KR20200126550A - Continuously measurable spectroscopic ellipsometer - Google Patents

Abstract

The present invention relates to a continuous-measurement spectroscopic ellipsometer capable of continuously acquiring a spectroscopic ellipsometry coefficient by continuously generating a pulse signal at a predetermined angle while continuously rotating a polarization generating module or an analyzer module, and continuously acquiring the amount of reflected light at each rotation angle. To this end, according to the present invention, the continuous-measurement spectroscopic ellipsometer for measuring characteristics of a sample by using a rotation angle of light, which is incident on or reflected from a surface of the sample, and the amount of reflected light includes: a light source configured to generate light; a polarization control module configured to polarize the light generated from the light source; an analyzer module configured to detect a polarization state of the light reflected from the surface of the sample; a rotation module configured to continuously rotate the polarization control module or the analyzer module at a predetermined speed; a photodetector configured to operate within a predetermined exposure time according to an external trigger signal to measure the amount of the light passing through the analyzer module; and a trigger generation module configured to generate a pulse signal having a predetermined angle according to the rotation of the polarization control module or the analyzer module to transmit the generated pulse signal to the photodetector as the external trigger signal.

Description

Spectroscopic ellipsometer capable of continuous measurement {CONTINUOUSLY MEASURABLE SPECTROSCOPIC ELLIPSOMETER}

The present invention relates to a spectroscopic ellipsometer, wherein the spectral ellipse coefficient can be continuously obtained by continuously obtaining a rotation angle of a polarization module and an amount of reflected light at each rotation angle while continuously rotating a polarization module. It is about the system.

Ellipsometry is variously used as a non-destructive measurement method in the industrial field using various thin films, and is particularly useful in non-destructively measuring the thickness of a thin film in the semiconductor field.

Ellipsometry is a method of measuring and analyzing the changed polarization state of the reflected light after incident light having a specific polarization state on a sample to determine the change in density, optical thickness, and complex orange index, which are the factors that changed the polarization. As, the device for this is called an elliptic system.

1 is a configuration diagram showing a conventional elliptic system, which generally includes a light source 10, a polarization generating module 20, an analyzer module 50, and a photo detector 60.

In addition, the conventional ellipsometer may further include focusing optical modules 30 and 40 that focus incident light incident on the sample S or reflected light reflected from the sample S, and each time a driving pulse is applied It includes motors 70 and 80 that rotate by an angle to rotate the polarization generating module 20 and the analyzer module 50 by unit angle.

According to this configuration, light generated from the light source 10 is incident on the sample S in a polarization-controlled state by the light generating module 20, and the light reflected from the sample S is incident on the analyzer module 50. Thus, the analyzer module 50 detects the polarization state, and the light that has passed through the analyzer module 50 is incident on the photo detector 60 to measure the intensity of the incident light as an electrical signal such as voltage or current. do.

These ellipses are classified into short-wavelength ellipsimeters and spectroscopic ellipsimeters according to the type of light source or the number of wavelengths used.

Short-wavelength ellipsometers mainly use light sources with one characteristic wavelength such as He-Ne lasers, and have a measurement speed of several ps to tens of ms, so they can be used in fields such as thin film deposition, etching, and heat treatment that require fast measurement. It is easy, but the refractive index of the material must be known in advance, and there is a problem that it cannot be applied to a multilayer thin film sample.

On the other hand, the spectroscopic ellipsometer uses a continuous wavelength band from ultraviolet (UV) to near infrared (NIR) using a white light source. Accordingly, since spectroscopy is performed using a spectrograph or a monochromator to obtain an elliptic constant in a wide wavelength band, the measurement speed is from several tens of seconds to several minutes.

In the process of applying a spectroscopic ellipsometer to analyze thin films in recent years, the use of spectroscopic ellipsometers is increasing to obtain measurement precision as well as the measurement speed, so a technique to increase the measurement speed of the spectroscopic ellipsometer is required. have.

In particular, since the semiconductor process requires a measurement speed of several seconds, efforts are being made to reduce the measurement speed of the spectroscopic ellipsometer.

In the case of a short-wavelength ellipsometer, the structure is simple because a light source having a specific wavelength such as a laser is used, and the measurement speed is fast because an elliptic constant of one wavelength is obtained. In general, the measurement speed of a short-wavelength ellipsometer has a speed of several ps to tens of ms because the rotation speed of the driving module of the analyzer module used to measure polarization or the reaction speed of the photo detector is determined.

To calculate the elliptic constant in the elliptic system, the amount of light detected by the photodetector and the rotation angle information of the analyzer module are used as shown in [Equation 1].

[Equation 1]

In the case of a short wavelength ellipsometer capable of high-speed measurement, information on the rotation angle can be obtained by connecting the encoder and the rotation module.

On the other hand, in the case of a spectroscopic ellipsometer, it is difficult to continuously rotate because the time to obtain the spectral light amount information for an angle is tens of ms to several seconds, so the light amount is measured after rotating the analyzer module at a certain angle and then rotating it again. Repeat the measurement process.

For this reason, since the measurement takes about tens of seconds, a method of obtaining an accurate rotation angle while enabling continuous rotation measurement is required.

In addition, in order to rotate the analyzer module at a certain angle, the step motor is repeatedly rotated and stopped at a certain angle. Therefore, acceleration/deceleration time for stopping and driving is required, making rapid rotation difficult as well as repeating stopping and driving. Therefore, it takes a long time to measure.

Korean Patent Registration No. 0992839 "Micro Spot Spectroscopy" Korean Patent Registration No. 11761251 "spectral ellipse analyzer" Korean Patent Registration No. 1949109 "Reconfigurable Spectral Ellipsometer"

An object of the present invention for solving the disadvantages of the background art is to continuously rotate a polarization generating module or an analyzer module to continuously generate a pulse signal at a certain angle, and to continuously acquire the reflected light amount at each rotation angle to obtain a spectral ellipse. It is to provide a spectroscopic ellipsometer capable of continuously measuring the coefficients that can be obtained continuously.

In order to solve the problem, the continuous measurable spectroscopic ellipsometer of the present invention is a spectroscopic ellipsometer that measures the characteristics of a sample using a rotation angle of light incident or reflected to the surface of a sample and an amount of reflected light. A polarization control module that polarizes the light generated from; An analyzer module for detecting a polarization state of light reflected from the sample surface or a rotation module for continuously rotating the polarization control module or the analyzer module at a constant speed; An external trigger to the photodetector by generating a pulse signal at a certain angle according to the rotation of the polarization control module or the polarization control module or the photodetector module, which operates according to a predetermined exposure time according to the external trigger signal and measures the amount of light that has passed through the analyzer module. It includes a trigger generation module that transmits a signal.

At this time, the trigger generation module includes an encoder that continuously rotates in synchronization with a polarizer module or an analyzer module and generates a pulse signal for measuring the amount of reflected light at regular intervals, and a control circuit that controls the pulse generation cycle and number of the encoder. I can.

Here, the control circuit may divide a pulse signal of equal intervals generated during one rotation of the encoder by 1/N at a set ratio and output it to the photo detector.

Alternatively, the trigger generation module continuously rotates by the motor drive and detects the disk and each tooth shape of the disk in which the number of teeth corresponding to the number of pulses generated on the outer circumferential direction is arranged in the circumferential direction, and generates a pulse signal every time the shape of the teeth is detected. It may include a photogate to generate.

According to the present invention, it is possible to significantly reduce the measurement time in the non-destructive measurement field by continuously obtaining the amount of reflected light at each rotation angle.

1 is a block diagram showing a conventional elliptic system.
2 is a configuration diagram of a spectroscopic ellipsometer capable of continuously measuring according to an embodiment of the present invention.
3 is a timing diagram of a control signal according to an embodiment of the present invention.
4 is a block diagram of a control circuit according to an embodiment of the present invention.
5 is a configuration diagram of a spectroscopic ellipsometer capable of continuous measurement according to another embodiment of the present invention.
6 is a configuration diagram of a trigger generation module of FIG. 5.

Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

2 is a configuration diagram of a spectroscopic ellipsometer capable of continuously measuring according to an embodiment of the present invention, and relates to a spectroscopic ellipsometer for measuring characteristics of a sample using a rotation angle of light incident or reflected to a surface of a sample and an amount of reflected light.

For this purpose, the continuously measurable spectroscopic ellipsometer of the present invention includes a light source 100, a polarization control module 200, an analyzer module 300, a trigger generation module 400, and a photo detector 500.

In addition, the spectroscopic ellipsometer capable of continuously measuring according to an embodiment of the present invention may further include focusing optical modules 600 and 700 focusing incident light incident on the sample S or reflected light reflected from the sample S. have.

The light source 100 is a light generating device irradiated to the sample S, and generates light in various wavelength bands from deep ultra violet (DUV) to near infrared rays.

The polarization control module 200 is disposed between the light source 100 and the sample, and polarizes the light generated from the light source 100 in a controlled polarization state. That is, since the light generated from the light source 100 generally appears as non-polarized light that cannot be expressed in a specific polarization state, the polarization control module 200 passes the light generated from the light source 100 to measure light controlled in a specific polarization state Polarized.

The sample S receives the polarization-controlled light and changes the polarization state according to optical characteristics. That is, the measurement light incident on the surface of the sample S reflects polarized light modified according to optical and structural characteristics such as refractive index and thickness of the sample.

The analyzer module 300 is disposed on a reflection path of light, and detects a change in a polarization state of light reflected from the sample surface.

Each of the motors 202 and 302 connected to the polarizer module 200 and the analyzer module 300 is selectively driven to continuously rotate any one of the polarizer module 200 and the checker module 300 at a constant speed. Let it.

Trigger generation module 400 is shown to be connected to the polarization control module 200 in the drawings of the embodiment of the present invention, but generates a pulse signal of a certain angle according to the rotation of the polarization control module 200 or the analyzer module 300 Thus, it is configured to transmit to the photodetector 500 as an external trigger signal.

The photo detector 500 measures the amount of light that has passed through the analyzer module by operating in accordance with a predetermined exposure time according to an external trigger signal received from the trigger generation module 400.

The trigger generation module 400 according to an embodiment of the present invention includes an encoder 402 and a control circuit 404.

The encoder 402 continuously rotates together with the polarization control module 200 or the analyzer module 300 and generates a pulse signal for measuring the amount of reflected light at regular intervals.

In the case of the encoder 402, more pulses are generated than necessary, and the pulse interval may be narrower than the exposure time of the amount of light that can be obtained from the spectrometer.

Accordingly, the control circuit 404 controls the period and number of times of pulse generation of the encoder 402 or the measurement period and number of times of measuring the amount of reflected light of the analyzer module.

Specifically, the encoder 402 generates a continuous pulse signal as shown in FIG. 3A, and the control circuit 404 generates a short period output from the encoder 402 as shown in FIG. 3B. A plurality of pulse signals are generated as a trigger signal of a long period.

That is, the control circuit 404 generates an external trigger signal by calculating the N encoder signals to be one trigger signal using an internal operation circuit according to the detection time period of the photo detector 500.

Exemplarily, the control circuit 404 bundles the eight pulse signals shown in Fig. 3(a) and generates one trigger signal as shown in Fig. 3(b) in order to obtain a desired exposure time of the amount of light. Can be reduced to 1/8.

Accordingly, the analyzer module 300 detects a change in the polarization state of the light reflected from the surface of the sample at each generation period of the external trigger signal generated by the control circuit 404, and the photodetector 500 is shown in 3(c). As described above, it operates according to the predetermined exposure time to measure the amount of light that has passed through the analyzer module 300.

As described above, in an embodiment of the present invention, the control circuit 404 generates a pulse signal of a plurality of units periodically generated by the encoder 402 as a single pulse signal in a bundle, and outputs the pulse signal to the photo detector 500. 404), for example, it can be reduced to 1/2, 1/4, 1/8, 1/16.

The control circuit 404 for this is composed of a buffer TTL 404a, a flip-flop TTL 404b, a NAND TTL 404c, and a division TTL 404d, as shown in FIG. 4.

The buffer TTL 404a serves to protect the entire control circuit and invert the high/low state of the signal when a high voltage signal is momentarily inputted along the pulse signal line coming from the encoder 402 (see FIG. 2).

The signal generated by the encoder 402 (refer to FIG. 2) includes a continuous pulse having a constant interval according to the rotation angle and a Tz signal that occurs once per rotation, of which the signal is transmitted to the flip-flop TTL 404b. .

The flip-flop TTL 404b receives a preparation signal for measurement from a computer or a controller and opens the gate when a Tz signal is received, and then emits a high signal, and inputs the emitted high signal to the NAND TTL 402c.

At this time, the pulse of the encoder 402 (refer to FIG. 2) occurs continuously during rotation and arrives at the NAND TTL 402c. Cannot pass.

On the other hand, when the high signal of the flip-flop TTL 404b operated by the Tz signal arrives, it is operated from this point and the continuous pulse of (402, see FIG. 2) can pass through the NAND TTL 402c.

Subsequently, the continuous pulse arriving at the divided TTL 402d is divided into 1/2, 1/4, 1/8, 1/16, etc. according to the setting of the divided TTL 402d to generate a continuous pulse. This divided signal is again input to the photodetector 500 (refer to FIG. 2) by an external trigger as shown in FIG. 3B.

In an embodiment of the present invention, the control circuit 404 is shown to be connected between the encoder 402 and the photodetector 500, but the control circuit 404 is between the analyzer module 300 and the photodetector 500. It can also be connected to.

As described above, according to an embodiment of the present invention, there is an advantage of shortening the measurement time compared to a configuration in which rotational driving and stopping of a polarizer module is repeated based on a pulse signal generated from an encoder according to a predetermined rotation angle. .

That is, according to an exemplary embodiment of the present invention, the measurement time can be shortened by periodically measuring the amount of light while continuously rotating the polarizer module at a constant speed.

In addition, as the rotation angle for calculating the spectral elliptic constant corresponds to a preset pulse period, the rotation angle can be accurately obtained, thereby securing the precision of the spectral elliptic constant.

5 is a configuration diagram of a spectroscopic ellipsometer capable of continuously measuring according to another embodiment of the present invention, and FIG. 6 is an exemplary view of the trigger generation module of FIG. It should be omitted.

5 and 6, a trigger generating module 800 according to another exemplary embodiment of the present invention includes an original plate 802 and a photogate 804.

The disk 802 is continuously rotated by motor driving, and a number of teeth corresponding to the number of pulse generations is arranged in the circumferential direction on the outer peripheral surface.

The photogate 804 detects each sawtooth shape of the original plate, generates a pulse signal each time the sawtooth shape is detected, and outputs it to the photodetector 500.

That is, in another embodiment of the present invention, a sawtooth shape is formed on the disk according to the number of desired light quantity measurements, and each time the sawtooth passes through the photogate 804, the photogate 804 detects it and transmits a pulse signal to the photodetector ( 500).

Accordingly, the photodetector 500 is triggered by the pulse signal of the photogate 804 to measure the amount of light incident on the analyzer polarizer module 300 200 rotating in the sample S.

Although the present invention has been described in connection with the above-mentioned preferred embodiments, it is possible to make various modifications or variations without departing from the spirit and scope of the invention. Accordingly, the scope of the appended claims will include such modifications or variations that fall within the gist of the present invention.

100: light source 200: polarization control module
202, 302: motor 300: analyzer module
400, 800: trigger generation module 402: encoder
404: control circuit 404a: buffer TTL
404b: flip-flop TTL 404c: NAND TTL
404d: division TTL 500: photo detector
600, 700: focusing optical module 802: original plate
804: photogate

Claims (4)

In a spectroscopic ellipsometer that measures the characteristics of a sample by using the rotation angle of light incident or reflected to the surface of the sample and the amount of reflected light,
A light source that generates light;
A polarization control module that polarizes the light generated by the light source;
An analyzer module for detecting a polarization state of light reflected from the sample surface;
A rotation module continuously rotating the polarization control module or the analyzer module at a constant speed;
An optical detector that measures the amount of light that has passed through the analyzer module by operating according to a predetermined exposure time according to an external trigger signal, and
And a trigger generation module that generates a pulse signal of a certain angle according to the rotation of the polarization control module or the analyzer module and transmits it to the photodetector as an external trigger signal.
The method of claim 1,
The trigger generation module
An encoder that continuously rotates in synchronization with the continuously rotating polarizer module or analyzer module and generates a pulse signal for measuring the amount of reflected light at regular intervals,
And a control circuit for controlling the pulse generation period and the number of times of the encoder.
The method of claim 1,
The control circuit divides the pulse signal of equal intervals generated during one rotation of the encoder by 1/N at a set ratio and outputs the divided pulse signal to the photodetector.
The method of claim 1,
The trigger generation module
A disk continuously rotated by a motor driving and having a number of teeth corresponding to the number of pulse generations arranged in the circumferential direction on the outer peripheral surface;
And a photogate configured to detect each sawtooth shape of the disk and generate a pulse signal each time the sawtooth shape is detected.

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