Laser Scatterometry for Process Characterization,

Laser scatterometry is a technique which involves shining a light beam on an area to be characterized and measuring the angular distribution of the light that is scattered from that area. A laser is used so that the incident light will be monochromatic and coherent. It is also valuable, in many applications, to be able to confine the probe beam to a selected area, with a diameter of 10 um or more. The scattered light distribution is typically measured either by scanning a detector over an arc, using a fixed array of photodiodes that are mounted along an arc, or by measuring the scattered light intensity distribution at a hemispherical screen when sample symmetry requires more than a one dimensional distribution measurement. In most cases, a single line measurement along a 90 deg arc is sufficient, either because of sample symmetry or because of the ability to align the sample in the direction of interest. The wavelength of the light used is a determining factor in the range of feature sizes that will be measured. Thus, different wavelength sources are sometimes valuable. Also, the angle of incidence of the probing light beam is a factor in the range of features that will be characterized.