AVS 51st International Symposium
    Electronic Materials and Processing Tuesday Sessions
       Session DI+PS-TuM

Paper DI+PS-TuM7
DFT Investigation of Initial HfO@sub 2@ Atomic Layer Deposition on Nitrided Silicon Surface

Tuesday, November 16, 2004, 10:20 am, Room 304C

Session: High-k Dielectrics: Growth and Processing
Presenter: Y. Xu, Stanford University
Authors: Y. Xu, Stanford University
C.B. Musgrave, Stanford University
Correspondent: Click to Email
The atomistic mechanism of the initial atomic layer deposition (ALD) reactions of hafnium oxide on a nitrided silicon surface was investigated using density functional theory (DFT). Reactions involving two different metal precursors are explored: Tetrakis-dimethylamido-hafnium (Hf[N(CH@sub 3@)@sub 2@]@sub 4@) and hafnium tetra chloride (HfCl@sub 4@). Hf[N(CH@sub 3@)@sub 2@]@sub 4@ forms no adsorbed complex on the nitrided Si substrate. The ALD ligand exchange reaction requires a barrier of 0.63eV and is exothermic by 0.22 eV. The adsorbed precursor state is not formed because the Hf atom of the precursor state has full s and d-shells and the amines are doubly bonded to Hf. Furthermore, the lone pair of nitrogen on the nitrided silicon surface is somewhat delocalized, reducing its ability to form dative bonds. Reaction between HfCl@sub 4@ and the nitrided silicon surface results in adsorbed HfCl@sub 4@ complex with an adsorption energy of 0.66 eV. The ligand exchange barrier is 1.33eV relative to the complex structure and the overall reaction is endothermic by 0.50 eV. Consequently, the alkylamide precursor is both kinetically and thermodynamically superior to HfCl@sub 4@ for the initial ALD reactions on the nitrided surface. We previously showed that for ALD of HfO@sub 2@, Hf[N(CH@sub 3@)@sub 2@]@sub 4@ appears to be a better choice than HfCl@sub 4@ both thermodynamically and kinetically. Thus Hf[N(CH@sub 3@)@sub 2@]@sub 4@ precursor performs better for both the initial reaction on the nitrided silicon surface and subsequent ALD of the HfO@sub 2@.