JP2000146836A - Refractive index measuring method utilizing transmission phenomenon of evanescent wave and its measuring device - Google Patents
Refractive index measuring method utilizing transmission phenomenon of evanescent wave and its measuring deviceInfo
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- JP2000146836A JP2000146836A JP32175398A JP32175398A JP2000146836A JP 2000146836 A JP2000146836 A JP 2000146836A JP 32175398 A JP32175398 A JP 32175398A JP 32175398 A JP32175398 A JP 32175398A JP 2000146836 A JP2000146836 A JP 2000146836A
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- refractive index
- substance
- light
- sample
- evanescent wave
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Abstract
Description
【０００１】[0001]
【発明の属する技術分野】本発明は、特に光通信デバイ
スや光センシングの分野で用いられる材料の屈折率測定
に有効な、エバネセント波の透過現象を利用する屈折率
測定方法およびその測定装置に関するものである。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for measuring a refractive index utilizing a transmission phenomenon of an evanescent wave, which is particularly effective for measuring the refractive index of a material used in the field of optical communication devices and optical sensing. It is.
【０００２】[0002]
【従来の技術】通常、材料の屈折率を測定する場合、エ
リプソメータや屈折率計が用いられている。アッベの屈
折率計では、サンプルより屈折率の高いプリズムをサン
プルに押し当て、プリズム側から光を入射して臨界角を
測定する事でサンプルの屈折率を測定することが可能で
あるが、バルク材料以外には適用できない。また、他の
屈折率測定法として、膜厚既知のサンプルの場合、ある
特定の波長の光を被測定物質に入射し、その透過光や反
射光について計算処理をすることで求めることができ
る。また、全反射における滲み出しであるエバネセント
波を用いて測定する方法として、表面プラズモンセン
サ、光導波路センサ、光漏洩モードセンサといった屈折
率計があり、これらの方法では、サンプルの厚さが既知
である必要はない。2. Description of the Related Art Usually, when measuring the refractive index of a material, an ellipsometer or a refractometer is used. Abbe's refractometer can measure the refractive index of a sample by pressing a prism with a higher refractive index than the sample onto the sample and irradiating light from the prism side and measuring the critical angle. It cannot be applied to materials other than materials. Further, as another method of measuring the refractive index, in the case of a sample having a known film thickness, it can be obtained by making light of a specific wavelength incident on the substance to be measured and calculating the transmitted light and reflected light. In addition, as a method of measuring using an evanescent wave which is a seepage in total reflection, there are refractometers such as a surface plasmon sensor, an optical waveguide sensor, and a light leakage mode sensor, and in these methods, the thickness of a sample is known. No need to be.
【０００３】[0003]
【発明が解決しようとする課題】しかし、このような従
来の屈折率測定方法およびその測定装置においては、被
測定物質の正確な厚さデータが必要な測定法の場合、測
定光の波長に合わせた厚さを持つサンプル（試料）が必
要となる。そのため、屈折率を測定する前段階として、
膜厚を測定したり、厚さ調整のためにサンプルを研磨す
る作業が必要であった。また、膜厚測定が非常に困難な
形状の物質を測定する場合には、形状の作り替えを行う
必要があり、作り替えた物質の屈折率が、実際に求めた
い物質の値と異なっている恐れもあった。However, in such a conventional method of measuring the refractive index and its measuring apparatus, in the case of a measuring method which requires accurate thickness data of the substance to be measured, it is necessary to adjust the wavelength to the wavelength of the measuring light. A sample having a different thickness is required. Therefore, as a step before measuring the refractive index,
Work to measure the film thickness and polish the sample for thickness adjustment was required. Also, when measuring a material having a shape that is very difficult to measure the film thickness, it is necessary to reshape the shape, and the refraction index of the reshaped material is different from the value of the material that is actually required. I was afraid.
【０００４】また、屈折率を測定する際にエバネセント
波を用いる方法では、膜厚測定は必要でないが、光導波
部分に直接被測定試料を押しつけて測定するため、必ず
複雑な計算処理および装置構成が必要である。さらに、
表面プラズモンセンサの場合には測定光の導入部分や検
出器部分に角度可変機構を設置する必要があること、光
導波路センサの場合には光の位相を求めなくてはならな
いため特別な光学系を必要とすることから、測定装置に
大がかりな特殊な装置が必要であった。また光漏洩モー
ドセンサにおいては、直接サンプルに測定光を導入する
ため、サンプルによる吸収がない場合には測定が不可能
となってしまう問題があった。In the method of using an evanescent wave for measuring the refractive index, it is not necessary to measure the film thickness. However, since the measurement is performed by directly pressing the sample to be measured on the optical waveguide portion, complicated calculation processing and device configuration are always required. is necessary. further,
In the case of a surface plasmon sensor, it is necessary to install an angle variable mechanism in the part where the measuring light is introduced and in the detector.In the case of an optical waveguide sensor, a special optical system must be used because the phase of the light must be obtained. Because of the necessity, a large-scale special device was required for the measuring device. Further, in the light leakage mode sensor, since the measurement light is directly introduced into the sample, there is a problem that the measurement becomes impossible if there is no absorption by the sample.
【０００５】また近年の通信や環境センシングの分野で
は、波長の長い赤外光領域の光の利用に注目が集まって
きている。これに伴い、材料の赤外領域の光に対する屈
折率や、赤外光透過材料自身の屈折率、また、バルク材
料ではなく薄膜化された材料そのままの状態で屈折率を
知りたいという欲求がある。しかし、赤外光領域の光に
対する屈折率の測定や、特に長波長の赤外光透過材料の
屈折率測定のための測定系は、従来の測定法をベースに
構築することには困難がともなった。その原因は、長波
長の赤外光を測定光とする場合、測定光導入用の光学材
料の屈折率が高いこと、またサンプルに直接、測定光を
導入することにある。さらに、数μｍ以上の長い波長の
赤外光を透過させる材料の中には人体への毒性を持つも
のがあるため、厚さ調整のための加工作業は避けたいと
いう欲求もあり、また、プロセスモニタとして利用する
ときや、屈折率センサとして他の装置類に組み込む際
に、小型化したいという要求があったが、それらに答え
られないという問題がある。In recent years, in the field of communication and environmental sensing, attention has been focused on the use of light in a long wavelength infrared light region. Along with this, there is a desire to know the refractive index of light in the infrared region of the material, the refractive index of the infrared light transmitting material itself, and the refractive index of the material as a thin film rather than a bulk material. . However, it is difficult to construct a measurement system for measuring the refractive index of light in the infrared light region, and particularly for measuring the refractive index of a long-wavelength infrared light transmitting material, based on a conventional measurement method. Was. This is because, when long wavelength infrared light is used as the measurement light, the refractive index of the optical material for introducing the measurement light is high, and the measurement light is directly introduced into the sample. Furthermore, since some materials that transmit infrared light having a long wavelength of several μm or more have toxicity to the human body, there is also a desire to avoid processing work for adjusting the thickness, When used as a monitor or when incorporated as a refractive index sensor into other devices, there has been a demand to reduce the size, but there is a problem that they cannot be answered.
【０００６】本発明は上述の課題を解決するためになさ
れたもので、試料の厚さデータを用いずに、また実測し
たデータを用いる複雑な計算処理を要さずに、薄膜状態
の試料の屈折率を測定することが可能なエバネセント波
の透過現象を利用する屈折率測定法およびその測定装置
を提供することを目的とする。SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it has been proposed that a thin film sample can be obtained without using thickness data of the sample and without complicated calculation processing using actually measured data. An object of the present invention is to provide a refractive index measuring method using an evanescent wave transmission phenomenon capable of measuring a refractive index, and a measuring device therefor.
【０００７】[0007]
【課題を解決するための手段】この目的を達成するた
め、本発明においては、測定光を透過する屈折率が既知
の第１の物質の平坦な面に、前記測定光を透過し前記第
１の物質よりも低屈折率の第２の物質からなり前記第１
の物質側から入射した前記測定光が前記第２の物質との
界面で全反射するときに生ずるエバネセント波の滲み出
し距離よりも小さな膜厚を有する屈折率と膜厚が既知の
薄膜を密着させ、該薄膜上に屈折率を求めたい試料を密
着させ、前記第１の物質と前記薄膜との界面で測定光を
全反射させてエバネセント波を発生させ、前記エバネセ
ント波のうち、前記薄膜を越えて前記試料中に滲み出し
て透過光に変化したエバネセント波の大きさを求めて前
記試料の屈折率を求める。In order to achieve the above object, according to the present invention, a first material having a known refractive index through which a measurement light is transmitted is provided on a flat surface of the first material, and the first light is transmitted through the first material. The second material having a lower refractive index than that of the first material.
A thin film having a known refractive index and a known film thickness smaller than the exudation distance of an evanescent wave generated when the measurement light incident from the material side is totally reflected at the interface with the second material is brought into close contact. A sample whose refractive index is to be obtained is brought into close contact with the thin film, and an evanescent wave is generated by totally reflecting measurement light at an interface between the first substance and the thin film. Then, the magnitude of the evanescent wave that oozes into the sample and changes into transmitted light is determined to determine the refractive index of the sample.
【０００８】また、前記試料がないときに前記第１の物
質と前記薄膜との界面で全反射して戻ってくる測定光の
強度と、前記試料を設置したときに前記第１の物質と前
記薄膜との界面で全反射して戻ってくる測定光の強度と
の差から、前記試料中に滲み出して透過光に変化したエ
バネセント波の大きさを求める。[0008] Further, the intensity of the measurement light which is totally reflected back at the interface between the first substance and the thin film when the sample is not present, and the intensity of the first substance and the first substance when the sample is set. The magnitude of the evanescent wave that oozes into the sample and changes into transmitted light is determined from the difference from the intensity of the measurement light that returns after being totally reflected at the interface with the thin film.
【０００９】また、前記第１の物質と前記薄膜との界面
での前記測定光の全反射を多数回繰り返すように、前記
測定光を前記第１の物質中を導波させ、その後前記第１
の物質より出射させて強度を測定する。Further, the measuring light is guided through the first material so that total reflection of the measuring light at the interface between the first material and the thin film is repeated many times.
And the intensity is measured.
【００１０】また、赤外光源、マイケルソン干渉計、検
出器、試料室を有するフーリエ変換赤外光光度計の試料
室内に、測定光の光路を誘導するプリズムと、上記プリ
ズム上に密着させた屈折率が既知の第１の物質と、上記
第１の物質上に密着させた上記第１の物質よりも低屈折
率でエバネセント波の滲み出し距離よりも小さな膜厚の
第２の物質からなる薄膜とを有する屈折率測定装置を用
いる。A prism for guiding an optical path of measurement light is provided in a sample chamber of a Fourier transform infrared photometer having an infrared light source, a Michelson interferometer, a detector, and a sample chamber, and the prism is brought into close contact with the prism. A first substance having a known refractive index and a second substance having a lower refractive index than the first substance adhered on the first substance and having a film thickness smaller than a seepage distance of an evanescent wave. A refractive index measuring device having a thin film is used.
【００１１】また、上記第１の物質にシリコンを用い、
上記第２の物質にＳｉＯ2を用いる。Further, silicon is used for the first substance,
SiO 2 is used as the second substance.
【００１２】[0012]
【発明の実施の形態】図１は本発明に係るエバネセント
波の透過現象を利用する屈折率測定法の実施の形態を示
す概念図である。図１（ａ）に示すように、測定光１を
透過する屈折率が既知の第１の物質（物質Ａ）と物質Ａ
よりも低屈折率の第２の物質（物質Ｂ）との界面２にお
いて測定光１が全反射するとき、エバネセント波３が生
じ、物質Ｂ中に滲み出す。このエバネセント波３は、数
１式に示すように、指数関数的に減衰しながら、界面２
から物質Ｂ内に入り込む。DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a conceptual diagram showing an embodiment of a refractive index measuring method using an evanescent wave transmission phenomenon according to the present invention. As shown in FIG. 1A, a first substance (substance A) having a known refractive index that transmits the measuring light 1 and a substance A
When the measurement light 1 is totally reflected at the interface 2 with the second substance (substance B) having a lower refractive index, an evanescent wave 3 is generated and seeps into the substance B. The evanescent wave 3 is exponentially attenuated while the interface 2
From the substance B.
【００１３】[0013]
【数１】 (Equation 1)
【００１４】ここで、Ｅは界面２からの距離がｄの時の
エバネセント波３の強度、Ｅ0はｄ＝０の時の強度、
ｎ1、ｎ2は物質Ａおよび物質Ｂの屈折率で、ｎijはｎi
／ｎjで表される相対屈折率を示している。Ｄは、エバ
ネセント波３の強度が１／ｅ（自然対数の底）まで減衰
したときの距離（滲み出し距離）であり、数２式によっ
て定義される。これは入射する光の波長λに依存する値
となる。Here, E is the intensity of the evanescent wave 3 when the distance from the interface 2 is d, E 0 is the intensity when d = 0,
n 1 and n 2 are the refractive indices of substance A and substance B, and n ij is n i
/ N j indicates a relative refractive index. D is the distance (leaching distance) when the intensity of the evanescent wave 3 has attenuated to 1 / e (the base of the natural logarithm), and is defined by Expression 2. This is a value that depends on the wavelength λ of the incident light.
【００１５】[0015]
【数２】 (Equation 2)
【００１６】更に、図１（ｂ）に示すように、物質Ｂを
エバネセント波３の滲み出し距離Ｄよりも小さい膜厚の
薄膜とし、エバネセント波３の到達範囲内に、もう一つ
の物質Ｃ（屈折率ｎ3）が存在する場合、エバネセント
波３がさらに外側の物質Ｃへと到達し、物質Ｃが測定さ
れるサンプル（試料）となる。これがエバネセント波の
透過現象であり、この物質Ｃへ透過する光の入射光に対
する強度比Ｔは、数３式によって表現される。Further, as shown in FIG. 1B, the substance B is formed into a thin film having a thickness smaller than the seeping distance D of the evanescent wave 3, and another substance C ( When the refractive index n 3 ) exists, the evanescent wave 3 reaches the further outer material C, and becomes a sample (material) from which the material C is measured. This is the transmission phenomenon of the evanescent wave, and the intensity ratio T of the light transmitted to the substance C with respect to the incident light is expressed by Expression 3.
【００１７】[0017]
【数３】 (Equation 3)
【００１８】ここで、ＴｓとＴｐは、それぞれ、入射光
のｓ偏光成分（入射面に対して垂直な成分）とｐ偏光成
分（入射面内に含まれる成分）であることを示してお
り、次の数４式によって求められる。Here, Ts and Tp represent the s-polarized component (the component perpendicular to the incident surface) and the p-polarized component (the component included in the incident surface) of the incident light, respectively. It is obtained by the following equation (4).
【００１９】[0019]
【数４】 (Equation 4)
【００２０】ただし、ｐs、ｐo、ｑs、ｑo、は数５式に
表すとおりであり、またｍp１１、ｍp１２、ｍp２１、
ｍp２２、ｍs１１、ｍs１２、ｍs２１、ｍs２２は、数
６式の特性行列ＭｐとＭｓの因子である。Here, p s , p o , q s , q o are as shown in Formula 5, and m p 11, m p 12, m p 21,
m p 22, m s 11, m s 12, m s 21, m s 22 is a factor of characteristic matrix Mp and Ms of equation (6).
【００２１】[0021]
【数５】 (Equation 5)
【００２２】[0022]
【数６】 (Equation 6)
【００２３】ただし、γd、ｐ、ｑは数７式で表され、
ｚは物質Ｂの厚さ、またｉは虚数根である。Here, γ d , p and q are expressed by the following equation (7).
z is the thickness of the substance B, and i is the imaginary root.
【００２４】[0024]
【数７】 (Equation 7)
【００２５】ここで、ｎ1、ｎ2、ｚ、入射角θ1が既知
のとき、数３式のＴｐ、Ｔｓは物質Ｃの屈折率（ｎ3）
の関数となる。したがって、ｎ3を求めるために物質Ｃ
の厚さを知る必要がない。測定光の波長λには、物質Ｂ
による強い吸収が無い範囲にあるものを適用する必要が
ある。また、利用できる光の波長範囲は、物質Ａ、物質
Ｂとして用いる材料によって制限され、さらに、測定可
能なｎ3の範囲は、ｎ1、ｎ2、ｚ、θ1によって制限され
る。したがって、測定系の設計において、用いる光学材
料とその組み合わせの選定作業が重要である。また、物
質Ｂの厚さであるｚの値は、エバネセント波の進入深さ
の基準であるＤの値よりも十分小さくしておく必要があ
る。透過光強度比Ｔと屈折率ｎ3の関係について、λ＝
２．０（μｍ）、ｎ1＝３．４５（シリコン）、ｎ2＝
１．４６（ＳｉＯ2）、ｚ＝１００（Å）、入射角θ1＝
４５゜を代入して求めると、図２の様になる。図に示す
ように、Ｔとｎ3との間に相関が認められるため、Ｔを
実測すれば物質Ｃの屈折率ｎ3が求められることにな
る。Here, when n 1 , n 2 , z and the incident angle θ 1 are known, Tp and Ts in the equation 3 are the refractive index (n 3 ) of the substance C.
Is a function of Therefore, to determine n 3 ,
You don't need to know the thickness. The substance B is included in the wavelength λ of the measurement light.
It is necessary to apply one that is in a range where strong absorption due to is not caused. The wavelength range of light that can be used is limited by the materials used as the substances A and B, and the range of n 3 that can be measured is limited by n 1 , n 2 , z, and θ 1 . Therefore, in designing a measurement system, it is important to select an optical material to be used and a combination thereof. Further, the value of z, which is the thickness of the substance B, needs to be sufficiently smaller than the value of D, which is a reference of the penetration depth of the evanescent wave. Regarding the relationship between the transmitted light intensity ratio T and the refractive index n 3 , λ =
2.0 (μm), n 1 = 3.45 (silicon), n 2 =
1.46 (SiO 2 ), z = 100 (Å), incident angle θ 1 =
FIG. 2 shows a result obtained by substituting 45 °. As shown in the figure, since a correlation is recognized between T and n 3 , if T is measured, the refractive index n 3 of the substance C can be obtained.
【００２６】次に測定方法について述べる。まず、屈折
率既知の物質Ａと物質Ｂを用意し、このとき物質Ｂは十
分厚さが小さく、かつ物質Ａと密着しているものとす
る。この時、測定光１が物質Ａと物質Ｂとの界面２で全
反射する角度θ1で導入されるように設置しておく。こ
こで、ｎ1、ｎ2、ｚ、θ1の値を数３〜７式に代入し、
図２にあるようなＴとｎ3の関係を表す曲線を求める。
Ｔの実測値であるＱの値は、物質Ｃで透過光４へ変化し
た光の量であり、検出器５が光を検知したときの出力値
Ｐから求める。屈折率既知の標準試料を物質Ｃとして測
定し、その時の検出器５の出力値Ｐを求める。検出器の
出力値Ｐの最大値Ｐｍａｘ（物質Ｃがない時の検出器５
の出力値）から出力値Ｐを引いた値（Ｐｍａｘ−Ｐ）
を、実測値Ｑとする。標準試料の実測値Ｑｉを、図２の
様にして求めた曲線に当てはめ、曲線のＴの値と実測値
Ｑｉとの相関を表す検量線を作成する。検量線が作成で
きたら、未知試料であるサンプルを物質Ｃとして設置
し、その時の検出器５の出力値ＰをＰｍａｘから差し引
き、実測値Ｑｓを求める。この実測値Ｑｓを、先に求め
た検量線にあてはめ、その横軸から屈折率が求められ
る。ただし、物質Ｃが、物質Ａと接触させたときに全反
射条件をみたす屈折率である場合には、実測値はゼロに
近い値を示す。図２で用いた様なパラメータの値の測定
装置においては、屈折率が２．４以下の場合に、物質Ａ
との全反射がおこる。よって、図２において実測値がゼ
ロに近い値の場合、屈折率を求める事はできないが、ｎ
3は２．４より小さい値である、ということが分かる。Next, the measuring method will be described. First, a substance A and a substance B having a known refractive index are prepared. At this time, it is assumed that the substance B has a sufficiently small thickness and is in close contact with the substance A. At this time, it is set so that the measurement light 1 is introduced at an angle θ 1 at which the measurement light 1 is totally reflected at the interface 2 between the substance A and the substance B. Here, the values of n 1 , n 2 , z, and θ 1 are substituted into Expressions 3 to 7, and
A curve representing the relationship between T and n 3 as shown in FIG. 2 is obtained.
The value of Q, which is the actual measured value of T, is the amount of light that has changed into the transmitted light 4 by the substance C, and is determined from the output value P when the detector 5 detects the light. A standard sample with a known refractive index is measured as the substance C, and the output value P of the detector 5 at that time is obtained. The maximum value Pmax of the output value P of the detector (the detector 5 when there is no substance C)
Output value) minus output value P (Pmax-P)
Is an actual measurement value Q. The measured value Qi of the standard sample is applied to the curve obtained as shown in FIG. 2, and a calibration curve representing the correlation between the T value of the curve and the measured value Qi is created. After the calibration curve has been created, a sample, which is an unknown sample, is set as the substance C, and the output value P of the detector 5 at that time is subtracted from Pmax to obtain an actually measured value Qs. The actually measured value Qs is applied to the previously obtained calibration curve, and the refractive index is obtained from the horizontal axis. However, when the substance C has a refractive index that satisfies the condition of total reflection when brought into contact with the substance A, the measured value shows a value close to zero. In the apparatus for measuring parameter values as used in FIG. 2, when the refractive index is 2.4 or less, the substance A
And total reflection occurs. Therefore, when the measured value is close to zero in FIG. 2, the refractive index cannot be obtained, but n
It can be seen that 3 is a value smaller than 2.4.
【００２７】近年、赤外光通信および近赤外・中赤外光
によるセンシング分野で注目されている、長波長の赤外
光を透過する材料について、屈折率測定を行った例を示
す。An example in which the refractive index of a material that transmits infrared light of a long wavelength, which has recently attracted attention in the field of infrared light communication and sensing using near-infrared light and mid-infrared light, is described.
【００２８】図３は本発明に係るエバネセント波の透過
現象を利用する屈折率測定装置の実施の形態を示す構成
図である。図に示すように、赤外光源６、マイケルソン
干渉計７、検出器８、試料室９を有するフーリエ変換赤
外光光度計の試料室９内に、測定光１の光路を誘導する
セレン化亜鉛のプリズム１０と、プリズム１０上に密着
させた屈折率が既知の第１の物質（物質Ａ）と、物質Ａ
上に密着させた物質Ａよりも低屈折率でエバネセント波
の滲み出し距離Ｄよりも小さな膜厚の第２の物質（物質
Ｂ）と、物質Ｂ上に測定サンプル（物質Ｃ）を固定して
いる。FIG. 3 is a block diagram showing an embodiment of a refractive index measuring apparatus utilizing the transmission phenomenon of an evanescent wave according to the present invention. As shown in the figure, selenization for guiding the optical path of the measurement light 1 into a sample chamber 9 of a Fourier transform infrared photometer having an infrared light source 6, a Michelson interferometer 7, a detector 8, and a sample chamber 9. A prism 10 made of zinc, a first substance (substance A) having a known refractive index adhered on the prism 10, and a substance A
A second sample (substance B) having a lower refractive index than the substance A adhered thereon and having a film thickness smaller than the exudation distance D of the evanescent wave, and a measurement sample (substance C) fixed on the substance B I have.
【００２９】赤外光透過材料は屈折率が大きいため、屈
折率が２．０以上の物質を測定する測定系を構築する。
フーリエ変換赤外光度計は、赤外光源６から赤外光を発
射し、スリットを通過してマイケルソン干渉計７に導入
され、ここから試料室９内におかれたサンプル（物質
Ｃ）に導入されて、この試料室９を通過した測定光１を
検出器８で検知し、その強度を測定する事ができる。つ
まり、サンプル内で測定光１が透過光４へ変換される
と、検出器８にて検知する測定光１の強度は小さくな
る。Since the infrared light transmitting material has a large refractive index, a measuring system for measuring a substance having a refractive index of 2.0 or more is constructed.
The Fourier transform infrared photometer emits infrared light from an infrared light source 6, passes through a slit and is introduced into a Michelson interferometer 7, from which a sample (material C) placed in a sample chamber 9 is provided. The measuring light 1 introduced and passed through the sample chamber 9 is detected by the detector 8 and its intensity can be measured. That is, when the measuring light 1 is converted into the transmitted light 4 in the sample, the intensity of the measuring light 1 detected by the detector 8 decreases.
【００３０】そこで、図３にあるような測定装置を構成
した。フーリエ変換赤外光光度計の試料室９に、入射角
４５度のセレン化亜鉛のプリズム１０をそのカット面に
対して測定光１が垂直に導入できるように設置し、Ｓｉ
Ｏ2が形成されたシリコンウェハーをセレン化亜鉛のプ
リズム１０上に、上面がＳｉＯ2となるようにシリコン
ウェハーを固定してある。すなわち、シリコンウェハー
が物質Ａ、ＳｉＯ2が物質Ｂとなる。次に、屈折率を求
めたい物質ＣをＳｉＯ2の上に押しつける。したがっ
て、物質Ｃ部分で透過光４が生じると、検出器８の検知
する強度が小さくなる。シリコンウェハーを透過できる
赤外光の波長は１．０〜６．２μｍであるので、図３の
測定系の場合、Ｄの値（エバネセント波の滲み出し距
離）は０．１８〜１．１５μｍとなる。物質ＢのＳｉＯ
2は、熱酸化法により膜厚制御を行いながら作製し、厚
さを上記Ｄの値より十分小さな１５０Å（屈折率１．４
６）とした。この時、物質Ａから物質Ｂへの測定光１の
入射角θ1は約２９度となり、これは、シリコンウェハ
ーとＳｉＯ2の屈折率によって規定される臨界角より大
きい。よって、シリコンウェハーとＳｉＯ2の界面２で
の全反射条件は満たされている。測定可能な屈折率範囲
は、また、この場合の物質Ａ（シリコン）の上部界面２
における全反射条件が屈折率１．７以下の物質であるか
ら、１．７以上である。測定光として適用可能な赤外光
は、シリコンを透過可能な波長範囲にあるものでなけれ
ばならないため、６．２μｍまで長い波長のものであ
る。Therefore, a measuring apparatus as shown in FIG. 3 was constructed. A zinc selenide prism 10 having an incident angle of 45 degrees was set in a sample chamber 9 of a Fourier transform infrared photometer so that the measurement light 1 could be introduced perpendicularly to the cut surface thereof.
A silicon wafer on which O 2 is formed is fixed on a prism 10 of zinc selenide so that the upper surface becomes SiO 2 . That is, the silicon wafer becomes the substance A, and the SiO 2 becomes the substance B. Next, a substance C whose refractive index is to be obtained is pressed onto SiO 2 . Therefore, when the transmitted light 4 occurs in the material C portion, the intensity detected by the detector 8 decreases. Since the wavelength of the infrared light that can pass through the silicon wafer is 1.0 to 6.2 μm, the value of D (the oozing distance of the evanescent wave) is 0.18 to 1.15 μm in the measurement system of FIG. Become. Material B SiO
2 is manufactured while controlling the film thickness by a thermal oxidation method, and the thickness is set to 150 ° (refractive index 1.4) sufficiently smaller than the value of D.
6). At this time, the incident angle θ 1 of the measurement light 1 from the substance A to the substance B is about 29 degrees, which is larger than the critical angle defined by the refractive indexes of the silicon wafer and SiO 2 . Therefore, the condition of total reflection at the interface 2 between the silicon wafer and SiO 2 is satisfied. The measurable refractive index range also depends on the upper interface 2 of the substance A (silicon) in this case.
Is a substance having a refractive index of 1.7 or less, and therefore is 1.7 or more. The infrared light applicable as the measurement light must be in a wavelength range that can transmit silicon, and therefore has a long wavelength up to 6.2 μm.
【００３１】次に、具体的な測定手順を説明する。始め
に検量線を作成するための、標準試料の吸収エネルギー
値を測定する。標準試料を物質ＣとしてＳｉＯ2の上に
設置した測定系を、フーリエ変換赤外分光装置の試料室
９内に設置する。標準試料には、鏡面研磨がなされたシ
リコン結晶（屈折率≒３．４）、ゲルマニウム結晶（屈
折率≒４．０）、セレン化亜鉛結晶（屈折率≒２．４）
を適用した。フーリエ変換赤外分光装置を用いて吸収測
定を行うと、図４のように赤外光の広い波長範囲にわた
ってエネルギー出力値を求めることができる。そこで、
屈折率を求めたい光の波長を任意に選び、ある波長での
出力値Ｐを読みとって、この値を検出器出力値の最大値
Ｐｍａｘ＝１００から差し引いて透過光強度比の実測値
Ｑｉを求める。このようにして得られた３つの標準試料
の実測値Ｑｉを、数７式から得られる曲線とフィッティ
ングし、検量線を決定する。Next, a specific measurement procedure will be described. First, the absorption energy value of a standard sample for preparing a calibration curve is measured. A measurement system in which a standard sample is set as a substance C on SiO 2 is set in a sample chamber 9 of a Fourier transform infrared spectrometer. The standard samples include mirror-polished silicon crystal (refractive index ≒ 3.4), germanium crystal (refractive index ≒ 4.0), and zinc selenide crystal (refractive index ≒ 2.4).
Was applied. When an absorption measurement is performed using a Fourier transform infrared spectrometer, an energy output value can be obtained over a wide wavelength range of infrared light as shown in FIG. Therefore,
The wavelength of the light whose refractive index is to be obtained is arbitrarily selected, the output value P at a certain wavelength is read, and this value is subtracted from the maximum value Pmax = 100 of the detector output value to obtain the actually measured value Qi of the transmitted light intensity ratio. . The measured values Qi of the three standard samples thus obtained are fitted to a curve obtained from the equation (7) to determine a calibration curve.
【００３２】以上の手順により、作成された検量線が図
５である。ここでは、波長が３．７０μｍの光を用い、
数７式に代入した値はλ＝３．７０（μｍ）、ｎ1＝
３．４２、ｎ2＝１．４６、ｚ＝１５０（Å）である。
標準試料のＱｉはプロットで示してある。FIG. 5 shows a calibration curve created by the above procedure. Here, light having a wavelength of 3.70 μm is used,
The values substituted into Equation 7 are λ = 3.70 (μm) and n 1 =
3.42, n 2 = 1.46, z = 150 (Å).
The Qi of the standard sample is shown in the plot.
【００３３】次に、未知試料のプラズマＣＶＤ法により
作製したシリコンカーバイド薄膜（基板はシリコンウェ
ハー）の屈折率を求めた。シリコンカーバイド薄膜をＳ
ｉＯ2と接するように配置し、このサンプルの出力値Ｑ
ｓを求めた。シリコンカーバイド膜の波長３．７μｍに
おけるＱｓは５７．９６となった。この値を図５の検量
線にあてはめると、屈折率は２．５８と求めることがで
きた。バルク形状のシリコンカーバイドの屈折率は、文
献によればおよそ２．５３である。ここで、サンプルの
シリコンカーバイド薄膜の屈折率が文献値に比べて高い
値として得られた理由は、サンプルのシリコンカーバイ
ド膜内に、化学量論比よりも大きな割合でシリコン元素
が存在しているためと考えられ、求められた値は妥当な
値である。Next, the refractive index of an unknown sample silicon carbide thin film (substrate is a silicon wafer) produced by the plasma CVD method was determined. Silicon carbide thin film S
It is arranged so as to be in contact with iO 2, and the output value Q of this sample is
s was determined. Qs of the silicon carbide film at a wavelength of 3.7 μm was 57.96. When this value was applied to the calibration curve in FIG. 5, the refractive index was determined to be 2.58. The refractive index of bulk silicon carbide is approximately 2.53 according to the literature. Here, the reason that the refractive index of the silicon carbide thin film of the sample was obtained as a value higher than the literature value is that the silicon element is present in the silicon carbide film of the sample at a ratio larger than the stoichiometric ratio. Therefore, the obtained value is an appropriate value.
【００３４】このように、膜厚測定を行うことなく未知
試料の屈折率を測定して材料分析手段として適用できる
ことが示された。As described above, it has been shown that the refractive index of an unknown sample can be measured without measuring the film thickness and the film can be applied as a material analysis means.
【００３５】以上の測定結果より明らかな様に、検量線
の作成のため測定する標準試料のプロットのずれはその
まま測定誤差となり、アッベの屈折率計に比べれば誤差
は大きいが、膜厚測定を行わずに簡便に屈折率測定が可
能である点で利便性の高い方法である。As is evident from the above measurement results, the deviation of the plot of the standard sample to be measured for the preparation of the calibration curve is a measurement error as it is. Although the error is large compared to the Abbe refractometer, the measurement of the film thickness is difficult. This is a highly convenient method in that the refractive index can be easily measured without performing it.
【００３６】上述のように、サンプルの厚さ測定、厚さ
調整作業、複雑な計算処理が不必要で、なおかつ、特殊
な大きな装置を構成せずにサンプル自身に吸収が無い場
合でも屈折率が測定可能な屈折率測定法を考案した。従
来の方式の様な、サンプル自身による光の全反射や、サ
ンプル内を透過する光を利用する方法とは異なり、光導
波部分とサンプル以外の物質との界面で生じる全反射光
から生成するエバネセント波の、サンプルによる吸収強
度を求め、これを利用して屈折率を求める方法である。
また、この方法を利用して、高屈折率の長波長の赤外光
を透過できる材料について、市販の赤外光度計をベース
とした赤外光領域の光に対する屈折率測定を可能とする
屈折率測定装置を新たに考案した。As described above, the measurement of the thickness of the sample, the work of adjusting the thickness, and the complicated calculation processing are unnecessary, and the refractive index can be maintained even if the sample itself has no absorption without configuring a special large apparatus. A measurable refractive index measurement method was devised. Unlike conventional methods that use total reflection of light by the sample itself or light that passes through the sample, evanescent light generated from the total reflection light generated at the interface between the optical waveguide portion and the substance other than the sample is different from the conventional method. This is a method in which the absorption intensity of a wave by a sample is determined, and the refractive index is determined using the absorption intensity.
In addition, using this method, a material that can transmit long-wavelength infrared light with a high refractive index can be used to measure the refractive index of light in the infrared region based on a commercially available infrared photometer. A rate measuring device was newly devised.
【００３７】すなわち、上述のエバネセント波の透過現
象を利用する屈折率測定法においては、サンプル（物質
Ｃ）の透過光強度比Ｔからサンプルの屈折率ｎ3を求め
るから、サンプルの厚さデータを用いずに、また実測し
たデータを用いる複雑な計算処理を要さずに、薄膜状態
のサンプルの屈折率ｎ3を測定することが可能となっ
た。また、サンプルの測定条件を考慮しながら測定系を
構築する必要があるが、測定光の全反射条件はサンプル
の屈折率ｎ3に依存しない。したがって、一度、測定系
を構築して計算を行えば、多種の物質の測定に容易に適
用できる利点がある。また、膜厚測定用の特別のサンプ
ルを用意する必要がなく、サンプルをそのままの形状で
測定することが可能なため、プロセス監視用測定法とし
ても適用でき、特に、表面状態と屈折率との相関がある
材料においては有用である。That is, in the refractive index measuring method utilizing the transmission phenomenon of the evanescent wave, the refractive index n 3 of the sample is obtained from the transmitted light intensity ratio T of the sample (substance C). without, also without requiring a complicated calculation processing using the actually measured data, it becomes possible to measure the refractive index n 3 of the sample of the thin film state. Further, it is necessary to construct a measurement system in consideration of the measurement conditions of the sample, but the total reflection condition of the measurement light does not depend on the refractive index n 3 of the sample. Therefore, once the measurement system is constructed and the calculation is performed, there is an advantage that it can be easily applied to the measurement of various kinds of substances. In addition, since it is not necessary to prepare a special sample for film thickness measurement and the sample can be measured in the same shape, it can be applied as a process monitoring measurement method. Useful for correlated materials.
【００３８】また、上述のエバネセント波の透過現象を
利用する屈折率測定装置においては、市販の赤外分光装
置を組み合わせ、赤外領域の光を用いた屈折率測定を簡
便に行うことができ、毒性の高い赤外光透過材料であっ
ても、屈折率について特別な加工無しに測定できる。ま
た、測定光の波長が可変でない光学計を用いても測定が
可能である。よって、このような屈折率測定法を適用し
て構築される屈折率測定装置は、将来的に小型システム
に組み込む際に適したものである。さらに、シリコンウ
ェハーを切り出して作製される導波路の部分を使い捨て
部品として適用することが可能である。今後、赤外光を
利用した通信システムやセンシングシステムの開発支援
装置の一つとして活用できると考えられる。また、試料
室部分の構成を市販の紫外・可視分光装置に組みこみな
おすだけで、赤外領域だけでなく、数百ｎｍの波長の領
域の光を測定光として用いる装置を構成できる。Further, in the above-described refractive index measuring device utilizing the transmission phenomenon of the evanescent wave, a commercially available infrared spectrometer can be combined to easily perform the refractive index measurement using light in the infrared region. Even a highly toxic infrared light transmitting material can measure the refractive index without special processing. Also, measurement can be performed using an optical meter whose wavelength of the measurement light is not variable. Therefore, a refractive index measuring device constructed by applying such a refractive index measuring method is suitable for being incorporated into a small system in the future. Further, it is possible to apply a waveguide portion formed by cutting out a silicon wafer as a disposable part. In the future, it can be used as one of the development support devices for communication systems and sensing systems using infrared light. Further, by simply incorporating the configuration of the sample chamber portion into a commercially available ultraviolet / visible spectrometer, it is possible to configure an apparatus that uses not only the infrared region but also light having a wavelength of several hundred nm as the measurement light.
【００３９】[0039]
【発明の効果】以上説明したように、本発明に係るエバ
ネセント波の透過現象を利用する屈折率測定法、その測
定装置においては、試料中に滲み出して透過光に変化し
たエバネセント波の大きさを求めて試料の屈折率を求め
るから、試料の厚さデータを用いずに、また実測したデ
ータを用いる複雑な計算処理を要さずに、薄膜状態の試
料の屈折率を測定することが可能である。As described above, in the refractive index measuring method utilizing the transmission phenomenon of the evanescent wave according to the present invention and the measuring apparatus, the magnitude of the evanescent wave oozing out into the sample and changing into the transmitted light is obtained. The refractive index of the sample can be measured without using the thickness data of the sample and without complicated calculation processing using the actually measured data. It is.
【図１】本発明に係るエバネセント波の透過現象を利用
する屈折率測定法の実施の形態を示す概念図である。FIG. 1 is a conceptual diagram showing an embodiment of a refractive index measuring method using an evanescent wave transmission phenomenon according to the present invention.
【図２】透過光強度比と屈折率の関係図である。FIG. 2 is a relationship diagram between a transmitted light intensity ratio and a refractive index.
【図３】本発明に係るエバネセント波の透過現象を利用
する屈折率測定装置の実施の形態を示す構成図である。FIG. 3 is a configuration diagram showing an embodiment of a refractive index measuring device utilizing an evanescent wave transmission phenomenon according to the present invention.
【図４】シリコン標準試料の吸収測定結果を示す図であ
る。FIG. 4 is a diagram showing an absorption measurement result of a silicon standard sample.
【図５】透過光強度比と屈折率の関係を示す検量線図で
ある。FIG. 5 is a calibration diagram illustrating a relationship between a transmitted light intensity ratio and a refractive index.
１ 測定光 ２ 界面 ３ エバネセント波 ４ 透過光 ５ 検出器 ６ 赤外光源 ７ マイケルソン干渉計 ８ 検出器 ９ 試料室 １０ プリズム DESCRIPTION OF SYMBOLS 1 Measurement light 2 Interface 3 Evanescent wave 4 Transmitted light 5 Detector 6 Infrared light source 7 Michelson interferometer 8 Detector 9 Sample room 10 Prism
Claims (5)
質の平坦な面に、前記測定光を透過し前記第１の物質よ
りも低屈折率の第２の物質からなり前記第１の物質側か
ら入射した前記測定光が前記第２の物質との界面で全反
射するときに生ずるエバネセント波の滲み出し距離より
も小さな膜厚を有する屈折率と膜厚が既知の薄膜を密着
させ、該薄膜上に屈折率を求めたい試料を密着させ、前
記第１の物質と前記薄膜との界面で測定光を全反射させ
てエバネセント波を発生させ、前記エバネセント波のう
ち、前記薄膜を越えて前記試料中に滲み出して透過光に
変化したエバネセント波の大きさを求めて前記試料の屈
折率を求めることを特徴とするエバネセント波の透過現
象を利用する屈折率測定法。A first material having a known refractive index that transmits the measuring light, and a second material having a lower refractive index than the first material that transmits the measuring light and having a lower refractive index than the first material; A thin film having a known thickness and a refractive index smaller than the exudation distance of the evanescent wave generated when the measurement light incident from the first material side is totally reflected at the interface with the second material is adhered to the thin film. Then, a sample whose refractive index is to be obtained is brought into close contact with the thin film, and the measurement light is totally reflected at the interface between the first substance and the thin film to generate an evanescent wave. A refractive index measuring method using a transmission phenomenon of an evanescent wave, wherein the magnitude of an evanescent wave that has transpired into the sample and changed into transmitted light is determined to determine the refractive index of the sample.
記薄膜との界面で全反射して戻ってくる測定光の強度
と、前記試料を設置したときに前記第１の物質と前記薄
膜との界面で全反射して戻ってくる測定光の強度との差
から、前記試料中に滲み出して透過光に変化したエバネ
セント波の大きさを求めることを特徴とする請求項１に
記載のエバネセント波の透過現象を利用する屈折率測定
法。2. The method according to claim 1, wherein the intensity of the measuring light which is totally reflected back at the interface between the first material and the thin film when the sample is absent and the intensity of the first material and the first material when the sample is set. 2. The magnitude of an evanescent wave that oozes into the sample and is converted into transmitted light from a difference from the intensity of the measurement light that is totally reflected at the interface with the thin film and returns. A refractive index measurement method using the transmission phenomenon of evanescent waves.
記測定光の全反射を多数回繰り返すように、前記測定光
を前記第１の物質中を導波させ、その後前記第１の物質
より出射させて強度を測定することを特徴とする請求項
２に記載のエバネセント波の透過現象を利用する屈折率
測定法。3. The measurement light is guided through the first material so that total reflection of the measurement light at the interface between the first material and the thin film is repeated many times. The refractive index measurement method using the transmission phenomenon of an evanescent wave according to claim 2, wherein the intensity is measured by emitting light from the substance.
試料室を有するフーリエ変換赤外光光度計の試料室内
に、測定光の光路を誘導するプリズムと、上記プリズム
上に密着させた屈折率が既知の第１の物質と、上記第１
の物質上に密着させた上記第１の物質よりも低屈折率で
エバネセント波の滲み出し距離よりも小さな膜厚の第２
の物質からなる薄膜とを有することを特徴とするエバネ
セント波の透過現象を利用する屈折率測定装置。4. An infrared light source, a Michelson interferometer, a detector,
A prism for guiding an optical path of measurement light, a first substance having a known refractive index closely adhered on the prism, and a first material having a refractive index in the sample chamber of a Fourier transform infrared photometer having a sample chamber;
A second material having a lower refractive index than the first material adhered onto the material and having a smaller film thickness than the oozing distance of the evanescent wave.
A refraction index measuring device utilizing an evanescent wave transmission phenomenon, characterized in that the device has a thin film made of the following materials.
２の物質にＳｉＯ2を用いることを特徴とする請求項４
に記載のエバネセント波の透過現象を利用する屈折率測
定装置。5. The method according to claim 4, wherein silicon is used as said first material and SiO 2 is used as said second material.
2. A refractive index measuring device utilizing the transmission phenomenon of an evanescent wave described in 1.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP32175398A JP2000146836A (en) | 1998-11-12 | 1998-11-12 | Refractive index measuring method utilizing transmission phenomenon of evanescent wave and its measuring device |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP32175398A JP2000146836A (en) | 1998-11-12 | 1998-11-12 | Refractive index measuring method utilizing transmission phenomenon of evanescent wave and its measuring device |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JP2000146836A true JP2000146836A (en) | 2000-05-26 |
Family
ID=18136071
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP32175398A Pending JP2000146836A (en) | 1998-11-12 | 1998-11-12 | Refractive index measuring method utilizing transmission phenomenon of evanescent wave and its measuring device |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP2000146836A (en) |
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-
1998
- 1998-11-12 JP JP32175398A patent/JP2000146836A/en active Pending
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|---|---|---|---|---|
| US7054514B2 (en) | 2001-11-22 | 2006-05-30 | Kabushiki Kaisha Toshiba | Optical waveguide sensor, device, system and method for glucose measurement |
| JP2003156432A (en) * | 2001-11-22 | 2003-05-30 | Toshiba Corp | Optical waveguide type biochemical sensor |
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