Takahiro Dazai

Guided self-assembly of Si-containing block copolymer with a topcoat surface treatment

Directed self-assembly (DSA) of block copolymers (BCPs) is one of candidate for next generation patterning technique. Many good demonstrations of DSA have been reported using polystyrene-block-poly(methyl methacrylate) (PS-b- PMMA) these days. On the other hands, BCPs which show high chi parameter are being developed because the BCPs can be formed smaller features than PS-b-PMMA. Si-containing BCPs are one of them. Moreover Si-containing BCPs show higher etch selectivity than PS-b-PMMA because of higher etch resistance of Si-containing block. Unfortunately, while Si-containing BCPs can be aligned by solvent annealing, they but cannot be aligned perpendicular to the substrate by thermal annealing. Because Si-containing block which has low surface energy achieves maximum interaction with air interface by forming a top parallel wetting layer to the substrate. One solution to control of surface energy on top surface is the use of Top-Coat (TC). It has been already demonstrated that TC with Si-containing BCP could form perpendicular pattern. The challenges are TC coating onto BCP film and TC stripping after annealing. In order to solve these problems, polarity-changeable type TC has been developed. The effect of TC materials to generate finger print of BCP has been reported. However, this TC process should combine with DSA process to form aligned patterns. Graphoepitaxy is one of the DSA technique to align BCP pattern using guide pattern. In this technique, the characteristic of guide pattern side wall is very important to control BCP pattern alignment for the Graphoepitaxy process. Also, in order to establish the process, there are two key parameters for the materials. One is BCP and guide pattern should have enough resistance to TC solvent through TC coating process. The other is TC can be removed easily with basic aqueous solution before BCP patterning. In this report, a detail of examination for TC Graphoepitaxy process will be discussed.

Studying the effects of chemistry and geometry on DSA hole-shrink process in three dimensions

Acquiring three-dimensional information becomes increasingly important for the development of block copolymer (BCP) directed self-assembly (DSA) lithography, as 2D imaging is no longer sufficient to describe the 3D nature of DSA morphology and probe hidden structures under the surface. In this study, using post-DSA membrane fabrication technique and STEM (scanning transmission electron microscopy) tomography we were able to characterize the 3D structures of BCP in graphoepitaxial DSA hole shrink process. Different DSA structures of singlets formed in templated holes with different surface chemistry and geometry were successfully captured and their 3D shapes were reconstructed from tomography data. The results reveal that strong PS-preferential sidewalls are necessary to create vertical DSA cylinders and that template size outside of process window could result in defective DSA results in three dimensions. Our study as well as the established 3D metrology would greatly help to develop a fundamental understanding of the key DSA factors for optimization of the graphoepitaxial hole shrink process.

Desirable material selection on self-aligned multi-patterning

For self-aligned multiple patterning, higher etch selectivity between mandrel and spacer is desired to lessen roughness, and thereby prevent pitch walk. We selected dual carbon layers as mandrels and silicon oxide films as spacers for a new self-aligned quadruple patterning process since they potentially provide infinite etch selectivity. We gained insolubility and etch selectivity between two carbon layers by infiltrating trimethylsilyldimethylamine into one of the carbon layers under the ambient atmosphere. Significantly, neither necking nor recess were observed when the spin-on-glass antireflective coating was removed. Thus, a SAQP scheme was developed and successfully demonstrated a sub15-nm halfpitch pattern. Additionally, this scheme improves affordability since all the processes can be performed in the ambient pressure within a coater module.

Ionic Liquids as Additives to Polystyrene-Block-Poly(Methyl Methacrylate) Enabling Directed Self-Assembly of Patterns with Sub-10 nm Features

Polystyrene- block-poly(methyl methacrylate) (PS- b-PMMA) is one of the prototypical block copolymers in directed self-assembly (DSA) research and development, with standardized protocols in place for processing on industrially relevant 300 mm wafers. Scaling of DSA patterns to pitches below 20 nm using PS- b-PMMA, however, is hindered by the relatively low Flory-Huggins interaction parameter, χ. Here, we investigate the approach of adding small amounts of ionic liquids (ILs) into PS- b-PMMA, which selectively segregates into the PMMA domain and effectively increases the χ parameter and thus the pattern resolution. The amount of IL additive is small enough to result in limited changes in PS- b-PMMAs surface and interfacial properties, thus maintaining industry-friendly processing by thermal annealing with a free surface. Three different ILs are studied comparatively regarding their compositional process window, capability of increasing χ, and thermal stability. By adding ∼3.1 vol % of the champion IL into a low-molecular-weight PS- b-PMMA ( Mn = 10.3k- b-9.5k), we demonstrated DSA on chemically patterned substrates of lamellar structures with feature sizes <8.5 nm. Compatibility of the PS- b-PMMMA/IL blends with the standardized processes that have been previously developed suggests that such blend materials could provide a drop-in solution for sub-10 nm lithography with the processing advantages of PS- b-PMMA.