Challenge toward breakage of RLS trade-off for EUV lithography by Photosensitized Chemically Amplified Resist (PSCAR) with flood exposure

Abstract

This paper proposes a promising approach to break the resolution (R), line-edge-roughness (LER), and sensitivity (S) trade-off (RLS trade-off) relationships that limit the ultimate lithographic performance of standard chemically amplified resists (CAR). This is accomplished in a process that uses a Photosensitized Chemically Amplified Resist TM (PSCAR TM) ** in combination with a flood-exposure in an in-line track connected to a pattern exposure tool. PSCAR is a modified CAR which contains a photosensitizer precursor (PP) in addition to other standard CAR components such as a protected polymer, a photo acid generator (PAG) and a quencher. In this paper, the PSCAR concept and the required conditions in resist formulation are carefully explained. In the PSCAR process, the sensitivity improvement is accomplished by PAG decomposition to selectively generate more acid at the pattern exposed areas during the flood exposure. The selective photosensitization happens through the excitation of the photosensitizer (PS) generated by the deprotection of the PP at the pattern exposed areas. A higher resist chemical gradient which leads to an improved resolution and lower LER values is also predicted using the PSCAR simulator. In the PSCAR process, the improved chemical gradient can be realized by dual acid quenching steps with the help of increased quencher concentration. Acid quenching first happens simultaneously with acid catalytic PP to PS reactions. As a result, a sharpened PS latent image is created in the PSCAR. This image is subsequently excited by the flood exposure creating additional acid products at the pattern exposed areas only. Much the same as in the standard CAR system, unnecessary acid present in the non-pattern exposed areas can be neutralized by the remaining quencher to therefore produce sharper acid latent images. EUV exposure results down to 15 nm half pitch (HP) line/space (L/S) patterns using a PSCAR resist indicate that the use of PSCAR has the potential to improve the sensitivity of the system while simultaneously improving the line-width-roughness (LWR) with added quencher and flood exposure doses. In addition, improved across-wafer critical dimension uniformity (CDU) is realized by the use of a PSCAR in combination with a flood exposure using pre α UV exposure module.

Estimation of resist sensitivity for extreme ultraviolet lithography using an electron beam

“…Based on the obtained results using an EB, [14][15][16] EUV pattern exposure with an UV flood exposure was carried out. [17][18][19][20] The reaction mechanisms and patterning of PSCAR TM were studied using an EB. 21,22 In this paper, we compare the EB and EUV exposures focusing on the resist sensitivity (i.e., deposition energy).…”

Photosensitized Chemically Amplified Resist (PSCAR) 2.0 for high-throughput and high-resolution EUV lithography: dual photosensitization of acid generation and quencher decomposition by flood exposure

“…PSCAR uses a flood exposure subsequent to an EUV pattern exposure to sensitize the decomposition of a photo acid generator (PAG). The preliminary results have been discussed in previous papers [13][14][15][16][17] .…”

“…In this section, we will review the basic PSCAR concept 13,14,16,17 as background information for PSCAR 2.0 shown in the following section. PSCAR photosensitizes acid generation in order to obtain higher sensitivities and enhanced contrast.…”

“…This PS photosensitizes PS-PAG decomposition and creates additional acid products. This photosensitization most likely occurs through electron transfer from excited states of PS to PAG 17,22 . The PS image can be improved by acid quenching in the first step and therefore the PS can create an improved acid image by photosensitization.…”

Relationship between Sensitization Distance and Photon Shot Noise in Line Edge Roughness Formation of Chemically Amplified Resists Used for Extreme Ultraviolet Lithography

“…Several methods to increase the quantum efficiency have been investigated. The increase in the reduction potential of an acid generator [11], acid amplification [12], photosensitized chemically amplified resist (PSCAR TM ) [13,14], and acid generation promoter [15] are candidates to enhance the (apparent) quantum efficiency. The photon shot noise is a significant concern in the sensitivity enhancement through the increase of the quantum efficiency.…”