JP2600393B2 - Manufacturing method of semiconductor acceleration sensor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a semiconductor acceleration sensor that detects acceleration of a vehicle or the like by a change in piezoresistance, and particularly relates to a semiconductor with a built-in stopper that can be formed by batch processing. The present invention relates to a method for manufacturing an acceleration sensor.

<< Conventional Technology >> As a conventional semiconductor acceleration sensor, for example, FIG.
There is one as shown in FIG. This sensor is described in IEEE TRANS.vol.ED-26DEC.1979, “A Batch-Fa
bricated Silicon Accelerometer ".

In the figure, reference numeral 1 denotes a P-type silicon substrate having a fixing portion 4. The silicon substrate 1 is selectively etched to remove a groove 10 portion, and a thin cantilever 2 is fixed at a predetermined position of the fixing portion 4. At its free end, a substantially square weight 3 is provided. A piezoresistor 5 is formed on the upper surface of the cantilever 2, and when the cantilever 2 bends due to the acceleration applied to the weight 3, the resistance of the piezoresistor 5 changes due to the stress. I have. A resistor 6 having the same structure as the piezoresistor 5 is also formed on the upper surface of a portion of the fixed portion 4 near the cantilever 2, and the piezoresistor 5 and the compensation resistor 6 are connected to each other to form a bridge circuit. I have. The silicon substrate 1 having such a structure can be manufactured by a batch process by an IC manufacturing process.

In FIG. 6, reference numerals 7 and 8 denote upper and lower stoppers provided above and below the weight portion 3, respectively. The stoppers 7 and 8 limit the displacement of the weight portion 3 in the vertical direction. In addition, the stress destruction of the cantilever 2 against excessive acceleration is prevented. Reference numeral 9 denotes a lead wire connected to the bridge circuit and provided to take out a piezoelectric output to the outside.

Hereinafter, an example of the manufacturing process of the silicon substrate 1 will be briefly described with reference to FIGS. 8 (a) to 8 (d).

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

Next, the epitaxial layer 12 is formed by ion implantation of boron or the like.
A P-type piezoresistor 15 is formed at a predetermined position in the <110> direction, and an SiO ₂ film 14 is formed on the epitaxial layer 12.
On the other hand, on the back surface of the silicon substrate 11, an etching resistant film 16 made of Si ₃ N ₄ or the like is applied and patterned (FIG. 2B). Thereafter, a position corresponding to the piezo resistor 15 of the SiO ₂ film 14 is formed. Next, contact etching and the formation of the wiring electrode 17 are performed (FIG. 3C).

Finally, while the N-type epitaxial layer 12 is biased to a positive potential, the silicon substrate 11 is silicon-etched with an anisotropic alkali etchant such as KOH or hydrazine. As a result, the etching of the P-type silicon substrate 11 proceeds so as to leave the (111) plane. In particular, the etching is performed up to the surface of the P-type element isolation diffusion region 13.
On the other hand, in the portion of the cantilever 2, only the N-type epitaxial layer 12 remains without being etched, and a wafer structure having the cantilever 2 and the weight 3 as shown in FIG. 7 is obtained (FIG. )).

After such a silicon wafer is divided into chips, stoppers 8, 9 are provided on both upper and lower surfaces as shown in FIG.
Is fixed by an adhesive or the like, whereby a semiconductor acceleration sensor with a built-in stopper as a product is finally completed.

<< Problems to be Solved by the Invention >> However, in such a semiconductor acceleration sensor, after the wafer / manufacturing process is completed, that is, after the cantilever 2 is formed, the upper and lower stoppers 8, 9 are bonded. Therefore, there were the following problems.

Since it is difficult to set the gap between the upper and lower stoppers with respect to the weight, it is difficult to provide an air damping function for preventing resonance.

Excessive acceleration during the wafer / manufacturing process can damage the cantilever, resulting in a significant decrease in product yield.

Since the upper and lower stoppers must be bonded each time for each wafer / chip, a great deal of labor is required and mounting costs are increased.

The present invention has been made in view of such a conventional problem, and an object thereof is to provide a gap between a fixed portion and a weight portion of a stopper which restricts the movement of the weight portion during a wafer manufacturing process. By forming by isotropic etching,
An object of the present invention is to provide a semiconductor acceleration sensor capable of easily adding an air damping function, improving a product yield and reducing a mounting cost.

<< Means for Solving the Problems >> In order to achieve the above object, the present invention fixes a base end of a cantilever to a fixing portion of a P-type silicon substrate, A piezoresistor is provided in the portion, a weight portion is fixed to the free end of the cantilever to form a groove between the weight portion and the fixing portion, and a protrusion is formed between the weight portion and the fixing portion. A semiconductor acceleration sensor provided with a plurality of stoppers each comprising a portion and a receiving portion facing the contact portion with a gap in the protruding portion, wherein an N ⁺ buried layer is formed in a portion corresponding to the gap on the substrate. Te, forming an N-type epitaxial layer on the substrate, forming a piezo resistor portion corresponding to the cantilever base end portion of the epitaxial layer, the portion corresponding to the groove of the epitaxial layer N ⁺ Forming a diffusion layer in contact with the N ⁺ buried layer; A step of anisotropically etching a portion corresponding to the outer peripheral edge of the recessed part; and a step of forming the voids and grooves by isotropically etching the N ⁺ buried layer and the N ⁺ diffusion layer. And

<< Operation >> In the manufacturing method of the present invention, the lateral gap of the stopper including the projecting 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 accuracy according to the thickness of the N ⁺ buried layer, and an air damping mechanism can be easily provided.

Further, at the time of manufacturing a wafer, the stopper is formed simultaneously with the cantilever and the weight by etching. For this reason,
Not only is the stopper bonding step unnecessary, but even if excessive acceleration is applied to the weight during the wafer manufacturing process,
The movement of the weight is limited to a predetermined range by the stopper. As a result, breakage of the cantilever due to excessive acceleration can be prevented.

<< Example >> Hereinafter, the present invention will be described with reference to the drawings.

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

First, the structure will be described. 20 is a P-type silicon substrate, 21 is an N-type epitaxial layer formed on the substrate 20, and 22 is a P-type piezoresistor formed on the surface of the N-type epitaxial layer 21 by boron ion implantation or the like. And 23, SiO ₂ films 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 fixedly connected to a fixing portion 26 by a cantilever 24 made of the N-type epitaxial layer 21. Most of the epitaxial layer of the weight portion 25 and the cantilever beam 24 are separated from the fixing portion 26 by a groove 27, and the separation groove 27 communicates with the back surface of the substrate through a lateral gap 39. . That is, the N-type epitaxial layer 21 has a plurality of protrusions 29 and the P-type silicon substrate 20.
A receiving portion 30 indicated by a hatched portion in FIG. 1 is formed in a portion corresponding to the lower surface of each protruding portion 29. As a result, the downward movement of the protrusion 29 is restricted.

A stopper 28 composed of such a protruding portion 29 and a receiving portion 30
Is formed so as to surround the outer peripheral edge of the substantially square weight portion 25, and the protruding portions 29 are alternately formed on the weight portion 25 and the fixing portion 26 as shown in FIG. As a result, the weight 25 is restricted not only in its downward movement but also in its upward movement, and during the wafer manufacturing process,
A plurality of stoppers 28 are formed inside the chip. The three-dimensional detailed structure of the stopper 28 is shown in FIG. In the figure, a hatched portion is a receiving portion 30, and a protruding portion 29 is provided so as to be able to contact the receiving portion 30.

4 (a) and 4 (b) show a manufacturing process of such an acceleration sensor with a built-in stopper.

First, an N ⁺ buried layer 38 of Sb or As is formed in a portion corresponding to the stopper gap 39 on the P-type (100) silicon substrate 20. Next, an N-type epitaxial layer 21 is formed on the silicon substrate 20 (FIG. 1A).

Next, an epitaxial layer is formed by ion implantation of boron or the like.
A P-type piezoresistor 22 is formed at a portion corresponding to the cantilever beam 21 of FIG. Further, a deep N ⁺ diffusion layer 31 reaching the N ⁺ buried layer 38 is formed in a portion corresponding to the groove 27 of the epitaxial layer 21.
Is formed by phosphorus deposition or ion implantation (FIG. 2B).

After that, an etching resistant film 32 made of Si ₃ N ₄ or the like is partially formed on the back surface of the silicon substrate 20 so that the substrate exposed surface is set to surround the four sides of the substantially square weight 25. Thus, contact etching and formation of a metal electrode (not shown) are performed, and while the N-type epitaxial layer 21 is biased to a positive potential, the P-type silicon substrate 20 is
Perform anisotropic electro-chemical etching with an alkaline etchant such as H, hydrazine, EDP (ethylene diamine pyrocatechol aqueous solution). Here, since the cantilever beam 24 and the weight portion 25 are oriented in the <110> direction, the anisotropic etching stops at the (111) plane in contact with the opening edge of the etching resistant film 32 on the back surface of the substrate. On the other hand,
This etching proceeds upward toward the surface of the substrate, and stops at the point where the N-type epitaxial layer 21 is reached.
Thus, when setting the thickness of the cantilever 24, the thickness can be arbitrarily set by controlling the thickness of the N-type epitaxial layer 21. Therefore, since the cantilever 24 having a predetermined thickness can be formed with high accuracy, the variation in the detection sensitivity can be reduced. (Figure (c)).

Further, the N ⁺ buried layer 38 and the deep N ⁺ diffusion layer 31 are etched with an isotropic Si etching solution (for example, HF: HNO ₃ : CH ₃ COOH = 1: 3: 8), thereby accelerating the acceleration built in the stopper. The sensor is completed. In this case, the N ⁺ layer (25 × 10 ¹⁸ cm ^-3 etching
The rate is more than 100 times that of the N ^- layer (10 ¹⁵ -10 ¹⁶ cm ^-3 ).

Here, instead of using the deep N ⁺ diffusion layer 31 described above,
Reactive ion etching before performing anisotropic etching
The groove 27 can also be formed by etching Si by RIE.

 The operation of this embodiment will be described 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 an acceleration in the vertical direction is applied to the weight portion 25, the cantilever 24 bends and stress is applied to the piezoresistor 22. Due to the piezoresistance effect generated thereby, the resistance value changes according to the intensity of the stress, and the acceleration is detected. In this case, even if an excessive acceleration is applied to the weight portion 25, the vertical displacement of the weight portion 25 can be limited by the stopper 28, so that the cantilever 24
Can be prevented from being destroyed.

In this manufacturing method, the thickness of the cantilever 24 can be freely created by etching, and at the same time, the stopper 28 can also be created, so that damage to the cantilever 24 during the wafer / manufacturing process can be prevented. Further, since the 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 about several μm, so that the air damping function for preventing resonance can be sufficiently realized. ,oil·
Dumping can be eliminated.

On the manufacturing side, the lateral gap 39 between the receiving portion 30 and the projecting portion 29 is formed by isotropic etching.
There is no need to consider stopping the etching on the (111) plane as in the case of conventional anisotropic etching, and the degree of freedom in setting the stopper can be significantly increased as compared with the conventional case.

 FIG. 5 shows another embodiment of the present invention.

This embodiment is a specific example applied to a so-called IC acceleration sensor in which peripheral circuits of a piezoresistive bridge such as an amplifier, a bridge bias circuit, and a temperature compensation circuit are integrated in a sensor chip. FIG. 5 shows only the NPN transistor 33 for simplicity.

The structure of the sensor section of this embodiment is the same as that of FIG. 2 of the above embodiment. The N-type epitaxial layer 21 is divided into a number of islands by a P ⁺ element isolation diffusion region 34, and circuit elements are incorporated in each island. I have. Then, a P-type base diffusion region 36 is formed on the N-type epitaxial layer 21, and an N ⁺ emitter diffusion region 35 is formed in the P-type base diffusion region 36.
Further, the N ⁺ diffusion layer 31 and the N ⁺ buried layer 38 of the collector electrode can be shared as a stopper formation region. Reference numeral 37 denotes a metal electrode connected to the piezo resistor 22.

The manufacturing process of the semiconductor acceleration sensor according to this embodiment is substantially the same as that of the above-described embodiment, and the description thereof is omitted. In this embodiment, since the N ⁺ buried layer 38 and the N ⁺ diffusion layer 31 of the bipolar process can be used as the N ⁺ region for etching for forming the stopper 28, the integrated acceleration sensor is extremely easy. This has the effect of being able to be created.

As has been described "the effect of the invention", according to the present invention, in a method of manufacturing a semiconductor acceleration sensor having a stopper consisting of a receiving part projecting portion that limits the vertical movement of the weight portion, N ⁺
Since the gap of the stopper can be formed narrow 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.

In addition, since the cantilever is not damaged even if an excessive acceleration acts during the wafer / manufacturing process, it is possible to reliably prevent a decrease in product yield. Further, since a mounting step for bonding the stopper is not required, there is an effect that the manufacturing cost can be reduced and the labor can be saved correspondingly.

[Brief description of the drawings]

FIG. 1 is a plan view showing an embodiment of a semiconductor acceleration sensor according to the present invention, FIG. 2 is a cross-sectional view taken along the line II-II, FIG. 3 is a perspective view showing a detailed structure of a stopper portion, and FIG. a)
To (d) are process diagrams showing a method for manufacturing the semiconductor acceleration sensor, FIG. 5 is a sectional view showing another embodiment of the present invention, and FIG.
7 and 8 are a sectional view and a plan view, respectively, showing a conventional semiconductor acceleration sensor, and FIGS. 8A to 8D are process diagrams showing a method for manufacturing the same. 20 P-type silicon substrate 21 N-type epitaxial layer 22 P-type piezoresistor 24 cantilever 25 weight 26 fixed part 27 groove 28 stopper 29 protruding part 30 receiving part 31 N ⁺ diffusion layer 34 P-type element isolation diffusion area 38 N ⁺ buried layer 39 void

Claims (1)

(57) [Claims] 1. A cantilever base end is fixed to a fixing part of a P-type silicon substrate, a piezoresistor is provided at the base end of the cantilever, and a weight part is provided at a free end of the cantilever. To form a groove between the weight portion and the fixed portion, and between the weight portion and the fixed portion, from the protruding portion and the receiving portion facing the contactable portion with a gap in the protruding portion. A semiconductor acceleration sensor provided with a plurality of stoppers, comprising: forming an N ⁺ buried layer in a portion corresponding to the gap on a substrate; and forming an N-type epitaxial layer on the substrate. Forming a piezoresistor at a portion corresponding to the base end of the cantilever, and forming an N ⁺ diffusion layer at a portion corresponding to the groove of the epitaxial layer so as to be in contact with the N ⁺ buried layer; a step of anisotropically etching a portion corresponding to the weight outer periphery of the substrate backside, the N ⁺ buried Forming the voids and the grooves by isotropically etching the embedded layer and the N ⁺ diffusion layer.