Characterization of rare earth oxides based MOSFET gate stacks prepared by metal-organic chemical vapour deposition

We have prepared rare earth oxides based MOSFET gate stacks using metal-organic chemical vapour deposition, MOCVD. Gd₂O₃, La₂O₃, Nd₂O₃ and Pr₆O₁₁ films with thickness 3–20 nm were deposited on silicon substrate at 500 °C. The films were characterized by X-ray diffraction, X-ray reflectivity, transmission electron microscopy and X-ray photoelectron spectroscopy. As a next step, Ru films were grown on the dielectric films at 300 °C as a gate electrode. Electrical characterization of the MOS structures was performed by capacitance–voltage measurements. The structures annealed at 430 °C in forming gas (90% N₂+10% H₂) exhibited dielectric constant ranging from 12 to 14. Typically, the films showed high values of fixed oxide charge density, . Fixed oxide charges can be decreased by post-deposition annealing in forming gas and in oxygen.     

Examination and evaluation of La2O3 as gate dielectric for sub-100 nm CMOS and DRAM technology

High-k gate dielectric La₂O₃ thin films have been deposited on Si(1 0 0) substrates by molecular beam epitaxy (MBE). Al/La₂O₃/Si metal-oxide–semiconductor capacitor structures were fabricated and measured. A leakage current of 3 × 10⁻⁹ A/cm² and dielectric constant between 20 and 25 has been measured for samples having an equivalent oxide thickness (EOT) 2.2 nm. The estimated interface state density D_it is around 1 × 10¹¹ eV⁻¹ cm⁻². EOT and flat-band voltage were calculated using the NCSU CVC program. The chemical composition of the La₂O₃ films was measured using X-ray photoelectron spectrometry and Rutherford backscattering. Current density vs. voltage curves show that the La₂O₃ films have a leakage current several orders of magnitude lower than SiO₂ at the same EOT. Thin La₂O₃ layers survive anneals of up to 900 °C for 30 s with no degradation in electrical properties.     

dc-Conduction mechanism in lanthanum–manganese oxide films grown on p-Si substrate

Thin films of (La–Mn) double oxide were prepared on p-Si substrates for electrical investigations. The samples have been characterised by X-ray fluorescence (XRF) and X-ray diffraction (XRD) methods. The XRF spectrum was used to determine the weight fraction ratio of Mn to La in the prepared samples. The XRD study shows the formation of grains of LaMnO₃ compound through a solid-state reaction for annealing at 800 °C. Samples used to study the electrical characteristics of the prepared films were constructed in form of a metal–oxide–Si MOS structures. Those MOS structures were characterised by the measuring their capacitance as a function of gate voltage C(V_g) in order to determine the oxide charge density Q_ox, the surface density of states D_it at the oxide/Si interface, and to extract the oxide voltage in terms of gate voltage. The extracted dielectric constant of the double oxide film is lower than that of pure La₂O₃ film and larger than that of pure Mn₂O₃ film, but the formation of LaMnO₃ grains by a solid-state reaction at 800 °C increases the relative permittivity to 11.5. These experimental conclusions might be useful to be used in the field of Si-oxide alternative technique. The leakage dc current density vs. oxide field J(E_ox) relationship for crystalline films follow the mechanism of Richardson–Schottky (RS), from which the field-lowering coefficient and the dynamic relative permittivity were determined. Nevertheless, the leakage current density measured in a temperature range of (293–363 K) was not controlled by the RS mechanism. It was observed that the temperature dependence of the leakage current in crystalline (La–Mn) oxide insulating films has metallic-like temperature behaviour, which might be important in the technical applications.     

Electrical properties of hafnium silicate films obtained from a single-source MOCVD precursor

In the present work, the potential of hafnium silicate (Hf_xSi_yO₂) films as an alternative gate dielectric to SiO₂ for future technology generations is demonstrated. Thermally stable Hf_xSi_yO₂ films are deposited from a single-source MOCVD precursor. I–V and C–V measurement data are presented and effects of post-deposition annealing on electrical properties are discussed. A 900 °C O₂-anneal shows best results in terms of leakage current characteristics and is, therefore, intensively investigated.     

Effect of rapid thermal annealing of sputtered aluminium nitride film in an oxygen ambient

Aluminium nitride (AlN) thin films were deposited by radio frequency (RF) magnetron sputtering on p-type silicon (Si) substrate of (1 0 0) orientation using only argon (Ar) gas at substrate temperature of 300 °C. In order to achieve improved electrical properties, we performed post-deposition rapid thermal annealing (RTA). Sputtered AlN films were annealed in an oxygen ambient at temperatures of 600, 700, and 800 °C using RTA for 30 min. The orientation of the AlN crystal in the film was investigated using X-ray diffraction (XRD). The characteristic spectra by functional group were analyzed by Fourier transformation infrared (FTIR) spectroscopy. The electrical properties of the AlN thin films were studied through capacitance–voltage (C–V) characteristics in metal–insulator–semiconductor (MIS) device using the films as insulating layers. The flatband voltages (V_FB) in C–V curves were found to depend on crystal orientations. Negative V_FB was found in the case when AlN (1 0 0) peak was found. Also, when AlN (1 0 3) peak was observed upon increasing the annealing temperature, the value of V_FB was positive and after annealing at 700 °C, AlN (1 0 3) peak intensity was found to be maximum and V_FB was as high as+6.5 V.     

Lanthanum germanate as dielectric for scaled Germanium metal–oxide–semiconductor devices

We report a study of La₂O₃ with lanthanum germanate (LGO) as interfacial layer, or LGO alone as a gate dielectric candidate for scaled germanium metal–oxide–semiconductor devices. Capacitance–voltage (C–V) analysis of as-deposited samples of various oxide thicknesses show a La₂O₃ with k value of ～24–27 with an interfacial LGO with k value of ～12. Upon O₂ annealing, the oxides fully transform into LGO without an interfacial layer. The paper also discusses flatband voltage (V_fb) shifts with oxide thickness, from which positive fixed charges in La₂O₃ can be deduced. It is also shown that these charges are strongly reduced upon the O₂ anneal and LGO formation.     

Electrical properties of atomic-layer-deposited La2O3 films using a novel La formamidinate precursor and ozone

La₂O₃ films were grown by atomic layer deposition technique using a novel formamidinate precursor, tris(N,N′-diisopropylformamidinato) lanthanum [La(ⁱPrfAMD)₃], with H₂O and O₃ as an oxidant. La₂O₃ films grown with H₂O in the film exhibited a parasitic chemical vapor deposition type growth possibly due to a La(OH)_x component. However, the use of O₃ as the oxidant revealed a stable ALD process window. A post-deposition annealing (PDA) of the deposited La₂O₃ films using O₃ significantly reduces leakage current density by four orders of magnitude relative to as-deposited samples. The dielectric constant of La₂O₃ films with a TaN metal gate is found to be ～29, which is higher than reported values for CVD and ALD La₂O₃ films.     

Probing stress effects in HfO2 gate stacks with time dependent measurements

Effects of constant voltage stress (CVS) on gate stacks consisting of an ALD HfO₂ dielectric with various interfacial layers were studied with time dependent sensing measurements: DC I–V, pulse I–V, and charge pumping (CP) at different frequencies. The process of injected electron trapping/de-trapping on pre-existing defects in the bulk of the high-κ film was found to constitute the major contribution to the time dependence of the threshold voltage (V_t) shift during stress. The trap generation observed with the low frequency CP measurements is suggested to occur within the interfacial oxide layer or the interfacial layer/high-κ interface, with only a minor effect on V_t.     

Effects of oxygen partial pressure on structural and electrical characteristics of HfAlO high-k gate dielectric grown on strained SiGe by pulsed-laser deposition

Dependence of oxygen partial pressures on structural and electrical characteristics of HfAlO (Hf:Al=1:1) high-k gate dielectric ultra-thin films grown on the compressively strained Si₈₃Ge₁₇ by pulsed-laser deposition were investigated. The microstructure and the interfacial structure of the HfAlO thin films grown under different oxygen partial pressures were studied by transmission electron microscopy, and the their electrical properties were characterized by capacitance–voltage (C−V) and conductance–voltage measurements. Dependence of interfacial layer thickness and C–V characteristics of the HfAlO films on the growth of oxygen pressure was revealed. With an optimized oxygen partial pressure, an HfAlO film with an effective dielectric constant of 16 and a low interface state density of 2.1×10¹⁰ cm⁻² eV⁻¹ was obtained.     

Electrical characterization of zirconium silicate films obtained from novel MOCVD precursors

In the present work, the potential of zirconium silicate (ZrSi_xO_y) films as an alternative gate dielectric to SiO₂ for future technology generations is demonstrated. Novel single-source precursors for MOCVD of zirconium silicate were synthesized and ZrSi_xO_y layers were deposited. I–V and C–V measurement data are presented and detected charge trapping phenomena are discussed.     

High temperature transport kinetics in heteroepitaxial LaFeO3 thin films

Heteroepitaxial LaFeO₃(1 1 0) thin films with a thickness of 150 nm were grown on LaAlO₃(0 0 1) by reactive sputtering in an inverted cylindrical magnetron geometry. Equilibrium conductivity was measured as a function of partial pressure of oxygen at T=1000 °C, and logσ plotted vs. logP(O₂) showed a minimum in conductivity for P(O₂)=10⁻¹¹ atm and a linear response between 10⁻¹⁰ and 1 atm. This linear response makes thin films of LaFeO₃ a promising material for oxygen sensor applications. We have also measured the time response of the film conductivity upon an abrupt change in the partial pressure of ambient oxygen from 10⁻² to 10⁻³ atm, which was determined at 60 s for T=700 °C and <3.5 s at T=1000 °C.     

Improvement of gate dielectric reliability for p+poly MOS devices using remote PECVD top nitride deposition on ultra-thin (2.4–6 nm) gate oxides

Dual layer dielectrics have been formed by remote PECVD deposition of ultra-thin (0.4–1.2 nm) nitrides onto thin thermal oxides grown on n-type Si(100) substrates. Activation of boron-implanted p+ polycrystalline silicon gate electrodes was accomplished by a high temperature anneal, 1–4 min at 1000°C. Boron penetration through the dielectric film to the n-type substrate was investigated by performing a quasi-static C–V analysis and monitoring the flatband voltage shift. Boron penetration was effectively stopped by a 0.8 nm nitride film, and partially stopped by a 0.4 nm nitride film. In addition, the charge to breakdown as monitored by the Q_bd value to 50% cumulative failure was highest for the device with the 0.8 nm top nitride, and decreased significantly in the thermal oxide. However there were essentially no differences in the mid-gap interface state densities, D_it, between oxide and nitride/oxide gate dielectric structures with Al gate. It is concluded that the 0.8 nm of plasma nitride was sufficient to block boron atom out-diffusion from a heavily implanted p+ poly-silicon gate electrode under the conditions of an aggressive implant activation anneal to improve the dielectric reliability.     

Structural and Electrical Properties of Ta ax La(1−a)x O y Thin Films

Effect of annealing temperature on the characteristics of sol–gel-driven Ta _ax La_(1?a)x O _y thin film spin-coated on Si substrate as a high-k gate dielectric was studied. Ta _ax La_(1?a)x O _y thin films with different amounts of a were prepared (as-prepared samples). X-ray diffraction measurements of the as-prepared samples indicated that Ta_0.3x La_0.7x O_y film had an amorphous structure. Therefore, Ta_0.3x La_0.7x O _y film was chosen to continue the present studies. The morphology of Ta_0.3x La_0.7x O _y films was studied using scanning electron microscopy and atomic force microscopy techniques. The obtained results showed that the size of grain boundaries on Ta_0.3x La_0.7x O _y film surfaces was increased with increasing annealing temperature. Electrical and optical characterizations of the as-prepared and annealed films were investigated as a function of annealing temperature using capacitance–voltage (C–V) and current density–voltage (J–V) measurements and the Tauc method. The obtained results demonstrated that Ta_0.3x La_0.7x O _y films had high dielectric constant (≈27), wide band gap (≈4.5 eV), and low leakage current density (≈10^?6 A/cm² at 1 V).     

Optical and electrical characterization of hafnium oxide deposited by liquid injection atomic layer deposition

Optical and electrical properties of a set of high-k dielectric HfO₂ films, deposited by liquid injection atomic layer deposition (LI-ALD) and post deposition annealed (PDA) in nitrogen (N₂) ambient at various temperatures (400–600 °C), were investigated. The films were prepared using the cyclopentadienyl of hafnium precursor [Cp₂Hf(CH₃)₂] with water deposited at 340 °C. The spectroscopic ellipsometric (SE) results show that the characteristics of the dielectric functions of these films are strongly affected by annealing temperatures. I–V results show that N₂-based PDA enhances the average energy depth of the shallow trapping defects from Poole–Frenkel conduction fitting. This also correlated with the measured increase in MOS capacitance–voltage hysteresis.     

Epitaxial Growth and Characterization of p-Type ZnO

N-doped p-type ZnO thin films were grown on c-sapphire substrates, semi-insulating GaN templates, and n-type ZnO substrates by metal organic chemical vapor deposition (MOCVD). Diethylzinc and oxygen were used as precursors for Zn and O, respectively, while ammonia (NH₃) and nitrous oxide (N₂O) were employed as the nitrogen dopant sources. X-ray diffraction (XRD) studies depicted highly oriented N-doped ZnO thin films. Photoluminescence (PL) measurements showed a main emission line around 380 nm, corresponding to an energy gap of 3.26 eV. Nitrogen concentration in the grown films was analyzed by secondary ion mass spectrometry (SIMS) and was found to be on the order of 10¹⁸ cm⁻³. Electrical properties of N-doped ZnO epilayers grown on semi-insulating GaN:Mg templates were measured by the Hall effect and the results indicated p-type with carrier concentration on the order of 10¹⁷ cm⁻³.     

Vibrational spectroscopy characterization of low-dielectric constant SiOC:H films prepared by PECVD technique

Low-dielectric constant SiOC:H films were prepared by plasma enhanced chemical vapour deposition (PECVD) from trimethyl-silane (H–Si–(CH₃)₃) and ozone (O₃) gas mixture. The samples were preliminarily annealed at 400 °C in N₂ atmosphere and then in N₂+He plasma. Afterwards, they were treated in vacuum at some fixed temperatures in the range between 400 and 900 °C. Structural investigations of the annealed films were carried out by means of vibrational spectroscopy techniques. FT-IR spectrum of a preliminarily treated sample shows absorption bands due to stretching modes of structural groups like Si–CH₃ at 1270 cm⁻¹, Si–O–Si at 1034 cm⁻¹ and C–H_x in the region between 2800 and 3000 cm⁻¹. No significant spectral change was observed in the absorption spectra of samples annealed up to 600 °C, indicating that the preliminarily treated film retains a substantial structural stability up to this temperature. Above 600 °C, absorption spectra show a strong quenching of H-related peaks while the band due to Si–O–Si anti-symmetric stretching mode shifts towards higher energy, approaching the value observed for thermally grown SiO₂. Raman spectra of samples treated at temperatures T500 °C exhibit both D and G bands typical of sp²-hybridised carbon, due to the formation of C–C bonds within the film which is accompanying the release of hydrogen. The intensity of D and G bands becomes more pronounced in samples annealed at higher temperatures, thus suggesting a progressive precipitation of carbon within the oxide matrix.     

Investigation of high-K gate stacks with epitaxial Gd2O3 and FUSI NiSi metal gates down to CET=0.86 nm

Novel gate stacks with epitaxial gadolinium oxide (Gd₂O₃) high-k dielectrics and fully silicided (FUSI) nickel silicide (NiSi) gate electrodes are investigated. Ultra-low leakage current densities down to 10^–7 A cm^–2 are observed at a capacitance equivalent oxide thickness of CET=1.8 nm. The influence of a titanium nitride (TiN) capping layer during silicidation is studied. Furthermore, films with an ultra-thin CET of 0.86 nm at a Gd₂O₃ thickness of 3.1 nm yield current densities down to 0.5 A cm⁻² at V_g=+1 V. The extracted dielectric constant for these gate stacks ranges from k=13 to 14. These results emphasize the potential of NiSi/Gd₂O₃ gate stacks for future material-based scaling of CMOS technology.     

Electrical characterization of hafnium oxide and hafnium-rich silicate films grown by atomic layer deposition

An electrical characterization comparative analysis between Al/HfO₂/n-Si and Al/Hf-Si-O/n-Si samples has been carried out. Hafnium-based dielectric films have been grown by means of atomic layer deposition (ALD). Interface quality have been determined by using capacitance–voltage (C–V), deep level transient spectroscopy (DLTS) and conductance transient (G-t) techniques. Our results show that silicate films exhibit less flat-band voltage shift and hysteresis effect, and so lower disordered induced gap states (DIGS) density than oxide films, but interfacial state density is greater in Hf–Si–O than in HfO₂. Moreover, a post-deposition annealing in vacuum under N₂ flow for 1 min, at temperatures between 600 and 730 °C diminishes interfacial state density of Hf–Si–O films to values measured in HfO₂ films, without degrade the interface quality in terms of DIGS.     

Mechanical stress in PECVD a-SiC:H: aging and plasma treatments effects

Hydrogenated amorphous silicon carbide (a-SiC:H) deposited by PECVD is one of the most promising dielectric diffusion barrier available in Cu—Ultra low k interconnections due to its low dielectric constant and good barrier ability. In this work, the mechanical stress evolution with time of a-SiC:H film exposed to room atmosphere is studied and compared with the behavior observed on other PECVD dielectrics (SiN, SiO₂, SiCN). For as-deposited a-SiC:H samples, a strong stress evolution with time toward compression is observed and the results are interpreted mainly in terms of surface reactivity and silanol buildup. Infrared spectroscopy analysis allows to confirm that the mechanical stress evolution and the OH content are linked. An oxidation of the hydrogenated amorphous silicon carbide film with time is also observed. Different plasma treatments (He, O₂ or H₂) are tested on a-SiC:H films to limit the stress drift with time. Each plasma treatments are able to limit the stress evolution of a-SiC:H films but the mechanisms are different in each case: densification of the film with He plasma treatment, formation of a dense oxide at the surface with O₂ plasma treatment and passivation of dangling bonds with H₂ plasma treatment.     

Realization of intrinsic p-type ZnO thin films by metal organic chemical vapor deposition

P-type ZnO thin films were grown on sapphire substrates with and without nitrous oxide (N₂O) by metal organic chemical vapor deposition (MOCVD). The intrinsic p-type ZnO films were achieved by controlling the Zn:O ratio in the range of 0.05–0.2 without N₂O flow. Secondary ion mass spectroscopy (SIMS) showed that the films contained little or no nitrogen (N) impurities for all samples. The p-type behavior of the samples should be due to the intrinsic acceptor-like defects V_Zn, for ZnO film grown without nitrous oxide, and N, occupying O sites as acceptors for ZnO film grown with nitrous oxide. The best p-type ZnO film has low resistivity of 0.369 Ω-cm, high carrier density of 1.62×10¹⁹ cm⁻³, and mobility of 3.14 cm²/V-s. The obtained p-type ZnO films possess a transmittance of nearly 100% in the visible region and strong near-band-edge emission.