JP5890712B2 - Semiconductor pressure sensor, manufacturing method thereof, and pressure detection device - Google Patents

Description

  The present invention relates to a technique for detecting an external action such as pressure or acceleration, and more particularly to a technique for detecting an external action using a piezoresistance effect.

  Semiconductor sensors fabricated using semiconductor materials such as single crystal silicon are highly sensitive to external actions (external forces) such as pressure and acceleration based on detection principles such as the piezoresistance effect, piezoelectric effect, and capacitance change. Widely used as a sensor to detect. A semiconductor sensor can be manufactured using a MEMS (Micro Electro Mechanical Systems) technique or an MST (Micro System Technology) technique, and thus has an advantage that it can be reduced in cost and reduced in size compared to a mechanical sensor or an optical sensor. Such a semiconductor sensor is incorporated in, for example, a measuring device such as a seismic sensor, a pedometer, and a portable terminal.

  The piezoresistive effect is a phenomenon in which the electrical resistance of a substance changes according to mechanical stress generated by an external action. In general, a piezoresistive semiconductor pressure sensor that uses a piezoresistive effect has a thin portion called a diaphragm, and a piezoresistive element is formed on the surface of the diaphragm. When the diaphragm is deformed by an external action, mechanical stress (hereinafter also simply referred to as “stress”) is generated according to the deformation (strain), and the electric resistance of the piezoresistive element changes according to the stress. To do. The change in electric resistance is converted into an electric signal and taken out. Such a piezoresistive semiconductor pressure sensor is disclosed in, for example, Japanese Patent Laid-Open No. 2006-30159 (Patent Document 1).

  In a conventional piezoresistive semiconductor pressure sensor, in order to improve detection sensitivity, a method of increasing the area of a diaphragm forming region or reducing the thickness of the diaphragm has been employed. However, when the area of the diaphragm formation region is large, it is difficult to reduce the chip size of the semiconductor pressure sensor. Further, if the diaphragm is made thinner, the mechanical strength of the diaphragm is lowered. Therefore, in the semiconductor pressure sensor (piezoresistive pressure sensor) disclosed in Patent Document 1, a groove is formed in a part of the diaphragm in the peripheral portion of the stress detection unit made of a piezoresistive element. When the diaphragm is distorted due to pressure, the groove concentrates the stress generated according to this strain on the stress detection part, so that the detection sensitivity can be improved without increasing the area of the diaphragm formation area. it can.

JP 2006-30159 A (paragraphs 0012 to 0017, paragraphs 0024 to 0026, FIG. 1 and the like)

  However, in the semiconductor pressure sensor of Patent Document 1, stress concentration is generated in the groove formed in the diaphragm every time pressure is applied from the outside, so that the mechanical strength (fatigue strength) of the diaphragm with respect to repeated stress is low. is there. For this reason, there is a concern that damage or cracks may occur in the groove portion of the diaphragm due to long-term use, or the maximum allowable pressure of the semiconductor pressure sensor becomes a low value. In order to avoid such a problem, the diaphragm may be thickened as a whole. However, if the diaphragm is thickened as a whole, the detection sensitivity cannot be improved.

  In view of the above, an object of the present invention is to provide a semiconductor pressure sensor that can improve detection sensitivity without sacrificing the mechanical strength of the diaphragm, a manufacturing method thereof, and a pressure detection device.

A semiconductor pressure sensor according to a first aspect of the present invention includes a diaphragm having a pressure receiving surface and a back surface facing the pressure receiving surface, a support surface that supports the back surface of the diaphragm via a buried insulating film, and a hollow portion. And a plurality of semiconductor piezoresistive elements formed on the pressure-receiving surface and having variable electric resistance according to distortion of the pressure-receiving surface, and the diaphragm-side one end of the hollow portion includes the diaphragm The diaphragm is sealed by the back surface, and the diaphragm has an outer peripheral portion supported by the support surface, and a thick portion having a weight portion that protrudes into the hollow portion and is thinner than the support substrate and has a hollow portion. And connecting the thick portion to the outer peripheral portion and a thin portion thinner than the thick portion, and the plurality of semiconductor piezoresistive elements are arranged on the outer peripheral side of the thin portion. A first semiconductor piezoresistive element formed on, characterized in that it comprises a second semiconductor piezoresistive element formed in the thick portion of the inner peripheral edge of the thin portion.

  A pressure detection device according to a second aspect of the present invention is based on the semiconductor pressure sensor according to the first aspect and a voltage signal indicating a change in electrical resistance of the plurality of semiconductor piezoresistive elements included in the semiconductor pressure sensor. And a calculation unit for calculating a value of the pressure applied to the semiconductor pressure sensor.

The third method of manufacturing a semiconductor pressure sensor in accordance with aspects of the present invention includes a support substrate, preparing a substrate including a semiconductor crystal layer formed over the buried insulating film on the support substrate, wherein the semiconductor crystal Forming a plurality of semiconductor piezoresistive elements by selectively introducing impurities into the surface layer of the layer; and selectively etching the back surface of the support substrate to form an annular recess having a predetermined depth; , selective anisotropic etching to expose the buried insulating film in a region corresponding to the annular recess to both of said annular recess in the region and a convex region surrounded by the annular recess of the rear surface of the support substrate and executes manner, the by removing the buried insulating film in the region corresponding to the annular recess, wherein the the supporting substrate at the same time to form a weight portion disposed in the hollow portion and the hollow portion semiconductive And forming a diaphragm including a crystalline layer, the diaphragm, and the outer peripheral portion which is supported by the supporting substrate, and a thick portion having a thinner weight portion from the supporting substrate with projecting into said hollow portion, The thick portion is connected to the outer peripheral portion and has a thin portion thinner than the thick portion, and the plurality of semiconductor piezoresistive elements are formed on the outer peripheral end of the thin portion on the outer peripheral side. And a second semiconductor piezoresistive element formed at an inner peripheral end of the thin portion on the thick portion side.

The fourth method of manufacturing a semiconductor pressure sensor in accordance with aspects of the present invention includes a support substrate, preparing a substrate including a semiconductor crystal layer formed over the buried insulating film on the support substrate, wherein the semiconductor crystal A step of selectively introducing impurities into a surface layer portion of the layer to form a plurality of semiconductor piezoresistive elements; a step of selectively etching the back surface of the support substrate to form a recess having a predetermined depth; After forming the recess, forming an etching mask that exposes a predetermined annular region in the recess of the support substrate, and a region corresponding to the annular region using the etching mask on the back surface of the support substrate wherein while executing anisotropic etching to expose the buried insulating film, by removing the buried insulating film in a region corresponding to the annular region, the middle to the support substrate And forming a diaphragm including the semiconductor crystal layer at the same time as forming a diaphragm and a weight part disposed in the hollow part, the diaphragm comprising: an outer peripheral part supported by the support substrate; and an inner part of the hollow part A plurality of semiconductor piezoresistive elements, each having a thick portion that protrudes from the support substrate and has a weight portion thinner than the support substrate, and a thin portion that connects the thick portion to the outer peripheral portion and is thinner than the thick portion. The first semiconductor piezoresistive element formed at the outer peripheral end of the thin portion on the outer peripheral portion side, and the second semiconductor piezoresistive element formed at the inner peripheral end of the thin portion on the thick portion side It is characterized by including.

  According to the present invention, stress concentrations (tensile stress and compressive stress) in opposite directions are generated at the outer peripheral end and the inner peripheral end of the beam section defined by the weight section according to the pressure acting on the pressure receiving surface of the diaphragm. And since the stress concentration of these reverse directions can be detected with the 1st and 2nd semiconductor piezoresistive element, the improvement of a detection sensitivity is realizable. Moreover, it is not necessary to form a groove in the stress concentration portion of the diaphragm. Therefore, detection sensitivity can be improved without sacrificing the mechanical strength of the diaphragm.

(A) is a figure which shows schematically the cross-section of the piezoresistive type semiconductor pressure sensor of Embodiment 1 which concerns on this invention, FIG.1 (B) is a top view of this semiconductor pressure sensor. (A), (B) is a top view which shows the structural example of the piezoresistive element of Embodiment 1. FIG. (A), (B) is sectional drawing of the piezoresistive element which shows the state which the diaphragm distorted according to the external pressure. FIG. 3 is an equivalent circuit diagram of a bridge circuit including the piezoresistive element according to the first embodiment. FIG. 3 is a functional block diagram schematically showing a configuration example of a pressure detection device according to the first embodiment. FIG. 5 is a schematic cross-sectional view of a semiconductor structure for illustrating a first manufacturing process of the semiconductor pressure sensor according to the first embodiment. It is a schematic sectional drawing of the semiconductor structure for demonstrating the 2nd manufacturing process of the semiconductor pressure sensor of Embodiment 1. FIG. It is a schematic sectional drawing of the semiconductor structure for demonstrating the 3rd manufacturing process of the semiconductor pressure sensor of Embodiment 1. FIG. It is a schematic sectional drawing of the semiconductor structure for demonstrating the 4th manufacturing process of the semiconductor pressure sensor of Embodiment 1. FIG. It is a schematic sectional drawing of the semiconductor structure for demonstrating the 5th manufacturing process of the semiconductor pressure sensor of Embodiment 1. FIG. It is a schematic sectional drawing of the semiconductor structure for demonstrating the 6th manufacturing process of the semiconductor pressure sensor of Embodiment 1. FIG. 6 is a diagram schematically showing a cross-sectional structure of a piezoresistive semiconductor pressure sensor that is a modification of the first embodiment. FIG. It is a figure which shows schematically the cross-section of the piezoresistive type semiconductor pressure sensor of Embodiment 2 which concerns on this invention. It is a schematic sectional drawing of the semiconductor structure for demonstrating the 1st manufacturing process of the semiconductor pressure sensor of Embodiment 2. FIG. It is a schematic sectional drawing of the semiconductor structure for demonstrating the 2nd manufacturing process of the semiconductor pressure sensor of Embodiment 2. FIG. It is a schematic sectional drawing of the semiconductor structure for demonstrating the 3rd manufacturing process of the semiconductor pressure sensor of Embodiment 2. FIG. It is a schematic sectional drawing of the semiconductor structure for demonstrating the 4th manufacturing process of the semiconductor pressure sensor of Embodiment 2. FIG. It is a schematic sectional drawing of the semiconductor structure for demonstrating the 5th manufacturing process of the semiconductor pressure sensor of Embodiment 2. (A) is a figure which shows schematically the cross-section of the piezoresistive type semiconductor pressure sensor of Embodiment 3 which concerns on this invention, (B) is a top view of this semiconductor pressure sensor. FIG. 10 is an equivalent circuit diagram of a bridge circuit that detects a change in electrical resistance of the piezoresistive element according to the third embodiment. FIG. 10 is a functional block diagram schematically illustrating a configuration example of a pressure detection device according to a third embodiment. It is sectional drawing of the piezoresistive element which shows the state which the diaphragm distorted according to acceleration.

  Hereinafter, various embodiments according to the present invention will be described with reference to the drawings. In the drawings, the same reference numerals are given to components having the same structure and the same function, and detailed description thereof is omitted.

Embodiment 1 FIG.
FIG. 1A is a diagram schematically showing a cross-sectional structure of a piezoresistive semiconductor pressure sensor 10 in the pressure detection device according to the first embodiment of the present invention, and FIG. 2 is a top view of the sensor 10. FIG. FIG. 1A shows a schematic cross section taken along line Ia-Ia of the semiconductor pressure sensor 10 of FIG. The semiconductor pressure sensor 10 is configured using a support substrate 21 </ b> P having a hollow portion 31. 1A and 1B, the Z-axis direction coincides with the thickness direction of the support substrate 21P, and the X-axis direction, the Y-axis direction, and the Z-axis direction are orthogonal to each other.

  The semiconductor pressure sensor 10 is referred to as a thin film 22 disposed on a support substrate 21P via an insulating film 23P, and a semiconductor piezoresistive element (hereinafter simply referred to as “piezoresistive element”) formed on the pressure receiving surface of the thin film 22. ) P1, P2, P3, P4 and a protective film 24 such as a nitride film covering these piezoresistive elements P1 to P4. For convenience of explanation, the protective film 24 of FIG. 1A is not shown in FIG.

  The thin film 22 forms a diaphragm of the semiconductor pressure sensor 10 and is made of a semiconductor crystal material such as single crystal silicon. As shown in FIGS. 1A and 1B, this thin film 22 connects a central portion 22m, a rectangular annular peripheral portion 22p supported by a support substrate 21P, and the central portion 22m to the peripheral portion 22p. And a rectangular annular beam portion (thin wall portion) 22b. The central portion 22m of the thin film 22 is coupled to the upper end of the weight portion 32 made of a laminate of the insulating film 23M and the semiconductor layer 21M, and the portion of the thin film 22 that is coupled to the weight portion 32 constitutes the central portion 22m. . As shown in FIG. 1A, the weight portion 32 is disposed so as to protrude into the hollow portion 31 of the support substrate 21P.

  One end on the pressure receiving surface side of the hollow portion 31 of the support substrate 21P is sealed with the thin film 22, and the other end opposite to the pressure receiving surface of the hollow portion 31 is sealed with a sealing member 25 such as a glass plate. Therefore, the hollow part 31 comprises the sealed airtight chamber.

  The diaphragm of the semiconductor pressure sensor 10 includes a thin film 22 and a weight portion 32. The peripheral part 22p of the thin film 22 constitutes the outer peripheral part of the diaphragm, the central part 22m and the weight part 32 of the thin film 22 constitute the thick part of the diaphragm, and the beam part 22b of the thin film 22 constitutes the thin part of the diaphragm. . The piezoresistive elements P1 and P4 are formed at the outer peripheral end of the thin portion 22b of the diaphragm, and the other piezoresistive elements P2 and P3 are formed at the inner peripheral end of the thin portion 22b. These piezoresistive elements P1, P2, P3, and P4 are arranged in a straight line substantially along the X-axis direction as shown in FIG.

  The electric resistances of the piezoresistive elements P1 to P4 change according to the distortion of the pressure receiving surface of the thin film 22 due to the piezoresistance effect. 2A and 2B are top views showing a configuration example of the piezoresistive elements P1 and P2. As shown in FIG. 2A, the piezoresistive element P1 includes a piezoresistive diffusion region 41 composed of a P-type impurity diffusion region introduced into the semiconductor crystal layer, and both ends of the piezoresistive diffusion region 41 in the extending direction. The contact regions 42A and 42B, which are high-concentration P-type impurity diffusion regions to be joined, are formed. On the contact regions 42A and 42B, metal wirings 43A and 43B such as aluminum that are in ohmic contact with the contact regions 42A and 42B, respectively, are formed. The other piezoresistive element P3 has substantially the same structure as the piezoresistive element P1. On the other hand, as shown in FIG. 2B, the piezoresistive element P2 includes a piezoresistive diffusion region 44 composed of a P-type impurity diffusion region introduced into the semiconductor crystal layer, and the extending direction of the piezoresistive diffusion region 44. It is composed of contact regions 45A and 45B which are high-concentration P-type impurity diffusion regions joined to both ends. On the contact regions 45A and 45B, metal wirings 46A and 46B such as aluminum that are in ohmic contact with the contact regions 45A and 45B, respectively, are formed. The other piezoresistive element P4 has substantially the same structure as the piezoresistive element P2.

  The movable part of the diaphragm is composed of a thick part consisting of a central part 22m and a weight part 32 and a beam part (thin part) 22b. When a difference occurs between the external pressure with respect to the diaphragm and the internal pressure in the hollow portion 31, the diaphragm is deformed in the positive direction or the negative direction in the Z-axis direction according to the pressure difference. FIG. 3A is a diagram showing a deformed state of the diaphragm when the external pressure is lower than the internal pressure, and FIG. 3B shows a deformed state of the diaphragm when the external pressure is higher than the internal pressure. FIG.

  When the external pressure is lower than the internal pressure, the movable portion of the diaphragm is deformed in the positive direction of the Z axis with respect to the support substrate 21P as shown in FIG. At this time, compressive stress acts on the piezoresistive elements P1 and P4 at the outer peripheral ends, and tensile stress acts on the piezoresistive elements P2 and P3 at the inner peripheral ends. On the other hand, when the external pressure is higher than the internal pressure, the movable portion of the diaphragm is deformed in the negative Z-axis direction with respect to the support substrate 21P as shown in FIG. At this time, tensile stress acts on the piezoresistive elements P1 and P4 at the outer peripheral ends, and compressive stress acts on the piezoresistive elements P2 and P3 at the inner peripheral ends. For example, it is possible to use a piezoresistive element in which the interatomic distance increases when subjected to the action of tensile stress and the electrical resistance value increases, and the interatomic distance decreases and the electrical resistance value decreases when subjected to compressive stress. it can.

A bridge circuit may be used as an electric circuit for detecting changes in the electric resistance of the piezoresistive elements P1 to P4. FIG. 4 is an equivalent circuit diagram of a Wheatstone bridge circuit which is an example of the bridge circuit of the present embodiment. As shown in FIG. 4, the piezoresistive elements P1, P2, P3, and P4 are connected in series in a ring shape. A GND voltage is applied (ie, grounded) to a connection point (node) between the piezoresistive elements P1 and P4, and a power supply voltage (reference voltage) VDD is applied to a connection point (node) between the piezoresistive elements P2 and P3. Applied. The connection point between the piezoresistive elements P1, P2 (node) outputs a signal voltage V ₊ to the outside, the connection point between the piezoresistive element P3, P4 (node), the signal voltage V _- outputs to the outside To do. When the electrical resistance (gauge resistance) of these piezoresistive elements P1, P2, P3, and P4 is represented by R1, R2, R3, and R4, respectively, the differential signal voltage Vo (= V ₊ −V ₋ ) is represented by the following equation. be able to.
Vo = [R1 / (R1 + R2) −R4 / (R3 + R4)] × VDD

  FIG. 5 is a functional block diagram schematically illustrating a configuration example of the pressure detection device 1 according to the first embodiment. The pressure detection device 1 converts the differential signal voltage Vo output from the semiconductor pressure sensor 10 into a pressure value Pv. As shown in FIG. 5, the pressure detection device 1 includes a drive circuit 14 that supplies a drive voltage to the semiconductor pressure sensor 10, a differential amplifier 11 that amplifies the differential output voltage Vo, and an output of the differential amplifier 11. A gain adjuster 12 that adjusts the gain, an A / D converter (ADC) 13 that converts the output of the gain adjuster 12 into a digital signal, and a desired frequency component is extracted from the output of the A / D converter 13. And a pressure calculation unit 17 that calculates a pressure value Pv based on the output of the filter unit 16.

  Next, a method for manufacturing the semiconductor pressure sensor 10 will be described with reference to FIGS. 6 to 11 are schematic cross-sectional views of a semiconductor structure for explaining a manufacturing process of the semiconductor pressure sensor 10.

  First, an SOI (Semiconductor-On-Insulator) substrate 20 as shown in FIG. 6 is prepared. The SOI substrate 20 includes a support substrate 21 made of a silicon material, a semiconductor crystal layer 22 formed on the support substrate 21, and a semiconductor crystal layer 22 interposed between the semiconductor crystal layer 22 and the support substrate 21. It has a buried insulating film 23 that is electrically separated from the support substrate 21. The semiconductor crystal layer 22 that forms the outermost layer of the SOI substrate 20 may be a single crystal silicon layer having a thickness of about several μm to several tens of μm, for example, and the buried insulating film 23 has a thickness of about several μm, for example. The silicon oxide film may be used.

  Next, piezoresistive elements P1, P2, P3, and P4 are formed on the surface of the semiconductor crystal layer 22 as shown in FIG. Specifically, using a photolithography technique, a P-type impurity such as boron is selectively introduced into the surface layer portion of the semiconductor crystal layer 22 to form a piezoresistive diffusion region, and then using a photolithography technique, A high concentration contact region is formed by selectively introducing a P-type impurity such as boron into the surface layer portion of the semiconductor crystal layer 22. And piezoresistive elements P1-P4 are producible by forming metal wirings, such as aluminum, on these contact regions, for example using sputtering method. Next, these piezoresistive elements P1, P2, P3, and P4 are connected to form a bridge circuit. Thereafter, a protective film 24 such as a nitride film is formed on the piezoresistive elements P1, P2, P3, and P4.

Next, after grinding and polishing the back surface of the wafer of FIG. 7, a mask layer 28 having an opening 28h is formed on the back surface as shown in FIG. Specifically, for example, an oxide film (SiO ₂ ) or a silicon nitride film (Si ₃ N ₄ ) is formed on the back surface by using a CVD (Chemical Vapor Deposition) method or a thermal oxidation method. The mask layer 28 can be formed by patterning the silicon nitride film.

  Next, as shown in FIG. 9, a resist pattern 27 is formed in the opening 28 h of FIG. 8, and etching is performed using the resist pattern 27 and the mask layer 28 as a mask to form a rectangular ring shape in a top view. The recessed part 21c which has is formed. At this time, the thickness of the weight portion 32 in FIG. 1 can be controlled by adjusting the step of the concave portion 21c. Thereafter, the resist pattern 27 is removed.

  After removing the resist pattern 27, the support substrate 21 is anisotropically etched in the vertical direction until the buried insulating film 23 is exposed using the mask layer 28 as an etching mask, as shown in FIG. At this time, the buried insulating film 23 functions as a stopper film for anisotropic etching. As anisotropic etching, for example, reactive ion etching (RIE) or anisotropic etching using a TMAH (tetramethylammonium hydroxide) aqueous solution or a KOH (potassium hydroxide) aqueous solution is used. be able to.

  Next, as shown in FIG. 11, the exposed portion of the buried insulating film 23 in the hollow portion 31 is removed by etching. At this time, when the buried insulating film 23 is made of a silicon oxide film, for example, the exposed portion of the buried insulating film 23 can be removed by etching using hydrogen fluoride or the like.

  Next, a sealing member 25 made of a glass material is bonded to the back surface of the support substrate 21P, for example, by an anodic bonding method, and the open end of the hollow portion 31 is sealed. As a result, as shown in FIG. 1A, the semiconductor pressure sensor 10 having the hollow portion 31 as an airtight chamber is manufactured. In the case where the hermetic chamber is formed in the hollow portion 31 in the subsequent packaging process, the process of attaching the sealing member 25 to the back surface of the support substrate 21P is unnecessary.

  By the way, in order to reduce the influence of the acceleration on the weight portion 32, it is desirable to form a hollow portion having a ring shape in the weight portion 32 to reduce the weight of the weight portion 32. FIG. 12 is a diagram schematically showing a cross-sectional structure of a semiconductor pressure sensor 10 </ b> A that is a modification of the semiconductor pressure sensor 10. As shown in FIG. 12, the semiconductor pressure sensor 10A includes a weight portion 32A including a semiconductor layer 21Ma having a hollow portion 21v at the center and an insulating film 23M. The configuration of the semiconductor pressure sensor 10A is the same as the configuration of the semiconductor pressure sensor 10 shown in FIGS. 1A and 1B except for the weight portion 32A. The cavity 21v in FIG. 12 can be formed by adding an etching process using a resist pattern as a mask to the manufacturing process shown in FIGS.

  As described above, the semiconductor pressure sensor 10 according to the first embodiment is configured so that when the movable portion of the diaphragm is distorted due to a pressure difference, the outer peripheral end and the inner end of the beam portion (thin portion) 22b partitioned by the weight portion 32 are used. Stress concentrations can be respectively generated at the peripheral ends, and these stress concentrations can be detected by the piezoresistive elements P1, P2, P3, and P4. The weight part 32 constituting the thick part of the diaphragm is less likely to be deformed with respect to external action than the thin part 22b of the diaphragm. For this reason, in particular, the stress acting on the piezoresistive elements P2 and P3 formed at the inner peripheral end of the beam portion 22b is generated by the distortion of the thin portion 22b having both ends of the weight portion 32 as fulcrums. Compared with the case where it is not formed, the stress is large. Therefore, detection sensitivity can be improved as compared with the case where the weight portion 32 is not formed.

  Moreover, it is not necessary to form a groove in the stress concentration portion of the diaphragm. For this reason, compared with the structure of patent document 1, the mechanical strength (fatigue strength) of the diaphragm with respect to repetitive stress is high, and it can raise rated pressure (the maximum pressure which can maintain desired performance continuously). Is possible.

  Therefore, the semiconductor pressure sensor 10 of the first embodiment can improve the detection sensitivity without sacrificing the mechanical strength of the diaphragm.

  Furthermore, when the cavity 21v is formed in the weight 32A as shown in FIG. 12, the influence of acceleration can be reduced. For this reason, it is possible to provide the semiconductor pressure sensor 10A that can improve the detection sensitivity without sacrificing the mechanical strength of the diaphragm even in a use situation where acceleration can occur.

Embodiment 2. FIG.
Next, a second embodiment according to the present invention will be described. FIG. 13 is a diagram schematically showing a cross-sectional structure of the piezoresistive semiconductor pressure sensor 10B according to the second embodiment. The basic structure of the semiconductor pressure sensor 10B of the present embodiment is almost the same as the basic structure of the semiconductor pressure sensor 10 of the first embodiment, except that a part of the manufacturing method is different.

  As shown in FIG. 13, the semiconductor pressure sensor 10 </ b> B has a hollow portion 31 and a weight portion 32 </ b> B disposed in the hollow portion 31, and the weight portion 32 </ b> B is the semiconductor pressure sensor 10 of the first embodiment. It arrange | positions in the hollow part 31 similarly to.

  Hereinafter, a method for manufacturing the semiconductor pressure sensor 10B of the second embodiment will be described. 14 to 18 are schematic cross-sectional views of the semiconductor structure for explaining the manufacturing process of the semiconductor pressure sensor 10B.

  First, as in the first embodiment, the SOI substrate 20 of FIG. 6 is prepared, and the piezoresistive elements P1 to P4 are formed on the upper surface of the semiconductor crystal layer 22 of the SOI substrate 20 as shown in FIG. Further, a protective film 24 is formed.

Next, after grinding and polishing the back surface of the wafer in FIG. 7, a mask layer 28B having an opening 28Bh is formed on the back surface as shown in FIG. Specifically, for example, an oxide film (SiO ₂ ) or a silicon nitride film (Si ₃ N ₄ ) is formed on the back surface by using a CVD method or a thermal oxidation method, and the oxide film or the silicon nitride film is patterned. Thus, the mask layer 28B can be formed.

  Next, as shown in FIG. 15, a recess 21d having a predetermined depth is formed by performing etching using the mask layer 28B as an etching mask. Subsequently, as shown in FIG. 16, a resist pattern 29 is formed in the recess 21d of FIG.

  Next, as shown in FIG. 17, using the resist pattern 29 and the mask layer 28B as an etching mask, the support substrate 21 is anisotropically etched in the vertical direction until the buried insulating film 23 is exposed. At this time, the buried insulating film 23 functions as a stopper film for anisotropic etching. As the anisotropic etching at this time, reactive ion etching (RIE) that realizes a high aspect ratio may be used. Thereafter, the resist pattern 29 is removed.

  Next, as shown in FIG. 18, the exposed portion of the buried insulating film 23 in the hollow portion 31 is removed by etching. At this time, when the buried insulating film 23 is made of a silicon oxide film, for example, the exposed portion of the buried insulating film 23 can be removed by etching using hydrogen fluoride. As a result, the support substrate 21P having the inner peripheral end face 21w that forms the hollow portion 31 and the weight portion 32B are formed.

  Next, a sealing member 25 made of a glass material is bonded to the back surface of the support substrate 21P, for example, by an anodic bonding method, and the open end of the hollow portion 31 is sealed. As a result, the semiconductor pressure sensor 10B having the hollow portion 31 shown in FIG. 13 as an airtight chamber is manufactured. In the case where the hermetic chamber is formed in the hollow portion 31 in the subsequent packaging process, the process of attaching the sealing member 25 to the back surface of the support substrate 21P is unnecessary.

  The semiconductor pressure sensor 10B having the same basic structure as the semiconductor pressure sensor 10 of the first embodiment can be manufactured by the manufacturing method described above.

  In the semiconductor pressure sensor 10B of the present embodiment, the thickness of the weight portion 32B is larger than that of the weight portion 32 of the semiconductor pressure sensor 10 of the first embodiment. The gap width is small. Thereby, when a very large external pressure is applied, the weight portion 32B functions as a stopper, so that the diaphragm can be prevented from being broken. The lower end of the weight portion 32B comes into contact with the sealing member 25 against a large external pressure, and the moving amount of the movable portion of the diaphragm is limited. Therefore, the diaphragm is prevented from being deformed until it is broken. Thereby, it is possible to achieve a significant improvement in the absolute maximum rated pressure (a value that may cause damage to the semiconductor pressure sensor 10B if this value is exceeded). The gap width between the lower end of the weight portion 32B and the sealing member 25 can be adjusted to, for example, a width of 20 μm or less by controlling the process conditions of the etching step (FIG. 15).

  Even when the manufacturing method according to Embodiment 1 is used, the thickness of the weight portion 32 can be increased and the weight portion 32 can function as a stopper. Specifically, the thickness of the weight portion 32 can be increased by increasing the aspect ratio of the annular recess 21c in the etching process for forming the structure of FIG.

Embodiment 3 FIG.
Next, a third embodiment according to the present invention will be described. FIG. 19A is a diagram schematically showing a cross-sectional structure of a piezoresistive semiconductor pressure sensor 10C in the pressure detection device according to the third embodiment of the present invention, and FIG. It is a top view of sensor 10C. FIG. 19A shows a schematic cross section taken along the line XIXa-XIXa of the semiconductor pressure sensor 10C of FIG. For convenience of explanation, the protective film 24 is not shown in FIG.

  The semiconductor pressure sensor 10C according to the present embodiment has a configuration capable of detecting acceleration together with pressure detection. The semiconductor pressure sensor 10C can be manufactured using the manufacturing method of the semiconductor pressure sensor 10 of the first embodiment or the manufacturing method of the semiconductor pressure sensor 10B of the second embodiment.

  As shown in FIG. 19A, the semiconductor pressure sensor 10C has a hollow portion 31 and a weight portion 32C arranged in the hollow portion 31, and the weight portion 32C is formed by the first and second embodiments. The semiconductor pressure sensors 10 and 10B are disposed in the hollow portion 31. The weight portion 32C includes a semiconductor layer 21Mc having a large thickness in order to secure a weight for acceleration detection.

  Further, as shown in FIG. 19B, on the upper surface (pressure receiving surface) of the semiconductor crystal layer 22, piezoresistive elements Px1, Px2, Px3, Px4 arranged linearly along the X-axis direction, Piezoresistive elements Py1, Py2, Py3, Py4 arranged linearly along the Y-axis direction and piezoresistive elements Pz1, Pz2, Pz3, Pz4 arranged linearly along the Y-axis direction are formed. ing. The piezoresistive elements Px1, Px4, Py1, Py4, Pz1, Pz4 are formed at the outer peripheral end of the thin part 22b of the diaphragm, and the piezoresistive elements Px2, Px3, Py2, Py3, Pz2, Pz3 are formed of the thin part 22b of the diaphragm. It is formed at the inner peripheral end.

FIG. 20 is an equivalent circuit diagram of a bridge circuit that detects changes in electrical resistance of the piezoresistive elements Px1 to Px4, Py1 to Py4, and Pz1 to Pz4. Piezoresistive element Px1~Px4 the positive supply voltage VDDx differential signal voltage Vxo using a GND voltage _- constitute a bridge circuit 50X that outputs ₍₌ Vx + -Vx). The piezoresistive element Py1~Py4 the positive supply voltage VDDy differential signal voltage Vyo using the GND voltage ₍₌ Vy + -Vy _-) constitute a bridge circuit 50Y for outputting, and piezoresistive element Pz1~Pz4 the positive supply voltage VDDz differential signal voltage Vzo using the GND voltage _- constitute a bridge circuit 50Z for outputting ₍₌ Vz + -Vz).

Piezoresistive elements Px1, Px2, Px3, _Rx 1 the electrical resistance of _{Px4, Rx 2, Rx 3,} Rx 4 and represent, piezoresistive elements Py1, Py2, Py3, _Ry 1 the electrical resistance of _Py4, Ry 2, Ry ₃ It represents a Ry4, when referring piezoresistive elements Py1, Py2, Py3, the electrical resistance of Py4 and _{Ry 1, Ry 2, Ry 3} , Ry 4, differential signal voltage Vxo, Vyo, VZO is expressed by the following equation be able to.
Vxo = [Rx ₁ / (Rx ₁ + Rx ₂ ) −Rx ₄ / (Rx ₃ + Rx ₄ )] × VDDx,
Vyo = [Ry ₁ / (Ry ₁ + Ry ₂ ) −Ry ₄ / (Ry ₃ + Ry ₄ )] × VDDy,
Vzo = [Rz ₁ / (Rz ₁ + Rz ₂ ) −Rz ₄ / (Rz ₃ + Rz ₄ )] × VDDz

  FIG. 21 is a functional block diagram schematically illustrating a configuration example of the pressure detection device 1C according to the third embodiment. The pressure detection device 1C detects the pressure value Pv and the acceleration Az in the Z-axis direction from the differential signal voltage Vzo output from the semiconductor pressure sensor 10C, and the differential signal voltage Vxo, output from the semiconductor pressure sensor 10C. The accelerations Ax and Ay in the X-axis direction and the Y-axis direction can be detected from Vyo.

  As shown in FIG. 21, the pressure detection device 1C includes a drive circuit 14C that supplies a drive voltage to the semiconductor pressure sensor 10C, and differential amplifiers 11X and 11Y that receive differential signal voltages Vxo, Vyo, and Yzo, respectively. , 11Z, gain adjusters 12X, 12Y, 12Z that receive the outputs of the differential amplifiers 11X, 11Y, 11Z, and A / D converters that convert the outputs of the gain adjusters 12X, 12Y, 12Z into digital signals ( ADC) 13X, 13Y, 13Z, and filter units 16X, 16Y and a filter bank 16Z.

The acceleration calculation units 17X and 17Y detect the X-axis direction acceleration Ax and the Y-axis direction acceleration Ay based on the outputs of the filter units 16X and 16Y, respectively. For example, as shown in FIG. 22, when acceleration in the X-axis positive direction (rightward) occurs, the support substrate 21P moves in the X-axis positive direction with respect to the weight portion 32C. Thus, the piezoresistive element Px1, Px3 compressive stress acts, because they act tensile stresses in the piezoresistive element Px2, Px4, electrical resistance _Rx 1, Rx ₃ piezoresistive elements Px1, Px3 reduces, The electrical resistance of the piezoresistive elements Px2 and Px4 will increase. The acceleration calculator 17X can convert such a change in electrical resistance into an acceleration Ax.

  The filter bank 16Z extracts a high frequency component and a low frequency component from the output of the A / D converter 13Z, applies the high frequency component to the acceleration calculation unit 17Z, and supplies the low frequency component to the pressure calculation unit 17. The acceleration calculation unit 17Z can calculate the Z-axis direction acceleration Az from the high frequency component, and the pressure calculation unit 17 can calculate the pressure value Pv in the Z-axis direction from the high frequency component. Since the pressure change with time is often more gradual than the acceleration change with time, the acceleration Az and the pressure Pv can be detected from one differential signal voltage Vzo by frequency analysis using the filter bank 16Z.

  Therefore, the semiconductor pressure sensor 10C according to the third embodiment can detect the accelerations Ax, Ay, Az and the pressure Pv with one chip.

Modifications of the first to third embodiments.
Although various embodiments according to the present invention have been described above with reference to the drawings, these are examples of the present invention, and various forms other than the above can be adopted. For example, the top view shape of the hollow portion 31 of the support substrate 21P and the top view shapes of the weight portions 32, 32B, and 32C are rectangular as shown in FIGS. 1 (B) and 19 (B). It is not limited to. For example, these shapes may be circular or elliptical.

  The semiconductor pressure sensors 10, 10A, 10B, and 10C of the first to third embodiments are absolute pressure sensors that detect the absolute pressure between the external pressure and the reference pressure using the pressure in the hermetic chamber as the reference pressure. Although configured, the present invention is not limited to this. If a member having an open end at the other end of the hollow portion 31 is used instead of the sealing member 25, a differential pressure sensor can be configured.

  P1 to P4, Px1 to Px4, Py1 to Py4, Pz1 to Pz4 Piezoresistive element, 1, 1C pressure detection device, 10, 10B, 10C semiconductor pressure sensor, 11, 11X, 11Y, 11Z differential amplifier, 12X, 12Y, 12Z gain adjuster, 13, 13X, 13Y, 13Z A / D converter (ADC), 14, 14C drive circuit, 16, 16X, 16Y filter unit, 16Z filter bank, 17 pressure calculation unit, 17X, 17Y, 17Z acceleration Arithmetic unit, 20 SOI substrate, 21 support substrate, 21M semiconductor layer, 21v cavity portion, 22 thin film (semiconductor crystal layer), 22m center portion, 22b beam portion (thin portion), 22p peripheral portion, 23 buried insulating film, 24 protection Membrane, 25 sealing member, 31 hollow part, 32, 32B, 3 C weight part, 41 and 44 piezoresistive diffused region, 42A, 42B, 45A, 45B contact region.

Claims (10)

A diaphragm having a pressure receiving surface and a back surface facing the pressure receiving surface;
A support surface for supporting the back surface of the diaphragm via the buried insulating film, a supporting substrate having a hollow portion,
A plurality of semiconductor piezoresistive elements formed on the pressure receiving surface and having a variable electrical resistance in accordance with distortion of the pressure receiving surface;
The diaphragm side one end of the hollow portion is sealed by the back surface of the diaphragm,
The diaphragm is
An outer periphery supported by the support surface;
A thick part having a weight part protruding into the hollow part and thinner than the support substrate and having a hollow part ,
The thick part is connected to the outer peripheral part and has a thin part thinner than the thick part,
The plurality of semiconductor piezoresistive elements are:
A first semiconductor piezoresistive element formed at the outer peripheral end of the thin portion on the outer peripheral side;
A semiconductor pressure sensor, comprising: a second semiconductor piezoresistive element formed at an inner peripheral end of the thin portion on the thick portion side. The semiconductor pressure sensor according to claim 1,
The thin portion is formed in an annular shape so as to surround the thick portion,
The outer peripheral part is formed in an annular shape so as to surround the thin part. A semiconductor pressure sensor. The semiconductor pressure sensor according to claim 2,
The plurality of semiconductor piezoresistive elements are:
A third semiconductor piezoresistive element formed at the outer peripheral end of the thin portion;
A fourth semiconductor piezoresistive element formed at the inner peripheral end of the thin portion,
The first and second semiconductor piezoresistive elements are arranged along a first direction parallel to the pressure-receiving surface,
The third and fourth semiconductor piezoresistive elements are arranged along a second direction parallel to the pressure-receiving surface and different from the first direction. A semiconductor pressure sensor according to any one of claims 1 3, wherein the hollow portion, and the diaphragm has a sealed on the opposite side the other end, constitutes the airtight chamber A semiconductor pressure sensor. A semiconductor pressure sensor according to any one of claims 1 4, wherein the semiconductor piezoresistive element, a semiconductor pressure sensor, characterized in that it comprises an impurity diffusion region which is introduced into the semiconductor crystal layer. 6. The semiconductor pressure sensor according to claim 5 , wherein the semiconductor crystal layer is a single crystal silicon layer. A semiconductor pressure sensor according to any one of claims 1 to 6 ;
An arithmetic unit that calculates a value of a pressure applied to the semiconductor pressure sensor based on a voltage signal indicating a change in electrical resistance of the plurality of semiconductor piezoresistive elements included in the semiconductor pressure sensor. Pressure detector. A semiconductor pressure sensor according to claim 3;
An arithmetic unit that calculates a value of a pressure applied to the semiconductor pressure sensor based on a voltage signal indicating a change in electrical resistance of the plurality of semiconductor piezoresistive elements included in the semiconductor pressure sensor;
The said calculating part calculates the value of the acceleration which acted on the said semiconductor pressure sensor by the frequency analysis of the said voltage signal with the value of the said pressure. The pressure detection apparatus characterized by the above-mentioned. A supporting substrate, a step of preparing a substrate including a semiconductor crystal layer formed over the buried insulating film on the support substrate,
A step of selectively introducing impurities into a surface layer portion of the semiconductor crystal layer to form a plurality of semiconductor piezoresistive elements;
Selectively etching the back surface of the support substrate to form an annular recess having a predetermined depth;
Selective anisotropic etching for exposing the buried insulating film in the region corresponding to the annular recess with respect to both the annular recess region and the convex region surrounded by the annular recess in the back surface of the support substrate. And removing the buried insulating film in a region corresponding to the annular recess, thereby forming a hollow portion and a weight portion disposed in the hollow portion at the same time as forming the semiconductor crystal layer. Forming a diaphragm including, and
The diaphragm is
An outer periphery supported by the support substrate;
A thick part protruding into the hollow part and having a weight part thinner than the support substrate ;
The thick part is connected to the outer peripheral part and has a thin part thinner than the thick part,
The plurality of semiconductor piezoresistive elements are:
A first semiconductor piezoresistive element formed at the outer peripheral end of the thin portion on the outer peripheral side;
And a second semiconductor piezoresistive element formed at an inner peripheral end of the thin portion on the thick portion side. A method for manufacturing a semiconductor pressure sensor, comprising: A supporting substrate, a step of preparing a substrate including a semiconductor crystal layer formed over the buried insulating film on the support substrate,
A step of selectively introducing impurities into a surface layer portion of the semiconductor crystal layer to form a plurality of semiconductor piezoresistive elements;
Selectively etching the back surface of the support substrate to form a recess having a predetermined depth;
After formation of the recess, forming an etching mask for exposing a predetermined annular area of the inside recess of the supporting substrate,
Anisotropic etching is performed to expose the buried insulating film in the region corresponding to the annular region using the etching mask on the back surface of the support substrate, and the buried insulating film in the region corresponding to the annular region by removing, and a step of forming a diaphragm including the semiconductor crystal layer and at the same time to form a weight portion disposed in the hollow portion and the hollow portion to the support substrate,
The diaphragm is
An outer periphery supported by the support substrate;
A thick part protruding into the hollow part and having a weight part thinner than the support substrate ;
The thick part is connected to the outer peripheral part and has a thin part thinner than the thick part,
The plurality of semiconductor piezoresistive elements are:
A first semiconductor piezoresistive element formed at the outer peripheral end of the thin portion on the outer peripheral side;
And a second semiconductor piezoresistive element formed at an inner peripheral end of the thin portion on the thick portion side. A method for manufacturing a semiconductor pressure sensor, comprising:

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