Patent ID: 6867855

Claim:
Apparatus for detecting a defect in the outer peripheral edge of a wafer, comprising: a rotary mechanism by which the wafer can be rotated; a wafer edge contact device disposed adjacent said rotary mechanism, said device including a string, a guide section that guides the string such that a length thereof is freely supported, a string support to which one end of the string is fixed, and a sensor operatively associated with the other end of said string so as to sense movement of said other end of the string when said length of the string is displaced and operative to produce signals indicative of the extent to which said length of string is displaced, and wherein said length of string can be placed in contact with an outer peripheral edge of a wafer readied in the apparatus for rotation by said rotary mechanism, whereby said string will be pulled by a defect at the outer peripheral edge of the wafer when the length of string is in contact with the outer peripheral edge and the wafer is rotated by said rotary mechanism; and a controller operatively connected to said sensor so as to receive the signals produced by said sensor.