B. Pichaud

30° Si(g) partial dislocation mobility in nitrogen-doped 4H-SiC

Well-controlled population of dislocations are introduced in 4H-SiC by bending in cantilever mode and annealing between 400 and 700°C. The introduced defects consist of double stacking faults, each bound by a pair of 30° Si(g) partial dislocations, and the expansion of which is asymmetric. The velocity of each individual 30° Si(g) pair is directly measured as a function of stress and temperature on the surface of samples etched after deformation. The activation energies of the 30° Si(g) partial dislocation pairs are strongly stress dependent, ranging between 1.25 and 1.7eV. These values are lower than the ones derived from plasticity experiments. This is probably because 30° Si(g) pairs and double stacking faults are generated in N-doped 4H-SiC (N=2×1018cm−3), with their development being promoted by quantum well action.Well-controlled population of dislocations are introduced in 4H-SiC by bending in cantilever mode and annealing between 400 and 700°C. The introduced defects consist of double stacking faults, each bound by a pair of 30° Si(g) partial dislocations, and the expansion of which is asymmetric. The velocity of each individual 30° Si(g) pair is directly measured as a function of stress and temperature on the surface of samples etched after deformation. The activation energies of the 30° Si(g) partial dislocation pairs are strongly stress dependent, ranging between 1.25 and 1.7eV. These values are lower than the ones derived from plasticity experiments. This is probably because 30° Si(g) pairs and double stacking faults are generated in N-doped 4H-SiC (N=2×1018cm−3), with their development being promoted by quantum well action.

Defects created in N-doped 4H-SiC in the brittle regime: Stacking fault multiplicity and dislocation cores

Defects introduced in N-doped 4H-SiC by surface scratching and bending at 823 K or 973 K were characterised by weak beam-dark field transmission electron microscopy (TEM), high-resolution TEM (HRTEM), large-angle convergent beam electron diffraction (LACBED), image analysis and dislocation core reconstructions. They consist of double stacking faults (DSFs) dragged by partial dislocation (PD) pairs in planes in which the Si–C dumbbells have the same orientation. The PDs forming a pair always have the same Burgers vectors. The reconstructions prove that their core composition depends on the dislocation character, the expansion direction and the orientation of the dumbbells in the glide planes. Only Si(g) are mobile, the lack of mobility of C(g) explaining why only three kinds of half-loops expand and why one DSF is always edged by two identical PDs. It is shown that the line morphology is not a sufficient criterion to determine the core composition. Although mechanical stresses were applied, additional thermodynamic and/or electronic driving forces influenced the DSF formation in our experiments.

Gettering of Diffused Au and of Cu and Ni Contamination in Silicon by Cavities Induced by High Energy He Implantation

Silicon samples were gold-diffused at different temperatures (870-950°C) and implanted with He ions at 1.6 MeV and fluences ranging from 2 × 10 16 up to 10 17 cm -2 . The implantation induced defects observed by conventional and high resolution cross section electron microscopy were found to be essentially cavities 10 to 100 nm in size which are faceted mainly along {111}, but also along {110} and {100} planes. The cavities are located at the sample depth predicted by the transport range of ions in matter simulation. Secondary ion mass spectroscopy profiles exhibit a shouldered shape with a maximum at the projected range. They demonstrate that the cavities are very efficient sinks for Au atoms; the shoulder of the profile could be related to the presence of smaller cavities and dislocations in the vicinity of the projected range. Gold concentration in the cavity area was below the detection limit of the energy dispersive spectroscopy technique, but both Cu and Ni contamination gave rise to silicides and could be chemically analysed. Cu 3 Si precipitates have grown in cavities as already reported in the literature, while NiSi 2 precipitates were observed for the first time in cavities.

Structural characterization of 6H- and 4H-SiC polytypes by means of cathodoluminescence and x-ray topography

The cathodoluminescence (CL) technique is used to analyse the radiative recombination properties of four distinct silicon carbide (SiC) samples: a 6H-SiC n+-type Lely wafer, two off-axis 4H-SiC epitaxial layers of n type and p type, and a ()-oriented 4H-SiC n+-type substrate. The CL spectra, recorded at various temperatures and at various excitation conditions, show strong differences between the polytypes, indicating a better homogeneous distribution of radiative centres inside the 6H polytype than in the 4H one, and also between the different orientations. For the ()-oriented 4H sample, luminescence features decrease when the excitation intensity increases, probably due to a more significant indirect transition band. The CL spectra also vary for the same sample, due to the impurity and the microscopic defect density variations. Comparisons between two local spectra taken in two distinct areas of the ()-oriented 4H sample, and with images obtained by x-ray topography in the same areas, allow us to establish that some structural defects are involved in luminescence centres. A deep centre involved in green luminescence (at 1.80?eV) is found to be associated with basal plane dislocations with the Burgers vector .

Influence of metal trapping on the shape of cavities induced by high energy He+ implantation

In He implantation induced cavities highly contaminated with metals (Au, Ni, Pt) we found that, when no three-dimensional structure is observed, the shape of the cavities can be strongly modified depending on the nature of the metal and on its trapped quantity. The equilibrium shape of cavities is the Wulff shape associated with the minimum surface energy which can be determined using the code WULFFMAN. On the basis of these computations the effect of a metal chemisorption may be accounted for. At very low coverage (far below 1%) there is no effect to be expected. At coverages between 1% and 10%, independent of the nature of the metal, a reduction of the specific surface energy of the vicinal surfaces may produce spherical cavities. Eventually for coverages close to one monolayer, the specific surface energy of the concerned metal will drive the cavities toward spherical or highly facetted shapes depending on whether the specific energy of the metal is smaller or higher than the vicinal one of silicon.

Dislocation motion by double-kink migration in a bent crystal. Velocity measurements in silicon

Abstract The motion of the side arms of a dislocation half-loop in a non-homogeneous strain field is considered in terms of the double-kink mechanism. It is shown that the side arm moves as a unit and remains parallel to the Peierls valleys. This leads to an association of the measured velocity in cantilever bending with the stress at the midpoint of the side arm.

Gettering of platinum by cavities induced in silicon by high energy implantation of He ions

Abstract Pt diffused diodes (p + n n + junctions) were manufactured on 75 μm n-type epitaxial Si wafers. Gettering of Pt by 3.1 MeV He-implantation induced defects was performed. The fleunce was 10 17 He/cm 2 . A post thermal annealing at 1050°C for 2 h gave rise to formation of a 0.2 μm cavity layer at the predicted projected range ( R p ) as measured by XTEM (cross sectional transmission electron microscopy). SIMS (secondary ion mass spectroscopy) crater profiles of both B and Pt revealed that the cavities are efficient sites to trap Pt atoms.

A model for dislocation glide with impurity dragging: Application to GaAs:0·2at. % In

Abstract To account for the occurrence of a dragging regime established previously in the case of GaAs: 0·2 at.% In, we propose a model based on the existence of two populations of kinks along the dislocation line: free kinks and kinks coupled with In atoms. With a simple hypothesis concerning the variation in obstacle incorporation with the distance travelled by the dislocation, the model gives a good description of experimental results and allows a high value of the additional barrier height for In dragging to be derived: β= 0·6eV. The evolution of the incorporation coefficient with temperature and stress is discussed.

Roles of Impurities and Implantation Depth on He + - Cavity Shape in Silicon

Silicon samples were implanted with He + ions at energies varying from 10keV to 1.55MeV using doses ranging from 1.45×10 16 cm -2 to 5×10 16 cm -2 to obtain similar He concentration at each projection range (R p ). In few samples, gold, platinum, nickel or silver was introduced prior to He + implantation by diffusion at temperatures ranging from 870°C to 1050°C. All samples were annealed in the 400°C–1050°C temperature range to determine the equilibrium stage of the growth of the cavity. The cavity characteristics (distribution, shape and size) were studied by cross section transmission electron microscopy (XTEM). Their morphology demonstrates the validity of the chemisorption hypothesis when they grow in silicon intentionally contaminated by metal. A consequence of the surface proximity on the cavity characteristics was verified and allows stepping forward two regimes of cavity growth: one, very fast, taking place in a He-free environment and another one, slower, occurring in a He-rich atmosphere.

Evolution Of Defects Induced By High Energy He Implantation In Gold-Diffused Silicon

Silicon samples were gold-diffused at different temperatures, implanted with He ions at 1.6 MeVand then annealed at 1050°C for 2 hours. The implantation induced-defect structure and their distributionin the depth of the sample, studied by conventional and high resolution cross section electron microscopy (HRXTEM) depend on the gold level introduced in the wafer prior to the gettering process. A high concentration of gold in silicon seems to influence the defect configuration in the cavity zone. Indeed, gold chemisorbed atcavities can homogenize the surface energy of their planes in different orientations, and can increase the cavity critical diameter beyond they become facetted. Secondary ion mass spectroscopy (SIMS) profiles exhibit ashouldered shape and a width closely related to the presence of the defects (observed by XTEM) which are veryefficient sinks both for gold and copper atoms. Unfortunately, the electrical improvement of the material (checked by minority carriers diffusion length measurements MCDL) is not achieved by this gettering process, probably due to the high metal impurity concentrations remaining out of the gettering zone, to the presence of AuCu complexes and η-Cu 3 Si precipitates identified by deep level transient spectroscopy (DLTS)measurements and HRXTEM observations respectively.