JP2010210402A - Mems sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a MEMS sensor that prevents damage to a movable section and has improved durability. <P>SOLUTION: In the MEMS sensor for joining a sensor chip substrate, where the movable section that is operated mechanically and a sensor element for electrically detecting the displacement of the movable section are formed, to a base substrate with a gap from the movable section, a recess is provided along a portion of the outer periphery of the movable section on a substrate junction surface. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a MEMS sensor, and more particularly to a structure for preventing impact damage.

  In recent years, MEMS sensors using micro electro mechanical systems (MEMS) have attracted attention in many technical fields such as accelerometers, optical communications, and biomedical systems. In general, a MEMS sensor is provided with a gap between a movable part that can be mechanically operated and a sensor chip substrate in which a sensor element that electrically detects displacement of the movable part is formed by a semiconductor microfabrication technique, and the movable part. And a base substrate (support substrate) bonded to the sensor chip substrate. Specifically, such a MEMS sensor can be applied to an acceleration sensor, an angular velocity sensor, and a pressure sensor. For example, Patent Document 1 discloses that a bending portion including a central portion and a beam portion extending in all directions from the outer peripheral edge of the central portion, a weight portion suspended and supported by a central portion via a neck portion, and an inner periphery Disclosed is a semiconductor acceleration sensor having a frame-like frame formed by connecting a beam portion to a side surface, and a support member that supports the lower surface of the frame and surrounds the outer peripheral edge of the weight portion through a cut portion. Has been.

JP 11-311631 A

  The MEMS sensor having the conventional structure has a hollow structure having a gap between the movable portion of the sensor chip substrate and the base substrate. Therefore, when an impact is applied from the base substrate side due to dropping or the like, the movable portion receiving the impact energy. Resonated and the movable part might be damaged.

  An object of the present invention is to obtain a MEMS sensor excellent in durability by preventing breakage of a movable part based on the above problem awareness.

  The present invention reaches the conclusion that the cause of damage to the movable part is that the impact energy received from the base substrate side is uniformly transmitted from the periphery of the movable part toward the center of the movable part, and the movable part is likely to resonate. It has been completed.

  That is, the present invention provides a sensor chip substrate on which a mechanically operable movable part and a sensor element for electrically detecting the displacement of the movable part are formed, and a gap is provided between the movable part and the base substrate. In the MEMS sensor formed by bonding, a concave portion is provided along a part of the outer periphery of the movable portion on the bonding surface of the sensor chip substrate and the base substrate.

  For example, when the movable portion is formed in a rectangular shape in a plan view, the concave portions can be formed in an L shape in a plan view along the outer periphery of each corner portion of the rectangular shape in the plan view. Or you may form in a plane L shape in alignment with the outer periphery of this corner | angular part in a pair of corner | angular part which opposes 180 degrees of this planar view rectangle. Alternatively, it may be formed in a straight line shape in plan view along each side on the outer periphery of a pair of sides facing each other at 180 ° of the plan view rectangle.

  In the case of a MEMS sensor that holds the gap between the movable part and the movable part in a vacuum state, it is practical that the concave part is vacuum-sealed by joining the sensor chip substrate and the base substrate.

  According to the present invention, the impact energy transmitted from the base substrate side to the movable portion is different in phase in the peripheral direction of the movable portion via the recess and acts to cancel out at the center of the movable portion. Resonance can be suppressed. Thereby, damage of a movable part can be prevented and the MEMS sensor excellent in durability can be obtained.

It is sectional drawing (sectional drawing which follows the II line | wire of FIG. 3) which shows 1st Embodiment which applied the MEMS sensor of this invention to the semiconductor pressure sensor. It is sectional drawing (sectional drawing which follows the II-II line | wire of FIG. 3) which shows the semiconductor pressure sensor. It is a top view which shows the semiconductor pressure sensor, and has shown typically the positional relationship of the recessed part provided in the board | substrate joint surface, and a diaphragm (and cavity). It is a schematic diagram explaining the interference of the energy which arises in the recessed part provided in the board | substrate joint surface. It is 2nd Embodiment which applied the MEMS sensor of this invention to the semiconductor pressure sensor, Comprising: It is a top view which shows the modification of the recessed part provided in a board | substrate joint surface. It is 3rd Embodiment which applied the MEMS sensor of this invention to the semiconductor pressure sensor, Comprising: It is a top view which shows the modification of the recessed part provided in a board | substrate joint surface. It is sectional drawing which follows the VII-VII line of FIG. It is sectional drawing which shows 4th Embodiment which applied the MEMS sensor of this invention to the semiconductor acceleration sensor. It is a top view which shows the semiconductor acceleration sensor. It is a graph which shows the result of having measured the maximum principal stress concerning a movable part edge along the elapsed time about the Example 1 at the time of the fall of a MEMS sensor. It is a graph which shows the result of having measured the maximum principal stress concerning a movable part edge along the elapsed time about the comparative example 1 at the time of dropping of a MEMS sensor. It is a graph which shows the result of having measured the maximum principal stress concerning a movable part edge along the elapsed time about the comparative example 2 at the time of dropping of a MEMS sensor. It is the graph which frequency-resolved and represented the graph of FIG. 12 is a graph obtained by frequency-resolving the graph of FIG. 11. 13 is a graph obtained by frequency-resolving the graph of FIG. It is sectional drawing and top view explaining Example 1 which provided the recessed part located in the outer peripheral part of a diaphragm on the board | substrate joint surface used for the measurement of FIG. It is sectional drawing and a top view explaining the comparative example 1 which does not comprise a recessed part in the board | substrate joint surface used for the measurement of FIG. It is sectional drawing and top view explaining the comparative example 2 which provided the recessed part located in the outer periphery of a diaphragm on the board | substrate joint surface used for the measurement of FIG.

  1 to 4 show a first embodiment of the present invention. 1 and 2 are sectional views showing a first embodiment in which the MEMS sensor of the present invention is applied to a semiconductor pressure sensor, and FIG. 3 is a plan view.

  A semiconductor pressure sensor 101, which is a MEMS sensor, is a diaphragm type semiconductor pressure sensor that detects an absolute pressure, and includes a pressure detection diaphragm (movable part) 21 and a cavity (gap) 20 that are deformed by external pressure. And a base substrate 30 bonded to the sensor chip substrate 10 so that the cavity 20 is vacuum-sealed.

The sensor chip substrate 10 is an SOI (silicon-on-insulator) substrate in which a first silicon substrate 11 and a second silicon substrate 12 are bonded together via a silicon oxide film (SiO ₂ ) 13. The first silicon substrate 11 has a circuit formation surface (upper surface in FIGS. 1 and 2) in which a plurality of pressure sensitive resistance elements 22 are embedded as sensor elements for electrically detecting the displacement of the diaphragm 21 by a semiconductor microfabrication technique. Have. The circuit formation surface is covered with a silicon oxide film except for the position above the plurality of pressure sensitive resistance elements 22. On the silicon oxide film, wirings 23 (FIG. 3) and pads 24 (FIGS. 2 and 3) conducting to the respective pressure sensitive resistance elements 22 are provided. Further, the pressure sensitive resistance elements 22, the wirings 23, and the silicon oxide film are It is insulated and protected by a passivation film made of silicon nitride (Si ₃ N ₄ ) (not shown). The pad 24 is exposed from the passivation film and can be connected to an external measuring device. In the present embodiment, a piezoresistor is used as the pressure-sensitive resistor element 22, but the present invention is not limited to this.

  In the sensor chip substrate 10, the cavity 20 is formed by removing part of the second silicon substrate 12 and the silicon oxide film 13 from the second silicon substrate 12 side by dry etching, and constitutes the upper surface of the cavity 20. The diaphragm 21 is formed by the silicon oxide film 13 and the first silicon substrate 11. The central axis X of the cavity 20 and the diaphragm 21 coincides with the plane center O of the sensor chip substrate 10 and the base substrate 30. As shown in FIG. 3, the diaphragm 21 has a rectangular shape in plan view, and a plurality of pressure sensitive resistance elements 22 are arranged so as to cover each side of the rectangular outline of the diaphragm 21. The planar shape of the diaphragm 21 may be any other shape as long as it is distorted by pressure, and the number and arrangement of the pressure sensitive resistance elements 22 can be arbitrarily set.

  The base substrate 30 is a silicon substrate that supports the sensor chip substrate 10. The base substrate 30 faces the cavity 20 in the center of the substrate and is joined to the exterior package 35 by a resin adhesive 36 on the back surface 30b opposite to the front surface 30a to be joined to the second silicon substrate 12 at the periphery of the substrate. .

  As shown in FIGS. 2 and 3, the joint surface between the sensor chip substrate 10 and the base substrate 31 is positioned on the outer periphery of the diaphragm 21 having a rectangular shape in plan view, and is a plane along the four corners of the diaphragm 21. Each of the L-shaped concave portions 41 is provided. The recess 41 is formed by subjecting the sensor chip substrate 10 to dry etching or mechanical polishing from the second silicon substrate 12 side, and is sealed in a vacuum state by joining the sensor chip substrate 10 and the base substrate 30. Yes.

  When the diaphragm 21 is distorted in accordance with the pressure applied to the outer surface of the semiconductor pressure sensor 101, the resistance values of the plurality of pressure sensitive resistance elements 22 change according to the degree of distortion. The midpoint potential of the configured bridge circuit is output to the measuring device as a sensor output. The measuring device is connected to the semiconductor pressure sensor 101 mounted on the exterior package 35 via each pad 24, and can measure the pressure based on the output (change in midpoint potential) of the semiconductor pressure sensor 101. .

  When the semiconductor pressure sensor 101 receives an impact from the exterior package 35 side due to dropping or the like, the impact energy E is transmitted from the base substrate 30 to the sensor chip substrate 10 and travels from the periphery of the diaphragm 21 toward the center. In this energy propagation path, the impact energy E causes interference at the joint 40 between the sensor chip substrate 10 and the base substrate 30, as shown in FIG. Therefore, the impact energy E that has interfered is transmitted to the sensor chip substrate 10 in the portion where the recess 40 is formed, and the impact energy from the base substrate 30 is directly transmitted to the sensor chip substrate 10 as it is in the portion where the recess 40 is not formed. . That is, the impact energy E transmitted to the peripheral edge of the diaphragm 21 has a difference in energy amount and phase in the peripheral direction depending on the presence or absence of the recess 40 in the joint surface between the sensor chip substrate 10 and the base substrate 30. The impact energy E having a different phase cancels out from the periphery of the diaphragm 21 toward the center, so that the impact energy E actually received at the center of the diaphragm 21 is reduced, thereby suppressing the resonance of the diaphragm 21 due to the impact. be able to.

  FIG. 5 is a plan view showing a second embodiment in which the MEMS sensor of the present invention is applied to a semiconductor pressure sensor. In the semiconductor pressure sensor 201 according to the second embodiment, the joint surface of the sensor chip substrate 10 and the base substrate 30 is positioned on the outer periphery of the diaphragm 21 having a rectangular shape in plan view, and the diagonal direction of the diaphragm 21 is (180 °). Only a pair of opposing corners is provided with an L-shaped recess 42 in plan view surrounding the corner. Thus, even if the concave portion 42 is formed on the substrate bonding surface so as to correspond to the pair of corner portions of the diaphragm 21, the presence of the concave portion 42 changes the propagation path of the impact energy E received from the base substrate 30, so that the diaphragm The impact energy transmitted to the periphery of 21 is not uniform. Thereby, impact energy having different phases is canceled out at the center of the diaphragm 21, and resonance of the diaphragm 21 due to impact can be suppressed. The configuration other than the recess 42 is the same as that of the first embodiment, and a cross-sectional view of the semiconductor pressure sensor 201 shown by cutting along the II-II line in FIG.

  6 and 7 are a plan view and a cross-sectional view showing a third embodiment in which the MEMS sensor of the present invention is applied to a semiconductor pressure sensor. In the semiconductor pressure sensor 301 shown in the third embodiment, a pair of parallel sides of the diaphragm 21 is positioned on the outer periphery of the diaphragm 21 having a rectangular shape in plan view on the joint surface of the sensor chip substrate 10 and the base substrate 30. A concave portion 43 that is linear in a plan view is provided along (a pair of sides facing each other by 180 °). Thus, even if the recess 43 is formed on the substrate bonding surface so as to correspond to the pair of sides of the diaphragm 21, the propagation path of the impact energy E received from the base substrate 30 changes due to the presence of the recess 43. The impact energy transmitted to the periphery of is not uniform. Thereby, impact energy having different phases is canceled out at the center of the diaphragm 21, and resonance of the diaphragm 21 due to impact can be suppressed. The configuration other than the recess 43 is the same as that of the first embodiment.

  The four recesses 41 of the first embodiment, the pair of recesses 42 of the second embodiment, and the pair of recesses 43 of the third embodiment are rotationally symmetric with respect to the central axis X of the diaphragm 21, respectively. Instead, the presence of the recesses 41, 42, and 43 in a part of the outer periphery makes it possible to vary the phase and energy amount of impact energy transmitted to the diaphragm 21 in the peripheral direction.

  In the first to third embodiments, the recesses 41, 42, and 43 may be formed on the base substrate 30 side, or may be formed on both the sensor chip substrate 10 and the base substrate 31. Since the recesses 41, 42, and 43 can be formed at the same time as the cavity 20 if they are formed in the sensor chip substrate 10, it is preferable because manufacturing becomes easy.

  8 and 9 are a sectional view and a plan view showing a fourth embodiment in which the MEMS sensor of the present invention is applied to a semiconductor acceleration sensor 401. FIG. The semiconductor acceleration sensor 401 is a diaphragm type semiconductor acceleration sensor, and is a sensor that electrically detects a movable portion 421 that is bent by an inertial force of a weight 423 when acceleration is applied, and a bending amount of the movable portion 421. A sensor chip substrate 410 on which an element 422 is formed is provided.

  The movable portion 421 has a rectangular shape in plan view as a whole surrounded by the outer frame frame 410A of the sensor chip substrate 410, and has a central portion 421a in a rectangular shape in plan view located at the center thereof, and an outside of the central portion 421a. The beam portion 421b extends from the periphery to the outer frame frame portion 410A of the sensor chip substrate 410, and a weight 423 is suspended and supported on the central portion 421a. As shown in FIG. 9, the plurality of sensor elements 422 are arranged so as to cover each side of the rectangular outline of the central portion 421a. In this embodiment, a piezoresistor is used as the sensor element 422, but the present invention is not limited to this. The planar shape of the central portion 421a may be any other shape as long as it is distorted by the inertia force of the weight 423, and the number and arrangement of the sensor elements 422 can be arbitrarily set.

  A gap 425 is formed around the weight 423 by removing the sensor chip substrate 410 from its back surface (the surface opposite to the surface on which the sensor element 422 is formed) by dry etching. The sensor chip substrate 410 and the base substrate 430 are bonded in a state where the gap 425 is generated. The base substrate 430 is a silicon substrate that serves as a support substrate for the sensor chip substrate 410. The base substrate 430 is bonded and fixed to the exterior package 435 with a resin adhesive 436 on the surface opposite to the bonding surface with the sensor chip substrate 410. The central axis X of the movable portion 421 (center portion 421a) and the plane center O of the sensor chip substrate 10 and the base substrate 30 coincide.

  As shown in FIGS. 8 and 9, the joint surface between the sensor chip substrate 410 and the base substrate 430 is positioned on the outer periphery of the movable portion 421 having a rectangular shape in plan view, that is, on the outer frame frame portion 410A. A concave portion 441 having an L shape in plan view is provided to surround each of the four corners of the movable portion 421. The concave portion 441 is formed by subjecting the sensor chip substrate 410 to dry etching processing or mechanical polishing processing from the back side thereof, and is closed by joining the sensor chip substrate 410 and the base substrate 430.

  When acceleration is applied to the weight 423, the semiconductor acceleration sensor 401 bends the movable portion 421 interlocked with the weight 423, and outputs a plurality of sensor elements 422 according to the amount of the bend (if the sensor element 422 is a piezoresistor, the resistance value). ) Changes, and the midpoint potential of the bridge circuit constituted by the plurality of sensor elements 422 is output to the measuring device as a sensor output. The measuring device can measure acceleration based on the output (change in midpoint potential) of the semiconductor acceleration sensor 401.

  When the semiconductor acceleration sensor 401 receives an impact from the exterior package 435 side due to dropping or the like, the impact energy E is transmitted from the base substrate 430 to the sensor chip substrate 410 and goes from the periphery of the central portion 421a to the center via the beam portion 421b. . In this energy propagation path, the impact energy E causes interference in the sealed recess 441 at the joint surface between the sensor chip substrate 410 and the base substrate 430, as in the first embodiment. Therefore, the impact energy E that has interfered is transmitted to the sensor chip substrate 410 in the portion where the recess 441 is formed, and the impact energy E from the base substrate 430 is directly applied to the sensor chip substrate 410 as it is in the portion where the recess 441 is not formed. It is transmitted. That is, the impact energy E transmitted to the periphery of the movable part 421 (center part 421a, beam part 421b) has an energy amount and a phase in the peripheral direction depending on the presence or absence of the recess 441 at the joint surface between the sensor chip substrate 410 and the base substrate 430. There is a difference. The impact energy E having a different phase cancels out at the center of the movable part 421 toward the center from the periphery of the movable part 421. Therefore, the impact energy E actually received by the central part 421a of the movable part 421 becomes small, and the movable part can be moved by the impact. The resonance of the part 421 can be suppressed.

  10 to 12 are graphs showing the results of measuring the maximum principal stress applied to the edge of the movable part along the elapsed time when the MEMS sensor is dropped. In this measurement, Example 1 (third embodiment) in which linear concave portions 43 along a pair of sides of the diaphragm 21 are provided on the substrate bonding surface shown in FIG. 16, and the concave portions are formed on the substrate bonding surface shown in FIG. Comparative Example 1 that was not provided, and Comparative Example 2 in which a recess 45 along each side was provided on the entire outer periphery of the diaphragm 21 on the substrate bonding surface shown in FIG. 10 to 12, the vertical axis indicates the maximum principal stress applied to the center position of each side of the contour of the diaphragm 21, and the horizontal axis indicates the elapsed time since the drop.

  As is clear from FIGS. 10 to 12, the impact received by the diaphragm 21 when dropped is smaller in the first embodiment than in the first and second comparative examples.

  13 to 15 are graphs obtained by frequency-resolving the graphs of FIGS. 10 to 12, respectively. The vertical axis | shaft of FIGS. 13-15 shows the signal value corresponding to the largest principal stress concerning the diaphragm 21, and the horizontal axis has shown the frequency.

  13 to 15, it can be seen that in both Example 1 and Comparative Examples 1 and 2, the resonance frequency of the diaphragm 21 due to impact is in the vicinity of 300 Hz and 1400 Hz. In Comparative Example 1 having no recess, the signal value is 7000 when the resonance frequency is 300 Hz, and the signal value is 4000 when the resonance frequency is 1400 Hz. On the other hand, in the first embodiment in which the concave portion 43 located at a part of the outer periphery of the diaphragm 21 is provided on the substrate bonding surface, the signal value is 4000 when the resonance frequency is 300 Hz, and the signal value is about 3200 when the resonance frequency is 1400 Hz. It is apparent that the stress received by the diaphragm 21 is reduced by providing the recess 43. In Comparative Example 2 in which the concave portion 45 located on the entire outer periphery of the diaphragm 21 is provided on the substrate bonding surface, the signal value is 6500 when the resonance frequency is 300 Hz, and the signal value is 5200 when the resonance frequency is 1400 Hz. It does n’t change that much.

  As is clear from the above, in the joint surface between the sensor chip substrate 10 (410) and the base substrate 30 (430), a concave portion (41, 42, 43,. By providing 441), the impact energy transmitted to the movable part can be reduced, and the resonance of the movable part due to the impact can be suppressed. As a result, it is possible to obtain a MEMS sensor that prevents damage to the movable part and has excellent durability.

  The embodiment in which the present invention is applied to the semiconductor pressure sensor or the semiconductor acceleration sensor has been described above. However, the present invention is not limited to the semiconductor type, and in addition to the capacitance type pressure sensor and the acceleration sensor, the bonded sensor chip substrate and the base substrate. In general, the present invention is applicable to MEMS sensors that generate air gaps between them. In the first to third embodiments, the present invention is applied to an absolute pressure sensor that detects an absolute pressure while the cavity is held in a vacuum state. The present invention is also applicable to a differential pressure sensor that detects a difference from a reference pressure.

101 201 301 Semiconductor pressure sensor (MEMS sensor)
10 Sensor chip substrate 11 First silicon substrate 12 Second silicon substrate 13 Silicon oxide film 20 Cavity (void)
21 Diaphragm (movable part)
22 Pressure sensitive resistance element (sensor element)
30 Base substrate 30a surface (bonding surface)
30b Back side (mounting side)
35 Exterior Package 36 Resin Adhesive 41, 42, 43 Recess 401 Semiconductor Acceleration Sensor (MEMS Sensor)
410 sensor chip substrate 410A outer frame frame 421 movable portion 421a center portion 421b beam portion 422 sensor element 423 weight 430 base substrate 435 exterior package 436 resin adhesive 441 recess E impact energy O plane center (substrate center)
X Center axis

Claims (5)

A MEMS sensor in which a mechanically operable movable part and a sensor chip substrate on which a sensor element for electrically detecting the displacement of the movable part is formed are joined to a base substrate with a gap provided between the movable part and the sensor chip substrate. In
A MEMS sensor, wherein a concave portion is provided along a part of an outer periphery of the movable portion on a joint surface between the sensor chip substrate and the base substrate. 2. The MEMS sensor according to claim 1, wherein the movable portion has a rectangular shape in a plan view, and the concave portion is formed in an L shape in a plan view along an outer periphery of each corner portion of the rectangular shape in the plan view. 2. The MEMS sensor according to claim 1, wherein the movable portion has a rectangular shape in plan view, and the concave portion has a planar L-shape along a periphery of the corner portion at a pair of corner portions facing each other at 180 ° of the rectangular shape in plan view. MEMS sensor formed by. 2. The MEMS sensor according to claim 1, wherein the movable portion has a rectangular shape in a plan view, and the concave portion has a linear shape in a plan view along each side on an outer periphery of a pair of sides facing each other at 180 ° of the rectangular shape in the plan view. The formed MEMS sensor. 5. The MEMS sensor according to claim 1, wherein the concave portion is vacuum-sealed. 6.

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