JP2001201417A - Diaphragm-type vacuum pressure sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small-sized vacuum pressure sensor, which can measure a pressure range of 0.01 to 133 Pa with high sensitivity by improving the linearity of the relation between pressure and electrostatic capacity. SOLUTION: The size and thickness of a diaphragm 2 formed on a conductive silicon substrate 1 and the interval between the diaphragm and a fixed electrode are limited. A 1st glass (case) 4 and a 2nd (pedestal) glass 6 are jointed with both the surfaces of the diaphragm 2 and silicon substrate, and the surface of the 1st glass 4 jointed with the conductive silicon substrate is formed into a recessed shape; and the internal surface of the recessed surface of the case 4 is so adjusted that the diaphragm and fixed electrode face each other at a prescribed interval and a hole, which links the diaphragm with the outside, is bored in the pedestal glass 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vacuum pressure sensor for detecting a value of an absolute pressure as a capacitance value for measuring a pressure in a vacuum device.

[0002]

2. Description of the Related Art As a vacuum pressure sensor capable of measuring a pressure range of 0.01 to 133 Pa in a vacuum device, a Pirani gauge and a metal diaphragm gauge are known in the prior art.

FIG. 3 shows a pressure detecting portion of a Pirani vacuum gauge. Platinum filament 1 inside case 9
0 is disposed, and the filament 10 is electrically heated. The pressure changes in accordance with the change in the number and momentum (temperature) of the gas molecules, but the temperature of the filament changes due to the change in the amount of gas molecules taking heat from the filament 10. In this Pirani vacuum gauge, power for keeping the temperature of the filament 10 constant is measured by a detection circuit,
The system converts pressure from power consumption.

FIG. 4 shows a detection portion of a metal diaphragm type vacuum gauge. A metal diaphragm 12 is provided in a case 11, and a central opposing electrode 15 is opposed to the metal diaphragm.
And the outer peripheral counter electrode 14 are arranged at a predetermined interval.
The space 13 is sealed in a vacuum, and the metal diaphragm 12 is displaced by a change in pressure, and the displacement at that time is detected by the central electrode 15 as a change in capacitance, so that the pressure can be measured (converted).

Further, a semiconductor pressure sensor as disclosed in Japanese Patent Application Laid-Open No. H11-248582 has been proposed. The outline thereof is, as shown in FIG. 5, a diaphragm 18 made of a semiconductor and a fixed electrode 19, and a space 23 is sealed. The diaphragm 18 is displaced by the change in pressure,
A capacitance value is measured between the movable electrode 20 and the fixed electrode 19, and is converted into a pressure value.

[0006]

The above prior art has the following problems.

[0007] The Pirani vacuum gauge has the disadvantage that the thermal conductivity and the specific heat vary depending on the type of gas to be measured, so that the measurement sensitivity changes and the pressure value varies depending on the type of gas.

In a metal diaphragm type vacuum gauge, the pressure value does not differ depending on the kind of gas to be measured like a Pirani vacuum gauge, but in order to enhance sensitivity, the thickness of the metal diaphragm 12 is extremely thin to 10 μm or less. And the film area is
It must be 0 cm ² . However, when the thickness of the metal diaphragm is extremely thin, it becomes difficult to process the metal diaphragm and to attach the metal diaphragm to the case 11, and when the area of the diaphragm 12 is large, the volume and surface area of the case 11 increase, and dead space increases. However, there is a disadvantage that the response to pressure changes is deteriorated (the sensitivity is reduced).

In a semiconductor pressure sensor, the pressure value does not differ depending on the type of gas to be measured as in a Pirani vacuum gauge, and since it is smaller than a metal diaphragm gauge, it has a small dead space and excellent responsiveness. However, 0.01
In order to obtain a pressure sensitivity of 0.01 Pa in a pressure range of ~ 133 Pa, the space 23 must be at least 0.01 Pa
It is necessary to seal in the following high vacuum. However, in Japanese Patent Application Laid-Open No. H11-248582, since the insulating resin 27 is used as a sealing material, it is difficult to keep the semiconductor pressure sensor at a high vacuum of 0.01 Pa or less due to a gas generated when the resin is cured. Impossible.

As described above, in the prior art, no vacuum pressure sensor has been manufactured in which the pressure sensitivity is maintained at this level (about 0.01 Pa) while maintaining a high vacuum state of 0.01 Pa or less.

There are further problems in achieving the above-mentioned problems. For example, in the pressure range of 0.01 to 133 Pa, linearity is not guaranteed between pressure and capacitance, and there is no proportional relationship between pressure change and increase / decrease of capacitance. Further, a pressure sensor using a semiconductor has a large temperature dependency, and the problem of this is that correction by a complicated compensation circuit as an electronic circuit is indispensable.

[0012] Further, for high-sensitivity pressure detection, 0.01
A technique for maintaining a high vacuum state of Pa or less is required, but a resin or the like that easily generates gas must not be used as a sealant.

The present inventors first focused on the improvement of the non-linearity of the diaphragm, and in order to improve the non-linearity, the thickness and area of the diaphragm and the distance between the diaphragm and the fixed electrode were set to optimal conditions. Was found to be indispensable, and a condition in which a pressure change and an increase or a decrease in capacitance were substantially proportional to each other was found, and the present invention was completed.

[0014]

In order to solve the above-mentioned problem, linearity is improved in relation between pressure and capacitance. Accordingly, it is an object of the present invention to provide a compact vacuum pressure sensor capable of measuring a pressure range of 0.01 to 133 Pa with a pressure sensitivity of 0.01 Pa.

According to a first aspect of the present invention, there is provided an electrostatic capacity type vacuum pressure sensor, wherein when the diaphragm formed on the conductive silicon substrate is square, the size of the diaphragm is 5 mm square or more and 15 mm square or less. And the thickness is 5 μm
As described above, the pressure range of 0.01 to 133 Pa can be measured by setting the predetermined interval provided between the fixed electrode and the diaphragm to be not more than 15 μm and not more than 20 μm.

According to a second aspect of the present invention, there is provided a diaphragm formed on a conductive silicon substrate, and a first glass (case) and a second glass substrate (pedestal glass) joined to both surfaces of the conductive silicon substrate. A surface of the first glass substrate which is joined to the diaphragm is formed in a concave shape, and a fixed electrode is formed on an inner surface of the concave portion of the first glass so as to face the diaphragm at a predetermined interval. And a hole for communicating with the outside is provided in the second glass substrate.

According to a third aspect of the present invention, the space defined by sealing the conductive silicon substrate and the first glass substrate having the concave portion formed therein to a high vacuum of 0.01 Pa or less. Vacuum pressure sensor.

According to a fourth aspect of the present invention, when the shape of the diaphragm is other than a square, it is substantially a regular pentagon, a substantially regular hexagon, a substantially regular octagon, a substantially regular decagon, or a substantially circular shape. Is a vacuum pressure sensor having an area and a thickness. Here, “approximately” means that when the central angle of the regular N-gon is θ (N), a deviation of 5% that can be expressed by central angle θ (N) = 360 / N ± 18 / N [degree] is acceptable. Say range.

The invention of claim 1 will be described.

In the case of a rectangular diaphragm, the distance between the fixed electrode and the diaphragm is set to 5 to 20 μm, and the size of the diaphragm is set to a specific area and thickness for the following reason.

First, the distance between the diaphragm and the fixed electrode is set to 20 μm or less. This is because if the interval is larger than 20 μm, the amount of change in the capacitance becomes small, and the detection accuracy by the electronic circuit cannot be increased.

The shape, size (area), and thickness of the diaphragm are limited to a range that satisfies the conditions for linearity in pressure change and capacitance. Referring to Table 1, the description will be made.
In the case where the material is a square made of silicon, appropriate requirements for the size and thickness of the diaphragm are those indicated by the double circles in Table 1. Table 1 shows qualitative experimental data showing the performance as a sensor in a combination of the size and thickness of the diaphragm. The thickness of the diaphragm is shown in the row (vertical) and the size of the diaphragm in the column (horizontal). Things.

[0023]

[Table 1]

In Table 1, the combination of the size and the thickness indicated by the symbol A indicates that when the diaphragm is subjected to a pressure of 133 Pa, the diaphragm cannot withstand the pressure.
It indicates that it will be damaged. For this reason, the combination indicated by the symbol A cannot be used for a vacuum pressure sensor.

The combination denoted by the symbol B is 0.01 to
This is a combination in which, in the pressure range of 133 Pa, the distortion of the diaphragm is large, and the pressure and the capacitance cause nonlinearity. For this reason, a diaphragm having a size and a thickness in the range of reference B cannot be applied to a pressure sensor.

The combination denoted by the symbol C is 0.01 to
This is a combination in which a pressure sensitivity of 0.01 Pa cannot be obtained in a pressure range of 133 Pa. Therefore, it cannot be used for a vacuum pressure sensor requiring high sensitivity.

In the combination denoted by the symbol D, when the distance between the diaphragm and the fixed electrode is 5 μm or less, the relationship between the pressure change and the capacitance is non-linear in a predetermined pressure range (0.01 to 133 Pa). If the interval is more than 5 μm, the pressure sensitivity is reduced and the measurement of the pressure of 0.01 Pa becomes impossible. For these reasons, it cannot be applied to the intended vacuum pressure sensor.

In the combination denoted by reference character E, the distance between the diaphragm and the fixed electrode must be set to 20 μm or more, so that the amount of change in capacitance required for detecting an electronic circuit cannot be obtained.

For the reasons described above, 0.01 to 133
In the pressure range of Pa, the linearity is established between the strain due to the pressure change of the diaphragm and the capacitance, and 0.0
The combination of the size and the thickness of the diaphragm that can obtain a pressure sensitivity of 1 Pa is determined by setting the distance between the diaphragm and the fixed electrode to 5-2.
As long as it is limited to 0 μm, it is limited to the region (range) indicated by the mark ◎ in Table 1.

To explain the invention of claim 2 and claim 3, the vacuum pressure sensor has the diaphragm of the requirement described in claim 1, and the structure of the vacuum pressure sensor is formed on a conductive silicon substrate. Said formed diaphragm,
A first glass (also serving as a case) and a second glass substrate (pedestal glass) joined to both surfaces of the conductive silicon substrate. Then, the surface of the first glass substrate that is joined to the diaphragm is formed in a concave shape,
The fixed electrode is formed on the inner surface of the first glass so as to face the recess with a predetermined distance (5 to 20 μm). Further, a hole for communicating with the diaphragm and the outside is provided in the second glass substrate.

As shown in FIG. 1, the space 5 (partitioned) is sealed in a vacuum by joining the conductive silicon substrate 1 and the first glass substrate (4) having the recess. A vacuum pressure sensor is assembled.

The fourth aspect of the present invention describes a case where the shape of the diaphragm is other than a square. In the case of a symmetrical shape in which the shape of the diaphragm is substantially a regular pentagon, a substantially regular hexagon, a substantially regular octagon, a substantially regular decagon, or a substantially circular shape, when the area and the thickness satisfy the relationship shown in Table 1, a good shape is obtained. Functions as a vacuum pressure sensor. On the other hand, in the case of a diaphragm with a shape lacking symmetry, for example, a rectangular diaphragm, the linearity is broken because the pressure and the amount of distortion of the diaphragm are not symmetrical, and there is no practicality, and the fabrication of the diaphragm is not easy. Also, the assembly tends to be complicated.

[0033]

The silicon diaphragm type vacuum pressure sensor constructed as described above has a linear relationship between pressure and capacitance in the pressure range of 0.01 to 133 Pa. Moreover, since the space between the diaphragm and the fixed electrode is sealed with a high degree of vacuum of 0.01 Pa or less,
Pressure sensitivity.

[0034]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A typical embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of a silicon diaphragm type vacuum pressure sensor of the present invention. The fixed electrode 3 provided in the concave portion of the case 4 is joined to the diaphragm 2 and the case 4 so as to face the diaphragm 2 with a gap of 10 μm. The size of the diaphragm 2 made from the conductive silicon substrate is a square of 10 mm square in this embodiment. And its thickness is 10 μm and it is electrically connected to the pin 7a.

The fixed electrode 3 is electrically connected to the pin 7b, and the capacitance can be measured by the pins 7a and 7b. Further, a gas adsorbent (getter agent) 8 is introduced into the space 5 to keep the space at a vacuum.

Next, a description will be given of manufacturing means for realizing the structure of the silicon diaphragm type vacuum pressure sensor according to the present invention. First, the production of the diaphragm 2 will be described. After a silicon dioxide film of about 1 μm is formed by thermally oxidizing the conductive silicon substrate 1, silicon of a target area is exposed using photolithography technology. By keeping the conductive silicon substrate 1 at a constant temperature, immersing it in an aqueous solution of caustic potassium (KOH) having a concentration of 30%, and leaving it for a predetermined time, only the exposed silicon portion can be etched. A diaphragm having a desired thickness can be manufactured.

Subsequently, the case (first glass substrate) 4
Is to deposit a chromium metal film and a gold metal film on the surface of a borosilicate glass plate, and then expose the borosilicate glass using a photolithography technique. The borosilicate glass is immersed in a hydrofluoric acid aqueous solution while being kept at a predetermined temperature, and immersed for a predetermined time, so that only the exposed portions of the borosilicate glass are etched so as to be concave. Further, the fixed electrode 3 having the same area as the diaphragm 2 is bonded to the concave portion of the borosilicate glass by the anodic bonding method.

The case 4 is bonded to the conductive silicon substrate by the anodic bonding method, and the diaphragm 2 and the fixed electrode 3 are opposed to each other. At this time, by adjusting the depth of the concave portion of the first glass substrate (case) 4 and the thickness of the fixed electrode 3,
A desired distance is set between the diaphragm and the fixed electrode.
When the diaphragm 2 and the first glass substrate 4 are joined together, this is performed in an atmosphere having a pressure of 0.001 Pa or less, and the getter agent 8 is further sealed in the first glass substrate 4 so as to form a space. The pressure can be kept at 0.01 Pa or less. Finally, a pin 7b for conducting with the fixed electrode and a pin 7 for conducting with the conductive silicon substrate 1.
a is bonded by a conductive adhesive, and the second glass substrate (pedestal glass) 6 is bonded.

FIG. 2 shows the relationship between the pressure and the capacitance value of the silicon diaphragm type vacuum pressure sensor manufactured as described above. At a pressure of 0.01 to 133 Pa, the change of the capacitance value has a linearity and exhibits a proportional relationship. Therefore, by measuring the capacitance value, the pressure at that time is uniquely determined.

[0040]

According to the present invention, the size of the diaphragm formed from the conductive silicon substrate is not less than 5 mm square and not more than 15 mm.
Square or less square mm or polygonal or circular having an area equivalent thereto, the thickness is 5μm or more,
When the distance is 15 μm or less and the distance between the diaphragm and the fixed electrode is 5 to 20 μm, in the pressure range of 0.01 to 133 Pa, the pressure exhibits a linearity in which the capacitance value is proportional. A vacuum pressure sensor capable of measuring pressure with a pressure sensitivity of 0.01 Pa can be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view of a silicon diaphragm type vacuum pressure sensor of the present invention.

FIG. 2 is a graph showing the relationship between the pressure and the capacitance value of the silicon diaphragm type vacuum pressure sensor of the present invention.

FIG. 3 is a sectional view of a Pirani vacuum gauge.

FIG. 4 is a sectional view of a metal diaphragm gauge.

FIG. 5 is an example showing a conventional semiconductor vacuum pressure sensor.

[Explanation of symbols]

 Reference Signs List 1 conductive silicon substrate 2 diaphragm 3 fixed electrode 4 first glass substrate (case) 5 space 6 second glass substrate (pedestal glass) 7a pin 7b pin 7c pin 8 getter material 9 case 10 filament 11 case 12 metal diaphragm 13 space 14 Outer peripheral counter electrode 15 Central counter electrode 16 Silicon substrate 17 Glass substrate 18 Diaphragm 19 Fixed electrode 20 Movable electrode 21 Leader 22 Frame 23 Space 24 Groove 25 Through hole 26 Pad 27 Insulating resin

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Nobuyuki Mukai 1189 Nippa-cho, Kohoku-ku, Yokohama-shi, Kanagawa Prefecture F-term (reference) 2F055 AA40 BB01 BB08 BB10 CC02 CC41 DD05 DD07 EE25 FF12 GG11 4M112 AA01 BA07 CA02 CA15 CA16 DA04 DA11 DA18 EA02 EA06 EA13 FA11 GA01

Claims (4)

[Claims] 1. A capacitance type sensor for measuring vacuum pressure, wherein when a diaphragm formed on a conductive silicon substrate is square, the size of the diaphragm is not less than 5 mm square and not more than 15 mm square. , Thickness of 5 μm or more, 15
A diaphragm-type vacuum pressure sensor which is capable of measuring a pressure range of 0.01 to 133 Pa by setting the distance between the fixed electrode and the diaphragm to 5 μm or more and 20 μm or less. 2. A semiconductor device comprising: a diaphragm formed on a conductive silicon substrate; and first and second glass substrates bonded to both surfaces of the conductive silicon substrate, wherein the first glass substrate is bonded to the diaphragm. The surface is formed in a concave shape, a fixed electrode is formed on the inner surface of the concave portion of the first glass so as to face the diaphragm at a predetermined interval, and a hole for communicating with the diaphragm and the outside is formed in the second glass substrate. The diaphragm-type vacuum pressure sensor according to claim 1, wherein the pressure sensor is provided. 3. The space defined (partitioned) is sealed in a vacuum by bonding the conductive silicon substrate and the first glass substrate having a concave portion.
Diaphragm type vacuum pressure sensor. 4. The area and thickness according to claim 1, wherein when the shape of the diaphragm is other than a square, the shape of the diaphragm is substantially regular pentagon, substantially regular hexagon, substantially regular octagon, substantially regular decagon, or substantially circular. Diaphragm type vacuum pressure sensor provided with.