JP3768854B2 - Plasma jet generator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The invention of this application relates to a plasma jet generator. More specifically, the invention of this application is such that high-density plasma is jetted out from a thin nozzle in a jet shape, and the material of the workpiece is not selected, and processing such as fusing, etching, thin film deposition, etc. on the local portion of the workpiece is performed. The present invention relates to a plasma jet generator that performs processing at high speed.
[0002]
[Prior art and its problems]
Conventionally, a plasma jet has been useful for processing and surface treatment such as fusing, etching, thin film deposition, etc. on a workpiece, and is also used in various other fields such as high-temperature treatment of harmful substances. .
[0003]
With respect to such a plasma jet, at present, a method using a DC arc discharge is well known for generating a fine plasma jet having a diameter of 2 mm or less. However, the method using direct-current arc discharge has various problems such as that the electrode is easily deteriorated, the reactive gas cannot be used, and the substrate is limited to a conductor. In addition, the electrodeless high-frequency inductively coupled thermal plasma generator known as another plasma generator is known to have a large aperture and require high power input. Since it is difficult to control a large amount of heat generated as a result of input, there has been no device that can irradiate a small area with plasma.
[0004]
Accordingly, the invention of this application has been made in view of the circumstances as described above, solves the problems of the prior art, and ejects high-density plasma in a jet form from a thin nozzle, thereby local regions of the workpiece. It is an object of the present invention to provide a new plasma jet generator capable of performing processing such as fusing, etching, thin film deposition, and surface treatment at high speed.
[0005]
[Means for Solving the Problems]
In order to solve the above-described problems, the invention of this application firstly includes a discharge tube, a solenoid antenna wound around a part of the discharge tube in the length direction, and the solenoid antenna. A high-frequency inductively coupled plasma jet generator equipped with a power supply for generating power for generating plasma, having a nozzle having a smaller inner diameter than the discharge tube at the end of the plasma output side of the discharge tube Provided is an electrodeless plasma jet generator characterized in that the inner diameter of the tube is 5 mm or less and is capable of discharging, and is driven by using a 30 to 300 MHz high frequency power source in the VHF band as the power source. To do.
[0006]
2ndly, the plasma jet generator of 1st invention WHEREIN: The minimum of the internal diameter of a discharge tube is 1.0 mm, The plasma jet generator characterized by the above-mentioned is provided.
[0007]
Third, in the plasma jet generator of the first or second invention, the inner diameter of the nozzle is 2 mm or less, and fourth, the plasma jet of any one of the first to third inventions In the generator, there is provided a plasma jet generator characterized in that the lower limit of the inner diameter of the nozzle is 0.4 mm .
[0008]
In addition, the fifth, the plasma jet generator of the first to fourth any one of the discharge tube to provide a plasma jet generator, characterized in that it consists of a quartz tube.
[0009]
According to a sixth aspect of the present invention, there is provided the plasma jet generator according to any one of the first to fifth aspects, wherein the nozzle is made of ceramics.
[0010]
Moreover, the seventh, the plasma jet generator of any of the first to sixth, the plasma jet and the reactive gas by irradiating the local region of a workpiece, etching, processing such as film deposition, surface Provided is a plasma jet generator characterized in that processing is performed .
[0011]
Eighth , the plasma jet generator according to any one of the first to sixth inventions is characterized in that it is operated at atmospheric pressure.
[0012]
More ninth, the plasma jet generator of any of the first to sixth, jet generator apparatus characterized by having an auxiliary high-voltage power supply for applying a high electric field in the vicinity of the antenna at the discharge starting I will provide a.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
The plasma jet generator of the invention of this application is a high-frequency inductively coupled plasma generator composed of a discharge tube, an antenna disposed near the discharge tube, and a power supply thereof, and is connected to one end of the discharge tube from the discharge tube. Also has a nozzle with a small inner diameter, the discharge tube is reduced to an inner diameter of 5 mm or less, and the nozzle inner diameter is set to 2 mm or less, thereby reducing the volume of plasma generated and reducing the power required for plasma generation. be able to. The ratio d / D between the inner diameter d of the nozzle and the inner diameter D of the discharge tube is in the range of 1 to 1/100.
[0014]
In the plasma generation in the narrow discharge tube as described above, the loss of electrons on the discharge tube wall becomes a problem. Therefore, the VHF band (30−30), which is an optimum frequency region in order to increase the efficiency of capturing electrons in an alternating electric field. By applying a high frequency of 300 MHz to the antenna, plasma generation with low power is possible. At this time, a solenoid antenna can be used as the antenna.
[0015]
As a result, the total amount of heat generated can be suppressed, and an electrodeless high frequency inductively coupled plasma jet generator capable of jetting high density plasma in the form of a jet from the tip of a thin nozzle can be realized.
[0016]
Further, in the plasma jet generator of the present invention, the discharge tube and made of a quartz tube, the small nozzle inner diameter than the discharge tube, which compared with the quartz consists of strong alumina or silicon nitride arsenide ceramic thermal By doing so, the nozzle can be used for a long time.
[0017]
Note that energy loss is suppressed when the distance between the tip of the nozzle and the center of the discharge tube is short, but it is possible to operate even when the distance is long (about 15 cm).
[0018]
Furthermore, the plasma jet generator according to the present invention can perform processing such as etching and film deposition, and surface treatment by irradiating a plasma jet and a reactive gas to a local portion of the workpiece. That is, since the reactive gas can be used, various effects can be obtained such as the processing accuracy can be increased and the processing speed can be increased in processing the workpiece by the action of the reactive gas.
[0019]
Furthermore, since the plasma jet generator of the present invention can be operated at atmospheric pressure, it can be operated without a vacuum exhaust device.
[0020]
It is also possible to add an auxiliary high-voltage power supply for applying a high electric field near the antenna at the start of discharge to the plasma jet generator. As the auxiliary high-voltage power source, for example, a kind of high-voltage pulse power source called a commercially available Tesla coil is operated near the antenna, and a pulse discharge current is allowed to flow in the vicinity of the antenna, thereby triggering the discharge.
[0021]
Embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Of course, the present invention is not limited to the following examples, and it goes without saying that various aspects are possible in detail.
[0022]
【Example】
<Example 1>
First, a miniaturized high-frequency inductively coupled plasma jet generator (1) as shown in FIG. 1 was prototyped. A discharge tube (2) made of a quartz tube with an outer diameter of 3 mm and an inner diameter of 1.5 mm is wound with 3 turns of a copper tube with an outer diameter of 2.5 mm that can be cooled by passing cooling water (3) through the inside, and a solenoid antenna ( 4). Argon gas (5) is introduced from one end of the discharge tube (2), opened to atmospheric pressure via a nozzle (6) disposed at the other end of the discharge tube (2), and 100 MHz from the VHF power source (9). When a high frequency in the VHF band was applied to the solenoid antenna (4) via the matching circuit (7), a plasma jet (8) extending in a frame shape could be generated.
[0023]
Next, in order to investigate the influence of the length and shape of the discharge tube (2) and the nozzle (6) on the plasma jet (8), the electron density and the excitation temperature were measured using emission spectroscopy.
[0024]
When the power of the VHF power source (9) is in the range of 5-500 W and the flow rate of the argon gas (5) is in the range of 0.2-15 liters / minute, the argon plasma jet (8) can be generated. When the power and gas flow rate were increased, the plasma jet length increased to a maximum of 15 mm.
[0025]
The electric power of the VHF power source (9) was kept constant at 200 W, and the spatial distribution of electron density was measured by changing the gas flow rate. The result is shown in FIG.
[0026]
As shown in the graph of FIG. 2, the electron density was 10 ¹⁵ cm ⁻³ or more at a gas flow rate of 6-10 liters / minute immediately below the solenoid antenna (4) (X = 7 mm). When the gas flow rate was increased, heat conduction to the wall was suppressed and the density was increased, and it was confirmed that the high-density portion directly under the solenoid antenna (4) spreads in the downstream area. The electron density of the jet portion of X = 25 mm is about half of that directly below the solenoid antenna (4) (X = 7 mm). Subsequent plasma measurement was performed at a position of X = 25 mm unless otherwise specified.
[0027]
Next, the effect of the pinch nozzle for reducing the diameter of the plasma jet (8) was examined. The graph in FIG. 3 shows the change in electron density according to the gas flow rate when (A) no nozzle and (B) nozzle are shown in the inset of FIG. In either case, the electron density tends to increase as the gas flow rate increases, and when the nozzle (6) is narrowed to an inner diameter of 0.2 mm, the flow velocity further increases, so the electron density increased rapidly. In addition to the effect of the flow velocity, in the case where there is a nozzle, it is considered that the electron density increases because the energy density increases because the volume of the plasma is reduced in the nozzle (6). Further, when the power dependence of the electron density was examined, as shown in FIG. 4, when the gas flow rate was kept constant at 2 liters / minute, the electrons with (B) nozzle were compared with those with (A) no nozzle. The density doubled, and a density as high as 10 ¹⁵ cm ⁻³ was obtained at about 300 W.
[0028]
Further, when the power dependence of the excitation temperature was examined, as shown in FIG. 5, the case with (B) nozzle was higher than the case with (A) no nozzle, and was 5000-6000K. This value is consistent with the relationship between the electron density and temperature of the argon plasma predicted from the Saha equation.
[0029]
When the apparatus is operated for a long time, the nozzle formed by thinly stretching the quartz tube is easily softened by heat. Therefore, it is more practical to use ceramics such as alumina or silicon nitride for the nozzle. Actually, a high-density, highly stable plasma jet can be generated for a long time by using a ceramic nozzle having a length of 20 mm and an inner diameter of 0.4 mmφ.
[0030]
The photograph of the example which applied this apparatus to the high precision plasma fusing is shown in FIG. As shown in FIG. 6 (A), a 30 μm thick stainless steel thin plate (10) was irradiated with an argon plasma jet (8) for 5 seconds at a power of 50 W, and an opening diameter of 0.4 mmφ was shown in FIG. 6 (B). A circular hole (11) could be processed. Moreover, the stainless steel thin plate (10) was able to be cut | disconnected by moving the stainless steel thin plate (10) which is a workpiece under a plasma jet (8) to a horizontal direction.
<Example 2>
FIG. 7 shows an experimental apparatus that was prototyped for irradiating a workpiece with a plasma jet in a reactive gas atmosphere. The plasma jet generator (1) includes a three-turn solenoid antenna (4) for supplying VHF power, a discharge tube (2) composed of a quartz tube having an outer diameter of 3.0 mm and an inner diameter of 1.0 mm, and an inner diameter disposed at the end thereof. A fine plasma jet (8) is ejected into a SUS container (12) which is composed of a 0.4 mm ceramic nozzle (6) and is provided immediately below the plasma jet generator (1). The substrate stage (13) immediately below the plasma jet (8) is movable in a horizontal plane. The inside of the container (12) is at atmospheric pressure, and the fact that it can operate without a vacuum exhaust device is a great advantage in practice.
[0031]
A fine plasma jet (8) was generated at a power of 250 W from a VHF power source (9) and an argon gas (5) flow rate of 9 liters / min to the discharge tube, and irradiated onto the silicon substrate (14) for 3 minutes. FIG. 8 shows the results of observation using a laser microscope of the difference in the processing shape depending on whether or not a small amount of SF ₆ was added at 2 cc / min.
[0032]
As shown in FIG. 8A, when only argon gas is used, physical etching occurs due to evaporation, so that the processed surface is very rough and the processing depth is 10 μm or less. On the other hand, as shown in FIG. 8B, when SF _{6 is} added, the processed surface is smooth due to the effect of chemical etching, and isotropically deep with a diameter of 0.5 mm substantially equal to the diameter of the plasma jet (8). A concave shape with a thickness of 30 μm was obtained. The etching rate of silicon increased with the amount of SF ₆ added. Further, when a substrate bias of 13.56 MHz is applied to the silicon substrate (14) and ions in the plasma are accelerated and irradiated onto the silicon substrate (14), the etching rate increases, and a processing depth of 1 mm or more per minute is obtained. Obtained.
[0033]
When a gas that is a raw material for thin film deposition such as methane gas is introduced instead of a gas that causes an etching reaction such as SF _6, the thin film deposition is performed only on the local area where the plasma jet (8) is irradiated onto the silicon substrate (14). Happened. Also, by moving the silicon substrate (14) under the plasma jet (8) while performing etching or thin film deposition, a two-dimensional or three-dimensional arbitrary shape can be directly processed on the silicon substrate (14). It was.
[0034]
FIG. 9 shows an experimental apparatus in which an auxiliary high-voltage power supply is added to the experimental apparatus shown in FIG. In FIG. 9, the high voltage pulse power supply (16) is operated near the solenoid antenna (4), and a pulse discharge current is caused to flow near the solenoid antenna (4), thereby triggering discharge. FIG. 9 is a diagram provided with a high-frequency power source (15) and a matching circuit (7) for accelerating and irradiating ions in plasma to the substrate stage (13).
[0035]
【The invention's effect】
As described above, according to the invention of this application, it is possible to generate a fine high-density plasma jet by low-power high-frequency discharge, and unlike the case of direct current discharge, the material of the workpiece such as metal, ceramics, plastic, etc. It is possible to provide a practical plasma jet generator for performing precision processing such as high-speed dry etching and film formation on a local part.
[Brief description of the drawings]
FIG. 1 is a schematic view of a high-frequency inductively coupled fine plasma jet generator according to the present invention.
FIG. 2 is a result of measuring a spatial distribution of electron density in the plasma jet generator of the present invention.
FIG. 3 is a diagram showing a structure with and without a nozzle in the plasma jet generator of the present invention, and a graph showing the gas flow rate dependence of electron density.
FIG. 4 is a graph showing the power dependence of the electron density when there is no nozzle and when there is a nozzle in the plasma jet generator of the present invention.
FIG. 5 is a graph showing the power dependence of the excitation temperature when there is no nozzle and when there is a nozzle in the plasma jet generator of the present invention.
FIG. 6 is a photograph showing an example in which the plasma jet generator of the present invention is applied to high-precision plasma fusing.
FIG. 7 is an experimental apparatus that was prototyped to irradiate a workpiece with a plasma jet in a reactive gas atmosphere.
FIG. 8 is a laser microscope image of the surface of a silicon substrate irradiated with a plasma jet when SF _{6 is} added.
9 is an experimental apparatus obtained by adding a high-voltage pulse power supply to the experimental apparatus of FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Plasma jet generator 2 Discharge tube 3 Cooling water 4 Solenoid antenna 5 Argon gas 6 Nozzle 7 Matching circuit 8 Plasma jet 9 VHF power source 10 Stainless steel thin plate 11 Circular hole 12 Container 13 Substrate stage 14 Silicon substrate 15 High frequency power source 16 High voltage pulse power source

Claims (9)

A high-frequency inductively coupled plasma jet comprising a discharge tube, a solenoid antenna wound around a part of the discharge tube in the length direction, and a power source for supplying electric power for generating plasma in the solenoid antenna The generator has a nozzle having a smaller inner diameter than the discharge tube at the end of the discharge tube on the plasma output side, and has a size capable of discharging when the inner diameter of the discharge tube is 5 mm or less. An electrodeless plasma jet generator, which is driven by using a high frequency power source in the VHF band of ˜300 MHz . 2. The plasma jet generator according to claim 1, wherein the lower limit of the inner diameter of the discharge tube is 1.0 mm . 3. The plasma jet generator according to claim 1, wherein an inner diameter of the nozzle is 2 mm or less . The plasma jet generator according to any one of claims 1 to 3, wherein the lower limit of the inner diameter of the nozzle is 0.4 mm . 5. The plasma jet generator according to claim 1, wherein the discharge tube comprises a quartz tube . 6. The plasma jet generator according to claim 1, wherein the nozzle is made of ceramics . In any of the plasma jet generator of claims 1 to 6, the plasma jet and the reactive gas by irradiating the local region of the workpiece, and no to perform etching, processing such as film deposition, surface treatment A plasma jet generator characterized by that. In any of the plasma jet generator of claims 1 to 6, the plasma jet generator being characterized in that none to operate at atmospheric pressure. 7. The plasma jet generator according to claim 1, further comprising an auxiliary high-voltage power supply for applying a high electric field in the vicinity of the antenna at the start of discharge.

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