JP4960965B2 - Method for manufacturing a suspended beam in a MEMS process - Google Patents

Description

  The present invention relates to the field of ink jet printing devices and discloses an ink jet printing system using a print head manufactured with micro electro mechanical system (MEMS) technology.

これらの出願及び特許の開示は、参照により本明細書に組み込まれる。 [Cross-reference of related applications]
Various methods, systems and devices relating to the present invention are disclosed in the following US patents / patent applications filed by the assignee or assignee of the present invention.

The disclosures of these applications and patents are incorporated herein by reference.

  The present invention includes discharging ink drops by forming a gas or vapor bubble in a bubble forming liquid. This principle is outlined in US Pat. Each pixel of the printed image is obtained from ink drops ejected from one or more ink nozzles. In recent years, inkjet printing has become increasingly popular, mainly due to its inexpensive and versatile nature. Many different aspects and techniques of inkjet printing are described in detail in the above cross-reference documents.

  Full immersion of the heater element in the ink dramatically improves the efficiency of the printhead. The heat dissipated to the underlying wafer substrate is much reduced, so that more input energy is used to generate bubbles that eject ink.

  A convenient way to suspend the heater element is to attach it to a sacrificial photoresist, which is then removed with a strip etch. Sacrificial material (SAC) is deposited in pits or trenches etched into the substrate adjacent to the electrodes. However, it is difficult to accurately match the mask to the side of the pit. Normally, when the masked photoresist is exposed, a gap is formed between the side of the pit and the SAC. When a layer of heater material is deposited, these gaps are refilled to form a (so-called) “stringer”. The stringer remains after the metal etch (forming the heater element) and the stripping etch (which eventually removes the SAC). Stringers can short circuit the heater and therefore cannot generate bubbles.

By creating a mask larger than the trench, SAC is deposited on the sidewalls so that no gaps are formed. Unfortunately, this creates a raised lip around the top of the trench. When a layer of heater material is deposited, it thins at the vertical or inclined surface of the lip. After metal etching and stripping etching, such a thin lip configuration remains and causes “hot spots” because the resistance increases due to local thinning. These hot spots affect the operation of the heater and usually shorten the life of the heater.
US Pat. No. 3,747,120 (Stemme)

Accordingly, the present invention provides a method of manufacturing a beam suspended in a MEMS process, the method comprising:
(A) etching a pit having a base and a sidewall into the substrate;
(B) attaching a sacrificial material to the surface of the substrate so as to refill the pits;
(C) removing the sacrificial material from a peripheral region of the pit and from the substrate surface surrounding the pit;
(D) reflowing the remaining sacrificial material in the pit so that the remaining sacrificial material is in contact with the sidewall;
(E) attaching a beam material to the substrate surface and to the reflowed sacrificial material;
(F) removing the reflowed sacrificial material to form the suspended beam.

  The suspended beam is preferably substantially planar. In a further preferred form, all parts of the suspended beam have substantially the same thickness.

  Optionally, the suspended beam is an inkjet nozzle actuator.

In a first aspect, the present invention provides a method of manufacturing a beam suspended in a MEMS process, the method comprising:
(A) etching a pit having a base and a sidewall into the substrate;
(B) attaching a sacrificial material to the surface of the substrate so as to refill the pits;
(C) removing the sacrificial material from a peripheral region of the pit and from the substrate surface surrounding the pit;
(D) reflowing the remaining sacrificial material in the pit so that the remaining sacrificial material is in contact with the sidewall;
(E) attaching a beam material to the substrate surface and to the reflowed sacrificial material;
(F) removing the reflowed sacrificial material to form the suspended beam.

  Optionally, the suspended beam is substantially planar.

  Optionally, all parts of the suspended beam have substantially the same thickness.

  Optionally, the suspended beam is an inkjet nozzle actuator.

  Optionally, the actuator is a heater element.

  Optionally, the heater element is suspended between a pair of electrodes.

  Optionally, the substrate is a silicon wafer.

  Optionally, the silicon wafer comprises at least one oxide layer.

  Optionally, the sacrificial material is a photoresist.

  Optionally, the photoresist is removed by exposure through a mask and subsequent development.

  Optionally, the surrounding region comprises an area adjacent to at least two of the side walls.

  Optionally, the surrounding area comprises an area adjacent to all of the side walls.

  Optionally, removal of the sacrificial material from the surrounding region results in a space between the remaining sacrificial material and at least two of the sidewalls of less than 1 micron.

  Optionally, removal of the sacrificial material from the surrounding region results in a space between the remaining sacrificial material and all of the sidewalls of less than 1 micron.

  Optionally, the reflow is performed by heating the sacrificial material.

  Optionally, the sacrificial material is treated to prevent further reflow before depositing the beam material.

  Optionally, the treatment comprises UV curing.

Optionally, the beam material is etched into a predetermined configuration after deposition.
Optionally, further MEMS process steps are performed after deposition of the beam material and before the removal of the reflowed sacrificial material.

  Optionally, the step of the further MEMS process includes forming an inkjet nozzle that includes the suspended beam.

In a second aspect, the present invention provides a method of manufacturing a plurality of inkjet nozzles on a substrate, each nozzle having a ceiling spaced from the substrate and a sidewall extending from the ceiling to the substrate. A nozzle chamber having one of the sidewalls having a chamber entrance for receiving ink from an ink conduit extending along the row of nozzles, the ink conduit having a plurality of ink inlets defined in the substrate. Receiving the ink from the method,
(A) providing a substrate having a plurality of trenches corresponding to the ink inlets;
(B) depositing a sacrificial material on the substrate to refill the trench and form a scaffold on the substrate;
(C) defining an opening in the sacrificial material that, when refilled with a ceiling material, is disposed to form a sidewall of the chamber and the ink conduit;
(D) depositing a ceiling material on the sacrificial material to simultaneously form the nozzle chamber and the ink conduit;
(E) etching nozzle openings through the ceiling material, each nozzle chamber having at least one nozzle opening;
(F) removing the sacrificial material.

  Optionally, each nozzle chamber includes an actuator that ejects ink through the nozzle opening.

  Optionally, the actuator is formed prior to manufacturing the nozzle chamber.

  Optionally, the substrate is a silicon wafer.

  Optionally, the silicon wafer comprises at least one oxide film layer.

  Optionally, the sacrificial material is a photoresist.

  Optionally, the opening is defined by exposing the photoresist through a mask followed by development.

  Optionally, the photoresist is UV cured prior to depositing the ceiling material, thereby preventing reflow of the photoresist during deposition.

  Optionally, the photoresist is removed by plasma ashing.

  In a further aspect, a method is further provided that includes etching an ink supply path from an opposite back side of the substrate, wherein the ink supply path is in fluid communication with the ink inlet.

  Optionally, each ink inlet has at least one priming feature extending from an individual edge, and the method further comprises at least one opening corresponding to the at least one priming feature in the photoresist. Including defining.

  Optionally, the at least one priming feature comprises a column of ceiling material extending from the edge.

  Optionally, each ink inlet has a plurality of priming features disposed around individual edges.

  Optionally, the plurality of priming features together form a cylindrical cage extending from the edge.

  Optionally, the chamber entrance includes at least one filter structure, and the method further comprises defining at least one opening in the photoresist corresponding to the at least one priming feature.

  Optionally, the at least one filter structure comprises a column of ceiling material extending from the substrate to the ceiling.

  Optionally, each room entrance includes a plurality of filter structures arranged across the entrance.

  Optionally, each room entrance includes a plurality of rows of filter structures arranged across the entrance.

  Optionally, the columnar filter structures are staggered.

In a third aspect, the present invention provides a method of manufacturing a plurality of inkjet nozzles on a substrate, each nozzle having a ceiling spaced from the substrate, and a sidewall extending from the ceiling to the substrate. A nozzle chamber having an entrance for receiving ink from at least one ink inlet defined in the substrate, wherein the at least one ink inlet extends from an individual edge. Having a priming feature, the method comprising:
(A) providing a substrate having a plurality of trenches corresponding to the ink inlets;
(B) depositing a sacrificial material on the substrate to refill the trench and form a scaffold on the substrate;
(C) defining an opening in the sacrificial material that, when refilled with a ceiling material, is disposed to form a sidewall of the chamber and the at least one priming feature;
(D) depositing a ceiling material on the sacrificial material to simultaneously form the nozzle chamber and the at least one priming feature;
(E) etching nozzle openings through the ceiling material, each nozzle chamber having at least one nozzle opening;
(F) removing the sacrificial material.

  Optionally, the at least one priming feature comprises a column of ceiling material extending from the edge.

  Optionally, each ink inlet has a plurality of priming features disposed around individual edges.

  Optionally, the plurality of priming features together form a cylindrical cage extending from the edge.

  Optionally, each nozzle chamber includes an actuator that ejects ink through the nozzle opening.

  Optionally, the actuator is formed prior to manufacturing the nozzle chamber.

  Optionally, the substrate is a silicon wafer.

  Optionally, the silicon wafer comprises at least one oxide layer.

  Optionally, the sacrificial material is a photoresist.

  Optionally, the opening is defined by exposing the photoresist through a mask followed by development.

  Optionally, the photoresist is UV cured prior to depositing the ceiling material, thereby preventing reflow of the photoresist during deposition.

  Optionally, the photoresist is removed by plasma ashing.

  In a further aspect, a method is further provided that includes etching an ink supply path from an opposite back side of the substrate, wherein the ink supply path is in fluid communication with the ink inlet.

  Optionally, the chamber entrance is defined in one of the side walls of the nozzle chamber.

  Optionally, the chamber entrance receives ink from an ink conduit extending along a row of nozzles, and step (c) further comprises defining a further opening in the sacrificial material, the further opening. Is arranged to form the ink conduit when refilled with ceiling material.

  Optionally, the ink conduit receives ink from the at least one ink inlet.

In a fourth aspect, the present invention provides a method of manufacturing a plurality of inkjet nozzles on a substrate, each nozzle having a ceiling spaced from the substrate and a sidewall extending from the ceiling to the substrate. And wherein one of the side walls has a chamber entrance for receiving ink from at least one ink inlet defined in the substrate, the chamber entrance including at least one filter structure, the method comprising: ,
(A) providing a substrate having a plurality of trenches corresponding to the ink inlets;
(B) depositing a sacrificial material on the substrate to refill the trench and form a scaffold on the substrate;
(C) defining an opening in the sacrificial material that, when refilled with ceiling material, is disposed to form sidewalls of the chamber and the at least one filter structure;
(D) depositing a ceiling material on the sacrificial material to simultaneously form the nozzle chamber and the at least one filter structure;
(E) etching nozzle openings through the ceiling material, each nozzle chamber having at least one nozzle opening;
(F) removing the sacrificial material.

  Optionally, the filter structure comprises a column of ceiling material extending from the substrate to the ceiling.

  Optionally, each room entrance includes a plurality of filter structures arranged across the entrance.

  Optionally, each room entrance includes a plurality of rows of filter structures arranged across the entrance.

  Optionally, the columnar filter structures are staggered.

  Optionally, each nozzle chamber includes an actuator that ejects ink through the nozzle opening.

  Optionally, the actuator is formed prior to manufacturing the nozzle chamber.

  Optionally, the substrate is a silicon wafer.

  Optionally, the silicon wafer comprises at least one oxide layer.

  Optionally, the sacrificial material is a photoresist.

  Optionally, the opening is defined by exposing the photoresist through a mask followed by development.

  Optionally, the photoresist is UV cured prior to depositing the ceiling material, thereby preventing reflow of the photoresist during deposition.

  Optionally, the photoresist is removed by plasma ashing.

  In a further aspect, a method is further provided that includes etching an ink supply path from an opposite back side of the substrate, wherein the ink supply path is in fluid communication with the ink inlet.

  Optionally, the chamber entrance receives ink from an ink conduit extending along a row of nozzles, and step (c) further comprises defining a further opening in the sacrificial material, the further opening. Is arranged to form the ink conduit when refilled with ceiling material.

  Optionally, the ink conduit receives ink from the at least one ink inlet.

In a fifth aspect, the present invention provides a method of forming a nozzle plate with low static friction of an ink jet print head, wherein the nozzle plate is defined within itself, each having a plurality of nozzles having individual nozzle edges. Having an opening, the method comprising:
(A) providing a partially manufactured printhead comprising a plurality of inkjet nozzle assemblies sealed with a ceiling material;
(B) partially etching the ceiling material to simultaneously define the nozzle edge and a plurality of static friction reducing features;
(C) etching the ceiling material to define the nozzle openings and thereby form the nozzle plate.

  Optionally, each nozzle edge comprises at least one protrusion around each nozzle opening.

  Optionally, each nozzle edge comprises a plurality of coaxial protrusions around each nozzle opening.

  Optionally, the at least one edge projection protrudes from the nozzle plate by at least 1 micron.

  Optionally, each static friction mitigating arrangement comprises a cylindrical protrusion on the nozzle plate.

  Optionally, each cylindrical protrusion protrudes from the nozzle plate by at least 1 micron.

  Optionally, each cylindrical projection is spaced from adjacent cylindrical projections by less than 2 microns.

  Optionally, each static friction mitigating arrangement comprises an elongated wall projection on the nozzle plate.

  Optionally, each wall projection projects at least 1 micron from the nozzle plate.

  Optionally, the wall protrusion is disposed on the nozzle plate to minimize ink color mixing.

  Optionally, the wall projections extend along the nozzle plate in parallel with the row of nozzles, and each nozzle in the row discharges the same color of ink.

  Optionally, the location of the nozzle edge and the static friction mitigation feature is defined by photolithography masking.

  Optionally, at least half of the surface area of the nozzle plate is tiled in a static friction reducing configuration.

  Optionally, the inkjet nozzle assembly is formed on a silicon substrate and the nozzle plate is spaced from the substrate.

  Optionally, the nozzle plate comprises a silicon nitride film, a silicon oxide film, a silicon oxynitride film, and aluminum nitride.

  Optionally, the nozzle assembly is sealed by CVD or PECVD deposition of the ceiling material.

  Optionally, the ceiling material adheres to the sacrificial scaffold.

  Optionally, each inkjet nozzle assembly has at least one nozzle opening associated with it for ejecting ink.

  Optionally, the nozzle plate is then treated with a hydrophobic material.

  The print head according to the present invention comprises a plurality of nozzles, a chamber corresponding to each nozzle and one or more heater elements. The smallest repeating unit of the print head has an ink supply inlet for supplying ink to one or more chambers. The entire nozzle array is formed by repeating these individual units. Such individual units are referred to herein as “unit cells”.

  Also, the term “ink” is used to mean a drainable liquid and is not limited to conventional inks including colored dyes. Examples of non-colored inks include fixing agents, infrared absorber inks, functionalized chemicals, adhesives, biological fluids, drugs, water and other solvents. The ink or drainable liquid is also not necessarily strictly liquid and may include a suspension of solid particles.

  Preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings.

  In the following description, corresponding reference numbers relate to corresponding parts. For convenience, the features indicated by each reference number are listed below.

MNN MPN serial parts list Nozzle unit cell 2. Silicon wafer 3. top aluminum metal layer in CMOS metal layer 4. Deactivation layer 5. Chemical vapor deposition oxide layer 6. Ink inlet opening in top aluminum metal layer 3 7. Pit port of uppermost aluminum metal layer 3 Pit 9 Electrode 10. 10. SACI photoresist layer Heater material (TiAlN)
12 Thermal actuator 13. Photoresist layer 14. 15. Ink inlet opening etched through the photoresist layer Ink inlet passage 16. 18. SAC2 photoresist layer Side wall opening of chamber 18. Front channel priming feature 19. 21. Barrier configuration at the ink inlet Room ceiling layer 21. Ceiling 22. Side wall 23. Ink conduit 24. Nozzle chamber 25. Elliptical nozzle edge 25 (a) inner lip 25 (b) outer lip 26. Nozzle opening 27. Ink supply channel 28. Contact part 29. Heater element 30. Foam cage 32. Bubble holding structure 34. Ink permeable structure 36. Bleeding hole 38. Ink chamber 40.2 row filter 42. Paper dust 44. Inkwell 46. A gap between the SACI and the trench sidewall 48. Trench sidewall 50. SACI raised lip around trench edge 52. Thinned inclined section of heater material 54. Low temperature spot between heater elements connected in series56. Nozzle plate 58. Cylindrical protrusion 60. Side wall ink openings 62. Ink refill opening
MEMS manufacturing process The MEMS manufacturing process builds a nozzle structure on a silicon wafer after CMOS processing is completed. FIG. 2 is a cut-out perspective view of the nozzle unit cell 100 after the CMOS process and before the MEMS process.

  During the CMOS processing of the wafer, four metal layers are deposited on the silicon wafer 2 with the metal layers filling between the interlayer dielectric (ILD) layers. The four metal layers are called M1, M2, M3 and M4 layers and accumulate in order on the wafer during CMOS processing. These CMOS layers provide all the drive circuitry and logic to operate the printhead.

  Within the completed printhead, each heater element actuator is connected to the CMOS via a pair of electrodes defined in the outermost M4 layer. Thus, the M4 CMOS layer is the basis for subsequent MEMS processing of the wafer. The M4 layer also defines bonding pads along the vertical edges of each printhead integrated circuit. These bonding pads (not shown) allow the CMOS to be connected to the microprocessor via wire bonds extending from the bonding pads.

  1 and 2 show an aluminum M4 layer 3 with a passivation layer 4 deposited thereon. (In these figures, only the M4 layer MEMS feature is shown, the main CMOS feature of the M4 layer is located outside the unit cell of the nozzle.) The M4 layer 3 has a thickness of 1 micron, Deposit on a 2 micron layer of CVD oxide 5. As shown in FIGS. 1 and 2, the M4 layer 3 has an ink inlet opening 6 and a pit opening 7. These openings define the location of ink inlets and pits that are subsequently formed in the MEMS process.

  Before the MEMS processing of the unit cell 1 begins, the bonding pads along the longitudinal edges of each printhead integrated circuit are defined by etching through the passivation layer 4. This etching exposes the M4 layer 3 at the bonding pad position. The unit cell 1 of the nozzle is completely masked with photoresist for this step and is therefore not affected by etching.

  Referring to FIGS. 3-5, the first stage of the MEMS process etches the pits 8 through the passivation layer 4 and the CVD oxide layer 5. This etch is defined using a layer of photoresist (not shown) exposed by the dark tone pit mask shown in FIG. The pit 8 has a depth of 2 microns as measured from the top of the M4 layer 3. Simultaneously with etching the pits 8, the electrode 9 is defined on either side of the pits by partially exposing the M4 layer 3 through the passivation layer 4. Within the completed nozzle, the heater element is suspended between the electrodes 9 across the pits 8.

  In the next step (FIGS. 6-8), the pits 8 are refilled with a first sacrificial layer of photoresist 10 (“SAC1”). A 2 micron layer of high speed photoresist is first stretched over the wafer and then exposed using the dark shade mask shown in FIG. The SAC1 photoresist 10 forms a scaffold for subsequent deposition of heater material across the electrode 9 on either side of the pit 8. As a result, it is important that the SAC1 photoresist 10 has a flat top surface that is flush with the top surface of the electrode 9. At the same time, the SAC1 photoresist must be completely refilled with pits 8 to avoid “stringers” of conductive heater material extending across the pits and shorting the electrodes 9.

  Typically, when a trench is refilled with photoresist, it is guaranteed that the photoresist refills against the trench walls, thus avoiding "stringers" in subsequent deposition steps. It is necessary to expose the photoresist to the outside. However, this technique results in a raised (or spiked) edge of the photoresist around the trench. This is undesirable because in subsequent attachment steps, the material will adhere unevenly to the raised edges. That is, the vertical or inclined surface of the edge of the photoresist that refills the trench has less material deposited than the horizontal plane. The result is a “resistance hot spot” in a region where the material is thinly deposited.

  As shown in FIG. 7, this process intentionally exposes the SAC1 photoresist 10 inside the perimeter wall of the pit 8 (eg, within 0.5 microns) using the mask shown in FIG. This ensures a flat top surface of the SAC1 photoresist 10 and avoids the formation of spike-like regions in the photoresist around the periphery of the pit 8.

  After the SAC1 photoresist 10 is exposed, the photoresist is reflowed by heating. Due to the reflow of the photoresist, this flows down to the wall of the pit 8 and refills it exactly. 9 and 10 show the SAC1 photoresist 10 after reflow. The photoresist has a flat top surface and is flush with the top surface of the M4 layer 3 forming the electrode 9. After reflow, the SAC1 photoresist 10 is UV cured and / or hard baked to avoid reflow during subsequent deposition steps of the heater material.

  11 and 12 show the unit cell after the 0.5 micron heater material 11 has been deposited on the SAC1 photoresist 10. Due to the reflow process described above, the heater material 11 is deposited in a uniform and planar layer on the electrode 9 and the SAC1 photoresist 10. The heater material can be composed of any suitable conductive material such as TiAl, TiN, TiAlN, TiAlSiN. A typical heater material deposition process may include sequentially depositing a 100 シ ー ド seed layer of TiAl, a 2500 Ｔｉ layer of TiAlN, an additional 100 シ ー ド layer of TiAl, and finally a further 2500 Ｔｉ layer of TiAlN. .

  Referring to FIGS. 13-15, in the next step, the layer of heater material 11 is etched to define the thermal actuator 12. Each actuator 12 has a contact 28 that establishes an electrical connection to an individual electrode 9 on either side of the SAC1 photoresist 10. The heater element 29 is stretched between the corresponding contacts 28.

  This etch is defined by a layer of photoresist (not shown) exposed using the dark shade mask shown in FIG. As shown in FIG. 15, the heater element 12 is a linear beam spanning between the pair of electrodes 9. However, the heater element 12 may alternatively employ other configurations as described in Applicant's US Pat. No. 6,755,509, the contents of which are incorporated herein by reference. For example, the configuration of a heater element 29 having a central air gap may be advantageous to minimize the deleterious effects of cavitation forces on the heater material if air bubbles collapse during ink ejection. Other forms of cavitation protection may be employed, such as “bubble aeration” and the use of self-inactivating materials. These cavitation management techniques are discussed in detail in US patent applications (Applicant's document MTC001US).

  In the next sequence of steps, the nozzle ink inlet is etched through the passivation layer 4, oxide layer 5 and silicon wafer 2. During CMOS processing, each metal layer has an ink inlet opening (see, for example, opening 6 in M4 layer 3 in FIG. 1) etched in preparation for this ink inlet etching. These metal layers, together with the inserted ILD layer, form a seal ring at the ink inlet and prevent ink from penetrating into the CMOS layer.

  Referring to FIGS. 16-18, a relatively thick layer of photoresist 13 is stretched over the wafer and exposed using the dark shade mask shown in FIG. The required photoresist 13 thickness depends on the selectivity of deep reactive ion etching (DRIE) used to etch the ink inlet. With the ink inlet opening 14 defined in the photoresist 13, the wafer is ready for a subsequent etching step.

In the first etching step (FIGS. 19 and 20), the dielectric layers (passivation layer 4 and oxide layer 5) are etched through the underlying silicon wafer. Any standard oxide etch (eg, O ₂ / C ₄ F ₈ plasma) may be used.

  In the second etching step (FIGS. 21 and 22), the same photoresist mask 13 is used to etch the ink inlet 15 through the silicon wafer 2 to a depth of 25 microns. This etch may use any standard anisotropic DRIE such as Bosch etch (see US Pat. Nos. 6,501,893 and 6,284,148). After the ink inlet 15 is etched, the photoresist layer 13 is removed by plasma ashing.

  In the next step, the ink inlet 15 is plugged with photoresist, and a second sacrificial layer of photoresist (“SAC2”) 16 is built on top of the SAC1 photoresist 10 and the passivation layer 4. The SAC2 photoresist 16 serves as a scaffold for subsequent accumulation of the ceiling material that forms the ceiling and sidewalls of each nozzle chamber. Referring to FIGS. 23-25, a high-speed photoresist layer of about 6 microns is stretched over the wafer and exposed using the dark shade mask shown in FIG.

  As shown in FIGS. 23 and 25, the mask exposes the sidewall openings 17 in the SAC2 photoresist 16 corresponding to the location of the chamber sidewalls and the ink conduit sidewalls. Openings 18 and 19 are exposed adjacent to the capped inlet 15 and the nozzle chamber inlet, respectively. These openings 18 and 19 are refilled with ceiling material in a subsequent ceiling attachment step, providing unique advantages in the nozzle design of the present invention. In particular, the opening 18 refilled with ceiling material acts as a priming feature that assists in drawing ink from the inlet 15 into each nozzle chamber. This will be described in more detail below. The opening 19 refilled with ceiling material acts as a barrier to the filter structure and fluid crosstalk. These help to prevent bubbles from entering the nozzle chamber and diffuse the pressure pulses generated by the thermal actuator 12.

  Referring to FIGS. 26 and 27, the next step is to deposit a 3 micron ceiling material 20 on the SAC2 photoresist 16 by PECVD. The ceiling material 20 refills the openings 17, 18 and 19 of the SAC2 photoresist 16 to form a nozzle chamber 24 having a ceiling 21 and side walls 22. An ink conduit 23 that supplies ink to each nozzle chamber is also formed during the deposition of the ceiling material 20. Also, if there is a priming feature and a filter structure (not shown in FIGS. 26 and 27), they are formed simultaneously. The ceilings 21, each corresponding to an individual nozzle chamber 24, are extended in rows across adjacent nozzle chambers to form a continuous nozzle plate. The ceiling material 20 may be made of any appropriate material such as a silicon nitride film, a silicon oxide film, a silicon nitride oxide film, or aluminum nitride.

  Referring to FIGS. 28-30, the next step is to define the elliptical nozzle edge 25 of the ceiling 21 by etching away the 2 micron ceiling material 20. This etch is defined using a layer of photoresist (not shown) exposed by the dark tone edge mask shown in FIG. The elliptical edge 25 comprises two coaxial edge lips 25a and 25b arranged on the individual thermal actuators 12.

  Referring to FIGS. 31-33, the next step is to define an elliptical nozzle opening 26 in the ceiling 21 by etching all through the remaining ceiling material 20 limited by the edge 25. This etch is defined using a layer of photoresist (not shown) exposed by the dark shade ceiling mask shown in FIG. The elliptical nozzle opening 26 is disposed on the thermal actuator 12 as shown in FIG.

With the MEMS nozzle feature now fully formed, the next step is to remove the SAC1 and SAC2 photoresist layers 10 and 16 by O ₂ plasma ashing (FIGS. 34-35). After ashing, the thermal actuator 12 is suspended in a single plane on the pit 8. By making the contact portion 28 and the heater element 29 adhere to the same surface, the electrode 9 is efficiently electrically connected.

  36 and 37 show the total thickness (150 microns) of the silicon wafer 2 after ashing of the SAC1 and SAC2 photoresist layers 10 and 16. FIG.

  Referring to FIGS. 38 to 40, after the front side MEMS processing of the wafer is completed, the ink supply channel 27 is etched from the back side of the wafer and aligned with the ink inlet 15 using standard anisotropic DRIE. This backside etch is defined using a photoresist layer (not shown) exposed by the dark shade mask shown in FIG. The ink supply channel 27 fluidly connects between the back side of the wafer and the ink inlet 15.

  Finally, referring to FIGS. 41 and 42, the wafer is thinned to 135 microns by backside etching. FIG. 43 is a cut-away perspective view of the completed printhead integrated circuit, showing three adjacent rows of nozzles. Each row of nozzles has an individual ink supply channel 27 that extends along its length and supplies ink to a plurality of ink inlets 15 in each row. The ink inlet supplies ink to each row of ink conduits 23, and each nozzle chamber receives ink from a common ink conduit in that row.

[Features and Advantages of Specific Embodiment]
The following discusses certain unique features of embodiments of the present invention, and the advantages of these features, with appropriate subheadings. The features are discussed in connection with all drawings relating to the present invention, unless the content specifically excludes the particular drawing and is not particularly related to the drawing referred to.

Low Loss Electrode As shown in FIGS. 41 and 42, the heater element 29 is suspended in the room. This ensures that the heater element is immersed in the ink during chamber priming. When the heater element is fully immersed in the ink, the efficiency of the printhead is dramatically improved. Very little heat is dissipated to the underlying wafer substrate, thus increasing the input energy used to generate bubbles that eject ink.

  To suspend the heater element, a contact is used to support the element in the raised position. Basically, the contacts at either end of the heater element can have vertical or inclined sections to connect the individual electrodes on the CMOS drive to the element in the raised position. However, heater material deposited on vertical or inclined surfaces is thinner than material on horizontal surfaces. In order to avoid undesirable resistance losses due to the thinned section, the contact portion of the thermal actuator needs to be relatively large. Larger contacts occupy a significant area on the wafer surface and limit nozzle packing density.

  In order to immerse the heater, the present invention etches the pits or trenches 8 between the electrodes 9 to reduce the level of the chamber floor. As discussed above, a sacrificial photoresist (SAC) layer 10 (see FIG. 9) is deposited in the trench to provide a scaffold for the heater element. However, if the SAC 10 is deposited in the trench 8 and simply covered with a layer of heater material (as described above in connection with FIG. 7), a stringer is placed in the gap 46 between the SAC 10 and the sidewall 48 of the trench 8. Can be formed. The gap is formed because it is difficult to accurately match the mask to the side of the trench 8. Normally, when the masked photoresist is exposed, a gap 46 is formed between the side of the pit and the SAC. If a heater material layer is deposited, these gaps are refilled to form a “stringer” (as is known). The stringer remains in the trench 8 after a metal etch (which forms the heater element) and a release etch (which eventually removes the SAC). Stringers can short circuit the heater and therefore cannot produce bubbles.

  52 and 53, a “traditional” technique for preventing stringers is illustrated. By making the UV mask exposing the SAC slightly larger than the trench 8, the SAC 10 is deposited on the side wall 48 and thus no gap is formed. Unfortunately, this creates a raised lip 50 around the top of the trench. When the heater material layer 11 is deposited (see FIG. 53), this is thinner on the vertical or inclined surface 52 of the lip 50. After metal etching and release etching, these thin lip structures 52 remain and cause “hot spots”. This is because resistance increases as the thickness is reduced locally. These hot spots affect the operation of the heater and usually shorten the life of the heater.

  As discussed above, Applicants have discovered that the reflow of SAC 10 closes gap 46 and thus the scaffold between electrodes 9 is completely flat. As a result, the entire thermal actuator 12 can be made flat. The planar structure of the thermal actuator prevents hot spots caused by vertical or inclined surfaces with the contact directly attached to the CMOS electrode 9 and the suspended heater element 29, so that the contact reduces resistance loss. It can be made much smaller without being so large. The low resistance loss maintains efficient operation of the suspended heater element, and the small contact size is convenient for packing the nozzle closer onto the printhead.

Multiple nozzles in each chamber Referring to FIG. 49, the unit cell shown has two separate ink chambers 38, each chamber having heater elements 29 extending between individual pairs of contacts 28. Have. An ink permeable structure 34 is disposed within the ink refill opening so that ink can enter the chamber, but upon activation, the structure 34 is sufficient to reduce backflow or fluid crosstalk to an acceptable level. Provides hydraulic resistance.

  Ink is supplied through the ink inlet 15 from the back side of the wafer. The priming feature 18 extends into the inlet opening so that the ink meniscus is not pinned to the periphery of the opening and does not stop the ink flow. Ink from the inlet 15 refills the lateral ink conduit 23 that feeds both chambers 38 of the unit cell.

  Each chamber 38 has two nozzles 25 instead of one nozzle per chamber. When the heater element 29 is activated (forms a bubble), two drops of ink are ejected from each nozzle 25, one drop at a time. Each individual drop of ink has a smaller volume than a single drop that is ejected if the chamber has only one nozzle. When a plurality of droplets are discharged simultaneously from one chamber, the print quality is improved.

  For each nozzle, the ejected drops are misoriented to some extent. Depending on the degree of misorientation, this can be detrimental to print quality. By providing a plurality of nozzles in the chamber, each nozzle ejects drops having a different misorientation in a relatively small volume. Some small drops that are misoriented in different directions are not as detrimental to print quality as a single relatively large drop that is misoriented. Applicants have found that they effectively “see” the dots from one drop with the average misalignment of each small eye drop and the overall misorientation greatly reduced.

  A multi-nozzle chamber can also eject droplets more effectively than a single nozzle chamber. The heater element 29 is a suspended elongated TiAlN beam, the bubbles it forms are likewise elongated. The pressure pulse generated by the elongated bubble causes ink to be ejected through a centrally located nozzle. However, some of the energy from the pressure pulse is dissipated due to hydraulic losses associated with the mismatch between the bubble geometry and that of the nozzle.

  Separating several nozzles 25 along the length of the heater element 29 reduces the geometric discrepancy between the bubble shape and the nozzle configuration through which the ejected ink passes. This reduces the hydraulic resistance to ink ejection, thereby improving the printhead efficiency.

Ink chamber refilled through adjacent ink chambers Referring to FIG. 46, two opposing unit cells are shown. In this embodiment, the unit cell has four ink chambers 38. The chamber is defined by the sidewall 22 and the ink permeable structure 34. Each chamber has its own heater element 29. The heater elements 29 are arranged and configured in pairs connected in series. Between each pair is a “cold spot” 54 with reduced resistance and / or increased heat sinking. This ensures that the bubbles do not agglomerate at the cold spot 54, so that the cold spot becomes a common contact between the outer contacts 28 of each pair of heater elements.

  Although the ink permeable structure 34 allows the chamber 38 to be refilled with ink after ejection of the drop, it can interfere with the pressure pulses from each heater element 29 and reduce fluid crosstalk between adjacent chambers. it can. It will be appreciated that this embodiment has many parallel to that shown in FIG. 49 discussed above. However, this embodiment effectively divides the relatively long chamber of FIG. 49 into two separate chambers. This aligns the foam geometry formed by the heater element 29 with the shape of the nozzle 25 and reduces hydraulic losses during drop ejection. This is achieved without reducing nozzle density, but adds some complexity to the manufacturing process.

  The conduits that distribute ink to each ink chamber of the array (ink inlet 15 and supply conduit 23) may occupy a significant percentage of the wafer area. This can be a limiting factor on the nozzle density on the print head. By making some chambers part of the ink flow path to other ink chambers while fully releasing each chamber from fluid crosstalk, the amount of lost wafer area to the ink supply conduit is reduced. .

Ink chamber with multiple actuators and individual nozzles Referring to FIG. 54, the unit cell shown has two chambers 38, each chamber having two heater elements 29 and two nozzles 25. Effective reduction of drop misorientation by using multiple nozzles per chamber has been discussed above with respect to the embodiment shown in FIG. The additional advantage of dividing one elongated chamber into separate chambers, each with its own actuator, will be described with respect to the embodiment shown in FIG. This embodiment achieves many of the advantages of the embodiment of FIG. 46 with a surprisingly uncomplicated design using multiple nozzles and multiple actuators in each chamber. With a simplified design, the overall dimensions of the unit cell can be reduced, thereby increasing the nozzle density. In the illustrated embodiment, the occupied area of the unit cell is 64 μm long and 16 μm wide.

  The ink permeable structure 34 is a single cylinder in the ink refill opening of each chamber 38, rather than three spaced cylinders as in the embodiment of FIG. One cylinder has a cross-sectional profile that reduces resistance to refill flow but increases resistance to sudden backflow due to an activation pressure pulse. Both heater elements in each chamber can be deposited simultaneously with contact 28 and cold spot feature 54. Ink is supplied to both chambers 38 from a common ink inlet 15 and supply conduit 23. These features can also reduce the footprint, which will be discussed in more detail below. The priming feature 18 is made integral with one of the chamber side wall 22 and the wall ink conduit 23. These features are dual purpose in nature and help to simplify manufacturing and make the design compact.

Multiple chambers and multiple nozzles per drive circuit In FIG. 54, the actuators are connected in series, thus starting together with the same drive signal, simplifying the CMOS drive circuit. In the unit cell of FIG. 46, the actuators of adjacent nozzles are connected in series in the same drive circuit. Needless to say, adjacent indoor actuators can also be connected in parallel. In contrast, if each chamber actuator becomes a separate circuit, the CMOS drive circuit becomes more complex and the size of the unit cell footprint increases. In a printhead design that addresses drop misorientation by replacing multiple relatively small drops, combining several actuators and their individual nozzles into a common drive circuit would reduce the printhead IC manufacturing. Efficiently realized in terms of both nozzle density.

By reducing the width of the high density thermal inkjet printhead unit cell, the printhead can have a nozzle pattern that previously had to reduce the nozzle density. Needless to say, the reduction in nozzle density has a corresponding effect on the size and / or print quality of the print head.

  Traditionally, the rows of nozzles are arranged in pairs, with each row of actuators extending in opposite directions. The rows are staggered with respect to each other, so the print resolution (dots per inch) is twice the nozzle pitch (nozzles per inch) along each row. By configuring the components of the unit cell so that the overall width of the unit is reduced, the same number of nozzles can be used instead of two alternating rows facing each other without sacrificing the print resolution (dpi). Can be arranged in rows. The embodiment illustrated in the accompanying drawings achieves a nozzle pitch of more than 1000 nozzles per inch (2.54 cm) in each linear row. With this nozzle pitch, the print resolution of the print head is better than the photo (1600 dpi) when two opposite staggered rows are considered, and a nozzle that ensures that the print head operating life is satisfactory There is enough capacity for redundancy, dead nozzle compensation, etc. As discussed above, the embodiment shown in FIG. 54 has an footprint that is 16 μm wide, so the nozzle pitch along a row is about 1600 nozzles per inch (2.54 cm). . Thus, the two staggered staggered rows are approximately 3200 d. p. i. Generate a resolution of.

  Recognizing certain advantages associated with narrowing unit cells, Applicants have focused on identifying and combining several features that reduce the associated dimensions of the structures in the printhead. For example, the elliptical nozzle, the ink inlet shift from the chamber, the geometric logic miniaturization, and the shortening of the drive FET (field effect transistor) were developed by the Applicant to derive some of the illustrated embodiments. It is a feature. Each feature that contributes to this deviates from the conventional wisdom of this technical field, such as reducing the FET drive voltage from the conventional 5V to 2.5V, which is widely used to shorten the length of the transistor. Needed.

Printhead surface with reduced stiction Static friction, or “stiction”, as it has become known, can “stick” dust particles to the nozzle plate, thereby clogging the nozzles. FIG. 50 shows a part of the nozzle plate 56. For clarity, the nozzle opening 26 and nozzle edge 25 are also shown. On the outer surface of the nozzle plate, a pattern is formed by cylindrical protrusions 58 extending a short distance from the surface of the plate. The nozzle plate can also be patterned with other surface configurations such as short-interval ridges, corrugations or bumps. However, it is easy to generate an appropriate UV mask for the cylindrical protrusions in the pattern shown, and etching the cylinder to the outer surface is simple.

  By reducing the co-action of static friction, the possibility of paper dust or other contaminants clogging the nozzles of the nozzle plate is reduced. When the pattern is formed in a configuration that protrudes outside the nozzle plate, the surface area with which the dust particles contact is limited. If the particles can only contact the outer edge of each component, the friction between the particles and the nozzle plate is minimal and therefore very unlikely to adhere. If the particles actually adhere, there is a high probability that they will be removed during the printhead maintenance cycle.

Inlet Priming Feature Referring to FIG. 47, two unit cells are shown extending in opposite directions relative to each other. The ink inlet passage 15 supplies ink to the four chambers 38 via the lateral ink conduits 23. Distributing ink to individual MEMS nozzles of an inkjet printhead through micron-scale conduits such as ink inlets 15 is complicated by factors that do not occur with macro-scale flow. A meniscus is formed which, depending on the geometry of the opening, can “pin” it very strongly to the lip of the opening. This is useful for print heads such as bleed holes that vent trapped bubbles but retain ink, but can be problematic when stopping ink flow to some chambers. This is most likely to occur when initially priming the print head with ink. When an ink meniscus is pinned to an ink inlet opening, the chamber supplied by that inlet remains unprimed.

  To protect against this, two priming features 18 are formed to extend through the face of the inlet opening 15. The priming feature 18 is a cylinder extending around the inlet 15 from the inside of a nozzle plate (not shown). A portion of each cylinder 18 is inside the circumference, so the surface tension of the ink meniscus at the ink inlet is formed in the priming feature 18 to draw ink out of the inlet. This allows the meniscus to “pull out the pin” from that section of the circumference and to flow toward the ink chamber.

  The priming feature 18 can take many forms, as long as it exhibits a surface that extends across the face of the opening. Further, the priming feature may be an integral part of other nozzle features as shown in FIG.

Ink Chamber Side Entrance Referring to FIG. 48, several adjacent unit cells are illustrated. In this embodiment, an elongated heater element 29 extends parallel to the ink distribution conduit 23. Accordingly, the elongated ink chamber 38 is similarly aligned with the ink conduit 23. A side wall opening 60 connects the chamber 38 to the ink conduit 23. Configuring the ink chamber to have a side inlet reduces the ink refill time. The inlet becomes wider and therefore the refill flow rate increases. Sidewall opening 60 has ink permeable structure 34 to maintain fluid crosstalk at an acceptable level.

Ink Chamber Inlet Filter Referring again to FIG. 47, the ink refill opening to each chamber 38 has a filter structure 40 that traps air bubbles or other contaminants. Bubbles and solid contaminants in the ink are detrimental to the MEMS nozzle structure. Solid contaminants clearly clog the nozzle openings and bubbles are highly compressible, so when trapped in the ink chamber, they can absorb pressure pulses from the actuator. This effectively disables ink ejection from the affected nozzles. By providing the filter structure 40 in the form of a row of obstructions extending across the direction of flow through the aperture and separating each row so that it is not registered with the obstruction of an adjacent row with respect to the direction of flow Without reducing the ink refill flow rate too much, the likelihood of contaminants entering the chamber 38 is reduced. The rows are offset from each other and the effect of introduced turbulence on the nozzle refill rate is minimal, but bubbles or other contaminants follow the relatively serpentine flow path and are retained by the obstruction 40 Is likely to be.

  The illustrated embodiment uses two rows of obstacles 40 in the form of a cylinder that extends between the wafer substrate and the nozzle plate.

Intermediate Color Surface Barrier of Multi-Color Inkjet Printhead Referring now to FIG. 51, the outer surface of the unit cell nozzle 56 as shown in FIG. 46 described above is shown. The nozzle opening 26 is positioned directly above the heater element (not shown) and a series of right-angled ink fountains 44 are formed in the nozzle plate 56 above the ink conduit 23 (see FIG. 46).

  Inkjet printers often have a maintenance station that caps the print head when not in use. To remove excess ink from the nozzle plate, the capper can be disengaged so as to be stripped from the outer surface of the nozzle plate. This promotes meniscus formation between the capper surface and the outer surface of the nozzle plate. Using the contact angle history for the angle at which the meniscus surface tension contacts the surface (for further details, see Applicant's co-pending USSN (document FND007US) incorporated herein by reference), the nozzle plate Most of the ink that wets the outside of the ink can be collected and pulled by a meniscus between the capper and the nozzle plate. The ink is conveniently deposited as a large bead at the point where the capper fully disengages from the nozzle plate. Unfortunately, some ink remains on the nozzle plate. If the print head is a multicolor print head, the residual ink remaining in or around a given nozzle opening may be different in color from the ink ejected by the nozzle. This is because the meniscus pulls ink across the entire surface of the nozzle plate. Contaminating ink from one nozzle with ink from another can cause visible artifacts in the print.

  A ridge arrangement 44 extending across the direction in which the capper is stripped from the nozzle plate removes and retains a portion of the ink in the meniscus. The spider does not collect all the meniscus ink, but greatly reduces the level of contamination of the nozzles with different color inks.

Bubbles entrained with bubble trap ink are very detrimental to the operation of the printhead. Air or generally gas is highly compressible and can absorb pressure pulses from the actuator. If the trapped bubble simply compresses in response to the actuator, no ink is ejected from the nozzle. The trapped bubbles can be purged from the print head with a forced flow of ink, but the purged ink must be blotted and the forced flow can also introduce fresh bubbles.

  The embodiment shown in FIG. 46 has a bubble trap at the ink inlet 15. The trap is formed by a bubble holding structure 32 and a vent 36 formed in the ceiling layer. The foam retention structure is a series of cylinders 32 spaced around the inlet 15. As discussed above, the ink priming feature 18 has two purposes and conveniently forms part of the bubble retention structure. In use, the ink permeable trap directs the bubbles to the vent where they are vented to the atmosphere. By trapping bubbles at the ink inlet and directing them to a small vent, they are effectively removed from the ink stream without leaking ink.

Supplying ink to the nozzles through conduits that extend from one side of the flow path wafers to the other at the ink inlet results in more wafer areas (on the ink discharge side) instead of a complex ink distribution system. It can have a nozzle. However, micron-scale holes etched deep through the wafer are prone to clogging with contaminants or bubbles. This depletes the nozzles fed from the affected inlet.

  As best illustrated in FIG. 48, a printhead according to the present invention has at least two ink inlets 15 that feed each chamber 38 via an ink conduit 23 between the nozzle plate and the underlying wafer. .

  Introducing an ink conduit 23 that feeds several chambers 38 and is itself fed from several ink inlets 15 reduces the possibility of nozzle clogging due to inlet clogging. When one inlet 15 is clogged, the ink conduits will draw more ink from other conduits on the wafer.

  Although the invention has been described with reference to particular embodiments, those skilled in the art will recognize that the invention can be implemented in many other forms.

4 is a diagram illustrating a partially manufactured unit cell of a MEMS nozzle array on a print head according to the present invention, the unit cell being a cross section taken along line AA in FIG. FIG. 2 is a perspective view of the partially manufactured unit cell of FIG. 1. FIG. 6 shows marks associated with etching of a heater element trench. It is sectional drawing of the unit cell after the etching of a trench. It is a perspective view of the unit cell shown in FIG. It is a figure which shows the mask accompanying attachment of the sacrificial photoresist shown in FIG. FIG. 5 shows the unit cell after deposition of a sacrificial photoresist trench with the gap between the sacrificial material edge and the trench sidewall partially enlarged. FIG. 8 is a perspective view of the unit cell shown in FIG. 7. FIG. 5 shows the unit cell after the sacrificial photoresist has been reflowed to close the gap along the trench sidewall. FIG. 10 is a perspective view of the unit cell shown in FIG. 9. It is sectional drawing which shows adhesion of a heater material layer. It is a perspective view of the unit cell shown in FIG. It is a figure which shows the mask accompanying metal etching of the heater material shown in FIG. It is sectional drawing which shows the metal etching which shape | molds a heater actuator. It is a perspective view of the unit cell shown in FIG. It is a figure which shows the mask accompanying the etching shown in FIG. FIG. 5 shows the deposition of a photoresist layer and subsequent etching of the ink inlet to the passivation layer on top of the CMOS drive layer. FIG. 18 is a perspective view of the unit cell shown in FIG. 17. FIG. 6 shows an oxidative etch through an passivation layer and a CMOS layer to an underlying silicon wafer. FIG. 20 is a perspective view of the unit cell shown in FIG. 19. It is a figure which shows the deep anisotropic etching to the silicon wafer of an ink entrance. It is a perspective view of the unit cell shown in FIG. It is a figure which shows the mask accompanying the photoresist etching shown in FIG. FIG. 5 is a diagram illustrating photoresist etching that forms openings in the chamber ceiling and sidewalls. It is a perspective view of the unit cell shown in FIG. It is a figure which shows adhesion of a side wall and a risk material. It is a perspective view of the unit cell shown in FIG. It is a figure which shows the mask accompanying nozzle edge part etching shown in FIG. It is a figure which shows the etching of the ceiling layer which forms the edge of a nozzle opening. FIG. 30 is a perspective view of the unit cell shown in FIG. 29. It is a figure which shows the mask accompanying nozzle opening etching shown in FIG. FIG. 6 shows etching of the ceiling material that forms an elliptical nozzle opening. It is a perspective view of the unit cell shown in FIG. It is a figure which shows the oxygen plasma release etching of the 1st and 2nd sacrificial layer. It is a perspective view of the unit cell shown in FIG. It is a figure which shows the unit cell after release etching, and also the side part which a wafer opposes. FIG. 37 is a perspective view of the unit cell shown in FIG. 36. It is a figure which shows the mask accompanying reverse etching shown in FIG. It is a figure which shows the reverse etching to the wafer of an ink supply flow path. FIG. 40 is a perspective view of the unit cell shown in FIG. 39. It is a figure which shows thinning a wafer by back surface etching. It is a perspective view of the unit cell shown in FIG. 2 is a partial perspective view of an array of nozzles on a print head according to the present invention. FIG. It is a figure which shows the top view of a unit cell. FIG. 45 is a perspective view of the unit cell shown in FIG. 44. FIG. 5 is a schematic plan view of two unit cells with the ceiling layer removed, but with a particular ceiling layer feature shown only in outline. FIG. 6 is a schematic plan view of two unit cells in which the ceiling layer is removed, but the nozzle openings are shown only by the outlines. It is a partial schematic plan view of a unit cell having an ink inlet opening on the side wall of the chamber. FIG. 4 is a schematic plan view of a unit cell in which the ceiling layer is removed, but the nozzle openings are illustrated only by contour lines. FIG. 6 is a partial plan view of a nozzle plate having a configuration for reducing stiction and paper dust particles. It is a partial top view of a nozzle plate with a residual ink fountain. FIG. 3 is a partial cross-sectional view showing the deposition of a prior art SACI photoresist used to avoid stringers. FIG. 53 is a partial cross-sectional view showing the deposition of a layer of heater material on the SACI photoresist scaffold deposited in FIG. It is a partial schematic plan view of a unit cell having a plurality of nozzles and actuators in each chamber.

Claims (20)

A method of manufacturing a beam suspended in a MEMS process, comprising:
(A) etching a pit having a base and a sidewall into the substrate;
(B) attaching a sacrificial material to the surface of the substrate so as to refill the pits;
(C) removing the sacrificial material from the surrounding area of the pit and from the surface of the substrate surrounding the pit;
(D) reflowing the remaining sacrificial material in the pit so that the remaining sacrificial material is in contact with the sidewall;
(E) attaching a beam material to the substrate surface and the reflowed sacrificial material;
(F) removing the reflowed sacrificial material to form the suspended beam. The method of claim 1, wherein the suspended beam is planar . The method of claim 1, wherein all parts of the suspended beam have the same thickness.   The method of claim 1, wherein the suspended beam is an actuator of an inkjet nozzle.   The method of claim 4, wherein the actuator is a heater element.   The method of claim 5, wherein the heater element is suspended between a pair of electrodes.   The method of claim 1, wherein the substrate is a silicon wafer.   The method of claim 7, wherein the silicon wafer comprises at least one oxide layer.   The method of claim 1, wherein the sacrificial material is a photoresist.   The method of claim 9, wherein the photoresist is removed by exposure through a mask and subsequent development.   The method of claim 1, wherein the surrounding region comprises an area adjacent to at least two of the sidewalls.   The method of claim 1, wherein the surrounding region comprises an area adjacent to all of the sidewalls.   The method of claim 1, wherein the removal of the sacrificial material from the surrounding region results in a space between the remaining sacrificial material and at least two of the sidewalls of less than 1 micron.   The method of claim 1, wherein the removal of the sacrificial material from the surrounding region results in a space between the remaining sacrificial material and all of the sidewalls being less than 1 micron.   The method of claim 1, wherein the reflow is performed by heating the sacrificial material.   The method of claim 1, wherein the sacrificial material is treated to prevent further reflow prior to deposition of beam material.   The method of claim 16, wherein the treatment comprises UV curing.   The method of claim 1, wherein the beam material is etched into a predetermined configuration after deposition.   The method of claim 1, wherein a further MEMS process step is performed after deposition of the beam material and before the removal of the reflowed sacrificial material.   The method of claim 19, wherein the step of the further MEMS process comprises forming an inkjet nozzle that includes the suspended beam.

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