Apparatus and method for dry etching

The present invention relates to an apparatus and a method for dry etching and more particularly to a dry etching apparatus equipped with an electrode structure having a convex-shaped surface as well as a dry etching method which makes use of the apparatus.

There have recently been required for the development of high precision techniques for processing materials such as quartz crystals, quartz and glass substances when producing, for instance, a subminiature quartz crystal oscillator such as a tuning fork-type quartz crystal oscillator and a thickness-shear mode quartz crystal resonator, an electrode, an element for optical applications, a surface acoustic wave device (an SAW device), a micro-sensor, and a micro-actuator and accordingly, it has gradually been difficult for the existing processing techniques, which have been conducted under wet conditions, to satisfy the foregoing requirements for the further precise processing.

For this reason, it would be considered to be effective to use the processing methods which make use of the dry etching technique, but such dry etching technique may suffer from such a problem that materials each having a high thermal expansion coefficient such as quartz crystal, quartz and glass materials are liable to undergo heat deformation due to the action of temperatures used in the dry etching processes. In some cases, the object to be processed would sometimes undergo cracking during the etching procedures due to such heat deformation of the object and thermal shocks acting on the same.

However, there has not yet been proposed any satisfactory technique for the solution of such a problem that an object to be processed undergoes cracking during the etching procedures due to such heat deformation and thermal shocks, possibly encountered when subjecting, to dry etching procedures, the object to be processed, which has a high thermal expansion coefficient.

For instance, a method has been known, in which a quartz crystal oscillator is produced according to the photo-lithography techniques and the chemical etching technique (see, for instance, Patent Document 1 specified below), but this method cannot always solve the foregoing problem.

Patent Document 1: Japanese Un-Examined Patent Publication Hei 5-315881 (see the section entitled “What is claimed is”).

It is an object of the present invention to solve the problems associated with the conventional dry etching techniques and more particularly to provide an apparatus and a method for dry etching, which can solve such a problem that an object to be processed undergoes cracking during the etching procedures due to the heat deformation thereof and thermal shocks acting on the same, possibly encountered when subjecting, to dry etching procedures, the object to be processed, which has a high thermal expansion coefficient.

The dry etching apparatus according to the present invention is characterized in that it is provided with an electrode structure having a convex-shaped surface. The use of such an electrode structure would permit the solution of the problem such that the object to be processed undergoes cracking during its dry etching because of the heat deformation thereof and thermal shocks acting thereon during the same.

The convex shape of the electrode structure used herein is characterized in that it means one concentric with the cross section of the structure and the height thereof falls within the range of from 0.2 to 1.0 mm. In this respect, if the height of the convex shape as measured from the bottom face thereof is less than 0.2 mm, there is observed a difference in temperature between the central and peripheral portions on the object to be processed during the etching procedures of the same or the temperature distribution on the surface thereof (i.e. the in-plane temperature distribution) becomes non-uniform and this in turn results in the heat deformation and cracking of the object. On the other hand, if the height of the convex shape as measured from the bottom face thereof is greater than 1.0 mm, the object may sometimes be cracked upon the chucking thereof to an electrode structure.

The dry etching apparatus according to the present invention has the following construction: a plasma-generation section is positioned within and at the upper portion of a vacuum chamber and a substrate electrode section is positioned within and at the bottom portion of the vacuum chamber; a high-frequency antenna coil for generating plasma, which is connected to a first high-frequency power source, is attached to the outside of the side wall of the plasma-generation section, which is constituted by a dielectric material; an electrode structure, to which a high-frequency bias electric power is applied through a second high-frequency power source, is fitted to the substrate electrode section; a counter (or opposite) electrode is arranged within the plasma-generation section in such a manner that it is opposed to the electrode structure; the counter or opposite electrode is a float electrode which is so designed that it is air-tightly fixed, through an insulator, preferably to an upper flange of the side wall of the plasma-generation section and that it is in a potentially floating state; and a magnetic field-establishing coil is positioned on the outside of the high-frequency antenna coil, and the dry etching apparatus is characterized in that the electrode structure has a convex-shaped surface. The convex shape of the electrode structure used herein is characterized in that it means one concentric with the cross section of the electrode structure and the height thereof falls within the range of from 0.2 to 1.0 mm. If the height of the convex shape is beyond the range specified above, the problems described above would arise.

Alternatively, the dry etching apparatus according to the present invention has the following construction: a plasma-generation section is positioned within and at the upper portion of a vacuum chamber and a substrate electrode section is positioned within and at the bottom portion of the vacuum chamber; a high-frequency antenna coil for generating plasma, which is connected to a first high-frequency power source, is attached to the outside of the side wall of the plasma-generation section, which is constituted by a dielectric material; an electrode structure, to which a high-frequency bias electric power is applied through a second high-frequency power source, is fitted to the substrate electrode section; a counter (or opposite) electrode is arranged within the plasma-generation section in such a manner that it is opposed to the electrode structure; the counter or opposite electrode is a float electrode which is so designed that it is air-tightly fixed, through an insulator, preferably to an upper flange of the side wall of the plasma-generation section and that it is in a potentially floating state; a magnetic field-establishing coil is positioned on the outside of the high-frequency antenna coil; and a variable condenser, which can serve as a branching device, is arranged in the course of an electric power supply path positioned between the antenna coil and the first high-frequency power source so as to ensure the connection of the first high-frequency power source with the counter electrode; and the dry etching apparatus is characterized in that the electrode structure has a convex-shaped surface. The convex shape of the electrode structure used herein is characterized in that it means one concentric with the cross section of the electrode structure and the height thereof falls within the range of from 0.2 to 1.0 mm. If the height of the convex shape is beyond the range specified above, the problems described above would arise.

The dry etching method according to the present invention comprises the step of subjecting, to dry-etching, an object to be processed, which is made of a material having a thermal expansion coefficient of not less than 30×10⁻⁷/° C. using the dry etching apparatus discussed above. There was not observed any cracking of the processed article thus obtained due to the heat deformation thereof and thermal shocks acting on the same, possibly encountered when an object to be processed is subjected to dry etching. The object to be processed is one made of, for instance, a quartz, quartz crystal or glass material.

According to the present invention, the surface shape of an electrode structure to be incorporated into a dry etching apparatus is so designed that it has a convex shape and accordingly, the present invention permits the solution of such a problem that an object to be processed undergoes cracking during its dry etching because of the heat deformation thereof and thermal shocks acting on the same, possibly encountered when subjecting an object to be processed having a high thermal expansion coefficient to a dry etching step.

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Components for use in a plasma chamber having reduced particle generation and method of making
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Etching a substrate: processes

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