JPH04114478A - Semiconductor device - Google Patents

Abstract

PURPOSE:To improve a semiconductor device in temperature characteristics of offset voltage by a method wherein a silicon semiconductor substrate is joined to another member, and the member concerned is formed of material other than silicon, which is specified in thermal expansion coefficient within a range of the operating temperature of a semiconductor device. CONSTITUTION:The surface of a silicon substrate 1 is coated with a protective film 5, such as a silicon oxide film, including a contact hole 6 reaching the surface of the substrate 1, and an aluminum electrode 7 is built on the contact hole 6. A pressure sensitive element 11 is electrostatically jointed to a base 8 provided with a pressure introducing hole 9 at its center. The base 8 is optionally set in height so as to prevent the thermal deformation of a member joined to the underside of the base 8 from affecting the output of the pressure sensitive element 11. The base 8 can be formed of various kinds of material other than silicon, where materials are possessed of a thermal expansion coefficient alpha[ deg.C<-1>] at a temperature of T[ deg.C] within an operating temperature range of a sensor, and alpha is so set as to satisfy a formula, alpha=aT+b, where 2.4X10<-9=a<=7.2X10<-9>[ deg.C<-2>] and 1.9X10<-9=b<=3.3X10<-6>[ deg.C<-1>].

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor device, and particularly to a semiconductor strain sensor such as a semiconductor pressure sensor or an acceleration sensor that is mounted on a vehicle and used in a wide temperature range.

[Prior Art] A semiconductor pressure sensor, which is a type of semiconductor strain sensor, is used, for example, to detect the intake pipe pressure of a vehicle engine, and is used to control the amount of fuel injection.

Semiconductor pressure sensors generally have a structure in which a part of a silicon substrate is a thin pressure-receiving diaphragm, and a pressure-sensitive element with a strain gauge resistor formed on the upper surface of the diaphragm is bonded to a pedestal. When pressure is applied to the diaphragm, the resistance value of the strain gauge changes (piezoresistance effect), and an output signal corresponding to the pressure is obtained.

For the pedestal that supports the pressure-sensitive element, a borosilicate glass-based material whose coefficient of thermal expansion is relatively similar to that of silicon, which is the substrate material, is often used for the purpose of alleviating thermal stress caused by the difference in coefficient of thermal expansion. It is bonded to a silicon substrate by electrostatic bonding (anodic bonding).

[Problems to be Solved by the Invention] However, since a vehicle-mounted pressure sensor has a wide operating temperature range, thermal distortion occurs in the joint surface due to a slight difference in thermal expansion coefficient between the two as the temperature changes.

This thermal strain is transmitted through the thick portion of the silicon substrate to the strain gauge on the diaphragm, and affects its output.

In other words, since a strain gauge outputs a strain output signal that is approximately proportional to the magnitude of strain, as a pressure sensor, a thermal strain signal is included in the signal component other than the pressure signal (hereinafter referred to as offset voltage). Become.

The magnitude of this thermal strain is temperature dependent, and the amount of change with respect to temperature is not constant within the operating temperature range of the sensor. This means that the offset voltage changes non-linearly with respect to temperature, which is difficult to correct using a simple electronic circuit.

Therefore, an object of the present invention is mainly to improve the temperature characteristics of offset voltage and to provide a highly accurate and reliable semiconductor device.

[Means for Solving the Problems] In order to solve the above problems, in the present invention, a silicon semiconductor substrate is bonded to another member, and the member is thermally expanded at a temperature T [°C] in the sensor use area. Coefficient α [℃']
is shown for α-aT, and 2.4X10 ≦a≦7.2 X 1.0-9[℃'
]1.9X10≦b≦3.3X10-6[℃-
1], and is made of a material other than silicon.

[Function] The coefficient of thermal expansion α [°C'] of silicon is expressed as b'2, 56 x 10-6 [°C'].

In the present invention, the thermal expansion coefficient α of other members to be bonded to the silicon semiconductor substrate is expressed as aT+b [°C-1],
Since the material is made of a material that is
)T+εO. In other words, thermal strain is expressed by a linear equation related to temperature T, and changes linearly with respect to temperature changes. Therefore, when obtaining output from a semiconductor substrate, thermal distortion components can be easily corrected.
Improves accuracy.

[Example] Hereinafter, an example in which the present invention is applied to a semiconductor pressure sensor will be described based on the drawings.

In FIG. 1, a silicon semiconductor substrate 1 has a central portion made thinner by etching to form a diaphragm 2, and a strain gauge resistor 3 is formed on the upper surface of the diaphragm 2 by a semiconductor process. Here, the strain gauge resistor 3 was formed by thermally diffusing impurities at predetermined locations on the upper surface of the diaphragm 2. This strain gauge resistor 3 is usually configured such that four pieces form a Wheatstone bridge, or two pieces form a half bridge.
A resistor portion is formed between these strain gauge resistors 3 and between the strain gauge resistor 3 and the aluminum electrode 7 by thermal diffusion, and there is no diffusion lead 4.

The surface of the silicon substrate 1 is covered with a protective film 5 such as a silicon oxide film.
A contact hole 6 reaching the substrate 1 is provided in a part of the protective film 5, and the aluminum electrode 7 is formed thereon. The entire structure including each part formed in this manner is referred to as a pressure sensitive element 11.

The pressure sensitive element 11 is electrostatically bonded to a pedestal 8 having a pressure introduction hole 9 in its center. The height of the pedestal 8 is appropriately set to such an extent that thermal strain caused by the member bonded to the lower part of the pedestal 8 does not affect the output of the pressure sensitive element 11.

The material constituting the pedestal 8, excluding silicon, has a coefficient of thermal expansion α [°C] at the temperature T [°C] within the sensor usage area.
°C'] is shown as α=aT+, 2.4X10'≦a≦
7, 2 X 10-9 [℃-2] 1.9 X 10-9≦
Various materials satisfying b≦3.3×10 −6 [° C. −11] can be suitably used.

Here, the influence of differences in thermal expansion coefficients of the materials of the pedestal 8 on thermal strain at the joint surface with silicon will be discussed.

First, the pedestal 8 is made of conventional material Pyrex (registered trademark: Corning Glass Code #7740, NazO
-8iO2-B203-based glass material>, the thermal strain when a strong bond such as electrostatic bonding with silicon is applied will be studied.

At this time, the thermal strain 1εT1 is expressed by the following formula, where T: temperature To: temperature at the time of bonding α, coefficient of thermal expansion α of conventional material, i: coefficient of thermal expansion of silicon. As shown in FIG.
6 x 10"6[℃'], so the thermal strain is ε0:T=0℃, and the thermal strain 1ε■1 has temperature dependence.The first equation in the above equation
The term is a quadratic component with respect to temperature T, which represents a non-linear component of the temperature dependence of thermal strain. Generally, 2
It can be said that the components of the second or higher order are non-linear components, and therefore, in order to eliminate the non-linearity of the temperature dependence of thermal strain, it is necessary to have no component of the second or higher order with respect to T. That is, if the coefficient of thermal expansion of the material of the pedestal 8 is α, then when α=aT+b [°C-1], if ai==a- is selected, then ε, -11(bb-b-)' r+εO.

It can be seen that the temperature-dependent nonlinearity is improved.

Note that if a = a- and b = b-, the thermal expansion coefficients of both will completely match and no thermal distortion will occur, but the purpose of the present invention of eliminating temperature-dependent nonlinearity can be achieved. In order to do this, it is sufficient that there is no component of aha-1, that is, the second or higher order of T.

Next, we will consider in what range a and b should be in order to obtain a good improvement effect. Assuming that the temperature-dependent nonlinearity should be halved compared to the case of using the above conventional material, a=a-±0.5 ta-a-1[℃-2]=
2.4X10'~7, 2X10-9["C-"]
In addition, if we try to suppress the magnitude of thermal strain to the conventional level, at T=O℃, the difference in thermal expansion coefficient between silicon and conventional material is approximately 0.7 x 10'["C-11"] From, b=b −±0.7×lO−6[℃−1=2.
6X10 ±0. 7X10-6 [℃-1 Colo = 1.9X10'~3, 3 X 10-'' [℃-1
]. From the above, the thermal expansion coefficient α [℃
-1] is shown by α=aT+b, 2.4X10'≦a≦7, 2X10-9[℃-"
]=9 1.9X10 ≦b≦3.3X10-6["C-']
If so, it can be seen that the nonlinearity of temperature characteristics can be improved.

Next, in order to confirm the effects of the present invention, verification was carried out using a sample (Example 1.2) having a coefficient of thermal expansion α (30°C to 150°C) shown in Table 1 and Figure 2 below. These are glass materials whose components are mixed so that they can be electrostatically bonded and have a slope of the temperature dependence of the coefficient of thermal expansion close to that of silicon (aha-).

Table 1 Using the glass materials of Example 1.2 as the material for the pedestal 8, the pressure sensor shown in FIG. 1 was prototyped. FIG. 3 shows the results of measuring the temperature dependence of the offset voltage fluctuation amount ΔVoF. As is clear from the figure, in the conventional material, the amount of offset voltage fluctuation △■OFF changes nonlinearly, whereas in Example 1.2, there is almost no nonlinearity and the temperature characteristics are significantly improved. It can be seen that

By the way, the magnitude of the offset voltage fluctuation is larger in Example 1, which is closer to the coefficient of thermal expansion of silicon than in Example 2, which may seem contradictory, but
This is considered to be because the strain gauge resistor 3 is also affected by thermal strain generated between the silicon substrate 1 and the protective film 5 formed of a silicon oxide film or the like.

Note that although a glass-based material is exemplified here as the material for the pedestal 8, it is not limited to a glass-based material as long as it is a material other than silicon that satisfies the above conditions.

Further, in this embodiment, the bonding between the silicon substrate 1 and the pedestal 8 of the pressure sensor has been described, but the bonded member is not limited to the pedestal, but the same applies to other uses and roles that are bonded to the silicon substrate 1. The effect of this can be obtained. Further, the bonding method does not need to be electrostatic bonding (anodic bonding).

In the above embodiment, the strain gauge resistor 3 and the diffusion lead 4 are formed by thermal diffusion, but other methods may be used, and the strain gauge resistor 3 does not need to constitute a bridge circuit.

Furthermore, the pedestal 8 may have a structure without the pressure introduction hole 9, and the protective film 5 and the aluminum electrode 6 may not be provided.

Although the above embodiments have been described with respect to pressure sensors, it is of course possible to apply the present invention to other semiconductor devices such as acceleration sensors.

[Effects of the Invention] As described above, according to the present invention, the member to be bonded to the silicon substrate is made of a material whose coefficient of thermal expansion has a predetermined temperature dependence. , there is no non-linearity with respect to temperature changes. Therefore, temperature correction can be easily performed when obtaining an output signal from a silicon substrate, and sensor accuracy can be significantly improved, making it useful as a strain sensor used in a wide temperature range, such as in a vehicle.

[Brief explanation of the drawing]

Figures 1 to 3 show an embodiment of the present invention, Figure 1 is an overall sectional view of a semiconductor pressure sensor, Figure 2 is a diagram showing the temperature dependence of the coefficient of thermal expansion, and Figure 3 is an offset diagram. FIG. 3 is a diagram showing the temperature dependence of voltage fluctuation amount. 1... Silicon substrate 2... Diaphragm 3... Strain gauge resistor 8... Pedestal (member) 11... Pressure sensitive element No. 2nd figure knitting T ['c] -+ 3rd figure trick T ['c] -m

Claims (1)

[Claims] Consisting of a silicon semiconductor substrate bonded to another member, the member has a coefficient of thermal expansion α [°C^-^1] at a temperature T [°C] in the region in which the semiconductor device is used, α= It is represented by aT+b, and 2.4×10^-^9≦a≦7.2×10^-^9[℃
^-^2] 1.9×10^-^6≦b≦3.3×10^
-^6 [°C^-^1], and is characterized by being made of a material other than silicon.