JPH0748566B2 - Acceleration sensor and manufacturing method thereof - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an acceleration sensor for detecting acceleration such as an earthquake, movement of an object, collision, and the like, and a manufacturing method thereof.

[Conventional technology]

FIG. 6 is a sectional view showing an example of a conventional acceleration sensor. In the figure, 1 is a silicon substrate, 2 is a groove formed by etching on the back surface side of the silicon substrate 1 in a square shape having a substantially trapezoidal cross section, and 3 is a trapezoid formed by forming the groove 2 in the silicon substrate 1. The island-shaped thick inertial mass portions 4 are thin-walled straining portions as movable portions that suspend and support the inertial mass portion 3 by forming the grooves 2 in the silicon substrate 1. The silicon chip 1, the groove 2, the inertial mass portion 3 and the strain generating portion 4 constitute the sensor chip 5. Further, 6 is an electrode lead-out portion formed on the front surface side of the silicon substrate 1, 7 is an upper cap fixedly arranged on the front surface side of the silicon substrate 1 by covering the inertial mass portion 3, and 8 is an inner surface of the upper cap 7. An upper electrode formed to face the inertial mass portion 3, a lower cap 9 fixedly arranged on the back surface side of the silicon substrate 1 so as to cover the inertial mass portion 3,
Reference numeral 10 is a lower electrode formed on the inner surface of the lower cap 9 so as to face the inertial mass portion 3, and 11 is a capacitance forming portion formed of a void portion.

In such a configuration, when acceleration is applied to the sensor,
The position of the inertial mass part 3 is displaced, the capacitance value is changed between the upper electrode 8 and the lower electrode 10 which face each other, and the acceleration is detected. On the other hand, if excessive acceleration is applied,
The upper and lower caps 7 and 9 play the role of stoppers, and have a structure that prevents damage due to excessive deformation of the strain-flexing part 4.

[Problems to be Solved by the Invention]

However, the acceleration sensor configured in this way is
The sensor chip 5, the upper cap 7, and the lower cap 9 are composed of three main constituent members, and these three constituent members have dimensional variations. There was a problem. That is, (a) it was extremely difficult to align the three components at the time of assembling.

(B) Since the completed dimensions of the gap between the upper cap 7 and the lower cap 9 and the sensor chip 5 greatly vary,
It is difficult to design a high-sensitivity acceleration sensor because it is necessary to allow a sufficient withstand voltage.

(C) Since the bottom surface of the inertial mass portion 3 is configured to directly contact the stopper, the degree of freedom in designing the shape of the inertial mass portion 3 and the shape of the lower plate is small.

Therefore, the present invention has been made to solve the above-described conventional problems, and an object thereof is to improve the sensitivity to acceleration and to make the acceleration sensor small in size and capable of mass production with high breakdown voltage, and to manufacture the same. To provide a method.

[Means for Solving the Problems]

In order to solve such a problem, in the acceleration sensor according to the present invention, a groove having an L-shaped cross-sectional structure having a constant gap width is formed in a silicon substrate, and a silicon thin-walled shape is formed on a surface portion of the silicon substrate. A pair of strain generating portions are formed, and a thick silicon inertial mass portion is suspended and supported between the strain generating portions.

Further, in the method of manufacturing an acceleration sensor according to the present invention, after forming a groove on one surface of the first silicon substrate, a second silicon substrate serving as a strain-generating portion is adhered on the groove, and the above-mentioned method is performed from the other surface. By forming a groove having an L-shaped cross-sectional structure by forming a groove connected to the groove of No. 3, a thin-walled silicon strain element is formed on the surface portion of the silicon substrate.

[Action]

In the present invention, the L-shaped groove is formed in the silicon substrate with a constant gap width with high accuracy.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a sectional view showing an embodiment of an acceleration sensor according to the present invention, and the same parts as those in the above-mentioned drawings are designated by the same reference numerals. In the figure, the back surface parallel to the front surface of the silicon substrate 1 is defined as the (110) plane of the crystal plane, and the back surface is along the <112> axis of the crystal plane in a direction perpendicular to the (110) plane of the crystal plane. A pair of L-shaped grooves 2a 'and 2b', which are etched by anisotropic etching and have a substantially inverted L-shaped cross section, are formed in parallel with a constant gap. Then, the inverted L-shaped grooves 2a ′, 2
Due to the formation of b ′, a pair of strain-generating portions 4a, 4b, which are thin portions of the silicon substrate 1, are formed on the upper portion of the silicon substrate 1, and between the pair of strain-generating portions 4a, 4b are almost formed. An inertial mass portion 3'consisting of a thick-walled portion of a silicon substrate 1 having a rectangular parallelepiped is supported and formed, and the inertial mass portion 3'is further formed.
A lower electrode 10 is formed so as to face the surface of the lower electrode.

With such a configuration, the inertial mass portion 3'is not a mesa type but a rectangular parallelepiped having an arbitrary size, so that the mass thereof is increased and the sensitivity can be improved. Also, a pair of grooves 2
By forming a ′ and 2b ′ in the inverted L shape on the silicon substrate 1, acceleration is applied to the capacitance forming portion 11, and the inertial mass portion 3 ′ is formed.
Even if the inertial force F is applied downward, as shown in FIG. 2, a pair of thin-walled strain generating portions 4a, 4b are formed at the respective corners 1a, 1b in the inverted L-shaped grooves 2a ', 2b'. Even if a large acceleration is applied due to the contact and support, and a large inertial force F'is applied to the inertial mass portion 3 ', as shown in FIG.
The a and 4b can contact the corners 1a and 1b with the fulcrums 4A and 4B as fulcrums, and can support the bottom of the inertial mass part 3'to the extent of contact with the base. Therefore, even with an excessive acceleration, the function as a final stopper having a two-step stance can be obtained, and it is possible to prevent destruction due to further deformation.

FIG. 4 is a cross-sectional view showing another embodiment of the acceleration sensor according to the present invention, and the same parts as those in the above-mentioned drawings are designated by the same reference numerals. In this figure, the point that is different from FIG. 1 is that the surface of the silicon substrate 1 is the (100) plane, and
Anisotropic etching is performed on the (0) plane to
10> The acceleration sensor is configured by forming the grooves 2a ″, 2b ″ along the axial direction.

Even in such a configuration, the same effect as described above can be obtained.

5 (a) to 5 (g) are sectional views of steps for explaining an embodiment of the method of manufacturing the acceleration sensor according to the present invention. In the figure, first, as shown in FIG. 3A, an etching mask material 2 such as Si ₃ N ₄ is formed on the surface of the P-type silicon substrate 1.
After depositing the film 1 on the etching mask material 21, the reverse L
A pair of window patterns 21a, 21b corresponding to the portions parallel to the surface of the silicon substrate 1 in the character-shaped grooves 2a ', 2b' are formed by patterning by the photolithography technique, and inside the pair of window patterns 21a, 21b. After anisotropic etching is performed with an etching liquid such as KOH to form the pair of grooves 22a and 22b, the etching mask material 21 is removed. Next, as shown in FIG. 3B, in the pair of grooves 22a, 22b, not shown in the portions of the inverted L-shaped grooves 2a ', 2b' which are perpendicular to the surface of the silicon substrate 1, for example, a thermal oxide film is formed. A mask material is deposited, and phosphorus or the like is thermally diffused on the surface of the silicon substrate 1 and in the pair of grooves 22a and 22b to form the n-type impurity diffusion layer 23. Next, an etching mask material of Si ₃ N ₄ is formed on the back surface side of the silicon substrate 1 by the same method as described above, and anisotropic etching is performed with KOH to form a groove 24 in the portion which becomes the inertial mass portion 3 '. To form. Next, as shown in FIG. 3D, on the silicon substrate 1 having the n-type impurity diffusion layer 23 formed on its surface,
A p-type silicon substrate 26 having an n-type epitaxial layer 25 formed on one surface is subjected to a fusion bond in an oxidizing atmosphere of, for example, 1000 to 1100 ° C. to form the n-type epitaxial layer 25.
The sides are directly joined and integrated. Next, the silicon substrate 26 having the n-type epitaxial layer 25 formed thereon is dipped in, for example, a KOH solution to form the silicon substrate 1 having the n-type impurity diffusion layer 23 formed thereon.
When a positive potential of about several to 10 V is applied to the etching, etching stops at the n-type epitaxial layer 25 as shown in FIG. 7E, and the silicon substrate 26 shown in FIG. Etching is removed. Next, as shown in FIG. 3F, after the lower electrode 10 and the electrode lead-out portion 6 are formed at predetermined positions on the surface of the n-type epitaxial layer 25, Si ₃ is formed on the back surface side of the silicon substrate 1 by the same method as described above. When an etching mask material of N ₄ is formed and dipped in a KOH solution, and etching is performed by applying a positive voltage of about several tens to several tens of volts to the n-type epitaxial layer 25, etching is performed on the n-type epitaxial layer 25 and the n-type epitaxial layer 25. Etching stops at the impurity diffusion layer 23, and a pair of inverted L-shaped grooves 26a, 26b communicating with the pair of grooves 22a, 22b described above are formed. Next, as shown in FIG. 2G, a Pyrex cap 7 having an upper electrode 8 formed on the inner surface of the n-type epitaxial layer 25 is bonded by an anodic bonding method to obtain an acceleration sensor equivalent to that shown in FIG. Will be completed.

According to such a method, the pair of inverted L-shaped grooves 2a 'and 2b' for suspending and supporting the inertial mass portion 3'is formed in the silicon substrate 1 by the anisotropic etching and electric field etching techniques of the silicon substrate 1. Since it can be formed by etching a pair of grooves 22a and 22b parallel to the surface of the silicon and vertical grooves 26a and 26b that communicate with each other, the surface of the silicon substrate 1 has a pair of strain generating portions.
4a and 4b can be formed with a high sensitivity structure, and this pair of strain generating portions 4a and 4b and the corner portions 1a and 1b that stop the excessive displacement of the inertial mass portion 3'can be formed at precise positions with high precision. it can. In addition, the above-described steps can be mass-produced because 500 to 1000 pieces can be formed at a time from a φ4 ″ wafer as in the normal IC manufacturing process.

〔The invention's effect〕

As described above, according to the present invention, a pair of L-shaped grooves having a constant gap width are formed in a silicon substrate, and a pair of silicon thin strain elements are formed on the surface portion of the silicon substrate. By supporting the thick silicon inertial mass between the pair of strain generating parts, high sensitivity and high withstand voltage can be achieved, and the degree of freedom in designing the contradictory characteristics of high sensitivity and high withstand voltage is greatly increased. Be expanded to. Further, the sensor chip having the lower electrode formed on the surface and the cap having the upper electrode formed on the inner surface are arranged to face each other, so that the main constituent members are reduced from the conventional three points to two points, and the size can be reduced. It is possible to obtain an extremely excellent effect such as

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the acceleration sensor according to the present invention, FIGS. 2 and 3 are sectional views for explaining the operation of the acceleration sensor of FIG. 1, and FIG. 4 is a sectional view of the acceleration sensor according to the present invention. 5 (a) to 5 (g) are sectional views of steps showing an embodiment of a method of manufacturing an acceleration sensor according to the present invention, and FIG. 6 shows a structure of a conventional acceleration sensor. It is sectional drawing shown. 1 ... Silicon substrate, 1a, 1b ... Corner, 2a ', 2a ", 2b',
2b "... Groove, 3 '... Inertia mass part, 4a, 4b ... Strain element, 4
A, 4B ...... fulcrum, 6 ...... electrode extraction part, 7 ...... upper cap, 8 ...... upper electrode, 10 ...... lower electrode, 11 ...... capacitance forming part, 21 ...... etching mask, 21a, 21b ...... Window pattern, 22a, 22b ... Groove, 23 ... N-type impurity diffusion layer, 24 ...
Groove, 25 ... n-type epitaxial layer, 26a, 26b ... Inverted L-shaped groove.

Claims (2)

[Claims] 1. A first groove having a constant gap width in a direction perpendicular to the surface of the silicon substrate on one surface of the silicon substrate, and a bottom portion of the first groove, the first groove being connected to the end surface direction of the silicon substrate. A second groove having a predetermined gap width in the direction parallel to the silicon substrate is formed on the other surface of the silicon substrate by providing a groove having an L-shaped cross section in the direction perpendicular to the silicon substrate. And a pair of silicon thin-walled strain generating portions, an inertial mass portion including a thick silicon portion suspended and supported along the direction of the first groove between the pair of strain generating portions, and the other of the silicon substrates. And a lower electrode formed on a surface of the surface opposite to the inertial mass portion and the second groove, and bonded to the other surface of the silicon substrate so as to cover the pair of strain-flexing portions. An insulating cap, and the insulating cap An acceleration sensor, comprising: an upper electrode disposed on the inner surface of the cup so as to face the lower electrode. 2. A step of forming a pair of second grooves parallel to a surface of the silicon substrate on one surface of a first first conductivity type silicon substrate, and a center in the pair of second grooves. A step of forming a second conductivity type impurity diffusion layer on one surface of the first first conductivity type silicon substrate except the side; and a step of forming the second conductivity type impurity diffusion layer on the other surface of the first first conductivity type silicon substrate. A step of forming a third groove having a corresponding positional relationship between the pair of second grooves, and a second first conductivity type silicon substrate having a second conductivity type epitaxial layer formed on one surface thereof Bonding the second conductivity type epitaxial layer to the second conductivity type impurity diffusion layer forming surface of the first first conductivity type silicon substrate, and the second first conductivity type silicon substrate. Is immersed in an etching solution and no positive potential is applied to the second conductivity type epitaxial layer. The step of etching away the first conductivity type portion of the second first conductivity type silicon substrate, and the positional relationship between the pair of second grooves on the surface of the second conductivity type epitaxial layer. A step of forming a lower electrode on the surface having the first conductive type silicon substrate, immersing the first first conductive type silicon substrate in an etching solution, and applying a positive potential to the second conductive type epitaxial layer; A predetermined portion in the groove of the first groove is etched to connect with the center side in the pair of second grooves.
And a step of adhering an insulative cap having an upper electrode formed in an inner recess on the surface of the second-conductivity-type epitaxial layer.