Takehiro Seshimo

Polarity-Switching Top Coats Enable Orientation of Sub–10-nm Block Copolymer Domains

Thermally Transforming Thin Films Nanoscale features can be created by the phase separation that occurs in block copolymers that join together polymer segments with different wetting properties. For applications such as lithography, it is useful to generate small features and to orient them through simple processing steps. Top-layer coatings should be able to help drive alignment, but it is difficult to coat a layer that also has strong enough interactions to influence assembly. Bates et al. (p. 775) developed a water-soluble polymer that can top-coat lamellaforming block copolymers and that transforms during thermal annealing into a neutral wetting layer that helps drive the formation of vertically oriented lamellae. A chemical reaction in a thin polymer film imposes orientational ordering of lamellar domains in an underlying film. Block copolymers (BCPs) must necessarily have high interaction parameters (χ), a fundamental measure of block incompatibility, to self-assemble into sub–10-nanometer features. Unfortunately, a high χ often results from blocks that have disparate interfacial energies, which makes the formation of useful thin-film domain orientations challenging. To mitigate interfacial forces, polymers composed of maleic anhydride and two other components have been designed as top coats that can be spin-coated from basic aqueous solution in the ring-opened, acid salt form. When baked, the anhydride reforms and switches polarity to create a neutral layer enabling BCP feature alignment not possible by thermal annealing alone. Top coats were applied to the lamella-forming block copolymers poly(styrene-block-trimethylsilylstyrene-block-styrene) and poly(trimethylsilylstyrene-block-lactide), which were thermally annealed to produce perpendicular features with linewidths of 15 and 9 nanometers, respectively.

Studies of the Photo Acid Generator Material Design for Chemically Amplified Photoresists

In current optical lithography, resolution is required to reach for 45 nm half-pitch and a chemically amplified resist (CAR) is used for a wide variety of applications. For ArF lithography beyond the 45 nm half-pitch, it is important to control pattern quality. The molecular design of a photo acid generator (PAG) is very important in the study to control not only acid strength but also acid diffusion length. Various novel PAGs that have different characteristics were synthesized for resist performance improvement. Acid molecular size was determined by molecular orbital (MO) calculation, and the acid diffusion coefficients (D) of these PAGs were evaluated by a bilayer method. As a result, it was found that acid diffusion coefficient (D) could not be controlled simply by adjusting anion molecular size. It may be presumed that the molecular interaction between acid generated by the exposure and polymer matrix areas is one of the most important key factors for controlling acid diffusion.

Photobase generator enabled pitch division: a progress report

Pitch division lithography (PDL) with a photobase generator (PBG) allows printing of grating images with twice the pitch of a mask. The proof-of-concept has been published in the previous paper and demonstrated by others. Forty five nm half-pitch (HP) patterns were produced using a 90nm HP mask, but the image had line edge roughness (LER) that does not meet requirements. Efforts have been made to understand and improve the LER in this process. Challenges were summarized toward low LER and good performing pitch division. Simulations and analysis showed the necessity for an optical image that is uniform in the z direction in order for pitch division to be successful. Two-stage PBGs were designed for enhancement of resist chemical contrast. New pitch division resists with polymer-bound PAGs and PBGs, and various PBGs were tested. This paper focuses on analysis of the LER problems and efforts to improve patterning performance in pitch division lithography.

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.

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.

Directed self-assembly of Si-containing and topcoat free block copolymer

Directed self-assembly (DSA) of block copolymers (BCPs) with conventional lithography is being thought as one of the potential patterning solution for future generation devices manufacturing. New BCP platform is required to obtain resolution below 10nm half pitch (HP), better roughness, and defect characteristics than PS-b-PMMA. In this study, we will introduce the newly developed Si-containing high chi BCP which can apply perpendicular lamellar orientation with topcoat free, mild thermal annealing under nitrogen process conditions. It will be also shown in experimental results of graphoepitaxy demonstration for L/S multiplication using new high chi BCP.

A study of the photo acid generator material design for chemically amplified photoresists

In current optical lithography, resolution is required to reach for 45 nm half-pitch and a chemically amplified resist (CAR) is used for a wide variety of applications. For ArF lithography beyond the 45 nm half-pitch, it is important to control pattern quality. The molecular design of a photo acid generator (PAG) is very important in the study to control not only acid strength but also acid diffusion length. Various novel PAGs that have different characteristics were synthesized for resist performance improvement. Acid molecular size was determined by molecular orbital (MO) calculation, and the acid diffusion coefficients (D) of these PAGs were evaluated by a bilayer method. As a result, it was found that acid diffusion coefficient (D) could not be controlled simply by adjusting anion molecular size. It may be presumed that the molecular interaction between acid generated by the exposure and polymer matrix areas is one of the most important key factors for controlling acid diffusion.