Method for forming a trench in a first semiconductor layer of a multi-layer system

A method for forming a trench in a first semiconductor layer of a multi-layer system, comprising the following steps:

• applying a mask layer onto the first semiconductor layer, at least one recess being formed in the mask layer in such a way that the first semiconductor layer is exposed within the recess;
• applying a protective layer, the protective layer completely covering or modifying the mask layer and the first semiconductor layer exposed within the recess;
• applying a second semiconductor layer onto the protective layer;
• etching the second semiconductor layer in such a way that the second semiconductor layer is completely removed in a subarea surrounding the recess of the mask layer, the protective layer acting as an etching stop, and the protective layer being exposed in the removed subarea;
• etching the protective layer in such a way that the first semiconductor layer is exposed within the recess;
• and
• forming the trench in the first semiconductor layer, the recess of the mask layer serving as an etching mask, and the trench being formed by a cyclical alternation between etching steps and passivation steps, material of the first semiconductor layer being successively removed by the etching steps, and a passivation of inner walls of the trench taking place by the passivation steps, and a first etching step of the etching steps being longer than subsequent etching steps of the etching steps so that a greater lateral material removal takes place at an upper edge of the trench than in areas situated beneath the upper edge.