JPH06302831A - Manufacture of strain gage - Google Patents

Abstract

PURPOSE:To provide a manufacturing method of a strain gage in which the degree of freedom of a process is high and whose detection accuracy and stability are good. CONSTITUTION:The surface on a part of one face of a first substrate 18 composed of single-crystal silicon of a p-type or an n-type is doped with low- concentration ions, the p-type is inverted into the n-type or the n-type is inverted into the p-type, and a low-concentration doped layer 19 is formed. Then, a second substrate 21 composed of single-crystal silicon of the same material as that of the first substrate 18 is bonded to a face on the side on which the low-concentration doped layer 19 of the first substrate 18 has been formed, an electrochemical etching operation is performed, regions other than the low- concentration doped layer 19 in the first substrate 18 are removed wholly, and the low-concentration doped layer 19 which has been left on the second substrate 21 by removing the first substrate 18 is used as a strain gage 22.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to micromachining,
The present invention relates to a method for manufacturing a strain gauge used for a scanning probe microscope, a pressure sensor, or the like.

[0002]

2. Description of the Related Art Conventionally, stylus, pressure sensor, etc. have been used as a strain gauge. Therefore, first, as a first conventional example, a method for manufacturing a stylus will be described with reference to FIG.
It will be described based on. First, S oxide is used as a masking material on the surface of the Si single crystal substrate 1 having a (100) plane orientation.
A film 2 made of i or the like is formed, an opening (not shown) is formed in the film 2 by photolithography, and the underlying Si single crystal substrate 1 is subjected to crystal axis anisotropic etching to form a pyramidal recess. 3 is formed (a). Next, after removing the film 2 by etching or the like,
A Si ₃ N ₄ film 4 is laminated over the entire surface including the concave portion 3,
Photolithographic etching is performed to form the cantilever 6 (b). Next, a glass 7 is formed on the Si ₃ N ₄ film 4.
Are joined by anodic bonding (c). Next, after mechanically cutting a part of the glass 7 from the cut portion 7a with a dicing saw, from the surface opposite to the surface having the Si ₃ N ₄ film 4,
Only the Si single crystal substrate 1 is etched using an etchant without immersing the Si ₃ N ₄ film 4 (d). Next, the metal film 8 is deposited from the surface side on which the glass 7 in which only the Si single crystal substrate 1 has been completely removed in this way is provided to form a light reflecting mirror (e). With such a series of processes, the SFM stylus having the projection 9 at the tip of the cantilever 6 can be manufactured. In the stylus thus manufactured, the protrusion 9 is formed at the position opposite to the fixing portion made of the glass 7, and therefore, when the protrusion 9 is brought close to the sample surface, only the protrusion 9 is attached. The measurement is easy without colliding with the sample surface.

Next, as a second conventional example, a specific example of the pressure sensor will be described. FIG. 10 shows the structure of the pressure sensor of the micro diaphragm. The manufacturing process of the pressure sensor will be described below. First, a first silicon nitride film (not shown) is formed on the silicon substrate 10, and a rectangular window is opened in the center. Next, an etch channel of polycrystalline silicon (not shown) is laminated so as to cover the rectangular window. Next, a second silicon nitride film 11 is laminated on the polycrystalline silicon etch channel,
A strain gauge 13 made of polycrystalline silicon is formed at a predetermined position on the diaphragm 12 made of silicon nitride.
Further, a third silicon nitride film 14 is laminated on the second silicon nitride film 11. Etching holes 15 are formed in the outer periphery of the diaphragm 12 so as to penetrate the second and third silicon nitride films 11 and 14 and reach the etching channel of polycrystalline silicon thereunder. Then, etching is performed through the etch hole 15 while removing the etch channel of polycrystalline silicon, thereby forming an inverted pyramid type cavity portion 16 in the silicon substrate 10. In this case, the undercut etching is performed using an anisotropic etching solution such as a KOH aqueous solution. Next, when all the etch channels of the polycrystalline silicon are removed, the anisotropic etching of the silicon substrate 10 automatically stops at the pyramidal cavity 16 surrounded by the (111) plane. Further, after forming an electrode 17 connected to the strain gauge 13 by vapor deposition of aluminum, a silicon nitride film is laminated on the entire surface of the substrate by plasma CVD to seal the etch hole 15, thereby making it desired. Microdiaphragms can be made. In this way, the microdiaphragm has the pyramidal cavity 16 that serves as a vacuum pressure reference chamber inside the substrate.
A micro-diaphragm made of silicon nitride is formed on the upper part of 6, and a strain gauge 13 made of poly (polycrystalline) silicon is wired on the micro-diaphragm, and the strain gauge 13 is connected to an electrode 17, whereby a pressure sensor is provided. Can be used as

[0004]

In the case of the first conventional example,
A cantilever (cantilever 6) made of Si ₃ N ₄ with a tip (protrusion 9) attached to the tip is integrally attached to the end face of the base (glass 7). However, in such manufacturing processes, strain gauges for measuring the "deflection" of the cantilever cannot be installed during the process. Therefore, in order to measure the deflection of the cantilever, it is necessary to use an optical method such as irradiating a laser beam from above the cantilever, and such an optical deflection measuring method is used for measuring a photosensitive material. Is not applicable, and there are problems with drift and reproducibility.

In the case of the second conventional example, the pressure is detected by using the strain gauge 13 made of polysilicon. Generally, according to the detection principle using such strain gauge 13, the material characteristic of polysilicon is used. Therefore, there arises a problem in detection accuracy variation and stability.

[0006]

According to a first aspect of the present invention, a portion of one surface of a first substrate made of p-type or n-type single crystal silicon is doped with a low concentration of ions to make the p-type n-type. Forming a low-concentration doping layer by inverting the n-type to the p-type and forming a low-concentration doping layer on the first substrate by forming a second substrate made of single crystal silicon of the same material as the first substrate. The surface of the first substrate is joined to the surface of the second substrate and electrochemical etching is performed to remove all regions of the first substrate except the low-concentration doping layer. The concentration doped layer was used as a strain gauge.

According to a second aspect of the present invention, a part of one surface of the first substrate made of p-type or n-type single crystal silicon is doped with a low concentration of ions to change p-type to n-type or n-type. The p-type is inverted to form a low-concentration doping layer, and high-concentration ions are doped around the low-concentration doping layer to form a high-concentration doping layer. And bonding the second substrate to the surface of the first substrate on the side where the low-concentration doping layer and the high-concentration doping layer are formed, and performing electrochemical etching to the low-concentration doping layer of the first substrate and All regions except the heavily doped layer are removed,
The low-concentration doping layer of the low-concentration doping layer and the high-concentration doping layer remaining on the second substrate after the removal of the first substrate is used as a strain gauge, and the high-concentration doping layer is a wiring for a strain gauge. Used as.

According to the invention of claim 3, claim 1 or 2
In the described invention, after electrochemical etching,
The second substrate in the region including the strain gauge was etched to form a thin beam.

According to a fourth aspect of the invention, in the first, second or third aspect of the invention, the probe is attached to a part of the second substrate in the region including the strain gauge.

[0010]

According to the first aspect of the invention, the strain gauge formed from the low-concentration doping layer can be provided at an arbitrary position on the surface of the silicon substrate, so that it is possible to increase the degree of freedom of the process. Since the strain gauge is made of single crystal silicon and has little variation in characteristics and high stability, it is possible to improve detection accuracy.

According to the second aspect of the present invention, the wiring made of the high-concentration doping layer can be formed at the same time as the strain gauge made of the low-concentration doping layer. Therefore, the process can be simplified and the characteristics of the strain gauge due to the wiring can be improved. The influence can be reduced, and the wiring can be used as a path for voltage application to the strain gauge during electrochemical etching.

According to the third aspect of the present invention, by forming the region where the strain gauge is formed thin, it is possible to improve the detection accuracy and resolution, and also to increase the directivity of the beam strain detection. .

In the invention of claim 4, the probe can be used as a probe of a probe type force microscope, and further, the detection accuracy and resolution of the force applied to the probe for detecting the force, and further, It is possible to improve the directivity of beam strain detection.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the invention described in claim 1 is shown in FIGS.
It will be described based on. The method of manufacturing the strain gauge will be described below with reference to FIG.
A description will be given based on (a) to (d). In (a), as the first substrate 18, a p-type single crystal silicon (p-Si) wafer doped with boron (B) or the like is used. The substrate thickness is 200 μm. Next, in (b), from the surface of the first substrate 18 to a depth of 1 μm, a width of 10 μm,
A region of 100 μm in length is doped with 10 ¹⁸ / cm ³ of phosphorus (P) to invert it into n-type, thereby forming a low concentration doping layer 19. Next, in (c), the second substrate 21 having an oxide film (SiO ₂ ) 20 having a thickness of 1 μm on both surfaces is bonded to the surface of the first substrate 18 on which the low-concentration doping layer 19 is formed. The second substrate 21 is made of a single crystal silicon wafer like the first substrate 18. Next, in (d), the p-Si of the first substrate 18 is electrochemically etched to leave only the low concentration doping layer 19. This allows
The low-concentration doping layer 19 having a thickness of 1 μm is fixed to the second substrate 21 and can function as the strain gauge 22. The first substrate 18 and the second substrate 21
Although p-Si was used as the material of the above, it is not limited to this, and n-Si may be used. In this case, the low-concentration doping layer 19 is inverted to p-type by doping.

Here, the electrochemical etching method performed in the step of FIG. 1D will be described. FIG. 2 shows a general method of electrochemical etching. Board 23
The n-Si film ₂ is formed by immersing a member in which the n-Si film 24 is formed on the front surface side of (p-Si) and the mask of the SiO ₂ film 25 is formed on the back surface side in the KOH aqueous solution 26.
4 is connected to the terminal of the power supply V on the positive (+) polarity side, and a negative (-)
It is configured by connecting the terminal on the polarity side to the Pt electrode 27. Thereby, as shown in FIG. 3, the strain gauge 22 of FIG. 1D can be manufactured by applying a voltage suitable for the etching stop of the pn junction. In the method of applying a voltage to the n-type strain gauge 22 portion in the etching method in this embodiment, an n-type region is separately formed by doping from the same portion to the wafer end, and the voltage is applied from the end. To do.

Therefore, the n-type strain gauge 22 thus obtained has a piezoresistance coefficient of about 90 × 10 ¹² cm ² /
It can be made to function with the characteristic of dyn, whereby the deflection of the second substrate 21 can be detected. In addition, the strain gauge 2 manufactured from the low concentration doping layer 19
Since 2 can be provided at any place on the surface of the silicon substrate, the degree of freedom in the process can be increased. Further, since the strain gauge 22 is made of single crystal silicon, it is possible to improve detection accuracy and stability. Further, since the strain gauge is formed on the oxide film (SiO ₂ ) on the second substrate 21, the element isolation between the plurality of strain gauges is performed by the oxide film, which allows the potential of the strain gauge to be set freely. The reliability of operation at high temperature and high temperature can be improved.

Next, an embodiment of the invention described in claim 2 will be described with reference to FIG. The description of the same parts as those in the first aspect of the present invention will be omitted, and the same reference numerals will be used for the same parts.

The steps shown in FIGS. 4 (a) to 4 (d) can be processed in the same manner as the steps shown in FIGS. 1 (a) to 1 (d), and only different points will be described below.
(B), the adjacent periphery of 10 ¹⁸ / cm ³ of low concentration lightly doped layer 19 of phosphorus, 10 ²² / cm ³
High-concentration doping layer 2
8 is formed. The high-concentration doping layer 28 has a depth of 1 μm from the surface and a width of 30 μm, and is inverted from p-type to n-type by doping. After that, in (c), the second substrate 21 is bonded, and then electrochemical etching is performed to obtain a shape as shown in (d). As a result, the low-concentration doping layer 19 which has been subjected to the low-concentration doping is strain gauge 2
The high-concentration doping layer 28 used as No. 2 and having a high-concentration doping can be used as the conductor wiring 29.

Therefore, in the embodiment of the invention described in claim 1, the wiring to the strain gauge 22 had to be separately performed by bonding wire or metal vapor deposition, and photolithography etching. Since the wiring 29 can be manufactured at the same time as the gauge 22 is manufactured, the process can be significantly shortened and the influence of the wiring 29 on the characteristics of the strain gauge 22 can be reduced. Further, by adopting such a process, the wiring 29 itself is resistant to damage and reliability can be improved. Further, by providing such a wiring 29, it can be used to apply a voltage to the entire n-type portion when performing electrochemical etching. Moreover, such a process can be applied not only to the strain gauge 22 but also to fabrication of a normal SOI electronic device.

Next, an embodiment of the invention described in claim 3 will be described with reference to FIG. The description of the same parts as those in the first and second aspects of the present invention is omitted, and the same parts are designated by the same reference numerals.

Here, among the steps of FIGS. 5A to 5G, the steps of (e) to (g) are newly added. (E) shows a state in which the direction of the second substrate 21 in (d) is reversed, and here, the oxide film 20 with the strain gauge 22 is formed into a cantilever shape by photolithography. Next, in (f), the second substrate 21
The oxide film 20 on the back surface side of is subjected to photolithography etching into a predetermined shape. Finally, in (g), a beam (cantilever) 30 can be produced by etching with hydrazine using the oxide film 20 as a mask, and a beam having a strain gauge 22 on the upper surface of this beam 30 is obtained. be able to. Note that the structure formed by etching the oxide film 20 is not limited to the cantilever as long as it is intended to measure the deflection with the strain gauge 22, and may be a membrane, for example.

Therefore, by adding the steps (e) to (g) and thinning the substrate region of the strain gauge 22, the detection accuracy and resolution can be improved.
It is possible to increase the directivity of beam strain detection. Further, in this case, since the beam 30 is manufactured after the strain gauge 22 is attached, damage due to the attachment of the strain gauge 22 can be reduced during the process.

Next, a first embodiment of the invention described in claim 4 will be described with reference to FIG. The description of the same parts as those in the first and second aspects of the present invention is omitted, and the same parts are designated by the same reference numerals.

Here, among the steps of FIGS. 6A to 6J, the steps of (e) to (g) are newly added. First, in (e), a 10 μm square hole 31 is formed in the oxide film 20 on the side where the strain gauge 22 is provided. next,
In (f), a pyramid-shaped hole 31 a is formed in the silicon of the second substrate 21 through the hole 31 by anisotropic etching of KOH. The single crystal strain gauge 22 is KO.
Si ₃ N ₄ , SiO to prevent etching by H
_2. Mask with Cr, etc. beforehand. Next, in (g), after depositing 0.5 μm of Cr from above the hole 31a,
Cr is photolithographically etched so as to leave a 20 μm square portion including the hole 31 of the oxide film 20. After this (h)
The steps of (j) to (j) of FIG.
It can be performed in the same manner as the steps (g) to (g). Thus, in (j), a cantilever having a tip (probe) 32 of Cr at the tip of the beam 30 can be manufactured. Also here, the structure formed by etching the oxide film 20 is not limited to the cantilever.

Next, a second embodiment of the invention described in claim 4 will be described with reference to FIG. The description of the same parts as those in the first embodiment is omitted, and the same reference numerals are used for the same parts.

Here, among the steps of FIGS. 7A to 7F, the step of forming the tip 32 of the step after (c) is changed. In FIG. 7C, the above-described FIG.
After performing the same process as above, an oxide film 20 of SiO ₂ is attached to the exposed surface of the p-Si wafer of the first substrate 18. next,
In (d), after the oxide film 20 is formed into a pedestal shape and photolithographically etched, the first substrate 18 of p-Si is electrochemically etched to leave only the n-type strain gauge 22.
Next, in (e) and (f), the same steps as (e) to (j) in FIG. 6 are performed. Specifically, a 10 μm square hole is opened in the oxide film 20 on the side where the strain gauge 22 is attached,
A pyramid-shaped hole is formed from the hole by anisotropic etching, Cr is deposited to a thickness of 0.5 μm, and the portion near the periphery of the hole is etched away to remove a shape as shown in (e). obtain. Finally, the second substrate 21
When all sides are removed by etching, a cantilever with a strain gauge 22 and a tip 32 as shown in (f) can be manufactured.

Next, a third embodiment of the invention described in claim 4 will be described with reference to FIG. The description of the same parts as those of the first and second embodiments will be omitted, and the same parts will be denoted by the same reference numerals.

Here, among the steps of FIGS. 8A to 8E, the step of forming the tip 32 of the step after (c) is changed. In (c), a pyramid-shaped pit 33 is formed in a part of the second substrate 21, the SiO ₂ oxide film 20 is deposited over the entire surface including the pit 33, and then the pit 33 of the second substrate 21 is formed. The surface on which the strain gauge 22 is formed and the surface on which the strain gauge 22 of the first substrate 18 is formed are joined. Next, in (d), the oxide film 20 of the first substrate 18 is photolithographically etched into a pedestal shape, and then p-
Electrochemical etching of Si leaves only the n-type strain gauge 22. Finally, in (e), the oxide film 20 on the side opposite to the bonding surface of the second substrate 21 and p-Si which is the substrate material thereof.
Thus, a cantilever with a tip (probe) 34 and a strain gauge 22 can be obtained.

As shown in the above-described first to third embodiments, a process is added to add tips 32 and 34.
Since the tips 32 and 34 can be used as the probe of the probe type force microscope,
Moreover, the detection accuracy and resolution of the force applied to the tips 32 and 34 for detecting the force and the directivity can be improved. In addition, tip 3 required for the probe force microscope
2, 34, the strain gauge 22 for detecting the force acting on the tips 32, 34, and the cantilever (beam 30) are all manufactured by a batch process, so that they can be processed with high reproducibility and high reliability. You can Further, since the strain gauge 22 and the tips 32 and 34 are formed in the cantilever of the probe manufactured by this process, the entire structure can be made compact and the detection stability can be improved.

[0030]

According to the first aspect of the present invention, the p-type is made n-type or n-type by doping a low concentration of ions on a part of one surface of the first substrate made of p-type or n-type single crystal silicon. The mold is inverted to a p-type to form a low-concentration doping layer, and a second substrate made of single crystal silicon of the same material as the first substrate is provided on the surface of the first substrate on which the low-concentration doping layer is formed. And removing all regions of the first substrate other than the low-concentration doping layer by performing electrochemical etching, removing the low-concentration doping layer remaining on the second substrate by removing the first substrate. Since it was used as a strain gauge, the strain gauge manufactured from the low-concentration doping layer can be provided at any place on the surface of the silicon substrate, and thus the process flexibility can be increased. The In which it is possible to achieve stability enhancing detection accuracy for.

According to a second aspect of the present invention, a portion of one surface of the first substrate made of p-type or n-type single crystal silicon is doped with a low concentration of ions to change p-type to n-type or n-type. p
Forming a low-concentration doping layer by reversing the mold, and forming a high-concentration doping layer by doping high-concentration ions around the low-concentration doping layer, and consisting of single crystal silicon of the same material as the first substrate A second substrate is bonded to the surface of the first substrate on which the low-concentration doping layer and the high-concentration doping layer are formed, and electrochemical etching is performed to perform the low-concentration doping layer and the first substrate. All regions except the high-concentration doping layer are removed, and the low-concentration doping layer of the low-concentration doping layer and the high-concentration doping layer remaining on the second substrate due to the removal of the first substrate is used as a strain gauge. Moreover, since the high-concentration doping layer is used as the wiring for the strain gauge, the wiring formed of the high-concentration doping layer is used as the strain gauge formed of the low-concentration doping layer. By simultaneously making the wiring, it is possible to simplify the process and reduce the influence of the wiring on the characteristics of the strain gauge, and also to make the wiring itself resistant to breakage and highly reliable. ,
The wiring can be used as a path for applying a voltage to a strain gauge when performing electrochemical etching.

According to a third aspect of the present invention, in the first or second aspect of the invention, after the electrochemical etching is performed, the second substrate in the region including the strain gauge is etched to form a thin beam. Improve accuracy and resolution, and
The directivity of strain detection of the beam can be enhanced, and since the beam is formed after the strain gauge is attached, damage to the beam during the process can be reduced.

According to a fourth aspect of the present invention, in the first, second or third aspect of the invention, the probe is attached to a part of the second substrate in the region including the strain gauge. Can be used as a probe of, and further, the detection accuracy and resolution of the force applied to the probe for the force detection, further, it is possible to enhance the directivity of the strain detection of the beam,
Since the probe can be manufactured in the process of manufacturing the strain gauge and the beam, the whole structure can be made compact and the detection stability can be improved.

[Brief description of drawings]

FIG. 1 is a process chart showing an embodiment of the invention described in claim 1.

FIG. 2 is a schematic diagram showing a method of electrochemical etching.

FIG. 3 is a characteristic diagram showing current-voltage characteristics.

FIG. 4 is a process drawing which is an embodiment of the invention according to claim 2;

FIG. 5 is a process drawing which is an embodiment of the invention according to claim 3;

FIG. 6 is a process chart which is a first embodiment of the invention according to claim 4;

FIG. 7 is a process drawing which is a second embodiment of the invention according to claim 4;

FIG. 8 is a process drawing which is a third embodiment of the invention according to claim 4;

FIG. 9 is a process chart showing a first conventional example.

FIG. 10 is a partially cutaway perspective view showing a second conventional example.

[Explanation of symbols]

 18 First Substrate 19 Low Concentration Doping Layer 21 Second Substrate 22 Strain Gauge 28 High Concentration Doping Layer 29 Wiring 30 Beam 32, 34 Probe

Claims (4)

[Claims] 1. A first substrate made of p-type or n-type single crystal silicon is partially doped with ions at a low concentration on one surface thereof to invert p-type to n-type or n-type to p-type. A low-concentration doping layer is formed, a second substrate made of single crystal silicon of the same material as the first substrate is bonded to the surface of the first substrate on which the low-concentration doping layer is formed, and electrochemical etching is performed. The entire region of the first substrate other than the low-concentration doping layer is removed, and the low-concentration doping layer remaining on the second substrate due to the removal of the first substrate is used as a strain gauge. Strain gauge manufacturing method. 2. A first substrate made of p-type or n-type single crystal silicon is partially doped with ions at a low concentration on one surface thereof to invert p-type to n-type or n-type to p-type. A low-concentration doping layer is formed, and a high-concentration ion is doped around the low-concentration doping layer to form a high-concentration doping layer, and a second substrate made of single crystal silicon of the same material as the first substrate is formed. Except for the low-concentration doping layer and the high-concentration doping layer of the first substrate, which is joined to the surface of the first substrate on which the low-concentration doping layer and the high-concentration doping layer are formed and electrochemically etched. Of the low-concentration doping layer and the high-concentration doping layer remaining on the second substrate by removing the first substrate as a strain gauge. A method for manufacturing a strain gauge, which is characterized in that the high-concentration doping layer is used as a wiring for a strain gauge. 3. The method for manufacturing a strain gauge according to claim 1, wherein the beam is formed by thinly etching the second substrate in the region including the strain gauge after performing the electrochemical etching. 4. The method for manufacturing a strain gauge according to claim 1, wherein the probe is attached to a part of the second substrate in a region including the strain gauge.