JPH05335596A - Semiconductor acceleration sensor and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a semiconductor acceleration sensor with a stopper which does not require any cost for mounting such as bonding for the stopper, controls gap with high accuracy and does not break even when an excessive acceleration is applied during wafer process. CONSTITUTION:A weight and side of weight which are displaced together during application of acceleration are defined by etching two layers in both sides of a triple-layer structure of an N type layer/oxide film/P type substrate to form grooves 27, 28, a part where both grooves are mutually off-set on the surface is provided and both grooves are connected by etching the oxide film 31 in the lateral direction. Thereby, the weight/side of weight may be displaced and the offset area works simultaneously as a built-in stopper.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor acceleration sensor with a stopper and a method for manufacturing the same.

[0002]

2. Description of the Related Art As a semiconductor acceleration sensor of this type,
"A Batch-Fabricated Silicon Accelerometer" (I
EEE TRANS. VOL. ED-26 DEC. 1979), which is shown in FIGS. 6 and 7. That is, the groove 10 is removed from the silicon wafer 1 by selective etching, and a thin cantilever 2 extending from the weight portion 3 and the fixing portion 4 to support the weight portion 3 is formed. A piezoresistor 5 is formed on the upper surface of the cantilever 2, and the resistance value changes due to the stress when the beam 2 is bent by the application of acceleration. Further, a piezoresistor 6 is formed on the upper surface of the fixed portion 4, and together with the resistor 5, a bridge circuit is formed. Stoppers 7 and 8 are provided on both upper and lower surfaces of the silicon wafer 1 to prevent the cantilever 2 from being damaged when an excessive acceleration is applied.

Such a silicon wafer is manufactured by the process shown in FIG. First, in step (a), an n-type epitaxial layer 12 is grown on a single crystal P-type (100) silicon substrate 11 to form a P-type diffusion layer region 13 reaching the substrate 11 from the surface. The P-type regions 13 are arranged so as to surround the weight portion 3 so as to form the grooves 10 in FIG. 7. A SiO ₂ film (silicon oxide film) 14 is formed on the n-type epitaxial layer 12.

Next, in the step (b), a P-type piezoresistor 15 is formed in the <110> direction by ion implantation of boron or the like, and an etching resistant film 16 such as Si ₃ N ₄ is deposited on the back surface. Perform patterning.

Then, in step (c), contact etching and formation of the wiring electrode 17 are performed. In the final step (d), when the silicon wafer is etched with an anisotropic alkaline etching solution while biasing the n-type epitaxial layer 12 to a positive potential, the P-type substrate 11 is etched so that the (111) plane remains, The surface is etched at the portion where the P-type region 13 is present. On the other hand, in the beam part, n
Only the mold epitaxial layer 12 remains without being etched, and the cantilever 2 supporting the weight portion 3 is obtained.

Through the above steps, the silicon wafer produced by the batch processing is thereafter divided into chips, and the upper and lower stoppers 7 and 8 are fixed by adhesion or the like to form an acceleration sensor with a stopper.

In addition, as a stopper to be built in the chip, the P-shaped region formed in the L shape is electro-formed by using a strongly alkaline anisotropic etching liquid while applying a positive voltage to the surrounding n-type region. The chemical etching method or the mixture ratio of the n + silicon embedded layer is HF: HN
A method has been proposed in which lateral selective etching is performed with a liquid of O ₃ : CH ₃ COOH = 1: 3: 8.

[0008]

However, in such a conventional semiconductor acceleration sensor, in the case of the stopper bonding method, the upper and lower stoppers are bonded after the wafer processing process is completed, that is, after the cantilever is formed. Since (1) excessive acceleration is applied during the wafer processing process, the cantilever will be damaged and the yield will be greatly deteriorated. (2) For bonding the upper and lower stoppers for each chip It takes a lot of work and the implementation cost becomes high,
(3) It is difficult to control the accuracy of the gap with the stopper, and it is difficult to stably obtain the air damping effect for preventing resonance.

Even in the chip built-in type, in the anisotropic etching method, the (111) plane which becomes the etch stop surface is generated in the middle of the process, and it is impossible to etch into an arbitrary shape. The selective etching method of the n + buried layer However, there is a problem that it is difficult to stably etch a large area because the liquid management is delicate, and none of them has been commercialized. It is therefore an object of the present invention to solve the above problems by making it possible to form stoppers without difficult obstacles during the wafer processing process.

[0010]

The present invention has a single crystal semiconductor layer formed on a single crystal semiconductor substrate via an insulating film, and the single crystal semiconductor substrate has a weight portion formed by a groove formed in the substrate. And a fixed portion, and the single crystal semiconductor layer has a weight side portion substantially corresponding to the weight portion, a fixed side portion substantially corresponding to the fixed portion, a fixed side portion and a weight by the groove formed in the layer. The groove is divided into a beam connecting a side portion, and each groove has a portion that is offset in a plane with respect to each other so that the weight portion and the fixed side portion or the fixed portion and the weight side portion overlap each other. At the same time as the formation, the insulating film was made to communicate with each other through the voids removed along the periphery of the weight portion, and the voids were removed by etching so that the weight portion could be displaced and the offset portion became a built-in stopper.

[0011]

1 and 2 show an embodiment of the present invention in which a single crystal n-type silicon layer 21 is formed on a single crystal P-type silicon substrate 20 via an insulating film 31, and a SiO ₂ film 23 is formed. Covered. The P-type substrate 20 is divided into a substantially square weight portion 33 and a fixed portion 34 by an etching groove 28 from the back surface, and the weight portion 33 is connected to and supported by the fixed portion 34 by a cantilever 22 made of an n-type layer. ..

The n-type layer 21 is separated by a groove 27 into a weight side portion 35 corresponding to the cantilever beam 22 and the weight portion 33, and a fixed side portion 36 corresponding to the fixed portion 34. The groove 27 is a plane groove 28. And a portion S that is offset from each other, and communicates with a groove 28 on the back surface of the substrate via a lateral gap 29. A piezoresistor 25 is formed on the surface of the cantilever 22 by ion implantation of boron or the like, and a resistance value change as an acceleration sensor is generated as an output based on the stress due to the deflection of the beam when acceleration is applied.

The offset between the grooves 27 and 28 has a plurality of protrusions 37 in which the n-type layer on the fixed side portion overlaps the weight portion 33, and the n-type layer on the weight side portion is on the fixed portion 34 of the substrate. It is formed by bending the upper groove 27 in FIG. 1 so as to have a plurality of protrusions 38 overlapping with each other. As shown in FIG. 3, the protrusion 3
The other side on which 7 (38) overlaps becomes a receiving portion 39 (40). The groove 28 may be bent, but it becomes a beam n
Since the shaping layer is formed to be thin, the groove 27 has an advantage that it can be processed more accurately even if the groove 27 has a complicated shape as illustrated.

As a result, a stopper is formed in the chip, and the upward displacement of the weight 33 in FIG. 2 is limited by the contact of the receiving portion 39 of the P-type substrate weight with the protrusion 37, Similarly, the downward displacement is limited by the protrusion 38 on the side of the n-type layer weight contacting the receiving portion 40 of the P-type substrate fixing portion.

The acceleration sensor described above is manufactured by the process shown in FIG. First, in step (A), the n-type layer 21 is formed on the (100) surface of the P-type silicon substrate 20 with the silicon oxide film SiO _{2 serving} as the insulating film 31 interposed therebetween. This three-layer formation is performed by implanting oxygen ions into the P-type silicon substrate 20 and annealing it to embed an oxide film in the substrate and then SIMOX.
After forming the structure, it can be obtained by epitaxially growing the n-type layer 21 or by adhering a second wafer having an oxide film formed on its surface to a sensor substrate wafer at a high temperature.

Next, in step (B), the surface of the n-type layer 21 is subjected to S
After covering with an iO ₂ film and ion-implanting into the portion which becomes the cantilever 22, a P-type piezoresistor 25 is formed, and then contact etching and aluminum wiring (not shown) are performed. Further, a groove 27 reaching the insulating film 31 is formed around the beam and the portion to be the weight by RIE (reactive ion etching), anisotropic etching with a strong alkaline solution, or isotropic etching with hydrofluoric nitric acid. On the other hand, the substrate 20
S is opened on the back surface of the so as to surround the part that becomes the weight part.
An etching resistant film 30 such as an i ₃ N ₄ film is formed.

In step (C), anisotropic etching is performed from the back surface of the substrate 20 with a strong alkaline liquid such as KOH, hydrazine, EDP (ethylene, diamine, pyrocatechol aqueous solution). Since the cantilever and the weight are oriented in the <110> direction, the etching stops at the (111) plane which is in contact with the opening edge 32 of the etching resistant film 30, while the etching progresses in the upward direction to form the buried oxide film. Insulating film 31
And stops, and the groove 28 is formed.

Finally, in step (D), the buried oxide film which is the insulating film 31 is laterally etched from the groove opening,
The groove 27 is formed through the groove 27 and the groove 28. As a result, the protrusion 37 (3
8) and the receiving portion 39 (40) is formed in the chip as an acceleration sensor.

Although the insulating film 31 is formed on the entire surface of the chip here, when SIMOX is used, the buried oxide film can be formed only on the portion where the stopper is provided by masking at the time of oxygen ion implantation.

In the semiconductor acceleration sensor manufactured as described above, when a vertical acceleration is applied to the weight portion 33, the cantilever 22 bends, and the stress changes the resistance value of the piezoresistor 25 to detect the acceleration. .. Here, since the thickness of the cantilever 22 can be controlled by the thickness of the n-type layer 21, it is possible to suppress variations in sensitivity of the acceleration sensor to be low.
When an excessive acceleration is applied, the stopper limits the displacement of the weight portion and thus prevents the cantilever from being damaged.

In this semiconductor acceleration sensor, peripheral circuits can be integrated in the same chip to form an IC sensor. That is, FIG. 5 shows a portion in which NPN transistors are integrated as elements of peripheral circuits such as an amplifier, a bridge bias circuit, and a temperature compensation circuit, which are built together with the same acceleration sensor unit as in FIG.

Circuit element separating groove 4 filled with an insulating agent
In the island of the n-type layer 21 surrounded by 3, the P-type region 44 is provided as a base, and the n + emitter region 45, n +
A collector region 46 is formed, and a metal electrode 47 of the piezoresistor 25 and a metal electrode 48 connected to each region of the transistor are provided on the SiO ₂ film 23. Reference numeral 49 is an n + region as an embedded collector having a low specific resistance. Then, such a circuit element is built in each island of the n-type layer divided into a large number. Therefore, an SOI structure in which each element is separated by an insulator can be easily obtained, and an IC sensor capable of operating at high temperature can be obtained.

An example using a cantilever has been described above, but the invention is not limited to this, and a cantilever or a type in which four sides of the weight portion are supported by four beams is also applicable.
Further, in order to detect the displacement of the weight portion, for example, not only the piezoelectric element formed on the surface portion of the n-type layer as an electric element but also the back surface portion of the weight portion P-type substrate or the weight side portion n-type layer surface portion. Even in the type in which the electrode for detecting the electrostatic capacitance is formed, the electric element can be formed before the gap 29 is formed.

[0024]

As described above, according to the present invention, a single-crystal semiconductor three-layer structure wafer sandwiching an insulating film is used to form grooves in two layers on both sides to define a portion which is displaced when acceleration is applied. , The two grooves on the plane are offset from each other, and the insulating film between them is used to connect the two grooves by a gap so that the offset portion serves as a stopper to prevent displacement beyond the gap. There is an effect like.

(1) It is not necessary to further mount the stopper after the chip is manufactured by adhering it, and the stopper can be built in by batch processing, and the manufacturing cost can be reduced. (2) Even if an excessive acceleration is applied during the wafer process, the displacement becomes possible and at the same time the stopper is formed in the chip.
Beam damage is prevented and yield is improved. (3) Since the gap of the stopper can be accurately controlled by the thickness of the insulating film 31, the air damping function can be exhibited to prevent the resonance of the beam, and the oil damping is also unnecessary.

Also, compared with the conventional in-chip stopper built-in type, unlike the anisotropic etching method (1
11) It is not necessary to consider the etching stop on the surface, and an extremely large etching rate selection ratio can be obtained by using a combination arrangement of silicon and an insulating film, particularly SiO _{2 as} compared with the lateral selective etching method of single crystal silicon. There is an advantage that the degree of freedom in designing the stopper is very high, such as the fact that it can be utilized and the lateral etching of the gap part can be performed accurately.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of the present invention.

FIG. 2 is a sectional view taken along line XX of FIG.

FIG. 3 is a perspective view showing a stopper portion.

FIG. 4 is a diagram showing a manufacturing process of an example.

FIG. 5 is a diagram showing another embodiment.

FIG. 6 is a diagram showing a conventional example.

7 is a cross-sectional view taken along line YY of FIG.

FIG. 8 is a diagram showing a manufacturing process of a conventional example.

[Explanation of symbols]

 20 P-type silicon substrate 21 n-type layer 22 cantilever 25 piezoresistive 27, 28 groove 29 void 30 etching resistant film 31 insulating film 33 weight part 34 fixing part 35 weight side part 36 fixing side part 37, 38 protrusion 39, 40 Receiver

Claims (7)

[Claims] 1. A single crystal semiconductor layer is formed on a single crystal semiconductor substrate via an insulating film, and the single crystal semiconductor substrate is divided into a weight portion and a fixed portion by a groove formed in the substrate. A beam connecting the weight side portion substantially corresponding to the weight portion, the fixed side portion substantially corresponding to the fixed portion, and the fixed side portion and the weight side portion by the groove formed in the single crystal semiconductor layer. And each of the grooves is formed so that the weight portion and the fixed side portion or the fixed portion and the weight side portion are overlapped with each other, and the insulating film has Are communicated with each other through the void removed along the periphery of the weight,
A semiconductor acceleration sensor comprising means for sensing the displacement of the weight portion. 2. The offset portion is formed by bending the groove formed in the semiconductor layer by projections alternately extending from the weight side portion and the fixed side portion. Semiconductor acceleration sensor. 3. The semiconductor acceleration sensor according to claim 1, wherein the insulating film is a silicon oxide film. 4. The semiconductor acceleration sensor according to claim 1, wherein the means for sensing the displacement of the weight portion includes a piezoresistor formed on the surface portion of the beam. 5. A first step of forming a wafer in which a single crystal semiconductor layer is provided on a main surface of a single crystal semiconductor substrate via an insulating film, wherein the semiconductor substrate of the wafer is etched from the back surface to the insulating film. Then, a groove is formed to divide the substrate into a weight portion and a fixed portion, and the semiconductor layer is etched from the upper surface until reaching the insulating film, and the semiconductor layer is provided with a weight side portion substantially corresponding to the weight portion. The weight portion and the fixed side portion are divided into a fixed side portion that substantially corresponds to the fixed portion and a beam that connects the fixed side portion and the weight side portion, and that has a portion that is offset on the plane with the groove. Or a second step of forming a groove so that the fixing portion and the weight side portion overlap with each other, and thereafter, the insulating film is laterally etched along the periphery of the weight portion to form a void for communicating the both grooves. It consists of the third step of forming, A method of manufacturing a semiconductor acceleration sensor and having a fourth step of forming an electrical elements for sensing the displacement of the weight portion in the surface portion of the semiconductor substrate or semiconductor layer. 6. The method of manufacturing a semiconductor acceleration sensor according to claim 5, wherein the insulating film in the first step is formed by ion implantation of oxygen into the semiconductor substrate. 7. The method of manufacturing a semiconductor acceleration sensor according to claim 5, wherein the first step is performed by adhering a semiconductor layer having an oxide film formed on the surface thereof to the semiconductor substrate.