Carbon nanotube based integrated circuit interconnects
Creators: name: AHMAD, MUHAMMAD
Publisher: name: University of Surrey
Year: 2013

description: Integrated circuits (ICs) with Cu based interconnects are facing various challenges
description: such as electromigration, metallization issues associated with high aspect ratio lines
description: and vias (vertical interconnect access), high current density requirements for future
description: interconnects, heat dissipation in interconnects etc., with miniaturization. Therefore,
description: the need of new materials for IC interconnects is at present emphasized. Carbon
description: nanotubes (CNTs) have evolved as a potential candidate due to their exceptional
description: properties such as high current carrying capacity, ballistic conduction, extraordinary
description: strength and bottom-up growth behaviour. Vertically aligned CNT bundles have been
description: suggested for via applications. For the fabrication of CNT based vias, low temperature
description: efficient growth of high quality and high density CNTs on metal lines are required.
description: However, the growth rate and quality of CNTs is largely degraded when the growth is
description: conducted below 700oC using conventional CVD techniques. A suitable technique
description: enabling the growth of CNTs in a buried catalyst arrangement is required in order to
description: exploit the true bottom-up growth behaviour of CNTs in high aspect ratio vias. The
description: prevention of the catalyst from oxidation upon exposure to the atmosphere and
description: improved adhesion of CNTs with substrate (which reduces the reliability) are needed.
description: Here, a novel state-of-the-art photo-thermal chemical vapour deposition
description: (PTCVD) system is used for the low temperature (below 450oC) growth of high
description: quality carbon nanotubes on metallic layers for the interconnect via applications. The
description: CNT growth on TiN (50 nm)/Al (10 nm) metallic layers is studied as function of
description: growth temperature, catalyst material and catalyst thickness where 3 nm of Fe film as
description: a catalyst material is found to be the best as compared with the other two commonly
description: used catalyst materials which are Ni and Co. The achieved growth rate of 8 μm/min is
description: the highest when compared with the other reports of low temperature grown CNTs. A
description: low temperature growth process for the production of highest quality (ID/IG = 0.13)
description: vertically aligned carbon nanotubes on TiN film is demonstrated. The dependence of
description: the CNT growth profile on the thickness of TiN film provides a unique opportunity to
description: fine tune the various parameters of CNTs such as quality, growth rate, diameter,
description: density etc. High quality catalysed growth of CNTs on Ti/Cu/TiN metallic structure
description: has been achieved. The effect of catalyst heat treatment time and temperature is
description: studied. By rapidly reaching 659oC at the top surface of the samples, the CNTs with
description: lengths in excess of 1 μm were grown in less than 4 min of total process time.
description: The resistance of a single 100 × 100 μm2 CNT based via is calculated as 0.42 _, which is
description: one of the best values reported for CNT based via. A new ‘protected catalyst’
description: technique for the growth of CNTs is demonstrated where a capping layer of TiN at the
description: top of Fe catalyst is used to protect the catalyst. The protected catalyst scheme can be
description: a breakthrough in many potential application areas of CNTs as it simultaneously
description: protects catalyst from oxidation, improves the surface adhesion of CNTs and allows
description: the etching of SiO2 in a buried catalyst scheme while keeping the catalyst unharmed.
description: The fabrication and characterisation of CNT based vias in a chain structure on
description: TiN and Ti/Cu/TiN metallic layers is demonstrated. All processes resulted in the
description: growth of vertically aligned and dense (1010 cm-2) CNTs in all vias giving 100% yield.
description: The current-voltage plots show ohmic behaviour for all structures and resistance of
description: the structures increases linearly with increasing number of vias. The resistance values
description: of 23 _ and 91 _ (resistivity = 1.1 × 10-2 _-cm) for 10x10 μm2 and 5x5 μm2 vias
description: obtained for CNT based vias show more than a factor of two improvement as
description: compared with the recently published reports. The improvement can be attributed to
description: the high quality of the CNTs. The CNT via structures of protected catalyst scheme
description: exhibit a significant improvement in resistance of the structures both in terms of the
description: resistance of metal strips (100 _) and via resistances (21 _ and 84 _ for 5x5 μm2 and
description: 10x10 μm2 vias). The growth of CNTs in deep vias is demonstrated. The vias of 3.5 to
description: 20 μm depth are fabricated in polyimide (PI-5878G) film coated on n-Si substrate.
description: The CNT growth of up to 50 μm height in the vias is demonstrated which can be used
description: in TSVs. Length controlled growth of carbon nanotubes in 20 μm deep vias is
description: demonstrated. Levelling of the CNTs with the surface of the sample and filling of the
description: via-holes with photoresist is demonstrated using etch-back techniques.