Electronic Defect and Contamination Monitoring in Si Wafers Using Spectrally Integrated Photocarrier Radiometry

Abstract

The ability of spectrally integrated room-temperature photocarrier radiometry to image electronic defects and contamination in silicon wafers is presented. Amplitude and phase imaging contrast is a result of signal sensitivity to local variations in the recombination lifetime of photoexcited carriers. Experimental frequency scans are fitted to carrier density-wave theory to simultaneously obtain the recombination lifetime, diffusivity, and surface recombination velocities ͑front and back͒. Lifetime measurements are combined with lateral surface scans to produce quantitative lifetime imaging. Contaminated boron-doped silicon wafers with iron concentration ϳ10 11 cm −3 on a baseline of ϳ5 ϫ 10 9 cm −3 have been successfully imaged and exhibit a much higher spatial resolution than surface photovoltage images. Recombination lifetime measurements before and after photodissociation of FeB pairs have been utilized for quantitative determination of iron concentration; however, lifetime accuracy limitations due to photodissociation by the excitation laser under medium-to-high optical injection levels required for photocarrier radiometric measurements compromise the accuracy of heavy ion ͑Fe͒ concentration measurements.

Thermal annealing induced photocarrier radiometry enhancement for ion implanted silicon wafers

“…The PCR experimental setup has been described in detail elsewhere. [7,8] Briefly, a 105 mW-power and 660 nm-wavelength semiconductor laser modulated by a function generator was used as an excitation source. A 10 nm-bandwidth bandpass filter centred at 660 nm was employed to block all unwanted radiation from the excitation source.…”

Effective interface state effects in hydrogenated amorphous-crystalline silicon heterostructures using ultraviolet laser photocarrier radiometry

“…They were subsequently demodulated with a lock-in amplifier (EG&G Princeton Applied Research, model 5210) and displayed as PCR amplitude and phase vs. modulation frequency. 16 The samples consisted of 290-lm thick CZ silicon wafers, on which i-a-Si:H nanolayers were deposited by DC saddle field plasma enhanced chemical vapor deposition (DCSF-PECVD) from silane gas precursor, chamber pressure of 160 mTorr, anode current 34.5 mA, substrate temperature 170 C, gas flow rate 30 sccm, and base vacuum <1 Â 10 À5 mTorr. The thicknesses of i-a-Si:H were 10, 30, and 90 nm for wafers #437, #438, and #439, respectively.…”

Quantitative Imaging of Defect Distributions in CdZnTe Wafers Using Combined Deep-Level Photothermal Spectroscopy, Photocarrier Radiometry, and Lock-In Carrierography

“…Rapidly growing applications of CdZnTe as a material suitable for X-ray and γ-ray detector fabrication − and for high-efficiency solar cells , have introduced the urgent need for characterization of photocarrier properties and their associated solid-state transport parameters, including their spatial distributions in wafer substrates, which affect charge transport and limit the performance of optoelectronic devices. Most popular diagnostic methods in use are current deep-level transient spectroscopy (I-DLTS), transient current technique (TCT), current and capacitance vs voltage ( I – V and C – V ) measurements, γ-ray spectroscopy, Hall measurements, and optical and thermal measurements. − Beyond those methodologies, photocarrier radiometry (PCR) is a nondestructive and noncontacting spectrally gated frequency-domain dynamic semiconductor photoluminescence (PL) diagnostic modality, which allows for the simultaneous nondestructive determination of electronic transport parameters in semiconductor substrates and devices. − Subsequently, lock-in carrierography (LIC) was introduced as a near-infrared (NIR) imaging extension of PCR, aimed at constructing quantitative images of carrier transport parameters. − Next, two-beam heterodyne LIC (HeLIC) was introduced to address the need for high-frequency photocarrier excitation, eliciting fast enough signal responses required to measure short recombination lifetimes and other fast photocarrier relaxation processes. HeLIC was developed to allow high-frequency dynamic imaging of optoelectronic material and device properties, which require sampling rates orders of magnitude higher than those achievable by the frame rates of today’s fastest NIR camera technologies. − Very recently, heterodyne PCR (HePCR) proved to be very sensitive to photocarrier emission/capture processes out of, and into, band-gap defect and impurity states: a newly discovered HePCR phenomenon giving rise to a frequency-domain heterodyne signal amplitude depression (“dip” or “notch”) accompanied by a 180° phase transition was attributed to a nonlinear kinetic mechanism of laser-excited harmonic carrier density waves (CDW) interacting with trap or defect states in Si wafers .…”