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vapour deposition (CVD) has been limited to R&D-scale use because only specialised and cost-prohibitive precursors have been available. Tin-containing materials are currently in demand as the electronics industry looks for ways to increase the speed of transistors.


In response, Dow Electronic Materials has introduced an electronic grade of a tin CVD precursor, stannic chloride, which has been successfully used by imec for the growth of germanium tin for use in stressors, high- mobility channels and other features of future semiconductor devices.


“We are very pleased that we found a tin precursor that enables the industrial production of GeSn for future generation electronic devices” says Egbert Woelk, Technology and Applications Manager at Dow Electronic Materials. “Together with our VAPORSTATION Central Delivery System, we have a turn-key solution to deliver our new tin precursor to any CVD tool on the market. This removes all barriers to using the new GeSn CVD process on a large scale in the latest generation CVD tools.”


In the past GeSn CVD was limited to using deuterated stannane, SnD4, which is costly to make and not available on a commercial basis. Silicon germanium (SiGe) is a desirable material for electronics and optoelectronics manufacturers, and the addition of tin increases the speed of transistors made from this material.


There is a growing interest in thin germanium or germanium-silicon materials containing tin to enhance semiconductor structures, such as the high-mobility channel that conducts current in transistors, and photonic devices, such as LEDs.


The viability of Dow’s material has been confirmed in a new CVD process developed by the Belgium-based nanoelectronics research centre imec. Using stannic chloride supplied by Dow Electronic Materials, imec


January / February 2012 www.compoundsemiconductor.net 117


has demonstrated the material’s viability in an industrial CVD process, overcoming the barrier of tin’s propensity to etch deposited material. Imec has produced high-content germanium tin epitaxial films (>8% tin content) with outstanding electronic and structural quality. This work has been described in the paper “Undoped and in-situ B doped GeSn epitaxial growth on Ge by atmospheric pressure- chemical vapor deposition”, by B. Vincent et al, Appl. Phys. Lett. 99, 152103 (2011).


According to imec, the CVD grown GeSn layer can also be used as a high-mobility channel material on germanium. A strained GeSn channel on germanium is also a possible candidate to be used in the device channel of future Ge-based metal-oxide semiconductor field-effect transistor (MOSFET) devices.


“The CVD growth of GeSn with commercially- available precursors will boost the research on high-mobility MOSFETs,” says Roger Loo, R&D Manager at imec. “Besides, it opens new routes for group-IV semiconductors research in other fields, such as photonics (having indirect- to-direct-bandgap transition expected for about 10% Sn incorporated in monocrystalline GeSn alloys) and photovoltaics (ternary SiGeSn alloys). The good results that we achieved with stannic chloride precursor convince us to continue our successful collaboration with Dow Electronic Materials,” adds Loo.


Imec recently presented the results of their development work at The 2nd GeSn Workshop: GeSn Developments for Future Applications, which was held in conjunction with the 7th International Conference on Si Epitaxy and Heterostructures 2011 in Leuven, Belgium.


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