Application of polysilazane to etch mask in pattern transfer processes for deep and vacuum UV lithography

摘要

A polysilazane was investigated as a precursor to a spin-on glass (SOG) used for a middle-layer in a tri-level resist system. Higher film density is required for the middle-layer in order to obtain higher etch resistance during the under-resist etching and prevent the acids in the resist from diffusing to the SOG, which induces deteriorating of resist patterns. High film density of the SOG was achieved by spin-coating the polysilazane solution. The compositions of the polysilazane baked at 200℃ and 300℃ are Si_(42)O_(34)C_4N_(20) and Si_(29)O_(65)C_1N_5, respectively. The polysilazane is converted to silicon-oxide likely structure by baking at 300℃. The film density of the SOG made from the polysilazane (SGPZ) is 2.07 g/cm~3, which was higher than 1.87 g/cm~3 of the conventional SOG made from a polysiloxsane. The etch resistance of the SGPZ baked at 300℃ which is expected not to volatilize the under-resist is unproved by 90% compared with that of the SOG made from the polysiloxsane baked at 300℃ due to the increased film density of the SGPZ. The refractive indices of the films are n =1.56, k = 0.01 (ArF) and n=1.68, k = 0.02 (F_2). Without the stacked films of SGPZ/under-resist, reflectivities to the resist are 56.2% (ArF) and 44.2% (F_2). By optimizing the SGPZ thickness, the reflectivity is reduced to less than 0.7% (ArF) and 0.4% (F_2). In conclusions, the polysilazane can be as the superior material for the SOG used for the middle-layer in the tri-level resist system.