JP5529577B2 - Electromechanical transducer and method for manufacturing the same - Google Patents

Description

The present invention relates to an electromechanical transducer such as a capacitive ultrasonic transducer that performs at least one of reception and transmission of elastic waves such as ultrasonic waves, and a method for manufacturing the electromechanical transducer, such as a highly sensitive two-dimensional sensor device. It is related with the technology applicable to realization.

In recent years, a capacitive electromechanical transducer manufactured using a micromachining process has been actively studied. A typical capacitive electromechanical transducer has a cell including a vibrating membrane supported with a distance from a lower electrode, and an upper electrode disposed on the surface of the vibrating membrane. This is used as, for example, a capacitive ultrasonic transducer (CMUT: Capacitive-Micromachined-Ultrasonic-Transducer). In general, a CMUT is composed of about 200 to 4000 elements, with a plurality of (usually about 100 to 3000) cells as one element (one element), and the CMUT itself is about several mm in size. The CMUT transmits and receives ultrasonic waves using a lightweight vibrating membrane, and can easily obtain a broadband characteristic having excellent broadband characteristics even in liquid or air. When this CMUT is used, diagnosis with higher accuracy than conventional medical diagnosis is possible, and therefore, it is attracting attention as a promising technology.

The operation principle of the capacitive electromechanical transducer will be described. When transmitting an elastic wave such as an ultrasonic wave, a minute AC voltage is superimposed on the DC voltage and applied between the lower electrode and the upper electrode. Thereby, the vibration film vibrates and an elastic wave is generated. When the elastic wave is received, the vibration film is deformed by the elastic wave, and the elastic wave signal is detected by the change in capacitance between the lower electrode and the upper electrode accompanying the deformation. In general, an electromechanical transducer in which a plurality of elements are arrayed is used to transmit and receive ultrasonic waves and sound waves.

As a technique related to arraying of electromechanical transducers, a technique in which a piezoelectric body and a circuit board are combined is proposed (see Patent Document 1). Also, an assembly of an electronic element array including a sensor array and an integrated circuit module is proposed. There is a proposal (see Patent Document 2).

JP 2000-298119 A JP 2008-147622 A

However, in order to manufacture a two-dimensional capacitive electromechanical transducer having a desired sensitivity in a desired frequency band with a high yield, the above-described array technology is not sufficient.

In view of the above problems, the electromechanical transducer according to the present invention has a plurality of elements each including a cell composed of at least a first electrode and a second electrode provided with a gap between the first electrode and the first electrode. Has the following characteristics. That is, the plurality of elements are arranged separately from each other and independently with respect to the corresponding processing circuits on the integrated circuit substrate on which the plurality of processing circuits are formed. In addition, it is mechanically and electrically coupled to the corresponding processing circuits so that signals can be input and output for each element.

Further, in view of the above problems, the electric machine of the present invention has a plurality of elements including at least a cell composed of the first electrode and the second electrode provided with a gap between the first electrode and the first electrode. The method for manufacturing the conversion device includes the following steps. A production process in which a plurality of elements are arranged on a substrate in multiple faces. A good element is selected and cut out from the plurality of elements fabricated on the substrate, and the corresponding processing circuits on the integrated circuit board on which the plurality of processing circuits are formed are separated from each other independently. Arrangement process to arrange. A coupling step of mechanically and electrically coupling the plurality of elements to the corresponding processing circuits so that signals can be input and output for each element.

According to the present invention, a non-defective chip that has been inspected in advance can be selected from a plurality of chips (elements) fabricated on a substrate and connected to a corresponding processing circuit on an integrated circuit substrate. Accordingly, it is possible to manufacture a two-dimensional capacitive electromechanical transducer having good sensitivity in a desired frequency band with no defect or high yield.

Sectional drawing of the electromechanical converter which concerns on Embodiment 1 of this invention. 3A and 3B illustrate a manufacturing process of Embodiment 1. 6 is a table showing conditions for forming a SiN film on a sensor chip used in Embodiment 1. 3A and 3B illustrate a manufacturing process of Embodiment 1. 3A and 3B illustrate a manufacturing process of Embodiment 1. 3A and 3B illustrate a manufacturing process of Embodiment 1. 3 is a graph showing resonance frequency characteristics of a plurality of sensor chips of Embodiment 1 and resonance frequency characteristics of the electromechanical transducer of Embodiment 1. FIG. 8A and 8B illustrate a manufacturing process according to Embodiment 2 of the present invention. 6 is a graph showing resonance frequency characteristics of the electromechanical transducer of Embodiment 2.

Hereinafter, embodiments of the present invention will be described. In the present invention, a good chip is selected from a plurality of chips (elements) fabricated on a substrate, cut out, and connected to a corresponding processing circuit on an integrated circuit substrate to constitute an electromechanical converter. It is. Based on this concept, the basic form of the electromechanical transducer of the present invention and the manufacturing method thereof has the configuration as described above. On the basis of this basic form, the following embodiments are possible.

The plurality of elements (elements) may include a plurality of elements having different resonance frequency characteristics. In general, in ultrasonic image diagnosis, a frequency to be detected differs depending on a target object, and a wider band is required. The resonance frequency is determined by the size of the cavity constituting the CMUT or the like, the gap between the electrodes, the physical property values (Young's modulus, Poisson's ratio) and the film thickness of the membrane film material. For this reason, a method of changing the cavity diameter is simple in order to have different resonance frequencies on the same substrate. However, in this method, it is unavoidable to arrange the transmission / reception structures depending on the respective cavity diameters within a certain area, or to arrange them inefficiently. The configuration including a plurality of elements having different resonance frequency characteristics as described above solves these problems and meets the above requirements. According to this configuration, it is possible to produce a plurality of types of sensor chips having sensitivity characteristics in different frequency bands by changing the hardness of the membrane film (vibrating film) (corresponding to the Young's modulus in physical properties) with the same cavity diameter. . In this way, it is possible to manufacture a two-dimensional capacitive electromechanical transducer having higher sensitivity in a desired frequency band with no defect or high yield.

In addition, the plurality of elements can be directly connected to the corresponding processing circuits on the integrated circuit substrate. In general, the load of electrical mounting increases with the two-dimensionalization, and the density cannot be increased by means such as wire bonding. Further, in CMUT and the like, vibration signals generated by ultrasonic waves are converted into changes in capacitance value. Therefore, if the parasitic capacitance of the device is large, the sensitivity characteristic is deteriorated accordingly, and the reduction of parasitic capacitance is a big problem. The structure directly connected on the integrated circuit board solves such a problem.

Embodiments of the present invention will be described below with reference to the drawings.
(Embodiment 1)
Embodiment 1 of the present invention will be described. The electromechanical transducer of this embodiment shown in FIG. 1 has a plurality of sensor chips that are elements including at least one cell. Each cell includes a lower electrode that is a first electrode and an upper electrode that is a second electrode provided to face each other with a cavity (gap) therebetween. The element is composed of one or more cells, and when the element has a plurality of cells, the cells in the element are electrically connected in parallel. The sensor chip includes a sensor chip 1 having a resonance frequency of 1 MHz, a sensor chip 2 having a resonance frequency of 5 MHz, and a sensor chip 3 having a resonance frequency of 10 MHz. These sensor chips are electrically mounted with bumps 4 and are electrically connected to the integrated circuit board 5. The gap between the sensor chips 1 to 3 and the integrated circuit board 5 and the gap between the sensor chips 1 to 3 are filled with an underfill 6 made of an insulating material, and a common upper wiring 7 is formed on the upper layer by inkjet drawing. The upper electrode of the cell is used as a common electrode. Since the plurality of sensor chips 1 to 3 are arranged separately and independently from each other and are directly connected to the corresponding element unit processing circuit on the integrated circuit board 5 by the bumps 4, the electromechanical conversion device is parasitic. Has almost no capacity.

A method for manufacturing the electromechanical transducer according to this embodiment will be described. 2A is a top view showing the arrangement of the sensor chip 9 used for the fabrication of this embodiment on the silicon substrate 8, and FIG. 2B is a sacrifice for forming the cavity 11 of each cell of the sensor chip 9. FIG. It is a top view which shows the formation process of a layer. Moreover, FIG.2 (c) is AA 'sectional drawing of the part used as the cell of FIG.2 (b). As shown in FIG. 2A, a sensor chip 9 of 2 mm square element units is arranged on a 4-inch silicon substrate 8 having a specific resistance value of 0.02 Ω · cm. This production is performed according to the following surface type MEMS method. In the sacrificial layer forming step to be the cavity 11 in FIGS. 2B and 2C, the chromium film 10 is formed on the 200 nm thick silicon substrate 8 and is formed into a cavity 11 having a diameter of 25 μm by photolithography. The sacrificial layer is patterned. Then, as shown in FIG. 2C, a SiN film 12 serving as a membrane film (vibration film) is formed on the silicon substrate 8 by a plasma CVD apparatus to a thickness of 400 nm. At this time, the physical property values of the SiN film 12 can be controlled by the SiH ₄ gas flow rate, the NH ₃ gas flow rate, the N ₂ gas flow rate, the frequency of the radio frequency (RF) power source, the RF power, and the substrate temperature as film formation parameters. The Young's modulus decreases as Si increases in the Si / N component ratio. Therefore, Young's modulus can be controlled by the flow ratio of SiH ₄ gas and NH ₃ gas. In the present embodiment, the silicon substrate 8 itself is used as the lower electrode. Further, the Young's modulus of the SiN film 12 serving as the membrane film was set to 100 GPa, 170 GPa, and 240 GPa, and the resonance frequencies of the sensor chip were set to 1 MHz, 5 MHz, and 10 MHz. That is, different SiN films 12 were formed on the three wafer substrates 8 by the recipes A, B, and C shown in FIG.

4A and 4B show the cavity forming process. Here, fine etching holes 13 communicating with each chromium film 10 are formed by dry etching in a part of the SiN film 12 formed on the patterned chromium film 10 which is a sacrificial layer for forming the cavity 11. . Then, the substrate is immersed in a cerium ammonium nitrate solution as an etchant to remove the chromium sacrificial layer 10 by etching, and a cavity (cavity) 14 is formed through washing with water and drying. Next, FIGS. 5A and 5B show the upper electrode forming step. Here, an aluminum film having a thickness of 400 nm is formed on the substrate by sputtering, and the sealing 16 of the etching hole 13 and the upper electrode pattern 17 are formed.

FIG. 6A shows a UBM (Under Bump Metal) layer forming process for electrical mounting. Here, the stencil mask 18 is aligned and set on the back surface of the wafer (substrate) 8 so that the holes formed in the stencil mask 18 correspond to the sensor chips 9. Then, titanium / nickel / gold (= UBM layer) 19 is formed by continuous film formation on each part of the wafer back surface corresponding to the sensor chip 9. In this way, a manufacturing process is performed in which a plurality of elements 9 are arranged on the substrate 8 in multiple positions.

Thereafter, a plurality of sensor chips 9 arranged on the wafer are inspected for a short circuit failure between the upper electrode and the lower electrode, a chromium removal failure, and the like. And the sensor chip 9 in which all the cells are non-defective was cut out and selected by dicing. Here, about 80% of non-defective sensor chips (elements) 9 were selected. FIG. 6B shows a form at the end of electrical mounting. In this electrical mounting step, the cream solder is transferred to the UBM layer 19 of the non-defective chip 9 by printing, and the bumps 4 are formed through a reflow furnace. On the other hand, cream solder is printed on the UBM layer 21 on the side of the integrated circuit board 5 in which a plurality of processing circuits 20 are arranged for each element. Then, after the sensor chip 9 is aligned and mounted on the UBM layer 21 of the corresponding processing circuit 20 with a flip chip bonder, the electrical connection is completed through a reflow furnace. Further, by utilizing capillary action, the underfill material 6 is filled between the sensor chip 9 and the integrated circuit substrate 5 and between the plurality of elements, and is heated and cured to complete the mechanical coupling. As described above, a good element is selected and cut out from the plurality of elements 9 formed on the substrate 8, and the corresponding processing circuit on the integrated circuit substrate 5 on which the plurality of processing circuits 20 are formed is selected. Thus, an arrangement step is performed in which the arrangement steps are performed separately from each other. In addition, a coupling step is performed in which the plurality of elements 9 are mechanically and electrically coupled to the corresponding plurality of processing circuits 20 so that signals can be input and output for each element.

FIG. 6C shows the final process. Here, in order to use the upper electrode of each cell of the electromechanical conversion device as a common electrode, the conductive paste 23 is discharged by the ink jet drawing machine 22 so that the upper electrode pattern 17 of each sensor chip 9 can be electrically connected. The common upper wiring 7 is drawn. Then, the common upper wiring 7 is heated and cured to complete the electrical mounting process. In this way, a wiring having one electrode of each cell of the plurality of elements 9 as a common electrode can be formed on the surface of the filled insulating material 6 by ink jet drawing. The reception characteristics of the two-dimensional capacitive electromechanical transducer of this embodiment produced in this way were measured with castor oil filled with castor oil. As a result, the widened frequency band shown in FIG. 7B was measured as the frequency band of the capacitive electromechanical transducer including the sensor chip 9 having the individual frequency band shown in FIG. 7A.

(Embodiment 2)
Next, Embodiment 2 of the present invention will be described. In the present embodiment, resonance frequency characteristics are controlled closer to each other. In the electromechanical transducer of this embodiment, the resonance frequency of each sensor chip is 1 MHz, 2 MHz, and 3 MHz. In order to realize such a resonance frequency, a method of changing the film thickness of a membrane film (vibration film) having the same Young's modulus is effective. In this embodiment, in order to use <100> single crystal silicon having a Young's modulus of 130 GPa as the membrane film of each cell, an electromechanical transducer is manufactured according to a silicon direct bonding MEMS method.

A manufacturing method of this embodiment will be described. FIG. 8A is a top view showing a multi-face arrangement on the silicon substrate 24 of the sensor chip (element) 25 used in the fabrication of this embodiment, and FIG. 8B is the formation of the oxide film 26 of the sensor chip 25. It is sectional drawing which shows a process. 8C is a cross-sectional view showing the etching process of the oxide film 26 of the sensor chip 25, FIG. 8D is a cross-sectional view showing the wafer bonding process in the sensor chip 25, and FIG. 5 is a cross-sectional view showing a process of forming a membrane film 31 of the sensor chip 25. FIG. Here, as shown in FIG. 8A, the sensor chip 25 of 2 mm square element units is arranged in a multi-sided manner on a 4-inch silicon substrate 24 having a specific resistance value of 0.02 Ω · cm. This production is performed according to the following junction type MEMS method. In the oxide film formation step of FIG. 8B, an oxide film 26 having a thickness of 200 nm is formed on the silicon substrate 24 by pyrogenic oxidation (1000 ° C., 90 minutes) in a thermal oxidation furnace. In the oxide film etching step of FIG. 8C, the oxide film 26 in the portion 27 that becomes the cavity is removed by RIE etching using CF ₄ gas. The wafer bonding process in FIG. 8D is a bonding process with the SOI substrate 28 having a silicon active layer having a crystal orientation <100>. Each of the substrates 24 and 28 is cleaned in advance and subjected to N ₂ plasma for 10 minutes. The exposed and activated surfaces are bonded together in an atmosphere of about 0.4 Pa with a vacuum bonding apparatus. Thereafter, heating is performed at 1100 ° C. for 2 hours to complete the bonding of the two silicon substrates 24 and 28. Here, bonding was performed using three types of SOI substrates 28 having different thicknesses of the silicon active layer 29 of 400 nm, 800 nm, and 1100 nm.

8E, after that, from the back surface of the SOI substrate 28, the back grinder and the KOH liquid are used to remove the BOX (embedded oxide film) layer 30. Finally, the BOX layer 30 is removed with hydrofluoric acid. Thus, a membrane film (vibration film) 31 of single crystal silicon is formed. Further, as in the first embodiment, a UBM layer for electrical mounting is formed, inspected, and a two-dimensional capacitive electromechanical transducer is manufactured using approximately 60% non-defective chips having three types of resonance frequencies. did. Similarly, as a reception characteristic, a highly sensitive reception characteristic was confirmed in a band of 5 MHz or less as shown in FIG. Thus, an electromechanical transducer having a highly sensitive resonance frequency characteristic in a relatively low frequency band is effective as a sensor device used for early detection of breast cancer and the like. According to this embodiment, a sensor device suitable for the purpose can be manufactured without any element defect or with a high yield.

In the above embodiment, the sensor chip is manufactured using the silicon substrate. However, the present invention is not limited to this, and a chip using another material (such as a glass substrate) may be used. Moreover, although bump connection was used in electrical mounting, it is also possible to employ mounting technology using a conductive adhesive, an anisotropic conductive film, or the like. Furthermore, the upper wiring forming method using an ink jet drawing apparatus can easily form wiring without breaking even on a relatively stepped surface, and wiring can be formed without using a large-scale apparatus such as a film forming apparatus or photolithography. This is a very effective method.

1, 2, 3, 9, 25 ... element (sensor chip), 5 ... integrated circuit substrate, 8, 24 ... substrate (silicon substrate), 12, 31 ... membrane membrane (vibrating membrane), 14, 27 ... cavity (cavity) Part), 17 ... upper electrode, 20 ... processing circuit

Claims (6)

An electromechanical transducer having a plurality of elements including at least a cell composed of a first electrode and a vibrating membrane including a second electrode provided with a gap between the first electrode,
The plurality of elements are separated from one another for each element, and are arranged independently on an integrated circuit board , and an insulating material is filled between the elements ,
The second electrodes between the plurality of elements are electrically connected by wiring provided on the insulating material,
Respectively, respectively, the electromechanical transducer, characterized in that it is mechanically and electrically coupled a plurality of processing circuits provided in the integrated circuit board of the plurality of elements.   The electromechanical transducer according to claim 1, wherein the plurality of elements includes a plurality of elements having different resonance frequency characteristics.   The electromechanical transducer according to claim 1, wherein the first electrode is made of a silicon substrate. A method of manufacturing an electromechanical transducer having a plurality of elements including at least a cell composed of a first electrode and a vibrating membrane including a second electrode provided with a gap between the first electrode and the first electrode. There,
A producing step of producing a plurality of elements on a substrate,
A switching Ride to process a desired element from among a plurality of elements made in said substrate,
An arrangement step of independently disposing each of the cut out elements on an integrated circuit substrate on which a plurality of processing circuits are formed;
Filling an insulating material between the elements;
Forming a wiring electrically connecting the second electrodes between the elements on the insulating material;
With
Wherein each a plurality of elements, respectively of said plurality of processing circuits, the mechanical and manufacturing method of electromechanical transducer according to claim electrically coupled to Turkey. Method for manufacturing electromechanical transducer according to claim 4, wherein the benzalkonium be formed by inkjet image the wiring. 6. The method of manufacturing an electromechanical transducer according to claim 4, wherein in the arranging step, elements having different resonance frequency characteristics are arranged.

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