# Patent

## Title
Method of fabricating printhead using metal film for protecting hydrophobic ink ejection face

## Abstract

A method of fabricating a printhead having a hydrophobic ink ejection face, the method comprising the steps of: (a) providing a partially-fabricated printhead comprising a plurality of nozzle chambers and a nozzle plate having relatively hydrophilic nozzle surface, the nozzle surface at least partially defining the ink ejection face of the printhead; (b) defining a plurality of nozzle openings in the nozzle plate; (c) depositing a hydrophobic polymeric layer onto the nozzle surface; (d) depositing a protective metal film onto the polymeric layer; (e) subjecting the printhead to an oxidizing plasma; and (f) removing the protective metal film, thereby providing a printhead having a relatively hydrophobic ink ejection face. Step (b) may be performed immediately after any of steps (a), (c) or (d).

## Background
CROSS REFERENCES TO RELATED APPLICATION
This application is a continuation-in-part application of U.S. application Ser. No. 11/685,084 filed on Mar. 12, 2007, now issued U.S. Pat. No. 7,794,613.
CROSS REFERENCES
The following patents or patent applications filed by the applicant or assignee of the present invention are hereby incorporated by cross-reference.


















09/575197
7079712
09/575123
6825945
09/575165
6813039
6987506


7038797
6980318
6816274
7102772
09/575186
6681045
6728000


7173722
7088459
09/575181
7068382
7062651
6789194
6789191


6644642
6502614
6622999
6669385
6549935
6987573
6727996


6591884
6439706
6760119
09/575198
6290349
6428155
6785016


6870966
6822639
6737591
7055739
09/575129
6830196
6832717


6957768
09/575162
09/575172
7170499
7106888
7123239
6405055


6628430
7136186
10/920372
7145689
7130075
7081974
7177055


10/919243
7161715
7154632
7158258
7148993
7075684
11/635526


11/650545
11/653241
11/653240
10/503924
7108437
6915140
6999206


7136198
7092130
7170652
6967750
6995876
7099051
11/107942


11/107943
11/209711
11/599336
7095533
6914686
7161709
7099033


11/124158
11/124196
11/124199
11/124162
11/124202
11/124197
11/124154


11/124198
11/124153
11/124151
11/124160
11/124192
11/124175
11/124163


11/124149
11/124152
11/124173
11/124155
11/124157
11/124174
11/124194


11/124164
11/124200
11/124195
11/124166
11/124150
11/124172
11/124165


11/124186
11/124185
11/124184
11/124182
11/124201
11/124171
11/124181


11/124161
11/124156
11/124191
11/124159
11/124176
11/124188
11/124170


11/124187
11/124189
11/124190
11/124180
11/124193
11/124183
11/124178


11/124177
11/124148
11/124168
11/124167
11/124179
11/124169
11/187976


11/188011
11/188014
11/482979
11/228540
11/228500
11/228501
11/228530


11/228490
11/228531
11/228504
11/228533
11/228502
11/228507
11/228482


11/228505
11/228497
11/228487
11/228529
11/228484
11/228489
11/228518


11/228536
11/228496
11/228488
11/228506
11/228516
11/228526
11/228539


11/228538
11/228524
11/228523
11/228519
11/228528
11/228527
11/228525


11/228520
11/228498
11/228511
11/228522
111/228515
11/228537
11/228534


11/228491
11/228499
11/228509
11/228492
11/228493
11/228510
11/228508


11/228512
11/228514
11/228494
11/228495
11/228486
11/228481
11/228477


11/228485
11/228483
11/228521
11/228517
11/228532
11/228513
11/228503


11/228480
11/228535
11/228478
11/228479
7079292
6227652
6213588


6213589
6231163
6247795
6394581
6244691
6257704
6416168


6220694
6257705
6247794
6234610
6247793
6264306
6241342


6247792
6264307
6254220
6234611
6302528
6283582
6239821


6338547
6247796
6557977
6390603
6362843
6293653
6312107


6227653
6234609
6238040
6188415
6227654
6209989
6247791


6336710
6217153
6416167
6243113
6283581
6247790
6260953


6267469
6588882
6742873
6918655
6547371
6938989
6598964


6923526
09/835448
6273544
6309048
6420196
6443558
6439689


6378989
6848181
6634735
6299289
6299290
6425654
6902255


6623101
6406129
6505916
6457809
6550895
6457812
7152962


6428133
11/144778
7080895
11/144844
7182437
11/599341
11/635533


11/607976
11/607975
11/607999
11/607980
11/607979
11/607978
09/517539


6566858
6331946
6246970
6442525
09/517384
09/505951
6374354


09/517608
6816968
6757832
6334190
6745331
09/517541
10/203559


10/203560
7093139
10/636263
10/636283
10/866608
10/902889
10/902833


10/940653
10/942858
11/706329
10/727181
10/727162
10/727163
10/727245


7121639
7165824
7152942
10/727157
7181572
7096137
10/727257


10/727238
7188282
10/727159
10/727180
10/727179
10/727192
10/727274


10/727164
10/727161
10/727198
10/727158
10/754536
10/754938
10/727227


10/727160
10/934720
7171323
11/272491
11/474278
11/488853
11/488841


10/296522
6795215
7070098
7154638
6805419
6859289
6977751


6398332
6394573
6622923
6747760
6921144
10/884881
7092112


10/949294
11/039866
7173739
6986560
7008033
11/148237
11/248435


11/248426
11/478599
11/499749
10/922846
7182422
11/650537
11/712540


10/854521
10/854522
10/854488
10/854487
10/854503
10/854504
10/854509


10/854510
7093989
10/854497
10/854495
10/854498
10/854511
10/854512


10/854525
10/854526
10/854516
10/854508
10/854507
10/854515
10/854506


10/854505
10/854493
10/854494
10/854489
10/854490
10/854492
10/854491


10/854528
10/854523
10/854527
10/854524
10/854520
10/854514
10/854519


10/854513
10/854499
10/854501
10/854500
10/854502
10/854518
10/854517


10/934628
7163345
11/499803
11/601757
11/706295
11/544764
11/544765


11/544772
11/544773
11/544774
11/544775
11/544776
11/544766
11/544767


11/544771
11/544770
11/544769
11/544777
11/544768
11/544763
10/728804


7128400
7108355
6991322
10/728790
7118197
10/728970
10/728784


10/728783
7077493
6962402
10/728803
7147308
10/728779
7118198


7168790
7172270
10/773199
6830318
10/773201
10/773191
10/773183


7108356
7118202
10/773186
7134744
10/773185
7134743
10/773197


10/773203
10/773187
7134745
7156484
7118201
7111926
10/773184


7018021
11/060751
11/060805
11/188017
7128402
11/298774
11/329157


11/490041
11/501767
11/499736
11/505935
11/506172
11/505846
11/505857


11/505856
11/524908
11/524938
11/524900
11/524912
11/592999
11/592995


11/603825
11/649773
11/650549
11/653237
6746105
10/407212
10/407207


10/683064
10/683041
6750901
6476863
6788336
11/097308
11/097309


11/097335
11/097299
11/097310
11/097213
11/210687
11/097212
7147306


11/545509
7156508
7159972
7083271
7165834
7080894
10/760218


7090336
7156489
10/760233
10/760246
7083257
10/760243
10/760201


10/760185
10/760253
10/760255
10/760209
7118192
10/760194
10/760238


7077505
10/760235
7077504
10/760189
10/760262
10/760232
10/760231


7152959
10/760190
7178901
10/760227
7108353
7104629
11/446227


11/454904
11/472345
11/474273
11/478594
11/474279
11/482939
11/482950


11/499709
11/592984
11/601668
11/603824
11/601756
11/601672
11/650546


11/653253
11/706328
11/706299
11/706965
11/246687
11/246718
11/246685


11/246686
11/246703
11/246691
11/246711
11/246690
11/246712
11/246717


11/246709
11/246700
11/246701
11/246702
11/246668
11/246697
11/246698


11/246699
11/246675
11/246674
11/246667
11/246684
11/246672
11/246673


11/246683
11/246682
11/003786
11/003616
11/003418
11/003334
11/003600


11/003404
11/003419
11/003700
11/003601
11/003618
11/003615
11/003337


11/003698
11/003420
6984017
11/003699
11/071473
11/003463
11/003701


11/003683
11/003614
11/003702
11/003684
11/003619
11/003617
11/293800


11/293802
11/293801
11/293808
11/293809
11/482975
11/482970
11/482968


11/482972
11/482971
11/482969
11/246676
11/246677
11/246678
11/246679


11/246680
11/246681
11/246714
11/246713
11/246689
11/246671
11/246670


11/246669
11/246704
11/246710
11/246688
11/246716
11/246715
11/293832


11/293838
11/293825
11/293841
11/293799
11/293796
11/293797
11/293798


11/293804
11/293840
11/293803
11/293833
11/293834
11/293835
11/293836


11/293837
11/293792
11/293794
11/293839
11/293826
11/293829
11/293830


11/293827
11/293828
11/293795
11/293823
11/293824
11/293831
11/293815


11/293819
11/293818
11/293817
11/293816
10/760254
10/760210
10/760202


10/760197
10/760198
10/760249
10/760263
10/760196
10/760247
7156511


10/760264
10/760244
7097291
10/760222
10/760248
7083273
10/760192


10/760203
10/760204
10/760205
10/760206
10/760267
10/760270
10/760259


10/760271
10/760275
10/760274
7121655
10/760184
10/760195
10/760186


10/760261
7083272
11/501771
11/583874
11/650554
11/706322
11/706968


11/014764
11/014763
11/014748
11/014747
11/014761
11/014760
11/014757


11/014714
11/014713
11/014762
11/014724
11/014723
11/014756
11/014736


11/014759
11/014758
11/014725
11/014739
11/014738
11/014737
11/014726


11/014745
11/014712
11/014715
11/014751
11/014735
11/014734
11/014719


11/014750
11/014749
11/014746
11/014769
11/014729
11/014743
11/014733


11/014754
11/014755
11/014765
11/014766
11/014740
11/014720
11/014753


11/014752
11/014744
11/014741
11/014768
11/014767
11/014718
11/014717


11/014716
11/014732
11/014742
11/097268
11/097185
11/097184
11/293820


11/293813
11/293822
11/293812
11/293821
11/293814
11/293793
11/293842


11/293811
11/293807
11/293806
11/293805
11/293810
11/518238
11/518280


11/518244
11/518243
11/518242
11/246707
11/246706
11/246705
11/246708


11/246693
11/246692
11/246696
11/246695
11/246694
11/482958
11/482955


11/482962
11/482963
11/482956
11/482954
11/482974
11/482957
11/482987


11/482959
11/482960
11/482961
11/482964
11/482965
11/482976
11/482973


11/495815
11/495816
11/495817
11/482980
11/563684
11/482953
11/482977


6238115
6386535
6398344
6612240
6752549
6805049
6971313


6899480
6860664
6925935
6966636
7024995
10/636245
6926455


7056038
6869172
7021843
6988845
6964533
6981809
11/060804


11/065146
11/155544
11/203241
11/206805
11/281421
11/281422
11/482981


7152972
11/592996
11/482967
11/482966
11/482988
11/482989
11/482982


11/482983
11/482984
11/495818
11/495819
11677049
11677050
11677051


11/482978
11/640356
11/640357
11/640358
11/640359
11/640360
11/640355


11/679786
11/544778
11/544779











FIELD OF THE INVENTION
The present invention relates to the field of printers and particularly inkjet printheads. It has been developed primarily to improve print quality and reliability in high resolution printheads.
BACKGROUND OF THE INVENTION
Many different types of printing have been invented, a large number of which are presently in use. The known forms of print have a variety of methods for marking the print media with a relevant marking media. Commonly used forms of printing include offset printing, laser printing and copying devices, dot matrix type impact printers, thermal paper printers, film recorders, thermal wax printers, dye sublimation printers and ink jet printers both of the drop on demand and continuous flow type. Each type of printer has its own advantages and problems when considering cost, speed, quality, reliability, simplicity of construction and operation etc.
In recent years, the field of ink jet printing, wherein each individual pixel of ink is derived from one or more ink nozzles has become increasingly popular primarily due to its inexpensive and versatile nature.
Many different techniques on ink jet printing have been invented. For a survey of the field, reference is made to an article by J Moore, “Non-Impact Printing: Introduction and Historical Perspective”, Output Hard Copy Devices, Editors R Dubeck and S Sherr, pages 207-220 (1988).
Ink Jet printers themselves come in many different types. The utilization of a continuous stream of ink in ink jet printing appears to date back to at least 1929 wherein U.S. Pat. No. 1,941,001 by Hansell discloses a simple form of continuous stream electro-static ink jet printing.
U.S. Pat. No. 3,596,275 by Sweet also discloses a process of a continuous ink jet printing including the step wherein the ink jet stream is modulated by a high frequency electro-static field so as to cause drop separation. This technique is still utilized by several manufacturers including Elmjet and Scitex (see also U.S. Pat. No. 3,373,437 by Sweet et al)
Piezoelectric ink jet printers are also one form of commonly utilized ink jet printing device. Piezoelectric systems are disclosed by Kyser et. al. in U.S. Pat. No. 3,946,398 (1970) which utilizes a diaphragm mode of operation, by Zolten in U.S. Pat. No. 3,683,212 (1970) which discloses a squeeze mode of operation of a piezoelectric crystal, Stemme in U.S. Pat. No. 3,747,120 (1972) discloses a bend mode of piezoelectric operation, Howkins in U.S. Pat. No. 4,459,601 discloses a piezoelectric push mode actuation of the ink jet stream and Fischbeck in U.S. Pat. No. 4,584,590 which discloses a shear mode type of piezoelectric transducer element.
Recently, thermal inkjet printing has become an extremely popular form of ink jet printing. The ink jet printing techniques include those disclosed by Endo et al in GB 2007162 (1979) and Vaught et al in U.S. Pat. No. 4,490,728. Both the aforementioned references disclosed ink jet printing techniques that rely upon the activation of an electrothermal actuator which results in the creation of a bubble in a constricted space, such as a nozzle, which thereby causes the ejection of ink from an aperture connected to the confined space onto a relevant print media. Printing devices utilizing the electro-thermal actuator are manufactured by manufacturers such as Canon and Hewlett Packard.
As can be seen from the foregoing, many different types of printing technologies are available. Ideally, a printing technology should have a number of desirable attributes. These include inexpensive construction and operation, high speed operation, safe and continuous long term operation etc. Each technology may have its own advantages and disadvantages in the areas of cost, speed, quality, reliability, power usage, simplicity of construction operation, durability and consumables.
In the construction of any inkjet printing system, there are a considerable number of important factors which must be traded off against one another especially as large scale printheads are constructed, especially those of a pagewidth type. A number of these factors are outlined below.
Firstly, inkjet printheads are normally constructed utilizing micro-electromechanical systems (MEMS) techniques. As such, they tend to rely upon standard integrated circuit construction/fabrication techniques of depositing planar layers on a silicon wafer and etching certain portions of the planar layers. Within silicon circuit fabrication technology, certain techniques are better known than others. For example, the techniques associated with the creation of CMOS circuits are likely to be more readily used than those associated with the creation of exotic circuits including ferroelectrics, gallium arsenide etc. Hence, it is desirable, in any MEMS constructions, to utilize well proven semi-conductor fabrication techniques which do not require any “exotic” processes or materials. Of course, a certain degree of trade off will be undertaken in that if the advantages of using the exotic material far out weighs its disadvantages then it may become desirable to utilize the material anyway. However, if it is possible to achieve the same, or similar, properties using more common materials, the problems of exotic materials can be avoided.
A desirable characteristic of inkjet printheads would be a hydrophobic ink ejection face (“front face” or “nozzle face”), preferably in combination with hydrophilic nozzle chambers and ink supply channels. Hydrophilic nozzle chambers and ink supply channels provide a capillary action and are therefore optimal for priming and for re-supply of ink to nozzle chambers after each drop ejection. A hydrophobic front face minimizes the propensity for ink to flood across the front face of the printhead. With a hydrophobic front face, the aqueous inkjet ink is less likely to flood sideways out of the nozzle openings. Furthermore, any ink which does flood from nozzle openings is less likely to spread across the face and mix on the front face—they will instead form discrete spherical microdroplets which can be managed more easily by suitable maintenance operations.
However, whilst hydrophobic front faces and hydrophilic ink chambers are desirable, there is a major problem in fabricating such printheads by MEMS techniques. The final stage of MEMS printhead fabrication is typically ashing of photoresist using an oxidizing plasma, such as an oxygen plasma. However, organic, hydrophobic materials deposited onto the front face are typically removed by the ashing process to leave a hydrophilic surface. Moreover, a problem with post-ashing vapour deposition of hydrophobic materials is that the hydrophobic material will be deposited inside nozzle chambers as well as on the front face of the printhead. The nozzle chamber walls become hydrophobized, which is highly undesirable in terms of generating a positive ink pressure biased towards the nozzle chambers. This is a conundrum, which creates significant demands on printhead fabrication.
Accordingly, it would be desirable to provide a printhead fabrication process, in which the resultant printhead has improved surface characteristics, without comprising the surface characteristics of nozzle chambers. It would further be desirable to provide a printhead fabrication process, in which the resultant printhead has a hydrophobic front face in combination with hydrophilic nozzle chambers.
SUMMARY OF THE INVENTION
In a first aspect the present invention provides a method of fabricating a printhead having a hydrophobic ink ejection face, the method comprising the steps of:
(a) providing a partially-fabricated printhead comprising a plurality of nozzle chambers and a nozzle plate having relatively hydrophilic nozzle surface, said nozzle surface at least partially defining the ink ejection face of the printhead;
(b) defining a plurality of nozzle openings in at least said nozzle plate;
(c) depositing a hydrophobic polymeric layer onto the nozzle surface;
(d) depositing a protective metal film onto at least said polymeric layer;
(e) subjecting said printhead to an oxidizing plasma; and
(f) removing said protective metal film,
thereby providing a printhead having a relatively hydrophobic ink ejection face, wherein step (b) is performed immediately after any of steps (a), (c) or (d).
Optionally, step (c) comprises the sub-steps of:

    
    
        (c)(i) depositing the hydrophobic polymeric layer onto the nozzle surface; and
        (c)(ii) photopatterning said polymeric layer so as to define a plurality of nozzle openings in said polymeric layer.
    
    


Optionally, photopatterning comprises UV-curing at least some of said polymeric material.
Optionally, step (d) comprises the sub-steps of:

    
    
        (d)(i) depositing a protective metal film onto at least said polymeric layer; and
        (d)(ii) defining a plurality of film openings in said metal film, said film openings being aligned with said nozzle openings.
    
    


Optionally, sub-step (d)(ii) comprises the further sub-steps of:

    
    
        (d)(ii)(1) depositing a mask on said protective metal film;
        (d)(ii)(2) patterning said mask so as to unmask said metal film in a plurality of film opening regions; and
        (d)(ii)(3) etching said unmasked nozzle opening regions to define said plurality of film openings.
    
    


Optionally, step (b) is performed immediately after step (c), and step (b) comprises: defining a plurality of nozzle openings in said nozzle plate and in said polymeric layer.
Optionally, said protective metal film is comprised of a metal selected from the group comprising: titanium and aluminium.
Optionally, said protective metal film has a thickness in the range of 10 nm to 1000 nm.
Optionally, step (f) is performed by wet or dry etching.
Optionally, step (f) is performed by a wet rinse using peroxide or acid.
Optionally, all plasma oxidizing steps are performed prior to removing said protective metal film in step (f).
Optionally, all backside MEMS processing steps are performed prior to removing said protective metal film in step (f).
Optionally, said backside MEMS processing steps include defining ink supply channels from a backside of said wafer, said backside being an opposite face to said ink ejection face.
Optionally, in said partially-fabricated printhead, a roof of each nozzle chamber is supported by a sacrificial photoresist scaffold, said method further comprising the step of ashing said photoresist scaffold prior to removing said protective metal film.
Optionally, oxidizing plasma is an oxygen ashing plasma.
Optionally, roof of each nozzle chamber is defined at least partially by said nozzle plate.
Optionally, said nozzle plate is spaced apart from a substrate, such that sidewalls of each nozzle chamber extend between said nozzle plate and said substrate.
Optionally, said hydrophobic polymeric layer is comprised of a polymeric material selected from the group comprising: polymerized siloxanes and fluorinated polyolefins.
Optionally, said polymeric material is selected from the group comprising: polydimethylsiloxane (PDMS) and perfluorinated polyethylene (PFPE).
In a further aspect the present invention provides a printhead obtained or obtainable by a method comprising the steps of:

    
    
        (a) providing a partially-fabricated printhead comprising a plurality of nozzle chambers and a nozzle plate having relatively hydrophilic nozzle surface, said nozzle surface at least partially defining the ink ejection face of the printhead;
        (b) defining a plurality of nozzle openings in at least said nozzle plate;
        (c) depositing a hydrophobic polymeric layer onto the nozzle surface;
        (d) depositing a protective metal film onto at least said polymeric layer;
        (e) subjecting said printhead to an oxidizing plasma; and
        (f) removing said protective metal film,

thereby providing a printhead having a relatively hydrophobic ink ejection face, wherein step (b) is performed immediately after any of steps (a), (c) or (d).

    
    





BRIEF DESCRIPTION OF THE DRAWINGS
Optional embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:
FIG. 1 is a partial perspective view of an array of nozzle assemblies of a thermal inkjet printhead;
FIG. 2 is a side view of a nozzle assembly unit cell shown in FIG. 1;
FIG. 3 is a perspective of the nozzle assembly shown in FIG. 2;
FIG. 4 shows a partially-formed nozzle assembly after deposition of side walls and roof material onto a sacrificial photoresist layer;
FIG. 5 is a perspective of the nozzle assembly shown in FIG. 4;
FIG. 6 is the mask associated with the nozzle rim etch shown in FIG. 7;
FIG. 7 shows the etch of the roof layer to form the nozzle opening rim;
FIG. 8 is a perspective of the nozzle assembly shown in FIG. 7;
FIG. 9 is the mask associated with the nozzle opening etch shown in FIG. 10;
FIG. 10 shows the etch of the roof material to form the elliptical nozzle openings;
FIG. 11 is a perspective of the nozzle assembly shown in FIG. 10;
FIG. 12 shows the oxygen plasma ashing of the first and second sacrificial layers;
FIG. 13 is a perspective of the nozzle assembly shown in FIG. 12;
FIG. 14 shows the nozzle assembly after the ashing, as well as the opposing side of the wafer;
FIG. 15 is a perspective of the nozzle assembly shown in FIG. 14;
FIG. 16 is the mask associated with the backside etch shown in FIG. 17;
FIG. 17 shows the backside etch of the ink supply channel into the wafer;
FIG. 18 is a perspective of the nozzle assembly shown in FIG. 17;
FIG. 19 shows the nozzle assembly of FIG. 10 after deposition of a hydrophobic polymeric coating;
FIG. 20 is a perspective of the nozzle assembly shown in FIG. 19;
FIG. 21 shows the nozzle assembly of FIG. 19 after photopatterning of the polymeric coating;
FIG. 22 is a perspective of the nozzle assembly shown in FIG. 21;
FIG. 23 shows the nozzle assembly of FIG. 7 after deposition of a hydrophobic polymeric coating;
FIG. 24 is a perspective of the nozzle assembly shown in FIG. 23;
FIG. 25 shows the nozzle assembly of FIG. 23 after photopatterning of the polymeric coating;
FIG. 26 is a perspective of the nozzle assembly shown in FIG. 25;
FIG. 27 is a side sectional view of an inkjet nozzle assembly comprising a roof having a moving portion defined by a thermal bend actuator;
FIG. 28 is a cutaway perspective view of the nozzle assembly shown in FIG. 27;
FIG. 29 is a perspective view of the nozzle assembly shown in FIG. 27;
FIG. 30 is a cutaway perspective view of an array of the nozzle assemblies shown in FIG. 27;
FIG. 31 is a side sectional view of an alternative inkjet nozzle assembly comprising a roof having a moving portion defined by a thermal bend actuator;
FIG. 32 is a cutaway perspective view of the nozzle assembly shown in FIG. 31;
FIG. 33 is a perspective view of the nozzle assembly shown in FIG. 31;
FIG. 34 shows the nozzle assembly of FIG. 27 with a polymeric coating on the roof forming a mechanical seal between a moving roof portion and a static roof portion;
FIG. 35 shows the nozzle assembly of FIG. 31 with a polymeric coating on the roof forming a mechanical seal between a moving roof portion and a static roof portion;
FIG. 36 shows the nozzle assembly of FIG. 21 after deposition of a protective metal film;
FIG. 37 shows the nozzle assembly of FIG. 36 after removal a the metal film from within the nozzle opening; and
FIG. 38 shows the nozzle assembly of FIG. 36 after backside MEMS processing to define an ink supply channel.



DESCRIPTION OF OPTIONAL EMBODIMENTS
The present invention may be used with any type of printhead. The present Applicant has previously described a plethora of inkjet printheads. It is not necessary to describe all such printheads here for an understanding of the present invention. However, the present invention will now be described in connection with a thermal bubble-forming inkjet printhead and a mechanical thermal bend actuated inkjet printhead. Advantages of the present invention will be readily apparent from the discussion that follows.
Thermal Bubble-Forming Inkjet Printhead
Referring to FIG. 1, there is shown a part of printhead comprising a plurality of nozzle assemblies. FIGS. 2 and 3 show one of these nozzle assemblies in side-section and cutaway perspective views.
Each nozzle assembly comprises a nozzle chamber 24 formed by MEMS fabrication techniques on a silicon wafer substrate 2. The nozzle chamber 24 is defined by a roof 21 and sidewalls 22 which extend from the roof 21 to the silicon substrate 2. As shown in FIG. 1, each roof is defined by part of a nozzle surface 56, which spans across an ejection face of the printhead. The nozzle surface 56 and sidewalls 22 are formed of the same material, which is deposited by PECVD over a sacrificial scaffold of photoresist during MEMS fabrication. Typically, the nozzle surface 56 and sidewalls 22 are formed of a ceramic material, such as silicon dioxide or silicon nitride. These hard materials have excellent properties for printhead robustness, and their inherently hydrophilic nature is advantageous for supplying ink to the nozzle chambers 24 by capillary action. However, the exterior (ink ejection) surface of the nozzle surface 56 is also hydrophilic, which causes any flooded ink on the surface to spread.
Returning to the details of the nozzle chamber 24, it will be seen that a nozzle opening 26 is defined in a roof of each nozzle chamber 24. Each nozzle opening 26 is generally elliptical and has an associated nozzle rim 25. The nozzle rim 25 assists with drop directionality during printing as well as reducing, at least to some extent, ink flooding from the nozzle opening 26. The actuator for ejecting ink from the nozzle chamber 24 is a heater element 29 positioned beneath the nozzle opening 26 and suspended across a pit 8. Current is supplied to the heater element 29 via electrodes 9 connected to drive circuitry in underlying CMOS layers 5 of the substrate 2. When a current is passed through the heater element 29, it rapidly superheats surrounding ink to form a gas bubble, which forces ink through the nozzle opening. By suspending the heater element 29, it is completely immersed in ink when the nozzle chamber 24 is primed. This improves printhead efficiency, because less heat dissipates into the underlying substrate 2 and more input energy is used to generate a bubble.
As seen most clearly in FIG. 1, the nozzles are arranged in rows and an ink supply channel 27 extending longitudinally along the row supplies ink to each nozzle in the row. The ink supply channel 27 delivers ink to an ink inlet passage 15 for each nozzle, which supplies ink from the side of the nozzle opening 26 via an ink conduit 23 in the nozzle chamber 24.
The MEMS fabrication process for manufacturing such printheads was described in detail in our previously filed U.S. application Ser. No. 11/246,684 filed on Oct. 11, 2005, the contents of which is herein incorporated by reference. The latter stages of this fabrication process are briefly revisited here for the sake of clarity.
FIGS. 4 and 5 show a partially-fabricated printhead comprising a nozzle chamber 24 encapsulating sacrificial photoresist 10 (“SAC1”) and 16 (“SAC2”). The SAC1 photoresist 10 was used as a scaffold for deposition of heater material to form the suspended heater element 29. The SAC2 photoresist 16 was used as a scaffold for deposition of the sidewalls 22 and roof 21 (which defines part of the nozzle surface 56).
In the prior art process, and referring to FIGS. 6 to 8, the next stage of MEMS fabrication defines the elliptical nozzle rim 25 in the roof 21 by etching away 2 microns of roof material 20. This etch is defined using a layer of photoresist (not shown) exposed by the dark tone rim mask shown in FIG. 6. The elliptical rim 25 comprises two coaxial rim lips 25a and 25b, positioned over their respective thermal actuator 29.
Referring to FIGS. 9 to 11, the next stage defines an elliptical nozzle aperture 26 in the roof 21 by etching all the way through the remaining roof material, which is bounded by the rim 25. This etch is defined using a layer of photoresist (not shown) exposed by the dark tone roof mask shown in FIG. 9. The elliptical nozzle aperture 26 is positioned over the thermal actuator 29, as shown in FIG. 11.
With all the MEMS nozzle features now fully formed, the next stage removes the SAC1 and SAC2 photoresist layers 10 and 16 by O2 plasma ashing (FIGS. 12 and 13). FIGS. 14 and 15 show the entire thickness (150 microns) of the silicon wafer 2 after ashing the SAC1 and SAC2 photoresist layers 10 and 16.
Referring to FIGS. 16 to 18, once frontside MEMS processing of the wafer is completed, ink supply channels 27 are etched from the backside of the wafer to meet with the ink inlets 15 using a standard anisotropic DRIE. This backside etch is defined using a layer of photoresist (not shown) exposed by the dark tone mask shown in FIG. 16. The ink supply channel 27 makes a fluidic connection between the backside of the wafer and the ink inlets 15.
Finally, and referring to FIGS. 2 and 3, the wafer is thinned to about 135 microns by backside etching. FIG. 1 shows three adjacent rows of nozzles in a cutaway perspective view of a completed printhead integrated circuit. Each row of nozzles has a respective ink supply channel 27 extending along its length and supplying ink to a plurality of ink inlets 15 in each row. The ink inlets, in turn, supply ink to the ink conduit 23 for each row, with each nozzle chamber receiving ink from a common ink conduit for that row.
As already discussed above, this prior art MEMS fabrication process inevitably leaves a hydrophilic ink ejection face by virtue of the nozzle surface 56 being formed of ceramic materials, such as silicon dioxide, silicon nitride, silicon oxynitride, aluminium nitride etc.
Nozzle Etch Followed by Hydrophobic Polymer Coating
As an alternative to the process described above, the nozzle surface 56 has a hydrophobic polymer deposited thereon immediately after the nozzle opening etch (i.e. at the stage represented in FIGS. 10 and 11). Since the photoresist scaffold layers must be subsequently removed, the polymeric material should be resistant to the ashing process. Preferably, the polymeric material should be resistant to removal by an O2 or an H2 ashing plasma. The Applicant has identified a family of polymeric materials which meet the above-mentioned requirements of being hydrophobic whilst at the same time being resistant to O2 or H2 ashing. These materials are typically polymerized siloxanes or fluorinated polyolefins. More specifically, polydimethylsiloxane (PDMS) and perfluorinated polyethylene (PFPE) have both been shown to be particularly advantageous. Such materials form a passivating surface oxide in an O2 plasma, and subsequently recover their hydrophobicity relatively quickly. A further advantage of these materials is that they have excellent adhesion to ceramics, such as silicon dioxide and silicon nitride. A further advantage of these materials is that they are photopatternable, which makes them particularly suitable for use in a MEMS process. For example, PDMS is curable with UV light, whereby unexposed regions of PDMS can be removed relatively easily.
Referring to FIG. 10, there is shown a nozzle assembly of a partially-fabricated printhead after the rim and nozzle etches described earlier. However, instead of proceeding with SAC1 and SAC2 ashing (as shown in FIGS. 12 and 13), at this stage a thin layer (ca 1 micron) of hydrophobic polymeric material 100 is spun onto the nozzle surface 56, as shown in FIGS. 19 and 20.
After deposition, this layer of polymeric material is photopatterned so as to remove the material deposited within the nozzle openings 26. Photopatterning may comprise exposure of the polymeric layer 100 to UV light, except for those regions within the nozzle openings 26. Accordingly, as shown in FIGS. 21 and 22, the printhead now has a hydrophobic nozzle surface, and subsequent MEMS processing steps can proceed analogously to the steps described in connection with FIGS. 12 to 18. Significantly, the hydrophobic polymer 100 is not removed by the O2 ashing steps used to remove the photoresist scaffold 10 and 16.
Hydrophobic Polymer Coating Prior to Nozzle Etch with Polymer Used as Etch Mask
As an alternative process, the hydrophobic polymer layer 100 is deposited immediately after the stage represented by FIGS. 7 and 8. Accordingly, the hydrophobic polymer is spun onto the nozzle surface after the rim 25 is defined by the rim etch, but before the nozzle opening 26 is defined by the nozzle etch.
Referring to FIGS. 23 and 24, there is shown a nozzle assembly after deposition of the hydrophobic polymer 100. The polymer 100 is then photopatterned so as to remove the material bounded by the rim 25 in the nozzle opening region, as shown in FIGS. 25 and 26. Hence, the hydrophobic polymeric material 100 can now act as an etch mask for etching the nozzle opening 26.
The nozzle opening 26 is defined by etching through the roof structure 21, which is typically performed using a gas chemistry comprising O2 and a fluorinated hydrocarbon (e.g. CF4 or C4F8). Hydrophobic polymers, such as PDMS and PFPE, are normally etched under the same conditions. However, since materials such as silicon nitride etch much more rapidly, the roof 21 can be etched selectively using either PDMS or PFPE as an etch mask. By way of comparison, with a gas ratio of 3:1 (CF4:O2), silicon nitride etches at about 240 microns per hour, whereas PDMS etches at about 20 microns per hour. Hence, it will be appreciated that etch selectivity using a PDMS mask is achievable when defining the nozzle opening 26.
Once the roof 21 is etched to define the nozzle opening, the nozzle assembly 24 is as shown in FIGS. 21 and 22. Accordingly, subsequent MEMS processing steps can proceed analogously to the steps described in connection with FIGS. 12 to 18. Significantly, the hydrophobic polymer 100 is not removed by the O2 ashing steps used to remove the photoresist scaffold 10 and 16.
Hydrophobic Polymer Coating Prior to Nozzle Etch with Additional Photoresist Mask
FIGS. 25 and 26 illustrate how the hydrophobic polymer 100 may be used as an etch mask for a nozzle opening etch. Typically, different etch rates between the polymer 100 and the roof 21, as discussed above, provides sufficient etch selectivity.
However, as a further alternative and particularly to accommodate situations where there is insufficient etch selectivity, a layer of photoresist (not shown) may be deposited over the hydrophobic polymer 100 shown in FIG. 24, which enables conventional downstream MEMS processing. Having photopatterned this top layer of resist, the hydrophobic polymer 100 and the roof 21 may be etched in one step using the same gas chemistry, with the top layer of a photoresist being used as a standard etch mask. A gas chemistry of, for example, CF4/O2 first etches through the hydrophobic polymer 100 and then through the roof 21.
Subsequent O2 ashing may be used to remove just the top layer of photoresist (to obtain the nozzle assembly shown in FIGS. 10 and 11), or prolonged O2 ashing may be used to remove both the top layer of photoresist and the sacrificial photoresist layers 10 and 16 (to obtain the nozzle assembly shown in FIGS. 12 and 13).
The skilled person will be able to envisage other alternative sequences of MEMS processing steps, in addition to the three alternatives discussed herein. However, it will be appreciated that in identifying hydrophobic polymers capable of withstanding O2 and H2 ashing, the present inventors have provided a viable means for providing a hydrophobic nozzle surface in an inkjet printhead fabrication process.
Metal Film for Protecting Hydrophobic Polymer Layer
We have described hereinabove three alternative modifications of a printhead fabrication process which result in the ink ejection face of a printhead being defined by a hydrophobic polymer layer.
As already described above, the modification relies on the resistance of certain polymeric materials to standard ashing conditions using, for example, an oxygen plasma. This characteristic of certain polymers allows final ashing steps to be performed without removing the hydrophobic coating on the nozzle plate. However, there remains the possibility of such materials being imperfectly resistant to ashing, particularly aggressive ashing conditions that are typical of final-stage MEMS processing of printheads. Furthermore, there is the possibility that some hydrophobic polymers do not fully recover their hydrophobicity after ashing, which is undesirable given that the purpose of modifying the printhead fabrication process is to maximize the hydrophobicity of the ink ejection face.
It would therefore be desirable to provide an improved process, whereby hydrophobic polymers that are imperfectly resistant to ashing may still be used to hydrophobize an ink ejection face of a printhead. This would expand the range of materials available for use in hydrophobizing printheads. It would further be desirable to maximize the hydrophobicity of the ink ejection face without relying on hydrophobic materials recovering their hydrophobicity post-ashing.
In an improved hydrophobizing modification, the hydrophobic polymeric layer is protected with a thin metal film e.g. titanium or aluminium. The thin metal film protects the hydrophobic layer from late-stage oxygen ashing conditions, and is removed in a final post-ashing step, typically using a peroxide or acid rinse e.g. H2O2 or HF rinse. An advantage of this process is that the polymer used for hydrophobizing the ink ejection face is not exposed to aggressive ashing conditions and retains its hydrophobic characteristics throughout the MEMS processing steps.
It will be appreciated that the metal film may be used to protect the hydrophobic polymer layer in any of the three alternatives described above for hydrophobizing the printhead. By way of example, the process outlined in connection with FIGS. 19 to 22 will now be described with a protective metal film modification.
Referring then to FIGS. 19 to 22, printhead fabrication proceeds exactly as detailed in these drawings. In other words, a thin layer (ca 1 micron) of hydrophobic polymeric material 100 is spun onto the nozzle surface 56, as shown in FIGS. 19 and 20. After deposition, this layer of polymeric material is photopatterned so as to remove the material deposited within the nozzle openings 26. Photopatterning may comprise exposure of the polymeric layer 100 to UV light, except for those regions within the nozzle openings 26. Accordingly, as shown in FIGS. 21 and 22, the printhead now has a hydrophobic nozzle surface with no hydrophobic material positioned within the nozzle openings 26.
Turning to FIG. 36, the next stage comprises deposition of a thin film (ca 100 nm) of metal 110 onto the polymeric layer 100. After deposition, the metal may be removed from within the nozzle opening 26 by standard metal etch techniques. For example, a conventional photoresist layer (not shown) may be exposed and developed, as appropriate, and used as an etch mask for etching the metal film 110. Any suitable etch may be used, such as RIE using a chlorine-based gas chemistry.
FIG. 37 shows the partially-fabricated printhead after etching the metal film 110. It will be seen that the hydrophobic polymer layer 100 is completely encapsulated by the metal film 110 and therefore protected from any aggressive late-stage ashing.
Subsequent MEMS processing steps can proceed analogously to the steps described in connection with FIGS. 12 to 18. Significantly, the hydrophobic polymer 100 is not removed by the O2 ashing steps used to remove the photoresist scaffold 10 and 16, because it is protected by the metal film 110.
After O2 ashing, the metal film is removed by a brief H2O2 or HF rinse, thereby revealing the hydrophobic polymer layer 100 in the completed printhead.
FIGS. 10 to 13 show frontside ashing of the wafer to remove all photoresist from within the nozzle chambers. In this case, it is of course necessary to define openings in the protective metal layer 110 so that the oxygen plasma can access the photoresist.
FIG. 38 exemplifies an alternative sequence of MEMS processing steps, which makes use of backside ashing and avoids defining openings in the protective metal layer 110. The wafer shown in FIG. 36 is subjected to backside MEMS processing so as to define ink supply channels 27 from the backside of the wafer. The resultant wafer is shown in FIG. 38. Once ink supply channels 27 are defined from the backside, then backside ashing can be performed to remove all frontside photoresist, including the scaffolds 10 and 16. The hydrophobic polymer layer 100 still enjoys protection from the ashing plasma. With the photoresist removed, the protective metal film 110 can simply be rinsed off with H2O2 or HF to provide the wafer shown in FIG. 17, except with a hydrophobic polymer layer covering the nozzle plate.
Of course, it will be appreciated that metal film protection of the polymer layer 100 may be performed prior to the nozzle opening etch. In this scenario, the metal film 110, the polymer layer 100 and the nozzle roof may be etched in simultaneous or sequential etching steps, using a top conventional photoresist layer as a common mask for each etch. Regardless, the polymer layer 100 still benefits from protection by the metal film 110 in subsequent ashing steps.
Thermal Bend Actuator Printhead
Having discussed ways in which a nozzle surface of a printhead may be hydrophobized, it will be appreciated that any type of printhead may be hydrophobized in an analogous manner. However, the present invention realizes particular advantages in connection with the Applicant's previously described printhead comprising thermal bend actuator nozzle assemblies. Accordingly, a discussion of how the present invention may be used in such printheads now follows.
In a thermal bend actuated printhead, a nozzle assembly may comprise a nozzle chamber having a roof portion which moves relative to a floor portion of the chamber. The moveable roof portion is typically actuated to move towards the floor portion by means of a bi-layered thermal bend actuator. Such an actuator may be positioned externally of the nozzle chamber or it may define the moving part of the roof structure.
A moving roof is advantageous, because it lowers the drop ejection energy by only having one face of the moving structure doing work against the viscous ink. However, a problem with such moving roof structures is that it is necessary to seal the ink inside the nozzle chamber during actuation. Typically, the nozzle chamber relies on a fluidic seal, which forms a seal using the surface tension of the ink. However, such seals are imperfect and it would be desirable to form a mechanical seal which avoids relying on surface tension as a means for containing the ink. Such a mechanical seal would need to be sufficiently flexible to accommodate the bending motion of the roof.
A typical nozzle assembly 400 having a moving roof structure was described in our previously filed U.S. application Ser. No. 11/607,976 filed on Dec. 4, 2006 (the contents of which is herein incorporated by reference) and is shown here in FIGS. 27 to 30. The nozzle assembly 400 comprises a nozzle chamber 401 formed on a passivated CMOS layer 402 of a silicon substrate 403. The nozzle chamber is defined by a roof 404 and sidewalls 405 extending from the roof to the passivated CMOS layer 402. Ink is supplied to the nozzle chamber 401 by means of an ink inlet 406 in fluid communication with an ink supply channel 407 receiving ink from a backside of the silicon substrate. Ink is ejected from the nozzle chamber 401 by means of a nozzle opening 408 defined in the roof 404. The nozzle opening 408 is offset from the ink inlet 406.
As shown more clearly in FIG. 28, the roof 404 has a moving portion 409, which defines a substantial part of the total area of the roof. Typically, the moving portion 409 defines at least 50% of the total area of the roof 404. In the embodiment shown in FIGS. 27 to 30, the nozzle opening 408 and nozzle rim 415 are defined in the moving portion 409, such that the nozzle opening and nozzle rim move with the moving portion.
The nozzle assembly 400 is characterized in that the moving portion 409 is defined by a thermal bend actuator 410 having a planar upper active beam 411 and a planar lower passive beam 412. Hence, the actuator 410 typically defines at least 50% of the total area of the roof 404. Correspondingly, the upper active beam 411 typically defines at least 50% of the total area of the roof 404.
As shown in FIGS. 27 and 28, at least part of the upper active beam 411 is spaced apart from the lower passive beam 412 for maximizing thermal insulation of the two beams. More specifically, a layer of Ti is used as a bridging layer 413 between the upper active beam 411 comprised of TiN and the lower passive beam 412 comprised of SiO2. The bridging layer 413 allows a gap 414 to be defined in the actuator 410 between the active and passive beams. This gap 414 improves the overall efficiency of the actuator 410 by minimizing thermal transfer from the active beam 411 to the passive beam 412.
However, it will of course be appreciated that the active beam 411 may, alternatively, be fused or bonded directly to the passive beam 412 for improved structural rigidity. Such design modifications would be well within the ambit of the skilled person.
The active beam 411 is connected to a pair of contacts 416 (positive and ground) via the Ti bridging layer. The contacts 416 connect with drive circuitry in the CMOS layers.
When it is required to eject a droplet of ink from the nozzle chamber 401, a current flows through the active beam 411 between the two contacts 416. The active beam 411 is rapidly heated by the current and expands relative to the passive beam 412, thereby causing the actuator 410 (which defines the moving portion 409 of the roof 404) to bend downwards towards the substrate 403. Since the gap 460 between the moving portion 409 and a static portion 461 is so small, surface tension can generally be relied up to seal this gap when the moving portion is actuated to move towards the substrate 403.
The movement of the actuator 410 causes ejection of ink from the nozzle opening 408 by a rapid increase of pressure inside the nozzle chamber 401. When current stops flowing, the moving portion 409 of the roof 404 is allowed to return to its quiescent position, which sucks ink from the inlet 406 into the nozzle chamber 401, in readiness for the next ejection.
Turning to FIG. 12, it will be readily appreciated that the nozzle assembly may be replicated into an array of nozzle assemblies to define a printhead or printhead integrated circuit. A printhead integrated circuit comprises a silicon substrate, an array of nozzle assemblies (typically arranged in rows) formed on the substrate, and drive circuitry for the nozzle assemblies. A plurality of printhead integrated circuits may be abutted or linked to form a pagewidth inkjet printhead, as described in, for example, Applicant's earlier U.S. application Ser. No. 10/854,491 filed on May 27, 2004 and Ser. No. 11/014,732 filed on Dec. 20, 2004, the contents of which are herein incorporated by reference.
An alternative nozzle assembly 500 shown in FIGS. 31 to 33 is similar to the nozzle assembly 400 insofar as a thermal bend actuator 510, having an upper active beam 511 and a lower passive beam 512, defines a moving portion of a roof 504 of the nozzle chamber 501.
However, in contrast with the nozzle assembly 400, the nozzle opening 508 and rim 515 are not defined by the moving portion of the roof 504. Rather, the nozzle opening 508 and rim 515 are defined in a fixed or static portion 561 of the roof 504 such that the actuator 510 moves independently of the nozzle opening and rim during droplet ejection. An advantage of this arrangement is that it provides more facile control of drop flight direction. Again, the small dimensions of the gap 560, between the moving portion 509 and the static portion 561, is relied up to create a fluidic seal during actuation by using the surface tension of the ink.
The nozzle assemblies 400 and 500, and corresponding printheads, may be constructed using suitable MEMS processes in an analogous manner to those described above. In all cases the roof of the nozzle chamber (moving or otherwise) is formed by deposition of a roof material onto a suitable sacrificial photoresist scaffold.
Referring now to FIG. 34, it will be seen that the nozzle assembly 400 previously shown in FIG. 27 now has an additional layer of hydrophobic polymer 101 (as described in detail above) coated on the roof, including both the moving 409 and static portions 461 of the roof. Importantly, the hydrophobic polymer 101 seals the gap 460 shown in FIG. 27. It is an advantage of polymers such as PDMS and PFPE that they have extremely low stiffness. Typically, these materials have a Young's modulus of less than 1000 MPa and typically of the order of about 500 MPa. This characteristic is advantageous, because it enables them to form a mechanical seal in thermal bend actuator nozzles of the type described herein—the polymer stretches elastically during actuation, without significantly impeding the movement of the actuator. Indeed, an elastic seal assists in the bend actuator returning to its quiescent position, which is when drop ejection occurs. Moreover, with no gap between a moving roof portion 409 and a static roof portion 461, ink is fully sealed inside the nozzle chamber 401 and cannot escape, other than via the nozzle opening 408, during actuation.
FIG. 35 shows the nozzle assembly 500 with a hydrophobic polymer coating 101. By analogy with the nozzle assembly 400, it will be appreciated that by sealing the gap 560 with the polymer 101, a mechanical seal 562 is formed which provides excellent mechanical sealing of ink in the nozzle chamber 501.
It will be appreciated by ordinary workers in this field that numerous variations and/or modifications may be made to the present invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects to be illustrative and not restrictive.

## Claims

1. A method of fabricating a printhead having a hydrophobic ink ejection face, the method comprising the steps of:
(a) providing a partially-fabricated printhead comprising a plurality of nozzle chambers and a nozzle plate having relatively hydrophilic nozzle surface, said nozzle surface at least partially defining the ink ejection face of the printhead;
(b) defining a plurality of nozzle openings in at least said nozzle plate;
(c) depositing a hydrophobic polymeric layer onto the nozzle surface;
(d) depositing a protective metal film onto at least said polymeric layer;
(e) subjecting said printhead to an oxidizing plasma; and
(f) removing said protective metal film,

thereby providing a printhead having a relatively hydrophobic ink ejection face,
wherein step (b) is performed immediately after any of steps (a), (c) or (d), and wherein no plasma oxidizing steps are performed after removing said protective metal film in step (f).

2. The method of claim 1, wherein step (b) is performed immediately after step (c), and step (b) comprises: defining a plurality of nozzle openings in said nozzle plate and in said polymeric layer.

3. The method of claim 1, wherein said protective metal film is comprised of a metal selected from the group comprising: titanium and aluminium.

4. The method of claim 1, wherein said protective metal film has a thickness in the range of 10 nm to 1000 nm.

5. The method of claim 1, wherein step (f) is performed by wet or dry etching.

6. The method of claim 1, wherein step (f) is performed by a wet rinse using peroxide or acid.

7. The method of claim 1, wherein, in said partially-fabricated printhead, a roof of each nozzle chamber is supported by a sacrificial photoresist scaffold, and wherein said photoresist scaffold by plasma oxidizing prior to removing said protective metal film.

8. The method of claim 1, wherein step (c) comprises the sub-steps of:
(c)(i) depositing the hydrophobic polymeric layer onto the nozzle surface; and
(c)(ii) photopatterning said polymeric layer so as to define a plurality of nozzle openings in said polymeric layer.

9. The method of claim 8, wherein photopatterning comprises UV-curing at least some of said polymeric material.

10. The method of claim 1, wherein step (d) comprises the sub-steps of:
(d)(i) depositing a protective metal film onto at least said polymeric layer; and
(d)(ii) defining a plurality of film openings in said metal film, said film openings being aligned with said nozzle openings.

11. The method of claim 10, wherein sub-step (d)(ii) comprises the further sub-steps of:
(d)(ii)(1) depositing a mask on said protective metal film;
(d)(ii)(2) patterning said mask so as to unmask said metal film in a plurality of film opening regions; and
(d)(ii)(3) etching said unmasked nozzle opening regions to define said plurality of film openings.

12. The method of claim 1, wherein one or more backside MEMS processing steps are performed after removing said protective metal film in step (f).

13. The method of claim 12, wherein said backside MEMS processing steps include defining ink supply channels from a backside of said wafer, said backside being an opposite face to said ink ejection face.

14. The method of claim 1, wherein a roof of each nozzle chamber is defined at least partially by said nozzle plate.

15. The method of claim 14, wherein said nozzle plate is spaced apart from a substrate, such that sidewalls of each nozzle chamber extend between said nozzle plate and said substrate.

16. The method of claim 1, wherein said hydrophobic polymeric layer is comprised of a polymeric material selected from the group comprising: polymerized siloxanes and fluorinated polyolefins.

17. The method of claim 16, wherein said polymeric material is selected from the group comprising: polydimethylsiloxane (PDMS) and perfluorinated polyethylene (PFPE).