Patent Application
20210252664
The invention relates to a method for machining, in particular polishing, a plate-shaped component, in particular an electrostatic holding apparatus or an immersion wafer panel, with a plane surface formed by end faces of a plurality of protruding burls. In particular, the invention relates to a method for polishing at least one of the burls of an electrostatic holding apparatus or an immersion wafer panel. The invention furthermore relates to a component machined with said method, in particular an electrostatic holding apparatus or an immersion wafer panel with a machined surface. Furthermore, the invention concerns a polishing apparatus for machining a plate-shaped component, in particular for executing said method. Applications of the invention lie in the production, repair or regeneration of components, in particular electrostatic holding apparatuses or immersion wafer panels.
Electrostatic holding apparatuses for electrostatic holding of components, also known as electrostatic wafer panels, electrostatic clamping devices, electrostatic clamps, ESCs or electrostatic chucks, are generally known. Electrostatic holding apparatuses are used for example in holding semiconductor wafers, in particular silicon wafers, in lithographic semiconductor machining, for example chip production.
Typically, an electrostatic holding apparatus comprises several plate-shaped or layered elements (see e.g. U.S. Pat. No. 4,502,094 or US 2013/0308116 A1), of which at least one plate-shaped element is provided with an electrode device via which the electrostatic holding forces are generated. At least one plate-shaped element is produced from a mechanically rigid ceramic to fulfil a carrier and cooling function. Furthermore, an electrostatic holding apparatus typically has at least one exposed surface, e.g. at its top side, which is formed by a plurality of protruding burls. The end faces of the burls form a support surface for the silicon wafer.
For use of the electrostatic holding apparatus for holding semiconductor wafers, e.g. in chip production, the support surface spanned by the burls must be as plane as possible since unevenness may lead to deformation of the semiconductor wafer and hence e.g. to faults in its structuring during chip production. Unevenness may occur if individual burls or burl groups protrude or are recessed (lowered) relative to their surroundings (local unevennesses), or if larger surface regions within the support surface have burl heights which differ from the burl heights in other surface regions (global unevenness). Local unevennesses of a few nanometers, e.g. protruding burls >10 nm, may already lead to unacceptable deformations of the semiconductor wafers.
It is known from practice to machine a surface of an electrostatic holding apparatus by ion beam etching. With this method however, only global unevenness can be corrected. In addition, ion beam etching is disadvantageous since it is complex and costly. Furthermore, magneto-rheological polishing is known, which is indeed suitable for correcting local unevenness, but when machining burl surfaces creates disruptive grinding marks. Finally, undesirable abrasion and grinding marks remain even with further locally acting mechanical polishing methods known in practice using polishing robots and micro-milling processes with hard tool tips. A further disadvantage of the conventional method is that the result may be sensitively dependent on the skills and experience of the user.
The above problems occur not only in machining of an electrostatic holding apparatus but also when machining other components, e.g. immersion wafer panels.
The objective of the invention is to provide an improved method for machining a plate-shaped component, in particular an electrostatic holding apparatus or immersion wafer panel, with which the disadvantages of conventional techniques are avoided. In particular, the method is to be adapted for correcting both local and global unevennesses and offering increased precision and reproducibility in adjusting the surface of the machined component, and/or is to be able to be executed independently of the skills and experience of the user, with reduced complexity, reduced cost and/or increased throughput.
Furthermore, the objective of the invention is to provide an improved component, in particular an improved electrostatic holding apparatus or immersion wafer panel, which is manufactured with said method and with which disadvantages of conventional techniques are avoided. In particular, the component is to be distinguished by improved local and global evenness, having fewer disruptive grinding marks and/or having a defined roughness on its surface. The objective of the invention is also to provide an improved polishing apparatus with which said method can be executed and with which the disadvantages of conventional techniques are avoided. In particular, the polishing apparatus is to be adapted for allowing the correction of local and global unevenness, achieving increased precision and reproducibility in the adjustment of the surface of the process component, and/or allowing operation independently of the skills and experience of the user with reduced complexity, reduced costs and/or increased throughput.
These objectives are respectively achieved by a method for machining a plate-shaped component, in particular an electrostatic holding apparatus or immersion wafer panel, a component machined using the method, and a polishing device of the invention.
According to a first general aspect of the invention, the above objective is achieved by a method for machining a plate-shaped component, in particular an electrostatic holding apparatus or an immersion wafer panel, wherein the plate-shaped component has at least one surface (also called the top side) formed by end faces of a plurality of protruding projections (burls). The end faces of the burls form a surface of the component which extends along a predefined reference plane. Using the method for machining the component, the heights of the burls are set such that the surface formed (spanned) by the end faces is substantially stepless, in particular plane.
The plate-shaped component machined according to the invention has a base plate which is composed integrally of one single plate-shaped element or preferably several plate-shaped elements, as known e.g. from electrostatic holding apparatuses or immersion wafer panels. Preferably, the base plate has a flat form with a top side and an underside. The burls are provided exclusively on the top side or on both the top side and the underside. End faces of the burls on the top side (and/or underside) extend respectively along the common reference plane. The reference plane is also referred to below as the x-y plane, wherein the burls extend in a direction perpendicular to the reference plane (z direction). Directions parallel to the reference plane also are indicated as lateral directions. The machining of the component comprises a mechanical material removal from the end face of at least one of the burls, in particular a height adjustment of the at least one burl, and where applicable includes polishing.
The component is arranged on a component carrier device and a mechanical polishing tool is arranged on a tool carrier device. The component carrier device and the tool carrier device are each a holder at which the component and polishing tool are positioned such that the end faces of the burls, or at least one working surface of the polishing tool, are exposed. The component and the polishing tool are positioned such that the end faces of the burls and the working surface of the polishing tool face to each other. The component and the polishing tool can be moved relative to each other by the component carrier device and/or the tool carrier device. The mutual relative movement of the component and the polishing tool is also known as a removal movement. The component and the polishing tool are positioned such that on execution of the removal movement, the polishing tool can act on the end faces of the burls. For example, the component may be positioned with the component carrier device stationarily and the polishing tool may be moved with the tool carrier device relative to the component. Alternatively, conversely, the polishing tool may be stationary and the component movable, or both the polishing tool and the component may be movable.
In the removal movement, the polishing tool and the component are moved relative to each other such that material is removed from the end face of at least one of the burls. The removal movement comprises in particular a plurality of partial removal movements, in which material is removed in steps from the end face of the at least one machined burl. The partial removal movements are preferably executed such that the end face(s) of the at least one burl is/are completely swept by the polishing tool.
According to the invention, the polishing tool, in particular the working surface of the polishing tool, is a composition of a binding material and polishing particles. The polishing particles are embedded in the binding material. The binding material consists of a shape-stable material, such as a plastic, which is elastically deformable (in particular compressible) on action of the polishing tool on the burls, in particular during execution of the removal movement. The polishing particles protrude from the binding material on the working surface of the polishing tool. The hardness of the binding material is less than the hardness of the burls, for example less than the hardness of SiSiC ceramic. The polishing particles consist of a material which is selected for removal of material from the burls. The polishing particles have a hardness which is greater than the hardness of the burls, for example greater than the hardness of SiSiC ceramic.
Furthermore, according to the invention, a force sensor device is provided. The force sensor device is preferably arranged on the tool carrier device, but alternatively may also be arranged on the component carrier device. The force sensor device is configured to measure a pressure force (contact pressure force) acting between the polishing tool and the at least one burl. The pressure force may be measured continuously during machining of the component or at specific measuring times. The pressure force is for example the force with which the polishing tool, when positioned in a compressed state on the end face of the at least one burl, acts on the end face of the burl. If several burls are being machined, the pressure force is the force with which the polishing tool acts on the end face of one of the burls. Alternatively or additionally, the pressure force may also be the force which acts laterally on a burl when the polishing tool meets the burl during the removal movement.
Furthermore, according to the invention, the tool carrier device and/or the component carrier device are adjusted to provide a predefined working value of the pressure force between the polishing tool and the at least one burl. The 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, but otherwise no damage occurs to the burls, in particular no breakage of material at the edges of the end face(s) or breakage of the burl(s).
According to the invention, a single burl may be machined locally e.g. lowered to the height of the adjacent burls. In practice, typically locally several adjacent burls or burls spaced apart from each other, or globally all burls of the component are machined, so that usually reference is made to the machining of several burls in the following.
According to the invention, advantageously a relatively soft polishing tool with a mean hardness lower than the hardness of the burls is used. During the removal movement, the polishing tool is partially compressed, wherein the polishing particles act on the burls. Advantageously, thereby the form of the polishing tool is not transferred to the end faces of the burls. Undesirable and/or non-reproducible machining marks, such as occur for example with the use of polishing robots with grinding tips or in magneto-rheological polishing, are avoided.
The working value of the pressure force, and hence the material removal which can be achieved per partial removal movement, is set by the position of the polishing tool relative to the burls depending on the mean hardness of the polishing tool. The working value of the pressure force is determined in particular by the vertical distance which is set during positioning of the polishing tool, laterally next to a burl, between the working surface of the uncompressed polishing tool and the plane of the end face of the burl (feed of the polishing tool). In other words, the feed is a distance dimension which is characteristic of the depth with which the polishing tool protrudes into the face spanned by the end faces of the burls.
The total material removal achieved during machining is established by the working value of the pressure force and the number of partial removal movements. Advantageously, in this way the precision and reproducibility of the material machining is increased in comparison with conventional techniques. The feed and the number of removal movements define two process parameters of the machining process, whereby the method advantageously can be automated relatively easily.
It is a further advantage of the invention that the size of the polishing tool can be freely selected. The polishing tool, in particular its working surface acting on the end faces of the burls, may have a size which is adapted to the lateral extent of the end faces, in particular their diameter. For example, the polishing tool may have the size of one single end face. The number of burls machined may be set by the working range of the removal movement. Depending on application of the invention therefore, even with a small polishing tool, by setting the working range of the removal movement (amplitude of partial movements), a local correction of burls can be made, even down to one single burl, or a correction of burl groups, or a global correction of all burls of the component. Alternatively, the polishing tool, in particular its working surface, may have a size which extends over end faces of several adjacent burls.
According to a preferred embodiment of the invention, the partial movements comprise translational movements of the polishing tool and burls relative to each other, particularly preferably translational movements of the polishing tool relative to the stationary burls. The translational movements, by deviation from magneto-rheological polishing and typical variants of manual machining, are targeted, non-rotating, for example linear, movements in the lateral direction, i.e. parallel to the x-y plane. Translational movement has the advantage over rotational movement that it avoids the formation of a preferential direction in the material removal, and hence clear grinding marks. Furthermore, with comparable pressure force, a translational movement achieves a greater material removal per partial movement than a corresponding rotational movement.
Particularly preferably, the partial movements, in particular the translational partial movements parallel to the reference plane of the component, have lateral movement directions of the polishing tool and burls relative to each other which change step by step. Advantageously, the step-by-step change of movement direction, for example of the polishing tool in the reference plane, avoids the creation of undesirably deep scratches on the end faces of the burls and promotes the formation of a stochastic roughness of the end faces.
It is particularly advantageous for avoiding preferential directions in material removal and for forming the stochastic roughness if the directions of successive partial movements of the polishing tool and burls relative to each other differ by a non-integral part of 360°, in particular in the range from 5° to 30°. Advantageously, thus even when the changing directions of the partial movements pass through a complete circle, this avoids material removal in existing marks and hence excessive deepening thereof.
According to a further preferred embodiment of the invention, the pressure force is measured by the force sensor device before the start of the movement of the polishing tool and the component relative to each other, and/or in predefined measuring phases in which the polishing tool is at rest following a plurality of partial movements on at least one of the burls. By measuring the pressure force under the condition of a resting polishing tool, measuring errors are avoided which could otherwise be caused by vibrations of a moving polishing tool.
According to a further, particularly advantageous variant of the invention, the polishing tool acts on the burls without a lapping agent. The burls are machined without a lapping agent. The polishing tool is dry when acting on the end faces of the burls. Advantageously, this simplifies the machining process and avoids post-machining steps to eliminate lapping agent residue.
A further important advantage of the invention is that polishing tools are commercially available in the form of high-gloss polishers from dental technology, which comprise a sufficiently soft binding material and a sufficiently high grain density of the polishing particles. Preferably, the binding material comprises a rubber-elastic plastic such as e.g. rubber or other elastomers, and/or the polishing particles are diamond, silicon and/or silicon carbide particles, for example with a size in the range from 2 μm to 10 μm, in particular 3 μm to 7 μm. The mean grain spacing of the polishing particles is preferably in the range from 10 μm to 15 μm. Polishing particles with sizes in this range have the advantage that a sufficiently low roughness for use of the component can be achieved.
According to further preferred embodiments of the invention, a polishing tool is used in which the binding material comprises a soft or medium-hard plastic. Particularly preferably, the binding material has a stiffness in the range from 5 N/mm to 30 N/mm. Polishing tools with a stiffness in this range have proved particularly advantageous for gentle machining of the burls, in particular for effective material removal from the end faces without breaking the edges of the end faces or breaking off whole burls.
Further advantages apply if, according to a variant of the method according to the invention, a machining region is set within the surface of the component, to which the movement of the polishing tool and the component relative to each other is restricted. In setting the machining region, any desired machining size from local correction to global correction may be predefined.
According to a second general aspect of the invention, the above objective is achieved by a plate-shaped component, in particular an electrostatic holding apparatus or immersion wafer panel, which as described above comprises a base plate and a plurality of protruding burls which are arranged on at least one side of the base plate, and the end faces of which form a plane surface of the component. The surface extends parallel to a predefined reference plane.
According to the invention, the end faces of the burls of the component according to the invention have a predefined roughness. The roughness takes the form of grinding marks with equal depth. The grinding marks are stochastically distributed and run laterally and parallel to the reference plane. Advantageously, the component according to the invention is distinguished by plane end faces of the burls parallel to the reference plane, equal heights of all burls in the z direction, and said roughness of the end faces. This combination of features of the burls is of particular advantage for the use of the component for holding semiconductor wafers. By deviation from components machined with conventional techniques, the grinding marks are formed evenly, i.e. they are distinguished by a substantially equal mark depth along the end faces. Preferably, the component according to the invention is produced with the method according to the first general aspect of the invention in its various embodiments.
According to a third general aspect of the invention, the above objective is achieved by a polishing apparatus for machining a plate-shaped component, in particular an electrostatic holding apparatus or an immersion wafer panel, wherein the component has a plane surface formed by end faces of a plurality of protruding burls. Preferably, the polishing apparatus is configured to execute the method according to the first general aspect of the invention in its various embodiments, and/or to produce a component according to the second general aspect of the invention in its various embodiments.
The polishing apparatus comprises a component carrier device, a tool carrier device and a drive device. The component carrier device is configured to receive the component temporarily during machining and to move it if required. The tool carrier device is configured to hold a mechanical polishing tool and where applicable to move the polishing tool. The component carrier device and the tool carrier device are designed for a mutual relative movement of the polishing tool and the component.
The component carrier device and/or the tool carrier device can be actuated with the drive device. The drive device is configured for moving the component and/or the polishing tool in order to execute a removal movement of the polishing tool and the component relative to each other. The component carrier device and/or the tool carrier device are configured for the preferably non-rotating removal movement, which comprises a plurality of partial movements with changing movement directions, parallel to the reference plane of the plane surface of the component. The plurality of partial movements are provided for material removal on the end faces of the burls.
According to the invention, the polishing tool comprises a shape-stable, deformable binding material and polishing particles. The polishing particles are embedded in the binding material. The binding material is preferably elastically deformable. Furthermore, according to the invention, a force sensor device is provided with which a pressure force can be measured which acts between the polishing tool and the burls of a component held by the component carrier device. Furthermore, according to the invention, a control device is provided with which the tool carrier device and/or the component carrier device can be set to a predefined working value of the pressure force between the polishing tool and the burls.
Preferably, the tool carrier device comprises a tool portal. The tool portal has special advantages in the positioning and movement of the polishing tool relative to the component to be machined on the component carrier device.
To summarize, the invention in its various aspects offers the following advantages. An automated correction of unevenness on semiconductor wafers, in particular wafer panels, is provided. The machining may take place substantially independently of the skills and experience of a user. Here a reproducible material removal on burls of the semiconductor wafer holder is possible at specific burl positions within the nanometer range. The invention offers the setting of reproducible engagement conditions for machining, in particular polishing, of the surface of the component, in particular of an electrostatic holding apparatus or immersion wafer panel. Particularly advantageously, automated machining is possible of the component surface e.g. of SiSiC, DLC and CrN surfaces, with a mean removal of less than 1 nm per machining step (partial removal movement). The use of a macroscopic tool with flexible binding of the binding material for microscopic mechanical correction in the single-digit nanometer range is possible thanks to the use of the force sensor, which may be used to create reproducible machining conditions.
Further details and advantages of the invention are described in the following with reference to the attached drawings. The drawings show in:
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.
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
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.
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.
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
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.
The polishing tool 221 at the lower end of the tool holder 224 has, as shown diagrammatically in further enlargement in
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.
To machine the component 100 with the method according to the invention in the polishing apparatus 200 according to
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.
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.
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.
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.
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.
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 Z0.
The feed Z0 is generally set e. g. in the range from 70 μm to 130 μm, particularly preferably around 100 μm. A feed Z0 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.
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.
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.
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.
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 Z1.
After the removal movement has been carried out on each desired burl 120, the machining of the component 100 is completed.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102020104238.8 | Feb 2020 | DE | national |
