JP2018059726A - Pressure sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To implement a pressure sensor which is miniaturized while maintaining sensitivity, without thinning of a silicon active layer.SOLUTION: A pressure sensor 1A relating to this invention is a semiconductor pressure sensor comprising: a silicon substrate 100 having a cavity 102 and a base part 101 surrounding the cavity 102; and a silicon active layer 120 formed on the silicon substrate 100 so as to cover the cavity 102. The silicon active layer 120 has a deformable movable part 121 disposed in a position corresponding to the cavity 102, a fixed part 122 disposed on the base part 101 and fixed to the base part 101, and a plurality of gauge resistances 124 to 127 formed at a peripheral edge of the movable part 121 to detect deformation of the movable part 121, and a silicon active layer non-formation part 123 where the silicon active layer 120 is not formed is provided on the base part 101 at least in the vicinity of the gauge resistances 124 to 127.SELECTED DRAWING: Figure 1

Description

The present invention relates to a pressure sensor.

A general piezoresistive pressure sensor includes, for example, an SOI substrate in which a silicon oxide film is formed in the middle in the thickness direction and a silicon active layer is formed on the main surface side as described in Patent Document 1, and a back surface of the SOI substrate. A diaphragm portion formed by providing a pressure introduction hole reaching the silicon oxide film from the surface, a gauge resistor formed on the main surface side in the silicon active layer for detecting deformation of the diaphragm portion, and on the silicon active layer And a formed surface oxide film. The gauge resistor is usually formed by diffusing impurities in the silicon active layer, and the four gauge resistors are usually connected to form a bridge circuit.

JP 2000-356560 A

In recent years, mobile electronic terminals, high-performance wristwatches, and the like have become more and more miniaturized, and pressure sensors mounted thereon are required to be further miniaturized while maintaining sensitivity to applied pressure. In order to maintain the sensitivity even when the area of the diaphragm portion is reduced due to downsizing, the diaphragm portion needs to be deformed to the same degree with respect to the same pressure, and as a means of the silicon active layer including the diaphragm portion, There is thinning. However, there is a manufacturing limitation in reducing the thickness of the silicon active layer.

Therefore, the problem to be solved by the present invention is to realize a pressure sensor that is downsized while maintaining sensitivity without reducing the thickness of the silicon active layer.

A pressure sensor according to the present invention is a semiconductor pressure sensor comprising a base substrate having a cavity and a base surrounding the cavity, and a silicon active layer formed on the base substrate so as to cover the cavity, The silicon active layer is disposed at a position corresponding to the cavity and can be deformed, a fixed portion disposed on the base and fixed to the base, and a periphery of the movable portion. A plurality of gauge resistors for detecting deformation, and a silicon active layer non-formation portion where the silicon active layer is not formed is provided at least in the vicinity of the gauge resistance above the base portion. And

  The pressure sensor according to the present invention is a semiconductor pressure sensor comprising a base substrate having a cavity and a base portion surrounding the cavity, and a silicon active layer formed on the base substrate so as to cover the cavity. The silicon active layer is formed at a position corresponding to the cavity and can be deformed, a fixed portion disposed on the base and fixed to the base, and a periphery of the movable portion. A plurality of gauge resistors for detecting deformation of the portion, and a silicon active layer non-forming portion where the silicon active layer is not formed is provided at least in the vicinity of the gauge resistance above the base portion Therefore, the stress generated near each gauge resistance of the silicon active layer when pressure is applied becomes difficult to relax, and the molecular level of each gauge resistance is reduced. Kicking distortion increases. As a result, it is possible to realize a miniaturized pressure sensor while maintaining sensitivity without reducing the thickness of the silicon active layer.

  The silicon active layer non-forming part may be provided over the entire periphery of the upper part of the base part.

  The silicon active layer non-formation part may be composed of a plurality of notches and may be provided apart from each other.

  An insulating layer may be formed between the base substrate and the silicon active layer.

The base substrate may have a bottom portion below the cavity.

According to the present invention, it is possible to realize a pressure sensor that is miniaturized while maintaining sensitivity without reducing the thickness of the silicon active layer.

It is a figure which shows 1st Embodiment of the pressure sensor which concerns on this invention, (a) is sectional drawing, (b) is a top view. It is a figure which shows 2nd Embodiment of the pressure sensor which concerns on this invention, (a) is sectional drawing, (b) is a top view. It is a figure which shows 3rd Embodiment of the pressure sensor which concerns on this invention, (a) is sectional drawing, (b) is a top view. It is a figure which shows the pressure sensor 10 of a comparative example, (a) is sectional drawing, (b) is a top view. It is a graph of the stress simulation of the pressure sensor 1A of this invention and the pressure sensor 10 of a comparative example.

  Hereinafter, a preferred embodiment of a pressure sensor according to the present invention will be described with reference to the drawings.

1A and 1B are views showing a first embodiment of a pressure sensor according to the present invention, in which FIG. 1A is a sectional view and FIG. 1B is a plan view.
As shown in FIG. 1, a pressure sensor 1A according to the present invention is formed by laminating a silicon substrate 100 as a base substrate, a silicon oxide film 110 as an insulating layer, and a silicon active layer 120 in this order. The silicon substrate 100 includes a cavity 102, a base 101 that surrounds the cavity 102, and a bottom 103 that is positioned below them. Here, the silicon active layer 120 is formed on the silicon substrate 100 via the silicon oxide film 110 so as to cover the cavity 102. In addition, the silicon active layer 120 is formed at a position corresponding to the cavity 102 and can be deformed, a fixed portion 122 disposed on the base 101 and fixed to the base 101, and formed on the periphery of the movable portion 121. And a plurality of gauge resistors 124 to 127 that detect deformation of the movable portion 121 and wiring 128 that electrically connects the gauge resistors 124 to 127. Furthermore, a silicon active layer non-forming portion 123 in which the silicon active layer 120 is not formed is provided over the entire periphery of the upper portion of the base 101. The silicon active layer non-forming part 123 is provided by removing the periphery of the silicon active layer 120 by wet etching, dry etching, or the like at the time of manufacture.

  In the pressure sensor 1A, the movable part 121 of the silicon active layer 120 and the silicon oxide film 110 immediately below the movable part 121 are integrated to operate as the diaphragm part 130. However, the silicon oxide film 110 is not essential, and when the silicon oxide film 110 is not present, only the movable part 121 of the silicon active layer 120 operates as the diaphragm part 130. The definition of the diaphragm portion is the same in the other embodiments.

  The gauge resistors 124 to 127 constitute a detection circuit that detects pressure fluctuation applied to the diaphragm section 130, and are connected to each other so as to constitute a so-called Wheatstone bridge circuit via the wiring 128. A land 129 for wire bonding is formed at an intermediate portion of the wiring 128.

  Such gauge resistors 124 to 127 are generally arranged near the center of each side of the diaphragm portion 130. In the vicinity of the center of each side of the diaphragm portion 130, both compressive and tensile stresses are easily applied to the gauge resistances 124 to 127, so that a pressure sensor 1A with high sensitivity can be obtained. Further, the gauge resistors 124 to 127 are arranged on the surface of the diaphragm portion 130 and can be formed by injecting a diffusion source such as boron into the silicon active layer 120, for example. The wiring 128 can be formed of a metal such as aluminum, or can be formed by injecting a diffusion source having a concentration higher than that of the gauge resistors 124 to 127.

Here, the operation principle of the pressure sensor 1A of the present invention will be described in comparison with the pressure sensor 10 of the comparative example. 4A and 4B are views showing a pressure sensor 10 of a comparative example, where FIG. 4A is a cross-sectional view and FIG. 4B is a plan view.
As shown in FIG. 4, the pressure sensor 10 of the comparative example is different from the pressure sensor 1 </ b> A in that no silicon active layer non-formation portion is provided on the base 401 of the silicon substrate 400. Therefore, the fixing portion 422 of the silicon active layer 420 is fixed to the entire upper portion of the base 401 via the silicon oxide film 410. Other structures and dimensions are the same as those of the pressure sensor 1A. In the pressure sensor 10, the silicon active layer 420 is not deleted during manufacturing.

  When the same pressure is applied to the pressure sensor 1A and the pressure sensor 10, the degree of deformation of the diaphragm portions 130 and 430 is the same. However, in the pressure sensor 1A, since the silicon active layer non-forming portion 123 is provided outside the gauge resistors 124 to 127 of the silicon active layer 120, the stress generated in the vicinity of the gauge resistors 124 to 127 is less likely to be relaxed. The strain at the molecular level of the gauge resistors 124 to 127 increases. As a result, the sensitivity of the pressure sensor 1A is improved.

2A and 2B are views showing a second embodiment of the pressure sensor according to the present invention, in which FIG. 2A is a sectional view and FIG. 2B is a plan view.
As shown in FIG. 2, in the pressure sensor 1B of the present invention, the silicon active layer non-forming portion 223 of the silicon active layer 220 is formed of notches as a plurality of openings, and the notches as the openings are formed of silicon. The active layer 220 is provided outside the gauge resistors 224 to 227 so as to be separated from each other. Other structures and dimensions are the same as those of the pressure sensor 1A. Here, the notch of the pressure sensor 1 </ b> B is a notch as an opening surrounded by the silicon active layer 220, but may be a notch reaching the periphery of the silicon active layer 220.

  The feature of the pressure sensor 1A is that it is easy to provide the silicon active layer non-forming portion 123, and the feature of the pressure sensor 1B is that the silicon active layer 220 is difficult to peel off. Further, the position and size of the silicon active layer non-formation portion of the silicon active layer are not limited to those shown in the pressure sensor 1A and the pressure sensor 1B, and are near the gauge resistance above the base portion of the silicon substrate. As long as the pressure is applied, the stress generated in the vicinity of the gauge resistance is less likely to be relaxed. That is, the vicinity of the gauge resistance means a position where the stress generated in the vicinity of the gauge resistance is difficult to be relaxed when pressure is applied.

3A and 3B are views showing a pressure sensor according to a third embodiment of the present invention, in which FIG. 3A is a sectional view and FIG. 3B is a plan view.
As shown in FIG. 3, the pressure sensor 1C of the present invention does not have a bottom, and the cavity 302 is opened downward. Other structures and dimensions are the same as those of the pressure sensor 1A. The pressure sensor 1A is used when detecting an absolute pressure, and the pressure sensor 1C is used when detecting a differential pressure.

  Next, simulations performed on the pressure sensor 1A and the pressure sensor 10 will be described. Specifically, when the same pressure is applied to the pressure sensor 1 </ b> A and the pressure sensor 10, simulation of stress analysis generated in each of the gauge resistances 124 to 127 and 424 to 427 was performed by the finite element method. The stress analysis simulation software used this time is “ANSYS Mechanical” of Cybernet System Co., Ltd.

In order to perform a stress analysis simulation, in general, the hook law expressed by the following equation is modified to optimize to individual simulation conditions, and then the simultaneous equations corresponding to the number of elements are changed. Do it by solving.

In addition, the dimensional conditions of this simulation are described. The silicon substrates 100 and 400, the cavities 102 and 402, the silicon oxide films 110 and 410, and the silicon active layers 120 and 420 in a top view are each assumed to be square, and FIG. 1 shows L11, L12, L13, M11, M12, M13, The dimensions shown as M14 and in FIG. 4 as L21, L22, L23, M21, M22, M23, M24 are as follows. That is, the pressure sensor 1A and the pressure sensor 10 are common except for L13 and L23.
The pressure sensor 1A
L11 (length of one side of the silicon substrate 100) = 500 μm
L12 (length of one side of cavity 102) = 300 μm
L13 (length of one side of silicon active layer 120) = 350 μm
M11 (thickness of the silicon substrate 100) = 200 μm
M12 (height of cavity 102) = 5 μm
M13 (thickness of the silicon oxide film 110) = 1 μm
M14 (thickness of the silicon active layer 120) = 13 μm,
The pressure sensor 10
L21 (the length of one side of the silicon substrate 400) = 500 μm
L22 (length of one side of cavity 402) = 300 μm
L23 (length of one side of silicon active layer 420) = 500 μm
M21 (thickness of silicon substrate 400) = 200 μm
M22 (height of cavity 402) = 5 μm
M23 (thickness of silicon oxide film 410) = 1 μm
M24 (thickness of the silicon active layer 420) = 13 μm.

Further, Table 1 shows the physical property conditions of this simulation, and is common to the pressure sensor 1A and the pressure sensor 10. As shown in Table 1, the physical property conditions of the silicon substrates 100 and 400 and the silicon active layers 120 and 420 are the same. Here, the physical property conditions of the gauge resistors 124 to 127 and 424 to 427 and the wirings 128 and 428 formed in the silicon active layers 120 and 420 are also the same. That is, since the gauge resistors 124 to 127 and 424 to 427 and the wirings 128 and 428 are originally the silicon active layers 120 and 420, the physical property conditions other than the conductivity can be regarded as the same.

  In addition, assuming that the gauge resistances 124 to 127 and 424 to 427 exist near the center of each side of the diaphragm portions 130 and 430, the stresses generated at these locations were calculated by simulation.

  FIG. 5 is a graph showing the stress generated at the location where the gauge resistances 124 and 424 of each pressure sensor are assumed to exist when the same pressure is applied to the pressure sensor 1A and the pressure sensor 10 from above. is there. From FIG. 5, it can be seen that the stress generated at the location where the gauge resistance 124 of the pressure sensor 1 </ b> A is assumed to be present is approximately twice as large as the stress generated at the location where the gauge resistance 424 of the pressure sensor 10 is assumed to be present.

  In this way, it is possible to realize a downsized pressure sensor while maintaining sensitivity without reducing the thickness of the silicon active layer.

  Although the pressure sensor of the present invention has been described above, the present invention is not limited to this, and can be appropriately changed without departing from the spirit of the invention.

1A, 1B, 1C, 10 ... Pressure sensor 100, 200, 300, 400 ... Silicon substrate 101, 201, 301, 401 ... Base 102, 202, 302, 402 ... Cavity 103, 203, 403 ... Bottom 110, 210, 310 410, silicon oxide films 120, 220, 320, 420 ... silicon active layers 121, 221, 321, 421 ... movable parts 122, 222, 322, 422 ... fixed parts 123, 223, 323 ... silicon active layer non-forming parts 124 ˜127, 224˜227, 324˜327, 424˜427... Gauge resistance 128, 228, 328, 428... Wiring 129, 229, 329, 429... Land 130, 230, 330, 430.

Claims (5)

A semiconductor pressure sensor comprising: a base substrate having a cavity and a base surrounding the cavity; and a silicon active layer formed on the base substrate so as to cover the cavity,
The silicon active layer is disposed at a position corresponding to the cavity and can be deformed, a fixed portion disposed on the base and fixed to the base, and a peripheral portion of the movable portion. A plurality of gauge resistors for detecting the deformation of
A semiconductor pressure sensor characterized in that a silicon active layer non-formation portion where the silicon active layer is not formed is provided at least in the vicinity of the gauge resistance above the base.   The semiconductor pressure sensor according to claim 1, wherein the silicon active layer non-forming portion is provided over the entire periphery of the upper portion of the base portion.   The semiconductor pressure sensor according to claim 1, wherein the silicon active layer non-formation portion includes a plurality of notches and is provided apart from each other. The semiconductor pressure sensor according to claim 1, wherein an insulating layer is formed between the base substrate and the silicon active layer.
  The semiconductor pressure sensor according to claim 1, wherein the base substrate has a bottom portion below the cavity.

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