| AVS 58th Annual International Symposium and Exhibition | |
| Plasma Science and Technology Division | Wednesday Sessions |
| Session PS+EM-WeA |
| Session: | Low-K Materials & Integration |
| Presenter: | Juline Shoeb, Iowa State University |
| Authors: | J. Shoeb, Iowa State University M.J. Kushner, University of Michigan |
| Correspondent: | Click to Email |
Porous dielectric materials offer lower capacitances that reduce RC time delays in integrated circuits. Typical low-k materials include SiOCH – silicon dioxide with carbon groups, principally CH3, lining the pores. Fluorocarbon plasmas are often used to etch low-k materials, a process that leaves a fluorocarbon polymer on the low-k surface that must be removed. With porosities as high as 0.5, pores which are internally connected provide pathways for reactive species to enter into the porous network. During cleaning using oxygen plasmas, reactions of O atoms with the CHx groups, can remove carbon as CO/CO2. After the process, H2O from air can form hydrophilic Si-OH which can further adsorb H2O through hydrogen bonding or physisorption.[1] As such, O2 plasmas can degrade the low k value of the porous SiCOH. Plasma cleaning with He/H2 mixtures causes less damage to SiCOH as reaction of H atoms with –CH3 is endothermic. These damage scenarios are complicated by the UV/VUV photons produced by the plasma. Photons produced by the plasma can break Si-C bonds and separate –CH3 radicals from SiO2 to enhance the C removal rate.[2] 130 nm photons of Ar/O2 plasmas can penetrate into SiCOH ≈100 nm but photons of He/H2 plasmas (<100 nm) penetrate ≈20 nm. As a result, VUV photons from O2 plasmas can produce Si-C bond scission approximately 5 times deeper in the low-k material compared to the VUV photons from He/H2 mixtures. These penetration depths are sensitive functions of porosity and interconnectivity. For example, penetration depth increases nearly linearly with increases in interconnectivity due to the alignment of pores. In this talk, we discuss results from modeling of the plasma damage of porous SiOCH in He/H2 and Ar/O2 plasmas. The HPEM (Hybrid Plasma Equipment Module) was employed to obtain the ion energy and angle distributions of reactive fluxes from inductively coupled plasmas. These are used as input to the MCFPM (Monte Carlo Feature Profile Module) with which profiles of the low-k materials after the plasma exposure are predicted. The role of photons in porous SiCOH damage and validation of numerical results will be discussed in terms of treatment time, interconnectivity and photon flux. Overall, we found that due to its lower photon penetration depth and less reactivity, He/H2 plasmas cause approximately 3 times less damage than Ar/O2 plasmas, which is in agreement with experiments.
1. J. Proost, E. Kondoh, G. Vereecke, M. Heyns, and K. Maex, J. Vac. Sci. Technol. B 16, 2091 (1998).
2. B. Jinnai, S. Fukuda, H. Ohtake, and S. Samukawa, J. Appl. Phys. 107, 43302 (2010).
* Work supported by Semiconductor Research Corp.