JP2007171042A - Physical quantity sensor and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily and surely inspect the airtightness of an airtight space, in a physical quantity sensor having the airtight space formed of a wafer level package, and to provide its manufacturing method. <P>SOLUTION: A sensor section 2, for outputting an electrical signal according to physical quantity to be measured, is formed in the airtight space R1 formed of the wafer level package by a semiconductor micromachining process. The physical quantity sensor comprises a pressure sensor 3, having an airtight chamber R2 adjacent to the airtight space R1 via a diaphragm 30 and a strain gage for measuring the amount of deformation of the diaphragm 30. The pressure sensor 3 enables inspection of the airtightness of the airtight space R1 that is required for maintaining the characteristics of the sensor section 2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a physical quantity sensor such as an acceleration sensor used for automobiles, airplanes, home appliances, and the like, and a manufacturing method thereof, and more particularly to a physical quantity sensor in which an airtight space is formed by wafer level packaging.

  Conventionally, a small and high-performance physical quantity sensor using a semiconductor and its processing technology has been developed and used. For example, there are physical quantity sensors such as an acceleration sensor, a pressure sensor, and a tilt sensor. These include a sensor unit formed on a semiconductor wafer using a semiconductor microfabrication technique and a cover unit that protects the sensor unit (see, for example, Patent Document 1).

  The sensor unit is manufactured and used in a state of being sealed in an airtight space in order to maintain accuracy and life. In recent years, in order to manufacture a physical quantity sensor having such an airtight space in a compact and efficient manner in large quantities, a large number of sensor portions are formed on one wafer, and the other wafers are bonded in an airtight state. A so-called wafer level packaging technique is used in which a space is formed and then diced into chips including each sensor unit. The physical quantity sensor that is separated into pieces with the airtight space is inspected for airtightness of the airtight space by a method such as a helium leak test, for example. Helium is often used as a probe gas because it has a small atomic radius and can easily enter fine gaps, and is small in the atmosphere.

Then, the helium leak test is performed, for example, based on whether helium gas is detected from the physical quantity sensor after the separated physical quantity sensor is left in a high-pressure helium gas atmosphere for a predetermined time. That is, if helium is detected from the physical quantity sensor, helium has entered the airtight space because the airtightness of the airtight space of the physical quantity sensor is incomplete and the remaining helium is detected. It is considered a good product.
JP 2001-071113 A

  However, the physical quantity sensor having an airtight space and the manufacturing method thereof manufactured using the helium leak test as described above have the following problems. In general, a helium leak test for measuring helium leaking from an airtight space requires time for adjusting the conditions for helium detection, and a large amount of physical quantity sensor test requires a long time. In addition, physical quantity sensors having an airtight space manufactured by wafer level packaging often have a small capacity in the airtight space due to the miniaturization thereof, and the effective time for the helium leak test is shortened, so that the inspection cannot be performed. There is also a problem.

  In other words, even if helium leaks into the airtight space of a defective airtight product that has a leak path to the airtight space, helium that has entered the airtight space is externally reduced at a rate determined by the leak rate of the helium and the capacity of the airtight space. Since it escapes and decreases, if a certain time is exceeded, helium leaks from the airtight portion, and helium cannot be detected even though it is defective. That is, the physical quantity sensor having a small airtight space has a shorter time allowed for taking out the physical quantity sensor from the high-pressure helium-filled space and conducting the airtightness test.

  An object of the present invention is to solve the above problems, and to provide a physical quantity sensor having an airtight space formed by a wafer level package and a method for manufacturing the same, in which the airtightness of the airtight space can be easily and reliably inspected. And

  In order to achieve the above object, the invention of claim 1 is directed to a physical quantity sensor in which a sensor unit that outputs an electric signal according to a physical quantity to be measured is formed by a semiconductor microfabrication process in an airtight space formed by a wafer level package. A pressure sensor having an airtight chamber adjacent to the airtight space via a diaphragm and a strain gauge for measuring the amount of deformation of the diaphragm, and maintaining the characteristics of the sensor unit by the pressure sensor. The required airtightness of the airtight space can be inspected.

  According to a second aspect of the present invention, there is provided a method of manufacturing a physical quantity sensor in which a sensor unit that outputs an electrical signal in accordance with a physical quantity to be measured is formed in a hermetic space formed by a wafer level package by a semiconductor microfabrication process. A step of forming a pressure sensor having an airtight chamber adjacent to the airtight space through a strain gauge and a strain gauge for measuring the amount of deformation of the diaphragm, and the pressure sensor formed by the step determines characteristics of the sensor unit. And an inspection process for measuring the airtightness of the airtight space necessary for maintenance.

  According to a third aspect of the present invention, in the method of manufacturing a physical quantity sensor according to the second aspect, the sensor unit includes a strain gauge, and the step of forming the strain gauge of the pressure sensor is performed by the strain of the sensor unit. It is performed simultaneously with the formation of the gauge.

  According to a fourth aspect of the present invention, in the physical quantity sensor manufacturing method according to the second or third aspect, the inspection step is performed by a probe inspection for a strain gauge of the pressure sensor.

  According to a fifth aspect of the present invention, in the method of manufacturing a physical quantity sensor according to the fourth aspect, the inspection step is performed simultaneously with a probe inspection for inspecting characteristics of the sensor unit.

  According to the first aspect of the present invention, since the pressure sensor is formed so as to be able to measure the pressure in the hermetic space according to the deformation amount of the diaphragm, the pressure change in the hermetic space can be measured. In addition, the airtightness of the airtight space can be inspected easily and reliably in a short time. The airtightness inspection of the airtight space using the pressure sensor can be performed, for example, by placing the physical quantity sensor in different pressure states and comparing the output of the pressure sensor measured in each state.

  According to the second aspect of the present invention, the method includes a step of forming a pressure sensor so that the pressure in the hermetic space can be measured by a deformation amount of the diaphragm, and an inspection step using the pressure sensor. The physical quantity sensor can measure the pressure change in the hermetic space and check the hermeticity of the hermetic space easily and reliably in a short time without using the helium leak test, and the manufacturing efficiency is improved as compared with the conventional sensor.

  According to the invention of claim 3, since the formation of the strain gauge of the pressure sensor is performed at the same time as the formation of the strain gauge of the sensor portion, it is possible to manufacture a low-cost physical quantity sensor with fewer man-hours than when separately formed. .

  According to the invention of claim 4, the evaluation of the airtightness of the airtight space can be performed in a shorter time and more easily than the helium leak test.

  According to the invention of claim 5, the setting for the inspection can be made common, and the physical quantity sensor can be evaluated and inspected efficiently.

  Hereinafter, a physical quantity sensor and a manufacturing method thereof according to an embodiment of the present invention will be described with reference to the drawings. 1A and 1B show an outline of a physical quantity sensor 1 according to an embodiment of the present invention, and FIG. 2 shows components of the physical quantity sensor 1. The physical quantity sensor 1 is formed by a wafer level package technique, and the physical quantity sensor 1 and its components shown in the following figures show the shape after the wafer is separated into pieces. In the following, acceleration is taken as an example of a physical quantity, and the physical quantity sensor 1 will be described on the assumption of an acceleration sensor.

  The physical quantity sensor 1 is a sensor in which a sensor unit 2 that outputs an electrical signal according to a physical quantity to be measured is formed in a hermetic space R1 formed by a wafer level package by a semiconductor microfabrication process. This physical quantity sensor 1 is a pressure sensor having a diaphragm 30, a strain gauge for measuring the amount of deformation thereof (described later in FIG. 4), an electrode 31, and a hermetic chamber R 2 adjacent to the hermetic space R 1 via the diaphragm 30. 3, and the pressure sensor 3 can inspect the airtightness of the airtight space R <b> 1 necessary for maintaining the characteristics of the sensor unit 2.

  The physical quantity sensor 1 is arranged so as to cover the sensor wafer 10 on which the sensor unit 2 and the pressure sensor 3 are formed, and the upper surface of the sensor unit 2 and the diaphragm 30 of the pressure sensor 3, without contacting the sensor wafer 10. A cover wafer 11 bonded at the outer peripheral portion and a lower cover wafer 12 bonded to the back surface of the sensor wafer 10 to form an airtight space R1 and an airtight chamber R2.

  The sensor wafer 10 is formed on a silicon substrate having a long rectangular outer shape, a sensor unit 2 for measuring a physical quantity (acceleration), a frame 10a surrounding the sensor unit 2, and an airtight chamber R2 formed adjacent to the sensor unit 2. A rectangular recess having an upper surface of the diaphragm 30 is formed.

  The airtight space R <b> 1 includes a bonding portion a between the outer peripheral portion of the upper surface of the sensor wafer 10 and the outer peripheral portion of the lower surface of the cover wafer 11, and an outer peripheral portion (lower surface of the frame 10 a) of the sensor portion 2 on the lower surface of the sensor wafer 10 and the upper surface of the lower cover wafer 12. It is the space sealed by the joint parts b and c. The sensor unit operates in the airtight space R1. The hermetic chamber R <b> 2 is a space surrounded by the diaphragm 30, the side wall of the sensor wafer 10, and the lower cover wafer 12. The hermetic chamber R <b> 2 is sealed by joints c and d between the lower surface of the sensor wafer 10 and the upper surface of the lower cover wafer 12.

  The sensor unit 2 includes a weight body 20 for detecting an inertial force against acceleration, a beam 21 extending from the weight body 20 in four directions to the frame body 10a, and supporting the weight body 20 from the frame body 10a side. And a strain gauge (FIG. 4) formed near the base of the beam 21 to electrically detect the deformation amount of the beam, for example, formed of a piezo element. The weight body 20, the beam 21, and the frame body 10a are configured by, for example, using a silicon semiconductor wafer as a material and processing it in an integrated state by a semiconductor micromachining technique (described later, FIG. 8). An electrical signal from the strain gauge is drawn from the central portion to the peripheral portion by electric wiring (not shown), and is taken out to the electrode 22 provided on the outer surface of the physical quantity sensor 1.

  The weight body 20 is composed of four mass portions having a center of gravity at a position away from the central portion so that the magnitude of the inertial force generated in the weight body 20 is reflected in the deformation of the beam 21 with high sensitivity. Note that each weight body 20 and each beam can be measured so that acceleration in an arbitrary direction in the three-dimensional space can be measured, that is, the weight body 20 can perform necessary and sufficient movements such as twisting, rotation, and parallel movement. A weight body 20 is formed at a position one step below the position of the beam 21 for the purpose of preventing interference with the beam 21. In addition, concave portions are formed in the lower surface of the cover wafer 11 and the upper surface of the lower cover wafer 12, respectively. These recesses form a movable space in the vertical direction of the weight body 20, and the bottom surface of the recess constitutes a stopper that prevents excessive movement of the weight body 20.

  Here, the dimension of each part of the physical quantity sensor 1 will be described. The external dimensions of the physical quantity sensor 1 are, for example, a vertical and horizontal dimension of 2.0 to 5.0 mm and a thickness of about 0.6 mm to 1.0 mm. Moreover, the thickness dimension of the weight body 20 is 300-500 micrometers, for example. The dimensions of the beam 21 are, for example, a length of about 300 to 700 μm, a width of about 60 to 150 μm, and a thickness of about 4 to 10 μm. The thickness of the beam 21 is set to a sufficiently small value with respect to the thickness of the weight body 20. The size of one side of the diaphragm 30 is, for example, about 50 μm to 1.0 mm.

  Next, the operation principle of the physical quantity sensor 1 as an acceleration sensor and the operation principle of the pressure sensor 3 will be described. 3A to 3C show the operation of the weight body, FIG. 4 shows the upper surface of the sensor wafer 10 showing the arrangement of the strain gauges on the sensor unit 2 and the diaphragm 30, and FIG. 5A shows the sensor. FIG. 5B shows positive and negative responses to the acceleration of each strain gauge, and FIG. 6 shows a bridge circuit used for electric signal detection of the pressure sensor 3.

  As shown in FIG. 3A, when the physical quantity sensor 1 receives acceleration in the direction of the arrow u parallel to the beam 21, the frame body 10a moves in the direction of the arrow u, and the weight body 20 is left behind. Receives an inertial force in the direction of v. Therefore, a compressive stress (for example, indicated by a + sign) is generated in the left beam 21, and a tensile stress (for example, indicated by a-sign) is generated in the right beam 21.

  3B, when the physical quantity sensor 1 receives acceleration in the direction of the arrow u that is not parallel to the beam 21, the weight body 20 is inertial in the direction of the arrow v inclined in the vertical direction. Receive power. Then, as shown in FIG. 3C, compressive stress and tensile stress are generated in the left and right beams 21, respectively. Therefore, if strain gauges are provided in the vicinity of both ends of each beam 21 and the degree of occurrence of compressive stress and tensile stress is measured, the inertial force acting on the weight body 20, and hence the acceleration received by the physical quantity sensor 1, can be measured. it can. For example, the strain gauge is formed of a resistor that changes its resistance by receiving strain.

  As shown in FIG. 4, the beam 21 of the sensor unit 2 of the sensor wafer 10 includes strain gauges X1 to X4 for measuring acceleration in the X direction made of a resistor long in the X direction and Y made of a resistor long in the Y direction. Directional strain measurement strain gauges Y1 to Y4 are arranged at the sensor inner end of the beam 21 serving as a stress concentration portion. Further, strain gauges Z1 to Z4 for acceleration measurement in the Z direction, which are made of resistors that are long in the Y direction, are arranged at the sensor outer end of the beam 21 serving as another stress concentration part. The hatching area S shown in FIG. 4 is a wiring area and a bonding area between the sensor wafer 10 and the cover wafer 11. Therefore, the inside of the hatching region S is the inside of the airtight space R1.

  Each strain gauge of the above-described sensor unit 2 has electrodes Xa, Xb, Ya, Yb, Za, Zb, arranged on the outer periphery of the sensor wafer 10 by electrical wiring (not shown) connected to both ends in the longitudinal direction. E1 and G are connected so as to form a bridge circuit shown in FIG. If the bridge circuit is formed in this way, for example, when the acceleration is applied to the X-axis, the resistance value balance of the bridge circuit is lost. Therefore, when a constant voltage is applied between the power supply electrode E1 and the ground electrode G, the electrode The potential difference between Xa and Xb changes according to the magnitude of the acceleration, and the acceleration can be detected as a voltage.

  Similarly, the change in stress with respect to the acceleration of each XYZ axis is as shown in FIG. 5B. Therefore, the physical quantity sensor 1 can detect the acceleration independently and simultaneously for each XYZ axis.

  In addition, strain gauges P <b> 1 to P <b> 4 that are long in the direction along one side of the square diaphragm 30 are arranged on the diaphragm 30 of the pressure sensor 3 of the sensor wafer 10. The arrangement location is the periphery of the diaphragm 30 where a large deformation can be obtained. These strain gauges form the bridge circuit shown in FIG. 6 on the electrodes Pa, Pb, E2, and G arranged on the outer periphery of the sensor wafer 10 by electrical wiring (not shown) connected to both ends in the longitudinal direction. To be connected.

  If the bridge circuit is formed as described above, for example, when there is a pressure change between the hermetic space R1 and the hermetic chamber R2, the diaphragm 30 is deformed and the resistance value balance of the bridge circuit is lost, so the power supply electrode E2 When a constant voltage is applied between the ground electrode G and the ground electrode G, the potential difference between the electrodes Pa and Pb changes according to the pressure change, and the pressure change can be detected as a voltage.

  Thus, according to the physical quantity sensor 1 of the present invention, the pressure sensor 3 is formed and provided so that the pressure in the airtight space R1 can be measured by the deformation amount of the diaphragm 30, so that the pressure change in the airtight space R1 is measured. Therefore, the airtightness of the airtight space R1 can be inspected easily and reliably in a short time without using the helium leak inspection. The airtightness inspection of the airtight space R1 using the pressure sensor 3 can be performed, for example, by placing the physical quantity sensor 1 in different pressure states and comparing the output of the pressure sensor 3 measured in each state.

  Next, the manufacturing process of the physical quantity sensor 1 will be described. FIG. 7 shows a schematic flow of a manufacturing process of the physical quantity sensor 1, and FIGS. 8A to 8D show main stages of the manufacturing process in a time series by cross sections of the physical quantity sensor 1. The SOI wafer shown in FIG. 8A is a wafer in which a silicon oxide film 1b, a silicon layer 1c, and a silicon oxide film 1d are stacked in this order on a silicon wafer 1a.

  First, an SOI wafer to be the sensor wafer 10 shown in FIG. 8A is prepared, and a strain gauge and diffusion wiring extending from the strain gauge to the peripheral portion are formed on the surface of the beam 21 forming region and the diaphragm 30 forming region. The wiring is formed by diffusion wiring technology (S1). At this time, the strain gauge for acceleration detection of the physical quantity sensor 1 and the strain gauge for pressure detection of the pressure sensor 3 are formed simultaneously.

  Next, metal wiring from the diffusion wiring to the electrode Xa and the like disposed on the outer periphery of the sensor wafer 10 is formed on the sensor wafer 10, and a bridge circuit for detecting acceleration and a bridge circuit for detecting airtightness are formed simultaneously ( S2).

  Next, as shown in FIG. 8 (b), the silicon wafer 1a portion of the sensor wafer 10 is etched by a semiconductor microfabrication process, and the sensor unit structure including the weight body 20 and the beam 21, and the airtight chamber. A pressure sensor structure comprising the concave portion R0 and the diaphragm 30 is formed (S3).

  Next, as shown in FIG. 6C, a separately formed lower cover wafer 12 is bonded to the lower surface of the sensor wafer 10 (S4). By forming the joints c and d between the sensor wafer 10 and the lower cover wafer 12, the hermetic chamber R2 is completed. By performing this bonding in a vacuum atmosphere, the hermetic chamber R2 is made a vacuum space.

  Next, as shown in FIG. 8D, the cover wafer 11 that is separately formed with the upper electrodes 22 and 31 and the through wiring (not shown) is bonded to the upper surface of the sensor wafer 10. Thereby, the bonded wafer of the physical quantity sensor 1 packaged in the wafer level is completed (S5). At the time of this bonding, the electrode Xa and the like (FIG. 4) formed on the sensor wafer 10 and the through electrode of the cover wafer 11 are electrically connected. The through electrode is connected to the upper electrode, whereby the output of each strain gauge is taken out to the outside. Further, the sensor wafer 10 and the cover wafer 11 are joined in a vacuum to form a vacuum-tight airtight space R1.

  Next, the physical quantity sensor 1 packaged in the wafer level is diced into individual chips of the physical quantity sensor 1 (S6). The separated physical quantity sensor 1 is simultaneously inspected for the airtightness of the airtight space R1 by the pressure sensor 3 simultaneously with the inspection of the basic characteristics of the acceleration sensor using a prober (S7).

  As described above, according to the method of manufacturing a physical quantity sensor of the present invention, the step of forming the pressure sensor 3 so that the pressure of the hermetic space R1 can be measured by the deformation amount of the diaphragm 30, and the inspection step by the pressure sensor 3 Therefore, the physical quantity sensor 1 manufactured by this manufacturing method can easily and reliably inspect the airtightness of the airtight space R1 in a short time by measuring the pressure change in the airtight space R1 without using the helium leak inspection. Manufacturing efficiency is improved. In addition, since the formation of the strain gauge of the pressure sensor 3 and the formation of the strain gauge of the sensor unit 2 are simultaneously performed in the same process, it is possible to manufacture a low-cost physical quantity sensor with fewer man-hours than when separately formed.

  The present invention is not limited to the above-described configuration, and various modifications can be made. For example, in the probe inspection, each physical quantity sensor 1 may be inspected in a wafer level state instead of being separated into pieces. By such a probe inspection at the wafer level, it is possible to evaluate the airtightness of the airtight space R1 together with the characteristic evaluation of the physical quantity sensor 1 for all the physical quantity sensors 1 on the wafer in a short time.

  When performing the above-described evaluation, a joint surface that forms each airtight space R1 in advance so that a leak path to the airtight space R1 having a leak is not closed by a side wall or the like that forms another airtight space R1. It is necessary to process the periphery of each physical quantity sensor 1 of the wafer level package so that the cross sections a, b, and c are exposed. By this processing, the inspection can be performed without missing the leaky airtight space R1. In this case, the measurement of the output of the pressure sensor 3 performed for the total number of physical quantity sensors 1 in the wafer level state is performed twice under a high pressure and a low pressure, and such a measurement result is obtained for each physical quantity sensor 1. By comparing, airtightness inspection can be performed in a short time and efficiently.

(A) is a top view of the physical quantity sensor which concerns on one Embodiment of this invention, (b) is the sectional view on the AA line of (a). The disassembled perspective view of a physical quantity sensor same as the above. (A) (b) is typical sectional drawing which shows the mode at the time of operation | movement of a physical quantity sensor same as the above, (c) is a distribution map of the beam direction of the stress corresponding to the state of (b). The top view of a sensor wafer which shows the sensor part of a physical quantity sensor same as the above, and the diaphragm of airtight space. (A) is a bridge circuit diagram used for the physical quantity sensor same as above, (b) is a response relationship diagram for the acceleration of the strain gauge of the physical quantity sensor. The bridge circuit figure used for the pressure sensor of a physical quantity sensor same as the above. The general | schematic flowchart of the manufacturing process of a physical quantity sensor same as the above. (A)-(d) is sectional drawing which shows the manufacturing process of a physical quantity sensor same as the above in time series.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Physical quantity sensor 2 Sensor part 3 Pressure sensor 30 Diaphragm R1 Airtight space R2 Airtight chamber X1-X4 Strain gauge Y1-Y4 Strain gauge Z1-Z4 Strain gauge P1-P4 Strain gauge

Claims (5)

A sensor unit that outputs an electrical signal according to a physical quantity to be measured is a physical quantity sensor formed by a semiconductor microfabrication process in an airtight space formed by a wafer level package,
A pressure sensor having an airtight chamber adjacent to the airtight space via a diaphragm and a strain gauge for measuring a deformation amount of the diaphragm, and the airtightness necessary for maintaining the characteristics of the sensor unit by the pressure sensor; A physical quantity sensor characterized in that the airtightness of a space can be inspected. A sensor unit that outputs an electrical signal according to a physical quantity to be measured is a method of manufacturing a physical quantity sensor formed by a semiconductor microfabrication process in an airtight space formed by a wafer level package,
Forming a pressure sensor having a hermetic chamber adjacent to the hermetic space via a diaphragm and a strain gauge for measuring a deformation amount of the diaphragm;
An inspection step of measuring the airtightness of the airtight space necessary for maintaining the characteristics of the sensor unit by the pressure sensor formed by the step. The sensor part is provided with a strain gauge,
The method of manufacturing a physical quantity sensor according to claim 2, wherein the step of forming the strain gauge of the pressure sensor is performed simultaneously with the formation of the strain gauge of the sensor unit.   The method of manufacturing a physical quantity sensor according to claim 2, wherein the inspection step is performed by a probe inspection on a strain gauge of the pressure sensor.   The method of manufacturing a physical quantity sensor according to claim 4, wherein the inspection step is performed simultaneously with a probe inspection for inspecting characteristics of the sensor unit.