JP3745700B2 - Antenna for generating microwave plasma - Google Patents

Description

但しωは２πｆ、ωpは２πｆ_pである。
【００１９】
即ち、（１）式で表されるインダクタンスＬ_m(ω)は、ａとｂとの比の大小により、負の値をとることができ、この場合にはプラズマは生成できない。そしてインダクタンスＬ _m ( ω )が負の値から正の値になるｂの値、即ち前記臨界厚さｂ_c以上被覆厚さの場合にプラズマを発生することができる。
【００２０】
前記アンテナ素子を配置する層と給電回路を形成する層との間にギャップを設けることができる。この場合、この部分を貫通する前記ガス通路を金属パイプなどで形成し、ギャップ部分に蒸着ガスが進入しないようにすることが好ましい。またギャップ部分は導体でシールする。
【００２１】
【発明の実施の形態】
以下添付の図面を参照する実施の形態を示し、本発明を具体的に説明する。
【００２２】
図1は第1実施の形態のマイクロ波生成用アンテナ(以下単にアンテナ)４をプラズマ処理装置５のチャンバ５ａに取り付け、例えばガラス板などの被処理材６の表面に化学的気相成長法（ＣＶＤ）により薄膜を生成させる装置の概要を示したものである。
【００２３】
アンテナ４の基本構造は、誘電体からなる基板７のギャップ８側に給電回路９（詳細は図２で説明）を、その反対側に導電層１０を配置し、前記ギャップ８の反対側には導体層１１にスロット３を形成し、その外側に誘電体１２を配置したものである。
【００２４】
そして第１実施の形態では、チャンバ５ａ内をアンテナ４によってガス分散室５ｂとプラズマ処理室５ｃとに分割し、ガス分散室５ｂ内の蒸着ガスをプラズマ処理室５ｃ内に導入する複数のガス通路１３をアンテナ４を貫通して形成した。
【００２５】
第１実施の形態のプラズマ処理装置５を大型液晶ディスプレイ用薄膜形成用として使用する場合には、真空ポンプ（図示せず）によってプラズマ処理室５ｃ内の真空度を通常１mmTorr〜１０Torrとし、被処理材６を加熱装置５ｄによって所定温度に加熱し、被処理材６の表面に薄膜を形成した。なお、図１に示す符号５ｅは試料台、５ｆはガス導入口、５ｇは真空排気口である。
【００２６】
アンテナの立体的構造を説明する前に、図２によってスロット３、給電回路９およびガス通路１３の平面的関係を説明する。図２において、各スロット３はいずれも２個づつ対にして一つのパワースプリッタ１４によって１本の伝送路９ａから分岐して供給する。そして、各パワースプリッタ１４（詳細は図１２により説明）に給電する伝送路９ａも亦、２分割型のパワースプリッタ１４により分割されたものであり、最終的に１本の伝送路に統合されてマイクロ波発生用高周波電源（いずれも図示せず）に接続するカスケード型の給電回路９を形成した。
【００２７】
図３に示す部分拡大図によってアンテナ４の構造を更に説明する。図３においてスロット３は前記説明のとおり導体層１１をエッチングなどにより形成し、スロット３にマイクロ波を供給する伝送路９ａの先端部９ｂがギャップ８を隔ててスロット３の所定位置に重なるように配置した。また導体層８は接地している。
【００２８】
スロット３の長さをマイクロ波の波長の１／２の長さとすると共振が起こり、電波として放射され、周囲に電離するガスが存在するとプラズマを発生させる。プラズマは導電性であるためスロットの両端が短絡される。したがって、導体層１１にプラズマ側に誘電体１２を被覆し、導体層１１をプラズマから絶縁することによりスロット３近辺の蒸着ガス中にマイクロ波を伝播させることができる。この場合、スロットラインを流れるマイクロ波とプラズマとの干渉の様子を図４に示すイメージ図によって説明する。なを、図３に示す符合１３ａはガス通路１３を形成する金属パイプである。
【００２９】
前記のとおり電波はスロット３の軸方向（以下スロットライン）に沿って伝播すると共に（図４Ａ）、直角方向に放射されプラズマ中にマイクロ波の侵入領域Ｐを形成する（図４ｂ）。スロットラインと直行する方向の前記マイクロ波侵入領域Ｐはスロット部分で深く、その他の部分では浅いものとなる（図４Ｃ）。
【００３０】
かかるマイクロ波侵入領域Ｐは、被覆している誘電体１２の厚さが薄すぎるとマイクロ波はスロット３に沿って伝播することができなくなり、また厚すぎると伝播は可能であるがプラズマ加熱の効率が悪くなる。即ち誘電体１２の厚さには臨界被覆厚さｔ_cがあり、この値よりやや厚めにすることが最も好ましい。以下この問題を順次説明する。
【００３１】
プラズマ加熱のマイクロ波周波数をfとする。高密度プラズマＣＶＤや高密度プラズマエッチングの場合、前記ｆの値は、生成するプラズマ周波数ｆｐより低いと仮定することができる。前記ｆ_pは次の数３式で算出することができる。
【００３２】
【数３】

式中ｎ_eは電子の単位体積中の数、−ｅは電子の電荷、ｍ_eは電子の質量、ε₀は真空の誘電率である。
【００３３】
本発明者による前記出願発明の棒状アンテナからなる大面積プラズマアンテナの数学的解析は、棒状アンテナ中を実際に電力が流れているので、直接数式モデルを作ることができた。それに対しスロットラインの数式モデルは、スロット３中を電力が流れていないので、次の手続によった。
【００３４】
即ち、スロット３には図５Ａに示す電界が実際に発生している。そこでこの電界を発生させる量として磁流Ｊ_m(z)を以下に説明する［数５］式によって定義し、電圧に対して磁圧ψ_m(z)を以下に説明する［数４］式により定義する。なおサフィックスｍは磁気についての量であること示しており、ｚは電波の伝播方向の座標を示す。
【００３５】
図５は、磁流Ｊ_m(z)と電界Ｅとの関をを示しており、これらの関係を数式モデルとして、図５Ｃに示すように磁流Ｊ_m(z)はスロット３の幅を直径とする円形の表面を均等に分散して流れるものとして扱い、図５ｃに示す円形断面磁流アンテナと生成しているプラズマとの関係を解析する際のモデルを図６に示す。
【００３６】
図６に基づく磁流路（断面）の伝送方程式を求めるため図７に示す積分路Ｃ₁，Ｃ₂を定義する。しかる後、♯１，♯２間の磁圧ψ_m(z)（磁気ポテンシャル）と、♯１の表面を流れる総磁流Ｊ_m(z)をそれぞれ［数４］式、［数５］式のように定義する。
【００３７】
【数４】

【００３８】
【数５】

但し式中サフィックスtは接線成分であることを示す。
【００３９】
以上の定義に基づいて伝送方程式を求めると次の[数６]式〜［数９］式が得られる。なお［数８］式は前記［数１］および［数２］と同じものである。
【００４０】
【数６】

【００４１】
【数７】

【００４２】
【数８】

【００４３】
【数９】

但しａは図７に示した磁流路の半径（スロット幅に同じ値）、ｂ（図６）の誘電体被覆半径、εは被覆誘電体の誘電率、μ₀は真空の透磁率、C₀は真空中の光速度、ωは２πｆ、ω_pは２πｆ_p、Ｆ(r)は［数１０］式で表される値、Ｋ₀(r)は変形ベッセル関数、ｌｎ(ｘ)は自然対数である。
【００４４】
【数１０】

［数８］式および［数９］式中の関数Ｆ(ｘ)をグラフに表すとｘが１以下と１以上とについて、それぞれ図８Ａおよび図８Ｂが得られる。
【００４５】
ここで注目すべきことは、［数８］式のＬ_m(ω)が、誘電体がない場合、即ちａ＝ｂのときに負の値になることである。ｂがａに比べて十分大きな値になればＬ_m(ω)は正の値になる。Ｌ_m(ω)が負の値のときにはアンテナに効率よくマイクロ波を給電することはできない。Ｌ_m(ω)が負から正になる臨界値ｂ_cが存在することを示している。
【００４６】
次にスロットライン伝送路について検討する。考察対象の磁流の流れる系においては、単位長さ当たりの直列インピーダンスをＺ_m、単位長さ当たりの並列アドミタンスＹ_mは［数１１］式、［数１２］式で与えられる。
【００４７】
【数１１】

【００４８】
【数１２】

このときの伝播定数γ、伝播速度ｖ、波長λは次のようになる。
【００４９】
【数１３】

【００５０】
【数１４】

【００５１】
【数１５】

アンテナ軸に沿った磁流分布は次のように表される。
【００５２】
【数１６】

［数１６］式の結果から、ｂ＜ｂ_cの場合γが正となり磁流分布は図９Ａのようになるため均一なプラズマの発生は望めない。ｂ＞ｂ_cの場合γが虚数となり、磁流分布は図９Ｂのように定在波を発生させることが可能となる。
【００５３】
次に磁流路の直径（実際はスロット３の幅）２ａを２ｍｍと０．２ｍｍとした場合について、誘電体１２の比誘電率を３および５(ガラスの値)、供給するマイクロ波の周波数が２．４５ＧＨｚとした場合について、［数８］式からプラズマ周波数ｆ_pに対する誘電体１２の臨界厚さｔｃ＝（ｂ_c−ａ）を求めた結果を図１０Ａおよび図１０Ｂに示す。
【００５４】
以上のようにしてアンテナ４を設計するに当たり、［数８］式を用いることによりスロット３を被覆する誘電体１２の厚さｔの基礎数値を求めることができる。本発明に関わるスロットアンテナは、棒状アンテナによる前記先行発明と異なり、プラズマ周波数が高くなるほど必要とするスロットを形成する導体層１１を覆う誘電体１２の厚さｔが大きくなることである。
【００５５】
本実施の形態に使用したパワースプリッタ１４の構造は、図１２に示すように、インピーダンスの整合のために、パワースプリッタ１４部分の伝送路９ａの特性インピーダンスを、伝送路９ａの特性インピーダンスＺ₀の２の平方根倍となるように線幅を変化させ、更に前記特性インピーダンスＺ₀の２倍の特性インピーダンスのバランス用抵抗Ｒを、分岐した側の伝送路９ａ間に取り付けたマイクロストリップラインで構成した。またバランス用抵抗Ｒは、高温に耐えるように炭化ケイ素SiCなどの耐熱性抵抗体を使用した。なお、第１実施の形態で採用した標準インピーダンスは５０Ωである。
【００５６】
次に図１３によって本発明の第２実施の形態について説明する。第２実施の形態はマイクロ波電極としてストリップ３′を使用したマイクロスプリットアンテナによって実施したものである。図においてストリップ３′および伝送路９ａは、それぞれ誘電体７，１５に形成した導体層からエッチング手段などにより形成することができる。なお図中の符合１６は伝送路９ａとストリップ３′とを繋ぐ伝播路、１７は誘電体１５を積層した導体層である。伝送路９ａと導体層１７とは相互に絶縁されている。その他、図１〜３に示したものと同様の部材には同じ符合を付し、説明を省略する。また、図１３にはガス通路の図示を省略した。
【００５７】
ストリップアンテナによる電界生成形態は、図１４に示すように、２個のスロット３を対にした第１実施の形態の場合の様子との類似性が得られるが、誘電体１２の厚さの決定方法とは異なるが、空間的に一様なプラズマを生成させ、長方形断面のプラズマを容易に作成させることができる。
【００５８】
【発明の効果】
以上説明したように本発明のマイクロ波プラズマ生成用アンテナは、導体層に形成したスロットまたは導体層からなるストリップからなる電極をマトリクス状にプラズマ発生領域全面に配置し、その表面を誘電体で被覆し、多段式パワー分配回路からマイクロ波を発生させる周波数の高周波電力を供給し、前記電極によってマイクロ波を共振させることによりエネルギーを全ての電極に均等に分配するようにしたので、空間的に一様且つ長方形状のプラズマを容易に作成することができる。したがって、大型テレビなどの液晶ディスプレイ製造工程において、高品質な膜を高速に造ることができ、且つ製膜装置を必要最小限のサイズにすることが可能となった。
【図面の簡単な説明】
【図１】本発明の第１実施の形態によるマイクロ波プラズマ生成用アンテナをプラズマ処理装置に組み込んだ様子を概念的に示す縦断面図である。
【図２】図１に示すアンテナのスロット部分の構造を示す部分斜視図である。
【図３】図１に示すアンテナをプラズマ処理室側から順次上の層を除去し、アンテナの平面構造を示した平面図である。
【図４】誘電体でスロットラインを覆う異によりプラズマ中を伝播が伝播可能となる様子を説明するための説明図であり、Ａはスロットと伝播の伝播方向とが一致する様子を示す図であり、Ｂは生成したプラズマと誘電体およびスロットの位置的関係を模型的に示す図であり、Ｃは前記Ｂの横断面により示した図である。
【図５】誘電体の厚さとスロットとの関係を導くためのスロットアンテナのモデル化を行う仮定を示す図であり、Ａはスロットに発生した電界発生のようすを示す図であり、ＢはＡと等価の電界を発生させる磁流平板アンテナのモデルに置き換えた図であり、ＣはＢと等価の円柱形磁流アンテナモデルに置き換え、数式で扱えるように下た場合の図である。
【図６】図５Ｃに示す磁流路の表面を磁流が流れる場合の数式モデルの各量の関係を示す図である。
【図７】安定したプラズマ画発生している領域を基準磁位源とし、磁流の流路（伝送路）断面と２つの積分路の関係を示す説明図である。
【図８】［数８］式および［数９］式中に示す関数Ｆ(ｘ)を横軸にｘ値をとった場合の対数メモリによるグラフ図であり、Ａはｘが１以下の場合を、Ｂはｘが１以上の場合を示しｔがものである。
【図９】誘電体の厚さによる電波の電波パターンを示すグラフ図であり、Ａは電波が遮蔽されて伝播しない場合の図であり、Ｂは電波が遮蔽されなくてプラズマ中を伝播する場合の様子を示す図であり、図の矢印は伝播方向を示している。
【図１０】スロットアンテナの誘電層厚さのプラズマ周波数依存性を示す図であって、誘電率３の誘電体を使用し、且つスロット幅に一致するアンテナ直径を２ｍｍとした場合の値であり、Ｂはアンテナ直径を０，２ｍｍとした場合の値である。
【図１１】図１０に続く図であって、スロットアンテナの誘電層厚さのプラズマ周波数依存性を示す図であって、Ａは誘電率５の誘電体を使用し、且つスロット幅に一致するアンデナ直径を２ｍｍとした場合の値であり、Ｂはアンテナ直径を０.２ｍｍとした場合の値である。
【図１２】本発明の第１実施の形態に使用したパワースプリッタの回路構成を説明するための平面図である。
【図１３】本発明の第２実施の形態によるマイクロストリップアンテナの部分斜視図である。
【図１４】マイクロストリップアンテナは２素子スロットアレイアンテナと投下であることを示す斜視図である。
【図１５】従来例によるラジアルスロットラインアンテナのスロット配置の一例を示す平面図である。
【符号に説明】
３ スロット
３′ ストリップ
４ アンテナ(マイクロ波プラズマ生成用アンテナ)
６ 被処理材
９ａ 伝送路
９ｂ 先端部
１２ 誘電体[0001]
[Field of the Invention]
The present invention relates to an electrode for generating a microwave plasma, and more particularly, to use it when a high-quality thin film that can be used for a display for a large liquid crystal television is generated by chemical vapor deposition (CVD). The present invention relates to an antenna for generating microwave plasma.
[0002]
[Prior art]
Since shortening of manufacturing time in semiconductor manufacturing technology leads to cost reduction, development of high-density plasma generation technology using microwaves is demanded in order to reduce plasma processing time to apply one CVD. In order to manufacture display devices for next-generation large-sized LCD TVs, flat and uniform high-density plasma generation technology has become the core technology.
[0003]
[Problems to be solved by the invention]
By the way, a technique using a radial line slot antenna is known as the high-density plasma generation technique. As the prior art, for example, what is described in Japanese Patent Application Laid-Open No. 2001-223098 is formed by expanding the diameter at the tip of the coaxial cable and forming it into a flat cylindrical shape. A plurality of slots are formed, and a front surface of the slot surface is covered with a microwave transmission body (dielectric material).
[0004]
As a known slot arrangement example according to the conventional example, for example, as shown in FIG. 15 attached to this specification, a radio wave is supplied from a coaxial cable in which a radio wave is supplied to the central part and a radio wave absorber (not shown) is arranged on the outer peripheral part. There is a radial line slot antenna 1 adapted to supply. As pointed out in the above publication, these conventional methods have a drawback that it is difficult to make the distribution of microwaves in the radial direction constant.
[0005]
In other words, part of the microwave injected from the center of the disk is radiated from the central slot and the rest propagates in the direction of increasing radius. Many microwaves are radiated from a certain slot, and since the radiation amount is reduced from a large radius, it is difficult to obtain radial uniformity. In order to solve this drawback, it is necessary to devise such as changing the slot size in the radial direction. This is because the antenna characteristics are related to the plasma density, and it is difficult to predict the radial distribution of the slot size at the time of design. is there.
[0006]
Therefore, the proposal disclosed in the publication discloses a plurality of waveguides concentrically and annularly arranged with their end portions closed by a microwave absorber, and a plurality of microwave radiation slots arranged at predetermined intervals on the side wall of the waveguide. The present invention relates to a plasma processing apparatus using a microwave antenna having a microwave transmission body disposed outside thereof.
[0007]
Japanese Laid-Open Patent Publication No. 2001-203098 discloses a conventional radial line slot antenna in which a slot is formed in a conductor layer formed by electroless plating on a dielectric plate. The illustrated slots are T-shaped, and all of the slots are inclined in the same direction with respect to the radial direction.
[0008]
The above-described microwave antenna has a problem that if the reflection occurs at the end of the waveguide, the microwave intensity distribution in the waveguide becomes complicated, and the slot design becomes complicated. There is a problem that the energy efficiency deteriorates when the body is attached.
[0009]
In addition, the radial line slot antenna has a circular shape as its name suggests, and is suitable for film formation processing and etching of wafers, but is not suitable for manufacturing rectangular thin films such as solar cells and liquid crystal displays.
[0010]
The inventor previously invented a high-frequency antenna capable of forming a thin film for a large area solar cell of 1 m × 1 m, and applied for a patent on September 14, 2002. The present invention relates to a plasma generating antenna in which a plurality of rod-shaped antennas insulated and coated with a dielectric material are arranged in a plane at predetermined intervals and are alternately fed from opposite directions. A method for determining the required thickness of body coating was proposed.
[0011]
However, in this large-area plasma generator using a rod-shaped antenna, it is difficult to control the plasma gas concentration in detail as in a liquid crystal display device and to increase the operating frequency in order to generate a thin film.
[0012]
Since the present invention generates uniform and high-density plasma that is controlled in detail, such as for the generation of thin films for large-screen liquid crystal displays, as described above, the power is generated using power in the microwave band (gigahertz band). An object of the present invention is to provide a microwave plasma generating antenna whose cross-sectional shape can be made rectangular.
[0013]
[Means for Solving the Problems]
The antenna for generating microwave plasma according to the present invention achieves the above object. The array antenna in which an array antenna including a plurality of antenna elements resonating with microwaves is used for plasma generation, and the plurality of elements are arranged. The surface is covered with a dielectric, and an energy supply network of a transmission path for supplying the microwave generating high frequency power is formed for each element, and the plurality of elements are arranged in a planar shape.
[0014]
The antenna element that can be used in the present invention is not particularly limited. For example, a slot antenna element, a microstrip antenna element, or the like can be used.
[0015]
The power supply circuit forming the energy supply network is not particularly limited. For example, high-frequency power supplied from a high-frequency power source is sequentially and equally divided into two by a power splitter, and the high-frequency energy supply terminal is provided for each of a plurality of antenna elements. A cascade-type power supply circuit that forms
[0016]
The method for supplying the plasma processing gas is not particularly limited, but in order to supply the plasma generating gas evenly through the slots arranged in a large number of planes, the plasma processing gas is supplied to the back side of the antenna, It can supply to the front side of this antenna from the several gas supply path which penetrates this antenna.
[0017]
When the slot width is a, the dielectric coating thickness is b, the dielectric constant of the coating dielectric is ε, the microwave frequency is f, the plasma frequency is f _p , and the radio wave propagation speed is c ₀ , [expression 2] type inductance L _m (omega) which is defined by (the [number 1] same as formula) the value of b that a positive value from a negative value, that is, b _c or more coating thickness.
[0018]
[Expression 2]

However ω is 2πf, ωp is 2πf _p.
[0019]
That is, the inductance L _m (ω) represented by the equation (1) can take a negative value depending on the ratio of a and b, and in this case, plasma cannot be generated. Plasma can be generated when the inductance L _m ( ω ) is a value of b from a negative value to a positive value, that is, the coating thickness is equal to or greater than the critical thickness b _c .
[0020]
A gap can be provided between the layer in which the antenna element is disposed and the layer in which the feeding circuit is formed. In this case, it is preferable that the gas passage penetrating this portion is formed by a metal pipe or the like so that the vapor deposition gas does not enter the gap portion. The gap is sealed with a conductor.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments will be described below in detail with reference to the accompanying drawings.
[0022]
FIG. 1 shows a first embodiment of a microwave generating antenna (hereinafter simply referred to as an antenna) 4 attached to a chamber 5a of a plasma processing apparatus 5, and a chemical vapor deposition method (on a surface of a material 6 to be processed such as a glass plate). The outline | summary of the apparatus which produces | generates a thin film by CVD) is shown.
[0023]
The basic structure of the antenna 4 is that a feeder circuit 9 (details will be described in FIG. 2) is disposed on the gap 8 side of the substrate 7 made of a dielectric, and a conductive layer 10 is disposed on the opposite side. A slot 3 is formed in the conductor layer 11, and a dielectric 12 is arranged outside thereof.
[0024]
In the first embodiment, the chamber 5a is divided into the gas dispersion chamber 5b and the plasma processing chamber 5c by the antenna 4, and a plurality of gas passages for introducing the vapor deposition gas in the gas dispersion chamber 5b into the plasma processing chamber 5c. 13 was formed through the antenna 4.
[0025]
When the plasma processing apparatus 5 of the first embodiment is used for forming a thin film for a large liquid crystal display, the degree of vacuum in the plasma processing chamber 5c is normally set to 1 mm Torr to 10 Torr by a vacuum pump (not shown). The material 6 was heated to a predetermined temperature by the heating device 5d, and a thin film was formed on the surface of the material 6 to be processed. In addition, the code | symbol 5e shown in FIG. 1 is a sample stand, 5f is a gas inlet, 5g is a vacuum exhaust port.
[0026]
Before describing the three-dimensional structure of the antenna, the planar relationship among the slot 3, the power feeding circuit 9, and the gas passage 13 will be described with reference to FIG. In FIG. 2, each of the slots 3 is supplied as a pair by branching from one transmission line 9a by one power splitter 14 in pairs. The transmission path 9a that feeds power to each power splitter 14 (details will be described with reference to FIG. 12) is also divided by the two-split power splitter 14, and is finally integrated into one transmission path. A cascade-type power supply circuit 9 connected to a microwave generation high-frequency power source (none of which is shown) was formed.
[0027]
The structure of the antenna 4 will be further described with reference to a partially enlarged view shown in FIG. In FIG. 3, the slot 3 is formed by etching the conductor layer 11 as described above, and the tip 9b of the transmission line 9a for supplying microwaves to the slot 3 is overlapped with a predetermined position of the slot 3 with the gap 8 therebetween. Arranged. The conductor layer 8 is grounded.
[0028]
Resonance occurs when the length of the slot 3 is ½ the wavelength of the microwave, and plasma is generated when there is a gas that is radiated as a radio wave and is ionized in the surroundings. Since the plasma is conductive, both ends of the slot are short-circuited. Therefore, microwaves can be propagated in the vapor deposition gas near the slot 3 by covering the conductor layer 11 with the dielectric 12 on the plasma side and insulating the conductor layer 11 from the plasma. In this case, the state of interference between the microwave flowing through the slot line and the plasma will be described with reference to an image diagram shown in FIG. Note that reference numeral 13 a shown in FIG. 3 is a metal pipe that forms the gas passage 13.
[0029]
As described above, the radio wave propagates along the axial direction of the slot 3 (hereinafter referred to as the slot line) (FIG. 4A), and is radiated in a perpendicular direction to form a microwave intrusion region P in the plasma (FIG. 4b). The microwave intrusion region P in the direction perpendicular to the slot line is deep at the slot portion and shallow at the other portions (FIG. 4C).
[0030]
In the microwave intrusion region P, if the thickness of the covering dielectric 12 is too thin, the microwave cannot propagate along the slot 3, and if it is too thick, propagation is possible, but plasma heating is not possible. Inefficiency. That is, the thickness of the dielectric 12 has a critical coating thickness t _c , and it is most preferable to make it slightly thicker than this value. This problem will be described in turn below.
[0031]
Let f be the microwave frequency of plasma heating. In the case of high-density plasma CVD or high-density plasma etching, it can be assumed that the value of f is lower than the generated plasma frequency fp. The f _p can be calculated by the following equation (3).
[0032]
[Equation 3]

Where n _e is the number of electrons in a unit volume, −e is the charge of the electrons, m _e is the mass of the electrons, and ε ₀ is the dielectric constant of the vacuum.
[0033]
In the mathematical analysis of the large-area plasma antenna composed of the rod-shaped antenna of the invention of the application by the present inventor, since electric power is actually flowing through the rod-shaped antenna, a mathematical model can be made directly. On the other hand, the mathematical model of the slot line is based on the following procedure because no power flows through the slot 3.
[0034]
That is, the electric field shown in FIG. 5A is actually generated in the slot 3. Therefore, the magnetic current J _m (z) is defined by the following [Formula 5] as an amount for generating this electric field, and the magnetic pressure ψ _m (z) with respect to the voltage is expressed by the following [Formula 4]. Defined by Note that the suffix m indicates the amount of magnetism, and z indicates the coordinates of the radio wave propagation direction.
[0035]
FIG. 5 shows the relationship between the magnetic current J _m (z) and the electric field E. Using these relationships as mathematical models, the magnetic current J _m (z) shows the width of the slot 3 as shown in FIG. 5C. FIG. 6 shows a model for analyzing the relationship between the circular cross-section magnetic current antenna shown in FIG. 5c and the generated plasma, treating a circular surface having a diameter as being distributed uniformly.
[0036]
In order to obtain the transmission equation of the magnetic flow path (cross section) based on FIG. 6, the integration paths C ₁ and C ₂ shown in FIG. 7 are defined. After that, the magnetic pressure ψ _m (z) (magnetic potential) between # 1 and # 2 and the total magnetic current J _m (z) flowing on the surface of # 1 are respectively expressed by [Equation 4] and [Equation 5]. Define as follows.
[0037]
[Expression 4]

[0038]
[Equation 5]

In the formula, the suffix t indicates a tangential component.
[0039]
When the transmission equation is obtained based on the above definition, the following [Expression 6] to [Expression 9] are obtained. In addition, [Formula 8] is the same as the above [Formula 1] and [Formula 2].
[0040]
[Formula 6]

[0041]
[Expression 7]

[0042]
[Equation 8]

[0043]
[Equation 9]

Where a is the radius of the magnetic flow path shown in FIG. 7 (the same value as the slot width), b (FIG. 6) is the dielectric coating radius, ε is the dielectric constant of the coating dielectric, μ ₀ is the vacuum permeability, C ₀ is the speed of light in vacuum, ω is 2πf, ω _p is 2πf _p , F (r) is a value expressed by the formula [10], K ₀ (r) is a modified Bessel function, and ln (x) is a natural value Logarithmic.
[0044]
[Expression 10]

When the function F (x) in the [Equation 8] and [Equation 9] is represented in the graph, FIGS. 8A and 8B are obtained for x of 1 or less and 1 or more, respectively.
[0045]
What should be noted here is that L _m (ω) in the formula [8] takes a negative value when there is no dielectric, that is, when a = b. If b becomes a value sufficiently larger than a, L _m (ω) becomes a positive value. When L _m (ω) is a negative value, microwaves cannot be efficiently fed to the antenna. It shows that there is a critical value b _{c in} which L _m (ω) changes from negative to positive.
[0046]
Next, the slot line transmission line is examined. In a system in which the magnetic current to be considered flows, the series impedance per unit length is Z _m , and the parallel admittance Y _m per unit length is given by [Equation 11] and [Equation 12].
[0047]
## EQU11 ##

[0048]
[Expression 12]

The propagation constant γ, propagation velocity v, and wavelength λ at this time are as follows.
[0049]
[Formula 13]

[0050]
[Expression 14]

[0051]
[Expression 15]

The magnetic current distribution along the antenna axis is expressed as follows.
[0052]
[Expression 16]

From the result of [Equation 16], when b <b _c , γ is positive and the magnetic current distribution is as shown in FIG. 9A, so that uniform plasma generation cannot be expected. For b> b _c gamma becomes imaginary, magnetic current distribution becomes possible to generate a standing wave as shown in FIG. 9B.
[0053]
Next, when the diameter of the magnetic flow path (actually, the width of the slot 3) 2a is 2 mm and 0.2 mm, the relative dielectric constant of the dielectric 12 is 3 and 5 (glass value), and the frequency of the supplied microwave is FIG. 10A and FIG. 10B show the result of obtaining the critical thickness tc = (b _c −a) of the dielectric 12 with respect to the plasma frequency f _p from the formula [8] for the case of 2.45 GHz.
[0054]
In designing the antenna 4 as described above, the basic value of the thickness t of the dielectric 12 covering the slot 3 can be obtained by using the equation [8]. The slot antenna according to the present invention is different from the above-described prior invention using a rod-shaped antenna in that the thickness t of the dielectric 12 covering the conductor layer 11 forming the required slot increases as the plasma frequency increases.
[0055]
As shown in FIG. 12, the structure of the power splitter 14 used in this embodiment is such that the characteristic impedance of the transmission line 9a in the power splitter 14 portion is changed to the characteristic impedance Z ₀ of the transmission line 9a for impedance matching. The line width is changed so that the square root is 2 times, and the resistance R for balancing the characteristic impedance twice the characteristic impedance Z ₀ is constituted by a microstrip line attached between the branched transmission lines 9a. . Moreover, the resistance R for balance used the heat resistant resistor, such as silicon carbide SiC, so that it might endure high temperature. The standard impedance adopted in the first embodiment is 50Ω.
[0056]
Next, a second embodiment of the present invention will be described with reference to FIG. The second embodiment is implemented by a micro split antenna using a strip 3 'as a microwave electrode. In the figure, the strip 3 'and the transmission line 9a can be formed by etching means or the like from conductor layers formed on the dielectrics 7 and 15, respectively. In the figure, reference numeral 16 is a propagation path connecting the transmission line 9a and the strip 3 ', and 17 is a conductor layer in which a dielectric 15 is laminated. The transmission line 9a and the conductor layer 17 are insulated from each other. In addition, the same code | symbol is attached | subjected to the member similar to what was shown in FIGS. 1-3, and description is abbreviate | omitted. Further, the gas passage is not shown in FIG.
[0057]
As shown in FIG. 14, the electric field generation form by the strip antenna is similar to the state of the first embodiment in which two slots 3 are paired, but the thickness of the dielectric 12 is determined. Although different from the method, a spatially uniform plasma can be generated, and a plasma having a rectangular cross section can be easily created.
[0058]
【The invention's effect】
As described above, the microwave plasma generating antenna of the present invention has electrodes formed of slots formed in a conductor layer or strips made of a conductor layer arranged in a matrix on the entire surface of the plasma generation region, and the surface is covered with a dielectric. Since the high-frequency power having a frequency for generating the microwave is supplied from the multistage power distribution circuit and the microwave is resonated by the electrodes, energy is evenly distributed to all the electrodes. And a rectangular plasma can be easily produced. Therefore, in the manufacturing process of a liquid crystal display such as a large-sized television, a high-quality film can be manufactured at high speed, and the film-forming apparatus can be made to the minimum necessary size.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view conceptually showing a state in which a microwave plasma generating antenna according to a first embodiment of the present invention is incorporated in a plasma processing apparatus.
2 is a partial perspective view showing a structure of a slot portion of the antenna shown in FIG. 1. FIG.
FIG. 3 is a plan view showing a planar structure of the antenna in which the upper layer of the antenna shown in FIG. 1 is sequentially removed from the plasma processing chamber side;
FIG. 4 is an explanatory diagram for explaining a state in which propagation can propagate through plasma due to a difference in covering a slot line with a dielectric, and A is a view showing a state in which a slot and a propagation direction of propagation coincide with each other. B is a diagram schematically showing the positional relationship between the generated plasma, the dielectric, and the slot, and C is a diagram showing the cross section of B.
FIGS. 5A and 5B are diagrams showing assumptions for modeling a slot antenna for deriving the relationship between the thickness of a dielectric and a slot, and FIG. 5A is a diagram showing how an electric field is generated in a slot; FIG. Is a diagram in which the model is replaced with a model of a magnetic current plate antenna that generates an electric field equivalent to, and C is a diagram in the case where the model is replaced with a cylindrical magnetic current antenna model equivalent to B and can be handled by mathematical expressions.
6 is a diagram showing the relationship between the quantities of the mathematical model when a magnetic current flows on the surface of the magnetic flow path shown in FIG. 5C. FIG.
FIG. 7 is an explanatory diagram showing a relationship between a cross section of a magnetic current flow path (transmission path) and two integration paths, with a region where a stable plasma image is generated as a reference magnetic potential source.
FIG. 8 is a graph using a logarithmic memory when the x value is taken on the horizontal axis of the function F (x) shown in [Formula 8] and [Formula 9], and A is when x is 1 or less. , B represents a case where x is 1 or more, and t represents the case.
FIGS. 9A and 9B are graphs showing radio wave patterns of radio waves depending on the thickness of a dielectric; A is a case where radio waves are shielded and do not propagate; and B is a case where radio waves are not shielded and propagate through plasma. The arrows in the figure indicate the propagation direction.
FIG. 10 is a diagram showing the plasma frequency dependence of the dielectric layer thickness of a slot antenna, using a dielectric with a dielectric constant of 3 and the antenna diameter corresponding to the slot width being 2 mm. , B are values when the antenna diameter is 0.2 mm.
FIG. 11 is a diagram subsequent to FIG. 10 showing the plasma frequency dependence of the dielectric thickness of the slot antenna, where A uses a dielectric with a dielectric constant of 5 and matches the slot width; The value is when the Andena diameter is 2 mm, and B is the value when the antenna diameter is 0.2 mm.
FIG. 12 is a plan view for explaining the circuit configuration of the power splitter used in the first embodiment of the present invention.
FIG. 13 is a partial perspective view of a microstrip antenna according to a second embodiment of the present invention.
FIG. 14 is a perspective view showing that the microstrip antenna is dropped with a two-element slot array antenna.
FIG. 15 is a plan view showing an example of a slot arrangement of a radial slot line antenna according to a conventional example.
[Explanation of symbols]
3 slot 3 'strip 4 antenna (antenna for generating microwave plasma)
6 Material 9a Transmission path 9b Tip 12 Dielectric

Claims (2)

An array antenna composed of a plurality of slot antenna elements that resonate with microwaves is used for plasma generation, and the surface of the array antenna on which the plurality of elements are arranged is covered with a dielectric, and the microwave generation is performed for each element. Forming an energy supply network of a transmission line that feeds high-frequency power of the microwave plasma generating antenna in which the plurality of elements are arranged in a planar shape, the dielectric coating thickness is such that the slot width is a, When the coating thickness of the dielectric is b, the dielectric constant of the coating dielectric is ε, the frequency of the microwave is f, the frequency of the plasma is f _p , and the propagation speed of radio waves is c ₀ , the following [ An antenna for generating microwave plasma, wherein the inductance L _m ( ω ) defined by the equation ( 1 ) is a value of b from a negative value to a positive value, that is, _bc or more.

However, the ω 2πf, is ω p is 2πf _p.  2. The microwave plasma generating antenna according to claim 1, wherein a plasma processing gas is supplied to a back side of the antenna and supplied to a front side of the antenna from a plurality of gas supply paths penetrating the antenna.

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