Foreign matter detection device

A foreign matter detection device for detecting a foreign matter on a test piece made of a first optically transmissible material with patterns made of a second optically transmissible material which can transmit the light less than said first transmissible material formed thereon, said device comprising:

• a first illumination means for emitting a coherent light having a first predetermined diameter to impinge on a first surface of said test piece at a predetermined incidence angle with respect to said first surface and to produce a reflected coherent light reflected from said first surface, said coherent light being polarized in a first direction parallel to said first surface of said test piece, said reflected coherent light being polarized in a second direction perpendicular to said first direction;
• a second illumination means for emitting an illumination light to illuminate a second surface opposed to said first surface of said test piece and to produce a transmitted light transmitted from said first surface;
• and
• an image forming means for forming a first image of said first surface based on said reflected coherent light and said transmitted light, whereby said reflected coherent light reflected from said pattern edge is added with said transmitted light passing through said pattern such that the light intensity distribution at said pattern edge is smoothed and that at said foreign matter is enhanced.