KR100960349B1 - Method of measuring thickness and refractive index of sample by using confocal optics and low-coherence interferometry, measurement apparatus using the same - Google Patents

Abstract

A method and apparatus for simultaneously measuring the thickness and refractive index of a sample are disclosed. Obtain a first relation regarding the thickness and phase refractive index of the sample through the confocal optical system using the light having the first center wavelength, and the thickness and the group refractive index of the sample through the low coherence interferometer using the light having the first center wavelength. Obtaining a second relation regarding the thickness and phase refractive index of the sample through a confocal optical system using the light having the second center wavelength, using the light having the second center wavelength, and Using a light having two center wavelengths, a fourth relationship relating to the thickness and group refractive index of the sample was obtained through a low coherence interferometer, and then, using the first to fourth relations, the thickness, phase refractive index, and group refractive index of the sample. A method of simultaneously measuring the thickness and the refractive index of the sample is configured to obtain. Therefore, there is no limitation on the sample to be measured, and a measuring method having a small measurement error and a device using the same as compared to the conventional method using a separate sample holder or assuming a phase refractive index and a group refractive index.

Confocal, coherence, refractive index, thickness, measurement

Description

METHOD OF MEASURING THICKNESS AND REFRACTIVE INDEX OF SAMPLE BY USING CONFOCAL OPTICS AND LOW-COHERENCE INTERFEROMETRY, MEASUREMENT APPARATUS USING THE SAME}

The present invention relates to a method and apparatus for simultaneously measuring the thickness and refractive index of a sample, and more particularly, to the thickness, phase refractive index, and the like of a sample without using a specially designed sample holder using a confocal optical system and a low coherence interferometer. A method and apparatus for measuring group refractive indices simultaneously.

Simultaneously measuring the thickness and refractive index of a sample can be used in many industries, such as optical engineering to study the optical properties of materials, optical tomography techniques to find the physical structure inside a sample, and medical engineering to measure the refractive index to affect the scattering coefficient of biological samples. Can be applied.

), 시료의 군 굴절률(group index;

) 및 상기 기준단 간의 위치차(

)의 관계식은 하기 수학식 1과 같이 정의된다. 또한, 여기에서 기준단 간의 위치차(

)는 시료의 광학적 두께로 정의된다.To this end, conventional studies using low coherence interferometry (LCI) (T. Tsuruta, et al., Proceedings of the International Commission for Optics Conference, pp. 369-372, 1974. and BLDanielson et al., Applied Optics., Vol. 30, No. 21, pp. 2976-2979, 1991. That is, the distance between each boundary constituting the sample and the position of the reference stage having the same optical path difference are obtained by detecting the interference signal, and then the relationship between the position difference of each reference stage, the physical thickness of the sample and the group refractive index of the sample is Find the physical thickness. At this time, the physical thickness of the sample (

), Group index of the sample;

) And the position difference between the reference stage (

) Is defined as in Equation 1 below. Also, here, the position difference between the

) Is defined as the optical thickness of the sample.

[Equation 1]

), 시료의 물리적 두께(

) 및 시료의 위상 굴절률(

)간의 관계는 하기 수학식 2와 같이 정의된다.In addition, conventional studies using confocal optics (CO) (T.Fukano, et al., Optics Letters., Vol. 21, No. 23, pp. 1942-1944, 1996., M. Ohmi) , et al., Proceedings of SPIE, the International Society for Optical Engineering, vol. 4185, pp. 288-291, 2000. and T. Fukano, et al., Applied Optics., vol. 38, no. 19, pp .4065 ~ 4073, 1999.) moves the sample along the optical axis until the light reflected at each interface constituting the sample becomes the maximum, the difference between the two positions where the reflected light becomes the maximum, the physical thickness of the sample, and the sample. The physical thickness is obtained by using the relationship between the phase refractive indices. At this time, the difference between the two positions (

), The physical thickness of the sample (

) And phase refractive index of the sample (

) Is defined as in Equation 2 below.

[Equation 2]

Here, NA represents a numerical aperture of the objective lens used in the confocal optical system. When NA is small, Equation 2 may be approximated by Equation 3 below.

&Quot; (3) "

)이 사용되고, 낮은 결맞음 간섭계에서는 군 굴절률(

)이 사용되어, 시료의 두께와 시료의 굴절률을 동시에 측정하기 위한 방법들이 필요해지게 되는데, 즉 상술한 두 식 이외에 최소한 하나 이상의 관계식이 더 요구되는 것이다.However, in the confocal optical system, the phase refractive index (

) Is used, and for low coherence interferometers the group refractive index (

), Methods are needed for simultaneously measuring the thickness of the sample and the refractive index of the sample, i.e., at least one or more relational expressions are required in addition to the above two equations.

Therefore, in order to obtain additional relations in addition to the above-described two equations, a specially manufactured sample holder is conventionally used, or a special equation representing a relationship between the group refractive index and the phase refractive index, such as US Patent No. 6,172,752, is assumed. Methods were used.

However, when using a specially made sample holder, the sample must first be fixed in the sample holder. Therefore, the sample must be cut to a size that can be placed in the holder. Therefore, the thickness of the measurable sample is quite limited. There is a problem that needs to be correctly aligned. In addition, even if the material of the sample is well known in the case of the method of assuming the relationship between the group refractive index and the phase refractive index, there is a problem that the measurement error is large for the unknown sample.

An object of the present invention for solving the above problems, by using a confocal optical system and a low coherence interferometer at the same time, using a light having two or more central wavelengths of the sample without cutting the sample having a variety of types and thickness It is to provide a measuring method for measuring the thickness and the phase refractive index and the group refractive index of the material constituting the sample with high accuracy.

Another object of the present invention for solving the above problems, using a confocal optical system and a low coherence interferometer at the same time, using a light having two or more central wavelengths of the sample without cutting a variety of types and thickness of the sample The present invention provides a measuring device for measuring physical thickness, phase refractive index, and group refractive index of materials constituting a sample with high accuracy.

The present invention for achieving the above object, in the method for simultaneously measuring the thickness and the refractive index of the sample using a confocal optical system and a low coherence interferometer, using the light having a first central wavelength, through the confocal optical system Obtaining a first relational expression relating to the thickness and phase refractive index of the sample; obtaining a second relational expression regarding the thickness and group refractive index of the specimen through the low coherence interferometer, using light having the first center wavelength; Obtaining a third relational expression regarding the thickness and phase refractive index of the sample through the confocal optical system using light having a second center wavelength different from the first center wavelength, using light having the second center wavelength Obtaining a fourth relational expression regarding the thickness and the group refractive index of the sample through the low coherence interferometer and the first If using a fourth relational expression, it provides a thickness of the sample, phase refractive index, the thickness of the sample, characterized in that, including a step of obtaining a group index of refraction and the refractive index of simultaneous measurements.

Here, the step of obtaining the first relation or the third relation relating to the thickness and the phase refractive index of the sample, the light having the first center wavelength or the second center wavelength is reflected and reflected on both boundary surfaces constituting the sample Using the distance difference between the objective lens constituting the confocal optical system and the sample at both points at which the optical power is maximized, the relationship between the thickness and the phase refractive index of the sample may be obtained.

In addition, obtaining a second relation or a fourth relation relating to the thickness and the group refractive index of the sample, the light reflected by the light having the first center wavelength or the second center wavelength reflected on both boundary surfaces constituting the sample When the power is maximized, the relationship between the thickness of the sample and the group refractive index may be obtained by using the distance difference of the reference mirror at the point where the interference fringe is detected on the reference mirror constituting the low coherence interferometer. have.

Here, the calculating of the thickness, phase refractive index, and group refractive index of the sample using the first to fourth relational expressions may be performed by using a relationship between the phase refractive index and the group refractive index.

Alternatively, obtaining the thickness, phase refractive index, and group refractive index of the sample by using the first to fourth relational expressions may include determining a dispersion parameter of the sample and using the relationship between the phase refractive index and the dispersion parameter of the sample. have.

According to another aspect of the present invention, there is provided a light generation unit for generating light having two or more central wavelengths, a light distribution unit for distributing light generated by the light generation unit, and light emitted from the light distribution unit. A first measurement unit and an optical distribution unit configured to transfer the objective lens and / or the sample so as to adjust a distance between the objective lens and the object, the object lens irradiated onto the sample, and measure the distance between the objective lens and the sample A second measurement unit configured to transfer the reference mirror to adjust the optical path difference between the reference mirror receiving the light distributed from the light reflected from the sample and the light reflected from the reference mirror, and measuring the position of the reference mirror A signal detector for measuring the optical power signal reflected from the sample and the interference fringe signal of the reference mirror, and the first measuring unit and the second measuring unit And a control unit for controlling the measurement unit, wherein the control unit passes the objective lens based on the optical power signal reflected from the sample detected by the signal detection unit while adjusting the distance between the objective lens and the sample through the first measurement unit. A distance difference between the objective lens and the sample is measured at both points where one light is focused on the interface of the sample, and the light passing through the objective lens through the second measuring unit is focused on the interface of the sample. At both points to form a position, the position of the objective lens and the sample is fixed and the reference mirror is transferred while measuring the position difference of the reference mirror from which the interference fringe signal is obtained by the signal detection unit, and through the light generating unit The distance between the objective lens and the sample and the interference fringe scene with light having a different center frequency A device for simultaneously measuring the thickness and refractive index of a sample configured to measure the physical thickness, phase refractive index, and group refractive index of the sample at the same time by measuring the positional difference of the reference mirror from which the arc is obtained.

Here, the light generation unit may include two or more light sources for generating light having different center wavelengths. Alternatively, the light generator may include at least one wavelength variable light source for generating light having different center wavelengths.

Here, the signal detector may include a lens, a pin-hole and a photo detector. Alternatively, the signal detector may include a beam parallelizer and an optical detector for the optical fiber.

Here, the optical path between the light generating unit and the light distribution unit, the light distribution unit and the objective lens, the light distribution unit and the reference mirror, the light distribution unit and the signal detection unit is formed using an optical fiber, and the light distribution The part may comprise an optical fiber type coupler.

Herein, the controller may be configured to adjust the distance between the objective lens and the sample through the first measurement unit and to use the points where the optical power signal reflected from the sample detected by the signal detector is substantially maximum. And the distance difference between the sample can be measured. Alternatively, the controller may be configured to adjust the distance between the objective lens and the sample through the first measuring unit, using the center points of the half widths of the optical power signals reflected from the sample detected by the signal detecting unit, to adjust the distance between the objective lens and the sample. The difference in distance between them can be measured.

Using the measuring method and the measuring device according to the present invention as described above using a confocal optical system and a low coherence interferometer at the same time, the physical thickness of the sample and the phase of the material constituting the sample without cutting the sample having a variety of types and thickness It is possible to measure the refractive index and the group refractive index together with high accuracy.

In particular, by using light having two or more center wavelengths by using a light generating unit that generates light having two or more center wavelengths, phase refractive index and group refractive index may be used by using a conventionally designed sample holder or by using a specific sample material. Beyond the limitations of assuming a relationship between them, there is a small limit on the measurable sample and an effect that can be performed without a specially designed sample holder.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a flowchart illustrating an embodiment of a method for simultaneously measuring the thickness and refractive index of a sample according to the present invention.

Referring to FIG. 1, an embodiment of a method for simultaneously measuring a thickness and a refractive index of a sample according to the present invention may be performed by using a light having a first center wavelength and using the confocal optical system to determine the thickness and phase refractive index of the sample. Obtaining a first relation relating to the thickness of the sample and a group refractive index using the low coherence interferometer, using the light having the first center wavelength (S110); By using light having a second center wavelength different from the first center wavelength, using the confocal optical system to obtain a third relation about the thickness and phase refractive index of the sample (S130), the second center wavelength Using the light having a light, using the low coherence interferometer to obtain a fourth relational expression about the thickness and the group refractive index of the sample (S140) and using the first to fourth relational expression, The thickness of the sample, the phase index may be configured by comprising a step (S150) to obtain the refractive index of the group.

2A and 2B are conceptual views illustrating a process of obtaining a relationship between a physical thickness of a sample and a phase refractive index in a method for simultaneously measuring a thickness and a refractive index of a sample according to the present invention.

Hereinafter, the step (S110) of obtaining the relation between the physical thickness and the phase refractive index of the sample in parallel with FIGS. 1, 2A and 2B will be described.

)를 가지는 시료(220)에 조사되게 된다. 이때, 대물렌즈(210)와 시료(220) 간의 거리를 대물렌즈(210)를 이동시키거나, 시료(220)를 이동시켜가면서 조절하게 되는데, 이때 대물렌즈(210)를 통과한 광이 시료(220)이 가지는 경계면(220-1)에 도달하게 될 경우에 대물렌즈(210)와 시료(220) 간의 거리(230)를 측 정하게 된다.Referring to FIG. 2A, the light generated from the light source passes through the light distribution unit, and half of the optical power is transmitted to the objective lens 210, and the thickness of the light has a predetermined focal length through the objective lens 210.

It is irradiated to the sample 220 having a). In this case, the distance between the objective lens 210 and the sample 220 is adjusted by moving the objective lens 210 or by moving the sample 220. In this case, the light passing through the objective lens 210 is controlled by the sample ( When the boundary surface 220-1 of 220 is reached, the distance 230 between the objective lens 210 and the sample 220 is measured.

Also, referring to FIG. 2B, the distance between the objective lens 210 and the sample 220 is adjusted again by moving the objective lens 210 or by moving the sample 220. In this case, the objective lens 210 is adjusted. When the light passing through reaches the rear surface of the sample 220, that is, the interface 220-2, the distance 240 between the objective lens 210 and the sample 220 is measured again.

On the other hand, the method for determining whether the light passing through the objective lens 210 has reached the boundary surfaces 220-1 and 220-2 of the sample 220 includes the light 220 passing through the objective lens 210. When focusing on the boundary surfaces 220-1 and 220-2, since the light reflected from the sample will have the maximum optical power, the reflected optical power can be determined by using a photo detector. That is, while adjusting the distance between the objective lens 210 and the sample 220, when the light reflected from the sample is detected as having the maximum power signal by the photodetector, the light passing through the objective lens 210 is detected by the sample 220. It may be determined that the boundary surfaces 220-1 and 220-2 of FIG.

라고 하고, 공기의 굴절률을 1, 시료(220)의 위상 굴절률을

라 정의하면, 스넬(Snell)의 법칙과 도 2a 및 도 2b에서 예시한 구조로부터 하기 수학식 4 및 수학식 5의 관계를 얻을 수 있다. In this case, the distance 230 between the objective lens 210 and the sample 220 measured in the state illustrated in FIG. 2A and the distance 240 between the objective lens 210 and the sample 220 measured in the state illustrated in FIG. 2B. Difference

The refractive index of air is 1, and the phase refractive index of the sample 220 is

In this case, the relationship between Equations 4 and 5 can be obtained from Snell's law and the structure illustrated in FIGS. 2A and 2B.

[Equation 4]

[Equation 5]

In this case, when the numerical aperture of the objective lens 210 is NA, the following Equation 6 may be derived from Equations 4 and 5 above.

&Quot; (6) "

를 구할 수도 있을 것이다. On the other hand, when the optical power signal reflected from the sample does not have a sharp peak characteristic, it may be difficult to find a peak point at which the optical power signal is maximized. Therefore, assuming the point having the maximum optical power signal as the center of the half width of the optical power signal received by the photodetector, and obtain the difference in the distance between the objective lens 210 and the sample 220 at these points

You can also get

In addition, the light generated from the light source passes through the light distribution unit, and half of the optical power is transmitted to the objective lens 210, while the other half of the optical power is transmitted to the reference mirror.

)로서, 이를 이용하여 하기 수학식 7의 시료의 물리적 두께(

)와 군굴절률(

) 간의 관계식을 얻을 수 있다.In the step (S120) of obtaining a relational expression regarding the thickness of the sample and the group refractive index, the reference is made while the light passing through the objective lens 210 focuses on both boundary surfaces 220-1 and 220-2 of the sample 220. By moving the mirror. That is, the optical path through which the light passing through the objective lens 210 is reflected from the sample in the state of focusing on both boundary surfaces 220-1 and 220-2 of the sample 220 and returns to the photo detector through the light distribution unit. When the objective lens 210 and the sample 220 is fixed, it is possible to check whether the interference fringe is generated while transferring the reference mirror. That is, the optical detector can identify the point where the optical path difference between the light reflected from the interface of the sample and the light reflected from the reference mirror is the same by the maximum interference fringe, and the difference between the two points is the optical distance of the sample. thickness(

, The physical thickness of the sample of Equation 7

) And group refractive index (

) Can be obtained.

[Equation 7]

), 위상굴절률(

) 및 군굴절률(

)를 측정하기 위해서는 상기 수학식 6과 수학식 7 이외의 또 다른 관계식을 얻어야 한다.At this time, the physical thickness of the sample (

), Phase refractive index (

) And group refractive index (

In order to measure), other relations other than Equations 6 and 7 must be obtained.

In the method for simultaneously measuring the thickness and refractive index of a sample according to the present invention, the measurement process is performed with light having different center wavelengths by using a plurality of light sources having different center wavelengths or by using a variable wavelength light source capable of converting the center wavelengths. By repeating again, other relations other than Equations 6 and 7 can be obtained.

That is, the second relational equation regarding the thickness and phase refractive index of the sample is again used by using light having a wavelength different from the light having the first center wavelength (second center wavelength) used in steps S110 and S120. That is, a step S130 of obtaining a third relational expression) and a step S140 of obtaining a second relational expression (ie, a fourth relational expression) regarding the thickness and the group refractive index of the sample are performed.

)을 가지는 광의 중심주파수(

)에 대한 식으로 고쳐쓰여질 수 있다. 즉, 상기 수학식 6과 수학식 7은 서로 다른 중심 파장을 가지는 두 가지 이상의 광에 대하여 각각 하기 수학식 8 및 하기 수학식 9와 같이 고쳐 쓰여질 수 있다. By using a plurality of light sources having different center wavelengths or using a variable wavelength light source capable of converting the center wavelengths, Equations 6 and 7 are different from each other.

Center frequency of light with

Can be rewritten as That is, Equations 6 and 7 may be rewritten as Equations 8 and 9 for two or more lights having different center wavelengths, respectively.

[Equation 8]

[Equation 9]

와

을 이용하여

와

(또한,

및

)을 각각

의 함수로서 기술하는 것이 가능해진다. 즉, 두 가지 광을 이용한 경우에는 일차함수로, 세가지 이상의 광을 이용한 경우에는 이차함수 이상으로

,

,

및

를 각각

의 함수(

,

,

,

)로 기술할 수 있을 것이다.In this case, at least two light sources having different wavelengths should be used, and the more accurate the number of light having different wavelengths can be obtained. If two kinds of light having different wavelengths are used, the equations 8 and 9 are obtained for each wavelength.

Wow

Using

Wow

(Also,

And

) Each

It can be described as a function of. In other words, if two types of light are used, the first function is used.

,

,

And

Each

Function in

,

,

,

).

), 위상굴절률(

) 및 군굴절률(

)을 구하는 방법은 다양하게 구성될 수 있으나, 대표적으로 다음의 두가지 방법으로 구해질 수 있다.At this time, the physical thickness of the sample using the equation (8) and (9)

), Phase refractive index (

) And group refractive index (

) Can be obtained in a variety of ways, but can be obtained in two ways.

1) Method using the relationship between phase refractive index and group refractive index

By using two kinds of light having different center wavelengths, the relationship between the phase refractive index and the group fracture rate can be expressed as follows.

[Equation 10]

)에 관하여 정리하면 하기 수학식 11을 얻을 수 있다. 여기에서, 상기 수학식 10에 포함된 미분항(

)은 앞서 언급된 바와 같이, 수학식 8에서

의 함수로 기술된

를 미분하는 것에 의해 얻어질 수 있다.Therefore, after substituting Equations 8 and 9 into Equation 10, the thickness (

), The following equation (11) can be obtained. Here, the derivative term included in Equation 10 (

), As mentioned above,

Described as a function of

By differentiating.

[Equation 11]

From here,

를 제외한 모든 값들은 측정에 의해서 얻어질 수 있는 값이므로, 상기 수학식 11에서

를 구한 다음, 이를 이용하여 다시 상기 수학식 8 및 수학식 9로부터 위상 굴절률과 군 굴절률을 구할 수가 있다.In Equation 11

Since all values except for are values that can be obtained by measurement, Equation 11

Then, the phase refractive index and the group refractive index can be obtained from the above Equations 8 and 9 again.

2) using distributed parameters

Dispersion parameters of the media constituting the sample can be obtained by comparing the interference signals generated at both interfaces of the sample with each other. That is, as illustrated in FIG. 2A, the interference signal generated by the light reflected from the front boundary 220-1 of the sample does not reflect the characteristics of the medium of the sample, but is illustrated in FIG. 2B. The interference signal generated by the light reflected from the boundary surface 220-2 reflects the characteristics of the sample medium because the reflected light is transmitted through the sample. Thus, by comparing the interference signals generated at both interfaces, the dispersion parameters of the medium constituting the sample can be obtained.

)의 제곱은 하기 수학식 12와 같이 정의된다.In this case, the dispersion parameter (

) Squared is defined by the following equation (12).

[Equation 12]

The phase refractive index of a sample can be obtained by substituting the obtained dispersion parameter into following formula (13).

[Equation 13]

By substituting the phase refractive index obtained through the equation (13) again into the equations (6) and (7), the physical thickness and the group refractive index value of the sample can also be obtained.

On the other hand, the simultaneous measurement of the thickness and refractive index of the sample according to the present invention can be described in more detail through a measuring device to which the measuring method according to the present invention is applied.

3 is a conceptual view illustrating an embodiment of a device for simultaneously measuring a thickness and a refractive index of a sample according to the present invention.

Referring to FIG. 3, an embodiment 300 of the apparatus for simultaneously measuring a thickness and a refractive index of a sample according to the present invention includes a light generator 310, a light distributor 320, an objective lens 330, and a first measurer. 340, the reference mirror 350, the second measurement unit 360, the signal detector 370, and the controller 380 may be configured.

The light generator 310 is a component for generating light having two or more different center wavelengths, and may include two or more light sources 311 for generating light having different center wavelengths. Alternatively, the light generator 310 may include at least one wavelength variable light source for generating light having different center wavelengths. In this case, the variable wavelength light source may be configured by attaching the variable wavelength filter to the ultra-wideband light source.

In addition, the light generating unit 310 is configured to include a lens 312 for converting the light irradiated from the light source 311 into parallel light.

The light distributor 320 is a component that distributes the light generated by the light generator 310. That is, half of the optical power distributed by the light distribution unit 320 is transmitted to the objective lens 330 side, and the other half of the optical power is transmitted to the reference mirror 350 side.

The objective lens 330 irradiates the sample 390 with the light transmitted from the light distribution unit 320 at a predetermined focal length. Meanwhile, the objective lens 330 illustrated in FIG. 3 is a component that performs the same role as the objective lens 210 described with reference to FIGS. 2A and 2B.

The first measuring unit 340 transfers the objective lens 330 and / or the sample 390 to adjust the distance between the objective lens 330 and the sample 390, and the objective lens 330 And a component for measuring the distance between the sample 390. That is, the first measurement unit 340 transfers the objective lens 330 with the sample 390 fixed, or transfers the sample 390 with the objective lens 330 fixed, and the objective lens 330. It is a component for adjusting the distance between the sample 390, and measuring the adjusted distance. That is, the first measuring unit 340 is a component that allows the signal detector 370 to measure the reflected light at the interface of the sample 390 while adjusting the distance between the sample 390 and the objective lens 330.

The reference mirror 350 is a component for generating an interference signal by receiving the light distributed from the light distribution unit 320.

The second measuring unit 360 transfers the reference mirror 350 to adjust the optical path difference between the light reflected from the sample 390 and the light reflected from the reference mirror 350, and the position of the reference mirror. Is a component that measures. That is, the second measuring unit 360 is a component that allows the signal detector 370 to measure the interference signal while transferring the reference mirror 350. The second measurement unit 360 may include a lens 361 that allows the light transmitted from the light distribution unit 320 to focus on the reference mirror 350.

The signal detector 370 is a component for detecting the optical power signal of the light that has passed through the objective lens 330 reflected from the sample 390 and detecting the interference signal reflected from the reference mirror 350.

The signal detector 370 may include a lens 371, a pin-hole 372, and a photo detector 373. The pin-hole 372 delivers only the light focused at the focus by the lens 371 to the photo detector 373.

Meanwhile, the signal detector 370 may be configured using a beam collimator, an optical fiber, and an optical detector for an optical fiber. In this case, a lens is also installed inside the beam parallelizer for the optical fiber, and the optical fiber is connected so that the core of the optical fiber can replace the role of the pin-hole. That is, the signal detector 37 may have a configuration in which the beam parallel for the optical fiber and the optical detector are connected as the optical fiber.

Figure 4a is a conceptual diagram for explaining another embodiment of the thickness and refractive index measurement apparatus of the sample according to the present invention.

Referring to FIG. 4A, unlike the embodiment 300 of the apparatus for simultaneously measuring the thickness and the refractive index of the sample according to the present invention illustrated in FIG. 3, the lens 351 is disposed in front of the reference mirror 350. The configuration 400 is omitted. In FIG. 4A, components using the same reference numerals as in FIG. 3 play the same role as the case of the embodiment 300 illustrated in FIG. 3, and a detailed description thereof will be omitted.

The configuration 400 illustrated in FIG. 4A is a method for obtaining the physical thickness, the phase refractive index, and the group refractive index of a sample, using 1) a method of using the relationship between the phase refractive index and the group refractive index and the method of using the dispersion parameter. It is a structure of a measurement apparatus possible in the case of using only the method of 1).

That is, in the case of using the method of using the dispersion parameter, as shown in FIG. 3, the same lens 361 as the objective lens 330 irradiating light onto the sample 390 is placed at the front end of the reference mirror 350. It is necessary to attach. That is, it is necessary to compensate the dispersion effect of the objective lens 330 by using the lens 361 so that the sample stage and the reference mirror stage have the same dispersion characteristics. However, 1) If the configuration of the measuring device using only the method using the relationship between the phase refractive index and the group refractive index is assumed, the configuration in which the lens in front of the reference mirror is omitted, as illustrated in FIG. 4A.

Figure 4b is a conceptual diagram for explaining another embodiment of the thickness and refractive index measurement apparatus of the sample according to the present invention.

Referring to FIG. 4B, an embodiment 500 according to the present invention is illustrated in which the light generator 310 includes an additional lens 313 and a pin-hole 314. Here, the role of the lens 313 and the pin-hole 314 is to acquire a more precise confocal signal from the signal detector 370. In FIG. 4B, components using the same reference numerals as in FIG. 3 play the same role as in the case of the embodiment 300 illustrated in FIG. 3 and detailed descriptions thereof will be omitted.

If the pin-hole 314 is not used, a focal point having a certain radius may be formed depending on the numerical aperture of the lens 313 even when the pin-hole is focused. In addition, since light having a certain radius is transmitted to the lens 312, light of non-parallel components is generated in the lens 312, and the non-parallel light component passes through the objective lens 330. 390) to make the thickness of the confocal signal thicker. Therefore, a more precise signal can be obtained by additionally including the lens 313 and the pin-hole 314 before the light source 311 included in the light generator 370.

4C is a conceptual view for explaining another embodiment of the apparatus for simultaneously measuring the thickness and the refractive index of a sample according to the present invention.

Referring to FIG. 4C, an embodiment 600 of configuring an optical path of a device for simultaneously measuring a thickness and a refractive index of a sample according to the present invention using an optical fiber is illustrated.

That is, the light generator 310, the light distributor 321, the light distributor 321, the objective lens 330, the light distributor 321, the reference mirror 350, and the light Optical paths 610, 620, 630, and 630 are formed between the distribution unit 321 and the signal detection unit 370 using optical fibers.

In the case of the embodiment 600 illustrated in FIG. 4C, an optical coupler may be used as the light distribution unit 321, which is more compact than the configuration illustrated in FIGS. 3, 4A, and 4B. There is an advantage that it can have a configuration of a measuring device. The role and detailed configuration of the components constituting the other measuring device are the same as those illustrated in FIGS. 3, 4A, and 4B, and thus, detailed descriptions thereof will be omitted.

5A is a graph illustrating an optical power signal measurement result for obtaining a relational expression regarding a thickness and a phase refractive index of a sample.

The horizontal axis (x axis) of the graph illustrated in FIG. 5A represents the distance between the objective lens 330 and the sample 390, and the vertical axis (y axis) represents the optical power signal detected by the signal detector 370. .

Referring to FIG. 5A, when the objective lens 330 focuses on the front boundary of the sample 390 in the measuring apparatus according to the present invention of FIGS. 3 and 4A to 4C, the signal detecting unit 370 detects the signal. The optical power signal 510 is illustrated. In addition, when the objective lens 330 focuses on the rear boundary of the specimen 390, the optical power signal 520 detected by the signal detector 370 is illustrated.

)로 측정될 수 있다.In this case, the difference 530 of the distance between the objective lens 330 and the sample 390 at both points where the peaks 510 and 520 of the optical power signal are detected is described with reference to FIG. The difference in distance between the objective lens 4 and the sample 6 to obtain a relationship between the thickness and the phase refractive index

Can be measured.

5B is a graph illustrating an interference signal measurement result for obtaining a relationship between a thickness of a sample and a group refractive index.

The horizontal axis (x axis) of the graph illustrated in FIG. 5b represents the position of the reference mirror 350, and the vertical axis (y axis) represents the magnitude of the interference signal detected by the signal detector 370.

Referring to FIG. 5B, in the measuring device according to the present invention of FIGS. 3 and 4A to 4C, the objective lens 330 and the sample (with the objective lens 330 focused on the front boundary of the sample 390). The interference signal 540 measured by the signal detector 370 is illustrated while the 390 is fixed and the reference mirror 350 is transferred. In addition, while the objective lens 330 is focused on the rear boundary of the specimen 390, the objective lens 330 and the specimen 390 are fixed, and the signal detection unit 370 is transported while the reference mirror 350 is transported. The interference signal 550 to be measured is illustrated.

)로 측정될 수 있다.At this time, the position difference 560 of the reference mirror in which the maximum two interference signals (540, 550) are measured is described with reference to Figure 1, the sample 390 for obtaining the relationship between the thickness of the sample and the group refractive index according to the present invention Optical thickness (

Can be measured.

Table 1 is a table illustrating the results measured by the method and apparatus for simultaneously measuring the thickness and refractive index of the sample according to the present invention.

BK7

Silica
Center wavelength [nm]

813
1030
813
1030

[mm]

[mm]
2.1385
2.1430
3.5055
3.5107

[mm]
4.9355

4.9182
7.4747
7.4522

및

측정값이 예시되어 있다.Referring to Table 1, two samples (BK7 and silica) were measured using light having a center wavelength of 813 nm and light having a center wavelength of 1030 nm, respectively.

And

The measurement is illustrated.

Table 2 is a result of comparing the calculated value and actual value of the thickness, phase refractive index, and group refractive index of the sample calculated by the method and apparatus for simultaneously measuring the thickness and refractive index of the sample according to the present invention.

Phase refractive index

Group refractive index
thickness
Measures

Actual value
Measures
Actual value
Measures
Actual value
BK7

813 nm
1.5119
1.5105
1.5264
1.5261

3.2333 mm


3.2340mm

1030nm

1.5087
1.5070
1.5211
1.5210
Silica
813nm

1.4550
1.4531
1.4654
1.4667

5.1007mm


5.0965 mm

1030nm

1.4528
1.4500
1.4610
1.4627

Referring to Table 2, 1) method of using the relationship between the phase refractive index and the group refractive index of the method for obtaining the physical thickness, phase refractive index and group refractive index of the sample described through Figure 1 using the measurement results illustrated in Table 1 above The result of comparing the calculated value and actual value of the thickness, phase refractive index, and group refractive index of the sample computed using is illustrated. Among the methods for obtaining the physical thickness, the phase refractive index, and the group refractive index of the sample described with reference to FIG. 1, similar results can be obtained when calculated using the method using the dispersion parameter, and thus the results thereof will be omitted.

The measured values measured using the method and apparatus according to the present invention shown in Table 2 were found to have an average error of 0.052% in thickness, 0.00198 in phase refractive index, and 0.00085 in group refractive index with respect to actual values.

및

을 광의 중심 파장의 함수로서 피팅(fitting)하고, 대물렌즈에 입사되는 빔의 크기에 따른 개구수까지 고려한다면 보다 더 정확한 결과를 얻을 수 있다.Since the measured values exemplified in Tables 1 and 2 are measured using two lights having different center wavelengths, a greater number of center wavelengths are used to accurately measure the light.

And

It is possible to obtain a more accurate result by fitting a as a function of the center wavelength of light and considering the numerical aperture according to the size of the beam incident on the objective lens.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the present invention as defined by the following claims It can be understood that

1 is a flowchart illustrating an embodiment of a method for simultaneously measuring the thickness and refractive index of a sample according to the present invention.

2A and 2B are conceptual views illustrating a process of obtaining a relationship between a physical thickness of a sample and a phase refractive index in a method for simultaneously measuring a thickness and a refractive index of a sample according to the present invention.

3 is a conceptual view illustrating an embodiment of a device for simultaneously measuring a thickness and a refractive index of a sample according to the present invention.

4A to 4C are conceptual views for explaining other embodiments of a thickness and refractive index measurement apparatus of a sample according to the present invention.

5A is a graph illustrating an optical power signal measurement result for obtaining a relational expression regarding a thickness and a phase refractive index of a sample.

5B is a graph illustrating an interference signal measurement result for obtaining a relationship between a thickness of a sample and a group refractive index.

Claims (15)

In the method for simultaneously measuring the thickness and the refractive index of the sample using a confocal optical system and a low coherence interferometer, First center wavelength (

Center angular frequency

The thickness of the sample through the confocal optical system using light having

) And a first relation relating to the phase refractive index; The thickness of the sample is passed through the low coherence interferometer using light having the first center wavelength.

) And a second relation relating to the group refractive index; A second center wavelength different from the first center wavelength (

Center angular frequency

The thickness of the sample through the confocal optical system using light having

) And a third relation for phase refractive index; The thickness of the sample is passed through the low coherence interferometer using light having the second center wavelength.

) And a fourth relation relating to the group refractive index and Using the first to fourth relational formula, the thickness of the sample (

), The method of measuring the thickness and the refractive index of the sample, characterized in that it comprises the step of obtaining the phase refractive index, group refractive index. The method of claim 1, Obtaining a first relational expression regarding the thickness and the phase refractive index of the sample, The difference between the distance between the objective lens constituting the confocal optical system and the sample at both time points at which the light having the first center wavelength is reflected on both boundary surfaces constituting the sample and the reflected light power is maximum (

), The thickness of the sample represented by the following equation (1)

) And phase refractive index (

A method for simultaneously measuring the thickness and refractive index of a sample, characterized by obtaining a relational expression of [Equation 1]

The method of claim 2, Obtaining a second relationship relating to the thickness and the group refractive index of the sample, When the light having the first center wavelength is reflected on both boundary surfaces constituting the sample and the reflected optical power is maximized, the reference mirror is detected at the point where the interference fringe is detected on the reference mirror constituting the low coherence interferometer. Distance difference

), The thickness of the sample represented by the following equation (2)

) And group refractive index (

A method for simultaneously measuring the thickness and refractive index of a sample, characterized by obtaining a relational expression of [Equation 2]

The method of claim 1, Obtaining a third relational expression regarding the thickness and the phase refractive index of the sample, The difference between the distance between the objective lens constituting the confocal optical system and the sample at both time points at which the light having the second center wavelength is reflected on both boundary surfaces constituting the sample and the reflected light power is maximum (

), The thickness of the sample represented by the following equation (3)

) And phase refractive index (

A method for simultaneously measuring the thickness and refractive index of a sample, characterized by obtaining a relational expression of &Quot; (3) "

The method of claim 4, wherein Obtaining a fourth relational expression regarding the thickness and the group refractive index of the sample, When the light having the second center wavelength is reflected on both boundary surfaces constituting the specimen and the reflected light power is maximized, the reference mirror is detected at the point where the interference fringe is detected on the reference mirror constituting the low coherence interferometer. Distance difference

), The thickness of the sample represented by the following equation (2)

) And group refractive index (

A method for simultaneously measuring the thickness and refractive index of a sample, characterized by obtaining a relational expression of [Equation 2]

The method of claim 1, Obtaining the thickness, phase refractive index, and group refractive index of the sample using the first to fourth relational expressions, includes using a relationship between the phase refractive index and the group refractive index represented by Equation 5 below. Simultaneous measurement of thickness and refractive index of a sample. [Equation 5]

(Wherein the above

Is the thickness of the sample (

) And the center frequency of light, approximated using the second and fourth equations for group index of refraction (

Group index of refraction defined by

Is a function of

Is the thickness of the sample (

) And the center frequency of light, approximated using the first and third equations for

Phase index of refraction defined by

Is a function of) The method of claim 1, Obtaining the thickness, phase refractive index, and group refractive index of the sample using the first to fourth relational expressions, the dispersion parameter of the sample represented by Equation 6

) To obtain the phase refractive index of the sample using the following equation (7). &Quot; (6) "

[Equation 7]

A light generator for generating light having two or more center wavelengths; A light distribution unit that distributes the light generated by the light generation unit; An objective lens for irradiating the sample with the light distributed by the light distribution unit; A first measuring unit configured to transfer the objective lens and / or the sample so as to adjust the distance between the objective lens and the sample, and measure a distance between the objective lens and the sample; A reference mirror to receive the light distributed by the light distribution unit; A second measuring unit configured to transfer the reference mirror so as to adjust an optical path difference between the light reflected from the sample and the light reflected from the reference mirror, and measure a position of the reference mirror; A signal detector for measuring the optical power signal reflected from the sample and the interference fringe signal of the reference mirror; And A control unit for controlling the first measurement unit and the second measurement unit; Based on the optical power signal reflected from the sample detected by the signal detector while adjusting the distance between the objective lens and the sample through the first measuring unit, the light passing through the objective lens focuses on the interface of the sample. Distance difference between the objective lens and the sample at both points (

), At both points where the light passing through the objective lens through the second measuring unit focuses on the boundary surface of the sample, the interference is detected by the signal detector while fixing the position of the objective lens and the sample and transporting the reference mirror. Position difference of the reference mirror from which the pattern signal is obtained (

), The light having different center frequencies through the light generator;

Wow

Measuring the thickness of each sample, the phase refractive index and the group refractive index simultaneously measuring the thickness and the refractive index of the sample, characterized in that. The method of claim 8, The light generating unit Apparatus for simultaneous measurement of thickness and refractive index of a sample comprising two or more light sources for generating light having different center wavelengths. The method of claim 8, The light generating unit An apparatus for simultaneously measuring a thickness and a refractive index of a sample including at least one wavelength variable light source for generating light having different center wavelengths. The method of claim 8, The signal detection unit lens; Pin-holes; And An apparatus for simultaneously measuring a thickness and a refractive index of a sample including a photo detector. The method of claim 8, The signal detection unit Beam parallelizers for optical fibers; And An apparatus for simultaneously measuring a thickness and a refractive index of a sample including a photo detector. The method of claim 8, An optical path is formed between the light generating unit and the light distribution unit, the light distribution unit and the objective lens, the light distribution unit and the reference mirror, the light distribution unit and the signal detection unit using an optical fiber, And the optical distribution unit comprises an optical fiber type coupler. The method of claim 8, The control unit may adjust the distance between the objective lens and the sample through the first measurement unit and use the points where the optical power signal reflected from the sample detected by the signal detection unit is substantially maximized. Simultaneous measurement of the thickness and refractive index of the sample, characterized in that for measuring the distance difference between. The method of claim 8, The controller may adjust the distance between the objective lens and the sample by adjusting the distance between the objective lens and the sample by using the center points of the half width of the optical power signal reflected from the sample detected by the signal detector. A device for measuring the thickness and refractive index of a sample, characterized by measuring the difference.

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