For etching trenches in single-crystal silicon, dry etch systems with different chamber geometries and chemistries are used. In this work the influence of the etch parameters and the oxide mask on the trench profile is investigated using a triode reactor system with chlorine as the reactive gas and additions of argon and nitrogen. It is shown that there are several possibilities for adjustment of the trench profile even if a heavily doped buried layer has to be etched. It is also demonstrated that unsymmetrical trenches or even sidewall trenching are caused by an unsuitable oxide mask.