KR102141228B1 - Method and apparatus for measuring physical quantity of a thin layer using terahertz spectroscopy - Google Patents

Abstract

The present disclosure relates to a thin film measuring apparatus for measuring a physical quantity of a thin film, and comprises: a terahertz wave generator for generating a broadband pulsed terahertz wave for irradiating a thin film sample; a detector detecting the terahertz wave reflected from the thin film sample after irradiation to the thin film sample; and a calculation device calculating the thickness and physical properties of the thin film through frequency analysis of a reflected wave signal detected by the detector. The thickness and physical properties of the thin film are simultaneously measured by a least squares method using a Drude model.

Description

METHOD AND APPARATUS FOR MEASURING PHYSICAL QUANTITY OF A THIN LAYER USING TERAHERTZ SPECTROSCOPY}

The present invention relates to a method and apparatus for measuring the physical quantity of a thin film based on terahertz wave spectroscopy technology, and more specifically, the thickness and physical properties of the thin film formed on the sample by irradiating terahertz waves to the sample and spectroscopically analyzing the reflected wave (electric conductivity) , Doping concentration, resistance).

In the manufacture of semiconductors, solar cell cells or secondary battery films, a process of forming a thin film layer of various materials on a substrate is essential. When forming a thin film by a technique such as CVD (Chemical Vapor Deposition) or ion doping, it is important to keep the physical properties such as the thickness and electrical conductivity of the thin film at a target value. If the thickness or physical properties of the thin film deviate from the target value, it may lead to product defects. Therefore, the technology of easily identifying good and bad products by measuring the thickness and physical properties of each thin film process is essential to increase the yield of the entire manufacturing process. .

In particular, epitaxial wafers for semiconductors are required for the manufacture of semiconductor devices such as microprocessors, image sensors, and power devices, and production continues to increase as the demand for the devices increases.

A semiconductor epitaxial wafer (epitaxial wafer) is further deposited or ion-doped with a silicon single crystal layer (secondary growth layer) with a thickness of several μm on a polished wafer silicon layer (primary growth layer) as shown in FIG. 1. will be. The epitaxial layer, which is a secondary growth layer formed on the polished primary growth layer, plays an important role in controlling electrical conductivity when making a semiconductor device. For example, secondary growth of a relatively low concentration of n-type or p-type, formed by implanting dopants through ion implantation or CVD on an n+ or p+ type primary high doped Si wafer. It is a layer.

As a target specification for the epi layer, the layer thickness and the doping concentration are very important. As shown in FIG. 2, the thickness is 2 to 80 μm, and the doping concentration is produced between 10 ¹⁴ and 10 ¹⁸ pieces/cm ^{3 according} to the design specifications. After measuring the physical quantity such as thickness and electrical conductivity of the produced epi wafer, only the epi wafer that meets the target specification is put into the next process.

As a conventional technique for measuring the doping concentration, there is a 4-point probe method in which a probe is contacted with a thin film to measure voltage by applying a voltage as shown in FIG. 3. It can cause particle generation. In addition, in order to minimize such damage, it is necessary to make slow contact with the thin film to be measured, so it takes too much measurement time (40sec/point), and it is difficult to obtain a doping concentration map for uniformity of the entire surface of the product.

Since electrical conductivity depends on the concentration of carriers such as holes or electrons, and electrical resistivity (ΩM) is the reciprocal of electrical conductivity, the doping concentration can be converted into conductivity or resistance. 4 is a graph showing a function relationship between the doping concentration and the specific resistance.

On the other hand, a conventional technique for precisely measuring the thickness of the opaque semiconductor thin film is an ellipsometer. However, this technology not only requires expensive equipment, but also has difficulty in accurately measuring thickness in the case of thin films that crystallize coherently with a substrate material, such as a semiconductor epitaxial layer. Also, the ellipsometer cannot measure the electrical conductivity (doping concentration), which is a property other than the thickness, so separate equipment is required to measure the properties.

As described above, since the thin film thickness and electrical conductivity (doping concentration) must be measured with separate equipment, expensive equipment must be provided separately for measuring two important factors, measurement time is long, and measurement accuracy is limited. There were disadvantages.

Registered Patent Publication No. 10-1788450

The present invention solves the above problems to provide an apparatus and method for simultaneously measuring the thickness and electrical conductivity (doping concentration) of a thin film.

The present invention seeks to reduce process time and process cost by quickly and accurately measuring the thickness and physical properties of the entire sample surface while overcoming the limitations and disadvantages of the conventional method for thin films.

Another object of the present invention is to provide a thin film measuring apparatus and method capable of reducing the facility space while ensuring uniformity (UNIFORMITY) of the thin film by securing a doping concentration map for the entire measuring surface within a short time.

In order to solve the above problems, the thin film measuring apparatus of the present invention includes a terahertz wave generator that generates a terahertz wave pulse; A precision stage that mounts the sample on which the thin film is formed; A detector that detects terahertz waves reflected by the sample; And a computing device that processes a signal detected by the detector. Preferably, the computing device calculates the physical quantity of the thin film based on the reflectance of the thin film.

The thin film measuring apparatus according to an aspect of the present invention further includes an optical system that focuses terahertz waves and irradiates them with a thin film sample, and guides the terahertz waves reflected from the thin film sample to a detector.

The computing device preferably calculates the physical quantity of the thin film based on the reflectance Rs simulated by the Drude model and the measured reflectance of the thin film calculated from the detected signal.

The arithmetic unit 500 divides the detected terahertz wave signal into a reference signal after FFT (fast Fourier transformation) conversion, and normalizes it to calculate the measured reflectance spectrum of the thin film, and to the Drude Model to approximate the measured reflectance spectrum. The physical quantity of the sample is calculated by simulating the reflectance spectrum Rs.

The terahertz wave is a broadband pulse having a center frequency of 1 to 100 terahertz, and the physical quantity of the thin film is preferably one or more of the thickness, doping concentration, electrical conductivity, and resistivity of the thin film.

The thickness of the thin film is 100 μm or less, and the thin film measuring device can simultaneously measure two or more physical quantities of the thin film.

According to another aspect of the present invention, a terahertz wave generator, a precision stage for mounting a thin film sample, a detector for detecting the reflected terahertz wave irradiated to the thin film sample, and a computing device for processing a signal detected by the detector It provides a method for measuring the physical quantity of the thin film using a thin film measuring device.

The measurement method includes: a terahertz wave generator generating a broadband terahertz pulse; Irradiating the terahertz pulse to a thin film sample; A detector detecting terahertz reflected waves reflected by the thin film sample; And calculating a physical quantity of the sample based on the reflectance calculated from the terahertz reflected wave.

It is preferable to calculate the physical quantity of the thin film based on the reflectance spectrum Rs simulated by the Drude model and the measured reflectance spectrum calculated from the reflected wave.

The calculating of the physical quantity of the sample may include: Fourier transforming the detected terahertz wave reflection wave; A normalization step of dividing the Fourier transformed terahertz wave reflected wave into a reference signal to calculate a measured reflectance spectrum of the thin film; And simulating a reflectance spectrum (Rs) by a Drude Model to approximate the measured reflectance spectrum.

The step of simulating the reflectance spectrum (Rs) includes: setting a film thickness d and a doping concentration N _A ; Calculating the simulated reflectance spectrum (Rs) by substituting the set film thickness d and the doping concentration N _A into the Drude Model; Quantifying a difference between a simulated reflectance spectrum (Rs) and the measured reflectance spectrum; Performing the iterative calculation while changing the film thickness d and the doping concentration N _A so that the quantified difference value is equal to or less than the reference value; And if the difference value is smaller than the reference value, determining the set film thickness d and the doping concentration N _A as the film thickness d of the sample and the doping concentration N _A and ending the calculation.

The quantification step is preferably to quantify the simulated reflectance spectrum (Rs) and the measured reflectance spectrum by the Drude Model by the least square method, but is not limited thereto, and may be performed by various other quantification methods.

The present invention provides a technique for simultaneously measuring film thickness and electrical conductivity with a high degree of precision required in a wafer epitaxial layer for mass production.

The present invention can also be used as an in-situ monitoring instrument for deposition equipment such as CVD (Chemical Vapor Deposition), ALD (Atomic Layer Deposition).

The present invention can also be used as a method for quickly measuring the uniformity of electrical conductivity over the entire area for products in which electrical properties are important, such as ITO (Indium Tin Oxide) or graphene.

The present invention can also reduce the cost and reduce the space occupied by the equipment by integrating a plurality of instruments that are being purchased at an expensive price into one.

If the present invention is used, quality control can be performed early through in-line monitoring of the semiconductor manufacturing process, thereby reducing the semiconductor defect rate and contributing to reducing waste of core materials such as rare earth.

1 is a view showing a cross-sectional structure of an epitaxial waiter for semiconductors.
2 is a view showing an example of the manufacturing specifications of the epitaxial wafer.
Figure 3 is a conceptual diagram of a conventional 4-point probe method for measuring the physical properties of the epiwafer, especially the doping concentration.
4 is a graph showing the correlation between the doping concentration and resistivity.
5 is a diagram showing a frequency region of terahertz (THz) waves.
6 is a graph showing a difference in absorption rate and absorption rate by frequency according to silicon doping concentration.
7 is a schematic diagram of a measurement device based on terahertz (THz) wave spectroscopy technology according to an embodiment of the present invention.
8 is a conceptual diagram schematically showing a terahertz (THz) wave generator.
9 is a perspective view of an embodiment of the apparatus for measuring the thickness and properties of a thin film based on terahertz spectrum of the present invention.
10 is a view schematically showing the behavior of the incident wave and the reflected wave of the terahertz wave pulse in the epi layer.
11 is a graph of the terahertz wave signal reflected from the epi wafer.
12 is a view showing a formula for the relationship between the reflectance, film thickness, and physical properties by the Drude Model.
13 is a view showing an equation by the Drude Model.
14 is a flowchart in which the computing device 500 calculates the film thickness d and the doping concentration N _A using a Drude Model.
15 is a graph showing a spectrum of reflected waves actually calculated by a Drude Model and a spectrum of reflected waves actually measured.
16 shows the measurement points and specifications of the epi-wafer to be measured.
17 are equations in which constant values are applied when a doping concentration of a silicon substrate is assumed to calculate reflectance by a Drude Model.
FIG. 18 is a graph showing reflectance by measured values, reflectance calculated by the Drude model, and the difference.
FIG. 19 is a table showing the physical quantity of the epi layer calculated as shown in the graph of FIG. 18 using the method and apparatus of the present invention, compared with a value measured using other devices.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art to which the present invention pertains may easily practice. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. In addition, in order to clearly describe the present invention in the drawings, parts irrelevant to the description are omitted, and like reference numerals are assigned to similar parts throughout the specification.

Throughout the specification, when a part is "connected" to another part, it is not only "directly connected", but also "electrically or communicatively connected" with another element in between. Also includes. Also, when a part “includes” a certain component, this means that other components may be further included instead of excluding other components, unless otherwise specified.

Hereinafter, the apparatus and method of the present invention will be described in detail with reference to the drawings.

As shown in FIG. 5, the terahertz wave has a tera-level frequency of 10 ¹² ~ 10 ¹⁴ Hz between the infrared and electromagnetic waves, and has a characteristic in which a transmission amount and a reflection amount vary according to an electrical characteristic of the object. Moreover, it is possible to transmit even an opaque sample that is not transmitted through normal light, and has a merit in that the thickness of the thin film layer can be measured because the wavelength is short compared to radio frequency.

Figure 6 shows the relationship between the absorption rate of electromagnetic waves in high-doped Si and low-doped Si in a silicon wafer, and it can be seen that the difference in absorption rate is the largest in the terahertz wave region. As can be seen in FIG. 6, the terahertz wave has a characteristic in that the absorption rate is greatly changed according to the doping concentration of an epitaxial layer doped on a silicon wafer, and thus the doping concentration (electric conductivity) can be measured with high sensitivity.

The present invention analyzes the reflected wave using the fact that the terahertz wave is irradiated to the epi wafer sample, and the reflected wave is changed according to the physical properties of the epi layer and the substrate layer, and the properties of the interface, so that the thickness and physical properties of the epi layer (thin film) are analyzed. Provided is a method and apparatus capable of simultaneously measuring (electric conductivity, doping concentration, resistance).

A thin film measuring apparatus based on terahertz wave spectroscopy technology according to an embodiment of the present invention includes: a terahertz wave generator for generating terahertz waves; An optical system for irradiating terahertz waves to a thin film sample and condensing the reflected waves; A terahertz wave detector that senses the terahertz wave reflected from the thin film sample; A spectroscopic analyzer that converts the detector signal into a frequency domain; And a Drude model calculation device for deriving the thickness and doping concentration of the thin film from the spectrometer data. The terahertz wave is characterized in that it is a broadband pulse.

7 is a schematic diagram of a thin film measuring apparatus based on terahertz wave spectroscopy technology of the present invention. Referring to FIG. 7, a terahertz wave generator 100, a first optical system 201 for irradiating terahertz waves generated from the terahertz wave generator as a sample, a precision stage capable of mounting a thin film sample and moving the XY axis ( 300), a second optical system 202 that guides the terahertz waves reflected by the sample to the detector, a detector 400 for detecting the reflected terahertz waves, and a signal detected by the detector to process the thin film. It includes a computing device 500 for calculating the thickness and physical properties.

The computing device 500 includes a spectroscopic analyzer that processes the terahertz wave reflected signal detected by the detector 400 and converts it into a frequency domain; And a Drude model calculator that calculates the thickness and doping concentration of the thin film from the frequency data derived by the spectrometer.

Hereinafter, the structure and operation method of each component will be described in detail.

The terahertz wave generator 100 includes a femtosecond pulse laser source, a photoconductor responsive to the femtosecond pulse light source, and optical rectification, as shown in FIGS. 7 and 8. ) Is a device that generates terahertz waves using a method. According to FIG. 8, a femtosecond pulse is irradiated to a terahertz emitter including a photoconductive antenna (PCA), and then a terahertz wave pulse is generated.

Meanwhile, according to FIG. 7, the femtosecond pulse from the femtosecond pulse light source is branched by a beam splitter, some of which are guided to a detector, functioning as a probe beam, and the other part through a delay stage through terahertz. It is irradiated to the emitter (THz emitter) and functions as a pump light for generating terahertz wave pulses. The terahertz wave pulse generated in the terahertz emitter by the femtosecond pulse is focused by the first optical system 201, irradiated to a specific location of the sample, and reflected by the upper and lower interfaces of the epi layer, and then by the second optical system 202. Guided to the detector 400, the intensity of the reflected light is detected. The probe beam reaches the detector prior to the terahertz wave reflected by the sample, and serves to set a reference point for terahertz wave detection.

10 is a diagram schematically showing the behavior of incident and reflected waves of a terahertz wave pulse in an epi layer. According to FIG. 10, the terahertz wave pulse from the terahertz wave generator 100 is irradiated to the sample, and transmits the first reflected wave (reflectance R ₁₂ ) reflected from the sample surface, that is, the upper surface of the epi layer, and the epi layer. After that, the second reflected wave (reflectance R ₂₃ ) reflected from the interface between the epi layer and the primary growth layer is overlapped to form the entire reflected wave (final reflectance R ₁₂₃ ). The second optical system 202 focuses the reflected terahertz wave (total reflected wave) on the sample to the detector 400, and the detector measures the intensity of the reflected wave.

When the thickness of the epi layer is as thin as several μm, the first reflected wave and the second reflected wave are not clearly separated in time and are detected with little time difference as shown in FIG. 11. Therefore, when using the conventional technique of calculating the thickness of the epi layer by identifying the time difference between the first and second reflected waves, the accuracy decreases when the thickness of the thin film is thin.

Therefore, there is a need for a method for obtaining film thickness and doping concentration from reflected wave waveforms that are not distinguished in the time axis. In the present invention, the difference between the simulated value using the Drude model and the actually detected reflected wave is quantified using a least square method, The film thickness and the doping concentration are obtained by taking a simulation value in which the difference is within a certain error.

12 shows Equations 1 to 3 of reflectance by Fresnel's equation and Equations 4 and 5 for obtaining physical properties by applying a Drude Model to a thin film layer. Reflectance R ₁₂₃ may be calculated by simulation using the equation of FIG. 12.

Referring to FIG. 12 in detail, in a structure having a low doped epi-layer (P-) layer (epi layer) on a high doped substrate (P+), which is a primary growth layer, the final reflectance of incident THz wave R ₁₂₃ Reflects the reflectance R ₁₂ of the first reflected wave reflected from the surface of the epi layer and the reflectance R ₂₃ of the second reflected wave reflected from the interface with the primary growth layer after passing through the epi layer and ?? _It is determined by the following equation (1) according to the relationship of ₂ .

(1)

(One)

(1-1)

(1-1)

는 2차 성장층(에피층)의 복소굴절율,

는 파장이고,

이고,

는 테라헤르츠파 펄스의 에피층(박막)으로의 입사각이다(도 10 참조). to be. Here, d is the thickness of the thin film (secondary growth layer),

Is the complex refractive index of the secondary growth layer (epi layer),

Is the wavelength,

ego,

Is the angle of incidence of the terahertz wave pulse to the epi layer (thin film) (see FIG. 10).

The following equation (1-1-1) can be derived from equation (1-1) in FIG. 12 using Snell's law of refraction and the law of trigonometric functions.

식 (1-1-1)

Equation (1-1-1)

On the other hand, the reflectance R ₁₂ can be represented by Equation (2) and the reflectance R ₂₃ by Equation (3), and the derivation of this equation is derived by applying Snell's law and trigonometric law to Fesnel's equation.

, 하부의 기판층의 복소굴절율

에 의해 결정됨을 알 수 있다.According to equations (1) to (3), the reflectance R ₁₂₃ is the incident angle θ ₁ , the refractive index n1 in vacuum, and the complex refractive index of the upper thin film to be measured.

, Complex refractive index of the underlying substrate layer

It can be seen that is determined by.

,

에 의해 R₁₂₃는 결정되는데, 이는 도 13에 기재된 Drude Model에 의해 산출된다.Since the angle of incidence and the refractive index in the vacuum are fixed, the complex refractive index

,

R ₁₂₃ is determined by, which is calculated by the Drude Model described in FIG. 13.

의 경우, 도 13에 기재된 Drude Model에 의하면, 2차 성장층의 복소굴절율(

)은 다음의 식 (4)와 같다.

In the case of, according to the Drude Model described in Figure 13, the complex refractive index of the secondary growth layer (

) Is as in the following equation (4).

Here, N _A is the doping concentration of the epi layer (secondary growth layer), ω is the angular frequency,

ρ _DC is the resistivity, ω _p is the plasma frequency, _ε0 is the dielectric constant in vacuum, m _eff is the effective mass of the charge carrier, ν is the collision frequency, and e is the electron charge. Other values are input, but N _A is arbitrarily set for simulation, which will be described later.

에 대해서도 동일한 식이 적용될 수 있고, 다만 각 값이 달라질 뿐이다. 즉, 1차 성장층(기판층)의 도핑 농도, 비저항, 플라즈마 주파수 등이 변수가 된다.

는 알려진 수치(상수값)와 기판층의 도핑농도를 입력하여 산출할 수 있다. 다만, 그 값을 확보하지 못한 경우 시뮬레이션 값으로 같이 넣어 산출되는 것도 고려될 수 있다. Complex refractive index of the substrate as the primary growth layer

The same equation can be applied to, but each value is only different. That is, the doping concentration, specific resistance, plasma frequency, etc. of the primary growth layer (substrate layer) are variables.

Can be calculated by inputting a known value (constant value) and the doping concentration of the substrate layer. However, if the value is not secured, it may be considered to be calculated by putting it as a simulation value.

는 Drude Model에 의해 도핑 농도 N_A에 의존하므로, d와 N_A를 가정하면 복소 함수로 반사율이 계산될 수 있다. 그러므로 Drude 모델에 의한 도핑 농도와, 막 두께를 가정하여 상기 식 1, 1-1-1, 2, 3, 4, 5를 이용한 시뮬레이션에 의해 반사율 스펙트럼을 산출할 수 있다. As can be seen in FIG. 12, the film thickness d of the epi layer is included in Equations 1 to 3 for obtaining the reflectance, and the complex refractive index of the thin film

Is dependent on the doping concentration N _A by the Drude Model, so assuming d and N _{A the} reflectance can be calculated as a complex function. Therefore, assuming the doping concentration and film thickness by the Drude model, the reflectance spectrum can be calculated by simulation using Equations 1, 1-1-1, 2, 3, 4, and 5 above.

On the other hand, the reflectance R ₁₂₃ is the reflectance of the entire terahertz reflected wave in which the first and second reflected waves are overlapped. The value detected by the detector is the intensity of the reflected wave that is not normalized, so the reflectance R ₁₂₃ = (measurement The reflected wave intensity of the sample)/(reflected wave intensity of the reference sample) is required as a reference. The intensity of the reflected wave as a reference is measured using a reference sample wafer. The reference sample is measured using a terahertz wave measuring device of the present invention for a wafer having a surface coated with a complete reflector, for example, gold.

The terahertz reflected wave detection value detected by the detector 400 is transmitted to the computing device 500, and the computing device 500 processes the terahertz wave signal reflected from the epi wafer sample to epitaxial the epi wafer from the above principle. Calculate the physical quantity of the layer.

After transforming into a frequency domain value by FFT (fast Fourier transformation) and dividing it into a reference signal and normalizing it, the reflectance for each frequency R ₁₂₃ is calculated. Here, the reference signal is obtained by converting the reflected wave intensity of the reference sample into a frequency domain value by fast Fourier transformation (FFT). The blue curve of FIG. 15 shows the reflectance spectrum (R ₁₂₃ ) for each frequency calculated by normalizing in this way.

14 is a flowchart in which the computing device 500 calculates the film thickness d and the doping concentration N _A using a Drude Model. Referring to FIG. 14, a method in which the computing device 500 calculates a film thickness d and a doping concentration N _A using a Drude Model includes: obtaining a terahertz reflected wave signal detected by a detector; Processing the acquired reflected wave signal by Fast Fourier Transformation (FFT); A normalization step of calculating the measured reflectance of the sample by dividing the signal converted by the FFT by a reference signal (the value of the reflected wave intensity of the separately detected reference sample FFT processed); And calculating the physical quantity of the sample by a least squares method by comparing the measured reflectance of the calculated sample with a simulation value Rs by the Drude Model.

The step of calculating the physical quantity of the sample by the least squares method includes: setting the film thickness d and the doping concentration N _A ; Calculating the simulated reflectance (Rs) by substituting the set film thickness d and the doping concentration N _A into the Drude Model, and calculating the least square method calculation value R ² by the difference between R ₁₂₃ and Rs; Checking whether the calculated value R ² by the least squares method is smaller than a reference value that is a predetermined error; And if the calculated value R ² is smaller than the reference value, which is a predetermined error, determining the set film thickness d and the doping concentration N _A as the film thickness d of the sample and the doping concentration N _A and ending the calculation. If the calculated value R ² is greater than or equal to a predetermined error, the step of calculating the physical quantity of the sample by the least squares method is repeated until a value smaller than the reference value is obtained.

_A method of calculating the film thickness d and the doping concentration N _A using the above-described Drude Model will be described in detail step by step with reference to FIG. 14.

First, the computing device 500 acquires the terahertz reflected wave signal detected by the detector. The detector detects terahertz reflected waves as electrical signals. The detected signal waveform represents reflected wave intensity in the time domain.

The spectrometer included in the computing device 100 converts the obtained reflected wave signal into a frequency domain signal by processing Fast Fourier Transformation (FFT). This FFT is performed by a spectroscopic analyzer, but may be performed by a single computing device without a separate spectroscopic analyzer. That is, the terahertz wave pulse is a broadband, and includes various frequency components, but the center frequency belongs to the terahertz region. The terahertz wave pulses irradiated to the epi layer are partially absorbed and reflected by the epi layer, but the absorption rate varies depending on the frequency component. The doping concentration/resistivity, which is the absorption factor for each frequency, is finally reflected in the reflectance for each frequency in the Drude Model, and the film thickness d is also? By reflectance.

In order to calculate the reflectance of the sample, the measured reflectance spectrum R ₁₂₃ is calculated through a normalization step of dividing the Fourier transformed reflected wave signal into a reference signal (a value obtained by performing FFT on the reflected light intensity of the reference sample) for each frequency.

Next, the random value d and the doping concentration N _A are substituted into the Drude Model to calculate the simulation value Rs of the reflectance, and the difference between R ₁₂₃ and Rs is calculated according to the least squares method, and the calculated value R ² by the least squares method. Iterative calculation is performed while changing film thickness d and doping concentration N _A until is within a predetermined error range. The process by the least squares method is a process performed by changing the variable value in order to find the variable value where the calculated value R ² is the minimum.

When the calculated result R ² falls within a predetermined error range, the film thickness d and the doping concentration N _A at that time are calculated as the film thickness and the doping concentration of the sample, and the calculation ends.

15 is a graph showing the measured value (R _123, blue) of the reflectance by frequency (horizontal axis), the simulation value (Rs, red) by the Drude Model, and the difference (green) between the two values. The graph shown in red is a simulated reflectance (Rs) calculated by substituting the film thickness d and the doping concentration N _A set by the calculator into the Drude Model (see equations 1 to 3 in FIG. 12).

Throughout this specification, Rs refers to a simulated reflectance in which R ₁₂₃ is calculated by Equation 1 of FIG. 12 based on the Drude model.

After calculating the thickness and the doping concentration of the thin film measured by the method and apparatus of the present invention, the specific resistance and electrical conductivity are simply calculated from the doping concentration based on the relationship of FIG. 4 showing the correlation between the doping concentration and the resistivity. can do.

As described above, the thin film thickness and physical property (doped concentration, electrical conductivity) measurement device based on the terahertz wave spectroscopy technology of the present invention can simultaneously measure the thickness and physical properties of the thin film by a single device, thereby saving space occupied by equipment. It is possible to measure physical quantity in a short time by detecting and calculating terahertz wave reflected light.

The precision stage on which the sample is mounted is capable of two-dimensional precision movement in the XY axis, so that the thickness and physical properties of the thin film can be measured in a non-contact manner in a short time on the entire surface of the epi wafer. That is, it can be used as an in-situ monitoring instrument for film-forming equipment such as CVD and ALD, thereby improving the quality control of the thin film manufacturing process. Hereinafter, using the method and apparatus of the present invention, the epilayer thickness and doping concentration of the actual epiwafer were measured.

16 to 17 show the process and results of measuring the physical quantity of the epiwafer using the method and apparatus for measuring the physical quantity of the thin film based on the terahertz wave spectroscopy technology of the present invention. 16 shows the measurement points and specifications of the epi-wafer to be measured. The upper table is the thickness and the doping concentration respectively measured by a method such as FTIR, CV, etc., and the lower right table is a value measured by the method of the present invention.

FIG. 17 is a constant value for obtaining ε by the Drude Model to calculate reflectance.

FIG. 18 is a graph showing the calculated value R ² by the least square method of the measured value and the calculated reflectance in order to compare and measure the simulation value and the measured value. The thickness and concentration of the epi layer calculated using the graph of FIG. 18 are as shown in the table of FIG. 19. 19 is a table showing values measured using other equipment and thicknesses and doping concentrations of epilayers calculated using the method and apparatus of the present invention.

As can be seen from the table, it can be confirmed that while measuring two physical quantities simultaneously, the measured values and errors by other equipment are very small.

The apparatus and method of the present invention can measure physical quantities such as graphene, ITO, solar cell, and secondary battery film as well as epi wafers.

In addition, the present invention can precisely measure the properties of thin films thinner than the wavelength of terahertz waves by using a measurement algorithm based on the Drude model.

The terahertz wave-based thin film measuring apparatus according to an embodiment of the present invention includes a dry chamber to prevent terahertz waves from being absorbed by water vapor in the atmosphere and deteriorating measurement accuracy, and optical systems are placed in the drying chamber. Can be installed.

In addition, ionizing waves such as X-Ray can affect atomic units in addition to thermal reactions to test samples, but terahertz waves are non-ionizing waves, so samples are tested at low energy levels. It has a very big advantage to do.

The above description of the present invention is for illustration only, and those skilled in the art to which the present invention pertains can understand that it can be easily modified to other specific forms without changing the technical spirit or essential features of the present invention. will be. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive. For example, each component described as a single type may be implemented in a distributed manner, and similarly, components described as distributed may be implemented in a combined form.

The scope of the present invention is indicated by the following claims rather than the above detailed description, and it should be interpreted that all changes or modified forms derived from the meaning and scope of the claims and equivalent concepts thereof are included in the scope of the present invention. do.

Claims (10)

A thin film measuring device for measuring the physical quantity of a thin film,
A terahertz wave generator that generates a terahertz wave pulse;
A precision stage that mounts the sample on which the thin film is formed;
A detector that detects terahertz waves reflected by the sample; And
Includes; a computing device for processing the signal detected by the detector,
The computing device calculates the physical quantity of the thin film by calculating the simulated reflectance to approximate the measured reflectance of the thin film calculated from the detected signal,
The simulation reflectance is calculated by assuming the film thickness and doping concentration of the thin film,
The physical quantity of the thin film is calculated based on the film thickness and the doping concentration when the difference between the simulated reflectance and the measured reflectance of the thin film is smaller than the reference value.
According to claim 1,
The optical system for focusing the terahertz wave to irradiate the thin film sample and guiding the terahertz wave reflected from the thin film sample to the detector.
The computing device sets the film thickness and doping concentration of the thin film, calculates the simulation reflectance by substituting the set film thickness and doping concentration into the Drude Model, and sets the film thickness when the difference between the simulated reflectance and the measured reflectance is less than the reference value. And a doping concentration is determined by a film thickness and a doping concentration of the thin film.
According to claim 1,
The arithmetic unit divides the detected terahertz wave signal into a reference signal after FFT (fast Fourier transformation) conversion and normalizes to calculate the measured reflectance spectrum of the thin film, and reflects the spectra by Drude Model to approximate the measured reflectance spectrum. A thin film measuring device that calculates the physical quantity of a thin film by simulating (Rs).
According to claim 1,
The terahertz wave is a broadband pulse having a center frequency of 1 to 100 terahertz,
The thin film measuring device, characterized in that the physical quantity of the thin film is at least one of the thickness, doping concentration, electrical conductivity, and resistivity of the thin film.
According to claim 1,
The computing device is a thin film measuring device characterized in that to quantify the difference between the simulated reflectivity and the actual reflectance of the thin film.
Terahertz wave generator, a precision stage for mounting a thin film sample, a thin film measuring device using a thin film measuring device including a detector for detecting the reflected terahertz wave irradiated on the thin film sample and a signal processing device detected by the detector As a method of measuring the physical quantity,
A terahertz wave generator generating a broadband terahertz pulse;
Irradiating the terahertz pulse to a thin film sample;
A detector detecting terahertz reflected waves reflected by the thin film sample; And
Including; calculating the physical quantity of the thin film by calculating a simulation reflectance to approximate the measured reflectance calculated from the terahertz reflected wave;
The simulation reflectance is calculated by assuming the film thickness and doping concentration of the thin film,
The physical quantity of the thin film is calculated based on the film thickness and the doping concentration when the difference between the simulated reflectance and the measured reflectance of the thin film is smaller than the reference value.
The method of claim 6,
The step of calculating the physical quantity of the thin film,
Setting a film thickness d and a doping concentration N _A of the thin film;
Calculating the simulated reflectance spectrum (Rs) by substituting the set film thickness d and the doping concentration N _A ; And
Characterized by including; simulated reflectance spectrum determining (Rs) and the measured spectral reflectance film thickness d and the doping concentration N _A the difference value is less than the reference value set to the film thickness d and the doping concentration N _A of the film Thin film measurement method.
The method of claim 6,
The step of calculating the physical quantity of the thin film,
Fourier transforming the detected terahertz reflected wave;
A normalization step of dividing the Fourier transformed terahertz reflected wave into a reference signal to calculate a measured reflectance spectrum of the thin film; And
And simulating a reflectance spectrum (Rs) by a Drude Model to approximate the measured reflectance spectrum.
The method of claim 8,
The step of simulating the reflectance spectrum (Rs),
Setting a film thickness d and a doping concentration N _A ;
Calculating the simulated reflectance spectrum (Rs) by substituting the set film thickness d and the doping concentration N _A into the Drude Model;
Quantifying a difference between a simulated reflectance spectrum (Rs) and the measured reflectance spectrum;
Performing the iterative calculation while changing the film thickness d and the doping concentration N _A so that the quantified difference value is equal to or less than the reference value; And
Thin film measurement methods comprising the; comprising: if the difference value is smaller than the reference value determines a film thickness d and the doping concentration N _A is set to a film thickness d and the doping concentration N _A of the sample and exit the calculation.
The method of claim 9,
The quantification step is a method for measuring a thin film, characterized in that the simulated reflectance spectrum (Rs) and the measured reflectance spectrum by the Drude Model are quantified by a least square method.

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