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Plasma-assisted atomic layer deposition (ALD) was used to deposit SiO2films in the temperature range of Tdep= 50–400°C on Si(100). H2Si[N(C2H5)2]2and an O2plasma were used as Si precursor and oxidant, respectively. The ALD growth process and material properties were characterized in detail. Ultrashort precursor doses (∼50 ms) were found to be sufficient to reach self-limiting ALD growth with a growth-per-cycle of ∼1.2 Å (Tdep= ∼200°C) leading to SiO2films with O/Si ratio of ∼2.1. Moreover, the plasma ALD process led to a high conformality (95–100%) for trenches with aspect ratios of ∼30. In addition, the electronic (interface) properties of ultrathin ALD SiO2films and ALD SiO2/Al2O3stacks were studied by capacitance-voltage and photoconductance decay measurements. The interface quality associated with SiO2was improved significantly by using an ultrathin ALD Al2O3capping layer and annealing. The interface defect densities decreased from ∼1×1012eV−1cm−2(at mid gap) for single layer SiO2to < 1011eV−1cm−2for the stacks. Correspondingly, ultralow surface recombination velocities < 3 cm/s were obtained for n-type Si. The density and polarity of the fixed charges associated with the stacks were found to be critically dependent on the SiO2thickness (1–30 nm).

Differences in Si surface passivation by aluminum oxide (Al2O3)films synthesized using H2Oand O3-based thermal atomic layer deposition (ALD) and plasma ALD have been revealed. A low interface defect density of Dit=∼1011eV−1cm−2was obtained after annealing, independent of the oxidant. This low Ditwas found to be vital for the passivation performance. Field-effect passivation was less prominent for H2O-based ALD Al2O3before and after annealing, whereas for as-deposited ALD films with an O2plasma or O3as the oxidants, the field-effect passivation was impaired by a very high Dit.

GdxHf1−xOythin films were deposited by atomic layer deposition (ALD) using tris(isopropyl-cyclopentadienyl) gadolinium [Gd(PirCp)3]and HfCl4in combination with H2Oas an oxidizer. Growth curves showed a nearly ideal ALD behavior. The growth per individual Gd(PirCp)3/H2Oor HfCl4/H2Ocycle was 0.55 Å, independent of the Gd/(Gd+Hf)composition xin the studied range. This indicates that the amount of HfO2deposited during a HfCl4/H2Ocycle was essentially identical to the amount of Gd2O3deposited during a Gd(PirCp)3/H2Ocycle, assuming identical atomic densities of the films independent of composition. The crystallization of GdxHf1−xOywith Gd/(Gd+Hf)contents xbetween 7 and 30% was studied. Films with x≳10%crystallized into a cubic/tetragonal HfO2-like phase during spike or laser annealing up to 1300°C, demonstrating that the cubic/tetragonal phase is thermally stable in this temperature range. A maximum dielectric constant of κ∼36was found for a Gd/(Gd+Hf)concentration of x∼11%.

Strontium titanate (STO) is a promising candidate as a high-kdielectric for dynamic random access memory application. STO thin films are deposited by atomic layer deposition using Sr(Bu3tCp)2, Ti(OMe)4, and H2Oas precursors. Growth and saturation behavior of STO and binary oxides are evaluated by ellipsometry thickness measurements. The precursor pulse ratio controls the amount of Sr and Ti incorporated in STO films. Stoichiometric SrTiO3is characterized by the lowest crystallization temperature and largest refractive index, density, and dielectric constant. An excess of Ti or Sr results in an increase in the crystallization onset temperature and contraction or expansion of the cubic cell constant of perovskite SrTiO3. Incorporation of more Sr in STO reduces the leakage current density but also increases the capacitance-equivalent thickness.

The requirements and development of high-k dielectric films for application in storage cells of future generation flash and Dynamic Random Access Memory (DRAM) devices are reviewed. Dielectrics with k-value in the 9-30 range are studied as insulators between charge storage layers and control gates in flash devices. For this application, large band gaps (> 6 eV) and band offsets are required, as well as low trap densities. Materials studied include aluminates and scandates. For DRAM metal-insulator-metal (MIM) capacitors, aggressive scaling of the equivalent oxide thickness (with targets down to 0.3 nm) drives the research towards dielectrics with k-values > 50. Due to the high aspect ratio of MIMCap structures, highly conformal deposition techniques are needed, triggering a substantial effort to develop Atomic Layer Deposition (ALD) processes for the deposition of metal gates and high-k dielectrics. Materials studied include Sr and Ba-based perovskites, with SrTiO3 as one of the most promising candidates, as well as tantalates, titanates and niobates.