Chemically amplified lithographic

A change of a polarity from a polar to nonpolar state (reverse polarity change) can be accomplished by the pinacol-pinacolone rearrangement and has been exploited in chemically amplified lithographic imaging [151, 348-350]. The pinacol rearrangement involves conversion of vie-diols to ketones or aldehydes with an acid as a catalyst (Fig. 115). 

H. Ito, Chemical amplification resists for microlithography, Adv. Polym. Set, 172, 149 (2005). Ito, Y. Maekawa, R. Sooriyakumaran, and E.A. Mash, Acid catalyzed dehydration A new mechanism for chemically amplified lithographic imaging, Polymers for Microelectronics, ACS Symp. Series 537, L.F. Thompson, C.G. Willson, and S. Tagawa, Eds., p. 64, American Chemical Society, Washington, DC. (1994). 

Acid Proliferation Reactions and Their Application to Chemically Amplified Lithographic Imaging... 

Polymer Properties and Lithographic Performance in Chemically Amplified Resins. 

The process control of the post-exposure bake that is required for chemically amplified resist systems deserves special attention. Several considerations are apparent from the previous fundamental discussion. In addition for the need to understand the chemical reactions and kinetics of each step, it is important to account for the diffusion of the acid. Not only is the reaction rate of the acid-induced deprotection controlled by temperature but so is the diffusion distance and rate of diffusion of acid. An understanding of the chemistry and chemical kinetics leads one to predict that several process parameters associated with the PEB will need to be optimized if these materials are to be used in a submicron lithographic process. Specific important process parameters include ... 

The problems met by chemically amplified photoresists are a) poor stability to environmental contaminations such as airborne amines b) sensitivity of lithographic parameters to PEB temperature variations c) poor stability during storage both after coating and after exposure d) side-directed diffusion... 

The industry roadmap specifies the need for chemically amplified resists that provide lithographic performance suitable to sustain their extension to 20 nm dimensional regime [522]. The ultimate resolution of 0.3 nm has been demonstrated by moving atoms at will with a scanning tunneling microscope [523] but the process is too slow to be economically feasible (one atom/min or... 

Figure 7.23 Common chemically amplified resist platforms based on poly (hydroxystyrene) and used in DUV lithographic applications. (Courtesy of R. Dammel.)...

H. Iwasaki, T. Itani, M. Fujimoto, and K. Kasama, Acid size effects of chemically amplified negative resist on lithographic performance, Proc. SPIE 2195, 164 172 (1994) U. Schedeli, N. Miinzel, H. Holzwarth, S.G. Slater, and O. Nalamasu, Relationship between physical properties and lithographic behavior in a high resolution positive tone deep UV resist, Proc. SPIE 2195, 98 110 (1994). 

HAMA), were polymerized. Each star-block copolymer had low polydispersity and approximately five mers per arm. All the resists used were chemically amplified with a 5% photo-add generator added, and they were exposed with an e-beam in order to have a first lithographic evaluation. They found that the star resist was 20% more sensitive than the linear resist and it also exhibited a lower LER that was greater than 10% in some cases. 

Photoacid diffusion behavior in t-BOC-blocked chemically amplified positive DUV resists under various conditions was studied. Based on the experimental results, it was confirmed that only one mechanism dominated the acid diffusion in the resist film, and two diffusion paths, i.e., the remaining solvent in the resist film and hydrophilic OH sites of base phenolic resin, existed. Moreover, the effects of molecular weight dispersion, acid structure, and additional base component on both acid-diffusion behavior and lithographic performance were revealed. Finally, the acid diffusion behavior in the resist film was clarified and the acid diffusion length that affected the resist performance could be controlled. 

In the present study, the chemical mechanism and the kinetics of acid initiated crosslinking reactions of epoxy novolac based chemically amplified resists are examined. FTIR and thermal analysis have been used as the basic methods for elucidating chemical mechanism. Lithographic results obtained in a number of different processing conditions are interpreted in the context of the proposed mechanism. 

Resist Chemistry. The basic chemistry of epoxy novolac based chemically amplified resists has been proposed in the past by Stewart et al. (9J. According to this the Bronsted acid generated either photochemically or through electron beam exposure from the onium salt induces acid catalysed polymerization of the epoxy functionality. This mechanism implies that the proton generated by the exposure is actually bound to the polymer. Since the lithography consequences of this mechanism are obvious we decided to seek possible experimental evidence for the proton binding in the resist film under conditions of lithographic interest. 

Diffusion vs. Reaction Controlled Kinetics Contrast curves obtained from e-beam experiments at the lithographically usefiil doses at 90 °C and 110 °C for different PER times show a very characteristic behavior for this epoxy chemistry based chemically amplified resist. The gel dose does not change in this PER temperature and time range whereas the contrast increases in the higher temperature and time regime (Figures 7 and 8). 

Further reduction of the wavelength to 193 nm (ArF excimer laser) has become the major thrust in the last several years, which has necessitated a development of new chemically amplified resists, spawning a massive research effort and providing enormous challenges and opportunities to resist chemists and engineers. X-ray and electron-beam lithographic technologies are also expected to come into the scene in the not-far future. 

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