The Disilicides of Tungsten, Molybdenum, Tantalum, Titanium, Cobalt, and Nickel, and Platinum Monosilicide: A Survey of Their Thermodynamic Properties Cite as: Journal of Physical and Chemical Reference Data 22, 1459 (1993); https:// doi.org/10.1063/1.555922 Submitted: 21 December 1992 . Published Online: 15 October 2009 M. S. Chandrasekharaiah, J. L. Margrave, and P. A. G. O’Hare ARTICLES YOU MAY BE INTERESTED IN Thermodynamic considerations in refractory metal-silicon-oxygen systems Journal of Applied Physics 56, 147 (1984); https://doi.org/10.1063/1.333738 Thermal and Electrical Conductivity of Graphite and Carbon at Low Temperatures Journal of Applied Physics 15, 452 (1944); https://doi.org/10.1063/1.1707454 Formation of thin films of NiSi: Metastable structure, diffusion mechanisms in intermetallic compounds Journal of Applied Physics 55, 4208 (1984); https://doi.org/10.1063/1.333021 Journal of Physical and Chemical Reference Data 22, 1459 (1993); https://doi.org/10.1063/1.555922 22, 1459 © 1993 American Institute of Physics for the National Institute of Standards and Technology. The Disilicides of Tungsten, Molybdenum, Tantalum, Titanium, Cobalt, and Nickel, and Platinum Monosilicide: A Survey of Their Thermodynamic Properties M. s. Chandrasekharaiah and J. L. Margrave HARC, Materials Science Research Center, 4802 Research Forest Drive, The Woodlands, TX 77381 and P. A. G. O'Hare Chemical Kinetics and Thennodynamics Division, National Institute of Standards and Technology, Gaithersburg, MD 20899-0001 Received December 21, 1992; revised manuscript received February 19, 1993 A critical evaluation is presented of the thermodynamic properties of six disiIi­ cides and one monosilicide that are important in the manutacture ot very large scale integrated circuits. Values of the standard molar enthalpies of formation 8fH~ at T = 298.15 K and po = 0.1 MPa are recommended as follows: WSh, - (79 ± 5) 1 1 kJ'mo]-l; MoSh, - (137 ± 4) kJ'mol- ; TiSiz, - (171 ± 11) kJ'mol- ; CoSh, - (103 1 1 1 ± 15) kJ'mol- ; NiSh, - (88 ± 12) kJ'mol- ; TaSh, - (120 ± 20) kJ'mol- ; and l PtSi, - (119 ± 7) kJ·mol- . Equations are given for the molar enthalpy increments of some of the silicides along with a few evaluated standard Gibbs free energies of formation. Brief descriptions of methods of synthesis and limited structural informa­ tion have also been included. Key words: chemical thermodynamics; cobalt' disilicide; enthalpy increments; evaluated properties; molybdenum disilicide; nickel disilicide; platinum monosiIicide; standard enthalpies of formation; stan­ dard Gibbs free energies of formation; tantalum disilicide; titanium disiHcide; tungsten disilicide. Contents 1. Introduction ................................ 1459 List of Tables 2. Tungsten Disilicide .......................... 1460 2.1. Preparative Methods .................... 1460 1. The standard molar enthalpy of formation of 2.2. Thermodynamic Properties .............. 1460 WSh(cr, 298.15 K) ........................... 1460 3. Molybdenum Disilicide ...................... 1461 2. The standard molar enthalpy of formation of 3.1. Preparative Methods .................... 1461 MoSh(cr, 298.15 K) .......................... 1462 3.2. Thermodynamic Properties .............. 1461 3. Enthalpy increments for MoSb(cr) ........... 1463 4. Titanium Disilicide .......................... 1463 4. The standard molar enthalpy of formation of 4.1. Preparative Methods .................... 1464 TiSh(cr, a, 298.15 K) ......................... 1464 4.2. Thermodynamic Properties .............. 1464 5. Enthalpy increments for TiSb(cr) ............ 1465 5. Cobalt and Nickel Disilicides ................ 1465 6. The standard molar enthalpies of formation of 5.1. Preparative Methods .................... 1465 CoSh(cr) and NiSh(cr) at 298.15 K ........... 1465 5.2. Thermodynamic Properties .............. 1465 7. Enthalpy increments for CoSh(cr) and NiSi1.857 6. Tantalum Disilicide ......................... 1466 (cr, a) ..................................... 1466 6.1. Preparative Methods .................... 1466 8. The standard molar enthalpy of formation of 6.2. Thermodynamic Properties .............. 1466 TaSiz(cr, 298.15 K) .......................... 1467 7. Platinum Monosilicide ....................... 1466 9. The standard molar enthalpy of formation of 7.1. Preparative Methods .................... 1466 PtSi(cr, 298.15 K) ........................... 1467 7.2. Thermodynamic Properties .............. 1467 8. References ............... _. _. _.. ______ . __ . __ 1467 1. Introduction There is a revival of interest in the chemistry of transi­ ©1993 by the U.S. Secretary of Commerce on behalf of the United States. This copyright is assigned to the American Institute of Physics tion-metal disilicides as a result of their use as intercon­ and the American Chemical Society. nects and gate materials in very-large-scale integrated Reprints available from ACS; see Reprints List at back of issue. (VLSI) circuits.1 Considerable R&D efforts have been 0047-2689/93/22(6)/1459/10/$10.00 1459 J. Phys. Chem. Ref. Data, Vol. 22, No.6, 1993 1460 CHANDRASEKHARAIAH, MARGRAVE, AND O'HARE expended in the preparation and measurement of the and Harshbarger7 calculated the equilibrium composi­ electrical properties of thin films of these disilicides, but tions under CVD conditions for deposition of WSh from much less attention has been paid to their thermody­ two different feed gases: (WF6 + Si~ + H2) and (WF6 namic properties. Without reliable thermodynamic infor­ + SiH2Ch + H2) at temperatures between 473 K and mation for these materials, any long-term compatibility 1073 K at p = 67 Pa. They showed that WSh film was the evaluation is of little value. only silicide phase formed in both cases. Blanquet et al. 8 Schlesinger recently surveyed in a general way the examined the optimum thermodynamic conditions for thermodynamic properties of metal silicides. His review CVD deposition of WSh at p = 0.1 MPa by means of in covered literature references exhaustively, but critical cs­ situ chlorination of W-films followed by reaction with timates of the uncertainties in the selected values are (Si~ + H2)' Dobkin et al.9 obtained high-quality films of lacking. The only other comprehensive review of the ther­ WSh by CVD from (WF6 + ShH6) or (SiH4 + H2 + N2) mochemical properties of metal silicides was published at p = 0.1 MPa and temperatures of the substrate be­ 3 about 20 years ago by Chart. ,4 tween 563 K and 583 K. Zhang et al.1O obtained WSix by In the present assessment, a thorough search was made low-pressure CVD from (WF6 +SiH4 + Ar), and WSh of the literature of the thermodynamic properties of the by annealing on Si substrates W films formed from WF6. 11 crystalline disilicides of tungsten, molybdenum, tantalum, Tungsten disilicide and similar films prepared by CVD titanium, cobalt, and nickel, and of the monosilicide of are usually characterized by standard surface techniques platinum, because those substances appear to predomi­ including Rutherford back-scattering. nate in modern VLSI designs. The thermochemical prop­ erties: standard molar enthalpy of formation at T = 2.2. Thermodynamic Properties 298.15 K, molar enthalpy increments relative to T = 298.15 K. and standard molar Gihhs free energies of for­ A recent ~ssesssment of the (W + Si) phase diagram mation are tabulated and appraised, and selected values by Nagender Naidu et al.12 showed WSh to be a con­ are recommended. That is the main thrust of the effort. gruently-melting intermediate phase that crystallized in In addition, for each disilicide, we have included short, by tetragonal form (tI6, space group I4/mmm, a = 0.3211 no means exhaustive, sections that list methods of synthe­ nm, C = 0.7868 nm; melting temperature 2433 ± 4 K). sis, structural information, and some details of the phase The only other solid phase observed in this system was diagram. the congruently melting (at T = 2593 ± 10 K) tetragonal WsSh, which has a small compositional homogeneity.Ap­ 2. Tungstel) Disilicide parently, W3Si does not exist. The direct-reaction calorimetric determination of the 2.1. Preparative Methods standard molar enthalpy of formation dfH~(WSh, 298.15 K) by Robins and Jenkins13 was, for many years, Tungsten disilicide, in common with the other disili­ the only experimental result for this quantity. O'Harel4 cides discussed in this survey, is generally prepared by di­ has recently determined AfH~ by fluorine-combustion 15 U recUy heating mixtures of stoichiometric amounts of pure calorimetry. Several estimates - ! of dfH~(WSh) have specimens of Si and the appropriate second element in a been published . Chart19 deduced the molar Gibbs free vacuum or inert atmosphere to about 1500 K, followed by energy of formation from Knudsen-effusion measure­ s s quenching to room temperature. Bondarenko et al. pre­ ments. Bondarenko et al. ,20 obtained the high-tempera­ pared single-phase WSh by the diffusion impregnation in ture enthalpy increments (1200 K to 2200 K) from vacuum of a tablet or thin sheet of tungsten with silicon. measurements with a drop calorimeter. A number of workers6- 11 used CVD techniques to All the values of the enthalpies of formation are col­ deposit thin (~50 J,Lm) films of WSh on silicon sub­ lected in Table 1. 6 strates. Hammar et al. laid tungsten films on prede­ Robins and Jenkins13 deduced AfH~(WSh) from the posited polycrystaHine Si in a CVD system at p = 47 Pa measured total enthalpy changes when compacted sam­ and T = 623 K, followed by annealing at 1073 K. Rode