Chemical vapor deposition of titanium nitride thin films from tetrakis(dimethylamido)titanium and hydrazine as a coreact
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Derk A. Wierda Department of Chemistry, Saint Anselm College, Manchester, New Hampshire 03102 (Received 3 April 2000; accepted 7 August 2000)
Hydrazine was used as a coreactant with tetrakis(dimethylamido)titanium for the low-temperature chemical vapor deposition of TiN between 50 and 200 °C. The TiN film-growth rates ranged from 5 to 45 nm/min. Ti:N ratios of approximately 1:1 were achieved. The films contain between 2 and 25 at.% carbon, as well as up to 36 at.% oxygen resulting from diffusion after air exposure. The resistivity of these films is approximately 104 ⍀ cm. Annealing the films in ammonia enhances their crystallinity. The best TiN films were produced at 200 °C from a 2.7% hydrazine–ammonia mixture. The Ti:N ratio of these films is approximately 1:1, and they contain no carbon or oxygen. These films exhibit the highest growth rates observed.
I. INTRODUCTION
Titanium nitride (TiN) belongs to the class of materials known as transition-metal nitrides, known for their refractory properties and high hardness.1,2 TiN is a golden yellow material with a high melting point of 2949 °C.2 It has a Vickers hardness of 2100 (kg mm−2), which is between that of alumina (2080 kg mm−2) and diamond (7600 kg mm−2).2 It is resistant to most corrosive environments, except at high temperatures when it will oxidize to form TiO2.1 TiN has a density of 5.4 g/cm3, a thermal conductivity of 0.33 W/cm °C, a coefficient of thermal expansion of 9.35 × 10−6 m/°C, and an electrical resistivity of 25 ⍀ cm.1–3 The high hardness and refractory properties make TiN useful for the hard-coatings industries, such as in cutting tools.3,4 Additionally, its metal-like conductivity in combination with the refractory properties makes it suitable for microelectronic applications.5 TiN serves as a diffusion barrier between metals and silicon, as well as an adhesion layer for tungsten, in metallization schemes of integrated circuits.6 Additionally, TiN is used as a antireflective coating on top of metal lines to minimize reflection during the lithography steps later in the process.6 TiN thin films can be deposited both by physical and chemical vapor deposition (CVD). Physical deposition methods, mostly reactive sputtering and pulsed laser deposition, have poor conformality in submicron feaa)
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J. Mater. Res., Vol. 15, No. 11, Nov 2000 Downloaded: 17 Mar 2015
tures on integrated circuits, and they do not offer the large area uniformity of coverage required in some hardcoatings applications.6,7 Therefore, CVD has received much attention for these applications because it offers superior conformality, as well as the ability to cover larger areas.4,8 The two most extensively used thermal CVD precursor systems are: (i) the inorganic halide, TiCl4 and ammonia;3,7,9–10 or (ii) the organometallic compounds, tetrakis(dimethylamido)titanium (TDMAT) or tetrakis(diethylamido)titanium (TDEAT) and ammonia.11–28 The first system requires temperatures too high (500– 700 °C) for most
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