Semiconductor pressure sensor and method for manufacturing the same

Abstract

The object of the present invention is to provide a semiconductor pressure sensor capable of detecting minute pressure with high accuracy and a method for manufacturing the same. The semiconductor pressure sensor of the present invention comprises: a first silicon substrate (1); a first silicon oxide film (2) disposed on the first silicon substrate (1) and constituting a closed space (3) together with the first silicon substrate (1); a second silicon substrate (4) disposed on the first silicon oxide film (2); a strain resistor (11) disposed on the surface of the second silicon substrate (4) opposite to the surface on which the first silicon oxide film (2) is disposed and located at a position overlapping the closed space (3) when viewed from above; a first electrode (7) electrically connected to one end of the strain resistor (11); and a second electrode (7) electrically connected to the other end of the strain resistor.

Description

Technical Field

[0001] The present invention relates to a diaphragm-type semiconductor pressure sensor for measuring minute pressure and a method for manufacturing the semiconductor pressure sensor. Background Art

[0002] Conventionally, a technique related to a diaphragm-type semiconductor pressure sensor is disclosed (for example, refer to Patent Document 1).

[0003] Patent Document 1: Japanese Patent Application Publication No. 2015-145801

[0004] For semiconductor pressure sensors that detect minute pressures, the diaphragm area needs to be increased and the thickness reduced in order to improve the detection sensitivity to pressure changes. For example, the diaphragm area is set to be less than or equal to 3 mm square and the thickness is set to be less than or equal to 20 μm.

[0005] In the current semiconductor pressure sensor, it is difficult to form or process a film on the back side of the diaphragm. In addition, in the current semiconductor pressure sensor, it is difficult to control the stress of the diaphragm because the laminated film provided only on the surface of the silicon substrate affects the stress characteristics of the diaphragm. Therefore, the slight pressure applied to the diaphragm is masked by the influence of the stress generated by the laminated film (deformation of the diaphragm), and the slight pressure cannot be detected with high accuracy. Summary of the invention

[0006] The present invention has been made to solve such a problem, and an object of the present invention is to provide a semiconductor pressure sensor capable of detecting minute pressure with high accuracy and a method for manufacturing the same.

[0007] In order to solve the above-mentioned problems, the semiconductor pressure sensor involved in the present invention comprises: a first silicon substrate; a first silicon oxide film, which is arranged on the first silicon substrate and constitutes a closed space together with the first silicon substrate; a second silicon substrate, which is arranged on the first silicon oxide film; a strain resistor, which is arranged on the surface of the second silicon substrate opposite to the surface on which the first silicon oxide film is arranged, and is located at a position overlapping with the closed space when viewed from above; a first electrode, which is electrically connected to one end of the strain resistor; and a second electrode, which is electrically connected to the other end of the strain resistor.

[0008] Effects of the Invention

[0009] According to the present invention, the semiconductor pressure sensor comprises: a first silicon oxide film, which is arranged on a first silicon substrate and constitutes a closed space together with the first silicon substrate; a second silicon substrate, which is arranged on the first silicon oxide film; a strain resistor, which is arranged on the surface of the second silicon substrate opposite to the surface on which the first silicon oxide film is arranged, and is located at a position overlapping with the closed space when viewed from above; a first electrode, which is electrically connected to one end of the strain resistor; and a second electrode, which is electrically connected to the other end of the strain resistor, so that tiny pressure can be detected with high precision. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is a plan view showing an example of the structure of the semiconductor pressure sensor according to the first embodiment.

[0011] Figure 2 yes Figure 1 A1-A2 section view.

[0012] Figure 3 yes Figure 1 B1-B2 cross-section diagram.

[0013] Figure 4 This is a flowchart showing an example of a manufacturing process of the semiconductor pressure sensor according to the first embodiment.

[0014] Figure 5 It is a plan view for explaining the manufacturing process of the semiconductor pressure sensor according to the first embodiment.

[0015] Figure 6 yes Figure 5 A1-A2 section view.

[0016] Figure 7 yes Figure 5 B1-B2 cross-section diagram.

[0017] Figure 8 It is a plan view for explaining the manufacturing process of the semiconductor pressure sensor according to the first embodiment.

[0018] Fig. 9 yes Figure 8 A1-A2 section view.

[0019] Fig.10 It is a plan view for explaining the manufacturing process of the semiconductor pressure sensor according to the first embodiment.

[0020] Fig.11 yes Fig.10 A1-A2 section view.

[0021] Fig.12 It is a plan view for explaining the manufacturing process of the semiconductor pressure sensor according to the first embodiment.

[0022] Fig.13 yes Fig.12 A1-A2 section view.

[0023] Fig.14 yes Fig.12 B1-B2 cross-section diagram.

[0024] Fig.15 yes Fig.12 A1-A2 section view.

[0025] Fig.16 yes Fig.12 A1-A2 section view.

[0026] Fig.17 It is a plan view for explaining the manufacturing process of the semiconductor pressure sensor according to the first embodiment.

[0027] Fig.18 yes Fig.17 A1-A2 section view.

[0028] Fig.19 yes Fig.17 B1-B2 cross-section diagram.

[0029] Fig. 20 It is a plan view showing an example of the structure of a semiconductor pressure sensor according to the second embodiment.

[0030] Fig.21 yes Fig. 20 A1-A2 section view.

[0031] Fig. 22 yes Fig. 20 B1-B2 cross-section diagram.

[0032] Fig.23 It is a plan view showing an example of the structure of a semiconductor pressure sensor according to the third embodiment.

[0033] Fig.24 yes Fig.23 A1-A2 section view.

[0034] Fig.25 yes Fig.23 B1-B2 cross-section diagram.

[0035] Fig.26 It is a plan view showing an example of the structure of a semiconductor pressure sensor according to the third embodiment.

[0036] Fig. 27 yes Fig.26 A1-A2 section view.

[0037] Fig.28 It is a plan view showing an example of the structure of a semiconductor pressure sensor according to a fourth embodiment.

[0038] Fig.29 yes Fig.28 A1-A2 section view.

[0039] Fig.30 yes Fig.28 B1-B2 cross-section diagram.

[0040] Fig.31 It is a cross-sectional view for explaining the manufacturing process of the semiconductor pressure sensor involved in the fourth embodiment.

[0041] Fig.32 It is a cross-sectional view for explaining the manufacturing process of the semiconductor pressure sensor involved in the fourth embodiment.

[0042] Fig.33 It is a cross-sectional view for explaining the manufacturing process of the semiconductor pressure sensor involved in the fourth embodiment.

[0043] Fig.34 It is a cross-sectional view for explaining the manufacturing process of the semiconductor pressure sensor involved in the fourth embodiment.

[0044] Fig.35 It is a cross-sectional view for explaining the manufacturing process of the semiconductor pressure sensor involved in the fourth embodiment. DETAILED DESCRIPTION

[0045] <Implementation Method 1>

[0046] <Structure>

[0047] Figure 1 This is a plan view showing an example of the structure of the semiconductor pressure sensor according to the first embodiment. Figure 2 yes Figure 1 A1-A2 section view. Figure 3 yes Figure 1 Next, refer to the B1-B2 section of Figures 1 to 3 , the structure of the semiconductor pressure sensor involved in embodiment 1 is described.

[0048] The first silicon substrate 1 may be of the first conductivity type (n type) or the second conductivity type (p type). In addition, since the first silicon substrate 1 is a base of an SOI (Silicon On Insulator) substrate, the thickness is set to about 200 to 900 μm.

[0049] The first silicon oxide film 2 is provided on the first silicon substrate 1, and has an outer edge portion, i.e., a thick film portion 2a, and an inner portion, i.e., a first thin film portion 2b. One surface of the thick film portion 2a is in contact with the first silicon substrate 1, and the other surface is in contact with the second silicon substrate 4. One surface of the first thin film portion 2b is opposite to the first silicon substrate 1 across the closed space 3, and the other surface is in contact with the second silicon substrate 4. In this way, the first silicon oxide film 2 and the first silicon substrate 1 together constitute the closed space 3.

[0050] The second silicon substrate 4 is of the first conductivity type (n type) and is provided on the first silicon oxide film 2. The diaphragm 10 corresponds to the portion of the second silicon substrate 4 overlapping the enclosed space 3 in plan view. That is, the diaphragm 10 and the enclosed space 3 are aligned in plan view.

[0051] If the pressure applied from the outside to the surface of the diaphragm 10 is set to P1, and the pressure in the closed space 3 is set to P2, the diaphragm 10 deforms in accordance with the pressure of (P2-P1). Specifically, since the pressure P1 applied from the outside to the surface of the diaphragm 10 is higher than the pressure P2 in the closed space 3, the diaphragm 10 deforms toward the first silicon substrate 1. Here, the first thin film portion 2b of the first silicon oxide film 2 functions as a stress adjustment film for the second silicon oxide film 5 and the protective film 6 present on the diaphragm 10. Therefore, by appropriately setting the film thickness of the first thin film portion 2b, the desired curved shape of the diaphragm 10 can be obtained.

[0052] In addition, the movable range of the diaphragm 10 can be determined by the interval between the first thin film portion 2b and the first silicon substrate 1 (the height of the closed space 3). Therefore, the interval between the first thin film portion 2b and the first silicon substrate 1 can be set by arbitrarily changing the thickness and shape of the first silicon oxide film 2 in such a manner that a stress greater than or equal to the breaking stress is not applied to the diaphragm 10 when excessive pressure is applied to the surface of the diaphragm 10 from the outside. In addition, in the first embodiment, the thickness of the first silicon oxide film 2 is about 0.5 to 5 μm, and the thickness of the diaphragm 10 on the second silicon substrate 4 is about 5 to 30 μm.

[0053] The gauge resistors 11a, 11b, 11c, and 11d are provided on the surface layer of the second silicon substrate 4 (the surface layer of the second silicon substrate 4 opposite to the surface on which the first silicon oxide film 2 is formed) and are located at a position overlapping with the diaphragm 10 when viewed from above. Specifically, the gauge resistors 11a, 11b, 11c, and 11d are as follows: Figure 1 As shown, they are provided on four sides defining the diaphragm 10. The strain resistors 11a, 11b, 11c, and 11d are of the second conductivity type (p-type) and are formed by ion implantation into the surface layer of the second silicon substrate 4.

[0054] The diffusion wirings 12a, 12b, 12c, and 12d are provided to contact one end or the other end of the strain resistors 11a, 11b, 11c, and 11d. For example, the diffusion wiring 12a (first diffusion wiring) contacts one end of the strain resistor 11a, and the diffusion wiring 12b (second diffusion wiring) contacts the other end of the strain resistor 11a. In addition, the one end and the other end described here may be interchanged. Figure 1 As shown, the strain resistors 11 a , 11 b , 11 c , and 11 d are connected to each other via diffusion wirings 12 a , 12 b , 12 c , and 12 d to form a Wheatstone bridge circuit.

[0055] If the diaphragm 10 is deformed due to the pressure difference (P1-P2) between the pressure P1 applied from the outside to the surface of the diaphragm 10 and the pressure P2 in the closed space 3, stress corresponding to the deformation amount of the diaphragm 10 is applied to the strain resistors 11a, 11b, 11c, and 11d, respectively. The strain resistors 11a, 11b, 11c, and 11d have the characteristic that the resistance value changes corresponding to the magnitude of the stress applied to themselves. Therefore, by connecting the strain resistors 11a, 11b, 11c, and 11d in a manner that constitutes a Wheatstone bridge circuit, the change in the resistance value of each of the strain resistors 11a, 11b, 11c, and 11d can be detected as an output voltage. The output voltage detected here is output to the outside from the electrodes 7a, 7b, 7c, and 7d respectively provided on the diffusion wiring 12a, 12b, 12c, and 12d. For example, the electrode 7a (the first electrode) is electrically connected to one end of the strain resistor 11a via the diffusion wiring 12a. In addition, the electrode 7 b (second electrode) is electrically connected to the other end of the strain resistor 11 a via the diffusion wiring 12 b .

[0056] In addition, the second silicon substrate 4 can be set to the second conductivity type (p type) and the strain resistors 11a, 11b, 11c, and 11d can be set to the first conductivity type (n type). However, in this case, the configuration of the strain resistors 11a, 11b, 11c, and 11d relative to the diaphragm 10 needs to be changed.

[0057] Since the purpose of the diffusion wiring 12a, 12b, 12c, 12d is to reduce the change in the resistance value of the diffusion wiring 12a, 12b, 12c, 12d when pressure is applied to the diaphragm 10, and to be used as wiring to connect the strain resistors 11a, 11b, 11c, 11d in a manner of forming a Wheatstone bridge circuit, it is necessary to set the resistance to be low. In the first embodiment, the diffusion surface concentration of the diffusion wiring 12a, 12b, 12c, 12d is set to 1e19-1e20 ions / cm 3In order to balance the resistance value, the change in resistance value corresponding to stress, and the temperature characteristics, the diffusion surface concentration of the strain resistors 11a, 11b, 11c, and 11d is set to 5e17 to 5e18 ions / cm 3 The diffusion depth is set to about 0.5 to 1.5 μm.

[0058] <Method of Detecting Pressure Using Diaphragm 10>

[0059] The pressure applied from the outside to the surface of the diaphragm 10 is defined as P1, and the pressure in the sealed space 3 is defined as P2. The sealed space 3 is a vacuum chamber, and the pressure P2 in the sealed space 3 is used as a reference pressure. Thus, the semiconductor pressure sensor according to the first embodiment has a function of measuring absolute pressure.

[0060] As described above, by bonding the first silicon substrate 1 and the second silicon substrate 4 via the first silicon oxide film 2 having the thick film portion 2a and the first thin film portion 2b, a cavity SOI substrate can be provided. Therefore, the bending shape of the diaphragm 10 can be controlled, the first silicon substrate 1 can be provided as a stopper structure, and a small pressure difference (P1-P2) can be detected.

[0061] The detection sensitivity to the pressure change can be controlled by the thickness of the diaphragm 10 and the area of ​​the diaphragm 10 when viewed from above. The thickness of the diaphragm 10 is determined by the thickness of the second silicon substrate 4. The area of ​​the diaphragm 10 is determined by the area of ​​the enclosed space 3 when viewed from above. In addition, the movable range of the diaphragm 10 can be controlled by the height of the enclosed space 3. The height of the enclosed space 3 is determined by the height difference between the thick film portion 2a and the first thin film portion 2b.

[0062] Thus, the movable range of the diaphragm 10 can be limited by making the first silicon substrate 1 forming the enclosed space 3 (the first silicon substrate 1 corresponding to the lower part of the enclosed space 3) function as a stopper in a manner that does not apply stress greater than or equal to the breaking strength to the diaphragm 10. Thus, the diaphragm 10 can be prevented from being damaged, and a semiconductor pressure sensor that is easy to operate can be obtained simply.

[0063] In addition, as a stress adjustment film of the second silicon oxide film 5 and the protective film 6 provided on the diaphragm 10, the first thin film portion 2b of the first silicon oxide film 2 is provided on the back side of the diaphragm 10. Thus, the stress applied to the diaphragm 10 is balanced, the desired curved shape of the diaphragm 10 is obtained, and the change of the curvature of the diaphragm 10 following the slight pressure change can be produced. In addition, if stress is applied to the strain resistors 11a, 11b, 11c, and 11d by slight pressure changes, their resistance values ​​change. Since the strain resistors 11a, 11b, 11c, and 11d are connected in a manner of forming a Wheatstone bridge circuit through the diffusion wiring 12a, 12b, 12c, and 12d, the output voltage changes correspondingly to the change of its own resistance value. By outputting such a change in the output voltage from the electrodes 7a, 7b, 7c, and 7d to the outside, slight pressure changes can be detected.

[0064] For example, in the case where the semiconductor pressure sensor can detect a pressure of about 1 atmosphere, the area of ​​the diaphragm 10 is set to 400 μm square, the thickness is set to 10 μm, and the height of the closed space 3 is set to about 1.5 μm, so that if a pressure of about 5 atmospheres is applied, the diaphragm 10 contacts the first silicon substrate 1. At this time, the first silicon substrate 1 functions as a stopper.

[0065] <Manufacturing method>

[0066] use Figures 4 to 19 A method for manufacturing the semiconductor pressure sensor according to the first embodiment will be described.

[0067] Figure 4 This is a flowchart showing an example of a manufacturing process of the semiconductor pressure sensor according to the first embodiment.

[0068] In step S1, if Figures 5 to 7 As shown, a first silicon oxide film 2 is formed on a second silicon substrate 4. The thickness of the first silicon oxide film 2 is about 0.5 to 5 μm. The first silicon oxide film 2 can be formed using a known technique. For example, by heating the second silicon substrate 4 at about 700 to 1100° C. in an oxygen environment, a silicon thermal oxide film (equivalent to the first silicon oxide film 2) is formed to transform the second silicon substrate into a silicon oxide film. Next, as Figure 6 As shown, the opening constituting the sealed space 3 is formed by performing photolithography and etching.

[0069] Then, if Figure 8 , 9As shown in FIG. 1 , an oxidation treatment is performed on the first silicon oxide film 2 and the second silicon substrate 4 formed as described above. Thus, a first silicon oxide film 2 having a thick film portion 2a and a first thin film portion 2b is formed. The thickness of the thick film portion 2a is about 0.01 to 2 μm. In order to make the first thin film portion 2b function as a stress control film of the diaphragm 10 formed in the subsequent process, the thickness of the first thin film portion 2b of the first silicon oxide film 2 is set to match the film stress characteristics of the second silicon oxide film 5 and the protective film 6 formed on the diaphragm 10 in the subsequent process.

[0070] like Fig. 9 As shown, the height difference between the thick portion 2a and the first thin portion 2b of the first silicon oxide film 2 corresponds to the height of the sealed space 3. That is, the movable range of the diaphragm 10 can be determined by the height difference between the thick portion 2a and the first thin portion 2b.

[0071] In step S2, if Fig.10 , 11 As shown in the figure, the first silicon substrate 1 and the second silicon substrate 4 are bonded to each other by laminating them with the first silicon oxide film 2 interposed therebetween and performing heat treatment. Thus, a closed space 3 is formed by the thick film portion 2a and the first thin film portion 2b of the first silicon oxide film 2 and the first silicon substrate 1. In addition, the closed space 3 becomes a vacuum chamber by bonding the first silicon substrate 1 and the second silicon substrate 4 in a vacuum environment. The pressure P2 of the closed space 3 thus formed is a reference pressure relative to the pressure P1 applied to the diaphragm 10 formed in a subsequent process.

[0072] In the above, the case where the first silicon substrate 1 and the second silicon substrate 4 are bonded after the first silicon oxide film 2 is formed on the second silicon substrate 4 is described, but the present invention is not limited thereto. For example, the thick film portion 2a may be formed on the first silicon substrate 1, the first thin film portion 2b may be formed on the second silicon substrate 4, and then the first silicon substrate 1 and the second silicon substrate 4 may be bonded.

[0073] In step S3, if Figures 12-14 As shown, the second silicon substrate 4 is polished to a desired thickness of the diaphragm 10. Thus, the portion of the second silicon substrate 4 overlapping the enclosed space 3 in a plan view functions as the diaphragm 10. By adjusting the thickness of the diaphragm 10, the pressure detection sensitivity can be controlled.

[0074] In addition, for example, Fig.13 Although the description has been given of a case where the first thin film portion 2 b of the first silicon oxide film 2 is formed so as to cover the entire back surface of the diaphragm 10 , the present invention is not limited thereto.

[0075] For example, you can also Fig.15As shown, the first silicon oxide film 2 has an opening at the center of the first thin film portion 2 b. With such a structure, the stress applied to the diaphragm 10 can be adjusted from the edge to the center of the diaphragm 10 .

[0076] In addition, for example, Fig.16 As shown, the first silicon oxide film 2 has an opening at a position overlapping with the edge of the diaphragm 10 when viewed from above, and has a second thin film portion 2c thicker than the first thin film portion 2b at the center of the first thin film portion 2b. With such a structure, the stress control of the diaphragm 10 can be adjusted from the back side of the diaphragm 10 in consideration of the film stress on the surface side of the diaphragm 10, so the curved shape of the diaphragm 10 can be controlled with further high precision.

[0077] In step S4, Figures 17 to 19 As shown, strain resistors 11 a , 11 b , 11 c , and 11 d and diffusion wirings 12 a , 12 b , 12 c , and 12 d are formed on the second silicon substrate 4 .

[0078] Specifically, the impurity injection is performed after the second silicon substrate 4 is subjected to oxidation treatment and photolithography treatment. Thereafter, the diffusion wirings 12a, 12b, 12c, and 12d are formed by performing annealing treatment and oxidation treatment. The diffusion wirings 12a, 12b, 12c, and 12d are low-resistance wirings for connecting the strain resistors 11a, 11b, 11c, and 11d to be formed next in a manner of forming a Wheatstone bridge. In the first embodiment, the impurity concentration injected is set to 5e14 to 5e15 ions / cm 2 The annealing temperature is set to about 1000 to 1100° C., and an oxidation treatment is performed to about 100 to 500 nm to form a diffusion layer with a diffusion depth of about 2 to 5 μm. Thus, low-resistance diffusion wirings 12a, 12b, 12c, and 12d are realized.

[0079] Next, after oxidation treatment and photolithography treatment, impurity injection is performed. After that, annealing treatment is performed to form strain resistors 11a, 11b, 11c, and 11d. The strain resistors 11a, 11b, 11c, and 11d are connected to each other through diffusion wiring 12a, 12b, 12c, and 12d to form a Wheatstone bridge circuit. In the first embodiment, the impurity concentration injected when forming the strain resistors 11a, 11b, 11c, and 11d is 1e13 to 1e14 ions / cm 2 If the impurity concentration is set low, the detection sensitivity for pressure changes becomes higher, but the temperature characteristics become worse. Therefore, the appropriate impurity concentration is set in consideration of the trade-off relationship between detection sensitivity and temperature characteristics.

[0080] In step S5, Figures 17 to 19 As shown, a second silicon oxide film 5 , electrodes 7 a , 7 b , 7 c , 7 d , and a protective film 6 are formed on a second silicon substrate 4 .

[0081] Specifically, after all the oxide films deposited when forming the diffusion wirings 12a, 12b, 12c, 12d and the strain resistors 11a, 11b, 11c, 11d are removed, the second silicon oxide film 5 is formed on the second silicon substrate 4. In this way, the second silicon oxide film 5 formed on the surface of the diaphragm 10 becomes flat, and the deformation characteristics of the diaphragm 10 corresponding to the pressure change become good. In addition, a PSG (Phospho Silicate Glass) film or a BPSG (Boro-Phospho Silicate Glass) film may be deposited on the second silicon oxide film 5 as a passivation film (not shown).

[0082] Next, in order to output electric signals to the outside from the diffusion wirings 12a, 12b, 12c, and 12d, photolithography and etching are performed to form contact holes (not shown). Thereafter, a metal film such as AlSi, AlCu, Al, or AlSiCu is deposited on the second silicon substrate 4 and then photolithography and etching are performed to form electrodes 7a, 7b, 7c, and 7d in the contact holes.

[0083] Next, the protective film 6 is formed. For example, a nitride film is deposited on the entire surface by plasma CVD (Chemical Vapor Deposition), and then photolithography and etching are performed to form the protective film 6 having openings only at desired positions (part of the surface of the electrodes 7a, 7b, 7c, 7d).

[0084] The semiconductor pressure sensor completed through the manufacturing steps of steps S1 to S5 is an absolute pressure sensor that uses the pressure P2 of the vacuum chamber, that is, the closed space 3 as a reference pressure and detects the pressure P1 applied to the surface of the diaphragm 10 .

[0085] <Effect>

[0086] According to Embodiment 1, the first thin film portion 2b of the first silicon oxide film 2 serving as a stress control film is provided on the back side of the diaphragm 10. Therefore, the first thin film portion 2b can achieve a balance between the stress of the second silicon oxide film 5 or the protective film 6 provided on the surface of the diaphragm 10, and the stress applied to the diaphragm 10 can be controlled to obtain a desired curved shape of the diaphragm 10.

[0087] Generally, when a pressure within the detection range of the semiconductor pressure sensor is applied to the diaphragm 10, the diaphragm 10 is controlled to bend toward the closed space 3. Thus, a minute pressure change can be detected with high accuracy as a change in the amount of bending of the diaphragm 10. The change in the amount of bending of the diaphragm 10 can be detected as a change in stress applied to the strain resistors 11a, 11b, 11c, and 11d provided on the four sides of the diaphragm 10, a change in the resistance value of the strain resistors 11a, 11b, 11c, and 11d, and a change in the output voltage of a Wheatstone bridge formed by connecting the strain resistors 11a, 11b, 11c, and 11d via diffused wirings 12a, 12b, 12c, and 12d.

[0088] As described above, according to the first embodiment, a semiconductor pressure sensor capable of detecting minute pressure with high accuracy can be obtained through a simple manufacturing process.

[0089] <Implementation Method 2>

[0090] Fig. 20 It is a plan view showing an example of the structure of a semiconductor pressure sensor according to the second embodiment. Fig.21 yes Fig. 20 A1-A2 section view. Fig. 22 yes Fig. 20 Next, refer to the B1-B2 section of Figures 20-22 , the structure of the semiconductor pressure sensor involved in embodiment 2 is described.

[0091] In the second embodiment, it is characterized in that a protective film stress adjustment groove 13 (first groove) is provided in the protective film 6 provided on the surface of the diaphragm 10. In other words, the protective film 6 has the protective film stress adjustment groove 13 provided at a position overlapping with the closed space 3 when viewed from above. Since the other structures are the same as those in the first embodiment, detailed description is omitted here.

[0092] Next, a method for forming the protective film stress adjustment groove 13 will be described. In addition, regarding the method for manufacturing the semiconductor pressure sensor according to the second embodiment, the manufacturing steps other than the step of forming the protective film stress adjustment groove 13 are the same as those of the first embodiment.

[0093] exist Figure 4 After the protective film 6 is formed in step S5, a photolithography process is performed, and the protective film is etched using a resist mask (not shown). Thus, a protective film stress adjustment groove 13 is formed in the protective film 6. Since the protective film stress adjustment groove 13 can be formed by the same process as the process of opening a part of the surface of the electrodes 7a, 7b, 7c, 7d, there is no need to add a process.

[0094] Thus, according to the second embodiment, by providing the protective film stress adjustment groove 13 in the protective film 6, the stress applied to the diaphragm 10 can be adjusted, so the bending shape of the diaphragm 10 can be controlled with higher accuracy. In addition, such a semiconductor pressure sensor can be easily obtained.

[0095] <Implementation Method 3>

[0096] Fig.23 It is a plan view showing an example of the structure of a semiconductor pressure sensor according to the third embodiment. Fig.24 yes Fig.23 A1-A2 section view. Fig.25 yes Fig.23 Next, refer to the B1-B2 section of Figures 23 to 25 , the structure of the semiconductor pressure sensor involved in embodiment 3 is described.

[0097] In the third embodiment, a groove 14 (second groove) is provided in the second silicon substrate 4 along the edge of the diaphragm 10. In other words, the second silicon substrate 4 has a groove 14 provided along the outer edge of the closed space 3 when viewed from above on the surface opposite to the surface provided with the first silicon oxide film 2. Since the other structures are the same as those in the second embodiment, detailed description is omitted here.

[0098] The groove 14 has a width of about 3 to 30 μm and a depth of about 0.3 to 3 μm.

[0099] Next, a method for forming the concave groove 14 will be described. In addition, regarding the method for manufacturing the semiconductor pressure sensor according to the third embodiment, the manufacturing steps other than the step of forming the concave groove 14 are the same as those of the second embodiment.

[0100] exist Figure 4 After the second silicon substrate 4 is polished in step S3, a photolithography process is performed, and the second silicon substrate 4 is etched using a resist mask (not shown). Thus, the groove 14 is formed in the second silicon substrate 4.

[0101] As another forming method different from the above, the recess 14 may be formed by locally oxidizing the portion where the recess 14 is to be formed by LOCOS (Local Oxidation of Silicon) oxidation to form an oxide film, and then removing the oxide film.

[0102] Thus, according to the third embodiment, by providing the groove 14 in the second silicon substrate 4, the same effect as the case of making the entire diaphragm 10 thinner can be obtained, so that the detection sensitivity of the diaphragm 10 for a small pressure change can be improved. In addition, since the area of ​​the diaphragm 10 can be reduced, the size of the semiconductor pressure sensor can be reduced, so that the cost can be reduced.

[0103] In addition, if Fig.26 , 27 As shown in FIG. 1 , a protective film stress adjustment groove 13 b may also be provided along the edge (groove 14) of the diaphragm 10. Fig.23 The protective film stress adjustment groove 13 is equivalent. By setting it as such a structure, the detection sensitivity of the diaphragm 10 for a small pressure change can be improved. In addition, the area of ​​the diaphragm 10 can be reduced.

[0104] In the above, the case where the groove 14 is provided in the structure described in the second embodiment is described, but the present invention is not limited to this. For example, the groove 14 may be provided in the structure described in the first embodiment.

[0105] <Implementation Method 4>

[0106] Fig.28 It is a plan view showing an example of the structure of a semiconductor pressure sensor according to a fourth embodiment. Fig.29 yes Fig.28 A1-A2 section view. Fig.30 yes Fig.28 Next, refer to the B1-B2 section of Figures 28-30 , the structure of the semiconductor pressure sensor involved in embodiment 4 is described.

[0107] In the fourth embodiment, it is characterized in that a diaphragm edge stress adjustment groove 15 (third groove) is provided on the second silicon substrate 4 along the edge of the back side of the diaphragm 10. In addition, it is characterized in that a pit 16 is provided in the central area of ​​the back side of the diaphragm 10. In other words, the second silicon substrate 4 has a diaphragm edge stress adjustment groove 15 provided on the surface on which the first silicon oxide film 2 is provided and provided on the inner periphery of the enclosed space 3 when viewed from above. In addition, the second silicon substrate 4 has a pit 16 provided on the surface on which the first silicon oxide film 2 is provided and provided in the center of the enclosed space 3 when viewed from above. Since the other structures are the same as those in the first embodiment, detailed descriptions are omitted here.

[0108] Next, use Figures 31-35 , a method for forming the diaphragm edge stress adjustment groove 15 and the pit 16 is described. In addition, regarding the manufacturing method of the semiconductor pressure sensor involved in the fourth embodiment, the manufacturing process other than the process of forming the diaphragm edge stress adjustment groove 15 and the pit 16 is the same as that of the first embodiment. Figures 31-35 The manufacturing process shown is similar to Figure 4 is equivalent to step S1.

[0109] First, if Fig.31 As shown, an oxide film 17 and a nitride film 18 are sequentially formed on the second silicon substrate 4. The thickness of the oxide film 17 and the nitride film 18 are both about 50 to 100 nm. After that, a photolithography process is performed, and only the nitride film 18 is etched using a resist mask (not shown). In the opening of the nitride film 18 formed by the etching process, the diaphragm edge stress adjustment groove 15 and the pit 16 are formed in the subsequent process.

[0110] Then, if Fig.32 As shown, the LOCOS oxide film 19 is formed by performing oxidation treatment. The oxide film thickness is about 500 to 1600 nm. As a result, the opening of the nitride film 18 is partially oxidized, so that the surface layer of the second silicon substrate 4 is also oxidized.

[0111] Then, if Fig.33 As shown, the LOCOS oxide film 19, the nitride film 18, and the oxide film 17 are sequentially etched and removed using hydrogen fluoride (HF) and hot phosphoric acid. As a result, the diaphragm edge stress adjustment groove 15 and the pit 16 are formed in the second silicon substrate 4.

[0112] Then, if Fig.34 , 35 As shown in FIG. 1 , a thick film portion 2 a and a first thin film portion 2 b of the first silicon oxide film 2 are formed.

[0113] Thus, according to the fourth embodiment, the diaphragm edge stress adjustment groove 15 (third groove) is provided on the second silicon substrate 4 along the edge of the back side of the diaphragm 10, thereby improving the strength of the diaphragm 10. In addition, since the edge of the diaphragm 10 can be thinned, the detection sensitivity of the diaphragm 10 to a small pressure change can be further improved. In addition, since the area of ​​the diaphragm 10 can be reduced, the size of the semiconductor pressure sensor can be reduced, so that the cost can be reduced.

[0114] Furthermore, by providing the recess 16 in the central region of the back surface of the diaphragm 10, when excessive pressure or impact is applied to the diaphragm 10 and the diaphragm 10 contacts the first silicon substrate 1, the contact area between the diaphragm 10 and the first silicon substrate 1 can be reduced. Thus, adhesion (adhesion) between the diaphragm 10 and the first silicon substrate 1 can be prevented.

[0115] Since the above-mentioned effects can be obtained without impairing the effects of the first embodiment, a semiconductor pressure sensor that has high reliability and can detect minute pressure changes with high accuracy can be easily obtained.

[0116] Furthermore, the various embodiments may be freely combined within the scope of the present invention, and the various embodiments may be appropriately modified or omitted.

[0117] Description of the label

[0118] 1 the first silicon substrate, 2 the first silicon oxide film, 2a the thick film portion, 2b the first thin film portion, 2c the second thin film portion, 3 the main opening portion, 4 the second silicon substrate, 5 the second silicon oxide film, 6 the protective film, 7a, 7b, 7c, 7d the electrodes, 10 the diaphragm, 11a, 11b, 11c, 11d the strain resistors, 12a, 12b, 12c, 12d the diffusion wiring, 13 the protective film stress adjustment groove, 13a the protective film stress adjustment groove, 13b the protective film stress adjustment groove, 14 the groove, 15 the diaphragm edge stress adjustment groove, 16 the pit, 17 the oxide film, 18 the nitride film, 19 the LOCOS oxide film.

Claims

1. A semiconductor pressure sensor, comprising: 1st silicon substrate; a first silicon oxide film disposed on the first silicon substrate and forming a closed space together with the first silicon substrate; a second silicon substrate disposed on the first silicon oxide film; a strain resistor provided on a surface layer of a surface of the second silicon substrate opposite to a surface provided with the first silicon oxide film and located at a position overlapping with the closed space when viewed from above; a first electrode electrically connected to one end of the strain resistor; and a second electrode electrically connected to the other end of the strain resistor, The surface of the first silicon substrate on which the first silicon oxide film is provided is flat.

2. The semiconductor pressure sensor according to claim 1, wherein: The first silicon oxide film has: a thick film portion, one surface of which is in contact with the first silicon substrate and the other surface of which is in contact with the second silicon substrate; and The first thin film portion has one surface facing the first silicon substrate via the sealed space and the other surface in contact with the second silicon substrate.

3. The semiconductor pressure sensor according to claim 1 or 2, wherein: Also features: a second silicon oxide film disposed on the second silicon substrate; and a protective film disposed on the second silicon oxide film, The protective film has a first groove provided at a position overlapping with the sealed space in a plan view.

4. The semiconductor pressure sensor according to claim 1 or 2, wherein: The second silicon substrate has a second groove provided on a surface opposite to the surface provided with the first silicon oxide film and along an edge of the sealed space in a plan view.

5. The semiconductor pressure sensor according to claim 2, wherein: The first silicon oxide film has an opening portion provided at the center of the first thin film portion, The second silicon substrate is arranged in a manner covering the opening. The sealed space is formed by the first silicon substrate, the thick film portion, the first thin film portion, and the second silicon substrate.

6. The semiconductor pressure sensor according to claim 2, wherein: The first silicon oxide film has a second thin film portion at the center of the first thin film portion that is thicker than the first thin film portion.

7. The semiconductor pressure sensor according to claim 1 or 2, wherein: The second silicon substrate has a third groove provided on the surface provided with the first silicon oxide film and provided on the inner periphery of the sealed space in a plan view.

8. The semiconductor pressure sensor according to claim 1 or 2, wherein: The second silicon substrate has a recess provided on the surface provided with the first silicon oxide film and provided at the center of the sealed space in a plan view.

9. A method for manufacturing a semiconductor pressure sensor, comprising the following steps: (a) preparing a first silicon substrate; (b) preparing a second silicon substrate; (c) forming a first silicon oxide film on the second silicon substrate in such a manner that the outer edge portion is thicker than the inner portion; (d) bonding the first silicon substrate and the second silicon substrate together in such a manner as to sandwich the first silicon oxide film; (e) forming a strain resistor by implanting impurities into a position overlapping the inner portion when viewed from above, with respect to a surface layer of the second silicon substrate opposite to the surface on which the first silicon oxide film is formed; (f) implanting impurities into a surface layer of a surface of the second silicon substrate opposite to the surface on which the first silicon oxide film is formed, thereby forming a first diffusion wiring in contact with one end of the strain resistor; (g) implanting impurities into a surface layer of a surface of the second silicon substrate opposite to the surface on which the first silicon oxide film is formed, thereby forming a second diffusion wiring in contact with the other end of the strain resistor; (h) forming a first electrode on the first diffusion wiring; as well as (i) A second electrode is formed on the second diffusion wiring.

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