JPH10221143A - Micro heater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a micro heater having high measurement accuracy, by restraining heat from scattering via an insulating film without lowering strength of a part where a heater wire is formed. SOLUTION: An insulating film 12 is provided at an upper face of a rectangular silicon substrate 10, on which a conductive film of a predetermined pattern is formed to constitute a heater wire 14. A basic structure of the micro heater is thus formed. Recessed parts 16a, 16b are formed at a predetermined position of the upper face of the insulating film 12 of the basic structure. Since the insulating film becomes thin at an area where the recessed parts are formed, the heat is hard to scatter and a current sent to the heater wire contributes to the generation of heat at the heater wire. The heat does not leak to the periphery through the insulating film. Accordingly, highly accurate measurements are enabled. Moreover, since the insulating film is present although it is thin, a peripheral part of the insulating film is totally connected to an inner peripheral face of an opening 10a, thereby restricting a decrease of strength in spite of the reduced thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a micro-heater which is used for detecting a temperature change of a detecting section as a change of an electric signal and measuring a physical quantity such as a flow rate, a flow velocity, a humidity, etc. of a gas or liquid. is there.

[0002]

2. Description of the Related Art FIG. 1 shows an example of a conventional micro heater. As shown in FIG. 1, an insulating film 2 is bonded and integrated on the upper surface of a substrate 1 having a flat rectangular shape. The portion of the insulating film 2 facing the opening 1a at the center of the substrate 1 serves as a detection unit. That is, the heater wire 3 is formed by forming a polycrystalline silicon film having a predetermined pattern on the surface of the insulating film 2.
The heater wire 3 serves as a detection unit.

In this micro heater, when the heater wire 3 is energized, the heater wire 3 generates heat. On the other hand, if a fluid flows around the sensor, the heat generated in the heater wire 3 is taken away, and the resistance value of the heater wire 3 changes. Since the temperature coefficient of the resistance of the heater wire 3 is known, the change in the temperature can be obtained from the change in the resistance value, and the flow velocity or the like is obtained from the change in the temperature (the amount of heat taken away).

A portion of the insulating film 2 facing the opening 1a of the substrate 1 has a flat surface as shown in FIG. 1A and a heater wire 3 as shown in FIG. There is one in which a through hole 2a is formed in an unformed region.

[0005]

However, the above-mentioned conventional micro heater has the following problems. That is, in the structure shown in FIG. 2A, even if the heater wire 3 generates heat when energized, the heat spreads along the insulating film 2 and proceeds even if there is no fluid flow around. May be robbed. Then, high-precision measurement cannot be performed.

On the other hand, in the structure shown in FIG.
Although there is no problem of heat diffusion, there is a problem that the portion of the insulating film 2 on which the heater wire 3 is formed is connected to the surroundings only at two opposing sides, is easily bent, and has a low strength.

In any type, the surface of the insulating film 2 on which the heater wire 3 is formed is a flat surface, and a polycrystalline silicon thin film is formed on the flat surface by patterning. Part protrudes from the surface of the insulating film, and a step is generated. Then, if dust is contained in the fluid to be measured, the dust adheres to the step portion, which causes a decrease in sensitivity.

SUMMARY OF THE INVENTION The present invention has been made in view of the above background, and has as its object to solve the above-described problems and to reduce the strength of a portion where a heater wire is formed without interposing an insulating film. And to provide a micro heater with high measurement accuracy. Another object of the present invention is to provide a micro-heater in which foreign matter such as dust does not adhere around the heater wire and high-precision measurement sensitivity does not deteriorate over a long period of time.

[0009]

In order to achieve the above object, the present invention provides a micro heater comprising an insulating film provided on a substrate and a heater wire provided on the insulating film. The film thickness at a predetermined position in the heater line non-formed area is configured to be thin.

In the embodiment, a structure for reducing the film thickness is realized by removing a predetermined region on at least one of the front surface and the back surface of the insulating film to form a concave portion. In general, since the protective film is formed on the surface of the insulating film, even if the insulating film is partially omitted, the protective film exists on the surface, and when a through hole is not formed as a whole,
This is included in the concept of reducing the thickness of the present invention. In other words, when there is no protective film, a part of the insulating film is removed so as to penetrate vertically, or even if there is a protective film, a part of the protective film is also removed and opened so as to penetrate vertically. In the case where it is present (as shown in FIG. 1B), it is not included.

With this configuration, heat diffusion is less likely to occur in a part of the insulating film where the thickness is reduced, and the thermal insulation is improved. Therefore, when the heater wire is energized to generate heat,
The diffusion of the heat and the escape of the heat are suppressed as much as possible, and the loss of the heat of the heater wire is based on the state of the fluid present in the surroundings, so that highly accurate measurement can be performed.

Further, even if the film thickness is partially reduced, it does not penetrate up and down and the entire periphery is connected to the substrate.
Since a large stress is not applied to a part of the insulating film, no crack or breakage occurs.

Further, the insulating film may be formed by forming a film using a single material, or may be formed by laminating a plurality of materials. If the thermal conductivity of the plurality of materials is different and the thermal conductivity of the plurality of materials is different, at least a predetermined position of the thin film having a high thermal conductivity is removed, so that the portion having the small thickness is formed. May be formed (claim 2). Here, in the embodiment, a nitride film and an oxide film are used as materials having different thermal conductivity, and the nitride film has higher thermal conductivity. Therefore, by removing the nitride film, thermal diffusion can be effectively suppressed even with the same film thickness.

On the premise of each of the above constitutions, a predetermined portion on the back side of the insulating film is removed to form a thin portion, and the front side of the insulating film is flat. (Claim 3). When the surface is flat, there is no step around the heater wire, and even if there is foreign matter such as dust in the fluid to be measured, such foreign matter will not be caught and accumulated around the heater wire. Therefore, the initial state can be maintained for a long time, and the high sensitivity state realized by the first and second aspects can be maintained without lowering the sensitivity.

[0015]

FIG. 2 shows a first embodiment of a micro-heater according to the present invention. As shown in the figure, the basic configuration is the same as the conventional one, and an insulating film (dielectric film) 12 is provided on the upper surface of a rectangular silicon substrate 10.
The silicon substrate 10 has a substantially rectangular shape in plan view, and the center is an opening 10a penetrating vertically. As shown in FIG. 1B, the insulating film 12 has a three-layer structure in which an oxide film 12a, a nitride film 12b, and an oxide film 12c are stacked in this order.

Then, a conductor film having a predetermined pattern is formed on the upper surface of the insulating film 12 (oxide film 12c). This conductor film is formed by patterning, for example, polycrystalline silicon into an appropriately bent linear shape, thereby forming the heater wire 14. Both ends of the heater wire 14 are connected to terminal portions 14a,
14a, the heater wire 14 is heated by energizing between the terminal portions 14a. Then, the flow rate of the fluid flowing on the upper surface side of the insulating film 12 (the side on which the heater wire 14 is formed) is detected. In this example,
As shown in FIG. 1B, an oxide film 15a is also formed on the lower surface of the silicon substrate 10, and a nitride film 1 is formed on the surface thereof.
5b is formed to enhance the insulating property and the long-term storage property. Since each of the above-described configurations is basically the same as the conventional configuration,
Detailed description is omitted.

Here, in the present invention, the concave portions 16a and 16b are formed at predetermined positions on the upper surface of the insulating film 12, and the thickness is partially reduced. That is, the opening 10 of the silicon substrate 10
In the portion of the insulating film 12 opposing a (inside the region indicated by the dashed line in the figure), it is formed in the region where the heater wire 14 is not formed. More specifically, when the fluid flows in the direction indicated by the arrow in the figure, the recess 16
a, and a concave portion 16b is provided on the upstream side.

The recesses 16a and 16b are formed by removing a predetermined region of the uppermost oxide film 12c constituting the insulating film 12. Thus, the intermediate nitride film 12b is exposed on the bottom surfaces of the concave portions 16a and 16b. In the present example, since the material constituting each layer is different, it can be easily performed by selective etching, and the depth of the concave portions 16a and 16b can be controlled with high accuracy. Moreover, since the etching is performed from one side, the number of processing steps can be reduced.

In this embodiment, the protective film 18 is formed so as to cover the surfaces of the heater wire 14 and the insulating film 12. The protective film 18 can be formed, for example, by forming an oxide film, but the material to be formed is not limited to this. The thickness of each film is, for example, the thickness of the insulating film 12 is about 1 μm, the thickness of the heater wire 14 is about 0.8 μm, and the thickness of the protection film 18 is 0.2 μm.
Degree.

With such a configuration, the concave portions 16a,
In the region where 16b is provided, the thickness of the insulating film 12 is small, so that heat diffusion is difficult. As a result, both terminal portions 14a,
The current passed between 14a directly contributes to the heat generation of the heater wire 14, does not escape to the surroundings via the insulating film 12, and enables highly accurate measurement.

Further, since the insulating film 12 having a small thickness exists, the insulating film 12 on which the heater wires 14 are formed is formed.
Are connected to the inner peripheral surface of the opening 10a, and even if the insulating film 12 is to be bent by applying pressure, the entire periphery of the inner peripheral surface of the opening 10a is Since the stress is evenly applied, cracks and other damages do not occur in the insulating film 12. Also, when comparing the oxide film and the nitride film, the nitride film has higher strength. Therefore, even if the thickness is reduced, a decrease in strength can be suppressed.

Here, the manufacturing process will be briefly described.
As shown in FIG. 3A, an oxide film 12a and an oxide film 12a are formed on the entire upper surface of the flat silicon substrate 10 by chemical vapor deposition.
A nitride film 12b and an oxide film 12c are sequentially laminated, and a polycrystalline silicon thin film 14 'is formed at a predetermined position on the upper surface of the oxide film 12c. Similarly, the oxide film 1 is also formed around the lower surface of the silicon substrate 10 (the frame portion to be finally left).
5a and a nitride film 15b are formed.

Next, the heater wire 14 and the terminal portion 14a (not shown) are formed by etching the polycrystalline silicon thin film 14 'to form a predetermined pattern.
Thereafter, a protective film 18 is formed by covering the entire upper surface with an oxide film by a chemical vapor deposition method. Further, a portion of the protective film 18 facing the terminal portion 14a is removed by etching to expose the terminal portion 14a, and then a metal is deposited on the exposed portion by vapor deposition, sputtering, or the like. As a result, an intermediate product as shown in FIG. And
The steps up to this point are the same as the conventional one.

After that, the silicon substrate 10 is
Deep etching using OH or the like is performed. Then, the upper surface of the silicon substrate 10 is covered with the protective film 18 and the periphery of the lower surface is also covered with the oxide film 15a and the nitride film 15b. The opening 10a is removed. Thereafter, a predetermined position is covered with a patterned mask and selectively etched to expose the exposed oxide film 14.
Is removed. As a result, as shown in FIG. 2B, the recesses 16a. 16b is formed.

It is not necessary to provide the recesses on both the upstream side and the downstream side of the heater wire 14 as shown in the figure, but only on the upstream side recess 16a or only on the downstream side recess 16b. May be. Further, as shown in FIG. 4, the heater wire 1 on the opposite side to the installation position of the terminal portion 14a is provided.
4, a recess 16c is also formed in the unformed region on the tip side, and two recesses 16a and 16b provided on the upstream side and the downstream side shown in FIG.
May be connected to form a generally U-shaped concave portion as a whole.

Further, the surface on which the concave portion 16 is formed is located above the insulating film 12 in the above-described example. However, the present invention is not limited to this. As shown in FIG. That is, the oxide films 12a and 12c may be selectively etched and removed. Alternatively, only the lower surface side may be removed.

Further, as shown in FIG. 6A, a plurality of small concave portions 16d may be provided in an unformed area around the heater wire 14. In this configuration, since there is a region R between the adjacent concave portions 16d where there is no concave portion and the film thickness is not reduced, the strength of the insulating film 12 can be maintained in the region R. Therefore, the recess 16d can be removed up to the nitride film 12b as shown in FIG. With such a configuration, since a nitride film having a high thermal conductivity is eliminated, thermal diffusion can be further suppressed, and thermal insulation properties can be improved.
Of course, as in each of the above embodiments, at least one of the upper and lower oxide films may be removed.

Further, in the example of FIG. 6, the recesses 16d are formed on all four sides around the heater wire 14. However, the type in which such a small recess 16d is formed, as shown in FIG. The heater wire 14 may be formed on three sides, as shown in FIG. 2, on the upstream side and the downstream side, or may be formed on one of the upstream side and the downstream side. The position is arbitrary. In addition, even when the recesses 16d are formed on the upstream side or the downstream side, the number and intervals of the recesses 16d are not limited to those shown in FIG.

As described above, the formation position and the like of the concave portion can be variously changed. In any case, the larger the region, area and depth of the concave portion can suppress the heat diffusion, and It is better that the relative formation position with respect to the heater wire 14 is closer to the heater wire 14 even if the size and shape of the heater wire 14 are the same.

FIG. 7 shows a second embodiment of the present invention. In the present embodiment, a concave portion is formed at a predetermined position of the above-mentioned insulating film 12, the thickness is reduced, and a main portion for improving thermal insulation is used in common.
The step on the four side surface is eliminated.

More specifically, the specific structure will be described while following the manufacturing process. After manufacturing the insulating film 12 having a three-layer structure, before forming the polycrystalline silicon film, the uppermost oxide film 12c is etched. To form a recess in advance in the formation region of the polycrystalline silicon thin film (heater wire, terminal portion)
A polycrystalline silicon thin film is deposited in the recess. As a result, as shown in FIG.
The surface of 2c is a flat surface. So after that,
Even if the protective film 18 is formed on the upper surface, the surface is still flat. Members corresponding to those in FIGS. 2 and 3 are denoted by the same reference numerals, and detailed description thereof will be omitted.

Then, similarly to FIG. 3B, the lower surface of the silicon substrate 10 is removed by etching to form an opening 10a.
oxide film 12a and nitride film 1 exposed through
By etching a predetermined position of 2b, the concave portion 16 is formed.
To form With such a configuration, there is no step between the heater wire 14 and the periphery thereof, dust or the like flowing with the fluid does not adhere, and the sensitivity does not decrease for a long time.

Although the nitride film 12b is removed by etching in the illustrated example, the oxide film 12c and the protective film 18 exist above the region where the concave portion 16 is formed.
Can maintain strength. Further, as a formation pattern of the concave portion 16, various modes can be adopted as in the above-described embodiments.

FIG. 8 shows a modification of the type in which the surface is flattened similarly to FIG. In this example, a polyimide resin is used for the protective film 20. That is, FIG.
As in (A), an oxide film 12 a is formed on a silicon substrate 10.
The heater wire 14 is formed by laminating a nitride film 12b and an oxide film 12c in this order, and patterning and providing a polycrystalline silicon thin film thereon. And usually,
When an oxide film is deposited thereon again, a polyimide resin 20 'is formed as shown in FIG. In the case of polyimide resin, by applying an appropriate thickness,
The step based on the thickness of the heater wire 14 is absorbed and its surface is made smoother, so that all surface positions are higher than the heater wire 14.

Next, after the polyimide resin 20 'is cured, the surface is ashed and flattened. At this time, a very thin polyimide resin is left on the upper surface of the heat wire 14 as a protective film. Thereafter, etching is appropriately performed from the bottom side of the silicon substrate 10 to form an opening 10a and a recess 16 as shown in FIG. By forming the protective film 20 with the polyimide resin in this manner,
Flattening can be easily performed, and it can be formed with high accuracy.

In the illustrated example, the concave portion 1 formed on the lower surface is shown.
6 denotes an oxide film 12a, a nitride film 12b and an oxide film 12b.
Since all of c is formed by etching to remove a predetermined region, the thermal insulating property is further improved. Of course, instead of removing all three layers like this,
Only two or one layer may be removed.

[0037]

As described above, in the micro heater according to the present invention, since the thickness of a part of the insulating film on which no heater wire is formed is reduced, the strength of the portion where the heater wire is formed is not reduced, and Thermal diffusion via the insulating film can be suppressed. As a result, a micro heater with high measurement accuracy can be configured.

Further, in the case of the structure as described in claim 3, there is no step around the heater wire, and even if foreign matter such as dust flows, it does not adhere to the periphery of the heater wire. The state of precision measurement sensitivity does not deteriorate over a long period of time.

[Brief description of the drawings]

FIG. 1 is a diagram showing a conventional example.

FIG. 2 is a diagram showing a first embodiment of a micro heater according to the present invention.

FIG. 3 is a diagram showing an example of the manufacturing process.

FIG. 4 is a diagram showing a modification.

FIG. 5 is a diagram showing still another modified example.

FIG. 6 is a diagram showing still another modified example.

FIG. 7 is a view showing a second embodiment of the micro heater according to the present invention.

FIG. 8 is a diagram showing a modified example thereof.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 Silicon substrate 12 Insulating film 14 Heater wire 16, 16a, 16b, 16c, 16d Concave part (portion where film thickness is reduced)

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masakazu Shiiki Omron Co., Ltd. (10) Hanazono Todocho, Ukyo-ku, Kyoto-shi (72) Inventor Kenichi Nakamura 1-5-20 Kaigan, Minato-ku, Tokyo Tokyo Gas (72) Inventor Tokudai Neda 1-5-20 Kaigan, Minato-ku, Tokyo Tokyo Gas Co., Ltd.

Claims (3)

[Claims] 1. A micro-heater comprising an insulating film provided on a substrate and a heater wire provided on the insulating film, wherein a film thickness at a predetermined position in a region where no heater wire is formed on the insulating film is reduced. Micro heater. 2. The insulating film is formed by laminating thin films of different types having different thermal conductivities, and forming the thin portion by removing at least a predetermined position of the thin film having a high thermal conductivity. The micro heater according to claim 1, wherein 3. The method according to claim 1, wherein a predetermined portion on the back side of the insulating film is removed to form a thin portion, and the front side of the insulating film is flat. The micro heater according to claim 1.