Highly sensitive thermally developable positive resist systems

Abstract

Acid-catalyzed thermal depolymerization of polyphthalaldehyde derivatives has been utilized in the design of highly sensitive, thermally developable, positive resist systems incorporating two stages of chemical amplification. Poly(4-chlorophthalaldehyde) mixed with triphenylsulfonium hexafluoroantimonate can be thermally developed to the substrate simply by heating the resist after exposure to <1 mJ/cm2 of 254-nm radiation or 1 μC/cm2 of 18-keV electron beam radiation. The images obtained by postbaking at 160 °C do not exhibit any thermal flow. Poly(4-trimethylsilylphthalaldehyde) (PSPA) sensitized with triphenylsulfonium triflate exhibits a high deep UV sensitivity of <2 mJ/cm2 and a high electron beam sensitivity of 1 to 2 μC/cm2 (20 keV) when the thermal development is performed at 100–130 °C. The high contrast (γ=4.3) of the PSPA resist allows thermal imaging of submicrometer features, which can then be transferred to the bottom planarizing layer by oxygen reactive ion etching (RIE). The combination of the thermal development and oxygen RIE pattern transfer provides a new mode of all dry bilayer processes.