Zr Silicate Films Research Articles

Trimethylsilylcyclopentadienyl tris(dimethylamino)zirconium as a single-source metal precursor for the atomic layer deposition of ZrxSi1 -xO4

Zr Silicate (ZrxSi1-xO4) films with a cation ratio of Zr:Si=3:1 were deposited by atomic layer deposition (ALD) using trimethylsilylcyclopentadienyl tris(dimethylamino)zirconium (SCTDMAZ) and ozone as a single-source metal precursor and oxidant, respectively. The resultant films showed low residual impurity concentration as well as excellent conformality over complex structures, implying that the growth is controlled by a surface-limited reaction and hence proper ALD growth behavior. The Zr-silicate films exhibited amorphous characteristics as deposited and after post-deposition annealing (PDA) up to temperatures of 800°C. After PDA the electrical properties of the amorphous Zr-silicate showed standard output values in the metal–insulator–semiconductor structure, with a low hysteresis of 0.04V and moderate dielectric constant of ~10. Accordingly, these experimental results suggest that SCTDMAZ is indeed a viable option as a single-source metal precursor for the ALD of Zr-silicate thin films.

Thermal stability and electrical properties of Zr silicate films for high-k gate-dielectric applications, as prepared by pulsed laser deposition

Zirconium silicate films with high thermal stability and good electrical properties have been prepared on n-Si(100) substrates and commercially available Pt-coated Si substrates to fabricate metal–insulator–metal (MIM) structures by the pulsed laser deposition (PLD) technique using a Zr0.69Si0.31O2-δ ceramic target. Rapid thermal annealing (RTA) in N2 was performed. X-ray diffraction indicated that the films annealed at 800 °C remained amorphous. Differential thermal analysis revealed that amorphous Zr silicate crystallized at 830 °C. X-ray photoelectron spectroscopy showed that RTA annealing of Zr silicate films at 900 °C led to phase separation. The dielectric constant has been determined to be about 18.6 at 1 MHz by measuring the Pt/Zr silicate/Pt MIM structure. The equivalent oxide thicknesses (EOTs) and the leakage-current densities of films with 6-nm physical thickness deposited in O2 and N2 ambient were investigated. An EOT of 1.65 nm and a leakage current of 31.4 mA/cm2 at 1-V gate voltage for the films prepared in N2 and RTA annealed in N2 at 800 °C were obtained. An amorphous Zr-rich Zr silicate film fabricated by PLD looks to be a promising candidate for future high-k gate-dielectric applications.

Atomic Layer Chemical Vapor Deposition (ALCVD) of Hf and Zr Silicate and Aluminate High-k Gate Dielectric for Next Generation Nano Devices

Among many deposition techniques, atomic layer deposition (ALD) is well suited for highly conformal and uniform ultrathin films with accurate thickness control over a large area. A number of ALD deposition processes have been used to grow mixed oxides like Hf or Zr silicate and aluminate thin films for high-k gate dielectrics needed in the next generation silicon transistors. Nano laminate mixing of each oxide by switching between two metal precursors with an oxidant like water can be used and film composition can be controlled by adjusting the number of each single oxide cycles. An alternating injection of metal alkoxides and chlorides without the injection of extra oxidants is another method. Single metal source, which contains both metal and Si (or Al), also can be adopted to form silicate or aluminate films. These processes will be overviewed in this article with our recent work on atomic layer deposition (ALD) of high-k gate dielectrics. It is important to select a proper set of precursors and each process should be evaluated and compared in terms of the reliability and film properties. In-situ diagnostic technique such as FT-IR is also helpful for the process development.

Spectroscopic characterization of high k dielectrics: Applications to interface electronic structure and stability against chemical phase separation

Extensive spectroscopic characterization of high k materials under consideration for replacing Si oxide as the gate dielectric in Si-based microelectronic devices has been accomplished. Band offset energies of Zr silicates with respect to Si have been determined as a function of silicate alloy composition by combining near-edge x-ray absorption fine structure spectroscopy, vacuum-ultraviolet spectroscopic ellipsometry, x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy, and ab initio calculations on cluster models. These studies provide insight that applies to both transition metal- and rare earth-based dielectrics, including binary oxides and silicate and aluminate alloys. Results have been used to estimate the electronic conduction through Hf silicate films as a function of alloy composition. Thermally induced chemical phase separation in Zr silicate films has been characterized using XPS, Fourier transform infrared spectroscopy, x-ray diffraction, high-resolution transmission electron microscopy, and extended x-ray absorption fine structure spectroscopy. Our results indicate separation into a noncrystalline, Si-rich phase and either nano- or microcrystalline ZrO2, depending on the original film stoichiometry.

Interfacial properties of ultra thin ZrxSi1−xO2 with compositional gradation grown on Si(100) using Zr[N(C2H5)2]4 and Si(OC4H9)4

Zr x Si 1−x O 2 films were deposited by using Zr[N(C2H5)2]4 and Si(OC4H9)4. Composition (x) of a 4 nm thick ZrxSi1−xO2 was investigated by Zr 3d, Si 2p, and O 1s x-ray photoelectron spectroscopy depth profiles. The Zr/(Zr+Si) ratio gradationally changed from ∼0.1 at the silicate film surface to ∼0.67 at the ZrxSi1−xO2-Si interface during Ar+ sputtering. An atomically flat interface with no sub-SiO2 interfacial layers was observed. The dielectric constants were approximately 9 for both Zr-silicate films as-deposited and annealed at 500 °C in oxygen ambient. When annealed in oxygen ambient, the flat band approached the ideal value in C–V curve. The leakage current density of the Zr-silicate films as-deposited and annealed at 500 °C was ∼5×10−4 and ∼3×10−8 A/cm2, respectively, at a bias of 1.0 V.

Characterization of interfacial layer of ultrathin Zr silicate on Si(100) using spectroscopic ellipsometry and HRTEM

Optical properties and the film thickness of interfacial layer formed between the ultrathin as-deposited Zr silicate films and the Si substrate were investigated by the variable-angle spectroscopic ellipsometry (SE), the high-resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS). Five Zr silicate films were deposited by using oxygen-based Zr(O i-Pr) 2(thd) 2 and Si(O t-Bu) 2(thd) 2 as precursors in a pulse-mode metalorganic chemical-vapor deposition (MOCVD) apparatus to investigate the influence of the choice of ambient gas (oxygen or NO) on the formation of the interfacial layers during the oxidation and the deposition of the Zr silicate films. HRTEM images clearly show the existence of the amorphous interfacial layer below the Zr silicate layer. The interfacial layers are found to be Zr-free from the XPS study. In SE analysis, the interfacial layers were described best as the mixture of SiO 2 and SiO in the Bruggeman effective medium approximation (BEMA). The evident reduction of the interfacial layer due to the intentionally grown ultrathin oxynitride buffer layer was observed for the Zr silicate film deposited under a carefully designed growing condition. Any source of oxygen during the growth of the film results in the thicker, but self-limited interfacial layer.

Electronic structure analysis of Zr silicate and Hf silicate films by using spatially resolved valence electron energy-loss spectroscopy

Electronic structures near the band gaps of Zr silicate and Hf silicate thin films were investigated experimentally and theoretically. We show that the electronic structure of Zr silicate can be reproduced by a superposition of the electronic structures of ZrO2 and SiO2. Similarly, the electronic structure of Hf silicate can be reproduced by a superposition of the electronic structures of HfO2 and SiO2. This indicates that, in these silicates, the lowest conduction band states are composed mostly of d states of Zr or Hf, and the valence band states mostly of O 2p states. The similarity of the electronic structures of these silicates can be attributed to the similarity of the chemical natures of Zr and Hf atoms. Consequently, when these silicate films are used as gate dielectrics in metal–oxide–semiconductor transistors, the gate leakage current could be strongly affected by d states of Zr or Hf.

Ultrathin Zirconium Silicate Films Deposited on Si(100) Using Zr ( O i ­ Pr ) 2 ( thd ) 2 , Si ( O t ­ Bu ) 2 ( thd ) 2 , and Nitric Oxide

Ultrathin Zr silicate films were deposited using and nitric oxide in a pulse-mode metallorganic chemical-vapor deposition apparatus with a liquid injection source. High resolution transmission electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy (XPS), and medium energy ion scattering were employed to investigate the structure, surface roughness, chemical state, and composition of the films. The nitric oxide used as oxidizing gas, instead of not only reduced the thickness of the interfacial layer but also removed the carbon contamination effectively from the bulk of the films. The as-deposited Zr silicate films with a Si:Zr ratio of 1.3:1 were amorphous, with an amorphous interfacial layer 0.3-0.6 nm thick. After a spike anneal in oxygen and a 60 s nitrogen anneal at 850°C, these films remained amorphous throughout without phase separation, but the interfacial layer increased in thickness. No evidence of and bonds were found in the films by XPS and carbon concentrations the detection limit, were obtained. The hysteresis, fixed charge density, and leakage current determined from capacitance-voltage analysis improved significantly after postdeposition anneals at 850°C and the films exhibited promising characteristics for deep submicrometer metal-oxide-semiconductor devices. © 2003 The Electrochemical Society. All rights reserved.

Depth profiling of ultrathin films using medium energy ion scattering

The medium energy ion scattering (MEIS) system at the University of Western Ontario has been modified by replacing the original one-dimensional position sensitive detector with a 2-D array. Calibration and analysis procedures for quantitative depth profiling are devised and established in this work: distortion correction, image tiling, charge state distribution of the scattered hydrogen ions, etc. The software to simultaneously control the sample manipulator (three orthogonal rotations), toroidal electrostatic analyzer and spectrum acquisition has been developed using LabView R . This development makes for easy sample alignment to the incident ion beam and automatically collects the step images. Additionally, the tiling procedure using corrected step images is accomplished within LabView R to produce a final energy–angle spectra. Our QUARK (quantitative analysis of Rutherford kinematics) spectrum simulation package has been modified to provide for non-linear least squares fitting to a measured MEIS energy spectrum. As a reference for quantitative analysis, a shallow Sb-implanted graphite sample was used with normalization to the height of the thick target carbon region by applying 1 H stopping power values from Konac et al. [Nucl. Instr. Meth. Phys. Res. B 136–138 (1998) 159]. To determine the system suitability for compositional analysis, Zr silicate films of thickness 2–7 nm on Si (1 0 0) substrates have been characterized by MEIS, RBS and NRA. The absolute areal densities of constituent elements are in good agreement (within 15%) among the three methods.

Wet chemical etching studies of Zr and Hf-silicate gate dielectrics

The etching properties of alternate gate dielectric candidates Hf and Zr silicate in hydrofluoric acid (HF) solutions are presented. As-deposited Hf silicate films were found to be more difficult to etch when compared with as-deposited Zr silicate films. After annealing, both Hf and Zr silicate are harder to etch than as-deposited films. Annealed Zr silicate films were the most difficult to remove in either concentrated, or diluted HF solutions. Film densification, along with crystallization of the silicate films near the Si interface are thought to be responsible for the etch rate change in these silicate systems. Alternate processes to remove remnant metal from the silicon surface after gate dielectric removal are also discussed. After annealing and dielectric film removal, remnant Zr and Hf concentrations near the Si surface of ∼1019/cm3 and ∼1016/cm3, respectively, were observed.

Interdiffusion studies for HfSixOy and ZrSixOy on Si

Metal incorporation into silicon substrates, and thermal stability of alternate gate dielectric candidates HfSixOy and ZrSixOy films after aggressive thermal annealing are reported. Considerable Zr incorporation is observed after furnace and rapid thermal annealing. No detectible Hf incorporation is observed for HfSixOy films annealed with the same conditions as the ZrSixOy films. Sputter deposited Hf silicate films showed superior thermal stability compared with chemical vapor deposited Zr silicate films. An alternate approach to obtain sub-nm resolution depth profiling of impurities in Si is also reported. Device performance associated with Zr incorporation into the channel is also discussed.

Spatially-resolved valence-electron energy-loss spectroscopy of Zr-oxide and Zr-silicate films

We examined electronic structures in Zr-oxide (ZrO2) and Zr-silicate (ZrxSi1−xO2) films deposited on Si substrates by using valence-electron energy-loss spectroscopy combined with scanning transmission electron microscopy (the electron probe diameter was about 0.3 nm). Our analysis indicated that both valence-electron excitations in ZrO2 and in SiO2 occurred in the ZrxSi1−xO2 films. Therefore, the band gaps in the ZrxSi1−xO2 films should be dominated by an energy gap between O 2p and Zr 4d states.

Electrical properties of Ru and RuO2 gate electrodes for Si-PMOSFET with ZrO2 and Zr-silicate dielectrics

In this work, we have studied the electrical and thermal stability of Ru and RuO2 electrodes on ZrO2 and Zr-silicate dielectrics. Very low resistivity Ru and rutile stoichiometric RuO2 films, deposited by reactive sputtering, were evaluated as gate electrodes on ultrathin ZrO2 and Zr-silicate (∼2.7 nm) films for Si-PMOS devices. Thermal and chemical stability of the electrodes were studied at annealing temperatures up to 800°C in N2 followed by a forming gas anneal. X-ray diffraction (XRD), transmission electron microscopy (TEM), and x-ray photoelectron spectroscopy (XPS) methods were used to study grain structure and interface reactions. Electrical properties were evaluated using MOS capacitors. The role of oxygen in these dielectrics was studied by comparing equivalent oxide thickness (EOT) changes as a function of annealing temperature for capacitors with ZrO2 and Zr-silicate dielectrics. For capacitors with Ru and RuO2 gate electrodes on both ZrO2 and Zr-silicate, excellent stability of EOT was detected. Flatband voltage and gate current as a function of annealing temperature were also studied. These studies indicate that Ru and RuO2 are promising gate electrodes for P-MOSFETs.

Thermal stability and diffusion in gadolinium silicate gate dielectric films

Gadolinium silicate films on Si(100) annealed in oxygen and vacuum at temperatures up to 800 °C were analyzed by Rutherford backscattering and narrow resonance nuclear profiling. Oxygen diffused into the film eliminating oxygen vacancies, but Si diffusion, previously observed in Al and Y oxides and in La and Zr silicate films, was absent. Higher-temperature annealing in oxygen resulted in the formation of an interfacial layer observable in high-resolution electron micrographs. Gd0.23Si0.14O0.63 films crystallize at temperatures between 1000 and 1050 °C. These observations combined with recent electrical measurements show that gadolinium silicate films may be a good candidate for the replacement of SiO2 in deep submicron metal–oxide–semiconductor gates.

Ultra-Thin Zirconium Silicate Filmsc With Good Physical And Electrical Properties For Gate Dielectric Applications

AbstractThe need for alternative gate dielectrics to replace conventional SiO2 is increasing to facilitate further CMOS scaling. One of the most promising materials for use as an alternative gate dielectric is Zr silicate due to its thermodynamic stability on Si and its good interface quality with Si. In this study, ultra-thin Zr silicate films (45 – 60 Å thick) with different Zr compositions have been deposited on Si using magnetron reactive co-sputtering. The Zr composition was kept below the stoichiometric value of about 16% to prevent precipitation of ZrO2and to have Si rich films for better interface quality. Films were rapid thermal annealed in N2 ambient up to 9000C and Pt was used as the gate electrode. Electrical characterization of these films was done using HP 4156 and HP 4194 parameter analyzers. Based on these studies, we demonstrate Zr silicate films with equivalent oxide thickness (EOT) of less than 14 Å with gate leakage significantly lower thanSiO2 of similar thickness and hysteresis of < 20mV ( in a sweep from –3 to 3 V). The films exhibit good thermal stability on Si even after 900 0C annealing as shown by a minimal increase in EOT with annealing. TEM and XPS analyses show high quality Zr silicate films that remain stable and amorphous even at 900 0C.