Cheol Jin Cho

Control of the initial growth in atomic layer deposition of Pt films by surface pretreatment

The controllability of the nucleation behavior of Pt in atomic layer deposition (ALD) by surface pretreatments with H2O, H2S, and NH3 was investigated. The H2O pretreatment on SiO2 and TiO2 surfaces had little effect on the nucleation of Pt. The H2S pretreatment on the SiO2 and TiO2 surfaces significantly delayed the nucleation of Pt on them, while the NH3 pretreatment on the TiO2 surface led to fluent nucleation of Pt. In particular, a continuous Pt film was successfully formed even at an ultrathin thickness of approximately 2.2 nm by NH3 pretreatment. This work suggests that the pretreatment with H2S and NH3 is an efficient way to control the nucleation of Pt in ALD without the support of any reactive species, such as plasma or O3. Such a strategy enables the easy control of the size and distribution density of Pt nanoparticles for a wide range of applications.

Evaluating the Top Electrode Material for Achieving an Equivalent Oxide Thickness Smaller than 0.4 nm from an Al-Doped TiO2 Film

The effects of Pt and RuO2 top electrodes on the electrical properties of capacitors with Al-doped TiO2 (ATO) films grown on the RuO2 bottom electrode by an atomic layer deposition method were examined. The rutile phase ATO films with high bulk dielectric constant (>80) were well-grown because of the local epitaxial relationship with the rutile structured RuO2 bottom electrode. However, the interface between top electrode and ATO was damaged during the sputtering process of the top electrode, resulting in the decrease in the dielectric constant. Postmetallization annealing at 400 °C was performed to mitigate the sputtering damage. During the postmetallization annealing, the ATO layer near the RuO2 top electrode/ATO interface was well-crystallized because of the structural compatibility between RuO2 and rutile ATO, while the ATO layer near the Pt top electrode/ATO interface still exhibited an amorphous-like structure. Despite the same thickness of the ATO films, therefore, the capacitors with RuO2 top electrodes showed higher capacitance compared to the capacitors with Pt top electrodes. Eventually, an extremely low equivalent oxide thickness of 0.37 nm with low enough leakage current density (<1 × 10(-7) A/cm(2) at 0.8 V) and physical thickness of 8.7 nm for the next-generation dynamic random access memory was achieved from ATO films with RuO2 top electrodes.

Ta-Doped SnO2 as a reduction–resistant oxide electrode for DRAM capacitors

Noble metal oxides, such as RuO2, have received attention as capacitor electrodes in dynamic random access memories (DRAMs). Noble metal oxides generally have a high work function compared to noble metals and enhance the crystallinity of dielectric materials grown on them, resulting in a lower leakage current and higher dielectric constants. Despite these advantages, noble metal oxides are easily reduced during the dielectric film, such as TiO2, growth on top or by annealing under a forming gas atmosphere, degrading the capacitor performance. In this work, Ta-doped SnO2 is suggested as a potential capacitor electrode for DRAMs. Ta-Doped SnO2 films have a high work function, comparable to that of RuO2, and induce the formation of a high-temperature phase with a high dielectric constant, namely rutile TiO2, at low temperatures. More importantly, the Ta-doped SnO2 films show suitable structural and chemical stabilities, even after annealing at 400 °C under a forming gas atmosphere. RuO2 films, on the other hand, turn into a mixture of RuO2 and Ru after annealing under the same conditions. These findings suggest that Ta-doped SnO2 could serve as capacitor electrodes in next-generation DRAMs.

Correct extraction of frequency dispersion in accumulation capacitance in InGaAs metal-insulator-semiconductor devices

The anomalous frequency dispersion of the accumulation capacitance, i.e. an increase in the accumulation capacitance at high frequencies, of Pt/Al2O3/InGaAs metal-oxide-semiconductor (MOS) capacitors was investigated in this study. The anomalous frequency dispersion can be attributed to the considerable effects of parasitic inductance at high frequencies. The effects of parasitic inductance were effectively suppressed by decreasing the capacitor area without changing the MOS structure. This suggests that a smaller capacitor area should be used to precisely characterize the capacitance-voltage behavior of InGaAs-based MOS devices.