JPH08162645A - Sensor for mechanical quantity - Google Patents

Abstract

PURPOSE: To enable easy manufacture without requiring an element isolation step, by isolating a strain portion by a semiconductor layer of a pn-junction diode or a semiconductor identical to the former semiconductor layer. CONSTITUTION: In a semiconductor substrate 1, a thin strain portion 3 is formed at a central part by wet etching, leaving a thick frame portion 2. In the strain portion 3, a gauge resistor 4 is provided, made of a semiconductor layer 8 and having a positive temperature coefficient of resistance for the resistance varying in response to the strain of the strain portion 3. Also in the strain portion 3, pn-junction diodes 6a, 6b are provided, made of the semiconductor layer 8 and having a negative temperature coefficient of resistance. In addition, a wiring conductor 11 for connecting the gauge resistor 4 with the pn-junction diodes 6a, 6b is provided on an insulation film 7 on the surface of the semiconductor substrate 1. The strain portion 3 is isolated by the semiconductor layer 8 of the pn-junction diodes 6a, 6b, or a semiconductor layer identical to the semiconductor layer 8. Thus, easy manufacture can be realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mechanical quantity sensor that can be used as a sensor for pressure detection, acceleration detection or the like by using a gauge resistance formed by a semiconductor layer.

[0002]

2. Description of the Related Art For example, JP-A-6-102118 and JP-A-160218.
Nos. 207871 and 207871 disclose a pressure sensor using a mechanical quantity sensor. This kind of pressure sensor
Pressure is generated by converting the resistance change of the gauge resistance due to the so-called piezoresistive effect, which is caused by the strain state of the strain sensitive part, to the strain generated in the strain sensitive part by the introduction of pressure. Is measured.

FIG. 7 shows a basic structure, which is an n-type silicon substrate (semiconductor substrate) having a peripheral thick-walled frame portion 2 serving as a fixed portion and a thin-walled diaphragm portion (strain sensitive portion) 3 in the center. 4), four gauge resistors 4 having a piezoresistive effect made of a p-type semiconductor layer are formed in the diaphragm portion 3 and the gauge resistors 4 (4a to 4d) are connected to the bridge circuit 5 as shown in FIG. By applying a power supply voltage (direct current) Vcc to this, the bridge circuit 5 responds to the pressure by changing the gauge resistance 4 due to the distorted state of the diaphragm portion 3 due to the difference in pressure between the front and back sides of the diaphragm portion 3. The output voltage Vo can be taken out.

[0004]

In such a pressure sensor, the positive resistance temperature coefficient TCR (Temperature Coeffi
cient of resistance), and its value is generally about 2000 ppm / ° C. Therefore, in the case of constant voltage driving, there is a problem that the sensitivity decreases as the ambient temperature increases.

On the other hand, it is known to connect a diode having a negative TCR in order to compensate for a resistance circuit having a positive TCR (see, for example, JP-A-3-228364 and JP-A-22-228364).
The present invention relates to a specific technique for forming the diode with a pn junction diode.

[0006]

In order to solve the above problems, the present invention provides a thin-walled strain-sensitive portion formed on a semiconductor substrate, and a strain-sensitive portion formed by a semiconductor layer on the strain-sensitive portion. A gauge resistance having a positive resistance temperature coefficient whose resistance value changes according to a strain state, a pn junction diode having a negative resistance temperature coefficient formed of a semiconductor layer in the strain sensitive portion, and a surface of the semiconductor substrate. A wiring conductor formed on the formed insulating film to connect the gauge resistor and the pn junction diode, and the semiconductor layer of the pn junction diode or the same semiconductor layer as the semiconductor layer. The strain sensitive portion is isolated.

In the pn junction diode, a direction in which a large amount of current flows is formed along a crystallographic direction in which the sensitivity of the semiconductor substrate is low.

A plurality of the pn junction diodes are electrically connected in series, and are formed so as to cancel out the sensitivity to the strain state as a whole.

[0009]

The pn junction diode has a rising voltage (a voltage at which a current flows) decreases when the ambient temperature rises, and acts as a resistance having a negative TCR equivalently under a constant current condition, and has a piezoresistive effect. Since the bridge circuit made up of resistors has a positive TCR, by combining these, it is possible to realize a mechanical quantity sensor having a small TCR, that is, less susceptible to the ambient temperature. In particular, since the strain sensitive portion is isolated by the semiconductor layer forming the pn junction diode or the same semiconductor layer as this semiconductor layer, the element isolation step is not required and the manufacturing can be easily performed.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The mechanical quantity sensor of the present invention will be described below with reference to the embodiment shown in FIGS. 1 to 5 applied to a pressure sensor. ing.

1 to 4 show an embodiment, in which a pn junction diode 6 is connected in series between a bridge circuit 5 and an input voltage (DC) Vcc. The pn junction diode 6 is not limited to one and may be two or more connected in series. The output voltage Vo corresponding to the pressure can be taken out from the bridge circuit 5 by the change of the gauge resistance 4 due to the strained state of the diaphragm portion 3 due to the difference in pressure between the front and back sides of the diaphragm portion 3 as in the above-mentioned conventional technique. is there.

The gauge resistor 4 made of a semiconductor layer formed by an appropriate method such as a diffusion method, an ion implantation method, or an epitaxial method has a positive TCR and has an ambient temperature (T1, T2, T2).
The current (I) -voltage (V) characteristic with respect to T3) is as shown in FIG. On the other hand, in the pn junction diode 6, as shown by the current (I) -voltage (V) characteristic of FIG. 3, the anode-cathode potential (rising voltage) at which the forward current sharply rises increases the ambient temperature (T1). → T2 → T3), and when a constant current is applied, the resistance has an apparently negative TCR.

Therefore, by combining the pn junction diode 6 having the negative TCR and the bridge circuit 5 having the positive TCR, the TCR equivalently as a whole is obtained.
You can get a small circuit of. According to the experiment, when a constant current is applied, the TCR of the pn junction diode 6 is
Since about −1600 to 2000 ppm / ° C. was obtained, temperature compensation according to the bridge circuit 5 can be performed by appropriately providing it.

In such a configuration, since the pn junction diode 6 is oriented in one direction, there is a limitation that it can be used only under the condition of forward current.
The width of the potential difference that can be compensated can be obtained to the required extent depending on the number of diodes, and theoretically there is no limitation.

Next, a method of manufacturing the pn junction diode 6 will be described with reference to FIG. As described above, the number of pn junction diodes 6 may be any, but a case where two pn junction diodes 6a and 6b are formed will be described.

First, the n-type silicon substrate 1, which is a semiconductor substrate, is left with the peripheral thick-walled frame portion 2 to be a fixed portion,
A central thin-walled diaphragm portion 3 serving as a strain sensitive portion is formed by an appropriate method such as wet etching with an alkaline etching solution such as KOH, and then an insulating film 7 made of silicon dioxide, silicon nitride or the like is provided on the front and back surfaces (see FIG. 4 a).

Next, in the diaphragm portion 3, it corresponds to two points of the gauge resistor 4 (only one point of the gauge resistor 4a is shown in FIG. 4) and two points of the p-type regions of the pn junction diodes 6a and 6b. Remove the insulating film 7 on the surface,
The semiconductor layer 8 (8a, 8b, 8c) is formed by using the p-type semiconductor material such as boron by the above-described appropriate method. Among these, the semiconductor layer 8c constitutes a gauge resistor 4a which will be described later, and the semiconductor layers 8a and 8b constitute pn junction diodes 6a and 6b which will be described later. In this case, the semiconductor layer 8 is the diaphragm portion 3
The diaphragm portion 3 is formed sufficiently deep to penetrate in the wall thickness direction, and the diaphragm portion 3 is isolated by at least the semiconductor layers 8a and 8b forming the pn junction diodes 6a and 6b (b in FIG. 4).

Next, after the insulating film 7 is formed again on the entire surface, the pn junction diode 6 is formed in the diaphragm portion 3.
Insulating film 7 on the surface corresponding to two parts of n-type regions of a and 6b
Are removed, and the semiconductor layer 9 (9a, 9b) is formed using an n-type semiconductor material such as phosphorus by the above-described appropriate method. Of these, the semiconductor layers 9a and 9b constitute pn junction diodes 6a and 6b described later (c in FIG. 4).

After forming the insulating film 7 on the entire surface again, the gauge resistor 4a and the pn junction diodes 6a, 6 are formed.
In order to make b the electric circuit configuration of FIG. 1, a contact hole 10 is provided in the insulating film 7, and a wiring conductor 11 made of aluminum or the like and patterned in a predetermined pattern is formed thereon (d in FIG. 4).

Since the diaphragm portion 3 is isolated in the same step by the semiconductor layer 8 constituting the pn junction diode 6 as described above, it is possible to easily manufacture the element without the need for a separate element isolation process. Wear.

Next, another method of manufacturing the pn junction diode 6 will be described with reference to FIG. As mentioned above, pn
Although the number of the junction diodes 6 may be any, the case of forming one of the pn junction diodes 6a will be described. The same or corresponding parts as those in the manufacturing method are designated by the same reference numerals.

First, the n-type silicon substrate 1, which is a semiconductor substrate, is left with the thick frame portion 2 around the periphery, which serves as a fixing portion,
The central thin-walled diaphragm portion 3 serving as the strain sensitive portion is formed by an appropriate method such as wet etching with an alkaline etching solution such as KOH, and then the insulating film 7 made of silicon dioxide, silicon nitride or the like is provided on the surface (FIG. 5). A).

Next, in the diaphragm portion 3, the insulating film 7 on the surface corresponding to the portion dividing the gauge resistance 4a described later from the pn junction diode 6a described later is removed,
The same semiconductor layers 8 (8d, 8e) as the semiconductor layer 8 (see FIG. 4) of the pn junction diode 6a are formed from the front and back sides of the silicon substrate 1 by the above-described method. in this case,
By providing until the semiconductor layers 8d and 8e are connected, the diaphragm portion 3 is isolated (see FIG. 5).
B).

Next, after forming the insulating film 7 on the entire surface again, in the diaphragm portion 3, the portion of the gauge resistor 4 (only one portion of the gauge resistor 4a is shown in FIG. 5) and the p of the pn junction diode 6a are formed. The insulating film 7 on the surface corresponding to each of the mold regions is removed, and the semiconductor layer 8 (8a, 8a,
8c) is formed. Of these, the semiconductor layer 8c constitutes the gauge resistor 4a, and the semiconductor layer 8a constitutes the pn junction diode 6a. Similarly, the insulating film 7 on the surface corresponding to the location of the n-type region of the pn junction diode 6a is removed, and the semiconductor layer 9a is formed by the above-described method using an n-type semiconductor material such as phosphorus. Thus, the semiconductor layers 8a and 9a form a pn junction diode 6a. After that, the insulating film 7 is formed on the entire surface again, and the contact hole 10 is formed in the insulating film 7 in order to form the gauge resistor 4a and the pn junction diode 6a into the electric circuit configuration of FIG. The wiring conductor 11 made of aluminum or the like is formed (FIG. 5C).

Then, the insulating film 7 is formed on the back surface of the silicon substrate 1.
Are formed (d in FIG. 5). The insulating film 7 on the back surface of the silicon substrate 1 can be formed at the same time when the semiconductor layer 8 is formed.

According to this method, since the semiconductor layer 8e can be formed from the back surface side of the silicon substrate 1, even a relatively thick (for example, about 10 μm) diaphragm 3 can be isolated in a short time. You can
Although the number of steps for isolation is increased, since it is performed using the same semiconductor layer 8 (8d, 8e) as the semiconductor layer 8 (8a) of the pn junction diode 6a, it is a separate dedicated step as an element isolation process. No preparation is required, and it can be used as part of the next step of forming the semiconductor layer 8 of the pn junction diode 6a, and does not significantly increase the process load.

The resistance value of the pn junction diode 6 may be affected by the strain state in the diaphragm portion 3, but the direction in which a large amount of current flows is along the crystallographic direction in which the semiconductor substrate 1 has low sensitivity. By being formed,
The influence can be mitigated.

A plurality of pn junction diodes 6 are electrically connected in series, and are formed in such a direction as to cancel the sensitivity to the strain state as a whole, so that the strain sensitive portion 3 is formed.
It is possible to mitigate the above-mentioned influence due to the strain state in the above.

FIG. 6 is a schematic circuit diagram showing the structure of another embodiment. In contrast to the direct current type of the above embodiment, FIG.
It is an exchange type. In this case, the pn junction diode 6
Are connected in parallel so that the first and second pn junction diodes 61 and 62 are in opposite directions to each other, and connect the variable resistor 12 between the bridge resistors 4c and 4d on the ground side. The operation and manufacturing process in such an embodiment are the same as those in the above embodiment, and will be omitted.

The present invention can be applied not only to the mechanical quantity sensor having the bridge circuit composed of a plurality of gauge resistors shown in each embodiment, but also to the mechanical quantity sensor having a single gauge resistance. In addition to the pressure sensor, the mechanical quantity sensor of the present invention can also be used as other sensors such as an acceleration sensor.

[0031]

According to the present invention, a thin-walled strain sensitive portion formed on a semiconductor substrate, and a positive electrode whose resistance value changes according to the strain state of the strain sensitive portion formed by a semiconductor layer on the strain sensitive portion. A gauge resistance having a temperature coefficient of resistance, a pn junction diode having a negative temperature coefficient of resistance formed of a semiconductor layer in the strain sensitive portion, and an insulating film formed on a surface of the semiconductor substrate. A wiring conductor that connects the gauge resistor and the pn junction diode, and the strain sensitive portion is isolated by the semiconductor layer of the pn junction diode or the same semiconductor layer as the semiconductor layer, The pn junction diode has a rising voltage that decreases as the ambient temperature rises, and acts equivalently as a resistor having a negative TCR under the condition of a constant current, and is a gauge resistor having a piezoresistive effect. The bridge circuit consists of a positive in TCR, and by combining these, TC
It is possible to realize a mechanical quantity sensor having a small R, that is, less susceptible to the ambient temperature.

In particular, since a plurality of pn junction diodes can be obtained in a series of steps without using a separate element isolation process, the steps can be simplified and the manufacturing cost can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic circuit diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a current-voltage characteristic diagram with respect to a temperature change of the gauge resistance according to the embodiment.

FIG. 3 is a current-voltage characteristic diagram with respect to a temperature change of the diode circuit according to the embodiment.

FIG. 4A to FIG. 4D are cross-sectional views of main parts for explaining the manufacturing process of the embodiment.

5A to 5D are cross-sectional views of a main part for explaining another manufacturing process of the embodiment.

FIG. 6 is a schematic circuit diagram showing the configuration of another embodiment of the present invention.

FIG. 7A is a cross-sectional view of an essential part showing the configuration of a conventional pressure sensor, and b is a plan view of the same.

FIG. 8 is a schematic circuit diagram showing the configuration of the same.

[Explanation of symbols]

 1 n-type silicon substrate (semiconductor substrate) 2 frame part 3 diaphragm part (distortion part) 4 (4a, 4b, 4c, 4d) gauge resistance 5 bridge circuit 6 (6a, 6b) pn junction diode 7 insulating film 8 (8a) , 8b, 8c, 8d, 8e) p-type semiconductor layer 9 (9a, 9b) n-type semiconductor layer 10 contact hole 11 wiring conductor

Claims (3)

[Claims] 1. A thin-walled strain sensitive portion formed on a semiconductor substrate, and a positive resistance temperature coefficient which is formed by a semiconductor layer on the strain sensitive portion and whose resistance value changes according to the strain state of the strain sensitive portion. , A pn junction diode having a negative temperature coefficient of resistance formed of a semiconductor layer in the strain sensitive portion, and the gauge resistor and the pn junction diode formed on an insulating film formed on the surface of the semiconductor substrate. and a wiring conductor connecting to the pn junction diode, wherein the strain sensitive section is isolated by the semiconductor layer of the pn junction diode or the same semiconductor layer as the semiconductor layer. Quantity sensor. 2. The pn junction diode is characterized in that a direction in which a large amount of current flows is formed along a crystal direction in which the sensitivity of the semiconductor substrate is low.
The mechanical quantity sensor described. 3. The mechanical quantity sensor according to claim 1, wherein a plurality of the pn junction diodes are electrically connected in series, and are formed so as to cancel the sensitivity to the strain state as a whole. .