U.S. patent number RE32,572 [Application Number 06/947,020] was granted by the patent office on 1988-01-05 for thermal ink jet printhead and process therefor.
This patent grant is currently assigned to Xerox Corporation. Invention is credited to Michael R. Campanelli, Donald J. Drake, William G. Hawkins.
United States Patent |
RE32,572 |
Hawkins , et al. |
January 5, 1988 |
Thermal ink jet printhead and process therefor
Abstract
Several fabricating processes for ink jet printheads are
disclosed, each printhead being composed of two parts aligned and
bonded together. One part is a substantially flat substrate which
contains on the surface thereof a lineal array of heating elements
and addressing electrodes, and the second part is a substrate
having at least one recess anisotropically etched therein to serve
as an ink supply manifold when the two parts are bonded together. A
lineal array of parallel grooves are formed in the second part, so
that one end of the grooves communicate with the manifold recess an
the other ends are open for use as an ink droplet expelling
nozzles. Many printheads can be made simultaneously by producing a
plurality of sets of heating elements array with their addressing
electrodes on a silicon wafer and by placing alignment marks
thereon at predetermined locations. A corresponding plurality of
sets of channels and associated manifolds are produced in a second
silicon wafer and, in one embodiment, alignment openings are etched
thereon at predetermined locations. The two wafers are aligned via
the alignment openings and alignment marks, then bonded together
and diced into many separate printheads. A number of printheads can
be fixedly mounted in a pagewidth configuration which confronts a
moving recording medium for pagewidth printing or individual
printheads may be adapted for carriage type ink jet printing.
Inventors: |
Hawkins; William G. (Webster,
NY), Drake; Donald J. (Rochester, NY), Campanelli;
Michael R. (Webster, NY) |
Assignee: |
Xerox Corporation (Stamford,
CT)
|
Family
ID: |
27110072 |
Appl.
No.: |
06/947,020 |
Filed: |
December 29, 1986 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
719410 |
Apr 3, 1985 |
04601777 |
Jul 22, 1986 |
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Current U.S.
Class: |
216/27; 216/2;
216/41; 216/52; 216/99; 347/63 |
Current CPC
Class: |
B41J
2/1604 (20130101); B41J 2/1623 (20130101); B41J
2/1628 (20130101); B41J 2/1642 (20130101); B41J
2/1631 (20130101); B41J 2/1635 (20130101); B41J
2/1629 (20130101) |
Current International
Class: |
B41J
2/16 (20060101); H01L 021/306 (); B44C 001/22 ();
C03C 015/00 (); C23F 001/02 () |
Field of
Search: |
;156/626,629,633,634,643,644,646,647,651,659.1,662,901,902 ;430/313
;346/1.1,14R |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
IBM Tech. Disclosure Bulletin, vol. 21, No. 6, Nov. 1978, Title,
"Two-Sided Groove Etching Method to Produce Silicon Ink Jet
Nozzles"; Authors; T. S. Kuan et al. .
Article, "Fabrication of Novel Three-Dimensional Microstructures by
the Anisotropic Etching of (100) and (110) Silicon", in the IEEE
Transactions on Electron Devices, vol. ED-25, No. 10 (Oct. 1978) by
Ernest Bassous..
|
Primary Examiner: Powell; William A.
Attorney, Agent or Firm: Chittum; Robert A.
Claims
We claim:
1. A method for fabricating a printhead for use in an ink jet
printing device, comprising the steps of:
(a) cleaning first and second silicon substrates, each having first
and second parallel surfaces, the substrate surfaces being {100}
planes;
(b) depositing a layer of insulating material on the surfaces of
the substrates;
(c) forming an equally spaced, linear array of resistive material
on the first surface of the first substrate for use as heating
elements and forming a pattern of electrodes on the same substrate
surface for enabling individual addressing of each heating element
with current pulses;
(d) photolithographically patterning the insulative layer on the
first surface of the second substrate to produce at least one via
therein for orientation dependent etching of at least one recess in
the second substrate bounded by {111} plane side walls;
(e) forming a plurality of equally spaced, parallel grooves in the
first surface of the second substrate, one end of the grooves
communicate with the recess and the other ends of the grooves are
open;
(f) applying an adhesive to the insulative layer on the first
surface of the second substrate, taking care not to permit the
adhesive to run into the recess or grooves;
(g) aligning the first and second substrates with their first
surfaces confronting and contacting each other, so that each groove
contains a heating element therein spaced a predetermined distance
from the groove open end; and
(h) curing the adhesive to bond the first and second substrates
together to form the printhead, wherein the recess serves as an ink
supplying manifold, the grooves serve as capillary filled channels,
and the groove open ends serve as the printhead nozzles.
2. The method of claim 1, wherein step (d) further comprises:
photolithographically patterning the insulative layer on the second
surface of the second substrate to enable orientation dependent
etching of a second recess in said second substrate bounded by
{111} plane side walls, this second recess is deep enough to
penetrate the floor of the recess in the first surface of the
second substrate to provide an aperture for use as a fill hole to
fill and maintain ink in said manifold.
3. The method of claim 1, wherein the method further comprises
providing means on each of the first and second substrates for
aligning them together.
4. The method of claim 3, wherein the means provided for alignment
is accurately dicing two adjacent corners on each substrate for use
in alignment of the two substrates in a jig.
5. The method of claim 3 wherein the means provided for alignment
is at least two patterned alignment marks on the first substrate
first surface with the heating elements and addressing electrodes,
the alignment marks being placed at predetermined locations and at
least two patterned via in the insulative layer on the first
surface of the second substrate at predetermined locations in order
for alignment pits to the etched in the second substrate, and
wherein an infrared aligner may be used to align the two substrates
by aid of the alignment marks and alignment pits.
6. The method of claim 1, wherein the via patterned in step (d) is
sized so that the orientation dependent etching etches entirely
through the second substrate, the open bottom of the recess being
for use as a fill hole for the subsequently formed manifold.
7. The method of claim 1, wherein the grooves of step (e) are
formed by concurrent orientation dependent etching with the recess
of step (d) by patterning a plurality of narrow, equally spaced,
elongated vias in the insulative layer spaced from and
perpendicular to the recess via, the etched grooves being bounded
by {111} plane side walls, the longer side walls converging to form
grooves with a V-shaped cross-section, and wherein both ends of the
grooves are diced open, so that the groove ends closer to the
recess are in communication therewith and the other ends are open
to serve as nozzles.
8. The method of claim 1, wherein the grooves of step (e) are
formed by concurrent orientation dependent etching with the recess
of step (d) by patterning a plurality of relatively narrow, equally
spaced, elongated vias in the insulative layer spaced from and
perpendicular to the recess via, the distance between the ends of
the grooves closer to the recess being shorter than the distance
between the other ends of the grooves from a one of the second
substrate edges, the etched grooves being bounded by {111} plane
side walls, and wherein the ends of the grooves adjacent the recess
are opened to the recess by first isotropic etching of the second
substrate for a period of time sufficient to permit undercutting of
the insulative layer between the grooves and the recess, cleaning
the second substrate to stop the isotropic etching process, and
then orientation dependent etching of the second substrate a second
time in order to open the grooves to the recess since the undercut
region is exposed to the orientation dependent etchant, the other
ends of the grooves being subsequently diced opened to form the
nozzles.
9. The method of claim 1, which further comprises the steps of:
(i) mounting the printhead on an insulating board having a
plurality of electrodes thereon which correspond in numbers to the
addressing electrodes of the printhead, the insulating board
electrodes having an input end and a terminal end;
(j) wirebonding each printhead electrode to a corresponding one of
the insulating board electrode input ends; and
(k) passivating the wirebonds with a silicone encapsulation
compound.
10. The method of claim 9, which further comprises the steps
of:
(l) attaching the insulating board and mounted printhead, after
their electrodes have been wirebonded and passivated, to an ink
supply cartridge in such a manner that the ink in the cartridge
maintains the ink in the printhead at a predetermined pressure, the
cartridge, insulating board, and printhead assembly being suitable
for installation in an ink jet printer.
11. A method for fabricating a plurality of printheads, each
printhead being usable in an ink jet printing device for emitting
and propelling ink droplets toward a recording medium, the method
comprising the steps of:
(a) cleaning first and second (100) silicon wafers, each having
first and second substantially parallel surfaces;
(b) depositing a layer of insulative material on the surfaces of
the wafers;
(c) forming a plurality of sets of equally spaced, linear arrays of
resistive material on the insulative layer on the first surface of
the first wafer for use as sets of heating elements, and forming a
plurality of sets of addressing electrodes on the same wafer
surface for enabling individual addressing of each heating element
with current pulse;
(d) photolithographically patterning the insulative layer on the
first surface of the second wafer to produce a plurality of set of
vias of predetermined sizes and at predetermined locations
thereon;
(e) anisotropic etching of the second wafer to produce sets of
recesses in its first surface, each recess being bounded by {111}
plane side walls;
(f) forming a plurality of sets of equally spaced, parallel grooves
through the first surface of the second wafer and its insulative
layer, each groove having a predetermined depth and first and
second ends, the first ends of each set of grooves communicating
with an associated one of the set of recesses, the second ends of
each set of grooves opening into another of the set of
recesses;
(g) applying an adhesive on the remaining unetched insulative layer
of the first surface of the second wafer, so that the adhesive does
not run into any of the grooves or recesses;
(h) aligning the first and second wafers with their first surfaces
confronting and contacting each other with the adhesive sandwiched
therebetween, the alignment assuring that each groove contains a
one of the heating elements spaced a predetermined distance from
the second open ends thereof;
(i) curing the adhesive to bond the first and second wafers
together, so that each recess in the set of recesses communicating
with a set of grooves serves as an ink supplying manifold, while
each set of grooves serves as capillary filling channels, with its
second open ends serving as nozzles; and
(j) dicing the bonded wafers into a plurality of individual
printheads, each printhead having a manifold, a set of channels
communicating with the manifold at one end thereof and having
nozzles at the other end with heating elements in each a
predetermined distance from the nozzles, and addressing electrodes
for selectively addressing the heating elements.
12. The method of claim 11, wherein the method further comprises
the step of:
providing means on each of the first and second wafers for aligning
them together.
13. The method of claim 12, wherein the means for providing
alignment is the accurate dicing of the wafers so that each has
intersecting edges that produce corners thereon for use in the
alignment of the two wafers in a jig.
14. The method of claim 12, wherein the means for providing
alignment is accomplished by the placement of at least two
alignment marks on the first surface of the first wafer during the
forming of the addressing electrodes in step (c), the alignment
marks being placed at predetermined locations on the first surface
of the first wafer, and wherein at least two relatively small vias
are patterned in the insulative layer of the first surface of the
second wafer at predetermined locations, in order that alignment
pits may be anisotropically etched therein during step (e), so that
alignment of the first and second wafers may be conducted by an
infrared aligner which would view the alignment marks and alignment
pits as opaque objects, while the silicon wafer surrounding the
alignment marks and pits would be viewed as transparent to the
infrared light of the infrared aligner.
15. The method of claim 12, wherein step (d) further comprises:
photolithographically patterning the insulating layer on the second
surface of the second wafer to produce a plurality of vias therein
at predetermined locations, so that at step (e), the vias in the
second wafer second surface are etched anisotropically concurrently
with those in the first surface of the second wafer.
16. The second of claim 15, wherein at least two of the vias in the
second surface of the second wafer are located and sized for
anisotropic etching through the wafer to produce alignment openings
suitable for enabling visual alignment of the second wafer with the
first wafer, and wherein the remainder of the vias in the second
surface of the second wafer are sized and positioned to coincide
with a selected one of the vias in each set of vias on the first
surface of the second wafer, in order that the anisotropic etching
during step (e) produces a through-hole in each of the selected
recesses of the first surface of the second wafer, this
through-hole later serving as an ink filling hole.
17. The method of claim 16, wherein step (c) further comprises the
forming of at least two alignment marks at predetermined locations
on the first surface of the first wafer for use with the alignment
openings in the second wafer for alignment therewith.
18. The method of claim 12, wherein the step of forming a plurality
of sets of grooves is accomplished by dicing.
19. The method of claim 12, wherein the step (f) of forming a
plurality of sets of grooves is accomplished by patterning a
plurality of sets of elongated vias in the insulative layer on the
first surface of the second wafer concurrently with the patterning
of the plurality of sets of vias during step (d), each set of
elongated vias being located adjacent but spaced from a selected
one of the vias of the set of vias of step (d) and being
perpendicular to the closest edge of the selected vias, and the
grooves being produced during step (e) wherein the second wafer is
anisotropically etched at all locations not protected by the
insulative layer to form recesses bounded by {111} plane side
walls, the elongated vias being sized to produce grooves that have
longer side walls which converge and make grooves with a V-shaped
cross-section but that have closed ends, the closed ends of the
grooves adjacent the selected recesses being opened to the selected
recess by dicing prior to step (g) and the other closed end of the
groove which is to serve eventually as nozzles being opened during
step (i) when the plurality of individual printheads are
obtained.
20. The method of claim 19, wherein the closed ends of the grooves
adjacent the selected recess are opened by isotropic etching the
second wafer for a period of time sufficient to undercut the
insulative layer between the grooves and its selected recess,
cleaning the second wafer to remove the isotropic etch, and then
anisotropic etching the second wafer again to open the grooves to
its selected recess. .Iadd.
21. A method for fabricating a printhead for use in an ink jet
printing device, comprising the steps of:
(a) cleaning a silicon substrate and a second substrate, each
having first and second parallel surfaces, the silicon substrate
surfaces being {100} planes;
(b) depositing a layer of etch resistant material on the surfaces
of the silicon substrate;
(c) forming an equally spaced, linear array of resistive material
on the first surface of the second substrate for use as heating
elements and forming a pattern of electrodes on the same second
substrate surface for enabling individual addressing of each
heating element with current pulses;
(d) patterning the etch resistant material on the first surface of
the silicon substrate to produce at least one via therein for
orientation dependent etching of at least one recess in silicon
substrate bounded by {111} plane side walls;
(e) forming a plurality of equally spaced, parallel grooves in the
first surface of the silicon substrate, one end of the grooves
communicate with the recess and the other ends of the grooves are
open; and
(f) aligning and bonding the silicon substrate and the second
substrate with their first surfaces confronting and contacting each
other, so that each groove contains a heating element therein
spaced a predetermined distance from the groove open end, whereby
the recess serves as an ink supplying manifold, the grooves serve
as capillary filled channels, and the groove open ends serve as the
printhead nozzles. .Iaddend. .Iadd.22. The method of claim 21,
wherein the second substrate is semiconductive; and wherein the
method further comprises depositing a layer of insulating material
on the surfaces of the second substrate prior to step (c).
.Iaddend. .Iadd.23. The method of claim 22, wherein the bonding in
step (f) is accomplished prior to the alignment by applying an
adhesive to the etch resistant material on the first surface of the
silicon substrate, taking care not to permit the adhesive to run
into the recess or grooves; and wherein the method further
comprises the step of curing the adhesive after the alignment of
the silicon substrate and second substrate in step (f) to bond said
substrates together to form the printhead. .Iaddend. .Iadd.24. The
method of claim 23, wherein the semiconductive second substrate is
silicon. .Iaddend. .Iadd.25. The method of claim 24, wherein the
first and second surfaces of the silicon second substrate are
{100}
planes. .Iaddend. .Iadd.26. A method for fabricating a plurality of
printheads, each printhead being usable in an ink jet printing
device for emitting and propelling ink droplets toward a recording
medium, the method comprising the steps of:
(a) cleaning a (100) silicon wafer and a similar sized substrate,
each having first and second substantially parallel surfaces;
(b) forming a layer of etch resistant material on the surfaces of
the wafer;
(c) forming a plurality of sets of equally spaced, linear arrays of
resistive material on the first surface of the second substrate for
use as sets of heating elements, and forming a plurality of sets of
addressing electrodes on the same substrate surface for enabling
individual addressing of each heating element with current
pulse;
(d) photolithographically patterning the etch resistant layer on
the first surface of the wafer to produce a plurality of sets of
vias of predetermined sizes and at predetermined locations
thereon;
(e) anisotropic etching of the wafer to produce sets of recesses in
its first surface, each recess being bounded by {111} plane side
walls;
(f) forming a plurality of sets of equally spaced, parallel grooves
through the first surface of the wafer and its etch resistant
layer, each groove having a predetermined depth and first and
second ends, the first ends of each set of grooves communicating
with an associated one of the set of recesses, the second ends of
each set of grooves opening into another of the set of
recesses;
(g) aligning and bonding the wafer and the substrate with their
first surfaces confronting and contacting each other, the alignment
assuring that each groove contains a one of the heating elements
spaced a predetermined distance from the second open ends thereof
and the bonding permanently attaching the wafer and substrate
together, so that each recess in the set of recesses communicating
with a set of grooves serves as an ink supplying manifold, while
each set of grooves serves as capillary filling channels, with it
second open ends serving as nozzles; and
(h) dicing the bonded wafers into a plurality of individual
printheads, each printhead having a manifold, a set of channels
communicating with the manifold at one end thereof and having
nozzles at the other end with heating elements in each a
predetermined distance from the nozzles, and addressing electrodes
for selectively addressing the heating elements.
.Iaddend. .Iadd.27. The method of claim 26, wherein the similar
sized substrate is semiconductive and wherein the method further
comprises the step of forming a layer of insulating material on the
surfaces of the similar sized substrate prior to step (c).
.Iaddend. .Iadd.28. The method of claim 27, wherein the bonding is
accomplished by the steps of: (i) applying an adhesive on the
remaining unetched etch resistant layer of the first surface of the
wafer so that the adhesive does not run into any of the grooves or
recesses and so that after alignment of the wafer and substrate,
the adhesive is sandwiched therebetween; and
(j) curing the adhesive to accomplish the permanent bonding of the
wafer and substrate together. .Iaddend. .Iadd.29. The method of
claim 28, wherein the semiconductive substrate is a second silicon
wafer. .Iaddend. .Iadd.30. The method of claim 29, wherein the
first and second surfaces of the second silicon wafer are {100}
planes. .Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to thermal ink jet printing, and more
particularly to a thermal ink jet printhead and process for
fabricating it.
2. Description of the Prior Art
Generally speaking, drop-on-demand ink jet printing systems can be
divided into two types. The type using a piezoelectric transducer
to produce a pressure pulse that expells a droplet from a nozzle or
the type using thermal energy to produce a vapor bubble in an
ink-filled channel that expels a droplet. This latter type is
referred to as thermal ink jet printing or bubble ink jet printing
and is the subject matter of the present invention. In existing
thermal ink jet printing, the printhead comprises one or more ink
filled channels, such as disclosed in U.S. Pat. No. 4,463,359 to
Ayata et al, communicating with a relatively small ink supply
chamber at one end and having an opening at the opposite end,
referred to as a nozzle. A thermal energy generator, usually a
resistor, is located in the channels near the nozzle a
predetermined distance therefrom. The resistors are individually
addressed with a current pulse to momentarily vaporize the ink and
form a bubble which expels an ink droplet. As the bubble grows, the
ink bulges from the nozzle and is contained by the surface tension
of the ink as a meniscus. As the bubble begins to collapse, the ink
still in the channel between the nozzle and bubble starts to move
towards the collapsing bubble, causing a volumetric contraction of
the ink at the nozzle and resulting in the separating of the
bulging ink as a droplet. The acceleration of the ink out of the
nozzle while the bubble is growing provides the momentum and
velocity of the droplet in a substantially straight line direction
towards a recording medium, such as paper.
In U.S. Pat. No. 4,463,359, a thermal ink jet printer is disclosed
having one or more ink-filled channels which are replenished by
capillary action. A meniscus is formed at each nozzle to prevent
ink from weeping therefrom. A resistor or heater is located in each
channel at a predetermined distance from the nozzles. Current
pulses representative of data signals are applied to the resistors
to momentarily vaporize the ink in contact therewith and form a
bubble for each current pulse. Ink droplets are expelled from each
nozzle by the growth of the bubbles which causes a quantity of ink
to bulge from the nozzle and break off into a droplet at the
beginning of the bubble collapse. The current pulses are shaped to
prevent the meniscus from breaking up and receding too far into the
channels, after each droplet is expelled. Various embodiments of
linear arrays of thermal ink jet devices are shown such as those
having staggered linear arrays attached to the top and bottom of a
heat sinking substrate and those having different colored inks for
multicolored printing. In one embodiment, a resistor is located in
the center of a relatively short channel having nozzles at both end
thereof. Another passageway is connected to the open-ended channel
and is perpendicular thereto to form a T-shaped structure. Ink is
replenished to the open-ended channel from the passageway by
capillary action. Thus, when a bubble is formed in the open-ended
channel, two different recording mediums may be printed
simultaneously.
U.S. Pat. No. 4,275,290 to Cielo et al discloses a thermally
activated liquid ink printing head having a plurality of orifices
in a horizontal wall of an ink reservoir. In operation, an electric
current pulse heats selected resistors that surround each orifice
and vaporizes the nonconductive ink. The vapor condenses on a
recording medium, such as paper, spaced above and parallel to the
reservoir wall, causing a dark or colored spot representative of a
picture element or pixel. Alternatively, the ink may be forced
above the orifice by partial vaporization of the ink, so that the
ink is transported by a pressure force provided by vapor bubbles.
Instead of partially or completely vaporizing the ink, it can be
caused to flow out of the orifices by reduction of the surface
tension of the ink. By heating the ink in the orifices, the surface
tension coefficient decreases and the meniscus curvature increases,
eventually reaching the paper surface and printing a spot. A
vibrator can be mounted in the reservoir to apply a fluctuating
pressure to the ink. The current pulse to the resistors are
coincident with the maximum pressure produced by the vibration.
Japanese patent application No. 51160 filed in Japan on May 10,
1974 by Hitachi, Ltd. and published after examination as
Publication No. 56-007874 on Feb. 20, 1981 discloses a method of
manufacturing an ink jet nozzle plate having one or more nozzles or
orifices therein. The method comprises growing a high resistance
silicon single crystal layer on a low resistance silicon single
crystal substrate, masking the high resistance silicon crystal with
silicon nitride (Si.sub.3 N.sub.4) having a photo-etched pattern of
the conical orifice to be produced, etching the high resistance
silicon with a crystal axis-dependent etching solution to form a
conical hole therein, oxidizing the surface of the high resistance
silicon, and removing the low resistance silicon.
U.S. Pat. No. 4,362,599 to Imaizumi et al discloses a method of
preparing a high-voltage, semiconductor device. The semiconductor
device is prepared by forming a silicon substrate of one conductor
type having a surface of the (100) crystal plane, opening a
rectangular window having sides parallel to the (100) crystal axis,
etching the interior of the rectangular window with an anisotropic
etching solution to form a recess or dent in the silicon substrate,
removing the oxide film and growing an epitaxial layer of silicon
having a conductor type opposite to that of the substrate over the
entire substrate surface, and masking the recess and etching the
epitaxial layer with an anisotropic etching solution to flatten the
surface of the epitaxial layer. The remainder of the semiconductor
device is produced on the flattened epitaxial layer. U.S. Pat. No.
4,106,976 to Chiou et al discloses a method of fabricating a nozzle
array structure comprising the steps of forming a uniformed layer
of inorganic membrane material, such as silicon dioxide or silicon
nitride, on the planar surface of a monocrystalline substrate, such
as silicon, preferential etching the substrate from the surface
opposite the one with the membrane to form an array of openings
therethrough, and etching the membrane to form orifices coaxially
with the substrate openings. The substrate surfaces are parallel
and oriented in the (100) crystallographic direction.
U.S. Pat. No. 4,157,935 to Solyst discloses a method of producing
nozzle arrays for ink jet printers from silicon wafers that do not
have parallel surfaces. The method comprises exposing the wafer to
a light source through a mask, wherein columnar light from the
light source is directed toward the wafer at a predetermined angle
with respect to the wafer structure and relative motion between the
light source and the wafer is produced; treating the wafer to
render it subject to anisotropic etching only in the non-exposed
areas; and anisotropically etching the wafer to produce uniform
orifices corresponding to the mask.
IBM Technical Disclosure Bulletin, Vol. 21, No. 6 dated November
1978 discloses differential etching of mutually perpendicular
grooves in opposite surfaces of a (100) oriented silicon wafer. An
array of nozzles formed when the depth of the grooves is equal to
one-half of the thickness of the wafer.
An article entitled "Fabrication of Novel Three-Dimensional
Microstructures by the Anisotropic Etching of (100) and (110)
Silicon" by Ernest Bassous, IEEE Transactions on Electron Devices,
Vol. ED-25, No. 10, dated October 1978 discusses the anisotropic
etching of single crystal silicon of (100) and (110) orientation
and the fabrication of three types of microstructures; viz., (1) a
high-precision circular orifice in a thin membrane for use as an
ink jet nozzle, (2) a multisocket miniature electrical connector
with octahedral cavities suitable for cryogenic applications, and
(3) multichannel arrays in (100) and (110) silicon. To make some of
these structures, a novel bonding technique to fuse silicon wafers
with phosphosilicate glass films was developed. The membrane-type
nozzles with circular orifices were fabricated by anisotropic
etching of holes in combination with a process which takes
advantage of the etch resistance of heavily doped p+ silicon in the
etchant.
U.S. Pat. No. 4,438,191 to Cloutier et al discloses a method of
making a monolithic bubble-driven ink jet printhead which
eliminates the need for using adhesives to construct multiple part
assemblies. The method provides a layered structure which can be
manufactured by standard integrated circuit and printed circuit
processing techniques. Basically, the substrate with the bubble
generating resistors and individually addressing electrodes have
the ink chambers and nozzles integrally formed thereon by standard
semiconductor processing.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an ink jet
printhead for high resolution printing that is more cost effective
to manufacture by allowing the concurrent fabrication of large
quantities of printheads from two substrates that are preferably
silicon wafers.
It is another object of this invention to provide a printhead
composed of two parts which are accurately aligned with each other
and bonded together.
It is still another object of this invention to form a plurality of
sets of bubble generating heating elements and their addressing
electrodes on one substrate and to form a corresponding plurality
of sets of ink channels and their ink supplying manifolds on
another substrate via anisotropic etching.
It is yet another object of this invention to provide means for
accurately aligning each of the plurality of sets of channels and
their associated manifolds with a corresponding set of heating
elements so that the two substrates may be bonded together and
diced to produce a plurality of individual printheads.
It is still a further object of this invention to provide a method
of batch fabricating sets of channels and their associated
manifolds wherein the channels are of highly uniform size and shape
with a pitch or center-to-center spacing corresponding to a pixel
density of up to 1000 spots per inch (spi).
In the present invention, a plurality of ink jet printheads are
fabricated from two (100) silicon wafers. In the preferred
embodiment, the printheads are of the thermal, drop-on-demand type
and adapted for carriage printing. A plurality of sets of heating
elements and their individually addressing electrodes are formed on
a surface of one of the wafers, and a corresponding plurality of
sets of parallel channels, each channel set communicating with a
manifold, are anisotropically etched in a surface of the other
wafer. A fill hole and alignment openings are etched in the other
surface of the wafer with the channels. Alignment marks are formed
at predetermined locations on the wafer surface having the heating
elements. The wafer surface with the channels are aligned with the
heating elements via the alignment openings and alignment marks and
bonded together. A plurality of individual printheads are obtained
by dicing the two bonded wafers. Each printhead is fixedly
positioned on one edge of an L-shaped electrode or daughter board
with the manifold fill hole exposed, so that the channel nozzles
are parallel to the daughter board edge. The printhead electrodes
are wire-bonded to corresponding electrodes on the daughter board.
The daughter board with printhead is mounted on an ink supply
cartridge. The ink cartridge may optionally be disposable. The
printhead fill hole is sealingly positioned over and coincident
with an aperture in the cartridge in order that ink may fill and
maintain ink in the printhead manifold and communicating
capillary-filled ink channels.
The printhead, daughter board, and cartridge combination may, for
example, be mounted on a carriage of an ink jet printer that is
adapted for reciprocation across the surface of a recording medium,
such as paper. The paper is stepped a predetermined distance each
time the printhead's reciprocating direction is reversed to print
another line. The array of printhead nozzles in this configuration
are parallel to the direction of movement of the recording medium
and perpendicular to the direction of traversal of the carriage.
Current pulses are selectively applied to the heating elements in
each channel from a controller in the printer in response to
receipt of digitized data signals by the controller. In a pagewidth
array configuration, of course, the array is fixed and oriented
perpendicular to the direction of movement of the recording medium.
During the printing operation, the recording medium continually
moves at a constant velocity.
The current pulses cause the heating elements to transfer thermal
energy to the ink which, as is well known in the art, vaporizes the
ink and momentarily produces a bubble. The heating element cools
after the passage of the current and the bubble collapses. The
nucleation and expansion of the bubble forms an ink droplet and
propels it towards the recording medium.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic isometric view of a carriage type thermal ink
jet printing system incorporating the present invention.
FIG. 2 is a plan view of the daughter board and fixedly mounted
printhead showing the electrodes terminals of the printhead
wire-bonded to the one end of the electrodes of the daughter
board.
FIG. 3 is an enlarged plan view of the printhead attached to the
daughter board as shown in FIG. 2.
FIG. 4 is an enlarged isometric view of a printhead mounted on the
daughter board showing the ink droplet emitting nozzles.
FIG. 5 is a schematic plan view of a wafer having a plurality of
heating element arrays and addressing electrodes, with one heating
element array and one alignment mark being shown enlarged.
FIG. 6A is a schematic plan view of a wafer having a plurality of
ink manifold recesses, with one manifold recess and one alignment
opening being shown enlarged.
FIG. 6B is an enlarged isometric view of one set of channels which
were later diced into one of the manifold recess walls of FIG.
6A.
FIG. 6C is an enlarged cross-sectional view of the wafer of FIG. 6A
as viewed along the line "C--C" thereof, showing an alignment
opening and a recess which will later form the fill hole.
FIG. 6D is a cross-sectional view of the enlarged manifold recess
of FIG. 6A as viewed along line "D--D" thereof.
FIG. 7 is a schematic plan view of a wafer having a plurality of
ink manifold recesses with the channels concurrently etched
therein; this alternate fabrication process also shows one enlarged
manifold recess and associated channels, as well as one enlarged
alignment opening.
FIG. 7A is an enlarged cross-sectional view of a channel recess as
viewed along line "A--A" in the enlarged manifold recess wall of
FIG. 7.
FIG. 8 is an alternate embodiment of FIG. 7 showing all etching
from one side of the wafer.
FIG. 8A is an enlarged cross-sectional view of a channel recess as
viewed along line "A--A" in the enlarged manifold recess wall of
FIG. 8.
FIG. 9a is an isometric view of an etched set of channels from FIG.
7 or 8 after the channels have been milled open.
FIG. 9B is an enlarged, partial top view of the channel recesses of
FIG. 8.
FIG. 10 shows an enlarged isometric view of the channel and
manifold wafer bonded to the wafer with the heating elements after
the excess channel wafer material has been removed.
DESCRIPTION OF THE PREFERRED EMBODIMENT
A typical carriage type, multicolor, thermal ink jet printing
device 10 is shown in FIG. 1. A linear array of ink droplet
producing channels is housed in each printhead 11 of each ink
supply cartridge 12 which may optionally be disposable. One or more
ink supply cartridges are replaceably mounted on a reciprocating
carriage assembly 14 which reciprocates back and forth in the
direction of arrow 13 on guide rails 15. The channels terminate
with orifices or nozzles aligned perpendicular to the carriage
reciprocating direction and parallel to the stepping direction of
the recording medium 16, such as paper. Thus, the printhead prints
a swath of information on the stationary recording medium as it
moves in one direction. Prior to the carriage and printhead
reversing direction, the recording medium is stepped by the
printing device a distance equal to the printed swath in the
direction of arrow 17 and then the printhead moves in the opposite
direction printing another swath of information. Droplets 18 are
expelled and propelled to the recording medium from the nozzles in
response to digital data signals received by the printing device
controller (not shown), which in turn selectively addresses the
individual heating elements, located in the printhead channels a
predetermined distance from the nozzles with a current pulse. The
current pulses passing through the printhead heating elements
vaporize the ink contacting the heating eleents and produce
temporary vapor bubbles to expel droplets of ink from the nozzles.
Alternatively, several printheads may be accurately juxtaposed to
form a pagewidth array of nozzles. In this configuration (not
shown), the nozzles are stationary and the paper moves
therepast.
In FIG. 1, several ink supply cartridges 12 and fixedly mounted
electrode boards or daughter boards 19 are shown in which each
sandwich therebetween a printhead 11, shown in dashed line. The
printhead is permanently attached to the daughter board and their
respective electrodes are wire-bonded together. A printhead fill
hole, discussed more fully later, is sealingly positioned against
and coincident with an aperture (not shown) in the cartridge, so
that ink from the cartridge is continuously supplied to the ink
channels via the manifold during operation of the printing device.
This cartridge is similar to and more fully described in U.S.
patent application Ser. No. 677,426 filed Dec. 3, 1984 by Ivan
Rezanka and assigned to the same assignee as this application.
Accordingly, U.S. application Ser. No. 677,426 is incorporated
herein by reference. Note that the lower portion 20 of each
daughter board 19 has electrode terminals 21 which extend below the
cartridge bottom 22 to facilitate plugging into a female receptacle
(not shown) in the carriage assembly 14. In the preferred
embodiment, the printhead contains 48 channels on 3 mil centers for
printing with a resolution of 300 spots per inch (spi). Such a high
density of addressing electrodes 23 on each daughter board is more
conveniently handled by having some of the electrodes terminate on
both sides. In FIG. 1, the side 24 shown is opposite the one
containing the printhead. The electrodes all originate on the side
with the printhead, but some pass through the daughter board. All
of the electrodes 23 terminate at daughter board end 20.
A plan view of the L-shaped daughter board 19 is shown in FIG. 2.
This view is of the side containing the printhead 11. The daughter
board electrodes 23 are on a one-to-one ratio with the electrodes
of the printhead and are wire-bonded thereto as better shown in
FIG. 3 and described later. The printhead fill hole 25 is readily
apparent in this FIG. 2. About half of the daughter board
electrodes 23 which are on the longer leg of the daughter board are
on the opposite surface thereof so that both sides of the daughter
board end portion 20 have substantially identical parallel arrays
of terminals 21. The electrodes on the opposite side of the
daughter board are electrically connected through the daughter
board at locations 26. An enlarged, plan view of the printhead 11
of FIG. 2 is shown in FIG. 3 bonded to the daughter board 19 with
the printhead electrode terminals 32 wire-bonded to one end of the
daughter board electrodes 23. The wire bonds 56 are installed
automatically by any standard wire bonding machine.
FIG. 4 is an enlarged schematic isometric view of the front face of
the printhead 11 showing the array of droplet emitting nozzles 27.
The lower electrically insulated substrate 28 has the heating
elements (not shown) and addressing electrodes 33 patterned on the
surface 30 thereof, while the upper substrate 31 has parallel
triangular cross-sectional grooves which extend in one direction
and penetrate through the upper substrate front edge 29. The other
end of the grooves communicate with a common internal recess, not
shown in this Figure. The floor of the internal recess has an
opening therethrough for use as an ink fill hole 25. The surface of
the upper substrate with the grooves are aligned and bonded to the
lower substrate 28 as described later, so that a respective one of
the plurality of heating elements is positioned in each channel,
formed by the grooves and the lower substrate. Ink enters the
manifold formed by the recess and the lower substrate through the
fill hole and, by capillary action, fills the channels. The ink at
each nozzle forms a meniscus, the surface tension of which prevents
the ink from weeping therefrom. The addressing electrodes 33 on the
lower substrate 28 terminate at terminals 32. The upper substrate
or channel plate 31 is smaller than that of the lower substrate or
heating element plate 28 in order that the electrode terminals 32
are exposed and available for wire-bonding to the electrodes of the
daughter boards, on which this printhead 11 is permanently
mounted.
In FIG. 5, a plurality of sets of bubble-generating, heating
elements 34 and their addressing electrodes 33 are patterned on the
polished surface of a single-side-polished, (100) silicon wafer 36.
One set of heating elements 34 and addressing electrodes 33
suitable for one ink jet printhead is enlarged. Prior to patterning
the multiple sets of printhead electrodes 33, the resistive
material that serves as the heating elements, and the common return
35, the polished surface to receive the heating elements and
addressing electrodes is coated with an underglaze layer, such as
SiO.sub.2, having a thickness of between 5000 .ANG. and one micron.
The resistive material may be a doped polycrystalline silicon which
may be deposited by chemical vapor deposition (CVD) or any other
well known resistive material such as ZrB.sub.2. The common return
and the addressing electrodes are aluminum leads deposited on the
underglaze layer and over the edges of the heating elements. The
common return ends 37 and addressing electrodes terminals 32 are
positioned at predetermined locations to allow clearance for
wire-bonding to the daughter board electrodes 23 after the channel
plate 31 (see FIG. 10) is attached to make the printhead. The
common return 35 and the addressing electrodes 33 are deposited to
a thickness of 0.5 to 3.0 microns, with the preferred thickness
being 1.5 microns. For electrode passivation, a 2 micron thick
phosphorus doped CVD SiO.sub.2 film (not shown) is deposited over
the entire plurality of sets of heating elements and addressing
electrodes and subsequently etched off of the terminal ends of the
common return and addressing electrodes for subsequent connection
with the daughter board electrodes by wire-bonding. This etching
may be by either the wet or dry etching method. Alternatively, the
electrode passivation may be accomplished by plasma deposited
Si.sub.3 N.sub.4.
If polysilicon heating elements are used, they may be subsequently
oxidized in steam or oxygen at a relatively high temperature of
about 1100.degree. C. for 50 to 80 minutes, prior to the deposition
of the aluminum leads, in order to convert a small fraction of the
polysilicon to SiO.sub.2. In such cases, the heating elements are
thermally oxidized to achieve an overglaze (not shown) of SiO.sub.2
of about 500 .ANG. to 1 micron which has good integrity with
substantially no pin holes.
A tantalum (Ta) layer (not shown) may optionally be deposited to a
thickness of about 1 micron on the oxidized polysilicon overglaze
or passivation layer for added protection thereof against the
cavitational forces generated by the collapsing ink vapor bubbles
during the printhead operation. The Ta layer is etched off all but
the heating elements using, for example, CF.sub.4 /O.sub.2 plasma
etching. For polysilicon heating elements, the aluminum common
return and addressing electrodes are deposited on the underglaze
oxide layer and over the opposing edges of the polysilicon heating
elements which have been cleared of oxide for the attachment of the
common return and electrodes.
At a convenient point after the underglaze is deposited, at least,
two alignment markings 38 are photolithographically produced at
prdetermined locations on separate lower substrates 28 which
substrates make up wafer 36. These alignment markings are used for
alignment of the plurality of upper substrates 31 having the
channels that make up wafer 39. The surface of the single sided
wafer 36 containing the plurality of sets of the heating elements
and addressing electrodes are bonded to the wafer 39 after
alignment between the wafers, as explained later.
In FIG. 6A, a two-sided-polished, (100) silicon wafer 39 is used to
produce the plurality of upper substrates 31 for the printhead.
After the wafer is chemically cleaned, a pyrolytic CVD silicon
nitride layer 41 (see FIG. 6C) is deposited on both sides. Using
conventional photolithography, a via for fill hole 25 for each of
the plurality of upper substrates 31 and, at least two vias for
alignment openings 40 at predetermined locations are printed on one
wafer side 42, opposite the side shown in FIG. 6A. The silicon
nitride is plasma etched off of the patterned vias representing the
fill holes and alignment openings. A potassium hydroxide (KOH)
anisotropic etch is used to etch the fill holes and alignment
openings. In this case, the {111} planes of the (100) wafer make an
angle of 54.7 degrees with the surface of the wafer. The fill holes
are small square surface patterns of about 20 mils per side, and
the alignment openings are about 60 to 80 mils square. Thus, the
alignment openings are etched entirely through the 20 mil thick
wafer, while the fill holes are etched to a terminating apex 43 at
about half way to three quarters through the wafer. The relatively
small square fill hole is invariant to further size increase with
continued etching, so that etching of the alignment openings and
fill holes are not significantly time constrained. This etching
takes about two hours and many wafers can be simultaneously
processed.
Next, the opposite side 44 of wafer 39 is photolithographically
patterned, using the previously etched alignment holes as a
reference, to form the relatively large rectangular recesses 45
that will eventually become the ink manifolds of the printheads.
Also patterned are two recesses 46 between the manifolds in each
substrate 31 and adjacent each of the shorter walls 51 of the
manifold recesses. Parallel elongated grooves 53 which are parallel
and adjacent each longer manifold recess wall 52 extend entirely
across the wafer surface 44 and between the manifold recesses of
adjacent substrates 31. The elongated grooves do not extend to the
edge of the wafer for reasons explained later. The tops 47 of the
walls delineating the manifold recesses are portions of the
original wafer surface 44 that still contain the silicon nitride
layer and forms the streets 47 on which adhesive will be applied
later for bonding the two wafers 36, 39 together. The elongated
grooves 53 and recesses 46 provide clearance for the printhead
electrode terminals during the bonding process discussed later. One
of the manifold recess walls 52 of each manifold will later contain
grooves 48 which will serve as ink channels as discussed with
reference to FIG. 6B. At this stage in the fabrication process, the
grooves 48 have not yet been formed, so that they are shown in
dashed line in FIG. 6A on the top of one of the longer manifold
recess walls 52 to assist in understanding where the future
channels will be produced. A KOH solution anisotropic etch is used
to produce the recess, but, because of the size of the surface
pattern, the etching process must be timed to stop the depth of the
recesses. Otherwise, the pattern size is so large that the etchant
would etch entirely through the wafer. The floor 45a of the
manifold recess 45 is determined at a depth where the etching
process is stopped. This floor 45a is low enough to meet or
slightly surpass the depth of the fill hole apex 43, so that an
opening is produced that is suitable for use as the ink fill hole
25.
Parallel grooves 48 are milled into a predetermined recess wall 52
by any dicing machine as is well known in the art. Each groove 48
shown in FIG. 6B is about 20 mils long and has a depth and width of
about 1 mil. The lineal spacing between axial centerlines of the
grooves are about 3 mils. The silicon nitride layer 41 on wafer
side 44 forms the bonding surfaces, as discussed earlier, and a
coating of an adhesive, such as a thermosetting epoxy, is applied
in a manner such that it does not run or spread into the grooves 48
or other recesses.
The alignment openings 40 are used with a vacuum chuck mask aligner
to align the channel wafer 39 via the alignment marks 38 on the
heating element and addressing electrode wafer 36. The two wafers
are accurately mated and tacked together by partial curing of the
adhesive. Alternatively, the heating element and channel wafers 36,
39 can be given precisely diced edges and than manually or
automatically aligned in a precision jig. The grooves 48
automatically are positioned by either alignment operation, so that
each one has a heating element therein located a predetermined
distance from the nozzles or orifices in channel plate edge 29 (see
FIG. 4). The two wafers are cured in an oven or a laminator to
permanently bond them together and then the channel wafer is milled
to produce individual upper substrates with the manifolds and ink
channels as shown in FIG. 10. Care is taken not to machine the
exposed printhead electrodes terminals 32 which surround the three
sides of the manifold that do not have the nozzles. The recesses 46
and elongated grooves greatly assist in preventing damage to the
printhead electrodes 33 and terminals 32 by spacing the upper
substrate therefrom.
The heating element wafer 36 is then diced to produce a plurality
of individual printheads which are bonded to the daughter board and
the printhead electrode terminals are wire bonded to the daughter
board electrodes.
An alternate fabrication embodiment is shown in FIG. 7, where the
channel grooves 48 are etched concurrently with the manifold recess
45, recess 46, and elongated grooves 53 which provide the clearance
for the printhead electrodes and terminals. The embodiment has like
index numerals for like parts and eliminates the need to dice
individual channels. This fabricating process requires that
parallel milling cuts be made at the end of the channel grooves
which are adjacent the manifold recess 45. The milling or dicing
cuts are perpendicular to the channel grooves. Of necessity, the
cut on the interior side of the manifold recess also cuts a gap 49
in the walls of the manifold recess. These very narrow cuts are
filled later during the application of a passivation layer which is
accomplished after the printhead is mounted on and wire bonded to
the daughter board. With the exception that the channel grooves are
etched instead of milled, this embodiment is substantially the same
as that described with reference to FIGS. 6A through 6D. The cut on
the exterior side of the channels is preferably accomplished after
the wafers are bonded together, in the step of dicing out the
individual printheads. Thus, the channels are opened and the
nozzles are formed in the perpendicular upper substrate face 29 as
the individual printheads are diced out of the wafers.
An enlarged cross-sectional view taken along line "A--A" of FIG. 7
is shown in FIG. 7A. A milling cut shown in dashed line has width
"t" to open the etched groove 48 to the manifold recess 45. In FIG.
7, the milling or dicing cut will form a gap 49 having width "t"
also shown in dashed line.
Anisotropic etching of (100) silicon wafers must always be
conducted through square or rectangular vias, so that the etching
is along the 111 planes. Thus, each recess or opening has walls at
54.7 degrees with the surface of the wafer. If the square or
rectangular opening is small with respect to the wafer thickness a
recess is formed. For example, a small etched rectangular surface
shape will produce an elongated, V-grooved recess with all walls at
54.7 degrees with the wafer surface. As is well known in the art,
only internal corners may be anisotropically etched. External or
convex corners do not have {111} planes to guide the etching and
the etchant etches away such corners very rapidly. This is why the
channels cannot be opened at their ends, but instead must be
completed by a separate process, such as milling. The channel
recesses may be opened by an isotropic etch of a short
predetermined time period, such as two minutes, to undercut the
thin nitride mask, followed by a short KOH anisotropic etch, for
example, for five minutes, to complete the opening of the channels.
Since the isotropic etching etches equally in all directions at the
same time, this removal of silicon must be taken into account when
the anisotropic etching is designed. Because the channels have been
isotropically then anisotropically etched opened, the channel walls
have been shortened but are still within the desired length of
about 20 mils.
In the preferred alternate fabrication embodiment of FIG. 8, all of
the etching is done from one side of the wafer 58. Therefore, only
a single-side-polished, (100) wafer 58 is required as was required
by the heating element wafer 36. On the chemically cleaned,
single-polished surface of the wafer, a layer 41 of pyrolytic CVD
silicon nitride is deposited. A mask for the plurality of the
manifolds, electrode clearances, channels and alignment openings
are printed on the silicon nitride layer using conventional
photolithography. The silicon nitride 41 is plasma etched from the
printed areas of the mask on surface of the wafer. Next, a KOH
anisotropic etch is used to each completely, the wafer. This takes
about two hours and many wafers can be simultaneously processed.
The etching depth depends upon the surface area of the wafer
exposed to the etchant. Only the recesses for the alignment opening
40 and the manifold 45 are sized so that the etchant etches through
the wafer. The channels 48 and the electrode terminal clearing
recesses 54 converge along the {111} planes and stop at a depth
short of the wafer thickness. The channel recesses 48 can be opened
to the manifold recess by a milling run perpendicular to the
channels to form a gap 49, as in the embodiment of FIG. 7. The gaps
49 extend across the wafer 58 as shown in dashed line and have a
thickness "t". The depth of the milling runs are sufficient to open
the channels to the manifold recess and one at least equal to the
depth of the V-grooves 48. The milling runs also slice through the
manifold recess walls 55 that perpendicularly connect to the recess
wall 57 with the channels, but this narrow opening is closed later
by the printhead passivation layer, so that the manifold produced
by the bonding together of the two wafer is sealed except for the
fill hole 25 and nozzles 27.
In this preferred embodiment, the channels are opened to the
manifold by short, for example, 2 minutes duration, isotropic
etching as discussed above with respect to FIG. 7. A well-known
isotropic etch is, for example, mixtures of HF/HNO.sub.3 /C.sub.2
H.sub.4 O.sub.2. As explained earlier, the isotropic etching
removes silicon from the surface contacting the etchant equally in
all directions. Thus, the silicon nitride layer forming the mask
for the anisotropic etching is undercut at the interior end of the
channel (i.e., the end adjacent the manifold recess) since it is
proposely made more narrow than the other end, if this technique is
to be used instead of dicing the channels open. Again, a short KOH
anisotropic etch then removes any silicon that might partially plug
the channel-manifold openings. After each etching process, the
wafers are cleared using, for example, demineralized water at room
temperature.
The original surface of the wafer with silicon nitride layer serves
as the bonding area for bonding the two wafers together, one having
the plurality of sets of channels with associated manifolds and the
other having the plurality of sets of heating elements and
addressing electrodes. The bonding area is coated with a
thermosetting epoxy resin and then the two wafers are aligned
together by using an infrared aligner-bonder which holds the
channel wafer and aligns the channel wafer with the heating element
wafer. Instead of using alignment holes 40 in the wafer 58,
alignment marks (not shown) on this water can be used such as,
small etched pits which, because of the angle of their sides
defined by the intersection of the {111} planes, are seen as opaque
patterns in an infrared microscope. The alignment marks 38 on the
wafer having the plurality of sets of heating elements 34 can be
aluminum patterns, for example, which are also infrared opaque.
Therefore, use of an infrared microscope with infrared opaque
markings on each wafer to be aligned is yet another alternative
technique to align the two wafers together.
Prior to the alignment of the two wafers, the steets 47 or tops of
the manifold recess walls are coated with a layer of adhesive, with
care being taken not to permit the adhesive to run or weep into the
channels 48.
The two wafers are tacked together and cured permanently in a
laminator. The printhead electrode terminals are cleared by milling
the wafer portions as shown in FIG. 10. Next, the heating element
wafer is diced into a plurality of individual printheads, which
operation also opens the channel ends opposite the manifold recess
45, forming the nozzles 27 in the freshly cut face 29. FIG. 9A is
an enlarged, isometric view of the finished printhead with the
lower substrate 28 with the heating elements removed to more
clearly show the V-shaped channels 48. Each printhead is
permanently mounted on a daughter board and the respective
electrodes are wire-bonded together. The wire bonds and pads or
terminals are coated with a passivation layer of silicone
encapsulation compound, such as Dow Corning 3-6550 RTV (Trademark).
This layer electrically isolates the electrodes and wire bonds.
FIG. 9B is an enlarged partial top view of the channel recesses 48
of FIG. 8 with the region 60 of isotropic-anisotropic etching of
the interior ends of the channels shown in dashed line with arrows
schematically representing the direction of the etching. Though the
isotropic etchant attacks all surface areas, only the region
involving the interior ends of the channel recesses 48 is depicted.
The silicon nitride layer 41, which forms the mask for the
anisotropic etching and serves as the streets 47 for the
application of the adhesive, is very narrow at the channel recess
ends which are adjacent the manifold recess 45. This distance is
shown as "X" distance, generally in the range of 0.2 to 1.0 mil. At
the other end, which will ultimately be the nozzles, the distance
"Y" is at least twice that of the "X" distance. Thus, while the
isotropic etching removes and undercuts the silicon nitride layer
at the channel interior ends, it cannot do so at the other wider
end. Having anticipated the enlargement and shortening of the
channels by using the technique of opening the channels to the
manifold by isotropic then anisotropic etching, the use of dicing
the interior channel ends to open them to the manifold is
avoided.
A variety of combinations of these process steps can be used to
fabricate a complete printhead. These combinations are illustrated
in Table I for processes using two major etching steps and in Table
II for processes using only one major etching step. The sequential
process steps in each Table are sequentially numbered. The steps
with the same numbers, but coupled with a letter of the alphabet,
are alternative steps in the fabricating process. Each subsequent
alternate step with like letters must be used for any one process.
For example, in Table I, step 6.a must be used when step 4.a is
selected rather than either step 6.b.1 or 6.6.2. Note that steps
6.b.1 and 6.b.2 are alternate optional steps for the process using
the step 4.b. If the subsequent alternative steps are optional with
either the step 4.a or 4.b, then both combinations of numbers and
letters are used as in step 8.(a.1 or b.1) and step 8(a.2 or b.2).
This numbering approach is used throughout both Table I and Table
II to present the various alternative fabricating processes.
TABLE I ______________________________________ TWO MAJOR ETCH
PROCESS ______________________________________ 1. deposit silicon
nitride on (100) wafers 2. pattern fill and alignment openings on
one wafer side by, for example, plasma etching to form mask. 3.
anisotropic etch fill and alignment openings. 4.a. pattern manifold
and electrode clearance recesses on other side of wafer. 4.b.
pattern manifold, channels, and electrode clearance recesses on
other side of wafer. 5. anisotropic etch these structures. 6.a.
dice individual channels. 6.b.1. dice channel recess ends adjacent
manifold recess to open them to manifold. 6.b.2. isotropically etch
to undercut nitride mask at channel end adjacent manifold, then
anisotropically etch to completely finish opening each channel end.
7. apply adhesive to channel plate. 8. (a.1. or b.1.) using etched
alignment openings, align wafer with alignment marks on associated
wafer containing heating elements and addressing electrodes, tack
together by partially curing adhesive. 8. (a.2. or b.2.) dice
precise edges on both wafer with etched structures and wafer
containing heating elements and addressing electrodes, align other
wafers using a jig and tack together by partially curing adhesive.
9. permanently bond wafers together by a thermocompressive means.
10. dice out individual printheads, this step also opens channel
ends opposite the manifold, with this open end being the nozzles.
11. mount printhead on daughter board and wirebond printhead
electrodes to electrodes of daughter board. 12. passivate wirebonds
with silicone encapsulation compound.
______________________________________
TABLE II ______________________________________ ONE MAJOR ETCH STEP
PROCESS ______________________________________ 1. deposit silicon
nitride on (100) wafers. 2.a. pattern all structures on one side of
wafers (manifolds, channels, alignment pits, etc. 2.b. use
two-sided aligner to simultaneously pattern fill and alignment
openings on one side of wafer and remaining structures (manifold,
channels, and electrode clearance recesses) on the other side. 3.
anisotropically etch all structures. 4.(a. or b.)
isotropically-anisotropically etch channel ends adjacent manifold
to open channels to associated manifold. 4.(a. or b.) dice channel
ends adjacent manifold to open channels to associated manifold. 5.
apply adhesive to nitride surface containing manifold and channels.
6.a.1. align wafer with channels and associated manifolds with a
wafer containing heating elements and addressing electrodes using
infrared aligner-bonder. use alignment pits on etched wafer with
aluminum marks on wafer with heating elements, tack wafers together
by partially curing adhesive. 6.(a.2. or dice edges on wafer with
channels and associated b.2.) manifolds and wafer with heating
elements and addressing electrodes, align in a jig, and tack wafers
together by partially curing adhesive. 6.b.1. using etched
alignment openings on etched wafer align with a wafer having
heating elements and addressing electrodes by using alignment marks
placed at predetermined locations on heating element wafer. 7.
permanently bond wafers together by thermocompressive means. 8.
dice out individual printheads; this opens channel ends opposite
manifold and forms nozzles. 9. mount each printhead on a daughter
board and wire bond printhead electrodes to daughter board
electrodes. 10. passivate wirebonds with silicone encapsulation
compound. ______________________________________
Several advantages are obtained by this fabrication approach. The
microfabrication of the channel plate batches by chemical
anisotropic etching in inexpensive and the channels are of uniform
size, independent of wafer thickness or various in thickness. The
channel placement is accurate, especially when delineated with
lithographic resolution. The heating elements are accurately
aligned in the channels because of the wafer to wafer alignment
using the alignment openings in the channel plate and the alignment
marks on the heating element plate or, alternatively, the infrared
opaque alignment marks. Since the heating elements and addressing
electrodes are patterned on silicon wafers, mating anisotropically
etched silicon channels and manifold eliminates any potential error
due to thermal expansion differences during printhead operation.
One major advantage is that batch processing is practical; 100
wafers of 100 mm diameter can be simultaneously etched with about
250 discrete printhead parts per wafer, thus providing around
50,000 parts per batch.
Many modifications are variations are apparent from the foregoing
description of the invention and all such modifications and
variations are intended to be within the scope of the present
invention.
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