Intriguing morphological evolution during chemical vapor deposition of HfS2 using HfCl4 and S on sapphire substrate
Journal
Applied Surface Science (APPL SURFACE SCI)
Date
2020.04.15
Abstract
For chemical vapor deposition (CVD) of HfS2, HfCl4 is commonly used as the Hf precursor, and a sapphire (Al2O3) substrate is preferred to improve film crystallinity. During the HfS2 CVD process using HfCl4 and S precursors on the sapphire substrate, we observed an anomalous morphological evolution due to a chemical interaction between the Al2O3 substrate and HfCl4, particularly when the substrate was exposed to HfCl4 vapor too early prior to the introduction of S. The excessive HfCl4-induced local chemical etching produced a serrated surface on the substrate, and pyramid-shaped HfO2 crystals (a by-product of chemical etching) and CVD-HfS2 flakes grew on the unetched and etched substrate surface regions, respectively. A mechanism for the observed morphological evolution is proposed based on thermodynamic and kinetic considerations, which emphasizes the importance of precursor supply timing to minimize the possible process-related defects.