5 research outputs found
Study of Tantalum nitride diffusion barrier films for coppper interconnect technology
As technology progressed to ultra - large scale integration leading to smaller and smaller devices, there are continuous challenges in the fields of materials, processes and circuit designs. Copper is the interconnect material of choice because of its low electrical resistivity and high electromigration resistance. However, copper is quite mobile in silicon at elevated temperatures. Therefore, to prevent the diffusion of copper into silicon, a diffusion barrier layer that has fewer grain boundaries, good adhesion to Si and Si02, high thermal and electrical stability with respect to Cu is necessary. Tantalum nitride compounds have been investigated as potential barrier materials. TaN has a very high melting point of 2950C. It is thermodynamically stable with respect to Cu and has good adhesion to the substrate. It has a dense microstructure and shows good resistance to heavy mobility of Cu in Si and has electrical stability at temperatures upto 750 C. The diffusion barrier properties of Ta and its nitrides for copper metallization at RIT have been investigated. The TaNx films were reactively sputter deposited on Si02 substrates at various N2/AJ- ratios. The influence of nitrogen partial pressure on the electrical and structural properties of the films is studied. It has been observed that as deposited pure Ta is tetragonal, which becomes bcc-Ta with small increase in N2 flow to 5% of the sputtering gas mixture. When the nitrogen flow is increased from 12 up to 20%, amorphous and a mixture of amorphous and crystalline Ta2N phase is formed. The amorphous phase crystallizes when annealed to higher temperatures. An fee- TaN phase is formed at N2 flow of 30%. At higher concentrations of N2; nitrogen rich compounds like Ta5N6, Ta3N5 are formed. During backend semiconductor processing, both Cu and TaN films are subjected to various annealing treatments in N2, 02, and Ar at relatively high temperatures. Since these treatments influence the stability of the metallization it was important to establish the effect of the ambients on the integrity of the copper interconnect. The Cu/TaN/Si02 films were annealed to various temperatures up to 600 C in N2, Ar ambients for 20 min and the thermal stability and barrier effectiveness of the films was studied. Annealing the films to temperatures above 500 C cause de-lamination of films at the Cu/TaN interface, which is attributed to the formation of copper oxides with a high density of voids. This was observed by XRD analyis and SEM. RBS spectra showed diffusion of tantalum into the surface of copper at temperatures ~ 500 to 600 C. Therefore we can conclude that cubic TaN films act as stable barrier films up to 500 C in an inert ambient
Reactive sputtering of tantalum Nitrides for Diffusion Barrier Layers
The objective of this project is to develop a robust process to deposit Tantalum nitride barrier layer for copper metallization. TaN films were reactively sputtered in a twin cathode AC inverted cylindrical magnetron configuration using the lonTech Cyclone sputtering system. The dependence of thickness, resistivity and phase changes as a function of N2 flow rate was studied. A designed experimental approach was used to optimize resistivity and the phases formed. A 10 sccm N2 flow (with 99 sccm Ar) deposited at 4 mTorr and 2 kW pressure gave an amorphous bcc-phase Ta(N) with a low resistivity of about 220 μ Ωcm. Further analysis would be done to study the barrier properties, after depositing copper and doing electrical, structural and chemical characterization
Conference of Microelectronics Research 2000
https://scholarworks.rit.edu/meec_archive/1009/thumbnail.jp
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Epitaxial regrowth based fabrication process for vertical cavity lasers
GaAs based oxide confined vertical-cavity surface-emitting lasers (VCSELs) have
demonstrated record performance in terms of low threshold current, high modulation
speed and high wall-plug efficiency. However, oxide-confined VCSELs have reliability
and non-uniformity problems that limit scaling to small active volumes for single mode
operation or to micro-cavity dimensions for quantum light sources. The optical mode is
also difficult to engineer since aperture geometries are limited. These limitations call for
the development of a new technology that provides full control of modal overlap with
optical gain, and this requires patterning of the VCSEL’s transverse mode- and current-confinement. A new approach presented in this dissertation demonstrates a very
important attribute in providing lithographically defined and self-aligned mode- and
current-confinement suitable for arbitrary patterning and size scaling, and for high reliability, is based on an all-epitaxial device. The fabrication process involves epitaxial
regrowth over shallow mesas to incorporate these intra-cavity patterns that have direct
overlap with the optical mode. These intracavity gratings are defined by lithography and
a selective etching process after the first stage of epitaxial growth. In this work, a
VCSEL with an intracavity grating has been realized that shows an increase in the slope
efficiency due to better matching of the gain and optical mode in comparison to a device
that lacks the grating. Using a similar regrowth process, a laser diode incorporating a
buried high index contrast GaAs-air (etched void) photonic pattern within the cavity has
also been demonstrated.
Epitaxial quantum dots (QDs) present new opportunities in semiconductor
light sources due to their charge localization and modified electronic density of states. It
is especially interesting to combine QDs with a microcavity VCSEL, since electronic and
photonic confinement become scalable in a device that can have important commercial
applications. This has been achieved in a buried heterostructure VCSEL that employs an
intracavity mesa to confine the quantum dots and optical mode to the same regions in the
cavity. Cavity quality factors as high as 33000 are measured, and ground state lasing is
demonstrated with a single quantum dot active layer for temperatures up to 110 K.Electrical and Computer Engineerin