A review is presented of the recent advances in the study of oxygen precipitation and of the main properties of oxide precipitates in silicon. After a general overview of the system ‘‘oxygen in silicon,’’ the thermodynamics and the kinetics of the precipitate formation are treated in detail, with major emphasis on the phenomenology; subsequently, the most important techniques for the characterization of the precipitates are illustrated together with the most interesting and recent results. Finally, the possible influence of oxygen precipitation on technological applications is stressed, with particular attention to recent results regarding device yield. Actually, the essential novelty of this review rests on the attempt to give an extended picture of what has been recently clarified by means of highly sophisticated diagnostic methods and of the influence of precipitation on the properties of semiconductor devices.

Oxygen precipitation in silicon

Indentation techniques have been extensively used for mechanical characterisation of materials. Development of instrumented indentation techniques at low and ultra low load levels has further improved their utility for understanding the mechanical responses of solids at micro and nano scales. The variation of hardness with the load/depth of indentation, known as indentation size effect, has led to difficulties in using hardness as a fundamental or characteristic mechanical property of materials. Detailed discussions are focused on the issue of indentation size effect in brittle and ductile solids. Various theoretical models accounting for the indentation mechanics are highlighted. The results obtained from these techniques with quasicrystals, bulk metallic glasses and nanomaterials are reviewed. The issues related to phase transformation during indentation tests are briefly discussed. The industrial use of the indentation technique has been pointed out. Some of the current issues and directions fo...

Micro- and nanoindentation techniques for mechanical characterisation of materials

The issue of bond rupture versus microplasticity as an essential mechanism of crack propagation in brittle solids is addressed. A detailed survey of existing theoretical and experimental evidence relating to this issue highlights the need for direct observations of events within the crack-tip “process zone”, at a level approaching 10 nm. Transmission electron microscopy is accordingly used to study arrested cracks about sharp-contact (Vickers indentation and particle impact) sites in Si, Ge, SiC and Al2O3. The nature of the deformation which accommodates the irreversible contact impression is first investigated, in the light of Marsh's proposal of an “equivalence” between indentation and crack-tip zone processes. Interfacial and tip regions of the surrounding cracks are then examined for any trace of a plasticity-controlled fracture process. Dislocation-like images are indeed evident at the crack planes, but these are shown to be totally inconsistent with any conventional slip mechanism. The close connection between the dislocation patterns and moire fringe systems along the cracks points to “lattice mismatch” contrast in association with a partial closure and healing operation at the interface. Analysis of all other details in the crack patterns, e.g. the presence of a crack-front contrast band indicative of a residual strain field and the disposition of interfacial fracture steps relative to the dislocation/moire system, reinforces this interpretation. It is concluded that the concept of an atomically sharp crack provides a sound basis for the theory of fracture of brittle solids.

Atomically sharp cracks in brittle solids: an electron microscopy study

Single crystalline silicon was plunge-cut using diamond tools at a low speed. Cross-sectional transmission electron microscopy and laser micro-Raman spectroscopy were used to examine the subsurface structure of the machined sample. The results showed that the thickness of the machining-induced amorphous layer strongly depends on the tool rake angle and depth of cut, and fluctuates synchronously with surface waviness. Dislocation activity was observed below the amorphous layers in all instances, where the dislocation density depended on the cutting conditions. The machining pressure was estimated from the micro-cutting forces, and a subsurface damage model was proposed by considering the phase transformation and dislocation behavior of silicon under high-pressure conditions.

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Fundamental investigation of subsurface damage in single crystalline silicon caused by diamond machining

Dislocation Dynamics and Mechanical Properties of Crystals

The specific features of the dislocation structure, occuring in the vicinity of indentations have been studied using Si single crystals under different conditions of deformation (at temperatures of 20 to 700 °C and loadings of 0.5 to 10 p). It is shown, that the deformation of crystals at temperatures of 350 to 650 °C results in twin formation with {111} twinning plane. Flat defects with {115} habit plane are revealed. They are shown to be platelets of a new phase, which is of the hexagonal structure with c = 6.31 A and a = 3.86 A. The possible mechanism of the phase transformation is discussed.



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Electron microscope investigation of the microplastic deformation mechanisms of silicon by indentation

It is shown that the starting stresses for dislocation glide and their electrical activity are determined by the temperature, dislocation velocity, and distance moved upon bringing them to the starting position and, also, on the sample cooling rate after deformation A correlation between starting is stresses and dislocation donor center concentration is observed It is shown that the result obtained is determined by the formation of complicated centers in the impurity atmospheres of both, mobile and immobile dislocations



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The effect of thermal treatment on the electrical activity and mobility of dislocations in Si

The properties of regions swept by a moving dislocation in silicon crystals are experimentally studied. The peculiarities of forming traces of various types behind dislocations observed by electron microscopy and chemical etching are investigated. These traces are found to arise as result of point defect redistribution by moving dislocations and change in their structural state in a volume swept by a dislocation. It is shown that the processes mentioned enable the slip plane to assume properties of a specific two-dimensional defect responsible for the appearance of the new mechanism of a charge carrier mobility anisotropy in the plastically deformed crystals.



[Russian Text Ignored]

On the real structure of monocrystalline silicon near dislocation slip planes

The experimental results are presented of a study of new extended defects morphology in Si. It is shown that the defects generated by moving 60 -dislocation lie in the dislocation slip plane. h110i and h112i axes of the defects are found and {113} and {115} habit planes are supposed. It is assumed that the peculiarities of the atomic structure of split 60 -dislocations are the source of local supersaturation of intrinsic point defects, mainly self-interstitials, which results in the formation of their agglomerates in the form of extended defects with specific crystallography. The defects were revealed also in SiGe crystals and in this way this phenomenon is supposed to generally exist for materials with diamond crystal lattice. The cardinal influence of Ge content on the defects nucleation proves the supposition about their self-interstitial nature.

V. G. Eremenko

Papers

Electron microscope investigation of the microplastic deformation mechanisms of silicon by indentation

The effect of thermal treatment on the electrical activity and mobility of dislocations in Si

On the real structure of monocrystalline silicon near dislocation slip planes

The Origin and Properties of New Extended Defects Revealed by Etching in Plastically Deformed Si and SiGe