JP2006133245A - Capacitance type acceleration sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a capacitance type acceleration sensor that eliminates the possibility that the opposite faces of a mass and a glass substrate adhere to each other during the anodic bonding of a silicon substrate and the glass substrate, making it impossible to measure acceleration because of malfunctioning. <P>SOLUTION: The capacitance type acceleration sensor includes the silicon substrate 1A formed with a pair of fixed electrodes 2A, 3A and a moving electrode 4A having a mass 4Aa disposed therebetween; and a pair of glass substrates 6A, 7A anodically bonded to both principal faces of the silicon substrate 1A. Gaps are formed between the mass 4Aa and the glass substrate 6A, 7A. At least one of the opposite faces of the mass 4Aa or the pair of glass substrates 6A, 7A on at least one of both principal faces of the mass 4Aa is coated with a silicon nitride film 11 serving as an adhesion prevention means for preventing the mass and the glass substrates from adhering to each other. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a capacitive acceleration sensor in which a pair of fixed electrodes and a movable electrode having a movable portion disposed therebetween are sealed with a pair of insulating protective covers, and a method of manufacturing the same, and in particular, the movable portion and The present invention relates to impact mitigation of a collision with the pair of insulating protective covers.

  The capacitive acceleration sensor has a structure in which the acceleration sensing part is formed in a silicon substrate, the silicon substrate is sandwiched between glass substrates, and is manufactured using semiconductor microfabrication technology. It is inexpensive and can be manufactured in large quantities, and has recently been widely used as an acceleration detection element such as an airbag sensor for automobiles.

Japanese Patent Laid-Open No. 8-32090 (FIG. 8)

  FIG. 10 is a plan view showing an acceleration sensing unit in a conventional capacitive acceleration sensor, and FIG. 11 is a schematic view showing a cross section AA in FIG. In the figure, reference numeral 1 designates a silicon substrate, and an acceleration sensing part and an outer frame 5 comprising fixed electrodes 2, 3 and a movable electrode 4 are formed by anisotropic etching of a silicon wafer. Reference numerals 6 and 7 denote a pair of glass substrates as protective covers fixed to both main surfaces of the silicon substrate 1, respectively, and are anodic bonded to the silicon substrate 1.

  The fixed electrode 2 includes a fixed electrode terminal portion 2a, and the fixed electrode 3 includes a fixed electrode terminal portion 3a. The movable electrode 4 connects the mass body 4a as a movable portion disposed between the fixed electrodes 2 and 3, the movable electrode terminal portion 4b as an anchor, and the mass body 4a and the movable electrode terminal portion 4b. The mass body 4a is opposed to the fixed electrodes 2 and 3 with a gap G therebetween. The outer frame 5 includes a GND terminal portion 5 a and is formed so as to surround the fixed electrodes 2 and 3 and the movable electrode 4. Further, a gap X is formed between the opposing surfaces of the mass body 4 a and the glass substrate 6 by etching the silicon substrate 1.

  The glass substrate 7 is formed with through-holes 7a so that the fixed electrode terminal portions 2a and 3a, the movable electrode terminal portion 4b and the GND terminal portion 5a can be externally connected, and the fixed electrode terminal portions 2a viewed from the through-holes 7a. 3a, the movable electrode terminal portion 4b, and the GND terminal portion 5a are deposited with an aluminum film 9, and a concave portion 7b is formed on the surface facing the mass body 4a to form a gap Y. Further, a gap Z is formed between the fixed electrodes 2, 3 and the movable electrode 4 and the outer frame 5, and the fixed electrodes 2, 3 and the movable electrode 4 are hermetically protected by the glass substrates 6, 7 and the outer frame 5. At the same time, the mass body 4a is supported via the beam 4c so as to be displaceable in parallel to the joint surface between the glass substrates 6 and 7 and the silicon substrate 1.

  The silicon substrate 1 has a high aspect ratio structure in which the width of the gap G between the fixed electrodes 2 and 3 and the mass body 4a and the width of the beam 4c of the mass body 4a are extremely small compared to the thickness. Both main surfaces are aligned with the (110) plane of the single crystal silicon wafer, and the crystal orientation perpendicular to the crystal plane is wet etched along the (111) plane. As is apparent from FIG. 10, the planar shape of the acceleration sensing unit is a parallelogram having an acute angle of about 70 degrees and an obtuse angle of about 110 degrees. Note that 10 is sandwiched between the silicon substrate 1 and the glass substrate 6 in a mask made of a silicon dioxide film deposited on the silicon substrate 1 when the gap G or the like is formed on the silicon substrate 1, and the removal step This is the portion that remains without being removed.

  Next, the operation of the acceleration sensing unit in this capacitive acceleration sensor will be described. The acceleration sensing unit uses a mass body 4a supported by a movable electrode terminal 4b as an anchor via a beam 4c so as to be displaceable, and the fixed electrode 2 facing the gap G having a predetermined width. 3 and the movable electrode 4 are used as a counter electrode of the capacitance C of the sensing unit.

  When acceleration is applied to the sensing unit in a direction that coincides with the displaceable direction of the mass body 4a, the dimension of the gap G changes due to the displacement of the mass body 4a, and the capacitance C changes according to the magnitude of the acceleration. The acceleration received by the sensing unit by measuring the change in the capacitance C is calculated by an external acceleration calculation means (not shown). The capacitance type acceleration sensor using the change of the capacitance C makes it possible to measure the acceleration in the direction coinciding with the displaceable direction of the mass body 4a and is put to practical use.

  The width of the beam 4c is narrow compared to its thickness, and it has a structure that is difficult to be displaced toward the glass substrates 6 and 7 perpendicular to the displaceable direction of the mass body 4a. If the mass body 4a collides with the opposing surfaces of the glass substrates 6 and 7, the mass body 4a is damaged, or when the silicon substrate 1 and the glass substrates 6 and 7 are anodic bonded, Even after it is adsorbed to either of the glass substrates 6 and 7 and the voltage application is stopped, the facing surfaces do not adhere to each other and may not be able to measure acceleration.

  Since the conventional capacitive acceleration sensor is configured as described above, there is a problem that the mass body 4a may collide with the opposing surfaces of the glass substrates 6 and 7 and be damaged due to, for example, dropping. It was. Further, when the anodic bonding of the silicon substrate 1 and the glass substrates 6 and 7 is performed, the facing surfaces of the mass body 4a and the glass substrates 6 and 7 do not adhere to each other, and there is a possibility that the acceleration may not be measured due to a malfunction. There was a point.

  The present invention has been made to solve the above-described problems, and the movable part is damaged due to dropping or the like, or the movable part does not adhere to the opposing surface of the protective cover and is not separated. It is an object of the present invention to obtain a capacitive acceleration sensor and a method for manufacturing the same that do not cause the possibility of measuring acceleration.

  According to a first aspect of the present invention, there is provided a capacitive acceleration sensor comprising: a movable electrode having a movable portion disposed between a pair of fixed electrodes; and a pair of protective covers disposed to face the movable portion via a gap. In the capacitive acceleration sensor provided, the pair of protective covers on at least one of the surfaces of the pair of protective covers facing the movable portion, or at least one of the surfaces of the movable portion facing the pair of protective covers, It has an adhesion preventing means for preventing adhesion of the surface facing the movable part.

  The capacitive acceleration sensor according to the second invention is the capacitive acceleration sensor according to the fourth invention, wherein the adhesion preventing means is made of a different material film different from the material of the protective cover attached to the surface of the protective cover. It is.

  A capacitive acceleration sensor according to a third aspect of the present invention is the capacitive acceleration sensor according to the fourth aspect of the present invention, wherein the adhesion preventing means forms the surface of the protective cover on a non-mirror surface.

  According to the first invention, the movable portion and the protection are provided on at least one of the opposed surfaces of the pair of protective covers facing the movable portion, or at least one of the opposed surfaces of the movable portion facing the pair of protective covers. Since an adhesion preventing means for preventing adhesion to the cover is provided, there is an effect that a highly reliable capacitive acceleration sensor that does not cause a malfunction due to inability to be separated even when the movable part is in close contact with the protective cover is obtained.

  According to the second aspect of the invention, since a film of a different material from the protective cover is attached to the surface of the protective cover as an adhesion preventing means, in the manufacturing process of the protective cover, the movable part and the protective cover are There is no risk of chemical bonding even if they are in close contact, and there is an effect that a capacitive acceleration sensor that can prevent the occurrence of defects during manufacture can be obtained at low cost.

  According to the third invention, since the surface of the protective cover is formed as a non-mirror surface as an adhesion preventing means, there is little possibility that the movable part cannot be separated even if the movable part is in close contact with the protective cover. Since it can be obtained easily and inexpensively in the manufacturing process of the protective cover, there is an effect that a highly reliable capacitive acceleration sensor can be obtained inexpensively.

Embodiment 1 FIG.
A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a schematic diagram showing a cross section of a capacitive acceleration sensor, FIG. 2 is a schematic diagram for explaining a manufacturing method of a glass substrate of the capacitive acceleration sensor, and FIG. 3 is a schematic diagram for explaining a manufacturing method of the capacitive acceleration sensor. . In the figure, the same reference numerals as those in the conventional example are the same as or equivalent to those in the conventional example. The plan view of the capacitive acceleration sensor is substantially the same as the conventional example shown in FIG.

  In FIG. 1, reference numeral 1A denotes a silicon substrate having a thickness of about 140 μm, and an acceleration sensing portion composed of fixed electrodes 2A, 3A and a movable electrode 4A and an outer frame 5A are formed by etching. 6A and 7A are borosilicate heat-resistant glass substrates having a thermal expansion coefficient close to that of silicon of approximately 400 μm as protective covers that are anodically bonded to both main surfaces of the silicon substrate 1A.

  The fixed electrode 2A includes a fixed electrode terminal portion 2Aa, and the fixed electrode 3A includes a fixed electrode terminal portion 3Aa. The movable electrode 4A includes a mass body 4Aa as a movable portion disposed between the fixed electrode 2A and the fixed electrode 3A, a movable electrode terminal portion (not shown) as an anchor, and the mass body 4Aa and the movable electrode. It is formed by a beam (not shown) connecting the terminal portion. The fixed electrodes 2A and 3A and the movable electrode terminal portion are bonded and fixed to the glass substrates 6A and 7A, and the mass body 4Aa is supported so as to be displaceable via the beam, and the outer frame 5A and the glass substrate 6A, The fixed electrodes 2A, 3A and the movable electrode 4A are hermetically protected by 7A.

  Mass body 4Aa has convex part 4Ab which projected on the glass substrate 6A side, and the cross-sectional shape of mass body 4Aa makes T shape. And the opposing surface 4Ac with glass substrate 6A is formed in the front-end | tip part of convex part 4Ab, and when mass body 4Aa is displaced to the glass substrate 6A side, opposing surface 4Ac of convex part 4Ab is glass substrate 6A. To restrict the displacement of the mass body 4Aa.

  That is, the beam supporting the mass body 4Aa has a narrow width compared to its thickness, and the mass body 4Aa has a structure that is difficult to be displaced toward the glass substrates 6A and 7A. If it is received, it may be displaced toward the glass substrates 6A and 7A, and may collide with them. If this displacement is large, the impact received will be great and the beam or mass 4Aa may be damaged. Therefore, a convex portion 4Ab that protrudes toward the glass substrate 6A is formed on the mass body 4Aa, and the convex portion 4Ab has a role as a stopper that regulates displacement toward the glass substrate 6A.

  Further, the glass substrate 6A is provided with a recess 6Aa having a depth of about 15 μm on the surface facing the convex portion 4Ab of the mass body 4Aa, and the bottom surface of the concave portion 6Aa buffers the impact caused by the collision with the convex portion 4Ab. An aluminum layer 8 having a thickness of about 5 μm as a buffer material is deposited by vapor deposition.

  The mass body 4Aa includes a facing surface 4Ad facing the fixed electrode 2A, and a facing surface 4Ae facing the fixed electrode 2A. The facing surfaces 4Ad and 4Ae have a length of about 3000 μm, a thickness of about 50 μm, and a width of the gap G. Has an elongated slit shape of about 5 μm.

  The glass substrate 7A has through-holes 7Aa at the positions of the fixed electrode terminal portions 2Aa and 3Aa, the movable electrode terminal portion (not shown), and the GND terminal portion (not shown) of the outer frame 5A. The aluminum film 9 is deposited on the fixed electrode terminal portions 2Aa, 3Aa, the movable electrode terminal portion, and the GND terminal portion of the outer frame 5A as viewed from the through holes 7Aa so as to be externally connected. Further, the glass substrate 7A has a concave portion 7Ab having a depth of about 20 μm on the surface facing the mass body 4Aa, and a convex portion 7Ac having a thickness of about 10 μm is formed in the center of the concave portion 7Ab.

  That is, a gap XA having a width of about 10 μm is formed between the convex portion 4Ab of the mass body 4Aa and the aluminum layer 8 deposited on the concave portion 6Aa of the glass substrate 6A, and the convex portion 7Ac of the mass body 4Aa and the glass substrate 7A. A gap YA having a width of about 10 μm is also formed between the two. A gap ZA is formed between the fixed electrodes 2A, 3A and the movable electrode 4A and the outer frame 5A.

  Next, a method for manufacturing the acceleration sensor shown in FIG. 1 will be described with reference to FIGS. FIG. 2A is a view showing a cross section of the completed glass substrate 6A. A sand blast is selectively performed on one main surface of the glass substrate 6A having a thickness of about 400 μm to form a recess 6Aa having a depth of about 15 μm. In addition, after depositing an aluminum layer 8 of about 5 μm on the recess 6Aa, the excess aluminum layer around the recess 6Aa is removed to complete the glass substrate 6A.

  2B to 2E show a method for manufacturing the glass substrate 7A. First, as shown in FIG. 2B, a mask 10A made of a resist film is provided except for a surface opposite to a mass body (4Aa in FIG. 1) on one main surface of a glass substrate 7A having a thickness of about 400 μm, and deepened by sandblasting. A recess 7Ab having a thickness of about 10 μm is formed. Next, as shown in FIG. 2C, a mask 10B made of a resist film is provided at the center of the recess 7Ab, and the depth of the recess 7Ab from the main surface is set to about 20 μm by sandblasting. A convex portion 7Ac having a thickness of 10 μm is formed.

  Further, as shown in FIG. 2D, a mask 10C made of a resist film is provided on the other main surface of the glass substrate 7A, a pair of fixed electrode terminal portions (not shown), a movable electrode terminal portion (not shown), Through holes 7Aa are respectively formed by sandblasting at positions corresponding to the terminal portions (not shown) of the frame, and a glass substrate 7A having a shape as shown in FIG. 2E is completed.

  Next, as shown in FIG. 3F, a mask 10D made of a silicon dioxide film is formed on one surface of a wafer-like silicon substrate 1A having a thickness of about 250 μm whose both surfaces are mirror-polished, and a narrow groove having a depth of about 50 μm. 1Aa and groove 1Ab are selectively formed by anisotropic etching.

  That is, the semiconductor wafer forming the silicon substrate 1A is a silicon wafer having a main surface crystal orientation of (110), and a mask 10D made of a silicon dioxide film is formed on this surface, for example, with a concentration of about 20% by weight. Using an anisotropic etching solution such as an aqueous potassium hydroxide solution, anisotropic etching is performed along the plane of the crystal orientation (111) to form the fine grooves 1Aa and 1Ab. At this time, wet etching is performed so that the depth of the narrow groove 1Aa is about 50 μm. However, the opening width of the simultaneously formed groove 1Ab is much wider than the opening width of the narrow groove 1Aa. It is formed considerably deeper than the groove 1Aa.

  Note that since the crystal orientation of the single crystal silicon wafer is perpendicular to the (110) plane and is etched along the (111) plane, the groove width w is extremely small compared to the groove depth d. A narrow groove 1Aa having such a high aspect ratio (for example, w / d <0.05) is formed.

  Next, as shown in FIG. 3G, the surface of the glass substrate 7A on which the recesses 7Ab are formed and the surface of the silicon substrate 1A on which the narrow grooves 1Aa and 1Ab are formed are brought into close contact with each other and bonded by anodic bonding. That is, the wafer-like silicon substrate 1A and the glass substrate 7A are aligned and brought into close contact with each other, and the glass substrate 7A side is the negative electrode (−) in an inert atmosphere, for example, at a high temperature of about 350 ° C. to 450 ° C. Then, for example, a DC voltage of about 200V to 1000V is applied so that the back surface of the silicon substrate 1A becomes a positive electrode (+), and the substrate is cooled after being held for several minutes to several hours. As a result, the contact portions between the silicon substrate 1A and the glass substrate 7A are bonded together and integrated.

  If the silicon dioxide film is about 1 μm as the mask 10D, the anodic bonding between the glass substrate 7A and the silicon substrate 1A is possible even when the silicon dioxide film is sandwiched between them. Anodic bonding is performed. Next, the silicon substrate 1A integrated with the glass substrate 7A is lapped off (ground) on the surface having a thickness of about 250 μm so that the groove 1Ab formed in the previous step is not exposed to a thickness of about 140 μm. Finish to a certain thickness.

  Next, as shown in FIG. 3H, a mask 10E made of a silicon nitride film that can be deposited at a relatively low temperature is provided on the surface of the silicon substrate 1A integrated with the glass substrate 7A so as to selectively form silicon anisotropy. Etching is performed so that the concave portion 1Ac having a depth of about 90 μm is formed at the central portion so that the surface of the mass body 4Aa facing the fixed electrodes 2A and 3A, that is, the gap G is formed with a thickness of about 50 μm. The groove 1Ae is formed, and the groove 1Ae is formed to communicate with the previously formed narrow groove 1Aa so that the gap G communicates with the groove 1Ae and the groove 1Ab previously formed. By forming the gap ZA, the silicon substrate 1A is separated into the fixed electrodes 2A, 3A, the mass body 4Aa having the convex portions 4Ab, the outer frame 5A, and the like.

  The reason why a silicon wafer having a thickness of about 250 μm was used as the material of the silicon substrate 1A is that it was easy to handle, and the glass substrate 7A and the integrated silicon substrate 1A were wrapped off to reduce the thickness. The reason is that since the glass substrate 7A has a thickness of about 400 μm and there is no problem in handling, the etching depth of the recess 1Ac is made as shallow as possible when forming the mass body 4Aa having a thickness of about 50 μm. .

  Next, after the exposed masks 10D and 10E of the silicon substrate 1A integrated with the glass substrate 7A are dissolved and removed, as shown in FIG. 3I, a recess 6Aa of the glass substrate 6A is formed on the surface of the silicon substrate 1A. The surface on which the aluminum layer 8 is deposited is brought into close contact with the anodic bonding. That is, in almost the same environment as in the case of anodic bonding between the silicon substrate 1A and the glass substrate 7A, a DC voltage is applied so that the glass substrate 7A side is a negative electrode (−) and the glass substrate 6A side is a positive electrode (+). To join directly. Next, as shown in FIG. 1, an aluminum thin film 9 having a thickness of about 3 μm is deposited on the surface of the silicon substrate 1A at a position where the glass substrate 7A can be seen through each through hole 7Aa, thereby completing the acceleration sensor.

  The above-described manufacturing method shown in FIG. 3 is characterized in that when the gap G for separating the fixed electrodes 2A, 3A and the mass body 4Aa is formed on one main surface of the silicon substrate 1A, as shown in FIG. Since 1A is before anodic bonding with the glass substrate 7A, the mask 10D for forming the narrow groove 1Aa requires high-temperature treatment at 1000 ° C. or higher, but has extremely excellent adhesion to the surface of the silicon substrate 1A. A silicon film can be formed, and in wet etching using a potassium hydroxide aqueous solution, the etching solution does not enter between the bonding surface of the silicon substrate 1A and the silicon dioxide film, and a gap with an extremely excellent high aspect ratio. G is obtained.

  The mass body 4Aa obtained as described above is used as the movable part mass of the sensing unit, and the fixed electrodes 2A and 3A that face each other at the gap G and the facing surfaces 4Ad and 4Ae of the mass body 4Aa that face the fixed electrodes 2A and 3A are sensed. The acceleration applied to the displaceable direction of the mass body 4Aa is measured by measuring the change in the capacitance C of the counter electrode.

Embodiment 2. FIG.
A second embodiment of the present invention will be described with reference to FIGS. FIG. 4 is a schematic diagram showing a cross section of a capacitive acceleration sensor, and FIG. 5 is a schematic diagram for explaining a manufacturing method of the capacitive acceleration sensor. The capacitive acceleration sensor shown in FIG. 4 is different from the capacitive acceleration sensor of Embodiment 1 shown in FIG. 1 in its manufacturing method, which will be described later, and the silicon substrate 1A is formed to a thickness of about 70 μm. Except for the point that the gold / chrome layer 8A is formed as a cushioning material provided in the recess 6Aa of the glass substrate 6A, that is, the point that the chromium layer is deposited on the recess 6Aa and the gold layer is deposited thereon. Except for this, the structure is the same as that shown in FIG. 1, and the description of the structure shown in FIG. 4 is omitted. Reference numeral 10F denotes a mask to be described later attached to the main surface of the silicon substrate 1A.

  Next, a method of manufacturing the acceleration sensor shown in FIG. 4 will be described based on FIGS. 5J to 5M. The manufacturing method of the first embodiment shown in FIG. 3 is that the order of forming the narrow groove 1Aa and the groove 1Ab for the silicon substrate 1A and the order of forming the recess 1Ac and the groove 1Ae are reversed. This is a major difference, and the other steps are almost the same as the manufacturing method shown in FIG.

  That is, as shown in FIG. 5J, a mask 10F made of a silicon dioxide film is provided on one surface of a silicon substrate 1A having a thickness of about 250 μm, and etching is performed to leave a convex portion 1Ad in the central portion. Recess 1Ac and groove 1Ae are formed, and as shown in FIG. 5K, mask 10F is re-deposited on the formation surface of recess 1Ac to form recess 6Aa in glass substrate 6A, and gold / chrome layer 8A is deposited. The surface and the formation surface of the recess 1Ac of the silicon substrate 1A are brought into close contact and integrated by anodic bonding, and then the surface of the silicon substrate 1A is wrapped off to a thickness of about 70 μm.

  Next, as shown in FIG. 5L, a mask 10G made of a silicon nitride film that can be formed at a relatively low temperature is provided on the surface of the silicon substrate 1A, and selective silicon anisotropic etching is performed to perform fine grooves 1Aa and 1Ab. And the gaps 1Ac and grooves 1Ae previously formed are communicated with each other to form the gap G and the gap ZA.

  Next, after the exposed masks 10F and 10G of the silicon substrate 1A integrated with the glass substrate 6A are dissolved and removed, as shown in FIG. 5M, the main surface of the silicon substrate 1A and the formation surface of the recess 7Ab in the glass substrate 7A Then, an aluminum thin film 9 having a thickness of about 3 μm is deposited on the silicon substrate 1A at a position seen from the through hole 7Aa of the glass substrate 7A to complete the acceleration sensor as shown in FIG.

  According to the above-described manufacturing method shown in FIG. 5, since the silicon substrate 1A is anodically bonded to the glass substrate 6A as the mask 10G for forming the narrow groove 1Aa, nitridation that can be formed at a relatively low temperature. A silicon film is formed. Since the etching for forming the narrow groove 1Aa is the last wet etching, there is no fear that the formed fine groove 1Aa is exposed to a subsequent etching solution and deformed, and the processing process is simplified.

  Further, since the recess 1Ac and the groove 1Ae formed by the first wet etching have a sufficiently wide opening width with respect to the etching depth, they can be formed at substantially the same depth by simultaneous etching. Accordingly, in order to form the mass body 4Aa having a thickness of about 50 μm, the silicon substrate 1A integrated with the glass substrate 6A is formed, the recess 1Ac and the groove 1Ae are formed to a depth of about 20 μm, and then the thickness is about 70 μm. Wrapping off was performed, and a very light mass 4Aa having a convex portion 4Ab thickness of about 20 μm was obtained.

  However, in the case of the manufacturing method shown in FIG. 5, since the buffer material layer provided in the recess 6Aa of the glass substrate 6A is exposed to the etching liquid in the subsequent process, the aluminum layer 8 can withstand the exposure of the etching liquid. Therefore, it is necessary to select a gold / chromium layer 8A having excellent resistance to the etching solution.

  In the manufacturing method according to the second embodiment shown in FIG. 5, silicon dioxide films are formed on both main surfaces of the silicon substrate 1A before integration with the glass substrate 6A, and after integration with the glass substrate 6A. If the gap G is formed using the formed silicon dioxide film as a mask without wrapping off, the gap G having the same high aspect ratio as that in the manufacturing method shown in FIG. 3 can be obtained.

  However, if a silicon wafer having a thickness of about 250 μm is used as the silicon substrate 1A, it is necessary to form the recess 1Ac and the groove 1Ae having a depth of about 200 μm in order to obtain the mass body 4Aa having a thickness of about 50 μm. In addition, a silicon wafer that is as thin as possible is selected as long as it is acceptable for handling.

  As described above, the capacitive acceleration sensor as the first embodiment or the second embodiment is subjected to careless handling before being put to practical use, for example, a large impact is applied due to dropping, and the mass body 4Aa is shown on the drawing. Even when it suddenly displaces in the vertical direction, that is, in the direction perpendicular to the surface of the silicon substrate 1A and collides with the opposing surface of the glass substrates 6A and 7A, it opposes the mass body 4Aa on the glass substrate 6A through a gap of about 10 μm An aluminum layer 8 or a gold / chrome layer 8A as a buffer material is deposited on the opposing surface, and shock is buffered, so that there is very little risk of damage due to collision.

  In the capacitive acceleration sensor as the first embodiment or the second embodiment, the aluminum layer 8 or the gold / chrome layer 8A as the buffer material is attached to the recess 6Aa of the glass substrate 6A. The deposition position is not limited to the concave portion 6Aa of the glass substrate 6A, and a similar impact resistance effect can be obtained even if it is formed on the convex portion 7Ac of the glass substrate 7A. Moreover, even if it forms in at least any one of the opposing surface 4Ac with the glass substrate 6A in convex part 4Ab of mass body 4Aa, and the opposing surface with the glass substrate 7A in mass body 4Aa, an impact-resistant effect is acquired.

  In particular, if it adheres to the recess 6Aa of the glass substrate 6A and also adheres to the surface 7Ad facing the mass body 4Aa of the projection 7Ac of the glass substrate 7A, a more reliable buffering effect can be obtained.

Embodiment 3 FIG.
A third embodiment of the present invention will be described with reference to FIG. FIG. 6 is a schematic diagram showing a cross section of a capacitive acceleration sensor. In FIG. 6, reference numeral 11 denotes a silicon nitride film as an adhesion preventing means provided on the surface of the convex portion 7Ac of the glass substrate 7A facing the mass body 4Aa of the movable electrode 4A. The capacitive acceleration sensor shown in FIG. 6 is the same as the capacitive acceleration sensor shown in FIG. 1 except that the silicon nitride film 11 as an adhesion preventing means is deposited on the glass substrate 7A. Description of the structure is omitted.

  The silicon nitride film 11 deposited on the convex portion 7Ac of the glass substrate 7A has a thickness of about 1 μm, and is mirror-finished while being exposed to a high temperature during the anodic bonding between the silicon substrate 1A and the glass substrate 7A. Even if the mass body 4Aa is adsorbed to the glass substrate 7A, the phenomenon that the mass body 4Aa and the glass substrate 7A are chemically bonded due to the presence of the silicon nitride film 11 can be prevented. It is possible to prevent the trouble that the operation cannot be performed without leaving and the acceleration cannot be measured.

  In the third embodiment shown in FIG. 6, the silicon nitride film 11 as the adhesion preventing means is deposited on the convex portion 7Ac of the glass substrate 7A, but the deposition position of the silicon nitride film 11 is the same as that of the glass substrate 7A. It is not limited to the convex portion 7Ac, but may be formed on the surface of the mass body 4Aa facing the glass substrate 7A, that is, of the facing surfaces of the mass body 4Aa and the glass substrate 6A or the glass substrate 7A during anodic bonding. Even if it is formed on any of the opposing surfaces on the side where it can be adsorbed, a corresponding adhesion preventing effect can be obtained.

  Further, the material for the adhesion preventing means need not be limited to the silicon nitride film 11 and may be a thin film made of a different material from the glass substrates 6A and 7A. For example, an aluminum layer 8 or a gold / chrome layer as a buffer material Even with 8A or the like, an adhesion preventing effect can be obtained.

Embodiment 4 FIG.
Embodiment 4 of the present invention will be described with reference to FIGS. FIG. 7 is a schematic diagram showing a cross section of a capacitive acceleration sensor, and FIGS. 8 and 9 are schematic diagrams for explaining a method of manufacturing the capacitive acceleration sensor. In FIG. 7, reference numeral 1B denotes a silicon substrate, and an acceleration sensing portion and an outer frame 5B made up of the fixed electrodes 2B and 3B and the movable electrode 4B are formed by etching. The glass substrates 6 and 7B made of borosilicate heat-resistant glass close to silicon are anodically bonded.

  The fixed electrode 2B includes a fixed electrode terminal portion 2Ba, the fixed electrode 3B includes a fixed electrode terminal portion 3Ba, and the movable electrode 4B serves as a movable portion disposed between the fixed electrode 2B and the fixed electrode 3B. It consists of a mass body 4Ba, a movable electrode terminal portion (not shown) as an anchor, and a beam (not shown) connecting the movable electrode terminal portion and the mass body 4Ba, and the mass body 4Ba faces the glass substrate 6 A recess 4Bb is formed on the surface. Further, the glass substrate 7B has an uneven surface 7Bd as a non-mirror surface formed by sandblasting with rough sand on the convex portion 7Bc as an adhesion preventing means for preventing adhesion with the mass body 4Ba on the surface of the convex portion 7Bc.

  A major difference from the first to third embodiments shown in FIGS. 1, 4 and 6 is that a recess 4Bb is formed on the surface of the mass body 4Ba facing the glass substrate 6, The concave portion 4Bb has a flat bottom surface, the peripheral edge portion 4Bc forms an inclined surface, and a gap G is opened on the inclined surface. As a result, the mass body 4Ba has a shape in which the central portion is hollowed out, and the mass body 4Ba having a reduced area specific mass of the opposing surfaces 4Bd and 4Be is obtained.

  Further, the glass substrate 7B is different from the glass substrate 7A shown in FIG. 6 in that a rough uneven surface 7Bd which is a non-mirror surface is formed on the surface of the convex portion 7Bc. The uneven surface 7Bd has a role as an adhesion preventing means for the mass body 4Ba as the silicon nitride film 11 as an adhesion preventing means for the glass substrate 7A shown in FIG.

  Next, a method for manufacturing the capacitive acceleration sensor shown in FIG. 7 will be described with reference to FIG. 8N is a process for manufacturing a silicon substrate 1B and a glass substrate 7B which are integrally joined, that is, a wafer-like silicon substrate having a mirror orientation of both sides and a thickness of about 250 μm and a crystal orientation of (110). The narrow groove 1Ba and the groove 1Bb are formed on one surface of 1B, and the concave surface 7Bb formation surface of the glass substrate 7B and the fine groove 1Ba and groove 1Bb formation surface of the silicon substrate 1B are formed by anodic bonding while leaving the mask 10D. The process of integrating and wrapping off the exposed surface of the silicon substrate 1B to a predetermined thickness is the same as the manufacturing method of the capacitive acceleration sensor as the first embodiment shown in FIG.

  First, as shown in FIG. 8O, a silicon nitride mask 10H is deposited on the surface of a silicon substrate 1B integrated with a glass substrate 7B, and a potassium hydroxide aqueous solution having a concentration of about 32% by weight or more is selectively used. By performing silicon anisotropic etching to form concave portions 1Bc and grooves 1Bd having a predetermined thickness and communicating with the previously formed narrow grooves 1Ba and grooves 1Bb, gaps G and gaps ZB are formed.

  This manufacturing method is characterized in that, when the recess 1Bc is formed, anisotropic etching is performed using a potassium hydroxide aqueous solution having a concentration of about 32% by weight or more as an anisotropic etching solution. That is, anisotropic etching is performed on a silicon wafer having a crystal orientation of (110) using a potassium hydroxide aqueous solution having a concentration of about 32% by weight or more along a plane having a crystal orientation of (111). As a result, as shown in an enlarged view in FIG. 8P, the cross-sectional shape of the recess 1Bc is such that the peripheral wall is vertical and the bottom surface is flat, and the inclined surface 1Be is at the end where the peripheral wall and the bottom surface are in contact. It is formed. Then, the inclined surface 1Be and the fine groove 1Ba formed in the previous etching process intersect and communicate with each other, and a gap G is formed.

  Thereafter, through the same manufacturing process as in the case of the first embodiment shown in FIG. 3, as shown in FIG. 7, a mass body 4Ba is provided in which the mass ratio of the facing surface to the fixed electrodes 2B and 3B is greatly reduced. A capacitive acceleration sensor is completed.

  In the manufacturing method shown in FIG. 8, the narrow groove 1Ba is formed before anodic bonding with the glass substrate 7B when the gap G is formed in the silicon substrate 1B, as in the manufacturing method of the first embodiment shown in FIG. Therefore, the mask 10D made of a silicon dioxide film having extremely excellent adhesion can be formed, and the etching solution does not enter the bonding surface between the silicon substrate 1B and the silicon dioxide film, so that a gap G having an excellent high aspect ratio can be obtained. .

  Next, another manufacturing method of the capacitive acceleration sensor shown in FIG. 7 will be described with reference to FIG. 8 differs from the manufacturing method shown in FIG. 8 in that the order of forming the narrow grooves 1Ba and 1Bb on the silicon substrate 1B and the order of forming the recesses 1Bc and 1Bd are reversed.

  That is, the mask 10H is deposited on the silicon substrate 1B, and anisotropic etching is selectively performed using an aqueous potassium hydroxide solution having a concentration of about 32% by weight or more as an anisotropic etching solution. Are formed in a concave portion 1Bc and a groove 1Bd having an inclined surface at the end where the peripheral wall and the bottom face are in contact with each other, and the mask 10H is re-deposited on the surface where the concave portion 1Bc is formed. After the silicon substrate 1B and the formation surface of the recess 1Bc are brought into close contact and integrated by anodic bonding, the silicon substrate 1B is wrapped to a predetermined thickness to obtain the one shown in FIG. 9Q.

  Next, as shown in FIG. 9R, a mask 10G made of a silicon nitride film is deposited on the surface of the silicon substrate 1B, and anisotropic etching is selectively performed to form narrow grooves 1Ba and grooves 1Bb. As shown in an enlarged manner, the inclined surface 1Be of the previously formed recess 1Bc and the narrow groove 1Ba are communicated to form a gap G. At the same time, as shown in FIG. 9R, the groove 1Bb and the groove formed in the previous etching step are formed. 1Bd communicates to form a gap ZB.

  Thereafter, through a manufacturing process similar to that of the first embodiment shown in FIG. 5, a capacitive acceleration sensor including the mass body 4Ba in which the area ratio mass of the surface facing the fixed electrodes 2B and 3B is greatly reduced is completed. . As shown in FIGS. 9R and 9S, the remaining portion of the mask 10H exists at a position sandwiched between the silicon substrate 1B and the glass substrate 6 and is different from that shown in FIG. There is no difference in performance.

  In the manufacturing method shown in FIG. 9, since the narrow groove 1Ba is formed after anodic bonding with the glass substrate 6 when the gap G is formed, a silicon nitride film that can be formed at a relatively low temperature is formed as the mask 10G. In addition, since the etching for forming the fine groove 1Ba is the last wet etching, the formed fine groove 1Ba is not exposed to a subsequent etching solution and is not deformed, and the processing process is simplified.

  As described above, the capacitive acceleration sensor as the fourth embodiment has a smaller mass and lighter weight than the area of the opposing surfaces 4Bd and 4Be facing the fixed electrodes 2 and 3 in the mass body 4Ba. Is relatively small and excellent in responsiveness, and the impact received by dropping is small, and troubles such as breakage are unlikely to occur.

  In the fourth embodiment shown in FIG. 7, the uneven surface 7Bd, which is a non-mirror surface, is formed on the surface of the convex portion 7Bc of the glass substrate 7B facing the mass body 4Ba as an adhesion preventing means. There is an effect of preventing the so-called adhesion that does not leave in close contact. If an adhesion preventing film such as the silicon nitride film 11 is formed on the uneven surface 7Bd, a further excellent adhesion preventing effect can be obtained by a synergistic effect.

  As described above, in the first to fourth embodiments, a heat-resistant glass substrate having a thermal expansion coefficient substantially equal to that of the silicon substrates 1A and 1B is used as the protective cover, but this is limited to a heat-resistant glass material. Any material that can mechanically protect and electrically insulate the acceleration sensing portions formed on the silicon substrates 1A and 1B may be used. For example, even if a silicon substrate is used, the surface of the silicon substrate may be used. A similar effect can be obtained if an insulating film such as a silicon oxide film is formed.

  In the first to fourth embodiments, a heat-resistant glass substrate having a thickness of about 400 μm is used. However, the thickness of the glass substrate is not necessarily limited to about 400 μm, for example, 50 μm to 1000 μm. It may be a range. That is, when the glass substrate has a lower limit of 50 μm or more, good handling properties can be obtained in a series of bonding work steps such as sandblasting, alignment with a silicon substrate and anodic bonding, and an upper limit of 1000 μm. When the thickness is as follows, anodic bonding is easy and it is difficult to cause bonding failure.

  In the first to fourth embodiments, the anisotropic etching of the silicon substrates 1A and 1B was performed by wet etching using an aqueous potassium hydroxide solution as an etchant when forming the acceleration sensing unit. The anisotropic etching of the silicon substrates 1A and 1B is not limited to wet etching. For example, even if dry etching using active gas plasma is performed, the silicon substrate 1A or 1B has a mass body or gap G with the same accuracy. can get.

  In the first to third embodiments, the protrusion 4Ab is formed on the mass body 4Aa and the cross-sectional shape of the mass body 4Aa is formed in a T shape. However, the cross-sectional shape of the mass body 4Aa is a T shape. For example, the same effect can be obtained by forming a plurality of narrow convex portions (not shown). Further, in the fourth embodiment, the mass body 4Ba is not formed to correspond to the above-described convex portion, but a convex portion (not shown) is provided at the substantially central portion of the mass body 4Ba facing the glass substrate 6 side. ) To restrict the displacement of the mass body 4Ba in the direction of the surface facing the glass substrate 6.

It is a schematic diagram which shows the cross section of the capacitive acceleration sensor as Embodiment 1 of this invention. It is a schematic diagram for description of the manufacturing method of the glass substrate in the capacitive acceleration sensor shown in FIG. It is a schematic diagram for description of a manufacturing method of the capacitive acceleration sensor shown in FIG. It is a schematic diagram which shows the cross section of the capacitive acceleration sensor as Embodiment 2 of this invention. It is a schematic diagram for description of the manufacturing method of the capacitive acceleration sensor shown in FIG. It is a schematic diagram which shows the cross section of the capacitive acceleration sensor as Embodiment 3 of this invention. It is a schematic diagram which shows the cross section of the capacitive acceleration sensor as Embodiment 4 of this invention. FIG. 8 is a schematic diagram for explaining a manufacturing method of the capacitive acceleration sensor shown in FIG. 7. It is a schematic diagram for description of another manufacturing method of the capacitive acceleration sensor shown in FIG. It is a top view of the conventional capacitive acceleration sensor. It is a schematic diagram which shows the cross section of the conventional capacitive acceleration sensor shown in FIG.

Explanation of symbols

1A, 1B silicon substrate, 1Aa, 1Ba narrow groove, 1Ac, 1Bc recess, 1Be inclined surface, 2A, 2B, 3A, 3B fixed electrode, 4A, 4B movable electrode, 4Aa, 4Ba movable part, 4Ab convex part, 4Bb concave part, 5A, 5B Outer frame, 6, 6A, 7A, 7B Glass substrate, 7Ac, 7Bc Convex, 7Bd Concavity and convexity, 8 Aluminum layer, 8A Gold / chromium layer, 11 Silicon nitride film

Claims (3)

  In the capacitive acceleration sensor comprising: a movable electrode having a movable portion disposed between a pair of fixed electrodes; and a pair of protective covers disposed to face each other with a gap between the movable portions. Prevention of adhesion of the opposed surfaces of the pair of protective covers and the movable portion to at least one of the opposed surfaces of the cover to the movable portion or at least one of the opposed surfaces of the movable portion to the pair of protective covers. A capacitive acceleration sensor comprising an adhesion preventing means.   2. The capacitive acceleration sensor according to claim 1, wherein the adhesion preventing means is made of a different material film different from the material of the protective cover deposited on the surface of the protective cover. 2. The capacitive acceleration sensor according to claim 1, wherein the adhesion preventing means is formed by forming the surface of the protective cover into a non-mirror surface.

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