JP2775578B2 - Acceleration sensor and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor and a method for manufacturing the same. The present invention particularly relates to an acceleration of a cantilever structure utilizing a piezoresistive effect by a p-type semiconductor formed on a silicon Si chip or a variable capacitor by electrodes formed on both main surfaces of the silicon Si chip. It is suitably used for sensors.

[0002]

2. Description of the Related Art As sensors for detecting acceleration, there are piezoresistive sensors, capacitive sensors and piezoelectric sensors. The piezoresistive type and the capacitive type are excellent in that a continuous acceleration can be detected unlike the piezoelectric type, and their general use is expected.

A piezoresistive acceleration sensor is structurally composed of, for example, a fixing portion 15, a weight 16, and a beam 17 for connecting the weight 16 and the fixing portion 15 with flexibility, as shown in FIG. It comprises a silicon Si chip 12 and two upper and lower silicon lids 13 and 14 that sandwich the fixing portion 15 and seal the weight 16 and the beam 17. The weight 16 is fixed to the fixing portion 15 by applying acceleration to the main body.
Relative to the reference. In the beam 17 of the tip 12, a strain gauge portion (not shown) whose electric resistance changes according to the amount of mechanical deformation of the beam 17 bent by the displacement of the weight 16
However, on the fixed portion 15 of the chip 12, an electric circuit (not shown) for guiding the electric signal of the gauge portion to the outside and an external electrode 18 are formed.

With such a structure, when acceleration is applied to the acceleration sensor 11, an inertial force acts on the weight 16 to displace the weight 16 in a direction opposite to the acceleration. The beam 17 bends in accordance with this displacement, and the electric resistance of the resistive element diffused and formed in the beam 17 changes due to the piezoresistance effect. The piezoresistive acceleration sensor 11 detects the amount of change in resistance and measures acceleration. In addition, stoppers 19 projecting toward the weight 16 are provided on the inner surfaces of the upper lid 13 and the lower lid 14 in order to prevent the beam 17 from being broken due to excessive displacement of the weight 16.

On the other hand, as shown in FIG. 6, for example, as shown in FIG. 6, the capacitive type acceleration sensor is composed of a silicon Si chip 22 comprising a fixed portion 25, a weight 26 and a beam 27, and a Pyrex glass. It comprises lids 23 and 24. The weight 26 is also similar to the piezoresistive type in that the weight 26 is relatively displaced with respect to the fixed portion 25 when acceleration is applied to the main body. However, no resistive element is formed in the beam 27 of the chip 22, and electrodes 28, 28 are respectively provided on the inner surfaces of the upper and lower lids 23, 24 facing both main surfaces of the weight 26.
29 are formed, and a gap is formed between the weight 26 and the electrodes 28 and 29 to form a capacitor.

When acceleration is applied to the sensor 21, the weight 26 is displaced as in the case of the piezo type. The distance between the weight 26 and the electrode 28 (29) changes according to this displacement. That is,
The distance between the weight 26 and the upper electrode 28 increases (or decreases), the distance between the weight 26 and the lower electrode 29 decreases (or increases), and a difference occurs between the upper and lower capacitances. Therefore, when a complementary square wave voltage is applied to the upper and lower electrodes 28 and 29, respectively, when no acceleration is applied, the output is canceled and the output becomes zero. However, when acceleration is applied, a square wave is output due to a capacitance difference. .
The capacitive acceleration sensor 21 detects the square wave and measures the acceleration. The method of manufacturing these piezoresistive and capacitive acceleration sensors will be briefly described as follows.

First, in the case of the piezoresistive type, a low resistance of a p-type semiconductor is formed on one main surface (plane orientation (100)) of a silicon Si wafer of an n-type semiconductor in the same manner as in a known semiconductor chip manufacturing method. Diffusion lead, piezoresistor and Al
Form electrodes. Next, after an Si oxide film is provided on the entire surface, rectangular annular Si is exposed on the surface opposite to the piezoresistor forming surface in a photolithography process. And
Anisotropic etching is performed from the exposed portion toward the piezoresistive surface with an aqueous solution of potassium hydroxide KOH.
By this etching, only a portion corresponding to the beam is left with a predetermined thickness (usually about 8 to 20 μm), and the other portions are pierced. In this manner, the inside of the hollowed portion becomes the weight, the outside is the fixed portion, and the thin portion left by a predetermined thickness becomes the beam. The wafer is removed from the etching solution, washed and dried, and
A lid is anodically bonded to both major surfaces of the chip. Thereafter, it is cut into individual chips. Thus, the acceleration sensor is completed.

In the case of the capacitive type, a silicon Si wafer having no low-resistance diffusion lead, piezoresistor, and Al electrode is prepared, and the main surfaces on both sides are arranged so that the portion corresponding to the beam is located at the center in the thickness direction. Other than performing more anisotropic etching,
It is manufactured through substantially the same process as the piezoresistive type.

[0009]

In any type of acceleration sensor, after the lid is joined to the chip, as described above, the stopper is provided on the inner surface of the lid toward the weight. As a result, the weight is not excessively displaced, so that the beam is prevented from being broken.

However, after the anisotropic etching, until the lid is joined, only the thin beam supports the weight. Therefore, when removing the wafer from the etchant,
When cleaning, cutting into individual chips or combining with a lid, even with great care, the beam is broken, and many defective chips are generated. As a result, the production yield of the conventional acceleration sensor was very low. However, increasing the thickness of the beam reduces the sensitivity of the sensor. That is, conventionally, there has been a problem that the improvement of the sensitivity of the sensor and the improvement of the yield cannot be compatible.

An object of the present invention is to provide a method of manufacturing an acceleration sensor which solves such a problem, prevents a beam from being broken in a manufacturing process, and can achieve both improvement in sensitivity and improvement in yield.

[0012]

[0013]

[0014]

The present invention achieves the above object.
The method for manufacturing an acceleration sensor according to the invention includes preparing a chip having a fixed portion, a weight, and a plurality of beams that flexibly connect the weight and the fixed portion, and sealing the weight and the beam of the chip with a lid. The method is characterized in that other beams are cut so that at least one desired beam remains. The chip preferably has a gage portion for generating a piezoresistive effect formed in the beam, and an electric circuit for guiding the electric resistance of the gage portion to the outside.

In this manufacturing method, it is desirable that the tip before cutting the beam has a geometrically symmetrical shape around the weight. Also desirable is that
This is the case where at least a portion of the lid that can be seen through the beam is made of glass, and the cutting is performed with a laser that passes through the glass.

[0016]

[Action] Until sealed with a lid, a plurality (for example, n pieces)
Since the weight is supported by the beam, the force acting on one beam even when an unexpected force is applied to the weight is reduced to 1 / n of that when the weight is supported by one beam. Therefore, the beam is not easily broken, and the thickness of the beam can be reduced. Further, after sealing with the lid, unnecessary beams are cut, so the number of beams before cutting may be increased or decreased according to the thickness of the beams.

In the case of a piezoresistive sensor in which a gauge portion that produces a piezoresistive effect is formed in a beam, the variation in the resistance value is reduced by leaving the beam whose resistance value falls within a specified range and cutting the other beams. can do. In particular, if the resistance in the beam is designed to be linearly different for each beam, the resistance in at least one of the beams matches the specified value even if the resistance value slightly varies. For example, it is designed so that the resistance value gradually increases in the arrangement order of the beams, and after sealing with the lid, the resistance value is measured in the arrangement order of the beams, and the beams where the resistance matches the specified value are left. ,
The other beams may be cut.

If the tip before cutting the beams has a geometrically symmetric shape about the weight, all beams have the same mechanical properties. Therefore, it is possible to reduce the variation in the flexibility of the beam between the chips. Further, there is no possibility that the beam to be cut is mistaken.

When at least a portion of the lid through which the beam can be seen is made of glass, and the beam is cut by a laser transmitting through the glass, the cutting operation can be performed instantaneously and accurately even if the area of the beam is minute. It is possible to execute.

[0020]

An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a piezoresistive acceleration sensor,
(A) is a plan view thereof, (B) is a cross-sectional view taken along the line X-Y of (A) viewed from the left, (C)
FIG. 3A is a cross-sectional view along the line PQ in FIG. FIG. 2 shows Si as a main component before assembling the acceleration sensor.
FIG. 3 is a plan view of the chip, FIG. 3 is a cross-sectional view of the chip bisected in the longitudinal direction, and FIG. 4 is a bottom view.

[Structure of Acceleration Sensor] A piezoresistive acceleration sensor (hereinafter, also simply referred to as “sensor”) 1 is a semiconductor having a plane orientation (100), a thickness of 300 μm, a long side of 5.0 mm, and a short side of 3.0 mm. It comprises an Si chip 2 and an upper lid 3 and a lower lid 4 made of Pyrex glass joined to the upper and lower main surfaces of the chip 2 respectively. The sensor 1 has a symmetrical shape with respect to the PQ line. Also, X-
It is symmetric about the Y line except for a part described later.

The chip 2 includes a rectangular frame-shaped fixing portion 5, a rectangular weight 6 relatively displaced with respect to the fixing portion 5 when acceleration is applied to the main body of the sensor 1, and the weight 6 and the fixing portion 5. And a beam 7 having a thickness of 8 μm and a width of 200 μm. The beam 7 has flexibility and the weight 6
Bends due to the displacement of In addition, a gauge portion 8 made of a p-type diffusion resistance that produces a piezoresistive effect according to the amount of deformation of the beam 7 is formed in the beam 7.

The weight 6 and the beam 7 are hermetically sealed by the upper lid 3 and the lower lid 4 sandwiching the fixing portion 5. Therefore, in order to detect the electric resistance of the gauge part 8, the lead 9 due to the p-type diffusion low resistance goes out of the upper lid 3 via the inside of the beam 7 in a bifurcated manner from the end of the weight 6, and It is formed up to the outer surface, and an electrode terminal 91 of Al is formed at the end of the lead 9.

On the other hand, at the symmetric position of the beam 7 about the XY line as a central axis, a mark 7 'obtained by cutting a beam having the same shape and the same quality as the beam 7 remains. The upper lid 3 and the lower lid 4 are thinner at the central portion of the inner surface than the outer peripheral portion, and at the central portion, four stoppers 31... It protrudes toward the weight 6 and limits the amplitude of the weight 6.

[Method of Manufacturing Acceleration Sensor] Sensor 1
Are roughly divided into (1) a step of preparing the chip 2 having the fixing portion 5, the weight 6, and the plurality of beams 7, (2) a step of hermetically sealing the weight 6 and the beam 7 with the upper and lower lids 3, 4. (3) Thereafter, it is manufactured through a step of cutting another beam so that at least one desired beam 7 remains. Hereinafter, description will be made in the order of steps.

First, the surface of a silicon Si wafer (not shown) having the (100) plane as a main surface is oxidized at a high temperature to provide a silicon oxide film. A photoresist is applied thereon, and the silicon Si is exposed to the pattern of the lead 9 through exposure and etching.

Next, the plurality of silicon Si wafers thus obtained are alternately arranged with a plurality of BN plates, placed on a quartz boat, and heated in a quartz tube at a temperature of 1 while flowing nitrogen gas.
Perform resistance heating at 100 ° C. Then, the exposed Si
Boron B diffuses into the wafer portion, and only that portion becomes a p-type semiconductor, and the portion covered with the silicon oxide film remains as an n-type semiconductor. By removing the oxide film in the portion corresponding to the gauge portion 8 in the same photolithography process and again diffusing boron B, a piezoresistor is formed in the gauge portion 8, and the p-type semiconductor portion connected to the Lead 9 is obtained. Thereafter, the oxide film at the electrode terminal installation portion is removed, Al is vapor-deposited on the entire surface, and four Al electrode terminals 91 are formed on the leads by a photolithography process (see FIG. 2).

Next, in order to obtain a large number of periodically arranged patterns having one dimension pattern in FIG. 4, a rectangular annular Si is formed on the surface opposite to the piezoresistor forming surface by a photolithography process. Expose. However, at this stage, a portion of the oxide film for forming the beam is left. And A
1) A protective plate is attached to the surface of the silicon Si wafer on the electrode terminal side so as not to be attacked by potassium hydroxide KOH, and then exposed from the exposed portion of the opposite surface toward the piezoresistance forming surface with an aqueous solution of potassium hydroxide KOH. First anisotropic etching is performed. Subsequently, the Si on the surface forming the beam
After the oxide film is removed by the photolithography process, the secondary anisotropic etching is similarly repeated.

By these etchings, only the portion corresponding to the beam 7 (in this example, two places on the left and right sides of the paper) is left with a thickness of 8 μm, and the other portions are penetrated into a trapezoidal cross section. In this case, since the (111) plane is harder to be etched than the (100) plane crystallographically, the etching solution is (11)
1) Plane direction, that is, with respect to the main surface of the wafer
Erosion in 7 ° direction. Therefore, by determining the area of the rectangular ring that exposes Si on the etching start surface, the etching can be performed accurately as calculated.
Thus, the weight 6 is on the inside of the hollow portion, the fixing portion 5 is on the outside, and the two thin portions left by a predetermined thickness become the beams 7, 7 (see FIG. 3).

After the wafer is taken out of the etching solution, the protective plate is removed, washed and dried, the upper and lower lids 3 and 4 are anodically bonded to both main surfaces of the Si chip. Then, the individual chips 2, 2,... 2 are cut.

Lastly, a probe of a resistance meter (not shown) is applied to the electrode terminal 91 to measure the resistance value of the left and right gauge portions 8. Then, the beam 7 whose resistance value is closer to the specified value (the left side of the drawing in this example) is left, and the other beam 7 is left.
(The right side) is irradiated with a YAG laser having an oscillation wavelength of 1.06 μm through the glass upper lid 3 to cut the beam. Thus, the acceleration sensor 1 is completed. The laser to be irradiated may be any light having a property of transmitting the upper lid 3 and capable of cutting silicon. For example, A laser may be used instead of the YAG laser.
It is also possible to use an r laser.

[Function and Effect] In the case of the acceleration sensor of this embodiment,
Before sealing with the upper and lower lids 3, 4, the two beams 7, 7
Since the weight 6 is supported at (FIGS. 2 to 4), even if an unexpected force is applied to the weight 6, the force acting on one beam is 1 / the value of the case of supporting with one beam. Reduce to 2. Therefore, the beam was not easily broken, and the thickness of the beam could be reduced. As a result, even if the thickness of the beam was reduced to 5 μm, a yield of 90% or more could be achieved.

Further, by leaving only the beam whose resistance value falls within the specified range and cutting the other beam, the variation in resistance could be reduced. As a result, variation in sensitivity to acceleration was reduced.

The chip 2 before cutting the beams 7, 7 is
Is geometrically symmetrical with respect to the center of the beam, so that any of the beams 7, 7 can be cut to satisfy the design specification conditions other than the resistance value.

Since the upper lid 3 is made of Pyrex glass and the beam is cut by a YAG laser penetrating the glass, the cutting operation can be performed instantaneously and accurately even if the area of the beam is fine. Further, since the upper lid 3 is made of Pyrex glass, it is possible to know the inside of the sensor after completion.

[0036]

As described above, according to the present invention, even if the beam is thinned, it is possible to prevent the beam of the acceleration sensor from being broken in the manufacturing process. Therefore, both improvement in sensor sensitivity and improvement in yield can be achieved.

[Brief description of the drawings]

FIG. 1 shows a piezoresistive acceleration sensor according to an embodiment;
(A) is a plan view thereof, (B) is a cross-sectional view taken along the line X-Y of (A) viewed from the left, (C)
FIG. 3A is a cross-sectional view along the line PQ in FIG.

FIG. 2 is a plan view of a Si chip as a main component of the acceleration sensor of FIG.

FIG. 3 is a cross-sectional view of the Si chip of FIG. 2 cut into two in the longitudinal direction.

FIG. 4 is a bottom view of a Si chip as a main component of the acceleration sensor of FIG.

FIG. 5 is a sectional view of a conventional piezoresistive acceleration sensor.

FIG. 6 is a sectional view of a conventional capacitive acceleration sensor.

[Explanation of symbols]

1,11,21 ... acceleration sensor 2,12,22
... Semiconductor Si chip 3,13,23 ... Top cover 4,14,24
… Lower lids 5,15,25… Fixed parts 6,16,26
... weight 7, 17, 27 ... beam 8
… Gauge part

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01P 15/12 H01L 29/84

Claims (5)

(57) [Claims] 1. A chip having a fixing portion, a weight, and a plurality of beams for connecting the weight and the fixing portion with flexibility is prepared, and after the weight and the beam of the chip are sealed with a lid, at least one of the chips is provided. A method of manufacturing an acceleration sensor, comprising cutting another beam so that a desired beam remains. 2. The acceleration according to claim 1 , wherein the prepared chip has a gauge portion for generating a piezoresistive effect formed in the beam, and an electric circuit for guiding the electric resistance of the gauge portion to the outside is wired. Manufacturing method of sensor. 3. The method for manufacturing an acceleration sensor according to claim 2 , wherein the resistance in the beam is designed to be linearly different for each beam. Wherein the chip before cutting the beam, in the manufacturing method for the acceleration sensor according to claim 1 has a geometrically symmetrical shape around the spindle. 5. A portion can be viewed at least the beam of the lid made of glass, a manufacturing method of an acceleration sensor according to claim 1, cutting is performed by a laser that transmits the glass.