Patent attributes
An array of conjugated quadratures of fields is measured interferometrically by a confocal interferometer and detector system wherein each conjugated quadratures comprises a difference of conjugated quadratures of fields of beams scattered/reflected or transmitted by a pair of spots in or on a substrate. The array of conjugated quadratures is measured jointly, i.e., simultaneously, and the components of each conjugated quadratures may be measured jointly. Each pair of spots generally has a relative displacement on the order of the three or more times the size of the spots in a direction nominally tangent to the surface of the substrate. The relative phases of the beams subsequently scattered/reflected or transmitted by the pair of spots on/in a substrate may be adjusted as a set by control of a single system parameter so that the conjugated quadratures of the array of conjugated quadratures are nominally zero, i.e., information may be obtained about the substrate with the interferometer and detector system operating in a dark field mode. Operation in a dark field mode leads to both reduced systematic and statistical errors in the information and increased throughput. The information may include the transverse derivative of a profile of one or more surfaces of a substrate; one-dimensional, two-dimensional, and three-dimensional transverse differential images of a substrate; critical dimensions of features or artifacts on or in a substrate, and the size and location of sub-wavelength defects in or on a substrate.
