Previous vacuum beam studies showed that methacrylate-based 193 nm photoresist (PR) will roughen due to the synergistic effects of ion bombardment, vacuum ultraviolet (VUV) photon and substrate heating [1]. The surface roughness and surface morphology is similar to that after inductively coupled argon plasma exposure under similar ion and VUV fluences and energies [2]. However, 193 nm PR is a heteropolymer, with three separate side-groups that could be photolyzed due to the plasma-generated VUV, and this could complicate analysis of roughening mechanisms. We therefore examined several associated homopolymers to better understand the role of the side groups in roughening under plasma exposure. We chose two homopolymers: 2-methyl-2-adamantyl methacrylate (MAMA, leaving group) and R-functionalized adamantly methacrylate (RAMA, polar group). At a substrate temperature of 65˚C, MAMA undergoes considerable loss of material under VUV-only exposure. In addition to the loss of CH2/CH3, C=O and C-O-C bonds in the polymer bulk observed by transmission Fourier transform infrared (FTIR) spectroscopy, mass spectroscopy analysis shows that the adamantane leaving group is lost from the film. In contrast, RAMA is relative insensitive to VUV irradiation. After simultaneous ion/VUV exposure at a substrate temperature of 65˚C, MAMA shows very high surface roughness while RAMA shows little surface roughening. The surface of MAMA is also significantly rougher than that of 193 nm PR processed under the same condition. It therefore appears that the leaving group in 193 nm PR, designed to cleave in the presence of photoacid during lithographic exposure and post-exposure bake, is the primary cause of 193 nm PR roughening, when combined with energetic ion bombardment, VUV irradiation and elevated heating.

 

[1] D. Nest, T.-Y. Chung, D. B. Graves, S. Engelmann, R. L. Bruce, F. Weilnboeck, G. S. Oehrlein, D. Y. Wang, C. Andes, and E. A. Hudson, Plasma Process. Polym. 6 (2009) 649.

[2] M. J. Titus, D. G. Nest, T.-Y. Chung, and D. B. Graves, J. Phys. D, Appl. Phys. 42 (2009) 245205.