Ichiro Tajima

Investigation of Hydrogen Plasma Etched Si Surfaces

Roughness of Si surfaces irradiated with a hydrogen electron cyclotron resonance plasma at several substrate temperatures was investigated using scanning electron microscopy and reflection high-energy electron diffraction (RHEED). When the substrate temperature is below 100°C, the surface remains smooth after irradiation for 10 min. However, at the higher temperatures, conelike projections are formed on the surface. By RHEED analysis, the facet orientation of the projections changes from (511) to (211) with growth of the roughness. These facet surfaces are composed of microsteps with {111} risers. The temperature dependence of the Si etch rate was also measured, so that the etch rate decreased with increase of the substrate temperature. IR spectroscopy and elastic recoil detection analysis were used to identify hydrogen penetration into the Si bulk. The temperature dependence of both the etch rate and the roughness formation will be discussed on the basis of the reduction of hydrogen atoms contributing to the etch reaction.

Effects of substrate temperature and bias potential on hydrogen plasma etching of silicon

Si masked by patterned SiO2 was etched using an electron cyclotron resonance hydrogen plasma. The dependence of the etch rate and the etched profile on substrate temperature and dc bias potential has been investigated, and an etch mechanism has been considered. The substrate temperature was varied between room temperature and 400 °C, and a bias potential between −100 and +100 V was applied. The etch rate of Si had the highest value at the lowest substrate temperature and decreased with increasing temperature. For the bias potential, the etch rate of Si had its peak value at 0 V. It decreased with increase of the potential which was either positive or negative. Si was also etched laterally when the substrate temperature was low. For the negative bias potential, the etched Si had a terrace on the border of a SiO2 mask. It is considered that the temperature dependence of the etch rate and the etched profile is caused by the action of hydrogen atoms, and the bias potential dependence is caused by the action o...

Selective Synthesis of Macrocyclic Oligoesters from a Bicyclic Oxalactone and Cation Transport through their Organic Liquid Membranes

Preparation of macrocyclic oligoesters has so far been achieved by two major approaches [1]. One is condensation of dibasic acid derivatives with glycols or dihalides, and the other is depolymerization of linear polyesters. However, the yield of macrocyclic oligoesters by these methods are generally unsatisfactory, and moreover, the product distribution is mostly controlled by intrinsic thermodynamic factors. In order to overcome these drawbacks, a new procedure using tin derivatives as covalent templates has been proposed recently for the synthesis of some macrocyclic tetraesters [2].

Selective preparation of a twenty-membered cyclic oligoester from 6,8-dioxabicyclo[3.2.1]octan-7-one

SummaryA twenty-membered macrocyclic oligoester consisting of alternating tetrahydropyran and ester moieties was prepared selectively by the cationic oligomerization of 6,8-dioxabicyclo[3.2.1]octan-7-one (1) in chloroform at −40°C with boron trifluoride etherate as an initiator. The solubility data of ten-, twenty-and thirty-membered cyclic oligomers of 1 in four different solvents, along with the significant time dependence of the product distribution, indicate that the formation of these cyclic oligomers is controlled primarily by solubility and kinetic factors.