2009 Volume 22 Issue 1 Pages 51-58
The image formation in conventional non-chemically amplified photoresists has been investigated and theorized. Image formation theories have been extended to chemically amplified KrF and ArF resists by introducing the effects of acid diffusion. After ArF immersion lithography, extreme ultraviolet (EUV) radiation is expected as an exposure tool for mass production of semiconductor devices. In EUV resists, secondary electrons play a major role in the sensitization of acid generators because the energy of EUV photons (92.5 eV) is higher than the ionization potential of resist materials. The effects of secondary electrons should be taken into account for the discussion of image formation in EUV resists. In this study, the dependence of chemical gradient on the aerial image contrast of incident photons was investigated on the basis of the sensitization mechanisms of chemically amplified EUV resists. The relationship between aerial image contrast and chemical gradient depends on the neutralization mechanisms, the rate constant for deprotection, quencher concentration, and dissolution point. To minimize line edge roughness, it is necessary to optimize not only quencher concentration but also dissolution point in accordance with the aerial image contrast.
