METHOD FOR FORMING THE ISOLATION LAYER OF SEMICONDUCTOR MEMORY DEVICE

A method for forming an isolation layer in a semiconductor memory device is provided to ensure a gap-fill margin by both using an HDP(High-Density Plasma) oxide layer manner and an HARP(High Aspect Ratio Process) manner. After a tunnel oxide layer(101), a polysilicon layer(102), a nitride layer(103) and an oxide layer are sequentially formed on a semiconductor substrate(100), the oxide layer, the nitride layer, the polysilicon layer and the tunnel oxide layer are etched to expose a predetermined region of the substrate. The exposed substrate is etched to form trenches(105), and then an HDP oxide layer(107), a sacrificial layer and an HSQ(Hydrogen Silses Quioxane) layer are formed on the entire surface of the substrate. The substrate is subjected to a low-selectivity etching process and high-selectivity etching process so that the HDP oxide layer remains in the trenches and the HSQ layer is fully removed from a peripheral region of the substrate. An insulating layer(110) formed on the entire surface to form an isolation layer.