Cl Incorporation at the Si / SiO2 Interface during the Oxidation of Si in HCl /  O 2 Ambients

Abstract

Transmission and analytical electron microscopy, nuclear backscattering, and secondary ion mass spectroscopy have been used to study the incorporation of C1 at the Si/SiO2 interface during the oxidation of Si. Oxidations were carried out in the range of 1100~176 for 10-120 min and with HC1 additions from 1-13%. It was found that a critical concentration of C1 (2 • 10~Scm -2) is required before a Cl-rich phase is observed. X-ray microanalysis indicates that the matrix in the interfacial region still contains at least about 2 • 1015 cm -2 as the Cl-rich phase forms. These two observations suggest that the Cl-rich phase formation takes place in order to reduce the reacted C1 supersaturation.in the SiO2 matrix. Agglomerates, whose growth occurs by thickening and/or coalescence phenomena, are the final morphology observed during the continuing C1 incorporation. Models relating Na-ion passivation to the Cl-rich phase are shown to require modification in terms of the microstructural development.The oxidation of silicon in chlorine-containing ambients is known to cause chlorine incorporation into the SiO2 near the Si/SiO2 interface il,. 2). For several oxidation conditions, phase separated regions have been observed (4-6). It has been asserted that both chlorine incorporation and sodium neutralization are related to the development of the Cl-rich phase formed at the Si/SiO2 interface (3-5).Recent CI concentration vs. distance profiles through the bulk oxide determined by secondary ion mass spectroscopy (SIMS) were interpreted to be the result of fieldaided diffusion (7). The profiles show the chlorine concentration to increase exponentially toward the Si/SiO2 interface where a peak occurs. Auger analysis-sputter profiles indicate the interface C1 peak is <~3 nm thick (7, 8). This peak is presumably the result of the Si/SiO2 interface acting as a "sink of the electrochemical potential" for C1 (7). Simple steady-state diffusion models have been proposed to describe the C1 incorporation as a function of oxide thickness (7-9).To improve the understanding of C1 incorporation, we have carried out detailed determinations of both the Si/SiO2 interface microstructure and the chlorine concentration and its lateral distribution along the interface. The interface morphology was determined by transmission electron microscopy (TEM). The total C1 content was obtained using nuclear backscattering (NBS) measurements (1, 2). The analytical electron microscope (AEM) [i.e. with the microscope operating in scanning transmission (STEM) mode] was .used to determine the local C1 concentration at the interface. The CI concentration profile was investigated in depth on several samples by SIMS. The effect of the initial oxide thickness on the chlorine incorporation process has also been studied. These results will be discussed with the objective of trying to understand the processes controlling chlorine incorporation. The relationship between the Cl-rich phase morphology and the Na-ion passivation models is briefly considered.