HIGHLY SELECTIVE CONTACT HOLE ETCHING USING ELECTRON-CYCLOTRON-RESONANCE PLASMA

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 O-2 addition in C4F8 + O-2 plasma using electron cyclotron resonance (ECR) discharge. In C-4 F-8 + O-2 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 O-2, dissociation of high-mass species such as C2F5 proceeds, and at about 20% O-2, 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.