U.S. patent application number 09/683542 was filed with the patent office on 2003-07-17 for methods for forming features in polymer layers.
Invention is credited to Andrews, John R., Burke, Cathie J., Markham, Roger G..
Application Number | 20030134444 09/683542 |
Document ID | / |
Family ID | 24744473 |
Filed Date | 2003-07-17 |
United States Patent
Application |
20030134444 |
Kind Code |
A1 |
Andrews, John R. ; et
al. |
July 17, 2003 |
METHODS FOR FORMING FEATURES IN POLYMER LAYERS
Abstract
12 Methods of forming features in polymeric materials by laser
ablation techniques alone, or by the combined use of laser ablation
techniques and photolithography, are disclosed. The methods can be
used to pattern non-photosensitized materials, as well as
photosensitized materials. The patterned features can have
different shapes, dimensions and aspect ratios in the same polymer
layer. Structures including the patterned features can include
multiple layers formed of photosensitized and/or
non-photosensitized polymer materials.
Inventors: |
Andrews, John R.; (Fairport,
NY) ; Burke, Cathie J.; (Rochester, NY) ;
Markham, Roger G.; (Webster, NY) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC.
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Family ID: |
24744473 |
Appl. No.: |
09/683542 |
Filed: |
January 16, 2002 |
Current U.S.
Class: |
438/21 ;
438/725 |
Current CPC
Class: |
B23K 2103/172 20180801;
B23K 2103/42 20180801; B23K 26/066 20151001; B41J 2/1623 20130101;
B23K 26/40 20130101; B23K 2103/50 20180801; B23K 2103/52 20180801;
B41J 2/1645 20130101; B41J 2/1634 20130101; B23K 26/389 20151001;
B41J 2/1631 20130101; B41J 2/1604 20130101; B29C 59/16 20130101;
B23K 26/382 20151001 |
Class at
Publication: |
438/21 ;
438/725 |
International
Class: |
H01L 021/00 |
Claims
What is claimed is:
1. A method of forming features in a polymer layer, comprising:
irradiating a polymer layer formed on a substrate with an ablation
laser to form at least one feature in the polymer layer; wherein
the polymer layer comprises a non-photosensitized material; wherein
the substrate comprises a material selected from the group
consisting of silicon, quartz, glass, ceramics and metals; and
wherein the at least one feature has (i) a width of from about 2
microns to about 1000 microns, and (ii) a height of from about 0.1
micron to about 1000 microns.
2. The method of claim 1, wherein the at least one feature has an
aspect ratio of at least about 5:1.
3. The method of claim 1, wherein the polymer layer has a thickness
of at least about 1 micron.
4. The method of claim 3, wherein the polymer layer has a thickness
of at least about 5 microns.
5. The method claim 1, wherein the at least one feature is a
portion of a channel.
6. The method claim 1, wherein the at least one feature comprises a
plurality of features.
7. A method of forming features in a polymer layer, comprising:
irradiating a polymer layer formed on a substrate with an ablation
laser to form a plurality of features in the polymer layer; wherein
the polymer layer comprises a non-photosensitized material; wherein
the substrate comprises a material selected from the group
consisting of silicon, quartz, glass, ceramics and metals; wherein
at least one of the features has (i) a width of from about 2
microns to about 1000 microns, and (ii) a height of from about 0.1
micron to about 1000 microns; and wherein at least two of the
features have a different height from each other.
8. The method of claim 7, wherein the at least one feature has an
aspect ratio of at least about 5:1.
9. The method of claim 7, wherein the polymer is an adhesive.
10. The method of claim 7, wherein the polymer layer has a
thickness of at least about 10 microns, and the at least one
feature has an aspect ratio of at least about 10:1.
11. The method of claim 7, wherein the polymer layer has a
thickness of at least about 5 microns.
12. The method claim 7, wherein the features are each at least a
portion of a channel.
13. The method claim 7, wherein the features are a plurality of
channels.
14. A method of forming features in a polymer layer, comprising:
forming a first portion of at least one feature in a polymer layer
formed on a substrate by photolithography, the polymer layer
comprising a photosensitized material; and irradiating the polymer
layer with an ablation laser to form a second portion of each at
least one feature in the polymer layer; wherein the first portion
and the second portion of at least one feature have a different
size from each other.
15. The method of claim 14, wherein the first portion and the
second portion of each feature have a different height in a
thickness direction of the polymer layer from each other.
16. The method of claim 14, wherein the second portion is a
nozzle.
17. The method of claim 14, wherein the polymer layer has a
thickness of at least about 5 microns, and the second portion of
each feature has an aspect ratio of at least about 5:1.
18. The method of claim 14, wherein the polymer layer has a
thickness of at least about 10 microns and the second portion of
each feature has an aspect ratio of at least about 10:1.
19. The method of claim 14, wherein: the substrate comprises a
heater wafer of an inkjet print head; and the method further
comprises forming a cover over the polymer layer; wherein the
features form ink flow passages in the ink jet print head.
20. The method of claim 14, comprising: forming a first portion of
each of at least a first feature and a second feature in the
polymer layer by photolithography; and irradiating the polymer
layer with an ablation laser to form a second portion of each of at
least the first feature and the second feature in the polymer
layer, wherein the second portion of the first feature has a
different height in a thickness direction of the polymer layer from
at least one of (i) the first portion of the first feature, (ii)
the first portion of the second feature, and the (iii) the second
portion of the second feature.
21. The method of claim 20, wherein the second portion of the first
feature has a different height from the first portion of the first
feature.
22. The method of claim 20, wherein the second portion of each
feature is a nozzle.
23. The method of claim 20, wherein the polymer layer has a
thickness of at least about 5 microns, and the second portion of
each feature has an aspect ratio of at least about 5:1.
24. The method of claim 20, wherein the polymer layer has a
thickness of at least about 10 microns and the second portion of
each feature has an aspect ratio of at least about 10:1.
25. The method of claim 20, wherein: the substrate comprises a
heater wafer of an ink jet print head; and the method further
comprises forming a cover over the polymer layer; wherein the
features form ink flow passages in the ink jet print head.
26. A method of forming features in a structure, the structure
including a substrate, and a first polymer layer comprising a
non-photosensitized material and a second polymer layer comprising
a photosensitized material formed over the substrate, the method
comprising: irradiating the first polymer layer with an ablation
laser to form a plurality of first features in the first polymer
layer; forming a first portion of each of a plurality of second
features in the second polymer layer by photolithography; and
irradiating the second polymer layer with the ablation laser to
form a second portion of each of the plurality of second features
in the second polymer layer, wherein the first portion and the
second portion of at least one second feature in the second polymer
layer have a different size from each other.
27. The method of claim 26, wherein the first portion and the
second portion of each second feature have a different height in a
thickness direction of the second polymer layer from each
other.
28. The method of claim 26, wherein the second portion of each
second feature is a nozzle.
29. The method of claim 26, wherein the second polymer layer has a
thickness of at least about microns, and the second portion of each
second feature of the second polymer layer has an aspect ratio of
at least about 5:1.
30. The method of claim 26, wherein the second polymer layer has a
thickness of at least about microns, and the second portion of each
second feature has an aspect ratio of at least about 10:1.
31. The method of claim 26, wherein: the substrate comprises a
heater wafer of an ink jet print head; and the method further
comprises forming a cover over the first polymer layer and second
polymer layer; wherein the features form ink flow passages in the
ink jet print head.
32. A structure, comprising: a substrate; a polymer layer over the
substrate, the polymer layer comprising a non-photosensitized
material; and a plurality of fluid flow channels in the polymer
layer, at least one of the fluid flow channels has (i) a width of
from about 5 microns to about 1000 microns, (ii) a height of from
about 25 microns to about 1000 microns in a thickness direction of
the polymer layer, and (iii) an aspect ratio of at least about
5:1.
33. The structure of claim 32, wherein at least two of the fluid
flow channels have a different height from each other.
34. The structure of claim 33, wherein the at least one of the two
fluid flow channels has an aspect ratio of at least about 10:1.
35. The structure of claim 33, wherein the at least two fluid flow
channels comprise at least a first channel and a second channel
formed in the polymer layer, at least a portion of the first
channel has a different height in the thickness direction of the
polymer layer from a height of the second channel.
36. The structure of claim 35, wherein the first channel comprises
a first portion having a first height and a second portion having a
second height different from the first height.
37. The structure of claim 35, wherein the first portion of the
first channel has a first width and the second portion of the first
channel has a second width different from the first width.
38. The structure of claim 32, wherein the structure is a thermal
ink jet print head.
39. The structure of claim 38, wherein: the substrate comprises a
heater wafer; and further comprising a cover formed over the
polymer layer.
40. A structure, comprising: a substrate; a polymer layer over the
substrate, the polymer layer comprising a photosensitized material;
and a plurality of features in the polymer layer, at least two of
the features have different heights from each other.
41. The structure of claim 40, wherein the features are fluid flow
channels.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention is directed to methods for forming structures
for microfluidic applications, and also to structures and devices
formed by the methods.
[0003] 2. Description of Related Art
[0004] Structures for microfluidic applications include passages in
which fluids are contained and flowed. In order to provide
controlled, uniform flow through the passages, it is important that
the passages have well-defined characteristics.
[0005] One exemplary type of structure that includes fluid flow
passages is the ink jet print head. Ink jet print heads typically
include a base, an intermediate layer formed over the base, and a
cover formed over the intermediate layer. The intermediate layer
and cover form channels and nozzles for flowing and discharging the
ink onto a recording medium to form images. Ink droplets are
ejected from the nozzles by applying energy to the ink to form the
droplets.
[0006] The intermediate layers in microfluidic devices include flow
passages that can be defined by openings, or features, having
various shapes and sizes, depending on their functions within the
device.
SUMMARY OF THE INVENTION
[0007] Fluid passages have been formed in structural layers of
microfluidic devices by different techniques. For example,
photosensitized materials have been used for structural layers
defining fluid flow passages in ink jet print heads.
Photolithographic techniques have been used to form these fluid
passages. However, such photolithographic techniques are not
completely satisfactory for at least the following reasons. First,
photolithographic techniques require the use of photosensitized
materials. Thus, the group of suitable materials that can be
patterned by conventional photolithographic techniques is limited.
Second, in order to form accurate features by conventional
photolithography techniques, very thin layers have been used. For
thicker layers, the accuracy of photolithography is reduced. Third,
it has been difficult to pattern features having different depths
and/or widths in a photosensitized material by
photolithography.
[0008] The features formed in a material can be characterized by
their aspect ratio. The aspect ratio of a feature is determined by
both its height and width. For a typical feature, however, there
will also be a certain amount of taper of the side walls defining
the feature. FIGS. 1 and 2 show two different opening
configurations that have aspect ratios defined by respectively
different relationships. FIG. 1 shows a layer 10 having a surface
12, and an opening 14 formed in the surface. The opening 14 has a
height h and width w. The height h can be less than or equal to the
thickness of the layer 10. The side walls 16 defining the opening
14 are perpendicular to the surface 12. For this opening
configuration, the aspect ratio can be defined as the ratio of the
height h to the width w of the opening; i.e.: h/w.
[0009] FIG. 2 shows a layer 20 formed on a substrate 22. The layer
20 has a thickness h and includes an upper surface 28, a lower
surface 30, and an opening 32 extending between the upper surface
28 and the lower surface 30. The opening 32 is defined by side
walls 34 which are tapered, such that the width of the opening 32
varies from a maximum width b' at the upper surface 28 to a minimum
width b" at the lower surface 30. The layer 20 has a width a' at
the upper surface 28 and a width a" at the lower surface 30. For
the opening 32 having tapered side walls, the average aspect ratio
of the opening 32 can be defined as: 2h/(b'+b"). Likewise, the
average aspect ratio of the wall between the openings can be
defined as: 2h/(a'+a").
[0010] Structural layers in devices may require aspect ratios
significantly greater than 1:1. In an ink jet print head, for
example, features having aspect ratios significantly greater than
1:1, as well as features having significantly different aspect
ratios, can be needed in different portions of the same device.
[0011] Conventional photolithography techniques have limited
applicability for forming features that are tall, but narrow (i.e.,
have high aspect ratios) in thick photosensitized material layers.
In addition, such techniques are unable to satisfactorily provide
features having different heights in the same layer.
[0012] This invention provides methods for forming features in
various different polymeric materials that can overcome the
above-described disadvantages of known photolithographic
techniques. Exemplary embodiments of the methods according to the
invention can form fine features in non-photosensitized materials.
Such embodiments can be used to form features in
non-photosensitized materials that have not previously been
achievable by known techniques. In addition, such methods can form
fine features in non-photosensitized materials, for which
photolithographic techniques are not suitable.
[0013] In addition, in exemplary embodiments of the methods
according to the invention, fine features with high aspect ratios
can be formed in non-photosensitized materials.
[0014] In addition, exemplary embodiments of the methods according
to this invention can form features having different depths or
widths in the same layer.
[0015] Furthermore, exemplary embodiments of the methods according
to this invention can form features having different shapes and
sizes in the same layer.
[0016] Thus, for example, in some embodiments, different portions
of the same feature can have different depths, shapes and/or sizes.
Accordingly, different portions of the same feature can provide
different fluid flow characteristics. In addition, in some
embodiments, different features can have different depths, widths,
shapes and/or sizes in the same structural layer. Accordingly,
different features of the same type can provide different fluid
flow characteristics in the same structural layer. In addition,
different types of features can be formed in the same structural
layer to provide further versatility with respect to fluid
flow.
[0017] Other exemplary embodiments of the methods according to the
invention can form features in photosensitized materials by the
combined use of laser ablation and photolithography. By combining
these two different techniques, the patterning of features, or
portions of features, that can be done by photolithography
techniques can be performed by photolithography, while other
features, or portions of the same feature, that previously have not
been satisfactorily achieved in photosensitive materials by
photolithography, can be formed by laser ablation. In embodiments,
photolithography and laser ablation can be combined to form
features in multi-layer structures including at least
photosensitized material layer and at least one non-photosensitized
material layer.
[0018] This invention also separately provides devices including
such features.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Various embodiments of this invention will be described in
detail, with reference to the following figures, wherein:
[0020] FIG. 1 illustrates an opening in a layer that includes
vertical side walls;
[0021] FIG. 2 illustrates a structure including an opening having
inwardly tapered side walls formed on a substrate;
[0022] FIG. 3 illustrates an inkjet print head die module of an ink
print head incorporating an exemplary embodiment of a patterned
polymer layer according to the invention;
[0023] FIG. 4 illustrates an exemplary embodiment of a patterned
polymer layer according to this invention;
[0024] FIG. 5 illustrates another exemplary embodiment of a
patterned polymer layer according to this invention;
[0025] FIG. 6 is a perspective view of an imagewise ablation
apparatus;
[0026] FIG. 7 is a perspective view of a flying spot scanning
cutting apparatus; and
[0027] FIG. 8 illustrates another exemplary embodiment of a
patterned polymer layer according to this invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0028] This invention provides methods that can form openings, or
features, in both non-photosensitized and photosensitized
materials. These materials can form portions of various
devices.
[0029] One exemplary device that includes openings, or features
that can be formed according to the invention is an ink jet print
head. FIG. 3 illustrates a portion of a thermal ink jet print head.
The illustrated ink jet print head die module 40 mounted on a heat
sink 42. The ink jet print head die module 40 comprises a base or
heater plate 44, an intermediate layer 46 formed over the heater
plate 44, and a cover or channel plate 48, formed over the
intermediate layer 46.
[0030] The heater plate 44 includes heating elements (not shown)
that are activated to heat ink contained in the ink jet print head
die module 40, to cause ink droplets to be ejected from nozzles 56.
The heater plate 44 can comprise any suitable substrate material,
including, for example, silicon, quartz, glass or ceramics.
[0031] The intermediate layer 46 has a thickness t. The
intermediate layer can be formed of any suitable photosensitized or
non-photosensitized material. Referring to FIG. 4, channels 50 are
formed in the intermediate layer 46. The upper surface 45 of the
heater plate 44 forms a floor of the channels 50. The channels 50
communicate with an ink reservoir 60 that contains a supply of ink.
The channels 50 include a portion having parallel side walls 52,
and a portion including nonparallel side walls 54. The side walls
54 define nozzles 56 having open ends 58. Ink droplets are ejected
from the open ends 58 of the nozzles 56 during operation of the
inkjet print head. The intermediate layer 46 includes features
configured to control the flow of ink through the channels 50 and
other flow passages of the ink jet print head die module 40.
[0032] The lower surface 49 of the channel plate 48 forms a top of
the channels 50. The channel plate 48 can comprise any suitable
material that is resistant to the ink. For example, the channel
plate 48 can comprise glass, quartz, plastics, silicon, metals,
polymers, and/or ceramics.
[0033] The channels 50 have a height H, which is measured
perpendicular to the upper surface 45 of the heater plate 44. In
the embodiment shown in FIG. 3, the channels 50 have a height H
that equals the thickness t of the intermediate layer 46. In other
embodiments, the height of the channels 50, as well as other
features formed in intermediate layer 46, can be less than the
thickness t.
[0034] As shown in FIG. 4, the channels 50 have a maximum width W
at the portion of the channels defined by the side walls 52 and a
minimum width W' at the open end 58. In accordance with the
invention, the channels 50, and other features formed in the
intermediate layer 46, can have high aspect ratios. For the
channels 50, the aspect ratio is defined by the ratio of the height
H to the width W, for embodiments in which the side walls 52, 54
are at least substantially vertical. The channels 50 have
substantially constant width portions defined by the side walls 52.
The angular range of the side walls 52, 54 is preferably
substantially vertical (90.degree.+5.degree.). However, the side
walls 52 and/or 54 can optionally be formed with tapered side
walls.
[0035] The invention provides methods that can form improved
features in both non-photosensitized materials and photosensitized
materials. These materials can be formed on various different
substrates. Furthermore, in multi-layer structures described below,
non-photosensitized materials and photosensitized materials can be
formed over each other. The features formed in the
non-photosensitized materials and photosensitized materials can
have various shapes and sizes. In some embodiments, the features
can have fine dimensions, i.e., sub-micron and micron size
dimensions. In addition, a wide range of feature sizes can be
provided in both non-photosensitized materials and photosensitized
materials. The features can have widths of from about 0.1 micron up
to 1 mm or even higher. In preferred embodiments, the features have
a width of at least about 1 micron. The features can also have
heights, or depths, of from about 0.1 micron up to about 1 mm or
even higher. In addition, as described below, the features can be
formed with high aspect ratios.
[0036] According to the invention, the features can also have
different heights or depths, as well as different aspect ratios,
within the same layer. For example, in the intermediate layer 46
shown in FIG. 4, the aspect ratio of the channels 50 varies along
the channel lengths. Particularly, the channels 50 have an aspect
ratio that increases from that of the remainder of the channel 50
in the direction toward the open ends 58. In embodiments, the
channels 50 can have an aspect ratio of at least about 5:1 in
selected portions of the channels, such as the portion defined by
the side walls 52. At the location of the open ends 58, the flow
cross-sectional area is significantly reduced and the aspect ratio
can be as high as at least about 10:1 at those locations.
[0037] In the ink jet print head die module 40 shown in FIG. 3, the
droplet volume is essentially controlled by the size of the open
ends 58. The required droplet volume for different fluids, such as
different colored inks, can be achieved by changing the size of
channel openings through which the different fluids respectively
flow. The ability to form features having different aspect ratios
enables the formation of channels having different sizes and shapes
in the same intermediate layer 46.
[0038] FIG. 5 shows another exemplary embodiment of an intermediate
layer 146 formed in an ink jet print head. In this embodiment,
channels 150 are formed in the intermediate layer 146. The channels
150 each include a portion having parallel side walls 152, a
portion having inwardly converging, non-parallel side walls 154,
and a portion having parallel side walls 155 adjacent to the open
ends 158. The side walls 154, 155 form nozzles 156.
[0039] In the intermediate layer 46, 146, the channels 50, 150 can
have various different shapes and sizes. For example, the open ends
of the nozzles can be square, rectangular, triangular, trapezoidal,
circular or any other suitable shape. In addition, other types of
features may be formed in the intermediate layer with various
shapes and sizes.
[0040] According to the invention, the intermediate layer 46 can
comprise any suitable polymeric material. The material forming the
intermediate layer can be formed on any suitable substrate
material, including, but not limited to silicon, quartz, glass,
ceramics, metals and plastics. The invention provides methods of
forming features in materials formed on such substrates. This
invention further provides methods that can form features in a
broad array of different material compositions, including
non-photosensitized materials and photosensitized materials.
[0041] Exemplary embodiments of the methods according to the
invention form entire features, or at least portions of features,
in non-photosensitized polymeric materials by laser ablation
techniques. Laser ablation can form features in thick
non-photosensitized polymer layers, i.e., layers having a thickness
of at least about 5 microns. For example, features can be formed in
non-photosensitized polymeric materials having a thickness up to
about 1000 microns. In some preferred embodiments, the
non-photosensitized materials that are patterned have a thickness
of from about 5 microns to about 250 microns. Polymeric materials
having such a thickness can advantageously be formed as single
layers in devices.
[0042] Laser ablation can be used to form features less than about
3 microns in size in non-photosensitized and photosensitized
materials polymeric materials.
[0043] In addition, exemplary embodiments of the methods according
to the invention can form such fine features having a high aspect
ratio in non-photosensitized polymeric materials, including thick
materials, by laser ablation techniques. For example, features
having an aspect ratio of from about 5:1 to at least about 20:1 can
be formed in thick non-photosensitized materials. In embodiments,
high-aspect ratio features also can be formed in photosensitized,
polymeric materials. The polymeric materials in which such features
are formed can have a thickness of at least about 0.1 micron, and
preferably from about 5 microns to about 50 microns.
[0044] In exemplary embodiments of the invention, laser ablation
can be used to form entire features, or at least portions of
features, that have different heights, or depths, in the same
layer.
[0045] Other exemplary embodiments of the methods according to the
invention can form features in photosensitized materials, such as
photoresist materials. In such embodiments, entire features, or at
least portions of features, in a layer can be formed by
photolithography, and laser ablation can then be used for secondary
patterning of the layer. Thus, features can be formed in
photoresist materials by a combination of photolithography and
secondary patterning by laser ablation. For example, in exemplary
embodiments, one or more portions of a given feature can be formed
by photolithography, and one or more other portions of that same
feature can be formed by laser ablation. Accordingly,
photolithography can be used to form entire features, or only
portions of features, that can be readily formed in a
photosensitized material layer by this technique. For example,
photolithography can be used to form features, or portions of
features, that have the same height in a photosensitized polymer
layer, or features, or portions of features, that have a low aspect
ratio, such as, for example, an aspect ratio up to about 1:1.
[0046] Accordingly, by using both photolithography and laser
ablation to form features in the same photosensitized polymer
layer, the benefits of each respective technique can be combined to
form features that could not previously be formed using
conventional photolithography techniques alone.
[0047] In addition, in exemplary embodiments of the invention,
multi-layer, patterned structures can be formed, that include at
least one photosensitized polymer layer, and also at least one
non-photosensitized polymer layer. For example, such structures can
include a photosensitized polymer layer that is patterned by at
least one of photolithography and laser ablation, and another
non-photosensitized material layer that is patterned by laser
ablation. The non-photosensitized layer(s) can be formed either
under or over the photosensitized polymer layer(s). For example, in
some embodiments, a photosensitized layer can be formed under
and/or over an adhesive layer (i.e., a non-photosensitized
material). It will be readily understood by those skilled in the
art that other multi-layer, patterned structures that include at
least one photosensitized polymer layer, also at least one
non-photosensitized material layer, can also be formed by methods
according to the invention.
[0048] In methods according to the invention that form entire
features in non-photosensitized materials by laser ablation,
various different non-photosensitized materials can be patterned.
For example, suitable materials for forming the intermediate layer
46 of the ink jet print head die module 40 should be resistant to
ink, have temperature stability and suitable rigidity, and be
diceable. Because non-photosensitized materials can also be
patterned, the methods according to the invention provide increased
versatility with respect to the selection of polymeric materials
that can be patterned and provide the above-described desired
properties, as compared to known methods that can only utilize
photosensitized materials.
[0049] Exemplary materials that can be patterned by laser ablation
techniques according to the invention include, for example,
adhesives, thermoplastics and thermoset plastics. An exemplary
thermoset plastic is polyimide. Exemplary adhesives include, but
are not limited to, epoxies, phenolics, acrylics, cyanoacrylates
and methacrylates. Such adhesives that can be applied on substrates
by, for example, spin coating, doctor blade coating, or film
transfer techniques. Exemplary thermoplastics that can be coated
and patterned according to the invention include, but are not
limited to, polyester, polysulfone, polyetheretherketones and
polyimides.
[0050] In embodiments of the methods according to the invention
that utilize both photolithography and laser ablation to form
features in the same layer, or in different layers of multi-layer
structures, suitable photosensitized materials that can be
patterned include, but are not limited to, materials that become
polyimide, polyarylene ether ketone, Vacrel, or bisbenzocyclobutene
or polymethylmethacrylate when cured. Such photoresist materials
can be applied to any suitable substrate by any suitable technique.
For example, photosensitized materials can be applied by coating.
The photosensitive material (photoresist) used to form the
intermediate layer 46 can be either a positive working resist or a
negative working resist.
[0051] As stated, entire features, or portions of features, can be
formed in non-photosensitized and photosensitized polymer layers by
laser ablation. Any suitable laser can be used, including, but not
limited to, solid state lasers such as Nd:YAG (neodymium:yttrium
aluminum garnet) lasers and their harmonics at shorter wavelength,
ultraviolet lasers such as excimer lasers, free electron lasers,
gas discharge lasers, such as argon ion or krypton ion lasers or
copper vapor lasers, infrared lasers such as RF (radio-frequency
discharge) CO.sub.2 lasers or TEA (transverse electric
discharge-atmospheric pressure) CO.sub.2 lasers, and the like.
[0052] The specific selection of a laser source will depend on the
composition and physical properties of the polymer material being
processed, the thickness of the polymer layer, the required spatial
resolution, the desired surface quality, and economic
considerations such as power consumption, equipment cost,
maintenance cost and processing speed. For example, excimer lasers
offer fine resolution, about 2 microns to about 5 microns and a
heat-affected zone of less than about 2 microns.
[0053] In exemplary embodiments of the methods of this invention,
the choice of the laser ablation method depends on the specific
characteristics of the laser and the material processing parameters
required. A preferred technique is the imagewise ablation method.
The imagewise ablation method is most appropriate for short pulse
and relatively low frequency (<1 kHz) gas discharge lasers, such
as excimer and TEA CO.sub.2 lasers. Referring to FIG. 6, in this
cutting system, the laser source 200 emits a laser beam 202, which
is processed through a variable attenuator 204 and beam shaping
stage 206. The laser beam 202 is imaged onto a mask 208 containing
the pattern of the features (not shown). The patterned laser beam
is then deflected by a deflecting mirror 210 and passes through a
lens 212, after which the illuminated mask is imaged onto a polymer
layer 217. The polymer layer 217 can be, for example, the
intermediate layer 46 formed on the channel plate 44 shown in FIG.
3. The polymer layer 217 is supported on a stage 218. In this
exemplary embodiment, the polymer layer 217 is transported in the
direction of the arrow 216, typically in a step-and-repeat
manner.
[0054] In this embodiment, the laser source 200, variable
attenuator 204, mask 208 and the stage 218 are each connected to a
controller 220. Further, the mask 208 can be moved in the x- and
y-directions by one or more actuators (not shown).
[0055] The laser beam 202 illuminates the mask 208 and forms a
laser light image of the region to be ablated on the polymer layer
217. An appropriate number of pulses from the laser source 200 can
remove unwanted material from the polymer layer 217. One or more
passes can be used to etch the polymer layer 217 to selected depths
at different locations of the polymer layer 217. For example, in
some embodiments, the polymer layer 217 can be etched through its
entire thickness, i.e., to the underlying substrate, such as the
channel plate 44. In other embodiments, the polymer layer 217 can
be etched to a selected depth that is less than the thickness of
the polymer layer 217 at selected regions of the polymer layer
217.
[0056] Alternatively, in other exemplary embodiments, an
illumination and imaging system can be provided that images the
desired features in a single die, in a single imaging process.
[0057] Another suitable technique for forming features in polymer
layers according to the invention is the flying spot scanning
technique. This technique is most appropriate for CW or high
frequency pulsed lasers such as the RF CO.sub.2 and Nd:YAG lasers.
In this method, shown generally in FIG. 7, a laser beam 300 emitted
from a laser source (not shown) passes through a beam expander 302.
The expanded laser beam reflects from a first deflecting mirror 304
that is operatively connected to an x-axis scanner 306, and a
second deflecting mirror 308 that is operatively connected to a
y-axis scanner 310. The reflected laser beam is then focused to a
tight spot by a f .crclbar. flat field scanning lens 312.
[0058] The focused laser beam spot 300 is scanned by the mirrors
304 and 308 onto a polymer layer 317, which is moved in the
direction of arrow 316. As a result, the laser beam 300 cuts
desired features in the polymer layer 317. By properly controlling
the scanning speed and the laser power, the cut depth of the
features can be selected.
[0059] In a modification of the flying spot method, which is not
shown, but will be readily apparent to those skilled in the art,
the laser beam is stationary and the polymer layer 317 is moved
along two axes parallel to the plane of the polymer layer 317.
[0060] To perform the laser ablation process according to this
invention, the energy characteristics of the laser source are
usually adjusted to provide the desired penetration depth and
cutting properties. For example, in exemplary embodiments where a
KrF excimer laser operating at 248 nm is used as the laser source,
the laser can effectively and precisely cut a polymer layer having
a thickness of from about 0.1 microns to about 1000 microns, and
preferably a thickness from about 5 microns to about 250 microns.
The energy density used to cut such layers can be from about 0.3
J/cm.sup.2 to about 30 J/cm.sup.2, and is preferably from about 0.5
J/cm.sup.2 to about 1.5 J/cm.sup.2. Increasing the energy density
will increase the aspect ratio that is achievable, with other
factors remaining constant.
[0061] Furthermore, it will be readily recognized that the laser
processing parameters may be adjusted within broad ranges to
account for the specific properties desired, the polymer materials
being patterned, the laser power, and method. For example, the
specific laser ablation process parameters, such as fluence,
intensity, and cutting speed will depend upon such factors as
wavelength and type of the laser, rate of irradiation, pulse width,
energy level, and the like. Based on this disclosure one skilled in
the art can select such processing parameters for a specific
material to be cut.
[0062] In the exemplary embodiment of the inkjet print head die
module 40 shown in FIG. 3, the channels 50 extend from the lower
surface 49 of the channel plate 48 completely through the thickness
of the intermediate layer 46, i.e., to the top surface 45 of the
heater plate 44. In some exemplary embodiments, the channels 50 are
formed entirely by laser ablation, preferably in
non-photosensitized materials.
[0063] The wider portions of the channels 50 defined by the side
walls 52 have a lower aspect ratio than the nozzles 56. The
portions of the channels 50 defined by the side walls 52 are
preferably formed by photolithography, while the nozzles 56 are
preferably formed by laser ablation. By combining both techniques,
fine nozzles 56 can be accurately and consistently formed in
polymer materials. By forming smooth and uniform nozzles, correct
drop volume, uniform drop volume and good directionality can be
achieved.
[0064] Exemplary embodiments of the methods according to this
invention can also be used to form features that extend through
only a portion of the thickness of polymer layers, to form lines,
trenches or other like features. Such embodiments are particularly
advantageous for non-photosensitized materials. For example, FIG. 8
shows another exemplary embodiment of a patterned layer including
channels 450, which include wide portions having parallel side
walls 452, a narrow portion having side walls 455 and connecting
the wide portions to each other, and a front portion including
non-parallel side walls 454, which define nozzles 456 having open
ends 458 for injecting ink. As shown, the sidewalls 452, 455 and
454, respectively, define a maximum width W, a minimum width W" and
an intermediate width W', of the channels 450. The wide portions
and the narrow portions of the channels can have different depths
with respect to each other. In addition, the front portion can have
a depth that differs from that of the wide portions and/or narrow
portions.
[0065] According to the invention, different portions of the same
channels 450 can extend entirely, or only partially through, the
thickness of the polymer layer. That is, different portions of the
same channels can have different vertical heights or depths
relative to each other. These different portions can also have
different widths relative to each other. For example, the narrow
portion of the channels 450 defined by the side walls 455 can have
a depth that is less than the thickness of the polymer layer (i.e.,
the narrow portions do not extend to the upper surface of the
underlying substrate), while the widest portions of the channels
450 defined by the side walls 452 can have a greater depth than the
narrow portion. For example, the widest portions of the channel can
have a depth equal to the thickness of the polymer layer. In this
manner, the narrow portion of the channels 450 can connect the
widest portions of the channel to control fluid flow in the
channels 450. In addition, the narrow portions of the channels 450
can have different widths and different depths in the same polymer
layer, in order to provide different, controlled fluid flow
characteristics in different channels of the same polymer
layer.
[0066] Furthermore, although the patterned polymer layers according
to the invention have been described above with respect to thermal
ink jet print heads, it will be readily understood by those skilled
in the art that patterned photoresist layers can be formed in other
types of ink jet print heads, such as acoustic ink jet print heads,
piezoelectric printheads, and other print heads that eject
materials (liquid/solid blends/mixtures/combinations, solids that
are in liquid phase when ejected, and the like), using methods
according to the invention.
[0067] In addition, the patterned non-photosensitive and
photosensitive material layers formed according to this invention
can be incorporated in various other types of micro-fluidic devices
that would benefit from having one more such layers including
different types of features, features with high aspect ratios,
features having different aspect ratios and/or features with
controlled shapes. Such devices include, but are not limited to,
micro-analytical devices and biomedical devices, in which
controlled fluid flow is needed.
[0068] While the invention has been described in conjunction with
the specific embodiments described above, it is evident that many
alternatives, modifications and variations are apparent to those
skilled in the art. Accordingly, embodiments of the invention as
set forth above are intended to be illustrative and not limiting.
Various changes can be made without departing from the spirit and
scope of the invention.
* * * * *