JPH0519088B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention detects strain corresponding to the measured pressure of a silicon vibrating beam placed in a hollow chamber formed using a silicon single crystal as a frequency signal. The present invention relates to a method of manufacturing a vibrating transducer, and more particularly, to a method of manufacturing a vibrating transducer that improves the method of creating a vacuum state for creating a good resonant state by creating a vacuum inside the hollow chamber.

<Prior Art> The vibration that forms the basis of the improvement of this invention is of the type in which the measured pressure is detected from the change in the resonance frequency of a vibrating beam formed on a silicon pressure receiving diaphragm, fixed at both ends, and excited by an excitation means. A type transducer is disclosed, for example, in Japanese Patent Application No. 59-42632 entitled "Pressure Sensor."

An outline of this vibrating transducer will be explained using FIGS. 4 to 6.

Figure 4 is a perspective view showing the configuration of this conventional pressure sensor with the cover removed, and Figure 5 is an
A cross-sectional view taken along the -X cross-section with the cover attached, and FIG. 6 is a partially omitted plan view.

In these figures, 1 is a cylindrical silicon substrate, and 2 is a pressure-receiving diaphragm that is formed by digging the center of this silicon substrate 1 to form a thin part to serve as a pressure-receiving part that receives the measurement pressure Pm. It is made by etching 1.

3 and 4 are formed on the pressure receiving diaphragm 2,
It is a vibrating beam whose both ends are fixed to a silicon substrate 1, and the vibrating beam 3 is located approximately at the center of the pressure receiving diaphragm 2, and the vibrating beam 4 is located at the periphery of the pressure receiving diaphragm 2, respectively.

Specifically, these vibrating beams 3 and 4 are, for example, n
A first P ⁺ -type epitaxial layer is formed on a silicon substrate 1 , a cut is made in the center to electrically separate the left and right sides, an n-type epitaxial layer is formed on this, and then a P + -type epitaxial layer is formed on top of the first P + -type epitaxial layer. ^{A +} type epitaxial layer is formed and the top thereof is protected with an oxide film SiO ₂ . The cavity 5 at the bottom of the vibrating beam 3 is formed by under-etching this n-type epitaxial layer.

For example, the vibrating beam 3 formed in this way has a length of l, a thickness of h, and a width of d, then l=
The sizes are approximately 100 μm, h = 1 μm, and d = 5 μm.

Vibration beam 3 formed on pressure receiving diaphragm 2
The periphery of the pressure-receiving diaphragm 2 is covered with, for example, a silicon cover 6 bonded to the pressure-receiving diaphragm 2 by anodic bonding or the like, and the internal space 7 is maintained in a vacuum state. Although not shown, the vibrating beam 4 side is also formed in the same way.

The vibrating beam 3, cover 6, cavity 5, internal space 7, etc. form a detection section D of the vibrating transducer.

In the above configuration, the first left and right vibrating beams 3 and 4, which are the second P ⁺ type epitaxial layers,
When an oscillation circuit is connected between the P ⁺ type epitaxial layers to cause oscillation, the vibrating beams 3 and 4 cause self-oscillation at their natural frequencies.

In this case, the internal space 7 of the cover 6 is made into a vacuum state and held in the vacuum of the vibrating beam 3, so that the Q value indicating the sharpness of resonance becomes large, making it easy to detect the resonance frequency.

The frequencies of this self-oscillation change in opposite directions in response to the tensile or compressive stress applied to the vibrating beam. As shown in FIG. 5, when the measurement pressure Pm is applied to the pressure receiving diaphragm 2, the vibrating beam 3 receives tensile stress and the vibrating beam 4 receives compressive stress.

Therefore, the natural frequencies of the vibrating beams 3 and 4 change differentially with respect to the measured pressure, and by calculating the difference between these, it is possible to know the measured pressure Pm with twice the sensitivity. can.

<Problems to be Solved by the Invention> However, in the conventional method of manufacturing a vibrating transducer, a separately made silicon film is placed on the top of the vibrating beam 3 formed on the thin pressure receiving diaphragm 2. Since the cover 5 must be joined by anodic bonding or the like, and the internal space formed by the cover 5 and the pressure receiving diaphragm 2 must be evacuated, the pressure characteristics or temperature characteristics of the vibrating transducer may deteriorate, resulting in a decrease in accuracy. There is a question of what causes it. Furthermore, in order to perform anodic bonding, it is necessary to maintain the temperature at a high temperature, for example, 450°C or higher.
For this reason, there is a problem of thermal expansion and stable processing is not possible.

<Means for solving the problems> In order to solve the above problems, the present invention has the following features:
This manufacturing method involves the following steps.

A protective film is formed on a silicon single crystal substrate,
After this, an opening is formed in a part of the first protective film using a patterned mask, and then a recess corresponding to this opening is formed in the first substrate, and the first substrate is placed on top of this recess. The lower half of the gap corresponding part, which has a conduction mode opposite to that of The upper half of the gap-corresponding part is formed by epitaxial growth on top of the protective film, and then the shell-corresponding part is integrally formed on top of these by epitaxial growth. By etching, an injection port for the etching liquid that reaches the previous gap corresponding part is formed in the previous shell corresponding part, and after this, the previous gap corresponding part is removed by etching to form a vibrator. With the temperature below 10 ^-6 Torr, a specific gas is used to seal the injection port to form a shell, and the surrounding area of the vibrator is 10 ^-1 ~
The pressure is maintained at approximately 10 ^-5 Torr.

<Effect> By following each step from above,
The shell and the vibrator covered by the shell are integrally fixed to the substrate, and the injection port is sealed with a specific gas to maintain a predetermined vacuum state inside, resulting in excellent pressure and temperature characteristics. It becomes a vibration type transducer.

<Example> Hereinafter, an example of the present invention will be described based on the drawings. FIG. 1 is a process diagram showing the manufacturing process of a detection section which is a main part of the vibrating transducer of the present invention. This shows the process of the detection part D' shown in the axial cross section of the vibrating beam corresponding to the detection part D in FIG.

FIG. 1A shows an n-type silicon substrate 8 which is a base for making the detection section D'.

Next, this silicon substrate 8 is thermally oxidized to form an oxide film (SiO ₂ ) 9 on its surface (FIG. 1B).Furthermore, in the step of FIG. Grooves 10 are formed by photoetching in the vertical direction.

In the process shown in Figure 1 (d), hydrogen gas is heated at a temperature of 1050°C.
A groove 11 is formed in the silicon substrate 8 through the groove 10 by etching in an atmosphere containing H ₂ and hydrochloric acid HCl.

Next, as shown in FIG.
10 ¹⁸ cm ^-3 in an atmosphere of hydrogen gas H ₂ at a temperature of 1050 ° C
The first epitaxial layer 12 is formed by selectively epitaxially using boron (P type) having a concentration of .

After this, as shown in FIG.
A second epitaxial layer 14, which will become the vibrating beam 13, is formed on the vibrating beam 13 by selectively epitaxially depositing boron (P type) at a concentration of 10 ²⁰ cm ^-3 in an atmosphere of hydrogen gas H ₂ at a temperature of 1050° C.

Even if the measurement pressure Pm is zero, the vibrating beam 13 must be given an initial tension, otherwise it will buckle due to the application of the measurement pressure Pm and become unable to be measured. Also, the covalent radius of silicon is 1.17 Å and that of boron is 0.88 Å, so if boron is partially implanted into silicon, that part will experience tensile strain.

Therefore, by utilizing this phenomenon, for example, by adjusting the concentration of boron in the second epitaxial layer 14, an initial tension can be applied to the second epitaxial layer 14, or by applying phosphorus in the n-type silicon substrate 8 (covalent bond radius is 1.10 Å). The initial tension is given by adjusting the concentration and taking into account the relative strain between the silicon substrate 8 and the second epitaxial layer 14.

Next, as shown in FIG.
In an atmosphere of hydrogen gas _H2 at a temperature of 1050 °C above
A third epitaxial layer 15 is formed by selectively epitaxially using boron (P type) with a concentration of 10 ¹⁸ cm ^-3 .

Furthermore, as shown in FIG.
In an atmosphere of hydrogen gas _H2 at a temperature of 1050 °C above
A fourth epitaxial layer 16 is formed by selectively epitaxially using phosphorus (n-type) with a concentration of 10 ¹⁷ cm ^-3 .

FIG. 1R shows that the _first epitaxial layer is removed after the selective epitaxial process shown in FIG. 12 and the third epitaxial layer 15 are shown.

In this etching process, although not shown,
The entire structure is immersed in an alkaline solution, and a peak voltage is applied from a DC pulse power source 17 so that the n-type silicon substrate 8 and the fourth epitaxial layer 16 have a positive potential with respect to the p-type second epitaxial layer 14. A positive pulse voltage with a value of 5V and a repetition period of about 0.04Hz is applied. By applying this voltage, an insoluble film is formed on the surfaces of the n-type silicon substrate 8 and the fourth epitaxial layer 16 and the etching rate is increased to the first level.
Since it is much slower than the epitaxial layer 12 and the third epitaxial layer 15, the first epitaxial layer 12 and the third epitaxial layer are
Epi layer 15 is removed. Furthermore, the second epi layer 14
Taking advantage of the phenomenon that when the concentration of doped boron is greater than 4×10 ¹⁹ , the etching rate is significantly slower than the normal rate for undoped silicon, the second epitaxial layer 14 is left in place as a whole, as shown in FIG. As shown in FIG. 3, it is formed to have an opening 18 in a part and a gap between the silicon substrate 8 and the second epitaxial layer 14.

FIG. 1 shows a sealing process for sealing the opening 18. After putting the entire body into a sputtering device 19 and making the inside a vacuum state of about 10 ^-6 Torr, argon (Ar), helium (He), or neon (Ne) is applied.
etc. into the sputtering device 19 at about 10 ^-3 Torr, and silicon (Si) or silicon dioxide (SiO ₂ )
etc. to fill the opening 18.

FIG. 1E shows the result of sealing the opening 18. The second epitaxial layer 14 is formed as the vibrating beam 13, with both ends thereof being integrally fixed to the silicon substrate 8, with a predetermined gap being maintained at the other ends. Vibration beam 1
The upper part of 3 is covered with a shell 20, and there is a hollow chamber 2 inside.
1 is formed. Since this hollow chamber 21 was formed in a vacuum state, it is in a vacuum state.

FIG. 2 is a process diagram in which a part of the process shown in FIG. 1 is changed.

The steps from I to I in FIG. 1 are the same, and then proceed to the step in FIG. 2 A.

The process shown in FIG. 3A is the same as the process shown in FIG.
8 is another sealing process. Put the material obtained in Fig. 1 into the plasma CVD device 22,
After making the inside a vacuum state of about 10 ^-6 Torr,
Hydrogen (H ₂ ) and silane (SiH ₄ ) are introduced, the silane is decomposed by plasma excitation, the opening 18 is filled with amorphous, polycrystalline, or single crystal silicon, and a vacuum of 10 ^-2 to ^{10 -3} Torr is created. Seal.

FIG. 2B shows the result of sealing in this manner. The second epitaxial layer 14 is formed as the vibrating beam 13, with both ends thereof being integrally fixed to the silicon substrate 8, with a predetermined gap being maintained at the other ends. Vibration beam 1
The upper part of 3 is covered with a shell 23, and there is a hollow chamber 2 inside.
1 is formed. Since this hollow chamber 21 was formed in a vacuum state, it is in a vacuum state.

The process shown in FIG. 3A is the same as the process shown in FIG.
This is the third sealing step. The material obtained in Fig. 1 is put into the molecular beam epitaxial device 24, and the inside thereof is brought to an ultra-high vacuum state, and then the silicon evaporated from the evaporation source is radiated in the form of a beam onto the silicon substrate 8, etc. The opening 18 is sealed by epitaxial growth.

FIG. 3B shows the result of sealing in this manner. The second epitaxial layer 14 is formed as the vibrating beam 13, with both ends thereof being integrally fixed to the silicon substrate 8, with a predetermined gap being maintained at the other ends. Vibration beam 1
The upper part of 3 is covered with a shell 25, and there is a hollow chamber 2 inside.
1 is formed. Since this hollow chamber 21 was formed in an ultra-high vacuum state, it is in an ultra-high vacuum state.

<Effects of the Invention> As specifically explained above in conjunction with the embodiments, according to the manufacturing method of the present invention, after the vibrating beam is integrally formed with a predetermined gap with respect to the silicon substrate, a pressure of 10 The injection port was sealed with a specific gas under ^-6 Torr to form a shell, and the pressure around the vibrating beam was maintained at around 10 ^-1 to ^{10 -5} Torr. Therefore, a vibrating transducer with excellent pressure characteristics and temperature characteristics can be realized. Furthermore, by going through the process of sealing the injection port with a specific gas, processing can be performed at a low temperature of 200°C or less, so there is little change in properties due to thermal expansion.

[Brief explanation of the drawing]

FIG. 1 is a process diagram showing the manufacturing process of the main part of the present invention, FIG. 2 is a process diagram showing a manufacturing process in which a part of the process in FIG. 1 is changed, and FIG. A process diagram showing the manufacturing process with some other changes; Fig. 4 is a perspective view showing the configuration of the detection section of a conventional pressure sensor with the cover removed; Fig. 5 is a cover taken along the line X-X in Fig. 4; Cross-sectional view with
FIG. 6 is a partially omitted plan view. 1...Silicon substrate, 2...Pressure receiving diaphragm,
3, 4... Vibration beam, 5... Cavity, 6... Cover, 7...
Internal space, 8... Silicon substrate, 12... First epi layer, 13... Vibration beam, 14... Second epi layer, 15... Third epi layer, 16... Fourth epi layer, 18... Opening, 1
9... Sputter device, 20, 23, 25... Ciel,
21...Hollow chamber, 22...Plasma CVD device, 24
...Molecular beam epitaxial equipment.

Claims (1)

[Claims] 1. Forming a protective film on a silicon single crystal substrate,
After this, an opening is formed in a part of the protective film using a patterned mask, and then a recess corresponding to the opening is formed in the substrate, and 2 the conduction of the substrate is formed on the recess. A lower half of the gap corresponding part having a conduction type opposite to the above-mentioned type is formed by epitaxial growth, a vibrator corresponding part adjusted to a predetermined concentration is formed on this, and this vibrator corresponding part and the protective film are further formed. 3. Forming the upper half of the gap-corresponding part by epitaxial growth on top of the above, further integrally forming a shell-corresponding part by epitaxial growth on these parts, 3. Next, by etching the protective film. An inlet for an etching liquid that reaches the gap corresponding part is formed in the shell corresponding part, and then the gap corresponding part is removed by etching to form a vibrator. 4 After this, the pressure is reduced to 10 ^-6 Torr or less. The inlet is sealed with a specific gas to form ^a shell in the ^state of A method of manufacturing a transducer, characterized in that: