AN FT-IR STUDY OF SILICON DIOXIDES FOR VLSI MICROELECTRONICS

SiO2 layers that are applied in VLSI (very large scale integration) microelectronics (gate dielectric, insulation, etc) are prepared in different ways: thermal, chemical vapour deposition (CVD), thermochemical. It has been investigated whether the composition, thickness, film stress and disorder of thin silicon dioxide can be characterised in a simple manner by Fourier-transform infrared absorption spectroscopy (FT-IR). In addition to the main absorption bands at 460 cm-1, 808 cm-1 and 1075 cm-1 (all transverse optical modes) spectral features at 1165 cm-1, 1200 cm-1 (LO4-TO4 pair) and 1230-1250 cm-1 (LO3 mode) have been analysed as a function of film thickness, preparation conditions, substrate and rapid thermal annealing. The position, full width at half maximum of the band at 1075 cm-1, the position of the LO3 mode and the intensity ratio of the LO4-TO4 pair and the LO3 mode can be related in a qualitative fashion to film stress, composition and disorder of the thin SiO2 films.