How do TiN film prepared by different methods compare?

1. How do TiN film prepared by different methods compare? S-69.4114 Thin film technologyHeikki ViljanenVTT Technical Research Centre of Finland

2. List of Contents • TiN and it’s properties & applications • Diffusion barrier layer for metal interconnects • TiN deposition methods • Sputter • CVD • ALD • Rapid thermal anneal • Comparison of the deposition methods • The future of TiN? • TSV

3. TiN properties Similar to other transition metal nitrides TaN -> PBL1 Chemical stability Thermal stability Conductivity Strong resistivity to diffusion of other atoms Resistance to form compounds with copper Most important applications One of the most widely used diffusion barrier layer materials both in Al and Cu metallizations Encapsulation layer (oxidation & corrosion) (Other applications similar to those of TaN) [1-6]

4. Important properties for TiN barriers Material properties Stoichiometry (Ti55N45 vs Ti45N55) Grain size Deposition method Deposition temperature below 350°C Step coverage (conformality) Pin holes, particles Stoichiometry Grain size Material properties after deposition Grain boundaries Short cut for impurity diffusion Oxygen plasma treatment Annealing Increase of grain size

5. Sputtered TiN (1/2) Reactive sputtering Nitrogen from the process gas The most widely used method Active research still going on TiN alloy target Ceramic target Smaller sputtering power because of cooling problems Only a fraction of the target’s nitrogen to the wafer Nitrogen atmosphere still needed Cosputtering from different sources ? [1-6] http://www.leb.e-technik.uni-erlangen.de/lehre/mm/images/deposition/sputtern.gif

6. Sputtered TiN (2/2) Excellent control over stoichiometry Better thermal stability than CVD films Bigger grain size than CVD films Slow process Typically few nanometers per minute Low resistivity: 27 and 33 µΩcm Ti resistivity (42 µΩcm) Barrier up to Depending on stoichiometry 750°C for 1 hour 900°C for 30s Poor step coverage http://www.peter-wolters.com/cmp/cmpmultilevel.htm [1-6]

7. CVD TiN TiCl4 with NH3 Good conformality Stoichiometric TiN 600-700°C Corrosion caused by Cl compounds Particle formation TEMAT with NH3 (MOCVD) 150-350°C Deposition rate 20-35 nm/min Better film quality Worse conformality Particle contamination TEMAT without NH3 (MOCVD) 250-350°C Deposition rate 15-33 nm/min Good conformality High carbon contamination High resistivity [7,8,10]

8. PECVD TiN TiCl4 with NH2 & H2 ECR-PECVD Deposition temperature 350-500°C Deposition rate @ 350°C = ~16 nm/min Grain size 20 nm (@ 350°C) 60µΩcm (when deposited @350°C) R.f.-PECVD Deposition temperature 400-620°C Deposition rate @ 400°C = ~17 nm/min 670µΩcm (when deposited @400°C) The fastests deposition rates CVD not suitable for TiN and TaN passivation layers for CMOS Popular in wear-resistant applications [7]

9. ALD TiN ALD guys step in where CVD guys failed Low process temperature Excellent step coverage A bit slower than PVD Low carbon & cloride contamination No particle contamination Higher resistivity than PVD Low deposition rate (max few nm/min) TiCl4 and NH3 450°C TEMAT with NH3 170-210°C 120µΩcm [9-12]

10. Rapid thermal anneal (RTA) RTA? Ti thin film is annealed in Nitrogen atmosphere Similar to doping of silicon The best thermal stability High temperature process Not a CMOS compatible process Might cause problems also with thin film stresses Not too popular [1]

11. Comparison of various methods

12. Comparison of various methods PVD Cheapest Simplest Best film quality Highest stability Poor conformality Aspect ratio below 5:1 CVD Conformal Impurities and particles or high process temperature Not a good option for electronics ALD Exlellent conformality No particle contamination Low temperature Not as good film quality as PVD Resistivity Impurities Grainsize

13. The future of TiN diffusion barrier (1/3) • Other diffusion barrier materials • Tantalum has lower resistivity than Titanium • Other compounds such as Ti-Si-N • Better barrier • Higher resistivity • The future of the diffusion barrier deposition methods • Future of electronics • Something else than transistor size needed to satisfy Moore’s law • Interconnection length • Copper • 3D integration • TSV

14. The future of diffusion barriers (2/3) http://sunnygreater.com/products/sputtering_targets http://taxdollars.freedomblogging.com/files/2008/10/fortune-teller-3.jpg http://www.ems007.com/articlefiles/50661-ScreenShot004.jpg

15. The future of TiN diffusion barriers (3/3) • Low aspect ratio • Sputtering • Shadow effect • Slower than ALD? • High aspect ratio • CVD of some other material? • ALD • Plating of conductor material? http://sunnygreater.com/products/sputtering_targets

16. TSV Diffusion barrier for tapered TSV Both seeding and diffusion barrier layer with Sputter Electroplating easy and conformal Only thin wafers - what about volume devices? The pitch is limited because of tapering Diffusion barrier for vertical TSV Not possible with sputter ALD the strongest candidate Seed layer for ECD also a problem ALD TiN could perhaps act also as a seed for ECD Electroless plating

17. Thank you! Any questions?

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