Invited Paper PS-ThM11
Plasma Surface Interactions for Low-k Material Etching

Thursday, October 21, 2010, 11:20 am, Room Aztec

Porous low-dielectric-constant (low-k) materials such as porous SiOCH film are essential for interlayer dielectric film in high performance ULSI devices. To establish extremely precise etching processes of the low-k film for the next generation devices, it is required to understand the surface reaction and damage formation mechanism during plasma processing, while developing a sophisticated methodology to control the etching and ashing processes. We developed an integrated monitoring system equipped with in-situ spectroscopic ellipsometry, Fourier transform infrared reflection absorption spectroscopy (FT-IR RAS), a substrate temperature monitor using an optical fiber-type low-coherence interferometer [1] and an absolute density monitor for H and N radicals [2,3]. The integrated monitoring system was installed in a dual frequency capacitively coupled plasma etch reactor and we investigated H₂/N₂ plasma interactions on the low-k film. The in-situ monitoring during the plasma etching or ashing is crucial for the clarification of damage mechanism because the damaged films are easily modified during air exposure. Furthermore, the effect of each particle, i.e. ions, photons and radicals, was investigated individually by ‘PAPE’ method [4] that uses small plates, such as Si, SiO₂ and MgF₂, on or above the film substrate during the plasma exposures. So far, we considered that damages on the p-SiOCH are determined by chemical reactions of H radicals that reduce the Si-CH₃ bonds and N radicals that have an effect of inhibition of the damages. It was also confirmed that a portion of Si-O-Si linear structure in the SiOCH film changed to network and cage structures with decrease in Si-CH₃ bond during the plasma exposure. The effects of the temperature during etching on the etch profile were also examined for a variety of H₂/N₂ gas mixture ratio. The higher the H radical density and the temperature, the lager the undercut in the low-k pattern profile. Especially, the temperature increase after plasma ignition was found to be a cause of the profile deformation. Based on the above results, we proposed an autonomously-controlled etch system that realized a real-time feedback control for the fine pattern etching while monitoring the wafer temperature, radical densities and so on. It was demonstrated that real-time radical-density control upon the temperature was effective for obtaining precise pattern profiles.

[1] K. Takeda, et al., J. Appl. Phys., 43, 7737 (2004).

[2] S. Takashima, et al., Appl. Phys. Lett., 75, (25), 3929 (1999).

[3] S. Takashima, et al., J. Vac. Sci. Technol., A 19, 599 (2001).

[4] S. Uchida, et al., J. Appl. Phys. 103, 073303 (2008).