Formation mechanism of crystallites in the as-deposited mixed-phase low pressure chemical vapor deposition silicon thin films

Abstract

Transmission electron microscopy study on the microstructure of silicon thin films, deposited at temperature ranges of 565 °C∼600 °C and at 200 mTorr by low pressure chemical vapor deposition and annealed at 570 °C, was carried out so that the formation mechanism of crystallites observed in as-deposited mixed-phase silicon thin films could be proposed. Crystallites were observed only at the Si/SiO2 interface in the as-deposited silicon thin film deposited at 570 °C for 28 min. Their size was about 20 nm and they had an irregular shape. Areal density of crystallites in the as-deposited film was about 4 × 1010/cm2, but that in the film deposited as an amorphous phase and annealed at 570 °C for 2 h was about 2×109/cm2. No remarkable crystal growth occurred in the film deposited at 570 °C for 28 min and then annealed at 570 °C for 1 h. Two kinds of crystallites were observed in the film annealed at 570 °C for 3 h. The first, observed only at the Si/SiO2 interface, had an irregular shape, and the second, grown through the entire thickness of the film, had an elongated elliptical shape. On the basis of above results, it was proposed that crystallites observed in as-deposited silicon thin films were formed not because silicon films deposited as an amorphous phase had been annealed during the deposition process, but because silicon films were deposited as a crystalline phase at the initial stage of the deposition process and then deposited as an amorphous phase after the initial stage of the deposition process.