GB2210536A

GB2210536A - Security tag for a sealed container

Info

Publication number: GB2210536A
Application number: GB8722613A
Authority: GB
Inventors: Christopher John Waters; Jonathan Burnie
Original assignee: Plessey Co Ltd
Current assignee: Plessey Co Ltd
Priority date: 1987-09-25
Filing date: 1987-09-25
Publication date: 1989-06-07
Anticipated expiration: 2007-09-25
Also published as: GB8722613D0; GB2210536B

Abstract

Security tags on sealed containers used for transporting silicon wafers between closed pollution-free environments have means responsive to the opening of the containers and means for reporting an unauthorised opening to a reader located at each of the environments. A processing station includes a transmitter (34) interrogating the tags and a receiver (36) receiving information including a report as to whether the container has been opened. The container is rejected, if it has been opened, and sent to a verification station. <IMAGE>

Description

CONTENTS TAG This invention relates to the provision of a tag on a closed container for indicating whether the container has been opened.

Particularly, this invention relates to a codable tag which can be coded (or re-coded) each time a container whereto it is applied is legitimately opened and closed but which indicates an intervening unauthorised opening and reclosing.

A manufacturing process in which such tags are advantageously employed is the fabrication of integrated circuits on silicon wafers. As is well known, the wafers are subjected to a plurality of process stages and it is essential that they should remain free from contamination on transfer between stages. A recently devised manufacturing process for the fabrication of integrated circuits involves the use of localised contamination free spaces and the carriage of the wafers between such spaces in sealed containers.

This process is described in an article entitled "SMIF: A technology for wafer cassette transfer in VLSI manufacturing" by Mihir Parikh and Ulrich Kaempf published in "Solid State Technology" July 1984.

A SMIF (Standard Mechanical Interface) box is used in the above described process. The box is arranged to be opened, loaded and closed mechanically in a pollution-free environment, to be transported around in a normal environment between process stations and then, again in a pollution-free environment, to be opened un-loaded, re-loaded and closed. The contents of the box comprises a plurality of silicon wafers. The process stations are locations at which a further stage in the process of fabrication of integrated circuits thereon is effected.

In our copending patent application No. filed simultaneously herewith, there is described verification apparatus for location at each of the process stations, for determining the contents of the boxes and for ensuring that the particular process at that station is appropriate to some or all of the wafers in the box.

In such circumstances, it is essential that, prior to opening the box (and possibly contaminating a pollution-free station), it should be verified that no unauthorised, accidental or incorrect opening has taken place subsequent to the last legitimate opening and closing of the box.

It is an object of the present invention to provide a sealed container, such as a SMIF box, with a security tag enabling detection of unauthorised opening of the container.

According to the present invention, there is provided a security tag for a sealed container comprising a first means cooperable with the container or its contents, the first means changing state on opening of the container or on removal of the contents thereof, a receiver for receiving an interrogation request and a transmitter for reporting the state of the first means upon receipt of the interrogation request.

The invention also provides a standard mechanical interface box for transporting silicon wafers between closed, pollution-free environments whereat the box may be opened, loaded, un-loaded or re-loaded with silicon wafers, the box including a security tag having first means arranged to change state on opening of the box to remove the contents thereof, a receiver for receiving an interrogation request, and a transmitter for responding to a received interrogation request for reporting the state of the first means.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic side view of a sealed container incorporating a security tag in accordance with the present invention; and Figure 2 is a block schematic circuit diagram of a preferred security tag and an associated tag reader in accordance with the present invention.

Referring to the drawings, there is shown a sealed container 10 in the form of a SMIF box. The container 10 is arranged for mechanical opening and closing in a pollution free atmosphere to avoid contamination of the contents. The contents comprise a cassette 12 holding a plurality of silicon wafers 14. The cassette 12 can be accessed, in use, by mechanical means for removing or replacing individual wafers, as required, once the container 10 has been opened.

Internally of the container 10, a microswitch 16 is provided.

The switch 16 is arranged to be held closed whilst the cassette 12 is in the container 10, but on opening the container 10 and displacing the cassette 12, the switch 16 is spring-loaded to move to its open position. The switch 16 is associated with an electronic circuit (as shown in Figure 2) and, on moving to its open portion, causes a bistable flip-flop of a sensor circuit 18 to be set to its alternate state.

A latch 20 is set by the sensor circuit 18 to indicate this alternate state. An address store 22 acts as a container identifier and holds a unique identifier of the particular container 10.

Both the latch 20 and the store 22 are connected to a message controller 24 arranged to receive and transmit messages to a reader 44 via a receiver 26 and a transmitter 28 powered by a power pack 30. There is a control circuit 32 which interfaces and controls the operation of the various circuit elements.

The receiver 26 and the transmitter 28 may operate at ultrasonic or infra-red frequencies.

Each time the container 10 arrives at a process station for opening, its security tag is checked by the reader 44 located at the station. The reader 44 includes a transmitter 34, a receiver 36, a signal generator 38 or a control circuit 40. A protocol converter 42 serves for communicating with a controlling host computer (not shown) via a comms line 46.

The reader 44 sends a request signal from the transmitter 34 to the receiver 26 to activate the message controller 24. In return, the message controller 24, under the control of the control circuit 32, sends, via the transmitter 28 and receiver 36, the identity of the container 10 from the address store 22 and the state of the flag latch 20. The identity is checked with the host computer via the converter 42 and the comms line 46. If the flag latch 20 has reported that the container 10 has not been opened, the container 10 is opened and some or all of the wafers 14 are removed from the cassette 12 to enable the process effected at the particular station to be carried out.

Thereafter, the wafers 14 or further wafers awaiting at the station are reloaded into the cassette 12 which is then reinserted into the container 10 and the latter is again sealed.

The reader 44 then transmits a signal via the transmitter 34 to the receiver 26 to reset the flag latch 20. The container 10 is then transported to the next process station.

If the flag latch 20 has reported that the container has been illegally or accidentally opened, the container is moved to a verification location where it is opened and the contents of the cassette 12 are individually removed and individually verified as disclosed in our aforesaid copending patent application.

The invention in not confined to the precise details of the foregoing example and variations may be made thereto. Whilst a power pack 30 has been shown, it will be appreciated that sufficient power could be transmitted by the reader 44 to enable interrogation to be effected. The latch 20 and switch 16 could then be purely mechanical or magnetic with no intervening power requirement. If a battery is employed in the power pack 30, it may be rechargeable and could be recharged by, for example ultrasonic energy transmitted thereto.

The verification location may be provide at or immediately adjacent the particular process location. However, it is preferred that only one verification location be provided for a whole manufacturing process.

Claims

1. A security tag for a sealed container comprising a first means cooperable with the container or its contents, the first means changing state on opening of the container or on removal of the contents thereof, a receiver for receiving an interrogation request and a transmitter for reporting the state of the first means upon receipt of the interrogation request.

2. A tag as claimed in claim 1 wherein second means are provided for holding a unique identifier, the transmitter being arranged also to transmit the unique identifier upon receipt of the interrogation request.

3. A tag as claimed in claim 1 or 2 further including rechargeable power supply means and wherein the receiver is arranged to receive and convert transmitted energy to recharge the power supply means.

4. A tag as claimed in claim 3 wherein the receiver and transmitter are arranged to operate at ultra-sonic frequencies.

5. A security tag for a sealed container substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.

6. A container adapted for mechanical opening and closing for loading, un-loading or reloading the contents thereof in closed environments and including a security tag as claimed in any preceding claim, the first means of the security tag cooperating with the contents from the container.

7. A standard mechanical interface box for transporting silicon wafers between closed, pollution-free environments whereat the box may be opened, loaded, un-loaded or re-loaded with silicon wafers, the box including a security tag having first means arranged to change state on opening of the box to remove the contents thereof, a receiver for receiving an interrogation request, and a transmitter for responding to a received interrogation request for reporting the state of the first means.

8. A standard mechanical interface box having a security tag and substantially as hereinbefore described with reference to and as illustrated in Figures 1 and 2 of the accompanying drawings.

9. A process station, in the multi-stage fabrication of integrated circuits in which silicon wafers are transported between stations whereat process stages are effected in closed pollution-free environments, the silicons wafers being so transported in sealed containers having interrogable security tags, the process station incorporating a reader having a transmitter for transmitting an interrogation request to a container located at the station, and a reveiver for receiving a unique identifier transmitted by the container and a report as to whether the container has been opened, and for rejecting, from the process station, a container which has been opened.