Investigation of stress in shallow trench isolation using UV micro-Raman spectroscopy

Abstract

We present an investigation of local mechanical stress in shallow trench isolation by UV micro-Raman spectroscopy. UV light (364 nm) penetrates only 15 nm into silicon. In contrast to conventional micro-Raman spectroscopy using visible light only the stress very close to the surface is monitored. In this way, local areas of high stress can be detected, that are not seen with longer wavelength light due to averaging. We demonstrate the advantages of the UV method by an investigation of the influence of different trench oxide densification ambients on the amount of mechanical stress in the silicon substrate. We find, that large mechanical stress up to 800 MPa is introduced at the active area edges during densification in steam ambient. This stress is caused by the formation and growth of a bird’s beak, which may lead to defect creation especially in small trenches. This investigation demonstrates the capability to use UV micro-Raman spectroscopy in ULSI technology.