JPH03237761A - Semiconductor strain sensor and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a semiconductor strain sensor which can be used at a high temperature and is suitable for a highly precise load cell, by electrically insulating a strain gauge plate forming a piezoresistance layer from a semiconductor single crystal substrate, by using an insulating film. CONSTITUTION:A silicon substrate 2 composed of silicon single crystal is bonded on a substratum 1 composed of pyrex. A silicon oxide film 3 as an insulating film is formed on the upper surface of the silicon substrate 2. On said film 3, a strain gauge plate 4 composed of silicon single crystal is bonded. A load transferring rod 5 of a squar pole type is bonded at the central part of a strain gauge plate 4. Even in the case where this semiconductor strain sensor is used in a high temperature atmosphere at 150 deg.C or higher, electric isolation between the silicon substrate 2 and the strain gauge plate 4 forming a piezoresistance layer is maintained, and load can be detected at a high temperature. Since a part 4 turning to the piezoresistance layer and a part 2 turning to the substrate are constituted of the same silicon single crystal, bonding stress or the like is hardly generated and reliability is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a semiconductor strain sensor suitable for application to a load cell.

"Conventional technology" Conventional semiconductor strain sensors of this type form a piezoresistive layer on the main surface of a silicon single crystal substrate by thermal diffusion, eviaxial growth, etc., and transmit load to the center of the piezoresistive layer. It was made by gluing together rods. Electrical insulation between the piezoresistive layer and the single-crystal silicon substrate is achieved by a PN junction formed within the single-crystal silicon substrate.

Furthermore, the load transmitting rods are bonded to the silicon single crystal substrate for each chip after the wafer is divided.

"Problem to be Solved by the Invention" However, electrical isolation using a PN junction has the problem that leakage current due to thermal excitation increases at high temperatures, and the upper limit temperature for use of semiconductor strain sensors is limited to 125°C to 150°C. was there. In recent years, in-vehicle sensors and industrial measuring instruments have been increasingly used in temperature ranges exceeding 200°C, but conventional semiconductor strain sensors have not been able to handle this.

For this reason, it is possible to bond piezoresistive semiconductor elements onto an insulating material substrate such as Pyrex glass without using a single-crystal silicon substrate, but this tends to cause changes in the characteristics of piezoresistive semiconductor elements due to bonding strain, crystal defects, etc. , there was a problem of lack of reliability.

In addition, in the case of a semiconductor strain sensor applied to a load cell, due to the structure in which a load transmission rod is joined to the center of the piezoresistive layer, the ratio of the length and width of the piezoresistive layer (gauge) is 1/w like in a diaphragm pressure sensor. cannot be set to zero, and the resistance value (gauge resistance value) of the piezoresistive layer must be set by controlling the thickness.For this reason, it is difficult to set the resistance value of the semiconductor strain sensor with high precision. There were also problems.

Furthermore, since the load transmitting rods are joined for each chip, there is a problem in that it requires a lot of man-hours and productivity is low.

The present invention was made to solve the above problems, and its purpose is to enable use at high temperatures,
Another object of the present invention is to provide a semiconductor strain sensor suitable for use in a high-precision load cell.

Another object of the present invention is to provide a method for manufacturing a semiconductor strain sensor with high productivity, and further to provide a semiconductor strain sensor that can increase the utilization of materials in the manufacturing method.

Means for Solving the Problems J In order to achieve the above object, the present invention uses a substrate made of a semiconductor single crystal with an insulating film formed on one surface, and a piezoresistive layer formed uniformly in the thickness direction. A strain gauge plate made of a semiconductor single crystal is directly bonded to each other with their surfaces in close contact with each other, and a load transmitting rod is further bonded to the upper surface of the strain gauge plate. provided.

Further, the manufacturing method includes a groove machining step of cutting a large number of vertical and horizontal grooves on one surface of a rod wafer that is a material of the load transmission rod, and forming a rectangular or square protrusion surrounded by the grooves; A bonding process in which the surface of the rod wafer on which the coating is formed is overlapped and directly bonded to the top surface of the gauge wafer, which is the material of the strain gauge plate, and the top surface of the bonded rod wafer is removed and the groove is formed. Provided is a method for manufacturing a semiconductor strain sensor, comprising: a removing step that leaves only the protruding portions surrounded by the wafer on a gauge wafer; and a cutting step of cutting the gauge wafer into each of the protruding portions by dicing. be done.

Furthermore, the semiconductor strain sensor manufactured by this method is
The shape of the substrate is rectangular or square, the shape of a cross section parallel to the joint surface of the load transmission rod is rectangular or square, and the edge of the substrate and the side peripheral surface of the load transmission rod are approximately Preferably, they are parallel.

"Operation" In the semiconductor strain sensor configured as described above, the strain gauge plate forming the piezoresistive layer and the semiconductor single crystal substrate are electrically insulated by the insulating film. Furthermore, since the substrate and the strain gauge plate are made of the same single crystal semiconductor with only impurities present, joint strain and crystal defects are less likely to occur at the joint.

Further, the resistance value of the piezoresistive layer is controlled by controlling the thickness of the strain gauge plate by polishing or the like.

Further, according to the manufacturing method, the rod wafer is bonded to the gauge wafer in its wafer state, and only the protruding portion of the rod wafer is left on the gauge wafer in the removal step. The protruding portion constitutes a load transmitting rod. That is, according to this manufacturing method, the strain gauge plate and the load transmission rod are joined in the form of a wafer.

Furthermore, in a semiconductor strain sensor in which the edge of the substrate and the side peripheral surface of the load transmission rod are approximately parallel, the trajectory of the dicing cutter in the gage wafer cutting process must pass through the portion of the rod wafer that was the trough. This makes it possible to form protrusions at a higher density without providing a blank section on the rod wafer for the dicing cutter to pass through.

"Example" Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a front view showing a first embodiment of the present invention, and FIG. 2 is a plan view.

A silicon substrate 2 made of silicon single crystal is bonded onto a substantially square pedestal 1 made of Pyrex glass (#7740). The −L surface of the silicon substrate 2 is covered with a silicon oxide film (Sin2 film) 3 with a thickness of approximately 0.5 to 1 μm.
is formed as an insulating film. The silicon oxide film 3
A strain gauge plate 4 made of silicon single crystal is bonded on top. The strain gauge plate 4 is a bulk type strain gauge having a predetermined conductivity type and crystal axis, such as a silicon single crystal having a P-type conductivity type, a (110) crystal plane, and a specific resistance of about 2 Ω-cm. Its thickness is about 10 to 20 microns. Note that the crystal axes of the strain gauge plate 4 and the silicon substrate I2 are aligned in the same direction.

A load transmitting rod 5 in the shape of a square prism is connected to the center of the strain gauge plate 4. The load transmission rod 5 is made of the same Pyrex glass (#7740) as the pedestal 1. Pyrex glass is used for these silicon substrates made of silicon single crystals2. This is because the coefficient of linear expansion is similar to that of the planned gauge plate 4. Further, on the strain gauge plate 4, electrodes 6 and 7 for voltage application and electrodes 8 and 9 for signal extraction are formed of an aluminum vapor-deposited film according to the direction of the crystal axis thereof.

A method of manufacturing a semiconductor strain sensor having the above configuration will be explained. First, a silicon single crystal substrate 2 is prepared, and a silicon oxide film (S+02 film) is formed on one surface by thermal oxidation.
3 is formed. Next, a bulk type strain gauge plate 4 made of silicon single crystal on which a piezoresistive layer is uniformly formed in the thickness direction by diffusing P-type impurities such as boron (B) is formed as described above. It is bonded to a silicon substrate 2 using a so-called silicon direct bonding technique. As techniques for directly bonding silicon, anodic bonding, direct bonding in a vacuum high temperature furnace, etc. are used.

Next, the upper surface of the joined strain gauge plate 4 is polished to a predetermined thickness! lIi adjustment. Then, a pedestal 1 made of Pyrex glass is hermetically bonded to a silicon substrate 2 by anodic bonding, and aluminum electrodes 6 to 6 are attached to the upper surface of the strain gauge plate 4.
Each of the zero or more steps in which 9 is deposited is processed in the wafer state.

Thereafter, the wafer is divided into individual elements (chips) by guising cutting, and a load transmitting rod 5 is bonded to the center by anodic bonding to complete a semiconductor strain sensor.

A method of using the semiconductor strain sensor having the above configuration will be explained. In the semiconductor strain sensor, a base 1 made of Pyrex glass and a load transmission rod 5 are bonded to a case body (not shown) constituting a load cell using a highly rigid adhesive and sealed inside the case body. For the joints of the case body, alloys such as Kovar and 42 alloy, which have a linear weight similar to Pyrex glass (1, 5), are used. Then, the hermetic seal terminal provided on the case body and the aluminum electrodes 6 to 9 of the semiconductor strain sensor are connected to gold (
Au) Connected by thin wire.

During use, a constant voltage of about 3 to 12 V is applied between the poles 6 and 7 for voltage application. When a load is applied between the load transmission rod 5 and the pedestal 1 through the case body of the load cell, the output voltage between the signal extraction electrodes 8 and 9 changes due to the viezoresistance effect of the silicon single crystal. The load is detected by this change in output voltage.

In the semiconductor strain sensor of this embodiment, a portion 4 serving as a piezoresistive layer and a portion 2 serving as a substrate are both made of silicon single crystal, and both portions 2 and 4 are made of an insulating film made of a silicon oxide film 3. Insulated.

Therefore, even when used in a high-temperature environment of 150° C. or higher, electrical isolation between the silicon substrate 2 and the strain gauge plate 4 forming the piezoresistive layer is maintained, making it possible to detect loads at high temperatures.

Further, since the portion 4 serving as the piezoresistive layer and the portion 2 serving as the substrate are made of the same silicon single crystal, reliability is increased even though bonding strain etc. occur.

Furthermore, since the thickness (gauge thickness) of the strain gauge plate 4, which becomes the piezoresistive layer, can be adjusted with an accuracy of about ±10% by adjustment such as polishing, the resistance i of the portion 4 of the piezoresistive layer can be adjusted.
f (gauge resistance value) can be controlled with high accuracy, and a highly accurate semiconductor strain sensor can be provided.

In the embodiment described above, Pyrex glass was used for the base 1, but it is not necessary to use glass; for example, crystallized glass can be used for this purpose.

35th! FIG. 1 is a front view showing the second embodiment. In this embodiment, the thickness of the silicon single crystal plate serving as the substrate 10 is made sufficiently large, so that the silicon substrate 10 itself not only holds the strain gauge plate 4 forming the piezoresistive layer, but also serves as a load cell case body. The pedestal 1 also functions to absorb and relieve thermal stress generated when bonded.

Furthermore, in all of the above embodiments, the silicon oxide film (Si0w film) 3 was used as the insulating film, but other insulating films such as a nitride film may be formed on the silicon substrate 2.

Fig. 4 is a plan view showing the third embodiment, and Fig. 5 is its V-
It is a v-line sectional view.

In this embodiment, the strain gauge plate 24 serving as a piezoresistive layer is patterned to have a pattern shape that allows current to flow uniformly only directly below the load transmitting rod 25, thereby improving sensor sensitivity.

The pattern of this strain gauge plate 24 is similar to that of the load transmitting rod 2.
The rod 25 extends vertically in the drawing with the width of the bottom surface of the rod 25, and is further bent left and right in the drawing to reach the bonding pot part, and the load transmitting rod 25 extends narrowly from the approximate center of the bottom surface to the left and right in the drawing and is bent. The other regions of the strain gauge plate 24 are removed by etching.

The aluminum electrodes 26 and 27 for voltage application have a shape extending from the bonding pot part to the full width of the load transmission rod 25.

Further, the shapes of the pedestal 21 and the silicon substrate 22 are square, and the shape of the cross section parallel to the joint surface of the load transmitting rod 25 joined on the strain gauge plate 24 is also different from that of the embodiment shown in FIG. , is considered to be a square. And pedestal 2
1 and edges 22A, 22B, 22C of the silicon substrate 22
, 22D and the side peripheral surfaces 25A, 25 of the load transmission rod 25.
B, 25C, and 25D are arranged and joined in parallel to each other.

The semiconductor strain sensor configured as described above is sealed in a case body forming a load cell, and the load applied to the load cell is transmitted between the load transmission rod 25 and the pedestal 21. Same as example.

During use, a predetermined voltage is applied between the voltage application electrodes 26 and 27. At this time, the width of the center part of the patterned strain gauge plate 24 is approximately equal to the width of the bottom surface of the load transmission rod 25, and the voltage application electrodes 26 and 27 are deposited extending to the full width. Therefore, current flows uniformly within the strain gauge plate 24 between the opposing voltage applying electrodes 26 and 27, and most of the current flows under the bottom surface of the load transmitting rod 25. When a load is applied between the load transmission rod 25 and the pedestal 21, a voltage is generated between the signal extraction electrodes 28 and 29 due to the piezoresistance effect, and the output voltage changes depending on the load. Since almost 100% of the current flowing through the gauge plate 24 flows under the bottom surface of the load transmitting rod 25, the conversion efficiency is high and the sensor sensitivity is significantly increased. In the embodiment shown in FIG. 2,
The strain gauge plate 4 has the same shape as the silicon substrate 2, and the t current flowing between the voltage application electrodes 6 and 7 spreads within the strain gauge plate 4 and also flows considerably to parts other than the bottom surface of the load transmitting rod 5. This is in contrast to the case where the conversion efficiency becomes low and a loss in output voltage occurs.

The first and second embodiments have the advantage that no etching process is required and the manufacturing process is simple, whereas the third embodiment has the advantage that the sensitivity of the sensor can be improved.

In the embodiment shown in FIG. 4, all unnecessary areas of the strain gauge plate 24 are removed by etching, but the point is that Tt
Since sensor sensitivity can be improved by limiting the area where the flow flows to just below the load transmitting rod 25, the groove portion 30 that divides the area is removed by etching, as shown in FIG. A strain gauge plate 24 consisting of a non-operating region 2 isolated by a gauge region 24A and a
4B may be separated. In this case, there is an advantage that the burden of etching is lightened.

The manufacturing method of the third embodiment shown in FIG. 4 will be explained.

First, a silicon oxide film (Si
o. A silicon single crystal substrate 22 on which a film> 23 is formed and a bulk type strain gauge plate 24 in which P-type impurities are diffused are bonded together using a silicon direct bonding technique to form a gauge wafer 42.

Next, the upper surface of the bonded strain gauge plate 24 is polished to a predetermined thickness (TI4). Everything up to this point is the same as the first embodiment.

Next, resin is applied to the upper surface of the strain gauge plate 24 in a wafer state, masking is applied, and a fourth layer is formed using etching technology.
A large number of patterns 24 shown in the figure are formed on a wafer.

The depth of etching is adjusted so that the strain gauge plate 24 is reliably removed and S i 021i 23 remains.

Next, a pedestal wafer 41 made of borosilicate glass such as Pyrex glass and serving as the pedestal 21 is bonded to the silicon substrate 22 portion of the gauge wafer 42 by anodic bonding. Aluminum electrodes 26, 27, 28, 29 are deposited at the locations.

Next, a rod wafer 43 that will become the load transmission rod 25 is prepared. FIG. 7 is a plan view showing the rod wafer 43, and FIG. 8 is a sectional view thereof.

The rod wafer 43 is a disc-shaped member made of borosilicate glass, typified by Pyrex glass (#7740) suitable for anodic bonding. On one side of the rod wafer 43, a large number of 71144 holes are formed vertically and horizontally by a diamond blade.
．． 45 are cut out, and a large number of square protrusions 46 surrounded by these 11144, 45 are formed on the surface.

Next, as shown in FIG. 9(a), the surface of the rod wafer 43 on which the edges 44 and 45 are formed is superimposed on the upper surface of the gauge wafer 42 bonded to the pedestal wafer 41, and bonded by an anodic bonding technique. do.

At this time, each protruding portion 46 of the rod wafer 43 is precisely positioned and bonded so as to accurately bond to the gauge plate portion 24 left by etching the gauge wafer 42.

Next, as shown in FIG. 9(b), the rod wafer 43
The upper surface portion is removed by lapping or dicing and lapping, and the protruding portion 4 surrounded by the grooves 44 and 45 is removed.
6 is left on the gauge wafer 42.

Next, as shown in FIG. 9(c), the gauge wafer 42
Then, the pedestal wafer 41 is cut by a guising cut into each protruding portion 46 and divided into each element (chip) to complete a semiconductor strain sensor. Each separated protruding portion 46 constitutes a load transmitting rod 25. do.

According to the above manufacturing method, since a large number of load transmission rods 25 can be bonded simultaneously in a wafer state, there is an advantage that the number of steps for manufacturing a semiconductor strain sensor can be reduced and productivity can be improved.

In addition, in the embodiment shown in FIG. 4, the edges 22A, 22B, 22C, 22D of the base and the silicon substrate 22 and the side peripheral surfaces 25A, 25B, 25C, 25D of the load transmission rod 25 are
are connected so that they are parallel. Therefore, during the dicing cut to separate and cut each chip, the dicing cutter can pass through the grooves 44 and 45 of the rod wafer 43, and the rod wafer 43 can be cut into the rod wafer 43 without having to take into account the passage of the dicing cutter. The protruding portions 46 can be formed with high density.

For example, as in the first embodiment shown in FIG. 2, if the load transmitting rods 5 are arranged at an angle of 45° to each side of the silicon substrate 2, as shown in FIG. , each protruding part 52 of the rod wafer 51 has to be roughly arranged. In this example, the center lines 53 and 54 of the groove for forming the protruding part 52 and the dicing cut for separating each chip Since the cutter trajectories 55 and 56 at the time are at an angle and do not match, blank portions 57 must be arranged in a staggered manner between the respective protruding portions 52 that become the load transmission rods 5. The distance between the rod wafers 51 increases, and the density of the protruding portions 52 on the rod wafer 51 decreases. The blank parts 57 arranged in a staggered manner are parts that cannot be used, and the corresponding parts on the gauge wafer are also parts that cannot be used and are lost, so the utilization rate of wafer material is reduced. This results in a decrease in productivity.

On the other hand, the embodiment shown in FIG. 4 or FIG. 6 has the advantage that the portion serving as the semiconductor strain sensor can be formed on the wafer with high density, and the utilization rate of the wafer material is increased.

"Effects of the Invention" In the present invention, the strain gauge plate configured as described above and made of a semiconductor single crystal is directly bonded to the substrate, and electrical isolation is achieved by an insulating film such as an oxide film or a nitride film. This enables stable use at high temperatures. Furthermore, it is easy to control the gauge resistance to control the gauge thickness, and there is an effect that a highly accurate semiconductor strain sensor suitable for a load cell can be provided.

Further, according to the manufacturing method of the present invention, it is possible to bond a large number of load transmitting rods to a strain gauge plate in a wafer state, reducing the number of man-hours and increasing productivity. .

Further, when the edge of the substrate and the side peripheral surface of the load transmitting rod are made substantially parallel to each other, there is an effect that the utilization rate of the material can be increased when manufacturing in the form of a wafer.

Strain gauge plate, 5,25. ,,Load transmission rod, 41
, , pedestal wafer 42. ,, gauge wafer,
43, Rod wafer, 44.45. ,, groove, 4
6. Protrusion part.

[Brief explanation of drawings]

FIG. 1 is a front view of a semiconductor strain sensor showing a first embodiment of the present invention, FIG. 2 is a plan view, FIG. 3 is a front view of a second embodiment, and FIG. 4 is a third embodiment. FIG. 5 is a plan view showing an example, FIG. 5 is a sectional view taken along the line v-v in FIG. 4, FIG. 6 is a plan view showing the fourth embodiment, and FIG. 7 is applied to the third embodiment. A plan view showing the rod wafer, FIG. 8 is a sectional view taken along the line ■-■ in FIG. 7, FIG. 9 is a sectional view showing the manufacturing process in the wafer state, and FIG. 10 is applied to the first embodiment. FIG. 3 is a plan view showing a rod wafer. 1100 pedestal, 2.22. ,,Silicon substrate, 3゜23,,,Silicon oxide film (insulating film), 4.24.
,. Fig. 1 Bow Fig. Fig. Fig. Fig. Fig. 7 Fig. Fig. Fig. Fig. 7

Claims (1)

[Claims] 1. A substrate made of a semiconductor single crystal on which an insulating film is formed on one surface, and a strain gauge plate made of a semiconductor single crystal on which a piezoresistive layer is uniformly formed in the thickness direction. A semiconductor strain sensor characterized in that the surfaces of the strain gauge plate are directly bonded in close contact, and a load transmission rod is further bonded to the upper surface of the strain gauge plate. 2. The method for manufacturing a semiconductor strain sensor according to claim 1, wherein a large number of vertical and horizontal grooves are cut on one surface of a rod wafer that is a material for the load transmission rod, and a rectangular or square protrusion surrounded by the grooves is formed. a bonding process of overlapping and directly bonding the groove-formed surface of the rod wafer to the top surface of the gauge wafer, which is the raw material for the strain gauge plate; and a top surface portion of the bonded rod wafer. A semiconductor device characterized by comprising: a removal process in which only the protruding portions surrounded by the grooves are left on the gauge wafer; and a cutting step of cutting the gauge wafer into each of the protruding portions by dicing. A method of manufacturing a strain sensor. 3. The semiconductor strain sensor according to claim 1, wherein the shape of the substrate is rectangular or square, and the shape of a cross section parallel to the joint surface of the load transmission rod is rectangular or square, and the edge of the substrate and the A semiconductor strain sensor characterized in that a side circumferential surface of a load transmitting rod is substantially parallel to the side circumferential surface of the load transmitting rod.