JP2008225190A - Surface shape processing method and surface shape processing device of multilayer film - Google Patents
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Abstract
Description
本発明は、多層膜の表面形状加工方法及び表面形状加工装置に関するものである。 The present invention relates to a surface shape processing method and a surface shape processing apparatus for a multilayer film.
近年の半導体微細加工技術の進歩に伴い、更なる微細化を目的として極端紫外線(EUV: Extreme Ultra Violet)を光源とすることが世界的に制定された(EUVリソグラフィ技術)。光による投影露光の解像力は光の回折限界で制限されるが、EUV光を用いれば従来の紫外線露光を大幅に上回る解像力が期待できる。 With recent advances in semiconductor microfabrication technology, it has been established worldwide that EUV (Extreme Ultra Violet) is used as a light source for further miniaturization (EUV lithography technology). The resolution of projection exposure by light is limited by the diffraction limit of light, but if EUV light is used, the resolution can be expected to greatly exceed conventional ultraviolet exposure.
極端紫外線やＸ線波長域では、物質の屈折率が1に非常に近く従来型の屈折あるいは反射を利用した光学素子を使用することは極めて困難である。そこで図１に示すような屈折率が異なる２種類以上の物質を超研磨基板上に交互に積層した多層膜反射鏡が使用される。多層膜反射鏡は強め合いの干渉効果を利用した反射増加膜であることから、周期膜厚は使用波長の1/2程度の厚さに精密に制御しなければならない。EUVリソグラフィで使用される波長13nm光に対しては、モリブデン(Mo)とシリコン(Si)を交互に数十層積層することで70%近い直入射反射率が得られる。多層膜を凹面、凸面あるいは非球面基板上に成膜した反射鏡を複数枚組み合わせることで拡大あるいは縮小光学系とする。その一例として図２に多層膜鏡を成膜した凹面、凸面鏡から成るシュバルツシルド光学系の模式図を示す。 In the extreme ultraviolet or X-ray wavelength region, it is extremely difficult to use an optical element using a conventional type of refraction or reflection, whose refractive index is very close to 1. Therefore, a multilayer film reflecting mirror in which two or more kinds of substances having different refractive indexes as shown in FIG. 1 are alternately stacked on a super-polished substrate is used. Since the multilayer mirror is a reflection increasing film that uses the interference effect of strengthening, the periodic film thickness must be precisely controlled to be about half the wavelength used. For light with a wavelength of 13 nm used in EUV lithography, a direct incidence reflectance of nearly 70% can be obtained by alternately laminating several tens of layers of molybdenum (Mo) and silicon (Si). An enlargement or reduction optical system is obtained by combining a plurality of reflecting mirrors each having a multilayer film formed on a concave, convex or aspherical substrate. As an example, FIG. 2 shows a schematic diagram of a Schwarzschild optical system composed of concave and convex mirrors formed with a multilayer mirror.
光学系の波面収差を抑え回折限界の性能を得るためには波面位相を精密に制御することが不可欠である。反射光学系の波面誤差は、反射による光路の折り返しによって基板の形状誤差の２倍となることからその形状精度はMarechal基準であるλ/28(λ: 使用波長)が要求される。複数枚の多層膜反射凹面鏡及び凸面鏡から成るEUV露光装置やEUV顕微鏡では一枚の多層膜鏡に要求される形状精度は0.1 nmオーダーとなる。 In order to suppress the wavefront aberration of the optical system and obtain diffraction limited performance, it is indispensable to precisely control the wavefront phase. Since the wavefront error of the reflection optical system is twice the shape error of the substrate due to the reflection of the optical path due to reflection, the shape accuracy is required to be Marechal reference λ / 28 (λ: wavelength used). In EUV exposure equipment and EUV microscopes composed of multiple multilayer reflective concave mirrors and convex mirrors, the shape accuracy required for a single multilayer mirror is on the order of 0.1 nm.
従来の研磨加工技術で曲面基板の形状精度0.1 nmを実現することは困難である。研磨技術に代わるものとしてイオンビームよる加工技術が開発されている。これは、細く絞ったイオンビームで基板上を走査し加工するものである。加工量(ミリング深さ)はイオンビームの滞在時間で決まるため、イオンビーム強度の時間安定性が要求されるが、現状では数%程度の不安定性があるため加工精度を保障できない。また、EUVリソグラフィなどに用いられる大口径の曲面基板の加工には長時間を要するため実用的ではない。 It is difficult to achieve a shape accuracy of 0.1 nm for curved substrates using conventional polishing technology. A processing technique using an ion beam has been developed as an alternative to the polishing technique. In this method, the substrate is scanned and processed with a finely focused ion beam. Since the processing amount (milling depth) is determined by the residence time of the ion beam, the time stability of the ion beam intensity is required, but at present, the processing accuracy cannot be guaranteed due to the instability of about several percent. In addition, it is not practical because it takes a long time to process a large-diameter curved substrate used for EUV lithography or the like.
例えばBK7ガラス基板にアルゴンイオンビームを1時間照射した場合、およそ200 nm程度ミリング除去することが出来る。このときの加速電圧は1kV、ビーム電流は0.13 mA/cm2 = 1.3μA/mm2である。直径2mmの収束イオンビームを用いるとするとこのとき得られるビーム電流は4.08μAである。この時、直径100 mmの基板全面を10 nmミリング除去するのに要する時間は、2500×10/200=125 時間となり、約５日掛かる計算となる。EUVリソグラフィで用いる大口径基板ではこの数倍の時間を要する。
本発明は、イオンビームを利用した多層膜のミリングにおいて、従来の欠点を除去し、サブナノメートル精度で反射波面の位相補正を実現するとともに加工時間の短縮を実現した多層膜の表面形状加工方法及び表面形状加工装置を提供することを課題とする。 The present invention eliminates the conventional drawbacks in milling a multilayer film using an ion beam, realizes phase correction of the reflected wavefront with sub-nanometer accuracy, and shortens the processing time, and a multilayer surface shape processing method It is an object to provide a surface shape processing apparatus.
上記の課題を解決するために本発明は、次のような多層膜の表面形状加工方法及び表面形状加工装置を提供するものである。
（１）屈折率に差がある複数の物質を周期的に積層した多層膜のイオンビームによるミリングに際し、反射位相変化の小さい方の物質を基準としてミリングの深さを検知することを特徴とする多層膜の表面形状加工方法。
（２）（１）に記載の多層膜の表面形状加工方法を実施する表面形状加工装置であって、該多層膜の全面を、一定の加工速度で、一括して加工除去できるミリング加工源と、該多層膜の直前に近接して配置固定されたミリング領域選択マスクと、ミリング深さを検知する機構とを備えることを特徴とする多層膜の表面形状加工装置。
（３）上記ミリング加工源は、一定の速度で加工する手段として、ミリング領域選択マスクを固定した該多層膜を高速で自転させ、ミリング加工流の空間密度分布と加工時間の積を一定にできるミリング加工流分布補正板を備えることを特徴とする（２）に記載の多層膜の表面形状加工装置。
（４）上記ミリング深さを検知する機構は、該多層膜と該多層膜に近接して固定されたミリング領域選択マスクとの間隙に放射される光を検知する手段を含むことを特徴とする（２）又は（３）に記載の多層膜の表面形状加工装置。
（５）上記ミリング深さを検知する機構は、該多層膜に流入又は流出するドレイン電流を検知する手段を含むことを特徴とする（２）又は（３）に記載の多層膜の表面形状加工装置。
（６）上記ミリング領域選択マスクの材質は、該多層膜の反射光に実質的に透明な物質で構成されていることを特徴とする（２）乃至（５）のいずれかに記載の多層膜の表面形状加工装置。
（７）上記ミリング領域選択マスクは、多層膜を構成する物質のいずれかで構成されることを特徴とする（２）乃至（６）のいずれかに記載の多層膜の表面形状加工装置。
（８）上記多層膜は、超研磨基板と基板上に形成された薄膜構造で構成され、薄膜構造がミリング深さを検知できる機構の要素を構成することを特徴とする（２）乃至（７）のいずれかに記載の多層膜の表面形状加工装置。
（９）上記多層膜は、超研磨基板と基板上に形成された反射増加多層膜で構成されることを特徴とする（２）乃至（７）のいずれかに記載の多層膜の表面形状加工装置。
In order to solve the above-mentioned problems, the present invention provides the following surface shape processing method and surface shape processing apparatus for a multilayer film.
(1) When milling with a multi-layer film in which a plurality of materials having different refractive indexes are periodically stacked, the depth of milling is detected with reference to the material with the smaller reflection phase change. A method for processing the surface shape of a multilayer film.
(2) A surface shape processing apparatus for performing the surface shape processing method for a multilayer film according to (1), wherein the entire surface of the multilayer film is processed and removed at a constant processing speed at a time. An apparatus for processing a surface shape of a multilayer film, comprising: a milling region selection mask arranged and fixed immediately in front of the multilayer film; and a mechanism for detecting a milling depth.
(3) The milling processing source can rotate the multilayer film with the milling region selection mask fixed at a high speed as a means for processing at a constant speed, thereby making the product of the spatial density distribution of the milling flow and the processing time constant. The multi-layer surface shape processing apparatus according to (2), further comprising a milling flow distribution correction plate.
(4) The mechanism for detecting the milling depth includes means for detecting light radiated to a gap between the multilayer film and a milling region selection mask fixed in proximity to the multilayer film. (2) The surface shape processing apparatus for a multilayer film according to (3).
(5) The surface shape processing of the multilayer film according to (2) or (3), wherein the mechanism for detecting the milling depth includes means for detecting a drain current flowing into or out of the multilayer film. apparatus.
(6) The multilayer film according to any one of (2) to (5), wherein the material of the milling region selection mask is made of a material that is substantially transparent to the reflected light of the multilayer film. Surface shape processing equipment.
(7) The apparatus for processing a surface shape of a multilayer film according to any one of (2) to (6), wherein the milling region selection mask is composed of any of the substances constituting the multilayer film.
(8) The multilayer film includes a super-polished substrate and a thin film structure formed on the substrate, and the thin film structure constitutes an element of a mechanism capable of detecting a milling depth (2) to (7) The surface shape processing apparatus for a multilayer film according to any one of the above.
(9) The multilayer film according to any one of (2) to (7), wherein the multilayer film includes a super-polished substrate and a reflection-enhancing multilayer film formed on the substrate. apparatus.
本発明によれば、厚さ数nmの多層膜の1周期毎のミリング除去により、サブナノメートル精度で反射波面の位相補正を実現できる。また大口径の多層膜全面にイオンビームを一括照射することが可能であり、1周期当たり数分でミリングできるため加工時間の大幅短縮を実現できる。さらに本発明の表面形状加工装置では、多層膜の所定の位置をミリング加工除去しているときに、除去している物質を分析装置により検知することができる。 According to the present invention, phase correction of the reflected wavefront can be realized with sub-nanometer accuracy by milling removal for each cycle of a multilayer film having a thickness of several nanometers. In addition, it is possible to irradiate the entire surface of a large-diameter multilayer film with an ion beam, and milling can be performed in a few minutes per cycle, thus significantly reducing processing time. Furthermore, in the surface shape processing apparatus of the present invention, when the predetermined position of the multilayer film is removed by milling, the removed substance can be detected by the analyzer.
本発明に係る多層膜の表面形状加工の原理を以下説明する。
基板の形状誤差をΔとすると反射光学系と屈折率nの透過光学系でそれぞれ2Δ、(1-n)Δの光路差を与える。極端紫外線や軟Ｘ線領域の屈折率nは1に極めて近く(1-n)は10-2から10-4程度である。ここで、多層膜の反射は多層膜全体からの総和であるから、表面付近の多層膜は透過膜としても機能するはずである。従って、多層膜による光路差は2(1-n)Δで与えられる。図３をもってその原理を説明する。
The principle of the surface shape processing of the multilayer film according to the present invention will be described below.
If the shape error of the substrate is Δ, the optical path difference of 2Δ and (1-n) Δ is given by the reflection optical system and the transmission optical system of refractive index n, respectively. The refractive index n in the extreme ultraviolet or soft X-ray region is extremely close to 1, and (1-n) is about 10 −2 to 10 −4 . Here, since the reflection of the multilayer film is the sum total from the entire multilayer film, the multilayer film near the surface should also function as a transmission film. Therefore, the optical path difference due to the multilayer film is given by 2 (1-n) Δ. The principle will be described with reference to FIG.
図３(a)に示すように、基板を厚さd除去すると、基板表面に垂直に進む光は2dだけ光路長が変化する。ここでファクター2は反射による効果を表す。次に図３(b)に示す多層膜1周期分をミリング除去した場合について考える。多層膜は透過膜としても機能するので、多層膜1周期分を透過し多層膜構造を含めた実効的な基板で反射する光の光路長は2(nAdA+nBdB)で与えられる。ここで、nA、nBはそれぞれ多層膜を構成する物質A、Bの屈折率を、dAとdBはそれぞれの膜厚を表し、dA+dB=dとする。一方、多層膜を除去した部分の光路長は2dである。従って、多層膜1周期分をミリング除去したことによる光路長の変化、すなわち、光路差OPDは、最表面を反射位相の基準とするとOPD=2d-2(nAdA+nBdB)となる。nA=nB=nと置けば、OPD=2(1-n)dとなる。極端紫外線及びＸ線領域の物質の屈折率は1に近いため、OPDは微小量となる。 As shown in FIG. 3 (a), when the substrate is removed by thickness d, the optical path length of light traveling perpendicular to the substrate surface changes by 2d. Here, factor 2 represents the effect of reflection. Next, consider a case where one cycle of the multilayer film shown in FIG. Since the multilayer film also functions as a transmission film, the optical path length of light that is transmitted through one period of the multilayer film and reflected by an effective substrate including the multilayer film structure is 2 (n A d A + n B d B ). Given. Here, n A and n B represent the refractive indexes of the substances A and B constituting the multilayer film, respectively, d A and d B represent the respective film thicknesses, and d A + d B = d. On the other hand, the optical path length of the portion from which the multilayer film is removed is 2d. Therefore, the change in the optical path length due to milling removal of one period of the multilayer film, that is, the optical path difference OPD is OPD = 2d-2 (n A d A + n B d B ) when the outermost surface is the reference of the reflection phase. It becomes. If n A = n B = n, OPD = 2 (1-n) d. Since the refractive index of the material in the extreme ultraviolet and X-ray region is close to 1, OPD is very small.
波長13 nmでMo/Si多層膜を用いた場合を例示して本発明の原理を説明する。極端紫外線及び軟Ｘ線領域での波長に対するSi、Moの屈折率は、それぞれnSi=1.00236、nMo=0.9314であり、直入射で用いる場合のそれぞれの膜厚はdSｉ=4.01 nm、dMo=2.64 nmである。これらの値を用いて光路差OPDを計算すると0.34 nmとなる。これは基板ミリングに換算すると0.17 nmである。つまり、多層膜1周期分6.65 nmをミリング除去すれば、基板を0.17 nmミリング除去したことと同等の効果が得られることを示す。 The principle of the present invention will be described by exemplifying a case where a Mo / Si multilayer film is used at a wavelength of 13 nm. The refractive indexes of Si and Mo with respect to wavelengths in the extreme ultraviolet and soft X-ray regions are n Si = 1.00236 and n Mo = 0.9314, respectively, and the film thicknesses when used at normal incidence are d Si = 4.01 nm and d Mo = 2.64 nm. Using these values, the optical path difference OPD is calculated to be 0.34 nm. This is 0.17 nm in terms of substrate milling. That is, if 6.65 nm is removed by milling for one cycle of the multilayer film, the same effect as that obtained by removing 0.17 nm from the substrate is obtained.
図４、５に60周期Mo/Si多層膜の最上層に30 nmのMo層を付加した場合のミリング除去による位相変化の計算結果を示す。ミリング厚さが30 nmに達するまでは除去量とともに位相は減少し、反射率は増加する。多層膜表面に達すると以後-1°/nmで位相が変化する。一方、反射率は干渉効果による周期的な変動を見せるだけでほとんど変化しない。反射率は積層数とともに増加し、ある積層数を超えると飽和して一定となることから、反射率が十分飽和するまで積層すれば、ミリングによる反射率の低下は生じない。位相変化を詳細に見てみると、Siの屈折率が1に極めて近いため、大きな反射位相変化はMo層のミリングで生じ、Si層のミリングでは反射位相も反射率もほとんど変化しない。つまり、Si層のミリング深さを精密に制御することなく、Si層が最表面層となる条件を検知すれば反射波面の高精度な位相補正を実現することができる。図６に形状誤差が有る多層膜凹面鏡の集光と多層膜を除去し反射波面の補正を行った後の多層膜凹面鏡の集光の模式図を示す。 FIGS. 4 and 5 show the calculation results of the phase change due to milling removal when a 30 nm Mo layer is added to the uppermost layer of the 60-period Mo / Si multilayer. The phase decreases with removal and the reflectivity increases until the milling thickness reaches 30 nm. After reaching the surface of the multilayer film, the phase changes at -1 ° / nm. On the other hand, the reflectivity hardly changes, only showing periodic fluctuations due to the interference effect. The reflectivity increases with the number of layers, and when it exceeds a certain number of layers, it becomes saturated and constant. Therefore, if the layers are stacked until the reflectivity is sufficiently saturated, the reflectance does not decrease due to milling. When the phase change is examined in detail, since the refractive index of Si is very close to 1, a large reflection phase change is caused by milling of the Mo layer, and the reflection phase and reflectivity hardly change in the milling of the Si layer. That is, highly accurate phase correction of the reflected wavefront can be realized by detecting the condition that the Si layer is the outermost surface layer without precisely controlling the milling depth of the Si layer. FIG. 6 shows a schematic diagram of the condensing of the multilayer concave mirror having a shape error and the condensing of the multilayer concave mirror after the multilayer film is removed and the reflected wavefront is corrected.
これまで述べたような多層膜のミリングによる波面補正は、回折限界の結像性能を実現できることから、顕微鏡や望遠鏡に有効であり、その適用波長は軟Ｘ線に限定されることなく可視光や赤外光にも有効である。例えば、可視光では、フィルタリングやホログラフィーのための位相制御、光通信に利用される赤外光では、光波の伝送特性を向上するための波面制御や位相補正などにも適用できる。また、これらの波長や反射鏡に限定することなく、多層膜を付加した素子、例えば透過フィルターなどにも適用することができる。 Wavefront correction by multilayer film milling as described above is effective for microscopes and telescopes because it can achieve diffraction-limited imaging performance, and its application wavelength is not limited to soft X-rays. It is also effective for infrared light. For example, in the case of visible light, phase control for filtering and holography can be applied, and in the case of infrared light used for optical communication, it can also be applied to wavefront control and phase correction for improving light wave transmission characteristics. Further, the present invention is not limited to these wavelengths and reflecting mirrors, and can be applied to an element to which a multilayer film is added, such as a transmission filter.
一方、高い解像力を持つ光学系には非球面基板の採用が必須であることから、基板の加工技術では、従来の研磨技術や収束イオンビームによる非球面加工が行われつつある。 On the other hand, since it is indispensable to use an aspherical substrate for an optical system having a high resolving power, conventional polishing techniques and aspherical processing using a focused ion beam are being performed in substrate processing techniques.
次に、本発明の表面形状加工装置について、図面を参照しながら説明する。
図７は多層膜の表面形状加工装置の概略図である。図７に示すように、表面形状加工装置は、２つの真空容器を有し、互いにゲートバルブを介して接続されている。一方の真空容器にはイオン源が設置され(以後、ガンチャンバーと呼ぶ)、もう一方には多層膜を有する反射鏡を設置固定するステージが配置されている(以後、ワークチャンバーと呼ぶ)。多層膜はイオン源から照射されるイオンビームに正対するように設置する。
Next, the surface shape processing apparatus of the present invention will be described with reference to the drawings.
FIG. 7 is a schematic view of a multilayer film surface shape processing apparatus. As shown in FIG. 7, the surface shape processing apparatus has two vacuum vessels and is connected to each other via a gate valve. One vacuum vessel is provided with an ion source (hereinafter referred to as a gun chamber), and the other is provided with a stage on which a reflecting mirror having a multilayer film is installed and fixed (hereinafter referred to as a work chamber). The multilayer film is installed so as to face the ion beam irradiated from the ion source.
また、多層膜の全面を一括でミリング加工するために、多層膜の直径と比べて大きな照射領域を持つイオンビームをイオン源から照射するものとする。また、イオンビームはミリング加工対象の表面粗さを抑えるために300V程度の低加速電圧で照射できる。多層膜の全面を実質的に一定の速度で加工するために、反射鏡を高速で自転させ、イオンビームの空間密度分布と加工時間の積を一定に出来るミリング加工流分布補正板を備える。また、ミリング加工する領域を指定するために、多層膜の表面の近傍にミリング領域選択マスクを固定する。このミリング領域選択マスクは反射鏡の回転ステージに固定され、多層膜とともに自転する。なお、ミリング領域によって複数枚のミリング領域選択マスクを用意し、位置の再現性良く且つ簡便に回転ステージに取り付け可能な構造とする。照射するイオンビームの安定化を図るため、ミリング領域選択マスクの交換時には、ゲートバルブを閉じ、ガンチャンバーの動作を保持したままワークチャンバーを大気開放することが可能である。 Further, in order to mill the entire surface of the multilayer film at once, an ion beam having an irradiation region larger than the diameter of the multilayer film is irradiated from the ion source. The ion beam can be irradiated with a low acceleration voltage of about 300 V in order to suppress the surface roughness of the object to be milled. In order to process the entire surface of the multilayer film at a substantially constant speed, a milling flow distribution correction plate capable of rotating the reflecting mirror at a high speed and making the product of the spatial density distribution of the ion beam and the processing time constant is provided. In addition, a milling region selection mask is fixed near the surface of the multilayer film in order to designate a region to be milled. This milling area selection mask is fixed to the rotary stage of the reflecting mirror and rotates together with the multilayer film. Note that a plurality of milling area selection masks are prepared according to the milling area, and the structure can be easily attached to the rotary stage with good position reproducibility. In order to stabilize the ion beam to be irradiated, when the milling region selection mask is replaced, the gate valve can be closed and the work chamber can be opened to the atmosphere while maintaining the operation of the gun chamber.
図８及び９に示すように、多層膜とミリング領域選択マスクの間のわずかな隙間から放射される光の分光スペクトルを計測するための検出器がワークチャンバーに設置される。また、ワークチャンバーには多層膜とミリング領域選択マスクの間のわずかな隙間から放射される光の全強度を計測するための検出器が、多層膜表面には多層膜に流入あるいは流出するドレイン電流を計測する計測器がそれぞれ多層膜回転ステージに固定設置される。 As shown in FIGS. 8 and 9, a detector for measuring a spectral spectrum of light emitted from a slight gap between the multilayer film and the milling region selection mask is installed in the work chamber. In addition, the work chamber has a detector for measuring the total intensity of light emitted from a slight gap between the multilayer film and the milling region selection mask, and a drain current flowing into or out of the multilayer film on the multilayer film surface. A measuring instrument for measuring is fixedly installed on the multilayer film rotation stage.
多層膜にイオンビームのような高エネルギーの粒子を照射すると、構成物質に起因した発光が見られる。すなわち、イオンビームを照射しながら分光スペクトル計測を行えば、多層膜の最表面に露出した物質を同定することができる。通常、Mo/Si多層膜の最表面はMo層であるから、ミリング開始はMoに起因した発光スペクトルが検出される。Mo層のミリング除去が完了すると、Moに起因したスペクトルに変わりSiに起因したスペクトルが検出される。Mo/Si多層膜のミリングによる反射位相変化はMo層で生じるため、Siに起因した発光スペクトルが現れた時点でミリングを終了すればよい。MoとSiに起因した発光スペクトルの変化は交互に現れることから、これらの変化をモニターし、Si起因の発光スペクトルが現れたときにミリングを終了すれば所望の波面補正効果が得られる。 When the multilayer film is irradiated with high energy particles such as an ion beam, light emission due to the constituent material is observed. That is, if a spectral spectrum measurement is performed while irradiating an ion beam, a substance exposed on the outermost surface of the multilayer film can be identified. Usually, since the outermost surface of the Mo / Si multilayer is a Mo layer, an emission spectrum caused by Mo is detected at the start of milling. When the removal of milling of the Mo layer is completed, the spectrum caused by Si is detected instead of the spectrum caused by Mo. Since the reflection phase change due to the milling of the Mo / Si multilayer film occurs in the Mo layer, the milling may be terminated when an emission spectrum due to Si appears. Since changes in the emission spectrum caused by Mo and Si appear alternately, if these changes are monitored and milling is terminated when the emission spectrum caused by Si appears, the desired wavefront correction effect can be obtained.
イオンビームを多層膜に照射すると多層膜の構成物質に起因した発光スペクトルが計測される。各波長における光強度を計測波長域に渡って足し合わせるとその総和は物質によって異なる。つまり、光全強度検出器からの信号強度変化はミリング物質の切り替わりで生じることから、切り替わる回数をカウントすれば、所望の層数分だけミリング除去することができる。 When the multilayer film is irradiated with an ion beam, an emission spectrum due to the constituent material of the multilayer film is measured. When the light intensity at each wavelength is added over the measurement wavelength range, the total sum varies depending on the substance. That is, the change in signal intensity from the optical total intensity detector is caused by the switching of the milling substance. Therefore, if the number of times of switching is counted, milling can be removed by the desired number of layers.
イオンビームが照射される領域に露出した物質に対応して、多層膜に流入あるいは流出するドレイン電流が変化する。すなわち、ミリング中のドレイン電流値変化はミリング領域に露出した物質に応じて変化するため、ドレイン電流変化をモニターすれば所望の層数分だけミリング除去することが出来る。 The drain current flowing into or out of the multilayer film changes corresponding to the material exposed to the region irradiated with the ion beam. That is, since the drain current value change during milling changes according to the material exposed in the milling region, if the drain current change is monitored, the milling can be removed by the desired number of layers.
本表面形状加工装置は、発光スペクトル計測、光全強度計測あるいはドレイン電流計測によって波面補正に必要な層数のミリング除去をカウントし、所望の層数に達した時に、イオンビーム照射を瞬時に停止する機構又は、ゲートバルブを瞬時に閉じる機構を持つ。 This surface shape processing device counts the milling removal of the number of layers necessary for wavefront correction by measuring the emission spectrum, measuring the total light intensity, or measuring the drain current. When the desired number of layers is reached, the ion beam irradiation is stopped instantaneously. Or a mechanism for instantaneously closing the gate valve.
イオン源の加速電極板がイオン流によって削られ、削られた加速電極板が多層膜に付着し影響を及ぼすことを防ぐため、加速電極板の材質は多層膜の反射光に実質的に透明な物質で構成されている。例えば、波長13 nm用Mo/Si多層膜のミリングには、モリブデン、ルテニウム、ロジウムなどを材質とする。また、炭素の窓波長域(4 nmから6 nm程度の波長域)では、カーボン、クロム、コバルトなどを、水の窓波長域(2 nmから4 nm程度の波長域)では、スカンジウムやクロムなどを材質とする。 In order to prevent the acceleration electrode plate of the ion source from being scraped by the ion flow and preventing the scraped acceleration electrode plate from adhering to and affecting the multilayer film, the material of the acceleration electrode plate is substantially transparent to the reflected light of the multilayer film. Consists of substances. For example, molybdenum, ruthenium, rhodium or the like is used for milling the Mo / Si multilayer film for a wavelength of 13 nm. In addition, carbon, chromium, cobalt, etc. are used in the carbon window wavelength range (4 nm to 6 nm wavelength range), and scandium, chromium, etc. are used in the water window wavelength range (2 nm to 4 nm wavelength range). Is the material.
多層膜のミリング加工領域を指定するミリング領域選択マスクの概念図を図１０に示す。ミリング加工を行う領域は、干渉計測などによって得られた反射波面マップによって決定する。ミリング領域選択マスクの開口部をイオン流が通過し、所定の位置のみミリング加工を行うことができる。ミリング領域選択マスクがイオン流によって削られ、削られたマスク構成物質が多層膜に付着し影響を及ぼすことを防ぐため、ミリング領域選択マスクの材質は多層膜の反射光に実質的に透明な物質を素材とする。例えば、波長13 nm用Mo/Si多層膜のミリングには、シリコン、モリブデン、ルテニウム、ロジウムなどを材質とする。また、炭素の窓波長域(4 nmから6 nm程度の波長域)では、カーボン、クロム、コバルトなどを、水の窓波長域(2 nmから4 nm程度の波長域)では、スカンジウムやクロムなどを材質とする。 FIG. 10 shows a conceptual diagram of a milling area selection mask for designating a milling area of the multilayer film. The area to be milled is determined by a reflected wavefront map obtained by interference measurement or the like. The ion flow passes through the opening of the milling region selection mask, and milling can be performed only at a predetermined position. In order to prevent the milling area selection mask from being scraped by the ion flow and preventing the mask constituent material from adhering to and affecting the multilayer film, the material of the milling area selection mask is a material that is substantially transparent to the reflected light of the multilayer film. Is the material. For example, silicon, molybdenum, ruthenium, rhodium, or the like is used as a material for milling the Mo / Si multilayer film for a wavelength of 13 nm. In addition, carbon, chromium, cobalt, etc. are used in the carbon window wavelength range (4 nm to 6 nm wavelength range), and scandium, chromium, etc. are used in the water window wavelength range (2 nm to 4 nm wavelength range). Is the material.
イオンビーム強度の分布補正板の概念図を図１１に示す。分布補正板がイオン流によって削られ、削られた分布補正板構成物質が多層膜に付着し影響を及ぼすことを防ぐため、分布補正板の材質は多層膜の反射光に実質的に透明な物質を素材とする。例えば、波長13 nm用Mo/Si多層膜のミリングには、シリコン、モリブデン、ルテニウム、ロジウムなどを材質とする。また、炭素の窓波長域(4 nmから6 nm程度の波長域)では、カーボン、クロム、コバルトなどを、水の窓波長域(2 nmから4 nm程度の波長域)では、スカンジウムやクロムなどを材質とする。分布補正板を設置しない状態で計測したイオン流の二次元強度分布を元に、ミリング対象範囲でミリング加工流の空間密度分布と加工時間の積が一定となるように分布補正板の形状を決定する。
ミリング領域選択マスク及びミリング加工流分布補正板は、サンドブラスト法、エッチング法、機械加工などによって作製する。
FIG. 11 shows a conceptual diagram of an ion beam intensity distribution correction plate. The material of the distribution correction plate is a material that is substantially transparent to the reflected light of the multilayer film in order to prevent the distribution correction plate from being scraped by the ion flow and the shaved distribution correction plate constituent material from adhering to and affecting the multilayer film. Is the material. For example, silicon, molybdenum, ruthenium, rhodium, or the like is used as a material for milling the Mo / Si multilayer film for a wavelength of 13 nm. In addition, carbon, chromium, cobalt, etc. are used in the carbon window wavelength range (4 nm to 6 nm wavelength range), and scandium, chromium, etc. are used in the water window wavelength range (2 nm to 4 nm wavelength range). Is the material. Based on the two-dimensional intensity distribution of the ion flow measured without the distribution correction plate installed, the shape of the distribution correction plate is determined so that the product of the spatial density distribution of the milling flow and the processing time is constant within the milling target range. To do.
The milling region selection mask and the milling process flow distribution correction plate are produced by a sandblast method, an etching method, a machining process, or the like.
本発明の表面加工装置によって、広い面積を持つ光学素子の表面を一括且つ低加速のイオンビームで加工することができる。従って、様々な表面形状及び非球面形状を創生できる表面形状加工装置、非球面光学素子、それを用いた光学系、顕微鏡、露光装置等を提供することができる。 With the surface processing apparatus of the present invention, the surface of an optical element having a large area can be processed at once with a low acceleration ion beam. Accordingly, it is possible to provide a surface shape processing apparatus, an aspherical optical element, an optical system using the same, a microscope, an exposure apparatus, and the like that can create various surface shapes and aspherical shapes.
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