JP2864700B2 - Semiconductor pressure sensor and method of manufacturing the same - Google Patents

Description

The present invention relates to a semiconductor pressure sensor having a diaphragm portion recessed by etching a single crystal silicon substrate having a plane orientation of approximately (110) and a method of manufacturing the same. About.

[Prior Art] An example of a conventional semiconductor pressure sensor is shown in FIG.

This semiconductor pressure sensor has a diaphragm portion 4a which is formed in a substantially square shape by anisotropically etching a single crystal silicon substrate 1a having a plane orientation of approximately (110). When the plane orientation is substantially (110), the strain gauges forming the bridge are provided at the peripheral part and the central part of the diaphragm part 4a.

As shown in FIG. 3, the non-diaphragm portion 7a of the substrate 1a is joined to a pedestal 3 made of, for example, Pyrex glass, and a pressure is introduced into the diaphragm portion 4a from outside through a pressure introducing hole 31 of the pedestal 3. .

The semiconductor pressure sensor disclosed in Japanese Patent Publication No. 60-13314 discloses a semiconductor pressure sensor having a surface orientation of (100) different from the surface of a semiconductor crystal.
Disclosed are octagonal diaphragm portions having sides parallel to different crystal axes. In a semiconductor pressure sensor having this plane orientation, it is general that all strain gauges are arranged around the diaphragm. Further, the above-mentioned publication discloses that adopting the above-described structure can provide an effect of eliminating local stress concentration and increasing the maximum value of the allowable applied pressure.

[Problems to be Solved by the Invention] In a semiconductor pressure sensor in which a single crystal silicon substrate as described above is joined to a pedestal having a different thermal expansion coefficient from the single crystal silicon substrate,
Conventionally, a thermal stress is generated in a diaphragm portion due to a difference in thermal expansion coefficient between the two, and an output (hereinafter, referred to as a thermal stress output) due to the thermal stress is generated in a bridge due to a variation in the thermal stress in a diaphragm surface. It is known. This thermal stress output is a signal component other than the pressure signal (hereinafter, referred to as an offset voltage). Although described later, the thermal stress output often has a non-linearity with respect to a temperature change. Difficulty compensating the performance has been a major obstacle to improving the accuracy of the semiconductor pressure sensor, and despite that, no effective solution has been hitherto shown.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a semiconductor pressure sensor and a method of manufacturing the same that can significantly improve the temperature compensation accuracy.

[Means for Solving the Problems] A semiconductor pressure sensor according to the present invention includes: a strain gauge provided on a diaphragm; a silicon crystal base having a plane orientation of approximately (110) as a base of the diaphragm; In a semiconductor pressure sensor including a pedestal joined to the base, the diaphragm portion may have a <100> axis, a <110> axis, and a <11> axis.
1> has an octagonal shape with two opposing sides each orthogonal to the axis,
In addition, the distance between two opposing sides orthogonal to the <100> axis is substantially equal to the distance between two opposing sides orthogonal to the <110> axis.

Here, that the plane orientation is substantially (110) means that the plane may be inclined, for example, by several degrees from the (110) plane.
Such an inclination is advantageous for reducing defects when epitaxial growth is performed on a substrate surface to integrate a transistor.

The following manufacturing method is used to manufacture the above-described semiconductor pressure sensor of the present invention.

That is, the method of manufacturing a semiconductor pressure sensor according to the present invention includes:
A method of manufacturing a semiconductor pressure sensor, comprising forming a thin diaphragm portion on a silicon substrate by anisotropically etching a silicon substrate having a plane orientation of approximately (110), wherein the etching has an octagonal etching opening. The silicon substrate is anisotropically etched from the etching opening using a mask for <100> axis and <110> axis.
Axis and two opposite sides orthogonal to the <111> axis, respectively, and <1
It is characterized in that an octagonal diaphragm portion is formed in which the distance between two opposing sides orthogonal to the 00> axis and the distance between two opposing sides orthogonal to the <110> axis are substantially equal.

[Operation and Effect of the Invention] The octagonal diaphragm portion disclosed in the present invention has a distance between two opposing sides perpendicular to the <100> axis and a distance between two opposing sides perpendicular to the <110> axis. A semiconductor pressure sensor having a silicon crystal base having a (110) surface orientation and a pedestal (hereinafter referred to as a (110) octagonal semiconductor pressure sensor) is a silicon pressure sensor having a substantially square diaphragm portion. Compared to a conventional semiconductor pressure sensor having a crystal base and a pedestal having a thermal expansion coefficient different from that of the base (hereinafter referred to as a square semiconductor pressure sensor), the distribution of thermal stress in the plane of the diaphragm is changed. It was found by calculation and trial production by the finite element method.

As a result, according to the (110) type octagonal semiconductor pressure sensor of the present invention, the output error can be made extremely small irrespective of the temperature fluctuation as compared with the related art.

Furthermore, in the (110) type octagonal semiconductor pressure sensor of the present invention, the distance between two opposing sides orthogonal to the <100> axis of the diaphragm portion is substantially equal to the distance between two opposing sides orthogonal to the <110> axis. Therefore, it is possible to reduce the variation of the thermal stress of each part in the surface of the diaphragm part and to improve the temperature characteristic.

In the present invention, the following manufacturing method is used to manufacture the above-described semiconductor pressure sensor of the present invention.

That is, a first method of manufacturing a semiconductor pressure sensor according to the present invention provides a semiconductor pressure sensor formed by forming a thin diaphragm portion on a silicon substrate having an approximately (110) plane orientation by anisotropically etching the silicon substrate. In a method of manufacturing a sensor, the silicon substrate is anisotropically etched from the etching opening using an etching mask having an octagonal etching opening, and the <100>
Axis, <110> axis, and <111> axis, each having two opposing sides orthogonal to each other, and the distance between the two opposing sides orthogonal to the <100> axis and <110>.
The octagonal diaphragm is formed so that the distance between two opposing sides perpendicular to the axis is substantially equal.

According to this manufacturing method, the above-described (110) octagonal semiconductor pressure sensor of the present invention can be favorably manufactured.

Embodiments (Embodiment 1) FIGS. 1 to 4 show one embodiment of the semiconductor pressure sensor of the present invention.
This will be described with reference to the drawings.

As shown in FIG. 3, the semiconductor pressure sensor includes a substrate 1 made of a single-crystal silicon chip having a diaphragm portion 4 and diced into a square having a side of about 3 mm.
And the pedestal 3 made of Pyrex glass (trade name) electrostatically bonded to the peripheral portion of the non-diaphragm portion 7, that is, the diaphragm portion 4. A pressure to be measured is introduced from the outside to the concave side of the diaphragm portion 4 through a pressure introducing hole 31 penetrated through the pedestal 3, while a constant reference pressure is applied to the flat surface side of the diaphragm portion 4.

The thickness of the substrate 1 is about 0.3 mm, the plane orientation is substantially (110), and an octagonal diaphragm portion 4 is recessed at the center of the substrate 1 by anisotropic etching.

Diaphragm part 4 has a thickness of about 40 μm and <10
It is defined by sides orthogonal to the 0>, <110>, and <111> axes. The length of the first side ι1 is about 0.54mm, the second side ι2
Has a length of about 0.84 mm and the length of the third side ι3 is about 0.48 mm.

Four strain gauges 2 are formed in the peripheral part and the central part of the diaphragm part 4 by impurity doping of a conductivity type opposite to that of the substrate 1, and as shown in FIG.
Bridge-connected.

Hereinafter, a manufacturing process of the semiconductor pressure sensor will be described.

Strain gauges 2a to 2d are formed on a single crystal silicon wafer having a plane orientation of approximately (110) by a normal semiconductor process technique, and thereafter, contact holes are formed, wiring, passivation, and bonding pads are formed. The arrangement of the strain gauges 2a to 2d is the same as the case of using the normal (110) plane, and the longitudinal direction of the gauge is set in the <110> direction so that the <110> axis passing through the center of the diaphragm part 4 is set as a symmetric axis. The strain gauges 2a and 2d are attached around the diaphragm 4
The strain gauges 2b and 2c are arranged at the center.

Next, as shown in FIG. 2, an etching mask such as an oxide film is formed on the back surface of the wafer by a photolithographic method, and anisotropically etched with a KOH aqueous solution or the like. In this manner, the diaphragm 4 having an octagon can be formed by straight lines perpendicular to the <100> axis, the <110> axis, and the <111> axis.

Next, the wafer is diced and electrostatically bonded to a Pyrex glass pedestal 3, and bonding pads and input / output pins (not shown) are bonded by gold wires or the like.

Since the structure and manufacturing process of this type of semiconductor pressure sensor are well known, further description is omitted.

Next, the thermal error offset voltage generated at the output terminal of the bridge (see FIG. 4) will be described.

The thermal error offset voltage is mainly caused by a difference in thermal expansion coefficient between the pedestal 3 and the substrate 1 and a difference in thermal expansion coefficient between the substrate 1 and a thermal oxide film, a passivation film, or the like attached to the substrate 1. The stress is caused by variation in the plane of the diaphragm.

FIG. 5 shows the distribution of the thermal stress in the radial direction obtained by analyzing the thermal stress by the Pyrex pedestal by the finite element method. A shows a thermal stress distribution in the radial direction in the semiconductor pressure sensor of this embodiment, and B shows a quadrangular semiconductor pressure sensor (see FIG. 8) in which the distance between corresponding sides of the diaphragm portion is equal to that of the semiconductor pressure sensor of this embodiment. 2) shows the thermal stress distribution in the radial direction in FIG.

Analysis conditions are: temperature difference 100 ° C, thermal expansion coefficient difference 1 × 10
⁻⁷ [° C. ⁻¹ ], and the pressure difference was set to 0.

As can be seen from FIG. 5, the semiconductor pressure sensor (A) of this embodiment has much smaller thermal stress variation in the plane of the diaphragm portion 4 than the conventional semiconductor pressure sensor (B). In particular, in the semiconductor pressure sensor of this embodiment, since the thermal stress was substantially equal between the central portion and the peripheral portion of the diaphragm portion 4, it was found that a thermal error output voltage was hardly generated in the bridge output Vout.

Therefore, in the octagonal semiconductor pressure sensor, the difference in thermal stress between the strain gauges 2b and 2c arranged at the center of the diaphragm 4 and the strain gauges 2a and 2d arranged at the periphery can be extremely small. , The thermal error offset voltage is greatly reduced.

In the bridge of FIG. 4, the total offset voltage Vout (p = 0) including the thermal error offset voltage is: Vout (p = 0) = Vin · (Rb · Rc−Ra · Rd) / ｛(Ra + Rb) · (Rc + Rd)｝ where Ra, Rb, Rc, and Rd are the strain gauges 2a, 2b,
The resistance values are 2c and 2d, and the pressure difference p applied to the diaphragm 4 is 0. The resistance values of the strain gauges 2a to 2d change together with the thermal stress due to variations in the temperature coefficient of resistance TCR of each strain gauge itself.

Now, in the range from room temperature to about 150 ° C., the coefficient of thermal expansion of Pyrex glass αp = 3.2 × 10
^-6 [℃ ^-1 ], temperature T [° C], thermal expansion coefficient αs of Si
≒ 4.8 × 10 ^-9 T + 2.6 × 10 ^-6 [℃ ^-1 ], the amount of thermal strain |
εT | And has temperature dependence. Here, TB is the temperature when the substrate 1 and the pedestal 3 are joined, and εo is the amount of thermal strain when the temperature T is 0 ° C.

The second-order component of the temperature T in the above equation represents a non-linear component of the temperature dependence of the thermal strain. As described above, this non-linear component is more important for temperature compensation than the absolute value of the thermal strain itself. Often a problem.

Each of these resistance values changes due to the temperature fluctuation of each of the strain gauges 2a to 2d. However, in the bridge connection, as can be understood from the equation of the offset voltage Vout (p = 0), Variations in the resistance values of the gauges 2a to 2d (particularly, differences in the amount of thermal strain between the peripheral portions 2a and 2d and the central portions 2b and 2c) actually appear as thermal error offset voltages (mainly thermal stress outputs).

Next, with respect to the semiconductor pressure sensor of this embodiment, test articles were manufactured in which the ratio of each side length of the diaphragm portion 4 was changed variously, and the amount of change of the thermal error offset voltage with respect to the temperature change was measured. As a comparative example, a rectangular product having the same distance between the sides was also manufactured, and the amount of change of the thermal error offset voltage with respect to the temperature change is set to 1, and is relatively displayed in FIG.

The test conditions are as follows: the pressure difference of the diaphragm part 4 is 0, the temperature change is 25 ° C. and 120 ° C., the length of the first side ι1 of the diaphragm part 4 is ι, the distance between the second sides parallel to each other and perpendicular to the first side. The distance between ι2 is L, the distance between both first sides ι1 parallel to each other is L ′, and L ′ / L is 1.04 (see FIG. 7).

From FIG. 6, it was found that when ι / L = 0.4, the fluctuation amount can be made almost zero. However, considering the influence of the passivation film and the like, if the scale such as the thickness of the diaphragm is changed, the graph shown in FIG. 6 may slightly change.

Modifications Although the strain gauges 2a to 2d are made by doping the single crystal silicon (110) surface with impurities, a polysilicon resistor provided on the diaphragm 4 may be used.

Alternatively, a single crystal silicon substrate having a (100) plane orientation may be bonded to the substrate 1 having a (110) plane orientation, and a strain gauge resistor may be formed on the (100) substrate.

As the etching method, various conventionally known methods can be adopted in addition to the KOH aqueous solution.

The pedestal 3 can employ a material other than Pyrex glass.

In this embodiment, four strain gauges 2a to
Although 2d is formed on the diaphragm 4, a so-called half-bridge circuit composed of any combination of the strain gauges 2a and 2b or 2c and 2d on the diaphragm 4 has the same effect.

(Effects of Embodiment) As described above, in the semiconductor pressure sensor of this embodiment, the distance between two opposing sides orthogonal to the <100> axis of the octagonal diaphragm portion having a plane orientation of substantially (110) is <110. >
The distance between the two opposing sides perpendicular to the axis is shown in FIG.
As shown in FIG. 7 and FIG. 7, since they are substantially equal, it is possible to reduce the variation of the thermal stress of each part in the surface of the diaphragm part and to suppress the variation of the output (thermal stress output) due to the temperature change.

In addition, the degree of influence of thermal stress can be arbitrarily changed by changing the ratio ι / L with respect to the length L of the first side of the diaphragm portion and the distance L between the two second sides of the diaphragm portion. Therefore, according to this embodiment, the thermal stress output can be arbitrarily changed as well as the thermal stress output can be arbitrarily changed, so that the thermal stress output is actively used for temperature compensation of the pressure sensitivity. And the offset voltage are completely different, so it is not a perfect compensation method.), And a semiconductor pressure sensor having an extremely small output fluctuation due to a temperature change can be manufactured.

[Brief description of the drawings]

FIG. 1 (a) is a plan view showing an embodiment of a substrate used for a semiconductor pressure sensor according to the present invention, and FIG. 1 (b) is AA in FIG. 1 (a).
FIG. 2 (c) is a sectional view taken along line CC of FIG. 1 (a), FIG. 2 (d) is a sectional view taken along line BB of FIG. 1 (a), and FIG. 2 is a plan view showing an etching mask used in the manufacture thereof. FIG. 3 is a cross-sectional view of the semiconductor pressure sensor of the above embodiment, FIG. 4 is a bridge connection circuit diagram, FIG. 5 is a diagram showing a thermal stress distribution in a radial direction, and FIG. FIG. 7 is a diagram showing the dimensions of the sample used in FIG. 6, FIG. 8A is a plan view of a substrate of a conventional semiconductor pressure sensor, and FIG. Sectional view, FIG.
Is a BB sectional view thereof. 1 ... substrate 2a-2d ... strain gauge 3 ... pedestal 4 ... diaphragm part

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-56-80174 (JP, A) JP-A-62-259476 (JP, A) JP-A-63-144582 (JP, A) (58) Investigation Field (Int.Cl. ⁶ , DB name) H01L 29/84 G01L 9/04 101

Claims (2)

(57) [Claims] A strain gauge provided on a diaphragm portion and a base of the diaphragm having a plane orientation substantially (11).
0) a semiconductor pressure sensor comprising a silicon crystal base and a pedestal joined to the base, wherein the diaphragm portion has a <100> axis, a <110> axis, and a <111> axis.
> Has an octagonal shape having two opposing sides each orthogonal to the axis, and the distance between the opposing two sides orthogonal to the <100> axis is substantially equal to the distance between the opposing two sides orthogonal to the <110> axis. Semiconductor pressure sensor. 2. A method for manufacturing a semiconductor pressure sensor, comprising forming a thin diaphragm portion on a silicon substrate by anisotropically etching a silicon substrate having a plane orientation of approximately (110), comprising: Using an etching mask having an opening, the silicon substrate is anisotropically etched from the etching opening to obtain a <100> axis, a <110> axis,
It has two opposing sides orthogonal to the <111> axis, and <100>
A method of manufacturing a semiconductor pressure sensor, comprising forming an octagonal diaphragm portion in which a distance between two opposing sides perpendicular to the axis and a distance between two opposing sides perpendicular to the <110> axis are substantially equal.