METHOD AND POLISHING APPARATUS FOR MACHINING A PLATE-SHAPED COMPONENT, AND PLATE-SHAPED COMPONENT, IN PARTICULAR ELECTROSTATIC HOLDING APPARATUS OR IMMERSION WAFER PANEL

Abstract

A method for machining a plate-shaped component, in particular an electrostatic holding device or an immersion wafer table, with a surface formed by end faces of protruding burls, including: mutual alignment of the component on a component carrier device and of a mechanical polishing tool on a tool carrier device, wherein the polishing tool and the component are arranged for relative movement to remove material from end face(s) of at least one burl. The polishing tool includes shape-stable, deformable binding agent and polishing particles therein. Pressure force between the polishing tool and the at least one burl is measured by a force sensor device. The tool carrier device and/or the component carrier device are set to a predefined working value of the pressure force such that material is removed from the end face during removal movement. Also disclosed are a plate-shaped component produced with the method, and a polishing device.

Claims

1. A method for machining a plate-shaped component, wherein the component has a plane surface formed by end faces of a plurality of protruding burls, with the steps: mutual alignment of the component arranged on a component carrier device and of a mechanical polishing tool arranged on a tool carrier device, wherein the mechanical polishing tool and the component are arranged so as to be movable relative to each other, and removal movement of the mechanical polishing tool and the component relative to each other such that with a plurality of partial movements, material is removed from an end face of at least one of the burls, wherein the mechanical polishing tool has a composition comprising a shape-stable, deformable binding agent and polishing particles embedded in the binding agent, a force sensor device is provided which can measure a pressure force acting between the mechanical polishing tool and the at least one burl, and at least one of the tool carrier device and the component carrier device is set to a predefined working value of the pressure force between the mechanical polishing tool and the at least one burl, wherein the predefined working value of the pressure force is selected such that during the removal movement, material is removed from the end face of the at least one burl.

2. The method according to claim 1, wherein the partial movements comprise translational movements of the mechanical polishing tool relative to the at least one burl.

3. The method according to claim 1, wherein the partial movements along the plane surface of the component have movement directions of the mechanical polishing tool relative to the at least one burl which change step by step.

4. The method according to claim 3, wherein the directions of successive partial movements of the mechanical polishing tool relative to the at least one burl differ by a non-integral part of 360°.

5. The method according to claim 4, wherein the directions of successive partial movements of the mechanical polishing tool relative to the at least one burl differ in a range from 5° to 30°.

6. The method according to claim 1, wherein the pressure force is measured by the force sensor device before starting the movement of the mechanical polishing tool and component relative to each other.

7. The method according to claim 1, wherein the pressure force is measured by the force sensor device in predefined measuring phases in which the mechanical polishing tool is at rest following a plurality of partial movements on the at least one burl.

8. The method according to claim 1, wherein the mechanical polishing tool acts on the at least one burl without a lapping agent.

9. The method according to claim 1, wherein the binding agent comprises a plastic and the polishing particles are comprised of diamond.

10. The method according to claim 1, wherein the binding agent has a stiffness in a range from 5 N/mm to 30 N/mm.

11. The method according to claim 1, with the further step setting a machining region within the surface of the component, to which the movement of the mechanical polishing tool and the component relative to each other is restricted.

12. The method according to claim 1, wherein the plate-shaped component comprises an electrostatic holding device.

13. The method according to claim 1, wherein the plate-shaped component comprises an immersion wafer table.

14. A plate-shaped component, comprising a base plate, and a plurality of protruding burls which are arranged on the base plate and end faces of which form a plane surface of the component, wherein an end face of at least one of the burls has a roughness in a form of polishing or lapping marks which run laterally and parallel to the surface of the component.

15. The plate-shaped component according to claim 14, comprising an electrostatic holding device.

16. The plate-shaped component according to claim 14, comprising an immersion wafer table.

17. A polishing device for machining a plate-shaped component, wherein the plate-shaped component has a plane surface formed by end faces of a plurality of protruding burls, comprising: a component carrier device configured to receive the plate-shaped component, a tool carrier device configured to receive a mechanical polishing tool, wherein the mechanical polishing tool and the plate-shaped component can be moved relative to each other by at least one of the tool carrier device and the component carrier device, and a drive device which acts on the at least one of the tool carrier device and the component carrier device and is configured for a removal movement of the mechanical polishing tool and the plate-shaped component relative to each other, such that with a plurality of partial movements, material is removed from an end face of at least one of the burls, wherein the mechanical polishing tool comprises a shape-stable, deformable binding agent and polishing particles embedded in the binding agent, the tool carrier device comprises a force sensor device which can measure a pressure force acting between the mechanical polishing tool and the at least one burl, and a control device is provided with which at least one of the tool carrier device and the component carrier device can be adjusted to a predefined working value of the pressure force between the mechanical polishing tool and the at least one burl.

18. The polishing device according to claim 17, wherein the tool carrier device comprises a tool portal.

19. The polishing device according to claim 17, wherein the polishing device is configured for machining an electrostatic holding device.

20. The polishing device according to claim 17, wherein the polishing device is configured for machining an immersion wafer table.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Further details and advantages of the invention are described in the following with reference to the attached drawings. The drawings show in:

[0039] FIG. 1: a schematic depiction of features of embodiments of a polishing apparatus according to the invention for executing the method according to the invention;

[0040] FIG. 2: a schematic illustration of the feed of a polishing tool relative to a burl; and

[0041] FIG. 3: exemplary images of burl end faces before (A) and after (B) application of the method according to the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0042] Features of preferred embodiments of the invention are described below with exemplary reference to the machining of an electrostatic holding apparatus with a plurality of burls on a single surface (top side), wherein in particular details of the polishing tool and its setting relative to the burls, and the execution of the removal movement, are described. As an example, reference is made to a polishing apparatus in the form of a portal machine. The implementation of the invention in practice is not however restricted to the use of the portal machine. Rather, the polishing apparatus may have a different configuration for the desired removal movement of the polishing tool and component relative to each other. Details of the electrostatic holding apparatus are not described since these are known in themselves from conventional electrostatic holding apparatuses. The application of the invention is not restricted to the machining of one or more burls of an electrostatic holding apparatus, but may apply accordingly to the machining of other components e.g. immersion wafer panels.

[0043] FIG. 1 shows in a schematic sectional view an embodiment of a polishing apparatus 200 according to the invention in the form of a tool portal. A lower platform (machine bed) of the tool portal forms a component carrier device 210. The lower platform is configured for temporarily holding the component 100 to be machined, and for this is provided e.g. with a plane platform surface and fixing elements (not shown). The component 100 is positioned reproducibly with sufficient precision in the horizontal plane by a corresponding receptacle.

[0044] The component 100 is for example a schematically depicted electrostatic holding apparatus with a base plate 110 and burls 120, the end faces 121 of which (see also FIG. 2) span a surface 130 of the component 100. In the illustration, the surface 130 extends in an x-y plane (reference plane) while the burls 120 extend in a z direction perpendicular to the x-y plane. In a practical example, on a surface with a lateral extent of 300 mm for example, the component 100 has a total number of up to 30,000 burls each with a diameter from 200 μm to 350 μm and a height in the z direction from 10 μm to 180 μm.

[0045] An upper portal portion of the tool portal forms a tool carrier device 220 on which the polishing tool 221 is attached by means of a drive slide 232. The upper portal portion is arranged so as to be displaceable by a portal drive 231 relative to the component carrier device 210 (lower platform) in the y direction, i.e. perpendicular to the drawing plane. The drive slide 232 is arranged so as to be displaceable in the x direction along the upper portal portion.

[0046] A force sensor device 240 is arranged on an underside of the drive slide 232, and a tool holder 224 with the polishing tool 221 is arranged at the force sensor device 240. The force sensor device 240, which comprises for example a load cell, serves to measure a pressure force of the polishing tool 221 relative to the burls 120 in the z direction. Particularly preferably, a 6-axis force sensor is used. The load cell is e.g. a dynamometer from manufacturer ATI for force measurement up to 10 mN. The tool holder 224 is provided for temporarily fixing the polishing tool 221 to the force sensor device 240 or the drive slide 232. Depending on application of the invention, a polishing tool 221 with suitable configuration (stiffness of binding material and hardness of polishing particles), with a respective tool holder 224 of suitable length in the z direction, may be selected and used on the force sensor device 240 or drive slide 232.

[0047] The portal drive 231 and the drive slide 232 form a drive device 230 with which the polishing tool 221 can be moved relative to the component 100. Using the drive slide 232, the polishing tool 221 can, in addition to mobility in the x direction, be moved in the z direction in order to adjust the feed of the polishing tool 221 relative to the burls 120 (see FIG. 2). With the portal drive 231, the polishing tool 221 is movable in the y direction. The removal movement of the polishing tool 221 relative to the burls 120 is executed by operation of the portal drive 231 and the drive slide 232.

[0048] The polishing apparatus 200 is provided with a control device 250 which is connected to the drive device 230 and the force sensor device 240, and is configured to measure the polishing tool 221 (in particular its setting in the z direction) and control the drive device 230 (in particular setting the partial removal movements). The control device 250 comprises for example a control computer.

[0049] The polishing tool 221 at the lower end of the tool holder 224 has, as shown diagrammatically in further enlargement in FIG. 2, a working surface in the form of a spheroidal surface, e.g. a hemispherical surface. The polishing tool 221 comprises a binding material 222 and polishing particles 223 embedded therein, and is for example a high-gloss polisher as known from dental technology (in particular a dental polisher). The binding material 221 is made of a rubber-elastic material, in particular rubber, and the polishing particles 223 comprise e.g. diamond, silicon and/or silicon carbide particles. The polishing particles 223 have a typical cross-sectional dimension in the range from 3 μm to 7 μm. The mean grain spacing of the polishing particles 223 lies in the range from 10 μm to 15 μm. Furthermore, the arrow in FIG. 2 indicates schematically the movements of the polishing tool 221 which can be executed with the drive slide 232, comprising the feed movement in the z direction towards the end face 121 of the exemplary burl 120 and the removal movement in the x-y plane parallel to the end face 121.

[0050] The configuration of the polishing tool is selected depending on the actual machining task, in particular depending on the material of the burl end faces, the desired machining speed and/or the desired roughness of the finished burl end faces after machining. For example, if the burls have a DLC coating or a CrN coating, or if a high machining speed is desired, a polishing tool with a higher stiffness (or binding hardness) of the binding material and a greater hardness of the polishing particles is selected than when machining burls with end faces of Si or SiSiC. If an increased roughness is to be set, correspondingly larger polishing particles are used.

[0051] To machine the component 100 with the method according to the invention in the polishing apparatus 200 according to FIG. 1, the following steps are provided.

[0052] Firstly, optionally, a preparation step is provided in which it is determined where correction is required on the burls 120 of the component 100. For example, the burl heights in the z direction are measured with optical or mechanical means in order to determine individual burls or burl groups which protrude relative to the desired height with respect to the surface 130.

[0053] Measurement with optical means may take place for example by electrostatic holding of a wafer on the burls and interferometric measurement of the wafer surface (functional measurement). Measurement with mechanical means may take place for example using a profilometer (e.g. Bruker Dektat Stylus Pro). Said measurements are preferably carried out when the component 100 is already arranged in the polishing apparatus 200. For this, the polishing apparatus 200 may be provided with an optical measuring device and/or a profilometer.

[0054] As a result of the preparation step, data are available comprising identification of the burls 120 to be machined, their positions in the x-y plane and optionally their heights in the z direction. For each burl 120 to be machined, the desired material removal in the z direction can be determined (in microns or nanometers). The preparation step may be omitted if the data on the burls to be machined are already available from other sources.

[0055] The burl coordinates to be machined and the necessary process parameters are read and the machining of the burls 120 begins. Individual burls may be machined successively, or groups of burls (or all burls) may be machined together.

[0056] Firstly, the polishing tool 221 is initially calibrated in order to determine its appropriate feed. Typically, the polishing tool is only recalibrated after a change. With known machining conditions, the feed may be predefined by the control device. During calibration, the polishing tool 221 is brought to an individual burl 120 and placed on its end face 121. Using the drive slide 232, the polishing tool 221 is pressed against the end face 121 in the z direction. On contact, the polishing tool 221 is elastically compressed.

[0057] The force sensor device 240 measures the force between the polishing tool 221 and the end face. When a predefined pressure force is reached, the current position of the polishing tool 221 is stored as a working position in the z direction for the next removal movement. Corresponding to the working position, in the uncompressed state (see FIG. 2), the polishing tool 221 protrudes below the plane of the end face 121, wherein the distance between the apex of the polishing tool 221 and the plane of the end face 121 is designated the feed Z.sub.0.

[0058] The feed Z.sub.0 is generally set e. g. in the range from 70 μm to 130 μm, particularly preferably around 100 μm. A feed Z.sub.0 in this range has proved particularly advantageous for controllability of the machining process, in particular for machining SiSiC or CrN. For other materials, such as e.g. when machining DLC, a different feed value may be preferred.

[0059] For simultaneous machining of several burls, the polishing tool 221 is placed on one of the burls 120 in order to calibrate the tool and set the feed. If the polishing tool 221 is larger than the end face 121 of a burl 120, the polishing tool 221 is accordingly placed on several end faces for calibration.

[0060] Then the removal movement of the polishing tool 221 relative to the burl 120 is carried out. The polishing tool 221 is moved repeatedly over the end face 121 with changing lateral directions in the x-y plane (so-called nano-plowing). On each partial removal movement, for example material of a thickness of 0.05 nm is removed. Each partial removal movement indeed produces nano-scratches on the end face 121, but because of the plurality of machining steps (a material removal which leads to a change in local flatness of 50 nm in the functional measurement, e.g. around 1000 partial removal movements), polishing or lapping marks are superposed with a stochastic roughness of the surface 121. FIG. 3 shows as an example photographic images of the end face of a burl with a diameter of 210 μm before (A) and after (B) execution of the removal movement of the polishing tool. FIG. 3B clearly shows the creation of a roughness of the end face by stochastically distributed polishing or lapping marks.

[0061] Each partial removal movement is a linear movement, in each case with a different direction in the x-y plane. With the drive device 230, the orientation of the partial removal movement in the x-y plane is adjusted by an angular step each time. Each angular step is a non-integral part of 360°. For example, an angular step in the range from 15° to 25° is selected, e.g. 17.5°. Smaller angular steps are avoided in order to avoid dragging individual polishing particles into existing nano-scratches from the preceding partial removal movement, and hence the creation of undesirably large grinding marks.

[0062] To compensate for abrasion of the polishing tool 221, the calibration may advantageously be repeated after a predefined number (e.g. 300 to 500) of partial removal movements, in order in each case to set a new updated feed Z.sub.1.

[0063] After the removal movement has been carried out on each desired burl 120, the machining of the component 100 is completed.

[0064] The features of the invention disclosed in the above description, the drawings and the claims may, both individually and in combination or sub-combination, be important for the realization of the invention in its various embodiments.