Infrared photocarrier radiometry of semiconductors:  Physical principles, quantitative depth profilometry, and scanning imaging of deep subsurface electronic defects

Abstract

Laser-induced infrared photocarrier radiometry ͑PCR͒ is introduced theoretically and experimentally through deep subsurface scanning imaging and signal frequency dependencies from Si wafers. A roomtemperature InGaAs detector (0.8-1.8 m) with integrated amplification electronics is used instead of the liquid-nitrogen-cooled HgCdTe photodetector (2-12 m) of conventional photothermal radiometry. PCR measures purely electronic carrier-wave ͑CW͒ recombination. The InGaAs detector completely obliterates the thermal-infrared emission band (8-12 m), unlike the known photothermal signal types, which invariably contain combinations of carrier-wave and thermal-wave infrared emissions due to the concurrent lattice absorption of the incident beam and nonradiative heating. The PCR theory is presented as infrared depth integrals of CW density profiles. Experimental aspects of this methodology are given, including the determination of photocarrier transport parameters through modulation frequency scans, as well as CW scanning imaging. The PCR coordinate scans at the front surface of 500Ϫm-thick Si wafers with slight back-surface mechanical defects can easily ''see'' and create clear images of the defects at modulation frequencies up to 100 kHz, at laser-beam optical penetration depth ϳ1 m below the surface ͑at 514 nm͒. The physics of the contrast mechanism for the nonthermal nature of the PCR signal is described: it involves self-reabsorption of CWrecombination-generated IR photons emitted by the photoexcited carrier-wave distribution depth profile throughout the wafer bulk. The distribution is modified by enhanced recombination at localized or extended defects, even as remote as the back surface of the material. The high-frequency, deep-defect PCR images thus obtained prove that very-near-surface ͑where optoelectronic device fabrication takes place͒ photocarrier generation can be detrimentally affected not only by local electronic defects as is commonly assumed, but also by defects in remote wafer regions much deeper than the extent of the electronically active thin surface layer.

Numerical Analysis of Piezoelectric Spectra of Zn1-x-yBexMnySe Mixed Crystals

“…Photothermal methods [1] have recently become a very useful tool for measurements of the optical and thermal parameters of semiconductors [2,3,5]. The significance of thermal phenomena becomes more and more important because of the problem of energy dissipation in miniaturized semiconducting devices.…”

Characterization of Arsenic Ultra-Shallow Junctions in Silicon Using Photocarrier Radiometry and Spectroscopic Ellipsometry

“…A. Woollam Co.). The PCR experimental setup has been described in detail elsewhere [7]. In a PCR experiment, a 405 nm wavelength semiconductor laser with an output power of ∼40 mW was used as the excitation source.…”

Photo-carrier and Electronic Studies of Silicon-Doped GaAs Grown by MBE Using PCR

“…According to the diffusion laws, they are moving away from the excitation region. If the IR emissions from the recombination region of the sample are filtered and focused onto a narrow-bandwidth IR detector, such as InGaAs which has a spectral bandwidth from 800 nm to 1800 nm, a PCR signal free of any thermal contribution can be obtained [1]. The diameter of the detecting area focused in our system is similar to the excitation area, about 40 µm.…”

“…Moreover, the distribution of impurities in the semiconductor is an important aspect in the manufacture of integrated circuits. Photo-carrier radiometry (PCR) is a new powerful technique that has been used to obtain different electronic transport parameters such as recombination lifetime, front and back surface recombination velocities, carrier diffusion coefficient [1,2], and the distribution of the impurities on semiconductor wafers [3]. Unlike other photothermal techniques like photothermal radiometry (PTR) or photo-modulated thermoreflectance (PMOR), PCR is only sensitive to the recombination of free photo-excited carrier density waves [1].…”