JP2016039476A - Capacitive transducer, and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique for achieving a structure capable of controlling the cell diameter of a capacitive transducer accurately, while suppressing a step between a connection and the vibrating membrane of a cell even when an inter-cell connection is formed.SOLUTION: A capacitive transducer has a plurality of cells each having a structure including a vibrating membrane 105 which includes a first electrode 102, and a second electrode 106 separated therefrom by a gap 109. The capacitive transducer is formed using a substrate where a first layer including a part becoming the first electrode, a second layer including a part becoming a gap be etching, and a third layer including a part of the vibrating membrane are formed. Connections 118, 119 for connection with a cell, and a groove 122 defining the cell are formed up to the third layer 115, and on the sidewall of the groove on the cell and connection side, an insulating film 112, i.e., a support for supporting the vibrating membrane and connection, is formed. The gap 109 is formed by etching the second layer, and the connection and cell are connected while being contained in the third layer commonly.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a manufacturing method using a capacitive transducer, a semiconductor process, or the like.

  Conventional ultrasonic transducers that use piezoelectric materials have been used in many cases, but in recent years, capacitive ultrasonic transducers (CMUTs) manufactured using semiconductor processes have attracted attention. ing. The capacitive transducer includes a plurality of cells having a structure including two parallel plate electrodes facing each other with a gap (cavity) therebetween, and ultrasonic waves are transmitted and received by vibration of a vibrating film including one electrode. . Such transducer fabrication methods can be broadly divided into a junction type and a sacrificial layer type. The junction type is, for example, a method of forming a cell structure by bonding an active layer silicon of an SOI (Silicon On Insulator) substrate to a vibration film and bonding a silicon substrate having a recess and an SOI substrate. On the other hand, the sacrificial layer type is formed by forming a first film called a sacrificial layer and covering the second film on the first film, removing the sacrificial layer of the first film, and forming a cavity. It is a method of forming.

  When generating ultrasonic waves that propagate in the air, such as an ultrasonic distance meter, the acoustic impedance of air is as low as about 1/3600 of the acoustic impedance of water, so ultrasonic waves are required to generate sufficient sound pressure. A large amplitude vibration of the element is required. Also, when generating ultrasonic waves such as those used in high-intensity focused ultrasound (HIFU) in medicine, a large sound pressure is required, and the ultrasonic element has a large amplitude. Vibration is necessary. In CMUT, it is necessary to increase the gap between the upper and lower electrodes in order to obtain vibration with a large amplitude. This gap is required from several μm to several hundred μm in order to produce a sound pressure that can be actually used.

  In a CMUT having such a large gap, it is important that the CMUT has a thickness capable of withstanding a large amplitude vibration and a stable mechanical characteristic. An example of using an active silicon film of an SOI substrate as a vibration film is an example. Non-Patent Document 1. Patent Document 1 describes an example in which a CMUT is formed using a single SOI substrate that does not require bonding. The method is a method of forming a CMUT using an active layer of an SOI substrate as a CMUT vibration film, a handle layer as a lower electrode, and a BOX layer (Buried oxide layer) as a sacrificial layer. is there.

JP 2009-165931 A

IEEE Transactions on Ultrasonics, Ferroelectronics and Frequency control, vol56, 2009, 193

  In the method of Patent Document 1, after the box layer of the sacrificial layer is patterned, a silicon nitride film is formed by LPCVD (Low Pressure Chemical Vapor Deposition) as the cell side wall of the CMUT. Then, this silicon nitride film functions as an etching stop layer when removing the box layer to form a cell structure. However, this method can form the cell diameter with high accuracy, but a step is generated in the electric wiring portion connecting the cells. Polysilicon or metal film is used as the electrical wiring part between cells, but if this method is used to form a CMUT with a wide gap as described above, the step in the electrical wiring part will have resistance and will be disconnected. there's a possibility that.

  Patent Document 1 also describes a method for forming a cell structure without patterning a box layer serving as a sacrificial layer. In this method, the cell diameter is controlled by the etching time of the sacrificial layer. In the method in which the cell diameter is controlled by the etching time of the sacrificial layer, there is a possibility that the uniformity within a substrate having a plurality of cell diameters and the reproducibility between production batches are lowered. As described above, the above-described manufacturing method has an advantage that the active layer of the SOI substrate can be used as the vibration film. However, when the box layer is patterned, there is a step in the electric wiring portion between the cells, and the wiring There is a possibility of increased resistance and disconnection. Moreover, when the box layer is not patterned, the uniformity of the cell diameter in the substrate tends to be low.

  In view of the above problems, the present invention provides a capacitance type having a plurality of cells each having a structure including a first electrode and a vibration film including a second electrode provided with a gap from the first electrode. A transducer having the following characteristics. That is, a first layer including a portion that becomes the first electrode, a second layer including a portion that is etched to become the gap, and a third layer including a portion that becomes at least a part of the vibration film, It is formed using a substrate laminated in this order in a flat plate shape, and a connecting portion connected to the cell and a groove defining the cell are formed through the third layer and the second layer to reach the first layer. An insulating film is formed on a side wall of the groove on the cell and the connection portion side, and an insulating film is formed as a support portion for supporting the vibration film and the connection portion, and between the first electrode and the second electrode. The gap is formed by etching the second layer, and the connection portion and the cell are connected so as to include the third layer in common.

  In addition, in view of the above problems, another capacitive transducer of the present invention includes a first electrode, a vibration film including a second electrode positioned with a gap from the first electrode, and the first electrode. A plurality of cells having a structure including a support portion that is positioned on the electrode and supports the vibration membrane, and the support portion supports the vibration membrane in contact with a side portion of the support portion. It is characterized by.

  According to the present invention, the cell diameter can be accurately controlled, and a structure in which a step between the connection portion and the vibration film is suppressed can be realized even when the connection portion between cells is formed.

The figure explaining one Embodiment of the capacitive transducer of this invention. 3A and 3B illustrate a capacitive transducer according to Embodiment 1 and a manufacturing method thereof. 3A and 3B illustrate a capacitive transducer according to Embodiment 1 and a manufacturing method thereof. 3A and 3B illustrate a capacitive transducer according to Embodiment 1 and a manufacturing method thereof. 6A and 6B illustrate a capacitive transducer according to a second embodiment and a manufacturing method thereof. 6A and 6B illustrate a capacitive transducer according to Example 3 and a manufacturing method thereof. 8A and 8B illustrate a capacitive transducer according to Example 4 and a manufacturing method thereof. 8A and 8B illustrate a capacitive transducer according to Example 4 and a manufacturing method thereof. 8A and 8B illustrate a capacitive transducer according to Example 4 and a manufacturing method thereof. FIG. 10 is a diagram illustrating a capacitive transducer according to a fifth embodiment. The whole block diagram which shows the example of the information acquisition apparatus containing the transducer of this invention.

  The present invention relates to a technique capable of achieving both control of a cell diameter of a capacitive transducer and suppression of a step in a connection portion. Therefore, in the present invention, a first layer including a portion to be a first electrode, a second layer including a portion to be etched to form a gap, and a third layer including a portion to be at least a part of the vibration film Are manufactured using a substrate laminated in this order in a flat plate shape. Then, a connecting portion connected to the cell and a groove defining the cell are formed through the third layer and the second layer to reach the first layer, and are connected to the vibration film on the side wall of the groove on the side of the cell and the connecting portion. An insulating film is formed as a support part for supporting the part, and the connection part and the cell are coupled together including the third layer. The substrate is, for example, an SOI substrate, but may be any substrate as long as the first layer, the second layer, and the third layer are made of materials that satisfy the above conditions. From another viewpoint, the capacitive transducer according to the present invention includes a first electrode, a vibration film including a second electrode positioned with a gap from the first electrode, A plurality of cells having a structure including a support portion that is positioned on the electrode and supports the vibrating membrane, and has the following characteristics. That is, the support portion supports the vibrating membrane in contact with the side portion of the support portion. Since the support portion supports the vibrating membrane in contact with the side portion of the supporting portion instead of the upper portion of the supporting portion, variation in transducer characteristics due to variation in height of the vibrating membrane due to variation in height of the supporting portion can be suppressed. In addition, since the variation in height of the vibration film is suppressed, disconnection of the wiring electrode formed on the upper surface of the vibration film is suppressed. In the configuration further comprising a connection portion coupled to the cell and a support portion that supports the connection portion, the support portion that supports the connection portion supports the connection portion in contact with the side portion of the support portion, and the connection portion. And the cells are connected including a common layer. In this case, the second electrode can be formed on the common layer of the cell, and the electrical wiring electrically connected to the second electrode can be formed on the common layer of the connection portion.

  A capacitive transducer according to an embodiment of the present invention will be described with reference to FIGS. FIG. 1A shows a cross-sectional view of the transducer of this embodiment, and FIG. 1B shows a top view of the transducer of this embodiment. 1A is a cross-sectional view taken along a dotted line A-A ′ in FIG.

  The structure of the present embodiment is described by showing one element including a plurality of cells, but may be a structure having a plurality of elements. As shown in FIG. 1B, the element includes three cells 101, 201, and 301 connected in series, but any number of cells may be included in the element. Here, as shown in FIG. 1A, the handle layer 115 of the SOI substrate including the handle layer 115, the box layer 116, and the active layer 117 is used as the first electrode 102. The handle layer is desirably a low-resistance silicon substrate, and preferably has a resistivity of 0.1 Ωcm or less. The active layer 117 of the SOI substrate becomes the vibration film 105. The thickness of the active layer 117 is determined by the desired mechanical properties of the transducer. The active layer 117 may also serve as the second electrode by itself. In order to make the conductivity better, a conductive film can be formed on the active layer.

  The vibration film 105 including the second electrode 106 formed by separating the first electrode 102 and the cavity 109 is supported by a sidewall insulating film 112 which is a support portion. As shown in FIG. 1 (a), the support part supports the vibrating membrane in contact with the side part of the support part. In addition to the reason described below, disconnection of the wiring electrode formed on the upper surface of the vibration film and an increase in resistance are suppressed because the variation in height of the vibration film is suppressed. The vibrating membrane 105 is substantially separated for each cell by the groove 122, and the cells are connected by the inter-cell connecting portion 118. Since the inter-cell connection portion 118 is also formed of the active layer 117 of the SOI substrate, there is no step between the cell vibration film 105 and the inter-cell connection portion 118. That is, the connection portion 118 is also supported in contact with the side portion of the side wall insulating film 112 that is a support portion, and the upper surface of the cell vibration film 105 and the upper surface of the inter-cell connection portion 118 are in the same plane. In this embodiment, the space below the active layer 117 of the inter-cell connection portion 118 is a cavity connected to the cell cavity 109. That is, the connection portion has a cross-linked structure in which the second layer portion is etched. However, the second box layer 116 may remain there.

  In the present embodiment, as shown in FIG. 1B, the second electrode (upper electrode) 106 on the cell vibrating membrane 105, the uppermost layer electrical connection (wiring) 131 of the adjacent inter-cell connection, the cell The electrical connection part (wiring) 132 of the inter-pad connection part 119 is composed of the same conductive film. Since the semiconductor active layer 117 of the SOI substrate has conductivity, it is possible to energize between cells and between the cell and the pad without providing the second electrode 106, but to further suppress the resistance value between the cells. For this, it is desirable to provide the second electrode 106 and the wiring 131. The second electrode and the wirings 131 and 132 are not necessarily the same conductive film. A conductive material such as metal or polycrystalline silicon can be used. As described above, since there is no step between the vibration film 105 and the inter-cell connecting portion 118 or the cell-pad connecting portion 119, the second electrode 106 and the uppermost layer electric connecting portion (wiring) 131 of the inter-cell connecting portion. There is no step between the electrical connection portion (wiring) 132 and the electrical connection portion (wiring) 132, and electrical connection can be made in the same plane, so that the possibility of disconnection is low.

  As shown in FIG. 1, a wiring pad 120 and a pad 121 (described later) are also prepared for inputting and outputting signals to and from this transducer. Since a firm pad is preferable when wiring, the pad 120 of the second electrode is formed on the vibration film 105 without the cavity 109 as shown in FIG. If the vibrating membrane 105 is sufficiently thick and sturdy, the second electrode pad 120 can be formed on the vibrating membrane 105 even if there is a cavity or cavity. Further, since the sidewall insulating film 112 is formed on the sidewall of the groove 122, the shape of the cell can be controlled by the shape of the groove 122. At least a part of the sidewall insulating film 112 is preferably a nitride film such as a silicon nitride film formed by LPCVD (Low Pressure Chemical Vapor Deposition).

  As shown in FIG. 1, the cavity 109 is connected to an external space through the etching hole 107. In the case of an ultrasonic sensor used in the air, the etching hole 107 does not need to be sealed. When the ultrasonic transducer is used in a liquid, it is preferable to seal the etching hole 107. The shape of the cavity is not limited to a circle but may be a polygon. Further, the arrangement positions of the cells and elements may be any. In order to improve the sensitivity of ultrasonic transmission and reception, it is preferable to arrange them more densely.

  The driving principle of this embodiment will be described. The first electrode 102 or the second electrode 106 is used as an electrode for applying a bias voltage or an electrode for applying an electric signal or extracting an electric signal. In FIG. 1B, the first electrode 102 is used as the electrode to which the bias voltage is applied, and the second electrode 106 is used as the signal extraction electrode, but this may be reversed. When ultrasonic waves are received by a capacitive transducer, a DC voltage is applied to the first electrode 102 by a voltage applying means (not shown). When the ultrasonic wave is received, the vibration film 105 having the second electrode 106 is deformed, so that the distance of the gap between the second electrode 106 and the first electrode 102 changes, and the capacitance changes. Due to this capacitance change, a current flows through the lead-out wiring, and an ultrasonic wave can be received as a voltage by a current-voltage conversion element (not shown).

  According to this embodiment, when the sacrificial box layer is removed, the cell diameter can be controlled by using the insulating film (silicon nitride film) on the side wall of the cell (side wall of the groove) as an etching stop layer. Furthermore, there is a connection by the active layer between adjacent cells, and a connection part without a step is formed, so that the disconnection of wiring between cells can be suppressed. Therefore, it is possible to easily manufacture a capacitive transducer that achieves both accurate cell diameter control and formation of inter-cell connection portions with reduced steps, using a single SOI substrate. A capacitive transducer can be realized.

Hereinafter, more specific examples will be described.
Example 1
In Example 1, a manufacturing method of a CMUT that does not seal an etching hole and covers a conductive film on a vibration film will be described. FIGS. 2-1 to 2-3 show a method for manufacturing the CMUT in the first embodiment.

  First, as shown in FIG. 2A, an SOI substrate is cleaned and prepared. The handle layer 115 is used as the first electrode (lower electrode) 102. The handle layer 115 is preferably a low-resistance silicon substrate for use as the first electrode, and here has a resistivity of 0.01 Ωcm. Thereafter, the SOI substrate is patterned in accordance with a desired cell shape, and dry etching is performed up to the active layer 117, the box layer 116, and the handle layer 115. Thus, as shown in FIG. 2-1 (b), a groove 122 is formed between the cells. However, the inter-cell connection part (connection part) 118 remains. From the viewpoint of satisfactorily forming the cavity by etching the box layer, the connecting portion 118 is preferably connected between the central portions of the cells, but may be formed at a location deviated from the central portion. Then, as shown in FIG. 2-1 (c), a silicon nitride film is formed on the substrate using LPCVD. This silicon nitride film becomes the subsequent sidewall insulating film 112. A silicon nitride film is also deposited on the back surface of the substrate, but is removed by dry etching.

  Next, patterning is performed on the substrate and etching is performed to form an etching hole 107. As shown in FIG. 2D, the etching hole 107 is formed by etching up to the handle layer 115. However, the etching hole 107 is used to remove the box layer 116 as a sacrificial layer. That's fine. FIG. 2-1 (e) is a horizontal plan view taken along the dotted line A-A 'at the box layer level in FIG. 2-1 (d). In other words, the range of A-A ′ in FIG. 2-1 (d) is a cross-sectional view taken along the dotted line A-A ′ in FIG. 2 (e).

  Next, as shown in FIG. 2-2 (f), the substrate is immersed in a BHF solution (Buffered Hydrogen Fluoride Acid) in order to remove the box layer which is a sacrificial layer. The BHF solution is removed by etching the silicon oxide film of the box layer through the etching hole 107, and the removed space becomes a cavity 109. The silicon nitride film 112 formed by LPCVD is hardly etched with the BHF solution, and functions as an etching stop layer to determine the cell shape.

  FIG. 2-2 (g) shows a horizontal plan view of the dotted line A-A 'at the box layer level in FIG. 2-2 (f). That is, the range of A-A ′ in FIG. 2-2 (f) is a cross-sectional view taken along the dotted line A-A ′ in FIG. 2-2 (g). As can be seen with reference to FIG. 2-2 (f) and FIG. 2-2 (g), the cell 101, the cell 201, and the cell 301 are connected by an inter-cell connection unit 118. The BHF solution flows into the etching hole 107, first the box layer in the cell 301 is removed, and then the box layer in the inter-cell flow path 130 is also removed, and the box layer in the cell 201 is removed through the flow path 130. To do. When the etching is performed up to the flow path 133 between the cell 101 and the pad 125, the etching is stopped. Thus, as shown in FIG. 2-2 (g), the box layer of the three cells is completely removed, and the shape of the cell can be controlled. The channel width of the channel 130 between the adjacent cells and the channel 133 between the cell and the pad 125 is preferably 3/2 or less of the effective diameter of the cell (the square root of the ratio of the cell area / circumferential ratio). Further, it is more preferable that the effective diameter of the cell is ½ or less. That is, the connection portion is narrower than the cell. The locations where the etching holes are formed are not limited to those described above. For example, an etching hole may be formed in each cell portion. In this case, it is possible to leave at least a part of the box layer of the inter-cell connecting portion 118 by controlling the etching time (see an example of FIG. 6 described later).

  Next, the substrate is washed and dried, and then thermal oxidation is performed to form a silicon thermal oxide film 103 as an insulating film as shown in FIG. In the step of forming the sidewall insulating film 112 which is the silicon nitride film, oxygen is blocked. On the other hand, in this step, a thermal oxide film (insulating layer 103) is formed only in a portion where silicon is exposed to the air. Since oxygen enters the cavity 109 through the etching hole 107, oxide insulating layers 103 are also formed above and below the cavity 109. By forming the insulating layer 103, when the CMUT is operated, a protective effect that a short-circuit does not occur even when a DC bias voltage larger than the collapse voltage is applied to contact the upper and lower electrodes can be obtained.

  Next, as shown in FIG. 2-2 (i), the insulating film 112 (silicon nitride film) on the substrate surface and the insulating film 103 (silicon oxide film) on the back surface of the substrate are removed by dry etching. Since dry etching has anisotropy, only the sidewall insulating film 112 on the sidewall can be left. The purpose of removing the nitride film on the substrate surface is to expose the vibrating film 105 of the single crystal silicon semiconductor, form a conductive film thereon, and wire the second electrode (upper electrode). The purpose of removing the oxide film on the back surface of the substrate is to expose the handle layer 115 serving as the first electrode (lower electrode) and to provide a pad for the first electrode (lower electrode). In this way, the electrical wiring of the upper and lower electrodes of the CMUT can be formed. In addition, the vibration film 105 including the second electrode (upper electrode) and the first electrode (lower electrode) 102 face each other at a short distance through the insulating film 103 and the cavity 109, so that the electromechanical conversion of the element is performed. Efficiency can be increased. In FIG. 2-2 (i), the nitride film on the surface of the substrate is not patterned in order to reduce the electric resistance value between cells and simplify the process. It may be patterned into an appropriate shape. Similarly, if the handle layer has a low resistance, the oxide film on the back surface of the substrate may be patterned into an appropriate shape according to the specification.

  Next, as shown in FIG. 2-3 (j), a conductive film on the vibration film 105 is formed on the surface of the substrate and patterned to form a second electrode (upper electrode) 106 and a pad 120 of the second electrode. Form. Then, the first electrode (lower electrode) pad 121 is formed on the back surface of the substrate and patterned. FIG. 2-3 (k) shows a top view of the A-A ′ range in FIG. 2-3 (j). In other words, the range A-A ′ in FIG. 2-3 (j) shows a cross-sectional view taken along the dotted line A-A ′ in FIG. 2-3 (k). As can be seen with reference to FIGS. 2-3 (j) and 2-3 (k), the second electrode (upper electrode) 106 of the cell, the inter-cell electrical connection 131, the pad 120 of the second electrode, Since all the electrical connection portions 132 between the cells and the pads are placed on the active layer 117, electrical connection without a step can be achieved.

(Example 2)
In Example 2, a method for manufacturing a CMUT in which an etching hole is sealed and a conductive film is formed on a vibration film will be described. FIG. 3 is a diagram for explaining a method of manufacturing a CMUT in Embodiment 2 of the present invention.

  In the CMUT manufacturing method of this embodiment, a substrate is first formed in the same manner as the steps shown in FIGS. 2-1 (a) to 2-2 (h) of the first embodiment. Thereafter, as shown in FIG. 3A, a sealing film 113 is formed on the surface of the substrate, and the etching hole 107 is sealed to form a sealing portion 108. The sealing film 113 is a silicon nitride film formed by PECVD (Plasma Enhanced Chemical Vapor Deposition). The sealing film may be a silicon oxide film, or a silicon nitride film or silicon oxide film formed by LPCVD. In FIG. 3A, the sealing film 113 in the sealing portion 108 closes the etching hole 107, but closes the cavity 109 near the etching hole by the diameter of the etching hole (for example, by increasing the diameter). It is also possible.

  Next, as shown in FIG. 3B, the sealing film 113 and the insulating film 112 on the substrate surface are removed by dry etching. The insulating film 103 (silicon oxide film) is also removed from the back surface of the substrate by dry etching. The purpose and effect are the same as the steps shown in FIG. Since dry etching has anisotropy, the sidewall of the cavity 109 is constituted by the sidewall insulating film 112 and the sealing film 113. That is, at least a part of the supporting portion of the vibration film is formed of a polycrystalline silicon film.

  Next, as shown in FIG. 3C, a conductive film is formed on the vibration film 105 and patterned to form a second electrode (upper electrode) 106 and a pad 120 of the second electrode. Then, a first electrode (lower electrode) pad 121 is formed on the back surface of the substrate and patterned. FIG. 3D shows a top view of the range A-A ′ shown in FIG. That is, the A-A ′ range in FIG. 3C is a cross-sectional view taken along the dotted line A-A ′ in FIG. Here, as can be seen from FIGS. 3C and 3D, the second electrode (upper electrode) 106 of the cell, the inter-cell electrical connection 131, the pad 120 of the second electrode, the cell and the pad Since all the electrical connection portions 132 are placed on the active layer 117, electrical connection without a step can be achieved.

(Example 3)
In Example 3, a method of manufacturing a CMUT in which the etching hole is sealed and the vibration film itself is the second electrode (upper electrode) will be described. FIG. 4 shows a method for producing a CMUT in Example 3.

  In the CMUT manufacturing method of this embodiment, first, a substrate is formed in the same manner as in the process up to the step shown in FIG. Thereafter, as shown in FIG. 4A, the insulating film 112 and the sealing film 113 are etched on the surface of the substrate to etch the second electrode (upper electrode) pad 120 with a conductive film. The back surface of the substrate is also patterned and etched on the insulating film 103 (oxide film) to form a pad 121 of the first electrode (lower electrode).

  FIG. 4B is a horizontal plan view of the dotted line A-A ′ at the box layer level in FIG. In other words, the range of A-A ′ in FIG. 4A is a cross-sectional view taken along the dotted line A-A ′ in FIG. According to the present embodiment, the vibration film itself that can seal the etching hole and is the active layer of the low-resistance semiconductor is used as the second electrode (upper electrode). Therefore, since the electrical connection part between the cells is also formed by the same active layer 117 as the vibration film, the possibility of disconnection is low.

Example 4
In the fourth embodiment, in addition to the features of the third embodiment (sealing of the etching holes and the vibrating membrane itself is the second electrode), the features of having insulating films with the same thickness above and below the vibrating membrane and the back surface of the substrate are taken out. It has the characteristic of having a through wiring. 5A to 5C are diagrams illustrating a method for manufacturing a CMUT according to the fourth embodiment.

  In the CMUT manufacturing method of the present embodiment, a substrate is first formed in the same manner as in the first embodiment up to the step shown in FIG. Thereafter, as shown in FIG. 5A, the entire surface of the substrate is dry-etched, and the insulating film 112 (nitride film) is removed leaving only the side walls. The purpose of removing the nitride film on the substrate surface is to expose the vibrating film 105 of the single crystal silicon semiconductor and then form a thermal oxide film in a thermal oxidation process.

  Next, as shown in FIG. 5B, an etching hole 107 is formed by patterning and dry etching. Thereafter, as shown in FIG. 5C, the sacrificial box layer 116 is removed. This process is the same as the process shown in FIGS. 2-2 (f) and 2-2 (g) of the first embodiment. FIG. 5-1 (d) shows a horizontal plan view of the dotted line A-A 'at the box layer level in FIG. 5-1 (c). That is, the range of A-A ′ in FIG. 5C is a cross-sectional view taken along the dotted line A-A ′ in FIG.

  Next, the substrate is thermally oxidized in the same manner as the process shown in FIG. 2-2 (h) of the first embodiment, and the silicon surface exposed to the atmosphere is exposed to silicon as shown in FIG. 5-2 (e). An insulating film 103 made of a thermal oxide film is formed. Since the thermal oxidation process is not a supply-controlled rate but a surface reaction-controlled rate, thermal oxide films can be formed on the upper and lower surfaces in the cavity 109 at the same rate. That is, the insulating films 103 above and below the vibration film 105 are formed simultaneously, and they have the same thickness and the same stress. Thus, a thermal silicon oxide film having the same thickness is formed on the surface facing the gap between the first electrodes and the surface facing the gap between the vibration films. Accordingly, since the vertical stress is balanced, there is an advantage that the vibration film 105 has little bending and is substantially horizontal. Next, the sealing film 113 is deposited in the same manner as in the step shown in FIG. 3A of the second embodiment, and the etching hole 107 is sealed as shown in FIG. 108 is formed.

  Next, dry etching is performed without patterning in the same manner as in the step shown in FIG. 3B of the second embodiment, and the sealing film 113 (silicon nitride) on the substrate surface as shown in FIG. Film). Since dry etching has anisotropy, the sidewall insulating film 112 and the sealing film 113 remain on the sidewall of the formed cavity 109.

  Next, as shown in FIG. 5-3 (h), patterning is performed on the surface of the substrate and dry etching is performed to form an etching hole 138. Then, an etching groove 136 around the through silicon via is formed on the back surface of the substrate by deep dry etching. In order to electrically connect the vibration film 105 serving as the second electrode 106 to the through silicon via 135 in the handle layer, the etching hole 138 needs to be dug up to the handle layer 115. That is, a signal generated in the vibration film 105 serving as the second electrode can be extracted to the back side of the substrate by the through silicon via 135. In order to insulate the through silicon via 135 from the handle layer 115 of the first electrode, the etching groove 136 needs to be dug up to the box layer 116. FIG. 5-3 (i) shows a horizontal plan view of the dotted line A-A ′ at the box layer level in FIG. 5-3 (h). In other words, the range A-A ′ in FIG. 5C is a cross-sectional view taken along the dotted line A-A ′ in FIG.

  Next, as shown in FIG. 5-3 (j), a conductive film is formed in the etching hole 138 to form a conductive through wiring portion 137. On the other hand, on the back surface of the substrate, the surface of the silicon through wiring 135 and a part of the surface of the first electrode 102 are etched to expose silicon, and a conductive film is formed to form the second electrode pad 120 and A pad 121 of the first electrode is formed. FIG. 5-3 (k) is a horizontal plan view of a dotted line A-A ′ at the box layer level in FIG. 5-3 (j). In other words, the range of A-A ′ in FIG. 5-3 (j) shows a cross-sectional view taken along the dotted line A-A ′ in FIG. 5-3 (k).

  In the first to fourth embodiments, when a plurality of cells are arranged in series, the cavities of the plurality of cells in series can be collectively formed by an etching process through a single etching hole. That is, if the etching hole 107 is arranged at a position opposite to the pad (or the through wiring portion), a plurality of cells adjacent in series can be formed, and the group of cells connected in series constitutes one element. Can do.

(Example 5)
In the above-described Examples 1 to 4, the example in which three adjacent cells are connected in series to the pad (or the through wiring portion) is shown. In the fifth embodiment, an example is shown in which three cells are not adjacently connected in series, but are connected in parallel to pads (or through wiring portions). FIG. 6 illustrating the CMUT of Example 5 shows a horizontal view of a box layer level in which three cells are connected in parallel to the through wiring portion. The CMUT in this embodiment is formed in the same manner as in the fourth embodiment. As shown in FIG. 6, the plurality of cells 101, 201, 301 are connected in parallel to one pad (or through wiring portion 137). According to this embodiment, a plurality of cells can be connected in parallel to the same pad (or through wiring portion).

(Other embodiments)
The transducer can be applied to a subject information acquisition apparatus such as an ultrasonic diagnostic apparatus. The transducer receives the acoustic wave from the subject, and uses the output electrical signal to obtain subject information that reflects the subject's optical characteristic values, such as the light absorption coefficient, and subject information that reflects the difference in acoustic impedance. it can.

  More specifically, an example of the information acquisition apparatus irradiates a subject with light (electromagnetic waves including visible light, infrared light, etc.). Thus, photoacoustic waves generated at a plurality of positions (parts) in the subject are received, and characteristic distributions indicating distributions of characteristic information respectively corresponding to the plurality of positions in the subject are acquired. The characteristic information acquired by the photoacoustic wave indicates characteristic information related to light absorption. The initial sound pressure of the photoacoustic wave generated by light irradiation, the light energy absorption density derived from the initial sound pressure, or the absorption coefficient And characteristic information reflecting the concentration of substances constituting the tissue. The substance concentration is, for example, oxygen saturation, total hemoglobin concentration, oxyhemoglobin or deoxyhemoglobin concentration. The information acquisition device can also be used for the diagnosis of human or animal malignant tumors, vascular diseases, etc., and the follow-up of chemical treatment. Therefore, the subject is assumed to be a living body, specifically, a diagnosis target such as a breast, neck or abdomen of a human or animal. As the light absorber inside the subject, there is a tissue having a relatively high absorption coefficient inside the subject. For example, if a part of the human body is a subject, there are oxyhemoglobin or deoxyhemoglobin, blood vessels containing many of them, tumors containing many new blood vessels, and plaques on the carotid artery wall. Furthermore, molecular probes that specifically bind to malignant tumors using gold particles or graphite, capsules that transmit drugs, and the like are also light absorbers.

  In addition to the reception of photoacoustic waves, the distribution of the acoustic characteristics in the subject is obtained by receiving the reflected waves from the ultrasonic echoes reflected by the ultrasound transmitted from the probe including the transducer in the subject. You can also The distribution relating to the acoustic characteristics includes a distribution reflecting the difference in acoustic impedance of the tissue inside the subject.

  FIG. 7A shows an information acquisition device using the photoacoustic effect. The pulsed light oscillated by the light source 2010 is applied to the subject 2014 via an optical member 2012 such as a lens, a mirror, or an optical fiber. The light absorber 2016 inside the subject 2014 absorbs the energy of the pulsed light and generates a photoacoustic wave 2018 that is an acoustic wave. The transducer 2020 of the present invention in the probe unit 2022 receives the photoacoustic wave 2018, converts it into an electrical signal, and outputs it to the front end circuit of the probe unit. The front-end circuit performs signal processing such as a preamplifier and sends it to the signal processing unit 2024 of the main body through the connection unit. The signal processing unit 2024 performs signal processing such as A / D conversion and amplification on the input electrical signal, and outputs the same to the data processing unit 2026 of the main body unit. The data processing unit 2026 acquires object information (characteristic information reflecting the optical characteristic value of the object such as a light absorption coefficient) as image data using the input signal. Here, the signal processing unit 2024 and the data processing unit 2026 are collectively referred to as a processing unit. The display unit 2028 displays an image based on the image data input from the data processing unit 2026. The probe unit 2022 and the main body unit may be integrated.

  FIG. 7B shows an information acquisition apparatus such as an ultrasonic echo diagnostic apparatus using acoustic wave reflection. The acoustic wave transmitted from the transducer 2120 of the present invention in the probe unit 2122 to the subject 2114 is reflected by the reflector 2116. The transducer 2120 receives the reflected acoustic wave (reflected wave) 2118, converts it into an electrical signal, and outputs it to the front end circuit in the probe unit. The front-end circuit performs signal processing such as a preamplifier and sends it to the signal processing unit 2124 of the main body through the connection unit. The signal processing unit 2124 performs signal processing such as A / D conversion and amplification on the input electrical signal, and outputs the same to the data processing unit 2126 of the main body. The data processing unit 2126 acquires object information (characteristic information reflecting a difference in acoustic impedance) as image data using the input signal. Here, the signal processing unit 2124 and the data processing unit 2126 are also referred to as a processing unit. The display unit 2128 displays an image based on the image data input from the data processing unit 2126. In this case, the probe unit 2122 and the main body unit may be integrated.

  The probe unit may be one that mechanically scans, or one that a user such as a doctor or engineer moves with respect to the subject (handheld type). In the case of a device that uses reflected waves as shown in FIG. 7B, a probe that emits an acoustic wave may be provided separately from the receiving probe. Further, the apparatus has both the functions of the apparatus of FIG. 7A and FIG. 7B, and the object information reflecting the optical characteristic value of the object and the object information reflecting the difference in acoustic impedance, Both of them may be acquired. In this case, the transducer 2020 in FIG. 7A may transmit not only the photoacoustic wave but also the acoustic wave and the reflected wave.

  101, 201, 301... Cell 102.. First electrode (lower electrode) 105.. Vibrating membrane 106. Second electrode (upper electrode) 109 109 cavity (gap) 112 Support portion (side wall insulating film, etching stop insulating film), 115.. Handle layer (first layer), 116.. Box layer (second layer), 117... Active layer (third layer), 118, 119.・ Connection part (cell-cell connection part, cell-pad connection part), 122 ..groove

Claims (22)

A capacitive transducer having a plurality of cells having a structure including a first electrode and a vibrating membrane including a second electrode provided with a gap from the first electrode,
A first layer including a portion to be the first electrode, a second layer including a portion to be etched to form the gap, and a third layer including a portion to be at least a part of the vibration film are in a plate shape Are formed using a substrate laminated in this order,
A connecting portion connected to the cell and a groove defining the cell are formed through the third layer and the second layer to reach the first layer;
An insulating film that is a support portion for supporting the vibration film and the connection portion is formed on a side wall of the groove on the cell and the connection portion side,
The gap between the first electrode and the second electrode is formed by etching the second layer;
The capacitance type transducer is characterized in that the connection portion and the cell are connected so as to include the third layer in common.   The capacitive transducer according to claim 1, wherein the substrate is an SOI substrate having a handle layer, a box layer, and an active layer.   3. The electrostatic capacitance type according to claim 2, wherein a thermal silicon oxide film having the same thickness is provided on a surface facing the gap of the first electrode and a surface facing the gap of the vibration film. Transducer.   4. The capacitive transducer according to claim 1, wherein the connection portion is narrower than the cell. 5.   5. The capacitive transducer according to claim 1, wherein the connection portion has a cross-linked structure in which a portion of the second layer is etched. 6.   The capacitive transducer according to claim 1, wherein at least a part of the support portion is formed of a nitride film.   The capacitive transducer according to any one of claims 1 to 6, wherein at least a part of the support portion is formed of a polycrystalline silicon film.   The second electrode is formed on the third layer of the cell, and an electrical wiring electrically connected to the second electrode is formed on the third layer of the connection portion. The capacitive transducer according to any one of claims 1 to 7, wherein A vibration film including a first electrode; a second electrode located at a distance from the first electrode; and a support portion located on the first electrode and supporting the vibration film. A capacitive transducer having a plurality of structured cells,
The capacitive transducer according to claim 1, wherein the supporting portion supports the vibrating membrane in contact with a side portion of the supporting portion. A connection part coupled to the cell; and a support part for supporting the connection part,
The support part supporting the connection part supports the connection part in contact with the side part of the support part,
The capacitive transducer according to claim 9, wherein the connection portion and the cell are connected to each other including a common layer.   The second electrode is formed on the common layer of the cell, and an electrical wiring electrically connected to the second electrode is formed on the common layer of the connection portion. The capacitive transducer according to claim 10, wherein   The capacitive transducer according to claim 9, wherein at least a part of the support portion is formed of a nitride film.   The capacitive transducer according to claim 9, wherein at least a part of the support portion is formed of a polycrystalline silicon film. A method for producing a capacitive transducer according to any one of claims 1 to 9,
Preparing the substrate;
Forming the groove by etching through the first layer and the second layer to the third layer;
Forming an insulating film constituting the support portion on the side wall of the groove;
Forming an etching hole for etching the second layer;
Etching the second layer through the etching holes to form the gap;
A manufacturing method characterized by comprising:   The manufacturing method according to claim 14, wherein the groove is formed by dry etching.   The manufacturing method according to claim 14, wherein the insulating film constituting the support portion is formed by LPCVD.   The manufacturing method according to claim 14, further comprising a step of sealing the etching hole.   The manufacturing method according to claim 14, wherein the substrate is an SOI substrate having a handle layer, a box layer, and an active layer.   19. The manufacturing method according to claim 18, further comprising the step of thermally oxidizing after etching the second box layer to form a thermal oxide film on a silicon surface exposed to the atmosphere. A capacitance type transducer according to any one of claims 1 to 19, and a processing unit that acquires and processes information on an object using an electrical signal output from the capacitance type transducer. And
The subject information acquisition apparatus, wherein the capacitive transducer receives an acoustic wave from a subject and outputs the electrical signal. Having a light source,
21. The subject information according to claim 20, wherein the capacitive transducer receives an acoustic wave generated by irradiating the subject with light oscillated from the light source and converts the acoustic wave into an electrical signal. Acquisition device.   The object information acquiring apparatus according to claim 20, wherein the capacitive transducer emits an acoustic wave to the object.