JP2001165733A - Flow sensor and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately measure the flow rate of a fluid by detecting the temperature change of the fluid with good response. SOLUTION: In a flow sensor wherein a flow rate detector 30 and a heater 40 are provided on the diaphragm 10 having a membrane structure formed on the cavity part 1a of a semiconductive substrate 1 and a fluid temperature detector 20 is provided on the semiconductive substrate 1, grooves 21 are formed on both sides of the wiring pattern of the fluid temperature detector 20. By this constitution, the response of the fluid temperature detector 20 becomes good and the temperature of a fluid can be detected with good response and, therefore, the flow rate of the fluid can be accurately detected as the flow sensor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a flow sensor for detecting a flow rate of a fluid and a method for manufacturing the same.

[0002]

2. Description of the Related Art As a flow sensor for detecting a flow rate of a fluid, a diaphragm having a thin film structure is formed on a cavity of a semiconductor substrate, and a micro heater (hereinafter simply referred to as a heater) and a flow rate detector are provided in the diaphragm.
A fluid temperature detector is provided in an area other than the diaphragm on the semiconductor substrate, and the temperature of the heater is controlled so as to be higher than the temperature detected by the fluid temperature detector by a predetermined temperature ΔT. Various proposals have been made for detecting the flow rate of a fluid based on this. The heater,
The flow rate detector and the fluid temperature detector are formed of a resistor film such as Pt (platinum).

[0003]

In the conventional structure described above, the fluid temperature detector for measuring the temperature of the fluid responds to the temperature of the fluid while thermally insulating it so as not to be affected by the heater. Need to measure well.

However, since the fluid temperature detector is formed in a region other than the diaphragm on the semiconductor substrate, when the fluid temperature changes, the heat capacity of the substrate influences and the fluid temperature can be measured with good response. Therefore, there is a problem that the flow rate cannot be measured accurately because the temperature difference ΔT from the heater is shifted.

In this case, it is conceivable that the fluid temperature detector is also provided on the thin film structure of the diaphragm. However, in order to thermally insulate the heater from the heater, the fluid temperature detector must be arranged separately from the heater. And the strength of the thin film structure is significantly reduced.

The present invention has been made in view of the above problems, and has as its object to accurately measure a fluid flow rate by detecting a change in fluid temperature with good responsiveness.

[0007]

In order to achieve the above object, according to the first aspect of the present invention, a fluid temperature detector (2) is provided.
The groove (21) is formed on both sides of the wiring pattern (0).

As a result, since the heat capacity is reduced, the temperature of the fluid can be detected with good responsiveness, and the flow rate can be accurately measured as a flow sensor.

In this case, it is preferable that the groove (21) is formed to have a depth reaching the inside of the substrate (1).

Further, when the hollow portion (22) communicating with the groove (21) is formed in the substrate (1), the heat capacity is further reduced and the responsiveness is improved. Can be good.

According to the fourth aspect of the present invention, the heating element (40) is provided on the first cavity (1a) formed in the substrate (1).
And a second cavity (2) formed in the substrate (1).
2) A fluid temperature detector (20) is provided on top.

As described above, the fluid temperature detector (20) is connected to the second
The heat capacity is also reduced by arranging on the hollow portion (22), and the temperature of the fluid can be detected with good responsiveness.

In this case, it is preferable that the second cavity (22) is formed inside the substrate (1).

According to the present invention, the flow sensor as described above can be appropriately manufactured.

The reference numerals in parentheses of the above-mentioned means indicate the correspondence with the concrete means described in the embodiments described later.

[0016]

(First Embodiment) FIG. 1 is a perspective view of a flow sensor according to a first embodiment of the present invention, and FIG.
1 shows a cross-sectional view taken along the line AA in FIG.

In this flow sensor, a silicon nitride film 11 and a silicon oxide film 12 serving as a lower insulating film are formed on a semiconductor substrate 1 formed of single crystal silicon or the like.
A fluid temperature detector 20 and a flow rate detector (temperature measuring element) 30 forming a thermometer are formed thereon, and a heater (heating element) 40 is formed thereon. Further, a silicon oxide film serving as an upper insulating film is formed thereon. It has a structure in which a film 13 and a silicon nitride film 14 are formed.

As shown in FIG. 2, a cavity 1a is formed in the semiconductor substrate 1, and a diaphragm 10 forming a thin film structure is formed on the cavity 1a. A heater 40 is provided.

The fluid temperature detector 20, the flow detector 30 and the heater 40 are arranged in that order from the upstream side in the direction of the flow of the fluid (indicated by the white arrow in FIG. 1). The pattern is formed by a resistor film made of a wiring material such as Pt.

The fluid temperature detector 20 detects the temperature of the fluid, and is disposed at a position sufficiently separated from the heater 40 so that the heat of the heater 40 does not affect the temperature detection. The heater 40 is controlled by a control circuit (not shown) so that the reference temperature is higher than the temperature detected by the fluid temperature detector 20 by a certain temperature.

In the flow sensor constructed as described above, when a fluid flows, the temperature of the fluid is changed to the fluid temperature detector 2.
The heater 40 is energized so that the reference temperature is measured at 0 and the reference temperature is higher by a certain temperature than the measured temperature. Then, the heat distribution of the heater 40 changes according to the magnitude of the flow of the fluid, and the change in the heat distribution causes the flow rate detector 3 to change.
The flow rate is detected by changing the resistance value of 0.

In this embodiment, as shown in FIG. 2, grooves 21 are formed on both sides of the wiring pattern of the fluid temperature detector 20. The groove 21 has a depth reaching the inside of the semiconductor substrate 1 (for example, a depth of about 50 μm from the surface of the semiconductor substrate 1). Since the fin structure in which the grooves 21 are provided on both sides of the wiring pattern of the fluid temperature detector 20 improves the thermal responsiveness and can measure the change in the fluid temperature with good response, Accurate flow measurement considering the change in conduction can be performed.

Next, a method of manufacturing the above-described flow sensor will be sequentially described with reference to the process diagrams shown in FIGS. 3 and 4 (the diagrams corresponding to the AA cross section in FIG. 1). [Step of FIG. 3 (a)] A single crystal silicon substrate 1 is used as a semiconductor substrate, and a silicon nitride film 11 is formed on one surface (front surface) thereof by LPCVD or the like, and a silicon oxide film 12 is formed thereon by CVD. It forms with.

By laminating the silicon oxide film 12 on the silicon nitride film 11 as described above, the adhesion with the wiring material formed on the silicon oxide film 11 is improved,
Further, when the thin film structure is formed, the moisture resistance of the thin film structure can be improved because the water-resistant silicon nitride film 12 is disposed outside. [Step of FIG. 3B] A Pt film is formed as a resistor material by 200
The Pt film is deposited on the silicon nitride film 12 by a vacuum evaporation machine at
The wiring pattern of the flow rate detector 30 and the heater 40 is patterned.

Here, the resistor material may be polysilicon, NiCr, TaN, SiC, W or the like. In this case, a single film is more preferable than a multilayer film. Further, a Ti layer or a Cr layer may be inserted as an adhesive layer between the silicon oxide film 12 and the Pt film for the purpose of increasing the adhesion, and the adhesive layer may also be inserted between the resistor material and the upper film. May be inserted. [Step of FIG. 3C] A silicon oxide film 13 is deposited for insulation between the fluid temperature detector 20, the flow detector 30, and the heater 40. [Step of FIG. 3D] A silicon nitride film 14 which is a surface protection film is formed. Thereafter, although not shown, openings are formed in the silicon nitride film 14 for forming electrode pads of the fluid temperature detector 20, the flow detector 30, and the heater 40. [Step of FIG. 4 (a)] A groove 21 is formed by anisotropic etching up to the silicon substrate 1 between the wirings of the fluid temperature detector 20 to form a fin structure. [Step of FIG. 4B] A mask material (for example, a silicon oxide film or a silicon nitride film) 15 is formed on the back surface of the silicon substrate 1.
Is formed, and the opening 16 is formed by etching. [Step of FIG. 4 (c)] The back side of the silicon substrate 1 is anisotropically etched until the silicon nitride film 11 is exposed to form a cavity 1a. At this time, the end point is detected by, for example, using TMAH (tetramethylammonium hydroxide) as an etching solution, so that the silicon nitride film 1
1 can be easily stopped because the etching rate is very low.

Thus, the flow sensor shown in FIGS. 1 and 2 can be manufactured. (Second Embodiment) In the above-described first embodiment, the structure in which the grooves 21 are formed on both sides of the wiring pattern of the fluid temperature detector 20 has been described. However, as shown in FIGS. If the hollow portion 22 communicating with the groove 21 is formed below the detection body 20, the heat capacity can be further reduced and the responsiveness can be improved.

In the embodiment shown in FIG. 5, the silicon substrate 1
Has a structure in which a cavity 21 communicating with the groove 21 is formed. After the anisotropic dry etching shown in FIG. 4A, isotropic etching (for example, plasma etching using SF6) is performed from the surface of the cavity 22 in this embodiment, and the silicon under the fluid temperature detector 20 is formed. It is formed by removing the substrate 1. In this case, since the silicon nitride film 14 and the silicon oxide film 13 serve as a mask material as they are, etching can be performed without adding a mask and by omitting steps such as photolithography. Also,
This structure has an advantage that it can be formed while maintaining the strength of the entire chip.

In the embodiment shown in FIG. 6, the silicon substrate 1
A cavity 22 communicating with the groove 21 and opening on the back surface of the silicon substrate 1 is formed. The cavity 22 in this embodiment is formed by etching both surfaces in the process of FIG. 4C, whereas only the back surface is etched in the first embodiment.

Here, by using TMAH or KOH as an etching solution, silicon (11
1) By utilizing the difference in etching rate between the surface and the other surface,
The etching shape can be accurately controlled. For this reason, the walls of the cavity 1a and the cavity 22 have the same inclination and are parallel to each other, so that the distance between the fluid temperature detector 20 and the heater 40 is smaller than when the same cavity is formed by etching from the back surface. Can be brought close to the point where there is no thermal effect, and the chip size can be reduced.

In the embodiment shown in FIG. 7, in order to prevent a decrease in chip strength in the embodiment shown in FIG.
Is not penetrated to the back surface, but is stopped halfway. The cavity 22 in this embodiment can be formed by combining etching of only the back surface and etching of both surfaces. Specifically, first, only the back surface is etched, a predetermined amount is etched, and then both surfaces are etched, so that the cavity 22 shown in FIG. 7 can be formed. In this case, the back surface may be etched after both surfaces are etched. However, in consideration of good controllability and the possibility of destruction of the fluid temperature detector 20 when the back surface is etched later, the back surface is etched first. Is more desirable. In the embodiment shown in FIG. 7, the process is more complicated than in the embodiment shown in FIG. 6, but the cavity 22 can be formed with better control than that in the embodiment shown in FIG.

It is desirable that the above-mentioned hollow portion 22 communicates with grooves 21 formed on both sides of the wiring pattern of the fluid temperature detector 20. Even when the cavity 22 is formed by communicating with the groove, the temperature of the fluid can be detected with good responsiveness.

Further, in the various embodiments described above, the thin film structure of the flow rate detector 30 and the heater 40 has a diaphragm type structure, but may have a bridge type structure. In addition, the flow rate detector 30 includes the heater 4
0 may be provided not only on one side but also on both sides. In this case, the flow rate is measured based on the detected temperature difference between the flow rate detectors 30 provided on both sides.

[Brief description of the drawings]

FIG. 1 is a perspective view of a flow sensor according to a first embodiment of the present invention.

FIG. 2 is a sectional view taken along the line AA in FIG.

FIG. 3 is a process chart showing a method of manufacturing the flow sensor according to the first embodiment of the present invention.

FIG. 4 is a process chart showing a process shown in FIG. 3;

FIG. 5 is a sectional view showing a first example of a flow sensor according to a second embodiment of the present invention.

FIG. 6 is a sectional view showing a second example of the flow sensor according to the second embodiment of the present invention.

FIG. 7 is a sectional view showing a third example of the flow sensor according to the second embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Silicon substrate, 1a ... Hollow part, 10 ... Diaphragm, 11 ... Silicon nitride film, 12 ... Silicon oxide film, 1
3 ... silicon oxide film, 14 ... silicon nitride film, 20 ... fluid temperature detector, 21 ... groove, 22 ... cavity, 30 ... flow rate detector, 40 ... heater.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroyuki Wado 1-1-1 Showa-cho, Kariya-shi, Aichi F-term in DENSO Corporation (reference) 2F035 EA08

Claims (13)

[Claims] A fluid temperature detector (20) and a heating element (4) formed by a wiring pattern are provided on one side of a substrate (1).
0) is provided, and the temperature of the heating element (40) is set to a reference temperature based on the temperature detected by the fluid temperature detection element (20). A flow sensor for detecting a flow rate of the fluid based on a change in heat distribution of a body (40), wherein grooves (21) are formed on both sides of a wiring pattern of the fluid temperature detecting body (20). A flow sensor. 2. The device according to claim 1, wherein the groove has a depth reaching the inside of the substrate.
3. The flow sensor according to claim 1. 3. The flow sensor according to claim 1, wherein a cavity (22) communicating with the groove (21) is formed in the substrate (1). 4. A fluid temperature detector (20) and a heating element (40) are provided on one surface side of the substrate (1), and the heat generation is performed based on the temperature detected by the fluid temperature detector (20). In the flow sensor, the temperature of the body (40) is set to a reference temperature, and the flow rate of the fluid is detected based on a change in heat distribution of the heating element (40) due to the flow of the fluid. The heating element (40) is disposed on a first cavity (1a) formed in the substrate (1), and the fluid temperature detector (20) is formed in the substrate (1). A flow sensor, wherein the flow sensor is disposed on the second cavity (22). 5. The flow sensor according to claim 3, wherein the second cavity (22) is formed inside the substrate (1). 6. The method for manufacturing a flow sensor according to claim 1, wherein a fluid temperature detector (20) and a heating element (40) are provided on one side of the substrate (1). ) Using a wiring pattern; and forming grooves (21) on both sides of the wiring pattern of the fluid temperature detector (20). 7. The method according to claim 6, wherein the etching is performed using a wiring pattern of the fluid temperature detector as a mask. 8. The method according to claim 6, wherein the etching is anisotropic etching. 9. A step of forming a cavity (22) communicating with the groove (21) by performing isotropic etching from one surface side of the substrate (1) after forming the groove (21). The method for manufacturing a flow sensor according to claim 8, comprising: 10. A method of manufacturing a flow sensor according to claim 4, wherein a fluid temperature detector (20) and a heating element (40) are formed on one surface of the substrate (1). A first part of the substrate (1) below the heating element (40)
Forming a second hollow portion (22) under the fluid temperature detector (20) while forming the hollow portion (1a). 11. The method according to claim 10, wherein after forming the groove in the substrate, isotropic etching is performed to form the second cavity. Manufacturing method of flow sensor. 12. The method according to claim 10, wherein after forming the groove in the substrate, anisotropic etching is performed to form the second hollow portion. Manufacturing method of flow sensor. 13. A method for manufacturing a flow sensor according to claim 4, wherein a fluid temperature detector (20) and a heating element (40) are formed on one surface of the substrate (1); A first cavity (1a) is formed in a region where the heating element (40) is formed from the other surface side of the substrate (1), and at the same time, the fluid temperature detection is formed from the other surface side of the substrate (1). Forming a second hollow portion (22) in the defined region.