Reactive ion etching of deep trenches in silicon with CF2Cl2 and O2

Silicon trenches are used for modern device isolation or three-dimensional capacitors in dynamic memories. For etching of deep trenches in silicon a process using a mixture of CF2Cl2 and O2 has been investigated. Competitive reactions in the trench favour deposition of SiO2-like material on the side walls and the cause anisotropic etching of the trenches under conditions necessary for high selectivity to the oxide mask and high silicon etch rates. In this paper, the influence of the oxygen concentratuin in the gas micture on the trench shape and on the contamination of the trench bottom is described. Further, the contribution of He addition in the etching gas for improving the anisotropy of trenches with a smooth is discussed. Finally, the results of initial investigations of structural effects on the trench process are shown, especially the dependence of the trench depth and shape on etching time for various mask sizes.