JPH04240776A - Semiconductor pressure sensor and its manufacture - Google Patents

Abstract

PURPOSE:To obtain a high-sensitivity semiconductor pressure sensor by a method wherein a piezoresistance forming a pressure-sensing resistance is formed on the face of an Si (110) wafer of a bonded body by the Si (110) wafer and by an Si (100) wafer and a diaphragm is formed on the Si (100) wafer by performing a selective etching operation reaching a bonded face or a part near it. CONSTITUTION:An Si (110) wafer 3 and an Si (100) wafer 4 are pasted and united; after that, a shaping operation or a polishing operation is executed to the wafer 3 so as to make it thin or the like. Then, a piezoresistance element as a pressure-sensing element is formed on the face of the wafer 3. Then, a required masking operation is executed to the face of the wafer 4; an anisotropic etching operation is executed selectively to the bonding interface to the wafer 3 or a part near it; a diaphragm 3a is formed.

Description

[Detailed description of the invention]

0001

[Purpose of the invention]

0002

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor pressure sensor and a method of manufacturing the same.

0003

[Prior Art] A piezoresistor, which is a pressure-sensitive resistor, is made of Si(1
00) A semiconductor pressure sensor formed in a thin area that is to be a diaphragm formed by etching on one principal surface (front surface) of a wafer or Si (110) wafer and from the other principal surface (back surface) is used in automobiles. It is used in a wide range of applications, including engine control, industrial plants, blood pressure monitors, and barometers. FIG. 7 shows a cross-sectional view of an example of the structure of the semiconductor sensor, in which 1 is a Si (100) wafer or Si (
110) 2 indicates a thin region that will become a diaphragm formed by selectively etching the other main surface (back surface) of the wafer.

0004

However, the semiconductor pressure sensor having the above structure generally has the following disadvantages. First, when using a Si (100) wafer 1, a structure is adopted in which a piezoresistor is formed on one main surface and anisotropic etching is performed on the other main surface to form a square diaphragm 2 that deforms under pressure. . The thickness of the diaphragm 2 is generally controlled by the etching time, but since the amount of etching required to form the diaphragm 2 is large, variations in the thickness of the diaphragm 2 are likely to occur even if temperature control is performed. There was a problem that the characteristics were uneven. Further, even if the size of the diaphragm and the formation position of the piezoresistance are optimized, the sensitivity is ultimately determined by the piezoresistance coefficient specific to the Si (100) wafer 1, so it is impossible to achieve higher sensitivity than that. On the other hand, when Si(110) wafer 1 is used, the piezoresistance coefficient is higher than that of Si(100) wafer 1.
A highly sensitive pressure sensor can be created. but,
(110) Due to the anisotropic etching characteristics of the surface, it is difficult to form a symmetrical and smooth diaphragm, and the thickness of the diaphragm is also difficult to form uniformly and has many variations, so there is a problem that the properties become uneven.

The present invention has been made in response to the above-mentioned circumstances, and aims to provide a semiconductor sensor that is highly sensitive, whose diaphragm thickness is uniformly and precisely controlled, and which always exhibits excellent required functions, and a method for manufacturing the same. purpose.

[0006]

[Structure of the invention]

[0007]

[Means for Solving the Problems] A semiconductor pressure sensor according to the present invention comprises a Si(110) wafer and a Si(100) wafer.
) A piezoresistor forming a pressure-sensitive resistor is formed on the Si(110) wafer surface of the bonded wafer, and a diaphragm is formed on the Si(100) wafer by selective etching that reaches the bonding interface or its vicinity. The manufacturing method includes a step of forming a bonded body of a Si(110) wafer and a Si(100) wafer;
A step of forming a piezoresistor forming a pressure-sensitive resistor, and
(100) The wafer is selectively etched to reach the bonding interface or its vicinity so that at least a portion of the wafer becomes Si(11
0) Forming a diaphragm made of a wafer.

[0008]

[Operation] In the semiconductor pressure sensor according to the present invention, S
High sensitivity was achieved by forming a piezoresistor forming a pressure-sensitive resistor on the i(110) wafer surface, and selective etching of the Si(100) wafer made at least a portion of the Si(110)
) A diaphragm with excellent characteristics is formed from the wafer, and the thickness of the formed diaphragm is also controlled with high precision, so variations in characteristics are completely eliminated.

[0009]

Embodiments An embodiment of the present invention will be described below with reference to FIGS. 1 to 6.

FIG. 1 shows a cross-sectional view of an example of the structure of a semiconductor pressure sensor according to the present invention, in which 3 is a Si (110) wafer on which a piezoresistor forming a pressure-sensitive resistor is formed on one principal surface;
4 is a Si(10
0) It is a wafer. However, the Si(100)
The wafer 4 is selectively etched to reach the bonding interface with the Si(110) wafer 3 or its vicinity to form a diaphragm 3a of a predetermined thickness.

The semiconductor pressure sensor having the above structure can be manufactured as follows. FIG. 2 is a flowchart showing an outline of the manufacturing process of a semiconductor pressure sensor.
) Wafer 3 and Si (100) wafer 4 are bonded together and integrated. In this bonding and integration, for example, at least the bonded surfaces of the n-type Si (110) wafer 3 and the n-type or p-type Si (100) wafer 4 are polished.
Volume No. 3 (1987) pp. 373-376)
The direct adhesion technique disclosed in et al. Note that after polishing the bonding surfaces in the bonding and integration process, the bonding and integration process is performed without performing any processing other than normal wafer processing. , the n-type Si
(110) It is preferable to make the bonding surface side of the wafer 3 a high concentration p+ layer or to form an oxide layer 5 in advance. Here, the Si(100) wafer 4 may be an n-type or a p-type depending on the means for stopping etching, and an oxide layer may be formed on the surface of the Si(100) wafer 4.

[0012] The Si(110) wafer 3 and the Si
(100) After bonding and integrating the wafer 4, if necessary, the wafer edge may be scraped off or the Si(110)
) The wafer 3 is subjected to shape shaping processing such as thinning (to about the thickness of the diaphragm) or polishing processing. Next, a piezoresistive element, which is a pressure-sensitive resistor, is formed on three surfaces of the integrated Si (110) wafer by a common method (process). Furthermore, the four surfaces of the Si (100) wafer are masked as required, and anisotropic etching is selectively performed at or near the bonding interface with the Si (110) wafer 3 to form a required diaphragm 3a. Etching is stopped in the following manner when forming the diaphragm 3a by anisotropic etching. That is,
Either stop the etching at the oxide layer 5 at the bonding interface, or
This can be achieved by stopping the etching at the p+ high concentration layer of the i(110) wafer 3 or by utilizing the characteristics of electrolytic etching.

To explain in more detail the means for stopping etching when forming the diaphragm 3a by anisotropic etching, when stopping at the oxide layer 5 at the bonding interface, the etchant for anisotropic etching stops etching at the oxide layer 5. This is the use of the property of almost stopping the action. That is, the bonding surface between Si(110) wafer 3 and Si(100) wafer 4, for example, Si(110) wafer 3
When an oxide layer 5 is formed on the surface in advance, etching stops at the oxide layer 5 as shown in FIG.
0) A diaphragm 3a consisting of 3 parts of the wafer is formed. When using this method, it is not appropriate to use an etchant that easily etches the oxide layer 5, such as an aqueous potassium hydroxide solution. Also, Si(110)
In order to stop the etching at the p+ high concentration layer of the wafer 3, the property of the anisotropic etching etchant that almost stops the etching at the p+ high concentration layer is utilized. That is, for example, boron or the like is implanted and diffused into the bonding or bonding surface side of the Si(110) wafer 3.
When the + high concentration layer 6 is formed, the etching stops at the p+ high concentration layer 6, as shown cross-sectionally in FIG.
Diaphragm 3 consisting of 3 parts of Si(110) wafer
a is formed.

Furthermore, when utilizing the characteristics of electrolytic etching, a Si(100) wafer 4 having a p-type conductivity is etched.
Using a bonded (bonded) n-type Si (110) wafer 3, anisotropic etching is performed using an etching system as shown cross-sectionally in FIG. Due to the characteristics of electrolytic etching, this anisotropic etching stops when three surfaces of the n-type Si(110) wafer are exposed, as shown cross-sectionally in FIG. A diaphragm 3a is formed. Furthermore, Figure 4
In the figure, 7 represents an anisotropic etching solution, 8 represents a platinum electrode, and 9 represents a power source.

As mentioned above, Si(110) wafer 3
and Si(100) wafer 4 bonded (bonded)
By selectively anisotropically etching the Si(100) wafer 4 side and leaving the Si(110) wafer 3 portion, a semiconductor pressure sensor having a diaphragm 3a with a uniform thickness can be easily and easily manufactured. Formed with good reproducibility. Although the diaphragm 3a was formed by anisotropic etching in the above example, a semiconductor pressure sensor having similar performance can also be obtained by isotropic etching using hydrofluoric nitric acid or isotropic electrolytic etching using dilute hydrofluoric acid. is configured. As shown in cross section in FIG. 6, the semiconductor pressure sensor 10 configured as described above is mounted and bonded to a pedestal 11 by conventional means, and further packaged for various pressure measurement or pressure distribution measurement. etc.

Although the structure of unit elements has been illustrated above as an example of the structure of a semiconductor pressure sensor, it goes without saying that there is no problem in arranging these unit elements in an array or a matrix. That is, the present invention is not limited to the embodiments exemplified above, and various modifications may be made without departing from the gist thereof.

[0017]

As explained above, according to the present invention, it is possible to provide a semiconductor pressure sensor or a multi-element semiconductor pressure sensor array which is highly sensitive and has no variation in sensitivity. In other words, by providing a semiconductor pressure sensor that exhibits high performance and highly reliable functions, the practical use of various applied devices for measuring and detecting pressure changes will be further promoted.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a structural example of a semiconductor pressure sensor according to the present invention.

FIG. 2 is a flowchart showing an example of the manufacturing process of the semiconductor pressure sensor according to the present invention.

FIG. 3 is a sectional view showing another structural example of the semiconductor pressure sensor according to the present invention.

FIG. 4 is a cross-sectional view schematically showing an embodiment of electrolytic etching in an example of the manufacturing process of the semiconductor pressure sensor according to the present invention.

FIG. 5 is a sectional view showing still another structural example of the semiconductor pressure sensor according to the present invention.

FIG. 6 is a cross-sectional view showing a configuration example of a pressure sensor using the semiconductor pressure sensor according to the present invention.

FIG. 7 is a cross-sectional view showing the structure of a conventional semiconductor pressure sensor.

[Explanation of symbols]

1...Si wafer 2...diaphragm 3...
Si(110) wafer 3a...Diaphragm 4...Si(100) wafer 5...Oxide layer 6...P+ high concentration layer
7...Anisotropic etching solution 8...Platinum electrode

Claims (2)

[Claims] Claim 1: Si(110) wafer and Si(
100) Si(110) of the wafer bonded body A piezoresistor forming a pressure-sensitive resistor is formed on the wafer surface, and Si(100)
) A semiconductor pressure sensor characterized in that a diaphragm is formed on a wafer by selective etching that reaches the bonding interface or its vicinity. [Claim 2] Si (110) wafer and S
i(100) wafer assembly, forming a piezoresistor forming a pressure-sensitive resistor, and forming the Si(100) wafer assembly.
00) Selective etching of the wafer to reach the bonding interface or its vicinity to make at least a portion of Si(110)
1. A method for manufacturing a semiconductor pressure sensor, comprising the step of forming a diaphragm made of a wafer.