Position measuring device and position measuring method in semiconductor single crystal manufacturing device

A position measuring device applied to a semiconductor single crystal manufacturing device for manufacturing a semiconductor single crystal by pulling up and growing the semiconductor single crystal from a melt housed in a crucible of a furnace, comprising:

• a thermal shield located above the melt and provided around the semiconductor single crystal, and having a rim at a lower end thereof;
• light emitting means for emitting light;
• light scanning means for performing scanning of the light emitted from the light emitting means along a radial direction of the crucible;
• light receiving means for receiving reflected light of the light emitted from the light emitting means and used to perform scanning by the light scanning means;
• first distance measuring means for sequentially measuring a distance between a reference point and a reflection point for each prescribed first scanning interval based on a sequential optical scanning position, an emitting position of the light emitting means, and a light receiving position of the light receiving means and according to a principle of triangulation while performing light scanning;
• first determination means for determining whether the distance measured by the first distance measuring means changes from a size corresponding to a distance between the reference point and the melt to a size corresponding to a distance between the reference point and the rim of the thermal shield, or changes from the size corresponding to the distance between the reference point and the rim of the thermal shield to the size corresponding to the distance between the reference point and the melt;
• second distance measuring means for sequentially measuring, when the first determination means determines that the measured distance changes, a distance between the reference point and a reflection point for each second scanning interval that is shorter than the first scanning interval, based on a sequential optical scanning position, an emitting position of the light emitting means, and a light receiving position of the light receiving means and according to the principle of triangulation while returning the optical scanning position for a predetermined amount in a direction opposite to the scanning direction and performing re-scanning of the light from the returned optical scanning position;
• second determination means for determining whether the distance measured by the second distance measuring means changes from the size corresponding to the distance between the reference point and the melt to the size corresponding to the distance between the reference point and the rim of the thermal shield, or changes from the size corresponding to the distance between the reference point and the rim of the thermal shield to the size corresponding to the distance between the reference point and the melt;
• and
• edge position judgment means for judging, when the second determination means determines that the measured distance changes, that light is reflected by an edge of the rim of the thermal shield at the optical scanning position at a point in time when the change is determined.