Material and process development of tri-level resist system in KrF and ArF lithography

A material and process development of a tri-level resist system is carried out to introduce the resist system into 130nm and 110nm device fabrication. The tri-level resist system consists of organic films as a bottom layer, spin-on- glass (SOG) as a middle layer and DUV photoresists as a top imaging layer. A wettability and an acidity of the SOG film are adjusted depending on the type of resist materials to obtain a desirable resist profile. The anti-reflective performance of the tri-level resist system is evaluated along with the lithographic performance. A light reflection (reflectivity) in the DUV photoresist film is reduced less than 0.5% for both KrF resist and ArF resist by choosing the nominal thickness of the SOG film and the bottom layer. A conventional DNQ-Novolak type MUV resist is used for the bottom layer in the KrF tri-level resist system. The MUV resist is thermally cured to avoid mixing with the SOG and to increase the optical density at 248nm wavelength. A newly developed spin-on-carbon film is used for the bottom layer in the ArF tri-level resist system. The spin-on-carbon has an excellent dry etch resistance because of its high carbon content (>90%). The dry etch rates of the MUV resist and the spin-on-carbon for CF4/O2/Ar etch chemistry (SiN RIE condition) are 372nm/min and 287nm/min respectively. A pattern transfer using the tri-level resist system is demonstrated for both L/S and hole structures.