JP4103016B2 - Inclined decel apparatus and ion beam forming method thereof - Google Patents

Description

この数式は、Ｄc ＝Ｄが望ましい。ここで、Ｌ₁ （第１の間隙），Ｌ₂ （第３の間隙）は、前側及び後側のギャップ長さであり、Ｌs は、２つの抑制電極間のドリフト空間である第２の間隙である。また、φは、ビーム基軸に対して第２の間隙で曲げられたイオンビームの偏向角度である。
ディセル装置は、概略的には、
Ｌd 〜Ｌ₁ ＋Ｌ₂ ＋Ｌs （６）
で与えられ、ここでＬd はディセル電極の長さである。
【００５１】
上記の全てのパラメータを変換することによって、商業的な高電流型イオン注入装置に一番適合するものを決定することができる。
ディセル装置を機械的に単純化すると、θ₁ ，θ₂ ，及びＤは、不変数とみなすことができ、さらに、ディセル電極は、ディセル比の広いレンジで作動すると考えれば、設計を単純化して、例えば、θ₁ ＝３０°、θ₂ ＝１５°とし、Ｄ＝２ｃｍ，Ｌ₁ ＝Ｌ₂ ＝１ｃｍ，Ｌs ＝８ｃｍとしたとき、現在の高電流型イオン注入装置において、Ｌd は約１０ｃｍとなる。
【００５２】
また、
【表１】

は、上記設計値におけるいくつかのエネルギーレベルにおける作動パラメータを示す表である。各電極の傾斜角度は、固定されており、それぞれのオフセット修正距離Ｄc は、互いに接近している。イオン注入装置の性能は、機械軸から１または２ｍｍだけのわずかなオフセットされただけでは影響を受けない。後側電極が接地電位（０電位）にあるとするならば、他の電極の電位を決定することができ、抑制電極の電位は、−（Ｕs −Ｕ₂ ）であり、前側電極の電位は、−（Ｕ₁ −Ｕ₂ ）である。
【００５３】
図５は、電極の傾斜角度が固定されている場合における傾斜ディセル装置の一例の詳細なグラフであり、オフセット修正距離と、ディセル比の関数として変化する抑制比を示している。これから、ディセル比が３より大きい場合には、オフセット修正距離が、ほんの僅かなだけ変化することが明らかである。この結果は、機械的構造を変更することなく、ディセル比の広範囲に渡って、傾斜ディセル装置３が動作可能であることを意味している。したがって、傾斜ディセル装置３は機械的に簡易に作製することができる。
【００５４】
空間電荷は、超低エネルギーのイオンビームの運動において、非常に大きな影響を与えるということが知られている。空間電荷の力に起因して、イオンビームの横方向への拡がりは、Ｕ^-3/2の関数で与えられる。したがって、傾斜ディセル装置の第３の間隙の後方のビーム伝搬は、その設計研究における非常に重要な問題となる。
【００５５】
電位差に起因して、傾斜ディセル装置３の第１と第３の２つの間隙は、また、横方向に集束する力もイオンビーム上に与えることになる。他の通常の電極のように、各間隙の電位差は、ビームの集束力の大きさを決定する。傾斜ディセル装置に関して、Ｕs ／Ｕ₁ の抑制比は、集束力の大きさを変更する手段を提供する。注意深いシミュレーションによる設計研究及び必要なビーム試験研究によって、傾斜ディセルのオフセット修正及び横方向の集束の両方を満足する抑制比を選択することができる。
【００５６】
図１において傾斜ディセル装置３の後段に置かれた可動式ファラデーカップ９は、物理的に許容される範囲内で可能な限りウエハ７に近設させて取り付けることが示唆されている。ファラデーカップ９から傾斜ディセル装置３までの距離は、長くなり、ファラデーカップ９からウエハ７までの距離が短くなる。このファラデーカップ９は、減速された超低エネルギービームにのみ働く。減速されたビームを調整しているとき、そのファラデーカップは機械軸１０上に位置している。
【００５７】
このファラーデカップ９の利点として、２つの面がある。第１には、作動中、オペレータは、ファラデーカップ９でのイオンビーム電流が最大となるように調整し、これによりオフセットは正しく修正され、イオンビームは機械軸１０に沿って進ませることができる。第２には、輸送経路が短くなるので、大部分のイオンビームがウエハに到達できる。低エネルギーの伝搬は困難なため、距離が長くなるとビーム損失が大きくなる。調整後、ファラデーカップ９は機械軸１０から引き離される。
【００５８】
次に、図６において、本発明における第２の実施の形態としての傾斜ディセル装置１００が示されている。機械的に単純構造にするために、２つの抑制電極は一緒に接続され、抑制ボックス２２を形成している。このボックスは、その表面に多くの溝が形成されており、真空達成率、すなわち、真空室からの空気排出の容易性が改善されている。抑制ボックス２２は、確実にその内部空間がフィールドフリー（零電界）である。
【００５９】
この良好な傾斜ディセル装置１００は、ディセルモード時の超低エネルギービームに動作するだけでなく、比較的高いエネルギービームに対して動作するドリフトモードにおいても、両立して動作可能である。この傾斜ディセル装置１００の好ましい機械的構造は、図７ａないし図７ｃに示されており、その好ましい形態において、３つの動作モードを有する。
【００６０】
傾斜ディセル装置１００は、前側電極２１、抑制ボックス２２及び後側電極２３の３つの主要部を含んでいる。その長さは、所定の商業的な高電流型イオン注入装置に最適となるように決定される。ディセルモードで動作しているときの電極の位置は、図７ａに示される。
【００６１】
この前側電極２１は、質量分析磁石２の焦点に位置している。前側電極２１は、二つの開口を有し、１つは、ボロン用の開口２５であり、他の１つは、リン用の開口２４である。両開口２４，２５は、高電流型イオン注入装置に備わる開口と同様の作用を呈する。選択されたイオンのために設けられる開口の１つは、機械軸１０から設計されたオフセット距離だけ離れた位置に置かれている。他の抑制ボックス２２と後側電極２３は、それらの設計位置に置かれている。終端に位置する後側電極２３の開口２８は、ちょうど機械軸１０上に位置する。また、これら３つの部材は、すべて設計された電位に接続されている。
【００６２】
前側電極２１の前で発生した中性粒子は、前開口２５と後開口２８が対向していないために、後側電極２３の開口２８を通過することができない。抑制ボックス２２内で発生したこれらの中性粒子は、最後の開口２８を通過することができるが、これらは、ウエハ７に到達する前に最終的にイオンビーム経路の壁に衝突する。したがって、イオン注入装置に傾斜ディセル装置１００を使用した場合、ウエハ等の加工物にイオン注入する際にエネルギー汚染が起こらない。
【００６３】
イオンビームは、第３の間隙から実際に減速される。これは、ウエハまでのビームの移動距離が、従来のディセル装置の場合の移動距離と比較して、傾斜ディセル電極の長さの分だけ短くなることを意味している。したがって、このビームの移動距離が短くなることによって、ウエハまでの輸送中に失われるイオンビームが少なくなり、それだけウエハに到達するイオンが増加し、傾斜ディセル電極１００によってビーム電流は、従来のディセルのビーム電流よりも高くなる。
【００６４】
図７ｂのように、ボロン用のドリフトモードで動作しているときには、電位が０のターンオフ状態になる。それから前側電極のボロン用開口２５は、機械軸１０上に位置するように合わせられ、また、抑制ボックス２２及び終端の後側電極２３は、機械軸１０から引き下げられている。このため、ボロンイオンのビームは、図７ｂに示すように、前側電極の開口２５を通過し、他の電極の影響を受けないでウエハまで直進することが可能となる。リンイオンのビームを使用する場合には、前側電極２１は、図７ｃに示されるように、軸１０上にリン用開口２４が位置するように再び調整される。このように、本発明の傾斜ディセル装置１００は、高電流型イオン注入装置のドリフトモードにおいて、ビーム経路の基軸上に所定のイオンを通過させる前側電極の開口を合わせるように調整できるので、傾斜ディセル電極は、ドリフトモードの操作に何ら悪影響を与えることがない。
【００６５】
次に、図８および図９において、本発明における第３の実施の形態としての傾斜ディセル装置２００が示されている。図８は、偏向角δθで、ディセル電極を通過するイオンビームの進行状態を示す原理図であり、図９は、このためのディセル電極３０〜３２の配置構造とイオンビームの進路を示している。この実施形態において、傾斜ディセル装置２００は、傾斜する３つのディセル電極で構成され、前側電極３０、抑制電極３１、後側電極３２からなる。各電極は、それぞれイオンビームが通過する開口３３，３４，３５を有している。前側電極３０は、機械軸（基軸）に垂直な軸に対してθ₁ 傾斜し、また後側電極３２はθ₂ 傾斜している。
【００６６】
図８において、質量分析磁石を通過したイオンビームは、偏向磁石によって、機械軸１０から偏向角δθだけ偏向した方向に進む。このイオンビームは、３つのディセル電極３０〜３２の開口を通過して、イオンと中性粒子が分離される。イオンは、各ディセル電極によってその進行方向が屈曲させられて、後側電極３２の開口から出るとき、イオンビームのオフセット距離Ｄが完全に修正されずに、機械軸１０から所定距離ｄ₁ だけ離れて機械軸と平行に進む。このため、第３の形態においては、上述したオフセット距離Ｄをゼロに修正する第１，第２の実施形態とは異なっている。
【００６７】
このように、オフセット距離Ｄをｄ₁ に修正する場合でも、イオンと中性粒子は分離される。すなわち、イオンは、機械軸１０から所定の距離だけ離れた状態でウエハ表面に衝突し、一方、中性粒子は、ディセル電極の影響を受けることなく開口を通過してまっすぐに進むが、ウエハに近い距離にあるスクラッパー(scraper) ５０によって、その進行が妨げられている。本形態では、中性粒子を捕捉するスクラッパー５０は、機械軸１０に直交した位置に配置されているが、ディセル電極３２を通過した中性粒子がウエハに到達できないように配置すれば良い。図８において、このスクレーパ５０に衝突する中性粒子と、ウエハ７に衝突する前にスクラッパーの延長線上を通過するイオンとの距離は、ｄ₂ だけ離れており、イオンは中性粒子と完全に分離してウエハ７に衝突する。
【００６８】
次に、図１０および図１１において、本発明における第４の実施の形態としての傾斜ディセル装置３００が示されている。この形態では、ディセル電極が２つであり、ディセル電極４０，４１の各開口４２，４３をイオンと中性粒子は共に通過する。これらの電極は、機械軸１０に垂直な軸に対してθ傾斜している。この場合も、イオンはディセル電極４０，４１によって減速されて開口内を屈曲して進み、中性粒子は、影響されずに直進する。このために、イオンと中性粒子は分離され、そして中性粒子はスクラッパー５０によって捕捉されてしまうが、イオンはウエハ７に到達できる。
【００６９】
【発明の効果】
以上述べたことから明らかなように、本発明の傾斜ディセル装置は、簡単なディセル電極の構造で、イオンビームの減速及び分離の両方を同時に兼ね備えているので、イオン注入装置を小型化し、かつエネルギー汚染を防止することができる。
【００７０】
また、この傾斜ディセル装置は、ディセル電極の長さ及び配置により、ウエハまでのビームの移動距離を短くし、さらにディセル比を飛躍的に大きくすることができるので、超低エネルギービームに対して大電流を供給することができる。さらに、傾斜ディセル装置自体も、操作が容易な機械的構造であるために単純化されている。
【００７１】
また、この傾斜ディセル装置は、ディセルモード以外に、高電流イオン注入装置のドリフトモードにおいても使用でき、完全に両立モードに対して適用できる。そのとき、ドリフトモードの操作に何ら影響を及ぼすことがない。
【図面の簡単な説明】
【図１】本発明に係る傾斜ディセル装置が設けられる高電流型イオン注入装置の概略図である。
【図２】イオンビームの減速及び中性粒子の分離を同時に実現するために、傾斜して配置した２つのディセル電極の原理を説明する図である。
【図３】４つの電極と３つの間隙を有する構造からなる本発明の第１の実施形態を示す傾斜ディセル装置の動作を説明するための図である。
【図４】図３における傾斜ディセル装置の構成を示す模式図である。
【図５】オフセット距離とディセル比の関係を示すグラフである。
【図６】本発明に係る第２の実施形態を示す３つのディセル電極を備える傾斜ディセル装置の構成を示す模式図である。
【図７】図６における本発明の傾斜ディセル装置における３つの動作モードを示し、(a) は、ディセルモード、(b) は、ボロンイオンビームのドリフトモード、(c) は、リンイオンビームのドリフトモード、における各ディセルの動作を説明するための図である。
【図８】本発明に係る第３の実施形態を示す３つのディセル電極を備える傾斜ディセル装置の動作を説明するための図である。
【図９】図８における傾斜ディセル装置の構成を示す模式図である。
【図１０】本発明に係る第４の実施形態を示す２つのディセル電極を備える傾斜ディセル装置の動作を説明するための図である。
【図１１】図１０における傾斜ディセル装置の構成を示す模式図である。
【符号の説明】
１ イオン源
２ 質量分析磁石
３ ディセル電極
４ フラグファラデーカップ
７ ウエハ
９ ファラデーカップ
１０ 機械軸（基軸）
１１ ドリフトモードのイオンビーム
１２ ディセルモードのイオンビーム
１７，１８，１９，２０ ディセル電極
２１ 前側電極
２２ 抑制ボックス
２３ 後側電極
２４，２５，２７，２８ 開口[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a decel apparatus and a method thereof capable of generating an ultra-low energy ion beam free from energy contamination and directly used in a high current ion implantation apparatus used in semiconductor manufacturing technology and the like. About.
[0002]
[Prior art]
The ion implantation apparatus generates ions such as B + and P + from an ion source to generate an ion beam.TheA semiconductor product is manufactured by implanting ions into one or a plurality of wafers formed and provided in an ion implantation chamber.
[0003]
Ions generated in and released from the ion source chamber are mass separated by the difference between mass and charge and are accelerated to form an ion beam. The ion beam has sufficient energy to implant ions into the wafer and is directed along the beam path into the ion implantation chamber and enters one or more wafers.
[0004]
In a conventional ion implantation apparatus, an IC (integrated circuit) can be manufactured by selective implantation using a mask or an inactive layer. The apparatus for this implantation technique is large, complex, expensive, and has limited capabilities in that it can implant ions with low energy.
[0005]
In the fabrication of integrated circuits, high current and ultra-low energy ion implantation will be required in the near future to form an Ultra-shallow junction. Therefore, the latest high current ion implanters used commercially need to extend their operating range to energies as low as 1 KeV (kiloelectron volts) or several hundred eV.
[0006]
In order to obtain a high current at ultra-low energy, the ion beam is typically extracted from the ion source with relatively high energy, then mass analyzed and transported to a location closer to the wafer. The ion beam is then decelerated to the required ultra-low energy. An apparatus for decelerating the ion beam is called decel. The decelerated ion beam is then conveyed to a target such as a wafer.
[0007]
Also, the charged ions that form the ion beam repel each other by so-called space charge forces, which become stronger at lower energies. Due to the force of this space charge, the lateral spread of the ion beam is
(√m / √q) × Iz² / U^3/2                     (1)
Is proportional to
[0008]
Here, the ion beam is assumed to be a uniform beam having a circular cross section. m and q are ion masses and charges, I is a beam current, U is a beam energy, and z is a passing distance of the ion beam. As is apparent, a shorter moving distance of the ion beam is suitable for obtaining a larger current.
[0009]
Thus, it is anticipated that a decel device will be provided to produce current commercial ion implanters that provide ultra-low energy beams at high currents. However, it is considered that this decel apparatus has two technical problems that are important as design problems.
[0010]
The first problem is due to energy contamination. This is because ions collide with the residual gas molecules before they reach the decel electrode, some ions become neutral particles, and after passing through the decel electrode, the energy of the ions is reduced, but the neutral particles Energy contamination is caused by high energy neutral particles reaching the wafer together with ions while maintaining energy. In addition, as the beam current is increased to increase the beam current, the harm of energy contamination becomes more serious. Therefore, ideally, a decel device having not only a deceleration function but also a separation function is most desirable. However, such decel devices have not been used in commercial high current ion implanters.
[0011]
The second problem is caused by a rapid increase in space charge force of the ultra-low energy beam. When the ion beam energy is lowered, the space charge force becomes extremely large and charged ions repel each other. For this reason, when the flight distance of the ion beam to the wafer becomes long, it becomes difficult to cause ions to reach the wafer. Therefore, it is necessary to shorten the distance from the decel apparatus to the wafer, and this shortening of the distance is very important in order to obtain an ultra-low energy beam with a large current. In order to solve this second problem, it is necessary to make the separation device for separating the neutral particles from the ion beam as compact as possible.
[0012]
In addition, a decel may be used in a medium current ion implanter that requires higher beam energy than that of a high current ion implanter. The conventional decel used in this medium current ion implantation apparatus or the like is an electrode having an opening that is positioned perpendicular to the traveling direction of the ion beam. Thus, neutral particles can pass through it.
[0013]
As described above, the separation device having the separation function is provided in the subsequent stage of the decel in order to remove energy contamination. Therefore, in order to separate the neutral particles from the ion beam, two types of apparatuses are generally used. The first device is an electrical deflection device in which the transverse electric field bends the ion beam and has no effect on the neutral particles. The ion beam and neutral particles are separated after passing a predetermined movement distance. The second apparatus is a magnet that bends the ion beam by a magnetic field transverse to the traveling direction of the ion beam, thereby separating the ion beam from the neutral particles.
[0014]
[Problems to be solved by the invention]
However, the first device diverges individual ions of the ion beam over a large area, which is a fatal defect for carrying ultra-low energy beams over long distances, and for our desired purpose. Cannot be used.
[0015]
In addition, the magnet as the second device is usually large and has a long distance to the wafer, so that the beam flight path becomes too long for use with an ultra-low energy beam.
[0016]
In addition, the above-described concept for obtaining a high current at ultra-low energy is based on the so-called energy contamination caused by high-energy neutral particles, so that a commercially available high-current ion implanter is available. Has never been applied to reality in the past.
[0017]
Harmful neutrals are generated in the front region of the decel electrode by collisions between ions and residual gas molecules. The neutral particles generated here pass straight through the decel electrode and reach the wafer. Neutral particles have higher energy than the decelerated ions, so they will enter deeper regions of the wafer. This is called energy contamination and becomes an essential problem when using the decel device.
[0018]
Energy contamination can in principle be removed by separating neutral particles from the ion beam.
[0019]
Therefore, an object of the present invention is to provide an ion beam forming method and a new tilted decel apparatus for the ion beam forming method that can simultaneously achieve deceleration of the ion beam and separation of neutral particles.
[0020]
[Means for Solving the Problems]
  In order to achieve the above object, the present invention has the structure described in each claim. The new decel device of the present invention will be referred to as a tilted decel device, which is tilted.pluralDiceLEThis is because the poles are not arranged perpendicular to the base axis of the beam path in the ion implanter.In addition, the basic axis used in this specification represents the central axis of the ion beam that reaches the wafer in a straight line from the mass analysis magnet.
[0021]
The present invention discloses a preferred structure of a tilted decel apparatus that can be used by incorporating it into current high current ion implanters. With this preferred structure, it is possible to obtain an ultra-low energy ion beam free of energy contamination at a current larger than that currently available. The inclined decelerating device is simple and easy to operate.
[0022]
The present invention provides a completely new decel device having both functions of ion beam deceleration and neutral particle separation. The length of the high energy portion of the tilt decel device in the present invention is the same as that of the conventional decel device. It is slightly longer than the length and has a structure suitable for shortening the flight distance of the decelerated beam to the wafer.
[0023]
  The tilted decel apparatus according to the present invention tilts a plurality of decel electrodes having openings in a beam path between a mass analyzing magnet and a wafer with respect to an axis perpendicular to a base axis of the beam path, and the plurality of decel electrodesDeviation of the opening of the front electrode and the opening of the rear electrode by a predetermined offset distancePlace and
  Adjust the mass spectrometry magnet to move away from the base axisLocatedAn ion beam passing through the opening of the front electrode is on the base axis in response to an ON operation of the plurality of decel electrodes.Located in the aboveRear electrodeOpeningFurther, a decel mode in which the ion beam travels toward the wafer on or parallel to the base axis of the beam path, and
  And turning off the plurality of decel electrodesThe opening of the front electrode configured to be positioned on the base axis by changing the position of the front electrode is an ion beam.To pass,AndA drift mode in which another decel electrode positioned behind the front electrode is positioned in a zero electric field space that is not affected by an electric field, and an ion beam that has passed through the opening of the front electrode travels along the base axis without being decelerated. And
  In the decel mode,An offset distance of the ion beam from the base axis at a position where the ion beam is incident on the plurality of decel electrodes and a deflection angle of the incident ion beam with respect to the base axis are determined and formed between the plurality of decel electrodes. By decelerating the ion beam and simultaneously separating neutral particles from the ion beam by generating an electric field in the gapDoIt is characterized by that.
[0024]
According to a further preferred configuration, there is a gap between at least two sets of decel electrodes and a gap in the drift space composed of suppression electrodes, which ensures beam movement through the decel electrodes and the beam to the wafer. It is possible to adjust the focusing force by changing a suppression ratio, which will be described later, at the design stage of the inclined decel device.
[0025]
  Also inclinedpluralIn the first gap between the electrodes of the decel electrode, the ion beam isAcceleration and deflectionNext, the ion beam travels through the second gap in the drift space in a direction approaching the base axis of the beam path, and further decelerates the ion beam in the third gap.And deflectionThe beam offset distance was corrected and the ion beam was tiltedpluralAfter passing through the decel electrode, it can be moved in parallel along the base axis of the beam path, and in this case, the offset distance D can be corrected to zero.
[0026]
In addition, since the front opening and the rear opening of the decel electrode are arranged to be deviated by a predetermined offset distance, neutral particles generated in front of the front electrode of the decel electrode are Further, the neutral particles generated in the suppression box that constitutes the suppression electrode finally do not collide with the wall before reaching the wafer. As a result, the neutral particles are prevented from colliding with the wafer, and energy contamination is not generated.
[0027]
Furthermore, according to the configuration of the present invention, in the case where the number of inclined decel electrodes is two to three, even if neutral particles can pass through the openings of the decel electrodes, ions and neutral particles are reliably separated. The neutral particles are captured before reaching the wafer, and only ions enter the wafer.
[0028]
Thus, according to the present invention, the neutral particles are almost completely separated from the ion beam. Therefore, if the ratio between the beam energy before deceleration and the beam energy after deceleration is referred to as the decel ratio, The ratio can be quite large. For example, if the decel ratio is 3, a beam from 3 KeV to 1 KeV can be produced, and if the decel ratio is 6, a beam from 3 KeV to 0.5 KeV can be produced, and the decel ratio is as high as about 8. 0.25 KeV can be made from 2 KeV.
[0029]
Furthermore, in order to increase the current of the decelerated ultra-low energy beam, the current can be increased before decelerating in the decel electrode so that the decel ratio becomes very large. Therefore, the new tilted decel device can reliably apply a large current to the ultra-low energy beam in the current high current ion implanter.
[0030]
The above objects, advantages and features of the present invention will be better understood on the basis of the detailed description and drawings illustrating the preferred embodiments of the present invention.
[0031]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram of a high current ion implantation apparatus including a tilted decel device 3 according to the first embodiment of the present invention. The tilted decel device 3 includes a plurality of decel electrodes 17, 18, 19, and 20. Is displayed. BACKGROUND ART An ion implantation apparatus is mainly used for performing ion implantation by colliding an ion beam against a semiconductor silicon wafer used in an integrated circuit. The ion beam 11 located on the mechanical axis is extracted from the ion source 1 and further bent by about 90 ° by the mass analysis magnet 2. At the focal point of the magnet 2 in the horizontal direction, the ion beam 11 is directed by the mass analysis magnet according to the difference in bending due to the mass difference, and passes through the mass separation hole provided in the mass analyzer. Thus, only necessary ions are separated.
[0032]
If necessary, since the beam size is small in the horizontal projection plane of the focal point, the decel electrodes 17 to 20 are provided at the focal point position. The openings of these decel electrodes also function as mass separation holes. For the above purpose, the front electrode 17 of the inclined decel device 3 of the present invention can be set at the focal position.
[0033]
In FIG. 1, these decel electrodes are arranged in pairs of two electrodes, and each pair of electrodes has an angle θ relative to an axis perpendicular to the base axis.₁ , Θ₂ Just tilted. In addition, each opening is located approximately at the center of each decel electrode, the opening width is substantially equal to the offset distance, and the dimension in the embodiment is about 2 cm. In general, the cross section of the beam is elliptical, and the longitudinal direction of the ellipse corresponds to the longitudinal direction of the opening. Therefore, the opening of the electrode is usually rectangular, and its vertical dimension is larger than the longitudinal opening width of the cross section of the ion beam.
[0034]
The ion beam may or may not be decelerated according to the on / off state of the decel electrodes 17-20. After passing through the decel electrodes 17 to 20, the ion beam finally reaches the wafer 7. On the back surface of the wafer 7, the disk Faraday cup 8 detects the sample current of the ion beam. Many other necessary devices are arranged between the inclined decel device 3 and the wafer 7.
[0035]
  The flag Faraday cup 4 shown in FIG. 1 measures the current of the ion beam while adjusting the beam. The electron reflector 5 stabilizes the influence of the plasma shower 6. The plasma shower 6 supplies electrons for reducing the charging of the wafer. Another movable Faraday cup 9To measure the beam current of an ultra-low energy ion beam,It has been suggested that it can be mounted as close to the wafer as is physically acceptable. The Faraday cup 9 facilitates the adjustment of the decelerated ultra-low energy beam and allows a large current to reach the wafer 7.
[0036]
Similarly, in the other embodiments, the new inclined decel device 3 according to the present invention is composed of a plurality of electrodes, and includes at least two electrodes. All electrodes are tilted with respect to an axis perpendicular to the base axis 10 of the beam path in order to achieve both separation and deceleration (or acceleration). When current commercial high current ion implanters are operating in the drift mode (non-decel mode), which is the main working mode, the decel electrode of the present invention has a suitable aperture as will be described later. Located in a field-free space. The center of the ion beam 11 always moves along the mechanical axis, ie the base axis 10 of the beam path. When the ion beam is operating in decel mode, to form a non-linear beam trajectory that can pass through all four apertures from the mass analyzing magnet 2 in front of the tilted decel device 3 to the wafer 7, The electrodes are adjusted as shown in FIG.
[0037]
Therefore, neutral particles cannot pass through the rearmost decel electrode 20, and no energy contamination occurs. The potential of each electrode 3 is adjusted to the design value. The mass spectrometry magnet 2 operates with a magnetic field strength slightly lower than the normal setting. By adjusting the mass analysis magnet 2, the ion beam 12 is positioned at a predetermined offset distance D from the mechanical shaft 10 and has a small deflection angle δθ at the end of the magnet 2.
[0038]
When the ion beam drifts and reaches the entrance of the decel electrode 3, the offset distance D increases with the deflection angle δθ. The total offset distance is required to be greater than or at least equal to the mass separation hole, which is on the order of 2 cm. The preferred tilting decelerating device 3 of the present invention corrects this offset distance through four decelerating electrodes and simultaneously decelerates the ion beam. After passing through the decel, the decelerated ion beam again moves along the mechanical axis 10 and reaches the surface of the wafer. The center of the ion beam in the decel mode is indicated by reference numeral 12 in FIG.
[0039]
The present invention proposes that the decel electrode is disposed at an angle in order to achieve both functions of separating neutral particles from the ion beam and decelerating the ion beam at the same time. FIG. 2 illustrates the principle of such a pair of inclined electrodes.
[0040]
In FIG. 2, the internal electric field E acts perpendicularly to the two electrodes 13 and 14. When both electrodes are inclined at the same angle, the electric field acts so that two component forces Ex and Ez work. The component force Ez is a conventional deceleration electric field. By this component force Ex, the traveling direction of the ion beam is bent, while the moving direction of the neutral particles (opposite to Ez) is kept straight. As a result, the ion beam is decelerated and separated from neutral particles.
[0041]
Depending on the potential difference between the two electrodes, the ions are decelerated or accelerated. Since the internal electric field leaks from the openings 15 and 16 provided in the electrodes, the electric field distribution is affected. However, the present invention believes that if the aperture is small compared to the size of the electrode, the overall effect of the electric field in the ion beam will not change clearly.
[0042]
However, in the preferred decel apparatus, a suppression electrode is provided between two pairs of electrodes in order to prevent electrons from being accelerated between the inclined decel electrodes having two electrodes as shown in FIG. Yes.
[0043]
This suppression electrode complicates the design of the decel device. The present invention provides a practical decel device having both this suppression function and the above two functions, ie, deceleration and separation. FIGS. 3 and 4 are diagrams showing how a tilted decel device having three gaps formed between four electrodes and each pair of electrodes operates. FIG. 3 corresponds to the tilted decel apparatus 3 used in the overall configuration of the ion implantation apparatus shown in FIG.
[0044]
That is, the four electrodes are divided into two sets. The first set of two electrodes 17, 18 are at an angle θ with respect to the mechanical axis 10.₁ Inclined to form a first gap. The second set of two electrodes 19, 20 has an angle θ with respect to the mechanical axis 10.₂ Inclined to form a third gap. Since the second and third electrodes 18 and 19 are suppressing electrodes and are at the same potential, a drift space without an electric field is formed as a second gap between the first set and the second set of electrodes. To do.
[0045]
For ease of explanation, the potential of each electrode will be expressed by a beam energy level. In FIG. 3, U₁ And U₂ Represents the beam energy before and after passing through the inclined decelerating device 3, and U₁ Is the energy level before passing through the decel electrode 17 and U₂ Is the energy level after passing through the decel electrode 20. Us is the beam energy level between the decel electrodes 18 and 19 acting as a suppression electrode. For these decel electrodes, usually Us> U₁ > U₂ The relationship holds. For convenience, U₁ / U₂ Is the decel ratio, and Us / U₁ Is defined as the suppression ratio.
[0046]
The ion beam enters the decel electrode with a deflection angle δθ and an offset distance D determined at the position where the ion beam enters the aperture of the decel electrode. In FIG. 3, the deflection angle δθ is an angle with respect to the base axis 10 of the incident ion beam, and the offset distance D indicates the distance that the ion beam is separated from the base axis 10 of the beam path. This ion beam is first accelerated and deflected in the first gap to the decel electrode 18 after entering the decel electrode 17. Then, the ion beam drifts in the drift space in the second gap between the decel electrodes 18 and 19, approaches the base axis 10, is decelerated in the third gap between the decel electrodes 19 and 20, and returns to the base axis 10. Will be deflected again. In the first embodiment, the offset distance is finally adjusted to zero.
[0047]
The initial offset distance and deflection angle in the ion beam are given by adjusting the mass analysis magnet 2. The first-order approximation value of the offset distance D and the deflection angle δθ at the entrance of the decel are given as follows.
[0048]
δθ = δR / R (2)
D = δR (1 + F / R)
Here, R is the radius of curvature of the magnet 2, F is the distance from the magnet to the decel electrode 17, D is the offset distance required for the decel electrode, δθ is the deflection angle, and δR is the offset distance at the exit of the magnet ( 1 and 3). Usually, since R is a value much larger than D, δθ and δR are considerably small values and do not affect the performance of the magnet.
[0049]
According to the so-called Snell's law, the angles have the following correlation:
√U₁ sin (θ₁ + Δθ) = √U sin (θ₁ + Δθ−φ) (3)
√Us sin (θ₂ -Φ) = √U₂ sinθ₂           (4)
By solving this equation of motion, it is possible to estimate the position of the decel electrode aligned with the focal point of the beam offset distance. The offset correction distance Dc is expressed by the following formula.
[0050]
[Expression 1]

In this formula, it is desirable that Dc = D. Where L₁ (First gap), L₂ (Third gap) is the gap length of the front side and the rear side, and Ls is the second gap which is a drift space between the two suppression electrodes. Φ is the deflection angle of the ion beam bent at the second gap with respect to the beam base axis.
The decelerating device is roughly
Ld to L₁ + L₂ + Ls (6)
Where Ld is the length of the decel electrode.
[0051]
By converting all of the above parameters, the best fit for a commercial high current ion implanter can be determined.
When the decelering device is mechanically simplified, θ₁ , Θ₂ , And D can be considered invariant, and further, assuming that the decel electrodes operate in a wide range of decel ratios, simplify the design, eg, θ₁ = 30 °, θ₂ = 15 °, D = 2cm, L₁ = L₂ = 1 cm and Ls = 8 cm, Ld is about 10 cm in the current high current ion implantation system.
[0052]
Also,
[Table 1]

These are tables showing operating parameters at several energy levels at the above design values. The inclination angle of each electrode is fixed, and the respective offset correction distances Dc are close to each other. The performance of the ion implanter is not affected by a slight offset of 1 or 2 mm from the machine axis. If the rear electrode is at ground potential (0 potential), the potential of the other electrode can be determined and the potential of the suppression electrode is-(Us -U₂ ) And the potential of the front electrode is-(U₁ -U₂ ).
[0053]
FIG. 5 is a detailed graph of an example of a tilted decel apparatus when the electrode tilt angle is fixed, showing the offset correction distance and the suppression ratio that varies as a function of the decel ratio. From this it is clear that when the decel ratio is greater than 3, the offset correction distance changes only slightly. This result means that the tilted decel device 3 can operate over a wide range of decel ratios without changing the mechanical structure. Therefore, the inclined decel device 3 can be easily manufactured mechanically.
[0054]
It is known that space charge has a very large influence on the motion of an ultra-low energy ion beam. Due to space charge forces, the lateral spread of the ion beam is U^-3/2Is given by the function Therefore, beam propagation behind the third gap of the tilted decel apparatus is a very important issue in the design study.
[0055]
Due to the potential difference, the first and third gaps of the tilted decel device 3 will also impart a lateral focusing force on the ion beam. Like other conventional electrodes, the potential difference across each gap determines the magnitude of the beam focusing force. Us / U for inclined decel equipment₁ The suppression ratio provides a means of changing the magnitude of the focusing force. Careful simulation design studies and required beam test studies can select a suppression ratio that satisfies both offset correction and lateral focusing of the tilted decel.
[0056]
In FIG. 1, it is suggested that the movable Faraday cup 9 placed at the rear stage of the inclined decel device 3 is attached as close to the wafer 7 as possible within a physically allowable range. The distance from the Faraday cup 9 to the inclined decel device 3 is increased, and the distance from the Faraday cup 9 to the wafer 7 is decreased. This Faraday cup 9 works only with a decelerated ultra-low energy beam. When adjusting the decelerated beam, the Faraday cup is located on the machine shaft 10.
[0057]
There are two aspects to this Faraday cup 9. First, during operation, the operator adjusts the ion beam current at the Faraday cup 9 to a maximum so that the offset is corrected correctly and the ion beam can be advanced along the machine axis 10. . Second, since the transport path is shortened, most of the ion beam can reach the wafer. Since propagation of low energy is difficult, the beam loss increases as the distance increases. After the adjustment, the Faraday cup 9 is pulled away from the machine shaft 10.
[0058]
Next, FIG. 6 shows an inclined decel device 100 as a second embodiment of the present invention. In order to make the structure mechanically simple, the two suppression electrodes are connected together to form a suppression box 22. The box has many grooves formed on the surface thereof, and the vacuum achievement rate, that is, the ease of air discharge from the vacuum chamber is improved. The inner space of the suppression box 22 is surely field free (zero electric field).
[0059]
This good tilted decel apparatus 100 can operate not only in the ultra-low energy beam in the decel mode but also in the drift mode that operates in a relatively high energy beam. The preferred mechanical structure of this tilted decel device 100 is shown in FIGS. 7a to 7c and in its preferred form has three modes of operation.
[0060]
The inclined decel device 100 includes three main parts: a front electrode 21, a suppression box 22, and a rear electrode 23. Its length is determined to be optimal for a given commercial high current ion implanter. The position of the electrodes when operating in decel mode is shown in FIG. 7a.
[0061]
The front electrode 21 is located at the focal point of the mass analysis magnet 2. The front electrode 21 has two openings, one is an opening 25 for boron, and the other is an opening 24 for phosphorus. Both openings 24 and 25 exhibit the same action as the opening provided in the high current ion implantation apparatus. One of the openings provided for the selected ions is located at a designed offset distance from the machine shaft 10. The other restraining box 22 and the rear electrode 23 are placed in their design positions. The opening 28 of the rear electrode 23 located at the end is just located on the machine shaft 10. These three members are all connected to the designed potential.
[0062]
The neutral particles generated in front of the front electrode 21 cannot pass through the opening 28 of the rear electrode 23 because the front opening 25 and the rear opening 28 do not face each other. These neutral particles generated in the suppression box 22 can pass through the last opening 28, but they eventually collide with the walls of the ion beam path before reaching the wafer 7. Therefore, when the tilted decel apparatus 100 is used for an ion implantation apparatus, energy contamination does not occur when ions are implanted into a workpiece such as a wafer.
[0063]
The ion beam is actually decelerated from the third gap. This means that the moving distance of the beam to the wafer becomes shorter by the length of the inclined decel electrode compared to the moving distance in the case of the conventional decel apparatus. Therefore, by shortening the moving distance of this beam, the ion beam lost during transportation to the wafer is reduced, and the number of ions reaching the wafer is increased accordingly. It becomes higher than the beam current.
[0064]
When operating in the drift mode for boron as shown in FIG. 7b, the potential is turned off. Then, the boron opening 25 of the front electrode is aligned so as to be positioned on the mechanical shaft 10, and the restraining box 22 and the rear electrode 23 at the end are pulled down from the mechanical shaft 10. Therefore, as shown in FIG. 7B, the boron ion beam passes through the opening 25 of the front electrode and can travel straight to the wafer without being influenced by other electrodes. When using a phosphorus ion beam, the front electrode 21 is again adjusted so that the phosphorus opening 24 is located on the shaft 10, as shown in FIG. 7c. As described above, the tilted decel device 100 of the present invention can be adjusted so that the opening of the front electrode through which predetermined ions pass is aligned on the base axis of the beam path in the drift mode of the high current ion implanter. The electrode has no adverse effect on drift mode operation.
[0065]
Next, FIGS. 8 and 9 show an inclined decel device 200 according to a third embodiment of the present invention. FIG. 8 is a principle diagram showing the state of travel of the ion beam passing through the decel electrode at the deflection angle δθ, and FIG. 9 shows the arrangement structure of the decel electrodes 30 to 32 and the path of the ion beam for this purpose. . In this embodiment, the tilted decel device 200 is composed of three tilted decel electrodes, and includes a front electrode 30, a suppression electrode 31, and a rear electrode 32. Each electrode has openings 33, 34 and 35 through which ion beams pass. The front electrode 30 is θ₁ The rear electrode 32 is inclined and θ₂ Inclined.
[0066]
In FIG. 8, the ion beam that has passed through the mass analysis magnet travels in a direction deflected by the deflection angle δθ from the mechanical axis 10 by the deflection magnet. The ion beam passes through the openings of the three decel electrodes 30 to 32 to separate ions and neutral particles. The ions are bent in the traveling direction by the respective decel electrodes, and when the ions exit the opening of the rear electrode 32, the offset distance D of the ion beam is not completely corrected, and the predetermined distance d from the mechanical axis 10 is obtained.₁ Only away and proceed parallel to the machine axis. For this reason, the third embodiment is different from the first and second embodiments in which the offset distance D is corrected to zero.
[0067]
Thus, the offset distance D is set to d₁ Even in the case of correction, the ions and neutral particles are separated. That is, the ions collide with the wafer surface at a predetermined distance from the mechanical axis 10, while the neutral particles pass straight through the opening without being affected by the decel electrode. Its progress is hindered by a scraper 50 at a close distance. In this embodiment, the scraper 50 that captures the neutral particles is disposed at a position orthogonal to the mechanical axis 10. However, the neutral particles that have passed through the decel electrode 32 may be disposed so as not to reach the wafer. In FIG. 8, the distance between the neutral particles colliding with the scraper 50 and the ions passing on the extension line of the scraper before colliding with the wafer 7 is d₂ The ions are completely separated from the neutral particles and collide with the wafer 7.
[0068]
Next, in FIG. 10 and FIG. 11, an inclined decel device 300 as a fourth embodiment of the present invention is shown. In this embodiment, there are two decel electrodes, and both ions and neutral particles pass through the openings 42 and 43 of the decel electrodes 40 and 41, respectively. These electrodes are inclined by θ with respect to an axis perpendicular to the mechanical axis 10. Also in this case, the ions are decelerated by the decel electrodes 40 and 41 and bend and advance in the opening, and the neutral particles go straight without being influenced. For this reason, ions and neutral particles are separated, and the neutral particles are trapped by the scraper 50, but the ions can reach the wafer 7.
[0069]
【The invention's effect】
As is apparent from the above description, the tilted decelerating device of the present invention has a simple decelerating electrode structure and combines both the deceleration and separation of the ion beam at the same time. Contamination can be prevented.
[0070]
In addition, this tilted decel device can shorten the distance of beam travel to the wafer and greatly increase the decel ratio due to the length and arrangement of the decel electrodes. A current can be supplied. Furthermore, the tilting decelerator itself is simplified because it is a mechanical structure that is easy to operate.
[0071]
In addition to the decel mode, this tilted decel apparatus can be used in the drift mode of a high current ion implantation apparatus, and can be completely applied to the compatible mode. At that time, there is no influence on the operation of the drift mode.
[Brief description of the drawings]
FIG. 1 is a schematic view of a high-current ion implantation apparatus provided with a tilted decel device according to the present invention.
FIG. 2 is a diagram for explaining the principle of two decel electrodes arranged at an angle in order to simultaneously realize ion beam deceleration and neutral particle separation;
FIG. 3 is a diagram for explaining the operation of the inclined decel device showing the first embodiment of the present invention having a structure having four electrodes and three gaps;
4 is a schematic diagram showing the configuration of the inclined decel device in FIG. 3. FIG.
FIG. 5 is a graph showing the relationship between offset distance and decel ratio.
FIG. 6 is a schematic diagram showing a configuration of an inclined decel device having three decel electrodes showing a second embodiment according to the present invention.
7 shows three operation modes in the tilted decel device of the present invention shown in FIG. 6, wherein (a) is a decel mode, (b) is a drift mode of a boron ion beam, and (c) is a phosphorous ion beam. It is a figure for demonstrating operation | movement of each decel in drift mode.
FIG. 8 is a diagram for explaining the operation of a tilted decel apparatus having three decel electrodes showing a third embodiment according to the present invention.
9 is a schematic diagram showing a configuration of the inclined decel device in FIG. 8. FIG.
FIG. 10 is a diagram for explaining the operation of a tilted decel apparatus having two decel electrodes showing a fourth embodiment according to the present invention.
11 is a schematic diagram showing a configuration of the inclined decel device in FIG.
[Explanation of symbols]
1 Ion source
2 Mass spectrometry magnet
3 Decel electrode
4 Flag Faraday Cup
7 Wafer
9 Faraday Cup
10 Machine shaft (base shaft)
11 Drift mode ion beam
12 ion beam in decel mode
17, 18, 19, 20 Decel electrode
21 Front electrode
22 Suppression box
23 Rear electrode
24, 25, 27, 28 opening

Claims (9)

In the beam path between the mass analysis magnet and the wafer, the plurality of decel electrodes having openings are inclined with respect to an axis perpendicular to the base axis of the beam path, and the openings and rear sides of the front electrodes in the plurality of decel electrodes Displace the electrode opening with a predetermined offset distance ,
An ion beam passing through the opening of the front electrode , which is positioned away from the base axis by adjusting the mass spectrometry magnet, is positioned on the base axis in accordance with the ON operation of the plurality of decel electrodes. A decel mode in which the ion beam travels toward the wafer through the opening of the side electrode and further on or parallel to the base axis of the beam path;
The plurality of decel electrodes are turned off, the position of the front electrode is changed, the opening of the front electrode configured to be positioned on the base axis is allowed to pass through the ion beam , and the front electrode A drift mode in which another decel electrode positioned behind is positioned in a zero electric field space that is not affected by an electric field, and the ion beam that has passed through the opening of the front electrode proceeds along the base axis without being decelerated, and
In the decel mode, an offset distance of the ion beam from the base axis at a position where the ion beam is incident on the plurality of decel electrodes and a deflection angle of the incident ion beam with respect to the base axis are determined, by generating an electric field in the gap formed between the decel electrode, tilting decel device compatibility mode and separating the deceleration and at the same time neutral ion beam from the ion beam.   The plurality of decel electrodes form first, second, and third gaps with respect to the traveling direction of the ion beam and realize a front side in order to achieve both correction of the offset distance of the ion beam and separation of the neutral particles. The inclined decel device according to claim 1, wherein a pair of suppression electrodes is arranged between the electrode and the rear electrode, and the second gap is a drift space without an electric field between the suppression electrodes.   3. The tilt decel device according to claim 1, wherein the offset distance and the deflection angle of the ion beam are determined by adjusting a mass analyzer provided in front of the plurality of decel electrodes. To adjust the beam is decelerated during operation, it is arranged at a position close to the wafer In the rear of the plurality of decel electrode, further provided with it a movable Faraday cups for measuring the beam current i Onbimu The inclined decel device according to any one of claims 1 to 3. A plurality of decel electrodes (17, 18, 19, 20; 21, 22, 23) inclined at predetermined intervals with respect to the traveling direction of the ion beam, and each of these decel electrodes has at least one opening ( 25, 26, 27, 28) , and a gap for decelerating or accelerating the ion beam between the electrodes located on the front side and the rear side, and a drift space without an electric field between the electrodes located between the electrodes. Forming a gap, and the front opening (25) of the front electrode is deviated from the rear opening (28) of the rear electrode by a predetermined offset distance (D). The inclined decel device according to 1 . In the beam path between the mass analysis magnet and the wafer, the plurality of decel electrodes having openings are inclined with respect to an axis perpendicular to the base axis of the beam path, and the openings and rear sides of the front electrodes in the plurality of decel electrodes Displace the electrode opening with a predetermined offset distance ,
The ion beam emitted from the mass analysis magnet is incident on the front electrode openings of the plurality of decel electrodes at a predetermined deflection angle and offset distance with respect to the base axis of the beam path,
During operation of the plurality of decel electrodes in the decel mode, an ion beam passing through the opening of the front electrode , which is positioned away from the base axis, is positioned on the base axis according to the on operation of the plurality of decel electrodes. to pass through the opening of the rear electrode, and further wherein towards the base shaft or on base shaft parallel to the wafer in the beam path to proceed an ion beam,
On the other hand, during the drift mode operation in which the plurality of decel electrodes are turned off , the ion beam passes through the opening of the front electrode configured to be positioned on the base axis by changing the position of the front electrode. to, and the other decel electrode positioned behind the front electrode is located in the space null field which is not affected by the electric field, along the base shaft without slowing the ion beam having passed through the opening of the front electrode Advancing the ion beam,
During the decel mode operation , ions and neutral particles of the ion beam passing through the plurality of decel electrodes are separated, and the separated neutral particles are captured before reaching the wafer, and only the ions collide with the wafer. The ion beam forming method characterized by comprising the steps of moving the ion beam that has passed through the plurality of inclined decel electrodes in a direction along the base axis. Each step during the operation of the decel mode includes accelerating and deflecting the ion beam in the first gap formed between the decel electrodes, and then the second direction in the direction in which the ion beam approaches the base axis of the beam path. 7. The method of forming an ion beam according to claim 6 , further comprising three steps of traveling in a drift space without an electric field as a gap and further decelerating and deflecting the ion beam in the third gap. One opening of the front electrode in a plurality of tilted decel electrodes is arranged at the position where the offset ion beam passes, and the ion beam line deflected by the front electrode and the base line of the beam path intersect at the rear side 7. The method of forming an ion beam according to claim 6 , wherein one of the suppression electrodes paired with the electrode is positioned to separate the ion beam from the neutral particles. The plurality of decel electrodes include a front electrode (21), a suppression electrode (22), and a rear electrode (23), and the suppression electrode (22) has a box structure having an internal space, and the front electrode (21) 8. The method of forming an ion beam according to claim 7 , further comprising openings (26, 27) in electrode walls facing the rear electrode and the rear electrode (23), respectively.

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