JP2650623B2 - Semiconductor acceleration sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microminiature semiconductor acceleration sensor using a cantilever formed on a semiconductor substrate.

[0002]

2. Description of the Related Art Recently, a very small semiconductor acceleration sensor formed on a semiconductor substrate has been developed. This semiconductor acceleration sensor is formed on a semiconductor substrate using a thin film technique such as etching, and detects acceleration by detecting a resistance change due to a piezoresistance effect of a semiconductor and a minute capacitance change due to displacement. It has become. Since these semiconductor acceleration sensors are formed using the thin film technology as described above, they are formed extremely small, for example, the length of the vibrating portion is about 100 μm, the thickness is about 1 μm, and the entire chip is about 1 mm square. And an integrated circuit can be formed on the same substrate as other elements. Examples of the semiconductor acceleration sensor as described above include, for example, “IEE Electron Devices, Vol. ED-26, No. 1
2, p. 1911, Dec. 1979 “A Batch-Fabricated Silicon Ac
celerometer ")".

FIGS. 2A and 2B show the above-described semiconductor acceleration sensor. FIG. 2A is a plan view of a cantilever and a piezoresistor, and FIG. 2B is a circuit diagram of a bridge circuit. In FIG. 2, the Si cantilever 11 is displaced when an acceleration is applied. As a result, stress is applied to the piezoresistor 12 formed at the base of the Si cantilever 11 and the resistance value of the piezoresistor 12 changes. By detecting the change in the resistance value, the acceleration can be detected.

As a circuit for detecting a change in the resistance value, for example, a bridge circuit as shown in FIG. 2B is used. In (b), reference numeral 12 denotes the same piezoresistor as in (a), and reference numerals 13 to 15 denote fixed resistors.
The resistors 13 to 15 can also be formed on the semiconductor acceleration sensor chip. In the bridge circuit shown in FIG. 2B, when an acceleration is applied, the resistance value R of the piezo resistor 12 changes to R + ΔR, and the other resistors 13 to
Assuming that the resistance value R of 15 does not change as it is and the applied voltage to the bridge is V, the output ΔV of the bridge is expressed by the following equation (1).

[0005]

(Equation 1)

As can be seen from the above equation (1), there is a problem in that the bridge circuit using one piezoresistor has low sensitivity.

Therefore, as a method of improving the sensitivity,
For example, a configuration as shown in FIG.
No. 9-158566). In FIG. 3, four piezoresistors 16 to 19 are formed in the vicinity of the support portion of the Si cantilever 11, and a bridge circuit 20 is formed by the four piezoresistors. Reference numerals 21 to 24 denote wirings for connecting the four piezoresistors to the outside, and use metal wirings such as Al. Of the four piezoresistors, 16 and 18 are formed perpendicular to the length of the Si cantilever, and 17 and 19 are formed parallel to the length of the Si cantilever. Therefore, the resistance changes when stress is applied to 16 and 18 and 17 and 19 are reversed. Therefore, when stress is applied to the Si cantilever beam by acceleration, when the resistance values of 16 and 18 of the four piezoresistors become R−ΔR, the resistance values of 17 and 19 become R + ΔR.
It becomes R. When a bridge circuit as shown in FIG. 3B is formed by the four piezoresistors 16 to 19, when the applied voltage of the bridge circuit is V, the output ΔV of the bridge circuit is expressed by the following equation (Equation 2). Is shown.

[0008]

(Equation 2)

As can be seen by comparing the above equation (2) with the above equation (1), the sensitivity of the configuration of FIG. 3 is quadrupled as compared with the configuration of FIG.

[0010]

As described above, with the configuration shown in FIG. 3, the sensitivity can be improved. However, in the configuration of FIG. 3, since the metal wires 21 to 24 made of Al or the like are used as the wires connected to the piezoresistors 16 to 19, the following problem occurs. That is, S
Due to the difference in the coefficient of thermal expansion between the cantilever 11 and the metal wiring layers 21 to 24, the thermal stress caused by this difference is reduced to the Si cantilever 1
The thermal stress applied to the four piezoresistors 16 to 19 differs depending on the direction, length, thickness, area, and the like of the metal wires 21 to 24. For this reason, when a temperature change occurs, in the semiconductor acceleration sensor, the offset temperature characteristic occurs in the resistance value of each piezo resistor due to the arrangement of the metal wirings 21 to 24, and a temperature drift occurs in the output voltage Vout of the bridge circuit. This causes a problem that a detection error occurs.

The present invention has been made to solve the problems of the prior art as described above, and has a high detection sensitivity.
It is an object of the present invention to provide a highly accurate semiconductor acceleration sensor having excellent reliability and stability.

[0012]

In order to achieve the above object, the present invention provides a method for manufacturing a semiconductor device, comprising:
In the vicinity of the support, four piezo resistors forming a bridge circuit
And each of the four piezoresistors forms a piezoresistor.
The ends of each are directly connected to the next one
Made is, the lead wires of the bridge circuit from the respective coupling portions, and a portion on at least the cantilever of the wiring, and configured to form a high-concentration diffusion layer formed on the semiconductor substrate.

[0013]

In the present invention, since the wiring connected to the piezoresistor is formed of a high-concentration diffusion layer having a thermal expansion coefficient equal to that of the semiconductor substrate, no thermal stress is generated by the wiring. Therefore, the resistance value of the piezoresistor is suppressed from changing due to temperature to the minimum value, the temperature drift of the voltage output from the bridge circuit is reduced, and the acceleration can be accurately detected. Also, as is apparent from the embodiment of FIG.
In the present invention, the ends of the four piezoresistors 16 to 19 formed near the support of the cantilever 11 are adjacent to each other.
It is formed in a shape that directly couples with the object. Sand
That is, each piezoresistor is directly joined, and there is no wiring between each piezoresistor. Such a structure is made possible by effectively utilizing the characteristics of the cantilever type acceleration sensor. That is, in the cantilever beam, the stress due to the acceleration is concentrated at a part (near the supporting part), so that the piezoresistors can be collected at the concentrated part, and the piezoresistors can be directly joined without wiring. It is. Thus, by directly joining the piezoresistors, it is possible to eliminate the problem that the detection sensitivity is reduced due to the wiring resistance, and the detection accuracy is reduced due to the offset caused by the variation in the resistance value of each wiring resistance. I can do it.

[0014]

1A and 1B are views showing an embodiment of the present invention, in which FIG. 1A is a plan view of a cantilever beam and a resistor forming portion, and FIG. 1B is a circuit diagram of a bridge circuit. In FIG. 1, Si cantilever 11
, Four piezoresistors 16 to 19 are formed near the support portion. The ends of these four piezoresistors are directly connected, and there is no connection wiring between the piezoresistors. Further, four fixed resistors 16 'to 19' are formed on the Si substrate 25 which is common to the Si cantilever 11. These four resistors 16 'to 19' are formed in portions where the Si cantilever 11 is not affected even if it is broken. The piezoresistors 16 to 19 and the resistors 16 'to 19' are connected in parallel one by one by wires 31 to 34 made of high concentration diffusion layers. The above four piezo resistors 16 to
19 are all formed on the cantilever 11. Also,
The wirings 31 to 34 wired to the piezo resistors 16 to 19 are:
It is formed of a high-concentration diffusion layer formed by diffusing impurities into a semiconductor substrate, and has the same thermal expansion coefficient as that of the Si cantilever 11. Therefore, no thermal stress is generated by the wirings 31 to 34. Therefore, the piezo resistance value is 16 to 1
In the resistance value of 9, the change due to temperature is suppressed to the minimum value, the temperature drift of the output voltage Vout of the bridge circuit is reduced, and the accuracy of acceleration detection is improved.

The above-described bridge circuit has a circuit configuration as shown in FIG. In the apparatus of FIG. 1, if the Si cantilever 11 is broken from the base and the four piezoresistors 16 to 19 are cut off, the potential of the output terminal is changed by the four fixed resistors 16 'to 19'. Will be determined. For example, if 16 'to 19' are all set to the same resistance value, when four piezoresistors are damaged,
The output voltage ΔV is fixed to 0. If the values of the four fixed resistors 16 'to 19' are set appropriately,
When the piezoresistors 16 to 19 are damaged, the output voltage ΔV
Can be set to be fixed to an arbitrary value. Therefore, the Si cantilever breaks and the piezo resistance 1
Even when 6 to 19 are disconnected, a stable value can be taken out as the output of the semiconductor acceleration sensor, and the value can be set to an arbitrary value. It can be determined that the acceleration sensor has been damaged. Therefore, it is possible to accurately detect the damage state of the semiconductor acceleration sensor with a simple detection circuit.

Next, the change in the sensitivity of the bridge circuit due to the connection of the resistors 16 'to 19' will be described. Assuming that the resistance values of the resistors 16 'to 19' are r, and the other conditions are the same as those in FIG.
The output voltage ΔV is expressed by the following (Equation 3).

[0017]

(Equation 3)

Accordingly, if the resistance value r of the resistors 16 'to 19' is sufficiently larger than the resistance value R of the piezo resistors 16 to 19, the expression (3) becomes equal to the expression (2). That is,
By making r sufficiently larger than R, the resistances 16 'to 1
The decrease in sensitivity due to connecting 9 'in parallel can be almost ignored. For example, assuming that the resistance value r of the resistors 16 'to 19' is 10 times the resistance value R of the piezo resistors 16 to 19, respectively,
The sensitivity is reduced by 10% as compared with the case where 19 'is not connected. If the decrease in sensitivity is within 10%, it is considered that there is no problem in practical use. Therefore, as described above, the resistance values of the resistors 16 'to 19' are changed to the piezoresistor 16 as described above.
It is desirable to make it 10 times or more of 19. In addition, as a method of forming the resistors 16 ′ to 19 ′, accuracy is high,
It is desirable to use an ion implantation method which can realize a high resistance value in a small area.

[0019]

As described above, in the present invention,
Since the wiring connected to the piezoresistor is formed of a high-concentration diffusion layer having a thermal expansion coefficient equal to that of the semiconductor substrate, no thermal stress is generated by the wiring. Therefore, the resistance value of the piezoresistor has an effect that the change due to the temperature is suppressed to the minimum value, the temperature drift of the voltage output from the bridge circuit is reduced, and the acceleration can be accurately detected. Also, by directly joining the four piezoresistors, it is possible to solve the problem that the detection sensitivity is reduced due to the wiring resistance, and the offset is caused due to the variation in the resistance value of each wiring resistance, thereby lowering the detection accuracy. Can be obtained.

[Brief description of the drawings]

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

FIG. 2 is an example of a conventional device.

FIG. 3 is another example of a conventional device.

[Explanation of symbols]

11 ... Si cantilever 16-19 ... Piezo resistor 16'-19 '... Resistance 21-24 ... Wiring 25 ... Si substrate 31-34 ... Wiring

Claims (1)

(57) [Claims] A piezoresistor is formed in the vicinity of a support portion of a cantilever having one end supported on a semiconductor substrate, and a change in a resistance value generated in the piezoresistor in accordance with the deflection of the cantilever. In a semiconductor acceleration sensor for detecting acceleration by detecting , a bridge is provided near a support portion of the cantilever on a semiconductor substrate.
Forming four piezoresistors constituting a circuit, and
Of the piezoresistors are such that the ends of each piezoresistor are next to each other.
It is shaped to direct binding as the lead-out wires of the bridge circuit from the respective coupling portions, and forming a high concentration diffusion layer portions on at least the cantilever, formed in said semiconductor substrate of said wiring A semiconductor acceleration sensor characterized in that: