JPH03255369A - Manufacture of semiconductor acceleration sensor - Google Patents

Abstract

PURPOSE:To easily realize air-damping function by a method wherein a gap of a stopper is formed narrow according to isotropic etching of an N built-in layer of a sensor having the stopper consisting of a projecting part to control the up-and-down movement of a weight part and a receiving part. CONSTITUTION:An N built-in layer 38 is formed on a P-type silicon substrate 20 at a part corresponding to a stopper gap 39. An N-type epitanial layer 21 is formed on the substrate 20. A piezoelectric resistance 22 is formed on the layer 21 at a part corresponding to a cantilever 24. An SiO2 film 23 is formed on the layer 21. The layer 21 is etched from the front surface to form a groove 27, and further an etching-resistant film 32 is partially formed on the rear sur face of the substrate 20. A part corresponding to an outer peripheral edge of a weight part 25 is subjected to anisotropic etching. Thereafter, the layer 38 is isotropiclly etched and the gap 39 is obtained. In this manner, the stopper gap is formed narrow by isotropically etching the N built-in layer, whereby the air damping function is easily realized.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a semiconductor acceleration sensor that detects the acceleration of a vehicle, etc. by changes in piezoresistors, and particularly relates to a semiconductor acceleration sensor with a built-in stopper that can be formed by batch processing. The present invention relates to a method of manufacturing an acceleration sensor.

(Prior Art) Examples of conventional semiconductor acceleration sensors include those shown in FIGS. 6 and 7, for example. Regarding this sensor,
IEEE TRANS, vow.

ED-26DEC, 1979, “A Batch-F
abricated 5ilicon Accel
erometer'.

In the figure, reference numeral 1 denotes a P-type silicon substrate having a fixing part 4. The silicon substrate 1 has a groove 10 removed by selective etching, and a thin cantilever beam 2 is fixed to a predetermined position of the fixing part 4. , a substantially square weight portion 3 is provided at its free end. A piezoresistor 5 is formed on the 1-plane of the cantilever beam 2, so that when the cantilever beam 2 is bent due to acceleration applied to the weight portion 3, the resistance value of the piezoresistor 5 changes due to the stress. It has become. A resistor 6 having the same structure as the piezoresistor 5 is also formed on the upper surface of the portion of the fixed part 4 near the cantilever 2, and these piezoresistors 5 and compensation resistors 6 are connected to each other to form a bridge circuit. There is. The silicon substrate 1 having such a structure can be manufactured by batch processing using an IC manufacturing process.

7 and 8 in FIG. 6 are upper and lower stoppers provided on the upper and lower sides of the bulge 3, respectively, and both stoppers 7 and 8 limit the displacement of the weight portion 3 in the 1-downward direction. By doing so, stress fracture of the cantilever beam 2 due to excessive acceleration is prevented.

Reference numeral 9 denotes a lead wire connected to the bridge circuit, which is provided for taking out the piezoelectric output to the outside.

An example of the manufacturing process of this silicon substrate 1 will be briefly explained below based on FIGS. 8(a) to 8(d).

First, an N-type epitaxial layer 12 is grown on a P-type (100) silicon substrate 11-1-, and this epitaxial layer 1
A P-type element isolation diffusion region 13 is formed from a part of the surface of 2 so as to reach the silicon substrate 11. This P-type element isolation diffusion region 13 is formed so as to surround the weight portion 3 as shown in FIG. 7 (FIG. 7(a)).

Next, the epitaxial layer 12 is formed by ion implantation of poron, etc.
A P-type piezoresistor 15 is formed at a predetermined position in the 110> direction, and a 5i02 film 14 is formed on the epitaxial layer 12. On the other hand, the back surface of the silicon substrate 11 has Si3N
An etching-resistant film 16 made of 4 or the like is deposited and patterned (FIG. 4(b)).

Thereafter, contact etching and formation of wiring electrodes 17 are performed on the 5i02 film 14 at positions corresponding to the piezoresistors 15 (FIG. 3(C)).

Finally, while biasing the N-type epitaxial layer 12 to a positive potential, the silicon substrate 11 is silicon etched using an anisotropic alkaline ethynchide solution such as KOH or hydrazine. As a result, the P-type silicon substrate 11 becomes (11
1) Etching proceeds so as to leave a surface, and in particular, the etching is performed to the surface of the P-type element isolation diffusion region 13. On the other hand, in the cantilever beam 2 part, the N-type epitaxial layer 1 also remains without being etched, and a wafer structure having the cantilever beam 2 and the weight part 3 as shown in FIG. 7 is obtained ((d) )).

After such a silicon wafer is divided into chips, stoppers 7.
are fixed with an adhesive or the like, thereby finally completing a semiconductor acceleration sensor with a built-in stopper as a product.

(Problem to be Solved by the Invention) However, in such a semiconductor acceleration sensor, the upper and lower stoppers 7 and 8 are bonded together after the wafer manufacturing process is completed, that is, after the cantilever beam 2 is formed. As a result, the following problems occurred.

■ Since it is difficult to set the air gap between the upper and lower stoppers relative to the weight, it is difficult to provide an air tamping function to prevent resonance.

■ During the wafer manufacturing process, the cantilever beam is damaged due to excessive acceleration, resulting in a significant drop in product yield.

■ Since the bottom stopper must be bonded each time for each wafer chip, it takes a lot of effort and increases the mounting cost.

On the other hand, the present applicant previously proposed a method for manufacturing a semiconductor acceleration sensor having a manufacturing process as shown in FIG. 9 (see Japanese Patent Application No. 1-248802, unpublished).

As shown in FIG. 5A, first, an N0 buried layer 18 is formed on the P-type silicon substrate 11 at a portion corresponding to the stopper gap 42, and then an N-type epitaxial layer 12 is formed on the silicon substrate 1. form. And epitaxial layer 12
A P-type piezoresistor 15 is formed in a portion corresponding to the cantilever beam 2. Further, a deep N0 diffusion layer 19 reaching the N0 buried layer 18 is formed in a portion corresponding to the groove 41 formed in this epitaxial layer 12.

Next, as shown in FIG. 2(b), an etching-resistant film 16 is partially formed on the back surface of the silicon substrate 11.
The exposed surface of the substrate is set so as to surround the four sides of the substantially square weight portion 3. Then, a metal electrode (not shown) is formed, and the P-type silicon substrate 11 is anisotropically etched while biasing the N-type epitaxial layer 12 to a positive potential. This etching progresses upward toward the surface of the substrate.
The process stops when it reaches the N-type epitaxial layer 12. Thereby, when setting the thickness of the cantilever beam 2, it can be set arbitrarily by controlling the thickness of the N-type epitaxial layer 12. In this way, the cantilever beam 2 having a predetermined thickness can be formed with high precision, so that variations in detection sensitivity can be reduced.

Then, as shown in FIG. 3(c), by isotropically etching the N0 buried layer 18 and the deep N0 diffusion layer 19,
An acceleration sensor with a built-in stopper is completed.

The following is an outline of the method for manufacturing a semiconductor acceleration sensor previously proposed by the applicant.

By the way, various circuit elements are formed in the N-type epitaxial layer 12-t. Therefore, in terms of packaging, the N-type epitaxial layer 12 is required to have a predetermined thickness.

On the other hand, if the N-type epitaxial layer 12 is made thicker, the N+ diffusion layer 19 formed in the N-type epitaxial layer 12 needs to be formed deeper. Technically difficult. If an attempt is made to form the diffusion layer 19 deeply, the concentration of the diffusion layer 19 becomes low near the buried layer 18, resulting in a problem that isotropic etching takes time.

This invention was made by focusing on these conventional problems, and its purpose is to easily add an air damping function between the fixed part and the weight part, and also to improve product yield and reduce mounting costs. It is an object of the present invention to provide a method for manufacturing a semiconductor acceleration sensor that can reduce the amount of stress and easily form deep grooves in an epitaxial layer.

(Means for Solving the Problems) In order to achieve the above-mentioned object, the present invention fixes the base end of a cantilever to a fixed part of a P-type silicon substrate, and A piezoresistance is provided in the section, a weight section is fixed to the free end of the cantilever beam, a groove is formed between the weight section and the fixed section, and a protrusion is provided between the weight section and the fixed section. A semiconductor acceleration sensor is provided with a plurality of stoppers each having a plurality of stoppers each comprising a part and a receiving part facing the protruding part so as to be able to come into contact with the protruding part,
forming an N type epitaxial layer on the substrate by forming an N+ buried layer in a portion corresponding to the void on the substrate; and providing a piezoresistor in a portion of the epitaxial layer corresponding to the base end of the cantilever. a step of etching the epitaxial layer from the surface side to form the groove; a step of anisotropically etching a portion of the back surface of the substrate corresponding to the outer periphery of the weight portion; The method is characterized by comprising a step of forming the voids by isotropic etching.

(Function) In the manufacturing method of the present invention, the lateral gap of the stopper consisting of the protruding portion and the receiving portion is formed by isotropically etching the N buried layer. Therefore, the gap of the stopper can be set with high precision according to the thickness of the N0 buried layer, and the air tongue pinking function can be easily provided.

Further, during wafer manufacturing, the stopper is formed by etching at the same time as the cantilever and the weight.

Therefore, not only is the stopper bonding process unnecessary, but even if excessive acceleration is applied to the weight part during the wafer manufacturing process, the movement of the weight part is limited within a predetermined range by the stopper. As a result, damage to the cantilever beam due to excessive acceleration can be prevented.

Moreover, since the grooves formed in the epitaxial layer are formed by etching from the surface side, deep grooves can be easily formed in a short time.

(Example) The present invention will be explained below based on the drawings.

FIG. 1 and FIG. 2 are a plan view and a sectional view, respectively, showing an embodiment of the present invention.

First, to explain the configuration, 20 is a P-type silicon substrate, 21
is an N-type epitaxial layer formed on this substrate 20,
22 is a P-type piezoresistance formed on the surface of the N-type epitaxial layer 21 by boron ion implantation or the like, and 23 is a 5i02 film formed on the N-type epitaxial layer 21.

The P-type silicon substrate 20 is divided into a substantially square weight portion 25 and a substantially square fixing portion 26 surrounding the weight portion 25 by etching from the back surface thereof.

The weight portion 25 is fixed and connected to a fixed portion 26 by a cantilever beam 24 made of the N-type epitaxial layer 21. Most of the epitaxial layer of the weight part 25 and the cantilever beam 24 is separated from the fixing part 26 by a groove 27, and this separation groove 27 communicates with the back side of the substrate via a lateral gap 39. . That is, N type epitaxial layer 2
] has a plurality of protrusions 29, and a receiving portion 30 shown by diagonal lines in FIG. 1 is formed in a portion of the P-type silicon substrate 20 corresponding to the lower surface of each protrusion 29. This restricts the downward movement of the protrusion 29.

The stopper 2 consists of such a protruding part 29 and a receiving part 30.
8 is formed along the outer peripheral edge of the substantially square weight portion 25 so as to surround it, and the protruding portions 29 are formed alternately on the weight portion 25 and the fixed portion 26 as shown in FIG. . As a result, the weight portion 25 is restricted not only in its downward movement but also in its upward movement, and a plurality of stoppers 28 are formed inside the chip during the wafer manufacturing process. The three-dimensional detailed structure of this stopper 28 is
As shown in the figure. In the figure, the shaded area is the receiving part 30, and the protruding part 29 is arranged so as to be able to come into contact with this.

The manufacturing process of such a stopper built-in acceleration sensor is shown in FIGS. 4(a) to 4(e).

First, a N"
A buried layer 38 is formed. Next, this silicon substrate 20
An N-type epitaxial layer 2] is formed on top (see figure (a)).
).

Next, a P-type piezoresistor 22 is formed in a portion of the epitaxial layer 21 corresponding to the cantilever 24 by boron ion implantation or the like, and a SiO2 layer is formed on the epitaxial layer 21.
The membrane 23 has a membrane shape 3 (FIG. 3(b)).

Then, grooves 27 are formed in the epitaxial layer 21,
This is formed by performing reactive ion etching (tE) or anisotropic etching with an alkaline etching solution on a portion corresponding to the groove 27 from the surface side of the epitaxial layer 21 (FIG. 3(C)). Thereby, even when the epitaxial layer 21 is thick, deep grooves can be easily formed.

Thereafter, by partially forming an etching-resistant film 32 made of 513N4 or the like on the back surface of the silicon substrate 20,
The exposed surface of the substrate is set so as to surround the four sides of the substantially square weight portion 25. Then, contact etching and formation of metal electrodes (not shown) are performed, and while biasing the N-type epitaxial layer 21 to a positive potential, the P-type silicon substrate 20 is coated with KOH, hydrazine, EDP (ethylene, etc.).
Anisotropic electrochemical etching is performed using an alkaline etching solution such as diamine/pyrocatechol aqueous solution. Here, the cantilever beam 24 and the weight portion 25 are <1
10> direction, the anisotropic etching stops at the (111) plane that contacts the opening edge of the etching-resistant film 32 on the back side of the substrate. On the other hand, this etching progresses upward toward the substrate surface and stops when it reaches the N-type epitaxial layer 21. This allows the cantilever beam 24
The thickness can be arbitrarily set by controlling the thickness of the N-type epitaxial layer 21. Therefore, the cantilever beam 24 with a predetermined thickness can be formed with high precision.
Variations in detection sensitivity can be reduced. (Same figure (
d)).

Furthermore, the N buried layer 38 is etched with an isotropic Si etching solution (
For example, HF: HNO3: CH3CO'0H=1:
By etching at a ratio of 3:8), an acceleration sensor with a built-in stopper is completed ((e) in the same figure). In this case, N
The etching rate of the "layer" (25x1018 cm-3) is more than 100 times that of the N-layer (1015-1016 cm-3).

The operation of this embodiment will be explained below.

The basic operation of detecting acceleration by the acceleration sensor having the above configuration is the same as that of the conventional example. That is, when vertical acceleration is applied to the weight portion 25, the cantilever beam 24 is bent and stress is applied to the piezoresistor 22.

Due to the resulting piezoresistance effect, the resistance value changes depending on the strength of stress, and acceleration is detected. In this case, even if excessive acceleration is applied to the weight portion 25,
Since the vertical displacement of the weight portion 25 can be restricted by the stopper 28, it is possible to prevent the cantilever beam 24 from breaking due to excessive stress.

In this manufacturing method, the thickness of the cantilever beam 24 can be freely created by etching, and the stopper 28 can also be created at the same time.
4 damage can be prevented. Further, since mounting of the stopper 28 is substantially unnecessary, the acceleration sensor can be manufactured at low cost. Furthermore, by setting the thickness of the N'' buried layer 38 to be thin, the gap 39 of the stopper 28 can be controlled to be as small as several micrometers, so the air damping function for preventing resonance can be fully realized. , making oil and damp pink unnecessary.

In addition, in terms of manufacturing, since the lateral gap 39 between the receiving part 30 and the protruding part 29 is formed by isotropic etching, the (111) gap is formed by isotropic etching.
There is no need to consider stopping etching on the surface, and the degree of freedom in setting the stopper can be significantly increased compared to the conventional method.

Furthermore, since the grooves 27 formed in the epitaxial layer 21 are directly formed from the surface side of the epitaxial layer 21 by reactive ion etching (RIE) or anisotropic etching using an alkaline etching solution, the epitaxial layer 21 is thick. deep grooves can be easily formed.

FIG. 5 shows another embodiment of the invention.

This embodiment uses sensor and peripheral circuits of the piezoresistive bridge, such as amplifiers, bridge bias circuits, and temperature compensation circuits.
This is a specific example applied to a so-called IC-based acceleration sensor integrated in a chip. In FIG. 5, only the NPN transistor 33 is shown for simplicity.

The structure of the sensor section in this example is the same as that shown in FIG.
It is divided into a large number of islands by 4, and circuit elements are incorporated in each of the 6 islands. Then, the N type epitaxial layer 21
A P-type base diffusion region 36 is formed thereon, and an N+ emitter diffusion region 35 is formed within the P-type base diffusion region 36. Note that 37 is a metal electrode connected to the piezoresistor 22.

The manufacturing process of the semiconductor acceleration sensor according to this example is as follows:
Since this embodiment is almost the same as the previous embodiment, the explanation thereof will be omitted.

In this embodiment, the bipolar process N' buried layer 38 can be used as the N' region for etching to form the stopper 28, making it extremely easy to fabricate an integrated acceleration sensor. It has this effect.

(Effects of the Invention) As described above, according to the present invention, in the method of manufacturing a semiconductor acceleration sensor equipped with a stopper consisting of a protruding portion and a receiving portion that limit the vertical movement of a weight portion, N”
Since the gap in the stopper can be narrowed by isotropic etching of the buried layer, the degree of freedom in designing the stopper is increased and the air damping function can be easily realized.

Moreover, since the grooves formed in the epitaxial layer are formed by etching from the surface side, deep grooves can be easily formed.

Further, since the cantilever beam will not be damaged even if excessive acceleration is applied during the wafer manufacturing process, a decrease in product yield can be reliably prevented. Furthermore, since a mounting process for adhering the stopper is not necessary, it is possible to reduce manufacturing costs and save labor accordingly.

[Brief explanation of drawings]

FIG. 1 is a plan view showing an embodiment of the semiconductor acceleration sensor according to the present invention, and FIG. 2 is a sectional view taken along the line ■-n. Figure 3 is a perspective view showing the detailed structure of the stopper part, Figure 4 (a)
~(e) are process diagrams showing a method for manufacturing a semiconductor acceleration sensor, FIG. 5 is a sectional view showing another embodiment of the present invention, and FIGS. 6 and 7 are sectional views showing conventional semiconductor acceleration sensors, respectively. , a plan view, FIGS. 8(a) to 8(d) are process diagrams showing the manufacturing method of the conventional sensor, and FIGS. 9(a) to (C) are manufacturing steps of the semiconductor acceleration sensor previously proposed by the applicant. FIG. 3 is a process diagram of the method. 20... P-type silicon substrate 21... N-type epitaxial layer 22... P-type piezoresistor 24... Cantilever beam 25... Weight part 26... Fixing part 27... Groove 28... ...Stopper 29...Protrusion 30...Receptacle 34...P type element isolation diffusion region 38...N+ buried layer 39...Void

Claims (1)

[Claims] 1. The base end of the cantilever beam is fixed to the fixed part of the P-type silicon substrate, a piezoresistor is provided at the base end of the cantilever beam, and a weight part is fixed to the free end of the cantilever beam. A groove is formed between the weight part and the fixed part, and a plurality of stoppers are provided between the weight part and the fixed part, each consisting of a protruding part and a receiving part facing the protruding part with a gap therebetween so as to be able to come into contact with the protruding part. a semiconductor acceleration sensor comprising the steps of: forming an N^+ buried layer on a substrate in a portion corresponding to the void, and forming an N-type epitaxial layer on the substrate; and the cantilevering of the epitaxial layer. A step of forming a piezoresistance in a portion corresponding to the base end of the beam, a step of etching the epitaxial layer from the front side to form the groove, and anisotropic etching a portion of the back surface of the substrate corresponding to the outer periphery of the weight portion. A method for manufacturing a semiconductor acceleration sensor, comprising: a step of isotropically etching the N^+ buried layer to form the void.