JP2005037309A - Vibration-type transducer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vibration-type transducer manufactured stably at a low cost. <P>SOLUTION: This vibration-type transducer is equipped with a vibrator 3 provided on a silicon monocrystal substrate 1, a shell 4 for forming a vacuum chamber in the substrate by surrounding the vibrator so as to keep a gap around the vibrator, an excitation means for exciting the vibrator, and an excitation detecting means for detecting the vibration of the vibrator. As to this transducer, when forming the vibrator out of silicon monocrystal and forming the vacuum chamber surrounding the vibrator, a silicon oxide film and a silicon nitride film are used as sacrificial layers on an upper part of the vibrator while electrically insulating the vibrator and the shell from each other. The vibrator and the shell are driven by capacitance, with these used as electrodes, to detect distortion given to the vibrator as a change in resonance frequency. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a vibratory transducer in which a fine beam (vibrator) is formed in a fine vacuum chamber, and strain applied to the vibrator is measured with high accuracy.

  The following is a prior art document of a vibratory transducer in which a fine vibrator is formed in a vacuum chamber and the strain applied to the vibrator is measured with high accuracy.

[Patent Document 1] Japanese Patent Laid-Open No. 5-332852 [Patent Document 2] Japanese Patent Laid-Open No. 7-30128 [Patent Document 2] Japanese Patent Laid-Open No. 9-008330 FIG. 17 is a cross-sectional view taken along the line AA in FIG.

In these drawings, 1 is a semiconductor single crystal substrate, and 2 is a measurement diaphragm provided on the semiconductor substrate 1 and receiving a measurement pressure Pm.
A strain detection sensor 3 is embedded in the measurement diaphragm 2 and uses a vibrating beam (vibrator) 3.

  Reference numeral 4 denotes a shell made of a semiconductor epitaxial growth layer for sealing, which seals the vibrator 3 to the measurement diaphragm 2. A portion surrounded by the shell 4 around the vibrator 3 is a vacuum chamber 5. The vibrator 3 is oscillated by the natural vibration of the vibrator 3 by a magnetic field generated by a permanent magnet (not shown) and a closed loop self-excited oscillation circuit (not shown) connected to the vibrator 3. It is configured.

  In the above configuration, when the measurement pressure Pm is applied to the measurement diaphragm 2, the axial force of the vibrator 3 changes and the natural frequency changes, so that the measurement pressure Pm can be measured by the change of the oscillation frequency.

18 to 23 are explanatory views showing an example of the manufacturing process of the conventional example of FIGS.
In FIG. 18, a silicon oxide or silicon nitride film 101 is formed on a substrate 1 cut into an N-type silicon (100) surface, and a required portion 102 of the film 101 is removed by photolithography.

In FIG. 19, etching is performed with hydrogen chloride in a hydrogen (H ₂ ) atmosphere at 1050 ° C., a required portion 102 formed in the substrate 1 is etched, and the film 101 is undercut to form a recess 103.

In FIG. 20, a selective epitaxial growth method is performed in a hydrogen (H ₂ ) atmosphere at 1050 ° C. by mixing hydrogen chloride gas into the source gas. That is,
a) The first epitaxial layer 104 corresponding to the lower half of the vacuum chamber 5 is selectively epitaxially grown with P-type silicon having a boron concentration of 10 ¹⁸ cm ⁻³ .

b) The second epitaxial layer 105 corresponding to the resonator 3 is selectively epitaxially grown on the surface of the first epitaxial layer 104 with P-type silicon having a boron concentration of 3 × 10 ¹⁹ cm ⁻³ so as to block the required portion 102. Let
c) The third epitaxial layer 106 corresponding to the upper half of the vacuum chamber 5 is selectively epitaxially grown on the surface of the second epitaxial layer 105 with P-type silicon having a boron concentration of 10 ¹⁸ cm ⁻³ .
d) The fourth epitaxial layer 107 corresponding to the shell 4 is selectively epitaxially grown on the surface of the third epitaxial layer 106 with P-type silicon having a boron concentration of 3 × 10 ¹⁹ cm ⁻³ .

In FIG. 21, the silicon oxide or silicon nitride film 101 is removed by etching with hydrofluoric acid (HF), and an etching inlet 108 is provided.
In FIG. 22, a positive pulse or a positive voltage is applied to the substrate 1 with respect to the fourth epitaxial layer 107, and an alkaline solution is injected from the etching inlet 108, and the first epitaxial layer 104 and the third epitaxial layer 106 are injected. Is removed by selective etching.

There is a difference in etching action between the second epitaxial layer 105 and the first epitaxial layer 104 or the third epitaxial layer 106 because the etching action is suppressed when the boron concentration is 3 × 10 ¹⁹ cm ⁻³ or more. It depends on what happens.

In FIG. 23, N-type silicon is epitaxially grown in hydrogen (H ₂ ) at 1050 ° C. to form an epitaxially grown layer 111 on the outer surfaces of the substrate 1 and the fourth epitaxial layer 107. For example, the etching inlet 108 is formed by thermal oxidation. Close.

  A vibratory transducer having a vibrator made of single crystal silicon has less variation in residual strain and is easy to control as compared with a polycrystalline material or an amorphous material. When the vibrator is made of single crystal silicon, the kind and concentration of impurities are changed by epitaxial growth or impurity diffusion as described above, and the vibrator is formed by selective etching.

  For this reason, a structure in which the sacrificial layer at the bottom of the vibrator is composed of an oxide film, or an electrical element (electrode that forms a piezoresistance or capacitance) is provided in the vibrator or at the bottom of the vibrator is realized. It is difficult or a complicated manufacturing process is required for realization, resulting in an increase in manufacturing cost. There is a problem.

  In a vibratory transducer, it is necessary to form a vibrator in a fine vacuum chamber in order to increase the mechanical Q value of the vibrator regardless of the constituent material of the vibrator. When a vibration type transducer is realized by a MEMS (Micro / Electro / Mechanical / Systems) technology, its structure is naturally limited, and a drive method and a detection method are preferably as simple as possible.

  In the case of electromagnetic drive / detection, if a permanent magnet is installed outside, it can be driven simply by energizing the vibrator, and it can be detected simply by measuring the induced current. However, there are problems such as the need for a permanent magnet and the need to position the magnet and the vibrator with high precision, which increase the manufacturing cost.

The present invention has been made to solve such problems,
a) The vibrator is composed of a single crystal to facilitate control of residual strain,
b) A substrate, a vibrator, and a vacuum chamber are formed monolithically by a semiconductor process,
c) An object of the present invention is to provide a vibratory transducer that can be manufactured inexpensively and stably by driving and detecting a vibrator by electrostatic capacitance and simplifying the drive and detection mechanism of the vibrator.

In order to achieve such a problem, the invention according to claim 1 of the present invention is:
A vibrator provided on a silicon single crystal substrate, a shell that surrounds the vibrator so as to maintain a gap around the vibrator and forms a vacuum chamber in the substrate, and an excitation that excites the vibrator And an excitation detecting means for detecting vibration of the vibrator, the vibrator is formed of a silicon single crystal and a vacuum chamber surrounding the vibrator is formed. A silicon oxide film and a silicon nitride film are used as sacrificial layers of the electrodes, the vibrator and the shell are electrically insulated, and the vibrator and the shell are used as electrodes to be driven by an electrostatic capacity to resonate the strain applied to the vibrator. It is detected as a change in frequency.

The invention according to claim 2
1) A step of forming a silicon oxide film on a silicon single crystal substrate.
2) The silicon oxide film is partially removed, the removed portion is undercut to form a recess D, and P ⁺ single crystal silicon and P ⁺⁺ single crystal silicon are sequentially grown in this recess by selective epitaxial growth. Process.
3) A step of forming a silicon oxide film on P ⁺⁺ single crystal silicon.
4) A step of forming a silicon nitride film on the substrate surface.
5) A step of forming P ⁺⁺ polysilicon on the substrate surface and forming an etching solution introduction hole in the P ⁺⁺ polysilicon.
6) A step of removing the silicon nitride film and the silicon oxide film.
7) A step of removing the P ⁺ single crystal silicon layer.
8) A step of closing the etching solution introduction hole to form a vacuum chamber.
9) A step of patterning P ⁺⁺ polysilicon to form an electrical wiring from the vibrator and shell to form an electrode for a bonding pad.
10) A step of thinning the silicon substrate from the back surface to form a diaphragm. It is characterized by including.

As is apparent from the above description, the present invention has the following effects.
1) Since the vibrator is made of single crystal silicon, the residual strain can be easily controlled.
2) When the vacuum chamber surrounding the vibrator is formed, since a silicon oxide film and a silicon nitride film are used as a sacrificial layer on the top of the vibrator, it is possible to etch a very narrow gap using HF as an etchant. HF can be easily etched even in a very narrow gap of 0.1 μm or less. As a result, a gap of 1 μm or less can be formed, and a desired capacitance between the vibrator / shell can be obtained.
3) Since the vibrator and shell are electrically insulated and driven / detected by the capacitance between the vibrator and shell, there is no need to form an electric element on the substrate side from the vibrator, and the structure is simple. Thus, it can be manufactured stably at low cost.
4) There is no need for an external permanent magnet required for the electromagnetic drive / detection method, and it can be manufactured stably at low cost.

FIGS. 1-10 is principal part structure explanatory drawing which shows an example of embodiment of this invention.
In the figure, components having the same functions as those of the conventional example shown in FIGS.
1 is a completed drawing, and FIGS. 2 to 10 are schematic production process diagrams. This will be described according to the manufacturing process.

In FIG. 2, a silicon oxide film 10a is formed on the N-type silicon single crystal substrate 1 and patterned.
The portion from which the oxide film has been removed is undercut to form a recess, and selective epitaxial growth is performed with P-type silicon having a boron concentration of 10 ¹⁸ cm ⁻³ to grow P ⁺ single crystal silicon 11. Next, a P ⁺⁺ single crystal silicon 12 is grown on the surface of the P ⁺ single crystal silicon 11 by closing the recess with P-type silicon having a boron concentration of 3 × 10 ¹⁹ cm ⁻³ . Later, the P ⁺ single crystal silicon layer becomes the gap under the vibrator, and the P ⁺⁺ single crystal silicon layer becomes the vibrator.

In FIG. 3, a silicon oxide film 10b is formed on the surface of the substrate including the P ⁺⁺ single crystal silicon 12 and patterned. The portion indicated by the recess D from which the oxide film has been removed becomes a grounding portion of the shell to the substrate.

In FIG. 4, a silicon nitride film 13 is formed on the substrate surface including the recess D and patterned. The silicon oxide film 10b and the silicon nitride film 13 on the P ⁺⁺ single crystal silicon 12a (vibrator) form a gap on the vibrator. The capacitance is determined by the film thickness and the area of the vibrator. Accordingly, by adjusting these values so that a desired capacitance can be obtained, the capacitance for driving and detecting the vibrator can be optimized.

In FIG. 5, P ⁺⁺ polysilicon 14 is formed on the entire surface, and an etching solution introduction hole E for sacrificial layer etching is formed by patterning. This P ⁺⁺ polysilicon will later become wiring for shell and electrode extraction. The wiring can also be formed by using P ⁺⁺ / P ⁺ single crystal silicon or by diffusing impurities into the silicon substrate before selective epitaxial growth. It is preferable to select the parasitic capacitance between the wiring and the silicon substrate to be the smallest.

  In FIG. 6, hydrofluoric acid is introduced from the etching solution introduction hole E to remove the silicon nitride film 14 and the silicon oxide film 12b. Since the etching rate of the silicon nitride film 14 is slow at the ground portion of the shell to the substrate, the silicon nitride film serves as an etching stop layer in the lateral direction.

In FIG. 7, the P ⁺ single crystal silicon layer 11 is removed by an alkaline solution (hydrazine, KOH, TMAH, etc.). At this time, the P ⁺⁺ single crystal silicon 12a and the P ⁺⁺ polysilicon 14 are not etched because impurities are introduced at a high concentration. Further, by applying a voltage of 1 to 2 V to the N-type silicon substrate during etching with an alkaline solution, it can be protected from being etched. The length direction of the vibrator is set as an etching stop by utilizing the slow etching rate in the <111> direction of the silicon single crystal.

In FIG. 8, a sealing member 15 (for example, SiO ₂ formed by sputtering, glass, etc.) is formed by sputtering, vapor deposition, CVD, epitaxial growth, etc. to close the etching solution introduction hole, and the fine vacuum chamber 5 is formed. Form. Prior to this step, it is possible to further stabilize the electrical insulation between the shell and the vibrator by a method such as forming a silicon oxide film on the vibrator surface and in the vacuum chamber by thermal oxidation or the like. In this case, a conductive material can be used as the sealing member.

In FIG. 9, P ⁺⁺ polysilicon 14 is patterned to form electrical wirings from the vibrator and shell, and to form bonding pad electrodes.
In FIG. 10, the silicon substrate is thinned from the back surface to form a diaphragm.
FIG. 11A is a plan view showing a state in which the P ⁺⁺ polysilicon 14 is patterned by being connected to the vibrator 12a and the shell 14 to form the electrical wiring 20 and the bonding Al electrode 21. FIG.

FIG. 11 (b) shows a circuit diagram of the vibratory transducer of the present invention.
In the figure, Vb is a bias voltage (constant voltage), Vi is a drive voltage (AC), R1 and R2 are wiring resistances, and R3 is a substrate resistance.
C1 is the capacitance between the vibrator / shell, C2 is the parasitic capacitance, and C3 and C4 are the capacitance between the wiring and the substrate. In the figure, the smaller the R3, C2, 3 and 4, the smaller the noise current. These values are determined by the wiring formation method, pattern, and the like. Therefore, these values are determined to be as small as possible.

  In the figure, when the capacitance C1 between the vibrator and the shell is constant, the amplitude of the output current is proportional to (C1 + C2) · Vi · ω when the frequency of Vi is ω. On the other hand, when C1 resonates at frequency ω, assuming that the change in C1 due to resonance is ΔC1, a current having an amplitude approximately proportional to ΔC1 · Vb · ω is added. The resonance frequency is detected from the increase in current.

  In FIG. 12, the vibrator is formed as an H type, and is divided into a driving capacitance and a detection capacitance. However, in this case, in order to electrically insulate the two shells (upper electrodes), a more complicated manufacturing method than the above-described manufacturing method is required. FIG. 4A is a plan view of the vibrator, and FIG. 4B is a cross-sectional view taken along the line AA in FIG.

FIGS. 13 to 15 show another embodiment for constituting the lower part of the vacuum chamber 5 and the vibrator 3. FIG. 13 shows that a P ⁺ diffusion layer 11 a is formed on the surface of the N-type silicon single crystal substrate 1. In this diffusion layer, a P ⁺⁺ diffusion layer 12b is formed.

FIG. 14 shows a P ⁺ epitaxial layer 11b formed on the surface of an N-type silicon single crystal substrate 1, a P ⁺⁺ epitaxial layer 12c formed on the epitaxial layer 11b, and patterned.

In FIG. 15, a P ⁺ diffusion layer 11a is formed on the surface of an N-type silicon single crystal substrate 1, and a P ⁺⁺ epitaxial layer 12d is formed on the diffusion layer 11a and patterned.

It is principal part structure explanatory drawing of the transducer which shows an example of embodiment of this invention. FIG. 2 is a production process diagram of FIG. 1. FIG. 2 is a production process diagram of FIG. 1. FIG. 2 is a production process diagram of FIG. 1. FIG. 2 is a production process diagram of FIG. 1. FIG. 2 is a production process diagram of FIG. 1. FIG. 2 is a production process diagram of FIG. 1. FIG. 2 is a production process diagram of FIG. 1. FIG. 2 is a production process diagram of FIG. 1. FIG. 2 is a production process diagram of FIG. 1. It is the wiring diagram and circuit diagram of FIG. It is a figure which shows the other Example of this invention. It is a figure which shows the other example of manufacture. It is a figure which shows the other example of manufacture. It is a figure which shows the other example of manufacture. It is structure explanatory drawing of the conventional example generally used. It is AA sectional drawing of FIG. FIG. 17 is a production process diagram of FIG. 16. FIG. 17 is a production process diagram of FIG. 16. FIG. 17 is a production process diagram of FIG. 16. FIG. 17 is a production process diagram of FIG. 16. FIG. 17 is a production process diagram of FIG. 16. FIG. 17 is a production process diagram of FIG. 16.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Measurement diaphragm 3 Vibrator 4 Shell 5 Vacuum chamber 10 Silicon oxide film 11 P ⁺ Single crystal silicon 12 P ⁺⁺ Single crystal silicon 13 Silicon nitride film 14 P ⁺⁺ Polysilicon 15 Sealing member 20 Wiring 21 Al pad

Claims (2)

  A vibrator provided on a silicon single crystal substrate, a shell that surrounds the vibrator so as to maintain a gap around the vibrator and forms a vacuum chamber in the substrate, and an excitation that excites the vibrator And an excitation detecting means for detecting vibration of the vibrator, the vibrator is formed of a silicon single crystal and a vacuum chamber surrounding the vibrator is formed. A silicon oxide film and a silicon nitride film are used as sacrificial layers of the electrodes, the vibrator and the shell are electrically insulated, and the vibrator and the shell are used as electrodes to be driven by an electrostatic capacity to resonate the strain applied to the vibrator. A vibratory transducer that is detected as a change in frequency. 1) A step of forming a silicon oxide film on a silicon single crystal substrate.
2) The silicon oxide film is partially removed, the removed portion is undercut to form a recess D, and P ⁺ single crystal silicon and P ⁺⁺ single crystal silicon are sequentially grown in this recess by selective epitaxial growth. Process.
3) A step of forming a silicon oxide film on P ⁺⁺ single crystal silicon.
4) A step of forming a silicon nitride film on the substrate surface.
5) A step of forming P ⁺⁺ polysilicon on the substrate surface and forming an etching solution introduction hole in the P ⁺⁺ polysilicon.
6) A step of removing the silicon nitride film and the silicon oxide film.
7) A step of removing the P ⁺ single crystal silicon layer.
8) A step of closing the etching solution introduction hole to form a vacuum chamber.
9) A step of patterning P ⁺⁺ polysilicon to form electrical wirings from the vibrator and shell to form electrodes for bonding pads.
10) A step of thinning the silicon substrate from the back surface to form a diaphragm. The manufacturing method of the vibration type transducer characterized by the above-mentioned.

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