Effect Of The Sequence Structure Of Polymer Mat On Block Copolymer Self-assembly

Directed self-assembly(DSA)of block copolymers(BCP),that offers sub-lithographic resolution and reduced process complexity,is a promising alternative patterning technique for sub-10 nm structures in semiconductor manufacturing.With appropriate interfacial energy between the substrate and the BCP,the block copolymer can form phase domains perpendicular to the substrate.To induce BCP to form long range ordering of structures,chemical patterns made by lithography process and the like are required.Compared to 1:1 DSA,DSA with density multiplication can augment the capability of the lithographic process beyond the current resolution limit,multiply the feature density,improve the pattern quality and reduce the fabrication cost.However,the defect density in density multiplication is still magnitudes larger than the target defect density of 0.01 cm2.In this paper,effect of the sequence structure of polymer mat on BCP self-assembly were studied,and the densities and elimination activation energy of defect types were calculated for the first time.In order to control the sequence structure of random polymer,a series of cross-linkable PS-r-PMMA with 20-91%PS fraction were firstly synthesized by nitroxide free radical polymerization,and the neutral window was confirmed between 51%and 66%PS fraction for PS-b-PMMA lamellar block copolymer.The random copolymer with 57%styrene content was selected as the reference,and other PS-r-PMMAs were blended into 57%by 1:1.The results show that the neutral mats for self-assembly of lamellar PS-b-PMMA can also be obtained by blends of two components outside the neutral window,and the average sequence length of the blend PS-r-PMMA is different from that of the reference group.Secondly,we developed a method by convolution algorithm to analysis the DSA structure and count the defects.Inspired by the general image processing method,image enhancement and template matching,a convolution algorithm is developed to detect defects in the SEM images of BCP films and count the densities of each types of defects.Defects and artificial noises are accurately distinguished as verified by hand.The dot,terminal point and junction defects are automatically counted without any error in most SEM images by this algorithm.In order to get the reliable and reproducible results,the ratio of the BCP period(Lo)to nanometers per pixel(NPP)needs to be>6.69 and the smallest image area is 1.5 um2.Direct comparison of the two algorithms on our workstation shows that the compute speed of the convolution algorithm is about 136-147 times faster than that of the adjacent pixel determination algorithm.At the same time,the DSA and self-assembly structure analysis platform with a graphical software of the assembly image processing was built,and the analysis functions of block copolymer microphase separation structure,such as defect analysis,correlation length calculation,line width/edge roughness analysis and roundness analysis,were realized.Finally,with the DSA and self-assembly structure analysis platform developed above,the effect of the sequence structure of polymer mat on BCP self-assembly was studied.In the first,the total defect densities removal time scope was determined in this part.From 190℃ to 230℃ most defects are removed in 60 s.After 180s,all the defect densities of the assembly structure almost no longer decrease.To compare the defect densities of BCP self-assembly structure between all random polymer mats and polyblend mats,230℃ and 5 min were selected and the results show that all kinds of defect densities are change slightly with random polymer components changed,while obvious increase or decrease are observed with the repeat unit number of short blocks increasing.After that,defect densities of BCP self-assembly structures on different random copolymer mats and polyblend mats decreases from 10 s to 45 s were also been traced in this paper.PS junction,PMMA terminal point and PMMA dot removal is the main reason that the total defects decrease while the defect densities of PMMA junction,PS terminal point and PS dot only fluctuate slightly.Meanwhile,the activation energy of PS junction and PMMA terminal removal were also been calculated.The activation energy of PS junction and PMMA terminal removal decreases with PS fraction of random copolymer mats or repeat unit number of polyblend mats increase.Finally,the simulation of BCP self-assembly on neutral surface with area wetting one of the BCP phases by self-consistent field were applied.Small area with enough force drives the BCP above form dot or terminal point defects and complex defect structure could form on a big area even with slight attraction force.