XRR: X-ray Reflectometry for Thin Films metrology

X-ray reflectometry (XRR) is gaining in popularity for the measurement of thickness, density and roughness of thin films. Unlike other techniques, multilayer structures can be determined, with no restriction on the crystalline nature of the films. The thicknesses can range from a few atomic layers to 1 micron of material. The measurement is fast (seconds) and can be applied for in-line product wafers metrology.

The measurement is performed at a glancing angle, with the specular reflection of the X-rays being detected by a detector. The intensity is recorded as a function of angle, and this information is modelled to determine the structure of the material in question.

The example above shows the fringe period which relates to the thickness of the layer (the thicker the layer, the shorter the period) and the critical angle, which is related to material density.

The simulation above shows a 2-layer structure, with the thickness, roughness and density determined for independent layers.