The package "fhi96md" is an efficient code to perform density-functional theory total-energy calculations for materials ranging from insulators to transition metals. The package employs first-principles pseudopotentials, and a plane-wave basis-set. For exchange and correlation both the local density and generalized gradient approximations are implemented. The code has a low storage demand and performs efficiently on low budget personal computers as well as high performance computers.

Density-functional theory calculations for poly-atomic systems: Electronic structure, static and elastic properties and ab initio molecular dynamics

Fabrication of monolithic lattice-mismatched semiconductor heterostructures with limited area regions having upper portions substantially exhausted of threading dislocations, as well as fabrication of semiconductor devices based on such lattice-mismatched heterostructures.

Lattice-Mismatched Semiconductor Structures with Reduced Dislocation Defect Densities and Related Methods for Device Fabrication

Surface structures and structural transformations are investigated upon femtosecond laser ablation (800 nm, 120 fs) from crystalline silicon (100) targets placed under ultra-high vacuum. After repetitive illumination with several thousand laser pulses at intensities below the single shot damage threshold, at normal incidence, the crater morphology indicates the development of periodic structures at the crater bottom, with the orientation depending on the laser beam polarization. Periods of 200 nm and 600–700 nm, respectively, are shorter than the laser wavelength and appear as a result of surface instability. The ablation dynamics monitored by time-of-flight mass spectrometry shows the emission of positive silicon ions and clusters with kinetic energies of about 7 eV. Raman spectroscopy reveals phase transformations in the irradiated spot from Si-I to the polymorphs Si-III, Si-IV, Si-XII, and amorphous silicon as well as a stable, uncommon phase of hexagonal Si-wurzite.

Sub–damage–threshold femtosecond laser ablation from crystalline Si: surface nanostructures and phase transformation

Methods of forming structures that include InP-based materials, such as a transistor operating as an inversion-type, enhancement-mode device. A dielectric layer may be deposited by ALD over a semiconductor layer including In and P. A channel layer may be formed above a buffer layer having a lattice constant similar to a lattice constant of InP, the buffer layer being formed over a substrate having a lattice constant different from a lattice constant of InP.

InP-Based Transistor Fabrication

Semiconductor structures include a trench formed proximate a substrate including a first semiconductor material. A crystalline material including a second semiconductor material lattice mismatched to the first semiconductor material is formed in the trench. Process embodiments include removing a portion of the dielectric layer to expose a side portion of the crystalline material and defining a gate thereover. Defects are reduced by using an aspect ratio trapping approach.

Tri-gate field-effect transistors formed by aspect ratio trapping

We have developed a method for studying the as-grown defect density spectra of Czochralski silicon wafers by infrared light scattering tomography. These spectra show the defect density vs. size or stability temperature. Different annealing procedures were used to reveal both parts of the spectra, one stable at high (1000 to 1280°C) and the other at low temperature (500 to 1000°C). The studies were performed on wafers grown in the vacancy-rich regime and on wafers with a stacking fault ring 150 and 200 mm in diam. In the as-grown state, only a very small part of the defect spectrum lies above the detection limit. In general, three main peaks appear in the spectrum. Their total height and exact positions are determined by the growth and cooling rates of the crystal, and by the initial concentration of interstitial oxygen. Due to the different locations of the maxima in the low temperature spectra, standard precipitation tests can be misleading for the estimation of the oxygen precipitation capability. A high temperature preanneal at 1000 or 1100°C shifts the low temperature part of the spectrum to smaller sizes. However, a dissolution of the grown-in defects was never detected. We conclude that during the nucleation anneals for internal gettering, only existing as-grown nuclei grow except under conditions when a time lag in nucleation is observed. The defect spectra provide a unique basis for the simulation of defect generation during wafer processing, and facilitate the selection of wafer material for a given technology. Furthermore, they provide the basis for effective generation of a bulk defect zone for internal gettering.

A Method for Studying the Grown‐In Defect Density Spectra in Czochralski Silicon Wafers

We have investigated the impact of rapid thermal annealing (RTA) induced vacancy supersaturation on oxide precipitation based as much as possible on experimental and theoretical values. Oxygen precipitation after RTA processing was found to be controlled by the initial concentration of interstitial oxygen in a sixth power dependency and frozen vacancies just in a cubic dependency. The formation of tensile strained nVO 2 clusters seems to be the favored process for coherent nucleation of oxide precipitates. The reduction of interstitial oxygen can be accurately modeled for the temperature range from 1150 to 1250°C using Ham's theory for precipitate growth and an empirical relation based on nucleation of oxide precipitates by agglomeration of VO 2 complexes. During RTA treatments at temperatures ≥ 1300°C vacancies seem to be consumed by other processes. Below RTA temperatures of 1150°C, oxide precipitation is dominated by shrunken as-grown precipitate nuclei because as-grown nuclei can be dissolved only at RTA temperatures ≥ 1150°C.

Analytical Modeling of the Interaction of Vacancies and Oxygen for Oxide Precipitation in RTA Treated Silicon Wafers

We present an approach in equilibrium theory for strain relief in small-area heteroepitaxial SiGe/Si structures, which includes surface and film-edge induced relaxation effects. With a view to computer simulation, the state of stress and shear components on the slip planes of strained mesa-like SiGe/Si systems are treated here in a simple analytical form in terms of strain and stress components, valid in linear elasticity. The two-dimensional analysis yields a complete description of the state of plane stress of small-area structural elements in a consistent manner. The present system of equations is generally sufficient to quantitatively determine the lowered stress components of stable, metastable, and plastically deformed finite strained layers. It is shown that there is a significant decrease in heteroepitaxial film stress as a function of material and size characteristics of the SiGe/Si system that allows one to increase substantially the critical layer thickness for loss of coherency for a given Ge content. The equilibrium theory proposed here provides guidance for computer simulation to configure stable small-area SiGe deposits for the development of technologies in which stress problems must be alleviated. A complete input deck for stress simulation including a run is given. The developed physics and computer simulation can be used for the design of small-geometry heterojunction bipolar transistors and SiGe channel MOSFETs, and for estimation of stress-related problems in sub-micron size devices.

State of stress and critical thickness of strained small-area SiGe layers

Additions of oxygen, boron, and phosphorus are well known to affect appreciabl y the dislocation dynamics in silicon single crystals. However, there are few reports on the effect of nitrogen on the mechanical strength, despite it’s using as dopant w hen growing large diameter silicon crystals CZ-Si. We have studied the effect of nitrogen (N ) doping on the plastic properties and mobility individual dislocations in 300 mm CZ-silicon. Three point loadings were used for dislocation mobility and starting stresses measurements in the t emperature range of 500 – 700 oC. It is shown that N-doping causes the decrease of dislocation mobility and increase starting stress. Possible mechanisms of hardening of silicon single crystals are discussed due to interaction of dislocations with impurities. Introduction The interaction of dislocations with intrinsic and impurity point defec ts in silicon single crystals is still being an object of an intensive study [1-3]. One of the reasons why researches in this domain are urgent is the trend toward increasing the diameter of silic on single crystals being grown [4, 5]. This contributes appreciably to the probability of formation and motion of dislocations in wafers in the process of high temperature technologic operations owing both to an increase of ther mal str sses and weight gain wafer themselves. Therefore, the problem of mecha nical strength of silicon wafers of larger diameter is of prime consideration. Currently nitrogen is of considerable use to strengthen silicon single crystals of larger diameter. It is well known that doping with nitrogen of silicon single cry stals significantly increases the upper and lower yield points. A number of works have been concerned with this f act [6, 7]. However, the effect of nitrogen doping on the mobility of individual dislocations in si licon is less studied. So, the authors of [7] showed that in a float-zone silicon single crystal ni rogen doping does not affect the velocity of individual dislocations but it leads to immobilization of dis locations while the crystal is kept under a low or zero applied stress at elevated temperatures. T he authors of [8] studied the effect of nitrogen doping on the process of formation and motion of dis locations from inner and surface (Knoop indentations) dislocation sources in CZ-Si. It was shown in a umber of works [9, 10] that nitrogen doping of CZ-Si leads to a diminution of the dislocat ion rosette around the indentation. Thus, today there are no data (or we are unaware of them) on the e ffect of nitrogen on the mobility and starting stress of individual dislocations in CZ-Si thoug , as is known, precisely the properties of individual dislocations make it possible to gain informati on on micromechanisms of the dopant-dislocation core interplay [11]. In this paper we have studie d the mobility of individual dislocations in nitrogen doped CZ-Si. This work is a follow-up to [6] where the macroplastic properties of the same silicon specimens were examined. Solid State Phenomena Online: 2003-09-30 ISSN: 1662-9779, Vols. 95-96, pp 465-472 doi:10.4028/www.scientific.net/SSP.95-96.465 © 2004 Trans Tech Publications Ltd, Switzerland All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications Ltd, www.scientific.net. (Semanticscholar.org-18/03/20,13:31:00) Experimental The specimens to be studied were cut from dislocation free 300 mm C zochralski silicon crystals doped with boron (10 ⋅cm) and nitrogen (3 ⋅10 cm ÷ 3⋅10 cm). The reference CZ-Si crystals were N-undoped with a concentration of N < 3⋅10 cm. The oxygen concentration was about 6.5⋅10 cm (FTIR, ASTM) for both. The specimens in the shape of rectangular prisms with the orie ntation of the faces (111), (112), (110) (the faces are listed in order of their area decreasing) measuring 30 ×4×1 mm, were cut with a diamond saw, mechanically polished with a diamond powder until an optically smooth surface was obtained and then chemically polished in a 7 HNO 3 + 1 HF solution to remove a 50-70 μm surface layer damaged at mechanical treatment. Dislocation mobility studies were carried out with specimens wit h individual dislocations hexagonal half-loops. Individual dislocations were introduced by indenting t he broad specimen face (111) with a diamond pyramid followed by loading through four-point bending a round the (112) axis. The loads on the pyramid in the process of indenting and on the spec imen upon its stressing were chosen such that preferentially individual dislocation half-loops f 10 – 20 μm in diameter, were generated in the specimen. For our crystals the conditions wer e as follows: the loading temperature = 600oC, the shear stress acting in the (111) glide plane τ = 50 MPa, the loading time ∆t = 10 min. After cooling the specimen within the furnace, the sites of the dislocation emergence on the surface were revealed by selective chemical etching (Sirt l etch: 1 CrO3 + 2 H2O + 3 HF). The specimen was then chemically polished for 1 min., the indentation bein g on longer the dislocation sources thereat, loaded again and the remaining individual dislocation h lf-loops were expanded to about 100 μm in diameter. After cooling the specimen within the furnace, the ind ntations were finally removed by chemical polishing after which dislocation loops w ere expanded up to 500-600 μm in diameter. After cooling and etching, the specimens were used for further deforming under required experimental conditions. In order to measure the dependence of the velocity of individual disloc ations V on the load the specimens were arranged in the furnace, heated to temperature , and loaded by three-point bending around the [112] axis for a time ∆ t. The specimen heating time to the test temperature T was 15 min. The loading time ∆ t was chosen such that the distance covered by the dislocations in the region of maximal shear stresses did not exceed 70 μm. The distances covered by individual dislocation L for the time ∆ t were revealed by the method of repeated selective etching. The three-point bending technique, giving the linear law of τ distribution along the direction normal to the bending axis, makes it possible to obtain the V(τ) dependence with one specimen in the process of one loading and to define the starting stresses τst for the motion of dislocations. The starting or unlocking stress τst [1,3] was defined as the maximal stress below that not a single dislocation moves. The measurements of L were performed with an optical microscope. Whereupon the velocities of dislocations were calculated, V = L / ∆ t. The deformation temperature T was controlled with a PtPtRh thermocouple and was maintained constant with an accuracy of ± 0.5 K throughout the run. We report in this paper the results obtained for 60o segments of dis location half-loops of the glide system (111) [001] at the compression side. Results and discussion Fig. 1 shows the stress dependences of velocity of individual 60o-disloca tions for undoped and nitrogen-doped CZ-Si obtained at temperature of 500o . It should be marked that each point in a figure corresponds to velocity of one dislocation at definite value of s hear stresses. One can see that 466 Gettering and Defect Engineering in Semiconductor Technology X

Influence of Nitrogen on Dislocation Mobility in Czochralski Silicon

NAA, TEM, DLTS, and EBIC investigations of Cu-contaminated CzSi with an intrinsic-gettering procedure realized by a multistep heat tretament demonstrate the efficiency of intrinsic gettering concerning redistribution to volume defects for Cu-contamination up to 1016 cm−3. The Cu-precipitation at the surface can still be suppressed for such contamination due to volume defects. However, in this case the concentration of contamination induced deep level centers at the surface is independent of the volums defect density. Only for Cu-contamination of about 1015 cm−3 the gettering effect is strong enough to prsrent the introduction of contamination induced deep levels at the surface.



Die Untersuchung von Cu-kontaminiertem CzSi nach einer fur die Intrinsic-Getterung typischen Mehrstufen-Warmebehandlung mittels Naa, TEM, DLTS und EBIC demonstriert die Wirksamkeit der Intrinsic-Getterung hinsichtlich Umverteilung zu den Volumendefekten bis zu einer Cu-Kontamination von 1016 cm−3. Die Ca-Prazipitation an dsr Oberflache kann infolge der Getter-wirksamkeit von Volumendefekten fur diese Kontamination noch unterdruckt werden. Die Konzentration kontaminationsinduzierter tiefer Storstellen an der Oberflache wird aber in diesem Fall schon nicht mehr reduziert. Nur fur eine Cu-Kontamination um 1015 cm−3 konnen infolge Mehrstufen-Warmebehandlung keine kontaminationsinduzierten tiefen Storstellen an der Oberflache mehr nachgewiesen werden.

Hans Richter

Papers

A Method for Studying the Grown‐In Defect Density Spectra in Czochralski Silicon Wafers

Analytical Modeling of the Interaction of Vacancies and Oxygen for Oxide Precipitation in RTA Treated Silicon Wafers

State of stress and critical thickness of strained small-area SiGe layers

Influence of Nitrogen on Dislocation Mobility in Czochralski Silicon

On the Intrinsic Gettering in Cu‐Contaminated CzSi