Loading and unloading station for a device for the processing of circular flat work-pieces, especially semiconductor wafers

The device comprises a carrier for a workpiece; the carrier can be moved along a vertical and a horizontal axis by use of a drive mechanism and has an approximately planar contact surface for the workpiece, whereby the workpiece can be held on the contact surface by a contact mechanism of the carrier, especially vacuum, a retaining ring on the carrier encircling the contact surface and projecting downwards beyond the contact surface and having an inner diameter which is slightly larger than the outer diameter of the workpiece. At least three centering cams are arranged on a circle, the centering cams can be moved synchronously and in a radial direction by use of a centering drive, the centering cams having a supporting surface oriented on the top. The supporting surface has an approximately vertical stop surface as well as a stop being radially outwards of the stop surface adapted to engage the outer side of the retaining ring, when the centering cams are radially moved towards each other and the carrier is set down until coming close to our onto the centering cams. A robot is provided so that a workpiece can be loaded on cams or removed from it, the outer diameter of the retaining ring and the position of the stop surface and of the stop being dimensioned such that the workpiece is arranged approximately in a centered way relative to the vertical axis of the carrier when the stops of the centering cams engage the retaining ring.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not Applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable.

BACKGROUND OF THE INVENTION

In the field of microelectronics, circuits are manufactured by means of superimposed and differently structured layers of different materials. In order to achieve the desired planarity, processing has to take place subsequent to each coating of a semiconductor wafer with a layer, for example an oxide layer, a tungsten layer or other metal layers, otherwise problems will occur, for example within lithographic processes, namely in the form of focus faults due to a low depth of sharpness of the UV stepper or in the form of fissures of the conductor paths.

A process used in the current semiconductor industry and designed for the planarisation exploits the so-called CMP process consisting in a chemical mechanical processing by means of a fluid (slurry), the chemically reactive part of the slurry being bound to transform the material into a polishable condition. The slurry contains an abrasive in form of colloidal abrasive particles.

A device for the chemical mechanical polishing of surfaces has been published in DE 197 19 503 A1. It comprised two polishing units with height adjustable vacuum carriers for one semiconductor wafer each which can be rotated about a vertical axis by a driving motor. The polishing units are guided independently from each other along two parallel guides extending approximately horizontally. Polishing tables driven in rotation are arranged below the guides and cooperate with the polishing units. At one end of the guides, at least one device is provided for the semiconductor wafers. Furthermore, loading and unloading devices for the semiconductor wafers are provided on the opposite side of the guides, towards the polishing units can be aligned and which can be reached by a transfer device. In most of the cases, the delivery and take over takes place by a robot.

During the transport of the wafers and the polishing process described above, the wafers are held by a chuck or a so-called carrier the task of which is to generate a homogenous pressure profile or different pressure profiles onto the rear side of the workpiece, the so-called loaded side, i.e. the side provided with the circuits, being oriented towards the polishing table. Usually, the carrier is held and moved by an actuation device turning the carrier around a vertical axis on the one hand and on the other hand moving it in a linear, vertical and horizontal direction.

In most cases, a wafer is held at the carrier by vacuum. First of all, the wafer must be brought into contact with the supporting or engagement surface of the carrier before the vacuum can transfer its holding force to the wafer. During the polishing process, the circular workpiece, for example the wafer, is stabilized by the outer rim of the carrier protruding beyond the supporting surface of the carrier and having an inner diameter which is slightly larger than the outer diameter of the wafer. In order to achieve high quality polishing results on the workpiece, especially in the radially marginal portion of the workpiece, it is absolutely necessary to dimension the protruding edge formed by a retaining ring in such a way that the circular space between the workpiece and the ring is minimized and uniform along the circumference.

BRIEF SUMMARY OF THE INVENTION

The invention is based on the objective to provide a loading and unloading station which positions the workpiece relative to the retaining ring in a way enabling a reliable reception of the workpiece. Furthermore, the loading and unloading station is to work in a failure tolerant way in order to compensate for tolerance inaccuracies. The loading and unloading station according to the invention may include a horizontal loading surface which can be moved by means of a first drive means along a vertical axis. One possible position of the vertical axis positions the loading surface at the same height as the supporting faces of the centering cams, another position is by far lower than the supporting surface of the centering cams. The transfer mechanism which is usually formed by a robot loads the workpiece on the supporting surface of the centering cams. The contact surface of the carrier can be oriented above the loading surface if provided so that the loading surface is capable of bringing the workpiece into contact with the contact surface of the carrier when being lifted. In any case, the workpiece has to be centered relative to the carrier. For doing so, the loading station has at least three centering cams arranged on a circle encircling the loading surface, preferably at equal circumferential spaces therebetween. By means of a centering drive, the centering cams can synchronously, radially be moved from the inside to the outside and vice versa the centering cams having a supporting surface upwardly directed for the workpiece which supporting surface including an upwardly extending stop surface. Furthermore, the centering cams are provided with a stop which is, in a radial position, located radially outward with respect to the stop face and which stop engages the retaining ring of the carrier when the centering cams are moved in a radially inward direction and the chuck or carrier is set down close to or onto the centering cams. The outer diameter of the retaining ring on the carrier and the position of the supporting surface and the stop are dimensioned in such a way that the workpiece is approximately centered relative to the vertical axis of the carrier when the stops of the centering cams are in engagement with the retaining ring.

The mechanical stops ensure automatic compensation for possible irregularities, such as tolerances with components and mounting, inaccuracies of positions and the reversal tolerance along the horizontal axis.

The centering cams can vertically be supported by means of a spring, thus enabling inaccuracies of the position during the vertical positioning to be compensated.

Preferably, the material of the supporting surface of the centering cams consists of an abrasive resistant synthetic. The loading surface is preferably concave, thus ensuring the guidance of the workpiece in the marginal portion. Furthermore, the concave form of the loading surface, in connection with the carrier, can also be used for the formation of a cleaning chamber. The contact surface of the carrier as known in the art has bores designed for the application of the vacuum on the workpiece. Moreover, various media, such as compressed air, water, slurry or nitrogen can be supplied. The loading surface can present appropriate draining bores for the draining of DI-water and residual slurry. To this end, it is also advantageous if the material of the loading surface is media proof in the range of pH1 to pH13.

Various construction modes are possible in order to form the centering cams. One of the possibilities consists in forming them as levers being supported for pivoting about a vertical axis and actuated for horizontal movement by the centering drive. Alternatively, the centering cams can also be moved in a linear direction. The centering drive can be realized by an electromechanic or pneumatic mechanism, for example.

It should be noted that for the invention the provision of the loading surface is not mandatory.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1to4depict a loading and unloading station as described in DE 199 11 295 A1, for example.FIGS. 1to4illustrate only one half on the left side of a vertical central axis10in a sectional view. One can recognize a loading plate12which can be positioned in a vertical direction by a lifting device14which is not illustrated in detail. Four centering cams16are arranged on a circle encircling the loading plate12. The centering cams16are supported by a slab18supported by a lower plate22by means of a spring20. A pneumatic centering drive24is arranged on the slab18, which centering drive is coupled with the centering cams16(Only one centering cam is illustrated inFIGS. 1to4), in order to move the centering cams16along the double arrow26. This movement can be in a linear direction. Alternatively, the centering cam16can also be a lever (not represented) which is pivotable about a vertical axis and is horizontally pivoted by the centering drive24.

On its top, the centering cam16is provided with a supporting surface28which is limited radially outward by a stop surface30. Moreover, there is a stop32on the centering cam16in the shape of a pin oriented upwardly which is located radially outwards of the stop surface30.

InFIGS. 2to4, one can recognize a carrier or chuck34, such as it is used for the holding and the transport of circular wafers. It can be moved both vertically and horizontally (also refer to DE 199 11 294) by drive means (not represented). At its lower side, the carrier34is provided with a contact surface36against which the workpiece is placed and where it is held by vacuum which can be applied by vacuum bores (not illustrated) in the contact surface36.

The circular carrier34has a circular retaining ring40at its circumference at the lower side. The exterior surface of the retaining ring40is aligned with the exterior surface of the carrier34. The lower portion of the retaining ring40is slightly protruding beyond the contact surface36. The inner diameter of the retaining ring40is dimensioned in order to be slightly larger than the outer diameter of a wafer42. Consequently, the retaining ring40restrains a wafer received (FIG.4).

The loading of the carrier34with a wafer42is as follows. A loading robot the details of which are not shown holds a wafer42as shown at46and deposits it onto the supporting surfaces28of the centering cams16. The stop surfaces30are positioned to allow the wafer42to be deposited without problems and without touching the stop surfaces30. During this process, the carrier34is in a lateral position thus not disturbing said operation.

Then, the carrier34is brought into a defined vertical position where its axis is oriented relative to the axis of the loading plate12or the center of the circle of the centering cams, respectively, and both axes coincide with the axis10. By the way, the carrier is provided with thin bores (not shown) by means of which various media can be supplied such a compressed air, vacuum, DI-water, slurry or nitrogen. When the vertical alignment is achieved, the carrier34is set down until the retaining ring40lies on the centering cams16(FIG.2), i.e. over the supporting surfaces28thereof. Then, the centering cams16are moved radially inwards until this movement is stopped by the stop pin32engaging the exterior side of the retaining ring40. During this process, the wafer42is centered relative to the carrier34. The radial space between the stop surfaces30of the centering cams16is dimensioned such that the wafer42is in a centered position between the stop surfaces30when the stop pin32engages the retaining ring40(FIG.3). It is appropriate for this operation that the drive of the centering cams16works synchronously.

Subsequently, the loading plate12is driven upwards and the wafer is made adjacent and brought into engagement with the contact surface42of the carrier34(FIG.4). The centering of the wafer described above has the effect that the small radial and annular space between the circumference of the wafer and the inner surface of the retaining ring40is constant. Irregularities, such as component and mounting tolerances, positioning inaccuracies, reversal tolerances along the horizontal axis, etc., are automatically compensated by means of the centering operation described above. After having brought the wafer42against the contact surface36, vacuum is generated via the internal bore or channels (not shown) of the carrier34in order to hold the wafer42. Then, the carrier34transports the wafer to a polishing section as described in DE 199 11 294 for example.

Unloading starts subsequent to the processing of the wafer42. To this end, the carrier34, which is again vertically oriented with respect to the loading plate12in a lower position thereof as represented in FIG.2. The centering cams16are moved radially outwardly so that the stop pins32have no contact any more with the retaining ring40. The carrier is in contact with the upper side of the loading table. The vacuum on the carrier34is switched off, compressed air and DI-water can be supplied through the internal bores in order to remove the wafer42from the carrier. The loading plate12takes the wafer42into a lower vertical position. Then, the wafer42lies on the supporting surfaces28of the centering cams16. The loading plate42can be designed on its upper loading surface as to support the workpiece only in marginal area (the loading table is concave). Subsequent to the removal of the wafer42, the station described above can also be used as a cleaning station for the carrier34. As already mentioned, the loading surface of the loading plate can be concave to this end and form a hollow space in conjunction with the carrier34when both parts are driven against each other, thus creating a cleaning chamber. In order to achieve a draining from this cleaning chamber, the loading plate12is provided with draining bores (not shown) for the draining of DI-water and residual slurry.

FIGS. 5 and 6show a realization mode for the centering cams. One can recognize four centering cams16aformed as levers and rotatable about a vertical axis50. The lever could be swung horizontally by means of the actuation device24thus radially shifting for example more or less the stop pin32. InFIG. 5, it is remote from the exterior of the retaining ring50of the carrier which is not represented. InFIG. 6, the stop pin52is adjacent to the retaining ring. The slight and still admissible offset between the vertical axis of the carrier34on the one hand and the axis of the centering device (shown) on the other hand is outlined at52in FIG.6.

In the realization mode according toFIGS. 7 and 8, the four centering cams16bcan radially be moved and are actuated by means of the actuation device24. The stop pin32inFIG. 7is remote from the retaining ring40, whereas it is adjacent to the retaining ring40in FIG.8.FIG. 8, in its turn, outlines an offset between the axes already described.