JP2023041549A - MEMS foreign matter detection element - Google Patents

Abstract

To provide a technology which is applicable to microscopic measurement devices such as MEMS flowrate measurement devices, and with which it is possible to detect a foreign matter included in fluid and thereby eliminate effects of the foreign matter in measurement, making higher accuracy measurement possible.SOLUTION: The present invention comprises: electrode parts (1a, 1b) for detection that include two comb-shaped electrode patterns (3, 4); electrode parts (11a, 11b) for reference that include two comb-shaped electrode patterns (3, 4); and a detection circuit (25) constructed by connecting the two electrode parts (1a, 1b) for detection and the two electrode parts (11a, 11b) for reference. The respective teeth (3a, 4a) in the two comb-shaped electrode patterns (3, 4) are arranged so as to be aligned in parallel to each other at a prescribed interval, and a dielectric layer (9) is interposed between the respective teeth (3a, 4a) in the two comb-shaped electrode patterns (3, 4) of the electrode parts (11a, 11b) for reference.SELECTED DRAWING: Figure 10

Description

The present invention relates to a MEMS foreign matter detection element manufactured in a semiconductor manufacturing process and capable of detecting foreign matter.

2. Description of the Related Art Conventionally, there has been known a flow rate measuring device that calculates the flow velocity or flow rate of a fluid. As such a flow rate measuring device, for example, a thermal type flow rate measuring device has been proposed, which is provided with a heater and a temperature sensor, and the temperature sensor detects the temperature distribution that changes with the flow of the fluid, thereby calculating the velocity or flow rate of the fluid. (See Patent Document 1, for example).

In the thermal flow rate measuring device described above, foreign matter such as dust adheres to the surface of the temperature sensor over time, affecting the temperature distribution detected by the temperature sensor, resulting in changes in flow rate measurement characteristics. There was a case. As a result, the accuracy of the flow rate measuring device may be degraded, and the usage environment of the flow rate measuring device itself may be limited to the measurement of clean gas. In addition, in the case where the heater and temperature sensor are provided on a membrane (thin film), the adhesion of foreign matter to the membrane changes the thermal conductivity and heat capacity of the membrane. becomes. For this reason, the flow rate measuring device is required to have resistance to foreign matter, or to have a function of detecting failure due to foreign matter.

The foreign matter detection element for detecting the presence of foreign matter is, for example, a sensor device having a capacitance-type detection electrode section and a processing circuit connected to the detection electrode section. The electrode fingers have a comb-like branching portion in which the electrode fingers face each other substantially in parallel at a predetermined interval to form a capacitance. A structure having one branched portion and a second branched portion having a second electrode width wider than the first electrode width is known. (For example, see Patent Document 1.)

The technology described in Patent Document 1 is applied, for example, to a developer container of a copier, etc., and is applicable regardless of the shape of the container, and is said to improve the powder amount measurement accuracy and noise resistance. have an effect. However, this technology particularly relates to a device for detecting the amount of powder filled in a developer container, such as the amount of developer contained in the developer container, etc., and detects foreign matter contained in fluid such as gas. It was difficult to detect.

Further, in the particulate matter detection device, the detection electrode is shaped like a comb tooth, and the comb rib portion of the comb tooth-shaped electrode is covered with a dielectric, thereby connecting one end of the comb tooth portion. A technique is known in which the distance between (comb rib portion) and the comb tooth portion facing it is made uniform to improve the measurement accuracy of the device. (See, for example, Patent Document 2.) However, the technology described in Patent Document 2 is mainly aimed at detecting particulate matter in the exhaust gas of automobiles, and requires a large-sized device such as a MEMS (Micro Electro Mechanical Systems) flow. It was difficult to apply to small devices such as sensors.

JP 2017-129470 A JP 2013-50577 A Japanese Patent No. 5542006

INDUSTRIAL APPLICABILITY The present invention has been made in view of the above problems, and can be applied to a micro-measurement device such as a MEMS flow rate measuring device. The purpose is to provide a technology that eliminates the

The present invention for solving the above problems is a MEMS foreign matter detection element for detecting foreign matter contained in fluid,
a silicon substrate;
a first insulating film formed on the silicon substrate;
a detection electrode section formed on the first insulating film and including a combination of two comb-shaped electrode patterns;
a reference electrode portion formed on the first insulating film and including a combination of two comb-shaped electrode patterns;
the two detection electrode portions, a first detection electrode portion and a second detection electrode portion, and the two reference electrode portions, a first reference electrode portion and a second reference electrode portion; a detection circuit constructed by connecting with a wiring pattern formed on the first insulating film;
with
The detection circuit is
an input terminal and a GND are connected by a first line in which the first detection electrode section and the first reference electrode section are connected in series from the input terminal side;
The input terminal and the GND are connected in parallel with the first line by a second line in which the second reference electrode section and the second detection electrode section are connected in series from the input terminal side. connected to
a first output end between the first detection electrode portion and the first reference electrode portion on the first line;
A circuit having a second output end between the second detection electrode portion and the second reference electrode portion on the second line,
In the combination of the two comb-teeth-shaped electrode patterns, the teeth of the two comb-teeth-shaped electrode patterns are arranged alternately in parallel at a predetermined interval,
The reference electrode section has a foreign matter suppression structure in which foreign matter is less likely to adhere between the teeth of the two comb-shaped electrode patterns, compared to the detection electrode section. , are MEMS foreign matter detection elements.

According to this, the foreign matter can be detected by the detection electrode portion which is formed in the semiconductor manufacturing process (MEMS manufacturing process) and which has a micro-sized comb-like electrode pattern. Then, it becomes possible to perform highly sensitive detection even for a particularly minute foreign matter contained in the normal atmosphere or the like. The fluid here includes fluids existing in nature such as air and water, as well as gases and liquids in which the concentration of specific components is intentionally increased.

Further, by detecting a phase difference or a voltage difference between the first output end and the second output end of the detection circuit, a change in capacitance at the first and second detection electrode portions is detected. Therefore, it is possible to detect adhesion of foreign matter more easily or accurately.

In addition, in the present invention, the reference electrode section has a foreign matter suppression structure in which foreign matter is less likely to adhere between the teeth of the two comb-shaped electrode patterns compared to the detection electrode section. By using the capacitance of the reference electrode portion having the foreign matter suppression structure as a reference, it is possible to accurately measure the change in capacitance caused by the two detection electrode portions. As a result, foreign matter can be detected more accurately.

Further, in the present invention, the foreign matter suppression structure may be a structure in which a dielectric layer is interposed between each tooth of the two comb-shaped electrode patterns of the reference electrode section.

According to this, it is possible to more reliably prevent foreign matter from adhering between the teeth of the two comb-shaped electrode patterns of the reference electrode section. Then, by using the capacitance of the reference electrode portion provided with the dielectric layer between the teeth of the two comb-shaped electrode patterns as a reference, foreign matter can be detected with higher accuracy. Become.

Further, in the present invention, the foreign substance suppressing structure is such that each tooth of the two comb-shaped electrode patterns of the reference electrode section is covered with the dielectric layer, and the dielectric layer has surface irregularities. may be 0.1 μm or less.

Here, in the case where the dielectric layer is interposed between the teeth of the two comb-shaped electrode patterns in the reference electrode section, for example, each of the two comb-shaped electrode patterns of the reference electrode section When the teeth of the dielectric layer are covered with the dielectric layer, the surface of the dielectric layer may have unevenness corresponding to the teeth of the comb-shaped electrode pattern. In such a case, foreign matter is likely to adhere to the irregularities, and there is a possibility that the electrostatic capacitance of the reference electrode portion may change due to the foreign matter.

In contrast, in the present invention, each tooth of the two comb-shaped electrode patterns of the reference electrode portion is covered with a dielectric layer, and the surface unevenness of the dielectric layer is set to 0.1 μm or less. As a result, it is possible to further suppress the adhesion of foreign matter to the dielectric layer, and it is possible to more reliably suppress the change in the capacitance due to the reference electrode portion.

Further, in the present invention, the two comb-shaped electrode patterns of the detection electrode unit are arranged so that the direction in which each tooth extends is perpendicular to the flow direction of the fluid,
In the foreign matter suppression structure, the directions in which the teeth of the two comb-shaped electrode patterns of the reference electrode section extend are the same as the directions of the teeth of the two comb-shaped electrode patterns of the detection electrode section. The structure may be arranged perpendicular to the extending direction.

According to this, it is possible to arrange so that the direction in which each tooth in the two comb-shaped electrode patterns of the reference electrode section extends is parallel to the flow direction of the fluid. This also more reliably prevents foreign matter from adhering between the teeth of the two comb-shaped electrode patterns of the reference electrode portion. As a result, by using the capacitance of the reference electrode portion, in which the dielectric layer is provided between the teeth of the two comb-shaped electrode patterns, as a reference, foreign matter can be detected with higher accuracy. becomes.

In the present invention, the number of teeth in the two comb-shaped electrode patterns of the reference electrode section is smaller than the number of teeth in the two comb-shaped electrode patterns of the detection electrode section. may be

Here, for example, a dielectric layer may be interposed between each tooth of the two comb-shaped electrode patterns of the reference electrode section, or a dielectric layer may be interposed between each tooth of the two comb-shaped electrode patterns of the reference electrode section. is covered with a dielectric layer, the electrostatic capacitance between the two comb-shaped electrode patterns of the reference electrode section increases.

On the other hand, if the capacitance of the two comb-shaped electrode patterns of the reference electrode section is approximately the same as the capacitance of the two comb-shaped electrode patterns of the detection electrode section, the initial It is possible to reduce the offset voltage detected by the detection circuit in this state, and to improve the detectability when a foreign object adheres. In contrast, in the present invention, the number of teeth in the two comb-shaped electrode patterns of the reference electrode section is made smaller than the number of teeth in the two comb-shaped electrode patterns of the detection electrode section. As a result, even when a dielectric layer is interposed between the teeth of the two comb-shaped electrode patterns of the reference electrode section, the two comb-shaped electrode patterns of the reference electrode section can be statically controlled. The capacitance can be set to a value approximately equal to the capacitance of the two comb-shaped electrode patterns of the detection electrode portion. As a result, it is possible to reduce the offset voltage detected by the detection circuit in the initial state, and to improve the detectability when a foreign object adheres.

Further, in the present invention, the interval between the teeth of the two comb-shaped electrode patterns of the reference electrode section is wider than the interval of the teeth of the two comb-shaped electrode patterns of the detection electrode section. may be As a result, even when a dielectric layer is interposed between each tooth of the two comb-shaped electrode patterns of the reference electrode section, the two comb-shaped electrode patterns of the reference electrode section can be set to a value approximately equal to the capacitance of the two comb-shaped electrode patterns of the detection electrode portion. As a result, it is possible to reduce the offset voltage detected by the detection circuit in the initial state, and to improve the detectability when a foreign object adheres.

Further, in the present invention, the two detection electrode portions and the two reference electrode portions are arranged in two rows and two rows on the first insulating film so as to be positioned diagonally to each other. It may be assumed that According to this, it is possible to shorten the length of the MEMS foreign matter detection element that intersects the flow of the fluid. In the case of arranging so as to be parallel to the flow direction of the reference electrode portion, it is possible to more reliably prevent foreign matter from adhering between the teeth of the two comb-shaped electrode patterns of the reference electrode portion. As a result, foreign matter can be detected more accurately.

Further, in the present invention, the two detection electrode portions and the two reference electrode portions may be arranged in a line on the first insulating film.

According to this, the shape of the MEMS foreign object detection element can be made into an elongated shape, and it is possible to facilitate incorporation into the flow path of the fluid.

Further, in the present invention, a first tooth root portion to which each tooth of the two comb tooth-shaped electrode patterns of the detection electrode portion is connected;
A second root portion to which the teeth of the two comb-shaped electrode patterns of the reference electrode portion are connected may be formed in common. According to this, it is possible to reduce the size of the MEMS foreign object detection element.

Further, in the present invention, a plurality of terminal portions for connecting the input terminal, the GND, the first output terminal and the second output terminal to the outside are further provided,
At least one of the plurality of terminal portions is arranged at an end portion in the extending direction of each tooth of the two comb-shaped electrode patterns of the detection electrode portion in the MEMS foreign matter detection element. good too.

According to this, by arranging the terminal portion at the end portion in the direction in which each tooth of the two comb tooth-shaped electrode patterns of the detection electrode portion extends in the MEMS foreign matter detection element, the terminal portion can be electrically connected to the terminal portion. Even when the wires are connected, it is possible to prevent disturbance of the flow of fluid in the vicinity of the teeth of the comb teeth, and it is possible to detect foreign substances with higher sensitivity.

Further, in the present invention, in the detection circuit,
By inputting a pulse-like voltage to the input terminal and detecting a potential difference between the first output terminal and the second output terminal, the two comb-shaped electrode patterns of the detection electrode section are detected. It is also possible to detect the capacitance between or the change in the capacitance. According to this, by detecting a dynamic signal, it is possible to detect the adhesion of foreign matter between the teeth of the two comb-shaped electrode patterns of the detection electrode unit, thereby further reducing the influence of noise. It is possible to perform detection that is difficult to receive.

In addition, in the present invention, it is possible to use the means for solving the above-described problems in combination as much as possible.

INDUSTRIAL APPLICABILITY According to the present invention, it can be applied to a micro-measurement device such as a MEMS flow measurement device, and by detecting foreign matter contained in a fluid, it is possible to eliminate the influence of the foreign matter on the measurement and perform more accurate measurement. becomes possible.

FIG. 2 is a diagram for explaining the basic principle of the foreign matter detection element according to Example 1 of the present invention; It is a figure which shows the basic structure of the foreign material detection element in Example 1 of this invention. 4 is a graph showing an example of changes in capacitance between two electrodes having a comb tooth structure in Example 1 of the present invention before and after a dust test. 1A and 1B are a cross-sectional view of a foreign object detection element and an enlarged cross-sectional view of teeth of an electrode in Example 1 of the present invention; It is a figure which shows the example of the usage state of the foreign material detection element in Example 1 of this invention. FIG. 4A is a first diagram showing a manufacturing process of the foreign matter detection element in Example 1 of the present invention; FIG. 2B is a second view showing the manufacturing process of the foreign object detection element in Example 1 of the present invention; FIG. 4 is a schematic diagram of a reference electrode in Example 2 of the present invention; FIG. 5 is a cross-sectional view of a reference electrode in Example 2 of the present invention; FIG. 10 is a diagram showing a bridge circuit using a foreign object detection element and a reference electrode in Example 2 of the present invention; 10 is a graph showing the result of confirming the foreign matter detection operation in the bridge circuit 25 in Example 2 of the present invention. FIG. 10 is a diagram showing a first arrangement mode of a foreign object detection element and a reference electrode in Example 2 of the present invention; FIG. 10 is a diagram showing a second arrangement mode of the foreign object detection element and the reference electrode in Example 2 of the present invention; FIG. 10 is a diagram showing a third arrangement mode of the foreign object detection element and the reference electrode in Example 2 of the present invention; FIG. 10 is a diagram showing a fourth arrangement mode of the foreign object detection element and the reference electrode in Example 2 of the present invention; FIG. 7 is a cross-sectional view of the foreign matter detection chip 10 in which the foreign matter detection element and the reference electrode are arranged side by side according to the second embodiment of the present invention; FIG. 10 is a first diagram showing a manufacturing process of the foreign matter detection element in Example 2 of the present invention; FIG. 10 is a second diagram showing a manufacturing process of the foreign matter detection element in Example 2 of the present invention; FIG. 10 is a third diagram showing a manufacturing process of the foreign matter detection element in Example 2 of the present invention; FIG. 10 is a first schematic diagram of a foreign object detection chip in Example 3 of the present invention; FIG. 10 is a second schematic diagram of the foreign matter detection chip in Example 3 of the present invention; FIG. 11 is a cross-sectional view of a foreign object detection chip in which a foreign object detection element and a flow rate measuring element are arranged side by side in Example 3 of the present invention; FIG. 11 is a first diagram showing a manufacturing process of the foreign matter detection element in Example 3 of the present invention; FIG. 10 is a second diagram showing the manufacturing process of the foreign matter detection element in Example 3 of the present invention; FIG. 10 is a third diagram showing the manufacturing process of the foreign matter detection element in Example 3 of the present invention;

<Application example>
Hereinafter, application examples of the present invention will be described with reference to the drawings.

As shown in FIG. 1, the foreign matter detection element according to this application example has a configuration in which when a foreign matter P is contained in fluid flowing around two electrodes 201 and 202 having different electric potentials, the foreign matter is detected between the electrodes 201 and 202. It is an element that utilizes the fact that the electrostatic capacitance generated by the electrodes 201 and 202 changes due to adhesion and deposition, and detects the presence of foreign matter by detecting the degree of change in the electrostatic capacitance.

A MEMS foreign matter detection element 1 (hereinafter also simply referred to as a foreign matter detection element) is manufactured by forming electrodes 3 and 4 on a silicon substrate 2 by a semiconductor manufacturing process (MEMS process), as shown in FIG. It is The electrodes 3 and 4 have a comb-teeth structure, and the teeth 3a and 4a of the comb-teeth structure of the electrodes 3 and 4 are arranged so as to be alternately arranged parallel to each other. When foreign matter is contained in the fluid flowing in the direction perpendicular to the direction in which the comb teeth extend (in the direction in which the comb teeth are arranged), and the foreign matter detection element 1 is exposed to this fluid, the electrodes 3 and 4 Foreign matter adheres and accumulates on the stepped portions of the teeth 3a and 4a. Foreign matter detection element 1 measures the change in capacitance between electrodes 3 and 4 .

In this application example, the surfaces of the teeth 3a, 4a are covered with a protective film 6 made of a non-conductive material, as shown in FIG. This can prevent electrical leakage between the teeth 3a and 4a (between the electrostatic electrodes) when the foreign matter contains a conductor. In this case, by using a silicon-based dielectric film such as SiO ₂ or SiN film as the protective film 6, it becomes easier to form a thin film in a semiconductor process.

In this application example, a base film 5 made of an insulating layer is formed between the teeth 3a, 4a and the substrate 2, and the width of the base film 5 is narrower than the width of the teeth 3a, 4a. It's becoming As a result, foreign matter can be easily caught and adhered to the recessed portion of the eaves, and the foreign matter detection sensitivity can be improved. As a result, the distance between the substrate 2 and the teeth 3a, 4a of the electrodes 3, 4 can be increased to reduce the effect of parasitic capacitance. In this application example, the height of the base film 5 is more preferably 0.1 μm to 5 μm. Further, the inter-tooth distance is more preferably 0.2 to 20 μm. .

FIG. 5 is a diagram showing an example of a usage state of the foreign object detection element 1. FIG. In this case, by forming a chip capacitor or the like on the printed circuit board 30, it is possible to easily form a foreign matter detection circuit. At this time, as shown in FIG. 5, the wires 7a and 7b connecting the electrode terminals 7 of the foreign object detection element 1 and the printed circuit board 30 are arranged perpendicular to the direction of movement of the fluid so as not to hinder the flow of the fluid. They are arranged so as to extend in the same direction from the electrode terminal 7 provided at the end of the direction.

In this application example, since the foreign matter detection element 1 is manufactured by the semiconductor manufacturing process, it is easy to reduce variations in manufacturing (dimensions) of the foreign matter detection element 1 . That is, since it is a processing technology for forming fine electronic circuits, it is possible to suppress dimensional variations to micron order or less, and to improve processing accuracy. Further, according to the foreign matter detection element 1 of this embodiment, fine particles and the like in the natural atmosphere can be detected with high sensitivity, and the size of the device can be greatly reduced. Furthermore, the manufacturing process can be automated, and the cost can be reduced.

As shown in FIG. 8, the measurement accuracy can be improved by using a reference electrode 11 having a structure in which the surface of an element having the same structure as that of the foreign matter detection element 1 is covered with a dielectric film 9. is. The reference electrode 11 is formed by covering the foreign matter detecting element 1 with a dielectric film 9, thereby making it difficult for foreign matter to adhere between the teeth 3a and 4a of the electrodes 3 and 4 of the reference electrode 11. FIG. That is, by comparing the change in the capacitance of the foreign object detection element 1 with the change in the capacitance of the reference electrode 11 to which foreign objects are less likely to adhere, it is possible to more accurately detect the adhesion of foreign objects.

As shown in FIG. 9A, in the reference electrode 11, the surface of the dielectric film 9 has steps 9a at portions corresponding to the electrodes 3 and 4 of the foreign matter detecting element 1 and the teeth 3a and 3b of the comb structure. However, since the space between the electrode teeth 3a and 4a is covered with the dielectric film 9, the change in capacitance due to foreign matter is greatly reduced. Further, as shown in FIG. 9B, after forming the dielectric film 9, the surface of the dielectric film 9 is planarized by CMP (Chemical Mechanical Polishing) or the like. Furthermore, it is possible to make it difficult for foreign matter to adhere, and to further reduce the change in the capacitance of the reference electrode 11 .

<Example 1>
In the following, foreign matter detection elements according to embodiments of the present invention will be described in more detail with reference to the drawings.

〔Basic principle〕
The basic principle of the foreign matter detection element according to this embodiment will be described with reference to FIG. 1(a) and 1(b) show cross-sectional views when electrodes 201 and 202 having a potential difference are arranged on a substrate 200. FIG. It is assumed that the electrodes 201 and 202 have a rod-like structure extending in the direction perpendicular to the plane of FIG. In this case, as shown in FIG. 1A, an electric field is generated between two electrodes 201 and 202 having different potentials, and the two electrodes generate capacitance.

As shown in FIG. 1(b), if foreign matter P is contained in the fluid such as air flowing around the electrodes 201 and 202, the foreign matter easily adheres to the stepped portions of the electrodes 201 and 202. FIG. As foreign matter adheres and accumulates between the electrodes 201 and 202, the capacitance generated at the electrodes 201 and 202 changes. By detecting the degree of this change, it is possible to detect the presence of a foreign object.

FIG. 2 shows the basic structure of the foreign matter detection element 1 in this embodiment. FIG. 2(a) shows the state before adhesion of foreign matter, and FIG. 2(b) shows the state after adhesion of foreign matter. In FIGS. 2(a) and 2(b), the upper figure is a perspective view of the entire device, and the lower figure is a sectional view seen from the direction of the white arrow. The foreign matter detection element 1 is manufactured by forming electrodes 3 and 4 on a silicon substrate 2 (hereinafter simply referred to as substrate 2) by a semiconductor manufacturing process (described later). The electrodes 3 and 4 have a comb-teeth structure, and the teeth 3a and 4a of the comb-teeth structure in the electrodes 3 and 4 are alternately arranged parallel to each other in the direction of arrangement, as shown in FIG. 2(a). are arranged side by side. Here, the distance between the teeth 3a and 4a (hereinafter also referred to as the inter-tooth distance) corresponds to the "predetermined distance" in this embodiment.

For example, if foreign matter is contained in fluid flowing in a direction perpendicular to the direction in which the comb teeth extend (the direction in which the comb teeth are arranged), and the foreign matter detection element 1 is exposed to this fluid, the electrodes 3 , 4, foreign matter adheres and accumulates on the stepped portions of the teeth 3a, 4a. Due to the presence of this foreign matter, the capacitance generated by the electrodes 3 and 4 changes. By measuring this change, it is possible to detect the presence or amount of foreign matter. In this embodiment, the electrodes 3 and 4 correspond to the detection electrode section.

FIG. 3 shows an example of changes in capacitance between two electrodes having a comb structure before and after the dust test. In the example shown in the figure, it was confirmed that the capacitance increased by 20% or more before and after the dust test.

The comb tooth structure of the electrodes 3 and 4 may have a thickness of 0.1 to 10 μm, a width of 0.1 to 10 μm, and an inter-tooth distance of 0.1 to 100 μm. Also, the tooth length may be 10 μm to 1 mm. Each may have 5 to 500 teeth. For example, if the thickness is 2 μm, the width is 2 μm, the distance between the teeth is 2 μm, the length of the opposing teeth is 400 μm, and the number of teeth is 50, a capacitance of 1 pF can be obtained in an area of 400 μm × 400 μm. can. In this case, it is possible to realize a very small element size of, for example, 500 μm×600 μm×400 μm (thickness).

It should be noted that the detection sensitivity and size of the foreign object detection element 1 of this embodiment vary depending on the inter-tooth distance. The inter-tooth distance is more preferably 0.2 to 20 μm. If the inter-tooth distance is reduced, the electrostatic capacity is increased, so that the capacitance change increases when a foreign object adheres, and the detection sensitivity is improved. Also, the electrodes themselves can be miniaturized. However, if the inter-tooth distance is too small, it will not be possible to trap large foreign objects. In addition, it is more likely to be affected by variations in processing dimensions. For these reasons, the inter-electrode distance of 0.2 μm or more is desirable. Contaminants smaller than 0.2 μm are considered to have little effect on the device. On the other hand, if the tooth-to-tooth distance is large, foreign matter of a larger size can be detected. In a case where a relatively large amount of foreign matter is contained, it can be said that a large inter-tooth distance is advantageous when the allowance for foreign matter is large. However, the electrodes themselves become large. From these, the inter-tooth distance of 20 μm or less is desirable. If the tooth-to-tooth distance is greater than 20 μm, the size of the device may increase if it is manufactured by a semiconductor process, and a sufficient change in capacitance may not be obtained when foreign matter adheres.

[Details of the cross-sectional view of the foreign object detection element]
FIG. 4 shows an example of a cross-sectional view of the foreign object detection element 1 and an enlarged cross-sectional view of the teeth 3a and 4a of the electrodes 3 and 4 in particular. The surfaces of the teeth 3a, 4a may be covered with a protective film 6 made of a non-conductive material, as shown in FIG. According to this, it is possible to prevent electrical leakage between the teeth 3a and 4a (between the electrostatic electrodes) when the foreign matter contains a conductor, and the protection of the circuit can be enhanced. In this case, by using a silicon-based dielectric film such as SiO ₂ or SiN film as the protective film 6, it becomes easier to form a thin film in a semiconductor process. This protective film 6 corresponds to the second insulating film in this embodiment.

In the cross section of the teeth 3a, 4a of the electrodes 3, 4, a base film 5 made of an insulating layer is formed between the teeth 3a, 4a and the substrate 2, and the width of the base film 5 is the width of the tooth 3a. , 4a. By doing so, it is possible to make it easier for foreign matter to be caught and attached to the portion recessed by the eaves, and it is possible to improve the detection sensitivity of foreign matter.

In this case, a parasitic capacitance occurs between the teeth 3a and 4a of the electrodes 3 and 4 via the silicon substrate. It is a factor that lowers the sensitivity. On the other hand, by forming the base film 5 between the electrode teeth 3a, 4a and the substrate 2, the distance between the substrate 2 and the teeth 3a, 4a of the electrodes 3, 4 is increased, and the effect of the parasitic capacitance is reduced. can be reduced.

Moreover, the detection sensitivity and productivity change depending on the height of the base film 5 that is the lower layer of the eaves structure. The height of the base film 5 is more preferably 0.1 μm to 5 μm. The low height of the base film 5 facilitates the manufacturing process. Time for film formation and etching is shortened. In addition, it is easy to control the amount of undercut (the distance in which etching progresses in the lateral direction) when fabricating the eaves structure in the semiconductor manufacturing process. On the other hand, if the height of the base film 5 is low, the parasitic capacitance of the substrate 2 becomes large, resulting in low electrical sensitivity. Moreover, since the total height of the base film 5 and the teeth 3a and 4a is low, the ability to trap foreign matter is deteriorated. For these reasons, the height of the base film 5 is preferably 0.1 μm or more.

On the other hand, if the height of the base film 5 is high, it is advantageous in terms of sensitivity. Since the step is increased, it becomes easier to catch foreign matter. Moreover, the parasitic capacitance of the substrate 2 can be reduced, and electrical sensitivity can be easily obtained. On the other hand, if the base film 5 is thick, film formation and etching for a long time are required in the manufacturing process, and it becomes difficult to secure the shape stability of the eaves structure. From these, a height of 5 μm or less is desirable.

FIG. 5 is a diagram showing an example of a usage state of the foreign object detection element 1. FIG. FIG. 5(a) is a top view of the foreign matter detection element 1 in use. FIG. 5B is a perspective view of the foreign matter detection element 1 mounted on the printed circuit board 30 in use. The foreign object detection element 1 is an element having a pair of comb-like electrodes 3 and 4 . In this case, it is possible to form a detection circuit by forming a chip capacitor or the like on the printed circuit board 30 . At this time, as shown in FIG. 5B, the wires 7a and 7b connecting the electrode terminals 7 of the foreign object detection element 1 and the printed circuit board 30 are arranged in the direction in which the fluid advances so as not to hinder the flow of the fluid. It is arranged so as to extend in the same direction from the electrode terminal 7 provided at the end in the vertical direction.

[Manufacturing Process of Foreign Matter Detection Element]
6 and 7, the manufacturing process of the foreign matter detection element 1 by the semiconductor manufacturing process will be described below.

(1) Process 1
As shown in FIG. 6A, a dielectric film (SiO ₂ ) 15 to be a base film 5 is formed with a thickness of 1 μm on a single crystal silicon substrate 12 to be a substrate 2 . Similarly, a dielectric film (SiO ₂ ) 15 is formed as an insulating layer on the bottom surface of the single crystal silicon substrate 12 . This dielectric film corresponds to the first insulating film in the present invention. Further, step 1 corresponds to the first insulating film forming step in this embodiment.

(2) Process 2
As shown in FIG. 6B, the electrodes 3 and 4 and the conductive film 13 that will become the electrode terminals 7 are formed. For example, a polycrystalline silicon (Poly-Si) film is formed with a thickness of 2 μm. This step corresponds to the conductive film forming step in this embodiment. After the film is formed, impurities are appropriately introduced to reduce the resistance value. After film formation, a pattern of electrodes 3 and 4 (teeth 3a and 4a) is formed by a patterning process (photolithography using a photomask, etching). In this case, for example, as described above, the tooth width is 2 μm and the inter-tooth distance is 2 μm. Each tooth may be 400 μm long. This step corresponds to the electrode forming step in this embodiment. Incidentally, the conductive film 13 may be formed of single crystal silicon or amorphous silicon in addition to polycrystalline silicon.

(3) Process 3
As shown in FIG. 7A, the dielectric film 15 around the electrodes 3 and 4 and the electrode terminals 7 is removed in a patterning process. At that time, when the dielectric film 15 of SiO ₂ is isotropically etched while masking the portions of the conductive film 13 of Poly-Si which will become the electrodes 3 and 4, an eaves structure as shown in FIG. 7A is formed. can do. For example, by isotropically etching the dielectric film 15 with a thickness of 1 μm, an undercut of 1 μm on one side can be generated in the base film 5 . Process 3 corresponds to the first etching process in this embodiment.

(4) Step 4
As shown in FIG. 7(b), a SiN film 16 having a thickness of 0.1 μm is formed over the entire surface to serve as the protective film 6 for the electrodes 3 and 4. Then, as shown in FIG. Similarly, a SiN film 16 is formed as a protective film 6 on the bottom surface of the single crystal silicon substrate 12 as well. At that time, by using the LPCVD method for film formation, the eaves structure can be coated satisfactorily. After that, the SiN film 16 around the electrodes 3 and 4 and the surface of the electrode terminal 7 and the SiN film 16 of the electrode terminal 7 are removed. Process 4 corresponds to the second insulating film forming process in this embodiment.

(5) Step 5
As shown in FIG. 7(c), an Au/Ti film 18 to be a metal film 8 is formed on the surface of the electrode terminal 7 with a thickness of 0.5 μm/0.1 μm and patterned.

Here, in the conventional technology described above, there was an example of using comb-teeth electrodes, but when capacitor electrodes are formed from comb-teeth electrodes, variations in capacitance tend to become a problem. This is because the distance between the electrodes and the thickness of the finished electrodes vary in the electrode manufacturing process. In particular, when attempting to miniaturize the sensor, the influence of dimensional variations tends to increase, which hinders miniaturization.

In order to solve such a problem, according to the present invention, since the foreign matter detection element 1 is manufactured by a semiconductor manufacturing process (semiconductor process), manufacturing (dimension) variations can be easily reduced. That is, since it is a processing technology for forming fine electronic circuits, it is possible to suppress dimensional variations to micron order or less, and to improve processing accuracy.

Further, in the prior art described above, the thickness of the comb teeth is 5 to 30 μm, the width is 30 to 400 μm, and the distance between the teeth is 30 to 400 μm. According to the foreign matter detection element 1 of the embodiment, fine particles in the natural atmosphere, which are not the exhaust gas of automobiles, etc., can be detected with high sensitivity, and the size of the apparatus can be greatly reduced. Furthermore, the manufacturing process can be automated, and the cost can be reduced.

<Example 2>
Next, Example 2 of the present invention will be described. In the second embodiment, in addition to the foreign matter detecting element 1 described in the first embodiment, a reference electrode is provided in order to facilitate detection of changes in capacitance between the electrodes 3 and 4 of the foreign matter detecting element 1. An example to add will be described.

The reference electrode 11 in this embodiment functions as a fixed capacitor formed with a structure to which foreign matter is less likely to adhere. FIG. 8 shows a schematic diagram of the reference electrode 11 in this embodiment. As shown in FIG. 8, the reference electrode 11 has a structure in which the surface of an element having a structure equivalent to that of the foreign matter detection element 1 is covered with a dielectric film 9 . By covering the foreign matter detecting element 1 with the dielectric film 9, the dielectric layer intervenes between the teeth 3a and 4a of the electrodes 3 and 4 in the reference electrode 11, making it difficult for foreign matter to adhere and preventing foreign matter from adhering. It is possible to make it difficult for the change in capacitance to occur. In this embodiment, each of the electrodes 3 and 4 corresponds to a reference electrode section.

FIG. 9 shows a cross-sectional view of the reference electrode 11 viewed in the direction of the white arrow in FIG. FIG. 9A shows an example in which a dielectric film 9 is simply formed on the surface of the foreign matter detection element 1. FIG. In this case, steps 9a are formed on the surface of the dielectric film 9 at portions corresponding to the electrodes 3 and 4 of the foreign matter detecting element 1 and the teeth 3a and 3b of the comb-tooth structure. Therefore, there is a possibility that foreign matter may adhere and accumulate on this step 9a. can be reduced and the capacitance detected at the reference electrode 11 can be used as a reference value for capacitance change.

FIG. 9B shows an example in which planarization is performed by CMP (Chemical Mechanical Polishing) or the like after forming the dielectric film 9 . By planarizing the dielectric film 9 in this way, it is possible to make it difficult for foreign matter to adhere to the surface of the dielectric film 9, and to further reduce the change in the capacitance of the reference electrode 11. is.

Advantages of using the reference electrode 11 are as follows: (1) By comparing the output from the foreign object detection element 1 and the output from the reference electrode 11, changes in capacitance in the foreign object detection element 1 are detected. It is easy to cancel variations in capacity. (2) It becomes possible to combine with various detection circuits, and it is easy to obtain sensitivity. etc. can be mentioned.

In the case of forming a capacitor with the comb-shaped electrodes 3 and 4, variations in capacitance tend to become a problem. This is because in the manufacturing process of the electrodes 3 and 4, the finished dimensions such as the inter-tooth distance and the thickness vary. In particular, when attempting to miniaturize the sensor, the influence of dimensional variations tends to increase, which hinders miniaturization.

In this embodiment, as the reference electrode 11, an element having the same structure as the foreign matter detection element 1 and the dielectric film 9 is formed thereon is used, so that manufacturing variations can be reduced. Furthermore, when they are manufactured on the same chip, manufacturing variations can be greatly reduced. This is because the major causes of manufacturing variations in the semiconductor manufacturing process are variations in film thickness and variations in patterning (exposure, etching), and these variations are small within the same chip. Moreover, the reference electrode 11 can be made smaller than when an external chip capacitor is used as the reference electrode, and the overall configuration can be made smaller. Also, it is possible to reduce the cost of parts.

An LC oscillation circuit, for example, can be given as an example of a detection circuit for detecting changes in capacitance. When it is connected in series with an external L (coil) and an AC signal is applied, it oscillates at the resonance frequency. When a foreign object adheres and the value of the capacitance C changes, the resonance frequency changes. By detecting the difference between the resonance frequency of the LC oscillation circuit by the reference electrode 11 and the frequency of the LC oscillation circuit by the foreign matter detection element 1, adhesion of foreign matter can be detected.

FIG. 10 shows a bridge circuit 25 using the foreign object detection element 1 and the reference electrode 11. As shown in FIG. In the example shown in FIG. 10, two foreign object detection elements 1 and two reference electrodes 11 constitute a bridge circuit 25, and supply an input signal to detect a change in capacitance. For example, a pulse voltage is input between INPUT and GND in the bridge circuit 25 . When a foreign object adheres, the electrostatic capacitances of C1 and C3 formed by the foreign object detection element 1 are increased, resulting in a difference in output power between OUT1 and OUT2. By detecting the phase difference or voltage difference between the outputs of OUT1 and OUT2, it is possible to detect a change in capacitance, that is, adhesion of foreign matter. The bridge circuit 25 shown in FIG. 10 is an example, and INPUT and GND may be reversed in FIG.

<Features of the bridge circuit>
By configuring the bridge circuit 25 using the foreign object detection element 1 and the reference electrode 11 as described above, the detection sensitivity is greatly improved. On the other hand, the point that four elements were required was a demerit. In contrast, in this embodiment, the two foreign matter detection elements 1 and the reference electrode 11 can be formed on one chip in the semiconductor manufacturing process, so the number of manufacturing steps does not change even if the number of elements increases. The area per element can be reduced, and the entire bridge circuit 25 can be miniaturized. Manufacturing variations of the four elements can be reduced. It is possible to achieve both improvement in measurement accuracy and improvement in production efficiency.

FIG. 11 shows the result of confirming the foreign matter detection operation in the bridge circuit 25 by circuit simulation. A bridge circuit is composed of C1, C2, C3, and C4. In the initial state (no foreign matter adhered), all were set to 1.0 pF. It is assumed that C1 and C3 are 1.05 pF in a state where foreign matter is attached. A voltage pulse wave was applied to the bridge circuit 25 in this state, and the outputs of OUT1 and OUT2 were confirmed. FIG. 11(a) shows changes in OUT1, OUT2, and OUT1-OUT2 when a pulse is input. FIG. 11(b) is an enlarged view of OUT1-OUT2. It can be seen that the difference between OUT1 and OUT2 is generated due to the change in capacitance between C1 and C3, and the presence of a foreign object can be detected.

<Arrangement Mode 1 of Foreign Matter Detection Element and Reference Electrode>
FIG. 12 shows an example in which a foreign object detection chip 10 has four electrodes, two foreign object detection elements 1a and 1b and two reference electrodes 11a and 11b. The reference electrodes 11a and 11b are covered with a dielectric film whose surface is indicated by a thick rectangle. In the example of FIG. 12, one pole of the foreign object detection element (tooth root portion to which each tooth is connected) and one pole of the reference electrode (tooth root portion to which each tooth is connected) are shared. As a result, the size of the foreign matter detection chip 10 can be reduced. In this case, the foreign matter detection chip 10 corresponds to a composite foreign matter detection element including the functions of the foreign matter detection elements 1a and 1b.

<Arrangement Mode 2 of Foreign Matter Detection Element and Reference Electrode>
FIG. 13 shows arrangement mode 2 of the foreign object detection element and the reference electrode. As shown in FIG. 13, the reference electrodes 11a and 11b are made smaller than the foreign matter detection elements 1a and 1b by, for example, reducing the number of teeth. Here, the dielectric film covering the reference electrodes 11a and 11b relatively increases the capacitance of the reference electrodes 11a and 11b. Therefore, the reference electrodes 11a and 11b can be configured to have a smaller capacitance than the foreign matter detection elements 1a and 1b.

As an example of a configuration for relatively reducing the capacitance of the reference electrodes 11a and 11b, (1) reducing the number of teeth of the reference electrodes 11a and 11b or shortening the length thereof can be considered. In this case, since the areas of the reference electrodes 11a and 11b can be reduced, the overall size of the foreign matter detection chip 10 can be reduced. In addition, (2) increasing the distance between the comb teeth of the reference electrodes 11a and 11b is conceivable. In this case, since the distance between the teeth is large, even if a foreign object adheres between the electrodes, it is difficult for the capacitance to change. Therefore, the stability of capacitance, which is required for the reference electrode, is enhanced.

When configuring a bridge circuit including the reference electrodes 11a and 11b and arranging them on one chip, the size of one of the foreign matter detection elements 1a and 1b is about 400 μm×400 μm, and the size of one of the reference electrodes 11a and 11b is about 400 μm×400 μm. is about 200 μm×400 μm, and the chip size can be about 1000 μm×700 μm×400 μm, enabling miniaturization.

<Arrangement Mode 3 of Foreign Matter Detection Element and Reference Electrode>
FIG. 14 shows arrangement mode 3 of the foreign object detection element and the reference electrode. As shown in FIG. 14, in this embodiment, the reference electrodes 11a and 11b are rotated 90 degrees with respect to the foreign matter detection elements 1a and 1b. As a result, when the direction of the teeth of the comb tooth structure of the foreign matter detection elements 1a and 1b is perpendicular to the direction of fluid flow, the direction of the teeth of the reference electrodes 11a and 11b can be parallel to the direction of fluid flow. . As a result, it is possible to further reduce the possibility of foreign matter adhering to the reference electrodes 11a and 11b.

<Arrangement Mode 4 of Foreign Matter Detection Element and Reference Electrode>
FIG. 15 shows arrangement mode 4 of the foreign object detection element and the reference electrode. As shown in FIG. 15, in this embodiment, foreign matter detection elements 1a and 1b and reference electrodes 11a and 11b are arranged in a line. FIG. 15(a) shows a mode in which the foreign matter detection elements 1a and 1b and the reference electrodes 11a and 11b are arranged in a line parallel to the flow direction of the fluid. FIG. 15(b) shows a mode in which the foreign matter detection elements 1a and 1b and the reference electrodes 11a and 11b are arranged in a line perpendicular to the flow direction of the fluid. According to this arrangement, the foreign matter detection chip 10 can be made into an elongated chip, so that it can be easily incorporated into the flow path. In FIG. 15(b), the electrode terminal 7 is arranged at the end of the foreign object detection chip 10 in the fluid flow direction, but is located downstream of the foreign object detection elements 1a and 1b and the reference electrodes 11a and 11b. It is configured so as not to hinder the detection of foreign matter.

Next, FIG. 16 shows a detailed cross-sectional view of the foreign matter detection chip 10 in which the foreign matter detection element 1 and the reference electrode 11 are arranged side by side. As described above, the teeth of each electrode in the foreign object detection element 1 have a canopy structure and the protective film 6 is formed thereon. Also, in the reference electrode 11 , the teeth of each electrode are covered with a dielectric film 9 .

[Manufacturing Process of Foreign Matter Detection Element]
17 to 19, the manufacturing process of the foreign object detection chip 10, in which the foreign object detection element 1 and the reference electrode 11 are arranged, according to the semiconductor manufacturing process will be described.

(1) Process 1
As shown in FIG. 17, a dielectric film (SiO ₂ ) 15 to be a base film 5 is formed with a thickness of 1 μm on a single crystal silicon substrate 12 to be a substrate 2 . Similarly, a dielectric film (SiO ₂ ) 15 is formed as an insulating layer on the bottom surface of the single crystal silicon substrate 12 .

(2) Process 2
As shown in FIG. 17, a conductive film 13 to be electrodes 3 and 4 is formed. For example, a polycrystalline silicon (Poly-Si) film is formed with a thickness of 2 μm. After the film is formed, impurities are appropriately introduced to reduce the resistance value. After film formation, a pattern of electrodes 3 and 4 (teeth 3a and 4a) is formed in a patterning process (photolithography using a photomask, etching). In this case, for example, as described above, the tooth width is 2 μm and the inter-tooth distance is 2 μm. Each tooth may be 400 μm long.

(3) Process 3
As shown in FIG. 18A, the dielectric film 15 around the electrodes 3 and 4 and the electrode terminals 7 is removed in the patterning process. At that time, when the dielectric film 15 of SiO ₂ is isotropically etched while masking the portions of the conductive film 13 of Poly-Si which will become the electrodes 3 and 4, an eaves structure as shown in FIG. 18(a) is formed. can do. For example, by isotropically etching the dielectric film 15 with a thickness of 1 μm, an undercut of 1 μm on one side can be introduced.

(4) Step 4
As shown in FIG. 18(b), a SiN film 16 having a thickness of 0.1 μm is formed over the entire surface to serve as the protective film 6 for the electrodes 3 and 4. Then, as shown in FIG. Similarly, a SiN film 16 is formed as a protective film 6 on the bottom surface of the single crystal silicon substrate 12 as well. At that time, by using the LPCVD method for film formation, the eaves structure can be coated satisfactorily. After that, the SiN film 16 around the electrodes 3 and 4 and the SiN film 16 of the electrode terminal 7 are removed.

(5) Step 5
As shown in FIG. 19A, a 3 μm-thick SiO ₂ film 19 to be the dielectric film 9 is formed so as to bury the comb-teeth electrode. This step corresponds to the dielectric layer forming step in this embodiment. By applying a CMP (Chemical Mechanical Polishing) method or the like after the film formation, the surface is flattened and becomes a more desirable shape for the reference electrode. This step corresponds to the planarization step in this embodiment.

(6) Step 6
As shown in FIG. 19(b), the portion filled between the teeth 3a and 4a of the electrodes 3 and 4 of the foreign matter detection element 1 and the SiO ₂ film 19 on the upper surface of the electrode terminal 7 are removed by photolithography. The electrode protective film 6 is made of SiN and the filling dielectric film 9 is made of SiO ₂ in order to obtain etching selectivity between the SiN film and the SiO ₂ film in this step. That is, this is for removing only the SiO ₂ film 19 and leaving the SiN film 16 .

(7) Step 7
As shown in FIG. 19(c), an Au/Ti film 18 to be the metal film 8 is formed on the electrode terminal portion with a thickness of 0.5 μm/0.1 μm and patterned.

<Example 3>
Next, Example 3 of the present invention will be described. In Example 3, an example in which the foreign matter detection element 1 described in Example 1 and the flow rate measurement element 21 are mounted together on one chip will be described.

FIG. 20 shows a schematic diagram of the foreign matter detection chip 20 in this embodiment. FIG. 20(a) is a plan view, and FIG. 20(b) is a cross-sectional view taken along the line AA. As shown in FIG. 20A, the foreign matter detection element 1 is arranged on the left side of the foreign matter detection chip 20 in the drawing, and the flow rate measurement element 21 is arranged on the right side thereof.

The flow measuring element 21 includes a microheater (also referred to as a heating section) 22 and two thermopiles (also referred to as a temperature detection section) 23a and 23b provided symmetrically with the microheater 22 interposed therebetween. That is, the microheater 22 and the two thermopiles 23a and 23b are arranged side by side in a predetermined direction. These are formed on an insulating thin film 24 as shown in FIG. A cavity 2a formed by etching or the like is provided in the substrate 2 below the microheater 22 and the thermopiles 23a and 23b.

The microheater 22 is a resistor made of polysilicon, for example. With no fluid flow, the temperature distribution around the microheater 22 is approximately uniform. On the other hand, when the fluid flows, the surrounding air moves, so the temperature on the downstream side of the microheater 22 becomes higher than on the upstream side. The flow rate measuring element 21 utilizes such uneven distribution of heater heat to output a value indicating the flow rate.

なお、Ｔｈはマイクロヒータ２２の温度（サーモパイル２３ａ、２３ｂにおけるマイクロヒータ２２側の端部の温度）、Ｔａはサーモパイル２３ａ、２３ｂにおけるマイクロヒータ２２から遠い側の端部の温度のうち低い方の温度、Ｖｆは流速の平均値、Ａ及びｂは所定の定数である。 The output voltage ΔV of the sensor element is expressed, for example, by the following equation (1).

Here, Th is the temperature of the microheater 22 (the temperature of the ends of the thermopiles 23a and 23b on the side of the microheater 22), and Ta is the temperature of the ends of the thermopiles 23a and 23b farther from the microheater 22, whichever is lower. , Vf is the mean value of the flow velocity, and A and b are predetermined constants.

Here, when the flow rate measuring element 21 and the foreign matter detecting element 1 are arranged on one chip, the following merits can be obtained. (Compared to the case of two chips) (1) The foreign matter detection element 1 itself is also smaller, and the mounting (assembly) area is also smaller than the case of two chips, so that the size can be significantly reduced. (2) As shown in FIG. 20(a), by providing comb-shaped electrodes over the entire width of the thermopiles 23a and 23b, it is possible to detect foreign matter in areas where the degree of influence on the flow rate measuring element 21 is large. (3) Since the foreign object detection element 1 is located in the immediate vicinity of the flow rate measurement element 21, the detection efficiency is good. In the case of two chips, the airflow state may change between the flow rate measurement chip and the foreign matter detection chip, but with one chip, the airflow state does not change between the elements, so the measurement accuracy can be improved. (4) Since the flow rate measuring element 21 and the foreign matter detecting element 1 can be manufactured in the same manufacturing process, the manufacturing cost can be kept lower than when they are manufactured separately. (5) The electrodes 3 and 4 in the foreign object detection element 1 can be made of the same film as the microheater 22 or the thermopiles 23a and 23b. This simplifies the manufacturing process, leading to improved productivity and reduced costs. (6) The foreign object detection element 1 is arranged upstream of the flow rate measurement element 21 . As a result, the sensitivity of foreign matter detection can be relatively increased. However, even when it is arranged downstream, it is significant when it is desired to lower the foreign matter detection sensitivity (to desensitize it). Foreign matter tends to adhere to the flow rate measuring element 21 first, but if the allowable amount of foreign matter is large, it may be arranged downstream.

FIG. 21 shows a schematic diagram of another aspect of the foreign matter detection chip 20 in this embodiment. FIG. 21(a) is a plan view, and FIG. 21(b) is a sectional view taken along the line AA. In this embodiment, as shown in FIG. 21(a), foreign matter detection elements 1a and 1b and reference electrodes 11a and 11b are arranged on the left side of the foreign matter detection chip 20, and a flow rate measuring element is arranged on the right side. 21 are arranged.

Thus, by forming the foreign matter detection elements 1a and 1b, the reference electrodes 11a and 11b, and the flow rate measurement element 21 on one chip by the semiconductor manufacturing process, it is possible to obtain a more remarkable effect of improving measurement accuracy and a cost advantage. It is possible.

Next, FIG. 22 shows a detailed cross-sectional view of the foreign matter detection chip 20 when the foreign matter detection element 1 and the flow rate measurement element 21 are arranged side by side. As described above, the teeth of each electrode in the foreign object detection element 1 have a canopy structure and the protective film 6 is formed thereon. In the flow measuring element 21, an insulating thin film 24 is formed by covering the microheater 22 and the two thermopiles 23a and 23b with a dielectric film.

[Manufacturing Process of Foreign Matter Detection Element]
23 to 25, the manufacturing process of the foreign matter detection chip 20, in which the foreign matter detection element 1 and the flow rate measuring element 21 are arranged, by the semiconductor manufacturing process will be described.

(1) Process 1
As shown in FIG. 23( a ), a dielectric film (SiO ₂ ) 15 to be a base film 5 is formed to a thickness of 1 μm on a single crystal silicon substrate 12 to be a substrate 2 . Similarly, a dielectric film (SiO ₂ ) 15 is formed as an insulating layer on the bottom surface of the single crystal silicon substrate 12 .

(2) Process 2
As shown in FIG. 23B, electrodes 3 and 4, a conductive film 13 to be microheaters 22 and thermopiles 23a and 23b are formed. For example, a polycrystalline silicon (Poly-Si) film is formed with a thickness of 2 μm. After film formation, impurities are appropriately introduced to reduce the resistance value. After film formation, patterns of electrodes 3, 4 (teeth 3a, 4a), microheater 22, and thermopiles 23a, 23b are formed in a patterning process (photolithography using a photomask, etching).

(3) Process 3
As shown in FIG. 24(a), the dielectric film 15 around the electrodes 3 and 4 is removed in the patterning process. At that time, when the dielectric film 15 of SiO ₂ is isotropically etched while masking the portions of the conductive film 13 of Poly-Si which will become the electrodes 3 and 4, an eaves structure as shown in FIG. 24(a) is formed. can do. For example, by isotropically etching the dielectric film 15 with a thickness of 1 μm, an undercut of 1 μm on one side can be introduced.

(4) Step 4
As shown in FIG. 24(b), a SiN film 16 having a thickness of 0.1 μm is formed over the entire surface to serve as a protective film 6 for the electrodes 3 and 4, the microheater 22, and the thermopiles 23a and 23b. At that time, by using the LPCVD method for film formation, the eaves structure can be coated satisfactorily. After that, the SiN film 16 of the SiN film 16 around the electrodes 3 and 4 is removed. At that time, the SiN film 16 is opened in a portion that contacts the Al film of the thermopile. An Al film 26 for thermopile is formed with a thickness of 0.2 μm, and then a pattern is formed. Although not shown, when forming the external terminals from an Al film, the external terminals are formed from the Al film at the same time.

(5) Step 5
As shown in FIG. 24(c), as shown in FIG. 19(a), a SiO ₂ film 19 to be the upper portion of the insulating thin film 24 is deposited to a thickness of 3 μm so as to bury the comb-teeth electrode. do. By applying a CMP (Chemical Mechanical Polishing) method or the like after the film formation, the surface is flattened and becomes a more desirable shape for the reference electrode.

(6) Step 6
As shown in FIG. 25(a), the portion of the SiO ₂ film 19 filled between the teeth 3a, 4a of the electrodes 3, 4 of the foreign matter detecting element 1 is removed by photolithography. The electrode protective film 6 is made of SiN and the filling dielectric film 9 is made of SiO ₂ in order to obtain etching selectivity between the SiN film and the SiO ₂ film in this step. That is, this is for removing only the SiO ₂ film 19 and leaving the SiN film 16 . Also, at this time, the SiO ₂ film 19 to be the upper portion of the insulating thin film 24 is left.

(7) Step 7
As shown in FIG. 25(b), a protective film 27 of SiN film is formed with a thickness of 0.1 μm on the outermost layer of the entire chip. This is to protect the SiO ₂ of the insulating thin film 14 from humidity, since the SiN film is excellent in moisture resistance. to form. At this time, the electrodes 3 and 4 are additionally provided with SiN films.

(8) Step 8
As shown in FIG. 25(c), a cavity 2a is formed by silicon etching. Etching is performed from the front side through etching holes (not shown) formed in the insulating thin film 24 .

(9) Step 9 (not shown)
An Au/Ti film 18 to be the metal film 8 is formed on the electrode terminal with a thickness of 0.5 μm/0.1 μm and patterned.

As described above, the electrodes 3 and 4 of the foreign object detection element 1 are made of the same material as the microheater 22 and the thermopiles 23a and 23b of the flow rate measurement element 21, thereby simplifying the manufacturing process. Materials that can be used at the same time are not necessarily polycrystalline silicon (Poly-Si) films, but metal films and silicon films are compatible with semiconductor processes and are easy to use. As the metal film, it is possible to use Al, Cu, Pt, Au, W, Mo, etc., which are used in the semiconductor manufacturing process.

When a silicon film is used, there is an advantage that the thickness of the electrodes 3 and 4 of the foreign matter detection element 1 can be easily increased. This is because if the electrodes 3 and 4 of the foreign matter detecting element 1 and the microheater 22 of the flow rate measuring element 21 are made of the same silicon film, even if the film thickness is increased, the heater resistance does not decrease so much. When forming the micro-heater 22 with a metal film, it is necessary to form the micro-heater 22 narrow and thin in order to prevent the resistance value from becoming too small. Since a silicon film has a higher resistance than a metal film, the film thickness can be increased. If the electrodes 3 and 4 in the foreign matter detection element 1 can be made thicker, the foreign matter detection sensitivity can be increased. In addition, it is easy to form a SiN film or a SiO ₂ film as a non-conductive film on the surface of the silicon film. Candidates for the material include monocrystalline silicon, polycrystalline silicon, amorphous silicon, and the like, which are used in semiconductor manufacturing processes.

There is an advantage that the thickness of the electrodes 3 and 4 of the foreign object detection element 1 can be easily increased. If the electrodes 3 and 4 of the foreign object detection element 1 and the microheater 22 of the flow rate measuring element 21 are formed from the same thin film layer, the thickness of the electrodes 3 and 4 is preferably 0.1 μm to 5 μm. when the film thickness is thin. Better productivity. Time for film formation and etching is shortened. (If the film thickness is the same for the flow sensor and the heater, the metal film tends to have a smaller film thickness in order to secure the resistance value.) On the other hand, if the film thickness is thin, the electrode The step between the teeth 3a and 4a of 3 and 4 becomes small, and there is a possibility that the sensitivity related to foreign matter detection may be lowered.

For these reasons, the thickness of the electrodes 3 and 4 of the foreign object detection element 1 is desirably 0.1 μm or more. If the thickness is smaller than 0.1 μm, the foreign matter detection sensitivity becomes excessively low. When the film thickness is large, the foreign matter detection sensitivity becomes large. As described above, when the electrodes 3 and 4 of the foreign matter detecting element 1 and the microheater 22 of the flow rate measuring element 21 have the same film thickness, the film thickness can be increased by using a silicon film as the material. becomes possible. On the other hand, in this case, productivity deteriorates. From these, it is desirable that the thickness of the electrodes 3 and 4 of the foreign object detection element 1 is 5 μm or less. If it is larger than 5 μm, it will be difficult to fabricate in the semiconductor manufacturing process.

The purpose of the foreign matter detection element 1 is to detect foreign matter and to discover a failure of the flow rate measuring element 21 . In fact, it can be used not only for failure detection but also for extending the sensor life and increasing accuracy by correcting the measurement result of the flow rate measuring element 21 . The degree of adherence of foreign matter is detected by the foreign matter detection element 1 and fed back to the control circuit of the flow rate measurement element 21 . When a large amount of foreign matter adheres, the applied power is increased in order to raise the heat generation temperature of the microheater 22 of the flow measuring element 21, or the sensitivity (flow rate output) of the thermopiles 23a and 23b of the flow measuring element 21 is amplified. By increasing the rate, deterioration of measurement performance can be suppressed.

In addition, in order to make it possible to compare the constituent elements of the present invention with the configurations of the embodiments, the constituent elements of the present invention are added below with the reference numerals of the drawings.
<Appendix 1>
A MEMS foreign matter detection element (1) for detecting foreign matter contained in a fluid,
a silicon substrate (2);
a first insulating film (5) formed on the silicon substrate (2);
detection electrode portions (1a, 1b) formed on the first insulating film (5) and including a combination of two comb-shaped electrode patterns (3, 4);
Reference electrode portions (11a, 11b) formed on the first insulating film (5) and including a combination of two comb-shaped electrode patterns (3, 4);
The two detection electrode parts (1a, 1b) of the first detection electrode part (1a) and the second detection electrode part (1b), the first reference electrode part (11a) and the second detection electrode part (11a) A detection circuit (25 )and,
with
The detection circuit (25)
The input terminal and GND are connected by a first line in which the first detection electrode section (1a) and the first reference electrode section (11a) are connected in series from the input terminal side,
The input terminal and the GND are connected by a second line in which the second reference electrode section (11b) and the second detection electrode section (1b) are connected in series from the input terminal side. connected in parallel with the first line;
a first output end between the first detection electrode portion and the first reference electrode portion on the first line;
A circuit having a second output end between the second detection electrode portion and the second reference electrode portion on the second line,
In the combination of the two comb-shaped electrode patterns (3, 4), the teeth (3a, 4a) of the two comb-shaped electrode patterns (3, 4) are alternately arranged in parallel at predetermined intervals. arranged side by side,
The reference electrode portions (11a, 11b) are each toothed (3a, 4a) in the two comb-tooth electrode patterns (3, 4) compared to the detection electrode portions (1a, 1b). A MEMS foreign matter detection element, characterized in that it has a foreign matter suppression structure (9) that makes it difficult for foreign matter to adhere therebetween.

1, 1a, 1b: foreign matter detection element 2: silicon substrate 3: electrode 3a: tooth 4: electrode 4a: tooth 5: base film 6: protective film 7: electrode terminal 9: dielectric film 10: foreign matter detection chip 11, 11a , 11b: reference electrode 21: flow rate measuring element 25: bridge circuit

Claims (11)

A MEMS foreign matter detection element for detecting foreign matter contained in a fluid,
a silicon substrate;
a first insulating film formed on the silicon substrate;
a detection electrode section formed on the first insulating film and including a combination of two comb-shaped electrode patterns;
a reference electrode portion formed on the first insulating film and including a combination of two comb-shaped electrode patterns;
the two detection electrode portions, a first detection electrode portion and a second detection electrode portion, and the two reference electrode portions, a first reference electrode portion and a second reference electrode portion; a detection circuit constructed by connecting with a wiring pattern formed on the first insulating film;
with
The detection circuit is
an input terminal and a GND are connected by a first line in which the first detection electrode section and the first reference electrode section are connected in series from the input terminal side;
The input terminal and the GND are connected in parallel with the first line by a second line in which the second reference electrode section and the second detection electrode section are connected in series from the input terminal side. connected to
a first output end between the first detection electrode portion and the first reference electrode portion on the first line;
A circuit having a second output end between the second detection electrode portion and the second reference electrode portion on the second line,
In the combination of the two comb-teeth-shaped electrode patterns, the teeth of the two comb-teeth-shaped electrode patterns are arranged alternately in parallel at a predetermined interval,
The reference electrode section has a foreign matter suppression structure in which foreign matter is less likely to adhere between the teeth of the two comb-shaped electrode patterns, compared to the detection electrode section. , MEMS foreign object detection elements. 2. The MEMS according to claim 1, wherein the foreign matter suppression structure is a structure in which a dielectric layer is interposed between each tooth of the two comb-shaped electrode patterns of the reference electrode section. Foreign object detection element. In the foreign matter suppression structure, each tooth of the two comb-shaped electrode patterns of the reference electrode section is covered with the dielectric layer, and the surface unevenness of the dielectric layer is 0.1 μm or less. 3. The MEMS foreign matter detection element according to claim 2, characterized by: The direction in which each tooth in the two comb tooth-shaped electrode patterns of the detection electrode unit extends is arranged so as to be perpendicular to the flow direction of the fluid,
In the foreign matter suppression structure, the directions in which the teeth of the two comb-shaped electrode patterns of the reference electrode section extend are the same as the directions of the teeth of the two comb-shaped electrode patterns of the detection electrode section. 4. The MEMS foreign matter detection element according to claim 1, wherein the element is arranged perpendicularly to the extending direction. The number of teeth in the two comb-shaped electrode patterns of the reference electrode section is smaller than the number of teeth in the two comb-shaped electrode patterns of the detection electrode section. 5. The MEMS foreign matter detection element according to any one of 1 to 4. The interval between the teeth in the two comb-shaped electrode patterns of the reference electrode unit is wider than the interval between the teeth in the two comb-shaped electrode patterns of the detection electrode unit,
The MEMS foreign object detection element according to any one of claims 1 to 4. The two detection electrode portions and the two reference electrode portions are arranged in two rows and two rows on the first insulating film so as to be positioned diagonally to each other. 7. The MEMS foreign matter detection element according to any one of claims 1 to 6. 7. The method according to any one of claims 1 to 6, wherein the two detection electrode portions and the two reference electrode portions are arranged in a line on the first insulating film. A MEMS foreign object detection element as described. a first tooth root portion to which each tooth of the two comb tooth-shaped electrode patterns of the detection electrode portion is connected;
9. The second tooth root portion to which the teeth of the two comb-shaped electrode patterns of the reference electrode portion are connected is formed in common. 10. The MEMS foreign matter detection element according to the item. further comprising a plurality of terminal portions for connecting the input terminal, the GND, the first output terminal and the second output terminal to the outside,
At least one of the plurality of terminal portions is arranged at an end portion in a direction in which each tooth of the two comb-shaped electrode patterns of the detection electrode portion extends in the MEMS foreign matter detection element. The MEMS foreign matter detection element according to any one of claims 1 to 9, wherein In the detection circuit,
By inputting a pulse-like voltage to the input terminal and detecting a potential difference between the first output terminal and the second output terminal, the two comb-shaped electrode patterns of the detection electrode section are detected. 11. The MEMS foreign matter detection element according to claim 1, wherein the capacitance between or a change in the capacitance is detected.

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