Yasuhisa Inao

Fabrication of half-pitch 32nm resist patterns using near-field lithography with a-Si mask

We evaluated the performances of Cr and amorphous Si (a-Si) films as light absorber materials for photomasks of near-field lithography on the basis of numerical studies using finite-difference time domain method and experimental results of fabrication process. With exposure experiments using both a Cr mask and an a-Si mask, fine performance of an a-Si near-field mask was demonstrated with respect to resolution. A half-pitch 32nm resist pattern of 120nm high was fabricated through the near-field lithography using the a-Si mask and a subsequent trilayer resist process.

Exposure dependence of the developed depth in nonadiabatic photolithography using visible optical near fields

We have developed new type of photolithography based on a nonadiabatic photochemical process that exposes an ultraviolet-photoresist using a visible optical near field. Investigating the exposure dependence of the developed depth using nonadiabatic photolithography, we found that the depth increased with the exposure threshold. To explain this result, the optical field intensity was simulated by using the finite-difference time-domain method. The evolution of the developed depth was proportional to the optical field intensity and its spatial gradient, agreeing closely with the simulated result that took into account the nonadiabatic processes. Another experimental result is to support our explanation, that in nonadiabatic photolithography, a component of the exposure progresses inside the photoresist.

Photo-deprotection resist based on photolysis of o-nitrobenzyl phenol ether; challenge to half-pitch 22 nm using near-field lithography

We propose a non chemically-amplified positive-tone photoresist based on photolysis of o-nitrobenzyl phenol ether (NBP). The increase in the amount of the phenolic hydroxyl group just after the exposure to the i-line propagation light is observed via IR spectroscopy. Using near-field lithography (NFL) combined with the NBP, we form half-pitch (hp) 32 nm line and space (L/S) patterns with lower line edge roughness (LER) than those of a chemically amplified resist (CAR). The high-resolution feature of the NBP is attributed to the photoreaction system without the acid diffusion, which is inherently involved in CARs, although the NBP requires six times as much exposure dose as the CAR does. A Hp 32 nm L/S patterns with 10 nm depths are successfully transferred to the 100 nm thick bottom-layer resist through the tri-layer resist process. Hp 22 nm L/S patterns with 10 nm depths are also fabricated on the top portion of a single-layer of NBP.