The energy landscape of a full atomic layer deposition cycle to grow a layer of SiO 2 on the hydroxylated SiO 2 (001) surface was systematically explored using density functional theory. A monoaminosilane-based compound, di(sec-butylamino)silane (DSBAS), was utilized as the silicon precursor with ozone acting as an oxidizing agent. The ALD cycle includes dissociative chemisorption of DSBAS, oxidation, and condensation for surface regeneration.Our results indicate that the dissociative chemisorption of DSBAS is kinetically facile. Upon oxidation by ozone, the layer grows with a SiO 2 crystalline morphology. The entire ALD cycle was found to be thermodynamically and kinetically favorable. This is important for growing dense and conformal SiO 2 thin films free of impurities and thus well-suited for low-temperature deposition of SiO 2 thin films.

Conformal and continuous silicon oxide films produced by atomic layer deposition (ALD) are enabling novel processing schemes and integrated device structures. The increasing drive toward lower temperature processing requires new precursors with even higher reactivity. The aminosilane family of precursors has advantages due to their reactive nature and relative ease of use. In this paper, the authors present the experimental results that reveal the uniqueness of the monoaminosilane structure [(R2N)SiH3] in providing ultralow temperature silicon oxide depositions. Disubstituted aminosilanes with primary amines such as in bis(t-butylamino)silane and with secondary amines such as in bis(diethylamino)silane were compared with a representative monoaminosilane: di-sec-butylaminosilane (DSBAS). DSBAS showed the highest growth per cycle in both thermal and plasma enhanced ALD. These findings show the importance of the arrangement of the precursor's organic groups in an ALD silicon oxide process.

A detailed reaction mechanism has been proposed for the full ALD cycle of Si3N4 deposition on the β-Si3N4(0001) surface using bis(diethylamino)silane (BDEAS) or bis(tertiarybutylamino)silane (BTBAS) as a Si precursor with NH3 acting as the nitrogen source. Potential energy landscapes were derived for all elementary steps in the proposed reaction network using a periodic slab surface model in the density functional approximation. Although the dissociative reactivity of BTBAS was slightly better than that of BDEAS, the thermal deposition process was still found to be an inherently high temperature process due to the high activation energies during the dissociative chemisorption of both precursors and the surface re-amination steps. These results underline the need to develop new precursors and alternative nitrogen sources when low temperature thermal silicon nitride films are targeted.

In situ Fourier transform infrared (FTIR) spectroscopy is used to investigate silicon dioxide deposition on OH-terminated oxidized Si(100) surfaces using two aminosilanes, di-sec-butylaminosilane (DSBAS) and bis­(tert-butylamino)­silane (BTBAS), with ozone as the coreactant. Both DSBAS and BTBAS readily react at 100 °C with surface −OH groups (loss at 3745 cm–1) with formation of Si–O–SiH3 and Si–O–SiH2–(NH t Bu), respectively, through elimination of secondary and primary amines. The (O−)­SiH3 structure is characterized by a strong Si–O–Si band at 1140 cm–1, and sharp (O−)­SiH3 stretch (2192 cm–1) and deformation (983 cm–1) bands. SiH3 remains stable up to 400 °C, at which point rearrangement into bidentate ((O−)2SiH2) and then tridentate ((O−)3SiH) bonding takes place through condensation reaction with neighboring OH or O groups. In contrast, the O–SiH2–(NH t Bu) structure obtained from BTBAS exposure at 100 °C loses its NH t Bu group at ∼350 °C, leading to a bidentate bonding ((O−)2SiH2) that remains stable up to 500 °C. In both cases, the transformation to bidentate and tridentate bonding depends on the initial OH concentration. The degree of ligand exchange during atomic layer deposition (ALD) with ozone also depends on the ozone flux. For a high enough flux (≥300 sccm, P ∼ 7.5 Torr), the ligand exchange is essentially complete, with the ozone pulse reacting with Si–H x [loss of vibrational bands at 2192 and 983 cm–1 for DSBAS, and at 2972, 2185, and 924 cm–1 for BTBAS] and forming surface Si–O–H (3745 cm–1). The initial Si–O–Si band at 1140 cm–1 broadens upon ozone exposure, consistent with the formation of a Si–O–Si network that extends the existing SiO2 substrate. In steady state, the ALD process is characterized by reaction of SiH x by ozone with the formation of OH, thus sustaining the ALD process, with densification of stoichiometric silicon oxide [transverse optical (TO) and longitudinal optical (LO) phonon modes at 1053 and 1226 cm–1].

We investigate theoretically using the finite difference time domain method acoustic wave propagation along waveguides in three-dimensional phononic crystals constituted of lead spherical inclusions on a face-centered cubic lattice embedded in an epoxy matrix. The transmission spectra of the perfect phononic crystal for transverse and longitudinal acoustic waves are shown to depend strongly on the direction of propagation. The crystal possesses an absolute band gap. Waveguides oriented along different crystallographic directions, namely the ͗100͘ and ͗111͘ directions, exhibit pass bands in the phononic crystal band gaps for both transverse and longitudinal polarizations.