JPH0146009B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention imparts thermal energy to a gas to be measured flowing in a capillary flow path as a heat transfer medium, and generates a temperature difference due to heat transfer by the gas to be measured. A resistor that outputs a voltage corresponding to the mass flow rate of the gas to be measured due to the difference in electrical resistance.
The present invention relates to a flow rate sensor provided on the outer wall of the capillary channel and a method for manufacturing the same.

The above-mentioned flow rate sensors include a so-called self-heating type in which two heating resistors are provided as resistors spaced apart in the direction of the capillary flow path, and a type in which one heating resistor is provided before and after the heating resistor. There is a so-called auxiliary heating type in which two heat-sensitive resistors are provided spaced apart in the direction of the capillary flow path, and in both cases, the resistors are connected to a bridge circuit.

In the former self-heating type, when a current is passed through the bridge circuit to heat the heating resistor and a gas to be measured is caused to flow through the capillary flow path, the upstream side of the gas to be measured is heated. Thermal energy is applied from the heating resistor, and heat is transferred to the downstream heating resistor using the gas to be measured as a heat transport medium. As a result, the electrical resistance value of the upstream heating resistor decreases and the electrical resistance value of the downstream heating resistor increases, causing the bridge circuit to become unbalanced. It outputs a voltage according to the mass flow rate, and in the latter auxiliary heating type, almost no current flows through both heat-sensitive resistors, and current flows through the heating resistor to generate heat. As a result, the thermal energy of the heating resistor is transferred to the downstream heat-sensitive resistor, and the mass of the gas to be measured is determined based on the difference in electrical resistance between the two heat-sensitive resistors due to this heat transfer. It outputs a voltage according to the flow rate.

Such flow rate sensors are widely used in the semiconductor industry and automobiles as mass flow meters to accurately measure the mass flow rate of fluids and mass flow controllers to accurately control the mass flow rate. It is widely used in the fields of industry, analytical instruments, and general industry, and especially in the semiconductor industry, where precise measurement and control of the flow rate of gas, which is a raw material for semiconductor manufacturing, has a significant impact on the quality and yield of semiconductors. Since then, mass flow controllers have already been introduced in large quantities into semiconductor manufacturing equipment, and even in sectors where they have not yet been introduced, there is a tendency to rapidly shift from the combination of needle valves and rotameters to mass flow controllers.

Therefore, there is a demand for a flow rate sensor that has uniform characteristics and does not change over time, and it is desired that such a sensor be supplied to the market at a low price, but it is difficult to meet the above requirements with the current technology. It was something that I couldn't do.

That is, conventionally, a flow rate sensor is manufactured by using a metal capillary tube with a circular cross section and having a capillary flow path with an inner diameter of about 0.2 mm to 1 mm, and wrapping a resistor around the outer circumference of the capillary flow path. There is a limit to automation of the work of winding the metal wire of the resistor around each capillary tube, so it has to be done manually, which has poor productivity and makes it difficult to mass-produce products with uniform characteristics. It was difficult and expensive to produce.

Furthermore, the metal wire of the resistor is coated with an organic substance for the purpose of insulation, and an adhesive of an organic compound is applied to fix the resistor after it has been wound. When a flow rate sensor is in use, the temperature of the resistor increases to about 120°C to 150°C due to the current flowing through the resistor, and under these conditions, organic substances gradually increase as time passes. It was inevitable that the deterioration would affect the output characteristics of the sensor, resulting in zero drift and changes in sensitivity over time, causing problems in terms of measurement stability.

The present invention has been made in view of the above-mentioned circumstances, and the first invention aims to provide a flow rate sensor that has uniform characteristics and does not change over time. The flow rate sensor based on this technology uses an inorganic insulating film on one side of a silicon crystal capillary base with a rectangular cross section that forms a capillary flow path.
A film-like resistor is formed on the insulating film by photolithography and etching, and a surface protection film of an inorganic material and a bonding plate for external wiring connection are provided on the resistor. It has characteristics.

In the second invention, it is possible to mass-produce flow rate sensors that have uniform characteristics and do not change over time.
Furthermore, the purpose of the present invention is to provide a method for manufacturing a flow rate sensor that allows the flow rate sensor to be manufactured at a low cost. and a plate-shaped lid that closes the groove to produce a silicon crystal capillary substrate having a large number of capillary channels in parallel;
Forming an insulating film of an inorganic material on one side plane of the capillary substrate, and forming a film-like resistor on the insulating film at a location corresponding to each of the capillary channels by photolithography and etching. Then, after providing a bonding plate for external wiring connection and a surface protection film made of an inorganic material to each of the resistors, the capillary substrate is cut and separated at the center adjacent to the capillary flow path, and a plurality of flow rate sensors are connected. It is characterized by the production of

Hereinafter, a procedure for manufacturing a flow rate sensor using the method of the present invention will be explained.

First, as shown in FIG.
Close the plate-shaped lid 2, also made of silicon crystal
Prepare.

Each of the plate-like base material 1 and the plate-like lid body 2 uses a wafer obtained by slicing a silicon ingot. Using a silicon wafer with a thickness of 400μ deep, 800μ wide, and 1100μ pitch grooves a... is used as the plate-like lid body 2. A 450μ thick silicon wafer is cut into a circle slightly narrower than the length of the grooves a... Although a silicon wafer of 300 mL is used, these dimensions can be changed in various ways.

Next, as shown in FIG.
The plate-like base material 1 and the lid 2 are bonded together with the grooves a closed by the capillary substrate 3, which is provided with a large number of capillary channels A in parallel.

When joining the lid 2 to the plate-like base material 1, as shown in FIG.
Gold films b and b are formed in advance on the bonding surfaces of by vacuum evaporation method, sputtering method, etc., and both 1 and 2 are overlapped at a predetermined position and kept under high temperature and high vacuum, and Apply pressure from above and below,
The base material 1 and the lid body 2 are bonded to each other by diffusion via the gold film b.

According to such diffusion bonding, the bonding surface is alloyed, so high mechanical strength can be expected, and no gas leakage is observed, so it has been adopted as a method to obtain excellent bonding. .

Next, as shown in FIG.
It may be on the bottom side. ), silicon dioxide by oxidation method or sputtering method, plasma
An insulating film c of an inorganic material such as silicon tetranitride is formed by a CVD (abbreviation for chemical vapor deposition) method.

Prior to the formation of the insulating film c, as shown in FIG.

In other words, a silicon wafer formed by slicing a silicon ingot has a
A process-affected layer reaching a depth of 30 to 60 μm has been formed, and the sliced surface is rough, so even if an insulating film c is formed on the surface, there is a risk that this will peel off, and the process By applying mechanical polishing treatment such as wrapping and polishing to the altered layer 2', or chemical polishing treatment using a chemical solution such as an alkali, the insulating film c
At this time, in order to reduce the heat capacity or to make the sensor sensitivity and characteristics good and uniform, the thickness of the capillary substrate 3 after polishing is adjusted. The back side of the base material 1 is also polished in order to make the thickness of the base material 1 a predetermined size.

Next, taking the auxiliary heating type as an example, as shown in FIG. A resistor 4 consisting of two heat-sensitive resistors 4b spaced apart from each other in the capillary flow direction before and after the heating resistor 4a is formed by photolithography and etching, respectively.

Specifically, using both ends of the groove a visible on both sides of the lid body 2 as a guide for positioning, for example, a nickel-chromium film for a heating resistor is placed at a predetermined position corresponding to the capillary flow path A, and a heat-sensitive resistor is For example, a nickel film is sequentially formed into a predetermined size by sputtering or the like (the order does not matter), and a photoresist is applied onto the film.

Then, a mask having a resistor pattern of a predetermined shape is applied to the photoresist, and exposure and development are performed to form an etching pattern on the photoresist.

Then, the resistor film is etched using an ion beam milling device or the like to form a resistor pattern of a predetermined shape. The photoresist is then removed by ion beam etching or a solvent to form heating and heat-sensitive resistors 4a, 4b, 4b in a predetermined pattern.

An example of the pattern of the heating and heat-sensitive resistors 4a, 4b is shown in FIG. Note that d in the figure is a film resistor portion, and e and e are bonding pads.

Next, as shown in FIG. 1G, in order to protect the heating and heat-sensitive resistors 4a, 4b, 4b from the influence of moisture in the outside air and the atmosphere, the film resistor portions excluding the bonding pads e... d...
A protective film f of an inorganic material such as silicon dioxide by a sputtering method or silicon tetranitride by a plasma CVD method is formed on the surface of the substrate.

Next, as shown in FIG. 5H, bonding plates 5 for connecting external wiring are provided in a connected state to the bonding pads e by, for example, the photolithography and etching described above. Gold is the most desirable material for the bonding plate 5 from the viewpoints of ease of bonding and chemical stability, but the material can be changed in various ways.

Next, as shown in FIG. 2, the capillary substrate 3 is cut along the vicinity of the cut-off part of the lid 2 (x ₁ in the figure), and the capillary channels A formed in parallel are further cut. Capillary substrate 3 at the center adjacent to...
(x ₂ in the figure), and in the capillary channels A and A on both sides, cut the circular arc portions A ₁ and A ₁ at points corresponding to the adjacent centers of the channels A (x ₃ in the figure). The capillary substrate 3 is cut out to form a capillary substrate 7 having a rectangular cross section.
By doing so, a plurality of auxiliary heating type flow rate sensors S can be manufactured from one capillary substrate 3. (See Figure 3.) In order to consolidate the external wiring connections of the bonding plates 5 into two locations and to further reduce the width of the flow rate sensor S, the bonding plates 5, 5 for heating resistors are connected to heat-sensitive resistors. 4b, 4b
I placed it so that it overlaps the top of the
After forming the protective film f, the bonding plate 5...
However, the heating resistor bonding plates 5, 5 are replaced with the heat sensitive resistors 4b,
If a configuration is adopted that does not overlap the bonding plates 4b, the protective film f may be formed after providing the bonding plates 5.

FIG. 5 shows a modification of the flow rate sensor S according to the present invention. Specifically, the resistor 4 is composed of resistors 4c and 4d that have a heating function and also have a heat-sensing function. Also in this configuration, the procedure for providing the protective film f and the bonding plate 5 is not limited.

Now, the electric circuit for the auxiliary heating type flow rate sensor S is as shown in FIG. 4, that is, it is configured so that almost no current flows through the heat-sensitive resistors 4b, 4b, and current flows through the heating resistor 4a. When the gas to be measured flows through the first capillary flow path A, the gas is heated by the heating resistor 4a, and the heat is transmitted to the downstream heat-sensitive resistor 4b. A difference occurs in the temperature resistance values of the resistors 4b, 4b, and both the heat-sensitive resistors 4b, 4
The balance of the bridge circuit with respect to b is disrupted, and a voltage corresponding to the mass flow rate of the gas to be measured is output to the terminals 6, 6.

The electric circuit for the self-heating type flow rate sensor S is as shown in FIG. When gas to be measured flows through the resistor 4c on the upstream side to the resistor 4d on the downstream side, heat moves from the resistor 4c on the upstream side to the resistor 4d on the downstream side, and as in the case of the auxiliary heating type, a voltage corresponding to the mass flow rate of the gas to be measured is applied to the terminal 6. , 6 is output,
In either type, the mass flow rate of the gas to be measured can be measured based on the output voltage, or the mass flow rate can be controlled based on the measurement results.

FIG. 6 shows a modification of the capillary substrate 3. This is a plate-shaped substrate 1 made of silicon crystal in which slit grooves a passing through the thickness are formed parallel to each other.
and two lids 2, 2, also made of silicon crystal, which close the grooves a of the base material 1 from above and below.

Note that it is possible to manufacture a single flow rate sensor S by partially changing the manufacturing procedure described above.

That is, as shown in FIG. 7, a capillary base material 7 made of silicon crystal having a rectangular cross section and having a capillary channel A formed therein is prepared by an appropriate means, and this capillary base material 7 is
By going through the same process as above, a single flow rate sensor S can be produced, and the plurality of sensors S thus produced have the same characteristics.

As explained above, according to the flow rate sensor of the first invention, since the resistor is provided on one side of the capillary base material having a rectangular cross section, the resistor can be easily automated by photolithography and etching. Accordingly, it is possible to form a wafer, thereby improving productivity.

Furthermore, since photolithography and etching are employed, it is possible to form a resistor with extremely good reproducibility of the resistance value, and since no organic material is used at all, the characteristics are uniform and there is no change over time. There is no.

Furthermore, it is conceivable to provide the resistor on one side of a capillary base material made of metal, for example, but since metal has a high coefficient of thermal expansion, the heat generated by the resistor may bend the capillary flow path. In this respect, by making the capillary base material made of silicon crystal, silicon has a coefficient of thermal expansion that is approximately 1/6 of that of metals such as iron, so there is a risk of measurement errors occurring due to bending. can be made extremely small and excellent measurement results can be obtained.

According to the method for manufacturing a flow rate sensor according to the second invention, a plurality of flow rate sensors having the above-mentioned excellent functions can be obtained at once. This became possible for the first time by forming a resistor on one side of the capillary substrate by photolithography and etching, which made it possible to mass-produce flow sensors, and eventually We have achieved a significant cost reduction for flow rate sensors.

[Brief explanation of drawings]

The drawings relate to a flow rate sensor and its manufacturing method according to the present invention, in which Figures 1 to 1 are explanatory diagrams showing the manufacturing procedure of the flow rate sensor, Figure 2 is an overall plan view before separating the flow rate sensor, and Figure 3 is an illustration of the flow rate sensor before it is separated. An enlarged sectional view of the resistor part, FIG. 4 is an explanatory diagram showing the flow rate sensor together with an electric circuit, FIG. 5 is an explanatory diagram of a modified example of the flow sensor, and FIG. 6 is a partially broken diagram showing a modified example of the capillary substrate. Exploded perspective view, No. 7
The figure is a partial perspective view of the capillary substrate. DESCRIPTION OF SYMBOLS 1... Plate-shaped base material, 2... Plate-shaped lid, 3... Capillary substrate, 4... Resistor, 5... Bonding plate, 7... Capillary base material, a... Groove, A... Capillary Channel, c...insulating film, f...protective film.

Claims (1)

[Claims] 1. Imparting thermal energy to the gas to be measured using the gas flowing in the capillary flow path as a heat transport medium, and reducing the electrical resistance value due to the temperature difference accompanying heat transfer by the gas to be measured. A flow sensor is provided with a resistor that outputs a voltage corresponding to the mass flow rate of the gas to be measured based on a difference on the outer wall of the capillary flow path, and the capillary flow path is formed by a silicon crystal capillary tube having a rectangular cross section. An insulating film made of an inorganic material is provided on one side of the base material, a film-like resistor is formed on the insulating film by photolithography and etching, and a surface protection film of an inorganic material is applied to the resistor. A flow rate sensor characterized by being provided with a membrane and a bonding plate for external wiring connection. 2. The resistor is composed of two heating resistors spaced apart in the direction of the capillary flow path, and the temperature difference between the two heating resistors caused by the imparting of thermal energy to the gas to be measured by the upper heating resistor is 2. The flow rate sensor according to claim 1, which outputs a voltage according to the mass flow rate of the gas to be measured based on a difference in the electrical resistance values of the heating resistors. 3. The resistor consists of one heating resistor and two heat-sensitive resistors spaced apart in the capillary flow direction before and after the heating resistor, and The mass of the gas to be measured is determined by the difference in electrical resistance between the two heat-sensitive resistors due to the difference in temperature caused by the provision of thermal energy and the provision of thermal energy to the heating element on the lower side of the gas to be measured after heating. The flow rate sensor according to claim 1, which outputs a voltage according to the flow rate. 4 The gas to be measured flowing in the capillary channel is used as a heat transfer medium to impart thermal energy to the gas to be measured, and the difference in electrical resistance value caused by the temperature difference accompanying heat transfer by the gas to be measured is used to generate the measured gas. A method for manufacturing a flow rate sensor in which a resistor that outputs a voltage corresponding to a mass flow rate of gas is provided on the outer wall of the capillary flow path, the method comprising a plate-like substrate in which a plurality of grooves of approximately the same size are formed parallel to each other. A capillary substrate made of silicon crystal having a large number of capillary channels in parallel is produced by diffusion bonding a material and a plate-like lid that closes the groove of the base material, and an inorganic At the same time as forming an insulating film of a substance, a film-like resistor is formed on the insulating film at a location corresponding to each of the capillary channels by photolithography and etching, and then a resistor in the form of a film is formed on each of the resistors. After providing a bonding plate for connecting external wiring and a surface protection film made of an inorganic material, the capillary substrate is cut and separated at the center adjacent to the capillary flow path to produce a plurality of flow rate sensors. How to manufacture a flow sensor. 5. The method of manufacturing a flow rate sensor according to claim 4, characterized in that, prior to forming the insulating film, the insulating film forming surface of the capillary flow path is polished.