Patent ID: 11923223
Assignee: DISCO CORPORATION
Field: Semiconductors (Electrical engineering)
Classification: CPC H | IPC H

Claim 6:
7. A method of determining whether or not there is an irregularity concerning a wafer stored in a cassette that has opposite side-walls in which a plurality of pairs of slots vertically spaced from one another are defined and that is capable of storing wafers in such a manner that each of the wafers is retained by a corresponding one of the pairs of slots, the pair of slots being positioned at a same height in confronting relation to each other, the method comprising:
a storing step of storing a value of an actual thickness of the wafer stored in the cassette and a threshold value representing an allowable range for a difference between a value of an apparent thickness of the wafer and the value of the actual thickness of the wafer;
a determining step of determining whether or not the difference between the value of the apparent thickness of the wafer and the value of the actual thickness of the wafer that has been stored in the storing step exceeds the threshold value, the value of the apparent thickness of the wafer being obtained by operating, while selectively lifting, lowering, and selectively rotating about a horizontal rotational axis a non-contact-type sensor for detecting a front portion of the wafer laterally of the wafer in the cassette that has an open front end, the non-contact-type sensor to detect whether or not there is the wafer in the cassette; and
a warning step of issuing a warning about an irregularity concerning the wafer stored in the cassette, if the determining step determines that the difference exceeds the threshold value.