Koji Izunome

Oxygen transport analysis in Czochralski silicon melt by considering the oxygen evaporation from the melt surface

Abstract Oxygen transport analysis of silicon melt in a silica crucible by considering the oxygen evaporation from the free surface was performed. The oxygen concentration stays in the region of 1015–1016 atoms/cm3 along the free surface and it strongly depends on the vertical flow under the free surface. It has been found that the oxygen distribution along the free surface affects the oxygen concentration in wafers obtained from grown crystals. The suction and the sweeping out flows at the peripheral region of the crystal are formed beneath the periphery of the crystal, and these oscillatory flows determine the oxygen concentration at the periphery of the crystal. Present results yielded good agreement with the experimental results of the radial oxygen distribution in grown crystals. Thus we established the method for prediction of the oxygen concentration in silicon crystal using the oxygen concentration conditions based on the experimental results for the free surface.

Oxygen transport from a silica crucible in Czochralski silicon growth

In this work, Czochralski silicon crystals were grown from a limited oxygen source crucible to determine the dominant flow of oxygen transport in silicon melt. The oxygen concentration in silicon crystal was found mainly to be controlled by the upward flow below the growth interface, with the crucible bottom as the dominant oxygen source. In this phenomenon, the region under the growth interface is assumed to remain rich in oxygen. Numerical simulation in the same system as that used in the experiment showed the same tendency. It also indicates that the concentration of this region strongly depends on the free surface region, whose concentration is to a large extent determined by dissolution from the crucible corner, which is heated to the highest temperature during crystal growth.

Surface modification of silicon (111) by annealing at high temperature in hydrogen

A vicinal silicon (111) surface exhibits well defined single steps after being annealed at 1200 °C in hydrogen, which is in sharp contrast with step bunches featuring the surface annealed in argon. As a temporary explanation for its ability to unzip the step bunches, we suggest that hydrogen destroys the faulted triangles of a [112] step, eliminates this kind of step, and eventually leaves the single [112] steps alone behind on the surface.

Oxygen precipitation in Czochralski‐grown silicon wafers during hydrogen annealing

In studying the effect of the ramping process on oxygen precipitation in Czochralski‐grown silicon wafers in hydrogen annealing, we have found that the oxygen precipitate density in the bulk region depends on the ramping‐up rate at temperatures between 900 and 1200 °C. Few oxygen defects are observed when the ramping‐up rate is 30 °C/min or more. Decreasing the ramping‐up rate exponentially increases the oxygen precipitate density. The nucleation for oxygen precipitates can therefore be controlled by adjusting the ramping‐up rate during hydrogen annealing.

Effect of Sn atoms on incorporation of vacancies in epitaxial Ge1−xSnx film grown at low temperature

The anomalous increase and decrease in the S-parameters of Doppler broadening spectroscopy in positron annihilation spectroscopy in a narrow range of Sn atom content were detected in a Ge1−xSnx thin film grown by MBE at low temperatures. The increase can be explained in terms of vacancies when the target content of 1.7% Sn atoms is incorporated in a Ge matrix, owing to the binding nature between them. However, the S-parameters were markedly decreased when the target content of Sn atoms in the film grown at the same temperature was 0.1%. These changes in the S-parameters correspond to the carrier concentrations obtained by Hall measurements.

Ultrathin-body Ge-on-insulator wafers fabricated with strongly bonded thin Al2O3/SiO2 hybrid buried oxide layers

An ultrathin-body Ge-on-insulator (GeOI) wafer having a bonded thin Al2O3/SiO2 hybrid buried oxide layer was fabricated using an epitaxially grown Ge film on Si as a Ge donor layer. The epitaxial Ge film was confirmed to have a negligibly low density of crystal-defect-induced p-type carriers and was successfully transferred to form the GeOI wafer. Strong Al2O3/SiO2 bonding effectively suppressed Ge exfoliation during the wafering process. The obtained device-grade GeOI layer and strong bonding strength between Al2O3 and SiO2 are potentially advantageous for future Si-based complementary metal–insulator–semiconductor (CMIS) fabrication processes utilizing large-diameter Si wafers.

Electrical Characterization of Wafer-Bonded Germanium-on-Insulator Substrates Using a Four-Point-Probe Pseudo-Metal--Oxide--Semiconductor Field-Effect Transistor

The electrical characteristics of wafer-bonded non-doped germanium-on-insulator (GOI) substrates were investigated using a four-point-probe pseudo-metal–oxide–semiconductor field-effect transistor. Annealing the wafer-bonded GOI substrates in vacuum strongly influenced their electrical characteristics. GOI samples annealed at temperatures below 500 °C exhibited n-channel depletion transistor operation, whereas GOI samples annealed at temperatures between 550 and 600 °C exhibited p-channel depletion transistor operation. The carrier mobility strongly depended on the sweep direction of the gate voltage; this characteristic disappeared after annealing at temperatures above 550 °C. The dependence of the electrical characteristics on the annealing temperature is explained in terms of the influence of the defect states on energy band bending near the interface.

Strain relaxation of patterned Ge and SiGe layers on Si(0 0 1) substrates

It was found that patterning of Ge and SiGe layers on Si(001) substrates principally leads to the strain anisotropy. The striped mesa structure readily induces elastic relaxation of the strained Ge and SiGe. Furthermore, a clear difference of strain relaxation mechanism depending on the dislocation introduction was confirmed. Introduction of 60deg dislocations is sensitive to the shape of patterned region, resulting in the anisotropic strain. On the other hand, the pure-edge dislocation network explicitly leads to isotropic strain relaxation even in the miniaturized region

Estimation of Surface Tension of Molten Silicon Using a Dynamic Hanging Drop

A new method to determine the surface tension of high-temperature liquids was developed using the rotation of a hanging drop. The measurement of surface tension of silicon melt was performed by observing the oscillation of a silicon droplet hanging from a SiC-coated carbon rod. The oscillation of the liquid drop was induced by a sudden high rotation speed above 570 rpm. The surface tension of molten silicon was estimated as 0.819 N/m at the melting point of 1415° C and its temperature coefficient was -0.308×10-3 N/mK. We concluded that the dynamic hanging drop method could be used to measure the surface tension of high-temperature liquids.

Light Point Defects on Hydrogen Annealed Silicon Wafer

In observing 0.1 µ m in size light point defects (LPDs) in Czochralski-grown silicon wafers in hydrogen annealing by scatterometer (Surfscan\circR SP1 and Surfscan 6200 from Tencor Instrument), we have found that the hydrogen annealed wafer has fewer defects on the surface, compared with a polished wafer. Assuming that LPDs are equal to Crystal Originated Particles (COPs) which are oxygen precipitates and/or vacancy-type defects, LPDs can therefore be reduced by evaporating oxygen from the surface, and migrating silicon-atoms onto the surface during hydrogen annealing at 1200° C for 1 h.