JP2680471B2 - Semiconductor pressure sensor and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a semiconductor pressure sensor used in a differential pressure transmitter and the like, and a manufacturing method thereof.

(Prior Art) As a semiconductor pressure sensor used in differential pressure transmitters,
Conventionally, the structure shown in FIG. 2 is known.

The semiconductor pressure sensor shown in this figure has a circular etching hole.
An N ⁺ type silicon substrate 102 on which 101 is formed, an N type epitaxial silicon 103 provided on the N ⁺ type silicon substrate 102, and a piezoresistor 104 formed on the N type epitaxial silicon 103 are provided. When pressure is applied to each surface of the N-type epitaxial silicon 103, the N-type epitaxial silicon 103 is deformed according to the pressure difference to change the resistance value of the piezoresistor 104, and this change is output as a pressure difference signal according to the pressure difference. To do.

Another semiconductor pressure sensor shown in FIG. 3 is also known.

The semiconductor pressure sensor shown in this figure has a circular etching hole.
An N-type silicon substrate 106 on which 105 is formed and a piezoresistor 107 formed on the N-type silicon substrate 106 are provided. When pressure is applied to each surface of the N-type silicon substrate 106, this pressure difference And the resistance value of the piezoresistor 107 is changed, and the change amount is output as a pressure difference signal according to the pressure difference.

As described above, each of the semiconductor pressure sensors described above utilizes the excellent elasticity of single crystal silicon, detects the stress in response to the pressure difference applied to both surfaces of the thin film silicon diaphragms 108 and 109, and outputs this as a pressure difference signal. .

(Problems to be Solved by the Invention) By the way, in such a semiconductor pressure sensor, as the size of the chip constituting the semiconductor pressure sensor is reduced, the pressure resistance is improved and the reliability against an excessive pressure is improved. Tend.

Then, in order to effectively utilize such advantages, it is necessary to reduce the chip size. When the chip size is reduced, the thin film silicon diaphragm 10 is accompanied by this.
N-type epitaxial silicon 103 and N constituting 8 and 109
The mold silicon substrate 106 must also be thin.

And such a thin film silicon diaphragm 108, 1
As a thin film technology for 09, wet etching such as hydrofluoric nitric acid etching and electrolytic etching has hitherto been attempted.

In this case, in the electrolytic etching, the electrode is connected to the substrate to be etched serving as the anode, and the diaphragm is formed with 5% fluorinated nitric acid.

At this time, a silicon nitride film is formed as a protective film on the etching surface, and a circular pattern corresponding to the size of the diaphragm is formed by photoetching.

Next, after removing the protective film on the surface to be etched and immersing it in an etching solution to form a thin film diaphragm, the protective film on the thick plate that remains unetched is removed and electrostatically bonded to the pedestal of Pyrex glass. Mounted on an outer container that can be bonded and measured with pressure.

However, in such a conventional configuration, there is a large amount of etching, and in order to form a desired thin film silicon diaphragm, it has to be immersed in an etching solution for a long time, which results from the incompleteness of electrode connection points. As a result, heat may be generated, and the variation in etching may increase due to the difference in series resistance due to the distance from the electrode connection point to the etching location of each thin film silicon diaphragm.

In addition, the thermal expansion coefficient of the silicon nitride film that is a protective film,
Due to the difference in the thermal expansion coefficient of the silicon dioxide film, which is the buffer film, cracks are likely to occur in the thin film, and if there are pinholes, etc., the connection surface with the pedestal will be roughened by an etching solution such as hydrofluoric nitric acid However, there was a problem that the reliability of the airtightness was impaired.

Furthermore, since the etching depth is almost proportional to the thickness of the silicon substrate, the side etching amount is large,
There is a problem that it is difficult to form a diaphragm smaller than 1 mmφ.

In view of the above circumstances, the present invention can shorten the etching time in isotropic etching, and can keep the non-etched silicon surface, which is the connection portion with the base, completely mirror-like, and also electrostatic. Provided are a semiconductor pressure sensor that can improve airtightness at the time of joining, can enhance high withstand voltage when an excessive pressure is applied, and can achieve miniaturization of a sensor chip, and a manufacturing method thereof. Is intended.

[Configuration of the invention]

(Means for Solving the Problem) In order to achieve the above object, the invention of claim 1 has a single crystal semiconductor substrate and an epitaxial layer on one surface of the substrate, It has an opening for introducing pressure, and inside the epitaxial layer, it has a circular thin film diaphragm with a cavity having a larger cross-sectional area parallel to the epitaxial layer than the area of the opening end on the epitaxial layer side of the opening. It has a feature.

The invention according to claim 2 is the semiconductor pressure sensor according to claim 1, wherein the single crystal semiconductor substrate is P-type,
The thick portion forming the periphery of the cavity is N-type.

According to the invention of claim 3, an opening for pressure introduction is formed by anisotropic etching of the single crystal semiconductor substrate of a wafer having a single crystal semiconductor substrate and an epitaxial layer on one surface of the substrate, A cavity having a larger cross-sectional area parallel to the epitaxial layer than the area of the opening end on the epitaxial layer side of the opening is formed inside the epitaxial layer by isotropic etching.

(Operation) With the above configuration, the semiconductor pressure sensor according to the present invention has an opening for introducing pressure into the single crystal semiconductor substrate,
By making a circular thin film diaphragm with a cavity larger than the opening inside the epitaxial layer, while shortening the etching time in isotropic etching,
The non-etched silicon surface that is the connection to the base is completely retained in a mirror shape, and the airtightness at the time of electrostatic bonding is improved, and the high pressure resistance at the time of excessive pressure application is strengthened, and the sensor chip is small in size. To achieve

Further, with the above structure, in the method for manufacturing a semiconductor pressure sensor according to the present invention, an opening for introducing pressure is formed by anisotropic etching of the single crystal semiconductor substrate of a wafer having a single crystal semiconductor substrate and an epitaxial layer. After that, by forming a cavity larger than the opening inside the epitaxial layer by isotropic etching, the etching time in the isotropic etching is shortened, and the unetched silicon surface to be the connection portion with the base is completely removed. In addition, the airtightness at the time of electrostatic bonding is improved, the high pressure resistance at the time of applying an excessive pressure is enhanced, and the miniaturization of the sensor chip is achieved.

(Embodiment) FIG. 1 is a manufacturing process diagram showing an embodiment of a semiconductor pressure sensor and a manufacturing method thereof according to the present invention.

When manufacturing the semiconductor pressure sensor according to the present invention, as shown in FIG. 1A, first, a silicon wafer 3 having an N-type epitaxial layer 2 on a low-concentration boron substrate (P-type silicon substrate) 1 is prepared.

Next, as shown in FIG. 1 (b), thermal oxide films 4 and 5 are formed on both sides of the silicon wafer 3, and then a diaphragm is formed on the N-type epitaxial layer 2 side by photoetching as shown in FIG. 1 (c). Pattern 6
Then, the oxide film 4 on the pattern 6 is removed.

Thereafter, as shown in FIG. 1 (d), high-concentration phosphorus is diffused to make the N type epitaxial layer 2 in the pattern 6 portion into an N ⁺⁺ layer 7, and then the oxide film 4 on the upper surface side is removed. .

Then, as shown in FIG. 1 (e), an N-type epitaxial layer 8 is grown on the upper surface side of the wafer 3 until a desired diaphragm thickness is obtained, and then a piezoresistor 9 is formed on a portion which will be a diaphragm 11, and P Pattern 10 for etching on the oxide film 5 formed on the lower surface of the silicon substrate 1
To form

Thereafter, as shown in FIG. 1 (f), the N-type epitaxial layer 8 is protected by wax or the like, and then the P-type silicon substrate 1 is etched using an anisotropic etching solution to reach the N ⁺⁺ layer 7. Form a hole 12. At this time, N ⁺⁺ layer 7
The size of the etching hole 12 at a predetermined size, for example 50
Keep below micron.

Then, as shown in FIG. 1 (g), the N ⁺⁺ layer 7 is etched using an isotropic etching solution to form a cavity 13, and the N-type epitaxial layer 8 on the cavity 13 is used as a diaphragm 11. After that, the oxide film 5 on the lower surface of the P-type silicon substrate 1 is removed. At this time, as can be seen from FIG. 1 (g), the cross-sectional area of the cavity 13 parallel to the epitaxial layer 2 is
It is larger than the area of the opening end of the etching hole 12 on the epitaxial layer side.

In this embodiment this way, after forming an etching hole 12 reaching the N ⁺⁺ layer 7 is etched by anisotropic etching solution P-type silicon substrate 1, N ⁺⁺ layer by isotropic etching solution 7 Is etched to form a cavity in the lower surface of the N type epitaxial layer 8 formed on the N ⁺⁺ layer 7.
Since the diaphragm 11 is formed by forming 13, it is possible to shorten the etching time in the isotropic etching, and to keep the non-etched silicon surface that is the connection part with the base completely mirror-like. Moreover, the airtightness at the time of electrostatic bonding can be improved.

Also, by thinning the N ⁺⁺ layer 7, the diaphragm 1
The displacement amount of 1 can be reduced to enhance the high withstand voltage when an excessive pressure is applied, and the thickness of the N type epitaxial layer 8 formed on the N ⁺⁺ layer 7 can be reduced. ,
As a result, the pressure detection sensitivity can be significantly improved, and at the same time, the chip size can be reduced to achieve the miniaturization of the sensor chip.

Further, the surface distance from the P-type silicon substrate 1 side (the distance from the point A of the P-type silicon substrate 1 to the point B of the N-type epitaxial layer 8 along the P-type silicon substrate 1 and the N-type epitaxial layers 2 and 8). 2) can be made large, the influence on the diaphragm 11 can be made extremely small even when a joining strain occurs when joining the P-type silicon substrate 1 and the base.

Further, in the above-mentioned embodiment, the cavity 13 is removed cleanly, but even if the boundary between the P-type silicon substrate 1 and the N ⁺⁺ layer 7 remains, the diaphragm 11 is removed.
As long as there is an etching hole 12 in the center of, the remainder of the cavity 13 does not adversely affect the displacement of the diaphragm 11,
When the N ⁺⁺ layer 7 is etched, the etching may be terminated by short etching to leave a boundary between the P type silicon substrate 1 having a low concentration and the N ⁺⁺ layer 7.

〔The invention's effect〕

As described above, according to the present invention, the etching time in isotropic etching can be shortened, and the unetched silicon surface to be the connection portion with the base can be kept completely in a mirror shape. The airtightness at the time of electrostatic bonding can be improved, the high withstand voltage at the time of applying an excessive pressure can be enhanced, and the sensor chip can be downsized.

Further, according to the present invention, since the thickness of the epitaxial layer becomes the thickness of the cavity, the thickness of the cavity can be accurately and freely controlled by controlling the thickness of the epitaxial layer. As a result, the withstand pressure can be increased to a pressure close to the limit at which the diaphragm is broken, and the diaphragm can be easily and uniformly manufactured to prevent damage.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an embodiment of a semiconductor pressure sensor and a manufacturing method thereof according to the present invention, FIG. 2 is a sectional view showing an example of a conventionally known semiconductor pressure sensor, and FIG. It is sectional drawing which shows another example of the semiconductor pressure sensor currently used. 1 ... Single crystal semiconductor substrate (P-type silicon substrate) 2, 8 ... Epitaxial layer (N-type epitaxial layer) 11 ... Circular thin film diaphragm (diaphragm) 12 ... Opening (etching hole) 13 ... Cavity

Claims (3)

(57) [Claims] 1. A single crystal semiconductor substrate and an epitaxial layer on one surface of the substrate, and an opening for introducing pressure into the single crystal semiconductor substrate. Inside the epitaxial layer, the opening of the opening is formed. A semiconductor pressure sensor having a circular thin film diaphragm with a cavity having a cross-sectional area parallel to the epitaxial layer larger than the area of the opening end on the epitaxial layer side. 2. The semiconductor pressure sensor according to claim 1, wherein the single crystal semiconductor substrate is P-type, and the thick portion forming the periphery of the cavity is N-type. 3. A single-crystal semiconductor substrate of a wafer having a single-crystal semiconductor substrate and an epitaxial layer on one surface of the substrate is anisotropically etched to form an opening for introducing pressure, and then isotropically etched. A method of manufacturing a semiconductor pressure sensor, wherein a cavity having a cross-sectional area parallel to the epitaxial layer larger than an area of an opening end of the opening on the epitaxial layer side is formed in the epitaxial layer.