JP2008172011A - Piezoresistive structure and external force detection sensor using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoresistive structure with improved reliability in performance. <P>SOLUTION: The piezoresistive structure 1 has a piezoresistive part 2 that is partially formed on the surface of a base 3 comprising a semiconductor and in which magnitude of electric resistance varies corresponding to stress changes. Either of the base 3 and the piezoresistive part 2 is formed into a p-type semiconductor while the other is formed into an n-type semiconductor. One-end 2H side of the piezoresistive part 2 is electrically connected to the high-potential side of a voltage application means while the other-end 2L side is electrically connected to the low-potential side of the voltage application means so as to apply a voltage to the piezoresistive part 2. In that state, in consideration of the thickness D of a depletion layer H at the PN junction part between the piezoresistive part 2 and the base 3, the piezoresistive part 2 is formed by changing the width or the thickness continuously or step by step so that an effective cross-sectional area of a current conduction path is equalized from the end part 2H on the high-potential side to the end part 2L on the low-potential side in the piezoresistive part 2. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a piezoresistive structure provided as, for example, a detection unit of an external force detection sensor and an external force detection sensor using the same.

  FIG. 5A is a schematic plan view showing an example of main components of an acceleration sensor that is one of the external force detection sensors, and FIG. 5B shows an A- shown in FIG. 5A. A schematic cross-sectional view of the acceleration sensor at a position corresponding to the portion A is shown. The acceleration sensor 30 shown in FIGS. 5 (a) and 5 (b) is arranged in a form that surrounds the weight part 31 arranged in a floating state and the circumferential surface of the weight part 31 with a space therebetween. 5, the cantilever 33 for supporting and fixing the weight portion 31 to the fixing portion 32 in a state displaceable in the Z-axis direction shown in FIG. 5B, and the cantilever 33. The detection unit 34, the external connection means 35 for electrically connecting the detection unit 34 and the like to the outside, and the weight unit 31 are spaced apart from each other on the upper side and the lower side of the weight unit 31 shown in FIG. And a sealing member 36 for forming a closed space for accommodating and arranging the weight portion 31.

In this example, the weight part 31, the fixing part 32, and the cantilever 33 are formed by processing an SOI (Silicon-On-Insulator) substrate 38. That is, the SOI substrate 38 is a substrate in which a support layer 39 made of silicon, an oxide layer 40 made of SiO _2, and an active layer 41 made of silicon are laminated and integrated. A through hole 42 penetrating from the support layer 39 side to the active layer 41 side is formed around the predetermined weight portion 31 formation region in the SOI substrate 38 so as to avoid the cantilever 33 formation region. 31 and the fixing | fixed part 32 are formed. Further, the support layer 39 in the formation region of the cantilever 33 in the SOI substrate 38 is removed, and the cantilever 33 is formed by the oxide layer 40 and the active layer 41. That is, the cantilever 33 is formed thinner than the weight portion 31 and the fixed portion 32 and is easily bent and deformed.

As described above, sealing members 36, which are glass substrates, are arranged on both upper and lower sides of the SOI substrate 38 on which the weight portion 31, the fixing portion 32, and the cantilever 33 are formed. . An adhesive layer 43 is laminated on the surface on the support layer 39 side and the surface on the active layer 41 side of the fixing portion 32 so as to surround the entire circumference of the region where the weight portion 31 is formed. The bonding layer 43 is bonded and integrated with the SOI substrate 38. The sealing member 36, the adhesive layer 43, and the fixing portion 32 form a closed space in which the weight portion 31 and the cantilever beam 33 are accommodated while being movable in the Z-axis direction. Note that reference numeral 44 in FIG. 5B indicates an insulating film (for example, a SiO ₂ film or a SiNx film) formed on the surface of the active layer 41.

  In this example, the weight part 31 and the cantilever 33 are movable parts that are deformed by an external force to be detected. That is, when acceleration in the Z-axis direction shown in FIG. 5B is generated as a detection target, the weight portion 31 is displaced in the Z-axis direction by the force resulting from the acceleration in the Z-axis direction, and the cantilever 33 is Deforms and deforms. The amount of displacement of the weight portion 31 and the amount of bending deformation of the cantilever beam 33 are in accordance with the magnitude of acceleration so that it increases as the acceleration increases.

  The configuration of the acceleration sensor 30 includes a configuration for detecting the amount of deformation of the cantilever 33 to detect the magnitude of acceleration. That is, the following detection unit 34 is formed on the cantilever 33. The detection unit 34 is configured to include four piezoresistive units 45 formed on the surface side of the cantilever 33 as shown in the enlarged view shown in FIG. The four piezoresistive portions 45 are arranged at the positions of the respective sides of the quadrangular shape and are electrically connected so as to form a quadrangular shape to form a bridge circuit. One of the four connection portions 46 (Vdd) of the bridge circuit is connected to the high potential side (for example, 5 V voltage supply side) of the voltage applying means, and to the pair of the connection portions 46 (Vdd). The connecting portions 46 (Vgnd) at the corner positions are respectively connected to the low potential side (for example, ground) of the voltage applying means. Furthermore, the remaining two connection portions 46 (Vo1, Vo2) are electrically connected to external force detection means (not shown), respectively.

  FIG. 7 shows a configuration example of the piezoresistive unit 45 together with peripheral components in a schematic cross-sectional view. In the configuration of the acceleration sensor 30, the active layer (silicon layer) 41 of the SOI substrate 38 is made of an n-type semiconductor, and the piezoresistive portion 45 is formed by doping a part of the surface of the active layer 41 with impurities. The p-type semiconductor is constituted. The piezoresistive portion 45 changes the magnitude of the electrical resistance in accordance with the stress change. Both ends of the piezoresistive portion 45 are connected to separate terminal portions 48, respectively.

  The terminal portion 48 includes a terminal portion 49 formed on a part of the surface of the active layer 41 and an electrode 50 that is joined to the terminal portion 49 and is electrically connected. The terminal portion 49 is made of a p-type semiconductor formed by doping a part of the surface of the active layer 41, and the terminal portion 49 has an electric resistance smaller than that of the piezoresistive portion 45. The impurity doping amount is adjusted. The electrode 50 is formed on the surface of the insulating film 44 laminated on the active layer 41, and a part of the electrode 50 is insulated through a contact hole 51 which is a through hole provided in the insulating film 44. The film 44 extends from the surface side of the active layer 41 to the surface side of the active layer 41 and is joined to the terminal portion 49 of the active layer 41. The terminal portion 48 is configured as described above. The electrode 50 of the terminal portion 48 is electrically connected to the wiring pattern 52.

  The four piezoresistive portions 45 are electrically connected via the terminal portion 48 and the wiring pattern 52 as described above to form a bridge circuit as shown in FIG. Further, on the surface of the insulating layer 44 laminated on the fixed portion 32, four electrodes are connected to the four connection portions 46 of the bridge circuit in a one-to-one relationship via wiring patterns (not shown). Pads 35A are formed with a space therebetween. Further, a through hole 35B reaching the electrode pad 35A from the surface side is formed in the sealing member 36 and the adhesive layer 43, and the inner wall surface of the through hole 35B and the through hole 35A on the surface of the sealing member 36 are formed. A conductor film 35C is formed at the opening edge. The electrode pad 35A, the through hole 35B, the conductor film 35C, and the wiring pattern constitute external connection means 35 for electrically connecting a bridge circuit as a detection unit accommodated in the closed space to the outside. Yes. Further, a voltage is applied to the piezoresistive portion 45 through the external connecting means 35, the connecting portion 46, the wiring pattern 52 and the terminal portion 48. Further, in this example, for example, a voltage having the same potential as that applied to the connection portion 46 (Vdd) of the bridge circuit is applied to the active layer 41 by an external connection means (not shown).

  In the configuration of the acceleration sensor 30, when the acceleration in the Z-axis direction is not generated, the electric resistances of the four piezoresistive portions 45 of the bridge circuit are in an equilibrium state and become the potential of the connecting portion 46 (Vo1, Vo2). It is formed so as not to cause a difference. On the other hand, when the acceleration in the Z-axis direction is generated and the cantilever beam 33 is bent and deformed, the magnitude of the electric resistance of each piezoresistive portion 45 is changed by the stress change caused by the bending deformation of the cantilever beam 33. In the piezoresistive portions 45a and 45c shown in FIG. 6, the direction of the energized current is in the direction along the X-axis direction, whereas in the piezoresistive portions 45b and 45c, the direction of the energized current is along the Y-axis direction. There is a difference in the energization direction of the current of the piezoresistive portion 45 as in the direction. When the magnitude of the electrical resistance of each piezoresistive portion 45 changes due to the bending deformation of the cantilever 33 due to the acceleration in the Z-axis direction due to this difference and the difference in the formation position of the piezoresistive portion 45, the bridge circuit of FIG. The equilibrium state of the electrical resistance of the four piezoresistive portions 45 is broken. As a result, a difference occurs in the potential of the connection part 46 (Vo1, Vo2) of the bridge circuit. This difference increases between the potential difference of the connecting portion 46 (Vo1, Vo2) and the bending deformation amount (magnitude of acceleration) of the cantilever beam 33 so that the bending deformation amount of the cantilever beam 33 increases. Since there is a correlation, the external force detection means connected to the connection part 46 (Vo1, Vo2) of the bridge circuit determines the magnitude of acceleration in the Z-axis direction based on the potential difference of the connection part 46 (Vo1, Vo2). Can be detected.

Japanese Unexamined Patent Publication No. 63-41079 JP 2003-329702 A

  By the way, in the configuration of the acceleration sensor 30, as shown in FIG. 6, each piezoresistive portion 45 has a uniform width from one end side to the other end side. Further, each piezoresistive portion 45 is formed by doping impurities into the active layer 41 almost evenly from one end side to the other end side. When no voltage is applied, each piezoresistive portion 45 is formed. 45 is formed to be equal in thickness (depth) from one end side to the other end side.

  However, when a voltage is applied to the piezoresistive portion 45, the following problem caused by the depletion layer of the PN junction occurs. That is, since the active layer 41 is an n-type semiconductor and the piezoresistive portion 45 is a p-type semiconductor, the active layer 41 and the piezoresistive portion 45 form a PN junction, and a depletion layer is formed at the PN junction portion. . For this reason, the thickness of the depletion layer increases as the potential difference between the PNs increases, and the thickness (depth) of the piezoresistive portion 45 decreases as the thickness of the depletion layer increases. For example, in FIG. 7, the end portion on the terminal portion 48H side of the piezoresistive portion 45 is on the high potential side, and the end portion on the terminal portion 48L side of the piezoresistive portion 45 is on the low potential side. 41 is configured to be applied with a voltage comparable to the voltage applied to the terminal portion 48H. When a voltage is applied to the piezoresistive portion 45, the potential difference between the terminal portion 48L side (low potential side) of the piezoresistive portion 45 and the active layer 41 (potential difference between PN) is the piezoresistive portion 45. The potential difference between the terminal portion 48H side (high potential side) and the active layer 41 becomes larger. For this reason, as shown in FIG. 7, the thickness D of the depletion layer H increases from the terminal portion 48H side toward the terminal portion 48L side, and the piezoresistive portion 45 increases with the change in the thickness D of the depletion layer H. The thickness decreases from the terminal portion 48H side toward the terminal portion 48L side.

  In other words, the piezoresistive portion 45 is formed so as to have the same width and the same thickness when hung from one end side to the other end side (hanging from the terminal portion 48H side to the terminal portion 48L side). When a voltage is applied between both ends of the piezoresistive portion 45, the thickness D of the depletion layer H at the PN junction portion between the piezoresistive portion 45 and the active layer 41 increases in the direction from the terminal portion 48H side toward the terminal portion 48L side. As a result, the thickness of the piezoresistive portion 45 changes in the direction of becoming thinner from the terminal portion 48H side toward the terminal portion 48L side, and is not the same thickness. That is, in a state where a voltage is applied to the piezoresistive portion 45, the effective cross-sectional area of the conduction path of the current flowing through the piezoresistive portion 45 becomes narrower from the terminal portion 48H side toward the terminal portion 48L side. For this reason, the magnitude of the electrical resistance of the piezoresistive portion 45 increases from the terminal portion 48H side toward the terminal portion 48L side, and is not uniform. Note that, as described above, the cross-sectional area of the piezoresistive portion 45 changes depending on the presence or absence of voltage application, and therefore, here, the piezoresistive portion when a voltage is applied to the piezoresistive portion 45 and a current is applied. The cross-sectional area of the 45 current conducting paths is indicated as the effective cross-sectional area.

  As described above, if the magnitude of the electrical resistance of the piezoresistive portion 45 is not uniform throughout the piezoresistive portion 45, it is difficult to give the piezoresistive portion 45 a set electrical resistance value. Further, for example, it becomes difficult to achieve a balanced state of the electric resistances of the four piezoresistive portions 45 constituting the bridge circuit as shown in FIG. 6, and further, the connection portions 46 (Vo1, Vo2) of the bridge circuit are made. The relationship between the potential difference (that is, the output value of the bridge circuit) and the magnitude of acceleration are likely to vary, which hinders performance improvement of the acceleration sensor 30.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a piezoresistive structure and an external force detection sensor that can be easily designed and can improve performance.

In order to achieve the above object, the present invention has the following configuration as means for solving the above problems. That is, the piezoresistive structure of the present invention is
A piezoresistive structure having a piezoresistive portion that is formed on a part of a surface of a base made of a semiconductor and changes in magnitude according to a stress change,
One of the base and the piezoresistive portion is a p-type semiconductor, and the other is an n-type semiconductor.
The piezoresistive portion is configured such that one end side is electrically connected to the high potential side of the voltage applying means, and the other end side is electrically connected to the low potential side of the voltage applying means, and the voltage is applied. When a voltage is applied to the piezoresistive portion, a depletion layer whose thickness increases as the potential difference between the PNs increases in the PN junction region between the piezoresistive portion and the base portion below the piezoresistive portion. Formed, the thickness of the piezoresistive portion becomes thinner as the thickness of the depletion layer increases,
The piezoresistor is continuously or stepwise so that the effective cross-sectional area of the current conduction path becomes equal from the high potential end to the low potential end in a state where the voltage is applied by the voltage applying means. It is characterized by being formed by changing the width or thickness.

The external force detection sensor of the present invention is
A movable part configured by a semiconductor and deformed by an external force to be detected;
A detector for detecting the magnitude of the external force by detecting the amount of deformation of the movable part that increases as the magnitude of the external force applied to the movable part increases;
An external force detection sensor having
The detection unit is a piezoresistive unit that constitutes the piezoresistive structure of the present invention formed based on the movable unit, and detects the amount of change in voltage due to the change in the electrical resistance of the piezoresistive unit as the magnitude of the external force. It is characterized by doing.

  In the present invention, in a state where a voltage is applied to the piezoresistive portion, the effective cross-sectional area of the current conduction path is continuously or stepwise from the high potential end to the low potential end of the piezoresistive portion. Piezoresistive portions are formed to be equal. In other words, considering the thickness of the depletion layer whose thickness changes due to voltage application to the piezoresistive portion, current conduction is performed continuously or stepwise from the high potential end to the low potential end of the piezoresistive portion. The piezoresistive portion is formed so that the effective cross-sectional areas of the passages are equal. For this reason, the piezoresistive portion can make the magnitude of the electrical resistance uniform throughout the entire state in the state where a voltage is applied. Thereby, it becomes easy to form a piezoresistive portion having an electrical resistance value as designed. Further, in the external force detection sensor provided with the piezoresistive structure of the present invention as the detection unit, the variation in the correlation between the output value of the detection unit and the magnitude of the external force is reduced, so that the external force detection sensor detects the external force. Reliability for performance can be increased.

  In addition, since the detection unit of the external force detection sensor has a configuration formed by a bridge circuit including four piezoresistive units having a configuration unique to the present invention, the electrical resistance of the four piezoresistive units of the bridge circuit It becomes easy to balance. In addition, it is possible to suppress variation in the correlation between the output value of the bridge circuit and the magnitude of the external force. Thereby, the reliability with respect to the performance of the external force detection sensor can be improved.

  Embodiments according to the present invention will be described below with reference to the drawings.

  FIG. 1A is a schematic plan view showing a piezoresistive portion constituting a piezoresistive structure according to an embodiment of the present invention, and FIG. A schematic cross-sectional view of the piezoresistive structure 1 at a position corresponding to the portion A is shown. The piezoresistive portion 2 of the piezoresistive structure 1 of this embodiment is composed of a p-type semiconductor formed by doping impurities into a part of the surface of a base 3 made of an n-type semiconductor, and responds to changes in stress. The magnitude of the electrical resistance changes. Both end sides 2H and 2L of the piezoresistive section 2 are joined to the terminal section 4 (4H and 4L) as shown in FIG. 1B. The terminal portions 4H and 4L have the same configuration as the terminal portion 48 (48H and 48L) shown in FIG. 7, and in this embodiment, the terminal portion 4H is a high voltage applying means (not shown). The terminal 4L is connected to the potential side (for example, 5V voltage supply side), and the low potential side (for example, ground) of the voltage applying means. A voltage is applied to the piezoresistive section 2 from the voltage applying means via the terminal sections 4H and 4L.

  In this embodiment, the base 3 is electrically connected to the high potential side of the voltage applying means. For this reason, when a voltage is applied to the piezoresistor 2 and the base 3 by the voltage applying means, the potential difference between the piezoresistor 2 and the base 3 (that is, the potential difference between PN) is the same as that of the piezoresistor 2. It becomes larger from the end 2H side which is the high potential side toward the end 2L side which is the low potential side. Thus, when a voltage is applied to the piezoresistive portion 2 and the base 3, the thickness D of the depletion layer H formed at the PN junction portion between the piezoresistive portion 2 and the base 3 is the end of the piezoresistive portion 2. The thickness of the piezoresistive portion 2 increases from the end 2H side to the end 2L side due to the thickness D of the depletion layer H. The thinner it becomes.

  In this embodiment, a voltage is applied to the piezoresistive portion 2 and the base 3, and the thickness D of the depletion layer H at the PN junction portion between the piezoresistive portion 2 and the base 3 is increased from the end 2H side of the piezoresistive portion 2 to the end. Even if the thickness d of the piezoresistive portion 2 decreases from the end portion 2H side toward the end portion 2L side, the electric resistance of the piezoresistive portion 2 increases as a whole. It has a configuration that is uniform over the range. That is, as shown in FIG. 1A, the piezoresistive portion 2 is continuously widened from the end 2H side toward the end 2L side, and a voltage is applied to the piezoresistive portion 2. In the state, the effective cross-sectional areas of the current conduction paths are equalized and the electric resistances are the same from the end 2H toward the end 2L.

  The piezoresistive structure 1 according to this embodiment is configured as described above. Next, an embodiment of an external force detection sensor including the piezoresistive structure 1 will be described. The external force detection sensor is an acceleration sensor, and has a configuration unique to the detection unit of the acceleration sensor. Other configurations are the same as those of the acceleration sensor 30 in FIG. 5 described above. In the description of the acceleration sensor according to this embodiment, the same components as those of the acceleration sensor 30 described above are denoted by the same reference numerals, and redundant description of the common portions is omitted.

  The detection part of the acceleration sensor of this embodiment has four piezoresistive parts 2 of the piezoresistive structure 1 described above. These four piezoresistive portions 2 are formed on the cantilever 33 with the active layer 41 of the SOI substrate 38 as the base 3 and constitute a bridge circuit 6 as shown in FIG. In other words, the four piezoresistive portions 2 (2a to 2d) are arranged at the positions of the respective sides of the quadrangular shape and are formed via the terminal portions 4 (the terminal portion 4 is not shown in FIG. 2) so as to form a quadrangular shape. Electrically connected. One connecting portion 7 (Vdd) of the four connecting portions 7 is connected to a high potential side (for example, 5 V voltage supply side) of a voltage applying means (not shown), and the diagonal of the connecting portion 7 (Vdd). The position connecting portion 7 (Vgnd) is connected to the low potential side (for example, ground) of the voltage applying means. The remaining connecting portions 7 (Vo1, Vo2) are external force detecting means (not shown) for detecting the magnitude of acceleration, which is an external force, based on the difference in potential output by the connecting portions 7 (Vo1, Vo2). )It is connected to the.

  In this bridge circuit 6, when a voltage is applied between the connecting portions 7 (Vdd) and 7 (Vgnd) by the voltage applying means, a PN junction between the piezoresistive portion 2 (2 a to 2 d) and the active layer 41 that is the base 3. The thickness D of the partial depletion layer H increases from the high potential side end 2H side to the low potential side end 2L side of the piezoresistive portion 2 (2a, 2d). 2b, 2c) the thickness increases from the high potential side end 2H side toward the low potential side end 2L side. For this reason, the thickness d of the piezoresistive portion 2 (2a to 2d) increases from the end 2H side to the end 2L side of the piezoresistive portion 2 (2a, 2d), and further, the piezoresistive portion 2 (2b, 2c). ) Becomes thinner from the end 2H side toward the end 2L side. In this embodiment example, the thickness D of the depletion layer H when a voltage is applied is taken into consideration so that the electric resistances of all the piezoresistive portions 2 (2a to 2d) are uniform throughout. 2, the piezoresistive portion 2 (2a, 2d) is widened from the end 2H side toward the end 2L side, and the piezoresistive portion 2 (2b, 2c) The width of the piezoresistive portion 2 (2a to 2d) is increased as the width of the piezoresistive portion 2 (2a to 2d) is increased. It is formed so that the effective area is the same.

  Below, an example of the manufacturing process of the acceleration sensor of this embodiment is demonstrated based on FIG. 3, FIG.

  First, formation regions such as the piezoresistive portion 2 and the terminal portion 4 (joining portion 49 of the terminal portion 48) of the piezoresistive structure 1 in the active layer 41 of the SOI substrate 38 as shown in FIG. Impurities are doped in the respective formation regions from the surface side of the active layer 41 to form the piezoresistive portion 2 and the terminal portion 4 (49) as shown in the enlarged view of FIG. In this step, as shown in FIG. 1A, the impurity doped region is controlled so that the piezoresistive portion 2 becomes wider as it goes from the one end 2H side to the other end 2L side. Resistor 2 is formed. Examples of the impurity doping method in this step include various methods such as a gas layer diffusion method, a solid layer diffusion method, and an ion implantation method, and any method may be used here.

Next, as shown in FIG. 3C, an insulating layer 44 is formed on the surface of the active layer 41 of the SOI substrate 38. The insulating layer 44 protects the surface of the active layer 41 and insulates the active layer 41 from the electrodes and wirings formed on the surface of the insulating layer 44. For example, when an oxide film such as SiO ₂ is formed as the insulating layer 44, the insulating layer 44 is formed by oxidizing the surface portion of the active layer 41 by, for example, a thermal oxidation method. When a SiNx film is formed as the insulating layer 44, the insulating layer 44 is stacked on the active layer 41 by, for example, a p-CVD method.

  After the formation of the insulating layer 44, as shown in FIG. 3D, a contact hole 51 (see FIG. 7 for example) is formed at a predetermined position of the insulating layer 44. The contact hole 51 can be formed using, for example, a photolithography technique. That is, first, a resist film is formed on the entire surface of the insulating layer 44, and then a resist film portion other than the contact hole forming region is formed using a contact hole forming position regulating mask disposed above the resist film. Cured by UV irradiation. Then, the uncured portion of the resist film, that is, the resist film portion in the conductor hole forming region is removed to form a through hole in the resist film. Thereafter, using the through hole of the resist film, the portion of the insulating film 44 where the through hole is disposed is removed by, for example, a dry etching method or a wet etching method to form the contact hole 51. Thereafter, the resist film is removed by, for example, an ashing technique. In this way, the contact hole 51 can be formed.

  After the contact hole 51 is formed in the insulating film 44, as shown in FIG. 3E, a conductor pattern formed with the electrode 50, the wiring pattern 52, the electrode pad 35A, and the like is formed on the surface of the insulating layer 44. This conductor pattern can also be formed using, for example, photolithography. For example, a conductor film is formed on the entire surface of the insulating layer 44 by a film formation technique such as sputtering, and then a resist film is formed on the entire surface of the conductor film. Then, the resist film portion in the conductor pattern forming region is cured by ultraviolet irradiation using a conductor pattern forming mask arranged on the upper side of the resist film. Then, the uncured portion of the resist film, that is, the resist film portion other than the conductor pattern formation region is removed. Thereafter, the portion of the conductor film where the resist film is not formed is removed by, for example, a dry etching method or a wet etching method to form a conductor pattern. In this manner, a conductor pattern that forms the electrode 50, the wiring pattern 52, the electrode pad 35A, and the like is formed on the surface of the insulating layer 44. Note that a part of the conductor material forming the conductor film enters the inside of the contact hole 51 in the step of forming the conductor film on the entire surface of the insulating layer 44. The conductor material (electrode 50) formed on the surface of the insulating layer 44 and the terminal portion 49 of the terminal portion 4 formed on the active layer 41 of the SOI substrate 38 by the conductive material that has entered the contact hole 51, for example. And a conduction path is formed.

After the conductor pattern is formed on the surface of the insulating layer 44, as shown in FIG. 4A, the through hole 42 is formed in the SOI substrate 38 by dry etching or wet etching to form the weight portion 31, and the SOI pattern is formed. The cantilever 33 is formed by removing the support layer 39 in the formation region of the cantilever 33 on the substrate 38 by dry etching or wet etching. In this manner, the weight portion 31, the fixing portion 32, and the cantilever 33 are formed on the SOI substrate 38. The support layer 39 and the active layer 41 that are Si layers and the oxide layer 40 that is a SiO ₂ layer are difficult to remove in the same etching step because the materials constituting the layers are different. Therefore, the etching of the support layer 39 and the active layer 41 and the etching of the oxide layer 40 are performed in separate steps. 4A to 4D, illustration of the piezoresistive portion 2, the terminal portion 4, the electrode 50, and the conductor pattern 52 is omitted.

  Thereafter, as shown in FIG. 4B, the adhesive layer 43 is laminated on the entire surface of the fixing portion 32 on the surface on the active layer 41 side and the surface on the support layer 39 side. Then, sealing members 36 made of glass substrates are arranged on both upper and lower sides of the SOI substrate 38 on which the weight portion 31, the fixing portion 32, and the cantilever 33 are formed, and are bonded to the SOI substrate 38 by the adhesive layer 43.

  Thereafter, as shown in FIG. 4 (c), a through hole 35B extending from the surface of the sealing member 36 to the electrode pad 35A is formed. As shown in FIG. 4 (d), the inside of the through hole 35B is formed. Conductive film 35C is formed on the wall surface and the opening edge.

  Through the manufacturing process as described above, an acceleration sensor that is an external force detection sensor can be manufactured.

  In addition, this invention is not limited to the form of the said embodiment, Various embodiments can be taken. For example, in this embodiment example, the piezoresistive portion 2 of the piezoresistive structure 1 is arranged from the one end 2H side so that the effective cross-sectional area of the current conduction path is uniform over the whole in a state where a voltage is applied. For example, the difference between the potential difference between the one end 2H side of the piezoresistive portion 2 and the base 3 and the potential difference between the other end 2L side and the base 3 has been described. When the change in the thickness of the depletion layer H that changes from the one end 2H side to the other end 2L side of the piezoresistive portion 2 is gradual, the piezoresistive portion 2 is connected to the other end 2L from the one end 2H side. It may be a form in which the width is gradually increased toward the side. In this embodiment, the width of the piezoresistive section 2 is changed from one end 2H side to the other end 2L side in order to make the effective cross-sectional area of the current conduction path of the piezoresistor section 2 uniform over the entire piezoresistor section 2. It was set as the structure widened continuously or in steps as it goes to. In other words, by adjusting the width of the piezoresistive portion 2, the effective cross-sectional area of the current conduction path of the piezoresistive portion 2 when a voltage is applied is made uniform, and the entire piezoresistive portion 2 is electrically Although the magnitudes of the resistances are made equal, for example, by adjusting the depth of the piezoresistive part 2, the electrical resistances may be made equal across the entire piezoresistive part 2. Good.

  In this embodiment, the piezoresistive structure 1 is provided as a detection unit of an acceleration sensor that is an external force detection sensor. For example, the piezoresistive structure 1 is provided as a detection unit for an angular velocity sensor that is an external force detection sensor. The external force detection sensor provided with the piezoresistive structure 1 is not limited to the acceleration sensor, and may be provided in an external force detection sensor other than the acceleration sensor. Further, in this embodiment, the detection unit of the external force detection sensor (acceleration sensor) is configured by a bridge circuit including four piezoresistive units 2, but the piezoresistive unit 2 is configured by a configuration other than the bridge circuit to detect external force. You may comprise the detection part of a sensor.

  Furthermore, in this embodiment, in the acceleration sensor, the SOI substrate 38 and the sealing member 36 that is a glass substrate are bonded by the adhesive layer 43, but the support layer 39 that is a silicon layer of the SOI substrate 38 and The active layer 41 and the sealing member 36 that is a glass substrate may be bonded by an anodic bonding method. In this case, for example, in order to form a gap between the weight portion 31 and the sealing member 36, a concave portion is formed in the sealing member 36 at a portion facing the weight portion 31. .

  Furthermore, in the configuration of the acceleration sensor which is an external force detection sensor in this embodiment, the active layer 41 (base 3) has the same voltage as the high potential side voltage applied to the connection portion 7 (Vdd) of the bridge circuit. For example, the active layer 41 (base 3) may be grounded to the ground. In this case, in a state where a voltage is applied to the piezoresistive portion 2, the piezoresistive portion 2 has a higher potential side (end portion 2H side) than a low potential side (end portion 2L side). The thickness D of the depletion layer H at the PN junction portion between the portion 2 and the base 3 is increased. Therefore, in this case, for example, the piezoresistive unit 2 is directed from the end 2L side to the end 2H side in order to equalize the effective cross-sectional area of the current conduction path in a state where a voltage is applied. Accordingly, the width is increased continuously or stepwise.

  Furthermore, in this embodiment, the detection unit of the acceleration sensor that is an external force detection sensor is configured by a bridge circuit having four piezoresistive units 2. For example, at least one of the four piezoresistive units 2 is used. Another piezoresistive portion may be connected in series to one piezoresistive portion to form one square side. Furthermore, for example, the detection unit of the acceleration sensor may be configured by only one piezoresistive unit, and if the detection unit of the external force detection sensor has at least one piezoresistive unit, the configuration is configured in a bridge circuit. It is not limited.

  Further, in this embodiment example, the piezoresistive portion 2 is formed of a p-type semiconductor and the base 3 (active layer 41) is formed of an n-type semiconductor. However, the piezoresistive portion 2 is formed of an n-type semiconductor, The base 3 (active layer 41) may be a p-type semiconductor.

It is a model figure for demonstrating one example of a characteristic piezoresistive part in the piezoresistive structure of the embodiment which concerns on this invention. In the external force detection sensor of the example of an embodiment, it is a figure for explaining one example of composition of the detecting part formed with the piezoresistive part shown in FIG. It is a flowchart of the manufacturing process for demonstrating the manufacturing process example of an external force detection sensor. FIG. 4 is a flowchart of a manufacturing process for explaining an example of the manufacturing process of the external force detection sensor following FIG. 3. It is a figure for demonstrating an example of the external force detection sensor provided with the piezoresistive part. It is a figure for demonstrating one prior art example of the piezoresistive part provided as a detection part of an external force detection sensor. It is typical sectional drawing showing the example of 1 structure of the piezoresistive part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piezoresistive structure 2 Piezoresistive part 3 Base 6 Bridge circuit 7 Connection part

Claims (3)

A piezoresistive structure having a piezoresistive portion that is formed on a part of a surface of a base made of a semiconductor and changes in magnitude according to a stress change,
One of the base and the piezoresistive portion is a p-type semiconductor, and the other is an n-type semiconductor.
The piezoresistive portion is configured such that one end side is electrically connected to the high potential side of the voltage applying means, and the other end side is electrically connected to the low potential side of the voltage applying means, and the voltage is applied. When a voltage is applied to the piezoresistive portion, a depletion layer whose thickness increases as the potential difference between the PNs increases in the PN junction region between the piezoresistive portion and the base portion below the piezoresistive portion. Formed, the thickness of the piezoresistive portion becomes thinner as the thickness of the depletion layer increases,
The piezoresistor is continuously or stepwise so that the effective cross-sectional area of the current conduction path becomes equal from the high potential end to the low potential end in a state where the voltage is applied by the voltage applying means. A piezoresistive structure characterized in that it is formed by changing its width or thickness. A movable part configured by a semiconductor and deformed by an external force to be detected;
A detector for detecting the magnitude of the external force by detecting the amount of deformation of the movable part that increases as the magnitude of the external force applied to the movable part increases;
An external force detection sensor having
The piezoresistive portion according to claim 1, wherein the detecting portion is formed based on a movable portion, and detects a change amount of a voltage due to a change in electric resistance of the piezoresistive portion as a magnitude of an external force. External force detection sensor. The detection unit is configured to include at least four piezoresistive units, and these four piezoresistive units are arranged at respective positions constituting each side of the quadrangular shape so as to form a square shape. To form a bridge circuit, and one of the four connection parts of the piezoresistive part of the bridge circuit is on the high potential side of the voltage application means and on the diagonal position of the connection part. The connecting portions are electrically connected to the low potential side of the voltage applying means, respectively, and the remaining two connecting portions detect the magnitude of the external force based on the potential difference detected by the two connecting portions. A configuration connected to the external force detection means,
Each of the piezoresistive portions is formed so that the effective cross-sectional areas of the current conduction paths of all the piezoresistive portions are equal when the voltage is applied to the four piezoresistive portions of the bridge circuit by the voltage applying means. The external force detection sensor according to claim 2, wherein:

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