phase image showing the expected higher sensitivity in terms of a greater extent of the damage region compared to the amplitude image. The results indicate that the change in carrier lifetime is the major contrast mechanism which can thus be calibrated and labeled as a free-carrier recombination lifetime image (under the same surface recombination conditions).

Combined photothermal and photoacoustic characterization of silicon–epoxy composites and the existence of a particle thermal percolation threshold

Abstract Photoacoustic (PA) and photothermal radiometric (PTR) detection were used to characterize thermal properties of silicon–epoxy composite materials in the volume range 0% x 50 μm ). PA detection was used to study the variation of the thermal diffusivity as a function of Si volume fraction, and PTR was used to determine the influence of the electronic carrier contribution to the thermal transport with the optical properties taken into consideration. The combined PA and PTR measurements show that there exists no linear relation between thermal diffusivity and silicon volume fraction. Thermal diffusivity and optical absorption coefficient measurements can be obtained by means of combined PA and PTR measurements. Both parameters exhibit anomalous behavior in the 16% Si volume fraction range, corroborating the existence of a particle percolation threshold for three-dimensional random close packed (rcp) solids.

Laser Infrared Photothermal Radiometric and ELYMAT Characterizations of p‐Si Wafers Annealed in the Presence of an External Electric Field

Laser infrared photothermal radiometry (PTR) was used as an analytical technique to measure the electronic transport parameters of p-Si wafers oxidized and thermally annealed under positive or negative external bias applied to the back surface. It was found that, following Fe contamination and recombination lifetime τ e , degradation in the oxidation and thermal-anneal furnace, both polarities of the external field result in significant minority carrier lifetime improvement, as well as in strong changes in the front-surface recombination velocity S 1 , of the samples, compared to a zerobias annealed reference sample. A qualitative model involving the passivating action of positive mobile ions (protons) trapped at the oxide-Si interface was advanced to explain the relative relations S 1 (+) > S 1 (0) > S 1 (-) . The lifetime relations τ e (+) > τ e (-) > τ e (0) obtained through both PTR and electrolytical metal tracer (ELYMAT) measurements were explained in terms of the relative abilities of positive and negative applied electric fields to prevent heavy metal ions from diffusing into the Si bulk and compromising the lifetime.