Semiconductor devices and methods of forming

Abstract

A middle contact etch stop layer (MCESL) with a multi-layered structure is formed over the interlayer-dielectric layer (ILD) and the gate structure of a semiconductor device, and an interconnect structure is then formed on the MCESL. The MCSEL includes a first dielectric layer (e.g., SiOCN), a second dielectric layer (e.g., SiOC), and a third dielectric layer (e.g., SiO) formed successively over the ILD and the gate structure. A dielectric constant of the first dielectric layer is higher than that of the second dielectric layer and that of the third dielectric layer. The first dielectric layer performs most of etch stopping function of the MCESL. The second dielectric layer helps to reduce the overall dielectric constant of the MCESL, and also functions as a buffer layer to reduce downward oxygen diffusion from the third dielectric layer into the gate structure. The third dielectric layer helps to achieve improved photolithography quality.

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