WO2013136856A1 - Thermal type fluid flow rate sensor and manufacturing method therefor - Google Patents

Abstract

In order to solve the problem of deflection and the like due to stress imbalance in a thermal type fluid flow rate sensor having wires with different wire widths to thereby provide the thermal type fluid flow rate sensor with higher flow rate measurement detection accuracy, a thermal type fluid flow rate sensor is provided with a heating resistor (3) having tensile stress, thermometric resistors (5a-5d) having tensile stress and having a wire width different from that of the heating resistor, and an insulating layer provided in layers above and below each of the heating resistor and thermometric resistors and including a plurality of first insulating films (15, 17) having tensile stress and a plurality of second insulating films (14, 16, 18) having compressive stress. In the insulating layer, the average value of stress in portions located above and below a wire with a wide wire width in the heating resistor or the thermometric resistors is set closer to the compression side than the average value of stress in portions located above and below a wire with a narrow wire width in the heating resistor or the thermometric resistors.

Description

Thermal fluid flow sensor and manufacturing method thereof

The present invention relates to a thermal fluid flow sensor and a manufacturing method thereof, and more particularly, to a thermal fluid flow sensor having a plurality of wires having different wiring widths and a manufacturing method thereof.

Currently, a thermal type fluid flow sensor used in an air flow meter for measuring an intake air amount provided in an electronically controlled fuel injection device of an internal combustion engine such as an automobile is mainly used because a thermal type can directly detect a mass air amount. It has become.

Among them, a thermal air flow sensor manufactured by semiconductor micromachining technology has attracted attention because it can reduce the cost and can be driven with low power.

As a prior art of such an airflow sensor, for example, there is one disclosed in Patent Document 1, and platinum (Pt) is used as a heating element (heater) and a temperature detection element (sensor), and Si and the lower part of the heater and sensor are used. In the diaphragm structure from which the film is removed, a technique is disclosed in which the upper and lower layers of the heater and the sensor are covered with an insulating film, and the combined stress of these insulating films is used as a slight tensile stress. In Patent Document 2, the upper layer and the lower layer of the heater and the sensor have a laminated structure of compressive stress and tensile stress, and this film structure is arranged symmetrically to form a structure that is resistant to thermal stress.

Further, Patent Document 3 is another conventional technique related to an airflow sensor. Patent Document 3 discloses a process of depositing a silicon oxide film to insulate between a fluid temperature detector (sensor) and a heater. At that time, the surface of the silicon oxide film is uneven due to the sensor and heater pattern, so CMP (Chemical-Mechanical-Polishing) is performed on the surface of the silicon oxide film to remove the unevenness, and the silicon oxide film is flattened. The process of doing is disclosed.

JP-A-11-194043 JP 2001-153705 A Japanese Patent Laid-Open No. 2001-165737

However, Patent Documents 1 and 2 describe the stress control of the entire diaphragm, but do not perform stress control considering the shape of the heater and the sensor. Therefore, with only the stress control technology disclosed in Patent Documents 1 and 2, the average stress on the wiring is not zero due to the stress of the metal material forming the heater and the sensor arranged in a limited region, and as a result, the diaphragm Even though the overall stress control is performed, warping occurs. Usually, heaters and sensors formed of the same material have different resistance values, so that the wiring widths thereof are also usually different. At this time, due to the stress of the wiring material, the greater the wiring width, the greater the warpage in the vicinity of the wiring. As a result, there is a problem that deflection due to stress imbalance occurs at the boundary between the thick wiring and the thin wiring, and the resistance values of the heater and the sensor change due to the thermal influence of the heater heating.

In addition, although patent document 3 has description about the planarization process using CMP, the special description and consideration about stress control are not disclosed.

Based on the above, an object of the present invention is to provide a thermal fluid flow sensor with higher detection accuracy of flow measurement in a thermal fluid flow sensor having wires of different wiring widths.

Of the means for solving the problems according to the present invention, typical examples are as follows.

First, a thermal fluid flow sensor comprising a heating layer having a tensile stress, a wiring layer provided with a temperature measuring resistor having a tensile stress and a wiring width different from that of the heating resistor, A plurality of first insulating films provided on the upper layer and the lower layer, each having a tensile stress, and an insulating layer on which a plurality of second insulating films each having a compressive stress are stacked, and the insulating layer generates heat The average value of the stress at the upper and lower portions of the wiring with the larger wiring width of the resistor or resistance temperature detector is located at the upper and lower portions of the wiring with the narrow wiring width of the heating resistor or the resistance temperature detector. It is characterized in that it is on the compression side with respect to the average value of the stress of the part to be.

Second, a thermal fluid flow sensor, a heating layer having a tensile stress, a wiring layer provided with a temperature measuring resistor having a tensile stress and a wiring width narrower than the heating resistor, A stress adjusting layer provided on the upper layer, having a compressive stress, and having a film thickness at an upper portion of a portion where the heating resistor is provided being thicker than a thickness of a portion where the resistance temperature detector is provided; .

Third, there is a method for manufacturing a thermal fluid flow sensor, in which (a) a plurality of first insulating films each having a tensile stress and a plurality of second insulations each having a compressive stress are formed on an upper layer of a semiconductor substrate. A step of forming an insulating layer including a film; (b) a heating resistor having a tensile stress on the upper layer of the semiconductor substrate; and a resistance temperature detector having a tensile stress and a wiring width different from that of the heating resistor; And (c) after step (b), the average value of the stress of the portions of the insulating layer located on the upper and lower portions of the wiring having a larger wiring width in the heating resistor or the resistance temperature detector And a step of making the compression side of the average value of the stress of the portion located above and below the thin wiring of the heating resistor or the resistance temperature detector.

The effects obtained by typical ones of the inventions disclosed in the present application will be briefly described. In a thermal fluid flow sensor having wirings with different wiring widths, a thermal fluid flow rate with higher detection accuracy of flow rate measurement. A sensor may be provided.

It is a principal part top view which shows an example of the thermal type fluid flow sensor which concerns on Example 1 of this invention. It is principal part sectional drawing which shows the manufacturing method of the thermal type fluid flow sensor which concerns on Example 1 of this invention. It is principal part sectional drawing which shows the manufacturing method of the thermal type fluid flow sensor which concerns on Example 1 of this invention. It is principal part sectional drawing which shows the manufacturing method of the thermal type fluid flow sensor which concerns on Example 1 of this invention. It is principal part sectional drawing which shows the manufacturing method of the thermal type fluid flow sensor which concerns on Example 1 of this invention. It is principal part sectional drawing which shows the manufacturing method of the thermal type fluid flow sensor which concerns on Example 1 of this invention. It is principal part sectional drawing which shows the thermal type fluid flow sensor which concerns on Example 1 of this invention, and its manufacturing method. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic layout diagram of a thermal air flow meter mounted with a thermal fluid flow sensor attached to an intake passage of an internal combustion engine such as an automobile according to Embodiment 1 of the present invention. It is the principal part top view which expanded a part of FIG. FIG. 10 is a main part cross-sectional view taken along line B-B ′ of FIG. 9. It is the circuit diagram which showed an example of the thermal type fluid flow sensor which concerns on Example 1 of this invention. It is explanatory drawing which showed the principal part sectional drawing (upper stage) and the displacement amount (lower stage) of the surface of the thermal type fluid flow sensor by a conventional system. It is explanatory drawing which showed the principal part sectional drawing (upper stage) of the thermal type fluid flow sensor which concerns on Example 1, and the displacement amount (lower stage) of the surface. It is explanatory drawing which showed the relationship between the cumulative energization time and resistance change rate in Example 1 of this invention and the thermal-type fluid flow sensor of a conventional system. It is principal part sectional drawing which shows the thermal type fluid flow sensor which concerns on Example 2 of this invention, and its manufacturing method. It is principal part sectional drawing which shows the thermal type fluid flow sensor which concerns on Example 3 of this invention, and its manufacturing method.

<Configuration of thermal fluid flow sensor>
An example of a plan view of the main part of the thermal fluid flow sensor according to the first embodiment is shown in FIG. A measuring element 1 which is a thermal fluid flow sensor according to the first embodiment includes a semiconductor substrate 2, a heating resistor 3, a heating resistor temperature measuring resistor 4, temperature measuring resistors 5a to 5d, and an air temperature measuring resistor. 6, heater temperature control resistors 7 and 8, terminal electrodes 9a9i, and lead wires 10a, 10b, 10c-1, 10c-2, 10d, 10e, 10f, 10g, 10h-1, 10h-2, 10i-1 10i-2 or the like.

The semiconductor substrate 2 is made of, for example, single crystal Si.

The heating resistor 3 is formed on the semiconductor substrate 2 via an insulating film, and the wiring width is, for example, about 1 μm to 150 μm.

The resistance temperature detector 4 for the heating resistor is used for temperature detection of the heating resistor 3, and the wiring width is, for example, about 0.3 μm to 10 μm.

The resistance temperature detector comprises two upstream resistance temperature detectors 5a and 5b and two downstream resistance temperature detectors 5c and 5d, and is used for temperature detection of air heated by the heating resistor 3.

The wiring width of the upstream side resistance thermometers 5a and 5b and the downstream side resistance thermometers 5c and 5d is, for example, about 0.3 μm to 10 μm. The air temperature measuring resistor 6 is used for measuring the air temperature, and the wiring width is, for example, about 0.3 μm to 10 μm. However, each of the upstream side resistance temperature detectors 5 a and 5 b, the downstream side resistance temperature detectors 5 c and 5 d, and the air temperature resistance temperature detector 6 has a wiring width narrower than that of the heating resistor 3. Formed.

The wiring width of the heater temperature control resistors 7 and 8 is, for example, about 0.3 μm to 10 μm.

The terminal electrodes 9a to 9i are used for connecting the signal of the temperature measuring element 1 to an external circuit.

The lead wiring 10a electrically connects the heating resistor 3 to the terminal electrode 9a, and the wiring width is, for example, about 5 μm to 500 μm.

The lead-out wiring 10b electrically connects the heating resistor 3 to the terminal electrode 9b, and the line width is, for example, about 5 μm to 500 μm.

The two lead wires 10c-1 and 10c-2 electrically connect the heater temperature control resistor 7 and the heater temperature control resistor 8 to the terminal electrode 9c, and the wire width is, for example, about 5 μm to 500 μm. .

The lead wiring 10d electrically connects the resistance temperature measuring resistor 4 and the heater temperature control resistor 7 to the terminal electrode 9d, and the wiring width is, for example, about 5 μm to 500 μm.

The lead wiring 10e electrically connects the air temperature measuring resistor 6 and the heater temperature control resistor 8 to the terminal electrode 9e, and the wiring width is, for example, about 5 μm to 500 μm.

The lead wiring 10f electrically connects the upstream resistance temperature detector 5a and the downstream resistance temperature detector 5c to the terminal electrode 9f, and the wiring width is, for example, about 1 μm to 500 μm.

The lead wiring 10g electrically connects the resistance temperature detector 4 for the heating resistor, the air temperature resistance resistor 6, the upstream side resistance temperature detector 5b, and the downstream side resistance temperature detector 5d to the terminal electrode 9g. The width is, for example, about 1 μm to 500 μm.

The two lead wires 10h-1 and 10h-2 electrically connect the upstream resistance temperature detector 5b and the downstream resistance temperature detector 5c to the terminal electrode 9h, and the wiring width is, for example, about 1 μm to 500 μm. .

The two lead wires 10i-1 and 10i-2 electrically connect the upstream resistance temperature detector 5a and the downstream resistance temperature detector 5d to the terminal electrode 9i, and the wiring width is, for example, about 1 μm to 500 μm. .

In addition, an opening 11 is provided in at least the heating resistor 3, the resistance thermometer 4 for the heating resistor, and the protective film on the temperature measuring resistor, and the lower Si substrate (semiconductor substrate 2) is removed from the diaphragm. Structure 12 is formed. At this time, due to the diaphragm structure 12, the outer periphery of the opening portion 11 of the protective film is approximately 50 μm or more inside from the outer periphery of the diaphragm structure 12 in a plane.

This measuring element 1 measures the air temperature of the air flow 13 with the air temperature measuring resistor 6, and compares the temperature difference with the increase in resistance of the resistance thermometer 4 for the heating resistor heated by the heating resistor 3 ( ΔTh) is calculated, and the resistance of the resistance temperature detectors 5 a, 5 b, 5 c, and 5 d is changed by the flow of air heated by the heating resistor 3. In addition, in order to match the resistance value of each resistor with the design value, a wiring structure with a folded meander pattern is adopted.

<Method for manufacturing thermal fluid flow sensor>
Next, an example of a manufacturing method of the thermal fluid flow sensor according to the first embodiment will be described in the order of steps with reference to FIGS. 2 to 7 are cross-sectional views of relevant parts corresponding to the line AA in FIG.

First, as shown in FIG. 2, a semiconductor substrate 2 made of single crystal Si is prepared. Subsequently, the insulating film 14 is formed on the main surface of the semiconductor substrate 2, and the insulating film 15, the insulating film 16, the insulating film 17, and the insulating film 18 are sequentially formed. The insulating film 14 is a silicon oxide film formed in, for example, a high-temperature furnace and has a thickness of about 200 nm. The insulating film 15 is a silicon nitride film using, for example, a CVD method and has a thickness of about 100 to 200 nm. These insulating film 14 and insulating film 15 are also formed on the back surface of the semiconductor substrate 2. The insulating film 16 is a silicon oxide film using, for example, a CVD method and has a thickness of about 300 to 500 nm. The insulating film 17 is a silicon nitride film using, for example, a CVD method or a plasma CVD method, and the film thickness is determined by the wiring pitch of the sensor portion, but is in the range of about 20 nm to 200 nm. The insulating film 18 is a silicon oxide film using, for example, a CVD method or a plasma CVD method, and has a thickness of 50 nm to 300 nm.

Here, the insulating film 14, the insulating film 16, and the insulating film 18 are films having a compressive stress (second insulating film), and the insulating film 15 and the insulating film 17 are films having a tensile stress (first insulating film). Membrane). The residual stress of the first insulating film is a tensile stress of about 700 MPa to 1200 MPa, for example, and the residual stress of the second insulating film is a compressive stress of about 50 MPa to 250 MPa, for example. The insulating film 15 and the insulating film 17 may be aluminum nitride films having a tensile stress of 500 MPa to 1200 MPa. In order to adjust the stress of each film after forming these insulating films, a heat treatment at about 1000 ° C. may be performed in a nitrogen atmosphere.

Next, as the metal film 19, a Mo (molybdenum) film is formed to a thickness of about 100 to 200 nm by sputtering, for example. At this time, in order to improve adhesion and crystallinity, the underlying insulating film 18 is etched by about 5 nm to 20 nm by a sputter etching method using Ar (argon) gas before the Mo film is deposited. The semiconductor substrate 2 is formed at a temperature of about 200 ° C. to 500 ° C. In order to further enhance the crystallinity of the Mo film, a heat treatment at about 1000 ° C. is performed in a nitrogen atmosphere in the furnace body or lamp heating apparatus after the Mo film is formed.

Next, as shown in FIG. 3, the metal film 19 is patterned by etching using a photolithography method, so that the heating resistor 3, the heating resistor temperature measuring resistor 4, the temperature measuring resistor (upstream temperature measuring device). Resistors 5a and 5b and downstream temperature measuring resistors 5c and 5d), air temperature measuring resistor 6, heater temperature control resistors 7 and 8, and lead wires 10a to 10i-2 are formed (however, FIG. 3). Then, the air temperature measuring resistor 6, the heater temperature control resistors 7, 8 and a part of the lead wiring are not shown). Since the metal film 19 is a film having a tensile stress, each of the wirings (3 to 10i-2) obtained by the patterning has a tensile stress, and the residual stress is a strong tensile stress of about 800 MPa, for example. . In addition, due to over-etching during processing of the metal film 19, the underlying insulating film 18 is etched at a maximum of about 50 nm in a portion where the metal film 19 is not present. Therefore, the step difference between the portion formed of the metal film 19 such as the heating resistor 3 and the portion where the insulating film 18 is etched by processing the metal film 19 is about 150 to 250 nm.

Thereafter, as the insulating film 20 serving as a stress adjusting layer, a silicon oxide film deposited by, for example, a CVD method or a low temperature CVD method using plasma using TEOS (tetraethoxysilane) is formed to a thickness of about 300 to 600 nm. However, the insulating film 20 is not particularly limited to those manufactured by these manufacturing methods, and may be a film having at least a compressive stress. In this example, a film (second film) in which the residual stress at room temperature becomes a compressive stress of about 50 MPa to 250 MPa.

Next, as shown in FIG. 4, the insulating film 20 is polished by using a CMP (Chemical Mechanical Polishing) method so that the film thickness is different between the heater and the sensor having different wiring widths of the underlying metal film. Here, the stress adjustment layer 37 refers to a layer having a relatively large compressive stress in an upper layer of a thick wiring and a relatively small compressive stress in an upper layer of a thin wiring among heaters or sensors having different wiring widths. Particularly in Examples 1 and 2, the insulating film 20 after the film thickness control is referred to as a stress adjustment layer 37.

Here, for example, in the conventional CMP method as disclosed in Patent Document 3, it is usual to make the film thickness on the wiring constant by flattening regardless of the wiring width. However, in the CMP method, when the insulating film on the wiring is polished, the insulating film on the thin wiring is polished relatively large and the insulating film is thinned, and the insulating film on the thick wiring is polished relatively small. There is a characteristic that the insulating film becomes thick. This characteristic can be utilized to eliminate local stress imbalances due to differences in heater and sensor wiring widths.

That is, in the present embodiment, particularly in the heating resistor 3, the heating resistor 4 for the heating resistor, and the temperature measuring resistors (the upstream temperature measuring resistors 5a and 5b and the downstream temperature measuring resistors 5c and 5d). Taking advantage of the above-mentioned characteristics of the CMP method while taking into account the pattern arrangement, the resistance temperature detector 4 for the heating resistor having a narrow wiring width, the resistance temperature detector (the upstream resistance temperature detectors 5a and 5b, and the downstream resistance temperature detector) 5c and 5d), by setting the conditions and the amount of polishing in which the polishing progresses quickly in the heating resistor 3 having a large wiring width and in which the polishing progresses slowly, the temperature measuring resistor 4 for the heating resistor, the resistance thermometer The body (upstream resistance temperature detectors 5a, 5b and downstream resistance temperature detectors 5c, 5d) is thin, the heating resistor 3 is thick, and the stress adjustment layer having a different thickness depending on the width of the underlying wiring from the same insulating film 20 37 can be formed. The polishing amount is preferably equal to or less than the thickness of the metal film 19. However, when the shaving amount of the base insulating film 18 at the time of processing the metal film 19 is large, the polishing amount including the shaving amount may be used. Thereafter, it is desirable to perform a heat treatment at about 1000 ° C. in order to improve stress adjustment and moisture resistance. By forming this stress adjustment layer, it is possible to reduce the difference in warpage amount that differs depending on the wiring width, to suppress the deflection at the boundary portion where the wiring width differs, and to reduce the heat generated by heating the heating resistor 3. The plastic deformation of influence can be reduced. Further, as compared with a process by dry etching which will be described later, there is an advantage that the corners of the unevenness of the insulating film generated at the upper part of each wiring can be rounded and the sensor characteristics are improved.

In the above description, the film thickness is adjusted by the CMP method based on the lower metal wiring width of the stress adjusting layer 37. As a modification of the process of FIG. 4, the insulating film 20 is formed and then the wiring is formed by photolithography. There is also a method of forming the stress adjustment layer 37 by thinning only a narrow sensor portion by dry etching. Although this method requires a step of forming a mask as compared with the step of FIG. 4, the amount of abrasion of the insulating film 20 can be adjusted by dry etching. There is an advantage that the error can be reduced.

Next, as shown in FIG. 5, an insulating film 21 and an insulating film 22 are sequentially formed. The insulating film 21 is a silicon nitride film deposited by, for example, a CVD method or a low temperature CVD method using plasma, and has a thickness of about 150 to 200 nm. The insulating film 22 is a silicon oxide film deposited by, for example, a CVD method or a low temperature CVD method using TEOS as a raw material and using plasma, and has a thickness of about 100 to 500 nm. The stress adjusting film 20 and the insulating film 22 which are silicon oxide films are films (second films) whose residual stress at room temperature is a compressive stress of about 50 MPa to 250 MPa, and the insulating film 21 which is a silicon nitride film. Is a film (first film) having a residual stress of about 700 MPa to 1200 MPa at room temperature. Further, when the insulating film 21 is a silicon nitride film formed by a low temperature CVD method using plasma, heat treatment is performed at a temperature of about 800 ° C. or higher, preferably about 1000 ° C., so as to obtain a desired tensile stress. The silicon oxide film that is the insulating film 22 is also preferably subjected to heat treatment after deposition because heat resistance is improved by performing heat treatment at about 1000 ° C. Next, the connection hole 23 for exposing a part of the lead wirings 10a to 10i-2 is formed by dry etching or wet etching using a photolithography method. In FIG. 5, illustration of the connection holes 23 other than the connection hole 23 reaching the lead wiring 10g is omitted. Thereafter, as the metal film 24, for example, an Al alloy film that fills the connection hole 23 with a thickness of about 1 μm is formed. In order to improve the contact with the lead wiring 10g, the surfaces of the lead wirings 10a to 10i-2 may be sputter-etched with Ar (argon) gas before the formation. Further, in order to ensure the contact, a barrier metal film such as a TiN (titanium nitride) film is formed as a third metal film before the Al alloy film is deposited, and a laminated film of the barrier film and the Al alloy film May be formed. Note that, when the barrier metal film at this time is formed relatively thick, the contact resistance increases. Therefore, the thickness is preferably about 20 nm. However, when the sufficient contact area can be taken and the problem of resistance increase can be avoided, the thickness of the barrier metal film can be 200 nm or less. Further, although the TiN film is exemplified as the barrier metal film, a TiW (titanium tungsten) film, a Ti (titanium) film, and a laminated film thereof may be used.

Next, as shown in FIG. 6, the metal film 24 is patterned by dry etching or wet etching using a photolithography method to form terminal electrodes 9a to 9i. Next, for example, a polyimide film is formed as the protective film 25 on the terminal electrodes 9a to 9i, and at least the heating resistor 3, the heating resistor 4 for the heating resistor, and the upper temperature measuring resistor are formed by etching using a photolithography method. Openings (not shown) for connecting the openings 11 and the terminal electrodes 9a to 9i to external circuits are formed on the bodies 5a, 5b and the lower resistance temperature detectors 5c, 5d. The protective film 25 may be a photosensitive organic film or the like, and the film thickness is about 2 to 3 μm.

Next, as shown in FIG. 7, a photoresist film pattern (not shown) is formed on the back surface of the semiconductor substrate 2 by photolithography, and the insulating film 14 and the insulating film 15 formed on the back surface are dry-etched. Or by wet etching. Next, using the remaining insulating film 14 and insulating film 15 as a mask, the semiconductor substrate 2 is wet-etched from the back surface with KOH (potassium hydroxide), TMAH (Tetramethylammonium hydroxide) or an aqueous solution containing these as a main component to form the diaphragm structure 12. Form. The diaphragm structure 12 is designed to be larger than the opening 11 of the protective film 25, and is preferably formed to be approximately 50 μm or more larger than all sides of the protective film 25 opening 11. The total film thickness of the insulating film (insulating film 14, insulating film 15, insulating film 16, insulating film 17, insulating film 18, insulating film 20, insulating film 21, and insulating film 22) constituted by this diaphragm structure 12 is 1. About 5 μm or more is desirable. If it is thinner than this, the strength of the insulating film constituted by the diaphragm structure 12 is lowered, and there is a high possibility that the insulating film is broken due to the collision of dust contained in the intake air of the automobile. However, since the film formed below the semiconductor substrate 2 in the insulating film 14 serves as a buffer film when dust collides from below, dust collides such that the lower surface of the chip is covered with a lead frame, for example. The insulating film 14 may be omitted if the configuration is such that it does not.

In the above embodiment, the thermal fluid flow sensor in which the metal film 19 to be the heating resistor 3 or the like is formed of Mo has been described. However, metals other than Mo, metal nitride compounds, metal silicide compounds, polycrystalline silicon Alternatively, it may be formed from polycrystalline silicon doped with phosphorus or boron as impurities. In the case of a metal, α-Ta (alpha tantalum), Ti (titanium), W (tungsten), Co (cobalt), Ni (nickel), Fe (iron), Nb (niobium), Hf (hafnium), Examples thereof include metals mainly composed of Cr (chromium) or Zr (zirconium). Examples of the metal nitride compound include TaN (tantalum nitride), MoN (molybdenum nitride), and WN (tungsten nitride). Examples of the metal silicide compound include MoSi (molybdenum silicide), CoSi (cobalt silicide), and NiSi (nickel silicide). As yet another example, polysilicon doped with phosphorus or boron can be exemplified.

<Configuration of thermal fluid flow meter>
FIG. 8 is a schematic layout diagram of a thermal air flow meter mounted with an intake passage of an internal combustion engine such as an automobile in which the thermal fluid flow sensor according to the present embodiment according to the first embodiment is mounted. The thermal air flow meter 26 includes the above-described measuring element 1 which is a thermal fluid flow sensor, a support body 27 including an upper part and a lower part, and an external circuit 28. The measuring element 1 is provided inside the air passage 29. It is arranged in the auxiliary passage 30 in The external circuit 28 is electrically connected to the terminal of the measuring element 1 through the support body 27. The intake air flows in the direction of the air flow indicated by the arrow (air flow 13) in FIG. 8 or in the opposite direction depending on the conditions of the internal combustion engine.

FIG. 9 is an enlarged plan view of a main part of a part (measuring element 1 and support 27) of FIG. 8 described above, and FIG. 10 is a cross-sectional view of the main part taken along line BB in FIG. As shown in FIGS. 9 and 10, the measuring element 1 is fixed on the lower support 27a, and the space between each of the terminal electrodes 9a to 9i of the measuring element 1 and the terminal electrode 31 of the external circuit 28 is as follows. For example, they are electrically connected by a wire bonding method using a gold wire 32 or the like. The terminal electrodes 9a to 9i, 31 and the gold wire 32 are protected by being covered with an upper support body 27b. The upper support 27b may be sealed and protected with a resin.

Next, the operation of the above-described thermal air flow meter 26 will be described with reference to FIG. FIG. 11 is a circuit diagram showing the measuring element 1 and the external circuit 28 according to the first embodiment. Reference numeral 33 denotes a power source, reference numeral 34 denotes a transistor for supplying a heating current to the heating resistor 3, and reference numeral 35 denotes A control circuit composed of an output circuit including an A / D converter or the like and a CPU (Central Processing 行 な う Unit) that performs arithmetic processing, and a reference numeral 36 is a memory circuit.

The circuit shown in FIG. 11 has two bridge circuits. One is a heater control bridge circuit composed of a heating resistor temperature measuring resistor 4, an air temperature measuring resistor 6, and heater control resistors 7, 8. The other is a temperature sensor bridge circuit comprising four resistance temperature detectors ( upstream resistance resistors 5a and 5b and downstream resistance resistors 5c and 5d).

In the measurement element 1 shown in FIG. 1, the terminal electrode 9c is electrically connected to both of the two heater temperature control resistors 7 and 8 via two lead wires 10c-1 and 10c-2. A predetermined potential Vref1 is supplied to the terminal electrode 9c. Further, the terminal electrode 9f is electrically connected to both the upstream resistance temperature detector 5a and the downstream resistance temperature detector 5c, and a predetermined potential Vref2 is supplied to the terminal electrode 9f. Further, the terminal electrode 9g is electrically connected to each of the air temperature measuring resistor 6, the heating resistor temperature measuring resistor 4, the upstream temperature measuring resistor 5b, and the downstream temperature measuring resistor 5d through the lead wire 10g. The terminal electrode 9g is set to the ground potential as shown in FIG.

A terminal electrode 9d electrically connected to both the heating resistor temperature measuring resistor 4 and the heater temperature control resistor 7 through the lead wiring 10d corresponds to the node A in FIG.

Further, the terminal electrode 9e electrically connected to both the air temperature measuring resistor 6 and the heater temperature control resistor 8 through the lead wiring 10e corresponds to the node B in FIG. A terminal electrode 9i electrically connected to both the upstream side resistance temperature detector 5a and the downstream side resistance temperature detector 5d via the two lead wires 10i-1 and 10i-2 is connected to the node in FIG. Corresponds to C. Further, the terminal electrode 9h electrically connected to both the upstream resistance temperature detector 5b and the downstream resistance temperature detector 5c via the two lead wires 10h-1 and 10h-2 is connected to the node in FIG. Corresponds to D.

In this embodiment, the ground potential of the heater bridge circuit and the temperature sensor bridge circuit is supplied by the common terminal electrode 9g. However, the terminal electrode may be increased and each terminal electrode may be set to the ground potential.

When the gas heated by the heating resistor 3 is higher than the intake air temperature by a certain temperature (ΔTh, for example, 100 ° C.), the heater control bridge circuit is connected to the node A (terminal electrode 9d) and the node B (terminal electrode 9e). The resistance values of the heating resistor temperature measuring resistor 4, the air temperature measuring resistor 6, and the heater control resistors 7, 8 are set so that the potential difference between them is 0V. When the constant temperature (ΔTh) deviates from the setting, a potential difference is generated between the node A and the node B, the transistor 34 is controlled by the control circuit 35 to change the current of the heating resistor 3, and the bridge circuit Is kept in an equilibrium state (potential difference between A and B is 0 V).

On the other hand, the temperature sensor bridge circuit is designed so that the distance from the heating resistor 3 to each of the resistance temperature detectors (the upstream resistance temperature detectors 5a and 5b and the downstream resistance temperature detectors 5c and 5d) is the same. Therefore, the potential difference between the node C (terminal electrode 9i) and the node D (terminal electrode 9h) becomes an equilibrium state and becomes 0V in the absence of wind regardless of heating by the heating resistor 3. When a voltage is applied to the heating resistor 3 and the intake air flows in the direction of the air flow 13, the temperature of the upstream resistance thermometers 5a and 5b heated by the heating resistor 3 decreases, and the downstream resistance thermometer The temperature of 5c, 5d becomes high, the resistance value of the resistance temperature detector is different between the upstream side and the downstream side, the balance of the temperature sensor bridge is lost, and a differential voltage is generated between the node C and the node D. This difference voltage is input to the control circuit 35, and the air flow rate (Q) obtained from the comparison table of the difference voltage and the air flow rate recorded in the memory 36 is processed and output. Even in the case where the air flow 13 is in the reverse direction, the air flow rate can be measured in the same manner, so that the reverse flow can be detected.

<Characteristics and Effects of Example 1>
Next, features and effects of the first embodiment will be described using the displacement amount of the diaphragm surface. The upper part of FIG. 12 is a cross-sectional view of a main part of a conventional thermal fluid flow sensor having a diaphragm structure which is a comparative example of the diaphragm structure according to the first embodiment (see FIG. 7). In the lower part of FIG. 12, the wiring width of the sensor wiring (upstream temperature sensing resistors 5a and 5b and downstream temperature sensing resistors 5c and 5d, and the heating resistor temperature sensing resistor 4) is about 1 μm, and the heater wiring ( The wiring width of the heating resistor 3) is about 5 μm. In the lower part of FIG. 12, the surface is measured by a palpation step meter, and the relative displacement at each surface position with reference to the uppermost silicon oxide film at the center of the diaphragm portion. The quantity is illustrated.

As shown in the upper cross-sectional view of FIG. 12, the conventional thermal fluid flow rate sensor does not perform the CMP process on the insulating film 20 (that is, the stress adjustment layer 37 is not formed), so that the wiring width is large. The film thickness is the same on the thick heater wiring and the sensor wiring with a narrow wiring width.

In the case of such a conventional thermal fluid flow sensor structure, the amount of displacement locally changes at the boundary between the sensor unit (heating resistor 4 for heating resistor) and the heater unit (heating resistor 3). The heater portion has a convex shape about 0.15 μm downward. At this time, the space width between the wirings is about 1 μm in both the sensor part and the heater part, and is small enough not to affect the displacement compared to each wiring. Is negligibly small. Therefore, the above-described local change in the displacement amount is caused by the difference in the wiring width of the metal film 19. Specifically, the metal film 19 usually has a tensile stress, and the Mo film used in the present invention has a strong tensile stress of particularly 800 MPa or more, so that it protrudes downward particularly in a heater portion having a large wiring width. The warpage which becomes a shape occurs remarkably, resulting in a displacement amount as shown in the lower part of FIG.

When there is a local change in the amount of displacement as described above, the heater part is likely to rise when the heater is heated, and the diaphragm is likely to be deformed. As a result, the resistance value changes. The above-mentioned constant temperature (ΔTh) as a reference is calculated from the resistance value of the resistance temperature detector 4 for the heating resistor, and when the thermal fluid flow sensor is operated according to the design value while the resistance value is changing. There is a concern that the detection accuracy is lowered due to a decrease in ΔTh, and the film structure is destroyed due to abnormal heating of the heater due to excessive current.

On the other hand, the upper part of FIG. 13 shows a cross-sectional view of the main part of the thermal fluid flow sensor according to the first embodiment, and the lower part of FIG. Measure the surface of the wiring ( upstream resistance thermometers 5a, 5b and downstream resistance thermometers 5c, 5d, the resistance thermometer 4 for the heating resistor) and the heater wiring (heating resistor 3) with a palpation step meter. The amount of displacement is shown.

In summary, the thermal fluid flow sensor according to the present invention includes a heating resistor (3) having tensile stress and a resistance temperature detector (4, 5a) having a tensile stress and a wiring width different from that of the heating resistor. 5d, or 6), and a plurality of first insulating films having tensile stress and a plurality of second insulating films having compressive stress, which are provided in the upper layer and the lower layer of each of the heating resistor and the resistance temperature detector, And an insulating layer. Here, the term “insulating layer” is used in the first embodiment to include the insulating films 14 to 18 and the stress adjusting layer 37. Furthermore, in Examples 2 and 3 to be described later, this is used to include the insulating film 20. And the average value of the stress of the part located in the upper part and the lower part of the wiring having a large wiring width of the heating resistor or the resistance thermometer in the insulating layer is the wiring width of the heating resistor or the resistance thermometer. It is characterized in that it is on the compression side with respect to the average value of the stress at the upper and lower portions of the thin wiring. Here, the term “upper part” is used as a word indicating the vertical upper direction with respect to the surface of the substrate 2 in each of the heating resistor and the resistance temperature detector, and the term “lower part” is used as a vertical direction with respect to the surface of the substrate 2. It is used as a word pointing down.

Further, the characteristics of the thermal fluid flow sensor common to the first and second embodiments will be described from another viewpoint. The heating resistor (3) having tensile stress and the wiring width larger than that of the heating resistor having tensile stress. Is a thin RTD (4, 5a to 5d, or 6), and is provided on the upper layer of the heating resistor and the RTD, has a compressive stress, and the film thickness above the portion where the heating resistor is provided Has a stress adjustment layer (37) thicker than the film thickness of the portion where the resistance temperature detector is provided.

Further, the characteristics of the thermal fluid flow sensor according to the first embodiment will be described from the viewpoint of the manufacturing method. (A) A plurality of first insulating films each having tensile stress on the upper layer of the semiconductor substrate, and A step of forming an insulating layer including a plurality of second insulating films having compressive stress (FIGS. 2 to 6); and (b) a heating resistor having tensile stress on the upper layer of the semiconductor substrate, and having tensile stress. After the step (FIG. 3) and (c) step (b) of forming a resistance temperature detector having a different wiring width from the heat resistance resistor, the heat resistance resistor or the resistance temperature detector of the insulating layer is formed. Of these, the average value of the stress at the top and bottom of the wiring with a large wiring width is the average value of the stress at the top and bottom of the wiring with a narrow wiring width of the heating resistor or resistance temperature detector. And the step of making the compression side (FIG. 6). To.

In addition, in Example 1 (same as in Example 2), in particular, the step (c) includes a step of polishing at least one of the plurality of second insulating films using a CMP method, or a plurality of steps. A step of removing at least one of the second insulating films located above the wiring having a narrow wiring width by dry etching (here, “removal” in the step (c)) Is not meant to completely remove the part, but to be partially removed or thinned).

In the case of the diaphragm structure of the thermal fluid flow sensor according to the present invention as described above, there is no local step between the heater portion and the sensor portion, and the diaphragm and the periphery are gently curved. The value is very small, about 0.05 μm. With such a gentle curve, even if the heater part rises due to the heat effect of the heater heating, the deformation of the entire diaphragm can be alleviated, so that the sensor wiring (the upstream resistance temperature detectors 5a, 5b and the downstream side) has a narrow wiring width. It is possible to suppress stress concentration that causes the side resistance temperature detectors 5c and 5d and the resistance temperature detector resistance element 4) to be plastically deformed.

Therefore, it is possible to prevent a change in the resistance value of the sensor unit and prevent problems such as a decrease in detection accuracy due to a decrease in ΔTh and a breakdown of the film structure due to abnormal heater heating due to excessive current.

Particularly in Example 1 (same as in Example 2), the thickness of the stress adjustment layer 37 is such that the upper part or the lower part of the heater part (heating resistor 3) is the sensor part (temperature measuring resistor 4, It is thicker than the upper or lower part of 5a to 5d, 6). Here, due to the characteristics of the stress adjusting layer, the vicinity of the heater portion where deflection due to thermal expansion is more likely to occur is protected by a thicker insulating film, and the strength of the diaphragm is improved. In particular, the heater portion is provided at the center side of the diaphragm than the normal sensor portion, that is, at a portion where the amplitude at the time of bending is particularly large, and thus the effect of the film thickness is particularly effective.

FIG. 14 shows the rate of change in resistance of the resistance temperature detector 4 for the heating resistor for each cumulative energization time of the acceleration test in which the heater section (heating resistor 3) is energized so that the temperature is about 600 ° C. The conventional thermal fluid flow sensor (the upper part of FIG. 12) is compared with the thermal fluid flow sensor of the present embodiment (the upper part of FIG. 13).

As shown in FIG. 14, in the conventional thermal fluid flow sensor, the resistance of the resistance temperature detector for the heating resistor changes suddenly at the beginning of energization, and the resistance gradually changes after 24 hours. Recognize. On the other hand, in the thermal fluid flow sensor of the present embodiment, the resistance change is gentle from the initial energization, and the initial resistance change seen in the conventional thermal fluid flow sensor can be suppressed. Recognize. From this result, in the conventional method, it is presumed that the plastic deformation of the resistance temperature detector 4 for the heating resistor due to the influence of the heater heating is accelerated in the initial stage of energization and appears as a resistance change.

Therefore, it is possible to obtain a highly reliable thermal fluid flow sensor by eliminating local deflection between the sensor unit and the heater unit.

In addition, compared with Example 2 described later, the thermal fluid flow sensor according to Example 1 is characterized in that the stress adjustment layer is provided in contact with the heating resistor and the resistance temperature detector. With such a feature, stress concentration associated with the steps of the insulating films 21 and 22 provided in the upper stage of the stress adjustment layer is alleviated, so that there is an advantage that the sensor characteristics are further improved.

The position where the stress adjustment layer is provided is not limited to just above the heater wiring and sensor wiring. In the second embodiment, a modified example in which the stress adjustment layer is formed on the uppermost layer of the diaphragm will be described as an example of a configuration in which the stress adjustment layer is formed except for the heater wiring and the sensor wiring.

FIG. 15 is an example of a thermal fluid flow sensor according to the second embodiment, and shows a cross-sectional view of the main part corresponding to the line AA in FIG.

In the thermal fluid flow sensor according to the second embodiment, a silicon oxide film deposited by a low temperature CVD method using plasma using a CVD method or TEOS as a raw material is formed on the heater and sensor as compared with the first embodiment. The process is the same up to the steps (FIGS. 2 to 3).

In Example 1, after that, the insulating film 20 was subjected to CMP to adjust the film thickness of the portions having different wiring widths. However, in the embodiment, the film thickness adjustment is not performed in this step, but the low temperature CVD method using plasma. The silicon nitride film insulating film 21 and the silicon oxide insulating film 22 deposited by the low temperature CVD method using plasma using a CVD method or TEOS as a raw material are formed. Here, film thickness adjustment (CMP or dry etching) similar to that of FIG. 4 is performed on the insulating film 22 to obtain a stress adjustment layer 37 having a film thickness that varies depending on the wiring width. Thereafter, after the formation of the connection hole 23 exposing a part of the lead wirings 10a to 10i-2, the lead wiring, the protective film 25, and the diaphragm 12 are formed as in the first embodiment.

By adopting the above structure, the compressive stress of the heater wiring portion becomes larger than the sensor wiring portion, the deflection of the sensor wiring portion and the heater wiring portion is eliminated, and the thermal influence at the time of heating the heater can be suppressed as in Example 1, Resistance change with time can be reduced.

The stress adjustment layer can be formed by a method other than controlling the film thickness of the insulating film. In Example 3, a structure in which a stress adjustment layer is newly provided only on the upper part of the sensor unit will be described.

FIG. 16 is an example of a thermal fluid flow sensor according to the third embodiment, and shows a cross-sectional view of the main part corresponding to the line AA in FIG.

The thermal fluid flow sensor of the third embodiment is equivalent to the step of forming the insulating film 22 as compared with the second embodiment, and is then nitrided by a low temperature CVD method using plasma as the stress adjustment layer 37. A silicon film is formed to a thickness of about 20 to 50 nm, and only the upper part of the sensor portion with a narrow wiring width is left by dry etching using a photolithography method. Thereafter, after the formation of the connection hole 23 exposing a part of the lead wirings 10a to 10i-2, the lead wiring, the protective film 25, and the diaphragm 12 are formed as in the first embodiment. The stress adjusting layer 37 is described as being on the sensor wiring, but may be a region including between the wirings.

As described above, in the thermal fluid flow sensor according to the third embodiment, the insulating layer is an insulating film having tensile stress, and is provided on the upper part of the wiring having a large wiring width (heater portion). It has a stress adjustment layer 37 that is not provided on the upper part of the (sensor part). Further, from the viewpoint of the manufacturing method, in the step (c) described above, at least one of the plurality of first insulating films included in the insulating layer is dried on the portion located above the wiring having a large wiring width. It is a process of removing by etching. With such a feature, the sensor wiring portion has a structure in which the compressive stress is reduced as compared with the heater wiring portion, and the same effects as those of the first and second embodiments can be obtained. Furthermore, since the stress can be adjusted by the amount of film formation of the stress adjustment layer 37 provided separately in the upper layer, the error in the design is further reduced, and a sensor with higher accuracy can be provided.

As mentioned above, the invention made by the present inventor has been specifically described based on the embodiment. However, the present invention is not limited to the embodiment, and various modifications can be made without departing from the scope of the invention. Needless to say.

For example, in the present specification, the heater part wiring (heating resistor) has been described as being thicker than the sensor part wiring (temperature measuring resistor). However, when the wiring of the sensor part is made thicker than the heater part, the present invention also includes a thermal fluid flow sensor using the “wiring with a wide wiring width” as the sensor part.

材料 Representative materials are illustrated as materials of each member, but the illustrated materials are main ones and do not exclude secondary elements, additives, additional elements, and the like. In particular, another material having the same kind of stress may be applied to a portion where the material is described from the aspect of stress (tensile stress or compressive stress).

In each embodiment, when referring to the number of elements (including the number, numerical value, quantity, range, etc.), unless otherwise specified, or in principle limited to a specific number, etc. The number is not limited to a specific number, and may be a specific number or more. Furthermore, in each embodiment, it is needless to say that its constituent elements (including element steps and the like) are not necessarily indispensable unless otherwise specified and clearly considered essential in principle. . In addition, regarding the constituent elements and the like, when “consisting of A” and “consisting of A” are stated, other elements are not excluded unless specifically indicated that only the elements are included. Similarly, when referring to the shape, positional relationship, etc. of components, etc., those that are substantially similar to or similar to the shape, etc., unless explicitly stated or otherwise considered otherwise apparent Etc. The same applies to the above numerical values and ranges.

In addition, as a general rule, those having the same function in all drawings are denoted by the same reference numerals, and repeated description thereof is omitted. In the drawings, even a plan view is partially hatched to make the drawings easy to see.

1: measurement element, 2: semiconductor substrate, 3: heating resistor, 4: resistance temperature detector for heating resistor, 5a, 5b: upstream resistance temperature detector, 5c, 5d: downstream resistance temperature detector, 6 : Air temperature measuring resistor, 7, 8: Heater temperature control resistor, 9a to 9i: Terminal electrodes, 10a, 10b, 10c-1, 10c-2, 10d, 10e, 10f, 10g, 10h-1, 10h-2, 10i-1, 10i-2: Lead-out wiring, 11: Opening, 12: Diaphragm structure, 13: Air flow, 14: Insulating film, 15: Insulating film, 16: Insulating film, 17: Insulating film 18: Insulating film, 19: Metal film, 20: Insulating film, 21: Insulating film, 22: Insulating film, 23: Connection hole, 24: Metal film, 25: Protective film, 26: Thermal air flow meter, 27 27a, 27b: support, 28: external circuit, 29: air passage, 30: secondary passage , 31: terminal electrodes, 32: gold, 33: Power, 34: transistor 35: control circuit, 36: Memory circuit 37: stress adjusting layer.

Claims (15)

1. A heating resistor having a tensile stress;
   A resistance temperature detector having a tensile stress and a wiring width different from that of the heating resistor, and
   An insulating layer provided on the upper layer and the lower layer of each of the heating resistor and the resistance temperature detector and including a plurality of first insulating films having tensile stress and a plurality of second insulating films having compressive stress; Have
   Of the insulating layer, an average value of stresses of portions of the heating resistor or the temperature measuring resistor located at the upper and lower portions of the wiring having a large wiring width is the heating resistor or the temperature measuring resistor. A thermal fluid flow sensor characterized in that it is on the compression side with respect to an average value of stresses at the upper and lower portions of the wiring having a narrow wiring width.
2. In claim 1,
   The insulating layer is an insulating film having a compressive stress, and further includes a stress adjustment layer in which a film thickness of an upper part of the wiring having a large wiring width is larger than a film thickness of an upper part of the wiring having a thin wiring width. A thermal fluid flow sensor.
3. In claim 2,
   The thermal fluid flow sensor, wherein the stress adjustment layer is provided in contact with the heating resistor and the resistance temperature detector.
4. In claim 2,
   The thermal fluid flow sensor, wherein the stress adjusting layer is made of a silicon oxide film.
5. In claim 1,
   The insulating layer is an insulating film having a tensile stress, and is further provided with a stress adjusting layer provided on an upper part of the wiring having a large wiring width and not provided on an upper part of the wiring having a small wiring width. Thermal fluid flow sensor.
6. In claim 5,
   The thermal fluid flow sensor, wherein the stress adjustment layer is made of a silicon nitride film or an aluminum nitride film.
7. In claim 1,
   The thermal fluid flow sensor according to claim 1, wherein a wiring width of the heating resistor is larger than a wiring width of the temperature measuring resistor.
8. In claim 1,
   The heating resistor and the resistance temperature detector are each composed mainly of molybdenum, alpha tantalum, titanium, tungsten, cobalt, nickel, iron, niobium, hafnium, chromium, zirconium, platinum, or beta tantalum. A metal nitride compound mainly containing any one of a film, tantalum nitride, molybdenum nitride, tungsten nitride, and titanium nitride, a metal silicide mainly containing any of tungsten silicide, molybdenum silicide, cobalt silicide, and nickel silicide 2. The thermal fluid flow sensor according to claim 1, wherein the thermal fluid flow sensor is a compound or polysilicon doped with phosphorus or boron.
9. A heating resistor having a tensile stress;
   A resistance temperature detector having a tensile stress and a wiring width narrower than the heating resistor,
   Provided in the upper layer of the heating resistor and the resistance temperature detector, has a compressive stress, and the thickness of the upper portion of the portion where the heating resistor is provided is larger than the thickness of the portion where the resistance temperature detector is provided. A thermal fluid flow sensor comprising a thick stress adjusting layer.
10. In claim 9,
    The thermal fluid flow sensor, wherein the stress adjusting layer is in contact with the heating resistor and the resistance temperature detector.
11. In claim 9,
    The thermal fluid flow sensor, wherein the stress adjusting layer is made of a silicon oxide film.
12. (A) forming an insulating layer including a plurality of first insulating films each having a tensile stress and a plurality of second insulating films each having a compressive stress on an upper layer of the semiconductor substrate;
    (B) forming a heating resistor having a tensile stress and a temperature measuring resistor having a tensile stress and having a wiring width different from that of the heating resistor on an upper layer of the semiconductor substrate;
    (C) After the step (b), an average value of stresses of portions of the insulating layer located in the upper part and the lower part of the wiring having a large wiring width in the heating resistor or the temperature measuring resistor is calculated as A thermal fluid flow sensor characterized by comprising a step of making the compressive side more than the average value of the stresses in the upper and lower portions of the wiring having a narrow wiring width of the heating resistor or the temperature measuring resistor. Manufacturing method.
13. In claim 12,
    The step (c) is a step of polishing at least one of the plurality of second insulating films by using a CMP method.
14. In claim 12,
    The step (c) is a step of removing, by dry etching, at least one of the plurality of second insulating films, the portion located above the wiring having a narrow wiring width. Manufacturing method of flow sensor.
15. In claim 12,
    In the thermal fluid, the step (c) is a step of removing at least one of the plurality of first insulating films located on the upper part of the wiring having a large wiring width by dry etching. Manufacturing method of flow sensor.

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