Development of plasma etching processes to pattern sub-15 nm features with PS-b-PMMA block copolymer masks: Application to advanced CMOS technology

Abstract

Pattern transfer using poly(styrene-block-methyl methacrylate) copolymer films and reactive ion etchingThe best strategies to transfer nanoholes formed from the self-assembly of Polystyren/ Polymethylmethacrylate (PS/PMMA) based block copolymers into a silicon substrate are investigated. The authors show that specific issues are associated with the plasma etching of materials through the PS masks obtained from self-assembly. Indeed, due to the nanometric size of sub-15 nm contact holes and to their inherently high aspect ratio (>5), plasma etching processes typically used to etch SiO 2 and silicon in the microelectronic industry must be revisited. In particular, processes where the etching anisotropy relies on the formation of passivation layer on the feature's sidewalls are not adapted to nanometric dimensions because these layers tend to fill the holes leading to etch stop issues. At the same time, the ion bombarding energy must be increased as compared to a typical process to overcome differential charging effects in high aspect-ratio nanoholes. However, by developing appropriate processes-such as synchronized pulsed plasmas-the authors show that it is possible to etch 70 nm deep holes into silicon by using block copolymers and a hard mask strategy. Another interesting observation resulting from these experiments is that for sub-15 nm holes, a critical dimension (CD)-dispersion of few nm leads to strong aspect ratio dependent etch rates. In addition, a careful analysis of the dispersion of the holes' CD after each plasma steps shows that the CD control is far from satisfying advanced CMOS technology requirements. A critical issue comes from the uncompleted PMMA removal from the PS/PMMA matrix during our self-assembly process: variable amount of PMMA remains in the PS holes, leading to microloading effects during the etching steps, which in turn generates CD-control loss. This problem perhaps can be solved by combining UV exposure to acetic acid treatment to provide PS masks free of PMMA residues before plasma etching.

Dissipative particle dynamics for directed self-assembly of block copolymers

“…With the advancement of modern technology, intricate designs of nanostructures with nanoscale feature sizes are needed for various applications. Self-assembly of block copolymers (BCPs) offers a feasible route to fabricate such nanopatterns with feature sizes ranging from 5-500nm [1][2][3][4][5][6][7][8][9][10][11] . Block copolymers are comprised of two or more chemically distinct subchains, which are linked together by covalent bonds.…”

Etched ion tracks in amorphous SiO2 characterized by small angle x-ray scattering: influence of ion energy and etching conditions

“…[10]. Conical pores of aspect ratio around 5:1 have been fabricated in Si by directed self-assembly of block copolymers (polystyrene-b-polymethylmethacrylate, PS-b-PMMA) [11,12] and in SiO 2 . [13], however these pores are not randomly distributed, and they have relatively wide size distributions and surface roughness inside the pore walls.…”

Dry-Etching Processes for High-Aspect-Ratio Features with Sub-10 nm Resolution High-χ Block Copolymers

“…The VUV fluence however, owing to self-absorption by H2, 21 is larger at lower pressure, where the ion flux is also higher, and the atomic flux is proportionally lower. Considering our intent of modifying both the PS and the PDMSB, a slower etch rate of the topcoat is rather beneficial, although the larger ion flux reduces the selectivity with PS (severely ion-limited etch rate 22 ). Provided the results observed on the effect of VUV on material modification during the etch process and that the limiting factor for etch-rate is the atomic hydrogen flux, we deduced that the etch rate will vary linearly with pressure and ICP power in the range of pressure and power relevant in the context.…”