Jonas Sundqvist

Ferroelectricity in yttrium-doped hafnium oxide

Structural and electrical evidence for a ferroelectric phase in yttrium doped hafnium oxide thin films is presented. A doping series ranging from 2.3 to 12.3 mol% YO1.5 in HfO2 was deposited by a thermal atomic layer deposition process. Grazing incidence X-ray diffraction of the 10 nm thick films revealed an orthorhombic phase close to the stability region of the cubic phase. The potential ferroelectricity of this orthorhombic phase was confirmed by polarization hysteresis measurements on titanium nitride based metal-insulator-metal capacitors. For 5.2 mol% YO1.5 admixture the remanent polarization peaked at 24 μC/cm2 with a coercive field of about 1.2 MV/cm. Considering the availability of conformal deposition processes and CMOS-compatibility, ferroelectric Y:HfO2 implies high scaling potential for future, ferroelectric memories.

Properties of hafnium oxide films grown by atomic layer deposition from hafnium tetraiodide and oxygen

Polycrystalline monoclinic HfO2 films were atomic layer deposited on Si(100) substrates by a nonhydrous carbon-free process of HfI4 and O2. The oxygen to hafnium ratio corresponded to the stoichiometric dioxide within the limits of accuracy of ion beam analysis. A 1.5–2.0 nm thick SiO2 interface layer formed between the HfO2 films and Si substrates. Hysteresis of the capacitance–voltage curves was observed in Al/HfO2/p-Si(100) structures with oxide grown in the substrate temperature range of 570–755 °C. The hysteresis ceased with an increase in O2 pressure. The effective permittivity of the dielectric layers varied between 12 and 16. The breakdown voltages were found to be lower in the case of higher oxygen doses and higher HfO2 deposition temperatures.

Effect of selected atomic layer deposition parameters on the structure and dielectric properties of hafnium oxide films

HfO2 films were atomic layer deposited from HfCl4 and H2O on Si(100) in the temperature range of 226–750°C. The films consisted of dominantly the monoclinic polymorph. Elastic recoil detection analysis revealed high residual chlorine and hydrogen contents (2–5at.%) in the films grown below 300–350°C. The content of residual hydrogen and chlorine monotonously decreased with increasing growth temperature. The effective permittivity insignificantly depended on the growth temperature and water partial pressure. Capacitance-voltage curves exhibited marked hysteresis especially in the films grown at 400–450°C, and demonstrated enhanced distortions likely due to the increased trap densities in the films grown at 700–750°C. Changes in water pressure led to some changes in the extent of crystallization, but did not induce any clear changes in the capacitance of the dielectric layer.

Atomic layer deposition of polycrystalline HfO2 films by the HfI4-O2 precursor combination

Atomic Layer Deposition of Polycrystalline HfO2 Films by the HfI4-O2 Precursor Combination.

Atomic Layer Deposition of Ruthenium Films from (Ethylcyclopentadienyl)(pyrrolyl)ruthenium and Oxygen

Ru films were grown by atomic layer deposition in the temperature range of 275―350°C using (ethylcyclopentadienyl)(pyrrolyl)ruthenium and air or oxygen as precursors on HF-etched Si, SiO 2 , ZrO 2 , and TiN substrates. Conformal growth was examined on three-dimensional silicon substrates with 20:1 aspect ratio. ZrO 2 promoted the nucleation of Ru most efficiently compared to other substrates, but the films roughened quickly on ZrO 2 with increasing film thickness. The minimum number of cycles required to form continuous and conductive metal layers could be decreased by increasing the length of the oxygen pulse. In order to obtain well-conducting Ru films growth to thicknesses of at least 8―10 nm on any surface was necessary. Resistivities in the ranges of 30―60 and 14―16 μΩ · cm were achieved for 4―6 and 10―15 nm thick films, respectively. Delamination became an issue in the Ru films grown to thicknesses about 10 nm and higher.

Hafnium tetraiodide and oxygen as precursors for atomic layer deposition of hafnium oxide thin films

Hafnium tetraiodide and oxygen as precursors for atomic layer deposition of hafnium oxide thin films

Atomic Layer Deposition of High-Permittivity Yttrium-Doped HfO2 Films

Yttrium-doped HfO 2 films were grown by atomic layer deposition via alternating HfO 2 and Y 2 O 3 growth cycles. Precursors used were (CpMe) 2 Hf(OMe)Me or Hf(NEtMe) 4 and (CpMe) 3 Y together with ozone. The 5-8 nm thick HfO 2 :Y films were amorphous in as-deposited state and crystallized as high-permittivity cubic/tetragonal polymorphs upon annealing. The best combination of low leakage current of 10 -7 A/cm 2 at 1 V and high capacitance was achieved with the films grown from Hf(NEtMe) 4 , with yttrium content being about 6-7 atom %. The highest permittivity values measured for these films reached 30.

Structural properties of as deposited and annealed ZrO2 influenced by atomic layer deposition, substrate, and doping

Thin ZrO2 films are of high interest as high-k material in dynamic random access memory (DRAM), embedded dynamic random access memory, and resistive random access memory as well as for gate oxides. Actually, ZrO2 is predicted to be the key material in future DRAM generations below 20 nm. Profound knowledge of pure and doped ZrO2 thin films, especially of the structural properties, is essential in order to meet the requirements of future devices. This paper gives a detailed overview about the structural properties of ZrO2 films in dependence of various process parameters. The study of atomic layer deposition (ALD) growth mechanisms of ZrO2 on a TiN-substrate in comparison to a Si-substrate covered with native oxide exhibits significant differences. Furthermore, the structural properties crystallinity, surface roughness, and film stress are studied after the ALD deposition in dependence of the process parameters deposition temperature, layer thickness, and underlying substrate. Remarkable dependencies of the ZrO2 crystallization temperatures on the substrates are figured out. The structural properties after various annealing steps are monitored as well. The influence of doping by SiO2 and Al2O3 is studied, which is primarily used to keep the thin films amorphous during deposition.

TEMAZ/O3 atomic layer deposition process with doubled growth rate and optimized interface properties in metal–insulator–metal capacitors

ZrO2 is of very high interest for various applications in semiconductor industry especially as high-k dielectric in metal–insulator–metal (MIM) capacitor devices. Further improvement of deposition processes, of material properties, and of integration schemes is essential in order to meet the strict requirements of future devices. In this paper, the authors describe a solution to solve one of the key challenges by reducing the process time of the bottle neck high-k atomic layer deposition (ALD). The authors extensively optimized the most common ALD process used for the ZrO2 deposition (TEMAZ/O3) resulting now in a doubled growth rate compared to the published growth rates of maximum 1 A/cycle. Chemical reactions explaining the origin of the high growth rate are proposed by theoretical process modelling. At the same time, the outstanding electrical properties of ZrO2 thin films could be preserved. Finally, the integration of the ZrO2 process in MIM capacitor devices with TiN electrodes was evaluated. Thereb...

Detailed leakage current analysis of metal–insulator–metal capacitors with ZrO2, ZrO2/SiO2/ZrO2, and ZrO2/Al2O3/ZrO2 as dielectric and TiN electrodes

ZrO2-based metal–insulator–metal capacitors are used in various volatile and nonvolatile memory devices as well as for buffer capacitors or radio frequency applications. Thus, process optimization and material tuning by doping is necessary to selectively optimize the electrical performance. The most common process for dielectric fabrication is atomic layer deposition which guarantees high conformity in three dimensional structures and excellent composition control. In this paper, the C–V and J–V characteristics of ZrO2 metal–insulator–metal capacitors with TiN electrodes are analyzed in dependence on the O3 pulse time revealing the optimum atomic layer deposition process conditions. Moreover, a detailed study of the leakage current mechanisms in undoped ZrO2 compared to SiO2- or Al2O3-doped ZrO2 is enclosed. Thereby, the discovered dependencies on interfaces, doping, layer thickness, and crystalline phases enable the detailed understanding and evaluation of the most suitable material stack for dynamic ra...