JPH03257303A - Measuring method of superposing accuracy - Google Patents

Abstract

PURPOSE:To measure the superposing accuracy by forming diffraction gratings on an upper and a lower films and forming an image by the passing diffraction light of a specific degree. CONSTITUTION:A diffraction grating 102 is formed on the surface of a sample 101. A monochromic parallel light 103 as an illuminating light is introduced by a beam splitter 104 into an optical system and applied to the surface of the sample 101 from a vertical direction. As a result, a diffraction light of zero degree, a diffraction light of a first degree 105 and a diffraction light of a higher degree are reflected. These relecting light pass through lenses 106, 107, 108, with forming a diffraction image on the focal plane of the lens 108. A filter 109 is put on the focal plane of the lens 108 and an aperture 110 is adjusted to the position where the diffraction light 105 passes. Accordingly, all the lights except the diffraction light 105 of the first degree are shut off. An image of the diffraction light 105 is formed on the focal plane by a lens 111 and a diffraction image 112 is detected. If the diffraction gratings are formed respectively on an upper and a lower films as patterns to be measured in a manner that the central gratings are aligned on the same line, the relative position of the upper and lower films can be detected from the diffraction image.

Description

Translated fromJapanese

【発明の詳細な説明】〔産業上の利用分野〕本発明は、半導体装置の製造技術に係り、特に多層配線
リソグラフィー技術において、半導体装置の下層膜と上
層膜とのパターンの一致の程度を知るために、重ね合せ
精度を測定する方法に関する。[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to semiconductor device manufacturing technology, and in particular, in multilayer wiring lithography technology, determining the degree of pattern matching between a lower layer film and an upper layer film of a semiconductor device. The present invention relates to a method for measuring overlay accuracy.

〔従来の技術〕[Conventional technology]

従来、この種の重ね合せ精度測定方法は、まず半導体装
置の下層膜および上層膜に形成された被測定パターンを
照明し、反射光を明視野または暗視野でカメラ等により
画像情報として取り込み、画像情報の明暗により各パタ
ーンのエツジ位置を決定する。下層および上層のパター
ンの各エツジ位置から上層パターンおよび下層パターン
の相対位置を求め、重ね合せ精度を測定していた。Conventionally, this type of overlay accuracy measurement method first illuminates the pattern to be measured formed on the lower layer film and upper layer film of a semiconductor device, and captures the reflected light as image information with a camera or the like in bright field or dark field. The edge position of each pattern is determined based on the brightness of the information. The relative positions of the upper layer pattern and the lower layer pattern were determined from the respective edge positions of the lower layer pattern and the upper layer pattern, and the overlay accuracy was measured.

〔発明が解決しようとする課題〕[Problem to be solved by the invention]

上述した従来の測定方法では、明視野では対物レンズの
開口角で決まる反射角度範囲の光を検知し、暗視野では
カメラの取付角度等で決まる反射角度の光を検知してい
るので、測定パターンの形状の影響を受けやすい欠点が
あった。In the conventional measurement method described above, in bright field, light is detected in the reflection angle range determined by the aperture angle of the objective lens, and in dark field, light is detected in the reflection angle range determined by the camera mounting angle, etc., so the measurement pattern The disadvantage was that it was easily affected by the shape of the

特に、明視野では、下層パターンは、通常、上層パター
ンを形成するための膜で被覆されているので、この上層
膜表面からの反射光が強い場合、下層パターンのエツジ
部の光の散乱による反射光強度が低下する。一方暗視野
ではエツジの散乱光を検出しているが、エツジ部での光
の散乱は、製造プロセスの影響により個々に大きく異な
るエツジ形状に強く依存するので、測定感度が不安定と
なり、測定不能となる場合も生ずる。In particular, in bright field, the lower layer pattern is usually covered with a film for forming the upper layer pattern, so if the reflected light from the surface of this upper layer film is strong, it will be reflected by the scattering of light at the edges of the lower layer pattern. Light intensity decreases. On the other hand, in dark field, scattered light from edges is detected, but since the scattering of light at edges strongly depends on the shape of the edges, which vary greatly due to the influence of the manufacturing process, measurement sensitivity becomes unstable and measurement becomes impossible. This may occur in some cases.

本発明の目的は、上記の欠点を除去した新規な重ね合せ
精度測定方法を提供することにある。An object of the present invention is to provide a new overlay accuracy measurement method that eliminates the above-mentioned drawbacks.

〔課題を解決するための手段〕[Means to solve the problem]

本発明の測定方法は、半導体装置の上層膜と下層膜の重
ね合せ精度を上層膜・下層膜に形成した回折格子を利用
して測定する方法であって、上層膜および下層膜のそれ
ぞれの回折格子の中心格子が同一線上に並ぶように配設
した回折格子を単色光で照明し、レンズにより焦点面上
に回折像を形成し、そのうちの特定次数の回折光のみを
透過させ、前記透過回折光を結像して、回折像から上層
膜・下層膜の相対位置を求めるものである。また、上層
膜・下層膜の回折格子を同一でなく、格子間隔の異なる
ものを使用し、特定次数の回折光のみ透過させるフィル
タの開口位置を、回折格子に合わせて変えるようにして
測定するようにもできる。The measurement method of the present invention is a method of measuring the overlay accuracy of an upper layer film and a lower layer film of a semiconductor device using a diffraction grating formed on the upper layer film and the lower layer film, and the method includes A diffraction grating arranged so that the central gratings of the grating are aligned on the same line is illuminated with monochromatic light, a diffraction image is formed on the focal plane by a lens, and only the diffracted light of a specific order is transmitted, and the transmitted diffraction It forms an image of light and determines the relative position of the upper layer film and the lower layer film from the diffraction image. In addition, the diffraction gratings of the upper and lower layers are not the same, but have different grating intervals, and the aperture position of the filter that transmits only the diffracted light of a specific order can be changed to match the diffraction grating. It can also be done.

〔作用〕[Effect]

本発明は、被測定パターンとして、回折格子を上層膜・
下層膜に形成する。しかし直接に形状画像を検知するも
のでなく、回折格子像のうち、特定次数の回折像を透過
させ、その光軸に対する位置を検知する。The present invention uses a diffraction grating as an upper layer film and a pattern to be measured.
Formed on the lower layer film. However, the shape image is not directly detected, but a diffraction image of a specific order among the diffraction grating images is transmitted, and its position with respect to the optical axis is detected.

また下層膜・上層膜の回折格子は、中心格子の位置が両
者が同一線上に配置しであるものであれば、異なる特性
の回折格子を用いることができる。Further, as the diffraction gratings for the lower layer film and the upper layer film, diffraction gratings having different characteristics can be used as long as the center gratings are arranged on the same line.

この場合回折光の結像面における位置を、両者が全く影
響をうけないように分離して測定されるので、相互の影
響を除外できる。In this case, the positions of the diffracted lights on the imaging plane are measured separately so that both are not affected at all, so mutual effects can be excluded.

〔実施例〕〔Example〕

以下、図面を参照して、本発明の一実施例につき説明す
る。第１図は実施例の光路図である。試料１０１０表面
に回折格子１０２が形成されている。単色平行光１０３
を照明光として、ビームスプリンタ１０４により光学系
内に導入し、試料１０１の表面を垂直な方向から照明す
る。回折格子１０２に照明光が照射されると０次と１次
回折光１０５と、高次の回折光が反射される。これらの
反射光は、レンズ１０６と、レンズ１０７と、レンズ１
０８を通り、レンズ１０８の焦点面上に回折像をつくる
。この焦点面にフィルタ１０９をおき、その開口部１１
０を１次回折光１０５が通る位置に合わせる。こうして
、１次回折光１０５以外は全て遮光し、１次回折光１０
５をレンズ１１１により焦点面（結像面１１３）上に結
像して得た像１．１２を検知器（図示していない）によ
り検知する。Hereinafter, one embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an optical path diagram of an embodiment. A diffraction grating 102 is formed on the surface of a sample 1010. Monochromatic parallel light 103
is introduced into the optical system by the beam splinter 104 as illumination light, and illuminates the surface of the sample 101 from a perpendicular direction. When the diffraction grating 102 is irradiated with illumination light, 0th-order and 1st-order diffracted lights 105 and higher-order diffracted lights are reflected. These reflected lights pass through lens 106, lens 107, and lens 1.
08 and creates a diffraction image on the focal plane of the lens 108. A filter 109 is placed on this focal plane, and its aperture 11
0 to the position through which the first-order diffracted light 105 passes. In this way, all light except the first-order diffracted light 105 is blocked, and the first-order diffracted light 10
5 onto the focal plane (imaging plane 113) by the lens 111, and an image 1.12 obtained is detected by a detector (not shown).

第２図は、本実施例の重ね合せ測定のために半導体装置
のウェーハ面上に設ける回折格子の例であり、（ａｌは
上層膜の回折格子、ｆｂｌは下層膜で、Ｘ方向に中心格
子のセンタ位置を一致させて並列させる。この図では、
図示のように重ね合せ誤差により、位置ずれ量ΔａＩ＋
Δａ２が発生した場合を示している。また上層膜と下層
膜とでは、回折格子を異ならしめている。それぞれ格子
幅２ｘ＋２Ｉ！２の格子２０１．２０２がＮ１個、Ｎ２
個、Ｘ方向に間隔ｄ、、ｄ２でり、、Ｌ２の幅まで配列
している。ここではＮＩ＝７．Ｎ２＝５としている。（
ａ）の回折格子を、第１図の光学系で測定する場合、照
明光の波長を人として、レンズ１０６．レンズ１０７、
レンズ１０８．レンズ１１１の各焦点距離をｆ、、ｆ２
．ｆ３．ｆ４とすると、回折格子が光軸に十分近ければ
フラウンホーファ回折となり、フィルタ１０９面での回
折像は光軸からの間隔ｄ＋’　＝（ｆ１ｆ＊／ｆｚ）λ
／　ｄ　＋　　　　　＋１１ｄ　、　ｌの点で極大値を
とり、また、この極大値と隣接する極小点との間隔ｔ２
　、　Ｌはｊ！＋’＝（ｆ＋・ｆ　３／　ｆ　ｚ）λ／
Ｎ＋ｄ＋　　　　（２＋となる。FIG. 2 is an example of a diffraction grating provided on the wafer surface of a semiconductor device for overlay measurement in this embodiment, (al is the diffraction grating of the upper layer film, fbl is the lower layer film, and the central grating is oriented in the X direction. Match the center positions of and arrange them in parallel.In this figure,
As shown in the figure, due to the overlay error, the amount of positional deviation ΔaI+
This shows a case where Δa2 occurs. Further, the upper layer film and the lower layer film have different diffraction gratings. Each grid width is 2x + 2I! 2 grids 201.202 are N1 pieces, N2
They are arranged at intervals of d, d2 in the X direction, up to a width of L2. Here NI=7. N2=5. (
When measuring the diffraction grating in a) using the optical system shown in FIG. 1, the wavelength of the illumination light is set to 106. lens 107,
Lens 108. Let each focal length of the lens 111 be f, , f2
．． f3. Assuming f4, if the diffraction grating is close enough to the optical axis, Fraunhofer diffraction will occur, and the diffraction image on the filter 109 surface will have a distance from the optical axis of d+' = (f1f*/fz)λ
/ d + +11d , the maximum value is taken at the point l, and the distance t2 between this maximum value and the adjacent minimum point is
, L is j! +'=(f+・f 3/ f z)λ/
N+d+ (becomes 2+.

照明光として波長λ−６３３ｎｍのＨｅ　−Ｎ　ｅレー
ザーを使用し、ｆ＋・ｆ’３／ｆ２＝５０ｍｍ、ｄｌ−
５μｍとすれば１次回折光の位置ｄ　、　ｒはｄ＋’−
６，３３ｍｍとなる。また、この例では格子数Ｎ、＝５
としているので、１次回折光と隣接する極小点との距離
β、′は１．２７ｍｍである。これよりフィルタ１０９
の開口部１１０を、光軸から６．３３ｍｍの位置に開口
幅１．２７ｍｍ以上とれば、１次回折光を全て通すこと
ができる。A He-Ne laser with a wavelength of λ-633 nm was used as the illumination light, f+・f'3/f2=50 mm, dl-
If it is 5 μm, the position d and r of the first-order diffracted light are d+'-
It will be 6.33mm. In addition, in this example, the number of lattices N, = 5
Therefore, the distance β,' between the first-order diffracted light and the adjacent minimum point is 1.27 mm. From this filter 109
If the opening 110 is located at a position 6.33 mm from the optical axis and has an opening width of 1.27 mm or more, all of the first-order diffracted light can pass through.

この１次回折光をレンズ１１１により結像すると、結像
面１１３内での光強度は第４図のように、光学系の最終
倍率をＭ　”　ｆ　ａ　／　ｆ　Ｉとしてｄ、　　＝　
（Ｍ／２）ｄの間隔で極大値をとる。また、これらの光強度の極大点
の結像面１１３内でのＸ方向の位相△ａ。When this first-order diffracted light is imaged by the lens 111, the light intensity within the imaging plane 113 is as shown in FIG. 4, where d, =
Maximum values are taken at intervals of (M/2)d. Furthermore, the phase Δa in the X direction of the maximum points of these light intensities within the imaging plane 113.

は、回折格子の位置が第１図に示すようにＸ方向に△ａ
、だけずれたときには、△ａｌ　　＝Ｍ△ａ１だけ拡大してずれる。この像を検知器で検出する。is, the position of the diffraction grating is △a in the X direction as shown in Figure 1.
, the deviation is expanded by Δal=MΔa1. This image is detected by a detector.

上記は上層膜の回折格子についてであるが、第２図（ｂ
ｌの下層膜の回折格子も同様にして検出できる。ただし
この回折格子は異なる格子間隔ｄ２を有し、（ａ）の回
折格子に対して中央格子の位置を設計上同一線上になる
ように配置してｙ方向に平行にずらしている。フィルタ
１０９としては、下層膜の１次回折光の位置に開口部を
設ける。これにより、結像面１１３内で各回折格子の像
の各位相△ａ、′、△ａ２″を測定し位相差△ａｌ′−
△ａ２を求めることで重ね合せ精度△ａ１−△ａ２が求
まる。倍率を５００倍、検知器の分解能が５μｍとする
と、試料面上で０．０１μｍの分解能で重ね合せ精度が
測定できる。The above is about the diffraction grating of the upper layer film.
The diffraction grating of the lower layer film of 1 can be detected in the same manner. However, this diffraction grating has a different grating interval d2, and the position of the central grating is designed to be on the same line as in the diffraction grating of (a), and is shifted in parallel to the y direction. As the filter 109, an opening is provided at the position of the first-order diffracted light of the lower layer film. As a result, each phase △a,', △a2'' of the image of each diffraction grating is measured within the imaging plane 113, and the phase difference △al'-
By determining Δa2, the overlay accuracy Δa1-Δa2 can be determined. When the magnification is 500 times and the resolution of the detector is 5 μm, the overlay accuracy can be measured on the sample surface with a resolution of 0.01 μm.

次に第３図により、本発明の実施例に用いるフィルタの
説明を行なう。フィルタ１０９面での回折像は、前述の
（１）式、（２）式で表されるので、開口部をそれに合
せて設ける。第３図の上部に下層膜回折格子の下部に上
層膜回折格子のフィルタがそれぞれ示されている。下層
膜用Ｘ軸スリット３０１と、ｙ軸スリット３０２が重な
った部分のみ開口部３０３となるようにする。Ｘ軸スリ
ット３０１は、ｙ軸方向にスライドすることで、Ｘ軸の
開口位置を調整でき、また上層膜用Ｘ軸スリット３０４
は、ｙ軸スリット３０２を重ねれば、上層膜用の開口部
をつくることができる。このようなフィルタを用いれば
、異なった格子間隔のものも測定できる。また下層膜用
Ｘ軸スリット３０１で下層の回折格子のみを測定し、Ｘ
軸スリットをスライドして上層膜用Ｘ軸スリット３０４
で上層の回折格子のみを測定すれば、結像面で、上層膜
と、下層膜の回折格子の像が干渉することがなく、回折
格子の配置の制約が少なくなる利点がある。第２図（ａ
ｌと（ｂｌの回折格子の中心格子の位置を同一線上に並
べて、さらに（ａ）、　（ｂｌをｙ方向にずらさず平行
に並べて配置するときには、格子の方向と測定方向との
直交度のずれによる重ね合せ精度測定誤差を排除できる
。Next, referring to FIG. 3, a filter used in an embodiment of the present invention will be explained. Since the diffraction image on the surface of the filter 109 is expressed by the above-mentioned equations (1) and (2), the apertures are provided accordingly. At the top of FIG. 3, the filters of the lower layer film diffraction grating and the upper layer film diffraction grating are shown below. Only the portion where the lower layer film X-axis slit 301 and the y-axis slit 302 overlap becomes an opening 303. The X-axis slit 301 can adjust the opening position of the X-axis by sliding in the y-axis direction.
By overlapping the y-axis slits 302, an opening for the upper layer film can be created. Using such a filter, it is also possible to measure objects with different grid spacings. In addition, only the lower layer diffraction grating is measured using the X-axis slit 301 for the lower layer film, and
Slide the axis slit to open the X-axis slit 304 for upper layer film.
If only the upper layer diffraction grating is measured, there is no interference between the images of the upper layer film and the lower layer film diffraction gratings on the imaging plane, which has the advantage of reducing restrictions on the arrangement of the diffraction gratings. Figure 2 (a
When the central grating positions of the diffraction gratings l and (bl are aligned on the same line, and (a) and (bl are arranged parallel to each other without shifting in the y direction, the difference in orthogonality between the grating direction and the measurement direction It is possible to eliminate overlay accuracy measurement errors caused by

〔発明の効果〕〔Effect of the invention〕

以上、説明したように本発明は、被測定パタンに回折格
子を用いて、これによる回折光を検知することにより、
パターンエツジ形状等の不安定な影響が少なく、回折格
子間隔寸法により決まる指向性の高い安定した回折光を
測定でき、安定した測定結果が得られる効果がある。ま
た、フィルタを用いて、測定方向の回折光のみが検知さ
れるようにすることにより、他方向の光による影響がな
く、回折格子と、それ以外の部分とのＳ／Ｎ比が向上し
、測定の信頼性が向上する効果がある。As explained above, the present invention uses a diffraction grating for the pattern to be measured and detects the diffracted light thereby.
This method has the effect of being able to measure stable diffracted light with high directivity determined by the diffraction grating spacing, with little influence of instability due to pattern edge shapes, etc., and stable measurement results. In addition, by using a filter so that only the diffracted light in the measurement direction is detected, there is no influence from light in other directions, and the S/N ratio between the diffraction grating and other parts is improved. This has the effect of improving measurement reliability.

また、フィルタの開口位置を上層膜回折格子と、下層膜
同格子に対し、それぞれの回折光の位置に別々に合せて
測定することにより、下層膜および、上層膜の回折格子
の配置に対する制約を少なくすることができる。In addition, by measuring the aperture position of the filter separately to the position of the diffracted light for the upper layer film diffraction grating and the lower layer film grating, constraints on the arrangement of the diffraction gratings of the lower layer film and the upper layer film can be resolved. It can be reduced.

【図面の簡単な説明】[Brief explanation of drawings]

第１図は本発明の実施例につき、光経路を示す図、第２
図は、重ね合せ精度測定用回折格子の１例の平面図、第
３図は実施例のフィルタの平面図、第４図は結像の光強
度分布を示す平面図である。１０１−一試料、　　１０２’−回折格子、１０３−照
明光、　ｌ　０４−ビームスプリ・７り、１０５−４次
回折光、１０６゜１０９１２０１０２０１０２０４１０７．１０８．ＩＩＬ−−−レンズ、フィルタ、　１
１０−開口部、回折像、　１１３−結像面、上層膜回折格子、下層膜回折格子、下層膜用Ｘ軸スリット、ｙ軸スリット、　　３０３−開口部、上層膜用Ｘ軸スリット。FIG. 1 is a diagram showing the optical path according to an embodiment of the present invention, and FIG.
The figure is a plan view of an example of a diffraction grating for overlay accuracy measurement, FIG. 3 is a plan view of a filter of the example, and FIG. 4 is a plan view showing the light intensity distribution of imaging. 101-One sample, 102'-Diffraction grating, 103-Illumination light, 104-Beam splitter, 105-4th order diffracted light, 106°109 12 01 02 01 02 04 107.108. IIL---lens, filter, 1
10-opening, diffraction image, 113-imaging surface, upper layer film diffraction grating, lower layer film diffraction grating, X-axis slit for lower layer film, y-axis slit, 303-opening, X-axis slit for upper layer film.

Claims (1)

Translated fromJapanese

【特許請求の範囲】１、半導体装置の上層膜と下層膜の重ね合せ精度を上層
膜・下層膜に形成した回折格子を利用して測定する方法
であって、上層膜および下層膜のそれぞれの回折格子の中心格子が
同一線上に並ぶように配設した回折格子を単色光で照明
し、レンズにより焦点面上に回折像を形成し、そのうち
の特定次数の回折光のみを透過させ、前記透過回折光を
結像して、回折像から上層膜・下層膜の相対位置を求め
ることを特徴とする重ね合せ精度測定方法。２、前記第１項において、下層膜と上層膜に形成した回
折格子として格子間隔の異なるものを使用し、特定次数
の回折光のみ透過させるフィルタの開口位置を、回折格
子に合わせて変えることを特徴とする請求項１記載の重
ね合せ精度測定方法。[Claims] 1. A method for measuring the overlay accuracy of an upper layer film and a lower layer film of a semiconductor device using a diffraction grating formed on the upper layer film and the lower layer film, the method comprising: A diffraction grating arranged so that the central gratings of the diffraction grating are aligned on the same line is illuminated with monochromatic light, a diffraction image is formed on the focal plane by a lens, and only the diffraction light of a specific order is transmitted. An overlay accuracy measuring method characterized by forming an image of diffracted light and determining the relative position of an upper layer film and a lower layer film from the diffraction image. 2. In item 1 above, use diffraction gratings with different grating spacings formed on the lower layer film and the upper layer film, and change the aperture position of the filter that transmits only diffracted light of a specific order according to the diffraction grating. The method for measuring overlay accuracy according to claim 1.