Spin-on pre metal dielectric (PMD) materials are being developed for memory and logic devices at 0.10 um design rules and beyond. The stringent design rules require a PMD material with a low thermal budget, excellent gap fill capability, and etch resistance similar to that of a thermal oxide. Spin-on PMD is being developed to meet these requirements as current PMD technologies of HDP CVD and BPSG reflow are constrained by void formation or high thermal budget requirement. One common challenge that faces spin-on PMD is inhomogeneous densification, or “corner etch”. In this paper EELS-STEM, FTIR, SEM and HF wet etching were used to study the mechanism of this phenomenon. This information provides a possible route for the development of spin-on PMD resins.