Tetrakis(dimethylamido)hafnium Adsorption and Reaction on Hydrogen Terminated Si(100) Surfaces

Abstract

The adsorption and reaction of tetrakis(dimethylamido)hafnium (TDMAH) on hydrogen terminated Si(100) were studied by using in situ attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), transmission IR, and quadrupole mass spectrometry (Q-MS). Surface and gas phase reactions were investigated at temperatures between 25 and 300 °C. Density functional theory (DFT) calculations benchmarked by coupled cluster calculations on small models were performed for gas phase decomposition via intramolecular insertion and β-hydride elimination as well as the adsorption and reaction of TDMAH onto a hydrogen terminated Si(100) surface. N−Si and CH2−Si bonds due to reactions on the Si windows were observed in transmission IR, while N−Ge and CH2−Ge bonds on a Ge internal reflectance element (IRE) were observed by ATR-FTIR at 25 and 100 °C. Also observed were the formation of Hf−H bonds and three-member-ring species on the Si surface; the former was confirmed by a control D2O exchange reaction experiment. Both transmission IR and Q-MS indicated the presence of decomposition products dimethylamine (DMA) and N-methyl methyleneimine (MMI). The calculated bond dissociation energies (BDE) at the CCSD(T)/CBS level roughly follow the order of Hf−O > Hf−N > N−H, C−H, Si−N > Si−H, Si−C > N−C, Hf−H > Hf−Si, and the BDEs of the same chemical bond can vary substantially in different molecules. The interface is predicted by DFT calculations to involve Hf−Si, Hf−N−Si, and/or HfNC-Si bonds. TDMAH decomposition products, such as MMI, can form a C−Si or N−Si bond with the silicon surface. The combined experimental and theoretical results suggest that insertion and β-hydride elimination reactions can occur during bidentate chemisorption on the H−Si(100) surface by forming N−Si bonds.

Synthesis and high-temperature evolution of single-phase amorphous Si–Hf–N ceramics

“…The FT-IR spectrum of TDMAH contains absorption bands corresponding to C-H bonds vibrations at 2948, 2822 and 2766 cm −1 ; the absorption bands at 932 and 1251 cm −1 are characteristic vibrations of TDMAH and were assigned to the Hf-N-C units. 24 The FT-IR spectra of the as-synthesized SiHfN precursors are also shown in Fig. 1a and reveal a decrease in the relative intensity of N H and Si H bands with the increase of TDMAH used for the modification of PHPS, indicating that a chemical reaction occurred between the PHPS and TDMAH.…”

“…For the reaction between Si H groups and TDMAH, Li et al 24 have studied the reaction between TDMAH and hydrogen terminated Si(1 0 0) surface. The reaction can follow three paths leading to the formation of (i) Hf Si (byproduct HNMe 2 ), (ii) Hf N Si (byproduct CH 4 ) or (iii) HfNC Si bonds (byproduct H 2 ), and the calculated reaction energies were 10.2 kcal/mol, −21.3 kcal/mol and 8.7 kcal/mol, respectively.…”

Atomic-scale simulation of ALD chemistry

“…HF or approximate DFT), thereby limiting the system size to <1000 atoms on today's computer hardware. Even so, error cancellation is poor when the wavefunction changes strongly at the transition state, so that chemical accuracy can only reliably be achieved by post-HF methods such as coupled cluster [10], [11] or configuration interaction [12], tractable for fewer than 100 atoms.…”

“…showing the inhibiting effect of passivation with sulfur [23], and for HfCl 4 on hydroxylated GaAs [67], decomposition reactions are computed to result in interfacial Si-C bonds [69], or Si-N and Si-CN bonds [11], which are important insights that can guide precursor choice for specific interface properties.…”

“…CVD reactions are generally responsible for an upper limit to the ALD temperature window and associated impurity levels in homodeposition, [84] and can explain heterodeposition by certain precursors and resulting interfaces with substrates [7], [11], [69], [53], [54] , [94], [95]. New ALD precursors should be designed so as to be thermally stable, minimising unwanted CVD-like decomposition during storage and delivery of the precursor.…”