| AVS 57th International Symposium & Exhibition | |
| Plasma Science and Technology | Tuesday Sessions |
| Session PS1-TuA |
| Session: | Advanced BEOL/Interconnect Etching II |
| Presenter: | J. Shoeb, Iowa State University |
| Authors: | J. Shoeb, Iowa State University M.J. Kushner, University of Michigan, Ann Arbor |
| 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. These processes leave a fluorocarbon polymer on the low-k surface that must be removed. This is often done with oxygen containing plasmas. With porosities as high as 0.5, pores open to the surface and which are internally connected provide pathways for reactive species to enter into the porous network. Reactions during plasma cleaning of, for example, O atoms with the CHx groups, can increase the k value of the material by removing C atoms. To maintain the low-k value, cleaning the CFx polymer and sealing of the surface must be performed without significantly altering the SiOCH material properties, and not removing the CHx groups. Plasma cleaning with He/H2 mixtures is capable of removing these CFx residues without harming the underlying low-k surface and can also strip off the hydrocarbone photoresist (PR) mask.
In this talk, we discuss results from modeling of the plasma cleaning and sealing of porous SiOCH in sequentially applied He/H2 and Ar/NH3 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 exposures are predicted.
We found that hot hydrogen atoms can remove the CFx polymer, generating mainly HF and fluorohydrocarbons such as CHF2. These hot H-atoms can simultaneously remove H from the surface resident CH3 groups thereby activating the SiOCH surface by creating C dangling bonds. He ions are also effective at breaking Si-O bonds creating dangling while also removing H-atoms from CH3 group, both of which activate the SiOCH surface. Unlike O2 plasma cleaning, the He/H2 clean creates more reactive CHx (x = 1,2) sites without significantly damaging the substrate. Following the He/H2 plasma cleaning, NH3 plasma treatment seals the pores by NHx (x=1,2 and 3) species passivating previously produced dangling bonds, forming Si-N and C-N bonds.[1] Initial results indicate that combined He/H2 and Ar/NH3 plasma treatment of SiOCH with pores having radii of 0.8 nm can seal nearly 100% of the surface pores.
* Work supported by Semiconductor Research Corp.
[1] A. M. Urbanowicz, M. R. Baklanov, J. Heijlen, Y. Travaly, and A. Cockburn, Electrochem. Solid-State Lett. 10, G76 (2007).