Highly Selective Contact Hole Etching Using Electron Cyclotron Resonance Plasma

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Abstract
The SiO2 etching process is one of the most significant processes in ultra-large-scale integration (ULSI) fabrication. In order to obtain fine contact holes, it is necessary to achieve both highly selective etching of SiO2 over other materials, and non-reactive ion etch (non-RIE) lag. We investigated the etching characteristics and the effect of O2 addition in C4F8+O2 plasma using electron cyclotron resonance (ECR) discharge. In C4F8+O2 plasma, we can obtain dense fluorocarbon films at low pressure, and films are more durable against ion bombardment than at high pressure. This film enables the suppression of O atoms to the Si surface, and the achievement of high SiO2-to-Si selectivity. By additional O2, dissociation of high-mass species such as C2F5 proceeds, and at about 20%O2, low-mass species, such as C, CF, and CF2, increase. Thus we can obtain high SiO2-to-Si selectivity and high-aspect-ratio fine contact holes.

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