JPH0755523A - Flow rate sensor - Google Patents

Abstract

PURPOSE:To provide a flow rate sensor having high responsiveness and a high mechanical strength by reducing the heat capacity and heat conduction. CONSTITUTION:A flow rate sensor is provided with a substrate 13, an insulating film 14 formed on the surface of the substrate 13, flow detection circuit conductors 15 formed on the surface of the film 14, and a conductor protecting film 16 formed on the surface of the film 14 so as to cover the conductors 15. In addition, a heat insulating space section 21 is formed in the substrate 13 at the part where the conductors 15 are positioned and a thin-walled section 23 is formed in the film 14 below the part where the conductors 15 are formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow rate sensor for detecting an extremely minute flow velocity of a fluid.

[0002]

2. Description of the Related Art Conventionally, as a flow rate sensor for detecting a minute flow velocity of a fluid, as shown in FIGS. 6A and 6B, for example, a flow rate sensor chip having a thin film structure portion having an extremely small heat capacity is formed. Things are known. This is because a pair of heating elements 5 and a heating element 5 for detecting a flow rate by a thin film forming technique and a thin film processing technique are provided in a thin film structure 4 in which two layers of an insulating film 2 and a conductor protective film 3 are laminated on a surface of a substrate 1. A flow rate detection circuit conductor 7 composed of the temperature sensitive resistors 6 is formed, and a space 8 for heat insulation is formed in a portion of the back surface of the substrate 1 where the flow rate detection circuit conductor 7 is located. This utilizes that the temperature difference between the upstream side and the downstream side of the flow rate detection circuit conductor 7 (in this case, the resistance value of the pair of temperature sensitive resistors 6, 6) changes according to the flow velocity.

In this flow rate sensor 9, in order to detect the flow velocity of a minute fluid, it is necessary to reduce the heat capacity of the area of the flow rate detecting circuit conductor 7 to detect a minute temperature change. The conductor 7 region has a thin film structure. Further, in order to detect a minute temperature change, it is necessary to block the inflow and outflow of heat between the flow rate detection circuit conductor 7 region and the substrate 1, and in order to improve the heat insulation property, it is necessary to use As shown in (a) and (b), a flow rate sensor 11 having a structure in which holes 10 for thermal insulation are provided in the peripheral portion of the heating element 5 and the temperature sensitive resistors 6 has also been manufactured.

[0004]

However, in the conventional flow rate sensor 9 shown in FIG. 6, in addition to the problem of the heat capacity of the flow rate detection circuit conductor 7 region itself, the two layers of the insulating film 2 and the conductor protective film 3 are provided. As a result, the amount of heat conduction between the flow rate detection circuit conductor 7 in the thin film structure 4 and the substrate 1 becomes large, or the insulation between the heating element 5 and the pair of temperature sensitive resistors 6, 6 in the area of the flow rate detection circuit conductor 7 is increased. There is a problem that the responsiveness of the sensor decreases due to an increase in the amount of heat conduction through the film 2, and in order to solve both of these problems, the film thickness of the thin film structure portion 4 should be thin. on the other hand,
The thinner the film thickness, the weaker the mechanical strength of the thin film structure portion 4 and the more likely it is to be damaged by impact.

Further, the holes 10 and 1 for heat insulation shown in FIG.
In the case of the flow rate sensor 11 provided with 0, ...
There is a problem that the thin film structure portion 4 is easily attached to the edge portion of 0, an abnormal operation of the sensor is likely to occur, and the mechanical strength of the thin film structure portion 4 is weaker than that of a sensor having a structure without holes. That is, in the case of any of the flow rate sensors, it is difficult to realize a flow rate sensor in which both the heat capacity or the amount of heat conduction is reduced to improve the responsiveness of the flow rate sensor and the mechanical strength is improved. there were.

The present invention has been made to solve the above problems, and provides a flow rate sensor having high responsiveness and high mechanical strength by reducing heat capacity or heat conduction. The purpose is to

[0007]

In order to achieve the above object, a flow sensor according to claim 1 is formed with a substrate, an insulating layer formed on the surface of the substrate, and an insulating layer formed in the insulating layer. A flow rate sensor comprising a flow rate detection circuit conductor, wherein a space portion for thermal insulation is formed in a portion of the substrate where the flow rate detection circuit conductor is located, wherein the flow rate detection circuit conductor of the insulating layer is formed. It is characterized in that a thin portion is formed in the open region.

According to a second aspect of the flow sensor, a substrate, an insulating layer formed on the surface of the substrate, a flow rate detection circuit conductor formed on the surface of the insulating layer, and a surface of the insulating layer are provided. A flow rate sensor comprising a conductor protection layer formed to cover the flow rate detection circuit conductor, wherein a space for thermal insulation is formed in a portion of the substrate where the flow rate detection circuit conductor is located, In the insulating layer, a thin portion is formed below the position where the flow rate detection circuit conductor is formed.

A flow sensor according to a third aspect of the present invention includes a substrate, an insulating layer formed on the surface of the substrate, a flow rate detection circuit conductor formed on the surface of the insulating layer, and a surface of the insulating layer. A flow sensor comprising a conductor protection layer formed so as to cover the flow rate detection circuit conductor, wherein a space for thermal insulation is formed in a portion of the substrate where the flow rate detection circuit conductor is located, One of the insulating layer and the conductor protection layer is formed in a peripheral portion of the flow rate detection circuit conductor with a cutout portion penetrating in the thickness direction, and the other is configured to cover the cutout portion. It is characterized by that.

[0010]

According to the flow rate sensor of the present invention, since the heat capacity of the flow rate detection circuit conductor region is reduced by the thin portion formed in the flow rate detection circuit conductor region, the flow rate detection circuit detects a minute temperature change. be able to. On the other hand, the portions other than the thin portion retain the mechanical strength of the flow rate sensor.

Further, according to the flow rate sensor of the second aspect, since the heat capacity of the flow rate detection circuit conductor area is reduced by the thin portion formed below the flow rate detection circuit conductor, the flow rate detection circuit has a small temperature. Changes can be detected. On the other hand, the portion other than the thin portion around the flow rate detection circuit conductor retains the mechanical strength of the flow rate sensor.

Further, according to the flow sensor of the third aspect, there is a portion (missing portion) where only one layer of the insulating layer or the conductor protective layer exists in the peripheral portion of the flow rate detection circuit conductor. By forming the portion, the amount of heat conduction inside and outside the flow rate detection circuit conductor is reduced, and the flow rate detection circuit can detect a minute temperature change. Further, the one-layer portion retains the mechanical strength of the flow sensor.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the flow rate sensor of the present invention will be described below with reference to FIGS. FIG. 1 shows (a) a plan view and (b) a cross-sectional view of the flow rate sensor of this embodiment. The flow rate sensor 12 includes a substrate 13 and a substrate 13 as shown in FIG. 1 (b). The insulating film 14 (insulating layer) formed on the surface of the substrate 13, the flow rate detecting circuit conductor 15 formed on the surface of the insulating film 14, and the flow rate detecting circuit conductor 1
5, a conductor protective film 16 (conductor protective layer) formed on the surface of the insulating film 14 and an insulating film 17 formed on the back surface side of the substrate 13. As shown in FIG. 1A, the flow rate detection circuit conductor 15 includes a heater 18 (heating element) and temperature-sensitive resistors 19 and 20 formed at positions on both sides of the heater 18 on the surface of the insulating film 14. (Upstream-side resistor 19, downstream-side resistor 20).

Then, the flow rate detection circuit conductor 15 of the substrate 13
A space 21 for thermal insulation exposing the insulating film 14 to the back side by partially removing the substrate 13 is formed in a portion corresponding to the lower part of the insulating film 14, the insulating film 14, the flow rate detection circuit conductor 15, and the conductor protection. The film 16 forms a thin film structure 22. Further, as shown in FIGS. 1A and 1B, in the insulating film 14 in the thin film structure portion 22, the thin portion 2 is formed below the pattern region of the flow rate detection circuit conductor 15.
3 is formed.

Next, a procedure for producing the flow rate sensor 12 having the above-mentioned structure will be described with reference to FIG. First, a 200 μm thick silicon substrate 13 is used as the substrate (see FIG.
(A)) A 500 nm-thickness silicon oxide film 24 is formed on the surface of the silicon substrate 13 by a thermal oxidation method, and the silicon oxide film 24 is patterned by a lithography technique. (FIG.2 (b)). The planar shape of the silicon oxide film 24 patterned here is finally
It is a planar shape of the thin portion 23 shown in FIG. 1A, and is a region where the flow rate detection circuit conductor 15 pattern is formed later.

Next, an insulating film 14 made of silicon nitride and having a thickness of 800 nm is deposited on the surface of the silicon substrate 13 by a method such as a sputtering method or a plasma CVD method (FIG. 3).
(C)). Then, the insulating film 14 on the silicon oxide film 24
The insulating film 14 is polished until the film thickness becomes 400 nm (FIG. 3D). On the other hand, a back surface insulating film 17 made of silicon nitride is deposited on the back surface of the silicon substrate 13 by a method such as a sputtering method or a plasma CVD method (FIG. 3D).
The back surface insulating film 17 is provided as a mask for etching when the heat insulating space 21 is formed in the silicon substrate 13, as described later.

Next, a metal film for forming the heater 18 and the temperature sensitive resistors 19 and 20 is formed on the surface of the insulating film 14 and processed into a desired circuit pattern shape by a lithography technique (FIG. 3 (e)). This metal film is made of Ni, Ni-
A film having a film thickness of 80 nm is formed using Fe, Pt, or the like by a vacuum deposition method, a sputtering method, or the like. Then, the conductor protective film 16 made of silicon nitride and having a film thickness of 100 nm is formed by the same method as the case of the insulating film 14 or the back surface insulating film 17 (FIG. 3F).

Next, the heater 18 and the temperature sensitive resistor 1
In order to form the heat insulating space portion 21 at the position where 9 and 20 are formed, the back surface insulating film 17 is patterned to remove the portions below the heater 18 and the temperature sensitive resistors 19 and 20, and the silicon surface 25 The back surface of the substrate 13 is exposed (FIG. 3G). Then, the substrate 13 is etched until the back surface of the insulating film 14 is exposed from the silicon surface 25 exposed by anisotropic etching to form the heat insulating space portion 21 (FIG. 3 (h)). A commonly used KOH (potassium hydroxide) solution is used as the anisotropic etching solution. This etching liquid has a property of etching silicon, but not of an insulating film such as silicon nitride or silicon oxide.

Next, as described above, since the silicon oxide film 24 is exposed when the heat insulating space 21 is formed, the silicon oxide film 24 is removed with buffered hydrofluoric acid (FIG. 3 (i)). ). At this time, the etching rate of silicon oxide with respect to buffered hydrofluoric acid is 10 times or more faster than that of silicon nitride. Therefore, only the silicon oxide film 24 can be selectively removed without etching the insulating film 14. Through the above procedure, it is possible to manufacture the flow rate sensor 12 in which the thickness of the insulating film 14 which is a part of the thin film structure portion 22 (flow rate detection circuit conductor 15 region) having a thickness of 900 nm is reduced to 400 nm.

The flow rate sensor 12 of this embodiment has a thin portion 23 formed in a part of the thin film structure portion 22 corresponding to the area of the flow rate detection circuit conductor 15, and the insulating film 1 below the heater 18 is formed.
Since 4 is thin, it is possible to reduce the heat capacity of the heater portion, so that it is possible to reduce the power consumption of the heater.
Furthermore, since the insulating film 14 below the temperature sensitive resistors 19 and 20 is also thin, the heat capacity of the temperature sensitive resistor portion can be reduced, so that the thermal response is improved and the flow rate sensor 12 has high sensitivity. You can

On the other hand, the portion of the thin film structure portion 22 other than the thin portion 23 has an effect of maintaining the mechanical strength of the thin film structure portion 22, and prevents the thin film structure portion 22 from being damaged by an impact or the like. You can That is, the flow rate sensor 12 of the present embodiment can have both good characteristics such as low power consumption and high sensitivity and high mechanical strength.

In this embodiment, as shown in FIG. 1A, the heater 18 and the pair of temperature sensitive resistors 19 and 20 are used.
Although the large-area thin-walled portions 23 are collectively formed in each region, the smaller the area of the thin-walled portions 23, the more the mechanical strength of the thin-film structure 22 can be improved.
For example, as shown in FIG. 3, the heater 26, the temperature sensitive resistor 2
The heater 26 and the temperature sensitive resistor 2 are maintained while maintaining the effect of the characteristic of reducing the heat capacity by changing the circuit patterns of 7 and 28.
Thin-walled portion 2 divided into small areas 7 and 28 respectively
It is also possible to further improve the mechanical strength by forming 9, 29, ....

Next, the second embodiment of the flow rate sensor in the present invention.
An example will be described with reference to FIGS. 4 and 5. FIG. 4 shows a perspective view (a) and a sectional view (b) of the flow sensor of the present embodiment. The flow rate sensor 31 has substantially the same configuration as that of the flow rate sensor 12 of the first embodiment.
As shown in (b), it comprises a substrate 13, an insulating film 14, a flow rate detection circuit conductor 15, and a conductor protection film 16. As shown in FIG. 4A, the flow rate detection circuit conductor 15 includes a heater 18 (heating element) and a pair of temperature-sensitive resistors 19 and 20 (upstream-side resistor 19, downstream-side resistor 20). It consists of

Then, as shown in FIG. 4B, the substrate 1
A space 21 for heat insulation is formed in a portion below the flow rate detection circuit conductor 15 of FIG. In addition, FIG.
As shown in (b), in the thin film structure portion 22 which is the area of the flow rate detection circuit conductor 15, the protective film 1 layer portion (missing portion) 30, 30, ... In which only the insulating film 14 is partially removed is a heater. 1
A large number are formed around the temperature sensor 8 and the temperature sensitive resistors 19 and 20. The planar shape of the protective film 1 layer portion 30 shown in FIG. 4A is the same as that of the flow sensor 1 shown in FIG.
The shape is the same as that of the hole 10 for heat insulation in FIG.

Next, the procedure for producing the flow rate sensor 31 having the above-mentioned structure will be described with reference to FIG. The specific specifications of each step are almost the same as those in the first embodiment, and detailed description thereof will be omitted. First, after depositing the insulating film 14 on the surface of the silicon substrate 13 (FIG. 5A), the insulating film 14 is deposited.
Is patterned to remove the insulating film 14 at the portion where the protective film 1 layer portion is to be formed (FIG. 5B). Next, the insulating film 14
After forming the metal film 32 forming the heater 18 and the temperature sensitive resistors 19 and 20 on the surface, it is processed into a circuit pattern shape (FIG. 5C).

Further, a conductor protection film 16 is deposited (see FIG. 5).
(D)), this conductor protection film 16 is patterned (FIG. 5E). The patterning is for removing the conductor protection film 16 at the terminal portion 33 of the heater 18 and the temperature sensitive resistors 19 and 20 and exposing the surface of the metal film 32 for bonding with a conductor or the like. Next, the back side of the silicon substrate 13 is etched to form the heat insulating space 2.
1 is formed (FIG. 5 (f)). By the procedure described above, the insulating film 1 is formed on the thin film structure portion 22 (flow rate detection circuit conductor 15 region).
It is possible to manufacture the flow rate sensor 31 in which the protective film 1-layer portion 30 including only the conductor protective film 16 is removed and the protective film 1 is removed.

In the flow rate sensor 31 of this embodiment, the protective film 1 layer portions 30, 30, ... Are formed on a part of the thin film structure portion 22 corresponding to the region of the flow rate detection circuit conductor 15. The protective film 1 layer portion is formed. The amount of heat conduction through 30, 30, ... Is reduced to less than half the amount of heat conduction through the two insulating film layers in the conventional flow sensor 9 shown in FIG. Therefore, the heat generated by the heater 18 is transferred to the temperature sensitive resistors 19 and 20 through the insulating film, or the heat is generated.
The rate of transmission from 0 to the substrate 13 is reduced, that is,
The heat insulating property is improved, and the flow rate sensor 31 can be made highly sensitive.

On the other hand, the protective film 1 layer portion 3 of the present flow sensor 31.
0, 30, ... Are the heat insulating holes 10, 10, ... In the conventional flow sensor 11 shown in FIG.
Since it corresponds to a shape filled with layers, it is possible to improve mechanical strength as compared with the flow rate sensor 11 of FIG.
It is possible to eliminate the problem that foreign matter adheres to the edge of the hole 10 and causes the sensor to malfunction. That is, the flow rate sensor 31 of this embodiment can have both good sensitivity and high mechanical strength.

In the present embodiment, when forming the protective film 1-layer portions 30, 30, ..., The insulating film 14 is patterned and removed, and the conductor protective film 16 is used to form the protective film 1-layer portions 30, 30 ,. .. are formed, the conductor protective film 16 may be patterned and removed to form the protective film 1 layer portions 30, 30, ... With the insulating film 14 instead of this structure.

[0030]

As described above in detail, the first aspect of the present invention is as follows.
Since the flow sensor described has the thin portion formed in the flow detection circuit conductor area, the heat capacity of the flow detection circuit conductor area becomes smaller than that of the conventional flow sensor in which the thin portion does not exist, and the heat of the flow detection circuit is reduced. Responsiveness is improved. On the other hand, the portions other than the thin portion retain the mechanical strength of the flow rate sensor. Therefore, the present flow rate sensor can have high responsiveness and high mechanical strength at the same time.

Further, in the flow sensor according to the second aspect, since the thin portion is formed at a position below the flow detecting circuit conductor, the flow detecting circuit conductor region is provided as compared with the conventional flow sensor in which the thin portion does not exist. The heat capacity of is reduced, and the thermal response of the flow rate detection circuit is improved. On the other hand, the portion other than the thin portion around the flow rate detection circuit conductor retains the mechanical strength of the flow rate sensor. Therefore, the present flow rate sensor can have high responsiveness and high mechanical strength at the same time.

Further, in the flow sensor according to the third aspect of the invention, there is a missing portion in which either the insulating layer or the conductor protection layer is missing in the peripheral portion of the flow detecting circuit conductor, and the missing portion has one layer. Since only the flow rate detecting circuit conductor area has two layers, the amount of heat conduction inside and outside the flow rate detecting circuit conductor area is smaller than that of the conventional flow rate sensor in which the flow rate detecting circuit conductor area is entirely composed of two layers. The thermal response of is improved. Also,
Since there is no defective portion such as a hole, the mechanical strength of the flow sensor is maintained. Therefore, this flow sensor
In addition to being highly responsive, it can have high mechanical strength.

[Brief description of drawings]

1A is a plan view showing a first embodiment of a flow rate sensor according to the present invention, and FIG. 1B is a sectional view taken along line AA in FIG.

FIG. 2 is a diagram showing a manufacturing procedure of the embodiment.

FIG. 3 is a plan view showing a modified example of the same embodiment.

4A is a perspective view showing a second embodiment of the flow rate sensor according to the present invention, and FIG. 4B is a sectional view taken along line BB in FIG. 4B.

FIG. 5 is a diagram showing a manufacturing procedure of the embodiment.

FIG. 6A is a perspective view showing an example of a conventional flow rate sensor,
(B) It is sectional drawing which follows CC line in (a).

7 (a) is a perspective view showing another example of a conventional flow rate sensor, and FIG. 7 (b) is a sectional view taken along the line D-D in FIG. 7 (a).

[Explanation of symbols]

 12, 31 Flow rate sensor 13 Substrate 14 Insulating film (insulating layer) 15 Flow rate detection circuit conductor 16 Conductor protective film (conductor protective layer) 21 Thermal insulation space 23 Thin portion 30 Protective film 1 layer (missing part)

Claims (3)

[Claims] 1. A substrate, an insulating layer formed on a surface of the substrate, and a flow rate detecting circuit conductor formed in the insulating layer, the portion of the substrate where the flow rate detecting circuit conductor is located. A flow sensor in which a space for heat insulation is formed in the flow sensor, wherein a thin portion is formed in a region of the insulating layer where the flow detection circuit conductor is formed. 2. A substrate, an insulating layer formed on the surface of the substrate, a flow rate detecting circuit conductor formed on the surface of the insulating layer, and a surface of the insulating layer covering the flow rate detecting circuit conductor. A flow sensor comprising a conductor protection layer formed, wherein a space portion for thermal insulation is formed in a portion of the substrate where the flow rate detection circuit conductor is located, wherein the flow rate detection circuit conductor is provided in the insulating layer. A flow rate sensor characterized in that a thin portion is formed below the position where is formed. 3. A substrate, an insulating layer formed on the surface of the substrate, a flow rate detecting circuit conductor formed on the surface of the insulating layer, and a surface of the insulating layer covering the flow rate detecting circuit conductor. In a flow rate sensor comprising a formed conductor protection layer, wherein a space portion for thermal insulation is formed in a portion of the substrate where the flow rate detection circuit conductor is located, the insulating layer or the conductor protection layer On either side,
A flow rate sensor, characterized in that a cutout portion penetrating in the thickness direction is formed at a peripheral portion of the flow detection circuit conductor, and the other portion covers the cutout portion.