The excellent mechanical and optical properties of diamond are well known but it shows extremely high dielectric breakdown, thermal conductivity and electron emissivity as well. In addition, diamond withstands any acid base or organic solvent up to ? 700°C. Chemical vapor deposition (CVD) of adherent polycristalline diamond films made practical applications economically feasible, but only in cases where coverage of small surfaces provide high added value. Such a possibility is the application of CVD diamond in micromachined silicon based sensors for highly corrosive environment. Diamond CVD is compatible this technology. The work carried out by the TUB and the RITPMS in this field will be presented.

Present work is intended to study the dependence of the homogeneity, the contamination state and the appearance of pinholes on various deposition parameters in diamond films deposited on monocrystalline and polycrystalline substrates. Such deposition parameters are the nucleation and the growing temperature in the ranges of 850-950°C and
750-900°C respectively. In addition the duration of nucleation and the duration of growing cycle were also varied. The nucleation normally lasts 15-25 minutes or 5-15 minutes dependent on the fact weather mono or polycrystalline substrate is used. The growing cycle on the other hand is a 4-8 hour long process in both cases. The concentration of methane was adjusted to the value of 0,5-1,5% during the whole growing process. Number of other experimental parameters were chosen to be constant, such as the power output of the microwave generator (750 W), the total pressure in the system (23 mbar), the nucleation bias (-200 V) and the total flowrate (100 m/min).

The compactness of diamond film on silicon monocrystalline substrate can readily be examined by means of chemical etching with basic solution. Regular rectangular etch patterns appear on the spots of the pinholes due to the anisotropy of Basic etching in (100) orientation crystal. These rectangles can readily be studied and counted by means of optical microscope.

The objective of the experiments is to find the technology of manufacturing graphite free diamond films with a pinhole density less than one in ten square centimetres. This can be used as an efficient chemical and mechanical protective coating on some micro sensor elements with surface area of 0,1-30 mm², operating in extreme harsh environments.

This work is sponsored by OTKA # TT 025346

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Magyar Anyagtudományi Egyesület