JPS63108762A - Manufacture of heat-insulating structure of sensor element - Google Patents

Abstract

PURPOSE:To prevent the generation of disconnections at stepped sections in a wiring by forming a diaphragm, an upper surface of which is shaped by SiO2, and forming a sensor element onto the SiO2 surface in the diaphragm. CONSTITUTION:When nitrogen is boiled frothed with an etchant, using silicon nitride or thermal oxide as a mask material onto an Si substrate 4 and the substrate 4 is etched, an indentation in depth of 5-100mum and width of approximately 45mum can be formed. The particulates of SiO2 are deposited onto the surface to which the indentation is shaped, and an SiO2 film in approximately 50mum thicker than the depth of the indentation is formed through heating. The shaped SiO2 film is polished to expose the surface of the Si substrate except the indentation. An silicon section being positioned at the position of the indentation and having an area smaller than the indentation is etched in an anisotropic manner from another surface of the surface of the Si substrate, and removed until etching reaches the surface of SiO2, thus forming a diaphragm, an upper section of which is shaped by the SiO2 film. An element requiring heat insulation is formed onto the diaphragm, a peripheral circuit controlling the element is shaped by the Si surface, and both the element and the circuit are connected by a metallic thin-film wiring. Accordingly, heat insulating structure having high mechanical reliability and the metallic thin-film wiring forming no stepped section between the surface of the Si substrate 4 and the SiO2 film 5 for heat insulation are acquired.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a method for manufacturing a structure for thermally insulating a sensor element on a silicon substrate.

``Prior art/problems to be solved by the invention'' Figure 1 shows a thermal insulation structure used in thermistors, Golay cells, thermopiles, etc. used as infrared light sensors (1). In FIG. 5, reference numeral 101 denotes a sensor element;
102 is a 5isN4 layer, 103 is a Sin layer, 104 is a Si, N layer, 105 is a Si plate, 106 is a Si3N4 layer
The layer 107 is a hole.

The substrate of the device is an n-type substrate with a (100) crystal orientation.

The thin film is S 13N 4s S 10
It has a three-layer structure of t and Si3N4. These thin films are made by CVD and have a total thickness of 2 to 4 μm. A hole 109 is formed in the substrate 105 by anisotropic etching to form a diaphragm structure. In this structure, the strength of the membrane part is low, causing problems in both reliability during manufacture and during use.Furthermore, the entire Si surface is covered with the membrane, so the peripheral circuitry can be built on the Si surface by removing the membrane. When formed, it is necessary to route the wiring through a level difference of several μm, which has the disadvantage of causing disconnection of the wiring.

As a thermal insulation structure for a gas sensor fabricated on a Si substrate, an SiO2 film obtained by thermally oxidizing Si or a SiO2 film obtained by CVD method! There is a bridge structure made of membrane (2)
. The bridge structure consists of a bridge-shaped 5-layer structure on a Si substrate with crystal orientation (100).
This method creates an iOz and undercuts it using anisotropic etching. The disadvantage of this structure is that the 5idt film produced by thermal oxidation or CVD is about 2 μm thick, and the bridge made of the Si film is extremely mechanically weak, and when a peripheral circuit is formed in the Si part, it is necessary to pass through a step of about 2 μm. This has the disadvantage that the wiring may break.

The purpose of the present invention is to form a SiO2 film on a Si substrate.
Solved the problem of weak mechanical strength of the thermal insulation structure made with 3N4 film etc. and the problem of disconnection in the wiring connecting the sensor element made on the thermal insulation structure and the peripheral circuit made on the Si substrate. An object of the present invention is to provide a method for manufacturing a thermal insulation structure of a sensor element.

References (1) Mie, Shiba 1) "Far-infrared sensor with Si lens" Confucian Technical Report ED83-134 p27 (2) Manchu, Mizu 1) "Low power high-speed response micro gas sensor" 32nd Japan Society of Applied Physics lecture Proceedings 31p A-3 "Means for solving the problems" The first invention of the present invention is to form a square or rectangular depression with a depth of 5 to 100 μm on a silicon substrate by etching, and then remove the silicon substrate. Fine particles of 5 iOy are deposited on top and heated to form a SiO layer thicker than the depth of the recess.
x film is formed, and then Sio,i is polished until the silicon surface other than the depression is exposed, and further, a silicon portion having an area smaller than the depression is anisotropically etched from the other side of the silicon substrate at the location of the depression. The diaphragm is removed until the 5-hot surface is reached, a diaphragm whose upper part is made of 5 iOz is formed, and a sensor element is formed on the SiO2 surface of the diaphragm.

In addition, the second invention is to form an SiO2 film through the same process as the first invention, and after polishing, remove the SiO2 film in the recessed portion.
A bridge is created between the two films by etching, and the Si below the bridge is removed by anisotropic etching to form a space.
A feature of this method is that the sensor element is formed on the bridge of the O2 film.

"Example" Example 1 FIG. 1 is a process diagram showing an example of the present invention, and FIG. 2 is a sectional view of a thermal insulation structure of a Senna element manufactured by the method shown in FIG. 1.

In Fig. 2, l is the sensor element (in the case of a gas sensor;
5hot thin film, ZnO thin film, Pd/ZnO Schottky diode, Pd gate FET element, etc., for infrared light sensors; thermistor, Golay cell, thermopile, etc.), 2 is a heater that heats the sensor element (only for gas sensors), 3 is an integrated circuit that controls the sensor, 4
is Si substrate, 5 is Sin! A SiO2 film with a thickness of approximately 40 μm was prepared by depositing and heating fine particles of
It is on the same plane as the surface of the iO2 film and there is no difference in level. 6 is a metal thin film wiring connecting the sensor and the integrated circuit, 7 is a bonding pad, 8 is a diaphragm space, 9 is a metal for a heat sink, and IO is an adhesive with good thermal conductivity for bonding Si and the metal for a heat sink.

Sensor element! The operation of a SnO thin film gas sensor will now be described. The heater 2 is energized and the sensor element l
Heat to 400°C. When the combustible gas comes into contact with the sensor element 1, the resistance of the sensor element 1 decreases, and the information is processed by the integrated circuit 3 through the wiring 6 to issue an alarm signal. Because of this structure, even if the sensor element l is heated to 400°C, it is thermally insulated by the SiO2 film diaphragm of approximately 40 μm, so that the integrated circuit 3 formed on the Si substrate 4 has no adverse effect on. In addition, the metal thin film wiring 6 has a step between the surface of the SiO2 film 5 and the surface of the Si substrate 4 (
Since they are connected, there will be no disconnection. 40 μm S
The iO2 film 5 is mechanically strong and highly reliable. As is clear from these results, it is possible to obtain thermal insulation with higher mechanical reliability compared to the conventional technology.
An improved effect was obtained in which metal thin film wiring without a step difference with the iO2 film 5 could be formed.

The method for manufacturing the thermal insulation structure is as shown in FIG. (
In the step 1), pyrocatechol 4 mol%, ethylenediamine 46.4 mol%,
1 while bubbling nitrogen with a mixture of 49.6 mol% water.
When boiled at 18°C and etched for 50 minutes, depressions with a depth of about 45 μm as seen in (1) can be formed. Next, apply 5iOy on the surface where the depression was formed in step (2).
fine particles are deposited and heated to form a SiO2 film of approximately 50 μm.

The SiO2 film formed in step (3) is polished to expose the Si substrate surface other than the depression. In step (4), S
From the other side of the i-substrate surface, at the location of the depression, a silicon portion with an area smaller than the depression is etched in the same manner as in step (1) until it reaches the 5iOy plane, and the upper part is etched with S.
A diaphragm made of an iO2 film is formed. (5)
In the process, an element requiring thermal insulation is formed on the diaphragm, a peripheral circuit for controlling the element is formed on the Si surface, and the two are connected by metal thin film wiring. By the above manufacturing method, a thermally insulating structure with high mechanical reliability and a metal thin film wiring without a step between the Si substrate 4 surface and the thermally insulating SiO2 film 5 were obtained. Note that if the thickness of the SiO2 film 5 is less than 5 μm, the mechanical reliability is poor, and if it is more than 100 μm, it becomes difficult to form and polish the SiO2 film.

Embodiment 2 FIG. 3 is a process diagram showing another embodiment of the present invention, and FIG.
This figure is a perspective view of the thermal insulation structure of the sensor element manufactured by the method shown in FIG. 3.

In FIG. 4, 11 is a space formed by removing Si under the SiO2 film by anisotropic etching, and 12 is a bridge made of a 5iOp film with a thickness of 40 μm, which connects the Si surface and Stow.
The surface of the membrane is on the same plane and there is no difference in level.

As in the first embodiment, the sensor element 1 formed on the SiO2 film bridge 12 is heated and operated, and information is processed by the integrated circuit 3 through the wiring 6. Because of this structure, even if the sensor element 1 is heated to 400° C., the heat will not be conducted to the integrated circuit 3 and will not have any effect. Also, metal thin film wiring 6
Since the surface of the bridge 12 made of the Si0g film and the surface of the Si substrate are on the same plane, no step breaks occur. 40 μm S
The bridge 12 made of iO is mechanically strong and highly reliable.

The method for manufacturing the thermal insulation structure shown in Fig. 4 is as shown in Fig. 3.
Steps (1) to (3) are the same as in Example 2. (4)
In the process, the surface on which the SiO2 film is formed is patterned by resist work so as to mask areas other than the 11 part in FIG. By undercutting, a bridge of 5iO8 film can be formed. In the step (5), an element requiring thermal insulation is formed on the 5iot film, a peripheral circuit for controlling the element is formed on the Si portion, and both are connected by metal wiring. By the above manufacturing method, a thermally insulating structure with high mechanical reliability and a Si surface and a thermally insulating S
A metal thin film wiring without a step difference from the iOx film was obtained.

"Effects of the Invention" According to the present invention, a Si substrate is etched to a depth of 5 to
After forming a 100 μm depression, a Si Oy film is formed to a depth greater than the depth of the depression, and then polished until the Si surface is exposed, and the Si surface and the SiO2 film are made on the same plane for anisotropic etching of the Si. Possibly a Sif of 5 to 100 μmn
The mechanical reliability of the thermal insulation structure is high because a diaphragm or bridge structure is fabricated using a film and this is used as a thermal insulation structure. It has the advantage of not causing cuts.

[Brief explanation of the drawing]

Figures 1 (1) to (5) are process diagrams showing one embodiment of the present invention, Figure 2 is a sectional view of the thermal insulation structure of the sensor element manufactured by the method shown in Figure 1, and Figure 3 (1). ~(5) are process diagrams showing another embodiment of the present invention, FIG. 4 is a perspective view of a thermal insulation structure of a sensor element manufactured by the method shown in FIG. 3, and FIG. 5 is a typical conventional sensor element. FIG. 2 is a cross-sectional view of a thermal insulation structure of l...Sensor element, 4...Si substrate,
5... SiO2 film, 11... Space, 1
2...SiO2 bridge. Applicant Nippon Telegraph and Telephone Corporation Figure 1 Figure 8

Claims (2)

[Claims] (1) Depth 5-100 by etching on silicon substrate
After forming a μm square or rectangular depression, SiO_2 fine particles are deposited on the silicon substrate and heated to form a SiO_2 film that is thicker than the depth of the depression. The silicon substrate was polished until it was exposed, and then from the other side of the silicon substrate, at the location of the depression, a silicon portion with an area smaller than the depression was removed by anisotropic etching until it reached the SiO_2 surface, and the upper part was formed of SiO_2. A method for manufacturing a thermal insulation structure for a sensor element, comprising forming a diaphragm and forming a sensor element on the SiO_2 surface of the diaphragm. (2) Depth 5 to 100 by etching on silicon substrate
After forming a μm square or rectangular depression, fine particles of SiO_2 are deposited on the silicon substrate and heated to form a SiO_2 film that is thicker than the depth of the depression, and then the SiO_2 film is removed so that the silicon surface above the depression is Polish until exposed, create a bridge by etching the SiO_2 film in the recessed part, remove Si under the bridge by anisotropic etching to form a space, and form a sensor element on the bridge of the SiO_2 film. A method for manufacturing a thermally insulating structure for a sensor element, characterized in that: