JP4134881B2 - Semiconductor acceleration sensor - Google Patents

Description

  The present invention relates to a semiconductor acceleration sensor that detects acceleration applied by converting stress into an electrical signal, and more particularly to a semiconductor acceleration sensor having excellent temperature characteristics.

  As this type of background art, for example, there is one proposed in Japanese Patent Laid-Open No. 2000-187040 (Patent Document 1), which is shown in FIG. FIG. 3A is an overall schematic plan view thereof, and FIG. 3B is a schematic cross-sectional view taken along line AA.

  This is formed of a semiconductor substrate made of silicon, and includes a support part 110, a bending part 120, a weight part 130, and a cut groove 140.

  The support part 110 supports the weight part 130, and is formed in a substantially rectangular shape in plan view. In addition, the inner side is opened in a substantially quadrangular shape in which each side is parallel to the peripheral edge of the support portion 110, and the support portion 110 is configured as a frame as a whole.

  The bending portion 120 is interposed between the support portion 110 and the weight portion 130 to suspend and support the weight portion 130, and is formed in a strip shape in a plan view, so that the thickness thereof has elasticity. It is formed in a thin shape. In addition, this is integrally formed with the support part 110 and protrudes inward from the upper surfaces of the four sides constituting the support part 110, and intersects and intersects near the inner center of the support part 110. Part 111 is configured.

  In addition, a plurality of piezoresistors (not shown) are formed in the vicinity of the intersection portion 111 and the support portion 110 on the surface of the bending portion 120. Here, the direction parallel to any one side of the support part 110 is defined as the X axis, the direction parallel to the other side intersecting the X axis at an angle of 90 ° is defined as the Y axis, and both the X axis and the Y axis. When the direction intersecting at an angle of 90 ° is the Z-axis, these piezoresistors are a set of four corresponding to the X-axis, Y-axis, and Z-axis in order to detect acceleration acting in the respective axial directions. As a Wheatstone bridge.

  The weight part 130 is idled according to the magnitude of the acting acceleration, and changes the amount of bending of the bending part 120. In other words, the force received by the weight part 130 is derived from Newton's equation of motion. In other words, the bending portion 120 is bent. This is located in the inner space of the support part 110 and supported by being suspended by the bending part 120, and its shape is on the lower surface (below FIG. 3B) in the thickness direction of the support part 110. It has a trapezoidal shape that becomes narrower in width, and has a substantially square shape in plan view.

  The cut groove 140 relieves stress generated when the support portion 110 and the upper cap (not shown) and the support portion 110 and the lower cap (not shown) are joined, and the shape thereof is in a cross-sectional view. It is formed in a V shape. In addition, a plurality of these are formed on each side of the support part 110, and are formed in a direction parallel to the bending part 120 integrated with each side. In addition, one end in the longitudinal direction of the cut groove 140 reaches the periphery of the support portion 110.

Therefore, according to the semiconductor acceleration sensor having the above-described configuration, when the support portion 110 and the upper cap and the support portion 110 and the lower cap are joined using anodic bonding, due to the difference in the linear expansion coefficient between the support portion 110 and each cap. Since the generated stress can be absorbed by the cut groove 140, the distortion generated in the bent portion 120 can be reduced and the temperature characteristics can be improved.
JP 2000-187040 A

  However, since such a semiconductor acceleration sensor has the cut groove 140 formed by anisotropic etching that depends on the crystal orientation of the semiconductor substrate using KOH or the like, its depth depends on the size and the breaking strength of the semiconductor acceleration sensor. It will be limited by. Therefore, there is a possibility that the stress generated at the joint portion, particularly the stress generated at the corner of the support portion 110, may be transmitted to the inner peripheral edge of the support portion 110 and act on the flexure portion 120. In situations where characteristics are required, accuracy may be insufficient.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a semiconductor acceleration sensor having improved temperature absorption characteristics and excellent temperature characteristics.

In order to achieve the above object, a semiconductor acceleration sensor according to a first aspect of the present invention comprises a semiconductor substrate having a first main surface and a second main surface, and includes a support portion having an inward opening and a base end portion. An elastic beam portion provided on the first main surface side of the support portion and extending in the opening, a weight portion that is suspended and supported by the beam portion and freely movable, and is provided on the beam portion and functions. A piezoresistor whose resistance value changes according to the acceleration to be performed, and the second main surface side of the support portion is provided so as to divide at least the second main surface, and the base end of the beam portion from the corner of the support portion And a relaxation means for absorbing the stress transmitted to the part , the semiconductor substrate is constituted by an SOI substrate, and the relaxation means is a concave body whose depth is drilled to the insulating layer of the SOI substrate. It is characterized by this.

According to this, when the second main surface side of the support portion is joined to another member, the stress transmitted from the joint portion, particularly the stress transmitted from the corner of the support portion where the stress is concentrated is transmitted. The path can be divided by the relaxation means to improve the stress absorption efficiency . Further, the depth of the relaxation means can be provided to almost the entire area in the thickness direction of the support portion, and silicon can be used as the depth control means. and since insulating layers having different etch rate is the etching stopper, Ru can suppress variation in depth of the relieving means.

  According to the semiconductor acceleration sensor of the present invention, the stress transmission efficiency can be improved by dividing the transmission path of the stress transmitted from the second main surface side of the support portion by the buffering means by the relaxation means. It is possible to improve the temperature characteristics by reducing the influence of the bending portion on the stress caused by the temperature change due to the difference in coefficient.

  Further, by using an SOI substrate as the semiconductor substrate, a concave body having a depth up to almost the entire region in the thickness direction of the support portion can be formed as a buffer means, and the depth of the concave body can be controlled by an insulating layer. Therefore, the variation in the depth of the buffer means can be suppressed, and as a result, the temperature characteristic can be improved and the variation in the temperature characteristic can be suppressed.

[First Embodiment]
The semiconductor acceleration sensor according to the first embodiment will be described with reference to FIG. FIG. 1A is a schematic perspective view thereof, and FIG. 1B is a schematic bottom view thereof.

In the semiconductor acceleration sensor of this embodiment, for example, an SOI substrate in which an active layer 13 made of silicon is laminated on a support layer 11 made of silicon (Si) via an insulating layer 12 made of, for example, silicon dioxide (SiO ₂ ). 1 is formed by processing a supporting part 2, a beam part 3, a weight part 4, a piezoresistor 5 and a relaxation means 6 as main components.

  Among these, the support part 2 becomes a base body of a semiconductor acceleration sensor, and supports the weight part 4 via the beam part 3. This is a frame having an inner side of the SOI substrate 1 and formed in a substantially square shape in plan view. The support portion 2 is composed of a support layer 11, an insulating layer 12, and an active layer 13, and the surface of the support layer 11 is connected to the piezoresistor 5, for example, from aluminum (Al). An electrode (not shown) is formed.

  The beam part 3 is suspended and supported so that the weight part 4 moves freely according to the acting acceleration. This is composed of the active layer 13 of the SOI substrate 1 and protrudes inwardly with the vicinity of the approximate center of each side of the support portion 2 as a base end portion 31, and in the vicinity of the center of the support portion 2. They are integrated with each other through the intersection 21. Further, the beam portion 3 has a strip shape in plan view, and has a thickness substantially equal to that of the active layer 13. In this embodiment, the thickness of the active layer 13 is set to about 5 μm, and at such a thickness, the beam portion 3 functions as an elastic body that is flexible in accordance with the acting acceleration.

  The weight portion 4 is guided according to the magnitude of the acting acceleration and changes the amount of bending of the beam portion 3. This is constituted by the support layer 11 of the SOI substrate 1, and is composed of a main weight portion 41 and four auxiliary weight portions 42.

  Among these, the main weight portion 41 is coupled to the lower surface of the intersecting portion 21 via the insulating layer 12. The shape thereof is a substantially square shape in plan view, the thickness thereof is substantially the same as the thickness of the support layer 11 of the support portion 2, and the lower surface of the main weight portion 41 forms the same plane as the lower surface of the support portion 2. .

  On the other hand, the auxiliary weight part 42 is formed integrally with each of the four corners of the main weight part 41, and is adjacent to the auxiliary weight part 42 when viewed from the active layer 13 side of the SOI substrate 1 in a state where acceleration is not applied. It forms so that it may be located in the area | region enclosed by the beam part 3 which fits, and the edge | side of the support part 2 which supports the beam part 3. FIG. The shape thereof is a substantially square shape in plan view, and the thickness thereof is substantially the same as that of the main weight portion 41.

  The piezoresistor 5 converts the amount of bending when the beam portion 3 is deformed by stress into an electric signal. This is formed on the surface of the beam portion 3, and more specifically, is disposed in the vicinity of the coupling portion between the beam portion 3 and the support portion 2 and in the vicinity of the coupling portion between the beam portion 3 and the intersection portion 21. Among these, the piezoresistor 5 in the vicinity of the intersection 21 responds to acceleration having a vector component in a direction parallel to the side of the support 2, for example, in a direction parallel to any one side of the support 2. When the X axis is defined and the direction perpendicular to the X axis and parallel to the side of the support portion 2 is defined as the Y axis, a set of Wheatstones is formed by four piezoresistors 5 on the support portion 2 parallel to the X axis. A bridge is formed, and a set of Wheatstone bridges is formed by four piezoresistors on the support portion 2 parallel to the Y axis. Furthermore, the piezoresistor 5 in the vicinity of the support portion 2 responds to acceleration having a vector component in a direction orthogonal to the X axis and the Y axis. For example, if this direction is defined as the Z axis, The four piezoresistors 5 in FIG. 1 constitute a set of Wheatstone bridges.

  The relaxing means 6 relaxes the stress generated by the difference in linear expansion coefficient when the support portion 2 is joined to a pedestal (not shown), a package (not shown) or the like. A concave body is connected to the outer peripheral edge and the other end is connected to the inner peripheral edge of the support portion 2. This is formed on the lower surface of the support portion 2, and the position thereof is orthogonal to the longitudinal direction of the side of the support portion 2 in the vicinity of the approximate center between the corner of the support portion 2 and the beam portion 3. It is arranged. Further, the relaxing means 6 is formed so that the depth of the concave body is substantially equal to the support layer 11 of the support portion 2 and the width parallel to the longitudinal direction of the side of the support portion 2 is about 10 μm. Each side of the portion 2 is divided between the corner of the support portion 2 and the beam portion 3. Thereby, the active layer 13 which comprises the support part 2 is comprised by the substantially square continuous cyclic | annular body, and the insulating layer 12 and the support layer 11 are divided | segmented by the relaxation means 6, and are comprised by eight lump bodies. It will be.

  Next, the manufacturing method will be described.

First, an SOI substrate 1 having a thickness of about 400 μm for the support layer 11, about 0.5 μm for the insulating layer 12, and about 5 μm for the active layer 13 is used for each layer. An oxide film made of silicon dioxide (SiO ₂ ) is formed.

  Next, a piezoresistor 5, a diffusion wiring (not shown), a metal wiring (not shown), and an electrode (not shown) are formed on the active layer 13. Among these, the piezoresistor 5 and the diffusion wiring are formed by first removing the oxide films at predetermined positions of the beam portion 3 and the support portion 2. For example, when the active layer has an n-type conductivity type, the conductivity type is A p-type impurity, for example, boron (B) is implanted into the support layer 11 using an ion implantation method or a deposit diffusion method. Subsequently, the impurity is thermally diffused for about 30 minutes in a mixed gas of water vapor and oxygen heated to about 1100 ° C. to finish the process.

  On the other hand, the metal wiring and electrode are formed by removing the oxide film at a predetermined position on the diffusion wiring to form a contact hole (not shown), and for example, aluminum (Al) on the oxide film of the active layer 13. Are stacked using a sputtering method. Subsequently, after applying a photoresist (not shown), patterning into a predetermined shape is completed.

Next, a photoresist is applied to the support layer 11, and the photoresist at the part that becomes the boundary between the support part 2 and the weight part 4 and the part that becomes the relaxation means 6 is removed, and inductively coupled plasma etching (ICP) is used. The support layer 11 is removed by etching until it reaches the insulating layer 12, thereby forming a concave body constituting the support portion 2, the weight portion 4, and the relaxing means 6. At this time, for example, sulfur hexafluoride (SF ₆ ) is used for the ICP.

  Next, a photoresist is applied to the active layer 13, the photoresist in a region surrounded by the adjacent beam portion 3 and the support portion 2 is removed, and the active layer 13 is etched using ICP to form an opening 22. To do.

  Finally, for example, a solution of hydrofluoric acid (HF) is sprayed in the form of a mist, and the insulating layer 12 that contacts the support layer 11 of the support portion 2 and the insulating layer 12 that contacts the main weight portion 41 of the weight portion 4. Etching is performed on the insulating layer 12 in other areas except for the weight portion 4 so as to be freely movable, thereby completing the semiconductor acceleration sensor.

  Thereafter, the semiconductor acceleration sensor can be used as an acceleration sensor device by being joined to a pedestal or package and electrically connected to the outside.

Here, for example, when the semiconductor acceleration sensor is bonded to a pedestal made of glass, the linear expansion coefficient of silicon (Si) constituting the semiconductor acceleration sensor is about 2.6 × 10 ⁻⁶ / K, and the linear expansion coefficient of the pedestal is Since it is about 2.8 × 10 ⁻⁶ / K, a stress is generated due to the difference in the linear expansion coefficient as the environmental temperature changes. However, according to the semiconductor acceleration sensor of the present embodiment, since the transmission path is divided by the concave body formed as the relaxation means 6 in the support portion 2 from the stress, particularly from the corner of the support portion where the stress is concentrated. The transmitted stress can be absorbed efficiently, and the influence of the beam portion 3 can be reduced to improve the temperature characteristics. In addition, since the semiconductor acceleration sensor is realized using the SOI substrate 1, the depth of the concave body can be provided equivalent to the thickness of the support layer 11, and the insulating layer 12 can be used as an etching stopper. Variations in the depth of the concave body can be suppressed, and as a result, variations in temperature characteristics of the semiconductor acceleration sensor can be suppressed.

  The relaxation means 6 is not limited to the one provided so as to be orthogonal to the longitudinal direction of the side of the support part 2. For example, the relaxation means 6 may be provided so as to cross obliquely. If the angle can be divided, the intersecting angle can be appropriately changed in design. Further, the formation position is not limited to the vicinity of the approximate center between the corners of each side of the support portion 2 and the beam portion 3, and can be arbitrarily selected. Moreover, if the space between the corners of each side of the support part 2 and the beam part 3 can be divided, a plurality of relaxation means 6 may exist between them.

[Second Embodiment]
A semiconductor acceleration sensor according to a second embodiment will be described with reference to FIG. FIG. 2 (a) is a schematic perspective view thereof, and FIG. 2 (b) is a schematic bottom view thereof.

  In the semiconductor acceleration sensor of the present embodiment, the predetermined portion of the support portion 7 is different from that of the first embodiment, and other components are substantially the same as those of the first embodiment. Are given the same numbers and their explanation is omitted.

  The support portion 7 of this embodiment differs from that of the first embodiment in a portion 71 sandwiched between the relaxing means 6 and including the proximal end portion 31 of the beam portion 3 in a plan view from the support layer 11 side. . This portion 71 is formed by removing the outer edge side thereof by etching and making it thinner than the width near the corner of the support portion 7, and the support layer 11 does not bend due to the weight of the weight portion 4 or the acting acceleration. The degree is set.

  Therefore, according to the semiconductor acceleration sensor of the present embodiment, since the transmission path is divided by the concave body formed as the relaxing means 6 in the support portion 7 from the stress, the stress is concentrated particularly from the corner of the support portion where the stress is concentrated. The transmitted stress can be efficiently absorbed, and the stress received directly by the portion 71 including the proximal end portion 31 of the beam portion 3 in the support portion 2 can be reduced, and the temperature characteristics can be further improved. Can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS The semiconductor acceleration sensor which concerns on the 1st Embodiment of this invention is shown, (a) is the schematic perspective view, (b) is the schematic bottom view seen from the support layer. The semiconductor acceleration sensor which concerns on the 2nd Embodiment of this invention is shown, (a) is the schematic perspective view, (b) is the schematic bottom view seen from the support layer. A conventional semiconductor acceleration sensor is shown, (a) is a schematic plan view thereof, and (b) is a schematic cross-sectional view taken along line AA.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 SOI substrate 12 Insulating layer 2 Support part 22 Opening part 3 Beam part 31 Base end part 4 Weight part 5 Piezoresistive 6 Relaxation means

Claims (2)

A semiconductor substrate having a first main surface and a second main surface;
A support that opens inward;
A beam portion having elasticity and extending in the opening by providing a base end portion on the first main surface side of the support portion;
A weight part that is suspended and supported by the beam part and freely movable;
Piezoresistor whose resistance value changes according to the acceleration applied and acting on the beam,
And a relaxation means that is provided on the second main surface side of the support portion so as to divide at least the second main surface and absorbs stress transmitted from the corner of the support portion to the base end portion of the beam portion. and it will be,
The semiconductor acceleration sensor according to claim 1, wherein the semiconductor substrate is an SOI substrate, and the relaxation means is a concave body having a depth drilled to an insulating layer of the SOI substrate . 2. The semiconductor acceleration sensor according to claim 1, wherein the semiconductor substrate is an SOI substrate, and the buffer means is a concave body having a depth drilled to an insulating layer of the SOI substrate.

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