WO2022088015A1 - 超声换能单元及其制备方法 - Google Patents

超声换能单元及其制备方法 Download PDF

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Publication number
WO2022088015A1
WO2022088015A1 PCT/CN2020/125147 CN2020125147W WO2022088015A1 WO 2022088015 A1 WO2022088015 A1 WO 2022088015A1 CN 2020125147 W CN2020125147 W CN 2020125147W WO 2022088015 A1 WO2022088015 A1 WO 2022088015A1
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WIPO (PCT)
Prior art keywords
pattern
layer
electrode
photoresist
ultrasonic transducer
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PCT/CN2020/125147
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English (en)
French (fr)
Inventor
花慧
李延钊
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京东方科技集团股份有限公司
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Application filed by 京东方科技集团股份有限公司 filed Critical 京东方科技集团股份有限公司
Priority to US17/427,358 priority Critical patent/US12030084B2/en
Priority to PCT/CN2020/125147 priority patent/WO2022088015A1/zh
Priority to CN202080002544.5A priority patent/CN114698410B/zh
Publication of WO2022088015A1 publication Critical patent/WO2022088015A1/zh

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
    • B06B—METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, e.g. FOR PERFORMING MECHANICAL WORK IN GENERAL
    • B06B1/00—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency
    • B06B1/02—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy
    • B06B1/0292—Electrostatic transducers, e.g. electret-type
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R7/00—Diaphragms for electromechanical transducers; Cones
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
    • B06B—METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, e.g. FOR PERFORMING MECHANICAL WORK IN GENERAL
    • B06B2201/00—Indexing scheme associated with B06B1/0207 for details covered by B06B1/0207 but not provided for in any of its subgroups
    • B06B2201/50—Application to a particular transducer type
    • B06B2201/51—Electrostatic transducer

Definitions

  • the present application relates to the technical field of semiconductors, and in particular, to an ultrasonic transducer unit and a preparation method thereof.
  • CMUT capacitive micromachined ultrasonic transducer
  • MEMS microelectromechanical system
  • the CMUT device preparation process is compatible with the process of CMOS integrated circuits. Usually, photolithography technology is used, and photoresist and film layer patterning process are used to prepare ultrasonic probes with high integration and large-scale arrays, which can meet the requirements of clinical medicine. The growing need for access to information.
  • the present disclosure provides an ultrasonic transducer unit and a preparation method thereof.
  • the ultrasonic transducer unit comprises: a substrate; a first electrode arranged on the substrate;
  • a diaphragm layer arranged on the first electrode; and a second electrode arranged on the diaphragm layer, the orthographic projection of the first electrode on the substrate and the orthographic projection of the second electrode on the substrate There is an overlapping area, and a closed cavity is formed at the overlapping area between the diaphragm layer and the first electrode; wherein, the material of the diaphragm layer is photoresist.
  • the ultrasonic transducer unit further includes a through hole penetrating the diaphragm layer and communicating with the cavity, and a filling pattern for filling the through hole.
  • the ultrasonic transducer unit further includes an insulating layer disposed on the first electrode and between the cavity, wherein the insulating layer is made of photoresist.
  • the photoresist includes DL-1000-C glue or SU8 glue.
  • the material of the diaphragm layer is DL-1000-C glue, and the thickness of the diaphragm layer is greater than or equal to 1.5 ⁇ m and less than or equal to 3 ⁇ m; or the material of the diaphragm layer is SU8 glue, And the thickness of the diaphragm layer is greater than or equal to 5 ⁇ m and less than or equal to 40 ⁇ m.
  • the material of the insulating layer is DL-1000-C glue, and the thickness of the insulating layer is greater than or equal to 1.5 ⁇ m and less than or equal to 3 ⁇ m; or the material of the insulating layer is SU8 glue, and the The thickness of the insulating layer is 5 ⁇ m or more and 40 ⁇ m or less.
  • the material for filling the pattern is amorphous silicon.
  • the ultrasonic transducer unit further includes a first electrode lead which is disposed on the substrate in the same layer as the first electrode and is electrically connected to the first electrode.
  • the orthographic projection of the cavity on the substrate is located in a first area
  • the substrate further includes a second area
  • the second area surrounds the first area
  • the diaphragm layer has a At least a portion of the insulating layer is in direct contact with at least a portion of the insulating layer in the second region; or the ultrasonic transducer unit further includes a support pattern disposed between the diaphragm layer and the insulating layer, the support pattern in the second area.
  • the material of the supporting pattern is photoresist.
  • the present disclosure also provides a method for preparing an ultrasonic transducer unit, comprising: forming a first electrode on a substrate; forming a sacrificial material pattern on the first electrode; forming a photoresist pattern on the sacrificial material pattern, wherein, The orthographic projection of the photoresist pattern on the substrate and the orthographic projection of the first electrode on the substrate have an overlapping area; the sacrificial material pattern is removed, so that the photoresist pattern and the A first electrode forms a closed cavity in the overlapping area; and a second electrode is formed on the photoresist pattern, wherein the orthographic projection of the second electrode on the substrate and the overlapping area are at least partially overlapping.
  • the material for forming the photoresist pattern includes DL-1000-C glue or SU8 glue.
  • forming the sacrificial material pattern on the first electrode includes: forming a first photoresist layer on the first electrode; exposing and developing and post-baking the first photoresist layer using a mask forming an insulating layer; and forming the sacrificial material pattern at least in the overlapping region on the insulating layer.
  • forming a photoresist pattern on the sacrificial material pattern includes: forming a second photoresist layer on the sacrificial material pattern and on the exposed portion of the insulating layer; and using a mask pair The second photoresist layer is subjected to exposure development and post-baking treatment to form the photoresist pattern having at least one through hole penetrating through the second photoresist layer.
  • removing the pattern of sacrificial material includes: removing the pattern of sacrificial material through the at least one via; and forming a fill pattern in the at least one via.
  • the orthographic projection of the cavity on the substrate is located in a first area
  • the substrate further includes a second area surrounding the first area and on the first electrode
  • Forming the sacrificial material pattern includes: forming a first photoresist layer on the first electrode; exposing the first photoresist layer with a mask, developing and post-baking to form an insulating layer; on the insulating layer forming a third photoresist layer, exposing, developing and post-baking the third photoresist layer to form a support pattern in the second region; and forming the sacrificial material pattern in the support pattern.
  • the method further includes forming a first electrode lead on the substrate that is in the same layer as the first electrode and is electrically connected to each other.
  • the sacrificial material pattern is a Mo or AlNd metal pattern; and removing the sacrificial material pattern includes removing the Mo or AlNd metal pattern using phosphoric acid and/or sulfuric acid.
  • the material of the insulating layer includes DL-1000-C glue or SU8 glue.
  • the material for supporting the pattern includes DL-1000-C glue or SU8 glue.
  • FIG. 1A shows a top view of an ultrasonic transducer unit according to an embodiment of the present disclosure
  • FIG. 1B shows a schematic cross-sectional view of an ultrasonic transducer unit according to an embodiment of the present disclosure
  • FIG. 1C shows a top view of an ultrasonic transducer unit according to an embodiment of the present disclosure
  • FIG. 1D shows a schematic cross-sectional view of an ultrasonic transducer unit according to an embodiment of the present disclosure
  • FIG. 2 shows a schematic structural diagram of an ultrasonic transducer unit according to an embodiment of the present disclosure
  • FIG. 3 shows a flowchart of a method for manufacturing an ultrasonic transducer unit according to an embodiment of the present disclosure
  • FIGS. 4A to 4F show schematic structural diagrams of a manufacturing process of an ultrasonic transducer unit according to an embodiment of the present disclosure
  • FIG. 5 shows a flowchart of a method for manufacturing an ultrasonic transducer unit according to an embodiment of the present disclosure
  • FIG. 6 shows a schematic structural diagram of a manufacturing process of an ultrasonic transducer unit according to an embodiment of the present disclosure.
  • the ultrasonic transducer unit of the present application may be a Capacitive Micro-machined Ultrasonic Transducer (CMUT), which generally includes a substrate (eg glass), a bottom electrode, an insulating layer, a diaphragm formed in sequence on the substrate layer and top electrode, wherein a closed cavity is formed between the insulating layer and the diaphragm layer.
  • CMUT Capacitive Micro-machined Ultrasonic Transducer
  • the ultrasonic transducer unit further includes a filling hole formed in the diaphragm layer when the cavity is formed, and a filling layer formed after filling the filling hole.
  • the insulating layer and the diaphragm layer in the related art are prepared from silicon nitride or silicon oxide, and the preparation of these layers must go through layer deposition, photoresist coating, and layer etching. , the step of removing the photoresist.
  • a low pressure chemical vapor deposition (LPCVD) process can be used to deposit a single layer of silicon nitride, a material, or a dry oxidation process and a low pressure chemical vapor deposition (LPCVD) process to deposit silicon dioxide and nitrogen. It is composed of a composite layer of two materials of silicon carbide.
  • a polysilicon thin film layer can be formed as a sacrificial material layer on the formed insulating layer and patterned. The size of the patterned polysilicon layer determines the size of the cavity of the ultrasonic transducer unit, for example, determines the thickness of the cavity .
  • a vibrating film of low residual stress silicon nitride is deposited on the patterned polysilicon layer and the exposed insulating layer, for example using a low pressure chemical vapor deposition (LPCVD) process, the thickness of the vibrating film may be selected, for example, in the range of 0.3 to 2 ⁇ m, This depends on the requirements for the output sound pressure of the ultrasonic transducer unit.
  • LPCVD low pressure chemical vapor deposition
  • etching holes such as An etched hole with a diameter of about 2 ⁇ m can be formed, and the silicon nitride in the etched hole area is etched away by dry etching technology, so that the etched hole is directly connected to the sacrificial material layer of polysilicon.
  • the photoresist needs to be removed.
  • the etching hole for forming the cavity in the diaphragm layer it is necessary to coat the photoresist on the silicon nitride layer or the silicon oxide layer.
  • the dry etching of the mask plate and the steps of removing the photoresist are complicated, occupy a lot of production equipment, and take a long time.
  • the present application proposes an ultrasonic transducer unit, the diaphragm layer of which is prepared by photoresist, that is, in the process of forming the cavity after the diaphragm layer is formed, only photoresist needs to be coated, and a mask is used. After the plate exposes and develops the photoresist, etching holes can be formed in the photoresist layer, which greatly simplifies the preparation process and improves the production efficiency. Compared with the silicon nitride film layer and the silicon oxide film layer in the related art, it can not only reduce the ductility of the material forming the photoresist layer, but also better as the diaphragm layer of the ultrasonic transducer unit. During the working process of the ultrasonic transducer unit, the diaphragm layer is not easily damaged, so that the formed ultrasonic transducer unit is more reliable.
  • the ultrasonic transducer unit includes: a substrate 10; a first electrode (bottom electrode) 11 arranged on the substrate 10; an insulating layer 12 arranged on the first electrode 11; a diaphragm layer 14 arranged on the insulating layer 12;
  • the second electrode (top electrode) 15 on the diaphragm layer 14, the orthographic projection of the first electrode 11 on the substrate 10 and the orthographic projection of the second electrode 15 on the bottom of the substrate 10 have overlapping areas, the diaphragm layer 14 and the first An electrode 11 is formed with a closed cavity 13 at the overlapping area.
  • the ultrasonic transducer unit further includes a through hole penetrating the diaphragm layer 14 to communicate with the cavity 13 and a filling pattern 18 for filling the through hole.
  • the through hole is used as a channel for the etching solution when the cavity 13 is formed.
  • the material of the diaphragm layer 14 is photoresist, such as DL-1000-C glue or SU8 glue.
  • DL-1000-C adhesive mainly contains polyimide, which is a positive photoresist, insoluble in organic solvents, stable to dilute acid, and the cross-linked polymer contained in it can be cut off by light to become soluble in the developing solvent.
  • SU8 is a negative photoresist, which forms a cross-linked polymer after exposure and is not easily dissolved by a solvent.
  • photoresist is used as the material of the diaphragm layer. Since the photoresist has good ductility as a film layer, the vibrating film layer is not easily damaged when the formed ultrasonic transducer unit is repeatedly vibrated during the operation.
  • the material and thickness of the diaphragm layer determine the operating frequency of the ultrasonic transducer unit. When the frequency is constant, the thickness of the diaphragm layer of the photoresist material is thicker than that of silicon nitride and/or silicon oxide, which will make the diaphragm layer more reliable during repeated vibrations in operation.
  • the thickness of the diaphragm layer When the material of the diaphragm layer is DL-1000-C glue, its thickness can be greater than or equal to 1.5 ⁇ m and less than or equal to 3 ⁇ m; when the material of the diaphragm layer is SU8 glue, its thickness can be greater than or equal to 5 ⁇ m and less than or equal to 40 ⁇ m. In the related art, when a silicon nitride material is used to form the diaphragm layer, the thickness thereof is usually between 0.3 ⁇ m and 2 ⁇ m.
  • the thickness of the diaphragm layer prepared by using the photoresist material is relatively thick, which further increases the product reliability of the ultrasonic transducer unit, and avoids the diaphragm layer being easily damaged due to multiple reciprocating motions.
  • SU8 glue is a transparent material. Using SU8 glue as the diaphragm layer material of the ultrasonic transducer unit can form a completely transparent ultrasonic transducer unit, thereby forming an ultrasonic transducer unit with higher transmittance.
  • the ultrasonic transducer unit of the embodiment shown in FIGS. 1A and 1B includes the insulating layer 12 , but the present disclosure is not limited thereto.
  • the ultrasonic transducer unit of the present disclosure may not include an insulating layer, but form a closed cavity between the diaphragm layer and the first electrode.
  • the material of the diaphragm layer is photoresist.
  • a metal material such as Mo (molybdenum) or AlNd (aluminum neodymium alloy) can be used as the sacrificial material.
  • the insulating layer 12 of non-metallic material formed on the first electrode can avoid the adverse effects on the first electrode by the processes used to form and remove the sacrificial material later.
  • the insulating layer 12 can be prepared with the same photoresist material (eg, DL-1000-C glue or SU8 glue) as the diaphragm layer 14 .
  • the material of the insulating layer 12 is DL-1000-C glue
  • its thickness can be greater than or equal to 1.5 ⁇ m and less than or equal to 3 ⁇ m
  • the material of the insulating layer 12 is SU8 glue
  • its thickness can be greater than or equal to 5 ⁇ m and less than or equal to 40 ⁇ m.
  • the ultrasonic transducer unit further includes a through hole penetrating through the diaphragm layer 14 of the photoresist material to pass through the cavity 13 , and a filling pattern 18 is formed in the through hole.
  • amorphous silicon may be used to fill the via hole, and the filling pattern may extend to the bottom of the cavity 13 through the via hole, as shown in FIG. 1B .
  • the present invention is not limited to this, for example, silicon nitride or the like can also be used as the filling material.
  • the ultrasonic transducer unit is in the transmitting state first, and then switches to the receiving state.
  • a forward DC bias voltage VDC is loaded between the second electrode 15 and the first electrode 11, and the diaphragm layer 14 will bend downward (the side close to the first electrode 11) under the electrostatic action .
  • an AC voltage VAC with a certain frequency f is applied between the second electrode 15 and the first electrode 11 to excite the diaphragm layer 14 to reciprocate in a large amount (closer to the first electrode).
  • One electrode 11 reciprocates in the direction of and away from the first electrode 11) to realize the conversion of electrical energy into mechanical energy, and the diaphragm layer 14 radiates energy to the medium environment to generate ultrasonic waves; some of the ultrasonic waves can be detected on the surface of the object to be measured. Reflection occurs and returns to the ultrasonic transducer unit for reception and detection by the ultrasonic transducer unit.
  • the ultrasonic transducer unit is in the receiving state, only a DC bias voltage is applied between the second electrode 15 and the first electrode 11, and the diaphragm layer 14 achieves a static equilibrium under the action of electrostatic force and film restoring force.
  • the diaphragm layer 14 When acting on the diaphragm layer 14, the diaphragm layer 14 is excited to vibrate, and the cavity spacing between the second electrode 15 and the first electrode 11 changes, causing the capacitance between the plates to change, thereby generating a detectable electrical signal, Detection of the received ultrasonic waves can be realized based on the electrical signal.
  • the substrate 10 may include a first region on which the orthographic projection of the cavity 13 is located and a second region surrounding the first region, as shown in FIGS. 1A and 1B , at least a portion of the diaphragm layer 14 and at least a portion of the insulating layer 12 . A portion is in direct contact with the second region.
  • the cavity 13 may be surrounded by photoresist material only.
  • the materials of the top, bottom and side surfaces of the cavity 13 are all photoresists such as DL-1000-C glue and SU8 glue.
  • the ultrasonic transducer unit may further include a first electrode lead 16 disposed on the substrate 10 in the same layer as the first electrode 11 , which is connected to the first electrode 11 is electrically connected to lead the first electrode 11 to the outside, so as to apply an electrical signal to the first electrode 11 when the ultrasonic transducer unit works.
  • the first electrode lead 16 may be provided with a through hole penetrating through the diaphragm layer 14 and the insulating layer 12 for connecting an external signal line.
  • FIGS. 1C and 1D respectively show a top view and a schematic cross-sectional view of an ultrasonic transducer unit according to an embodiment of the present disclosure, wherein FIG. 1D is a cross-sectional view taken along the line AA' shown in FIG. 1C .
  • the cavity 13 of the ultrasonic transducer unit shown in FIGS. 1C and 1D includes a central portion 25 and one or more cavities extending outwardly from the central portion 25 as its cavities.
  • the branched connecting portion 26 in which through holes penetrating the diaphragm layer 14 to communicate with the cavity 13 and filling patterns 18 filling the through holes are provided on the connecting portion 26 , that is, in the region other than the central portion 25 .
  • This structure can reduce the influence of the filling pattern 18 on the vibration of the diaphragm layer 14, so that it has better vibration performance.
  • the orthographic projection of the cavity on the substrate in the embodiment shown in FIGS. 1A and 1B is a hexagon
  • the orthographic projection of the cavity on the substrate in the embodiment shown in FIGS. 1C and 1D is a hexagon
  • the present application is not limited thereto, for example, the orthographic projection of the cavity on the substrate 1 may be a square or a circle.
  • FIG. 2 shows a schematic cross-sectional view of an ultrasonic transducer unit according to an embodiment of the present disclosure.
  • the ultrasonic transducer unit includes a first electrode 5 , an insulating layer 6 , a diaphragm layer 8 and a second electrode 9 which are provided on the substrate 10 .
  • a vibration cavity is enclosed by a support pattern 7 , such as a ring-shaped hollow support pattern 7 , and the orthographic projection of the cavity on the substrate 10
  • the substrate 10 further includes a second area, and the second area surrounds the first area.
  • the support pattern 7 is located in the second area.
  • the diaphragm layer 8 is formed on the support pattern 7 to close the vibration cavity, thereby forming the closed cavity 11 .
  • the ultrasonic transducer unit also includes a through hole formed through the diaphragm layer 8 and passing through the cavity, and a filling pattern 12 formed in the through hole.
  • the material of the diaphragm layer 8 is photoresist, such as DL-1000-C glue or SU8 glue.
  • photoresist such as DL-1000-C glue or SU8 glue.
  • the ductility of the diaphragm layer of the photoresist material of the present application is better, and can be used at specific frequencies.
  • the thicker photoresist material makes the diaphragm layer more reliable during repeated vibrations during operation and is not easily damaged.
  • the material of the insulating layer 6 and the supporting pattern 7 can also be photoresist, such as DL-1000-C glue or SU8 glue.
  • the thickness of the diaphragm layer when the material of the diaphragm layer is DL-1000-C glue, its thickness is greater than or equal to 1.5 ⁇ m and less than or equal to 3 ⁇ m; when the material of the diaphragm layer is SU8 glue, its thickness is greater than or equal to 5 ⁇ m and less than or equal to 3 ⁇ m. is equal to 40 ⁇ m.
  • the thickness of the insulating layer is DL-1000-C glue, and the thickness of the insulating layer is greater than or equal to 1.5 ⁇ m and less than or equal to 3 ⁇ m; when the material of the insulating layer is SU8 glue, the thickness of the insulating layer is greater than or equal to 5 ⁇ m and less than or equal to 3 ⁇ m is equal to 40 ⁇ m.
  • the ultrasonic transducer unit may further include electrode leads disposed on the substrate 10 in the same layer as the first electrodes 5 and electrically connected to the first electrodes 5, for leading the first electrodes 5 to the outside, In order to apply an electrical signal to the first electrode 5 when the ultrasonic transducer unit is working.
  • FIG. 3 shows a flowchart of a method for manufacturing an ultrasonic transducer unit according to an embodiment of the present disclosure.
  • the preparation method includes the following steps S11 to S18.
  • a first electrode is formed on the substrate, and the material of the first electrode is, for example, AlNd or Au.
  • step S12 an insulating layer is formed on the first electrode.
  • a non-metallic material such as silicon nitride and/or silicon oxide can be used to form the insulating layer, for example, an insulating material layer can be formed on the substrate on which the first electrode is formed; photoresist layer; using a mask to expose and develop the photoresist layer to form a photoresist pattern; etch the insulating material layer to form an insulating layer, and remove the photoresist pattern.
  • a photoresist material such as DL-1000-C glue or SU8 glue can also be used to form the insulating layer, for example, DL-1000-C glue or SU8 glue is directly coated on the substrate on which the first electrode is formed
  • the photoresist material layer of the glue is exposed and developed by using a mask plate to form a photoresist pattern, which is used as an insulating layer.
  • DL-1000-C adhesive for example, it can be denatured by post-baking at 200°C to 300°C for about 1 hour, so that the post-baking DL-1000-C adhesive is resistant to acid and acetone; for SU8 adhesive, for example, you can It is denatured by post-baking at 90°C to 100°C for about 2 to 6 minutes, so that the post-baking SU8 glue is resistant to acid and acetone. After the post-baking treatment, adverse effects on the formed insulating layer caused by the subsequent patterning process can be avoided.
  • a sacrificial material pattern is formed on the insulating layer in a region overlapping with the first electrode, wherein the sacrificial material pattern exposes a part of the insulating layer.
  • a metal material such as Mo or AlNd can be used to form the sacrificial material pattern 200 , and the thickness of the sacrificial material pattern will determine the thickness of the cavity, as shown in FIG. 4A .
  • a metal material layer such as Mo or AlNd is formed on the substrate formed with the insulating layer 12; secondly, a photoresist, such as AZ5214 or AZ4620 series photoresist, is coated on the metal material layer, Then, the photoresist is exposed and developed by using a mask; the metal material layer is etched to form a sacrificial material pattern 200, and the formed sacrificial material pattern partially overlaps with the first electrode 11, as shown in FIG. 4A and FIG. 4B .
  • a photoresist layer is formed on the sacrificial material pattern and the exposed portion of the insulating layer.
  • a photoresist layer may be formed that completely covers the sacrificial material pattern and covers exposed portions of the insulating layer, as shown in FIGS. 4C and 4D .
  • DL-1000-C glue or SU8 glue can be used to form the photoresist layer, and the thickness of the photoresist layer of DL-1000-C glue can be greater than or equal to 1.5 ⁇ m and less than or equal to 3 ⁇ m; and if Using SU8 glue, its thickness can be greater than or equal to 5 ⁇ m and less than or equal to 40 ⁇ m.
  • a photoresist layer is directly formed on the sacrificial material pattern 200 , the photoresist layer covers the side and front surface of the sacrificial material layer 200 , and completely covers the sacrificial material pattern 200 .
  • step S15 at least one through hole exposing a part of the sacrificial material pattern is formed in the photoresist layer to form a photoresist pattern, and then the photoresist pattern is post-baked to form a diaphragm layer .
  • a through hole 100 penetrating the photoresist layer 4 is formed in the photoresist layer 14 .
  • the photoresist layer 14 is exposed and developed using a mask to form at least one through hole as an etching hole, and a part of the sacrificial material layer 200 is exposed, so that the sacrificial material layer 200 is subsequently removed through the through hole to form the cavity 13 .
  • a photoresist layer with a specific pattern with filled holes will be formed after exposure and development. After post-baking treatment, the formed photoresist pattern is resistant to acid corrosion. , alcohol-resistant acetone and other cleaning and degumming solutions. As shown in FIG. 4E , in this step, a through hole 17 penetrating the diaphragm layer 14 and the insulating layer 12 may be formed at the same time, so as to expose the first electrode lead 16 .
  • step S16 the sacrificial material pattern is removed through the at least one through hole.
  • a sacrificial material pattern of a sacrificial material such as Mo or AlNd may be removed through the through hole 100 using a sulfuric acid and/or phosphoric acid etching solution, as shown in FIG. 4F .
  • step S17 a filling pattern is formed in the through hole.
  • the material for filling the pattern can be, for example, amorphous silicon, as shown in FIG. 1 .
  • step S18 a second electrode is formed on the photoresist pattern in a region overlapping with the first electrode.
  • a metal layer such as AlNd or Au can be coated first, and then a photoresist such as AZ5214 or AZ4620 can be coated on the metal layer, which is formed by exposure and development.
  • a photoresist such as AZ5214 or AZ4620
  • the pattern of the first electrode or the second electrode, and then acetone or the like can be used to remove the photoresist used here, and this removal will not cause any influence or damage to the diaphragm layer and the insulating layer.
  • the preparation method further includes forming a first electrode lead 16 on the substrate 10 while forming the first electrode 11 on the substrate 10 , and the first electrode lead 16 is electrically connected to the first electrode 11 for The first electrode 11 is externally connected to a signal line to apply an electrical signal to the first electrode 11 .
  • the method may further include forming a through hole 17 penetrating the insulating layer 12 and the diaphragm layer 14 to expose the first electrode
  • the lead 16 is convenient for external signal lines.
  • the diaphragm layer of the formed ultrasonic transducer unit will be more reliable during repeated vibrations of operation.
  • the ultrasonic transducer unit prepared by the above method includes an insulating layer, but the ultrasonic transducer unit of the present disclosure may not include the above-mentioned insulating layer.
  • the method for preparing the ultrasonic transducer unit may include directly forming a sacrificial material pattern on the first electrode, and then forming a photoresist pattern serving as a diaphragm layer on the sacrificial material pattern. The other steps are similar to the above steps, and are not repeated here.
  • FIG. 5 shows a flowchart of a method for manufacturing an ultrasonic transducer unit according to an embodiment of the present disclosure.
  • the preparation method includes the following steps S21 to S28.
  • a first electrode is formed on the substrate, and the first electrode material is, for example, AlNd or Au.
  • step S22 an insulating layer is formed on the first electrode.
  • a non-metallic material such as silicon nitride and/or silicon oxide can be used to form the insulating layer, for example, an insulating material layer can be formed on the substrate on which the first electrode is formed; The photoresist layer is exposed and developed by using a mask to form a photoresist pattern; the insulating material layer is etched to form an insulating layer, and then the photoresist is removed.
  • a photoresist material such as DL-1000-C glue or SU8 glue can also be used to form the insulating layer, for example, DL-1000-C glue or SU8 glue is directly coated on the substrate on which the first electrode is formed
  • the photoresist material layer of the glue is exposed and developed by using a mask plate to form a photoresist pattern, which is used as an insulating layer.
  • the patterned insulating layer formed after exposure and development is subjected to post-baking treatment, so that the formed photoresist pattern is resistant to acid corrosion and corrosion. Alcohol acetone and other cleaning and degumming solutions to avoid damage in subsequent processes.
  • an annular support pattern is formed on the insulating layer.
  • an annular support pattern 7 is formed, as shown in FIG. 6 .
  • a circular or polygonal annular support pattern can be formed, the support pattern 7 defines an area on the substrate where a closed cavity is to be formed, and the height of the support pattern will determine the height of the cavity to be formed (eg, 140 nm to 400nm), the area of the support pattern also determines the size of the cavity.
  • the selection of the material of the support pattern needs to be considered, and the consideration of the selection is that it must be compatible with the process used to etch away the sacrificial material inside to form the cavity.
  • DL- 1000-C or SU8 photoresist In this embodiment, for example, DL- 1000-C or SU8 photoresist.
  • This embodiment is different from the embodiment shown in FIGS. 4A to 4E in that the support pattern 7 for defining the size of the cavity 13 is separately formed, which improves the freedom of the manufacturing process.
  • a sacrificial material pattern is formed in the annular support pattern.
  • a metal material such as Mo or AlNd can be used to form the sacrificial material pattern 110 , and the thickness of the sacrificial material pattern 110 will determine the thickness of the cavity, as shown in FIG. 6 .
  • photoresist can also be selected as the material of the support pattern 7 . That is, the same material can be selected to form the insulating layer 6, the support pattern 7 and the diaphragm layer 8 to be formed later.
  • SU8 glue or DL-1000-C glue can be used to form the support pattern layer.
  • a ring-shaped support pattern 7 will be formed. After post-baking treatment, the formed support pattern 7 is resistant to acid corrosion and alcohol and acetone. Wait for cleaning and degumming solution to avoid its damage in subsequent processes.
  • a photoresist pattern exposing a portion of at least one through hole of the sacrificial material pattern is formed on the sacrificial material pattern and the support pattern, and then the photoresist pattern is post-baked to form vibration film layer.
  • DL-1000-C glue or SU8 glue can be used to form a photoresist layer, and the thickness of the photoresist layer of DL-1000-C glue can be greater than or equal to 1.5 ⁇ m and less than or equal to 1.5 ⁇ m. 3 ⁇ m; and if SU8 glue is used, the thickness of the photoresist layer can be greater than or equal to 5 ⁇ m and less than or equal to 40 ⁇ m.
  • the photoresist layer can be exposed and developed by using a mask to form the pattern of the diaphragm layer 8 as shown in FIG. 6 .
  • a photoresist pattern with filling holes 120 will be formed after exposure and development.
  • the formed diaphragm layer is resistant to acid corrosion and alcohol. Acetone and other cleaning and degumming solutions.
  • step S26 the sacrificial material pattern is removed through the at least one through hole.
  • a sacrificial material such as Mo or AlNd can be removed using, for example, sulfuric acid and/or phosphoric acid through the via 120 .
  • step S27 a filling pattern is formed in the through hole.
  • the filling material may be, for example, amorphous silicon, as shown in FIG. 2 .
  • step S28 a second electrode is formed on the lithographic pattern in an area overlapping with the first electrode.
  • a metal layer such as AlNd or Au is firstly coated, and then a photoresist such as AZ5214 or AZ4620 can be coated on the metal layer, and the first electrode is formed by exposure and development.
  • the pattern of the first electrode or the second electrode can then be removed using a solution such as acetone to remove the photoresist used here, and this removal will not cause any influence or damage to the diaphragm layer and insulating layer.
  • a photoresist material such as DL-1000-C glue or SU8 glue
  • DL-1000-C glue or SU8 glue is used as the material of the diaphragm layer of the ultrasonic transducer unit.
  • the ductility of the vibrating film layer of the photoresist material of the present application is better, and in order to obtain a certain frequency, a thicker photolithography can be used.
  • Glue material so the diaphragm layer will be more reliable and not easy to be damaged during repeated vibration during operation.
  • the diaphragm layer when forming the diaphragm layer, it is only necessary to coat the photoresist, and the photoresist is exposed and developed and then baked to form the required diaphragm layer pattern.
  • the pattern of the film layer is formed with through holes that pass through the pattern of the sacrificial material. Therefore, compared with the prior art, when forming a diaphragm layer such as silicon nitride and/or silicon oxide material, it is necessary to first form a silicon nitride and/or silicon oxide material layer, apply photoresist, expose and develop, and etch nitrogen.
  • the method for preparing an ultrasonic transducer unit in the present application is simpler and saves process procedures.
  • the insulating layer in the present disclosure can also be formed by using the photoresist for forming the diaphragm layer, which can further reduce the fabrication complexity and process procedures.

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Abstract

本申请公开一种超声换能单元及其制备方法，其中所述超声换能单元包括：基底；设置在基底上的第一电极；设置在第一电极上的绝缘层；设置在绝缘层上的振膜层,其中所述振膜层和所述绝缘层之间形成有封闭空腔；以及设置在振膜层上的第二电极；其中，所述振膜层的材料为光刻胶。本公开的超声换能单元采用光刻胶作为绝缘层和/或振膜层的材料，可以获得性能更加好的超声换能单元。

Description

超声换能单元及其制备方法 技术领域
本申请涉及半导体技术领域，尤其涉及一种超声换能单元及其制备方法。
背景技术
使用微机电系统(MEMS)工艺制备的电容式微机械超声换能器(CMUT)的声阻抗较低且可以调节，因此制造超声探头的时候不需要添加阻抗匹配层，不仅减少了探头制造的难度，也提升了带宽。CMUT器件制备工艺与CMOS集成电路的工艺相兼容，通常使用光刻蚀技术，采用光刻胶配合膜层图形化工艺来制备高集成度、大规模阵列的超声探头，可以满足临床医学领域中对信息获取日益增长的需求。
发明内容
本公开提供了一种超声换能单元及其制备方法。
所述一种超声换能单元,包括:基底；设置在基底上的第一电极；
设置在第一电极上的振膜层；以及设置在振膜层上的第二电极，所述第一电极在所述基底上的正投影和所述第二电极在所述基底上的正投影存在重叠区域，所述振膜层和所述第一电极在所述重叠区域处形成有封闭空腔；其中，所述振膜层的材料为光刻胶。
在一个实施例中，所述超声换能单元还包括贯穿所述振膜层并与空腔连通的通孔，以及填充所述通孔的填充图形。
在一个实施例中，所述超声换能单元还包括设置在第一电极上和所述空腔之间的绝缘层，其中，所述绝缘层的材料为光刻胶。
在一个实施例中，所述光刻胶包括DL-1000-C胶或者SU8胶。
在一个实施例中，所述振膜层的材料为DL-1000-C胶，以及所述振膜层的厚度大于等于1.5μm并且小于等于3μm；或者所述振膜层的材料为SU8胶，以及所述振膜层的厚度大于等于5μm并且小于等于40μm。
在一个实施例中，所述绝缘层的材料为DL-1000-C胶，以及所述绝缘层的厚度大于等于1.5μm并且小于等于3μm；或者所述绝缘层的材料为SU8胶，以及所述绝缘层的厚度大于等于5μm并且小于等于40μm。
在一个实施例中,所述填充图形的材料为非晶硅。
在一个实施例中，所述超声换能单元还包括与所述第一电极同层设置在基底上并且与所述第一电极电连接的第一电极引线。
在一个实施例中，所述空腔在所述基底上的正投影位于第一区域，所述基底还包括第二区域，所述第二区域围绕所述第一区域，所述振膜层的至少一部分和所述绝缘层的至少一部分在所述第二区域直接接触；或者所述超声换能单元还包括设置在所述振膜层和所述绝缘层之间的支撑图形，所述支撑图形位于所述第二区域。
在一个实施例中，所述支撑图形的材料为光刻胶。
本公开还提供了一种制备超声换能单元的方法，包括：在基底上形成第一电极；在第一电极上形成牺牲材料图形；在所述牺牲材料图形上形成光刻胶图形，其中，所述光刻胶图形在所述基底上的正投影与所述第一电极在所述基底上的正投影存在重叠区域；去除所述牺牲材料图形，以使得所述光刻胶图形和所述第一电极在所述重叠区域出形成封闭空腔；以及在所述光刻胶图形上形成第二电极，其中，所述第二电极在所述基底上的正投影与所述重叠区域至少部分重叠。
在一个实施例中，形成所述光刻胶图形的材料包括DL-1000-C胶或者SU8胶。
在一个实施例中，在第一电极上形成牺牲材料图形包括：在第一电极上形成第一光刻胶层；采用掩膜板对所述第一光刻胶层进行曝光显影以及后烘处理以形成绝缘层；以及至少在绝缘层上的所述重叠区域形成所述牺牲材料图形。
在一个实施例中，在所述牺牲材料图形上形成光刻胶图形包括：在所述牺牲材料图形上和所述绝缘层的暴露部分上形成第二光刻胶层；以及采用掩膜板对所述第二光刻胶层进行曝光显影以及后烘处理以形成具有至少一个贯穿所述第二光刻胶层的通孔的所述光刻胶图形。
在一个实施例中，去除所述牺牲材料图形包括：通过所述至少一个通孔去除所述牺牲材料图形；以及在所述至少一个通孔中形成填充图形。
在一个实施例中，所述空腔在所述基底上的正投影位于第一区域，所述基底还包括第二区域，所述第二区域围绕所述第一区域，以及在第一电极上形成牺牲材料图形包括：在第一电极上形成第一光刻胶层；采用掩膜板对所述第一光刻胶层进行曝光显影以及后烘处理以形成绝缘层；在所述绝缘层上形成第三 光刻胶层，对所述第三光刻胶层进行曝光显影以及后烘处理以在所述第二区域形成支撑图形；以及在所述支撑图形中形成所述牺牲材料图形。
在一个实施例中，在基底上形成第一电极的步骤的同时，所述方法还包括在基底上形成与所述第一电极同层且彼此电连接的第一电极引线。
在一个实施例中，所述牺牲材料图形为Mo或AlNd金属图形；以及去除所述牺牲材料图形包括利用磷酸和/或硫酸去除Mo或AlNd金属图形。
在一个实施例中，所述绝缘层的材料包括DL-1000-C胶或者SU8胶。
在一个实施例中，所述支撑图形的材料包括DL-1000-C胶或者SU8胶。
附图说明
下面将参照附图对本公开的实施例进行详细介绍。
图1A示出了根据本公开实施例的超声换能单元的俯视图；
图1B示出了根据本公开实施例的超声换能单元的截面示意图；
图1C示出了根据本公开实施例的超声换能单元的俯视图；
图1D示出了根据本公开实施例的超声换能单元的截面示意图；
图2示出了根据本公开实施例的超声换能单元的结构示意图；
图3示出了根据本公开实施例的超声换能单元的制备方法的流程图；
图4A至图4F示出了根据本公开实施例的超声换能单元的制备过程的结构示意图；
图5示出了根据本公开实施例的超声换能单元的制备方法的流程图；以及
图6示出了根据本公开实施例的超声换能单元的制备过程的结构示意图。
具体实施方式
为使本领域技术人员更好地理解本公开的技术方案，下面结合附图和具体实施方式对本公开进行详细描述。
本申请的超声换能单元可以为电容式微机械超声换能器(Capacitive Micro-machined Ultrasonic Transducer,CMUT)，其通常包括基底(例如玻璃)、在基底上依次形成的底电极、绝缘层、振膜层和顶电极，其中在绝缘层和振膜层之间形成有密闭空腔。超声换能单元还包括形成所述空腔时在振膜层中形成 的填充孔以及对填充孔进行填充后形成的填充层。
在超声换能单元制备过程中，相关技术中绝缘层和振膜层由氮化硅或氧化硅来制备，这些膜层的制备都须经历膜层沉积、涂胶光刻胶、膜层刻蚀、去除光刻胶的步骤。
例如，在制备绝缘层时，可以使用低压力化学气相沉积(LPCVD)工艺沉积单层氮化硅一种材料或者使用干式氧化工艺及低压力化学气相沉积(LPCVD)工艺沉积二氧化硅与氮化硅两种材料的复合层构成。在形成的绝缘层上可以形成多晶硅薄膜层作为牺牲材料层，并且对其进行图形化，经过图形化的多晶硅层的尺寸决定了超声换能单元的空腔的尺寸，例如决定了空腔的厚度。在图形化的多晶硅层和暴露出的绝缘层上例如使用低压力化学气相沉积(LPCVD)工艺沉积低残余应力的氮化硅的振动薄膜，振动薄膜厚度例如可以选择处于0.3至2μm的范围内，这取决于对超声换能单元输出声压的要求。
接下来，为了去除图形化的多晶硅层而形成空腔，首先在氮化硅的振动薄膜上涂覆光刻胶，然后利用掩膜板对氮化硅的振动薄膜进行刻蚀形成腐蚀孔，例如可以形成直径约2μm的腐蚀孔，利用干法刻蚀技术将腐蚀孔区域内的氮化硅蚀刻掉，使得腐蚀孔直通到多晶硅的牺牲材料层，这个步骤后需要去除光刻胶。
如上所述，在相关技术中，在振膜层中形成用于形成空腔的腐蚀孔时，需要在氮化硅层或氧化硅层上涂覆光刻胶，经过光刻胶涂覆、利用掩膜板的干法刻蚀和去除光刻胶的步骤，这个工序复杂，占用生产设备较多，耗时较长。
为此，本申请提出了一种超声换能单元，其振膜层由光刻胶制备，即，在形成振膜层后形成空腔的过程中，仅仅需要涂覆光刻胶，利用掩膜板对光刻胶进行曝光显影后，即可在光刻胶层中形成腐蚀孔，这极大地简化了制备工艺，提高了生产效率。相对于相关技术中的氮化硅膜层和氧化硅膜层而言，不仅仅能够降低形成光刻胶层材料的延展性更好，因此其作为超声换能单元的振膜层而言，在超声换能单元工作过程中，振膜层不易损坏，使得形成的超声换能单元更加可靠。
图1A和图1B分别示出了根据本公开的超声换能单元的俯视图和截面示意图，其中图1B是沿着图1A所示的AA’截取所获得的截面图。该超声换能单元包括：基底10；设置在基底10上的第一电极(底电极)11；设置在第一电极11上的绝缘层12；设置在绝缘层12上的振膜层14；设置在振膜层14上的第二 电极(顶电极)15，第一电极11在基底10上的正投影和第二电极15在基10底上的正投影存在重叠区域，振膜层14和第一电极11在所述重叠区域处形成有封闭空腔13。该超声换能单元还包括贯穿振膜层14从而与空腔13连通的通孔和填充所述通孔的填充图形18。该通孔用作形成空腔13时的刻蚀液的通道。
在本申请中，振膜层14的材料为光刻胶，例如DL-1000-C胶或者SU8胶。DL-1000-C胶主要含聚酰亚胺，其属于正性光刻胶，不溶于有机溶剂，对稀酸稳定，其所包含的交联聚合物能通过光照而被截断从而变得可溶于显影溶剂。SU8就属于负性光刻胶，其在曝光后形成了交联聚合物，不容易被溶剂溶解。
与相关技术中通常采用氮化硅和/或氧化硅形成振膜层的超声换能单元相比，在本申请中，采用光刻胶作为振膜层的材料。由于光刻胶作为膜层的延展性较好，因此所形成的超声换能单元在操作过程中进行反复振动时振膜层不易损坏。振膜层的材料和厚度对超声换能单元的工作频率起决定作用。在频率一定时，相对于氮化硅和/或氧化硅而言，光刻胶材料的振膜层的厚度较厚，这将会使得振膜层在操作的反复振动时会更加可靠。
在振膜层的材料为DL-1000-C胶时，其厚度可以大于等于1.5μm且小于等于3μm；在振膜层的材料为SU8胶时，其厚度可以大于等于5μm且小于等于40μm。相关技术中采用氮化硅材料形成振膜层时，其厚度通常在0.3μm至2μm之间。因此，在一定频率下，采用光刻胶材料制备的振膜层厚度相对较厚，这进一步增加了超声换能单元的产品可靠性，以避免振膜层多次往复运动而易于损坏的发生。
另外，SU8胶是透明的材料，利用SU8胶作为超声换能单元的振膜层材料，可以形成完全透明的超声换能单元，从而形成透过率更高的超声换能单元。
图1A和图1B示出的实施例的超声换能单元包括了绝缘层12，但是本公开不限于此。本公开的超声换能单元可以不包括绝缘层，而是在振膜层和第一电极之间形成密闭空腔。
在本申请中，振膜层的材料为光刻胶。在形成空腔时，为了避免对光刻胶材料的振膜层产生不利影响，可以采用诸如Mo(钼)或AlNd(铝钕合金)金属材料作为牺牲材料。此时，为了避免对第一电极11造成不利影响，在第一电极上形成的非金属材料的绝缘层12可以避免之后形成牺牲材料和去除牺牲材料时所用的工艺对第一电极的不利影响。在一个实施例中，绝缘层12可以与振膜层14一样，采用光刻胶材料(例如DL-1000-C胶或者SU8胶)制备。在绝缘层12 的材料为DL-1000-C胶时，其厚度可以大于等于1.5μm且小于等于3μm；在绝缘层12的材料为SU8胶时，其厚度可以大于等于5μm且小于等于40μm。
如图1B所示，该超声换能单元还包括贯穿光刻胶材料的振膜层14以直通空腔13的通孔，在该通孔中形成有填充图形18。在一个实施例中，可以采用非晶硅来填充通孔，该填充图形可以通过所述通孔延伸至空腔13的底部，如图1B所示。但是本发明不限于此，例如还可以采用氮化硅等作为填充材料。
在进行超声波检测时，超声换能单元先处于发射状态，再切换至接收状态。当处于发射状态时，在第二电极15和第一电极11之间加载正向直流偏置电压VDC，振膜层14将在静电作用下向下(靠近第一电极11的一侧)弯曲变形。在此基础上，在第二电极15和第一电极11之间施加一定频率f(f的大小根据实际需要来设定)的交流电压VAC，激励振膜层14大幅度往复运动(在靠近第一电极11的方向和远离第一电极11的方向上进行往复运动)，实现电能向机械能的转换，振膜层14向介质环境辐射能量，产生超声波；其中，部分超声波可在待测对象的表面发生反射，并返回至超声换能单元，以供超声换能单元进行接收、检测。当超声换能单元处于接收状态时，在第二电极15和第一电极11之间只加载直流偏置电压，振膜层14在静电力和薄膜回复力的作用下达到静态平衡，当有声波作用在振膜层14上时，激励振膜层14振动，第二电极15和第一电极11之间的空腔间距发生变化，引起板间电容量的变化，从而产生可检测的电信号，基于该电信号可实现对接收到的超声波的检测。
基底10可包括空腔13在其上的正投影所处的第一区域和围绕第一区域的第二区域，如图1A和1B所示，振膜层14的至少一部分和绝缘层12的至少一部分在所述第二区域直接接触。在一个实施例中，所述空腔13可以仅由光刻胶材料围成。换句话说，在绝缘层13由光刻胶材料制备时，空腔13的顶面、底面和侧面的材料均为诸如DL-1000-C胶和SU8胶的光刻胶。
另外，在一个实施例中，如图1A和图1B所示，超声换能单元还可包括与第一电极11同层设置在基底10上的第一电极引线16，其与所述第一电极11电连接，用于将第一电极11引出至外部，以便在超声换能单元工作时对第一电极11施加电信号。第一电极引线16上可以设有贯穿振膜层14和所述绝缘层12的通孔，以用于外接信号线。
图1C和图1D分别示出了根据本公开实施例的超声换能单元的俯视图和截面示意图，其中图1D是沿着图1C所示的AA’线截取所获得的截面图。与图1A 和图1B所示的实施例不同的是，图1C和图1D示出的超声换能单元的空腔13包括中心部25和一个或多个从中心部25向外延伸的作为其分支的连接部26，其中贯穿振膜层14从而与空腔13连通的通孔和填充所述通孔的填充图形18设置在连接部26上，即设置在中心部25以外的区域。这种结构可以减轻填充图形18对振膜层14的振动的影响，使其具有较佳的振动性能。
图1A和图1B所示出的实施例的空腔在基底上的正投影为六边形，图1C和图1D所示出的实施例的空腔在基底上的正投影为六边形，但是本申请不限于此，例如空腔在基底1上的正投影可以为正方形或圆形。
图2示出了根据本公开实施例的超声换能单元的截面示意图。如图2所示，在该实施例中，超声换能单元包括设置在基底10上的第一电极5、绝缘层6、振膜层8和第二电极9。与图1A至图1D所示的实施例不同，在该实施例中，通过支撑图形7，例如环状的中空的支撑图形7，来围成振动空腔，空腔在基底10上的正投影为第一区域，基底10还包括第二区域，而第二区域围绕第一区域，如图所示，支撑图形7位于第二区域。振膜层8形成在支撑图形7上来封闭振动空腔，从而形成封闭空腔11。该超声换能单元也包括贯穿振膜层8形成的直通空腔的通孔以及在通孔中形成的填充图形12。
在该实施例中，振膜层8的材料为光刻胶，例如DL-1000-C胶或者SU8胶。相对于常规的采用氮化硅和/或氧化硅形成的振膜层的超声换能单元相比，本申请的光刻胶材料的振膜层的延展性更好，并且在特定频率下可以采用较厚的光刻胶材料，因此使得振膜层在操作时的反复振动时会更加可靠，不容易损坏。另外，在该实施例中，绝缘层6和支撑图形7的材料也可以为光刻胶，例如DL-1000-C胶或者SU8胶。
在该实施例中，在振膜层的材料为DL-1000-C胶时，其厚度大于等于1.5μm并且小于等于3μm；在振膜层的材料为SU8胶时，其厚度大于等于5μm并且小于等于40μm。在绝缘层的材料为DL-1000-C胶，以及所述绝缘层的厚度大于等于1.5μm并且小于等于3μm；在绝缘层的材料为SU8胶时，所述绝缘层的厚度大于等于5μm并且小于等于40μm。
图2所示的实施例的其他构造与图1所示的实施例相同，在此不进行赘述。在一个实施例中，该超声换能单元还可包括与第一电极5同层设置在基底10上的并且与第一电极5电连接的电极引线，用于将第一电极5引出至外部， 以便在超声换能单元工作时对第一电极5施加电信号。
图3示出了根据本公开实施例的超声换能单元的制备方法的流程图。该制备方法包括如下步骤S11至S18。
在步骤S11中，在基底上形成第一电极，第一电极材料例如为AlNd或者Au。
在步骤S12中,在第一电极上形成绝缘层。
在一个实施例中，可以采用如氮化硅和/或氧化硅等的非金属材料形成绝缘层，例如，可以在形成有第一电极的基底上形成绝缘材料层；在绝缘材料层上形成光刻胶层；利用掩膜板对光刻胶层进行曝光显影，形成光刻胶图形；对绝缘材料层进行刻蚀形成绝缘层，并且去除光刻胶图形。
在一个实施例中，也可以采用例如DL-1000-C胶或者SU8胶的光刻胶材料形成绝缘层，例如，在形成有第一电极的基底上直接涂覆DL-1000-C胶或者SU8胶的光刻胶材料层；利用掩膜板对光刻胶材料层进行曝光显影，形成光刻胶图形，作为绝缘层。在采用例如DL-1000-C胶或者SU8胶的光刻胶材料形成绝缘层时，对曝光显影后形成的光刻胶图形进行后烘处理，使得所形成的绝缘层耐酸腐蚀，耐酒精丙酮等清洗和去胶液，从而避免在后续的工艺中被破坏。对于DL-1000-C胶，例如可以采用200℃至300℃下后烘大约1小时来对其进行变性，使得后烘处理后的DL-1000-C胶耐酸耐丙酮；对于SU8胶，例如可以采用90℃至100℃下后烘大约2至6分钟来对其进行变性，使得后烘处理后的SU8胶耐酸耐丙酮。经过后烘处理，可以避免后续形成图形工艺对所形成的绝缘层造成不利影响。
在步骤S13中,在绝缘层上与第一电极重叠的区域形成牺牲材料图形，其中所述牺牲材料图形暴露出所述绝缘层的一部分。在一个实施例中，可以采用Mo或AlNd等金属材料形成牺牲材料图形200，该牺牲材料图形的厚度将决定空腔的厚度，如图4A所示。
在一个实施例中，首先，在形成有包括绝缘层12的基底上形成Mo或AlNd等金属材料层；其次，在金属材料层上涂覆光刻胶，例如AZ5214或者AZ4620系列的光刻胶，然后利用掩膜板对光刻胶进行曝光显影；对金属材料层进行刻蚀形成牺牲材料图形200，所形成的牺牲材料图形与第一电极11部分重叠，如图4A和图4B所示。
在步骤S14中,在所述牺牲材料图形和所述绝缘层的暴露部分上形成光刻 胶层。例如，所形成的光刻胶层可以完全覆盖牺牲材料图形，并且覆盖绝缘层的暴露部分，如图4C和图4D所示。在一个实施例中，可以采用例如DL-1000-C胶或者SU8胶形成光刻胶层，DL-1000-C胶的光刻胶层厚度可以大于等于1.5μm且小于等于3μm范围内；而如果采用SU8胶，其厚度可以大于等于5μm且小于等于40μm范围内。在该实施例中，在牺牲材料图形200上直接形成光刻胶层，该光刻胶层覆盖了牺牲材料层200的侧面和正面，将牺牲材料图形200完全覆盖。
在步骤S15中，在所述光刻胶层中形成暴露所述牺牲材料图形的一部分的至少一个通孔以形成光刻胶图形，然后对光刻胶图形进行后烘处理，从而形成振膜层。例如如图4E所示，在光刻胶层14中形成穿透光刻胶层4的通孔100。具体地，利用掩膜板对光刻胶层14进行曝光显影来形成至少一个通孔作为腐蚀孔，暴露牺牲材料层200的一部分，以便后续借由该通孔去除牺牲材料层200形成空腔13。在使用SU8胶或DL-1000-C胶来形成振膜层时，曝光显影后会形成特定带填充孔的图形的光刻胶层，经后烘处理后，所形成的光刻胶图形耐酸腐蚀，耐酒精丙酮等清洗和去胶液。如图4E所示，该步骤还可以同时形成了贯穿振膜层14和绝缘层12的通孔17，以暴露第一电极引线16。
在步骤S16中，通过所述至少一个通孔去除所述牺牲材料图形。在一个实施例中，例如可以通过通孔100采用硫酸和/或磷酸腐蚀液来去除例如Mo或AlNd的牺牲材料的牺牲材料图形，如图4F所示。
在步骤S17中，在所述通孔中形成填充图形。填充图形的材料例如可以为非晶硅，如图1所示。
在步骤S18中，在所述光刻胶图形上与所述第一电极重叠的区域形成第二电极。
在本公开中，在制备第一电极或第二电极时，可以先涂覆一层金属层，例如AlNd或Au，然后可以在金属层上涂覆例如AZ5214或者AZ4620光刻胶，通过曝光显影形成第一电极或第二电极的图形，然后可以采用丙酮等来去除此处所使用的光刻胶，而这种去除不会对振膜层和绝缘层造成任何影响和损害。
如图4A所示，所述制备方法还包括在基底10上形成第一电极11的同时在基底10上形成第一电极引线16，该第一电极引线16电连接至第一电极11，用于将第一电极11外接至信号线，以对第一电极11施加电信号。另外，在对用于形成振膜层的光刻胶层曝光显影形成通孔的同时，所述方法还可以包括形 成穿透绝缘层12和振膜层14的通孔17，以暴露第一电极引线16，便于外接信号线。
在一个实施例中，在绝缘层与振膜层一样由光刻胶制备时，所形成的超声换能单元的空腔的侧面和顶面均为光刻胶材料，由于光刻胶材料的延展性较好，因此所形成的超声换能单元的振膜层在操作的反复振动时会更加可靠。
如上方法制备的超声换能单元包括绝缘层，但是本公开的超声换能单元可以不包括上述的绝缘层。在此情况下，制备超声换能单元的方法可以包括在第一电极上直接形成牺牲材料图形，然后在牺牲材料图形上形成用作振膜层的光刻胶图形。其他步骤类似于如上所述的各步骤，在此不再赘述。
图5示出了根据本公开实施例的超声换能单元的制备方法的流程图。该制备方法包括如下步骤S21至S28。
在步骤S21中，在基底上形成第一电极，第一电极材料例如为AlNd或者Au。
在步骤S22中，在第一电极上形成绝缘层。
在一个实施例中，可以采用如氮化硅和/或氧化硅等的非金属材料形成绝缘层，例如，可以在形成有第一电极的基底上形成绝缘材料层；在绝缘材料层上形成光刻胶层；利用掩膜板对光刻胶层进行曝光显影，形成光刻胶图形；对绝缘材料层进行刻蚀形成绝缘层，然后去除光刻胶。
在一个实施例中，也可以采用例如DL-1000-C胶或者SU8胶的光刻胶材料形成绝缘层，例如，在形成有第一电极的基底上直接涂覆DL-1000-C胶或者SU8胶的光刻胶材料层；利用掩膜板对光刻胶层进行曝光显影，形成光刻胶图形，作为绝缘层。在采用例如DL-1000-C胶或者SU8胶的光刻胶材料形成绝缘层时，对曝光显影后形成的图案化的绝缘层进行后烘处理，使得所形成的光刻胶图形耐酸腐蚀，耐酒精丙酮等清洗和去胶液，从而避免在后续的工艺中被破坏。
在步骤S23中，在绝缘层上形成环状的支撑图形。在此步骤中，形成环状的支撑图形7，如图6所示。例如，可以形成圆环或者多边形环状的支撑图形，该支撑图形7在基板上限定了要形成封闭空腔的区域，该支撑图形的高度将决定要形成的空腔的高度(例如，140nm至400nm)，该支撑图形的面积也决定了空腔的大小。该支撑图形的材料选择是需要考虑的，其选择的考虑依据是必须与用于腐蚀掉其内部的牺牲材料形成空腔时所用到的工艺兼容，在该实施例 中，例如也可以选择DL-1000-C胶或者SU8胶的光刻胶。该实施例与图4A至图4E所示的实施例不同，单独形成了用于限定空腔13尺寸的支撑图形7，提高了制备工艺的自由度。
在步骤S24中，在所述环状的支撑图形中形成牺牲材料图形。在一个实施例中，可以采用Mo或AlNd等金属材料形成牺牲材料图形110，该牺牲材料图形110的厚度将决定空腔的厚度，如图6所示。在Mo或AlNd金属作为牺牲材料时，也可选择光刻胶作为支撑图形7的材料。即，可以选择相同的材料形成绝缘层6、支撑图形7以及随后要形成的振膜层8。例如，可以使用SU8胶或DL-1000-C胶来形成支撑图形层，曝光显影后会形成环状的支撑图形7，然后经后烘处理后，所形成的支撑图形7耐酸腐蚀，耐酒精丙酮等清洗和去胶液，以避免后续工艺其被破坏。
在步骤S25中，在所述牺牲材料图形和所述支撑图形上形成暴露部分所述牺牲材料图形的至少一个通孔的光刻胶图形，然后对光刻胶图形进行后烘处理，以形成振膜层。在一个实施例中，在此步骤中，可以采用例如DL-1000-C胶或者SU8胶形成光刻胶层，DL-1000-C胶的光刻胶层的厚度可以大于等于1.5μm且小于等于3μm；而如果采用SU8胶，光刻胶层的厚度可以大于等于5μm且小于等于40μm。可以利用掩膜板对光刻胶层进行曝光显影，形成如图6所示的振膜层8的图形。在使用SU8胶或DL-1000-C胶来形成振膜层时，曝光显影后会形成带填充孔120的光刻胶图形，经后烘处理后，所形成的振膜层耐酸腐蚀，耐酒精丙酮等清洗和去胶液。
在步骤S26中，通过所述至少一个通孔去除所述牺牲材料图形。在一个实施例中，例如可以通过通孔120采用硫酸和/或磷酸来去除例如Mo或AlNd等金属的牺牲材料。
在步骤S27中，在所述通孔中形成填充图形。填充材料例如可以为非晶硅，如图2所示。
在步骤S28中，在所述光刻图形上与所述第一电极重叠的区域形成第二电极。
在本公开中，在制备第一电极或第二电极时，先涂覆一层金属层，例如AlNd或Au，然后可以在金属层上涂覆例如AZ5214或者AZ4620光刻胶，通过曝光显影形成第一电极或第二电极的图形，然后可以采用丙酮等溶液去除此处所使用的光刻胶，而这种去除不会对振膜层和绝缘层造成任何影响和损害。
如上所述，在本申请中，采用光刻胶材料作为超声换能单元的振膜层的材料，例如DL-1000-C胶或者SU8胶。相对于相关技术的采用氮化硅和/或氧化硅形成的振膜层，本申请的光刻胶材料的振膜层的延展性更好，并且为了获得一定频率，可以采用较厚的光刻胶材料，因此振膜层在操作时的反复振动时会更加可靠，不容易损坏。
另外，在制备超声换能单元的方法中，形成振膜层时，仅仅需要涂覆光刻胶，并且对光刻胶进行曝光显影后烘即可形成所需要的振膜层图形，例如，振膜层图形形成有直通牺牲材料图形的通孔。因此，相对于现有技术中形成例如氮化硅和/或氧化硅材料的振膜层时需要先形成氮化硅和/或氧化硅材料层、涂覆光刻胶、曝光显影、刻蚀氮化硅和/或氧化硅形成振膜层图形相比，本申请中的制备超声换能单元的方法更加简单，节省了工艺程序。另外，本公开中的绝缘层也可以采用形成振膜层的光刻胶来形成，这样可以进一步降低制备复杂性和工艺程序。
可以理解的是，以上实施方式仅仅是为了说明本公开的原理而采用的示例性实施方式，然而本公开并不局限于此。对于本领域内的普通技术人员而言，在不脱离本公开的精神和实质的情况下，可以做出各种变型和改进，这些变型和改进也视为本公开的保护范围。

Claims (20)

  1. 一种超声换能单元,包括:
    基底；
    设置在基底上的第一电极；
    设置在第一电极上的振膜层；以及
    设置在振膜层上的第二电极，所述第一电极在所述基底上的正投影和所述第二电极在所述基底上的正投影存在重叠区域，所述振膜层和所述第一电极在所述重叠区域处形成有封闭空腔；其中,
    所述振膜层的材料为光刻胶。
  2. 根据权利要求1所述的超声换能单元，还包括贯穿所述振膜层并与空腔连通的通孔，以及填充所述通孔的填充图形。
  3. 根据权利要求1或2所述的超声换能单元，还包括设置在第一电极上和所述空腔之间的绝缘层，其中，所述绝缘层的材料为光刻胶。
  4. 根据权利要求1至3中任一项所述的超声换能单元，其中，
    所述光刻胶包括DL-1000-C胶或者SU8胶。
  5. 根据权利要求4所述的超声换能单元，其中，所述振膜层的材料为DL-1000-C胶，以及所述振膜层的厚度大于等于1.5μm并且小于等于3μm；或者
    所述振膜层的材料为SU8胶，以及所述振膜层的厚度大于等于5μm并且小于等于40μm。
  6. 根据权利要求4或5所述的超声换能单元，其中，所述绝缘层的材料为DL-1000-C胶，以及所述绝缘层的厚度大于等于1.5μm并且小于等于3μm；或者
    所述绝缘层的材料为SU8胶，以及所述绝缘层的厚度大于等于5μm并且小于等于40μm。
  7. 根据权利要求2所述的超声换能单元,其中,所述填充图形的材料为非晶硅。
  8. 根据权利要求1至7中任一项所述的超声换能单元，还包括与所述第一电极同层设置在基底上并且与所述第一电极电连接的第一电极引线。
  9. 根据权利要求3至8中任一项所述的超声换能单元，其中，
    所述空腔在所述基底上的正投影位于第一区域，所述基底还包括第二区域，所述第二区域围绕所述第一区域，
    所述振膜层的至少一部分和所述绝缘层的至少一部分在所述第二区域直接接触；或者所述超声换能单元还包括设置在所述振膜层和所述绝缘层之间的支撑图形，所述支撑图形位于所述第二区域。
  10. 根据权利要求9所述的超声换能单元，其中，所述支撑图形的材料为光刻胶。
  11. 一种制备超声换能单元的方法，包括：
    在基底上形成第一电极；
    在第一电极上形成牺牲材料图形；
    在所述牺牲材料图形上形成光刻胶图形，其中，所述光刻胶图形在所述基底上的正投影与所述第一电极在所述基底上的正投影存在重叠区域；
    去除所述牺牲材料图形，以使得所述光刻胶图形和所述第一电极在所述重叠区域出形成有封闭空腔；以及
    在所述光刻胶图形上形成第二电极，其中，所述第二电极在所述基底上的正投影与所述重叠区域至少部分重叠。
  12. 根据权利要求11所述的方法，其中，形成所述光刻胶图形的材料包括DL-1000-C胶或者SU8胶。
  13. 根据权利要求11或12所述的方法，其中，在第一电极上形成牺牲材 料图形包括：
    在第一电极上形成第一光刻胶层；
    采用掩膜板对所述第一光刻胶层进行曝光显影以及后烘处理以形成绝缘层；以及
    至少在绝缘层上的所述重叠区域形成所述牺牲材料图形。
  14. 根据权利要求13所述的方法，其中，在所述牺牲材料图形上形成光刻胶图形包括：
    在所述牺牲材料图形上和所述绝缘层的暴露部分上形成第二光刻胶层；以及
    采用掩膜板对所述第二光刻胶层进行曝光显影以及后烘处理以形成具有至少一个贯穿所述第二光刻胶层的通孔的所述光刻胶图形。
  15. 根据权利要求14所述的方法，其中，去除所述牺牲材料图形包括：
    通过所述至少一个通孔去除所述牺牲材料图形；以及
    在所述至少一个通孔中形成填充图形。
  16. 根据权利要求11或12所述的方法，其中，所述空腔在所述基底上的正投影位于第一区域，所述基底还包括第二区域，所述第二区域围绕所述第一区域，以及
    在第一电极上形成牺牲材料图形包括：
    在第一电极上形成第一光刻胶层；
    采用掩膜板对所述第一光刻胶层进行曝光显影以及后烘处理以形成绝缘层；
    在所述绝缘层上形成第三光刻胶层，对所述第三光刻胶层进行曝光显影以及后烘处理以在所述第二区域形成支撑图形；以及
    在所述支撑图形中形成所述牺牲材料图形。
  17. 根据权利要求11至16中任一项所述的方法，其中，在基底上形成第一电极的步骤的同时，所述方法还包括在基底上形成与所述第一电极同层且彼此电连接的第一电极引线。
  18. 根据权利要求11至17中任一项所述的方法，其中，所述牺牲材料图形为Mo或AlNd金属图形；以及
    去除所述牺牲材料图形包括利用磷酸和/或硫酸去除Mo或AlNd金属图形。
  19. 根据权利要求13至16中任一项所述的方法，其中，所述绝缘层的材料包括DL-1000-C胶或者SU8胶。
  20. 根据权利要求16所述的方法，其中，所述支撑图形的材料包括DL-1000-C胶或者SU8胶。
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