Background
One of the major challenges in thin film growth and application is the precise control of the film thickness. X-ray reflectivity is a fast and accurate—yet non-destructive—technique to measure the film thickness. The technique relies on the interference effect of the X-ray waves scattered at the top and bottom surfaces of the film. The interval between the interference fringes, often called thickness fringes, is inversely proportional to the thickness of the film. As a consequence, higher resolution optics are required to measure thicker films.
Investigation
The SmartLab diffractometer offers automatically aligned, variable resolution (0.002 to 0.1° divergence) optical capabilities for optimal performance over a range of film thicknesses. In the figure below, a 180 nm AlN thin film deposited on a sapphire substrate is measured with both 0.1 and 0.01° resolution. Only the 0.01° resolution curve shows clear interference fringes. By fitting the curve, the actual thickness of the AlN film is determined to be 174 nm.
