JP3577601B2 - Atmospheric pressure glow discharge plasma treatment method - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to an atmospheric pressure glow discharge plasma processing method, and more particularly to an atmospheric pressure glow discharge plasma processing method for forming a uniform processing layer or thin film on the surface of a substance to be processed by the atmospheric pressure glow discharge processing.
[0002]
[Prior art]
Plasma excitation is performed at atmospheric pressure to form a hydrophilic treatment layer on the surface of the substance, or plasma is excited at atmospheric pressure by adding a small amount of reactive organic vapor to radical polymerization on the surface of the substance. A processing method for forming a thin film by such a method is already known, for example, as described in Japanese Patent Publication No. 3-236425 or Japanese Patent Publication No. 4-74525.
[0003]
In each of these methods, the air in a container in which a solid dielectric is disposed on at least one of the parallel electrodes is replaced with an inert gas such as helium gas or a mixed gas of argon gas and helium gas. Then, a high-frequency high voltage is applied between the parallel electrodes to generate a glow discharge to excite the plasma. FIG. 1 shows an example of an apparatus for performing this processing method.
[0004]
In FIG. 1, an upper electrode 2 and a lower electrode 6 are arranged in a vessel 1 having a gas inlet 3 and a gas outlet 4 so as to face each other in parallel. The surfaces of these electrodes are covered with a dielectric 5 and one of the electrodes is heated by a heating power supply. Using such a device, an inert gas or an inert gas mixed with a trace amount of a reactive gas is introduced from the gas inlet 3, while the air in the container is discharged from the gas outlet 4 and the inside of the container is discharged. Under an inert gas atmosphere, a glow discharge is performed by applying a high frequency voltage between both electrodes. The surface of the substance located between the two electrodes is plasma-treated by the glow discharge.
[0005]
If the plasma treatment is performed in a state where the inside of the container is an inert gas, the surface of the substance located between the parallel electrodes is cleaned, that is, ashing is performed, and the hydrophilicity of the surface is significantly improved, and the contact angle is reduced.
In addition, when a reactive gas or a liquid at room temperature or an organic substance that is sublimable at room temperature is mixed with an inert gas, radical reaction or radical polymerization is caused by the energy of plasma, and a thin film is formed on the surface of the material.
[0006]
These methods are extremely economical because no high vacuum is required. However, since the frequency is usually 1KHz to 100KHz and the voltage is 1000V to 6000V as a high frequency high voltage, creeping discharge occurs on the surface of the dielectric, and the tip is easier to discharge. And the energy of the excited plasma also tends to change. In the case of hydrophilization, this problem causes uneven contact angles on the surface of the substance to be treated and appears as uneven leakage. In the case of forming a thin film, it appears as uneven thickness of the thin film. A processed film cannot be obtained.
In particular, such a phenomenon is not preferable for an electronic material for forming a thin film on the surface of a silicon wafer since a coating as uniform as possible is required.
[0007]
[Problems to be solved by the invention]
As a result of the inventor's efforts to remedy this drawback, when applying a high-frequency high voltage, by alternately applying a reverse voltage direct current and a high-frequency for a certain period of time, the present inventors have made a remarkable improvement compared to the conventional high-frequency high voltage alone. It has been found that the discharge is made uniform, the surface of the material is not hydrophilized at all, and the formation of a thin film is made uniform in thickness, and the present invention has been completed. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a glow-discharge plasma processing method in which unevenness of plasma processing which is apt to occur due to the intensity of glow discharge due to electric discharge or tip discharge is solved, and a method of applying a high-frequency voltage is improved.
[0008]
[Means for Solving the Problems]
The gist of the present invention is to provide a plasma reactor having an electrode in which a solid dielectric is disposed on the surface of at least one of the opposed parallel electrodes, an inert gas in the reactor, or an inert gas. Atmospheric pressure at which a reactive gas is introduced, a voltage is applied between the electrodes to excite the atmospheric pressure glow-discharge plasma, and the surface of the substance to be treated positioned between the opposing electrodes is hydrophilized or a thin film is formed. In the glow discharge plasma processing method, a glow discharge is generated by alternately applying a high frequency voltage and a DC reverse voltage to a high voltage side as a voltage for generating the glow discharge, thereby generating a glow discharge. This is a plasma processing method.
[0009]
Hereinafter, the present invention will be described in more detail.
The processing conditions of the processing method for hydrophilizing the surface of the substance to be treated or forming a thin film by the atmospheric pressure glow discharge in the present invention, or the substance to be treated and the like do not differ from the conventional treatment method. However, the present invention is characterized in that a high frequency voltage and a DC reverse voltage are alternately applied as a method of applying a voltage for generating an atmospheric pressure glow discharge.
FIGS. 2 and 3 show an example of a basic circuit of this voltage application method. That is, a high-frequency power source exchanges a direct current into an alternating current (high frequency) by an inverter, boosts a voltage by a transformer to obtain a high voltage (FIG. 2), rectifies the obtained voltage, and supplies a negative voltage bias power source. It is made (FIG. 3) and supplied to the high voltage side electrode instantaneously through a switching circuit such as a flip-flop during the glow discharge process. By alternately performing this operation, the process is continued without stopping the discharge. The bias voltage may be generated by another power supply.
[0010]
When the processing time is 30 seconds, the normal high voltage is repeated for 5 seconds and the negative DC voltage is repeated for 1 second five times to perform the processing for 30 seconds.
The application time of the negative voltage is 0.1 to 5 seconds, preferably 0.5 to 2 seconds. If the time is shorter than 0.1 second, the effect is small, and if it is longer than 5 seconds, the discharge becomes unstable.
Next, the present invention will be described more specifically with reference to Examples and Comparative Examples.
[0011]
[Examples and Comparative Examples]
Comparative Example 1
The surface of the fluororesin Teflon was treated for hydrophilicity using the plasma processing apparatus shown in FIG.
As the Teflon, FEP which is the least wet was used. When one drop of water is dropped on the surface of this material, when it is untreated, the contact angle is 103 degrees and almost close to a polka dot.
The electrode used was a stainless steel 80 mm diameter with a mica plate having a diameter of 100 mm and a thickness of 0.2 mm as a dielectric. In this example, the same dielectric was attached to both surfaces of the parallel electrode. An FEP film having a size of 100 mm × 100 mm and a thickness of 0.1 mm was placed on the lower electrode, and the air in the processing apparatus was replaced with a mixed gas of 40 parts of helium and 60 parts of argon. In this state, a high frequency voltage of 5 kHz and 4000 V was applied between the parallel electrodes. The gap between the electrodes is 8 mm. It is generated by a blue-violet glow discharge and is energized as it is for 20 seconds after being excited by plasma, and then taken out and measured for a contact angle of the surface. As shown in FIG. 4A, the contact angle is in a range of 30 ° to 50 °. There was some unevenness.
[0012]
Example 1
The same mixture gas was used in the same apparatus as in Comparative Example 1, but the applied voltage was 5 KHz, 4000 V high-frequency voltage for 4 seconds, followed by 4000 V DC negative voltage for 1 second, and repeated for 20 seconds. And plasma treatment was performed. When a direct current was applied without any change in the generation of glow discharge, blue-violet light was felt slightly weak.
Then, the FEP film obtained by the treatment was taken out and the contact angle was measured in the same manner. As shown in FIG. 4B, it was well understood that the FEP film was in the range of 30 ° to 35 ° and extremely averaged. .
[0013]
Example 2
Using a device similar to that shown in Comparative Example 1, a silicon wafer having a diameter of 60 mm was positioned on the lower electrode, and the temperature of the lower electrode was raised to 200 ° C. to heat the silicon wafer to the same temperature. Helium gas was used as an inert gas, and a small amount of methane gas as a reactive gas was mixed. The mixing ratio is 93 parts of helium and 7 parts of methane. The air in the container was replaced with the above mixed gas, and when completely replaced, a high frequency voltage of 5 KHz and 2500 V was applied between the electrodes. A beautiful purple-red glow discharge is generated and plasma is excited. The energization was continued for 5 minutes to form a thin film on the surface of the wafer. After 5 minutes, the wafer was taken out with tweezers and illuminated on the surface of the wafer. The formed thin film emitted an interference color and appeared rainbow-colored. The thin part of the film is blue, the thick part is red, and the intermediate thickness is green, which looks like concentric circles, indicating that the film is not uniform.
The voltage application method was changed in exactly the same manner, and a high frequency voltage of 5 KHz and 2500 V was applied for 10 seconds, followed by a negative voltage of DC 2500 V for 1 second, and the applied voltage was repeated for 5 minutes. Observation of the surface revealed that the interference color was almost yellow-red, not iridescent, and that a very uniform thin film was formed.
[0014]
Example 3
A 50 mm square, 0.5 mm thick glass plate was placed on the lower electrode using the same device as in Comparative Example 1, and 99 parts of argon gas was used as an inert gas to cause a glow discharge. 6 ppm of acetone and 1 part of CF ₄ as a reactive gas were mixed, and the air in the container was replaced with the mixed gas.
When the replacement was completed, a high frequency voltage of 8 kHz and 3500 V was applied. A beautiful yellow-pink glow discharge is generated to excite the plasma. Electricity was supplied for 2 minutes. After the treatment, the glass plate was taken out and its contact angle was measured.
Next, in exactly the same manner, a high frequency voltage of 8 kHz and 2500 V was applied for 8 seconds, and a negative voltage of 2500 V DC was applied for 2 minutes with a repetition of 2 seconds. No change was observed in the glow discharge. After the treatment, the glass plate was taken out and the contact angle was measured, and the treatment was substantially uniform at 50 to 55 degrees with little unevenness.
[0015]
【The invention's effect】
As described above, in the present invention, the high-frequency voltage and the DC reverse voltage are alternately applied to the high voltage side to generate a glow discharge. In the case where a uniform hydrophilic processing layer is formed and a thin film is formed without causing uneven contact angles and in the presence of a reactive gas and an inert gas, a uniform processing film is formed, for example, silicon. This is particularly effective when a uniform film is formed on the surface of a wafer, for example.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of an apparatus for performing plasma processing by atmospheric pressure glow discharge.
FIG. 2 is a circuit diagram showing an example of high voltage generation in the present invention.
FIG. 3 is a circuit diagram showing an example of an applied voltage according to the present invention.
FIG. 4 shows the measurement results of the contact angle of the surface obtained by Comparative Example 1 and Example 1.
A is Comparative Example 1 and B is Example 1.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Container 5 Dielectric 2 Upper electrode 6 Lower electrode 3 Gas inlet 7 Heating power supply 4 Gas outlet

Claims (2)

An inert gas, or an inert gas and a reactive gas, are introduced into a plasma reactor having an electrode in which a solid dielectric is provided on the surface of at least one of the opposed parallel electrodes. In the atmospheric pressure glow discharge plasma processing method of applying a voltage between the electrodes to excite the atmospheric pressure glow discharge plasma and hydrophilizing the surface of the substance to be treated positioned between the opposed electrodes, or forming a thin film, As the glow discharge generating voltage, a high frequency voltage and a DC reverse voltage of the same voltage obtained by rectifying the current of the high frequency voltage are alternately applied to a high voltage side electrode to generate a glow discharge. Atmospheric pressure glow discharge plasma processing method. 2. The atmospheric pressure glow discharge plasma processing method according to claim 1, wherein the application time of the DC reverse voltage is 0.1 seconds to 5 seconds.

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