Growth and integration challenges for carbon nanotube interconnects

• One MWCNT per contact hole meets ITRS conductivity requirement for sub-15 nm DRAM contact technology.
• Termination of CNT growth limits CNT length below 500 °C.
• Improved CNT contact resistance and yield across 200 mm wafer upon adding ALD Al2O3.
• Catalyst particle density close to 1012 cm−2achieved on TiN.

This paper discusses the current status and the challenges associated with the fabrication of carbon nanotube (CNT) interconnects. This application needs innovative technological solutions for realizing high quality CNT growth at low growth temperatures. In addition, the CNT integration process should be CMOS compatible while at the same time it should preserve the quality of the CNT. We show that the CNT length at low growth temperatures is limited as a result of growth termination. Moreover, the carbon forest population below 500 °C contains predominately multi-walled CNT (MWCNT). We show that generating Ni catalyst particles from a thin film only reaches densities of 1012 cm−2 on TiN. Under the assumption that each particle yields a CNT, the resulting CNT density is still at least one order of magnitude too low to compete with Cu vias in local interconnects. For DRAM and Flash contacts, one MWCNT per contact hole is sufficient to satisfy the contact resistance requirement set by the ITRS roadmap. In order to protect the CNTs during the integration process, we evaluated different oxide encapsulations of the CNT and its impact on the electrical performance for 150 nm CNT contacts metallized with Cu single damascene top contact. The yield plots show an improved yield and contact resistance when using an additional Al2O3 layer to encapsulate the CNT. The comparison of our electrical results with theory indicates there is still room for improvement in CNT quality and contact resistance.

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