Mechanism of k -value Reduction of PECVD Low- k Films Treated with He/H 2 Ash Plasma

1. Mechanism of k-value Reduction of PECVD Low-k Films Treated with He/H2 Ash Plasma A.M. Urbanowicz, M. Cremel, K. Vanstreels, D. Shamiryan, S. De Gendt, M.R. Baklanov Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France

2. Outline • Introduction • organic removal from low-k by He/H2-DSP* ash • detection of porogen residues by UV spectroscopic ellipsometry • Experimental • Results • depth of porogen residue removal for different low-k’s • mechanism of k-value reduction by He/H2-DSP* • effect of porogen residue removal on mechanical properties • Conclusions • Recommendations for future work *DSP – downstream plasma Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France

3. Organic material embedded in low-k matrix is removed by He/H2-DSP without Si-CH3 group breakage 1 Photresist removal with “zero damage” residue removal TOFSIMS shows carbon removal, but it does not come from Si-CH3, as FTIR shows 1A. M. Urbanowicz, et al., in 25th Advanced Metallization Conference, San Diego, CA, 2008 2A. M. Urbanowicz, et al., in Electrochemical and Solid State Letters, 12(8), 2009 Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France

4. UV ellipsometry is very sensitive to presence of porogen in low-k films • SiOC:H matrix has silmilar optical properties toSiO2 • Porogen residue (a-C) contains sp2 orbitals (C=C) which have transtion band ~4.5 eV (275 nm) SiOC:H matrix P. Marsik, A. Urbanowicz et al., AMC 2008 proc., p. 543-549 (2009) Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France

5. Experiment PECVD PECVD UV curing: Porogen residue removal Ash: 20 – 700 s porogen Porogen residue Spin-on Spin-on Organic removal? Silica nanoparticles UV curing Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France

6. He/H2-DSP removes organic content from all films Spectroscopic ellipsometry Pristine films properties Porogen residue content Before After • Observations: • PECVD with k~2.3 contains • more porogen residues • Spin-on contains minimal amount of organics N Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France

7. Depth of porogen residue removal decreases logarithmically with time Mass balance on 300 mm wafers UV-spectroscopic ellipsometry • Observation: • Depth of porogen residue removal increases with film porosity Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France

8. Depth of porogen residue removal decreases logarithmically with time Mass balance on 300 mm wafers UV-spectrocopic ellipsometry • Observation: • Depth of porgen residue removal increases with film porosity Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France

9. Overash results in k-value reduction, but.. Hg-probe • Observation • SOG and CVD 2.5: Longer times cause k-value increase Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France

10. k-value increase for longer over-ash times can be explained by minor polar group incorporation N2-purged FTIR • Observation • FTIR shows minor polar groups incorporation for all treated films Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France

11. Final k-value is determined by 2 competing phenomena: density reduction and polar group incorporation Debye’s equation Polar groups incorporation Density reduction Mass balance on 300 mm wafers FTIR k k Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France

12. CVD 2.3 show the highest k-value reduction accopanied by mechanical properties degradation Nano-indentation Hg-probe • Observations: • No mechanical properties reduction for CVD 2.5 and SOG 2.3 film while sinficant mechanical properties degradation for CVD 2.3 • The highest k-value reduction for CVD 2.3 Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France

13. 3 effectsof He/H2-DSP overash due to porogen residue/organics removal and silianol incoroporation Nano indentation and Hg-probe II I Ref I – k and YM ~ const CVD 2.5 (T<100 s) II - k and YM ~ const CVD 2.5 (T>100 s) and SOG 2.3) III - k and YM  CVD 2.3 Ref Ref Ref III Ref Ref Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France

14. Conclusions • Mechanism of k-value reduction of PECVD low-k’sexposed at He/H2-DSP ash is a superposition of two competing phenomena: • porogen residue removalresults in k-value reduction • minor silanol group incorporation results in k-value increase • Reduction of k-value by removing porogen residue is beneficial (T<100 s)for PECVD with k=2.5 since no degradation of their mechanical propertiesis observed • Depth of porogen removal decreases logarithmically with time. Can be as high as: • ~70 nm for PECVD (k=2.5) with 25% open porosity • ~160 nm for PECVD (k=2.3) with >32 % open porosity Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France

15. Future plans • Effect of He/H2-DSP ash modification on subsequent damascene processing steps: • chemical or physical-chemical cleaning • barrier deposition • Fabrication of porogen-residue-free PECVD films by porogen removal by He/H2-DSP before UV curing step Adam Urbanowicz PESM 2010, 4-5 March, Grenoble, France