表征超大规模集成电路互连纳米薄膜硬度特性的声表面波的频散特性

利用声表面波(SAW)的频散特性来表征超大规模集成电路(ULSI)互连系统中低介电常数(k)薄膜的物性具有准确、快速、对材料无损伤等突出优点.研究了Si(100)衬底上淀积低k薄膜的分层结构中，SAW沿任意方向传播的色散关系.引入坐标变换后，单层薄膜特征矩阵从9阶降到6阶，双层薄膜特征矩阵从15阶降到10阶，大幅度提高了计算速度，有利于生产ULSI过程中的在线监测. 关键词： 超大规模集成电路 声表面波 传输方向 频散特性     

Characterization of the interface between the Hf-based high-k thin film and the Si using spatially resolved electron energy-loss spectroscopy

The interfacial structures of HfO₂ and HfAlO thin films on Si have been investigated using spatially resolved electron energy-loss spectroscopy. We have found that interfaces are not atomically sharp, and variation in the symmetry of the local atomic coordination lasts for a couple of monolayers for both the as-deposited HfO₂ and the HfAlO samples. Annealing of the HfO₂ film in the oxygen environment leads to the formation of a thick SiO₂/SiO_x stack layer in-between the original HfO₂ and the Si substrate. As a comparison, the interfacial stability is significantly improved by Al incorporation into the HfO₂ film (forming HfAlO), which effectively reduced/eliminated the interfacial silicon oxide formation during the oxygen annealing process. The mechanism of the high-k film/substrate stabilization by Al incorporation is discussed based on the experimental results.     

Maxima of the spectral reflectance ratio of polarized waves used to measure the thickness of a nonabsorbing thin film

A simple method to determine the thickness of a nonabsorbing thin film on an absorbing substrate from maxima of the ratio between the spectral reflectances of p- and s-polarized components reflected from the thin-film structure is presented. The spectral reflectance ratio, which can be measured in a simple polarimetry configuration at a fixed angle of incidence, consists of maxima whose number and positions depend on the thickness of a thin film. An approximative linear relation between the thin-film thickness and a wavelength of the maximum of the reflectance ratio for a specific angle of incidence is revealed, provided that the wavelength-dependent refractive index of the thin film is known and the substrate is weakly absorbing. The relation permits the calculation of the thickness from the measured spectral reflectance ratio by using one maximum only, as is demonstrated theoretically for a SiO₂ thin film on a Si substrate. The application of this method is demonstrated experimentally for the same thin-film structure with different thicknesses of the SiO₂ thin film. The results are compared with those given by the algebraic fitting method, and very good agreement is confirmed.     

Dielectric properties of continuous composition spreaded MgO-Ta2O5 thin films

The dielectric properties of MgO-Ta₂O₅ continuous composition spread (CCS) thin films were investigated. The MgO-Ta₂O₅ CCS thin films were deposited on Pt/Ti/SiO₂/Si substrates by off-Axis RF magnetron sputtering system, and then the films were annealed at 350 °C with rapid thermal annealing system in vacuum. The dielectric constant and loss of MgO-Ta₂O₅ CCS thin films were plotted via 1500 micron-step measuring. The specific point of Ta₂O₅-MgO CCS thin film (post annealed at 350 °C) showing superior dielectric properties of high dielectric constant (k ∼ 28) and low dielectric loss (tan δ < 0⋅004) at 1 MHz were found in the area of 3-5 mm apart from Ta₂O₅ side on the substrate. The cation's composition of thin film was Mg:Ta = 0.4:2 at%.     

Optical and electrical properties of plasma-oxidation derived HfO2 gate dielectric films

High-k gate dielectric HfO₂ thin films have been deposited on Si(1 0 0) by using plasma oxidation of sputtered metallic Hf thin films. The optical and electrical properties in relation to postdeposition annealing temperatures are investigated by spectroscopic ellipsometry (SE) and capacitance-voltage (C-V) characteristics in detail. X-ray diffraction (XRD) measurement shows that the as-deposited HfO₂ films are basically amorphous. Based on a parameterized Tauc-Lorentz dispersion mode, excellent agreement has been found between the experimental and the simulated spectra, and the optical constants of the as-deposited and annealed films related to the annealing temperature are systematically extracted. Increases in the refractive index n and extinction coefficient k, with increasing annealing temperature are observed due to the formation of more closely packed thin films and the enhancement of scattering effect in the targeted HfO₂ film. Change of the complex dielectric function and reduction of optical band gap with an increase in annealing temperature are discussed. The extracted direct band gap related to the structure varies from 5.77, 5.65, and 5.56 eV for the as-deposited and annealed thin films at 700 and 800 °C, respectively. It has been found from the C-V measurement the decrease of accumulation capacitance values upon annealing, which can be contributed to the growth of the interfacial layer with lower dielectric constant upon postannealing. The flat-band voltage shifts negatively due to positive charge generated during postannealing.     

Formation of silicon nanodots from dysprosium-doped amorphous SiCxOy films grown by hot-filament assisted chemical vapor deposition of CH3SiH3 and Dy(DPM)3 gas jets

We report on Si nanodot formation by chemical vapor deposition (CVD) of ultrathin films and following oxidation. The film growth was carried out by hot-filament assisted CVD of CH₃SiH₃ and Dy(DPM)₃ gas jets at the substrate temperature of 600 °C. The transmission electron microscopy observation and X-ray photoelectron spectroscopy analysis indicated that ∼35 nm Dy-doped amorphous silicon oxycarbide (SiC_xO_y) films were grown on Si(1 0 0). The Dy concentration was 10-20% throughout the film. By further oxidation at 860 °C, the smooth amorphous film was changed to a rough structure composed of crystalline Si nanodots surrounded by heavily Dy-doped SiO₂.     

Soft X-ray photoemission study of nitrogen diffusion in TiN/HfO:N gate stacks

The impact of HfO:N post nitridation anneal (PNA) and gate fabrication on the physico-chemical properties of the TiN/HfO:N/SiO₂/Si stack are investigated using Soft X-ray Photoelectron Spectroscopy (S-XPS) and Vacuum UltraViolet Spectroscopic Ellipsometry (VUV-SE). Defects created in the high-k during plasma nitridation are passivated by PNA under O₂. Both oxygen and nitrogen diffusion is observed towards the bottom SiO₂/Si interface together with a regrowth of the SiO₂. These defects play a major role regarding nitrogen diffusion during gate fabrication. Without PNA, no diffusion is observed because O and N atoms are trapped inside the high-k. With PNA and simultaneous defects passivation, nitrogen from both metal gate and high-k diffuses towards the bottom SiO₂/Si interface.     

Surface morphology characterization of pentacene thin film and its substrate with under-layers by power spectral density using fast Fourier transform algorithms

Surface morphology of pentacene thin films and their substrates with under-layers is characterized by using atomic force microscopy (AFM). The power values of power spectral density (PSD) for the AFM digital data were determined by the fast Fourier transform (FFT) algorithms instead of the root-mean-square (rms) and peak-to-valley value. The PSD plots of pentacene films on glass substrate are successfully approximated by the k-correlation model. The pentacene film growth is interpreted the intermediation of the bulk and surface diffusion by parameter C of k-correlation model. The PSD plots of pentacene film on Au under-layer is approximated by using the linear continuum model (LCM) instead of the combination model of the k-correlation model and Gaussian function. The PSD plots of SiO₂ layer on Au under-layer as a gate insulator on a gate electrode of organic thin film transistors (OTFTs) have three power values of PSD. It is interpreted that the specific three PSD power values are caused by the planarization of the smooth SiO₂ layer to rough Au under-layer.     

Structural investigation of thin tetracene films on flexible substrate by synchrotron X-ray diffraction

Structural properties of tetracene thin films grown by vacuum sublimation on a flexible Mylar^© substrate have been investigated by means of synchrotron X-ray diffraction. The films are polycrystalline and are made up of crystalline domains oriented with the (0 0 l) planes almost parallel to the substrate and completely misoriented around the surface normal. Two crystallographic phases (α and β thin film phases) have been identified. They differ for the d_h k l interplanar spacing, both larger than that of the bulk. As a comparison, results from tetracene films grown on SiO₂ have been reported to investigate the different charge transport properties of films grown on Mylar and on SiO₂ substrates.     

Dielectric and piezoelectric properties of the Ba0.92Ca0.08Ti0.95Zr0.05O3 thin films grown on different substrate

Lead free Ba_0.92Ca_0.08Ti_0.95Zr_0.05O₃ (BCZT) thin films were deposited on Pt/Ti/SiO₂/Si and LaNiO₃(LNO)/Pt/Ti/SiO₂/Si substrates by a sol–gel processing technique, respectively. The effects of substrate on structure, dielectric and piezoelectric properties were investigated in detail. The BCZT thin films deposited on LNO/Pt/Ti/SiO₂/Si substrates exhibit (100) orientation, larger grain size and higher dielectric tunability (64%). The BCZT thin films deposited on Pt/Ti/SiO₂/Si exhibit (110) orientation, higher Curie temperature (75 °C), better piezoelectric property (d₃₃ of 50 pm/V) and lower dielectric loss (0.02). The differences in dielectric and piezoelectric properties in the two kinds of oriented BCZT films should be attributed to the difference of structure, in-plane stress and polarization rotation in orientation engineered BCZT films.     

Structural and optical properties of nitrogen-incorporated HfO2 gate dielectrics deposited by reactive sputtering

High-k HfO_xN_y thin films with different nitrogen-incorporation content have been fabricated on Si (1 0 0) substrate by means of radio-frequency reactive sputtering method. Analyses from X-ray diffraction (XRD) and atomic force microscopic have indicated that the increase of the crystallization temperature of HfO₂ thin films and the decrease of the roughness root-mean-square value of HfO₂ thin films due to the incorporation of nitrogen. Based on a parameterized Tauc-Lorentz (TL) dispersion model, the optical properties of the HfO_xN_y thin films related to different nitrogen-incorporation content are systematically investigated by spectroscopic ellipsometer. Increase in the refractive index and the extinction coefficient and reduction in band gap with increase of nitrogen-incorporation content are discussed in detail.     

Surface acoustic wave device properties of (B, Al)N films on 128° Y-X LiNbO3 substrate

A c-axis orientated aluminium nitride (AlN) film on a 128° Y-X lithium niobate (LiNbO₃) surface acoustic wave (SAW) device which exhibit a large electromechanical coupling coefficient (k²) and a high SAW velocity property, is needed for future communication applications. In this study, a c-axis orientated (B, Al)N film (with 2.6 at.% boron) was deposited on a 128° Y-X LiNbO₃ substrate by a co-sputtering system to further boost SAW device properties. The XRD and TEM results show that the (B, Al)N films show highly aligned columns with the c-axis perpendicular to the substrate. The hardness and Young's modulus of (B, Al)N film on 128° Y-X LiNbO₃ substrates are at least 17% and 7% larger than AlN films, respectively. From the SAW device measurement, the operation frequency characteristic of (B, Al)N film on 128° Y-X LiNbO₃ is higher than pure AlN on it. The SAW velocity also increases as (B, Al)N film thickness increases (at fixed IDT wavelength). Furthermore, the k² of (B, Al)N on the IDT/128° Y-X LiNbO₃ SAW device shows a higher value than AlN on it.     

Physical and electrical characteristics of a high-k Yb2O3 gate dielectric

High-k ytterbium oxide (Yb₂O₃) gate dielectrics were deposited on Si substrate by reactive sputtering. The structural features of these films after postdeposition annealing treatment were studied by X-ray diffraction and X-ray photoelectron spectroscopy. It is found that the Yb₂O₃ gate dielectrics annealed at 700 °C exhibit a larger capacitance value, a lower frequency dispersion and a smaller hysteresis voltage in C-V curves compared with other annealing temperatures. They also show negligible charge trapping under high constant voltage stress. This phenomenon is mainly attributed to the decrease in the amorphous silica thickness.     

The interface reaction of high-k La2Hf2O7/Si thin film grown by pulsed laser deposition

The La₂Hf₂O₇ films have been deposited on Si (1 0 0) substrate by using pulsed laser deposition (PLD) method. X-ray diffraction (XRD) demonstrates that the as-grown film is amorphous and crystallizes after 1000 °C annealing. The interface structure is systematically studied by Synchrotron X-ray reflectivity (XRR), Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). Silicide, silicate and SiO_x formations from interfacial reaction are observed on the surface of the Si substrate in the as-grown film. The impact of silicide formation on the electrical properties is revealed by capacitance-voltage (C-V) measurements. By post-deposition annealing (PDA), silicide can be effectively eliminated and C-V property is obviously improved.     

Thickness measurement of a thin hetero-oxide film with an interfacial oxide layer by X-ray photoelectron spectroscopy

The general equation T_ove = L cos  θ ln(R_exp/R₀ + 1) for the thickness measurement of thin oxide films by X-ray photoelectron spectroscopy (XPS) was applied to a HfO₂/SiO₂/Si(1 0 0) as a thin hetero-oxide film system with an interfacial oxide layer. The contribution of the thick interfacial SiO₂ layer to the thickness of the HfO₂ overlayer was counterbalanced by multiplying the ratio between the intensity of Si⁴⁺ from a thick SiO₂ film and that of Si⁰ from a Si(1 0 0) substrate to the intensity of Si⁴⁺ from the HfO₂/SiO₂/Si(1 0 0) film. With this approximation, the thickness levels of the HfO₂ overlayers showed a small standard deviation of 0.03 nm in a series of HfO₂ (2 nm)/SiO₂ (2-6 nm)/Si(1 0 0) films. Mutual calibration with XPS and transmission electron microscopy (TEM) was used to verify the thickness of HfO₂ overlayers in a series of HfO₂ (1-4 nm)/SiO₂ (3 nm)/Si(1 0 0) films. From the linear relation between the thickness values derived from XPS and TEM, the effective attenuation length of the photoelectrons and the thickness of the HfO₂ overlayer could be determined.     

Optical characterization of band gap graded ZnMgO films

We investigated the optical properties of compositionally graded Zn_1?xMg_xO (g-ZnMgO) films using spectroscopic ellipsometry. The g-ZnMgO and ZnO films were grown on Pt/Ti/SiO₂/Si substrates by ultrasonic spray pyrolysis. We simulated a uniformly graded optical band gap layer on the Pt substrate to reproduce the experimental result. The band gap of the bottommost layer of the g-ZnMgO film was estimated to be ～3.22 eV, the same as the undoped ZnO film. Then we considered a linearly increasing band gap with the film composition, and obtained a band gap of ～3.56 eV for the topmost layer of the film. In addition, the exciton peak showed a strong increase for the topmost layer of the film suggesting an important role of doping.     

New approach to the growth of SiOx nanowire bunch using Au catalyst and SiNx film on Si substrate

SiO_x nanowire bunches were fabricated on a SiN_x film with Au catalytic metal in the presence of an Ar flow of 50 sccm at 1150 °C. The resulting samples were characterized by field-emission scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy. A SiN_x film serves as a barrier to the diffusion of Si atoms from the Si substrate to the catalytic Au metal, where a substrate is a Si source material for SiO_x nanowire (NW) growth. Using this process, we could temporally control the initial growth step of SiO_x NWs and easily grow the NW bunch.     

Surface chemical states of barium zirconate titanate thin films prepared by chemical solution deposition

Ba(Zr_0.05Ti_0.95)O₃ (BZT) thin films grown on Pt/Ti/SiO₂/Si(1 0 0) substrates were prepared by chemical solution deposition. The structural and surface morphology of BZT thin films has been studied by X-ray diffraction (XRD) and scanning electron microscope (SEM). The results showed that the random oriented BZT thin film grown on Pt/Ti/SiO₂/Si(1 0 0) substrate with a perovskite phase. The SEM surface image showed that the BZT thin film was crack-free. And the average grain size and thickness of the BZT film are 35 and 400 nm, respectively. Furthermore, the chemical states and chemical composition of the films were determined by X-ray photoelectron spectroscopy (XPS) near the surface. The XPS results show that Ba, Ti, and Zr exist mainly in the forms of BZT perovskite structure.     

Substrate effects on the oxygen gas sensing properties of SnO2/TiO2 thin films

In this study, SnO₂/TiO₂ thin films are fabricated on SiO₂/Si and Corning glass 1737 substrates using a R.F. magnetron sputtering process. The gas sensing properties of these films under an oxygen atmosphere with and without UV irradiation are carefully examined. The surface structure, morphology, optical transmission characteristics, and chemical compositions of the films are analyzed by atomic force microscopy, scanning electron microscopy and PL spectrometry. It is found that the oxygen sensitivity of the films deposited on Corning glass 1737 substrates is significantly lower than that of the films grown on SiO₂/Si substrates. Therefore, the results suggest that SiO₂/Si is an appropriate substrate material for oxygen gas sensors fabricated using thin SnO₂/TiO₂ films.     

Microstructure of Fe film on Si grown by MOCVD

Fe epitaxial films were grown on Si(100) substrate by MOCVD using thermal decomposition of iron pentacarbonyl, Fe(CO)₅. X-ray diffraction and XPS spectroscopy were used to study the structure of the epitaxial film. The results indicate that single crystal Fe film and iron oxide-iron-silicon multilayer structure can be grown on Si (100) substrate. We have also discussed the relation between microstructure and MOCVD process.