JP3936159B2 - Optical measuring apparatus, optical measuring method, optical film thickness detecting method, and semiconductor manufacturing method - Google Patents

Description

ここで、Ｎはデータ総数、Ｐは未知のパラメータ数（上述した例では、未知のパラメータをＳｉＮ膜の光学的膜厚ｎＤとしてＰ＝２）である。
【００３８】
第１実施形態では、簡単な構成で、空気中での実測反射率の他に、連続して純水中での実測反射率も得ることができ、各測定環境の間でフィッティングすることになる。したがって、空気中での実測反射率のみで膜厚計算を行うよりも、容易に高い精度での解析が実現される。
【００３９】
＜第２実施形態＞
第２実施形態では、半導体製造プロセスにおいて、化学的機械的研磨（ＣＭＰ）直後にロールスポンジ洗浄を行う面上に膜厚測定装置を取り付けて、残膜の厚さを求めるとともに、下層の膜厚も測定する適用例を説明する。
【００４０】
図３は、第２実施形態にかかる光学測定装置を示す。第２実施形態の光学測定装置は、光源（不図示）および分光反射率計（不図示）を含む分光光学系２３０と、光学窓２０３を有するノズル２０４と、ノズル２０４に接続され、３つに分岐する供給管２１０と、供給管２１０の分岐点近傍に位置する３つのバルブ２１１、２１２、２１４を含む。分光光学系２３０と光学窓２０３とは、光ファイバ２０６で接続されている。各分岐管２２１、２２２、２２３からは、対応するバルブ２１１、２１２、２１４を介して、それぞれ、空気、純水、イソプロピルアルコールが供給されるようになっている。
【００４１】
第２実施形態では、測定するサンプルは、Ｓｉ基板２０１上に約１５０ｎｍのＳｉＮ薄膜２０２を成膜し、溝２１６を設けた後、この溝２１６をＳｉＯ₂膜２１５で埋め込んだものをＣＭＰ研磨し、ＳｉＮ薄膜２０２上のＳｉＯ₂膜２１５を除去したものである。すなわち、ＳｉＯ₂膜２１５の研磨が適正に行われているかどうかを検査、確認するために、ＳｉＮ薄膜２０２上に残存するＳｉＯ₂膜２１５の膜厚を測定する必要がある。
【００４２】
しかしこの場合、ＳｉＮ薄膜２０２上に残存するＳｉＯ₂膜２１５の膜厚は１０ｎｍ以下の極薄膜であるうえに、ＳｉＮ膜２０２とＳｉＯ₂膜２１５の屈折率は近いため、通常の垂直入射分光反射率測定では、正確な膜厚測定は困難であった。
【００４３】
そこで、本実施形態では、ＣＭＰ研磨後の純水での研磨面のロールスポンジ洗浄と同時に、純水中で膜厚測定を行い、その後連続して測定環境を変えることにより精密な残膜測定を行う。
【００４４】
図４に示すように、ＳｉＯ₂膜２１５が研磨されたウエハ２２０上に洗浄用の純水（不図示）が供給され、ロールスポンジ２３２が回転しながら、研磨面２１７を洗浄する。このとき、ウエハ２２０も、ウエハ回転コロ２３３で回転され、全体にわたって均一に洗浄が行われる。
【００４５】
この洗浄工程において、まず、第２バルブ２１２と第３バルブ２１３を開にし、第１バルブ２１１と第４バルブ２１４と閉にして、純水を供給し、光学窓２０３とＣＭＰ研磨面２１７との間の測定環境２１８を、洗浄環境と同様の純水で満たす。ノズル２０４はＣＭＰ研磨面２１７から約２ｍｍのところに配置し、第１実施形態と同様に、純水環境中で、ウエハ表面からの反射干渉光を測定する。測定光は、光ファイバ２０６を伝播し、光学窓２０３からウエハ表面に垂直入射する。第２実施形態では、測定光は、ＣＭＰ研磨面２１７、ＳｉＮ膜２０２とＳｉＯ₂膜２１５との界面、ＳｉＮ膜２０２とＳｉ基板２０１との界面などで反射し、それぞれ干渉して分光光学系に導かれる。
【００４６】
次に、ウエハ洗浄終了後に、第２バルブ２１２を閉じ、第３バルブ２１４を開にしてイソプロピルアルコール（ＩＰＡ）を供給し、測定環境２１８を異なる媒質で満たす。上述したのと同様の手順で、イソプロピルアルコール中で反射率を測定する。この測定が終了したら、第４バルブ２１４を閉じてイソプロピルプロピルアルコールの供給を止め、ウエア上のイソプロピルアルコールを蒸発、乾燥させる。乾燥を促進するために、第１バルブ２１１を開にして、ノズル２０４から高圧空気を吹き付ける。ウエハが十分に乾燥した後、空気で満たされた測定環境２１８中で、再度反射干渉光を測定する。この方法によれば、純水、イソプロピルアルコール、空気中のそれぞれで測定した反射率スペクトルが得られる。
【００４７】
３つの実測値を得た後、ＳｉＮ膜２０２と、ＳｉＯ₂膜２１５のそれぞれの予測膜厚値を変化させながら３つの測定雰囲気での反射率計算式に代入し、３つの実測値と、対応する計算値が最小となるようにフィッティング計算することによって、ＳｉＮ膜２０２と、ＳｉＯ₂膜２１５の双方の膜厚を解として求める。なお、第２実施形態では、空気、純水、ＩＰＡ、Ｓｉ基板の屈折率および消衰係数と、ＳｉＮ膜２０２、ＳｉＯ₂膜２１５の消衰係数は既知とし、ＳｉＮ膜２０２の膜厚Ｄ₁と屈折率ｎ₁、ＳｉＯ₂膜２１５の膜厚Ｄ₃と屈折率ｎ₃を未知のパラメータとして変化させる。
【００４８】
第２実施形態によれば、半導体製造プロセスで重要になりつつあるＣＭＰ研磨後の残膜を、その下層の膜厚とともに、正確かつ簡単な方法で求めることが可能になる。研磨面洗浄の雰囲気を利用しつつ、実測パラメータも増やすことができるので測定効率が良く、同時に膜厚検出精度も向上する。
【００４９】
＜第３実施形態＞
図５は、第３実施形態に係る光学測定装置を示す。第３実施形態では、第１実施形態とほぼ同様の装置を用いて、第２実施形態のサンプルを測定する例を説明する。
【００５０】
第３実施形態に係る光学側定装置は、光源３０５と、光源側に光学窓３０３を有するノズル３０４と、光源３０５と光学窓３０３の間の光軸上に位置するハーフミラー３０６と、ハーフミラー３０６の光軸上に位置する分光反射率計３０７と、ノズル３０４に接続され、２つに分岐する供給管３１０と、供給管３１０の分岐点近傍に位置するマスフローコントローラ（ＭＦＣ）３１１、３１２と、供給管３１０上に位置する屈折率計３０８を含む。
【００５１】
第１実施形態と同様に、光源３０５、ハーフミラー３０６、分光反射率計３０７で光学系３３０を構成する。この光学系３３０は、光源３０５から試料であるＣＭＰ研磨面３１７に光を垂直入射させ、各層の表面で反射された反射干渉光をハーフミラー３０６によって分光反射率計３０７に導いて反射率を測定する。
【００５２】
ノズル３０４の先端は、ＣＭＰ研磨面３１７の表面から約２ｍｍ離れた位置に設定され、光学窓３０３とＣＭＰ研磨面３１７の間に、光軸を含む測定環境３１４が形成される。ノズル３０４には、第１分岐管３２１を介して純水が接続され、第２分岐管３２２を介してＩＰＡが接続される。
【００５３】
第３実施形態では、ＭＦＣ３１１と３１２で純水とＩＰＡの流量を調節して混合比を変えることによって、測定環境３１４を任意の媒質で満たし、任意の数の測定環境で、連続して反射干渉光を側定することを可能にする。
【００５４】
具体的には、
(１) 純水のみを１リットル／分の流量で流して反射率の測定を行う
(２) その後、純水を０．８リットル／分、ＩＰＡを０．２リットル／分（すなわち、純水とＩＰＡの混合比８：２）になるようにＭＦＣを調整して測定する
(３) その後、純水を０．６リットル／分、ＩＰＡを０．４リットル／分（すなわち、純水とＩＰＡの混合比６：４）になるようにＭＦＣを調整して測定する
(４) その後、純水を０．４リットル／分、ＩＰＡを０．６リットル／分（すなわち、純水とＩＰＡの混合比４：６）になるようにＭＦＣを調整して測定する
(５) その後、純水を０．２リットル／分、ＩＰＡを０．８リットル／分（すなわち、純水とＩＰＡの混合比２：８）になるようにＭＦＣを調整して測定する
(６) その後、ＩＰＡのみを１リットル／分の流量で供給して測定する
というふうに、６つの異なる測定環境を連続して作り上げる。測定環境を満たす媒質がそれぞれ異なるため、その屈折率も異なる。各測定環境３１４での屈折率は、純水とＩＰＡの混合比から計算により求めてもよいが、より正確な値をリアルタイムで求められるように、インラインの屈折率計３０８を供給管３１０上に設ける。これにより、流量比の変動による屈折率の変動の影響を排除した、より精密な膜厚検出が可能になる。
【００５５】
第３実施形態では、２つのＭＦＣを調整することによって、６つの異なる測定環境を連続して創出し、フィッティングのための実測値の数を増やしたが、混合比を６以上に変化させて測定環境を変えることももちろん可能である。
【００５６】
また、第３実施形態では、２つの異なる液体を混合させたが、同じ相の物質であれば、容易かつ均一に混合するので、２つの異なる気体、たとえば、空気とアルゴン、あるいは空気と水素など混合させることによって、異なる測定環境を連続して作り上げてもよい。
【００５７】
いずれの場合も、各測定環境における実測値と、計算による反射率とをフィッティングすることによって、ＣＭＰ研磨後の残膜（ＳｉＯ2膜３１５）の膜厚と、その下層のＳｉＮ膜３０２の膜厚の双方をきわめて高い精度で検出することができる。
【００５８】
第３実施形態では、簡単な構成で連続して任意の数の測定環境で反射率の測定ができるので、より高い精度で膜厚検出が可能になる。しかも、測定対象となる膜の屈折率以外の他の物理的性質、たとえば消衰係数等をも未知のパラメータとして、実測パラメータの数をさらに増やすこともできる。また、インラインの屈折率計を用いた場合は、測定環境を満たす媒質の屈折率変動誤差を排除し、より正確な測定が可能になる。
【００５９】
さらに、研磨後の洗浄工程と同時に膜厚検査を行うことができるので、作業効率に優れる。
以上、第１実施形態から第３実施形態を、半導体基板上に形成された膜厚の測定と関連づけて説明したが、本発明は、半導体基板上の膜厚の測定に限定されず、トレンチの深さ測定や、ピエゾ素子、超音波弾性素子、電子部品等に形成される薄膜配線、絶縁膜など、任意の膜厚測定に適用できる。
【００６０】
さらに、半導体装置の検査工程のみならず、任意の機械部品や、電気部品の膜厚検査にも適用できる。
【００６１】
【発明の効果】
以上述べたように、本発明によれば、複雑な光学系を必要とせず、簡単な構成で、きわめて薄い膜厚も精度よく検出することが可能になる。
【００６２】
測定環境を連続的かつ迅速に変えることが可能なため、多くの環境での反射率測定を短時間で行うことができる。
【００６３】
半導体製造工程に適用した場合は、同一試料で多数の測定パラメータが得られるため、極めて薄い膜厚の測定だけでなく、製造プロセスのばらつきや膜、基板等の光学定数の変動を考慮した精密な光学解析が可能になる。
【図面の簡単な説明】
【図１】本発明の第１実施形態に係る光学測定装置と、それを利用した膜厚測定の例を示す図である。
【図２】垂直入射光による反射干渉光を利用した薄膜測定の原理を示す図である。
【図３】本発明の第２実施形態に係る光学測定装置と、それを利用した膜厚測定の例を示す図である。
【図４】図３の装置で、ＣＭＰ研磨後の洗浄工程で残膜を測定する例を示す図である。
【図５】本発明の第３実施形態に係る光学測定装置と、それを利用した膜厚測定の例を示す図である。
【符号の説明】
１０１、２０１、３０１ Ｓｉ基板
１０２、２０２、３０２ ＳｉＮ膜
１０３、２０３、３０３ 光学窓
１０４、２０４、３０４ ノズル
１０５、３０５ 光源
１０６、３０６ ハーフミラー
１０７、３０７ 分光反射率計
１１０、２１０、３１０ 供給管
１１１、１１２、１１３、２１１、２１２、２１３、２１４ バルブ
１１４、２１８、３１４ 測定環境
１２１、１２２、２２１、２２２、２２３、３２１、３２２ 分岐管
１３０、２３０、３３０ 光学系
２１５、３１５ ＳｉＯ₂膜
２１６、３１６ 溝
２１７、３１７ ＣＭＰ研磨面
３０８ 屈折率計
３１１、３１２ マスフローコントローラ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical measurement apparatus and an optical measurement method, and more particularly to a spectral reflection interference measurement apparatus and measurement method for film thickness measurement required in a semiconductor manufacturing process, and a semiconductor manufacturing method using the same.
[0002]
[Prior art]
Semiconductor devices use a wide variety of surface protective films, metal thin films for electrodes, plating of component materials, and the like, and their film thickness control is very important for ensuring operational reliability.
[0003]
In addition, along with the high integration and miniaturization of semiconductor elements, insulating film planarization technology using CMP technology has emerged, and not only an interlayer process for polishing an interlayer insulating film, but also STI (shallow trench isolation), buried gate, etc. CMP is also being applied to these layers. As the end point detection in the final stage of the CMP process, the amount of polishing is managed by optically measuring the remaining film.
[0004]
There are various methods for measuring the film thickness depending on the physical properties of the film. When measuring a transparent film having a known refractive index, such as SiO ₂ or SiN on the Si surface, a film thickness measuring apparatus using a normal incidence spectral reflection interferometer having a relatively simple apparatus configuration is generally used. .
[0005]
[Problems to be solved by the invention]
However, in the interference spectroscopy measurement at normal incidence, since the actual measurement value is only the reflectance, it is difficult to analyze multivariables. When the sample film is a multilayer, the multiple reflection interference light reflected at all the interfaces is measured, so that more variables need to be obtained and the analysis becomes more difficult.
[0006]
Therefore, an optical constant of a thin film or a substrate to be measured, that is, an optical thickness (nD; where n is a refractive index and D is a physical film thickness) of a medium (film) is assumed (predicted) in advance. In many cases, the thickness of the thin film is obtained by performing fitting calculation so that the difference between the calculated reflectance obtained by sequentially changing the predicted film thickness value and the actually measured reflectance is minimized. However, if the optical constants used for the calculation and the measured optical constants of the sample are different due to problems such as manufacturing process variations and instability, the fitting calculation will not be successful and an accurate film thickness will not be obtained. There may not be.
[0007]
In order to perform fitting more accurately and obtain an accurate film thickness, it is conceivable to increase the actual measurement parameters. For example, a multiple incidence angle measurement method that measures various incident angles, or a completely polarized light whose polarization state is known is incident on a sample with a flat surface, and changes in the polarization state of reflected light are captured. There is an ellipsometry for obtaining optical constants. However, these methods require a complicated optical system as compared with the normal incidence reflectivity measurement.
[0008]
Therefore, in the present invention, while using a normal incidence spectral reflection interferometer with a simple optical system as it is, by changing the measurement environment, by obtaining a plurality of reflectance measurement values, increase the parameters for analysis, Provided are an optical measurement apparatus and an optical measurement method that facilitate analysis and enable accurate film thickness fitting.
[0009]
Moreover, the optical film thickness detection method using such a measuring method and the semiconductor manufacturing method which applied this to the inspection process of a semiconductor manufacturing process are provided.
[0010]
[Means for Solving the Problems]
In one aspect of the present invention, an optical measurement device includes an optical system including a light source and a spectral reflectometer, a nozzle having an optical window that transmits light from the light source onto the sample, and two or more branch pipes connected to the nozzle. And a flow rate adjusting means provided in each of the branch pipes, and the nozzle is set at a position facing the sample, and a different medium is provided between the optical window and the sample surface. By satisfying, different measurement environments are formed .
[0011]
The flow rate adjusting means is any means that can supply a different medium via a nozzle to the space between the optical window and the sample surface, such as a valve or a mass flow controller.
[0012]
This apparatus can continuously fill the space through which the measurement light passes with different media while using the conventional normal incidence optical system as it is. Since the types of parameters necessary for optical measurement can be easily increased with a simple configuration, the accuracy of measurement can be improved.
[0013]
In another aspect of the present invention, an optical measurement method is provided. This optical measurement method includes the following steps.
[0014]
(A) a step of arranging an optical window so as to face the sample;
(B) filling the space between the optical window and the sample surface with the first medium;
(C) irradiating the sample with measurement light through the optical window and the first medium in the space, and measuring reflected interference light from the sample;
(D) filling the space with a second medium different from the first medium;
(E) A step of irradiating the sample with measurement light through the optical window and the second medium in the space and measuring reflected interference light from the sample.
[0015]
According to this optical measurement method, different measurement environments are created, and reflected environment light is measured in each environment. Therefore, accurate measurement can be performed by increasing the types of parameters required for measurement.
[0016]
In still another aspect of the present invention, an optical film thickness detection method is provided. This film thickness detection method includes the following steps.
[0017]
(A) a step of arranging an optical window so as to face a sample on which a first thin film is formed on a substrate;
(B) filling a space between the optical window and the first thin film with the first medium;
(C) irradiating the sample with measurement light through the optical window and the first medium filling the space, and measuring the first reflected interference light from the sample;
(D) filling the space with a second medium different from the first medium;
(E) irradiating the sample with measurement light through the optical window and the second medium filling the space, and measuring the second reflected interference light from the sample; and
(F) A step of detecting the thickness of the first thin film based on the first and second reflected interference lights.
[0018]
This film thickness detection method can change the measurement environment and increase the number of parameters required for the calculation. Therefore, when the film thickness is extremely thin, the refractive index of the film to be detected and the refractive index of the lower layer (or substrate) Even when the rates are close, the film thickness can be detected with high accuracy.
[0019]
In still another aspect of the present invention, a semiconductor manufacturing method in which optical film thickness measurement is applied to a film thickness inspection process is provided. The semiconductor manufacturing method includes the following steps.
[0020]
(A) forming a first thin film on the wafer;
(B) arranging the optical window so as to face the first thin film;
(C) Filling the space between the optical window and the first thin film with the first medium, irradiating the wafer with measurement light through the first medium filling the optical window and the space, Measuring the reflected interference light of 1;
(D) Filling the space with a second medium different from the first medium, irradiating the wafer with measurement light via the optical window and the second medium filling the space, Measuring two reflected interference lights; and
(E) detecting the film thickness of the first thin film based on the first and second reflected interference lights;
[0021]
According to this semiconductor manufacturing method, by changing the measurement environment on the same wafer, it is possible to obtain a plurality of parameters required for measurement, so taking into account variations in manufacturing processes and variations in optical constants in thin films, substrates, etc. Precise film thickness inspection is possible.
[0022]
In still another aspect of the present invention, a semiconductor manufacturing method in which optical film thickness measurement is applied to the final polishing process is provided. This semiconductor manufacturing method includes the following steps.
[0023]
(A) forming a first layer on the wafer;
(B) forming a second layer different from the first layer on the first layer;
(C) polishing the second layer;
(D) a step of arranging an optical window so as to face the polished wafer;
(E) Filling the space between the optical window and the wafer with the first medium, irradiating the wafer with the measuring light through the first medium filling the optical window and the space, and the first reflection from the wafer Measuring interference light,
(F) Filling the space with a second medium different from the first medium, irradiating the wafer with measurement light through the optical medium and the second medium filling the space, Measuring second reflected interference light; and
(G) A step of detecting a film film of the second layer remaining after the polishing based on the first and second reflected interference lights.
[0024]
According to this semiconductor manufacturing method, the film thickness inspection in the planarization process corresponding to the high integration of the semiconductor device can be performed continuously and accurately at the final stage of polishing.
[0025]
Other features and advantages of the present invention will become more apparent from the detailed description given below with reference to the drawings.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
<First Embodiment>
FIG. 1 shows an optical measurement apparatus according to the first embodiment of the present invention. In the first embodiment, an example in which the film thickness of the SiN thin film 102 formed on the Si substrate 101 is measured will be described.
[0027]
The optical measurement apparatus according to the first embodiment includes a light source 105, a nozzle 104 having an optical window 103 on the light source side, a half mirror 106 positioned on the optical axis between the light source 105 and the optical window 103, and a half mirror. A spectral reflectometer 107 located on the optical axis, a supply pipe 110 connected to the nozzle 104 and bifurcated, and valves 111 and 112 located near the branch point of the supply pipe 110 are included.
[0028]
The light source 105, the half mirror 106, and the spectral reflectometer 107 constitute a spectral optical system 130. In this optical system, light is vertically incident on a sample SiN thin film 102 from a light source 105, and reflected interference light reflected on the surface of each layer is guided to a spectral reflectometer 107 by a half mirror 106, and the reflectance is measured. It is a normal incidence type spectral reflection optical system.
[0029]
The tip of the nozzle 104 is set at a position 2 mm away from the surface of the SiN thin film 102, and a measurement environment 114 including an optical axis is formed between the optical window 103 and the SiN thin film 102. In order to increase the actual measurement parameters, the reflected light is measured by changing the medium that satisfies the measurement environment 114. In the first embodiment, air and pure water are used as the medium that satisfies the measurement environment. Therefore, the supply pipe 110 has a first branch pipe 121 for introducing air and a second branch pipe 122 for introducing pure water.
[0030]
A first valve 111 for introducing air is provided in the first branch pipe 121, and a second valve 112 for introducing pure water is installed in the second branch pipe 122. Further, the supply pipe 110 is provided with a third valve (supply pipe valve) 113. By switching these valves, the medium satisfying the measurement environment 114 is continuously switched, and two reflectances (measurement parameters) can be obtained continuously without changing the arrangement of the measurement apparatus itself.
[0031]
In the reflectance measurement procedure, first, the second valve 112 for pure water is closed, and the first valve 111 for air and the third valve 113 of the supply pipe are opened. The measurement environment 114 is filled with air, and the spectrum of reflected light is measured in the air. At this time, the light from the light source 105 passes through the half mirror 106 and the optical window 103, passes through the air that satisfies the measurement environment 114, and enters the SiN thin film 102 perpendicularly.
[0032]
Part of the incident light is reflected on the surface of the SiN thin film 102 and part of it is transmitted. Part of the transmitted light is further reflected on the surface of the Si substrate 101. A part of the light transmitted through the Si substrate 101 is further reflected on the back surface of the substrate, but for convenience of explanation, the reflection on the back surface of the Si substrate 101 is not considered. Therefore, the return light is interference light of reflected light at the interface between the SiN thin film 102 and air and at the interface between the SiN thin film 102 and the Si substrate 101. The return light is reflected by the half mirror 106 and guided to the spectral reflectometer 107.
[0033]
Subsequently, the air valve 111 is closed, the pure water valve 112 and the supply pipe valve 113 are opened, and pure water is supplied to the measurement environment 114 between the optical window 103 and the sample (SiN film 102) at a flow rate of 1. Supply at 0 liter / min and fill the light path with pure water. When there are no more bubbles in the optical path, measure the reflectance in pure water.
[0034]
FIG. 2 is a diagram for explaining the thin film measurement theory. Refractive index N ₂ = n ₂ −ik ₂
A thickness D ₁ and a refractive index N ₁ = n ₁ −ik ₁ It is assumed that light is incident at an incident angle of 0 °. Here, k ₁ and k ₂ are extinction coefficients of the SiN film 102 and the Si substrate 101. The reflectance R ^meas measured by the spectral reflectometer 107 in FIG. 1 is the reflectance of interference light between the reflected light r1 on the surface of the SiN film 102 and the reflected light r2 on the surface of the Si substrate 101.
[0035]
In order to calculate the reflectance of the SiN film 102 in the configuration of the first embodiment, in addition to the respective refractive indexes n and extinction coefficients k of the Si substrate 101, the SiN film 102, air, and pure water, the SiN film 102 is calculated. The film thickness D ₁ is required. Now, Si substrate 101, the air, respectively the refractive index and extinction coefficient of pure water, as the extinction coefficient k ₁ of the SiN film 102 are known, can be assigned to the formula. On the other hand, regression calculation is performed using the film thickness D ₁ and the refractive index n ₁ of the SiN film 102 as unknown parameters.
[0036]
The reflectance R ^meas obtained by the measurement and the calculated reflectance R ^cal obtained from the predicted film thickness value are compared, and the calculation is performed while changing the predicted film thickness value of the SiN film 102 until they match. Repeat the curve fitting. The measurement value and the calculated value are fitted by minimizing the following unbiased estimation amount.
[0037]
[Expression 1]

Here, N is the total number of data, and P is the number of unknown parameters (in the above-described example, P = 2 where the unknown parameter is the optical film thickness nD of the SiN film).
[0038]
In the first embodiment, with a simple configuration, in addition to the measured reflectance in the air, the measured reflectance in pure water can be continuously obtained, and fitting is performed between the measurement environments. . Therefore, an analysis with higher accuracy can be realized more easily than when the film thickness is calculated using only the measured reflectance in the air.
[0039]
Second Embodiment
In the second embodiment, in the semiconductor manufacturing process, a film thickness measuring device is attached on the surface where roll sponge cleaning is performed immediately after chemical mechanical polishing (CMP) to obtain the thickness of the remaining film, and the film thickness of the lower layer. An application example for measuring the above will also be described.
[0040]
FIG. 3 shows an optical measurement apparatus according to the second embodiment. The optical measurement apparatus according to the second embodiment includes a spectroscopic optical system 230 including a light source (not shown) and a spectroscopic reflectometer (not shown), a nozzle 204 having an optical window 203, and a nozzle 204 connected to the three. It includes a supply pipe 210 that branches off and three valves 211, 212, and 214 located near the branch point of the supply pipe 210. The spectroscopic optical system 230 and the optical window 203 are connected by an optical fiber 206. Air, pure water, and isopropyl alcohol are supplied from the branch pipes 221, 222, and 223 through corresponding valves 211, 212, and 214, respectively.
[0041]
In the second embodiment, as a sample to be measured, a SiN thin film 202 having a thickness of about 150 nm is formed on a Si substrate 201, a groove 216 is provided, and then the groove 216 embedded with a SiO ₂ film 215 is subjected to CMP polishing. The SiO ₂ film 215 on the SiN thin film 202 is removed. That is, it is necessary to measure the film thickness of the SiO ₂ film 215 remaining on the SiN thin film 202 in order to inspect and confirm whether the SiO ₂ film 215 is properly polished.
[0042]
However, in this case, the thickness of the SiO ₂ film 215 remaining on the SiN thin film 202 is an extremely thin film of 10 nm or less, and the refractive indexes of the SiN film 202 and the SiO ₂ film 215 are close to each other. In the rate measurement, accurate film thickness measurement was difficult.
[0043]
Therefore, in this embodiment, the film thickness is measured in pure water at the same time as the roll sponge cleaning of the polished surface with pure water after CMP polishing, and then a precise residual film measurement is performed by continuously changing the measurement environment. Do.
[0044]
As shown in FIG. 4, cleaning water (not shown) is supplied onto the wafer 220 on which the SiO ₂ film 215 has been polished, and the polishing surface 217 is cleaned while the roll sponge 232 rotates. At this time, the wafer 220 is also rotated by the wafer rotating roller 233, and cleaning is performed uniformly throughout.
[0045]
In this cleaning process, first, the second valve 212 and the third valve 213 are opened, the first valve 211 and the fourth valve 214 are closed, pure water is supplied, and the optical window 203 and the CMP polishing surface 217 are contacted. The measurement environment 218 is filled with pure water similar to the cleaning environment. The nozzle 204 is disposed approximately 2 mm from the CMP polished surface 217, and measures reflected interference light from the wafer surface in a pure water environment, as in the first embodiment. The measurement light propagates through the optical fiber 206 and enters the wafer surface perpendicularly from the optical window 203. In the second embodiment, the measurement light is reflected at the CMP polished surface 217, the interface between the SiN film 202 and the SiO ₂ film 215, the interface between the SiN film 202 and the Si substrate 201, and interferes with each other to enter the spectroscopic optical system. Led.
[0046]
Next, after the wafer cleaning is completed, the second valve 212 is closed, the third valve 214 is opened, and isopropyl alcohol (IPA) is supplied to fill the measurement environment 218 with a different medium. The reflectance is measured in isopropyl alcohol by the same procedure as described above. When this measurement is completed, the fourth valve 214 is closed to stop the supply of isopropylpropyl alcohol, and the isopropyl alcohol on the wear is evaporated and dried. In order to accelerate drying, the first valve 211 is opened and high pressure air is blown from the nozzle 204. After the wafer is sufficiently dried, the reflected interference light is measured again in the measurement environment 218 filled with air. According to this method, reflectance spectra measured in pure water, isopropyl alcohol, and air can be obtained.
[0047]
After obtaining three actual measurement values, the predicted film thickness values of the SiN film 202 and the SiO ₂ film 215 are changed and substituted into the reflectance calculation formulas in the three measurement atmospheres. By performing fitting calculation so that the calculated value to be minimized is obtained, the film thicknesses of both the SiN film 202 and the SiO ₂ film 215 are obtained as solutions. In the second embodiment, the refractive index and extinction coefficient of air, pure water, IPA, and Si substrate, and the extinction coefficients of the SiN film 202 and SiO ₂ film 215 are known, and the film thickness D _{1 of the} SiN film 202 is determined. And the refractive index n ₁ , the film thickness D ₃ of the SiO ₂ film 215 and the refractive index n ₃ are changed as unknown parameters.
[0048]
According to the second embodiment, the remaining film after CMP polishing, which is becoming important in the semiconductor manufacturing process, can be obtained together with the film thickness of the lower layer by an accurate and simple method. The measurement parameters can be increased while using the polishing surface cleaning atmosphere, so that the measurement efficiency is good and the film thickness detection accuracy is improved at the same time.
[0049]
<Third Embodiment>
FIG. 5 shows an optical measurement apparatus according to the third embodiment. In the third embodiment, an example will be described in which the sample of the second embodiment is measured using an apparatus substantially the same as that of the first embodiment.
[0050]
The optical side fixing device according to the third embodiment includes a light source 305, a nozzle 304 having an optical window 303 on the light source side, a half mirror 306 positioned on the optical axis between the light source 305 and the optical window 303, and a half mirror. A spectral reflectometer 307 located on the optical axis 306; a supply pipe 310 connected to the nozzle 304 and bifurcated; and mass flow controllers (MFCs) 311 and 312 located near the branch point of the supply pipe 310; A refractometer 308 located on the supply tube 310.
[0051]
As in the first embodiment, the optical system 330 is configured by the light source 305, the half mirror 306, and the spectral reflectometer 307. In this optical system 330, light is vertically incident from a light source 305 to a CMP polishing surface 317 as a sample, and reflected interference light reflected on the surface of each layer is guided to a spectral reflectometer 307 by a half mirror 306 to measure the reflectance. To do.
[0052]
The tip of the nozzle 304 is set at a position about 2 mm away from the surface of the CMP polishing surface 317, and a measurement environment 314 including an optical axis is formed between the optical window 303 and the CMP polishing surface 317. Pure water is connected to the nozzle 304 via the first branch pipe 321, and IPA is connected via the second branch pipe 322.
[0053]
In the third embodiment, the MFCs 311 and 312 adjust the flow rates of pure water and IPA to change the mixing ratio, thereby filling the measurement environment 314 with an arbitrary medium and continuously reflecting interference in an arbitrary number of measurement environments. Allows you to determine the light.
[0054]
In particular,
(1) Measure the reflectivity by flowing pure water only at a flow rate of 1 liter / min.
(2) Thereafter, the MFC is adjusted and measured so that the pure water is 0.8 liter / minute and the IPA is 0.2 liter / minute (that is, the mixing ratio of pure water and IPA is 8: 2).
(3) Thereafter, the MFC is adjusted and measured so that the pure water is 0.6 liter / minute and the IPA is 0.4 liter / minute (that is, the mixing ratio of pure water and IPA is 6: 4).
(4) Thereafter, the MFC is adjusted and measured so that the pure water is 0.4 liter / minute and the IPA is 0.6 liter / minute (that is, the mixing ratio of pure water and IPA is 4: 6).
(5) Thereafter, the MFC is adjusted and measured so that the pure water is 0.2 liter / minute and the IPA is 0.8 liter / minute (that is, the mixing ratio of pure water and IPA is 2: 8).
(6) After that, six different measurement environments are continuously created, such as measuring by supplying only IPA at a flow rate of 1 liter / min. Since the medium satisfying the measurement environment is different, the refractive index is also different. The refractive index in each measurement environment 314 may be obtained by calculation from the mixing ratio of pure water and IPA, but an inline refractometer 308 is provided on the supply pipe 310 so that a more accurate value can be obtained in real time. Provide. This makes it possible to detect the film thickness more precisely without the influence of the refractive index fluctuation caused by the flow ratio fluctuation.
[0055]
In the third embodiment, by adjusting two MFCs, six different measurement environments were created in succession and the number of actual measurement values for fitting was increased, but the measurement was performed by changing the mixing ratio to 6 or more. It is of course possible to change the environment.
[0056]
In the third embodiment, two different liquids are mixed. However, if they are in the same phase, they are easily and uniformly mixed, so two different gases, for example, air and argon, or air and hydrogen, etc. By mixing, different measurement environments may be created continuously.
[0057]
In any case, by fitting the measured value in each measurement environment and the calculated reflectance, the film thickness of the remaining film (SiO 2 film 315) after CMP polishing and the film thickness of the SiN film 302 underneath are polished. Both can be detected with extremely high accuracy.
[0058]
In the third embodiment, since the reflectance can be measured continuously in an arbitrary number of measurement environments with a simple configuration, the film thickness can be detected with higher accuracy. In addition, the physical parameters other than the refractive index of the film to be measured, such as the extinction coefficient, can be used as unknown parameters to further increase the number of actually measured parameters. In addition, when an inline refractometer is used, more accurate measurement is possible by eliminating the refractive index fluctuation error of the medium that satisfies the measurement environment.
[0059]
Furthermore, since the film thickness inspection can be performed simultaneously with the cleaning process after polishing, the working efficiency is excellent.
As described above, the first to third embodiments have been described in relation to the measurement of the film thickness formed on the semiconductor substrate. However, the present invention is not limited to the measurement of the film thickness on the semiconductor substrate. The present invention can be applied to any film thickness measurement such as depth measurement, piezo elements, ultrasonic elastic elements, thin film wirings formed on electronic components, and insulating films.
[0060]
Furthermore, the present invention can be applied not only to the inspection process of semiconductor devices but also to film thickness inspection of arbitrary mechanical parts and electrical parts.
[0061]
【The invention's effect】
As described above, according to the present invention, an extremely thin film thickness can be accurately detected with a simple configuration without requiring a complicated optical system.
[0062]
Since the measurement environment can be changed continuously and quickly, the reflectance measurement in many environments can be performed in a short time.
[0063]
When applied to semiconductor manufacturing processes, many measurement parameters can be obtained with the same sample, so not only extremely thin film thickness measurements, but also precise measurements that take into account variations in manufacturing processes and optical constants such as films and substrates. Optical analysis becomes possible.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an example of an optical measurement apparatus according to a first embodiment of the present invention and film thickness measurement using the same.
FIG. 2 is a diagram showing the principle of thin film measurement using reflected interference light by vertically incident light.
FIG. 3 is a diagram illustrating an optical measurement apparatus according to a second embodiment of the present invention and an example of film thickness measurement using the same.
4 is a diagram showing an example in which a residual film is measured in a cleaning process after CMP polishing with the apparatus of FIG. 3;
FIG. 5 is a diagram illustrating an optical measurement apparatus according to a third embodiment of the present invention and an example of film thickness measurement using the same.
[Explanation of symbols]
101, 201, 301 Si substrate 102, 202, 302 SiN film 103, 203, 303 Optical window 104, 204, 304 Nozzle 105, 305 Light source 106, 306 Half mirror 107, 307 Spectral reflectometer 110, 210, 310 Supply tube 111, 112, 113, 211, 212, 213, 214 Valve 114, 218, 314 Measurement environment 121, 122, 221, 222, 223, 321, 322 Branch pipes 130, 230, 330 Optical system 215, 315 SiO ₂ film 216 316 Groove 217, 317 CMP polishing surface 308 Refractometer 311, 312 Mass flow controller

Claims (17)

An optical system including a light source and a spectral reflectometer;
A nozzle having an optical window for transmitting light from the light source onto the sample;
A supply pipe connected to the nozzle and having two or more branch pipes, each supplying a different medium;
A flow rate adjusting means provided in each of the branch pipes , wherein the nozzle is set at a position facing the sample, and different measurement environments are obtained by filling the optical window and the sample surface with different media. Optical measuring device forming .   The optical measurement apparatus according to claim 1, wherein the optical system further includes an optical unit that guides reflected interference light reflected by the sample to the spectral reflectometer.   The optical measurement apparatus according to claim 1, wherein the flow rate adjusting unit is a valve.    The optical measurement apparatus according to claim 1, wherein the flow rate adjusting unit is a mass flow controller. The optical measurement apparatus according to claim 4 , further comprising a refractometer provided on the supply pipe.   The optical measurement apparatus according to claim 2, wherein the optical unit is a half mirror.   The optical measurement apparatus according to claim 2, wherein the optical unit is an optical fiber. Arranging an optical window to face the sample;
Filling a space between the optical window and the sample surface with a first medium;
Irradiating measurement light on the sample through the optical window and the first medium, and measuring reflected interference light from the sample;
Filling the space with a second medium different from the first medium;
Irradiating measurement light on the sample through the optical window and the second medium, and measuring reflected interference light from the sample. The step of filling the space with the second medium, by switching the valve provided on the tube that is connected to a nozzle communicating with the space, in claim 8, characterized in that to supply the second medium The optical measurement method described. 9. The optical system according to claim 8 , wherein the step of filling the space with the second medium supplies the second medium by changing a mixing ratio of two or more substances supplied to the space. Measuring method. The optical measurement method according to claim 10 , further comprising a step of measuring refractive indexes of the first medium and the second medium. Disposing an optical window so as to face a sample on which a first thin film is formed on a substrate;
Filling a space between the optical window and the first thin film with a first medium;
Irradiating the sample with measurement light through the optical window and the first medium, and measuring first reflected interference light from the sample;
Filling the space with a second medium different from the first medium;
Based on the steps of irradiating the sample with measurement light through the optical window and the second medium and measuring second reflected interference light from the sample, and the first and second reflected interference light And a step of detecting the thickness of the first thin film. The thickness detection step, according to claim 12, wherein the determination of the thickness by fitting the first and second reflectance of the reflection interference light obtained by the measurement, and was calculated reflectance Optical film thickness detection method. Forming a first thin film on the wafer;
Disposing an optical window so as to face the first thin film;
A space between the optical window and the first thin film is filled with a first medium, measurement light is irradiated onto the wafer through the optical window and the first medium, and the first light from the wafer is irradiated. Measuring the reflected interference light of
The space is filled with a second medium different from the first medium, the measurement light is irradiated onto the wafer through the optical window and the second medium, and the second reflection from the wafer. Measuring interference light; and
Detecting the film thickness of the first thin film based on the first and second reflected interference lights;
A semiconductor manufacturing method comprising: Forming a first layer on the wafer;
Forming a second layer different from the first layer on the first layer;
Polishing the second layer;
Disposing an optical window to face the polished wafer;
A space between the optical window and the wafer is filled with a first medium, measurement light is irradiated onto the wafer through the optical window and the first medium, and first reflection from the wafer is performed. Measuring interference light; and
The space is filled with a second medium different from the first medium, the measurement light is irradiated onto the wafer through the optical window and the second medium, and the second reflection from the wafer. Measuring the interference light and detecting the film thickness of the second layer remaining after the polishing based on the first and second reflected interference lights;
A semiconductor manufacturing method comprising: After the polishing step, further comprising cleaning the wafer surface;
The method of manufacturing a semiconductor device according to claim 15 , wherein the step of measuring the first reflected interference light is performed together with the cleaning. 16. The semiconductor manufacturing method according to claim 15 , wherein the film thickness detecting step detects the film thickness of the first layer together with the film thickness of the remaining second layer.

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