JP3087334B2 - Semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device and, more particularly, to a diaphragm formed by anisotropically etching a semiconductor substrate having a principal surface having a predetermined small angle with respect to the (110) and (100) planes. And a plurality of strain gages symmetrically arranged on the diaphragm.

[0002]

2. Description of the Related Art An example of a conventional semiconductor pressure sensor is shown in FIG.
And FIG. In this sensor, a strain gauge 2a having a bridge structure is symmetrically arranged on the front main surface of a (110) silicon substrate 1a, and the silicon substrate 1a is formed into a truncated quadrangular pyramid shape from the back main surface with the center of symmetry as an etching center. The thin diaphragm portion 4a is recessed by anisotropic etching.

Therefore, the center of the anisotropic etching start surface (this surface is defined by the photomask pattern) S2 (hereinafter referred to as the etching start surface center s) and the midpoint (hereinafter referred to as the center of each strain gauge 2a). (Hereinafter referred to as the gage center g) g
Is coincident when viewed in a direction perpendicular to the plane direction of the main surface.
The diaphragm portion 4a bends due to a pressure difference acting on both main surfaces, whereby the resistance value of the strain gauge changes and a signal voltage is output from the output terminal of the bridge.

[0004]

If a semiconductor integrated circuit including a bipolar transistor conventionally implemented by an external circuit is mounted on the above-mentioned silicon substrate 1a for the purpose of signal amplification and temperature compensation, the size of the semiconductor pressure sensor can be reduced. Is possible. The manufacture of this bipolar transistor involves n ⁺
It is necessary to form an epitaxial layer on a silicon substrate 1a after forming a buried layer of the like, then, transient
Alignment mark with other diffusion layer to form star
Click in order to be visible on the silicon surface, it is necessary to use a substrate having a so-called off-angle tilted several degrees against the principal (110) plane.

When a substrate having such an off-angle is subjected to anisotropic etching, a pair of slopes rising obliquely from each side of the diaphragm portion 4a (for example, FIGS. 18 and 19).
In (18) and (19), the inclination angle changes with respect to the main surface direction by the off-angle. For example, when the off angle is 3 ° in FIGS. 18 and 19, the slope 18 is 32.3 ° and the slope 19 is 38.3 ° with respect to the main surface.

Therefore, the center of the diaphragm portion 4a (the center of the anisotropic etching end surface S1; hereinafter, the center of the etching start surface s) which coincides with the above-mentioned gage center g in the direction perpendicular to the main surface. Etching end surface center b
), So that a pair of strain gauges (particularly, the diaphragm portion 4
The strain gauges 2a and 2a at the central portion of a do not have equal distortion-resistance characteristics, and undesirably affect the output characteristics of the bridge.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide a semiconductor device in which a strain gauge is bridge-arranged in a diaphragm portion formed by anisotropic etching on a silicon substrate having an off-angle. To improve
That is the purpose.

[0008]

According to the present invention, there is provided a semiconductor device comprising:
A diaphragm formed by anisotropically etching a semiconductor substrate whose main surface has a predetermined off-angle with respect to one of the (110) and (100) planes, and a plurality of symmetrically arranged with respect to the diaphragm In a semiconductor device having a strain gage, the center of symmetry of each of the strain gages coincides with the center of the bottom of the diaphragm as viewed in a direction perpendicular to the main surface.

In a preferred embodiment, the polygon formed on the etching start surface of the substrate by the anisotropic etching has an asymmetric shape by a half turn, and the diaphragm has a symmetrical shape by a half turn. Have. Here, a semiconductor device to which the present invention is directed is a semiconductor device including a semiconductor pressure sensor, a semiconductor humidity sensor, and a diaphragm portion formed by anisotropic etching and a strain gauge having a bridge configuration symmetrically arranged therewith. Includes all equipment.

[0010]

According to the present invention, each strain gauge has:
The diaphragm portions are symmetrically arranged at predetermined intervals and are bridge-connected to each other, so that the center of the gage, which is the midpoint of each of the strain gauges, is in a conventional manner when viewed in a direction perpendicular to the main surface. It coincides with the center of the etching end surface, not the center of the etching start surface.

As a result, even if the center of the etching start plane is deviated from the center of the etching end plane in the direction perpendicular to the main surface due to the anisotropic etching of the silicon substrate, the center of the diaphragm actually formed, ie, the center of the etching end plane. b
Are arranged symmetrically with respect to the main surface direction, and the output characteristics do not vary among the respective strain gauges.

Therefore, according to the present invention, in a semiconductor device in which a strain gauge is bridge-arranged in a diaphragm portion recessed by anisotropic etching on a silicon substrate having an off angle, it is comparable to a silicon substrate having no off angle. The bridge output accuracy can be realized. Further, since the silicon substrate of the present invention has an off-angle, it is possible to align the buried layer with another diffusion layer, and therefore, it is important to have an epitaxial layer in terms of characteristics. Such a bipolar transistor can be integrated on the same chip, and a sense amplifier circuit and a temperature compensation circuit of the strain gauge can be mounted using the bipolar transistor.

The rate of change in resistance of the strain gauge with respect to stress is not so large, and the S / N ratio to the output voltage of the bridge cannot ignore the influence of various noises applied to the wiring between the strain gauge and the sense amplifier. According to the present invention, while ensuring the excellent transistor characteristics by epitaxial layer, since it is greatly shortened capable to <br/> Rukoto by integration of both the wiring length between the bipolar sense amplifier and strain gauges, conventionally compared to be such to both separate body, it is possible to improve significantly SN ratio.

There are also various advantages in cost.

[0015]

(Embodiment 1) One embodiment of a semiconductor pressure sensor according to the present invention will be described with reference to FIGS. Here, FIG. 1 is an enlarged plan view of a diaphragm portion of the semiconductor pressure sensor, and FIG.
FIG. 3 is a schematic sectional view showing the structure of the semiconductor pressure sensor, FIG. 3 is a bridge circuit diagram thereof, FIG. 4 is a sectional view taken along line AA of FIG. 1, and FIG. 5 is a sectional view taken along line BB of FIG. , FIG. 6 shows C in FIG.
2 shows a cross-sectional view taken along line C of FIG.

As shown in FIG. 2, this semiconductor pressure sensor has a substrate 1 made of a single crystal silicon chip having a diaphragm 4 and diced into a square having a side of about 3 mm.
And a pedestal 3 made of Pyrex glass (trade name) electrostatically bonded to the non-diaphragm portion 7 of the substrate 1, that is, the periphery of the diaphragm portion 4. A pressure to be measured is introduced from the outside to the concave surface 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 (110), and as shown in FIG.
Off angle. An octagonal diaphragm portion 4 is formed at the center of the substrate 1 by anisotropic etching. The details of the shape of the diaphragm section 4 will be described later. The front main surface S3 of the diaphragm section 4 (FIG. 2)
4), four strain gauges 2 (see FIG. 1) are formed by impurity doping of the opposite conductivity type to the substrate 1 at the peripheral portion and the central portion. As shown in FIG. In FIG. 3, Vin is a DC power supply voltage applied to the bridge, and Vout is an output signal voltage.

On the other hand, a bipolar integrated circuit 5 is formed on the front main surface S3 (see FIG. 2) of the non-diaphragm portion 7 of the substrate 1. The bipolar integrated circuit 5 has a sense amplifier for amplifying the voltage of the bridge output, a temperature compensating circuit for temperature compensating the signal voltage output from the sense amplifier, a power amplifying circuit for further amplifying the temperature compensated signal voltage. However, since the details of these circuit structures deviate from the gist of the present invention, description thereof will be omitted.

Hereinafter, the detailed structure of the diaphragm section 4 will be described. The thickness of the diaphragm part 4 is about 40 μm,
The bottom surface of the diaphragm portion 4, that is, the etching end surface S1
Is divided by eight sides L1 to L8. Here, the length of the sides L1 and L5 is about 0.84 mm, and the sides L2 and L5
4, the length of L6 and L8 is about 0.48 mm, the sides L3 and L3
7 is set to about 0.54 mm.

On the other hand, in the etching start surface S2 of the substrate 1, a hexagonal concave portion having sides d1 to d6 is formed by the anisotropic etching, and the hexagonal concave portion is formed at right angles to the etching start surface S2. Sides L2 and d2, sides L4 and d
3, the sides L6 and d5, and the sides L8 and d6 are substantially the same (slightly shifted due to the off-angle), and the sides L1 and d1, and the sides L5 and d4 are parallel to each other.

What is particularly important in this embodiment is that the strain gauges 2 are symmetrically arranged about the center point of the diaphragm portion 4 defined by the etching end surface S1, that is, the center b of the etching end surface. That is. Further, despite the fact that the etching start surface S2 of the substrate 1 has an off-angle, the sides L1 and L5, L2 and L
6, L3 and L7, and L2 and L8 are formed to have the same length. Therefore, the diaphragm portion 4 has the same shape even when rotated by 180 degrees around the center b of the etching end surface, which is the center thereof, and the respective strain gauges 2 return to the original arrangement by the rotation of 180 degrees.

However, on the etching start surface S2 of the substrate 1, mutually parallel sides d1 and d4 are formed to have different lengths. Here, for comparison, the diaphragm portion 4 in the case of performing anisotropic etching using a rotationally symmetrical photomask using a (110) substrate having no off angle is used.
FIG. 7 shows the shape of (110) with an off angle of 3 °.
FIG. 8 shows the shape of the diaphragm portion 4 when anisotropic etching is performed using a substrate and a rotationally symmetric photomask.

In FIG. 7, in order to make the diaphragm portion 4 of FIG. 1 have the same shape, it is natural that the sides d1 and d4 on the etching start surface S2 should be equal in length. As a result, side L1 = L5. However, when the (110) wafer having an off-angle of 3 ° is anisotropically etched using the same mask pattern as shown in FIG. 7 (that is, the sides d1 and d4 have the same length), as shown in FIG. If the sides d1 and d4 are equal in length, the side L1 is shorter than the side L5,
As a result, the center s of the etching start surface and the center g of the gage are shifted from the center b of the etching end surface.

In this embodiment, the etching end surface center b
That is, the side d1 and the side d4 are adjusted so that the diaphragm center is aligned with the gage center g and the sides L1 and L5 are made equal in length. Note that the diaphragm shape is 8
The square shape is more effective in improving the offset temperature characteristics of the pressure sensor than the square shape. Next, the sides d1 and d
4, a method of calculating a distance Δx between an intermediate point in the x direction (center s of the etching start plane in the present invention) and the center b of the etching end plane, that is, the center g of the gage, will be described.

First, the shift amount Δx is Where e is the etching depth of the anisotropic etching and α is the off-angle.

Further, L ₁ the lengths of the sides L1, the length L ₂ of the side L2, l ₁ the length of a side d1, if the length of the side d4 and l _2, And if L ₁ = L ₂ , Thus, a photomask pattern may be manufactured as described above.

Here, 35.3 ° is tan ⁻¹ (1 / √).
Means 2). Hereinafter, a manufacturing process of the semiconductor pressure sensor will be described with reference to FIGS. 3 on the (110) plane
A P-type silicon substrate 10 having an off-angle of .degree. Is prepared, and a high-concentration N-type region 31 for a collector or the like is buried in a predetermined region (non-diaphragm portion 7 where the diaphragm portion 4 is not formed) on the surface thereof. A low concentration N-type epitaxial layer 32 for a collector region or the like is grown on the surface of the silicon substrate 1 by a photolithography / impurity diffusion process (see FIG. 9).

Next, a high-concentration P-type region 33 for PN junction isolation of a bipolar transistor is formed by impurity diffusion, followed by a P-type base region 34 and a high-concentration N-type emitter region 35. , High concentration N-type collector region 36
Are formed by oxidation / photolithography and impurity diffusion, respectively (see FIG. 10). Further, the diaphragm part 4
The low-concentration N-type epitaxial layer 32 is divided by a high-concentration P-type region 33 into a region where
2a is formed, and a high-concentration P-type region 37 is linearly formed as a strain gauge 2 in the strain gauge accommodation region 32a (see FIG. 12). Note that the strain gage 2 may be formed in the same step as the P-type base region 34, or the strain gage 2 may be formed in the same step as the high-concentration N-type emitter region 35.

Next, a contact hole is opened in the silicon oxide film 38 formed on the surface of the substrate 1 to form an electrode wiring 39, for example, a PSG film 4 for passivation.
0 is deposited (see FIGS. 11 and 12). Of course, in the manufacturing process of the above-described bipolar transistor and strain gage 2, various resistors and the like are manufactured to form a desired bipolar integrated circuit.

Next, the above-mentioned octagonal photoresist 42 is formed in a predetermined region on the back main surface of the wafer on which the insulating film 41 such as an oxide film is formed (see FIG. 13). After selectively opening an insulating film 41 to serve as an etching mask such as a film (see FIG. 14) and removing the photoresist 42, the silicon substrate 10 is subsequently anisotropically etched with a KOH aqueous solution or the like, as shown in FIG. An octagonal diaphragm section 4 is formed (see FIG. 15).

Next, the wafer is diced and electrostatically bonded to a Pyrex glass pedestal 3, and bonding pads and unillustrated input / output pins are bonded by gold wires or the like (see FIG. 2). Embodiment 2 FIG. 16 shows a semiconductor pressure sensor according to another embodiment.

The semiconductor pressure sensor of this embodiment is the same as that of the first embodiment.
In comparison with the above, the (100) silicon substrate 1 is employed. Also in this embodiment, the center s of the etching start surface which is the center of the concave portion in the anisotropic etching start surface S2 (this surface is defined by the photomask pattern) is the center of the diaphragm portion 4, that is, the center of the etching end surface. b shifts by Δx ′.

Therefore, the center g of the gage, which is an intermediate point from each strain gage, coincides with the center b of the etching end surface. In each of the above embodiments, the strain gage 2 is formed by doping impurities on the single crystal silicon (110) surface. However, a polysilicon resistor provided on the diaphragm 4 may be used.

As the etching method, in addition to the KOH aqueous solution, various conventionally known methods can be adopted. The pedestal 3 can employ a material other than Pyrex glass. Further, the present invention is applicable regardless of the shape of the pedestal 3 and the presence or absence of the pressure introducing hole 31.

It is to be noted that Δx ′ in this case having an off angle of α = 3 ° on the (100) plane is: Is changed. Here, 54.7 ° is (90 ° −tan ^−1).
(1 / √2).

[Brief description of the drawings]

FIG. 1 is a partial plan view showing one embodiment of a semiconductor pressure sensor using the present invention;

FIG. 2 is a sectional view of the sensor of FIG. 1,

FIG. 3 is an equivalent circuit diagram of the sensor of FIG. 1;

4 is an AA cross-sectional view of the sensor of FIG.

FIG. 5 is a cross-sectional view taken along the line BB of the sensor of FIG. 1;

FIG. 6 is a CC cross-sectional view of the sensor of FIG. 1;

FIG. 7 is a partial plan view of a semiconductor pressure sensor of a comparative example without an off angle,

FIG. 8 is a partial plan view of a semiconductor pressure sensor of a comparative example with an off-angle;

FIG. 9 is a cross-sectional view illustrating a manufacturing process.

FIG. 10 is a sectional view showing a manufacturing process.

FIG. 11 is a cross-sectional view showing a manufacturing process.

FIG. 12 is a sectional view showing a manufacturing process;

FIG. 13 is a sectional view showing a manufacturing process.

FIG. 14 is a sectional view showing a manufacturing process;

FIG. 15 is a sectional view showing a manufacturing process.

FIG. 16 is a partial plan view showing another embodiment of the semiconductor pressure sensor;

FIG. 17 is a cross-sectional view of the sensor of FIG. 16 taken along the line AA.

FIG. 18 is a partial plan view showing an example of a conventional semiconductor pressure sensor;

19 is a cross-sectional view of the sensor of FIG. 18 taken along the line AA.

[Explanation of symbols]

 1 is a substrate, 2 is a strain gauge, 4 is a diaphragm,

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 29/84 G01L 9/04 101 H01L 21/306 H01L 29/04

Claims (2)

(57) [Claims] A diaphragm formed by anisotropically etching a semiconductor substrate having a predetermined off angle with respect to one of the (110) and (100) planes;
In a semiconductor device having a plurality of strain gauges symmetrically arranged on the diaphragm, a center of symmetry of each strain gauge coincides with a center of a bottom of the diaphragm when viewed in a direction perpendicular to the main surface. A semiconductor device, comprising: 2. A polygon formed on an etching start surface of a substrate by said anisotropic etching has an asymmetric shape by a half turn, and said diaphragm has a symmetric shape by a half turn. 13. The semiconductor device according to claim 1.