Automated photomask inspection apparatus

A method of inspecting objects formed on substrates, comprising the steps of:

• transporting a substrate such that a surface thereof to be inspected moves within an inspection plane;
• providing means defining a first optical axis intersecting said inspection plane;
• directing a beam of light along said first optical axis and focusing said beam of light to illuminate a spot of a selected size on the substrate to be inspected;
• sweeping said beam of light in oscillatory fashion such that the illuminated spot moves from one side to another of a path defined by the intersection of the optical axis with the substrate surface as said substrate surface is moved within said inspection plane whereby care areas of the substrate including at least one of said objects are scanned in swaths the width of which is determined by the beam sweep limits;
• detecting changes in the intensity of said beam of light caused by its intersection with areas of the inspected substrate as said beam of light is either transmitted or reflected by said substrate, and developing scan signals corresponding thereto;
• sampling said scan signals to produce sample signals;
• and
• comparing said sample signals to corresponding reference signals and identifying differences therebetween.

An optical inspection system for inspecting objects formed on substrates selected from the group consisting of photomasks, reticles, phase shift masks and semiconductor wafers including a plurality of supposedly identical patterned objects disposed in an ordered array on a surface thereof, comprising:

• a laser for providing a pixel illuminating beam of light;
• an optical system defining a first optical axis along which said pixel illuminating beam of light is to be initially passed;
• a stage for moving a substrate to be inspected such that a surface thereof moves within an inspection plane intersected by said optical axis and such that as the substrate is moved the point of intersection traces a serpentine path over a portion of the substrate including at least one of the objects;
• a beam deflector disposed along said first optical axis and operative to deflect said beam of light in oscillatory fashion such that said beam of light sweeps back and forth across said path from one side to another and in a direction generally transverse to said path such that, as the substrate is carried, the deflection of said beam of light from one side of said path to the other defines a scanning swath over the portion of the substrate;
• a light detector for detecting changes in the intensity of said beam of light caused by pixel areas of the inspected substrate illuminated by said beam of light as said beam of light is either transmitted or reflected by said substrate, said light detector being responsive to the detected changes in intensity and operative to develop scan signals corresponding thereto;
• an electronic circuit for storing first scan signals developed as said scanning swath passes over a first of the patterned objects and for comparing the stored first scan signals to second scan signals developed as the scanning swath passes over a second of the patterned objects whereby differences therebetween may be used to identify defects in the inspected substrate;
• and
• a recorder for recording the locations of said defects on said substrate.

An optical inspection system for inspecting objects formed on substrates selected from the group consisting of photomasks, reticles, phase shift masks and semiconductor wafers, comprising:

• a stage for carrying a substrate to be inspected such that a surface of said substrate moves in a particular manner within an inspection plane;
• a laser for providing a pixel illuminating beam of light;
• an optical system defining a first optical axis intersecting said inspection plane and along which said pixel illuminating beam of light is initially passed, said optical system including a variable magnification subsystem for focusing said beam of light to a pixel defining spot on the substrate to be inspected;
• a beam deflector disposed along said first optical axis and operative to deflect said beam of light in oscillatory fashion whereby said pixel defining spot is caused to sweep across the surface of said substrate from one side to another of the path traced by the intersection of said optical axis with said substrate as said substrate is moved in said particular manner, and in a direction transverse to said path, as the substrate is carried along said path, the limits of deflection of said beam of light from one side of said path to the other defining the width of a scanning swath over a care area of the substrate including at least a portion of one of said objects;
• at least one light detector for detecting changes in the intensity of said beam of light caused by its intersection with the inspected substrate as said beam of light is either transmitted or reflected by said substrate, said light detector being responsive to the detected changes in intensity and operative to develop scan signals corresponding thereto, said light detector including a signal sample for sampling said scan signals to produce pixel sample signals;
• and
• an electronic comparator for comparing said pixel sample signals to corresponding reference signals whereby differences therebetween may be used to identify defects in the inspected substrate.

An optical inspection system for inspecting objects formed on substrates such as photomasks, reticles, phase shift masks and semiconductor wafers, comprising:

• a stage for carrying a substrate to be inspected such that a surface of said substrate moves in a particular manner within an inspection plane;
• a laser for providing a pixel illuminating beam of light;
• an optical system defining a first optical axis intersecting said inspection plane and along which said pixel illuminating beam of light is initially passed, said optical system being operative to focus said beam of light to illuminate a pixel defining spot on the substrate to be inspected, the spot size determining at least one dimension of a pixel of the substrate;
• a beam deflector disposed along said first optical axis and operative to deflect said beam of light in oscillatory fashion whereby said pixel defining spot is caused to sweep across the surface of said substrate from one side to another of a path traced by the intersection of said optical axis with said substrate as said substrate is moved in said particular manner, and in a direction transverse to said path as the substrate is carried along said path, the limits of deflection of said beam of light from one side of said path to the other defining the width of a scanning swath over care areas of the substrate including at least a portion of one of said objects;
• at least one light detector for detecting changes in the intensity of said beam of light caused by its intersection with pixel areas of the inspected substrate as said beam of light is either transmitted or reflected by said substrate, said light detector being responsive to the detected changes in intensity and operative to develop scan signals corresponding thereto;
• an electronic comparator for comparing said scan signals to corresponding reference signals whereby differences therebetween may be used to identify defects in the inspected substrate;
• a recorder for recording the substrate locations of said defects;
• a controller for subsequently causing said stage to reposition and hold the inspected substrate at a previously recorded location of a selected defect;
• an oscillatory reflector disposed along said optical axis for causing a portion of said optical axis to sweep back and forth along a portion of said path in cooperation with said beam deflector whereby a selected segment of a swath is repetitively scanned and said light detector continuously generates display signals representative of the selected defect;
• and
• a display device responsive to said display signals and operative to provide a visual display of substrate area covered by the swath segment and including the selected defect.

An optical inspection system for inspecting objects formed on substrates selected from the group consisting of photomasks, reticles, phase shift masks and semiconductor wafers, comprising:

• a laser for providing a pixel illuminating beam of light;
• an optical system defining a first optical axis along which said pixel illuminating beam of light is to be passed;
• a stage for moving a substrate to be inspected such that a surface thereof is carried within an inspection plane intersected by said optical axis and such that the point of intersection traces a serpentine path over at least a portion of the substrate including at least one of the objects to be inspected;
• a beam deflector disposed along said first optical axis and operative to deflect said pixel illuminating beam of light in oscillatory fashion such that said beam of light sweeps back and forth across said path from one side to another and in a direction generally transverse to said path such that, as the substrate is carried, the deflection of said beam of light from one side of said path to the other defines a scanning swath over the portion of the substrate;
• a light detector for detecting changes in the intensity of said beam of light caused by pixel areas of the inspected substrate illuminated by said beam of light as said beam of light is either transmitted or reflected by said substrate, said light detector being responsive to the detected changes in intensity and operative to develop scan signals corresponding thereto;
• and
• an electronic comparator for comparing said scan signals to corresponding reference signals whereby differences therebetween may be used to identify defects in the inspected substrate, and for recording the location of said defects on said substrate.