A novel thermally-stable zirconium amidinate ALD precursor for ZrO2 thin films

ZrO₂ thin films were deposited by the atomic layer deposition process on Si substrates using tetrakis(N,N′-dimethylacetamidinate) zirconium (Zr-AMD) as a Zr precursor and H₂O as an oxidizing agent. Tetrakis (ethylmethylamino) zirconium (TEMA-Zr) was also evaluated for a comparative study. Physical properties of ALD-derived ZrO₂ thin films were studied using ellipsometry, grazing incidence XRD (GI-XRD), high resolution TEM (HRTEM), and atomic force microscopy (AFM). The ZrO₂ deposited using Zr-AMD showed a better thermal stability at high substrate temperature (>300 °C) compared to that using TEMA-Zr. GI-XRD analysis reveals that after 700 °C anneal both ZrO₂ films enter tetragonal phase. The electrical properties of N₂-annealed ZrO₂ film using Zr-AMD exhibit an EOT of 1.2 nm with leakage current density as low as 2 × 10⁻³ A/cm² (@V_fb−1 V). The new Zr amidinate is a promising ALD precursor for high-k dielectric applications.     

Optical properties of Zr and ZrO2 films deposited by laser ablation

Optical properties of Zr and ZrO₂ films in the energy range from 1.5 to 100 eV were obtained by quantitative analysis of reflection electron energy loss spectroscopy (REELS) and ellipsometry. The films were prepared on (1 1 1) silicon substrates by reactive laser ablation using a zirconium target. For the growth of ZrO₂ films a pressure of 5 mTorr of oxygen in the growth chamber was used. The substrate temperature during deposition was . The deposits were studied ex situ by X-ray diffraction (XRD) and in situ by X-ray photoelectron spectroscopy (XPS) and REELS. The ZrO₂ films were found to be polycrystalline with monoclinic structure. The XPS results showed that the oxygen pressure used is the optimal control to produce ZrO₂ films by laser ablation. A gap of 5 eV for the ZrO₂ film was measured by REELS.     

Highly (1 0 0)-oriented Pb(Zr0.20Ti0.80)O3/(Pb1−xLax)Ti1−x/4O3 multilayered thin films prepared by RF magnetron sputtering

The Pb(Zr_0.20Ti_0.80)O₃/(Pb_1−xLa_x)Ti_1−x/4O₃ (x = 0, 0.10, 0.15, 0.20) (PZT/PLT_x) multilayered thin films were in situ deposited on the Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) substrates by RF magnetron sputtering technique with a PbO_x buffer layer. With this method, all PZT/PLT_x multilayered thin films possess highly (1 0 0) orientation. The PbO_x buffer layer leads to the (1 0 0) orientation of the multilayered thin films. The effect of the La content in PLT_x layers on the dielectric and ferroelectric properties of the PZT multilayered thin films was systematically investigated. The enhanced dielectric and ferroelectric properties are observed in the PZT/PLT_x (x = 0.15) multilayered thin films. The dielectric constant reaches maximum value of 365 at 1 KHz for x = 0.15 with a low loss tangent of 0.0301. Along with enhanced dielectric properties, the multilayered thin films also exhibit large remnant polarization value of 2P_r = 76.5 μC/cm², and low coercive field of 2E_c = 238 KV/cm.     

Microstructure and electrical characteristics of Ba0.65Sr0.35TiO3 thin films etched in CF4/Ar/O2 plasma

Radio frequency magnetron sputtered Ba_0.65Sr_0.35TiO₃ (BST) thin films were etched in CF₄/Ar/O₂ plasma by magnetically enhanced reactive ion etching technique. The etching characteristics of BST films were characterized in terms of microstructure and electrical properties. Atomic force microscopy and X-ray diffraction results indicate that the microstructure of the etched BST film is degraded because of the rugged surface and lowered intensities of BST (1 0 0), (1 1 0), (1 1 1) and (2 0 0) peaks compared to the unetched counterparts. Dielectric constant and dielectric dissipation of the unetched, etched and postannealed-after-etched BST film capacitors are 419, 346, 371, 0.018, 0.039 and 0.031 at 100 kHz, respectively. The corresponding dielectric tunability, figure of merit and remnant polarization are 19.57%, 11.56%, 17.25%, 10.87, 2.96, 5.56, 3.62 μC/cm², 2.32 and 2.81 μC/cm² at 25 V, respectively. The leakage current density of 1.75 × 10⁻⁴ A/cm² at 15 V for the etched BST capacitor is over two orders of magnitude higher than 1.28 × 10⁻⁶ A/cm² for the unetched capacitor, while leakage current density of the postannealed-after-etched capacitor decreases slightly. It means that the electrical properties of the etched BST film are deteriorated due to the CF₄/Ar/O₂ plasma-induced damage. Furthermore, the damage is alleviated, and the degraded microstructure and electrical properties are partially recovered after the etched BST film is postannealed at 923 K for 20 min under a flowing O₂ ambience.     

Microstructure and dielectric response of SrTiO3/NdGaO3 interdigitated capacitors

Epitaxial strontium titanate (SrTiO₃ or STO) thin films were prepared by an off-axis pulsed laser deposition technique on neodymium gallate (NdGaO₃ or NGO) substrates held at temperature of 820 °C. This technique allows different film growth rates in a deposition. Coplanar capacitors were fabricated and dielectric responses were measured at 1 MHz and at 2 GHz, and from 300 K to 4 K. The electric field tunability of the dielectric constant and loss tangent were taken with a range of electric field. The structure and morphology of the films were analyzed using high-resolution X-ray diffractometry and atomic force microscopy, respectively. The results showed that the films are crystalline with (1 0 0) orientation and the grains are columnar. Increased in-plane grain size and reduced surface to volume ratio were found to play a major role in improved performance of the film coplanar capacitors. The film with the growth rate of approximate 40 Å/min showed the highest change in the dielectric constant with an electric field of 4 V/μm. The film also showed the largest in-plane grain size of about 3000 Å.     

MOS devices with tetragonal ZrO2 as gate dielectric formed by annealing ZrO2/Ge/ZrO2 laminate

A Ge-stabilized tetragonal ZrO₂ (t-ZrO₂) film with permittivity (κ) of 36.2 was formed by depositing a ZrO₂/Ge/ZrO₂ laminate and a subsequent annealing at 600 °C, which is a more reliable approach to control the incorporated amount of Ge in ZrO₂. On Si substrates, with thin SiON as an interfacial layer, the SiON/t-ZrO₂ gate stack with equivalent oxide thickness (EOT) of 1.75 nm shows tiny amount of hysteresis and negligible frequency dispersion in capacitance-voltage (C-V) characteristics. By passivating leaky channels derived from grain boundaries with NH₃ plasma, good leakage current of 4.8 × 10⁻⁸ A/cm² at V_g = V_fb − 1 V is achieved and desirable reliability confirmed by positive bias temperature instability (PBTI) test is also obtained.     

Plasma-enhanced flexible metal-insulator-metal capacitor using high-k ZrO2 film as gate dielectric with improved reliability

We demonstrate a new flexible metal-insulator-metal capacitor using 9.5-nm-thick ZrO₂ film on a plastic polyimide substrate based on a simple and low-cost sol-gel precursor spin-coating process. The surface morphology of the ZrO₂ film was investigated using scan electron microscope and atomic force microscope. The as-deposited ZrO₂ film under suitable treatment of oxygen (O₂) plasma and then subsequent annealing at 250 °C exhibits superior low leakage current density of 9.0 × 10⁻⁹ A/cm² at applied voltage of 5 V and maximum capacitance density of 13.3 fF/μm² at 1 MHz. The as-deposited sol-gel film was completely oxidized when we employed O₂ plasma at relatively low temperature and power (30 W), hence enhancing the electrical performance of the capacitor. The shift (Zr 3d from 184.1 eV to 184.64 eV) in X-ray photoelectron spectroscopy of the binding energy of the electrons towards higher binding energy; clearly indicates that the O₂ plasma reaction was most effective process for the complete oxidation of the sol-gel precursor at relatively low processing temperature.     

Etching characteristics and plasma-induced damage of Ba0.65Sr0.35TiO3 thin films etched in CF4/Ar/O2 plasma

Sol-gel-derived Ba_0.65Sr_0.35TiO₃ (BST) thin films were etched in CF₄/Ar/O₂ plasma using magnetically enhanced reactive ion etching technology. The maximum etch rate of BST film is 8.47 nm/min when CF₄/Ar/O₂ gas mixing ratio is equal to 9/36/5. X-ray photoelectron spectroscopy analysis indicates the accumulation of fluorine-containing by-products on the etched surface due to their poor volatility, resulting in (Ba,Sr)-rich and (Ti,O)-deficient etched surface. Compared to the unetched counterparts, the etched Ba 3d_5/2, Ba 3d_3/2, Sr 3d_5/2, Sr 3d_3/2, Ti 2p_3/2, Ti 2p_1/2 and O 1s photoelectron peaks shift towards higher binding energy regions by amounts of 1.31, 1.30, 0.60, 0.79, 0.09, 0.46 and 0.50 eV, respectively. X-ray diffraction (XRD) analysis reveals that intensities of the etched BST (1 0 0), (1 1 0), (2 0 0) and (2 1 1) peaks are lowered and broadened. Raman spectra confirm that the Raman peaks of the etched film shift towards lower wave number regions with the values of 7, 6, 4 and 4 cm⁻¹, and the corresponding phonon lifetimes are longer than those of the unetched film because of the plasma-induced damage. When the etched films are postannealed at 650 °C for 20 min under an O₂ ambience, the chemical shifts of Ba 3d, Sr 3d, Ti 2p and O 1s peaks, the variations for atomic concentrations of Ba, Sr, Ti and O, and the Raman redshifts are reduced, while the corresponding XRD peak intensities increase. It is conceivable that the plasma-induced damage of the etched film could be partially recovered during the postannealing process.     

In situ crystallisation in ZrO2 thin films during high temperature X-ray diffraction

The crystallisation behaviour of ZrO₂ thin films on Si(0 0 1) wafers, deposited either by ALCVD or by evaporation, was studied by using high temperature grazing incidence X-ray diffraction. The tests indicate that the crystallisation temperature of the ZrO₂ films is depending on the film thickness, but below 500°C. The possibility of using these films as high-k gate stacks is discussed, with respect to the crystallisation temperatures measured in the films.     

Enhanced thermoelectric properties of poly(3,4-ethylenedioxythiophene) thin films treated with H2SO4

Poly(3,4-ethylenedioxythiophene)–tosylate–polyethylene glycol–polypropylene glycol–polyethylene glycol (PEDOT–Tos–PPP) films were prepared via a vapor phase polymerization (VPP) method. The thermoelectric (TE) properties of the films before and after treated with H₂SO₄ at different concentrations were measured at 295 K. The TE properties of the films have been significantly improved by the H₂SO₄ treatment. For example, after treated with H₂SO₄ at 1 M, the electrical conductivity of the film has increased remarkably from 944 to 1750 S cm⁻¹, the Seebeck coefficient of the film reduced slightly from 16.5 to 14.6 μV K⁻¹, and the thermal conductivity decreased from 0.495 to 0.474 W/mK. Hence, the ZT value at 295 K has increased from 0.016 to 0.024. The electrical conductivity (Seebeck coefficient) of the untreated and 1 M H₂SO₄ treated PEDOT-Tos-PPP films decreases (increases) with increasing temperature from 295 to 375 K. And the power factor of the films monotonically increases with temperature. The power factor at 375 K of the 1 M H₂SO₄ treated film is almost twice as high as that at 295 K. Atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS) analyses, and the thickness measurement of the films indicate that the tri-block copolymer PPP have been removed from the PEDOT-Tos-PPP films after the H₂SO₄ treatment, and the UV–Vis-NIR absorption spectroscopy and Raman spectroscopy analyses reveal an increasing in the doping level in the PEDOT chains after the H₂SO₄ treatment. Therefore, the TE properties enhancement may be attributed to the combined effects of the removal of the insulating PPP from the PEDOT-Tos-PPP film, increase the doping level and conformational change of the PEDOT chains resulted from the H₂SO₄ treatment.