Sidewall image transfer structures

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

• forming a semiconductor fin;
• forming a layer of sacrificial gate material on an initial oxide layer on the semiconductor fin;
• forming a first sacrificial mandrel on the layer of sacrificial gate material and forming a second sacrificial mandrel on the layer of sacrificial gate material, where the first sacrificial mandrel is formed from a first sacrificial material and the second sacrificial mandrel is formed from a second sacrificial material;
• forming a first oxide layer on the first sacrificial mandrel and a second oxide layer on the second sacrificial mandrel, the first oxide layer having a thickness that is less than the second oxide layer;
• removing the first sacrificial mandrel and the second sacrificial mandrel to define a first spacer and a second spacer, the first spacer having a width that is less than a width of the second spacer;
• removing exposed portions of the layer of sacrificial gate material to expose the initial oxide layer on the semiconductor fin and form a first sacrificial gate and a second sacrificial gate over channel regions of the semiconductor fin;
• forming a spacer adjacent to the first sacrificial gate and a spacer adjacent to the second sacrificial gate;
• depositing an insulator layer over a source/drain region;
• removing the first sacrificial gate and the second sacrificial gate to form a first cavity and a second cavity that expose channel regions of the semiconductor fin;
• and
• forming a first gate stack in the first cavity and a second gate stack in the second cavity.