Patent ID: 7109511

Claim:
A wafer prealignment apparatus comprising: a wafer rotation means that can rotate a substantially circular wafer while holding the wafer on a table having a vertical rotational axis; a rotation sensing means for sensing a rotational angle of the wafer rotation means and transforming it into an electrical signal; a light projecting means for projecting light onto an edge of the wafer held by the wafer rotation means; a CCD linear sensor that consists of a great many pixels linearly arranged each of which has a fixed order and that reads a stored electric charge in order from a first pixel in accordance with a transfer pulse signal and then sequentially outputs stored electric charges of all pixels as electrical signals; and a signal processing means that repeatedly senses an edge position of the wafer at a plurality of arbitrary points over an outer circumference of the wafer and stores it in a built-in memory when a signal of the CCD linear sensor and a signal of the rotation sensing means are received, and, based on a sensed value thereof, calculates at least one of an orientation flat position, a notch position, and a center position of the wafer; wherein a photodiode is provided within a range where the light projecting means projects light and in the vicinity of the first pixel of the CCD linear sensor, and the signal processing means includes a luminous energy signal processing section for receiving a signal of the photodiode and sensing a quantity of light, a wafer edge sensing section for receiving a signal of the CCD linear sensor and sensing an edge of the wafer, a comparison judgment means for determining the presence or absence of the wafer by making a comparison between a luminous energy value of the photodiode and a signal of the wafer edge sensing section, and an output means for imparting a result thereof to an outside element.