Control of ion-flux and ion-energy in direct inductively coupled plasma reactor for interfacial-mixing plasma-enhanced atomic layer deposition Available to Purchase

The effects of low-energy (<15 eV) high-flux O₂⁺ ion bombardment on the properties of Al₂O₃ films deposited on 3D nanostructures by plasma-enhanced atomic layer deposition (PE-ALD) were investigated. High-dose O₂⁺ ion bombardment (>10¹⁷ cm⁻² cycle⁻¹) during the oxidation steps caused interfacial mixing, and AlSiO_x films with abrupt interfaces were formed on Si surfaces. Interfacially mixed AlSiO_x films were selectively formed on single-crystal Si, amorphous Si, and degraded SiO₂ surfaces, whereas normal ALD Al₂O₃ films were formed on thermally grown SiO₂ surfaces. At the same time, the interfacially mixed AlSiO_x films were selectively formed on the horizontal top and bottom faces of the 3D nanostructures, whereas normal ALD Al₂O₃ films were formed on the vertical sidewalls. The morphology and thickness of the film deposited on the amorphous Si surface were the same as those on the single-crystal Si surface. The interfacially mixed AlSiO_x film possessed rough surface morphology and a layered structure of Al-/Si-/Al-rich AlSiO_x layers. The low-energy high-flux O₂⁺ ion bombardment condition required for the interfacial-mixing ALD was realized in a direct inductively coupled plasma (ICP) reactor with a self-resonant planar coil, in which high-density plasma was excited near the substrate. The O₂⁺ ion flux was found to be controllable over a wide range through variation in the O₂ pressure. The ratio of O₂⁺ ion flux at 0.01 Torr to that at 1 Torr was 289. The steep decrease of the ion flux with increasing pressure was attributed to the decrease of electron density in the upstream plasma for intensifying electron energy loss and the decrease of the ambipolar diffusion coefficient in the downstream plasma. A comparison of electron densities near the substrate and those at the presheath edge calculated from measured positive ion fluxes using the Bohm criterion revealed that negative ions, which significantly affect the positive ion flux, scarcely exist near the substrate. The interfacial-mixing PE-ALD has the potential to realize area-selective and topographically selective depositions, which are key technologies for fabricating next-generation electronic devices with 3D nanostructures. The direct ICP reactor is suitable for realizing selective deposition using the interfacial-mixing ALD.