JP2015194443A - Method for manufacturing differential pressure detecting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a differential pressure detecting element, capable of suppressing the formation of a notch affecting deflection characteristics of a cantilever part in the vicinity of the hinge of the cantilever part to detect a flow rate with high accuracy.SOLUTION: The method for manufacturing a differential pressure detecting element including a cantilever part comprises the steps of: forming a depression on one surface of a first silicon substrate; preparing a second silicon substrate having an insulation layer formed on one surface to join the one surface of the first silicon substrate to the one surface of the second silicon substrate; forming a piezoresistance layer on the other surface of the second silicon substrate; forming a metal layer on the piezoresistance layer of the second silicon substrate; etching the second silicon substrate until the insulation layer is exposed from the other surface side of the second silicon substrate; forming a via hole from the other surface of the first silicon substrate to the depression by a dry etching method; and removing the insulation layer exposed on the bottom surface of the via hole.

Description

  The present invention relates to a method for manufacturing a differential pressure detecting element having a cantilever portion.

  As a differential pressure detecting element, a cantilever portion having a piezoresistive layer and a substrate that supports the cantilever portion so as to be elastically deformable, and the cantilever portion protrudes into a pressure introducing hole formed in the substrate are known. (See, for example, Patent Document 1). The differential pressure detecting element can measure the fluid pressure from the deformation amount of the cantilever part that is deformed by the pressure difference between the one surface side and the other surface side of the cantilever part.

  FIG. 9 is a diagram schematically showing the differential pressure detection element disclosed in Patent Document 1. As shown in FIG. The differential pressure detecting element 50 shown in FIG. 9 is a stacked body in which a silicon substrate 51, an insulating layer 52, a silicon layer 53, a piezoresistive layer 54, and a metal layer 55 are stacked in this order, and the piezoresistive layer 54 and the silicon layer 53 are stacked. Thus, a cantilever portion 58 having a predetermined shape is formed.

  10A to 10E are diagrams showing a manufacturing process of the conventional differential pressure detecting element 50 shown in FIG. First, an SOI (Silicon On Insulator) substrate 57 in which a silicon substrate 51, an insulating layer 52, and a silicon layer 53 are sequentially stacked is prepared. Then, an impurity element is diffused to a certain depth of the silicon layer 53 to form a piezoresistor 54. As a result, a laminated body in which the silicon substrate 51, the insulating layer 52, the silicon layer 53, and the piezoresistive layer 54 are formed is prepared (FIG. 10A).

  Next, a metal layer 55 is formed on the piezoresistive layer 54, and the metal layer 55 is patterned by etching. The metal layer 55 remaining in the predetermined pattern becomes the electrodes 55a and 55b and the wiring 55c (FIG. 10B).

  Next, a part of the silicon layer 53 and the piezoresistive layer 54 in a region to be a gap 57 described later is etched (FIG. 10C).

  Next, the silicon substrate 51 is etched from the back surface of the silicon substrate 51 (the surface on which the insulating layer 52 to the piezoresistive layer 54 are not formed) to form via holes 56. Etching of the silicon substrate 51 proceeds until the insulating layer 52 is exposed. As a result, a via hole 56 whose bottom surface is the silicon oxide layer 52 is formed (FIG. 10D).

In order to form the via hole 56, a DRIE (Deep Reactive Ion Etching) method is generally used. The procedure is as follows. First, an etching mask is formed on the back surface of the silicon substrate 51 by opening a portion where the via hole 56 is to be formed. Next, the silicon substrate 51 exposed in the opening region of the etching mask is etched using the reaction gas 1 in which SF ₆ and O ₂ are mixed, and the etching is advanced until the insulating layer 52 is reached. The insulating layer 52 is a silicon oxide (SiO ₂ ) thin film having a thickness of about 0.5 μm to 3.0 μm. Since silicon oxide is not decomposed into the reactive gas 1, it functions as an etching stopper. The etching of the silicon substrate 51 is terminated when the bottom surface of the via hole 56 reaches the insulating layer 52.

  After the via hole 56 is formed, the insulating layer 52 on the bottom surface of the via hole 56 is removed by RIE (Reactive Ion Etching) method (FIG. 10E). A fluorine-based reaction gas 2 is used as the reaction gas. When the etching of the insulating layer 52 is completed, a cantilever portion 58 composed of the silicon layer 53 and the piezoresistive layer 54 is formed. Thereby, the differential pressure detecting element 50 is completed.

JP2012-145356

  However, the conventional method for manufacturing a differential pressure detecting element has the following problems.

  In the formation of the via hole 56 shown in FIG. 10D, when the etching of the silicon substrate 51 by the DRIE method reaches the insulating layer 52, the dry etching of the silicon substrate 51 is terminated at that point. However, in the actual manufacturing process, the etching rate becomes unstable as the via hole 56 approaches the insulating layer 52, so that the via hole may not reach the silicon oxide layer 52 in some cases. Therefore, in an actual manufacturing process, it is necessary to perform etching over a longer time than expected from theoretical calculation, and to form the via hole 56 with the insulating layer 52 exposed on the bottom surface with good reproducibility.

  Due to the above-described circumstances, the silicon substrate 51 is exposed to long-time dry etching. However, in this case, a notch (recess) 60 may be formed on the side wall near the bottom surface of the via hole 56. This notch 60 is due to abnormal etching of the silicon substrate 51. Charges in the plasma are accumulated in the insulating layer 52 at the bottom of the via hole, and reaction radicals approaching the insulating layer 52 are coulombs of the charges accumulated in the insulating layer 52. It is thought to be formed by rebounding to the side wall side under the force.

  The notch 60 formed by the abnormal etching remains even after the differential pressure detecting element 50 is completed. As shown in FIG. 9, since the notch 60 is formed in the vicinity of the hinge of the cantilever part 58, there is a possibility of affecting the bending characteristics of the cantilever part 58. In addition, since the notch 60 is also formed near the free end of the cantilever part 58, when the width of the gap 57 is wide enough to allow the airflow to flow, turbulence occurs in the airflow passing through the gap 57, and the cantilever part 58 is formed. May affect the deflection characteristics of the. Therefore, the differential pressure detecting element 50 in which the notch 60 is formed has a problem that it is difficult to accurately measure the flow rate.

  The present invention has been made in view of such circumstances. In the vicinity of the hinge of the cantilever part, the formation of a notch that affects the bending characteristics of the cantilever part is suppressed, and the differential pressure capable of detecting the flow rate with high accuracy. It is an object to provide a method for manufacturing a detection element.

The method for manufacturing a differential pressure detecting element of the present invention is a method for manufacturing a differential pressure detecting element provided with a cantilever part, the step of forming a recess on one surface of the first silicon substrate (step S1),
Preparing a second silicon substrate having an insulating layer formed on one surface and bonding one surface of the first silicon substrate and one surface of the second silicon substrate (step S2);
(2) forming a piezoresistive layer on the other surface of the silicon substrate (step S4);
Forming a metal layer on the piezoresistive layer of the second silicon substrate (step S5);
Etching the second silicon substrate until the insulating layer is exposed from the other surface side of the second silicon substrate (step S6);
Forming a via hole from the other surface of the first silicon substrate to the recess by a dry etching method (step S7);
Removing the insulating layer exposed in the via hole from the other surface side of the first silicon substrate (step S8);
It is characterized by having.

  According to the method of manufacturing a differential pressure detecting element of the present invention, in the step of forming a via hole in the first silicon substrate (step S7), the via hole is formed until reaching the concave portion, so that it is not affected by the insulating layer. The first silicon substrate is etched at a stable etching rate with good reproducibility. Therefore, it is possible to suppress the formation of a notch near the hinge of the cantilever part.

In the method for manufacturing the differential pressure detecting element, it is preferable that a step (Step S3) of thinning the second silicon substrate is provided between Step S2 and Step S4.
In this case, the step of thinning the second silicon substrate (step S2) between the step of bonding the first silicon substrate and the second silicon substrate (step S2) and the step of forming the piezoresistive layer (step S4). Since S3) is performed, a thin plate-like cantilever part can be easily formed.

In the above-described method for manufacturing the differential pressure detecting element, in step S1, an alignment mark is formed on one surface of the first silicon substrate at the same time as forming the recess.
In this case, in step S1, since the concave mark is formed and the alignment mark is formed on one surface of the first silicon substrate, the metal layer and the cantilever part can be easily patterned using the alignment mark formed in step S1. Can do.

  According to the method for manufacturing a differential pressure detecting element of the present invention, formation of a notch that affects the bending characteristics of the cantilever part is suppressed in the vicinity of the hinge of the cantilever part. Therefore, it is possible to provide a method for manufacturing a differential pressure detecting element capable of detecting a flow rate with high accuracy.

FIG. 1 is a cross-sectional view of a differential pressure detecting element according to an embodiment of the present invention. FIG. 2 is a plan view of the differential pressure detecting element in the embodiment of the present invention. FIG. 3 is a diagram of a flow rate measuring device configured using the differential pressure detecting element in the embodiment of the present invention. FIG. 4A and FIG. 4B are diagrams for explaining the operation of the differential pressure detecting element in the embodiment of the present invention. FIG. 5 is a process flow diagram of the manufacturing method of the differential pressure detecting element in the embodiment of the present invention. 6A to 6D are cross-sectional views showing step S1 to step S4 in FIG. FIGS. 7A to 7D are cross-sectional views showing steps S5 to S8 in FIG. 8A to 8D are cross-sectional views showing steps S5 to S8 in FIG. FIG. 9 is a cross-sectional view of a conventional differential pressure detecting element. FIG. 10 is a diagram showing a conventional method for manufacturing a differential pressure detecting element.

  Hereinafter, modes for carrying out the present invention will be described.

(Differential pressure detection element)
The differential pressure detecting element 10 of the present embodiment will be described with reference to FIGS.
FIG. 1 is a cross-sectional view of the differential pressure detecting element 10, and FIG. 2 is a plan view of the differential pressure detecting element 10. The cross-sectional structure taken along the line AA ′ in FIG. 2 corresponds to the cross-sectional view in FIG. FIG. 3 shows an example of the flow rate measuring device 1 using the differential pressure detecting element 10.

  The differential pressure detecting element 10 of this embodiment can be used as the flow rate measuring device 1 shown in FIG. 3, for example. The flow rate measuring device 1 shown in FIG. 3 has a function of measuring the flow rate of the fluid flowing through the main channel 2. The flow rate measuring device 1 includes a bypass path 3 provided side by side with the main flow path 2, a differential pressure detection element 10 in the bypass path 3, and a flow rate calculation unit 5 electrically connected to the differential pressure detection element 10. It is equipped with. One end and the other end of the bypass path 3 are connected to the upstream side and the downstream side of the main flow path 2, respectively.

  In FIG. 3, the fluid flows in the direction indicated by the arrow F in the main flow path 2. A specific example of the fluid flowing through the main flow path 2 is a gas such as air. The direction in which the fluid flows is not limited to the direction of the arrow F shown in the main flow path 2 in FIG. 3, and may flow in the direction opposite to the direction of the arrow F.

  A differential pressure detecting element 10 provided in the bypass 3 is a cantilever type differential pressure detecting element. As will be described later, the differential pressure detecting element 10 includes a frame portion 17 and a cantilever portion 18, and a gap 19 is provided between the frame portion 17 and the cantilever portion 18.

  One end of the bypass path 3 is connected to the upstream side of the main flow path 2 and communicates with the inside of the main flow path 2 through the opening 3a. Similarly, the other end of the bypass path 3 is connected to the downstream side of the main flow path 2 and communicates with the inside of the main flow path 2 through the opening 3b. A differential pressure detecting element 10 having a cantilever portion 18 formed therein is provided in the bypass passage 3, and the pressure receiving surface of the cantilever portion 18 is perpendicular to the direction in which the bypass passage 3 extends.

The pressure of the fluid flowing in the main flow path 2 is transmitted to the pressure detection element 10 through the bypass 3 from the openings 3a and 3b. More specifically, the pressure Pa in the upstream opening 3 _a is applied to the one surface 18 _a of the cantilever portion 18, and the pressure P _b in the downstream opening 3 _b is applied to the other surface 18 _b of the cantilever portion 18. At this time, when there is a pressure difference between the pressure P _a and the pressure P _b, the cantilever portion 18 is deformed. For example, if P _a <P _b , the cantilever portion 18 is deformed so as to bend toward the one surface 18a side, that is, the opening 3a side. Conversely, if P _a > P _b , the cantilever portion 18 is deformed so as to bend toward the other surface 18b side, that is, the opening 3b side. If P _a = P _b , the cantilever portion 18 is not bent and is kept flat.

Pressure sensing element 10, the deformation amount of the cantilever portion 10, detects a pressure difference between the pressure P _a and the pressure P _b. The detected differential pressure value is transmitted to the flow rate calculation unit 5 and converted into a flow rate of the fluid flowing in the main flow path 2 by a predetermined coefficient. Then, the flow rate data calculated by the flow rate calculation unit 5 is output from the flow rate measuring device 1 as the flow rate of the fluid flowing in the main flow path 2.

  As shown in FIG. 1, the differential pressure detecting element 10 includes a first silicon substrate 11, an insulating layer 12, a silicon layer 13, a piezoresistive layer 15, a frame portion 17 including a metal layer 16, a silicon layer 13, and a piezoresistive layer. This is a MEMS (Micro Electro Mechanical Systems) element including a cantilever portion 18 made of 15.

  The frame portion 17 included in the differential pressure detecting element 10 is formed in a substantially square shape having an opening in the center in plan view, and includes a first silicon substrate 11, an insulating layer 12, a silicon layer 13, a piezoresistive layer 15, It is a laminated body in which the metal layers 16 are sequentially laminated. The cantilever portion 18 is a thin plate composed of two layers, a silicon layer 13 and a piezoresistive layer 15.

  As shown in FIG. 2, the cantilever portion 18 is formed to protrude from one side of the four sides of the rectangular opening of the frame portion 17. The cantilever portion 18 is integrally connected to the frame portion 17 by hinges 20a and 20b. The cantilever portion 18 is not connected to the frame portion 17 except for the hinges 20 a and 20 b, and a gap (gap) 19 is provided between the cantilever portion 18 and the frame portion 17. The width of the gap 19 is preferably about 0.1 [μm] to 10 [μm]. Piezoresistors 15a and 15b are formed in the hinges 20a and 20b, respectively.

  The metal layer 16 of the differential pressure detecting element 10 functions as an electrode or wiring for measuring the electric resistance value of the piezoresistors 15a and 15b. More specifically, the metal layer 16 is separated into three regions: an electrode 16a connected to the piezoresistor 15a, an electrode 16b connected to the piezoresistor 15b, and a wiring 16c connecting the piezoresistors 15a and 15b. Is formed. The electrode 16a and the electrode 16b are electrically separated by a groove 22 formed by exposing the silicon layer 13. Thus, an electric circuit is formed in which the electrode 16a, the piezoresistor 15a, the wiring 16c, the piezoresistor 15b, and the electrode 16b are connected in series.

(Operation of differential pressure detection element)
Next, the operation of the differential pressure detecting element 10 of this embodiment will be described with reference to FIG. FIG. 4A is a view showing a flat state without the cantilever portion 18 being deformed. FIG. 4B is a view showing a state where the cantilever portion 18 is bent and deformed. The pressure P _a on the side of one surface 18a of the cantilever portion 18, in the case where there is no pressure difference between the pressure P _b of a side of the other surface 18b, the cantilever section 18 without deforming, to the main surface of the silicon substrate Are almost parallel. If there is a pressure difference between the pressure P _b of the pressure P _a and the other surface 18b side of the one surface 18a side of the cantilever portion 18, the cantilever portion 18 deflects to the side of lower pressure. The deformation of the cantilever part 18 is an elastic deformation around the hinge 20 that is the base of the cantilever part 18.

When the cantilever portion 18 is deformed, a distortion stress is generated in the hinge 20. When strain stress is generated in the hinge 20, the electrical resistance values of the piezoresistors 15a and 15b of the hinge portion 20 change due to the piezoresistive effect. The amount of change in the electrical resistance value of the piezoresistors 15a and 15b corresponds to the magnitude of strain stress generated in the hinges 20a and 20b. That is, the hinge 20a in response to a pressure difference between the pressure _{P b} of the side of the pressure _{P a} and the other surface 18b side of the one surface 18a of the cantilever portion 18, the strain stress of 20b is changed, the degree of piezoresistive 15a of the change , 15b, the amount of change in the electrical resistance value. Changes in the resistance values of the piezoresistors 15a and 15b are detected by a signal processing IC provided separately from the differential pressure detecting element 10 through a wiring (not shown), and further converted into a flow rate of the fluid flowing in the main flow path 2 by a predetermined coefficient. The The change in resistance value of the piezoresistors 15a and 15b can be detected by examining the change in the resistance value of the circuit between the electrode 16a and the electrode 16b described above.

(Differential pressure detection element manufacturing method)
Next, a method for manufacturing the differential pressure detecting element 10 of the present embodiment will be described with reference to FIGS. FIG. 5 is a process diagram showing a method for manufacturing the differential pressure detecting element 10 of the present invention, and FIGS. 6 (a) to 6 (d) and FIGS. It is sectional drawing in a step (S1-S8). Steps S1 to S4 in FIG. 5 correspond to FIGS. 6A to 6D, and steps S5 to S8 in FIG. 5 correspond to FIGS. 7A to 7D.

First, in step S <b> 1 of FIG. 5, as shown in FIG. 6A, the first silicon substrate 11 is prepared, and the recess 30 is formed on one surface of the first silicon substrate 11. When the differential pressure detecting element 10 is completed, the recess 30 serves as a pressure introduction hole 21 that transmits pressure to the other surface 18b side of the cantilever 18. The first silicon substrate 11 is a silicon wafer generally used in the technical field of semiconductor device manufacturing, and various wafers can be adopted regardless of the inch diameter and the substrate thickness. Although not particularly limited, the inch diameter of the first silicon substrate 11 is, for example, 4 to 8 inches, and the thickness is, for example, 100 μm to 1 mm. The recess 30 has a rectangular shape in plan view, and has a size of, for example, 100 μm × 100 μm and a depth of 50 μm. The recess 30 can be formed using a conventionally known etching technique. When the recess 30 is formed by dry etching, SF ₆ or the like can be used as the main gas as an etching gas. In the case of forming by a wet etching method, an etching solution using a KOH aqueous solution or a TMAH aqueous solution can be used.

  In step S <b> 1, an alignment mark 31 is formed on one surface of the first silicon substrate 11 simultaneously with the formation of the recess 30. The alignment mark 31 is a fine groove whose cross-sectional shape is, for example, a cross shape. This alignment mark 31 is a region that becomes the gap 19 that is formed in the pattern processing of the metal layer 55 performed in step S5 described later and step S6. This is used as a mark for mask position adjustment during pattern processing. The alignment mark 31 is formed on the frame portion 17 of the differential pressure detecting element 10 as shown in FIG. Alternatively, if the first silicon substrate is a silicon wafer, it may be formed in a dead space on the outer periphery of the wafer.

  Next, in step S <b> 2 of FIG. 5, as shown in FIG. 6B, a second silicon substrate 14 having an insulating layer 12 on one side and a silicon layer 13 on the other side is prepared, and one surface of the first silicon substrate 11 is prepared. And both substrates are bonded so that one surface of the second silicon substrate 14 faces. By bonding both the substrates, the concave portion 30 of the first silicon substrate 11 and the fine groove of the alignment mark 31 are sealed by the second silicon substrate 14. As a method of bonding the first silicon substrate 11 and the second silicon substrate 14, for example, a fusion bonding method can be adopted. With the fusion bonding method, it is possible to directly bond one surface of the first silicon substrate and one surface of the second silicon substrate without using an adhesive or the like.

Specifically, the insulating layer 12 of the second silicon substrate 14 is a thin film of silicon oxide (SiO ₂ ). The insulating layer 12 may be formed on a silicon wafer similar to the first silicon substrate 11 by a technique such as a thermal oxidation method or a CVD method, or a commercially available silicon wafer in which a silicon oxide thin film is formed in advance is used. May be. Although not particularly limited, the insulating layer 12 has a thickness of about 0.5 to 3 μm.

  Next, in step S3 of FIG. 5, the second silicon substrate 14 is thinned as shown in FIG. 6C. More specifically, the thickness of the second silicon substrate 14 is reduced by polishing the silicon layer 13 on the other surface side of the second silicon substrate 14 to reduce the thickness. Thinning of the second silicon substrate 14, that is, a method of reducing the thickness of the silicon layer 13, is, for example, a mechanical polishing method such as back grinding, a chemical polishing method such as wet etching, a chemical mechanical polishing method (CMP method), or silicon. A method of forming a damaged layer in the crystal and removing the damaged layer as a starting point can be employed. The thickness of the silicon layer 13 after thinning is about 0.3 μm. If the silicon layer 13 of the second silicon substrate 14 prepared in step S2 is sufficiently thin, the process may proceed to step S4 after step S2 without polishing the silicon layer 13 in step S3. . Further, the first silicon substrate 11 may be thinned in step S3. Further, RCA cleaning may be performed after thinning.

  Next, in step S4 of FIG. 5, as shown in FIG. 6D, the piezoresistive layer is formed on the other surface side of the second silicon substrate 14 after step S3, that is, on the side of the silicon layer 13 with reduced thickness. 15 is formed. The piezoresistive layer 15 is formed by doping the silicon layer 13 with an impurity element. When the impurity element is doped from the other surface side of the second silicon substrate, the region doped with the impurity element is converted into the piezoresistive layer 15, and the region not doped with the impurity element remains as the silicon layer 13. Examples of the technique for doping the silicon layer 13 with an impurity element include a thermal diffusion method (Irmal Diffusion) and an ion implantation method (Ion Implantation). When the n-type piezoresistive layer 15 is formed, phosphorus or the like is doped, and when the p-type piezoresistive layer 15 is formed, boron or the like is doped. After the piezoresistive layer 15 is formed, the second silicon substrate 14 has a three-layer structure of the insulating layer 12, the silicon layer 13, and the piezoresistive layer 15. After the piezoresistive layer 15 is formed, the thickness of the silicon layer 13 is 0.15 μm, for example, and the thickness of the piezoresistive layer 15 is 0.15 μm, for example.

  Next, in step S5 of FIG. 5, a metal layer 16 is formed on the piezoresistive layer 15 as shown in FIG. The material used for the metal layer 16 is, for example, Au, Al, Cr, Ni, Pd, or a combination thereof. The metal layer 16 can be formed by a sputtering method, a vacuum evaporation method, a plating method, or the like. Subsequently, the metal layer 16 is pattern-etched into the shapes of the electrodes 16a and 16b and the wiring 16c using a resist mask. The pattern etching of the metal layer 16 is generally performed by a wet etching method, and an etching solution may be appropriately selected according to the metal material used for the metal layer 16. Finally, when the resist mask is removed, the metal patterns of the electrodes 16a and 16b and the wiring 16c are completed. The position adjustment of the resist mask used for pattern etching of the metal layer 16 is performed using the alignment mark 31 formed in step S2 as a mark.

Next, in step S6 of FIG. 5, as shown in FIG. 7B, the piezoresistive layer 15 and the silicon layer 13 in the region to be the gap 19 and the groove 22 are removed. In order to selectively etch only the region that becomes the gap 19 and the groove 22, after removing the resist mask used in step S 5, a resist mask is formed by opening the region that becomes the gap 19 and the groove 22. The piezoresistive layer 15 and the silicon layer 13 in the opening region are etched. In order to etch the piezoresistive layer 15 and the silicon layer 13, a dry etching method or a wet etching method can be employed, but the width of the gap 19 is about 0.1 [μm] to 10 [μm]. Therefore, it is preferable to employ a dry etching method suitable for fine processing. As a reaction gas used for dry etching, for example, SF ₆ gas can be employed. In step S6, the piezoresistive layer 15 and the silicon layer 13 are etched, and the insulating layer 12 remains. The position adjustment of the resist mask used for forming the gap 19 and the groove 22 is performed using the alignment mark 31 formed in step S2 as a mark. Although the alignment mark 31 is covered with the insulating layer 12, the silicon layer 13, the piezoresistive layer 15, and the metal layer 16, since the thickness of these is as thin as several tens of nm, the alignment mark 31 is visually recognized. be able to. If the first silicon substrate is a silicon wafer and an alignment mark is formed in the outer peripheral area, the alignment mark can be easily seen by removing the silicon layer 13 in the outer peripheral area in advance. Alignment can be done.

Next, in step S <b> 7 of FIG. 5, as shown in FIG. 7C, a via hole 32 is formed from the other surface side of the first silicon substrate 11 toward the recess 30. In order to form the via hole 32, a resist mask having an opening in a region where the via hole 32 is formed is formed on the other surface of the first silicon substrate 11, and the first silicon substrate 11 is etched using the resist mask. . The via hole 32 can be formed by a dry etching method, and the DRIE (Deep Reactive Ion Etching) method, which excels in anisotropic etching with a high aspect ratio, is the most suitable. As an etching apparatus, a dry etching apparatus whose electrode structure is a parallel plate type is mainly used. As the reaction gas, SF ₆ or the like can be used. Etching of the first silicon substrate 11 proceeds until the via hole 32 reaches the recess 30. By forming the via hole 32, the other surface side of the first silicon substrate 11 communicates with the recess 30. On the bottom surface of the via hole 32, the insulating layer 12 of the second silicon substrate 14 is exposed.

Next, in step S8 of FIG. 5, as shown in FIG. 7D, the insulating layer 12 exposed on the bottom surface of the via hole 32 is removed from the other surface side of the first silicon substrate 11 by etching. Etching of the insulating layer 12 made of silicon oxide is performed by a wet etching method or a dry etching method. The etching solution in the case of the wet etching method is, for example, a mixed solution of hydrofluoric acid and nitric acid. The reaction gas in the case of the dry etching method is, for example, CF ₄ , C ₂ F ₆ , C ₄ F ₆ , C ₄ F ₈ , SF ₆ , or NF ₃ . By removing the insulating layer 12 exposed on the bottom surface of the via hole 32 from the other surface side of the first silicon substrate 11, a cantilever portion 18 composed of two layers of a piezoresistive layer 15 and a silicon layer 13, a cantilever portion 18 and a frame portion A gap 19 between them is also formed. A pressure introducing hole 21 is formed on the other surface 18 b side of the cantilever portion 18. The inner surface of the pressure introducing hole 21 is constituted by the inner surface of the via hole 32, the inner surface of the recess 30 formed in step S1, and the inner surface of the insulating layer 14 after etching in step S8. As shown in FIG. 7D, each inner surface is a flat surface that is flush with the other.

  When using the pressure detection element 10, it is preferable that the shape of the via hole 32 and the shape of the recess 30 in plan view are the same so that the pressure is smoothly transmitted toward the cantilever portion 18. If the shape of the via hole 32 and the shape of the recess 30 are the same, an unnecessary step is not formed on the inner surface of the pressure introducing hole 21 after the differential pressure detecting element 10 is completed. As a result, the air pressure is smoothly transmitted toward the cantilever portion 18 without causing turbulence of the airflow due to the step.

  However, as described above, in order to make the shape of the via hole 32 formed in step S7 the same as that of the concave portion 30, a high degree of processing accuracy is required, which may be difficult to realize. In that case, a via hole 32 having a diameter different from the diameter of the recess 30 may be used.

  8A to 8D are cross-sectional views corresponding to steps S5 to S8 in the process diagram shown in FIG. As shown in FIG. 8, after finishing step S5 and step S6 (FIGS. 8A and 8B), the diameter D2 of the via hole 32 formed in step S7 (FIG. 8C) is the recess 30. It is larger than the diameter D1. When it is difficult to form the via hole 32 with high processing accuracy, the diameter D2 of the via hole 32 may be formed larger than the diameter D1 of the recess 30 as shown in FIG.

  Steps S1 to Step S8 described above are the method for manufacturing the differential pressure detecting element 10 of the present embodiment. According to the method for manufacturing the differential pressure detecting element 10 of the present embodiment, in step S7 in which the via hole 32 is formed in the first silicon substrate 11, the recess 30 is previously formed below the insulating layer 12 that becomes the cantilever portion 18. Therefore, the via hole 32 may be formed until the recess 30 is reached. That is, the first silicon substrate 11 does not have to be etched until the insulating layer 12 is reached as in the prior art. Since the first silicon substrate 11 does not have to be etched until it reaches the insulating layer 12, the etching rate does not become unstable as it approaches the insulating layer 12 as in the prior art. The via hole 32 having a predetermined shape can be formed with high reproducibility at a stable etching rate from the surface to the recess 30. Therefore, since it is not necessary to etch the first silicon substrate for a long time in order to form the via hole 32 as in the prior art, a notch (abnormal etching of the first silicon substrate) generated in the side wall near the bottom of the via hole is formed. It is never done. Therefore, according to the present embodiment, the differential pressure detecting element 10 capable of measuring the flow rate with high accuracy can be manufactured without forming a notch in the vicinity of the hinge 20 of the cantilever portion 18.

(Industrial applicability)
INDUSTRIAL APPLICABILITY The present invention can be used for manufacturing a cantilever-type differential pressure detecting element formed using a silicon wafer.

DESCRIPTION OF SYMBOLS 1 ... Flow measuring device 2 ... Main flow path 3 ... Bypass path 3a, 3b ... Opening 5 ... Flow rate calculation part 10 ... Differential pressure detection element 11 ... 1st silicon substrate 12 ... Insulating layer 13 ... Silicon layer 14 ... Second silicon substrate 15 ... Piezoresistive layer 15a, 15b ... Piezoresistor 16 ... Metal layer 16a, 16b ... Electrode 16c ... -Wiring 17 ... Frame part 18 ... Cantilever part 19 ... Gap 20 ... Hinge 21 ... Pressure introduction hole 22 ... Groove 30 ... Concave part 31 ... Alignment mark 32 ...・ Beer hole 33 ・ ・ ・ Step

Claims (3)

A method of manufacturing a differential pressure detecting element having a cantilever part,
Forming a recess on one surface of the first silicon substrate (step S1);
Preparing a second silicon substrate having an insulating layer formed on one surface, and bonding one surface of the first silicon substrate and one surface of the second silicon substrate (step S2);
Forming a piezoresistive layer on the other surface of the two silicon substrate (step S4);
Forming a metal layer on the piezoresistive layer of the second silicon substrate (step S5);
Etching the second silicon substrate until the insulating layer is exposed from the other surface side of the second silicon substrate (step S6);
Forming a via hole from the other surface of the first silicon substrate to the recess by a dry etching method (step S7);
Removing the insulating layer exposed at the bottom of the via hole (step S8);
The manufacturing method of the differential pressure | voltage detection element provided with.   2. The method for manufacturing a differential pressure detecting element according to claim 1, further comprising a step (Step S3) of thinning the second silicon substrate between Step S2 and Step S4.   3. The method of manufacturing a differential pressure detecting element according to claim 1, wherein in the step S <b> 1, an alignment mark is formed on one surface of the first silicon substrate simultaneously with the formation of the recess.

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