Effect of annealing temperature on the formation of silicon nanocrystals in a nitride matrix

Abstract

Superlattices of silicon nanocrystals or quantum dots (QDs) are fabricated by depositing alternating layers of stoichiometric and sub-stoichiometric silicon nitride by dual-mode PECVD and subsequent high temperature annealing. NH3, SiH4 and Ar are used as processing gases. The formation of QDs is monitored for varying annealing temperatures using TEM and GI-XRD. Samples composed of 50 bi-layers are grown under the same conditions and annealed for two hours at temperatures ranging between 600 and 1150°C. A 50 bi-layer superlattice structure of silicon nanocrystals with an estimated average grain size of approximately 4 nm was achieved at 1000°C. The use of FTIR spectroscopy as a complementary technique for verifying the formation of silicon nanocrystals in a nitride matrix is investigated. The IR absorbance spectra for samples containing silicon nanocrystals show a distinct shoulder at 1080 cm-1 corresponding to the Si-O-Si stretching mode possibly due to oxidation. Preliminary evidence is also presented showing the possible formation of α-Si3N4 nanocrystals at 1100 and 1150°C.