Papers

AVS2001 Session PS2+TF+SE-TuA: PECVD/IPVD

Tuesday, October 30, 2001 2:00 PM in Room 104

Tuesday Afternoon

Start	Invited?	Item
2:00 PM		PS2+TF+SE-TuA-1 Mechanisms Involved in the PECVD of Thin Films in Low Pressure Organosilicon Plasmas A. Granier, A. Goullet, K Aumaille, G. Borvon (Institut des Matériaux Jean Rouxel, France); C. Vallee (LEMD, France); G. Turban (Institut des Matériaux Jean Rouxel, France) Low pressure organosilicon plasmas are widely used for the deposition of thin organic and inorganic films, used for their dielectric, optical and barrier properties. The organosilicon precursors such as tetraethoxysilane (TEOS), hexamethyldisiloxane (HMDSO) or tetramethylsilane (TMS) are used either pure or mixed with Ar, He, O₂ or N₂. The subject of this talk is to present the state of knowledge on the mechanisms involved in the low pressure (1 to 50 mTorr) organosilicon plasmas namely, both homogeneous and heterogeneous reactions. Since the data related to organosilicon reactions are relatively poor, information has to be deduced from experiments. Systematic plasma analyses have been carried out in low pressure RF inductively coupled TEOS and HMDSO based plasma by optical emission spectroscopy, Langmuir probes and mass spectrometry coupled with real time monitoring of the film growth by ellipsometry. It is deduced that electrons are more efficient than O atoms to break HMDSO and TEOS molecules. Organosilicon dissociation rates higher than 90% are easily reached. It is likely that the by-products of the electron impact dissociation are light H and CH₃ radicals and big fragments directly issued from the organosilicon molecule. On the other hand, in order to get better insight in heterogeneous reactions with O, H atoms, organosilicon film have been exposed to pure Ar, oxygen and hydrogen plasmas. It is demonstrated that oxygen atoms are very efficient to oxidize the organic part of the films, and that a 50 nm thick organosilicon film can be totally transformed into a porous silica film, upon exposition to an oxygen plasma.
2:40 PM		PS2+TF+SE-TuA-3 Electron Cyclotron Resonance Plasma Enhanced Chemical Vapor Deposition (ECR-PECVD) of ZrO₂ on Silicon B.O. Cho, J. Wang, S.X. Lao, J.P. Chang (University of California, Los Angeles) ZrO₂ is one of the most promising high dielectric constant (k) materials to replace SiO₂ in ultra large scale integration chip fabrication because of its wide band gap and low leakage current level. We developed an ECR-PECVD process to deposit ZrO₂ with zirconium tetra-tert-butoxide (Zr(OC₄H₉)₄) as an organometallic precursor, Ar as a carrier of the precursor vapor, and O₂ as an oxidant. Quadrupole mass spectroscopy, optical emission spectroscopy (OES), and Langmuir probe were used to characterize the plasma. The mechanisms of precursor decomposition and oxidation reactions including Zr-ligand bond dissociation and ZrO formation were investigated by analyzing the radical appearance potentials. The decomposition and oxidation reactions in the plasma were mainly controlled by the flow rate ratio of O₂ to Ar (O₂/Ar), varying between 0 and 10, and the electron temperature of 2-8 eV with the typical value of 3-4 eV. The OES intensity ratio of C₂ at 516.52 nm to O at 777.42 nm linearly scaled with the incorporated carbon concentration in the deposited film, which were determined by x-ray photoelectron spectroscopy and secondary ion mass spectroscopy. Since carbon incorporation greatly influenced the electrical performance of the film, low carbon-content, stoichiometric, and amorphous ZrO₂ was obtained at O₂/Ar>1 without substrate heating. We also deposited the film at elevated substrate temperatures around 400 °C with the controlled substrate bias to obtain carbon-free amorphous ZrO₂. The as-deposited ZrO₂ film between Al electrode and Si in capacitor devices showed good capacitance-voltage and current-voltage characteristics, which yielded k=22 and J=4x10^-5A/cm² at -1.5 V, respectively. Scanning electron micrograph (SEM) showed that highly conformal film deposition could be achieved over 300 nm diameter cylindrical memory structure with an aspect ratio of 4.
3:00 PM		PS2+TF+SE-TuA-4 Deposition of a-C:H Films: Plasma Chemistry and Material Properties J. Benedikt, K.G.Y. Letourneur (Eindhoven University of Technology, The Netherlands); M. Wisse (Free University, The Netherlands); D.C. Schram, M.C.M. van de Sanden (Eindhoven University of Technology, The Netherlands) Remote Ar-C₂H₂ plasma created by means of a cascaded arc is used for fast rate deposition of hard hydrogenated amorphous carbon films (a-C:H, rate up to 50 nm/s, hardness up to 14 GPa). First the densities of the radicals have been investigated in detail using cavity ring down absorption spectroscopy (CRDS). C₂, CH, C and H radicals were spectroscopically identified and measured as a function of C₂H₂ gas flow admixture. C₂H radical is still not spectrally resolved but broad band absorption observed around 250, 276 and 431 nm can be ascribed to this radical. The main mechanism of the dissociation of acetylene and other radicals in the plasma is a charge exchange reaction with argon ion and subsequent dissociative recombination of the molecular ion with an electron. Thus the composition of the plasma depends strongly on the amount of argon ions (and electrons) available in comparison with the amount of acetylene molecules injected. A plug-down model of plasma chemistry was made to simulate measured densities and to find creation channels of the different radicals. Second in-situ real time ellipsometry was used during deposition to measure the refractive index and the growth rate of the films. Clear correlation between plasma composition and the properties of the film was observed. Both the refractive index (which is in our case correlated with hardness) and the growth rate increase with increasing acetylene flow. The highest values are reached when the acetylene flow into the chamber is equal or higher than the argon ion flow emanating from the plasma source. In this case the C₂H radical is dominantly present in the plasma and is the main growth precursor of our films.
3:20 PM		PS2+TF+SE-TuA-5 Study of SiO_xN_y Films Deposited by Radio-Frequency Plasma Assisted Electron Cyclotron Resonance J.D. Brewer (University of North Carolina at Chapel Hill); A. Raveh (NRCN Division of Chemistry, Israel); E.A. Irene (University of North Carolina at Chapel Hill) New techniques for the development of higher dielectric constant materials as a passivation layer of silicon remains a challenge. To this end, a radio-frequency (RF) plasma process, in combination with an electron cyclotron resonance (ECR) plasma, was employed at low pressures (100-1000 mTorr) and low substrate temperatures (100-300°C) to grow silicon oxynitride thin films on p-type Si (100) wafers. N₂ and O₂ were used as gas sources to allow separate control of the amount of N and O ions and radicals, thus affording control of film stoichiometry. Films were produced with an ECR power of 300 W and an RF bias range of 0 to -80 V. The ability to tailor film properties such as; composition, interface states, morphology and structure was made possible by varying plasma processing parameters. Spectroscopic ellipsometry, atomic force microscopy, Auger electron spectroscopy, x-ray photoelectron spectroscopy and capacitance-voltage measurements were performed on the silicon oxynitride layers. The nitrogen to oxygen ratio in the silicon oxynitride films was found to depend on competitive processes between N⁺ and O^- species. Less negative voltages (> -20 V) produced a greater content of oxide due to a larger concentration of O^- ions, while more negative voltages (< -50 V) produced NO and N⁺ ions and radicals forming a greater content of nitride in the films. In addition, the effects of pressure, flow-rate ratio, time, temperature and ECR power on the fabricated film properties will be presented.
4:20 PM		PS2+TF+SE-TuA-8 An In Situ Study of the Interactions of Atomic Deuterium with Hydrogenated Amorphous Silicon Thin Films Using Multiple Total Reflection Fourier Transform Infrared Spectroscopy S. Agarwal (University of California, Santa Barbara); A. Takano (Fuji Electric Corporate Research and Development, Ltd., Japan); M.C.M. van de Sanden (Eindhoven University of Technology, The Netherlands); D. Maroudas, E.S. Aydil (University of California, Santa Barbara) Atomic hydrogen plays a crucial role in the deposition of amorphous hydrogenated silicon (a-Si:H) from silane containing discharges which are often diluted with hydrogen. However, during the deposition process the role of atomic hydrogen cannot be isolated from the other radicals impinging onto the surface. In order to isolate the effect of H atoms, as deposited a-Si:H films were exposed to a deuterium plasma and subsequent compositional and structural changes in the film were studied using in situ multiple total reflection Fourier transform infrared (MTR-FTIR) spectroscopy. The use of atomic deuterium generated by the plasma allowed us to observe both the abstraction-passivation reaction and the insertion reaction since the stretching modes of SiH_x (x = 1,2,3) and SiD_x (x = 1,2,3) appear at different wavenumbers. a-Si:H thin films were deposited in an inductively coupled plasma reactor at 200 °C. The deposited films were exposed to a series of one second deuterium plasma pulses at different substrate temperatures. In situ MTR-FTIR was used to observe the changes in the film after each pulse. Peak assignments were made and the IR data was deconvoluted for both the SiH_x and SiD_x part of the spectrum. Removal of surface hydrides is very fast and there is no activation barrier for the abstraction-passivation reaction in agreement with atomistic calculations of this barrier. The modification of the bulk film through abstraction and insertion reactions is limited by diffusion of D. Moreover, we find evidence for the presence of a thin sub-surface region (<30 Å) that has a higher concentration of silicon di- and trihydrides and strained silicon-silicon bonds. Insertion into the Si-SiH₂ bonds in this layer is faster than insertion into Si-SiH.
4:40 PM		PS2+TF+SE-TuA-9 A New and Fast In-situ Spectroscopic Infrared Absorption Measurement Technique for Submonolayer Detection at High Growth Rate M.F.A.M. van Hest, A. Klaver, M.C.M. van de Sanden (Eindhoven University of Technology, The Netherlands) Silicon oxide like films are deposited at high rate (up to 200 nm/s) using an expanding thermal plasma (Cascaded arc) in combination with hexamethyldisiloxane (HMDSO) and oxygen as deposition precursors. In general Fourier transform infrared (FTIR) reflection spectroscopy is a useful tool for in situ analysis of the film deposition growth process. However this technique is difficult to apply when the film deposition rate is reaching high values (10 to 100 nm/s). When studying submonolayer growth, the time resolution of a FTIR setup is too long (typical 0.1 - 1 s). So another technique has to be used to improve the time resolution. The heart of the new technique is a grating mounted on a laser scanner, which oscillates at a frequency of up to 300 Hz. Only a small part of the infrared spectrum will reach the detector (MCT). The rotation angle is limited and therefore the spectral bandwidth with respect to a FTIR spectroscope is small (200 cm^-1 at 1000 cm^-1), but the time resolution improved (1.7 to 10 ms). A cascaded arc is used as a light source, because if its high radiation temperature it produces more infrared light than a glowbar. To make submonolayer absorption detectable, single reflection is not sufficient; therefore attenuated total reflection (ATR) crystals are used as substrates. These crystals make multiple (50) interactions of the infrared beam with the depositing film possible, leading to a higher measured absorption. The set up will be presented in detail as well as the first results of the in situ study of the film growth of silicon oxide like films. Together with the in situ study also a plasma post treatment study has been performed. With this the resistance of the deposited films towards an argon/oxygen plasma has been studied. This study shows that the deposited films contain a significant amount of carbon, which can be removed by post treatment.
5:00 PM		PS2+TF+SE-TuA-10 Reaction Mechanism of PECVD to Produce Low Dielectric Constant Thin Films Y. Shimogaki (University of Tokyo, Japan) Ever growing device integration now requires low dielectric constant materials for inter metal dielectrics to improve speed performance of ULSIs. SiO:F (fluorinated silicon oxide) and a-C:F (amorphous fluoro carbon) films produced by PECVD are the major candidates for this purpose. In case of SiO:F film deposition from SiH₄/N₂O/CF₄, we found that fluorine addition to SiO₂ reduces Si-OH bonds which are the major dielectric component in SiO₂ films by PECVD. Fluorine addition also reduces growth rate and improved step coverage. We have examined the gas flow rate dependency of the growth rate by keeping the other process parameters constant. The growth rate of SiO:F film increased and the step coverage profile became poor by increasing gas flow rate. We have extracted suitable reaction kinetics to explain these phenomena. The reaction mechanism, which contains two major species in film deposition, obtained from this experimental approach well explained the step coverage behavior. In case of a-C:F film deposition from C₂F₄, the film growth rate decreased by increasing the gas flow rate. This is due to the gas phase reactions that produce main film precursors, like as CF₃⁺ ion and CF₂ radical. We also evaluated the contribution of ionic species and neutral radical species using step coverage into micron scale features. We found that radical species contributes to have uniform step coverage, but most of the film forming species are ionic ones and they contribute to make thermally stable films.