JPH07207468A - Etching device and etching method - Google Patents

Abstract

PURPOSE:To execute etching with stable low-temp. plasma under a middle pressure without being affected by the insulation characteristic/resistance value of a substrate and to improve etching efficiency by grounding the surface of a work piece to prevent electrification. CONSTITUTION:Gas consisting essentially of a rare gas added with a halogen element is introduced into a discharge space 15 between a central conductor 11 constituted to a concentrical cylindrical shape and an outside conductor 12. High-frequency energy is then impressed thereto to form the plasma under a pressure of 5 to 150Torr. A conductive film is deposited and formed on a part of the surface of the substrate 1 and is grounded as an electrode thin film 18 at the time of etching the surface of the substrate 1 which is the work piece by using this plasma. As a result, the etching treatment stable over a wide range is executed and the substrate 1 is treated without exposing the substrate to a high temp.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention uses a plasma generator capable of stably discharging at a medium pressure of 5 to 150 Torr and capable of obtaining discharge plasma at low temperature.
The present invention relates to a method of performing stable etching regardless of the insulating property / resistance value of a substrate in the etching performed without heating the substrate.

[0002]

2. Description of the Related Art Atmospheric pressure is an insulator at low electric fields,
When a high electric field such as direct current, alternating current, or impulse is applied, dielectric breakdown occurs and current starts to flow (self-sustaining discharge). Self-sustaining discharge is divided into corona discharge, glow discharge, and arc discharge. In the case of a uniform electric field, when it goes to self-sustaining discharge, all the roads are destroyed immediately, and it goes to glow discharge or arc discharge.
In the case of an unequal electric field, first, only local parts where the electric field is strong are dielectrically broken down, and corona discharge occurs. After that, if the electric field is further increased, the road will be destroyed. In general, in atmospheric pressure air, when the whole road is destroyed, the arc discharge is often made rapidly without passing through glow discharge. This is because arc discharge is characterized by thermionic emission (existence of cathode luminescent spots) due to electrode heating caused by incident ions, but at high pressure the number of ions incident on the electrode is higher than at low pressure, so it is extremely It is considered that the electrode is heated in a short time and thermions are emitted. It is known that glow discharge occurs when the current is 2 A or less, but the controllability is not good.
Arc discharge is generally used for applications such as welding and cutting.

Arc discharge utilizes the high electrode temperature and the positive column temperature (gas temperature) to melt the workpiece,
It is used for fusing. In the processing method using arc discharge, the temperature of the portion to be processed is usually as high as 2000 to 6000K, and the workpiece cannot be processed at a low temperature (for example, room temperature).

Therefore, in order to enable substrate processing and processing at room temperature, an attempt has been made to generate a low temperature plasma by causing a stable discharge at atmospheric pressure (SK).
anazawa et.al. J.Phys.D: Appl.Phys.21 (1988) 838-84
0). To generate stable low-temperature plasma at atmospheric pressure 1. Fill the discharge space with He 2. Insert an insulator between electrodes (in the discharge path) 3. At least one electrode It is known as a necessary condition that the frequency of the applied electric field is 3 kHz or higher. The insulator is inserted between the electrodes so that the discharge does not shift to arc discharge, and the applied electric field frequency of 3 kHz or more is for passing a current through the insulator.The electrode shape is needle-like or brush-like. The reason is that the electric field is made non-uniform to facilitate the initiation of discharge.

The plasma obtained by the above method is 1
It has a temperature below 00 degrees. It has also been attempted to etch the surface of an organic substance such as polyimide or an inorganic substance such as silicon by using this atmospheric pressure low temperature plasma. However, although these methods are carried out at atmospheric pressure, they have been complicated in that they have to undergo a step of once depressurizing the reaction space to a vacuum and then filling it with a gas such as helium. Further, the processing of the substrate is performed uniformly on the substrate, and there is a drawback that it is not possible to selectively process a minute area. Further, since the region where plasma is generated is limited to a very small region, it is difficult to use plasma in a large area.

Further, since the plasma at atmospheric pressure has a high probability of collision between particles due to the atmospheric pressure (that is, the mean free path is short), the probability of electron-ion recombination in space also becomes high. As a result, the plasma does not spread spatially and disappears rapidly as the potential gradient decreases, and the number of radicals reaching the substrate becomes extremely small. To prevent this, the substrate should be brought as close as possible to the discharge region. However, in the vicinity of the discharge region, radical density greatly changes with a slight change in distance, which causes another problem that controllability is significantly deteriorated. Will occur.

Further, the above-mentioned conventional etching method using glow discharge at atmospheric pressure has a problem that the work piece is charged when the work piece is an insulator. Since the electric charge that reaches the workpiece is mainly electrons, if the workpiece is charged, the electrons will not reach the workpiece. As a result, the number of radicals that reach the object to be processed along with the electrons is reduced, so that the etching efficiency is reduced.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to solve various problems in glow discharge at atmospheric pressure, and to enable efficient etching even if the work piece is an insulator.

[0009]

In the present invention, the reaction pressure is set to 5
The first feature is that the pressure is set to 150 Torr. Further, in order to release the charge on the surface of the work piece, an electrode is provided on the whole or a part of the surface of the work piece, and by setting this electrode to the ground potential, electrons from the plasma are sequentially released to the outside. It is characterized in that etching is performed by plasma while maintaining the initial condition without being charged.

Further, in the present invention, by using a gas containing a rare gas containing a halogen element as a main component,
It is characterized in that stable discharge is generated at normal pressure and etching is performed without exposing the workpiece to high temperature. Helium, argon, neon, krypton, or xenon can be used as the rare gas.

Further, the present invention is characterized in that a conductive film is provided on the surface of the workpiece to prevent the charging phenomenon of the workpiece and enhance the etching efficiency.

FIG. 1 shows a conceptual diagram of the etching apparatus of the present invention. In FIG. 1, a central conductor (11) which is an inner electrode
A cylindrical insulator (13) is arranged between the outer conductor (12) and the outer conductor (12), and the center conductor (11) and the outer conductor (1)
2) and are used as electrodes, and an AC electric field is applied to them as electromagnetic energy from the AC power supply (14). A gas containing helium as a main component is supplied to the discharge space (15) in a cylinder (1
It is supplied from 7) through the flow controller (16) in a flow state. Although only one cylinder is shown, it goes without saying that a gas supply system is provided as necessary to add a halogen element to helium. The substrate (1) to be etched is a paramagnetic substrate holder (2).
Held in.

The substrate (1) is placed on the substrate holder (2). An electrode thin film (18) serving as a ground electrode is deposited on the surface of the substrate (1). This electrode thin film (1
As the material of 8), a conductive material, preferably a highly conductive material such as gold, platinum or graphite, is vapor-deposited and used. The electrode thin film (18) is made of gold or platinum when etching is performed by adding a halogen element to helium.
It is desirable to prevent 8) from being easily etched. Since gold, platinum, or the like is a metal that is difficult to be etched by a halogen-based element, the surface of the insulating substrate to be etched must not be completely covered. Therefore, the electrode thin film (18) is preferably deposited on the edge portion of the substrate. This electrode thin film (18)
It is not necessary to use a metal vapor-deposited thin film, and a paste-like or adhesive tape-like highly conductive material (for example, a paste such as graphite or gold, an adhesive conductive tape such as graphite or copper) may be applied to the edge portion of the substrate. A method of using a coating on the center may be used.

Further, the electrode thin film (18) can obtain a certain effect only by disposing it on a part of the substrate.
This is because the electric charge on the surface of the workpiece can be released to some extent by the presence of the conductive material on the surface of the workpiece.

Since the central conductor (11) is directly exposed to plasma, metals such as tungsten and tantalum which are strong against spatter are effective. In addition, helium-based gas is fluorine,
When a gas containing a halogen element having a strong etching action such as chlorine is added, since gold, platinum and the like are metals that are difficult to be etched by the halogen element as described above, the central conductor (11) is composed of gold, platinum and the like. Or coat the surface. It is desirable that the outer diameter of the central conductor (11) and the inner diameter of the outer conductor (12) satisfy the following equation.

[0016]

[Equation 1]

This consists of a central conductor (11) and an outer conductor (1
Conditions where the electric field between 2) becomes unequal (corona generation condition)
Is a condition that makes it easy to start discharge. The above conditions are only desirable conditions, and even if the ratio of the above equation is smaller than 3 and is close to 1, (actually, the cylindrical insulation is provided between the center conductor (11) and the outer conductor (12)). Since the body (13) is inserted, it does not become 1), but since the discharge can cause the glow discharge without passing through the corona discharge, the present invention is not particularly limited by this condition.

The cylindrical insulator (13) is provided so that the discharge does not transfer to an arc discharge between the electrodes, and its material is an inorganic substance such as quartz glass or alumina.
Organic substances such as Teflon, polyimide, polyethylene, and polyethylene terephthalate can be used. Since there is a possibility that the temperature will rise to some extent when exposed to electric discharge, quartz glass, alumina, etc., which have high heat resistance, are effective. Further, the larger the dielectric constant of the insulator is, the higher the voltage applied to the gap between the central conductor and the insulator is, so that the discharge is more easily started. Therefore, alumina and soda glass are effective. The thickness of the cylindrical insulator depends on the relative permittivity of the insulator, and if the gap between the center conductor and the insulator is too large, it exceeds the practical output voltage of the AC power supply. Appropriate. That is, the gap between the insulator and the center electrode is 50 mm or less, preferably 10 mm.
It is desirable that it is less than or equal to mm.

The lower limit of the frequency of the AC power supply is determined by the capacitive susceptance generated by the insulator inserted in the discharge path. That is, the capacitance C per unit length is expressed by the series combined capacitance of the gap capacitance Cg between the center conductor and the insulator and the insulator capacitance Ci, and

[0020]

[Equation 2]

[0021] However, the center conductor radius is a, the insulator inner diameter is b, the outer electrode inner diameter is c, and the dielectric constant of the insulator is ε,
Let εo be the dielectric constant of a vacuum. The electric field applied between the concentric cylindrical electrodes is divided by the ratio of Cg and Ci. It has been confirmed by experiments that the discharge is stable if the susceptance value ωC due to the insulator is 10 ⁻⁶ [S] or more.

It is necessary that the rare gas-containing gas supplied to the discharge space (15) contains 70% or more of the rare gas. Ne, Ar, Kr, Xe as rare gas
Can be used. Gases of halogen compounds necessary for etching include CF ₄ , CCl ₄ , and N.
F ₃ or the like can be used. There is an experimental fact that when CF ₄ is used as the additive gas, no discharge occurs when the CF ₄ concentration is 4% or more. However, if the CF ₄ concentration is 0.5% or less, almost no etching can be performed. A carbon film can be formed by adding a hydrocarbon gas such as CH ₄ or C ₂ H ₄ . Furthermore, a silicon film can be formed by using SiH ₄ or the like.

As described above, the reaction gas is mixed with the rare gas and introduced into the discharge space. In addition, the long life of the metastable excited atoms of the rare gas is utilized to cause radicals of the rare gas to flow into the substrate. There is also a method in which radicals of a halogen compound are generated by transporting to a region such as a surface where a reaction is desired, and supplying a halogen-based reaction gas as an etching gas to the region through an external nozzle or the like. In this case, ions do not reach the region to be reacted and only radicals can be supplied, so that no current flows in the reaction target. Therefore, a living body can be selected as the reaction target. That is, it is possible to scrape the teeth and nails by radicals of the etching gas supplied as needed.

The plasma generator of the present invention can control the reaching distance of radicals by controlling the flow rate of the supply gas. If the flow rate of the supply gas is increased, the flow velocity is increased in proportion to the flow rate, and the reaching distance of the radicals is lengthened.

The object to be etched, that is, the object to be processed may be not only the substrate outside the discharge region but also the electrode itself in the discharge space. It can also be used to form needles with very sharp tips.

[0026]

By setting the reaction pressure to a medium pressure of 5 to 150 Torr, plasma treatment can be performed over a wider range compared to atmospheric pressure discharge, and practical application can be achieved with an even simpler vacuum exhaust device. . Further, by providing the ground electrode on the surface of the workpiece, the charge on the surface of the workpiece can be released, and even if the workpiece is an insulator, it is possible to avoid a decrease in etching efficiency due to charging.

[0027]

【Example】

Example 1 FIG. 2 shows a sectional view of the plasma generator of the present invention. The coaxial cylindrical electrode is composed of a central conductor (11), a cylindrical insulator (13), and an outer conductor (29). Although not clear in the figure, the cylindrical insulator (13) is
It is installed close to 9). In this example, the central conductor (11) was made of stainless steel, the cylindrical insulator (13) was made of quartz glass, and the outer conductor (29) was made of stainless steel. The center conductor (11) is connected to the MHV coaxial connector (21),
An AC electric field is applied from an AC power source via a coaxial cable (not shown) connected to the V coaxial plug (21), and electromagnetic energy is supplied between the center conductor (11) and the outer conductor (29). . The central conductor (11) and the cylindrical insulator (1
The gas containing helium (helium is used as a rare gas in this embodiment) as a main component supplied during 3) is supplied from the gas inlet port (20) and is made of a Teflon insulator (22).
It flows through between (27). Teflon insulator (2
2) (27) also has a role of preventing discharge in unnecessary places. The cases (23) (28) are tightening jigs (25) (2
It is fixed by 6). The housings (23) and (28) and the fastening jigs (25) and (26) are made of stainless steel and are kept at the ground potential together with the outer conductor (29).

The introduced gas containing helium as a main component is sealed by an O-ring (24) so as not to leak from the gaps between the components. In addition, a gap between the cylindrical insulator (13) and the outer conductor (29) is filled with a conductive metal foil (not shown).

As the work piece (1), the (100) plane of a P type Si substrate was used. This board (1) has a resistance of 0.01 Ωcm, 0.4 Ωcm, 10 Ωcm, 50 Ωcm, 100 Ωcm
Each of these was prepared, and the difference in etching efficiency due to the difference in electrical resistance of the workpiece was investigated. The substrate holder (2) was made of Pyrex glass (thickness 1.1 mm).

A gold thin film having a width of about 2 mm was vapor-deposited on the end of the substrate (1) on the side of the etching surface to form an electrode thin film (1
8). A schematic diagram around the electrode thin film is shown in FIG. FIG. 3 shows a state in which a grounded electrode thin film (18) is formed on the periphery of the substrate (1) to be etched and the surface to be etched is irradiated with a plasma beam. Since the electrode thin film (18) is provided, it is possible to prevent the substrate (1), which is the workpiece, from being charged by the electrons that reach the substrate (1) according to the plasma beam.

The electrode thin film (18) is made up of casings (23) (2
8) and tightening jigs (25) (26), outer conductor (2)
With 9) it is kept at ground potential. In this embodiment,
The electrode thin film (18) was maintained at the installation potential by electrically connecting it to the outer conductor (29) through the contact terminal in contact with the electrode thin film (18). Further, it is possible to provide the electrode thin film (18) without being used as a ground electrode and electrically connected to any place, but the same effect as when it is grounded cannot be obtained.

The distance between the substrate (1) and the central conductor (11) is 2
mm. The diameter of the central conductor is 5 mm, the outer diameter of the insulator is 12 mm, and the thickness of the insulator is 1 mm.

Helium was added to the above apparatus at 99.5 sccm.
And CF ₄ are supplied at 0.5 sccm and the pressure in the plasma generation region is 100 Torr, a stable discharge is obtained when 500 W of high frequency power of 13.56 MHz is applied and this discharge is performed for 10 minutes. Held
In this state, the Si substrate having various resistances described above was etched for 10 minutes. As a result, it was confirmed that constant etching was obtained regardless of the resistance of the substrate. When the temperature of the plasma was measured with a thermocouple, it was about 100 degrees. From this, the temperature of the surface of the workpiece is estimated to be 100 degrees or less.

Comparative Example In this comparative example, in order to confirm the effect of installing the ground electrode on a part of the surface of the workpiece, the electrode thin film (18) in Example 1 was not provided,
The experimental results when the same etching as in Example 1 is performed will be described.

In this comparative example, a plasma generator,
The etching conditions are the same as in Example 1 except that the electrode thin film (18) is not present. Regarding the etching depth with respect to the resistance value of the substrate in this comparative example, the etching rate tended to decrease rapidly as the resistance value of the substrate increased. That is, it was confirmed that the etching ability of the substrate was greatly influenced by the resistance value of the substrate.

From the results of this comparative example, the electrode thin film (18)
It is concluded that the etching efficiency with respect to the work piece having a large electric resistance is extremely reduced if the step is not provided. At the same time, from the results of Example 1, when the electrode thin film (18) is provided and the surface of the workpiece (Si substrate (1) in this case) is at ground potential, regardless of the electrical resistance of the workpiece,
It became clear that etching was possible. From this, it has been clarified that the insulating material can be efficiently etched.

[Embodiment 2] This embodiment shows an example in which etching is attempted when an electrode thin film is provided on the surface of a ceramic substrate. In this example, an alumina substrate having a purity of 99.5% was used as the substrate material to be processed. The method for installing the electrode thin film is the same as that in the first embodiment. The alumina substrate was etched under the same experimental conditions as in Example 1. As a result, it was confirmed that etching is possible by removing the charging phenomenon by installing the electrode thin film. As a result of this example, it was clarified that various plasma insulators shown in FIG. 2 used in Example 1 can be used for etching various insulators.

[0038]

As described above, when the grounded electrode is provided on the surface of the work piece, it is stabilized by using the plasma generator at the pressure of 5 to 150 Torr regardless of the electric resistance value of the target material. An etching effect can be obtained. Then, etching can be efficiently performed by an apparatus that does not require a large-scale vacuum exhaust apparatus.

[Brief description of drawings]

FIG. 1 shows a schematic view of a plasma generator of the present invention.

FIG. 2 shows an embodiment of the plasma generator of the present invention.

FIG. 3 is a schematic view of the vicinity of an electrode thin film in the device of the example.

[Explanation of symbols]

 1 Substrate 2 Substrate Holder 11 Center Conductor 12 Outer Conductor 13 Cylindrical Insulator 14 High Frequency Power Supply 15 Discharge Space 16 Flow Controller 17 Cylinder 18 Electrode Thin Film 20 Gas Inlet 21 MHV Coaxial Plug 22 Teflon Insulator 23 Insulator 24 O Ring 25 Tightening jig 26 Tightening jig 27 Teflon insulator 28 Case 29 Outer conductor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kenji Ito 398 Hase, Atsugi, Kanagawa Prefecture Semiconductor Conductor Energy Laboratory Co., Ltd.

Claims (4)

[Claims] 1. An outer electrode and an inner electrode each having a concentric cylindrical shape, and a cylindrical insulator inserted in a gap between the outer electrode and the inner electrode to generate plasma at a pressure of 5 to 150 Torr. 1. An etching apparatus for performing plasma etching according to claim 1, wherein the surface of the workpiece is grounded so that the surface of the workpiece to be etched has a ground potential. 2. A surface of an object to be processed is etched by applying electromagnetic energy to a gas containing a rare gas to which a halogen element is added, which is held at a pressure of 5 to 150 Torrno, as a main component to form plasma, and using the plasma. An etching method, characterized in that a ground electrode is provided on the surface of the workpiece in order to maintain the surface of the workpiece at a ground potential. 3. The etching method according to claim 2, wherein the ground electrode is formed by depositing a conductive thin film on a part of the surface of the workpiece. 4. A plasma is formed by applying electromagnetic energy to a gas containing a noble gas to which a halogen element is added, which is held at a pressure of 5 to 150 Torr, as a main component, and the plasma is used. An etching method for etching, characterized in that a conductive film is formed on a part of the surface of the object to be etched in order to release electric charges charged on the surface of the object to be processed.