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.

A new type of Photosensitized Chemically Amplified Resist TM (PSCAR TM) ** : "PSCAR 2.0," is introduced in this paper. PSCAR 2.0 is composed of a protected polymer, a "photo acid generator which can be photosensitized" (PS-PAG), a "photo decomposable base (quencher) which can be photosensitized" (PS-PDB) and a photosensitizer precursor (PP). With this PSCAR 2.0, a photosensitizer (PS) is generated by an extreme ultraviolet (EUV) pattern exposure. Then, during a subsequent flood exposure, PS selectively photosensitizes the EUV exposed areas by the decomposition of a PS-PDB in addition to the decomposition of PS-PAG. As these pattern-exposed areas have the additional acid and reduced quencher concentration, the initial quencher loading in PSCAR 2.0 can be increased in order to get the same target critical dimensions (CD). The quencher loading is to be optimized simultaneously with a UV flood exposure dose to achieve the best lithographic performance and resolution. In this work, the PSCAR performance when different quenchers are used is examined by simulation and exposure experiments with the 16 nm half-pitch (HP) line/space (L/S, 1:1) patterns. According to our simulation results among resists with the different quencher types, the best performance was achieved by PSCAR 2.0 using PS-PDB with the highest possible chemical gradient resulting in the lowest line width roughness (LWR). PSCAR 2.0 performance has furthermore been confirmed on ASML's NXE:3300 with TEL TM 's standalone pre-alpha flood exposure tool at imec. The initial PSCAR 2.0 patterning results on NXE:3300 showed the accelerated photosensitization performance with PS-PDB. From these results, we concluded that the dual sensitization of PS-PAG and PS-PDB in PSCAR 2.0 have a potential to realize a significantly improved resist performance in EUV lithography.

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