| 摘要 |
A wafer cassette mapper detects the presence or absence of a wafer in a particular corresponding pair of slots in a wafer cassette, as well as a cross slotted condition in which a wafer is not aligned in a corresponding pair of slots. The wafer cassette mapper includes a base member for receiving a standard slotted wafer cassette, the base member supporting a transmitter/receiver module adjacent the rear of the wafer cassette. The transmitter/receiver module includes two vertical columns of light emitting apertures, coupled to an infrared transmitter array, and a single vertical column, between the two columns of light emitting apertures, of light receiving apertures coupled to an infrared receiver array. Corresponding light emitting apertures in each of the two columns are positioned to illuminate the rear edge of each of the wafers in the wafer cassette at an angle that will cause the diffused reflected light to enter an associated one of the light receiving apertures. Alternate ones of the light emitting apertures are positioned to illuminate the vertical space between each of the wafer slots of the cassette, and a corresponding alternate one of the light receiving apertures detects light reflected by a cross slotted wafer that is positioned in this otherwise unoccupied space. Control circuitry selectively interrogates the infrared receiver array during a period of time in which the infrared transmitter array is turned on in order to determine if a particular light receiving aperture has received light reflected by a particular wafer. Logic circuitry then processes this information for each wafer slot of the wafer cassette to determine if a wafer is present, absent or cross slotted.
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