JPH11126909A - Manufacture of semiconductor acceleration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a semiconductor acceleration sensor having a deflection part with accuracy in thickness. SOLUTION: On a first main face of a silicon substrate 1, a p<+> -type buried sacrificial layer 3 extended from the edge of a central part 1a of the substrate 1 to the outer part is formed, and an epitaxial layer 4 with a thickness corresponding to a deflection part 11 to be deflected at acceleration time is formed. A metal wiring 14, an upper stopper junction electrode 15, a movable electrode 16, and an electrode pad are formed in a given position on the epitaxial-layer formed side of the silicon substrate 1. A part, corresponding to the circumferential part of a weight part 12 for deflecting the deflection part 11 at the acceleration time, is treated in an anisotropic etching step from a second main face of the substrate 1 to form a cut part 8 reaching the p<+> -type buried sacrificial layer 3 from the second main face. Then, the p<+> -type buried sacrificial layer 3 is removed in an isotropic etching step, and the epitaxial layer 4 is changed into a deflection part 11 supported by each frame 10 on both sides and connected to a central part 12a of the weight part 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a doubly supported semiconductor acceleration sensor for use in automobiles, aircraft, home appliances, and the like.

[0002]

2. Description of the Related Art FIG. 8 is a schematic sectional view showing a manufacturing process of a conventional semiconductor acceleration sensor. First, a silicon nitride film 25 is formed on both surfaces of the silicon substrate 24a (FIG. 8).
(A)) a flexible portion 11 described later on one surface of the silicon substrate 24a and a flexible portion 11 when acceleration is applied on the other surface.
The openings 25a and 25b are formed by etching away the silicon nitride film 25 at locations respectively corresponding to the outer peripheral edges of the weight portion 12 that bends (FIG. 8B).

Subsequently, using the silicon nitride film 25 in which the openings 25a and 25b are formed as a mask, the silicon substrate 2
The recesses 26a and 26b are formed by etching 4a, and the silicon nitride film 25 on the surface of the silicon substrate 24a on which the bent portion 11 is formed is removed by etching. Then, the silicon substrate 24b is bonded to the surface of the silicon substrate 24a from which the silicon nitride film 25 has been removed (FIG. 8C), and the silicon substrate 24b is thinned by grinding or etching to a thickness corresponding to the bent portion 11. (FIG. 8D).

Next, a portion corresponding to the bent portion 11 of the thinned silicon substrate 24b has a conductivity type opposite to that of the silicon substrate 24b, and a resistance change due to the deflection is formed into a bridge circuit to generate an electric signal. Piezoresistor to convert 2
7 and diffusion wiring 28 electrically connected to piezoresistor 27
Are formed by impurity diffusion (FIG. 8E).

Next, the piezoresistor 2 of the silicon substrate 24b is
A protective film 29 is formed on the formation surface side, and the protective film 29 at a desired location on the diffusion wiring 28 is removed by etching to form a contact hole, and the metal wiring 14 is formed so as to fill the contact hole.

Finally, using the silicon nitride film 25 in which the opening 25b is formed as a mask, potassium hydroxide (KO) is used.
H) Anisotropically etching the silicon substrate 24a using an alkaline etchant such as a solution to form the notch 8 communicating from the concave portion 26b on one surface of the silicon substrate 24a to the concave portion 26a on the other surface. And a flexible member 11 connected to the weight 12, a center of the weight 12, and both ends of which are supported by a frame 10 formed of a silicon substrate 24 b, and a support member 13 for supporting a lower surface of the frame 10. (FIG. 8F).

In the semiconductor acceleration sensor, the acceleration to be detected is transmitted to the flexure 11 as flexure, and the flexure 11
The resistance value of the piezoresistor 27 is changed by bending and converted into an electric signal.

Accordingly, the sensitivity of the semiconductor acceleration sensor is governed by the thickness of the bending portion 11, and is deteriorated as the thickness increases, and is affected by the variation in the thickness. That is, in the manufacturing process of the semiconductor acceleration sensor, it is important to uniformly and accurately control the thickness of the bending portion 11.

[0009]

However, in the method of manufacturing a semiconductor acceleration sensor as described above, the bending portion 11 is connected to the center of the weight portion 12 and both ends thereof are connected to the frame 14.
A semiconductor acceleration sensor having a double-supported beam structure supported by the silicon substrate 24a can be manufactured.
4b, the silicon substrate 24b is thinned into a thin film to a thickness corresponding to the bent portion 11, and the thickness of the silicon substrate 24b varies. It was difficult.

The present invention has been made in view of the above points, and an object of the present invention is to provide a method of manufacturing a semiconductor acceleration sensor capable of accurately forming the thickness of a bent portion. It is in.

[0011]

According to the first aspect of the present invention,
Forming, on one main surface of the semiconductor substrate having one main surface and two main surfaces, a high-concentration impurity region extending outward from an outer edge of at least a portion of a central portion of the semiconductor substrate; and one main surface of the semiconductor substrate A step of forming an epitaxial layer with a thickness corresponding to a bending portion that bends when an acceleration is applied; and forming an electrode at a predetermined position on the epitaxial layer forming surface side of the semiconductor substrate and electrically connecting the electrode to the electrode. Forming a metal wiring, and performing anisotropic etching from the two main surface sides of the semiconductor substrate to a portion corresponding to an outer peripheral edge of a weight portion that bends the bent portion when acceleration is applied, to the high-concentration impurity region. A step of forming a notch which reaches, and removing the high-concentration impurity region by isotropic etching through the notch, and connecting to the center of the weight to connect both ends of the epitaxy. The deflection unit, which is supported by a frame formed by Le layer and a step of forming an epitaxial layer.

According to a second aspect of the present invention, in the method for manufacturing a semiconductor acceleration sensor according to the first aspect, a step of forming a slit by etching a desired portion of the epitaxial layer after forming the bent portion is provided. It is characterized by having.

According to a third aspect of the present invention, in the method for manufacturing a semiconductor acceleration sensor according to the first or second aspect,
The epitaxial layer is provided with a step of forming a high-concentration connection layer having a high impurity concentration connected to the high-concentration impurity region, and the slit is formed by etching and removing the high-concentration connection layer. It is assumed that.

According to a fourth aspect of the present invention, in the method of manufacturing a semiconductor acceleration sensor according to the third aspect, the high-concentration connecting layer and the high-concentration impurity region are continuously removed by etching. It is.

According to a fifth aspect of the present invention, in the method of manufacturing a semiconductor acceleration sensor according to any one of the first to fourth aspects, the wiring forming surface side of the semiconductor substrate is etched before the high-concentration impurity region is removed by etching. And a step of forming a protective film for protecting against erosion by the method.

According to a sixth aspect of the present invention, in the method of manufacturing a semiconductor acceleration sensor according to the fifth aspect, a chromium film, a silicon nitride film, or a fluorine resin is used as the protective film.

According to a seventh aspect of the present invention, in the method of manufacturing a semiconductor acceleration sensor according to any one of the first to sixth aspects, a step of reducing the thickness of the weight portion by etching is provided. .

According to an eighth aspect of the present invention, in the method of manufacturing a semiconductor acceleration sensor according to any one of the first to seventh aspects, the metal wiring is connected to a center line passing through the center of gravity of the weight portion and perpendicular to the semiconductor acceleration sensor. Are arranged so as to be rotationally symmetric with respect to.

According to a ninth aspect of the present invention, in the method of manufacturing a semiconductor acceleration sensor according to any one of the first to eighth aspects, the impurity concentration of the high-concentration impurity region is reduced on one main surface of the semiconductor substrate. It is a feature.

According to a tenth aspect of the present invention, in the method for manufacturing a semiconductor acceleration sensor according to the ninth aspect, the impurity concentration of one main surface of the semiconductor substrate in the high-concentration impurity region is 5 × 10 ¹⁹ cm ⁻³ or less. It is characterized by having.

According to an eleventh aspect of the present invention, in the method for manufacturing a semiconductor acceleration sensor according to the ninth or tenth aspect, the high-concentration impurity region is formed by impurity deposition and thermal diffusion, and is subjected to wet oxidation or pyrolysis. By performing genic oxidation, the impurity concentration of the high-concentration impurity region is reduced on one main surface of the semiconductor substrate.

According to a twelfth aspect of the present invention, in the method of manufacturing a semiconductor acceleration sensor according to the ninth or tenth aspect, the high-concentration impurity region is formed by ion-implanting impurities directly into one main surface of the semiconductor substrate. The high-concentration impurity region having a low impurity concentration is formed on one main surface of the semiconductor substrate by performing an annealing process.

According to a thirteenth aspect of the present invention, in the method for manufacturing a semiconductor acceleration sensor according to the ninth or tenth aspect, after forming the high-concentration impurity region, one of the semiconductor substrates in the high-concentration impurity region is formed. The surface is doped with an impurity of a conductivity type opposite to a conductivity type of the high concentration impurity region.

According to a fourteenth aspect of the present invention, in the method for manufacturing a semiconductor acceleration sensor according to any one of the ninth to thirteenth aspects, the impurity concentration of at least the epitaxial layer in the semiconductor substrate and the epitaxial layer is adjusted during epitaxial growth. It is characterized in that the concentration of impurities taken into the epitaxial layer is made higher than the maximum value by autodoping.

[0025]

Embodiments of the present invention will be described below with reference to the drawings. In the following embodiments, the invention is also applied to a case where the conductivity type is reversed.

FIGS. 1 to 3 are schematic sectional views showing a manufacturing process of a semiconductor acceleration sensor according to an embodiment of the present invention. FIG. 4 is a partially broken view of the semiconductor acceleration sensor according to the embodiment. FIG. 5 is a schematic plan view showing a state of the semiconductor acceleration sensor according to the present embodiment as viewed from above. FIG. 1 is a cross-sectional view of FIG.
FIG. 2 shows a schematic cross-sectional view at A ′, FIG. 2 shows a schematic cross-sectional view at BB ′ in FIG. 5, and FIG. 3 shows a schematic cross-sectional view at FIG.

First, a silicon oxide film 2 is formed on an n-type silicon substrate 1 as a semiconductor substrate by thermal oxidation or the like.
By etching the silicon oxide film 2, a substantially long opening extending outward from the outer edge of the rectangular central portion 1a of the silicon substrate 1 and separated by an equal angle (90 °) is provided. 2a is formed.

The opening 2a may be formed at a location surrounding the center 1a. Subsequently, the opening 2a
Using the silicon oxide film 2 on which is formed as a mask, a p-type impurity such as boron (B) is deposited and thermally diffused or ion-implanted and annealed to perform a p + -type buried sacrificial layer 3 as a high-concentration impurity region. (Fig. 1
(A), FIG. 2 (a), FIG. 3 (a)), silicon oxide film 2
Is removed by etching.

In the present embodiment, the p + -type buried sacrificial layer 3 is formed on the silicon substrate 1, but n-type impurities such as phosphorus (P) are deposited and thermally diffused or ion-implanted and annealed. The n + type buried sacrificial layer may be formed by performing the processing.

The p + type buried sacrificial layer 3 has a central portion 1a.
May extend from the entire outer edge of the to completely surround the portion, or may extend from a portion of the outer edge. When extending from the whole, the p + -type buried sacrificial layer 3 may have an annular shape, for example, the central portion 1a is circular and p
The + type embedded sacrificial layer 3 is an annular portion between a concentric circle formed by a circle concentric with the central portion 1a and the central portion 1a is an inner square, and the p + type embedded sacrificial layer 3 is concentric with the central portion 1a. And it may be formed by the outer square having the same orientation, and may be an annular portion between the inner square and the outer square. Further, the p + -type buried sacrificial layer 3 may be a portion formed by a portion between the circular central portion 1a and the outer square or a portion formed by a combination of the opposite portions. Alternatively, an elliptical shape may be used.

The p + type buried sacrificial layer 3 has a central portion 1a.
When extending from a part of the outer edge of the p + type buried sacrificial layer 3
May be substantially elongated layers spaced at equal angles (eg, 90 °) around the central portion 1a, in which case the p + -type buried sacrificial layer 3 is Are formed (ie, cross at the center 1a). In other words, the p + type buried sacrificial layer 3 may extend radially from the central portion 1a, and the number thereof is not limited.

Next, on the surface of the silicon substrate 1 on which the p + -type buried sacrificial layer 3 is formed (hereinafter, this surface is referred to as the surface), an n-type is formed with a thickness corresponding to a later-described bending portion 11 which bends when an acceleration is applied. The epitaxial layer 4 is formed on both sides,
A silicon oxide film 5 is formed by pyrogenic oxidation or the like, and a silicon nitride film 6 is formed on the silicon oxide film 5 by a low-pressure CVD method or the like, and corresponds to an outer peripheral edge of a later-described weight portion 12 on the back surface of the silicon substrate 1. The opening 7 is formed by etching and removing the silicon oxide film 5 / silicon nitride film 6 at the portion to be formed (FIGS. 1 (b), 2 (b), 3 (b)).

In this embodiment, the silicon oxide film 5 / silicon nitride film 6 is formed. However, the present invention is not limited to this, and only the silicon nitride film 6 may be formed. However, by forming the silicon oxide film 5 / silicon nitride film 6, the internal stress of each film can be compressed and pulled (or reversed) to reduce the warpage of the beam portion 11a described later.

Next, using the silicon oxide film 5 / silicon nitride film 6 having the opening 7 formed therein as a mask, anisotropic etching of the silicon substrate 1 using an alkaline etchant such as a potassium hydroxide (KOH) solution. Is performed until reaching the p + -type buried sacrificial layer 3 to form the cut portion 8 (FIGS. 1C and 2C).

Next, an etchant is introduced from the cut portion 8, the p + -type buried sacrificial layer 3 is removed by isotropic etching for etching in all directions to form a cut groove 9, and the epitaxial layer 4 is formed. Frame 10 composed of: a flexible portion 11 composed of an epitaxial layer 4 having both ends (beam portions 11a) supported by the frame 10; and a silicon substrate 1 having a central portion 12a supported by a central portion of the flexible portion 11. And a supporting member 13 made of the silicon substrate 1 surrounding the weight portion 12 and supporting the lower surface side of the frame 10 (the joint surface side between the silicon substrate 1 and the epitaxial layer 4).

At this time, the etching rate of the isotropic etching is higher in the p + -type buried sacrificial layer 3 than in the epitaxial layer 4 having a low impurity concentration, and only the epitaxial layer 4 remains selectively. , P + -type buried sacrificial layer 3 can be selectively removed.

In this embodiment, as an etchant for performing isotropic etching, an acidic solution composed of hydrofluoric acid or the like (50% hydrofluoric acid aqueous solution: 69% nitric acid aqueous solution: acetic acid =
1: 1 to 3: 8).

Next, metal wiring 14, upper stopper bonding electrode 15, movable electrode 16 and electrode pad 17 are formed of gold (Au) on silicon nitride film 9 on the front side (FIG. 1).
(D), FIG. 2 (d), FIG. 3 (c)). At this time, the metal wiring 14, the upper stopper bonding electrode 15, the movable electrode 16 and the electrode pad 17 may be formed via a chromium (Cr) film or the like in order to enhance the adhesion to the underlying layer. Also, metal wiring 1
4. Aluminum (Al) may be used for the upper stopper bonding electrode 15, the movable electrode 16, and the electrode pad 17. Further, the metal wiring 14, the upper stopper bonding electrode 15,
As a method of forming the movable electrode 16 and the electrode pad 17, a method of forming a metal layer by performing vapor deposition or sputtering or the like and patterning it into a predetermined shape by using a photolithography technique and an etching technique, or a method of previously forming a metal wiring 14, an upper stopper After a resist or the like is formed at a position other than the positions where the bonding electrode 15, the movable electrode 16 and the electrode pad 17 are formed,
There is a method of forming a metal layer by performing vapor deposition or sputtering and removing a resist or the like, a so-called lift-off method, and the like.

Next, a wiring protection film 18 such as a chromium film, a silicon nitride film, and a fluororesin is formed on the front surface side, and as shown in FIG.
An opening 18a is formed in a portion of the inner side surface excluding the portion where the beam portion 11a is formed (FIGS. 1 (e), 2 (e), 3).
(D)).

Next, reactive ion etching (RI) is performed using the wiring protection film 18 in which the opening 18a is formed as a mask.
E: Reactive Ion Etching) or the like is formed. At this time, the slit 19 adjacent to the beam portion 11a is formed until reaching the cut groove 9, and the slit 19 on the inner side surface of the frame 10 is formed until reaching the cut portion 8.

In this embodiment, the beam 11a is used.
The slits 19 are simultaneously formed in the portion adjacent to the frame 10 and the inner side surface of the frame 10. However, the present invention is not limited to this.
After the formation, the slit 19 may be formed at a position adjacent to the beam portion 11a (or vice versa). However, if the slits 19 are formed on the inner side surface of the frame 10 and then formed at positions adjacent to the beam portions 11a, the cut grooves 9 will not be etched by RIE or the like.

In the present embodiment, the slit 19 is formed after the p + type buried sacrificial layer 3 is removed by etching. However, the present invention is not limited to this. The mold embedded sacrificial layer 3 may be removed by etching.

Further, the slit 19 of the epitaxial layer 4
If a high-concentration connection layer connected to the p + -type buried sacrificial layer 3 is formed in advance by deposition of p-type or n-type impurities and thermal diffusion or ion implantation and annealing at the formation location, the accuracy can be further improved. A slit 19 can be formed. In this case, the high-concentration connection layer and the p + -type buried sacrificial layer 3 can be continuously removed by etching, so that the cut groove 9 and the slit 19 can be formed without increasing the number of steps.

Here, the boundary between the beam portion 11a and the center portion of the bending portion 11 and the boundary between the beam portion 11a and the frame 10 are provided with slits 19 whose edges have a curved shape in order to avoid stress concentration. It is desirable to form.

Finally, the wiring protection film 18 on the front surface and the silicon oxide film 5 / silicon nitride film 6 on the rear surface are removed by etching (FIGS. 1F, 2F and 3E), and the weight is removed. A lower stopper 20 having a concave portion 20a at a position corresponding to the portion 12 is joined to the support member 13 by anodic bonding or the like, has a concave portion 21a at a position corresponding to the weight portion 12, and is formed so as to face the movable electrode 16. The upper stopper 21 having the fixed electrode 22 is bonded to the upper stopper bonding electrode 15 by anodic bonding or the like (FIGS. 1 (g), 2 (g), 3).
(F)). Here, the fixed electrode 2 is provided on the upper stopper 21.
2 and a contact hole 23 for making contact with the electrode pad 17 are formed.

In this embodiment, the slit 1
Although the lower stopper 20 is joined to the support member 13 after the formation of 9, the slit is not limited to this, and the slit 19 may be formed after the lower stopper 20 is joined to the support member 13. .

Further, in the present embodiment, as shown in FIG. 4, the slit 19 is formed at a position adjacent to the beam portion 11a and on the inner side surface of the frame 10, but the present invention is not limited to this. For example, as shown in FIG.
Epitaxial layer 4 between flexure 11 and frame 10
May be removed by etching to form a slit. In this case, the movable electrode 16 is formed on the upper surface side (the surface on which the epitaxial layer 4 is formed) of the weight portion 12.

In the method of manufacturing the semiconductor acceleration sensor according to the present embodiment, the outer peripheral edge of the weight portion 12 is formed by anisotropic etching from the back surface of the silicon substrate 1, and the bent portion 11 is formed at the center of the silicon substrate 1. The p + -type buried sacrificial layer 3 provided around the portion 1a is formed by removing the p + -type buried sacrificial layer 3 by isotropic etching, and the p + -type buried sacrificial layer 3 is etched compared to the silicon substrate 1 and the epitaxial layer 4. Since the speed is high, the epitaxial layer 4 is not etched so much when the p + type buried sacrificial layer 3 is removed by etching, and the thickness of the bent portion 11 can be formed with high accuracy.
A semiconductor acceleration sensor having a double-supported beam structure with little variation in sensitivity can be manufactured stably.

Further, since the p + type buried sacrificial layer 3 is removed by etching to form the cut groove 19, the bending of the bending portion 11 given by the weight portion 12 is concentrated on the beam portion 11a, and the movable electrode 16 and the fixed electrode 11 are fixed. The rate of change of the capacitance formed by the electrodes 22 increases, and the sensitivity can be improved.

Further, since the slit 19 is formed only at the portion adjacent to the beam portion 11a and on the inner side surface of the frame 10 (excluding the portion where the beam portion 11a is formed), the weight portion 12 is formed.
The upper surface side of the epitaxial layer 4 can also be used as a weight portion, the volume of the weight portion 12 can be increased, the mass of the weight portion 12 can be increased, and the sensitivity can be improved.

In this embodiment, the two beams 1
Although the metal wirings 14 are formed in 1a, for example, as shown in FIG. 7, four metal wirings 14 are arranged rotationally symmetrically with respect to a center line passing through the center of gravity of the weight portion 12 and perpendicular to the sensor. By doing so, the metal wirings 14 are formed evenly on the four beam portions 11a, so that a structure in which thermal distortion is evenly applied and an offset hardly occurs can be obtained.

In the present embodiment, if the bottom surface of the weight portion 12 (on the side different from the surface on which the epitaxial layer 4 is formed) is etched to reduce the thickness of the weight portion 12, a flat lower stopper may be used. Therefore, the step of forming the concave portion in the lower stopper becomes unnecessary, and the cost can be reduced.

In this embodiment, four beam portions 11a are formed. However, the present invention is not limited to this. Any number of beam portions such as eight beams and twelve beams are formed. May be.

In the present embodiment, when a silicon nitride film is used as the wiring protection film 18, the silicon nitride film 6 on the surface does not have to be formed. In this case, the wiring protection film 18 on the electrode pad 17 is previously thinned by etching, and the entire surface of the wiring protection film 18 is etched after the p + type buried sacrificial layer 3 is removed by etching. If the etching is stopped, portions other than the electrode pads 17 will be covered with the silicon nitride film, and the moisture resistance can be improved.

Here, when the epitaxial layer 4 is formed after the formation of the p + -type buried sacrificial layer 3, the surface of the silicon substrate 1 is completely exposed at the beginning of the epitaxial growth. There is a problem that impurities in the layer 3 escape into the atmosphere in which the epitaxial layer 4 is formed and are simultaneously taken in during the epitaxial growth.
This phenomenon is generally called auto-doping. However, as the impurity concentration of the p + -type buried sacrificial layer 3 becomes higher, the degree of the phenomenon becomes larger, and the impurity concentration of the p + -type buried sacrificial layer 3 becomes particularly high. In this case, an inversion layer that is a p + -type impurity region is formed by auto-doping near the interface between the silicon substrate 1 and the epitaxial layer 4 even in a region where the p + -type impurity region should not be formed by design. As a method of solving this problem, there is a method of lowering the impurity concentration of the p + -type buried sacrificial layer 3 near the surface of the silicon substrate 1. For example, there are the following three methods.

(1) Deposition and thermal diffusion are performed using the silicon oxide film with the opening formed as a mask, and wet oxidation or pyrogenic oxidation is performed to form a silicon oxide film at the position where the opening is formed. At this time,
Impurities near the surface of the silicon substrate of the p + type buried sacrificial layer are taken into the silicon oxide film.

(2) Using the silicon oxide film with the opening formed as a mask, ion implantation and annealing are directly performed on the silicon substrate. Here, it is known that the peak of the distribution of impurities immediately after ion implantation appears a little deeper than the implantation surface due to the channeling effect, and this distance is determined by the type of impurity and the acceleration energy at the time of implantation. Assuming the same concentration, the deeper the peak position, the lower the impurity concentration on the silicon substrate surface.

(3) An impurity of the conductivity type opposite to that of the p + type buried sacrificial layer is doped in the vicinity of the silicon substrate surface of the p + type buried sacrificial layer. As a result, p-type and n-type impurities are present in the vicinity of the substrate surface of the p + -type buried sacrificial layer. Therefore, when the epitaxial layer is formed, each of the impurities simultaneously escapes into the atmosphere during the epitaxial growth and epitaxially grows. It is taken into the layer, and both are offset, so that the formation of the inversion layer can be suppressed.

In the above three methods, the impurity concentration on the substrate surface of the p + type buried sacrificial layer is 5 × 10 ¹⁹
cm ^-3 or less.

In addition to the above-described method, as a method for preventing the formation of the inversion layer, at least the impurity concentration of the epitaxial layer in the silicon substrate and the epitaxial layer is adjusted by the impurity doped into the epitaxial layer by autodoping during epitaxial growth. If the concentration is higher than the concentration of the impurity, the incorporated impurities can be offset, the formation of the inversion layer can be completely prevented, and the impurities can be transferred to the epitaxial layer side through the surface of the silicon substrate. Diffusion can also be suppressed.

[0061]

According to the first aspect of the present invention, a high-concentration impurity region extending outward from at least a portion of an outer edge of a central portion of a semiconductor substrate is formed on one main surface of a semiconductor substrate having one main surface and two main surfaces. A step of forming, a step of forming an epitaxial layer on one main surface of the semiconductor substrate with a thickness corresponding to a bending portion that bends when an acceleration is applied, and forming an electrode and a electrode at a predetermined position on the epitaxial layer forming surface side of the semiconductor substrate. A step of forming a metal wiring electrically connected to the electrode, and anisotropically etching the portion corresponding to the outer peripheral edge of the weight portion that bends the bent portion when applying acceleration from the two main surface sides of the semiconductor substrate, Forming a notch reaching the high-concentration impurity region; removing the high-concentration impurity region through the notch by isotropic etching; Forming a bent portion supported by the frame formed by the epitaxial layer, so that an epitaxial layer of a desired thickness can be formed, and the high-concentration impurity region is formed in the epitaxial layer and the semiconductor substrate. On the other hand, the etching rate at the time of isotropic etching is very high, the epitaxial layer is hardly etched at the time of removing the high-concentration impurity region by etching, and the thickness of the bent portion can be accurately formed. A method for manufacturing a semiconductor acceleration sensor can be provided.

According to a second aspect of the present invention, in the method of manufacturing a semiconductor acceleration sensor according to the first aspect, a step of forming a slit by forming a bent portion and then etching a desired portion of the epitaxial layer is provided. In addition, the bending provided by the weight portion is concentrated on the bending portion, and the sensitivity can be improved.

According to a third aspect of the present invention, in the method of manufacturing a semiconductor acceleration sensor according to the first or second aspect,
In the epitaxial layer, a step of forming a high-concentration connection layer having a high impurity concentration connected to the high-concentration impurity region was provided, and a slit was formed by etching and removing the high-concentration connection layer. Since the etching rate is higher than that of the epitaxial layer, the epitaxial layer is not much etched, and the bent portion can be formed with high accuracy.

According to a fourth aspect of the present invention, in the method of manufacturing a semiconductor acceleration sensor according to the third aspect, the high-concentration connecting layer and the high-concentration impurity region are continuously etched and removed, so that the number of steps is increased. Without forming a slit.

According to a fifth or sixth aspect of the present invention, in the method of manufacturing a semiconductor acceleration sensor according to any one of the first to fourth aspects, before the high concentration impurity region is removed by etching, Forming a protective film such as a chromium film, a silicon nitride film, and a fluororesin that protects the electrodes from erosion due to etching, the electrodes and metal wirings are eroded by etching when the high-concentration impurity regions are removed by etching. Can be prevented.

According to a seventh aspect of the present invention, in the method of manufacturing a semiconductor acceleration sensor according to the first to sixth aspects, a step of reducing the thickness of the weight portion by etching is provided. It can be joined to the two main surfaces of the semiconductor substrate, and the cost can be reduced.

According to an eighth aspect of the present invention, in the method for manufacturing a semiconductor acceleration sensor according to any one of the first to seventh aspects, the metal wiring is connected to a center line passing through the center of gravity of the weight portion and perpendicular to the semiconductor acceleration sensor. Since they are arranged rotationally symmetrically, a structure in which thermal strain is evenly applied and an offset hardly occurs can be obtained.

According to a ninth aspect of the present invention, in the method of manufacturing a semiconductor acceleration sensor according to any one of the first to eighth aspects, the impurity concentration of the high-concentration impurity region is reduced on one main surface of the semiconductor substrate. Initially, the amount of impurities that escape from the high-concentration impurity region into the atmosphere can be reduced, and the formation of an inversion layer by autodoping and the diffusion of impurities into the epitaxial layer can be suppressed.

According to a tenth aspect of the present invention, in the method of the ninth aspect, the impurity concentration on one main surface of the semiconductor substrate in the high-concentration impurity region is set to 5%.
Since × was 10 ^{1 9} cm ^-3 or less, it is possible to reduce the amount of impurities to escape into the atmosphere from the high concentration impurity regions in the epitaxial growth beginning, formation and inversion layer due to auto-doping, the impurity into the epitaxial layer Diffusion can be suppressed.

According to an eleventh aspect of the present invention, in the method for manufacturing a semiconductor acceleration sensor according to the ninth or tenth aspect, the high-concentration impurity region is formed by impurity deposition and thermal diffusion, and is wet oxidized or pyrogenic. By performing the oxidation, the impurity concentration of the high-concentration impurity region is reduced on one main surface of the semiconductor substrate, so that the amount of impurities that escape from the high-concentration impurity region into the atmosphere at the beginning of epitaxial growth can be reduced. Formation of an inversion layer by doping and diffusion of impurities into the epitaxial layer can be suppressed.

According to a twelfth aspect of the present invention, in the method for manufacturing a semiconductor acceleration sensor according to the ninth or tenth aspect, the high-concentration impurity region is directly ion-implanted and annealed in one main surface of the semiconductor substrate. Is performed, a high-concentration impurity region having a low impurity concentration is formed on one main surface of the semiconductor substrate, so that the amount of impurities that escape from the high-concentration impurity region into the atmosphere at the beginning of epitaxial growth can be reduced. In addition, it is possible to suppress formation of an inversion layer by auto doping and diffusion of impurities into the epitaxial layer.

According to a thirteenth aspect of the present invention, in the method for manufacturing a semiconductor acceleration sensor according to the ninth or tenth aspect, after forming the high-concentration impurity region, one main surface of the semiconductor substrate in the high-concentration impurity region is provided. Since the impurity of the conductivity type opposite to the conductivity type of the high-concentration impurity region is doped, the impurities of the first conductivity type and the second conductivity type simultaneously escape into the atmosphere during the epitaxial growth and are taken into the epitaxial layer. Thus, the two are cancelled, and the formation of the inversion layer can be suppressed, and at the same time, the diffusion of impurities into the epitaxial layer can be suppressed.

According to a fourteenth aspect of the present invention, in the method for manufacturing a semiconductor acceleration sensor according to the ninth to thirteenth aspects, the impurity concentration of at least the epitaxial layer of the semiconductor substrate and the epitaxial layer is adjusted by autodoping during epitaxial growth. Since the impurity concentration taken into the epitaxial layer is higher than the maximum value, the impurities of the first conductivity type and the second conductivity type can be offset, and the formation of the inversion layer can be completely prevented.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a manufacturing process of a semiconductor acceleration sensor according to one embodiment of the present invention.

FIG. 2 is a schematic sectional view illustrating a manufacturing process of the semiconductor acceleration sensor according to the embodiment.

FIG. 3 is a schematic sectional view illustrating a manufacturing process of the semiconductor acceleration sensor according to the embodiment.

FIG. 4 is a schematic perspective view showing a partially broken state of the semiconductor acceleration sensor according to the embodiment.

FIG. 5 is a schematic plan view showing a state of the semiconductor acceleration sensor according to the embodiment as viewed from above.

FIG. 6 is a schematic perspective view showing a partially broken state of a semiconductor acceleration sensor according to another embodiment of the present invention.

FIG. 7 is a schematic plan view showing a state of the semiconductor acceleration sensor according to the embodiment as viewed from above.

FIG. 8 is a schematic sectional view showing a manufacturing process of a semiconductor acceleration sensor according to a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Silicon substrate 1a Central part 2 Silicon oxide film 2a Opening 3 p + type buried sacrificial layer 4 Epitaxial layer 5 Silicon oxide film 6 Silicon nitride film 7 Opening 8 Notch 9 Cut groove 10 Frame 11 Flexure 11a Beam 12 Weight Part 12a central part 13 supporting member 14 metal wiring 15 upper stopper bonding electrode 16 movable electrode 17 electrode pad 18 wiring protective film 19 slit 20 lower stopper 20a concave part 21 upper stopper 21a concave part 22 fixed electrode 23 contact hole 24a, 24b silicon substrate 25 silicon Nitride film 25a, 25b Opening 26a, 26b Depression 27 Piezoresistor 28 Diffusion defeat 29 Protective film

Claims (14)

[Claims] A step of forming a high-concentration impurity region extending outwardly from an outer edge of at least a part of a central portion of the semiconductor substrate on one main surface of the semiconductor substrate having one main surface and two main surfaces; Forming an epitaxial layer on one main surface of the substrate with a thickness corresponding to a bending portion that bends when an acceleration is applied; and forming an electrode at a predetermined position on the epitaxial layer forming surface side of the semiconductor substrate and electrically connecting the electrode to the electrode. Forming a metal wiring to be electrically connected, and anisotropically etching the portion corresponding to the outer peripheral edge of the weight portion that gives flexure to the flexure portion when applying acceleration from the two main surface sides of the semiconductor substrate, Forming a cut portion reaching the high-concentration impurity region; removing the high-concentration impurity region through the cut portion by isotropic etching; connecting to the center of the weight portion; Forming a bent portion supported by a frame formed by the epitaxial layer using the epitaxial layer. 2. The method according to claim 1, further comprising the step of forming a slit by etching a desired portion of the epitaxial layer after forming the bending portion. 3. A step of forming a high-concentration connection layer having a high impurity concentration connected to the high-concentration impurity region in the epitaxial layer, and forming the slit by etching away the high-concentration connection layer. The method for manufacturing a semiconductor acceleration sensor according to claim 1 or 2, wherein 4. The method for manufacturing a semiconductor acceleration sensor according to claim 3, wherein said high-concentration connecting layer and said high-concentration impurity region are continuously removed by etching. 5. The method according to claim 1, further comprising a step of forming a protective film for protecting the wiring formation surface side of the semiconductor substrate from erosion due to etching before the high-concentration impurity region is removed by etching. A method for manufacturing a semiconductor acceleration sensor according to claim 4. 6. The method according to claim 5, wherein a chromium film, a silicon nitride film, or a fluororesin is used as the protective film. 7. The method for manufacturing a semiconductor acceleration sensor according to claim 1, further comprising a step of reducing the thickness of said weight portion by etching. 8. The semiconductor device according to claim 1, wherein the metal wiring is arranged symmetrically with respect to a center line passing through a center of gravity of the weight portion and perpendicular to the semiconductor acceleration sensor.
A method for manufacturing a semiconductor acceleration sensor according to claim 7. 9. An impurity concentration of the high concentration impurity region,
9. The method of manufacturing a semiconductor acceleration sensor according to claim 1, wherein the first surface of the semiconductor substrate is lowered. 10. The method of manufacturing a semiconductor acceleration sensor according to claim 9, wherein an impurity concentration in one main surface of said semiconductor substrate in said high-concentration impurity region is set to 5 × 10 ¹⁹ cm ⁻³ or less. 11. The high-concentration impurity region is formed by deposition and thermal diffusion of an impurity, and by performing wet oxidation or pyrogenic oxidation, the impurity concentration of the high-concentration impurity region is reduced by one of the semiconductor substrates. The surface is lowered at the surface thereof.
0. A method for manufacturing a semiconductor acceleration sensor according to item 0. 12. The high-concentration impurity region having a low impurity concentration on one main surface of the semiconductor substrate by directly performing ion implantation and annealing of the impurity on the one main surface of the semiconductor substrate. The method for manufacturing a semiconductor acceleration sensor according to claim 9, wherein a region is formed. 13. After forming the high-concentration impurity region, one main surface of the semiconductor substrate in the high-concentration impurity region is doped with an impurity having a conductivity type opposite to a conductivity type of the high-concentration impurity region. The method of manufacturing a semiconductor acceleration sensor according to claim 9, wherein the method is performed. 14. The semiconductor substrate and the epitaxial layer, wherein at least the impurity concentration of the epitaxial layer is higher than the maximum impurity concentration taken into the epitaxial layer by autodoping during epitaxial growth. Claims 9 to 1
4. The method for manufacturing a semiconductor acceleration sensor according to 3.