Method of measuring orientation flat width of single crystal ingot

A method of measuring the orientation flat width of a single crystal ingot by the use of an apparatus including an optical non-contact type displacement measuring device having a sensor, means for fixing the orientation fiat of the single crystal ingot facing to the sensor, means for scanning the sensor in the direction normal to the major axis of the single crystal ingot and means for measuring the scanning distance, comprising the steps of:

• (a) detecting the boundary points between the orientation flat and the round surface of the single crystal ingot from the displacement to be measured by scanning the sensor while detecting the distance between the sensor and the ingot surface including the orientation flat;
• (b) measuring the scanning distance A of the sensor from the first boundary point detection position to the second boundary point detection position;
• (c) detecting the first distance 1.sub.1 from the first boundary point to the sensor and the second distance 1.sub.2 from the sensor to the second boundary point to obtain B=.vertline.1.sub.1 -1.sub.2 .vertline.;
• and
• (d) calculating the orientation flat width C in accordance with the following equation (1):
• C.sup.2 =A.sup.2 +B.sup.2 ( 1).