Electron-enhanced SiO₂ atomic layer deposition at 35 °C using disilane and ozone or water as reactants

Electrons can enhance SiO₂ atomic layer deposition (ALD) at low temperatures using disilane (Si₂H₆) and either ozone (O₃/O₂) or water (H₂O) as reactants. SiO₂ electron-enhanced ALD (EE-ALD) was demonstrated at 35 °C by exposing the sample to sequential electron, oxygen reactant, and Si₂H₆ exposures. The reaction sequence was electron beam exposure for 3 s, purge for 5 s, O₃/O₂ or H₂O exposure at 0.5–1.0 Torr for 3 s, purge for 10 s, Si₂H₆ exposure at 100 mTorr for 1 s, and purge for 15 s. The electron exposure was an electron current of ∼150 mA for 3 s. The electrons were produced by a hollow cathode plasma electron source typically operating with a grid bias of ≈−300 V. These electrons could irradiate a sample area of ∼2 × 2 cm². In situ spectroscopic ellipsometry measurements determined that SiO₂ EE-ALD films nucleated rapidly and deposited linearly versus number of EE-ALD cycles. The SiO₂ EE-ALD growth rate was 0.89 Å/cycle using O₃/O₂ and 0.88 Å/cycle using H₂O. The SiO₂ growth rate was also self-limiting at higher electron and Si₂H₆ exposures. In addition, SiO₂ EE-ALD films were grown by changing the reaction sequence or codosing the electrons with the oxygen reactant. The SiO₂ EE-ALD films could be grown on conducting silicon wafers or insulating SiO₂ films. SiO₂ EE-ALD is believed to be possible on insulating SiO₂ films because the secondary electron yield for SiO₂ at electron energies of ∼100–300 eV is greater than unity. Under these conditions, the SiO₂ film charges positive during electron exposure and then pulls back secondary electrons to maintain charge neutrality. The SiO₂ EE-ALD films had properties that were comparable with thermal SiO₂ oxides. The refractive indices of the SiO₂ EE-ALD films were similar at n = 1.44 ± 0.02 for various process conditions and equivalent to the refractive index of a wet thermal SiO₂ oxide film. In addition, all the SiO₂ EE-ALD films yielded etch rates in dilute buffered oxide etch solution that were only slightly higher than the etch rate of a thermal SiO₂ oxide film. SiO₂ EE-ALD should be useful to deposit high-quality SiO₂ films for various applications at low temperatures.