Paper HI-WeA7
Characterization of Structural Changes During HIM and SEM Imaging of Organic Films

Wednesday, November 9, 2016, 4:20 pm, Room 104A

Acrylic organic films of 100 nm thick were spin coated on Si substrates, and then a helium ion or electron beam was irradiated at a dose of 2X10¹⁵ at 30 kV and 1x10¹⁷/cm² at 0.7 kV of an adequate observation condition, respectively.Morphological and structural changes after the beam irradiations were characterized by AFM, IR, Raman, and TOF-SIMS. Although the helium beam energy is higher, the combination of the lower helium ion current and the longer range of the ions means that the power density to the organic materials is nearly a factor of 10³ lower with the 30 keV helium ion beam than it is with the 0.7 keV electron beam [1]. One might therefore expect the materials to shrink less and be less damaged during HIM imaging than during SEM imaging.

AFM showed less decrease in the film thickness in a case of the ion than the electron. It indicated that the electrons might damage the film heavier than the helium ions. IR showed larger signal intensity decrease with less peak broadening and OH system remained in a case of the electrons, while it was completely destroyed in the helium ions case. Raman showed more amorphous carbon in the helium ions irradiated film, which was probably formed by destruction of CH system. Those results mean that helium ions irradiations brought about less surface morphological transformation while it resulted in larger chemical change in a deeper region of the film than the electron irradiations. This phenomenon is probably because heavier helium ions with higher energy came into deeper than electrons to the organic film cutting chains of the organic material with amorphous. TOF-SIMS showed the similar results for larger decrease of signal intensities of CH and CHO systems by the electron irradiation. Those results mean there were a lot of trade-off between irradiations of helium ions and electrons. Based on the above results with optimization, cross sections of filling of the organic materials into trenches were imaged by the HIM and SEM. As described, helium ions damaged the organic materials heavier in depth direction than electrons, while it kept original surface morphology with less transformation or shrink, so imaging of the filled organic materials into trenches by the HIM presumably shows more realistic than the SEM imaging.

T. Iijima and S. Migita are acknowledged for the usage of helium ion microscope at AIST SCR station.

References

[1] S. Ogawa, et al., “Helium ion secondary electron mode microscopy for interconnect material Imaging”, Jpn. J. Appl. Phys. 49 04DB12 (2010)