U.S. patent application number 12/330028 was filed with the patent office on 2009-08-27 for apparatus and method for producing microcomponents and use of.
This patent application is currently assigned to R3T GmbH Rapid Reactive Radicals Technology. Invention is credited to Josef MATHUNI.
Application Number | 20090212018 12/330028 |
Document ID | / |
Family ID | 40291145 |
Filed Date | 2009-08-27 |
United States Patent
Application |
20090212018 |
Kind Code |
A1 |
MATHUNI; Josef |
August 27, 2009 |
Apparatus and method for producing microcomponents and use of
Abstract
An apparatus and the use of such an apparatus and method for
producing microcomponents with component structures are presented
which are generated in a process chamber on a substrate according
to the LIGA method for example and are stripped from the enclosing
photoresist with the help of a cooled remote plasma source.
Inventors: |
MATHUNI; Josef; (Munchen,
DE) |
Correspondence
Address: |
BAKER & HOSTETLER LLP
WASHINGTON SQUARE, SUITE 1100, 1050 CONNECTICUT AVE. N.W.
WASHINGTON
DC
20036-5304
US
|
Assignee: |
R3T GmbH Rapid Reactive Radicals
Technology
|
Family ID: |
40291145 |
Appl. No.: |
12/330028 |
Filed: |
December 8, 2008 |
Current U.S.
Class: |
216/69 ;
156/345.27; 156/345.37; 156/345.41; 156/345.51 |
Current CPC
Class: |
H01J 37/32357 20130101;
B81C 2201/032 20130101; B81C 99/0085 20130101 |
Class at
Publication: |
216/69 ;
156/345.41; 156/345.37; 156/345.51; 156/345.27 |
International
Class: |
B44C 1/22 20060101
B44C001/22 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 12, 2007 |
DE |
102007059717.9 |
Claims
1. A method for producing microcomponents with component structures
which are produced on a substrate by using the LIGA method for
example, with the microcomponents being stripped in an etching
chamber from photoresist based on epoxy resin, characterized in
that the photoresist is stripped in a controlled manner with a
cooled remote plasma source by chemical etching through increased
density of the radicals, with the temperatures of the
microcomponents being monitored individually and the temperature
curves being subjected to an individual recognition of the end
point.
2. A method according to claim 1, wherein the individual
temperature measurement is made in real time via thermal sensors
which are in mechanical contact via a thermostatized work plate
distributed beneath the positions of the microcomponents either
with the substrate itself or with a substrate holder on which the
substrate is disposed.
3. A method according to claim 1, wherein the substrate is pressed
in a planar manner with the help of a contact means such as wax for
example against the substrate holder which rests in a planar way on
the thermostatized work plate (3) and is severed again after the
end of the stripping process, through which the reaction heat is
dissipated during the stripping process from the substrate to the
substrate holder and from there via its bottom side to the
thermostatized work plate, so that the substrate is not damaged as
a result of the thermal and mechanical loading.
4. A method according to claim 1, wherein the individually
transmitted temperature curves are used as evaluation criteria for
individually recognizing the end point, with the temperature rising
with the start of the stripping process from an initial temperature
as a result of reaction heat following the reaction of the
photoresist with the radicals to an equilibrium temperature and
remaining stable as long as the reaction occurs and decreasing with
the end of the stripping process to an end temperature, through
which the recognition of the end point is linked to the decreasing
flank of the temperature curve.
5. A method according to claim 1, wherein the density of the
radicals in the plasma is increased with the help of an external
microwave source for promoting a higher stripping rate of the
photoresist.
6. A method according to claim 1, wherein an external plasma
chamber for providing the remote plasma for the benefit of lower
thermal loading of the microcomponents disposed in an etching
chamber is cooled with a coolant, through which the microcomponents
already stripped of photoresist can easily remain in the etching
chamber until the end of all stripping processes is recognized on
the basis of the individually transmitted temperature curves and
the etching process is thus terminated in due time.
7. A method according to claim 1, wherein the individual end point
recognition signalizes the end of each stripping process via a
display of a monitoring device, so that the respectively finished
stripped microcomponent can optionally be removed from the etching
chamber.
8. An apparatus for producing microcomponents with component
structures according to the method according to claim 1, wherein a
microwave source is arranged for increasing the density of the
radicals outside of the etching chamber.
9. An apparatus according to claim 8, wherein a plasma chamber
which is cooled with a coolant is arranged outside of the etching
chamber.
10. An apparatus claim 8, wherein a substrate is connected in a
planar way with a substrate holder via a contact means such as via
wax for example and is detachable again after the stripping
process.
11. An apparatus according to claim 8, wherein at least one thermal
sensor is arranged in the thermostatized work plate beneath the
positions of the microcomponents either underneath a substrate or
underneath a substrate holder on which the substrate is
disposed.
12. An apparatus according to claim 1, wherein a monitoring device
displays the temperature curves transmitted individually by the
thermal sensors and individually monitors and signalizes the end
points of the stripping processes.
13. The use of an apparatus according to claim 8 for producing
microcomponents with component structures by using the LIGA method
for example, characterized in that a cooled remote plasma source
with a high density of the radicals is used for stripping
photoresist for microcomponents.
Description
BACKGROUND OF THE INVENTION
[0001] The invention relates to an apparatus for producing
microcomponents with component structures which are generated in a
process chamber on a substrate according to the LIGA method. The
invention further relates to a method for producing microcomponents
with component structures in which the microcomponents are
generated in provided substrates and thereafter are relieved from
the enclosing material sections, such that the material sections
can be etched away (stripped). The invention further relates to the
use of such an apparatus and method for stripping or removing the
material sections enclosing the microcomponents.
[0002] Apparatuses and methods of this kind with which
microcomponents are produced for the clock industry are well known
from the state of the art. Methods are frequently used here which
are based on a combination of lithography and electroplating. These
methods are generally well known as LIGA methods. In such a "LIGA"
method, a photoresist can be applied at first to a substrate such
as a wafer or the like. A negative resist with the designation SU-8
can be used as a photoresist.
[0003] The substrate can concern a silicon wafer for example which
comprises a thin gold layer on its surface on which microcomponents
can grow especially well. The photoresist is applied to this
silicon wafer. It especially covers the gold layer and can be
exposed there selectively by means of a suitable exposure system
and a mask. The unexposed places of the photoresist layer are
removed in a subsequent development step.
[0004] In a subsequent electroplating process, a metal such as
nickel or gold can be allowed to grow on the thus prepared
substrate surface, with the respective metal beginning to grow on
the places stripped of the photoresist layer. Depending on the
intended application, growth can be stopped when the grown metal
structure grows slightly beyond the photoresist layer.
[0005] Photoresist SU-8 comes with the disadvantage that the
removal of the cross-linked SU-8 structures between metal
structures deposited by electroplating is currently very complex.
SU-8 is based on epoxy resin which in the cross-linked state is
very stable against organic and inorganic etchants. Photoresist is
removed by means of currently known etchants either very slowly or
in such a way that the metallic microcomponents are also attacked
and thus become useless.
[0006] Mechanical removal of the photoresist from the
microcomponent is not only laborious and cost-intensive, but also
causes a high rejection rate due to the extremely small dimensions
of the microcomponents. Some complex structural shapes cannot even
be produced at all under these conditions.
[0007] Conventional plasma methods progress on the one hand very
slowly and on the other hand the metal is attacked by ions and
electrons. The etching process needs to be interrupted frequently
because the substrates otherwise will become too hot.
[0008] In previous methods, the end of the stripping process, i.e.
the removal of the photoresist, is determined on the basis of
integral temperature measurement by means of emission spectroscopy,
which entails very high costs. When photoresist is removed in an
etching chamber in batch operations from several microcomponents on
the respective substrates, it was only possible to date to
recognize the start of the etching process by means of a rise in
the integral process temperature and the global end of the etching
process by means of the drop in the integral process temperature.
It was not possible to individually monitor the individual
substrates which may have differently thick layers of photoresist
and thus require differently long stripping periods. It was further
not possible to recognize in time whether an individual substrate
will become too hot due to a bad contact to the substrate holder
for example which rests on a work plate and will thus be
damaged.
[0009] WO 2004/104704 A2 discloses a lithographic method for
producing microcomponents. It is tried to form etching chambers in
a constructional way, through which removal of SU-8 is facilitated.
Several intermediate steps are added as a result of additional
bonding layers, support structures, masks and exposure steps,
through which construction and production of the microcomponents
becomes more laborious.
SUMMARY OF THE INVENTION
[0010] From all the aforementioned disadvantages of the state of
the art, the invention is based on the object of ensuring that the
photoresist is to be stripped as easily, efficiently and reliably
as possible, so that rejects are minimized.
[0011] The simplicity of production shall be achieved by utilizing
and combining already existing techniques and systems with as few
as possible, but effective additional steps. Efficiency of
production shall be raised by the possibility of simultaneous
treatment of several substrates in an etching chamber and by
reducing the stripping duration through an increased removal rate
of the photoresist. The reliability of the production and thus the
reduction in the number of the damaged microcomponents shall be
implemented with the help of individual temperature monitoring and
lowering the substrate temperature and by avoiding aggressive
etchants.
[0012] The object of the invention is achieved in respect of its
method in such a way that the photo-resist is stripped with the
help of a cooled remote plasma source by chemical etching due to
the increased density of the radicals, with the temperature of the
microcomponents being monitored individually and the progression of
the temperature being subjected to the recognition of an end
point.
[0013] The use of a remote plasma source for stripping photoresist
offers the advantage that no ions or electrons will reach the
substrate and place a thermal load on the same. The radicals strip
the photoresist through pure chemical etching. The density of
radicals is increased by using a microwave source such as the one
from R3T GmbH. A suitable apparatus by means of which the etching
process as explained above can be performed especially well is
described in the patent specification DE 198 47 848 C1. The
apparatus described there comprises a generator for generating
electromagnetic waves such as a microwave generator. The
electromagnetic waves can be used to form excited and/or ionized
particles in a plasma zone. At least the excited particles are
conveyed by means of a suitable feed line to the etching chamber in
order to trigger there the desired etching process on the surfaces
of the substrates. Since the plasma chamber of the source is cooled
with a coolant such as water, a cooled beam of radical particles of
high radical density is introduced for stripping into the etching
chamber, through which a high removal rate is achieved which rises
with the density of the radicals on the one hand, and the thermal
loading of the substrates, apart from the unavoidable reaction
heat, is minimized on the other hand.
[0014] For an especially advantageous embodiment of the invention,
thermal sensors are distributed over the entire work area for
individually checking the local substrate temperatures. They are
held in a resilient manner in the work plate, so that a mechanical
and thus thermal contact is ensured with the bottom side of a
substrate holder on which the substrate is located. It is
understood that the substrate can also be placed directly on the
work plate, and in this case the thermal sensors would have direct
contact with the bottom side of the substrate. It has been seen
that as a result of the temperature data measured in real time,
especially on each of the substrates, it is possible to draw
precise conclusions on the progress of the etching process,
advantageously on each of the substrates.
[0015] The term "substrate" describes any structure which can be
used as a carrier on which the microstructures can grow. Widely
used as silicon wafers which can be provided with a thin gold
layer, with said gold layer being used as a starting layer from
which the microstructures will grow. In the present connection, the
term wafer shall generally be used synonymously for the term
"substrate".
[0016] "Substrate holders" shall mean such structures which can
produce contact between the substrates and the work plate. A
substrate is applied to their upper side by means of a contact
means and the work plate is located on its bottom side. It is
ensured that heat from the substrates which become hot as a result
of reaction heat is forwarded via the contact means to the
substrate holder and from there to the work plate. Furthermore, a
substrate holder is used for horizontally planar positioning of a
substrate in an etching chamber.
[0017] Any devices are suitable as a "work plate" on which the
provided substrates can be arranged either with or with a substrate
holder within the etching chamber. Ideally, a cooling medium flows
through the work plate in order to thus enable the removal of the
process heat from the etching chamber.
[0018] The term "etching chamber" describes any device in which the
production of microstructures can be made. In such a chamber, a
photoresist layer can be removed from a substrate surface and/or a
microstructure surface for example.
[0019] The term "contact means" describes any means which is
suitable of improving the contact between the provided substrates
and the substrate holders, so that temperature differences between
the provided substrates and the work plate can be compensated in a
better way than without such contact means. It is understood that
such contact means can be realized in many ways as long as an
especially intimate contact is produced between the substrate and
the substrate holder.
[0020] In accordance with the invention, these contact means
provide a substantially better contact between the provided
substrates and the substrate holders, so that critical thermal
energy present in the substrates and/or the microstructures can be
dissipated in a substantially better way into the work plate, thus
considerably reducing a thermal loading of the substrates, and the
microstructures in particular, in an advantageous manner. The
likelihood is reduced or ideally excluded that the microstructures
to be produced are damaged or even rendered useless as a result of
critical temperature conditions.
[0021] When the contact means comprise wax, it is possible to
produce a very intensive contact between the provided substrates
and substrate holders by means of the wax in an especially simple
constructional way. Moreover, the wax can be removed easily from
the substrates or the microstructures that have grown thereon when
an etching process has been completed for example and the
microstructures are to be relieved of further impurities.
[0022] Wax as a contact means allows compensating in a very
effective way for very small uneven portions on the bottom side of
the substrate and/or the upper side of the substrate holder caused
by possible production faults or undesirable particles, so that the
substrate is aligned in an horizontally planar way and is thus
provided with optimal contact to the substrate holder and thus to
the work plate, thus producing a favorable thermal contact for heat
dissipation.
[0023] It is further especially advantageous to use the
individually transmitted temperature curves as evaluation criteria
for individual recognition of the end points. The transmitted
temperatures rise at the beginning of the stripping process from a
starting temperature such as the temperature of the work plate to
the respective temperature maximum as a result of reaction heat and
remain stable as long as the reaction progresses. With the end of
the stripping process, the temperatures start to decrease rapidly.
The start, middle, end or other suitable places of the decreasing
flank of the individual temperature curve is recognized as the
individual end point of the stripping process.
[0024] Ideally, a monitoring device which can be a computer or the
like for example and displays and monitors the temperatures
individually sent by the thermal sensors signalizes the end of the
stripping process either acoustically and/or visually, so that the
operator optionally removes the finished stripped microcomponent
from the etching chamber or waits until further microcomponents
have been completely stripped.
[0025] It would also be possible to arrange the monitoring device
in such a way that the stripping process is controlled
automatically.
[0026] The object of the invention is achieved by means of the
apparatus in such a way that a microwave source is arranged outside
of the etching chamber to increase the density of the radicals.
[0027] The arrangement of a plasma chamber outside of the etching
chamber is further advantageous. Ideally, said plasma chamber is
cooled with a cooling medium. Water or other agents are considered
as cooling medium for example which are able to dissipate heat from
the plasma chamber.
[0028] A remote plasma method can preferably be used in this
connection in which the plasma is generated advantageously outside
of an etching chamber and ideally no ions and/or electrons reach a
substrate within the etching chamber. The substrate is
advantageously not additionally thermally loaded by these ions or
electrons. In particular, an already cooled radical particle beam
with a density of radicals can be provided favorably especially
with the apparatus as described above from the patent specification
DE 198 47 848 C1.
[0029] The arrangement of the spring-supported thermal sensors in
the work place beneath the substrate positions is especially
advantageous. The thermal sensors have contact with the bottom side
of the substrate holder or with the bottom side of the substrate
when no substrate holders are used. Ideally, a spring-supported
thermal sensor is associated with each employed substrate or
substrate holder. Individual temperature measurement and monitoring
of each substrate in real time are thus ensured.
[0030] Ideally, a monitoring device will be used which will
individually display the temperatures in real time determined by
the thermal sensors and will monitor them by means of suitable
criteria. The monitoring comprises the determination of the end
points and signaling the termination of the stripping processes. It
shall further be monitored whether a stripping process will run
according to a pre-determined scheme. If malfunctions occur such as
the overheating of a substrate, the monitoring device will
signalize this malfunction and will initiate suitable measures so
that the substrate will not be damaged.
[0031] The arrangement of a monitoring device at a location which
need not necessarily be close to the plasma chamber is further
advantageous. The operator can conveniently observe the stripping
process in real time from his/her office. When a completed
stripping process is signalized via the monitoring device, the
operator can decide whether or not this completed microcomponent is
removed from the etching chamber.
[0032] As a result of the advantages explained above, the
application of the described apparatus and method is well-suited
for stripping photoresist for microcomponents with component
structures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] The invention is explained below in closer detail by
reference to an embodiment shown in the drawings, which show
schematically:
[0034] FIG. 1 shows a sectional enlarged view of a microcomponent
on a substrate produced according to the LIGA method;
[0035] FIG. 2 shows a sectional view of an apparatus for producing
microcomponents;
[0036] FIG. 3 shows a detailed view of the work plate of FIG. 2,
and
[0037] FIG. 4 shows an exemplary visualization of three temperature
curves of three substrates.
DETAILED DESCRIPTION
[0038] FIG. 1 shows a microcomponent on a substrate 14 produced
according to the LIGA method. Photoresist 1 encloses the metal 2
which was electroplated to a gold layer 3 which is used as a
starter layer.
[0039] The apparatus 10 for producing microstructures (not shown
here) as shown in FIG. 2 comprises an etching chamber 12 in which a
thermostatized work plate 13 is arranged.
[0040] A microwave source 18 is arranged outside of the etching
chamber 12. Furthermore, a water-cooled plasma chamber 11 is shown
which is also located outside of the etching chamber 12. The
microwave source 18 can be used to produce cooled remote plasma 19
in the water-cooled plasma chamber 11. A detailed description of
how the present remote plasma process works in detail shall be
omitted in this case because the remote plasma process concerns a
well-known method. A respectively suitable apparatus and
respectively suitable methods are also described in detail in the
initially mentioned patent specification DE 198 47 848 C1.
[0041] In the present case, the generated remote plasma 19 is
advantageously already cooled by means of the water-cooled plasma
chamber 11, so that in this way an advantageous reduction in
temperature can already be realized concerning the etching process
yet to be explained.
[0042] The present remote plasma method can be controlled by means
of the apparatus 10 shown here in such a way that a cooled radical
particle beam 20 will reach the etching chamber 12 with an
especially high density of radicals.
[0043] As is also mainly shown in the illustration according to
FIG. 3, substrates 14 are arranged on a thermostatized work plate
13. In the sectional views of this specific embodiment, two
substrates 14 are placed by means of two substrate holders 15 on
the work plate 13. Reaction heat which is produced during an
etching process for example in which areas of material (not shown
here) such as the photoresist layer SU-8 are etched away from the
substrates 14 can be dissipated away from the substrates 14 in an
especially advantageous manner. This dissipation of the reaction
heat is achieved especially well when the two substrate holders 15
are made of thermally well-conducting material. To ensure that the
heat transmission can be achieved over the full surface area from
the illustrated substrates 14 to the substrate holders 15, a
contact means 16 (see FIG. 3 in particular) is each arranged
between the substrates 14 and the respective substrate holders 15.
These layers of contact means are also used for horizontally planar
positioning of the substrates 14 on the substrate holders 15 in the
etching chamber 12. The contact means 16 in this embodiment is made
of wax.
[0044] The wax layers are used to position the substrates 14 in a
fixed but detachable way and individually above the respective
substrate holders 15. Both the wax layers as well as the substrate
holders 15 especially represent means within the terms of the
invention for placing in a planar way the provided substrates 14 on
the thermostatized work plate 13.
[0045] The wax layers ensure very advantageously that the already
mentioned reaction heat is dissipated from the substrates 14 and
thus also from the microstructures (not shown here explicitly) to
be produced, so that especially the microstructures are also
thermally loaded in a lesser way, as a result of which the
rejection of microstructures can be reduced advantageously.
[0046] Moreover, spring-supported thermal sensors 17 are provided
in the thermostatized work plate 13 which can be used to detect the
current temperatures directly on the substrate holders 15.
[0047] This ensures advantageously to realize a monitoring of the
actually existing temperatures directly on the substrate holders 15
and thus also on the substrates 14 and the respective
microstructures.
[0048] A thermal sensor 17 is preferably associated with each
substrate holder 15 and each substrate 14 which is arranged on the
work plate 13. It can thus reliably and permanently be ensured that
each of the existing thermal sensors 17 is in operative contact
with the associated substrate holder 15.
[0049] When the thermal sensors 17 are held in a resilient or
spring-supported manner, as shown in FIG. 3, it can be ensured
especially well that the thermal sensors 17 are always pressed with
sufficient force against the substrate holders 15.
[0050] Since there is a direct connection between the temperatures
applied to the substrates 14 and the presence of photoresist that
still needs to be etched away, it is possible to draw conclusions
on the basis of the determined temperature data on how far the
etching process has already progressed on one of the substrates 14,
as already described above. In particular, due to a rapidly falling
temperature during the etching process it is possible to recognize
whether an etching process has already finished on one of the
substrates 14 because no reaction heat is then produced on this
substrate.
[0051] In order to enable a respective evaluation of the
temperature data detected by means of the thermal sensors 17 it is
advantageous when the present apparatus 10 comprises a suitable
monitoring device which offers the possibility for visualizing the
detected temperature data by means of display means 24.
[0052] The present example visually shows in the display means 24 a
first temperature curve 21 of a substrate 14, a second temperature
curve 22 of another substrate 14 and a third temperature curve 23
of a third substrate (not shown here).
[0053] The temperature curves 21, 22 and 23 show the respective
temperatures on the respective substrates 14 over a specific period
of time. It is described on the basis of the first temperature
curve 21 in which phase the first substrate 14 is located. At the
beginning of the etching process, the substrate 14 on which the
first spring-supported thermal sensor 17 is arranged has an initial
temperature 21a which is close to the temperature of the
thermostatized work plate. With the start of the stripping process,
the temperature on the substrate 14 rises to an equilibrium
temperature 21b. The equilibrium temperature will occur when the
temperature gradient occurring towards the work plate 13 is
dissipating the reaction heat from the substrate 14. The
equilibrium temperature remains virtually constant as long as the
stripping process occurs in this substrate 14. Once the substrate
14 has been stripped of photoresist, the temperature will start to
drop. The start, middle, end or other suitable places of the
decreasing flank of the temperature curve can be recognized as the
end point of the stripping process 21c. The possibility for setting
an optimal etching duration is given by suitable setting of the end
point recognition.
[0054] The present apparatus can be used to display different
temperatures and different temperature curves 21, 22, 23 in
connection with each of the substrates 14, so that an evaluation of
the respectively occurring etching process on the respective
substrate 14 can be made rapidly and securely. Reasons for the
different temperature curves can be differently running reactions
on the respective substrate 14 which may indicate differently thick
layers of resist.
* * * * *