JPH05340959A - Fabrication of semiconductor acceleration sensor - Google Patents

Abstract

PURPOSE:To fabricate an acceleration sensor in which movable and fixed electrodes are formed on a same substrate and the movable electrode displaces in parallel with a silicon substrate. CONSTITUTION:An epitaxial layer 24 is formed on a silicon substrate 23 and two trenches are made therein. An oxide 26 is then formed on the side wall of the trench followed by formation of an epitaxial layer 70 therein. The epitaxial layer 70 is then partially implanted with impurities to form fixed electrodes 16, 17. The epitaxial layer 24 is subsequently removed selectively followed by selective removal of the silicon substrate 23 immediately below a movable electrode 15, the oxide 26, and the fixed electrodes 16, 17. subsequently, the oxide 26 is removed thus isolating the movable electrode 15 from the fixed electrodes 16, 17. Acceleration can be detected by detecting the capacitances of the fixed electrodes 16, 17.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor for detecting acceleration applied to an object, and more particularly to a method of manufacturing an acceleration sensor having a semiconductor structure.

[0002]

2. Description of the Related Art There is a conventional semiconductor acceleration sensor as disclosed in Japanese Patent Laid-Open No. 3-146872, which will be described with reference to FIG.

Beams 7, movable electrodes 5, and supporting members 8 are formed on a silicon substrate 1 by anisotropic etching. The movable electrode 5 is supported by the support member 8 by the beam 7,
The movable electrode 5 is displaced upward or downward in the drawing due to the bending. The silicon substrate 1 is sandwiched by the upper glass plate 2 and the lower glass plate 3 in close contact with each other in the vertical direction of the drawing. On the silicon substrate 1 side of the upper glass plate 2, an upper fixed electrode 4 is formed with a predetermined gap with the movable electrode 5. Similarly, a lower fixed electrode 6 is formed on the silicon substrate 1 side of the lower glass plate 3 with a predetermined gap with the movable electrode 5. A predetermined voltage is applied to the movable electrode 5 and the upper and lower fixed electrodes 4 and 6, and a predetermined capacitance is generated between the movable electrode 5 and the upper and lower fixed electrodes 4 and 6 by the application of this voltage. ..

If acceleration is applied to the acceleration sensor as shown in FIG. 22 and the acceleration sensor moves upward in the drawing, the movable electrode 5 is displaced downward in the drawing. Due to the displacement of the movable electrode 5, the gap between the movable electrode 5 and the upper and lower fixed electrodes 4 and 6 is changed, so that the electrostatic capacitance is changed, and this change is detected and applied to the acceleration sensor. Acceleration can be detected. Alternatively, the voltage applied between the movable electrode 5 and the upper and lower fixed electrodes 4 and 6 may be changed so that the capacitance does not change, and the acceleration applied to the acceleration sensor can be detected from the amount of change. it can.

[0005]

However, the conventional acceleration sensor has a silicon substrate on which movable electrodes are formed,
Adheres to the glass plate on which the upper and lower fixed electrodes are formed,
Since the structure is such that the gap between the movable electrode and the fixed electrode is joined to form a predetermined value, it is difficult to manage the gap such that the gap is made as designed. Therefore, when the voltage is applied to the electrodes, the applied voltage needs to be corrected in accordance with the gap, which is troublesome.

Further, in order to detect the displacement of the movable electrode in the direction perpendicular to the silicon substrate, only one-dimensional acceleration can be detected, and two-dimensional acceleration sensors having different displacement directions are mounted on the same silicon substrate. There was a problem that it could not be formed.

The present invention solves the above problems by providing a method of manufacturing an acceleration sensor in which a movable electrode and a fixed electrode are formed on the same substrate, and the displacement direction of the movable electrode is displaced parallel to the silicon substrate. Has a purpose.

[0008]

According to a first aspect of the present invention, in a method of manufacturing a semiconductor acceleration sensor having a beam and a movable electrode supported by the beam, a first epitaxial layer is formed on a semiconductor substrate. A step of selectively removing the first epitaxial layer up to the surface of the semiconductor substrate to form two symmetrical rectangular parallelepiped trenches, and forming an oxide film on the sidewalls of the two trenches. A step, a step of stacking a second epitaxial layer on the semiconductor substrate at the bottom of the two trenches in which the oxide film is formed, and a step of forming a fixed electrode on at least a part of opposing surfaces of the two second epitaxial layers. And the first
A step of selectively removing a part of the epitaxial layer to reach the surface of the semiconductor substrate to form the beam and the movable electrode; and at least a semiconductor substrate directly below the movable electrode and a semiconductor directly below the fixed electrode. It is composed of a step of simultaneously removing the substrate and the semiconductor substrate directly below the oxide film formed between the movable electrode and the fixed electrode, and a step of removing the oxide film.

According to a second aspect of the present invention, in a method of manufacturing a semiconductor acceleration sensor having a beam and a movable electrode supported by the beam, a step of forming a first epitaxial layer on a semiconductor substrate, and the first step. The epitaxial layer is selectively removed to reach the surface of the semiconductor substrate to form a substantially rectangular parallelepiped trench, a step of forming an oxide film on the side wall of the trench, and a step of forming a trench bottom portion where the oxide film is formed. Stacking a second epitaxial layer on a semiconductor substrate to form a first electrode, and selectively removing the first electrode to form the beam and the movable electrode, and the first epitaxial layer By selectively removing the two predetermined regions at the symmetrical positions of 2 to reach the semiconductor substrate.
Forming three symmetrical substantially rectangular parallelepiped third epitaxial layers, and forming fixed electrodes on at least a part of opposing surfaces of the two third epitaxial layers,
At least a step of simultaneously removing at least the semiconductor substrate immediately below the movable electrode, the semiconductor substrate immediately below the fixed electrode, and the semiconductor substrate immediately below the oxide film sandwiched between the movable electrode and the fixed electrode; It was composed of a step of removing the oxide film.

[0010]

Since the semiconductor acceleration sensor is manufactured in the above process, the gap between the movable electrode and the fixed electrode is formed by self-alignment of the semiconductor substrate, so that the gap can be easily controlled. .. Further, since this gap can be narrowed, the detection sensitivity can be improved.

Further, in order to detect lateral acceleration with respect to the semiconductor substrate, an acceleration sensor for detecting two-dimensional acceleration can be formed on the same semiconductor substrate.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

A first embodiment will be described with reference to FIGS.

FIG. 1 is a diagram showing the configuration of the first embodiment.
1A is a plan view, and FIG. 1B is a cross-sectional view taken along the line AA of FIG.

The movable electrode 15 is formed by the beam 14 on the silicon substrate 11
And the displacement direction of the movable electrode 15 is
Direction. The fixed electrodes 16 and 17 have a predetermined gap with respect to the movable electrode 15 so as to sandwich the movable electrode 15. Further, epitaxial layers 70 are adjacent to the side surfaces of the fixed electrodes 16 and 17 that are not on the movable electrode 15 side. In addition, fixed electrode 16,
Each of 17 is formed so as not to come into contact with the silicon substrate 23.

When a voltage is applied to the movable electrode 15 and the fixed electrodes 16 and 17, the movable electrode 15 and the fixed electrodes 16 and 17 have a predetermined capacitance. When acceleration is applied to the acceleration sensor, the movable electrode 15 is displaced leftward or rightward in the drawing with the beam 14 as a fulcrum. The displacement changes the electrostatic capacitance, and the acceleration can be detected by detecting the change.

Next, a method of manufacturing the acceleration sensor shown in FIG. 1 will be described with reference to FIGS.

FIG. 2A is a plan view and FIG. 2B is FIG.
It is an AA sectional view of (a).

The epitaxial layer 24 is formed on the silicon substrate 23, and the rear surface of the silicon substrate 23 and the epitaxial layer are formed.
Oxide films 25 and 20 are formed on the upper surface of 23, respectively. Next, the oxide film 20 formed on the upper surface of the epitaxial layer 23 is selectively etched to remove the oxide film 20, and further the portion of the epitaxial layer 24 from which the oxide film 20 has been removed is removed to form the trenches 21 and 22.
To form a structure as shown in FIG.

Next, as shown in the sectional view of FIG. 3, the entire surface (including the sidewalls of the trenches 21 and 22) of the structure shown in FIG. 2 is oxidized to deposit an oxide film 60.

Next, as shown in the sectional view of FIG. 4, only the oxide film 60 on the upper surface of the epitaxial layer 24 and on the upper surface of the silicon substrate 23 at the bottom of the trenches 21 and 22 is removed by etching. At this time, since the oxide films 20 and 60 formed on the epitaxial layer 24 are thicker than the oxide film 60 formed on the bottoms of the trenches 21 and 22, the surface of the silicon substrate 23 at the bottoms of the trenches 21 and 22 is Even if exposed, the oxide film 20 on the upper surface of the epitaxial layer 24 remains.

Next, as shown in FIG. 5, a silicon substrate 23
The epitaxial layers 23 are grown in the trenches 21, 22 whose surfaces are exposed by thermal oxidation or the like, and the trenches 21,
Epitaxial layers 70 are formed in the respective 22.

Next, the epitaxial layer 70 shown in FIG.
Impurities are injected and diffused into the epitaxial layer 70 portion so as to include the surfaces facing each other, and the fixed electrodes 16 and 17 are formed respectively.
Further, although the fixed electrodes 16 and 17 are formed by injecting and diffusing impurities in the present embodiment, it suffices that the electrodes are formed, so that they may be formed by depositing aluminum or the like.
However, in this case, the height of the epitaxial layer 70 formed in FIG. 5 in the drawing direction is formed lower than that of the present embodiment, and the fixed electrode is deposited (deposited) on the surface of the epitaxial layer 70. Then an oxide film on the surface of this structure
Forming 26. Further, the oxide film 25 formed on the back surface of the silicon substrate 23 is selectively removed by etching to form it as shown in FIG.

Next, the manufacturing process shown in FIG. 7 is performed. Figure 7
7A is a plan view, and FIG. 7B is a sectional view taken along line BB of FIG. 7A. The sectional view shown in FIG. 7B is a sectional view of a portion different from the portions shown in FIGS.

The oxide film 26 on the surface of the epitaxial layer 24 and the oxide film 25 on the back surface of the silicon substrate 23 are selectively etched, and the oxide film 26 on the epitaxial layer 24 is patterned to selectively select the epitaxial layer 24. To form trenches 27, 28 and trench 29.

Next, the manufacturing process shown in FIG. 8 is performed. Figure 8
8A is a cross-sectional view taken along the line AA shown in FIGS. 2 to 6, and FIG. 8B is a line BB taken along the line BB shown in FIG. 7.
A sectional view is shown.

The surface oxide film 26 on the epitaxial layer 24 is protected by a resin or the like, the pattern of the oxide film 25 on the back surface is used as a mask, and the silicon substrate 23 is removed from the back surface by anisotropic etching. Then, the resin is removed. This silicon substrate 23 is removed by etching as shown in FIG.
The process is performed so that the fixed electrodes 16 and 17 formed in the step shown in (3) and the portion of the silicon substrate 23 that is not removed by etching are not in contact with each other. This is to electrically separate the movable electrode 15 and the fixed electrodes 16 and 17.

Next, the manufacturing process shown in FIG. 9 is performed. Figure 9
FIG. 9A is a sectional view taken along the line AA, and FIG.
It is a B sectional view.

The oxide film 25 and the oxide film 26 on the back surface of the silicon substrate 23 are removed by etching, so that the movable electrode 15 supported by the silicon substrate 23 and the epitaxial layer 24 via the beam 14 and the fixed electrodes 16 and 17 are removed. Then, the acceleration sensor as shown in FIG. 1 is formed.

Next, the relationship between the acceleration applied to the acceleration sensor of this embodiment and the electrostatic capacitance between the movable electrode 15 and the fixed electrodes 16 and 17 will be described with reference to FIG.

When acceleration is generated in the acceleration sensor, the rate of change of capacitance per 1 G of acceleration ΔC / C is Δ
C / C≅5 GML ³ / 4dEbt ³ (1) However, M: mass of the movable electrode 15, b: length (thickness) of the movable electrode 15 in the substrate direction, t: width of the beam 14, L: beam
The distance from the center of gravity g of the member composed of 14 and the movable electrode 15 to the mounting portion of the beam 14, E: Young's modulus of the movable electrode 15, d: the gap between the movable electrode 15 and the fixed electrode 16 or 17, G: gravity It is acceleration.

The capacitance change is converted into an electric signal by a detection circuit composed of a transistor or the like, and the generated acceleration is detected.

As described above, as shown in FIGS. 1 to 10, since the gap d between the movable electrode 15 and the fixed electrodes 16 and 17 is formed by self-alignment of the semiconductor substrate, management of this gap is performed. And the gap can be narrowed. Therefore, from equation (1) above, acceleration 1
Since the rate of change in capacitance per G can be increased, a highly sensitive acceleration sensor can be provided.

Further, in order to detect lateral acceleration with respect to the silicon substrate 23, as shown in FIG. 11, an acceleration sensor for detecting two-dimensional acceleration can be formed on the same silicon substrate. Have.

Next, a second embodiment will be described with reference to FIGS.

FIG. 12 is a diagram showing the configuration of this embodiment.
12A is a plan view, and FIG. 12B is a sectional view taken along line AA of FIG. 12A.

The movable electrode 30 is formed on the silicon substrate 33 by the beam 29.
The movable electrode 30 is supported by the
Direction. The fixed electrodes 31 and 32 have a predetermined gap with respect to the movable electrode 30 so as to sandwich the movable electrode 30. Epitaxial layers 71 are adjacent to the side surfaces of the fixed electrodes 31 and 32 that are not on the movable electrode 30 side.

When a voltage is applied to the movable electrode 30 and the fixed electrodes 31 and 32, there is a predetermined electrostatic capacitance between the movable electrode 30 and the fixed electrodes 31 and 32. When acceleration is applied to the acceleration sensor, the movable electrode 30 is displaced leftward or rightward in the drawing with the beam 29 as a fulcrum. The capacitance changes due to the displacement of the movable electrode 30, and the acceleration can be detected by detecting this change.

Next, the acceleration sensor shown in FIG.
The manufacturing process of this embodiment will be described with reference to FIG.

FIG. 13A is a plan view and FIG. 13B is FIG.
It is an AA sectional view of (a).

The epitaxial layer 35 is formed on the silicon substrate 36, and the oxide films 38 and 37 are formed on the back surface of the silicon substrate 36 and the upper surface of the epitaxial layer 35, respectively. Next, the oxide film 37 on the epitaxial layer 35 is selectively removed by etching, and the part of the epitaxial layer 35 from which the oxide film 37 has been removed is removed to form one trench 34.

Next, as shown in FIG. 14, the entire surfaces of the epitaxial layer 35 and the silicon substrate 36 (including the sidewalls of the trench 34) are oxidized to deposit an oxide film 61.

Then, as shown in FIG. 15, only the oxide film 61 on the upper surface of the epitaxial layer 35 and on the upper surface of the silicon substrate 36 at the bottom of the trench 34 is removed by etching. At this time, since the oxide films 37 and 61 formed on the epitaxial layer 35 are thicker than the oxide film 61 formed on the bottom of the trench 34, even if the surface of the silicon substrate 36 at the bottom of the trench 34 is exposed. The oxide film 37 on the upper surface of the epitaxial layer 35 remains.

Next, as shown in FIG. 16, a silicon substrate 36
The movable electrode 40 is formed by growing an epitaxial layer in the trench 34 whose surface is exposed by thermal oxidation or the like.

Then, as shown in FIG. 17, the surfaces of the epitaxial layer 35 and the movable electrode 40 are oxidized to form an oxide film 39. 17 (a) is a plan view, and FIG. 17 (b) is A in FIG. 17 (a).
FIG.

Next, the trench 43 is formed by selectively removing the oxide film 39 and the epitaxial layer 35 at the portions apart from both side surfaces of the movable electrode 40 by a predetermined distance. The epitaxial layer from the movable electrode 40 to the trench 43 is referred to as an epitaxial layer 71, which is distinguished from the above-described epitaxial layer 35.
Next, the fixed electrodes 31 and 32 are formed by selectively injecting and diffusing impurities into the epitaxial layer 35 from the movable electrode 40 to the trench 43 on the movable electrode 40 side. It suffices that the fixed electrodes 31 and 32 include the facing surfaces of the epitaxial layer 70, and the epitaxial layers from the movable electrode 40 to the trench 43.
Impurities may be injected and diffused into the entire region of 71 to form the fixed electrode. Further, although the fixed electrodes 31 and 32 are formed by implanting and diffusing impurities in the present embodiment, it is sufficient that the electrodes are formed, so that they may be formed by another method. Then, the oxide film 38 on the back surface of the silicon substrate 36 is selectively removed,
An oxide film 44 is formed.

Further, as shown in the sectional view of FIG. 18C, trenches 41 and 42 are formed in the epitaxial layer 35 at the same time when the trench 43 shown in FIG. 18B is formed. Further, the oxide film 38 formed on the back surface of the epitaxial layer 35 is selectively etched and removed.

Next, the step shown in FIG. 19 is performed. 19A is a sectional view taken along the line AA of FIG. 18A, and FIG. 19B is a sectional view taken along the line BB of FIG. 18A.

The oxide film 39 on the upper surface of the epitaxial layer 35 is protected by a resin or the like, and the pattern of the oxide film 38 on the back surface of the silicon substrate 36 is used as a mask to remove the silicon substrate 36 from below by anisotropic etching. After that, the resin is removed. The silicon substrate 36 is removed by etching so that the fixed electrodes 31 and 32 do not come into contact with the portions of the silicon substrate 36 that are not removed by etching. This is to electrically separate the movable electrode 40 and the fixed electrodes 31 and 32.

Next, the oxide film 38 and the oxide film 39 on the back surface of the silicon substrate 36 are removed to form an acceleration sensor as shown in FIG.

Thus, as shown in FIGS. 12 to 20, since the gap between the movable electrode 30 and the fixed electrodes 31 and 32 is formed by self-alignment of the semiconductor substrate, this gap is managed. This can be done easily and this gap can be narrowed. Further, since a plurality of acceleration sensors can be formed on the same substrate, two-dimensional acceleration can be detected.

Next, a third embodiment will be described with reference to FIG.

This embodiment is an embodiment in which the movable electrode 62 and the fixed electrodes 63 and 64 are comb-shaped so that a large capacitance change due to a minute displacement of the movable electrode 62 can be obtained. Since the method of detecting the acceleration is the same as in the first and second embodiments, a detailed description will be omitted here. Since the manufacturing method of this embodiment is similar to that of the first and second embodiments, detailed description thereof will be omitted here.

In the above embodiment, the fixed electrodes 16 and 17 in the first embodiment and the movable electrode 30 in the second embodiment are formed by epitaxial growth and impurity diffusion. A CVD method, an electrolytic plating method, or an electroless plating method may be used.

[0055]

As described above, since the gap between the fixed electrode and the movable electrode can be formed by self-alignment of the semiconductor substrate, this gap can be easily managed. .. Further, since the gap can be narrowed, the detection sensitivity when acceleration occurs can be improved. Further, since a plurality of acceleration sensors can be formed on the same substrate, there is an effect that two-dimensional acceleration can be detected.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a first embodiment of the present invention.

FIG. 2 is a diagram showing a manufacturing process of the first embodiment of the present invention.

FIG. 3 is a diagram showing a manufacturing process of the first embodiment of the present invention.

FIG. 4 is a view showing a manufacturing process of the first embodiment of the present invention.

FIG. 5 is a diagram showing a manufacturing process of the first embodiment of the present invention.

FIG. 6 is a diagram showing a manufacturing process of the first embodiment of the present invention.

FIG. 7 is a diagram showing a manufacturing process of the first embodiment of the present invention.

FIG. 8 is a view showing a manufacturing process of the first embodiment of the present invention.

FIG. 9 is a view showing a manufacturing process of the first embodiment of the present invention.

FIG. 10 is a diagram for explaining the operation of the first embodiment.

FIG. 11 is a diagram showing a structure in which two acceleration sensors are formed on the same semiconductor substrate.

FIG. 12 is a diagram showing a manufacturing process of a third embodiment of the present invention.

FIG. 13 is a view showing a manufacturing process of the third embodiment of the present invention.

FIG. 14 is a diagram showing a manufacturing process of a third embodiment of the present invention.

FIG. 15 is a view showing a manufacturing process of the third embodiment of the present invention.

FIG. 16 is a view showing a manufacturing process of the third embodiment of the present invention.

FIG. 17 is a view showing the manufacturing process of the third embodiment of the present invention.

FIG. 18 is a view showing a manufacturing process of the third embodiment of the present invention.

FIG. 19 is a view showing a manufacturing process of the third embodiment of the present invention.

FIG. 20 is a diagram showing a manufacturing process of the third embodiment of the present invention.

FIG. 21 is a diagram showing a fourth embodiment of the present invention.

FIG. 22 is a diagram showing a conventional acceleration sensor.

[Explanation of symbols]

1, 23, 36 ... Silicon substrate 5, 15, 30, 62 ... Movable electrode 4, 6, 16, 17, 31, 32, 63, 64 ... Fixed electrode

Claims (2)

[Claims] 1. A method of manufacturing a semiconductor acceleration sensor having a beam and a movable electrode supported by the beam, the method comprising: forming a first epitaxial layer on a semiconductor substrate;
Selectively removing the epitaxial layer to the surface of the semiconductor substrate to form two substantially rectangular parallelepiped trenches, forming oxide films on the sidewalls of the two trenches, and forming the oxide film. Stacking a second epitaxial layer on the semiconductor substrate at the bottom of the two trenches in which the trenches are formed, forming fixed electrodes on at least a part of the facing surfaces of the two second epitaxial layers, and the first epitaxial layer A step of selectively removing a part of the layer to reach the surface of the semiconductor substrate to form the beam and the movable electrode; and at least a semiconductor substrate immediately below the movable electrode and a semiconductor substrate immediately below the fixed electrode. And a step of simultaneously removing the semiconductor substrate immediately below the oxide film formed between the movable electrode and the fixed electrode,
A step of removing the oxide film, and a method of manufacturing a semiconductor acceleration sensor. 2. A method of manufacturing a semiconductor acceleration sensor having a beam and a movable electrode supported by the beam, the method comprising: forming a first epitaxial layer on a semiconductor substrate;
A step of selectively removing the epitaxial layer to the surface of the semiconductor substrate to form a substantially rectangular parallelepiped trench;
A step of forming an oxide film on the sidewall of the trench, a step of stacking a second epitaxial layer on the semiconductor substrate at the bottom of the trench where the oxide film is formed to form a first electrode, and a step of forming the first electrode. Electrodes are selectively removed to form the beam and the movable electrode, and two predetermined regions at symmetrical positions of the first epitaxial layer are selectively removed to reach the semiconductor substrate to obtain two symmetrical regions. The third of the substantially rectangular parallelepiped shape
A step of forming an epitaxial layer, a step of forming a fixed electrode on at least a part of the facing surfaces of the two third epitaxial layers, a semiconductor substrate at least under the movable electrode and a semiconductor under the fixed electrode. A step of simultaneously removing the substrate and the semiconductor substrate immediately below the oxide film sandwiched between the movable electrode and the fixed electrode;
A step of removing the oxide film, and a method of manufacturing a semiconductor acceleration sensor.