TWI900377B - Ellipsometry and operation method of the same - Google Patents

Abstract

An ellipsometry includes a light source, a polarizer, a sample platform, a phase retarder, a analyzer, a detector. The light source is configured to emit an unpolarized light. The polarizer receives the unpolarized light and transforms the unpolarized light to a polarized light with known polarization. The sample platform is used to support a sample to be inspected. The polarized light is emitted onto a surface of the sample to be inspected. The phase retarder is configured to modulate a phase difference between S polarization and P polarization of the polarized beam. A fast axis of the phase retarder is parallel with a S-polarization of the polarized light. The analyzer is configured to receive a reflection light reflected from the surface of the sample. The phase retarder is located between the polarizer and the analyzer to reduce the variability of film thickness measurements of the same to be inspected. The detector is configured to receive the reflection light passed through the analyzer.

Description

Ellipsometer and its operation method

The present disclosure relates to an ellipsometer and a method of operating the same.

In response to industry demands such as in-situ film thickness measurement in the atomic layer deposition (ALD) process, the thickness of the atomic layer is approximately 0.25 nm, and thinner film thickness needs to be measured.

Existing ellipsometer configurations reduce the variability of film thickness measurements on test samples by placing a polarizer with adjustable energy and phase. This involves adjusting the angle during measurement and performing multiple measurements to achieve optimal results. This process is complex and cannot be conveniently applied to existing ellipsometer configurations.

In view of this, how to provide an ellipsometer and its operation method that can solve the above-mentioned problems is still one of the research directions that urgently needs to be studied.

Another technical aspect of the present disclosure is an ellipsometer.

In one embodiment, the ellipse meter includes a light source, a polarizer, a sample stage, a phase retarder, an analyzer, and a detector. The light source is configured to emit an unpolarized light beam. The polarizer receives the unpolarized light beam and converts the unpolarized light beam into a polarized light beam with a known polarization state. The sample stage is used to support the sample to be tested, wherein the polarized light beam is incident on the surface of the sample to be tested. The phase retarder is configured to adjust the phase difference between the S polarization and the P polarization of the polarized light beam, and the fast axis of the phase retarder is parallel to the S polarization component of the polarized light beam. The analyzer is configured to receive a reflected light beam reflected from the surface of the sample to be tested, wherein the phase retarder is located between the polarizer and the analyzer to reduce the film thickness variability of the thin film to be tested. The detector is configured to receive the reflected light beam passing through the analyzer.

In one embodiment, the phase retarder is located between the polarizer and the sample to be measured.

In one embodiment, the phase delay device is located between the sample to be measured and the analyzer.

In one embodiment, the film thickness of the sample to be tested is less than or equal to 4 nm.

In one embodiment, the phase delay angle of the phase delayer is greater than or equal to 60 degrees and less than or equal to 80 degrees.

In the embodiments described in paragraphs [0007] to [0010], the analyzer is a rotating type.

In one embodiment, the ellipse further comprises a polarizer that is a combination of a linear polarizer and a phase modulator.

In one embodiment, the phase delay device is located between the sample to be measured and the analyzer.

In one embodiment, the phase retarder is located between the polarizer of the combination of the linear polarizer and the phase modulator and the sample to be measured.

In the embodiments of paragraphs [0012] to [0014], the polarizer is of a fixed type.

Another embodiment of the present disclosure is a method for operating an elliptical instrument, which is applied to the aforementioned elliptical instrument.

In one embodiment, the operating method of the ellipsometer includes emitting an unpolarized light beam toward a sample to be tested placed on a sample stage via a light source; receiving the unpolarized light beam via a polarizer and converting the unpolarized light beam into a polarized light beam with a known polarization state; adjusting the phase difference between the S polarization and the P polarization of the polarized light beam via a phase retarder, wherein the fast axis of the phase retarder is parallel to the S polarization component of the polarized light beam, and the phase delay angle of the phase retarder is a fixed value; receiving a reflected light beam reflected from the surface of the sample to be tested via a polarizer and performing polarization analysis; and converting the reflected light beam into an electrical signal via a detector.

In one embodiment, adjusting the phase difference of a polarized light beam by a phase delayer further includes setting a phase delay angle of the phase delayer between 60 degrees and 80 degrees.

In one embodiment, adjusting the phase difference between the S-polarization and the P-polarization of the polarized light beam by using a phase retarder further includes placing the phase retarder in a rotating analyzer ellipsometer structure.

In one embodiment, adjusting the phase difference between the S-polarization and the P-polarization of the polarized light beam by a phase retarder further includes placing the phase retarder between the polarizer and the sample to be measured.

In one embodiment, adjusting the phase difference between the S-polarization and the P-polarization of the polarized light beam by using a phase delay device further includes placing the phase delay device between the sample to be measured and the analyzer.

In one embodiment, the operating method of the ellipse meter further includes modulating the phase difference between the S-polarization and P-polarization of the polarized light beam by a phase modulator located between the linear polarizer and the sample to be measured, wherein the linear polarizer and the phase modulator are combined to form a polarizer.

In one embodiment, adjusting the phase difference between the S-polarization and P-polarization of the polarized light beam by a phase retarder further includes placing the phase retarder in a phase modulation ellipse structure.

In one embodiment, adjusting the phase difference between the S-polarization and P-polarization of the polarized light beam by using a phase delay further includes placing the phase delay between the sample to be measured and the analyzer.

In one embodiment, adjusting the phase difference between the S-polarization and P-polarization of the polarized light beam by a phase retarder further includes placing the phase retarder between a polarizer of a combination of a linear polarizer and a phase modulator and a sample to be measured.

In the aforementioned embodiments, the disclosed ellipsometer reduces variability in the thickness measurement of extremely thin films by placing a phase retarder within the existing rotating analyzer ellipsometer or phase modulation ellipsometer configuration, aligning the fast axis with the S-polarization component of polarized light. In the disclosed ellipsometer operating method, the phase retarder's phase retardation angle is a fixed value, eliminating the need for repeated angle testing during the measurement process to achieve the desired effect.

The following drawings illustrate various embodiments of the present invention. For the sake of clarity, many practical details are described in the following description. However, it should be understood that these practical details should not be used to limit the present invention.

FIG1 is a schematic diagram of an ellipse meter 100 according to an embodiment of the present disclosure. The ellipse meter 100 includes a light source 110, a polarizer 120, a sample stage 130, a phase delay device 140, an analyzer 150, and a detector 160.

Light source 110 is configured to emit an unpolarized light beam L1. Polarizer 120 receives unpolarized light beam L1 and converts it into a polarized light beam L2 having a known polarization state. In some embodiments, polarizer 120 is a linear polarizer. In other embodiments, polarizer 120 may be a combination of a linear polarizer and a phase modulator. Sample stage 130 is used to support a sample 132 to be tested. Polarized light beam L2 is incident on the surface of sample 132 to be tested.

Phase retarder 140 is configured to adjust the phase difference between the S-polarization and P-polarization of polarized light beam L2. Analyzer 150 is configured to receive reflected light beam L3 reflected from the surface of sample 132. Phase retarder 140 is positioned between polarizer 120 and analyzer 150 to reduce film thickness variability of sample 132.

The analyzer 150 is a rotating analyzer. In this embodiment, the analyzer 150 is a rotating analyzer. The detector 160 is configured to receive the reflected light beam L4 passing through the analyzer 150.

The ellipsometry 100 is equivalent to adding a phase delay device 140 between the rotating-analyzer ellipsometry ( _PSAR ) structure and the sample 132 to be tested. In this embodiment, the phase delay device 140 is located between the polarizer 120 and the sample 132 to be tested.

Figure 2 illustrates a polarized light beam L2 incident on a sample 132. An incident plane 134 is defined as a plane perpendicular to the surface of the sample 132. The incident light (polarized light beam L2) and the reflected light beam L3 are located on either side of the incident plane 134. Arrow S indicates the S-polarization direction of the polarized light beam L2.

The fast axis of phase retarder 140 is parallel to the S-polarization component of polarized light beam L2. The phase delay angle of phase retarder 140 is greater than or equal to 60 degrees and less than or equal to 80 degrees. The phase delay angle of phase retarder 140 is not adjustable. Phase retarder 140 can produce relative phase delays between the two mutually perpendicular S-polarization and P-polarization components in the vibration direction of polarized light beam L2, thereby changing the polarization characteristics of the light. In this embodiment, phase retarder 140 is located between polarizer 120 and sample 132 to be tested.

The ellipsometer 100 measures film thickness according to the ellipsometer equation (1), where Ψ is the amplitude ratio and ∆ is the phase difference. rp is the P-polarization amplitude intensity, and rs is the S-polarization amplitude intensity. When the film thickness is extremely thin, sin∆ approaches zero. The noise is relatively low, limiting the thinnest thickness that can be measured. (1)

Figure 4 shows a simulated comparison of the measurement variability of phase difference as a function of film thickness between an ellipsometer 100 according to an embodiment of the present disclosure and a conventional ellipsometer. The simulation conditions used in Figure 4 include a sample 132 placed on a silicon substrate with a refractive index of 1.46, an incident wavelength of 633 nm, an incident angle of 70 degrees, and thicknesses ranging from 0 nm to 4 nm. The measurement variability data was simulated at a signal-to-noise ratio of 1000:1. The delay phase γ of the phase retarder 140 of the present disclosure is 80 degrees, as an example.

The polarization optics mathematical description of the PSA _R configuration is as follows:

The polarization mathematical description of the ellipsometer 100 disclosed herein is as follows:

Compared to the conventional ellipsometer's retardation measurement variability curve C1, which shows how the retardation varies with film thickness, the ellipsometer 100 exhibits low variability even at extremely thin film thicknesses. In other words, by aligning the fast axis of the phase retarder 140 with the S-polarization of the polarized light beam L2, the variability in the measurement of extremely thin film thicknesses can be reduced.

FIG3 is a schematic diagram of an ellipsemeter 100a according to another embodiment of the present disclosure. Ellipsemeter 100a is similar to ellipsemeter 100 in FIG1 , except that the phase delay 140 of ellipsemeter 100a is positioned between the sample 132 to be measured and the analyzer 150. Ellipsemeter 100a and ellipsemeter 100 have the same technical functions and are not further described here.

FIG5 is a schematic diagram of an ellipse 100b according to another embodiment of the present disclosure. Ellipse 100b includes a light source 110, a linear polarizer 120b, a sample stage 130, a phase retarder 140, an analyzer 150, a detector 160, and a phase modulator 170. Phase modulator 170 is located between linear polarizer 120b and phase retarder 140. Linear polarizer 120b and phase modulator 170 form a polarizer. In this embodiment, analyzer 150 is fixed.

Ellipsometry 100b is equivalent to adding a phase delayer 140 between the structure of a phase-modulation ellipsometry (PMSA) and the sample 132 to be tested. In this embodiment, the phase delayer 140 is located between the phase modulator 170 and the sample 132 to be tested.

Figure 6 shows a simulated comparison of the measurement variability of phase difference as a function of film thickness between an ellipsometer 100b according to an embodiment of the present disclosure and a conventional ellipsometer. The simulation conditions used in Figure 6 include a sample 132 placed on a silicon substrate with a refractive index of 1.46, an incident wavelength of 633 nm, an incident angle of 70 degrees, and a thickness range of 0 nm to 4 nm for the sample 132. The phase delay angle of the phase modulator 170 is 70 degrees. The measurement variability data was simulated under a signal-to-noise ratio of 1000:1. The delay phase γ of the phase retarder 140 of the present disclosure is 75 degrees, as an example.

The polarization optical mathematical description of the Phase Modulated Ellipsometer (PMSA) architecture is as follows:

The polarization mathematical description of the elliptical polarizer 100b disclosed herein is as follows:

Compared to the conventional ellipsometer's retardation measurement variability curve C4, which shows a phase difference measurement variability curve C3, ellipsometer 100b exhibits low variability even at extremely thin film thicknesses. In other words, by aligning the fast axis of the phase retarder 140 with the S-polarization of the polarized light beam L2, the variability in the measurement of extremely thin film thicknesses can be reduced.

FIG7 is a schematic diagram of an elliptometer 100c according to another embodiment of the present disclosure. In this embodiment, a phase delay 140 is positioned between a sample 132 to be tested and an analyzer 150. Elliptometer 100c and elliptometer 100b have the same technical functions and are not further described here.

It should be understood that the connection relationship and function of the components already described will not be repeated, and will be described first. The following describes the operation method of the elliptical instrument, which can be applied to the elliptical instrument of any of the above embodiments.

The operation method of the ellipse meter begins with the light source 110 emitting an unpolarized light beam L1 toward the sample 132 to be tested placed on the sample stage 130. Then, the polarizer 120 receives the unpolarized light beam L1 and converts the unpolarized light beam L1 into a polarized light beam L2 with a known polarization state.

Next, the phase difference between the S-polarization and P-polarization components of polarized light beam L2 is adjusted using phase retarder 140. In this step, the fast axis of phase retarder 140 is parallel to the S-polarization component of polarized light beam L2, and the phase retarder angle of phase retarder 140 is fixed. The phase retarder angle of phase retarder 140 is a fixed value between 60 and 80 degrees.

When the ellipsometer is a rotating analyzer ellipsometer, this step is equivalent to placing the phase retarder 140 between the rotating analyzer ellipsometer and the sample 132 to be measured. The phase retarder 140 can be placed between the polarizer 120 and the sample 132 to be measured, or between the sample 132 to be measured and the analyzer 150. This improves film thickness variability without changing the existing structure.

When the ellipse is a phase-modulation ellipse, this step is equivalent to placing the phase delay 140 between the phase-modulation ellipse and the sample 132 under test. The phase delay 140 can be placed between the phase modulator 170 and the sample 132 under test, or between the sample 132 under test and the analyzer 150. This improves film thickness variability without changing the existing structure.

Next, the reflective beam L3 reflected from the surface of the sample 132 is received by the analyzer 150 and polarization analyzed. Finally, the detector 160 converts the reflective beam L4 after passing through the analyzer 150 into an electrical signal, resulting in a measurement result with low film thickness variability.

In summary, the disclosed ellipsometer reduces the variability in the thickness measurement of extremely thin films by placing a phase retarder within the existing rotating analyzer or phase modulation ellipsometer architecture, with the fast axis aligned with the S-polarization component of polarized light. In the disclosed ellipsometer operating method, the phase retarder's phase retardation angle is a fixed value, eliminating the need for repeated angle testing during the measurement process to achieve the desired effect.

Although the present invention has been disclosed in the form of embodiments as described above, this is not intended to limit the present disclosure. Anyone skilled in the art may make various changes and modifications without departing from the spirit and scope of the present disclosure. Therefore, the scope of protection of the present disclosure shall be determined by the scope of the attached patent application.

100, 100a, 100b, 100c: Ellipsometer 110: Light source 120: Polarizer 120b: Linear polarizer 130: Sample stage 132: Sample to be measured 134: Incident plane 140: Phase retarder 150: Analyzer 160: Detector 170: Phase modulator L1: Unpolarized beam L2: Polarized beam L3, L4: Reflected beam S: Arrow C1, C2, C3, C4: Curves

Figure 1 is a schematic diagram of an ellipsometer according to an embodiment of the present disclosure. Figure 2 is a schematic diagram of a polarized light beam incident on a sample to be measured. Figure 3 is a schematic diagram of an ellipsometer according to another embodiment of the present disclosure. Figure 4 is a simulated comparison of the measurement variation of the phase difference as a function of film thickness between an ellipsometer according to an embodiment of the present disclosure and a conventional ellipsometer. Figure 5 is a schematic diagram of an ellipsometer according to another embodiment of the present disclosure. Figure 6 is a simulated comparison of the measurement variation of the phase difference as a function of film thickness between an ellipsometer according to an embodiment of the present disclosure and a conventional ellipsometer. Figure 7 is a schematic diagram of an ellipsometer according to another embodiment of the present disclosure.

100: Elliptical instrument

110: Light Source

120: Polarizer

130: Sample table

132: Sample to be tested

140: Phase Delay

150: Polarizer

160: Detector

L1: Unpolarized beam

L2: Polarized beam

L3, L4: Reflected beams

Claims (19)

An ellipsometer includes: a light source configured to emit an unpolarized light beam; a polarizer configured to receive the unpolarized light beam and convert it into a polarized light beam with a known polarization state; a sample stage configured to support a sample to be tested, wherein the polarized light beam is incident on the surface of the sample to be tested; a phase retarder configured to adjust the phase difference between the S-polarization and P-polarization components of the polarized light beam, wherein a fast axis of the phase retarder is parallel to an S-polarization component of the polarized light beam, and the phase retarder angle is not adjustable; an analyzer configured to receive a reflected light beam reflected from the surface of the sample to be tested, wherein the phase retarder is located between the polarizer and the analyzer to reduce film thickness variability of the sample to be tested; and a detector configured to receive the reflected light beam passing through the analyzer. The ellipsometer as claimed in claim 1, wherein the phase delay device is located between the polarizer and the sample to be measured. The ellipsometer as claimed in claim 1, wherein the phase delay device is located between the sample to be measured and the polarizer. The elliptical instrument as described in claim 1, wherein a phase delay angle of the phase delay device is greater than or equal to 60 degrees and less than or equal to 80 degrees. The ellipse as claimed in claim 1, wherein the polarizer is a combination of a linear polarizer and a phase modulator. The ellipsometer of claim 5, wherein the phase modulator is located between the linear polarizer and the sample to be measured. The ellipsometer as described in claim 6, wherein the phase delay device is located between the sample to be measured and the polarizer. The ellipsometer as described in claim 6, wherein the phase delay device is located between the phase modulator and the sample to be measured. The ellipsometer as described in claim 1, wherein the polarizer is of a rotating type or a fixed type. The elliptical polarizer as described in claim 1, wherein the polarizer is a linear polarizer. A method for operating an ellipsometer is applied to the ellipsometer described in claim 1, and the method for operating the ellipsometer includes: emitting an unpolarized light beam toward a sample to be tested placed on a sample stage by a light source; receiving the unpolarized light beam by a polarizer and converting the unpolarized light beam into a polarized light beam with a known polarization state; adjusting the phase difference between the S polarization and the P polarization of the polarized light beam by a phase delay device, wherein a fast axis of the phase delay device is parallel to an S polarization component of the polarized light beam, and a phase delay angle of the phase delay device is not adjustable and is a fixed value; receiving a reflected light beam reflected from the surface of the sample to be tested by a polarizer and performing polarization analysis; and converting the reflected light beam into an electrical signal by a detector. The operating method of the ellipsometer as described in claim 11, wherein adjusting the phase difference of the polarized light beam by the phase delay device further includes: making the phase delay angle of the phase delay device between 60 degrees and 80 degrees. The operating method of the ellipsometer as described in claim 11, wherein adjusting the phase difference of the polarized light beam by the phase retarder further includes: placing the phase retarder in a rotating analyzer ellipsometer structure. The operating method of the ellipsometer as described in claim 13, wherein adjusting the phase difference of the polarized light beam by the phase retarder further includes: placing the phase retarder between the polarizer and the sample to be measured. The operating method of the ellipsometer as described in claim 13, wherein adjusting the phase difference of the polarized light beam by the phase delay device further includes: placing the phase delay device between the sample to be measured and the polarizer. The operating method of the ellipse meter as described in claim 11, wherein the polarizer includes a linear polarizer and a phase modulator, and the operating method of the ellipse meter further includes: changing the phase difference between the S polarization and the P polarization of the polarized light beam by the phase modulator located between the linear polarizer and the sample to be measured. The operating method of the ellipsometer as described in claim 16, wherein adjusting the phase difference of the polarized light beam by the phase retarder further includes: placing the phase retarder in a phase modulation ellipsometer structure. The operating method of the ellipsometer as described in claim 17, wherein adjusting the phase difference of the polarized light beam by the phase delay device further includes: placing the phase delay device between the sample to be measured and the polarizer. The operating method of the ellipsometer as described in claim 17, wherein adjusting the phase difference of the polarized light beam by the phase delay device further includes: placing the phase delay device between the phase modulator and the sample to be measured.