CN114620673A - Ultrasonic transducer cell with CMUT combined with MEMS pressure sensor, array and manufacturing method - Google Patents
Ultrasonic transducer cell with CMUT combined with MEMS pressure sensor, array and manufacturing method Download PDFInfo
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Abstract
The invention discloses an ultrasonic transducer unit, an array and a manufacturing method of a CMUT combined MEMS pressure sensor. The invention also discloses a manufacturing method of the ultrasonic transducer unit of the CMUT combined MEMS pressure sensor, which adopts the active wafer bonding and thinning technology to stack the CMOS wafer and the MEMS pressure sensor wafer so as to manufacture the CMUT-on-CMOS, thereby realizing the three-dimensional framework of vertical interconnection and obviously improving the chip integration level.
Description
Technical Field
The invention relates to the technical field of MEMS-on-CMOS high-density monolithic integrated semiconductor sensors, in particular to a novel structure and a processing technology for integrating a three-dimensional CMUT (micro-machined structure) with an MEMS pressure sensor.
Background
In recent years, with the rapid development of ultrasonic products and applications, piezoelectric microstructure ultrasonic transducers have been widely used. But low ultrasonic transducer signal response is a common problem. Under the existing ultrasonic transducer unit architecture, through the optimization of the film thickness and the structural layout, the sensitivity can be improved to a certain degree, but the improvement amplitude still needs to be improved.
On the other hand, after a traditional MEMS silicon-based piezoresistance Sensor (Piezo-Resistive Sensor) is optimized, the pressure sensitivity can exceed that of the existing PZT or aluminum nitride ultrasonic transducer. If the MEMS pressure sensor can be combined with the ultrasound transducer unit to superimpose the output signal of the MEMS pressure sensor on the output signal of the ultrasound transducer, the sensitivity can be enhanced, for example, the sensitivity of the existing ultrasound transducer can be enhanced by 100-. However, the structure and process flow of the conventional MEMS pressure sensor are very different from those of the conventional ultrasonic transducer device, and monolithic integration is difficult to achieve.
MEMS pressure sensor:
MEMS pressure sensors have found widespread use. A typical MEMS pressure sensor structure and equivalent circuit schematic is shown in fig. 1. Wherein (a) is a layout design plan view and a cross-sectional view; there are four silicon resistors, formed by P + diffusion regions in an N-well, laid out in a silicon single crystal film (Membrane) over a closed cavity volume (Sealed cavity). Under the external pressure, the Membrane film deforms due to the space provided by the cavity body. The resistance value of the deformed P + silicon resistor changes, the change of the resistance value is in direct proportion to the external pressure, and if the design is reasonable, a linear relation is formed in a certain pressure range. (b) Is a bridge circuit diagram formed by four piezoresistors interconnected, and the connection can maximize the output voltage signal Vout of the MEMS pressure sensor.
FIG. 2 is a three-dimensional structure of a typical semiconductor process fabricated MEMS pressure sensor: piezoresistor (R in the figure)1，R2，R3) Is made in the silicon epitaxial thin layer and is positioned above the cavity body. Under the external pressure, the silicon thin layer on the cavity body deforms, the resistance value of the silicon material changes due to the piezoelectric effect, and the piezoelectric sensing is realized in the process. The semiconductor material is a silicon single crystal with a crystal orientation (100), a P-type silicon substrate, an N-type epitaxial layer or forms N-well isolation. The piezoresistor is formed by P + diffusion in the N trap. The position of the diffusion resistor layout is as close as possible to the position where the Membrane generates the maximum deformation, and this position can be simulated by software (such as Commol simulation)n) is determined. The cavity shown provides room for the Membrane to deform under pressure. The lowest air outlet hole is designed for the pressure sensor with the Membrane having great deformation, and is used for eliminating the damping effect of air. For ultrasonic applications, the deformation of the Membrane is very small and no vent holes may be used.
An ultrasonic transducer:
the Ultrasonic transducers are classified into PMUT (piezoelectric micro Ultrasonic transducers) and CMUT (capacitive micro Ultrasonic transducers), and the schematic structural diagrams thereof are shown in fig. 3, where CMUT is on the left and PMUT is on the right. The commonality is that they are both designed with a movable Membrane, they are both designed with a hollow cavity, and they are both designed with two electrodes. The difference is that the CMUT is designed with upper and lower electrodes similar to capacitors, the upper electrode can move, and the lower electrode is fixed. After alternating current is applied to two poles of the capacitor to generate different charges, the like charges repel and the opposite charges attract, so that the upper electrode vibrates. The PMUT is excited by an electric field, and the atomic lattice of the piezoelectric material is displaced, so that the material expands or contracts along the direction of the displacement of the lattice, thereby vibrating up and down in the vertical direction. The PMUT upper and lower electrodes move simultaneously.
A typical CMUT piezoelectric ultrasound transducer structure is shown in fig. 4, and comprises: substrate material 110, cavity body 120, mechanical layer 130, lower metal layer 112, and upper metal layer 114.
The traditional MEMS pressure sensor architecture and process flow have great difference with the existing ultrasonic transducer device architecture and process flow, namely CMUT or PMUT, and monolithic integration is difficult to realize.
Disclosure of Invention
The invention aims to provide a novel architecture integrating a MEMS pressure sensor and a CMUT (micro-machined device) and a process flow thereof, wherein the output signals of the MEMS pressure sensor and the CMUT are superposed through a specific structure, so that the sensitivity of receiving signals is obviously improved. Meanwhile, three-dimensional vertical interconnection is utilized, the size of the CMUT unit is not increased, and the area of a chip is not increased.
In order to achieve the object, an embodiment of the present invention provides an ultrasonic transducer cell of a CMUT combined MEMS pressure sensor, which is formed by bonding a first wafer and a second wafer, where a silicon substrate layer of the first wafer is pre-fabricated with a first CMOS circuit and a first CMOS circuit metal interconnection layer required by the CMUT, and a silicon substrate layer of the second wafer is pre-fabricated with a MEMS piezoresistor bridge interconnection circuit; a cavity body is arranged right below the center of the MEMS piezoresistor bridge type interconnection circuit layout in the substrate material layer of the first wafer or the second wafer, and the CMUT and the MEMS pressure sensor share the cavity body; thinning the back of a silicon substrate layer of the second wafer to form a monocrystalline silicon thin layer, wherein the monocrystalline silicon thin layer is used as the silicon substrate of the MEMS piezoresistor and also used as a mechanical layer of the CMUT; a first metal wiring layer is arranged in a substrate material layer of the first wafer, and a second metal wiring layer and an MEMS pressure sensor metal interconnection layer are arranged in a substrate material layer of the second wafer; a lower metal layer of the CMUT is arranged in a substrate material layer of the first wafer below the cavity body, and an upper metal layer of the CMUT is arranged in a substrate material layer of the second wafer above the cavity body; the first wafer and the second wafer are electrically connected through vertical interconnection among the upper metal layer, the lower metal layer, the MEMS pressure sensor metal interconnection layer, the first metal wiring layer, the second metal wiring layer and the first CMOS circuit metal interconnection layer, and the process includes superposing an output signal of the MEMS pressure sensor into an output signal of the CMUT.
Another embodiment of the present invention provides an array chip characterized by comprising a plurality of said CMUT associated MEMS pressure sensor ultrasound transducer cells.
Another embodiment of the present invention provides a method for manufacturing an ultrasonic transducer cell with a CMUT integrated with a MEMS pressure sensor, which is characterized by comprising the steps of:
preparing a first wafer and a second wafer, respectively forming silicon substrate layers, manufacturing a first CMOS circuit and a first CMOS circuit metal interconnection layer on the first wafer silicon substrate layer, and manufacturing an MEMS piezoresistor bridge type interconnection circuit on the second wafer silicon substrate layer;
respectively depositing substrate material layers on a first wafer silicon substrate layer and a second wafer silicon substrate layer, manufacturing a first metal wiring layer, a second metal wiring layer, an MEMS pressure sensor metal interconnection layer, an upper metal layer and a lower metal layer of a CMUT, and respectively manufacturing vertical interconnection structures for realizing the electrical connection inside the first wafer and the second wafer;
manufacturing a cavity body on the substrate material layer of the first wafer or the second wafer;
bonding the first wafer and the second wafer;
thinning the back of the second wafer silicon substrate layer to form a monocrystalline silicon thin layer;
manufacturing a vertical interconnection structure for realizing electrical connection between the first wafer and the second wafer;
depositing an oxide layer and an additional metal interconnection layer on the monocrystalline silicon thin layer;
vertical interconnect structures are fabricated that enable electrical connection between the additional metal interconnect layer and the first wafer and/or the second wafer.
The invention has the beneficial effects that:
the ultrasonic transducer unit of the CMUT combined MEMS pressure sensor adopts active wafers (a first wafer with a CMOS circuit required by the CMUT and a second wafer with the MEMS pressure sensor) to perform fusion bonding and thinning, then the ultrasonic transducer is manufactured, an MEMS pressure resistor is positioned in a mechanical layer of the ultrasonic transducer, the MEMS pressure sensor and the ultrasonic transducer share a cavity body, a three-dimensional vertically interconnected three-dimensional framework is adopted, three-dimensional monolithic integration of the MEMS pressure sensor, a CMUT array and the CMOS circuit is realized, an output signal of the MEMS pressure sensor is superposed to an output signal of the ultrasonic transducer, the overall response is improved, and the sensitivity of an ultrasonic probe is effectively enhanced. The invention adopts a three-dimensional vertical interconnection three-dimensional framework, does not increase the size of the CMUT unit, does not increase the area of the chip, and obviously improves the integration level of the chip.
Drawings
FIG. 1 is a schematic diagram of a prior art MEMS pressure sensor structure and equivalent circuit, wherein (a) is a layout plan view and a cross-sectional view, and (b) is a bridge circuit diagram formed by interconnecting four piezoresistors;
FIG. 2 is a schematic diagram of a three-dimensional structure of a MEMS pressure sensor fabricated by a prior art semiconductor process;
FIG. 3 is a schematic view of a prior art ultrasonic transducer configuration;
figure 4 is a schematic diagram of a prior art CMUT structure;
fig. 5 is a structural diagram of an ultrasonic transducer unit of the CMUT combined with the MEMS pressure sensor of the first embodiment;
FIG. 6 is a cross-sectional view of a first wafer according to one embodiment;
FIG. 7 is a schematic cross-sectional view of a second wafer according to one embodiment;
FIG. 8 is a process flow diagram of an embodiment three CMOS circuit fabrication process;
FIG. 9 is a flowchart of an embodiment three MEMS pressure sensor fabrication process;
FIG. 10 is a schematic view illustrating bonding of a third wafer and a second wafer according to one embodiment;
FIG. 11(a) is one exemplary illustration of a vertical interconnect structure of a first wafer and a second wafer according to an embodiment;
FIG. 11(b) is a second exemplary diagram of the vertical interconnect structure of the first wafer and the second wafer according to the first embodiment;
FIG. 12 is a third exemplary diagram of vertical interconnect structures of the first wafer and the second wafer according to the third embodiment;
FIG. 13 is a schematic diagram of the output signal of the MEMS pressure sensor in the fourth embodiment;
FIG. 14 is a schematic diagram of the CMUT output signals in the fourth embodiment;
fig. 15 is a schematic diagram of signal superposition in the fourth embodiment;
fig. 16 is a circuit diagram for superimposing signals in the fourth embodiment.
Detailed Description
Example one
As shown in fig. 5, the present embodiment provides an ultrasonic transducer cell of a CMUT integrated MEMS pressure sensor, which is formed by low temperature fusion bonding of a first wafer and a second wafer through a substrate material layer, where 122 is a bonding interface. The first wafer and the second wafer are active wafers, wherein a first CMOS circuit 160-1 and a first CMOS circuit metal interconnection layer 201 required for CMUT operation are prefabricated in a silicon substrate layer 160 of the first wafer, for example, high voltage pulse generation, a pulse modulation circuit, a signal amplifier, etc. required for driving the CMUT are generated, so the first wafer is called a CMOS wafer. MEMS piezoresistor bridge interconnection circuits of the MEMS pressure sensors are prefabricated in the silicon substrate layer 130 of the second wafer, and in the figure, R-101 and R-102 represent MEMS piezoresistors, so that the second wafer is called an MEMS piezoresistor wafer. A MEMS pressure sensor unit has 4 MEMS piezoresistors, and when the layout of layout is adopted, the resistors are distributed at the position where the mechanical layer has larger mechanical deformation and are interconnected to form a resistor bridge circuit, and the bridge circuit can maximize the output voltage signal of the piezoelectric sensor. And thinning the back of the silicon substrate layer of the second wafer to form a monocrystalline silicon thin layer, wherein the thickness of the monocrystalline silicon thin layer is 1-6 microns, and the monocrystalline silicon thin layer is used as a silicon substrate of the MEMS piezoresistor and also used as a mechanical layer of the CMUT.
The ultrasonic transducer unit adopts the design that the CMUT and the MEMS pressure sensor share the cavity body, the cavity body is arranged right below the layout center of the MEMS piezoresistor bridge type interconnection circuit, and the cavity body not only provides space for the mechanical vibration of the Membrane film in the CMUT, but also provides space for the deformation of the Membrane film in the MEMS pressure sensor. The cavity body may be disposed in a substrate material layer of a first wafer (as shown in fig. 6, 10, 11(a), and 11 (b)), or may be disposed in a substrate material layer of a second wafer (as shown in fig. 5 and 12), the cavity body is located right below the center of the layout of the MEMS piezoresistive bridge interconnection circuit after the two wafers are bonded, and the MEMS piezoresistive bridge interconnection circuit is distributed at the boundary between the cavity body and the silicon substrate and located right above the cavity body. In this embodiment, the cavity is disposed in the second wafer substrate material layer, the 4 MEMS piezoresistors are symmetrically distributed around the cavity (as shown in fig. 1 (a)), and the center position of the cavity overlaps with the arrangement center position of the four resistors.
A first metal wiring layer 202 is arranged in the substrate material layer of the first wafer, and a second metal wiring layer 302 and a MEMS pressure sensor metal interconnection layer 301 are arranged in the substrate material layer of the second wafer. A lower metal layer 112 of the CMUT is disposed in a substrate material layer of the first wafer below the cavity body 120, and an upper metal layer 114 of the CMUT is disposed in a substrate material layer of the second wafer above the cavity body 120; the first wafer and the second wafer are electrically connected through vertical interconnection among the upper metal layer 114, the lower metal layer 112, the MEMS pressure sensor metal interconnection layer 301, the first metal wiring layer 202, the second metal wiring layer 302, and the first CMOS circuit metal interconnection layer 201, and the electrical connection includes superimposing an output signal of the MEMS pressure sensor into an output signal of the CMUT, thereby effectively enhancing the sensitivity of ultrasonic detection.
An oxide layer 600 is arranged above a mechanical layer of the CMUT, an additional metal interconnection layer 401 is arranged above the oxide layer 600, the additional metal interconnection layer 401 is vertically connected to a metal layer of the first wafer and/or the second wafer through the TOV 400, the additional metal interconnection layer 401 increases connection efficiency through the TOV 400, flexible design of circuit connection is facilitated, and the additional metal interconnection layer 401 can be used for realizing metal interconnection between CMUT cells required by array wiring, and required power supply lines, ground lines, and the like.
According to the ultrasonic transducer unit, the output signals of the MEMS pressure sensor are superposed into the output signals of the CMUT through the vertical interconnection between the first wafer and the second wafer. The vertical interconnection structure between the first wafer and the second wafer can be realized by Through silicon Oxide vias (TOV, Through Oxide Via, as shown in the black part in the figure), metal connection holes, metal lead holes, and the like. The vertical interconnection structure between the first wafer and the second wafer has a plurality of connection combinations, and those skilled in the art can flexibly design the vertical interconnection structure according to the circuit layout, and fig. 11(a), 11(b) and 12 respectively illustrate one of the possible connection combinations.
In this embodiment, the connection combination manner shown in fig. 12 is adopted, the lower metal layer 112 of the CMUT is interconnected with the first metal wiring layer 202, and the upper metal layer 114 of the CMUT is interconnected with the MEMS pressure sensor metal interconnection layer 301; the MEMS piezoresistor bridge interconnection circuit is interconnected with the MEMS pressure sensor metal interconnection layer 301, the MEMS pressure sensor metal interconnection layer 301 and the second metal wiring layer 302 are vertically interconnected through a metal connection hole 312, the second metal wiring layer 302 is vertically interconnected with the first metal wiring layer 202 through a TOV, and the first metal wiring layer 202 and the first CMOS circuit metal interconnection layer 201 are vertically interconnected through a metal connection hole 212, so that respective internal electrical connection of the first wafer and the second wafer and electrical connection between the first wafer and the second wafer are realized, and an output signal of the MEMS pressure sensor is superimposed into an output signal of the CMUT. And the first CMOS circuit of the first wafer silicon substrate layer comprises a circuit structure for realizing superposition of the output signal of the MEMS pressure sensor and the output signal of the CMUT.
The interconnection between the lower metal layer 112 of the CMUT and the first metal wiring layer 202, and the upper metal layer 114 of the CMUT and the MEMS pressure sensor metal interconnection layer 301 can be realized by different flexible connection manners. In this embodiment, the connection in the vertical direction is adopted. The upper metal layer 114 is vertically interconnected with the first metal wiring layer 202 through the TOV, the first metal wiring layer 202 is vertically interconnected with the second metal wiring layer 302 through the TOV, and the second metal wiring layer 302 is vertically interconnected with the MEMS pressure sensor metal interconnection layer 301 through the metal connection hole 312, so that interconnection between the upper metal layer 114 of the CMUT and the MEMS pressure sensor metal interconnection layer 301 can be realized. The lower metal layer 112 is vertically interconnected with the first CMOS circuit metal interconnection layer 201 through a metal connection hole, and the first CMOS circuit metal interconnection layer 201 is vertically interconnected with the first metal wiring layer 202 through a metal connection hole 212, so that interconnection between the lower metal layer 112 of the CMUT and the first metal wiring layer 202 can be realized.
According to the requirements of CMOS circuit design, the first metal wiring layer 202 and the second metal wiring layer 302 may include more than one metal wiring layer, and the metal wiring layers may be vertically interconnected through structures such as TOV, metal connection hole, metal lead hole, etc., wherein the top metal wiring layer of the first metal wiring layer is vertically interconnected with the second metal wiring layer 302, and the bottom metal wiring layer is vertically interconnected with the first CMOS circuit metal interconnection layer 201. The top layer metal wiring of the second metal wiring layer is vertically interconnected with the MEMS pressure sensor metal interconnection layer 301, and the bottom layer metal wiring is vertically interconnected with the first metal wiring layer 202. The present embodiment gives only an example in which the first metal wiring layer and the second metal wiring layer have one metal wiring layer, respectively.
When the bonding is completed and the second wafer is thinned, the electrical connection between the first wafer and the second wafer is realized by manufacturing the TOV, wherein the TOV includes necessary power lines, ground lines, signal lines, control line connections and the like. Firstly, photoetching corrosion penetrates through the second wafer, silicon side surface oxidation, oxide layer deposition and CMP polishing are carried out, further, photoetching corrosion penetrates through silicon dioxide, and the MEMS pressure sensor metal interconnection layer 301 of the second wafer, the second metal wiring layer 302 of the second wafer and the first metal wiring layer 202 of the first wafer are corroded. According to the design requirement of circuit connection, the TOV is mainly connected with a power line, a ground line, a signal line, a control line and the like.
In order to highlight the TOV connection between the two wafers, the drawings of the second metal wiring layer and the interconnection structures between the second metal wiring layer and the MEMS pressure sensor metal interconnection layer and between the second metal wiring layer and the MEMS pressure sensor metal interconnection layer are omitted in fig. 11(a) and 11(b), and the example of fig. 12 may be referred to for the design of the interconnection structures between the second metal wiring layer and the MEMS pressure sensor metal interconnection layer and between the second metal wiring layer and the first metal wiring layer.
As shown in fig. 11(a), the left TOV is connected to the first metal wiring layer 202, and further connected to the ground gnd (ground) through the first CMOS circuit metal interconnection layer 201; the intermediate TOV is connected to the MEMS pressure sensor metal interconnect layer 301 as part of the piezoresistive interconnect; the right TOV is connected to the MEMS pressure sensor metal interconnect layer 301, which in turn is connected to the first metal wiring layer 202, the first CMOS circuit metal interconnect layer 201, and finally to the power supply line VDD. The upper ends of the TOVs are respectively connected to the additional metal layers according to an electrical connection design.
As shown in fig. 11(b), the left TOV is connected to the first metal wiring layer 202 and the first CMOS circuit metal interconnection layer 201, and is connected to the first wafer CMOS circuit, and the middle TOV is connected to the MEMS pressure sensor metal interconnection layer 301, and is further connected to the first metal wiring layer 202 and the first CMOS circuit metal interconnection layer 201, and is connected to the first wafer CMOS circuit, so as to implement signal transmission. The right TOV is connected to the control terminal of the first wafer CMOS circuit in the same connection way as the middle TOV. The upper ends of the TOVs are respectively connected to the additional metal layers according to an electrical connection design.
In this embodiment, a second CMOS circuit 300-1 is further prefabricated in the second wafer silicon substrate layer, and the second CMOS circuit 300-1 is interconnected with the MEMS pressure sensor metal interconnection layer 301. The second CMOS circuit 300-1 includes a differential amplifier, a two-stage low noise amplifier, etc. required for the MEMS piezoresistor bridge interconnect circuit.
Regarding the vertical connection between the metal layers in the present invention, this embodiment only illustrates a partial way of implementing the vertical connection, and according to the teaching of this embodiment, a person skilled in the art can flexibly arrange, and the implementation way is not limited to this embodiment.
Example two
The present embodiment provides an array chip including a plurality of ultrasonic transducer cells of the CMUT integrated MEMS pressure sensor of the first embodiment. The design of the array chip for product application comprises a linear array and an area array, wherein the linear array of 1X128 bits is taken as an example, 128 ultrasonic transducer units are arranged, the lower metal layer of each unit is connected to a common ground wire, and the upper metal layer of each unit is respectively connected to a 128-bit signal wire. In the transmission mode, the 128-bit signal line is supplied with a high level at a designed timing, and an ultrasonic wave is transmitted. In a receiving mode, a 128-bit CMUT + MEMS PRS (piezoelectric-Resistive-Sensor) combination unit is used, and the CMUT and the MEMS PRS respectively acquire piezoelectric signals and send the piezoelectric signals to an adder for superposition and amplification.
EXAMPLE III
The present embodiment provides a method for manufacturing an ultrasonic transducer cell of a CMUT combined with a MEMS pressure sensor according to the first embodiment, and the main process route includes:
a first wafer fabricating the CMOS circuitry required for CMUT, a second wafer fabricating the MEMS pressure sensor;
manufacturing a cavity body from the second wafer;
the CMOS wafer and MEMS wafer are face-to-face fusion bonded;
performing special back thinning on the bonded second wafer to form a mechanical layer required by the CMUT array and a silicon substrate of the MEMS piezoresistor, with the MEMS pressure sensor in the mechanical layer;
the CMUT array is vertically interconnected with the MEMS pressure sensor and the CMOS circuit, implementing a MEMS-on-CMUT-on-CMOS architecture, comprising:
TOV process to achieve device interconnection between the first and second wafers;
routing process steps required for CMUT arrays, fabrication of arrays;
the method for manufacturing the ultrasonic transducer unit of the CMUT combined MEMS pressure sensor specifically comprises the following steps:
the CMOS circuit is fabricated using standard processes in the industry, and the process flow is shown in fig. 8.
Step 2, depositing a substrate material layer on a silicon substrate layer of a first wafer, and manufacturing a first CMOS circuit metal interconnection layer, a first metal wiring layer and a vertical interconnection structure in the first wafer;
and 3, preparing a second wafer, forming a silicon substrate layer, manufacturing an MEMS piezoresistor bridge type interconnection circuit, depositing a substrate material layer on the silicon substrate layer of the second wafer, and manufacturing an MEMS pressure sensor metal interconnection layer, a second metal wiring layer and a vertical interconnection structure in the second wafer.
According to the requirements of CMOS circuit design, the first and second metal wiring layers can comprise more than one layer of metal wiring, and the metal wiring layers can be vertically interconnected through metal lead holes to form a multilayer metal wiring vertical interconnection architecture. The process flow of the embodiment provides great flexibility for the number of wiring layers.
And 4, manufacturing a cavity body in the second wafer substrate material layer. The specific method comprises the following steps: and photoetching to form a Cavity pattern, and corroding the substrate material by adopting a plasma chemical vapor to form a Cavity.
Since the cavity body of the first embodiment is disposed on the second wafer, the manufacturing process of the cavity body of the first embodiment is located at the end of the second wafer preparation process. If the cavity body is disposed on the first wafer, the fabrication process for the cavity body may be correspondingly placed at the end of the first wafer fabrication process.
FIG. 7 is a cross-sectional view of a MEMS piezoresistor fabricated on a second wafer. The P + piezoresistor is arranged in the isolated N-Well (or N type epitaxial layer), and when external pressure is applied, the P + piezoresistor changes the resistance value to generate a piezoelectric signal.
The process flow for manufacturing the MEMS piezoresistor on the second wafer is shown in fig. 9, and mainly includes the following steps:
(1) preparing a P-type silicon material;
(2) forming a thin silicon dioxide layer;
(3) photoetching, ion implantation and diffusion to form N-Well;
(4) photoetching to form a piezoresistance pattern area;
(5) p + ion implantation;
(6) removing the photoresist and performing rapid annealing;
(7) depositing silicon oxide at low temperature;
(8) photoetching to form a piezoresistor contact hole;
(9) depositing interconnection metal, and photoetching, corroding and forming;
(10) silicon dioxide is deposited and CMP polishing is carried out.
When the MEMS piezoresistor and the CMOS circuit are manufactured on the second wafer at the same time, the standard CMOS process flow in the industry may be adopted, and the standard process flow may be used as much as possible to manufacture the MEMS piezoresistor, and the local process of the MEMS piezoresistor may be adjusted according to specific requirements, which is not described herein again.
And 5, performing low-temperature melt bonding on the first wafer and the second wafer to form a bonding interface 122, as shown in fig. 10.
Step 6, thinning the back of the second wafer silicon substrate layer to form a monocrystalline silicon thin layer;
after fusion bonding and thinning, the MEMS pressure sensor is left in a monocrystalline silicon thin layer, namely a CMUT unit mechanical layer, and a cavity body is positioned right below the center of the layout of the MEMS piezoresistor bridge type interconnection circuit, so that a space is provided for mechanical vibration of a Membrane film in the CMUT on one hand, and a space is also provided for deformation of the Membrane film in the MEMS pressure sensor on the other hand.
After step 6 is completed, the main cell structure of the CMUT is also completed. The thickness of the thin layer of formed monocrystalline silicon is very important for the performance and long-term operational reliability of the CMUT, and also has a significant influence on the performance of the CMUT cell and the MEMS pressure sensor, such as the pressure sensitivity in the CMUT receiving mode. The advantages of the single-crystal silicon mechanical layer, in addition to providing excellent mechanical performance and yield of mass production, can be used to locally adjust the thickness of the mechanical layer above the CMUT cavity (for example, adding a silicon etching mask) in the conventional CMOS process, so as to optimize the performance of the CMUT and the MEMS pressure sensor, which is not described herein.
And 7, performing a TOV process for vertically interconnecting the first wafer and the second wafer. There are various connection combinations of TOVs when connecting two wafers, and fig. 11(a) and 11(b) show two examples of connection combinations. When manufacturing the TOV, photoetching and corroding silicon on the design position of the TOV, carrying out oxygen plasma treatment, continuing silicon dioxide deposition, CMP, photoetching and connecting holes, and corroding the silicon dioxide. Thereafter, a metal (e.g., metal tungsten) is deposited to make electrical connection. The TOV also reserves contact sites for the CMUT array and the required power and ground lines while connecting the two wafers.
After TOV, an oxide layer 600 is deposited, and an additional metal interconnect layer 401 is deposited, lithographically, and etched. The additional metal interconnect layer 401 increases the connection efficiency of the cell interior including with the CMOS wafer through the TOV 400, and at the same time, the additional metal interconnect layer 401 implements the metal interconnects between CMUT cells required for array routing, and power supply lines, ground lines, etc. required for the array.
Therefore, the three-dimensional monolithic integration of the MEMS pressure sensor, the CMUT array and the CMOS circuit is realized by adopting the three-dimensional vertically interconnected stereo architecture, the superposition of the output signal of the MEMS pressure sensor and the output signal of the CMUT unit is realized, and the sensitivity of the ultrasonic transducer unit is improved.
Example four
The superposition of the output signal of the MEMS pressure sensor and the output signal of the CMUT cell belongs to the superposition of two analog small signals, and there are various implementation methods.
Referring to fig. 13, a typical MEMS pressure sensor uses four piezoresistors to form a bridge circuit, a current source provides a stable bias, and the bridge circuit outputs a piezoelectric signal Vout to a low-noise amplifier circuit for amplification.
Referring to fig. 14, a CMOS auxiliary circuit block diagram of the CMUT cell in transmit (Transmitter) and receive (Receiver) mode. In a receiving mode, after receiving the ultrasonic reflection wave, the CMUT unit generates a small analog signal, and extracts a low-voltage small analog signal V through a high-low voltage level shift circuitRX_outAnd the output is sent to a low noise amplifier for amplification.
In the present embodiment, the output signal of the MEMS pressure sensor and the output signal of the CMUT are subjected to signal amplitude superposition by an addition operational amplifier, and the principle of the superposition is shown in fig. 15. When the configuration resistance value is Rf＝R1＝R2＝R3Then, an addition operation is implemented, in which case Vo＝－(Vi1+Vi2+Vi3)。
As shown in FIG. 16, the output signal Vout of the MEMS pressure sensor is stored and controlled at the first input terminal of the summing operational amplifier via the timing control signal Clk1, while the output signal V of the CMUT isRX_outAfter voltage conversion and filtering, the time sequence control signal Clk2 is stored and controlled at the second input end of the addition operational amplifier, a signal Vo is obtained through addition, differential superposition and amplification, and the signal Vo replaces the output signal V of the original CMUTRX_outAnd the output signal of the integrated ultrasonic transducer unit is input into a low-noise amplifying circuit for amplification. Compared with the CMUT used alone in the prior art, the present embodiment adds the addition circuit for realizing signal superposition to the CMOS circuit portion supporting the CMUT operation in the first wafer, and designs the corresponding circuit connection, so that the piezoelectric signal output by the MEMS pressure sensor can be superposed to the input of the CMUTAnd (4) outputting signals, thereby improving the signal to noise ratio and greatly improving the sensitivity of the CMUT.
Claims (12)
1. An ultrasonic transducer unit of a CMUT combined MEMS pressure sensor is characterized by being formed by bonding a first wafer and a second wafer, wherein a first CMOS circuit (160-1) and a first CMOS circuit metal interconnection layer (201) required by the CMUT are prefabricated in a silicon substrate layer (160) of the first wafer, and an MEMS piezoresistance bridge interconnection circuit is prefabricated in a silicon substrate layer (130) of the second wafer; a cavity body (120) is arranged in the substrate material layer of the first wafer or the second wafer and is right below the center of the MEMS piezoresistor bridge-type interconnection circuit layout, and the CMUT and the MEMS pressure sensor share the cavity body (120); thinning the back side of a silicon substrate layer (130) of the second wafer to form a monocrystalline silicon thin layer, wherein the monocrystalline silicon thin layer is used as a silicon substrate of the MEMS piezoresistor and also used as a mechanical layer of the CMUT; a first metal wiring layer (202) is arranged in a substrate material layer of the first wafer, and a second metal wiring layer (302) and a MEMS pressure sensor metal interconnection layer (301) are arranged in a substrate material layer of the second wafer; a lower metal layer (112) of the CMUT is disposed in a substrate material layer of the first wafer below the cavity body (120), and an upper metal layer (114) of the CMUT is disposed in a substrate material layer of the second wafer above the cavity body (120); the first wafer and the second wafer are electrically connected through vertical interconnection among the upper metal layer (114), the lower metal layer (112), the MEMS pressure sensor metal interconnection layer (301), the first metal wiring layer (202), the second metal wiring layer (302) and the first CMOS circuit metal interconnection layer (201), and the electrical connection includes superimposing an output signal of the MEMS pressure sensor into an output signal of the CMUT.
2. The CMUT integrated MEMS pressure sensor ultrasound transducer cell of claim 1, wherein the structure implementing the vertical interconnect comprises a through silicon oxide via, a metal connection hole, a metal wire via.
3. The CMUT in combination with the ultrasound transducer cell of the MEMS pressure sensor of claim 1, wherein the MEMS pressure sensor metal interconnect layer (301) is vertically interconnected with the second metal wiring layer (302) by a metal connection hole or a metal lead hole, the second metal wiring layer (302) is vertically interconnected with the first metal wiring layer (202) by a through silicon oxide via, the first metal wiring layer (202) is vertically interconnected with the first CMOS circuit metal interconnect layer (201) by a metal connection hole or a metal lead hole.
4. The CMUT in combination with an ultrasound transducer cell of a MEMS pressure sensor as claimed in claim 1, wherein the lower metal layer (112) of the CMUT is interconnected with the first metal wiring layer (202), and the upper metal layer (114) of the CMUT is interconnected with the MEMS pressure sensor metal interconnect layer (301).
5. The CMUT integrated MEMS pressure sensor ultrasound transducer cell of claim 1, characterized in that the first and second metal wiring layers (202, 302) each comprise at least one layer of vertically interconnected metal wiring.
6. The CMUT in combination with an ultrasound transducer cell of a MEMS pressure sensor as claimed in claim 1, characterized in that an oxide layer (600) is arranged above the mechanical layer of the CMUT, an additional metal interconnect layer (401) is arranged above the oxide layer (600), the additional metal interconnect layer (401) is vertically connected to the metal layer of the first wafer and/or the second wafer by through-silicon-oxide vias.
7. The CMUT integrated MEMS pressure sensor ultrasound transducer cell of claim 1, wherein the thickness of the thin layer of single crystal silicon is 1-6 microns.
8. The CMUT in combination with the ultrasonic transducer cell of the MEMS pressure sensor of claim 1, characterized in that the second wafer silicon substrate layer has prefabricated therein a second CMOS circuit (300-1), the second CMOS circuit (300-1) being interconnected with the MEMS pressure sensor metal interconnect layer (301).
9. An array chip characterized by comprising a plurality of CMUT-coupled MEMS pressure sensor ultrasound transducer cells of any of claims 1-8.
10. A method of manufacturing an ultrasound transducer cell with a CMUT bonded to a MEMS pressure sensor according to any of claims 1-8, comprising the steps of:
preparing a first wafer and a second wafer, respectively forming silicon substrate layers, manufacturing a first CMOS circuit and a first CMOS circuit metal interconnection layer on the first wafer silicon substrate layer, and manufacturing an MEMS piezoresistor bridge type interconnection circuit on the second wafer silicon substrate layer;
respectively depositing substrate material layers on the silicon substrate layers of the first wafer and the second wafer, manufacturing a first metal wiring layer, a second metal wiring layer, an MEMS pressure sensor metal interconnection layer, an upper metal layer and a lower metal layer of a CMUT, and respectively manufacturing vertical interconnection structures for realizing the electrical connection inside the first wafer and inside the second wafer;
manufacturing a cavity body on the substrate material layer of the first wafer or the second wafer;
bonding the first wafer and the second wafer;
thinning the back of the silicon substrate layer of the second wafer to form a monocrystalline silicon thin layer;
manufacturing a vertical interconnection structure for realizing electrical connection between the first wafer and the second wafer;
depositing an oxide layer and an additional metal interconnection layer on the monocrystalline silicon thin layer;
vertical interconnect structures are fabricated that enable electrical connection between the additional metal interconnect layer and the first wafer and/or the second wafer.
11. The method of manufacturing an ultrasonic transducer cell of a CMUT integrated MEMS pressure sensor of claim 10, wherein the first wafer and the second wafer are bonded using low temperature fusion.
12. The method of manufacturing an ultrasonic transducer cell of a CMUT integrated MEMS pressure sensor of claim 10, further comprising: a second CMOS circuit and its interconnect structure with the MEMS pressure sensor metal interconnect layer are fabricated in a second wafer silicon substrate layer.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114871084A (en) * | 2022-07-06 | 2022-08-09 | 南京声息芯影科技有限公司 | Digital signal output PMUT unit, chip and ultrasonic equipment |
| CN115117049A (en) * | 2022-07-06 | 2022-09-27 | 南京声息芯影科技有限公司 | CMUT unit, chip and ultrasonic equipment of digital signal output |
| CN118031814A (en) * | 2024-04-11 | 2024-05-14 | 山东誉中新材料股份有限公司 | Hardware height measurement device |
Citations (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102353610A (en) * | 2011-06-10 | 2012-02-15 | 西安交通大学 | Capacitance micro-machining ultrasonic sensor for measuring density and production method thereof |
| CN102620878A (en) * | 2012-03-15 | 2012-08-01 | 西安交通大学 | Capacitive micromachining ultrasonic sensor and preparation and application methods thereof |
| WO2016040333A2 (en) * | 2014-09-08 | 2016-03-17 | Invensense, Inc. | Integrated piezoelectric microelectromechanical ultrasound transducer (pmut) on integrated circuit (ic) for fingerprint sensing |
| CN107764439A (en) * | 2016-08-19 | 2018-03-06 | 上海丽恒光微电子科技有限公司 | The preparation method of pressure sensor |
| CN109244232A (en) * | 2018-09-13 | 2019-01-18 | 徐景辉 | MEMS PZT (piezoelectric transducer) and production method |
| CN113441379A (en) * | 2021-08-27 | 2021-09-28 | 南京声息芯影科技有限公司 | PMUT-on-CMOS unit suitable for high-density integration, array chip and manufacturing method |
| CN113560158A (en) * | 2021-08-27 | 2021-10-29 | 南京声息芯影科技有限公司 | Piezoelectric micromechanical ultrasonic transducer, array chip and manufacturing method |
| CN113666327A (en) * | 2021-08-27 | 2021-11-19 | 南京声息芯影科技有限公司 | SOC (system on chip) PMUT (passive optical network) suitable for high-density system integration, array chip and manufacturing method |
| TW202200967A (en) * | 2020-06-16 | 2022-01-01 | 鴻海精密工業股份有限公司 | Method for making array ultrasonic sensor and array ultrasonic sensor |
-
2022
- 2022-03-18 CN CN202210271258.XA patent/CN114620673B/en active Active
Patent Citations (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102353610A (en) * | 2011-06-10 | 2012-02-15 | 西安交通大学 | Capacitance micro-machining ultrasonic sensor for measuring density and production method thereof |
| CN102620878A (en) * | 2012-03-15 | 2012-08-01 | 西安交通大学 | Capacitive micromachining ultrasonic sensor and preparation and application methods thereof |
| WO2016040333A2 (en) * | 2014-09-08 | 2016-03-17 | Invensense, Inc. | Integrated piezoelectric microelectromechanical ultrasound transducer (pmut) on integrated circuit (ic) for fingerprint sensing |
| CN107764439A (en) * | 2016-08-19 | 2018-03-06 | 上海丽恒光微电子科技有限公司 | The preparation method of pressure sensor |
| CN109244232A (en) * | 2018-09-13 | 2019-01-18 | 徐景辉 | MEMS PZT (piezoelectric transducer) and production method |
| TW202200967A (en) * | 2020-06-16 | 2022-01-01 | 鴻海精密工業股份有限公司 | Method for making array ultrasonic sensor and array ultrasonic sensor |
| CN113441379A (en) * | 2021-08-27 | 2021-09-28 | 南京声息芯影科技有限公司 | PMUT-on-CMOS unit suitable for high-density integration, array chip and manufacturing method |
| CN113560158A (en) * | 2021-08-27 | 2021-10-29 | 南京声息芯影科技有限公司 | Piezoelectric micromechanical ultrasonic transducer, array chip and manufacturing method |
| CN113666327A (en) * | 2021-08-27 | 2021-11-19 | 南京声息芯影科技有限公司 | SOC (system on chip) PMUT (passive optical network) suitable for high-density system integration, array chip and manufacturing method |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114871084A (en) * | 2022-07-06 | 2022-08-09 | 南京声息芯影科技有限公司 | Digital signal output PMUT unit, chip and ultrasonic equipment |
| CN115117049A (en) * | 2022-07-06 | 2022-09-27 | 南京声息芯影科技有限公司 | CMUT unit, chip and ultrasonic equipment of digital signal output |
| CN115117049B (en) * | 2022-07-06 | 2024-06-25 | 南京声息芯影科技有限公司 | Digital signal output CMUT unit, chip and ultrasonic equipment |
| CN118031814A (en) * | 2024-04-11 | 2024-05-14 | 山东誉中新材料股份有限公司 | Hardware height measurement device |
| CN118031814B (en) * | 2024-04-11 | 2024-06-11 | 山东誉中新材料股份有限公司 | Hardware height measurement device |
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|---|---|
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