Preparation and properties of boron doped diamond films

Boron doped diamond films were deposited on the silicon substrate by hot-filament chemical vapour deposition (HFCVD). The effects of boron source flow on the conductivity, grain size, crystal direction and residual stress of boron doped diamond films were investigated. The results show that the resistance of diamond films decreases rapidly with increasing boron flux. After a certain flow rate, the defects and impurities increase and hinder the further decline of resistance. The boron flow increases gradually in 0-25 mL/min, and the average grain size of the diamond film increases from 3.5 to 8.3 μm. The boron element promotes the growth of (111) crystal surface. When the boron flow rate continues to increase to 35 mL/min, the promotion effect on the (111) crystal surface weakens and the grain size decreases. Therefore, the surface defects increase and the integrity is lost. The X-ray diffraction analysis shows that with the increase of boron flow, the diffraction peak area ratios of the diamond film (111) surface and (110) surface increase first and then decrease, and that the maximum value is reached when the boron flow rate is 20 mL/min. The residual stress of boron doped diamond film is compressive stress. When the flow rate of boron source is less than 10 mL/min, the stress decreases with the increase of flow rate, and the stress increases with the increase of flow rate when the flow rate is more than 30 mL/min.