JP2008224525A - Triaxial acceleration sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce initial offsets having small offset fluctuations, into an area and at low cost of a manufactured triaxial acceleration sensor. <P>SOLUTION: The triaxial acceleration sensor has a frame section and a spindle section formed in first and second layers; a beam section formed in the first layer, and having two pairs of beams for supporting the spindle within the frame; a semiconductor piezoelectric element provided in the beam section; and wiring for connecting them. A frame protrusion and a spindle protrusion, protruded toward the center of the beam section rather than connection ends of the beam section, are formed on a plane opposite to a plane of the second layer for connecting the first layer at both ends of the beam section. Since shapes of etching grooves match at both ends of the beam section, it is easy to match shapes of connections, and fluctuations in the output due to a stress can be reduced. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a semiconductor acceleration sensor for detecting acceleration used in automobiles, aircraft, portable terminal devices, toys and the like.

Accelerometers are often used for air bag operation and capture the impact of automobile collision as acceleration. In automobiles, the 1-axis or 2-axis function was sufficient to measure the X-axis and Y-axis accelerations. Further, since the acceleration to be measured is very large, an acceleration sensor element for detecting the acceleration is also sturdily manufactured. Recently, it is often used for portable terminal devices, robots, and the like, and a three-axis acceleration sensor for measuring X-, Y-, and Z-axis accelerations has been required in order to detect spatial movement. In addition, it is required to be small with high resolution in order to detect minute acceleration.

Acceleration is a method of converting the movement of the flexible part into an electrical signal. It is roughly divided into a piezoresistive type, a capacitance type, and a piezoelectric type. The sensor output size, response frequency characteristics, electromagnetic noise resistance, and output linearity It is selected considering the detection of static acceleration, temperature characteristics, etc. Since microfabrication is required due to the demand for small size and high sensitivity, a piezoresistive three-axis acceleration sensor that forms a piezoresistor by forming a shape on a silicon substrate using photolithography technology and implanting impurities into silicon using semiconductor technology is put to practical use Has been.

The applicant has filed a large number of applications regarding a piezoresistive element type three-axis acceleration sensor. Patent Document 1 to Patent Document 6 clarify the shape of the weight portion, the shape of the beam portion, the arrangement of the piezoresistive elements, the connection method of the piezoresistive elements, the shape of the joint between the beam portion and the frame portion, and the like. 9 is an exploded perspective view of the triaxial acceleration sensor, FIG. 10a) is a cross-sectional view in the hh ′ direction of FIG. 9, and FIG. 10b) is a plan view of the sensor chip. In the triaxial acceleration sensor 20, the sensor chip 2 and the regulating plate 3 are fixed to the case 1 with an adhesive 16 such as resin at a predetermined interval. The chip terminal 4 of the sensor chip 2 is connected to the case terminal 6 by a wire 5, and the sensor signal is taken out from the external terminal 7. A case lid 8 is fixed to the case 1 with an adhesive 17 such as AuSu solder and sealed. A triaxial acceleration sensor element 9 is formed on the sensor chip 2. The triaxial acceleration sensor element 9 includes a beam portion 12 that forms a pair with a square frame portion 10 and a weight portion 11.
1 is held in the center of the frame portion 10 by two pairs of beam portions 12. A piezoresistive element is formed on the beam portion 12. An X-axis piezo 13 and a Z-axis piezo 15 are provided for one pair of beams, and Y is provided for the other pair of beams.
A shaft piezo 14 is formed. The distance g4 between the lower surface of the weight part 11 and the inner bottom surface of the case 1 and the distance g3 between the upper surface of the weight part 11 and the regulating plate 3 in FIG. The amount of movement of the portion 11 is restricted to prevent the beam portion 12 from being damaged. Since the basic structure of the piezoresistive element type three-axis acceleration sensor of the present application is the same as those of these patent documents, detailed description will be omitted unless otherwise specified.

As a manufacturing method of the above three-axis acceleration sensor element, since the thickness of the beam portion needs to be processed with high accuracy, a thin silicon layer is laminated on the surface of a thick silicon layer via a silicon oxide film layer. In general, an SOI (Silicon on Insulator) wafer is used. The thickness of the thin silicon layer is obtained by using the silicon oxide film layer as an etching stop and processing the shape of the beam part etc. in the thin silicon layer, then processing the groove in the thick silicon layer to separate the frame part and the weight part. A structure in which the weight portion is supported by the frame portion by the beam portion can be manufactured.

JP 2003-172745 A Japanese Patent Laid-Open No. 2003-279592 JP 2004-184373 A JP 2006-098323 A JP 2006-098321 A WO2005 / 062060 A1

In a piezoresistive element type three-axis acceleration sensor, both a downsizing and high sensitivity can be achieved by providing a notch in the weight and connecting a beam to the notch. For example, Patent Literature 7 to Patent Literature 10 describe the acceleration sensor having such a structure. The typical structure is shown in FIG.
Shown in The sensor chip 21 has a notch in the portion of the weight portion 11 to which the beam portion 12 is connected. Thereby, even if the weight part 11 is formed inside the frame part 10, the length of the beam part 12 can be increased, and a sensor with high sensitivity can be obtained even in a small area.

Japanese Patent Laid-Open No. 11-214705 JP 2002-296293 A JP 2003-101032 A JP-A-9-237902

By arranging the beam along the diagonal of the sensor chip, both miniaturization and high sensitivity can be achieved.
For example, Patent Documents 8 and 11 describe the acceleration sensor having such a structure. By arranging the beams on the diagonal line, the length of the beams can be increased, and the sensitivity can be increased even with the same chip area.

JP 2006-170962 A

In the acceleration sensor described in Patent Document 12, the base of the beam portion is connected to the frame portion and the weight portion through a connection region having the same thickness as the beam portion. Thereby, even when an excessive acceleration is applied, it is possible to make it difficult to break at the root of the beam.

JP 2004-198280 A

If the conventional acceleration sensor has a structure in which the thin base portion of the beam portion is directly connected to the thick weight portion and the frame portion, the stress is concentrated on the base portion of the beam portion, so that there is a problem that impact resistance is lowered. Therefore, it has been devised to provide a connection region having the same thickness as the beam portion in the frame portion and the weight portion. If the connection region is sufficiently wider than the beam portion, the connection area between the weight portion and the frame portion can be increased, and the impact resistance is improved. This structure is described in detail in Patent Document 12.

However, the shape of the connection region has a considerable influence on the characteristics of the sensor. On the surface of the beam and connection area, there are wiring that connects the piezoresistive elements, insulation between the wiring and the silicon layer, or an insulating film for protecting the piezoresistive elements, and a protective film on the wiring. It is formed. A metal material such as aluminum is used for the wiring, and a silicon oxide film or a silicon nitride film is used for the insulating film or the protective film. Because these materials have different coefficients of thermal expansion from silicon,
When the temperature rises during film formation and then returns to room temperature, a large stress is generated. Since the weight portion and the frame portion are thick, they are hardly deformed even by such stress, but the beam portion and the connection region have the same thickness and are thin, so that deformation occurs. Since the deformation of the connection region also affects the deformation of the continuous beam portion, the stress generated in the piezoresistive element is also affected. Since the piezoresistive element is arranged near the base of the beam part where the stress changes greatly, there is a possibility that the stress balance of the piezoresistive elements on both sides may change if the shape of the connection region on the weight side and the frame side is different. . In the conventional acceleration sensor, the acceleration is detected by the balance change of the bridge circuit composed of the piezoresistive elements arranged at the four bases of the beam portion to be paired. When the initial stress of the film is changed and the stress of the film fluctuates,
This also causes the offset to fluctuate.

In order to suppress the variation of the offset, it is desirable to process the shape of the connecting portion at both ends of the beam, but it is not easy in practice. When the SOI is used, a groove that separates the weight portion and the frame portion is processed by dry etching from the back surface of the thick silicon layer (the surface opposite to the bonding surface with the thin silicon layer). A weight portion is formed. At this time, there is a problem in that the etching gas concentration is not constant and the processing speed is different at portions where the pattern shapes of the processing grooves are different. At the root of the beam part, the shape of the connection area at both ends of the beam part is determined by the end point position of the etching process. There is a risk that the side and the frame side will not be the same. In the structure of the conventional example shown in FIG. 11, the shape of the processed groove pattern is an end portion of a notch shape on the weight side,
Since the frame side is different from the T-shape, the above problem is likely to occur. Such a change in the machining speed due to the difference in the shape of the machining groove can be reduced by extremely slowing the machining speed. However, since the cost increases due to an increase in work time, it is not practical to use in the mass production process.

It is an object of the present invention to solve the above-described problems and to realize an acceleration sensor with small variations and fluctuations in characteristics at a small size and at a practical cost.

The triaxial acceleration sensor of the present invention is composed of a first layer and a second layer, and is formed in a frame portion and a weight portion formed from the first layer to the second layer, and in the first layer, and the weight portion is placed in the frame portion. A three-axis acceleration sensor having a beam portion composed of two pairs of beams to be supported, a semiconductor piezoresistive element provided in the beam portion, and a wiring connecting them, the frame portion and the weight portion of the beam portion In the connection region, the frame-side protruding portion and the weight-side protruding portion protruding from the connecting end of the beam portion toward the center of the beam portion on both sides of the beam portion are at least the connection surfaces with the first layer of the second layer It is preferable that it is formed on the opposite surface.

In the processing method using the aforementioned SOI wafer, the thin silicon layer corresponds to the first layer and the thick silicon layer corresponds to the second layer. By providing a weight-side protrusion and a frame-side protrusion on the second layer surface (the surface opposite to the connection surface with the first layer) for starting the groove processing of the second layer, the shape of the groove on the frame-side is T-shaped. Without both, the connection part on the frame part side and the weight part side becomes the end of the groove, so that the processing pattern can be made similar,
Even on the inner surface of the second layer (the connection surface with the first layer), which is the end point of processing, the end positions are easily aligned on the weight side and the frame side.

In the triaxial acceleration sensor of the present invention, it is preferable that the frame side protrusion and the weight side protrusion have the same distance between the side facing the beam portion of the portion protruding on both sides of the beam portion on the frame side and the weight side. .

The widths of the groove patterns on the surface of the second layer on the frame portion side and on the weight portion side match, and the end shape on the inner surface of the second layer, which is the processing end, can be made more consistent.

In the triaxial acceleration sensor of the present invention, it is preferable that the beam portion is connected to the frame portion and the weight portion via a connection region formed wider in the first layer than the beam portion.

By providing the connection region, the area of the connection part between the weight part and the frame part can be made larger than when the beam part is directly connected, and the impact resistance is improved. The connection region can be formed by setting the position of the etching end portion of the inner surface of the second layer at the end portion of the beam portion to be outside the end portion position of the first layer. If the shape of the connection region at both ends of the beam portion is different, a difference in deformation due to the influence of the thin film stress occurs, and offset deviation and fluctuation are likely to occur. In the present invention, since the processing groove patterns at both ends of the beam portion are matched, the etching end position on the inner surface of the second layer can be matched at both ends, so that offset deviation and fluctuation hardly occur.

In the triaxial acceleration sensor of the present invention, it is preferable that the length protruding from the connection end of the beam portion is shorter in the frame side protruding portion than in the weight side protruding portion.

In order to completely match the processed groove patterns on both sides of the beam portion, it is preferable to make the protruding lengths along the beam longitudinal direction of the weight side protruding portion and the frame side protruding portion equal. If it is within the allowable range of the etching rate, the frame-side protruding portion can be shortened. Moreover, it is preferable to form a protrusion part more than the length as long as the protrusion part space | interval (distance between the side surfaces which a protrusion part opposes) of the both sides of a beam part. By shortening the length of the frame-side protruding portion, even if the size of the frame portion and the length of the beam portion are the same, the area of the weight portion can be increased and the sensitivity can be improved.

In the triaxial acceleration sensor of the present invention, it is preferable that the inside of the frame portion is substantially square and the beam portion is arranged along a diagonal line of the square.

When the beam part is arranged in a direction perpendicular or parallel to each side of the substantially square with respect to the substantially square frame part, when the frame side protruding part is formed in the frame part, the beam part protrudes from the frame part. In order to maintain the strength by ensuring the width of the part over a certain circumference, the size of the sensor chip is increased. Therefore, by arranging the beam portions in the diagonal direction, the projection of the beam portions to the frame portions can be arranged at the corners, so that the effect of the present invention can be obtained without increasing the sensor chip.

The connection portion between the beam portion, the frame portion, and the weight portion does not need to be at right angles, and the fracture resistance of the connection portion can be increased by adopting an arc shape or a chamfered shape.

According to the acceleration sensor of the present invention, since the dry etching processing speed can be made uniform and the shape of both ends of the beam portion can be made the same, the initial offset due to the stress of the film such as the insulating film or wiring, the time variation thereof, etc. And a small acceleration sensor excellent in impact resistance can be provided.

Hereinafter, the present invention will be described in detail based on examples with reference to the drawings. In order to make the explanation easy to understand, the same reference numerals are used for the same parts and parts.

The acceleration sensor according to the first embodiment of the present invention will be described below with reference to FIGS.
FIG. 1 shows the structure of the sensor chip of the acceleration sensor of the first embodiment, FIG. 1a) is a sectional view, FIG. 1b) is a plan view seen from the first surface of the sensor chip, and FIG. 2
It is the top view seen from the surface. FIG. 2 is a diagram illustrating the connection area. FIG. 2a) shows the first embodiment, and FIGS. 2b) to 2d) are modifications of this embodiment. FIG. 3 is an exploded perspective view of the connection region of the connection region, and shows the positional relationship between the frame portion, the weight portion, and the beam portion of the first layer and the second layer. The sensor chip 30 of FIG. 1 is a sensor chip in an acceleration sensor assembled as in the conventional example of FIG. 9, for example. The present invention is characterized by the structure of this sensor chip. This will be described in detail.

In the sensor chip 30 of the first embodiment, a weight portion 32 is supported in a frame portion 31 by a first beam portion 33a and a second beam portion 33b each formed of two beams. The first beam portion 33a and the second beam portion 33b are hereinafter collectively referred to as a beam portion 33. When the X and Y axes are set in the plane direction of the sensor chip 30 and the Z axis is set in the vertical direction, the X is placed on the first beam portion 33a formed along the X axis.
The Y-axis piezo 14 for detecting the Y-axis direction acceleration was formed on the second beam portion 33b formed along the Y-axis, and the X-axis piezo 13 of the piezoresistive element for detecting the axial acceleration. Z for Z-axis acceleration detection
The shaft piezo 15 may be on either beam portion, but in this embodiment, it is formed on the first beam portion 33a.
Four piezoresistive elements were formed in the vicinity of the base of the pair of beams for each axis, and connected by wiring not shown to constitute a bridge circuit. When the acceleration is applied, a force is applied to the weight portion 32 to be displaced, and the beam portion 33 is deformed to change the electric resistance of the piezoresistive element. 4 for each axis
The potential difference caused by the difference in resistance change between the two piezoresistive elements can be detected as an acceleration value by taking it out with a bridge circuit.

The manufacturing method and dimensional relationship of the acceleration sensor element will be briefly described. An SOI wafer having a silicon layer of about 1 μm and a silicon layer of about 6 μm on a silicon layer of about 400 μm thickness was used. The silicon oxide film layer was used as an etching stop layer for dry etching, and the structure was formed on two silicon layers. Hereinafter, the thinner silicon layer is referred to as the first layer 41, the thicker silicon layer is referred to as the second layer 42, and the surface of the first layer that is not bonded to the silicon oxide film layer is referred to as the first surface 43.
The surface of the second layer is referred to as a second surface 44, and the connection surface through the silicon oxide film layer is referred to as a third surface 45. Patterning was performed with a photoresist, and boron was implanted into the first layer at 1 to ³ × 10 ¹⁸ atoms / cm ³ to form a piezoresistive element. The wiring connected to the piezoresistive element was formed using a metal sputtering and dry etching apparatus. Next, after forming a photoresist mask on the first surface of the first layer, the shapes of the beam portion, the weight portion, and the frame portion were processed by dry etching. 2nd layer second
After forming a photoresist mask on the surface, the shapes of the weight portion and the frame portion were processed by dry etching. The silicon oxide film layer remaining between the first layer and the second layer was removed by wet etching. Since a large number of chips are produced on one wafer, the sensor chip 30 is obtained by singulation by dry etching or dicing.

As a feature of the present invention, the shape of the frame portion 31 and the weight portion 32 viewed from the second surface 44 is changed to the beam portion 3.
The frame-side protruding portion 35 and the weight-side protruding portion 36 are provided in the connection region between the three frame portions 31 and the weight portion 32. The frame-side protruding portion 35 is on the frame portion side of the beam portion 33, and the frame-side connection portion 37 of the beam portion 33.
It protrudes toward the weight portion 32 side. Similarly, the weight side protruding portion 36 is on the weight portion side of the beam portion 33, and protrudes toward the frame portion side (the center direction side in the longitudinal direction of the beam portion) from the weight side connection portion 38 of the beam portion 33.

In the acceleration sensor having the structure as in the present embodiment, the center of gravity of the weight portion 32 is sufficiently separated from the position of the beam portion 33 in order to obtain sufficient detection sensitivity for acceleration in the X-axis and Y-axis directions. Since it is necessary, the second layer 42 needs to be thick. When the thick second layer 42 is dry-etched, an error is likely to occur between the photoresist formation and the processing shape as the processing depth increases, and the processing groove end shape on the third surface 45 that is the processing end is The shape of the photoresist mask formed on the second surface 44 is different. In particular, as described above, there is a problem that the etching rate is different because the etching gas concentration is not constant at the portion where the shape pattern of the processed groove is different. When the etching rate is different, a difference occurs in the amount of overetching, so that the shape of the processing end portion of the frame portion 31 or the weight portion 32 is deviated from the desired shape.

In this embodiment, a frame side protrusion 35 is provided on the frame side, and a weight side protrusion 36 is provided on the weight side. The frame-side protruding portion interval a and the weight-side protruding portion interval b, which are distances between protruding portions protruding on both sides of the beam portion 33
Were set to the same value. The frame-side protruding portion length d and the weight-side protruding portion length e were also set to the same value. As a result, the processing groove shape patterns on the frame side and the weight side are made to coincide and the etching rate is made the same, so that the end shape on the third surface 45 can also be made to coincide. As a result, an acceleration sensor with little variation and fluctuation in characteristics was realized.

Further, the processing groove width c for separating the weight portion and the frame portion is also set to the same value as the frame side protruding portion interval a and the weight side protruding portion interval b, so that the etching rate can be made constant in the entire processing groove pattern. As a result, it is possible to reduce the over-etching and process with high accuracy.

FIG. 2 is a plan view for explaining the structure around the connection portion of the beam portion in more detail. The outline of each part on the first surface 43 is indicated by a solid line, and the outline on the third surface 45 is indicated by a dotted line. FIG. 2 a) shows the shape of the first embodiment, wherein the end shape of the processing groove on the frame side and the weight side is an arc shape, and the first surface 43 and the third surface 45 are external shapes on the side of the protruding portion. The lines match. Since the etching rate at the end of the processed groove decreases at the corner portion, even if the shape pattern on the second surface 44 is a straight line, the third surface 45 is likely to be arcuate, and the shape pattern on the second surface 44 is previously circular. It may be arcuate. In order for the side portions to roughly match, the second layer 42 is processed in consideration of the taper of the second layer 42.
The outer shape pattern of the surface 44 was formed closer to the beam portion 33 than the outer shape pattern of the first surface 43.

FIG. 3 shows an exploded perspective view of the connection region, and the frame portion 31 and the weight portion 32 of the first layer 41 and the second layer 42,
The positional relationship of the beam portion 33 is shown in an easily understandable manner. At the connection end portion of the beam portion 33, the processing end of the second layer 42 is located farther from the beam than the connection end of the beam, so the beam portion 33, the weight portion 32, and the frame portion 3.
1 and a connection region having a thickness of the first layer 41 is interposed therebetween. Although the processing end of the second layer 42 is a stress concentration portion, the connection area is increased by connecting via a connection region wider than the beam portion 33, and the structure is less likely to be damaged by impact.

In this embodiment, since the shape pattern of the machining groove is matched on the frame side and the weight side, the position of the machining end can be easily matched on the frame side and the weight side. It was possible to match. As a result, the deformation due to the stress of the insulating film and wiring formed on the surface of the connection region becomes the same on the frame side and the weight side, and the stress generated in the piezoresistor arranged near the root on the beam part is also on the weight side. Since the balance is achieved on the frame side, the amount of change in the balance of the bridge circuit for detecting acceleration can be minimized. Due to this effect, the amount of offset variation considered to be due to the change in the initial offset amount and the stress of the insulating film or wiring formed on the surface of the connection region can be reduced to about ½ of the conventional amount.

A silicon oxide film, a silicon nitride film, or the like is used as an insulating film or a protective film on the beam portion 33. Since these materials have a smaller coefficient of thermal expansion than silicon in the beam portion, when an insulating film or the like is formed on the upper surface of the beam portion at a high temperature and then returned to room temperature, the beam portion is deformed into a convex shape due to stress. Although metal materials such as aluminum and copper are used for the wiring, these metal materials have a larger coefficient of thermal expansion than silicon, so that the beam portion is deformed into a concave shape when the temperature rises. Since the connection region is subjected to such deformation, and these deformations extend over the entire beam portion, stress is also generated in the piezoresistive element formed on the surface of the beam portion. When the deformation amount of the connection region is different between the frame side and the weight side, the stress generated in the piezoresistive element on the frame side and the weight side becomes unbalanced, which causes a characteristic variation. In the present invention, since the shape of the connection region is the same on the frame side and the weight side, the beam portion 33 and the frame portion 31, and the beam portion 33 and the weight portion 32.
Since the connection conditions are the same, the amount of deformation in the connection region of the frame portion and the weight portion is the same, and the balance can be maintained at both ends of the beam portion.

The shape of the periphery of the connecting portion of the beam portion 33 is not limited to that shown in FIG.
The shape of d) can be taken. The shape of FIG. 2 b) in which the taper angle at the time of dry etching of the second layer is increased or the amount of overetching is increased so that the processing end is inserted from the outer shape of the first layer 41. As shown in FIG. 2c), the second layer 42 protrudes beyond the first layer at the side of the protrusion. The structure of FIG. 2d) in which the width of the tip of the processing groove is widened can be obtained.

In the first embodiment, the connecting portion between the beam portion 33 and the frame portion 31 and between the beam portion 33 and the weight portion 32 has a substantially arc shape, but is not limited thereto. The effects of the present invention can be obtained even with right angles, chamfered shapes, and irregular shapes. By adopting an arc shape or a chamfered shape, it is possible to increase the fracture strength at the connection portion.

A sensor chip according to a second embodiment of the present invention is shown in FIG. FIG. 4 shows the second sensor chip.
It is the top view seen from the surface 44 side. The difference from the first embodiment is that the frame-side protruding portion length d is shorter than the weight-side protruding portion length e. In the first embodiment, it is described that the processing groove pattern on the frame side and the weight side can be substantially matched by setting the frame side protrusion length d = the weight side protrusion length e. But,
By making the frame-side protruding portion length d longer than the frame-side protruding portion interval a, even if the weight-side protruding portion length e is larger than the frame-side protruding portion length d, the processing groove pattern on the frame portion side and the weight portion side Can be substantially matched. By reducing the frame-side protruding portion length d as in the present embodiment, the area of the weight portion 32 can be increased even if the size of the frame portion 31 and the length of the beam portion 33 are the same. I was able to improve.

FIG. 5 shows a sensor chip according to a third embodiment of the present invention. FIG. 5 shows the second sensor chip.
It is the top view seen from the surface 44 side. The difference between the first and second embodiments is that the outer contour line on the inner side of the frame portion 31 is spread outward and the outer contour line of the weight portion 32 is expanded outward along the outer contour line. In the first and second embodiments, the position of the front end of the frame-side protruding portion 35 is the position of the outer line inside the frame portion 31, and the beam-side connecting portion 37 protrudes into the frame portion 31. It was. In the present embodiment, in the portions other than the frame-side protruding portion 35 of the frame portion 31, the inner outline is extended to the same position as the beam-side connecting portion 37, and the weight portion 32 is also extended along with it. Thereby, the area of the weight part 32 can be enlarged while maintaining the minimum width dimension for maintaining the rigidity of the frame part 31, and the sensitivity can be further improved.

FIG. 6 shows a sensor chip according to a fourth embodiment of the present invention. FIG. 6 shows the second sensor chip.
It is the top view seen from the surface 44 side. The weight part 32 can be efficiently arranged by arranging the beam part 33 inside the substantially square frame part 31 in the diagonal direction of the square. The beam portion 33 was arranged at an angle of 45 degrees with respect to the inner outline 46 of the frame portion 31. Therefore, the frame side connection portion 37 of the beam portion 33 is in the center of the square side in the first to third embodiments, but in the square corner in this embodiment.

As shown in the third embodiment, when it is considered to arrange the weight portion 32 with an area as large as possible inside the frame portion 31, in this embodiment, the frame-side protruding portion 35 can be arranged at the corner. Thus, the weight portion 32 and the beam portion 33 can be efficiently arranged in the chip area, and the size of the sensor chip for realizing the acceleration sensor having the same sensitivity can be reduced.

The overall configuration of the acceleration sensor of the present invention is not limited to the configuration shown in FIG. As a fifth embodiment, an acceleration sensor in which wafer level packaging is applied to a sensor chip 30 will be described with reference to cross-sectional views of FIGS. As shown in FIG. 7, the first cap 70 and the second cap 71 were joined to the top and bottom of the sensor chip 30. First cap 70
The second cap 71 has a cavity 72 in the center, and is joined to the sensor chip 30 at the periphery. The joint portion is disposed outside the sensor element formation region of the sensor chip 30,
Therefore, the sensor element is protected in an airtight package surrounded by the first cap 70 and the second cap 71 so that the characteristics of the sensor element do not fluctuate due to the influence of humidity or foreign matter.

The first cap 70 and the second cap 71 have an appropriate interval between the sensor element weight part 32 and the beam part 33 by restricting the displacement of the weight part 32 when excessive acceleration is applied. Serves as a regulating plate to prevent damage. A chip protective film 73 is formed on the surface of the sensor chip 30.
The wiring 74 connecting the chip terminal 4 disposed outside the hermetic package and the piezoresistive element (not shown) is drawn from the bottom of the chip protective film 73 to the outside of the hermetic package. For the first cap 70 and the second cap 71, a silicon wafer was used, and the cavity 72 was processed by anisotropic etching or dry etching of silicon. The sensor chip 30 and the first cap 70 and the second cap 71 were joined at the wafer level, and after joining, the sensor chip package 75 was separated into individual pieces. The bonding method was Au / Sn solder bonding, and the width of the bonding portion was 60 μm. In addition, solder bonding and eutectic bonding of various metals, surface activated bonding, anodic bonding, low melting point glass bonding, and the like can be used. Since it is necessary to expose the chip terminal 4 when dividing into individual pieces, a cavity is formed in the upper region of the chip terminal 4 in the first cap 70, and only the first cap 70 is first dicing. The chip terminal 4 was exposed by cutting at the part 76. Then, sensor chip 30
The second cap 71 was cut into pieces by the second dicing part 77.

Since the sensor element is protected in an airtight package, an inexpensive plastic package that is generally used can be applied to the entire sensor package. A configuration example using a metal lead frame and resin sealing is shown in FIG. The IC chip 80 was bonded to the chip support plate 78 of the metal lead frame 85 with a first adhesive 79 made of resin, and the sensor chip package 75 was bonded to the IC chip 80 with a second adhesive 81 made of resin. Then, the chip terminal 4 of the sensor chip package 75, the IC terminal 82 of the IC chip 80, and the IC terminal 8
2 and the external terminal 83 of the metal lead frame 85 were connected by an Au wire 5 and then sealed with an epoxy sealing resin 84.

In this mounting structure using a wafer level package, a cap can be connected along the outer periphery of the sensor chip with a thin bonding width of, for example, about 60 μm, and fixing to the package can be performed via the cap. On the other hand, in the structure shown in FIG. 9, it is necessary to apply at least two resin adhesives on the sensor chip and connect the caps. As in the sensor chip shown in the fourth embodiment, in the structure in which the beams are arranged diagonally and the corners of the sensor chip are effectively used, it is difficult to secure the adhesive application area. Especially suitable.

It is sectional drawing which shows the structure of the sensor chip of a 1st Example, and the top view seen from the 1st surface side and the 2nd surface side. It is a top view of the beam part periphery seen from the 1st surface side. It is a disassembled perspective view of a connection area. It is the top view seen from the 2nd surface side of the sensor chip of a 2nd example. It is the top view seen from the 2nd surface side of the sensor chip of a 3rd example. It is the top view seen from the 2nd surface side of the sensor chip of the 4th example. It is sectional drawing which shows the structure of the sensor chip package of 5th Example. It is sectional drawing which shows the structure of the acceleration sensor of 5th Example. It is a perspective view which shows the whole structure of the conventional triaxial acceleration sensor. It is sectional drawing of the conventional triaxial acceleration sensor, and the top view of a sensor chip. It is a perspective view which shows the structure of the conventional sensor chip.

Explanation of symbols

1 case, 2 sensor chip,
3 Regulatory plate, 4 chip terminal,
5 wires, 6 case terminals,
7 External terminal, 8 Case lid,
9 3-axis acceleration sensor element, 10 frame part,
11 weight, 12 beam,
13 X-axis piezo, 14 Y-axis piezo,
15 Z-axis piezo, 16 first adhesive,
17 second adhesive, 20 triaxial acceleration sensor,
21 sensor chip, 30 sensor chip,
31 frame part, 32 weight part,
33 beam portion, 33a first beam portion,
33b 2nd beam part, 35 frame side protrusion part,
36 weight side protrusion, 37 frame side connection,
38 weight side connection part, 41 1st layer,
42 second layer, 43 first surface,
44 2nd surface, 45 3rd surface,
46 frame part inner outline, 70 first cap,
71 second cap, 72 cavities,
73 Chip protection film, 74 wiring,
75 sensor chip package, 76 first dicing part,
77 first dicing part, 78 chip support plate,
79 First adhesive, 80 IC chip,
81 first adhesive, 82 IC terminal,
83 external terminals, 84 sealing resin,
85 Metal lead frame.

Claims (5)

A frame portion and a weight portion formed from the first layer and the second layer, and formed from the first layer to the second layer, and two pairs of beams formed in the first layer and supporting the weight portion in the frame portion. And a semiconductor piezoresistive element provided on the beam portion, and a wiring for connecting the semiconductor piezoresistive elements. In a connection region between the frame portion and the weight portion of the beam portion, On both sides, a frame side protruding portion and a weight side protruding portion protruding toward the center of the beam portion from the connection end of the beam portion are formed at least on the surface opposite to the connection surface with the first layer of the second layer. A three-axis acceleration sensor. 2. The distance between the side surfaces of the frame-side protruding portion and the weight-side protruding portion that protrude from both sides of the beam portion and that face the beam portion is equal on the frame side and the weight side. Accelerometer. 3. The beam part according to claim 1, wherein the beam part is connected to the frame part and the weight part via a connection region formed wider in the first layer than the beam part. Axial acceleration sensor. The triaxial acceleration sensor according to any one of claims 1 to 3, wherein a length protruding from the connection end of the beam portion is shorter in the frame side protruding portion than in the weight side protruding portion. 5. The triaxial acceleration sensor according to claim 1, wherein the inside of the frame portion has a substantially square shape, and the beam portion is disposed along a diagonal line of the square.

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