JP6028677B2 - Force sensing element - Google Patents

Description

  The technology disclosed in the present specification relates to a force sensing element that utilizes the piezoresistance effect of a semiconductor crystal.

  Force sensing elements utilizing the piezoresistance effect of semiconductor crystals have been developed. FIG. 5 illustrates a force detection element 100 to which the technique disclosed in Patent Document 1 is applied. The force detection element 100 includes a semiconductor substrate 110, a pair of electrode constellations 122 and 124, and a force transmission block 130. Grooves 112A and 112B are formed on the surface of the semiconductor substrate 110, and a mesa step 113 extends across the grooves 112A and 112B. On the surface of the semiconductor substrate 110 including the mesa step 113, a gauge portion 114 into which p-type impurities are introduced is formed. One end of the gauge portion 114 is exposed in the through hole 122 a of the first electrode constellation portion 122, and the other end is exposed in the through hole 124 a of the second electrode constellation portion 124. An electrode (not shown) formed on the surface of the first electrode constellation portion 122 is electrically connected to one end of the gauge portion 114 through the through hole 122a. An electrode (not shown) formed on the surface of the second electrode constellation portion 124 is electrically connected to the other end of the gauge portion 114 through the through hole 124a. The force transmission block 130 is joined so as to come into contact with the top surface of the mesa step 113 and the surface of the peripheral edge 115 of the grooves 112A and 112B.

  In the force detection element 100, when compressive stress is applied to the mesa step 113 via the force transmission block 130, the electrical resistance of the gauge portion 114 formed on the mesa step 113 changes due to the piezoresistance effect. Therefore, an output signal corresponding to the compressive stress can be obtained by applying a constant current or applying a constant voltage to the gauge portion 114 via the electrodes formed on the pair of electrode constellation portions 122 and 124. .

JP 2004-132911 A

  FIG. 6 shows a longitudinal distribution of compressive stress applied to the mesa step 113. As described above, the compressive stress applied to the mesa step 113 is small at the end where the mesa step 113 is connected to the peripheral edge 115 of the grooves 112A and 112B and has a large distribution at the center. The breaking strength of the mesa step 113 depends on the maximum compressive stress applied to the mesa step 113. On the other hand, the sensitivity of the force detection element 100 depends on the average value of the compressive stress applied to the mesa step 113. Therefore, as shown in FIG. 6, if the difference between the maximum compressive stress and the minimum compressive stress applied to the mesa step 113 is large, the difference between the maximum compressive stress applied to the mesa step 113 and the average value also increases, and the force sensing element 100 The trade-off relationship between reliability and sensitivity becomes a problem.

  The technology disclosed in the present specification aims to make the longitudinal distribution of the compressive stress applied to the mesa step uniform and improve the trade-off relationship between the reliability and sensitivity of the force detection element.

  One embodiment of the force sensing element disclosed in this specification includes a semiconductor substrate having a gauge portion formed in a mesa step extending across a groove, and a top surface of the mesa step and a peripheral portion of the groove. It has a force transmission block that contacts the surface. The mesa step extends along the first direction between the first end connected to the peripheral edge of the groove and the second end connected to the peripheral edge of the groove. When measured along a second direction orthogonal to the first direction, the distance from the first end to the peripheral edge of the groove is the first distance, and the distance from the second end to the peripheral edge of the groove is the second. The third distance is shorter than the first distance and the second distance, where the distance from the intermediate portion between the first end and the second end to the peripheral edge of the groove is the third distance.

  In the force detection element of the above form, the distribution in the longitudinal direction of the compressive stress applied to the mesa step is made uniform. Thereby, in the force detection element of the said form, the trade-off relationship between reliability and a sensitivity is improved.

FIG. 1 schematically shows a perspective view of the force detection element of the embodiment. FIG. 2 schematically shows a cross-sectional view corresponding to the line II-II in FIG. 1 in the force detection element of the embodiment. FIG. 3 schematically shows a plan view of the force detection element of the embodiment. FIG. 4 schematically shows a plan view of an example of a modification of the force detection element of the embodiment. FIG. 5 schematically shows a perspective view of a conventional force detection element. FIG. 6 shows a plan view of a conventional force detection element and a distribution of compressive stress applied to a mesa step.

The technical features disclosed in this specification will be summarized below. The items described below have technical usefulness independently.
(Feature 1) One embodiment of the force detection element disclosed in the present specification may include a semiconductor substrate and a force transmission block. The semiconductor substrate may have a gauge portion formed at a mesa step extending across the groove. The force transmission block may contact the top surface of the mesa step and the surface of the peripheral edge of the groove. The mesa step may extend along the first direction between the first end connected to the peripheral edge of the groove and the second end connected to the peripheral edge of the groove. Thus, the gauge part of a force detection element may be comprised by the uniaxial. When measured along a second direction orthogonal to the first direction, the distance from the first end to the peripheral edge of the groove is the first distance, and the distance from the second end to the peripheral edge of the groove is the second. The third distance may be shorter than the first distance and the second distance, where the distance is the third distance from the intermediate portion between the first end and the second end to the peripheral edge of the groove.
(Feature 2) The third distance may be the shortest distance from the mesa step to the peripheral edge of the groove when measured along the second direction. According to this embodiment, the longitudinal distribution of the compressive stress applied to the mesa step is satisfactorily uniform, and the trade-off relationship between the reliability and sensitivity of the force detection element is improved.
(Feature 3) When measured along the second direction, the longest distance of the distance from the mesa step to the peripheral edge of the groove may be the first distance and the second distance. According to this embodiment, the longitudinal distribution of the compressive stress applied to the mesa step is satisfactorily uniform, and the trade-off relationship between the reliability and sensitivity of the force detection element is improved.
(Feature 4) The width of the mesa step in the second direction may be wider at the intermediate portion than at the first end and the second end. The maximum width of the mesa steps in the second direction may be formed in the intermediate portion. The minimum width of the mesa steps in the second direction may be formed at the first end and the second end.
(Feature 5) The width of the mesa step in the second direction may gradually increase or discontinuously increase between the first end portion and the intermediate portion. Similarly, the width of the mesa step in the second direction may gradually increase or discontinuously increase between the second end portion and the intermediate portion. The width of the mesa step in the second direction may be adjusted as appropriate so that the longitudinal distribution of the compressive stress applied to the mesa step is made uniform.
(Characteristic 6) The peripheral edge portion of the groove existing away from the mesa step in the second direction may protrude in a convex shape toward the mesa step. The top part of the convex peripheral part (which can also be said to be a local maximum) may be arranged corresponding to the intermediate part of the mesa step when observed along the second direction.

  As shown in FIGS. 1 to 3, the force detection element 1 includes a semiconductor substrate 10, a pair of electrode constellations 22 and 24, and a force transmission block 30.

  The semiconductor substrate 10 is n-type single crystal silicon, and the surface thereof is a (110) crystal plane. On the surface of the semiconductor substrate 10, substantially rectangular grooves 12A and 12B are formed. The grooves 12A and 12B are defined by a pair of first peripheral edge portions 15a and a pair of second peripheral edge portions 15b. The pair of first peripheral edge portions 15a extends in parallel to the first direction (the <110> direction of the semiconductor substrate 10, hereinafter referred to as the longitudinal direction). The pair of second peripheral edge portions 15b extends in parallel to a second direction (a <100> direction of the semiconductor substrate 10 and hereinafter referred to as a width direction) orthogonal to the first direction. Further, a mesa step 13 extending along the longitudinal direction between the second peripheral edge portions 15b of the grooves 12A and 12B is formed on the surface of the semiconductor substrate 10. For convenience, one of the grooves 12A and 12B divided by the mesa step 13 will be referred to as “12A” and the other as “12B”.

The mesa step 13 protrudes in a mesa shape from the bottom surface of the grooves 12A and 12B, and its height is about 0.5 to 5 μm. The top surface of the mesa step 13 is located on the same plane as the surface of the peripheral edge 15 of the grooves 12A and 12B. In other words, the mesa step 13 is formed as a remaining portion in which the grooves 12A and 12B are formed on the surface of the semiconductor substrate 10 by using, for example, a dry etching technique. On the surface of the semiconductor substrate 10 including the mesa step 13, a gauge portion 14 into which p-type impurities are introduced is formed. The impurity concentration of the gauge part 14 is about 1 × 10 ¹⁸ to 1 × 10 ²¹ cm ⁻³ . The gauge portion 14 is substantially insulated from the n-type semiconductor substrate 10 by a pn junction.

  The pair of electrode constellations 22 and 24 are disposed on the surface of the semiconductor substrate 10 with the grooves 12A and 12B interposed therebetween, and are disposed at positions other than the range in which the force transmission block 30 is disposed. An insulator is used as the material of the pair of electrode constellations 22 and 24. In one example, an oxide film is used. A through hole 22 a is formed in the first electrode constellation 22. One end of the gauge portion 14 is formed to extend from the mesa step 13 along the longitudinal direction of the surface of the semiconductor substrate 10 below the first electrode constellation portion 22 and is exposed from the through hole 22a. An electrode (not shown) formed on the surface of the first electrode constellation portion 22 is connected to one end of the gauge portion 14 through the through hole 22a. A through hole 24 a is formed in the second electrode constellation portion 24. The other end of the gauge portion 14 is formed by extending the surface of the semiconductor substrate 10 below the second electrode constellation portion 24 along the longitudinal direction from the mesa step 13, and is exposed from the through hole 24a. An electrode (not shown) formed on the surface of the second electrode constellation portion 24 is connected to the other end of the gauge portion 14 through the through hole 24a.

  The force transmission block 30 has a rectangular parallelepiped shape, and glass is used as the material thereof. The lower surface of the force transmission block 30 is bonded to the top surface of the mesa level difference 13 and the surface of the peripheral edge portion 15 of the grooves 12A and 12B by using, for example, electrostatic bonding. The force transmission block 30 is joined to the peripheral edge 15 over the entire periphery of the peripheral edge 15 of the grooves 12A and 12B. For this reason, the grooves 12 </ b> A and 12 </ b> B and the mesa step 13 are sealed by the force transmission block 30.

  In the force detection element 1, when compressive stress is applied to the mesa step 13 via the force transmission block 30, the electrical resistance of the gauge portion 14 formed on the mesa step 13 changes due to the piezoresistance effect. Therefore, an output signal corresponding to the compressive stress can be obtained by applying a constant current or applying a constant voltage to the gauge portion 14 via the electrodes formed on the pair of electrode constellations 22 and 24. .

  As shown in FIG. 3, the mesa step 13 is characterized in that the width in the width direction changes along the longitudinal direction. Here, one end portion where the mesa step 13 is connected to the second peripheral portion 15b is referred to as a first end portion 13a, and the other end portion where the mesa step 13 is connected to the second peripheral portion 15b is referred to as a second end portion 13b. That's it. Further, when measured along the longitudinal direction, a portion of the mesa step 13 where the distance from the first end portion 13a is equal to the distance from the second end portion 13b is referred to as an intermediate portion 13c. The force detection element 1 has a point-symmetric form with respect to the intermediate portion 13 c of the mesa step 13. For this reason, in the following, it should be noted that the description of the first end portion 13a also serves as the description of the equivalent second end portion 13b.

  As shown in FIG. 3, in the force detection element 1, the width W13c of the intermediate portion 13c is configured to be wider than the width W13a of the first end portion 13a. Further, in this example, the width W13c of the intermediate portion 13c is the maximum, and the width W13a of the first end portion 13a is the minimum. The width of the mesa step 13 gradually increases from the first end portion 13a toward the intermediate portion 13c. For example, the width of the mesa step 13 is preferably set based on the stress when the width of the mesa step is constant (see FIGS. 5 and 6). Specifically, when the width of the mesa step is constant (see FIGS. 5 and 6), the compressive stress applied to the middle part of the mesa step (corresponding to the left end of the stress distribution in FIG. 6) is P1, and the mesa step When the compressive stress applied to the end portion (corresponding to the right end of the stress distribution in FIG. 6) is P2, the width W13c of the intermediate portion 13c and the width W13a of the first end portion 13a of the mesa step 13 of this embodiment are P1. : P2 = W13c: It is desirable to set W13a. It is desirable that the width between the intermediate portion 13c and the first end portion 13a of the mesa step 13 is set similarly.

  For this reason, in the force detection element 1, when measured in the width direction, the distance W12c between the intermediate portion 13c and the first peripheral portion 15a is the first distance between the mesa step 13 and the first peripheral portion 15a. It is configured to be shorter than the distance W12a between the end portion 13a and the first peripheral edge portion 15a. Further, in this example, the distance W12c between the intermediate portion 13c and the first peripheral portion 15a is the minimum, and the distance W12a between the first end portion 13a and the first peripheral portion 15a is the maximum. The distance W12c between the intermediate portion 13c and the first peripheral edge portion 15a is evaluated as Wo−W13c / 2 when the distance between the center line of the mesa step 13 and the first peripheral edge portion 15a is Wo. Can do. Similarly, the distance W12a between the first end portion 13a and the first peripheral edge portion 15a can be evaluated as Wo−W13a / 2.

  With such a configuration, the compressive stress applied to the intermediate portion 13c of the mesa step 13 and the compressive stress applied to the first end portion 13a are compared with the case where the width of the mesa step is constant (see FIGS. 5 and 6). The difference becomes smaller. Thereby, the compressive stress applied to the mesa step 13 is made uniform in the longitudinal direction, and the difference between the maximum compressive stress applied to the mesa step 13 and the average value of the compressive stress is reduced. As a result, the trade-off relationship between the reliability and sensitivity of the force detection element 1 is improved.

  In the modified force detection element 2 shown in FIG. 4, the width of the mesa step 13 is constant along the longitudinal direction. On the other hand, the first peripheral edge 15 a protrudes in a convex shape toward the mesa step 13. The top portion of the first peripheral edge portion 15a is formed at a position corresponding to the intermediate portion 13c of the mesa step 13 when observed in the width direction. Also in this example, the distance between the intermediate portion 13c of the mesa step 13 and the first peripheral portion 15a is shorter than the distance between the first end portion 13a of the mesa step 13 and the first peripheral portion 15a. For this reason, the compressive stress applied to the mesa step 13 is made uniform in the longitudinal direction, and the difference between the maximum compressive stress applied to the mesa step 13 and the average value of the compressive stress is reduced. As a result, the trade-off relationship between the reliability and sensitivity of the force detection element 2 is improved. In the force detection element 2 as well, like the force detection element 1, the width of the mesa step 13 may change along the longitudinal direction.

  Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above. The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or the drawings can achieve a plurality of objects at the same time, and has technical usefulness by achieving one of the objects.

10: Semiconductor substrate 12A, 12B: Groove 13: Mesa step 14: Gauge part 15: Peripheral part 22, 24: Electrode constellation part 30: Force transmission block

Claims (3)

A semiconductor substrate having a gauge portion formed in a mesa step extending across the groove;
A force transmission block that contacts the top surface of the mesa step and the peripheral surface of the groove;
The mesa step extends along a first direction between a first end connected to the peripheral edge of the groove and a second end connected to the peripheral edge of the groove;
When measured along a second direction orthogonal to the first direction, the distance from the first end to the peripheral edge of the groove is defined as a first distance, and the peripheral edge of the groove from the second end The second distance is the distance to the portion, and the third distance is the distance from the intermediate portion between the first end portion and the second end portion to the peripheral edge portion of the groove. A force sensing element shorter than the first distance and the second distance.   The force detection element according to claim 1, wherein a width of the mesa step in the second direction is wider at the intermediate portion than at the first end portion and the second end portion.   The force detection element according to claim 1, wherein the peripheral edge portion of the groove that is separated from the mesa step in the second direction protrudes in a convex shape toward the mesa step.

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