| 摘要 |
A conductivity-type sensor, typically for use in a wafer sorting system, for detecting the conductivity-type of semiconductor wafers. In measuring conductivity, a two-contact probe is applied to the semiconductor wafer and any static charge which may have been accumulated on the wafer is initially discharged at an accelerated rate. The charge state is measured and an acceptable level of discharge requires repeated indications of discharge below a predetermined level. Discharging and charge measurement is repeated a predetermined number of times as necessary to accomplish discharging or the wafer identified as defective. The conductivity-type of the discharged wafer is read from the rectified polarity of an oscillating signal applied to the contacts. A valid indication of conductivity-type requires two consecutive readings of the same conductivity-type. The consecutive readings can be either the first reading of a new wafer identical with the reading of a previous wafer or two consecutive identical readings on the same wafer. Each reading, to be considered an acceptable reading of conductivity-type requires five consecutive, identical conductivity measurements over a predetermined time interval. Failure of such criteria produces a wafer defect indication.
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