LPCVD Si3N4 growth retardation on silicon native oxide compared with in situ HF vapour-deglazed silicon substrates
The advantages offered by clustered tools, which eliminate parasitic oxidation of silicon as currently observed in classical open furnaces, allow for a more in-depth study of the influence of a complete native oxide deglaze on the silicon nitride deposition. In this study it is found that silicon wafers, kept under vacuum without native oxide etching, tend to show Si3N4 growth retardation whereas gaseous HF etched wafers simultaneously processed do not. Although the linear growth rate is equivalent on both substrates, the final nitride thickness shows a difference of about 5 nm, hence, depending on the substrate pretreatment, nucleation inhibition is observed. Since Auger profiles display an oxygen free but less abrupt Si3N4/Si interface on the deglazed wafers, a silicon-rich interface layer introducing a refractive index gradient in the film provides apparently thicker layers by ellipsometric measurements of very thin nitride deposited on deglazed silicon (<10 nm). However, while nothing is deposited on native oxide, a nitride layer measured at 3.4 nm on deglazed mono shows a remarkable oxidation resistance similar to 2.3 nm pure nitride, whereas a 5-6 nm nitride measured on native oxide after 7 minutes more deposition time is slightly less resistant. This demonstrates not only that nitride is deposited on in situ deglazed mono without nucleation retardation but also that. as a consequence of this, these very thin films have a more homogeneous thickness.