KR101980785B1 - Back Plate Structure for a MEMS Acoustic Sensor and a Method for fabricating the same - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a back plate structure of a capacitive MEMS acoustic sensor used as a component of a microphone, and a method of manufacturing the same. Due to the difference in the residual stresses of the membranes, the deflection of the back plate is reduced to increase the space to vibrate the membrane, and the dimple portion that prevents the membrane from adhering to the back plate also has a conductive film acting as the back plate electrode to increase the MEMS acoustic sensor capacitance. BACKGROUND OF THE INVENTION A capacitive MEMS acoustic sensor that reduces noise by lowering acoustic resistance of a back plate relates to a back plate structure and a method of manufacturing the same.

Description

Back Plate Structure for a MEMS Acoustic Sensor and a Method for fabricating the same

The present invention relates to a capacitive MEMS acoustic sensor used as a component of a microphone, and removes the phenomenon that the back plate sags toward the membrane due to the difference in residual stress of each layer constituting the back plate. The present invention relates to a back plate structure of a MEMS acoustic sensor, and a method of manufacturing the same, in which an electrode is also inserted into a dimple portion which increases the thickness and prevents the membrane from being attached to the back plate, thereby increasing the capacitance and reducing the acoustic resistance of the back plate.

MEMS (Micro-electromechanical Systems) is a system that includes small (several microns to hundreds of microns) electric machines manufactured using the precision manufacturing techniques of microelectronics. The main examples of MEMS are pressure sensors, vibration accelerometers and acoustic sensors.

The microphone acts as a transducer that converts a voice signal into an electrical signal. It consists of an acoustic sensor that detects a change in sound pressure caused by sound waves, and a readout circuit that converts the detected change into an electrical signal. Used for cordless phones, personal audio equipment, and more. More than 20 years after the first silicon-based microphones were introduced, advances in silicon processing technology have resulted in inexpensive products with high reproducibility and precision for mass production.

The most commonly used acoustic sensor of a microphone is a product that operates on a capacitive principle, and is classified into two types. Among them, ECM (Electret Condenser Microphone) was first commercialized as a capacitive acoustic sensor, and then implemented as MEMS.

The electret of the ECM refers to a polarized dielectric and is a component mounted on the charge storage layer. The ability to accumulate charge eliminates the need for bias voltages. The first ECM was published in 1984 by Hohm and Gerhard-Multhaupt. The electret's charge is vulnerable to soldering temperatures and degrades due to long-term drift, affecting microphone sensitivity. Thus, there have been attempts to apply Teflon to silicon microphones, which have excellent characteristics as electrets, but there are many difficulties in applying Teflon to standard mass production processes.

 MEMS acoustic sensors, on the other hand, do not use electret materials, and must apply a bias voltage to accumulate charge. MEMS acoustic sensors do not deteriorate due to high temperature soldering, and they can reduce the size and manufacturing cost of acoustic sensors.

MEMS acoustic sensors are manufactured in fine mechanical structures using CMOS processes. A micro air gap is created between the two plate electrodes, the membrane and the back plate, which acts as a dielectric material. The back plate may serve to mitigate air damping by forming a plurality of acoustic holes. When sound waves act on the membrane, they change the gap of the air gap, causing a change in capacitance between the membrane and the back plate. The microphone's readout circuit converts the change in capacitance caused by sound waves into an electrical signal.

To date, MEMS microphone manufacturers have continually improved the structure and material of membranes and back plates to improve sensitivity and lower noise levels. In order to increase the sensitivity and signal-to-noise ratio (SNR), the capacitance of the acoustic sensor with the change in sound pressure should be large and the noise generated should be small. To increase the change in capacitance, the sensor capacitance value formed by the membrane and the back plate, which are facing each other, must be large, and there must be enough space for the membrane to vibrate.

1 is a cross-sectional view of a conventional conventional capacitive MEMS acoustic sensor.

The back plate 30 is generally formed by bonding a back plate conductive film 30b forming an electrode and a back plate non-conductive film 30a connected to a substrate to form a support structure. At this time, due to the difference in residual stress between the back plate conductive film 30b and the non-conductive film 30a, the deformation of the central portion of the back plate 30 to form a convex surface convex downward toward the membrane 20 is caused. Happens.

When the bias voltage is applied to the membrane conductive film 20b in such a state, electric charges are generated between the two electrodes while charges are accumulated in the membrane conductive film 20b and the back plate conductive film 30b, so that the membrane 20 is formed on the back plate 30. The upwardly convex parabolic surface of the membrane 20 is formed as a vertex by being pulled up in the) direction.

As a result, the center of the back plate 30 and the membrane 20 approaches each other so that the space 10 for the membrane 20 to vibrate is reduced, and the distance between the membrane 20 and the back plate 30 is smaller than that of the center. Because of the long distance, the capacitance per unit area is reduced and hardly contributes to the change of capacitance.

In this state, when the sound pressure is applied by the sound waves, the membrane parabolic vertices move up and down, but the entire membrane 20 still maintains the convex parabolic shape.

As a result, in order to increase the sensitivity and SNR, the deflection of the back plate 30 should be reduced to increase the space for the membrane 20 to vibrate and to reduce the gap difference between the membrane 20 and the back plate 30 at the periphery and the center part.

However, when the gap between the membrane 20 and the back plate 30 is narrowed, the membrane 20 may be attached to the back plate 30, and thus, the bag 20 may be attached to the back plate to prevent the membrane 20 from being attached to the back plate. The dimple 33 may be formed on the plate 30. When the conductive film is present in the dimple 33, the charge of the membrane 20 is discharged through the dimple when the membrane 20 contacts the dimple 33. Since the dimple 33 cannot form a conductive film, there is a disadvantage in that the acoustic sensor capacitance is reduced by that amount.

On the other hand, the thickening of the back plate 30 can be considered a method of increasing the rigidity of the back plate 30 to reduce the degree of bending, in this case there is a disadvantage that the acoustic resistance of the acoustic hole increases.

Acoustic resistance (R _a) In order to pass the sound through the back plate 30 to the membrane 20, to exist in a number of acoustic holes 32, the back plate 30, the acoustic holes is expressed by the following equation.

Where μ is the viscosity of air,

l : length of acoustic hole (thickness of back plate),

n : number of acoustic holes,

r : radius of the acoustic hole

The acoustic resistance ( R _a ) causes thermal noise and reduces SNR, so the acoustic resistance should be reduced as much as possible. μ is a constant with respect to the properties of the air, so there is no room for improvement. To reduce l , the thickness of the back plate 30 must be reduced, but doing so reduces the rigidity of the back plate. Increasing n or increasing r reduces the acoustic resistance, but the smaller the electrode area, the smaller the capacitance of the sensor.

Therefore, increasing the thickness of the back plate increases the acoustic resistance, so this method is limited. Rather, it is possible to reduce the sag of the back plate without reducing the capacitance of the acoustic sensor while reducing the acoustic resistance by reducing the thickness of the back plate. I need a way.

Korean Patent Publication No. 10-2013-0039504 (published Apr. 22, 2013) discloses a method for improving a phenomenon in which a central portion of a back plate bends toward a membrane due to a difference in residual stress. Referring to FIG. This will be described.

In FIG. 2, the fixed electrodes 120, 121, and 122 cover the acoustic chamber 110, which becomes the back plate 123, and the membrane 136 is positioned as an upper electrode which is a diaphragm. A fixing pin 112 is provided at the lower end of the lower back plate 123 to prevent sagging of the back plate 123.

However, in this method, there is a process difficulty of digging a fixing groove deeply to manufacture the fixing pin 112, and the membrane 136, which is a vibration plate vibrating by sound, may be directly exposed to the outside and be damaged during the process. Even during operation of the acoustic sensor, it may be damaged by foreign particles or moisture.

In addition, Korean Patent Publication No. 10-2014-0028467 (published on March 10, 2014) discloses another method for improving a phenomenon in which the center of the back plate bends toward the membrane due to the difference in residual stress. This will be explained.

In FIG. 3, the etch stop wall 216 is formed by deeply etching the upper portion of the substrate 210 and embedding the etch stop material to improve the deflection. After depositing a first sacrificial layer (not shown), a membrane 220 which is a diaphragm is formed on the first sacrificial layer. Next, a second sacrificial layer (not shown) is deposited and a back plate 230, which is the fixed electrodes 230a and 230b, is formed on the second sacrificial layer. Finally, the first sacrificial layer and the second sacrificial layer are removed and the substrate 210 under the lower electrode is etched to form the rear acoustic chamber 212. At this time, since the etch is prevented by the etch stop wall 216 inserted at first, the back plate support 214 is formed in the center to support the back plate 230 through the exhaust hole 224 of the membrane.

However, this method also needs to etch as deep as the depth of the acoustic chamber 212 in order to install the etch stop wall 216, but the narrow and deep etching and the filling of narrow and deep grooves are difficult to apply to mass production. have.

Therefore, the deflection of the back plate 30 is increased to increase the capacitance of the acoustic sensor to improve the sensitivity and SNR of the acoustic sensor and to reduce the gap between the membrane 20 and the back plate 30 at the periphery and the center of the acoustic sensor. There is a need for technology that can be reduced or prevented.

In addition, in order to increase the acoustic sensor capacitance and increase the space for the membrane 20 to vibrate, and to reduce thermal noise, it is necessary to develop a technology for reducing the acoustic resistance to improve the sensitivity and SNR of the acoustic sensor.

Further, in order to prevent the membrane 20 from adhering to the back plate 30, a technique capable of suppressing the reduction of the area of the back plate conductive film 30b by the dimples 33 formed in the back plate 30 is prevented. Need development

1. Domestic Patent Publication No. 10-2013-0039504 (published Apr. 22, 2013) 2. Korean Patent Publication No. 10-2014-0028467 (Published March 10, 2014)

In order to solve the problems of the prior art, the present invention increases the capacitance of the acoustic sensor in order to improve the sensitivity and SNR of the acoustic sensor and the gap between the membrane 20 and the back plate 30 at the periphery and the center of the acoustic sensor. An object of the present invention is to provide a back plate structure of MEMS acoustic sensor and a method of manufacturing the same, which can simultaneously reduce or prevent sagging of the back plate 30.

In addition, the present invention provides a back plate structure of a MEMS acoustic sensor that can reduce acoustic resistance to increase acoustic sensor capacitance, increase the space for the membrane 20 to vibrate, and reduce thermal noise to improve the sensitivity and SNR of the acoustic sensor. It is an object to provide a manufacturing method.

In addition, the present invention can suppress that the area of the back plate conductive film 30b is reduced by the dimples 33 formed in the back plate 30 to prevent the membrane 20 from being attached to the back plate 30. An object of the present invention is to provide a MEMS acoustic sensor back plate and a method of manufacturing the same.

Method for manufacturing a back plate of the MEMS acoustic sensor according to an embodiment of the present invention to achieve the above object, the step of depositing a sacrificial layer on the membrane; Depositing a first silicon film on the sacrificial layer; Doping the conductive portion of the first silicon film to be an electrode; Removing a portion of the sacrificial layer to a depth equal to the height of the dimple while etching a portion of the first silicon film to be the dimple to a predetermined diameter; Depositing a non-conductive film on the first silicon film; Forming a lower end of an acoustic hole by etching the non-conductive film and the first silicon film with a single photomask while drilling the film to a predetermined size; Depositing a second silicon film on the non-conductive film; Etching the second silicon film to perforate the same or larger size than the first silicon film and the non-conductive film to form an upper end of the acoustic hole; And removing the sacrificial layer.

In addition, if the method helps to offset the bending force up and down by the residual stress difference after the step of depositing the second silicon film, the second silicon film is doped with the same shape as the electrode portion of the first silicon film. And conducting conductors.

According to another aspect of the present invention, there is provided a method for manufacturing a back plate of a MEMS acoustic sensor, including: depositing a sacrificial layer on an upper portion of a membrane; Depositing a first non-conductive film on the sacrificial layer; Depositing a silicon film on the first non-conductive film; Doping the electrode portion of the silicon film to conduct a conductor; Forming a lower end of the acoustic hole by etching the silicon film and the first non-conductive film with a single photomask while drilling the film to a predetermined size; Depositing a second non-conductive film on the silicon film; Etching the second non-conductive film to perforate the same or larger size than the first non-conductive film and the silicon film to form an upper end of an acoustic hole; And removing the sacrificial layer.

The method may further include, after the sacrificial layer deposition, removing the sacrificial layer by etching the dimple at a position where a dimple is to be formed.

On the other hand, in order to achieve the above object, the back plate structure of the MEMS acoustic sensor according to an embodiment of the present invention is manufactured by the above-described methods, and the junction between the first non-conductive film and the conductive film and the second non-conductive film The bending phenomenon in the vertical direction due to the residual stress difference generated at the junction of the conductive film is canceled with each other because the forces are generated symmetrically at the same time.

In addition, the back plate structure is characterized in that the upper end of the sound hole is formed larger than the lower end of the sound hole.

According to the present invention, in order to improve the sensitivity and SNR of the acoustic sensor, the capacitance of the acoustic sensor is increased, and the deflection of the back plate 30 is reduced or prevented, thereby increasing the space for the membrane to vibrate and the membrane 20 at the periphery and the center of the acoustic sensor. And back plate structure of the MEMS acoustic sensor to reduce the gap between the back plate 30 and a method of manufacturing the same is provided.

In addition, according to the present invention, the back plate of the MEMS acoustic sensor can increase the acoustic sensor capacitance to increase the sensitivity and SNR of the acoustic sensor and reduce the acoustic resistance in order to reduce the thermal noise while increasing the space for the membrane 20 to vibrate. A structure and a method of manufacturing the same are provided.

Further, according to the present invention, in order to prevent the membrane 20 from being attached to the back plate 30, the area of the back plate electrode 30b is reduced by the dimple 33 formed in the back plate 30. Provided are a back plate structure of a MEMS acoustic sensor and a method of manufacturing the same.

1 is a cross-sectional view of a conventional conventional capacitive MEMS acoustic sensor.
Figure 2 is a cross-sectional view of the MEMS acoustic sensor of the prior art by adding a fixing pin to reduce the deflection of the back plate.
3 is a cross-sectional view of the MEMS acoustic sensor of the prior art in which the support is inserted in the center of the acoustic chamber to reduce the deflection of the back plate.
4 is a cross-sectional view of a MEMS acoustic sensor according to an embodiment of the present invention.
5A to 5L are back plate process diagrams for the MEMS acoustic sensor according to the embodiment of FIG. 4.
6 is a cross-sectional view of a MEMS acoustic sensor according to another embodiment of the present invention.
7A to 7I are diagrams illustrating a manufacturing process of a back plate for a MEMS acoustic sensor according to the embodiment of FIG. 6.

Hereinafter, with reference to the accompanying drawings will be described in detail the present invention through the preferred embodiment of the present invention.

4 is a cross-sectional view of a MEMS acoustic sensor according to an embodiment of the present invention.

A membrane 320, which is a diaphragm supported by the membrane support part 340, is formed on an upper portion of the substrate 350 on which the back chamber 360 is formed, and a back plate supported by the back plate support part 342 is formed thereon. 330 is formed.

The membrane 320 is formed by stacking a membrane conductive film 322 serving as an electrode on the membrane nonconductive film 321 connected to and supported by the membrane support 340. In order to simplify the process, a method may be used in which a pure silicon film is doped to conduct an electrode by doping only an electrode part.

The back plate 330 forms first silicon films 332a and 332b on the back plate support part 342 and conducts doping to form the electrode portion 332a. The non-conductive film 331 is deposited thereon, and finally, the second silicon films 333a and 333b are deposited again, and doped in the same form as the electrode portions 332a of the first silicon film to form the corresponding portions 333a of the second silicon film. Conductor Since the upper silicon film does not need to be used as an electrode, doping may be omitted if there is no contribution to symmetrical residual stress at the interface.

In the back plate 330, a plurality of sound holes 370 are formed to transmit external sound to the membrane 320 through the back plate 330, and protrusion dimples 380 are formed at lower portions of the back plate 330. ) Is formed to prevent the membrane 320 from adhering to the back plate 330 during operation of the acoustic sensor.

When the bias voltage is applied to the membrane conductive film 322 in this state, electric charges are generated between the two electrodes while charges of opposite polarities are accumulated in the membrane conductive film 322 and the back plate electrode 332a, so that the membrane 320 becomes the back plate. Pulled up in the direction of 330, an upwardly convex parabolic surface having a center point of the membrane 320 as a vertex is formed.

The externally applied sound arrives at the membrane 320 through the plurality of acoustic holes 370 formed in the back plate 330 and vibrates the membrane 320. Then, as the distance between the membrane 320 and the back plate 330 changes, the capacitance changes, resulting in an output signal corresponding to the change in capacitance due to the bias voltage applied to the membrane 320.

As shown in FIG. 1, if the non-conductive film 30a is bonded to the back plate 30 having a double structure on the conductive film 30b, the back plate 30 sags toward the membrane 20 due to the difference in residual stress. Although the phenomenon occurs, the back plate 330 of FIG. 4 has a triple structure in which the silicon films 332a, 332b, 333a, and 333b are formed on the upper and lower portions of the nonconductive film 331. Even if a force bending up or down at each bonding surface occurs due to the difference in the residual stress of the silicon film, the force is generated symmetrically at the same time, thereby canceling each other out.

Therefore, according to the structure of the back plate 330 of FIG. 4 according to an embodiment of the present invention, the phenomenon that the back plate 330 sags downward due to the bending caused by the difference in residual stress may be prevented.

On the other hand, in order to reduce the acoustic resistance, the length of the sound hole, that is, the overall thickness of the back plate 330 or the sound hole 370 should increase the radius, in order to maintain the stiffness at a constant level, the overall thickness of the back plate 330. In order to substantially increase the radius of the acoustic hole 370, the acoustic sensor of FIG. 4 is a bottom portion of the acoustic hole including the back plate non-conductive film 331 and the first silicon film 332a. The radius of 372 is maintained and the back plate second silicon film 333a is partially removed to increase only the radius of the acoustic hole upper portion 371.

As such, when the radius of the upper end of the acoustic hole 371 increases, the acoustic resistance of the entire acoustic hole 370 is substantially reduced.

In the MEMS acoustic sensor according to the exemplary embodiment of the present invention illustrated in FIG. 4, the bending force due to the residual stress generated between the back plate silicon films 332a, 332b, 333a, and 333b and the non-conductive film 331 is symmetrically. By offsetting the deflection of the back plate 330 by making and offsetting it can reduce the thickness of the back plate 330 while ensuring the vibration space of the membrane 320 Sound resistance can be reduced. In addition, the thermal noise of the acoustic sensor may be reduced by increasing the radius of the acoustic hole upper end 371 of the back plate second silicon films 333a and 333b to reduce the acoustic resistance.

5A to 5L are diagrams illustrating a manufacturing process of a back plate for a MEMS acoustic sensor according to the embodiment of FIG. 4.

The back plate manufacturing process disclosed in FIGS. 5A to 5L provides a method of manufacturing a dimple while etching the three-layer back plate of FIG. 4 and etching the radius of the upper end of the acoustic hole 371 to be larger than the lower end of the acoustic hole 372.

In the acoustic sensor manufacturing process, first, the sacrificial layer 500 is deposited on the membrane as shown in FIG. 5A, and the back plate first silicon layer 332b is deposited on the membrane as shown in FIG. 5B. Next, as shown in FIG. 5C, the electrode portion 332a of the first silicon film 332b is doped to be conductive. Thereafter, as shown in FIG. 5D, the silicon film where the dimple is to be formed is etched and removed to etch the sacrificial layer 500 to a depth equal to the height of the dimple. Next, as shown in FIG. 5E, the non-conductive film 331 is deposited on the first silicon films 332a and 332b.

Next, as shown in FIG. 5F, the lower portion of the sound hole is formed by etching the upper non-conductive film 331 and the first silicon films 332a and 332b in accordance with the size of the sound hole lower portion 372 at the position of the sound hole. A hole is deposited and a second silicon film 333b is deposited on the structure as shown in FIG. 5G. Then, as illustrated in FIG. 5H, the second silicon film 333b is etched using the photo mask to match the size of the upper portion of the acoustic hole 371. Finally, as shown in FIG. 5I, when the sacrificial layer 500 is removed, an acoustic hole having a structure having an upper and a lower part in a form in which the upper end diameter is larger than the lower end diameter is completed.

On the other hand, if necessary to make the difference in the residual stress of the upper and lower interfaces symmetrically, as shown in FIG. 5J, the corresponding portion 333a of the second silicon film may also be doped to correspond to the electrode portion 332a of the first silicon film. Then, as illustrated in FIG. 5K, the second silicon film 333a is etched using the photo mask to match the size of the upper portion of the acoustic hole 371. Finally, as shown in FIG. 5L, when the sacrificial layer 500 is removed, an acoustic hole having a structure having an upper portion and a lower portion having a larger upper diameter than the lower diameter is completed.

In the above back plate manufacturing process, the diameter of the upper end of the acoustic hole 372 of the second silicon films 333a and 333b should be larger than the diameter of the lower end of the acoustic hole 371 below the non-conductive film 331. At this time, since the area of the first silicon film electrode facing the membrane 320 is determined by the diameter of the lower end of the acoustic hole, there is no change in capacitance, but the diameter of the upper end of the acoustic hole 371 is larger than that of the lower end of the acoustic hole 372. This reduces the overall acoustic resistance.

6 is a cross-sectional view of a MEMS acoustic sensor according to another embodiment of the present invention.

A membrane 320, which is a diaphragm supported by the membrane support part 340, is formed on an upper portion of the substrate 350 on which the acoustic chamber 360 or the back chamber is formed, and is supported by the back plate support part 342 thereon. The back plate 330 is formed, and the membrane 320 is formed by stacking a membrane conductive film 322 serving as an electrode on the membrane nonconductive film 321 connected to and supported by the membrane support 340. A plurality of sound holes 370 are formed in the 330 to transmit external sound to the membrane 320 through the back plate 330, and protrusion dimples 380 are formed in lower portions of the back plate 330. Formed to prevent the membrane 320 from being attached to the back plate 330 during operation of the acoustic sensor is the same as the embodiment in FIG.

6, the back plate silicon films 332a and 332b are formed between the back plate non-conductive films 331 and 334 that are connected to the back plate support 342 to form the support structure. There is a structural difference in that it includes.

When the bias voltage is applied to the membrane conductive film 322 in this state, electric charges are generated between the two electrodes while charges of opposite polarities are accumulated in the electrode conductive part 332a of the membrane conductive film 322 and the back plate silicon film, thereby generating the membrane 320. Pulled up in the direction of the back plate 330, an upwardly convex parabolic surface having a center point of the membrane 320 as a vertex is formed.

The externally applied sound arrives at the membrane 320 through the plurality of acoustic holes 370 formed in the back plate 330 and vibrates the membrane 320. Then, as the distance between the membrane 320 and the back plate 330 changes, the capacitance changes, resulting in an output signal corresponding to the change in capacitance due to the bias voltage applied to the membrane 320.

As shown in FIG. 1, if the non-conductive film 30a is joined to the conductive film 30b, the double plate back plate 30 is warped due to a difference in residual stress, so that the back plate 30 sags toward the membrane 20. Although the phenomenon occurs, the back plate 330 of FIG. 6 has a triple structure in which the non-conductive films 331 and 334 are formed on the upper and lower portions of the silicon films 332a and 332b. Even if a force bent up or down at each joint surface due to the difference of residual stresses, the force is generated symmetrically at the same time, thereby canceling each other out.

Therefore, according to the structure of the back plate 330 of FIG. 6 according to an embodiment of the present invention, the back plate 330 may be prevented from sagging due to the bending caused by the difference in the residual stress.

On the other hand, in order to reduce the acoustic resistance, the length of the sound hole, that is, the overall thickness of the back plate 330 or the sound hole 370 should increase the radius. In order to maintain the rigidity at a constant level, the overall thickness of the back plate 330 is required. 6, the acoustic sensor of FIG. 6 eventually reduces the bottom of the acoustic hole including the back plate silicon layers 332a and 332b and the first non-conductive layer 334 in order to substantially increase the radius of the acoustic hole 370. The radius of the portion 372 was maintained as it is, and only the radius of the upper portion 371 of the acoustic hole of the back plate second non-conductive film 331 was adopted.

As such, when the radius of the upper end of the acoustic hole 371 is increased, the acoustic resistance of the entire acoustic hole 370 is substantially reduced as in the embodiment of FIG. 4.

In the MEMS acoustic sensor illustrated in FIG. 6, the back plate 330 is symmetrically offset by the bending force caused by the residual stress generated between the back plate silicon films 332a and 332b and the non-conductive films 331 and 334. Since the deflection of the deflection of the membrane 320 to secure the vibration space may not increase the thickness of the back plate 330 as a whole has the effect of reducing the acoustic resistance.

In addition, since the electrode 332a of the back plate silicon film may be left at a position corresponding to the dimple 380, the capacitance of the acoustic sensor may be increased, and a portion of the back plate upper non-conductive film 331 may be removed to remove the upper portion of the sound hole. The thermal noise of the acoustic sensor can be reduced by increasing the radius of 371 to reduce the acoustic resistance.

7A to 7I are diagrams illustrating a manufacturing process of a back plate for a MEMS acoustic sensor according to the embodiment of FIG. 6.

In the back plate manufacturing process disclosed in FIGS. 7A to 7I, the diameter of the upper end of the acoustic hole 371 may be smaller than the lower end of the acoustic hole 372 while maintaining the back plate electrode 332a in the dimple while manufacturing the three-layer back plate of FIG. 6. Give a way to etch big.

In the manufacturing process of the acoustic sensor, first, the sacrificial layer 700 is deposited on the membrane as shown in FIG. 7A, and the sacrificial layer 700 is etched by the height of the dimple in the portion to be manufactured as shown in FIG. 7B. The back plate first non-conductive film 334 is deposited on top of it, as shown in FIG. 7C. Subsequently, a silicon film 332b is deposited on the first non-conductive film 334 as shown in FIG. 7D and doped as shown in FIG. 7E to conduct the electrode portion 332a.

Next, as shown in FIG. 7F, the lower silicon film 332a and the first non-conductive film 334 are etched in the same shape with the single photomask, and then the lower portion 372 of the acoustic hole is drilled. The second nonconductive film 331 is deposited on the substrate.

Then, as illustrated in FIG. 7H, the upper portion of the acoustic hole 371 is drilled larger than the diameter of the lower portion of the acoustic hole 372 while etching the second non-conductive film 331 using the photo mask.

Finally, as shown in FIG. 7I, when the sacrificial layer 700 is removed, an acoustic hole having a larger upper diameter than the lower diameter is completed.

At this time, since the area of the intermediate electrode interacting with the electrode of the membrane 320 is determined by the diameter of the lower end of the acoustic hole, there is no change in capacitance, but the diameter of the upper end of the acoustic hole 371 is larger than that of the lower end of the acoustic hole 372. This reduces the overall acoustic resistance.

In the case of the triple structure back plate 330 illustrated in FIG. 6, since the intermediate silicon film electrode 332a is present at a portion corresponding to the dimple 380, there is no decrease in capacitance due to the formation of the dimple 380. Since the dimple 380 at the lower end is formed of the non-conductive film 334, even if the membrane conductive film 322 contacts the dimple 380, the charge of the membrane 320 is not discharged through the dimple 380. Do not. As a result, the capacitance of the acoustic sensor is increased as compared to the back plate 30 of the prior art shown in FIG. 1, in which an electrode corresponding to the dimple 380 is not formed, thereby improving the sensitivity of the acoustic sensor.

Although not shown, the back plate structure of the dual structure MEMS acoustic sensor shown in FIG. 1 may be partially changed to configure the back plate structure to include an acoustic hole having a larger diameter at the upper end than the lower end.

Method for producing such a back plate structure, the step of depositing a sacrificial layer on the membrane; Depositing a silicon film on the sacrificial layer; Doping the electrode portion of the silicon film to conduct a conductor; Drilling a lower end of the acoustic hole while etching the silicon film; Depositing a non-conductive film on the silicon film; Drilling the upper end of the acoustic hole of the non-conductive film while etching the non-conductive film to have a diameter larger than the diameter of the lower end of the acoustic hole of the silicon film; And removing the sacrificial layer, whereby the etched silicon film and the non-conductive film form an acoustic hole having a top diameter larger than the bottom diameter.

In this way, the overall acoustic resistance is lowered by the acoustic hole having the upper diameter larger than the lower diameter, so that the thermal noise of the acoustic sensor can be reduced and the SNR can be improved.

Meanwhile, in the above embodiment, a method of depositing a pure silicon film and doping to form a back plate electrode is disclosed. Alternatively, an electrode portion may be formed by depositing a conductive material film on a non-conductive film.

In addition, in the present specification, the present invention has been described through one embodiment of the present invention, but the scope of the present invention is not limited to the disclosed embodiments, and modifications or changes are possible within the scope of the appended claims. It will be apparent to those skilled in the art to which the present invention pertains, and therefore, the scope of the present invention should not be limited by the disclosed embodiments but should be determined by the claims.

310: air gap
320: membrane
321: membrane non-conductive membrane
322: membrane conductive film
330: back plate
331: back plate non-conductive film
332a and 333a: electrode portions of the back plate silicon film
332b and 333b: non-electrode portion of back plate silicon film
334: back plate non-conductive film
340: membrane support
342 back plate support
350: substrate, silicon substrate
360: acoustic chamber, back chamber
370: sound hall
372: lower end of the acoustic hole
371: top of the sound hole
380: Dimple

Claims (8)

Depositing a sacrificial layer over the membrane;
Depositing a first silicon film on the sacrificial layer;
Doping the conductive portion of the first silicon film to be an electrode;
Removing a portion of the sacrificial layer to a depth equal to the height of the dimple while etching a portion of the first silicon film to be the dimple to a predetermined diameter;
Depositing a non-conductive film on the first silicon film;
Etching the non-conductive film and the first silicon film with a single photomask to perforate a predetermined size to form a lower end of the acoustic hole;
Depositing a second silicon film on the non-conductive film;
Etching the second silicon film to punch the second silicon film to a size larger than that of the first silicon film and the non-conductive film to form an upper end of the acoustic hole; And
Removing the sacrificial layer;
MEMS acoustic sensor back plate structure manufacturing method comprising a. The method according to claim 1,
Doping and conducting a portion of the second silicon film to be an electrode after the depositing the second silicon film;
MEMS acoustic sensor back plate structure manufacturing method further comprising a. delete delete Depositing a sacrificial layer over the membrane;
Depositing a first non-conductive film on the sacrificial layer;
Depositing a silicon film on the first non-conductive film;
Doping the electrode portion of the silicon film to conduct a conductor;
Etching the silicon film and the first non-conductive film with a single photomask to perforate a predetermined size to form a lower end of the acoustic hole;
Depositing a second non-conductive film on the silicon film;
Etching the second non-conductive film to perforate the same or larger size than the first non-conductive film and the silicon film to form an upper end of an acoustic hole; And
Removing the sacrificial layer;
MEMS acoustic sensor back plate structure manufacturing method comprising a. The method according to claim 5,
After the sacrificial layer deposition step, removing the sacrificial layer by the height of the dimple at the position where the dimple is to be formed;
Method for producing a back plate structure of the MEMS acoustic sensor further comprises. delete delete

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