JP2006078191A - Semiconductor sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor sensor capable of inhibiting suitably lowering a proof amount against the destruction of a thin film structural part caused by defects regardless of positions of the defects. <P>SOLUTION: The flow sensor FS is constituted by providing a semiconductor substrate 10, and on the hollow part H of the semiconductor substrate 10 the thin film structured part MB is formed. At the neighbor of the four corner part of the thin film structured part MB, the upstream heater Rha and the downstream heater Rhb are formed with a part of the conductor film 20 which functions as a reinforcement member of the thin film structured part MB. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a semiconductor sensor that measures a predetermined physical quantity using a resistor formed on a thin film structure such as a membrane or a diaphragm provided on a semiconductor substrate.

  Conventionally, for example, a flow sensor is known as this type of semiconductor sensor. This flow sensor senses the flow rate of the fluid by utilizing the fact that the heat generated by the heating element (resistor) formed in the thin film structure is taken away by the fluid flowing in the vicinity of the heating element. That is, of the heat generated by the heating element, the amount of heat taken away by the fluid increases as the flow rate of the fluid increases, so the flow rate of the fluid in the vicinity of the heating element can be measured based on the amount of heat taken away by the fluid.

  On the other hand, as such a flow sensor and a flow meter using the flow sensor, for example, one described in Patent Document 1 is known. Hereinafter, the flow sensor and the flow meter described in Patent Document 1 will be described with reference to FIGS. 7 and 8.

  FIG. 7 shows the overall structure of the flow sensor. As shown in FIG. 7, the flow sensor FS includes a semiconductor substrate 10. On the semiconductor substrate 10, an upstream heater Rha, a downstream heater Rhb, an upstream thermometer Rka, and a downstream thermometer Rkb are formed by patterning the conductor film 20. Of these, the upstream heater Rha and the downstream heater Rhb serve as temperature sensing elements that sense their own temperature based on a change in resistance value of the heating element, in addition to the function as a heating element that generates heat when current is supplied. It also has the function of. On the other hand, the upstream side thermometer Rka and the downstream side thermometer Rkb have a function of sensing the environmental temperature of the flow sensor FS. The upstream heater Rha, the downstream heater Rhb, the upstream thermometer Rka, and the downstream thermometer Rkb are connected to a signal generation circuit SG (FIG. 8) and pads P1 to P6, which will be described later, via leads L1 to L6. They are connected via bonding wires W1 to W6.

  The semiconductor substrate 10 has a cavity H. The hollow portion H is opened in a rectangular region indicated by a one-dot chain line in FIG. 7 on the back surface side of the semiconductor substrate 10, and the opening area is reduced toward the upper surface side of the semiconductor substrate 10, The upper surface of the semiconductor substrate 10 is formed in the shape of a rectangular region indicated by a broken line in FIG. A thin film structure MB is formed on the cavity H, and an upstream heater Rha and a downstream heater Rhb are formed so as to bridge the cavity H.

An equivalent circuit of a flow meter provided with the flow sensor FS having such a structure is shown in FIG.
As shown in FIG. 8, the flow meter FM includes the flow sensor FS having the above-described configuration and a signal generation circuit SG that generates an electrical signal based on the detection result of the flow sensor FS.

  Among these, the flow sensor FS senses the flow rate of the fluid based on the heat generated by the fluid (such as intake air) among the heat generated by the upstream heater Rha and the downstream heater Rhb. The flow sensor FS senses the flow direction of the fluid based on the difference in the amount of heat taken away by the fluid among the heat generated by the upstream heater Rha and the downstream heater Rhb.

  On the other hand, the signal generation circuit SG generates a detection signal corresponding to the sensing result of the fluid flow rate and fluid flow direction by the flow sensor FS. Specifically, the flow sensor is configured so that the temperature difference between the upstream heater Rha and the upstream thermometer Rka and the temperature difference between the downstream heater Rhb and the downstream thermometer Rkb are set to predetermined values (for example, “200 ° C.”). Controls the current supplied to the FS. And based on the electric power consumed by this flow sensor FS, the detection signal according to the flow volume of the said fluid and the distribution direction of the fluid is produced | generated.

  Specifically, the flow sensor FS and the signal generation circuit SG include an upstream Wheatstone bridge UHB in which an upstream heater Rha and a resistor R1a, an upstream thermometer Rka and a resistor R2a are connected in parallel, and a downstream heater. A downstream Wheatstone bridge circuit DHB in which Rhb and a resistor R1b, a downstream thermometer Rkb, and a resistor R2b are connected in parallel is provided. In the upstream Wheatstone bridge UHB, the voltage drop at the upstream heater Rha and the voltage drop at the upstream thermometer Rka are taken into the differential amplifier circuit UOP. In order to establish the equilibrium condition, the transistor UT is controlled in accordance with the difference between these voltage drops. Such an operation is the same in the downstream Wheatstone bridge DHB including the transistor DT and the differential amplifier circuit DOP. Further, the voltage drop at the upstream heater Rha and the voltage drop at the downstream heater Rhb are taken into the differential amplifier circuit COP, and a signal corresponding to the difference between the two voltage drops is received by the differential amplifier circuit. Generated by COP. Then, after this signal is amplified by the amplifier circuit AC, it is output to the outside through the terminal P7 of the signal generation circuit SG. That is, the detection signal output via the terminal P7 is a detection signal for the flow rate and the flow direction of the fluid.

  By the way, in such a flow sensor, when there are pinholes or scratches in the constituent film constituting the thin film structure part, or defects such as particles between the constituent films, the pressure difference or fluid between the surface and the back surface of the thin film structure part. The resistance of the thin film structure part to external stresses such as the collision of dust inside, that is, the external stress (destructive resistance) that causes the thin film structure part to break down decreases. For this reason, in manufacturing the flow sensor, screening for selecting and removing the defective thin film structure is performed. This screening is performed, for example, by applying a uniform pressure to the entire surface of the thin film structure portion using air, oil, or the like so as to destroy chips below a predetermined value.

  However, it is generally difficult to select and remove all defects in the thin film structure by such screening. Therefore, conventionally, in order to suppress a decrease in breakdown tolerance due to the defect, a reinforcing member is provided in the thin film structure portion to increase the rigidity of the thin film structure portion. As an example of such a flow sensor, for example, one described in Patent Document 2 is known.

FIG. 9 shows a thin film structure portion of the flow sensor described in Patent Document 2. In this flow sensor, a thin film structure 112 formed on a cavity 111 of a semiconductor substrate 110 includes a heating element 113 and a temperature sensing element 114 that senses the temperature upstream of the heating element 113, and a thin film. The reinforcing member 115 is provided in the vicinity of the center of the side located on the downstream side of a part of the peripheral part of the structure part 112, specifically, the side constituting the peripheral part of the thin film structure part 112. The reinforcing member 115 increases the rigidity of the thin film structure portion 112.
JP-A-16-191299 JP-A-15-202257

  By the way, the stress acting on the peripheral portion of the thin film structure portion due to the pressure at the time of screening generally has a characteristic that it is larger near the center of each side constituting the peripheral portion and smaller as it is closer to the four corners of the thin film structure portion. Therefore, when screening a thin film structure having uniform rigidity, if the defect is near the center of the side constituting the peripheral edge of the thin film structure, it can be selected and removed. If the defects are in the vicinity of the four corners of the thin film structure, they cannot be selected and removed. On the other hand, the degree of stress applied when actually used as a flow sensor is not necessarily uniform over the entire thin film structure, unlike the screening. For this reason, when stress concentrates on the defects near the four corners, the thin film structure may be destroyed starting from the defects near the four corners. In other words, a reduction in the breakdown tolerance of the thin film structure due to defects near the four corners is inevitable.

  Under such circumstances, in the case of the flow sensor described in Patent Document 2, although the rigidity of the thin film structure portion 112 is surely increased by the reinforcing member 115 provided in the thin film structure portion 112, the thin film structure by the reinforcing member 115 is provided. The rigidity of the portion 112 is improved only in the vicinity of the center of the side constituting the peripheral portion of the thin film structure portion 112. For this reason, even when the reinforcing member 115 is provided, a reduction in breakdown resistance due to defects near the four corners that cannot be removed by screening is still inevitable.

  Such a situation is not limited to the flow sensor but is generally common to other semiconductor sensors in which a semiconductor substrate is provided with a thin film structure such as a membrane or a diaphragm.

  The present invention has been made in view of the above circumstances, and the object thereof is a semiconductor sensor capable of suitably suppressing a reduction in the breakdown resistance of a thin film structure portion caused by the defects without depending on the position where the defects enter. Is to provide.

  In order to achieve such an object, according to the first aspect of the present invention, there is provided a semiconductor sensor comprising a resistor in a thin film structure portion having a rectangular shape formed on a semiconductor substrate and measuring a predetermined physical quantity using the resistor. As described above, the reinforcing member is formed in the vicinity of the four corners of the thin film structure portion so as to straddle two adjacent sides of each side constituting the peripheral portion of the thin film structure portion.

  According to the said structure, the film thickness of the thin film structure part in the four corner vicinity improves by the said reinforcement member formed in the four corner vicinity of a thin film structure part, and the rigidity in the four corner vicinity of the said thin film structure part is improved. That is, even if there are defects near the four corners that cannot be selected by screening, the reduction in the fracture resistance is compensated by the rigidity of the reinforcing members formed near the four corners. On the other hand, there is no problem with respect to defects in portions other than the vicinity of the four corners where the reinforcing member is not formed because they are destroyed during screening and are accurately selected. Therefore, whatever the position where the defect enters, it is possible to suppress a reduction in the breakdown tolerance of the thin film structure portion due to the defect.

  Further, in the semiconductor sensor according to claim 1, for example, according to the invention according to claim 2, the reinforcing member is formed by a part of wiring constituting the resistor, thereby forming the resistor. Since it becomes possible to form a reinforcing member together with the process to perform, it becomes unnecessary to provide a new process for forming a reinforcing member, and an increase in man-hours can be suppressed.

  Further, in the semiconductor sensor according to claim 1, as in the invention according to claim 3, for example, the reinforcing member is formed as a dummy wiring electrically separated from the wiring configuring the resistor. Thus, since the resistor and the reinforcing member are thermally insulated, it is possible to improve the heat generation efficiency of the heat generator and to reduce power consumption.

  Further, in the semiconductor sensor according to claim 3, for example, according to the invention according to claim 4, the resistor is made of the same material and in the same layer as the resistor, thereby forming the resistor. Since the reinforcing member as the dummy wiring can be formed together with the forming step, an increase in man-hours can be suppressed.

  Moreover, in the semiconductor sensor according to any one of claims 1 to 4, in forming the reinforcing member, for example, according to the invention according to claim 5, each side constituting the peripheral portion of the thin film structure portion is formed. It is effective to form a region from the end to “¼” of the length of the same side as the vicinity of the four corners.

  As a result of the experiment by the inventor, it has been confirmed that, among the stresses applied to the thin film structure part at the time of screening, the region where the screening effect cannot be expected is from the end of each side to a length of “1/4”. Yes. For this reason, by providing a reinforcing member with a region from the end of each side of the thin film structure portion to a length of “¼” in the vicinity of the four corners, it is possible to suppress a decrease in fracture resistance with a necessary and sufficient reinforcing member. Will be able to.

  In addition, as a semiconductor sensor in any one of Claims 1-5, like the invention of Claim 6, for example, in the thin film structure part, as the resistor, a heating element, and the vicinity of the heating element A flow sensor in which a temperature sensing element for detecting temperature is formed can be employed.

  Hereinafter, an embodiment in which a semiconductor sensor according to the present invention is applied to a flow sensor used in a flow meter for detecting an intake air amount of an in-vehicle internal combustion engine will be described with reference to FIGS. Note that the same reference numerals are used for elements having the same functions as those of the conventional flow sensor described above, and the detailed description thereof is omitted.

  FIG. 1 shows the overall structure of the flow sensor of the present embodiment. As shown in FIG. 1, the flow sensor FS includes a semiconductor substrate 10. On the semiconductor substrate 10, an upstream heater Rha, a downstream heater Rhb, an upstream thermometer Rka, and a downstream thermometer Rkb are formed by patterning the conductor film 20. The upstream heater Rha, the downstream heater Rhb, the upstream thermometer Rka, and the downstream thermometer Rkb are connected to the signal generation circuit SG and the pads P1 to P6 shown in FIG. They are connected via bonding wires W1 to W6.

  The semiconductor substrate 10 has a cavity H. The hollow portion H is opened in a rectangular region indicated by a one-dot chain line in FIG. 1 on the back surface side of the semiconductor substrate 10, and the opening area is reduced toward the upper surface side of the semiconductor substrate 10, The upper surface of the semiconductor substrate 10 is formed in the shape of a rectangular region indicated by a broken line in FIG. A thin film structure MB is formed on the cavity H, and an upstream heater Rha and a downstream heater Rhb are formed so as to bridge the cavity H. The thin film structure MB is formed to be thinner than other parts of the flow sensor FS, so that the heat capacity is kept low, and thermal insulation from other parts of the flow sensor FS is prevented. Secured.

  FIG. 2 shows a cross-sectional structure of the thin film structure portion taken along line AA shown in FIG. As shown in FIG. 2, the conductor film 20 constituting the upstream heater Rha and the downstream heater Rhb is laminated on the semiconductor substrate 10 so as to be sandwiched between the lower insulating film 30 and the upper insulating film 40. The thin film structure MB is formed on the cavity H by the conductor film 20, the lower insulating film 30, and the upper insulating film 40. The lower insulating film 30 and the upper insulating film 40 are made of a silicon nitride film, a silicon oxide film or the like, and the conductor film 20 is made of a metal film such as platinum (Pb) or n-type or p-type polysilicon (PolySi). . Further, a back film 50 made of, for example, a silicon nitride film is formed on the back side of the semiconductor substrate 10.

  In the flow sensor FS having such a configuration, screening for selecting and removing defective thin film structures is performed. Hereinafter, the stress distribution of the thin film structure MB during the screening will be described. In the present embodiment, a method of uniformly applying pressure to the entire surface of the thin film structure MB using air or oil is adopted, and the periphery of the thin film structure MB at the time of screening is used. FIG. 3 shows the stress distribution along one side.

  As shown in FIG. 3, when a uniform pressure is applied to the thin film structure MB, the stress is greater at the center of each side constituting the peripheral edge of the thin film structure MB, and from the center toward the four corners. Stress is reduced. In particular, in the region from the four corners (ends of each side) of the thin film structure part MB to the length of “1/4” of the length of one side, the stress is not expected to have a screening effect.

  Therefore, in the present embodiment, a region from the end of each side where the stress decreases to a length of “¼” is defined as a four-corner region (near the four corners), and the four-corner region is reinforced. Specifically, as shown in FIG. 1, a part of the conductor film 20 constituting the upstream heater Rha, the downstream heater Rhb, and the like is provided in the four corner regions. The conductor film 20 provided in the four corner regions is formed in such a manner as to straddle two adjacent sides of each side constituting the thin film structure part MB. As a result, the four corner regions where the conductor film 20 is formed are configured to be thicker than the other portions, and the conductor film 20 functions as a reinforcing member in the four corner regions of the thin film structure MB. It will be.

Next, a manufacturing method of the flow sensor FS will be described.
First, an insulating film made of a silicon nitride film, a silicon oxide film, or a composite film of these is laminated on the semiconductor substrate 10 by, for example, chemical vapor deposition (CVD) to form the lower insulation serving as a base film. A film 30 is formed.

  Next, a metal film made of platinum, n-type or p-type polysilicon or the like is laminated on the lower insulating film 30. Then, this metal film is etched to form patterns of the upstream heater Rha, the downstream heater Rhb, the upstream thermometer Rka, and the downstream thermometer Rkb, and at the portions corresponding to the four corner regions of the thin film structure MB. Etching is performed so that the metal film remains. Thereby, the conductor film 20 of the aspect shown by FIG. 1 is formed.

  Next, the upper insulating film 40 is formed by laminating an insulating film made of a silicon nitride film, a silicon oxide film, or a composite film thereof on the lower insulating film 30 on which the conductor film 20 is formed. Then, the upper insulating film 40 is etched to form contacts leading to the lead portions L1 to L6 of the conductor film 20, and the pads P1 to P6 are formed by forming and etching an aluminum layer thereon. To do.

  Next, a silicon nitride film or the like is formed on the back surface of the semiconductor substrate 10 by plasma CVD, and only the region where the thin film structure MB is to be formed is etched to form the back film 50. Then, the cavity H and the thin film structure MB are formed by etching the semiconductor substrate 10 with a potassium hydroxide solution (KOH solution) using the back film 50 as a mask. Thus, the flow sensor FS is manufactured. In this embodiment, when the thin film structure MB is formed, the semiconductor substrate 10 is etched without leaving the semiconductor substrate 10, but a certain amount of the semiconductor substrate 10 is left in consideration of the rigidity of the thin film structure MB. It may be.

  And after manufacturing the said flow sensor FS, the said flow sensor FS and the said signal generation circuit SG (FIG. 8) are electrically connected by the bonding wires W1-W6. Thereby, a flow meter is manufactured.

As described above, according to the present embodiment, the effects listed below can be obtained.
(1) A part of the conductor film 20 is formed in the four corner regions of the thin film structure MB so as to extend over two adjacent sides of each side constituting the peripheral edge of the thin film structure MB. For this reason, the film thickness of the thin film structure MB in the four corner regions is improved by the conductor film 20, and thus the rigidity in the vicinity of the four corners of the thin film structure MB is increased. That is, even when there is a defect in the four corner regions that cannot be selected by screening, a reduction in the breakdown resistance is compensated by the rigidity of the conductor film 20 formed in the four corner regions. On the other hand, the defects except for the four corner regions where the conductive film 20 is not formed are broken down at the time of screening and are accurately selected. Therefore, whatever the position where the defect enters, it is possible to suppress a decrease in the breakdown tolerance of the thin film structure MB due to the defect.

  (2) Further, since the four corner regions are reinforced by using a part of the conductor film 20 constituting the upstream heater Rha and the like, the upstream heater Rha and the downstream heater Rhb and the like are also combined in the patterning process. Thus, a part of the conductor film 20 can be formed in the four corner regions. Therefore, it is not necessary to provide a new process for reinforcing the four corner regions, and an increase in man-hours can be suppressed.

  (3) A region from the end of each side constituting the peripheral portion of the thin film structure MB to a length of “¼” of the side is defined as a four-corner region, and the four-corner region is reinforced using the conductor film 20. It was. That is, the four corner regions where the screening effect cannot be expected are reinforced using the conductor film 20. For this reason, it is possible to suppress a decrease in the breakdown resistance of the thin film structure MB with the necessary and sufficient conductor film 20.

In addition, the said embodiment can also be changed and implemented as follows.
In the above embodiment, the case where only the four corner regions of the thin film structure MB are reinforced by a part of the conductor film 20 has been described. For example, as shown in FIG. As for the two sides extending along the line, it is not necessary to etch the conductor film 20 in forming the upstream heater Rha and the downstream heater Rhb. Therefore, these two sides may be reinforced using the conductor film 20. Good. The point is that the conductor film 20 may be formed in the four corner regions of the thin film structure MB so as to extend over the two adjacent sides of the peripheral edge of the thin film structure MB.

  In the above embodiment, the four corner regions of the thin film structure MB are reinforced using a part of the conductor film 20 constituting the upstream heater Rha, the downstream heater Rhb, etc., for example, as shown in FIG. As described above, the dummy wirings DH may be formed in the four corner regions of the thin film structure MB to reinforce the four corner regions. When this configuration is adopted, the same effect as in the above embodiment can be obtained, and the upstream heater Rha, the downstream heater Rhb, and the dummy wiring DH are thermally insulated from each other. In addition, the heat generation efficiency of the downstream heater Rhb can be improved, thereby contributing to the reduction of power consumption. Note that, when the four corner regions are reinforced by the dummy wirings DH, an increase in man-hours can be suppressed by forming the dummy wirings DH using the same material and the same layer as the conductor film 20.

  As shown in FIG. 6, when reinforcing the four corner regions of the thin film structure MB, the reinforcement by the dummy wiring DH and the reinforcement by a part of the conductor film 20 can be combined. At this time, the lead portions L2 and L3 and the lead portions L4 and L5 are electrically connected by adopting a configuration in which two regions near the pads P1 to P6 among the four corner regions are reinforced by the dummy wiring DH. The dummy wiring DH can be easily formed using the boundary portion to be separated.

  In the above embodiment, the conductor film 20 constituting the upstream heater Rha, the downstream heater Rhb, etc. is sandwiched between the lower insulating film 30 and the upper insulating film 40, but the lower side of the conductor film 20 as necessary. Alternatively, an intermediate layer made of an insulating film may be formed on the upper side or both sides. Here, when an intermediate layer is provided below the conductor film 20, the adhesion of the conductor film 20 can be improved by the intermediate layer, and the cavity H is formed by etching the semiconductor substrate 10. It can be used as a stopper film when performing. On the other hand, when an intermediate layer is provided on the upper side of the conductor film 20, the step on the surface of the thin film structure MB due to the conductor film 20 can be reduced, so that the flow of the fluid that is the detection target of the flow rate and the flow direction is inhibited It becomes difficult to do.

  In the above embodiment, the region of “¼” from the four corners of the thin film structure MB is reinforced by the conductor film 20 as four corners (near the four corners), but the rigidity required for the thin film structure MB The size of the four corner regions may be appropriately changed according to the above.

  In the above embodiment, the upstream heater Rha and the downstream heater Rhb function not only as a heating element but also as a temperature sensing element. However, the upstream heater Rha and the downstream heater Rhb are different from the above. The present invention may be applied to a flow sensor that is provided with a warm body and functions only as a heating element with respect to the upstream heater Rha and the downstream heater Rhb.

  In the above embodiment, the flow sensor having the upstream heater Rha and the downstream heater Rhb in the thin film structure MB is shown. For example, the thin film structure of the conventional flow sensor (FIG. 9) described above, etc. The present invention may be applied to a flow sensor having another thin film structure.

  In the above embodiment, the flow sensor is shown as the semiconductor sensor. However, the present invention is not limited to the flow sensor as long as it is a semiconductor sensor having a thin film structure such as a membrane diaphragm.

The top view which shows the whole structure of a flow sensor as one Embodiment of the semiconductor sensor concerning this invention. Sectional drawing of the thin film structure part of the said flow sensor at the time of cut | disconnecting along the AA line shown in FIG. The graph which shows the stress distribution concerning the thin film structure part of the said flow sensor at the time of screening. The top view which shows the modification of the thin film structure part of the flow sensor of the embodiment. The top view which shows another modification of the thin film structure part of the flow sensor of the embodiment. The top view which shows another modification of the thin film structure part of the flow sensor of the embodiment. The top view which shows the whole structure of the conventional flow sensor. The circuit block diagram of the conventional flow meter. The top view which shows the thin film structure part of the conventional flow sensor.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Semiconductor substrate, 20 ... Conductor film, 30 ... Lower insulating film, 40 ... Upper insulating film, 50 ... Back surface film, DH ... Dummy wiring, FS ... Flow sensor, H ... Cavity, L1-L6 ... Bonding wire, MB Thin film structure, P1 to P6, pad, Rha, upstream heater, Rhb, downstream heater, Rka, upstream thermometer, Rkb, downstream thermometer, SG, signal generation circuit.

Claims (6)

In a semiconductor sensor comprising a resistor in a rectangular thin film structure formed on a semiconductor substrate and measuring a predetermined physical quantity using the resistor,
Reinforcing members are formed near the four corners of the thin film structure portion so as to straddle two adjacent sides of each edge constituting the peripheral portion of the thin film structure portion. The semiconductor sensor according to claim 1, wherein the reinforcing member is formed by a part of a wiring constituting the resistor. The semiconductor sensor according to claim 1, wherein the reinforcing member is formed as a dummy wiring that is electrically separated from a wiring configuring the resistor. The semiconductor sensor according to claim 3, wherein the reinforcing member is made of the same material as the resistor and is formed in the same layer. 5. The reinforcing member is formed from the end of each side constituting the peripheral portion of the thin film structure portion to “¼” of the length of the side as the vicinity of the four corners. The semiconductor sensor according to item. The semiconductor sensor according to any one of claims 1 to 5, wherein the resistor is configured as a flow sensor formed in the thin-film structure as a heating element and a temperature sensing element that senses a temperature in the vicinity of the heating element.

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