Atomic Layer Deposition of Silicon Dioxide Using Aminosilanes Di-<i>sec</i>-butylaminosilane and Bis(<i>tert</i>-butylamino)silane with Ozone

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-<i>sec</i>-butylaminosilane (DSBAS) and bis­(<i>tert</i>-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^<i>t</i>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^<i>t</i>Bu) structure obtained from BTBAS exposure at 100 °C loses its NH^<i>t</i>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, <i>P</i> ∼ 7.5 Torr), the ligand exchange is essentially complete, with the ozone pulse reacting with Si–H_<i>x</i> [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_<i>x</i> 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]