Abstract:
A double-disk polishing machine, particularly for tooling semiconductor wafers, comprising a machine housing, an upper and a lower working disk, carrier disks for the lower and upper working disks either of which is connected to a vertical driving shaft which, in turn, are rotatably supported in the machine housing by means of roller bearings and are adapted to be driven by a motor via a gear mechanism wherein cooling channels to which a coolant is fed are formed in each carrier disk, characterized in that each of the carrier disks is mounted with the aid of fastening means on a circumferential ring of a wheel-shaped basic carrier which, in turn, is connected to the driving shaft, the radius on which said fastening means lie which connect said basic carrier to said carrier disk is approximately on half the width of the ring-shaped working disk and said basic carrier for the upper working disk is connected to the shaft or to carrier disk in such a way that the inclination of the upper working disk automatically adapts itself to that of the lower working disk when the two working disks bear under a pressure against the interposed workpieces.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not Applicable 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     The invention relates to a double-disk polishing machine, particularly for tooling semiconductor wafers. 
     Polishing machines of this type are generally known. The semiconductor wafers being worked on two sides become larger and larger when new types are being developed. This creates the requirement for the working disks to have smaller and smaller deviations from geometry if the dimensional accuracy required is to be observed. 
     In manufacturing wafers polished on two sides with minimum geometrical deviations and good surface characteristics, accuracy in running and dimensional stability of the lower working disk (polishing plate) is a critical factor. In meeting such requirements, solutions for supporting the lower polishing plate have become known which partially are rather expensive, e.g. a hydrodynamic or hydrostatic support. 
     It is an object of the invention to create a double-disk polishing machine, particularly for tooling semiconductor wafers, which provides a support for the lower polishing plate at a relatively lower expenditure, which also makes it possible to precisely tool semiconductor wafers, which have a larger diameter, to the desired extent. 
     BRIEF SUMMARY OF THE INVENTION 
     A substantial feature of the invention is that the working disks, which are formed as ring disks, be sustained in an approximately central way. The basic carrier used for this purpose is connected to the corresponding carrier disk via appropriate fastening means. According to an aspect of the invention, the basic carrier may be designed as a radially spoked wheel the boss of which is in a rotary connection with the driving shaft. Ultimately, the upper working disk of the invention is suspended in such a way that it automatically adapts itself to the inclination of the lower working disk when it changes. This support for the upper working disk may be achieved by a ball-and-socket joint which simultaneously is designed for the transfer of a torque, for example by appropriate teeth intermeshing between the bearing components. As an alternative, a plurality of cylinder units may be disposed between the ring of the basic carrier and the carrier disk, the cylinder spaces of which are filled with a hydraulic medium and are connected to each other so that an “oscillation” of the upper working disk is also possible in this suspension mount. 
     The invention is based on the findings that even relatively small variations in temperature will result already in changes to the dimensions of the carrier disks. For example, if it is impossible for the carrier disks to freely expand when the temperature rises there is the risk that they will deform and, thus, loose their planarity. Therefore, another aspect of the invention provides that the fastening means between the basic carrier and the carrier disk also allow a relative radial motion. If thermal expansions occur, which naturally are different amongst the components, they will not lead to a deformation of the carrier disk which has an adverse effect on the planarity of the working surface. 
     In an inventive aspect of the double-disk polishing machine, the shaft of the lower working disk has several axially parallel channels to which cooling water is fed and is discharged therefrom by means of a stationary feeding device. The cooling operation described helps in obtaining high temperature stability for the driving shaft, whereby different axial forces caused by temperature changes and, hence, dimensional changes to the driving shaft affecting the working disk will not occur. 
     According to another aspect of the invention, the main driving shaft is supported by means of two spaced-apart tapered-roller bearings. The tapered-roller bearings are appropriately dimensioned relatively large and are provided with opposed taper angles so that there is a large stiffness and low flexibility when changes in load occur during the polishing operation. The tapered-roller bearings are preferably biased against each other and against the shaft by means of a nut screwed onto the shaft. 
     The arrangement of cooling channels on the upper surface of a carrier disk, on which the polishing or working disk is mounted, is known per se. In an aspect of the invention, the cooling channel in the driving shaft is connected to the upper cooling channels of the carrier disk via respective channel portions. Thus, only a single transfer of coolant is required from the stationary machine housing to the rotary parts. Preferably, another axially parallel cooling channel is provided in the driving shaft, which defines the return line of the circulating coolant. 
     According to another aspect of the invention, the underside of the carrier disk also has cooling channels which preferably are connected to the axial cooling channels in the driving shaft in the same way as the upper cooling channels are. Adjusting the temperature of the coolant of the lower cooling channels (At between top and bottom) also permits to influence the geometry of the carrier disk which is known to be firmly connected, in turn, to the working disk, which will also have an effect on the geometry of the working disk. This is advantageous for differing conditions of the polishing process. Both the upper and lower cooling labyrinths may be cooled separately from each other, using different temperatures. 
     The driving shaft is driven by an electric motor, preferably via a gear mechanism which, according to an aspect of the invention, has straight radial intermeshing teeth. Preferably, a high quality of the intermeshing teeth is provided. This also makes it possible to exclude axial forces and vibrations acting on the driving shaft. 
     As mentioned earlier, the carrier disks may be mounted, in turn, on a wheel-shaped basic carrier which, in turn, is connected to the respective driving shaft. The basic carrier is preferably designed in the shape of a cart-wheel wherein the carrier disk is connected, preferably by screws, to the outer ring of the basic carrier at the ends of the spokes. Spacer disks may be provided in making the bolted joint, which serve for balancing the axial run-outs of the basic carrier. What is achieved by the central arrangement of the actuator is that the polishing disks do not non-uniformly deform when the load required for polishing is applied, but uniformly move downwards and upwards with no change to the geometry of the polishing disks. 
     In spite of precise assembly, it is impossible to completely avoid inaccuracies and warpings, especially on the lower working disk. In order to produce the initial geometry of the polishing disk upon completion of assembly, another aspect of the invention provides that the machine housing has mounting means on diametrically opposed sides of the lower working disk to mount a bridge-like turn-off device which, in a bridge-shaped guide, carries a carriage holding a turn-off tool, which is radially with respect to the working disk moved by a linear drive. When a polishing plate is mounted, which was made in a relatively precise way before, its geometry may be affected by warpings or the like during assembly in the machine. As a result, the lapping operation performed in the machine will take an exceptionally long time unless it is preferred to dismount the polishing disk again and to rework it, which will then also be afflicted by an uncertainty because the polishing surface might happen to have lost its precision again after re-assembly. Lapping by dressing rings does not permit to correct a radial run-out. Lapping allows to adjust the polishing disk in a convex or concave direction. Resurfacing the polishing disk inside the machine will eliminate all inaccuracies in the manufacture of the components used such as the basic carrier, polishing-disk carrier, and polishing disk. In addition, a considerable advantage of time will be obtained. For the turn-off procedure, the polishing-disk carrier with the polishing disk is brought to the processing temperature before by the heated cooling water. 
     Turn-off devices of the type described are basically known, but have not been directly used on polishing machines hitherto. In an aspect of the invention, the mounting means have an approximately horizontal contact area on one side of the lower polishing plate and sustaining means adjustable in height on the opposed side. The horizontal contact area defines a reference plane and the inclination of the line along which the tool moves radially may be adjusted with the aid of the adjustable sustaining means. In some cases, a funnel-shaped configuration is desirable for the working surface of the polishing plate. This can readily be achieved by means of the construction described. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     The invention is now described with reference to an embodiment shown in the drawings. 
     FIG. 1 shows a sectional view of a polishing machine according to the invention. 
     FIG. 2 shows a view similar to FIG. 1 with a turn-off device shown in addition. 
     FIG. 3 shows an enlarged view of the central part of the polishing machine of FIG.  1 . 
     FIG. 4 shows a section through a modified embodiment of a polishing machine according to the invention. 
     FIG. 5 shows the detail  5  of FIG.  4 . 
     FIG. 6 shows a modified embodiment of the upper polishing plate of a polishing machine according to the invention. 
     FIG. 7 shows the detail  7  of FIG.  6 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     While this invention may be embodied in many different forms, there are described in detail herein specific preferred embodiments of the invention. This description is an exemplification of the principles of the invention and is not intended to limit the invention to the particular embodiments illustrated. 
     Referring to FIGS. 1 and 2, merely the lower part of a double-disk polishing machine is illustrated, which includes a ring-shaped polishing disk  10 . The ring-shaped polishing disk  10  is mounted on a ring-shaped carrier disk  14  by means of screws  12 . Carrier disk  14  has cooling channels  16  formed in its upper surface. 
     A basic carrier  18  has a boss  20 , spokes  22 , and an outer circumferential ring  24  which interconnects the spokes at the outside. Carrier disk  14  is firmly connected to circumferential ring  24  by means of screws  26 . A flat ring  28  is disposed between the circumferential ring  24  and the underside of carrier disk  14 . It covers cooling channels  30  at the underside of carrier disk  14 . Spacer washers  32  are arranged between ring  28  and circumferential ring  32 . The mounting of carrier disk  14  on circumferential ring  24  is located on half the radial width of polishing disk  10 . As a result, loading forces applied in the direction of arrows  34  do not cause any non-uniform deformation of polishing disk  10 . 
     Boss  20  of basic carrier  18  is connected by means of screws to a driving shaft  36 , which vertically extends downwardly through a gearbox casing  38 . Gearbox casing  38  has a cover  40  and a shell  42 . The cover and shell each support a tapered-roller bearing  44  with the taper angles directed opposite to each other. The upper tapered-roller bearing  44  abuts against a radial flange of shaft  36  and the lower tapered-roller bearing  44  is biased on shaft  36  by means of a nut  46 . This construction enables the tapered-roller bearings to be biased towards each other. 
     The hollow driving shaft  36  has a first axially parallel channel  36 . In its lower region, driving shaft  36  is surrounded by a distributor ring  48  which is disposed in a stationary way in machine housing  50 . Connected to distributor ring  48  is a nipple  52  which, in turn, is connected to a coolant line (not shown) which, in turn, leads to a coolant source. Nipple  52  is aligned with a radial bore  54  which ends in a continuous circular groove  56  at the inside of the ring. The continuous circular groove  56  is aligned with a continuous circular groove  58  of shaft  35  which, in turn, is in communication with a radial bore  60 . Hence, coolant introduced in nipple  52  will flow into the axially parallel channel  46  and, thence, into an oblique bore  62  in boss  20  and, from the oblique bore, into a channel portion  64  which is connected to the upper cooling channels  16  via a line  66  and another channel portion  68 . A parallel line  70  passes through a bore in ring  70  such that a connection is also made to the lower cooling channels  30 . Return flow is effected through a line  72 , which is passed through a bore of ring  28 , in communication with lower cooling channels  30  and a line  74  which is in communication with the upper cooling channels  16  via a bore. The lines lead to the second axially parallel channel  76  in driving shaft  36 , which is connected to another circular groove  80  in the distributor ring  48  via a second radial bore  78 . The circular groove  80  is connected, in a way not shown, to another nipple through which the coolant may exit, possibly back into a reservoir of the coolant source. 
     Centrally seated on shaft  36  is a spur gear  82  which is in engagement with a pinion  84 , which is driven by a motor  86  via a worm gear mechanism  88 . The intermeshing teeth between spur gear  82  and pinion  84  is straight and of a high precision. 
     Coaxially extending through driving shaft  36  is a second shaft  90  which, via a toothed belt, is connected at its lower end to a gear  92  which is driven by a driving gear  96  seated on the shaft of a second motor  98 . Shaft  90  has connected to it, at its upper end, an inner pinned rim  100  (the mechanical connection of which is not described in detail because it does not contain any particularity). The pinned rim  100  has a series of pins  101  uniformly spaced in the circumferential direction. Another pinned rim  102  including pins  104  is sustained on the piston rod of a lifting cylinder  108  via a bearing component  106 . In case of need, the pinned rim  102  may be driven like the pinned rim  100 . Pins  101  and  104  drive toothed runner disks (not shown) resting on the polishing disk  10 , which receive the wafers. This is also known as such. 
     Boss  20  and cover  40  of gearbox casing  38  have provided between them a labyrinth sealing not denoted in detail, which is intended to prevent contaminants from entering the gearbox casing. 
     As can be seen from FIG. 2 machine housing  50  has a shoulder  110  which has an upper contact area  112  which is located slightly lower than the upper surface of polishing disk  10 . A turn-off device  114  has a bridge-like carrier element  116  extending diametrically across polishing disk  10 , which ends in a frame portion  118  which is adapted to be attached to shoulder  110  by means of screws  120 . At its other end, carrier element  116  has a lug  122  across which device  114  sustains itself. A screw  124  is connected to a spacer  126  which, in turn, is screwed to a bearing portion  130  of machine housing  50  by means of a screw  128 . The height and the angle of bridge-like carrier  116  may be adjusted by turning the screw  124 . 
     The bridge-like carrier  116  serves as a guide for a carriage  132  not described in detail, which holds a pin-like turn-off tool  134  of a known design. A driving spindle  136  in the carrier element  116  connects with a driving motor  138  and, in addition, is in communication with carriage  132 . This communication is constituted by a ball-screw drive, which enables tool  134  to be moved radially with respect to polishing disk  10  at a relatively low friction. 
     After polishing disk  10  is installed in place in the above-described way turn-off device  114  is mounted, after which polishing disk  10  undergoes tooling. Prior to this, it was brought to the operating temperature by means of the heated coolant mentioned. This measure can compensate all tolerances which result because of the structure and the parts that the polishing disk  10  carries. Therefore, the lapping process which succeeds may be performed within a minimum period. 
     The geometry of the driving shaft and carrier disk may be kept to a desired rate by means of the cooling measures described such that changes which even occur irrespective of such measures do not affect the geometry of polishing disk  10 . When carrier disk  14  is cooled as well the geometry of polishing disk  10  may be acted on in the desired way to a limited extent. Likewise, the cooling system described will also help in adjusting a certain temperature in polishing disk  10 , which is of significance for the turn-off operation. 
     By adopting the measures discussed in the specification including the turn-off of the polishing disk in the machine it is possible to achieve an axial height run-out of a polishing disk, as referred to the center of rotation, of less than ± 1 m and less than ± 10 m at a short distance from the outer diameter of the polishing disk, at a polishing-disk diameter of 1,535 mm. These values virtually have no longer an adverse effect on the surface quality of the polished wafers. 
     In the polishing machine of FIG. 4, the arrangement of the lower polishing disk and the drive are configured in the same way as for the embodiment of FIG.  1 . Therefore, no detailed reference is intended to be made thereto here. However, what is discerned is that the polishing disk  10 , for example, also contains a cooling labyrinth which cooperates with the cooling labyrinth of carrier disk  14 . A particular characteristic, however, is the way of attaching carrier disk  14  to ring  24  of basic carrier  18  as illustrated in FIG.  5 . Polishing disk  10  is attached to carrier disk  14  by means of fastening screws  12  (also see FIG.  1 ). Likewise, ring  24  is attached to carrier disk  14  by means of fastening screws  26  disposed at uniform circumferential spacings. Now, a particular characteristic is that the fastening screw is surrounded by a sleeve  150  which is disposed in appropriately widened bore portions of carrier disk  14  and ring  24 . When ring  24  and carrier disk  14  are screwed together sleeve  150  will be exposed to an axial stress. However, the sleeve is in the bore at a radial play and also has a radial play with respect to screw  12  so that a limited relative radial motion may take place between the two elements. Hence, a one-sided thermal expansion of basic carrier  18  and ring  24 , on one hand, and carrier disk  14 , on the other, does not result in a deformation of carrier disk  14  and, thus, a deformation of polishing disk  10 . 
     An upper polishing plate  160  of FIG. 4 has a polishing disk  162 , a carrier disk  164 , and a basic carrier  166 . The interconnection of these elements corresponds to the one for the lower polishing plate so that no detailed reference will be made thereto here. A boss  168  of basic carrier  166  is suspended from a driving shaft  170 . Seated at the lower end of driving shaft  170  is a bearing ball  172  which interacts with a bearing shell  174  in boss  168 . This permits the whole polishing plate  160  to oscillate to a limited extent and the working surface of polishing disk  162  to automatically adapt itself to the respective inclination of the working surface of the lower polishing plate. Since a torque also requires to be transmitted via shaft  170  the bearing components  172 ,  174  have curved intermeshing teeth via which the transmission of the torque is effected, but which also allows the oscillation of polishing plate  160 . 
     As can be further discerned polishing disk  162  has a series of axially parallel through bores  176  which are aligned with corresponding through bores in carrier disk  164  and to which lines  178  are connected, through which a polishing agent is passed to the working surface of polishing disk  162 . Disposed on boss  168  is a distribution device  180  for the polishing agent, which has three concentrically arranged ring-shaped channels  182  in which the polishing agent is, which is delivered downwardly by the action of gravity. 
     Even in attaching basic carrier  166  to carrier disk  164  the procedure adopted is the same as the one described in conjunction with FIGS. 1 to  3 , viz. the central attachment of the ring of basic carrier  166  with carrier disk  164 . Again, attachment is effected by means of screws  184  which interact with clamping sleeves  186  as was described in conjunction with FIG. 5, which are radially movable to a limited extent or allow a relative motion between screw  184  and sleeve  186  in order that no inadmissible deformation of carrier disk  164  and, hence, of polishing disk  162  be entailed by deformations of carrier  166 . 
     The structure of the polishing plate of FIGS. 6 and 7 is largely equal to the one of the upper polishing plate of FIG. 4. A difference from FIG. 4 is that boss  168   a  of basic carrier  166   a  is firmly connected to shaft  170   a  and, therefore, no oscillation is possible at this point contrary to what the case was for the embodiment of FIG.  4 . 
     A particular characteristic of the embodiment of FIG. 6 consists in the way of attaching carrier disk  164  to basic carrier  166   a , i.e. to its outer ring. This is illustrated in detail in FIG.  1 . As can be discerned from FIG. 7, a piston cylinder unit  192  is disposed between ring  190  and carrier disk  164 . Arranged in a through bore of ring  190  is a spherical sliding guide  194  through which a hollow piston rod  196  is passed. At its upper end, piston rod  196  holds a piston  198 , which is sealingly kept moving inside a cylinder  200 . Cylinder  200  is firmly connected to ring  190 . Passed through piston  198  and the hollow piston rod  196  is a fastening screw  202 . It is screwed into a threaded bore of carrier disk  164 . On the contrary, piston rod  196  is radially movable in the corresponding bore of carrier disk  164  so that a radial relative motion is possible between basic carrier  166   a  and carrier disk  164  because of the connection shown. 
     Both the piston-rod space and the other cylinder space of all piston cylinder units  192  are in communication with each other via lines  204  and  206  as is suggested in FIG.  6 . Thus, polishing plate  160  is floatingly suspended from basic carrier  166   a  and, like the polishing plate of FIG. 4, is adapted to automatically change its inclination while adapting itself to the change in inclination of the working surface of polishing disk  10  of the lower polishing disk of FIG.  4 . 
     The above Examples and disclosure are intended to be illustrative and not exhaustive. These examples and description will suggest many variations and alternatives to one of ordinary skill in this art. All these alternatives and variations are intended to be included within the scope of the attached claims. Those familiar with the art may recognize other equivalents to the specific embodiments described herein which equivalents are also intended to be encompassed by the claims attached hereto.