Takashi Yunogami

Etching technique for ruthenium with a high etch rate and high selectivity using ozone gas

We have studied the characteristics of ruthenium etching reactions and the etch selectivity of Ru to photoresist in ozone gas. The Ru was etched at a maximum etch rate of 950 nm/min at between 100 and 150  °C by the formation of a volatile product, RuO4. However, the etch rate decreased at temperatures above 150 °C, since the formation of RuO2 on the Ru surface hindered the etching reaction. A comparison between the etching reaction of Ru and that of photoresist revealed that Ru was etched predominantly by ozone, whereas the photoresist was etched predominantly by atomic oxygen. This difference in etching behavior enables us to control the etch selectivity between Ru and photoresist. Below 150 °C, the Ru/photoresist selectivity was higher than 40 due to a small amount of atomic oxygen. Conversely, above 300 °C, the selectivity of photoresist/Ru was higher than 40 due to RuO2 formation. Therefore, a high degree of selectivity was achieved by manipulating the temperature.

Anisotropic etching of RuO2 and Ru with high aspect ratio for gigabit dynamic random access memory

Anisotropic RuO2 and Ru etching technology for gigabit dynamic random access memory has been developed using high density O2+10% Cl2 plasma in an inductively coupled plasma etching system. Under the conditions of low pressure, high gas flow rate, and large overetching times, we have demonstrated 0.2 μm wide patterns in 0.3-μm-thick RuO2/Ru films and 0.1 μm wide patterns in 0.45-μm-thick Ru films, both with an almost perpendicular taper angle of 89°.

Radiation damage in SiO2/Si induced by low‐energy electrons via plasmon excitation

We have found definite evidence which proves that radiation damage in SiO2/Si induced by low‐energy electrons is caused by plasmon excitation in SiO2. The SiO2/Si sample was irradiated by accelerated thermoelectrons, and the flat‐band voltage shift, ΔVFB, of the sample was measured by the C‐V method. The effective charge generation yield, Rf, in SiO2/Si was evaluated from the ΔVFB and the electron dose. The effective positive charges were measured in p‐type SiO2/Si, and the effective negative charges were measured in n‐type SiO2/Si. This is because interface states behave like positive charges in p‐type SiO2/Si and negative charges in n‐type SiO2/Si. The Rf in p‐type SiO2/Si oscillated as a function of the incident electron energy of 5–150 eV with several clear peaks. These peaks correspond to the quantum energy of a bulk plasmon or a surface plasmon. Both plasmons decay into electron‐hole pairs. The holes that escape from recombination with the electrons are trapped at the SiO2/Si interface and cause eff...

Lower plasma‐induced damage in SiO2/Si at lower temperatures

We found that the radiation damage induced in a SiO2/Si system during plasma processing depends strongly on the specimen temperature. The surfaces of the SiO2 have been exposed to a microwave plasma at different temperatures and the resultant damage has been evaluated by capacitance‐voltage (C‐V) measurements. The flatband voltage shift (ΔVFB) for the specimen exposed to the plasma at 126 K has been found to be only 1/3 of that at 300 K. In case of vacuum ultraviolet photon irradiation through a thin Al film, the ΔVFB for the irradiation at 126 K has been only 1/5 of that at 300 K. It is believed that this lower plasma‐induced damage at the lower temperature is due to the small mobility of hole in SiO2 at lower temperatures. Plasma etching at low temperature has the advantage of low damage generation in the SiO2/Si structures.