Application of UV Irradiation in Removal of Post-etch 193 nm Photoresist
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1156-D02-09
Application of UV irradiation in removal of post-etch 193 nm photoresist Q. T. Le1, E. Kesters1, L. Prager2, M. Lux1, P. Marsik1, and G. Vereecke1 1 Imec, Kapeldreef 75, 3001 Leuven, Belgium 2 Leibniz-Institut für Oberflächenmodifizierung, Permoserstr. 15, 04318 Leipzig, Germany. ABSTRACT This study focused on the effect of UV irradiation on modification of polymethyl methacrylate-based photoresist, and then on wet photoresist (PR) removal of patterned structure (single damascene structure). Three single-wavelength UV sources were considered for PR treatment, with λ = 172, 222, and 283 nm. Modification of blanket PR was characterized using Fourier-transform infrared spectroscopy (FTIR; chemical change), spectroscopic ellipsometry (SE; thickness change), and dissolution in organic solvent (solubility change). While for patterned samples, scanning electron microscopy (SEM) was used for evaluation of cleaning efficiency. In comparison to 172 nm, the PR film irradiated by 222 nm and 283 nm photons resulted in formation of higher concentration in C=C bond. Immersion tests using pure N-methyl pyrrolidone (NMP) at 60 °C for 2 min showed that some improvement in PR removal was only observed for PR films treated by 283 nm UV for short irradiation times. Irradiation by photons at the other two wavelengths did not result in an enhancement of removal efficiency. The PR film treated by 222 nm photons was chosen for further study with O3/H2O vapor at 90°C. Experimental results showed a complete PR and BARC removal for UV-treated PR, which can be explained by C=C bond cleavage by the oxidizer. INTRODUCTION In Back-End-of-Line processing, the remaining photoresist (PR) layer after plasma etch is traditionally removed using plasma process. However, dry ashing of PR degrades porous low-k dielectrics [1-3]. To minimize damage to low-k material, wet alternative methods using solvent for removal of PR layer are gaining a renewed interest. The etch plasma used to pattern the dielectric stack leads to formation of a “crust” layer at the PR surface. The presence of the crust makes a complete removal of PR impossible using a pure organic solvent, especially for small features, i.e., ½ pitch ≤90 nm. Indeed, the crust, most likely composed of cross-linked polymer, is not soluble in organic solvents [4-6]. PR removal becomes even more challenging with reduced critical dimensions. A wet process combining the chemical action of organic solvents (bulk PR dissolution) with physical forces (for mechanically removal of plasma-induced crust) was shown to be able to remove PR on a structure of 150 nm ½ pitch but not for 90 nm ½ pitch [5,7]. Over the past years, ozone dissolved in water was shown to be an efficient process in the removal of organic contamination and PR layers [8, 9]. This process is regarded as a more environmentally friendly process, with lower costs, compared to traditional processes. In a recent study [10], we have shown that UV treatment of PR at certain wavelengths generates C=C bonds, and represents a convenient way
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