Low Resistivity Titanium Nitride Thin Films ALD realized by RASIRC Brute® Hydrazine vaporization technology

TiN ALD is one of the most important ALD processes in high volume manufacturing in the semiconductor industry for more than 15 years. Most Tier 1 ALD equipment manufacturers (e.g. ASM International, Tokyo Electron , Applied Materials, Lam Research, Kokusai, Jusung Engineering, Wonik IPS, Picosun) has TiN ALD and PEALD in their process portfolio for 300 mm wafer productions targeting the Logic, 3DNAND and DRAM fab customers (e.g. Intel, Samsung, TSMC, SK Hynix, Micron, Globalfoundries, Toshiba, TI) because the metallic film has proven to be highly flexible metal film due to:

• Relatively cheap precursor, mainly TiCl4 and TDMAT, as compared to the much more expensive precursors with lower vapor pressure for tantalum metal nitrides (PDMAT) and metals like Co (CCTBA) and Ru (RuCp´s). 
• High vapor pressure and reactivity allowing fast conformal processing bay both CVD, pulsed CVD and ALD for TiCl4/NH3 based processes 
• Possibility to tune low resistivity films however at relatively high temperatures (TiCl4/NH3) not allowing for BEOL thermal budget requirements (<390 °C) 
• Excellent barrier properties hindering metal diffusion (TDMAT and TiCl4) 
• Metal gate work function tuning by doping and partial controlled oxidation 
• Oxygen gettering driving excess oxygen from the gate oxide channel interface into the metal gate reducing the CMOS device EOT. 
• Mini Batch and Large Batch processing capability (e.g. TEL Indy, ASM A412, Kokusai ALDina, Picosun Sprinter)

Due to low resistivity, titanium nitride (TiN) thin films are in production as the diffusion barrier for Cu, Co and W as well as the gate metal barrier in CMOS. However, as mentioned, for high aspect ratio features, thermal ALD deposition  is needed because of high conformality. Therefore, it is very important to develop thermal ALD TiN processes further to improve the capacitor electrode, barrier and CMOS metal gate properties to perfection.

Cheng-Hsuan Kuo and co-workers at UCSanDiego in the Kummel research group, has recently concluded a study on TiN ALD utilizing the RASIRC BruteÒ Hydrazine (N2H2) vaporizer technology, which is presented this week at IEEE SISC December 16-18 (LINK).

In the work, titanium tetrachloride (TiCl₄) and anhydrous hydrazine (Rasirc, Brute Hydrazine^Ò) were employed as the precursors with ultra-high purity nitrogen purge gas.

• The TiN ALD chamber was connected to an in-vacuo Auger Electron Spectrometer (RBD Instruments), which was used to determine the atomic composition of ALD. (Fig. 1)
• The sample was biased at -100V DC and Ar plasma (50W) was used to remove the surface oxides and impurities. (Fig. 2)
• To determine resistivity, four-point probe (Ossila) measurements were performed on TiN thin films on degreased SiO₂ substrates. (Fig. 3)
• Scanning electron microscopy (SEM), ellipsometry, and X-ray reflectivity (XRR) were used to measure TiN film thicknesses. (Fig. 4)

Fig.1 Auger Electron Spectroscopy of TiN at different sputtering time.(oxygen and carbon contents are listed)

Fig. 2 Oxygen concentration and resistivity vs pulse length at 300 °C 

Fig. 3. Oxygen concentration and resistivity vs pulse length at 350 °C 

Fig.4 X-Ray Reflectivity (XRR) of the 350 oC TiN film with optimal pulse lengths 

To conclude, these experiments indicate that minimizing oxygen concentration is key in producing TiN thin films with desirable electrical properties.

The optimal resistivity of the TiN deposited at 350^oC was 160 micro-ohm-cm which is the lowest reported resistivity of any TiN film deposited by thermal ALD.  As stated above the importance of 3D process capability can be met by having TiN thin films synthesized by using thermal ALD and post-plasma treatment reducing oxygen concentration and impurities potentially in very high aspect ratio structures such as contact holes, FinFET, Gate all around FETs, vias, DRAM capacitors structures as well as 3DNAND metal gates and contacts.

References

[1] C. H. Ahn. et al. Metals and Materials International, 7 (2001)

[2] Steven Wolf et al. Applied Surface Science 462 (2018)

Acknowledgements

This work was supported in part by the SRC

LINKS

UCSanDiego 

Kummel research group

EEE SISC December 16-18 (LINK).