JPH07201511A - Microbridge shaped thin film element - Google Patents

Abstract

PURPOSE:To eliminate restriction on design and bridge area in formation of a bridge by using photosensitive glass, having SiO2 as the main component, as a substrate. CONSTITUTION:After a micropattern 2 has been transferred to a sheet of both side polished photosensitive glass 3, the photo-sensed part is crystallized by heat treatment. Then, after the above-mentioned sheet of glass has been flattend into a thin film manufacturing substrate 3 by conducting precise polishing, a dielectric thin film 5 for bridge formation is deposited. Then, a Pt thin film resistor 6 is formed, it is patterned using a thin film heater as a temperature measuring resistor, and a functional thin film element is formed on the bridge. Then, after a passivation film 7 has been deposited, a pad and an etching hole are provided, and a microbridge 1 is formed by conducting an etching treatment at room temperature. Then, the hole penetrating the substrate 3 connects a thermosetting type epoxy adhesive film or sheet to the back side of the substrate 3, and a chip cutting operation is conducted. As a result, bridge width is increased and high integration is obtained easily.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a thin film device having a microbridge shape.

[0002]

2. Description of the Related Art Si for forming a beam (micro bridge)
In a device in which a dielectric film is deposited on a substrate and then a beam (micro bridge) is formed by anisotropic etching of Si, various characteristics of the thermal sensor (low power consumption, high response speed, (Multifunctionalization) has been dramatically improved. By forming various sensor elements in the form of a thin film on the microbridge, it is effective for a sensor that detects changes in physical properties by using heat as a medium, because thermal insulation can be easily performed. The structure of these microsensors is shown in Fig. 1.
Shown in. For example, in Japanese Examined Patent Publication No. 3-52028, S
A thermal gas mass flow meter is manufactured by forming a micro bridge on an i-wafer substrate. Anisotropic etching on a Si substrate has a corrosion rate (etching rate) of the substrate Si to an alkali of (100), (110) plane and (11) plane.
1) It is a processing method that uses different things in terms of surface. Therefore, if a Si (100) substrate is used as the substrate, the substrate surface is substantially parallel to the (100) plane, and the microbridge can be processed at an angle that is not parallel to the (110) axis direction. Previously developed microsensors (11
0) and has a shape suspended at an angle of 45 °. This is selected at 45 ° in order to efficiently etch Si under the bridge in the process of processing and to form the largest bridge on the limited substrate area. Therefore, in the microfabrication using the Si substrate, the current situation is that the bridge formation (design) is restricted.
For example, when this element is used in a gas mass flowmeter, there is a proportional relationship between the increase in heat radiation area (bridge area) and the sensitivity, and it is desirable to increase the heat radiation area. Also, in the gas flow direction detection and mass flowmeter in which the heating elements are arranged on the bridge and the temperature measurement elements are symmetrically arranged at both ends, if the heat radiation area is small, the heat balance saturation phenomenon at high flow rate causes Narrowing becomes a problem.

Increasing the heat dissipation area of a Si substrate is subject to the following restrictions. A bridge is formed at 45 ° to the (110) axis. The etching hole consists of two sets of right-angled isosceles triangles each having a side length l, and the hypotenuse of the right-angled isosceles triangle is (1
10) It is placed on the axis, and the distance between the two bases is placed so that it has a value close to √2l. The formation of a bridge in such an etching hole gives the maximum bridge area in principle. The progress of etching is shown in FIG. In the figure, the arrow A indicates that the etching does not proceed with the appearance of the (111) plane (the etching rate is different from that of the other planes by about two orders of magnitude, so it is expressed as not progressing). The lateral etching indicated by the depth directions B and B'progresses at substantially the same rate. The lateral etching proceeds so that the (111) plane appears until the point P is reached, and when the etching on both sides overlaps at the point P, the etching in the C direction proceeds. The end of etching ends when a substantially square shape with two triangular vertices of the etching hole as diagonal lines is formed. Now, assuming that the thickness of the substrate is infinitely large, consider formation of a bridge width of 1000 μm designed at l = 500 μm / sin 45 °. After reaching the point P in the lateral direction (500 μm) until P ′ (500
μm) advance to P ″ (500 μm)
Then, a similar distance of 1500 μm is etched in the depth direction of the substrate. In reality, the thickness of the substrate is finite,
500 μm is generally used for a 4-inch Si wafer.
A hole penetrating the substrate is formed during the formation of the 000 μm bridge. The through holes are not preferable in the subsequent bonding process using a die bonder. Therefore, when the Si substrate is used, the bridge area is also restricted.

[0004]

[Object] A first object of the present invention is to design a thin film device having a microbridge structure for forming a bridge,
Also, the device characteristics are improved without restricting the bridge area. A second object is to cover the holes of the substrate formed in the production of the thin film element and to improve the joining process of the element.

[0005]

According to a first aspect of the present invention, a dielectric film and a functional thin film element formed on the dielectric film are provided on a substrate, and the substrate is partially removed. In the thin film device in which the functional thin film device formed on the body film forms one or a plurality of microbridges, the substrate is made of Si.
In a thin film element, which is a photosensitive glass containing O ₂ as a main component. The photosensitive glass used in the present invention is such that a metal colloid precursor is deposited (exposure) by irradiation with energetic light such as ultraviolet rays, and the metal colloid becomes a crystal nucleus by heat treatment to cause crystallization only in the exposed portion (development). In this way, the glass that crystallizes only the exposed area is an etching agent,
For example, dissolution with a hydrofluoric acid aqueous solution has different speeds in a crystalline portion and an amorphous portion, and as a result, anisotropic etching is possible. The microfabrication by this method has good compatibility with the semiconductor manufacturing process and can be performed without any restrictions on the bridge design.

A second aspect of the present invention is a beam (micro bridge).
A film or sheet is joined to the bottom surface of the thin film element substrate having a substrate through hole formed in the substrate for preparation, and the through hole is closed and mounted. Regarding thin film devices.
The microbridge of the thin film sensor of the present invention may have a bridge structure or a cantilever structure floating in the air on a substrate, or both of them. Next, a method for producing the thin film element of the present invention and its configuration will be specifically described as examples based on the drawings.

[0007]

EXAMPLE An example will be described with reference to FIG. Photosensitive glass 3 [HOYA photosensitive glass PEG3 (trade name)] was used. Transfer the micropattern to the photosensitive glass 3 whose both surfaces have been polished (this creates a latent image 4 in the glass by irradiating it with ultraviolet rays C through the photomask 2).
(A). The exposed portion (latent image 4) is crystallized by an appropriate heat treatment. This accelerates the dissolution rate in the aqueous solution of hydrofluoric acid. The temperature of heat development was 600 ° C.
Next, precision polishing is performed to remove deformation due to heat history,
After ensuring sufficient smoothness as the thin film forming substrate 3 (b), the dielectric thin film 5 for bridge formation is deposited (c). The dielectric thin film 5 may be formed by depositing a silicon nitride film, which is familiar with processes such as Si semiconductor devices, by the CVD method, or by depositing a tantalum pentoxide film by the reactive sputtering method. In order to get a self-solid as a bridge,
The film thickness of this dielectric thin film was 1.5 μm or more. It has been confirmed that in the reactive sputtering film formation of tantalum pentoxide, the internal stress of the film becomes a relatively small value depending on the sputtering conditions, and the stress hardly remains by the heat treatment at 500 ° C. after the deposition. Therefore, in this example, this tantalum pentoxide film was deposited and heat-treated. Then Pt
If the thin film resistor 6 is formed and a thermal gas mass flowmeter is manufactured, this Pt thin film resistor is patterned as a thin film heater and a temperature measuring resistor, and a metal oxide semiconductor and a metal oxide semiconductor are formed on the metal oxide semiconductor. In a gas sensor using a noble metal such as platinum (Pt) or palladium (Pd) as a catalyst, a thin film functional element is further formed on this bridge (d). Basically, this means that at least a thin film functional element is formed on the bridge, and various microsensors can be produced by this. Next, after depositing the passivation film 7, a pad and an etching hole were opened (e), and etching was performed at room temperature with an 8 wt% hydrofluoric acid aqueous solution to form a bridge. As shown in this step, the Si substrate had restrictions on its crystal orientation, bridge area, etc. However, this does not occur in this embodiment. Next, a hole penetrating the substrate was bonded (g) with a thermosetting epoxy-based adhesive film or sheet (thickness 40 μm, thermosetting temperature 170 ° C.) on the back surface of the substrate, and thereafter, chips were cut out and mounted. However, the film or sheet to be bonded to the back surface of the substrate is not limited to the thermosetting epoxy adhesive film or sheet, and any film or sheet can be used as long as it can be bonded by heat or an adhesive. .

[0008]

According to the present invention, by expanding the bridge width, it is possible to expand the dynamic range of sensitivity in, for example, a thermal gas mass flowmeter, and further, another gas sensor,
Also in a microsensor such as a humidity sensor, it is possible to easily integrate a plurality of functional thin film elements, and the function of the element can be improved. In addition, by closing the through holes of the substrate by joining the sheets, it is possible to manufacture without causing any defect in the mounting process.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a plane of an example of a microbridge type gas mass flowmeter.

FIG. 2 is a diagram illustrating an example of processing by Si anisotropic etching.

FIG. 3 is a diagram illustrating the progress of bridge formation by Si anisotropic etching. (A) is a diagram in which two sets of isosceles right triangle etching holes are arranged on a Si substrate. (B) It is a figure explaining that the horizontal etching of said (a) progresses to P point. (C) It is a diagram explaining that after the laterally traveling etching of (b) reaches point P, etching proceeds to point P ′. (D) It is a figure explaining the end time of etching.

FIG. 4 is a diagram illustrating a configuration of a thin film element manufactured in an example and a manufacturing process thereof. (A) A step of irradiating the photosensitive glass with ultraviolet rays through a mask pattern is shown. (B) A step of performing precision polishing on a substrate having a heat-sensitive photosensitive latent image portion is shown. (C) A step of depositing a dielectric thin film is shown. (D) A step of depositing and patterning a Pt thin film is shown. (E) A step of depositing a passivation film and opening an etching hole is shown. (F) A step of removing the substrate by etching to form a bridge is shown. (G) A step of joining and mounting a thermosetting epoxy adhesive film is shown.

[Explanation of symbols]

 1 Micro Bridge 2 Mask Pattern 3 Photosensitive Glass 4 Photosensitive Latent Image Part 5 Dielectric Film 6 Pt Thin Film Resistor 7 Passivation Film 8 Thermosetting Epoxy Adhesive Film A (110) Axial Direction (Direction of Etching) B Depth Direction Etching direction B'Depth direction Etching direction C UV irradiation (exposure)

Claims (3)

[Claims] 1. A dielectric film and a functional thin film element formed on the dielectric film on a substrate, wherein the substrate is partially removed, and the dielectric film and the dielectric film are formed on the dielectric film. A thin film element in which the functional thin film formed one or a plurality of microbridges, wherein the substrate is photosensitive glass containing SiO ₂ as a main component. 2. The thin film element according to claim 1, wherein the functional thin film is patterned by using a Pt thin film resistor as a thin film heater and a resistance temperature detector. 3. The thin film element according to claim 1, wherein a film or sheet is bonded to the back surface of the substrate through the substrate through hole.