JPH11281446A - Flow rate detecting element and flow rate sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase flow rate measuring accuracy and reliability by reducing the fluctuation of a resistance value caused by humidity in a thermo-sensitive flow rate detecting element or a flow rate sensor. SOLUTION: A thermo-sensitive flow rate detecting element is provided with an insulating supporting film 2 formed on the surface of a flat plate-like substrate 1, and a thermo-sensitive resisting film 11 (heat generation section) formed on the supporting film 2. A silicon oxide film 18 as an insulating film is formed on the thermo-sensitive resisting film 11 or the supporting film 2, and a protective film 3 is formed on the silicon oxide film 18. The incursion of external humidity into the thermo-sensitive resisting film 11 is prevented by the silicon oxide film 18, the fluctuation of a resistance value caused by the humidity of the thermo-sensitive resisting film 11 is thereby reduced, and the measuring accuracy and reliability of the flow rate detecting element or a flow rate sensor using this element are increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow rate detecting element for measuring a flow rate or a flow rate of a fluid based on a heat transfer phenomenon from a heating element or a portion heated by the heating element to the fluid, and to use the flow rate detecting element. The present invention relates to a flow sensor which is used for measuring an intake air amount of an internal combustion engine, for example.

[0002]

2. Description of the Related Art The heat transfer amount is determined by utilizing a substantially unique functional relationship established between the flow rate or flow rate of a fluid and the heat transfer amount from a heating element disposed in the fluid to the fluid. 2. Description of the Related Art A heat-sensitive flow rate detecting element that detects a flow rate or a flow rate of a fluid based on the flow rate, or a flow rate sensor using the flow rate detecting element has been widely used for detecting an intake air amount of an internal combustion engine.

FIGS. 11 and 12 are an elevation sectional view and a plan view, respectively, of a conventional heat-sensitive flow rate detecting element for detecting a flow rate of air disclosed in Japanese Patent Publication No. 5-7659. . 11 and 12, 1 is a flat substrate made of a silicon semiconductor, 2 is an insulating support film made of silicon nitride, 4 is a heating resistor made of permalloy which is a heat-sensitive resistor, and 5 and Reference numeral 6 denotes a temperature measuring resistor made of permalloy, which is a heat-sensitive resistor, and reference numeral 3 denotes an insulating protective film made of silicon nitride.
An air space 9 is provided in the flat substrate 1 in the vicinity of the film-forming portions of the heating resistor 4 and the temperature measuring resistors 5 and 6, thereby forming a bridge 13. The air space 9
It is formed by removing a part of the silicon semiconductor from the opening 8 using an etchant that does not damage the silicon nitride. The two temperature measuring resistors 5 and 6 are arranged in a plane in the flow direction of the measurement fluid with the heating resistor 4 interposed therebetween. Reference numeral 7 denotes a comparative resistor made of permalloy, which is a heat-sensitive resistor.

In such a conventional flow rate detecting element, the heating current applied to the heating resistor 4 is detected by a control circuit (not shown), for example, by the flat resistor 1 detected by the comparison resistor 7.
Is controlled to be a constant temperature 200 ° C. higher than the temperature of Here, since the air space 9 exists below the heating resistor 4, the heat generated by the heating resistor 4 is hardly transmitted to the comparison resistor 7, and the temperature of the comparison resistor 7 becomes substantially equal to the temperature of the air. ing.

The heat generated by the heat generating resistor 4 is transmitted to the temperature measuring resistors 5 and 6 via the support film 2, the protective film 3 or the heat-sensitive resistance film. As shown in FIG. 12, the temperature measuring resistor 5 and the temperature measuring resistor 6 are arranged at positions symmetrical to each other with respect to the heating resistor 4, so that when there is no air flow, the temperature measuring resistor 5 and the temperature measuring resistor 5 are measured. No difference occurs in the resistance value of the temperature resistor 6. However, when there is an air flow, the upstream temperature measuring resistor is cooled by air, while the downstream temperature measuring resistor is more affected by the heat transmitted from the heat generating resistor 4 to the air. Is not cooled. For example, when the air flow in the direction indicated by the arrow 10 occurs, the temperature measuring resistor 5 on the upstream side has a lower temperature than the temperature measuring resistor 6 on the downstream side, and the difference between the two resistance values is the flow rate or flow rate of the air. The larger the is, the larger it is. Therefore, by detecting the difference between the resistance values of the resistance temperature detectors 5 and 6, the flow velocity or the flow rate of the air can be measured. When the direction of the air flow is opposite to the direction of the arrow 10, the temperature of the upstream temperature measuring resistor 6 becomes lower than that of the downstream temperature measuring resistor 5, so that it is necessary to detect the direction of the air flow. Is also possible.

The conventional flow rate detecting element shown in FIGS. 11 and 12 is a bridge type thermal type flow rate detecting element. In addition, a diaphragm type thermal type flow rate detecting element has been widely used. FIG. 13 and FIG. 14 are an elevational sectional view and a plan view of a conventional diaphragm type thermosensitive flow rate detecting element, respectively. 13 and FIG. 14, the members 1 to 10 correspond to FIG. 11 and FIG.
Are substantially the same as those of the bridge type flow rate detecting element shown in FIG. Reference numeral 12 denotes a recess formed by removing a part of the flat substrate 1 by etching or the like from the surface of the flat substrate 1 opposite to the surface on which the support film 2 is attached. is there. Accordingly, the diaphragm 14 is formed between the supporting film 2 and the protective film 3 with the heating resistor 4 and the temperature measuring resistors 5 and 6 interposed therebetween. According to such a configuration, higher strength can be obtained as compared with the bridge type flow rate detecting element shown in FIGS. 11 and 12, but the response is inferior due to the diaphragm 14 being supported all around. There is such a feature.
The principle of detecting the flow velocity or flow rate of air is the same as that of the bridge type flow rate detection element.

[0007]

By the way, when such a conventional thermosensitive flow rate detecting element is actually used,
The temperature measuring resistors 5 and 6 may change due to factors other than temperature, for example, humidity. In such a case, a phenomenon occurs in which the detection accuracy and reliability of the flow rate detecting element decrease.
Conventional bridge type and diaphragm type flow rate detecting elements are formed using a thin film forming process.
Heat generation resistance and temperature measurement resistance
16 are surrounded by a support film and a protective film having a thickness of 0.5 to 2 μm.
As shown in (1), there is a problem that the resistance value of the heat-sensitive resistance film using platinum fluctuates (drifts) under the influence of the humidity of the outside air. As described above, when the resistance value of the heat-sensitive resistive film changes due to the influence of the humidity of the outside air, there arises a problem that the flow rate detection accuracy and reliability of the flow rate detection element decrease.

The present invention has been made to solve the above-mentioned conventional problems, and can suppress or prevent a change in the resistance value of a heat-sensitive resistive film due to humidity, and can be manufactured by a simple manufacturing process. An object or a problem to be solved is to obtain a flow rate detection element or a flow rate sensor.

[0009]

As shown in FIG. 15, the inventor of the present application has proposed that when a metal film such as platinum is used as the heat-sensitive resistance film 11 in the conventional heat-sensitive flow rate detecting element, it is formed by a sputtering method. Protection film 3 made of silicon nitride
Above the thermal resistance film 11, a columnar porous structure 1
5 was found. This is the thermal resistance film 1
Since the protective film 3 in the portion where no 1 exists, that is, the protective film 3 directly formed on the support film 2 is not a columnar porous structure 15, the crystal orientation of the heat-sensitive resistive film 11 It is considered that the structure of the protective film 3 above the heat-sensitive resistive film 11 has changed (altered) due to the influence of. Therefore, it is considered that the resistance change (resistance drift) due to the humidity of the heat-sensitive resistance film 11 shown in FIG. 16 is caused by the movement of moisture (moisture) through the columnar porous structure 15. Then, in order to prevent a change in the resistance value of the heat-sensitive resistive film 11 due to a change in the humidity of the outside air, the protective film 3 above the heat-sensitive resistive film 11 or the columnar porous structure 15 is provided on the surface of the heat-sensitive resistive film 11. That is, it is only necessary to prevent the moisture that moves through the air from reaching. The present invention has been made based on such knowledge of the present inventor.

Thus, the flow rate detecting element according to the first aspect of the present invention comprises: (a) a flat base material; (b) an insulating support film disposed on the surface of the base material; A plurality of heat generating portions made of a heat-sensitive resistive film arranged on the support film (arranged in the direction of the flow of the measurement fluid) and supported by the support film; and (d) the heat generating portions arranged on the heat generating portion. (E) the flow rate of the measurement fluid (e) based on the amount corresponding to the difference between the heating currents of the upstream and downstream heating portions when viewed in the flow direction of the measurement fluid. (F) an insulating intermediate film (insulating film) that prevents movement of moisture (moisture) between the heating element (thermosensitive resistance film) and the protective film. ) Is interposed.

In the flow rate detecting element thus configured, since an insulating intermediate film (insulating film) is interposed between the heat-generating portion (heat-sensitive resistance film) and the protective film, the surface of the heat-generating portion is formed on the surface of the heat-generating portion. The moisture that reaches can be reduced. For this reason,
Fluctuations in the resistance of the heat generating portion can be reduced, and the accuracy and reliability of the flow measurement can be improved. Further, since such a flow rate detecting element has a simple structure, it can be easily manufactured.

A flow rate detecting element according to a second aspect of the present invention is the flow rate detecting element according to the first aspect, wherein the intermediate film has an amorphous structure. In this flow rate detecting element, since an intermediate film (insulating film) having an amorphous structure is interposed between the heat-generating portion (thermosensitive resistance film) and the protective film, the crystal orientation of the heat-generating portion is set in the protective film above it. Transfer is prevented. For this reason, the protective film above the heat generating portion does not become a column-shaped porous structure, and it is possible to more reliably prevent moisture from entering through the protective film. Therefore, the variation in the resistance value of the heat generating portion can be further reduced, and the accuracy and reliability of the flow rate measurement can be further improved.

A flow rate detecting element according to a third aspect of the present invention is the flow rate detecting element according to the first aspect, characterized in that the intermediate film is non-hygroscopic (has no hygroscopicity). is there. In this flow rate detecting element, since a non-hygroscopic intermediate film (insulating film) is interposed between the heat-generating portion (heat-sensitive resistance film) and the protective film, the ingress of moisture through the protective film is more reliably prevented. The variation of the resistance value of the heat generating portion can be further reduced, and the accuracy and reliability of the flow measurement can be further improved.

A flow rate detecting element according to a fourth aspect of the present invention is the flow rate detecting element according to any one of the first to third aspects, wherein the intermediate film is present only above the heating element. It is assumed that. In this flow rate detecting element, only the intermediate film (insulating film) is interposed between the protective film and the heat generating portion (thermosensitive resistance film), so that the material cost is reduced. In this case as well, it is possible to prevent moisture from penetrating through the protective film, reduce the resistance value fluctuation of the heat generating portion, and improve the flow rate measurement accuracy and reliability. . Also, in this case, the intermediate film does not need to be an insulator, and the range of material selection can be widened, and the process can be simplified, and the cost can be reduced.

The flow rate detecting element according to a fifth aspect of the present invention is the flow rate detecting element according to the first aspect, wherein the intermediate film is not interposed between the heating element (thermosensitive resistance film) and the protective film, and Is characterized in that an upper layer film for preventing movement of moisture is formed thereon. In this flow rate detection element, the diffusion of moisture to the protection film can be reduced by the upper layer film formed on the protection film, the resistance value fluctuation of the heat generating portion can be reduced, and the flow rate measurement accuracy and Reliability can be improved. Since the flow rate detecting element has a simple structure, it can be easily manufactured.

A flow rate detecting element according to a sixth aspect of the present invention is the flow rate detecting element according to the fifth aspect, characterized in that the upper layer film is highly hygroscopic (has high hygroscopicity). is there. In this flow rate detecting element, since the highly hygroscopic upper layer film is formed on the protective film, the diffusion of moisture into the protective film can be reduced, and the resistance value fluctuation of the heat generating portion (thermosensitive resistance film) can be reduced. Can be further reduced, and the flow measurement accuracy and reliability can be further improved.

A flow rate detecting element according to a seventh aspect of the present invention is the flow rate detecting element according to the fifth aspect, wherein the upper layer film is non-hygroscopic (has no hygroscopicity). It is. In this flow rate detecting element, since the non-hygroscopic upper layer film is formed on the protective film, the transmission of moisture to the protective film can be reduced, and the resistance value fluctuation of the heat generating portion (thermosensitive resistance film) can be reduced. Can be further reduced, and the flow measurement accuracy and reliability can be further improved.

The flow rate detecting element according to an eighth aspect of the present invention is the flow rate detecting element according to the fifth aspect, wherein the upper layer film has high water repellency (has high water repellency). is there. In this flow rate detection element, since the high water-repellent upper layer film is formed on the protective film, it is possible to prevent the transmission of moisture to the protective film, and to change the resistance value of the heat generating portion (thermosensitive resistance film). Can be further reduced, and flow measurement accuracy and reliability can be improved.

A flow rate detecting element according to a ninth aspect of the present invention is the flow rate detecting element according to any one of the first to eighth aspects, wherein the base material is formed in a region corresponding to the heat generating portion (thermosensitive resistive film). Are partially removed to form a diaphragm structure. Since the flow rate detecting element has a diaphragm structure, heat transfer from the heat generating portion to the fluid is promoted, and flow rate measurement accuracy and reliability are further enhanced.

According to a tenth aspect of the present invention, a flow rate sensor detects a flow rate of a measurement fluid using the flow rate detecting element according to any one of the first to ninth aspects. It is a feature. That is, a flow rate sensor is formed using the flow rate detection element according to any one of the first to ninth aspects. According to this flow sensor, the flow rate or flow rate of the fluid can be accurately detected regardless of the humidity.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is an elevational sectional view of a flow rate detecting element according to Embodiment 1 of the present invention. In FIG. 1, reference numeral 1 denotes a flat substrate made of, for example, a silicon wafer having a thickness of about 400 μm, and a support film 2 made of a silicon nitride film having a thickness of about 1 μm is formed on the flat substrate 1 by a sputtering method or the like. Is formed. Further, on the support film 2, a heat-sensitive resistance film 11 (a heat-generating portion such as a heat-generating resistor or a temperature-measuring resistor) made of, for example, platinum having a thickness of 0.2 μm is deposited by a vapor deposition method, a sputtering method, or the like. The heat-sensitive resistive film 11 is a current path formed by performing patterning using a photolithography method, a wet etching method, a dry etching method, or the like. Then, a third insulating film (intermediate film) is formed on the heat-sensitive resistive film 11 or the support film 2.
A silicon oxide film 18 having a thickness of about 0.2 μm is formed by a sputtering method. Further, the silicon oxide film 1
8, a protective film 3 made of a silicon nitride film having a thickness of about 0.8 μm is formed by a sputtering method or the like.

Further, an etching hole 17 is formed on the back surface protective film 16 formed on the surface (back surface) of the flat substrate 1 opposite to the surface on which the support film 2 is formed by photolithography or the like. After the formation, a portion of the flat substrate 1 is removed by performing, for example, alkali etching or the like to form the concave portion 12, thereby forming the diaphragm 14.

As shown in FIG. 1, a silicon oxide film 18 serving as a third insulating film is interposed between the heat-sensitive resistive film 11 and the protective film 3 thereabove. 11 is reduced by about 50% as compared with the case where the silicon oxide film 18 is not provided. In the first embodiment, a sputtered silicon oxide film is used as the third insulating film. However, similar effects can be obtained by using silicon nitride or the like as a material other than silicon oxide. The method for forming the film is not limited to the sputtering method, but may be an evaporation method or the like. Also,
In all the embodiments described below, including the first embodiment, a diaphragm type flow detecting element is described as an example, but it goes without saying that the same effect can be obtained in the case of a bridge type flow detecting element. .

Embodiment 2 FIG. FIG. 2 is an elevational sectional view of a flow rate detecting element according to a second embodiment of the present invention. FIG.
Numeral 1 is a flat substrate made of, for example, a silicon wafer having a thickness of about 400 μm, and a support film 2 made of a silicon nitride film having a thickness of about 1 μm is formed on the flat substrate 1 by a sputtering method or the like. Have been. Further, on the support film 2, a heat-sensitive resistor film 11 (heat-generating portion such as a heat-generating resistor or a temperature-measuring resistor) made of, for example, 0.2 μm-thick platinum is deposited by a vapor deposition method, a sputtering method, or the like. This heat-sensitive resistive film 11
Is a current path formed by performing patterning using a photoengraving method, a wet etching method, a dry etching method, or the like. Further, a silicon oxide film 19 having a thickness of about 0.2 μm is formed as a third insulating film (intermediate film) on the heat-sensitive resistance film 11 or the support film 2 by a CVD method. The silicon oxide film 19 formed by this CVD method has an amorphous structure. Further, a protective film 3 made of a silicon nitride film having a thickness of about 0.8 μm is formed on the silicon oxide film 19 by a sputtering method or the like.

Further, an etching hole 17 is formed by photolithography or the like on the back surface protective film 16 formed on the surface (back surface) of the flat substrate 1 opposite to the surface on which the support film 2 is formed. After that, a portion of the flat substrate 1 is removed by performing, for example, alkali etching or the like to form the concave portion 12, thereby forming the diaphragm 14.

As shown in FIG. 2, a third layer having an amorphous structure between the heat-sensitive resistive film 11 and the protective film 3 thereabove.
The silicon oxide film 19 prevents the crystal orientation of the thermal resistance film 11 from being transferred to the upper protective film 3 by the silicon oxide film 19. This makes it difficult for the protective film 3 to become a columnar porous structure, prevents moisture from being transmitted to the heat-sensitive resistance film 11, and reduces the resistance drift of the heat-sensitive resistance film 11 with respect to humidity without providing the silicon oxide film 19. Is reduced by about 80%. In the second embodiment, a CVD silicon oxide film is used as the third insulating film. However, a similar effect can be expected with another material having an amorphous structure. Further, the film formation method is not limited to the CVD method, and other film formation methods such as an evaporation method capable of giving an amorphous structure can be used.

Embodiment 3 FIG. 3 is an elevational sectional view of a flow rate detecting element according to a third embodiment of the present invention. FIG.
Numeral 1 is a flat substrate made of, for example, a silicon wafer having a thickness of about 400 μm, and a support film 2 made of silicon nitride having a thickness of about 1 μm is formed on the flat substrate 1 by a sputtering method or the like. ing. Further, on the support film 2, a heat-sensitive resistive film 11 made of platinum or the like having a thickness of, for example, 0.2 μm is deposited by a vapor deposition method, a sputtering method, or the like. The heat-sensitive resistive film 11 is a current path formed by performing patterning using a photolithography method, a wet etching method, a dry etching method, or the like. Further, on the heat-sensitive resistive film 11 or the support film 2, as a third insulating film (intermediate film), an SOG (Spin O
n Glass) film 20 is formed by spin coating. This SOG film 20 contains Si and O as main components.
(For example, SOG manufactured by Tokyo Ohka, Type-2: for Si-Film),
By performing annealing at 600 to 800 ° C. or more after coating formation, the hygroscopicity is almost eliminated. Furthermore, SOG
On the film 20, a protective film 3 made of a silicon nitride film having a thickness of about 0.8 μm is formed by a sputtering method or the like.

Further, an etching hole 17 is formed on the back surface protective film 16 formed on the surface (back surface) of the flat substrate 1 opposite to the surface on which the support film 2 is formed by photolithography or the like. After that, a portion of the flat substrate 1 is removed by performing, for example, alkali etching or the like to form the concave portion 12, thereby forming the diaphragm 14.

As shown in FIG. 3, a SOG film 20 as a third insulating film having no hygroscopic property is sandwiched between the heat-sensitive resistance film 11 and the protective film 3 thereabove. Therefore, the passage of moisture from the outside is prevented by the SOG film 20 on the heat-sensitive resistance film 11. As a result, the resistance drift of the heat-sensitive resistive film 11 with respect to humidity is reduced by the SOG film 20
Is reduced by about 70% as compared with the case where no is provided. Further, according to this configuration, even if the protective film 3 does not exist on the SOG film 20, it is hardly affected by humidity, so that there is no problem even if the process is terminated only by SOG coating. In this case, the process is simplified and the cost is reduced. In the third embodiment, the SOG coating film is used as the third insulating film. However, the same effect can be expected with another material that does not transmit moisture. Further, the film formation method is not limited to spin coating, and other film formation methods such as a vapor deposition method can be used.

Embodiment 4 FIG. 4 is an elevational sectional view of a flow rate detecting element according to a fourth embodiment of the present invention. FIG.
Numeral 1 is a flat substrate made of, for example, a silicon wafer having a thickness of about 400 μm, and a support film 2 made of silicon nitride having a thickness of about 1 μm is formed on the flat substrate 1 by a sputtering method or the like. ing. Further, a heat-sensitive resistive film 1 made of platinum or the like having a thickness of, for example, 0.2 μm is formed on the support film 2.
1 is deposited by a vapor deposition method, a sputtering method, or the like. Further, as a third film (intermediate film) on the heat-sensitive resistance film 11,
An amorphous silicon film 21 having a thickness of about 0.2 μm is formed by a plasma CVD method. Here, the amorphous silicon film 21 and the heat-sensitive resistive film 11 are simultaneously patterned by photolithography, wet etching or dry etching, thereby forming a current path. Further, the amorphous silicon film 21
Alternatively, a protective film 3 made of a silicon nitride film having a thickness of about 0.8 μm is formed on the support film 2 by a sputtering method or the like.

Further, an etching hole 17 is formed on the back surface protective film 16 formed on the surface (back surface) of the flat substrate 1 opposite to the surface on which the support film 2 is formed by photolithography or the like. After that, a portion of the flat substrate 1 is removed by performing, for example, alkali etching or the like to form the concave portion 12, thereby forming the diaphragm 14.

As shown in FIG. 4, an amorphous silicon film 2 having an amorphous structure only on the heat-sensitive resistance film 11
1 is formed so that the heat-sensitive resistive film 1
It is difficult for the protective film 3 on 1 to become a column-shaped porous structure. This prevents the transmission of moisture to the heat-sensitive resistive film 11 and reduces the resistance drift of the heat-sensitive resistive film 11 with respect to humidity by about 80% as compared with the case where the amorphous silicon film 21 is not provided. Further, according to this structure, it is not necessary to use an insulating film as the third film, and the range of choice of the type of film to be used is widened, which is advantageous in terms of process and cost.

Embodiment 5 FIG. FIG. 5 is an elevational sectional view of a flow rate detecting element according to a fifth embodiment of the present invention. FIG.
1 is a flat substrate made of, for example, a silicon wafer having a thickness of about 400 μm, and a support film 2 made of a silicon nitride film having a thickness of about 1 μm is formed on the flat substrate 1 by a sputtering method or the like. Is formed. Further, the support membrane 2
A heat-sensitive resistance film 11 made of platinum or the like having a thickness of, for example, 0.2 μm is formed thereon by a vapor deposition method, a sputtering method, or the like. The heat-sensitive resistive film 11 is patterned by using a photolithography method, a wet etching method, a dry etching method, or the like, thereby forming a current path. Then, on the heat-sensitive resistive film 11 or the support film 2, a thickness of about 0.
A protective film 3 made of 5 μm silicon nitride is formed by a sputtering method or the like.

Further, a silicon nitride film 22 having a thickness of about 0.5 μm is formed on the protective film 3 as a third film (upper layer film) by a sputtering method or the like. The silicon nitride film 22 formed by the sputtering method is not formed by continuous film formation, but is formed by once exposing to the atmosphere.
Further, after an etching hole 17 is formed on the back surface protective film 16 formed on the surface (back surface) of the flat substrate 1 opposite to the surface on which the support film 2 is formed by photoengraving or the like. For example, by performing alkali etching or the like, a part of the flat base material 1 is removed to form the concave portion 12, thereby forming the diaphragm 14.

By forming the film structure as shown in FIG. 5, the columnar porous structure 15 of the protective film 3 becomes the third porous structure.
A discontinuous surface is formed at the interface with the silicon nitride film 22, which is the film (upper layer film). This prevents moisture from entering the heat-sensitive resistive film 11 and reduces the resistance drift of the heat-sensitive resistive film 11 with respect to humidity by about 50% as compared with the case where the silicon nitride film 22 is not provided.

Embodiment 6 FIG. FIG. 6 is an elevational sectional view of a flow rate detecting element according to a sixth embodiment of the present invention. FIG.
Numeral 1 is a flat substrate made of, for example, a silicon wafer having a thickness of about 400 μm, and a support film 2 made of a silicon nitride film having a thickness of about 1 μm is formed on the flat substrate 1 by a sputtering method or the like. Have been. Further, on the support film 2, a heat-sensitive resistive film 11 made of platinum or the like having a thickness of, for example, 0.2 μm is deposited by a vapor deposition method, a sputtering method, or the like.
The heat-sensitive resistive film 11 is patterned by using a photolithography method, a wet etching method, a dry etching method, or the like, thereby forming a current path. And
About 0.5 μm thick on the heat-sensitive resistive film 11 or the support film 2
The protective film 3 made of a silicon nitride film having a thickness of m is formed by a sputtering method or the like.

Further, a phosphorus (P) -doped SOG having a thickness of about 0.2 μm is formed on the protective film 3 as a third film (upper layer film).
(Spin On Glass) film 23 is formed. This SOG
The film 23 has Si, O and P as main components (for example, SOG, Type-2: P-doped, P-Si-Film manufactured by Tokyo Ohka).
), And is solidified by annealing at 450 ° C. or higher after coating. Since the SOG film 23 contains phosphorus (P), it has high hygroscopicity. Further, after an etching hole 17 is formed on the back surface protective film 16 formed on the surface (back surface) of the flat substrate 1 opposite to the surface on which the support film 2 is formed by photoengraving or the like. For example, a portion of the flat substrate 1 is removed by performing, for example, alkali etching or the like to form the concave portion 12, thereby forming the diaphragm 14.

With the film structure shown in FIG. 6, the P-doped SOG film 23 as the third film has high hygroscopicity. The SOG film 23 has an action of absorbing external moisture, thereby preventing moisture from entering the heat-sensitive resistive film 11 through the columnar porous structure 15 of the support film 3, and the humidity of the heat-sensitive resistive film 11. Is about 40% lower than that in the case where the SOG film 23 is not provided.
Reduced.

Embodiment 7 FIG. 7 is an elevational sectional view of a flow rate detecting element according to a seventh embodiment of the present invention. FIG.
In the figure, reference numeral 1 denotes a flat substrate made of, for example, a silicon wafer having a thickness of about 400 μm, and a support film 2 made of silicon nitride having a thickness of about 1 μm is formed on the flat substrate 1 by a sputtering method or the like. Have been. Further, on the support film 2, a heat-sensitive resistive film 11 made of platinum or the like having a thickness of, for example, 0.2 μm is deposited by a vapor deposition method, a sputtering method, or the like.
The heat-sensitive resistive film 11 is patterned by using a photolithography method, a wet etching method, a dry etching method, or the like, thereby forming a current path. And
About 0.8 μm thick on the heat-sensitive resistive film 11 or the support film 2
The protective film 3 made of m silicon nitride is formed by a sputtering method or the like.

Further, on the protective film 3, an SOG (Spin On Glass) film 24 having a thickness of about 0.2 μm is formed as a third film (upper layer film). The SOG film 24 contains Si and O as main components (for example, SOG, Type
-2: for Si-Film), annealing at 600 to 800 ° C. or higher after coating formation almost eliminates hygroscopicity. Further, the back surface protective film 16 formed on the surface (rear surface) of the flat substrate 1 opposite to the surface on which the support film 2 is formed is etched into the etching hole 1 by a method such as photolithography.
After the formation of the recesses 7, a portion of the flat substrate 1 is removed by performing, for example, alkali etching or the like, thereby forming the recesses 1.
2 are formed, whereby the diaphragm 14 is formed.

By adopting the film structure shown in FIG. 7, the SOG film 24 as the third film does not have a hygroscopic property. The SOG film 24 has an effect of preventing moisture from passing through the protective film 3, thereby preventing moisture from entering the heat-sensitive resistance film 11 through the columnar porous structure 15, and Is about 70% lower than that without the SOG film 24.
Reduced.

Embodiment 8 FIG. FIG. 8 is an elevational sectional view of a flow rate detection element according to Embodiment 8 of the present invention. FIG.
1 is a flat substrate made of, for example, a silicon wafer having a thickness of about 400 μm, and a support film 2 made of a silicon nitride film having a thickness of about 1 μm is formed on the flat substrate 1 by a sputtering method or the like. Is formed. Further, the support membrane 2
A heat-sensitive resistance film 11 made of platinum or the like having a thickness of, for example, 0.2 μm is formed thereon by a vapor deposition method, a sputtering method, or the like. The heat-sensitive resistive film 11 is patterned by using a photolithography method, a wet etching method, a dry etching method, or the like, thereby forming a current path. Further, the heat-sensitive resistive film 11 or the support film 2 has a thickness of about 0.
A protective film 3 made of a 9 μm silicon nitride film is formed by a sputtering method or the like.

Further, a fluorinated carbon film 25 having a thickness of about 0.1 μm and containing C and F as main components is formed as a third film (upper layer film) on the protective film 3 by a sputtering method. This fluorinated carbon film 25 has high water repellency. An etching hole 17 is formed on the back surface protective film 16 formed on the surface (back surface) of the flat substrate 1 opposite to the surface on which the support film 2 is formed by photolithography or the like.
Is formed, a portion of the flat substrate 1 is removed by performing, for example, alkali etching or the like, so that the concave portions 12 are formed.
Is formed, whereby the diaphragm 14 is formed.

With the film structure shown in FIG. 8, the fluorinated carbon film 25 as the third film has high water repellency. The fluorinated carbon film 25 has an effect of preventing moisture from passing into the protective film 3, thereby preventing moisture from entering the heat-sensitive resistance film 11.
1 is reduced by about 70% as compared with the case where the fluorinated carbon film 25 is not provided. This water-repellent third film is not limited to the fluorinated carbon film, but may be any film having the same water-repellency. The same effect can be obtained by modifying the surface of the protective film 3 to be water-repellent by fluorination or the like.

Embodiment 9 FIG. FIGS. 9 and 10 are a front view and a side cross-sectional view, respectively, showing one embodiment of a flow sensor using the flow detection element according to each of the above embodiments. 9 and 10, reference numeral 31 denotes a flow detecting element, reference numeral 32 denotes a detection pipeline, reference numeral 33 denotes a main passage which is a fluid passage, reference numeral 34 denotes a grid-shaped rectifier,
Reference numeral 5 denotes a case in which a control circuit is housed, and reference numeral 36 denotes a connector for supplying power to the flow rate sensor and extracting output. As described above, by incorporating the flow rate detection elements according to the first to eighth embodiments, a flow rate sensor having the same effects as those of the flow rate detection elements according to the respective embodiments can be obtained.

[0046]

According to the present invention, the following remarkable effects can be obtained. That is, according to the flow rate detecting element according to the first aspect of the present invention, the intermediate film as the third insulating film is interposed between the heat generating portion (thermosensitive resistance film) and the protective film on the heat generating portion. In addition, it is possible to reduce moisture reaching the surface of the heat generating part, reduce fluctuations in resistance value of the heat generating part, and improve flow measurement accuracy and reliability. Further, since the flow rate detecting element has a simple structure, it can be manufactured by a simple manufacturing process.

According to the flow rate detecting element according to the second aspect of the present invention, the intermediate film, which is the third insulating film having an amorphous structure, is provided between the heat-generating portion (heat-sensitive resistance film) and the protective film on the heat-generating portion. Since it is sandwiched, the crystal orientation of the heat generating portion is prevented from being transferred to the upper protective film. For this reason, the protective film does not become a column-shaped porous structure, it is possible to prevent moisture from entering through the protective film, it is possible to further reduce the fluctuation of the resistance value of the heat generating portion, and to improve the flow measurement accuracy and reliability. It can be further improved.

According to the flow rate detecting element of the third aspect of the present invention, the intermediate film which is the third insulating film having no hygroscopic property between the heat-generating portion (heat-sensitive resistive film) and the protective film thereabove. , The moisture can be prevented from entering the heat-generating portion through the protective film, the resistance value fluctuation of the heat-generating portion can be further reduced, and the flow measurement accuracy and reliability can be further improved. it can.

According to the flow rate detecting element according to the fourth aspect of the present invention, the intermediate film as the third film is interposed between the protective film and the heat generating portion (thermosensitive film) only. In addition, it is possible to effectively prevent moisture from entering the heat-generating part through the protective film while reducing material costs, further reduce fluctuations in the resistance of the heat-generating part, and improve flow rate measurement accuracy and reliability. Can be done. In this case, the intermediate film, which is the third film, does not need to be an insulator, so that a wider range of materials can be selected, and thus the process can be simplified and the cost can be reduced.

According to the flow rate detecting element of the fifth aspect of the present invention, since the upper film as the third film is formed on the protective film, it is possible to reduce the diffusion of moisture into the protective film. As a result, it is possible to reduce the variation in the resistance value of the heat generating portion (heat-sensitive resistive film), and to improve the flow measurement accuracy and reliability.

According to the flow rate detecting element of the sixth aspect of the present invention, since the upper film, which is the third film having high hygroscopicity, is formed on the protective film, the diffusion of moisture into the protective film is performed. Can be reduced, the fluctuation of the resistance value of the heat generating portion (heat-sensitive resistive film) can be reduced, and the accuracy and reliability of the flow measurement can be improved.

In the flow rate detecting element according to the seventh aspect of the present invention, since the upper layer, which is the third layer having no hygroscopicity, is formed on the protective layer, the transmission of moisture to the protective layer is performed. , The fluctuation of the resistance value of the heat generating portion (thermosensitive resistance film) can be further reduced, and the accuracy and reliability of the flow measurement can be further improved.

According to the flow rate detecting element according to the eighth aspect of the present invention, since the upper film, which is the third film having high water repellency, is formed on the protective film, the transfer of moisture to the protective film is achieved. Can be eliminated, the fluctuation in the resistance value of the heat generating portion (thermosensitive resistance film) can be further reduced, and the accuracy and reliability of the flow measurement can be improved.

According to the flow rate detecting element according to the ninth aspect of the present invention, since it has a diaphragm structure, heat transfer from the heat generating portion to the fluid is promoted, and the flow rate measurement accuracy and reliability are further enhanced.

According to the flow rate sensor according to the tenth aspect of the present invention, since the above flow rate detecting elements are used, a flow rate sensor having the same effect as these flow rate detecting elements can be obtained. That is, according to this flow sensor, the flow rate or flow rate of the fluid can be accurately detected regardless of the humidity.

[Brief description of the drawings]

FIG. 1 is an elevational sectional view of a flow rate detecting element according to a first embodiment of the present invention;

FIG. 2 is an elevational sectional view of a flow rate detecting element according to a second embodiment of the present invention;

FIG. 3 is an elevational sectional view of a flow rate detecting element according to a third embodiment of the present invention;

FIG. 4 is an elevational sectional view of a flow rate detecting element according to a fourth embodiment of the present invention;

FIG. 5 is an elevational sectional view of a flow rate detecting element according to a fifth embodiment of the present invention;

FIG. 6 is an elevational sectional view of a flow rate detecting element according to a sixth embodiment of the present invention;

FIG. 7 is an elevational sectional view of a flow rate detecting element according to a seventh embodiment of the present invention;

FIG. 8 is an elevational sectional view of a flow rate detecting element according to an eighth embodiment of the present invention.

FIG. 9 is a front view of a flow rate sensor according to a ninth embodiment of the present invention.

10 is a side sectional view of the flow sensor shown in FIG. 9;

FIG. 11 is an elevational sectional view of a conventional bridge-type thermosensitive flow rate detecting element.

FIG. 12 is a plan view of the conventional flow rate detecting element shown in FIG.

FIG. 13 is an elevational sectional view of a conventional diaphragm-type thermosensitive flow rate detecting element.

FIG. 14 is a plan view of the conventional flow rate detecting element shown in FIG.

FIG. 15 is an elevational sectional view of a conventional flow rate detecting element.

FIG. 16 is a diagram showing the relationship between the humidity of outside air and the drift in resistance of a conventional flow rate detecting element.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Plate-shaped base material, 2 Support film, 3 Protective films, 4 Heat generation resistance, 5 RTD, 6 RTD, 7 Comparative Resistance, 8
Opening, 9 air space, 10 arrow, 11 thermal resistance film, 12 recess, 13 bridge, 14 diaphragm, 15 columnar porous structure, 16 back protective film, 17 etching hole, 18 sputtered silicon oxide film, 19 CVD oxidation Silicon film, 20 non-doped SOG film, 21 amorphous silicon film, 22 sputtered silicon nitride film, 23 phosphorus-doped SOG film, 24
Non-doped SOG film, 25 fluorinated carbon film, 31
Flow detection element, 32 detection pipeline, 33 main passage, 34
Rectifier, 35 cases, 36 connectors.

 ────────────────────────────────────────────────── ─── Continued on front page (72) Inventor Kazuhiko Tsutsumi 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Electric Corporation

Claims (10)

[Claims] 1. A substrate comprising: a flat substrate; an insulating support film disposed on a surface of the substrate; and a heat-sensitive resistive film disposed on the support film and supported by the support film. And a protective insulating film disposed on the heating section to protect the heating section, wherein the heating current of the upstream and downstream heating sections in the flow direction of the measurement fluid is measured. A heat-sensitive flow rate detection element that measures the flow rate of the measurement fluid based on the amount corresponding to the difference, wherein an insulating intermediate film that prevents movement of moisture is provided between the heating element and the protective film. A flow rate detecting element characterized by being sandwiched. 2. The flow detecting element according to claim 1, wherein the intermediate film has an amorphous structure. 3. The flow detecting element according to claim 1, wherein the intermediate film is non-hygroscopic. 4. The flow detecting element according to claim 1, wherein the intermediate film is provided only above the heating element. 5. A plurality of substrates each comprising a flat substrate, an insulating support film disposed on the surface of the substrate, and a heat-sensitive resistive film disposed on the support film and supported by the support film. And an insulating protective film disposed on the heating section to protect the heating section. The heating current of the heating section on the upstream and downstream sides in the flow direction of the measurement fluid. A heat-sensitive flow rate detecting element that measures the flow rate of the measurement fluid based on an amount corresponding to the difference between the two, wherein an upper layer film that prevents movement of moisture is formed on the protective film. Flow detection element. 6. The flow rate detecting element according to claim 5, wherein the upper layer film has high hygroscopicity. 7. The flow rate detecting element according to claim 5, wherein the upper layer film is non-hygroscopic. 8. The flow rate detecting element according to claim 5, wherein the upper layer film has high water repellency. 9. The flow rate detecting element according to claim 1, wherein the base material is partially removed in a region corresponding to the heat generating portion to form a diaphragm structure. 10. A flow rate sensor, wherein the flow rate of a measurement fluid is detected using the flow rate detection element according to claim 1. Description: