KR20040046205A - Method of adjusting polarized light and measuring method of thickness of thin layer using the same - Google Patents

Abstract

PURPOSE: A method of adjusting polarized light and a method for measuring the thickness of a thin film using the same are provided to be capable of improving process reliability and exactness. CONSTITUTION: The first light obtained by carrying out the first polarization process for predetermined light is embodied(10). Whether the embodied first light generates line polarization, or not, is decided(20). The line polarization is generated by collimating the first light(30). Preferably, the predetermined light is HENE short wavelength laser beam, wherein the HENE short wavelength laser beam is generated by discharging the mixed gas of helium gas and neon gas. The embodiment of the first light is performed by measuring the voltage for the first light using a voltmeter.

Description

Polarization control method and thin film thickness measurement method using the same {METHOD OF ADJUSTING POLARIZED LIGHT AND MEASURING METHOD OF THICKNESS OF THIN LAYER USING THE SAME}

The present invention relates to a polarization control method and a thickness measurement method of a semiconductor device. More specifically, the present invention relates to a polarization control method through aiming a polarizing device and a method for measuring thin film thickness of a semiconductor device using the same.

As semiconductor devices become super-integrated, the thickness of thin films formed on semiconductor substrates becomes thinner and thinner, and there is a need for a thickness measurement method capable of accurately measuring the thickness of such thin films. Specifically, the thickness of the thin film formed in the semiconductor device is present in a variety of thickness from about 50 ㎛ to about 500 Å or less, and the thickness and composition analysis for the film quality that is repeatedly etched and deposited in such a range of thickness This should be done, the representative method used for the component analysis and thickness measurement is the method using an ellipsometer (ellipsometer).

Ellipsometer is one of special photometers. It is a precision measuring instrument used to study surface and thin film structure, physical properties, and material properties by measuring changes in polarization state of light. In other words, since ellipsometers use light, they have almost no limitations on the medium, so they can be measured in vacuum, air or even fluids. It has the advantage of not affecting the sample (nondestructive).

In addition, since ellipsometers measure two constants, amplitude and phase simultaneously, compared to general optical equipment that only depends on light intensity, such as reflectance and transmittance measurements, the two-phase sample consisting of medium and substrate alone is Kramers-Cro The refractive index (n), which is the real part of the complex refractive index of the base layer, and the extinction coefficient (k), which is the imaginary part, can be simultaneously determined without using the relationship between Kramers-Kronig, etc. Since the phase value reacts very sensitively to the oxide film or the surface layer, the atomic monolayer as well as the atomic partial coverage can be analyzed precisely.

As described above, since the polarization state of the reflected light or the transmitted light is sensitively changed depending on the physical properties and the structure of the sample, the information on the physical properties and the structure of the sample can be obtained by measuring and analyzing the change in the polarization state. It is widely used in thin film analysis including the measurement of thickness and thickness distribution.

The principle of such an elliptic analysis device will be described below with reference to the drawings. 1 is a schematic diagram showing a process of polarizing light in such an elliptical analysis device.

Referring to FIG. 1, light is polarized twice by two polarizers before reaching a sample such as a thin film. The two polarizers are a polarizer and a compensator. The polarizer is a polarizer that generates linearly polarized light, and the compensator is a polarizer that converts light passing through the polarizer into circularly polarized light. The light from these two polarizers is transmitted through the thin film to perform component analysis and thickness measurement.

Korean Patent Laid-Open Publication No. 10-2001-0107735 (published Dec. 7, 2001) discloses an elliptic analysis measurement method for a sample accommodated in a chamber or the like using the ellipsometer described above. Specifically, a method is described for completing an elliptic analysis measurement, for example, between two fabrication steps or at the end of one of the steps, without taking the sample out of the chamber to measure the physical properties of the sample. According to the above method, the measurement of physical properties in the chamber can be performed, thereby preventing contamination of the integrated circuit during fabrication and at the same time preventing contamination of the regulated air in the chamber.

In addition, Korean Patent Laid-Open Publication No. 10-2001-0022767 (published on March 26, 2001) includes a light source (or laser generator) for transmitting an entrance ray and a polarized entrance light for a substrate. And a receiving optical body having a transmission optical body leading to the point of incidence, and an analyzer for guiding a reflection ray formed at the measuring point to a photo receiver. The use of an ellipsometer describes an elliptic measuring device that can be easily adjusted and handled even where it is difficult to access, and can produce accurate measurement results even where different radii change.

However, the above-described inventions do not provide a solution to the problem caused by the aiming state of the polarizer in the evaluation of a semiconductor thin film requiring measurement of an ultra-fine thin film. In other words, each polarizer should be aimed so that the polarizer and the compensator of the polarizer generate the desired polarization. If the aim is wrong, an error of about 2 Å in measuring the thickness of the ultra-thin film of about 1 to 500 microseconds is wrong. May occur, and this measurement error affects the deterioration of the semiconductor device.

2A and 2B are graphs illustrating a phenomenon that occurs when a polarizer is misaligned.

Referring to FIGS. 2A and 2B, when the polarizer and the compensator are incorrectly aimed, the refractive index is hunted in the data of a certain level or more (FIG. 2A), or the refractive index is saturated in the data of the predetermined level or more (FIG. 2B). Is generated. Therefore, it is required to form a light that is difficult to observe visually and to determine whether the light passing through the polarization element is changed to a desired polarization state, and a polarization control method for aiming the polarization element and a thickness measurement method using the same.

Accordingly, a first object of the present invention is to provide a polarization control method capable of easily performing polarization aim by shaping polarization.

A second object of the present invention is to provide a method for measuring the thickness of a thin film using the polarization control method.

1 is a schematic diagram showing a process of polarizing light in an elliptical analysis device.

2A and 2B are graphs illustrating a phenomenon that occurs when a polarizer is misaligned.

3 is a flowchart illustrating a polarization control method according to a first embodiment of the present invention.

4A to 4D are graphs showing polarization states before and after aiming the polarizer.

5A and 5B are graphs showing polarization states before and after compensator aiming.

6 is a flowchart illustrating a thickness measuring method according to a second embodiment of the present invention.

In order to achieve the first object of the present invention described above, the present invention comprises the steps of shaping the first light obtained by the first polarized light, determining whether the shaped first light is linearly polarized, and the result of determining the linearly polarized light When the linearly polarized light is not generated, the method provides a polarization control method including aiming the first light to generate linearly polarized light.

As the light, a helium-neon (HENE) short wavelength laser is used, and the first polarized light is polarized by passing the light through a polarizer at phases of 0 to 90 ° and 180 to 270 ° to generate first light. The first light is shaped by measuring the voltage. And aiming of said 1st light is performed by rotating the polarizer drum of a polarizer.

In order to achieve the above-described second object of the present invention, the present invention comprises the steps of shaping the first light obtained by first polarizing the light, determining whether the shaped first light is linearly polarized, the linearly polarized light is determined as a result of the linearly polarized light Otherwise, aiming the first light to generate linearly polarized light, and transmitting the generated linearly polarized light to a sample to measure the thickness of the sample.

According to the present invention, it is possible to accurately measure the thickness of the thin film of the semiconductor device to improve the reliability and accuracy of the process.

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

3 is a flowchart illustrating a polarization control method according to a first embodiment of the present invention.

Referring to FIG. 3, a polarization control method according to an embodiment of the present invention includes a step 10 of shaping a first light obtained by first polarizing light.

As the light, it is preferable to use a helium-neon (HENE) short wavelength laser (λ = 633 nm) formed by discharging a mixed gas of helium gas and neon gas. According to the measuring principle of the instrument using a short wavelength laser, two types of light are inputted, one is linear polarization for measuring the thickness of a thick thin film and the other is circular polarization for measuring the thickness of an ultra-thin film of about 1000 mW or less.

First polarization is performed by passing such light through a polarizer at phases of 0 to 90 degrees and 180 to 270 degrees to generate first light. In the elliptic system in which the helium-neon short wavelength laser is used, circularly polarized light is generated, and the circularly polarized light is first polarized through a polarizer to be 45 ° compensated linearly polarized light. A portion of this linearly polarized light (phase 135 ° or less) is applied to a relatively thick sample of 1000 kPa to 50 μm to measure the correct thickness.

The shaping of the first light is performed by measuring the voltage with a voltmeter. In order to measure the thick thin film by inputting the first light passed through the polarizer to the sample, accurate linearly polarized light should be generated. However, since it is difficult to identify the light with the eyes, it is difficult to determine whether the light passed through the polarizer has changed to the desired linearly polarized light. There is a difficult problem. Therefore, it is necessary to shape the first light, which forms the light by applying a digital voltmeter to the ellipsometer.

Specifically, in the method of checking the polarization state of an ellipsometer, a digital voltmeter is connected to a photo diode output terminal jack of an ellipsometer, and the digital voltmeter is set to AV (VOLTAGE). Thereafter, while rotating the polarizer drum at intervals of 5 degrees by hand, the measured voltage is shown for each rotated interval.

Referring to FIG. 3, the polarization control method according to the first embodiment of the present invention includes a step 20 of determining whether the shaped first light is linearly polarized.

4A is a graph showing the polarization state before aiming the polarizer in which the first light is shaped.

Referring to FIG. 4A, a linearly polarized signal when light passing through a polarizer passes through an analyzer drum is shown for each phase. However, even with reference to FIG. 4A, the degree of distortion of the waveform cannot be accurately determined by the eye. Therefore, it is necessary to represent the same data in an analog form and determine the same.

Figure 4b is a graph showing the polarization state in analog form before aiming the polarizer.

Referring to Figure 4b, it can be seen that the distortion of the waveform occurred in the phase (D1) around 220 ° and 280 to 300 °. If there is such a distortion and linear polarization is not normally generated, there is a problem that the ellipsometer cannot accurately measure the thickness of the sample, and thus it is necessary to improve it.

Referring to FIG. 3, in the polarization control method according to the first exemplary embodiment of the present invention, when linear polarization is not generated as a result of the determination of linear polarization, the polarization control method includes aiming the first light to generate linear polarization 30.

When the linear polarization is not generated as a result of determining whether the linear polarization occurs, the linear polarizer is generated by aiming the polarizer. Specifically, when the light passing through the polarizer causes distortion without generating normal linearly polarized light, the distortion can be removed by aiming to rotate the polarizing drum.

FIG. 4C is a graph showing the polarization state after collimating the polarizer, and FIG. 4D is a graph representing the data shown in FIG. 4C in an analog form.

Referring to FIGS. 4C and 4D, it can be seen that distortions generated at phases around 220 ° and 280 to 300 °, which can be observed in FIGS. 4A and 4B, are removed (D1 ′). Since normal linearly polarized light is generated without distortion, it is possible to accurately measure the thickness of a relatively thick thin film having a thickness of about 1000 mW to 50 m by using the linear polarized light.

Referring to FIG. 3, in the polarization control method according to the first embodiment of the present invention, after generating the linearly polarized light, forming the second light obtained by secondly polarizing the linearly polarized light (40), and the shaped agent The method may further include determining whether the second light is circularly polarized (50), and generating circularly polarized light by aiming the second light when the circularly polarized light is not determined. Since circularly polarized light needs to be generated in order to measure the thickness of an ultra-thin film of about 1000 mW or less, circularly polarized light is generated by secondly polarizing the linearly polarized light that has passed through the polarizer.

The process of obtaining the second light by second polarizing the linearly polarized light generated by aiming the first light is performed by passing the linearly polarized light through a compensator to generate the circularly polarized light compensated by 90 °. The compensator is a polarizing element compensating 45 ° linearly polarized light by 90 ° for light emitted through the polarizer to form circularly polarized light, and operates at a phase of 90 to 180 ° and 270 to 360 °.

Theoretically, whether or not to perform accurate circular polarization of 90 ° is based on Equation 1 below.

---- Equation 1

In Formula 1, n ₀ is normal light, n _e is abnormal light, and t is the thickness of the plate.

As a result of substituting each numerical value into Equation 1, when the value of p is close to 90 °, the compensator generates circularly polarized light. For example, in the present invention, when using a laser having a wavelength of 633 를, assuming that π = 3.1415, n _e -n _o = 0.00482, t = 0.032, the value of ρ ≒ 1.53 is obtained and substituted with a delta value of about 87.6 °, it can be judged to be almost in agreement with the exact theoretical value of 90 °.

However, since it is not easy to visually determine the degree of polarization of light, a technique is needed to shape the polarized invisible light and determine the polarization state. Similar to the method of shaping a light, a digital voltmeter is connected to the photodiode output jack of an ellipsometer, the digital voltmeter is set to AV (VOLTAGE), and the compensator is rotated by 5 ° by hand. At this time, the voltage is recorded for each interval rotated, and the second light is shaped by graphically displaying the recorded voltages at intervals of 5 ° from phases 5 ° to 360 °.

Referring to FIG. 3, the polarization control method according to the first embodiment of the present invention may further include determining whether the shaped second light is circularly polarized.

4A is a graph showing the polarization state before aiming the compensator.

Referring to FIG. 4A, it can be seen that there is a distortion in the shape of the circle between phases 0 ° to 85 ° (D2) in the graph of light passing through the compensator, which is distorted. If there is such a distortion and does not generate accurate circularly polarized light, there is a problem that the thickness measurement of the ultra-thin film formed in the semiconductor device is inaccurate.

3, the polarization control method according to an embodiment of the present invention further comprises the step of generating circularly polarized light by aiming the second light when the circularly polarized light is not determined as a result of determining the circularly polarized light (60). Can be.

When distortion is generated without accurate circular polarization, aiming of the compensator is performed by aligning the mica film of the compensator to generate circular polarization. Specifically, the compensator is a flat round plate, which is indistinguishable from the eye, but in reality, materials with different refractive indices are bonded. When the laser passes through the mica film, two normal and extraordinary rays are used. The characteristics of the shape of the light indicate that the instrument is aimed so that the position of the mica film can be rotated with a driver to generate a 90 ° polarization.

In another aspect, the present invention provides a method for measuring the thickness of a thin film, such as a semiconductor device using the above-described polarization control method.

6 is a flowchart illustrating a thin film thickness measuring method according to a second exemplary embodiment of the present invention.

Referring to FIG. 6, the method for measuring thin film thickness of the present invention comprises the steps of shaping the first light obtained by first polarizing light (10), determining whether the shaped first light is linearly polarized (20), and the linearly polarized light. If it is determined whether or not linear polarization is not generated, measuring the thickness of the sample by transmitting the polarization control process and the generated linear polarized light having a step of aiming the first light to generate linear polarization (30) through a sample (100). It includes.

Generation of linearly polarized light is performed by the polarization control method according to the first embodiment of the present invention described above. The generated linearly polarized light is transmitted to the sample, and the thickness of the sample is measured by analyzing the transmitted light by using an analyzer and a photodetector. The analyzer is a device used to investigate the degree of polarization of the light or the direction of the polarization plane, the photodetector is a device that detects the optical signal and converts it into an electrical signal having the same information, the analyzer and the light By measuring the change in polarization state according to the sample transmission through a detector to measure the thickness of a relatively thick thin film of 1000 ~ 50㎛.

In addition, the present invention provides a thickness measurement method for measuring the thickness of the sample of less than 1000 kPa.

Referring to FIG. 6, in the method of measuring the thickness of an ultra-thin film of a semiconductor device, after generating the linearly polarized light, forming the second light obtained by secondly polarizing the linearly polarized light (40), and whether the shaped second light is circularly polarized Determining (50), and if the circularly polarized light determination result, if the circularly polarized light is not generated further comprises the step of aiming the second light to generate circularly polarized light (60), the thickness measurement of the sample is generated The circularly polarized light is transmitted through the sample (200).

Shaping the second light 40, determining whether the second light is circularly polarized (50), aiming the second light to generate circularly polarized light (50) is the polarization control method of the first embodiment It is based on the method of generating circularly polarized light. Then, the generated circularly polarized light is transmitted to a sample of an ultra-thin film of 1000 Å or less, and then the thickness of the sample is measured by analyzing the transmitted light through a analyzer and a photodetector.

It is possible to generate an accurate circular polarization through the aim as described above, and when applied to the semiconductor manufacturing process it is possible to measure the exact thickness of the ultra-thin film formed on the semiconductor device.

According to the present invention, it is possible to determine whether proper polarization is generated by shaping light that cannot be recognized by the naked eye, and to control it, and when it is applied to a semiconductor manufacturing process, accurate thickness and component analysis of a thin film of a semiconductor device can be performed. It is possible to improve the reliability and accuracy of the.

Although described above with reference to a preferred embodiment of the present invention, those skilled in the art will be variously modified and changed within the scope of the invention without departing from the spirit and scope of the invention described in the claims below I can understand that you can.

Claims (10)

Shaping the first light obtained by first polarizing the light; Determining whether the shaped first light is linearly polarized; And And linearly polarizing the first light to generate linearly polarized light when the linearly polarized light is not determined. The method of claim 1, wherein the light is a helium-neon (HENE) short wavelength laser formed by discharging a mixed gas of helium gas and neon gas. 2. The method of claim 1, wherein said first polarization is effected by passing said light through a polarizer at phases of 0 to 90 degrees and 180 to 270 degrees to generate first light. The polarization control method according to claim 1, wherein the shaping of the first light is performed by measuring a voltage with a voltmeter. The polarization control method according to claim 1, wherein the aiming of the first light is performed by rotating a polarizer drum of the polarizer. The method of claim 1, wherein after generating the linearly polarized light Shaping the second light obtained by aiming the first light by polarizing the second polarized light, determining whether the shaped second light is circularly polarized, and determining whether the circularly polarized light is circularly polarized. Otherwise, aiming the second light to generate circularly polarized light. 7. The method of claim 6, wherein the second polarization is performed by passing the linearly polarized light generated by aiming the first light through a compensator at phases of 90 to 180 degrees and 270 to 360 degrees to generate second light. Polarization control method. The polarization control method according to claim 6, wherein the aiming of the second light is performed by rotating a mica film of the compensator. Shaping the first light obtained by first polarizing the light; Determining whether the shaped first light is linearly polarized; Aiming to generate the linearly polarized light by aiming the first light when the linearly polarized light is not determined as the result of the linearly polarized light determination; And And measuring the thickness of the sample by transmitting the generated linearly polarized light through a sample. 10. The method of claim 9, wherein after generating the linearly polarized light Shaping the second light obtained by aiming the first light by polarizing the second polarized light, determining whether the shaped second light is circularly polarized, and determining whether the circularly polarized light is circularly polarized. Otherwise, aiming the second light to generate circularly polarized light, The thickness measurement of the sample is a thin film thickness measuring method, characterized in that carried out by transmitting the generated circularly polarized light to the sample.