Ryuji Takeda

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 1200u2009°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.

Outdiffusion of impurity atoms from silicon crystals and its dependence upon the annealing atmosphere

The outdiffusion of boron, antimony, and phosphorus from the bare silicon wafer at 1200u2009°C, especially its dependence upon the annealing atmosphere, has been studied with spreading resistance and secondary ion mass spectroscopy (SIMS). It is found that the boron outdiffusion proceeds when the crystal is annealed in hydrogen, but is completely suppressed in argon even if the doping concentration is as high as 3×1018 cm−3 and the annealing time is as long as 2 h. The dramatic dependence upon the atmosphere has not been observed for the other impurities and is temporarily related with the desorption process of boron atoms from the surface.

Determination of silicon evaporation rate at 1200 °C in hydrogen

Separation by implanted oxygen silicon wafers have been investigated with cross‐sectional transmission electron microscopy after annealing at 1200u2009°C in argon as well as in hydrogen. It is observed that the buried oxide has experienced little change in the thickness, which is ascribed to the low hydrogen solubility in the crystal (about 3×1015 cm−3) and provides a natural mark to measure the thickness variation of the top silicon directly. The evaporation rate as determined in this method is less than 0.1 nm/min with an accuracy of ±0.1 nm/min, at least two orders of magnitude lower than reported in previous investigations.

Double‐crystal x‐ray diffraction from silicon film on insulator

This letter describes a simple and straightforward approach to the thickness measurement of silicon film on insulator, whose double‐crystal x‐ray diffraction curve is found of a sinusoidal slit function, as predicted by the dynamical scattering theory.

Effect of Hydrogen for Preservation of Reconstructed Surfaces

It is well known that a smooth surface of Si wafers can be obtained by Si surface reconstruction via high-temperature annealing. However, there remains a possibility of smooth Si surfaces deteriorating by accidental oxidation (called reflow oxidation) during the unloading process, i.e., taking out Si wafers from a vertical furnace after high-temperature annealing. Therefore, we considered it important to investigate the atomic-scale effects of oxidation on surface steps and terraces on Si wafers during the unloading process. We examined the effect of unloading temperature on oxide formation on Si (100) and Si (110) surfaces. The change in surface roughness was also measured. Our results indicated a significant improvement in the root mean square values of the surface roughness of terraces on the reconstructed surface. Moreover, this improvement was dependent on the decrease in the oxidation layer thickness in the case of low-temperature unloading. Furthermore, for suppressing reflow oxidation, we replaced the injected Ar gas with H2 in the cooling process during high-temperature Ar annealing and evaluated the thickness of the reflow oxidation layer and surface structure of Si (100) and Si (110). H2 annealing during the cooling process resulted in the formation of H-terminated Si surfaces, and this formation effectively suppressed reflow oxidation. However, the H2 atmosphere also caused etching of the reconstructed Si surfaces. Atomic force microscopy measurements revealed that in spite of the etching, Si (100) and Si (110) surface roughness drastically decreased because of subsequent roughness variation, regarded as being caused by oxidation. In the case of Si (110), characteristic line oxidation was effectively suppressed, resulting in a smooth terrace-and-step structure. In summary, the obtained results suggested that our method is effective for restraining the increase in atomic-scale surface roughness due to oxidation.

A novel configuration of atomic steps observed on vicinal silicon (100) surface annealed in a hydrogen atmosphere

Abstract The vicinal silicon (100) surface with a misorientation of 0.05° towards [011] and [001] has been investigated with atomic force microscopy after annealing at 1200°C in argon and hydrogen. For the samples tilted towards [011], while the surfaces annealed in argon are featured with the alternate smooth and rough steps of monolayer height (S steps), which unambiguously correlate themselves with the so-called (Sa + Sb) structure, the hydrogen annealing, in contrast, generates a configuration of orthogonal S steps. Through an analysis of the surface tilted towards [001], we show that a miscut toward an arbitrary direction can be accommodated by two identical S steps developed independently along two perpendicular {011} axes if the crystal is annealed in hydrogen. On the contrary, a surface annealed in argon shows no conformability with the misorientation towards an axis other than {011}. It is believed that the formation of the orthogonal S steps is a chemically driven process resulting from the rela...