Chemisorption of Tetrakis(dimethylamido)titanium on Si(100)-2 × 1: C−H and C−N Bond Reactivity Leading to Low-Temperature Decomposition Pathways

Abstract

Tetrakis(dimethylamido)titanium, Ti[N(CH3)2]4 or TDMAT, is a metal alkylamide precursor often used in the deposition of titanium nitride films. The mechanisms of decomposition of TDMAT upon its adsorption on the Si(100)-2 × 1 surface are investigated by infrared (IR) spectroscopy, temperature-programmed desorption (TPD), and density functional methods. Two experimental observations, the formation of Si−H bonds at temperatures as low as 220 K and methane desorption at temperatures below 400 K, indicate the scission of C−H and C−N bonds. The unusual low-temperature reactivity of these bonds is explained in terms of bond activation due to the zwitterionic character of the silicon−silicon dimers of the Si(100)-2 × 1 surface. Silicon surface atoms with predominantly nucleophilic character are able to attract hydrogen atoms, forming Si−H bonds. Silicon surface atoms with electrophilic character are able to form N−Si dative bonds that weaken the C−N bond, favoring its scission. Density functional calculations support this model, finding that the C−H scission is favored thermodynamically and kinetically provided that the TDMAT molecule has already undergone dissociative adsorption via N−Ti bond scission. Several decomposition pathways are considered, and in all cases the surface products are stabilized upon the formation of Si−C bonds, which agrees with the formation of an interface with high carbon content when metalorganic precursors are employed. The repercussion of these facile mechanisms of decomposition on the first stages of film deposition is discussed.