Papers

ICMCTF2002 Session F5-1: Characterization of Thin Film Growth Mechanism and Evolving Film Properties

Thursday, April 25, 2002 8:30 AM in Room San Diego

Thursday Morning

Start	Invited?	Item
8:30 AM		F5-1-1 Production of AlN on Al Substrates B. Ruiz, U. Figueroa (ITESM-CEM, Mexico); S. Rodriguez (Escuela Superior Militar de Ingenieria, Mexico); O. Salas (ITESM, Mexico on sabbatical to Colorado School of Mines); J. Oseguera (ITESM-CEM, MEXICO) A method has been developed to produce AlN on Al substrates. The approach includes an initial cleaning stage to eliminate the impervious alumina layer from the substrate surface and then an ion nitriding treatment which is performed at a temperature close to the melting point of the substrate. A critical factor during the process is the oxygen partial pressure which has to be kept to a minimum. The treated samples were characterized by scanning electron microscopy + EDS and by x-ray diffraction.
8:50 AM		F5-1-2 Electrical Properties of Metal-Ferroelectric-Insulator-Semiconductor(MFIS) Using Sol-gel Derived SrBi₂Ta₂O₉ Film and Ultra-thin Si₃N₄ Buffer Layer C.H. Huang (National Chiao Tung University, Taiwan, ROC); T.Y. Tseng (National Chiao Tung University, Taiwan); C.H. Chien, M.J. Yang, C.C. Leu (National Nano Device Laboratories, Taiwan, ROC); T.C. Chang (National Sun Yat-Sen University, Taiwan, ROC); P.T. Liu (National Nano Device Laboratory, Taiwan, ROC); T.Y. Huang (Department Of Electronics Engineering, Taiwan, ROC); X.C. Lian (National Sun Yat-Sen University, Taiwan, ROC) The electrical properties of the MFIS memories with stacked gate configuration of ferroelectric Pt/SrBi₂Ta₂O₉/Si₃N₄/p-Si(100) were investigated. 245nm-thick SBT thin films were spin-coated on the SiN/Si substrate followed by 1 min. rapid thermal crystallization annealing at the temperatures regime of 700~800°C. In an attempt to operate memory at low voltage with sufficient large memory window, various ultra thin Si₃N₄ buffer layers in thickness of 3.5, 2, and 0.9nm were employed. SiN buffer layers were deposited by means of LPCVD with the exception of surface nitridation for 0.9nm SiN thin film. >From the results of C-V measurements, the memory window can be as large as 1V at the bias amplitude of 5 V without optimization for the sample with 0.9 nm SiN buffer layer. Complete perovskite crystalline structure can also be affirmed by the spectra of X-ray Diffraction measurements. The leakage current, which plays an very important role in the data retention, of Pt/SBT(245nm)/ Si₃N₄(0.9nm)/p-Si(100) is as low as 1.2 x 10^-7 A/cm2 at 100kV/cm. Optimization and scaling of SBT thin films are believed to be effective in pursuing extremely low voltage operation, high-density and liable 1T nonvolatile ferroelectric random access memories.
9:10 AM		F5-1-3 Deposition of Oxides Using a Novel rf- Wave Resonance Plasma Source L. Kleinen, J. Degenhardt, H.J. Steffen, M. Weiler (CCR Technology, Germany) Plasma assisted vapor deposition is a very promising tool for high rate, low temperature deposition of oxide and nitride layers, even on temperature sensitive substrates like polymers. Using a wave resonant excitation mechanism in an inductively coupled rf-discharge by superimposing a weak magnetic field in the range of 1-2 mT has been proven to be a very efficient technique in the oxidation of metal chlorides like titanium (IV) chloride (TiCl₄) and metal organic precursors like hexamethyldisiloxane (HMDSO) to form the respective metal oxides. Due to the high degree of dissociation of 80%, and a degree of ionization of 20% accompanied by plasma densities of up to 10¹³ per cm³, a very efficient activation of the precursor molecules is achieved. In the current study, the plasma parameters during deposition were correlated with the properties of the layers, i.e. stress, optical properties and mass composition. These investigations were carried out for several different precursor molecules. It was shown that the plasma assisted oxidation of vaporized precursors leads to almost stress free oxide films which are fully oxidized and have excellent optical properties. Deposition rates of up to 5 nm/s were achieved. Also, the plasma species during deposition were analyzed using optical emission spectroscopy. This analytical method yields important information on the layer forming plasma particle flux. This information can also be correlated with the film properties.
9:30 AM		F5-1-4 Amorphous and Crystalline W-N Thin Films Prepared by rf Sputtering Peichuen Jiang, J.S. Chen (National Cheng Kung University, Taiwan, ROC) W-N films have been deposited by reactive rf (radio frequency) sputtering from a tungsten target in an Ar-N₂ gas mixture. The microstructure, chemical bonding state, composition and electrical resistivity of the films are investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and four-point probe. The electrical resistivity of W-N films increases, while the deposition rate decreases, when the nitrogen partial flow rate increases. Crystalline W₂N phase is obtained with ~25% of N₂ partial flow rate. XRD reveals amorphous character for the W-N films sputtered at low (<10%) or high (>50%) N₂ partial flow rates. XPS and AES analyses indicate that the W 4f bonding state and the film composition vary with increasing N₂ partial flow rate. By reducing the sputtering power, we have found that a lower N₂ flow is required to obtain the W-N films with equivalent resistivity and microstructure to that of W-N films sputtered with high power. The growth mechanism responsible for the amorphous-crystalline-amorphous structural transition of the sputtered W-N thin films will be discussed.
9:50 AM		F5-1-5 Microwave Plasma Oxidation of Thin Aluminium Layers: Determination of Diffusion Coefficient and Sputter Coefficient A. Quade, H. Steffen, R. Hippler, H. Wulff (University of Greifswald, Germany) A new method is presented to characterize the film growth mechanism of the oxidation process of thin aluminium films activated by a microwave plasma. The oxide formation involves a diffusion and sputter process. The oxidation was investigated in a 2.45 GHz microwave discharge (SLAN) under different plasma parameters, for example, microwave power and gas type. A quantitative determination of the part of activated oxygen species in the different gas-mixtures by means of a potentiometric solid-state electrolyte cell was used successfully. The Al-layers were plasma treated up to 9 hrs with interruptions every hour. After every hour samples were characterized by means of GIXR and GIXRD. For the quantitative description of the growing alumina layer the total film thickness (GIXR) and the peak integral intensity of Al(111) reflection (GIXRD) were measured time-controlled. A mathematical model based on FickÂ´s second law was developed to determine the diffusion coefficient D and the sputter coefficient S. The stoichiometric composition of the oxidized coatings were investigated by XPS and FTIR. From the temperature dependence of D between 423 K and 573 K the activation energies of the diffusion process for different plasma powers were calculated. This study integrates into the complex and difficult topic of mechanism of plasma-wall-interaction.
10:30 AM		F5-1-7 The Influence of pH on the Growth Morphology of (Ba, Sr)TiO₃ Thin Films prepared by Sol-gel Technique Seema Agarwal, G.L. Sharma (Indian Institute of Technology Delhi, India) Nanocrystalline (Ba, Sr)TiO₃ (BST)thin films were prepared by sol-gel technique using titanium isopropoxide and 2-ethyl hexonate precursors for barium and strontium. The pH value of the solution was adjusted by adding ammonium hydroxide. The films were prepared at 7.4, 9.0 and 9.5 pH values and sintered at 700Â°C for one hour in air. The grazing angle x-ray diffraction (XRD) of the these films taken in the range of 20-60° reveals the formation of nanocrystallites. The orientation of the crystallites in the film changes with the increasing pH value of the solution. While the intensity of all the observed peaks increases as we go from low to high pH value, the increase of (110) peak intensity is very prominent. The Atomic force microscopy (AFM) studies of theses films indicate a decrease in the grain size with increase in pH. It can be concluded that the pH value of the spinning solution has a very significant role on the growth of BST thin films by sol-gel technique.
10:50 AM		F5-1-8 Structure of Sputtered Silicon Suboxide Single- and Multi-Layers N. Tomozeiu (University of Utrecht, The Nertherlands); E.E.van Faassen, W.M. Arnoldbik, A.M. Vredenberg, F.H.P.M. Habraken (University of Utrecht, The Netherlands) Incorporation of oxygen atoms in the silicon matrix has a great influence on the physical properties of the obtained material. Photoemissions studies [1] on evaporated SiO_x have shown that for x>1.3 the distribution of Siⁿ⁺ (0x layers, obtained by sputter deposition in an Ar-O₂ mixture the structure for x<1.2 is best described by a random bonding distribution of Si-Si and Si-O bonds. Using a-SiO₂/a-Si multilayer structures, we have tried to simulate a two phases model. All samples have the same total thickness (250 nm) and the thickness/layer is between 2 nm and 126 nm. The thickness and composition of all structures have been verified by high resolution RBS. Decreasing the thickness of the individual layers, the IR spectrum of the Si-O-Si stretching vibration mode changes drastically in peak characteristics (shape, width and position). The fit of the IR spectra with two gaussians shows a SiO₂ contribution (peak position at 1068 cm-1) and another one at 1030 cm-1 , assigned to SiO_x from interfaces. Indeed, for the last contribution, a linear increase of the peak area with number of interfaces is observed. The density of paramagnetic centers amounts to about 10²⁰ cm^-3. A-Si dangling bonds defects are present in all samples. E' centers, specific for SiO₂ , were found in samples with thick SiO₂ layers, while samples with a layer thickness smaller than 16 nm, have a defect with g factor ranging between 2.002 and 2.004. We found that a two phases model with a-Si and/or SiO₂ clusters smaller than 3 nm can not be simulated via sputtering deposition, presumably because of the mixing during deposition by energetic particles or because of transient effects during deposition at the interfaces. [1] A.Barranco et al., J.Vac.Sci. Technol. A 19(1), 136 (2001)
11:10 AM		F5-1-9 The Role of Methyl Radicals in the Formation of (100) and (111) Oriented Diamond Films: FTIR Study. E Titus, M.K. Singh, K.N.N Unni, P.K Tyagi, D.S Misra (Indian Institute of Technology, Bombay, India) Optical applications of free-standing polycrystalline diamond wafers formed by Chemical Vapor Deposition (CVD) techniques are attractive owing to the wide range of transparency, hardness, chemical inertness and durability of diamond. Many efforts have been devoted and various models have been presented to explain the growth mechanism of diamond (100) and (111). To judge which model is correct requires experimental support. Here we have used FTIR technique in order to study the growth mechanism. Diamond films were formed on Si(100) substrates using Chemical Vapor Deposition (CVD Technique. Deposition was carried out with 0.8% CH4 in balance hydrogen at average substrate temperature of 880Â°C. Diamond films with dominant (100) texture were grown with a temperature gradient across the Si (100) substrates. The films grown at similar conditions but without temperature gradient across the substrates show (111) orientation. Chromium thin film was deposited as heater by thermal evaporation on the backside of the substrates for the generation of the gradient. FTIR studies show novel features in the films. Quantitative analysis was carried out to measure the H content in the films.
11:30 AM		F5-1-10 Influence of Particle Bombardment on the Growth of Calcium Phosphate (CaP) Coatings: Monte Carlo Simulations and Depositions Through an Aperture B. Feddes (University of Nijmegen, The Nertherlands); A.M. Vredenberg (University of Utrecht, The Netherlands); G.J.C. Wolke, J.A. Jansen (University of Nijmegen, The Netherlands) Calcium phosphate (CaP) coatings on implants are known to improve their biological performance. In previous work we showed that for RF magnetron sputter deposited coatings, the formation of an interface with a polymer is controlled by the bombardment of energetic particles. In this paper we investigate the type of particles and its influence on the interface and growing film. Coatings were deposited from a Ca₅(PO₄)₃OH target in 5.010^-4 - 5.010^-3 mbar Ar. Depositions through a small aperture were performed to produce an image that resembles the erosion profile of the sputtering target. Ca and P lateral profiles were determined using Rutherford Backscattering Spectrometry (RBS). In addition, the sputtering process was simulated using a monte carlo computer code, that calculates the trajectories of atoms and ions from target to substrate. From the measured and calculated lateral profiles at various pressures, it is concluded that the majority of Ca and P particles is deposited as neutrals. Further, we compared the amount of deposited Ca and P on the aperture to the amount deposited behind the aperture. On the aperture, 2-3 times less material is present. In addition, the Ca/P ratio is high (1.7 - 3.0) on the aperture, while it is low (0.6 - 1.2) behind it. Thus, the material behind the aperture seems to be protected against energetic particles, while on the aperture, material (preferentially P) is lost by sputtering. The rate with which material is sputtered away seems to correlate with the negative self bias of the target. Therefore, bombardment by accelerated ions (from target or plasma) seems to determine to a large extent the structure of the formed coating or interface. We found that depositions with and without aperture in combination with monte carlo simulations are a powerful tool to find the extent in which particle bombardment influences the growth of the coating or interface. In our case, the structure of the growing film is to a great extent determined by bombardment with ions coming from the target or plasma.
11:50 AM		F5-1-11 Investigation on Profile Distortion of Porous Silica after Photoresist Ashing Process T.C. Chang (National Sun Yat-Sen University, Taiwan, ROC); C.W. Chen (National Chiao Tung University, Taiwan, ROC); P.T. Liu (National Nano Device Laboratory, Taiwan, ROC); Y.S. Mor, T.M. Tsai (National Chiao Tung University, Taiwan, ROC); Y.J. Mei (Ching-Yun Institute of Technology, Taiwan, ROC); Y.T. Tseng (National Chiao Tung University, Taiwan, ROC) We have investigated the impact of O₂-plasma ashing on patterned porous silica (k=2.0). After the O₂-plasma ashing, we observed the pattern profile of porous silica was distorted. This is due to the oxidation of hydrophobic groups and formation of Si-OH bonds in the bulk. Silanol groups would attract each other and absorbed the polar moisture molecular through hydrogen bounding interaction. The silano groups on the surface of siloxane network give rise to surface distortions. The aim of perfect pattern transfer is not achieved while the profile was out of our desired pattern profiles. To confirm the mechanism of profile distortion, a varying temperature measurement of residue stress was carried out. Compared with as-cured film, the residue stress of O₂-ashing porous film increased significantly and an irreversible evolution of thermal stress appeared during the measurement cycle. Based on FTIR spectra analysis, this can be attributed to the moisture desorption and the gelation of Si-OH bounds.