JP2004069596A - Semiconductor pressure sensor and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase an output and reliability of a semiconductor pressure sensor constructed by forming a piezoresistor on a semiconductor board. <P>SOLUTION: A laminate board formed by layering silicone layers 12 via an insulating layer 13 is arranged on the semiconductor board 11, and a part of the silicone layer 12 left by patterning of the silicone layers 12 is constructed as the piezoresistor 14 projected on the insulating layer 13. On the piezoresistor 14, a glass member 20 bound by anodic connection is mounted. A pressure applied to the glass member 20 is turned into an electrical signal by means of the piezoresistor 14. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a semiconductor pressure sensor having a piezoresistor formed on a semiconductor substrate and a method of manufacturing the same.
[0002]
[Prior art]
Conventionally, as a semiconductor pressure sensor of this type, for example, a sensor described in Japanese Patent Application Laid-Open No. 6-302836 has been proposed. This device forms a bridge structure of a strain gauge, which is a piezoresistor, on a semiconductor wafer, and a glass member is anodically bonded on this piezoresistor, and converts the pressure applied to the glass member to an electric signal by the piezoresistor. It is.
[0003]
[Problems to be solved by the invention]
By the way, in the conventional semiconductor pressure sensor, the piezoresistor formed on the semiconductor substrate is a layer formed by ion implantation or the like and having a conductivity type different from that of the semiconductor substrate. And electrical insulation is provided.
[0004]
Because of such a structure having a PN junction, it is necessary to supply a current in a direction opposite to the PN junction when the glass member is anodically bonded, and there is a problem that the PN junction is deteriorated. Further, characteristic deterioration due to leakage at a high temperature due to the use of the PN junction and fluctuation of characteristics due to the use of the deteriorated PN junction occur. As described above, in the conventional device, various problems due to the PN junction occur, and the reliability of the sensor may be impaired.
[0005]
Further, in a conventional semiconductor pressure sensor, an applied pressure is converted into an electric signal by a piezo resistor, but further increase in output is desired. This is because in order to accurately detect pressure, it is necessary to increase the signal generated from the piezoresistor due to the pressure.
[0006]
In view of the above problems, an object of the present invention is to increase the output and improve the reliability of a semiconductor pressure sensor having a piezoresistor formed on a semiconductor substrate.
[0007]
[Means for Solving the Problems]
The present inventors have studied an increase in output in a semiconductor pressure sensor. In order to increase the signal from the piezoresistor, we considered increasing the stress per unit area generated by pressure in the piezoresistor.
[0008]
FIG. 4 and FIG. 5 are diagrams showing a manufacturing process of a sensor prototyped by the present inventors as such a semiconductor pressure sensor. First, as shown in FIG. 4A, an n-type silicon substrate 100 whose plane orientation is, for example, a (110) plane is prepared.
[0009]
Next, as shown in FIG. 4B, a photomask 101 is formed on one surface of the silicon substrate 100, and an impurity such as B (boron) is ion-implanted, so that a predetermined region on one surface of the silicon substrate 100 is A P + layer 102 serving as a resistor is formed.
[0010]
Next, as shown in FIG. 4C, the silicon substrate 100 is etched by RIE (reactive ion etching) or the like while a predetermined region of the P + layer 102 is masked with a photomask 103 on one surface of the silicon substrate 100. . As a result, a projection is formed on one surface of the silicon substrate 100, and the projection becomes the piezoresistor 104 and the wiring section 105.
[0011]
Next, as shown in FIG. 4D, one surface of the silicon substrate 100 is covered with an oxide film 106 by thermal oxidation or the like to protect the PN junction exposed on the side surface of the step. I do.
[0012]
Next, as shown in FIGS. 5A and 5B, a part of the oxide film 106 is removed by etching to form a contact hole 107, and an electrode 108 made of aluminum or the like is patterned through the contact hole 107. Form.
[0013]
Finally, as shown in FIG. 5C, a glass member 109 is mounted on the piezoresistor 104 by anodic bonding. For example, anodic bonding is performed using the glass member 109 as a negative electrode and the silicon substrate 100 as a positive electrode.
[0014]
In the semiconductor pressure sensor as a prototype manufactured in this way, since the piezoresistor 104 has a protruding shape, the contact area with the glass member 109 is larger than that of the conventional piezoresistive layer formed in the substrate surface. As a result, a configuration of a piezoresistor having a large stress (strain) per unit area can be realized. Therefore, the output of the sensor can be increased.
[0015]
However, this prototype also has the following problems. In order to surely form the piezoresistor 104 having a projection shape (mesa shape), as shown in FIG. 4C, the step D of the projection is, for example, about 3 μm, and the PN junction is also exposed on the side surface of the step. I do. Such a step is a relatively large step in a semiconductor manufacturing process.
[0016]
Therefore, when the oxide film 106 for protecting the exposed PN junction is formed, there arises a problem that coverage of the oxide film 106 at the step portion cannot be ensured, and the yield of the sensor may be reduced.
[0017]
In addition, since the prototype also has a PN junction, various problems caused by the PN junction cannot be avoided. From the above, the present inventors have conducted intensive studies to realize a configuration having a piezoresistor having a projection shape but not having a PN junction, and have led to the creation of the present invention.
[0018]
That is, according to the first aspect of the present invention, there is provided a laminated substrate (10) in which a semiconductor layer (12) is laminated on a semiconductor substrate (11) with an insulating layer (13) interposed therebetween. The portion of the semiconductor layer (12) remaining by patterning the layer (12) is configured as a piezoresistor (14) projecting above the insulating layer (13), and is formed on the piezoresistance (14). A semiconductor pressure sensor, wherein a glass member (20) is mounted by anodic bonding, and a pressure applied to the glass member (20) is converted into an electric signal by the piezoresistor (14).
[0019]
According to this, since the piezoresistor formed of the semiconductor layer is formed in a projection shape (mesa shape) protruding above the insulating layer, the piezoresistor has a large stress per unit area. In this piezoresistor, electrical insulation is ensured by the insulating layer in the vertical direction, that is, the thickness direction of the substrate, and by air in the lateral direction, that is, the direction of the substrate surface.
[0020]
For this reason, the semiconductor pressure sensor of the present invention does not require a PN junction for electrical insulation as in the related art, and has a configuration that does not actually have a PN junction. Since the PN junction does not exist, the problem of the PN junction deterioration due to the anodic bonding of the glass member does not occur in the first place.
[0021]
Further, in the sensor of the present invention, even when the piezoresistor has a projection shape, since there is no PN junction as in the prototype, an oxide film for protecting the PN junction as in the prototype is formed. It becomes unnecessary. Therefore, the problem of a decrease in sensor yield can be avoided.
[0022]
Therefore, according to the present invention, it is possible to provide a semiconductor pressure sensor capable of increasing output and improving reliability.
[0023]
According to the third aspect of the present invention, a laminated substrate (10) is prepared by laminating a semiconductor layer (12) on a semiconductor substrate (11) via an insulating layer (13). 12) forming a portion of the semiconductor layer (12) remaining by patterning as a piezoresistor (14); mounting a glass member (20) on the piezoresistor (14) and performing anodic bonding; And a step.
[0024]
According to the present invention, it is possible to provide a manufacturing method capable of appropriately manufacturing the pressure sensor according to the first aspect.
[0025]
Further, as described in the second and fourth aspects of the present invention, a semiconductor layer made of silicon can be used.
[0026]
It should be noted that reference numerals in parentheses of the above-described units are examples showing the correspondence with specific units described in the embodiments described later.
[0027]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention shown in the drawings will be described. FIG. 1 is a diagram showing a schematic sectional configuration of a semiconductor pressure sensor S1 according to an embodiment of the present invention. Although not limited, the pressure sensor S1 can be applied, for example, as a combustion pressure sensor that measures the combustion pressure in an automobile engine.
[0028]
The pressure sensor S1 has a laminated substrate 10 formed by laminating a silicon layer 12 made of silicon as a semiconductor layer on a semiconductor substrate 11 made of silicon or the like via an insulating layer 13.
[0029]
The laminated substrate 10 of this example is an SOI (silicon-on-insulator) substrate 10, and a second silicon layer 11 as a silicon layer via a buried oxide film 13 as an insulating layer on a first silicon layer 11 as a semiconductor substrate 11. Of the silicon layer (SOI layer) 12 of FIG.
[0030]
The silicon layer 12 is patterned, and the remaining portion of the silicon layer 12 is configured as a piezoresistor 14 and a wiring portion 15 protruding above the insulating layer 13. The piezoresistor 14 and the wiring portion 15 having a projection shape (mesa shape) on the insulating layer 13 constitute a bridge circuit such as a Wheatstone bridge.
[0031]
An electrode 16 made of aluminum or the like for extracting a signal from the bridge circuit is formed in a predetermined region on the wiring portion 15. On the piezoresistor 14 as a strain gauge, a glass member 20 made of glass is mounted by anodization.
[0032]
The pressure sensor S1 is housed in, for example, a sensor case (not shown) and attached near an automobile engine so that a combustion pressure from a combustion chamber of the engine is applied to the glass member 20.
[0033]
For example, a rod member moved by the diaphragm is brought into contact with an upper portion of the glass member 20 through a metal diaphragm that receives the combustion pressure in the combustion chamber, so that the combustion pressure is increased via the rod member. Is applied from above.
[0034]
The pressure applied to the glass member 20 is applied to the piezoresistor 14, and the piezoresistor 14 is distorted. Then, the balance of the bridge circuit constituted by the piezoresistor 14 changes, and an electric signal based on this change is output from the electrode 16 on the wiring section 15.
[0035]
Here, for example, the electrode 16 is connected to a wiring member (not shown) by a bonding wire or the like, and the converted pressure electric signal is output from the electrode 16 to an external circuit or the like via the wiring member. Has become. Thus, the combustion pressure is detected.
[0036]
As described above, the pressure sensor S1 of the present embodiment uses a new laminated substrate 10 such as an SOI substrate as a semiconductor substrate, and uses the silicon layer 12 on the insulating layer 13 in the laminated substrate 10 to form a protrusion (mesa-shaped). The main feature is that the piezo resistor 14 is formed.
[0037]
According to this, the piezoresistor 14 made of the silicon layer 12 is formed in a projecting shape (mesa shape) projecting above the insulating layer 13, so that the piezoresistor 14 has a large stress per unit area. . This is the same reason as described in the prototype shown in FIGS.
[0038]
In the piezoresistor 14, electrical insulation is ensured by the insulating layer 13 in the vertical direction in FIG. 1, that is, in the thickness direction of the laminated substrate 10 (substrate thickness direction), and in the lateral direction in FIG. In the plane direction (substrate plane direction), electrical insulation is ensured by air.
[0039]
Therefore, the semiconductor pressure sensor S1 of the present embodiment does not require a PN junction for electrical insulation as in the related art, and has a configuration that does not actually have a PN junction.
[0040]
Since the PN junction does not exist, the PN junction deteriorates due to the anodic bonding of the glass member 20 as described above, the characteristic deteriorates due to the leakage at a high temperature due to the use of the PN junction, and the deteriorated PN junction also occurs. There is no problem that may degrade the reliability of the sensor, such as a change in characteristics due to use.
[0041]
Further, in the pressure sensor S1 of the present embodiment, even when the piezoresistor 14 has a projection shape, since there is no PN junction existing in the prototype as shown in FIGS. It is not necessary to form the oxide film 106 for protecting the PN junction. Therefore, the problem of a decrease in the yield of the sensor S1 can be avoided.
[0042]
Therefore, according to the present embodiment, it is possible to provide the semiconductor pressure sensor S1 that can increase the output and improve the reliability.
[0043]
Next, a method for manufacturing the pressure sensor S1 will be described with reference to FIGS. FIG. 2 is a process diagram sequentially showing the present manufacturing process in a cross section corresponding to FIG.
[0044]
First, as shown in FIG. 2A, a laminated substrate 10 is prepared by laminating a silicon layer 12 on a semiconductor substrate 11 with an insulating layer 13 interposed therebetween. Here, impurities such as B (boron) are introduced into the surface of the silicon layer 12 of the laminated substrate 10 to be the piezoresistor 14 and the wiring portion 15 by deposition diffusion, ion implantation, or the like. A desired concentration exhibiting a piezoresistive effect may be achieved.
[0045]
Next, as shown in FIG. 2B, an electrode 16 is formed by forming a film of aluminum or the like by sputtering or vapor deposition and patterning the film using photolithographic technology.
[0046]
Next, as shown in FIG. 2C, the remaining silicon layer 12 is formed as a piezoresistor 14 and a wiring portion 15 by patterning the silicon layer 12 using dry etching or the like.
[0047]
Next, as shown in FIG. 2D, the glass member 20 is mounted on the piezoresistor 14 and anodically bonded. At this time, for example, the upper surface of the glass member 20 and the lower surface of the semiconductor substrate 11 are sandwiched by an electrode for anodic bonding (not shown), and a current is applied by using the glass member 20 as a negative electrode and the semiconductor substrate 11 as a positive electrode. Perform anodic bonding. Thus, the semiconductor pressure sensor S1 shown in FIG. 1 is completed.
[0048]
(Other embodiments)
FIG. 3 shows a schematic sectional configuration of a semiconductor pressure sensor S2 according to another embodiment of the present invention. The sensor S2 shown in FIG. 3 is different from the sensor S1 shown in FIG. 1 in that an oxide film 17 for flattening the surface is formed on the surface of the silicon layer 12.
[0049]
Depending on the impurities diffused into the silicon layer 12, irregularities may occur on the surface of the silicon layer 12, which may cause a problem in anodic bonding.
[0050]
In such a case, as shown in FIG. 3, if the oxide film 17 is formed after the silicon layer 12 is patterned in FIG. Then, if anodic bonding is performed via the flat oxide film 17 and the glass member 20 is mounted, bondability of anodic bonding can be ensured. This is the unique effect of the sensor S2 in FIG.
[0051]
Note that, in the sensor using the laminated substrate 10 such as the SOI substrate of the present invention, even if the piezoresistor 14 has a protruding shape, there is no PN junction as present in the prototypes shown in FIGS. The size of the step due to the protrusion can be made smaller than that of the prototype. For example, while the step of the prototype is about 3 μm, in the present invention, the size of the step is the thickness of the silicon layer 12 and can be about 1 μm.
[0052]
Such a step in the pressure sensor of the present invention is a step which is usually present in a semiconductor manufacturing process, and does not cause any problem. For this reason, even if the oxide film 17 as shown in FIG. 3 is formed, the coverage at the step portion of the oxide film 17 is insufficient, or the electrode film is left unetched when the electrode 16 is subsequently formed by patterning. This problem can be avoided as much as possible.
[0053]
In the present invention, the semiconductor layer laminated on the semiconductor substrate via the insulating layer in the laminated substrate may be a semiconductor layer other than the silicon layer, for example, a layer of germanium or gallium.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view of a semiconductor pressure sensor according to an embodiment of the present invention.
FIG. 2 is a process chart showing a method for manufacturing the semiconductor pressure sensor shown in FIG.
FIG. 3 is a schematic sectional view of a semiconductor pressure sensor as another embodiment of the present invention.
FIG. 4 is a diagram showing a manufacturing process of a semiconductor pressure sensor prototyped by the present inventors.
FIG. 5 is a view showing a manufacturing step following FIG. 4;
[Explanation of symbols]
10 laminated substrate, 11 semiconductor substrate, 12 silicon layer, 13 insulating layer,
14: Piezoresistance, 20: Glass member.

Claims (4)

A laminated substrate (10) formed by laminating a semiconductor layer (12) on a semiconductor substrate (11) via an insulating layer (13);
A portion of the semiconductor layer (12) remaining by patterning the semiconductor layer (12) is configured as a piezoresistor (14) protruding above the insulating layer (13);
A glass member (20) is mounted on the piezoresistor (14) by anodic bonding,
A semiconductor pressure sensor wherein a pressure applied to the glass member (20) is converted into an electric signal by the piezoresistor (14). The semiconductor pressure sensor according to claim 1, wherein the semiconductor layer (12) is made of silicon. A laminated substrate (10) is prepared by laminating a semiconductor layer (12) on a semiconductor substrate (11) via an insulating layer (13).
Forming a portion of the semiconductor layer (12) remaining by patterning the semiconductor layer (12) as a piezoresistor (14);
Mounting a glass member (20) on the piezoresistor (14) and performing anodic bonding. 4. The method according to claim 3, wherein the semiconductor layer is made of silicon.

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