Controlling the morphology of polycrystalline diamond films via seed density: Influence on grain size and film texture

Abstract

Controlling the morphology of polycrystalline diamond (PCD) films is crucial for various applications, including thermal management and quantum sensors. PCD films are typically produced by plasma-enhanced chemical vapor deposition on substrates seeded with nanodiamonds. Different film morphologies can be achieved by controlling growth rates of crystal-forming facets, which is commonly managed through deposition temperature and hydrocarbon concentration in the plasma. However, the impact of seed density on film morphology remains largely unexplored. In this study, we observed that reducing seed density on silicon substrates has a similar effect on PCD film morphology as increasing hydrocarbon concentration in the plasma. Specifically, as seed density decreases, deposition rate increases, and film texture transitions from (1 1 1) to (1 0 0), followed by the formation of large grains with (1 0 0) facets surrounded by clusters of small grains. These changes were observed using electron microscopy, Raman spectroscopy, and X-ray diffraction. To explain our results, we hypothesize that the silicon–plasma interface surrounding the growing diamond seeds acts as a diamond precursor source. Our proposed explanation requires relatively long precursor migration lengths compared to those assumed in standard diamond deposition theory. Finally, we also propose two new mechanisms for diamond precursor adsorption based on well-established physical phenomena and recent publications. Our findings may open new avenues in diamond research, applicable not only to polycrystalline but also to single-crystal diamond deposition.