Photobase generator assisted pitch division

Abstract

The drive to sustain the improvements in productivity that derive from following Moore's law has led the semiconductor industry to explore new technologies that enable production of smaller and smaller features on semiconductor device. Pitch division techniques and double exposure lithography are approaches that print features beyond the fundamental resolution limit of state-of-art lenses by modifying the lithographic process. This paper presents a new technique that enables pitch division in the printing of gratings using only a single exposure that is fully compatible with the current manufacturing tools. This technique employs a classical photoresist polymer together with a photoactive system that incorporates both a photoacid generator (PAG) and a photobase generator (PBG). The PBG is added to the resist formulation in higher molar concentration than the PAG, but has a base production rate that is slower than the acid production rate of the PAG. The PBG functions as a dose-dependent base quencher, which neutralizes the acid in high dose exposure regions but not in the low dose regions. This photoactive system can be exploited in the design of both positive tone and negative tone resist formulations that provide a developed image of a grating that is twice the frequency of the grating on the mask. A simulation of this process was performed for a 52 nm line and space pattern using PROLITH and customized codes. The results showed generation of a 26 nm half pitch relief image after development. Through this new technique, a 45 nm half pitch line and space pattern was experimentally achieved with a mask that produces a 90 nm half pitch aerial image. This corresponds to a k 1 factor of 0.13. The principles, the materials design and the first lithographic evaluations of this system are reported.

Polymer-bound photobase generators and photoacid generators for pitch division lithography

“…2 The mechanism of the photolysis that produces base is well characterized. 6 The target PBG monomer, 2NO was synthesized as shown in Figure 3.…”

“…2 The PAG monomer, TDF was a generous gift from Central Glass, Ltd in Japan. A polymerization reaction using the PBG monomer was performed as shown in Figure 5.…”

“…2 Even though pitch division was achieved, the line edge roughness (LER) of the resulting pattern was larger than the current standard. (Figure 2) There have been many studies designed to improve LER, which can be categorized into two groups, one is reducing the polymer "pixel" size, and the other is binding additives to polymers to minimize diffusion.…”

Photobase generator enabled pitch division: a progress report

“…The dual-tone is achieved by including both a photoacid generator (PAG) and a photobase generator (PBG) into the resist polymer formulation. The details of this concept are described in the early papers [2,3].…”

“…These particular acid generations kinetics can produce a dual tone response. In order to successfully capture the dual tone response, the image contrast needs to be higher than the E-factor which was defined in the previous paper [3] as (E n -E 0 ) / (E n + E 0 ).…”