Method for forming a
semiconductor device (200), comprising: Providing a substrate (208) comprising a plurality of first
semiconductor layers and a plurality of second
semiconductor layers arranged over the substrate (208), wherein the first and second semiconductor
layers (222, 220) have different material compositions and are arranged alternately with each other; Structuring the first semiconductor layers (222) and the second semiconductor layers (220) to form a first fin (212c) and a second fin (212b, 212d); Removing the first semiconductor layers (222) from the first fin (212c) and the second fin (212b), such that a first section of the structured second semiconductor layers (220) becomes first floating nanostructures (220) in the first fin (212c), and a second section of the structured second semiconductor layers (220) becomes second floating nanostructures (220) in the second fin (212b);
Doping a threshold-modifying
impurity into the first suspended nanostructures (220) in the first fin (212c), wherein the
doping of the threshold-modifying
impurity includes the application of a
plasma-assisted low-temperature
doping process; Forming a first
gate stack (260c) over the first fin (212c), wherein a section of the first
gate stack (260c) envelops the first floating nanostructures (220), thereby forming a first
transistor with a first
threshold voltage; and Forming a second
gate stack (260b) over the second fin (212b), wherein a section of the second gate stack (260b, 260d) envelops the second floating nanostructures (220), thereby forming a second
transistor with a second
threshold voltage which is higher than the first
threshold voltage.