Speckle reduction track filter apparatus for optical inspection of patterned substrates

An inspection device for substrates, such as patterned semiconductor wafers, having periodic features of a type diffracting light into a Fourier plane or surface comprising,

• a plurality of sources of illumination generating beams directed at a common region in a substrate, the substrate having a repetitive pattern of periodic features, as well as aperiodic contaminants and defects, said periodic features having a spacing diffracting light from said beams in a plurality of spectral lines found in a plurality of spectral dispersion orders, each order of spectral lines forming an elongated band,
• each beam having an aperture stop to control its angular diversity as it impinges on the substrate,
• a mainly transmissive spatial filter, disposed in the Fourier plane of light diffracted from the substrate, the filter having a plurality of spaced apart opaque tracks blocking said bands of light of said plurality of sources of illumination but transmitting light scattered from said aperiodic features, each track radiating from an imaginary point,
• a two dimensional imaging sensor located a distance from said spatial filter in a position receiving light transmitted through said spatial filter, and
• means for delivering light passing through the spatial filter to said imaging sensor.

An inspection device for substrates, such as patterned semiconductor wafers, having periodic features of a type diffracting light into a Fourier plane or surface comprising,

• a single source of monochromatic illumination generating a beam directed along an optical axis at a substrate, the substrate having a repetitive pattern of periodic features, as well as aperiodic contaminants and defects,
• an elongated slit-shaped aperture stop disposed along said optical axis with said beam focused to pass therethrough and onto said periodic features of the substrate, said periodic features having a spacing diffracting light from said beam in a plurality of lines found in a plurality of dispersion orders, each order of lines forming an elongated band,
• a mainly transmissive spatial filter, disposed in the Fourier plane of light diffracted from the substrate, the filter having a plurality of spaced apart opaque tracks blocking said bands of light associated with the slit-shaped aperture stop but transmitting light scattered from said aperiodic features, each track radiating from an imaginary point,
• a two dimensional imaging sensor located a distance from said spatial filter in a position receiving light transmitted through said spatial filter, and
• means for delivering light passing through the spatial filter to said imaging sensor.