28 nm pitch of line/space pattern transfer into silicon substrates with chemo-epitaxy Directed Self-Assembly (DSA) process flow

• We demonstrated DSA pattern transfer with 20–25 nm of block-copolymer.
• We developed several approaches to increase the etch selectivity of PS towards PMMA.
• We introduced SiCl4 encapsulation prior to Si3N4 hardmask etch.
• LWR/LER of 2.5–2.6 nm can be demonstrated.
• DSA trenches of 67 nm depth and 15 nm width can be created.

Directed Self-Assembly (DSA) using block-copolymer (BCP) materials is considered as an alternative to Extreme Ultra-Violet (EUV) lithography for sub-14 nm half pitch technology. A BCP with natural periodicity of 28 nm was assembled on 84 nm pitch pre-pattern. 3X feature multiplication can be achieved with the chemo-epitaxy DSA flow. The BCP thickness should be thin in order to reduce the self-assembly defectivity. As a consequence, plasma etch process to transfer such thin polymer material to subsequent underlayer becomes a challenging task. The main purpose of this paper is to study the DSA pattern transfer capability of 20–25 nm BCP layer aiming at silicon fin patterning through the Si3N4 hardmask. Alternative Ar/O2 and Ar plasmas were developed to increase the selectivity of PMMA to PS, and as well as reducing hydrogen passivation plasma for neutral brush layer etch. A SiCl4 encapsulation process was introduced to increase the selectivity towards Polystyrene during the Si3N4 hardmask patterning. Finally, DSA full pattern transfer to create 14 nm half-pitch line trenches with the silicon depth of 67 nm was achieved. Line width roughness (LWR) and line edge roughness (LER) of 2.56 nm and 2.64 nm respectively were achieved after PMMA removal. This DSA-based 14 nm half pitch line and space enable the building of fin structures meeting future 7 nm-technology node (N7) design rules.

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