JPH0740045B2 - Semiconductor acceleration sensor - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor acceleration sensor having a stopper structure that can be formed by batch processing.

[Prior art]

A conventional semiconductor acceleration sensor is, for example, an IEEE Electron Devices (IEEE Ele
ctron Devices, vol.ED-26, No.12, p.1911, Dec.1979
"A Batch-Fabricated Silicon Accelerometer").

FIG. 2 is a perspective view of the above device and AA ′, BB ′.
FIG. In FIG. 2, 21 is a Si substrate, 22 is a Si cantilever, 23 is a Si weight, 24 is a void, and 25 is a piezoresistor.

In the semiconductor acceleration sensor shown in FIG. 2, when the acceleration is applied, the Si weight 23 is displaced, and thereby the Si cantilever 22 is distorted. A piezoresistor 25 is formed on the surface of the Si cantilever 22, and when strain occurs in the Si cantilever 22, the resistance value of the piezoresistor 25 changes due to the piezoresistive effect. Acceleration can be detected by detecting the change in the resistance value.

Further, as a mounting structure of the above-mentioned sensor chip, a structure as shown in FIG. 3 (perspective view and XX ′ sectional view) is shown. This is a structure to prevent the cantilever from breaking due to excessive acceleration such as dropping.
It has a structure in which the Si substrate 21 having the above is sandwiched by two stoppers, a lower stopper 26 and an upper stopper 27.

[Problems to be solved by the invention]

However, the acceleration sensor having the above structure has the following problems.

First of all, in the above structure, since there is no function of suppressing the displacement of the weight between the formation of the beam and the formation of the stopper, it is necessary to take great care in handling the chip. If the value is bad, there is a problem that the material is destroyed and the yield is reduced.

Secondly, there is a problem that the stopper forming process becomes complicated and the cost increases. That is, one of the purposes of forming the acceleration sensor with a semiconductor is to reduce the cost per chip by batch processing. As is clear from IC manufacturing, many chips are formed on a wafer and processed at the same time. By doing so, it is possible to produce a product of stable quality and low cost, but the structure in which the upper and lower stoppers are bonded to each other after forming the beam as shown in FIG. 3 causes a significant increase in cost.

Thirdly, there is a problem of difficulty in forming a stopper. That is, in the structure shown in FIG. 3, the distance between the stopper and the weight must be controlled with an accuracy of several μm to several tens of μm depending on the design of the beam, and high accuracy is required for forming the stopper and adhering to the chip. There is a problem in that a high stopper manufacturing technique and a stopper bonding technique are required, resulting in a high mounting cost.

Furthermore, in the acceleration sensor as described above, a weight such as a metal may be added to the upper surface of the Si weight 23 in order to reduce the sensitivity of the other axis, but the thickness of such a metal weight inevitably varies. Since it occurs, it is difficult to precisely set the distance between the weight and the stopper (the distance between the metal weight formed on the upper surface of the Si weight 23 in FIG. 3 and the upper stopper 27), and therefore a stopper with a high precision effect can be obtained. There is also the problem that it will be difficult to realize.

The present invention has been made to solve various problems of the prior art as described above, and it is possible to form a stopper during sensor chip formation, that is, during a wafer process.
An object of the present invention is to provide a semiconductor acceleration sensor which has stable and uniform performance, is inexpensive, and is suitable for mass production.

[Means for Solving the Problem] In order to solve the above problem, in the present invention, when the acceleration detection direction, that is, the direction in which the beam portion is distorted is a vertical direction, it faces the fixed portion of the weight portion. A single or a plurality of first protrusions provided integrally with the weight portion, and a portion integrally provided with the fixing portion at a portion of the fixing portion facing the weight portion; It is configured to include a single protrusion or a plurality of second protrusions which are overlapped with each other at a predetermined interval in the vertical direction and are spaced apart from each other.

With the above-mentioned configuration, in the present invention,
When an excessive acceleration is applied and the displacement of the mutual position of the weight part and the fixed part becomes large, the first projection part and the second projection part hit and prevent further displacement.
The beams can be effectively protected from damage.

Example of Invention

FIG. 1 is a diagram showing an embodiment of the present invention, which is a plan view and A-
An A'sectional view and a BB 'sectional view are shown.

In Fig. 1, a Si cantilever 13 having a Si weight 12 at one end is
A piezoresistor 14 is formed on the surface of the Si cantilever 13, which is fixed to the Si support portion (fixing portion) 11. The process up to this point is the same as the conventional example shown in FIG.

In the peripheral portion of the Si weight 12 and the predetermined region of the Si support portion 11 on the Si weight 12 side, the first protrusions 15 on the Si weight side,
The second protruding portion 16 on the Si support portion side is formed as follows. That is, the first protrusion 15 and the second protrusion 16 are
And the second protrusions are formed so as to overlap each other with a predetermined gap 17 therebetween.

The way of overlapping is as follows:
As shown on the right side of the B ′ cross-sectional view, the first protrusion 15 has the second protrusion 16
There is a way of overlapping so that the second projecting portion 16 is on the first projecting portion 15 as shown on the left side of the BB ′ sectional view of FIG. The first protrusion 15 and the second protrusion 16 are formed so as to have one side.

Next, the operation will be described.

When the acceleration in the α ₁ direction (direction from the front to the back of the paper) shown in FIG. 1 is applied, the Si weight 12 is displaced in the opposite direction to α ₁ , and the Si weight 12 is shown in the left side of the BB ′ sectional view in FIG. 1 protrusion
A space 17 between the second protrusion 16 and the second protrusion 16 is narrowed. When an excessive acceleration is applied, the first protrusion 15 and the second protrusion contact each other, so that the displacement of the Si weight 12 is stopped.
Therefore, excessive stress is not applied to the Si cantilever 13, and damage to the Si cantilever 13 can be prevented.

Similarly, when an excessive acceleration in the α ₁ direction (direction from the back surface to the front surface of the paper) is applied, AA ′ in FIG.
In the right side of the sectional view and the right side of the BB 'sectional view, the first protrusion 15 is the second
Since it hits the protrusion 16, the displacement of the Si weight 12 is stopped.

The size of the gap 17 between the first and second protrusions can be set arbitrarily, and this value determines the range of measurable applied acceleration.

Next, FIG. 4 is a view showing a first embodiment of the manufacturing process of the apparatus of FIG.

In Fig. 4, first, in (a), the p-type S of the <100> plane is used.
A lower n-type Si layer 42 having a predetermined thickness and a lower etching p-type Si window 43 are formed on the i substrate 41. As a method of forming the lower n-type Si layer 42, there are a thermal diffusion method, an epitaxial growth method and the like.
In order to form the lower etching p-type Si window 43, a method using thermal diffusion and a method of leaving the lower etching p-type Si window 43 in advance when the lower n-type Si layer 42 is formed by the thermal diffusion method are used. There is a method of diffusion.

Next, in (b), a p-type Si layer 44 is formed on the lower n-type Si layer 42 and the lower etching p-type Si window 43 by a thermal diffusion method or an epitaxial growth method. The thickness of the p-type Si layer 44 determines the first and second protrusion voids 17.

Next, in (c), an upper n-type Si layer 45 and an upper etching p-type Si window 46 are formed on the p-type Si layer 44. As a forming method, the same method as the lower n-type Si layer 42 and the lower etching p-type Si window 43 can be used.

Next, in (d), a piezoresistor 14 is formed in a predetermined region by using a thermal diffusion method, and then a SiO ₂ film or a Si ₃ N ₄ film serving as a Si etching mask is formed in a predetermined region on the back surface. After that, p-type Si is selectively etched using an electro-chemical etching method using an alkaline etching solution with the lower n-type Si layer 42 and the upper n-type Si layer 43 as anodes. Details of the electro-chemical etching method are described in JP-A-61-97572 (manufacturing method of semiconductor acceleration sensor) and the like.

As a result of the above etching, Si support 11, Si weight 12, Si
The cantilever 13, the first protrusion 15, and the second protrusion 16 serving as a stopper are simultaneously formed.

As described above, in this embodiment, since the stopper for preventing Si cantilever bending can be formed during the wafer process,
The yield is improved and the mounting cost is reduced because it is not necessary to form a stopper later.

Further, since the precision of the stopper is determined by the thickness of the p-type Si layer formed during the wafer process, it can be formed with extremely high precision.

Furthermore, one of the features of the above process is
The stopper may be formed at the same time when the Si cantilever 13 is formed by using the chemical etching method. Therefore, no special process is required to form the stopper, and the stopper can be easily formed.

In the manufacturing process of FIG. 4, in order to form the first protrusion 15 and the second protrusion 16, the lower n-type Si layer 42 and the p-type Si layer 42 are formed.
Layer 44 and upper n-type Si layer 45 are used, but lower n-type Si
The layer 42, the p-type Si layer 44, and the upper n-type Si layer 45 do not necessarily have to be formed on the entire surface, and may be formed only in the region where the stopper structure is formed. As an example thereof, there is a structure as shown in FIG.

Further, the p-type Si layer 44 is necessary only when the first protrusion 15 and the second protrusion 16 are formed, and the p-type Si layer 44 may be completely etched away after the formation.
An example thereof is shown in FIG.

Further, the present invention can be applied not only to the cantilever structure shown in FIG. 1 but also to a plurality of beam structures such as a cantilever beam shown in FIG. I can.

Next, FIG. 8 is a diagram showing a second embodiment of the manufacturing method of the present invention.

In FIG. 8, first, in (a), the p-type S of the <111> plane is
A lower n-type Si layer 42 having a predetermined thickness and a lower etching p-type Si window 43 are formed on the i substrate 41.

Next, in (b), a SiO ₂ layer 50 is formed on the lower n-type Si layer 42 and the lower etching p-type Si window 43 by using the oxygen ion implantation method, and the Si layer is further formed on the SiO ₂ layer 50. 45 is formed using an epitaxial growth method. The thickness of the SiO ₂ layer 50 determines the gap 17 between the first and second protrusions.

Next, in (c), an upper etching window 46 is formed in a predetermined region of the Si layer 45. As the etching window 46, p-type Si is used.
When using, it can be formed by using a thermal diffusion method. When SiO ₂ is used for the etching window 46, it is formed by thermally oxidizing a predetermined region of the Si layer 45.

Next, in (d), a piezoresistor 14 is formed in a predetermined region using a thermal diffusion method, and then a SiO ₂ film or a Si ₃ N ₄ film to be a mask for Si etching is formed in a predetermined region on the back surface of the Si substrate. Then, using an electro-chemical etching method in which the lower n-type Si layer 42 and the Si layer 45 are used as anodes and an alkaline etching solution is used, a predetermined region on the back surface of the Si substrate and a lower etching p
Etch the shaped Si window 43. Etching window 46 is p-type Si
In the case of, the etching is carried out simultaneously at this time.

Finally, the SiO ₂ layer 50 is etched. Etching window 46
When SiO ₂ is SiO _2, the etching window 46 is also etched at the same time.

As a result of the above wafer process, Si support 11, Si
The weight 12, the Si cantilever 13, the first protrusion 15, and the second protrusion 16 acting as a stopper are simultaneously formed.

Next, a third embodiment of the manufacturing method of the present invention will be described.

As a conventional method of manufacturing a semiconductor acceleration sensor, for example, there is one as shown in FIG.

This conventional example is an electro-chemical method disclosed in JP-A-61-97572 (method for manufacturing a semiconductor acceleration sensor).
It is a method of manufacturing the semiconductor acceleration sensor shown in FIG. 2 using an etching method. The electro-chemical etching method in this case is a method of selectively etching p-type Si using n-type Si as an anode and an alkaline etching solution.

In FIG. 9, first, in (a), the p-type S of the <100> plane is used.
On the i substrate 141, an n-type Si layer 128 having a predetermined thickness and a p-type Si window 129 are formed.
To form. The n-type Si layer 128 is formed by a thermal diffusion method or an epitaxial growth method, and the p-type Si window 129 is formed so that the p-type Si window 129 remains in advance when the thermal diffusion method or the n-type Si layer 128 is formed by the thermal diffusion method. It is formed by a method of performing diffusion. Further, a piezoresistor 25 is formed in a predetermined region on the n-type Si layer 128 by using a thermal diffusion method.

Next, in (b), S is applied to a predetermined area on the back surface of the p-type Si substrate 141.
After forming a SiO ₂ film or a Si ₃ N ₄ film as an i-etching mask, a p-type Si film is selectively formed by an electro-chemical etching method using an alkaline etching solution with the n-type Si layer 128 as an anode. Etch. As a result, Si
The support portion 21, the Si weight 23, the Si cantilever 22, and the void 24 are formed at the same time.

However, in such a conventional method of manufacturing a semiconductor acceleration sensor, the anisotropy of electro-chemical etching is so strong that the etching stops at the <111> plane, so that it is shown in a partially enlarged view of FIG. 10 (a). As shown in FIG.
Since the stress tends to concentrate on the Y and Y'points, the Si cantilever easily breaks due to the concentration of stress, and etching stops at the <111> plane.
There was a problem that the shape of Si could not be etched and the structure that could be processed was limited.

The present embodiment solves the above-mentioned problems by using isotropic etching that can selectively etch p-type Si.

FIG. 12 is an embodiment diagram showing the above manufacturing method.

In FIG. 12, first, in (a), a lower n-type Si layer 242 having a predetermined thickness and a lower etching p-type are formed on a p-type Si substrate 221.
Form Si window 243. As a method of forming the lower n-type Si layer 242, there are a thermal diffusion method and an epitaxial growth method. As a method of forming the p-type Si window 243 for lower etching,
A method using thermal diffusion and a p-type Si window 243 for lower etching are previously prepared when the lower n-type Si layer 242 is formed by the thermal diffusion method.
There is a method of diffusing so that there is left.

Next, in (b), the p-type Si layer 244 is formed on the lower n-type Si layer 242 and the lower etching p-type Si window 242 by a thermal diffusion method or an epitaxial growth method. The thickness of the p-type Si layer 244 determines the gap 17 between the first and second protrusions.

Next, in (c), the upper n-type Si layer 245 is formed on the p-type Si layer 244.
And a p-type Si window 246 for upper etching is formed. This formation method includes a lower n-type Si layer 242 and a lower etching p-type.
There is a method similar to the shape Si window 243.

Next, in (d), after forming the piezoresistor 14 in a predetermined region by using a thermal diffusion method, a SiO ₂ film or a Si ₃ N ₄ film serving as a mask is formed in a predetermined region on the back surface of the p-type Si substrate 221. To do. next,
The p-type Si is made porous by using an anodic treatment method in hydrofluoric acid. The porous step is described in JP-A-48-10
2988 in detail.

Next, in (e), the porous p-type Si is isotropically etched and the oxide film formed by oxidizing is etched. As a result, Si support 11, Si weight 12, Si cantilever 13,
First protrusion 15 and second protrusion acting as a stopper
16 are formed at the same time.

In the above manufacturing method, since the etching process is isotropic etching, unlike the case of using anisotropic etching as in the conventional example, a corner portion where stress is concentrated such as the Y portion is formed. Not done. That is, when manufactured by the manufacturing process of this embodiment, as shown in the Y part of FIG. 10 (b), it has a rounded shape, and stress is higher than that of the Y part of FIG. 10 (a). You can see that the structure is not concentrated.

As described above, the stress is less likely to be concentrated, and thus the withstand capacity of the Si cantilever is increased.

Further, in the case of the embodiment of FIG. 12 described above, since the etching is isotropic, there is no stopping of etching due to the <111> plane, and therefore etching of any structure can be performed.

The embodiment of FIG. 12 shows that the Si cantilever beam 13 is formed at the same time that the stopper for preventing the Si cantilever beam from being bent is formed. Even when this embodiment is applied to, since the structure is such that stress is not concentrated, the withstand capacity of the Si cantilever can be improved.

In the case of this embodiment as well, similar to the embodiment of FIG. 4, the lower n-type Si layer 242, the p-type Si layer 244 and the upper n-type Si layer 242 are formed.
The layer 245 does not necessarily have to be formed on the entire surface, and may be formed only in the region where the stopper structure is formed. As an example thereof, there is a structure as shown in FIG.

Further, the p-type Si layer 244 is necessary only when the second protrusion 16 of the first protrusion 15 is formed, and the p-type Si layer 244 is formed after the formation.
It doesn't matter if they are all etched away. As an example thereof, there is a structure as shown in FIG.

Next, FIG. 13 is a diagram of a fourth embodiment of the manufacturing method of the present invention.

In Fig. 13, first, in (a), p-type Si on the <100> plane is shown.
A high-concentration p ⁺ buried region 322 is formed in a predetermined region on the substrate 321.

Next, in (b), the entire surface has a predetermined thickness (for example, 10 μm).
The n-type Si layer 323 is grown epitaxially.

Next, in (c), the second p is formed in a partial region of the n-type Si layer 323.
The mold region 324 is formed by diffusion. At this time, high concentration p ⁺
Buried region 322 also diffuses upward at the same time, and the upper portion of high-concentration p ⁺ buried region 322 and the lower portion of p type region 324 are connected.

Next, in (d), a high concentration n ⁺ region 325 is formed in a predetermined region. The high-concentration n ⁺ region 325 is a region that will later become a protrusion.

Further, the high-concentration n ⁺ region 325 may be formed as necessary for ohmic contact of the n-type Si layer 323 at the time of electro-chemical etching performed later.

Next, in (e), p-type impurities are diffused in a predetermined region to form a piezoresistor 14. An insulating film such as SiO ₂ or Si ₃ N ₄ is formed on the surface as a surface protective film 326.

Next, in (f), the surface holding film 326 in a predetermined region of the surface is
Are removed by photoetching.

Next, in (g), the piezoresistive lead-out wiring 327 and the voltage application electrode 328 for the subsequent electro-chemical etching are formed. As the material of the wiring 327 and the electrode 328, a single layer film or a composite film of a metal such as Al, Cr, Au, Ti, Ni is used.

Next, in (h), a SiO ₂ film or a Si ₃ N ₄ film is formed as a Si etching mask 329 in a predetermined region on the back surface.

Next, in (i), Si etching is performed using the voltage applying electrode 328 as an anode and an electro-chemical etching method using an alkaline etching solution. As a result, the sensor chip has a fixed portion (support portion) 11, Si weight 12, Si
A cantilever 13, a first protrusion 15, a second protrusion 16, and a gap 17 between the first and second protrusions are formed. At this time, the size of the void 17 is determined by the difference in diffusion between the p-type region 324 and the high-concentration n ⁺ region 325.

In this embodiment, the voltage application electrode 328 was formed at the same time as the formation of the piezoresistive lead wiring 327 when performing the electro-chemical etching, but the present invention is not limited to this, and after the wiring 327 is formed, A method of forming an electrode 328 on the entire surface after sandwiching an insulating film or the like is also possible.

In addition, in FIG. 13 (i), a metal weight is placed on the Si weight 12.
The structure with 30 removed is shown. Examples of the method of forming the metal weight 30 include a plating method, an adhesion method, and a method of adhering by melting solder or the like.

〔The invention's effect〕

As described above, according to the present invention, when the displacement of the mutual position of the weight portion and the fixed portion becomes large due to the application of excessive acceleration, the first protrusion portion and the second protrusion portion are contacted with each other. Since the above displacement is prevented, it is possible to effectively protect the beam portion from damage.

Further, since a stopper for preventing the Si cantilever from being bent can be formed during the wafer process, the yield is improved, and since it is not necessary to form the stopper later, the mounting cost is reduced.

Further, since the precision of the stopper is determined by the thickness of the p-type Si layer formed during the wafer process, it can be formed with extremely high precision.

Furthermore, using the electro chemical etching method
By forming the Si cantilever and the stopper at the same time, the stopper can be easily formed without requiring a special step for forming the stopper.

Also, in the case of the embodiment of FIG. 12, since the etching process is isotropic etching, it is possible to form a structure in which the corners where stress concentrates are not formed, thereby improving the withstand capacity of the Si cantilever. It can be done. Further, since the etching is isotropic, there is no stopping of etching due to the <111> plane, and it is possible to carry out etching of any structure.

[Brief description of drawings]

FIG. 1 is an embodiment of the present invention, FIGS. 2 and 3 are examples of a conventional apparatus, and FIG. 4 is a first embodiment of the manufacturing method of the present invention. 7 is an application example of FIG. 4, FIG. 8 is a second embodiment of the manufacturing method of the present invention, and FIG.
FIG. 10 shows a conventional manufacturing method, FIG. 10 shows a partially enlarged view of FIG. 9, FIG. 11 shows problems of the prior art, and FIG. 12 shows a third embodiment of the manufacturing method of the present invention. FIG. 13 and FIG. 13 are diagrams of a fourth embodiment of the manufacturing method of the present invention. <Explanation of symbols> 11 …… Si support (fixed part) 12 …… Si weight 13 …… Si cantilever 14 …… Piezo resistance 15 …… Si 1st protrusion on the weight side 16 …… Si support side 2nd protrusion 17 ... Air gap between the 1st and 2nd protrusions

Claims (1)

[Claims] 1. A single or a plurality of beam portions that are distorted when an acceleration is applied, a single weight portion formed by connecting to one end of the beam portion, and an outer periphery of the weight portion connected to the other end of the beam portion. In the semiconductor acceleration sensor formed on the semiconductor substrate, the fixed portion formed so as to surround with a predetermined interval and the piezoresistive portion formed on the beam portion, the acceleration detection direction, that is, the beam portion is When the distorting direction is a vertical direction, a single or a plurality of first protrusions provided integrally with the weight portion at a portion of the weight portion facing the fixing portion, and the weight portion of the fixing portion. Is provided integrally with the fixing portion at a portion facing
A semiconductor acceleration sensor, comprising: a protrusion and a single or a plurality of second protrusions at least partially overlapping each other at a predetermined interval in the vertical direction.