JP4746804B2 - Plasma generation method and plasma generation apparatus - Google Patents

Description

【００３３】
図４は、Ｈブリッジスイッチング回路７の等価回路を示す。図３に示すように、第２の半導体スイッチング素子ＳＷ２をＯＦＦにするときの時間幅は、第１の半導体スイッチング素子ＳＷ１をＯＮにするときの時間幅よりも前後に長く、また第３の半導体スイッチング素子ＳＷ３をＯＦＦにするときの時間幅は、第４の半導体スイッチング素子ＳＷ４をＯＮにするときの時間幅よりも前後に長くする。
【００３４】
図４において、まず、ＳＷ１がＯＦＦになってからＳＷ１がＯＮになると、Ｉ１の方向に電流が流れ、負荷が正に充電される。次に、ＳＷ１がＯＦＦになってからＳＷ２がＯＮになると、ＳＷ２とＤ３を通ってＩ２の方向に電流が流れるので、負荷のリーケージインダクタンス及び浮遊容量分がＳＷ２とＤ３で強制的にリセットされる。
【００３５】
この後、ＳＷ３がＯＦＦになってからＳＷ４がＯＮになると、Ｉ３の方向に電流が流れ、負荷が負に充電される。次に、ＳＷ３がＯＦＦになってからＳＷ４がＯＮになると、Ｉ４の方向に電流が流れ、負荷のリーケージインダクタンス及び浮遊容量分がＳＷ２とＤ３で強制的にリセットされる。
【００３６】
このような動作を表１に従って説明すると、次のとおりである。
▲１▼では、ＳＷ２とＳＷ３はゲート信号を入力されてＯＮとなり、負荷の両端はショートされた状態となる。
【００３７】
▲２▼では、ＳＷ２のゲート信号がＯＮされ、少し遅れてＳＷ１にゲート信号が入力されてこれがＯＮになると、ＳＷ３はＯＦＦのままであるため、ＳＷ１から負荷を通ってＩ１方向に電流が流れ、負荷を正に充電する。
【００３８】
▲３▼では、ＳＷ１へのゲート信号入力が終わってこれがＯＦＦとなってから、ＳＷ２へ再びゲート信号が入力されてこれが再びＯＮになるので、負荷に充電された電荷分は、ＳＷ２とＤ３を通ってディスチャージする。その結果、▲１▼と同じ状態に戻ることになる。
【００３９】
▲４▼では、ＳＷ３がＯＦＦとなり、少し遅れてＳＷ４にゲート信号が入力されてこれがＯＮになると、ＳＷ２はＯＮのままであるため、ＳＷ４から負荷を通ってＩ３方向に電流が流れ、負荷を負に充電する。
【００４０】
▲５▼では、ＳＷ４へのゲート信号入力が終わってこれがＯＦＦとなってから、ＳＷ３へ再びゲート信号が入力されてこれが再びＯＮになるので、負荷に充電された電荷分は、ＳＷ３とＤ２を通ってディスチャージする。その結果、▲３▼と同じ状態に戻ることになる。
【００４１】
このようにＳＷ１とＳＷ２との組、ＳＷ３とＳＷ４の組がそれぞれ同時にＯＮにならないように、デッドタイムを与えて▲１▼〜▲５▼と順番にスイッチングすることにより、入力信号（ゲート信号）に比例した波形の出力信号（ある時間間隔をおいた正負一対のパルス）が得られる。その場合、負荷側の浮遊容量及びリーケージインダクタンスは、上記のようなスイッチング動作によってリセットされるので、歪みの無い出力波形が得られる。
【００４２】
上記のようなスイッチング動作をするＨブリッジスイッチング回路７の出力は、図２において、第１と第２の半導体スイッチング素子ＳＷ１・ＳＷ２の中点を一方の極、第３と第４の半導体スイッチング素子ＳＷ３・ＳＷ４の中点を他方の極として取り出され、コンデンサＣを介して高圧トランス３の一次側に印加される。
【００４３】
次に、ゲートドライブ回路１１を制御してＨブリッジスイッチング回路７から正負一対のパルスを繰り返し出力させるとともに、その周期及びパルス幅を調整する前段の回路について、図５のタイミングチャートを参照して説明する。
【００４４】
電圧制御発振器（ＶＣＯ）１２は、図５（１）に示すような矩形波を繰り返し出力する。その繰り返し周波数は繰り返し周波数設定器１３にて調整できる。
【００４５】
第１のワンショットマルチバイブレータ１４は、図５（２）に示すように、電圧制御発振器１２の出力（ＶＣ０出力）の立ち上がりで立ち上がるパルスを出力する。そのパルス幅は第１のパルス幅設定器１５にて調整できる。
【００４６】
遅延回路１６は、図５（３）に示すように、第１のワンショットマルチバイブレータ１４のパルスの立ち下がりにより立ち上がる一定時間幅（デッドタイム）のパルスを出力する。
【００４７】
第２のワンショットマルチバイブレータ１７は、図５（４）に示すように、遅延回路１６の出力の立ち上がりで立ち上がるパルスを出力する。そのパルス幅は第２のパルス幅設定器１８にて調整できる。
【００４８】
第１のワンショットマルチバイブレータ１４からのパルスは第１のＡＮＤゲート１９、第２のワンショットマルチバイブレータ１７からのパルスは第２のＡＮＤゲート２０にそれぞれ入力される。これらＡＮＤゲート１９・２０には、起動スイッチ２１にてオン・オフされる起動・停止回路２２からの出力が入力されており、それがオンになっているときに、第１・第２のワンショットマルチバイブレータ１４・１７のパルスが、第３・第４のＡＮＤゲート２３・２４にそれぞれ入力される。
【００４９】
第３のＡＮＤゲート２３の出力は、第１の遅延用ＡＮＤ回路２５及び第１の遅延用ＮＡＮＤ回路２６へ入力され、第４のＡＮＤゲート２４の出力は、第２の遅延用ＡＮＤ回路２７及び第２の遅延用ＮＡＮＤ回路２８へ入力される。図５の（５）、（６）、（７）、（８）にこれらＡＮＤ回路２５、ＮＡＮＤ回路２６、ＡＮＤ回路２７、ＮＡＮＤ回路２８の出力波形を示し、その出力に従い、ゲートドライブ回路１１がＨブリッジスイッチング回路７の４個の半導体スイッチング素子ＳＷ１・ＳＷ２・ＳＷ３・ＳＷ４のためのゲートパルスを出力して、これらが前述のようにスイッチングする。
【００５０】
従って、図５（９）に示すように、Ｈブリッジスイッチング回路７から、ある時間間隔をおいた正負一対のパルスがある繰り返し周波数で正負のパルス波として出力されることになる。その繰り返し周波数は繰り返し周波数設定器１３にて調整でき、またパルス幅は、パルス幅設定器１５・１８にて正負それぞれ調整できる。
【００５１】
この正負のパルス波は、コンデンサＣを介して高圧トランス３の一次側に印加され、高圧トランス３が持つＬＣ成分により、共振した減衰振動波が間欠的に繰り返す高圧の減衰振動波形周期波となる。高圧トランス３の二次側は、接地から浮かしてあるので、一対の電極１・２にそれぞれ印加される高圧の電圧は、図５（１０）、（１１）に示すように、高圧トランス３の二次側の中点に対して正負が完全に逆位相となる。これら図５（１０）、（１１）に示す波形は、電極１・２間が放電しない状態での波形である。パルス幅設定器１５・１８にてパルス幅を調整することにより、高圧トランス３のＬＣ成分にマッチングする共振条件にすることができる。
【００５２】
電極１・２間でアーク放電が開始して、図５（１４）に示すように放電電流が流れると、その放電電流の最大波高値又はその付近で共振ズレが生じ、電極１・２間に印加される以降の減衰振動波が相殺して消滅するため、アーク放電は瞬時に中断する。その際の電極１・２にそれぞれ印加される電圧波形を図５（１２）、（１３）にそれぞれ示す。
【００５３】
上記のように、電極１・２には、共振した減衰振動波が間欠的に繰り返す逆位相の高圧の減衰振動波形周期波が印加されるが、その印加と休止を次のように間欠的に行えるようにもなっており、次にはその動作について図６のタイミングチャートを参照して説明する。
【００５４】
バースト波発振器２９は、図６（２）に示すように、電圧制御発振器１２による同図（１）に示すような繰り返し周波数よりもはるかに低い周波数の矩形波を出力し、それが連続・間欠動作切替スイッチ３０をオンにしたときに、ＮＡＮＤゲート３１を介して第３及び第４のＡＮＤゲート２３・２４に入力される。例えば、前者の繰り返し周波数を１００ＫＨｚとすると、後者の周期は１ＫＨｚで、バースト波発振器２９の出力がＨＩＧＨのときに、図６（３）、（４）に示すように、第３及び第４のＡＮＤゲート２３・２４から繰り返し周波数に応じた前述のようなパルスが出力される。そして、その間だけＨブリッジスイッチング回路７から正負のパルス波が図６（５）のように出力され、図６（６）、（７）のように一対の電極１・２に、共振した減衰振動波が間欠的に繰り返す逆位相の高圧の減衰振動波形周期波が印加され、アーク放電開始直後に図６（８）のように急峻に上昇する放電電流が流れることにより、共振ズレが生じてアーク放電が瞬時に中断する。このような動作が電圧制御発振器１２による繰り返し周波数で繰り返され、またその周期よりはるかに低い周期で運転・休止が反復される。
【００５５】
一対の電極１・２間に送風するファン５は、商用周波数で動作するシーケンス回路３２により駆動される。
【００５６】
次に、本発明者らが行った本発明の実験例について説明する。
基材に対する濡れ性の改善テストを行い、濡れ性を接触角計（エルマ製Ｇ−１／２ＭＧ型）で測定した。印加電圧の測定は、ソニーテクトロニクス製高電圧プローブＰ−６０１５型、電流の測定にはヒアソン製４１００型を用いた。基材としてはＰＥＴフィルム、金属の場合は銅、アルミニウム、ステンレスを用いた。
【００５７】
［実験例１］
電極１・２間の距離を１３ｍｍとし、処理する基材６としてＰＥＴフィルムを使って濡れ性改善を行った。送風するガスは空気を用いた。表２は、繰り返し周波数を変化させたときの接触角のデータで、２０ＫＨｚ以上で改質され、３５〜４０ＫＨｚで改質が飽和している。処理時間は３０ＫＨｚ以上で改質し、時間を１秒かけても改質は良くならず飽和していることが判る。表３は、周波数を２０ＫＨｚに固定し、出力を上げインバータであるＨブリッジスイッチング回路７の電力に対する接触角のデータで、電力を上げれば良くなることが判った。表４は、周波数を２０ＫＨｚに固定、電力を４９７Ｗに固定のもとで、プラズマ中に基材を照射する距離を変えたときのデータ、つまり電極から基材までの距離（処理距離）に対する接触角のデータで、２０ｍｍのときが一番良い結果となっている。
【００５８】
【表２】

【００５９】
【表３】

【００６０】
【表４】

【００６１】
［実験例２］
電極間距離を４ｍｍとし、ＰＥＴフィルムに対して濡れ性改善を行った。送風するガスは空気を用いた。表５は、繰り返し周波数を変化させたときの接触角のデータで、２０ＫＨｚ以上で改善され、３５〜４０ＫＨｚで改質が飽和している。実験例１の表と比較すると、実験例２の電極の方が改質性能が良く、プラズマ照射電力密度が高い電極が効果的である。表６は、周波数を２０ＫＨｚに固定し、出力を段階的に上げた場合のインバータの電力に対する接触角のデータで、電力を上げれば良くなることが判った。
また、電極間の距離を４ｍｍとした場合、照射電力５００Ｗ印加が限度であったので、照射電力を上げるには電極間距離を広げることが必要となることが判る。
【００６２】
【表５】

【００６３】
【表６】

【００６４】
［実験例３］
同様の方法において、処理する金属として銅、アルミニウム、ステンレスを用い、電極間距離を５ｍｍと１０ｍｍにした場合の濡れ性データを表７に示す。
【００６５】
【表７】

【００６６】
［実験例４］
ＩＴＯ透明電極接続端子を端部に設けた液晶ディスプレイ用パネル（大きさ５０ｍｍ×３０ｍｍ）において、その電極接続端子を実験例１と同一条件で、空気を用いてプラズマ処理を行った。次いで、異方導電性フィルムを介してポリイミドフィルム（５０ミクロン厚）で構成される駆動回路を熱圧着した。この熱圧着の条件は、温度１７０℃、圧力３ＭＰａ、時間２０秒とした。そして、上記のよにして接合されたパネルと回路体とを互いに逆方向に引っ張って剥離強度を測定した結果、プラズマ処理を行わない場合に比べて約２倍の剥離強度が得られた。
【００６７】
以上の結果から、発振周波数は繰り返し周波数を高く（４０ＫＨｚ以上）すると、接触角は飽和し、プラスチック基材が熱によって溶けてしまう結果となり、最適繰り返し周波数は１０〜２０ＫＨｚが最も良いと言うことが判った。また、金属を改質するには、繰り返し周波数の持つ連続信号で行うと、金属の一部に集中してしまうので、バースト動作させる必要が有るということが判った。電極間距離に対しては、距離を離せばプラズマの広がりは大きく広がるが、処理するには１秒以上かかり、均一な処理ができにくいことが判った。電極間距離を狭くするとプラズマの広がりは狭くなるが、処理時間が短縮でき、０．１〜０．２秒間で即改質されることが判った。
【００６８】
【発明の効果】
以上詳述したように本発明によれば、連続使用しても電極が加熱されて高温プラズマになるようなことはなく、処理時間を短縮できるとともに、安定した低温プラズマにより処理品質を向上させることができ、また異常放電により被処理物にダメージを与えることもなく、更にプラズマ発生の制御が容易であるのに加え装置規模も小さくできる。
【図面の簡単な説明】
【図１】本発明のプラズマ発生装置によるプラズマ処理例を示す図である。
【図２】本発明のプラズマ発生装置の一例のブロック図である。
【図３】同プラズマ発生装置中のＨブリッジスイッチング回路の等価回路図である。
【図４】同回路のスイッチング動作のタイミングチャートである。
【図５】図２の回路の動作を示すタイミングチャートである。
【図６】同じくバースト動作のタイミングチャートである。
【符号の説明】
１・２ 電極
３ 高圧トランス
４ プラズマ
５ ファン
６ 基材
７ Ｈブリッジスイッチング回路（インバータ）
ＳＷ１、ＳＷ２、ＳＷ３、ＳＷ４ 半導体スイッチング素子
Ｄ１、Ｄ２、Ｄ３、Ｄ４ ダイオード
Ｃ コンデンサ
８ 整流回路
９ 直流安定化電源回路
１０ 出力設定器
１１ ゲートドライブ回路
１２ 電圧制御発振器（ＶＣ０）
１３ 繰り返し周波数設定器
１４ ワンショットマルチバイブレータ
１５ パルス幅設定器
１６ 遅延回路
１７ ワンショットマルチバイブレータ
１８ パルス幅設定器
１９・２０ ＡＮＤゲート
２１ 起動スイッチ
２２ 起動・停止回路
２３・２４ ＡＮＤゲート
２５ 遅延用ＡＮＤ回路
２６ 遅延用ＮＡＮＤ回路
２７ 遅延用ＡＮＤ回路
２８ 遅延用ＮＡＮＤ回路
２９ バースト波発振器
３０ 連続・間欠動作切替スイッチ
３１ ＮＡＮＤゲート
３２ シーケンス回路[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a plasma generation method and a plasma generation apparatus capable of performing various treatments such as modification, cleaning, sterilization, disinfection, and cutting of an object to be processed under atmospheric pressure using plasma. More specifically, the present invention relates to a plasma generation method and a plasma generation apparatus in which a high voltage is applied between a pair of opposed electrodes to forcibly cause arc discharge, gas is supplied between these electrodes, and the discharge is expanded by the wind force. It is.
[0002]
[Prior art]
Conventionally, in this type of plasma generator used to modify a substrate, for example, to improve wettability, a commercial frequency voltage or a high frequency (about 30 KHz) voltage is boosted by a high voltage transformer, and the opposite electrodes It is carried out by applying simultaneously between them. However, even if the applied voltage is a commercial frequency or a high frequency, it is a sinusoidal continuous wave, and the voltage wave that rises after the discharge start voltage is continuously applied to the electrode as it is. Then, since the electrode is heated to become high-temperature plasma, it is used in intermittent operation (for example, ON / OFF using a low-frequency signal to perform burst operation), and the step-up transformer is used in a leakage manner. There is a disadvantage that the capacity of the resin becomes very large and heavy, and because it takes intermittent operation to take more than 1 second to improve the wettability of the base material. There was a limit.
[0003]
In addition, when processing a conductive or semiconductive material such as a metal or a semiconductor, abnormal discharge occurs toward the objects to be processed, causing damage to these objects to be processed.
[0004]
[Problems to be solved by the invention]
The present invention does not cause the electrode to be heated and become high-temperature plasma even if it is continuously used, and the processing time can be shortened, the processing quality can be improved by stable low-temperature plasma, and it can be covered by abnormal discharge. An object of the present invention is to provide a plasma generation method and a plasma generation apparatus that can easily control the generation of plasma without damaging a processed material and can reduce the scale of the apparatus.
[0005]
[Means for Solving the Problems]
The plasma generation method of the present invention is a method in which a high voltage is applied between a pair of opposed electrodes to forcibly cause arc discharge, and gas is supplied between these electrodes to expand the discharge by the wind force. A high voltage applied between a pair of electrodes is caused to resonate for each damped vibration wave as a damped vibration wave periodic wave that is generated repeatedly and repeatedly. Intermittent arc discharge is generated by interrupting the arc discharge.
[0006]
That is, in the present invention, the voltage applied between the pair of electrodes is not a sinusoidal continuous wave, but a damped vibration waveform by intermittent repetition of the damped vibration wave, and is resonated for each damped vibration wave. Then, for each damped vibration wave, the remainder of the damped vibration wave applied between the pair of electrodes is canceled by using the LC component or the like of the high-voltage transformer to generate a resonance shift with the occurrence of arc discharge ( The arc discharge is interrupted instantaneously by making a leakage). By repeating such an operation intermittently with the repetition period of the damped vibration wave, stable low-temperature plasma can be generated while suppressing heating of the electrode.
[0007]
As specific means, there are the following forms.
In the invention according to claim 2, the positive and negative phases of the high-voltage damped oscillation wave applied between the pair of electrodes are opposite in phase.
[0008]
That is, the high-voltage damped oscillatory wave applied between the pair of electrodes can be made independent of the ground-to-ground relationship by making one of the positive and negative phases out of phase without grounding one of them.
This is because when the base material is modified, when plasma is irradiated to the base material, it is irrelevant to the ground contact, so that current can flow between the electrodes without electric shock, and the base material can be modified. In addition, the reverse-phase voltage is applied at the same time as long as the potential difference between the electrodes is equal to or higher than the discharge start voltage. By floating the secondary side of the high-voltage transformer from the ground, the voltage applied between the pair of electrodes can be reversed in phase.
[0009]
In the invention according to claim 3, a pair of positive and negative pulses with a certain time interval is supplied to the primary side of the high-voltage transformer at a certain repetition frequency, and the damped vibration resonated for each damped vibration wave from the secondary side of the high-voltage transformer. A waveform periodic wave is output and applied between a pair of electrodes.
[0010]
When the voltage waveform applied between a pair of electrodes is an orderly continuous wave such as a sine wave, the applied voltage remains and discharge current continues after the start of discharge, as described above. It becomes plasma. Therefore, using the LC component of the high-voltage transformer, a pair of positive and negative pulses is made a damped oscillation wave that resonates on the primary side of the high-voltage transformer, and if a resonance shift occurs due to the occurrence of arc discharge on the secondary side, the resonance occurs. The damped oscillatory wave disappears instantly after the start of discharge. If this is performed for each damped vibration wave and is repeated intermittently without making it a continuous wave, stable low-temperature plasma can be generated.
[0011]
In the invention according to claim 4, the pulse width of the pair of positive and negative pulses is adjusted to vary the frequency of the damped vibration wave.
As described above, a pair of positive and negative pulses is set as a damped oscillation wave by the LC component of the high-voltage transformer. However, if there is no adjustment element, the resonance frequency cannot be adjusted to match the LC component of the high-voltage transformer. Therefore, by adjusting the pulse width of a pair of positive and negative pulses, a resonating damped oscillation wave is obtained.
[0012]
In the invention according to claim 5, the voltage rise time of each damped oscillating wave resonated is 1 μs or less.
In order to generate low-temperature plasma using arc discharge, as described above, low-temperature plasma cannot be obtained unless the applied voltage immediately after arc discharge is set to zero. In addition, when using a commercial frequency, since the rise time is slow, a strong electric field cannot be generated instantaneously, so that the plasma generation efficiency is poor and an excessive voltage must be applied. In order to clear this drawback, it is better to make the rise time as short as possible. However, in view of the switching characteristics of the semiconductor switching element for generating a pair of positive and negative pulses, the voltage rise time of the damped oscillatory wave should be 1 μs or less. Is preferred.
[0013]
In the invention which concerns on Claim 6, the repetition period of a damped vibration wave shall be 10-50 KHz.
The repetition frequency of the damped vibration wave varies depending on the material of the base material to be modified, but the repetition frequency is set to 10 to 50 KHz because the modification time can be shortened. 20 KHz.
[0014]
In the invention which concerns on Claim 7, the distance between a pair of electrodes shall be 1-15 mm.
When the distance between the electrodes is increased, the plasma irradiation range is elongated and widened, but it takes time for modification. However, since the irradiation range is widened, a large modification area of the substrate can be secured. On the other hand, when the distance between the electrodes is reduced, the plasma does not spread but concentrates in a narrow range. The advantage in this case is that the modification time of the substrate to be modified is shortened and the modification can be performed in a short time. Accordingly, the distance between the electrodes may be adjusted according to the conditions of the base material to be modified, but a range of 1 to 15 mm is practical.
[0015]
In the invention which concerns on Claim 8, a damped oscillatory wave is intermittently applied between a pair of electrodes with a frequency lower than the repetition frequency.
If the material to be reformed is metal, arc discharge concentrates on a part of the metal if it is performed only with damped vibration waves that occur repeatedly, but it cannot be reformed, but it is generated intermittently at a cycle lower than the repetition cycle. Thus, even if the metal is irradiated, the plasma can be irradiated uniformly.
[0016]
The plasma generator of the present invention applies a high voltage between a pair of opposing electrodes to forcibly cause arc discharge, and sends gas between these electrodes to expand the discharge by the wind force. A positive / negative pulse wave generation circuit that generates a pair of positive and negative pulses at a certain repetition frequency and a positive / negative pulse wave that is input to the primary side, and each damped oscillation wave has a positive / negative / inverse phase that resonates. A high-voltage transformer that outputs a damped vibration waveform periodic wave from the secondary side and applies it between a pair of electrodes, and for each damped vibration wave, causes a resonance shift with the occurrence of arc discharge and interrupts the arc discharge. Thus, intermittent arc discharge is obtained.
[0017]
Boosting using a commercial frequency as in the past with a high-frequency positive / negative pulse wave generation circuit using a switching circuit that switches at high speed with a narrow pulse width and a high-voltage transformer that can easily boost the voltage using the signal Therefore, it is not necessary to use a large leakage type high-voltage transformer, and it is possible to provide a plasma generation power source that is lightweight, small and highly efficient.
[0018]
As specific means, there are the following forms.
In the invention according to claim 10, the positive / negative pulse wave generation circuit includes four first to fourth circuits, wherein the first and fourth are upper arms, the second is a lower arm for the first, and the third is a lower arm for the fourth. These semiconductor switching elements are H-bridge connected, and positive and negative pulse waves are generated using an H-bridge switching circuit in which a diode is connected in parallel to each semiconductor switching element.
[0019]
Therefore, in the H-bridge switching circuit as the inverter unit, a switching operation without distortion is possible, and a narrow pulse width can be adjusted. Therefore, a damped oscillation wave having a rise time of 1 μs or less can be easily generated.
[0020]
In the invention according to claim 11, the positive / negative pulse wave generation circuit adjusts the pulse width of the gate pulse for the four semiconductor switching elements of the H bridge switching circuit to thereby output a positive / negative pair output from the H bridge switching circuit. There is provided pulse width setting means for adjusting the pulse width of these pulses to vary the frequency of the damped vibration wave.
[0021]
Therefore, it is possible to accurately adjust the resonance frequency to match the LC component of the high-voltage transformer and to instantly generate a resonance deviation immediately after the start of arc discharge.
[0022]
In the invention according to claim 12, the positive / negative pulse wave generation circuit adjusts the period of the gate pulse for the four semiconductor switching elements of the H bridge switching circuit to thereby output a pair of positive and negative signals output from the H bridge switching circuit. Repeating frequency setting means for adjusting the repetition frequency of the pulse to set the repetition frequency of the damped vibration wave is provided.
[0023]
Therefore, since the repetition frequency of the damped vibration wave can be easily adjusted, plasma processing suitable for the material of the base material to be modified can be performed.
[0024]
According to the thirteenth aspect of the present invention, the burst frequency is such that gate pulses for the four semiconductor switching elements of the H-bridge switching circuit are intermittently input to the gate drive circuit of the H-bridge switching circuit at a period lower than that frequency. Setting means is provided.
[0025]
Therefore, even if the material to be modified is a metal, uniform processing is possible.
[0026]
According to the present invention, low-temperature plasma treatment is possible, so surface modification of an object to be treated such as plastic, ceramic, metal, or glass (improves wettability and improves adhesiveness such as adhesives and inks). In addition, it can be widely applied to the cleaning of organic substances and dirt adhering to the surface, sterilization and disinfection, and cutting of plastic substrates.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described in detail with reference to the drawings.
[0028]
In the embodiment of the present invention, as shown in FIG. 1, a pair of J-shaped electrodes 1 and 2 face each other with their bent portions inside, and a circuit as shown in FIG. From the secondary side of the high-voltage transformer 3 in the final stage, a high voltage as will be described later is applied to forcibly arc discharge to generate plasma 4, and air is blown by the fan 5 between these electrodes 1 and 2. Then, the discharge is expanded by the wind force, that is, the plasma 4 is expanded while the electrodes 1 and 2 are cooled, and the substrate 6 that is the object to be processed is irradiated with the plasma 4 to modify the surface of the substrate 6.
[0029]
The gas to be fed is not particularly limited, but preferably, air, nitrogen, argon, helium, carbon dioxide alone or in combination is used. For example, a small amount of a reactive gas such as hydrogen, ammonia, nitrous oxide, or water vapor can be added. The addition amount is not particularly limited, but usually 0.1 volume% to 10 volume% is effective. The electrodes 1 and 2 may be made of a material that does not easily rust, such as tungsten, stainless steel, or brass.
[0030]
In the circuit shown in FIG. 2, an H-bridge switching circuit (inverter) 7 for generating positive and negative pulse waves applied to the primary side of the high-voltage transformer 3 will be described first. As shown in FIG. 2, the H-bridge switching circuit 7 includes first, second, third, and fourth semiconductor switching elements SW1, SW2, SW3, and SW4, SW1 and SW4 as upper arms, and SW2. Is a lower arm to SW1 and SW3 is a lower arm to SW4 (two semiconductor modules such as MOS-FETs are H bridges), and diodes D1, D2, D3 and D4 are connected to each semiconductor switching element. Each is connected in parallel. As a power source for the H bridge switching circuit 7, a DC power source using a rectifier circuit 8 that rectifies a commercial frequency voltage and a DC stabilized power source circuit 9 is used. The output voltage of the DC stabilized power supply circuit 9 can be adjusted by the output setter 10.
[0031]
The H bridge switching circuit 7 is turned on and off in five ON / OFF states (1), (2), (3), (4), and (5) shown in the following Table 1 by the gate drive circuit 11 and the preceding circuit. The switching operation is sequentially repeated in the combination mode. FIG. 3 shows the output from between the middle point of the first and second semiconductor switching elements SW1 and SW2 and the middle point of the third and fourth semiconductor switching elements SW3 and SW4 by such a switching operation. 5 is a timing chart of positive and negative alternating pulses.
[0032]
[Table 1]

[0033]
FIG. 4 shows an equivalent circuit of the H-bridge switching circuit 7. As shown in FIG. 3, the time width when turning OFF the second semiconductor switching element SW2 is longer than the time width when turning ON the first semiconductor switching element SW1, and the third semiconductor The time width when turning off the switching element SW3 is set to be longer than the time width when turning on the fourth semiconductor switching element SW4.
[0034]
In FIG. 4, first, when SW1 is turned on after SW1 is turned off, a current flows in the direction of I1, and the load is charged positively. Next, when SW2 is turned on after SW1 is turned off, a current flows in the direction I2 through SW2 and D3, so that the leakage inductance and stray capacitance of the load are forcibly reset by SW2 and D3. .
[0035]
Thereafter, when SW4 is turned on after SW3 is turned off, a current flows in the direction of I3, and the load is charged negatively. Next, when SW4 is turned on after SW3 is turned off, a current flows in the direction of I4, and the leakage inductance and stray capacitance of the load are forcibly reset by SW2 and D3.
[0036]
Such an operation will be described according to Table 1 as follows.
In (1), SW2 and SW3 are turned on when a gate signal is input, and both ends of the load are short-circuited.
[0037]
In (2), when the gate signal of SW2 is turned ON and a gate signal is input to SW1 with a slight delay and is turned ON, SW3 remains OFF, so that current flows from SW1 through the load in the I1 direction. , Charge the load positively.
[0038]
In (3), after the gate signal input to SW1 is finished and turned off, the gate signal is inputted again to SW2, and this is turned on again. Discharge through. As a result, it returns to the same state as (1).
[0039]
In (4), when SW3 is turned off and a gate signal is input to SW4 after a short delay and is turned on, SW2 remains on, so current flows from SW4 through the load in the direction I3, Charge negatively.
[0040]
In (5), after the gate signal input to SW4 is finished and turned off, the gate signal is inputted again to SW3 and this is turned on again. Therefore, the charges charged in the load are switched between SW3 and D2. Discharge through. As a result, it returns to the same state as (3).
[0041]
In this way, the dead signal is given so as to prevent the pair of SW1 and SW2 and the pair of SW3 and SW4 from being turned on at the same time, and switching is performed in order from (1) to (5). Output signal (a pair of positive and negative pulses with a certain time interval) is obtained. In that case, since the stray capacitance and the leakage inductance on the load side are reset by the switching operation as described above, an output waveform without distortion can be obtained.
[0042]
The output of the H-bridge switching circuit 7 that performs the switching operation as described above is shown in FIG. 2 with the middle point of the first and second semiconductor switching elements SW1 and SW2 as one pole, and the third and fourth semiconductor switching elements. The midpoint of SW3 and SW4 is taken out as the other pole and applied to the primary side of the high-voltage transformer 3 via the capacitor C.
[0043]
Next, referring to the timing chart of FIG. 5, a description will be given of a preceding circuit that controls the gate drive circuit 11 to repeatedly output a pair of positive and negative pulses from the H-bridge switching circuit 7 and adjusts the cycle and pulse width. To do.
[0044]
The voltage controlled oscillator (VCO) 12 repeatedly outputs a rectangular wave as shown in FIG. The repetition frequency can be adjusted by the repetition frequency setting unit 13.
[0045]
As shown in FIG. 5B, the first one-shot multivibrator 14 outputs a pulse that rises at the rising edge of the output of the voltage controlled oscillator 12 (VC0 output). The pulse width can be adjusted by the first pulse width setting unit 15.
[0046]
As shown in FIG. 5 (3), the delay circuit 16 outputs a pulse having a fixed time width (dead time) that rises when the pulse of the first one-shot multivibrator 14 falls.
[0047]
The second one-shot multivibrator 17 outputs a pulse that rises at the rising edge of the output of the delay circuit 16, as shown in FIG. The pulse width can be adjusted by the second pulse width setting unit 18.
[0048]
A pulse from the first one-shot multivibrator 14 is input to the first AND gate 19, and a pulse from the second one-shot multivibrator 17 is input to the second AND gate 20. The outputs from the start / stop circuit 22 that is turned on / off by the start switch 21 are input to the AND gates 19 and 20, and the first and second ones are turned on when the AND gates 19 and 20 are turned on. The pulses of the shot multivibrators 14 and 17 are input to the third and fourth AND gates 23 and 24, respectively.
[0049]
The output of the third AND gate 23 is input to the first delay AND circuit 25 and the first delay NAND circuit 26, and the output of the fourth AND gate 24 is the second delay AND circuit 27 and This is input to the second delay NAND circuit 28. (5), (6), (7), and (8) of FIG. 5 show the output waveforms of these AND circuit 25, NAND circuit 26, AND circuit 27, and NAND circuit 28. According to the output, the gate drive circuit 11 The gate pulses for the four semiconductor switching elements SW1, SW2, SW3, and SW4 of the H-bridge switching circuit 7 are output, and these are switched as described above.
[0050]
Therefore, as shown in FIG. 5 (9), a pair of positive and negative pulses with a certain time interval are output as positive and negative pulse waves at a certain repetition frequency from the H bridge switching circuit 7. The repetition frequency can be adjusted by the repetition frequency setting unit 13, and the pulse width can be adjusted by the pulse width setting units 15 and 18.
[0051]
The positive and negative pulse waves are applied to the primary side of the high-voltage transformer 3 via the capacitor C, and become a high-pressure damped oscillation waveform periodic wave in which the resonant damped oscillation wave is intermittently repeated by the LC component of the high-voltage transformer 3. . Since the secondary side of the high-voltage transformer 3 is floating from the ground, the high-voltage voltage applied to the pair of electrodes 1 and 2 is as shown in FIGS. 5 (10) and 5 (11). Positive and negative are completely opposite in phase to the midpoint on the secondary side. These waveforms shown in FIGS. 5 (10) and (11) are waveforms in a state where the electrodes 1 and 2 are not discharged. By adjusting the pulse width with the pulse width setting devices 15 and 18, a resonance condition matching the LC component of the high-voltage transformer 3 can be obtained.
[0052]
When an arc discharge starts between the electrodes 1 and 2 and a discharge current flows as shown in FIG. 5 (14), a resonance deviation occurs at or near the maximum peak value of the discharge current, Since the damped vibration wave after application cancels and disappears, arc discharge is interrupted instantaneously. The voltage waveforms applied to the electrodes 1 and 2 at that time are shown in FIGS. 5 (12) and 5 (13), respectively.
[0053]
As described above, the electrodes 1 and 2 are applied with a high-frequency damped oscillation waveform having a reverse phase in which the resonating damped oscillation wave repeats intermittently. The application and pause are intermittently performed as follows. Next, the operation will be described with reference to the timing chart of FIG.
[0054]
As shown in FIG. 6 (2), the burst wave oscillator 29 outputs a rectangular wave having a frequency much lower than the repetition frequency shown in FIG. When the operation changeover switch 30 is turned on, it is input to the third and fourth AND gates 23 and 24 via the NAND gate 31. For example, if the former repetition frequency is 100 KHz, the latter period is 1 KHz, and when the output of the burst wave oscillator 29 is HIGH, as shown in FIGS. The AND gates 23 and 24 output pulses as described above corresponding to the repetition frequency. During this period, positive and negative pulse waves are output from the H-bridge switching circuit 7 as shown in FIG. 6 (5), and the damped oscillation resonated with the pair of electrodes 1 and 2 as shown in FIGS. 6 (6) and 6 (7). When a periodic wave of high-pressure damped oscillation waveform with opposite phases that repeats intermittently is applied, and a discharge current that rises sharply as shown in FIG. 6 (8) flows immediately after the start of arc discharge, a resonance shift occurs and the arc Discharging stops instantaneously. Such an operation is repeated at the repetition frequency by the voltage controlled oscillator 12, and the operation / pause is repeated at a period much lower than the period.
[0055]
The fan 5 that blows air between the pair of electrodes 1 and 2 is driven by a sequence circuit 32 that operates at a commercial frequency.
[0056]
Next, experimental examples of the present invention conducted by the present inventors will be described.
A test for improving the wettability with respect to the substrate was performed, and the wettability was measured with a contact angle meter (G-1 / 2MG type manufactured by ELMA). The applied voltage was measured using a Sony Tektronix high voltage probe P-6015 type, and the current was measured using a Hierson model 4100. As the substrate, PET film was used, and in the case of metal, copper, aluminum, and stainless steel were used.
[0057]
[Experimental Example 1]
The distance between the electrodes 1 and 2 was 13 mm, and wettability was improved using a PET film as the substrate 6 to be treated. Air was used as the gas to be blown. Table 2 shows contact angle data when the repetition frequency is changed. The contact angle is modified at 20 KHz or more, and the modification is saturated at 35 to 40 KHz. It can be seen that the treatment time is improved at 30 KHz or more, and even when the time is increased to 1 second, the modification is not improved and is saturated. Table 3 shows the contact angle data with respect to the power of the H-bridge switching circuit 7 which is an inverter with the frequency fixed at 20 KHz and the output increased. Table 4 shows data when the distance to irradiate the substrate in the plasma is changed with the frequency fixed at 20 KHz and the power fixed at 497 W, that is, the contact with respect to the distance from the electrode to the substrate (processing distance). In the corner data, 20 mm is the best result.
[0058]
[Table 2]

[0059]
[Table 3]

[0060]
[Table 4]

[0061]
[Experiment 2]
The distance between the electrodes was set to 4 mm, and wettability was improved with respect to the PET film. Air was used as the gas to be blown. Table 5 shows contact angle data when the repetition frequency is changed. The contact angle data is improved at 20 KHz or more, and the reforming is saturated at 35 to 40 KHz. Compared with the table of Experimental Example 1, the electrode of Experimental Example 2 has better reforming performance, and the electrode with higher plasma irradiation power density is more effective. Table 6 shows the contact angle data with respect to the inverter power when the frequency is fixed at 20 KHz and the output is increased step by step.
In addition, when the distance between the electrodes is 4 mm, the application of the irradiation power of 500 W is the limit, and thus it can be understood that it is necessary to increase the distance between the electrodes in order to increase the irradiation power.
[0062]
[Table 5]

[0063]
[Table 6]

[0064]
[Experiment 3]
Table 7 shows wettability data when copper, aluminum, and stainless steel are used as the metal to be processed and the distance between the electrodes is 5 mm and 10 mm in the same method.
[0065]
[Table 7]

[0066]
[Experimental Example 4]
In a liquid crystal display panel (size: 50 mm × 30 mm) provided with ITO transparent electrode connection terminals at the ends, the electrode connection terminals were subjected to plasma treatment using air under the same conditions as in Experimental Example 1. Subsequently, the drive circuit comprised with a polyimide film (50 micron thickness) was thermocompression-bonded through the anisotropic conductive film. The thermocompression bonding conditions were a temperature of 170 ° C., a pressure of 3 MPa, and a time of 20 seconds. Then, as a result of measuring the peel strength by pulling the panel and circuit body joined as described above in opposite directions, a peel strength about twice that of the case where the plasma treatment was not performed was obtained.
[0067]
From the above results, it can be said that when the repetition frequency is increased (40 KHz or more), the contact angle is saturated and the plastic substrate is melted by heat, and the optimum repetition frequency is best at 10 to 20 KHz. understood. Further, it has been found that, in order to modify the metal, if a continuous signal having a repetition frequency is used, the metal concentrates on a part of the metal, so that it is necessary to perform a burst operation. With respect to the distance between the electrodes, the spread of the plasma is greatly increased if the distance is increased, but it took 1 second or more to process, and it was found that uniform processing was difficult. When the distance between the electrodes is narrowed, the spread of the plasma is narrowed, but the processing time can be shortened, and it was found that the plasma is immediately modified in 0.1 to 0.2 seconds.
[0068]
【The invention's effect】
As described above in detail, according to the present invention, the electrodes are not heated and become high-temperature plasma even when continuously used, and the processing time can be shortened and the processing quality can be improved by stable low-temperature plasma. In addition, there is no damage to the object to be processed due to abnormal discharge, and furthermore, the generation of plasma can be easily controlled and the apparatus scale can be reduced.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of plasma processing by a plasma generator of the present invention.
FIG. 2 is a block diagram of an example of a plasma generator according to the present invention.
FIG. 3 is an equivalent circuit diagram of an H-bridge switching circuit in the plasma generator.
FIG. 4 is a timing chart of the switching operation of the circuit.
FIG. 5 is a timing chart showing the operation of the circuit of FIG.
FIG. 6 is a timing chart of the burst operation.
[Explanation of symbols]
1.2 Electrodes
3 High voltage transformer
4 Plasma
5 fans
6 Base material
7 H bridge switching circuit (inverter)
SW1, SW2, SW3, SW4 Semiconductor switching element
D1, D2, D3, D4 Diode
C capacitor
8 Rectifier circuit
9 DC stabilized power supply circuit
10 Output setting device
11 Gate drive circuit
12 Voltage controlled oscillator (VC0)
13 Repeater frequency setting device
14 One-shot multivibrator
15 Pulse width setting device
16 Delay circuit
17 One-shot multivibrator
18 Pulse width setting device
19.20 AND gate
21 Start switch
22 Start / stop circuit
23.24 AND gate
25 AND circuit for delay
26 NAND circuit for delay
27 AND circuit for delay
28 NAND circuit for delay
29 Burst Wave Oscillator
30 Continuous / intermittent operation switch
31 NAND gate
32 Sequence circuit

Claims (14)

In a plasma generation method in which a high voltage is applied between a pair of opposing electrodes to forcibly cause arc discharge, gas is supplied between these electrodes, and the discharge is expanded by the wind force, the plasma is applied between the pair of electrodes. A high voltage is resonated for each damped vibration wave as a damped vibration waveform that is generated intermittently by a damped vibration wave, and for each damped vibration wave, a resonance shift occurs along with the occurrence of arc discharge, and the arc discharge is interrupted. A plasma generation method characterized by causing intermittent arc discharge. 2. The plasma generation method according to claim 1, wherein the high-voltage damped oscillation wave applied between the pair of electrodes has an opposite phase in positive and negative. A pair of positive and negative pulses with a certain time interval is supplied to the primary side of the high-voltage transformer at a certain repetition frequency, and a damped oscillation waveform periodic wave resonated for each damped oscillation wave is output from the secondary side of the high-voltage transformer. The plasma generating method according to claim 2, wherein the plasma is applied between the electrodes. 4. The plasma generation method according to claim 3, wherein the frequency of the damped oscillation wave is varied by adjusting the pulse width of a pair of positive and negative pulses. The plasma generation method according to claim 1, 2, 3, or 4, wherein the voltage rising time of each damped oscillation wave resonated is 1 µs or less. 6. The plasma generation method according to claim 1, wherein a repetition period of the damped vibration wave is 10 to 50 KHz. The plasma generating method according to claim 1, 2, 3, 4, 5, or 6, wherein the damped vibration wave is intermittently applied between the pair of electrodes at a frequency lower than the repetition frequency. 8. The plasma generating method according to claim 1, wherein a distance between the pair of electrodes is 1 to 15 mm. In a plasma generator in which a high voltage is applied between a pair of opposing electrodes to forcibly cause arc discharge, and gas is supplied between these electrodes to expand the discharge by the wind force, a pair of positive and negative with a certain time interval Positive and negative pulse wave generation circuit that generates a pulse with a certain repetition frequency, and the positive and negative pulse waves are input to the primary side, and for each damped vibration wave, a resonating damped vibration waveform periodic wave with positive and negative phases is generated from the secondary side. It is equipped with a high-voltage transformer that outputs and applies between a pair of electrodes, and for each damped vibration wave, a resonant shift occurs with the occurrence of arc discharge, and the arc discharge is interrupted to make intermittent arc discharge. A plasma generator characterized by the above. The positive and negative pulse wave generation circuit has the first and fourth upper arms, the second is the lower arm for the first, the third is the lower arm for the fourth, and the first to fourth semiconductor switching elements are H-bridge connected. In addition, the positive and negative pulse waves are generated by using an H-bridge switching circuit in which a diode is connected in parallel to each semiconductor switching element. The positive / negative pulse wave generation circuit adjusts the pulse width of the pair of positive and negative pulses output from the H bridge switching circuit by adjusting the pulse width of the gate pulse for the four semiconductor switching elements of the H bridge switching circuit. 11. The plasma generator according to claim 10, further comprising pulse width setting means for varying the frequency of the damped vibration wave. A positive / negative pulse wave generation circuit adjusts the repetition frequency of a pair of positive and negative pulses output from the H bridge switching circuit by adjusting the period of the gate pulse for the four semiconductor switching elements of the H bridge switching circuit. The plasma generator according to claim 10 or 11, further comprising repetition frequency setting means for setting a repetition frequency of the damped vibration wave. Burst frequency setting means for intermittently inputting gate pulses for four semiconductor switching elements of the H-bridge switching circuit to the gate drive circuit of the H-bridge switching circuit at a period lower than the frequency is provided. The plasma generator according to claim 10, 11 or 12. The plasma generator according to claim 10, 11, 12, or 13, wherein a distance between the pair of electrodes is 1 to 15 mm.

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