JPWO2005090909A1

JPWO2005090909A1 - Film thickness measuring apparatus and film thickness measuring method

Info

Publication number: JPWO2005090909A1
Application number: JP2006511098A
Authority: JP
Inventors: 梅田　倫弘; 倫弘梅田; 裕也武田; 秀昭長崎
Original assignee: Tokyo University of Agriculture and Technology NUC
Current assignee: Tokyo University of Agriculture and Technology NUC
Priority date: 2004-03-19
Filing date: 2004-03-19
Publication date: 2008-02-07
Anticipated expiration: 2024-03-19
Also published as: JP4427654B2; WO2005090909A1

Abstract

基材（２）上に液膜（３）を備えた被測定試料（４）を設置台（５）に設置し、設置台（５）に対して垂直に変位するＺ軸変位機構（６）に固定された水晶振動子（１１）をその電極に交流信号を供給して振動させ、水晶振動子（１１）の電極に流れる電流を電流検出器（１３）で検出してその振動振幅を測定し、水晶振動子（１１）に接触して振動する先端が尖鋭化された針状のプローブ（１０）を水晶振動子（１１）とともにＺ軸変位機構（６）で液膜（３）に接近させ、プローブ（１０）が液膜（３）の表面に接触して振動振幅が減少する第１の位置を測定し、プローブ（１０）をさらに液膜（３）を貫通して基材（２）に接近させ、プローブ（１０）が基材（２）に接触して振動振幅が減少する第２の位置を測定し、第１の位置と第２の位置の差を液膜（３）の膜厚とすることを特徴とする膜厚測定方法及び前記測定方法を可能とする膜厚測定装置を提供する。本発明によれば、屈折率等の物性値が未知であっても液膜の膜厚を測定できる。A Z-axis displacement mechanism (6) in which a sample to be measured (4) provided with a liquid film (3) on a base (2) is placed on an installation base (5) and displaced perpendicularly to the installation base (5). A crystal oscillator (11) fixed to the electrode is vibrated by supplying an AC signal to the electrode, and a current flowing through the electrode of the crystal oscillator (11) is detected by a current detector (13) to measure the vibration amplitude. Then, the needle-like probe (10) having a sharpened tip that vibrates in contact with the crystal resonator (11) is brought close to the liquid film (3) by the Z-axis displacement mechanism (6) together with the crystal resonator (11). The probe (10) contacts the surface of the liquid film (3) and the first position where the vibration amplitude decreases is measured, and the probe (10) further penetrates the liquid film (3) to form the substrate (2 ) To measure the second position where the probe (10) contacts the substrate (2) and the vibration amplitude decreases, and the first position and the first position Providing a film thickness measuring apparatus capable of film thickness measuring method and the measuring method of the difference in position, characterized in that the thickness of the liquid film (3). According to the present invention, the film thickness of a liquid film can be measured even if a physical property value such as a refractive index is unknown.

Description

本発明は、固体物上の液体薄膜の膜厚を測定する技術に係り、特に、薄膜の物性値を必要としない膜厚測定装置および膜厚測定方法に関する。 The present invention relates to a technique for measuring the film thickness of a liquid thin film on a solid material, and more particularly to a film thickness measuring apparatus and a film thickness measuring method that do not require physical properties of the thin film.

近年、半導体製造におけるフォトレジストや摩擦潤滑における潤滑油等の液体薄膜は、固体薄膜と同様に産業上の各種分野において幅広く用いられている。
これらの産業においては、粘性のある液体薄膜の膜厚管理は、液体薄膜の性能を発揮するために極めて重要であり、これまでに光学的手法や超音波を用いた方法などが用いられている。
光学的手法には、光波干渉法を利用して薄膜の表面と裏面からの反射光によって得られる干渉縞から膜厚を測定することができる。
一般に単色光では、波長を超える厚さに対しては干渉縞が複数発生し、いわゆるアンビギュイティに起因して膜厚が確定しない。このため、多波長光や白色光を光源とする分光光度計による方法が試みられている。
しかしながら、光波干渉法により得られる膜厚は光学的な長さであるため、物理的な長さに変換するためには、光が伝搬する媒質の屈折率が予め知られている必要がある。このため、使用する光源の波長に対する屈折率が知られていないと正確な膜厚測定ができないこととなる。
一方、膜厚だけでなく屈折率も同時に測定できる手法として、楕円偏光解析法（エリプソメトリ）が開発されている。この手法は、偏光状態の知られた光を測定試料に入射させてその偏光状態の変化を分析することによって膜厚だけでなく屈折率も比較的高精度に測定できる手法である。
しかしながら、この手法は、半導体表面の酸化膜や蒸着膜等のように光源波長に比べて厚さが薄い膜に対して有効であり、数百ｎｍ以上の厚さの膜に対しては適用が難しいという制約がある。
これらの光学的手法に対して、超音波を利用したり、電気的な静電容量を計測する方法があるが、いずれも光波干渉法と同様に薄膜の物性値（例えば音速や誘電率）が予め知られている必要がある。
本発明は上記の点を考慮してなされたもので、光学的手法によらずまた超音波や静電容量を用いるものではなく、従って屈折率等の薄膜の物性値を予め知らなくても膜厚を精度良く測定できる膜厚測定装置および膜厚測定法を提供することを目的とする。In recent years, liquid thin films such as photoresists in semiconductor manufacturing and lubricating oils in friction lubrication have been widely used in various industrial fields as well as solid thin films.
In these industries, film thickness control of viscous liquid thin films is extremely important for demonstrating the performance of liquid thin films, and so far optical methods and methods using ultrasonic waves have been used. .
For the optical technique, the film thickness can be measured from interference fringes obtained by the reflected light from the front and back surfaces of the thin film using light wave interferometry.
In general, with monochromatic light, a plurality of interference fringes are generated for a thickness exceeding the wavelength, and the film thickness is not determined due to so-called ambiguity. For this reason, a method using a spectrophotometer using multi-wavelength light or white light as a light source has been tried.
However, since the film thickness obtained by the light wave interferometry is an optical length, the refractive index of the medium through which the light propagates needs to be known in advance in order to convert it to a physical length. For this reason, if the refractive index with respect to the wavelength of the light source to be used is not known, accurate film thickness measurement cannot be performed.
On the other hand, ellipsometry has been developed as a method for simultaneously measuring not only the film thickness but also the refractive index. This method is a method in which not only the film thickness but also the refractive index can be measured with relatively high accuracy by making light whose polarization state is known enter a measurement sample and analyzing the change in the polarization state.
However, this method is effective for a film having a thickness smaller than the wavelength of the light source, such as an oxide film or a vapor deposition film on a semiconductor surface, and is not applicable to a film having a thickness of several hundred nm or more. There is a restriction that it is difficult.
In contrast to these optical methods, there are methods that use ultrasonic waves and measure electrical capacitance. However, as with the light wave interferometry, the physical properties of the thin film (for example, the speed of sound and dielectric constant) are the same. Need to be known in advance.
The present invention has been made in consideration of the above points, and does not depend on an optical method, and does not use ultrasonic waves or capacitance. Therefore, the film can be formed without knowing the physical properties of the thin film such as the refractive index in advance. An object of the present invention is to provide a film thickness measuring apparatus and a film thickness measuring method capable of accurately measuring the thickness.

上記目的を達成するために、請求項１記載の膜厚測定装置は、基材面に液膜が形成された被測定試料を設置する設置台と、設置台の上面に対して垂直な方向に変位するＺ軸変位機構と、設置台を保持する水平保持部と、Ｚ軸変位機構を保持する垂直保持部と、水平保持部と垂直保持部とを固定的に連接する固定連接機構と、Ｚ軸変位機構に固定され、設置台の上面に対して垂直方向の軸を有し、設置台に近い方の端が先鋭化された針状のプローブと、Ｚ軸変位機構に固定され、被測定試料とＺ軸変位機構の間に前記プローブと接触して配設された電極を有する水晶振動子と、水晶振動子の電極に交流信号を供給する信号発生器と、水晶振動子の電極から発生する電流を検出する電流検出器と、Ｚ軸変位機構によるＺ軸変位値と電流検出器から得られる水晶振動子の電流値とから液膜の膜厚を解析する膜厚解析装置と、を備えたことを特徴とするものである。
本発明によれば、プローブの先端部を振動させつつ液膜に接近させ、液膜に接触させた後さらに基材面に接触させる。プローブの先端部が液膜に接触する位置では振動振幅が大きく減衰する。またプローブ先端部が液膜を貫通し基材面に接触する位置でも振動振幅は大きく減衰する。振動振幅が大きく減衰する２つの位置から液膜の膜厚を測定する。本発明によれば、液膜の物理長を測定することができるため、液膜の屈折率等の物性値を知らなくとも液膜の膜厚を直接測定することが可能な膜厚測定装置を提供することができる。
また、請求項２ないし３に記載の発明によれば、Ｚ軸変位機構による垂直方向の変位量を、圧電アクチュエータによって高精度で設定できるため、膜厚測定精度の高い膜厚測定装置を提供することができる。
また、請求項４に記載の発明によれば、液膜に貫通させるにプローブは、その先端部が１００ｎｍ以下と極めて尖鋭化されたプローブであるため、液膜の貫通穴の径はおおよそ１００ｎｍ程度となり、貫通穴の影響が無視できる程度に小さな膜厚測定装置を提供することができる。
また、請求項５に記載の発明によれば、音叉型水晶振動子は、例えば腕時計用の水晶振動子として広く用いられているものであり、簡素かつ容易に入手できるため、低コストな膜厚測定装置を提供することができる。
また、請求項６に記載の発明によれば、水晶振動子に供給する信号の周波数を、公称共振周波数の近傍の所定範囲で変化させることによって、水晶振動子固有の共振周波数に設定することができるため、プローブの振動振幅を高感度で検出でき、その結果高精度の膜厚測定装置を提供することができる。
また、請求項７ないし８に記載の発明によれば、参照信号を用いた同期検波方式、或いは参照信号を用いたロックイン増幅器によって電流を検出する方式であるため、水晶振動子の電流のＳＮ比（信号対雑音電力比）を向上させることができる。このため、微弱な水晶振動子の電流を高ＳＮ比で検出でき、その結果高精度の膜厚測定装置を提供することができる。
また、請求項９に記載の発明によれば、Ａ／Ｄ変換器、Ｄ／Ａ変換器およびパーソナルコンピュータによってデジタルデータ解析が可能となり、簡素かつ低コストな膜厚測定装置を提供することができる。
また、請求項１０に記載の発明によれば、振動振幅が大きく減衰する位置を微分処理によってピーク点に変換できるため、液膜表面位置と基材表面位置の決定がデータ解析上容易化され、高効率化された膜厚測定装置を提供することができる。
また、請求項１１に記載の発明によれば、液膜上の任意の点において膜厚を二次元的に測定することができる膜厚測定装置を提供することができる。
さらに、上記目的を達成するために、本発明に係る膜厚測定方法は、請求項１２に記載したように、基材面に液膜が形成された被測定試料を設置する設置台と、設置台を保持する水平保持部と、設置台の上面に対して垂直な方向に設置台を変位させるＺ軸変位機構と、水平保持部と垂直保持部とを固定的に連接する固定連接機構と、垂直保持部に固定され、設置台の上面に対して垂直方向の軸を有し、設置台に近い方の端が先鋭化された針状のプローブと、垂直保持部に固定され、被測定試料と垂直保持部の間に前記プローブと接触して配設された、電極を有する水晶振動子と、水晶振動子の電極に交流信号を供給する信号発生器と、水晶振動子の電極から発生する電流を検出する電流検出器と、Ｚ軸変位機構によるＺ軸変位値と前記電流検出器から得られる前記水晶振動子の電流値とから前記液膜の膜厚を解析する膜厚解析装置と、を備えたことを特徴とするものである。
また、請求項１３に記載の発明によれば、基材面に液膜が形成された被測定試料を設置台に設置し、液膜の表面に対して垂直な方向に軸を有し液膜に近いほうの先端が尖鋭化されたプローブと、プローブに接触させた水晶振動子とを、液膜の表面から所定距離に離して配設し、水晶振動子の電極に信号発生器から交流信号を供給して水晶振動子を振動させ、水晶振動子の電極に流れる電流を電流検出器で検出することによって前記水晶振動子の振動振幅を測定するとともに、水晶振動子との接触によって振動する前記プローブを、水晶振動子とともに液膜の表面に対して垂直な方向に、Ｚ軸変位機構を用いて液膜の表面に接近させ、プローブの先端が前記液膜の表面に接触したことによって前記振動振幅が減少する第１の位置を測定し、プローブを、さらに液膜を貫通して前記基材に接近させ、プローブの先端が前記基材の表面に接触したことによって振動振幅が減少する第２の位置を測定し、第１の位置と第２の位置の差をもって液膜の膜厚とする事を特徴とするものである。
また、請求項１４ないし１５に記載の発明によれば、Ｚ軸変位機構による垂直方向の変位量を、圧電アクチュエータによって高精度で設定できるため、膜厚測定精度の高い膜厚測定方法を提供することができる。
また、請求項１６に記載の発明によれば、液膜に貫通させるにプローブは、その先端部が１００ｎｍ以下と極めて尖鋭化されたプローブであるため、液膜の貫通穴の径はおおよそ１００ｎｍ程度となり、貫通穴の影響が無視できる程度に小さな膜厚測定方法を提供することができる。
また、請求項１７に記載の発明によれば、音叉型水晶振動子は例えば腕時計用の水晶振動子として広く用いられているものであり、簡素かつ容易に入手できるため、低コストな膜厚測定方法を提供することができる。
また、請求項１８に記載の発明によれば、水晶振動子に供給する信号の周波数を、共振周波数に設定することができるため、プローブの振動振幅を高感度で検出でき、その結果高精度の膜厚測定方法を提供することができる。
また、請求項１９ないし２０に記載の発明によれば、参照信号を用いた同期検波方式、或いは参照信号を用いたロックイン増幅器によって電流を検出する方式であるため、水晶振動子の電流のＳＮ比（信号対雑音電力比）を向上させることができる。このため微弱な水晶振動子の電流を高ＳＮ比で検出でき、その結果高精度の膜厚測定方法を提供することができる。
また、請求項２１に記載の発明によれば、Ａ／Ｄ変換器、Ｄ／Ａ変換器、パーソナルコンピュータによってデジタルデータ解析が可能なため、簡素かつ低コストな膜厚測定を提供することができる。
また、請求項２２に記載の発明によれば、振動振幅が大きく減衰する位置を微分処理によってピーク点に変換できるため、液膜表面位置と基材表面位置の決定がデータ解析上容易化され、高効率化された膜厚測定方法を提供することができる。
また、請求項２３に記載の発明によれば、設置台をプローブに垂直な面内で移動させることによって、液膜上の任意の点において膜厚を二次元的に測定することができる膜厚測定方法を提供することができる。In order to achieve the above object, a film thickness measuring apparatus according to claim 1 is provided with an installation table on which a sample to be measured having a liquid film formed on a substrate surface is installed, and in a direction perpendicular to the upper surface of the installation table. A Z-axis displacement mechanism that displaces, a horizontal holding part that holds the installation base, a vertical holding part that holds the Z-axis displacement mechanism, a fixed connecting mechanism that fixedly connects the horizontal holding part and the vertical holding part, and Z Fixed to the shaft displacement mechanism, has an axis perpendicular to the upper surface of the installation table, and has a needle-like probe with a sharpened end closer to the installation table and a Z-axis displacement mechanism fixed to the measurement target Generated from a crystal resonator having an electrode disposed in contact with the probe between the sample and the Z-axis displacement mechanism, a signal generator for supplying an AC signal to the electrode of the crystal resonator, and an electrode of the crystal resonator A current detector for detecting the current to be generated, a Z-axis displacement value by the Z-axis displacement mechanism, and a current detector And the film thickness analyzer for analyzing the thickness of the liquid film from the current value of the crystal oscillator to be, and is characterized in that it comprises a.
According to the present invention, the tip of the probe is caused to vibrate while being brought close to the liquid film, brought into contact with the liquid film, and further brought into contact with the substrate surface. The vibration amplitude is greatly attenuated at the position where the tip of the probe contacts the liquid film. Further, the vibration amplitude is greatly attenuated even at the position where the probe tip penetrates the liquid film and contacts the substrate surface. The film thickness of the liquid film is measured from two positions where the vibration amplitude is greatly attenuated. According to the present invention, since the physical length of the liquid film can be measured, a film thickness measuring device capable of directly measuring the film thickness of the liquid film without knowing the physical property value such as the refractive index of the liquid film. Can be provided.
In addition, according to the second to third aspects of the present invention, since the amount of vertical displacement by the Z-axis displacement mechanism can be set with high accuracy by the piezoelectric actuator, a film thickness measuring device with high film thickness measuring accuracy is provided. be able to.
According to the invention described in claim 4, since the tip of the probe penetrating the liquid film is a sharpened probe whose tip is 100 nm or less, the diameter of the through hole of the liquid film is about 100 nm. Thus, it is possible to provide a film thickness measuring device that is small enough to ignore the influence of the through hole.
Further, according to the invention described in claim 5, the tuning fork type crystal resonator is widely used as a crystal resonator for a wristwatch, for example, and can be obtained simply and easily. A measuring device can be provided.
According to the invention described in claim 6, the frequency of the signal supplied to the crystal resonator can be set to a resonance frequency unique to the crystal resonator by changing in a predetermined range near the nominal resonance frequency. Therefore, the vibration amplitude of the probe can be detected with high sensitivity, and as a result, a highly accurate film thickness measuring device can be provided.
Further, according to the invention described in claims 7 to 8, since the current is detected by the synchronous detection method using the reference signal or the lock-in amplifier using the reference signal, the SN of the current of the crystal resonator is detected. The ratio (signal to noise power ratio) can be improved. For this reason, it is possible to detect a weak current of the crystal resonator with a high SN ratio, and as a result, it is possible to provide a highly accurate film thickness measuring apparatus.
According to the ninth aspect of the invention, digital data analysis can be performed by an A / D converter, a D / A converter, and a personal computer, and a simple and low-cost film thickness measuring device can be provided. .
In addition, according to the invention described in claim 10, since the position where the vibration amplitude is greatly attenuated can be converted into the peak point by differential processing, the determination of the liquid film surface position and the substrate surface position is facilitated in data analysis, A highly efficient film thickness measuring apparatus can be provided.
Moreover, according to the invention of Claim 11, the film thickness measuring apparatus which can measure a film thickness two-dimensionally in the arbitrary points on a liquid film can be provided.
Furthermore, in order to achieve the above object, the film thickness measuring method according to the present invention includes, as described in claim 12, an installation table for installing a sample to be measured in which a liquid film is formed on a substrate surface, A horizontal holding unit for holding the table, a Z-axis displacement mechanism for displacing the installation table in a direction perpendicular to the upper surface of the installation table, a fixed connection mechanism for fixedly connecting the horizontal holding unit and the vertical holding unit, A needle-like probe fixed to the vertical holding unit and having an axis perpendicular to the upper surface of the installation table and having a sharp end near the installation table, and a sample to be measured fixed to the vertical holding unit A crystal oscillator having an electrode, a signal generator for supplying an AC signal to the electrode of the crystal oscillator, and an electrode of the crystal oscillator. A current detector for detecting current, a Z-axis displacement value by the Z-axis displacement mechanism, and the current detection Is characterized in that the current value of the crystal oscillator obtained from vessel equipped with a film thickness analyzer for analyzing the thickness of the liquid film.
According to the invention described in claim 13, the sample to be measured having a liquid film formed on the surface of the substrate is placed on the setting table, and the liquid film has an axis in a direction perpendicular to the surface of the liquid film. A probe with a sharp tip near the tip and a crystal unit in contact with the probe are placed at a predetermined distance from the surface of the liquid film, and an AC signal is sent from the signal generator to the crystal unit electrode. To measure the vibration amplitude of the crystal resonator by detecting the current flowing through the electrode of the crystal resonator with a current detector, and to vibrate by contact with the crystal resonator When the probe is brought close to the surface of the liquid film using a Z-axis displacement mechanism in a direction perpendicular to the surface of the liquid film together with the crystal oscillator, the vibration of the probe is brought into contact with the surface of the liquid film. Measure the first position where the amplitude decreases, And the second position where the vibration amplitude decreases when the tip of the probe contacts the surface of the base material is measured. The difference between the two positions is the film thickness of the liquid film.
According to the fourteenth to fifteenth aspects of the present invention, since the amount of vertical displacement by the Z-axis displacement mechanism can be set with high accuracy by the piezoelectric actuator, a film thickness measuring method with high film thickness measurement accuracy is provided. be able to.
According to the invention described in claim 16, since the tip of the probe penetrating the liquid film is a sharpened probe whose tip is 100 nm or less, the diameter of the through hole of the liquid film is about 100 nm. Thus, it is possible to provide a film thickness measuring method that is small enough to ignore the influence of the through hole.
According to the invention described in claim 17, the tuning fork type crystal resonator is widely used as a quartz resonator for a wristwatch, for example, and can be obtained simply and easily. A method can be provided.
Further, according to the invention described in claim 18, since the frequency of the signal supplied to the crystal resonator can be set to the resonance frequency, the vibration amplitude of the probe can be detected with high sensitivity, and as a result, high accuracy. A film thickness measuring method can be provided.
In addition, according to the present invention, the current is detected by the synchronous detection method using the reference signal or the lock-in amplifier using the reference signal. The ratio (signal to noise power ratio) can be improved. Therefore, it is possible to detect a weak crystal resonator current with a high S / N ratio, and as a result, it is possible to provide a highly accurate film thickness measurement method.
Further, according to the invention described in claim 21, since digital data analysis can be performed by an A / D converter, a D / A converter, and a personal computer, it is possible to provide a simple and low-cost film thickness measurement. .
Further, according to the invention described in claim 22, since the position where the vibration amplitude is greatly attenuated can be converted into the peak point by differential processing, the determination of the liquid film surface position and the substrate surface position is facilitated in data analysis, A highly efficient film thickness measuring method can be provided.
According to the invention described in claim 23, the film thickness can be measured two-dimensionally at an arbitrary point on the liquid film by moving the installation base in a plane perpendicular to the probe. A measurement method can be provided.

第１図は、本発明に係る膜厚測定装置の一実施形態の構成を示す図である。
第２図は、本発明に係る膜厚測定装置の水晶振動子とプローブの位置関係を説明する図である。
第３図は、本発明に係る膜厚測定装置および膜厚測定方法の測定原理を説明する図である。
第４図は、本発明に係る膜厚測定装置の水晶振動子の振動振幅を検出する方法を説明する図である。
第５図は、本発明に係る膜厚測定装置の水晶振動子を流れる電流が減衰するメカニズムを説明する図である。
第６図は、本発明に係る膜厚測定装置の電流検出器の一実施形態を説明する図である。
第７図は、本発明に係る膜厚測定装置の電流検出器をロックインアンプとしたときの水晶振動子と信号発生器との接続関係を説明する図である。
第８図は、本発明に係る膜厚測定装置のプローブを光ファイバから加工して製作するときの概略工程を説明した図である。
第９図は、本発明の実施例に示した膜厚測定時における膜厚測定装置の接続系統を示す図である。
第１０図は、本発明の実施例に示した膜厚測定の結果について示したものである。FIG. 1 is a diagram showing a configuration of an embodiment of a film thickness measuring apparatus according to the present invention.
FIG. 2 is a view for explaining the positional relationship between the crystal resonator and the probe of the film thickness measuring apparatus according to the present invention.
FIG. 3 is a diagram for explaining the measurement principle of the film thickness measuring apparatus and the film thickness measuring method according to the present invention.
FIG. 4 is a diagram for explaining a method of detecting the vibration amplitude of the crystal resonator of the film thickness measuring apparatus according to the present invention.
FIG. 5 is a diagram for explaining the mechanism by which the current flowing through the crystal resonator of the film thickness measuring apparatus according to the present invention is attenuated.
FIG. 6 is a diagram for explaining an embodiment of a current detector of the film thickness measuring apparatus according to the present invention.
FIG. 7 is a diagram for explaining the connection relationship between the crystal resonator and the signal generator when the current detector of the film thickness measuring apparatus according to the present invention is a lock-in amplifier.
FIG. 8 is a diagram for explaining a schematic process when the probe of the film thickness measuring device according to the present invention is manufactured from an optical fiber.
FIG. 9 is a diagram showing a connection system of the film thickness measuring apparatus at the film thickness measurement shown in the embodiment of the present invention.
FIG. 10 shows the results of film thickness measurement shown in the examples of the present invention.

本発明に係る膜厚測定装置および膜厚測定方法の実施形態について、添付図面を参照して説明する。
（第１の実施形態）
第１図は、本発明に係る膜厚測定装置の第１の実施形態の概要を示す図である。
この膜厚測定装置１は、基材２の表面に液膜３が形成された被測定試料４を設置するための設置台５と、液膜３の表面に対して垂直方向に変位可能なＺ軸変位機構６とを有する。
設置台５は、水平保持部７によって保持される。Ｚ軸変位機構６は垂直保持部８によって保持される。水平保持部７と垂直保持部８は固定連接機構９によって連接され、両者の相対位置関係は固定される。
プローブ１０は、プローブ固定具１０ａによってＺ軸変位機構６に固定される。プローブ１０の軸は液膜３に対して垂直になるように固定される。
プローブ１０と被測定試料４の間には水晶振動子１１が配設される。水晶振動子１１は、水晶振動子固定具１１ａによってＺ軸変位機構６に固定される。
水晶振動子１１は電極１１ｂおよび電極１１ｃの２つの電極を備える。一方の電極（例えば電極１１ｂ）は、電流検出器１３に接続される。他方の電極（例えば電極１１ｃ）は信号発生器１４に接続される。電流検出器１３には、信号発生器１４の出力信号の一部を分岐して得られる参照信号１３ａが接続される。
電流検出器１３は、検出された電流値をデジタルデータに変換するためにＡ／Ｄ変換器１５に接続される。Ａ／Ｄ変換器１５の出力は膜厚解析装置１６に接続される。
膜厚解析装置１６は、Ｚ軸変位量をアナログ量（例えば電圧値）に変換するためのＤ／Ａ変換器（Ｚ）１７に接続される。さらに、Ｄ／Ａ変換器（Ｚ）１７の出力は、Ｚ軸変位機構６を駆動するためのＺ軸ドライバ１８に接続される。
設置台５は、Ｘ軸変位機構２０或いはＹ軸変位機構２１の少なくともいずれか一方によって、Ｚ軸に垂直な面内を移動可能なように構成されてもよい。
この場合、Ｘ軸変位機構２０には、Ｘ軸ドライバ２０ａが接続され、Ｘ軸ドライバ２０ａは、Ｄ／Ａ変換器（Ｘ）２０ｂを介して膜厚解析装置１６に接続される。
同様に、Ｙ軸変位機構２１には、Ｙ軸ドライバ２１ａが接続され、Ｙ軸ドライバ２１ａは、Ｄ／Ａ変換器（Ｙ）２１ｂを介して膜厚解析装置１６に接続される。
第１図ないし第３図を用いて本発明に係る膜厚測定装置および膜厚測定方法の測定原理について説明する。
まず第１図に示した設置台５の上に被測定試料４を設置する。被測定試料４は、基材２の表面に液膜３が形成されたものである。液膜３の膜厚が本発明の測定対象である。
液膜を形成する液体の材質については特に制約はない。また、材質の物性値、例えば屈折率や誘電率等が未知であってもかまわない。さらに、液膜の厚みについても特に制限はない。この点が従来の光学的手法を用いた膜厚測定方法とはまったく異なるところである。
液膜３の表面に対して垂直方向に軸をもつプローブ１０が配設される。プローブ１０は液膜３側の先端が先鋭化されたものである。プローブ１０は、第１図に示したようにプローブ固定具１０ａによってＺ軸変位機構６に固定される。
プローブ１０の先鋭化された先端は、Ｚ軸変位機構６によって、被測定試料４の液膜３に接近し、さらには液膜３を貫通して基材２の表面に接触するまでＺ軸方向、即ち液膜３に垂直な方向に移動させることができるようなっている。
一方、水晶振動子１１も水晶振動子固定具１１ａによってＺ軸変位機構６に固定される。このため、水晶振動子１１はプローブ３と相対的な位置関係を保ちながらＺ軸変位機構６によってＺ軸方向に移動する。
水晶振動子１１の形状は限定されるものではないが、例えば音叉のように２つの対称な突起を有する音叉型水晶振動子は、腕時計などの基準発信器として広く流通しており、入手性やコストの面で好ましい。
水晶振動子１１が音叉型水晶振動子の場合、プローブ１０は、第１図に示したように軸上の一点が水晶振動子１１の中央凹部に内側から接触させるように位置決めされる。この際、プローブ１０を音叉形状の「突起に接触」させることが重要であり、接触させる位置は第１図に限定されるものではない。
例えば、第２図に示したように、水晶振動子１１とプローブ１０の位置関係は第２Ａ図（第１図の位置関係に対応）の他、第２Ｂ図或いは第２Ｃ図の位置関係であってもよい。要するに「突起に接触」させればよい。
ちなみに、音叉型水晶振動子の２つの突起の内側の間隔は、典型的には約０．２ｍｍ（２００μｍ）であり、プローブ１０の水晶振動子に接触する部分での直径は典型的には約１２５μｍである。また音叉型水晶振動子の外形は長辺が約４ｍｍ、短辺が約３．５ｍｍ程度の小型のものである。
水晶振動子１１は電極１１ｂおよび電極１１ｃからなる二つの電極を有している。電極１１ｂおよび電極１１ｃの電極間に交流信号、例えば正弦波信号を印加すると、水晶振動子の有する圧電効果によって振動する。特に水晶振動子１１の共振周波数近傍の周波数をもつ信号を印加したときに振動振幅は大きくなる。
この際、主たる振動成分の振動方向は、いわゆる音叉と同様に、２つの突起が開いたり閉じたりする方向で振動する。
水晶振動子１１を振動させると、これに接触しているプローブ１０もあわせて振動させることができる。
第３図は、本発明の膜厚測定方法の原理を説明するために、プローブ１０の先端部と被測定試料４との位置関係（接近距離）を示す図と、その位置関係（接近距離）に対応したプローブ１０の振動振幅を示す模式的なグラフを合わせて示したものである。
プローブ１０の先端部と被測定試料４との位置関係（接近距離）が第３図の領域１２ａのとき、即ち、プローブ１０の先端が被測定試料４の表面から十分はなれているときは、プローブ１０の振動振幅は一定値を保つ。
プローブ１０の先端部が液膜３の表面に接触するとプローブ１０の振動振幅は減衰する（領域１２ｂ）。
この原因は、プローブ１０の先端部が液膜３の表面からせん断力（シア・フォース）を受けるためとされている（例えば、非特許文献１参照）。
Ｓｈｅａｒ−ＦｏｒｃｅＤｅｔｅｃｔｉｏｎｂｙＲｅｕｓａｂｌｅＱｕａｒｔｓＴｕｎｉｎｇＦｏｒｋｗｉｔｈｏｕｔＥｘｔｅｒｎａｌＶｉｂｒａｔｉｏｎ：Ｓ．Ｏｈｋｕｂｏ，Ｓ．Ｙａｍａｚａｋｉ，Ａ．Ｔａｋａｙａｎａｇｉ，Ｙ．ＯｈｔａｎｉａｎｄＮ．Ｕｍｅｄａ：ＯＰＴＩＣＡＬＲＥＶＩＥＷＶｏｌ．１０，ＮＯ．２（２００３）ｐ１２８−１３０
領域１２ｃは、プローブ１０の先端が、液膜３の中を移動している領域である。この領域１２ｃでは、プローブ１０の振動振幅は、ほぼ一定の振動振幅が維持される。
プローブ１０をさらに基材に接近させ、プローブ１０の先端が基材２の表面に接触すると、基材２の表面から領域１２ｂと同様にせん断力を受けプローブ１０の振動振幅はさらに大きく減衰する。これが領域１２ｄと示した領域である。
第３図のグラフからわかるように、プローブ１０の振動振幅は領域１２ｂと領域１２ｄで大きな減衰を示す。領域１２ｂは、プローブ１０の先端が液膜３の表面に接触する領域であり、領域１２ｄは基材２の表面に接触する領域である。
したがって、領域１２ｂの中央値に該当する接近距離Ｄ_ｂと領域１２ｄの中央値に該当する接近距離Ｄ_ｄの差が液膜３の膜厚を示すことになる。
後述する実施例によれば、領域１２ｂと領域１２ｄにおける振動振幅の減衰特性は非常に急峻であるため、接近距離Ｄ_ｂ、Ｄ_ｄは容易に求めることが可能である。
ところで、第３図のグラフを得るためには、プローブ１０の振動振幅を検出するための手段が不可欠である。
第４図ないし第７図を用いてプローブ１０の振動振幅を検出するメカニズムを説明する。
第４Ａ図は、水晶振動子１１にプローブ１０を接触させているだけの状態を示している。水晶振動子１１の電極１１ｂと電極１１ｃに信号発生器１４から正弦波信号を印加すると水晶振動子１１が持つ圧電効果によって水晶振動子１１とこれに接触したプローブ１０はともに振動を開始する（第４Ｂ図）。
また、水晶振動子１１の電極１１ｂと電極１１ｃには正弦波電流が流れる。水晶振動子１１は、等価的に共振回路を形成すると考えることができるから、水晶振動子の正弦波電流は共振周波数の近傍で極大値をとる。
一方、水晶振動子１１の振動振幅も共振周波数の近傍で極大となり、水晶振動子１１に流れる正弦波電流値の大きさと振動振幅の大きさには１対１の対応関係が存在する。
したがって、水晶振動子１１の電極１１ｂと電極１１ｃに流れる正弦波電流の大きさを第４Ｃ図に示した電流検出器１３で検出することによって、水晶振動子１１の振動振幅、ひいてはプローブ１０の振動振幅を検出することが可能となる。
プローブ１０の先端部が液膜３或いは基材２の表面に接触するとその表面からせん断力を受けてプローブ１０の振動振幅は減衰する。この結果プローブ１０に接触している水晶振動子１１の振動振幅も減衰し、水晶振動子１１に流れる正弦波電流の大きさも減衰することになる。
したがって、プローブ１０の振動振幅の減衰状態も電流検出器１３で検出できる。
水晶振動子１１に流れる正弦波電流の減衰は第５図に模式的に示した共振特性の変化からも説明することができる。
第５図のグラフは水晶振動子１１の共振特性を示したものであり、横軸に共振周波数近傍の周波数を、縦軸に水晶振動子１１に流れる正弦波電流の大きさを示しでいる。第５図に実線で示したグラフは、プローブ１０が液膜３の表面から離れている状態での共振特性を示したものである。水晶振動子１１に印加される周波数は例えば実線で示した共振特性の共振周波数ｆ_０の近傍ｆｃに設定される。
プローブ１０の先端部が液膜３に接すると、液膜３の表面からせん断力をうける。このせん断力は振動振幅を減少させる方向に働くもので、水晶振動子に伝達される。この結果、水晶振動子の共振周波数を決定する弾性定数等のファクターが変化し、共振特性が例えば破線でしめしたグラフのように変化する。
このため、水晶振動子１１に印加している周波数ｆｃにおける正弦波電流はＩａからＩｂに減衰することになる。
上述したメカニズムによって、プローブ１０の振動振幅の変化を水晶振動子１１に接続した電流検出器１３で検出することが可能となり、第３図に示したグラフの縦軸の情報を取得することができる。
ところで、水晶振動子１１の電極に流れる電流の大きさは非特許文献１のｆｉｇ．４に示されるように例えば１５０ｎＡ以下と非常に小さいものである。
このような微小な電流を検出するためには、信号対雑音電力比（Ｓ／Ｎ）を十分向上させることが可能な電流検出方式が必要となる。
信号対雑音電力比を向上させることが可能な電流検出方式を備えた電流検出器であればその方式を特に限定するものではないが、例えば、水晶振動子１１に印加される信号の一部を信号発生器１４から分岐させてこれを参照信号１３ａとし、電流検出器１３の入力１３ｂと参照信号を同期検波することによって信号対雑音電力比を向上させる方式は、本発明に好ましい電流検出器の一形態である。
第６図は、同期検波方式による電流検出器の動作原理を示す一例である。第６図の動作原理自体は周知であるため説明は省略する。
第７図は、本発明に係る電流検出器１３の一形態として、ロックインアンプ１３を用いて構成し、信号発生器１４と水晶振動子１１の電極１１ｂ、１１ｃとの接続関係をあわせて示したものである。
信号発生器１４の電流は、電極１１ｃから水晶振動子１１に入力され、電極１１ｂからロックインアンプ１３に入力される。さらにグランド線１１ｈを介して信号発生器１４に戻る。
ロックインアンプ１３も動作原理自体は第６図に示した同期検波方式を取り入れているものである。
第８図は、本発明にかかるプローブ１０の好ましい一形態として、光ファイバーを用いた光ファイバープローブ１０の製造方法の一例を示したものである。
光ファイバーの先端部を先鋭化する手法には、化学エッチングによる方法や溶融延伸法等種々の方法が周知である。
図８は、溶融延伸法による光ファイバの尖鋭化の工程を概念的に示したものである。図８Ａは、溶融する前の光ファイバの構造を示したもので、例えば直径が約１０μｍのコア２３ａと、直径が約１２５μｍのクラッド２３ｂからなる。
この光ファイバを、例えば炭酸ガスレーザによって熱を加えながら溶融延伸する（図８Ｂ）。この結果、光ファイバは、図８Ｃに示したように分断され、分断点は非常に尖鋭化されたものとなる。
この尖鋭化された部分をプローブ１０の先端部として用いるものである。
本発明にかかる光ファイバープローブ１０は、その先端部が例えば先端直径１００ｎｍ以下にテーパ状に加工できるものであればいずれの手法によるものでもよい。
例えば、米国サッター社の炭酸ガスレーザを用いたピペットプラーと呼ばれる市販の加工装置を用いてもよい。
次に、Ｚ軸変位機構６について説明する。
本発明に係る膜厚測定装置或いは膜厚測定方法では、第３図の測定原理を示すグラフから明らかなように、プローブ１０の振動振幅（縦軸）の測定と同時に、プローブ１０の先端部のＺ軸上の相対的な変位量、即ち被測定試料４の液膜３の表面あるいは基材２の表面に対する接近距離（横軸）の測定が必要となる。
プローブ１０の先端部を被測定試料４に接近させるためにＺ軸変位機構６を用いる。
Ｚ軸変位機構６の好ましい実施形態は、Ｚ方向の位置決め粗く行う粗調整機構６ａとＺ軸方向の位置設定を高精度で行う圧電アクチュエータ６ｂの組み合わせである。圧電アクチュエータ６ｂにＺ軸移動台６ｃが固定され、このＺ軸移動台６ｃにプローブ１０と水晶振動子１１が固定されてＺ軸方向に移動する。
圧電アクチュエータ６ｂは、より具体的には、ＰＺＴ系圧電セラミクスを用いた圧電アクチュエータが好ましい。
圧電アクチュエータ６ｂは、例えば高電圧増幅器によって構成されるＺ軸ドライバ１８によって駆動される。
Ｚ軸ドライバ１８に予め校正された電圧を印加することによって圧電アクチュエータ６ｂを駆動させ、プローブ１０をＺ軸方向に移動させることができる。
Ｚ軸ドライバ１８に印加される電圧は、膜厚解析装置１６が指示するＺ軸変位量データをＤ／Ａ変換器（Ｚ）１７でアナログ電圧に変換したものである。
膜厚解析装置１６が指示するＺ軸変位量データと、Ｚ軸変位機構６で変位する実際のＺ軸の変位量との関係を予め校正しておくことによって、膜厚解析装置１６が指示するＺ軸変位量データを実際のＺ軸の変位量とみなすことができる。
あるいは、位置センサを組み込んだフィードバック方式の圧電アクチュエータ６ｂを用いれば、校正の必要もない。
いずれも膜厚解析装置１６が指示するＺ軸変位量データが、第３図のグラフの接近距離（横軸）に該当する。
この他、膜厚解析装置１６が指示するＺ軸変位量データとは独立に、プローブ１０或いはＺ軸変位機構６の変位量を、例えば位置センサで測定し、この測定データを膜厚解析装置１６に取り込んでこれを接近距離とする方式であっても良い。
膜厚解析装置１６は、例えば汎用のパーソナルコンピュータ１６を用いて構成できるが、これに限定されるものではない。専用の膜厚解析装置１６を構築しても良い。
膜厚解析装置１６の主たる機能は、プローブ１０の被測定試料４に対する接近距離（Ｚ軸変位量データ）とそれに対応するプローブ１０の振動振幅データを取得し、データを記録することである。
さらに、記録したデータを例えば第３図に示したようなグラフとして表示器やプリンタに出力できることが好ましい。
また、プローブ１０の振動振幅が大きく減衰する２つの領域（第３図のグラフでは領域１２ｂと領域１２ｄに該当）のそれぞれの中心値を求め、その差を被測定試料４の液膜３の膜厚として記録、表示或いはプリンタ出力しても良い。
さらにまた、前記領域１２ｂと領域１２ｄの中心値を求める手法として、プローブ１０の振動振幅データを接近距離で数値的な微分処理を行い、領域１２ｂと領域１２ｄにおいて現れるそれぞれのピークにおける２つの接近距離の差をもって液膜３の膜厚とする方法でもよい。
（第２の実施形態）
第１の実施形態は、被測定試料４を載せた設置台５を固定させ、プローブ１０および水晶振動子１１をＺ軸変位機構６によって変位させる形態である。
これに対して、第２の実施形態は、プローブ１０および水晶振動子１１を固定させ、被測定試料４を載せた設置台をＺ軸変位機構６によって変位させる形態である。
第２の実施形態と第１の実施形態は、被測定試料４と、プローブ１０および水晶振動子１１とのどちらを固定し、どちらを変位させるかの差があるだけであり、膜厚測定の原理はいずれも異なるところはない。
また、プローブ１０を振動させる方法、振動振幅を検出する方法、Ｚ軸変位機構６によってプローブ１０と被測定試料４を接近させる方法等いずれも第１の実施形態と同じである。よって、これらの説明は省略する。
（第３の実施形態）
第３の実施形態では、設置台５をＺ軸とは垂直な面内で移動させ、被測定試料４の液膜３の膜厚を一点だけでなく、複数の点で測定できるように膜厚測定装置１を構成するものである。また、かかる膜厚測定装置１による膜厚測定方法を提供するものである。
このため、Ｚ軸と直角をなす軸（Ｘ軸）に変位可能なＸ軸変位機構２０を設け、Ｘ軸変位機構２０と設置台５を連接させることによって、設置台５をＸ軸方向に変位させるものである。
さらに、Ｚ軸とＸ軸の双方に直角をなす軸（Ｙ軸）に変位可能なＹ軸変位機構２１を設け、Ｘ軸変位機構２０とＹ軸変位機構２１とを連接させることにより、設置台５をＸ軸とＹ軸の双方に、即ち二次元的に移動させる構成としても良い。
また、第３の実施形態は、第１の実施形態あるいは第２の実施形態のいずれかの実施形態と組み合わせたものであってもよい。Embodiments of a film thickness measuring apparatus and a film thickness measuring method according to the present invention will be described with reference to the accompanying drawings.
(First embodiment)
FIG. 1 is a diagram showing an outline of a first embodiment of a film thickness measuring apparatus according to the present invention.
This film thickness measuring apparatus 1 includes an installation table 5 for installing a sample 4 on which a liquid film 3 is formed on the surface of a substrate 2, and a Z that can be displaced in a direction perpendicular to the surface of the liquid film 3. And an axial displacement mechanism 6.
The installation table 5 is held by the horizontal holding unit 7. The Z-axis displacement mechanism 6 is held by the vertical holding unit 8. The horizontal holding part 7 and the vertical holding part 8 are connected by a fixed connecting mechanism 9, and the relative positional relationship between them is fixed.
The probe 10 is fixed to the Z-axis displacement mechanism 6 by a probe fixture 10a. The axis of the probe 10 is fixed so as to be perpendicular to the liquid film 3.
A crystal resonator 11 is disposed between the probe 10 and the sample 4 to be measured. The crystal resonator 11 is fixed to the Z-axis displacement mechanism 6 by a crystal resonator fixture 11a.
The crystal unit 11 includes two electrodes, an electrode 11b and an electrode 11c. One electrode (for example, electrode 11b) is connected to the current detector 13. The other electrode (for example, electrode 11c) is connected to the signal generator 14. A reference signal 13 a obtained by branching a part of the output signal of the signal generator 14 is connected to the current detector 13.
The current detector 13 is connected to the A / D converter 15 in order to convert the detected current value into digital data. The output of the A / D converter 15 is connected to the film thickness analyzer 16.
The film thickness analyzer 16 is connected to a D / A converter (Z) 17 for converting the Z-axis displacement amount into an analog amount (for example, a voltage value). Further, the output of the D / A converter (Z) 17 is connected to a Z-axis driver 18 for driving the Z-axis displacement mechanism 6.
The installation base 5 may be configured to be movable in a plane perpendicular to the Z axis by at least one of the X axis displacement mechanism 20 and the Y axis displacement mechanism 21.
In this case, an X-axis driver 20a is connected to the X-axis displacement mechanism 20, and the X-axis driver 20a is connected to the film thickness analysis device 16 via a D / A converter (X) 20b.
Similarly, a Y-axis driver 21a is connected to the Y-axis displacement mechanism 21, and the Y-axis driver 21a is connected to the film thickness analyzer 16 via a D / A converter (Y) 21b.
The measurement principle of the film thickness measuring apparatus and film thickness measuring method according to the present invention will be described with reference to FIGS.
First, the sample 4 to be measured is installed on the installation table 5 shown in FIG. The sample 4 to be measured has a liquid film 3 formed on the surface of the substrate 2. The film thickness of the liquid film 3 is a measurement object of the present invention.
There are no particular restrictions on the material of the liquid that forms the liquid film. Further, the physical property value of the material, for example, the refractive index or the dielectric constant may be unknown. Further, the thickness of the liquid film is not particularly limited. This is completely different from the film thickness measurement method using the conventional optical method.
A probe 10 having an axis perpendicular to the surface of the liquid film 3 is disposed. The probe 10 has a sharpened tip on the liquid film 3 side. As shown in FIG. 1, the probe 10 is fixed to the Z-axis displacement mechanism 6 by a probe fixture 10a.
The sharpened tip of the probe 10 is moved close to the liquid film 3 of the sample 4 to be measured by the Z-axis displacement mechanism 6 and further penetrates the liquid film 3 and contacts the surface of the substrate 2 in the Z-axis direction. That is, it can be moved in a direction perpendicular to the liquid film 3.
On the other hand, the crystal resonator 11 is also fixed to the Z-axis displacement mechanism 6 by the crystal resonator fixture 11a. Therefore, the crystal unit 11 is moved in the Z-axis direction by the Z-axis displacement mechanism 6 while maintaining a relative positional relationship with the probe 3.
Although the shape of the crystal unit 11 is not limited, for example, a tuning fork type crystal unit having two symmetrical protrusions such as a tuning fork is widely distributed as a reference transmitter such as a wristwatch. It is preferable in terms of cost.
When the crystal unit 11 is a tuning fork type crystal unit, the probe 10 is positioned so that one point on the axis contacts the central recess of the crystal unit 11 from the inside as shown in FIG. At this time, it is important to bring the probe 10 into “contact with the protrusion” of the tuning fork shape, and the contact position is not limited to FIG.
For example, as shown in FIG. 2, the positional relationship between the crystal unit 11 and the probe 10 is the positional relationship of FIG. 2B or 2C in addition to FIG. 2A (corresponding to the positional relationship of FIG. 1). May be. In short, it is only necessary to “contact the protrusion”.
Incidentally, the interval between the two protrusions of the tuning fork type crystal resonator is typically about 0.2 mm (200 μm), and the diameter of the portion of the probe 10 in contact with the crystal resonator is typically about 125 μm. The tuning fork type crystal resonator has a small external shape with a long side of about 4 mm and a short side of about 3.5 mm.
The crystal unit 11 has two electrodes including an electrode 11b and an electrode 11c. When an AC signal, for example, a sine wave signal is applied between the electrodes 11b and 11c, it vibrates due to the piezoelectric effect of the crystal resonator. In particular, when a signal having a frequency near the resonance frequency of the crystal unit 11 is applied, the vibration amplitude increases.
At this time, the vibration direction of the main vibration component vibrates in the direction in which the two protrusions open and close, as in the so-called tuning fork.
When the crystal unit 11 is vibrated, the probe 10 in contact therewith can be vibrated together.
FIG. 3 is a diagram showing the positional relationship (approach distance) between the tip of the probe 10 and the sample 4 to be measured and the positional relationship (approach distance) in order to explain the principle of the film thickness measuring method of the present invention. 6 is a schematic graph showing the vibration amplitude of the probe 10 corresponding to the above.
When the positional relationship (approach distance) between the tip of the probe 10 and the sample 4 to be measured is the region 12a in FIG. 3, that is, when the tip of the probe 10 is sufficiently separated from the surface of the sample 4 to be measured. The vibration amplitude of 10 keeps a constant value.
When the tip of the probe 10 contacts the surface of the liquid film 3, the vibration amplitude of the probe 10 is attenuated (region 12b).
This is because the tip of the probe 10 receives a shearing force (shear force) from the surface of the liquid film 3 (see, for example, Non-Patent Document 1).
Shear-Force Detection by Reusable Quartz Tuning Fork Without External Vibration: Ohkubo, S .; Yamazaki, A .; Takayanagi, Y. et al. Ohtani and N.M. Umeda: OPTICAL REVIEW Vol. 10, NO. 2 (2003) p128-130
The region 12 c is a region where the tip of the probe 10 is moving in the liquid film 3. In this region 12c, the vibration amplitude of the probe 10 is maintained at a substantially constant vibration amplitude.
When the probe 10 is further brought closer to the base material and the tip of the probe 10 comes into contact with the surface of the base material 2, the vibration amplitude of the probe 10 is further attenuated by receiving a shearing force from the surface of the base material 2 similarly to the region 12 b. This is the area indicated as area 12d.
As can be seen from the graph of FIG. 3, the vibration amplitude of the probe 10 shows large attenuation in the regions 12b and 12d. The region 12 b is a region where the tip of the probe 10 is in contact with the surface of the liquid film 3, and the region 12 d is a region where the surface is in contact with the surface of the substrate 2.
Therefore, the difference between the approach distance D _b corresponding to the median value of the region 12 _b and the approach distance D _d corresponding to the median value of the region 12 _d indicates the film thickness of the liquid film 3.
According to an example described later, the vibration amplitude attenuation characteristics in the region 12b and the region 12d are very steep, so that the approach distances D _b and D _d can be easily obtained.
Incidentally, in order to obtain the graph of FIG. 3, means for detecting the vibration amplitude of the probe 10 is indispensable.
A mechanism for detecting the vibration amplitude of the probe 10 will be described with reference to FIGS.
FIG. 4A shows a state in which the probe 10 is simply brought into contact with the crystal resonator 11. When a sine wave signal is applied from the signal generator 14 to the electrodes 11b and 11c of the crystal unit 11, both the crystal unit 11 and the probe 10 in contact with the crystal unit 11 start to vibrate due to the piezoelectric effect of the crystal unit 11 (first). FIG. 4B).
Further, a sine wave current flows through the electrodes 11b and 11c of the crystal unit 11. Since it can be considered that the crystal unit 11 equivalently forms a resonance circuit, the sine wave current of the crystal unit takes a maximum value in the vicinity of the resonance frequency.
On the other hand, the vibration amplitude of the crystal unit 11 also becomes maximum near the resonance frequency, and there is a one-to-one correspondence between the magnitude of the sine wave current value flowing through the crystal unit 11 and the magnitude of the vibration amplitude.
Therefore, by detecting the magnitude of the sine wave current flowing through the electrodes 11b and 11c of the crystal resonator 11 by the current detector 13 shown in FIG. 4C, the vibration amplitude of the crystal resonator 11, and hence the vibration of the probe 10 is detected. The amplitude can be detected.
When the tip of the probe 10 contacts the surface of the liquid film 3 or the substrate 2, the vibration amplitude of the probe 10 is attenuated by receiving a shearing force from the surface. As a result, the vibration amplitude of the crystal unit 11 in contact with the probe 10 is also attenuated, and the magnitude of the sine wave current flowing through the crystal unit 11 is also attenuated.
Accordingly, the current detector 13 can also detect the attenuation state of the vibration amplitude of the probe 10.
The attenuation of the sine wave current flowing through the crystal unit 11 can also be explained from the change in resonance characteristics schematically shown in FIG.
The graph of FIG. 5 shows the resonance characteristics of the crystal resonator 11, the horizontal axis indicates the frequency near the resonance frequency, and the vertical axis indicates the magnitude of the sine wave current flowing through the crystal resonator 11. The graph shown by the solid line in FIG. 5 shows the resonance characteristics when the probe 10 is away from the surface of the liquid film 3. Frequency applied to the crystal oscillator 11 is set in the vicinity fc of the resonance frequency f ₀ of the resonance characteristics indicated by the solid line, for example.
When the tip of the probe 10 comes into contact with the liquid film 3, a shearing force is applied from the surface of the liquid film 3. This shearing force acts in the direction of decreasing the vibration amplitude, and is transmitted to the crystal unit. As a result, factors such as elastic constants that determine the resonance frequency of the crystal resonator change, and the resonance characteristics change, for example, as shown by a broken line graph.
For this reason, the sine wave current at the frequency fc applied to the crystal unit 11 is attenuated from Ia to Ib.
With the mechanism described above, it is possible to detect a change in the vibration amplitude of the probe 10 with the current detector 13 connected to the crystal unit 11, and to acquire information on the vertical axis of the graph shown in FIG. .
By the way, the magnitude of the current flowing through the electrode of the crystal unit 11 is shown in FIG. As shown in FIG. 4, it is very small, for example, 150 nA or less.
In order to detect such a minute current, a current detection method capable of sufficiently improving the signal-to-noise power ratio (S / N) is required.
The current detector is not particularly limited as long as it is a current detector having a current detection method capable of improving the signal-to-noise power ratio. For example, a part of a signal applied to the crystal unit 11 is obtained. A method of improving the signal-to-noise power ratio by branching from the signal generator 14 to be the reference signal 13a and synchronously detecting the input 13b of the current detector 13 and the reference signal is a current detector preferable for the present invention. It is one form.
FIG. 6 is an example showing the operating principle of a current detector based on the synchronous detection method. Since the operation principle itself of FIG. 6 is well known, description thereof is omitted.
FIG. 7 shows a connection relationship between the signal generator 14 and the electrodes 11b and 11c of the crystal unit 11 which is configured by using a lock-in amplifier 13 as an embodiment of the current detector 13 according to the present invention. It is a thing.
The current of the signal generator 14 is input from the electrode 11 c to the crystal unit 11 and input from the electrode 11 b to the lock-in amplifier 13. Furthermore, it returns to the signal generator 14 via the ground line 11h.
The lock-in amplifier 13 also adopts the synchronous detection method shown in FIG.
FIG. 8 shows an example of a method for manufacturing the optical fiber probe 10 using an optical fiber as a preferred embodiment of the probe 10 according to the present invention.
As a method for sharpening the tip of the optical fiber, various methods such as a method by chemical etching and a melt drawing method are well known.
FIG. 8 conceptually shows the process of sharpening the optical fiber by the melt drawing method. FIG. 8A shows the structure of the optical fiber before melting, and it includes, for example, a core 23a having a diameter of about 10 μm and a clad 23b having a diameter of about 125 μm.
This optical fiber is melt-drawn while applying heat, for example, with a carbon dioxide laser (FIG. 8B). As a result, the optical fiber is divided as shown in FIG. 8C, and the dividing point is very sharpened.
This sharpened portion is used as the tip of the probe 10.
The optical fiber probe 10 according to the present invention may be of any technique as long as the tip can be processed into a tapered shape with a tip diameter of 100 nm or less, for example.
For example, a commercially available processing device called a pipette puller using a carbon dioxide laser manufactured by Sutter, USA may be used.
Next, the Z-axis displacement mechanism 6 will be described.
In the film thickness measuring apparatus or the film thickness measuring method according to the present invention, as is clear from the graph showing the measurement principle of FIG. 3, the vibration amplitude (vertical axis) of the probe 10 is measured simultaneously with the measurement of the tip of the probe 10. It is necessary to measure the relative displacement on the Z-axis, that is, the approach distance (horizontal axis) of the sample 4 to be measured with respect to the surface of the liquid film 3 or the surface of the substrate 2.
A Z-axis displacement mechanism 6 is used to bring the tip of the probe 10 closer to the sample 4 to be measured.
A preferred embodiment of the Z-axis displacement mechanism 6 is a combination of a coarse adjustment mechanism 6a that performs rough positioning in the Z direction and a piezoelectric actuator 6b that performs position setting in the Z-axis direction with high accuracy. A Z-axis moving table 6c is fixed to the piezoelectric actuator 6b, and the probe 10 and the crystal unit 11 are fixed to the Z-axis moving table 6c and move in the Z-axis direction.
More specifically, the piezoelectric actuator 6b is preferably a piezoelectric actuator using PZT-based piezoelectric ceramics.
The piezoelectric actuator 6b is driven by a Z-axis driver 18 configured by a high voltage amplifier, for example.
By applying a voltage calibrated in advance to the Z-axis driver 18, the piezoelectric actuator 6 b can be driven and the probe 10 can be moved in the Z-axis direction.
The voltage applied to the Z-axis driver 18 is obtained by converting the Z-axis displacement amount data instructed by the film thickness analysis device 16 into an analog voltage by the D / A converter (Z) 17.
The film thickness analysis apparatus 16 instructs by calibrating in advance the relationship between the Z-axis displacement amount data instructed by the film thickness analysis apparatus 16 and the actual Z-axis displacement amount displaced by the Z-axis displacement mechanism 6. The Z-axis displacement amount data can be regarded as an actual Z-axis displacement amount.
Alternatively, if a feedback type piezoelectric actuator 6b incorporating a position sensor is used, calibration is not necessary.
In either case, the Z-axis displacement data indicated by the film thickness analyzer 16 corresponds to the approach distance (horizontal axis) in the graph of FIG.
In addition, the displacement amount of the probe 10 or the Z-axis displacement mechanism 6 is measured by, for example, a position sensor independently of the Z-axis displacement amount data instructed by the film thickness analysis device 16, and this measurement data is measured with the film thickness analysis device 16. It is also possible to adopt a method of taking this into an approach distance.
The film thickness analysis device 16 can be configured using, for example, a general-purpose personal computer 16, but is not limited thereto. A dedicated film thickness analyzer 16 may be constructed.
The main function of the film thickness analyzer 16 is to acquire the approach distance (Z-axis displacement amount data) of the probe 10 with respect to the sample 4 to be measured and the vibration amplitude data of the probe 10 corresponding thereto, and record the data.
Furthermore, it is preferable that the recorded data can be output to a display or printer as a graph as shown in FIG.
Further, the center value of each of the two regions (corresponding to the region 12b and the region 12d in the graph of FIG. 3) where the vibration amplitude of the probe 10 is greatly attenuated is obtained, and the difference is obtained as the film of the liquid film 3 of the sample 4 to be measured. The thickness may be recorded, displayed, or output by a printer.
Furthermore, as a method for obtaining the center values of the region 12b and the region 12d, the vibration amplitude data of the probe 10 is numerically differentiated by the approach distance, and two approach distances at respective peaks appearing in the region 12b and the region 12d are obtained. The method of making the film thickness of the liquid film 3 with the difference of
(Second Embodiment)
In the first embodiment, the installation base 5 on which the sample 4 to be measured is placed is fixed, and the probe 10 and the crystal unit 11 are displaced by the Z-axis displacement mechanism 6.
On the other hand, in the second embodiment, the probe 10 and the crystal resonator 11 are fixed, and the installation base on which the sample 4 to be measured is placed is displaced by the Z-axis displacement mechanism 6.
In the second embodiment and the first embodiment, there is only a difference in which the sample 4 to be measured, the probe 10 or the quartz crystal resonator 11 is fixed and which is displaced. There is no difference in the principle.
Also, the method of vibrating the probe 10, the method of detecting the vibration amplitude, the method of bringing the probe 10 and the sample 4 to be measured closer by the Z-axis displacement mechanism 6 and the like are all the same as in the first embodiment. Therefore, these descriptions are omitted.
(Third embodiment)
In the third embodiment, the installation base 5 is moved in a plane perpendicular to the Z axis, and the film thickness of the liquid film 3 of the sample 4 to be measured is measured not only at one point but also at a plurality of points. The measuring device 1 is constituted. Moreover, the film thickness measuring method by this film thickness measuring apparatus 1 is provided.
Therefore, an X-axis displacement mechanism 20 that can be displaced on an axis (X-axis) perpendicular to the Z-axis is provided, and the installation table 5 is displaced in the X-axis direction by connecting the X-axis displacement mechanism 20 and the installation table 5 together. It is something to be made.
Furthermore, a displaceable Y-axis displacement mechanism 21 is provided on an axis (Y-axis) perpendicular to both the Z-axis and the X-axis, and the X-axis displacement mechanism 20 and the Y-axis displacement mechanism 21 are connected to each other, thereby 5 may be configured to move in both the X axis and the Y axis, that is, two-dimensionally.
In addition, the third embodiment may be combined with either the first embodiment or the second embodiment.

次に、本発明に係る膜厚測定装置および膜厚測定方法によって、実際に液膜の膜厚を測定した結果を第９図および第１０図に示す。
第９図は、測定に用いた膜厚測定装置１の系統を示したものである。
本測定では、プローブ１０と水晶振動子１１を固定し、被測定試料４を設置する設置台５をＺ軸方向（垂直方向）に変位させる構成とした。
また、設置台５を変位させるＺ軸変位機構６としては、粗調整機構としては高精度のモータ駆動方式の駆動機構を、また、精調整機構としてはＰＺＴ圧電アクチュエータを用いた。ＰＺＴ圧電アクチュエータのドライバ（Ｚ軸ドライバ１８）には高電圧発生器を用いた。
信号発生器１４は市販のファンクションジェネレータを用いた。また電流検出器１３も同様に市販のロックインアンプを用い、ファンクションジェネレータの出力を分岐させて参照信号（リファレンス信号）とした。
プローブ１０は、光ファイバーを溶融延伸法によって先端を尖鋭化させたものを用いた。
水晶振動子１１は、腕時計用の音叉型水晶振動子で公称共振周波数が３２．７６８ｋＨｚのものを用いた。
また、膜厚解析装置１６としては、Ａ／Ｄ変換器１５およびＤ／Ａ変換器１７が内蔵されている汎用のパーソナルコンピュータを用いた。
被測定試料４は、基材２としてはガラス基盤を、また液膜３としては切削油を用いた。
第１０図に本測定による膜厚の測定結果を示す。
第１０Ａ図に示したグラフは、横軸が接近距離（Ａｐｐｒｏａｃｈｄｉｓｐｌａｃｅｍｅｎｔ）を、縦軸がプローブ１０の正規化振動振幅（Ａｍｐｒｉｔｕｄｅｒａｔｉｏ）を示したものである。正規化振動振幅は、振動振幅をプローブ１０が液膜から十分離れているときの振動振幅で正規化したものである。
第１０Ａ図に示したグラフからわかるように、プローブ１０の先端が液膜に接触した点（横軸の３００ｎｍ付近）と、ガラス基板に接触した点（横軸の１４００ｎｍ付近）の２点において振動振幅が大きく減衰していることが明確に認識できる。
この２点の差（１１００ｎｍ）が液膜３の膜厚に該当するものである。
第１０Ｂ図は、振動振幅の減衰する位置をより容易に識別できるように、第１０Ａ図と同一の正規化振動振幅データを接近距離で数値的に微分処理したものである。
第１０Ｂ図から明らかなように、振動振幅が大きく減衰する２つの接近距離において鋭いピークが現れている。この２つのピークにおける接近距離の差（１１００ｎｍ）が液膜３の膜厚である。Next, the results of actually measuring the film thickness of the liquid film by the film thickness measuring apparatus and the film thickness measuring method according to the present invention are shown in FIG. 9 and FIG.
FIG. 9 shows the system of the film thickness measuring apparatus 1 used for the measurement.
In this measurement, the probe 10 and the crystal resonator 11 are fixed, and the installation base 5 on which the sample 4 to be measured is placed is displaced in the Z-axis direction (vertical direction).
In addition, as the Z-axis displacement mechanism 6 for displacing the installation base 5, a high-precision motor drive type drive mechanism is used as the coarse adjustment mechanism, and a PZT piezoelectric actuator is used as the fine adjustment mechanism. A high voltage generator was used for the driver of the PZT piezoelectric actuator (Z-axis driver 18).
As the signal generator 14, a commercially available function generator was used. Similarly, a commercially available lock-in amplifier is used for the current detector 13 and the output of the function generator is branched to be a reference signal (reference signal).
As the probe 10, an optical fiber whose tip was sharpened by a melt drawing method was used.
As the crystal unit 11, a tuning fork type crystal unit for wristwatches having a nominal resonance frequency of 32.768 kHz was used.
Further, as the film thickness analysis device 16, a general-purpose personal computer in which the A / D converter 15 and the D / A converter 17 are incorporated is used.
In the sample 4 to be measured, a glass substrate was used as the substrate 2 and a cutting oil was used as the liquid film 3.
FIG. 10 shows the measurement results of the film thickness by this measurement.
In the graph shown in FIG. 10A, the horizontal axis represents the approach distance, and the vertical axis represents the normalized vibration amplitude (Amplitude) of the probe 10. The normalized vibration amplitude is obtained by normalizing the vibration amplitude with the vibration amplitude when the probe 10 is sufficiently separated from the liquid film.
As can be seen from the graph shown in FIG. 10A, vibration occurs at two points: the point where the tip of the probe 10 is in contact with the liquid film (around 300 nm on the horizontal axis) and the point where it is in contact with the glass substrate (around 1400 nm on the horizontal axis). It can be clearly recognized that the amplitude is greatly attenuated.
The difference between these two points (1100 nm) corresponds to the film thickness of the liquid film 3.
FIG. 10B is a result of numerically differentiating the same normalized vibration amplitude data as in FIG. 10A by the approach distance so that the position where the vibration amplitude attenuates can be more easily identified.
As is apparent from FIG. 10B, sharp peaks appear at two approach distances where the vibration amplitude is greatly attenuated. The difference in the approach distance (1100 nm) between these two peaks is the film thickness of the liquid film 3.

半導体製造におけるフォトレジスト、摩擦潤滑を目的とした潤滑油、塗装工程における乾燥前の塗装膜等、広い産業分野にわたって液膜は使用されている。液膜の膜厚測定に基づく膜厚管理は液膜の性能を発揮させるために極めて重要である。
従来これらの膜厚測定には光学的手法や超音波あるいは静電容量を用いたものが使用されているが、これらの方法によって膜厚を求めるには、屈折率等に代表される膜厚の物性値が必要である。またエリプソメトリによる膜厚測定法は膜厚と屈折率を同時に測定できるが、測定可能な膜厚が数百ｎｍ以下という制約がある。
本発明によれば、先端が１００ｎｍ程度に尖鋭化されたプローブを用いて液膜の膜厚を測定するものであり、液膜に与える影響が無視できる程に小さく、かつ屈折率等の物性値が未知であっても膜厚の測定が可能である膜厚測定装置および膜厚測定方法を提供することができる。
また、測定可能な膜厚も測定原理上の制約はなく、数百ｎｍを超える膜厚であっても測定可能であり、広い産業分野に利用できる。Liquid films are used in a wide range of industrial fields such as photoresists in semiconductor manufacturing, lubricating oils for frictional lubrication, and coating films before drying in coating processes. Film thickness management based on the measurement of the thickness of the liquid film is extremely important in order to exhibit the performance of the liquid film.
Conventionally, these film thickness measurements have been performed using optical techniques, ultrasonic waves, or electrostatic capacity. In order to obtain the film thickness by these methods, the film thickness represented by the refractive index or the like is used. Physical property values are required. The film thickness measurement method using ellipsometry can measure the film thickness and the refractive index at the same time, but has a limitation that the measurable film thickness is several hundred nm or less.
According to the present invention, the film thickness of a liquid film is measured using a probe whose tip is sharpened to about 100 nm, and its influence on the liquid film is so small that the influence on the liquid film is negligible, and a physical property value such as a refractive index. It is possible to provide a film thickness measuring apparatus and a film thickness measuring method capable of measuring the film thickness even when the thickness is unknown.
Further, the measurable film thickness is not limited by the measurement principle, and even a film thickness exceeding several hundred nm can be measured and can be used in a wide range of industrial fields.

Claims

An installation table on which a sample to be measured having a liquid film formed on the substrate surface is installed;
A Z-axis displacement mechanism that is displaced in a direction perpendicular to the upper surface of the installation table;
A horizontal holding unit for holding the installation table;
A vertical holding portion for holding the Z-axis displacement mechanism;
A fixed connection mechanism for fixedly connecting the horizontal holding unit and the vertical holding unit;
A needle-like probe fixed to the Z-axis displacement mechanism, having an axis perpendicular to the upper surface of the installation table, and having an end closer to the installation table sharpened;
A crystal resonator having an electrode fixed to the Z-axis displacement mechanism and disposed in contact with the probe between the sample to be measured and the Z-axis displacement mechanism;
A signal generator for supplying an AC signal to the electrodes of the crystal unit;
A current detector for detecting a current generated from an electrode of the crystal unit;
A film thickness analysis device for analyzing the film thickness of the liquid film from the Z axis displacement value by the Z axis displacement mechanism and the current value of the crystal resonator obtained from the current detector;
A film thickness measuring apparatus comprising:

The Z-axis displacement mechanism is driven by an electric signal, and has two types of displacement mechanisms: a Z-axis coarse displacement mechanism that is roughly displaced in a direction perpendicular to the upper surface of the installation table, and a Z-axis fine displacement mechanism that is finely displaced. The film thickness measuring apparatus according to claim 1, wherein:

The film thickness measuring device according to claim 2, wherein the Z-axis fine displacement mechanism is a piezoelectric actuator.

2. The film thickness measuring apparatus according to claim 1, wherein the probe is a probe obtained by processing one end of an optical fiber having a predetermined length on a taper and sharpening the tip diameter to 100 nm or less.

2. The film thickness measuring apparatus according to claim 1, wherein the crystal resonator is a tuning fork crystal resonator.

The signal generator is a signal generator that generates a sine wave, the frequency of which can change at least 10% or more of the resonance frequency from above and below the resonance frequency of the crystal resonator. The film thickness measuring device according to the first item of the range.

The current detector receives a reference signal obtained by branching a part of the output signal of the signal generator, and detects a current value by a method of synchronously detecting the input signal of the current detector using the reference signal. The film thickness measuring device according to claim 1, wherein the film thickness measuring device is a current detector.

2. The current detector according to claim 1, wherein the current detector is a current detector using a lock-in amplifier that uses a signal obtained by branching a part of the output signal of the signal generator as a reference signal. Film thickness measuring device.

The film thickness analyzer is
An A / D converter for converting the analog output of the current detector into current data;
A D / A converter for converting Z-axis displacement data for setting a displacement amount of the Z-axis displacement mechanism into a voltage value;
A personal computer comprising: means for converting the current data into a vibration amplitude ratio of the probe; and a film thickness analysis means for analyzing the film thickness of the liquid film from the vibration amplitude ratio and the Z-axis displacement data;
The film thickness measuring apparatus according to claim 1, wherein the film thickness measuring apparatus comprises:

The film thickness analysis means analyzes the film thickness of the liquid film from a vibration amplitude change rate obtained by differentiating the vibration amplitude ratio with the Z-axis displacement data and the vertical displacement data. The film thickness measuring device according to claim 9,

2. The film thickness measuring apparatus according to claim 1, wherein the installation table is configured to be driven in a plane perpendicular to a displacement direction of the Z-axis displacement mechanism.

An installation table on which a sample to be measured having a liquid film formed on the substrate surface is installed;
A horizontal holding unit for holding the installation table;
A Z-axis displacement mechanism for displacing the installation table in a direction perpendicular to the upper surface of the installation table;
A fixed connection mechanism for fixedly connecting the horizontal holding unit and the vertical holding unit;
A needle-like probe fixed to the vertical holding unit, having an axis in a direction perpendicular to the upper surface of the installation table, and having a sharpened end closer to the installation table;
A quartz crystal unit having an electrode fixed to the vertical holding unit and disposed between the sample to be measured and the vertical holding unit in contact with the probe;
A signal generator for supplying an AC signal to the electrodes of the crystal unit;
A current detector for detecting a current generated from an electrode of the crystal unit;
A film thickness analysis device for analyzing the film thickness of the liquid film from the Z axis displacement value by the Z axis displacement mechanism and the current value of the crystal resonator obtained from the current detector;
A film thickness measuring apparatus comprising:

Place the sample to be measured with a liquid film formed on the substrate surface on the installation base,
From the surface of the liquid film, a probe having an axis in a direction perpendicular to the surface of the liquid film and having a sharpened tip closer to the liquid film, and a crystal unit in contact with the probe Arranged at a predetermined distance,
Supply an AC signal from a signal generator to the electrodes of the crystal unit to vibrate the crystal unit,
While measuring the vibration amplitude of the crystal resonator by detecting the current flowing through the electrode of the crystal resonator with a current detector,
The probe that vibrates by contact with the crystal unit is caused to approach the surface of the liquid film using a Z-axis displacement mechanism in a direction perpendicular to the surface of the liquid film together with the crystal unit,
Measuring a first position where the vibration amplitude decreases due to the tip of the probe contacting the surface of the liquid film;
The probe further penetrates the liquid film and approaches the substrate;
Measuring a second position where the vibration amplitude decreases due to the tip of the probe contacting the surface of the substrate;
A film thickness measuring method, wherein a difference between the first position and the second position is a film thickness of the liquid film.

The Z-axis displacement mechanism is driven by an electrical signal, and has two types of displacement mechanisms: a Z-axis coarse displacement mechanism that is coarsely displaced in a direction perpendicular to the upper surface of the installation table, and a Z-axis fine displacement mechanism that is finely displaced. The film thickness measuring method according to claim 13, wherein:

The film thickness measuring method according to claim 14, wherein the Z-axis fine displacement mechanism is a piezoelectric actuator.

The film thickness measuring method according to claim 13, wherein the probe is a probe obtained by processing one end of an optical fiber having a predetermined length into a taper shape and sharpening a tip diameter to 100 nm or less.

The film thickness measuring method according to claim 13, wherein the crystal resonator is a tuning fork crystal resonator.

14. The film thickness measuring method according to claim 13, wherein the AC signal is a sine wave, and the vibration of the crystal resonator is vibrated at a resonance frequency at which the output of the current detector is maximized. .

The current detector receives a reference signal obtained by branching a part of the output signal of the signal generator, and detects a current value by a method of synchronously detecting the input signal of the current detector using the reference signal. The film thickness measuring method according to claim 13, wherein the film thickness measuring method is a current detector.

14. The current detector according to claim 13, wherein the current detector is a current detector using a lock-in amplifier using a signal obtained by branching a part of the output signal of the signal generator as a reference signal. Film thickness measurement method.

The output of the current detector is A / D converted into current data, the Z axis displacement data for displacing the Z axis displacement mechanism is converted into an electrical signal by D / A conversion, and a personal computer is used. 14. The film thickness of the liquid film is analyzed from the vibration amplitude ratio and the Z-axis displacement data after converting the current data into the vibration amplitude ratio of the probe. Film thickness measurement method.

The film thickness measuring method according to claim 21, wherein the first position and the second position are obtained by differentiating the vibration amplitude data with the Z-axis displacement data.

14. The film thickness measurement according to claim 13, wherein the film thickness is measured at a plurality of points by moving the installation base in a plane perpendicular to the displacement direction of the Z-axis displacement mechanism. Method.