Single-crystal silicon coimplanted by helium and hydrogen: Evolution of decorated vacancylike defects with thermal treatments

Abstract

Si p-type ͑100͒ samples were coimplanted at room temperature with He + ions at 30 keV with a dose of 1 ϫ 10 16 ions/ cm 2 and successively with H + ions at 24 keV with a dose of 1 ϫ 10 16 ions/ cm 2 . A series of samples was thermally treated for 2 h from 100 to 900°C at 100°C steps to study the evolution of pointlike and extended defects by two complementary techniques: positron Doppler broadening spectroscopy and transmission electron microscopy. Depth profiling the samples with a positron beam led to the identification of five different traps and the evolution of their profile distributions with thermal treatments. The positron traps were identified as decorated vacancy clusters of different sizes. Their decoration by implanted ions and in some case by oxygen was probed by coincidence Doppler broadening spectroscopy. Up to 300°C annealing temperature positrons probe three distributions of different decorated defects covering regions of the sample down to 400-450 nm. Starting from 300°C annealing temperature no defects were revealed by positrons in the region next to the peak of the implanted ions distributions positioned around 280 nm, where extended defects are expected; this indicates complete filling of the defects by H and He. From 300 to 600°C decorated vacancy clusters of different sizes appear progressively in the region below 280 nm, with a distribution moving deeper into the sample. Comparison with previous measurements on He-implanted samples points out the chemical action of H. Hydrogen atoms interact with the previous damage by He, producing more stabilized vacancylike defects distributed through the damage region of the sample. Electron microscopy shows the transformation of the extended defects from platelets to blisters and cavities.

Depth Profiling of Defects in He Implanted SiO2

“…1, and (b) the S parameter of native oxide grown on Si is about 0.94 and its coincidence DB-PAS spectra resemble that of quartz [22,25]. Besides observations (a) and (b) there is the fact that at the SiO 2 /Si interface and at the SiO 2 surface the contribution from annihilation with O electrons (broadening of the 511 keV annihilation line) is higher.…”

“…These defects must be mostly divacancies stabilized by He or/and platelets partially filled by He [22]. In the region where He density is higher (around the peak of the He distribution, 270 nm) the vacancy-like and the extended defects (platelets) are expected to be decorated by the presence of He [22,26]. The positron probes He decorated defects with an effective open volume smaller than a single monovacancy in Si.…”

“…Samples were implanted keeping the sample holder at 77 K with He + ions at 30 keV with a dose of 5 × 10 15 ions/cm −2 . At this energy, the He depth distribution is peaked around 270 nm [22]. The density of the beam current was about 8 µA cm −2 and the sample holder was tilted by 7…”

Splitting kinetics of Si0.8Ge0.2 layers implanted with H or sequentially with He and H

“…Recent and in-depth characterization of quite similar samples by positron Dopler broadening spectroscopy ͑DBS͒ suggests that hydrogen atoms interact with the damage previously created by He implantation, producing more stabilized vacancylike defects, a finding consistent with our own observations. 14 Diffusivity arguments only cannot be brought to the forefront to explain the different behaviors in splitting kinetics between Si and SiGe after sequential implantation since we ruled them out to compare splitting characteristics between H-only and sequential implantations in two materials. The migration length of He is larger in SiGe than in Si as measured by our SIMS results.…”

Caracterización de nanoestructuras sub-superficiales utilizando espectroscopía de aniquilación de positrones

“…En consecuencia, la aniquilación de positrones con electrones de alto momentum, es decir con electrones de las últimas capas del carozo iónico, se refleja en las "colas" del pico de aniquilación de 511keV. En un sólido, los electrones pertenecientes al carozo iónico mantienen las características atómicas [13] por lo tanto, la señal correspondiente a la aniquilación de positrones con electrones del carozo iónico puede ser utilizada para obtener información sobre las especies químicas que rodean el sitio de aniquilación [11,14]. La probabilidad de aniquilación de positrones con estos electrones es muy baja ya que los positrones son repelidos por el carozo iónico y, por lo tanto, su señal es comparable a la del fondo (background).…”