U.S. patent application number 10/791828 was filed with the patent office on 2005-09-08 for method for manufacturing a workpiece and torque transducer module.
Invention is credited to Gu, Yingru, Li, Leping, Moser, Werner.
Application Number | 20050197048 10/791828 |
Document ID | / |
Family ID | 34911714 |
Filed Date | 2005-09-08 |
United States Patent
Application |
20050197048 |
Kind Code |
A1 |
Li, Leping ; et al. |
September 8, 2005 |
Method for manufacturing a workpiece and torque transducer
module
Abstract
A method for manufacturing a workpiece and a torque transducer
module for material removal techniques, are disclosed, where
machining friction varies in dependency of machining depth and the
torque/deformation of a shaft is monitored for controlling material
removal. The module has a body extending along a central axis and
two end portions. Each end portion is part of an axial mount for a
respective part to be axially mounted thereto. The module also
includes a strain gage sensor arrangement with at least one
electric output.
Inventors: |
Li, Leping; (Poughkeepsie,
NY) ; Moser, Werner; (Gebertingen, CH) ; Gu,
Yingru; (Hyde Park, NY) |
Correspondence
Address: |
ANTONELLI, TERRY, STOUT & KRAUS, LLP
1300 NORTH SEVENTEENTH STREET
SUITE 1800
ARLINGTON
VA
22209-3873
US
|
Family ID: |
34911714 |
Appl. No.: |
10/791828 |
Filed: |
March 4, 2004 |
Current U.S.
Class: |
451/8 ; 29/595;
310/321 |
Current CPC
Class: |
B24B 37/013 20130101;
Y10T 29/49007 20150115; B24B 49/16 20130101 |
Class at
Publication: |
451/008 ;
310/321; 029/595 |
International
Class: |
B24B 049/00; B24B
051/00 |
Claims
1. A method for manufacturing a workpiece comprising the steps of:
providing a substrate having a substantially flat surface; removing
material from said surface by moving said surface of said substrate
relative to on and along a polishing surface; said moving including
a rotation about an axis by a shaft driven in a predetermined
manner; providing along said shaft a shaft section having a
predetermined torque/deformation characteristic, said
characteristic of said section being independent of
torque/deformation characteristic of said shaft; monitoring
deformation of said shaft section as a torque indicative signal;
controlling said removing in dependency of said torque indicative
signal; manufacturing said workpiece from said substrate having
said material removed.
2. The method of claim 1, wherein said shaft carries at one end
thereof said substrate.
3. The method of claim 1, wherein said substrate has at least one
material interface between two different materials and
substantially parallel to said surface, thereby monitoring when
said removing reaches said interface by said monitoring of said
deformation.
4. The method of claim 3, said controlling comprising disabling
said removing when reaching said interface is detected.
5. The method of claim 1, further comprising monitoring said
deformation by monitoring strain along said section.
6. The method of claim 5, further comprising monitoring said strain
by means of a strain sensor arrangement mounted to said section and
generating an electric output signal.
7. The method of claim 6, further comprising transmitting a signal
dependent on said output signal from said rotating section to a
system which is stationary with respect to said section and
performing analogue to digital signal conversion of a signal
dependent on said output signal before performing said
transmitting.
8. The method of claim 1, further comprising providing at least a
part of said shaft with a first hollow inner space and providing at
least a part of said section with a second hollow inner space, said
first and second hollow inner spaces being in communication,
monitoring said deformation with a sensor arrangement mounted on
said section and generating an electric output signal and
transmitting a signal dependent on said output signal to a system
stationary with respect to said rotating section through said first
and second hollow spaces being in communication.
9. The method of claim 1, further comprising providing at least a
part said shaft with a first hollow inner space and providing at
least a part of said section with a second hollow inner space, said
first and second hollow spaces being in communication, monitoring
said deformation by a sensor arrangement mounted on said section
and providing electric supply to said sensor arrangement via said
first and second hollow spaces in communication.
10. The method of claim 1, comprising monitoring said deformation
by means of a sensor arrangement mounted on said section and
generating an electric output signal, transmitting a signal
dependent from said electric output signal from said rotating
section to a system stationary with respect to said section via a
slide contact arrangement.
11. The method of claim 10, further comprising performing said
transmitting via at least two independent sliding contact
arrangements.
12. The method of claim 1, said shaft having an outer diameter,
further comprising providing said section with an outer diameter
smaller than said diameter of said shaft.
13. The method of claim 1, wherein said workpiece is a
semiconductor workpiece.
14. The method of claim 1, wherein said workpiece is a low-scale or
ultra-low-scale integrated microelectronic workpiece.
15. The method of claim 1, further comprising performing said
removal by chemical mechanical polishing, thereby applying a slurry
to said polishing surface.
16. A torque transducer module comprising a body extending along a
central axis and having two end portions, each of said end portions
being a part of an axial mount for a respective part to be axially
mounted thereto, a strain gage sensor arrangement with at least one
electric output.
17. The transducer module of claim 16, further comprising at least
one recess along said body, said sensor arrangement being mounted
within said recess.
18. The module of claim 17, wherein said recess is defined between
said two end portions.
19. The module of claim 16, said body being cylindrical with
respect to said axis, said end portion being substantially
cylindrical rims projecting from said body, said end portions and
said body forming a cylindrical part substantially of I-shape in an
axial cross-section with a reduced diameter cylindrical recess.
20. The module of claim 16, wherein said strain gage sensor
arrangement is mounted within a recess in the outer surface of said
body and further comprising a removable cover for said recess.
21. The module of claim 16, further comprising an analogue to
digital converter arrangement with an input operationally connected
to said at least one electric output.
22. The module of claim 16, further comprising an axially extending
hollow space open at at least one of said end portions.
23. The module of claim 22, further comprising electrical leads in
said hollow space being at least one of power supply leads for said
sensor arrangement and of signal transmission leads operationally
connected to said electric output of said sensor arrangement.
24. A mechanical surface machining apparatus, especially polishing
or grinding apparatus, comprising a rotatable transmission shaft
coupled to a drive, a torque transducer module with a body and two
end portions, at least one of said transmission shaft, of said end
portions being mounted to an end portion, said module having a
strain gage sensor arrangement with at least one electric output,
said transmission shaft and at least a part of said body being
hollow, electrical leads in said hollow shaft and said hollow body
operationally connected to said sensor arrangement.
25. The apparatus of claim 24, wherein said transducer module is a
transducer module comprising a body extending along a central axis
and having two end portions, each of said end portions being a part
of an axial mount for a respective part to be axially mounted
thereto, a strain gage sensor arrangement with at least one
electric output.
26. The apparatus of claims 24, further comprising a slip-ring
contact arrangement between said shaft and a part of said apparatus
stationary with respect to said rotatable transmission shaft, said
electric leads being operationally connected to said slip-ring
contact arrangement.
27. The apparatus of claim 26, wherein at least one of said leads
is operationally connected to at least two independent slip-ring
contact arrangements for redundant signal transmission between said
shaft and said part.
28. A method for monitoring the load presented by a material on a
rotating shaft in intimate contact with said material comprising:
providing along said shaft a shaft section having a predetermined
torque/deformation characteristic, said characteristic of said
section being independent of torque/deformation characteristic of
said shaft; monitoring deformation of said shaft section as a load
indicative signal.
Description
[0001] The present invention resulted from needs encountered in
context with endpoint detection when polishing substrates in
semiconductor processing. Thereby removing of material has often to
be disabled as soon as a material interface separating one material
from another is reached.
[0002] Nevertheless, the present invention is not restricted to
endpoint detection in context with polishing during semiconductor
processing, but may be applied to all material removal techniques
along a substantially flat plane, where the machining friction
varies in dependency of machining depth. Thus, the present
invention may be applied
[0003] for endpoint detection of mechanical surface machining.
Thereby the resistance which is presented by the workpiece to the
machining tool varies unsteadily at such endpoint when a material
interface is reached;
[0004] for continuous monitoring of mechanical surface machining
whenever the resistance which is presented by the workpiece to the
machining tool varies as a function of depth of machining material
removal.
[0005] As machining polishing and grinding are primarily
considered, thereby especially Chemical Mechanical Polishing
(CMP).
[0006] The invention may thus also be applied to polishing or
grinding processing of optical workpieces during manufacturing,
thereby and more generically to such machining of workpieces where
thin coatings have selectively to be removed. It may also be
applied to grinding in the pharmaceutical industry to control the
particle sizes or size distribution as realized by grinding.
[0007] The invention may further be applied to non-surface
machining, where the mechanical load on a rotating drive varies in
time and is significant for a characteristic to be monitored. This
is the case e.g. in monitoring varying viscosity of a material.
Thus, the invention may also be applied e.g. for monitoring
polymerization endpoint or progress in polymer synthesis.
[0008] In spite of the fact that the present invention may be
applied to a large scale of techniques, we will base the
description primarily on considerations in polishing--thereby in
CMP technique.
[0009] A significant part of yield loss in Ultra-Large-Scale
Integration (ULSI) and Very-Large-Scale-Integration (VLSI)
microelectronics fabrication can be traced to problems associated
with process control. Aggressive shrink of device dimension or
increase of package density, or densely packaged workpieces
becoming larger as in TFT, LCD and similar manufacturing art,
places an increasing demand on process control.
[0010] In situ real-time and closed loop process control is
recognized as a most effective solution for producing in time,
production with high yield and of high quality products. It plays a
critical role in achieving market competitiveness.
[0011] In the field of semiconductor processing CMP was first
introduced as a process to remove and planarize a top layer of
material in context with lithography patterning. It also provides a
reliable way to form interconnects e.g. in copper and to form
Shallow Trench Isolation (STI).
[0012] FIG. 1 shows schematically and simplified a typical
polishing apparatus as applied for CMP. A turntable 1 is rotatably
driven by a motor drive and with a predetermined drive
characteristics, as with a controlled rotational speed .OMEGA.,
around an axis A.sub.1. It carries on its surface a polishing pad
3. A transmission shaft 5 with an axis A.sub.5 parallel to axis
A.sub.1 is, in the embodiment of FIG. 1, arranged eccentrically
with respect to the axis A.sub.1. Transmission shaft 5 is mounted
to a substrate carrier 7 carrying a substrate 9 to be polished. The
transmission shaft 5 and thus substrate 9 is rotated about axis
A.sub.5 with a predetermined controlled drive from a drive motor
(not shown), e.g. at a controlled rotational speed .omega.. Between
polishing tab 3 and waver 9 there is applied a predetermined
controlled force F. For CMP and as schematically shown in FIG. 1
and well known in this art a slurry 11 is dispatched to the surface
of the polishing pad 3. For some applications axis A.sub.5 is
additionally moved toward and from axis A.sub.1 in a controlled
manner.
[0013] In the FIGS. 2A to 2C there is shown a typical application
for CMP realized e.g. by an arrangement as shown in FIG. 1. The
surface S.sub.10 of a workpiece substrate 10 has been patterned
e.g. by applying a photo resist, pattern-development of the resist
and dry etching areas free of photo resist down e.g. to a dry-etch
stop ES. The structured surface S.sub.10 is then coated e.g. by a
vacuum coating process with a material m.sub.1. Thereafter a second
material m.sub.2 is deposited filling the coated structure and
covering the overall surface as shown in FIG. 2A.
[0014] According to FIG. 2B and by means of polishing, especially
of CMP as with the apparatus of FIG. 1, material m.sub.2 is removed
up to reaching a material interface I.sub.1,2 at which material
m.sub.1 transits along distinct areas AE.sub.1,2 into material
m.sub.2. Reaching this interface I.sub.1,2 may be detected. If the
removing process is disabled then the remaining structure is that
shown in FIG. 2B. If additionally the areas AE.sub.m1 of material
m.sub.1 have to be removed, the polishing process is continued up
to reaching the material interface I.sub.1S between material
m.sub.1 and substrate material. Then the removing process is
disabled leading to the remaining structure as shown in FIG.
2C.
[0015] Very often it is crucial to stop the CMP process or more
generically to react by varying parameters of such process at a
selected material along a stack of at least one film on the
substrate. Over-polishing, i.e. excessive removal of material,
leads to device failure and loss of processing yield.
Under-polishing, i.e. insufficient removal of material, requires
that the polishing process be repeated which is tedious and costly
due to significant reduction of production yield. Thus, it is of
high importance to monitor polishing depth, thereby at least
monitoring when polishing reaches a predetermined material
interface.
[0016] Several approaches are known to resolve this problem. A
first approach resides on simple timing. Thereby the process
endpoint, i.e. reaching a predetermined material interface, is
determined just by trial and error. Often over- or under-polishing
occurs due to process parameter drift, changing properties of the
workpiece to be polished etc.
[0017] A second approach resides on measuring the thickness of the
unpolished workpiece, to determine polishing removal rate and to
set processing time according to the removal rate and the desired
removal depth. Due to the fact that frequent adjustment and
readjustment of the polishing time is necessary and removal rate
fluctuation may hardly be monitored during processing, this
approach is far from being satisfactory.
[0018] A further approach is to monitor audio-sound which may
change in a distinct manner at material interfaces. This approach
has not gained industrial applicability.
[0019] In a still further approach polishing pad temperature is
sensed which depends on the heat produced during polishing. This
approach has only found industrial application for some specific
tasks.
[0020] A still further approach is based on induction-sensing
systems, which only work when dealing with electrically conductive
surfaces.
[0021] From the U.S. Pat. Nos. 5,036,015, 5,069,002 and 5,308,438
and further from the U.S. Pat. No. 5,639,388 an approach is known
which is based on monitoring the torque with which e.g. shaft 5 of
the embodiment of FIG. 1 is loaded. Whenever a rotational movement
contributes to the relative movement of workpiece to be polished
and polishing surface the rotating transmission shaft for such
rotation is loaded with a torque which is dependent on the friction
between the instantaneous surface of the workpiece being polished
and the polishing surface. As this friction varies with the
material or materials and with the surface ratio of areas of such
materials, of the workpiece surface being polished, the torque
which is loading such transmission shaft is significant for the
instantaneously prevailing material and/or the ratio of areas of
different materials which simultaneously are exposed to
polishing.
[0022] According to the prior art documents mentioned, torque is
monitored by monitoring the current of an electric motor loaded by
such torque. Monitoring such motor current is of limited accuracy,
especially when materials changing of low friction as e.g. Tungsten
or Titanium Nitride are to be polished, more generically only small
frictional changes during the polishing process. Additionally,
accuracy of this approach is significantly affected by the fact
that small changes or large signals have to be monitored, which
leads to significant Signal to Noise problems.
[0023] Nevertheless, the present invention does reside on the
generic approach of monitoring torque loading of such transmission
shaft, the rotation of which at least contributing to the relative
polishing movement between workpiece to be polished and a polishing
surface.
[0024] Under this aspect there is known from the U.S. Pat. No.
6,213,846 to monitor the angle of torsion along a predetermined
axial extent of such shaft due by the torque loading. Without
teaching how to realize it is proposed to directly mount on or in
the shaft a sensor detecting such deformation. More explicitly this
document teaches to apply coaxial rings of reflective portions
spaced in axial direction at the outer surface of the shaft and to
measure the torque-dependent difference of angle torsion at the
respective axially spaced loci by monitoring phase difference of
laser beam reflection at the portions of the rings.
[0025] This approach suffers nevertheless from a severe drawback.
For each transmission shaft a tedious calibration is required and
very accurate mount of the reflector rings.
[0026] It is an object of the present invention to remedy such
drawback and to propose an improved method for manufacturing a
plate-like workpiece making use of surface polishing. This object
is reached according to the present invention by the method for
manufacturing a workpiece which comprises the steps of
[0027] providing a substrate which has a substantially flat
surface
[0028] removing material from said surface by moving the surface of
the substrate relative to, on and along a polishing surface,
wherein
[0029] the relative moving includes a rotation about an axis by a
selected transmission shaft which is motor-driven in a
predetermined manner;
[0030] there is provided along the transmission shaft a transducer
shaft section which has a predetermined torque to specific torsion
angle characteristic, which characteristic of the section being
independent of torque to torsion angle specific characteristic of
the transmission shaft;
[0031] monitoring a torsion angle at the section as a torque
indicative signal;
[0032] controlling removing in dependency of the torque indicative
signal and
[0033] manufacturing the workpiece from the substrate having
material removed by said removing.
[0034] Definition
[0035] We understand by the term "specific angle of torsion" the
angle of torsion per unit of axial extent of the shaft or shaft
section.
[0036] Thus, the present intention departs from the recognition
that the torque to torsion angle characteristic as exploited in the
U.S. Pat. No. 6,213,846 varies with varying cross-section of the
transmission shaft as well as with the material thereof, further
with operating time of such shaft and respective material fatigue.
This makes in fact calibration necessary for every specific
transmission shaft before processing.
[0037] According to the present invention this problem is resolved
generically by applying along the transmission shaft a preferably
exchangeable shaft section, whereat the addressed characteristic is
independent of the characteristic of the transmission shaft and
thus of its cross-sectional area, of its material and of its
fatigue status. Thereby, it becomes possible to apply one and the
same transducer shaft section to different shafts, e.g. of
different material, different cross-sections and/or fatigue status
without any need of recalibrating for accurate torque monitoring by
torsion angle detection. The addressed transducer shaft section is
tailored on one hand for optimum compromise of angle detection
accuracy and mechanical stability to torque loading and to axial
force loading.
[0038] Although it is possible not to apply to the transmission
shaft the workpiece to be polished but the polishing pad, in a
preferred embodiment the substrate or workpiece to be polished is
carried and rotated by the transducer shaft.
[0039] In spite of the fact that, generically, the manufacturing
method according to the present invention may be applied for
monitoring polishing or, more generically, a material removal
progress, as long as such progress varies the torque loading the
transmission shaft, in a most preferred embodiment the method
according to the present invention is applied where the substrate
has at least one material interface between two different materials
and substantially parallel to the surface of the substrate, whereby
by monitoring the addressed deformation, i.e. angle of torsion, one
monitors when material removing reaches such interface. Thus, a
more generalized "endpoint" detection is realized. Reaching the
interface is detected as endpoint of removing the first material
and as an indication as to where the removal process stands. With
this information removing is controlled dependent on the
application of the polishing process. Removing may e.g. go on, e.g.
transiting from a situation according to FIG. 2B to that of FIG. 2C
after having detected that I.sub.1,2 has been reached. Possibly the
removal process parameters are varied after I.sub.1,2 has been
reached, e.g. relative movement, slurry composition and flow-rate
in CMC processing etc. Nevertheless, in a preferred embodiment when
reaching a material interface is detected the removal process is
disabled.
[0040] In a further most preferred embodiment the
deformation--torsion angle--is monitored by monitoring strain along
the transducer section. Thereby, in a most preferred embodiment
strain is monitored by means of the strain sensor arrangement which
is mounted to the transducer section and which generates an
electric output signal. With an eye on the optical phase-shift
measurements according to the U.S. Pat. No. 6,213,846, providing
according to the present invention a dedicated transducer shaft
section as outlined above, allows providing a sophisticated
electronic sensor arrangement generating directly an electric
output signal to such section, because one and the same transducer
section is most flexibly applicable to different transmission
shafts for different machining requirements.
[0041] Thus, a further most preferred embodiment of the method
according to the present invention is economically feasible, namely
transmitting a signal which is dependent on the output signal of
the sensor arrangement from the rotating transducer section to a
system which is stationary with respect to the transducer section
and thereby performing analogue to digital signal conversion of a
signal dependent on the sensor output signal before performing the
addressed transmission. Thereby, possibly after preamplification,
filtering etc. the analogue output signal of the sensor arrangement
is digitized before the critical signal transmission from moving
shaft to stationary system is performed. Any signal distortion due
to such transmission may easily be restored at the stationary
system side due to the fact that the transmitted signal is
digitalized.
[0042] In a still further preferred embodiment at least a part of
the transmission shaft or possibly the entire transmission shaft is
provided with a hollow inner space. The section is also provided
with a hollow inner space. Both hollow spaces are brought in
communication. A signal which is dependent on the output signal of
the sensor arrangement is led toward the stationary system via the
hollow spaces e.g. by having electrical or optical leads from the
sensor arrangement running along these hollow spaces.
[0043] The same hollow shaft technique is preferably used for
electric power supply to the sensor arrangement, whereby in a less
preferred embodiment it is possible to electrically supply such
sensor arrangement by a battery or accumulator arrangement
integrated into the transducer shaft section or even in a hollow
space within the neighboring transmission shaft.
[0044] In spite of the fact that it is absolutely possible to
transmit a signal which is dependent on the output signal of the
sensor arrangement wirelessly to the system stationary with respect
to the transducer shaft section, it has turned out that in a most
preferred embodiment such signal transmission is performed via a
rotating slide contact arrangement. This is especially true if such
signal to be transmitted has already been digitalized. Thereby,
such slide contact arrangement is further preferably realized with
at least two independent sliding contact arrangements forming
redundant transmission paths for the measuring signal to be
transmitted from rotary to stationary system.
[0045] In view of the fact that the addressed and inventively
applied transducer shaft section has a significantly shorter axial
extent than the transmission shaft and that the transmission shaft
and the transducer shaft section are loaded by the same axial force
F as of FIG. 1 the transducer sections is conceived for high torque
to torsion angle resolution. Bending of this section due to axial
force may be neglected. In a most preferred embodiment the
transducer section has an outer diameter which is smaller than the
outer diameter of the transmission shaft, thereby improving the
addressed resolution.
[0046] Further, in a most preferred embodiment, the workpiece being
manufactured by the method according to the present invention is a
semiconductor workpiece, thereby preferably a Low-Scale or
Ultra-Low-Scale Integrated microelectronic workpiece. Further
preferred, the addressed material removal is performed by CMP,
thereby applying a slurry to the polishing surface.
[0047] A torque transducer module especially suited for realizing
the method of manufacturing according to the present invention
comprises a body which extends along a central axis and which has
two end portions. Each of the end portions is a part of an axial
mount for a respective part to be axially mounted thereto. The
module further comprises a strain gage sensor arrangement with at
least one electric output. The module allows flexible mount to one
end face of the transmission shaft as was described, the other end
portion of the module being mounted to a substrate carrier or
possibly a polishing table. Alternatively, the transducer module
according to the present invention is mounted on both sides to
respective parts of the transmission shaft.
[0048] Due to the fact that a strain gage sensor arrangement with
an electric output is integrated in the module a most compact,
self-contained concept for torque monitoring is provided, which may
flexibly be mounted to rotating shafts for a polishing process
being loaded by a torque which varies in dependency of polishing
conditions as was already explained.
[0049] Preferred embodiments of the torque transducer module
according to the present invention are further claimed in the
claims 17 to 23.
[0050] A mechanical surface machining, especially polishing or
grinding apparatus according to the present invention comprises a
rotatable transmission shaft which is coupled to a drive. It
further comprises a torque transducer module--preferable as has
been addressed above--which module has a body and two end portions.
At least one of the end portions of the transducer module is
mounted to a respective end portion of the transmission shaft. The
module has further a strain gage sensor arrangement with at least
one electric output.
[0051] At the apparatus according to the present invention the
transmission shaft and at least a part of the body of the torque
transducer module are hollow. Electrical leads are provided in and
along the hollow shaft and the hollow body and are operationally
connected to the sensor arrangement. Further preferred embodiments
of the polishing apparatus according to the present invention are
specified in dependent claims 25 to 27.
[0052] The present invention further provides for a method for
monitoring the load presented by a material on a rotating shaft
which is in intimate contact with the material, whereby there is
provided along the shaft a shaft section which has a predetermined
torque/deformation characteristic. The torque/deformation
characteristic of the section is independent of torque/deformation
characteristic of the shaft. Deformation of the shaft section is
monitored as a load indicative signal.
[0053] The present invention under the aspect of method for
manufacturing, torque transducer module and polishing apparatus is
additionally exemplified in the following description with the help
of further figures.
[0054] The further figures show by way of examples:
[0055] FIG. 3 simplified and schematically, the principal of the
present invention, exemplified at a torque transmission shaft
arrangement for polishing;
[0056] FIG. 4 by means of a simplified signal flow/functional block
diagram incorporating a part of the shaft arrangement of the
embodiment according to FIG. 3, signal sensing and exploitation
according to the present invention;
[0057] FIG. 5 still in a simplified and schematic representation, a
cross-sectional view of a transducer module according to the
present invention, mounted to an apparatus according to the present
invention, thereby providing for manufacturing of workpieces
according to the invention or to load monitoring according to the
invention;
[0058] FIG. 6 in a simplified schematic representation in analogy
to that of FIG. 5, a further preferred embodiment of a transducer
module according to the present invention to be mounted to an
apparatus according to the present invention, thereby providing for
manufacturing of workpieces according to the present invention or
to load monitoring according to the invention, and
[0059] FIG. 7 over the time axis torque and torque derivative as
measured with a transducer module according to the present
invention as indicative for reaching subsequently two material
interfaces.
[0060] In FIG. 3 there is shown, most simplified and schematically,
an apparatus according to the present invention incorporating a
torque transducer module according to the present invention and
operating the manufacturing method according to the present
invention. A substrate 30 has a substantially flat surface 32 to be
machined. The substrate is moved relative to a polishing surface
34, as upon a table 1 according to FIG. 1, by rotation .omega.. A
rotational drive is applied to the substrate 30 via a shaft
arrangement 36. A substrate carrier table 38 is mounted to one end
of shaft arrangement 36 and a drive motor M is operationally
coupled to the shaft arrangement 36. There is applied a
predetermined axial force F via the shaft arrangement 36 onto the
substrate 30 for efficient machining i.e. polishing of the surface
32 along polishing surface 34. Thereby, at least a part of force F
may be generated by the weight of shaft arrangement 36 and
substrate carrier 38.
[0061] The shaft arrangement 36 comprises a transmission shaft 39.
In the embodiment of FIG. 3 the shaft 39 is of two parts 39a, 39b
which have been made e.g. by cutting a one-piece shaft 39 in two
parts. Coaxially with transmission shaft 39 a transducer shaft
section 40 is provided, which is preferably removably and
exchangeably mounted to transmission shaft 39 as schematically
shown at the end portions of the transducer shaft section 40, at
41.
[0062] Due to rotation of the surface 32 on and along polishing
surface 34 the shaft arrangement 36 experiences a loading torque T.
This torque T causes, as perfectly known to the skilled artisan,
the shaft arrangement 36 to be twisted by a torsion angle. Per unit
of axial extent, the shaft arrangement is twisted by the specific
torsion angle .phi., which latter is dependent on material, shape
and dimension of the shaft arrangement at an axial locus
considered. If we consider a slice 37 of thickness "1" of the shaft
arrangement 36 at locus x.sub.37, it is the material of this slice
37 and the cross-section shape and dimension of that slice which
govern the angle .phi..sub.39 at a specific value of torque T.
[0063] Assuming that the transmission shaft 39 has a constant
cross-section Q along the axis A.sub.36 and material does not
change along that axis A.sub.36 the transmission shaft 39 has a
characteristic of .phi..sub.39(T), e.g. as qualitatively
exemplified in FIG. 3. The transducer section 40 of shaft
arrangement 36 is conceived to have a .phi..sub.40(T)
characteristic which is independent of the .phi.39(T)
characteristic of the transmission shaft 39.
[0064] Whereas the transmission shaft 39 is conceived for standing
the loading torque T, the axial force F and to provide by its axial
extent L transmission-coupling from drive M to table 38, the
transducer shaft section 40 of significantly smaller axial extent
l<<L has in fact one task, namely to provide for a steep
d.phi..sub.40/dT-slope. It just must stand force F, but its short
extent l results in negligible problems of bending.
[0065] The .phi..sub.40(T) Characteristics at the section 40 is
selectively tailored by respective selection of material and/or
cross-sectional shape. The characteristic .phi..sub.40(T) will not
change when the transducer section, now as a flexibly applicable
module, is applied to different transmission shafts 39 with
different .phi..sub.39(T) characteristics.
[0066] As shown in FIG. 4, still schematically, there is mounted a
sensor arrangement 42 preferably with a commercially available
strain gage on the transducer section 40. It generates an output
signal A.sub.42 which is dependent on specific torsion angle
.phi..sub.40 at section 40. The output signal A.sub.42 is
operationally connected to a control unit 44 which controls
generically the polishing process in dependency of the output
signal A.sub.42.
[0067] As by signal A.sub.42 real-time monitoring of .phi..sub.40
as a torque indicative entity is realized, which torque is
indicative of the instantaneously prevailing characteristic of the
polishing process, the unit 44 may be conceived with a difference
forming unit 45. One input thereof is operationally connected to
the output of sensor arrangement 42, the second to a setting unit
46 for a desired value of angle .phi..sub.40 and thus of torque.
The output of unit 45 is operationally connected to at least one
control input of a unit 48, which adjusts the polishing process.
Unit 48 may comprise at least one of motor drive M, force F
generating unit 48a, slurry composition or flow control unit 48b.
Thus a negative feedback control loop for the polishing process is
realized whereat the signal A.sub.42 is the measured value and the
parameter set at unit 46 is the desired torque-indicative value
.phi..sub.40W(T.sub.W).
[0068] In an open loop control manner, e.g. when A.sub.42 shall
just be indicative of reaching a material interface (endpoint
detection) the control unit 45 disables the polishing process, when
A.sub.42 experiences e.g. a predetermined, preset time derivative
as shown in dashed lines in FIG. 4.
[0069] Although the surface of the substrate to be polished could
possibly be provided instead of polishing surface 34 of FIG. 3, the
polishing surface being provided at table 38, in a most preferred
embodiment and as exemplified in FIG. 3 the substrate 30 to be
treated is mounted to the rotating shaft arrangement 36.
[0070] In FIG. 5 there is shown in a simplified cross-sectional
representation on one hand of a preferred form of realization of
the transducer shaft section as was previously described, but, on
the other hand, realized by a transducer module according to the
present invention and further applied to the transmission shaft of
a polishing apparatus according to the invention. According to FIG.
5 the transducer shaft section is formed by a transducer module 50.
The transducer module 50 comprises a hollow cylindrical base body
52. At both ends the base body 52 has respective end portions 54a
and 54b which respectively form a part of a mount for coaxially
mounting portions of transmission shaft 39 on both sides according
to FIG. 3, or as shown in FIG. 5 a transmission shaft 39 on one
side and a workpiece carrier table 7 according to FIG. 1 to the
other side of module 50. The respective coaxial mounts are
established by screwing, possibly quick connectors, as e.g.
bayonets, as long as such mounts are capable of transmitting the
loading torque T.
[0071] As shown in FIG. 5 the outer diameter .phi..sub.50 of the
main part of cylindrical base body 50 is selected smaller than the
outer diameter .phi..sub.39 of the transmission shaft 39, combined
with a selected material of base body 52, providing for the desired
.phi..sub.50(T) characteristic independent and mostly different
from the characteristic .phi..sub.39(T) of the transmission shaft
39.
[0072] There is provided a recess 56 in the base body 52,
preferably at the outside surface of body 52 and in a most
preferred form, as shown in FIG. 5, defined between the end
portions 54 which latter define for projecting rim portions 58.
[0073] Within recess 56 the sensor arrangement 60 is mounted,
preferably comprising strain gages affixed to the outer cylindrical
surface of base body 52. The electric output signal as
schematically shown at an electric output A.sub.60 of the strain
gage sensor arrangement 60 is operationally connected, possibly via
a filtering and/or preamplifier stage (not shown), to the analogue
input of an analogue to digital converter unit 62. Thus, the
sensing and signal processing electronics are mounted to the base
body 52, as shown in FIG. 5 preferably in an appropriately provided
recess along the outer surface of base body 52. There is further
provided a cover 64 which is, for the embodiment of FIG. 5,
cylindrical and may be slided in axial direction over the recess
56. O-ring seals are preferably provided so as to seal the recess
56 with the sensing electronics therein from industrial
environment.
[0074] The cover 64 is preferably made of a metal shielding
electromagnetic disturbances from the industrial surrounding.
[0075] The output A.sub.62 of the analogue to digital converter
unit 62 is preferably fed through the wall of base body 52 into
hollow inner space 70.sub.52 of body 52. The output signal of the
sensing electronics, preferably in digitized form, is led via a
conductor lead 72 along hollow space 70.sub.52, then along a hollow
space 70.sub.39 of transmission shaft 39 to an end portion 73 of
shaft 39.
[0076] As schematically shown in FIG. 5 shaft arrangement 36 is
driven e.g. via a gear arrangement 74 relative to a stationary
system 76. Signal transmission from lead 72 in the rotary shaft
system to stationary system 76 is preferably performed, as
schematically shown in FIG. 5, via a sliding ring contact
arrangement 78. Thereby, coaxially to axis A.sub.36 contact rings
80 are provided on the rotary system side and contact rings 82,
aligned with rings 80, on the stationary system side. In a
preferred embodiment bridging contact between the rings 80 and 82
is established by conductive balls 84. Lead 72 is connected to one,
preferably and as shown in FIG. 5 to more than one contact ring 80,
and the digitized electrical signal is transmitted via one or
preferably more than one sliding contact to the stationary system
side 76, there to be exploited as has been exemplified
schematically in FIG. 4.
[0077] By the fact that on one hand the analogue output signal of
the sensor arrangement or a signal dependent therefrom is first
converted to digital form, dealing with that signal is
significantly simplified in view of introducing noise and
distortions and allows the addressed transmission of this signal by
friction contact from the dynamic rotary system to the stationary
system. Providing redundancy by at least double-parallel
transmission reduces transmission resistance and additionally
improves uninterrupted signal transmission.
[0078] The electronic in recess 56 is supplied with electric energy
preferably via the arrangement 78 as shown in the figure.
[0079] It must be emphasized that instead of the preferred rolling
contact arrangement, as realized by the balls 84, a mere sliding
system for signal transmission may be provided where contact
between the rims 80 and 82 is established in a sliding rather than
in a rolling manner.
[0080] In FIG. 6 there is shown a further embodiment of a
transducer shaft section or module according to the present
invention. The transducer shaft section 90 comprises a hollow
cylindrical support 92. The base body 94 which is at both end
portions 94a and 94b rigidly mounted to shaft 39--as by screw-bolts
95--defines for a cylindrical recess 96 which is closed towards
hollow space 98 by the support 92. The sensor arrangement 60 is
mounted to the base body 94 within recess 96, wherein there is
further mounted the sensor electronic with the analogue to digital
converter unit 62. The support 82 has in fact only the task of
closing recess 86 towards the hollow space 88 and may contribute to
the support for electronic unit with converter unit 62. It is
supported and sealed by and towards base body 94 at sealing and
fixating areas 91.
[0081] With a transducer module substantially as has been
exemplified with the help of FIG. 5 the signal at lead 72 was
monitored on the stationary system 76. With respect to dimensioning
the following was valid (s. FIG. 5):
[0082] .PHI..sub.50: 26.54 mm
[0083] .PHI..sub.51, inner diameter: 22.54 mm
[0084] Shaft Diameter .PHI..sub.39: 46.99 mm
[0085] Both the shaft 39 as well as the base body 52 of the
transducer module were made from hardened high-grade steel.
[0086] As sensor arrangement, exemplified by reference Nr. 60 in
FIGS. 5 and 6, a metal-film based strain gauge arrangement may be
used, a semiconductor based strain gauge or a piezo-electric strain
gauge. Nevertheless most preferably a Fiber-Optic Bragg Grating
strain gauge arrangement is used. Such strain gauges are
commercially available from Fisco Technologies, Sainte-Foy (Quebec)
Canada and described for application in Application Note, Fisco
Technologies, Doc: APN-FPI-9901 and in J. D. Muhs, "Fiber Optic
Sensors: Providing Cost-Effective Solutions to Industry Needs", Oak
Ridge National Laboratory, US Department of Energy, November
2002.
[0087] The transducer module may further be implemented in the
shaft driving the workpiece to be machined e.g. polished or in the
shaft driving the machining table e.g. with the polishing pad. In a
further embodiment one transducer module is implemented in the
shaft driving the workpiece, one transducer module is implemented
in the shaft driving the machining table.
[0088] The shaft driving the workpiece is rotating or rotatingly
oscillating whereas the machining pad may rotate or may be moved
linearly possibly in an oscillating manner. Further the sensing
arrangement 60 may be mounted to the outer surface of the
transducer module as shown in FIG. 5, or may be mounted to the
inner surface of the transducer module as shown in FIG. 6.
[0089] Still further the signal transmission arrangement--between
rotating system and stationary system as exemplified in FIG. 5--for
signal transmission as well as for supply-power transmission, based
on a contacting ring arrangement, may be realised as a slip-ring
arrangement or as a roll-ring arrangement. As shown in FIG. 5 the
contacting rings may be realised in a plane one inside the other
thus with different diameters or staggered in axial direction
preferably with equal diameters."
[0090] FIG. 7 shows a typical measurement result when a workpiece
was machined by CMP which workpiece provided for two subsequent
material interfaces I.sub.A and I.sub.B. In FIG. 7 the time axis is
scaled in seconds and the signal axis S is scaled in torque
(inch*pounds). Course (a) is directly the torque-dependent signal,
whereas course (b) is its time derivative (see FIG. 4). It may
clearly be seen that the torque (a) is constant up to reaching the
first material interface I.sub.A at time t.sub.IA. Sharp slopes of
torque and its time derivative very accurately indicate reaching
the first material interface I.sub.A.
[0091] Then the torque remains substantially constant up to second
material interface I.sub.B, which is reached at time t.sub.IB. Here
again sharp slopes in torque and its derivative indicate very
accurately reaching the second material interface I.sub.B. Both
torque slopes at the respective material interfaces may accurately
be exploited as machining endpoints.
[0092] As may be seen in FIG. 7 torque was set to be zero at first
surface machining. The rotational speed of polishing was 60
rpm.
[0093] With the method, the module and the apparatus according to
the present invention, it becomes possible to most accurately
monitor the torque applied to a transmission shaft and especially
for most accurate controlling polishing operation, especially CMP.
Due to the exchangeability of the addressed transducer module
calibration efforts are minimized and interruption of a
manufacturing process is minimized. Whenever a transducer module is
recognized causing problems, such module may quickly be
exchanged.
* * * * *