Procedure and Facility for Handling and Transport of Wafers in Ultra-Clean Rooms

This invention concerns a procedure for handling plate-form discs which must be processed in ultra-clean rooms and which have to be transported to various stations as is the case in particular for wafers for integrated circuits. In the production of wafers several pre-treatments and several post-treatments are usually necessary. If the processing stations are integrated in the main working room, they make it more difficult to keep the room clean. If the processing stations are external, it is difficult to bring the wafers in a clean state into the main working room.

Although this invention can be used for other plate-form discs too, it is described here exclusively in relation to the example of handling and transport of wafers.

In order to subject the wafers to various processing steps such as one or several cleaning steps, coating steps, surface treatment, etc., they are usually brought to the respective processing stations individually or in conventional commercial carriers in which they stand vertically. Modern wafer production requires clean room class 1 or even 0.1 for this purpose. It is extremely difficult to maintain this degree of cleanliness in large rooms, especially if moving machinery parts are operating in this room or persons working therein have to move around. Thus it is appropriate to carry out the unavoidable preliminary and subsequent tasks on the wafers in rooms which are separated from the main processing station, because it is then easier to keep the main processing room free from dust. However, separation of the stations for pre-processing and post-processing entails the disadvantage that the wafers must be introduced into the main room and taken out of it again under ultra-clean conditions.

It is the purpose of this invention to create a procedure for handling wafers and similar plate-form discs requiring a high degree of cleanliness and for transporting them to work stations in ultra-clean rooms, involving lower costs, less effort and permitting universal application and programmed control, and to specify a facility for carrying out the procedure.

Thus the invention also provides a facility for carrying out the procedure of the invention, whereby this facility serves for handling plate-form discs, in particular wafers for integrated circuits, in ultra-clean rooms with at least one workstation. The facility according to the invention comprises a chamber which is maintained under ultra-clean room conditions, for example with clean room class 1 or 0.1, and in which a straight horizontally extended rail is provided which has storage positions for depositing standard commercial carriers containing vertically standing wafers, whereby their disc plane is oriented vertically with respect to the longitudinal direction of the rail. The chamber furthermore contains a lifting device which is movable in single working plane, the xy-plane, on a cross-slide whereby the working plane passes essentially vertically through the longitudinal direction of the rail. This lifting device has a supporting device, preferentially in the from of a fork, which extends at right angles, i.e., in the z-direction, with respect to the working plane and can grasp under the floor of a carrier to lift the carrier from its storage place. In the course of an upward movement in the y-direction the carrier is raised through a distance greater than the height of a carrier so that in the course of a subsequent movement in the longitudinal direction of the rail, i.e., in the x-direction, it can be lifted over neighboring carriers on the rail in order to be moved to a carrying basket which is located on the extension of the rail but beyond the latter. If the carrier which is to be transported is the first one on the rail, it is also possible to raise it only slightly and then to transport it to the carrying basket. In the carrying basket the carrier is lowered by movement of the cross-slide in the y-direction. The carrying basket is then turned through 90.degree. by a turning device on whose shaft it is mounted, such that the formerly vertical wafers now lie horizontal in the carrier turned through 90.degree.. A working device in the form of a tongue can then be moved to the carrying basket with the wafers in such a way that the tongue grasps under a horizontally lying wafer or grips it by suction vacuum from above or in some other way, pulling it out of the carrier and taking it to a workstation within the chamber. The tongue deposits the wafer at such a workstation for processing.

After processing, the tongue can lift up this wafer and bring it in an analogous manner to further workstations, or it can bring it back directly to the carrier and take another wafer from the carrier which is then processed too.

The tongue is mounted preferentially on the xy-cross-slide and is controlled too by the control system for the cross-slide.

When all the wafers of a carrier according to a predefined program have been processed, the turning device turns the carrying basket back through 90.degree. so that the lifting device can then take the carrier with the processed wafers back to its storage place.

When the device according to the invention is used for carrying out the preliminary tasks before the main treatment of a wafer, the wafer after pre treatment at the workstation in the chamber can be introduced into the main processing room through an airlock. After processing in the main room, the wafer is either taken out of the main processing room, or back through the airlock into the chamber of the device according to the invention, for post treatment.

There is no limitation on the number of storage places on the rail, and it is also possible to provide any desired number of workstations inside the chamber. The greater the number of storage places for carriers provided, the longer must be the rail and thus the longer becomes the chamber. For a shorter chamber, a single exhaust suction device suffices to maintain freedom from dust inside the chamber. If necessary, several adjacent exhaust suction devices in tandem must be provided for long chambers.

The implementation forms of the device according to the invention clearly show that the device for handling and transporting wafers permits standardization in a simple way, in that the device comprises a chamber with a certain number of storage places for carriers and a certain number of workstations, of which only a portion is used under process control as required when no smaller standard chamber is available. Such a chamber can be connected to the main processing room via an airlock, for pre-processing or post-processing operations.

The high degree of cleanliness inside the chamber can be maintained relatively easily because all driving devices are placed outside the chamber and only the xy-cross-slide for the lifting device and the working tongue are moved inside the chamber, and a rotating bushing from the exterior is used for tilting the carrying basket between its two end stop positions. Furthermore, in special cases it is even possible to attach a gripper to the cross-slide so that no additional drive is required for this gripper. Only an actuating cylinder must be moved inside the chamber for moving the airlock, whereby the drive unit can be mounted outside the chamber.

Movement of the cross-slide of the lifting device is appropriately carried out with two servo motors controlled in the x-and y-direction.

The working device is appropriately constructed in the form of a double-walled supporting tongue forming a pocket, which can be evacuated and which has a hole on the upper or lower side. When vacuum is applied, a wafer is held against the hole on the tongue by the reduced pressure. The vacuum inside the supporting tongue is controlled in the familiar way via a reservoir vacuum with a vacuum line in which a control valve is located. When a wafer is held on the underside of the tongue by vacuum, it can be deposited on the station after arrival over a workstation simply by switching off the vacuum. If a wafer must be brought to a workstation with the aid of a gripper, it is deposited by the tongue and then taken up again by the gripper.

The working head on the cross-slide of the lifting device is a U-shaped bent arm whose U-plane is at right angles to the xy-workplane and at right angles to the longitudinal direction of the rail. The upper leg of the "U" constitutes the supporting device which can lift a carrier. The center leg of the "U" is vertical with clearance in front of the carrier walls. The bottom leg of the "U" is directly connected to the cross-slide. This arrangement has the advantage that it does not interfere with the movement of the cross-slide or of the supporting device on the rotating bushing for the carrying basket.

The connection between the supporting device itself, i.e., usually a fork which grasps under the floor of a carrier, with the drive for the cross-slide, may be shaped differently, as long as this connection does not come into conflict with the rotating bushing for tilting the carrying basket.

A particular advantage of this invention is that encoded information on the base or floor of a carrier can be recognized and evaluated for identification and control of the carrier. A hole coding on a rib on the floor of a carrier can be sensed in a known manner by a known sensing device. The presence or absence of an opening in the floor rib of the carrier can be recognized using light of various wavelengths, lasers, long wavelength electromagnetic radiation or other means. For this purpose, a light emitting diode and receiver diode combination, or a transmitter/receiver or emitter/sensor pair is located in opposite walls of a slot in the supporting device, e.g., in the two prongs of a take-up form or on the carrier edge. Preferentially, the same numbers of pairs are provided in a row, as the number of holes corresponding to the code.

The sensed code signals are used preferentially in digitized form.

A further digitization of control signals is obtained in a simple manner when stepping motors are used for moving the cross-slide and the rotating device for the carrying basket. The entire control of handling and transport of carriers and wafers inside the chamber can easily be carried out with a process computer, making possible a completely automated action sequence of the work steps inside the chamber.

The invention will be explained in more detail below with reference to the attached drawings.

FIG. 1 is a schematic depiction to explain transport of a carrier to the carrying basket with the lifting device;

FIG. 2 shows the carrying basket with a carrier after the tilting operation;

FIG. 3 is an enlarged view of a floor section of a carrier with engaged fork of the lifting device.

FIG. 4 is a cross section taken through a longitudinal center line of tongue 13 shown in FIG. 1.

FIG. 5 is a left side view of the arrangement depicted in FIG. 1 shwong rail 1 in cross-section, and U-shaped arm 3 in its carrier lifting and transporting positionis shown by solid lines, and in a non-carrier engaging mode by broken lines.

In the device according to the invention, the chamber which forms a clean room of class 1 or 0.1 in the known manner contains a rail 1 with storage places A, B, C, D and E for carriers a, b, c, d and e in which wafers 2 stand vertically. These carriers with wafers have been brought into the chamber under dust-free conditions via an airlock.

A lifting device for carriers comprises a U-shaped arm 3, one of whose legs constitutes a supporting device in the form of a fork 4. Calling the horizontal longitudinal direction of the rail 1 the x-direction and the vertical, i.e., the elevation direction in which a carrier is lifted, the y-direction, then the xy-plane (corresponding to the plane of the paper in the drawing) is the actual working plane. The U-shaped arm 3 extends at right angles to the working plane and at right angles to the longitudinal direction of the rail (i.e., at right angles to the x-direction), thus it extends in the yz-plane. In FIG. 1 the middle leg of the "U" is shown as a rectangle viewed from above, the supporting device 4 forms the upper leg of the "U" and the lower leg of the "U" establishes a connection to a xy-cross-slide. The U-shaped arm 3 can be moved in the x-direction and in the y-direction controlled by this cross-slide. Arm 3 fits through a forwardly directed (i.e. out of the paper) opening 1a in rail 1. Opening 1a is U-shaped and has upwardly tapered post 1b, with an inwardly slanted surface, at its four corners for adjusting the carrier into position accurately as it is lowered onto rail 1.

FIG. 1 shows in continuous line the U-shaped arm 3 which has lifted up a carrier b from the storage position B through a distance greater than the height of the carrier walls. The broken line indicates the position of the U-shaped arm 3 before the lifting process.

In the next working step the cross-slide is moved in the x-direction until the carrier b resting on the U-shaped arm 3 is above a carrying basket 5. By moving the cross-slide downwards in the y-direction, the U-shaped arm 3 with the carrier on it lowers to such an extent that the carrier is deposited in the carrying basket 5. The U-shaped arm 3 is moved further downwards in the y-direction to avoid impediment of the carrying basket 5 in the following swivel process. By swiveling the carrying basket 5 about a turning axis 6 in the z-direction, the carrier is turned through 90.degree. in the carrying basket so that the wafers come to lie horizontal.

The turning axis 6 is located approximately in the center of the carrying basket to ensure that vibration of the wafers is minimized during the swivel operation.

The turning device for the carrying basket 5 has a simple construction because it only has to turn the carrying basket through 90.degree. between two end stops. When the wafers are in horizontal position as shown in FIG. 2, a working device, e.g., in the form of a flat tongue, can be moved between the end of the rail 1 and the carrying basket 5 such that it takes a wafer out of the carrier. The encoding of the wafer is simple because it corresponds to the height of the wafer within the carrier.

FIG. 3 shows with an enlarged scale the floor of a carrier which has the notches 7 and 8 into which the fork 4 of the U-shaped arm 3 engages. The wall parts of the fork prongs contain a light source 9 and a receiver 10. The receiver detects a light signal when a hole 12 is present in the ridge 11 on the carrier floor. A carrier can be encoded with a row of holes in the ridge 11. This code can be read by a row of emitter/receiver pairs preferentially using a combination of light emitting diodes and receiver diodes.

Because each carrier can be recognized by its code on its floor and each wafer in a carrier can be recognized by its height before taking it out of the carrier and placing it into the carrying basket 5 for the processing steps, every wafer in the chamber of the device according to the invention is individually identifiable. Thus it is possible to treat each wafer individually under automated control according to a predefined program.

On the U-shaped arm 3 a supporting tongue 13 is mounted as working device such that its principal plane is horizontal as shown in FIG. 1 so that it can grasp the wafers 2 (FIG. 2) lying horizontal in the turned over carrying basket 5 and take out a wafer. FIG.4 shows doubled walled tongue 13 as having upper and lower walls 13a and 13b, an evaluation opening 13c for creating a vacuum to produce suction through opening 14 in upper wall 13a and/or opening 15 in lower wall 13b. Either one or both of openings 14 and 15 can be provided. Takeout of individual wafers and their transport within the chamber is controlled too via the controlling device for the xy-cross-slide, through the connection of the supporting tongue 13 via the U-shaped arm 3 to the xy-cross-slide.

In this arrangement the workstations too lie in the xy-plane.

The procedure described with reference to FIG. 1, in which a certain carrier b is taken from the storage position B, lifted through a distance greater than the height of a side-wall of a carrier, to lift it over the carrier a in the depicted case and then to further transport it in the x-direction to the carrying basket 5, from where it is returned in reverse sequence of events to its resting position B after processing of its wafers, can also be modified as follows:

The first carrier a is raised slightly, brought in the x-direction to the carrying basket 5 and then lowered. As shown in FIG. 1, for this purpose the height of the front edge of the carrying basket 5 is less than the height of the rear edge and less than the side-wall of a carrier. While the wafers of the carrier a are being processed, the cross-slide takes the lifting device back to the rail and lets the carriers b, c, d and e advance by one position in cyclic sequence, thus to the positions A, B, C and D. Position E remains empty. After processing the carrier a, it is placed in the empty position E. Operation with a simpler control program is possible in this cyclic processing of the waiting carriers.