Koji Sueoka

Morphology and growth process of thermally induced oxide precipitates in Czochralski silicon

The morphology and growth process of oxide precipitates in Czochralski silicon have been studied with prolonged thermal treatments up to 700 h at intermediate temperatures (700–900 °C). It was found with transmission electron microscopy observation that (i) the morphology of precipitates changes from platelet to aggregation of polyhedra at both 800 and 900 °C during isothermal heat treatment, and (ii) the growth of platelet precipitates follows a t1/2 law.

Morphology and size distribution of oxide precipitates in as‐grown Czochralski silicon crystals

The morphology and size distribution of oxide precipitates in as‐grown Czochralski (CZ) silicon crystals, with growth rates of about 1.1 mm/min, have been studied using infrared light scattering tomography (LST). The following results were obtained. (1) The morphology of oxide precipitates in as‐grown CZ silicon is polyhedral. (2) The length of the side of the polyhedral precipitates is about 80 nm. According to their morphology and size distribution, it was concluded that they were formed in the high temperature range (≥1000 °C) during crystal growth.

OXYGEN DIFFUSION IN HEAVILY ANTIMONY-, ARSENIC-, AND BORON-DOPED CZOCHRALSKI SILICON WAFERS

The effect of dopant-type, antimony (Sb), arsenic (As), and boron (B), on the outdiffusion of oxygen in heavily doped Czochralski (Cz) silicon wafers has been investigated using secondary ion mass spectroscopy. The results indicate that, although oxygen diffusion in Cz silicon is retarded in heavily B- and As-doped wafers during low temperature annealing (800 °C), it is not influenced by heavy Sb doping. This indicates that charge effects and atom size effects have negligible influence on the diffusion of oxygen. The B and As diffusion retardation effect is attributed to the existence of dopant-oxygen complexes. The oxygen solubility was largest in the most heavily B-doped samples annealed at low temperature.

Defect Formation Behaviors in Heavily Doped Czochralski Silicon

To reveal a difference of defect formation behaviors, i.e. grown-in void formation during crystal growth and oxide precipitation in nand p-type silicon, we have investigated by using heavily boron-and arsenic-doped silicon crystals. The density of void defects in heavily boron doped silicon was decreased with a shrinking OSF-ring, but in arsenic doped silicon were increased with resistivities below 3.3mΩcm. On the other hand, for oxygen precipitation, the nucleation rate in boron doped silicon was enhanced with increasing resistivities, while decreased by one tenth in reference to lightly doped silicon for resistivities up to 4.4mΩcm in arsenic doped silicon. These contrastive phenomena between n- and p-type cannot be explained with a growth model of precipitates by an accelerated diffusion of oxygen in silicon. We believed that the nucleation rate of oxide precipitates related to a dependence of point defects on fermi level closely.

A Model for the Formation of Oxidation-Induced Stacking Faults in Czochralski Silicon

The mechanism of oxidation-induced stacking fault (OSF) formation in Czochralski silicon (CZ-Si) crystals was investigated by transmission electron microscopy observations of the initial stages of OSF growth. OSFs were observed to be always generated at one of the edges of platelet oxygen precipitates. We observed previously that these platelet oxygen precititates had an expansive strain field in the direction parallel to the precipitate plate and a compressive strain field normal to the plate. Silicon self-interstitials having compressive strain are probably attracted to the expansive strain field of the precipitates, and condense to form stacking faults. A new model for OSF generation is presented taking into consideration the strain field around self-interstitials and oxygen precipitates.

Effect of rapid thermal annealing on oxide precipitation behavior in silicon crystal

Abstract Oxide precipitation behavior after rapid thermal annealing (RTA) in Ar, N2 or O2 ambient was investigated. Lightly boron-, nitrogen- or carbon-doped p-CZ silicon wafers with a diameter of 200 mm ( [ O i ]=11.5–13.9×10 17 atoms / cm 3 (old ASTM)) were prepared as samples. RTA temperature and cooling rate were changed between 1280 and 1200 °C, and between 70 and 5 °C/s, respectively. From the result of in Ar ambient, it was found that (1) M-like depth profile of precipitate density was observed in the lightly boron-doped wafer, (2) width of precipitate denuded zone (DZ) was decreased in the nitrogen-doped wafer compared with the lightly boron-doped wafer and (3) DZ width in the carbon-doped wafer was comparable to lightly boron-doped wafer. From the calculated result of the depth profile of vacancy (V) and silicon interstitial (I) concentrations, CV and CI, it was clarified that the relationships of thermal equilibrium concentration and the diffusion constant of point defects are to be C V ∗ >C I ∗ and DV

Analysis of Local Lattice Strain Around Oxygen Precipitates in Czochralski-Grown Silicon Wafers Using Convergent Beam Electron Diffraction

The local lattice strain field around oxygen precipitates in Czochralski-grown silicon (CZ-Si) wafers has been measured quantitatively using convergent beam electron diffraction (CBED). As a result of the strain analysis from higher-order Laue zone patterns in the CBED disk, strain of the silicon lattices was found in the vicinity of oxygen precipitates, i.e., platelet type and polyhedral type. The strain along the normal direction to the precipitate is compressive, and the strain along the parallel direction to the precipitate is tensile. The lattice strain field around the precipitate decreases monotonically as a function of distance from the precipitate/matrix interface. Further, the morphological change in the growth process of the precipitate is important for the formation of the local lattice strain.

Effect of heavy boron doping on the lattice strain around platelet oxide precipitates in Czochralski silicon wafers

The effect of heavy boron doping on local lattice strain around platelet oxide precipitates in Czochralski silicon wafers was investigated quantitatively by convergent beam electron diffraction (CBED). Lightly boron doped (p−) polished wafers, including platelet precipitates with density of about 5×109/cm3 and with an edge length of about 500 nm, were prepared with an isothermal annealing at 800 °C for 700 h. Heavy boron doped (p/p+) epitaxial wafers, including an almost equal precipitate density and length to p− wafers, were also prepared with an isothermal annealing at 800 °C for 200 h. It was found by strain analysis from high-order Laue zone patterns in the CBED disk that (i) the type of lattice strain was coincident in p− and p/p+ wafers: the strain along the normal direction of the platelet precipitate was compressive, while the strain along the parallel direction of the platelet was tensile; (ii) the strain in p/p+ wafers was smaller than that in p− wafers; and (iii) the punched-out dislocations we...