Perfect Silicon Single Crystals Research Articles

X-ray measurement of minute lattice strain in perfect silicon crystals

Abstract The residual strain still present in nearly perfect silicon single crystals has been measured quantitatively by using double crystal topography at high reflexion orders. High quality float zone crystals from different suppliers were found to vary in residual strain from 2 × 10−8 to 100 × 10−8. No direct correlation with resistivity or choice of dopant was found for slightly doped crystals. The possible correlation of the local strain variation with the presence of swirls is discussed. The high sensitivity strain measurements are very useful to measure in a quantitative manner the degree of lattice perfection of so-called nearly perfect crystals. The results are already useful for neutron interferometry and, possibly, may become so for microintegration of devices.

Observation of small defects in silicon crystal by diffuse x-ray scattering

Two kinds of diffuse x-ray scattering due to defects were observed from a very perfect silicon single crystal. One forms the shape of a cigar, elongated along the [111] direction, and the other is a disk, which is broad and perpendicular to the [111] direction. The cigar-shaped diffuse scattering is asymmetric around the 111 relp with respect to the Bragg peak. Fourier transforms reveal two types of defects; platelike defects [200 Å (φ) ×30 Å (t)] of vacancy type and needlelike defects (400 A (l)). The platelike defect dimensions are in fairly good agreement with those of B-swirl defects observed by de Kock et al. The platelike defects also have a close correlation with the crystal pulling direction. They are contained predominantly in the (111) planes for a crystal grown along the [111] direction.

High-resolution diffuse X-ray scattering study from nearly perfect silicon single crystals

High-resolution measurements of diffuse X-ray scattering (DXS) have been made at and above room temperature around 111, 333, 444 and 555 reciprocal lattice points (relps) using highly collimated Mo Kα 1 and Cu Kα 1 radiations with the specimen set in (1, -1, 1) symmetrical Bragg geometry. The distribution of DXS intensity around different relps has shown that at temperatures up to at least 573 K the contribution of thermal DXS to the observed DXS is very small. This is apparently due to the high value of the Debye temperature (640 K) of silicon. A remarkable feature of these results is that for the same value of the scattering vector |K ∗ | the DXS intensity is different for the parallel and antiparallel orientations of K ∗ relative to R ∗ . The amount of anisotropy varied from sample to sample and depended on the thermal history of the specimen. This and the other features show that the observed DXS is predominantly due to point defects and their aggregates. A typical size parameter for the aggregates is 3000 to 10 000 A .

Diffuse x-ray scattering from small defects in a very perfect silicon single crystal

Two kinds of diffuse x-ray scattering were found in a very perfect silicon single crystal. One of them forms a cigar shape, extending along the [111] direction. The other is a disk shape whose normal is also parallel to the [111] direction in reciprocal space. Both diffuse scatterings are predominant along the crystal pulling [111] direction. From simple Fourier inversion of the shapes of the diffuse scatterings, it is concluded that the platelike defects and needlelike defects are the origins of the diffuse scatterings. The platelike defects observed differ from those observed by Patel for Czochralski silicon with heat treatment.

Precipitation of copper in silicon

The structure and morphology of precipitates of copper, decorating dislocations in high-purity nearly perfect silicon single crystals were determined by high-voltage (1 MV) transmission electron microscopy and are discussed in light of the covalent bond formation by copper in silicon. The precipitates are observed to form during cooling, in clusters or colonies, on and around dislocations. They are spherical, 50–500 Å in size, and exhibit parallel moiré fringes. Those which are heterogeneously nucleated on dislocations are always found to be in the larger size range. Dislocations are thought to be present prior to precipitation and they climb down, emitting vacancies for precipitating substitutional copper atoms, and thus become heavily jogged. No ``rel-rod'' streaks are found in diffraction patterns. Only a few extra spots are found and then only when the precipitate density is very high (5×1014/cm3). The crystal structure of the precipitates was determined by combined analyses of moiré spacings and the few extra spots. It is found to be diamond cubic (B3 type, a0=5.72 Å), isomorphous with the structure (A4). The B3 structure is derived from the diamond cubic (A4) silicon lattice by replacing corner (000) and face-center (1/2 1/2 0, 1/2 0 1/2, 0 1/2 1/2) sites by copper atoms. The precipitate has a chemical composition of Cu–Si and is not stable at room temperature but is thought to be stabilized by strain energy of the precipitate/matrix system. The new interpretation of covalency of copper in the diamond cubic silicon is given on the basis of stereochemical considerations. The proposed tetrahedral coordination of copper atoms implies d10sp3 orbitals which are rationalized in terms of state of ionization (triple acceptor) of copper in silicon. The choice of conductivity type, reduction in conductivity after precipitation, and quick recovery time in depletion-capacitance measurements are qualitatively explained in terms of the proposed covalency of copper.

Comparison of experimental andn-beam calculated intensities for glancing incidence high-energy electron diffraction

Rocking curves for the 2nd to 7th order reflections of the systematic set from the (111) planes of a highly perfect silicon single crystal have been obtained in an ultra-high-vacuum reflection electron diffraction camera operated at 40 keV. These have been compared with the profiles computed with an n-beam dynamic high-energy electron diffraction theory adapted to the Bragg case at glancing incidence. It is shown that, for the 333 reflection, six nodes of the hhh row from {\bar 111} up to 444 are adequate to take into account the systematic multiple beam interference effects. The calculated widths are found to agree with the observed widths within the experimental error for all reflections. The peak reflectivities computed initially for a perfect semi-infinite crystal are systematically higher than the experimental values, by a factor of 7 for the 222 node, decreasing to near agreement for the 777 node. Possible reasons for such discrepancies are discussed. Neither inelastic scattering effects nor reasonable changes in the silicon lattice potential near the surface can bring the observed and calculated intensities into agreement. The discrepancy can be considerably reduced for all orders of reflection, however, when the non-flat nature of the surface is considered.

329. Angular dependence of external x-ray photoeffect in perfect germanium and silicon single crystals: V N Schemelov et al, Fiz Tverd Tela, 12 (8), Aug 1970, 2495–2497 ( in Russian)

329. Angular dependence of external x-ray photoeffect in perfect germanium and silicon single crystals: V N Schemelov et al, Fiz Tverd Tela, 12 (8), Aug 1970, 2495–2497 ( in Russian)

Precision Density Measurement of Silicon.

The densities of 22 large highly perfect silicon single crystals have been measured by hydrostatic weighing in water, yielding an average value of An experimental precision has been achieved which exceeds the accuracy with which the absolute density of water is known. The effect of variations of the water surface tension force on the suspension wire has been mimized by using a 0.001 in. suspension wire coated with platinum black, and by doing a large number of repeated weighings of each crystal.

Single crystal diffraction patterns of germanium. Part II

The rocking curves of Ge (111), (220), (333) for CuKα1 radiation were measured by means of the triple-crystal diffractometer. Perfect silicon single crystals, cut parallel to the (111) plane were used in the monochromator part of the triple-crystal diffractometer. The results prove the suitability of such a monochromator for studying diffraction patterns.