Abrading – Machine – Rotary tool
Reexamination Certificate
2000-03-10
2001-10-09
Hail, III, Joseph J. (Department: 3723)
Abrading
Machine
Rotary tool
C451S041000, C451S060000, C451S268000, C451S285000, C451S287000
Reexamination Certificate
active
06299514
ABSTRACT:
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 te
Hail III Joseph J.
McDonald Shantese
Peter Wolters Werkzeugmachinen GmbH
Vidas Arrett & Steinkraus P.A.
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