Abstract : The aim of this work is to understand how PS-b-PMMA thin films presenting vertically oriented cylindrical PMMA nanodomains self-assemble. These films are used to organize discrete nano-objects with small dimensions (diameter ~ 20 nm) and in high density (~1011/cm ²).
It is shown that the vertical cylinder phase is indirectly formed during thermal annealing starting from a homogeneous phase. First, a disordered cylinder phase is created within the film, followed by the nucleation and growth of the vertical cylinder phase . This implies the presence of defects at the grain boundaries so that the obtained films present an hexatic order according to KTHNY theory.
For defect sites, the unit cell could adopt an anisotropic configuration due to the stress of the lattice. In this case, in order to minimize the free energy of the system, the PMMA domain deforms commensurately with the unit cell and adopts an elliptical or a lozenge-like cross section, in good agreement with strong segregation considerations. However, these strained configurations reveal to be metastable so that thermal fluctuations could induce a transition from a distorted column to two other circular columns. This phenomenon has been used to explain the motion of dislocations.
Finally, we use these films as a mask to realize, by etching plasma, Si/SiGe nano-pillars or MOS capacities with Pt nanocristals.