L. I. Fedina

Extended Defects Formation in Si Crystals by Clustering of Intrinsic Point Defects Studied by in-situ Electron Irradiation in an HREM

(a) Institute of Semiconductor Physics, Russian Academy of Sciences,Pr. akad. Lavrentyeva 13, 630090 Novosibirsk, RussiaFax: (3832)331080, e-mail: fedina@thermo.isp.nsc.ru(b) University of Antwerp, RUCA EMAT, Groenenborgerlaan 171, B-2020 Antwerpen,Belgium(c) IMEC, B-3001 Leuven, Belgium(Received October 5, 1998)In situ irradiation experiments in a high resolution electron microscope JEOL-4000EX at roomtemperature resulted in discovery of the isolated and combined clustering of vacancies and self-interstitial atoms on {111}- and {113}-habit planes both leading to an extended defect formation inSi crystals. The type of the defect is strongly affected by the type of supersaturation of point de-fects depending on the crystal thickness during electron irradiation. Because of the existence of en-ergy barriers against recombination of interstitials with the extended aggregates of vacancies, a largefamily of intermediate defect configurations (IDCs) is formed on {113}- and {111}-habit planes at alow temperature under interstitial supersaturation in addition to the well-known {113}-defects ofinterstitial type. The formation of metastable IDCs inside vacancy aggregates prevents a way ofrecombination of defects in extended shape.

Excimer laser and rapid thermal annealing stimulation of solid-phase nucleation and crystallization in amorphous silicon films on glass substrates

The solid-phase crystallization process in thin amorphous silicon films on glass substrates was studied with application of excimer laser annealing (ELA) and rapid thermal annealing (RTA) for stimulation of nucleation. Use of ELA allowed us to create homogeneous polycrystalline silicon films on glass with grain sizes up to at temperatures below C. Use of RTA reduced the incubation time of nucleation from 100 to 6 h. The textured silicon films on glass with predominant orientation (110) and sizes of textured areas up to were manufactured using excimer laser stimulation of nucleation. The influence of the mechanical stress mechanism on grain orientation was suggested, and it was theoretically shown that internal stresses retard the nucleation process. The addition of deformation to the chemical potential difference was estimated for nucleation in amorphous silicon as 11.4 meV per nucleated atom.

On the mechanism of {111}-defect formation in silicon studied by in situ electron irradiation in a high resolution electron microscope

Abstract The initial stages of point defect cluster formation on {111} habit planes in Si crystals have been investigated during in situ electron irradiation in a high resolution electron microscope to elucidate their nature and origin. It was observed that 〈110〉 interstitial chains located in {111} planes at regular spacing are formed by the agglomeration of self-interstitial atoms to the core of vacancy or interstitial Frank partial dislocation loops and by the insertion of interstitial chains between two perfect {111} planes. Based on experimental and calculated high resolution electron microscopy images a structural model for the {111}-defect is proposed which includes a regular sequence of double five-membered and single eight-membered rings in which no dangling bonds are involved. A dependence of the displacement vector of the {111}-defect on the formation mechanism is observed. An isolated {111}-defect is characterized by the fully relaxed atomic structure with a displacement vector of (a/5)〈111〉. ...

Precise surface measurements at the nanoscale

Availability of self-assembly effects occurring at the atomically clean Si(1 1 1) surface during high temperature anneals in an ultrahigh vacuum chamber for fabrication of a precise calibrator at nanoscale measurements is discussed. These effects provide formation of ordered monatomic step arrays assembled by step bunches divided by almost singular surface areas with widely spaced monatomic steps suitable for calibration of atomic force microscopes. The monatomic step height at the Si(1 1 1) surface and its replication by the native oxide layer was attested by the high-resolution transmission electron microscopy followed by Digital Micrograph analysis and found to be equal to interplanar spacing (0.314 nm) in the volume of Si crystal with ±0.001 nm of accuracy. Excellent replication of the monatomic step height by oxide film covering the Si surface makes available precise AFM calibration at the nanoscale at ambient conditions. The averaged step height measured by AFM scanning of 1 × 1 µm2 is found to be 0.314 ± 0.003 nm (~1% of uncertainty). However, when the scan area becomes bigger than 2 × 2 µm2, the height measurement uncertainty increases sharply 15 times (0.310 ± 0.034 nm). We assume that this is due to differences between piezo element calibrations at small and large scan areas. The height measurement uncertainty for step bunches with well-defined quantity of steps (28) even at a large scan area (18 × 18 µm2) turns out to be 0.3%.

Precise measurements of nanostructure parameters

The precision of measurements performed by atomic-force microscopy (AFM) and high-resolution electron microscopy (HREM) for solving problems of metrology and diagnostics of solid nanostructures is discussed. The HREM-measured height of a monatomic step on a Si(111) surface covered by a thin natural oxide film is demonstrated to be 0.314 ± 0.001 nm. The same accuracy is ensured by AFM measurements through controlling the Si surface relief with heating in ultra-high vacuum on specially created test objects with the distance between the steps being approximately 2 µm. It is shown that the geometric phase method can be used to quantify the strains in the crystal lattice of strained heterostructures on the basis of HREM images with accuracy to 10−4%, and in situ irradiation by electrons in HREM measurements can be used to visualize ordered clusterization of vacancies and self-interstitial atoms in {113} planes in Si samples.

Instability of the Distribution of Atomic Steps on Si(111) upon Submonolayer Gold Adsorption at High Temperatures

The gold adsorption effect on the distribution of monatomic steps on the (111) silicon surface is studied in situ by ultrahigh vacuum reflection electron microscopy at temperatures of 850–1260°C. A new effect of the instability of silicon surface morphology has been detected. This effect leads to the redistribution of regular steps (RSs) to step bunches (STs) and vice versa on a surface covered with a gold submonolayer. For the crystal heated by directly passing an electric current, the behavior of the RS ⇔ SB morphological transitions on the silicon surface is investigated as a function of the gold coverage and the direction of the heating current. Thus, isothermal annealing at 900°C is accompanied by the following transitions on the silicon surface with predeposited 0.75 monolayer gold coverage: RS (0.72) ⇒ SB (0.42) ⇒ RS (0.24) ⇒ SB (0.07) RS ⇒ (0). The numbers given in parentheses are estimated values of the critical gold coverage measured in the monolayers at which the morphological transitions are observed. A change in the direction of the electric current used to heat the crystal leads to the reversible changes RS ⇒ SB and SB ⇒ RS at the same values of the critical gold coverage.

High-precision nanoscale length measurement

Modern lithographical methods used to create linear measures for nanometer-range dimensions and the main factors which limit the applications of such gages have been analyzed in the paper. Prospects for developing high-precision measures based on an atomically structured crystalline surface (containing monoatomic steps) whose parameters are bound to the crystallographic parameters of the crystal (traceable to the length measure) are shown. A method which can be used to create such measures based on controlling the surface morphology of monocrystalline silicon at an atomic level due to the effects of self-organization arising at the atomically clean surface as a result of annealing in ultrahigh vacuum is proposed. A description of the set of high-precision gages of vertical dimensions STEPP-IFP-1 in a size range of 0.31–31 nm with an error in the whole interval of gages of less than 0.05 nm is presented. The set of high-precision gages after carrying out state testing is included into the state registry of measuring means as measuring type no. 48115-11 (Federal Agency on Technical Regulating and Metrology order no. 6290 of October 31, 2011).

New Compositionally-Ordered GeSi Nano Dots Fabricated with 1250 keV Electrons

Transformation of uniformly strained GexSi1-x layers into GeSi dots of 3 ~ 7 nm which are compositionally ordered by one or concurrently two sets of {111} planes was carried out for the first time under non-equilibrium conditions induced by 1.25 MeV electron irradiation at Tc ≥ 200 oC in the high voltage electron microscope (JEM-ARM1300S). This microscope installed in the KBSI is characterized by an excellent point-to-point resolution of 0.12 nm allowing obtaining detailed information on chemical ordering at specific parameters of defocus (-800 Å) and crystal thickness (200~250 Å) determined by extensive HRTEM image simulation for the ordered dots.

Nucleation of two-dimensional Si islands near a monatomic step on an atomically clean Si(111)-(7×7) surface

The process of nucleation of 2D islands near a monatomic step at the initial stage of growing of a silicon film on the Si(111)-(7 × 7) surface is studied by means of in situ ultrahighvacuum reflection electron microscopy. The dependence of the depletion region width W near the step, where no islands are formed, on the deposition rate R is described by the expression W2 ∝ R-χ with the exponent χ = 1.18 and χ = 0.63 at temperatures of 650 and 680 °C, respectively. It is demonstrated that the change in χ is associated with the step structure, which provides the transformation from the growth kinetics limited by attachment of adatoms to the step to that limited by diffusion of adatoms. A competition of the processes of nucleation and attachment to the step leads to an increase in the critical size of the island nucleus from i = 1 far from the step to i = 3–5 near the step and to i = 6–8 on the terrace of critical width for 2D nucleation.

Adatom concentration distribution on an extrawide Si(111) terrace during sublimation

The formation of an adsorption layer on the Si(111) surface during sublimation at temperatures of 1000–1100 °C and subsequent quenching at T = 750 °C is studied by methods of insitu ultrahigh-vacuum reflection electron microscopy and exsitu atomic force microscopy. The adatom concentration distribution on an extrawide (~60 μm) atomically flat terrace is determined for the first time, and the diffusion length xs = 31±2 μm at T = 1000 °C is obtained. The analysis of the temperature dependence of the equilibrium concentration of adatoms near a monatomic step allows pioneering measurements of the energy necessary for adatom detachment from the step and attachment to the terrace Ead ≈ 0.68 eV. Based on these results, the energy parameters for some atomic processes on the Si(111) surface are estimated.