JPH01127928A - Vibration type distortion sensor - Google Patents

Abstract

PURPOSE:To maintain the prescribed sensitivity by mixing other atom. having a covalent binding radius being different from a covalent binding radius of a main atom. for constituting a substrate into the substrate and applying a stable initial tension to a vibration beam. CONSTITUTION:A vibration beam 9 of silicon whose cross section is rectangular is fixed to both ends of a silicon substrate 8, and holds a prescribed internal to the substrate 8 except said both ends. In such a state, in the substrate 8, other atom. having a small covalent binding radius against an atom having a prescribed covalent binding radius which is mixed into the vibration beam 9 is mixed, therefore, the initial tension is applied to the vibration beam 9, the upper part of the vibration beam 9 is covered with a shell 10 of silicon and a hollow chamber 11 is formed and its inside is held in a vacuum, and to the bottom part of the substrate 8, a permanent magnet 12 is fixed and a DC magnetic flux is applied to the vibration beam 9. Subsequently, by combining a vibration type distortion sensor with an exciting circuit, and applying the measuring pressure Pm to the periphery of the substrate 8, the tension in the axial direction of the vibration beam 9 is varied and the resonance frequency is varied, therefore, by detecting it, the pressure Pm can be known.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention provides a vibration i! The present invention relates to a vibrating strain sensor that detects strain corresponding to a measured pressure of I@ as a frequency signal, and particularly relates to a vibrating strain sensor having a vibrating beam to which initial tension is applied.

<Prior art> A vibrating strain sensor using string vibration is disclosed in, for example, Japanese Patent Application Laid-Open No.
No. 56880, F. illumination device.

What is disclosed herein is that when a diaphragm receives the differential pressure and detects the differential pressure from the change in tension applied to the vibrating wire, a pair of flat wires surrounding the vibrating wire are used to give initial tension to the vibrating wire. It uses interconnected washer-like zero springs to tension the vibration wire, and uses differences in the expansion coefficients of the materials to prevent changes in tension due to leakage.

Further, a vibrating strain sensor using a semiconductor is disclosed in, for example, Japanese Patent Application No. 59-42632 entitled "Pressure Sensor".

An outline of this vibrating strain sensor will be explained using FIGS. 7 to 9.

Fig. 7 is a perspective view showing the structure of this conventional vibrating strain sensor with the cover removed, Fig. 8 is a sectional view taken along the xx section in Fig. 9 with the cover attached, and Fig. 7 is partly omitted. FIG.

In these figures, 1 is a cylindrical silicon substrate, and 2 is a pressure-receiving diaphragm which is formed by digging the center of this silicon substrate 1 to form a thin part and serving as a pressure-receiving part that receives measurement pressure PlK. It is made by etching 1.

3.4 is a vibrating beam formed on the pressure receiving diaphragm 2 and having both ends fixed to the silicon substrate 1; the vibrating beam 3 is located approximately at the center of the pressure receiving diaphragm 2, and the vibrating beam 4 is located at the periphery of the pressure receiving diaphragm 2. are located in each.

Specifically, these IIII beams 3.4 are made by forming a first P-type epitaxial layer on the n-type silicon substrate 1, and electrically separating the left and right sides by cutting in the center of the first P-type epitaxial layer. After forming an n-type epitaxial layer on this layer, a P-type epitaxial layer is further formed, and an oxide film of 5tO2 is formed on this layer.
Protect with. The cavity 5 at the bottom of the vibrating beam 3 has this n
A shaped epitaxial layer is formed by underetching.

The vibrating beam 3 formed in this way has a certain length, for example!
, if the thickness is h1 and the width is d, then! =100am, h-1
The size is about 1d-5 μm.

The periphery of the vibrating beam 3 formed on the pressure receiving diaphragm 2 is covered with, for example, a silicon cover 6 bonded to the pressure receiving diaphragm 2 by anodic bonding or the like, and this internal space 7 is maintained in a vacuum state. Although not shown, the vibrating beam 4 side is also formed in the same way.

The vibrating VJ beam 3, cover 6, cavity 5, internal space 7, etc. form a detection section of the vibrating transducer.

In the above configuration, when an oscillation circuit is connected between the first left and right P-type epitaxial layers to cause oscillation with respect to the vibration beam 3 (4), which is the second P-type epitaxial layer, the vibration Beam 3 (4) causes self-oscillation at its natural frequency.

In this case, the internal space 7 of the cover 6 is made into a vacuum state and the vibrating beam 3 is held in vacuum, so Q
The value increases, making it easier to detect the resonance frequency.

As shown in Fig. 8, the measured pressure Pu is
, the vibrating beam 3 receives tensile stress and the vibrating beam 4 receives compressive stress.

Therefore, the natural frequencies of the vibrating beams 3 and 4 vary differentially with respect to the measured pressure, and by exploiting these differences, the measured pressure P1 can be determined with twice the sensitivity.

<Problems to be Solved by the Invention> However, such conventional vibrating strain sensors, the former mechanical vibrating strain sensors, have a complicated tension application structure and are difficult to maintain tension stability. Many elements must be controlled in order to maintain the initial tension, and the structure of the former mechanical vibrating strain sensor is simpler than that of the former semiconductor type vibrating strain sensor, but it maintains the initial tension. Since no special measures have been taken to prevent this, there is a drawback that the sensitivity to pressure varies. Furthermore, there is a drawback that buckling occurs when the compression T is applied.

Means for Solving the Problems> In order to solve the above problems, the present invention measures the resonant frequency of a semiconductor vibrating beam whose both ends are fixed to a semiconductor substrate. In a vibrating strain sensor that measures strain applied to both ends, other atoms with a covalent bond radius different from the covalent bond radius of the main atoms constituting the substrate are mixed into the substrate to apply initial tension to the vibrating beam. It was designed to be given.

Effect> Other atoms with a covalent bond radius different from that of the main atoms constituting the substrate are mixed into this substrate, and an initial tension is applied to the vibrating beam whose both ends are bonded to the substrate, and a predetermined sensitivity is achieved. maintain.

<Example> Hereinafter, an example of the present invention will be described based on the drawings. FIG. 1 is a configuration diagram showing one embodiment of the present invention.
FIG. 1(a) is a longitudinal sectional view thereof, and FIG. 1(b) is a horizontal sectional view showing the Y-Y cross section in FIG. 1(a).

Reference numeral 8 denotes a silicon substrate, and a silicon vibration beam 9 having a rectangular cross section is fixed to both ends of this silicon substrate 8, and is fixed at a predetermined distance from the silicon substrate 8 except for these two ends. In this silicon substrate 8, an initial tension is applied to the vibrating beam 9 by mixing other atoms having a smaller covalent bond radius with respect to atoms having a predetermined covalent bond radius mixed in the vibrating beam 9.

The top of this crossbeam 9 is covered with a silicone shell 10 to form a hollow chamber 11, the inside of which is maintained in a vacuum.

A permanent magnet 12 is fixed to the bottom of the silicon substrate and applies DC magnetic flux to the vibrating beam 9, so that the vibration of the vibrating beam 9 can be detected electrically.

FIG. 2 is an explanatory view of the manufacturing process showing an enlarged view of the essential parts of the vibrating strain sensor in FIG. 1. FIG.

Reference numeral 13 denotes a P-type silicon holding substrate having a fourth degree of 1Q I 70 where 1li1 degree is 1Q I 70 of Hou 1 (B).

First, on top of this, lQ2'cm' of boron and 5×10"c
A P+ type silicon epitaxial layer doped with m-3 or more germanium (Ge) is formed as the first epitaxial layer 14.

Next, on the first epitaxial layer 14, an N-type silicon epitaxial layer doped with phosphorus (P) is formed on the second epitaxial layer 11.
2115.

Thirdly, a rectangular beam rectangular region 16 is formed on the second epitaxial layer 15 to become a P+ type vibrating beam 9 doped with 10 cm of boron by impurity diffusion, ion implantation, selective epitaxial method, etc. .

Fourth, a thermal oxide film (Si02) 17 is formed as a mask when etching the peripheral portion of the beam region 16, and then a window 18 is opened by photolithography.

In this manner, the intermediate step before etching shown in FIG. 2(a) is completed.

Next, the process proceeds to the etching step shown in FIG. 2(b). Second
When the semi-finished product obtained in the intermediate step shown in Figure (a) is immersed in an alkaline solution and etched, the boron concentration is 1Q"cm.
-' beam wX region 16 and P+ first epitaxial layer 14
Since the bottom surface (bottom surface) is not etched with alkaline solution, the vibrating beam 9 is formed apart from the surroundings except for both ends of the rectangular shape as shown.

Furthermore, portions of the holding substrate 13 are removed by etching from the back side, and the first epitaxial Jll! 14 and the thickness of the second epitaxial layer 115 can be obtained.

This silicon substrate 8 can also be used as a diaphragm for detecting differential pressure or the like by removing the permanent magnet 12 and providing it at a different position.

Vibration vJ@9 is 1f! when, for example, measurement pressure Pt is applied to the vibration type strain sensor. Although it is necessary to apply an initial tension to the auxiliary beam 9 so as not to cause buckling, the following describes how the initial tension is applied to the vibrating beam 9 with the above configuration.

FIG. 3 shows the covalent bond radius R9 of various impurities and purities and the covalent bond radius R8L of silicon with respect to the covalent bond t! of various impurities. It represents the relationship Rt/Rst. FIG. 4 shows the change in lattice constant with respect to impurities of 1li1 degree.

From this figure, the covalent bond radius of silicon < St ) is 1.
Phosphorus (P) is 1.10A and boron (B) for 17 people.
At 0.88 people, it is smaller than silicon, and germanium (
It can be seen that Ge) is 1.22A, which is larger than silicon.

Therefore, by taking a weighted average of the covalent bond radii of these dopants and silicon with respect to l1fi, the covalent bond radius of that part is calculated, and it is understood that distortion occurs when two layers with different values come into contact. Become. For example, when boron or phosphorus is implanted into silicon, this part shrinks, and the degree of shrinkage is shown in Figure 4. For example, when boron has a concentration of 101026O', the change in lattice constant is 2×
10-3, while the lattice constant of silicon is 5.43
Since there is only one person, it is approximately 4X10-4 (-2X10-ko1
5.431). To provide a shrinkage of 4×10″4 or more, boron may be implanted proportionally between implants.

Considering the above points, the beam region 16 contains 10" of boron.
Since it is doped with cm4, the lattice is very shrunken. Meanwhile, the second epitaxial! 15 is Rin in 1Q
Since it is doped to the extent of I Ic r71,
The shrinkage is smaller than the beam area 16, so @gA area 16
This causes tensile strain. However, since the second epitaxial layer 15 is an epitaxial layer formed on the first epitaxial layer 14 which is P+, it is influenced by the first epitaxial layer 14. If the first epitaxial layer 14 were a layer doped only with boron, the lattice of this layer would shrink in the same way as the beam regions 16, and the second epitaxial layer 15 would also be compressed, creating sufficient tension in the beam regions 16. Therefore, the first epitaxial layer ll!g14, which is P+, is simultaneously doped with germanium, which has a larger covalent bond radius than silicon, to expand the lattice and prevent the tension from being relaxed.

Furthermore, by increasing the concentration of germanium or by mixing germanium into the second epitaxial layer 15, the tension can be further increased.

As described above, any initial tension can be applied to the vibrating beam 9.

FIG. 5 is an overall configuration diagram showing a configuration in which the vibrating strain sensor shown in FIG. 1 is combined with an excitation circuit for exciting it.

19 is a vibrating strain sensor shown in FIG. 1 that detects the measured pressure, and 20 is an excitation circuit that excites the vibrating strain sensor 19 and extracts changes in its resonance frequency.

Lead wires i are connected from both ends of the vibrating beam 9 of the vibrating strain sensor 19.
t and 12 are drawn out to terminals T+ and T2, respectively.

The excitation unit 20 includes a transformer 21 with a center tap, an amplifier 22, a comparison resistor 23, and the like. The series circuit of the vibrating beam 9 and the comparison resistor 23 connected via the terminals T+ and T2 includes the secondary winding III n of the transformer 21.
2 voltages are applied.

Further, an amplifier 22 is connected between the connection point of the vibrating beam 9 and the comparison resistor 23 and the primary winding n1 of the transformer 21 to provide positive feedback, and the oscillation frequency is output from the output end of the amplifier 22 through the terminal T3. To detect.

Since a DC ta field is applied to the vibration a@9 from the permanent magnet 12, an AC current 1 is applied to the vibration beam 9 as shown in FIG.
When flowing, an electromagnetic force acts on the #J beam 9, causing it to vibrate. Since the hollow space 11 is maintained in a vacuum state, this vibration has a high Q value of several hundred to several tens of thousands, and has a large amplitude when it resonates. Therefore, when positive feedback is applied to the transformer 21 via the amplifier 22, the system self-oscillates at different natural frequencies due to the distortion of the vibrating beam 9.

Measurement pressure Pt applied from around the silicon substrate 8, etc.
The tension in the axial direction of the vibrating beam 9 changes due to the compressive strain determined by the inherent volumetric compressibility of the silicon St&- which constitutes the silicon substrate 8 due to u, and the resonant frequency f changes, so from this change in the oscillation frequency f, The measured pressure PIL can be known.

The above explanation is mainly based on a configuration in which strain is detected from the difference in oscillation frequency caused by applying measuring pressure from the outside of the vibrating strain sensor and the vibrating beam shrinks. However, the configuration is not limited to this, and for example, /Can also be used for pressure sensors, acceleration sensors, etc.

Furthermore, although boron, phosphorus, and germanium have been described as examples of atoms to be implanted, the present invention is not limited to these.

Furthermore, the material of the vibration a@ or the substrate on which it is fixed is not limited to silicon; for example, GaXITL (+-
χ) Tension is generated even when a vibrating beam of GaAs is formed.

Effect of Stretching 1-2> As specifically explained above with reference to the examples, according to the present invention, it is possible to stably apply an initial tension of any magnitude simply by controlling impurities.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the configuration of one embodiment of the present invention, Fig. 2 is an explanatory diagram explaining the process of manufacturing the vibrating strain sensor shown in Fig. 1, and Fig. 3 is a covalent bonding of various impurities. A characteristic diagram showing the radius and the ratio of the covalent bond radius of various impurities to the covalent radius of silicon, FIG. 4 is a characteristic diagram showing the change in lattice constant with respect to impurity concentration, and FIG.
A block diagram showing an excitation circuit that excites the constrained strain C sensor, FIG. 6 is an explanatory diagram explaining the excitation state shown in FIG. 5, and FIG. 7 is a perspective view showing the configuration of a conventional vibrating bulge pressure sensor. Figure 8 is a sectional view taken along line XX in Figure 7 with the cover attached;
FIG. 9 is a plan view of FIG. 8 with some parts omitted. 1.8... Silicon substrate, 2... Pressure receiving diaphragm, 3.4.9... Vibration beam, 11... Hollow chamber, 12...
... Permanent magnet, 13... Holding substrate, 14... First epitaxial layer, 15... Second epitaxial layer, 1
6...Beam area, 19...Vibration strain hinge, 20...
・Excitation circuit. Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] In a vibrating strain sensor that measures the strain applied to both ends of a semiconductor vibrating beam by measuring the resonance frequency of a semiconductor vibrating beam whose both ends are fixed to a semiconductor substrate, the main atoms constituting the substrate are shared. A vibrating strain sensor characterized in that another atom having a covalent bond radius different from the bond radius is mixed into the substrate to apply an initial tension to the vibrating beam.