JP2016138797A - Micro-heater and sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a micro-heater and a sensor capable of relaxing a heat expansion generated in an insulating layer that forms a diaphragm structure, suppressing a stress applied to the insulating layer and a heating resistance element, suppressing heat escape from the heating resistance element, and cutting power consumption.SOLUTION: A micro-heater 500 comprising: a semiconductor substrate 100 having a hollow part 130 formed therein so as to penetrate the semiconductor substrate 100 from a surface to a bottom surface; an insulating layer 200 provided on the surface of the semiconductor substrate so as to close a surface side of the hollow part; and a heating resistance element 400 buried in a region, which corresponds to the hollow part, of the insulating layer, is configured such that when the micro-heater is viewed along a penetration direction of the hollow part, a plurality of through-holes 200h each formed from a polygon is formed into a honeycomb state is formed in a region, which does not overlap the heating resistance element, of the corresponding region, a width W1 of each of bridge parts 200b1 to 200b3 sandwiched between the adjacent through-holes is constant and the adjacent bridge parts are not aligned linearly in a region which is equal to or higher than 50% of a sum of lengths of the bridge parts 200b1 to 200b3.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a microheater mounted on a semiconductor substrate having a diaphragm structure and a sensor employing the microheater.

  In recent years, research on fuel cells has been actively conducted as a high-efficiency, clean energy source due to social demands such as environmental protection and nature conservation. Among them, solid polymer fuel cells (PEFCs) and hydrogen internal combustion engines are expected as energy sources for home use and on-vehicle use due to advantages such as low temperature operation and high output density. In these systems, for example, hydrogen, which is a flammable gas, is used as a fuel, so detection of gas leakage is cited as one of the important issues.

As a gas detection device that detects the gas concentration of the combustible gas present in this type of detected atmosphere, a gas detection element is arranged in the detected atmosphere, and this gas detection element is subjected to its own temperature change (heat generation). There is known a heat conduction type gas sensor provided with a heating resistor element whose resistance value changes (see, for example, Patent Document 1).
This gas sensor is composed of a micro heater (gas detection element) in which an insulating layer that forms a diaphragm by closing a cavity provided in a semiconductor substrate is provided, and a heating resistor element is disposed on the insulating layer. Then, when the heating resistor element is energized and the heating resistor element generates heat, heat conduction to the combustible gas (gas heat conduction) occurs. Therefore, when the temperature of the gas sensor is controlled to a constant temperature, the temperature of the heating resistor element changes due to heat conduction and the resistance value changes, so that the gas to be detected can be detected based on the change amount.
The gas detection element is manufactured by using a MEMS technique, and has a configuration in which an insulating layer for forming a diaphragm is provided on a substrate and a heating resistor element is disposed on the insulating layer. As a result, heat escape from the heating resistor element to the substrate is reduced at the diaphragm portion, so that the heat of the heating resistor element is easily transferred to the gas to be detected.

  By the way, in the gas sensor (microheater) described in Patent Document 1, a large number of circular through holes are provided in a holding member (corresponding to the insulating layer) having a membrane structure. FIG. 13 shows an example in which a plurality of circular through holes 1002h are provided in a portion of the holding member (insulating layer) 1002 of the gas sensor 1000 where the heating resistor element 1004 is avoided. As a result, gas can flow through the through hole 1002h to the upper surface side and the back surface side of the holding member 1002, so that the gas that has arrived at the sensor region does not stay, and unexpected stress is applied to the holding member 1002 by the gas. Is no longer applied. Patent Document 1 describes that a polygon may be used as the through hole 1002h.

Japanese Patent Laying-Open No. 2010-230385 (FIG. 6, paragraphs 0026 and 0138)

By the way, when the heating resistor element 1004 generates heat, the holding member 1002 constituting the diaphragm is thermally expanded toward the outside in the surface direction (the direction of arrow E in FIG. 13), but the space (room for deformation) of the thermally expanded holding member 1002 is deformed. ), Stress is generated in the holding member 1002 itself, and stress is also applied to the heating resistor element 1004, and the holding member 1002 and the heating resistor element 1004 may be damaged or disconnected.
In this case, as shown in an enlarged view 14 of FIG. 13, a bridging portion 1002b is formed at a portion sandwiched between two adjacent through holes 1002h. The bridging portion 1002b has a narrower width than the holding member 1002 when the through hole 1002h is not provided, and thus is easily deformed. For this reason, even if the holding member 1002 is thermally expanded, the bridging portion 1002b is contracted and deformed in each direction of the surface direction to absorb the thermal expansion of the holding member 1002, and the generation of stress can be suppressed.
However, in the case of the technique described in Patent Document 1, since the through hole 1002 is a circular hole, the widths W1 to W3 of the bridging portion 1002b vary depending on the position of the bridging portion 1002b. The deformation of the bridging portion 1002b is concentrated in the narrowest and easily deformable width W1, and the deformation in the wide W2 portion is small. For this reason, there exists a problem that the deformation amount as the whole bridge | crosslinking part 1002b becomes small, and the absorption effect of thermal expansion also becomes small. Further, in the portion of the wide width W2, there is a problem that heat of the heating resistor element 1004 is easily transferred to the outside of the holding member 1002, and the heat escape of the heating resistor element 1004 is increased and power consumption is increased.

  On the other hand, as shown in FIG. 15, when a rectangular (square) through hole 1102h is provided in the holding member 1102, the width W1 of each of the bridging portions 1102b1 to 1102b3 is constant regardless of the position. However, in this case, since the adjacent bridging portions 1102b1 to 1102b3 are arranged on a straight line (arrow E1 in FIG. 15), the bridging portions 1102b1 to 1102b3 are connected in the direction along the straight line (left and right direction in FIG. 15). Functions as one wide member and is difficult to deform. As a result, the deformation is concentrated in the direction in which the through holes 1102h are interposed between the bridging portions and the bridging portions are not connected to each other (arrow E2 in FIG. 15), and the deformation amount as a whole of the bridging portion is also reduced. Also, the effect of absorbing thermal expansion is reduced. Further, in the direction of the arrow E1 where the bridging portions 1102b1 to 1102b3 are connected, the heat of the heating resistor element 1004 can be easily transferred to the outside of the holding member 1102, and the heat escape of the heating resistor element 1004 is further increased, resulting in higher power consumption. Become.

  Therefore, the present invention relaxes the thermal expansion generated in the insulating layer that forms the diaphragm structure, reliably suppresses stress applied to the insulating layer and the heating resistor element, and suppresses heat escape from the heating resistor element. An object is to provide a microheater with reduced power consumption and a sensor employing the microheater.

  In order to solve the above problems, a microheater according to the present invention includes a semiconductor substrate formed with a cavity penetrating between a surface and a bottom surface, and the surface of the semiconductor substrate so as to close a surface side of the cavity. A microheater comprising: an insulating layer provided thereon; and a heating resistance element embedded in a corresponding portion of the insulating layer with respect to the cavity, wherein the microheater is arranged along a penetration direction of the cavity When viewed, the plurality of polygonal through holes are formed in a honeycomb shape in a region that does not overlap the heating resistor element in the corresponding part, and the total length of the bridging portions sandwiched between the adjacent through holes The width of the cross-linked portion is constant at a site of 50% or more with respect to each other, and the adjacent cross-linked portions are not aligned on a straight line

According to this micro heater, since the through hole communicates with the cavity and allows gas to flow, the contact area between the heating resistor element and the gas to be detected increases, and heat is further detected at the heating resistor element adjacent to the through hole. It becomes easy to be transmitted to gas. For this reason, the heat transfer rate from the heating resistance element to the gas to be detected is increased, and the detection accuracy of the gas to be detected can be improved.
Furthermore, since the width of the bridging portion is constant at a site of 50% or more with respect to the total length of the bridging portion, the bridging portion is deformed almost uniformly. As a result, when the heating resistor element generates heat and the insulating layer constituting the diaphragm is thermally expanded toward the outside in the surface direction, each of the bridge portions contracts and deforms in each direction of the surface direction. As the amount of deformation increases, the effect of absorbing thermal expansion increases, and the stress applied to the insulating layer and the heating resistor element can be reliably suppressed.
In addition, the heat of the heating resistor element is prevented from being concentrated from a part of the wide bridge portion and transmitted to the outside of the insulating layer, and the heat of the heating resistor element is transmitted uniformly and widely from the bridge portion. The heat transfer path is a long distance through a plurality of bridging portions. For this reason, it becomes difficult for the heat of the heating resistance element to escape to the outside, and the power consumption can be reduced.
Further, since the adjacent bridging portions are not arranged in a straight line, it is avoided that the bridging portions are connected in the direction along the straight line and become difficult to be deformed as one wide member. As a result, each of the bridging portions contracts and deforms in each direction of the plane direction, so that the amount of deformation of the entire bridging portion increases and the effect of absorbing thermal expansion increases.
Further, when the respective bridging portions are connected in a straight line, this straight line becomes the shortest heat transfer path to the outside of the insulating layer, and the heat of the heating resistor element easily escapes to the outside. On the other hand, since each bridge | crosslinking part does not line up on a straight line, the heat transfer path | route of a heating resistive element becomes a long distance via a some bridge | crosslinking part. For this reason, it becomes difficult for the heat of the heating resistance element to escape to the outside, and the power consumption can be reduced.
The “honeycomb shape” refers to a shape in which a large number of through-holes are formed in a goblet shape.

In the microheater according to the present invention, two or more through-holes are formed, and each of the two through-holes is formed by connecting the centers of gravity of the two through-holes adjacent to each other in two different directions. With respect to the side, when the area of the rectangular inner region having the two sides as opposite sides is S1, and the total opening area of the four through holes included in the inner region is S2, the aperture ratio (S2 / S1) is It is good that it is 69% or more.
Even if the width of the cross-linked portion is constant at a site of 50% or more, if the width itself is too thick, deformation at the cross-linked portion may be difficult. And a bridge | crosslinking part becomes easy to deform | transform, so that a width | variety is made relatively small with respect to the diameter of a through-hole. Therefore, the relative width dimension of the width of the bridging portion is defined by the opening ratio (S2 / S1) with respect to the diameter of the through hole (the total diameter of all the through holes according to the number of through holes). By setting the ratio to 69% or more, the width of the crosslinked portion can be relatively reduced, and the crosslinked portion is more easily deformed. Further, when the microheater is used for a long period of time, impurities such as organic silicon are deposited on the bridging portion, and the heat escape from the heating resistor element tends to increase. Therefore, when the aperture ratio is 69% or more, the area ratio of the cross-linked portion in the insulating layer is relatively small, so that heat escape from the heating resistor element can be further suppressed to further reduce power consumption.

In the microheater of the present invention, the polygon may be a regular hexagon or a combination of a plurality of regular hexagons.
According to this microheater, it is possible to easily manufacture a microheater in which the width of the bridging portion is constant at a portion of 50% or more and the adjacent bridging portions are not arranged in a straight line.

  The sensor of the present invention includes the micro heater.

  According to the present invention, the thermal expansion generated in the insulating layer forming the diaphragm structure portion of the microheater is alleviated, the stress applied to the insulating layer and the heating resistance element is surely suppressed, and the heat escape from the heating resistance element is prevented. It is possible to reduce power consumption.

It is a top view which shows the structure of the microheater which concerns on embodiment of this invention. It is sectional drawing of the microheater along the AA line and BB line in FIG. It is a top view which shows the through-hole and bridge | crosslinking part which were formed in the insulating layer. It is a top view which shows the method of prescribing | regulating an aperture ratio. It is a figure showing the manufacturing process of a microheater. It is a figure following FIG. It is a figure following FIG. It is a figure following FIG. 1 is an overall configuration diagram of a gas sensor to which a micro heater is applied. It is a top view which shows the modification of a through-hole. It is a top view which shows another modification of a through-hole. It is a top view which shows another modification of a through-hole. It is a top view which shows the structure of the conventional microheater which provided the circular through-hole in the membrane structure. It is a top view which shows the stress which arises in the through-hole vicinity of FIG. It is a top view which shows the structure of the conventional microheater which provided the square through-hole in the membrane structure.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a plan view of the microheater 500, and FIG. 2 is an end view of each of the AA line cutting part and the BB line cutting part of FIG. In FIG. 1, the left-right direction of the paper surface is the left-right direction of the plan view. In FIG. 2, the vertical direction of the paper surface is the vertical direction of the sectional view.
The microheater 500 constitutes a gas detection element of a (gas) sensor that detects the hydrogen gas concentration.

As shown in FIG. 1, the microheater 500 has a flat plate shape (square shape in plan view), and electrodes 430, 440, 88, and 89 are formed at the four corners of the surface, respectively, and near the center of the other surface (back surface). In addition, a diaphragm constituting portion having a rectangular shape in plan view, which will be described later in detail, is formed.
As shown in FIG. 2, the microheater 500 includes a semiconductor substrate 100 made of a silicon substrate, an insulating layer 200 formed along the surface (upper surface in FIG. 2) 110 of the semiconductor substrate 100, and the semiconductor substrate 100. And a back-side insulating film 300 formed on the back surface (lower surface in FIG. 2) 120.
Then, on the back surface side of the insulating layer 200, a part of the semiconductor substrate 100 is removed in the shape of an eight-shaped section (in a pyramid shape (quadrangular pyramid shape)) in the plate thickness direction of the semiconductor substrate 100, so that FIG. As shown in FIG. In the insulating layer 200, the corresponding portion of the semiconductor substrate 100 corresponding to the cavity portion 130 includes the heating resistor element 400 embedded in the corresponding portion to form a diaphragm structure portion.

Further, a region (thin film portion) corresponding to the cavity 130 in the insulating layer 200, more specifically, between the lower thin film 210 and the upper thin film 220, that is, between the two compressive stress films 212 and 221, is a spiral. A heating resistance element 400 patterned in a shape is embedded.
The heating resistance element 400 is a resistor whose resistance value changes due to its own temperature change depending on the temperature of the gas to be detected (specifically, heat conduction to the combustible gas). The heating resistance element 400 is made of a conductive material having a large temperature resistance coefficient, and is made of platinum (Pt) in this embodiment. When detecting hydrogen gas as a combustible gas, the amount of heat taken from the heating resistor element 400 by heat conduction to the hydrogen gas is in accordance with the hydrogen gas concentration. From this, it is possible to detect the hydrogen gas concentration based on the change in the electrical resistance value in the heating resistor element 400.
Then, by providing the heating resistor element 400 in the diaphragm structure, the heating resistor element 400 is thermally insulated from the surroundings, so that the temperature is raised or lowered in a short time. For this reason, the heat capacity of the micro heater 500 can be reduced.
Since the change in resistance value of the heating resistor element 400 is affected by the temperature of the gas to be detected, the electrical resistance of the heating resistor element 400 is determined using the temperature detected based on the electrical resistance value of the resistance temperature detector 80 described later. By correcting the concentration of the detected gas detected based on the value change, the detection accuracy of the detected gas concentration can be improved.

The insulating layer 200 includes a lower thin film 210 and an upper thin film 220.
The lower thin film 210 has a tensile stress film 211 and a compressive stress film 212. A tensile stress film 211 made of silicon nitride (Si ₃ N ₄ ) is laminated on the surface 110 of the semiconductor substrate 100, and a compressive stress film 212 made of silicon oxide (SiO ₂ ) is laminated on the surface of the tensile stress film 211. Yes.
The upper thin film 220 includes a compressive stress film 221 and a tensile stress film 222. The compressive stress film 221 made of silicon oxide (SiO ₂ ) is laminated on the surface of the compressive stress film 212, and the tensile stress film 222 made of silicon nitride (Si ₃ N ₄ ) is laminated on the surface of the compressive stress film 221. Yes.

A back side insulating film 300 made of silicon nitride (Si ₃ N ₄ ) is formed along the back surface 120 of the semiconductor substrate 100. Further, in the back side insulating film 300, the corresponding part with respect to the cavity 130 is removed to form an opening of the cavity 130.
As a result, a portion of the back surface of the tensile stress film 211 of the insulating layer 200 corresponding to the cavity 130 is exposed to the outside through the opening of the cavity 130.
Note that a portion of the semiconductor substrate 100 other than the cavity portion 130 is hereinafter referred to as a substrate portion 140.
The tensile stress film 222 that forms the outermost layer is provided so as to cover the heating resistance element 400, the resistance temperature detector 80, and the wiring film 16 in order to prevent contamination and damage.
The microheater 500 is about several mm (for example, 3 mm × 3 mm) both vertically and horizontally, and is manufactured by, for example, a micromachining technique (micromachining process) using a silicon semiconductor substrate.

Returning to FIG. 1, the left and right ends of the heating resistor element 400 are connected via a left wiring film 410 and a right wiring film 420 (FIG. 2) that form wirings embedded in the same plane as the plane on which the heating resistor element 400 is formed. Are connected to the left electrode 430 and the right electrode 440, respectively. The left electrode 430 is a ground electrode. Both electrodes 430 and 440 are wiring lead portions connected to the heating resistor element 400 and are exposed through the contact holes 223 and 224 (FIG. 2), and are formed of, for example, aluminum (Al) or gold (Au). Has been.
The left wiring film 410 is a thin film on the surface of the compressive stress film 212 at a position corresponding to the substrate portion 140 of the semiconductor substrate 100 between the lower thin film 210 and the upper thin film 220, that is, between the two compressive stress films 212 and 221. It is formed in a shape. On the other hand, the right wiring film 420 is formed as a thin film on the surface of the compressive stress film 212 at a position corresponding to the substrate portion 140 of the semiconductor substrate 100 between the two compressive stress films 212 and 221.
Further, the left electrode 430 is formed on the left wiring film 410 through the contact hole 223 formed in the upper thin film 220. Similarly, the right electrode 440 is formed on the right wiring film 420 through the contact hole 224 formed in the upper thin film 220.

The resistance temperature detector 80 is for detecting the temperature of a gas (detected gas or the like) existing in the space where the microheater 500 is arranged, and as shown in FIG. ) Is embedded between the compressive stress film 221 and the tensile stress film 222. The resistance temperature detector 80 is made of a conductive material whose electric resistance value changes in proportion to the temperature (in this embodiment, the resistance value increases as the temperature rises). In this embodiment, platinum (Pt) It is formed with.
The resistance thermometer 80 is connected to the electrode 88 and the ground electrode 89 via a wiring film (not shown) embedded in the same plane as the plane on which the resistance thermometer 80 is formed. The electrode 88 and the ground electrode 89 are exposed through a contact hole (not shown), and are formed of, for example, aluminum (Al) or gold (Au).

Furthermore, a plurality of through-holes 200h made of the same polygon (regular hexagon in this embodiment) are formed in a region of the insulating layer 200 that avoids the formation site of the heating resistor element 400.
Since the through hole 200h communicates with the cavity 130 and allows gas to flow, the contact area between the heating resistor element 400 and the gas to be detected increases, and heat is further detected in the heating resistor element 400 adjacent to the through hole 200h. It becomes easy to be transmitted to. For this reason, the heat transfer rate from the heating resistance element 400 to the gas to be detected is increased, and the detection accuracy of the gas to be detected can be improved. In addition, the corner | angular part (vertex) of a polygon does not necessarily need to be an acute angle, The rounded shape may be sufficient.

Moreover, as shown in FIG. 3, each through-hole 200h1-200h3 is arrange | positioned so that the edge | side of an own and the edge | side of an adjacent through-hole may become parallel. Accordingly, the width W1 of the bridging portions 200b1 to 200b3 formed by the insulating layer 200 sandwiched between adjacent through holes is constant at any position. Specifically, the insulating layer 200 sandwiched between the adjacent through holes 200h1 and 200h2 forms the bridging portion 200b1, and the insulating layer 200 sandwiched between the adjacent through holes 200h1 and 200h3 forms the bridging portion 200b2 and is adjacent to the through hole. The insulating layer 200 sandwiched between the holes 200h2 and 200h2 forms a bridging portion 200b3.
And these adjacent bridge | crosslinking parts 200b1-200b3 are connected by each edge | side of the connection part 200c which consists of an equilateral triangle whose one side is W1, and each bridge | crosslinking part 200b1-200b3 is mutually 120 degree | times centering on the connection part 200c. It extends radially at an angle, and the bridging portions 200b1 to 200b3 do not line up in a straight line. Here, not being aligned on a straight line means that there is always an inflection point between the adjacent bridge portions 200b1 to 200b3.

Thus, since the width W1 of the bridging portions 200b1 to 200b3 is constant at any position, the bridging portions 200b1 to 200b3 are deformed almost uniformly. As a result, when the heating resistance element 400 generates heat and the insulating layer 200 constituting the diaphragm thermally expands toward the outside in the surface direction (the direction of arrow E in FIGS. 2 and 3), each of the bridging portions is in the surface direction. Therefore, the amount of deformation of the entire bridging portion is increased, the thermal expansion absorption effect is increased, and the stress applied to the insulating layer 200 and the heating resistor element 400 can be reliably suppressed. As described above, since the stress applied to the insulating layer 200 and the heating resistor element 400 can be reliably suppressed, the heat resistance and durability of the microheater are improved.
Note that the width W1 of the bridging portions 200b1 to 200b3 may be constant at a portion of 50% or more with respect to the total length of the bridging portions. If the portion of 50% or more is constant with respect to the total length of the cross-linked portions, the stress can be sufficiently suppressed at this constant portion. However, as described above, it is preferable that the width W1 of the bridge portions 200b1 to 200b3 is constant at any position (that is, 100% with respect to the total length of the bridge portions). In addition, it is preferable that the width W1 of the certain portion is narrower than the width of the other portion of the bridging portion because the certain portion is easily deformed.
Further, the heat of the heating resistor element 400 is prevented from being concentrated from a part of the wide bridging portion and transmitted to the outside of the insulating layer 200, and the heat of the heating resistor element 400 is evenly and widely transmitted from the bridging portion. The heat transfer path (arrows H1 and H2 in FIG. 3) of the heating resistor element 400 is a long distance through a plurality of bridging portions. For this reason, it becomes difficult for the heat of the heating resistance element 400 to escape to the outside, and power consumption can be reduced.

Further, since the adjacent bridging portions 200b1 to 200b3 are not arranged on a straight line (arrow E in FIG. 3), the bridging portions 200b1 to 200b3 are connected in a direction along the straight line to be deformed as one wide member. Difficulty is avoided. As a result, each of the bridging portions contracts and deforms in each direction of the plane direction, so that the amount of deformation of the entire bridging portion increases and the effect of absorbing thermal expansion increases.
Furthermore, when each bridge | crosslinking part 200b1-200b3 is connected on a straight line, this straight line becomes the shortest heat transmission path | route to the exterior of the insulating layer 200, and the heat | fever of the heating resistive element 400 tends to escape outside. On the other hand, in this embodiment, since each bridge | crosslinking part 200b1-200b3 does not line up on a straight line, the heat transfer path (arrow H1, H2 of FIG. 3) of the heating resistive element 400 is long through several bridge | crosslinking parts. Distance. For this reason, it becomes difficult for the heat of the heating resistance element 400 to escape to the outside, and power consumption can be reduced.

  In addition, although the connection part 200c consists of an equilateral triangle with the length of one side W1, the distance of the side of each through-hole 200h1-200h3 (specifically vertex of each through-hole 200h1-200h3) and the connection part 200c is W1. The following (shorter than W1). For this reason, the connection part 200c is wider than each bridge | crosslinking part 200b1-200b3, and it does not become difficult to deform | transform, and the connection part 200c does not prevent the deformation | transformation of each bridge | bridging part 200b1-200b3.

By the way, even if the width W1 of the bridging portions 200b1 to 200b3 is constant at a portion of 50% or more, if the width W1 itself is too thick, deformation at the bridging portion may be difficult. That is, as the width W1 is relatively decreased with respect to the diameters of the through holes 200h1 to 200h3, the bridging portion is easily deformed. Therefore, as a preferred embodiment of the present invention, the relative width dimension of the width W1 is defined by the following aperture ratio (S2 / S1).
Specifically, as shown in FIG. 4, a single through hole 200h1 is used as a starting point, and through holes 200h2 adjacent to one direction (vertical direction in FIG. 4) D1 are combined to form two through holes 200h1 and 200h2. A side L1 is formed by connecting the centroids G1 and G2. Similarly, the through-hole 200h3 starting from the through-hole 200h1 and adjacent to a direction D2 different from the direction D1 (diagonal right-down direction in FIG. 4) is combined to connect the centers of gravity G1 and G3 of the two through-holes 200h1 and 200h3. The side L2 is constituted by
Then, when the area of the rectangular inner region R having two sides L1 and L2 as opposite sides is S1, and the total opening area of the four through holes 200h1 to 200h4 included in the inner region R is S2, the aperture ratio is ( S2 / S1).

When the aperture ratio (S2 / S1) is 69% or more, the width W1 can be made relatively small with respect to the diameter of the through hole (the total diameter of all the through holes according to the number of through holes). The bridging portion sandwiched between the adjacent through holes is more easily deformed. In addition, when the microheater is used for a long period of time, impurities such as organic silicon are deposited on the bridging portion, and the heat escape from the heating resistor element 400 tends to increase. Therefore, when the aperture ratio is 69% or more, the area ratio of the cross-linking portion is relatively small in the insulating layer 200, so that heat escape from the heating resistor element 400 can be further suppressed to further reduce power consumption. it can.
The upper limit of the aperture ratio is not particularly limited, but the upper limit is about 91% due to the dimensional accuracy of the through holes and the bridging portion, manufacturing problems, and the like.

Next, the manufacturing process of the micro heater 500 will be described with reference to FIGS. 5-8, about each process, each end surface state in the AA line cutting | disconnection part and BB line cutting | disconnection part of the microheater in FIG. 1 is represented. The micro heater 500 is manufactured using micro machine technology.
(1) Film Forming Step of Tensile Stress Film 211 and Back Side Insulating Film 300 First, as shown in FIG. 5, a cleaned silicon substrate is prepared as a semiconductor substrate 100, and a tensile layer made of silicon nitride is formed on the surface of the semiconductor substrate 100. The stress film 211 is formed with a predetermined film thickness (for example, 0.2 μm) by a low pressure CVD method (LP-CVD method). Note that when the tensile stress film 211 is formed, the insulating film 300 is also formed in a thin film on the back surface 120 of the semiconductor substrate 100.
(2) Compression Stress Film 212 Formation Step Next, as shown in FIG. 5, a compression stress film 212 made of silicon oxide is formed on the surface of the tensile stress film 211 by a plasma CVD method to a predetermined thickness (for example, 0. 1 μm).

(3) Film Formation Step of Heating Resistance Element 400 and Left and Right Both Side Wiring Films 410 and 420 Next, as shown in FIG. 6, a thin platinum film is formed on the surface of the compressive stress film 212 by sputtering of platinum (Pt). After the film formation, the platinum film is subjected to a patterning process to integrally form the heating resistance element 400 and the left and right wiring films 410 and 420 on the surface of the compressive stress film 212.

(4) Compressive Stress Film 221 Formation Process Next, as shown in FIG. 7, the surface of the compressive stress film 212 is made of silicon oxide so as to cover the heating resistance element 400 and the left and right wiring films 410 and 420. The compressive stress film 221 is formed with a predetermined film thickness (for example, 0.1 μm) by plasma CVD.
(5) Film Formation Step of Tensile Stress Film 222 Further, a tensile stress film 222 made of silicon nitride is formed on the surface of the compression stress film 221 with a predetermined film thickness (for example, 0.2 μm) by low-pressure CVD. As a result, the upper thin film 220 composed of the compressive stress film 221 and the tensile stress film 222 is separated from the tensile stress film 211 and the compressive stress film 212 on the basis of the heating resistance element 400, in other words, between the two compressive stress films 212 and 221. The lower thin film 210 is formed symmetrically.
Note that when the tensile stress film 222 is formed, the insulating film 300 is also formed into a thin film on the back surface 120 of the semiconductor substrate 100.

(6) Step of forming electrodes and through-holes Next, as shown in FIG. 8, in the upper thin film 220 after the tensile stress film 222 is formed, the corresponding portions for the left and right wiring films 410 and 420 Contact holes 223 and 224 are formed by etching. Accordingly, the left and right wiring films 410 and 420 are exposed to the outside through the corresponding contact holes 223 and 224 on the respective surfaces.
Next, a contact metal film made of gold (Au) or the like is formed on the surface of the tensile stress film 222 including the insides of the contact holes 223 and 224 by sputtering. Further, the contact metal film is subjected to patterning processing and etching processing, and left and right side electrodes 430 and 440 are formed in the contact holes 223 and 224, respectively.
Further, the through-hole 200h is formed by patterning and dry etching in a region of the insulating layer 200 where the heating resistor element 400 is not formed.
The through hole 200h penetrates the upper thin film 220 and the lower thin film 210 constituting the insulating layer 200, but terminates at the surface 110 without penetrating the semiconductor substrate 100.

(7) Cavity Formation Process Next, after the formation of the electrodes and the through holes, the backside insulating film 300 is subjected to patterning processing and etching processing required to form the cavity 130. Here, the etching site 130E that forms the cavity 130 is outside in the surface direction from the site where the heating resistor element 400 and the through hole 200h are formed.
Next, an etching process is performed on the semiconductor substrate 100 using an anisotropic etching solution (for example, TMAH). Thereby, the cavity 130 communicating with the through hole 200h is formed in the semiconductor substrate 100 (see FIG. 2), and the manufacture of the microheater 500 is completed.

Next, the gas sensor 1 to which the micro heater 500 according to the embodiment of the present invention is applied will be described with reference to FIG. FIG. 9 is an overall configuration diagram of the gas sensor 1. The micro heater 500 constitutes a heat conduction type gas detection element for detecting the hydrogen gas concentration. The gas sensor 1 detects the concentration of combustible gas using a heat conduction type gas detection element. For example, the gas sensor 1 is installed in a cabin of a fuel cell vehicle and detects the leakage of hydrogen. Used.
In FIG. 1, only the resistance temperature detector 80 is illustrated in the microheater 500 that forms the gas detection element.

As shown in FIG. 9, the gas sensor 1 includes a gas detection element and a control circuit 90 that drives and controls the gas detection element. The control circuit 90 includes a gas detection circuit 91 and a temperature measurement circuit 93. The control circuit 90 (except for the heating resistor element 400 and the resistance temperature detector 80) and the microcomputer 94 are configured on a single circuit board, and the gas detection element is configured separately from the circuit board. Yes.
The gas detection circuit 91 amplifies the Wheatstone bridge 911 configured by the heating resistor element 400 provided in the gas detection element and the fixed resistors 95, 96, and 97, and the potential difference obtained from the Wheatstone bridge 911. An operational amplifier 912 is provided.
When a resistor whose resistance value increases with an increase in its own temperature is used as the heating resistor element 400, the operational amplifier 912 has a heating resistor element so that the temperature of the heating resistor element 400 is maintained at a predetermined temperature. When the temperature of 400 rises, the output voltage is lowered, and when the temperature of the heating resistor element 400 is lowered, the output voltage is raised.

Since the output of the operational amplifier 912 is connected to the Wheatstone bridge 911, when the temperature of the heating resistor element 400 rises above a predetermined temperature, the output of the operational amplifier 912 is output to lower the temperature of the heating resistor element 400. And the voltage applied to the Wheatstone bridge 911 decreases. At this time, the voltage of the right electrode 440 (see FIG. 1) constituting the end of the Wheatstone bridge 911 is detected by the microcomputer 94 as the output of the gas detection circuit 91, and the output value detected by the microcomputer 94 is It is subjected to arithmetic processing for detecting combustible gas contained in the detection gas.
The temperature measurement circuit 93 amplifies a potential difference obtained from the temperature measuring resistor 80 provided in the gas detection element, the Wheatstone bridge 931 configured by the fixed resistors 101, 102, and 103, and the Wheatstone bridge 931. An operational amplifier 933. The output of the operational amplifier 933 is detected by the microcomputer 94, and the output value detected by the microcomputer 94 is used to measure the temperature of the gas to be detected. Further, in order to detect the combustible gas contained in the gas to be detected. It is used for the arithmetic processing.

  The processing for calculating the concentration of the combustible gas executed by the microcomputer 94 based on the output value of the control circuit 90 having the above configuration is as follows. First, a CPU (not shown) provided in the microcomputer 94 is substantially proportional to the combustible gas concentration from the output value of the gas detection circuit 91 based on a program stored in a storage device (not shown) provided in the microcomputer 94. The first output value is output. Since the first output value includes an output change due to an ambient temperature change in the detection space of the gas sensor 1, the second output is obtained by correcting the first output value based on the output from the temperature measurement circuit 93. Output the value. Further, the microcomputer 94 determines the concentration of the combustible gas contained in the detected gas based on the relationship between the second output value stored in the storage device (not shown) of the microcomputer 94 and the concentration of the combustible gas. Is output. Thus, since the 1st output value is amended based on the output of temperature measuring circuit 93, combustible gas can be detected with sufficient accuracy. In addition, the process which calculates the density | concentration of combustible gas is not restricted to said thing, What is necessary is just to use a well-known means suitably.

It goes without saying that the present invention is not limited to the above-described embodiment, but extends to various modifications and equivalents included in the spirit and scope of the present invention.
For example, as shown in FIG. 10, a polygon having a combination of three regular hexagons may be used as the through hole. In the example of FIG. 10, the through holes 250 h 1 to 250 h 3 are arranged in the insulating layer 250 so that the sides of the through holes 250 h 1 to 250 h 3 are parallel to the sides of the adjacent through holes. The insulating layer 250 sandwiched between the adjacent through holes 250h1 and 250h2 forms the bridging portion 250b1, the insulating layer 250 sandwiched between the adjacent through holes 250h1 and 250h3 forms the bridging portion 250b2, and the adjacent through holes 250h2. The insulating layer 250 sandwiched between 250h3 forms a bridging portion 250b3. The width W1 of the bridging portions 250b1 to 250b3 is constant at any position.
Moreover, these adjacent bridge | crosslinking parts 250b1-250b3 are connected by each edge | side of the connection part 250c which consists of equilateral triangles, and each bridge | crosslinking part 250b1-250b3 is radially extended at an angle of 120 degree | times centering on the connection part 250c. The bridging portions 250b1 to 250b3 are not aligned on a straight line.
Thus, also in the example of FIG. 10, the width W1 of the bridging portions 250b1 to 250b3 is constant at any position, and the adjacent bridging portions 250b1 to 250b3 are not aligned in a straight line.

In addition, although the connection part 250c consists of an equilateral triangle whose one side is longer than W1, the distance between the side of each through hole 250h1 to 250h3 (including the vertex of each through hole 250h1 to 250h3) and the connection part 250c is W1. is there. For this reason, the connection part 250c is wider than each bridge | crosslinking part 250b1-250b3, and it does not become difficult to deform | transform, and the connection part 250c does not prevent a deformation | transformation of each bridge | crosslinking part 250b1-250b3.
In the example of FIG. 10, the bridging portion 250b2 is bent in a U shape so as to be symmetric with respect to the symmetry line 250bx, and the length of the symmetry line 250bx is wider than the width W1 (the same applies to the other bridging portions). However, since the symmetry line 250bx is a line and does not constitute a surface, the symmetry line 250bx does not hinder the deformation of the bridging portion 250b2.

Moreover, as shown in FIG. 11, you may use the polygon of the shape which combined seven regular hexagons as a through-hole. In the example of FIG. 11, the through holes 260 h 1 to 260 h 3 are arranged in the insulating layer 260 so that the sides of the through holes 260 h 1 to 260 h 3 are parallel to the sides of the adjacent through holes. The insulating layer 260 sandwiched between the adjacent through holes 260h1 and 260h2 forms the bridge portion 260b1, the insulating layer 260 sandwiched between the adjacent through holes 260h1 and 260h3 forms the bridge portion 260b2, and the adjacent through holes 260h2, An insulating layer 260 sandwiched between 260h3 forms a bridging portion 260b3. And the width | variety of bridge | bridging part 260b1-260b3 is constant in any position.
The adjacent bridge portions 260b1 to 260b3 are connected at each side of the connecting portion 260c formed of an equilateral triangle, and the bridge portions 260b1 to 260b3 extend radially at an angle of 120 degrees with respect to the connection portion 260c. The bridging portions 260b1 to 260b3 are not aligned on a straight line.
Thus, also in the example of FIG. 11, the width of the bridging portions 260b1 to 260b3 is constant at any position, and the adjacent bridging portions 260b1 to 260b3 are not aligned in a straight line.

In addition, although the connection part 260c consists of an equilateral triangle whose length of one side is longer than the width | variety of a bridge | bridging part, it is the same as that of the case of the connection part 250c not preventing the deformation | transformation of each bridge | bridging part 260b1-260b3.
In the example of FIG. 11, the bridging portion 260b2 is bent at two positions so as to be symmetric with respect to two symmetric lines 260bx, and the length of the symmetric line 260bx is wider than the width of the bridging portion (the other bridging portions The same). However, the symmetry line 260bx does not hinder the deformation of the bridging portion 260b2, as in the case of the symmetry line 250bx.

Moreover, as shown in FIG. 12, you may use the polygon of the shape which combined four regular hexagons as a through-hole. In the example of FIG. 12, the through holes 270 h 1 to 270 h 3 are arranged in the insulating layer 270 so that the sides of the through holes 270 h 1 to 270 h 3 are parallel to the sides of the adjacent through holes. The insulating layer 270 sandwiched between the adjacent through holes 270h1 and 270h2 forms the bridging portion 270b1, the insulating layer 270 sandwiched between the adjacent through holes 270h1 and 270h3 forms the bridging portion 270b2, and the adjacent through holes 270h2, An insulating layer 270 sandwiched between 270h3 forms a bridging portion 270b3. And the width | variety of bridge | crosslinking part 270b1-270b3 is constant in any position.
Further, these adjacent bridge portions 270b1 to 270b3 are connected at each side of the connecting portion 270c formed of an equilateral triangle, and the respective bridge portions 270b1 to 270b3 extend radially at an angle of 120 degrees with respect to the connection portion 270c. The bridging portions 270b1 to 270b3 do not line up on a straight line.
Thus, also in the example of FIG. 12, the width of the bridging portions 270b1 to 270b3 is constant at any position, and the adjacent bridging portions 270b1 to 270b3 are not aligned on a straight line.

In addition, although the connection part 270c consists of an equilateral triangle whose length of one side is longer than the width | variety of a bridge | bridging part, it is the same as that of the case of the connection part 250c not preventing the deformation | transformation of each bridge | bridging part 270b1-270b3.
In the example of FIG. 12, the bridging portion 270b2 is bent at two places so as to be symmetric with respect to the two symmetrical lines 270bx, and the length of the symmetrical line 270bx is wider than the width of the bridging portion (the bridging portion 270b1 is also The same). However, the symmetry line 270bx does not hinder the deformation of the bridging portion 270b2, as in the case of the symmetry line 250bx.
In the example of FIG. 12, the bridging portion 270b3 extends straight in the horizontal direction (left-right direction in FIG. 12), and the shape is different from the bridging portions 270b1 and 270b2.

Furthermore, when the vertex of the polygon that forms the through-hole (the intersection of two adjacent sides) is rounded, the stress concentration on the vertex is reduced compared to the case where the vertex is sharp, so when the bridge is deformed It is possible to suppress problems such as breaking at the apex.
In the example of FIG. 1, the through hole 200h is not provided in the gap 400G of the heating pattern adjacent to the heating resistor element 400. However, when the diameter of the through hole 200h is smaller than the width of the gap 400G, the gap 400G Alternatively, a through hole 200h may be provided.
Further, the formation of the contact hole in FIG. 8 and the formation of the through hole may be performed simultaneously.
Moreover, although the said embodiment demonstrated the case where hydrogen gas was detected, the gas sensor of this invention can also detect another kind of combustible gas.

1 Gas sensor (sensor)
100 Semiconductor substrate 130 Cavity part 200, 250, 260, 270 Insulating layer 200b1-200b3, 250b1-250b3, 260b1-260b3, 270b1-270b3 Cross-linking part 200h, 200h1-200h4, 250h1-250h3, 260h1-260h3, 270h1-270h3 Hole 400 Heating resistance element 500 Micro heater W1 Bridge width D1, D2 Two different directions of through-hole G1, G2, G3 Center of gravity of through-hole L1, L2 Two sides configured by connecting the center of gravity of through-hole R 2 sides The inner area of the rectangle with the opposite side

Claims (4)

A semiconductor substrate formed with a cavity penetrating between the front surface and the bottom surface;
An insulating layer provided on the surface of the semiconductor substrate so as to close the surface side of the cavity,
In a microheater comprising a heating resistance element embedded in a corresponding portion of the insulating layer with respect to the cavity,
When the micro heater is viewed along the penetration direction of the cavity,
A plurality of polygonal through holes are formed in a honeycomb shape in a region that does not overlap with the heating resistor element in the corresponding portion,
A micro-heater in which the width of the bridging portion is constant and the adjacent bridging portions are not aligned in a straight line at a portion of 50% or more of the total length of the bridging portions sandwiched between the adjacent through holes. . Four or more through-holes are formed, and two sides are formed by connecting the centers of gravity of two through-holes that are adjacent to each other in two different directions, starting from one through-hole.
The opening ratio (S2 / S1) is 69% or more, where S1 is the area of the rectangular inner region having the two opposite sides and S2 is the total opening area of the four through holes included in the inner region. The micro heater according to claim 1.   The micro heater according to claim 1 or 2, wherein the polygon is a regular hexagon or a combination of a plurality of regular hexagons.   A sensor comprising the microheater according to claim 1.

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