METHOD FOR FORMING TRANSISTOR STRUCTURES

According to an aspect of the present inventive concept there is provided a method for forming a first and a second transistor structure, wherein the first and second transistor structures are spaced apart by an insulating wall (108), and the method comprising:forming on a semiconductor layer of the substrate a first semiconductor layer stack (102) and a second semiconductor layer stack (104), each layer stack comprising in a bottom-up direction a sacrificial layer and a channel layer (114), wherein the layer stacks are spaced apart by a trench extending into the semiconductor layer substrate, the trench being filled with an insulating wall material to form the insulating wall; andprocessing the layer stacks to form the first and second transistor structures in the first and second device regions, respectively, the processing comprising forming source and drain regions and forming gate stacks;the method further comprising, prior to said processing:by etching removing the sacrificial layer of each layer stack to form a respective cavity (122) on either sides of the insulating wall underneath the channel layer of the first and second layer stack, the channel layers being supported by the insulating wall; anddepositing a bottom insulating material (124) in said cavities;wherein, subsequent to said processing, the bottom insulating material forms a bottom insulating layer underneath the source region, the drain region and the channel regions on either side of the insulating wall.