JP2003240618A - Flow sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance heat transfer efficiency by sufficiently thinning the thickness of an insulating film with excellent yield, and to improve sensitivity and responsiveness of a sensor. <P>SOLUTION: A passage 8 for a measuring fluid 7 is formed by a sensor body 2 and a sensor chip 3. A flow velocity detection means 12 and a peripheral temperature detection means 16 are formed on the face on the opposite side to the passage 8 side of the sensor chip 3 through an electrical insulating film 13. The sensor chip 3 is formed from a stainless steel product manufactured by dissolving/casting, by a vacuum induction melting method, a steel ingot dissolved/cast by an ordinary solution process, and by dissolving/casting it again by a vacuum arc remelting method, and the surface thereof is polished. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow sensor used for measuring the flow velocity or flow rate of a fluid flowing in a flow channel, and more particularly to a thermal type flow sensor.

[0002]

2. Description of the Related Art A thermal type flow sensor for measuring the flow velocity or flow rate of a fluid has a sensor chip equipped with a flow velocity detecting means installed in a pipe in parallel with the flow of the fluid to be measured to generate heat. Electricity caused by the flow generated in the spatial temperature distribution of the fluid due to the heat generated from the body (heater), which is detected by a temperature sensor (indirect heating type) or the heat of the heating element is removed by the fluid. Change or resistance change is detected (self-heating type) to measure the flow velocity or flow rate (eg, Japanese Patent Application Laid-Open No. 4-295724, Japanese Patent Publication No. 6-25684, and Japanese Patent Application Laid-Open No. 8-25684). 1460
No. 26 publication).

A sensor chip of a flow sensor is generally one in which a temperature detecting means is formed on one surface of a substrate by a photolithography technique and an etching technique. As the substrate material, silicon, glass or the like is usually used, but when corrosion resistance and mechanical strength are required, a metal substrate made of stainless steel or the like is used. In this case, since the sensor chip is a conductor, the flow velocity detecting means made of a conductor is formed on the electric insulating film after the electric insulating film is formed in the insulating film forming step. The present invention particularly relates to a thermal flow sensor using a stainless steel sensor chip.

In order to form a flow velocity detecting means on the surface of a stainless steel substrate through an electric insulating film, an electric insulating film such as a silicon oxide film or a silicon nitride film is usually formed by a plasma CVD method, and a temperature detection is performed on the electric insulating film. The means is formed by photolithography technology and etching technology. A general-purpose stainless steel material, which is a substrate material, has Al ₂
Since many impurities (particles) and defects (pinholes) such as O ₃ and SiO ₂ are present and lacking in cleanliness, the thickness of the electrical insulating film must be adjusted in order to manufacture a sensor with high yield and high breakdown voltage. Need to thicken.

[0005]

As described above, in the flow sensor in which the flow velocity detecting means is formed on the stainless steel sensor chip, the electric insulating film is formed on the substrate surface by the plasma CVD method, and the flow velocity detecting means is formed thereon. Were formed by photoetching. Generally, since the electric insulating film has a low thermal conductivity, it is desirable to form the electric insulating film as thin as possible within a range in which electric insulation between the sensor chip and the flow velocity detecting means can be achieved. However, general purpose stainless steel materials (eg,
The sensor chip formed of SUS304, SUS316 series stainless steel) has many particles and defects, and it is necessary to improve the insulation between the sensor chip and the flow velocity detection unit formed on the sensor chip through the electric insulating film. The electric insulation film must be thickened. In the case of a thermal type flow sensor, increasing the film thickness of the electrical insulating film lowers the heat transfer efficiency in the plate thickness direction and increases the heat capacity, so there is a problem that the sensitivity and responsiveness of the sensor cannot be improved. It was

The present invention has been made in order to solve the above-mentioned conventional problems, and an object of the present invention is to make it possible to sufficiently reduce the thickness of the electric insulating film with good yield and to improve sensitivity and responsiveness. It is to provide a flow sensor which is improved.

[0007]

To achieve the above object, a first invention comprises a sensor chip having a diaphragm part forming a part of a flow path of a fluid to be measured, and the diaphragm part on the flow path side. In a flow sensor in which a flow velocity detecting means is provided on the surface opposite to the surface through an electric insulating film, the sensor chip is a steel ingot melted and cast by a normal melting method and melted and cast by a vacuum induction melting method. Further, the diaphragm is formed of a stainless steel material manufactured by melting and casting by a vacuum arc remelting method, and at least a surface of the diaphragm opposite to the flow path side is polished.

In the first aspect of the present invention, the sensor chip is made of a stainless steel material formed by vacuum induction melting a steel ingot melted and cast by a normal melting method and then vacuum arc remelting. The number of particles and defects is extremely small, and the thickness of the electric insulating film can be reduced.

A second invention comprises a sensor chip having a diaphragm portion forming a part of a flow path of a fluid to be measured,
In a flow sensor in which a flow velocity detecting means is provided on the surface of the diaphragm portion opposite to the flow path side through an electric insulating film, the sensor chip is an electroslab formed by melting and casting a steel ingot melted by a normal melting method. It is formed of a stainless steel material manufactured by melting and casting by a remelting method, and at least the surface of the diaphragm opposite to the flow path side is polished.

In the second invention, since the sensor chip is made of a stainless steel material formed by remelting a steel ingot melted and cast by a normal melting method by an electroslab remelting method, particles and defects are formed. Is extremely small, and the thickness of the electric insulating film can be reduced.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below in detail based on the embodiments shown in the drawings. FIG. 1 is a sectional view showing an embodiment of a flow sensor according to the present invention, and FIG. 2 is a plan view of a sensor chip. In these figures, a flow sensor indicated by reference numeral 1 as a whole is provided with a sensor body 2, a sensor chip 3 installed on the sensor body 2, and a sensor chip 3 arranged on the sensor body 2 with a spacer 4 interposed therebetween. It is composed of a printed circuit board 5 and the like located above the sensor chip 3.

The sensor body 2 is made of a metal plate made of stainless steel, and has a protrusion 2A integrally formed at the center of the upper surface.
And two flow path holes 9 and 10 that form a flow path 8 for a fluid to be measured (hereinafter, also referred to as a fluid) 7 together with the recess 6 of the sensor chip 3. The flow path holes 9 and 10 are formed of through-holes, one end of which is open toward both ends of the protruding portion 2A in the longitudinal direction, and the other end of which is open to the lower surface of the sensor body 2.

The sensor chip 3 is formed in a rectangular plate shape having substantially the same size as the protrusion 2A of the sensor body 2, and the recess 6 is formed at the center of the lower surface. The formed surface forms a thin diaphragm portion 3A, and a thick fixing portion 3B surrounding the diaphragm portion 3A is joined to the upper surface of the protrusion 2A by YAG laser welding or the like. The diaphragm portion 3A has a plate thickness of about 50 to 150 μm,
A flow velocity detecting means 12 described later is provided at the center of the surface. The recess 6 is an ellipse elongated in the longitudinal direction of the sensor chip 3, and communicates with the flow passage holes 9 and 10 at both ends. An upper surface 3a on the side opposite to the passage 8 side of the sensor chip 3 on which the flow velocity detecting means 12 is provided.
Are mirror-polished.

As the material of the sensor chip 3, a material having a lower thermal conductivity than silicon and having high heat resistance, corrosion resistance and rigidity, specifically stainless steel is used.
However, since a general-purpose stainless steel material manufactured by a normal melting / refining method has a large amount of particles, defects, and released gas and lacks in cleanliness, it is used as a chip material for the flow sensor 1 used in a semiconductor manufacturing apparatus or the like. Not suitable.

Therefore, in the present invention, a stainless steel material manufactured by remelting a stainless steel material manufactured by a normal melting / refining method by a special melting method is used as a chip material.

As a method for producing a stainless steel material by the special melting method, a vacuum induction melting method (VIM) and a subsequent vacuum arc remelting method (VAR) are used to perform double vacuum melting, which is an electroslab remelting method (ESR). )
There are two types of casting.

The VIM method is a method for producing a steel ingot by remelting a steel ingot melted and cast by a normal atmospheric melting furnace and pouring it into a mold.

In the VAR method, an arc is generated between a consumable electrode and molten steel in a mold in a vacuum water-cooled copper mold, the generated heat remelts the electrode and continuously solidifies it in the mold. This is a method for producing a steel ingot.

The ESR method is a method of manufacturing a steel ingot while melting the electrode material by resistance heat of molten slag in a cold mold.

According to such a special melting method, since the molten steel is cut off from the atmosphere, the degassing effect is excellent.
It has the feature that oxide-based inclusions (particles) can be removed and high-quality steel with high cleanliness can be manufactured.

The steel ingot produced by the special melting method is forged or hot rolled into a stainless steel material having a predetermined thickness. Further, the stainless steel material is cut into a predetermined size, the upper surface 3a is mirror-polished, and the recess 6 is formed at the center of the lower surface 3b, whereby the above-mentioned stainless steel sensor chip 3 is manufactured.

The diaphragm portion 3A of the sensor chip 3 is
If the thickness is 50 μm or less, the strength decreases, which is not preferable. Further, if the thickness is 150 μm or more, the sensor chip 3
Since the efficiency of heat transfer between the fluid 7 and the flow velocity detecting means 12 is reduced, the amount of heat transfer (heat loss) in the direction parallel to the surface of the sensor chip 3 is increased, and the heat capacity is also increased. Not preferable.

An electric insulating film 13 is formed on the entire upper surface 3a of the sensor chip 3, and six electrode pads 14 (14a-1) are formed on the surface of the electric insulating film 13.
4f) and the metal thin film 15 for wiring, the flow velocity detecting means 12 and the ambient temperature detecting means 16 are formed by a well-known thin film forming technique. For example, it is formed by depositing a material such as platinum on the electric insulating film 13 and etching it into a predetermined pattern. The flow velocity detecting means 12 and the ambient temperature detecting means 16 form the wiring metal thin film 15 on the electrode pad 14. Are electrically connected to each other.

The flow velocity detecting means 12 and the ambient temperature detecting means 16 will be described in detail.
One heating element (resistive heater) 20 and two temperature sensors 21
A and 21B constitute an indirectly heated flow velocity detecting means. The heating element 20 is located substantially at the center of the diaphragm portion 3A. The two temperature sensors 21A and 21B are arranged so as to be respectively located on the upstream side and the downstream side in the flow direction of the fluid 7 with the heating element 20 interposed therebetween. The ambient temperature detecting means 16 is used to compensate for a change in the ambient temperature, that is, the temperature of the fluid 7, and is arranged outside the diaphragm portion 3A on the upstream side.
However, it is not limited to the upstream side, but may be the downstream side, one side in the width direction of the sensor chip 3, or the diaphragm portion 3A. The pattern width of the heating element 20 is 10 to 50 μm, and the pattern widths of the temperature sensors 21A and 21B and the ambient temperature detecting means 16 are 5 to 10 μm.
A degree is preferable. Further, the diaphragm portion 3A and the thick fixing portion 3B surrounding the diaphragm portion 3A may be separately formed and integrated by thermal diffusion bonding, laser welding or the like.

The electric insulating film 13 is formed of a silicon oxide (SiO ₂ ) film, a silicon nitride film, an aluminum oxide film, polyimide, etc. having a thickness of about 1 μm. The silicon oxide film is formed, for example, by sputtering or CVD.
Alternatively, it is formed by SOG (spin on glass) or the like. The silicon nitride film is formed by sputtering, CVD or the like. The reason why the film thickness of the electric insulating film 13 can be reduced to about 1 μm or less is that the sensor chip 3 is made of the stainless steel material manufactured by the special melting method described above. That is, the stainless steel material manufactured by the special melting method has excellent cleanliness, and has less particles and pinholes than ordinary steel materials, so that an electric insulating film can be formed uniformly. This is because it does not need to be thick. For example, the electrical insulating film 13 may be formed thin within a range in which a withstand voltage of about 100 to 500 V and an insulating property of several hundreds MΩ or more can be secured between the sensor chip 3 and the flow velocity detecting means 12 made of a conductor. .

The printed circuit board 5 arranged on the sensor body 2 via the spacer 4 has a circular hole 26 larger than the third diaphragm portion 3A in the center, and a plurality of circular holes 26 are formed on the surface of the printed circuit board 5. Wiring patterns 27 are formed by printing, and the electrode pads 14 of the sensor chip 3 are electrically connected to the wiring patterns 27 by bonding wires (not shown). The spacer 4 is made of stainless steel like the sensor body 2,
It is made of aluminum or synthetic resin, and is fixed to the sensor body 2 with screws, an adhesive, or the like.

FIG. 3 is a diagram showing a constant temperature difference circuit of the flow sensor 1. In the figure, the heating element 20, the ambient temperature detecting means 16 and the three fixed resistors R1, R2 and R3 form a bridge circuit, and this and an operational amplifier (OP1) form a constant temperature difference circuit. OP1 receives the midpoint voltage of the resistor R1 of the bridge circuit and the heating element 20 as an inverting input, and the midpoint voltage of the resistors R2 and R3 as a non-inverting input. The output of OP1 is commonly connected to one ends of resistors R1 and R2. The resistors R1, R2 and R3 are the heating elements 2
The resistance value is set so that 0 is always higher than the ambient temperature detecting means 16 by a constant temperature.

FIG. 4 is a diagram showing a sensor output circuit of the flow sensor 1. In the figure, two temperature sensors 21
A and 21B and the two fixed resistors R4 and R5 form a bridge circuit, and this and OP2 form a sensor output circuit.

In such a flow sensor 1, as shown in FIG.
When the fluid 7 is made to flow in the direction of the arrow in FIG. 2 while the heating element 20 is heated to a certain higher temperature than the ambient temperature by energizing the bridge circuit of the constant temperature difference circuit shown in FIG. Since the heat is taken away in proportion to the flow velocity, the heating element 20 is also taken away with the heat and the resistance value decreases.
Therefore, the balanced state of the bridge circuit is lost, but OP1
Since a voltage corresponding to the voltage generated between the inverting input and the non-inverting input is applied to the bridge circuit, the amount of heat generated by the heating element 20 increases so as to compensate for the heat taken by the fluid 7. As a result, the resistance value of the heating element 20 increases, and the bridge circuit returns to the equilibrium state. Therefore, a voltage corresponding to the flow velocity is applied to the bridge circuit in the balanced state. As a method of using the constant temperature difference circuit of FIG. 3, it is possible to output the terminal voltage of the heating element 20 among the voltages applied to the bridge circuit as a voltage output by sharing the sensor with the heater.

When the temperature distribution near the heating element 20 is destroyed by the flow of the fluid 7, a temperature difference occurs between the temperature sensor 21A located upstream of the heating element 20 and the temperature sensor 21B located downstream thereof. The sensor output circuit shown in FIG. 4 detects the voltage difference or resistance value difference. The temperature difference between the two temperature sensors 21A and 21B is proportional to the flow velocity of the fluid 7. Therefore, if the relationship between the flow path cross-section average flow velocity or flow rate and the temperature difference, that is, the voltage difference or the resistance value difference detected by the sensor output circuit is calibrated in advance, the actual flow from the voltage difference or the resistance value difference is obtained. It is possible to measure the average flow velocity or flow rate of the road section. The configurations of the flow velocity detecting means 12 and the ambient temperature detecting means 16 are not limited to the above-mentioned embodiment, and various changes can be made. Further, the ambient temperature detecting means 16 is arranged at a place where the fluid temperature can be detected without being affected by the heat from the heating element.

FIG. 5 is a sectional view showing another embodiment of the present invention. This embodiment is applied to a flow sensor of a type called a header type. The header type flow sensor 30 is to be fitted into the sensor mounting hole 32 provided in the pipe wall of the pipe 31 through which the fluid 7 flows from the outside and fixed by welding or the like. The sensor body 33, the sensor chip 34, and the mounting plate 35. And constitute a container, and the printed circuit board 36 is housed inside. The sensor body 33 is formed of stainless steel in a cylindrical shape with both ends open, and the back side opening facing the inside of the pipe 31 is closed by the sensor chip 34.

The sensor chip 34 is formed of stainless steel into a thin plate having a plate thickness of about 50 to 150 μm, and the outer peripheral edge portion is joined to the opening on the back side of the sensor body 33 by YAG laser welding or the like. The joint portion forms the diaphragm portion 34A. An electrically insulating film 13 is formed on the surface of the diaphragm portion 34A opposite to the surface in contact with the fluid 7, as in the above-described embodiment, and one heating element (resistive heater) and two temperature sensors are formed thereon. An indirect heating type flow velocity detecting means 12, which is composed of ,, an electrode pad, a wiring metal thin film, and an ambient temperature detecting means 16 are formed.
As the material of such a sensor chip 34, as in the case of the sensor chip 3 in the above-described embodiment, a stainless steel material manufactured by a normal melting / refining method is further added to a vacuum induction melting method (VIM). A stainless steel material manufactured by performing double vacuum melting by the subsequent vacuum arc remelting method (VAR) or melting and casting by the electroslab remelting method (ESR) is used. The ambient temperature detecting means 16 is arranged so as to detect the fluid temperature without being affected by the heat from the heating element.

A wiring pattern is formed on the printed circuit board 36, and the flow velocity detecting means 12 and the ambient temperature detecting means 16 formed on the sensor chip 34 are formed on the wiring pattern by a metal thin film for wiring and an electrode pad. Are connected via wire bonds or the like. Further, a lead pin 38 for taking out to the outside is connected to the wiring pattern.

The mounting plate 35 is attached to the sensor body 33.
Is integrally formed on the front surface side of the
It is welded to the wall of pipe 1. It should be noted that the O-ring may be used for attachment with screws or the like. In addition, the sensor body 33
The sensor chip 34 and the sensor chip 34 may be integrally formed.

It will be apparent that the header type flow sensor 30 having such a structure can also obtain the same effect as that of the above-described embodiment.

[0036]

As described above, according to the flow sensor of the present invention, the stainless steel material manufactured by remelting and casting the steel ingot melted and cast by the normal melting method by the special melting method is used as the sensor chip. Since it is used as the material of (1), there are few particles and defects from the sensor chip, and the film thickness of the electrical insulating film formed on the surface of the sensor chip can be reduced to, for example, about 1 μm or less. Therefore, the heat transfer efficiency in the plate thickness direction of the sensor chip is improved and the heat capacity can be reduced, so that the sensitivity and responsiveness of the sensor can be improved. In particular, it is possible to provide a flow sensor suitable for use in a semiconductor manufacturing apparatus or an ultra high vacuum apparatus.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a flow sensor according to the present invention.

FIG. 2 is a plan view of a sensor chip.

FIG. 3 is a diagram showing a constant temperature difference circuit of a flow sensor.

FIG. 4 is a diagram showing a sensor output circuit.

FIG. 5 is a sectional view showing another embodiment of the present invention.

[Explanation of symbols]

1 ... Flow sensor, 2 ... Sensor body, 3 ... Sensor chip, 4 ... Spacer, 5 ... Printed circuit board, 6 ... Recessed part, 7 ...
Fluid, 8 ... Flow path, 12 ... Flow velocity detecting means, 13 ... Electrical insulating film, 16 ... Ambient temperature detecting means, 20 ... Heating element (heater), 21A, 21B ... Temperature sensor, 30 ... Flow sensor, 31 ... Piping, 32 ... Sensor mounting hole, 33 ... Sensor body, 34 ... Sensor chip, 35 ... Mounting plate.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shouji Kamiten             2-12-19 Shibuya, Shibuya-ku, Tokyo Stock market             Takeyama F term (reference) 2F035 EA04 EA08

Claims (2)

[Claims] 1. A sensor chip having a diaphragm part forming a part of a flow path of a fluid to be measured, wherein a flow velocity detecting means is provided on a surface of the diaphragm part opposite to the flow path side via an electric insulating film. In the provided flow sensor, the sensor chip is manufactured by melting and casting a steel ingot melted and cast by a normal melting method by a vacuum induction melting method, and further melting and casting by a vacuum arc remelting method. A flow sensor formed of a stainless steel material, wherein at least a surface of the diaphragm opposite to the flow path side is polished. 2. A sensor chip having a diaphragm portion forming a part of a flow path of a fluid to be measured is provided, and a flow velocity detecting means is provided on a surface of the diaphragm portion opposite to the flow path side via an electric insulating film. In the provided flow sensor, the sensor chip includes a steel ingot melted and cast by an ordinary melting method and melted by an electroslab remelting method.
A flow sensor formed of a stainless steel material produced by casting, wherein at least a surface of the diaphragm opposite to the flow path side is polished.