ICMCTF1998 Session H4: Silicides

Tuesday, April 28, 1998 8:30 AM in Sunrise Room

Tuesday Morning

Start	Invited?	Item
8:30 AM	Invited	H4-1 Advanced Salicides for 0.10 μm CMOS: Co Salicide Processes with Low Diode Leakage and Ti Salicide Processes with Direct Formation of Low Resistivity C54 TiSi₂ J.A. Kittl, Q.Z. Hong, H. Yang, N. Yu, S.B. Samavedam, M.A. Gribelyuk (Texas Instruments) The scaling of CMOS technologies to 0.10 μm and beyond imposes increasingly demanding constraints to self-aligned silicide (salicide) processes. For high performance devices, it is essential that salicide processes achieve low gate and source/drain sheet resistance as well as low silicide to source/drain diffusion contact resistance, and maintain low junction leakage. This becomes more difficult as junction depths and linewidths are scaled. In this paper we present an overview of the development of advanced Ti and Co salicide processes at Texas Instruments, with implementations into a high performance 0.10 μm CMOS technology. For Co salicide, the main scaling issue is diode leakage on shallow junctions. We discuss the optimization of Co deposition and RTP variables for low diode leakage, and impact on devices. For conventional Ti salicide processes, the main scaling issue is sheet resistance on narrow lines due to incomplete high resistivity C49 TiSi₂ to low resistivity C54 TiSi₂ transformation. We present XRD and HRTEM studies that indicate that direct growth of C54 TiSi₂ bypassing the C49 phase can be achieved at low temperatures with the addition of metallic impurities. The nucleation mechanism and growth kinetics are analyzed as well as the effect of substrate crystallinity on phase formation. One-step RTP Ti salicide processes with metallic impurities are evaluated, demonstrating a process with low sheet resistance to 0.06 μm gate lengths. Successful implementations into a 0.10 μm flow are achieved both for Co salicide or Ti salicide processes.
9:10 AM		H4-3 Selective Deposition of TiSi₂ on Ultra-thin Silicon-on-Insulator (SOI) Wafers J.-S. Maa, B. Ulrich, S.T. Hsu, G. Stecker (Sharp Microelectronics Technology) Titanium silicide has been selectively deposited by chemical vapor deposition on ultrathin SOI devices using gas mixture of titanium tetrachloride, silane, dichlorosilane, and hydrogen. The selectivity to oxide is very good, the silicide film is observed deposited only on the source/drain and gate regions. There is no bridging problem from the overgrowth of silicide across the oxide spacers. The thickness of SOI silicon is from 250 angstroms to 500 angstroms. The polysilicon thickness is 3500 angstroms. Silicide film up to about 1000 angstroms forms successfully on very thin SOI layer as well on the thicker polysilicon line. There is no degradation of the silicide film due to the thickness of the thin SOI film. Titanium silicide formed on submicron polysilicon lines also has similar sheet resistance as on 10 micron lines. The deposition temperature is in the range of 750 degree Celsius to 800 degree Celsius, which shows the line stability up to about 800 degree Celsius. Active devices have been fabricated, and is discussed in this paper.
9:30 AM		H4-4 Ion Beam Synthesis of Calcium and Magnesium Silicides Studied by Auger Electron Spectroscopy H.J. Steffen (National Research Institute for Metals, Japan); S. Harada (Kyushu University, Japan); H. Tanoue (Electrotechnical Laboratory, Japan); T. Motooka (Kyushu University); Y. Makita (Electrotechnical Laboratory); S. Hofmann (National Research Institute for Metals, Japan) This study explores the possibility of growing new semiconductor materials by high-dose implantation of Calcium and Magnesium into silicon and subsequent annealing. Of special interest is the formation of the Zintl phases Ca₂Si with the orthorhombic structure and Mg₂Si with the cubic CaF₂ structure which have band gap energies of ca. 1.9 and 0.8 eV, respectively. Ca⁺ and Mg⁺ ions with kinetic energy of 200 keV were implanted into (100) silicon at a substrate temperature between 400 and 500 K with doses of 1x 10¹⁷ and 3 x 10¹⁸ Ca⁺/cm² and 1.3 x 10¹⁸ Mg⁺/cm². Calcium implanted samples were tempered at 800 and 1000 K and Mg samples of 1100 K for 30 min., respectively. Auger electron spectroscopy in combination with rotational sputter depth profiling provided detailed information about the depth-dependent composition, the different chemical states of the elements and the phases formed. The analysis reveals, in accordance with x-ray diffraction measurements, the existence of a continuous cubic Mg₂Si layer for the as-implanted state and after tempering. In contrast, Ca₂Si is only formed during implantation but the annealing above 800 K results in a dissolution of this phase and the formation of hexagonal CaSi₂ at 1000 K.
9:50 AM		H4-5 Ion Beam Induced Formation of Ta-Silicides M.M. Milosavljevi@aa c@, N.B. Bibi@aa c@, D.P. Perusko (VINCA Institute of Nuclear Sciences, Yugoslavia); N.B. Barradas, C.J. Jeynes (University of Surrey, United Kingdom) The effects of As and Xe ion irradiation on Ta thin films deposited on silicon substrates were investigated. Thin Ta films were deposited on (100) Si wafers to the thickness of 50, 70 and 100 nm, by d.c. ion sputtering. After deposition the Ta/Si samples were implanted at room temperture with 350 keV As⁺ and 300 keV Xe⁺ ions, to the doses from 1x10 ¹⁵ ions cm ^-2 to 2.5x10¹⁶ ions cm^-2. The different Ta layer thickness and the different implanted ions gave a variety ot the ion ranges with respect to the Ta/Si interface. Characterization of samples was performed by Rutherford Backscattering Spectroscopy (RBS), X-ray Diffraction Spectrometry (XRD), Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The results have reviled ion beam mixing of Ta and Si components practically for all the implanted doses. Particularly for higher doses and thinner Ta layers, an almost comlete formation of Ta-silicide phase was observed. In our analysis we have determined the component interactions and the formed silicide phases with respect to the ion species, doses and ranges. We have compared these results with our previous investigations of ion beam mixing of Pd/Si and TiN/Ti/Si and found an interesting behavior. Atlhough during thermal diffusion Ta-silicides are formed at temperatures above 900°C, their behavior during ion beam mixing is similar as in the cases of the low temperature forming metal-silicides.
10:50 AM		H4-8 The Effects of the Process Parameters on the Electrical and Microstructural Characteristics of the CrSi Thin Resistor Films, Part I F. Wu, A. Mclaurine, K.E. Henson (Medtronic, Inc. Micro-Rel Division) The effects of process parameters, such as target composition, sputtering pressure, reactive gas partial pressure, deposition rate, anneal temperature, on the electrical and microstructrual characteristics of CrSi thin resistor films in VLSI application was investigated in this paper. it was observed that the higher metallic compostion in target, low deposition rate, lower nitrogen partial pressure, and higher anneal temperature shifts TCR close to positive direction. The relationships between TCR and anneal temperature, TCR and nitrogen partial pressure, TCR and anneal environment were studied. Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), and Fourier Transform Infrared Reflection (FTIR) analysis were conducted to explore the microstructure of the films and the in situ anneal TEM analysis was performed to study the change of the microstructure of the films during anneal. The TEM images show that CrSi films from sputtering has typical cermet film microstructure which consists of darker island regions embedded in lighter boundary medium regions. In si situ TEM anneal analysis, as the temperature increases, the microstructure remains largely unchanged when the anneal temperature lower than 700 degree C. At 700 degree C, the diffraction pattern from the pure Ar sputtered sample indicates that a change is occurring in the film around this temperature. No such change was observed in the reactive sputtered sample at the same temperature. This may be the explanation of that TCR of the pure Ar sputtered sample changes from negative to positive but the TCR of the reactive sputtered sample does not change sign while the anneal temperature changes from 400 degree C to 600 degree C.
11:30 AM	Invited	H4-10 Low Temperature Formation of C54-TiSi₂ Using Titanium Alloys C. Lavoie, C. Cabral, Jr., L. Clevenger, J.M.E. Harper, F.M. D'Heurle, R. Roy, K.L. Saenger (IBM T.J. Watson Research Center) The phase transformation of TiSi2 from the C49 to the C54 structure has been shown to be weakly driven and sparsely nucleated resulting in difficulty forming the low resistivity C54 phase in the submicrometer dimensions used in microelectronics. We demonstrate that the transformation temperature can be lowered by more than 100C by alloying the titanium with small amounts of refractory metals prior to the reaction with silicon. Titanium alloy blanket films, containing from 1to 20% molybdenum, tantalum or niobium were deposited on polycrystalline and silicon (100) substrates. The films were annealed at constant ramp rates during which x-ray diffraction and sheet resistance were simultaneously monitored. To attain acceptable diffracted intensities in order to determine the phase transformation temperature during annealing at RTA rates, the experiment is performed at X20C beamline of the National Synchrotron Light Source where the x-ray intensity is about 4 orders of magnitude larger than with a standard rotating anode system. Although the addition of Mo, Ta and Nb all similarly reduce the transformation temperature, the sheet resistance of the final silicide varied not only with alloy concentration but also with alloy type. While the Mo additions lead to a large increase in resistivity, Ta or Nb additions kept the C54 resistivity to acceptable levels. Titanium tantalum alloys were also used to form C54 TiSi2 on arsenic doped Si(100) and polycrystalline silicon isolated regions of line widths ranging from 0.56 um down to 0.13 um. For both blanket and fine line samples, the transformation temperature was found to be lower by over 100C. As the concentration of Ta, Nb or Mo in the titanium alloy increases, or as line width decreases, we also observed an additional x-ray diffraction peak consistent with the higher resistivity C40 silicide phase. From the lower transformation temperatures and the increased fraction of C54 transformed in fine line samples, it is shown that alloying the titanium increases the density of nucleation sites for the C49 to C54 transformation. The role of the C40 phase as a template site is also addressed.