Low pressure chemical vapor deposition of B-N-C-H films from triethylamine borane complex
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H. J. Boeglin and R. Shalvoy Olin Chemicals Research, Cheshire, Connecticut 06410 (Received 19 April 1994; accepted 18 October 1994)
In this study, films consisting of B-N-C-H have been synthesized by low pressure chemical vapor deposition using the liquid precursor triethylamine borane complex (TEAB) both with and without ammonia. When no NH 3 is present, the growth rate was observed to follow an Arrhenius behavior in the temperature range of 600 to 800 °C with an apparent activation energy of 11 kcal/mol. A linear dependence of growth rate is observed as a function of square root of flow rate for the TEAB range of 20 to 60 seem, indicating that the reaction rate is controlled by the adsorption of borane. The addition of NH 3 to TEAB had the effect of lowering the deposition temperature down to 300 °C and increasing the apparent activation energy to 22 kcal/mol. Above 650 °C, the carbon concentration of the deposits increased significantly, reflecting the breakup of the amine molecule. X-ray diffraction measurements indicated the films to be in all cases amorphous. Infrared spectra of the films showed absorption peaks representing the vibrational modes of B-N, B-N-B, B-H, and N-H. The index of refraction varied between 1.76 and 2.47, depending on composition of the films. Films deposited with no NH 3 above 700 °C were seen to be compressive while films below that temperature were tensile. In the range of 350 to 475 °C, the addition of NH3 to TEAB resulted in films that were mildly tensile, while below 325 °C and above 550 °C, the films were found to be compressive. Both the hardness and Young's modulus of the films decreased with higher temperatures, reflecting the influence of the carbon presence.
I. INTRODUCTION Films consisting of B-N offer an attractive combination of properties that include high mechanical strength, good optical and x-ray transparency, chemical inertness, thermal stability, and a dielectric constant that can vary over the wide range of 2.7 to 7.7, depending on deposition conditions.1"17 These properties make the material useful as a chemical mechanical polishing (CMP) stop for global planarization of integrated circuits, as a low dielectric constant insulator to reduce the wiring capacitance between interlevel metals, and as a gate insulator as well as passivation layer for InP MIS devices.18-19 B-N films are also useful as protective coatings for tools, as efficient x-ray detection windows for light elements, and as diffusion sources of boron.2'20 B-N films have been synthesized by numerous physical21 as well as chemical vapor deposition (CVD)1-7'22"24 techniques. CVD is generally preferred in applications where superior step coverage is required. A wide range of boron precursors such as diborane,1'2'7'8-2224 decaborane,6 boron trichloride,3"5'20-23 320 http://journals.cambridge.org
J. Mater. Res., Vol. 10, No. 2, Feb 1995 Downloaded: 25 Mar 2015
borazine,25 and triethylboron26 have been used with ammonia for the film synthesis. In this study, a novel liquid precursor source consisting o
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