JPS63271975A - Pressure sensor and manufacture thereof - Google Patents

Abstract

PURPOSE:To render a sensor small in size and high in accuracy by a method wherein a light emitting and a photodetective element are connected through the intermediary of a diaphragm formed of the photoconductive material which is provided on and around a recessed part on a substrate so as to constitute a lightguide path. CONSTITUTION:A light emitting element 11 and a photodetector 12 are connected through a diaphragm 10 consisting of silicon oxide films 6 and 8 and a silicon nitride film 7 which are provided on and around a recessed part 3 so as to constitute a light guide path. Therefore the outputted light from the light emitting element 11 is detected by the photodetector 12 through the intermediary of the light guide path of the diaphragm 10 provided on and around the recessed part 3 on the substrate 1, where the deformation of the diaphragm 10 based on the state of pressure is detected by the photodetector 12 as the variation of the detected light volume, so that pressure is detected. By these processes, a sensor can be rendered to be small in size and high in accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a pressure sensor and a method of manufacturing the same.

(Prior art and problems) Taking advantage of the fact that the resistance value changes due to the piezoresistance effect when mechanical stress is applied, the wall thickness of a part of a single crystal silicon substrate is reduced to form a thin comb diaphragm. A pressure sensor is used that measures pressure by forming a strain gauge in the epitaxial layer formed on the tire flam with a diffusion layer, etc., deforming the strain gauge by the pressure applied to the diaphragm, and detecting the change in resistance value due to the piezoresistive effect. It is being

However, depending on this method, there are limits to the miniaturization and high precision of the sensor.

(Objective of the Invention) The object of the present invention is to solve the above-mentioned problems, and to provide a pressure sensor that is different in structure from the conventional pressure sensor 9 and is excellent in size and precision, and a method for manufacturing the same. be.

(Means for Solving the Problems) A first invention includes a substrate having a recess in a part thereof, and a diaphragm made of an optical waveguide material formed on and around the recess and forming an optical waveguide. , and a light emitting/receiving element connected via the diaphragm.
The gist is:

The second invention includes a step of forming four parts on the main surface of the first substrate, a step of forming an optical waveguide layer serving as a GUI A7 flam on the main surface of the semiconductor single crystal substrate, and a step of forming the four parts on the main surface of the first substrate. a step of joining the surface and the main surface of the semiconductor single crystal substrate;
etching from the other surface side of the semiconductor single crystal substrate to form a diaphragm made of the optical waveguide layer on the main surface of the first substrate; and connecting a light emitting/receiving element via the diaphragm. The gist thereof is a method of manufacturing a pressure sensor 17 comprising:

(Function) The light output from the light emitting element is received by the light receiving element via the leading wave path of the diaphragm formed on and around the recessed part of the substrate, and the deformation of the diaphragm according to the pressure state causes the light receiving element to The pressure is detected as a change in the amount of light received.

(Example) An example embodying the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of the pressure sensor of the present invention, FIG. 2 is a plan view thereof, and FIGS. 3(a) to 3(k) are sectional views for explaining the manufacturing process thereof.

First, to explain the manufacturing process, Fig. 3(a) shows -ff(
100) plane, a silicon oxide film (Si 02 >2) is formed in a predetermined region on the main surface of the first single crystal silicon substrate 1 as shown in FIG. Using an anisotropic etching solution such as potassium hydroxide (KOH) as a mask, etching was performed as shown in the same figure (
A recess 3 as shown in C) is formed. Note that the crystal plane of the substrate used here may be (110), or...
It may also be made of Pyrex glass, sapphire, or the like with recesses formed therein.

Further, a BPSG film 4 is formed in a predetermined region on the first single crystal silicon substrate 1 (silicon oxide film 2) (FIG.
)).

On the other hand, as shown in Figures (e) and (f), for example, a second single crystal silicon of N type conductivity with a resistivity of 3 to 50 cm and a crystal plane of (100) or (110) is used. A silicon oxide film 6 is formed on the main surface of substrate 5. Roughly, as shown in the figure (g), a silicon nitride film (Si 3 N4 ) 7 is formed on this silicon oxide film 6,
On top of that, another part of the silicon oxide film 8 is formed (see FIG.
h)). A BPSG film 9 is formed on this silicon oxide film 8 in a predetermined region as shown in FIG. 2(i). This B
The PSG film 9 is formed so as to overlap the BPSG film 4 of the first single crystal silicon substrate 1 in a state shown in FIG.

Then, as shown in FIG. 12(j), the second single crystal silicon substrate 1 is aligned on the main surface of the first single crystal silicon substrate 1 using, for example, an infrared microscope so that the upper and lower patterns overlap as set. The BPSG film 9 formed on the substrate 5 is placed. At this time, the peripheral portions of the first and second single-crystal silicon substrates (or wafers thereof) 1 and 5 are melted and bonded using a laser in a vacuum for temporary bonding.

After that, it is heated to about 1000'C in vacuum and BPS
G film 4.9 is melted and the first. Second single crystal silicon substrate 1
, 5. In this embodiment, a weight is placed on the substrate to ensure complete adhesion.

In addition, 1st. Although a BPSG film is used as an adhesion (bonding) layer for bonding the second single crystal silicon substrate 1.5, other low melting point glasses may also be used, or the bonding of the two may be performed using a low melting point glass. The method is not limited to melt bonding of melting point glass, and for example, bonding may be performed by removing the silicon oxide film 2 and using a so-called anode (7 no-decker bonding). You can also join directly.

Then, the other main surface (back surface) of the first single crystal silicon substrate 1
is covered with wax or the like (not shown), and a foreign substance containing, for example, ethylenediamine (260m>, pyrocaterol (450), and water (120d>) as main components is applied from the other main surface (back side) of the second single crystal silicon substrate 5. The second single-crystal silicon substrate 5 is etched away using an orthotropic etching solution (see figure (k)). At this time, the etching progresses selectively in the N-type conductivity region, leaving almost no silicon oxide layer 6. The silicon nitride film 7 remains unetched.
becomes the core, and the silicon oxide films 6 and 8 become the core! ;) Dyle frame (optical waveguide layer 10
) are arranged on and around the recess 3 of the first single crystal silicon substrate 1.

First, a light emitting element 11 is arranged at one end of the optical waveguide layer 10 (on the left side in Figures 1 and 2), a light receiving element 12 is arranged at the other end (on the right side in Figures 1 and 2), and the optical waveguide layer 10 ( The light emitting/receiving elements 11 and 12 are connected via a diaphragm. In this embodiment, the light emitting element 11 uses a semiconductor laser that outputs light (laser) from the active layer 11a by applying voltage to both upper and lower end surfaces (electrodes 11b) of the PN junction (active layer) 11a. In addition, a photodiode having a PN junction and an N layer 12a is used as the light receiving element 12, and light is transmitted to the PN junction based on the detection of the current value between the N+7m 12a and the P layer 12b. m of the light emitting element 11 and the light receiving element 12 is detected.
Adhesive is used for adhesion.

Bonding is done by melting SiO2 or the like or by soldering.In order to achieve accurate bonding, the light-emitting cable 11 is turned on and the light-receiving cable 12 becomes immovable when the voltage (or current) detected by the light-receiving cable 12 reaches its maximum. I'm trying to keep it fixed.

In this embodiment, a semiconductor laser is used as the light emitting element 11, and a photodiode is used as the light receiving element 12, but other elements may be used in combination.

Further, after forming the optical waveguide layer 10 on the substrate 1, the light emitting element 11 and the light receiving element 12 were arranged and fixed on the substrate 1, but either one or both of the elements 11 and 12 were integrated on the same substrate 1. The pixel elements 11 and 12 are formed on the optical waveguide layer 10.
You can also connect it with

The pressure sensor subjected to 'tAJa in this way is first
First, light outputted from the light emitting element 11 without applying pressure is received by the light receiving element 12 via the leading wave layer (diaphragm) 10, and the current value at that time is converted into a voltage or the like and is used as an initial value. Next, when external pressure is applied to the leading wave layer 10 (diaphragm), the leading wave path is deflected. Then, a loss occurs before the light output from the light-emitting element 11 reaches the light-receiving element 12, and the current value becomes smaller by the amount of pressure applied than the initial current value when no pressure is applied, so it is necessary to compare it with the reference value. can measure pressure.

That is, in the standard state, since no pressure is applied, the core (silicon nitride film 7) of the leading wave layer (diaphragm) 10
) inside the core and the reflective film (silicon oxide film 6, 8)
The light propagates while being totally reflected at the interface with the light receiving element 12, and is detected as a current (voltage value) proportional to the amount of light received by the light receiving element 12. When pressure is applied to the diaphragm and the optical waveguide is distorted in this reference state, the light that was totally reflected in the reference state is not totally reflected due to the distortion (below the critical angle) and propagates to the light receiving system 12. The amount of light 1 emitted decreases. Since the current (voltage) decreases based on this amount of decrease, pressure is detected based on this current (voltage) detection.

In this way, in this embodiment, the structure is different from the conventional pressure sensor, and the recess 3 is formed from the substrate on the diaphragm side, and the recess 3 can be made small, resulting in a small pressure sensor. .

In addition, by forming the optical waveguide layer 10, which serves as a diaphragm, to be thin, it is possible to obtain a highly accurate sensor for applied pressure, and the structure allows for optical detection of deformation of the leading waveguide, resulting in high precision. Are better. Furthermore, by using different optical waveguide materials forming the optical waveguide layer 10, the sensitivity can be set as desired.

Note that the present invention is not limited to the above embodiments, and may be implemented as follows.

(B) In the above embodiment, the silicon nitride film 7 was used as the core of the diaphragm, and the silicon oxide films 6 and 8 were used as the reflective films covering the core. However, in the combination U of the core and the reflective film, light is totally reflected. Other materials may be used as long as a material having a smaller refractive index than the core can be used as the reflective film. For example, the core is quartz glass, which has the lowest right loss in the visible or near-infrared region and has the lowest refractive index among optical glasses, and silicone containing boron (B) and fluorine ('). It is advisable to use a modified membrane or an organic material such as Punsujik as the anti-fouling membrane.

(b) In the above embodiment, the same material (silicon oxide F36.8> was used above and below the core (silicon nitride film 7) to equalize the difference in refractive index at the interface between the core and the reflective film. The difference in refractive index at the upper and lower boundary surfaces of the reflective film may be changed. For example, when pressure is applied from above, the refractive index of the upper reflective film may be changed to increase the loss of light at the curved part. It is also possible to use a film having a refractive index smaller than that of the lower anti-f) J film. Naturally, in this case, the sensitivity of the sensor to pressure from above becomes better.

(c) In the above embodiment, the light emitting element 11 and the light receiving element 12 were provided on the substrate 1, but as shown in FIG.
3 may be connected to a light emitting element formed separately from the main body (substrate 1). The optical fiber 13 is supported on the substrate 1 by solder 14 as shown in FIG.
The optical fiber 13 may be formed on the substrate 1 to facilitate alignment of the optical axes of the waveguide and the optical fiber 13, and then bonded together with an adhesive. In this sensor, the structure of the pressure sensor body can be simplified and the pressure sensor body can be made more compact.

Roughly speaking, as shown in FIG.
Even if it is made to be a separate body from the board 1), it is not possible. This sensor can be further miniaturized and can be stacked more easily.

Effects of the Invention As detailed above, the pressure sensor of the present invention has a different structure from conventional pressure sensors and is smaller.

It exhibits the effect of making it excellent in increasing viscosity.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a pressure sensor embodying the present invention, FIG. 2 is a plan view of a pressure sensor 9, and FIGS.
) is a sectional view for explaining the manufacturing process of the pressure sensor, FIG. 4 is a sectional view of another example of the pressure sensor V, and FIG. 5 is a sectional view of another example of the pressure sensor. In the figure, 1 is a first single crystal silicon substrate, 3 is a recess, 5 is a second single crystal silicon substrate, 6 is a silicon oxide film, 7 is a silicon nitride film, 8 is a silicon oxide film, 11 is a light emitting element, 12 is a light receiving element, and 13 is an optical fiber. Patent applicant Nippondenso Co., Ltd. Agent
Patent Attorney On 1) Hironobu Figure 1 Figure 2

Claims (1)

[Claims] 1. A substrate having a recess in a part thereof, a diaphragm made of an optical waveguide material formed on and around the recess and forming an optical waveguide, and connected via the diaphragm. A pressure sensor comprising: a light-emitting light-receiving element; 2. The pressure sensor according to claim 1, wherein the light emitting element and the light receiving element are both arranged on the substrate at both ends of the diaphragm. 3. A patent claim in which the light emitting and receiving element is arranged on one end of a diaphragm on a substrate, and the light emitting element is connected to the other end of the diaphragm through an optical fiber separately from the substrate. The pressure sensor according to the range 1 above. 4. The pressure sensor according to claim 1, wherein the light emitting element and the light receiving element are both connected to both ends of the diaphragm through optical fibers separately from the substrate. 5. forming a recess on the main surface of the first substrate; forming an optical waveguide layer serving as a diaphragm on the main surface of the semiconductor single crystal substrate; a step of bonding the main surface of the substrate; a step of etching from the other surface side of the semiconductor single crystal substrate to form a diaphragm made of the optical waveguide layer on the main surface of the first substrate; and a step of forming a light emitting/receiving element. A method for manufacturing a pressure sensor, comprising the step of connecting via the diaphragm.