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Carbon nanotubes technology on Si IC's

Final Report Summary - CARBONCHIP (Carbon nanotubes technology on Si IC's)

The microelectronics industry has adopted carbon nanotube (CNT)-based devices as an important and high potential route for post-complementary metal oxide semiconductor (CMOS) nanoelectronics. CARBONCHIP is a Specific Targeted Research Project (STREP) project funded by the European Commission (EC) that addresses the potential of integrated CNT technology. Through an interdisciplinary approach, comprising collaborating researchers from university, research centres and industrial partners, CARBONCHIP is investigating catalysis, growth and integration of CNTs on-chip while considering up-scalability and compatibility and taking advantage of existing electrical functions and / or patterns on Si. This work is complemented by the development of methodologies for CNT analysis on-chip.

CARBONCHIP addresses the potential of the integrated CNT technology through an interdisciplinary approach based on research and development in (i) CNT catalysis, (ii) CNT growth, (iii) on-chip CNT technology (iv) related analysis methodology for control of CNT properties and (v) CNT devices for nanoelectronics. In this respect, specific challenges include achieving catalyst control (in terms of activity and selectivity) and optimising single-wall carbon nanotube (SWCNT) synthesis (in terms of density, properties and location). Additional challenges include providing a methodology for analysis of CNTs integrated into Si structures and taking advantage of existing electrical functions and / or patterns on Si.

There are three industrial participants in CARBONCHIP to address the challenge and feasibility of applying CNTs in front-end-of-line (FEOL) and back-end-of-line (BEOL) Si technology at an industrial scale. It was the vision of the project to integrate the knowledge of materials science and nanomanufacturing as a key enabler for future CNT-based nanoelectronics. To this end, CARBONCHIP contributes to a roadmap of CNT-based devices in FEOL and BEOL, extending Moore's law towards the year 2020 and beyond. CARBONCHIP also addresses the materials properties, the related fabrication process and analysis methodology. These aspects are explicit objectives of the work packages (WPs). The real innovation in nanotechnology based on CNTs in the long term is the interdisciplinary research approach to enable integration of CNT technology with Si technology.

The consortium consists of an industrial end user, two renowned research centres, two small-to-medium enterprises (SMEs) and a university. The strength of this consortium is that it combines basic research from the university and innovative product development of SMEs to the end user, through the state-of-the-art research and development infrastructure of research institutes.

WP1 deals with the growth of CNTs on unpatterned substrates using standard, structured, and grafted catalysts combine in an effort to construct a chemical vapour deposition (CVD) phase diagram for CNT growth. During the project PVD thin film catalyst technology deposited by IBS has been developed and mastered up to a thickness of 0.5 nm. It has been demonstrated that this technology can be used at a wafer level integration thanks to its reproducibility and homogeneity. This technology has been used to develop different CNT growth processes. They include a rather low temperature (640 degrees Celsius) SWCNT process on silicon substrate which gives SW with a diameter in the range of 0.8 to 1.3 nm and a small diameter MWCNT process which allows growing dense forests (density between 5 1011 and 1012 cm-2) of 4 nm diameter tubes at a temperature of 580 degrees Celsius.

The results from WP1 together with those of WP3, the grafting of SWCNTs on unpatterned substrates, converge in WP2 where the different CVD growth processes and selected catalysts are used to guide a process flow for the integration of horizontal and vertical CNTs on patterned Si. Similar to WP1, in WP2, analysis methods are key to developing a successful approach to SWCNT growth on patterns leading to device characterisation in WP4.

In WP 3 the capabilities of electro-grafting as an innovative technology for the deposition of ex-situ grown CNTs was evaluated. We have explored a variety of methods for the surface or end modification of nanotubes; both physical (ball-milling and plasma) and chemical (by reaction with amines and diazonium salts). WP4 aimed to demonstrate electrically the compatibility of CNTs with Si technology. Test structures were designed and manufactured to enable growth and placement of the CNTs in WP2 in order to achieve suitable structures for electrical testing and characterisation including a methodology to perform statistical analysis on the quality of the grown CNTs and their contacts. From these results a material-based roadmap has been produced in conjunction with the International Technology Roadmap for Semiconductors (ITRS).

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