JP3234652B2 - Acceleration sensor and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor (including an angular acceleration sensor) suitable for detecting an angle change due to camera shake of a camera, a camera video or the like, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Currently, acceleration sensors mainly used include a piezoelectric type using a piezoelectric effect and a strain gauge type using a metal resistor or a semiconductor. Attempts have also been made to fabricate cantilevers using silicon micromechanics technology, add weight to the tip, and produce a small acceleration sensor. For example, KE Petersen et al. ("Michromechanica
l Accelerometer Integrated with Mos Detection Circ
uity "IEEE Trans. Electron Devices, vol.ED-29, p2
3, 1982) proposes a method of detecting acceleration using a change in capacitance.

FIG. 6 is a perspective view showing an example of a conventional acceleration sensor. This acceleration sensor is a silicon substrate 10
An electrode 104 and an elastic support beam 103 are formed on the substrate 1 by microfabrication. The elastic support beam 103 is made of an oxide film, a metal electrode 105 is formed on the upper surface, and the sensitivity to acceleration is increased by the weight 102 provided at the tip. A change in capacitance between the electrode 104 and the metal electrode 105 is detected by a detection circuit 106 to detect acceleration. Further, as an arrangement form of the metal electrode 105, a weight 10
2 has a configuration in which metal electrodes are also arranged on the upper surface (Suzuki, "Semiconductor Capacitance-type Acc
elerometer with PWM Electrostatic Servo Techniqu
e ", Sensors and Actuators, A21-A23 (1990), pp316-31
9).

As described above, an acceleration sensor using silicon is inexpensive with excellent mass productivity due to the photolithography technique. On the other hand, the angular acceleration is detected by, for example, arranging a plurality of such two translational acceleration sensors separated by a predetermined distance and obtaining the difference from the detected acceleration. In this case, the weight 102 of two or more acceleration sensors
And the mechanical properties such as the spring constant of the elastic support beam 103 need to be substantially the same.

However, a silicon wafer used as a base material for manufacturing an acceleration sensor has a thickness error of about several μm between wafers in the current mechanical polishing and polishing using a surface reaction. Therefore, the mass of the weight 102 of the acceleration sensor varies, and the characteristics of the individual acceleration sensors vary.

In an acceleration sensor of the type integrally formed of silicon, an elastic support beam employs anisotropic etching utilizing a difference in the etching rate of a crystal orientation plane with an alkali etchant such as a potassium hydroxide aqueous solution for a silicon substrate. Since the thickness of the elastic support beam 103 is determined by the etchant concentration, the heating temperature, and the like, it is necessary to manage the alkali etchant with high accuracy in order to improve the thickness error accuracy.

FIG. 7 is a perspective view showing an example of a main part of a conventional angular acceleration sensor. The main part of the angular acceleration sensor has a frame-shaped silicon substrate 111, a weight 112, and elastic support beams 113 that support rotation on both sides of the weight on a rotation axis substantially passing through the center of gravity of the weight. In such a main part,
By incorporating electrodes, a detection circuit, and the like, an angular acceleration sensor can be obtained. FIG. 8 is an exploded perspective view illustrating an angular acceleration sensor in which both surfaces of the main part shown in FIG. 7 are sandwiched between glass plates with electrodes. In this figure, 114
Is a detection direction of angular acceleration, 115 is a glass plate, 116 is a shallow groove formed on the glass plate, and 117 is a fixed electrode. When receiving the angular acceleration, the elastic support beam 113 is twisted, and the weight 112 rotates in the detection direction 114. At this time, a change in capacitance occurs between the silicon substrate and both electrodes, and this change in capacitance is detected by a detection circuit to determine the acceleration.

However, in such an angular acceleration sensor, the alignment accuracy when the weight 112 and the elastic support beam 113 are formed appears as a deviation of the center of the rotation axis, and the balance between the left and right weights 112 becomes imbalanced. The accuracy of detecting the angular acceleration is reduced. Because of this,
In an angular acceleration sensor, it is essential to improve alignment accuracy more than an acceleration sensor.

[0009]

[0010]

[0011]

[0012]

[0013]

SUMMARY OF THE INVENTION The present invention has been made to solve each of the problems in the prior art as described above.

[0014] The purpose of the present invention is a small structure, to provide a method acceleration sensor capable of detecting direct accurately conveniently acceleration and angular acceleration (including angular acceleration sensor), and that it can be manufactured easily It is in.

[0015]

[0016]

The above objects can be achieved by the present invention described below.

According to the present invention, there is provided an acceleration sensor comprising a base, a weight, and an elastic support beam for supporting the weight on the base, which are formed from an integral silicon base material, wherein the weight has the mass of the weight. Providing a groove or film for adjustment , and
A member having a through hole on the surface of the groove or the membrane
Is an acceleration sensor characterized in that the through hole is located at a position corresponding to the membrane , or a groove or a membrane for adjusting the spring constant of the elastic support beam is provided in the elastic support beam. An acceleration sensor characterized by the following. Furthermore the groove or film, a manufacturing method of an acceleration sensor having a step of forming by vapor phase etching or deposition through the through hole of the member.

[0018]

In the present invention, the term "acceleration sensor" is used to mean not only a mere acceleration sensor but also an angular acceleration sensor unless otherwise specified. In the case of the configuration of the angular acceleration sensor, for example, the elastic support beam may be an elastic support beam on a rotation axis substantially passing through the center of gravity of the weight and rotatably supporting the weight on both sides of the weight.

[0020]

According to the acceleration sensor of the present invention, the torque proportional to the acceleration or the angular acceleration around the axis acts on the weight due to the inertia moment of the weight, and the weight is displaced or distorted against the elastic force against the bending or torsion of the support beam. The rotation is used to detect acceleration. And the acceleration sensor of the present invention, even if there is a manufacturing error or an error of the silicon base material,
Since the mechanical characteristics of the mass of the weight and the spring constant of the elastic support beam are adjusted by the groove or the film, the sensor has uniform characteristics and high detection accuracy .

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in more detail with reference to the drawings and embodiments.

<Embodiment 1> FIG. 1 is a cross-sectional view illustrating an embodiment of an acceleration sensor having a weight adjusting groove for a weight. In this acceleration sensor, a silicon substrate is anisotropically etched to form a weight 12 and an elastic support beam 13 having a desired shape, the remaining portion is used as a silicon substrate 11, and a separate silicon plate 14 is adhered to a lower portion thereof. Consisting of The silicon plate 14 has a through hole 15, and the weight 12 has a through hole 1.
A groove is formed at a position corresponding to 5. This is the mass adjusting groove 17. The mass adjusting groove 17 is provided in the through hole 1.
5 is formed by partially removing the lower surface of the weight 12 by etching. Further, a glass plate 16 is adhered to the lower surface of the silicon plate 14 to cover the through hole 15.

FIG. 2 is a cross-sectional view illustrating a process for forming the mass adjusting groove 17 of the acceleration sensor shown in FIG. The outline of this process consists of forming the mass adjusting groove 17 by etching and removing the weight 12 through the through hole 15 as shown in FIGS.
Such a process such as etching through the through hole 15 is simple in process, and is suitable as a method for forming a groove, a film or the like in the present invention. Hereinafter, the concretely implemented items are shown for each process.

[Step shown in FIG. 2A] A main part of an acceleration sensor comprising a base 11, a weight 12, and an elastic support beam 13 for supporting the weight on the base is first prepared. This is produced by subjecting a plate-shaped silicon substrate to a known anisotropic etching. The elastic support beam 13 is made of an n-type diffusion layer. On the elastic support beam 13, a p-type diffusion layer serving as a strain gauge for detecting acceleration applied to the weight 12 by deflection of the beam is formed by an ion implantation method. Further, the surface of the silicon substrate 11 is subjected to reduced pressure CVD in a mixed gas atmosphere of ammonia and dichlorosilane gas.
A silicon nitride film is formed by the method.

The production of the weight 12 and the elastic support beam 13 was performed as follows. A silicon substrate having a weight pattern formed on a silicon nitride film is immersed in a 30% aqueous solution of potassium hydroxide heated to 80 ° C., and subjected to electrolytic etching while applying a voltage of 1.5 V to the n-type diffusion layer. Etch stop technology using pn junction only for diffusion layer (R. Huste
r, Sensors and Actuators, A21-A23 (1990) pp899-90
3), and a weight was formed at the same time. Next, using CF ₄ as an etching gas from the other surface of the silicon base material, the resist was patterned using photolithography so as to leave the weight 12 and the beam 13, and a part of the n-type diffusion layer was removed by etching. . Finally, the silicon nitride film was removed with hot phosphoric acid to obtain a weight 12 and an elastic support beam 13 having desired shapes.

A silicon plate (plate-like member) 14 having a through hole 15 is disposed below the weight 12 on the lower surface of the substrate 11 which is a member composed of the base 11, the weight 12, and the elastic support beam 13. Thus, an acceleration sensor (grooves not formed) shown in FIG. 2A was obtained. This through hole 15
It was formed by etching in a 30% aqueous solution of potassium hydroxide heated at 80 ° C. through a pattern for through holes in a silicon nitride film by silicon crystal isomer etching. The silicon nitride film was removed by hot phosphoric acid. Further, as a method for bonding the silicon substrate 11 and the silicon plate 14, a silicon direct bonding technique (M. Shimbo,
J. Appl. Phys., 60 (8), 15, 1986, pp 2987-2989) by heating in a furnace at 1000 ° C. for 1 hour.

[Step shown in FIG. 2 (b)] The weight 12 was partially removed by etching through the through hole 15 of the acceleration sensor (with no groove formed) manufactured as described above. This etching removal is performed to adjust the mass of the weight 12 to a desired value. Etching was performed for 20 minutes by reactive etching using SF ₆ as an etching gas and the silicon plate 14 as a mask. The gas pressure during the etching was 5 Pa, the input power was 150 W, and the silicon etching rate at that time was 4500 ° / min. Under these conditions, the mass adjusting groove 17 was formed, and the weight of the weight 12 was adjusted. In the embodiment illustrated here, the depth of the mass adjusting groove 17 is determined by measuring the thickness of the base 11 in advance. However, for example, a method of measuring the mass of the base 11 in advance may be used. Applicable.

[Step shown in FIG. 2C] In the acceleration sensor in which the groove 17 is formed as described above, the through hole 15 is closed by bonding a glass plate 16 to the lower surface of the silicon plate 14 as required. Here, as the glass plate 16, Pyrex glass having a thermal expansion coefficient similar to that of silicon was used. As a method for bonding the glass plate 16 to the silicon plate 14, a so-called anodic bonding method was used. In this anodic bonding, a negative voltage (300 V) is applied to the Pyrex glass (glass plate 16) side by heating to a temperature of about 400 ° C.
It is joined by electrostatic force acting on the interface between glass and silicon.

The acceleration sensor shown in FIG. 1 was obtained by the processes of FIGS. 2A to 2C described above. The silicon substrate 11 is p-type and has a thickness of 505 μm, and phosphorus is implanted and diffused into one surface by ion implantation at 5 μm, and the elastic support beam 13 is composed of this n-type diffusion layer. The acceleration sensor obtained according to this embodiment has a
The sensitivity was the same as that of a conventional acceleration sensor having no groove 17 made of a silicon substrate having a thickness of m.
That is, for example, even if there is an error of about +5 μm in the thickness of the base material, the groove 17 is formed so as to have the same mechanical characteristics as an acceleration sensor manufactured from an appropriate base material having a thickness of 500 μm, and the mass of the weight 12 is To obtain a uniform and precise product.

In this embodiment, reactive etching is employed as an etching method for forming a weight, but the present invention is not limited to this. That is, various methods such as plasma etching (PE) and vapor phase etching using a photo-excitation process can be adopted as a method of performing etching through the through-hole 15.

As the etching using this photoexcitation process, for example, a silicon substrate is placed in a chlorine gas as a reactive gas, and the reactive gas is excited by an Ar laser to react with silicon and perform etching (DJ Ehrlic).
h, Applied Physics Letters, No. 38, 1981, p1018),
Alternatively, it is performed by using an optical excitation process such as etching with SF ₆ gas and an excimer laser such as ArF or KrF (Fujii, 18th International Conference on Solid State Devices, 1986, p201). The light source used may be any light source that has sufficient energy to excite the reactive gas or that has sufficient power to heat the silicon substrate and react with the reactive gas. In the case of vapor phase etching, Cl containing Br, Cl, and F that can react with silicon is used.
Reactive gas species such as ₂ , Br ₂ , CF ₄ , NF ₃ , SF ₆ and CF ₂ Cl ₂ are used.

In this embodiment, a groove for adjusting the weight of the weight is formed. However, a film may be formed instead of the groove if desired.

<Embodiment 2> FIG. 3 is a cross-sectional view illustrating an embodiment of an acceleration sensor provided with a spring constant adjusting film of an elastic support beam. In this acceleration sensor, a silicon substrate is anisotropically etched to form a weight 22 and an elastic support beam 23 having a desired shape, the remaining portion is used as a silicon substrate 11, and a separate silicon plate 24 is adhered to a lower portion thereof. Consisting of
The silicon plate 24 has a through hole 25, and a film is formed on the elastic support beam 23 at a position corresponding to the through hole 25. This is the spring constant adjusting film 28. This film 28
Is formed by performing a film forming process on the lower surface of the elastic support beam 23 through the through hole 25. Further, a glass plate 26 is adhered to the lower surface of the silicon base 21 to cover the through hole 25.

FIG. 4 is a cross-sectional view illustrating a process for forming the spring constant adjusting film 23 of the acceleration sensor shown in FIG. The outline of this process is to form the spring constant adjusting film 23 on the lower surface of the spring constant adjusting film 23 through the through hole 25 by a known film forming method, as shown in FIGS. Hereinafter, the points that are specifically implemented are shown for each step.

[Step shown in FIG. 4A] A main part of an acceleration sensor comprising a base 21, a weight 22, and an elastic support beam 23 for supporting the weight on the base is first prepared. In the silicon substrate 21, a p-type diffusion layer serving as a strain gauge is formed by an ion implantation method as in the first embodiment, and a silicon vaginalized film is formed by low-pressure CVD. The weight 22 and the elastic support beam 23 were manufactured in the same manner as in Example 1 except that electrolytic etching was performed. However, elastic support beam 2
The thickness 3 was prepared by terminating the etching when the thickness of the anisotropically etched silicon became about 5 μm.

The thickness of the elastic support beam 23 was 4.5 μm when its cross section was observed with a scanning electron microscope. The thickness control of the elastic support beam depends on the etching time, the concentration of the potassium hydroxide solution and the temperature of the solution, and it is difficult to adjust the thickness with high accuracy. Through hole 25 of silicon plate 24
The method of forming the silicon substrate 21 and the bonding method between the silicon substrate 21 and the silicon plate 24 were the same as those in the first embodiment. Through hole 2
5 is disposed below the elastic support beam 23.

[Step shown in FIG. 4 (b)]
5, the spring constant adjusting film 28 was deposited on the lower surface of the elastic support beam 23 until the spring constant of the elastic support beam 23 reached a desired value. As a film deposition method, an SiO ₂ film was deposited in a 12 mTorr argon atmosphere by a sputtering method using a SiO ₂ target. By using the silicon plate 24 as a mask, there is no film deposition other than on the elastic support beam 23.
The deposition rate of the SiO ₂ film was 250 ° / min and 3000
Å Deposited. In the embodiment shown here, the thickness of the spring constant adjusting film 28 was determined from the deviation of the desired value by measuring the natural frequency of the elastic support beam 23 having the weight 22.

[Step shown in FIG. 4 (c)] With respect to the acceleration sensor having the film 28 formed as described above,
The glass plate 2 is placed on the lower surface of the silicon plate 24 on which the iO ₂ film is deposited.
6, the through hole 15 was closed. Here, as the glass plate 26, Pyrex glass having a thermal expansion coefficient similar to that of silicon was used. An anodic bonding method was used as a method for bonding the glass plate 26 to the silicon plate 24.
This anodic bonding was performed by heating to a temperature of about 400 ° C. and applying a negative voltage (800 V) to the Pyrex glass (glass plate) 26 side.

The acceleration sensor shown in FIG. 3 was obtained by the processes of FIGS. 4A to 4C described above. This silicon substrate 21 has an n-type thickness of 500 μm. The acceleration sensor obtained according to the present embodiment has the same sensitivity to acceleration as an acceleration sensor manufactured using a silicon substrate having an elastic support beam composed of an n-type diffusion layer formed by using an etch stop technique using a pn junction. Had become. That is, even if there is a thickness error of the beam 23 generated when the elastic support beam is formed, the beam is adjusted by providing the spring constant adjusting film 28, and a uniform and accurate acceleration sensor is obtained.

In this embodiment, the film is formed for adjusting the spring constant of the elastic support beam. However, a groove may be formed instead of the film if desired.

<Example 3> A main part similar to the main part of the angular acceleration sensor previously shown in FIG. 7 was manufactured. That is, a rectangular flat weight is supported inside the frame-shaped silicon base at the midpoint of each of the two long sides of the weight via the elastic support beam. The weight, the elastic support beam, and the frame-shaped substrate are integrally formed from a silicon substrate by anisotropic etching, and the thickness of the elastic support beam is controlled by using the same electrolytic etching as in the first embodiment. I have. The silicon substrate used was 500 m thick.

FIG. 5 is a sectional view showing a structure in which such a member is sandwiched between glass plates with electrodes. In this embodiment,
Glass plates 36 are bonded on the upper and lower sides of the frame-shaped silicon substrate 31. A portion of the glass plate 36 that is to be in contact with the weight 32 is slightly etched, and electrodes 39 and 39 ′ are formed on surfaces of the glass plate 36 and the weight 32 that face each other. The angular acceleration is detected by detecting a change in capacitance corresponding to a change in the distance between the opposing electrodes 39. A through hole 35 is formed in the lower glass plate 36, and a mass adjusting film 37 is formed on a part of the lower surface on one side of the weight 32 through the through hole 35. The elastic support beam 33 is 3 μm from the position where the weight is symmetric,
It is shifted to the 9 side. Hereinafter, the points that were specifically implemented are shown in the order of steps.

The through hole 35 of the glass plate 36 is formed by laser machining, sand blasting, and electrolytic discharge machining in a potassium hydroxide solution (S. Shoji, Technical Digest of the 9th Sens).
or Symposium, 1990, pp27-30). The adhesion between the base 31 and the two glass plates 36 was performed by an anodic bonding method. As the glass plate 36, Pyrex glass having a thermal expansion coefficient similar to that of silicon was used. At this time, the temperature of the anodic bonding was 400 ° C., and the voltage was 300 V.
In the angular acceleration sensor (film not formed) formed in this manner, a difference is generated between the capacitance of the upper and lower electrodes 39 and the capacitance of the electrode 39 '. This occurs because the position of the center of gravity of the weight and the position of the support by the beam are shifted by shifting the position of the elastic support beam.

Next, aluminum (A1) was deposited to a thickness of 5 μm on the lower surface on one side of the weight 32 through the through hole 35 by an electron beam evaporation method, which is one of the vacuum evaporation methods. By using the glass plate 36 having the through-hole 35 as a mask, film deposition on one side of the weight 32 was eliminated. As a result, the above-mentioned difference in capacitance is improved, and a value equivalent to the difference in capacitance when the arrangement of the midpoint of the weight and the elastic support beam is matched to 0.5 μm, which is the alignment accuracy range in photolithography. It became.

According to the angular acceleration sensor of this embodiment,
By adjusting the thickness of the mass adjusting film, it is possible to adjust the mass of the weight with high accuracy regardless of the magnitude of the alignment accuracy error caused by photolithography.

In this embodiment, the through hole 35 is provided only on one side of the glass plate 36, and the mass adjusting film is formed on one side of the weight. May be formed with a mass adjusting film.

In this embodiment, aluminum is deposited by the electron beam evaporation method as the mass adjusting film 37 for adjusting the weight of the weight. Other metals other than can be deposited. The main thin film production methods include resistance heating, vacuum evaporation using an electron beam, etc.
A sputtering method, a CVD method such as low-pressure CVD or plasma CVD may be used. It goes without saying that the film deposition method shown here may be used for a film for adjusting the spring constant of the elastic support beam.

In this embodiment, the film for adjusting the weight of the weight is formed, but a groove may be formed in the same manner as in the first embodiment.

[0049]

[0050]

[0051]

[0052]

[0053]

[0054]

[0055]

[0056]

[0057]

[0058]

[0059]

[0060]

[0061]

[0062]

[0063]

[0064]

[0065]

[0066]

As described above, the acceleration sensor shown in each embodiment is
Further, by incorporating predetermined electrodes, a detection circuit, and the like, it becomes very useful as a semiconductor (angular) acceleration sensor made of silicon.

[0068]

The acceleration sensor (including the angular acceleration sensor) of the present invention described above has a small and simple structure, and has a mechanical characteristic with a groove or a film formed on a part of a weight or an elastic support beam. Are uniform, and the acceleration or the angular acceleration can be directly and accurately detected. Further, according to a manufacturing method by etching or film formation through a through hole, this acceleration sensor can be easily manufactured.

[0069]

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an acceleration sensor according to a first embodiment.

FIG. 2 is a cross-sectional view illustrating a method of manufacturing the acceleration sensor according to the first embodiment.

FIG. 3 is a cross-sectional view illustrating an acceleration sensor according to a second embodiment.

FIG. 4 is a cross-sectional view illustrating a method of manufacturing the acceleration sensor according to the second embodiment.

FIG. 5 is a cross-sectional view illustrating an angular acceleration sensor according to a third embodiment.

FIG. 6 is a perspective view showing an example of a conventional acceleration sensor.

FIG. 7 is a perspective view showing an example of a main part of a conventional angular acceleration sensor.

FIG. 8 is an exploded perspective view showing an example of a configuration of a conventional angular acceleration sensor.

[Explanation of symbols]

 11, 21, 31 Silicon base 12, 22, 32 Weight 13, 23, 33 Elastic support beams 14, 24, Silicon plate 15, 25, 35 Through hole 16, 26, 36 Glass plate 17 Mass adjustment groove 37 Mass adjustment Membrane 28 Spring constant adjusting membrane 39, 39 'very  Reference Signs List 101 silicon substrate 102 weight 103 elastic support beam 104, 105 electrode 106 detection circuit 111 frame-shaped silicon substrate 112 weight 113 elastic support beam 114 angular acceleration measurement direction 115 glass substrate 116 groove 117very

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-166770 (JP, A) JP-A-4-13972 (JP, A) JP-A-4-181781 (JP, A) JP-A-2- 293669 (JP, A) JP-A-3-255369 (JP, A) JP-A-3-23676 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01P 15/00-15 / 125 H01L 29/84 H01L 21/3063

Claims (4)

(57) [Claims] 1. An acceleration sensor comprising a base (11), a weight (12), and an elastic support beam (13) for supporting the weight on the base, the acceleration sensor comprising:
A groove (1) for adjusting the mass of the weight is provided in the weight (12).
7) Or a film is provided , and the groove of the substrate (11, 21) is provided .
Or a member having through holes (15, 25) on the membrane side surface
(14, 24) at the position corresponding to the groove or film.
An acceleration sensor which is joined so that a through hole is located . 2. An acceleration sensor comprising a base (21), a weight (22), and an elastic support beam (23) for supporting the weight on the base, formed from an integral silicon base,
The elastic support beam (23) is provided with a groove or film (28) for adjusting the spring constant of the elastic support beam , and the base (1)
The through holes (15, 2)
The member (14, 24) having 5) is paired with the groove or the membrane.
An acceleration sensor which is joined so that the through hole is located at a corresponding position . 3. A method for manufacturing an acceleration sensor according to claim 1 , wherein the through-holes (15, 2) of the member are provided.
5) A method of manufacturing an acceleration sensor, comprising a step of forming a groove by vapor-phase etching the weight or the elastic supporting beam through the step 5). 4. A method for manufacturing an acceleration sensor according to claim 1 , wherein the through holes (15, 2) of the member are provided.
5) A method for manufacturing an acceleration sensor, comprising a step of forming the film on the weight or the elastic support beam through the method.