Lateral shift measurement using an optical technique

Abstract

Alignment of layers during manufacture of a multi-layer sample is controlled by applying optical measurements to a measurement site in the sample. The measurement site includes two diffractive structures located one above the other in two different layers, respectively. The optical measurements include at least two measurements with different polarization states of incident light, each measurement including illuminating the measurement site so as to illuminate one of the diffractive structures through the other. The diffraction properties of the measurement site are indicative of a lateral shift between the diffractive structures. The diffraction properties detected are analyzed for the different polarization states of the incident light to determine an existing lateral shift between the layers.

What is claimed is: 
     
         1 . A structure configured for overlay measurement on a sample, said structure comprising two pairs of diffractive structures of predetermined geometries, wherein
 said two pairs of diffractive structures are formed by two diffractive structures spaced-apart from one another along an X-axis and two diffractive structures spaced-apart from one another along a Y-axis,   the diffractive structures of each pair are spaced-apart from one another along the Y-axis or the X-axis, respectively, and comprise patterns of features aligned along the X-axis or the X-axis, respectively, with a predetermined lateral shift between the patterns in the structures in accordance with a predetermined model of simulated diffraction effects from incident light interaction with laterally shifted diffractive structures of a pair of such structures of said predetermined geometries, thereby enabling direct overlay measurement of a lateral shift between layers in the sample from diffraction of incident light from said two pairs of diffractive structures.