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In situ boron doping during heteroepitaxial growth of diamond on Ir/YSZ/Si

In situ boron doping of heteroepitaxial diamond films grown by microwave plasma chemical vapor deposition on Ir/YSZ/Si (001) is investigated. The study comprises the analysis of the gas phase by optical emission spectroscopy (OES) and measurements of B doped films by secondary ion mass spectroscopy (SIMS), cathodoluminescence (CL), and X‐ray diffraction (XRD). The OE intensity of BH species scales linearly with the concentration of the boron precursor trimethylboron (TMB) in the feed gas. Addition of CO2 as an oxygen source causes a proportional reduction of the BH signal. At a ratio C:O = 1, a reduction factor of ∼50 is obtained. It is shown for two diamond samples that the boron incorporation drops nearly identical to the BH emission intensity. We conclude that the influence of oxygen on boron incorporation is a pure gas phase effect. In contrast, CN and BH emission indicate a negligible interaction between N2 and TMB added to the feed gas. At the same time, preliminary growth rate measurements show that the boron background pressure in the chamber after growth with TMB completely cancels the growth acceleration by nitrogen up to N2 concentrations of 100 ppm which points to the dominance of surface processes. Heteroepitaxial diamond films grown on Ir at 50 mbar between 720 and 900 °C contain high intrinsic stress that varies from −2.2 GPa compressive at the lowest to slightly tensile at the highest deposition temperature. The observed behavior is similar to former work at 200 mbar in which effective climb of dislocations was suggested as responsible mechanism. Addition of boron rather enhances the stress formation than causing a relaxation. The B concentration in the heteroepitaxial films is deduced by SIMS, CL, and XRD and correlated with the TMB concentration in the gas phase.