Jeffrey M. Gaskell

Thermal stability of neodymium aluminates high-κ dielectric deposited by liquid injection MOCVD using single-source heterometallic alkoxide precursors

Thin films of neodymium aluminate (NdAlOx) have been deposited by liquid injection metalorganic chemical vapor deposition (MOCVD) using the bimetallic alkoxide precursor [NdAl(OPri)6(PriOH)]2. The effects of high-temperature postdeposition annealing on NdAlOx thin films are reported. The as-deposited thin films are amorphous in nature. X-ray diffraction (XRD) and medium energy ion scattering (MEIS) show, respectively, no crystallization or interdiffusion of metal ions into the substrate after annealing at 950°C. The capacitance-voltage (C-V) and current-voltage (I-V) characteristics of the thin films exhibited good electrical integrity following annealing. The dielectric permittivity (κ) of the annealed NdAlOx was 12, and a density of interface states at flatband (Dit) of 4.01 × 1011 cm-2 eV-1 was measured. The deposited NdAlOx thin films are shown to be able to endure high-temperature stress and capable of maintaining excellent dielectric properties.

Dielectric relaxation of lanthanum doped zirconium oxide

Lanthanum doped zirconium oxide (Lax–Zr1−xO2−δ) films, with La contents, up to x=0.35, were studied. Films were annealed at 900 °C to crystallize them into phases with higher κ-values. Increasing the La content suppressed the monoclinic phase and stabilized the tetragonal or cubic phase. The highest dielectric constant was obtained for a lightly doped film with a La content of x=0.09, for which a κ-value of 40 was obtained. This was accompanied by a significant dielectric relaxation, following a single Curie–von Schweidler power-law dependency with frequency, changing to a mixed Curie–von Schweidler and Kohlrausch–Williams–Watts relationships after annealing. The dielectric relaxation was most severe for lightly doped films, which had the highest κ-values. The dielectric relaxation appears to be related to the size of crystal grains formed during annealing, which was dependent on the doping level.

Deposition of lanthanum zirconium oxide high-κ films by liquid injection atomic layer deposition

Thin films of lanthanum zirconium oxide, LaxZr1−xO2−δ (x=0.22,0.35,0.63), have been grown by liquid injection atomic layer deposition using [(PriCp)3La] and [(MeCp)2ZrMe(OMe)] precursors. At lower La atomic fractions (x=0.22) films were stabilized in the cubic phase after annealing at 700°C in air. At higher La atomic fractions (x>0.35), the films remained amorphous after annealing. The films deposited showed good dielectric properties with low hysteresis voltages and negligible flatband voltage shifts. The relative permittivity (κ) ranged from 11 to 14 with leakage current densities at 1MVcm−1 in the range of 2.6×10−6–5.3×10−7Acm−2.

High-k materials and their response to gamma ray radiation

The radiation response of four different high-k materials has been investigated by irradiating them using a 979 MBq Cs137 γ-ray source and a dose absorption rate of 0.71rad(Si)∕s. Acceptorlike electron traps and donorlike traps were observed in HfO2 and ZrO2 metal-oxide-semiconductor capacitors originating from radiation-induced defects. A lower density of donor-like traps were created in LaAlO3 and NdAlO3 capacitors, but both electron and hole trapping play a role in shifting the flat band voltage. The radiation hardness of the LaAlO3 and NdAlO3 thin films is similar to thermal SiO2 but better than the HfO2 and ZrO2.

Liquid injection ALD and MOCVD of lanthanum aluminate using a bimetallic alkoxide precursor

Lanthanum aluminate has been deposited for the first time by liquid injection atomic layer deposition (ALD) using a bimetallic alkoxide precursor, [LaAl(OiPr)6(iPrOH)]2 with H2O as oxygen source. The ALD growth rate was constant in the temperature range 160–300 °C, but ALD growth was not fully self-limiting. Comparisons are made with film growth by liquid injection MOCVD. Auger electron spectroscopy (AES) showed that the films contained no detectable C contamination (detection limit ∼0.5%) and XRD showed that films remained amorphous at temperatures below 850 °C. Films grown by ALD were all La deficient with La : Al ratios of 0.50–0.61; films grown by MOCVD at 300 and 450 °C have La : Al ratios of 1.24 and 0.84, respectively. C–V and leakage current data for films grown by ALD and MOCVD are presented and a LaAlOx film (La : Al = 0.54) film had a permittivity (k) of ∼13.

Frequency dispersion and dielectric relaxation of La2Hf2O7

Thin films of La2Hf2O7 have been deposited by liquid injection atomic layer deposition and post-deposition annealed at 900°C. The dielectric frequency dispersion was more serious for thinner films which is attributed to the effect of a lossy interfacial layer between the La2Hf2O7 dielectric and silicon substrate. The effect of the interfacial layer was modeled based on a dual-frequency measurement technique. The dielectric relaxation of the La2Hf2O7 thin films was modelled using both the Curie-von Schweidler and Havriliak-Negami relationships. Post deposition annealing in nitrogen at 900°C for 15min improved dielectric relaxation and reduced the dielectric loss.

Permittivity enhancement and dielectric relaxation of doped hafnium and zirconium oxide

The frequency dispersion of La doped zirconia and cerium doped hafnia films is considered. Doping at concentration of approximately 10% stabilizes crystalline phases with higher-k values. The dielectric relaxation of La doped zirconia films is more severe than the cerium doped hafnia.

High-k dielectrics' radiation response to X-ray and γ-ray exposure

Radiation-induced degradation of HfO<inf>2</inf>, ZrO<inf>2</inf>, LaAlO<inf>3</inf>, and NdAlO<inf>3</inf> thin films was studied and compared based on a Fe⁵⁵ X-ray source and Cs¹³⁷ γ-ray source. After the X-ray exposure of a total dose of 100krad, negative VFB shifts were observed in these thin films, whereas after the γ-ray exposures of the same dose, positive VFB shifts was observed.

Liquid Injection MOCVD of Rare-Earth Oxides Using New Alkoxide Precursors

High purity lanthanum oxide and praseodymium oxide thin films (C 3 ] and [Pr(mmp) 3 ] in toluene-solution (mmp = OCMe 2 CH 2 OMe). 1 H NMR solution studies have shown that the addition of donor species, such as tetraglyme (CH 3 O(CH 2 CH 2 O) 4 CH 3 ) or mmpH prevent molecular aggregation and help stabilise the precursors.