| AVS 66th International Symposium & Exhibition | |
| Thin Films Division | Tuesday Sessions |
| Session TF+AP-TuM |
| Session: | ALD and CVD: Precursors and Process Development |
| Presenter: | Taiki Kato, Tokyo Electron Technology Solutions Limited, Japan |
| Authors: | T. Kato, Tokyo Electron Technology Solutions Limited, Japan Z. Ni, Tokyo Electron Technology Solutions Limited, Japan M. Matsukuma, Tokyo Electron Technology Solutions Limited, Japan H. Nakamura, Tokyo Electron Technology Solutions Limited, Japan Y. Ideno, Tokyo Electron Technology Solutions Limited, Japan Y. Serizawa, Tokyo Electron Technology Solutions Limited, Japan |
| Correspondent: | Click to Email |
TiN is an important barrier metal for semiconductor devices. Nevertheless, it is difficult to form low-electrical-resistance TiN films at low temperature with existing thermal TiCl4/NH3 ALD processes. To overcome this difficulty, we tried a new azotizing gas MMH (Monomethylhydrazine: CH3NHNH2) instead of NH3 and achieved low electrical resistance TiN (~1 mW.cm) under 300 deg C deposition temperature. XPS and AFM observations revealed that the film deposited with TiCl4/MMH has smaller Cl concentration and is smoother than the one deposited with TiCl4/NH3. In this study, we analyzed the TiCl4/MMH ALD reactions to clarify the process improvement mechanism when using MMH. Furthermore, we also analyzed the reactivity of TiCl4 with NH3 and with novel azotizing gases HZ (Hydrazine: H2NNH2) and UDMH (Unsymmetrical dimethylhydrazine: (CH3)2NNH2) for future process development.
To analyze surface azotizing reactions, we used density functional theory calculation software, DMol3. Surface reaction analysis of TiCl2 termination revealed that the azotizing reactions removed Cl from the substrate by HCl gas generation and MMH was more reactive as an azotizing gas than NH3. These results explained the experimental phenomenon in which MMH can remove Cl from a TiN film more efficiently than NH3 and improve the film’s roughness and electrical resistance. HZ and UDMH are also more reactive than NH3 and are candidates for future azotizing gases.
Next, we analyzed gas phase decomposition reactivity of these agents for clarification of ALD process windows. This analysis is conducted by GRRM (Global Reaction Route Mapping) program which can search for reaction paths automatically. Gas decomposition reaction paths search revealed that ALD processes of TiCl4 / HZ, MMH and UDMH are feasible under 400 deg C.
Furthermore, we analyzed azotizing gas chain reactivity for safe conservation estimation. This analysis is calculated by a molecular dynamics simulator, ADF ReaxFF. We inspected the chain reactivity of HZ, MMH, and UDMH densely packed in a tight container at high temperature. Reaction MD simulations showed that UDMH is the safest, followed by MMH then HZ.
In summary, we developed a new thermal TiN ALD process with TiCl4/MMH instead of existing NH3. Our simulation studies suggest that MMH, HZ and UDMH can remove Cl from TiN film more efficiently than NH3 and improve the film roughness and the electrical resistance. Other reaction paths analyses show that the novel azotizing agents also have ALD temperature process windows under 400 degC and that the safe conservation trend HZ < MMH < UDMH. These hydrazine-like agents are promising azotizing precursors for low temperature ALD.