Method for forming a semiconductor device structure

A method for forming a semiconductor device structure, the method comprising:

• forming a layer stack on a substrate, the layer stack comprising sacrificial layers of a first semiconductor material and channel layers of a second semiconductor material, the channel layers alternating the sacrificial layers;
• forming over the layer stack a plurality of parallel and regularly spaced core lines;
• forming spacer lines on side surfaces of the core lines, wherein a width of the spacer lines is such that gaps are formed between spacer lines formed on neighboring core lines;
• forming first trenches extending through the layer stack by etching the layer stack while using the core lines and the spacer lines as an etch mask;
• forming insulating walls in the first trenches and in the gaps by completely filling the first trenches and the gaps with insulating wall material;
• subsequent to forming the insulating walls, removing the core lines selectively to the spacer lines and the insulating walls;
• subsequent to removing the core lines, forming second trenches extending through the layer stack by etching the layer stack while using the spacer lines and the insulating walls as an etch mask, thereby forming a plurality of pairs of fin structures, each pair of fin structures comprising a first device layer stack and a second device layer stack separated by a respective insulating wall;
• and
• modifying at least one of the first device layer stack or the second device layer stack such that the first device layer stack is an n-type device and the second device layer stack is p-type device.