Abstract
A detailed investigation to understand the mechanism of the resist action at a fundamental level is essential for future Extreme Ultraviolet Lithography (EUVL) resists. The photodynamics study of a newly developed hybrid nonchemically amplified 2.15%-MAPDSA–MAPDST resist using synchrotron radiation excitation at 103.5 eV (12 nm) is presented. Antimony was incorporated in the resist as a heavy metal absorption center in the form of antimonate (2.15%). The results showed the fast decomposition rate of the radiation sensitive sulfonium triflate. HR-XPS and sulfur L-NEXAFS spectra of the copolymer films revealed that after irradiation the Ar–S+–(CH3)2 sulfonium group bonded to the phenyl ring resisted the EUV excitation. Those results confirmed the polarity switching mechanism from hydrophilic sulfonium triflates to hydrophobic aromatic sulfides obtained in previous results. The inorganic component SbF6− included in the resist formulations as an EUV absorption enhancer was particularly illustrative of the photofragmentation process. F 1s and O 1s HR-XPS spectra showed that fluorine remains linked to the antimony, even after 15 min of irradiation. A change of the antimony oxidation state was also observed with an increase in irradiation time. The presence of the heavy metal may control the high energy deposited on the resist which finally led to very well resolved 20 nm isolated line patterns by EUVL. The 10 times improved sensitivity compared with previous poly-MAPDST resists studied in the past showed the potential of this class of hybrid resists for next generation semiconductor industry applications.
Highlights
The signal that merges, when the irradiation time increases may be assigned to a –CH2–S–CH2– functional group, i.e., a R–S+–(CH3)[2] sulfonium group bonded to the phenyl ring in the case of the 2.15% MAPDSA–MAPDST pristine resist
A detailed photodynamic study was carried out using synchrotron radiation (SR) as an excitation source as well as high surface sensitive analytical tools (NEXAFS and X-ray photoelectron spectroscopy (XPS) spectroscopy)
The investigation clearly showed a fast decomposition rate of the radiation sensitive sulfonium tri ate followed with important changes in the ester group
Summary
Which causes chemical and morphological changes in the resist surface. One of the key challenges in EUVL is simultaneously meeting resist performance targets like sensitivity, resolution, etch resistance, and line edge roughness (LER).[15]. A mechanism investigation on Hf-based hybrid photoresists have been performed by studying the in uence of surface organic ligands on the physicochemical properties of the hybrids resists.[19] In spite, the authors studied the NPs size dependence with the ultraviolet (UV) irradiation time; they were able to correlate the UV data with the EUVL pattering results They showed a relationship between the very high sensitivity to EUV radiation with the NPs size that nally led to high sensitivity and high resolution patterns. In the last years we have studied the photofragmentation of several n-CAR homopolymers and co-polymers under EUV synchrotron radiation (SR) excitation.[4,9,15,16,21] The obtained results showed that the photodegradation processes affected mainly the tri ate group and the carbon backbone of the resists In those works it was hypothesized that the neutral sul de Ar–S–CH3 is formed a er irradiation rendering the irradiated area insoluble in the developer. Near-edge X-ray absorption ne structure (NEXAFS) and X-ray photoelectron spectroscopy (XPS) were used as highly sensitive surface analytical techniques for characterization to follow the surface chemical changes a er EUV irradiation
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