A negative resist for KrF excimer laser lithography

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Abstract
The design and preparation of a series of negative resists for KrF excimer laser lithography are described. Each resist is composed of poly(hydroxystyrene) and an aromatic azide. The base resin shows high transmittance of 62%/μm at 248 nm, when p‐ethylphenyl p‐azidophenylsulfonate. 4‐azido‐4α‐methoxy‐chalcone, 1‐(4 azidobenzylidene)‐3‐(α‐hydroxy‐4‐azidobenzyl)‐indene, 4,4α‐diazido‐3,3α‐dimethoxybiphenyl, or 1‐(4‐azidostyryl)‐5, 5‐dimethyl‐2‐cyclohexen‐1‐one is employed as a sensitizer. These azides are obtained by red‐shifting the absorption maxima to lower energy regions than the exposing wavelength of 248 nm. Transmittance of resists can be controlled from 10 to 30%. The resist is exposed with a KrF excimer laser stepper and developed in an alkaline solution. Sensitivities of about 15 mJ/cm2 are observed. A good, subhalf‐micron resist profile is achieved.The photochemical reaction mechanisms of poly(hydroxystyrene) and 4,4α‐diazido‐3,3α‐dimethoxybiphenyl were studied at 248 nm and 313 nm exposure. Quantum yield for photodecomposition at 248 nm is seven times larger than that at 313 nm, but dissolution‐inhibition effects are larger at 313 nm exposure. Consequently, the resist shows higher sensitivity at 313 nm than at 248 nm.