Solid State Phenomena Vols. 131-133

Abstract: We investigated the development of dislocation-related DLTS spectra in n-CZ-Si crystals with small (about 7.104 cm-2) number of long individual dislocations depending on the distance L that dislocations traveled during deformation at 600oC and on the velocity of dislocations. We found that a typical dislocation-related DLTS signal appeared only when dislocations traveled a significant distance that is more than 150-200μm, and it depended strongly on dislocation velocity. The results were interpreted on the assumption that the DLTS signal corresponds to some core defects and atomic impurities accumulated on the dislocations during their slow motion. At high concentration of deep level defects on dislocations a strange “negative DLTS” signal was observed. This can be explained by electron tunneling between deep defects along dislocations.

Abstract: The impact of nickel on minority carrier recombination lifetime has been studied in ptype CZ silicon using SPV and μ-PCD techniques. The results show that small oxide precipitates can be used to improve drastically the detection limit of nickel. This is explained by the decoration of oxide precipitates by nickel, which results in the enhanced recombination activity. In the absence of oxide precipitates or other related bulk microdefects nickel precipitates preferably to wafer surfaces, which does not have such a high impact on the measured recombination lifetime, at least on a low concentration level. Low temperature anneal at 180°C or light illumination of the wafers after nickel in-diffusion did not reveal any further change in lifetime in any of the wafers, which may indicate that nickel precipitates efficiently during air-cooling from high temperature.

Abstract: Current-voltage characteristics of Schottky-type Ag/Porous Silicon (Ag/PS) structures in normal air, humid ambient and in different hydrogen-containing solutions (distilled water, freshwater, Black sea-water, ethanol ad methanol) have been investigated. Generation of the opencircuit voltage (Voc), short-circuit current (Jsc) up to 560 mV and 0.5mA/cm2, respectively, on placing Ag/PS structures in hydrogen-containing solutions was discovered. This phenomenon is reversible, i.e. placing and removal of Ag/PS structures cell from hydrogen-containing solutions is accompanied by response and recovery of the Voc and Jsc parameters. It is shown that the thermal annealing of the Ag/PS structure at 200oC for 10 min is accompanied by somewhat changes and stabilization of Voc and Jsc parameters of Ag/PS sensors. The possible mechanisms related with hydrogen-stimulated generation of voltage and diffusion-stimulated stabilization of the sensing parameters of Ag/PS Schottky-type structures is suggested. Data received in this work indicate on perspectivity of using Ag/PS structures as both the gas sensors and hydrogen cells.

Abstract: The main goal of this work is to demonstrate the correlation between the density and type of surface defects arising during the formation of a buried nitrogen-containing layer in Si wafers, and the number of buried defects formed by different dose hydrogen preimplantation. Standard commercial 12 ⋅cm boron-doped and 4.5 ⋅cm phosphorous-doped Cz Si wafers were subjected to hydrogen ion implantation at room temperature with the energy 100 keV and doses 1⋅1015 - 4⋅1016 at/cm2. Then nitrogen was introduced into silicon from a DC plasma source at a temperature of 300 oС. Finally, all samples were subjected to 2 h vacuum annealing at 900 oС. The experiments have shown that the density and type of the surface defects depend significantly on the dose of hydrogen implantation, parameters of N+-plasma treatment, and conductivity type of silicon. Optimization of the above-mentioned parameters makes it possible to create the substrates containing a buried dielectric SixNy layer and having a practically defect-free surface.

Abstract: The effect of high-energy hydrogen and helium implantation and subsequent annealing on generation of radiation defects and shallow donors in the low-doped oxygen-rich FZ n-type silicon was investigated. Samples were implanted with 7 MeV 4He2+ or 1.8 MeV 1H+ to fluences ranging from 1x109 to 3x1011 cm-2 and 1.4x1010 to 5x1012cm-2, resp., and then isochronally annealed for 30 minutes in the temperature range up to 550°C. Results show that radiation damage produced by helium ions remarkably enhances formation of thermal donors (TDs) when annealing temperature exceeds 375°C, i.e. when the majority of vacancy-related recombination centers anneals out. The excess concentration of TDs is proportional to the helium fluence and peaks at 1.6x1014cm-3 if annealing temperature reaches 475°C. Proton irradiation itself introduces hydrogen donors (HDs) which form a Gaussian peak at the proton end-of-range. Formation and annealing of shallow and deep hydrogen-related levels are strongly influenced by electric field at annealing temperatures below 175°C. If annealing temperature exceeds 350°C, HDs disappear and the excessive shallow doping is caused, as in the case of helium irradiation, by radiation enhanced TDs.

Abstract: Complexes formed by low dose irradiation with electron (1015-16/cm2) and He (5x1012- 5x1013/cm2) in the relatively low carbon concentration (1016/cm3) MCZ silicon were investigated by highly sensitive and quantitative IR absorption analysis. CiOi and VO were the main complexes in all cases. The concentration of these complexes was about 1015/cm3, or 10% of included carbon in the highest case. Loss of almost equal amount of Cs was observed. The concentration of CiOiI was one order of magnitude lower. Upon annealing, these lines weakened and almost disappeared at 400 oC. There were some absorption lines introduced by the annealing. VO2 was strongest among them and CsOi related structure was also confirmed. There were absorption lines at 954.9 and 962.6 cm-1 appeared after annealing at 300 oC.

Abstract: In this paper we present a detailed investigation of peculiarities of dislocation related D1/D2 bands behavior in silicon doped with Cu. For this purpose float zone grown (FZ) p-type silicon with B-doping 2.85·1015cm-3 was deformed by 3-point bending method at 950flC up to dislocation density of 2±0.2·106 cm-2. The deformed samples were contaminated with Cu up to several concentrations from 6·1013 cm-3 to 5·1016 cm-3. The variation in dislocation related spectra were traced after different thermal treatments. A decrease of D1/D2 bands intensity in quenched samples was observed even after their storage at room temperature. Taking into account the fact that Cu has a high mobility even at room temperature the decrease of D1/D2 bands intensity can be attributed to passivation of corresponding luminescence centers by Cu atoms. The influence of Cu contamination on D2 band is much more complicated as compared to D1 band. New line in position about 883 meV was observed as a result of storage of samples at room temperature and subsequent isochronous anneals. It was observed that D1/D2 band luminescence sharply increased in 30K – 50K range in samples with high Cu doping level. In addition the line in about 830 meV position became stronger at these temperatures whereas its intensity was negligible at 6K.

Abstract: Nitrogen in silicon is known to affect dramatically the properties of voids. A plausible mechanism could be vacancy trapping by nitrogen interstitial species, mostly by the minor monomeric species (N1) with only a negligible contribution of the major dimeric species (N2). However, a more careful analysis of the published data shows that in Czochralski silicon no vacancy trapping occurs at the void formation stage (around 1100oC). The implication is that the trapping reaction, V + N1, although favoured thermodynamically, is of a negligible rate. Therefore, the nitrogen effect on voids in Czochralski Si is entirely due to nitrogen adsorption at the void surface. Quite a different mechanism operates in Float-Zoned crystals where voids are formed at lower T. Here vacancy trapping by N2 seems to be responsible for void suppression.

Abstract: Oxygen precipitation in Si is a complex set of processes which has been studied over many years. Here we review theoretical work relating to the precipitation process. At temperatures around 450°C oxygen atoms become mobile and form a family of thermal double donors. The structure of these defects and the origin of their electrical activity is discussed. At temperature around 650°C these donors disappear and there is a growth of SiO2 precipitates along with rod like defects which are extended defects involving Si interstitials. At higher temperatures these collapse into dislocation loops. The structure and electrical properties of the rod like defect are described and compared with those of dislocations.

Abstract: Interstitial iron and iron-acceptor pairs are well studied but undesirable defects in Si as they are strong recombination centers which resist hydrogen passivation. Thermal anneals often result in the precipitation of Fe. Relatively little information is available about the interactions between Fe and native defects or common impurities in Si. We present the results of first-principles calculations of Fe interactions with native defects (vacancy, self-interstitial) and common impurities such as C, O, H, or Fe. The goal is to understand the fundamental chemistry of Fe in Si, identify and characterize the type of complexes that occur. We predict the configurations, charge and spin states, binding and activation energies, and estimate the position of gap levels. The possibility of passivation is discussed.