JPH0712940U - Semiconductor pressure sensor - Google Patents

Abstract

(57) [Summary] [Purpose] Since the output voltage is proportional to the difference between the radial stress σr of the diaphragm and the circumferential stress σθ, the circumferential stress σr near the gauge is reduced. , Get a large output voltage. [Arrangement] Two adjacent gauges 3a of the differential pressure detection gauges (piezoresistive elements) 3A and 3B in the radial and tangential directions, which are respectively arranged near the outer periphery of the surface of the diaphragm portion 2, are adjacent to the respective gauge portions 3a. Shallow grooves 11a and 11b are formed on both sides.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a semiconductor pressure sensor that detects a differential pressure or pressure.

[0002]

[Prior art]

 Conventionally, as this type of semiconductor pressure sensor, one using a Si (silicon) semiconductor diaphragm is known. This Si diaphragm type semiconductor pressure sensor forms a gauge acting as a piezoresistive region on the surface of a substrate made of a semiconductor crystal (hereinafter referred to as a semiconductor substrate) by an impurity diffusion or ion implantation technique, and also by vapor deposition of Al or the like. It is configured by forming a lead and removing a part of the back surface by etching to form a thin part with a thickness of about 20 μm to 60 μm, that is, a diaphragm part. Applying measurement pressure to the front and back surfaces of the diaphragm part, respectively. When the diaphragm is deformed, the specific resistance of the gauge changes, and the output voltage accompanying the resistance change at this time is detected to measure the differential pressure or pressure.

FIGS. 4 and 5 are a plan view and a cross-sectional view showing a conventional example of such a semiconductor pressure sensor. The semiconductor substrate 1 is made of (100) -faced n-type single crystal Si, and its back surface is formed by etching. It is equipped with a thin disk-shaped pressure sensitive diaphragm part 2 which is sensitive to differential pressure or pressure by removing the central part, and which acts as a piezo region on the surface side of this diaphragm part 2 to detect differential pressure or pressure. Pressure detecting gauges 3 (3A, 3B) are provided and electrostatically bonded onto the back plate 4. The back plate 4 is formed of Pyrex glass, ceramics, or the like having a thermal expansion coefficient similar to that of the semiconductor substrate 1, and the back plate 4 has a recessed portion 5 formed on the back surface of the semiconductor substrate 1 in the center thereof. A through hole 6 for guiding one of the pressures P1 and P2 (P1) to be measured is formed on the back surface side.

The differential pressure detection gauge 3 is located near the peripheral edge portion where the radial and circumferential stresses generated in the diaphragm portion 2 at the time of applying a differential pressure or pressure on the surface of the pressure sensitive diaphragm portion 2 are maximum. Four are formed by the diffusion or ion implantation method, and by connecting to the Wheelstone bridge, the differential pressure signals of the pressures P1 and P2 to be measured applied to the front and back surfaces of the diaphragm part 2 are output differentially. To do. Measuring differential pressure or pressure is maximum ^{140Kgf / cm 2, 420Kgf / cm} 2 approximately, respectively. Further, the two differential pressure detection gauges 3A in the radial direction out of the four differential pressure detection gauges 3 form a folded-back gauge, so that a predetermined sheet resistance can be obtained at a low concentration (10 ¹⁹ pieces / cm ³ ). Two gauge parts 3a, 3a parallel to the <110> crystal axis direction having the maximum piezoresistive coefficient in the crystal plane orientation (100) and one end of these gauge parts 3a, 3a are connected to each other. It is composed of a portion 3b and two lead-out portions 3c and 3c connected to the other ends of the gauge portions 3a and 3a, respectively, and the connecting portion 3b and the lead-out portions 3c and 3c affect the gauge portions 3a and 3a. In order to exclude it, a high concentration (10 ²¹ pieces / cm ³ ) conductive type (p ⁺ type) semiconductor material region is generally formed. On the other hand, the two tangential-direction differential pressure detection gauges 3B do not form a folded gauge, have a predetermined sheet resistance at a low concentration (10 ¹⁹ pieces / cm ³ ), and have a piezo crystal orientation in the crystal plane orientation (100). One gauge portion 3a parallel to the <110> crystal axis direction having the maximum resistance coefficient, and a high-concentration (10 ²¹ pieces / cm ³ ) conductivity type (p ²¹ ) connected to the end of the gauge portion 3a. ⁽⁺ Type) It is composed of two lead-out portions 3c and 3c forming a semiconductor material region.

The piezoresistance coefficient of the differential pressure detecting gauge 3 decreases as the doping amount of impurities into the semiconductor substrate 1 increases for both p-type and n-type. Therefore, the impurity concentration is set low in order to increase the rate of change of the specific resistance of the differential pressure detection gauge 3 to increase the sensitivity to pressure and obtain a large output voltage. Further, the piezoresistance coefficient differs between the p-type and the n-type, and the p-type is larger. Therefore, it is general to provide the p-type resistance layer on the n-type semiconductor.

The output voltage of the differential pressure detection gauge 3 varies depending on the shape and thickness of the diaphragm portion 2, the formation position of the differential pressure detection gauge 3, the orientation of the gauge itself, and the like. For example, regarding the orientation, when a gauge is provided on Si with a crystal plane orientation (001), the direction in which the piezoresistive coefficient becomes maximum is the <110> crystal axis direction, so differential pressure detection is performed in this direction. It is desirable to form a working gauge 3.

In FIG. 4, 7a and 7b are leads made of aluminum formed by vapor deposition, and one ends of these leads 7a and 7b are connected to the lead-out portions 3c and 3c, respectively. Reference numeral 8 is a terminal portion for extracting the differential pressure signal, and 9 is a power source terminal portion for detecting the differential pressure.

FIG. 6 is a diagram showing a stress distribution on the diaphragm portion, in which the vertical axis represents the stress σr in the radial direction and the stress σθ in the circumferential direction, and the horizontal axis represents the distance from the center of the diaphragm portion. The output voltage of the differential pressure detecting gauge 3 is proportional to the stress difference | σr−σθ |. As is clear from the figure, this difference is the largest in the vicinity of the circumference, and therefore the gauge 3 is formed on the peripheral portion of the diaphragm portion 2.

[0009]

[Problems to be solved by the device]

 In the conventional semiconductor pressure sensor described above, improvement of detection sensitivity is a major issue. Therefore, the differential pressure detecting gauge 3 is formed so as to be sensitive to the pressure in the crystal axis direction (<110>) where the piezoresistive coefficient in the crystal plane orientation (001) is maximum, and the stress difference | σr − A gauge 3 is formed around the diaphragm portion having the largest σθ | to obtain a large output voltage. In this case, regarding the stress generated in the diaphragm portion 2, when the stress σr in the radial direction is increased or the stress σθ in the circumferential direction is decreased, the difference in stress becomes larger and a large output voltage can be obtained. To increase the radial stress σ r, the diaphragm part 2 should be made thinner, but in that case the breaking pressure becomes smaller, and when etching the diaphragm part there is a problem that it is difficult to control the thickness. There was a limit to making the thickness below (20 to 50 μm).

Therefore, the present invention has been made in view of the above-mentioned conventional problems, and the thickness of the entire diaphragm portion is not changed, and the thickness in the vicinity of the gauge portion is reduced to reduce the circumferential direction in the vicinity of the gauge portion. It is an object of the present invention to provide a semiconductor pressure sensor capable of increasing the difference between the stresses σr and σθ by absorbing or reducing the stress σθ of, and obtaining a large output voltage.

[0011]

[Means for Solving the Problems]

 In order to solve the above-mentioned object, the present invention forms a thin portion by forming a concave portion on the back surface of a substrate made of a semiconductor crystal, and a pair of piezoresistors is formed on the main surface of the thin portion in the radial direction and the tangential direction, respectively. In a semiconductor pressure sensor provided with an element, shallow grooves are formed adjacent to the piezoresistive element on both sides in the circumferential direction thereof.

[0012]

[Action]

 The shallow groove in the diaphragm absorbs or reduces the stress σθ in the circumferential direction near the piezoresistive element. Therefore, in the piezoresistive element, the stress σθ in the circumferential direction is reduced and | σr−σθ | is increased.

[0013]

【Example】

 Hereinafter, the present invention will be described in detail with reference to the embodiments shown in the drawings. 1 is a plan view showing an embodiment of a semiconductor pressure sensor according to the present invention, and FIG. 2 is an enlarged sectional view taken along line II-II of FIG. The same components as those in FIGS. 4 and 5 are designated by the same reference numerals, and the description thereof will be omitted. This embodiment is adjacent to the gauge portions 3a of the differential pressure detecting gauges (piezoresistive elements) 3A and 3B, which are arranged in pairs near the outer periphery of the surface of the diaphragm portion 2, respectively. Shallow grooves 11a and 11b are formed on both sides in the direction. The diaphragm portion 2 has the same thickness as the conventional one, that is, about 20 to 60 μm, and the depth of the shallow grooves 11a and 11b is about several μm. Therefore, the shallow grooves 11a and 11b do not affect the strength of the entire diaphragm portion. The circumferential length L of the shallow grooves 11a and 11b is about 5 times the width W (about 20 μm) of the gauge portion 3a. The other structure is the same as that of the conventional semiconductor pressure sensor shown in FIGS.

FIG. 3 is a diagram showing a stress distribution in the vicinity of the shallow groove of the diaphragm portion 2. As is clear from this figure, the stress σθ in the circumferential direction (in the direction of the arrow in FIG. 2) near the gauge portion 3a is reduced because it is blocked by the shallow groove 11a. On the other hand, since the radial stress σ r near the gauge portion 3 a is orthogonal to the circumferential stress σ θ, it is not blocked by the shallow grooves 11 a and 11 b and is not affected. Therefore, in the portion 2a (see FIG. 2) of the diaphragm portion 2 where the piezoresistive element 3A (the same applies to 3B) is formed, the circumferential stress σθ decreases and | σr−σθ | increases. As a result, since the output voltage is proportional to | σr −σθ |, it is possible to obtain a larger output than the conventional sensor described above.

In the above embodiment, the semiconductor substrate 1 is made of n-type silicon and the piezoresistive region, the gate portion 3a, is made of p-type silicon. However, this is a piezoresistor made of p-type silicon. Compared to the n-type, the one used has better linearity of pressure-resistance, the (001) plane where the piezoresistance coefficient becomes maximum, and the output in both the forward and reverse directions with good symmetry in the <110> crystal axis direction. Although it can be taken out, the present invention is not limited to this, and it goes without saying that an n-type piezoelectric region may be formed on a p-type substrate.

[0016]

[Effect of device]

 As described above, in the semiconductor pressure sensor according to the present invention, since the shallow grooves are formed adjacent to the piezoresistive element on both sides in the circumferential direction, the stress in the circumferential direction near the piezoresistive element is reduced. Can be absorbed or reduced by. Therefore, the stress applied to the piezoresistive element is only the stress in the radial direction, and a large output voltage can be obtained, and the detection sensitivity of the sensor can be improved.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of a semiconductor pressure sensor according to the present invention.

FIG. 2 is an enlarged sectional view taken along line II-II in FIG.

FIG. 3 is a diagram showing a stress distribution in the vicinity of a shallow groove of a diaphragm portion.

FIG. 4 is a plan view showing a conventional example of a semiconductor pressure sensor.

FIG. 5 is a sectional view of the sensor.

FIG. 6 is a diagram showing a stress distribution in a diaphragm portion.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 2 Diaphragm part (thin part) 3A Radial differential pressure detection gauge 3B Tangent direction differential pressure detection gauge 3a Gauge part 3b Connecting part 3c Lead-out part 4 Back plate 5 Recessed parts 11a, 11b Shallow groove

Claims (1)

[Scope of utility model registration request] 1. A semiconductor device comprising a substrate made of a semiconductor crystal, a recess formed on a back surface of the substrate to form a thin portion, and a main surface of the thin portion provided with a pair of piezoresistive elements in a radial direction and a tangential direction, respectively. In the sensor, a semiconductor pressure sensor characterized in that shallow grooves are formed adjacent to the piezoresistive element on both sides in the circumferential direction thereof.