CN112974197A - Capacitive ultrasonic transducer and preparation method thereof - Google Patents
Capacitive ultrasonic transducer and preparation method thereof Download PDFInfo
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- CN112974197A CN112974197A CN201911304640.0A CN201911304640A CN112974197A CN 112974197 A CN112974197 A CN 112974197A CN 201911304640 A CN201911304640 A CN 201911304640A CN 112974197 A CN112974197 A CN 112974197A
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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
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Abstract
The invention relates to the technical field of ultrasonic transducers and discloses a preparation method of a capacitive ultrasonic transducer and the capacitive ultrasonic transducer. The preparation method of the capacitive ultrasonic transducer comprises the following steps: sequentially forming a first sacrificial layer and a second sacrificial layer on a substrate, wherein the compactness of the first sacrificial layer is smaller than that of the second sacrificial layer; forming a vibration film layer on the second sacrificial layer, and forming a through hole in the vibration film layer; and etching the first sacrificial layer and the second sacrificial layer through the via hole to form a cavity structure. The preparation method can greatly reduce the time for forming the cavity structure of the capacitive ultrasonic transducer on the premise of ensuring the preparation yield of the capacitive ultrasonic transducer, thereby improving the preparation efficiency of the capacitive ultrasonic transducer.
Description
Technical Field
The invention relates to the technical field of ultrasonic transducers, in particular to a capacitive ultrasonic transducer and a preparation method thereof.
Background
Ultrasonic imaging refers to detecting a target object by using ultrasonic beams, detecting and storing received echo or transmitted wave signals, and then obtaining information such as a target distance, a contour and an internal structure according to different imaging modes, and finally displaying the information in an image mode. The ultrasonic transducer is one of the key components of ultrasonic imaging, and as a transducer device, the main functions of the ultrasonic transducer are as follows: in the transmitting stage, the transducer converts the input electric energy into mechanical energy under the action of an excitation signal and transmits the mechanical energy out, so that the ultrasonic wave is transmitted; in the receiving stage, the transducer converts the sound waves into electric signals to realize the receiving of the ultrasonic waves.
The Capacitive Micromachined Ultrasonic Transducer (CMUT) is the most rapidly developed ultrasonic transducer in recent years, and has the advantages of simple structure, small size, flexible design, high sensitivity, and the like.
Disclosure of Invention
The invention discloses a preparation method of a capacitive ultrasonic transducer and the capacitive ultrasonic transducer, and particularly provides the following technical scheme:
a method of making a capacitive ultrasound transducer, comprising:
sequentially forming a first sacrificial layer and a second sacrificial layer on a substrate, wherein the compactness of the first sacrificial layer is smaller than that of the second sacrificial layer;
forming a vibration film layer on the second sacrificial layer, and forming a through hole in the vibration film layer;
and etching the first sacrificial layer and the second sacrificial layer through the via hole to form a cavity structure.
In the preparation method of the capacitive ultrasonic transducer, two sacrificial layers, namely a first sacrificial layer and a second sacrificial layer, are sequentially formed on a substrate, and as the first sacrificial layer (the bottom sacrificial layer) is less compact, namely loose, corrosive liquid flows and diffuses fast in the first sacrificial layer and has large contact area, the layer (the first sacrificial layer) can be corroded rapidly; and with the increase of the corrosion speed of the first sacrificial layer by the corrosive liquid, the contact area between the corrosive liquid and the second sacrificial layer (the upper sacrificial layer) is gradually increased, so that the second sacrificial layer can be corroded in a large area, and the corrosion efficiency of the second sacrificial layer is further improved. In addition, the second sacrificial layer (the upper sacrificial layer) is high in compactness, namely, is compact, so that the vibration film layer formed on the film layer is smooth and compact, and the yield of the capacitive ultrasonic transducer can be further ensured. In summary, the preparation method can greatly reduce the time for forming the cavity structure of the capacitive ultrasonic transducer on the premise of ensuring the preparation yield of the capacitive ultrasonic transducer, thereby improving the preparation efficiency of the capacitive ultrasonic transducer.
Optionally, the first sacrificial layer and the second sacrificial layer are made of the same material.
Optionally, the forming a first sacrificial layer and a second sacrificial layer on the substrate in sequence specifically includes:
forming a first layer of SiO2 by a first plasma chemical vapor deposition process;
forming a second layer of SiO2 on the first layer of SiO2 by a second plasma chemical vapor deposition process having a lower reaction pressure, and/or a higher radio frequency power, and/or SiH than the first plasma chemical vapor deposition process4The gas flow is high.
Optionally, the forming a first sacrificial layer and a second sacrificial layer on the substrate in sequence specifically includes:
forming a first layer of ZnO by adopting a metal organic compound chemical vapor deposition process;
and forming a second ZnO layer on the first ZnO layer by adopting a magnetron sputtering process.
Optionally, the thickness of the first sacrificial layer is greater than the thickness of the second sacrificial layer.
Optionally, a thickness ratio of the first sacrificial layer to the second sacrificial layer is 1.5 to 4.
Optionally, projections of the first sacrificial layer and the second sacrificial layer on the substrate are overlapped.
Optionally, the substrate base plate includes a glass substrate.
Optionally, after the etching the first sacrificial layer and the second sacrificial layer through the via hole to form a cavity structure, the method further includes:
filling the via hole of the vibrating membrane layer;
forming a top electrode on the vibration film layer; the projection of the top electrode on the substrate base plate is positioned in the projection of the cavity structure on the substrate base plate, and the projection of the top electrode and the projection of the through hole on the substrate base plate are not overlapped.
Optionally, before the sequentially forming the first sacrificial layer and the second sacrificial layer on the substrate, the method further includes:
forming a bottom electrode on a substrate base plate;
an etch stop layer is formed on the bottom electrode.
Drawings
Fig. 1 is a flowchart of a method for manufacturing a capacitive ultrasonic transducer according to an embodiment of the present invention;
fig. 2 is a schematic structural diagram of a capacitive ultrasonic transducer after a diaphragm layer is formed in preparation according to an embodiment of the present invention;
fig. 3 is a schematic structural diagram of a capacitive ultrasonic transducer according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The embodiment of the invention provides a preparation method of a capacitive ultrasonic transducer, as shown in fig. 1, the method comprises the following steps:
102, forming a vibration film layer on the second sacrificial layer, and forming a through hole in the vibration film layer;
and 103, etching the first sacrificial layer and the second sacrificial layer through the via hole to form a cavity structure.
The above-mentioned preparation method can be specifically a preparation method of a Capacitive Micromachined Ultrasonic Transducer (CMUT), in the preparation method, as shown in fig. 2, two sacrificial layers, namely a first sacrificial layer 21 and a second sacrificial layer 22, are sequentially formed on a substrate base plate 1, since the compactness of the first sacrificial layer (bottom sacrificial layer) 21 is small, i.e. loose, the flowing and diffusion of the corrosive liquid in the interior thereof is fast, the contact area is large, and the corrosion of the layer (first sacrificial layer 21) can be rapidly completed; further, as the etching rate of the first sacrificial layer 21 by the etching solution increases, the contact area between the etching solution and the second sacrificial layer (upper sacrificial layer) 22 gradually increases, and the second sacrificial layer 22 can be etched in a large area, thereby further improving the etching efficiency of the second sacrificial layer 22. In addition, the compactness of the second sacrificial layer (the upper sacrificial layer) 22 is relatively high, that is, relatively dense, so that the vibrating membrane layer 3 formed on the membrane layer is flat and dense, and the yield of the capacitive ultrasonic transducer can be further ensured. In summary, the preparation method can greatly reduce the time for forming the cavity structure of the capacitive ultrasonic transducer on the premise of ensuring the preparation yield of the capacitive ultrasonic transducer, thereby improving the preparation efficiency of the capacitive ultrasonic transducer.
Specifically, the compactness of the film layer can be expressed by the etching speed, and the lower the etching speed is, the more compact the film is, namely the greater the compactness is; conversely, the looser the less dense. Specifically, the etching rate of the first sacrificial layer may be more than 2 times that of the second sacrificial layer.
In addition, the compactness of the film layer is specifically represented by the porosity and the pore size in the film layer, and the smaller the porosity and the pore size, the better the compactness of the film layer is; on the contrary, the film layer is poorer in compactness.
Specifically, in the present application, the compactness of the first sacrificial layer is smaller than that of the second sacrificial layer, the porosity and the pore size of the first sacrificial layer are both large, and the first sacrificial layer has a relatively obvious pore structure under an atomic force microscope, and the diameter of the pore can be larger than 100 nm; the porosity and the pore size of the second sacrificial layer are small, the surface has no obvious pore structure, but shows a plurality of particles with similar sizes, and the particles are uniformly and densely distributed on the membrane surface without obvious defects.
In one embodiment, as shown in FIG. 2, the first sacrificial layer 21 and the second sacrificial layer 22 are made of the same material.
Specifically, the material of the first sacrificial layer 21 and the second sacrificial layer 22 may be silicon oxide (SiO)2) Or zinc oxide (ZnO).
Specifically, as shown in fig. 2 and fig. 3, in step 103, the first sacrificial layer 21 and the second sacrificial layer 22 may be etched by using a wet etching process to form the cavity structure 20.
Specifically, the material of the first sacrificial layer 21 and the second sacrificial layer 22 is SiO2In this case, a Buffered Oxide etching solution (BOE) may be used for wet etching. When the material of the first sacrificial layer 21 and the second sacrificial layer 22 is ZnO, NH may be used4And performing wet etching on the CL aqueous solution.
In a specific embodiment, step 101, sequentially forming a first sacrificial layer and a second sacrificial layer on a substrate base plate may specifically include:
forming a first layer of SiO by a first plasma enhanced chemical vapor deposition Process (PECVD)2；
Forming a second layer of SiO by a second plasma CVD process2On which a second SiO layer is formed2The second plasma chemical vapor deposition process has lower reaction pressure and/or higher radio frequency power and/or SiH than the first plasma chemical vapor deposition process4The gas flow is high.
Specifically, in the Plasma Enhanced Chemical Vapor Deposition (PECVD) process, the reaction pressure is reduced, or the radio frequency power is increased, or SiH is increased4Gas flow rate, both of which can cause SiO to be formed2The compactness of the film layer is improved; furthermore, in the embodiment of the present application, the first Plasma Enhanced Chemical Vapor Deposition (PECVD) process may be set to have a higher reaction pressure, a lower rf power, and SiH4The gas flow is low, and the first SiO layer is formed by deposition2The density is small; during the second plasma CVD process, the reaction pressure can be reduced, the radio frequency power can be increased, and SiH can be increased4Adjustment of one or more of gas flow ratesSo that the second layer SiO is formed2The film layer is compact.
In another specific embodiment, step 101, sequentially forming a first sacrificial layer and a second sacrificial layer on a substrate base plate may specifically include:
forming a first layer of ZnO by using a Metal Organic Chemical Vapor Deposition (MOCVD) process; the first ZnO film layer obtained by the process step has good looseness and poor compactness;
and depositing a second ZnO layer on the first ZnO layer by adopting a magnetron sputtering process (Sputter). The second ZnO layer obtained by the process step has better compactness.
Of course, in the embodiment of the present invention, the materials and the preparation processes of the first sacrificial layer and the second sacrificial layer are not limited to the above embodiment, and two sacrificial layers with different compactness may be obtained by other materials or process flows. For example, two layers of SiN may also be formed by two PECVD processes, respectivelyxA film layer, wherein the reaction temperature in the first PECVD process is lower than 200 ℃, and a first SiN layer is obtainedxThe film layer has good looseness, the reaction temperature in the second PECVD process is higher than 250 ℃, and the second SiN layer is obtainedxThe compactness of the film layer is better.
In one specific embodiment, as shown in fig. 2, the thickness of the first sacrificial layer 21 is greater than the thickness of the second sacrificial layer 22.
Specifically, the first sacrificial layer 21 has small compactness and high etching speed, and the thickness of the first sacrificial layer 21 is set to be larger than that of the second sacrificial layer 22, so that the etching process time is favorably shortened, and the preparation efficiency is improved; however, in order to ensure flatness and compactness of the diaphragm layer 3 formed on the second sacrificial layer 22, the thickness of the second sacrificial layer 22 cannot be too thin.
Specifically, the ratio of the thicknesses of the first sacrificial layer 21 and the second sacrificial layer 22 may be 1.5 to 4: 1.
taking the manufacturing process of the capacitive micromachined ultrasonic transducer with the center frequency of 3.5MHz as an example, the sum of the thicknesses of the first sacrificial layer 21 and the second sacrificial layer 22 may be about 140nm, wherein the thickness of the first sacrificial layer 21 may account for 80% of the sum of the thicknesses of the two layers, which is about 112nm, and the thickness of the second sacrificial layer 22 may account for 20% of the sum of the thicknesses of the two layers, which is about 28 nm.
In a specific embodiment, as shown in fig. 2 and fig. 3, a projection of the first sacrificial layer 21 on the substrate base plate 1 coincides with a projection of the second sacrificial layer 22 on the substrate base plate 1, so that it can be ensured that the diaphragm layer 3 is completely formed on the second sacrificial layer 22, and is flat and dense; moreover, after the etching of the first sacrificial layer 21 is completed, the bottom surface of the second sacrificial layer 22 can be completely contacted with the etching solution, so that the etching speed of the second sacrificial layer 22 can be increased, and the etched cavity structure 20 has a regular shape and a smooth edge. In addition, the patterns of the first sacrificial layer 21 and the second sacrificial layer 22 are overlapped, so that the deposition processes of the first sacrificial layer 21 and the second sacrificial layer 22 can share one mask plate, and the cost can be effectively saved.
In a specific embodiment, the substrate base plate 1 includes a glass substrate.
Most of the existing CMUTs use silicon wafer substrates (6 inches in size and 150mm in diameter), are expensive and small in size, and are not beneficial to mass production; in the embodiment of the invention, the large-size high-temperature glass is used as the substrate for depositing the film layer, thereby being beneficial to mass production.
Specifically, as shown in fig. 2 and 3, before step 101, that is, before forming the first sacrificial layer 21 and the second sacrificial layer 22 on the substrate base plate 1 in sequence, the method further includes the following steps:
forming a bottom electrode 4 on a base substrate 1;
an etching stopper layer (insulating layer) 5 is formed on the bottom electrode 4.
Specifically, as shown in fig. 2 and 3, after step 103, that is, after the first sacrificial layer 21 and the second sacrificial layer 22 are etched through the via 30 to form the cavity structure 20, the method further includes the following steps:
filling the via hole 30 of the diaphragm layer 3 with a filling material 6;
a top electrode 7 is formed on the diaphragm layer 3. Specifically, the projection of the top electrode 7 on the substrate base plate 1 is located in the projection of the cavity structure 20 on the substrate base plate 1.
Further, as shown in fig. 3, after the top electrode 7 is prepared, the following steps may be further included: a passivation layer 8 is prepared on the top electrode 7.
Specifically, the method for manufacturing a capacitive ultrasonic transducer according to the embodiment of the present invention may generally include the following steps: depositing a bottom electrode on a substrate → preparing an etching stop layer (insulating layer) → depositing a sacrificial layer → forming a vibration film layer and opening a via hole → etching the sacrificial layer by using the via hole to form a cavity → sealing the etching hole → preparing a top electrode → depositing a passivation layer.
Specifically, the preparation method according to the embodiment of the present application may further include other steps, for example, as shown in fig. 3, before the top electrode 7 is prepared, windows are formed on the etch stop layer (insulating layer) 5 and the vibration film layer 3 for preparing the lead-out wire of the bottom electrode 4, and these steps may be completed by using a conventional process, which is not described herein again.
Specifically, as shown in fig. 3, a capacitance structure is formed between the bottom electrode 4 and the top electrode 7, the top electrode 7 is located on the vibrating membrane layer 3, and under the action of sound waves, the top electrode 7 can vibrate and deform along with the vibrating membrane layer 3, so that the electric quantity on the capacitance structure changes, and the conversion from mechanical energy to electric energy is realized. Conversely, the input electric energy can be converted into mechanical energy through the action of the excitation signal and then transmitted out.
Specifically, as shown in fig. 2 and 3, a plurality of vias 30 are provided in the diaphragm layer 3 for etching the sacrificial layer, and projections of the top electrode 7 on the substrate base plate 1 do not overlap projections of the plurality of vias 30 on the substrate base plate 1. Therefore, the top electrode 7 formed on the vibrating membrane layer 3 can be ensured to be flat and compact, and the yield of the capacitive ultrasonic transducer can be further ensured.
Specifically, as shown in fig. 2 and 3, the projection of the top electrode 7 is located in the central region of the projection of the cavity structure 20, and the projections of the plurality of vias 30 may be disposed around the projection of the top electrode 7 and uniformly distributed.
In addition, the embodiment of the invention also provides a capacitive ultrasonic transducer, and particularly, the capacitive ultrasonic transducer is prepared by adopting the preparation method of any one of the above.
Specifically, the capacitive ultrasonic transducer (CMUT) provided by the embodiment of the present invention can greatly reduce the time for forming the cavity structure of the CMUT on the premise of ensuring the product yield, thereby improving the preparation efficiency of the CMUT.
It will be apparent to those skilled in the art that various changes and modifications may be made in the embodiments of the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.
Claims (10)
1. A method for manufacturing a capacitive ultrasonic transducer, comprising:
sequentially forming a first sacrificial layer and a second sacrificial layer on a substrate, wherein the compactness of the first sacrificial layer is smaller than that of the second sacrificial layer;
forming a vibration film layer on the second sacrificial layer, and forming a through hole in the vibration film layer;
and etching the first sacrificial layer and the second sacrificial layer through the via hole to form a cavity structure.
2. The production method according to claim 1, wherein the first sacrificial layer and the second sacrificial layer are the same in material.
3. The method according to claim 2,
the method for forming the first sacrificial layer and the second sacrificial layer on the substrate comprises the following steps of:
forming a first layer of SiO by a first plasma chemical vapor deposition process2；
Forming a second layer of SiO by a second plasma CVD process2On which a second SiO layer is formed2The second plasma CVD process has a lower reaction pressure and/or a higher RF power than the first plasma CVD process, andor SiH4The gas flow is high.
4. The method according to claim 2, wherein the sequentially forming a first sacrificial layer and a second sacrificial layer on the substrate specifically comprises:
forming a first layer of ZnO by adopting a metal organic compound chemical vapor deposition process;
and forming a second ZnO layer on the first ZnO layer by adopting a magnetron sputtering process.
5. The method of claim 1, wherein a thickness of the first sacrificial layer is greater than a thickness of the second sacrificial layer.
6. The method according to claim 5, wherein a ratio of the thicknesses of the first sacrificial layer and the second sacrificial layer is 1.5 to 4: 1.
7. the method of claim 1, wherein projections of the first sacrificial layer and the second sacrificial layer on a substrate coincide.
8. The method of any one of claims 1-7, wherein the substrate base plate comprises a glass substrate.
9. The method of any one of claims 1-7, wherein after the etching the first sacrificial layer and the second sacrificial layer through the via to form a cavity structure, further comprising:
filling the via hole of the vibrating membrane layer;
forming a top electrode on the vibration film layer; the projection of the top electrode on the substrate base plate is positioned in the projection of the cavity structure on the substrate base plate, and the projection of the top electrode and the projection of the through hole on the substrate base plate are not overlapped.
10. The production method according to any one of claims 1 to 7, further comprising, before the sequentially forming the first sacrificial layer and the second sacrificial layer on the base substrate:
forming a bottom electrode on a substrate base plate;
an etch stop layer is formed on the bottom electrode.
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| KR101414531B1 (en) * | 2011-04-06 | 2014-07-03 | 캐논 가부시끼가이샤 | Electromechanical transducer and method of producing the same |
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