Paper PS-TuA12
On the Absence of Post-Plasma Etch Surface and Line Edge Roughness in Vinylpyridine Resists

Tuesday, November 10, 2009, 5:40 pm, Room A1

Reducing formation of line edge roughness during photoresist mask pattern transfer by plasma etching is becoming increasingly important as the critical dimensions of devices continue to shrink. We have found that using a nitrogen-containing polymer, poly(4-vinylpyridine) (P4VP), as resist completely eliminated plasma-induced surface and line edge roughening for pattern transfer process conditions that produced significant roughness in a wide variety of other polymers in Ar-containing gas discharges of various gas chemistries and over long plasma exposure times. This effect was investigated by considering the influence of the plasma species (ions, neutrals, VUV) as well as the polymer structure and comparing results with polymers that were prone to surface roughening, such as polystyrene. Material modification was characterized by in situ ellipsometry, X-ray photoelectron spectroscopy, and atomic force microscopy. Plasma-induced modifications in the polymer film are shown to cause changes in the mechanical properties at the surface leading to the development of residual stresses that creates surface roughness after plasma etching. We also investigated how nitrogen in the polymer structure as well as the gas discharge influences the mechanical stresses at the surface. Patterned films were also plasma-exposed to the same conditions and characterized by scanning electron microscope. The absence of surface roughness in P4VP is shown to eliminate LER in 3D features. Finally, we provide a comprehensive model to show how the difference in the plasma surface modification in P4VP compared to polymers such as polystyrene leads to elimination of surface roughening.