JPH04313275A - Semiconductor pressure sensor - Google Patents

Abstract

PURPOSE:To improve output characteristics and temperature characteristics and at the same time simplify a production process regarding a cross-type semiconductor pressure sensor utilizing a property that directional property appears at a specific resistance when an Si single-crystal body is compressed in a certain face direction. CONSTITUTION:An Si single-crystal body 2 which has a piezo resistance coefficient pi63' and becomes a gauge by allowing a specific crystal surface to be formed as a surface where a compression force is applied to is constituted by using a wafer in SOI structure. The gauge element is formed by etching, etc., from an Si single-crystal layer 3c of a wafer 3 in SOI structure. Therefore, a specific resistance and a thickness of the Si single-crystal body 2 which becomes the guide element are prescribed by the specific resistance and thickness of Si single-crystal layer of the wafer 3 in SOI structure, thus eliminating lapping process of the Si single-crystal body 2 and at the same time preventing a pn junction from being formed.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to an orthogonal semiconductor pressure sensor that detects compressive force by utilizing the piezoresistance effect of a Si single crystal. Insu
The present invention relates to a semiconductor pressure sensor constructed using a wafer with a wafer structure.

0002

[Prior Art] Conventional pressure sensors use adhesives to form a Wheatstone bridge circuit by attaching a plurality of strain-generating bodies to a strain-generating body using an adhesive to measure the distortion of a strain-generating body that occurs in response to an applied compressive force. The voltage was transmitted to an electrically connected strain gauge and detected as the magnitude of the voltage output generated based on the change in resistance of the strain gauge. In recent years, the strain gauges used for this purpose have also been made of silicon (Silicon).
Semiconductor strain gauges made of semiconductor single crystals, mainly Si (hereinafter referred to as Si), have become mainstream. However, semiconductor pressure sensors, which are made by attaching a plurality of semiconductor strain gauges to a strain body using an adhesive and connecting them to form a Wheatstone bridge circuit, require complicated and high know-how to manufacture, especially when attaching them. There are large variations in characteristics, resulting in high costs, and the adhesive used for pasting causes negative effects such as creep and hysteresis, and does not ensure strain transmission, which significantly reduces the reliability of semiconductor pressure sensors. Ta.

[0003] Therefore, in order to eliminate the above-mentioned drawbacks, the following methods have been adopted. In this method, a plurality of strain gauges are constructed using a single Si crystal, in other words, a pair of output electrodes and an input electrode are provided in a single Si crystal, each intersecting with the other.
Preferably, they are arranged in orthogonal directions. On top of that,
When a compressive force is applied perpendicular to the crystal plane of the Si single crystal, the compressive force is detected using the piezoresistance effect of the Si single crystal based on compressive strain. be. This type of orthogonal semiconductor pressure sensor has
The following first type and second type are known.

A first type of conventional orthogonal semiconductor pressure sensor is shown in FIG. In the figure, a Si single crystal 12 having a piezoresistance coefficient π63', which is a gauge element of a semiconductor pressure sensor 11, has an upper surface (110) as a crystal plane.
For example, a silicon piece having a substantially square horizontal cross section is cut out from a Si wafer so as to form a plane. This Si single crystal 12 is a high resistance material containing a low concentration of impurities such as boron, and its thickness is set to several tens to hundreds of μm depending on the impurity concentration and input resistance. , the thickness and impurity concentration are assumed to be uniform.

[0005] Furthermore, on the upper surface of this Si single crystal body 12,
A pair of opposing input electrodes 14, 15 and output electrodes 16, 17 made of metal such as aluminum are formed by vacuum deposition, plating, or the like. The direction of the input electrodes 14 and 15 and the direction of the output electrodes 16 and 17 are respectively 4 from the <001> direction.
5° direction and 45° direction from the outside direction

[0006]

[Outside 1]

It is formed as follows. Input electrodes 14 and 15 are formed along most of the opposing sides of the joint surface between the upper surface of the Si single crystal 12 and the upper pedestal 18, which will be described later. On the other hand, as is clear from FIG. 4, the output electrodes 16 and 17 are formed such that the portions facing the other opposing sides of the bonding surface have a small width at the center of each side with good positional accuracy. has been done.

Furthermore, an upper pedestal 18 and a lower pedestal 19 having an insulating property and having a thickness of about 1 mm are bonded to the upper and lower surfaces of the Si single crystal body 12 by, eg, electrostatic bonding. There is. The upper pedestal 18 reliably absorbs the compressive force W applied from above to the Si single crystal 1.
2, and the lower pedestal 19 reliably supports the Si single crystal 12 so that pressure other than the compressive force when the compressive force W acts does not have an adverse effect.

[0009] In this way, since the compressive force is applied to the crystal plane of the Si single crystal through the pedestal, which is a compressive force transmitting material, there is no negative effect on the output characteristics caused by the adhesive, and the compressive force is reduced. It is possible to effectively utilize the piezoresistance effect of the Si single crystal against the compressive force, and it is possible to obtain a voltage output proportional to the compressive force. The operating principle of voltage detection will be specifically explained below based on FIG. 6.

As mentioned above, a compressive force W is applied to the Si single crystal 12 having a piezoresistance coefficient π63' in the vertical direction.
, the mutually orthogonal resistance components RL and RR of the Si single crystal body 12 change, and the compressive force W
A voltage output ΔV corresponding to the voltage can be obtained. That is, when no compressive force W is applied, RL and R
Since R 2 are equal, the current flows straight between the input electrodes 14 and 15 and no voltage is produced between this and the vertical output electrodes 16 and 17. However, when a compressive force W is applied, RL and RR change depending on the force as shown in Figure 6(b) and become different values, so current flows more easily to the smaller resistance component. Since the current density distribution changes and the voltage distribution changes accordingly, the output electrodes 16,
A voltage is generated between 17.

That is, in FIG. 6, the distance between the opposing sides where the input electrodes 14 and 15 are provided in the Y direction is a, and the distance between the opposing sides where the output electrodes 16 and 17 are provided in the X direction is b. , a current is passed between the input electrodes 14 and 15, and the output electrode 1
By extracting the voltage output ΔV from 6 and 17,
If a compressive force W is applied perpendicularly to the crystal plane of the single crystal 12, Z
Compressive stress acting in the direction σz = (W/A, W: compressive force, A
The voltage output ΔV obtained in the Si single crystal 12 in which .

[0012] ΔV=b・ρ・J2・π63′・σz
(1) In the equation (1), ρ is the specific resistance of the Si single crystal 12, J2 is the current velocity, and π63' is the piezoresistance coefficient. In addition, input electrode 1
Assuming that a voltage of V is applied between 4 and 15, equation (1) can be written as equation (2) below.

[0013] ΔV=(b/a)・V・π63′・σz
...(2) As above, the compressive force W
A voltage output proportional to can be obtained very easily. and,
The first type of semiconductor pressure sensor has a lower pedestal 19
After bonding the Si crystal body 12 having an appropriate crystal orientation and specific resistance on top, the thickness of the Si single crystal body 12 that will become the gauge element is thinned by lapping to optimize the input resistance. I was adjusting the resistance. Next, input electrodes 14, 15
, the output electrodes 16 and 17 were formed on the upper surface of the Si single crystal 12, and then the upper pedestal 18 was bonded.

A second type of conventional semiconductor pressure sensor is shown in FIG. As shown in the figure, the second type semiconductor sensor 21 does not have a structure in which a Si single crystal 12 is bonded to a lower pedestal 19 like the first type semiconductor sensor 11, but uses a thick Si single crystal substrate. In this configuration, a gauge element is formed by an impurity region 22 formed by doping 23 with impurity at a high concentration. In other words, the Si single crystal substrate 23 has p
If it is a type, the gauge element is formed by forming the impurity region 22 by doping with an n-type impurity. On the other hand, in the first type of semiconductor pressure sensor 11, the entire Si single crystal 12 serves as a gauge element. Similar to the first type, the upper surface of the gauge element is formed to be a crystal plane in a predetermined direction, and after input electrodes 24, 25 and output electrodes 26, 27 are formed in a predetermined direction, the upper pedestal 28 are joined. The operating principle is common to both.

[0015]

[Problem to be Solved by the Invention] First of the above conventional structures
In the type of semiconductor pressure sensor 11, the gauge element made of Si single crystal 12 is configured to sense only compressive (or tensile) stress in the vertical direction.
When compressive force W is applied, the force is not applied uniformly,
The Si single crystal body 12 is bent, resulting in shear stress and lateral stress. As a result, the detected output voltage ΔV was about 2/3 of the theoretical value, and the linearity of the output characteristic was also impaired.

[0016] Furthermore, the input resistance of the gauge element is optimized by
This was done by adjusting the thickness of the Si single crystal 12 that becomes the gauge element, but there is a limit to the thinning of this Si single crystal 12 by wrapping, and therefore the resistivity of the gauge element cannot be freely selected. There wasn't. Furthermore, Si single crystal 1
There was a drawback that thinning by wrapping No. 2 itself was time-consuming.

Furthermore, in the second type of semiconductor pressure sensor 21 having the above conventional structure, a gauge element is formed using a pn junction formed by doping a thick Si single crystal substrate 23 with a high concentration of impurity. ing. Therefore, compared to the first type of semiconductor pressure sensor 11, there is no bonding process between the lower pedestal 19 and the Si single crystal body 12, and there is no lapping process for the Si single crystal body 12. This has the advantage that the specific resistance of the gauge element can be easily adjusted and the current flow path can be regulated. but,
Since the gauge element is formed of a pn junction, the leakage current from this pn junction increases as the temperature rises, and in the high temperature range (above about 150°C), the pn junction is damaged and the voltage output ΔV cannot be obtained. There was a drawback that there was no Also,
The influence on the output due to the generation of shear stress and lateral stress cannot be eliminated, and it also has the drawbacks of low output sensitivity and poor linearity.

SUMMARY OF THE INVENTION In view of the above-mentioned conventional problems, it is an object of the present invention to provide a semiconductor pressure sensor that has improved output characteristics and temperature characteristics, and also simplifies the manufacturing process.

[0019]

[Means for Solving the Problems] In order to achieve the above object, the orthogonal type semiconductor pressure sensor of the present invention has a piezoresistance coefficient π63' and a specific crystal plane is formed as a surface to which a compressive force is applied. An orthogonal semiconductor pressure sensor that uses a Si single crystal as a gauge element and detects a compressive force applied perpendicular to the crystal plane by utilizing the piezoresistance effect of the Si single crystal. It is characterized in that a wafer with a silicon-on-insulator (SOI) structure is used for formation, and the Si single-crystal body serving as the gauge element is formed from the Si single-crystal layer of the wafer with the silicon-on-insulator (SOI) structure.

[0020]

[Operation] As described above, when a wafer with a silicon-on-insulator (SOI) structure is used to form a gauge element, and the Si single crystal that becomes the gauge element is formed from a Si single-crystal layer with a silicon-on-insulator (SOI) structure. The specific resistance and thickness of the Si single crystal material serving as the gauge element are defined by the specific resistance and thickness of the Si single crystal layer of the wafer having a silicon-on-insulator (SOI) structure. Therefore, S
The manufacturing process is simplified because the wrapping process of the single crystal is eliminated, and the compressive force applied to the gauge element is ideal, resulting in improved output characteristics and high accuracy. Furthermore, since no pn junction is formed, temperature characteristics are improved.

[0021]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram of a semiconductor pressure sensor according to an embodiment of the present invention.

In the figure, a Si single crystal 2 which is a gauge element of a semiconductor pressure sensor 1 has an upper surface 2a which is a crystal plane.
is formed to be a (100) plane. This Si
The single crystal body 2 is made of silicon on insulator (Sili
con On Insulator (hereinafter referred to as SOI) structure wafer 3, that is, Si single crystal layer 3a,
Using an SOI substrate with a total thickness of several hundred μm on which an i-oxide film (SiO2) 3b is formed and a Si single crystal layer 3c is formed on it,
The uppermost Si single crystal layer 3c is formed into a predetermined size by etching or the like. In addition, Si single crystal 2
The specific resistance and thickness of the piezoresistance coefficient π63′ and its temperature characteristics are determined comprehensively, and the optimum value (for example, several Ω・cm, several μm to several (10 μm).

[0023] Also, the opposing 2 of the Si single crystal 2
A pair of input electrodes 4, 5 made of a metal film such as aluminum or platinum are formed on one side surface, and a pair of output electrodes 6, 7 made of a metal film similar to the above are formed on the other two opposing sides, for example, by vacuum evaporation. It is formed using techniques such as or plating. The direction of the input electrodes 4 and 5 and the direction of the output electrodes 6 and 7 are respectively 45 degrees from the <001> direction and 45 degrees from the outside direction.

[0024]

[Outside 2]

It is formed as follows. Here input electrode 4
, 5 are provided with contact portions 4a, 5a that cover the side edges of the upper surface 2a from the side surfaces of the Si single crystal body 2, whereas the output electrodes 6, 7 are provided at the center of the side surface of the Si single crystal body 2. Contact portions 6a and 7a are provided so as to traverse only a small portion of the portion and cover part of the side edges and upper surface thereof. Regarding the contact width of the contact portions 6a and 7a, it is necessary to detect a slight potential distribution of the Si single crystal 2 in order to extract the output efficiently, and as this width increases, the output sensitivity decreases. So the smaller the better.

Furthermore, on the upper surface 2a of the Si single crystal 2,
Contact portions 4a and 5a of the input electrodes 4 and 5 and output electrode 6
, 7, an insulating pedestal 8 made of glass, ceramic, or the like is bonded so as not to overlap with the contact portions 6a, 7a (Fig. 1(a) shows the state before bonding). )
. This bonding is, for example, anodic bonding (electrostatic bonding), eutectic bonding,
This is done using techniques such as glass bonding, which do not use adhesives, which may cause adverse effects on output characteristics such as creep or hysteresis.

Next, an example of a method for manufacturing the semiconductor pressure sensor 1 of this embodiment having the above structure will be explained below with reference to FIGS. 1 and 2. First, the top layer of Si, which will become the gauge element,
A wafer 3 having an SOI structure is prepared by setting the specific resistance and thickness of the single crystal layer 3c to predetermined values in advance (see FIG. 2(a)).
)). This resistivity and thickness are the piezoresistance coefficient π63'
As described above, the magnitude of resistivity and its temperature characteristics, and the magnitude of resistivity and its temperature characteristics are comprehensively judged and set to the optimum value.

Next, a master pattern for etching is formed using, for example, a photolithography method, and etching is performed through this mask to leave a Si single crystal body 2 of a predetermined size that will become a gauge element. Remove other parts. Alternatively, it can be formed with extremely high precision by using ultrafine processing technology such as ultrasonic processing or laser processing.

Furthermore, input electrodes 4, 5 and output electrodes 6,
7 is formed into a predetermined shape as shown in FIG. 1, that is, a contact portion 4a, on the Si oxide film 3b of the SOI structure wafer 3, and on the side and side edges of the top surface 2a of the Si single crystal 2 formed by etching or the like. , 5a cover the side edges of the upper surface 2a from the side surfaces of the Si single crystal 2, and the contact portions 6a, 7a cross only a small part of the center of the side surfaces of the Si single crystal 2, and the contact portions 6a, 7a cover the side edges of the upper surface 2a from the side surfaces of the Si single crystal 2. Form to cover part of the upper edge. For example, after forming the electrode pattern, a mask is formed on the metal film deposited by vacuum evaporation or plating on the entire upper surface of the Si oxide film 3b and the Si single crystal 2, and then etching is performed. This can be done by selectively removing the metal film.

Thereafter, the pedestal 8 is bonded so as not to overlap the above-mentioned two electrode arrangement portions on the upper surface 2a of the Si single crystal body 2 (
Figure 2(b)). In the above, S serving as the gauge element
Although the case where there is one single crystal 2 has been explained, if there are many S
It goes without saying that this can be done simultaneously for the i single crystal formation region, and then the wafer can be cut into individual regions.

In the semiconductor pressure sensor having the above structure, since the Si single crystal 2 formed in the above direction has a piezoresistance coefficient π63', the input electrodes 4,
5, by passing a current or applying a voltage between the upper pedestal 8
When a compressive force is applied in the vertical direction to the Si single crystal 2 through the compressive force, a voltage is generated between the output electrodes 6 and 7 in response to the force. It has already been mentioned that pressure can be detected by detecting this voltage (see FIG. 6).

As described above, this embodiment uses SOI to form a gauge element of a semiconductor pressure sensor that takes advantage of the fact that when a Si single crystal is compressed along a certain surface direction, the specific resistance appears directional. Using the wafer 3 having the SOI structure, a gauge element is formed from the uppermost Si single crystal layer 3c of the wafer 3 having the SOI structure. Therefore, as long as a wafer 3 with an SOI structure having a Si single crystal layer 3c with specific resistance and thickness set to predetermined values is prepared, the conventional lapping process of Si single crystal and thinning by lapping can be performed. In addition to eliminating the restriction, the restriction on the thickness of the gauge element can be relaxed. In other words, the selection range of the specific resistance of the gauge element is widened, and the specific resistance can be controlled with high precision. In addition, since the gauge element is formed by removing the Si single crystal other than the part that will become the gauge element, it is possible to completely define the current flow path, leading to improved output characteristics. There is no leakage current even at temperatures above 150°C, and heat resistance is improved. Furthermore, since the compressive force applied to the gauge element is ideal, the Si single crystal 2 has a simple compressive stress σz
This makes it possible to effectively utilize the piezoresistance effect that occurs only when using a conventional method, thereby achieving improved output characteristics and high accuracy.

FIG. 3(a) shows that a current is applied to the input electrodes 4 and 5 to apply a voltage to apply a vertical compressive force, and the output electrodes 6 and 5 are
This shows the magnitude of the voltage output obtained from 7.
The solid line is for this example, and the chain line is for the conventional first type and second type.
The output characteristics of this type of semiconductor pressure sensor are shown. It can be seen that in the case of this example, a linear and practically improved voltage output proportional to the compressive force is obtained.

FIG. 3(b) is a graph showing the change in sensitivity to temperature rise, where the solid line represents the semiconductor of this embodiment, the chain line represents the conventional first type semiconductor, and the dashed-dotted line represents the conventional second type semiconductor. Shows the temperature characteristics of the pressure sensor. The sensitivity of both the first type and the second type fluctuates with temperature changes, and in particular the type with the second pn junction, where the sensitivity rapidly decreases when the temperature exceeds about 150°C, in this example ,
It can be seen that substantially constant sensitivity is maintained even in the high temperature range (approximately 150° C. or higher), which is a significant improvement.

In the embodiment shown in FIGS. 1 and 2, the Si single crystal 2 serving as the gauge element is formed by leaving only a predetermined dimension from the Si single crystal layer 3c of the wafer 3 having an SOI structure.
Although the other portions were formed by removing them by etching or the like, they may be left without being removed. In this case, the linearity of the output characteristics and the sensitivity to temperature rise are slightly inferior to those in which parts other than the part that will become the gauge element are removed, but steps such as etching can be omitted, so the number of man-hours can be reduced. .

[0036] Also, the gauge element is mounted on a wafer 3 having an SOI structure.
When forming the Si single crystal layer 3c by removing other portions by etching or the like, it may be removed in the following shape. That is, as shown in FIG. 4, a hatched portion 3'c of the Si single crystal layer 3c is removed, and then electrode pads 4', 5', 6', and 7' are formed in the remaining portions. In this way, even if the joining position of the upper pedestal 8 deviates somewhat, the change in output characteristics due to this joining deviation is small. In the embodiment shown in FIGS. 1 and 2, electrodes 4a, 5a, 6a, and 7 are partially disposed on the upper surface of the Si single crystal 2 serving as a gauge element.
In order to join the upper pedestal 8 between the parts a, it is necessary to position it accurately. With the shape shown in FIG. 4, there is no need to form electrodes on the gauge element, and the area is also slightly increased, eliminating the need for accurate positioning of the upper seat 8.

Furthermore, the following method of forming a gauge element can also be considered. That is, this is a method in which an impurity diffusion process is performed on the wafer 3 having an SOI structure, and areas other than the lead wire formation portion are removed by etching or the like. The SOI structure wafer 3 is doped with impurities to some extent, but S
When a lead wire is formed using i, it is better to increase the impurity concentration and reduce the resistance in the lead wire forming portion for better sensitivity. Therefore, as shown in FIG.
The Si single crystal layer 3c other than ' is subjected to impurity diffusion treatment to increase the impurity concentration (dot portion 13c in Fig. 5(a)).
The low-resistance portion is then removed by etching or the like, leaving the lead wire formation portion (FIG. 5(b), removal of portion 13'c). After that, the electrodes are bonded. By using the low resistance portion as a lead wire, characteristics can be improved and man-hours can be reduced.

[0038] The above manufacturing method is just an example,
It is not limited to this.

[0039]

Effects of the Invention As described above, according to the present invention, a wafer with an SOI structure is used and a gauge element is formed from the Si single crystal layer of the SOI structure wafer, so that the ratio of the Si single crystal layer of the SOI structure wafer is reduced. The specific resistance and thickness of the Si single crystal that becomes the gauge element are determined by the resistance and thickness, and it is possible to improve output characteristics and temperature resistance characteristics, and to simplify the manufacturing process.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a semiconductor pressure sensor according to an embodiment of the present invention, in which (a) is a perspective view with the upper pedestal separated, and (b) is a plan view with the upper pedestal separated.

FIG. 2 is a diagram showing a manufacturing method of the embodiment of FIG. 1 of the present invention,
(a) is a cross-sectional view of a wafer having an SOI structure, and (b) is a vertical cross-sectional view of an embodiment of the present invention.

FIG. 3 is a graph for comparing the characteristics of the present invention and a conventional semiconductor pressure sensor, in which (a) is the output characteristic; (b) is the output characteristic;
is the temperature characteristic.

4 is a diagram showing another configuration example of the gauge element of the semiconductor pressure sensor of FIG. 1. FIG.

5 is a diagram showing still another configuration example of the gauge element of the semiconductor pressure sensor in FIG. 1, in which (a) is a diagram showing diffusion of impurities, and (b) is a diagram showing removal by etching etc. .

FIG. 6 is a diagram showing a conventional first type semiconductor pressure sensor, in which (a) is a perspective view, (b) is a plan view, and (c) is a perspective view.
is a front view.

FIG. 7 is a diagram showing a conventional second type semiconductor pressure sensor, in which (a) is a perspective view, (b) is a plan view with the upper pedestal omitted, and (c) is a front view.

8 is a diagram for explaining the operating principle of the semiconductor pressure sensor shown in FIG. 6, in which (a) RL = RR; (b)
is the case when RL > RR.

[Explanation of symbols]

1 Semiconductor pressure sensor 2 Si single crystal (gauge element) 3
Wafer 3c Si with SOI structure
single crystal layer

Claims (1)

[Claims] Claim 1: A Si single crystal having a piezoresistance coefficient π63' and a specific crystal plane formed as a surface to which a compressive force is applied is used as a gauge element, and the piezoresistance effect of the Si single crystal is utilized. In an orthogonal semiconductor pressure sensor that detects compressive force applied perpendicularly to the crystal plane, a wafer with a silicon-on-insulator (SOI) structure is used to form the gauge element, and a Si single crystal that becomes the gauge element is used. The silicon-on-insulator (SOI)
) A semiconductor pressure sensor characterized in that it is formed from a Si single crystal layer of a wafer structure.