W. Schröter

Precipitation behaviour of nickel in silicon

Abstract The precipitation behaviour of nickel in silicon after rapid cooling (at about 103 Ks−1) from high temperatures (850-850°C) has been studied using high-resolution transmission electron microscopy. It is shown that (1) coherent platelets on Si{111} planes are formed, which consist of two {111} layers of NiSi2 and (2) the precipitate-matrix interface is built up by Si-Si bonds. It is proposed that these precipitates, in which all nickel atoms have a deficient coordination, are formed as a compromise to maximize the energy degradation rate. It is estimated that a major fraction of the total content is contained in these precipitates. Further annealing of samples quenched from 1050°C leads to a considerable increase in the particle thickness, leaving the diameter of the platelets almost unaffected. This behaviour is attributed to the reduction in interfacial energy. It is found that the precipitate orientation depends on the annealing temperature, that is, we obtain (1) the same orientation as the si...

Structural and Electrical Properties of Metal Silicide Precipitates in Silicon

This paper summarizes current understanding of structural and electronic properties of metal silicide precipitates in silicon and their interrelation. Combined studies of high-resolution transmission electron microscopy and deep level transient spectroscopy together with numerical simulations show that the bounding dislocation of nickel silicide platelets is the key to understand their rapid growth and electrical properties. Different misfit relaxation phenomena govern the structural evolution of copper silicide precipitates from their early stages to the well-known colony growth. This evolution involves different types of secondary defects indicating that the deep band-like states observed throughout this process are associated with the silicide precipitates themselves.

Steady-state deformation at intermediate and high temperatures

Abstract Experimental data of steady-state deformation obtained either in creep or in constant strain-rate experiments, which extend from high to intermediate temperatures, become increasingly available in the literature. While in many cases the high-temperature regime can be explained by the well-known power-law models, the incorporation of the results at intermediate temperatures is still under discussion. It is the aim of the present work to show by a careful analysis of the above mentioned data, that the jog-dragging model put forward by Barrett and Nix can account for the whole temperature range considered here and that the activation enthalpy of steady-state deformation is that of lattice self-diffusion.

Mechanisms and computer modelling of transition element gettering in silicon

Abstract This paper starts out by summarising the modelling and computer simulation of phosphorus diffusion gettering (PDG) of Au. The mobilisation of precipitated impurity atoms is discussed in the light of the silicon interstitial supersaturation provided by the phosphorus diffusion (PD). We then extend the gettering model to Co using bulk solubility data of highly P-doped Si, and find satisfactory agreement with experimental profiles of the total Co-concentration. Yet the pointed disagreement between the CoP/Cos-ratio obtained through simulation and Mosbauer data leads to the conclusion that, in the case of phosphorus silicate glass (PSG) growth, segregation alone cannot unambigiously account for the observed gettering efficiency. Instead, it is proposed that PD induced silicide formation provides a more suitable explanation of the high efficiency of PDG accompanied with PSG growth.

Sensitivity limits of strain mapping procedures using high‐resolution electron microscopy

Strain detection limits achieved by several approaches of strain mapping differing in the procedure of determining positions of intensity maxima have been compared. Algorithms which simultaneously take into account the two‐dimensional intensity distribution around maximum positions yield similar detection limits and are superior to those performing successive one‐dimensional cuts. Investigations of the effect of image recording imply that the use of photographic plates is superior to direct image recording using a slow‐scan CCD camera because of larger sampling rates and a larger field of view. It is finally shown that the choice of specimen preparation technique substantially affects the strain detection limit with cleaved samples yielding results which are a factor of about three better than ion‐milled samples.

DLTS study of the influence of plastic deformation on deep levels in n‐type CdTe

Abstract Using transient capacitance spectroscopy, deep-level defects which are introduced by plastic deformation in n‐type CdTe have been looked for. Within the range 0·1–0·75 eV below the conduction-band edge, one line at Ee -0·72 eV associated with deformation-induced defects has been found. The characteristics of this line are different from those associated with isolated point defects : its shape is strongly asymmetric and its amplitude varies non-exponentially with duration of the filling pulse. These characteristics are well known from deep-level transient spectroscopy (DLTS) measurements on deformed elemental semiconductors. The defect concentrations correspond well to the dislocation densities. Further changes in transient capacitance spectra of deformed samples have not been detected (detection limit 1012cm−3).

Analysis of high resolution transmission electron microscope images of crystalline-amorphous interfaces.

For the analysis of images of homogeneous crystalline-amorphous interfaces we propose to average them along the interface obtaining the averaged interface image or the averaged intensity profile. Due to averaging, contrast components with the periodicity of the crystalline area of the image are extracted. Thus, the contrast features originating from the random overlap of the projected potentials of atoms in the amorphous layer are suppressed. It is shown that averaged images can be simulated by the multi-slice method using the novel approach to model the near interfacial amorphous structure by its mean atomic density distribution in front of the crystalline boundary. The crystalline structure is represented by its known atomic positions. We apply the proposed method to the investigation of the near interfacial short-range order in the c-Si/ a-Ge crystalline-amorphous interface.

New Analysis of the Yield Point of Germanium

The interpretation of the yield point of germanium is still an unsolved question and, for more than a decade, no new information or suggestion on this problem has become known to the authors. In the present paper the available data are again analyzed, together with measurements of the strain rate at the inflection point of the creep curve, and taking into account investigations of the dislocation velocity. A consistent picture can be obtained by assuming that at least two (perhaps three) different regimes are involved. At temperatures above about 600°C, the lower yield stress obeys Haasens model with a strain-rate exponent of 1/2.9 and an activation energy of 1.74 eV. At lower temperatures experimental evidence indicates different strain-rate and temperature dependences. A new phenomenological decription is discussed, but a conclusive model is difficult to establish. The underlying activation energy, however, can be derived as approximately 1.85 eV. Arguments are presented which may elucidate the origin of the problems arising for the low-temperature measurements.

The effect of the translational symmetry of crystalline silicon on the structure of amorphous germanium in the interfacial region

The structure of an amorphous Ge layer near an interface with a Si(111) crystal was studied by quantitative high-resolution electron microscopy. It was found that the translational symmetry of a Si crystal leads to the crystal-like order in the positions of Ge atoms in the interfacial region, the width of which is about 1.4 nm. In this region, the average orientation of interatomic bonds tilted with respect to the interface compensates for the difference in the bond lengths in crystalline Si and amorphous Ge and is responsible for the tetragonal distortion of the most likely atomic positions.

Diffusion of gallium along small-angle grain boundaries in germanium

Abstract Diffusion profiles of gallium in germanium containing a small-angle symmetric tilt boundary have been determined as a function of temperature and misorientation angle. The observed diffusion tails cannot be described in terms of the phono-monological pipe diffusion or grain-boundary diffusion models. The results may be understood by diffusion along a second phase, containing Ge, which forms around the dislocations, and in which the solubility of gallium is about 102 103 times that in the unperturbed germanium matrix.