Low Temperature Chemical Vapor Deposition of Titanium Nitride Thin Films With Hydrazine and Tetrakis-(dimethylamide)Tita
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CARMELA JR.*, and DERK A. WIERDA** *Materials AMATO-WIERDA*, Science Program, EDWARD University T.ofNORTON, New Hampshire, Durham, NH 03824, ccawa~cisunix.unh.edu "Department of Chemistry, Saint Anselm College, Manchester, NH 03102 ABSTRACT Hydrazine and tetrakis-(dimethylamido)titanium have been used as precursors for the low temperature chemical vapor deposition of TiN thin films between 50'C and 200'C at growth rates between 5 to 35 nm/min. At hydrazine to TDMAT ratios of 50:1 and 100:1 the resulting films show an increase in the Ti:N ratio with increasing deposition temperature. They contain 2% carbon, and varying amounts of oxygen up to 36% as a result of diffusion after air exposure. The low temperature growth is improved when hydrazine-ammonia mixtures containing as little as 1.9% hydrazine are used. Their Ti:N ratio is almost 1:1 and they contain no carbon or oxygen according to RBS. The TiN films grown from pure hydrazine or the hydrazine-ammonia mixture have some crystallinity according to x-ray diffraction and their resistivity is on the order of 104 p%2 cm. The low temperature growth is attributed to the weak N-N bond in hydrazine and its strong reducing ability. In these films, the Ti:N ratio is approximately 1:1.
INTRODUCTION TiN thin films can be deposited both by physical and chemical vapor deposition. Physical deposition methods, mostly reactive sputtering and pulsed laser deposition, have poor conformality in sub-micron features on integrated circuits, and they do not offer the large area uniformity of coverage required in some hard coatings applications. 1-8 Sputtered TiN is currently used in ULSI devices to prevent the interaction between the aluminum interconnect metal and the silicide contact layers on silicon. However, this TiN technology does not meet all the resistivity and conformality requirements of future devices with copper metallization. 3-5 This has lead to investigations of CVD TiN barriers with improved barrier properties, including conformality and large coating areas. Primarily two precursor s1ystems have been used: TiCI4 and ammonia, or tetrakis(dimethylamido)titanium and ammonia. " The first system requires temperatures too high (500-700 °C) for most device applications. In the case of the organometallic precursors, it is possible to obtain films with a combination of low impurity levels, low resistivity, and sufficient conformality for 0.25 pm technology. We present here the low temperature chemical vapor deposition of TiN between 50-200 'C by using hydrazine (N 2H4) as the nitrogen source precursor, along with tetrakis(dimethylamido)titanium (TMT). This is significantly lower than the 300-450 'C temperatures typically reported for this process. In addition, as little as 1.9% (molar percent) hydrazine in a hydrazine-ammonia mixture is required to obtain TiN films at these temperatures. These lower deposition temperatures may provide TiN films with improved step coverage for sub-0.25 pm metallization schemes, since conformality is expected to improve with decreasing deposition
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