U.S. patent application number 17/173651 was filed with the patent office on 2021-08-19 for method and polishing apparatus for machining a plate-shaped component, and plate-shaped component, in particular electrostatic holding apparatus or immersion wafer panel.
The applicant listed for this patent is Berliner Glas KGaA Herbert Kubatz GmbH & Co.. Invention is credited to Jan MEWIS.
Application Number | 20210252664 17/173651 |
Document ID | / |
Family ID | 1000005405030 |
Filed Date | 2021-08-19 |
United States Patent
Application |
20210252664 |
Kind Code |
A1 |
MEWIS; Jan |
August 19, 2021 |
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.
Inventors: |
MEWIS; Jan; (Berlin,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Berliner Glas KGaA Herbert Kubatz GmbH & Co. |
Berlin |
|
DE |
|
|
Family ID: |
1000005405030 |
Appl. No.: |
17/173651 |
Filed: |
February 11, 2021 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B24B 37/26 20130101;
B24B 7/228 20130101; B24B 37/042 20130101; B24B 37/245
20130101 |
International
Class: |
B24B 7/22 20060101
B24B007/22; B24B 37/26 20060101 B24B037/26; B24B 37/04 20060101
B24B037/04; B24B 37/24 20060101 B24B037/24 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 18, 2020 |
DE |
102020104238.8 |
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.degree..
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.degree.
to 30.degree..
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
BACKGROUND OF THE INVENTION
[0001] 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.
[0002] 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.
[0003] 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.
[0004] 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.
[0005] 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.
[0006] The above problems occur not only in machining of an
electrostatic holding apparatus but also when machining other
components, e.g. immersion wafer panels.
[0007] 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.
[0008] 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.
[0009] 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.
BRIEF SUMMARY OF THE INVENTION
[0010] 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.
[0011] 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.
[0012] 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.
[0013] 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.
[0014] 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.
[0015] 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.
[0016] 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).
[0017] 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.
[0018] 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.
[0019] 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.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] 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.degree., in particular in the range from
5.degree. to 30.degree.. 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.
[0025] 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.
[0026] 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.
[0027] 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 .mu.m to 10 .mu.m, in particular 3 .mu.m to 7
.mu.m. The mean grain spacing of the polishing particles is
preferably in the range from 10 .mu.m to 15 .mu.m. Polishing
particles with sizes in this range have the advantage that a
sufficiently low roughness for use of the component can be
achieved.
[0028] 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.
[0029] 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.
[0030] 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.
[0031] 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.
[0032] 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.
[0033] 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.
[0034] 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.
[0035] 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.
[0036] 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.
[0037] 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.
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 .mu.m to 350 .mu.m and a height in
the z direction from 10 .mu.m to 180 .mu.m.
[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 .mu.m to 7
.mu.m. The mean grain spacing of the polishing particles 223 lies
in the range from 10 .mu.m to 15 .mu.m. 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
.mu.m to 130 .mu.m, particularly preferably around 100 .mu.m. 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 .mu.m 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.degree.. For example, an angular
step in the range from 15.degree. to 25.degree. is selected, e.g.
17.5.degree.. 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.
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