ICMCTF2003 Session HP: Symposium H Poster Session

Metal chloride complexes with primary and secondary phosphines have been used as single-source precursors for the deposition of metal phosphide thin films by CVD, as they promote the elimination of HCl e.g. TiCl_4.2CyPH₂ for deposition of TiP.¹ We are interested in the development of precursors for the deposition of germanium phosphides, whose properties remain largely unexplored, and have thus focussed on the synthesis of the corresponding germanium adducts. Thin films of germanium phosphides of varying stiochiometry have been produced from dual-source APCVD, using GeX4 (X = Cl, Br) and CyPH₂ as reagents. An excess of phosphine generates phosphorus-rich films (GeP₂), whereas an excess of the germanium precursor leads to germanium-rich films (Ge₂P). The adduct chemistry is not, however, simple and species such as GeCl_4.2CyPH₂ have not been isolated. Cy(H)PGeCl₃ is formed from CyPH₂ and GeCl4, but only when the metal chloride is in excess. Reaction of GeCl4 with either CyPH₂ or Ph2PH (1:1) in ether leads to the isolation of the rare primary and secondary phosphonium salts, [CyPH₃]+[GeCl₃]- or [Ph₂PH₂]+[GeCl₃]-.

¹T. S. Lewkebandara, J. W. Proscia, and C. H. Winter, Chem. Mater., 1995, 7, 1053.

The control of wettability of solid surfaces has attracted much attention due to its potential applications in various industrial fields. Wettability is governed by the two factors, that is, surface energy and morphology. It is important to provide water-repellency to polymeric substrates as well as other materials. In this paper, we report on the fabrication of polymeric substrates with ultra water-repellency. The water-repellency of the treated polymeric substrates is discussed in terms of their nanotextures and chemical compositions.

Ultra water-repellent polymeric substrates were fabricated by a two-step plasma process. First, polymeric substrates were treated with oxygen plasma in order to provide a proper nanotexture and to terminate the surfaces with proper functional groups. Subsequently, a hydrophobic layer was coated on the nanotextured polymer surfaces by plasma-enhanced CVD using tetramethylsilane or trimethylmethoxysilane as a source in order to reduce their surface energies. A capacitively-coupled RF discharge system was used for both the oxygen plasma treatment and the hydrophobic coating.

Polyethylene terephthalate and polycarbonate substrates modified by using oxygen plasma and TMS-coating were certainly ultra water-repellent, showing the water contact angle was greater than 150°. Optical transmittance of the modified substrates was over 90 % in the visible range.

Great efforts recently have led to the development of surface acoustic wave (SAW) devices that operate at high frequencies, present low insertion loss, and retain superior performance of previous SAW devices. The operation frequency of SAW device is limited mainly due to restrictions in the photolithographic process. ZnO multi-layers coupled with polycrystalline diamond have exhibited phase velocities as large as 10 km/s, which enables to fabricate high-frequency (> 1 GHz) SAW devices without requiring submicron process technologies. In addition, thin film AlN rather than diamond may practically be more advantageous for implementing such high frequency SAW devices, although its phase velocity (~ 6.33 km/s) is lower than that of diamond. This is due to its lower deposition temperature (< 300°C), compatibility with well-developed Si technologies, and controllable material properties. However, there have been few studies on the ZnO/AlN structure. Furthermore, no experimental results are reported in literature that regards the fabrication and characterization of SAW devices based on the ZnO/AlN multilayer.

In this work, high frequency SAW devices with an IDT/ZnO/AlN/Si configuration are fabricated and characterized. Especially, the effect of the AlN buffer layer on the orientation of ZnO films as well as the performance of ZnO/AlN-SAW devices is investigated. AlN films are deposited on Si (100) employing both plasma-assisted MBE and RF reactive sputtering. ZnO films are prepared using RF sputtering at a nominal condition of RF power = 100 W, O₂/(Ar+O₂) ratio = 10 %, and substrate temperature (T_sub) = 200°C. For deposited AlN and ZnO films, texture coefficient (TC) for (002)-orientation, crystallite size, and full width at half maximum (FWHM) for (002)-peak are estimated from XRD spectra, of which all results are characterized in terms of deposition conditions used for preparing AlN films. The ZnO film grown on AlN buffer layer which is prepared at RF power = 350 W, N₂/Ar ratio = 10/20, and T_sub= 250°C exhibits the highest TC value (~ 100 %). Surface morphology and RMS surface roughness of deposited ZnO films are also measured using field emission SEM and AFM. ZnO/AlN-SAW devices are fabricated using a lift-off method and their frequency response characteristics are examined in terms of deposition conditions for the AlN buffer. Fabricated ZnO/AlN-SAW devices with 1µmm width-IDTs exhibit phase velocity = 4.8 ~ 5.1 km/s (corresponding operation frequency = 1.0 ~ 1.2 GHz), insertion loss < 17 dB, and side-lobe rejection level > 35 dB.

A film bulk acoustic resonator (FBAR) has become one of the most promising components for the realization of microwave monolithic integrated circuits (MMICs) in high performance frequency control devices of a few GHz-band wireless communication systems. This is mainly due to its small size and high device performance. The most critical factor that determines the characteristics of the FBAR is the material property of piezoelectric thin films, which is directly related to the preferred orientation of deposited piezoelectric films. Among the recently-introduced piezoelectric thin films for FBAR devices, AlN is considered to have strong potential mainly due to its high bulk velocity (~ 10 km/s) and compatibility with standard Si technologies. In addition, for fabrication of FBAR devices, selection of bottom electrode metals is very essential for achieving a high-quality AlN film since the difference in lattice parameters and crystalline structures between the AlN film and the bottom electrode may significantly affect the growth behavior of grown AlN film. However, there have been no systematic studies regarding the influence of bottom electrode metals on properties of piezoelectric films and characteristics of FBARs.

The purpose of this research is to elucidate the effect of the bottom electrode in AlN-based FBARs on the crystal orientation of AlN films as well as the frequency response characteristic of FBAR devices. AlN films are deposited using RF sputtering on various metal substrates (bottom electrodes) including Al, Cu, Ti, and Mo. Crucial deposition parameters and their ranges used to prepare AlN film are as follows; RF power = 150 ~ 450 W, substrate temperature (T_sub) = RT ~ 550°C, and Ar/N₂ratio = 5/25 ~ 25/5. The crystal orientation, texture coefficient (TC) for (002)-orientation, crystallite size, surface morphologies, and RMS roughness of deposited AlN films are measured using XRD, field-emission SEM, and AFM techniques. These are characterized in terms of bottom electrodes. FBAR devices with Al/AlN/metal(Al, Cu, Ti, Mo) configuration are also fabricated and their frequency responses (S₁₁) are compared. It is found that the AlN film deposited on Mo substrate exhibits the highest TC value (~ 90 %) for (002)-orientation, the largest crystallite size (~ 42 nm), and the smallest surface roughness (~ 85 nm). The FBAR device using Mo electrode is also found to have a superior performance (return low ~ 15 dB at 3.05 GHz). It is concluded that the positive role of Mo-electrode for high-quality AlN and high peformance FBAR may be attributed to the smaller lattice mismatch between AlN film and Mo electrode.

Many studies have focused on high-speed recording in phase-change optical discs to increase the data transfer rate. In order to increase the data transfer rate of phase-change optical recording discs, a number of phase change materials with fast crystallization speed were developed and a complicated disc structure with additional interface layers to enhance the crystallization speed of the recording media was employed. Recently, it has been reported that a superlattice-like phase-change recording layer can be adopted within the phase change layer instead of the conventional single layer structure to accelerate the crystallization speed and enhance the structural stability of the phase-change layer. However, there has been no detailed report on the dependence of crystallization behaviors and optical constants of phase-change recording media on the superlattice-like structure.

In this work, the relationships between superlattice-like structure and crystallization behaviors of phase-change optical media were discussed. A superlattice-like phase-change recording layer of GeTe/Sb₂Te₃ was deposited using electron beam evaporator. The transmission electron microscopy (TEM) and glancing angle x-ray diffraction (GAXRD) were used to characterize the crystallization behaviors. Optical constants were also investigated by using spectroscopic ellipsometer and UV-VIS spectrometer.

Nano-sized monodispersed colloidal silica and polystyrene Latex with controlled sizes (100nm, 200nm, 300nm) have been prepared by Stüber process and emulsion polymerization. Shape and monodispersity of synthesized colloidal particles were observed by Scanning electron microscopy(SEM) and laser light scattering particle analyzer. These monodisperse colloidal particles readily self-assemble into robust two and three-dimensionally ordered crystalline colloidal arrays (CCAs) and CCAs is obtained by controlling the related experimental parameters for the assembly, including concentration of colloidal particles, pH of solution, volume ratio of solvent (water and ethanol).

We have determined a simple method for the fabrication of macroporous structures in the patterned templates using two different sites of monodispersed colloids. That is, utilizing capaillary forces and convective flux, ultrafine particles are directly used to assembly themselves in the voids of patterned template and macroporous structures can be produced after removing the particles. Scanning electron microscopy(SEM) of these materials illustrates hexagonally ordered packing of monodispersed spherical colloids in the patterned templates.

Electrical tunable dielectric devices rely on the variation of a ferroelectric materials dielectric constant with application of an electric field. The requirements of Ferroelectric materials are low dielectric constant, high tunability, low losses and low leakage current. We investigated on the structural, electrical properties of (Pb_{0.5√sub 0.5})TiO₃ thin films on the Al₂O₃ substrate prepared using Sol-Gel method. The dielectric measurements were conducted in the Coplanar Waveguide (CPW) configuration. From the XRD analysis, the peak in the XRD pattern of PST thin films on the Al₂ O₃ substrate was shown epitaxial growth. The low loss (~0.001) and high tunability (~60%) were obtained for (Pb_{0.5√sub 0.5})TiO₃ thin films on the Al₂ O₃ substrate measured at 1 GHz.

¹This work was supported by Korea Research Foundation Grant (KRF-2001-042-E00042).

Photochemical deposition is one of deposition technique of thin films, easily applicable to the deposition of oxides including some metals such as (Pb, La)(Zr, Ti) O₃. The photochemical deposition, unlike sol-gel procedure, is not based on chemical reaction including hydrolysis and condensation, but forms metallic state through the removal of organic ligands by exposure to UV. And this metal usually turns to oxide through the oxidation reaction with atmospheric oxygen during the exposure to UV. This technique is suitable for the control of stoichiometry and furthermore lithographically producing a pattern without the requirement of separated etching procedure

Homogeneous lanthanum doped lead zirconate titanate(PLZT) thin films were prepared by photochemical deposition technique. PLZT films were investigated to reduce the amount of oxygen vacancies in the films by doping a suitable amount of La ions and by optimizing the annealing conditions. Fourier transform infra-red (FT-IR) was used to monitor the photochemical reaction after exposure to UV of spin-coated PLZT films. Scanning electron microscopy was used to observe the image of self-patterned PLZT films. X-ray diffraction and ellipsometry were used to provide the information about the crystalline structure and thickness of the films after anneal. The effects of La doping on the microstructure and the ferroelectric properties of PLZT films were explained. Also, the electrical properties of the films were discussed with their physical-chemical properties.

There is an increased research activity to search appropriate thin film materials for dynamic random access memories and microwave dielectric applications. Among the various dielectric films, the BST thin film was noticed as the most promising material due to its high dielectric constant and paraelectricity at normal operating temperature. Although BST possesses a satisfactorily high dielectric constant, it was known that a post heat treatment at a high temperature was essential to obtain good electrical property. However, the heat treatment at high temperature can cause deleterious effects on an electrode, barrier metal, and contact plug. Strontium titanate (ST) is one of the few titanates, which is cubic at room temperature. But, the dielectric constant is lower than BST. The addition of lead into strontium titanate makes its dielectric constant higher and the temperature of crystallization lower. Therefore, PST thin film can be a promising material due to its high dielectric constant and paraelectricity at normal operating temperature. However, there is no report on the characteristics and mechanism of PST thin films during etching process. In this study, Inductively coupled plasma etching system was used for etching PST because of its high plasma density, low process pressure and easy control bias power. The etching characteristics of PST thin films were investigated in terms of etch rates and selectivity as a function of gas mixing ratio, rf power, dc bias voltage and chamber pressure. The Cl₂/Ar plasmas were characterized by optical emission spectroscopy (OES) and Langmuir probe analysis. The chemical states on the etched surface were investigated with x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS). Scanning electron microscopy (SEM) was used to investigate the etching profile.

¹This work was supported by Korea Research Foundation Grant (KRF-2001-042-E00042) .