| AVS 57th International Symposium & Exhibition | |
| Plasma Science and Technology | Wednesday Sessions |
| Session PS1-WeA |
| Session: | Plasma Surface Interactions (Fundamentals & Applications) II |
| Presenter: | F. Weilnboeck, University of Maryland |
| Authors: | F. Weilnboeck, University of Maryland R. Bruce, University of Maryland G.S. Oehrlein, University of Maryland T.-Y. Chung, University of California, Berkeley D.B. Graves, University of California, Berkeley M. Li, Dow Electronic Materials D. Wang, Dow Electronic Materials E.A. Hudson, Lam Research Corporation |
| Correspondent: | Click to Email |
Plasma radiation in the ultraviolet (UV) and vacuum ultraviolet (VUV) spectral range is a fundamental component of plasma processes used for pattern transfer of nanometer structures. Photons in this wavelength range can lead to severe modification of photoresist (PR) materials in depths exceeding 100nm. We studied the material modifications of fully formulated 193nm PR by plasma photon radiation in Ar plasma discharges. A novel filter approach was applied allowing to probe PR surface modifications in real time by in-situ ellipsometry during plasma processing while protecting the PR against ion bombardment. Different filter materials enable to test dependencies on wavelength ranges of the plasma radiation from visible to VUV light. Material modifications were also characterized by Fourier transform infrared spectroscopy and scanning electron microscopy. By combining these data with optical multilayer ellipsometric simulations, material thickness reduction and changes in optical properties could be understood on a molecular level.
Radiation in the UV/VUV spectral range was found to modify the PR at a depth of ~100nm leading to thickness reduction of up to 12nm, whereas radiation in the VIS spectral range modifies the entire film (~400nm) leading to marginal changes in the film thickness. The thickness reduction is caused by material loss, mainly by detachment and loss of lactone, and to a larger extent by densification of up to 9% following the detachment of the PR pendant groups.
Radiation exposure also leads to a change in film optical properties which is discussed in terms of a bond polarizability model. This enables correlation of the measured data with changes of the PR structure on a molecular level. For exposure of the PR to UV/VUV radiation it was found that besides loss of lactone and detachment of the PR pendant groups a significant amount of C-C bonds were lost which can be directly correlated to changes in the polymer structure by chain scissioning reactions.
Real time measurements allow for extracting the temporal evolution of material removal, densification and changes in film optical properties as a function of photon flux and degree of modification. It was found that material modification can be separated into two fundamentally different regimes. In the initial exposure period to plasma radiation in the UV/VUV spectral range changes in film properties are rapid and mainly limited by the photon flux. For extended exposure times modification is flux dependent but limited by the unmodified material remaining in the film after the initial exposure period.