Adsorption and desorption kinetics of tetrakis(dimethylamino)titanium and dimethylamine on TiN surfaces

Abstract

Titanium nitride (TiN) can be deposited using the organometallic precursor tetrakis(dimethylamino)titanium (Ti[N(CH 3) 2] 4) (TDMAT). Deviations from conformal TiN film growth have been observed in trench structures using TDMAT. This nonconformal deposition may be associated with readsorption and site blocking by the dimethylamine (HN(CH 3) 2) (DMA) reaction product. To understand the deviations from conformal TiN deposition in trench structures, the adsorption and desorption kinetics for TDMAT and DMA were measured on a sputter-deposited TiN surface using laser induced thermal desorption (LITD) techniques. The LITD measurements revealed that DMA has a higher sticking coefficient than TDMAT. The sticking coefficients for both TDMAT and DMA were also dependent on surface coverage. The initial sticking coefficient for TDMAT is S 0=0.23 with a coverage-dependence approximated by S( θ)=0.25 exp(−4.7 θ) where θ is the normalized surface coverage. The initial sticking coefficient for DMA is S 0=0.70 and the coverage-dependence is approximated by S( θ)=0.86 exp(−3.7 θ). The observed desorption kinetics of DMA following TDMAT and DMA exposures on TiN were also coverage-dependent. The isothermal desorption measurements could be fit using a simple first-order desorption rate expression, k d= ν dexp[− E d( θ)/ RT] where E( θ) is the coverage-dependent desorption energy, E d( θ)= E 0− E 1 θ. Assuming a desorption preexponential of ν d=1×10 13 s −1, the observed isothermal desorption measurements for DMA desorption following both TDMAT and DMA exposures could be fit using E 0=29.1 kcal mol −1 and E 1=8.2 kcal mol −1. These measured adsorption and desorption kinetics are consistent with DMA readsorption as a major contributor to nonconformal TiN growth in trench structures using TDMAT.