Optical defect inspection apparatus

Abstract

A laser beam oscillated from a laser source is folded in its path by first and second plane mirrors and enters a beam expander. The surface of each plane mirror is deteriorated with illumination by the laser beam and the reflectance is reduced. To avoid a light quantity of the laser beam entering the beam expander from being reduced below a reference value, when the laser beam is illuminated over a certain time, a position on each of the first and second plane mirrors at which the laser beam is illuminated is changed by a structure for rotating and/or translating a reflecting surface of each plane mirror on a plane, which includes the plane mirror, while an optical axis is kept same. The useful life of each plane mirror can be prolonged without displacing the optical axis itself by overcoming the problem that when the laser beam is employed as the light source and a thin beam with a high illumination density is illuminated to the same position on each of the first and second plane mirrors for a long time, the surface of the plane mirror is deteriorated, the reflectance is reduced, and the light quantity cannot be held at a required level.

1 . An optical defect inspection apparatus including a beam deflection mechanism comprising: 
 a laser source;    a first reflecting mirror for reflecting a laser beam emitted from said laser source at a predetermined angle; and    a second reflecting mirror for reflecting again the laser beam reflected by said first reflecting mirror and producing a laser beam which advances in a predetermined direction with respect to the laser beam emitted from said laser source,    wherein said optical defect inspection apparatus further includes a reflecting mirror moving mechanism for moving at least one of said first reflecting mirror and said second reflecting mirror while an angle of incidence and an angle of reflection of the laser beam are maintained same.    
   
   
       2 . The optical defect inspection apparatus according to  claim 1 , wherein at least one of the predetermined angle at which the laser beam is reflected by said first reflecting mirror and the predetermined angle at which the laser beam is reflected by said second reflecting mirror is substantially 90 degrees, and 
 said reflecting mirror moving mechanism moves at least one of said first reflecting mirror and said second reflecting mirror such that a reflecting surface of the moved reflecting mirror is kept in a substantially parallel condition.    
   
   
       3 . The optical defect inspection apparatus according to  claim 1 , wherein at least one of the predetermined angle at which the laser beam is reflected by said first reflecting mirror and the predetermined angle at which the laser beam is reflected by said second reflecting mirror is substantially 90 degrees, and 
 said reflecting mirror moving mechanism rotates at least one of said first reflecting mirror and said second reflecting mirror such that a reflecting surface of the moved reflecting mirror is kept in a substantially parallel condition.    
   
   
       4 . The optical defect inspection apparatus according to  claim 3 , wherein said reflecting mirror moving mechanism includes a mechanism for linearly moving at least one of said first reflecting mirror and said second reflecting mirror such that the reflecting surface of the moved reflecting mirror is kept in a substantially parallel condition.  
   
   
       5 . The optical defect inspection apparatus according to any one of  claims 1  to  4 , wherein said optical defect inspection apparatus further includes a light quantity measuring mechanism for measuring a light quantity of the laser beam reflected by at least one of said first reflecting mirror and said second reflecting mirror.