Microloading Effect in Highly Selective SiO2 Contact Hole Etching Employing Inductively Coupled Plasma

Abstract

The highly selective SiO2 etching achieved in the downstream region of the inductively coupled plasma (ICP) employing C4F8+H2 was studied regarding polymer film deposition characteristics. Polymer deposition into as-etched 0.5 µ m holes at floating potential showed an overhang feature with C4F8 alone and a conformal one with C4F8+30%H2. When as-etched 0.5 µ m holes were subjected to C4F8+30%H2 plasma, the film thickness on bottom surfaces increased rapidly with increasing self-bias voltages. This result demonstrated that high selectivity in holes less than 0.8 µ m was achieved by deposition of resputtered film on the side wall onto the bottom. To analyze the bottom Si surface in deep holes, a simulated experiment was also performed using a capillary plate with 10 µ mφ (aspect ratio 40); the Si surface masked by the plate was exposed to plasma, then the Si surface was measured by X-ray photoemission spectroscopy (XPS). Etching occurred on the Si surface covered by the fluorine-rich polymer in C4F8 alone, and carbon-rich film was deposited on the Si surface with addition of 30%H2. The latter explains the origin of high selectivity.