In situ spectroscopic ellipsometry analyses of hafnium diboride thin films deposited by single-source chemical vapor deposition

In situ spectroscopic ellipsometry was used to analyze hafnium diboride thin films deposited by chemical vapor deposition from the single-source precursor Hf (B H4) 4. By modeling the film optical constants with a Drude-Lorentz model, the film thickness, surface roughness, and electrical resistivity were measured in situ. The calculated resistivity for amorphous films deposited at low temperature ranged from 340 to 760 μ cm. These values are within 25% of those measured ex situ with a four-point probe, indicating the validity of the optical model. By modeling the real-time data in terms of film thickness and surface roughness, the film nucleation and growth morphology were determined as a function of substrate type, substrate temperature, and precursor pressure. The data show that at low precursor pressures (∼ 10-6 Torr) and at low substrate temperatures (<300 °C), the onset of growth is delayed on both Si and Si O2 surfaces due to the difficulty of nucleation. A higher substrate temperature or precursor pressure reduces this delay. At low temperatures the film morphology is a sensitive function of the precursor pressure because site-blocking effects change the reaction probability; the authors show that the morphology of newly grown film can be reversibly transformed from dense smooth to rough columnar by decreasing the precursor pressure.