17 May 2019

Growth facilities

The Microwave plasma Chemical Vapour Deposition (MPCVD) method is used to grow a wide variety  diamond layers at Cadiz University. With this method, microwaves ignite methane gas and an abundance of hydrogen gas at low pressure to generate a hot plasma with reactive particles which perform the diamond growth. One home build NIRIM system  makes it possible to grow single crystal on a diamond substrates of 3×3 or 2×2 mm size.

If the amount of dopants is tuned during the MECVD process, diamond can have the properties of an electronic insulator, semiconductor, metal and even a superconductor. Boron, is the main dopant used in MPCVD system is used. With this growth reactor it is possible to obtain boron doped homoepiatxial diamond layers with boron concentration range between 10+16-10+21 at/cm3 with high  crystalline quality.

The growth chamber consists of an inner and an outer fused silica (quartz) tube, the sample holder is placed on the top of the inner quartz tube at the intersection with the waveguide. A
microwave plasma generator (Metal Process model G2V2) operating at a standard frequency of 2.45 GHz supplies an adjustable microwave power in the range of 0 to 2000 Watt. The horizontal position of the plasma can be adjusted by the hollow-faced piston (standing wave tuning); the reflected power (water cooled with the isolator) can be minimized by adapting the impedance. The growth chamber is connected to a pump system underneath, consisting of a primary pump and a turbo molecular pump. While the primary pump is used for the circulation of the gas mixture, the secondary pump ensures a base pressure below 10-5 Torr before introduction of the gas mixture and therefore prevents incorporation of other impurities.

MPCVD reactor

Electron Beam Evaporation (or e-beam evaporation) is a powerful physical vapor deposition process that allows the user to evaporate materials that are difficult or even impossible to process using standard resistive thermal evaporation. Electron beam deposition uses a magnet to focus electrons to form a beam, which is then directed towards a crucible that contains the material of interest. The energy of the electron beam is transferred to the material, which causes it to start evaporating. Many metals, such as gold, will melt first and then start evaporating, while ceramics will sublimate. The material vapors then travel out of the crucible and coat the substrate.

The Nexdep e-beam equipment with its 400mmx40mm baseplate, it can accommodate up to 8 soures and wide variety of PVD processes. In our particular case, the target materials are, Ti, Pt, Au and Zr. Using additional gasses (O2) during the sputtering process compound materials can by achieved (e.g. oxide materials…). Both applications can be used to perform metallic deposition and oxide layers for power devices (MOSFET, Schottky) and ohmic contacts.

 

E-beam sputtering

An alternative to Molecular Plasma Enhaced Chemical Vapor Deposition is based on linear antenna PECVD (LAPECVD) technology. This technology permits to obtain more stables and homogeneous  plasma conditions during the growth than MPDVD one as well as to introduce larger substrates 10x10cm). 

Facility required in the ERC budget: it is a NCS-600 system consists of a water cooled vacuum chamber containing the planar microwave plasma source, a process gas distribution system and a substrate stage. The microwave generator comprises two power supplies with two microwave magnetron heads, one on each side of the plasma source which can deliver up to 3 kW each at a frequency of 2.45 GHz, either in continuous wave mode or in pulsed mode.  The microwaves are transported from the microwave heads to four parallel coaxial antennas via rectangular wave guides and a cascaded coaxial power divider on each side. The coaxial plasma line is basically a coaxial transmission line, where the outer conductor is the conductive plasma discharge which forms on the outer surface of a dielectric tube. This tube acts as the vacuum-to-atmosphere interface for the microwaves. Unlike the commonly the CVD the coaxial plasma line approach allows the plasma to be in direct contact with the vacuum-to-atmosphere interface. The contact between the plasma and the vacuum-to-atmosphere interface allows for thecoating very large areas (square metres), since the quartz tubes distribute the plasma evenly along their length. Thus the growth of larger carbon fiber substrates under the same growing conditions and at same time can be carry out.  

Home made LAPECVD reactor