MICROLOADING EFFECT IN HIGHLY SELECTIVE SIO2 CONTACT HOLE ETCHING EMPLOYING INDUCTIVELY-COUPLED PLASMA

The highly selective SiO2 etching achieved in the downstream region of the inductively coupled plasma (ICP) employing C4F8+H-2 was studied regarding polymer film deposition characteristics. Polymer deposition into as-etched 0.5 mu m holes at floating potential showed an overhang feature with C4F8 alone and a conformal one with C-4 F-8+30% H-2. When as-etched 0.5 mu m holes were subjected to C4F8+30% H-2 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 mu 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 mu m phi (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% H-2. The latter explains the origin of high selectivity.