Preparation and properties of SiO2–SiO x heterostructures formed by uninterrupted processing by remote plasma enhanced chemical vapor deposition

Abstract

Heterostructures of SiO2 and SiOx are formed by remote plasma enhanced chemical vapor deposition without switching or interrupting the gases and their flow through the deposition chamber, or the radio-frequency (rf) power. Selectively exciting the process gases, e.g., only oxygen (O2) or both O2 and silane (SiH4) simultaneously, produces SiO2 or SiOx, respectively. Only when the plasma afterglow extends into the chamber, thereby activating silane, do suboxides form. Control of the plasma afterglow is accomplished with the plasma bias assembly, located between the plasma tube and the deposition region, and heterostructures are formed by switching the grid bias between floating and grounded states. We have examined the deposited heterostructures by transmission electron microscopy (TEM) and find the oxide/suboxide transition is abrupt. Electrical properties of the suboxide layers in metal/SiO2/Sio1/SiO2/n-Si structures have been investigated by C–V measurements. Three different structures, having oxide thicknesses of ∼20, 40, and 84 Å deposited onto the c-Si substrate have been investigated; the suboxide layer is 150 Å and the second oxide is fixed at 165 Å. Application of a +5 V gate bias allows electrons to tunnel through the 20 and 40 Å oxides into the suboxide, but the 84 Å oxide prevents any tunnel injection. The electrical characteristics of the metal/SiO2/SiO1/SiO2/n-Si structures are controlled by the tunneling of electrons into, and out of the suboxide layers.