ICMCTF1998 Session H2: Advanced Dielectrics and Planarization: Materials and Processes

Thursday, April 30, 1998 8:30 AM in Sunrise Room

Thursday Morning

Start	Invited?	Item
8:30 AM	Invited	H2-1 Optimisation of Low Dielectric Constant Flowfill Layers for Advanced Intermetal Applications. S. McClatchie, K. Beekmann, A. Kiermasz (Trikon Technologies Ltd, United Kingdom) It has been shown previously that low dielectric constant insulating layers can be deposited using a process technology known as "Low-k Flowfill". This process uses a chemical vapour deposition (CVD) reaction between methyl-silane (CH₃-SiH₃) and hydrogen peroxide (H₂O₂) to form a methyl doped silicon oxide. Layers deposited using this technique exhibit a dielectric constant < 3.0 and remain stable upon annealing at temperatures of up to 500 degrees Celsius. The layers also exhibit excellent gap-filling capabilities, being able to completely fill 0.1 micron features with up to 4 to 1 aspect ratios. This paper considers the application of the Low-k Flowfill material as an intermetal dielectric, and examines some of the integration issues raised. Future device technologies may require dielectric constants lower than those achieved using the methyl-silane/hydrogen peroxide chemistry to date. In order to meet these requirements the possibility of enhancing the basic methyl-silane/hydrogen peroxide chemistry, to achieve dielectric constants < 2.5, is described.
9:10 AM		H2-3 The Effects of Plasma Treatment for Low Dielectric Constant Hydrogen Silsesquioxane (HSQ) T.C. Chang (National Nano Device Laboratory, ROC.); B.T. Liu, Y.J. Mei, C.-C. Chang (National Chiao Tung University, ROC); W. Wu, M.-S. Tsai, B.T. Dai (National Nano Device Laboratory, ROC); F.M. Pan (National Nano Device Laboratory, ROC.) Low density material such as hydrogen silsesquioxane (HSQ) can offer lower dielectric constant. With HSQ, a low value of K can be achieved if the density of Si-H bonds is maintained at a high level and the formation of -OH bonds and absorption or creation of water in the film is minimized. In this work , we study the hydrogen plasma to improve the quality of HSQ. In addition, the effect of N₂ and O₂ plasma post-treatment are investigated The leakage current of HSQ decreases with increasing the H₂ plasma treatment time. However, the leakage current of HSQ decreases with increasing the N₂ and O₂ plasma treatment time. A model is proposed to explain the role of hydrogen in the HSQ. The role of hydrogen to the low dielectric HSQ is to passivate the surface of porous HSQ. If the surface is not passivated by hydrogen, much of those dangling bonds will remain on the surface. Dangling bonds can easily absorb moisture and form -OH bonds which will result in increasing the dielectric constant. In addition, the dangling bonds will increase leakage current. Both H₂ annealing and H₂ plasma treatment are provide hydrogen to passivate the surface and to reduce the dangling bonds. On the other hand, the N₂ and O₂ plasma treatment will reduce the hydrogen passivation of HSQ. As a result, both the leakage current and dielectric constant increase with increasing the N₂ and O₂ plasma treatment time.
9:30 AM		H2-4 Enhancing the Thermal Stability of Low Dielectric Constant Hydrogen Silsesquioxane (HSQ) by Ion Implantation Y.J. Mei (National Chaio Tung University, ROC); M.F. Chou, C.-C. Chang (National Chiao Tung University, ROC); T.C. Chang, J.S. Tsang, M.-S. Tsai, W. Wu (National Nano Device Laboratory, ROC); W. Lur (United Microelectronics Corp., ROC); F.Y. Shih, H. Huang (Dow Corning Taiwan Inc., ROC) A continuous reduction in chip size and increase in chip complexity is shifting the interconnection technology towards multilevel metallization. However, RC delay contributed from multilevel interconnect becomes important issue to limit performance of VLSI. A lower dielectric constant insulator is needed to counter the problems of parastic capacitance delays and cross talk across layers. Low density material such as hydrogen silsesquioxane (HSQ) can offer lower dielectric constant. However, the thermal stability is not good for HSQ. In addition, fluorine doping of oxide (SiOF) has been found to lower the dielectric constant of the thin films. Therefor, the fluorine play an important role in silicon oxide based low-k material In this work , we study the F implantation to improve the thermal stability of HSQ. The thermal stability of as-cured HSQ is about 400^OC. Both leakage current and dielectric constant of HSQ rapidly increase with increasing the annealing temperature. On the other hand, the leakage current of F-implanted HSQ reduces with increasing the annealing temperature. The dielectric constant of F-implanted HSQ keep almost constant. The thermal stability of HSQ is enhanced to as high as 500^OC by F ion implantation. A model is proposed to explain the effect of F-implantation in the HSQ.
9:50 AM		H2-5 Uncooled Thin Film Infrared Imaging Device with Aerogel Thermal Isolation: Deposition and Planarization Techniques J.A. Ruffner, P.G. Clem, B.A. Tuttle, C.J. Brinker, C.S. Sriram, R.W. Schwartz, W.L. Warren (Sandia National Laboratories); J.A. Bullington (AMMPEC) We have successfully integrated a thermally insulating silica aerogel thin film into a new uncooled monolithic thin film infrared imaging device. Compared to other technologies (e.g. microbridge), use of an aerogel layer provides superior thermal isolation of the pyroelectric imaging element from the relatively massive heat sinking integrated circuit. This results in significantly higher thermal and temporal resolutions. We have calculated noise equivalent temperature differences ranging from 0.04 to 0.10 °C based on pyroelectric coefficients measured from a variety of PLZT compositions used as pyroelectric imaging elements in monolithic structures. In addition, use of aerogels results in an easier, less expensive fabrication process and a more robust device. Fabrication of these monolithic devices entails a number of deposition processes including ambient temperature/pressure sol-gel deposition of the aerogel, sputter deposition of the electrodes, and solution chemistry deposition of the PLZT imaging elements. Uniform pyroelectric response is achieved across the device by use of appropriate planarization techniques involving the aerogel, electrode, and imaging element layers. These deposition and planarization techniques are described. In addition, characterization of the individual layers and monolithic structure using scanning electron microscopy, atomic force microscopy, thermal conductivity measurements and Byer- Roundy techniques is discussed. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000.
10:30 AM	Invited	H2-7 Precursor Selection for Plasma Deposited Fluorinate Amorphous Carbon Films T.W. Mountsier, J.A. Samuels (Novellus Systems, Inc.) PECVD Fluorinated amorphous carbon (FIAC) has shown promise as a low-k, intermetal dielectric (IMD) material. It has been demonstrated that electrical, thermal, and mechanical performance may be tailored by adjusting the amount of fluorine present in the film. There are a wide variety of fluorocarbon precursors available for the deposition of these films, each with a characteristic fluorine:carbon ratio. Additionally, hydrogen and/or various hydrocarbons can be included to lower the effective F:C ratio. The resulting film fluorine content is almost entirely dependent on this input chemistry. In this study, we examine films deposited from a number of different input chemistries; with F:C ratios ranging from 3:1 down below 1:1. The properties of FlAC depend strongly on the amount of fluorine present in the film. In general, films with lower fluorine content exhibit better thermal stability and mechanical strength, but tend to be higher in dielectric constant and give greater current leakage. We also found film performance to be influenced by deposition temperature, particularly thermal stability. The best case films were deposited at high temperature (400°C) such that they could withstand prolonged exposure to high temperature. Fluorine content was low (<45 atomic %) and the dielectric constant ranged from 2.7 to 2.9. Characterization was not limited to the FlAC material itself, but also included interactions with other dielectric films (e.g., amorphous carbon, silicon nitride, silicon dioxide, and silicon carbide).
11:10 AM		H2-9 Properties of Low Dielectric Constant Fluorinated SiO₂ Films Prepared by Plasma Enhanced Chemical Vapor Deposition K.H. Kim (Louisiana State University); D.H. Kwon (Kyungil University, South Korea); G.S. Lee (Louisiana State University) The chemical and electrical properties of fluorinated silicon oxide films prepared by plasma enhanced chemical vapor deposition at 180C were studied. The deposition of these films was made by flowing 0-48 sccm of CF₄ as the fluorine source into the deposition process of silicon oxide films using 2 sccm of Si₂H₆ and 100 sccm of N₂O. It was observed that the deposition rate of these films decreased as the fluorine concentration increased; meanwhile, the P-etch rate of these films increased as the fluorine concentration increased. It was also observed that the thickness of the films without fluorine slightly decreased with post- deposition anneal; meanwhile, the thickness slightly increased with the addition of fluorine. The FTIR spectroscopy showed that the characteristic peak around 940 cm^-1 due to the Si-F stretching bonds became bigger as the fluorine concentration increased. The FTIR spectroscopy also showed that the Si-O stretching frequency increased but its full width at half maximum decreased as the CF₄ concentration increased. The high frequency C-V measurements on the MOS capacitors fabricated with these films showed that the relative dielectric constant decreased from 4.13 to 3.52 as the fluorine concentration increased from 0 to 48 sccm. The I-V measurements on the MOS capacitors showed that the leakage current density of the films decreased as the fluorine concentration increased. The effective oxide charge density as well as the result of the dielectric breakdown measurements of the films will be also discussed.
11:30 AM		H2-10 Process Development for PECVD High Temperature Nitride and Delta Nitride Films M. Mudholkar, M. Deshpande, J.H. Huang, S. Raoux, D. Silvetti, D. Cheung (Applied Materials Inc.) In this paper we discuss the application of DxZ+ reactor to plasma enhanced CVD processes including high temperature nitride and dual frequency delta nitride films. The DxZ+ chamber offers unique advantages over conventional DxZ chamber in terms of its high temperature processing ability and bottom power dual frequency configuration, employing an embedded RF electrode. The high temperature nitride film is intended for PMD barrier layer and spacer applications. The DxZ+ plasma process offers unique CVD capability with wide process window, good film uniformity and low hydrogen content. Recent process developments and results from a 5000 wafer burn-in will be discussed. Recent advances in dual frequency delta nitride process using bottom power DxZ+ will be elaborated. The bottom bias provides precise control over the ion energy, allowing independent control of process parameters for good step coverage, excellent conformality, pinhole performance and sidewall integrity.
11:50 AM		H2-11 High Temperature Sub-atmospheric CVD Ozone/TEOS Process Characterization for Shallow Trench Isolation Application L.-Q. Xia, S. Nemani, S. Pichai, S. Chandran, F. Campana, E. Yieh (Applied Materials, Inc.) Shallow Trench Isolation (STI) has recently gained extensive attention in advanced VLSI device fabrication to replace traditional local oxidation of silicon (LOCOS) for device dimension below 0.25 μm. Among all different candidates, USG (Undoped Silicon Glass) process using TEOS/Ozone chemistry has been proven to yield void free trench fill due to its flow like gap fill capability. However, the current USG process deposited at low temperature (< 400⁰C) has the intrinsic drawback of (1) low film density, which requires extra furnace anneal after deposition and may potentially cause voiding inside the trench due to film shrinkage; (2) surface sensitivity, which exhibits strong dependence of film properties on substrate structure. Therefore process improvements are necessary to develop a high quality film to meet the STI trench fill requirements. In this study, we report a complete characterization for high temperature USG process, aiming at providing a solution for STI trench isolation. The experiments were conducted in Applied Materials Centura^TM SACVD Gigafill chamber, which is capable of high temperature TOES/O³ deposition. The significance of various process parameters was extensively studied, including deposition temperature, chamber pressure and gas flows. It is found that the USG film properties as well as gap fill capability can be greatly enhanced at high deposition temperature (>550⁰C). No void opens up for 0.18μm gap size at 3:1 aspect ratio even after high temperature anneal and harsh acid decoration. Upon variation of O³ to TEOS ratio, the surface sensitivity could also be reduced dramatically. No additional surface treatment and/or deposition is necessary. In conclusion, our study indicates that O³/TEOS process can be optimized for void free gap fill, CMP compatibility and strong etch resistance for STI application.
12:10 PM		H2-12 MOS Capacitor Characteristics of Plasma Oxide on Partially Strained SiGeC Films S.K. Ray (Indian Institute of Technology, India); L.K. Bera (Indian Institute of Technology, India); S. John (The University of Texas, Austin); C.K. Maiti (Indian Institute of Technology, India); S.K. Banerjee (The University of Texas, Austin) The band alignment and the valence band offset in partially strained Si_1-x-yGe_xC_y alloy are favorable for novel PMOSFET/MODFET applications, as it reduces the possiblity of process induced strain relaxation, while confining the holes in the valence band quantum well. However, the conventional thermal oxidation of the alloy gives rise to selective oxidation of Si, resulting in Ge pile up at the oxide-semiconductor interface. The electrical and interfacial properties of a low temperature (below 200⁰C) microwave plasma grown oxides on partially strain-compensated Si_1-x-yGe_xC_y (Ge:C = 20:1 and 40:1) with and without a Si cap layer is presented. The epitaxial layers of Si_1-x-yGe_xC_y were grown by UHVCVD on an epitaxial Si-buffer layer at 550^OC using SiH₄, GeH₄ and Ch₃SiH₃. High resolution X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy and atomic force microscopy (AFM), have shown the growth of strain-compensated epitaxial layer with C incorporated in the substitutional sites. Oxide films were grown in an oxygen plasma (700 W, 2.45 GHz) at a pressure of 1.0 Torr with 12 sccm O₂ flow for 2 minutes, resulting in a film thickness of 70-80Å without any Ge segregation. Electrical properties of the grown oxides were studied through Al-gate MOS capacitance-voltage (C-V), conductance-voltage (G-V), current voltage (I-V) and constant current stressing characteristics. Well-behaved C-V characteristics are observed even for uncapped capacitors with high C(1%) content. Fixed oxide charge density and mid-gap interface trap density are found to be 2.9x10¹¹/cm² and 8.8x10¹¹/cm²/eV, respectively for directly oxidized Si_0.79Ge_0.2C_0.01 film. The oxide on samples with low C (0.5%) concentration exhibits hole trapping, whereas electron trapping is observed for oxides on alloys containing 1%C. Oxides grown directly on the 1%C alloy exhibit reduced fixed oxide charge density, electron trapping and stress-induced charge build-up compared to that on a Si-capped sample with the same C concentration. However, the interface trap density and leakage current density are found to be lower for Si-capped samples.