Diamond deposition on copper: studies on nucleation, growth, and adhesion behaviours

Abstract

This paper presents a systematic study on diamond growth on copper by microwave plasma chemical vapour deposition (MPCVD). It includes the following four main parts. 1. Effect of substrate pre-treatment on diamond nucleation. 2. Effect of deposition conditions on diamond nucleation and growth. 3.Preparation of free-standing diamond films using copper substrate. 4. Adherent diamond coating on copper using an interlayer. In the first part we show that diamond nucleation on copper is strongly affected by the substrate pre-treatment. The residues of abrasives left in the surface of the copper substrate play an important role in the diamond nucleation. In the second part we show that the diamond growth rate increases with microwave power and gas pressure. The effect of the microwave power is mainly an effect of substrate temperature. Increasing methane concentration results in a higher nucleation density and higher growth rate, but at the cost of a lower film quality. Gas flow rate has little influence on the diamond nucleation density and growth rate. In the third part we demonstrate the possibility of preparing large area free-standing diamond films using copper substrate, which has nearly no carbon affinity and usually leads to weak adhesion of the diamond films. The normally observed film cracking phenomenon is discussed and a two-step growth method is proposed for stress release. In the fourth part we show that adherent diamond coating on copper can be obtained using a titanium interlayer. Residual stress in the films is evaluated by Raman spectroscopy. It is found that with increase in the film thickness, the diamond Raman line shifts from higher wave numbers to lower, approaching 1332 cm−1. The stress variation along the depth of the film is also analysed using Airy stress theory.