Bisazidobiphenyls/Novolak Resin Negative Resist Systems for i-Line Phase-Shifting Lithography

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Abstract
Bisazidobiphenyls have been evaluated as photosensitive compounds of negative resists for i-line phase-shifting lithography. The optical parameters of the bisazidobiphenyl resists such as Dill's A, B, and C parameters, molar absorption coefficients, and quantum yields are measured to select an appropriate bisazidobiphenyl for an i-line negative resist. The quantum yields of bisazidobiphenyls strongly depend on the substituents on the aromatic rings and vary between 0.25 and 0.83. The resist sensitivities are proportional to the product of ε and φ, which means the nitrenes produced from each bisazidobiphenyl have the same reactivity with novolak resin. 2,7-Diazidofluorene (azide 6), which has the largest ε·φ, gives the highest sensitivity. However, the resist using a mixture of azide 6 and 4,4'-diazido-3,3'-dimethoxybiphenyl (azide 1) is subjected to lithographic evaluation because azide 6 has low solubility in the casting solvents. The new resist resolves 0.275-µm line-and-space patterns in 1-µm-thick film when it is exposed with an i-line stepper in conjunction with a phase-shifting mask. The required dose of the new resist for imaging is 240 mJ/cm2.

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