Rotating compensator spectroscopic ellipsometry (RCSE) and its application to high-k dielectric film HfO 2

Abstract

High-k gate dielectric films with equivalent oxide thickness (EOT) of 3 nm or less are becoming the main theme of research and development in ultra-large-scale integrated circuits industry with device dimensions scaled down to less than 130 nm. Among the high-k gate dielectric materials hafnium dioxide (HfO<SUB>2</SUB>) is very promising with its high dielectric constant (approximately 30) and stability in contact with Si. The samples were prepared with a DC magnetron-reactive sputtering method and subsequently annealed in the furnace with a temperature range of 500- 850 degree(s)C. The thickness of the HfO<SUB>2</SUB> varied from 3.5- 18nm with a hafnium silicate interface layer of approximately 1 nm. The electrical measurement showed that the breakdown voltage is inversely proportional to the physical thickness, suggesting the breakdown process occur at the HfO<SUB>2</SUB> thin film rather than in the interface layer. To measure the physical thickness of hafnium dioxide and hafnium silicate interface simultaneously, a research grade bench top rotating compensator spectroscopic ellipsometry (RCSE) in the wavelength range of 195-915 nm was used. The dispersion of HfO<SUB>2</SUB> film was characterized with a two-peak critical point (CP) model and the dispersion of the interface layer of hafnium silicate was characterized with a five-peak CP model. An interface layer thickness of 0.7-2 nm was found for all hafnium dioxide films on Si, depending on the process conditions such as annealing temperature and oxygen flow rate. The same wafers measured by RCSE were later studied by transmission electron microscopy (TEM). The thickness of hafnium dioxide and hafnium silicate determined by TEM is in good agreement with the noninvasive RCSE method.