JP2002286567A - Diaphragm sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide structure reduced in a thermal stress error, in a diaphragm sensor using an SOI substrate. SOLUTION: Piezoelectric resistance elements 5-8 are provided in a diaphragm area 3 side with respect to a position 4a separated by 10 μm from a boundary line 3a between a diaphragm area 3 and an outer circumference 4 to an outer circumference 4 side. Since a position more distant from the diaphragm area 3 to its outside is affected more easily by a strain to increase the thermal stress error, the error is reduced because the resistance elements 5-8 are provided in the position hardly affected by the strain caused by thermal stress by forming the structure hereinbefore. The diaphragm sensor of the present invention is used mainly for on-vehicle use, and satisfies 1.3% FS or less which is within an allowable range of the thermal stress error in an electronic control unit(ECU), by reducing the thermal stress error, as shown in a graph of Fig. 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diaphragm sensor using an SOI substrate, and more particularly to a structure in which a thermal stress error is reduced.

[0002]

2. Description of the Related Art Conventionally, in a piezo type diaphragm sensor, a first semiconductor layer (SOI layer), a second semiconductor layer, and a first semiconductor layer are used as semiconductor substrates in order to be usable at a higher temperature. There is a device using an SOI substrate having an insulating layer formed between the first semiconductor layer and the second semiconductor layer.

[0003] When an SOI substrate is used, a parasitic capacitance which is a cause of fluctuation in temperature characteristics of a sensor can be reduced by an insulating layer provided inside the SOI substrate, thereby stabilizing the temperature characteristics of the sensor. And the sensor can be used under high temperature.

[0004] A diaphragm sensor as described above is an SO sensor.
A thin diaphragm is formed at the center of the I-substrate, and a plurality of piezoresistors whose resistance value changes in response to the application of stress are formed on the surface of the SOI substrate, and a bridge is formed by the plurality of piezoresistors. A circuit is configured.

When a stress is applied to the diaphragm, the diaphragm is distorted, and the applied stress is detected by changing the resistance value of the piezoresistive element.

A glass pedestal is joined to the lower part of the SOI substrate by anodic bonding, and the SOI substrate is supported by the glass pedestal.

[0007]

However, a diaphragm sensor using an SOI substrate has a problem that a thermal stress error increases as compared with a diaphragm sensor formed using only a bulk silicon substrate.

Specifically, the SOI substrate has a first
In the step of bonding the semiconductor layer to the insulating layer and the second semiconductor layer, the semiconductor layer warps into a curved shape.

As a cause of this, the joining step is performed at 110
Since the heat treatment is performed at a high temperature of about 0 ° C., when the temperature is returned from the high temperature to the room temperature after the bonding step, the SOI substrate is warped due to a difference in linear expansion coefficient between the semiconductor layer made of silicon and the insulating layer. It is.

[0010] The SO thus warped in a curved shape as described above.
When the I substrate is bonded to the glass pedestal by anodic bonding,
Although the warpage of the SOI substrate is reduced,
Since the piezoresistive element formed on the surface of the substrate is also deformed, an error has occurred.

As a result, when the operating temperature of the sensor changes, the SOI substrate and the glass pedestal are distorted due to the difference in linear expansion coefficient between the SOI substrate and the glass pedestal.
Although a thermal stress error occurs, the thermal stress error is larger in a diaphragm sensor using an SOI substrate than in a diaphragm sensor formed using only a bulk silicon substrate.

In view of the above problems, an object of the present invention is to provide a diaphragm sensor using an SOI substrate.
An object of the present invention is to provide a structure in which a thermal stress error is reduced.

[0013]

According to a first aspect of the present invention, there is provided a diaphragm sensor comprising: an SOI substrate having a quadrangular diaphragm formed on one surface; and a diaphragm region having a reduced thickness in a cross section of the SOI substrate. An outer peripheral portion having a thickness greater than that of the diaphragm region in the cross section of the SOI substrate, a resistance element having a piezoresistive effect formed on the other surface of the SOI substrate, and a pedestal portion joined to the SOI substrate. The diaphragm sensor is characterized in that the resistance element is provided on the diaphragm region side at a position 10 μm away from the boundary line between the diaphragm region and the outer periphery toward the outer periphery.

[0014] Since the position farther outward from the diaphragm region is more susceptible to distortion and the thermal stress error increases, the above-described structure causes the resistance element to be affected by distortion due to thermal stress. Since it is provided at a difficult position, a thermal stress error can be reduced.

Although the diaphragm sensor of the present invention is often used in a vehicle, the reduced thermal stress error can satisfy the allowable range of the thermal stress error in the electronic control unit (ECU).

[0016] The diaphragm sensor according to claim 2 is
The resistance element is provided on the diaphragm region side from a position 5 μm away from the boundary line between the diaphragm region and the outer peripheral portion toward the outer peripheral portion.

Theoretically, the position of the resistive element may be the same as in the first aspect of the present invention. In this case, however, in actuality, when the position at which the resistive element is formed varies, the electronic control is performed. The thermal stress error in the device (ECU) may exceed the allowable range.

Therefore, it is preferable that the resistance element is provided on the diaphragm area side at a position 5 μm away from the boundary line between the diaphragm area and the outer circumference part toward the outer circumference part in consideration of the variation in the formation position of the resistance element.

The diaphragm sensor according to claim 3 is
It is characterized in that the film thickness of the diaphragm region is set to 40 μm or less.

When the film thickness of the diaphragm region changes, the value of the thermal stress difference also changes, so that the film thickness of the diaphragm region is reduced to 40 μm or less, and the arrangement position of the resistance element according to claim 1 or 2. By applying
The allowable range of the thermal stress error in the electronic control unit (ECU) can be reliably satisfied.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment in which the present invention is applied to a semiconductor pressure sensor will be described below with reference to the drawings.

The semiconductor pressure sensor according to the present embodiment is
For example, it is used to detect the pressure of intake air in an intake manifold in a vehicle engine.

FIG. 1 shows a cross-sectional structure of the semiconductor pressure sensor of the present embodiment, and FIG. 2 shows a plan structure of a main part of the semiconductor pressure sensor of the present embodiment. Note that FIG. 2 is a simplified diagram viewed from the arrow A in FIG.

First, as shown in FIG. 1, a first semiconductor layer 1a made of silicon is used as a semiconductor substrate.
And a second semiconductor layer 1 similarly formed of silicon.
b (SOI layer) and an SOI substrate 1 having a buried oxide film 1c formed between the first semiconductor layer 1a and the second semiconductor layer 1b.

A concave portion 2 is formed at the center of the second semiconductor layer 1b, whereby a diaphragm region 3 having the thinnest film thickness at the bottom surface of the concave portion 2 in the cross section of the SOI substrate 1 is formed. At the same time, an outer peripheral portion 4 that is thicker than the thickness of the diaphragm region 3 is formed around the diaphragm region 3.

In this embodiment, the diaphragm region 3
Has a thickness of 27 μm.

The outer peripheral portion 4 includes a region where the concave portion 2 is inclined and a region where the SOI substrate 1 and the glass pedestal 14 are joined.

The recess 2 is formed, for example, by forming a mask having a predetermined pattern on the back surface (on the side of the second semiconductor layer 1b) of the SOI substrate 1 and using an etching solution such as KOH (potassium hydroxide). The second semiconductor layer 1b is formed by performing anisotropic etching.

Here, in the SOI substrate 1 used in the present embodiment, at least the plane orientation of the surface on which the concave portion 2 is formed is a (100) plane, and the planar shape of the diaphragm region 3 is a regular square. .

As shown in FIG. 2, the surface (on the side of the first semiconductor layer 1a) of the SOI substrate 1 is made of a P-type impurity such as boron by a semiconductor process such as diffusion or ion implantation. Piezoresistive elements 5, 6, 7, 8
Are formed.

The resistance values of the piezoresistive elements 5 to 8 change when the diaphragm region 3 is distorted in accordance with the applied pressure.

Note that these piezoresistive elements 5 to 8 have the same resistance value, and are connected in full bridge by diffusion wiring and aluminum wiring (not shown).

At the end of the surface of the SOI substrate 1, a pad for outputting an electric signal to the outside is formed.

In this case, the midpoint potential of the piezoresistive elements 5 and 7 decreases in accordance with the applied pressure, and conversely, the midpoint potential of the piezoresistive elements 6 and 8 increases in accordance with the applied pressure. Is set to

As shown in FIG. 1, a trench 9 is formed in a predetermined region of the first semiconductor layer 1a, and the trench 9 is filled with SiO ₂ 10 so that the surface of the SOI substrate 1 ( On the first semiconductor layer 1a), an insulating oxide film 11, an aluminum wiring 12, and a protective film 13 made of a silicon nitride film and a silicon oxide film are formed.

Further, a glass pedestal 14 is bonded to the lower part of the SOI substrate 1 by anodic bonding, whereby
The SOI substrate 1 is in a state of being supported by the glass pedestal 14.

In such a semiconductor type pressure sensor,
If distortion occurs due to factors other than the applied pressure to be measured, it becomes an error factor of the sensor characteristics.

For example, when the operating temperature of the sensor changes, the SOI substrate 1 and the glass pedestal 14 are distorted due to the difference in linear expansion coefficient between the SOI substrate 1 and the glass pedestal 14, and the distortion propagates to the diaphragm region 3. As a result, the resistance values of the piezoresistive elements 5 to 8 change, which causes a thermal stress error.

Therefore, in the present embodiment, as shown in FIGS. 1 and 2, the piezoresistive elements 5 to 8 are separated from the boundary 3a between the diaphragm region 3 and the outer peripheral portion 10 by 10 μm toward the outer peripheral portion 4 side. From the position 4a to the diaphragm area 3 side.

For example, in the present embodiment, the ends of the piezoresistive elements 5 to 8 are provided at a position 4 μm away from the boundary 3 a between the diaphragm region 3 and the outer periphery 4 toward the outer periphery 4.

Since the position farther away from the diaphragm region 3 is more susceptible to distortion and the thermal stress error increases, the piezoresistive elements 5 to 8 have the structure according to the present embodiment. Since it is provided at a position that is hardly affected by distortion due to thermal stress, a thermal stress error can be reduced.

The semiconductor type pressure sensor of the present embodiment is often used for a vehicle, but by reducing the thermal stress error, as shown in the graph of FIG.
1.3% F which is the allowable range of the thermal stress error in CU)
S or less can be satisfied.

The graph in FIG. 3 shows a diaphragm edge (diaphragm area) when a piezoresistive element having a longitudinal length of 65 μm is used at a maximum temperature of 120 ° C. at a general sensor mounting position. This is an experimental value obtained by measuring a thermal stress error due to a change in the distance from the boundary 3a) between the outer periphery 3 and the outer peripheral portion 4.

As shown in the graph of FIG. 3, the piezoresistive elements 5 to 8 are moved from the boundary 3a between the diaphragm region 3 and the outer peripheral portion 4 to the outer peripheral portion 4 by a distance of 10 μm from the boundary 4a to the diaphragm region 3 side. , It is possible to satisfy 1.3% FS or less, which is the allowable range of the thermal stress error in the electronic control unit (ECU).

However, theoretically, as described above, the piezoresistive elements 5 to 8 are placed at a position 4 μm away from the boundary 3 a between the diaphragm region 3 and the outer peripheral portion 4 toward the outer peripheral portion 4.
A may be provided on the diaphragm region 3 side from the position a. However, in this case, when variations occur in the positions where the piezoresistive elements 5 to 8 are formed, an allowable thermal stress error in the electronic control unit (ECU) is allowed. It may exceed the range of 1.3% FS.

Therefore, considering the variation in the formation positions of the piezoresistive elements 5 to 8, the ends of the piezoresistive elements 5 to 8 are separated from the boundary 3a between the diaphragm region 3 and the outer peripheral part 4 by the outer peripheral part 4 side. It is preferable to provide it on the diaphragm region 3 side from a position separated by 5 μm.

In this embodiment, the thickness of the diaphragm region 3 is set to 40 μm or less.

When the film thickness of the diaphragm region 3 changes,
Since the value of the thermal stress difference also changes, the electronic control unit (ECU) is controlled by setting the film thickness of the diaphragm region 3 to 40 μm or less and applying the above-described arrangement positions of the piezoresistive elements 5 to 8. 1.3) FS, which is the allowable range of the thermal stress error in (1), can be surely satisfied.

Here, the manufacturing process of the semiconductor pressure sensor of the present embodiment will be briefly described with reference to FIG.

First, as shown in FIG.
An I substrate 1 is prepared.

The SOI substrate 1 has a first semiconductor layer 1a made of silicon, a second semiconductor layer 1b (SOI layer) also made of silicon, a first semiconductor layer 1a and a second semiconductor layer 1a. Buried oxide film 1c formed between the semiconductor layer 1b.

Subsequently, as shown in FIG.
On the surface of the OI substrate (on the side of the first semiconductor layer 1a), a mask material such as a silicon nitride film or polysilicon is deposited, an isolation region is patterned and etched, and a trench 9 is formed to a desired depth. The trench 9 is filled with SiO ₂ 10.

Thus, electronic elements such as piezoresistive elements and diodes formed on the SOI substrate after the trench forming step can be electrically isolated.

Subsequently, as shown in FIG.
Piezoresistive elements 6 and 7 made of a P-type impurity such as boron are formed in a predetermined region on the surface of the OI substrate 1 (on the side of the first semiconductor layer 1a) by, for example, a semiconductor process such as diffusion or ion implantation.

In practice, as shown in FIG. 2, piezoresistive elements 5 and 8 are also formed.

Subsequently, as shown in FIG.
On the surface of the OI substrate 1 (on the side of the first semiconductor layer 1a), an insulating oxide film 1 for insulating and separating the aluminum wiring 12 and the SOI substrate 1
1. A protective film 13 made of an aluminum wiring 12 for transmitting a pressure applied through a pad portion to the outside, a silicon nitride film, and a silicon oxide film for preventing deterioration of device characteristics due to external air such as humidity.

Subsequently, as shown in FIG.
A mask having a predetermined pattern is formed on the back surface (the second semiconductor layer 1b side) of the OI substrate 1, and anisotropic etching is performed on the second semiconductor layer 1b using an etching solution such as KOH (potassium hydroxide). Then, a recess 2 having a square shape in a plan view is formed in the center of the second semiconductor layer 1b.

As a result, in the cross section of the SOI substrate 1, the diaphragm region 3 having the smallest film thickness is formed on the bottom surface of the concave portion 2, and the film of the diaphragm region 3 is formed around the diaphragm region 3. An outer peripheral portion 4 that is thicker than the thickness is formed.

Finally, as shown in FIG.
By bonding the glass pedestal 14 to the lower part of the OI substrate 1 by anodic bonding, the semiconductor pressure sensor of the present embodiment is completed.

The present invention is not limited to the above embodiment, but can be applied to various modes.

For example, the present invention is not limited to the semiconductor type pressure sensor as in the present embodiment, but can be applied to other physical quantity sensors such as an acceleration sensor having a diaphragm and a resistance element having a piezoresistive effect. is there.

In this embodiment, a full bridge circuit having one piezoresistive element as one side is formed. However, it is not particularly necessary to limit the number of piezoresistive elements.
A full bridge circuit having one piezoresistive element on one side may be formed.

In this embodiment, the full bridge circuit is formed by the piezoresistive element. However, the same effect can be obtained by forming a half bridge circuit.

[Brief description of the drawings]

FIG. 1 is a diagram showing a cross-sectional structure of a semiconductor pressure sensor according to the present embodiment.

FIG. 2 is a diagram showing a planar structure of a main part of the semiconductor pressure sensor of the present embodiment. FIG. 2 is a view taken in the direction of the arrow A in FIG.

FIG. 3 is a graph showing a relationship between a distance from a diaphragm edge and a thermal stress error.

FIGS. 4A to 4F are diagrams showing a manufacturing process of the semiconductor pressure sensor of the present embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... SOI board | substrate, 1a ... 1st semiconductor layer, 1b ... 2nd semiconductor layer, 1c ... buried oxide film, 2 ... recessed part 3 ... Diaphragm area | region, 3a ... Boundary line between a diaphragm area and an outer peripheral part, 4 ... Outer peripheral portion, 4a: Position 10 μm away from the boundary line toward the outer peripheral portion, 5, 6, 7, 8: Piezoresistive element, 9: Trench, 10: SiO ₂ , 11: Insulating oxide film, 12: Aluminum wiring, 13 ... protective film, 14 ... glass pedestal,

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2F055 AA40 BB20 CC02 DD05 EE14 FF01 GG15 GG16 4M112 AA02 BA01 CA03 CA04 CA09 CA11 DA04 EA11 EA13 FA09

Claims (3)

[Claims] An SOI substrate having a quadrangular diaphragm formed on one surface; a diaphragm region having a reduced thickness in a cross section of the SOI substrate;
An outer peripheral portion having a greater thickness than the diaphragm region in a cross section of the I substrate, a resistive element having a piezoresistive effect formed on the other surface of the SOI substrate;
In a diaphragm sensor having a pedestal portion bonded to a substrate, the resistance element is provided on the diaphragm region side from a position 10 μm away from the boundary line between the diaphragm region and the outer peripheral portion toward the outer peripheral portion. A diaphragm sensor. 2. The device according to claim 1, wherein the resistance element is provided on the diaphragm region side from a position 5 μm away from the boundary line between the diaphragm region and the outer periphery portion toward the outer periphery portion. Diaphragm sensor. 3. The film thickness of the diaphragm region is 40 μm.
The diaphragm sensor according to claim 1, wherein: