Real-time measurements of plasma photoresist modifications: The role of plasma vacuum ultraviolet radiation and ions
Weilnboeck Florian, Nirav Kumar, Gottlieb Oehrlein, Ting-Ying Chung, D Graves, Mingqi Li, Eric A. Hudson, Eric C. Benck
Plasma-induced roughness development of photoresist (PR) can be due to synergistic interactions of surface modifications introduced by ions, bulk material modifications by ultraviolet (UV)/vacuum ultraviolet (VUV) radiation, and increased temperature. While previous work identified the individual contributions of energetic ions and UV/VUV radiation, the dynamics of the concurrent modifications remained unclear. We studied the interactions of plasma radiation and ions with 193nm PR and 248nm PR in Ar plasma by in-situ ellipsometry. Ellipsometry provides valuable information on changes in film thickness and material optical properties in real-time during plasma processing. MgF2, sapphire, and glass optical filters were used to reduce the plasma-material interactions to the radiation component of a selected wavelength range in the UV/VUV spectral region. Ar plasma radiation and its transmission through different optical filters were characterized by VUV spectroscopy. This characterization allowed for the identification of the relative contribution of specific wavelength ranges to the overall material modification in direct plasmas. Exposure of 193nm PR to plasma UV/VUV radiation led to film thickness reduction and an increase in the refractive index (Ñ) which was enhanced for shorter wavelengths. For direct plasma exposure at low maximum ion energy (Eion≤25 eV), radiation effects dominated and bulk material modifications saturated after ≈30 s. By comparison, for 248nm PR film thickness reduction and increase of Ñ were modest and were only seen for UV/VUV exposure with wavelength lower than 142 nm. Both material surfaces remained relatively smooth during 60 s exposure to plasma radiation (0.3 mm to 0.6 nm RMS roughness) independent of radiation wavelengths used. For direct Ar plasma exposure involving energetic ion bombardment (Eion≤125 eV), a graphitic surface layer was established within 3 s to 5 s. During this time period ≈30% of the saturation UV/VUV modificatio
, Kumar, N.
, Oehrlein, G.
, Chung, T.
, Graves, D.
, Li, M.
, Hudson, E.
and Benck, E.
Real-time measurements of plasma photoresist modifications: The role of plasma vacuum ultraviolet radiation and ions, Journal of Vacuum Science and Technology B, [online], https://doi.org/10.1116/1.3697752
(Accessed December 8, 2023)