Theoretical Study On Directed Self-assembly Of Block Copolymer In Rectangular Confinement

Moore's law is the observation that the number of transistors in a dense integrated circuit doubles approx-imately every two years.It means the semiconductor industry continuously pursues approaches to fabricating nanostructures with higher resolution and throughput at lower cost.As an important manufacturing process of semiconductor,lithography is approaching its physical limit for fabricating large-scale defect-free geometrical-ly simple patterns and device-orientated,irregular structures with sub-10nm node.New strategy of fabricating large-scale perfectly ordered patterns via directed self-assembly of block copolymer becomes the most realistic and possible technology that is feasible to fabricate nanoimprint template to manufacture integrated circuits of semi-conductor industry.Block copolymer(BCP),a kind of macromolecules which is jointed via covalent bonds by two or more homopolymers,can self-assembly into nano-scale periodic morphologies(5-100nm).However,as a typical system of soft matter,block copolymer is often interfered by thermal fluctuations result-ing in the formation of defective morphologies.Therefore,it has become a hot topic to direct the self-assembly of block copolymer to form large-scale ordered nanostructures.Directed self-assembly(DSA)of block copolymer is one of the most effective methods to form long-range order of BCP domains.Geometrically confined systems and topographical or chemical guiding pattern on the substrate have been devised to guide the self-assembly of block copolymers to form the desired nanostructures with controllable orientation.In this thesis,the heterogeneous nucleation process during the phase separation of binary blends of the AB diblock and the C(AB/C blends)homopolymer induced by rectangular confinement is systematic studied by cell dynamics simulation based on the Time-Dependent Ginzburg-Landau theory.By tailoring the surface potentials of the sidewalls,large-scale ordered hexagonal pattern is achieved,and the problem of angle mismatch between the square well and the hexagonal lattice is resolved.Relevant parameters and tolerance window of rectangular sizes and field strength for ordered structures has been discussed by our simulation.Meanwhile,the dynamical behavior of the single defect in the system is also analyzed.In chapter one,we give an introduction to the background and progress of the studies on the directed self-assembly of block copolymers.In chapter two,we introduce widely used theoretical methods on block copolymer researching and Time-dependent Ginzburg-Landau(TDGL)Theory for AB/C binary model is de-scribed in detail.In chapter three,the self-assembly process of AB/C blends induced by rectangular confinement is sys-tematic studied by cell dynamics simulation based on the TDGL,and large-scale ordered hexagonal patterns is achieved via heterogeneous nucleation.Firstly,we examine the occurrence of heterogeneous nucleation in a square well with a uniform surface potential.Three typical cases of nucleations are observed with various field strengths,including the two types of corner-induced nucleations and one type of side-induced nucleations.In these cases,the defects are unavoidably generated on the boundaries of domain grains with dissimilar ori-entations.This implies an intrinsic difficulty of yielding the perfect hexagonal patterns with the rectangular confinement whose sidewalls have a uniform surface potential.Then we turn to the case in which one pair of parallel sidewalls,for example,at the x direction,has a stronger surface potential than the other.In this case,the two sidewalls at the x direction result in lines of nucleation domains at their surfaces,whereas the others at the y direction ensure that the domain grains possess correlated positions at the x direction.Our simulations predict a parameter window of the field strengths for the effective direction toward the perfect pattern.Furthermore,we have discussed tolerance to the rectangular sizes,the DSA scheme based on the heterogeneous nucleation that occurred in the rectangular well with tailored surface potentials exhibits a strong tolerance to the rectangular sizes.The results may provide a facile route to prepare large-scale ordered patterns via a simple rectangular confinement.In chapter four,we have tracked the mobility,approach,and annihilation of defects in hexagonally packed cylinder-forming AB/C blends.Penta-hepta defects can be categorized into two types(slip-type and climb-type)according to the dynamical behavior of defects,and samples for each type are also provided.Reaction condition is given to better explain reactions which result from defect-defect encounters in block copolymer.It is hoped that the results provide a new idea for eliminating the defect.