JPH1144705A - Semiconductor acceleration sensor and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a satisfactory sensitivity of a sensor even when a sensor chip is miniaturized. SOLUTION: This semiconductor acceleration sensor has a sensor chip 1 constituted of a thick weight section 2 displaced when applied with acceleration, a thick support section 3 formed to surround the weight section 2 at the prescribed interval with the weight section 2, thin beam sections 4-7 supporting the weight section 2 on the support section 3, and piezoelectric resistors 8-11 formed on the beam sections 4-7. The cross-shaped weight section 2 has projections 2a, 2b between the first and second beam sections 4, 5 and between the third and fourth beam sections 6-7 respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a semiconductor acceleration sensor for detecting acceleration in an automobile or the like and a method of manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, in a semiconductor acceleration sensor of this type, a thick weight portion which is displaced by receiving an acceleration, and a thick wall portion which is formed at a predetermined distance from the weight portion and surrounds the weight portion. A support portion, a thin beam portion supporting the weight portion on the support portion, and a sensor chip having a piezoresistor formed on the beam portion are provided, and the acceleration is detected based on a change in the resistance value of the piezoresistance. Various things have been proposed.

For example, Japanese Patent Application Laid-Open No. Hei 4-356971 discloses a structure in which two beams and two opposite sides of a rectangular weight are supported by two beams in order to detect minute acceleration. Has been proposed.

[0004]

In such a semiconductor acceleration sensor, there is a demand for downsizing of the sensor chip. In order to reduce the size of the sensor chip, it is necessary to increase the sensitivity of the sensor and reduce the size of chip components such as weights and beams. Here, the sensitivity of the sensor is
In the case of a doubly supported structure in which the length of the beam portion is determined by the length, thickness, width, weight of the weight portion, and the like, both sides of the weight portion are supported by the support portion, the sensitivity S of the sensor is expressed by Formula 1. Is done.

[0005]

(Equation 1)

In this equation 1, k is a piezo coefficient, E
Is the Young's modulus, m is the weight of the weight, l is the length of the beam, d is the thickness of the beam, and b is the width of the beam. Therefore, the present invention focuses on the weight of the weight portion and adopts a structure in which the weight portion can be made heavy, so that the sensitivity of the sensor can be improved even if the sensor chip is reduced in size, and a method of manufacturing the same. The purpose is to provide.

[0007]

Means for Solving the Problems The present inventors have, for example,
As in a semiconductor acceleration sensor disclosed in Japanese Patent Application Laid-Open No. 4-356971 and the like, two opposing sides of a rectangular weight and a support are supported by two beams, respectively. Area. That is,
The region is a region where the weight portion is not originally formed,
If the structure is such that the weight portion protrudes from the region, the weight portion can be made heavy.

The present invention has been made based on such an idea. According to the first aspect of the present invention, the weight portion (2) is provided.
Two beams (4, 5 or 6, 7) between the support and the support (3)
Are formed in parallel, and the weight portion (2) has a protruding portion (2a or 2b) protruding between the two beam portions. By providing the protruding portion (2a or 2b) of the weight portion between the two parallel beam portions as described above,
The weight portion is made heavy, and the sensitivity of the sensor can be improved.

According to the second aspect of the present invention, the support portion (3) has a shape having a plurality of sides (3a to 3d), and is formed between one side (3a or 3b) of the support portion and the weight. Two beam portions (4, 5 or 6, 7) are formed between the two beam portions, and the weight portion projects between the two beam portions (2a or 2a).
b). With this configuration, as in the first aspect of the invention, the weight portion is made heavy,
The sensitivity of the sensor can be improved.

According to the third aspect of the present invention, the support portion (3) has a shape composed of four sides (3a to 3d), and has a weight corresponding to two opposite sides (3a, 3b) of the support portion. Two beam portions (4 to 7) are formed between the two protruding portions (2 to 7).
a, 2b), and has a cross shape when viewed from the thickness direction.

According to this structure, in the double-supported structure in which the weight portion is supported from both sides by the beam portion, the weight portion can be made heavy and the sensitivity of the sensor can be improved similarly to the first aspect of the invention. . In the invention according to claim 4,
The weight part is configured to be supported by the support part (3) only by the first to fourth beam parts (4 to 7), and the weight part is composed of the first and second beam parts (4, 7). 5) The first projecting between
And a second projecting portion (2b) projecting between the third and fourth beam portions (6, 7), and a direction orthogonal to the projecting direction of the first and second projecting portions. The third and fourth projections (2c, 2d) protruding from each other are formed in a cross shape when viewed from the thickness direction.

According to this configuration, as in the third aspect of the invention, the weight can be made heavy and the sensitivity of the sensor can be improved. According to the fifth aspect of the present invention, the coating film (25) is formed on the surface of the silicon substrate with a pattern for forming a cross-shaped weight portion and a thick portion of the support portion, and the silicon substrate is anisotropically etched. The semiconductor acceleration sensor according to claim 3 or 4 can be appropriately manufactured.

In this case, a single crystal silicon substrate (20) having a {100} plane as the surface is used as the silicon substrate, and the coating film (25) is cross-shaped at the weight portion. By patterning into a shape that has a shape compensating part that is aligned with the {110} plane orientation at the corners of the shape in addition to the shape corresponding to the shape, a cross-shaped weight can be formed without causing corner undercutting problems. A part can be formed.

[0014]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a first embodiment of the present invention. In this embodiment, a vehicle VSC (Vehicle Stab) in which the detection range of acceleration is set to about ± 1 G is used.
ility control), which is used to detect small acceleration values such as rolls during running with high accuracy in order to perform stable running control of automobiles. It is.

FIG. 1 shows the external configuration of a sensor chip in a semiconductor acceleration sensor, and FIGS. 2 and 3 show the external configuration of the entire semiconductor acceleration sensor and its cross-sectional configuration. As shown in FIG. 1, the sensor chip 1 has a thick weight portion 2 that is displaced by receiving an acceleration, and a thick wall portion formed to surround the weight portion 2 with a predetermined interval from the weight portion 2. A support portion (frame portion) 3, thin beam portions (beam portions) 4 to 7 supporting the weight portion 2 on the support portion 3, and piezoresistance (diffusion resistance) as a resistor formed in the beam portions 4 to 7. ) 8-11.

The supporting portion 3 has a rectangular shape composed of four sides 3a to 3d. The first side 3a of the supporting portion 3 and the weight 2
The first and second beam portions 4 and 5 are formed in parallel between the third and fourth beam portions 6 and 7 between the second side 3 b of the support portion 3 and the weight portion 2. Is formed. And the first to fourth
The beam portions 4 to 7 support the weight 2 from both sides.

The weight portion 2 includes first and second beam portions 4,
5, a first projecting portion 2a projecting between the third, fourth beam portions 6, 7 and a projecting direction of the first and second projecting portions 2a, 2b. And third and fourth protruding portions 2c and 2d that protrude in a direction perpendicular to the direction of the arrow. Thus, between the first and second beam portions 4 and 5 and the third and fourth beam portions 6 and 7
By providing the first and second protrusions 2a and 2b between them, the weight 2 can be made heavy and the sensitivity of the sensor can be improved.

As shown in FIG. 3, the sensor chip 1 comprises a p-type silicon substrate 13 and an n-type epitaxial layer 14 formed thereon. And
When acceleration is generated in a direction perpendicular to the substrate surface, the weight 2 is displaced in its thickness direction, and the beams 4 to 7 are distorted. The acceleration is detected by changing the resistance values of the piezoresistors 8 to 11 according to the amount of distortion. That is, the piezo resistors 8 to 11
Constitutes a full-bridge circuit as shown in FIG. 5, and a voltage corresponding to the acceleration is output from a connection point between the piezoresistor 8 and the piezoresistor 10 and a connection point between the piezoresistor 9 and the piezoresistor 10. An acceleration is detected based on the output voltage.

In the above-described sensor chip 1, the chip size is 3.6 mm × 3.6 mm and the thickness is 3 mm.
It is about 00 μm. The beam portions 4 to 7 have a thickness of 4.3 to 6.3 μm with a thickness of about 5.3 μm as a center value.
The width dimension is formed in a range of about 140 to 180 μm with a center value of 160 μm, and the length dimension is formed in a range of about 530 to 570 μm with a center value of 550 μm. The weight 2 is 1.8
It is set to be about mg.

By setting such dimensions, S
The / N ratio was improved, and the value of the temperature coefficient of sensitivity TCS (ppm / ° C.) as a whole characteristic could be made ± 300 ppm / ° C. or less. As a result, when used as a semiconductor acceleration sensor for VSC, the operating temperature range is-
In a wide range of about 30 ° C. to 80 ° C., the degree of fluctuation of temperature can be suppressed to a predetermined value or less. It could be suppressed to 2% or less.

As shown in FIGS. 2 and 3, the sensor chip 1 has a silicon pedestal (having a thickness of about 1.8 mm).
15 is fixed. The silicon pedestal 15 is fixed on a ceramic substrate 16. In this case, the adhesive 1 is applied between the sensor chip 1 and the silicon pedestal 15 and between the silicon pedestal 15 and the ceramic substrate 16.
7 and fixed by adhesive. The adhesive 17 includes gold-plated beads 17b in which resin particles are gold-plated on a base adhesive 17a. The base adhesive 17a uses a silicone resin, which is a kind of flexible resin, and the silicone resin has an elastic modulus of about 1 MPa.

The sensor chip 1 and the silicon pedestal 15
Gold-plated beads 17b of adhesive 17 provided between
Is a gold-plated polydivinylbenzene resin having a shape of, for example, about 8 μm, and is blended in the base adhesive 17a so as to be 0.1 wt% or less. The elastic modulus of the resin beads 17b is about 4.8 GPa. The resin beads 17b of the adhesive 17 provided between the silicon pedestal 15 and the ceramic substrate 16 are, for example, 28
0.54 wt in base adhesive 17a with a particle size of about μm
%.

With the configuration shown in FIGS. 2 and 3,
The sensor chip 1 is adhered and fixed on the silicon pedestal 15, whereby the weight 2 is moved to the silicon pedestal 15.
And the thickness of the adhesive 17 (for example, 8 μm to 15 μm).
(about μm). By providing such a gap, an air damper using air as a damper when the weight portion 2 receives an excessive acceleration can be obtained.

Next, a manufacturing process of the above-described sensor chip 1 will be described with reference to FIGS. 5 to 10.
1 shows an AA cross section of FIG. First, as shown in FIG. 5, a single-crystal p-type silicon wafer 20 having a plane orientation of {100} is prepared, and an n-type epitaxial layer 21 is formed on the p-type silicon wafer 20.

The p ⁺ diffusion layer 2 serving as a piezo resistor is provided in a predetermined region in the surface layer portion of the n-type epitaxial layer 21.
Form 2 Further, an n ⁺ diffusion layer 23 is formed in a predetermined region in a surface portion of the n-type epitaxial layer 21. n ⁺
The diffusion layer 23 serves as an electrode contact at the time of electrochemical etching, and is removed with the formation of the upper separation groove (indicated by reference numeral 37 in FIG. 8).

Thereafter, an oxide film (not shown) is formed on the epitaxial layer 21 and a predetermined region is opened. An aluminum wiring (not shown) is arranged thereon to make contact with a predetermined region of the p ⁺ diffusion layer 22. Thereafter, a passivation film (not shown) made of a silicon oxide film or the like is deposited, and a predetermined region of the passivation film is opened to form a contact hole for wire bonding. Further, a current-carrying aluminum contact portion for contacting n ⁺ diffusion layer 23 is provided. Then, a resist film (or PIQ film) 24
Is formed on the entire surface, and a predetermined region is opened.

Then, a plasma nitride film 25 is formed on the entire back surface of the p-type silicon wafer 20, and the plasma nitride film 25 is photo-patterned into a desired shape using a resist and a mask (photomask). This photo patterning will be described in more detail with reference to FIGS. As shown in FIG. 12, a resist film 26 is applied on the deposited plasma nitride film 25 by spinning, and an anisotropic etching mask 27 is prepared. FIG. 11 shows a plan view of the anisotropic etching mask 27.
As shown in FIG. 12, the anisotropic etching mask 27 has a glass substrate 28 on which a Cr thin film 29 having a predetermined shape is arranged.

In FIG. 11, an anisotropic etching mask 27 has a rectangular annular frame portion 30 and a cross-shaped portion 3 formed inside the frame portion 30 and having a shape corresponding to the cross shape of the weight portion 2.
1 and a rectangular 8 formed at the corner of the cross-shaped portion 31
Shape compensators 32a, 32b, 32c, 32d, 32
e, 32f, 32g, and 32h. Shape compensation unit 3
Each of 2a to 32h is formed so that one side is aligned with, for example, the (011) plane orientation of silicon and one side orthogonal to the side is aligned with the (01-1) plane orientation of silicon, and (011) The length of the side aligned with the plane orientation is longer than the length of the side aligned with the (01-1) plane orientation. Thus, the anisotropic etching mask 23
Are provided with rectangular shape compensating portions 32a to 32h that are aligned with the (011) plane direction and the (01-1) plane direction at the corners of the cross-shaped portion 31, and have different lengths in each direction. It has a shape. Note that “1” in the plane orientation
"-" Indicates that a bar is attached to 1 as shown in the drawing.

Then, as shown in FIG. 12, the resist film 26 is irradiated with light through an anisotropic etching mask 23.
After photo patterning, the exposed plasma nitride film 25 is removed. As a result, the plasma nitride film 25 as a coating film has the same shape as that shown in FIG. 11, that is, a frame portion, a cross portion formed inside the frame portion, and a corner portion of the cross portion. (011) plane orientation and (0
1-1) It is patterned into a shape having eight rectangular shape compensating portions aligned with the plane orientation. In other words, the plasma nitride film 25 is patterned by the anisotropic etching using the patterned plasma nitride film 25 so as to form the weight 2 and the support 3 having a cross shape.

After patterning of the plasma nitride film 25, as shown in FIG. 6, the surface of the epitaxial layer 21 is adhered to a support plate 34 made of alumina while being protected by a wax 33, and then immersed in an etching solution. To perform electrochemical etching. A platinum electrode is extended on the support plate 34. The tip of the platinum electrode is brought into contact with the aluminum contact portion, and the epitaxial layer 21 and the p-type silicon wafer 20 are energized through the n ⁺ diffusion layer 23. The above electrochemical etching is performed. In this electrochemical etching, the etching stops at the pn junction between the p-type silicon wafer 20 and the n-type epitaxial layer 21,
As a result, a lower isolation groove 35 is formed in the p-type silicon wafer 20.

In this electrochemical etching, there is a problem in that a so-called corner undercut (corner drop: oblique side wall at a corner) is formed under the plasma nitride film 25 as a coating film. In order to deal with such a problem of corner undercut, a technique of adding a square shape compensating portion as a corner undercut compensating pattern to the corner of the coating film is referred to as “Si micromachining advanced technology” (1992). ), Science Forum, pp. 117-118. Therefore,
In the present embodiment, by applying the technology, as described above, the plasma nitride film 25 is formed into a shape having eight rectangular shape compensating portions at the corners of the cross-shaped portion, so that the corner undercut is formed. Is made as small as possible. FIG. 13 shows the state after performing anisotropic etching.
The back surface shape of the weight part 2 and the support part 3 which have a cross shape is shown.

After performing the anisotropic etching, the plasma nitride film 25 is removed with hydrofluoric acid as shown in FIG. Then, the support plate 34 is placed on a hot plate, the wax 33 is softened, the n-type epitaxial layer 21 is separated from the support plate 34, and the separated p-type silicon wafer 20 is immersed in an organic solvent to wash the wax 33. . Thereafter, a resist 36 is applied to the entire back surface of the p-type silicon wafer 20.

Then, as shown in FIG.
The epitaxial layer 21 is dry-etched from the opening 4 to form an upper isolation groove 37 communicating with the lower isolation groove 35. Subsequently, as shown in FIG. 9, the resist 36 is removed with an organic solvent to remove the upper separation groove 37 and the lower separation groove 35.
Is formed. FIG. 1
As shown in (1), a weight 2, a support 3, and beams 4 to 7 are formed.

Then, as shown in FIG. 10, the resist film 24 is removed by oxygen plasma ashing. Finally, dicing is performed to form a chip, and the sensor chip 1 is obtained. In the above-described embodiment, a double-support structure in which the weight portion 2 is supported by the support portion 3 by the beam portions 4 to 7 has been described, but the present invention can also be applied to a cantilever structure. That is, the weight portion is supported by the support portion only with the two parallel beam portions, and the weight portion protrudes from the two beam portions. Also in this case, since the weight can be made heavy, the sensitivity of the sensor can be improved.

The weight 2 may have any shape other than the cross shape, as long as a protrusion is formed between the two beams. Also, the support portion 3 may have a shape other than a square shape, as long as the weight portion 2 can be supported. Further, as disclosed in Japanese Patent Application Laid-Open No. 4-356971, the support portion may be constituted by first and second support portions.

Further, in the above-described embodiment, the one in which the acceleration in the thickness direction of the weight portion 2 is detected in one axis direction has been described. However, for example, the third and fourth protrusions of the weight portion 2 are provided. A beam portion is also provided between 2c and 2d and the support portion 3, and when acceleration is applied to the weight portion 2 from an oblique direction, XY
You may comprise so that acceleration of three Z-axis directions may be detected.

In the above embodiment, the semiconductor acceleration sensor of the type in which the acceleration is detected by the piezoresistors 8 to 11 formed in the beam portions 4 to 7 has been described, but the present invention is not limited to this type. For example, silicon pedestal 15
A capacitor is formed between the surface of the weight portion 2 and the opposing surface of the weight portion 2, and the acceleration is detected based on a change in the capacitance of the capacitor when the weight portion 2 is displaced by the application of the acceleration. The output increases as the area of 2 increases. Such a capacitive acceleration sensor may be used.

In the various embodiments described above, the shape of the shape compensating portions 32a to 32h in a single-crystal silicon wafer having a plane orientation of {100}, and one side of the shape compensating portion (0
11) In the plane orientation, it has been described that one side perpendicular to the side is aligned with the (01-1) plane orientation of silicon. However, the shape of the compensation units 32a to 32h is changed, for example, by setting one side to (01-1). -1) In the plane direction, one side orthogonal to the side is defined as (01)
-1-) plane orientation, one side is (01-1-) plane orientation, one side orthogonal to the side is (011-) plane orientation, and one side is (011-) plane orientation. , One that is orthogonal to that side
The sides may be formed so as to be aligned with each other such as the (011) plane orientation.

Note that {} indicating the plane orientation of silicon is:
A plane having equivalent symmetry. For example, in cubic symmetry, {110} as described in claim 6 is (11)
0), (1-1-0), (1-10), (11-0),
(101), (1-01-), (1-01), (101)
−), (011), (01-1-), (01-1),
(011-) represents all.

[Brief description of the drawings]

FIG. 1 is a diagram showing an external configuration of a sensor chip 1 in a semiconductor acceleration sensor according to one embodiment of the present invention.

FIG. 2 is a diagram showing an external configuration of a semiconductor acceleration sensor according to one embodiment of the present invention.

FIG. 3 is a diagram showing a cross-sectional configuration of a semiconductor acceleration sensor according to one embodiment of the present invention.

FIG. 4 is a diagram illustrating a configuration of a circuit that outputs a voltage according to acceleration by piezoresistors 8 to 11 illustrated in FIG. 1;

FIG. 5 is a process chart showing a manufacturing process of the sensor chip 1 shown in FIG.

FIG. 6 is a process chart showing a manufacturing step following FIG. 5;

FIG. 7 is a process chart showing a manufacturing process following FIG. 6;

FIG. 8 is a process chart showing a manufacturing step following FIG. 7;

FIG. 9 is a process diagram showing a manufacturing process following FIG. 8;

FIG. 10 is a process chart showing a manufacturing process following FIG. 9;

FIG. 11 shows a plasma nitride film 25 in the step shown in FIG.
FIG. 4 is a plan view showing an etching mask used in the etching of FIG.

12 is a diagram showing a step of patterning and forming a resist on the plasma nitride film 25 using the etching mask shown in FIG.

FIG. 13 is a view showing a back surface shape of the thick portion of the weight portion 2 and the support portion 3 having a cross shape after electrochemical etching is performed in the step shown in FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Sensor chip, 2 ... Weight part, 3 ... Support part, 4-7 ...
Beam part, 8-11 ... Piezo resistance.

Claims (6)

[Claims] A thick weight portion displaced by an acceleration; a thick support portion formed to surround the weight portion at a predetermined distance from the weight portion; A thin beam portion (4 to 4) for supporting the weight portion on the support portion;
7) and a sensor chip (1) having a detection unit (8 to 11) for detecting acceleration based on the displacement of the weight unit (2), and detecting acceleration based on a detection output of the detection unit. In the semiconductor acceleration sensor, the two beam portions are formed in parallel between the weight portion and the support portion, and the weight portion has a protrusion (2a) projecting between the two beam portions. , 2b). 2. A thick weight portion (2) that is displaced by receiving an acceleration, and a thick support portion (3) formed to surround the weight portion at a predetermined distance from the weight portion. A sensor chip including a thin beam portion (4 to 7) for supporting the weight portion on the support portion, and a detection portion (8 to 11) for detecting acceleration based on displacement of the weight portion (2). 1) a semiconductor acceleration sensor configured to detect acceleration based on a detection output of the detection unit, wherein the support unit has a shape having a plurality of sides (3a to 3d); The two beam portions are formed between a side and the weight portion, and the weight portion has a protruding portion (2a, 2b) protruding between the two beam portions. Semiconductor acceleration sensor. 3. A thick weight portion (2) displaced by acceleration, and a thick support portion (3) formed to surround the weight portion at a predetermined distance from the weight portion. A sensor chip including a thin beam portion (4 to 7) for supporting the weight portion on the support portion, and a detection portion (8 to 11) for detecting acceleration based on displacement of the weight portion (2). 1) The semiconductor acceleration sensor according to claim 1, wherein the acceleration is detected based on a detection output of the detection unit. The support unit has a shape including four sides (3a to 3d). The two beam portions are formed between two opposing sides (3a, 3b) and the weight portion, respectively, and the weight portion has a protruding portion (2a, 2b) protruding between the respective beam portions. ) And has a cross shape when viewed from the thickness direction. Semiconductor acceleration sensor that. 4. A thick weight portion (2) which is displaced by receiving an acceleration, and four sides (3a to 3d) which surround the weight portion with a predetermined distance from the weight portion. A thick support portion (3); thin first and second thin portions formed between the first side (3a) of the support portion and the weight portion, and supporting the weight portion on the first side. And a second side (3b) facing the first side of the support portion.
And the thin third and fourth beam portions (6, 7) formed between the first and fourth beam portions and formed between the weight portions and supporting the weight portion on the second side. And a resistor (8 to 11) formed, wherein the weight portion is the first to fourth resistors.
A semiconductor chip provided with a sensor chip (1) supported by the support portion only by the beam portion, and detecting acceleration based on a change in the resistance value of the resistor; 1, the first projecting between the second beam portions
Projecting portion (2a), a second projecting portion (2b) projecting between the third and fourth beam portions, and projecting in a direction orthogonal to the projecting direction of the first and second projecting portions. A semiconductor acceleration sensor having third and fourth protrusions (2c, 2d) and having a cross shape when viewed from the thickness direction. 5. The method for manufacturing a semiconductor acceleration sensor according to claim 3, wherein the silicon substrate has an epitaxial layer.
0), a coating film (25) is formed on the surface of the silicon substrate with a pattern for forming the cross-shaped weight portion and the support portion, and the silicon substrate is anisotropically etched. Forming a groove extending through the anisotropically etched region and a predetermined region in the predetermined region of the epitaxial layer to form the cross-shaped weight, the beam, and the support. A method for manufacturing a semiconductor acceleration sensor. 6. The silicon substrate is a single-crystal silicon substrate having a {100} plane as a surface, wherein the coating film has a shape corresponding to a cross shape of the weight and a corner portion of the shape. The method for manufacturing a semiconductor acceleration sensor according to claim 5, wherein patterning is performed into a shape having a shape compensating portion aligned with a {110} plane orientation.