JPH0442834B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to, for example, an improvement in a method for manufacturing a microscopic cavity which is a main component of a pressure sensor.

<Prior Art> Conventionally, capacitance pressure sensors and piezoresistive pressure sensors using silicon (Si) semiconductors are mainly known as pressure sensors. Regarding the structure of these pressure sensors, capacitive pressure sensors have a structure in which a cavity is provided on the substrate, a fixed electrode is formed at the bottom of the cavity, and a deformable movable electrode is formed at the top of the cavity. There is. Pressure is detected by utilizing the change in capacitance between the movable electrode and the fixed electrode due to the displacement of the movable electrode due to the application of pressure. On the other hand, a piezoresistive pressure sensor has a structure in which a diaphragm is formed above a cavity chamber and a resistance layer is provided on the diaphragm. By applying pressure, the diaphragm is displaced, and the resulting strain in the resistance layer is detected as a change in the resistance value of the resistance layer due to the piezoresistance effect. The cavity is an important component in these capacitive and piezoresistive pressure sensors, and has conventionally been manufactured as follows.

(1) Method using electrostatic adhesion (2) Method using adhesion using low melting point glass (3) Method using wet etching <Problem to be solved by the invention> Method using electrostatic adhesion is based on concavely processed glass or This is a method of bonding a Si wafer onto a substrate by applying high voltage under heat. Since no adhesive is used, bonding distortion is small and cavities can be created with good dimensional accuracy, but it is susceptible to surface viscosity and surface contamination. It has the disadvantage that adhesion is greatly affected and reproducibility is poor.

The method of adhesion using low melting point glass involves forming a thin film of low melting point glass by sputtering etc. on a glass or Si wafer processed into a concave shape, and then bonding the glass or Si wafer processed into a concave shape and the substrate by heating. Alternatively, a thick film of patterned low-melting point glass is formed on a substrate by screen printing, and a glass or Si wafer is bonded thereon under heating to form a cavity. The method using low melting point glass has the advantage of being able to easily form a cavity, but it also has the drawbacks of large adhesion distortion due to the low melting point glass, poor dimensional accuracy, and poor reproducibility. There is. The wet etching method is a method in which a cavity is created by anisotropically etching the Si wafer with an ethylenediamine-based or potassium hydroxide-based aqueous solution.Since a Si substrate is used, the cavity cannot be created in the semiconductor process. It also has the advantage that the signal processing circuit can be formed on the same chip. However, since the etching solution uses ethylene diamine or an alkaline aqueous solution such as potassium hydroxide, sufficient care must be taken in terms of safety and hygiene when handling it, and it also has the disadvantage that it is difficult to control the composition of the etching solution. There is. Furthermore, the wet etching method has the disadvantage that it is difficult to produce fine and complex cavities due to problems such as diffusion of the etching solution and generation of bubbles during etching.

FIG. 3 is a diagram showing a cross-sectional structure when a cavity is created by a conventional wet etching method.

In FIG. 3, a polysilicon film or a glass film is formed on a silicon substrate 21 in a hollow portion 22, and after patterning, an insulating film 2 such as a silicon nitride film with excellent etching resistance is applied thereon.
Layer 3. Next, the silicon substrate 21 is etched from the back side with an ethylenediamine-based or potassium hydroxide-based etching solution to form pores 24, and then polysilicon or glass is wet-etched to form cavities 22. Techiru. As shown in FIG. 3, cavities created by conventional wet etching usually have pores located in the center of the cavity. This is because the polysilicon or glass in the cavity is etched through the pores, resulting in insufficient diffusion of the etching solution, and also due to air bubbles generated during etching sealing part of the cavity. In order to prevent uniform etching, the pores were placed in the center to create a uniform cavity.

As described above, with conventional wet etching methods, it is difficult to create cavities with complex shapes.Furthermore, since the etching composition changes as etching progresses, the etching rate fluctuates, resulting in poor reproducibility. However, since the etching solution is heated before use, there are problems in terms of safety and hygiene, such as the need to be careful about the steam generated. These problems are caused by the fact that a wet etching method is used to dissolve and remove the polysilicon film, glass film, etc. in the cavity.

On the other hand, plasma etching, sputter etching, and the like are known as dry etching methods that can replace conventional wet etching methods, and these methods perform etching using products in plasma or spatter atoms. However, if the cavity, that is, the part to be etched, communicates with the outside through pores, and if the shape of the cavity is complex, it is difficult for plasma products or spatter atoms to reach the details of the cavity, so the fine cavity is etched using a dry process. It is very difficult to form by etching.

As described above, the conventional cavity manufacturing method has many problems with respect to reproducibility, dimensional accuracy, ease, etc.

An object of the present invention is to provide a novel cavity manufacturing method devised to solve these problems.

<Means and effects for solving the problems> In order to achieve the above object, the method for producing a microcavity chamber of the present invention includes forming a pattern of a sublimable or thermally decomposable material by patterning it in a specific shape on a substrate. a step of forming a patterned film, a step of covering the patterned film with a heat-resistant substance, a step of forming a pore in the substrate that reaches the patterned film,
The method is configured to include a step of removing the patterned film made of the above-mentioned sublimable or thermally decomposable substance through the pores by heating the patterned film.

That is, the present invention uses a material that sublimates or decomposes when heated as a material provided in a portion that will become a cavity, and utilizes the fact that this material is evaporated and removed through pores when heated. This is to create a. As the sublimable or decomposable substance, naphthalene, aluminum, ammonium formate, iodine, polyα-methylstyrene, etc. are preferably used.

<Example> Hereinafter, a case where polyα-methylstyrene is used as an example of the present invention will be described with reference to the drawings.

FIGS. 1a to 1d are diagrams each showing a process for forming microcavities on a field effect transistor (EET) using polyα-methylstyrene.

First, a spacer is placed on the silicon substrate 1.
An insulating film 2 such as SiO ₂ or Si ₃ N ₄ is formed, and the insulating film on the gate region of the EET is etched (Fig. 1a). Next, a methyl solve acetate film of polyα-methylstyrene is deposited on the silicon wafer 1. By spin-coating a solution, forming a film, and flattening and etching the polyα-methylstyrene, the structure shown in FIG.
The polyα-methylstyrene 3 is surrounded by an insulating film 2 as a spacer, and the thickness of the polyα-methylstyrene 3 and the insulating film 2 are equal to each other, as shown in FIG.
Furthermore, after forming an aluminum, nickel, or SiO ₂ film (diaphragm) 4 on these films, the silicon 1 is etched on the back side of the silicon wafer 1 to form a thin film that reaches the edge of the patterned polyα-methylstyrene 3. A hole 5 is provided (Fig. 1c),
Finally, by heating at a temperature of 150° C. or higher in vacuum, the polyα-methylstyrene 3 shown in FIG. Figure 1 d). In addition, in FIGS. 1a to 1d, 7 is a source region and 8 is a drain region.

When a cavity is fabricated using polyα-methylstyrene, as shown in Figure 1d, the pores can be placed at the end of the cavity, and conventional wet etching as shown in Figure 3 can be used. As a result, fine cavities can be created without the pores being located in the center, unlike when creating cavities.

Next, the fact that a cavity can be easily produced even when the shape of the cavity is complicated will be explained using a second embodiment shown in FIGS. 2a to 2d.

Figure 2a shows polyα-methylstyrene as a substrate 1.
After laminating a heat-resistant film 14 such as an Al film or a Ni film on the patterned polyα-methylstyrene 12 and 13, the two cavities are formed in series. A pore 15 is formed in the substrate 11 by etching, reaching only the back surface of the cavity on one side of the part (Fig. 2b), and then vacuum heating is performed at a temperature of 150°C or higher. The polyα-methylstyrene 12 is decomposed and removed, forming a cavity 18 (FIG. 2c),
When vacuum heating is further performed, the other polyα-methylstyrene 13 in the continuous cavity is also decomposed and removed, forming two continuous cavities 18 and 19 (FIG. 2d).

In this way, even when the cavity shape is complicated, if the cavity has one pore 17 communicating with the outside, the cavity shape can be formed by heating.

In these Examples, polyα-methylstyrene used was a polymer with a degree of polymerization of about 360;
- The degree of polymerization of methylstyrene is preferably in the range of about 50 to about 5000. If the degree of polymerization is too low, the softening point of polyα-methylstyrene will be low, resulting in poor pattern accuracy during pattern formation, and if the degree of polymerization is too high, the viscosity of the solution will become too large, making coating difficult.

<Effects of the Invention> As described above, the method of forming fine cavities using a substance that is sublimated or decomposed and removed by heating according to the present invention can easily form cavities without using wet etching. Furthermore, it is possible to form cavities ranging from simple to complex shapes, and is very effective when producing devices using cavities, especially pressure sensors and the like.

[Brief explanation of the drawing]

1a to d each illustrate a process for producing a cavity using polyα-methylstyrene as an embodiment of the present invention, and FIGS. 2a to d each illustrate another embodiment of the present invention. FIG. 3, which is a diagram illustrating an example manufacturing process, is a diagram showing a schematic cross section of a cavity manufactured by a conventional method. 1...Silicon substrate, 2...Insulating film (spacer), 3...Patterned polyα-methylstyrene,
4... Coating membrane (diaphragm), 5... Pore, 6
... formed cavity, 11 ... substrate, 12, 13
...Patterned polyα-methylstyrene, 14...
...Coating membrane (diaphragm), 17... Pore, 18
...First cavity, 19...Second cavity.

Claims (1)

[Scope of Claims] 1. A step of forming a patterned film of a sublimable or thermally decomposable substance by patterning it into a specific shape on a substrate; a step of covering the patterned film with a heat-resistant material; forming pores in the substrate that reach the patterned film; and removing the patterned film through the pores by heating the patterned film made of the sublimable or thermally decomposable substance. A method for producing a microscopic cavity characterized by: 2 The above sublimable or thermally decomposable substance has a polymerization degree of 50
5,000 to 5,000.