Density Of Grown-in Defects Research Articles

Size effects in vapor-solid-solid Ge nanowire growth with a Ni-based catalyst

We report a dramatic size effect on the morphology of Ge nanowires synthesized by low-temperature vapor-solid-solid (VSS) growth using a NiGe catalyst. Nanowires with diameter greater than 25 nm are 〈111〉-oriented, have a high density of grown-in defects, and exhibit frequent kinking. However, nanowires with diameter below 25 nm are straight, despite also having a substantial density of crystal defects. The latter wires grow preferentially in the 〈110〉 direction. The absence of kinking in the small nanowires coincides with the observation of a low-energy, epitaxial NiGe/Ge interface. Our results show that the occurrence of (1) this solid-solid epitaxial interface and (2) the low-energy sidewall facets of the 〈110〉 wire orientation strongly bias the Ni-Ge binary system toward kink-free nanowire growth in the VSS regime. We further demonstrate that kinking in larger nanowires occurs via multiple twinning events facilitated by the slow growth and anisotropic catalyst/wire interfaces typical of VSS growth. Such effects are expected in other VSS systems where a range of nanowire morphologies are observed.

Large modification of crystal–melt interface shape during Si crystal growth by using electromagnetic Czochralski method (EMCZ)

Large-diameter, high-quality Si wafers are required for further advance of ultra large-scale integrated circuit (ULSI) device processing. Therefore, a new crystal growth technique is needed to obtain large-diameter, high-quality Si crystals containing homogeneously distributed oxygen and reduction of grown-in defect density in the concentration required for ULSI device processing. To address this requirement, we developed a new crystal growth technique using electromagnetic force (EMF), which we call the electromagnetic Czochralski (EMCZ) method. Using the EMCZ method, we were able to grow defect-free Si crystals of 200 mm diameter with a higher pulling rate rather than those grown under the conventional CZ crystal growth conditions. High-speed pulling of defect-free crystals by the EMCZ method is due to large modifications of the crystal–melt interface. In this method, the interface shape is largely modified to the upward convexly toward the crystal. The large upward convex shape of the crystal–melt interface during EMCZ growth results from the temperature distribution at the interface by the controlled melt flow generated by the EMF. We confirmed this large modification of interface shape by experiments and numerical simulations. The mechanism of this modification of interface shape is discussed from the viewpoint of melt flow around the growing interface.

Effects of CZSi furnace modification on density of grown-in defects

During large diameter Czochralski silicon growth, heat zone and argon flow influence the formation of defects in silicon crystal by changing the distribution of temperature. Different silicon crystals with various density of grown-in defects were grown by replacing the popular heater with the composite heater and changing the popular argon flow into a controlled flow. The experimental results have been explained well by the numeric simulation of argon flow.

Dependence of gate oxide integrity on grown-in defect density in Czochralski grown silicon

The dependence of the gate oxide integrity on the grown-in defect density is demonstrated using Czochralski grown crystals with different as grown defect densities and by varying the gate oxide thickness in the range of 5–25 nm. The Poisson distribution −ln(1−F)=ϱ AA gate (F: ratio of failures, ϱ A: area defect density, A gate: gate area) is modified to −ln(1−F)=0.45ϱ Bt oxA gate to be able to involve the bulk defect density ϱ B and the thickness of the gate oxide t ox. The good agreement of that model with experimental data is proved comparing the density of infrared light scattering tomography defects and flow pattern defects with the gate oxide integrity yield.

Formation of Grown-in Defects during Czochralski Silicon Crystal Growth

The formation behavior of grown-in defects in Czochralski silicon (CZ-Si) crystals was investigated using two crystals that were quenched during growth but in one case after crystal growth had been halted for 5 h. The distributions of grown-in defect density and size, and their micro-structures were analyzed as a function of temperature during crystal growth just before quenching by means of an optical precipitate profiler (OPP) and an atomic force microscope (AFM) coupled with a laser particle counter. The formation of grown-in defects, which are considered to be octahedral voids, was found to consist of two dominant processes. The first step involves rapid void growth in a narrow temperature range of about 30° C below 1100° C and the subsequent step consists of an oxide film growth on the inner surface of the void during the cooling process to about 900° C after void formation. It was also found that the growth of the oxide film in the voids is rate-limited by the diffusion rate of oxygen atoms in silicon. In addition, it is strongly suggested that void formation in such a narrow temperature range is due to a rapid agglomeration of vacancies.

Influence of the thermal history of melts on the formation of grown-in defects in silicon

We have investigated the influence of time-dependent changes of melt properties on the formation of grown-in defects in silicon single crystals grown by the Czochralski method. It is found that the density of grown-in defects increases if the crystal is pulled immediately after melting. The results indicate that the change in the state of melts can influence the formation of grown-in defects in silicon single crystals.