W.F.A. Besling

Island growth in the atomic layer deposition of zirconium oxide and aluminum oxide on hydrogen-terminated silicon: Growth mode modeling and transmission electron microscopy

Atomic layer deposition (ALD) is used in applications where inorganic material layers with uniform thickness down to the nanometer range are required. For such thicknesses, the growth mode, defining how the material is arranged on the surface during the growth, is of critical importance. In this work, the growth mode of the zirconium tetrachloride∕water and the trimethyl aluminum∕water ALD process on hydrogen-terminated silicon was investigated by combining information on the total amount of material deposited with information on the surface fraction of the material. The total amount of material deposited was measured by Rutherford backscattering, x-ray fluorescence, and inductively coupled plasma–optical emission spectroscopy, and the surface fractions by low-energy ion scattering. Growth mode modeling was made assuming two-dimensional growth or random deposition (RD), with a “shower model” of RD recently developed for ALD. Experimental surface fractions of the ALD-grown zirconium oxide and aluminum oxid...

Growth and characterization of atomic layer deposited WC0.7N0.3 on polymer films

Atomic layer deposition (ALD) of tungsten carbide nitride (WC0.7N0.3) on a low-k (dielectric constant) dielectric aromatic polymer material is investigated. It is feasible to deposit thin WC0.7N0.3 films on polymers, but applying a nitrogen–oxygen (N2–O2) based plasma to the surface prior to ALD can significantly enhance the growth. The creation of polar surface groups by the plasma treatment is derived from the water contact angle and from O 1s to C 1s peak ratio extracted from x-ray photoelectron spectroscopy. Rutherford backscattering spectra and contact angle measurements revealed a typical ALD growth with at least two successive regimes. The first is controlled by the substrate surface, while during the last a constant amount of ALD material is added with each cycle. The plasma treatments create adsorption sites on the surface and therefore effectively enhance the growth and shorten the duration of the first regime. This observation is attributed to an improved initial ALD precursor adsorption. Howev...

RF Characterization and Analytical Modelling of Through Silicon Vias and Coplanar Waveguides for 3D Integration

High-aspect ratio (12.5) through silicon vias (TSV) made in a silicon interposer have been electrically characterized in the direct current (dc) and microwave regimes for 3D interconnect applications. The vias were micro-machined in silicon, insulated, and filled with copper employing a bottom-up copper electroplating technique in a “via-first” approach. DC via resistance measurements show good agreement with the theoretical expected value (~ 16 mΩ) . Radio-frequency (RF) measurements up to 50 GHz have been performed on coplanar waveguides located on the back-side of the wafers and connected to the front-side with TSVs. The S-parameters indicate clearly the beneficial impact of double sided ground planes of the RF signals. The via resistance extracted from impedance measurements is in good agreement with dc values, while the inductance (53 pH) and capacitance (2.4 pF) of the TSV are much lower than conventional wire bonding, which makes the use of TSV very promising for 3D integration. An advanced analytical model is proposed for the interconnect system with vias and lines and shows very good agreement with the experimental data with a limited number of fitting parameters. This work gives a proof of concept for high aspect ratio TSV manufacturing and new insights to improve 3D interconnect modeling for systems-in-package applications in the microwave regime.

Atomic layer deposition of WxN/TiN and WNxCy/TiN nanolaminates

Abstract Diffusion barrier materials, such as TiN, W x N, WN x C y and their nanolaminates were deposited by atomic layer deposition method. TiN film exhibited excellent properties, but W x N film exhibited high resistivity despite the low residue concentration. Both TiN and W x N films suffered from serious incompatibility with the copper metal. WN x C y film was deposited by introducing triethylboron as a reducing agent for tungsten. Excellent film properties were obtained, including very good compatibility with the copper metal, evident as strong adhesion and no pitting on the copper surface. Nanolaminate barrier stacks of W x N/TiN and WN x C y /TiN were successfully deposited. TiN deposition did not cause copper pitting when thin WN x C y film was deposited underneath.

Charge conduction mechanisms of atomic-layer-deposited Er2O3 thin films

The charge transport mechanism through atomic-layer-deposited erbium oxide thin films has been analyzed with current-voltage (I-V) measurements. At low electric field, i.e., below 3 MV/cm, the charge conduction through 10 nm thick Er2O3 films is dominated by Poole–Frenkel electron injection. However, Fowler–Nordheim tunneling of holes also occurs at higher electric fields through the oxide. Various electronic and material parameters such as the trap density, activation energy of the traps, and interface defect density are extracted from the I-V and parallel conductance (GP) measurements as a function of frequency.

Thermal stability and scalability of Zr-aluminate-based high-k gate stacks

It is demonstrated that a narrow composition range exists in the ZrAl/sub x/O/sub y/ mixed oxide system between 25 and 50 mol% Al/sub 2/O/sub 3/, where the crystallization temperature exceeds 950/spl deg/C and at the same time the k-values remain larger than 12. In this composition range, enhanced thermal stability for better integration of the ZrAl/sub x/O/sub y/ gate dielectric in a conventional poly-Si device process is observed. It is also shown that thin interfacial oxides strongly enhance the electrical stability while allowing for thickness scaling down to /spl sim/1 nm, providing gate leakage current reductions of two to three orders of magnitude.

Maxwell–Wagner instability in bilayer dielectric stacks

The Maxwell–Wagner effect, the enhanced charge migration to the interface of a stack of two dielectrics with different conductances, is shown to cause asymmetric leakage current and electrical breakdown behavior for different electrode polarities. For this purpose, metal-insulator-silicon capacitors were fabricated consisting of bilayered silicon dioxide–lanthanum zirconate dielectric stacks. Maxwell–Wagner instability and Debye polarization can be distinguished upon comparing electron injection from both sides of the stack. The Maxwell–Wagner charges have relaxation times that are nearly five orders of magnitude larger than the Debye polarization, suggesting the long-lasting influence of these trapped charges in nanolaminated dielectric systems.The Maxwell–Wagner effect, the enhanced charge migration to the interface of a stack of two dielectrics with different conductances, is shown to cause asymmetric leakage current and electrical breakdown behavior for different electrode polarities. For this purpose, metal-insulator-silicon capacitors were fabricated consisting of bilayered silicon dioxide–lanthanum zirconate dielectric stacks. Maxwell–Wagner instability and Debye polarization can be distinguished upon comparing electron injection from both sides of the stack. The Maxwell–Wagner charges have relaxation times that are nearly five orders of magnitude larger than the Debye polarization, suggesting the long-lasting influence of these trapped charges in nanolaminated dielectric systems.

Integration and performances of an alternative approach using copper silicide as a self-aligned barrier for 45 nm technology node Cu interconnects

Simulated signal propagation performances including crosstalk and delay time were investigated for self-aligned barriers on copper, highlighting the benefits of introducing these barriers for the 65 and 45 nm technology nodes. As an alternative to electrolessly deposited alloys, a self-aligned barrier technique based on controlled Si enrichment of Cu and named CuSiN was introduced. Promising performances in terms of copper barrier efficiency, interconnect compatibility, integration (line and via resistances, leakage currents, coupling capacitances), and reliability were shown.

Plasma-Assisted ALD of TiN/Al2O3 Stacks for MIMIM Trench Capacitor Applications

In this paper we report on the overall plasma-assisted ALD processes of Al2O3 and TiN conducted in a single reactor chamber and at a single temperature (340 oC). The individual Al2O3 and TiN films in the stack were consecutively deposited in such a way that they were separated by purge intervals ranging from 15 to 300 s. Time-resolved mass spectrometry, TOF-SIMS depth profiles and C-V measurements of the deposited stacks show practically no evidence of precursor cross-contamination by the individual TiN and Al2O3 deposition steps. Based on these results and previous work on planar plasma-assisted ALD TiN/Al2O3/Si MOS capacitor structures, the way was paved to deposit a TiN/Al2O3/TiN/Al2O3 stack on high aspect ratio (~ 17) structures in silicon. Step coverages of at least ~ 90 % and ~ 40 % are consistently obtained for the deposited Al2O3 and TiN layers, respectively. The trench capacitors demonstrated leakage current densities of 10-8 – 10-7 A/cm2, a capacitance density of 180 nF/mm2 and dielectric breakdown field values of 6 – 9 MV/cm.

Silicon out-diffusion and aluminum in-diffusion in devices with atomic-layer deposited La2O3 thin films

The use of aluminum as an electrode in metal-insulator-semiconductor devices containing lanthanum oxide is impaired by unacceptable leakage current levels. Time of flight secondary ion mass spectroscopy depth profiling shows a significant amount of silicon out-diffusion from the substrate and aluminum in-diffusion towards the oxide. By using titanium nitride as the electrode, the silicon out-diffusion is suppressed, which improves the device performance. This indicates that, despite the larger coordination number of the lanthanum ions in the oxide, aluminum acts as a sink for silicon, thus driving the out-diffusion of silicon.