Microstructural studies of diamond thin films grown by electron cyclotron resonance-assisted chemical vapor deposition

A detailed investigation of the correlation among intrinsic stress (σ_in1), nonuniform stress (σ_nu), and phonon lifetime (1/Γ) was performed in order to obtain a coherent and comprehensive picture of the microstructure of diamond thin films grown by the electron cyclotron resonance-assisted chemical vapor deposition (ECR-CVD) technique. It was found that the diamond growth taking place by the ECR-CVD is different to that taking place by the microwave CVD and hot-filament CVD. Point and line defects, rather than sp² C bonds, were found to be the dominant source of both nonuniform stress and reduced phonon lifetime. The surface relaxation mechanism in these films yields sp² C at the expense of strained sp³ C, resulting in a trade off between diamond yield and crystalline quality. The diamond precursor that spontaneously forms on the unseeded substrates yielded higher quality diamond than planted diamond seeds. The grain boundary relaxation model proposed by Hoffman accounts well for the observed behavior of the intrinsic stress, thus indicating that microstructural restructuration takes place at the grain boundaries when sufficient time and thermal energy are provided.