JPH01162159A - Semiconductor acceleration sensor - Google Patents

Abstract

PURPOSE:To prevent damage to a beam part, by a method wherein a first protrusion contacts a second protrusion to block further displacement of mutual position between a weight part and a fixed part as the displacement increases with the application of an excess acceleration. CONSTITUTION:An Si cantilever beam 13 having an Si weight 12 at one end thereof is fixed on an Si support 11 to form a piezo-resistance 14 on the surface of the Si cantilever beam 13. As acceleration with a direction alpha1 is applied, the Si weight 12 is displaced in the direction opposite to that alpha1 to narrow a gap 17 between the first and second protrusions 15 and 16. Then, when an excessive acceleration is applied, both the protrusions contact each other to check a displacement of the Si weight 12. Thus, no excessive stress works on the Si cantilever beam 13 to prevent damage to the Si cantilever beam 13. Likewise, even when an excessive acceleration with a direction alpha2 is applied, the displacement of the Si weight 12 can be stopped.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application 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]

As a conventional semiconductor acceleration sensor, for example, IE Electron Devices
Electron Devices, vol, E D
-26°No, 12. p, 1911. Dec, 1
979 “ABatch-Fabricate
d5ilicon Accelerometer”)
There are things listed in.

FIG. 2 is a perspective view of the above device and A-A', B-B'
FIG. In FIG. 2, 21 is a Si substrate, 22
is a Si cantilever, 23 is a Si weight, and 24 is a void.

25 is a piezoresistor.

In the semiconductor acceleration sensor shown in FIG. 2, when acceleration is applied, the Si weight 23 is displaced, thereby causing strain in the Si cantilever 22. A piezoresistance 25 is formed on the surface of this Si cantilever 22, and the Si cantilever 2
When distortion occurs in piezoresistor 2, the piezoresistor 2
The resistance value of 5 changes. Acceleration can be detected by detecting this change in resistance value.

Moreover, as a mounting structure of the above-mentioned sensor chip, a structure as shown in FIG. 3 (a perspective view and a sectional view taken along the line xx') is shown. This is a structure to prevent the cantilever beam from breaking due to excessive acceleration such as falling, and the Si substrate 21 having the Si cantilever beam 22 and the Si weight 23 is moved to the lower stopper 26. It has a structure in which it is sandwiched between two stoppers, the upper stopper 27.

[Problem that the invention seeks to solve]

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

First of all, in the above structure, there is no function to suppress the displacement of the weight between the formation of the beam and the formation of the stopper, so it is necessary to pay great attention to the handling of the chip. If the quality is poor, there is a problem that the beam will be destroyed and the yield will be lowered.

Second, there is a problem that the stopper forming process becomes complicated and the cost increases. In other words, one of the purposes of forming acceleration sensors using semiconductors is to reduce the cost per chip through batch processing, and as is clear in IC manufacturing, many chips are made on a wafer and processed simultaneously. This makes it possible to produce products with stable quality and low cost, but in a structure in which the upper and lower stoppers are bonded together after the beam is formed as shown in FIG. 3, the cost increases significantly.

Thirdly, there is the problem of difficulty in forming the stopper.

That is, in the structure shown in FIG. 3, depending on the beam design, the distance between the stopper and the weight must be controlled with an accuracy of several points to several tens of points, and high precision is required for forming the stopper and adhering it to the chip. This requires advanced stopper manufacturing technology and stopper adhesion technology, which poses a problem in that the mounting cost also increases.

Furthermore, in the above-mentioned acceleration sensor, a weight made of metal or the like is sometimes added to the top surface of the Si weight 23 in order to reduce the sensitivity of other axes, but the thickness of such metal weight inevitably varies. Therefore, it is difficult to accurately set the distance between the weight and the stopper (the distance between the metal weight formed on the top surface of the Si weight 23 and the upper stopper 27 in Fig. 3). There is also the problem that it becomes difficult to realize.

The present invention has been made in order 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 wafer processing.
The purpose of the present invention is to provide a semiconductor acceleration sensor that has stable and uniform performance, has a single force, is inexpensive, and is suitable for mass production.

[Means to solve the problem]

In order to solve the above problem, in the present invention, when the direction of acceleration detection, that is, the direction in which the beam part is distorted, is the vertical direction, a part of the weight part facing the fixed part is integrated with the weight part. one or more first protrusions provided at
It is configured to include the protrusion and one or more second protrusions that at least partially overlap each other at a predetermined interval in the vertical direction.

With the above configuration, in the present invention,
When excessive acceleration is applied and the mutual positional displacement between the weight part and the fixed part becomes large.

Since the first protrusion and the second protrusion contact each other and prevent further displacement, the beam can be effectively protected from damage.

[Embodiment of the Invention] Fig. 1 shows an embodiment of the present invention, and shows a plan view and an A-
An A' sectional view and a BB' sectional view are shown.

In FIG. 1, a Si cantilever beam 13 having an 81 weight 12 at one end is fixed to an S1 support part (fixed part) 11, and a piezoresistor 14 is formed on the surface of the Si cantilever beam 13. . The process up to this point is the same as the conventional example shown in FIG.

A first protrusion 15 on the Si weight side and a second protrusion 16 on the Si support part side are formed in the peripheral part of the SL weight 12 and a predetermined area of the Si support part 11 on the Si weight 12 side, respectively, as follows. has been done. That is, the first protrusion 15 and the second protrusion 16 have a predetermined gap 1 between the first and second protrusion.
They are formed so as to overlap with each other via 7.

The way they overlap is on the right side of the AA' sectional view in Figure 1, or on the B-
The first protrusion 15 overlaps with the second protrusion 16 as shown on the right side of the B-B' cross-sectional view, and the second protrusion 16 overlaps as shown on the left side of the B-B' cross-sectional view of FIG. The first protrusion 15 and the second protrusion 16 are formed so as to overlap with each other so as to be on top of the first protrusion 15, and in both ways.

Next, the effect will be explained.

When an acceleration is applied in the α□ force direction shown in FIG. The gap 17 between the protrusion 15 and the second protrusion 16 is narrowed.

When excessive acceleration is applied, the first protrusion 15 and the second protrusion 16 contact each other, so that the Si weight 12
displacement is stopped. Therefore, excessive stress is not applied to the Si cantilever beam 13, and damage to the Si cantilever beam 13 can be prevented.

Similarly, if excessive acceleration is applied in the α2 direction (direction from the back surface to the front surface of the paper),
Since the first protrusion 15 hits the second protrusion 16 on the right side of the cross-sectional view or on the right side of the BB' cross-sectional view, displacement of the Si weight 12 is stopped.

Furthermore, the size of the gap 17 between the first and second protrusions can be set arbitrarily, and the range of applied acceleration that can be measured is determined by this value.

Next, FIG. 4 is a diagram showing a first embodiment of the manufacturing process of the device shown in FIG. 1.

In FIG. 4, first, in (a), a lower n-type S1 layer 42 of a predetermined thickness and a p-type Si window 43 for lower etching are formed on a p-type Si substrate 41 of the <i o o> plane. . Methods for forming the lower n-type Si layer 42 include thermal diffusion, epitaxial growth, and the like. Also, p-type Si for lower etching.
In order to form the window 43, a method using thermal diffusion and a method using the lower n
There is a method of performing diffusion in advance so that a p-type Si window 43 for lower etching remains when forming the Si layer 42 by thermal diffusion.

Next, in (b), a p-type Si layer 44 is formed on the lower n-type Si layer 42 and the lower p-type Si window 43 for etching using a thermal diffusion method or an epitaxial growth method.

The gap 17 between the first and second protrusions is determined by the thickness of the p-type Si layer 44.

Next, in (C), an upper n-type Si layer 45 and an upper p-type S1 window 46 for etching are formed on the p-type Si layer 44. As for the formation method, the same method as that for the lower n-type Si layer 42 and the lower p-type Si window 43 for etching can be used.

Next, in (d), after forming the piezoresistor 14 in a predetermined area using a thermal diffusion method, a Sio film, or a Si3N film, which will serve as a mask for Si etching is formed in a predetermined area on the back surface, and then , lower n-type Si layer 42 and upper n-type Si layer 4
Using an electrochemical etching method using alkaline etching solution with No. 3 as an anode, p-type S
Electrochemical etching is performed.
For details on the etching method, please refer to Japanese Patent Application Laid-open No. 61-9757.
No. 2 (Method for manufacturing semiconductor acceleration sensor), etc.

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

As mentioned above, in this example, a stopper to prevent Si cantilever beams from breaking can be formed during the wafer process, which improves the yield.Furthermore, since there is no need to form a stopper later, mounting costs are reduced. do.

Further, since the accuracy of the stopper is determined by the thickness of the p-type Si layer formed during the wafer process, it is possible to form the stopper with extremely high accuracy.

Furthermore, one of the characteristics of the above process is that electro
The stopper may be formed at the same time as the Si cantilever 13 is formed using a chemical etching method. Therefore, no special process is required to form the stopper,
A stopper can be easily formed.

In the manufacturing process shown in FIG. 4, in order to form the first protrusion 15 and the second protrusion 16, the lower n-type Si layer 42 is
．． Although the p-type Si layer 44 and the upper n-type T layer 45 are used, the lower n-type Si layer 42, the p-type Si layer 44, and the upper n-type S1 layer 45 do not necessarily need to be formed over the entire surface. The stopper structure may be formed only in the area where the stopper structure is to be formed.An example of this is the structure shown in FIG.

Further, the p-type Si layer 44 is necessary only when forming the first protrusion 15 and the second protrusion 16, and after the formation, the p-type Si layer 44 is
FIG. 6 shows an example in which it is acceptable for the i-layer 44 to be completely etched away.

Furthermore, the present invention is not only applicable to the cantilever structure shown in FIG. I can do it.

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

In FIG. 8, first, in (a), a lower n-type Si layer 42 of a predetermined thickness is formed on a (111)-plane p-type S1 substrate 41.
A p-type Si window 43 for lower etching is formed.

Next, in (b), an SiO□ layer 50 is formed on the lower n-type Si layer 42 and the lower p-type Si window 43 for etching by using an oxygen ion implantation method, and then an 810□ layer 50 is formed on the 5103 layer 50.
Layer 45 is formed using an epitaxial growth method. The gap 17 between the first and second projections is determined by the thickness of the layer 50.

Next, in (C), an upper etching window 46 is formed in a predetermined region of the 81 layer 45. When using p-type Si as the etching window 46, it can be formed using a thermal diffusion method. In addition, Si is used as the etching window 46.
n, is formed by thermally oxidizing a predetermined region of the 81 layer 45.

Next, in (d), after forming a piezoresistor 14 in a predetermined area using a thermal diffusion method, a piezoresistor 14 is formed in a predetermined area on the back surface of the Si substrate.
1. Sin serves as an etching mask.

A film or Si, N film is formed, and then an electrochemical etching method is used using an alkaline etching solution with the lower n-type Si layer 42 and 81 layer 45 as anodes.
P-type Sl window 4 for etching a predetermined area on the backside of the Si substrate and the lower part
Etch 3. If the etching window 46 is p-type S1, it is etched at the same time.

Finally, the Sin layer 50 is etched. When the etching window 46 is Sin, the etching window 46 is also etched at the same time.

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

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

As for the conventional manufacturing method of semiconductor acceleration sensor.

For example, there is one shown in FIG.

This conventional example is a method of manufacturing the semiconductor acceleration sensor shown in FIG. 2 using the electrochemical etching method disclosed in Japanese Patent Application Laid-Open No. 61-97572 (Method of Manufacturing a Semiconductor Acceleration Sensor). In this case, the electrochemical etching method is a method in which p-type Si is selectively etched using an alkaline etching solution using n-type Si as an anode.

In FIG. 9, first, in (a), p of the <100> plane
An n-type Si layer 128 of a predetermined thickness is formed on the S1-type substrate 141.
A p-type Si window 129 is formed. The n-type Si layer 128 is formed by thermal diffusion or epitaxial growth, and the p-type S1 window 129 is formed by thermal diffusion or by epitaxial growth.
8 by the thermal diffusion method, the p-type Si window 12 is
It is formed by a method of diffusion so that 9 remains. Furthermore, a piezoresistor 25 is formed in a predetermined region on the n-type Si layer 128 using a thermal diffusion method.

Next, in (b), Si is deposited on a predetermined region of the back surface of the p-type Si substrate 141 to serve as a mask for Si etching.

After forming the film or 513N4 film, electroetching is performed using an alkaline etching solution with the n-type Si layer 128 as an anode.
The p-type Si is selectively etched using a chemical etching method, and as a result, the Si supporting portion 21. Si
Weight 23, Si cantilever 22, and void 24 are formed simultaneously.

However, in such a conventional manufacturing method for semiconductor acceleration sensors, the anisotropy of electrochemical etching is strong and etching stops at the <111) plane, so the partially enlarged view in Fig. 10(a) As shown, the ninth
Because the structure is such that stress tends to concentrate at Y and Y points in the figure,
Si cantilevers tend to break due to stress concentration, ■(11
1) Since etching stops at the surface, it is not possible to etch p-type Si having a structure as shown in FIG. 11, for example, and there are limitations on the structures that can be processed.

This embodiment solves the above problem 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), the p-type Si substrate 2
A lower n-type Si layer 242 of a predetermined thickness and a p-type Si window 243 for lower etching are formed on 21. This lower n-type S
Methods for forming the i-layer 242 include thermal diffusion and epitaxial growth. Also, the p-type Si window 243 for lower etching
There are two methods for forming the lower n-type Si layer 242 using thermal diffusion, and a method in which diffusion is performed by leaving a p-type Si window 243 for lower etching in advance when forming the lower n-type Si layer 242 by thermal diffusion. .

Next, in (b), a p-type film 1244 is formed on the lower n-type Si layer 242 and the lower etching p-type Si window 243 using a thermal diffusion method or an epitaxial growth method. The gap 17 between the first and second protrusions is determined by the thickness of the p-type Si layer 244.

Next, in (C), an upper n-type S
An i-layer 245 and a p-type Si window 246 for upper etching are formed. This formation method may be the same as that for the lower n-type Si layer 242 and the lower etching p-type Si window 243.

Next, in (d), after forming the piezoresistor 14 in a predetermined region using a thermal diffusion method, a Sun, film, or Si serving as a mask is formed in a predetermined region on the back surface of the p-type Si substrate 221.

After forming the N4 film, p-type Si is made porous using an anodic treatment method in hydrofluoric acid. The porous process is described in detail in JP-A-48-102988.

Next, in (e), the porous p-type Si is isotropically etched, and the oxide film formed after oxidation is etched. As a result, the Si support part 11, the Si weight 12, the S
The i-cantilever beam 13, the first protrusion 15 and the second protrusion 16 acting as a stopper are formed at the same time.

In the above manufacturing method, since the etching process is isotropic etching, unlike the case where anisotropic etching is used as in the conventional example, corners where stress is concentrated, such as the Y part described above, are formed. Not done.

That is, when manufactured according to the manufacturing process of this example, the shape is rounded as shown in the Y section in FIG. 10(b), and the stress is lower than that in the Y section in FIG. 10(a). You can see that it has a structure that does not concentrate.

In this way, the resistance of the Si cantilever increases because stress is difficult to concentrate.

Furthermore, in the case of the embodiment shown in FIG. 12, since the etching is isotropic, the etching does not stop at the (111) plane, and therefore it is possible to perform etching of any structure.

The embodiment shown in FIG. 12 shows a case in which a stopper for preventing the Si cantilever from breaking is formed at the same time as the Si cantilever 13 is formed, but the conventional structure of the device as shown in FIG. Even when this embodiment is applied to, the structure is such that stress is not concentrated, so the withstand capacity of the Si cantilever can be improved.

In addition, in the case of this embodiment as well, as in the embodiment shown in FIG. Instead, the stopper structure may be formed only in the region where the stopper structure is to be formed.An example of this is the structure shown in FIG.

Further, the p-type Si layer 244 is necessary only when forming the first protrusion 15 and the second protrusion 16, and it does not matter if the p-type Si layer 244 is completely etched away after the formation. An example of this is the structure shown in FIG. 6 above.

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

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

Next, in (b), a predetermined thickness (for example, 10,
) is epitaxially grown.

Next, in (c), a second
A p-type region 324 is formed by diffusion. At this time, the high concentration p + buried region 322 is also diffused upward at the same time, and the upper part of the high concentration p + buried region 322 and the lower part of the p type region 324 are connected.

Next, in (d), a high concentration n+ area 25 is placed in a predetermined area.
form. This high concentration n+ region 25 is a region that will later become a protrusion.

Furthermore, this high concentration n1 region 325 is used as the n-type Si layer 3 during electrochemical etching to be performed later.
23 may be formed as needed for ohmic contact.

Next, in (e), a p-type impurity is diffused into a predetermined region to form a piezoresistor 14. In addition, on the surface, 5i
An insulating film such as Oa, SL, N4, etc. is the surface protection film 32.
6.

Next, in (f), the surface protective film 32 in a predetermined area on one surface is
6 is removed by photoetching.

Next, in (g), a piezoresistor lead-out wiring 327 and a voltage application electrode 328 for later electrochemical etching are formed. This wiring 327 and electrode 328
The materials of fiJ-m are Cr, Au, and Ti.

A single layer film or a composite film of metal such as N1 is used.

Next, in (h), a sio film or a 513N4 film is formed as a Si etching mask 329 in a predetermined region of the back surface.

Next, in (i), Si etching is performed using an electrochemical etching method using an alkaline etching solution with the voltage application electrode 328 as an anode.As a result, the sensor chip has a fixed part (supporting part) 11 , Si weight 12. A Si cantilever 13, a first projection 15, a second projection 16, and a gap 17 between the first and second projections 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 25.

Note that in this embodiment, the voltage application electrode 328 was formed at the same time as the piezoresistor lead-out wiring 327 when performing electrochemical etching, but the invention is not limited to this; after the wiring 327 is formed, A method of sandwiching an insulating film or the like and then forming the electrode 328 on the entire surface is also possible.

Further, FIG. 13(i) shows a structure in which a metal weight 30 is placed on the Si weight 12. Methods for forming the metal weight 30 include a plating method, an adhesion method, and a method of melting and adhering solder.

〔Effect of the invention〕

As explained above, in the present invention, when excessive acceleration is applied and the displacement of the relative positions of the weight part and the fixed part becomes large, the first protrusion part and the second protrusion part come into contact with each other. Since the above displacement is prevented, the beam portion can be effectively protected from damage.

Furthermore, since a stopper for preventing the Si cantilever from breaking can be formed during the wafer process, the yield rate is improved, and since there is no need to form the stopper later, the mounting cost is reduced.

Further, since the accuracy of the stopper is determined by the thickness of the p-type Si layer formed during the wafer process, it is possible to form the stopper with extremely high accuracy.

Furthermore, by forming the stopper at the same time as forming the Si cantilever using an electrochemical etching method, the stopper can be easily formed without requiring any special process. can.

In addition, in the case of the example shown in Fig. 12, since the etching process is isotropic etching, it is possible to create a structure that does not form corners where stress is concentrated, thereby improving the resistance of the Si cantilever. I can do it. Also, because the etching is isotropic.

Etching does not stop due to the (111) plane, and it becomes possible to perform etching of any structure.

[Brief explanation of the drawing]

FIG. 1 is a diagram of an embodiment of the present invention, FIGS. 2 and 3 are diagrams of an example of a conventional device, FIG. 4 is a diagram of a first embodiment of the manufacturing method of the present invention, and FIGS. 7 shows an example of application of FIG. 4, FIG. 8 shows a second embodiment of the manufacturing method of the present invention, FIG. 9 shows a conventional manufacturing method, and FIG. 10 shows a part of FIG. 9. An enlarged view, FIG. 11 is a diagram showing problems in the prior art, FIG. 12 is a diagram of a third embodiment of the manufacturing method of the present invention, and FIG. 13 is a diagram of a fourth embodiment of the manufacturing method of the present invention. be. <Explanation of symbols> 11...Si support part (fixed part) 12...Si weight 13...Si cantilever 14...Piezo resistor 15...First protrusion part 16 on the SL weight side ...Second protrusion 17 on the S1 support side...Gap between the first and second protrusion

Claims (1)

[Claims] one or more beams that are distorted when acceleration is applied; a single weight portion connected to one end of the beam portion; In a semiconductor acceleration sensor formed on a semiconductor substrate, a fixing portion formed to open and surround the beam portion and a piezoresistive portion formed on the beam portion align the acceleration detection direction, that is, the direction in which the beam portion is distorted, in the vertical direction. In the case of It is characterized by comprising one or more second protrusions that are provided integrally with the fixing part and that are at least partially overlapped with each other at a predetermined interval in the vertical direction from the first protrusion. Semiconductor acceleration sensor.