U.S. patent application number 11/384562 was filed with the patent office on 2007-09-20 for manufacturing optical elements.
This patent application is currently assigned to HEPTAGON OY. Invention is credited to Stephan Heimgartner, Markus Rossi, Hartmut Rudmann, Susanne Westenhofer.
Application Number | 20070216048 11/384562 |
Document ID | / |
Family ID | 38066646 |
Filed Date | 2007-09-20 |
United States Patent
Application |
20070216048 |
Kind Code |
A1 |
Rudmann; Hartmut ; et
al. |
September 20, 2007 |
Manufacturing optical elements
Abstract
A method of manufacturing an element using a replication tool,
including the steps of providing a replication tool that defines
the shape of the element; providing a substrate; pressing the tool
against the substrate, with a replication material located between
the tool and the substrate; confining the replication material to a
predetermined area of the substrate, which predetermined area
exceeds the desired area of the element on covering the substrate,
in at least one direction along the surface of the substrate by
less than a predetermined distance.; hardening (e.g. curing) the
replication material to form the element.
Inventors: |
Rudmann; Hartmut;
(Unterlunkhofen, CH) ; Heimgartner; Stephan;
(Luzern, CH) ; Westenhofer; Susanne; (Wettswil,
CH) ; Rossi; Markus; (Jona, CH) |
Correspondence
Address: |
RANKIN, HILL, PORTER & CLARK LLP
4080 ERIE STREET
WILLOUGHBY
OH
44094-7836
US
|
Assignee: |
HEPTAGON OY
Espoo
FI
|
Family ID: |
38066646 |
Appl. No.: |
11/384562 |
Filed: |
March 20, 2006 |
Current U.S.
Class: |
264/1.7 ;
425/174.4; 425/385 |
Current CPC
Class: |
B29L 2011/0016 20130101;
Y10S 425/808 20130101; B29C 43/021 20130101; B29C 2043/3652
20130101; B29D 11/00365 20130101; B29D 11/00307 20130101; B29C
43/36 20130101 |
Class at
Publication: |
264/001.7 ;
425/174.4; 425/385 |
International
Class: |
B29D 11/00 20060101
B29D011/00 |
Claims
1. A method of manufacturing an element by means of a replication
tool, comprising the steps of: providing a replication tool that
defines the shape of the element; providing a substrate; pressing
the replication tool against the substrate, with a replication
material in a liquid or viscous or plastically deformable state
located between the replication tool and the substrate; confining
the replication material to a predetermined area of the substrate,
which predetermined area exceeds a desired area of the element on
the substrate, in at least one direction along a surface of the
substrate by less than a predetermined distance; hardening the
replication material to form the element.
2. The method of claim 1, wherein the replication tool comprises a
plurality of sections each defining an element to be replicated,
the method comprising the further step of: applying a volume of
replication material locally and individually, at a lateral
position of each section, to at least one of the replication tool
and the substrate prior to pressing the replication tool against
the substrate.
3. The method of claim 2, wherein the replication tool is chosen to
comprise a plurality of cavities each defining the shape of one
element or a group of elements, each cavity being limited, at least
in one lateral direction, by a flat section, an inner edge being
formed between the cavity and the flat section, the replication
tool further comprising at least one overflow volume and an outer
edge between the flat section and the overflow volume, and wherein
said volume of replication material is larger than a volume of the
cavity.
4. The method of claim 3, wherein the flat section is asymmetrical
with respect to a central axis of the element or group of
elements.
5. The method of claim 2, comprising the further steps of confining
flow of the replication material towards at least one side of the
replication tool by a spacer that touches the substrate; and
enabling the flow of the replication material towards another side
of the replication tool by an overflow channel.
6. The method of claim 1, comprising the further step of
controlling flow of the replication material by at least one of
capillary forces and of surface tension.
7. The method of claim 6, comprising the further step of applying a
pre-determined volume of replication material, and limiting flow of
the replication material by at least one of capillary forces and
surface tension acting at a discontinuity of the replication
tool.
8. The method of claim 7, wherein a cavity in the replication tool
defines the shape of the element and includes a buffer volume along
at least one side of the element, which buffer volume is separated
from an element volume by an inner edge, wherein the pre-determined
volume of replication material is smaller than a volume of the
cavity, and wherein the method comprises the further step of
limiting the flow of the replication material into the buffer
volume by at least one of capillary forces or surface tension
acting at the inner edge.
9. The method of claim 2, wherein the replication tool is chosen to
comprise a plurality of cavities each defining the shape of one
element or a group of elements, comprising the further step of when
pressing the replication tool against the substrate, an inclined
spacer displaces the replication material towards one of said
cavities.
10. A replication tool for replicating an element from a
replication material, the replication tool comprising a replication
side, a plurality of cavities on the replication side, each
defining the shape of one element or a group of elements, the
replication tool further comprising at least one spacer portion,
protruding, on the replication side, from the cavities, and further
comprising means for confining the replication material to a
predetermined area of the tool, when the tool is pressed against a
substrate, which predetermined area exceeds a desired volume of the
element in at least one direction along the surface of the
substrate by less than a predetermined distance.
11. The replication tool of claim 10, the cavity comprising an
element volume and a further volume at a periphery of the element
volume, boundaries of the further volume comprising discontinuities
for selectively controlling flow of the replication material by
means of at least one of capillary forces and of surface
tension.
12. The replication tool of claim 11, comprising an edge
dimensioned to stop the flow of the replication material at one
side of the cavity; and an overflow channel enabling the flow of
the replication material towards another side of the cavity.
13. The replication tool of claim 10, each cavity being limited, at
least in one lateral direction, by a flat section serving as the
spacer portion, an inner edge between the cavity and the flat
section, an overflow volume and an outer edge between the flat
section and the overflow volume.
14. The replication tool of claim 10, further comprising a buffer
volume at at least one side of an element volume defined by at
least one of said cavities, the buffer volume and the element
volume defining, at their common boundary, an inner edge for
inhibiting the flow of the replication material into the buffer
volume.
15. The replication tool of claim 14, comprising further edges in
the surface of the buffer volume for inhibiting the flow of the
replication material into the buffer volume.
16. The replication tool of claim 10, further comprising an
inclined spacer at at least one side of at least one of said
cavities.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention is in the field of manufacturing miniature
optical or mechanical elements, in particular refractive optical
elements or diffractive micro-optical elements, by means of a
replication process that includes embossing or molding steps. More
concretely, it deals with a method of replicating an optical
element and a replication tool therefore.
[0003] 2. Description of the Related Art
[0004] Replicated optical elements include diffractive and/or
refractive micro-optical elements for influencing an optical beam
in any pre-defined manner, refractive elements such as lenses,
potentially at least partially reflecting elements etc.
[0005] When optical elements are produced by replication, there is
often a basic configuration involving a substrate and replication
material on a surface thereof, which replication material is shaped
and hardened in the course of a replication process. Often, the
dimension perpendicular to the named substrate surface, the
thickness or height of the replicated structures, also termed
z-dimension, is important and must be well-defined and controlled.
Since the other dimensions of the element are defined by the
replication tool, this being the nature of the replication process,
the volume of the replicated element is alsowell defined. However,
small volumes of dispensed liquid or viscous material are generally
difficult and costly to control. Since elements that are only
partially filled are defective and lost, it is therefore
advantageous to dispense excess replication material. By this, one
makes sure that also for replication material volumes that
fluctuate between different elements, no or only few elements are
lost.
[0006] Of special interest are the wafer-scale fabrication
processes, where an array of optical elements is fabricated on a
disk-like ("wafer-") structure, which subsequently to replication
is separated ("diced") into the individual elements or stacked on
other wafer-like elements, and after stacking separated into the
individual elements, as for example described in WO 2005/083 789.
`Wafer scale` refers to the size of disk like or plate like
substrates of sizes comparable to semiconductor wafers, such as
disks having diameters between 2 in. (5.08 cm.) and 12 in. (30.48
cm.) In conventional wafer-scale replication processes, replication
material for the entire, wafer-scale replica is disposed on the
substrate in a single blob. However, there might be areas sideward
of the element where replication material is not wanted in later
replication steps. In certain applications, the fabricated elements
must, for example, be used in combination with other elements, and
the residual material will impair the function of the combined
structure. In a co-pending application "Method and Tool for
Manufacturing Optical Elements" by the same inventors and filed on
the same day as the present application, an array replication
method is disclosed according to which for every optical element or
sub-group of optical elements to be created, a blob of replication
material is dispensed in an array like manner, either on the
substrate or on the tool.
[0007] In such an array replication process, excess material will
ooze out sideward from the element volume. For example, miniature
optical lenses may be replicated above the surface of a wafer
carrying semiconductor chips each embodying a CCD or CMOS-camera
sensor array. The residual material, if it covers critical areas,
may interfere with further processing steps of the stack comprising
the semiconductor wafer and the lenses, e.g. bonding.
[0008] WO 2004/068198, by the same applicant, herewith incorporated
by reference in its entirety, describes a replication process for
creating micro-optical elements. A structured (or micro-structured)
element is manufactured by replicating/shaping (molding or
embossing or the like) a 3D structure in a preliminary product
using a replication tool. The replication tool comprises a spacer
portion protruding from a replication surface. A replicated
micro-optical element is referred to as replica.
[0009] The spacer portions allow for an automated and accurate
thickness control of the deformable material on the substrate. They
may comprise "leg like" structures built into the tool. In
addition, the spacers prevent the deformation of the micro optical
topography since the spacers protrude further than the highest
structural features on a tool.
[0010] The spacer portion is preferably available in a manner that
is `distributed` over at least an essential fraction of the
replication tool, for example over the entire replication tool or
at the edge. This means that features of the spacer portion are
present in an essential fraction of the replication tool, for
example, the spacer portion consists of a plurality of spacers
distributed over the replication surface of the replication tool.
The spacers allow for an automated and accurate thickness control
of the replication material layer.
[0011] The replication process may be an embossing process, where
the plastically deformable or viscous or liquid replication
material for the product to be shaped is placed on a surface of a
substrate, which can have any size. In the embossing step, the
spacer portions abut against the top surface of the substrate. This
surface, thus, serves as a stop face for the embossing.
[0012] For these reasons, the replication process described in WO
2004/068198 is one particularly advantageous possibility of
controlling the thickness (height, z-dimension) of the replicated
elements. Other ways of controlling the z-dimension include
measuring the distance between a tool plane and a substrate plane
and actively adjusting this distance at different places by a
robot.
[0013] For the reasons stated above, the embossing step causes
residual material to remain in the areas between the elements, and,
for example, also around the periphery of each of the elements. If
the replication tool comprises a spacer portion, this may also be
true for the spacer area surrounding an element.
BRIEF SUMMARY OF THE INVENTION
[0014] It is therefore an object of the invention to create a
method of replicating an element and a replication tool of the type
mentioned initially, which overcomes the disadvantages mentioned
above.
[0015] According to a first aspect of the invention, a method of
manufacturing an element by means of a replication tool is
provided, the method comprising the steps of: [0016] providing a
replication tool that defines the shape of the element; [0017]
providing a substrate; [0018] pressing the tool and the substrate
against each other, with a replication material in a liquid or
viscous or plastically deformable state located between the tool
and the substrate; [0019] confining the replication material to a
predetermined area of the substrate, which predetermined area
exceeds the desired area of the element on the substrate, in at
least one direction along the surface of the substrate by less than
a predetermined distance; [0020] hardening the replication material
to form the element.
[0021] The replication material is confined between the tool and
the surface of the substrate. By confining the replication material
to only part of the substrate surface, the resulting element will,
after hardening by e.g. curing, only cover part of the substrate.
The element will not extend to cover the substrate in predetermined
areas, leaving them free for e.g. bonding.
[0022] The replication tool may comprise a spacer portion. In such
a tool, at least one cavity of the tool defines a replication
surface with negative structural features, being a negative of at
least some of the structural features of the element to be
produced. The cavity contains the element volume and may
additionally comprise at least one buffer and/or overflow volume.
The spacer or spacer portions protrude from the replication
surface. In the embossing process, the spacer or spacer portions
abut against the substrate and/or float on a thin basis layer of
replication material.
[0023] The force by which the tool and the substrate are pressed
against each other may be chosen based on specific requirements.
For example, the force may be just the weight of the replication
tool lying, by way of spacer portions abutting the substrate
surface and/or floating on a thin basis layer of replication
material, on the substrate. Alternatively, the substrate may lie on
the replication tool. The force may, according to yet another
alternative, be higher or lower than the weight and may, for
example, be applied by a mask aligner or similar device which
controls the distance of the substrate and the replication tool
during the replication process.
[0024] Before the replication tool and the substrate are brought
together for the embossing process, replication material in a
liquid or viscous or plastically deformable state is placed on the
replication tool and/or the substrate. The replication tool may
comprise a plurality of sections each defining an element to be
replicated. Then, preferably the method comprises applying a
(possibly pre-defined) volume of replication material locally and
individually, at laterally displaced positions, each position
corresponding to one section, to at least one of the tool and the
substrate prior to pressing the tool against the substrate. This
allows providing a plurality of cavities, each corresponding to an
optical element, with an optimal amount of replication material. By
this, the volume of surplus replication material that must be
removed or diverted from the critical areas is reduced or
eliminated, as compared to the case where a plurality of elements
would be formed from a single blob of replication material.
[0025] While the replication tool and the substrate are in the
replication position in which the replication tool and the
substrate are brought together, for example the replication tool is
placed on the substrate, the replication material is hardened.
Depending on the replication material chosen, it may be hardened by
curing, for example UV curing. As an alternative, it may be
hardened by cooling. Depending on the replication material chosen,
other hardening methods are possible. Subsequently, the replication
tool and the replication material are separated from each other.
For most applications, the replication material remains on the
substrate. The optical element typically is a refractive or
diffractive optical element, but also may e.g. have a
micromechanical function, at least in regions.
[0026] The element volume covers a part of the substrate and
constitutes the functional part of the element. The remainder of
the cured replication material may fill a volume at the sides of
the element, i.e. the region of space adjacent to both the
substrate and the functional part of the element, and does not
interfere with the function of the element. The invention allows
for controlling how far the replication material may move along the
substrate at each side of the element volume.
[0027] In a preferred embodiment of the invention, the flow of the
replication material is controlled and/or limited by capillary
forces and/or surface tension. This exploits the property of
geometric features to further or to hinder the flow of the
replication material between the tool and the substrate.
[0028] As an example, the replication tool may be chosen to
comprise a plurality of cavities, each defining the shape of one
element or a group of elements, each cavity being limited, at least
in one lateral direction, by a flat section. An inner edge is
formed between the cavity and the flat section. The replication
tool further comprises a plurality of overflow volumes or one
contiguous overflow volume between the cavities. An outer edge is
formed between the flat section and the overflow volume. The
dispensed replication material (per cavity) is chosen to be larger
than the volume of the cavity. The flat section then serves as a
floating (non-contact) spacer, which preferably surrounds the
cavity. The outer edge constitutes a discontinuity, stopping a flow
the replication material. Without such discontinuities, capillary
forces would cause the replication material to eventually drain the
replication material from the element volume.
[0029] The cavity, in this example, may for example consist of the
element volume only. It may be dome-shaped so that the element is a
convex refractive lens adjacent to which a thin base layer is
formed, the base layer being what replication material remains
underneath the floating spacer.
[0030] Even in the case of a cylinder symmetric optical element,
the shape of the flat section, when seen in the direction
perpendicular to the substrate surface, e.g. along a central axis
of the element, may be asymmetrical so that a bulge of replication
material forming along the outer edge in the overflow volume is
farther away from the replication element towards one side of the
element than towards an other side.
[0031] Here and in the following, for the sake of convenience, the
dimension perpendicular to the surface of the substrate, which
comprises an essentially flat surface is denoted as "height". In
actual practice, the entire arrangement may also be used in an
upside down configuration or also in a configuration where the
substrate surface is vertical or at an angle to the horizontal. The
according direction perpendicular to the surface is denoted
z-direction. The terms "periphery", "lateral" and "sides" relate to
a direction perpendicular to the z-direction.
[0032] In another example, control of the flow is done by a cavity
in the tool defining the shape of the element, and the cavity
including a buffer volume along at least one side of the element,
which buffer volume is separated from the element volume by an
inner edge. Furthermore, the predetermined volume of replication
material applied individually to the element volume of the cavity
is smaller than the volume of the cavity. This causes the inner
edge to limit the flow of the replication material into the buffer
volume by capillary forces acting at the inner edge and by surface
tension.
[0033] Especially, the predetermined volume of replication material
may be about the volume of the element volume (or slightly smaller
or slightly larger). The element volume is the volume of the
functional element, extending from the outer shape of the element
defined by the tool on one side to the substrate on the other side.
The replication material will then be stopped by fluid forces
acting at the inner edge from flowing into the buffer volume.
[0034] In yet another preferred embodiment of the invention, when
pressing the tool against the substrate, an inclined spacer
displaces the replication material towards the element volume, and
in particular, a buffer volume adjacent to the element volume. The
inclined spacer has an inclined surface that is to be brought into
contact with the surface of the substrate. The inclined surface,
when no pressure is applied, touches the substrate at an outer
periphery, and in regions closer to the element volume gradually
moves away from the substrate. When, during embossing or molding,
pressure is applied to the tool, the tool, being slightly elastic,
is deformed, and the inclined surface causes replication material
to be displaced from under the inclined spacer.
[0035] In a preferred embodiment of the invention, the method
comprises the further steps of: [0036] confining the flow of the
replication material towards at least one side of the tool by a
contact spacer that touches the substrate; and [0037] enabling the
flow of the replication material towards another side of the tool
by an overflow channel.
[0038] This allows for the diverting of the replication material
away from the critical areas and guiding it to an overflow volume
located in a noncritical area.
[0039] Also according to the invention, a replication tool for
replicating an element from a replication material is provided, the
replication tool comprising a replication side, a plurality of
cavities on the replication side, each defining the shape of one
element or a group of elements, the replication tool further
comprising at least one spacer portion, protruding, on the
replication side, from the cavities, the replication tool further
comprising means for confining the replication material to a
predetermined area of the tool, when the tool is pressed against a
substrate, whose predetermined area exceeds the desired volume of
the element in at least one direction along the surface of the
substrate by less than a predetermined distance.
[0040] Such means for confining the replication material, or flow
confining features are constituted by the inner edge, the buffer
volume, the outer edge, the spacer and the inclined spacer; each of
them alone, or several of them in combination. They may be combined
to form a "multi-tiered" flow confinement, which, according to the
amount of replication material actually present, stops the flow at
an earlier or a later limit. This allows control of the flow
despite inaccuracies when dispensing the replication material to
individual cavities or onto corresponding individual locations on
the substrate.
[0041] In other words, the cavity comprises an element volume and a
further volume, at a periphery of the element volume, the
boundaries of the further volume comprising discontinuities for
selectively inhibiting and/or enabling capillary flow of the
replication material when pressing the tool against the substrate,
with the replication material in between.
[0042] In a further preferred embodiment, the replication tool
comprises a spacer dimensioned to stop the flow of the replication
material by touching the substrate at one side of the cavity and an
overflow channel enabling the flow of the replication material
towards another side of the cavity.
[0043] In a further preferred embodiment, the replication tool
comprises a buffer volume at at least one side of the element
volume defined by the cavity, the buffer volume and the element
volume defining, at their common boundary, an inner edge for
inhibiting the flow of the replication material into the buffer
volume.
[0044] In a further preferred embodiment, the replication tool
comprises further edges in the surface of the buffer volume for
inhibiting the flow of the replication material into the buffer
volume. The further edges follow the shape of the inner edge at
least roughly in parallel curves.
[0045] The tool comprises a plurality of cavities, thus preferably
allowing for the simultaneous manufacture of an array of elements
on a common substrate. This common substrate preferably is part of
an opto-electronic or micro-opto-electronic assembly comprising
optical and electronic elements produced on a wafer scale and later
diced into separate units.
[0046] Features of the method claims may be combined with features
of the device claims and vice versa.
[0047] The replica (for example a micro-optical element or
micro-optical element component or an optical micro-system) may be
made of epoxy. The hardening step, which is done while the
replication tool is still in place may then be an UV curing step.
UV light curing is a fast process that allows for good control of
the hardening process. The skilled person will know other materials
and other hardening processes.
[0048] "Optical" elements include elements that are capable of
influencing electromagnetic radiation not only in the visible part
of the spectrum. Especially, optical elements include elements for
influencing visible light, Infrared radiation, and potentially also
UV radiation. The word "wafer" in this text does not mean any
restriction as to the shape of the substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0049] The subject matter of the invention will be explained in
more detail in the following text with reference to preferred
exemplary embodiments, which are illustrated in the attached
drawings, which schematically show:
[0050] FIGS. 1 and 2 cross sections through tools placed on a
substrate;
[0051] FIG. 3 an elevated view of the arrangement of FIG. 2;
[0052] FIG. 4 an example of an alternative geometrical shape of a
transition between a buffer volume and an overflow volume;
[0053] FIGS. 5-9 cross sections through further tools;
[0054] FIG. 10 an elevated view of the arrangement of FIG. 9;
and
[0055] FIG. 11 a flow diagram of the method according to the
invention.
[0056] The reference symbols used in the drawings, and their
meanings, are listed in summary form in the list of reference
symbols. In principle, identical parts are provided with the same
reference symbols in the figures.
DETAILED DESCRIPTION OF THE INVENTION
[0057] FIG. 1 schematically shows a cross section through a tool 10
placed on a substrate 12. The tool 10 forms a cavity 8 that defines
the shape of the element to be formed by an element volume 1. In
the shown case, the optical element is simply a refractive lens.
The element volume 1 lies between the tool 10 and the substrate 12.
It is surrounded by a protruding element of the tool 10 which here
is denoted as a floating spacer 14. A flat surface 17 of the spacer
runs approximately parallel to the surface of the substrate 12 and
here is at a distance of about 5 .mu.m to 15 .mu.m therefrom.
Underneath the floating spacer 14, between the flat surface 17 and
the substrate 12, a small buffer volume 3 forms. Between the
element volume 1 and the buffer volume 3, the tool 10 comprises an
inner edge 2. Between the buffer volume 3 and an overflow volume 5,
the tool 10 comprises an outer edge 4.
[0058] The main function of the floating spacer 14 is to pull out
excess material by capillary forces. The flow stops at the outer
edge 4 and forms a bulge 18 and therefore prevents the element
volume 1 from being emptied by the capillary forces. In this way,
the width of the floating spacer 14 and the shape and size of the
overflow volume 5 define where excess material is to go. Therefore,
by keeping the replication material volume below a certain maximum
volume, the replication material is confined.
[0059] The inner edge 2 constitutes a first discontinuity, stopping
the flow at an outer boundary of the replication material 13, as is
also shown in following Figures. The outer edge 4 constitutes a
second discontinuity, stopping the replication material 13 from
flowing to the buffer volume 5 adjacent to the buffer volume 3.
Without such discontinuities, capillary forces would cause the
replication material 13 to continuously flow along the channel
formed by the buffer volume 3, eventually draining the replication
material 13 from the element volume 1.
[0060] FIG. 2 shows a variation of the above principle. In this
variation, the floating spacer 14 surrounding the element volume 1
is asymmetric. By this, the excess material can be transported to
areas where it is not disturbing other processes. A top view of the
configuration of FIG. 2 is shown in FIG. 3. The bulge 18 may, for
example, be approximately constant in its cross section. By the
asymmetric shape of the floating spacer, the length of the outer
edge 4 is increased. For these reasons, the asymmetric solution
allows confinement by the replication material especially well in
one desired direction, corresponding to the lower left corner in
the sketched configuration, as may be especially desired in
configurations with an off-center optical element.
[0061] The tool preferably comprises, as it may in the embodiment
of FIG. 1 and in all of the hereafter-described embodiments,
multiple sections each corresponding to an element to be
replicated. The sections are arranged array-like, for instance, in
a grid with grid 11 lines corresponding to cutting or dicing lines
for later separation of the substrate 12 carrying the manufactured
optical elements or corresponding to bonding areas where other
elements are later to be bonded to.
[0062] As shown in FIGS. 2 and 3, an asymmetry of material flow
between different directions can be implemented in a way that is
based on different distances. However, it is also possible to
influence the replication material flow by other means such as
different surface properties at different locations or by
geometrical shape. The outside portions of the spacers 14 can be
formed in a way so that differing surface tensions can be used to
control the excess liquid. An example is shown in FIG. 4. The
spacer 14 at one side comprises a geometrical feature 20 that
causes the flow towards this side to be different from the flow
towards the other side.
[0063] FIG. 5 shows a cross section of a tool 10 with replication
material 13 just filling the element volume 1 and being contained
by the discontinuity of the inner edge 2 between the element volume
1 and the buffer volume 3. The length of the buffer volume 3
preferably lies in the range of 100 to 300 or 500 or 800
micrometers.
[0064] In FIG. 5, the buffer volume 3 is within the cavity 8. Also,
the z-dimension and thus the element height and ultimately the
element volume are fixed by a contact spacer 9 surrounding the
cavity 8. The contact spacer 9 may, for example, be of the kind
described in WO 2004/068198. FIG. 5, thus, shows an example, where
the replication material is confined by a combination of an exact
dispensing of the replication material volume corresponding to the
element volume 1 (or to a slightly smaller or larger volume) and
the effect of surface tension in combination with the impact of an
edge 2.
[0065] The embodiment relying on a more or less exact dispensing of
the replication material and a geometrical element (such as an
edge) limiting the replication material flow in at least one
direction by means of surface tension and/or capillary forces,
thus, does not rely on there being a contact spacer surrounding the
cavity. This is illustrated in FIG. 6. FIG. 6 shows part of a cross
section of a tool 10 in which on one side, an (optional) elevated
spacer section 14 is shown. In such an embodiment, the z-dimension
is defined in another way, for example, by contact spacers on an
other side (not shown) or at another, for example, peripheral
lateral position, by active distance adjusters and/or controllers,
or other means.
[0066] FIG. 7 shows a cross section of a tool 10 with further edges
17 formed at the surface of the buffer volume 3. These further
edges 17 confine the flow of the replication material 13, and come
into action depending on the total volume of the replication
material 13, which may vary when applying the replication material
13 individually with a doser, such as a dosing syringe, to the
cavity 8, to the substrate 12 at locations opposite to the cavities
8, or generally, if no spacers and thus no cavities are present, on
the lateral positions of the elements to be replicated, either to
the substrate or to the replication tool or to both.
[0067] FIG. 8 shows part of a cross section of a tool 10 that has
an inclined spacer 15 prior to being pressed against the substrate
12. The arrow shows the direction of flow of the replication
material 13 under the inclined spacer 15, as it is being
compressed. Usually, the weight of the replication tool, with
optional additional weights, is sufficient to generate the required
pressure. The buffer volume 3 takes up the replication material 13
displaced from under the inclined spacer 15. In this embodiment, it
is the inclined spacer that limits the flow.
[0068] FIG. 9 schematically shows a cross section through a tool 10
placed on a substrate 12. FIG. 10 shows a corresponding elevated
view. The tool 10 comprises a cavity 8 that defines the shape of
the element to be formed by an element volume 1. The element volume
1 lies between the tool 10 and the substrate 12, and is surrounded
by a buffer volume 3. Between the element volume 1 and the buffer
volume 3, the tool 10 comprises an inner edge 2. Between the buffer
volume 3 and an overflow volume 5, and between the buffer volume 3
and a free volume 6, the tool 10 comprises an outer edge 4, 4'. The
buffer volume 3 constitutes an outlet or overflow channel 16 for
surplus material, in the case that the amount of replication
material 13 exceeds the volume of the element volume 1.
[0069] For cases in which a large volume tolerance is required, the
cavity 8 comprises an overflow volume 5 on one side of the element
volume 1. On the other side, the outer edge 4, or the free volume 6
or the spacer 9 defines the limit of flow for the replication
material 13, keeping the replication material 13 away from critical
areas of the substrate. This outer edge 4, together with the outer
limit of the overflow volume 5, defines a predetermined area 7 that
gives the maximum area of substrate 12 that can be covered by the
replication material 13.
[0070] The outer edge 4, 4' is shaped differently between the
transition 4 from the buffer volume 3 to the free volume 6 on the
one hand and the transition 4' from the buffer volume 3 to the
overflow volume 5 on the other hand, so that surface tension and/or
capillary forces cause excess replication material to flow into the
overflow volume 5 but not to the free volume 6. For example, the
outer edge 4, 4' may be sharper at the transition to the free
volume 6 and rounder at the transition to the overflow volume
5.
[0071] The tool 10 here rests on (optional) contact spacers 9
placed against the substrate 12. The function of the free volume 6,
which is not to be filled by replication material, is, in
combination with the outer edge 4, to stop the flow of the
replication material and also to thereby prevent it from flowing
underneath the contact spacer 9. Depending on the viscosity of the
replication material, surface tension and capillary forces, this
may not be necessary, and the flow may be stopped by the contact
spacer itself. In that case, the contact spacer may be immediately
adjacent to the element volume 1, without there being a need for
the buffer volume and the free volume 6.
[0072] Since the overflow volume 5 is higher than the buffer volume
3, following a discontinuity or step in height at the outer edge 4,
capillary forces are no longer relevant (For the sake of
convenience, the dimension perpendicular to the surface of the
substrate 12 is denoted as "height". In actual practice, the entire
arrangement may also be used upside down.). The overflow volume 5
will simply be filled in accordance with the surplus replication
material 13 volume.
[0073] In an exemplary embodiment of the invention, a diameter of
the element volume 1 is between 1 and 2 millimeters and has a
height around 250 micrometers, the height of the buffer volume 3,
i.e. the distance between the cavity 8 and the substrate 12 in the
region of the buffer volume 3 is ca. 10 micrometers, the length of
the buffer volume 3, i.e. the distance from the inner edge 2 to the
outer edge 4 is ca. 50 to 200 micrometers.
[0074] FIG. 11 shows a flow diagram of the method described.
[0075] While the invention has been described in present preferred
embodiments of the invention, it is distinctly understood that the
invention is not limited thereto, but may be otherwise variously
embodied and practised within the scope of the claims.
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