Routes towards large area, low pressure nanodiamond growth via pulsed microwave linear antenna plasma chemistry
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ybold Optics Dresden GmbH, Dresden, Germany Institute of Physics, Academy of Sciences of the Czech Republic, v.v.i, Prague 8, Czech Republic IMOMEC division, IMEC, Institute for Materials Research, University Hasselt, Wetenschapspark 1, B3590 Diepenbeek, Belgium 2
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ABSTRACT Current experimental configurations for MW PECVD diamond growth do not allow simple up-scaling towards large areas, which is essential for microelectronic industries and other applications. Another important issue is the reduction of the substrate temperature during diamond growth to enhance the compatibility with wafer processing technologies. Such advantages are provided by MW-linear antenna (LA) plasma applicators, allowing a scalable concept for diamond growing plasmas. In the present work we introduce a novel construction of LA MW applicators designed for nanodiamond growth by using plasmas ranging from continuous wave (CW) to high repetition rates pulsed modes (up to 20 kHz) which advantages are discussed in detail. INTRODUCTION Due to its excellent properties diamond layers in the form of nanocrystalline has been identified as having potential industrial uses from MEMs devices to biomedical devices and to protective coatings. The growth of such layers has been described in [1, 2 and 3]. Typically the conditions for growth are a mix of H2 and CH4 using microwave plasma enhanced (MW PECVD). To maximise the industrial potential of NCD layers it is necessary to grow on large areas and at temperatures compatible with the substrate. Microwave plasma enhanced discharges used for the growth of diamond need to operate at high pressures (few mbar up to several hundred mbar) since growth rates are low [4]. Ball or hemisphere type plasma discharges of several cm diameter fed by several kW of power are extremely destructive. Therefore atmosphere-to-vacuum interfaces need to stay clear of such plasma discharges. However, this is not easy to achieve since the power density is usually highest at the inner surface of the interface and that is where the plasma will ignite preferably. Microwaves can be used to overcome this by using transversal magnetic (E) modes of propagating microwaves in cylindrical waveguides which have a concentration of electric field around the axis of symmetry of the cylinder (the plasma discharge vessel) and to ensure the atmosphere to vacuum interface is not located near this region of the cylinder. The plasma would then ignite and remain at the area of highest electric field. TM01 (or E01) is the preferred mode of operation and is easy to create by terminating a coaxial line by letting the inner conductor end and the wave will propagate without the inner conductor. Typical MW PECVD systems using the above method, with reasonable growth rates, are restricted to an area of diameter of 15cm and with growth temperatures above 600°C and therefore is unattractive for industrial scale production of NCD In the described work we use coaxial plasma lines which are similar in the way that the outer conductor of a coaxial line is replaced
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