JP3153710B2 - Glass for silicon pedestal and silicon substrate type sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor pressure sensor,
The present invention relates to a silicon pedestal glass suitable as a pedestal glass for joining and fixing a silicon single crystal base material used for an acceleration sensor, an X-ray lithography mask, a micromachine, and the like. Further, the present invention relates to a silicon-based sensor such as a semiconductor pressure sensor using the silicon pedestal glass.

[0002]

2. Description of the Related Art As an example of a typical use of a unit in which a silicon base material is held by a glass for a silicon pedestal,
2. Description of the Related Art A silicon-based pressure sensor that detects an external force such as pressure is known. This silicon-based pressure sensor has
There are various types depending on the method of converting the strain generated in the diaphragm made of silicon single crystal into an electric signal. A semiconductor pressure sensor utilizing the piezoresistive effect is a representative example, and is widely used in the automobile industry and the FA equipment industry. Specifically, it is used as a sensor of an automatic control system for controlling a fuel flow rate and a hydraulic pressure in order to measure the pressure and flow rate of a gas or a liquid [Japanese Patent Laid-Open No. 4-11447].
No. 8, 4-83139]. The characteristic of this type of semiconductor pressure sensor is that a semiconductor circuit is formed on the surface of a thin-film silicon single crystal substrate formed to be elastically deformable, and a part of a strain gauge is formed to form a diaphragm. It was done. The mechanism of the pressure detection is that when a pressure is applied to the silicon single crystal substrate, a strain is generated, and the specific resistance of the strain gauge changes according to the strain. It is converted into change and measured.

[0003] A holding member for holding a diaphragm made of a silicon single crystal substrate of the semiconductor pressure sensor includes:
Anodic bonding to a silicon substrate is possible, and the thermal expansion coefficient (31-33 × 10 ⁻⁷⁾ is relatively similar to that of the silicon substrate.
/ ° C). The anodic bonding is a technique in which a silicon substrate and glass are heated to 300 to 600 ° C. and a voltage is applied to bond the two to each other.

[0004] The borosilicate glass used as the pedestal glass is, as a specific example, 81.0% SiO ₂ expressed by weight%.
%, Al ₂ O ₃ 2.0%, Na ₂ O 4.0% and B ₂ O
₃ is 13.0%, and a borosilicate glass having a coefficient of thermal expansion of 31 × 10 ^-7 / ° C. However, the borosilicate glass has poor compatibility with the thermal expansion of the silicon crystal, and has been one obstacle to improving the performance of the obtained device. Even though borosilicate glass has a similar thermal expansion coefficient to silicon crystal, it is only in a very limited range (from room temperature to around 240 ° C.). That is, 240 ° C
Until the vicinity, the borosilicate glass has a larger coefficient of thermal expansion than the silicon substrate, but it agrees at around 240 ° C, and over 240 ° C, the silicon substrate has a larger thermal expansion coefficient than the borosilicate glass. Becomes smaller. Moreover, when the coefficient of thermal expansion changes, the ratio of the amount of change in the coefficient of thermal expansion / the amount of change in the temperature is not uniform. This tendency is particularly remarkable at high temperatures.

In FIG. 1, the vertical axis represents the elongation rate α (α is ΔL / L
Represented by × 10 ^-4, L is the total length of the sample at room temperature, [Delta] L indicates the amount of elongation from room temperature at a measurement temperature. ), The horizontal axis is temperature T
And the elongation curve of the borosilicate glass and the elongation curve of the silicon crystal. As shown in FIG. 1, the elongation curve of the borosilicate glass intersects with the elongation curve of the silicon crystal at around 240 ° C., and the elongation of the borosilicate glass is larger at room temperature to 240 ° C., and is higher than 240 ° C. In the figure, the elongation rate of the silicon crystal is larger. Therefore, at about 400 ° C. or higher, which is suitable for anodic bonding with the silicon substrate, the difference in thermal expansion coefficient between the borosilicate glass and the silicon substrate becomes extremely large, 1.3 × 10 ⁻⁴ or more. A large residual strain (residual deformation) is generated in the subsequent silicon substrate. When such a silicon substrate with a glass for a silicon pedestal (hereinafter, referred to as a silicon substrate with a pedestal) is applied to a sensor, a complicated temperature compensation circuit is required.

Further, in order to obtain a high-precision pressure sensor, the silicon base material expands and contracts due to a temperature change. Therefore, it is avoided that the silicon substrate in a no-load state is distorted due to thermal stress caused by the temperature change. There is a need. Therefore, the semiconductor pressure sensor is put to practical use with a temperature compensation circuit. However, borosilicate glass has a non-uniform thermal expansion coefficient variation / temperature variation depending on the temperature range, and when applied to a silicon-based sensor, the variation of the offset variation of the temperature compensation circuit per unit temperature is small. Non-uniformity due to temperature (offset voltage does not change linearly with temperature). Therefore, a temperature compensation circuit capable of performing complicated control is required, and in practice, accurate pressure measurement may be difficult, and a measurement error may be caused.

[0007]

SUMMARY OF THE INVENTION The present inventors have found that the necessity of a complicated temperature compensation circuit is that the sign of the difference between the elongation rate of borosilicate glass and the elongation rate of silicon crystal is positive at a certain temperature. From negative to negative or from negative to positive. And a glass other than borosilicate glass,
In a desired temperature range (from room temperature to about 400 ° C.), the elongation curve approximates the elongation curve of the silicon crystal;
Further, a glass in which the sign of the difference in the elongation percentage from the silicon crystal does not reverse was examined. As a result, a composition region of glass belonging to aluminoborosilicate glass satisfying the above conditions was found, and a patent application was previously filed (Japanese Patent Application Laid-Open No. 4-83733). In this glass, no large residual strain occurred after anodic bonding, and the offset voltage showed a linear change with temperature.

However, as a result of further studies on various applications, the present inventors have found that the aluminoborosilicate base glass has disadvantages. One of the applications is that the base glass is required to have high heat resistance and excellent chemical durability in applications that are exposed to high-temperature exhaust gas such as a pressure sensor. However, in some cases, the heat resistance and the chemical durability of the pedestal glass are insufficient.

In general, a complicated circuit is often formed on a silicon wafer that is anodically bonded to a pedestal glass by using a lithography technique. For forming a circuit, a wet or dry etching step is generally incorporated in the process. In this case, components scattered from the glass due to the etching may remain in the apparatus, causing various adverse effects. As a result of the study by the present inventors, it has been found that a component causing various adverse effects is an alkali metal contained in glass. Further, an element using the pedestal glass may be subjected to a high-temperature treatment during the process depending on the application. However, the element may be deteriorated by the high temperature treatment. As a result of the study by the present inventors, it was found that the deterioration of the device was caused by migration of the alkali metal contained in the glass.

Accordingly, an object of the present invention is to provide excellent compatibility with the thermal expansion of a silicon crystal, enable anodic bonding of a silicon crystal to a base material, do not contain an alkali metal such as sodium, and have high heat resistance. It is an object of the present invention to provide a pedestal glass having chemical durability. In particular, an object of the present invention is to provide a silicon pedestal glass having high heat resistance and chemical durability, in which, when anodic bonding with a silicon base material, residual strain generated by cooling from a heated state is controlled. It is in.

Further, an object of the present invention is to provide an offset voltage that shows a linear change with respect to temperature, controls residual strain,
Another object of the present invention is to provide a silicon pedestal glass having high heat resistance and high chemical durability.

Another object of the present invention is to provide a silicon-based pressure sensor or a silicon-based pressure sensor which is easy to perform temperature compensation and has better performance than the conventional one.

[0013]

SUMMARY OF THE INVENTION The present invention, the content of each component, SiO ₂ 50-65 wt% Al ₂ O ₃ 12 to 28 wt% _{(however, SiO 2 + Al 2 O 3} 65~85 wt% ) 0-20% by weight MgO ZnO 0 wt% B ₂ O ₃ 0-20 wt% (however, a glass is _{MgO + ZnO + B 2 O 3} 10~30 wt%), at least the anodic bonding heating temperature zone, and elongation alpha ₁ due to thermal expansion of the glass,
The present invention relates to a glass for a silicon pedestal, wherein a ratio α ₁ / α _{2 of} an elongation percentage α ₂ due to thermal expansion of a silicon base material bonded to the glass is a value in a range of 0.8 to 1.2.

Further, the present invention provides an elongation α ₁ at least in a use temperature range of glass bonded to a silicon substrate.
The difference (α ₁ −α ₂ ) between the glass and the elongation α ₂ is zero or a positive value, or zero or a negative value. .

According to the present invention, an external force applied to a silicon substrate, which includes a silicon substrate and a silicon pedestal glass that elastically deforms the silicon substrate, is detected from the amount of deformation of the silicon substrate. The present invention relates to a silicon base type pressure sensor, wherein the silicon base glass is the silicon base glass of the present invention.

Conventional silicon pedestal glass contains an alkali (alkali metal) component for anodic bonding with silicon. However, the present inventors have unexpectedly found a glass having a novel composition that is capable of anodic bonding despite being substantially free of an alkali component. Further, the present inventors have studied the content of each component in order to adjust that the alkali component is not substantially contained. As a result, the aluminosilicate glass having a predetermined composition matches the thermal expansion of the silicon crystal. Found to be excellent in properties. Since the glass of the present invention is an aluminosilicate glass and does not contain an alkali component, it has high heat resistance and excellent chemical durability. Hereinafter, the present invention will be specifically described.

First, the reasons for limiting each component will be described. still,
In this specification, "%" is "% by weight" unless otherwise specified. SiO ₂ is a basic component of glass,
If it is less than 0%, not only the expansion coefficient becomes too large, but also the chemical durability is deteriorated. If it exceeds 65%, the viscosity becomes too high and melting becomes difficult, so it is limited to 50 to 65%. Optimal range of SiO ₂ is 50 to 60%. A
l ₂ O ₃ is a component essential for obtaining an elongation percentage curve similar to that of a silicon crystal, and is a component that provides high heat resistance and excellent chemical durability. However, if it is less than 12%, the tendency of phase separation increases and the viscosity in the high temperature region increases.
It is essential that the content be 12% or more. If it exceeds 28%, the devitrification resistance deteriorates. Optimal range of Al ₂ O ₃ is 18 to 25%. SiO ₂ and Al ₂ O ₃ is 65 to 85% in the content. If the total amount is less than 65%, the coefficient of thermal expansion becomes too large, and if it exceeds 85%, glass melting becomes difficult.

MgO, ZnO and B ₂ O ₃ are components that provide a stable glass, and the glass of the present invention contains at least one of these three components. MgO has the effect of increasing the coefficient of thermal expansion and decreasing the viscosity.
%, The coefficient of thermal expansion becomes too large. ZnO has the effect of improving the chemical durability, but when it exceeds 10%, the tendency of phase separation increases. B ₂ O ₃ has the effect of improving the meltability and lowering the viscosity, but when it exceeds 20%, the tendency of phase separation increases. MgO, the optimal range of ZnO and B ₂ O ₃ is 8-16%, respectively, which is 1-5% and 1-12%. However, the total amount of MgO, ZnO and B ₂ O ₃ is 10
-30%.

The glass of the present invention contains the above-mentioned components, and additionally contains La ₂ O ₃ , BaO, SrO, CaO, Pb
O, ZrO ₂ , TiO ₂ , P ₂ O ₅ , As ₂ O ₃ and Sb ₂ O ₃
And La, Ba, Sr, Ca, Pb, Z
At least one component selected from the group consisting of fluorides of r, Ti, P, As and Sb is used to improve devitrification resistance, melting property, chemical durability, etc., adjust the coefficient of thermal expansion, remove defoamer, etc. For the purpose,
It can be added in a range of 25% by weight or less of the glass. The content of the above components is preferably 10% by weight or less.

Further, in the glass of the present invention, at least in the anodic bonding heating temperature zone, the ratio of the expansion rate α ₁ due to the thermal expansion of the glass to the expansion rate α ₂ due to the thermal expansion of the silicon crystal bonded to the glass. α ₁ / α ₂ is 0.8
１．２1.2. Within this range, the matching of the thermal expansion characteristics with the silicon crystal is good. That is, when performing anodic bonding with a silicon substrate, it is possible to control residual strain generated by cooling from a heated state. The above-mentioned anodic bonding heating temperature zone varies depending on various conditions, for example, 300 ° C to 600 ° C, usually 350 ° C to
The range is 450 ° C.

Further, the glass of the present invention can be used at least in a use temperature range of glass bonded to a silicon crystal.
The difference (α ₁ −α ₂ ) between the two elongation percentages is either zero or a positive value, or zero or a negative value. That is, in the temperature range from room temperature to 400 ° C., the sign of the difference in elongation (α ₁ −α ₂ ) does not reverse.
This makes it possible to provide a pedestal glass that does not require a complicated temperature compensation circuit when a silicon-based sensor is used. That is, it is possible to obtain a silicon-based sensor in which the offset voltage changes linearly with temperature. The above-mentioned operating temperature range varies depending on the use of the silicon-based sensor, for example, -50 ° C to 250 ° C.
° C, usually in the range of room temperature to about 200 ° C.

The glass of the present invention may be made of silica powder, alumina, aluminum hydroxide,
It can be produced by appropriately selecting and using magnesium carbonate, zinc white, boric acid, lanthanum oxide, barium nitrate and the like. For example, a glass material is weighed in a predetermined amount in accordance with a desired glass composition, a mixed batch weighed is put into a heat-resistant container such as a platinum crucible, and heated and melted at 1500 to 1600 ° C., After stirring to homogenize and defoam, the glass of the present invention can be obtained by casting in a mold preheated to an appropriate temperature and slowly cooling.

Hereinafter, the sensor of the present invention using the pedestal glass of the present invention will be described. The sensor of the present invention
For example, it is a silicon-based sensor that can be used for a semiconductor device such as a semiconductor pressure sensor and an acceleration sensor. The case of a semiconductor pressure sensor will be described with reference to FIG. 1 is a pressure-sensitive chip (silicon base material) made of silicon crystal. The pressure-sensitive chip 1 is anodically bonded in a state where the pressure-sensitive chip 1 overlaps with the pedestal glass 2 whose center is perforated. A strain sensing resistance gauge 6 is provided on the upper surface of the pressure-sensitive chip. The thermal expansion coefficient of the silicon crystal of the pressure-sensitive chip 1 is 3
For example, Kovar having a thermal expansion coefficient of 46 × 10 ⁻⁷ / ° C. is used for the stem of 3 × 4 ⁻⁷ / ° C. The difference in thermal expansion between the pressure-sensitive chip 1 and the stem 3 is reduced by the base glass 2. The stem 3 is provided with a lead pin 5 penetrating therethrough. The lead pin 5 is sealed with a permetic seal made of glass, and the space 8 between the stem 3 and the cap 4 is sealed with resistance welding. For this reason, the pressure in the space surrounded by the stem 3 and the cap 4 shows a constant value corresponding to the temperature at that time.

Bonding 7 between the pressure-sensitive chip 1 and the pedestal glass 2 is performed by anodic bonding. The anodic bonding is performed by using a silicon crystal plate, which is a pressure-sensitive chip, as an anode and a pedestal glass as a cathode while applying a pressure between the polished silicon crystal plate and the pedestal glass, at a temperature of several hundred degrees (for example, 300 to
(600 ° C.) at a DC voltage of several hundred volts. By such an anodic bonding, both can be adhered with high confidentiality in a short time without using an adhesive. In the conventional pedestal glass, it has been considered that the presence of mobile carrier ions is necessary for anodic bonding. Alkali ions have been used as mobile carrier ions. However, since the pedestal glass of the present invention has the above-described composition, anodic bonding is possible even though it does not contain alkali ions.

When the pressure of the medium to be measured is applied to the semiconductor pressure sensor, which is the silicon substrate type sensor of the present invention shown in FIG. 3, from the direction of arrow P to the thin diaphragm surface of the pressure-sensitive chip 1, the pressure in the cap 4 is increased. The diaphragm surface is deformed according to the difference from the above, and the gauge resistance changes. This change in the resistance value is detected by a full bridge circuit or the like including the strain-resisting resistance gauge 6, and a very small pressure can be detected with high sensitivity.

The pedestal glass of the present invention is useful for various applications requiring anodic bonding with silicon. For example, it can be used for a flow path of an inkjet printer or an analytical instrument, an X-ray mask, an X-ray connector, a microscope, a display, a microphone, a hot cathode electron beam, and the like.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments. Examples 1 to 7 Glass raw materials (for example, silica powder, alumina, aluminum hydroxide, magnesium carbonate, zinc white, boric acid, lanthanum oxide, nitric acid, etc.) so that the finally obtained glass composition has the composition shown in Table 1. Barium) is appropriately selected, the raw materials are weighed so that the weight when converted to oxides is 12 kg, and mixed with a mixer. At 1600
After melting at 16 ° C. for 16 hours, homogenizing and defoaming, the mixture was cast into a mold made of cast iron and gradually cooled to obtain a glass block.

Example 1 of the obtained glass blocks
Elongation rate from room temperature to 500 ° C.
FIG. 2 shows the elongation curve obtained. The elongation rate curve of the glass of Example 1 almost coincided with the elongation rate curve of the silicon crystal. Although the elongation rate curve of the glass of Example 2 slightly deviated from the elongation rate curve of the silicon crystal, the curve shape was similar to the curve of the silicon crystal. None of the curves of the sample glass intersect the curves of the silicon crystal. Further, at any temperature in the measurement temperature range, the elongation rate α ₁ ′ of the glass of Example 1 and the elongation rate of Example 2
The ratios α ₁ ′ / α ₂ and α ₁ ″ / α ₂ of the elongation rate α ₁ ″ of the glass and the elongation rate α ₂ of the silicon crystal are 0.8 to 0.8.
1.2. Further, the differences (α ₁ ′ −α ₂ ) and (α ₁ ″ −α ₂ ) between the elongation percentage and the silicon crystal are zero or negative values over the entire measurement temperature range, and the signs of the differences are reversed. I never did.

The same measurement was performed for the glasses of Examples 3 to 7, and the ratio α ₁ / α _{2 to} the elongation rate α ₂ of the silicon crystal was in the range of 0.8 to 1.2 for all the glasses. And the difference in elongation percentage from the silicon crystal (α ₁ −
The sign of α ₂ ) did not reverse over the entire measurement temperature range. Table 1 shows the heat resistance and chemical durability of the glass of the present invention.
Were good. The coefficient of expansion in Table 1 is the average coefficient of linear expansion between 30 ° C. and 400 ° C. (× 10
⁻⁷ / ° C.) and water resistance of powdered glass (particle size 420 to 5)
(90 μm) in a pure water at 100 ° C. for 20 hours. The heat resistance is indicated by a transition temperature (° C.).

[0030]

[Table 1]

Further, the glass obtained in Example 1 was cut into a predetermined shape and subjected to a perforation process to obtain a pedestal glass.
The pedestal glass and the silicon wafer were aligned and superposed, and anodically bonded at 450 ° C. and 1 kV. Both were firmly joined over the entire surface. Further, the same anodic bonding was performed on the glasses of Examples 2 to 7.
As a result, it was confirmed that anodic bonding was possible in each case.

Example 8 The glass obtained in Example 1 was cut into a predetermined shape, and a hole was formed to obtain a pedestal glass. The pedestal glass and the silicon wafer are aligned and overlapped to form a 45
Anodic bonding was performed at 0 ° C. and 1 kV. A pressure element shown in FIG. 3 was produced by a conventional method using a pedestal glass obtained by anodically bonding the obtained silicon wafer. It was confirmed that the obtained pressure element had a small offset voltage variation and its temperature dependence was linear. This not only indicates that the temperature can be corrected with a simple electronic circuit, but also means that the pressure element is highly accurate and highly reliable.

[0033]

According to the glass for a silicon pedestal of the present invention, the elongation curve due to thermal expansion is close to the curve of the silicon crystal. Furthermore, at least in the range of room temperature to 500 ° C., the difference in elongation between the glass of the present invention and the silicon crystal is:
It is either zero or a positive value, or zero or a negative value, and the sign of the difference is not reversed. Therefore, the silicon pedestal glass of the present invention has excellent consistency with the thermal expansion characteristics of the silicon crystal. Further, the silicon pedestal glass of the present invention is a glass that can be subjected to anodic bonding and is excellent in heat resistance and chemical durability. further,
The silicon-based sensor using the glass of the present invention as the silicon pedestal glass has excellent zero-point moving temperature characteristics because the residual distortion of the pedestal glass is small, and the offset voltage shows a linear change with temperature. And a highly accurate element such as a pressure-sensitive element or an acceleration element can be provided. In addition, contamination due to alkali in the element processing step can be eliminated, which has a great advantage for related industries.

[Brief description of the drawings]

FIG. 1 is a graph showing the elongation percentage of borosilicate glass and silicon crystal due to thermal expansion.

FIG. 2 is a graph showing an elongation rate due to thermal expansion of glass of Examples 1 and 2 and an elongation rate due to thermal expansion of a silicon crystal.

FIG. 3 is an explanatory sectional view of a semiconductor pressure sensor as an example of the sensor of the present invention.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI H01L 29/84 H01L 29/84 Z (56) References JP 5-9039 (JP, A) JP 4-83733 ( JP, A) JP-A-61-281041 (JP, A) JP-A-64-61329 (JP, A) JP-A-6-56469 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , (DB name) C03C 3/083 G01L 1/22 G01L 9/04 101 H01L 21/02 H01L 29/84

Claims (8)

(57) [Claims] 1. A content of each component, SiO ₂ 50-65 wt% Al ₂ O ₃ 12 to 28 wt% (however, SiO2 + Al ₂ O ₃ 65~85 wt%) MgO 0-20% by weight ZnO 0-10 wt% B ₂ O ₃ 0 to 20 wt% _{(however, MgO + ZnO + B 2 O} 3 10~30 % by weight) a glass is, at least in anodic bonding heating temperature zone, of the glass heat the growth rate α ₁ due to expansion,
A silicon pedestal glass, wherein a ratio α ₁ / α _{2 of} an elongation percentage α ₂ due to thermal expansion of the silicon base material bonded to the glass is in a range of 0.8 to 1.2. _2. The difference (α ₁ −α ₂ ) between the elongation percentage α ₁ and the elongation percentage α ₂ is zero or a positive value or at least in at least the operating temperature range of the glass bonded to the silicon substrate. The glass according to claim 1, wherein the glass has a negative value. 3. The content of each component is 50 to 60% by weight of SiO ₂ , 18 to 25% by weight of Al ₂ O ₃ (however, SiO ₂ + Al ₂ O ₃ 68 to 85% by weight) MgO 8 to 16% by weight ZnO 1 to 5% by weight B ₂ O ₃ 1-12 wt% _{(however, MgO + ZnO + B 2 O} 3 10~30 wt%), and and the total amount of the component is 90% or more according to claim 2 or 3 glass according. 4. La ₂ O ₃ , BaO, SrO, CaO, P
bO, ZrO ₂ , TiO ₂ , P ₂ O ₅ , As ₂ O ₃ and Sb ₂
Group consisting of O ₃ , and La, Ba, Sr, Ca, P
The glass according to any one of claims 1 to 3, further comprising at least one component selected from the group consisting of fluorides of b, Zr, Ti, P, As and Sb. 5. A silicon substrate for detecting an external force applied to the silicon substrate from a deformation amount of the silicon substrate, comprising a silicon substrate and a silicon pedestal glass for holding the silicon substrate elastically deformable. A silicon substrate type sensor, wherein the glass for silicon pedestal is the glass for silicon pedestal according to any one of claims 1 to 4. 6. The silicon substrate type sensor according to claim 5, wherein the silicon substrate and the silicon pedestal glass are anodically bonded in a state where the silicon substrate and the silicon pedestal glass are overlapped. 7. The silicon-based pressure sensor according to claim 5, wherein the external force is pressure. 8. A temperature compensating circuit, comprising: a strain gauge for detecting an amount of deformation of the silicon base material; and a temperature compensation circuit for electrically correcting a strain generated in the silicon base material to a reference value based on an offset variation amount. 8. The silicon-based pressure sensor according to claim 7, wherein the controller adjusts a variation per unit temperature of an offset variation in an operating temperature range of the sensor to be substantially constant.