Keiji Horioka

Beam induced deposition of an ultraviolet transparent silicon oxide film by focused gallium ion beam

We have deposited a silicon oxide (SiOx) film with a high optical transmittance in the DUV region by a focused ion beam induced deposition technique using a gallium ion beam and a mixture of oxygen and TMCTS(1,3,5,7‐tetramethylcyclotetrasiloxane) as a source gas. The optical transmittance of a 0.3 μm thick film is higher than 90% at the wavelength of 250 nm. The transmittance of the deposited SiOx film depends on both the source gas and ion beam irradiation conditions. A scaling to explain the transmittance along with the ion beam conditions is proposed.

Smoothing of the Si surface using CF4/O2 down‐flow etching

Changes in surface morphology have been studied for Si surfaces treated with CF4/O2 down‐flow etching. It has been found that rough Si surfaces can be smoothed and Si trench corners can be rounded off using this CF4/O2 down‐flow etching. A SiFxOy layer is formed on the Si surface etched by a down‐flow discharged CF4/O2 gas mixture in high O2 concentration. A thick SiFxOy layer is formed at the concave part of the surface, which prevents fluorine atoms from reacting with Si. On the other hand, Si etching proceeds fast at the convex part covered with a thin SiFxOy layer. As a result, a rough Si surface is smoothed and trench corners are rounded off. By applying this treatment to a polycrystalline silicon surface, the leakage current of a SiO2 film grown on it is much reduced.

Highly selective etching of polycrystalline silicon on silicon dioxide at low wafer temperature, employing magnetron plasma

A mechanism for highly selective etching of phosphorus‐doped polycrystalline silicon (n+ poly‐Si) on SiO2 by employing a Cl2 magnetron plasma reactor at low wafer temperatures was investigated. Only the SiO2 etch rate drops rapidly in the magnetron plasma at low wafer temperatures below 0 °C. X‐ray photoelectron spectroscopy analysis revealed that only the SiO2 surface etched at lower temperatures was covered with silicon chloride or/and oxychloride compounds. The highly dense magnetron plasma decomposes the etched products into unsaturated molecules such as SiCl, SiCl2, and their oxides. These species have a large dipole moment and a higher sticking probability on SiO2 than on Si because the SiO2 bond is also ionic, and thus attracts a dipole molecule by Coulomb force. Thus, only the SiO2 surface was protected by a thin film from chlorine ion bombardment at a certain temperature range in the magnetron plasma. This protection film suppressed SiO2 etching, and a high selectivity of n+ poly‐Si/SiO2 has been...