JP2003098025A - Semiconductor sensor and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly sensitive semiconductor sensor hardly generating a leakage current even in a high temperature environment over 120 deg.C, capable of adjusting easily the impurity concentration in the depth direction of a piezo resistance element, and its manufacturing method. SOLUTION: This semiconductor sensor is constituted as follows. After removing an oxide film formed on a silicon substrate except a part where the piezo resistance element is to be formed, an n-type or p-type epitaxial layer having a desired impurity concentration is developed, to thereby develop single-crystal silicon on the part except the oxide film and polycrystal silicon on the oxide film respectively. In the state where the polycrystal silicon formed on the oxide film is removed, the epitaxial layer is developed until the single-crystal silicon developed from the part except the oxide film covers the oxide film and has the desired thickness. Hereby, the single-crystal silicon having the desired impurity concentration is formed on the oxide film, and the single-crystal silicon is used as the piezo resistance element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor sensor utilizing the piezoresistive effect, and more particularly to a highly sensitive semiconductor sensor adapted for use at a high temperature of 120 ° C. or higher and a manufacturing method thereof.

[0002]

2. Description of the Related Art A conventional semiconductor sensor utilizing the piezoresistive effect forms a p-type (or n-type) piezoresistive element in an n-type (or p-type) silicon substrate by a diffusion method or an ion implantation method. Was.

[0003]

However, this method has a problem that when the temperature is higher than 120 ° C., the leakage current from the PN junction increases and the measurement accuracy deteriorates significantly.

Further, by forming polycrystalline silicon on an insulating film formed on the surface of a silicon substrate and forming a piezoresistive element there, the silicon substrate and the piezoresistive element are electrically separated by the insulating film. However, although a method of preventing a leakage current due to a PN junction is also taken, since the crystallinity of polycrystalline silicon is inferior to that of single crystal silicon, the output sensitivity of the piezoresistive element with respect to stress such as pressure is significantly reduced. There was a problem.

Further, by using an SOI wafer or the like, it is possible to suppress the decrease in sensitivity depending on the crystallinity, but since the piezoresistive element is formed by the diffusion method or the ion implantation method, the piezoresistive element The impurity concentration in the depth direction is not uniform, and the impurity concentration of the piezoresistive element in the vicinity of the interface between silicon and the oxide film, which receives the largest stress, is generally low, so the piezoresistive effect is fully exerted. However, there is a problem that the sensitivity is lowered as a result.

The present invention has been made in view of the above-mentioned conventional drawbacks.
It was made to eliminate these drawbacks.
To obtain a highly sensitive semiconductor sensor and a manufacturing method thereof, in which a leakage current hardly occurs even in a high temperature environment of 20 ° C. or higher, and the impurity concentration in the depth direction of a piezoresistive element can be easily adjusted. Has an aim.

The objects and novel features of the present invention will become more fully apparent by reading the following description in light of the accompanying drawings. However, the drawings are only for explanation and do not limit the technical scope of the present invention.

[0008]

In order to achieve the above object, the present invention is a semiconductor sensor in which a piezoresistive element is arranged in a strain-generating part formed on a silicon substrate, and an oxide film is formed on the silicon substrate. After removing the oxide film leaving a portion for forming a piezoresistive element, n of a desired impurity concentration is obtained.
-Type or p-type epitaxial layer is grown so that single-crystal silicon is formed on the portion other than on the oxide film.
Polycrystalline silicon is grown on the oxide film, and the polycrystalline silicon formed on the oxide film is removed, and the single crystal silicon grown from a portion other than the oxide film covers the oxide film. The epitaxial layer is grown to a desired thickness to form single crystal silicon having a desired impurity concentration on the oxide film, and the single crystal silicon grown on a portion other than the oxide film is removed. By covering the single crystal silicon formed on the oxide film with an insulating film, the single crystal silicon is used as a piezoresistive element to form a semiconductor sensor.

Further, in a method of manufacturing a semiconductor sensor in which a piezoresistive element is arranged in a strained portion formed on a silicon substrate, a step of forming an oxide film on the silicon substrate and a portion for forming this piezoresistive element on the oxide film. And removing the polycrystalline silicon grown on the oxide film by growing an n-type or p-type epitaxial layer having a desired impurity concentration and removing the polycrystalline silicon grown on the oxide film from the silicon substrate. Covering with single crystal silicon grown from, and growing single crystal silicon of a desired thickness on the oxide film,
A method of manufacturing a semiconductor sensor is configured by including a step of removing single crystal silicon grown on a portion other than the oxide film and a step of covering the single crystal silicon formed on the oxide film with an insulating film. ing.

[0010]

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

In the drawings showing an example of the embodiment of the present invention shown in FIGS. 1 and 2, reference numeral 1 denotes a p-type silicon substrate, and stress is applied to a thin strained portion 9 formed in a substantially central portion thereof. Detectable piezoresistive elements 3a, 3b, 3c, 3d are arranged, and lead portions 5a, 5b, made of a conductor such as aluminum,
, 5h, and electrically connected to the electrode pads 7a, 7b, 7c, 7d made of a conductor such as aluminum.

The structure will now be described in detail with reference to FIG. 3 showing the manufacturing process of the present invention.

(1) p-type (100) plane silicon substrate 1
An oxide film 25a having a thickness of 0.5 μm or less is formed on the surface of (2) by a method such as thermal oxidation. Here, since the oxide film is formed by thermal oxidation, the oxide film 25b is also formed on the back surface of the silicon substrate 1. However, by using a method such as CVD, only the front surface of the silicon substrate 1 is formed. Alternatively, the oxide film 25a can be formed.

(3) The oxide film 25a is removed (patterned) except for the portions where the piezoresistive elements 3a, 3b, 3c and 3d are formed, so that the silicon substrate 1 other than this region is exposed.

(4) An epitaxial layer doped with impurities such as boron so as to have an appropriate impurity concentration (for example, about 2 × 10 18 / cubic cm) as a piezoresistive element is epitaxially grown on a silicon substrate. 1
And on the oxide film 25a. At this time, as shown in FIG. 4, the single crystal silicon 21 depending on the crystal orientation of the silicon substrate 1 is formed on the silicon substrate 1 by the oxide film 25a.
Polycrystalline silicon 2 with no specific crystal orientation on top
3 each grow.

(5) The polycrystalline silicon 23 formed on the oxide film 25a is removed by etching. At this time, the single crystal silicon 2 formed on the silicon substrate 1
1 is also partially etched as shown in FIG.

By repeating the epitaxial growth steps (6) and (4) and the etching step of the polycrystalline silicon 23 (5), the polycrystalline silicon 23 formed on the oxide film 25a is removed and the silicon substrate is removed. 1. The single crystal silicon 21 grown from above covers the oxide film 25a,
By growing the epitaxial layer to have a desired thickness, the single crystal silicon 21 having a desired impurity concentration is formed on the oxide film 25a as shown in FIG.

(7) The single crystal silicon 21 formed on a portion other than the oxide film 25a is removed by etching.
At this time, it is desirable to pattern the single crystal silicon 21 so that the outer edge of the oxide film 25a is slightly exposed.

(8) Single crystal silicon 2 is formed on the oxide film 25a.
By performing thermal oxidation in the state in which 1 is formed, the processing strain in the epitaxial growth process and the like is removed, and an oxide film is formed on the front and back surfaces of the silicon substrate 1 and the surface of the single crystal silicon 21. 25c) the single crystal silicon 21 covered with the piezoresistive elements 3a, 3b, 3
c and 3d.

(9) to (12) are the manufacturing method of the thin strain element 9 and the piezoresistive elements 3a, 3b, 3c, 3
1 shows an example of a method for manufacturing the contact hole 11 for electrically connecting the electrode pad 7a, 7b, 7c, 7d to the electrode pad 7a, 7b, 7c, 7d, but it is a known technique and various manufacturing methods can be applied. Therefore, the description is omitted.

As described above, in the semiconductor sensor of the present invention, single crystal silicon epitaxially grown with a desired crystal orientation and a desired impurity concentration is formed into a desired shape and then an insulating film (oxidized here) is formed. Since it is covered with a film) and this single crystal silicon is used as a piezoresistive element, it is spatially independent of other piezoresistive elements and is electrically insulated including the silicon substrate. It is possible to suppress the leakage current from the surface of the piezoresistive element due to the influence of, for example, and since it does not have a PN junction, it is possible to suppress the leakage current even in a high temperature environment of 120 ° C. or higher. .

Further, since it is grown as a single crystal by epitaxial growth, the crystallinity of the piezoresistive element is good, and an epitaxial layer doped with a predetermined amount of impurities is grown so as to have a desired impurity concentration. Therefore, since the impurity concentration can be appropriately controlled even in the cross-sectional depth direction of the piezoresistive element, it is configured so that the optimum piezoresistive effect can be obtained at the portion where the stress is highest, It is possible to easily adjust the impurity concentration in the depth direction of the piezoresistive element according to various characteristics, such as configuring the contact resistance at the part that is electrically connected to the lead part (contact hole) to be the smallest. You can

The semiconductor sensor shown in FIGS. 1 to 6 has been described by taking as an example the structure of a pressure sensor that exclusively detects the pressure of gas or liquid. However, the strain sensor formed on the silicon substrate has piezoelectric elements. If it is a semiconductor sensor that uses a piezoresistive effect and has a resistive element, an acceleration sensor, inclinometer, etc.
Needless to say, the present invention is not limited to various semiconductor sensors, but is not limited to the crystal orientation of the silicon substrate, the shape (pattern) of the piezoresistive element, the shape of the strain generating portion, and the like.

In addition, an example is shown in which, after patterning single crystal silicon, an oxide film by thermal oxidation is formed on the surfaces of the silicon substrate and the piezoresistive element, and a nitride film is formed thereon. It is also possible to directly form another insulating film without forming an oxide film by the above method.

[0025]

As described above in detail, the following effects can be obtained in the present invention.

(1) In a semiconductor sensor in which a piezoresistive element is arranged in a strain generating portion formed on a silicon substrate, an oxide film is formed on the silicon substrate, and the oxide film is removed except for the portion where the piezoresistive element is formed. After that, an n-type or p-type epitaxial layer having a desired impurity concentration is grown to grow single crystal silicon on a portion other than the oxide film and polycrystalline silicon on the oxide film. By removing the polycrystalline silicon formed on the oxide film, the epitaxial layer is grown until the single crystal silicon grown from a portion other than the oxide film covers the oxide film to a desired thickness. Formed on the oxide film after forming single crystal silicon having a desired impurity concentration on the oxide film and removing the single crystal silicon grown on a portion other than the oxide film. By covering the single crystal silicon with the insulating film, which constitutes the semiconductor sensor by the single-crystal silicon piezoresistive element, 120 ° C.
Even under the above high temperature environment, almost no leakage current is generated, the impurity concentration in the depth direction of the piezoresistive element can be easily adjusted, and a highly sensitive semiconductor sensor can be obtained.

(2) In a method of manufacturing a semiconductor sensor in which a piezoresistive element is arranged in a strained portion formed on a silicon substrate, a step of forming an oxide film on the silicon substrate and a piezoresistive element formed from this oxide film. A step of removing the remaining portion, and a step of growing an n-type or p-type epitaxial layer having a desired impurity concentration and removing the polycrystalline silicon grown on the oxide film, the oxide film is placed on the silicon substrate. Covering with single crystal silicon grown from above and growing single crystal silicon of a desired thickness on the oxide film;
By including a step of removing the single crystal silicon grown on a portion other than the oxide film, and a step of covering the single crystal silicon formed on the oxide film with an insulating film,
A method of manufacturing a semiconductor sensor having the effect (1) can be obtained.

[Brief description of drawings]

FIG. 1 is a plan view of a semiconductor sensor according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view seen from a II-II direction in FIG.

FIG. 3 is a diagram showing a manufacturing process of the semiconductor sensor according to the first embodiment of the invention.

FIG. 4 is an enlarged view of part A of FIG.

5 is a partially enlarged view of portion B of FIG.

FIG. 6 is a partially enlarged view of a C portion of FIG.

[Explanation of symbols]

1: Silicon substrate, 3a, 3b, 3c, 3d: Piezoresistive element, 5a, 5b, 5c, 5d, 5e, 5f, 5g,
5h: Lead part, 7a, 7b, 7c, 7d: Electrode pad, 9: Strain element, 11: Contact hole, 21: Single crystal silicon, 23: Polycrystalline silicon, 25a, 25b, 25c, 25d: Oxide film, 27
a, 27b: nitride film.

Claims (2)

[Claims] 1. In a semiconductor sensor in which a piezoresistive element is arranged in a strained portion formed on a silicon substrate, an oxide film is formed on the silicon substrate, and the oxide film is removed except for a portion where the piezoresistive element is formed. After that, by growing an n-type or p-type epitaxial layer having a desired impurity concentration, single crystal silicon is grown on a portion other than the oxide film, and polycrystalline silicon is grown on the oxide film. By removing the polycrystalline silicon formed on the oxide film, by growing the epitaxial layer until the single crystal silicon grown from a portion other than the oxide film covers the oxide film to a desired thickness, After forming single crystal silicon having a desired impurity concentration on the oxide film and removing the single crystal silicon grown on a portion other than the oxide film,
A semiconductor sensor, wherein the single crystal silicon formed on the oxide film is covered with an insulating film to form the single crystal silicon as a piezoresistive element. 2. A method of manufacturing a semiconductor sensor in which a piezoresistive element is arranged in a strain-generating part formed on a silicon substrate, a step of forming an oxide film on the silicon substrate, and a portion where the oxide film forms a piezoresistive element. And removing the polycrystalline silicon grown on the oxide film by growing an n-type or p-type epitaxial layer having a desired impurity concentration and removing the polycrystalline silicon grown on the oxide film from the silicon substrate. Covering the oxide film with single crystal silicon having a desired thickness, removing the single crystal silicon grown on a portion other than the oxide film, and forming the oxide film And a step of covering the single crystal silicon formed above with an insulating film.