A Novel T-Shaped Shallow Trench Isolation Technology

Abstract

This paper describes a novel T-shaped shallow trench isolation (STI) technology, which has the same effective isolation length with conventional STI but significantly reduced aspect ratio. The T-shaped STI is formed using 2-step trench etches. After the formation of the 1st trench of a relatively low aspect ratio, oxide spacer is formed inside the trench sidewall. And the 2nd trench is made to ensure an effective isolation length. When T-shaped STI is filled with undoped silicate glass (USG) and high density plasma (HDP) oxide, the mouth of 2nd trench is closed by the overhang of filling materials so that the effective aspect ratio of T-shaped STI can be lowered. We evaluated the electrical characteristics of T-shaped STI. Also, we performed simulation of the stress distribution and the junction profile. T-shaped STI has shown comparable characteristics to conventional STI and no electrical or physical degradation was found. We have adopted this technology to 512 Mbit flash memory (0.5 µm cell pitch) and obtained excellent structural and electrical properties. In addition, we obtained the excellent gap filling ability even for the 1 Gbit flash memory (0.34 µm cell pitch) and beyond.