JP2006275702A - Diaphragm type pressure sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a diaphragm type pressure sensor excellent in reproducibility of measurement value and capable of correct pressure measurement and prevented from effects of fluctuation of circumferential temperature. <P>SOLUTION: The diaphragm type pressure sensor is characteristically manufactured by bonding the first insulative substrate and the silicon substrate formed with the diaphragm, and the silicon substrate and the second insulative substrate provided with a ventilation hole, either of insulative substrate has smaller heat expansion coefficient than the coefficient of heat expansion of the silicon substrate at the bonding temperature, and the temperature expansion coefficient of the other silicon substrate is nearer to that of the silicon substrate than the former insulative substrate. The thickness of the former insulative substrate is characteristically thinner than that of the latter insulative substrate. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a diaphragm-type pressure sensor, and more particularly to a diaphragm-type pressure sensor that is excellent in pressure measurement stability and is not easily affected by environmental temperature changes.

  A capacitance type pressure sensor will be described as an example of a conventional diaphragm type pressure sensor. For example, as shown in the schematic cross-sectional view of FIG. 4, the capacitive pressure sensor includes a first glass substrate 10 on which a measurement electrode 11 is formed, a silicon substrate 20 on which a diaphragm 21 is formed, and a vent 31. The pressure reference chamber 1 and the pressure measurement chamber 2 are formed on both sides of the diaphragm 21. In the pressure reference chamber 1, for example, a non-evaporable getter 3 is disposed, and the inside is kept in a vacuum.

  This pressure sensor is mounted on, for example, a metal adapter 4 via an O-ring 5 and fixed by a pressing plate 6. The adapter is connected to the gauge port of the vacuum chamber. The pressure in the vacuum chamber is applied to the pressure measurement chamber 2 of the sensor through the vent 31, and the diaphragm 21 is bent according to the pressure difference between the pressure measurement chamber 2 and the pressure reference chamber 1. Accordingly, by measuring the capacitance between the diaphragm 21 and the measuring electrode 11 with the terminal pins 12 and 13, the amount of deflection of the diaphragm, that is, the pressure in the vacuum chamber can be measured.

Micromachine technology is used for manufacturing such a pressure sensor. In addition, an anodic bonding method is usually used for bonding the first and second glass substrates and the silicon substrate, and is heated to 300 to 450 ° C., and is about several hundreds V to 1 kV between the silicon substrate and the glass substrate. By applying this voltage, both substrates can be firmly bonded without using an adhesive. However, if bonding is performed at such a high temperature, a large stress is generated on the silicon substrate, particularly the diaphragm, when the temperature is returned to room temperature, and the measured values are not reproducible, or the measured values change due to fluctuations in ambient temperature around the sensor As the glass substrate, glass (for example, Pyrex (registered trademark) glass) whose material has a thermal expansion amount close to silicon at the bonding temperature is generally used.
JP 2001-255225 A JP-A-6-66658

  In recent years, as semiconductor devices and electronic components become more functional and denser, the manufacturing process needs to be more sophisticated and pressure sensors are required to have higher measurement accuracy under various process conditions. became. However, with the conventional capacitive pressure sensor shown in FIG. 4, it is not possible to sufficiently meet these high demands, and measurement due to variations between sensors, reproducibility of pressure measurement values, and fluctuations in environmental temperature. Errors and the like have become prominent problems. In addition, a configuration has been proposed in which a reference electrode is arranged around the measurement electrode for temperature compensation to compensate for a variation in capacitance caused by a temperature change, but the configuration with the reference electrode alone is sufficient. However, there is a need for a pressure sensor that is less temperature dependent.

  Therefore, the present inventors made trial manufactures of pressure sensors under various manufacturing conditions using various glass substrates, and studied to solve the above problems. Here, for example, in order to reduce stress, when glass having a thermal expansion coefficient very close to that of silicon (Asahi Techno Glass Co., Ltd., SW-Y, etc.) is used, contrary to expectation, a low pressure range of 100 Pa or less in particular. As a result, it was found that the measurement value was not reproducible and stable measurement could not be performed, and the environmental temperature dependency was not particularly improved. That is, it has been found that it is difficult to produce a pressure sensor capable of high-precision measurement by simply using a glass substrate having a material having a similar coefficient of thermal expansion at the bonding temperature. Furthermore, when a material and a joining condition that apply a compressive stress to the silicon substrate are selected, similarly, the reproducibility of the measured value is lost. In addition, even when tensile stress was applied, the sensitivity to pressure decreased as the tensile stress increased, and the variation of the measured value with respect to the environmental temperature tended to increase.

Based on these findings, in order to optimize the tensile stress of the silicon diaphragm, further studies on the materials and thicknesses of the first and second glass substrates, bonding conditions, etc. are made, and as a result, the measured values are stabilized and the temperature is stabilized. The present inventors have found a sensor structure that can reduce the influence of the above, and thus completed the present invention.
The above-mentioned problems and other circumstances related to the capacitance type pressure sensor include other pressure sensors using a diaphragm, for example, a semiconductor resistance element type in which a piezoresistive element is formed on the diaphragm, and a vibration type using a resonance frequency of the diaphragm. The same applies to other sensors.

  In view of such circumstances, an object of the present invention is to provide a diaphragm type pressure sensor that is excellent in reproducibility of measurement values and capable of accurate pressure measurement. Furthermore, it aims at providing the diaphragm type | mold pressure sensor with the high measurement accuracy which suppressed the influence of environmental temperature change.

The diaphragm type pressure sensor according to the present invention includes a first insulating substrate, a silicon substrate on which a diaphragm is formed, and a second insulating substrate on which a vent is formed, and the diaphragm and the first insulating substrate. A pressure reference chamber and a pressure measurement chamber are respectively formed between the pressure vent and the vent, and a displacement amount of a diaphragm displaced according to a pressure applied to the pressure measurement chamber from the outside through the vent is measured to obtain the pressure. In the diaphragm type pressure sensor, one of the first and second insulating substrates applies a first tensile stress to the silicon substrate at an environmental temperature, and the other insulating substrate A tensile stress or a compressive stress, which is smaller than the first stress, is applied to the silicon substrate at an environmental temperature so that the tensile stress always acts on the diaphragm. Further variation with respect to temperature of the second stress is characterized by being configured to be smaller than the change amount with respect to the temperature of the first stress.
Thus, in order to apply a tensile stress (first stress) to the silicon substrate in the environmental temperature region of pressure measurement, for example, by selecting the material and the bonding temperature, one insulating substrate can select silicon in the environmental temperature region. By selecting a material, for example, by selecting a material so that a tensile stress can always be applied to the diaphragm and the other insulating substrate hardly applies a stress (second stress) to the silicon substrate in the environmental temperature region. It becomes possible to reduce the temperature dependence of the tensile stress applied to the silicon diaphragm at the temperature. By adopting such a configuration, it is possible to perform stable pressure measurement with reproducibility, and to reduce variations in measurement values due to fluctuations in environmental temperature, thereby enabling more accurate measurement. If the stress applied to the diaphragm as a whole is a tensile stress, the second stress is not limited to a tensile stress but may be a compressive stress.

More specifically, a first insulating substrate, a silicon substrate on which a diaphragm is formed, and a second insulating substrate on which a vent hole is formed are joined, and the diaphragm, the first insulating substrate, and the ventilation are joined. A diaphragm-type pressure that forms a pressure reference chamber and a pressure measurement chamber between each of them and determines the pressure by measuring the amount of displacement of the diaphragm that is displaced according to the pressure applied to the pressure measurement chamber from the outside through the vent In the sensor, one of the first and second insulating substrates has a thermal expansion coefficient smaller than that of the silicon substrate at a bonding temperature, and the other insulating substrate is It has a thermal expansion coefficient closer to that of the silicon substrate than that of the one insulating substrate at an environmental temperature.
That is, with the sensor structure having the above relationship regarding the thermal expansion coefficients of the first and second insulating substrates, an appropriate tensile stress is always applied to the silicon diaphragm in the environmental temperature range of pressure measurement. As a result, stable measurement with reproducibility becomes possible. Furthermore, in the environmental temperature range, it is possible to suppress changes in tensile stress due to environmental temperature fluctuations, and as a result, variations in measured values due to environmental temperature fluctuations are reduced, resulting in more accurate measurements. It becomes possible.

Further, the thickness of the one insulating substrate is smaller than the thickness of the other insulating substrate.
As described above, with the sensor structure having the above relationship with respect to the thicknesses of the first and second insulating substrates, the thin insulating substrate mainly applies an appropriate tensile stress to the silicon substrate, A thick insulating substrate applies almost no tensile stress to the silicon substrate, and acts to suppress the change in the tensile stress of the silicon substrate due to changes in the environmental temperature to a small extent, allowing an appropriate tensile stress to act on the silicon diaphragm with better controllability. In addition, it is possible to suppress a change in the tensile stress of the silicon diaphragm accompanying a change in environmental temperature. As a result, it is possible to stably perform highly accurate measurement with high reproducibility by reducing variations in measurement values due to environmental temperature fluctuations.
Here, the stress caused by the thick insulating substrate is small even if it is a compressive stress, and the stress applied to the diaphragm as a whole of the sensor may be a tensile stress.

  Details of the reason why the temperature dependence of the measured value is improved by selecting the thermal expansion coefficient of the thick insulating substrate closer to the thermal expansion coefficient of the silicon substrate at the ambient temperature of the pressure measurement is clear at present. However, it is thought as follows. That is, since the thermal expansion coefficient is close between the thick insulating substrate and the silicon substrate, it can be considered that both are thermally integrated and thick with respect to the thin substrate having a small thermal expansion coefficient. Here, even if a thin insulating substrate with a small thermal expansion coefficient is bonded to the silicon substrate, the thermal expansion characteristics of the thick integrated substrate consisting of the thick insulating substrate and the silicon substrate are dominant, and the environmental temperature fluctuates. However, it is considered that the stress applied to silicon hardly changes, and as a result, variations in measured pressure values are suppressed.

At the environmental temperature, the change amount with respect to the temperature of the difference in thermal expansion coefficient between the other insulating substrate and the silicon substrate is larger than the change amount with respect to the temperature of the difference in thermal expansion coefficient between the one insulating substrate and the silicon. It is preferable to make it smaller.
By adopting such a configuration, for example, even when the environmental temperature fluctuates, the other substrate (for example, a thick insulating substrate) expands and contracts in the same manner as a silicon substrate. As a result, the temperature can be measured with high accuracy and less influenced by the environmental temperature.
Further, the difference in coefficient of thermal expansion at 10 to 50 ° C. between the other insulating substrate and the silicon substrate is preferably 5 ppm or less. Thereby, the temperature dependence of the pressure measurement value can be further reduced.

  In the present invention, the bonding between the one insulating substrate and the silicon substrate is preferably performed at a higher temperature and before the bonding between the other insulating substrate and the silicon substrate. As a result, the tensile stress on the silicon diaphragm can be controlled more precisely. For example, even when the same material is used for the two insulating substrates, an appropriate tensile stress is applied to the silicon diaphragm. Is possible.

In the present invention, the environmental temperature is the temperature of the environment in which the pressure sensor is used. Therefore, it differs depending on the purpose of use of the sensor and is not necessarily limited to the vicinity of room temperature. The coefficient of thermal expansion at a predetermined temperature refers to the ratio (ΔL / L ₀ ) between the reference value L _{0 at} 0 ° C. and the amount of thermal expansion ΔL (= L−L ₀ ) at the predetermined temperature.

  According to the present invention, that is, by adopting a configuration in which a minimum tensile stress is applied to the silicon diaphragm, a pressure sensor with high reproducibility of measurement can be manufactured with high yield, and the productivity of the high-precision pressure sensor is greatly improved. Can be made.

   In addition, by making the thermal expansion coefficient of a thick insulating substrate in the pressure measurement temperature range substantially the same as that of a silicon substrate, the temperature dependence of the measured value can be greatly reduced. For example, a heater or the like is used in a vacuum vessel However, even in a system in which the ambient temperature around the sensor fluctuates, highly accurate and stable pressure measurement is possible, and a pressure sensor can be provided that is compatible with production of highly functional devices and the like.

  Hereinafter, the present invention will be described in detail with reference to examples.

    One structural example of the capacitive sensor of the present invention is shown in the schematic cross-sectional view of FIG. As shown in the figure, the capacitance type pressure sensor of the present embodiment is formed with a first insulating substrate 10 on which a measurement electrode 11 is formed, a silicon substrate 20 on which a diaphragm 21 is formed, and a vent 31. A pressure reference chamber 1 and a pressure measurement chamber 2 are formed on both sides of the diaphragm 21. In the pressure reference chamber 1, for example, a non-evaporable getter 3 is disposed, and the inside is kept in a vacuum.

  This pressure sensor is manufactured as follows, for example. The first insulating substrate 10 on which the measurement electrode 11 is formed and the silicon substrate 20 on which the recess for the pressure reference chamber is formed are overlapped and heated to about 300 to 450 ° C. in a vacuum. A voltage of ˜1 kV is applied, and both are bonded by an anodic bonding method. Thereby, the pressure reference chamber 1 is formed. Subsequently, after the diaphragm 21 is formed by etching from the opposite side of the pressure reference chamber 1 of the silicon substrate, it is overlapped with the second insulating substrate 30 in which the vent 31 is formed, and similarly bonded by anodic bonding. Finally, the terminal pins 12 and 13 are attached to complete the pressure sensor.

In this embodiment, the first insulating substrate is thinner than the second insulating substrate. Further, a coefficient of thermal expansion (ΔL / L ₀ ) at the bonding temperature of the first insulating substrate is selected to be smaller than that of the silicon substrate. Further, the thermal expansion coefficient of the second insulating substrate in the environmental temperature range where pressure measurement is performed is selected so as to be a value closer to the thermal expansion coefficient of the silicon substrate than the first insulating substrate. By selecting an insulating substrate with such a material and thickness, the stress applied to the diaphragm when returning to room temperature, for example, can always be a small tensile stress, and measurement reproducibility can be obtained and stable measurement is performed. Is possible. In addition, variations in measured values due to environmental temperature fluctuations can be suppressed. Here, at the environmental temperature, the change amount with respect to the temperature of the difference in thermal expansion coefficient between the second insulating substrate and the silicon substrate is larger than the change amount with respect to the temperature of the difference in thermal expansion coefficient between the first insulating substrate and silicon. By reducing the size, it becomes possible to perform temperature measurement with higher accuracy with the influence of the environmental temperature being further reduced.

  Specifically, the thickness of each substrate is, for example, 0.2 to 0.5 mm for a silicon substrate, 0.5 to 0.8 mm for a first insulating substrate, and 1 to 3 mm for a second insulating substrate. Are preferably used. In addition, as a material of the insulating substrate, from the viewpoint of applying an appropriate tensile stress to the silicon diaphragm, glass similar in thermal expansion characteristics to the silicon substrate, for example, Pyrex (registered trademark), SW-Y glass and SW made by Asahi Techno Glass -YY glass, HOYA SD-1 glass and SD-2 glass are preferably used, and are selected so as to satisfy the above-mentioned relationship of thermal expansion coefficients.

As a combination of glasses satisfying the above relationship of thermal expansion coefficients, for example, a combination of Pyrex glass as the first insulating substrate and SW-Y glass as the second insulating substrate can be given. The thermal expansion characteristics of these glass substrates and silicon substrates are shown in FIGS. 2 and 3, and the operation of a sensor manufactured using these glass substrates will be described below.
2 and 3 show thermal expansion coefficient characteristics of 300 to 450 ° C. and 0 to 50 ° C., respectively, as an example of the thermal expansion coefficient in the bonding temperature range and the pressure measurement temperature (environment temperature) range.

  As shown in FIG. 2, the thermal expansion coefficient of Pyrex glass at the bonding temperature is smaller than that of SW-Y glass, and the thermal expansion coefficient of SW-Y glass is substantially the same as that of silicon. Here, when the thicknesses of Pyrex, silicon substrate and SW-Y are 0.7 mm, 0.5 mm and 2.0 mm, respectively, silicon and Pyrex glass are anodically bonded and then returned to room temperature. Will be added. On the other hand, since the thermal expansion coefficients of SW-Y glass and silicon substrate are very close, even when the temperature is returned to room temperature, almost no stress is generated between silicon and SW-Y glass. Therefore, as a whole, an appropriate tensile stress can be applied to the diaphragm.

  As shown in FIG. 3, even in the environmental temperature range, the thermal expansion coefficient of SW-Y glass is closer to that of silicon than Pyrex glass, and the difference in thermal expansion coefficient from silicon is 5 ppm or less. Accordingly, since it is considered that the thick SW-Y glass and the silicon substrate function as one body thermally, the influence of the thin Pyrex substrate is reduced, and the tensile stress can be kept substantially constant even when the environmental temperature changes. That is, even if the environmental temperature varies, the distortion of the diaphragm can be suppressed, and the variation in the measured value can be suppressed.

  In addition, when SW-Y glass having a thermal expansion characteristic very close to that of silicon is used for both the first and second insulating substrates, the reproducibility of measured values in the low-pressure region is reduced, It was said that the variation of would be likely to increase. This is because the thermal expansion coefficient at the bonding temperature is very close, so if there is a temperature distribution in the silicon substrate and the SW-Y glass at the time of bonding, the magnitude of expansion between the silicon and the glass is reversed according to the distribution, and the room temperature It is considered that the reproducibility of the measured value was lowered due to a partial compression stress that was caused by this.

The pressure sensor of this example has a configuration in which the first insulating substrate is thinner than the second insulating substrate and the coefficient of thermal expansion (ΔL / L ₀ ) at the junction temperature is smaller than that of silicon. On the contrary, the second insulating substrate may have a thin plate thickness and a thermal expansion coefficient smaller than that of silicon.

In Example 1, the thermal expansion coefficients of the first and second insulating substrates were selected and the tensile stress of the diaphragm was adjusted. In this example, the pressure was adjusted by changing the bonding temperature with the silicon substrate. The sensor will be described.
In this embodiment, a case where Pyrex glass is used for both the first and second insulating substrates will be described. The first glass substrate (for example, 0.7 mm thick) and the silicon substrate (for example, 0.5 mm) are bonded at, for example, 400 ° C., and the silicon substrate and the second glass substrate (for example, 2 mm plate) are bonded at, for example, 300 ° C. To produce a pressure sensor.

As is clear from FIG. 2, the thermal expansion coefficient of Pyrex glass tends to be closer to that of silicon as the temperature becomes lower. Accordingly, a tensile stress is generated on the first glass substrate side bonded at 400 ° C. on the silicon substrate bonded at 400 ° C. relative to the second glass substrate side bonded at 300 ° C. Less stress is generated on the surface. That is, since the stress applied to the silicon substrate by the second glass substrate, which is a thick substrate, is small, the strain of the entire pressure sensor can be reduced while maintaining the tensile stress of the silicon substrate. Temperature dependence can be improved.
In the present embodiment, the first and second glass substrates are made of the same material, but needless to say, different materials may be used. In this case, the tensile stress can be controlled more precisely, and the degree of freedom in sensor design increases.

  In the above embodiments, the case of the capacitive sensor has been described. However, the resistance of the semiconductor piezoresistive element on the diaphragm changes due to the distortion (that is, the pressure) of the diaphragm. Needless to say, the present invention can also be applied to a pressure sensor such as a semiconductor resistance element type and a vibration type that utilizes the fact that the resonance frequency of the diaphragm changes due to strain due to pressure. Further, the bonding method is not limited to anodic bonding, and any bonding method may be used as long as heating is performed at the time of bonding.

It is typical sectional drawing which shows an example of the diaphragm type | mold pressure sensor of this invention. It is a graph which shows the thermal expansion coefficient characteristic in a joining temperature range. It is a graph which shows the thermal expansion coefficient characteristic in the environmental temperature range of a pressure measurement. It is a typical sectional view showing an example of the conventional diaphragm type pressure sensor.

Explanation of symbols

1 reference pressure chamber,
2 Pressure measurement chamber,
3 Non-evaporable getter,
4 adapters,
5 O-ring,
6 holding plate,
10 first insulating substrate;
11 Measuring electrode,
12, 13 terminal pin 20 silicon substrate,
21 Diaphragm,
30 second insulating substrate;
31 Vent.

Claims (6)

A first insulating substrate, a silicon substrate on which a diaphragm is formed, and a second insulating substrate on which a vent is formed are joined, and the diaphragm and the first insulating substrate and the vent are respectively connected. In the diaphragm type pressure sensor that forms a pressure reference chamber and a pressure measurement chamber, and measures the displacement amount of the diaphragm that is displaced according to the pressure applied to the pressure measurement chamber from the outside through the vent, and obtains the pressure,
One of the first and second insulating substrates applies a first stress of tensile stress to the silicon substrate at an environmental temperature, and the other insulating substrate has the silicon substrate at the environmental temperature. A tensile stress or a compressive stress second stress smaller than the first stress is applied to the diaphragm so that a tensile stress always acts on the diaphragm, and the change amount of the second stress with respect to the temperature is the first stress. 1. A diaphragm type pressure sensor characterized by being configured to be smaller than an amount of change of stress of 1 with respect to temperature. A first insulating substrate, a silicon substrate on which a diaphragm is formed, and a second insulating substrate on which a vent is formed are joined, and the diaphragm and the first insulating substrate and the vent are respectively connected. In the diaphragm type pressure sensor that forms a pressure reference chamber and a pressure measurement chamber, and measures the displacement amount of the diaphragm that is displaced according to the pressure applied to the pressure measurement chamber from the outside through the vent, and obtains the pressure,
One of the first and second insulating substrates has a thermal expansion coefficient smaller than that of the silicon substrate at a bonding temperature, and the other insulating substrate has an environmental temperature. A diaphragm type pressure sensor having a coefficient of thermal expansion closer to that of a silicon substrate than that of the one insulating substrate.   3. The diaphragm type pressure sensor according to claim 2, wherein the thickness of the one insulating substrate is thinner than the thickness of the other insulating substrate.   At the environmental temperature, the change amount with respect to the temperature of the difference in thermal expansion coefficient between the other insulating substrate and the silicon substrate is larger than the change amount with respect to the temperature of the difference in thermal expansion coefficient between the one insulating substrate and the silicon. The diaphragm type pressure sensor according to claim 2 or 3, wherein the diaphragm type pressure sensor is small.   The diaphragm type pressure sensor according to any one of claims 2 to 4, wherein a difference in coefficient of thermal expansion at 10 to 50 ° C between the other insulating substrate and the silicon substrate is 5 ppm or less.   6. The bonding between the one insulating substrate and the silicon substrate is performed at a higher temperature and before the bonding between the other insulating substrate and the silicon substrate. The diaphragm type pressure sensor according to any one of the above.

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