JP2833257B2 - Semiconductor acceleration sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cantilever type semiconductor acceleration sensor, more precisely, a fixed portion formed by digging a recess and a groove in a semiconductor plate, and a flexible cantilever having one end supported by the fixed portion. And a movable mass portion connected to the other end.

[0002]

2. Description of the Related Art A sensor using a semiconductor device has an advantage that it can be formed in a very small size of several mm square or less and can be formed together with an associated circuit in an integrated circuit chip. , Pressure, acceleration, etc., have been widely adopted. In order to detect these physical quantities, it is necessary to create a flexible portion in the sensor. The flexible structure is roughly classified into a diaphragm and a cantilever. The latter, which can take large amounts, is more suitable. Hereinafter, a typical conventional example of this cantilever type semiconductor acceleration sensor will be briefly described with reference to FIG.

FIG. 4A is a top view of an acceleration sensor built in a small semiconductor plate 10 or a chip.
Is a sectional view taken along the line XX. As shown in FIG. 1B, the semiconductor plate 10 is, for example, n-type, and a deep recess 4 and a shallow recess 5 are dug from the back side thereof, and from the front side.
As shown in (a), the groove 6 is cut and connected to most of the recess 4 to form a frame-shaped fixing portion 20, a cantilever portion 30 supported at one end thereof, and a mass portion 40 connected to the other end. And are formed. A typical acceleration sensor has a mass 40 as shown in the figure.
Is supported only from one side, and the acceleration in the z direction shown in FIG.
Detect from zero deflection.

This bending is detected by a strain gauge 50 which is a p-type piezoresistive layer opposite to the semiconductor plate 10 diffused on the surface of the cantilever 30 as shown in FIG. 4 (b). Actually, it is preferable to make two as shown by 51 and 52 in FIG. 7A, and it is better to diffuse them in a folded pattern as shown in FIG. To derive the terminal,
As shown in FIG. 1B, an aluminum electrode film 12 connected to the end of the strain gauge 50 is arranged in a predetermined pattern in a window opened in an insulating film 11 such as an oxide film covering the surface of the semiconductor plate 10 as shown in FIG. Then, an end portion of the electrode film 10 is exposed in a window opened in the protective film 13 made of silicon nitride or the like covering the same to form a connection pad P. further,
Resistance layer 53 which is a p-type layer having the same configuration as strain gauges 51 and 52
And 54 are diffused to derive terminals as shown in the figure.

The acceleration sensor configured as described above is
Usually, the semiconductor plate 10 is used in a state of being joined to a pedestal 14 of glass, semiconductor, or the like as shown in FIG. At this time, as shown in FIG. 5, two strain gauges 51, 52 are bridge-connected together with two resistance layers 53, 54 having the same resistance value, and the voltage V
The detection signal DS is taken out in the state given.

[0006]

The above-described semiconductor acceleration sensor can be formed into a small chip having a size of 2 to 3 mm. By mounting this chip in an electronic circuit or an integrated circuit device, its mass as shown in FIG. When the acceleration in the z direction is applied to the portion 40, the cantilever portion 30 is bent and, for example, a collision of a car can be reliably detected. However, when acceleration is applied in a direction oblique to the z direction, the component in the z direction is reduced, so that the detection sensitivity is reduced. There is a problem that is considerably reduced.

In order to solve this problem, it is sufficient to use two or three chips of an acceleration sensor whose sensitivity is orthogonal to each other and synthesize their detection signals. It takes time and space for installation. Further, with the above-described structure, it is impossible to incorporate acceleration sensors having different sensitivity directions into the integrated circuit device.

In order to solve such a problem, an object of the present invention is to enable a semiconductor acceleration sensor to detect accelerations in two different directions.

[0009]

According to the first aspect of the present invention, the above-mentioned object is attained by the above-mentioned strain gauge for detecting the bending in the thickness direction of the cantilever portion, and between the fixed portion and the mass portion. And a fixed part facing the gap and an electrode layer formed by diffusion of a high impurity concentration in the mass part. The deflection in the width direction of the cantilever part is detected from a change in capacitance between the electrode layers. Provide a capacitance sensor,
This is achieved by detecting accelerations in two directions perpendicular to each other by a strain gauge and a capacitance sensor.

It is preferable that the electrode layer that diffuses into the mass part is extended to the fixed part via the cantilever part, and a connection terminal for this electrode layer is led out from the extended part.

Further, in the second invention of the present invention, the above-mentioned strain gauge for detecting the deflection in the thickness direction formed on the surface portion of the cantilever portion is a first strain gauge,
In addition, a second strain gauge is provided at the center in the thickness direction of the end portion in the width direction of the cantilever portion to detect the bending in the width direction created by embedding and diffusing, and the first and second strain gauges are used. The purpose is likewise achieved by detecting accelerations in two directions perpendicular to each other.

[0012]

The first invention of the present invention takes advantage of the fact that a very thin groove can be cut with a width of about 1 μm on a semiconductor plate by a recent etching technique, and this groove is formed between a pair of electrode layers. By forming the capacitance sensor as a narrow gap, it has succeeded in detecting minute deflection in the width direction of the cantilever sharply.

According to a second aspect of the present invention, the second strain gauge described in the preceding paragraph is formed at an end of the cantilever portion in the width direction to enable detection of a slight deflection in the width direction, By embedding the second strain gauge in the center of the thickness direction of the strain gauge on the surface of the cantilever portion, the first and second strain gauges are mounted on the surface portion of the cantilever portion. Can be detected independently of each other.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. 1 and 2 show embodiments of the first and second inventions of the present invention, and FIG. 3 shows a manufacturing method corresponding to the embodiment of FIG. 2, respectively. Therefore, the same parts as those in the description before will be omitted.

FIG. 1A is a top view of the semiconductor acceleration sensor according to the first invention, FIG. 1B is a cross-sectional view taken along the line XX, and FIG. 1C is a view taken along the line YY. It is sectional drawing. The acceleration sensor is a small type of 2-3mm square, and the semiconductor plate 10 for it is
Also in this example having a thickness of 200 to 300 μm, an n-type one is used. From now on, the fixed part 20, the cantilever part 30, and the mass part 40
As described above, a deep recess 4 and a shallow recess 5 are dug from the back side and the groove 6 is cut from the front side, as in the conventional case. To provide a very narrow gap 71 between the mass parts 40, the groove 6 and the gap 71
Is advantageously cut by dry etching or reactive ion etching. The gap length of the gap 71 is as short as possible and is set to about 0.5 to 1 μm.

The cantilever 30 has a thickness of, for example, 10
~ Tens of μm, width 200-500 μm, length 300-500 μ
m, and the mass part 40 is formed in a size of 500 × 1000 μm, the interval between the lower surface of FIG. 1 (b) and the pedestal 14 is set to about several tens μm, and the strong impact force in the thickness direction z causes the cantilever 30 to move. The mass portion 40 is received by the pedestal 14 in order to prevent the mass portion 40 from being broken when it is largely bent.

The strain gauge 50 for detecting the bending of the cantilever portion 30 in the thickness direction z is also a p-type piezoresistor in the illustrated example, for example, with an impurity concentration of 10 ¹⁷ atoms / cm ³ and 1-3.
It is diffused to the surface of the cantilever 30 at a depth of μm, and its diffusion pattern is, for example, 200 to 300 μm with a width of 10 to 30 μm.
It is preferable that a p-type connection layer having a high impurity concentration be diffused into the bent portion of the pattern in the same manner as in the connection portion with the electrode film 12 at the end. In practice, it is desirable to form a pair of piezoresistors 51 and 52 for the strain gauge 50 as in the prior art.

The electrode layers 72 and 73 for the capacitance sensor are p-type in the example shown, and are diffused to a depth of at least 10 μm as shown in FIG. 1C with a high impurity concentration of 10 ²⁰ atoms / cm ³ or more. Is done. In practice, a single p-type layer is diffused and placed, and the groove 6 and the gap
By cutting 71, an electrode layer 72 on the fixed part 20 side and an electrode layer 73 on the mass part 40 side are separated.

As shown in the figure, the capacitance sensor 70 including the gap 71 and the electrode layers 72 and 73 is preferably formed at both ends in the width direction of the mass part 40. When the acceleration in the width direction y is applied, the cantilever portion 30 bends in the width direction and the capacitance values of the pair of capacitance sensors 70 increase and decrease in opposite directions. Is connected to an AC mixing bridge, the acceleration can be detected sharply.

As shown in FIG. 1A, the electrode layer 72 on the mass part 40 extends through the widthwise end of the cantilever part 30 to the fixing part 20 at the base thereof, where the connection pad P It is convenient to connect to the connected electrode film 12.

In FIG. 2 showing an embodiment of the second invention,
FIG. 3A is a top view of the acceleration sensor, and FIG.
FIG. 3C is an enlarged cross-sectional view of only the cantilever portion 30 as viewed in the direction of the arrow YY. Also in this example, the fixing portion 20, the cantilever portion 30, and the mass portion 40 are formed by digging the recesses 4 and 5 in the semiconductor plate 10 and cutting the groove 6, but the thickness of the cantilever portion 30 is reduced. The thickness is about 30 μm which is slightly thicker than that of FIG. 1, and the width is 500 μm or more which is slightly wider. It is not necessary to provide a narrow gap between the mass part 40 and the fixing part 20 as in the case of FIG.

The first strain gauge 50 for the second invention
May be diffused to the surface of the cantilever portion 30 in the same manner as in FIG. 1, but it is desirable to provide it as close to the center in the width direction as possible. The major difference from the first invention is that the second invention
The strain gauge 60 is buried in the center in the thickness direction of the end in the width direction of the cantilever 30 and is formed by diffusion. For this reason, as shown in FIG. An n-type epitaxial layer 2 is grown on the substrate, and the second strain gauge 60 is buried between the two layers in a p-type, and both ends of the second strain gauge 60 are p-type high impurity concentration connection layers 60a. Is connected to the electrode film 12. The strain gauge 60 is not limited to the example shown in the figure, and may be embedded and diffused in a folded pattern.

The second strain gauge 60 is also constituted by a pair of embedded piezo resistors 61 and 62, as shown in FIG. It is desirable that the resistance layers 63 and 64 together form a bridge circuit.

As can be easily understood, in the acceleration sensor of FIG. 2 according to the second invention, the bending of the cantilever 30 when the acceleration in the width direction y shown in FIG. The first strain gauge 50 can detect the deflection when the acceleration in the thickness direction z in FIG. Furthermore, since the first strain gauge 50 is formed on the surface of the cantilever 30 and the second strain gauge 60 is formed at the center in the thickness direction, the first strain gauge 50 is formed in the direction combining the width direction y and the thickness direction z. The deflection in the thickness direction and the deflection in the width direction of the cantilever 30 when the acceleration is applied are measured by the first strain gauge 50 and the second strain gauge, respectively.
Can be detected independently of each other by the strain gauge 60 of the first embodiment.

Next, a method of manufacturing the acceleration sensor according to the second invention will be described with reference to FIG. FIGS. 2 (a) to 2 (f) show states of main processes.
It is sectional drawing corresponding to (b). First, in the first step of FIG. 3A, the second strain gauge 60 is placed on the surface of the n-type substrate 1.
P-type layer with an impurity concentration of about 10 ¹⁷ atoms / cm ³
Diffuses very shallowly.

In FIG. 3B, an n-type epitaxial layer 2 is first grown on a substrate 1 to a thickness of about 5 to 10 μm to form a wafer 3. As a result, the second strain gauge 60 is buried under the epitaxial layer 2 and becomes a piezoresistive having a diffusion depth of 2 to 3 μm at the temperature at which the epitaxial layer 2 is grown. Next, the connection layer 60a having a high impurity concentration is diffused from the surface of the wafer 3 so as to reach both ends of the strain gauge 60.
Of the strain gauge 50 and the resistance layer indicated by 53 in this cross section are simultaneously diffused in p-type, and a p-type high impurity concentration connection layer is appropriately diffused to the ends thereof.

Further, an electrode film 12 is provided on an insulating film 11 covering the surface of the wafer 3 and connected to a second strain gauge 60 and the like. The end portion of the electrode film 12 exposed at this time is set as a connection pad P, as shown in FIG. Thus, the main steps from the front side of the wafer 3 are completed.

FIG. 3C shows a process of excavating the recess 4.
For this reason, a photoresist film M1 is applied to the back surface of the wafer 3, a window of a predetermined pattern is formed by a photo process, and the recess 4 is generally dug in a circular pattern by wet etching using this as a mask. FIG. 3 (d) shows a step of digging the recess 5, in which a window corresponding to the outer contour of the recess 4 is formed in another photoresist film M2 applied to the back surface of the wafer 3, and a wet pattern is formed using the window as a mask. The recess 5 is dug by etching, and the recess 4 is also dug deeper as shown in the figure. This completes the digging from the back side.

FIG. 3 (e) shows a groove cutting process for the groove 6, and this time, the groove 6 is formed as shown in FIG. 2 (a) by a dry etching method using the photoresist film M3 formed on the front surface side of the wafer 3 as a mask. It is cut in the C-shaped pattern shown and communicated with the recess 4. As a result, the fixed portion 20, the cantilever portion 30, and the mass portion 40 are formed in the pattern shown in FIG. 2A, and the process of incorporating the acceleration sensor into the wafer 3 is completed.

FIG. 3F shows a process of attaching the base 14 to the base 14. For the pedestal 14, a glass plate or a semiconductor plate is used. For example, after the front surface of the pedestal 14 and the back surface of the wafer 3 are mirror-finished, the clean surfaces are electrostatically attracted to each other to electrostatically bond them. When the pedestal 14 is a semiconductor plate, soldering may be used. After this mounting process, the wafer 3 is
The semiconductor acceleration sensor shown in FIG.

The manufacturing method of the acceleration sensor shown in FIG. 1 is the same as that of FIG. 1 except that the wafer 3 is made of only the substrate 1 and the gap 71 for the capacitance sensor 70 is cut very narrowly together with the groove 6. Etc. are mainly different.

1 and 2, the accelerations in the width direction y and the thickness direction z applied to the mass portion 40 can be detected independently of each other as described above. When detecting the applied acceleration, an acceleration detection value most suitable for the purpose can be created by synthesizing the acceleration detection signals in the y direction and the z direction by the above-described bridge circuit or the like in a manner according to the application. As can be easily understood, if two acceleration sensors whose width directions y are orthogonal to each other are incorporated in the same chip and their acceleration detection signals are used independently or appropriately in combination, the acceleration received from any direction is obtained. Can be detected in a desired manner.

[0033]

As described above, in the first aspect of the present invention,
A strain gauge that detects the deflection in the thickness direction created on the surface of the cantilever part, a narrow gap formed between the fixed part and the mass part, and the fixed part and the mass part facing it Combined with a capacitive sensor that consists of an electrode layer and detects the bending of the cantilever in the width direction,
In the second invention of the present invention, the first strain gauge for detecting the deflection in the thickness direction formed on the surface portion of the cantilever portion and the central portion in the thickness direction of the end portion in the width direction of the cantilever portion are formed by diffusion. The following effects can be obtained by combining with the second strain gauge for detecting the bent in the width direction.

(A) A single cantilever-type semiconductor acceleration sensor can detect acceleration in the width direction of a conventional cantilever in addition to acceleration in the thickness direction.

(B) Since the acceleration in the thickness direction and the acceleration in the width direction can be detected independently of each other, by appropriately combining or combining the two acceleration detection signals, the acceleration detection having the desired sensitivity directivity optimal for the application or purpose can be performed. You can extract the output.

(C) If two acceleration sensors are formed in the same chip with different sensitivity directions, accelerations received from all directions can be detected.

Although the semiconductor acceleration sensor according to the present invention is not always suitable for high accuracy, it can be constructed in a very small size in addition to the above, can be easily incorporated into an integrated circuit device together with related circuits, and can be mounted on an electronic device. In this case, there is a feature that space and labor can be saved, and the effect that the acceleration can be detected with an arbitrary directional sensitivity characteristic when applied to an application such as collision detection of an automobile can be exhibited.

[Brief description of the drawings]

FIG. 1 shows an embodiment of a semiconductor acceleration sensor according to the first invention of the present invention. FIG. 1 (a) is a top view of the acceleration sensor, and FIG.
(b) is a sectional view taken along the line XX, and (c) is a sectional view taken along the line YY.

FIG. 2 shows an embodiment of the semiconductor acceleration sensor according to the second invention of the present case, and FIG. 2 (a) is a top view of the acceleration sensor, and FIG.
(b) is a sectional view taken along the line XX, and (c) is a sectional view taken along the line YY.

FIG. 3 is a view showing the manufacturing method of the semiconductor acceleration sensor of FIG. 2;
It is sectional drawing of the wafer illustrated in (a)-(f) in the state for every main process.

4A and 4B show a semiconductor acceleration sensor according to the prior art, wherein FIG. 4A is a top view thereof, and FIG. 4B is a cross-sectional view thereof along XX.

FIG. 5 is a circuit diagram of a detection circuit corresponding to the acceleration sensor of FIG.

[Explanation of symbols]

 4 Concave part 5 Concave part 6 Groove 10 Semiconductor plate 20 Fixed part 30 Cantilever part 40 Mass part 50 Strain gauge or first strain gauge 51 Piezo resistance for strain gauge 52 Piezo resistance for strain gauge 60 Second strain gauge 61 Strain gauge Piezoresistor 62 Piezoresistor for strain gauge 70 Capacitance sensor 71 Gap for capacitance sensor 72 Electrode layer for capacitance sensor 73 Electrode layer for capacitance sensor y Width direction of cantilever z Thickness direction of cantilever

Claims (3)

(57) [Claims] 1. A fixed portion formed by digging a recess and a groove in a semiconductor plate, a flexible cantilever portion having one end supported by the fixed portion, and a movable mass portion connected to the other end of the cantilever portion. And a strain gauge for detecting a thickness-direction deflection of the cantilever portion created by diffusion in the surface portion of the cantilever portion, and a narrow gap formed between the fixed portion and the mass portion. And a capacitance sensor comprising an electrode layer formed by diffusion of a high impurity concentration in the fixed portion facing the gap and the mass portion by diffusion of a high impurity concentration, and detecting a widthwise deflection of the cantilever portion from a change in capacitance between the electrode layers. A semiconductor acceleration sensor provided with a strain gauge and a capacitance sensor for detecting accelerations applied to the mass part in two directions perpendicular to each other. 2. The sensor according to claim 1, wherein the electrode layer for the mass portion extends to the fixed portion through the cantilever portion and is diffused, and a terminal is derived from the electrode layer extended to the fixed portion. A semiconductor acceleration sensor. 3. A fixed portion formed by digging a recess and a groove in a semiconductor plate, a flexible cantilever portion having one end supported by the fixed portion, and a movable mass portion connected to the other end of the cantilever portion. A first strain gauge for detecting a deflection in a thickness direction of the cantilever portion formed by diffusion in a surface portion of the cantilever portion, and a thickness direction of an end portion in a width direction of the cantilever portion. A second strain gauge is provided at the center to detect the bending of the cantilever in the width direction, which is formed by buried diffusion. The first and second strain gauges detect accelerations in two directions perpendicular to each other applied to the mass. A semiconductor acceleration sensor characterized in that: