Browse Prior Art Database

Intelligent Wafer Cassette Serial Number Reader

IP.com Disclosure Number: IPCOM000036338D
Original Publication Date: 1989-Sep-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 3 page(s) / 38K

Publishing Venue

IBM

Related People

Kazi, AM: AUTHOR [+7]

Abstract

The article describes a system to control, track and log wafer carriers by means of an electronic reader that can obtain the serial number of a carrier and report it to a local computer.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 53% of the total text.

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Intelligent Wafer Cassette Serial Number Reader

The article describes a system to control, track and log wafer carriers by means of an electronic reader that can obtain the serial number of a carrier and report it to a local computer.

When processing silicon wafers, it is common practice to transport a number of these wafers between stations in plastic cassettes. In order to control, track, and log aspects of the process, it is necessary to have a reliable means to identify these plastic carriers. This process has been automated by means of the electronic reader, disclosed herein, that can obtain the serial number of a carrier and report it to a local computer.

The carriers are identified by patterns on the legs of the cassettes in which a hole or the absence of a hole may be sensed to develop a serial number. This method is used because these cassettes are, at times, immersed in chemical baths. By drilling or not drilling holes at specific locations on the leg of the cassette, a through-beam sensing scheme may be used, without having to address the environment that the cassette may be subjected to.

Through-beam sensing consists of a light emitter and light detector pair that will develop an electrical signal based on the amount of light reaching the receiver from the transmitter. These electrical signals are interpreted digitally so that a zero voltage represents a logic zero and five volts represents a logic one. Based on the amount of light detected at the receiver, either a zero or a one will be generated. Ideally, if a hole exists in the cassette the receiver will indicate one logic level, and if no hole exists, the other logic level will be indicated. Depending upon the implementation, a logic one could represent a hole or vice versa. The problems associated with the current design occur from the fact that the sensors can only differentiate between two specific states, that of transistor- to- transistor logic (TTL) levels. If the translucency of the cassette changes or the transmitters are not installed correctly, then the resulting signal may be misinterpreted.

The solution to the problem is to provide an embedded computer such as t...