Takeshi Kagatsume

HSQ process development for a superior resolution and a reasonable sensitivity for an EB master-mold for nanoimprint lithography

Half-pitch (hp) 11 to 7.5nm will be resolution requirement for 3 to 5 years later in lithography technology. In specific, hp16nm in 2015 and hp11nm in 2019 for flash memory, bit pitch (bp) 18nm in 2015, bp15nm in 2018 for HDD patterned media, such extremely fine patterning capability is expected. We have been studying a positive resist ZEP520A particularly on its developers and process for the last 5 years. And, its resolution limit is hp16nm in lines and spaces pattern and bp22nm bit patterns for patterned media, in a large and practical patterning area (Figure 1). ZE520A is an option to pursue the resolution limit for the future. However, since it is a positive-tone resist, dark erosion is significant between holes particularly on bp25nm and below, even when the highest resolution developer of an alcohol and a fluoro-carbon mixture is used. ZEP holes in the nearest were not isolated but connected due to excess dark erosion, which seemed to be caused by EB back-scattering and fogging. If a negative-tone resist is employed, it would cause residue instead between pillars. However, the residue can be eliminated by etching back to the bottom, and the pillars can be remained without defects (Figure 2).

Cold-development tool and techniquefor the ultimate resolution of ZEP520A to fabricate an EB master moldfor nano-imprint lithography for 1Tbit/inch2 BPM development

Cold-development is well-known for resolution enhancement on ZEP520A. Dipping a wafer in a developer solvent chilled by a freezer, such a typical method had been employed. But, it is obvious that the dip-development method has several inferiorities such as developer temperature instability, temperature inconsistency between developer and a wafer, water-condensation on drying. We then built a single wafer spin-develop tool, and established a process sequence, to solve those difficulties. And, we tried to see their effect down to -10degC over various developers. In specific, we tried to make hole patterns in hexagonal closest packing in 40nm, 35nm, 30nm, 25nm pitch, and examined holes pattern quality and resolution limit by varying setting temperature from room temperature to -10degC in the cold-development, as well as varying developer chemistry from the standard developer ZED N-50 (n-amyl acetate, 100%) to MiBK and IPA mixture which was a rinsing solvent mixture originally. We also examined the other developer (poor solvent mixture) we designed, N-50 and fluorocarbon (FC) mixture, MiBK and FC mixture, and IPA+FC mixture. This paper describes cold-development tool and technique, and its results down to minus (-) 10degC, for ZEP520A resolution enhancement to obtain 1Xnm bits (holes) in 25nm pitch to fabricate an EB master mold for Nano-Imprinting Lithography for 1Tbit/in2 bit patterned media (BPM) in HDD development and production.

Challenges for quality 15nm groove patterning with ZEP520A for a master fabrication for track pitch 50nm full-surface DTR-Media

Discrete Track Recording Media (DTR-Media) requires 50nm track pitch patterns and a mold as the start for 1 Tb/inch2 areal density, which is a quality 15nm groove (trench) and beyond. Last year, 14nm groove was achieved with a newly designed solvent developer for ZEP520A, we reported in PMJ 2009. But, we still need to pursue extreme high resolution such as 10nm groove or 12.5nm dot array for bit patterns with ZEP520A since no alternative was found so far. To improve ZEP520 resolution, we just keep trying to find a new developer with a lower development speed for ZEP520 than the previous one. Then, a Fluoro-Carbon was selected from various candidates. It was proved that ZEP520 and the Fluoro-Carbon developer provided 11nm groove resolution at an exposure dose of 1800μC/cm2. Furthermore, the mixture of the Fluoro-Carbon and Solvent B provided the same 11nm groove resolution at a higher sensitive, i.e. less exposure dose than the Fluoro-Carbon and even the Solvent B.

A single-nanometer nanoimprint-mask fabrication by EB lithography followed by nanoimprinting and self-aligned double-patterning

As a new scheme of a master-mold (imprint-mask) fabrication, half pitch (hp) 12nm lines and spaces (L/S) pattern was fabricated from hp 24nm L/S resist mandrels, which was prepared by EB writing as well as nanoimprinting, and followed by self-aligned double-pattering (SADP) technique. It was observed that line width roughness (LWR, 3 sigma value) was reduced and improved by a single and multiple nanoimprinting to make hp24nm resist mandrels in the new scheme. We have studied the phenomena and then revealed that the resist patterns of nanoimprinting had more sharp and smooth shoulders as well as bottom edges than EB resist patterns. Those seemed to be reflected to better LWR and LWR reduction by nanoimprinting. The new scheme has advantages of resolution enhancement and better pattern quality of LWR on a mold (mask) for nanoimprint lithography, with comparing to a conventional and single EB lithography.

A master-mold fabrication by electron beam lithography followed by nanoimprinting and self-aligned double patterning

As a new scheme of master-mold fabrication, a half pitch (hp) 12 nm line and space (L/S) pattern was fabricated from hp 24 nm L/S resist mandrels, which were prepared by electron beam (EB) writing as well as nanoimprinting, followed by the self-aligned double-patterning (SADP) technique. It was observed that the line width roughness (LWR) was reduced and improved by single and multiple nanoimprintings in the new scheme of the master-mold fabrication to make hp 24 nm resist mandrels. We have studied the phenomena and revealed that the resist pattern of nanoimprinting had sharper and smoother shoulders and bottom edges in cross section than those of the EB resist. These shoulder shapes of nanoimprinting seemed to be reflected in its LWR improvement. The new scheme has advantages of resolution enhancement and better pattern quality of LWR on a master mold for nanoimprint lithography, in comparison with conventional optical and EB lithography technologies.