Papers

ICMCTF2002 Session H2-1: Thin Films for Next Generation Devices

Tuesday, April 23, 2002 8:30 AM in Room Royal Palm 4-6

Tuesday Morning

Start	Invited?	Item
8:30 AM		H2-1-1 Ohmic Metallization Technology for Wide Band-Gap Semiconductors A.A. Iliadis, A. Inumpudi, L. Liu, R.D. Vispute, T. Venkatesan (University of Maryland); K.A. Jones (Army Research Laboratory) The development of high quality ohmic metallizations on wide band-gap semiconductors is of critical importance to the performance of high power, high temperature electronic and optoelectronic devices. In this work, ohmic contact formation on p-type 6H-SiC and n-type ZnO using a novel approach of focused ion beam (FIB) surface-modification and direct-write metal deposition, and the properties of such focused ion beam assisted "cold" non-annealed contacts will be reported. The process uses different doses of Ga focused ion beam to modify the surface by incorporating Ga ions within a shallow (30nm) surface layer, and then uses the Ga ion beam in-situ to break up a Pt-organometallic compound for the direct-write deposition of Pt on the modified surface. Contact resistance measurements by the transmission line method, produced values as low as 3x10^-4 Ω cm² without any annealing. An optimum Ga surface-modification dosage window is determined, within which the current transport mechanism of these contacts was found to proceed mainly by tunneling through the Pt-Ga-Semiconductor interface layer.
9:10 AM		H2-1-3 Ti-Cr-Al-O Thin Film Resistors A.F. Jankowski, J.P. Hayes (Lawrence Livermore National Laboratory) Thin films of Ti-Cr-Al-O are produced for use as a resistor material. The films are rf sputter deposited from ceramic targets using a reactive working gas mixture of Argon and Oxygen. Resistivity values from 10⁴ to 10¹⁰ Ohm-cm are measured for Ti-Cr-Al-O films less than 1µm thick. The film resistivity can be discretely selected through control of the target composition and the deposition parameters. The application of Ti-Cr-Al-O as a thin film resistor is found to be thermodynamically stable, unlike other metal-oxide films. The Ti-Cr-Al-O film can be used as a vertical resistor, for example, as a layer beneath a field emission cathode in a flat panel display. Also, it can be used as a lateral resistor to control surface emissivity, for example, as a coating on an insulating material such as a vertical wall support in flat panel displays.
9:30 AM		H2-1-4 Characterizations of Organic Thin Film Transistors Fabricated on SiN_x Films by Non-photolithographic Processes M.H. Choo, S. Im (Yonsei University, Korea) We report on the electrical characteristics of organic pentacene TFTs fabricated on SiNx films. The pentacene thin films were deposited on 250 nm thick-SiNx layers by thermal evaporation at various temperatures. The nitride had been formed on p-Si by PECVD. Source and drain contact were made by Au evaporation. All the processes were non-photolithographic employing two shadow masks for TFT-patterning. The width and length of the TFT were 500 µm and 55 µm, respectively. The on/off ratio of the TFT was about 10⁵ and maximum saturation current, I_D was as high as about 1 µmA at the drain bias of -20V and at the gate bias of -40V. >From √(-I_D)-V_G characteristics, the field effect mobility of about 0.023 cm²/V-s and the threshold voltage of about -22V were obtained at V_D=-20V. The subthreshold slope was estimated to be about 3.8V/decade. In the present study three different types of TFTs were prepared to be compared one another; symmetric bottom-contacted, symmetric top-contacted, and asymmetric top-contacted. Among three types, the asymmetric top-contacted TFT exhibited the most excellent behavior and it will be discussed in detail.
9:50 AM		H2-1-5 Growth and Properties of Titania Thin Films Obtained by Magnetron Sputtering D. Kuo, K. Tzeng (National Dong Hwa University, Taiwan, ROC) Amorphous titania thin films were prepared on glass and silicon substrates by magnetron sputtering. These films were studied by choosing different substrate temperatures, rf powers, and annealing temperatures. The as-deposited films had high dielectric constants of 100-500 and high dielectric losses. The dielectric properties of annealed titania films depended on the deposition temperature, rf growth power, and annealing temperature. Titania films with high dielectric constants and low losses was obtained at 200° and 150 watts w/o low annealing temperatures. Mechanical properties, e.g. hardness, internal stress, and adhesion, of the titania films were evaluated. Optical properties, e.g. refractive index and optical transmittance, were also measured.
10:30 AM		H2-1-7 Ohmic Metallization of n-Type GaN N. Mohammed (Howard University)
11:10 AM		H2-1-9 Ionized Physical Vapor Deposition of TiN Barrier Layers with the Presence of Metal-Organic Precursors: Chemical Enhanced Physical Vapor Deposition (CEPVD) Ning Li, J.P. Allain, D.N. Ruzic (University of Illinois, Urbana-Champaign) TiN films have been mainly used as the diffusion barrier layers between Al or W with Si in ultra-large scale integrated (ULSI) devices. High aspect ratio trenches with sub-half-micron dimensions can be covered conformally by means of chemical vapor deposition (CVD). However ionized physical vapor deposition (IPVD) is able to produce TiN films of low resistivity and dense textures which are essential in reducing electromigration. A Ti target is sputtered by inert gas (Ar) and reactive gas (N2) in combination with a secondary inductively coupled plasma (ICP). A proper dose of metal-organic precursor gas (TDMAT) with a reactive (N2) carrier gas added to the region of the plasma sheath can partially interact with the accelerated metal ions and take advantages of both IPVD and CVD parameter regimes. Energetic ion bombardment promotes the film adhesion and purity as well as generates films of stable crystallographic orientation at a low substrate temperature. In addition precursor molecules gain energy through collisions with ion flux and dissociate at a lower temperature. Both liners and films are produced on Silicon wafers at different TDMAT and carrier gas flow rate, rf incident powers, bias voltage and substrate temperatures. Resistivity is evaluated by a four-point probe. Deposition rate and ionization fraction are measured in a gridded energy analyzer and a quartz crystal microbalance (QCM). SEM pictures visualize the surface structure of the films and liners. Film composition and microstructure are characterized by XPS and XRD, respectively. TEM are used to examine the cross-section properties of the liner.
11:30 AM		H2-1-10 Radiation Effect of Vacuum Ultraviolet from H₂ and O₂ Plasmas on SiO₂ Aerogel Film S-B. Jung, H-H. Park (Yonsei University, Korea) The decrease in device feature size leads to keep on investigating low-k material for interlayer dielectric. SiO₂ aerogel film has been drawn attention as an excellent candidate due to its ultra low dielectric constant. To meet the process requirement for integration, especially etching, the behavior of SiO₂ aerogel film exposed to plasma should be investigated. In plasma, chemical reaction, reactive ion bombardment, and radiation of vacuum ultraviolet (VUV) occurred. There have a few studies on the etching and plasma treatment of SiO₂ aerogel film, however, till now the sole role of VUV radiation on SiO₂ aerogel film has not been fully studied.In this work, the radiation effect of VUV on SiO₂ aerogel film has been investigated. The plasma sources used in this study were H₂ and O₂. For these experiments, lithium fluoride single crystal with a cutoff wavelength of 104 nm was used for the control of chemical reaction and reactive ion bombardment effects on SiO₂ aerogel film. As a comparison, SiO₂ aerogel films could be exposed to VUV and plasma, respectively. X-ray photoelectron spectroscopy and Fourier transform infrared analyses were performed to characterize the bonding states. The micro-structural behavior was monitored using scanning electron microscope.
11:50 AM		H2-1-11 Investigations of Non-selective and Inverse-selective Process on Cu Damascene CMP in Colloidal Silica-based Slurry Y.L. Wang (Taiwan Semiconductor Manufacturing Company, Taiwan, ROC); S.-Y. Chiu (National Chiao Tung University, Taiwan, ROC); T.-C. Wang (Taiwan Semiconductor Manufacturing Company, Taiwan, ROC); K.Y. Lo (National Chiyi University, Taiwan, ROC) The damascene process is regarded to be an essential and critical step for producing fine Cu lines, and the chemical mechanical polishing of copper and barrier metals is the key to establishing this process. In Cu damascene CMP process, the first step were designed and optimized for polishing copper and stops on barrier. Additionally, the second step removes the barrier metal and buffs the oxide to compensate for dishing and erosion. In order to provide damascene metal lines with high accuracy and at a high yield, the optimization of chemical characteristics of slurries and the CMP conditions have been investigated for achieving a large removal rate while suppressing dishing and erosion. From our preliminary investigations on the polishing behavior of Cu, Ta, and oxide thin film, non-selective and inverse-selective slurries are carried out for 2-step Cu damascene CMP by adding proper additives in colloidal silica based slurries. Therefore, the four phenomena that determine the usefulness of the CMP process-non-uniformity, rounding, metal dishing and oxide erosion- have been characterized for various pattern geometry on the planarization of the step height in the field area, the decision of the end-point for the first step and the removal selectivity of Cu/Ta/Ox for the second step by using noval formulated colloidal silica based slurries.