JP2016176741A - Acceleration sensor and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an acceleration sensor having a beam part the thickness of which varies to thereby prevent variation in amount of deflection in the beam part and is capable of outputting stable signals, and to provide a manufacturing method thereof.SOLUTION: The acceleration sensor has a beam part 12a, which includes: an active layer 20c formed over the upper face of the base layer 20a being interposed by an oxide film layer 20b; a first insulator layer 20d formed over the upper face of the active layer 20c; and a first metal layer 200b formed over the upper face of the first insulator layer 20d. The surface roughness of the lower plane of the beam part 12a: Ra=0.01 μm or less.SELECTED DRAWING: Figure 7

Description

  The present invention relates to an acceleration sensor used in a vehicle or the like and a manufacturing method thereof.

  FIG. 10 is a side sectional view of the conventional acceleration sensor 1.

  In FIG. 10, a conventional acceleration sensor 1 includes a weight portion 2, an outer frame portion 3, a beam portion 4 having one end connected to the outer frame portion 3 and the other end connected to the weight portion 2, and a weight portion 2. The upper substrate 8 connected to the outer frame portion 3 so as to oppose, the self-diagnosis electrode 7 formed on the upper surface of the weight portion 2, and the upper substrate 8 formed at a position facing the self-diagnosis electrode 7 It was comprised with the counter electrode 6. FIG.

  As a prior art document related to the invention of this application, for example, Patent Document 1 is known.

JP-A-6-148230

  However, in the conventional acceleration sensor 1 described above, when the thickness of the beam portion 2 changes, the bending amount of the beam portion 2 changes, and as a result, the output signal of the acceleration sensor 1 changes. Was.

  The present invention solves the above-described conventional problems, and provides an acceleration sensor with a stable output signal and a method for manufacturing the same, in which the amount of bending of the beam portion does not vary due to the change in the thickness of the beam portion. It is intended.

  According to the first aspect of the present invention, an active layer is provided on the upper surface of the base layer via an oxide film layer, a first insulating layer is provided on the upper surface of the active layer, and an upper surface of the first insulating layer is further provided. A frame portion provided with a first metal layer, a beam portion having one end connected to the frame portion, the base layer, the oxide film layer, the active layer, and the first insulating layer, and a detection portion provided on the upper surface; And a weight portion connected to the other end of the beam portion and provided with the base layer, the oxide film layer, the active layer, and the first insulating layer, and the surface roughness of the lower surface of the beam portion is set to Ra = 0. It is set to 01 μm or less.

  According to this configuration, since the surface roughness of the lower surface of the beam portion is small, the amount of change in the thickness of the beam portion is small, and thus the amount of deflection of the beam portion does not fluctuate. Has the effect of stabilizing.

  According to a second aspect of the present invention, after the first insulating layer is formed on the upper surface of the active layer in the base layer in which the active layer is provided in advance through the oxide film layer, the first insulating layer is formed on the upper surface of the first insulating layer. Forming a first metal layer, forming a second insulating layer on the top surface of the first metal layer, and then forming a second metal layer on the top surface of the second insulating layer; Forming a resist film at a predetermined position of the base layer and then removing the base layer and the oxide film layer; and forming a resist film at a predetermined position of the active layer and then removing the active layer. And a protective film is formed on the lower surface of the active layer before removing the active layer. According to this method, the protective film formed on the lower surface of the active layer has an effect of preventing the lower surface of the beam portion from being roughened during etching.

  According to a third aspect of the present invention, the step of removing the active layer includes a step of repeating etching and deposition, and the gas flow rates of the etching and deposition are substantially equal. For example, the lower surface of the beam portion can be prevented from becoming rough during etching, and the lower surface of the beam portion can be protected by deposition.

  In the acceleration sensor of the present invention, an active layer is provided on the upper surface of the base layer via an oxide film layer, a first insulating layer is provided on the upper surface of the active layer, and a first metal is provided on the upper surface of the first insulating layer. A frame portion provided with a layer; a beam portion having one end connected to the frame portion, the base layer, the oxide film layer, the active layer, and the first insulating layer; and a detection portion provided on an upper surface; A weight portion connected to the other end and provided with the base layer, the oxide film layer, the active layer, and the first insulating layer is provided, and the surface roughness of the lower surface of the beam portion is Ra = 0.01 μm or less. It is. According to this configuration, since the surface roughness of the lower surface of the beam portion is small, the amount of change in the thickness of the beam portion 2 is small, and thus the amount of deflection of the beam portion 2 does not fluctuate. This has the effect of providing a stable acceleration sensor.

1 is an exploded perspective view of an acceleration sensor according to an embodiment of the present invention. Top view of the detection element of the acceleration sensor Side view of the acceleration sensor Circuit diagram showing the detection circuit of the acceleration sensor Side sectional view of a contact portion formed on the upper surface of the base layer through the active layer in the acceleration sensor Manufacturing process diagram of acceleration sensor in one embodiment of the present invention Manufacturing process diagram of the acceleration sensor Manufacturing process diagram of the acceleration sensor The figure which shows the surface roughness of the back surface of the beam part in the sensor of the same acceleration Cross-sectional view of a conventional acceleration sensor

  Hereinafter, an acceleration sensor according to an embodiment of the present invention will be described with reference to the drawings.

  1 is an exploded perspective view of an acceleration sensor according to an embodiment of the present invention, FIG. 2 is a top view of a detection element in the acceleration sensor, FIG. 3A is a cross-sectional view taken along line AA ′ of FIG. b) is an enlarged view of the detection element 20 of FIG.

As shown in FIGS. 1, 2, and 3, the acceleration sensor 10 includes a detection element 20, an upper lid 30 connected to the upper surface of the detection element 20, and a weight portion provided on the lower surface of the detection element 20. The surface roughness of the lower surface of the beam portion is Ra = 0.01 μm or less.
The detection element 20 includes a support substrate 12, a weight portion 13, a first beam portion 14a and a second beam portion 14b, one end of which is connected to the support substrate 12 and the other end of which is connected to the weight portion 13, and a weight. A self-diagnosis electrode 16 formed on the upper surface of the portion 13 and a ground electrode 18 formed on the support substrate 12 are provided.

  Here, the support substrate 12 is located on the outer peripheral side of the detection element 20, and the shape thereof is formed in, for example, a substantially rectangular frame shape. The weight 12 in the detection element 20 is surrounded by a frame 12 a extending from the support substrate 12. In addition, a first beam portion 14 a and a second beam portion 14 b are provided inside the support substrate 12.

  Each of the first beam portion 14 a and the second beam portion 14 b has one end connected to the support substrate 12 and the other end connected to the weight portion 13. Although FIG. 1 shows a structure having a pair of beams, the present invention is not limited to this. For example, a structure in which the weight portion 13 is supported by one or three beam portions may be used.

  The weight portion 13 is connected to the tips of the first beam portion 14 a and the second beam portion 14 b and is located inside the support substrate 12. Further, a groove surrounding the weight portion 13 is provided between the weight portion 13 and the support substrate 12. Thereby, a gap is formed between the weight portion 13 and the support substrate 12, and the weight portion 13 is supported by the first beam portion 14a and the second beam portion 14b so as to be displaceable in the Z-axis direction. .

  The detection element 20 includes a base layer 20a made of silicon, an oxide film layer 20b made of an insulating layer of a silicon oxide film on the base layer 20a, an active layer 20c that is a silicon layer on the oxide film layer 20b, and an active layer 20c. And a first insulating layer 20d provided thereon.

  The upper lid 30 includes a counter electrode 17 formed at a position facing the self-diagnosis electrode 16. Moreover, the detection part 14c is formed on the 1st beam part 14a, and the detection part 14d is formed on the 2nd beam part 14b. The self-diagnosis electrode 16 is connected to the electrode pad on the support substrate 12 via the wiring on the first beam portion 14a and the second beam portion 14b.

  Further, the support substrate 12, the weight portion 13, the first beam portion 14a, the second beam portion 14b, and the upper lid 30 can be made of silicon, fused quartz, alumina, or the like. Preferably, by using silicon, a small acceleration sensor can be obtained by using a fine processing technique.

  In addition, as a method for bonding the support substrate 12 and the upper lid 30, bonding with an adhesive, metal bonding, room temperature bonding, anodic bonding, or the like can be used. Among these, an adhesive such as an epoxy resin or a silicon resin is used as the adhesive. By using a silicon-based resin as the adhesive, the stress due to the curing of the adhesive itself can be reduced.

  As the detection units 14c and 14d, a strain resistance method can be used. The sensitivity of the acceleration sensor 10 can be improved by using a piezoresistor as the strain resistance. Moreover, the temperature characteristic of the acceleration sensor 10 can be improved by using a thin film resistance method using an oxide film strain resistor as the strain resistance method.

  FIG. 4 is a circuit diagram showing a detection circuit of the acceleration sensor 10.

  R1 is a resistor corresponding to the detector 14c, R4 is a piezoresistor corresponding to the detector 14d, and R2 and R3 are reference piezoresistors provided on the support substrate 12. As shown in FIG. 4, R1, R2, R3, and R4 are connected in a bridge shape, and a voltage is applied between a pair of opposing connection points Vdd and GND to detect a change in voltage between Vout1 and Vout2. Thus, the acceleration applied to the acceleration sensor 10 can be detected.

  In the above configuration, when acceleration in the Z-axis direction acts on the acceleration sensor 10, the weight portion 13 is swung by the inertial force (external stress) acting on the weight portion 13, and the beam portion is distorted and deformed due to this. . As a result, stress is applied to the detection units 14c and 14d. Thereby, since the resistance value of the piezoresistor changes according to the external stress due to acceleration, the current flowing through the piezoresistor also changes according to the resistance value. For this reason, the acceleration (inertial force) acting on the detection element 20 can be detected by using the current flowing through the piezoresistor as a detection signal.

  Returning to FIG. 3, the lower lid 40 has a recess 41 in a portion facing the weight portion 13. The lower lid 40 is formed using a silicon material. The upper lid 30 is also formed using a silicon material.

Hereinafter, the self-diagnosis function will be described with reference to FIGS.
As shown in FIG. 3, when performing a self-diagnosis, a voltage V is applied between the self-diagnosis electrode 16 and the counter electrode 17 from the diagnosis circuit. As a result, an electrostatic force is generated between the self-diagnosis electrode 16 and the counter electrode 17, and the weight portion 13 is attracted to the upper lid 30. Due to the displacement of the weight part 13, the resistance R1 corresponding to the detection part 14c and the resistance R4 corresponding to the detection part 14d are lowered. Therefore, the output voltage Vout of the bridge circuit is detected and it can be confirmed that the bridge circuit is operating normally.

  FIG. 5 is a side sectional view of another contact portion formed on the upper surface of the base layer of the acceleration sensor according to one embodiment of the present invention via an active layer.

  In the contact portion 11, a first metal layer 200b made of, for example, chromium or an alloy containing chromium is provided in the first opening 20f provided in the first insulating layer 20d. The first metal layer 200b serves as an adhesion layer for preventing the active layer 20c from interdiffusing into the second metal layer 200a. In order to insulate the first metal layer 200b from the second metal layer 200a, a second insulating layer 20e is provided. Further, as shown in FIG. 2, the second metal layer 200a is connected to the ground electrode 18 provided in the detection element 20 via the wiring 18a.

  With this configuration, even if the weight 13 is charged during self-diagnosis, the charge is activated in the active layer 20c in the weight 13, the active layer 20c in the beams 14a and 14b, and the contact 11 in the frame 12a. Since it can be dropped to the ground via the layer 20c, the first metal layer 200b, the second metal layer 200a, the wiring 18a, and the ground electrode 18, for example, an electric field is generated in the space formed by the active layer 20c and the counter electrode 17 Can be suppressed, and as a result, the electrostatic force for operating the weight portion 13 is stabilized and normal self-diagnosis can be performed.

  Thus, in the contact portion 11b when the first metal layer 200b is provided, the first opening 20f provided in the first insulating layer 20d and the second opening provided in the second insulating layer 20e. 20g is provided at the same position. The second opening 20g provided in the second insulating layer 20e is preferably larger than the first opening 20f provided in the first insulating layer 20d. (That is, in FIG. 5, D2 <D1, or the second opening 20g provided in the second insulating layer 20e is perpendicular to the first opening 20f rather than the first opening 20f provided in the first insulating layer 20d. In this configuration, the contact resistance between the second metal layer 200a and the first metal layer 200b can be reduced, and charging of the weight portion 13 can be more efficiently suppressed.

  Below, an example of the manufacturing process of the contact part formed in the upper surface of the base layer of this embodiment example through an active layer is demonstrated based on FIG.

  First, as shown in FIG. 6A, a first insulating layer 20d is formed on the surface of the active layer 20c. The first insulating layer 20d protects the surface of the active layer 20c and insulates the active layer 20c. For example, when an oxide film such as SiO2 is formed as the first insulating layer 20d, the first insulating layer 20d is formed by oxidizing the surface portion of the active layer 20c by, for example, a thermal oxidation method.

  Next, as shown in FIG. 6B, a first opening 20f is formed at a predetermined position of the first insulating layer 20d. The first opening 20f can be formed using, for example, a photolithography technique. That is, first, a resist film is formed on the entire surface of the first insulating layer 20d, and then a resist other than the contact hole formation region is utilized using a contact hole formation position regulating mask disposed above the resist film. The film portion is cured by ultraviolet irradiation. Then, the uncured portion of the resist film, that is, the resist film portion in the contact hole formation region is removed, and a hole reaching the first insulating layer 20d is formed in the resist film. Thereafter, the portion of the first insulating layer 20d at the position where the hole portion of the resist film is formed is removed through the hole portion of the resist film by, for example, a dry etching method or a wet etching method to form a contact hole. Thereafter, the resist film is removed by, for example, an ashing technique. In this way, the first opening 20f can be formed using the photolithography technique.

  Next, as shown in FIG. 6C, a first metal layer 200b as an adhesion layer is formed. This metal layer is also formed on the entire surface of the first insulating layer 20d by a film formation technique such as sputtering.

  Next, as shown in FIG. 6D, a second insulating layer 20e is formed on the surface of the first metal layer 200b. The second insulating layer 20e protects the surface of the first metal layer 200b, and is formed on the surface of the second insulating layer 20e. The electrode made of Vdd, GND, Vout1, and Vout2 shown in FIG. A piezoresistor R1 corresponding to the detector 14c, a piezoresistor R4 corresponding to the detector 14d, piezoresistors R2 and R3 provided on the support substrate 12, and a wire connecting them to form a bridge circuit, and a first metal This is for insulating the layer 200b.

  When a SiN film is formed as the second insulating layer 20e, the second insulating layer 20e is stacked on the first metal layer 200b by, for example, a CVD (Chemical Vapor Deposition) method.

  Next, as shown in FIG. 6E, a second opening 20g is formed at a predetermined position of the second insulating layer 20e. The second opening 20g can also be formed by using the photolithography technique described above.

  Next, as shown in FIG. 6F, a second metal layer 200a is formed. The second metal layer 200a is also formed on the entire surface of the second insulating layer 20e by a film formation technique such as sputtering.

  Next, as shown in FIG. 7A, after forming a resist film (not shown) at a predetermined position of the second metal layer 200a, dry etching is performed until the active layer 20c remains. The second metal layer 200a, the second insulating layer 20e, and the first metal layer 200b are removed.

  Next, as shown in FIG. 7B, after the wafer is mounted upside down, a resist film (not shown) is formed at a predetermined position on the lower surface of the base layer 20a, and further, dry etching is performed. Then, the base layer 20a is removed, and the oxide film layer 20b is removed by wet etching.

  Next, as shown in FIG. 7C, a protective film 220 is formed on the lower surfaces of the active layer 20c and the base layer 20a.

  Next, as shown in FIG. 7D, after attaching the wafer upside down, a resist film (not shown) is formed at a predetermined position of the active layer 20c, and further dry etching is performed. The active layer 20c is penetrated.

  Here, considering the case where the manufacturing conditions for removing the active layer 20c are adjusted, in the conventional acceleration sensor manufacturing method, when the etching is repeated several tens of times, the etching gas flow rate is set to 400 [sccm]. In addition, the deposition gas flow rate was set to 150 [sccm]. Therefore, as shown in FIG. 8A, the etching gas flows to the lower surface of the active layer 20c, and a rough portion 210 having a surface roughness Ra = 0.57 [μm] is formed on the lower surface of the active layer 20c. It has occurred. For this reason, the thickness of the first beam portion 14a and the second beam portion 14b is reduced, and the first beam portion 14a and the second beam portion 14b are easily bent.

  In the acceleration sensor manufacturing method according to one embodiment of the present invention, before removing the active layer, a protective film is formed on the lower surface of the active layer, and the etching gas flow rate is set to 300 [sccm]. Since the gas flow rate at the position is substantially equal to 300 [sccm], the etching gas flows into the lower surfaces of the first beam portion 14a and the second beam portion 14b to reduce the surface roughness of the rough portion 210. It has the effect of being able to.

  That is, as shown in FIG. 9, the surface roughness Ra = 0.01 [μm] can be set on the lower surface of the active layer 20c by changing the etching gas flow rate as compared with the conventional one.

  Further, by forming a protective film 220 on the lower surfaces of the active layer 20c and the base layer 20a, as shown in FIG. 8B and FIG. 9, the surface roughness Ra = 0.005 [μm] of the rough portion 210. Until it is reduced.

  The acceleration sensor and the manufacturing method thereof according to the present invention have an effect that it is possible to provide an acceleration sensor with a stable output signal in which the amount of bending of the beam portion does not vary due to the change in the thickness of the beam portion. It is useful as an acceleration sensor used in vehicles and the like.

12a Frame part 13 Weight part 14a First beam part 14b Second beam part 14c, 14d Detection part 20a Base layer 20b Oxide film layer 20d, 20e Insulating layer 20c Active layer 200a, 200b Metal layer 210 Rough part 220 Protective film

Claims (3)

An active layer is provided on the upper surface of the base layer via an oxide film layer, a first insulating layer is provided on the upper surface of the active layer, and a first metal layer is provided on the upper surface of the first insulating layer; A beam portion having one end connected to the frame portion, the base layer, the oxide film layer, the active layer, and the first insulating layer and a detection portion provided on the upper surface; and the other end of the beam portion; An acceleration sensor comprising: a weight portion provided with the base layer, an oxide film layer, an active layer, and a first insulating layer, wherein the surface roughness of the lower surface of the beam portion is Ra = 0.01 μm or less. Forming a first insulating layer on the upper surface of the active layer in the base layer previously provided with the active layer via the oxide film layer, and then forming a first metal layer on the upper surface of the first insulating layer; Forming a second insulating layer on the upper surface of the first metal layer, and then forming a second metal layer on the upper surface of the second insulating layer; and forming a resist film at a predetermined position of the base layer And removing the base layer and the oxide film layer, and forming a resist film at a predetermined position of the active layer and then removing the active layer, and before the active layer is removed, A method of manufacturing an acceleration sensor in which a protective film is formed on the lower surface of the layer. 3. The method of manufacturing an acceleration sensor according to claim 2, wherein the step of removing the active layer includes a step of repeating etching and deposition, and the gas flow rates of the etching and deposition are substantially equal.

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