Method and apparatus for inspecting substrates

A method for detecting defects on a workpiece, said method comprising:

• providing a first signal indicative of the slope of said workpiece;
• providing a second signal that is the integral of said first signal;
• comparing said first signal against at least a first threshold value;
• and
• comparing said second signal against at least a second threshold value, wherein if said first signal exceeds said first threshold value or said second signal exceeds said second threshold value a defect is considered to be present in said workpiece.

Method comprising:

• moving a workpiece;
• reflecting first radiant energy off a first side of said workpiece;
• reflecting second radiant energy off a second side of said workpiece;
• generating a first signal indicative of the slope of the surface of said first side in response to said reflected first radiant energy;
• generating a second signal indicative of the slope of the surface of said second side in response to said reflected second radiant energy;
• and
• generating a third signal indicative of the integral of a combination of said first and second signals, said third signal representing the presence of defects in said first and second sides of said workpiece.

Apparatus comprising:

• a first circuit for generating a first signal indicative of the slope of the surface of a workpiece;
• and
• a second circuit for generating a second signal that is the integral of the first signal;
• a third circuit for sensing whether a defect is present on said surface in response to said second signal;
• and
• a fourth circuit for sensing whether a defect is present on said surface in response to said first signal independent of said second signal.

Apparatus comprising:

• a first circuit for generating a first signal indicative of the slope of the surface of a workpiece;
• a second circuit for generating a second signal that is the integral of the first signal;
• and
• a comparator comparing the first and second signals to one or more reference signals to detect whether there is a defect on the surface of the workpiece.

Apparatus comprising:

• a first circuit for generating a first signal indicative of the slope of the surface of a first side of a workpiece;
• a second circuit for generating a second signal indicative of the slope of the surface of a second side of the workpiece;
• and
• an integrator for generating a third signal corresponding to the integral of the first signal combined with the second signal.

Apparatus comprising:

• a first circuit for generating a first signal indicative of the slope of the surface of a first side of a workpiece;
• a second circuit for providing a first integral signal that is the integral of the first signal;
• a third circuit for generating a second signal indicative of the slope of the surface of a second side of the workpiece;
• a fourth circuit for providing a second integral signal that is the integral of the second signal;
• and
• a circuit for combining the first and second integral signals.